source: draft-ietf-httpbis/latest/p1-messaging.xml @ 187

Last change on this file since 187 was 187, checked in by julian.reschke@…, 13 years ago

Fix typo in ALPHA rule (we're still using the RFC2616's syntax); addresses #36.

  • Property svn:eol-style set to native
File size: 179.0 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="ALPHA"/>
814<x:anchor-alias value="DIGIT"/>
815<x:anchor-alias value="CTL"/>
816<x:anchor-alias value="CR"/>
817<x:anchor-alias value="LF"/>
818<x:anchor-alias value="SP"/>
819<x:anchor-alias value="HTAB"/>
820<x:anchor-alias value="CRLF"/>
821<x:anchor-alias value="LWS"/>
822<x:anchor-alias value="TEXT"/>
823<x:anchor-alias value="HEX"/>
824<x:anchor-alias value="token"/>
825<x:anchor-alias value="separators"/>
826<x:anchor-alias value="comment"/>
827<x:anchor-alias value="ctext"/>
828<x:anchor-alias value="quoted-string"/>
829<x:anchor-alias value="qdtext"/>
830<x:anchor-alias value="quoted-pair"/>
831<t>
832   The following rules are used throughout this specification to
833   describe basic parsing constructs. The US-ASCII coded character set
834   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
835</t>
836<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><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"/>
837  OCTET          = %x00-FF
838                   ; any 8-bit sequence of data
839  CHAR           = %x00-7F
840                   ; any US-ASCII character
841  ALPHA          = %x41-5A | %x61-7A
842                   ; A-Z | a-z
843  DIGIT          = %x30-39
844                   ; any US-ASCII digit "0".."9"
845  CTL            = %x00-1F | %x7F
846                   ; (octets 0 - 31) and DEL (127)
847  CR             = %x0D
848                   ; US-ASCII CR, carriage return (13)
849  LF             = %x0A
850                   ; US-ASCII LF, linefeed (10)
851  SP             = %x20
852                   ; US-ASCII SP, space (32)
853  HTAB           = %x09
854                   ; US-ASCII HT, horizontal-tab (9)
855  DQUOTE         = %x22
856                   ; US-ASCII double-quote mark (34)
857</artwork></figure>
858<t>
859   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
860   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
861   tolerant applications). The end-of-line marker within an entity-body
862   is defined by its associated media type, as described in &media-types;.
863</t>
864<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
865  CRLF           = CR LF
866</artwork></figure>
867<t>
868   HTTP/1.1 header field values can be folded onto multiple lines if the
869   continuation line begins with a space or horizontal tab. All linear
870   white space, including folding, has the same semantics as SP. A
871   recipient &MAY; replace any linear white space with a single SP before
872   interpreting the field value or forwarding the message downstream.
873</t>
874<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
875  LWS            = [CRLF] 1*( SP | HTAB )
876</artwork></figure>
877<t>
878   The TEXT rule is only used for descriptive field contents and values
879   that are not intended to be interpreted by the message parser. Words
880   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
881   <xref target="ISO-8859-1"/> only when encoded according to the rules of
882   <xref target="RFC2047"/>.
883</t>
884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
885  TEXT           = &lt;any OCTET except CTLs, but including LWS&gt;
886</artwork></figure>
887<t>
888   A CRLF is allowed in the definition of TEXT only as part of a header
889   field continuation. It is expected that the folding LWS will be
890   replaced with a single SP before interpretation of the TEXT value.
891</t>
892<t>
893   Hexadecimal numeric characters are used in several protocol elements.
894</t>
895<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEX"/>
896  HEX            = "A" | "B" | "C" | "D" | "E" | "F"
897                 | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
898</artwork></figure>
899<t>
900   Many HTTP/1.1 header field values consist of words separated by LWS
901   or special characters. These special characters &MUST; be in a quoted
902   string to be used within a parameter value (as defined in
903   <xref target="transfer.codings"/>).
904</t>
905<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="separators"/>
906  token          = 1*&lt;any CHAR except CTLs or separators&gt;
907  separators     = "(" | ")" | "&lt;" | "&gt;" | "@"
908                 | "," | ";" | ":" | "\" | DQUOTE
909                 | "/" | "[" | "]" | "?" | "="
910                 | "{" | "}" | SP | HTAB
911</artwork></figure>
912<t>
913   Comments can be included in some HTTP header fields by surrounding
914   the comment text with parentheses. Comments are only allowed in
915   fields containing "comment" as part of their field value definition.
916   In all other fields, parentheses are considered part of the field
917   value.
918</t>
919<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
920  comment        = "(" *( ctext | quoted-pair | comment ) ")"
921  ctext          = &lt;any TEXT excluding "(" and ")"&gt;
922</artwork></figure>
923<t>
924   A string of text is parsed as a single word if it is quoted using
925   double-quote marks.
926</t>
927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
928  quoted-string  = ( DQUOTE *(qdtext | quoted-pair ) DQUOTE )
929  qdtext         = &lt;any TEXT excluding DQUOTE and "\">
930</artwork></figure>
931<t>
932   The backslash character ("\") &MAY; be used as a single-character
933   quoting mechanism only within quoted-string and comment constructs.
934</t>
935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
936  quoted-pair    = "\" CHAR
937</artwork></figure>
938</section>
939</section>
940
941<section title="Protocol Parameters" anchor="protocol.parameters">
942
943<section title="HTTP Version" anchor="http.version">
944<t>
945   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
946   of the protocol. The protocol versioning policy is intended to allow
947   the sender to indicate the format of a message and its capacity for
948   understanding further HTTP communication, rather than the features
949   obtained via that communication. No change is made to the version
950   number for the addition of message components which do not affect
951   communication behavior or which only add to extensible field values.
952   The &lt;minor&gt; number is incremented when the changes made to the
953   protocol add features which do not change the general message parsing
954   algorithm, but which may add to the message semantics and imply
955   additional capabilities of the sender. The &lt;major&gt; number is
956   incremented when the format of a message within the protocol is
957   changed. See <xref target="RFC2145"/> for a fuller explanation.
958</t>
959<t>
960   The version of an HTTP message is indicated by an HTTP-Version field
961   in the first line of the message. HTTP-Version is case-sensitive.
962</t>
963<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/>
964  HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
965</artwork></figure>
966<t>
967   Note that the major and minor numbers &MUST; be treated as separate
968   integers and that each &MAY; be incremented higher than a single digit.
969   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
970   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
971   &MUST-NOT; be sent.
972</t>
973<t>
974   An application that sends a request or response message that includes
975   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
976   with this specification. Applications that are at least conditionally
977   compliant with this specification &SHOULD; use an HTTP-Version of
978   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
979   not compatible with HTTP/1.0. For more details on when to send
980   specific HTTP-Version values, see <xref target="RFC2145"/>.
981</t>
982<t>
983   The HTTP version of an application is the highest HTTP version for
984   which the application is at least conditionally compliant.
985</t>
986<t>
987   Proxy and gateway applications need to be careful when forwarding
988   messages in protocol versions different from that of the application.
989   Since the protocol version indicates the protocol capability of the
990   sender, a proxy/gateway &MUST-NOT; send a message with a version
991   indicator which is greater than its actual version. If a higher
992   version request is received, the proxy/gateway &MUST; either downgrade
993   the request version, or respond with an error, or switch to tunnel
994   behavior.
995</t>
996<t>
997   Due to interoperability problems with HTTP/1.0 proxies discovered
998   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
999   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
1000   they support. The proxy/gateway's response to that request &MUST; be in
1001   the same major version as the request.
1002</t>
1003<t>
1004  <list>
1005    <t>
1006      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
1007      of header fields required or forbidden by the versions involved.
1008    </t>
1009  </list>
1010</t>
1011</section>
1012
1013<section title="Uniform Resource Identifiers" anchor="uri">
1014<t>
1015   URIs have been known by many names: WWW addresses, Universal Document
1016   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
1017   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
1018   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
1019   simply formatted strings which identify--via name, location, or any
1020   other characteristic--a resource.
1021</t>
1022
1023<section title="General Syntax" anchor="general.syntax">
1024<t>
1025   URIs in HTTP can be represented in absolute form or relative to some
1026   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
1027   forms are differentiated by the fact that absolute URIs always begin
1028   with a scheme name followed by a colon. For definitive information on
1029   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
1030   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
1031   and <xref target="RFC1808"/>). This specification adopts the
1032   definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
1033   "host", "abs_path", "query", and "authority" from that specification:
1034</t>
1035<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"/>
1036  absoluteURI   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1037  authority     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
1038  path-absolute = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1039  port          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1040  query         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
1041  relativeURI   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
1042  uri-host      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1043</artwork></figure>
1044<t>
1045   HTTP does not place any a priori limit on the length of
1046   a URI. Servers &MUST; be able to handle the URI of any resource they
1047   serve, and &SHOULD; be able to handle URIs of unbounded length if they
1048   provide GET-based forms that could generate such URIs. A server
1049   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
1050   than the server can handle (see &status-414;).
1051</t>
1052<t>
1053  <list>
1054    <t>
1055      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
1056      above 255 bytes, because some older client or proxy
1057      implementations might not properly support these lengths.
1058    </t>
1059  </list>
1060</t>
1061</section>
1062
1063<section title="http URL" anchor="http.url">
1064<t>
1065   The "http" scheme is used to locate network resources via the HTTP
1066   protocol. This section defines the scheme-specific syntax and
1067   semantics for http URLs.
1068</t>
1069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
1070  http-URL = "http:" "//" uri-host [ ":" port ]
1071             [ path-absolute [ "?" query ]]
1072</artwork></figure>
1073<t>
1074   If the port is empty or not given, port 80 is assumed. The semantics
1075   are that the identified resource is located at the server listening
1076   for TCP connections on that port of that host, and the Request-URI
1077   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
1078   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
1079   the path-absolute is not present in the URL, it &MUST; be given as "/" when
1080   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1081   receives a host name which is not a fully qualified domain name, it
1082   &MAY; add its domain to the host name it received. If a proxy receives
1083   a fully qualified domain name, the proxy &MUST-NOT; change the host
1084   name.
1085</t>
1086</section>
1087
1088<section title="URI Comparison" anchor="uri.comparison">
1089<t>
1090   When comparing two URIs to decide if they match or not, a client
1091   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
1092   URIs, with these exceptions:
1093  <list style="symbols">
1094    <t>A port that is empty or not given is equivalent to the default
1095        port for that URI-reference;</t>
1096    <t>Comparisons of host names &MUST; be case-insensitive;</t>
1097    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
1098    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
1099  </list>
1100</t>
1101<t>
1102   Characters other than those in the "reserved" set (see
1103   <xref target="RFC2396"/>) are equivalent to their ""%" HEX HEX" encoding.
1104</t>
1105<t>
1106   For example, the following three URIs are equivalent:
1107</t>
1108<figure><artwork type="example">
1109   http://example.com:80/~smith/home.html
1110   http://EXAMPLE.com/%7Esmith/home.html
1111   http://EXAMPLE.com:/%7esmith/home.html
1112</artwork></figure>
1113</section>
1114</section>
1115
1116<section title="Date/Time Formats" anchor="date.time.formats">
1117<section title="Full Date" anchor="full.date">
1118<t>
1119   HTTP applications have historically allowed three different formats
1120   for the representation of date/time stamps:
1121</t>
1122<figure><artwork type="example">
1123   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1124   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1125   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1126</artwork></figure>
1127<t>
1128   The first format is preferred as an Internet standard and represents
1129   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1130   <xref target="RFC822"/>). The other formats are described here only for
1131   compatibility with obsolete implementations.
1132   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1133   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1134   only generate the RFC 1123 format for representing HTTP-date values
1135   in header fields. See <xref target="tolerant.applications"/> for further information.
1136</t>
1137<t><list><t>
1138      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1139      accepting date values that may have been sent by non-HTTP
1140      applications, as is sometimes the case when retrieving or posting
1141      messages via proxies/gateways to SMTP or NNTP.
1142</t></list></t>
1143<t>
1144   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1145   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1146   equal to UTC (Coordinated Universal Time). This is indicated in the
1147   first two formats by the inclusion of "GMT" as the three-letter
1148   abbreviation for time zone, and &MUST; be assumed when reading the
1149   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1150   additional LWS beyond that specifically included as SP in the
1151   grammar.
1152</t>
1153<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"/>
1154  HTTP-date    = rfc1123-date | rfc850-date | asctime-date
1155  rfc1123-date = wkday "," SP date1 SP time SP "GMT"
1156  rfc850-date  = weekday "," SP date2 SP time SP "GMT"
1157  asctime-date = wkday SP date3 SP time SP 4DIGIT
1158  date1        = 2DIGIT SP month SP 4DIGIT
1159                 ; day month year (e.g., 02 Jun 1982)
1160  date2        = 2DIGIT "-" month "-" 2DIGIT
1161                 ; day-month-year (e.g., 02-Jun-82)
1162  date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
1163                 ; month day (e.g., Jun  2)
1164  time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
1165                 ; 00:00:00 - 23:59:59
1166  wkday        = "Mon" | "Tue" | "Wed"
1167               | "Thu" | "Fri" | "Sat" | "Sun"
1168  weekday      = "Monday" | "Tuesday" | "Wednesday"
1169               | "Thursday" | "Friday" | "Saturday" | "Sunday"
1170  month        = "Jan" | "Feb" | "Mar" | "Apr"
1171               | "May" | "Jun" | "Jul" | "Aug"
1172               | "Sep" | "Oct" | "Nov" | "Dec"
1173</artwork></figure>
1174<t>
1175      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1176      to their usage within the protocol stream. Clients and servers are
1177      not required to use these formats for user presentation, request
1178      logging, etc.
1179</t>
1180</section>
1181</section>
1182
1183<section title="Transfer Codings" anchor="transfer.codings">
1184<t>
1185   Transfer-coding values are used to indicate an encoding
1186   transformation that has been, can be, or may need to be applied to an
1187   entity-body in order to ensure "safe transport" through the network.
1188   This differs from a content coding in that the transfer-coding is a
1189   property of the message, not of the original entity.
