source: draft-ietf-httpbis/latest/p1-messaging.xml @ 197

Last change on this file since 197 was 197, checked in by fielding@…, 12 years ago

RFC4288 is not a normative ref; related to #55

  • Property svn:eol-style set to native
File size: 180.6 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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           = %x01-7F
840                   ; any US-ASCII character, excluding NUL
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 title="Product Tokens" anchor="product.tokens">
1334<t>
1335   Product tokens are used to allow communicating applications to
1336   identify themselves by software name and version. Most fields using
1337   product tokens also allow sub-products which form a significant part
1338   of the application to be listed, separated by white space. By
1339   convention, the products are listed in order of their significance
1340   for identifying the application.
1341</t>
1342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1343  product         = token ["/" product-version]
1344  product-version = token
1345</artwork></figure>
1346<t>
1347   Examples:
1348</t>
1349<figure><artwork type="example">
1350    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1351    Server: Apache/0.8.4
1352</artwork></figure>
1353<t>
1354   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1355   used for advertising or other non-essential information. Although any
1356   token character &MAY; appear in a product-version, this token &SHOULD;
1357   only be used for a version identifier (i.e., successive versions of
1358   the same product &SHOULD; only differ in the product-version portion of
1359   the product value).
1360</t>
1361</section>
1362
1363</section>
1364
1365<section title="HTTP Message" anchor="http.message">
1366
1367<section title="Message Types" anchor="message.types">
1368<t>
1369   HTTP messages consist of requests from client to server and responses
1370   from server to client.
1371</t>
1372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1373  HTTP-message   = Request | Response     ; HTTP/1.1 messages
1374</artwork></figure>
1375<t>
1376   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1377   message format of <xref target="RFC2822"/> for transferring entities (the payload
1378   of the message). Both types of message consist of a start-line, zero
1379   or more header fields (also known as "headers"), an empty line (i.e.,
1380   a line with nothing preceding the CRLF) indicating the end of the
1381   header fields, and possibly a message-body.
1382</t>
1383<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1384  generic-message = start-line
1385                    *(message-header CRLF)
1386                    CRLF
1387                    [ message-body ]
1388  start-line      = Request-Line | Status-Line
1389</artwork></figure>
1390<t>
1391   In the interest of robustness, servers &SHOULD; ignore any empty
1392   line(s) received where a Request-Line is expected. In other words, if
1393   the server is reading the protocol stream at the beginning of a
1394   message and receives a CRLF first, it should ignore the CRLF.
1395</t>
1396<t>
1397   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1398   after a POST request. To restate what is explicitly forbidden by the
1399   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1400   extra CRLF.
1401</t>
1402</section>
1403
1404<section title="Message Headers" anchor="message.headers">
1405<t>
1406   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1407   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1408   entity-header (&entity-header-fields;) fields, follow the same generic format as
1409   that given in <xref target="RFC2822" x:fmt="of" x:sec="2.1"/>. Each header field consists
1410   of a name followed by a colon (":") and the field value. Field names
1411   are case-insensitive. The field value &MAY; be preceded by any amount
1412   of LWS, though a single SP is preferred. Header fields can be
1413   extended over multiple lines by preceding each extra line with at
1414   least one SP or HTAB. Applications ought to follow "common form", where
1415   one is known or indicated, when generating HTTP constructs, since
1416   there might exist some implementations that fail to accept anything
1417   beyond the common forms.
1418</t>
1419<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"/>
1420  message-header = field-name ":" [ field-value ]
1421  field-name     = token
1422  field-value    = *( field-content | LWS )
1423  field-content  = &lt;field content&gt;
1424                   ; the OCTETs making up the field-value
1425                   ; and consisting of either *TEXT or combinations
1426                   ; of token, separators, and quoted-string
1427</artwork></figure>
1428<t>
1429   The field-content does not include any leading or trailing LWS:
1430   linear white space occurring before the first non-whitespace
1431   character of the field-value or after the last non-whitespace
1432   character of the field-value. Such leading or trailing LWS &MAY; be
1433   removed without changing the semantics of the field value. Any LWS
1434   that occurs between field-content &MAY; be replaced with a single SP
1435   before interpreting the field value or forwarding the message
1436   downstream.
1437</t>
1438<t>
1439   The order in which header fields with differing field names are
1440   received is not significant. However, it is "good practice" to send
1441   general-header fields first, followed by request-header or response-header
1442   fields, and ending with the entity-header fields.
1443</t>
1444<t>
1445   Multiple message-header fields with the same field-name &MAY; be
1446   present in a message if and only if the entire field-value for that
1447   header field is defined as a comma-separated list [i.e., #(values)].
1448   It &MUST; be possible to combine the multiple header fields into one
1449   "field-name: field-value" pair, without changing the semantics of the
1450   message, by appending each subsequent field-value to the first, each
1451   separated by a comma. The order in which header fields with the same
1452   field-name are received is therefore significant to the
1453   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1454   change the order of these field values when a message is forwarded.
1455</t>
1456</section>
1457
1458<section title="Message Body" anchor="message.body">
1459<t>
1460   The message-body (if any) of an HTTP message is used to carry the
1461   entity-body associated with the request or response. The message-body
1462   differs from the entity-body only when a transfer-coding has been
1463   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1464</t>
1465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1466  message-body = entity-body
1467               | &lt;entity-body encoded as per Transfer-Encoding&gt;
1468</artwork></figure>
1469<t>
1470   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1471   applied by an application to ensure safe and proper transfer of the
1472   message. Transfer-Encoding is a property of the message, not of the
1473   entity, and thus &MAY; be added or removed by any application along the
1474   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1475   when certain transfer-codings may be used.)
1476</t>
1477<t>
1478   The rules for when a message-body is allowed in a message differ for
1479   requests and responses.
1480</t>
1481<t>
1482   The presence of a message-body in a request is signaled by the
1483   inclusion of a Content-Length or Transfer-Encoding header field in
1484   the request's message-headers. A message-body &MUST-NOT; be included in
1485   a request if the specification of the request method (&method;)
1486   explicitly disallows an entity-body in requests.
1487   When a request message contains both a message-body of non-zero
1488   length and a method that does not define any semantics for that
1489   request message-body, then an origin server &SHOULD; either ignore
1490   the message-body or respond with an appropriate error message
1491   (e.g., 413).  A proxy or gateway, when presented the same request,
1492   &SHOULD; either forward the request inbound with the message-body or
1493   ignore the message-body when determining a response.
1494</t>
1495<t>
1496   For response messages, whether or not a message-body is included with
1497   a message is dependent on both the request method and the response
1498   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1499   &MUST-NOT; include a message-body, even though the presence of entity-header
1500   fields might lead one to believe they do. All 1xx
1501   (informational), 204 (No Content), and 304 (Not Modified) responses
1502   &MUST-NOT; include a message-body. All other responses do include a
1503   message-body, although it &MAY; be of zero length.
1504</t>
1505</section>
1506
1507<section title="Message Length" anchor="message.length">
1508<t>
1509   The transfer-length of a message is the length of the message-body as
1510   it appears in the message; that is, after any transfer-codings have
1511   been applied. When a message-body is included with a message, the
1512   transfer-length of that body is determined by one of the following
1513   (in order of precedence):
1514</t>
1515<t>
1516  <list style="numbers">
1517    <x:lt><t>
1518     Any response message which "&MUST-NOT;" include a message-body (such
1519     as the 1xx, 204, and 304 responses and any response to a HEAD
1520     request) is always terminated by the first empty line after the
1521     header fields, regardless of the entity-header fields present in
1522     the message.
1523    </t></x:lt>
1524    <x:lt><t>
1525     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1526     is present, then the transfer-length is
1527     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1528     unless the message is terminated by closing the connection.
1529    </t></x:lt>
1530    <x:lt><t>
1531     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1532     decimal value in OCTETs represents both the entity-length and the
1533     transfer-length. The Content-Length header field &MUST-NOT; be sent
1534     if these two lengths are different (i.e., if a Transfer-Encoding
1535     header field is present). If a message is received with both a
1536     Transfer-Encoding header field and a Content-Length header field,
1537     the latter &MUST; be ignored.
1538    </t></x:lt>
1539    <x:lt><t>
1540     If the message uses the media type "multipart/byteranges", and the
1541     transfer-length is not otherwise specified, then this self-delimiting
1542     media type defines the transfer-length. This media type
1543     &MUST-NOT; be used unless the sender knows that the recipient can parse
1544     it; the presence in a request of a Range header with multiple byte-range
1545     specifiers from a 1.1 client implies that the client can parse
1546     multipart/byteranges responses.
1547    <list style="empty"><t>
1548       A range header might be forwarded by a 1.0 proxy that does not
1549       understand multipart/byteranges; in this case the server &MUST;
1550       delimit the message using methods defined in items 1, 3 or 5 of
1551       this section.
1552    </t></list>
1553    </t></x:lt>
1554    <x:lt><t>
1555     By the server closing the connection. (Closing the connection
1556     cannot be used to indicate the end of a request body, since that
1557     would leave no possibility for the server to send back a response.)
1558    </t></x:lt>
1559  </list>
1560</t>
1561<t>
1562   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1563   containing a message-body &MUST; include a valid Content-Length header
1564   field unless the server is known to be HTTP/1.1 compliant. If a
1565   request contains a message-body and a Content-Length is not given,
1566   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1567   determine the length of the message, or with 411 (Length Required) if
1568   it wishes to insist on receiving a valid Content-Length.
1569</t>
1570<t>
1571   All HTTP/1.1 applications that receive entities &MUST; accept the
1572   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1573   to be used for messages when the message length cannot be determined
1574   in advance.
1575</t>
1576<t>
1577   Messages &MUST-NOT; include both a Content-Length header field and a
1578   transfer-coding. If the message does include a
1579   transfer-coding, the Content-Length &MUST; be ignored.
1580</t>
1581<t>
1582   When a Content-Length is given in a message where a message-body is
1583   allowed, its field value &MUST; exactly match the number of OCTETs in
1584   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1585   invalid length is received and detected.
1586</t>
1587</section>
1588
1589<section title="General Header Fields" anchor="general.header.fields">
1590<t>
1591   There are a few header fields which have general applicability for
1592   both request and response messages, but which do not apply to the
1593   entity being transferred. These header fields apply only to the
1594   message being transmitted.
1595</t>
1596<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1597  general-header = Cache-Control            ; &header-cache-control;
1598                 | Connection               ; <xref target="header.connection"/>
1599                 | Date                     ; <xref target="header.date"/>
1600                 | Pragma                   ; &header-pragma;
1601                 | Trailer                  ; <xref target="header.trailer"/>
1602                 | Transfer-Encoding        ; <xref target="header.transfer-encoding"/>
1603                 | Upgrade                  ; <xref target="header.upgrade"/>
1604                 | Via                      ; <xref target="header.via"/>
1605                 | Warning                  ; &header-warning;
1606</artwork></figure>
1607<t>
1608   General-header field names can be extended reliably only in
1609   combination with a change in the protocol version. However, new or
1610   experimental header fields may be given the semantics of general
1611   header fields if all parties in the communication recognize them to
1612   be general-header fields. Unrecognized header fields are treated as
1613   entity-header fields.
1614</t>
1615</section>
1616</section>
1617
1618<section title="Request" anchor="request">
1619<t>
1620   A request message from a client to a server includes, within the
1621   first line of that message, the method to be applied to the resource,
1622   the identifier of the resource, and the protocol version in use.
1623</t>
1624<!--                 Host                      ; should be moved here eventually -->
1625<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1626  Request       = Request-Line              ; <xref target="request-line"/>
1627                  *(( general-header        ; <xref target="general.header.fields"/>
1628                   | request-header         ; &request-header-fields;
1629                   | entity-header ) CRLF)  ; &entity-header-fields;
1630                  CRLF
1631                  [ message-body ]          ; <xref target="message.body"/>
1632</artwork></figure>
1633
1634<section title="Request-Line" anchor="request-line">
1635<t>
1636   The Request-Line begins with a method token, followed by the
1637   Request-URI and the protocol version, and ending with CRLF. The
1638   elements are separated by SP characters. No CR or LF is allowed
1639   except in the final CRLF sequence.
