source: draft-ietf-httpbis/latest/p1-messaging.xml @ 239

Last change on this file since 239 was 239, checked in by julian.reschke@…, 15 years ago

Resolve #51: make it obvious from the BNF that most of the date formats that must be accepted are indeed obsolete (closes #51).

  • Property svn:eol-style set to native
File size: 191.2 KB
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="obsolete-date"/>
1177  <x:anchor-alias value="rfc1123-date"/>
1178  <x:anchor-alias value="rfc850-date"/>
1179  <x:anchor-alias value="asctime-date"/>
1180  <x:anchor-alias value="date1"/>
1181  <x:anchor-alias value="date2"/>
1182  <x:anchor-alias value="date3"/>
1183  <x:anchor-alias value="rfc1123-date"/>
1184  <x:anchor-alias value="time"/>
1185  <x:anchor-alias value="wkday"/>
1186  <x:anchor-alias value="weekday"/>
1187  <x:anchor-alias value="month"/>
1189   HTTP applications have historically allowed three different formats
1190   for the representation of date/time stamps:
1192<figure><artwork type="example">
1193   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1194   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1195   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1198   The first format is preferred as an Internet standard and represents
1199   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1200   <xref target="RFC822"/>). The other formats are described here only for
1201   compatibility with obsolete implementations.
1202   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1203   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1204   only generate the RFC 1123 format for representing HTTP-date values
1205   in header fields. See <xref target="tolerant.applications"/> for further information.
1208      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1209      accepting date values that may have been sent by non-HTTP
1210      applications, as is sometimes the case when retrieving or posting
1211      messages via proxies/gateways to SMTP or NNTP.
1214   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1215   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1216   equal to UTC (Coordinated Universal Time). This is indicated in the
1217   first two formats by the inclusion of "GMT" as the three-letter
1218   abbreviation for time zone, and &MUST; be assumed when reading the
1219   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1220   additional LWS beyond that specifically included as SP in the
1221   grammar.
1223<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="obsolete-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"/>
1224  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> | <x:ref>obsolete-date</x:ref>
1225  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> | <x:ref>asctime-date</x:ref>
1226  <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"
1227  <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"
1228  <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>
1229  <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>
1230                 ; day month year (e.g., 02 Jun 1982)
1231  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1232                 ; day-month-year (e.g., 02-Jun-82)
1233  <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> ))
1234                 ; month day (e.g., Jun  2)
1235  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
1236                 ; 00:00:00 - 23:59:59
1237  <x:ref>wkday</x:ref>        = "Mon" | "Tue" | "Wed"
1238               | "Thu" | "Fri" | "Sat" | "Sun"
1239  <x:ref>weekday</x:ref>      = "Monday" | "Tuesday" | "Wednesday"
1240               | "Thursday" | "Friday" | "Saturday" | "Sunday"
1241  <x:ref>month</x:ref>        = "Jan" | "Feb" | "Mar" | "Apr"
1242               | "May" | "Jun" | "Jul" | "Aug"
1243               | "Sep" | "Oct" | "Nov" | "Dec"
1246      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1247      to their usage within the protocol stream. Clients and servers are
1248      not required to use these formats for user presentation, request
1249      logging, etc.
1254<section title="Transfer Codings" anchor="transfer.codings">
1255  <x:anchor-alias value="parameter"/>
1256  <x:anchor-alias value="transfer-coding"/>
1257  <x:anchor-alias value="transfer-extension"/>
1259   Transfer-coding values are used to indicate an encoding
1260   transformation that has been, can be, or may need to be applied to an
1261   entity-body in order to ensure "safe transport" through the network.
1262   This differs from a content coding in that the transfer-coding is a
1263   property of the message, not of the original entity.
1265<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1266  <x:ref>transfer-coding</x:ref>         = "chunked" | <x:ref>transfer-extension</x:ref>
1267  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
1269<t anchor="rule.parameter">
1270  <x:anchor-alias value="attribute"/>
1271  <x:anchor-alias value="parameter"/>
1272  <x:anchor-alias value="value"/>
1273   Parameters are in  the form of attribute/value pairs.
1275<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"/>
1276  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
1277  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1278  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
1281   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1282   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1283   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1286   Whenever a transfer-coding is applied to a message-body, the set of
1287   transfer-codings &MUST; include "chunked", unless the message is
1288   terminated by closing the connection. When the "chunked" transfer-coding
1289   is used, it &MUST; be the last transfer-coding applied to the
1290   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1291   than once to a message-body. These rules allow the recipient to
1292   determine the transfer-length of the message (<xref target="message.length"/>).
1295   Transfer-codings are analogous to the Content-Transfer-Encoding
1296   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1297   binary data over a 7-bit transport service. However, safe transport
1298   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1299   the only unsafe characteristic of message-bodies is the difficulty in
1300   determining the exact body length (<xref target="message.length"/>), or the desire to
1301   encrypt data over a shared transport.
1304   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1305   transfer-coding value tokens. Initially, the registry contains the
1306   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1307   "gzip", "compress", and "deflate" (&content-codings;).
1310   New transfer-coding value tokens &SHOULD; be registered in the same way
1311   as new content-coding value tokens (&content-codings;).
1314   A server which receives an entity-body with a transfer-coding it does
1315   not understand &SHOULD; return 501 (Not Implemented), and close the
1316   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1317   client.
1320<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1321  <x:anchor-alias value="chunk"/>
1322  <x:anchor-alias value="Chunked-Body"/>
1323  <x:anchor-alias value="chunk-data"/>
1324  <x:anchor-alias value="chunk-extension"/>
1325  <x:anchor-alias value="chunk-ext-name"/>
1326  <x:anchor-alias value="chunk-ext-val"/>
1327  <x:anchor-alias value="chunk-size"/>
1328  <x:anchor-alias value="last-chunk"/>
1329  <x:anchor-alias value="trailer-part"/>
1331   The chunked encoding modifies the body of a message in order to
1332   transfer it as a series of chunks, each with its own size indicator,
1333   followed by an &OPTIONAL; trailer containing entity-header fields. This
1334   allows dynamically produced content to be transferred along with the
1335   information necessary for the recipient to verify that it has
1336   received the full message.
1338<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"/>
1339  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1340                   <x:ref>last-chunk</x:ref>
1341                   <x:ref>trailer-part</x:ref>
1342                   <x:ref>CRLF</x:ref>
1344  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1345                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1346  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEX</x:ref>
1347  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1349  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1350  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1351  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
1352  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1353  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1356   The chunk-size field is a string of hex digits indicating the size of
1357   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1358   zero, followed by the trailer, which is terminated by an empty line.
1361   The trailer allows the sender to include additional HTTP header
1362   fields at the end of the message. The Trailer header field can be
1363   used to indicate which header fields are included in a trailer (see
1364   <xref target="header.trailer"/>).
1367   A server using chunked transfer-coding in a response &MUST-NOT; use the
1368   trailer for any header fields unless at least one of the following is
1369   true:
1370  <list style="numbers">
1371    <t>the request included a TE header field that indicates "trailers" is
1372     acceptable in the transfer-coding of the  response, as described in
1373     <xref target="header.te"/>; or,</t>
1375    <t>the server is the origin server for the response, the trailer
1376     fields consist entirely of optional metadata, and the recipient
1377     could use the message (in a manner acceptable to the origin server)
1378     without receiving this metadata.  In other words, the origin server
1379     is willing to accept the possibility that the trailer fields might
1380     be silently discarded along the path to the client.</t>
1381  </list>
1384   This requirement prevents an interoperability failure when the
1385   message is being received by an HTTP/1.1 (or later) proxy and
1386   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1387   compliance with the protocol would have necessitated a possibly
1388   infinite buffer on the proxy.
1391   A process for decoding the "chunked" transfer-coding
1392   can be represented in pseudo-code as:
1394<figure><artwork type="code">
1395    length := 0
1396    read chunk-size, chunk-extension (if any) and CRLF
1397    while (chunk-size &gt; 0) {
1398       read chunk-data and CRLF
1399       append chunk-data to entity-body
1400       length := length + chunk-size
1401       read chunk-size and CRLF
1402    }
1403    read entity-header
1404    while (entity-header not empty) {
1405       append entity-header to existing header fields
1406       read entity-header
1407    }
1408    Content-Length := length
1409    Remove "chunked" from Transfer-Encoding
1412   All HTTP/1.1 applications &MUST; be able to receive and decode the
1413   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1414   they do not understand.
1419<section title="Product Tokens" anchor="product.tokens">
1420  <x:anchor-alias value="product"/>
1421  <x:anchor-alias value="product-version"/>
1423   Product tokens are used to allow communicating applications to
1424   identify themselves by software name and version. Most fields using
1425   product tokens also allow sub-products which form a significant part
1426   of the application to be listed, separated by white space. By
1427   convention, the products are listed in order of their significance
1428   for identifying the application.
1430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1431  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1432  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1435   Examples:
1437<figure><artwork type="example">
1438    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1439    Server: Apache/0.8.4
1442   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1443   used for advertising or other non-essential information. Although any
1444   token character &MAY; appear in a product-version, this token &SHOULD;
1445   only be used for a version identifier (i.e., successive versions of
1446   the same product &SHOULD; only differ in the product-version portion of
1447   the product value).
1453<section title="HTTP Message" anchor="http.message">
1455<section title="Message Types" anchor="message.types">
1456  <x:anchor-alias value="generic-message"/>
1457  <x:anchor-alias value="HTTP-message"/>
1458  <x:anchor-alias value="start-line"/>
1460   HTTP messages consist of requests from client to server and responses
1461   from server to client.
1463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1464  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> | <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1467   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1468   message format of <xref target="RFC2822"/> for transferring entities (the payload
1469   of the message). Both types of message consist of a start-line, zero
1470   or more header fields (also known as "headers"), an empty line (i.e.,
1471   a line with nothing preceding the CRLF) indicating the end of the
1472   header fields, and possibly a message-body.
1474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1475  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1476                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1477                    <x:ref>CRLF</x:ref>
1478                    [ <x:ref>message-body</x:ref> ]
1479  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> | <x:ref>Status-Line</x:ref>
1482   In the interest of robustness, servers &SHOULD; ignore any empty
1483   line(s) received where a Request-Line is expected. In other words, if
1484   the server is reading the protocol stream at the beginning of a
1485   message and receives a CRLF first, it should ignore the CRLF.