1190</t>
1191<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1192  transfer-coding         = "chunked" | transfer-extension
1193  transfer-extension      = token *( ";" parameter )
1194</artwork></figure>
1195<t>
1196   Parameters are in  the form of attribute/value pairs.
1197</t>
1198<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"/>
1199  parameter               = attribute "=" value
1200  attribute               = token
1201  value                   = token | quoted-string
1202</artwork></figure>
1203<t>
1204   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1205   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1206   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1207</t>
1208<t>
1209   Whenever a transfer-coding is applied to a message-body, the set of
1210   transfer-codings &MUST; include "chunked", unless the message is
1211   terminated by closing the connection. When the "chunked" transfer-coding
1212   is used, it &MUST; be the last transfer-coding applied to the
1213   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1214   than once to a message-body. These rules allow the recipient to
1215   determine the transfer-length of the message (<xref target="message.length"/>).
1216</t>
1217<t>
1218   Transfer-codings are analogous to the Content-Transfer-Encoding
1219   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1220   binary data over a 7-bit transport service. However, safe transport
1221   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1222   the only unsafe characteristic of message-bodies is the difficulty in
1223   determining the exact body length (<xref target="message.length"/>), or the desire to
1224   encrypt data over a shared transport.
1225</t>
1226<t>
1227   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1228   transfer-coding value tokens. Initially, the registry contains the
1229   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1230   "gzip", "compress", and "deflate" (&content-codings;).
1231</t>
1232<t>
1233   New transfer-coding value tokens &SHOULD; be registered in the same way
1234   as new content-coding value tokens (&content-codings;).
1235</t>
1236<t>
1237   A server which receives an entity-body with a transfer-coding it does
1238   not understand &SHOULD; return 501 (Not Implemented), and close the
1239   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1240   client.
1241</t>
1242
1243<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1244<t>
1245   The chunked encoding modifies the body of a message in order to
1246   transfer it as a series of chunks, each with its own size indicator,
1247   followed by an &OPTIONAL; trailer containing entity-header fields. This
1248   allows dynamically produced content to be transferred along with the
1249   information necessary for the recipient to verify that it has
1250   received the full message.
1251</t>
1252<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"/>
1253  Chunked-Body   = *chunk
1254                   last-chunk
1255                   trailer-part
1256                   CRLF
1257 
1258  chunk          = chunk-size [ chunk-extension ] CRLF
1259                   chunk-data CRLF
1260  chunk-size     = 1*HEX
1261  last-chunk     = 1*("0") [ chunk-extension ] CRLF
1262 
1263  chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
1264  chunk-ext-name = token
1265  chunk-ext-val  = token | quoted-string
1266  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1267  trailer-part   = *(entity-header CRLF)
1268</artwork></figure>
1269<t>
1270   The chunk-size field is a string of hex digits indicating the size of
1271   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1272   zero, followed by the trailer, which is terminated by an empty line.
1273</t>
1274<t>
1275   The trailer allows the sender to include additional HTTP header
1276   fields at the end of the message. The Trailer header field can be
1277   used to indicate which header fields are included in a trailer (see
1278   <xref target="header.trailer"/>).
1279</t>
1280<t>
1281   A server using chunked transfer-coding in a response &MUST-NOT; use the
1282   trailer for any header fields unless at least one of the following is
1283   true:
1284  <list style="numbers">
1285    <t>the request included a TE header field that indicates "trailers" is
1286     acceptable in the transfer-coding of the  response, as described in
1287     <xref target="header.te"/>; or,</t>
1288
1289    <t>the server is the origin server for the response, the trailer
1290     fields consist entirely of optional metadata, and the recipient
1291     could use the message (in a manner acceptable to the origin server)
1292     without receiving this metadata.  In other words, the origin server
1293     is willing to accept the possibility that the trailer fields might
1294     be silently discarded along the path to the client.</t>
1295  </list>
1296</t>
1297<t>
1298   This requirement prevents an interoperability failure when the
1299   message is being received by an HTTP/1.1 (or later) proxy and
1300   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1301   compliance with the protocol would have necessitated a possibly
1302   infinite buffer on the proxy.
1303</t>
1304<t>
1305   A process for decoding the "chunked" transfer-coding
1306   can be represented in pseudo-code as:
1307</t>
1308<figure><artwork type="code">
1309    length := 0
1310    read chunk-size, chunk-extension (if any) and CRLF
1311    while (chunk-size &gt; 0) {
1312       read chunk-data and CRLF
1313       append chunk-data to entity-body
1314       length := length + chunk-size
1315       read chunk-size and CRLF
1316    }
1317    read entity-header
1318    while (entity-header not empty) {
1319       append entity-header to existing header fields
1320       read entity-header
1321    }
1322    Content-Length := length
1323    Remove "chunked" from Transfer-Encoding
1324</artwork></figure>
1325<t>
1326   All HTTP/1.1 applications &MUST; be able to receive and decode the
1327   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1328   they do not understand.
1329</t>
1330</section>
1331</section>
1332
1333</section>
1334
1335<section title="HTTP Message" anchor="http.message">
1336
1337<section title="Message Types" anchor="message.types">
1338<t>
1339   HTTP messages consist of requests from client to server and responses
1340   from server to client.
1341</t>
1342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1343  HTTP-message   = Request | Response     ; HTTP/1.1 messages
1344</artwork></figure>
1345<t>
1346   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1347   message format of <xref target="RFC2822"/> for transferring entities (the payload
1348   of the message). Both types of message consist of a start-line, zero
1349   or more header fields (also known as "headers"), an empty line (i.e.,
1350   a line with nothing preceding the CRLF) indicating the end of the
1351   header fields, and possibly a message-body.
1352</t>
1353<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1354  generic-message = start-line
1355                    *(message-header CRLF)
1356                    CRLF
1357                    [ message-body ]
1358  start-line      = Request-Line | Status-Line
1359</artwork></figure>
1360<t>
1361   In the interest of robustness, servers &SHOULD; ignore any empty
1362   line(s) received where a Request-Line is expected. In other words, if
1363   the server is reading the protocol stream at the beginning of a
1364   message and receives a CRLF first, it should ignore the CRLF.
1365</t>
1366<t>
1367   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1368   after a POST request. To restate what is explicitly forbidden by the
1369   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1370   extra CRLF.
1371</t>
1372</section>
1373
1374<section title="Message Headers" anchor="message.headers">
1375<t>
1376   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1377   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1378   entity-header (&entity-header-fields;) fields, follow the same generic format as
1379   that given in <xref target="RFC2822" x:fmt="of" x:sec="2.1"/>. Each header field consists
1380   of a name followed by a colon (":") and the field value. Field names
1381   are case-insensitive. The field value &MAY; be preceded by any amount
1382   of LWS, though a single SP is preferred. Header fields can be
1383   extended over multiple lines by preceding each extra line with at
1384   least one SP or HTAB. Applications ought to follow "common form", where
1385   one is known or indicated, when generating HTTP constructs, since
1386   there might exist some implementations that fail to accept anything
1387   beyond the common forms.
1388</t>
1389<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"/>
1390  message-header = field-name ":" [ field-value ]
1391  field-name     = token
1392  field-value    = *( field-content | LWS )
1393  field-content  = &lt;field content>
1394                   ; the OCTETs making up the field-value
1395                   ; and consisting of either *TEXT or combinations
1396                   ; of token, separators, and quoted-string
1397</artwork></figure>
1398<t>
1399   The field-content does not include any leading or trailing LWS:
1400   linear white space occurring before the first non-whitespace
1401   character of the field-value or after the last non-whitespace
1402   character of the field-value. Such leading or trailing LWS &MAY; be
1403   removed without changing the semantics of the field value. Any LWS
1404   that occurs between field-content &MAY; be replaced with a single SP
1405   before interpreting the field value or forwarding the message
1406   downstream.
1407</t>
1408<t>
1409   The order in which header fields with differing field names are
1410   received is not significant. However, it is "good practice" to send
1411   general-header fields first, followed by request-header or response-header
1412   fields, and ending with the entity-header fields.
1413</t>
1414<t>
1415   Multiple message-header fields with the same field-name &MAY; be
1416   present in a message if and only if the entire field-value for that
1417   header field is defined as a comma-separated list [i.e., #(values)].
1418   It &MUST; be possible to combine the multiple header fields into one
1419   "field-name: field-value" pair, without changing the semantics of the
1420   message, by appending each subsequent field-value to the first, each
1421   separated by a comma. The order in which header fields with the same
1422   field-name are received is therefore significant to the
1423   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1424   change the order of these field values when a message is forwarded.
1425</t>
1426</section>
1427
1428<section title="Message Body" anchor="message.body">
1429<t>
1430   The message-body (if any) of an HTTP message is used to carry the
1431   entity-body associated with the request or response. The message-body
1432   differs from the entity-body only when a transfer-coding has been
1433   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1434</t>
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1436  message-body = entity-body
1437               | &lt;entity-body encoded as per Transfer-Encoding&gt;
1438</artwork></figure>
1439<t>
1440   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1441   applied by an application to ensure safe and proper transfer of the
1442   message. Transfer-Encoding is a property of the message, not of the
1443   entity, and thus &MAY; be added or removed by any application along the
1444   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1445   when certain transfer-codings may be used.)
1446</t>
1447<t>
1448   The rules for when a message-body is allowed in a message differ for
1449   requests and responses.
1450</t>
1451<t>
1452   The presence of a message-body in a request is signaled by the
1453   inclusion of a Content-Length or Transfer-Encoding header field in
1454   the request's message-headers. A message-body &MUST-NOT; be included in
1455   a request if the specification of the request method (&method;)
1456   explicitly disallows an entity-body in requests.
1457   When a request message contains both a message-body of non-zero
1458   length and a method that does not define any semantics for that
1459   request message-body, then an origin server &SHOULD; either ignore
1460   the message-body or respond with an appropriate error message
1461   (e.g., 413).  A proxy or gateway, when presented the same request,
1462   &SHOULD; either forward the request inbound with the message-body or
1463   ignore the message-body when determining a response.
1464</t>
1465<t>
1466   For response messages, whether or not a message-body is included with
1467   a message is dependent on both the request method and the response
1468   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1469   &MUST-NOT; include a message-body, even though the presence of entity-header
1470   fields might lead one to believe they do. All 1xx
1471   (informational), 204 (No Content), and 304 (Not Modified) responses
1472   &MUST-NOT; include a message-body. All other responses do include a
1473   message-body, although it &MAY; be of zero length.
1474</t>
1475</section>
1476
1477<section title="Message Length" anchor="message.length">
1478<t>
1479   The transfer-length of a message is the length of the message-body as
1480   it appears in the message; that is, after any transfer-codings have
1481   been applied. When a message-body is included with a message, the
1482   transfer-length of that body is determined by one of the following
1483   (in order of precedence):
1484</t>
1485<t>
1486  <list style="numbers">
1487    <x:lt><t>
1488     Any response message which "&MUST-NOT;" include a message-body (such
1489     as the 1xx, 204, and 304 responses and any response to a HEAD
1490     request) is always terminated by the first empty line after the
1491     header fields, regardless of the entity-header fields present in
1492     the message.
1493    </t></x:lt>
1494    <x:lt><t>
1495     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1496     is present, then the transfer-length is
1497     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1498     unless the message is terminated by closing the connection.
1499    </t></x:lt>
1500    <x:lt><t>
1501     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1502     decimal value in OCTETs represents both the entity-length and the
1503     transfer-length. The Content-Length header field &MUST-NOT; be sent
1504     if these two lengths are different (i.e., if a Transfer-Encoding
1505     header field is present). If a message is received with both a
1506     Transfer-Encoding header field and a Content-Length header field,
1507     the latter &MUST; be ignored.
1508    </t></x:lt>
1509    <x:lt><t>
1510     If the message uses the media type "multipart/byteranges", and the
1511     transfer-length is not otherwise specified, then this self-delimiting
1512     media type defines the transfer-length. This media type
1513     &MUST-NOT; be used unless the sender knows that the recipient can parse
1514     it; the presence in a request of a Range header with multiple byte-range
1515     specifiers from a 1.1 client implies that the client can parse
1516     multipart/byteranges responses.
1517    <list style="empty"><t>
1518       A range header might be forwarded by a 1.0 proxy that does not
1519       understand multipart/byteranges; in this case the server &MUST;
1520       delimit the message using methods defined in items 1, 3 or 5 of
1521       this section.
1522    </t></list>
1523    </t></x:lt>
1524    <x:lt><t>
1525     By the server closing the connection. (Closing the connection
1526     cannot be used to indicate the end of a request body, since that
1527     would leave no possibility for the server to send back a response.)
1528    </t></x:lt>
1529  </list>
1530</t>
1531<t>
1532   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1533   containing a message-body &MUST; include a valid Content-Length header
1534   field unless the server is known to be HTTP/1.1 compliant. If a
1535   request contains a message-body and a Content-Length is not given,
1536   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1537   determine the length of the message, or with 411 (Length Required) if
1538   it wishes to insist on receiving a valid Content-Length.
1539</t>
1540<t>
1541   All HTTP/1.1 applications that receive entities &MUST; accept the
1542   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1543   to be used for messages when the message length cannot be determined
1544   in advance.
1545</t>
1546<t>
1547   Messages &MUST-NOT; include both a Content-Length header field and a
1548   transfer-coding. If the message does include a
1549   transfer-coding, the Content-Length &MUST; be ignored.
1550</t>
1551<t>
1552   When a Content-Length is given in a message where a message-body is
1553   allowed, its field value &MUST; exactly match the number of OCTETs in
1554   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1555   invalid length is received and detected.
1556</t>
1557</section>
1558
1559<section title="General Header Fields" anchor="general.header.fields">
1560<t>
1561   There are a few header fields which have general applicability for
1562   both request and response messages, but which do not apply to the
1563   entity being transferred. These header fields apply only to the
1564   message being transmitted.
1565</t>
1566<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1567  general-header = Cache-Control            ; &header-cache-control;
1568                 | Connection               ; <xref target="header.connection"/>
1569                 | Date                     ; <xref target="header.date"/>
1570                 | Pragma                   ; &header-pragma;
1571                 | Trailer                  ; <xref target="header.trailer"/>
1572                 | Transfer-Encoding        ; <xref target="header.transfer-encoding"/>
1573                 | Upgrade                  ; <xref target="header.upgrade"/>
1574                 | Via                      ; <xref target="header.via"/>
1575                 | Warning                  ; &header-warning;
1576</artwork></figure>
1577<t>
1578   General-header field names can be extended reliably only in
1579   combination with a change in the protocol version. However, new or
1580   experimental header fields may be given the semantics of general
1581   header fields if all parties in the communication recognize them to
1582   be general-header fields. Unrecognized header fields are treated as
1583   entity-header fields.
