source: draft-ietf-httpbis/latest/p1-messaging.xml @ 238

Last change on this file since 238 was 238, checked in by julian.reschke@…, 15 years ago

Resolve #64: quoted-pair: disallow escaping of NUL, CR and LF (closes #64).

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "April">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x=''/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x=''/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x=''/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x=''/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x=''/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email></email>
73      <uri></uri>
74    </address>
75  </author>
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email></email>
88      <uri></uri>
89    </address>
90  </author>
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email></email>
104    </address>
105  </author>
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email></email>
118    </address>
119  </author>
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email></email>
132      <uri></uri>
133    </address>
134  </author>
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email></email>
146    </address>
147  </author>
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email></email>
162      <uri></uri>
163    </address>
164  </author>
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email></email>
178      <uri></uri>
179    </address>
180  </author>
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email></email>       
193      <uri></uri>     
194    </address>
195  </author>
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list ( The current issues list is
218    at <eref target=""/>
219    and related documents (including fancy diffs) can be found at
220    <eref target=""/>.
221  </t>
222  <t>
223    This draft incorporates those issue resolutions that were either
224    collected in the original RFC2616 errata list (<eref target=""/>),
225    or which were agreed upon on the mailing list between October 2006 and
226    November 2007 (as published in "draft-lafon-rfc2616bis-03").
227  </t>
231<section title="Introduction" anchor="introduction">
233   The Hypertext Transfer Protocol (HTTP) is an application-level
234   protocol for distributed, collaborative, hypermedia information
235   systems. HTTP has been in use by the World-Wide Web global
236   information initiative since 1990. The first version of HTTP, commonly
237   referred to as HTTP/0.9, was a simple protocol for raw data transfer
238   across the Internet with only a single method and no metadata.
239   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
240   the protocol by allowing messages to be in the format of MIME-like
241   messages, containing metadata about the data transferred and
242   modifiers on the request/response semantics. However, HTTP/1.0 did
243   not sufficiently take into consideration the effects of hierarchical
244   proxies, caching, the need for persistent connections, or name-based
245   virtual hosts. In addition, the proliferation of incompletely-implemented
246   applications calling themselves "HTTP/1.0" necessitated a
247   protocol version change in order for two communicating applications
248   to determine each other's true capabilities.
251   This document is Part 1 of the seven-part specification that defines
252   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
253   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
254   requirements that enable reliable implementations and adding only
255   those new features that will either be safely ignored by an HTTP/1.0
256   recipient or only sent when communicating with a party advertising
257   compliance with HTTP/1.1.
258   Part 1 defines those aspects of HTTP/1.1 related to overall network
259   operation, message framing, interaction with transport protocols, and
260   URI schemes.
263   This document is currently disorganized in order to minimize the changes
264   between drafts and enable reviewers to see the smaller errata changes.
265   The next draft will reorganize the sections to better reflect the content.
266   In particular, the sections will be organized according to the typical
267   process of deciding when to use HTTP (URI schemes), overall network operation,
268   connection management, message framing, and generic message parsing.
269   The current mess reflects how widely dispersed these topics and associated
270   requirements had become in <xref target="RFC2616"/>.
273<section title="Purpose" anchor="intro.purpose">
275   Practical information systems require more functionality than simple
276   retrieval, including search, front-end update, and annotation. HTTP
277   allows an open-ended set of methods and headers that indicate the
278   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
279   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
280   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
281   method is to be applied. Messages are passed in a format similar to
282   that used by Internet mail <xref target="RFC2822"/> as defined by the Multipurpose
283   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
286   HTTP is also used as a generic protocol for communication between
287   user agents and proxies/gateways to other Internet systems, including
288   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
289   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
290   access to resources available from diverse applications.
294<section title="Requirements" anchor="intro.requirements">
296   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
297   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
298   document are to be interpreted as described in <xref target="RFC2119"/>.
301   An implementation is not compliant if it fails to satisfy one or more
302   of the &MUST; or &REQUIRED; level requirements for the protocols it
303   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
304   level and all the &SHOULD; level requirements for its protocols is said
305   to be "unconditionally compliant"; one that satisfies all the &MUST;
306   level requirements but not all the &SHOULD; level requirements for its
307   protocols is said to be "conditionally compliant."
311<section title="Terminology" anchor="intro.terminology">
313   This specification uses a number of terms to refer to the roles
314   played by participants in, and objects of, the HTTP communication.
317  <iref item="connection"/>
318  <x:dfn>connection</x:dfn>
319  <list>
320    <t>
321      A transport layer virtual circuit established between two programs
322      for the purpose of communication.
323    </t>
324  </list>
327  <iref item="message"/>
328  <x:dfn>message</x:dfn>
329  <list>
330    <t>
331      The basic unit of HTTP communication, consisting of a structured
332      sequence of octets matching the syntax defined in <xref target="http.message"/> and
333      transmitted via the connection.
334    </t>
335  </list>
338  <iref item="request"/>
339  <x:dfn>request</x:dfn>
340  <list>
341    <t>
342      An HTTP request message, as defined in <xref target="request"/>.
343    </t>
344  </list>
347  <iref item="response"/>
348  <x:dfn>response</x:dfn>
349  <list>
350    <t>
351      An HTTP response message, as defined in <xref target="response"/>.
352    </t>
353  </list>
356  <iref item="resource"/>
357  <x:dfn>resource</x:dfn>
358  <list>
359    <t>
360      A network data object or service that can be identified by a URI,
361      as defined in <xref target="uri"/>. Resources may be available in multiple
362      representations (e.g. multiple languages, data formats, size, and
363      resolutions) or vary in other ways.
364    </t>
365  </list>
368  <iref item="entity"/>
369  <x:dfn>entity</x:dfn>
370  <list>
371    <t>
372      The information transferred as the payload of a request or
373      response. An entity consists of metainformation in the form of
374      entity-header fields and content in the form of an entity-body, as
375      described in &entity;.
376    </t>
377  </list>
380  <iref item="representation"/>
381  <x:dfn>representation</x:dfn>
382  <list>
383    <t>
384      An entity included with a response that is subject to content
385      negotiation, as described in &content.negotiation;. There may exist multiple
386      representations associated with a particular response status.
387    </t>
388  </list>
391  <iref item="content negotiation"/>
392  <x:dfn>content negotiation</x:dfn>
393  <list>
394    <t>
395      The mechanism for selecting the appropriate representation when
396      servicing a request, as described in &content.negotiation;. The
397      representation of entities in any response can be negotiated
398      (including error responses).
399    </t>
400  </list>
403  <iref item="variant"/>
404  <x:dfn>variant</x:dfn>
405  <list>
406    <t>
407      A resource may have one, or more than one, representation(s)
408      associated with it at any given instant. Each of these
409      representations is termed a `variant'.  Use of the term `variant'
410      does not necessarily imply that the resource is subject to content
411      negotiation.
412    </t>
413  </list>
416  <iref item="client"/>
417  <x:dfn>client</x:dfn>
418  <list>
419    <t>
420      A program that establishes connections for the purpose of sending
421      requests.
422    </t>
423  </list>
426  <iref item="user agent"/>
427  <x:dfn>user agent</x:dfn>
428  <list>
429    <t>
430      The client which initiates a request. These are often browsers,
431      editors, spiders (web-traversing robots), or other end user tools.
432    </t>
433  </list>
436  <iref item="server"/>
437  <x:dfn>server</x:dfn>
438  <list>
439    <t>
440      An application program that accepts connections in order to
441      service requests by sending back responses. Any given program may
442      be capable of being both a client and a server; our use of these
443      terms refers only to the role being performed by the program for a
444      particular connection, rather than to the program's capabilities
445      in general. Likewise, any server may act as an origin server,
446      proxy, gateway, or tunnel, switching behavior based on the nature
447      of each request.
448    </t>
449  </list>
452  <iref item="origin server"/>
453  <x:dfn>origin server</x:dfn>
454  <list>
455    <t>
456      The server on which a given resource resides or is to be created.
457    </t>
458  </list>
461  <iref item="proxy"/>
462  <x:dfn>proxy</x:dfn>
463  <list>
464    <t>
465      An intermediary program which acts as both a server and a client
466      for the purpose of making requests on behalf of other clients.
467      Requests are serviced internally or by passing them on, with
468      possible translation, to other servers. A proxy &MUST; implement
469      both the client and server requirements of this specification. A
470      "transparent proxy" is a proxy that does not modify the request or
471      response beyond what is required for proxy authentication and
472      identification. A "non-transparent proxy" is a proxy that modifies
473      the request or response in order to provide some added service to
474      the user agent, such as group annotation services, media type
475      transformation, protocol reduction, or anonymity filtering. Except
476      where either transparent or non-transparent behavior is explicitly
477      stated, the HTTP proxy requirements apply to both types of
478      proxies.
479    </t>
480  </list>
483  <iref item="gateway"/>
484  <x:dfn>gateway</x:dfn>
485  <list>
486    <t>
487      A server which acts as an intermediary for some other server.
488      Unlike a proxy, a gateway receives requests as if it were the
489      origin server for the requested resource; the requesting client
490      may not be aware that it is communicating with a gateway.
491    </t>
492  </list>
495  <iref item="tunnel"/>
496  <x:dfn>tunnel</x:dfn>
497  <list>
498    <t>
499      An intermediary program which is acting as a blind relay between
500      two connections. Once active, a tunnel is not considered a party
501      to the HTTP communication, though the tunnel may have been
502      initiated by an HTTP request. The tunnel ceases to exist when both
503      ends of the relayed connections are closed.
504    </t>
505  </list>
508  <iref item="cache"/>
509  <x:dfn>cache</x:dfn>
510  <list>
511    <t>
512      A program's local store of response messages and the subsystem
513      that controls its message storage, retrieval, and deletion. A
514      cache stores cacheable responses in order to reduce the response
515      time and network bandwidth consumption on future, equivalent
516      requests. Any client or server may include a cache, though a cache
517      cannot be used by a server that is acting as a tunnel.
518    </t>
519  </list>
522  <iref item="cacheable"/>
523  <x:dfn>cacheable</x:dfn>
524  <list>
525    <t>
526      A response is cacheable if a cache is allowed to store a copy of
527      the response message for use in answering subsequent requests. The
528      rules for determining the cacheability of HTTP responses are
529      defined in &caching;. Even if a resource is cacheable, there may
530      be additional constraints on whether a cache can use the cached
531      copy for a particular request.
532    </t>
533  </list>
536  <iref item="upstream"/>
537  <iref item="downstream"/>
538  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
539  <list>
540    <t>
541      Upstream and downstream describe the flow of a message: all
542      messages flow from upstream to downstream.
543    </t>
544  </list>
547  <iref item="inbound"/>
548  <iref item="outbound"/>
549  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
550  <list>
551    <t>
552      Inbound and outbound refer to the request and response paths for
553      messages: "inbound" means "traveling toward the origin server",
554      and "outbound" means "traveling toward the user agent"
555    </t>
556  </list>
560<section title="Overall Operation" anchor="intro.overall.operation">
562   HTTP is a request/response protocol. A client sends a
563   request to the server in the form of a request method, URI, and
564   protocol version, followed by a MIME-like message containing request
565   modifiers, client information, and possible body content over a
566   connection with a server. The server responds with a status line,
567   including the message's protocol version and a success or error code,
568   followed by a MIME-like message containing server information, entity
569   metainformation, and possible entity-body content. The relationship
570   between HTTP and MIME is described in &diff2045entity;.
573   Most HTTP communication is initiated by a user agent and consists of
574   a request to be applied to a resource on some origin server. In the
575   simplest case, this may be accomplished via a single connection (v)
576   between the user agent (UA) and the origin server (O).
578<figure><artwork type="drawing">
579       request chain ------------------------&gt;
580    UA -------------------v------------------- O
581       &lt;----------------------- response chain
584   A more complicated situation occurs when one or more intermediaries
585   are present in the request/response chain. There are three common
586   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
587   forwarding agent, receiving requests for a URI in its absolute form,
588   rewriting all or part of the message, and forwarding the reformatted
589   request toward the server identified by the URI. A gateway is a
590   receiving agent, acting as a layer above some other server(s) and, if
591   necessary, translating the requests to the underlying server's
592   protocol. A tunnel acts as a relay point between two connections
593   without changing the messages; tunnels are used when the
594   communication needs to pass through an intermediary (such as a
595   firewall) even when the intermediary cannot understand the contents
596   of the messages.
598<figure><artwork type="drawing">
599       request chain --------------------------------------&gt;
600    UA -----v----- A -----v----- B -----v----- C -----v----- O
601       &lt;------------------------------------- response chain
604   The figure above shows three intermediaries (A, B, and C) between the
605   user agent and origin server. A request or response message that
606   travels the whole chain will pass through four separate connections.
607   This distinction is important because some HTTP communication options
608   may apply only to the connection with the nearest, non-tunnel
609   neighbor, only to the end-points of the chain, or to all connections
610   along the chain. Although the diagram is linear, each participant may
611   be engaged in multiple, simultaneous communications. For example, B
612   may be receiving requests from many clients other than A, and/or
613   forwarding requests to servers other than C, at the same time that it
614   is handling A's request.
617   Any party to the communication which is not acting as a tunnel may
618   employ an internal cache for handling requests. The effect of a cache
619   is that the request/response chain is shortened if one of the
620   participants along the chain has a cached response applicable to that
621   request. The following illustrates the resulting chain if B has a
622   cached copy of an earlier response from O (via C) for a request which
623   has not been cached by UA or A.
625<figure><artwork type="drawing">
626          request chain ----------&gt;
627       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
628          &lt;--------- response chain
631   Not all responses are usefully cacheable, and some requests may
632   contain modifiers which place special requirements on cache behavior.
633   HTTP requirements for cache behavior and cacheable responses are
634   defined in &caching;.
637   In fact, there are a wide variety of architectures and configurations
638   of caches and proxies currently being experimented with or deployed
639   across the World Wide Web. These systems include national hierarchies
640   of proxy caches to save transoceanic bandwidth, systems that
641   broadcast or multicast cache entries, organizations that distribute
642   subsets of cached data via CD-ROM, and so on. HTTP systems are used
643   in corporate intranets over high-bandwidth links, and for access via
644   PDAs with low-power radio links and intermittent connectivity. The
645   goal of HTTP/1.1 is to support the wide diversity of configurations
646   already deployed while introducing protocol constructs that meet the
647   needs of those who build web applications that require high
648   reliability and, failing that, at least reliable indications of
649   failure.
652   HTTP communication usually takes place over TCP/IP connections. The
653   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
654   not preclude HTTP from being implemented on top of any other protocol
655   on the Internet, or on other networks. HTTP only presumes a reliable
656   transport; any protocol that provides such guarantees can be used;
657   the mapping of the HTTP/1.1 request and response structures onto the
658   transport data units of the protocol in question is outside the scope
659   of this specification.
662   In HTTP/1.0, most implementations used a new connection for each
663   request/response exchange. In HTTP/1.1, a connection may be used for
664   one or more request/response exchanges, although connections may be
665   closed for a variety of reasons (see <xref target="persistent.connections"/>).
670<section title="Notational Conventions and Generic Grammar" anchor="notation">
672<section title="Augmented BNF" anchor="notation.abnf">
674   All of the mechanisms specified in this document are described in
675   both prose and an augmented Backus-Naur Form (BNF) similar to that
676   used by <xref target="RFC822ABNF"/>. Implementors will need to be familiar with the
677   notation in order to understand this specification. The augmented BNF
678   includes the following constructs:
681   name = definition
682  <list>
683    <t>
684      The name of a rule is simply the name itself (without any
685      enclosing "&lt;" and "&gt;") and is separated from its definition by the
686      equal "=" character. White space is only significant in that
687      indentation of continuation lines is used to indicate a rule
688      definition that spans more than one line. Certain basic rules are
689      in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc. Angle
690      brackets are used within definitions whenever their presence will
691      facilitate discerning the use of rule names.