1488   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1489   after a POST request. To restate what is explicitly forbidden by the
1490   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1491   extra CRLF.
1495<section title="Message Headers" anchor="message.headers">
1496  <x:anchor-alias value="field-content"/>
1497  <x:anchor-alias value="field-name"/>
1498  <x:anchor-alias value="field-value"/>
1499  <x:anchor-alias value="message-header"/>
1501   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1502   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1503   entity-header (&entity-header-fields;) fields, follow the same generic format as
1504   that given in <xref target="RFC2822" x:fmt="of" x:sec="2.1"/>. Each header field consists
1505   of a name followed by a colon (":") and the field value. Field names
1506   are case-insensitive. The field value &MAY; be preceded by any amount
1507   of LWS, though a single SP is preferred. Header fields can be
1508   extended over multiple lines by preceding each extra line with at
1509   least one SP or HTAB. Applications ought to follow "common form", where
1510   one is known or indicated, when generating HTTP constructs, since
1511   there might exist some implementations that fail to accept anything
1512   beyond the common forms.
1514<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"/>
1515  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1516  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1517  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> | <x:ref>LWS</x:ref> )
1518  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1519                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1520                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1521                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1524   The field-content does not include any leading or trailing LWS:
1525   linear white space occurring before the first non-whitespace
1526   character of the field-value or after the last non-whitespace
1527   character of the field-value. Such leading or trailing LWS &MAY; be
1528   removed without changing the semantics of the field value. Any LWS
1529   that occurs between field-content &MAY; be replaced with a single SP
1530   before interpreting the field value or forwarding the message
1531   downstream.
1534   The order in which header fields with differing field names are
1535   received is not significant. However, it is "good practice" to send
1536   general-header fields first, followed by request-header or response-header
1537   fields, and ending with the entity-header fields.
1540   Multiple message-header fields with the same field-name &MAY; be
1541   present in a message if and only if the entire field-value for that
1542   header field is defined as a comma-separated list [i.e., #(values)].
1543   It &MUST; be possible to combine the multiple header fields into one
1544   "field-name: field-value" pair, without changing the semantics of the
1545   message, by appending each subsequent field-value to the first, each
1546   separated by a comma. The order in which header fields with the same
1547   field-name are received is therefore significant to the
1548   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1549   change the order of these field values when a message is forwarded.
1553<section title="Message Body" anchor="message.body">
1554  <x:anchor-alias value="message-body"/>
1556   The message-body (if any) of an HTTP message is used to carry the
1557   entity-body associated with the request or response. The message-body
1558   differs from the entity-body only when a transfer-coding has been
1559   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1561<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1562  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1563               | &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1566   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1567   applied by an application to ensure safe and proper transfer of the
1568   message. Transfer-Encoding is a property of the message, not of the
1569   entity, and thus &MAY; be added or removed by any application along the
1570   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1571   when certain transfer-codings may be used.)
1574   The rules for when a message-body is allowed in a message differ for
1575   requests and responses.
1578   The presence of a message-body in a request is signaled by the
1579   inclusion of a Content-Length or Transfer-Encoding header field in
1580   the request's message-headers. A message-body &MUST-NOT; be included in
1581   a request if the specification of the request method (&method;)
1582   explicitly disallows an entity-body in requests.
1583   When a request message contains both a message-body of non-zero
1584   length and a method that does not define any semantics for that
1585   request message-body, then an origin server &SHOULD; either ignore
1586   the message-body or respond with an appropriate error message
1587   (e.g., 413).  A proxy or gateway, when presented the same request,
1588   &SHOULD; either forward the request inbound with the message-body or
1589   ignore the message-body when determining a response.
1592   For response messages, whether or not a message-body is included with
1593   a message is dependent on both the request method and the response
1594   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1595   &MUST-NOT; include a message-body, even though the presence of entity-header
1596   fields might lead one to believe they do. All 1xx
1597   (informational), 204 (No Content), and 304 (Not Modified) responses
1598   &MUST-NOT; include a message-body. All other responses do include a
1599   message-body, although it &MAY; be of zero length.
1603<section title="Message Length" anchor="message.length">
1605   The transfer-length of a message is the length of the message-body as
1606   it appears in the message; that is, after any transfer-codings have
1607   been applied. When a message-body is included with a message, the
1608   transfer-length of that body is determined by one of the following
1609   (in order of precedence):
1612  <list style="numbers">
1613    <x:lt><t>
1614     Any response message which "&MUST-NOT;" include a message-body (such
1615     as the 1xx, 204, and 304 responses and any response to a HEAD
1616     request) is always terminated by the first empty line after the
1617     header fields, regardless of the entity-header fields present in
1618     the message.
1619    </t></x:lt>
1620    <x:lt><t>
1621     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1622     is present, then the transfer-length is
1623     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1624     unless the message is terminated by closing the connection.
1625    </t></x:lt>
1626    <x:lt><t>
1627     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1628     decimal value in OCTETs represents both the entity-length and the
1629     transfer-length. The Content-Length header field &MUST-NOT; be sent
1630     if these two lengths are different (i.e., if a Transfer-Encoding
1631     header field is present). If a message is received with both a
1632     Transfer-Encoding header field and a Content-Length header field,
1633     the latter &MUST; be ignored.
1634    </t></x:lt>
1635    <x:lt><t>
1636     If the message uses the media type "multipart/byteranges", and the
1637     transfer-length is not otherwise specified, then this self-delimiting
1638     media type defines the transfer-length. This media type
1639     &MUST-NOT; be used unless the sender knows that the recipient can parse
1640     it; the presence in a request of a Range header with multiple byte-range
1641     specifiers from a 1.1 client implies that the client can parse
1642     multipart/byteranges responses.
1643    <list style="empty"><t>
1644       A range header might be forwarded by a 1.0 proxy that does not
1645       understand multipart/byteranges; in this case the server &MUST;
1646       delimit the message using methods defined in items 1, 3 or 5 of
1647       this section.
1648    </t></list>
1649    </t></x:lt>
1650    <x:lt><t>
1651     By the server closing the connection. (Closing the connection
1652     cannot be used to indicate the end of a request body, since that
1653     would leave no possibility for the server to send back a response.)
1654    </t></x:lt>
1655  </list>
1658   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1659   containing a message-body &MUST; include a valid Content-Length header
1660   field unless the server is known to be HTTP/1.1 compliant. If a
1661   request contains a message-body and a Content-Length is not given,
1662   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1663   determine the length of the message, or with 411 (Length Required) if
1664   it wishes to insist on receiving a valid Content-Length.
1667   All HTTP/1.1 applications that receive entities &MUST; accept the
1668   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1669   to be used for messages when the message length cannot be determined
1670   in advance.
1673   Messages &MUST-NOT; include both a Content-Length header field and a
1674   transfer-coding. If the message does include a
1675   transfer-coding, the Content-Length &MUST; be ignored.
1678   When a Content-Length is given in a message where a message-body is
1679   allowed, its field value &MUST; exactly match the number of OCTETs in
1680   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1681   invalid length is received and detected.
1685<section title="General Header Fields" anchor="general.header.fields">
1686  <x:anchor-alias value="general-header"/>
1688   There are a few header fields which have general applicability for
1689   both request and response messages, but which do not apply to the
1690   entity being transferred. These header fields apply only to the
1691   message being transmitted.
1693<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1694  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1695                 | <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1696                 | <x:ref>Date</x:ref>                     ; <xref target=""/>
1697                 | <x:ref>Pragma</x:ref>                   ; &header-pragma;
1698                 | <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1699                 | <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1700                 | <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1701                 | <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1702                 | <x:ref>Warning</x:ref>                  ; &header-warning;
1705   General-header field names can be extended reliably only in
1706   combination with a change in the protocol version. However, new or
1707   experimental header fields may be given the semantics of general
1708   header fields if all parties in the communication recognize them to
1709   be general-header fields. Unrecognized header fields are treated as
1710   entity-header fields.
1715<section title="Request" anchor="request">
1716  <x:anchor-alias value="Request"/>
1718   A request message from a client to a server includes, within the
1719   first line of that message, the method to be applied to the resource,
1720   the identifier of the resource, and the protocol version in use.
1722<!--                 Host                      ; should be moved here eventually -->
1723<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1724  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1725                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1726                   | <x:ref>request-header</x:ref>         ; &request-header-fields;
1727                   | <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1728                  <x:ref>CRLF</x:ref>
1729                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1732<section title="Request-Line" anchor="request-line">
1733  <x:anchor-alias value="Request-Line"/>
1735   The Request-Line begins with a method token, followed by the
1736   Request-URI and the protocol version, and ending with CRLF. The
1737   elements are separated by SP characters. No CR or LF is allowed
1738   except in the final CRLF sequence.
1740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1741  <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>
1744<section title="Method" anchor="method">
1745  <x:anchor-alias value="Method"/>
1747   The Method  token indicates the method to be performed on the
1748   resource identified by the Request-URI. The method is case-sensitive.
1750<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1751  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1755<section title="Request-URI" anchor="request-uri">
1756  <x:anchor-alias value="Request-URI"/>
1758   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1759   identifies the resource upon which to apply the request.
1761<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1762  <x:ref>Request-URI</x:ref>    = "*"
1763                 | <x:ref>absoluteURI</x:ref>
1764                 | ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1765                 | <x:ref>authority</x:ref>
1768   The four options for Request-URI are dependent on the nature of the
1769   request. The asterisk "*" means that the request does not apply to a
1770   particular resource, but to the server itself, and is only allowed
1771   when the method used does not necessarily apply to a resource. One
1772   example would be
1774<figure><artwork type="example">
1775    OPTIONS * HTTP/1.1
1778   The absoluteURI form is &REQUIRED; when the request is being made to a
1779   proxy. The proxy is requested to forward the request or service it
1780   from a valid cache, and return the response. Note that the proxy &MAY;
1781   forward the request on to another proxy or directly to the server
1782   specified by the absoluteURI. In order to avoid request loops, a
1783   proxy &MUST; be able to recognize all of its server names, including
1784   any aliases, local variations, and the numeric IP address. An example
1785   Request-Line would be:
1787<figure><artwork type="example">
1788    GET HTTP/1.1
1791   To allow for transition to absoluteURIs in all requests in future
1792   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1793   form in requests, even though HTTP/1.1 clients will only generate
1794   them in requests to proxies.