1584</t>
1585</section>
1586</section>
1587
1588<section title="Request" anchor="request">
1589<t>
1590   A request message from a client to a server includes, within the
1591   first line of that message, the method to be applied to the resource,
1592   the identifier of the resource, and the protocol version in use.
1593</t>
1594<!--                 Host                      ; should be moved here eventually -->
1595<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1596  Request       = Request-Line              ; <xref target="request-line"/>
1597                  *(( general-header        ; <xref target="general.header.fields"/>
1598                   | request-header         ; &request-header-fields;
1599                   | entity-header ) CRLF)  ; &entity-header-fields;
1600                  CRLF
1601                  [ message-body ]          ; <xref target="message.body"/>
1602</artwork></figure>
1603
1604<section title="Request-Line" anchor="request-line">
1605<t>
1606   The Request-Line begins with a method token, followed by the
1607   Request-URI and the protocol version, and ending with CRLF. The
1608   elements are separated by SP characters. No CR or LF is allowed
1609   except in the final CRLF sequence.
1610</t>
1611<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1612  Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1613</artwork></figure>
1614
1615<section title="Method" anchor="method">
1616<t>
1617   The Method  token indicates the method to be performed on the
1618   resource identified by the Request-URI. The method is case-sensitive.
1619</t>
1620<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1621  Method         = token
1622</artwork></figure>
1623</section>
1624
1625<section title="Request-URI" anchor="request-uri">
1626<t>
1627   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1628   identifies the resource upon which to apply the request.
1629</t>
1630<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1631  Request-URI    = "*"
1632                 | absoluteURI
1633                 | ( path-absolute [ "?" query ] )
1634                 | authority
1635</artwork></figure>
1636<t>
1637   The four options for Request-URI are dependent on the nature of the
1638   request. The asterisk "*" means that the request does not apply to a
1639   particular resource, but to the server itself, and is only allowed
1640   when the method used does not necessarily apply to a resource. One
1641   example would be
1642</t>
1643<figure><artwork type="example">
1644    OPTIONS * HTTP/1.1
1645</artwork></figure>
1646<t>
1647   The absoluteURI form is &REQUIRED; when the request is being made to a
1648   proxy. The proxy is requested to forward the request or service it
1649   from a valid cache, and return the response. Note that the proxy &MAY;
1650   forward the request on to another proxy or directly to the server
1651   specified by the absoluteURI. In order to avoid request loops, a
1652   proxy &MUST; be able to recognize all of its server names, including
1653   any aliases, local variations, and the numeric IP address. An example
1654   Request-Line would be:
1655</t>
1656<figure><artwork type="example">
1657    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1658</artwork></figure>
1659<t>
1660   To allow for transition to absoluteURIs in all requests in future
1661   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1662   form in requests, even though HTTP/1.1 clients will only generate
1663   them in requests to proxies.
1664</t>
1665<t>
1666   The authority form is only used by the CONNECT method (&CONNECT;).
1667</t>
1668<t>
1669   The most common form of Request-URI is that used to identify a
1670   resource on an origin server or gateway. In this case the absolute
1671   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1672   the Request-URI, and the network location of the URI (authority) &MUST;
1673   be transmitted in a Host header field. For example, a client wishing
1674   to retrieve the resource above directly from the origin server would
1675   create a TCP connection to port 80 of the host "www.example.org" and send
1676   the lines:
1677</t>
1678<figure><artwork type="example">
1679    GET /pub/WWW/TheProject.html HTTP/1.1
1680    Host: www.example.org
1681</artwork></figure>
1682<t>
1683   followed by the remainder of the Request. Note that the absolute path
1684   cannot be empty; if none is present in the original URI, it &MUST; be
1685   given as "/" (the server root).
1686</t>
1687<t>
1688   The Request-URI is transmitted in the format specified in
1689   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1690   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1691   properly interpret the request. Servers &SHOULD; respond to invalid
1692   Request-URIs with an appropriate status code.
1693</t>
1694<t>
1695   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1696   received Request-URI when forwarding it to the next inbound server,
1697   except as noted above to replace a null path-absolute with "/".
1698</t>
1699<t>
1700  <list><t>
1701      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1702      meaning of the request when the origin server is improperly using
1703      a non-reserved URI character for a reserved purpose.  Implementors
1704      should be aware that some pre-HTTP/1.1 proxies have been known to
1705      rewrite the Request-URI.
1706  </t></list>
1707</t>
1708</section>
1709</section>
1710
1711<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1712<t>
1713   The exact resource identified by an Internet request is determined by
1714   examining both the Request-URI and the Host header field.
1715</t>
1716<t>
1717   An origin server that does not allow resources to differ by the
1718   requested host &MAY; ignore the Host header field value when
1719   determining the resource identified by an HTTP/1.1 request. (But see
1720   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1721   for other requirements on Host support in HTTP/1.1.)
1722</t>
1723<t>
1724   An origin server that does differentiate resources based on the host
1725   requested (sometimes referred to as virtual hosts or vanity host
1726   names) &MUST; use the following rules for determining the requested
1727   resource on an HTTP/1.1 request:
1728  <list style="numbers">
1729    <t>If Request-URI is an absoluteURI, the host is part of the
1730     Request-URI. Any Host header field value in the request &MUST; be
1731     ignored.</t>
1732    <t>If the Request-URI is not an absoluteURI, and the request includes
1733     a Host header field, the host is determined by the Host header
1734     field value.</t>
1735    <t>If the host as determined by rule 1 or 2 is not a valid host on
1736     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1737  </list>
1738</t>
1739<t>
1740   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1741   attempt to use heuristics (e.g., examination of the URI path for
1742   something unique to a particular host) in order to determine what
1743   exact resource is being requested.
1744</t>
1745</section>
1746
1747</section>
1748
1749
1750<section title="Response" anchor="response">
1751<t>
1752   After receiving and interpreting a request message, a server responds
1753   with an HTTP response message.
1754</t>
1755<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1756  Response      = Status-Line               ; <xref target="status-line"/>
1757                  *(( general-header        ; <xref target="general.header.fields"/>
1758                   | response-header        ; &response-header-fields;
1759                   | entity-header ) CRLF)  ; &entity-header-fields;
1760                  CRLF
1761                  [ message-body ]          ; <xref target="message.body"/>
1762</artwork></figure>
1763
1764<section title="Status-Line" anchor="status-line">
1765<t>
1766   The first line of a Response message is the Status-Line, consisting
1767   of the protocol version followed by a numeric status code and its
1768   associated textual phrase, with each element separated by SP
1769   characters. No CR or LF is allowed except in the final CRLF sequence.
1770</t>
1771<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1772  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1773</artwork></figure>
1774
1775<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1776<t>
1777   The Status-Code element is a 3-digit integer result code of the
1778   attempt to understand and satisfy the request. These codes are fully
1779   defined in &status-codes;. The Reason-Phrase is intended to give a short
1780   textual description of the Status-Code. The Status-Code is intended
1781   for use by automata and the Reason-Phrase is intended for the human
1782   user. The client is not required to examine or display the Reason-Phrase.
1783</t>
1784<t>
1785   The first digit of the Status-Code defines the class of response. The
1786   last two digits do not have any categorization role. There are 5
1787   values for the first digit:
1788  <list style="symbols">
1789    <t>
1790      1xx: Informational - Request received, continuing process
1791    </t>
1792    <t>
1793      2xx: Success - The action was successfully received,
1794        understood, and accepted
1795    </t>
1796    <t>
1797      3xx: Redirection - Further action must be taken in order to
1798        complete the request
1799    </t>
1800    <t>
1801      4xx: Client Error - The request contains bad syntax or cannot
1802        be fulfilled
1803    </t>
1804    <t>
1805      5xx: Server Error - The server failed to fulfill an apparently
1806        valid request
1807    </t>
1808  </list>
1809</t>
1810<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"/>
1811  Status-Code    = 3DIGIT
1812  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
1813</artwork></figure>
1814</section>
1815</section>
1816
1817</section>
1818
1819
1820<section title="Connections" anchor="connections">
1821
1822<section title="Persistent Connections" anchor="persistent.connections">
1823
1824<section title="Purpose" anchor="persistent.purpose">
1825<t>
1826   Prior to persistent connections, a separate TCP connection was
1827   established to fetch each URL, increasing the load on HTTP servers
1828   and causing congestion on the Internet. The use of inline images and
1829   other associated data often require a client to make multiple
1830   requests of the same server in a short amount of time. Analysis of
1831   these performance problems and results from a prototype
1832   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1833   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1834   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1835   T/TCP <xref target="Tou1998"/>.
1836</t>
1837<t>
1838   Persistent HTTP connections have a number of advantages:
1839  <list style="symbols">
1840      <t>
1841        By opening and closing fewer TCP connections, CPU time is saved
1842        in routers and hosts (clients, servers, proxies, gateways,
1843        tunnels, or caches), and memory used for TCP protocol control
1844        blocks can be saved in hosts.
1845      </t>
1846      <t>
1847        HTTP requests and responses can be pipelined on a connection.
1848        Pipelining allows a client to make multiple requests without
1849        waiting for each response, allowing a single TCP connection to
1850        be used much more efficiently, with much lower elapsed time.
1851      </t>
1852      <t>
1853        Network congestion is reduced by reducing the number of packets
1854        caused by TCP opens, and by allowing TCP sufficient time to
1855        determine the congestion state of the network.
1856      </t>
1857      <t>
1858        Latency on subsequent requests is reduced since there is no time
1859        spent in TCP's connection opening handshake.
1860      </t>
1861      <t>
1862        HTTP can evolve more gracefully, since errors can be reported
1863        without the penalty of closing the TCP connection. Clients using
1864        future versions of HTTP might optimistically try a new feature,
1865        but if communicating with an older server, retry with old
1866        semantics after an error is reported.
1867      </t>
1868    </list>
1869</t>
1870<t>
1871   HTTP implementations &SHOULD; implement persistent connections.
1872</t>
1873</section>
1874
1875<section title="Overall Operation" anchor="persistent.overall">
1876<t>
1877   A significant difference between HTTP/1.1 and earlier versions of
1878   HTTP is that persistent connections are the default behavior of any
1879   HTTP connection. That is, unless otherwise indicated, the client
1880   &SHOULD; assume that the server will maintain a persistent connection,
1881   even after error responses from the server.
1882</t>
1883<t>
1884   Persistent connections provide a mechanism by which a client and a
1885   server can signal the close of a TCP connection. This signaling takes
1886   place using the Connection header field (<xref target="header.connection"/>). Once a close
1887   has been signaled, the client &MUST-NOT; send any more requests on that
1888   connection.
1889</t>
1890
1891<section title="Negotiation" anchor="persistent.negotiation">
1892<t>
1893   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1894   maintain a persistent connection unless a Connection header including
1895   the connection-token "close" was sent in the request. If the server
1896   chooses to close the connection immediately after sending the
1897   response, it &SHOULD; send a Connection header including the
1898   connection-token close.
1899</t>
1900<t>
1901   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1902   decide to keep it open based on whether the response from a server
1903   contains a Connection header with the connection-token close. In case
1904   the client does not want to maintain a connection for more than that
1905   request, it &SHOULD; send a Connection header including the
1906   connection-token close.
1907</t>
1908<t>
1909   If either the client or the server sends the close token in the
1910   Connection header, that request becomes the last one for the
1911   connection.
1912</t>
1913<t>
1914   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1915   maintained for HTTP versions less than 1.1 unless it is explicitly
1916   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1917   compatibility with HTTP/1.0 clients.
1918</t>
1919<t>
1920   In order to remain persistent, all messages on the connection &MUST;
1921   have a self-defined message length (i.e., one not defined by closure
1922   of the connection), as described in <xref target="message.length"/>.
1923</t>
1924</section>
1925
1926<section title="Pipelining" anchor="pipelining">
1927<t>
1928   A client that supports persistent connections &MAY; "pipeline" its
1929   requests (i.e., send multiple requests without waiting for each
1930   response). A server &MUST; send its responses to those requests in the
1931   same order that the requests were received.
1932</t>
1933<t>
1934   Clients which assume persistent connections and pipeline immediately
1935   after connection establishment &SHOULD; be prepared to retry their
1936   connection if the first pipelined attempt fails. If a client does
1937   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1938   persistent. Clients &MUST; also be prepared to resend their requests if
1939   the server closes the connection before sending all of the
1940   corresponding responses.
1941</t>
1942<t>
1943   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1944   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1945   premature termination of the transport connection could lead to
1946   indeterminate results. A client wishing to send a non-idempotent
1947   request &SHOULD; wait to send that request until it has received the
1948   response status for the previous request.
1949</t>
1950</section>
1951</section>
1952
1953<section title="Proxy Servers" anchor="persistent.proxy">
1954<t>
1955   It is especially important that proxies correctly implement the
1956   properties of the Connection header field as specified in <xref target="header.connection"/>.
1957</t>
1958<t>
1959   The proxy server &MUST; signal persistent connections separately with
1960   its clients and the origin servers (or other proxy servers) that it
1961   connects to. Each persistent connection applies to only one transport
1962   link.
1963</t>
1964<t>
1965   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1966   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1967   discussion of the problems with the Keep-Alive header implemented by
1968   many HTTP/1.0 clients).
1969</t>
1970</section>
1971
1972<section title="Practical Considerations" anchor="persistent.practical">
1973<t>
1974   Servers will usually have some time-out value beyond which they will
1975   no longer maintain an inactive connection. Proxy servers might make
1976   this a higher value since it is likely that the client will be making
1977   more connections through the same server. The use of persistent
1978   connections places no requirements on the length (or existence) of
1979   this time-out for either the client or the server.
1980</t>
1981<t>
1982   When a client or server wishes to time-out it &SHOULD; issue a graceful
1983   close on the transport connection. Clients and servers &SHOULD; both
1984   constantly watch for the other side of the transport close, and
1985   respond to it as appropriate. If a client or server does not detect
1986   the other side's close promptly it could cause unnecessary resource
1987   drain on the network.
1988</t>
1989<t>
1990   A client, server, or proxy &MAY; close the transport connection at any
1991   time. For example, a client might have started to send a new request
1992   at the same time that the server has decided to close the "idle"
1993   connection. From the server's point of view, the connection is being
1994   closed while it was idle, but from the client's point of view, a
1995   request is in progress.