692    </t>
693  </list>
696   "literal"
697  <list>
698    <t>
699      Quotation marks surround literal text. Unless stated otherwise,
700      the text is case-insensitive.
701    </t>
702  </list>
705   rule1 | rule2
706  <list>
707    <t>
708      Elements separated by a bar ("|") are alternatives, e.g., "yes |
709      no" will accept yes or no.
710    </t>
711  </list>
714   (rule1 rule2)
715  <list>
716    <t>
717      Elements enclosed in parentheses are treated as a single element.
718      Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
719      foo elem" and "elem bar elem".
720    </t>
721  </list>
724   *rule
725  <list>
726    <t>
727      The character "*" preceding an element indicates repetition. The
728      full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and at most
729      &lt;m&gt; occurrences of element. Default values are 0 and infinity so
730      that "*(element)" allows any number, including zero; "1*element"
731      requires at least one; and "1*2element" allows one or two.
732    </t>
733  </list>
736   [rule]
737  <list>
738    <t>
739      Square brackets enclose optional elements; "[foo bar]" is
740      equivalent to "*1(foo bar)".
741    </t>
742  </list>
745   N rule
746  <list>
747    <t>
748      Specific repetition: "&lt;n&gt;(element)" is equivalent to
749      "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element).
750      Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
751      alphabetic characters.
752    </t>
753  </list>
756   #rule
757  <list>
758    <t>
759      A construct "#" is defined, similar to "*", for defining lists of
760      elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
761      &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
762      (",") and &OPTIONAL; linear white space (LWS). This makes the usual
763      form of lists very easy; a rule such as
764    </t>
765    <t>
766         ( *LWS element *( *LWS "," *LWS element ))
767    </t>
768    <t>
769      can be shown as
770    </t>
771    <t>
772         1#element
773    </t>
774    <t>
775      Wherever this construct is used, null elements are allowed, but do
776      not contribute to the count of elements present. That is,
777      "(element), , (element) " is permitted, but counts as only two
778      elements. Therefore, where at least one element is required, at
779      least one non-null element &MUST; be present. Default values are 0
780      and infinity so that "#element" allows any number, including zero;
781      "1#element" requires at least one; and "1#2element" allows one or
782      two.
783    </t>
784  </list>
787   ; comment
788  <list>
789    <t>
790      A semi-colon, set off some distance to the right of rule text,
791      starts a comment that continues to the end of line. This is a
792      simple way of including useful notes in parallel with the
793      specifications.
794    </t>
795  </list>
798   implied *LWS
799  <list>
800    <t>
801      The grammar described by this specification is word-based. Except
802      where noted otherwise, linear white space (LWS) can be included
803      between any two adjacent words (token or quoted-string), and
804      between adjacent words and separators, without changing the
805      interpretation of a field. At least one delimiter (LWS and/or
806      separators) &MUST; exist between any two tokens (for the definition
807      of "token" below), since they would otherwise be interpreted as a
808      single token.
809    </t>
810  </list>
814<section title="Basic Rules" anchor="basic.rules">
815<t anchor="core.rules">
816  <x:anchor-alias value="OCTET"/>
817  <x:anchor-alias value="CHAR"/>
818  <x:anchor-alias value="ALPHA"/>
819  <x:anchor-alias value="DIGIT"/>
820  <x:anchor-alias value="CTL"/>
821  <x:anchor-alias value="CR"/>
822  <x:anchor-alias value="LF"/>
823  <x:anchor-alias value="SP"/>
824  <x:anchor-alias value="HTAB"/>
825  <x:anchor-alias value="DQUOTE"/>
826   The following rules are used throughout this specification to
827   describe basic parsing constructs. The US-ASCII coded character set
828   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
830<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"/>
831  <x:ref>OCTET</x:ref>          = %x00-FF
832                   ; any 8-bit sequence of data
833  <x:ref>CHAR</x:ref>           = %x01-7F
834                   ; any US-ASCII character, excluding NUL
835  <x:ref>ALPHA</x:ref>          = %x41-5A | %x61-7A
836                   ; A-Z | a-z
837  <x:ref>DIGIT</x:ref>          = %x30-39
838                   ; any US-ASCII digit "0".."9"
839  <x:ref>CTL</x:ref>            = %x00-1F | %x7F
840                   ; (octets 0 - 31) and DEL (127)
841  <x:ref>CR</x:ref>             = %x0D
842                   ; US-ASCII CR, carriage return (13)
843  <x:ref>LF</x:ref>             = %x0A
844                   ; US-ASCII LF, linefeed (10)
845  <x:ref>SP</x:ref>             = %x20
846                   ; US-ASCII SP, space (32)
847  <x:ref>HTAB</x:ref>           = %x09
848                   ; US-ASCII HT, horizontal-tab (9)
849  <x:ref>DQUOTE</x:ref>         = %x22
850                   ; US-ASCII double-quote mark (34)
852<t anchor="rule.CRLF">
853  <x:anchor-alias value="CRLF"/>
854   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
855   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
856   tolerant applications). The end-of-line marker within an entity-body
857   is defined by its associated media type, as described in &media-types;.
859<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
860  <x:ref>CRLF</x:ref>           = <x:ref>CR</x:ref> LF
862<t anchor="rule.LWS">
863  <x:anchor-alias value="LWS"/>
864   HTTP/1.1 header field values can be folded onto multiple lines if the
865   continuation line begins with a space or horizontal tab. All linear
866   white space, including folding, has the same semantics as SP. A
867   recipient &MAY; replace any linear white space with a single SP before
868   interpreting the field value or forwarding the message downstream.
870<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
871  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> | <x:ref>HTAB</x:ref> )
873<t anchor="rule.TEXT">
874  <x:anchor-alias value="TEXT"/>
875   The TEXT rule is only used for descriptive field contents and values
876   that are not intended to be interpreted by the message parser. Words
877   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
878   <xref target="ISO-8859-1"/> only when encoded according to the rules of
879   <xref target="RFC2047"/>.
881<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
882  <x:ref>TEXT</x:ref>           = %x20-7E | %x80-FF | <x:ref>LWS</x:ref>
883                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
886   A CRLF is allowed in the definition of TEXT only as part of a header
887   field continuation. It is expected that the folding LWS will be
888   replaced with a single SP before interpretation of the TEXT value.
890<t anchor="rule.HEX">
891  <x:anchor-alias value="HEX"/>
892   Hexadecimal numeric characters are used in several protocol elements.
894<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEX"/>
895  <x:ref>HEX</x:ref>            = "A" | "B" | "C" | "D" | "E" | "F"
896                 | "a" | "b" | "c" | "d" | "e" | "f" | <x:ref>DIGIT</x:ref>
898<t anchor="rule.token.separators">
899  <x:anchor-alias value="tchar"/>
900  <x:anchor-alias value="token"/>
901  <x:anchor-alias value="separators"/>
902   Many HTTP/1.1 header field values consist of words separated by LWS
903   or special characters. These special characters &MUST; be in a quoted
904   string to be used within a parameter value (as defined in
905   <xref target="transfer.codings"/>).
907<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/>
908  <x:ref>separators</x:ref>     = "(" | ")" | "&lt;" | "&gt;" | "@"
909                 | "," | ";" | ":" | "\" | <x:ref>DQUOTE</x:ref>
910                 | "/" | "[" | "]" | "?" | "="
911                 | "{" | "}" | <x:ref>SP</x:ref> | <x:ref>HTAB</x:ref>
913  <x:ref>tchar</x:ref>          = "!" | "#" | "$" | "%" | "&amp;" | "'" | "*"
914                 | "+" | "-" | "." | "^" | "_" | "`" | "|" | "~"
915                 | <x:ref>DIGIT</x:ref> | <x:ref>ALPHA</x:ref>
916                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
918  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
920<t anchor="rule.comment">
921  <x:anchor-alias value="comment"/>
922  <x:anchor-alias value="ctext"/>
923   Comments can be included in some HTTP header fields by surrounding
924   the comment text with parentheses. Comments are only allowed in
925   fields containing "comment" as part of their field value definition.
926   In all other fields, parentheses are considered part of the field
927   value.
929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
930  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> | <x:ref>quoted-pair</x:ref> | <x:ref>comment</x:ref> ) ")"
931  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
933<t anchor="rule.quoted-string">
934  <x:anchor-alias value="quoted-string"/>
935  <x:anchor-alias value="qdtext"/>
936   A string of text is parsed as a single word if it is quoted using
937   double-quote marks.
939<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
940  <x:ref>quoted-string</x:ref>  = ( <x:ref>DQUOTE</x:ref> *(<x:ref>qdtext</x:ref> | <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref> )
941  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
943<t anchor="rule.quoted-pair">
944  <x:anchor-alias value="quoted-pair"/>
945  <x:anchor-alias value="quoted-text"/>
946   The backslash character ("\") &MAY; be used as a single-character
947   quoting mechanism only within quoted-string and comment constructs.
949<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
950  <x:ref>quoted-text</x:ref>    = %x01-09 |
951                   %x0B-0C |
952                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
953  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
957<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
958  <x:anchor-alias value="request-header"/>
959  <x:anchor-alias value="response-header"/>
960  <x:anchor-alias value="accept-params"/>
961  <x:anchor-alias value="entity-body"/>
962  <x:anchor-alias value="entity-header"/>
963  <x:anchor-alias value="Cache-Control"/>
964  <x:anchor-alias value="Pragma"/>
965  <x:anchor-alias value="Warning"/>
967  The ABNF rules below are defined in other parts:
969<figure><!-- Part2--><artwork type="abnf2616">
970  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
971  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
973<figure><!-- Part3--><artwork type="abnf2616">
974  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
975  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
976  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
978<figure><!-- Part6--><artwork type="abnf2616">
979  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
980  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
981  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
987<section title="Protocol Parameters" anchor="protocol.parameters">
989<section title="HTTP Version" anchor="http.version">
990  <x:anchor-alias value="HTTP-Version"/>
992   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
993   of the protocol. The protocol versioning policy is intended to allow
994   the sender to indicate the format of a message and its capacity for
995   understanding further HTTP communication, rather than the features
996   obtained via that communication. No change is made to the version
997   number for the addition of message components which do not affect
998   communication behavior or which only add to extensible field values.
999   The &lt;minor&gt; number is incremented when the changes made to the
1000   protocol add features which do not change the general message parsing
1001   algorithm, but which may add to the message semantics and imply
1002   additional capabilities of the sender. The &lt;major&gt; number is
1003   incremented when the format of a message within the protocol is
1004   changed. See <xref target="RFC2145"/> for a fuller explanation.
1007   The version of an HTTP message is indicated by an HTTP-Version field
1008   in the first line of the message. HTTP-Version is case-sensitive.
1010<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/>
1011  <x:ref>HTTP-Version</x:ref>   = "HTTP" "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
1014   Note that the major and minor numbers &MUST; be treated as separate
1015   integers and that each &MAY; be incremented higher than a single digit.
1016   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
1017   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
1018   &MUST-NOT; be sent.
1021   An application that sends a request or response message that includes
1022   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
1023   with this specification. Applications that are at least conditionally
1024   compliant with this specification &SHOULD; use an HTTP-Version of
1025   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
1026   not compatible with HTTP/1.0. For more details on when to send
1027   specific HTTP-Version values, see <xref target="RFC2145"/>.
1030   The HTTP version of an application is the highest HTTP version for
1031   which the application is at least conditionally compliant.
1034   Proxy and gateway applications need to be careful when forwarding
1035   messages in protocol versions different from that of the application.
1036   Since the protocol version indicates the protocol capability of the
1037   sender, a proxy/gateway &MUST-NOT; send a message with a version
1038   indicator which is greater than its actual version. If a higher
1039   version request is received, the proxy/gateway &MUST; either downgrade
1040   the request version, or respond with an error, or switch to tunnel
1041   behavior.
1044   Due to interoperability problems with HTTP/1.0 proxies discovered
1045   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
1046   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
1047   they support. The proxy/gateway's response to that request &MUST; be in
1048   the same major version as the request.
1051  <list>
1052    <t>
1053      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
1054      of header fields required or forbidden by the versions involved.
1055    </t>
1056  </list>
1060<section title="Uniform Resource Identifiers" anchor="uri">
1062   URIs have been known by many names: WWW addresses, Universal Document
1063   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
1064   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
1065   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
1066   simply formatted strings which identify--via name, location, or any
1067   other characteristic--a resource.
1070<section title="General Syntax" anchor="general.syntax">
1071  <x:anchor-alias value="absoluteURI"/>
1072  <x:anchor-alias value="authority"/>
1073  <x:anchor-alias value="fragment"/>
1074  <x:anchor-alias value="path-absolute"/>
1075  <x:anchor-alias value="port"/>
1076  <x:anchor-alias value="query"/>
1077  <x:anchor-alias value="relativeURI"/>
1078  <x:anchor-alias value="uri-host"/>
1080   URIs in HTTP can be represented in absolute form or relative to some
1081   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
1082   forms are differentiated by the fact that absolute URIs always begin
1083   with a scheme name followed by a colon. For definitive information on
1084   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
1085   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
1086   and <xref target="RFC1808"/>). This specification adopts the
1087   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
1088   "host", "abs_path", "query", and "authority" from that specification:
1090<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"/>
1091  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1092  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
1093  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
1094  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1095  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1096  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
1097  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
1098  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1101   HTTP does not place any a priori limit on the length of
1102   a URI. Servers &MUST; be able to handle the URI of any resource they
1103   serve, and &SHOULD; be able to handle URIs of unbounded length if they
1104   provide GET-based forms that could generate such URIs. A server
1105   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
1106   than the server can handle (see &status-414;).
1109  <list>
1110    <t>
1111      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
1112      above 255 bytes, because some older client or proxy
1113      implementations might not properly support these lengths.
1114    </t>
1115  </list>
1119<section title="http URL" anchor="http.url">
1120  <x:anchor-alias value="http-URL"/>
1122   The "http" scheme is used to locate network resources via the HTTP
1123   protocol. This section defines the scheme-specific syntax and
1124   semantics for http URLs.
1126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
1127  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
1128             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
1131   If the port is empty or not given, port 80 is assumed. The semantics
1132   are that the identified resource is located at the server listening
1133   for TCP connections on that port of that host, and the Request-URI
1134   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
1135   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
1136   the path-absolute is not present in the URL, it &MUST; be given as "/" when
1137   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1138   receives a host name which is not a fully qualified domain name, it
1139   &MAY; add its domain to the host name it received. If a proxy receives
1140   a fully qualified domain name, the proxy &MUST-NOT; change the host
1141   name.
1145<section title="URI Comparison" anchor="uri.comparison">
1147   When comparing two URIs to decide if they match or not, a client
1148   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
1149   URIs, with these exceptions:
1150  <list style="symbols">
1151    <t>A port that is empty or not given is equivalent to the default
1152        port for that URI-reference;</t>
1153    <t>Comparisons of host names &MUST; be case-insensitive;</t>
1154    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
1155    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
1156  </list>
1159   Characters other than those in the "reserved" set (see
1160   <xref target="RFC2396"/>) are equivalent to their ""%" HEX HEX" encoding.
1163   For example, the following three URIs are equivalent:
1165<figure><artwork type="example">
1173<section title="Date/Time Formats" anchor="date.time.formats">
1174<section title="Full Date" anchor="">
1175  <x:anchor-alias value="HTTP-date"/>
1176  <x:anchor-alias value="rfc1123-date"/>
1177  <x:anchor-alias value="rfc850-date"/>
1178  <x:anchor-alias value="asctime-date"/>
1179  <x:anchor-alias value="date1"/>
1180  <x:anchor-alias value="date2"/>
1181  <x:anchor-alias value="date3"/>
1182  <x:anchor-alias value="rfc1123-date"/>
1183  <x:anchor-alias value="time"/>
1184  <x:anchor-alias value="wkday"/>
1185  <x:anchor-alias value="weekday"/>
1186  <x:anchor-alias value="month"/>
1188   HTTP applications have historically allowed three different formats
1189   for the representation of date/time stamps:
1191<figure><artwork type="example">
1192   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1193   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1194   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1197   The first format is preferred as an Internet standard and represents
1198   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1199   <xref target="RFC822"/>). The other formats are described here only for
1200   compatibility with obsolete implementations.