1797   The authority form is only used by the CONNECT method (&CONNECT;).
1800   The most common form of Request-URI is that used to identify a
1801   resource on an origin server or gateway. In this case the absolute
1802   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1803   the Request-URI, and the network location of the URI (authority) &MUST;
1804   be transmitted in a Host header field. For example, a client wishing
1805   to retrieve the resource above directly from the origin server would
1806   create a TCP connection to port 80 of the host "" and send
1807   the lines:
1809<figure><artwork type="example">
1810    GET /pub/WWW/TheProject.html HTTP/1.1
1811    Host:
1814   followed by the remainder of the Request. Note that the absolute path
1815   cannot be empty; if none is present in the original URI, it &MUST; be
1816   given as "/" (the server root).
1819   The Request-URI is transmitted in the format specified in
1820   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1821   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1822   properly interpret the request. Servers &SHOULD; respond to invalid
1823   Request-URIs with an appropriate status code.
1826   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1827   received Request-URI when forwarding it to the next inbound server,
1828   except as noted above to replace a null path-absolute with "/".
1831  <list><t>
1832      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1833      meaning of the request when the origin server is improperly using
1834      a non-reserved URI character for a reserved purpose.  Implementors
1835      should be aware that some pre-HTTP/1.1 proxies have been known to
1836      rewrite the Request-URI.
1837  </t></list>
1842<section title="The Resource Identified by a Request" anchor="">
1844   The exact resource identified by an Internet request is determined by
1845   examining both the Request-URI and the Host header field.
1848   An origin server that does not allow resources to differ by the
1849   requested host &MAY; ignore the Host header field value when
1850   determining the resource identified by an HTTP/1.1 request. (But see
1851   <xref target=""/>
1852   for other requirements on Host support in HTTP/1.1.)
1855   An origin server that does differentiate resources based on the host
1856   requested (sometimes referred to as virtual hosts or vanity host
1857   names) &MUST; use the following rules for determining the requested
1858   resource on an HTTP/1.1 request:
1859  <list style="numbers">
1860    <t>If Request-URI is an absoluteURI, the host is part of the
1861     Request-URI. Any Host header field value in the request &MUST; be
1862     ignored.</t>
1863    <t>If the Request-URI is not an absoluteURI, and the request includes
1864     a Host header field, the host is determined by the Host header
1865     field value.</t>
1866    <t>If the host as determined by rule 1 or 2 is not a valid host on
1867     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1868  </list>
1871   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1872   attempt to use heuristics (e.g., examination of the URI path for
1873   something unique to a particular host) in order to determine what
1874   exact resource is being requested.
1881<section title="Response" anchor="response">
1882  <x:anchor-alias value="Response"/>
1884   After receiving and interpreting a request message, a server responds
1885   with an HTTP response message.
1887<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1888  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1889                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1890                   | <x:ref>response-header</x:ref>        ; &response-header-fields;
1891                   | <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1892                  <x:ref>CRLF</x:ref>
1893                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1896<section title="Status-Line" anchor="status-line">
1897  <x:anchor-alias value="Status-Line"/>
1899   The first line of a Response message is the Status-Line, consisting
1900   of the protocol version followed by a numeric status code and its
1901   associated textual phrase, with each element separated by SP
1902   characters. No CR or LF is allowed except in the final CRLF sequence.
1904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1905  <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>
1908<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1909  <x:anchor-alias value="Reason-Phrase"/>
1910  <x:anchor-alias value="Status-Code"/>
1912   The Status-Code element is a 3-digit integer result code of the
1913   attempt to understand and satisfy the request. These codes are fully
1914   defined in &status-codes;.  The Reason Phrase exists for the sole
1915   purpose of providing a textual description associated with the numeric
1916   status code, out of deference to earlier Internet application protocols
1917   that were more frequently used with interactive text clients.
1918   A client &SHOULD; ignore the content of the Reason Phrase.
1921   The first digit of the Status-Code defines the class of response. The
1922   last two digits do not have any categorization role. There are 5
1923   values for the first digit:
1924  <list style="symbols">
1925    <t>
1926      1xx: Informational - Request received, continuing process
1927    </t>
1928    <t>
1929      2xx: Success - The action was successfully received,
1930        understood, and accepted
1931    </t>
1932    <t>
1933      3xx: Redirection - Further action must be taken in order to
1934        complete the request
1935    </t>
1936    <t>
1937      4xx: Client Error - The request contains bad syntax or cannot
1938        be fulfilled
1939    </t>
1940    <t>
1941      5xx: Server Error - The server failed to fulfill an apparently
1942        valid request
1943    </t>
1944  </list>
1946<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"/>
1947  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1948  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1956<section title="Connections" anchor="connections">
1958<section title="Persistent Connections" anchor="persistent.connections">
1960<section title="Purpose" anchor="persistent.purpose">
1962   Prior to persistent connections, a separate TCP connection was
1963   established to fetch each URL, increasing the load on HTTP servers
1964   and causing congestion on the Internet. The use of inline images and
1965   other associated data often require a client to make multiple
1966   requests of the same server in a short amount of time. Analysis of
1967   these performance problems and results from a prototype
1968   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1969   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1970   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1971   T/TCP <xref target="Tou1998"/>.
1974   Persistent HTTP connections have a number of advantages:
1975  <list style="symbols">
1976      <t>
1977        By opening and closing fewer TCP connections, CPU time is saved
1978        in routers and hosts (clients, servers, proxies, gateways,
1979        tunnels, or caches), and memory used for TCP protocol control
1980        blocks can be saved in hosts.
1981      </t>
1982      <t>
1983        HTTP requests and responses can be pipelined on a connection.
1984        Pipelining allows a client to make multiple requests without
1985        waiting for each response, allowing a single TCP connection to
1986        be used much more efficiently, with much lower elapsed time.
1987      </t>
1988      <t>
1989        Network congestion is reduced by reducing the number of packets
1990        caused by TCP opens, and by allowing TCP sufficient time to
1991        determine the congestion state of the network.
1992      </t>
1993      <t>
1994        Latency on subsequent requests is reduced since there is no time
1995        spent in TCP's connection opening handshake.
1996      </t>
1997      <t>
1998        HTTP can evolve more gracefully, since errors can be reported
1999        without the penalty of closing the TCP connection. Clients using
2000        future versions of HTTP might optimistically try a new feature,
2001        but if communicating with an older server, retry with old
2002        semantics after an error is reported.
2003      </t>
2004    </list>
2007   HTTP implementations &SHOULD; implement persistent connections.
2011<section title="Overall Operation" anchor="persistent.overall">
2013   A significant difference between HTTP/1.1 and earlier versions of
2014   HTTP is that persistent connections are the default behavior of any
2015   HTTP connection. That is, unless otherwise indicated, the client
2016   &SHOULD; assume that the server will maintain a persistent connection,
2017   even after error responses from the server.
2020   Persistent connections provide a mechanism by which a client and a
2021   server can signal the close of a TCP connection. This signaling takes
2022   place using the Connection header field (<xref target="header.connection"/>). Once a close
2023   has been signaled, the client &MUST-NOT; send any more requests on that
2024   connection.
2027<section title="Negotiation" anchor="persistent.negotiation">
2029   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2030   maintain a persistent connection unless a Connection header including
2031   the connection-token "close" was sent in the request. If the server
2032   chooses to close the connection immediately after sending the
2033   response, it &SHOULD; send a Connection header including the
2034   connection-token close.
2037   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2038   decide to keep it open based on whether the response from a server
2039   contains a Connection header with the connection-token close. In case
2040   the client does not want to maintain a connection for more than that
2041   request, it &SHOULD; send a Connection header including the
2042   connection-token close.
2045   If either the client or the server sends the close token in the
2046   Connection header, that request becomes the last one for the
2047   connection.
2050   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2051   maintained for HTTP versions less than 1.1 unless it is explicitly
2052   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2053   compatibility with HTTP/1.0 clients.
2056   In order to remain persistent, all messages on the connection &MUST;
2057   have a self-defined message length (i.e., one not defined by closure
2058   of the connection), as described in <xref target="message.length"/>.
2062<section title="Pipelining" anchor="pipelining">
2064   A client that supports persistent connections &MAY; "pipeline" its
2065   requests (i.e., send multiple requests without waiting for each
2066   response). A server &MUST; send its responses to those requests in the
2067   same order that the requests were received.
2070   Clients which assume persistent connections and pipeline immediately
2071   after connection establishment &SHOULD; be prepared to retry their
2072   connection if the first pipelined attempt fails. If a client does
2073   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2074   persistent. Clients &MUST; also be prepared to resend their requests if
2075   the server closes the connection before sending all of the
2076   corresponding responses.
2079   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2080   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2081   premature termination of the transport connection could lead to
2082   indeterminate results. A client wishing to send a non-idempotent
2083   request &SHOULD; wait to send that request until it has received the
2084   response status for the previous request.
2089<section title="Proxy Servers" anchor="persistent.proxy">
2091   It is especially important that proxies correctly implement the
2092   properties of the Connection header field as specified in <xref target="header.connection"/>.
2095   The proxy server &MUST; signal persistent connections separately with
2096   its clients and the origin servers (or other proxy servers) that it
2097   connects to. Each persistent connection applies to only one transport
2098   link.
2101   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2102   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
2103   discussion of the problems with the Keep-Alive header implemented by
2104   many HTTP/1.0 clients).
2108<section title="Practical Considerations" anchor="persistent.practical">
2110   Servers will usually have some time-out value beyond which they will
2111   no longer maintain an inactive connection. Proxy servers might make
2112   this a higher value since it is likely that the client will be making
2113   more connections through the same server. The use of persistent
2114   connections places no requirements on the length (or existence) of
2115   this time-out for either the client or the server.
2118   When a client or server wishes to time-out it &SHOULD; issue a graceful
2119   close on the transport connection. Clients and servers &SHOULD; both
2120   constantly watch for the other side of the transport close, and
2121   respond to it as appropriate. If a client or server does not detect
2122   the other side's close promptly it could cause unnecessary resource
2123   drain on the network.