1996</t>
1997<t>
1998   This means that clients, servers, and proxies &MUST; be able to recover
1999   from asynchronous close events. Client software &SHOULD; reopen the
2000   transport connection and retransmit the aborted sequence of requests
2001   without user interaction so long as the request sequence is
2002   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2003   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2004   human operator the choice of retrying the request(s). Confirmation by
2005   user-agent software with semantic understanding of the application
2006   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2007   be repeated if the second sequence of requests fails.
2008</t>
2009<t>
2010   Servers &SHOULD; always respond to at least one request per connection,
2011   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2012   middle of transmitting a response, unless a network or client failure
2013   is suspected.
2014</t>
2015<t>
2016   Clients that use persistent connections &SHOULD; limit the number of
2017   simultaneous connections that they maintain to a given server. A
2018   single-user client &SHOULD-NOT; maintain more than 2 connections with
2019   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2020   another server or proxy, where N is the number of simultaneously
2021   active users. These guidelines are intended to improve HTTP response
2022   times and avoid congestion.
2023</t>
2024</section>
2025</section>
2026
2027<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2028
2029<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2030<t>
2031   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2032   flow control mechanisms to resolve temporary overloads, rather than
2033   terminating connections with the expectation that clients will retry.
2034   The latter technique can exacerbate network congestion.
2035</t>
2036</section>
2037
2038<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2039<t>
2040   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2041   the network connection for an error status while it is transmitting
2042   the request. If the client sees an error status, it &SHOULD;
2043   immediately cease transmitting the body. If the body is being sent
2044   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2045   empty trailer &MAY; be used to prematurely mark the end of the message.
2046   If the body was preceded by a Content-Length header, the client &MUST;
2047   close the connection.
2048</t>
2049</section>
2050
2051<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2052<t>
2053   The purpose of the 100 (Continue) status (see &status-100;) is to
2054   allow a client that is sending a request message with a request body
2055   to determine if the origin server is willing to accept the request
2056   (based on the request headers) before the client sends the request
2057   body. In some cases, it might either be inappropriate or highly
2058   inefficient for the client to send the body if the server will reject
2059   the message without looking at the body.
2060</t>
2061<t>
2062   Requirements for HTTP/1.1 clients:
2063  <list style="symbols">
2064    <t>
2065        If a client will wait for a 100 (Continue) response before
2066        sending the request body, it &MUST; send an Expect request-header
2067        field (&header-expect;) with the "100-continue" expectation.
2068    </t>
2069    <t>
2070        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2071        with the "100-continue" expectation if it does not intend
2072        to send a request body.
2073    </t>
2074  </list>
2075</t>
2076<t>
2077   Because of the presence of older implementations, the protocol allows
2078   ambiguous situations in which a client may send "Expect: 100-continue"
2079   without receiving either a 417 (Expectation Failed) status
2080   or a 100 (Continue) status. Therefore, when a client sends this
2081   header field to an origin server (possibly via a proxy) from which it
2082   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2083   for an indefinite period before sending the request body.
2084</t>
2085<t>
2086   Requirements for HTTP/1.1 origin servers:
2087  <list style="symbols">
2088    <t> Upon receiving a request which includes an Expect request-header
2089        field with the "100-continue" expectation, an origin server &MUST;
2090        either respond with 100 (Continue) status and continue to read
2091        from the input stream, or respond with a final status code. The
2092        origin server &MUST-NOT; wait for the request body before sending
2093        the 100 (Continue) response. If it responds with a final status
2094        code, it &MAY; close the transport connection or it &MAY; continue
2095        to read and discard the rest of the request.  It &MUST-NOT;
2096        perform the requested method if it returns a final status code.
2097    </t>
2098    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2099        the request message does not include an Expect request-header
2100        field with the "100-continue" expectation, and &MUST-NOT; send a
2101        100 (Continue) response if such a request comes from an HTTP/1.0
2102        (or earlier) client. There is an exception to this rule: for
2103        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2104        status in response to an HTTP/1.1 PUT or POST request that does
2105        not include an Expect request-header field with the "100-continue"
2106        expectation. This exception, the purpose of which is
2107        to minimize any client processing delays associated with an
2108        undeclared wait for 100 (Continue) status, applies only to
2109        HTTP/1.1 requests, and not to requests with any other HTTP-version
2110        value.
2111    </t>
2112    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2113        already received some or all of the request body for the
2114        corresponding request.
2115    </t>
2116    <t> An origin server that sends a 100 (Continue) response &MUST;
2117    ultimately send a final status code, once the request body is
2118        received and processed, unless it terminates the transport
2119        connection prematurely.
2120    </t>
2121    <t> If an origin server receives a request that does not include an
2122        Expect request-header field with the "100-continue" expectation,
2123        the request includes a request body, and the server responds
2124        with a final status code before reading the entire request body
2125        from the transport connection, then the server &SHOULD-NOT;  close
2126        the transport connection until it has read the entire request,
2127        or until the client closes the connection. Otherwise, the client
2128        might not reliably receive the response message. However, this
2129        requirement is not be construed as preventing a server from
2130        defending itself against denial-of-service attacks, or from
2131        badly broken client implementations.
2132      </t>
2133    </list>
2134</t>
2135<t>
2136   Requirements for HTTP/1.1 proxies:
2137  <list style="symbols">
2138    <t> If a proxy receives a request that includes an Expect request-header
2139        field with the "100-continue" expectation, and the proxy
2140        either knows that the next-hop server complies with HTTP/1.1 or
2141        higher, or does not know the HTTP version of the next-hop
2142        server, it &MUST; forward the request, including the Expect header
2143        field.
2144    </t>
2145    <t> If the proxy knows that the version of the next-hop server is
2146        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2147        respond with a 417 (Expectation Failed) status.
2148    </t>
2149    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2150        numbers received from recently-referenced next-hop servers.
2151    </t>
2152    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2153        request message was received from an HTTP/1.0 (or earlier)
2154        client and did not include an Expect request-header field with
2155        the "100-continue" expectation. This requirement overrides the
2156        general rule for forwarding of 1xx responses (see &status-1xx;).
2157    </t>
2158  </list>
2159</t>
2160</section>
2161
2162<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2163<t>
2164   If an HTTP/1.1 client sends a request which includes a request body,
2165   but which does not include an Expect request-header field with the
2166   "100-continue" expectation, and if the client is not directly
2167   connected to an HTTP/1.1 origin server, and if the client sees the
2168   connection close before receiving any status from the server, the
2169   client &SHOULD; retry the request.  If the client does retry this
2170   request, it &MAY; use the following "binary exponential backoff"
2171   algorithm to be assured of obtaining a reliable response:
2172  <list style="numbers">
2173    <t>
2174      Initiate a new connection to the server
2175    </t>
2176    <t>
2177      Transmit the request-headers
2178    </t>
2179    <t>
2180      Initialize a variable R to the estimated round-trip time to the
2181         server (e.g., based on the time it took to establish the
2182         connection), or to a constant value of 5 seconds if the round-trip
2183         time is not available.
2184    </t>
2185    <t>
2186       Compute T = R * (2**N), where N is the number of previous
2187         retries of this request.
2188    </t>
2189    <t>
2190       Wait either for an error response from the server, or for T
2191         seconds (whichever comes first)
2192    </t>
2193    <t>
2194       If no error response is received, after T seconds transmit the
2195         body of the request.
2196    </t>
2197    <t>
2198       If client sees that the connection is closed prematurely,
2199         repeat from step 1 until the request is accepted, an error
2200         response is received, or the user becomes impatient and
2201         terminates the retry process.
2202    </t>
2203  </list>
2204</t>
2205<t>
2206   If at any point an error status is received, the client
2207  <list style="symbols">
2208      <t>&SHOULD-NOT;  continue and</t>
2209
2210      <t>&SHOULD; close the connection if it has not completed sending the
2211        request message.</t>
2212    </list>
2213</t>
2214</section>
2215</section>
2216</section>
2217
2218
2219<section title="Header Field Definitions" anchor="header.fields">
2220<t>
2221   This section defines the syntax and semantics of HTTP/1.1 header fields
2222   related to message framing and transport protocols.
2223</t>
2224<t>
2225   For entity-header fields, both sender and recipient refer to either the
2226   client or the server, depending on who sends and who receives the entity.
2227</t>
2228
2229<section title="Connection" anchor="header.connection">
2230  <iref primary="true" item="Connection header" x:for-anchor=""/>
2231  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2232<t>
2233   The Connection general-header field allows the sender to specify
2234   options that are desired for that particular connection and &MUST-NOT;
2235   be communicated by proxies over further connections.
2236</t>
2237<t>
2238   The Connection header has the following grammar:
2239</t>
2240<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2241  Connection = "Connection" ":" 1#(connection-token)
2242  connection-token  = token
2243</artwork></figure>
2244<t>
2245   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2246   message is forwarded and, for each connection-token in this field,
2247   remove any header field(s) from the message with the same name as the
2248   connection-token. Connection options are signaled by the presence of
2249   a connection-token in the Connection header field, not by any
2250   corresponding additional header field(s), since the additional header
2251   field may not be sent if there are no parameters associated with that
2252   connection option.
2253</t>
2254<t>
2255   Message headers listed in the Connection header &MUST-NOT; include
2256   end-to-end headers, such as Cache-Control.
2257</t>
2258<t>
2259   HTTP/1.1 defines the "close" connection option for the sender to
2260   signal that the connection will be closed after completion of the
2261   response. For example,
2262</t>
2263<figure><artwork type="example">
2264    Connection: close
2265</artwork></figure>
2266<t>
2267   in either the request or the response header fields indicates that
2268   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2269   after the current request/response is complete.
2270</t>
2271<t>
2272   An HTTP/1.1 client that does not support persistent connections &MUST;
2273   include the "close" connection option in every request message.
2274</t>
2275<t>
2276   An HTTP/1.1 server that does not support persistent connections &MUST;
2277   include the "close" connection option in every response message that
2278   does not have a 1xx (informational) status code.
2279</t>
2280<t>
2281   A system receiving an HTTP/1.0 (or lower-version) message that
2282   includes a Connection header &MUST;, for each connection-token in this
2283   field, remove and ignore any header field(s) from the message with
2284   the same name as the connection-token. This protects against mistaken
2285   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2286</t>
2287</section>
2288
2289<section title="Content-Length" anchor="header.content-length">
2290  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2291  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2292<t>
2293   The Content-Length entity-header field indicates the size of the
2294   entity-body, in decimal number of OCTETs, sent to the recipient or,
2295   in the case of the HEAD method, the size of the entity-body that
2296   would have been sent had the request been a GET.
2297</t>
2298<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2299  Content-Length    = "Content-Length" ":" 1*DIGIT
2300</artwork></figure>
2301<t>
2302   An example is
2303</t>
2304<figure><artwork type="example">
2305    Content-Length: 3495
2306</artwork></figure>
2307<t>
2308   Applications &SHOULD; use this field to indicate the transfer-length of
2309   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2310</t>
2311<t>
2312   Any Content-Length greater than or equal to zero is a valid value.
2313   <xref target="message.length"/> describes how to determine the length of a message-body
2314   if a Content-Length is not given.
2315</t>
2316<t>
2317   Note that the meaning of this field is significantly different from
2318   the corresponding definition in MIME, where it is an optional field
2319   used within the "message/external-body" content-type. In HTTP, it
2320   &SHOULD; be sent whenever the message's length can be determined prior
2321   to being transferred, unless this is prohibited by the rules in
2322   <xref target="message.length"/>.
2323</t>
2324</section>
2325
2326<section title="Date" anchor="header.date">
2327  <iref primary="true" item="Date header" x:for-anchor=""/>
2328  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2329<t>
2330   The Date general-header field represents the date and time at which
2331   the message was originated, having the same semantics as orig-date in
2332   <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"/>;
2333   it &MUST; be sent in rfc1123-date format.
2334</t>
2335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2336  Date  = "Date" ":" HTTP-date
2337</artwork></figure>
2338<t>
2339   An example is
2340</t>
2341<figure><artwork type="example">
2342    Date: Tue, 15 Nov 1994 08:12:31 GMT
2343</artwork></figure>
2344<t>
2345   Origin servers &MUST; include a Date header field in all responses,
2346   except in these cases:
2347  <list style="numbers">
2348      <t>If the response status code is 100 (Continue) or 101 (Switching
2349         Protocols), the response &MAY; include a Date header field, at
2350         the server's option.</t>
2351
2352      <t>If the response status code conveys a server error, e.g. 500
2353         (Internal Server Error) or 503 (Service Unavailable), and it is
2354         inconvenient or impossible to generate a valid Date.</t>
2355
2356      <t>If the server does not have a clock that can provide a
2357         reasonable approximation of the current time, its responses
2358         &MUST-NOT; include a Date header field. In this case, the rules
2359         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2360  </list>
2361</t>
2362<t>
2363   A received message that does not have a Date header field &MUST; be
2364   assigned one by the recipient if the message will be cached by that
2365   recipient or gatewayed via a protocol which requires a Date. An HTTP
2366   implementation without a clock &MUST-NOT; cache responses without
2367   revalidating them on every use. An HTTP cache, especially a shared
2368   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2369   clock with a reliable external standard.
2370</t>
2371<t>
2372   Clients &SHOULD; only send a Date header field in messages that include
2373   an entity-body, as in the case of the PUT and POST requests, and even
2374   then it is optional. A client without a clock &MUST-NOT; send a Date
2375   header field in a request.
2376</t>
2377<t>
2378   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2379   time subsequent to the generation of the message. It &SHOULD; represent
2380   the best available approximation of the date and time of message
2381   generation, unless the implementation has no means of generating a
2382   reasonably accurate date and time. In theory, the date ought to
2383   represent the moment just before the entity is generated. In
2384   practice, the date can be generated at any time during the message
2385   origination without affecting its semantic value.
2386</t>
2387
2388<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2389<t>
2390   Some origin server implementations might not have a clock available.
2391   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2392   values to a response, unless these values were associated
2393   with the resource by a system or user with a reliable clock. It &MAY;
2394   assign an Expires value that is known, at or before server
2395   configuration time, to be in the past (this allows "pre-expiration"
2396   of responses without storing separate Expires values for each
2397   resource).