1201   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1202   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1203   only generate the RFC 1123 format for representing HTTP-date values
1204   in header fields. See <xref target="tolerant.applications"/> for further information.
1207      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1208      accepting date values that may have been sent by non-HTTP
1209      applications, as is sometimes the case when retrieving or posting
1210      messages via proxies/gateways to SMTP or NNTP.
1213   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1214   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1215   equal to UTC (Coordinated Universal Time). This is indicated in the
1216   first two formats by the inclusion of "GMT" as the three-letter
1217   abbreviation for time zone, and &MUST; be assumed when reading the
1218   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1219   additional LWS beyond that specifically included as SP in the
1220   grammar.
1222<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"/>
1223  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> | <x:ref>rfc850-date</x:ref> | <x:ref>asctime-date</x:ref>
1224  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> "GMT"
1225  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> "GMT"
1226  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
1227  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
1228                 ; day month year (e.g., 02 Jun 1982)
1229  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1230                 ; day-month-year (e.g., 02-Jun-82)
1231  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> | ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
1232                 ; month day (e.g., Jun  2)
1233  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
1234                 ; 00:00:00 - 23:59:59
1235  <x:ref>wkday</x:ref>        = "Mon" | "Tue" | "Wed"
1236               | "Thu" | "Fri" | "Sat" | "Sun"
1237  <x:ref>weekday</x:ref>      = "Monday" | "Tuesday" | "Wednesday"
1238               | "Thursday" | "Friday" | "Saturday" | "Sunday"
1239  <x:ref>month</x:ref>        = "Jan" | "Feb" | "Mar" | "Apr"
1240               | "May" | "Jun" | "Jul" | "Aug"
1241               | "Sep" | "Oct" | "Nov" | "Dec"
1244      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1245      to their usage within the protocol stream. Clients and servers are
1246      not required to use these formats for user presentation, request
1247      logging, etc.
1252<section title="Transfer Codings" anchor="transfer.codings">
1253  <x:anchor-alias value="parameter"/>
1254  <x:anchor-alias value="transfer-coding"/>
1255  <x:anchor-alias value="transfer-extension"/>
1257   Transfer-coding values are used to indicate an encoding
1258   transformation that has been, can be, or may need to be applied to an
1259   entity-body in order to ensure "safe transport" through the network.
1260   This differs from a content coding in that the transfer-coding is a
1261   property of the message, not of the original entity.
1263<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1264  <x:ref>transfer-coding</x:ref>         = "chunked" | <x:ref>transfer-extension</x:ref>
1265  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
1267<t anchor="rule.parameter">
1268  <x:anchor-alias value="attribute"/>
1269  <x:anchor-alias value="parameter"/>
1270  <x:anchor-alias value="value"/>
1271   Parameters are in  the form of attribute/value pairs.
1273<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"/>
1274  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
1275  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1276  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
1279   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1280   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1281   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1284   Whenever a transfer-coding is applied to a message-body, the set of
1285   transfer-codings &MUST; include "chunked", unless the message is
1286   terminated by closing the connection. When the "chunked" transfer-coding
1287   is used, it &MUST; be the last transfer-coding applied to the
1288   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1289   than once to a message-body. These rules allow the recipient to
1290   determine the transfer-length of the message (<xref target="message.length"/>).
1293   Transfer-codings are analogous to the Content-Transfer-Encoding
1294   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1295   binary data over a 7-bit transport service. However, safe transport
1296   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1297   the only unsafe characteristic of message-bodies is the difficulty in
1298   determining the exact body length (<xref target="message.length"/>), or the desire to
1299   encrypt data over a shared transport.
1302   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1303   transfer-coding value tokens. Initially, the registry contains the
1304   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1305   "gzip", "compress", and "deflate" (&content-codings;).
1308   New transfer-coding value tokens &SHOULD; be registered in the same way
1309   as new content-coding value tokens (&content-codings;).
1312   A server which receives an entity-body with a transfer-coding it does
1313   not understand &SHOULD; return 501 (Not Implemented), and close the
1314   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1315   client.
1318<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1319  <x:anchor-alias value="chunk"/>
1320  <x:anchor-alias value="Chunked-Body"/>
1321  <x:anchor-alias value="chunk-data"/>
1322  <x:anchor-alias value="chunk-extension"/>
1323  <x:anchor-alias value="chunk-ext-name"/>
1324  <x:anchor-alias value="chunk-ext-val"/>
1325  <x:anchor-alias value="chunk-size"/>
1326  <x:anchor-alias value="last-chunk"/>
1327  <x:anchor-alias value="trailer-part"/>
1329   The chunked encoding modifies the body of a message in order to
1330   transfer it as a series of chunks, each with its own size indicator,
1331   followed by an &OPTIONAL; trailer containing entity-header fields. This
1332   allows dynamically produced content to be transferred along with the
1333   information necessary for the recipient to verify that it has
1334   received the full message.
1336<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"/>
1337  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1338                   <x:ref>last-chunk</x:ref>
1339                   <x:ref>trailer-part</x:ref>
1340                   <x:ref>CRLF</x:ref>
1342  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1343                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1344  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEX</x:ref>
1345  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1347  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1348  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1349  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
1350  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1351  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1354   The chunk-size field is a string of hex digits indicating the size of
1355   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1356   zero, followed by the trailer, which is terminated by an empty line.
1359   The trailer allows the sender to include additional HTTP header
1360   fields at the end of the message. The Trailer header field can be
1361   used to indicate which header fields are included in a trailer (see
1362   <xref target="header.trailer"/>).
1365   A server using chunked transfer-coding in a response &MUST-NOT; use the
1366   trailer for any header fields unless at least one of the following is
1367   true:
1368  <list style="numbers">
1369    <t>the request included a TE header field that indicates "trailers" is
1370     acceptable in the transfer-coding of the  response, as described in
1371     <xref target="header.te"/>; or,</t>
1373    <t>the server is the origin server for the response, the trailer
1374     fields consist entirely of optional metadata, and the recipient
1375     could use the message (in a manner acceptable to the origin server)
1376     without receiving this metadata.  In other words, the origin server
1377     is willing to accept the possibility that the trailer fields might
1378     be silently discarded along the path to the client.</t>
1379  </list>
1382   This requirement prevents an interoperability failure when the
1383   message is being received by an HTTP/1.1 (or later) proxy and
1384   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1385   compliance with the protocol would have necessitated a possibly
1386   infinite buffer on the proxy.
1389   A process for decoding the "chunked" transfer-coding
1390   can be represented in pseudo-code as:
1392<figure><artwork type="code">
1393    length := 0
1394    read chunk-size, chunk-extension (if any) and CRLF
1395    while (chunk-size &gt; 0) {
1396       read chunk-data and CRLF
1397       append chunk-data to entity-body
1398       length := length + chunk-size
1399       read chunk-size and CRLF
1400    }
1401    read entity-header
1402    while (entity-header not empty) {
1403       append entity-header to existing header fields
1404       read entity-header
1405    }
1406    Content-Length := length
1407    Remove "chunked" from Transfer-Encoding
1410   All HTTP/1.1 applications &MUST; be able to receive and decode the
1411   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1412   they do not understand.
1417<section title="Product Tokens" anchor="product.tokens">
1418  <x:anchor-alias value="product"/>
1419  <x:anchor-alias value="product-version"/>
1421   Product tokens are used to allow communicating applications to
1422   identify themselves by software name and version. Most fields using
1423   product tokens also allow sub-products which form a significant part
1424   of the application to be listed, separated by white space. By
1425   convention, the products are listed in order of their significance
1426   for identifying the application.
1428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1429  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1430  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1433   Examples:
1435<figure><artwork type="example">
1436    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1437    Server: Apache/0.8.4
1440   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1441   used for advertising or other non-essential information. Although any
1442   token character &MAY; appear in a product-version, this token &SHOULD;
1443   only be used for a version identifier (i.e., successive versions of
1444   the same product &SHOULD; only differ in the product-version portion of
1445   the product value).
1451<section title="HTTP Message" anchor="http.message">
1453<section title="Message Types" anchor="message.types">
1454  <x:anchor-alias value="generic-message"/>
1455  <x:anchor-alias value="HTTP-message"/>
1456  <x:anchor-alias value="start-line"/>
1458   HTTP messages consist of requests from client to server and responses
1459   from server to client.
1461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1462  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> | <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1465   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1466   message format of <xref target="RFC2822"/> for transferring entities (the payload
1467   of the message). Both types of message consist of a start-line, zero
1468   or more header fields (also known as "headers"), an empty line (i.e.,
1469   a line with nothing preceding the CRLF) indicating the end of the
1470   header fields, and possibly a message-body.
1472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1473  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1474                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1475                    <x:ref>CRLF</x:ref>
1476                    [ <x:ref>message-body</x:ref> ]
1477  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> | <x:ref>Status-Line</x:ref>
1480   In the interest of robustness, servers &SHOULD; ignore any empty
1481   line(s) received where a Request-Line is expected. In other words, if
1482   the server is reading the protocol stream at the beginning of a
1483   message and receives a CRLF first, it should ignore the CRLF.
1486   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1487   after a POST request. To restate what is explicitly forbidden by the
1488   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1489   extra CRLF.
1493<section title="Message Headers" anchor="message.headers">
1494  <x:anchor-alias value="field-content"/>
1495  <x:anchor-alias value="field-name"/>
1496  <x:anchor-alias value="field-value"/>
1497  <x:anchor-alias value="message-header"/>
1499   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1500   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1501   entity-header (&entity-header-fields;) fields, follow the same generic format as
1502   that given in <xref target="RFC2822" x:fmt="of" x:sec="2.1"/>. Each header field consists
1503   of a name followed by a colon (":") and the field value. Field names
1504   are case-insensitive. The field value &MAY; be preceded by any amount
1505   of LWS, though a single SP is preferred. Header fields can be
1506   extended over multiple lines by preceding each extra line with at
1507   least one SP or HTAB. Applications ought to follow "common form", where
1508   one is known or indicated, when generating HTTP constructs, since
1509   there might exist some implementations that fail to accept anything
1510   beyond the common forms.
1512<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"/>
1513  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1514  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1515  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> | <x:ref>LWS</x:ref> )
1516  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1517                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1518                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1519                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1522   The field-content does not include any leading or trailing LWS:
1523   linear white space occurring before the first non-whitespace
1524   character of the field-value or after the last non-whitespace
1525   character of the field-value. Such leading or trailing LWS &MAY; be
1526   removed without changing the semantics of the field value. Any LWS
1527   that occurs between field-content &MAY; be replaced with a single SP
1528   before interpreting the field value or forwarding the message
1529   downstream.
1532   The order in which header fields with differing field names are
1533   received is not significant. However, it is "good practice" to send
1534   general-header fields first, followed by request-header or response-header
1535   fields, and ending with the entity-header fields.
1538   Multiple message-header fields with the same field-name &MAY; be
1539   present in a message if and only if the entire field-value for that
1540   header field is defined as a comma-separated list [i.e., #(values)].
1541   It &MUST; be possible to combine the multiple header fields into one
1542   "field-name: field-value" pair, without changing the semantics of the
1543   message, by appending each subsequent field-value to the first, each
1544   separated by a comma. The order in which header fields with the same
1545   field-name are received is therefore significant to the
1546   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1547   change the order of these field values when a message is forwarded.
1551<section title="Message Body" anchor="message.body">
1552  <x:anchor-alias value="message-body"/>
1554   The message-body (if any) of an HTTP message is used to carry the
1555   entity-body associated with the request or response. The message-body
1556   differs from the entity-body only when a transfer-coding has been
1557   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1560  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1561               | &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1564   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1565   applied by an application to ensure safe and proper transfer of the
1566   message. Transfer-Encoding is a property of the message, not of the
1567   entity, and thus &MAY; be added or removed by any application along the
1568   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1569   when certain transfer-codings may be used.)
1572   The rules for when a message-body is allowed in a message differ for
1573   requests and responses.
1576   The presence of a message-body in a request is signaled by the
1577   inclusion of a Content-Length or Transfer-Encoding header field in
1578   the request's message-headers. A message-body &MUST-NOT; be included in
1579   a request if the specification of the request method (&method;)
1580   explicitly disallows an entity-body in requests.
1581   When a request message contains both a message-body of non-zero
1582   length and a method that does not define any semantics for that
1583   request message-body, then an origin server &SHOULD; either ignore
1584   the message-body or respond with an appropriate error message
1585   (e.g., 413).  A proxy or gateway, when presented the same request,
1586   &SHOULD; either forward the request inbound with the message-body or
1587   ignore the message-body when determining a response.
1590   For response messages, whether or not a message-body is included with
1591   a message is dependent on both the request method and the response
1592   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1593   &MUST-NOT; include a message-body, even though the presence of entity-header
1594   fields might lead one to believe they do. All 1xx
1595   (informational), 204 (No Content), and 304 (Not Modified) responses
1596   &MUST-NOT; include a message-body. All other responses do include a
1597   message-body, although it &MAY; be of zero length.
1601<section title="Message Length" anchor="message.length">
1603   The transfer-length of a message is the length of the message-body as
1604   it appears in the message; that is, after any transfer-codings have
1605   been applied. When a message-body is included with a message, the
1606   transfer-length of that body is determined by one of the following
1607   (in order of precedence):
1610  <list style="numbers">
1611    <x:lt><t>
1612     Any response message which "&MUST-NOT;" include a message-body (such
1613     as the 1xx, 204, and 304 responses and any response to a HEAD
1614     request) is always terminated by the first empty line after the
1615     header fields, regardless of the entity-header fields present in
1616     the message.
1617    </t></x:lt>
1618    <x:lt><t>
1619     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1620     is present, then the transfer-length is
1621     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1622     unless the message is terminated by closing the connection.
1623    </t></x:lt>
1624    <x:lt><t>
1625     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1626     decimal value in OCTETs represents both the entity-length and the
1627     transfer-length. The Content-Length header field &MUST-NOT; be sent
1628     if these two lengths are different (i.e., if a Transfer-Encoding
1629     header field is present). If a message is received with both a
1630     Transfer-Encoding header field and a Content-Length header field,
1631     the latter &MUST; be ignored.
1632    </t></x:lt>
1633    <x:lt><t>
1634     If the message uses the media type "multipart/byteranges", and the
1635     transfer-length is not otherwise specified, then this self-delimiting
1636     media type defines the transfer-length. This media type
1637     &MUST-NOT; be used unless the sender knows that the recipient can parse
1638     it; the presence in a request of a Range header with multiple byte-range
1639     specifiers from a 1.1 client implies that the client can parse
1640     multipart/byteranges responses.
1641    <list style="empty"><t>
1642       A range header might be forwarded by a 1.0 proxy that does not
1643       understand multipart/byteranges; in this case the server &MUST;
1644       delimit the message using methods defined in items 1, 3 or 5 of
1645       this section.
1646    </t></list>
1647    </t></x:lt>
1648    <x:lt><t>
1649     By the server closing the connection. (Closing the connection
1650     cannot be used to indicate the end of a request body, since that
1651     would leave no possibility for the server to send back a response.)
1652    </t></x:lt>
1653  </list>
1656   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1657   containing a message-body &MUST; include a valid Content-Length header
1658   field unless the server is known to be HTTP/1.1 compliant. If a
1659   request contains a message-body and a Content-Length is not given,
1660   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1661   determine the length of the message, or with 411 (Length Required) if
1662   it wishes to insist on receiving a valid Content-Length.
1665   All HTTP/1.1 applications that receive entities &MUST; accept the
1666   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1667   to be used for messages when the message length cannot be determined
1668   in advance.