2126   A client, server, or proxy &MAY; close the transport connection at any
2127   time. For example, a client might have started to send a new request
2128   at the same time that the server has decided to close the "idle"
2129   connection. From the server's point of view, the connection is being
2130   closed while it was idle, but from the client's point of view, a
2131   request is in progress.
2134   This means that clients, servers, and proxies &MUST; be able to recover
2135   from asynchronous close events. Client software &SHOULD; reopen the
2136   transport connection and retransmit the aborted sequence of requests
2137   without user interaction so long as the request sequence is
2138   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2139   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2140   human operator the choice of retrying the request(s). Confirmation by
2141   user-agent software with semantic understanding of the application
2142   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2143   be repeated if the second sequence of requests fails.
2146   Servers &SHOULD; always respond to at least one request per connection,
2147   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2148   middle of transmitting a response, unless a network or client failure
2149   is suspected.
2152   Clients that use persistent connections &SHOULD; limit the number of
2153   simultaneous connections that they maintain to a given server. A
2154   single-user client &SHOULD-NOT; maintain more than 2 connections with
2155   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2156   another server or proxy, where N is the number of simultaneously
2157   active users. These guidelines are intended to improve HTTP response
2158   times and avoid congestion.
2163<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2165<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2167   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2168   flow control mechanisms to resolve temporary overloads, rather than
2169   terminating connections with the expectation that clients will retry.
2170   The latter technique can exacerbate network congestion.
2174<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2176   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2177   the network connection for an error status while it is transmitting
2178   the request. If the client sees an error status, it &SHOULD;
2179   immediately cease transmitting the body. If the body is being sent
2180   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2181   empty trailer &MAY; be used to prematurely mark the end of the message.
2182   If the body was preceded by a Content-Length header, the client &MUST;
2183   close the connection.
2187<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2189   The purpose of the 100 (Continue) status (see &status-100;) is to
2190   allow a client that is sending a request message with a request body
2191   to determine if the origin server is willing to accept the request
2192   (based on the request headers) before the client sends the request
2193   body. In some cases, it might either be inappropriate or highly
2194   inefficient for the client to send the body if the server will reject
2195   the message without looking at the body.
2198   Requirements for HTTP/1.1 clients:
2199  <list style="symbols">
2200    <t>
2201        If a client will wait for a 100 (Continue) response before
2202        sending the request body, it &MUST; send an Expect request-header
2203        field (&header-expect;) with the "100-continue" expectation.
2204    </t>
2205    <t>
2206        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2207        with the "100-continue" expectation if it does not intend
2208        to send a request body.
2209    </t>
2210  </list>
2213   Because of the presence of older implementations, the protocol allows
2214   ambiguous situations in which a client may send "Expect: 100-continue"
2215   without receiving either a 417 (Expectation Failed) status
2216   or a 100 (Continue) status. Therefore, when a client sends this
2217   header field to an origin server (possibly via a proxy) from which it
2218   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2219   for an indefinite period before sending the request body.
2222   Requirements for HTTP/1.1 origin servers:
2223  <list style="symbols">
2224    <t> Upon receiving a request which includes an Expect request-header
2225        field with the "100-continue" expectation, an origin server &MUST;
2226        either respond with 100 (Continue) status and continue to read
2227        from the input stream, or respond with a final status code. The
2228        origin server &MUST-NOT; wait for the request body before sending
2229        the 100 (Continue) response. If it responds with a final status
2230        code, it &MAY; close the transport connection or it &MAY; continue
2231        to read and discard the rest of the request.  It &MUST-NOT;
2232        perform the requested method if it returns a final status code.
2233    </t>
2234    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2235        the request message does not include an Expect request-header
2236        field with the "100-continue" expectation, and &MUST-NOT; send a
2237        100 (Continue) response if such a request comes from an HTTP/1.0
2238        (or earlier) client. There is an exception to this rule: for
2239        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2240        status in response to an HTTP/1.1 PUT or POST request that does
2241        not include an Expect request-header field with the "100-continue"
2242        expectation. This exception, the purpose of which is
2243        to minimize any client processing delays associated with an
2244        undeclared wait for 100 (Continue) status, applies only to
2245        HTTP/1.1 requests, and not to requests with any other HTTP-version
2246        value.
2247    </t>
2248    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2249        already received some or all of the request body for the
2250        corresponding request.
2251    </t>
2252    <t> An origin server that sends a 100 (Continue) response &MUST;
2253    ultimately send a final status code, once the request body is
2254        received and processed, unless it terminates the transport
2255        connection prematurely.
2256    </t>
2257    <t> If an origin server receives a request that does not include an
2258        Expect request-header field with the "100-continue" expectation,
2259        the request includes a request body, and the server responds
2260        with a final status code before reading the entire request body
2261        from the transport connection, then the server &SHOULD-NOT;  close
2262        the transport connection until it has read the entire request,
2263        or until the client closes the connection. Otherwise, the client
2264        might not reliably receive the response message. However, this
2265        requirement is not be construed as preventing a server from
2266        defending itself against denial-of-service attacks, or from
2267        badly broken client implementations.
2268      </t>
2269    </list>
2272   Requirements for HTTP/1.1 proxies:
2273  <list style="symbols">
2274    <t> If a proxy receives a request that includes an Expect request-header
2275        field with the "100-continue" expectation, and the proxy
2276        either knows that the next-hop server complies with HTTP/1.1 or
2277        higher, or does not know the HTTP version of the next-hop
2278        server, it &MUST; forward the request, including the Expect header
2279        field.
2280    </t>
2281    <t> If the proxy knows that the version of the next-hop server is
2282        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2283        respond with a 417 (Expectation Failed) status.
2284    </t>
2285    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2286        numbers received from recently-referenced next-hop servers.
2287    </t>
2288    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2289        request message was received from an HTTP/1.0 (or earlier)
2290        client and did not include an Expect request-header field with
2291        the "100-continue" expectation. This requirement overrides the
2292        general rule for forwarding of 1xx responses (see &status-1xx;).
2293    </t>
2294  </list>
2298<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2300   If an HTTP/1.1 client sends a request which includes a request body,
2301   but which does not include an Expect request-header field with the
2302   "100-continue" expectation, and if the client is not directly
2303   connected to an HTTP/1.1 origin server, and if the client sees the
2304   connection close before receiving any status from the server, the
2305   client &SHOULD; retry the request.  If the client does retry this
2306   request, it &MAY; use the following "binary exponential backoff"
2307   algorithm to be assured of obtaining a reliable response:
2308  <list style="numbers">
2309    <t>
2310      Initiate a new connection to the server
2311    </t>
2312    <t>
2313      Transmit the request-headers
2314    </t>
2315    <t>
2316      Initialize a variable R to the estimated round-trip time to the
2317         server (e.g., based on the time it took to establish the
2318         connection), or to a constant value of 5 seconds if the round-trip
2319         time is not available.
2320    </t>
2321    <t>
2322       Compute T = R * (2**N), where N is the number of previous
2323         retries of this request.
2324    </t>
2325    <t>
2326       Wait either for an error response from the server, or for T
2327         seconds (whichever comes first)
2328    </t>
2329    <t>
2330       If no error response is received, after T seconds transmit the
2331         body of the request.
2332    </t>
2333    <t>
2334       If client sees that the connection is closed prematurely,
2335         repeat from step 1 until the request is accepted, an error
2336         response is received, or the user becomes impatient and
2337         terminates the retry process.
2338    </t>
2339  </list>
2342   If at any point an error status is received, the client
2343  <list style="symbols">
2344      <t>&SHOULD-NOT;  continue and</t>
2346      <t>&SHOULD; close the connection if it has not completed sending the
2347        request message.</t>
2348    </list>
2355<section title="Header Field Definitions" anchor="header.fields">
2357   This section defines the syntax and semantics of HTTP/1.1 header fields
2358   related to message framing and transport protocols.
2361   For entity-header fields, both sender and recipient refer to either the
2362   client or the server, depending on who sends and who receives the entity.
2365<section title="Connection" anchor="header.connection">
2366  <iref primary="true" item="Connection header" x:for-anchor=""/>
2367  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2368  <x:anchor-alias value="Connection"/>
2369  <x:anchor-alias value="connection-token"/>
2371   The Connection general-header field allows the sender to specify
2372   options that are desired for that particular connection and &MUST-NOT;
2373   be communicated by proxies over further connections.
2376   The Connection header has the following grammar:
2378<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2379  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2380  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2383   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2384   message is forwarded and, for each connection-token in this field,
2385   remove any header field(s) from the message with the same name as the
2386   connection-token. Connection options are signaled by the presence of
2387   a connection-token in the Connection header field, not by any
2388   corresponding additional header field(s), since the additional header
2389   field may not be sent if there are no parameters associated with that
2390   connection option.
2393   Message headers listed in the Connection header &MUST-NOT; include
2394   end-to-end headers, such as Cache-Control.
2397   HTTP/1.1 defines the "close" connection option for the sender to
2398   signal that the connection will be closed after completion of the
2399   response. For example,
2401<figure><artwork type="example">
2402    Connection: close
2405   in either the request or the response header fields indicates that
2406   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2407   after the current request/response is complete.
2410   An HTTP/1.1 client that does not support persistent connections &MUST;
2411   include the "close" connection option in every request message.
2414   An HTTP/1.1 server that does not support persistent connections &MUST;
2415   include the "close" connection option in every response message that
2416   does not have a 1xx (informational) status code.
2419   A system receiving an HTTP/1.0 (or lower-version) message that
2420   includes a Connection header &MUST;, for each connection-token in this
2421   field, remove and ignore any header field(s) from the message with
2422   the same name as the connection-token. This protects against mistaken
2423   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2427<section title="Content-Length" anchor="header.content-length">
2428  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2429  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2430  <x:anchor-alias value="Content-Length"/>
2432   The Content-Length entity-header field indicates the size of the
2433   entity-body, in decimal number of OCTETs, sent to the recipient or,
2434   in the case of the HEAD method, the size of the entity-body that
2435   would have been sent had the request been a GET.
2437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2438  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2441   An example is
2443<figure><artwork type="example">
2444    Content-Length: 3495
2447   Applications &SHOULD; use this field to indicate the transfer-length of
2448   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2451   Any Content-Length greater than or equal to zero is a valid value.