2398</t>
2399</section>
2400</section>
2401
2402<section title="Host" anchor="header.host">
2403  <iref primary="true" item="Host header" x:for-anchor=""/>
2404  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2405<t>
2406   The Host request-header field specifies the Internet host and port
2407   number of the resource being requested, as obtained from the original
2408   URI given by the user or referring resource (generally an HTTP URL,
2409   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2410   the naming authority of the origin server or gateway given by the
2411   original URL. This allows the origin server or gateway to
2412   differentiate between internally-ambiguous URLs, such as the root "/"
2413   URL of a server for multiple host names on a single IP address.
2414</t>
2415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2416  Host = "Host" ":" uri-host [ ":" port ] ; <xref target="http.url"/>
2417</artwork></figure>
2418<t>
2419   A "host" without any trailing port information implies the default
2420   port for the service requested (e.g., "80" for an HTTP URL). For
2421   example, a request on the origin server for
2422   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2423</t>
2424<figure><artwork type="example">
2425    GET /pub/WWW/ HTTP/1.1
2426    Host: www.example.org
2427</artwork></figure>
2428<t>
2429   A client &MUST; include a Host header field in all HTTP/1.1 request
2430   messages. If the requested URI does not include an Internet host
2431   name for the service being requested, then the Host header field &MUST;
2432   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2433   request message it forwards does contain an appropriate Host header
2434   field that identifies the service being requested by the proxy. All
2435   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2436   status code to any HTTP/1.1 request message which lacks a Host header
2437   field.
2438</t>
2439<t>
2440   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2441   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2442   for other requirements relating to Host.
2443</t>
2444</section>
2445
2446<section title="TE" anchor="header.te">
2447  <iref primary="true" item="TE header" x:for-anchor=""/>
2448  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2449<t>
2450   The TE request-header field indicates what extension transfer-codings
2451   it is willing to accept in the response and whether or not it is
2452   willing to accept trailer fields in a chunked transfer-coding. Its
2453   value may consist of the keyword "trailers" and/or a comma-separated
2454   list of extension transfer-coding names with optional accept
2455   parameters (as described in <xref target="transfer.codings"/>).
2456</t>
2457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2458  TE        = "TE" ":" #( t-codings )
2459  t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2460</artwork></figure>
2461<t>
2462   The presence of the keyword "trailers" indicates that the client is
2463   willing to accept trailer fields in a chunked transfer-coding, as
2464   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2465   transfer-coding values even though it does not itself represent a
2466   transfer-coding.
2467</t>
2468<t>
2469   Examples of its use are:
2470</t>
2471<figure><artwork type="example">
2472    TE: deflate
2473    TE:
2474    TE: trailers, deflate;q=0.5
2475</artwork></figure>
2476<t>
2477   The TE header field only applies to the immediate connection.
2478   Therefore, the keyword &MUST; be supplied within a Connection header
2479   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2480</t>
2481<t>
2482   A server tests whether a transfer-coding is acceptable, according to
2483   a TE field, using these rules:
2484  <list style="numbers">
2485    <x:lt>
2486      <t>The "chunked" transfer-coding is always acceptable. If the
2487         keyword "trailers" is listed, the client indicates that it is
2488         willing to accept trailer fields in the chunked response on
2489         behalf of itself and any downstream clients. The implication is
2490         that, if given, the client is stating that either all
2491         downstream clients are willing to accept trailer fields in the
2492         forwarded response, or that it will attempt to buffer the
2493         response on behalf of downstream recipients.
2494      </t><t>
2495         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2496         chunked response such that a client can be assured of buffering
2497         the entire response.</t>
2498    </x:lt>
2499    <x:lt>
2500      <t>If the transfer-coding being tested is one of the transfer-codings
2501         listed in the TE field, then it is acceptable unless it
2502         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2503         qvalue of 0 means "not acceptable.")</t>
2504    </x:lt>
2505    <x:lt>
2506      <t>If multiple transfer-codings are acceptable, then the
2507         acceptable transfer-coding with the highest non-zero qvalue is
2508         preferred.  The "chunked" transfer-coding always has a qvalue
2509         of 1.</t>
2510    </x:lt>
2511  </list>
2512</t>
2513<t>
2514   If the TE field-value is empty or if no TE field is present, the only
2515   transfer-coding  is "chunked". A message with no transfer-coding is
2516   always acceptable.
2517</t>
2518</section>
2519
2520<section title="Trailer" anchor="header.trailer">
2521  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2522  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2523<t>
2524   The Trailer general field value indicates that the given set of
2525   header fields is present in the trailer of a message encoded with
2526   chunked transfer-coding.
2527</t>
2528<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2529  Trailer  = "Trailer" ":" 1#field-name
2530</artwork></figure>
2531<t>
2532   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2533   message using chunked transfer-coding with a non-empty trailer. Doing
2534   so allows the recipient to know which header fields to expect in the
2535   trailer.
2536</t>
2537<t>
2538   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2539   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2540   trailer fields in a "chunked" transfer-coding.
2541</t>
2542<t>
2543   Message header fields listed in the Trailer header field &MUST-NOT;
2544   include the following header fields:
2545  <list style="symbols">
2546    <t>Transfer-Encoding</t>
2547    <t>Content-Length</t>
2548    <t>Trailer</t>
2549  </list>
2550</t>
2551</section>
2552
2553<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2554  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2555  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2556<t>
2557   The Transfer-Encoding general-header field indicates what (if any)
2558   type of transformation has been applied to the message body in order
2559   to safely transfer it between the sender and the recipient. This
2560   differs from the content-coding in that the transfer-coding is a
2561   property of the message, not of the entity.
2562</t>
2563<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2564  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2565</artwork></figure>
2566<t>
2567   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2568</t>
2569<figure><artwork type="example">
2570  Transfer-Encoding: chunked
2571</artwork></figure>
2572<t>
2573   If multiple encodings have been applied to an entity, the transfer-codings
2574   &MUST; be listed in the order in which they were applied.
2575   Additional information about the encoding parameters &MAY; be provided
2576   by other entity-header fields not defined by this specification.
2577</t>
2578<t>
2579   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2580   header.
2581</t>
2582</section>
2583
2584<section title="Upgrade" anchor="header.upgrade">
2585  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2586  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2587<t>
2588   The Upgrade general-header allows the client to specify what
2589   additional communication protocols it supports and would like to use
2590   if the server finds it appropriate to switch protocols. The server
2591   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2592   response to indicate which protocol(s) are being switched.
2593</t>
2594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2595  Upgrade        = "Upgrade" ":" 1#product
2596</artwork></figure>
2597<t>
2598   For example,
2599</t>
2600<figure><artwork type="example">
2601    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2602</artwork></figure>
2603<t>
2604   The Upgrade header field is intended to provide a simple mechanism
2605   for transition from HTTP/1.1 to some other, incompatible protocol. It
2606   does so by allowing the client to advertise its desire to use another
2607   protocol, such as a later version of HTTP with a higher major version
2608   number, even though the current request has been made using HTTP/1.1.
2609   This eases the difficult transition between incompatible protocols by
2610   allowing the client to initiate a request in the more commonly
2611   supported protocol while indicating to the server that it would like
2612   to use a "better" protocol if available (where "better" is determined
2613   by the server, possibly according to the nature of the method and/or
2614   resource being requested).
2615</t>
2616<t>
2617   The Upgrade header field only applies to switching application-layer
2618   protocols upon the existing transport-layer connection. Upgrade
2619   cannot be used to insist on a protocol change; its acceptance and use
2620   by the server is optional. The capabilities and nature of the
2621   application-layer communication after the protocol change is entirely
2622   dependent upon the new protocol chosen, although the first action
2623   after changing the protocol &MUST; be a response to the initial HTTP
2624   request containing the Upgrade header field.
2625</t>
2626<t>
2627   The Upgrade header field only applies to the immediate connection.
2628   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2629   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2630   HTTP/1.1 message.
2631</t>
2632<t>
2633   The Upgrade header field cannot be used to indicate a switch to a
2634   protocol on a different connection. For that purpose, it is more
2635   appropriate to use a 301, 302, 303, or 305 redirection response.
2636</t>
2637<t>
2638   This specification only defines the protocol name "HTTP" for use by
2639   the family of Hypertext Transfer Protocols, as defined by the HTTP
2640   version rules of <xref target="http.version"/> and future updates to this
2641   specification. Any token can be used as a protocol name; however, it
2642   will only be useful if both the client and server associate the name
2643   with the same protocol.
2644</t>
2645</section>
2646
2647<section title="Via" anchor="header.via">
2648  <iref primary="true" item="Via header" x:for-anchor=""/>
2649  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2650<t>
2651   The Via general-header field &MUST; be used by gateways and proxies to
2652   indicate the intermediate protocols and recipients between the user
2653   agent and the server on requests, and between the origin server and
2654   the client on responses. It is analogous to the "Received" field of
2655   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2656   avoiding request loops, and identifying the protocol capabilities of
2657   all senders along the request/response chain.
2658</t>
2659<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"/>
2660  Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2661  received-protocol = [ protocol-name "/" ] protocol-version
2662  protocol-name     = token
2663  protocol-version  = token
2664  received-by       = ( uri-host [ ":" port ] ) | pseudonym
2665  pseudonym         = token
2666</artwork></figure>
2667<t>
2668   The received-protocol indicates the protocol version of the message
2669   received by the server or client along each segment of the
2670   request/response chain. The received-protocol version is appended to
2671   the Via field value when the message is forwarded so that information
2672   about the protocol capabilities of upstream applications remains
2673   visible to all recipients.
2674</t>
2675<t>
2676   The protocol-name is optional if and only if it would be "HTTP". The
2677   received-by field is normally the host and optional port number of a
2678   recipient server or client that subsequently forwarded the message.
2679   However, if the real host is considered to be sensitive information,
2680   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2681   be assumed to be the default port of the received-protocol.
2682</t>
2683<t>
2684   Multiple Via field values represents each proxy or gateway that has
2685   forwarded the message. Each recipient &MUST; append its information
2686   such that the end result is ordered according to the sequence of
2687   forwarding applications.
2688</t>
2689<t>
2690   Comments &MAY; be used in the Via header field to identify the software
2691   of the recipient proxy or gateway, analogous to the User-Agent and
2692   Server header fields. However, all comments in the Via field are
2693   optional and &MAY; be removed by any recipient prior to forwarding the
2694   message.
2695</t>
2696<t>
2697   For example, a request message could be sent from an HTTP/1.0 user
2698   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2699   forward the request to a public proxy at p.example.net, which completes
2700   the request by forwarding it to the origin server at www.example.com.
2701   The request received by www.example.com would then have the following
2702   Via header field:
2703</t>
2704<figure><artwork type="example">
2705    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2706</artwork></figure>
2707<t>
2708   Proxies and gateways used as a portal through a network firewall
2709   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2710   the firewall region. This information &SHOULD; only be propagated if
2711   explicitly enabled. If not enabled, the received-by host of any host
2712   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2713   for that host.
2714</t>
2715<t>
2716   For organizations that have strong privacy requirements for hiding
2717   internal structures, a proxy &MAY; combine an ordered subsequence of
2718   Via header field entries with identical received-protocol values into
2719   a single such entry. For example,
2720</t>
2721<figure><artwork type="example">
2722    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2723</artwork></figure>
2724<t>
2725        could be collapsed to
2726</t>
2727<figure><artwork type="example">
2728    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2729</artwork></figure>
2730<t>
2731   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2732   under the same organizational control and the hosts have already been
2733   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2734   have different received-protocol values.
2735</t>
2736</section>
2737
2738</section>
2739
2740<section title="IANA Considerations" anchor="IANA.considerations">
2741<t>
2742   TBD.
2743</t>
2744</section>
2745
2746<section title="Security Considerations" anchor="security.considerations">
2747<t>
2748   This section is meant to inform application developers, information
2749   providers, and users of the security limitations in HTTP/1.1 as
2750   described by this document. The discussion does not include
2751   definitive solutions to the problems revealed, though it does make
2752   some suggestions for reducing security risks.
2753</t>
2754
2755<section title="Personal Information" anchor="personal.information">
2756<t>
2757   HTTP clients are often privy to large amounts of personal information
2758   (e.g. the user's name, location, mail address, passwords, encryption
2759   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2760   leakage of this information.
2761   We very strongly recommend that a convenient interface be provided
2762   for the user to control dissemination of such information, and that
2763   designers and implementors be particularly careful in this area.
2764   History shows that errors in this area often create serious security
2765   and/or privacy problems and generate highly adverse publicity for the
2766   implementor's company.
2767</t>
2768</section>
2769
2770<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2771<t>
2772   A server is in the position to save personal data about a user's
2773   requests which might identify their reading patterns or subjects of
2774   interest. This information is clearly confidential in nature and its
2775   handling can be constrained by law in certain countries. People using
2776   HTTP to provide data are responsible for ensuring that
2777   such material is not distributed without the permission of any
2778   individuals that are identifiable by the published results.
2779</t>
2780</section>
2781
2782<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2783<t>
2784   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2785   the documents returned by HTTP requests to be only those that were
2786   intended by the server administrators. If an HTTP server translates
2787   HTTP URIs directly into file system calls, the server &MUST; take
2788   special care not to serve files that were not intended to be
2789   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2790   other operating systems use ".." as a path component to indicate a
2791   directory level above the current one. On such a system, an HTTP
2792   server &MUST; disallow any such construct in the Request-URI if it
2793   would otherwise allow access to a resource outside those intended to
2794   be accessible via the HTTP server. Similarly, files intended for
2795   reference only internally to the server (such as access control
2796   files, configuration files, and script code) &MUST; be protected from
2797   inappropriate retrieval, since they might contain sensitive
2798   information. Experience has shown that minor bugs in such HTTP server
2799   implementations have turned into security risks.
2800</t>
2801</section>
2802
2803<section title="DNS Spoofing" anchor="dns.spoofing">
2804<t>
2805   Clients using HTTP rely heavily on the Domain Name Service, and are
2806   thus generally prone to security attacks based on the deliberate
2807   mis-association of IP addresses and DNS names. Clients need to be
2808   cautious in assuming the continuing validity of an IP number/DNS name
2809   association.
2810</t>
2811<t>
2812   In particular, HTTP clients &SHOULD; rely on their name resolver for
2813   confirmation of an IP number/DNS name association, rather than
2814   caching the result of previous host name lookups. Many platforms
2815   already can cache host name lookups locally when appropriate, and
2816   they &SHOULD; be configured to do so. It is proper for these lookups to
2817   be cached, however, only when the TTL (Time To Live) information
2818   reported by the name server makes it likely that the cached
2819   information will remain useful.