1671   Messages &MUST-NOT; include both a Content-Length header field and a
1672   transfer-coding. If the message does include a
1673   transfer-coding, the Content-Length &MUST; be ignored.
1676   When a Content-Length is given in a message where a message-body is
1677   allowed, its field value &MUST; exactly match the number of OCTETs in
1678   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1679   invalid length is received and detected.
1683<section title="General Header Fields" anchor="general.header.fields">
1684  <x:anchor-alias value="general-header"/>
1686   There are a few header fields which have general applicability for
1687   both request and response messages, but which do not apply to the
1688   entity being transferred. These header fields apply only to the
1689   message being transmitted.
1691<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1692  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1693                 | <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1694                 | <x:ref>Date</x:ref>                     ; <xref target=""/>
1695                 | <x:ref>Pragma</x:ref>                   ; &header-pragma;
1696                 | <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1697                 | <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1698                 | <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1699                 | <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1700                 | <x:ref>Warning</x:ref>                  ; &header-warning;
1703   General-header field names can be extended reliably only in
1704   combination with a change in the protocol version. However, new or
1705   experimental header fields may be given the semantics of general
1706   header fields if all parties in the communication recognize them to
1707   be general-header fields. Unrecognized header fields are treated as
1708   entity-header fields.
1713<section title="Request" anchor="request">
1714  <x:anchor-alias value="Request"/>
1716   A request message from a client to a server includes, within the
1717   first line of that message, the method to be applied to the resource,
1718   the identifier of the resource, and the protocol version in use.
1720<!--                 Host                      ; should be moved here eventually -->
1721<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1722  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1723                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1724                   | <x:ref>request-header</x:ref>         ; &request-header-fields;
1725                   | <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1726                  <x:ref>CRLF</x:ref>
1727                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1730<section title="Request-Line" anchor="request-line">
1731  <x:anchor-alias value="Request-Line"/>
1733   The Request-Line begins with a method token, followed by the
1734   Request-URI and the protocol version, and ending with CRLF. The
1735   elements are separated by SP characters. No CR or LF is allowed
1736   except in the final CRLF sequence.
1738<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1739  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>Request-URI</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1742<section title="Method" anchor="method">
1743  <x:anchor-alias value="Method"/>
1745   The Method  token indicates the method to be performed on the
1746   resource identified by the Request-URI. The method is case-sensitive.
1748<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1749  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1753<section title="Request-URI" anchor="request-uri">
1754  <x:anchor-alias value="Request-URI"/>
1756   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1757   identifies the resource upon which to apply the request.
1759<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1760  <x:ref>Request-URI</x:ref>    = "*"
1761                 | <x:ref>absoluteURI</x:ref>
1762                 | ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1763                 | <x:ref>authority</x:ref>
1766   The four options for Request-URI are dependent on the nature of the
1767   request. The asterisk "*" means that the request does not apply to a
1768   particular resource, but to the server itself, and is only allowed
1769   when the method used does not necessarily apply to a resource. One
1770   example would be
1772<figure><artwork type="example">
1773    OPTIONS * HTTP/1.1
1776   The absoluteURI form is &REQUIRED; when the request is being made to a
1777   proxy. The proxy is requested to forward the request or service it
1778   from a valid cache, and return the response. Note that the proxy &MAY;
1779   forward the request on to another proxy or directly to the server
1780   specified by the absoluteURI. In order to avoid request loops, a
1781   proxy &MUST; be able to recognize all of its server names, including
1782   any aliases, local variations, and the numeric IP address. An example
1783   Request-Line would be:
1785<figure><artwork type="example">
1786    GET HTTP/1.1
1789   To allow for transition to absoluteURIs in all requests in future
1790   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1791   form in requests, even though HTTP/1.1 clients will only generate
1792   them in requests to proxies.
1795   The authority form is only used by the CONNECT method (&CONNECT;).
1798   The most common form of Request-URI is that used to identify a
1799   resource on an origin server or gateway. In this case the absolute
1800   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1801   the Request-URI, and the network location of the URI (authority) &MUST;
1802   be transmitted in a Host header field. For example, a client wishing
1803   to retrieve the resource above directly from the origin server would
1804   create a TCP connection to port 80 of the host "" and send
1805   the lines:
1807<figure><artwork type="example">
1808    GET /pub/WWW/TheProject.html HTTP/1.1
1809    Host:
1812   followed by the remainder of the Request. Note that the absolute path
1813   cannot be empty; if none is present in the original URI, it &MUST; be
1814   given as "/" (the server root).
1817   The Request-URI is transmitted in the format specified in
1818   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1819   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1820   properly interpret the request. Servers &SHOULD; respond to invalid
1821   Request-URIs with an appropriate status code.
1824   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1825   received Request-URI when forwarding it to the next inbound server,
1826   except as noted above to replace a null path-absolute with "/".
1829  <list><t>
1830      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1831      meaning of the request when the origin server is improperly using
1832      a non-reserved URI character for a reserved purpose.  Implementors
1833      should be aware that some pre-HTTP/1.1 proxies have been known to
1834      rewrite the Request-URI.
1835  </t></list>
1840<section title="The Resource Identified by a Request" anchor="">
1842   The exact resource identified by an Internet request is determined by
1843   examining both the Request-URI and the Host header field.
1846   An origin server that does not allow resources to differ by the
1847   requested host &MAY; ignore the Host header field value when
1848   determining the resource identified by an HTTP/1.1 request. (But see
1849   <xref target=""/>
1850   for other requirements on Host support in HTTP/1.1.)
1853   An origin server that does differentiate resources based on the host
1854   requested (sometimes referred to as virtual hosts or vanity host
1855   names) &MUST; use the following rules for determining the requested
1856   resource on an HTTP/1.1 request:
1857  <list style="numbers">
1858    <t>If Request-URI is an absoluteURI, the host is part of the
1859     Request-URI. Any Host header field value in the request &MUST; be
1860     ignored.</t>
1861    <t>If the Request-URI is not an absoluteURI, and the request includes
1862     a Host header field, the host is determined by the Host header
1863     field value.</t>
1864    <t>If the host as determined by rule 1 or 2 is not a valid host on
1865     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1866  </list>
1869   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1870   attempt to use heuristics (e.g., examination of the URI path for
1871   something unique to a particular host) in order to determine what
1872   exact resource is being requested.
1879<section title="Response" anchor="response">
1880  <x:anchor-alias value="Response"/>
1882   After receiving and interpreting a request message, a server responds
1883   with an HTTP response message.
1885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1886  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1887                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1888                   | <x:ref>response-header</x:ref>        ; &response-header-fields;
1889                   | <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1890                  <x:ref>CRLF</x:ref>
1891                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1894<section title="Status-Line" anchor="status-line">
1895  <x:anchor-alias value="Status-Line"/>
1897   The first line of a Response message is the Status-Line, consisting
1898   of the protocol version followed by a numeric status code and its
1899   associated textual phrase, with each element separated by SP
1900   characters. No CR or LF is allowed except in the final CRLF sequence.
1902<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1903  <x:ref>Status-Line</x:ref> = <x:ref>HTTP-Version</x:ref> <x:ref>SP</x:ref> <x:ref>Status-Code</x:ref> <x:ref>SP</x:ref> <x:ref>Reason-Phrase</x:ref> <x:ref>CRLF</x:ref>
1906<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1907  <x:anchor-alias value="Reason-Phrase"/>
1908  <x:anchor-alias value="Status-Code"/>
1910   The Status-Code element is a 3-digit integer result code of the
1911   attempt to understand and satisfy the request. These codes are fully
1912   defined in &status-codes;.  The Reason Phrase exists for the sole
1913   purpose of providing a textual description associated with the numeric
1914   status code, out of deference to earlier Internet application protocols
1915   that were more frequently used with interactive text clients.
1916   A client &SHOULD; ignore the content of the Reason Phrase.
1919   The first digit of the Status-Code defines the class of response. The
1920   last two digits do not have any categorization role. There are 5
1921   values for the first digit:
1922  <list style="symbols">
1923    <t>
1924      1xx: Informational - Request received, continuing process
1925    </t>
1926    <t>
1927      2xx: Success - The action was successfully received,
1928        understood, and accepted
1929    </t>
1930    <t>
1931      3xx: Redirection - Further action must be taken in order to
1932        complete the request
1933    </t>
1934    <t>
1935      4xx: Client Error - The request contains bad syntax or cannot
1936        be fulfilled
1937    </t>
1938    <t>
1939      5xx: Server Error - The server failed to fulfill an apparently
1940        valid request
1941    </t>
1942  </list>
1944<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"/>
1945  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1946  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1954<section title="Connections" anchor="connections">
1956<section title="Persistent Connections" anchor="persistent.connections">
1958<section title="Purpose" anchor="persistent.purpose">
1960   Prior to persistent connections, a separate TCP connection was
1961   established to fetch each URL, increasing the load on HTTP servers
1962   and causing congestion on the Internet. The use of inline images and
1963   other associated data often require a client to make multiple
1964   requests of the same server in a short amount of time. Analysis of
1965   these performance problems and results from a prototype
1966   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1967   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1968   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1969   T/TCP <xref target="Tou1998"/>.
1972   Persistent HTTP connections have a number of advantages:
1973  <list style="symbols">
1974      <t>
1975        By opening and closing fewer TCP connections, CPU time is saved
1976        in routers and hosts (clients, servers, proxies, gateways,
1977        tunnels, or caches), and memory used for TCP protocol control
1978        blocks can be saved in hosts.
1979      </t>
1980      <t>
1981        HTTP requests and responses can be pipelined on a connection.
1982        Pipelining allows a client to make multiple requests without
1983        waiting for each response, allowing a single TCP connection to
1984        be used much more efficiently, with much lower elapsed time.
1985      </t>
1986      <t>
1987        Network congestion is reduced by reducing the number of packets
1988        caused by TCP opens, and by allowing TCP sufficient time to
1989        determine the congestion state of the network.
1990      </t>
1991      <t>
1992        Latency on subsequent requests is reduced since there is no time
1993        spent in TCP's connection opening handshake.
1994      </t>
1995      <t>
1996        HTTP can evolve more gracefully, since errors can be reported
1997        without the penalty of closing the TCP connection. Clients using
1998        future versions of HTTP might optimistically try a new feature,
1999        but if communicating with an older server, retry with old
2000        semantics after an error is reported.
2001      </t>
2002    </list>
2005   HTTP implementations &SHOULD; implement persistent connections.
2009<section title="Overall Operation" anchor="persistent.overall">
2011   A significant difference between HTTP/1.1 and earlier versions of
2012   HTTP is that persistent connections are the default behavior of any
2013   HTTP connection. That is, unless otherwise indicated, the client
2014   &SHOULD; assume that the server will maintain a persistent connection,
2015   even after error responses from the server.
2018   Persistent connections provide a mechanism by which a client and a
2019   server can signal the close of a TCP connection. This signaling takes
2020   place using the Connection header field (<xref target="header.connection"/>). Once a close
2021   has been signaled, the client &MUST-NOT; send any more requests on that
2022   connection.
2025<section title="Negotiation" anchor="persistent.negotiation">
2027   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2028   maintain a persistent connection unless a Connection header including
2029   the connection-token "close" was sent in the request. If the server
2030   chooses to close the connection immediately after sending the
2031   response, it &SHOULD; send a Connection header including the
2032   connection-token close.
2035   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2036   decide to keep it open based on whether the response from a server
2037   contains a Connection header with the connection-token close. In case
2038   the client does not want to maintain a connection for more than that
2039   request, it &SHOULD; send a Connection header including the
2040   connection-token close.
2043   If either the client or the server sends the close token in the
2044   Connection header, that request becomes the last one for the
2045   connection.
2048   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2049   maintained for HTTP versions less than 1.1 unless it is explicitly
2050   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2051   compatibility with HTTP/1.0 clients.
2054   In order to remain persistent, all messages on the connection &MUST;
2055   have a self-defined message length (i.e., one not defined by closure
2056   of the connection), as described in <xref target="message.length"/>.
2060<section title="Pipelining" anchor="pipelining">
2062   A client that supports persistent connections &MAY; "pipeline" its
2063   requests (i.e., send multiple requests without waiting for each
2064   response). A server &MUST; send its responses to those requests in the
2065   same order that the requests were received.
2068   Clients which assume persistent connections and pipeline immediately
2069   after connection establishment &SHOULD; be prepared to retry their
2070   connection if the first pipelined attempt fails. If a client does
2071   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2072   persistent. Clients &MUST; also be prepared to resend their requests if
2073   the server closes the connection before sending all of the
2074   corresponding responses.
2077   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2078   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2079   premature termination of the transport connection could lead to
2080   indeterminate results. A client wishing to send a non-idempotent
2081   request &SHOULD; wait to send that request until it has received the
2082   response status for the previous request.
2087<section title="Proxy Servers" anchor="persistent.proxy">
2089   It is especially important that proxies correctly implement the
2090   properties of the Connection header field as specified in <xref target="header.connection"/>.
2093   The proxy server &MUST; signal persistent connections separately with
2094   its clients and the origin servers (or other proxy servers) that it
2095   connects to. Each persistent connection applies to only one transport
2096   link.
2099   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2100   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
2101   discussion of the problems with the Keep-Alive header implemented by
2102   many HTTP/1.0 clients).
2106<section title="Practical Considerations" anchor="persistent.practical">
2108   Servers will usually have some time-out value beyond which they will
2109   no longer maintain an inactive connection. Proxy servers might make
2110   this a higher value since it is likely that the client will be making
2111   more connections through the same server. The use of persistent
2112   connections places no requirements on the length (or existence) of
2113   this time-out for either the client or the server.
2116   When a client or server wishes to time-out it &SHOULD; issue a graceful
2117   close on the transport connection. Clients and servers &SHOULD; both
2118   constantly watch for the other side of the transport close, and
2119   respond to it as appropriate. If a client or server does not detect
2120   the other side's close promptly it could cause unnecessary resource
2121   drain on the network.
2124   A client, server, or proxy &MAY; close the transport connection at any
2125   time. For example, a client might have started to send a new request
2126   at the same time that the server has decided to close the "idle"
2127   connection. From the server's point of view, the connection is being
2128   closed while it was idle, but from the client's point of view, a
2129   request is in progress.
2132   This means that clients, servers, and proxies &MUST; be able to recover
2133   from asynchronous close events. Client software &SHOULD; reopen the
2134   transport connection and retransmit the aborted sequence of requests
2135   without user interaction so long as the request sequence is
2136   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2137   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2138   human operator the choice of retrying the request(s). Confirmation by
2139   user-agent software with semantic understanding of the application
2140   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2141   be repeated if the second sequence of requests fails.
2144   Servers &SHOULD; always respond to at least one request per connection,
2145   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2146   middle of transmitting a response, unless a network or client failure
2147   is suspected.
2150   Clients that use persistent connections &SHOULD; limit the number of
2151   simultaneous connections that they maintain to a given server. A
2152   single-user client &SHOULD-NOT; maintain more than 2 connections with
2153   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2154   another server or proxy, where N is the number of simultaneously
2155   active users. These guidelines are intended to improve HTTP response
2156   times and avoid congestion.
2161<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2163<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2165   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2166   flow control mechanisms to resolve temporary overloads, rather than
2167   terminating connections with the expectation that clients will retry.
2168   The latter technique can exacerbate network congestion.
2172<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2174   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2175   the network connection for an error status while it is transmitting
2176   the request. If the client sees an error status, it &SHOULD;
2177   immediately cease transmitting the body. If the body is being sent
2178   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2179   empty trailer &MAY; be used to prematurely mark the end of the message.
2180   If the body was preceded by a Content-Length header, the client &MUST;
2181   close the connection.
2185<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2187   The purpose of the 100 (Continue) status (see &status-100;) is to
2188   allow a client that is sending a request message with a request body
2189   to determine if the origin server is willing to accept the request
2190   (based on the request headers) before the client sends the request
2191   body. In some cases, it might either be inappropriate or highly
2192   inefficient for the client to send the body if the server will reject
2193   the message without looking at the body.