1640</t>
1641<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1642  Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1643</artwork></figure>
1644
1645<section title="Method" anchor="method">
1646<t>
1647   The Method  token indicates the method to be performed on the
1648   resource identified by the Request-URI. The method is case-sensitive.
1649</t>
1650<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1651  Method         = token
1652</artwork></figure>
1653</section>
1654
1655<section title="Request-URI" anchor="request-uri">
1656<t>
1657   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1658   identifies the resource upon which to apply the request.
1659</t>
1660<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1661  Request-URI    = "*"
1662                 | absoluteURI
1663                 | ( path-absolute [ "?" query ] )
1664                 | authority
1665</artwork></figure>
1666<t>
1667   The four options for Request-URI are dependent on the nature of the
1668   request. The asterisk "*" means that the request does not apply to a
1669   particular resource, but to the server itself, and is only allowed
1670   when the method used does not necessarily apply to a resource. One
1671   example would be
1672</t>
1673<figure><artwork type="example">
1674    OPTIONS * HTTP/1.1
1675</artwork></figure>
1676<t>
1677   The absoluteURI form is &REQUIRED; when the request is being made to a
1678   proxy. The proxy is requested to forward the request or service it
1679   from a valid cache, and return the response. Note that the proxy &MAY;
1680   forward the request on to another proxy or directly to the server
1681   specified by the absoluteURI. In order to avoid request loops, a
1682   proxy &MUST; be able to recognize all of its server names, including
1683   any aliases, local variations, and the numeric IP address. An example
1684   Request-Line would be:
1685</t>
1686<figure><artwork type="example">
1687    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1688</artwork></figure>
1689<t>
1690   To allow for transition to absoluteURIs in all requests in future
1691   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1692   form in requests, even though HTTP/1.1 clients will only generate
1693   them in requests to proxies.
1694</t>
1695<t>
1696   The authority form is only used by the CONNECT method (&CONNECT;).
1697</t>
1698<t>
1699   The most common form of Request-URI is that used to identify a
1700   resource on an origin server or gateway. In this case the absolute
1701   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1702   the Request-URI, and the network location of the URI (authority) &MUST;
1703   be transmitted in a Host header field. For example, a client wishing
1704   to retrieve the resource above directly from the origin server would
1705   create a TCP connection to port 80 of the host "www.example.org" and send
1706   the lines:
1707</t>
1708<figure><artwork type="example">
1709    GET /pub/WWW/TheProject.html HTTP/1.1
1710    Host: www.example.org
1711</artwork></figure>
1712<t>
1713   followed by the remainder of the Request. Note that the absolute path
1714   cannot be empty; if none is present in the original URI, it &MUST; be
1715   given as "/" (the server root).
1716</t>
1717<t>
1718   The Request-URI is transmitted in the format specified in
1719   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1720   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1721   properly interpret the request. Servers &SHOULD; respond to invalid
1722   Request-URIs with an appropriate status code.
1723</t>
1724<t>
1725   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1726   received Request-URI when forwarding it to the next inbound server,
1727   except as noted above to replace a null path-absolute with "/".
1728</t>
1729<t>
1730  <list><t>
1731      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1732      meaning of the request when the origin server is improperly using
1733      a non-reserved URI character for a reserved purpose.  Implementors
1734      should be aware that some pre-HTTP/1.1 proxies have been known to
1735      rewrite the Request-URI.
1736  </t></list>
1737</t>
1738</section>
1739</section>
1740
1741<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1742<t>
1743   The exact resource identified by an Internet request is determined by
1744   examining both the Request-URI and the Host header field.
1745</t>
1746<t>
1747   An origin server that does not allow resources to differ by the
1748   requested host &MAY; ignore the Host header field value when
1749   determining the resource identified by an HTTP/1.1 request. (But see
1750   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1751   for other requirements on Host support in HTTP/1.1.)
1752</t>
1753<t>
1754   An origin server that does differentiate resources based on the host
1755   requested (sometimes referred to as virtual hosts or vanity host
1756   names) &MUST; use the following rules for determining the requested
1757   resource on an HTTP/1.1 request:
1758  <list style="numbers">
1759    <t>If Request-URI is an absoluteURI, the host is part of the
1760     Request-URI. Any Host header field value in the request &MUST; be
1761     ignored.</t>
1762    <t>If the Request-URI is not an absoluteURI, and the request includes
1763     a Host header field, the host is determined by the Host header
1764     field value.</t>
1765    <t>If the host as determined by rule 1 or 2 is not a valid host on
1766     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1767  </list>
1768</t>
1769<t>
1770   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1771   attempt to use heuristics (e.g., examination of the URI path for
1772   something unique to a particular host) in order to determine what
1773   exact resource is being requested.
1774</t>
1775</section>
1776
1777</section>
1778
1779
1780<section title="Response" anchor="response">
1781<t>
1782   After receiving and interpreting a request message, a server responds
1783   with an HTTP response message.
1784</t>
1785<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1786  Response      = Status-Line               ; <xref target="status-line"/>
1787                  *(( general-header        ; <xref target="general.header.fields"/>
1788                   | response-header        ; &response-header-fields;
1789                   | entity-header ) CRLF)  ; &entity-header-fields;
1790                  CRLF
1791                  [ message-body ]          ; <xref target="message.body"/>
1792</artwork></figure>
1793
1794<section title="Status-Line" anchor="status-line">
1795<t>
1796   The first line of a Response message is the Status-Line, consisting
1797   of the protocol version followed by a numeric status code and its
1798   associated textual phrase, with each element separated by SP
1799   characters. No CR or LF is allowed except in the final CRLF sequence.
1800</t>
1801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1802  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1803</artwork></figure>
1804
1805<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1806<t>
1807   The Status-Code element is a 3-digit integer result code of the
1808   attempt to understand and satisfy the request. These codes are fully
1809   defined in &status-codes;. The Reason-Phrase is intended to give a short
1810   textual description of the Status-Code. The Status-Code is intended
1811   for use by automata and the Reason-Phrase is intended for the human
1812   user. The client is not required to examine or display the Reason-Phrase.
1813</t>
1814<t>
1815   The first digit of the Status-Code defines the class of response. The
1816   last two digits do not have any categorization role. There are 5
1817   values for the first digit:
1818  <list style="symbols">
1819    <t>
1820      1xx: Informational - Request received, continuing process
1821    </t>
1822    <t>
1823      2xx: Success - The action was successfully received,
1824        understood, and accepted
1825    </t>
1826    <t>
1827      3xx: Redirection - Further action must be taken in order to
1828        complete the request
1829    </t>
1830    <t>
1831      4xx: Client Error - The request contains bad syntax or cannot
1832        be fulfilled
1833    </t>
1834    <t>
1835      5xx: Server Error - The server failed to fulfill an apparently
1836        valid request
1837    </t>
1838  </list>
1839</t>
1840<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"/>
1841  Status-Code    = 3DIGIT
1842  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
1843</artwork></figure>
1844</section>
1845</section>
1846
1847</section>
1848
1849
1850<section title="Connections" anchor="connections">
1851
1852<section title="Persistent Connections" anchor="persistent.connections">
1853
1854<section title="Purpose" anchor="persistent.purpose">
1855<t>
1856   Prior to persistent connections, a separate TCP connection was
1857   established to fetch each URL, increasing the load on HTTP servers
1858   and causing congestion on the Internet. The use of inline images and
1859   other associated data often require a client to make multiple
1860   requests of the same server in a short amount of time. Analysis of
1861   these performance problems and results from a prototype
1862   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1863   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1864   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1865   T/TCP <xref target="Tou1998"/>.
1866</t>
1867<t>
1868   Persistent HTTP connections have a number of advantages:
1869  <list style="symbols">
1870      <t>
1871        By opening and closing fewer TCP connections, CPU time is saved
1872        in routers and hosts (clients, servers, proxies, gateways,
1873        tunnels, or caches), and memory used for TCP protocol control
1874        blocks can be saved in hosts.
1875      </t>
1876      <t>
1877        HTTP requests and responses can be pipelined on a connection.
1878        Pipelining allows a client to make multiple requests without
1879        waiting for each response, allowing a single TCP connection to
1880        be used much more efficiently, with much lower elapsed time.
1881      </t>
1882      <t>
1883        Network congestion is reduced by reducing the number of packets
1884        caused by TCP opens, and by allowing TCP sufficient time to
1885        determine the congestion state of the network.
1886      </t>
1887      <t>
1888        Latency on subsequent requests is reduced since there is no time
1889        spent in TCP's connection opening handshake.
1890      </t>
1891      <t>
1892        HTTP can evolve more gracefully, since errors can be reported
1893        without the penalty of closing the TCP connection. Clients using
1894        future versions of HTTP might optimistically try a new feature,
1895        but if communicating with an older server, retry with old
1896        semantics after an error is reported.
1897      </t>
1898    </list>
1899</t>
1900<t>
1901   HTTP implementations &SHOULD; implement persistent connections.
1902</t>
1903</section>
1904
1905<section title="Overall Operation" anchor="persistent.overall">
1906<t>
1907   A significant difference between HTTP/1.1 and earlier versions of
1908   HTTP is that persistent connections are the default behavior of any
1909   HTTP connection. That is, unless otherwise indicated, the client
1910   &SHOULD; assume that the server will maintain a persistent connection,
1911   even after error responses from the server.
1912</t>
1913<t>
1914   Persistent connections provide a mechanism by which a client and a
1915   server can signal the close of a TCP connection. This signaling takes
1916   place using the Connection header field (<xref target="header.connection"/>). Once a close
1917   has been signaled, the client &MUST-NOT; send any more requests on that
1918   connection.
1919</t>
1920
1921<section title="Negotiation" anchor="persistent.negotiation">
1922<t>
1923   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1924   maintain a persistent connection unless a Connection header including
1925   the connection-token "close" was sent in the request. If the server
1926   chooses to close the connection immediately after sending the
1927   response, it &SHOULD; send a Connection header including the
1928   connection-token close.
1929</t>
1930<t>
1931   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1932   decide to keep it open based on whether the response from a server
1933   contains a Connection header with the connection-token close. In case
1934   the client does not want to maintain a connection for more than that
1935   request, it &SHOULD; send a Connection header including the
1936   connection-token close.
1937</t>
1938<t>
1939   If either the client or the server sends the close token in the
1940   Connection header, that request becomes the last one for the
1941   connection.
1942</t>
1943<t>
1944   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1945   maintained for HTTP versions less than 1.1 unless it is explicitly
1946   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1947   compatibility with HTTP/1.0 clients.
1948</t>
1949<t>
1950   In order to remain persistent, all messages on the connection &MUST;
1951   have a self-defined message length (i.e., one not defined by closure
1952   of the connection), as described in <xref target="message.length"/>.
1953</t>
1954</section>
1955
1956<section title="Pipelining" anchor="pipelining">
1957<t>
1958   A client that supports persistent connections &MAY; "pipeline" its
1959   requests (i.e., send multiple requests without waiting for each
1960   response). A server &MUST; send its responses to those requests in the
1961   same order that the requests were received.
1962</t>
1963<t>
1964   Clients which assume persistent connections and pipeline immediately
1965   after connection establishment &SHOULD; be prepared to retry their
1966   connection if the first pipelined attempt fails. If a client does
1967   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1968   persistent. Clients &MUST; also be prepared to resend their requests if
1969   the server closes the connection before sending all of the
1970   corresponding responses.
1971</t>
1972<t>
1973   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1974   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1975   premature termination of the transport connection could lead to
1976   indeterminate results. A client wishing to send a non-idempotent
1977   request &SHOULD; wait to send that request until it has received the
1978   response status for the previous request.
1979</t>
1980</section>
1981</section>
1982
1983<section title="Proxy Servers" anchor="persistent.proxy">
1984<t>
1985   It is especially important that proxies correctly implement the
1986   properties of the Connection header field as specified in <xref target="header.connection"/>.
1987</t>
1988<t>
1989   The proxy server &MUST; signal persistent connections separately with
1990   its clients and the origin servers (or other proxy servers) that it
1991   connects to. Each persistent connection applies to only one transport
1992   link.
1993</t>
1994<t>
1995   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1996   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1997   discussion of the problems with the Keep-Alive header implemented by
1998   many HTTP/1.0 clients).