2820</t>
2821<t>
2822   If HTTP clients cache the results of host name lookups in order to
2823   achieve a performance improvement, they &MUST; observe the TTL
2824   information reported by DNS.
2825</t>
2826<t>
2827   If HTTP clients do not observe this rule, they could be spoofed when
2828   a previously-accessed server's IP address changes. As network
2829   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2830   possibility of this form of attack will grow. Observing this
2831   requirement thus reduces this potential security vulnerability.
2832</t>
2833<t>
2834   This requirement also improves the load-balancing behavior of clients
2835   for replicated servers using the same DNS name and reduces the
2836   likelihood of a user's experiencing failure in accessing sites which
2837   use that strategy.
2838</t>
2839</section>
2840
2841<section title="Proxies and Caching" anchor="attack.proxies">
2842<t>
2843   By their very nature, HTTP proxies are men-in-the-middle, and
2844   represent an opportunity for man-in-the-middle attacks. Compromise of
2845   the systems on which the proxies run can result in serious security
2846   and privacy problems. Proxies have access to security-related
2847   information, personal information about individual users and
2848   organizations, and proprietary information belonging to users and
2849   content providers. A compromised proxy, or a proxy implemented or
2850   configured without regard to security and privacy considerations,
2851   might be used in the commission of a wide range of potential attacks.
2852</t>
2853<t>
2854   Proxy operators should protect the systems on which proxies run as
2855   they would protect any system that contains or transports sensitive
2856   information. In particular, log information gathered at proxies often
2857   contains highly sensitive personal information, and/or information
2858   about organizations. Log information should be carefully guarded, and
2859   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2860</t>
2861<t>
2862   Proxy implementors should consider the privacy and security
2863   implications of their design and coding decisions, and of the
2864   configuration options they provide to proxy operators (especially the
2865   default configuration).
2866</t>
2867<t>
2868   Users of a proxy need to be aware that they are no trustworthier than
2869   the people who run the proxy; HTTP itself cannot solve this problem.
2870</t>
2871<t>
2872   The judicious use of cryptography, when appropriate, may suffice to
2873   protect against a broad range of security and privacy attacks. Such
2874   cryptography is beyond the scope of the HTTP/1.1 specification.
2875</t>
2876</section>
2877
2878<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2879<t>
2880   They exist. They are hard to defend against. Research continues.
2881   Beware.
2882</t>
2883</section>
2884</section>
2885
2886<section title="Acknowledgments" anchor="ack">
2887<t>
2888   This specification makes heavy use of the augmented BNF and generic
2889   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
2890   reuses many of the definitions provided by Nathaniel Borenstein and
2891   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2892   specification will help reduce past confusion over the relationship
2893   between HTTP and Internet mail message formats.
2894</t>
2895<t>
2896   HTTP has evolved considerably over the years. It has
2897   benefited from a large and active developer community--the many
2898   people who have participated on the www-talk mailing list--and it is
2899   that community which has been most responsible for the success of
2900   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2901   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2902   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2903   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2904   VanHeyningen deserve special recognition for their efforts in
2905   defining early aspects of the protocol.
2906</t>
2907<t>
2908   This document has benefited greatly from the comments of all those
2909   participating in the HTTP-WG. In addition to those already mentioned,
2910   the following individuals have contributed to this specification:
2911</t>
2912<t>
2913   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2914   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2915   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2916   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2917   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2918   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2919   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2920   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2921   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2922   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2923   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2924   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2925   Josh Cohen.
2926</t>
2927<t>
2928   Thanks to the "cave men" of Palo Alto. You know who you are.
2929</t>
2930<t>
2931   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2932   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2933   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2934   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2935   Larry Masinter for their help. And thanks go particularly to Jeff
2936   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2937</t>
2938<t>
2939   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2940   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2941   discovery of many of the problems that this document attempts to
2942   rectify.
2943</t>
2944</section>
2945
2946</middle>
2947<back>
2948
2949<references title="Normative References">
2950
2951<reference anchor="ISO-8859-1">
2952  <front>
2953    <title>
2954     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
2955    </title>
2956    <author>
2957      <organization>International Organization for Standardization</organization>
2958    </author>
2959    <date year="1998"/>
2960  </front>
2961  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
2962</reference>
2963
2964<reference anchor="Part2">
2965  <front>
2966    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
2967    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2968      <organization abbrev="Day Software">Day Software</organization>
2969      <address><email>fielding@gbiv.com</email></address>
2970    </author>
2971    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2972      <organization>One Laptop per Child</organization>
2973      <address><email>jg@laptop.org</email></address>
2974    </author>
2975    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2976      <organization abbrev="HP">Hewlett-Packard Company</organization>
2977      <address><email>JeffMogul@acm.org</email></address>
2978    </author>
2979    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2980      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2981      <address><email>henrikn@microsoft.com</email></address>
2982    </author>
2983    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2984      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2985      <address><email>LMM@acm.org</email></address>
2986    </author>
2987    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2988      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2989      <address><email>paulle@microsoft.com</email></address>
2990    </author>
2991    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2992      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2993      <address><email>timbl@w3.org</email></address>
2994    </author>
2995    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2996      <organization abbrev="W3C">World Wide Web Consortium</organization>
2997      <address><email>ylafon@w3.org</email></address>
2998    </author>
2999    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3000      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3001      <address><email>julian.reschke@greenbytes.de</email></address>
3002    </author>
3003    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3004  </front>
3005  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3006  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3007</reference>
3008
3009<reference anchor="Part3">
3010  <front>
3011    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3012    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3013      <organization abbrev="Day Software">Day Software</organization>
3014      <address><email>fielding@gbiv.com</email></address>
3015    </author>
3016    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3017      <organization>One Laptop per Child</organization>
3018      <address><email>jg@laptop.org</email></address>
3019    </author>
3020    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3021      <organization abbrev="HP">Hewlett-Packard Company</organization>
3022      <address><email>JeffMogul@acm.org</email></address>
3023    </author>
3024    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3025      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3026      <address><email>henrikn@microsoft.com</email></address>
3027    </author>
3028    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3029      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3030      <address><email>LMM@acm.org</email></address>
3031    </author>
3032    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3033      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3034      <address><email>paulle@microsoft.com</email></address>
3035    </author>
3036    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3037      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3038      <address><email>timbl@w3.org</email></address>
3039    </author>
3040    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3041      <organization abbrev="W3C">World Wide Web Consortium</organization>
3042      <address><email>ylafon@w3.org</email></address>
3043    </author>
3044    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3045      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3046      <address><email>julian.reschke@greenbytes.de</email></address>
3047    </author>
3048    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3049  </front>
3050  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3051  <x:source href="p3-payload.xml" basename="p3-payload"/>
3052</reference>
3053
3054<reference anchor="Part5">
3055  <front>
3056    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3057    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3058      <organization abbrev="Day Software">Day Software</organization>
3059      <address><email>fielding@gbiv.com</email></address>
3060    </author>
3061    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3062      <organization>One Laptop per Child</organization>
3063      <address><email>jg@laptop.org</email></address>
3064    </author>
3065    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3066      <organization abbrev="HP">Hewlett-Packard Company</organization>
3067      <address><email>JeffMogul@acm.org</email></address>
3068    </author>
3069    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3070      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3071      <address><email>henrikn@microsoft.com</email></address>
3072    </author>
3073    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3074      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3075      <address><email>LMM@acm.org</email></address>
3076    </author>
3077    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3078      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3079      <address><email>paulle@microsoft.com</email></address>
3080    </author>
3081    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3082      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3083      <address><email>timbl@w3.org</email></address>
3084    </author>
3085    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3086      <organization abbrev="W3C">World Wide Web Consortium</organization>
3087      <address><email>ylafon@w3.org</email></address>
3088    </author>
3089    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3090      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3091      <address><email>julian.reschke@greenbytes.de</email></address>
3092    </author>
3093    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3094  </front>
3095  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3096  <x:source href="p5-range.xml" basename="p5-range"/>
3097</reference>
3098
3099<reference anchor="Part6">
3100  <front>
3101    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3102    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3103      <organization abbrev="Day Software">Day Software</organization>
3104      <address><email>fielding@gbiv.com</email></address>
3105    </author>
3106    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3107      <organization>One Laptop per Child</organization>
3108      <address><email>jg@laptop.org</email></address>
3109    </author>
3110    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3111      <organization abbrev="HP">Hewlett-Packard Company</organization>
3112      <address><email>JeffMogul@acm.org</email></address>
3113    </author>
3114    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3115      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3116      <address><email>henrikn@microsoft.com</email></address>
3117    </author>
3118    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3119      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3120      <address><email>LMM@acm.org</email></address>
3121    </author>
3122    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3123      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3124      <address><email>paulle@microsoft.com</email></address>
3125    </author>
3126    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3127      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3128      <address><email>timbl@w3.org</email></address>
3129    </author>
3130    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3131      <organization abbrev="W3C">World Wide Web Consortium</organization>
3132      <address><email>ylafon@w3.org</email></address>
3133    </author>
3134    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3135      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3136      <address><email>julian.reschke@greenbytes.de</email></address>
3137    </author>
3138    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3139  </front>
3140  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3141  <x:source href="p6-cache.xml" basename="p6-cache"/>
3142</reference>
3143
3144<reference anchor="RFC822ABNF">
3145  <front>
3146    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3147    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3148      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3149      <address><email>DCrocker@UDel-Relay</email></address>
3150    </author>
3151    <date month="August" day="13" year="1982"/>
3152  </front>
3153  <seriesInfo name="STD" value="11"/>
3154  <seriesInfo name="RFC" value="822"/>
3155</reference>
3156
3157<reference anchor="RFC2045">
3158  <front>
3159    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3160    <author initials="N." surname="Freed" fullname="Ned Freed">
3161      <organization>Innosoft International, Inc.</organization>
3162      <address><email>ned@innosoft.com</email></address>
3163    </author>
3164    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3165      <organization>First Virtual Holdings</organization>
3166      <address><email>nsb@nsb.fv.com</email></address>
3167    </author>
3168    <date month="November" year="1996"/>
3169  </front>
3170  <seriesInfo name="RFC" value="2045"/>
3171</reference>
3172
3173<reference anchor="RFC2047">
3174  <front>
3175    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3176    <author initials="K." surname="Moore" fullname="Keith Moore">
3177      <organization>University of Tennessee</organization>
3178      <address><email>moore@cs.utk.edu</email></address>
3179    </author>
3180    <date month="November" year="1996"/>
3181  </front>
3182  <seriesInfo name="RFC" value="2047"/>
3183</reference>
3184
3185<reference anchor="RFC2119">
3186  <front>
3187    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3188    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3189      <organization>Harvard University</organization>
3190      <address><email>sob@harvard.edu</email></address>
3191    </author>
3192    <date month="March" year="1997"/>
3193  </front>
3194  <seriesInfo name="BCP" value="14"/>
3195  <seriesInfo name="RFC" value="2119"/>
3196</reference>
3197
3198<reference anchor="RFC2396">
3199  <front>
3200    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3201    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3202      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3203      <address><email>timbl@w3.org</email></address>
3204    </author>
3205    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3206      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3207      <address><email>fielding@ics.uci.edu</email></address>
3208    </author>
3209    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3210      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3211      <address><email>masinter@parc.xerox.com</email></address>
3212    </author>
3213    <date month="August" year="1998"/>
3214  </front>
3215  <seriesInfo name="RFC" value="2396"/>
3216</reference>
3217
3218<reference anchor="RFC4288">
3219  <front>
3220    <title>Media Type Specifications and Registration Procedures</title>
3221    <author initials="N." surname="Freed" fullname="N. Freed">
3222      <organization>Sun Microsystems</organization>
3223      <address>
3224        <email>ned.freed@mrochek.com</email>
3225      </address>
3226    </author>
3227    <author initials="J." surname="Klensin" fullname="J. Klensin">
3228      <organization/>
3229      <address>
3230        <email>klensin+ietf@jck.com</email>
3231      </address>
3232    </author>
3233    <date year="2005" month="December"/>
3234  </front>
3235  <seriesInfo name="BCP" value="13"/>
3236  <seriesInfo name="RFC" value="4288"/>
3237</reference>
3238
3239<reference anchor="USASCII">
3240  <front>
3241    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3242    <author>
3243      <organization>American National Standards Institute</organization>
3244    </author>
3245    <date year="1986"/>
3246  </front>
3247  <seriesInfo name="ANSI" value="X3.4"/>
3248</reference>
3249
3250</references>
3251
3252<references title="Informative References">
3253
3254<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3255  <front>
3256    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3257    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3258      <organization/>
3259    </author>
3260    <author initials="J." surname="Gettys" fullname="J. Gettys">
3261      <organization/>
3262    </author>
3263    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3264      <organization/>
3265    </author>
3266    <author initials="H." surname="Lie" fullname="H. Lie">
3267      <organization/>
3268    </author>
3269    <author initials="C." surname="Lilley" fullname="C. Lilley">
3270      <organization/>
3271    </author>
3272    <date year="1997" month="September"/>
3273  </front>
3274  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3275</reference>
3276
3277<reference anchor="Pad1995">
3278  <front>
3279    <title>Improving HTTP Latency</title>
3280    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3281      <organization/>
3282    </author>
3283    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3284      <organization/>
3285    </author>
3286    <date year="1995" month="December"/>
3287  </front>
3288  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3289  <annotation>
3290    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3291    which is available at <eref target="http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/HTTPLatency.html"/>.