2196   Requirements for HTTP/1.1 clients:
2197  <list style="symbols">
2198    <t>
2199        If a client will wait for a 100 (Continue) response before
2200        sending the request body, it &MUST; send an Expect request-header
2201        field (&header-expect;) with the "100-continue" expectation.
2202    </t>
2203    <t>
2204        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2205        with the "100-continue" expectation if it does not intend
2206        to send a request body.
2207    </t>
2208  </list>
2211   Because of the presence of older implementations, the protocol allows
2212   ambiguous situations in which a client may send "Expect: 100-continue"
2213   without receiving either a 417 (Expectation Failed) status
2214   or a 100 (Continue) status. Therefore, when a client sends this
2215   header field to an origin server (possibly via a proxy) from which it
2216   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2217   for an indefinite period before sending the request body.
2220   Requirements for HTTP/1.1 origin servers:
2221  <list style="symbols">
2222    <t> Upon receiving a request which includes an Expect request-header
2223        field with the "100-continue" expectation, an origin server &MUST;
2224        either respond with 100 (Continue) status and continue to read
2225        from the input stream, or respond with a final status code. The
2226        origin server &MUST-NOT; wait for the request body before sending
2227        the 100 (Continue) response. If it responds with a final status
2228        code, it &MAY; close the transport connection or it &MAY; continue
2229        to read and discard the rest of the request.  It &MUST-NOT;
2230        perform the requested method if it returns a final status code.
2231    </t>
2232    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2233        the request message does not include an Expect request-header
2234        field with the "100-continue" expectation, and &MUST-NOT; send a
2235        100 (Continue) response if such a request comes from an HTTP/1.0
2236        (or earlier) client. There is an exception to this rule: for
2237        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2238        status in response to an HTTP/1.1 PUT or POST request that does
2239        not include an Expect request-header field with the "100-continue"
2240        expectation. This exception, the purpose of which is
2241        to minimize any client processing delays associated with an
2242        undeclared wait for 100 (Continue) status, applies only to
2243        HTTP/1.1 requests, and not to requests with any other HTTP-version
2244        value.
2245    </t>
2246    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2247        already received some or all of the request body for the
2248        corresponding request.
2249    </t>
2250    <t> An origin server that sends a 100 (Continue) response &MUST;
2251    ultimately send a final status code, once the request body is
2252        received and processed, unless it terminates the transport
2253        connection prematurely.
2254    </t>
2255    <t> If an origin server receives a request that does not include an
2256        Expect request-header field with the "100-continue" expectation,
2257        the request includes a request body, and the server responds
2258        with a final status code before reading the entire request body
2259        from the transport connection, then the server &SHOULD-NOT;  close
2260        the transport connection until it has read the entire request,
2261        or until the client closes the connection. Otherwise, the client
2262        might not reliably receive the response message. However, this
2263        requirement is not be construed as preventing a server from
2264        defending itself against denial-of-service attacks, or from
2265        badly broken client implementations.
2266      </t>
2267    </list>
2270   Requirements for HTTP/1.1 proxies:
2271  <list style="symbols">
2272    <t> If a proxy receives a request that includes an Expect request-header
2273        field with the "100-continue" expectation, and the proxy
2274        either knows that the next-hop server complies with HTTP/1.1 or
2275        higher, or does not know the HTTP version of the next-hop
2276        server, it &MUST; forward the request, including the Expect header
2277        field.
2278    </t>
2279    <t> If the proxy knows that the version of the next-hop server is
2280        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2281        respond with a 417 (Expectation Failed) status.
2282    </t>
2283    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2284        numbers received from recently-referenced next-hop servers.
2285    </t>
2286    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2287        request message was received from an HTTP/1.0 (or earlier)
2288        client and did not include an Expect request-header field with
2289        the "100-continue" expectation. This requirement overrides the
2290        general rule for forwarding of 1xx responses (see &status-1xx;).
2291    </t>
2292  </list>
2296<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2298   If an HTTP/1.1 client sends a request which includes a request body,
2299   but which does not include an Expect request-header field with the
2300   "100-continue" expectation, and if the client is not directly
2301   connected to an HTTP/1.1 origin server, and if the client sees the
2302   connection close before receiving any status from the server, the
2303   client &SHOULD; retry the request.  If the client does retry this
2304   request, it &MAY; use the following "binary exponential backoff"
2305   algorithm to be assured of obtaining a reliable response:
2306  <list style="numbers">
2307    <t>
2308      Initiate a new connection to the server
2309    </t>
2310    <t>
2311      Transmit the request-headers
2312    </t>
2313    <t>
2314      Initialize a variable R to the estimated round-trip time to the
2315         server (e.g., based on the time it took to establish the
2316         connection), or to a constant value of 5 seconds if the round-trip
2317         time is not available.
2318    </t>
2319    <t>
2320       Compute T = R * (2**N), where N is the number of previous
2321         retries of this request.
2322    </t>
2323    <t>
2324       Wait either for an error response from the server, or for T
2325         seconds (whichever comes first)
2326    </t>
2327    <t>
2328       If no error response is received, after T seconds transmit the
2329         body of the request.
2330    </t>
2331    <t>
2332       If client sees that the connection is closed prematurely,
2333         repeat from step 1 until the request is accepted, an error
2334         response is received, or the user becomes impatient and
2335         terminates the retry process.
2336    </t>
2337  </list>
2340   If at any point an error status is received, the client
2341  <list style="symbols">
2342      <t>&SHOULD-NOT;  continue and</t>
2344      <t>&SHOULD; close the connection if it has not completed sending the
2345        request message.</t>
2346    </list>
2353<section title="Header Field Definitions" anchor="header.fields">
2355   This section defines the syntax and semantics of HTTP/1.1 header fields
2356   related to message framing and transport protocols.
2359   For entity-header fields, both sender and recipient refer to either the
2360   client or the server, depending on who sends and who receives the entity.
2363<section title="Connection" anchor="header.connection">
2364  <iref primary="true" item="Connection header" x:for-anchor=""/>
2365  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2366  <x:anchor-alias value="Connection"/>
2367  <x:anchor-alias value="connection-token"/>
2369   The Connection general-header field allows the sender to specify
2370   options that are desired for that particular connection and &MUST-NOT;
2371   be communicated by proxies over further connections.
2374   The Connection header has the following grammar:
2376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2377  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2378  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2381   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2382   message is forwarded and, for each connection-token in this field,
2383   remove any header field(s) from the message with the same name as the
2384   connection-token. Connection options are signaled by the presence of
2385   a connection-token in the Connection header field, not by any
2386   corresponding additional header field(s), since the additional header
2387   field may not be sent if there are no parameters associated with that
2388   connection option.
2391   Message headers listed in the Connection header &MUST-NOT; include
2392   end-to-end headers, such as Cache-Control.
2395   HTTP/1.1 defines the "close" connection option for the sender to
2396   signal that the connection will be closed after completion of the
2397   response. For example,
2399<figure><artwork type="example">
2400    Connection: close
2403   in either the request or the response header fields indicates that
2404   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2405   after the current request/response is complete.
2408   An HTTP/1.1 client that does not support persistent connections &MUST;
2409   include the "close" connection option in every request message.
2412   An HTTP/1.1 server that does not support persistent connections &MUST;
2413   include the "close" connection option in every response message that
2414   does not have a 1xx (informational) status code.
2417   A system receiving an HTTP/1.0 (or lower-version) message that
2418   includes a Connection header &MUST;, for each connection-token in this
2419   field, remove and ignore any header field(s) from the message with
2420   the same name as the connection-token. This protects against mistaken
2421   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2425<section title="Content-Length" anchor="header.content-length">
2426  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2427  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2428  <x:anchor-alias value="Content-Length"/>
2430   The Content-Length entity-header field indicates the size of the
2431   entity-body, in decimal number of OCTETs, sent to the recipient or,
2432   in the case of the HEAD method, the size of the entity-body that
2433   would have been sent had the request been a GET.
2435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2436  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2439   An example is
2441<figure><artwork type="example">
2442    Content-Length: 3495
2445   Applications &SHOULD; use this field to indicate the transfer-length of
2446   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2449   Any Content-Length greater than or equal to zero is a valid value.
2450   <xref target="message.length"/> describes how to determine the length of a message-body
2451   if a Content-Length is not given.
2454   Note that the meaning of this field is significantly different from
2455   the corresponding definition in MIME, where it is an optional field
2456   used within the "message/external-body" content-type. In HTTP, it
2457   &SHOULD; be sent whenever the message's length can be determined prior
2458   to being transferred, unless this is prohibited by the rules in
2459   <xref target="message.length"/>.
2463<section title="Date" anchor="">
2464  <iref primary="true" item="Date header" x:for-anchor=""/>
2465  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2466  <x:anchor-alias value="Date"/>
2468   The Date general-header field represents the date and time at which
2469   the message was originated, having the same semantics as orig-date in
2470   <xref target="RFC2822" x:fmt="of" x:sec="3.6.1"/>. The field value is an HTTP-date, as described in <xref target=""/>;
2471   it &MUST; be sent in rfc1123-date format.
2473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2474  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2477   An example is
2479<figure><artwork type="example">
2480    Date: Tue, 15 Nov 1994 08:12:31 GMT
2483   Origin servers &MUST; include a Date header field in all responses,
2484   except in these cases:
2485  <list style="numbers">
2486      <t>If the response status code is 100 (Continue) or 101 (Switching
2487         Protocols), the response &MAY; include a Date header field, at
2488         the server's option.</t>
2490      <t>If the response status code conveys a server error, e.g. 500
2491         (Internal Server Error) or 503 (Service Unavailable), and it is
2492         inconvenient or impossible to generate a valid Date.</t>
2494      <t>If the server does not have a clock that can provide a
2495         reasonable approximation of the current time, its responses
2496         &MUST-NOT; include a Date header field. In this case, the rules
2497         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2498  </list>
2501   A received message that does not have a Date header field &MUST; be
2502   assigned one by the recipient if the message will be cached by that
2503   recipient or gatewayed via a protocol which requires a Date. An HTTP
2504   implementation without a clock &MUST-NOT; cache responses without
2505   revalidating them on every use. An HTTP cache, especially a shared
2506   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2507   clock with a reliable external standard.
2510   Clients &SHOULD; only send a Date header field in messages that include
2511   an entity-body, as in the case of the PUT and POST requests, and even
2512   then it is optional. A client without a clock &MUST-NOT; send a Date
2513   header field in a request.
2516   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2517   time subsequent to the generation of the message. It &SHOULD; represent
2518   the best available approximation of the date and time of message
2519   generation, unless the implementation has no means of generating a
2520   reasonably accurate date and time. In theory, the date ought to
2521   represent the moment just before the entity is generated. In
2522   practice, the date can be generated at any time during the message
2523   origination without affecting its semantic value.
2526<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2528   Some origin server implementations might not have a clock available.
2529   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2530   values to a response, unless these values were associated
2531   with the resource by a system or user with a reliable clock. It &MAY;
2532   assign an Expires value that is known, at or before server
2533   configuration time, to be in the past (this allows "pre-expiration"
2534   of responses without storing separate Expires values for each
2535   resource).
2540<section title="Host" anchor="">
2541  <iref primary="true" item="Host header" x:for-anchor=""/>
2542  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2543  <x:anchor-alias value="Host"/>
2545   The Host request-header field specifies the Internet host and port
2546   number of the resource being requested, as obtained from the original
2547   URI given by the user or referring resource (generally an HTTP URL,
2548   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2549   the naming authority of the origin server or gateway given by the
2550   original URL. This allows the origin server or gateway to
2551   differentiate between internally-ambiguous URLs, such as the root "/"
2552   URL of a server for multiple host names on a single IP address.
2554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2555  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2558   A "host" without any trailing port information implies the default
2559   port for the service requested (e.g., "80" for an HTTP URL). For
2560   example, a request on the origin server for
2561   &lt;; would properly include:
2563<figure><artwork type="example">
2564    GET /pub/WWW/ HTTP/1.1
2565    Host:
2568   A client &MUST; include a Host header field in all HTTP/1.1 request
2569   messages. If the requested URI does not include an Internet host
2570   name for the service being requested, then the Host header field &MUST;
2571   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2572   request message it forwards does contain an appropriate Host header
2573   field that identifies the service being requested by the proxy. All
2574   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2575   status code to any HTTP/1.1 request message which lacks a Host header
2576   field.
2579   See Sections <xref target="" format="counter"/>
2580   and <xref target="" format="counter"/>
2581   for other requirements relating to Host.
2585<section title="TE" anchor="header.te">
2586  <iref primary="true" item="TE header" x:for-anchor=""/>
2587  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2588  <x:anchor-alias value="TE"/>
2589  <x:anchor-alias value="t-codings"/>
2591   The TE request-header field indicates what extension transfer-codings
2592   it is willing to accept in the response and whether or not it is
2593   willing to accept trailer fields in a chunked transfer-coding. Its
2594   value may consist of the keyword "trailers" and/or a comma-separated
2595   list of extension transfer-coding names with optional accept
2596   parameters (as described in <xref target="transfer.codings"/>).
2598<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2599  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2600  <x:ref>t-codings</x:ref> = "trailers" | ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2603   The presence of the keyword "trailers" indicates that the client is
2604   willing to accept trailer fields in a chunked transfer-coding, as
2605   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2606   transfer-coding values even though it does not itself represent a
2607   transfer-coding.
2610   Examples of its use are:
2612<figure><artwork type="example">
2613    TE: deflate
2614    TE:
2615    TE: trailers, deflate;q=0.5
2618   The TE header field only applies to the immediate connection.
2619   Therefore, the keyword &MUST; be supplied within a Connection header
2620   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2623   A server tests whether a transfer-coding is acceptable, according to
2624   a TE field, using these rules:
2625  <list style="numbers">
2626    <x:lt>
2627      <t>The "chunked" transfer-coding is always acceptable. If the
2628         keyword "trailers" is listed, the client indicates that it is
2629         willing to accept trailer fields in the chunked response on
2630         behalf of itself and any downstream clients. The implication is
2631         that, if given, the client is stating that either all
2632         downstream clients are willing to accept trailer fields in the
2633         forwarded response, or that it will attempt to buffer the
2634         response on behalf of downstream recipients.
2635      </t><t>
2636         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2637         chunked response such that a client can be assured of buffering
2638         the entire response.</t>
2639    </x:lt>
2640    <x:lt>
2641      <t>If the transfer-coding being tested is one of the transfer-codings
2642         listed in the TE field, then it is acceptable unless it
2643         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2644         qvalue of 0 means "not acceptable.")</t>
2645    </x:lt>
2646    <x:lt>
2647      <t>If multiple transfer-codings are acceptable, then the
2648         acceptable transfer-coding with the highest non-zero qvalue is
2649         preferred.  The "chunked" transfer-coding always has a qvalue
2650         of 1.</t>
2651    </x:lt>
2652  </list>
2655   If the TE field-value is empty or if no TE field is present, the only
2656   transfer-coding  is "chunked". A message with no transfer-coding is
2657   always acceptable.
2661<section title="Trailer" anchor="header.trailer">
2662  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2663  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2664  <x:anchor-alias value="Trailer"/>
2666   The Trailer general field value indicates that the given set of
2667   header fields is present in the trailer of a message encoded with
2668   chunked transfer-coding.
2670<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2671  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2674   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2675   message using chunked transfer-coding with a non-empty trailer. Doing
2676   so allows the recipient to know which header fields to expect in the
2677   trailer.
2680   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2681   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2682   trailer fields in a "chunked" transfer-coding.