2452   <xref target="message.length"/> describes how to determine the length of a message-body
2453   if a Content-Length is not given.
2456   Note that the meaning of this field is significantly different from
2457   the corresponding definition in MIME, where it is an optional field
2458   used within the "message/external-body" content-type. In HTTP, it
2459   &SHOULD; be sent whenever the message's length can be determined prior
2460   to being transferred, unless this is prohibited by the rules in
2461   <xref target="message.length"/>.
2465<section title="Date" anchor="">
2466  <iref primary="true" item="Date header" x:for-anchor=""/>
2467  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2468  <x:anchor-alias value="Date"/>
2470   The Date general-header field represents the date and time at which
2471   the message was originated, having the same semantics as orig-date in
2472   <xref target="RFC2822" x:fmt="of" x:sec="3.6.1"/>. The field value is an HTTP-date, as described in <xref target=""/>;
2473   it &MUST; be sent in rfc1123-date format.
2475<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2476  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2479   An example is
2481<figure><artwork type="example">
2482    Date: Tue, 15 Nov 1994 08:12:31 GMT
2485   Origin servers &MUST; include a Date header field in all responses,
2486   except in these cases:
2487  <list style="numbers">
2488      <t>If the response status code is 100 (Continue) or 101 (Switching
2489         Protocols), the response &MAY; include a Date header field, at
2490         the server's option.</t>
2492      <t>If the response status code conveys a server error, e.g. 500
2493         (Internal Server Error) or 503 (Service Unavailable), and it is
2494         inconvenient or impossible to generate a valid Date.</t>
2496      <t>If the server does not have a clock that can provide a
2497         reasonable approximation of the current time, its responses
2498         &MUST-NOT; include a Date header field. In this case, the rules
2499         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2500  </list>
2503   A received message that does not have a Date header field &MUST; be
2504   assigned one by the recipient if the message will be cached by that
2505   recipient or gatewayed via a protocol which requires a Date. An HTTP
2506   implementation without a clock &MUST-NOT; cache responses without
2507   revalidating them on every use. An HTTP cache, especially a shared
2508   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2509   clock with a reliable external standard.
2512   Clients &SHOULD; only send a Date header field in messages that include
2513   an entity-body, as in the case of the PUT and POST requests, and even
2514   then it is optional. A client without a clock &MUST-NOT; send a Date
2515   header field in a request.
2518   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2519   time subsequent to the generation of the message. It &SHOULD; represent
2520   the best available approximation of the date and time of message
2521   generation, unless the implementation has no means of generating a
2522   reasonably accurate date and time. In theory, the date ought to
2523   represent the moment just before the entity is generated. In
2524   practice, the date can be generated at any time during the message
2525   origination without affecting its semantic value.
2528<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2530   Some origin server implementations might not have a clock available.
2531   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2532   values to a response, unless these values were associated
2533   with the resource by a system or user with a reliable clock. It &MAY;
2534   assign an Expires value that is known, at or before server
2535   configuration time, to be in the past (this allows "pre-expiration"
2536   of responses without storing separate Expires values for each
2537   resource).
2542<section title="Host" anchor="">
2543  <iref primary="true" item="Host header" x:for-anchor=""/>
2544  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2545  <x:anchor-alias value="Host"/>
2547   The Host request-header field specifies the Internet host and port
2548   number of the resource being requested, as obtained from the original
2549   URI given by the user or referring resource (generally an HTTP URL,
2550   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2551   the naming authority of the origin server or gateway given by the
2552   original URL. This allows the origin server or gateway to
2553   differentiate between internally-ambiguous URLs, such as the root "/"
2554   URL of a server for multiple host names on a single IP address.
2556<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2557  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2560   A "host" without any trailing port information implies the default
2561   port for the service requested (e.g., "80" for an HTTP URL). For
2562   example, a request on the origin server for
2563   &lt;; would properly include:
2565<figure><artwork type="example">
2566    GET /pub/WWW/ HTTP/1.1
2567    Host:
2570   A client &MUST; include a Host header field in all HTTP/1.1 request
2571   messages. If the requested URI does not include an Internet host
2572   name for the service being requested, then the Host header field &MUST;
2573   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2574   request message it forwards does contain an appropriate Host header
2575   field that identifies the service being requested by the proxy. All
2576   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2577   status code to any HTTP/1.1 request message which lacks a Host header
2578   field.
2581   See Sections <xref target="" format="counter"/>
2582   and <xref target="" format="counter"/>
2583   for other requirements relating to Host.
2587<section title="TE" anchor="header.te">
2588  <iref primary="true" item="TE header" x:for-anchor=""/>
2589  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2590  <x:anchor-alias value="TE"/>
2591  <x:anchor-alias value="t-codings"/>
2593   The TE request-header field indicates what extension transfer-codings
2594   it is willing to accept in the response and whether or not it is
2595   willing to accept trailer fields in a chunked transfer-coding. Its
2596   value may consist of the keyword "trailers" and/or a comma-separated
2597   list of extension transfer-coding names with optional accept
2598   parameters (as described in <xref target="transfer.codings"/>).
2600<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2601  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2602  <x:ref>t-codings</x:ref> = "trailers" | ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2605   The presence of the keyword "trailers" indicates that the client is
2606   willing to accept trailer fields in a chunked transfer-coding, as
2607   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2608   transfer-coding values even though it does not itself represent a
2609   transfer-coding.
2612   Examples of its use are:
2614<figure><artwork type="example">
2615    TE: deflate
2616    TE:
2617    TE: trailers, deflate;q=0.5
2620   The TE header field only applies to the immediate connection.
2621   Therefore, the keyword &MUST; be supplied within a Connection header
2622   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2625   A server tests whether a transfer-coding is acceptable, according to
2626   a TE field, using these rules:
2627  <list style="numbers">
2628    <x:lt>
2629      <t>The "chunked" transfer-coding is always acceptable. If the
2630         keyword "trailers" is listed, the client indicates that it is
2631         willing to accept trailer fields in the chunked response on
2632         behalf of itself and any downstream clients. The implication is
2633         that, if given, the client is stating that either all
2634         downstream clients are willing to accept trailer fields in the
2635         forwarded response, or that it will attempt to buffer the
2636         response on behalf of downstream recipients.
2637      </t><t>
2638         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2639         chunked response such that a client can be assured of buffering
2640         the entire response.</t>
2641    </x:lt>
2642    <x:lt>
2643      <t>If the transfer-coding being tested is one of the transfer-codings
2644         listed in the TE field, then it is acceptable unless it
2645         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2646         qvalue of 0 means "not acceptable.")</t>
2647    </x:lt>
2648    <x:lt>
2649      <t>If multiple transfer-codings are acceptable, then the
2650         acceptable transfer-coding with the highest non-zero qvalue is
2651         preferred.  The "chunked" transfer-coding always has a qvalue
2652         of 1.</t>
2653    </x:lt>
2654  </list>
2657   If the TE field-value is empty or if no TE field is present, the only
2658   transfer-coding  is "chunked". A message with no transfer-coding is
2659   always acceptable.
2663<section title="Trailer" anchor="header.trailer">
2664  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2665  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2666  <x:anchor-alias value="Trailer"/>
2668   The Trailer general field value indicates that the given set of
2669   header fields is present in the trailer of a message encoded with
2670   chunked transfer-coding.
2672<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2673  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2676   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2677   message using chunked transfer-coding with a non-empty trailer. Doing
2678   so allows the recipient to know which header fields to expect in the
2679   trailer.
2682   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2683   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2684   trailer fields in a "chunked" transfer-coding.
2687   Message header fields listed in the Trailer header field &MUST-NOT;
2688   include the following header fields:
2689  <list style="symbols">
2690    <t>Transfer-Encoding</t>
2691    <t>Content-Length</t>
2692    <t>Trailer</t>
2693  </list>
2697<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2698  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2699  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2700  <x:anchor-alias value="Transfer-Encoding"/>
2702   The Transfer-Encoding general-header field indicates what (if any)
2703   type of transformation has been applied to the message body in order
2704   to safely transfer it between the sender and the recipient. This
2705   differs from the content-coding in that the transfer-coding is a
2706   property of the message, not of the entity.
2708<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2709  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2712   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2714<figure><artwork type="example">
2715  Transfer-Encoding: chunked
2718   If multiple encodings have been applied to an entity, the transfer-codings
2719   &MUST; be listed in the order in which they were applied.
2720   Additional information about the encoding parameters &MAY; be provided
2721   by other entity-header fields not defined by this specification.
2724   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2725   header.
2729<section title="Upgrade" anchor="header.upgrade">
2730  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2731  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2732  <x:anchor-alias value="Upgrade"/>
2734   The Upgrade general-header allows the client to specify what
2735   additional communication protocols it supports and would like to use
2736   if the server finds it appropriate to switch protocols. The server
2737   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2738   response to indicate which protocol(s) are being switched.
2740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2741  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2744   For example,
2746<figure><artwork type="example">
2747    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2750   The Upgrade header field is intended to provide a simple mechanism
2751   for transition from HTTP/1.1 to some other, incompatible protocol. It
2752   does so by allowing the client to advertise its desire to use another
2753   protocol, such as a later version of HTTP with a higher major version
2754   number, even though the current request has been made using HTTP/1.1.
2755   This eases the difficult transition between incompatible protocols by
2756   allowing the client to initiate a request in the more commonly
2757   supported protocol while indicating to the server that it would like
2758   to use a "better" protocol if available (where "better" is determined
2759   by the server, possibly according to the nature of the method and/or
2760   resource being requested).
2763   The Upgrade header field only applies to switching application-layer
2764   protocols upon the existing transport-layer connection. Upgrade
2765   cannot be used to insist on a protocol change; its acceptance and use
2766   by the server is optional. The capabilities and nature of the
2767   application-layer communication after the protocol change is entirely
2768   dependent upon the new protocol chosen, although the first action
2769   after changing the protocol &MUST; be a response to the initial HTTP
2770   request containing the Upgrade header field.
2773   The Upgrade header field only applies to the immediate connection.
2774   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2775   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2776   HTTP/1.1 message.