3292  </annotation>
3293</reference>
3294
3295<reference anchor="RFC822">
3296  <front>
3297    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3298    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3299      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3300      <address><email>DCrocker@UDel-Relay</email></address>
3301    </author>
3302    <date month="August" day="13" year="1982"/>
3303  </front>
3304  <seriesInfo name="STD" value="11"/>
3305  <seriesInfo name="RFC" value="822"/>
3306</reference>
3307
3308<reference anchor="RFC959">
3309  <front>
3310    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3311    <author initials="J." surname="Postel" fullname="J. Postel">
3312      <organization>Information Sciences Institute (ISI)</organization>
3313    </author>
3314    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3315      <organization/>
3316    </author>
3317    <date month="October" year="1985"/>
3318  </front>
3319  <seriesInfo name="STD" value="9"/>
3320  <seriesInfo name="RFC" value="959"/>
3321</reference>
3322
3323<reference anchor="RFC1123">
3324  <front>
3325    <title>Requirements for Internet Hosts - Application and Support</title>
3326    <author initials="R." surname="Braden" fullname="Robert Braden">
3327      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3328      <address><email>Braden@ISI.EDU</email></address>
3329    </author>
3330    <date month="October" year="1989"/>
3331  </front>
3332  <seriesInfo name="STD" value="3"/>
3333  <seriesInfo name="RFC" value="1123"/>
3334</reference>
3335
3336<reference anchor="RFC1305">
3337  <front>
3338    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3339    <author initials="D." surname="Mills" fullname="David L. Mills">
3340      <organization>University of Delaware, Electrical Engineering Department</organization>
3341      <address><email>mills@udel.edu</email></address>
3342    </author>
3343    <date month="March" year="1992"/>
3344  </front>
3345  <seriesInfo name="RFC" value="1305"/>
3346</reference>
3347
3348<reference anchor="RFC1436">
3349  <front>
3350    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3351    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3352      <organization>University of Minnesota, Computer and Information Services</organization>
3353      <address><email>fxa@boombox.micro.umn.edu</email></address>
3354    </author>
3355    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3356      <organization>University of Minnesota, Computer and Information Services</organization>
3357      <address><email>mpm@boombox.micro.umn.edu</email></address>
3358    </author>
3359    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3360      <organization>University of Minnesota, Computer and Information Services</organization>
3361      <address><email>lindner@boombox.micro.umn.edu</email></address>
3362    </author>
3363    <author initials="D." surname="Johnson" fullname="David Johnson">
3364      <organization>University of Minnesota, Computer and Information Services</organization>
3365      <address><email>dmj@boombox.micro.umn.edu</email></address>
3366    </author>
3367    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3368      <organization>University of Minnesota, Computer and Information Services</organization>
3369      <address><email>daniel@boombox.micro.umn.edu</email></address>
3370    </author>
3371    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3372      <organization>University of Minnesota, Computer and Information Services</organization>
3373      <address><email>alberti@boombox.micro.umn.edu</email></address>
3374    </author>
3375    <date month="March" year="1993"/>
3376  </front>
3377  <seriesInfo name="RFC" value="1436"/>
3378</reference>
3379
3380<reference anchor="RFC1630">
3381  <front>
3382    <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>
3383    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3384      <organization>CERN, World-Wide Web project</organization>
3385      <address><email>timbl@info.cern.ch</email></address>
3386    </author>
3387    <date month="June" year="1994"/>
3388  </front>
3389  <seriesInfo name="RFC" value="1630"/>
3390</reference>
3391
3392<reference anchor="RFC1737">
3393  <front>
3394    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3395    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3396      <organization>Xerox Palo Alto Research Center</organization>
3397      <address><email>masinter@parc.xerox.com</email></address>
3398    </author>
3399    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3400      <organization>MIT Laboratory for Computer Science</organization>
3401      <address><email>sollins@lcs.mit.edu</email></address>
3402    </author>
3403    <date month="December" year="1994"/>
3404  </front>
3405  <seriesInfo name="RFC" value="1737"/>
3406</reference>
3407
3408<reference anchor="RFC1738">
3409  <front>
3410    <title>Uniform Resource Locators (URL)</title>
3411    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3412      <organization>CERN, World-Wide Web project</organization>
3413      <address><email>timbl@info.cern.ch</email></address>
3414    </author>
3415    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3416      <organization>Xerox PARC</organization>
3417      <address><email>masinter@parc.xerox.com</email></address>
3418    </author>
3419    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3420      <organization>University of Minnesota, Computer and Information Services</organization>
3421      <address><email>mpm@boombox.micro.umn.edu</email></address>
3422    </author>
3423    <date month="December" year="1994"/>
3424  </front>
3425  <seriesInfo name="RFC" value="1738"/>
3426</reference>
3427
3428<reference anchor="RFC1808">
3429  <front>
3430    <title>Relative Uniform Resource Locators</title>
3431    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3432      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3433      <address><email>fielding@ics.uci.edu</email></address>
3434    </author>
3435    <date month="June" year="1995"/>
3436  </front>
3437  <seriesInfo name="RFC" value="1808"/>
3438</reference>
3439
3440<reference anchor="RFC1900">
3441  <front>
3442    <title>Renumbering Needs Work</title>
3443    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3444      <organization>CERN, Computing and Networks Division</organization>
3445      <address><email>brian@dxcoms.cern.ch</email></address>
3446    </author>
3447    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3448      <organization>cisco Systems</organization>
3449      <address><email>yakov@cisco.com</email></address>
3450    </author>
3451    <date month="February" year="1996"/>
3452  </front>
3453  <seriesInfo name="RFC" value="1900"/>
3454</reference>
3455
3456<reference anchor="RFC1945">
3457  <front>
3458    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3459    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3460      <organization>MIT, Laboratory for Computer Science</organization>
3461      <address><email>timbl@w3.org</email></address>
3462    </author>
3463    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3464      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3465      <address><email>fielding@ics.uci.edu</email></address>
3466    </author>
3467    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3468      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3469      <address><email>frystyk@w3.org</email></address>
3470    </author>
3471    <date month="May" year="1996"/>
3472  </front>
3473  <seriesInfo name="RFC" value="1945"/>
3474</reference>
3475
3476<reference anchor="RFC2068">
3477  <front>
3478    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3479    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3481      <address><email>fielding@ics.uci.edu</email></address>
3482    </author>
3483    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3484      <organization>MIT Laboratory for Computer Science</organization>
3485      <address><email>jg@w3.org</email></address>
3486    </author>
3487    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3488      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3489      <address><email>mogul@wrl.dec.com</email></address>
3490    </author>
3491    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3492      <organization>MIT Laboratory for Computer Science</organization>
3493      <address><email>frystyk@w3.org</email></address>
3494    </author>
3495    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3496      <organization>MIT Laboratory for Computer Science</organization>
3497      <address><email>timbl@w3.org</email></address>
3498    </author>
3499    <date month="January" year="1997"/>
3500  </front>
3501  <seriesInfo name="RFC" value="2068"/>
3502</reference>
3503
3504<reference anchor="RFC2145">
3505  <front>
3506    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3507    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3508      <organization>Western Research Laboratory</organization>
3509      <address><email>mogul@wrl.dec.com</email></address>
3510    </author>
3511    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3512      <organization>Department of Information and Computer Science</organization>
3513      <address><email>fielding@ics.uci.edu</email></address>
3514    </author>
3515    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3516      <organization>MIT Laboratory for Computer Science</organization>
3517      <address><email>jg@w3.org</email></address>
3518    </author>
3519    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3520      <organization>W3 Consortium</organization>
3521      <address><email>frystyk@w3.org</email></address>
3522    </author>
3523    <date month="May" year="1997"/>
3524  </front>
3525  <seriesInfo name="RFC" value="2145"/>
3526</reference>
3527
3528<reference anchor="RFC2324">
3529  <front>
3530    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3531    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3532      <organization>Xerox Palo Alto Research Center</organization>
3533      <address><email>masinter@parc.xerox.com</email></address>
3534    </author>
3535    <date month="April" day="1" year="1998"/>
3536  </front>
3537  <seriesInfo name="RFC" value="2324"/>
3538</reference>
3539
3540<reference anchor="RFC2616">
3541  <front>
3542    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3543    <author initials="R." surname="Fielding" fullname="R. Fielding">
3544      <organization>University of California, Irvine</organization>
3545      <address><email>fielding@ics.uci.edu</email></address>
3546    </author>
3547    <author initials="J." surname="Gettys" fullname="J. Gettys">
3548      <organization>W3C</organization>
3549      <address><email>jg@w3.org</email></address>
3550    </author>
3551    <author initials="J." surname="Mogul" fullname="J. Mogul">
3552      <organization>Compaq Computer Corporation</organization>
3553      <address><email>mogul@wrl.dec.com</email></address>
3554    </author>
3555    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3556      <organization>MIT Laboratory for Computer Science</organization>
3557      <address><email>frystyk@w3.org</email></address>
3558    </author>
3559    <author initials="L." surname="Masinter" fullname="L. Masinter">
3560      <organization>Xerox Corporation</organization>
3561      <address><email>masinter@parc.xerox.com</email></address>
3562    </author>
3563    <author initials="P." surname="Leach" fullname="P. Leach">
3564      <organization>Microsoft Corporation</organization>
3565      <address><email>paulle@microsoft.com</email></address>
3566    </author>
3567    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3568      <organization>W3C</organization>
3569      <address><email>timbl@w3.org</email></address>
3570    </author>
3571    <date month="June" year="1999"/>
3572  </front>
3573  <seriesInfo name="RFC" value="2616"/>
3574</reference>
3575
3576<reference anchor="RFC2821">
3577  <front>
3578    <title>Simple Mail Transfer Protocol</title>
3579    <author initials="J." surname="Klensin" fullname="J. Klensin">
3580      <organization>AT&amp;T Laboratories</organization>
3581      <address><email>klensin@research.att.com</email></address>
3582    </author>
3583    <date year="2001" month="April"/>
3584  </front>
3585  <seriesInfo name="RFC" value="2821"/>
3586</reference>
3587
3588<reference anchor="RFC2822">
3589  <front>
3590    <title>Internet Message Format</title>
3591    <author initials="P." surname="Resnick" fullname="P. Resnick">
3592      <organization>QUALCOMM Incorporated</organization>
3593    </author>
3594    <date year="2001" month="April"/>
3595  </front>
3596  <seriesInfo name="RFC" value="2822"/>
3597</reference>
3598
3599<reference anchor='RFC3977'>
3600  <front>
3601    <title>Network News Transfer Protocol (NNTP)</title>
3602    <author initials='C.' surname='Feather' fullname='C. Feather'>
3603      <organization>THUS plc</organization>
3604      <address><email>clive@demon.net</email></address>
3605    </author>
3606    <date year='2006' month='October' />
3607  </front>
3608  <seriesInfo name="RFC" value="3977"/>
3609</reference>
3610
3611<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3612  <front>
3613  <title>Analysis of HTTP Performance Problems</title>
3614  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3615    <organization/>
3616  </author>
3617  <date/>
3618  </front>
3619</reference>
3620
3621<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3622  <front>
3623  <title>Analysis of HTTP Performance</title>
3624  <author initials="J." surname="Touch" fullname="Joe Touch">
3625    <organization>USC/Information Sciences Institute</organization>
3626    <address><email>touch@isi.edu</email></address>
3627  </author>
3628  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3629    <organization>USC/Information Sciences Institute</organization>
3630    <address><email>johnh@isi.edu</email></address>
3631  </author>
3632  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3633    <organization>USC/Information Sciences Institute</organization>
3634    <address><email>katia@isi.edu</email></address>
3635  </author>
3636  <date year="1998" month="Aug"/>
3637  </front>
3638  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3639  <annotation>(original report dated Aug. 1996)</annotation>
3640</reference>
3641
3642<reference anchor="WAIS">
3643  <front>
3644    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3645    <author initials="F." surname="Davis" fullname="F. Davis">
3646      <organization>Thinking Machines Corporation</organization>
3647    </author>
3648    <author initials="B." surname="Kahle" fullname="B. Kahle">
3649      <organization>Thinking Machines Corporation</organization>
3650    </author>
3651    <author initials="H." surname="Morris" fullname="H. Morris">
3652      <organization>Thinking Machines Corporation</organization>
3653    </author>
3654    <author initials="J." surname="Salem" fullname="J. Salem">
3655      <organization>Thinking Machines Corporation</organization>
3656    </author>
3657    <author initials="T." surname="Shen" fullname="T. Shen">
3658      <organization>Thinking Machines Corporation</organization>
3659    </author>
3660    <author initials="R." surname="Wang" fullname="R. Wang">
3661      <organization>Thinking Machines Corporation</organization>
3662    </author>
3663    <author initials="J." surname="Sui" fullname="J. Sui">
3664      <organization>Thinking Machines Corporation</organization>
3665    </author>
3666    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3667      <organization>Thinking Machines Corporation</organization>
3668    </author>
3669    <date month="April" year="1990"/>
3670  </front>
3671  <seriesInfo name="Thinking Machines Corporation" value=""/>
3672</reference>
3673
3674</references>
3675
3676
3677<section title="Internet Media Types" anchor="internet.media.type.http">
3678<t>
3679   In addition to defining HTTP/1.1, this document serves
3680   as the specification for the Internet media type "message/http" and
3681   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3682</t>
3683<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3684<iref item="Media Type" subitem="message/http" primary="true"/>
3685<iref item="message/http Media Type" primary="true"/>
3686<t>
3687   The message/http type can be used to enclose a single HTTP request or
3688   response message, provided that it obeys the MIME restrictions for all
3689   "message" types regarding line length and encodings.
3690</t>
3691<t>
3692  <list style="hanging" x:indent="12em">
3693    <t hangText="Type name:">
3694      message
3695    </t>
3696    <t hangText="Subtype name:">
3697      http
3698    </t>
3699    <t hangText="Required parameters:">
3700      none
3701    </t>
3702    <t hangText="Optional parameters:">
3703      version, msgtype
3704      <list style="hanging">
3705        <t hangText="version:">
3706          The HTTP-Version number of the enclosed message
3707          (e.g., "1.1"). If not present, the version can be
3708          determined from the first line of the body.
3709        </t>
3710        <t hangText="msgtype:">
3711          The message type -- "request" or "response". If not
3712          present, the type can be determined from the first
3713          line of the body.