1999</t>
2000</section>
2001
2002<section title="Practical Considerations" anchor="persistent.practical">
2003<t>
2004   Servers will usually have some time-out value beyond which they will
2005   no longer maintain an inactive connection. Proxy servers might make
2006   this a higher value since it is likely that the client will be making
2007   more connections through the same server. The use of persistent
2008   connections places no requirements on the length (or existence) of
2009   this time-out for either the client or the server.
2010</t>
2011<t>
2012   When a client or server wishes to time-out it &SHOULD; issue a graceful
2013   close on the transport connection. Clients and servers &SHOULD; both
2014   constantly watch for the other side of the transport close, and
2015   respond to it as appropriate. If a client or server does not detect
2016   the other side's close promptly it could cause unnecessary resource
2017   drain on the network.
2018</t>
2019<t>
2020   A client, server, or proxy &MAY; close the transport connection at any
2021   time. For example, a client might have started to send a new request
2022   at the same time that the server has decided to close the "idle"
2023   connection. From the server's point of view, the connection is being
2024   closed while it was idle, but from the client's point of view, a
2025   request is in progress.
2026</t>
2027<t>
2028   This means that clients, servers, and proxies &MUST; be able to recover
2029   from asynchronous close events. Client software &SHOULD; reopen the
2030   transport connection and retransmit the aborted sequence of requests
2031   without user interaction so long as the request sequence is
2032   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2033   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2034   human operator the choice of retrying the request(s). Confirmation by
2035   user-agent software with semantic understanding of the application
2036   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2037   be repeated if the second sequence of requests fails.
2038</t>
2039<t>
2040   Servers &SHOULD; always respond to at least one request per connection,
2041   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2042   middle of transmitting a response, unless a network or client failure
2043   is suspected.
2044</t>
2045<t>
2046   Clients that use persistent connections &SHOULD; limit the number of
2047   simultaneous connections that they maintain to a given server. A
2048   single-user client &SHOULD-NOT; maintain more than 2 connections with
2049   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2050   another server or proxy, where N is the number of simultaneously
2051   active users. These guidelines are intended to improve HTTP response
2052   times and avoid congestion.
2053</t>
2054</section>
2055</section>
2056
2057<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2058
2059<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2060<t>
2061   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2062   flow control mechanisms to resolve temporary overloads, rather than
2063   terminating connections with the expectation that clients will retry.
2064   The latter technique can exacerbate network congestion.
2065</t>
2066</section>
2067
2068<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2069<t>
2070   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2071   the network connection for an error status while it is transmitting
2072   the request. If the client sees an error status, it &SHOULD;
2073   immediately cease transmitting the body. If the body is being sent
2074   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2075   empty trailer &MAY; be used to prematurely mark the end of the message.
2076   If the body was preceded by a Content-Length header, the client &MUST;
2077   close the connection.
2078</t>
2079</section>
2080
2081<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2082<t>
2083   The purpose of the 100 (Continue) status (see &status-100;) is to
2084   allow a client that is sending a request message with a request body
2085   to determine if the origin server is willing to accept the request
2086   (based on the request headers) before the client sends the request
2087   body. In some cases, it might either be inappropriate or highly
2088   inefficient for the client to send the body if the server will reject
2089   the message without looking at the body.
2090</t>
2091<t>
2092   Requirements for HTTP/1.1 clients:
2093  <list style="symbols">
2094    <t>
2095        If a client will wait for a 100 (Continue) response before
2096        sending the request body, it &MUST; send an Expect request-header
2097        field (&header-expect;) with the "100-continue" expectation.
2098    </t>
2099    <t>
2100        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2101        with the "100-continue" expectation if it does not intend
2102        to send a request body.
2103    </t>
2104  </list>
2105</t>
2106<t>
2107   Because of the presence of older implementations, the protocol allows
2108   ambiguous situations in which a client may send "Expect: 100-continue"
2109   without receiving either a 417 (Expectation Failed) status
2110   or a 100 (Continue) status. Therefore, when a client sends this
2111   header field to an origin server (possibly via a proxy) from which it
2112   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2113   for an indefinite period before sending the request body.
2114</t>
2115<t>
2116   Requirements for HTTP/1.1 origin servers:
2117  <list style="symbols">
2118    <t> Upon receiving a request which includes an Expect request-header
2119        field with the "100-continue" expectation, an origin server &MUST;
2120        either respond with 100 (Continue) status and continue to read
2121        from the input stream, or respond with a final status code. The
2122        origin server &MUST-NOT; wait for the request body before sending
2123        the 100 (Continue) response. If it responds with a final status
2124        code, it &MAY; close the transport connection or it &MAY; continue
2125        to read and discard the rest of the request.  It &MUST-NOT;
2126        perform the requested method if it returns a final status code.
2127    </t>
2128    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2129        the request message does not include an Expect request-header
2130        field with the "100-continue" expectation, and &MUST-NOT; send a
2131        100 (Continue) response if such a request comes from an HTTP/1.0
2132        (or earlier) client. There is an exception to this rule: for
2133        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2134        status in response to an HTTP/1.1 PUT or POST request that does
2135        not include an Expect request-header field with the "100-continue"
2136        expectation. This exception, the purpose of which is
2137        to minimize any client processing delays associated with an
2138        undeclared wait for 100 (Continue) status, applies only to
2139        HTTP/1.1 requests, and not to requests with any other HTTP-version
2140        value.
2141    </t>
2142    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2143        already received some or all of the request body for the
2144        corresponding request.
2145    </t>
2146    <t> An origin server that sends a 100 (Continue) response &MUST;
2147    ultimately send a final status code, once the request body is
2148        received and processed, unless it terminates the transport
2149        connection prematurely.
2150    </t>
2151    <t> If an origin server receives a request that does not include an
2152        Expect request-header field with the "100-continue" expectation,
2153        the request includes a request body, and the server responds
2154        with a final status code before reading the entire request body
2155        from the transport connection, then the server &SHOULD-NOT;  close
2156        the transport connection until it has read the entire request,
2157        or until the client closes the connection. Otherwise, the client
2158        might not reliably receive the response message. However, this
2159        requirement is not be construed as preventing a server from
2160        defending itself against denial-of-service attacks, or from
2161        badly broken client implementations.
2162      </t>
2163    </list>
2164</t>
2165<t>
2166   Requirements for HTTP/1.1 proxies:
2167  <list style="symbols">
2168    <t> If a proxy receives a request that includes an Expect request-header
2169        field with the "100-continue" expectation, and the proxy
2170        either knows that the next-hop server complies with HTTP/1.1 or
2171        higher, or does not know the HTTP version of the next-hop
2172        server, it &MUST; forward the request, including the Expect header
2173        field.
2174    </t>
2175    <t> If the proxy knows that the version of the next-hop server is
2176        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2177        respond with a 417 (Expectation Failed) status.
2178    </t>
2179    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2180        numbers received from recently-referenced next-hop servers.
2181    </t>
2182    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2183        request message was received from an HTTP/1.0 (or earlier)
2184        client and did not include an Expect request-header field with
2185        the "100-continue" expectation. This requirement overrides the
2186        general rule for forwarding of 1xx responses (see &status-1xx;).
2187    </t>
2188  </list>
2189</t>
2190</section>
2191
2192<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2193<t>
2194   If an HTTP/1.1 client sends a request which includes a request body,
2195   but which does not include an Expect request-header field with the
2196   "100-continue" expectation, and if the client is not directly
2197   connected to an HTTP/1.1 origin server, and if the client sees the
2198   connection close before receiving any status from the server, the
2199   client &SHOULD; retry the request.  If the client does retry this
2200   request, it &MAY; use the following "binary exponential backoff"
2201   algorithm to be assured of obtaining a reliable response:
2202  <list style="numbers">
2203    <t>
2204      Initiate a new connection to the server
2205    </t>
2206    <t>
2207      Transmit the request-headers
2208    </t>
2209    <t>
2210      Initialize a variable R to the estimated round-trip time to the
2211         server (e.g., based on the time it took to establish the
2212         connection), or to a constant value of 5 seconds if the round-trip
2213         time is not available.
2214    </t>
2215    <t>
2216       Compute T = R * (2**N), where N is the number of previous
2217         retries of this request.
2218    </t>
2219    <t>
2220       Wait either for an error response from the server, or for T
2221         seconds (whichever comes first)
2222    </t>
2223    <t>
2224       If no error response is received, after T seconds transmit the
2225         body of the request.
2226    </t>
2227    <t>
2228       If client sees that the connection is closed prematurely,
2229         repeat from step 1 until the request is accepted, an error
2230         response is received, or the user becomes impatient and
2231         terminates the retry process.
2232    </t>
2233  </list>
2234</t>
2235<t>
2236   If at any point an error status is received, the client
2237  <list style="symbols">
2238      <t>&SHOULD-NOT;  continue and</t>
2239
2240      <t>&SHOULD; close the connection if it has not completed sending the
2241        request message.</t>
2242    </list>
2243</t>
2244</section>
2245</section>
2246</section>
2247
2248
2249<section title="Header Field Definitions" anchor="header.fields">
2250<t>
2251   This section defines the syntax and semantics of HTTP/1.1 header fields
2252   related to message framing and transport protocols.
2253</t>
2254<t>
2255   For entity-header fields, both sender and recipient refer to either the
2256   client or the server, depending on who sends and who receives the entity.
2257</t>
2258
2259<section title="Connection" anchor="header.connection">
2260  <iref primary="true" item="Connection header" x:for-anchor=""/>
2261  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2262<t>
2263   The Connection general-header field allows the sender to specify
2264   options that are desired for that particular connection and &MUST-NOT;
2265   be communicated by proxies over further connections.
2266</t>
2267<t>
2268   The Connection header has the following grammar:
2269</t>
2270<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2271  Connection = "Connection" ":" 1#(connection-token)
2272  connection-token  = token
2273</artwork></figure>
2274<t>
2275   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2276   message is forwarded and, for each connection-token in this field,
2277   remove any header field(s) from the message with the same name as the
2278   connection-token. Connection options are signaled by the presence of
2279   a connection-token in the Connection header field, not by any
2280   corresponding additional header field(s), since the additional header
2281   field may not be sent if there are no parameters associated with that
2282   connection option.
2283</t>
2284<t>
2285   Message headers listed in the Connection header &MUST-NOT; include
2286   end-to-end headers, such as Cache-Control.
2287</t>
2288<t>
2289   HTTP/1.1 defines the "close" connection option for the sender to
2290   signal that the connection will be closed after completion of the
2291   response. For example,
2292</t>
2293<figure><artwork type="example">
2294    Connection: close
2295</artwork></figure>
2296<t>
2297   in either the request or the response header fields indicates that
2298   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2299   after the current request/response is complete.
2300</t>
2301<t>
2302   An HTTP/1.1 client that does not support persistent connections &MUST;
2303   include the "close" connection option in every request message.
2304</t>
2305<t>
2306   An HTTP/1.1 server that does not support persistent connections &MUST;
2307   include the "close" connection option in every response message that
2308   does not have a 1xx (informational) status code.
2309</t>
2310<t>
2311   A system receiving an HTTP/1.0 (or lower-version) message that
2312   includes a Connection header &MUST;, for each connection-token in this
2313   field, remove and ignore any header field(s) from the message with
2314   the same name as the connection-token. This protects against mistaken
2315   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2316</t>
2317</section>
2318
2319<section title="Content-Length" anchor="header.content-length">
2320  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2321  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2322<t>
2323   The Content-Length entity-header field indicates the size of the
2324   entity-body, in decimal number of OCTETs, sent to the recipient or,
2325   in the case of the HEAD method, the size of the entity-body that
2326   would have been sent had the request been a GET.
2327</t>
2328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2329  Content-Length    = "Content-Length" ":" 1*DIGIT
2330</artwork></figure>
2331<t>
2332   An example is
2333</t>
2334<figure><artwork type="example">
2335    Content-Length: 3495
2336</artwork></figure>
2337<t>
2338   Applications &SHOULD; use this field to indicate the transfer-length of
2339   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2340</t>
2341<t>
2342   Any Content-Length greater than or equal to zero is a valid value.
2343   <xref target="message.length"/> describes how to determine the length of a message-body
2344   if a Content-Length is not given.