2779   The Upgrade header field cannot be used to indicate a switch to a
2780   protocol on a different connection. For that purpose, it is more
2781   appropriate to use a 301, 302, 303, or 305 redirection response.
2784   This specification only defines the protocol name "HTTP" for use by
2785   the family of Hypertext Transfer Protocols, as defined by the HTTP
2786   version rules of <xref target="http.version"/> and future updates to this
2787   specification. Any token can be used as a protocol name; however, it
2788   will only be useful if both the client and server associate the name
2789   with the same protocol.
2793<section title="Via" anchor="header.via">
2794  <iref primary="true" item="Via header" x:for-anchor=""/>
2795  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2796  <x:anchor-alias value="protocol-name"/>
2797  <x:anchor-alias value="protocol-version"/>
2798  <x:anchor-alias value="pseudonym"/>
2799  <x:anchor-alias value="received-by"/>
2800  <x:anchor-alias value="received-protocol"/>
2801  <x:anchor-alias value="Via"/>
2803   The Via general-header field &MUST; be used by gateways and proxies to
2804   indicate the intermediate protocols and recipients between the user
2805   agent and the server on requests, and between the origin server and
2806   the client on responses. It is analogous to the "Received" field of
2807   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2808   avoiding request loops, and identifying the protocol capabilities of
2809   all senders along the request/response chain.
2811<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"/>
2812  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2813  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2814  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2815  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2816  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) | <x:ref>pseudonym</x:ref>
2817  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2820   The received-protocol indicates the protocol version of the message
2821   received by the server or client along each segment of the
2822   request/response chain. The received-protocol version is appended to
2823   the Via field value when the message is forwarded so that information
2824   about the protocol capabilities of upstream applications remains
2825   visible to all recipients.
2828   The protocol-name is optional if and only if it would be "HTTP". The
2829   received-by field is normally the host and optional port number of a
2830   recipient server or client that subsequently forwarded the message.
2831   However, if the real host is considered to be sensitive information,
2832   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2833   be assumed to be the default port of the received-protocol.
2836   Multiple Via field values represents each proxy or gateway that has
2837   forwarded the message. Each recipient &MUST; append its information
2838   such that the end result is ordered according to the sequence of
2839   forwarding applications.
2842   Comments &MAY; be used in the Via header field to identify the software
2843   of the recipient proxy or gateway, analogous to the User-Agent and
2844   Server header fields. However, all comments in the Via field are
2845   optional and &MAY; be removed by any recipient prior to forwarding the
2846   message.
2849   For example, a request message could be sent from an HTTP/1.0 user
2850   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2851   forward the request to a public proxy at, which completes
2852   the request by forwarding it to the origin server at
2853   The request received by would then have the following
2854   Via header field:
2856<figure><artwork type="example">
2857    Via: 1.0 fred, 1.1 (Apache/1.1)
2860   Proxies and gateways used as a portal through a network firewall
2861   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2862   the firewall region. This information &SHOULD; only be propagated if
2863   explicitly enabled. If not enabled, the received-by host of any host
2864   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2865   for that host.
2868   For organizations that have strong privacy requirements for hiding
2869   internal structures, a proxy &MAY; combine an ordered subsequence of
2870   Via header field entries with identical received-protocol values into
2871   a single such entry. For example,
2873<figure><artwork type="example">
2874    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2877        could be collapsed to
2879<figure><artwork type="example">
2880    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2883   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2884   under the same organizational control and the hosts have already been
2885   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2886   have different received-protocol values.
2892<section title="IANA Considerations" anchor="IANA.considerations">
2894   <cref>TBD.</cref>
2898<section title="Security Considerations" anchor="security.considerations">
2900   This section is meant to inform application developers, information
2901   providers, and users of the security limitations in HTTP/1.1 as
2902   described by this document. The discussion does not include
2903   definitive solutions to the problems revealed, though it does make
2904   some suggestions for reducing security risks.
2907<section title="Personal Information" anchor="personal.information">
2909   HTTP clients are often privy to large amounts of personal information
2910   (e.g. the user's name, location, mail address, passwords, encryption
2911   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2912   leakage of this information.
2913   We very strongly recommend that a convenient interface be provided
2914   for the user to control dissemination of such information, and that
2915   designers and implementors be particularly careful in this area.
2916   History shows that errors in this area often create serious security
2917   and/or privacy problems and generate highly adverse publicity for the
2918   implementor's company.
2922<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2924   A server is in the position to save personal data about a user's
2925   requests which might identify their reading patterns or subjects of
2926   interest. This information is clearly confidential in nature and its
2927   handling can be constrained by law in certain countries. People using
2928   HTTP to provide data are responsible for ensuring that
2929   such material is not distributed without the permission of any
2930   individuals that are identifiable by the published results.
2934<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2936   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2937   the documents returned by HTTP requests to be only those that were
2938   intended by the server administrators. If an HTTP server translates
2939   HTTP URIs directly into file system calls, the server &MUST; take
2940   special care not to serve files that were not intended to be
2941   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2942   other operating systems use ".." as a path component to indicate a
2943   directory level above the current one. On such a system, an HTTP
2944   server &MUST; disallow any such construct in the Request-URI if it
2945   would otherwise allow access to a resource outside those intended to
2946   be accessible via the HTTP server. Similarly, files intended for
2947   reference only internally to the server (such as access control
2948   files, configuration files, and script code) &MUST; be protected from
2949   inappropriate retrieval, since they might contain sensitive
2950   information. Experience has shown that minor bugs in such HTTP server
2951   implementations have turned into security risks.
2955<section title="DNS Spoofing" anchor="dns.spoofing">
2957   Clients using HTTP rely heavily on the Domain Name Service, and are
2958   thus generally prone to security attacks based on the deliberate
2959   mis-association of IP addresses and DNS names. Clients need to be
2960   cautious in assuming the continuing validity of an IP number/DNS name
2961   association.
2964   In particular, HTTP clients &SHOULD; rely on their name resolver for
2965   confirmation of an IP number/DNS name association, rather than
2966   caching the result of previous host name lookups. Many platforms
2967   already can cache host name lookups locally when appropriate, and
2968   they &SHOULD; be configured to do so. It is proper for these lookups to
2969   be cached, however, only when the TTL (Time To Live) information
2970   reported by the name server makes it likely that the cached
2971   information will remain useful.
2974   If HTTP clients cache the results of host name lookups in order to
2975   achieve a performance improvement, they &MUST; observe the TTL
2976   information reported by DNS.
2979   If HTTP clients do not observe this rule, they could be spoofed when
2980   a previously-accessed server's IP address changes. As network
2981   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2982   possibility of this form of attack will grow. Observing this
2983   requirement thus reduces this potential security vulnerability.
2986   This requirement also improves the load-balancing behavior of clients
2987   for replicated servers using the same DNS name and reduces the
2988   likelihood of a user's experiencing failure in accessing sites which
2989   use that strategy.
2993<section title="Proxies and Caching" anchor="attack.proxies">
2995   By their very nature, HTTP proxies are men-in-the-middle, and
2996   represent an opportunity for man-in-the-middle attacks. Compromise of
2997   the systems on which the proxies run can result in serious security
2998   and privacy problems. Proxies have access to security-related
2999   information, personal information about individual users and
3000   organizations, and proprietary information belonging to users and
3001   content providers. A compromised proxy, or a proxy implemented or
3002   configured without regard to security and privacy considerations,
3003   might be used in the commission of a wide range of potential attacks.
3006   Proxy operators should protect the systems on which proxies run as
3007   they would protect any system that contains or transports sensitive
3008   information. In particular, log information gathered at proxies often
3009   contains highly sensitive personal information, and/or information
3010   about organizations. Log information should be carefully guarded, and
3011   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3014   Proxy implementors should consider the privacy and security
3015   implications of their design and coding decisions, and of the
3016   configuration options they provide to proxy operators (especially the
3017   default configuration).
3020   Users of a proxy need to be aware that they are no trustworthier than
3021   the people who run the proxy; HTTP itself cannot solve this problem.
3024   The judicious use of cryptography, when appropriate, may suffice to
3025   protect against a broad range of security and privacy attacks. Such
3026   cryptography is beyond the scope of the HTTP/1.1 specification.
3030<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3032   They exist. They are hard to defend against. Research continues.
3033   Beware.
3038<section title="Acknowledgments" anchor="ack">
3040   This specification makes heavy use of the augmented BNF and generic
3041   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
3042   reuses many of the definitions provided by Nathaniel Borenstein and
3043   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3044   specification will help reduce past confusion over the relationship
3045   between HTTP and Internet mail message formats.
3048   HTTP has evolved considerably over the years. It has
3049   benefited from a large and active developer community--the many
3050   people who have participated on the www-talk mailing list--and it is
3051   that community which has been most responsible for the success of
3052   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3053   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3054   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3055   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3056   VanHeyningen deserve special recognition for their efforts in
3057   defining early aspects of the protocol.
3060   This document has benefited greatly from the comments of all those
3061   participating in the HTTP-WG. In addition to those already mentioned,
3062   the following individuals have contributed to this specification:
3065   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3066   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3067   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3068   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3069   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3070   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3071   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3072   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3073   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3074   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3075   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3076   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3077   Josh Cohen.
3080   Thanks to the "cave men" of Palo Alto. You know who you are.
3083   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3084   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3085   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3086   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3087   Larry Masinter for their help. And thanks go particularly to Jeff
3088   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3091   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3092   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3093   discovery of many of the problems that this document attempts to
3094   rectify.