3714        </t>
3715      </list>
3716    </t>
3717    <t hangText="Encoding considerations:">
3718      only "7bit", "8bit", or "binary" are permitted
3719    </t>
3720    <t hangText="Security considerations:">
3721      none
3722    </t>
3723    <t hangText="Interoperability considerations:">
3724      none
3725    </t>
3726    <t hangText="Published specification:">
3727      This specification (see <xref target="internet.media.type.message.http"/>).
3728    </t>
3729    <t hangText="Applications that use this media type:">
3730    </t>
3731    <t hangText="Additional information:">
3732      <list style="hanging">
3733        <t hangText="Magic number(s):">none</t>
3734        <t hangText="File extension(s):">none</t>
3735        <t hangText="Macintosh file type code(s):">none</t>
3736      </list>
3737    </t>
3738    <t hangText="Person and email address to contact for further information:">
3739      See Authors Section.
3740    </t>
3741                <t hangText="Intended usage:">
3742                  COMMON
3743    </t>
3744                <t hangText="Restrictions on usage:">
3745                  none
3746    </t>
3747    <t hangText="Author/Change controller:">
3748      IESG
3749    </t>
3750  </list>
3751</t>
3752</section>
3753<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3754<iref item="Media Type" subitem="application/http" primary="true"/>
3755<iref item="application/http Media Type" primary="true"/>
3756<t>
3757   The application/http type can be used to enclose a pipeline of one or more
3758   HTTP request or response messages (not intermixed).
3759</t>
3760<t>
3761  <list style="hanging" x:indent="12em">
3762    <t hangText="Type name:">
3763      application
3764    </t>
3765    <t hangText="Subtype name:">
3766      http
3767    </t>
3768    <t hangText="Required parameters:">
3769      none
3770    </t>
3771    <t hangText="Optional parameters:">
3772      version, msgtype
3773      <list style="hanging">
3774        <t hangText="version:">
3775          The HTTP-Version number of the enclosed messages
3776          (e.g., "1.1"). If not present, the version can be
3777          determined from the first line of the body.
3778        </t>
3779        <t hangText="msgtype:">
3780          The message type -- "request" or "response". If not
3781          present, the type can be determined from the first
3782          line of the body.
3783        </t>
3784      </list>
3785    </t>
3786    <t hangText="Encoding considerations:">
3787      HTTP messages enclosed by this type
3788      are in "binary" format; use of an appropriate
3789      Content-Transfer-Encoding is required when
3790      transmitted via E-mail.
3791    </t>
3792    <t hangText="Security considerations:">
3793      none
3794    </t>
3795    <t hangText="Interoperability considerations:">
3796      none
3797    </t>
3798    <t hangText="Published specification:">
3799      This specification (see <xref target="internet.media.type.application.http"/>).
3800    </t>
3801    <t hangText="Applications that use this media type:">
3802    </t>
3803    <t hangText="Additional information:">
3804      <list style="hanging">
3805        <t hangText="Magic number(s):">none</t>
3806        <t hangText="File extension(s):">none</t>
3807        <t hangText="Macintosh file type code(s):">none</t>
3808      </list>
3809    </t>
3810    <t hangText="Person and email address to contact for further information:">
3811      See Authors Section.
3812    </t>
3813                <t hangText="Intended usage:">
3814                  COMMON
3815    </t>
3816                <t hangText="Restrictions on usage:">
3817                  none
3818    </t>
3819    <t hangText="Author/Change controller:">
3820      IESG
3821    </t>
3822  </list>
3823</t>
3824</section>
3825</section>
3826
3827<section title="Tolerant Applications" anchor="tolerant.applications">
3828<t>
3829   Although this document specifies the requirements for the generation
3830   of HTTP/1.1 messages, not all applications will be correct in their
3831   implementation. We therefore recommend that operational applications
3832   be tolerant of deviations whenever those deviations can be
3833   interpreted unambiguously.
3834</t>
3835<t>
3836   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3837   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3838   accept any amount of SP or HTAB characters between fields, even though
3839   only a single SP is required.
3840</t>
3841<t>
3842   The line terminator for message-header fields is the sequence CRLF.
3843   However, we recommend that applications, when parsing such headers,
3844   recognize a single LF as a line terminator and ignore the leading CR.
3845</t>
3846<t>
3847   The character set of an entity-body &SHOULD; be labeled as the lowest
3848   common denominator of the character codes used within that body, with
3849   the exception that not labeling the entity is preferred over labeling
3850   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3851</t>
3852<t>
3853   Additional rules for requirements on parsing and encoding of dates
3854   and other potential problems with date encodings include:
3855</t>
3856<t>
3857  <list style="symbols">
3858     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3859        which appears to be more than 50 years in the future is in fact
3860        in the past (this helps solve the "year 2000" problem).</t>
3861
3862     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3863        Expires date as earlier than the proper value, but &MUST-NOT;
3864        internally represent a parsed Expires date as later than the
3865        proper value.</t>
3866
3867     <t>All expiration-related calculations &MUST; be done in GMT. The
3868        local time zone &MUST-NOT; influence the calculation or comparison
3869        of an age or expiration time.</t>
3870
3871     <t>If an HTTP header incorrectly carries a date value with a time
3872        zone other than GMT, it &MUST; be converted into GMT using the
3873        most conservative possible conversion.</t>
3874  </list>
3875</t>
3876</section>
3877
3878<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3879<t>
3880   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3881   simplify the process of date comparison. Proxies and gateways from
3882   other protocols &SHOULD; ensure that any Date header field present in a
3883   message conforms to one of the HTTP/1.1 formats and rewrite the date
3884   if necessary.
3885</t>
3886</section>
3887
3888<section title="Compatibility with Previous Versions" anchor="compatibility">
3889<t>
3890   It is beyond the scope of a protocol specification to mandate
3891   compliance with previous versions. HTTP/1.1 was deliberately
3892   designed, however, to make supporting previous versions easy. It is
3893   worth noting that, at the time of composing this specification
3894   (1996), we would expect commercial HTTP/1.1 servers to:
3895  <list style="symbols">
3896     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3897        1.1 requests;</t>
3898
3899     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3900        1.1;</t>
3901
3902     <t>respond appropriately with a message in the same major version
3903        used by the client.</t>
3904  </list>
3905</t>
3906<t>
3907   And we would expect HTTP/1.1 clients to:
3908  <list style="symbols">
3909     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3910        responses;</t>
3911
3912     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3913        1.1.</t>
3914  </list>
3915</t>
3916<t>
3917   For most implementations of HTTP/1.0, each connection is established
3918   by the client prior to the request and closed by the server after
3919   sending the response. Some implementations implement the Keep-Alive
3920   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3921</t>
3922
3923<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3924<t>
3925   This section summarizes major differences between versions HTTP/1.0
3926   and HTTP/1.1.
3927</t>
3928
3929<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">
3930<t>
3931   The requirements that clients and servers support the Host request-header,
3932   report an error if the Host request-header (<xref target="header.host"/>) is
3933   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3934   are among the most important changes defined by this
3935   specification.
3936</t>
3937<t>
3938   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3939   addresses and servers; there was no other established mechanism for
3940   distinguishing the intended server of a request than the IP address
3941   to which that request was directed. The changes outlined above will
3942   allow the Internet, once older HTTP clients are no longer common, to
3943   support multiple Web sites from a single IP address, greatly
3944   simplifying large operational Web servers, where allocation of many
3945   IP addresses to a single host has created serious problems. The
3946   Internet will also be able to recover the IP addresses that have been
3947   allocated for the sole purpose of allowing special-purpose domain
3948   names to be used in root-level HTTP URLs. Given the rate of growth of
3949   the Web, and the number of servers already deployed, it is extremely
3950   important that all implementations of HTTP (including updates to
3951   existing HTTP/1.0 applications) correctly implement these
3952   requirements:
3953  <list style="symbols">
3954     <t>Both clients and servers &MUST; support the Host request-header.</t>
3955
3956     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3957
3958     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3959        request does not include a Host request-header.</t>
3960
3961     <t>Servers &MUST; accept absolute URIs.</t>
3962  </list>
3963</t>
3964</section>
3965</section>
3966
3967<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3968<t>
3969   Some clients and servers might wish to be compatible with some
3970   previous implementations of persistent connections in HTTP/1.0
3971   clients and servers. Persistent connections in HTTP/1.0 are
3972   explicitly negotiated as they are not the default behavior. HTTP/1.0
3973   experimental implementations of persistent connections are faulty,
3974   and the new facilities in HTTP/1.1 are designed to rectify these
3975   problems. The problem was that some existing 1.0 clients may be
3976   sending Keep-Alive to a proxy server that doesn't understand
3977   Connection, which would then erroneously forward it to the next
3978   inbound server, which would establish the Keep-Alive connection and
3979   result in a hung HTTP/1.0 proxy waiting for the close on the
3980   response. The result is that HTTP/1.0 clients must be prevented from
3981   using Keep-Alive when talking to proxies.
3982</t>
3983<t>
3984   However, talking to proxies is the most important use of persistent
3985   connections, so that prohibition is clearly unacceptable. Therefore,
3986   we need some other mechanism for indicating a persistent connection
3987   is desired, which is safe to use even when talking to an old proxy
3988   that ignores Connection. Persistent connections are the default for
3989   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3990   declaring non-persistence. See <xref target="header.connection"/>.
3991</t>
3992<t>
3993   The original HTTP/1.0 form of persistent connections (the Connection:
3994   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3995</t>
3996</section>
3997
3998<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3999<t>
4000   This specification has been carefully audited to correct and
4001   disambiguate key word usage; RFC 2068 had many problems in respect to
4002   the conventions laid out in <xref target="RFC2119"/>.
4003</t>
4004<t>
4005   Transfer-coding and message lengths all interact in ways that
4006   required fixing exactly when chunked encoding is used (to allow for
4007   transfer encoding that may not be self delimiting); it was important
4008   to straighten out exactly how message lengths are computed. (Sections
4009   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4010   <xref target="header.content-length" format="counter"/>,
4011   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4012</t>
4013<t>
4014   The use and interpretation of HTTP version numbers has been clarified
4015   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4016   version they support to deal with problems discovered in HTTP/1.0
4017   implementations (<xref target="http.version"/>)
4018</t>
4019<t>
4020   Transfer-coding had significant problems, particularly with
4021   interactions with chunked encoding. The solution is that transfer-codings
4022   become as full fledged as content-codings. This involves
4023   adding an IANA registry for transfer-codings (separate from content
4024   codings), a new header field (TE) and enabling trailer headers in the
4025   future. Transfer encoding is a major performance benefit, so it was
4026   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4027   interoperability problem that could have occurred due to interactions
4028   between authentication trailers, chunked encoding and HTTP/1.0
4029   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4030   and <xref target="header.te" format="counter"/>)
4031</t>
4032</section>
4033
4034<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4035<t>
4036  Clarify that HTTP-Version is case sensitive.
4037  (<xref target="http.version"/>)
4038</t>
4039<t>
4040  Remove reference to non-existant identity transfer-coding value tokens.
4041  (Sections <xref format="counter" target="transfer.codings"/> and
4042  <xref format="counter" target="message.length"/>)
4043</t>
4044<t>
4045  Clarification that the chunk length does not include
4046  the count of the octets in the chunk header and trailer.
4047  (<xref target="chunked.transfer.encoding"/>)
4048</t>
4049<t>
4050  Fix BNF to add query, as the abs_path production in
4051  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4052  (<xref target="request-uri"/>)
4053</t>
4054<t>
4055  Clarify exactly when close connection options must be sent.
4056  (<xref target="header.connection"/>)
4057</t>
4058</section>
4059</section>
4060
4061<section title="Change Log (to be removed by RFC Editor before publication)">
4062
4063<section title="Since RFC2616">
4064<t>
4065  Extracted relevant partitions from <xref target="RFC2616"/>.
4066</t>
4067</section>
4068
4069<section title="Since draft-ietf-httpbis-p1-messaging-00">
4070<t>
4071  Closed issues:
4072  <list style="symbols">
4073    <t>
4074      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4075      "HTTP Version should be case sensitive"
4076      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4077    </t>
4078    <t>
4079      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4080      "'unsafe' characters"
4081      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4082    </t>
4083    <t>
4084      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4085      "Chunk Size Definition"
4086      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4087    </t>
4088    <t>
4089      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4090      "Message Length"
4091      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4092    </t>
4093    <t>
4094      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4095      "Media Type Registrations"
4096      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4097    </t>
4098    <t>
4099      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4100      "URI includes query"
4101      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4102    </t>
4103    <t>
4104      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4105      "No close on 1xx responses"
4106      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4107    </t>
4108    <t>
4109      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4110      "Remove 'identity' token references"
4111      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4112    </t>
4113    <t>
4114      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4115      "Import query BNF"
4116    </t>
4117    <t>
4118      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4119      "qdtext BNF"
4120    </t>
4121    <t>
4122      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4123      "Normative and Informative references"
4124    </t>
4125    <t>
4126      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4127      "RFC2606 Compliance"
4128    </t>
4129    <t>
4130      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4131      "RFC977 reference"
4132    </t>
4133    <t>
4134      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4135      "RFC1700 references"
4136    </t>
4137    <t>
4138      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4139      "inconsistency in date format explanation"
4140    </t>
4141    <t>
4142      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4143      "Date reference typo"
4144    </t>
4145    <t>
4146      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4147      "Informative references"
4148    </t>
4149    <t>
4150      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4151      "ISO-8859-1 Reference"
4152    </t>
4153    <t>
4154      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4155      "Normative up-to-date references"
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  Other changes:
4161  <list style="symbols">
4162    <t>
4163      Update media type registrations to use RFC4288 template.
4164    </t>
4165    <t>
4166      Use names of RFC4234 core rules DQUOTE and HTAB,
4167      fix broken ABNF for chunk-data
4168      (work in progress on <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4169    </t>
4170  </list>
4171</t>
4172</section>
4173
4174<section title="Since draft-ietf-httpbis-p1-messaging-01">
4175<t>
4176  Closed issues:
4177  <list style="symbols">
4178    <t>
4179      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4180      "Bodies on GET (and other) requests"
4181    </t>
4182    <t>
4183      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4184      "rel_path not used"
4185    </t>
4186  </list>
4187</t>
4188<t>
4189  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4190  <list style="symbols">
4191    <t>
4192       Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4193       "trailer-part").
4194    </t>
4195    <t>
4196       Avoid underscore character in rule names ("http_URL" ->
4197       "http-URL", "abs_path" -> "path-absolute").
4198    </t>
4199    <t>
4200       Add rules for terms imported from URI spec ("absoluteURI", "authority",
4201       "path-absolute", "port", "query", "relativeURI", "host) -- these will
4202       have to be updated when switching over to RFC3986.
4203    </t>
4204    <t>
4205       Synchronize core rules with RFC5234.
4206    </t>
4207    <t>
4208       Get rid of prose rules that span multiple lines.
4209    </t>
4210    <t>
4211       Get rid of unused rules LOALPHA and UPALPHA.
4212    </t>
4213  </list>
4214</t>
4215</section>
4216
4217</section>
4218
4219</back>
4220</rfc>
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