2345</t>
2346<t>
2347   Note that the meaning of this field is significantly different from
2348   the corresponding definition in MIME, where it is an optional field
2349   used within the "message/external-body" content-type. In HTTP, it
2350   &SHOULD; be sent whenever the message's length can be determined prior
2351   to being transferred, unless this is prohibited by the rules in
2352   <xref target="message.length"/>.
2353</t>
2354</section>
2355
2356<section title="Date" anchor="header.date">
2357  <iref primary="true" item="Date header" x:for-anchor=""/>
2358  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2359<t>
2360   The Date general-header field represents the date and time at which
2361   the message was originated, having the same semantics as orig-date in
2362   <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"/>;
2363   it &MUST; be sent in rfc1123-date format.
2364</t>
2365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2366  Date  = "Date" ":" HTTP-date
2367</artwork></figure>
2368<t>
2369   An example is
2370</t>
2371<figure><artwork type="example">
2372    Date: Tue, 15 Nov 1994 08:12:31 GMT
2373</artwork></figure>
2374<t>
2375   Origin servers &MUST; include a Date header field in all responses,
2376   except in these cases:
2377  <list style="numbers">
2378      <t>If the response status code is 100 (Continue) or 101 (Switching
2379         Protocols), the response &MAY; include a Date header field, at
2380         the server's option.</t>
2381
2382      <t>If the response status code conveys a server error, e.g. 500
2383         (Internal Server Error) or 503 (Service Unavailable), and it is
2384         inconvenient or impossible to generate a valid Date.</t>
2385
2386      <t>If the server does not have a clock that can provide a
2387         reasonable approximation of the current time, its responses
2388         &MUST-NOT; include a Date header field. In this case, the rules
2389         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2390  </list>
2391</t>
2392<t>
2393   A received message that does not have a Date header field &MUST; be
2394   assigned one by the recipient if the message will be cached by that
2395   recipient or gatewayed via a protocol which requires a Date. An HTTP
2396   implementation without a clock &MUST-NOT; cache responses without
2397   revalidating them on every use. An HTTP cache, especially a shared
2398   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2399   clock with a reliable external standard.
2400</t>
2401<t>
2402   Clients &SHOULD; only send a Date header field in messages that include
2403   an entity-body, as in the case of the PUT and POST requests, and even
2404   then it is optional. A client without a clock &MUST-NOT; send a Date
2405   header field in a request.
2406</t>
2407<t>
2408   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2409   time subsequent to the generation of the message. It &SHOULD; represent
2410   the best available approximation of the date and time of message
2411   generation, unless the implementation has no means of generating a
2412   reasonably accurate date and time. In theory, the date ought to
2413   represent the moment just before the entity is generated. In
2414   practice, the date can be generated at any time during the message
2415   origination without affecting its semantic value.
2416</t>
2417
2418<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2419<t>
2420   Some origin server implementations might not have a clock available.
2421   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2422   values to a response, unless these values were associated
2423   with the resource by a system or user with a reliable clock. It &MAY;
2424   assign an Expires value that is known, at or before server
2425   configuration time, to be in the past (this allows "pre-expiration"
2426   of responses without storing separate Expires values for each
2427   resource).
2428</t>
2429</section>
2430</section>
2431
2432<section title="Host" anchor="header.host">
2433  <iref primary="true" item="Host header" x:for-anchor=""/>
2434  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2435<t>
2436   The Host request-header field specifies the Internet host and port
2437   number of the resource being requested, as obtained from the original
2438   URI given by the user or referring resource (generally an HTTP URL,
2439   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2440   the naming authority of the origin server or gateway given by the
2441   original URL. This allows the origin server or gateway to
2442   differentiate between internally-ambiguous URLs, such as the root "/"
2443   URL of a server for multiple host names on a single IP address.
2444</t>
2445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2446  Host = "Host" ":" uri-host [ ":" port ] ; <xref target="http.url"/>
2447</artwork></figure>
2448<t>
2449   A "host" without any trailing port information implies the default
2450   port for the service requested (e.g., "80" for an HTTP URL). For
2451   example, a request on the origin server for
2452   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2453</t>
2454<figure><artwork type="example">
2455    GET /pub/WWW/ HTTP/1.1
2456    Host: www.example.org
2457</artwork></figure>
2458<t>
2459   A client &MUST; include a Host header field in all HTTP/1.1 request
2460   messages. If the requested URI does not include an Internet host
2461   name for the service being requested, then the Host header field &MUST;
2462   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2463   request message it forwards does contain an appropriate Host header
2464   field that identifies the service being requested by the proxy. All
2465   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2466   status code to any HTTP/1.1 request message which lacks a Host header
2467   field.
2468</t>
2469<t>
2470   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2471   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2472   for other requirements relating to Host.
2473</t>
2474</section>
2475
2476<section title="TE" anchor="header.te">
2477  <iref primary="true" item="TE header" x:for-anchor=""/>
2478  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2479<t>
2480   The TE request-header field indicates what extension transfer-codings
2481   it is willing to accept in the response and whether or not it is
2482   willing to accept trailer fields in a chunked transfer-coding. Its
2483   value may consist of the keyword "trailers" and/or a comma-separated
2484   list of extension transfer-coding names with optional accept
2485   parameters (as described in <xref target="transfer.codings"/>).
2486</t>
2487<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2488  TE        = "TE" ":" #( t-codings )
2489  t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2490</artwork></figure>
2491<t>
2492   The presence of the keyword "trailers" indicates that the client is
2493   willing to accept trailer fields in a chunked transfer-coding, as
2494   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2495   transfer-coding values even though it does not itself represent a
2496   transfer-coding.
2497</t>
2498<t>
2499   Examples of its use are:
2500</t>
2501<figure><artwork type="example">
2502    TE: deflate
2503    TE:
2504    TE: trailers, deflate;q=0.5
2505</artwork></figure>
2506<t>
2507   The TE header field only applies to the immediate connection.
2508   Therefore, the keyword &MUST; be supplied within a Connection header
2509   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2510</t>
2511<t>
2512   A server tests whether a transfer-coding is acceptable, according to
2513   a TE field, using these rules:
2514  <list style="numbers">
2515    <x:lt>
2516      <t>The "chunked" transfer-coding is always acceptable. If the
2517         keyword "trailers" is listed, the client indicates that it is
2518         willing to accept trailer fields in the chunked response on
2519         behalf of itself and any downstream clients. The implication is
2520         that, if given, the client is stating that either all
2521         downstream clients are willing to accept trailer fields in the
2522         forwarded response, or that it will attempt to buffer the
2523         response on behalf of downstream recipients.
2524      </t><t>
2525         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2526         chunked response such that a client can be assured of buffering
2527         the entire response.</t>
2528    </x:lt>
2529    <x:lt>
2530      <t>If the transfer-coding being tested is one of the transfer-codings
2531         listed in the TE field, then it is acceptable unless it
2532         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2533         qvalue of 0 means "not acceptable.")</t>
2534    </x:lt>
2535    <x:lt>
2536      <t>If multiple transfer-codings are acceptable, then the
2537         acceptable transfer-coding with the highest non-zero qvalue is
2538         preferred.  The "chunked" transfer-coding always has a qvalue
2539         of 1.</t>
2540    </x:lt>
2541  </list>
2542</t>
2543<t>
2544   If the TE field-value is empty or if no TE field is present, the only
2545   transfer-coding  is "chunked". A message with no transfer-coding is
2546   always acceptable.
2547</t>
2548</section>
2549
2550<section title="Trailer" anchor="header.trailer">
2551  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2552  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2553<t>
2554   The Trailer general field value indicates that the given set of
2555   header fields is present in the trailer of a message encoded with
2556   chunked transfer-coding.
2557</t>
2558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2559  Trailer  = "Trailer" ":" 1#field-name
2560</artwork></figure>
2561<t>
2562   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2563   message using chunked transfer-coding with a non-empty trailer. Doing
2564   so allows the recipient to know which header fields to expect in the
2565   trailer.
2566</t>
2567<t>
2568   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2569   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2570   trailer fields in a "chunked" transfer-coding.
2571</t>
2572<t>
2573   Message header fields listed in the Trailer header field &MUST-NOT;
2574   include the following header fields:
2575  <list style="symbols">
2576    <t>Transfer-Encoding</t>
2577    <t>Content-Length</t>
2578    <t>Trailer</t>
2579  </list>
2580</t>
2581</section>
2582
2583<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2584  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2585  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2586<t>
2587   The Transfer-Encoding general-header field indicates what (if any)
2588   type of transformation has been applied to the message body in order
2589   to safely transfer it between the sender and the recipient. This
2590   differs from the content-coding in that the transfer-coding is a
2591   property of the message, not of the entity.
2592</t>
2593<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2594  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2595</artwork></figure>
2596<t>
2597   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2598</t>
2599<figure><artwork type="example">
2600  Transfer-Encoding: chunked
2601</artwork></figure>
2602<t>
2603   If multiple encodings have been applied to an entity, the transfer-codings
2604   &MUST; be listed in the order in which they were applied.
2605   Additional information about the encoding parameters &MAY; be provided
2606   by other entity-header fields not defined by this specification.
2607</t>
2608<t>
2609   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2610   header.
2611</t>
2612</section>
2613
2614<section title="Upgrade" anchor="header.upgrade">
2615  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2616  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2617<t>
2618   The Upgrade general-header allows the client to specify what
2619   additional communication protocols it supports and would like to use
2620   if the server finds it appropriate to switch protocols. The server
2621   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2622   response to indicate which protocol(s) are being switched.
2623</t>
2624<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2625  Upgrade        = "Upgrade" ":" 1#product
2626</artwork></figure>
2627<t>
2628   For example,
2629</t>
2630<figure><artwork type="example">
2631    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2632</artwork></figure>
2633<t>
2634   The Upgrade header field is intended to provide a simple mechanism
2635   for transition from HTTP/1.1 to some other, incompatible protocol. It
2636   does so by allowing the client to advertise its desire to use another
2637   protocol, such as a later version of HTTP with a higher major version
2638   number, even though the current request has been made using HTTP/1.1.
2639   This eases the difficult transition between incompatible protocols by
2640   allowing the client to initiate a request in the more commonly
2641   supported protocol while indicating to the server that it would like
2642   to use a "better" protocol if available (where "better" is determined
2643   by the server, possibly according to the nature of the method and/or
2644   resource being requested).
2645</t>
2646<t>
2647   The Upgrade header field only applies to switching application-layer
2648   protocols upon the existing transport-layer connection. Upgrade
2649   cannot be used to insist on a protocol change; its acceptance and use
2650   by the server is optional. The capabilities and nature of the
2651   application-layer communication after the protocol change is entirely
2652   dependent upon the new protocol chosen, although the first action
2653   after changing the protocol &MUST; be a response to the initial HTTP
2654   request containing the Upgrade header field.
2655</t>
2656<t>
2657   The Upgrade header field only applies to the immediate connection.
2658   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2659   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2660   HTTP/1.1 message.
2661</t>
2662<t>
2663   The Upgrade header field cannot be used to indicate a switch to a
2664   protocol on a different connection. For that purpose, it is more
2665   appropriate to use a 301, 302, 303, or 305 redirection response.
2666</t>
2667<t>
2668   This specification only defines the protocol name "HTTP" for use by
2669   the family of Hypertext Transfer Protocols, as defined by the HTTP
2670   version rules of <xref target="http.version"/> and future updates to this
2671   specification. Any token can be used as a protocol name; however, it
2672   will only be useful if both the client and server associate the name
2673   with the same protocol.
2674</t>
2675</section>
2676
2677<section title="Via" anchor="header.via">
2678  <iref primary="true" item="Via header" x:for-anchor=""/>
2679  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2680<t>
2681   The Via general-header field &MUST; be used by gateways and proxies to
2682   indicate the intermediate protocols and recipients between the user
2683   agent and the server on requests, and between the origin server and
2684   the client on responses. It is analogous to the "Received" field of
2685   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2686   avoiding request loops, and identifying the protocol capabilities of
2687   all senders along the request/response chain.