2685   Message header fields listed in the Trailer header field &MUST-NOT;
2686   include the following header fields:
2687  <list style="symbols">
2688    <t>Transfer-Encoding</t>
2689    <t>Content-Length</t>
2690    <t>Trailer</t>
2691  </list>
2695<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2696  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2697  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2698  <x:anchor-alias value="Transfer-Encoding"/>
2700   The Transfer-Encoding general-header field indicates what (if any)
2701   type of transformation has been applied to the message body in order
2702   to safely transfer it between the sender and the recipient. This
2703   differs from the content-coding in that the transfer-coding is a
2704   property of the message, not of the entity.
2706<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2707  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2710   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2712<figure><artwork type="example">
2713  Transfer-Encoding: chunked
2716   If multiple encodings have been applied to an entity, the transfer-codings
2717   &MUST; be listed in the order in which they were applied.
2718   Additional information about the encoding parameters &MAY; be provided
2719   by other entity-header fields not defined by this specification.
2722   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2723   header.
2727<section title="Upgrade" anchor="header.upgrade">
2728  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2729  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2730  <x:anchor-alias value="Upgrade"/>
2732   The Upgrade general-header allows the client to specify what
2733   additional communication protocols it supports and would like to use
2734   if the server finds it appropriate to switch protocols. The server
2735   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2736   response to indicate which protocol(s) are being switched.
2738<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2739  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2742   For example,
2744<figure><artwork type="example">
2745    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2748   The Upgrade header field is intended to provide a simple mechanism
2749   for transition from HTTP/1.1 to some other, incompatible protocol. It
2750   does so by allowing the client to advertise its desire to use another
2751   protocol, such as a later version of HTTP with a higher major version
2752   number, even though the current request has been made using HTTP/1.1.
2753   This eases the difficult transition between incompatible protocols by
2754   allowing the client to initiate a request in the more commonly
2755   supported protocol while indicating to the server that it would like
2756   to use a "better" protocol if available (where "better" is determined
2757   by the server, possibly according to the nature of the method and/or
2758   resource being requested).
2761   The Upgrade header field only applies to switching application-layer
2762   protocols upon the existing transport-layer connection. Upgrade
2763   cannot be used to insist on a protocol change; its acceptance and use
2764   by the server is optional. The capabilities and nature of the
2765   application-layer communication after the protocol change is entirely
2766   dependent upon the new protocol chosen, although the first action
2767   after changing the protocol &MUST; be a response to the initial HTTP
2768   request containing the Upgrade header field.
2771   The Upgrade header field only applies to the immediate connection.
2772   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2773   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2774   HTTP/1.1 message.
2777   The Upgrade header field cannot be used to indicate a switch to a
2778   protocol on a different connection. For that purpose, it is more
2779   appropriate to use a 301, 302, 303, or 305 redirection response.
2782   This specification only defines the protocol name "HTTP" for use by
2783   the family of Hypertext Transfer Protocols, as defined by the HTTP
2784   version rules of <xref target="http.version"/> and future updates to this
2785   specification. Any token can be used as a protocol name; however, it
2786   will only be useful if both the client and server associate the name
2787   with the same protocol.
2791<section title="Via" anchor="header.via">
2792  <iref primary="true" item="Via header" x:for-anchor=""/>
2793  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2794  <x:anchor-alias value="protocol-name"/>
2795  <x:anchor-alias value="protocol-version"/>
2796  <x:anchor-alias value="pseudonym"/>
2797  <x:anchor-alias value="received-by"/>
2798  <x:anchor-alias value="received-protocol"/>
2799  <x:anchor-alias value="Via"/>
2801   The Via general-header field &MUST; be used by gateways and proxies to
2802   indicate the intermediate protocols and recipients between the user
2803   agent and the server on requests, and between the origin server and
2804   the client on responses. It is analogous to the "Received" field of
2805   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2806   avoiding request loops, and identifying the protocol capabilities of
2807   all senders along the request/response chain.
2809<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"/>
2810  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2811  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2812  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2813  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2814  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) | <x:ref>pseudonym</x:ref>
2815  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2818   The received-protocol indicates the protocol version of the message
2819   received by the server or client along each segment of the
2820   request/response chain. The received-protocol version is appended to
2821   the Via field value when the message is forwarded so that information
2822   about the protocol capabilities of upstream applications remains
2823   visible to all recipients.
2826   The protocol-name is optional if and only if it would be "HTTP". The
2827   received-by field is normally the host and optional port number of a
2828   recipient server or client that subsequently forwarded the message.
2829   However, if the real host is considered to be sensitive information,
2830   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2831   be assumed to be the default port of the received-protocol.
2834   Multiple Via field values represents each proxy or gateway that has
2835   forwarded the message. Each recipient &MUST; append its information
2836   such that the end result is ordered according to the sequence of
2837   forwarding applications.
2840   Comments &MAY; be used in the Via header field to identify the software
2841   of the recipient proxy or gateway, analogous to the User-Agent and
2842   Server header fields. However, all comments in the Via field are
2843   optional and &MAY; be removed by any recipient prior to forwarding the
2844   message.
2847   For example, a request message could be sent from an HTTP/1.0 user
2848   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2849   forward the request to a public proxy at, which completes
2850   the request by forwarding it to the origin server at
2851   The request received by would then have the following
2852   Via header field:
2854<figure><artwork type="example">
2855    Via: 1.0 fred, 1.1 (Apache/1.1)
2858   Proxies and gateways used as a portal through a network firewall
2859   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2860   the firewall region. This information &SHOULD; only be propagated if
2861   explicitly enabled. If not enabled, the received-by host of any host
2862   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2863   for that host.
2866   For organizations that have strong privacy requirements for hiding
2867   internal structures, a proxy &MAY; combine an ordered subsequence of
2868   Via header field entries with identical received-protocol values into
2869   a single such entry. For example,
2871<figure><artwork type="example">
2872    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2875        could be collapsed to
2877<figure><artwork type="example">
2878    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2881   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2882   under the same organizational control and the hosts have already been
2883   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2884   have different received-protocol values.
2890<section title="IANA Considerations" anchor="IANA.considerations">
2892   <cref>TBD.</cref>
2896<section title="Security Considerations" anchor="security.considerations">
2898   This section is meant to inform application developers, information
2899   providers, and users of the security limitations in HTTP/1.1 as
2900   described by this document. The discussion does not include
2901   definitive solutions to the problems revealed, though it does make
2902   some suggestions for reducing security risks.
2905<section title="Personal Information" anchor="personal.information">
2907   HTTP clients are often privy to large amounts of personal information
2908   (e.g. the user's name, location, mail address, passwords, encryption
2909   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2910   leakage of this information.
2911   We very strongly recommend that a convenient interface be provided
2912   for the user to control dissemination of such information, and that
2913   designers and implementors be particularly careful in this area.
2914   History shows that errors in this area often create serious security
2915   and/or privacy problems and generate highly adverse publicity for the
2916   implementor's company.
2920<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2922   A server is in the position to save personal data about a user's
2923   requests which might identify their reading patterns or subjects of
2924   interest. This information is clearly confidential in nature and its
2925   handling can be constrained by law in certain countries. People using
2926   HTTP to provide data are responsible for ensuring that
2927   such material is not distributed without the permission of any
2928   individuals that are identifiable by the published results.
2932<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2934   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2935   the documents returned by HTTP requests to be only those that were
2936   intended by the server administrators. If an HTTP server translates
2937   HTTP URIs directly into file system calls, the server &MUST; take
2938   special care not to serve files that were not intended to be
2939   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2940   other operating systems use ".." as a path component to indicate a
2941   directory level above the current one. On such a system, an HTTP
2942   server &MUST; disallow any such construct in the Request-URI if it
2943   would otherwise allow access to a resource outside those intended to
2944   be accessible via the HTTP server. Similarly, files intended for
2945   reference only internally to the server (such as access control
2946   files, configuration files, and script code) &MUST; be protected from
2947   inappropriate retrieval, since they might contain sensitive
2948   information. Experience has shown that minor bugs in such HTTP server
2949   implementations have turned into security risks.
2953<section title="DNS Spoofing" anchor="dns.spoofing">
2955   Clients using HTTP rely heavily on the Domain Name Service, and are
2956   thus generally prone to security attacks based on the deliberate
2957   mis-association of IP addresses and DNS names. Clients need to be
2958   cautious in assuming the continuing validity of an IP number/DNS name
2959   association.
2962   In particular, HTTP clients &SHOULD; rely on their name resolver for
2963   confirmation of an IP number/DNS name association, rather than
2964   caching the result of previous host name lookups. Many platforms
2965   already can cache host name lookups locally when appropriate, and
2966   they &SHOULD; be configured to do so. It is proper for these lookups to
2967   be cached, however, only when the TTL (Time To Live) information
2968   reported by the name server makes it likely that the cached
2969   information will remain useful.
2972   If HTTP clients cache the results of host name lookups in order to
2973   achieve a performance improvement, they &MUST; observe the TTL
2974   information reported by DNS.
2977   If HTTP clients do not observe this rule, they could be spoofed when
2978   a previously-accessed server's IP address changes. As network
2979   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2980   possibility of this form of attack will grow. Observing this
2981   requirement thus reduces this potential security vulnerability.
2984   This requirement also improves the load-balancing behavior of clients
2985   for replicated servers using the same DNS name and reduces the
2986   likelihood of a user's experiencing failure in accessing sites which
2987   use that strategy.
2991<section title="Proxies and Caching" anchor="attack.proxies">
2993   By their very nature, HTTP proxies are men-in-the-middle, and
2994   represent an opportunity for man-in-the-middle attacks. Compromise of
2995   the systems on which the proxies run can result in serious security
2996   and privacy problems. Proxies have access to security-related
2997   information, personal information about individual users and
2998   organizations, and proprietary information belonging to users and
2999   content providers. A compromised proxy, or a proxy implemented or
3000   configured without regard to security and privacy considerations,
3001   might be used in the commission of a wide range of potential attacks.
3004   Proxy operators should protect the systems on which proxies run as
3005   they would protect any system that contains or transports sensitive
3006   information. In particular, log information gathered at proxies often
3007   contains highly sensitive personal information, and/or information
3008   about organizations. Log information should be carefully guarded, and
3009   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3012   Proxy implementors should consider the privacy and security
3013   implications of their design and coding decisions, and of the
3014   configuration options they provide to proxy operators (especially the
3015   default configuration).
3018   Users of a proxy need to be aware that they are no trustworthier than
3019   the people who run the proxy; HTTP itself cannot solve this problem.
3022   The judicious use of cryptography, when appropriate, may suffice to
3023   protect against a broad range of security and privacy attacks. Such
3024   cryptography is beyond the scope of the HTTP/1.1 specification.
3028<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3030   They exist. They are hard to defend against. Research continues.
3031   Beware.
3036<section title="Acknowledgments" anchor="ack">
3038   This specification makes heavy use of the augmented BNF and generic
3039   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
3040   reuses many of the definitions provided by Nathaniel Borenstein and
3041   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3042   specification will help reduce past confusion over the relationship
3043   between HTTP and Internet mail message formats.
3046   HTTP has evolved considerably over the years. It has
3047   benefited from a large and active developer community--the many
3048   people who have participated on the www-talk mailing list--and it is
3049   that community which has been most responsible for the success of
3050   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3051   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3052   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3053   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3054   VanHeyningen deserve special recognition for their efforts in
3055   defining early aspects of the protocol.
3058   This document has benefited greatly from the comments of all those
3059   participating in the HTTP-WG. In addition to those already mentioned,
3060   the following individuals have contributed to this specification:
3063   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3064   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3065   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3066   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3067   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3068   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3069   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3070   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3071   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3072   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3073   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3074   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3075   Josh Cohen.
3078   Thanks to the "cave men" of Palo Alto. You know who you are.
3081   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3082   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3083   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3084   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3085   Larry Masinter for their help. And thanks go particularly to Jeff
3086   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3089   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3090   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3091   discovery of many of the problems that this document attempts to
3092   rectify.
3099<references title="Normative References">
3101<reference anchor="ISO-8859-1">
3102  <front>
3103    <title>
3104     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3105    </title>
3106    <author>
3107      <organization>International Organization for Standardization</organization>
3108    </author>
3109    <date year="1998"/>
3110  </front>
3111  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3114<reference anchor="Part2">
3115  <front>
3116    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3118      <organization abbrev="Day Software">Day Software</organization>
3119      <address><email></email></address>
3120    </author>
3121    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3122      <organization>One Laptop per Child</organization>
3123      <address><email></email></address>
3124    </author>
3125    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3126      <organization abbrev="HP">Hewlett-Packard Company</organization>
3127      <address><email></email></address>
3128    </author>
3129    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3130      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3131      <address><email></email></address>
3132    </author>
3133    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3134      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3135      <address><email></email></address>
3136    </author>
3137    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3138      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3139      <address><email></email></address>
3140    </author>
3141    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3142      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3143      <address><email></email></address>
3144    </author>
3145    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3146      <organization abbrev="W3C">World Wide Web Consortium</organization>
3147      <address><email></email></address>
3148    </author>
3149    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3150      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3151      <address><email></email></address>
3152    </author>
3153    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3154  </front>
3155  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3156  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3159<reference anchor="Part3">
3160  <front>
3161    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3162    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3163      <organization abbrev="Day Software">Day Software</organization>
3164      <address><email></email></address>
3165    </author>
3166    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3167      <organization>One Laptop per Child</organization>
3168      <address><email></email></address>
3169    </author>
3170    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3171      <organization abbrev="HP">Hewlett-Packard Company</organization>
3172      <address><email></email></address>
3173    </author>
3174    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3175      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3176      <address><email></email></address>
3177    </author>
3178    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3179      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3180      <address><email></email></address>
3181    </author>
3182    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3184      <address><email></email></address>
3185    </author>
3186    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3187      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3188      <address><email></email></address>
3189    </author>
3190    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3191      <organization abbrev="W3C">World Wide Web Consortium</organization>
3192      <address><email></email></address>
3193    </author>
3194    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3195      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3196      <address><email></email></address>
3197    </author>
3198    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3199  </front>
3200  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3201  <x:source href="p3-payload.xml" basename="p3-payload"/>
3204<reference anchor="Part5">
3205  <front>
3206    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3207    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3208      <organization abbrev="Day Software">Day Software</organization>
3209      <address><email></email></address>
3210    </author>
3211    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3212      <organization>One Laptop per Child</organization>
3213      <address><email></email></address>
3214    </author>
3215    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3216      <organization abbrev="HP">Hewlett-Packard Company</organization>
3217      <address><email></email></address>
3218    </author>
3219    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3220      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3221      <address><email></email></address>
3222    </author>
3223    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3224      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3225      <address><email></email></address>
3226    </author>
3227    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3228      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3229      <address><email></email></address>
3230    </author>
3231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3232      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3233      <address><email></email></address>
3234    </author>
3235    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3236      <organization abbrev="W3C">World Wide Web Consortium</organization>
3237      <address><email></email></address>
3238    </author>
3239    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3240      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3241      <address><email></email></address>
3242    </author>
3243    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3244  </front>
3245  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3246  <x:source href="p5-range.xml" basename="p5-range"/>
3249<reference anchor="Part6">
3250  <front>
3251    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3252    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3253      <organization abbrev="Day Software">Day Software</organization>
3254      <address><email></email></address>
3255    </author>
3256    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3257      <organization>One Laptop per Child</organization>
3258      <address><email></email></address>
3259    </author>
3260    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3261      <organization abbrev="HP">Hewlett-Packard Company</organization>
3262      <address><email></email></address>
3263    </author>
3264    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3265      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3266      <address><email></email></address>
3267    </author>
3268    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3269      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3270      <address><email></email></address>
3271    </author>
3272    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3273      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3274      <address><email></email></address>
3275    </author>
3276    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3277      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3278      <address><email></email></address>
3279    </author>
3280    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3281      <organization abbrev="W3C">World Wide Web Consortium</organization>
3282      <address><email></email></address>
3283    </author>
3284    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3285      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3286      <address><email></email></address>
3287    </author>
3288    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3289  </front>
3290  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3291  <x:source href="p6-cache.xml" basename="p6-cache"/>
3294<reference anchor="RFC822ABNF">
3295  <front>
3296    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3297    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3298      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3299      <address><email>DCrocker@UDel-Relay</email></address>
3300    </author>
3301    <date month="August" day="13" year="1982"/>
3302  </front>
3303  <seriesInfo name="STD" value="11"/>
3304  <seriesInfo name="RFC" value="822"/>
3307<reference anchor="RFC2045">
3308  <front>
3309    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3310    <author initials="N." surname="Freed" fullname="Ned Freed">
3311      <organization>Innosoft International, Inc.</organization>
3312      <address><email></email></address>
3313    </author>
3314    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3315      <organization>First Virtual Holdings</organization>
3316      <address><email></email></address>
3317    </author>
3318    <date month="November" year="1996"/>
3319  </front>
3320  <seriesInfo name="RFC" value="2045"/>
3323<reference anchor="RFC2047">
3324  <front>
3325    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3326    <author initials="K." surname="Moore" fullname="Keith Moore">
3327      <organization>University of Tennessee</organization>
3328      <address><email></email></address>
3329    </author>
3330    <date month="November" year="1996"/>
3331  </front>
3332  <seriesInfo name="RFC" value="2047"/>
3335<reference anchor="RFC2119">
3336  <front>
3337    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3338    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3339      <organization>Harvard University</organization>
3340      <address><email></email></address>
3341    </author>
3342    <date month="March" year="1997"/>
3343  </front>
3344  <seriesInfo name="BCP" value="14"/>
3345  <seriesInfo name="RFC" value="2119"/>
3348<reference anchor="RFC2396">
3349  <front>
3350    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3351    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3352      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3353      <address><email></email></address>
3354    </author>
3355    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3356      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3357      <address><email></email></address>
3358    </author>
3359    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3360      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3361      <address><email></email></address>
3362    </author>
3363    <date month="August" year="1998"/>
3364  </front>
3365  <seriesInfo name="RFC" value="2396"/>
3368<reference anchor="USASCII">
3369  <front>
3370    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3371    <author>
3372      <organization>American National Standards Institute</organization>
3373    </author>
3374    <date year="1986"/>
3375  </front>
3376  <seriesInfo name="ANSI" value="X3.4"/>
3381<references title="Informative References">
3383<reference anchor="Nie1997" target="">
3384  <front>
3385    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3386    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3387      <organization/>
3388    </author>
3389    <author initials="J." surname="Gettys" fullname="J. Gettys">
3390      <organization/>
3391    </author>
3392    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3393      <organization/>
3394    </author>
3395    <author initials="H." surname="Lie" fullname="H. Lie">
3396      <organization/>
3397    </author>
3398    <author initials="C." surname="Lilley" fullname="C. Lilley">
3399      <organization/>
3400    </author>
3401    <date year="1997" month="September"/>
3402  </front>
3403  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3406<reference anchor="Pad1995">
3407  <front>
3408    <title>Improving HTTP Latency</title>
3409    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3410      <organization/>
3411    </author>
3412    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3413      <organization/>
3414    </author>
3415    <date year="1995" month="December"/>
3416  </front>
3417  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3418  <annotation>
3419    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3420    which is available at <eref target=""/>.