3101<references title="Normative References">
3103<reference anchor="ISO-8859-1">
3104  <front>
3105    <title>
3106     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3107    </title>
3108    <author>
3109      <organization>International Organization for Standardization</organization>
3110    </author>
3111    <date year="1998"/>
3112  </front>
3113  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3116<reference anchor="Part2">
3117  <front>
3118    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3119    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3120      <organization abbrev="Day Software">Day Software</organization>
3121      <address><email></email></address>
3122    </author>
3123    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3124      <organization>One Laptop per Child</organization>
3125      <address><email></email></address>
3126    </author>
3127    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3128      <organization abbrev="HP">Hewlett-Packard Company</organization>
3129      <address><email></email></address>
3130    </author>
3131    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3132      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3133      <address><email></email></address>
3134    </author>
3135    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3136      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3137      <address><email></email></address>
3138    </author>
3139    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3140      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3141      <address><email></email></address>
3142    </author>
3143    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3144      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3145      <address><email></email></address>
3146    </author>
3147    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3148      <organization abbrev="W3C">World Wide Web Consortium</organization>
3149      <address><email></email></address>
3150    </author>
3151    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3152      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3153      <address><email></email></address>
3154    </author>
3155    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3156  </front>
3157  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3158  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3161<reference anchor="Part3">
3162  <front>
3163    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3164    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3165      <organization abbrev="Day Software">Day Software</organization>
3166      <address><email></email></address>
3167    </author>
3168    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3169      <organization>One Laptop per Child</organization>
3170      <address><email></email></address>
3171    </author>
3172    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3173      <organization abbrev="HP">Hewlett-Packard Company</organization>
3174      <address><email></email></address>
3175    </author>
3176    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3177      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3178      <address><email></email></address>
3179    </author>
3180    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3181      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3182      <address><email></email></address>
3183    </author>
3184    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3185      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3186      <address><email></email></address>
3187    </author>
3188    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3189      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3190      <address><email></email></address>
3191    </author>
3192    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3193      <organization abbrev="W3C">World Wide Web Consortium</organization>
3194      <address><email></email></address>
3195    </author>
3196    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3197      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3198      <address><email></email></address>
3199    </author>
3200    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3201  </front>
3202  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3203  <x:source href="p3-payload.xml" basename="p3-payload"/>
3206<reference anchor="Part5">
3207  <front>
3208    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3209    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3210      <organization abbrev="Day Software">Day Software</organization>
3211      <address><email></email></address>
3212    </author>
3213    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3214      <organization>One Laptop per Child</organization>
3215      <address><email></email></address>
3216    </author>
3217    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3218      <organization abbrev="HP">Hewlett-Packard Company</organization>
3219      <address><email></email></address>
3220    </author>
3221    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3222      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3223      <address><email></email></address>
3224    </author>
3225    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3226      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3227      <address><email></email></address>
3228    </author>
3229    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3230      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3231      <address><email></email></address>
3232    </author>
3233    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3234      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3235      <address><email></email></address>
3236    </author>
3237    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3238      <organization abbrev="W3C">World Wide Web Consortium</organization>
3239      <address><email></email></address>
3240    </author>
3241    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3242      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3243      <address><email></email></address>
3244    </author>
3245    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3246  </front>
3247  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3248  <x:source href="p5-range.xml" basename="p5-range"/>
3251<reference anchor="Part6">
3252  <front>
3253    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3254    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3255      <organization abbrev="Day Software">Day Software</organization>
3256      <address><email></email></address>
3257    </author>
3258    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3259      <organization>One Laptop per Child</organization>
3260      <address><email></email></address>
3261    </author>
3262    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3263      <organization abbrev="HP">Hewlett-Packard Company</organization>
3264      <address><email></email></address>
3265    </author>
3266    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3267      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3268      <address><email></email></address>
3269    </author>
3270    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3271      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3272      <address><email></email></address>
3273    </author>
3274    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3275      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3276      <address><email></email></address>
3277    </author>
3278    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3279      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3280      <address><email></email></address>
3281    </author>
3282    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3283      <organization abbrev="W3C">World Wide Web Consortium</organization>
3284      <address><email></email></address>
3285    </author>
3286    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3287      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3288      <address><email></email></address>
3289    </author>
3290    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3291  </front>
3292  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3293  <x:source href="p6-cache.xml" basename="p6-cache"/>
3296<reference anchor="RFC822ABNF">
3297  <front>
3298    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3299    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3300      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3301      <address><email>DCrocker@UDel-Relay</email></address>
3302    </author>
3303    <date month="August" day="13" year="1982"/>
3304  </front>
3305  <seriesInfo name="STD" value="11"/>
3306  <seriesInfo name="RFC" value="822"/>
3309<reference anchor="RFC2045">
3310  <front>
3311    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3312    <author initials="N." surname="Freed" fullname="Ned Freed">
3313      <organization>Innosoft International, Inc.</organization>
3314      <address><email></email></address>
3315    </author>
3316    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3317      <organization>First Virtual Holdings</organization>
3318      <address><email></email></address>
3319    </author>
3320    <date month="November" year="1996"/>
3321  </front>
3322  <seriesInfo name="RFC" value="2045"/>
3325<reference anchor="RFC2047">
3326  <front>
3327    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3328    <author initials="K." surname="Moore" fullname="Keith Moore">
3329      <organization>University of Tennessee</organization>
3330      <address><email></email></address>
3331    </author>
3332    <date month="November" year="1996"/>
3333  </front>
3334  <seriesInfo name="RFC" value="2047"/>
3337<reference anchor="RFC2119">
3338  <front>
3339    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3340    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3341      <organization>Harvard University</organization>
3342      <address><email></email></address>
3343    </author>
3344    <date month="March" year="1997"/>
3345  </front>
3346  <seriesInfo name="BCP" value="14"/>
3347  <seriesInfo name="RFC" value="2119"/>
3350<reference anchor="RFC2396">
3351  <front>
3352    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3353    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3354      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3355      <address><email></email></address>
3356    </author>
3357    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3358      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3359      <address><email></email></address>
3360    </author>
3361    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3362      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3363      <address><email></email></address>
3364    </author>
3365    <date month="August" year="1998"/>
3366  </front>
3367  <seriesInfo name="RFC" value="2396"/>
3370<reference anchor="USASCII">
3371  <front>
3372    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3373    <author>
3374      <organization>American National Standards Institute</organization>
3375    </author>
3376    <date year="1986"/>
3377  </front>
3378  <seriesInfo name="ANSI" value="X3.4"/>
3383<references title="Informative References">
3385<reference anchor="Nie1997" target="">
3386  <front>
3387    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3388    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3389      <organization/>
3390    </author>
3391    <author initials="J." surname="Gettys" fullname="J. Gettys">
3392      <organization/>
3393    </author>
3394    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3395      <organization/>
3396    </author>
3397    <author initials="H." surname="Lie" fullname="H. Lie">
3398      <organization/>
3399    </author>
3400    <author initials="C." surname="Lilley" fullname="C. Lilley">
3401      <organization/>
3402    </author>
3403    <date year="1997" month="September"/>
3404  </front>
3405  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3408<reference anchor="Pad1995">
3409  <front>
3410    <title>Improving HTTP Latency</title>
3411    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3412      <organization/>
3413    </author>
3414    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3415      <organization/>
3416    </author>
3417    <date year="1995" month="December"/>
3418  </front>
3419  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3420  <annotation>
3421    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3422    which is available at <eref target=""/>.
3423  </annotation>
3426<reference anchor="RFC822">
3427  <front>
3428    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3429    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3430      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3431      <address><email>DCrocker@UDel-Relay</email></address>
3432    </author>
3433    <date month="August" day="13" year="1982"/>
3434  </front>
3435  <seriesInfo name="STD" value="11"/>
3436  <seriesInfo name="RFC" value="822"/>
3439<reference anchor="RFC959">
3440  <front>
3441    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3442    <author initials="J." surname="Postel" fullname="J. Postel">
3443      <organization>Information Sciences Institute (ISI)</organization>
3444    </author>
3445    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3446      <organization/>
3447    </author>
3448    <date month="October" year="1985"/>
3449  </front>
3450  <seriesInfo name="STD" value="9"/>
3451  <seriesInfo name="RFC" value="959"/>
3454<reference anchor="RFC1123">
3455  <front>
3456    <title>Requirements for Internet Hosts - Application and Support</title>
3457    <author initials="R." surname="Braden" fullname="Robert Braden">
3458      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3459      <address><email>Braden@ISI.EDU</email></address>
3460    </author>
3461    <date month="October" year="1989"/>
3462  </front>
3463  <seriesInfo name="STD" value="3"/>
3464  <seriesInfo name="RFC" value="1123"/>
3467<reference anchor="RFC1305">
3468  <front>
3469    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3470    <author initials="D." surname="Mills" fullname="David L. Mills">
3471      <organization>University of Delaware, Electrical Engineering Department</organization>
3472      <address><email></email></address>
3473    </author>
3474    <date month="March" year="1992"/>
3475  </front>
3476  <seriesInfo name="RFC" value="1305"/>
3479<reference anchor="RFC1436">
3480  <front>
3481    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3482    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3483      <organization>University of Minnesota, Computer and Information Services</organization>
3484      <address><email></email></address>
3485    </author>