2688</t>
2689<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"/>
2690  Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2691  received-protocol = [ protocol-name "/" ] protocol-version
2692  protocol-name     = token
2693  protocol-version  = token
2694  received-by       = ( uri-host [ ":" port ] ) | pseudonym
2695  pseudonym         = token
2696</artwork></figure>
2697<t>
2698   The received-protocol indicates the protocol version of the message
2699   received by the server or client along each segment of the
2700   request/response chain. The received-protocol version is appended to
2701   the Via field value when the message is forwarded so that information
2702   about the protocol capabilities of upstream applications remains
2703   visible to all recipients.
2704</t>
2705<t>
2706   The protocol-name is optional if and only if it would be "HTTP". The
2707   received-by field is normally the host and optional port number of a
2708   recipient server or client that subsequently forwarded the message.
2709   However, if the real host is considered to be sensitive information,
2710   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2711   be assumed to be the default port of the received-protocol.
2712</t>
2713<t>
2714   Multiple Via field values represents each proxy or gateway that has
2715   forwarded the message. Each recipient &MUST; append its information
2716   such that the end result is ordered according to the sequence of
2717   forwarding applications.
2718</t>
2719<t>
2720   Comments &MAY; be used in the Via header field to identify the software
2721   of the recipient proxy or gateway, analogous to the User-Agent and
2722   Server header fields. However, all comments in the Via field are
2723   optional and &MAY; be removed by any recipient prior to forwarding the
2724   message.
2725</t>
2726<t>
2727   For example, a request message could be sent from an HTTP/1.0 user
2728   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2729   forward the request to a public proxy at p.example.net, which completes
2730   the request by forwarding it to the origin server at www.example.com.
2731   The request received by www.example.com would then have the following
2732   Via header field:
2733</t>
2734<figure><artwork type="example">
2735    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2736</artwork></figure>
2737<t>
2738   Proxies and gateways used as a portal through a network firewall
2739   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2740   the firewall region. This information &SHOULD; only be propagated if
2741   explicitly enabled. If not enabled, the received-by host of any host
2742   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2743   for that host.
2744</t>
2745<t>
2746   For organizations that have strong privacy requirements for hiding
2747   internal structures, a proxy &MAY; combine an ordered subsequence of
2748   Via header field entries with identical received-protocol values into
2749   a single such entry. For example,
2750</t>
2751<figure><artwork type="example">
2752    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2753</artwork></figure>
2754<t>
2755        could be collapsed to
2756</t>
2757<figure><artwork type="example">
2758    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2759</artwork></figure>
2760<t>
2761   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2762   under the same organizational control and the hosts have already been
2763   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2764   have different received-protocol values.
2765</t>
2766</section>
2767
2768</section>
2769
2770<section title="IANA Considerations" anchor="IANA.considerations">
2771<t>
2772   TBD.
2773</t>
2774</section>
2775
2776<section title="Security Considerations" anchor="security.considerations">
2777<t>
2778   This section is meant to inform application developers, information
2779   providers, and users of the security limitations in HTTP/1.1 as
2780   described by this document. The discussion does not include
2781   definitive solutions to the problems revealed, though it does make
2782   some suggestions for reducing security risks.
2783</t>
2784
2785<section title="Personal Information" anchor="personal.information">
2786<t>
2787   HTTP clients are often privy to large amounts of personal information
2788   (e.g. the user's name, location, mail address, passwords, encryption
2789   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2790   leakage of this information.
2791   We very strongly recommend that a convenient interface be provided
2792   for the user to control dissemination of such information, and that
2793   designers and implementors be particularly careful in this area.
2794   History shows that errors in this area often create serious security
2795   and/or privacy problems and generate highly adverse publicity for the
2796   implementor's company.
2797</t>
2798</section>
2799
2800<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2801<t>
2802   A server is in the position to save personal data about a user's
2803   requests which might identify their reading patterns or subjects of
2804   interest. This information is clearly confidential in nature and its
2805   handling can be constrained by law in certain countries. People using
2806   HTTP to provide data are responsible for ensuring that
2807   such material is not distributed without the permission of any
2808   individuals that are identifiable by the published results.
2809</t>
2810</section>
2811
2812<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2813<t>
2814   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2815   the documents returned by HTTP requests to be only those that were
2816   intended by the server administrators. If an HTTP server translates
2817   HTTP URIs directly into file system calls, the server &MUST; take
2818   special care not to serve files that were not intended to be
2819   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2820   other operating systems use ".." as a path component to indicate a
2821   directory level above the current one. On such a system, an HTTP
2822   server &MUST; disallow any such construct in the Request-URI if it
2823   would otherwise allow access to a resource outside those intended to
2824   be accessible via the HTTP server. Similarly, files intended for
2825   reference only internally to the server (such as access control
2826   files, configuration files, and script code) &MUST; be protected from
2827   inappropriate retrieval, since they might contain sensitive
2828   information. Experience has shown that minor bugs in such HTTP server
2829   implementations have turned into security risks.
2830</t>
2831</section>
2832
2833<section title="DNS Spoofing" anchor="dns.spoofing">
2834<t>
2835   Clients using HTTP rely heavily on the Domain Name Service, and are
2836   thus generally prone to security attacks based on the deliberate
2837   mis-association of IP addresses and DNS names. Clients need to be
2838   cautious in assuming the continuing validity of an IP number/DNS name
2839   association.
2840</t>
2841<t>
2842   In particular, HTTP clients &SHOULD; rely on their name resolver for
2843   confirmation of an IP number/DNS name association, rather than
2844   caching the result of previous host name lookups. Many platforms
2845   already can cache host name lookups locally when appropriate, and
2846   they &SHOULD; be configured to do so. It is proper for these lookups to
2847   be cached, however, only when the TTL (Time To Live) information
2848   reported by the name server makes it likely that the cached
2849   information will remain useful.
2850</t>
2851<t>
2852   If HTTP clients cache the results of host name lookups in order to
2853   achieve a performance improvement, they &MUST; observe the TTL
2854   information reported by DNS.
2855</t>
2856<t>
2857   If HTTP clients do not observe this rule, they could be spoofed when
2858   a previously-accessed server's IP address changes. As network
2859   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2860   possibility of this form of attack will grow. Observing this
2861   requirement thus reduces this potential security vulnerability.
2862</t>
2863<t>
2864   This requirement also improves the load-balancing behavior of clients
2865   for replicated servers using the same DNS name and reduces the
2866   likelihood of a user's experiencing failure in accessing sites which
2867   use that strategy.
2868</t>
2869</section>
2870
2871<section title="Proxies and Caching" anchor="attack.proxies">
2872<t>
2873   By their very nature, HTTP proxies are men-in-the-middle, and
2874   represent an opportunity for man-in-the-middle attacks. Compromise of
2875   the systems on which the proxies run can result in serious security
2876   and privacy problems. Proxies have access to security-related
2877   information, personal information about individual users and
2878   organizations, and proprietary information belonging to users and
2879   content providers. A compromised proxy, or a proxy implemented or
2880   configured without regard to security and privacy considerations,
2881   might be used in the commission of a wide range of potential attacks.
2882</t>
2883<t>
2884   Proxy operators should protect the systems on which proxies run as
2885   they would protect any system that contains or transports sensitive
2886   information. In particular, log information gathered at proxies often
2887   contains highly sensitive personal information, and/or information
2888   about organizations. Log information should be carefully guarded, and
2889   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2890</t>
2891<t>
2892   Proxy implementors should consider the privacy and security
2893   implications of their design and coding decisions, and of the
2894   configuration options they provide to proxy operators (especially the
2895   default configuration).
2896</t>
2897<t>
2898   Users of a proxy need to be aware that they are no trustworthier than
2899   the people who run the proxy; HTTP itself cannot solve this problem.
2900</t>
2901<t>
2902   The judicious use of cryptography, when appropriate, may suffice to
2903   protect against a broad range of security and privacy attacks. Such
2904   cryptography is beyond the scope of the HTTP/1.1 specification.
2905</t>
2906</section>
2907
2908<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2909<t>
2910   They exist. They are hard to defend against. Research continues.
2911   Beware.
2912</t>
2913</section>
2914</section>
2915
2916<section title="Acknowledgments" anchor="ack">
2917<t>
2918   This specification makes heavy use of the augmented BNF and generic
2919   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
2920   reuses many of the definitions provided by Nathaniel Borenstein and
2921   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2922   specification will help reduce past confusion over the relationship
2923   between HTTP and Internet mail message formats.
2924</t>
2925<t>
2926   HTTP has evolved considerably over the years. It has
2927   benefited from a large and active developer community--the many
2928   people who have participated on the www-talk mailing list--and it is
2929   that community which has been most responsible for the success of
2930   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2931   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2932   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2933   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2934   VanHeyningen deserve special recognition for their efforts in
2935   defining early aspects of the protocol.
2936</t>
2937<t>
2938   This document has benefited greatly from the comments of all those
2939   participating in the HTTP-WG. In addition to those already mentioned,
2940   the following individuals have contributed to this specification:
2941</t>
2942<t>
2943   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2944   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2945   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2946   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2947   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2948   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2949   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2950   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2951   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2952   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2953   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2954   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2955   Josh Cohen.
2956</t>
2957<t>
2958   Thanks to the "cave men" of Palo Alto. You know who you are.
2959</t>
2960<t>
2961   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2962   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2963   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2964   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2965   Larry Masinter for their help. And thanks go particularly to Jeff
2966   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2967</t>
2968<t>
2969   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2970   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2971   discovery of many of the problems that this document attempts to
2972   rectify.