3421  </annotation>
3424<reference anchor="RFC822">
3425  <front>
3426    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3427    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3428      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3429      <address><email>DCrocker@UDel-Relay</email></address>
3430    </author>
3431    <date month="August" day="13" year="1982"/>
3432  </front>
3433  <seriesInfo name="STD" value="11"/>
3434  <seriesInfo name="RFC" value="822"/>
3437<reference anchor="RFC959">
3438  <front>
3439    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3440    <author initials="J." surname="Postel" fullname="J. Postel">
3441      <organization>Information Sciences Institute (ISI)</organization>
3442    </author>
3443    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3444      <organization/>
3445    </author>
3446    <date month="October" year="1985"/>
3447  </front>
3448  <seriesInfo name="STD" value="9"/>
3449  <seriesInfo name="RFC" value="959"/>
3452<reference anchor="RFC1123">
3453  <front>
3454    <title>Requirements for Internet Hosts - Application and Support</title>
3455    <author initials="R." surname="Braden" fullname="Robert Braden">
3456      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3457      <address><email>Braden@ISI.EDU</email></address>
3458    </author>
3459    <date month="October" year="1989"/>
3460  </front>
3461  <seriesInfo name="STD" value="3"/>
3462  <seriesInfo name="RFC" value="1123"/>
3465<reference anchor="RFC1305">
3466  <front>
3467    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3468    <author initials="D." surname="Mills" fullname="David L. Mills">
3469      <organization>University of Delaware, Electrical Engineering Department</organization>
3470      <address><email></email></address>
3471    </author>
3472    <date month="March" year="1992"/>
3473  </front>
3474  <seriesInfo name="RFC" value="1305"/>
3477<reference anchor="RFC1436">
3478  <front>
3479    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3480    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3481      <organization>University of Minnesota, Computer and Information Services</organization>
3482      <address><email></email></address>
3483    </author>
3484    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3485      <organization>University of Minnesota, Computer and Information Services</organization>
3486      <address><email></email></address>
3487    </author>
3488    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3489      <organization>University of Minnesota, Computer and Information Services</organization>
3490      <address><email></email></address>
3491    </author>
3492    <author initials="D." surname="Johnson" fullname="David Johnson">
3493      <organization>University of Minnesota, Computer and Information Services</organization>
3494      <address><email></email></address>
3495    </author>
3496    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3497      <organization>University of Minnesota, Computer and Information Services</organization>
3498      <address><email></email></address>
3499    </author>
3500    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3501      <organization>University of Minnesota, Computer and Information Services</organization>
3502      <address><email></email></address>
3503    </author>
3504    <date month="March" year="1993"/>
3505  </front>
3506  <seriesInfo name="RFC" value="1436"/>
3509<reference anchor="RFC1630">
3510  <front>
3511    <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>
3512    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3513      <organization>CERN, World-Wide Web project</organization>
3514      <address><email></email></address>
3515    </author>
3516    <date month="June" year="1994"/>
3517  </front>
3518  <seriesInfo name="RFC" value="1630"/>
3521<reference anchor="RFC1737">
3522  <front>
3523    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3524    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3525      <organization>Xerox Palo Alto Research Center</organization>
3526      <address><email></email></address>
3527    </author>
3528    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3529      <organization>MIT Laboratory for Computer Science</organization>
3530      <address><email></email></address>
3531    </author>
3532    <date month="December" year="1994"/>
3533  </front>
3534  <seriesInfo name="RFC" value="1737"/>
3537<reference anchor="RFC1738">
3538  <front>
3539    <title>Uniform Resource Locators (URL)</title>
3540    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3541      <organization>CERN, World-Wide Web project</organization>
3542      <address><email></email></address>
3543    </author>
3544    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3545      <organization>Xerox PARC</organization>
3546      <address><email></email></address>
3547    </author>
3548    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3549      <organization>University of Minnesota, Computer and Information Services</organization>
3550      <address><email></email></address>
3551    </author>
3552    <date month="December" year="1994"/>
3553  </front>
3554  <seriesInfo name="RFC" value="1738"/>
3557<reference anchor="RFC1808">
3558  <front>
3559    <title>Relative Uniform Resource Locators</title>
3560    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3561      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3562      <address><email></email></address>
3563    </author>
3564    <date month="June" year="1995"/>
3565  </front>
3566  <seriesInfo name="RFC" value="1808"/>
3569<reference anchor="RFC1900">
3570  <front>
3571    <title>Renumbering Needs Work</title>
3572    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3573      <organization>CERN, Computing and Networks Division</organization>
3574      <address><email></email></address>
3575    </author>
3576    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3577      <organization>cisco Systems</organization>
3578      <address><email></email></address>
3579    </author>
3580    <date month="February" year="1996"/>
3581  </front>
3582  <seriesInfo name="RFC" value="1900"/>
3585<reference anchor="RFC1945">
3586  <front>
3587    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3588    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3589      <organization>MIT, Laboratory for Computer Science</organization>
3590      <address><email></email></address>
3591    </author>
3592    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3593      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3594      <address><email></email></address>
3595    </author>
3596    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3597      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3598      <address><email></email></address>
3599    </author>
3600    <date month="May" year="1996"/>
3601  </front>
3602  <seriesInfo name="RFC" value="1945"/>
3605<reference anchor="RFC2068">
3606  <front>
3607    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3608    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3609      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3610      <address><email></email></address>
3611    </author>
3612    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3613      <organization>MIT Laboratory for Computer Science</organization>
3614      <address><email></email></address>
3615    </author>
3616    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3617      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3618      <address><email></email></address>
3619    </author>
3620    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3621      <organization>MIT Laboratory for Computer Science</organization>
3622      <address><email></email></address>
3623    </author>
3624    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3625      <organization>MIT Laboratory for Computer Science</organization>
3626      <address><email></email></address>
3627    </author>
3628    <date month="January" year="1997"/>
3629  </front>
3630  <seriesInfo name="RFC" value="2068"/>
3633<reference anchor="RFC2145">
3634  <front>
3635    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3636    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3637      <organization>Western Research Laboratory</organization>
3638      <address><email></email></address>
3639    </author>
3640    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3641      <organization>Department of Information and Computer Science</organization>
3642      <address><email></email></address>
3643    </author>
3644    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3645      <organization>MIT Laboratory for Computer Science</organization>
3646      <address><email></email></address>
3647    </author>
3648    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3649      <organization>W3 Consortium</organization>
3650      <address><email></email></address>
3651    </author>
3652    <date month="May" year="1997"/>
3653  </front>
3654  <seriesInfo name="RFC" value="2145"/>
3657<reference anchor="RFC2324">
3658  <front>
3659    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3660    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3661      <organization>Xerox Palo Alto Research Center</organization>
3662      <address><email></email></address>
3663    </author>
3664    <date month="April" day="1" year="1998"/>
3665  </front>
3666  <seriesInfo name="RFC" value="2324"/>
3669<reference anchor="RFC2616">
3670  <front>
3671    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3672    <author initials="R." surname="Fielding" fullname="R. Fielding">
3673      <organization>University of California, Irvine</organization>
3674      <address><email></email></address>
3675    </author>
3676    <author initials="J." surname="Gettys" fullname="J. Gettys">
3677      <organization>W3C</organization>
3678      <address><email></email></address>
3679    </author>
3680    <author initials="J." surname="Mogul" fullname="J. Mogul">
3681      <organization>Compaq Computer Corporation</organization>
3682      <address><email></email></address>
3683    </author>
3684    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3685      <organization>MIT Laboratory for Computer Science</organization>
3686      <address><email></email></address>
3687    </author>
3688    <author initials="L." surname="Masinter" fullname="L. Masinter">
3689      <organization>Xerox Corporation</organization>
3690      <address><email></email></address>
3691    </author>
3692    <author initials="P." surname="Leach" fullname="P. Leach">
3693      <organization>Microsoft Corporation</organization>
3694      <address><email></email></address>
3695    </author>
3696    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3697      <organization>W3C</organization>
3698      <address><email></email></address>
3699    </author>
3700    <date month="June" year="1999"/>
3701  </front>
3702  <seriesInfo name="RFC" value="2616"/>
3705<reference anchor="RFC2821">
3706  <front>
3707    <title>Simple Mail Transfer Protocol</title>
3708    <author initials="J." surname="Klensin" fullname="J. Klensin">
3709      <organization>AT&amp;T Laboratories</organization>
3710      <address><email></email></address>
3711    </author>
3712    <date year="2001" month="April"/>
3713  </front>
3714  <seriesInfo name="RFC" value="2821"/>
3717<reference anchor="RFC2822">
3718  <front>
3719    <title>Internet Message Format</title>
3720    <author initials="P." surname="Resnick" fullname="P. Resnick">
3721      <organization>QUALCOMM Incorporated</organization>
3722    </author>
3723    <date year="2001" month="April"/>
3724  </front>
3725  <seriesInfo name="RFC" value="2822"/>
3728<reference anchor='RFC3977'>
3729  <front>
3730    <title>Network News Transfer Protocol (NNTP)</title>
3731    <author initials='C.' surname='Feather' fullname='C. Feather'>
3732      <organization>THUS plc</organization>
3733      <address><email></email></address>
3734    </author>
3735    <date year='2006' month='October' />
3736  </front>
3737  <seriesInfo name="RFC" value="3977"/>
3740<reference anchor="RFC4288">
3741  <front>
3742    <title>Media Type Specifications and Registration Procedures</title>
3743    <author initials="N." surname="Freed" fullname="N. Freed">
3744      <organization>Sun Microsystems</organization>
3745      <address>
3746        <email></email>
3747      </address>
3748    </author>
3749    <author initials="J." surname="Klensin" fullname="J. Klensin">
3750      <organization/>
3751      <address>
3752        <email></email>
3753      </address>
3754    </author>
3755    <date year="2005" month="December"/>
3756  </front>
3757  <seriesInfo name="BCP" value="13"/>
3758  <seriesInfo name="RFC" value="4288"/>
3761<reference anchor="Spe" target="">
3762  <front>
3763  <title>Analysis of HTTP Performance Problems</title>
3764  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3765    <organization/>
3766  </author>
3767  <date/>
3768  </front>
3771<reference anchor="Tou1998" target="">
3772  <front>
3773  <title>Analysis of HTTP Performance</title>
3774  <author initials="J." surname="Touch" fullname="Joe Touch">
3775    <organization>USC/Information Sciences Institute</organization>
3776    <address><email></email></address>
3777  </author>
3778  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3779    <organization>USC/Information Sciences Institute</organization>
3780    <address><email></email></address>
3781  </author>
3782  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3783    <organization>USC/Information Sciences Institute</organization>
3784    <address><email></email></address>
3785  </author>
3786  <date year="1998" month="Aug"/>
3787  </front>
3788  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3789  <annotation>(original report dated Aug. 1996)</annotation>
3792<reference anchor="WAIS">
3793  <front>
3794    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3795    <author initials="F." surname="Davis" fullname="F. Davis">
3796      <organization>Thinking Machines Corporation</organization>
3797    </author>
3798    <author initials="B." surname="Kahle" fullname="B. Kahle">
3799      <organization>Thinking Machines Corporation</organization>
3800    </author>
3801    <author initials="H." surname="Morris" fullname="H. Morris">
3802      <organization>Thinking Machines Corporation</organization>
3803    </author>
3804    <author initials="J." surname="Salem" fullname="J. Salem">
3805      <organization>Thinking Machines Corporation</organization>
3806    </author>
3807    <author initials="T." surname="Shen" fullname="T. Shen">
3808      <organization>Thinking Machines Corporation</organization>
3809    </author>
3810    <author initials="R." surname="Wang" fullname="R. Wang">
3811      <organization>Thinking Machines Corporation</organization>
3812    </author>
3813    <author initials="J." surname="Sui" fullname="J. Sui">
3814      <organization>Thinking Machines Corporation</organization>
3815    </author>
3816    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3817      <organization>Thinking Machines Corporation</organization>
3818    </author>
3819    <date month="April" year="1990"/>
3820  </front>
3821  <seriesInfo name="Thinking Machines Corporation" value=""/>
3827<section title="Internet Media Types" anchor="">
3829   In addition to defining HTTP/1.1, this document serves
3830   as the specification for the Internet media type "message/http" and
3831   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3833<section title="Internet Media Type message/http" anchor="">
3834<iref item="Media Type" subitem="message/http" primary="true"/>
3835<iref item="message/http Media Type" primary="true"/>
3837   The message/http type can be used to enclose a single HTTP request or
3838   response message, provided that it obeys the MIME restrictions for all
3839   "message" types regarding line length and encodings.
3842  <list style="hanging" x:indent="12em">
3843    <t hangText="Type name:">
3844      message
3845    </t>
3846    <t hangText="Subtype name:">
3847      http
3848    </t>
3849    <t hangText="Required parameters:">
3850      none
3851    </t>
3852    <t hangText="Optional parameters:">
3853      version, msgtype
3854      <list style="hanging">
3855        <t hangText="version:">
3856          The HTTP-Version number of the enclosed message
3857          (e.g., "1.1"). If not present, the version can be
3858          determined from the first line of the body.
3859        </t>
3860        <t hangText="msgtype:">
3861          The message type -- "request" or "response". If not
3862          present, the type can be determined from the first
3863          line of the body.
3864        </t>
3865      </list>
3866    </t>
3867    <t hangText="Encoding considerations:">
3868      only "7bit", "8bit", or "binary" are permitted
3869    </t>
3870    <t hangText="Security considerations:">
3871      none
3872    </t>
3873    <t hangText="Interoperability considerations:">
3874      none
3875    </t>
3876    <t hangText="Published specification:">
3877      This specification (see <xref target=""/>).
3878    </t>
3879    <t hangText="Applications that use this media type:">
3880    </t>
3881    <t hangText="Additional information:">
3882      <list style="hanging">
3883        <t hangText="Magic number(s):">none</t>
3884        <t hangText="File extension(s):">none</t>
3885        <t hangText="Macintosh file type code(s):">none</t>
3886      </list>
3887    </t>
3888    <t hangText="Person and email address to contact for further information:">
3889      See Authors Section.
3890    </t>
3891                <t hangText="Intended usage:">
3892                  COMMON
3893    </t>
3894                <t hangText="Restrictions on usage:">
3895                  none
3896    </t>
3897    <t hangText="Author/Change controller:">
3898      IESG
3899    </t>
3900  </list>
3903<section title="Internet Media Type application/http" anchor="">
3904<iref item="Media Type" subitem="application/http" primary="true"/>
3905<iref item="application/http Media Type" primary="true"/>
3907   The application/http type can be used to enclose a pipeline of one or more
3908   HTTP request or response messages (not intermixed).
3911  <list style="hanging" x:indent="12em">
3912    <t hangText="Type name:">
3913      application
3914    </t>
3915    <t hangText="Subtype name:">
3916      http
3917    </t>
3918    <t hangText="Required parameters:">
3919      none
3920    </t>
3921    <t hangText="Optional parameters:">
3922      version, msgtype
3923      <list style="hanging">
3924        <t hangText="version:">
3925          The HTTP-Version number of the enclosed messages
3926          (e.g., "1.1"). If not present, the version can be
3927          determined from the first line of the body.
3928        </t>
3929        <t hangText="msgtype:">
3930          The message type -- "request" or "response". If not
3931          present, the type can be determined from the first
3932          line of the body.
3933        </t>
3934      </list>
3935    </t>
3936    <t hangText="Encoding considerations:">
3937      HTTP messages enclosed by this type
3938      are in "binary" format; use of an appropriate
3939      Content-Transfer-Encoding is required when
3940      transmitted via E-mail.
3941    </t>
3942    <t hangText="Security considerations:">
3943      none
3944    </t>
3945    <t hangText="Interoperability considerations:">
3946      none
3947    </t>
3948    <t hangText="Published specification:">
3949      This specification (see <xref target=""/>).
3950    </t>
3951    <t hangText="Applications that use this media type:">
3952    </t>
3953    <t hangText="Additional information:">
3954      <list style="hanging">
3955        <t hangText="Magic number(s):">none</t>
3956        <t hangText="File extension(s):">none</t>
3957        <t hangText="Macintosh file type code(s):">none</t>
3958      </list>
3959    </t>
3960    <t hangText="Person and email address to contact for further information:">
3961      See Authors Section.
3962    </t>
3963                <t hangText="Intended usage:">
3964                  COMMON
3965    </t>
3966                <t hangText="Restrictions on usage:">
3967                  none
3968    </t>
3969    <t hangText="Author/Change controller:">
3970      IESG
3971    </t>
3972  </list>
3977<section title="Tolerant Applications" anchor="tolerant.applications">
3979   Although this document specifies the requirements for the generation
3980   of HTTP/1.1 messages, not all applications will be correct in their
3981   implementation. We therefore recommend that operational applications
3982   be tolerant of deviations whenever those deviations can be
3983   interpreted unambiguously.
3986   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3987   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3988   accept any amount of SP or HTAB characters between fields, even though
3989   only a single SP is required.
3992   The line terminator for message-header fields is the sequence CRLF.
3993   However, we recommend that applications, when parsing such headers,
3994   recognize a single LF as a line terminator and ignore the leading CR.
3997   The character set of an entity-body &SHOULD; be labeled as the lowest
3998   common denominator of the character codes used within that body, with
3999   the exception that not labeling the entity is preferred over labeling
4000   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4003   Additional rules for requirements on parsing and encoding of dates
4004   and other potential problems with date encodings include:
4007  <list style="symbols">
4008     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4009        which appears to be more than 50 years in the future is in fact
4010        in the past (this helps solve the "year 2000" problem).</t>
4012     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4013        Expires date as earlier than the proper value, but &MUST-NOT;
4014        internally represent a parsed Expires date as later than the
4015        proper value.</t>
4017     <t>All expiration-related calculations &MUST; be done in GMT. The
4018        local time zone &MUST-NOT; influence the calculation or comparison
4019        of an age or expiration time.</t>
4021     <t>If an HTTP header incorrectly carries a date value with a time
4022        zone other than GMT, it &MUST; be converted into GMT using the
4023        most conservative possible conversion.</t>
4024  </list>
4028<section title="Conversion of Date Formats" anchor="">
4030   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
4031   simplify the process of date comparison. Proxies and gateways from
4032   other protocols &SHOULD; ensure that any Date header field present in a
4033   message conforms to one of the HTTP/1.1 formats and rewrite the date
4034   if necessary.
4038<section title="Compatibility with Previous Versions" anchor="compatibility">
4040   It is beyond the scope of a protocol specification to mandate
4041   compliance with previous versions. HTTP/1.1 was deliberately
4042   designed, however, to make supporting previous versions easy. It is
4043   worth noting that, at the time of composing this specification
4044   (1996), we would expect commercial HTTP/1.1 servers to:
4045  <list style="symbols">
4046     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4047        1.1 requests;</t>
4049     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4050        1.1;</t>
4052     <t>respond appropriately with a message in the same major version
4053        used by the client.</t>
4054  </list>
4057   And we would expect HTTP/1.1 clients to:
4058  <list style="symbols">
4059     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4060        responses;</t>
4062     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4063        1.1.</t>
4064  </list>
4067   For most implementations of HTTP/1.0, each connection is established
4068   by the client prior to the request and closed by the server after
4069   sending the response. Some implementations implement the Keep-Alive
4070   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4073<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4075   This section summarizes major differences between versions HTTP/1.0
4076   and HTTP/1.1.
4079<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4081   The requirements that clients and servers support the Host request-header,
4082   report an error if the Host request-header (<xref target=""/>) is
4083   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4084   are among the most important changes defined by this
4085   specification.
4088   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4089   addresses and servers; there was no other established mechanism for
4090   distinguishing the intended server of a request than the IP address
4091   to which that request was directed. The changes outlined above will
4092   allow the Internet, once older HTTP clients are no longer common, to
4093   support multiple Web sites from a single IP address, greatly
4094   simplifying large operational Web servers, where allocation of many
4095   IP addresses to a single host has created serious problems. The
4096   Internet will also be able to recover the IP addresses that have been
4097   allocated for the sole purpose of allowing special-purpose domain
4098   names to be used in root-level HTTP URLs. Given the rate of growth of
4099   the Web, and the number of servers already deployed, it is extremely
4100   important that all implementations of HTTP (including updates to
4101   existing HTTP/1.0 applications) correctly implement these
4102   requirements:
4103  <list style="symbols">
4104     <t>Both clients and servers &MUST; support the Host request-header.</t>
4106     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4108     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4109        request does not include a Host request-header.</t>
4111     <t>Servers &MUST; accept absolute URIs.</t>
4112  </list>
4117<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4119   Some clients and servers might wish to be compatible with some
4120   previous implementations of persistent connections in HTTP/1.0
4121   clients and servers. Persistent connections in HTTP/1.0 are
4122   explicitly negotiated as they are not the default behavior. HTTP/1.0
4123   experimental implementations of persistent connections are faulty,
4124   and the new facilities in HTTP/1.1 are designed to rectify these
4125   problems. The problem was that some existing 1.0 clients may be
4126   sending Keep-Alive to a proxy server that doesn't understand
4127   Connection, which would then erroneously forward it to the next
4128   inbound server, which would establish the Keep-Alive connection and
4129   result in a hung HTTP/1.0 proxy waiting for the close on the
4130   response. The result is that HTTP/1.0 clients must be prevented from
4131   using Keep-Alive when talking to proxies.
4134   However, talking to proxies is the most important use of persistent
4135   connections, so that prohibition is clearly unacceptable. Therefore,
4136   we need some other mechanism for indicating a persistent connection
4137   is desired, which is safe to use even when talking to an old proxy
4138   that ignores Connection. Persistent connections are the default for
4139   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4140   declaring non-persistence. See <xref target="header.connection"/>.
4143   The original HTTP/1.0 form of persistent connections (the Connection:
4144   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4148<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4150   This specification has been carefully audited to correct and
4151   disambiguate key word usage; RFC 2068 had many problems in respect to
4152   the conventions laid out in <xref target="RFC2119"/>.
4155   Transfer-coding and message lengths all interact in ways that
4156   required fixing exactly when chunked encoding is used (to allow for
4157   transfer encoding that may not be self delimiting); it was important
4158   to straighten out exactly how message lengths are computed. (Sections
4159   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4160   <xref target="header.content-length" format="counter"/>,
4161   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4164   The use and interpretation of HTTP version numbers has been clarified
4165   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4166   version they support to deal with problems discovered in HTTP/1.0
4167   implementations (<xref target="http.version"/>)
4170   Transfer-coding had significant problems, particularly with
4171   interactions with chunked encoding. The solution is that transfer-codings
4172   become as full fledged as content-codings. This involves
4173   adding an IANA registry for transfer-codings (separate from content
4174   codings), a new header field (TE) and enabling trailer headers in the
4175   future. Transfer encoding is a major performance benefit, so it was
4176   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4177   interoperability problem that could have occurred due to interactions
4178   between authentication trailers, chunked encoding and HTTP/1.0
4179   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4180   and <xref target="header.te" format="counter"/>)
4184<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4186  The CHAR rule does not allow the NUL character anymore (this affects
4187  the comment and quoted-string rules).  Furthermore, the quoted-pair
4188  rule does not allow escaping NUL, CR or LF anymore.
4189  (<xref target="basic.rules"/>)
4192  Clarify that HTTP-Version is case sensitive.
4193  (<xref target="http.version"/>)
4196  Remove reference to non-existant identity transfer-coding value tokens.
4197  (Sections <xref format="counter" target="transfer.codings"/> and
4198  <xref format="counter" target="message.length"/>)
4201  Clarification that the chunk length does not include
4202  the count of the octets in the chunk header and trailer.
4203  (<xref target="chunked.transfer.encoding"/>)
4206  Fix BNF to add query, as the abs_path production in
4207  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4208  (<xref target="request-uri"/>)
4211  Clarify exactly when close connection options must be sent.
4212  (<xref target="header.connection"/>)
4217<section title="Change Log (to be removed by RFC Editor before publication)">
4219<section title="Since RFC2616">
4221  Extracted relevant partitions from <xref target="RFC2616"/>.
4225<section title="Since draft-ietf-httpbis-p1-messaging-00">
4227  Closed issues:
4228  <list style="symbols">
4229    <t>
4230      <eref target=""/>:
4231      "HTTP Version should be case sensitive"
4232      (<eref target=""/>)
4233    </t>
4234    <t>
4235      <eref target=""/>:
4236      "'unsafe' characters"
4237      (<eref target=""/>)
4238    </t>
4239    <t>
4240      <eref target=""/>:
4241      "Chunk Size Definition"
4242      (<eref target=""/>)
4243    </t>
4244    <t>
4245      <eref target=""/>:
4246      "Message Length"
4247      (<eref target=""/>)
4248    </t>
4249    <t>
4250      <eref target=""/>:
4251      "Media Type Registrations"
4252      (<eref target=""/>)
4253    </t>
4254    <t>
4255      <eref target=""/>:
4256      "URI includes query"
4257      (<eref target=""/>)
4258    </t>
4259    <t>
4260      <eref target=""/>:
4261      "No close on 1xx responses"
4262      (<eref target=""/>)
4263    </t>
4264    <t>
4265      <eref target=""/>:
4266      "Remove 'identity' token references"
4267      (<eref target=""/>)
4268    </t>
4269    <t>
4270      <eref target=""/>:
4271      "Import query BNF"
4272    </t>
4273    <t>
4274      <eref target=""/>:
4275      "qdtext BNF"
4276    </t>
4277    <t>
4278      <eref target=""/>:
4279      "Normative and Informative references"
4280    </t>
4281    <t>
4282      <eref target=""/>:
4283      "RFC2606 Compliance"
4284    </t>
4285    <t>
4286      <eref target=""/>:
4287      "RFC977 reference"
4288    </t>
4289    <t>
4290      <eref target=""/>:
4291      "RFC1700 references"
4292    </t>
4293    <t>
4294      <eref target=""/>:
4295      "inconsistency in date format explanation"
4296    </t>
4297    <t>
4298      <eref target=""/>:
4299      "Date reference typo"
4300    </t>
4301    <t>
4302      <eref target=""/>:
4303      "Informative references"
4304    </t>
4305    <t>
4306      <eref target=""/>:
4307      "ISO-8859-1 Reference"
4308    </t>
4309    <t>
4310      <eref target=""/>:
4311      "Normative up-to-date references"
4312    </t>
4313  </list>
4316  Other changes:
4317  <list style="symbols">
4318    <t>
4319      Update media type registrations to use RFC4288 template.
4320    </t>
4321    <t>
4322      Use names of RFC4234 core rules DQUOTE and HTAB,
4323      fix broken ABNF for chunk-data
4324      (work in progress on <eref target=""/>)
4325    </t>
4326  </list>
4330<section title="Since draft-ietf-httpbis-p1-messaging-01">
4332  Closed issues:
4333  <list style="symbols">
4334    <t>
4335      <eref target=""/>:
4336      "Bodies on GET (and other) requests"
4337    </t>
4338    <t>
4339      <eref target=""/>:
4340      "Updating to RFC4288"
4341    </t>
4342    <t>
4343      <eref target=""/>:
4344      "Status Code and Reason Phrase"
4345    </t>
4346    <t>
4347      <eref target=""/>:
4348      "rel_path not used"
4349    </t>
4350  </list>
4353  Ongoing work on ABNF conversion (<eref target=""/>):
4354  <list style="symbols">
4355    <t>
4356      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4357      "trailer-part").
4358    </t>
4359    <t>
4360      Avoid underscore character in rule names ("http_URL" ->
4361      "http-URL", "abs_path" -> "path-absolute").
4362    </t>
4363    <t>
4364      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4365      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4366      have to be updated when switching over to RFC3986.
4367    </t>
4368    <t>
4369      Synchronize core rules with RFC5234 (this includes a change to CHAR
4370      which now excludes NUL).
4371    </t>
4372    <t>
4373      Get rid of prose rules that span multiple lines.
4374    </t>
4375    <t>
4376      Get rid of unused rules LOALPHA and UPALPHA.
4377    </t>
4378    <t>
4379      Move "Product Tokens" section (back) into Part 1, as "token" is used
4380      in the definition of the Upgrade header.
4381    </t>
4382    <t>
4383      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4384    </t>
4385    <t>
4386      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4387    </t>
4388  </list>
4392<section title="Since draft-ietf-httpbis-p1-messaging-02">
4394  Closed issues:
4395  <list style="symbols">
4396    <t>
4397      <eref target=""/>:
4398      "WS in quoted-pair"
4399    </t>
4400  </list>
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