2973</t>
2974</section>
2975
2976</middle>
2977<back>
2978
2979<references title="Normative References">
2980
2981<reference anchor="ISO-8859-1">
2982  <front>
2983    <title>
2984     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
2985    </title>
2986    <author>
2987      <organization>International Organization for Standardization</organization>
2988    </author>
2989    <date year="1998"/>
2990  </front>
2991  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
2992</reference>
2993
2994<reference anchor="Part2">
2995  <front>
2996    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
2997    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2998      <organization abbrev="Day Software">Day Software</organization>
2999      <address><email>fielding@gbiv.com</email></address>
3000    </author>
3001    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3002      <organization>One Laptop per Child</organization>
3003      <address><email>jg@laptop.org</email></address>
3004    </author>
3005    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3006      <organization abbrev="HP">Hewlett-Packard Company</organization>
3007      <address><email>JeffMogul@acm.org</email></address>
3008    </author>
3009    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3010      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3011      <address><email>henrikn@microsoft.com</email></address>
3012    </author>
3013    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3014      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3015      <address><email>LMM@acm.org</email></address>
3016    </author>
3017    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3018      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3019      <address><email>paulle@microsoft.com</email></address>
3020    </author>
3021    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3022      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3023      <address><email>timbl@w3.org</email></address>
3024    </author>
3025    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3026      <organization abbrev="W3C">World Wide Web Consortium</organization>
3027      <address><email>ylafon@w3.org</email></address>
3028    </author>
3029    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3030      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3031      <address><email>julian.reschke@greenbytes.de</email></address>
3032    </author>
3033    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3034  </front>
3035  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3036  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3037</reference>
3038
3039<reference anchor="Part3">
3040  <front>
3041    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3042    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3043      <organization abbrev="Day Software">Day Software</organization>
3044      <address><email>fielding@gbiv.com</email></address>
3045    </author>
3046    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3047      <organization>One Laptop per Child</organization>
3048      <address><email>jg@laptop.org</email></address>
3049    </author>
3050    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3051      <organization abbrev="HP">Hewlett-Packard Company</organization>
3052      <address><email>JeffMogul@acm.org</email></address>
3053    </author>
3054    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3055      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3056      <address><email>henrikn@microsoft.com</email></address>
3057    </author>
3058    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3059      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3060      <address><email>LMM@acm.org</email></address>
3061    </author>
3062    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3063      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3064      <address><email>paulle@microsoft.com</email></address>
3065    </author>
3066    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3067      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3068      <address><email>timbl@w3.org</email></address>
3069    </author>
3070    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3071      <organization abbrev="W3C">World Wide Web Consortium</organization>
3072      <address><email>ylafon@w3.org</email></address>
3073    </author>
3074    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3075      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3076      <address><email>julian.reschke@greenbytes.de</email></address>
3077    </author>
3078    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3079  </front>
3080  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3081  <x:source href="p3-payload.xml" basename="p3-payload"/>
3082</reference>
3083
3084<reference anchor="Part5">
3085  <front>
3086    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3087    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3088      <organization abbrev="Day Software">Day Software</organization>
3089      <address><email>fielding@gbiv.com</email></address>
3090    </author>
3091    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3092      <organization>One Laptop per Child</organization>
3093      <address><email>jg@laptop.org</email></address>
3094    </author>
3095    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3096      <organization abbrev="HP">Hewlett-Packard Company</organization>
3097      <address><email>JeffMogul@acm.org</email></address>
3098    </author>
3099    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3100      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3101      <address><email>henrikn@microsoft.com</email></address>
3102    </author>
3103    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3104      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3105      <address><email>LMM@acm.org</email></address>
3106    </author>
3107    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3108      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3109      <address><email>paulle@microsoft.com</email></address>
3110    </author>
3111    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3112      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3113      <address><email>timbl@w3.org</email></address>
3114    </author>
3115    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3116      <organization abbrev="W3C">World Wide Web Consortium</organization>
3117      <address><email>ylafon@w3.org</email></address>
3118    </author>
3119    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3120      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3121      <address><email>julian.reschke@greenbytes.de</email></address>
3122    </author>
3123    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3124  </front>
3125  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3126  <x:source href="p5-range.xml" basename="p5-range"/>
3127</reference>
3128
3129<reference anchor="Part6">
3130  <front>
3131    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3132    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3133      <organization abbrev="Day Software">Day Software</organization>
3134      <address><email>fielding@gbiv.com</email></address>
3135    </author>
3136    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3137      <organization>One Laptop per Child</organization>
3138      <address><email>jg@laptop.org</email></address>
3139    </author>
3140    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3141      <organization abbrev="HP">Hewlett-Packard Company</organization>
3142      <address><email>JeffMogul@acm.org</email></address>
3143    </author>
3144    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3145      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3146      <address><email>henrikn@microsoft.com</email></address>
3147    </author>
3148    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3149      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3150      <address><email>LMM@acm.org</email></address>
3151    </author>
3152    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3153      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3154      <address><email>paulle@microsoft.com</email></address>
3155    </author>
3156    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3157      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3158      <address><email>timbl@w3.org</email></address>
3159    </author>
3160    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3161      <organization abbrev="W3C">World Wide Web Consortium</organization>
3162      <address><email>ylafon@w3.org</email></address>
3163    </author>
3164    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3165      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3166      <address><email>julian.reschke@greenbytes.de</email></address>
3167    </author>
3168    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3169  </front>
3170  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3171  <x:source href="p6-cache.xml" basename="p6-cache"/>
3172</reference>
3173
3174<reference anchor="RFC822ABNF">
3175  <front>
3176    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3177    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3178      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3179      <address><email>DCrocker@UDel-Relay</email></address>
3180    </author>
3181    <date month="August" day="13" year="1982"/>
3182  </front>
3183  <seriesInfo name="STD" value="11"/>
3184  <seriesInfo name="RFC" value="822"/>
3185</reference>
3186
3187<reference anchor="RFC2045">
3188  <front>
3189    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3190    <author initials="N." surname="Freed" fullname="Ned Freed">
3191      <organization>Innosoft International, Inc.</organization>
3192      <address><email>ned@innosoft.com</email></address>
3193    </author>
3194    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3195      <organization>First Virtual Holdings</organization>
3196      <address><email>nsb@nsb.fv.com</email></address>
3197    </author>
3198    <date month="November" year="1996"/>
3199  </front>
3200  <seriesInfo name="RFC" value="2045"/>
3201</reference>
3202
3203<reference anchor="RFC2047">
3204  <front>
3205    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3206    <author initials="K." surname="Moore" fullname="Keith Moore">
3207      <organization>University of Tennessee</organization>
3208      <address><email>moore@cs.utk.edu</email></address>
3209    </author>
3210    <date month="November" year="1996"/>
3211  </front>
3212  <seriesInfo name="RFC" value="2047"/>
3213</reference>
3214
3215<reference anchor="RFC2119">
3216  <front>
3217    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3218    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3219      <organization>Harvard University</organization>
3220      <address><email>sob@harvard.edu</email></address>
3221    </author>
3222    <date month="March" year="1997"/>
3223  </front>
3224  <seriesInfo name="BCP" value="14"/>
3225  <seriesInfo name="RFC" value="2119"/>
3226</reference>
3227
3228<reference anchor="RFC2396">
3229  <front>
3230    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3232      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3233      <address><email>timbl@w3.org</email></address>
3234    </author>
3235    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3236      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3237      <address><email>fielding@ics.uci.edu</email></address>
3238    </author>
3239    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3240      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3241      <address><email>masinter@parc.xerox.com</email></address>
3242    </author>
3243    <date month="August" year="1998"/>
3244  </front>
3245  <seriesInfo name="RFC" value="2396"/>
3246</reference>
3247
3248<reference anchor="USASCII">
3249  <front>
3250    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3251    <author>
3252      <organization>American National Standards Institute</organization>
3253    </author>
3254    <date year="1986"/>
3255  </front>
3256  <seriesInfo name="ANSI" value="X3.4"/>
3257</reference>
3258
3259</references>
3260
3261<references title="Informative References">
3262
3263<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3264  <front>
3265    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3266    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3267      <organization/>
3268    </author>
3269    <author initials="J." surname="Gettys" fullname="J. Gettys">
3270      <organization/>
3271    </author>
3272    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3273      <organization/>
3274    </author>
3275    <author initials="H." surname="Lie" fullname="H. Lie">
3276      <organization/>
3277    </author>
3278    <author initials="C." surname="Lilley" fullname="C. Lilley">
3279      <organization/>
3280    </author>
3281    <date year="1997" month="September"/>
3282  </front>
3283  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3284</reference>
3285
3286<reference anchor="Pad1995">
3287  <front>
3288    <title>Improving HTTP Latency</title>
3289    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3290      <organization/>
3291    </author>
3292    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3293      <organization/>
3294    </author>
3295    <date year="1995" month="December"/>
3296  </front>
3297  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3298  <annotation>
3299    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3300    which is available at <eref target="http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/HTTPLatency.html"/>.
3301  </annotation>
3302</reference>
3303
3304<reference anchor="RFC822">
3305  <front>
3306    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3307    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3308      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3309      <address><email>DCrocker@UDel-Relay</email></address>
3310    </author>
3311    <date month="August" day="13" year="1982"/>
3312  </front>
3313  <seriesInfo name="STD" value="11"/>
3314  <seriesInfo name="RFC" value="822"/>
3315</reference>
3316
3317<reference anchor="RFC959">
3318  <front>
3319    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3320    <author initials="J." surname="Postel" fullname="J. Postel">
3321      <organization>Information Sciences Institute (ISI)</organization>
3322    </author>
3323    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3324      <organization/>
3325    </author>
3326    <date month="October" year="1985"/>
3327  </front>
3328  <seriesInfo name="STD" value="9"/>
3329  <seriesInfo name="RFC" value="959"/>
3330</reference>
3331
3332<reference anchor="RFC1123">
3333  <front>
3334    <title>Requirements for Internet Hosts - Application and Support</title>
3335    <author initials="R." surname="Braden" fullname="Robert Braden">
3336      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3337      <address><email>Braden@ISI.EDU</email></address>
3338    </author>
3339    <date month="October" year="1989"/>
3340  </front>
3341  <seriesInfo name="STD" value="3"/>
3342  <seriesInfo name="RFC" value="1123"/>
3343</reference>
3344
3345<reference anchor="RFC1305">
3346  <front>
3347    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3348    <author initials="D." surname="Mills" fullname="David L. Mills">
3349      <organization>University of Delaware, Electrical Engineering Department</organization>
3350      <address><email>mills@udel.edu</email></address>
3351    </author>
3352    <date month="March" year="1992"/>
3353  </front>
3354  <seriesInfo name="RFC" value="1305"/>
3355</reference>
3356
3357<reference anchor="RFC1436">
3358  <front>
3359    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3360    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3361      <organization>University of Minnesota, Computer and Information Services</organization>
3362      <address><email>fxa@boombox.micro.umn.edu</email></address>
3363    </author>
3364    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3365      <organization>University of Minnesota, Computer and Information Services</organization>
3366      <address><email>mpm@boombox.micro.umn.edu</email></address>
3367    </author>
3368    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3369      <organization>University of Minnesota, Computer and Information Services</organization>
3370      <address><email>lindner@boombox.micro.umn.edu</email></address>
3371    </author>
3372    <author initials="D." surname="Johnson" fullname="David Johnson">
3373      <organization>University of Minnesota, Computer and Information Services</organization>
3374      <address><email>dmj@boombox.micro.umn.edu</email></address>
3375    </author>
3376    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3377      <organization>University of Minnesota, Computer and Information Services</organization>
3378      <address><email>daniel@boombox.micro.umn.edu</email></address>
3379    </author>
3380    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3381      <organization>University of Minnesota, Computer and Information Services</organization>
3382      <address><email>alberti@boombox.micro.umn.edu</email></address>
3383    </author>
3384    <date month="March" year="1993"/>
3385  </front>
3386  <seriesInfo name="RFC" value="1436"/>
3387</reference>
3388
3389<reference anchor="RFC1630">
3390  <front>
3391    <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>
3392    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3393      <organization>CERN, World-Wide Web project</organization>
3394      <address><email>timbl@info.cern.ch</email></address>
3395    </author>
3396    <date month="June" year="1994"/>
3397  </front>
3398  <seriesInfo name="RFC" value="1630"/>
3399</reference>
3400
3401<reference anchor="RFC1737">
3402  <front>
3403    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3404    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3405      <organization>Xerox Palo Alto Research Center</organization>
3406      <address><email>masinter@parc.xerox.com</email></address>
3407    </author>
3408    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3409      <organization>MIT Laboratory for Computer Science</organization>
3410      <address><email>sollins@lcs.mit.edu</email></address>
3411    </author>
3412    <date month="December" year="1994"/>
3413  </front>
3414  <seriesInfo name="RFC" value="1737"/>
3415</reference>
3416
3417<reference anchor="RFC1738">
3418  <front>
3419    <title>Uniform Resource Locators (URL)</title>
3420    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3421      <organization>CERN, World-Wide Web project</organization>
3422      <address><email>timbl@info.cern.ch</email></address>
3423    </author>
3424    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3425      <organization>Xerox PARC</organization>
3426      <address><email>masinter@parc.xerox.com</email></address>
3427    </author>
3428    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3429      <organization>University of Minnesota, Computer and Information Services</organization>
3430      <address><email>mpm@boombox.micro.umn.edu</email></address>
3431    </author>
3432    <date month="December" year="1994"/>
3433  </front>
3434  <seriesInfo name="RFC" value="1738"/>
3435</reference>
3436
3437<reference anchor="RFC1808">
3438  <front>
3439    <title>Relative Uniform Resource Locators</title>
3440    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3441      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3442      <address><email>fielding@ics.uci.edu</email></address>
3443    </author>
3444    <date month="June" year="1995"/>
3445  </front>
3446  <seriesInfo name="RFC" value="1808"/>
3447</reference>
3448
3449<reference anchor="RFC1900">
3450  <front>
3451    <title>Renumbering Needs Work</title>
3452    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3453      <organization>CERN, Computing and Networks Division</organization>
3454      <address><email>brian@dxcoms.cern.ch</email></address>
3455    </author>
3456    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3457      <organization>cisco Systems</organization>
3458      <address><email>yakov@cisco.com</email></address>
3459    </author>
3460    <date month="February" year="1996"/>
3461  </front>
3462  <seriesInfo name="RFC" value="1900"/>
3463</reference>
3464
3465<reference anchor="RFC1945">
3466  <front>
3467    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3468    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3469      <organization>MIT, Laboratory for Computer Science</organization>
3470      <address><email>timbl@w3.org</email></address>
3471    </author>
3472    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3473      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3474      <address><email>fielding@ics.uci.edu</email></address>
3475    </author>
3476    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3477      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3478      <address><email>frystyk@w3.org</email></address>
3479    </author>
3480    <date month="May" year="1996"/>
3481  </front>
3482  <seriesInfo name="RFC" value="1945"/>
3483</reference>
3484
3485<reference anchor="RFC2068">
3486  <front>
3487    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3488    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3489      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3490      <address><email>fielding@ics.uci.edu</email></address>
3491    </author>
3492    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3493      <organization>MIT Laboratory for Computer Science</organization>
3494      <address><email>jg@w3.org</email></address>
3495    </author>
3496    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3497      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3498      <address><email>mogul@wrl.dec.com</email></address>
3499    </author>
3500    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3501      <organization>MIT Laboratory for Computer Science</organization>
3502      <address><email>frystyk@w3.org</email></address>
3503    </author>
3504    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3505      <organization>MIT Laboratory for Computer Science</organization>
3506      <address><email>timbl@w3.org</email></address>
3507    </author>
3508    <date month="January" year="1997"/>
3509  </front>
3510  <seriesInfo name="RFC" value="2068"/>
3511</reference>
3512
3513<reference anchor="RFC2145">
3514  <front>
3515    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3516    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3517      <organization>Western Research Laboratory</organization>
3518      <address><email>mogul@wrl.dec.com</email></address>
3519    </author>
3520    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3521      <organization>Department of Information and Computer Science</organization>
3522      <address><email>fielding@ics.uci.edu</email></address>
3523    </author>
3524    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3525      <organization>MIT Laboratory for Computer Science</organization>
3526      <address><email>jg@w3.org</email></address>
3527    </author>
3528    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3529      <organization>W3 Consortium</organization>
3530      <address><email>frystyk@w3.org</email></address>
3531    </author>
3532    <date month="May" year="1997"/>
3533  </front>
3534  <seriesInfo name="RFC" value="2145"/>
3535</reference>
3536
3537<reference anchor="RFC2324">
3538  <front>
3539    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3540    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3541      <organization>Xerox Palo Alto Research Center</organization>
3542      <address><email>masinter@parc.xerox.com</email></address>
3543    </author>
3544    <date month="April" day="1" year="1998"/>
3545  </front>
3546  <seriesInfo name="RFC" value="2324"/>
3547</reference>
3548
3549<reference anchor="RFC2616">
3550  <front>
3551    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3552    <author initials="R." surname="Fielding" fullname="R. Fielding">
3553      <organization>University of California, Irvine</organization>
3554      <address><email>fielding@ics.uci.edu</email></address>
3555    </author>
3556    <author initials="J." surname="Gettys" fullname="J. Gettys">
3557      <organization>W3C</organization>
3558      <address><email>jg@w3.org</email></address>
3559    </author>
3560    <author initials="J." surname="Mogul" fullname="J. Mogul">
3561      <organization>Compaq Computer Corporation</organization>
3562      <address><email>mogul@wrl.dec.com</email></address>
3563    </author>
3564    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3565      <organization>MIT Laboratory for Computer Science</organization>
3566      <address><email>frystyk@w3.org</email></address>
3567    </author>
3568    <author initials="L." surname="Masinter" fullname="L. Masinter">
3569      <organization>Xerox Corporation</organization>
3570      <address><email>masinter@parc.xerox.com</email></address>
3571    </author>
3572    <author initials="P." surname="Leach" fullname="P. Leach">
3573      <organization>Microsoft Corporation</organization>
3574      <address><email>paulle@microsoft.com</email></address>
3575    </author>
3576    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3577      <organization>W3C</organization>
3578      <address><email>timbl@w3.org</email></address>
3579    </author>
3580    <date month="June" year="1999"/>
3581  </front>
3582  <seriesInfo name="RFC" value="2616"/>
3583</reference>
3584
3585<reference anchor="RFC2821">
3586  <front>
3587    <title>Simple Mail Transfer Protocol</title>
3588    <author initials="J." surname="Klensin" fullname="J. Klensin">
3589      <organization>AT&amp;T Laboratories</organization>
3590      <address><email>klensin@research.att.com</email></address>
3591    </author>
3592    <date year="2001" month="April"/>
3593  </front>
3594  <seriesInfo name="RFC" value="2821"/>
3595</reference>
3596
3597<reference anchor="RFC2822">
3598  <front>
3599    <title>Internet Message Format</title>
3600    <author initials="P." surname="Resnick" fullname="P. Resnick">
3601      <organization>QUALCOMM Incorporated</organization>
3602    </author>
3603    <date year="2001" month="April"/>
3604  </front> 
3605  <seriesInfo name="RFC" value="2822"/>
3606</reference>
3607
3608<reference anchor='RFC3977'>
3609  <front>
3610    <title>Network News Transfer Protocol (NNTP)</title>
3611    <author initials='C.' surname='Feather' fullname='C. Feather'>
3612      <organization>THUS plc</organization>
3613      <address><email>clive@demon.net</email></address>
3614    </author>
3615    <date year='2006' month='October' />
3616  </front>
3617  <seriesInfo name="RFC" value="3977"/>
3618</reference>
3619
3620<reference anchor="RFC4288">
3621  <front>
3622    <title>Media Type Specifications and Registration Procedures</title>
3623    <author initials="N." surname="Freed" fullname="N. Freed">
3624      <organization>Sun Microsystems</organization>
3625      <address>
3626        <email>ned.freed@mrochek.com</email>
3627      </address>
3628    </author>
3629    <author initials="J." surname="Klensin" fullname="J. Klensin">
3630      <organization/>
3631      <address>
3632        <email>klensin+ietf@jck.com</email>
3633      </address>
3634    </author>
3635    <date year="2005" month="December"/>
3636  </front>
3637  <seriesInfo name="BCP" value="13"/>
3638  <seriesInfo name="RFC" value="4288"/>
3639</reference>
3640
3641<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3642  <front>
3643  <title>Analysis of HTTP Performance Problems</title>
3644  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3645    <organization/>
3646  </author>
3647  <date/>
3648  </front>
3649</reference>
3650
3651<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3652  <front>
3653  <title>Analysis of HTTP Performance</title>
3654  <author initials="J." surname="Touch" fullname="Joe Touch">
3655    <organization>USC/Information Sciences Institute</organization>
3656    <address><email>touch@isi.edu</email></address>
3657  </author>
3658  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3659    <organization>USC/Information Sciences Institute</organization>
3660    <address><email>johnh@isi.edu</email></address>
3661  </author>
3662  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3663    <organization>USC/Information Sciences Institute</organization>
3664    <address><email>katia@isi.edu</email></address>
3665  </author>
3666  <date year="1998" month="Aug"/>
3667  </front>
3668  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3669  <annotation>(original report dated Aug. 1996)</annotation>
3670</reference>
3671
3672<reference anchor="WAIS">
3673  <front>
3674    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3675    <author initials="F." surname="Davis" fullname="F. Davis">
3676      <organization>Thinking Machines Corporation</organization>
3677    </author>
3678    <author initials="B." surname="Kahle" fullname="B. Kahle">
3679      <organization>Thinking Machines Corporation</organization>
3680    </author>
3681    <author initials="H." surname="Morris" fullname="H. Morris">
3682      <organization>Thinking Machines Corporation</organization>
3683    </author>
3684    <author initials="J." surname="Salem" fullname="J. Salem">
3685      <organization>Thinking Machines Corporation</organization>
3686    </author>
3687    <author initials="T." surname="Shen" fullname="T. Shen">
3688      <organization>Thinking Machines Corporation</organization>
3689    </author>
3690    <author initials="R." surname="Wang" fullname="R. Wang">
3691      <organization>Thinking Machines Corporation</organization>
3692    </author>
3693    <author initials="J." surname="Sui" fullname="J. Sui">
3694      <organization>Thinking Machines Corporation</organization>
3695    </author>
3696    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3697      <organization>Thinking Machines Corporation</organization>
3698    </author>
3699    <date month="April" year="1990"/>
3700  </front>
3701  <seriesInfo name="Thinking Machines Corporation" value=""/>
3702</reference>
3703
3704</references>
3705
3706
3707<section title="Internet Media Types" anchor="internet.media.type.http">
3708<t>
3709   In addition to defining HTTP/1.1, this document serves
3710   as the specification for the Internet media type "message/http" and
3711   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3712</t>
3713<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3714<iref item="Media Type" subitem="message/http" primary="true"/>
3715<iref item="message/http Media Type" primary="true"/>
3716<t>
3717   The message/http type can be used to enclose a single HTTP request or
3718   response message, provided that it obeys the MIME restrictions for all
3719   "message" types regarding line length and encodings.
3720</t>
3721<t>
3722  <list style="hanging" x:indent="12em">
3723    <t hangText="Type name:">
3724      message
3725    </t>
3726    <t hangText="Subtype name:">
3727      http
3728    </t>
3729    <t hangText="Required parameters:">
3730      none
3731    </t>
3732    <t hangText="Optional parameters:">
3733      version, msgtype
3734      <list style="hanging">
3735        <t hangText="version:">
3736          The HTTP-Version number of the enclosed message
3737          (e.g., "1.1"). If not present, the version can be
3738          determined from the first line of the body.
3739        </t>
3740        <t hangText="msgtype:">
3741          The message type -- "request" or "response". If not
3742          present, the type can be determined from the first
3743          line of the body.
3744        </t>
3745      </list>
3746    </t>
3747    <t hangText="Encoding considerations:">
3748      only "7bit", "8bit", or "binary" are permitted
3749    </t>
3750    <t hangText="Security considerations:">
3751      none
3752    </t>
3753    <t hangText="Interoperability considerations:">
3754      none
3755    </t>
3756    <t hangText="Published specification:">
3757      This specification (see <xref target="internet.media.type.message.http"/>).
3758    </t>
3759    <t hangText="Applications that use this media type:">
3760    </t>
3761    <t hangText="Additional information:">
3762      <list style="hanging">
3763        <t hangText="Magic number(s):">none</t>
3764        <t hangText="File extension(s):">none</t>
3765        <t hangText="Macintosh file type code(s):">none</t>
3766      </list>
3767    </t>
3768    <t hangText="Person and email address to contact for further information:">
3769      See Authors Section.
3770    </t>
3771                <t hangText="Intended usage:">
3772                  COMMON
3773    </t>
3774                <t hangText="Restrictions on usage:">
3775                  none
3776    </t>
3777    <t hangText="Author/Change controller:">
3778      IESG
3779    </t>
3780  </list>
3781</t>
3782</section>
3783<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3784<iref item="Media Type" subitem="application/http" primary="true"/>
3785<iref item="application/http Media Type" primary="true"/>
3786<t>
3787   The application/http type can be used to enclose a pipeline of one or more
3788   HTTP request or response messages (not intermixed).
3789</t>
3790<t>
3791  <list style="hanging" x:indent="12em">
3792    <t hangText="Type name:">
3793      application
3794    </t>
3795    <t hangText="Subtype name:">
3796      http
3797    </t>
3798    <t hangText="Required parameters:">
3799      none
3800    </t>
3801    <t hangText="Optional parameters:">
3802      version, msgtype
3803      <list style="hanging">
3804        <t hangText="version:">
3805          The HTTP-Version number of the enclosed messages
3806          (e.g., "1.1"). If not present, the version can be
3807          determined from the first line of the body.
3808        </t>
3809        <t hangText="msgtype:">
3810          The message type -- "request" or "response". If not
3811          present, the type can be determined from the first
3812          line of the body.
3813        </t>
3814      </list>
3815    </t>
3816    <t hangText="Encoding considerations:">
3817      HTTP messages enclosed by this type
3818      are in "binary" format; use of an appropriate
3819      Content-Transfer-Encoding is required when
3820      transmitted via E-mail.
3821    </t>
3822    <t hangText="Security considerations:">
3823      none
3824    </t>
3825    <t hangText="Interoperability considerations:">
3826      none
3827    </t>
3828    <t hangText="Published specification:">
3829      This specification (see <xref target="internet.media.type.application.http"/>).
3830    </t>
3831    <t hangText="Applications that use this media type:">
3832    </t>
3833    <t hangText="Additional information:">
3834      <list style="hanging">
3835        <t hangText="Magic number(s):">none</t>
3836        <t hangText="File extension(s):">none</t>
3837        <t hangText="Macintosh file type code(s):">none</t>
3838      </list>
3839    </t>
3840    <t hangText="Person and email address to contact for further information:">
3841      See Authors Section.
3842    </t>
3843                <t hangText="Intended usage:">
3844                  COMMON
3845    </t>
3846                <t hangText="Restrictions on usage:">
3847                  none
3848    </t>
3849    <t hangText="Author/Change controller:">
3850      IESG
3851    </t>
3852  </list>
3853</t>
3854</section>
3855</section>
3856
3857<section title="Tolerant Applications" anchor="tolerant.applications">
3858<t>
3859   Although this document specifies the requirements for the generation
3860   of HTTP/1.1 messages, not all applications will be correct in their
3861   implementation. We therefore recommend that operational applications
3862   be tolerant of deviations whenever those deviations can be
3863   interpreted unambiguously.
3864</t>
3865<t>
3866   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3867   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3868   accept any amount of SP or HTAB characters between fields, even though
3869   only a single SP is required.
3870</t>
3871<t>
3872   The line terminator for message-header fields is the sequence CRLF.
3873   However, we recommend that applications, when parsing such headers,
3874   recognize a single LF as a line terminator and ignore the leading CR.
3875</t>
3876<t>
3877   The character set of an entity-body &SHOULD; be labeled as the lowest
3878   common denominator of the character codes used within that body, with
3879   the exception that not labeling the entity is preferred over labeling
3880   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3881</t>
3882<t>
3883   Additional rules for requirements on parsing and encoding of dates
3884   and other potential problems with date encodings include:
3885</t>
3886<t>
3887  <list style="symbols">
3888     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3889        which appears to be more than 50 years in the future is in fact
3890        in the past (this helps solve the "year 2000" problem).</t>
3891
3892     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3893        Expires date as earlier than the proper value, but &MUST-NOT;
3894        internally represent a parsed Expires date as later than the
3895        proper value.</t>
3896
3897     <t>All expiration-related calculations &MUST; be done in GMT. The
3898        local time zone &MUST-NOT; influence the calculation or comparison
3899        of an age or expiration time.</t>
3900
3901     <t>If an HTTP header incorrectly carries a date value with a time
3902        zone other than GMT, it &MUST; be converted into GMT using the
3903        most conservative possible conversion.</t>
3904  </list>
3905</t>
3906</section>
3907
3908<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3909<t>
3910   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3911   simplify the process of date comparison. Proxies and gateways from
3912   other protocols &SHOULD; ensure that any Date header field present in a
3913   message conforms to one of the HTTP/1.1 formats and rewrite the date
3914   if necessary.
3915</t>
3916</section>
3917
3918<section title="Compatibility with Previous Versions" anchor="compatibility">
3919<t>
3920   It is beyond the scope of a protocol specification to mandate
3921   compliance with previous versions. HTTP/1.1 was deliberately
3922   designed, however, to make supporting previous versions easy. It is
3923   worth noting that, at the time of composing this specification
3924   (1996), we would expect commercial HTTP/1.1 servers to:
3925  <list style="symbols">
3926     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3927        1.1 requests;</t>
3928
3929     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3930        1.1;</t>
3931
3932     <t>respond appropriately with a message in the same major version
3933        used by the client.</t>
3934  </list>
3935</t>
3936<t>
3937   And we would expect HTTP/1.1 clients to:
3938  <list style="symbols">
3939     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3940        responses;</t>
3941
3942     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3943        1.1.</t>
3944  </list>
3945</t>
3946<t>
3947   For most implementations of HTTP/1.0, each connection is established
3948   by the client prior to the request and closed by the server after
3949   sending the response. Some implementations implement the Keep-Alive
3950   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3951</t>
3952
3953<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3954<t>
3955   This section summarizes major differences between versions HTTP/1.0
3956   and HTTP/1.1.
3957</t>
3958
3959<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">
3960<t>
3961   The requirements that clients and servers support the Host request-header,
3962   report an error if the Host request-header (<xref target="header.host"/>) is
3963   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3964   are among the most important changes defined by this
3965   specification.
3966</t>
3967<t>
3968   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3969   addresses and servers; there was no other established mechanism for
3970   distinguishing the intended server of a request than the IP address
3971   to which that request was directed. The changes outlined above will
3972   allow the Internet, once older HTTP clients are no longer common, to
3973   support multiple Web sites from a single IP address, greatly
3974   simplifying large operational Web servers, where allocation of many
3975   IP addresses to a single host has created serious problems. The
3976   Internet will also be able to recover the IP addresses that have been
3977   allocated for the sole purpose of allowing special-purpose domain
3978   names to be used in root-level HTTP URLs. Given the rate of growth of
3979   the Web, and the number of servers already deployed, it is extremely
3980   important that all implementations of HTTP (including updates to
3981   existing HTTP/1.0 applications) correctly implement these
3982   requirements:
3983  <list style="symbols">
3984     <t>Both clients and servers &MUST; support the Host request-header.</t>
3985
3986     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3987
3988     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3989        request does not include a Host request-header.</t>
3990
3991     <t>Servers &MUST; accept absolute URIs.</t>
3992  </list>
3993</t>
3994</section>
3995</section>
3996
3997<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3998<t>
3999   Some clients and servers might wish to be compatible with some
4000   previous implementations of persistent connections in HTTP/1.0
4001   clients and servers. Persistent connections in HTTP/1.0 are
4002   explicitly negotiated as they are not the default behavior. HTTP/1.0
4003   experimental implementations of persistent connections are faulty,
4004   and the new facilities in HTTP/1.1 are designed to rectify these
4005   problems. The problem was that some existing 1.0 clients may be
4006   sending Keep-Alive to a proxy server that doesn't understand
4007   Connection, which would then erroneously forward it to the next
4008   inbound server, which would establish the Keep-Alive connection and
4009   result in a hung HTTP/1.0 proxy waiting for the close on the
4010   response. The result is that HTTP/1.0 clients must be prevented from
4011   using Keep-Alive when talking to proxies.
4012</t>
4013<t>
4014   However, talking to proxies is the most important use of persistent
4015   connections, so that prohibition is clearly unacceptable. Therefore,
4016   we need some other mechanism for indicating a persistent connection
4017   is desired, which is safe to use even when talking to an old proxy
4018   that ignores Connection. Persistent connections are the default for
4019   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4020   declaring non-persistence. See <xref target="header.connection"/>.
4021</t>
4022<t>
4023   The original HTTP/1.0 form of persistent connections (the Connection:
4024   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4025</t>
4026</section>
4027
4028<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4029<t>
4030   This specification has been carefully audited to correct and
4031   disambiguate key word usage; RFC 2068 had many problems in respect to
4032   the conventions laid out in <xref target="RFC2119"/>.
4033</t>
4034<t>
4035   Transfer-coding and message lengths all interact in ways that
4036   required fixing exactly when chunked encoding is used (to allow for
4037   transfer encoding that may not be self delimiting); it was important
4038   to straighten out exactly how message lengths are computed. (Sections
4039   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4040   <xref target="header.content-length" format="counter"/>,
4041   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4042</t>
4043<t>
4044   The use and interpretation of HTTP version numbers has been clarified
4045   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4046   version they support to deal with problems discovered in HTTP/1.0
4047   implementations (<xref target="http.version"/>)
4048</t>
4049<t>
4050   Transfer-coding had significant problems, particularly with
4051   interactions with chunked encoding. The solution is that transfer-codings
4052   become as full fledged as content-codings. This involves
4053   adding an IANA registry for transfer-codings (separate from content
4054   codings), a new header field (TE) and enabling trailer headers in the
4055   future. Transfer encoding is a major performance benefit, so it was
4056   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4057   interoperability problem that could have occurred due to interactions
4058   between authentication trailers, chunked encoding and HTTP/1.0
4059   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4060   and <xref target="header.te" format="counter"/>)
4061</t>
4062</section>
4063
4064<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4065<t>
4066  The CHAR rule does not allow the NUL character anymore (this affects
4067  the comment and quoted-string rules).
4068  (<xref target="basic.rules"/>)
4069</t>
4070<t>
4071  Clarify that HTTP-Version is case sensitive.
4072  (<xref target="http.version"/>)
4073</t>
4074<t>
4075  Remove reference to non-existant identity transfer-coding value tokens.
4076  (Sections <xref format="counter" target="transfer.codings"/> and
4077  <xref format="counter" target="message.length"/>)
4078</t>
4079<t>
4080  Clarification that the chunk length does not include
4081  the count of the octets in the chunk header and trailer.
4082  (<xref target="chunked.transfer.encoding"/>)
4083</t>
4084<t>
4085  Fix BNF to add query, as the abs_path production in
4086  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4087  (<xref target="request-uri"/>)
4088</t>
4089<t>
4090  Clarify exactly when close connection options must be sent.
4091  (<xref target="header.connection"/>)
4092</t>
4093</section>
4094</section>
4095
4096<section title="Change Log (to be removed by RFC Editor before publication)">
4097
4098<section title="Since RFC2616">
4099<t>
4100  Extracted relevant partitions from <xref target="RFC2616"/>.
4101</t>
4102</section>
4103
4104<section title="Since draft-ietf-httpbis-p1-messaging-00">
4105<t>
4106  Closed issues:
4107  <list style="symbols"> 
4108    <t>
4109      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4110      "HTTP Version should be case sensitive"
4111      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4112    </t>
4113    <t>
4114      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4115      "'unsafe' characters"
4116      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4117    </t>
4118    <t>
4119      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4120      "Chunk Size Definition"
4121      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4122    </t>
4123    <t>
4124      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4125      "Message Length"
4126      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4127    </t>
4128    <t>
4129      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4130      "Media Type Registrations"
4131      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4132    </t>
4133    <t>
4134      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4135      "URI includes query"
4136      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4137    </t>
4138    <t>
4139      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4140      "No close on 1xx responses"
4141      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4142    </t>
4143    <t>
4144      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4145      "Remove 'identity' token references"
4146      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4147    </t>
4148    <t>
4149      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4150      "Import query BNF"
4151    </t>
4152    <t>
4153      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4154      "qdtext BNF"
4155    </t>
4156    <t>
4157      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4158      "Normative and Informative references"
4159    </t>
4160    <t>
4161      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4162      "RFC2606 Compliance"
4163    </t>
4164    <t>
4165      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4166      "RFC977 reference"
4167    </t>
4168    <t>
4169      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4170      "RFC1700 references"
4171    </t>
4172    <t>
4173      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4174      "inconsistency in date format explanation"
4175    </t>
4176    <t>
4177      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4178      "Date reference typo"
4179    </t>
4180    <t>
4181      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4182      "Informative references"
4183    </t>
4184    <t>
4185      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4186      "ISO-8859-1 Reference"
4187    </t>
4188    <t>
4189      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4190      "Normative up-to-date references"
4191    </t>
4192  </list>
4193</t>
4194<t>
4195  Other changes:
4196  <list style="symbols"> 
4197    <t>
4198      Update media type registrations to use RFC4288 template.
4199    </t>
4200    <t>
4201      Use names of RFC4234 core rules DQUOTE and HTAB,
4202      fix broken ABNF for chunk-data
4203      (work in progress on <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4204    </t>
4205  </list>
4206</t>
4207</section>
4208
4209<section title="Since draft-ietf-httpbis-p1-messaging-01">
4210<t>
4211  Closed issues:
4212  <list style="symbols"> 
4213    <t>
4214      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4215      "Bodies on GET (and other) requests"
4216    </t>
4217    <t>
4218      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4219      "rel_path not used"
4220    </t>
4221  </list>
4222</t>
4223<t>
4224  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4225  <list style="symbols"> 
4226    <t>
4227      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4228      "trailer-part").
4229    </t>
4230    <t>
4231      Avoid underscore character in rule names ("http_URL" ->
4232      "http-URL", "abs_path" -> "path-absolute").
4233    </t>
4234    <t>
4235      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4236      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4237      have to be updated when switching over to RFC3986.
4238    </t>
4239    <t>
4240      Synchronize core rules with RFC5234 (this includes a change to CHAR
4241      which now excludes NUL).
4242    </t>
4243    <t>
4244      Get rid of prose rules that span multiple lines.
4245    </t>
4246    <t>
4247      Get rid of unused rules LOALPHA and UPALPHA.
4248    </t>
4249    <t>
4250      Move "Product Tokens" section (back) into Part 1, as "token" is used
4251      in the definition of the Upgrade header.
4252    </t>
4253  </list>
4254</t>
4255</section>
4256
4257</section>
4258
4259</back>
4260</rfc>
Note: See TracBrowser for help on using the repository browser.