3486    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3487      <organization>University of Minnesota, Computer and Information Services</organization>
3488      <address><email></email></address>
3489    </author>
3490    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3491      <organization>University of Minnesota, Computer and Information Services</organization>
3492      <address><email></email></address>
3493    </author>
3494    <author initials="D." surname="Johnson" fullname="David Johnson">
3495      <organization>University of Minnesota, Computer and Information Services</organization>
3496      <address><email></email></address>
3497    </author>
3498    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3499      <organization>University of Minnesota, Computer and Information Services</organization>
3500      <address><email></email></address>
3501    </author>
3502    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3503      <organization>University of Minnesota, Computer and Information Services</organization>
3504      <address><email></email></address>
3505    </author>
3506    <date month="March" year="1993"/>
3507  </front>
3508  <seriesInfo name="RFC" value="1436"/>
3511<reference anchor="RFC1630">
3512  <front>
3513    <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>
3514    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3515      <organization>CERN, World-Wide Web project</organization>
3516      <address><email></email></address>
3517    </author>
3518    <date month="June" year="1994"/>
3519  </front>
3520  <seriesInfo name="RFC" value="1630"/>
3523<reference anchor="RFC1737">
3524  <front>
3525    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3526    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3527      <organization>Xerox Palo Alto Research Center</organization>
3528      <address><email></email></address>
3529    </author>
3530    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3531      <organization>MIT Laboratory for Computer Science</organization>
3532      <address><email></email></address>
3533    </author>
3534    <date month="December" year="1994"/>
3535  </front>
3536  <seriesInfo name="RFC" value="1737"/>
3539<reference anchor="RFC1738">
3540  <front>
3541    <title>Uniform Resource Locators (URL)</title>
3542    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3543      <organization>CERN, World-Wide Web project</organization>
3544      <address><email></email></address>
3545    </author>
3546    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3547      <organization>Xerox PARC</organization>
3548      <address><email></email></address>
3549    </author>
3550    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3551      <organization>University of Minnesota, Computer and Information Services</organization>
3552      <address><email></email></address>
3553    </author>
3554    <date month="December" year="1994"/>
3555  </front>
3556  <seriesInfo name="RFC" value="1738"/>
3559<reference anchor="RFC1808">
3560  <front>
3561    <title>Relative Uniform Resource Locators</title>
3562    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3563      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3564      <address><email></email></address>
3565    </author>
3566    <date month="June" year="1995"/>
3567  </front>
3568  <seriesInfo name="RFC" value="1808"/>
3571<reference anchor="RFC1900">
3572  <front>
3573    <title>Renumbering Needs Work</title>
3574    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3575      <organization>CERN, Computing and Networks Division</organization>
3576      <address><email></email></address>
3577    </author>
3578    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3579      <organization>cisco Systems</organization>
3580      <address><email></email></address>
3581    </author>
3582    <date month="February" year="1996"/>
3583  </front>
3584  <seriesInfo name="RFC" value="1900"/>
3587<reference anchor="RFC1945">
3588  <front>
3589    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3590    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3591      <organization>MIT, Laboratory for Computer Science</organization>
3592      <address><email></email></address>
3593    </author>
3594    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3595      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3596      <address><email></email></address>
3597    </author>
3598    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3599      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3600      <address><email></email></address>
3601    </author>
3602    <date month="May" year="1996"/>
3603  </front>
3604  <seriesInfo name="RFC" value="1945"/>
3607<reference anchor="RFC2068">
3608  <front>
3609    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3610    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3611      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3612      <address><email></email></address>
3613    </author>
3614    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3615      <organization>MIT Laboratory for Computer Science</organization>
3616      <address><email></email></address>
3617    </author>
3618    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3619      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3620      <address><email></email></address>
3621    </author>
3622    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3623      <organization>MIT Laboratory for Computer Science</organization>
3624      <address><email></email></address>
3625    </author>
3626    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3627      <organization>MIT Laboratory for Computer Science</organization>
3628      <address><email></email></address>
3629    </author>
3630    <date month="January" year="1997"/>
3631  </front>
3632  <seriesInfo name="RFC" value="2068"/>
3635<reference anchor="RFC2145">
3636  <front>
3637    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3638    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3639      <organization>Western Research Laboratory</organization>
3640      <address><email></email></address>
3641    </author>
3642    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3643      <organization>Department of Information and Computer Science</organization>
3644      <address><email></email></address>
3645    </author>
3646    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3647      <organization>MIT Laboratory for Computer Science</organization>
3648      <address><email></email></address>
3649    </author>
3650    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3651      <organization>W3 Consortium</organization>
3652      <address><email></email></address>
3653    </author>
3654    <date month="May" year="1997"/>
3655  </front>
3656  <seriesInfo name="RFC" value="2145"/>
3659<reference anchor="RFC2324">
3660  <front>
3661    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3662    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3663      <organization>Xerox Palo Alto Research Center</organization>
3664      <address><email></email></address>
3665    </author>
3666    <date month="April" day="1" year="1998"/>
3667  </front>
3668  <seriesInfo name="RFC" value="2324"/>
3671<reference anchor="RFC2616">
3672  <front>
3673    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3674    <author initials="R." surname="Fielding" fullname="R. Fielding">
3675      <organization>University of California, Irvine</organization>
3676      <address><email></email></address>
3677    </author>
3678    <author initials="J." surname="Gettys" fullname="J. Gettys">
3679      <organization>W3C</organization>
3680      <address><email></email></address>
3681    </author>
3682    <author initials="J." surname="Mogul" fullname="J. Mogul">
3683      <organization>Compaq Computer Corporation</organization>
3684      <address><email></email></address>
3685    </author>
3686    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3687      <organization>MIT Laboratory for Computer Science</organization>
3688      <address><email></email></address>
3689    </author>
3690    <author initials="L." surname="Masinter" fullname="L. Masinter">
3691      <organization>Xerox Corporation</organization>
3692      <address><email></email></address>
3693    </author>
3694    <author initials="P." surname="Leach" fullname="P. Leach">
3695      <organization>Microsoft Corporation</organization>
3696      <address><email></email></address>
3697    </author>
3698    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3699      <organization>W3C</organization>
3700      <address><email></email></address>
3701    </author>
3702    <date month="June" year="1999"/>
3703  </front>
3704  <seriesInfo name="RFC" value="2616"/>
3707<reference anchor="RFC2821">
3708  <front>
3709    <title>Simple Mail Transfer Protocol</title>
3710    <author initials="J." surname="Klensin" fullname="J. Klensin">
3711      <organization>AT&amp;T Laboratories</organization>
3712      <address><email></email></address>
3713    </author>
3714    <date year="2001" month="April"/>
3715  </front>
3716  <seriesInfo name="RFC" value="2821"/>
3719<reference anchor="RFC2822">
3720  <front>
3721    <title>Internet Message Format</title>
3722    <author initials="P." surname="Resnick" fullname="P. Resnick">
3723      <organization>QUALCOMM Incorporated</organization>
3724    </author>
3725    <date year="2001" month="April"/>
3726  </front>
3727  <seriesInfo name="RFC" value="2822"/>
3730<reference anchor='RFC3977'>
3731  <front>
3732    <title>Network News Transfer Protocol (NNTP)</title>
3733    <author initials='C.' surname='Feather' fullname='C. Feather'>
3734      <organization>THUS plc</organization>
3735      <address><email></email></address>
3736    </author>
3737    <date year='2006' month='October' />
3738  </front>
3739  <seriesInfo name="RFC" value="3977"/>
3742<reference anchor="RFC4288">
3743  <front>
3744    <title>Media Type Specifications and Registration Procedures</title>
3745    <author initials="N." surname="Freed" fullname="N. Freed">
3746      <organization>Sun Microsystems</organization>
3747      <address>
3748        <email></email>
3749      </address>
3750    </author>
3751    <author initials="J." surname="Klensin" fullname="J. Klensin">
3752      <organization/>
3753      <address>
3754        <email></email>
3755      </address>
3756    </author>
3757    <date year="2005" month="December"/>
3758  </front>
3759  <seriesInfo name="BCP" value="13"/>
3760  <seriesInfo name="RFC" value="4288"/>
3763<reference anchor="Spe" target="">
3764  <front>
3765  <title>Analysis of HTTP Performance Problems</title>
3766  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3767    <organization/>
3768  </author>
3769  <date/>
3770  </front>
3773<reference anchor="Tou1998" target="">
3774  <front>
3775  <title>Analysis of HTTP Performance</title>
3776  <author initials="J." surname="Touch" fullname="Joe Touch">
3777    <organization>USC/Information Sciences Institute</organization>
3778    <address><email></email></address>
3779  </author>
3780  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3781    <organization>USC/Information Sciences Institute</organization>
3782    <address><email></email></address>
3783  </author>
3784  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3785    <organization>USC/Information Sciences Institute</organization>
3786    <address><email></email></address>
3787  </author>
3788  <date year="1998" month="Aug"/>
3789  </front>
3790  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3791  <annotation>(original report dated Aug. 1996)</annotation>
3794<reference anchor="WAIS">
3795  <front>
3796    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3797    <author initials="F." surname="Davis" fullname="F. Davis">
3798      <organization>Thinking Machines Corporation</organization>
3799    </author>
3800    <author initials="B." surname="Kahle" fullname="B. Kahle">
3801      <organization>Thinking Machines Corporation</organization>
3802    </author>
3803    <author initials="H." surname="Morris" fullname="H. Morris">
3804      <organization>Thinking Machines Corporation</organization>
3805    </author>
3806    <author initials="J." surname="Salem" fullname="J. Salem">
3807      <organization>Thinking Machines Corporation</organization>
3808    </author>
3809    <author initials="T." surname="Shen" fullname="T. Shen">
3810      <organization>Thinking Machines Corporation</organization>
3811    </author>
3812    <author initials="R." surname="Wang" fullname="R. Wang">
3813      <organization>Thinking Machines Corporation</organization>
3814    </author>
3815    <author initials="J." surname="Sui" fullname="J. Sui">
3816      <organization>Thinking Machines Corporation</organization>
3817    </author>
3818    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3819      <organization>Thinking Machines Corporation</organization>
3820    </author>
3821    <date month="April" year="1990"/>
3822  </front>
3823  <seriesInfo name="Thinking Machines Corporation" value=""/>
3829<section title="Internet Media Types" anchor="">
3831   In addition to defining HTTP/1.1, this document serves
3832   as the specification for the Internet media type "message/http" and
3833   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3835<section title="Internet Media Type message/http" anchor="">
3836<iref item="Media Type" subitem="message/http" primary="true"/>
3837<iref item="message/http Media Type" primary="true"/>
3839   The message/http type can be used to enclose a single HTTP request or
3840   response message, provided that it obeys the MIME restrictions for all
3841   "message" types regarding line length and encodings.
3844  <list style="hanging" x:indent="12em">
3845    <t hangText="Type name:">
3846      message
3847    </t>
3848    <t hangText="Subtype name:">
3849      http
3850    </t>
3851    <t hangText="Required parameters:">
3852      none
3853    </t>
3854    <t hangText="Optional parameters:">
3855      version, msgtype
3856      <list style="hanging">
3857        <t hangText="version:">
3858          The HTTP-Version number of the enclosed message
3859          (e.g., "1.1"). If not present, the version can be
3860          determined from the first line of the body.
3861        </t>
3862        <t hangText="msgtype:">
3863          The message type -- "request" or "response". If not
3864          present, the type can be determined from the first
3865          line of the body.
3866        </t>
3867      </list>
3868    </t>
3869    <t hangText="Encoding considerations:">
3870      only "7bit", "8bit", or "binary" are permitted
3871    </t>
3872    <t hangText="Security considerations:">
3873      none
3874    </t>
3875    <t hangText="Interoperability considerations:">
3876      none
3877    </t>
3878    <t hangText="Published specification:">
3879      This specification (see <xref target=""/>).
3880    </t>
3881    <t hangText="Applications that use this media type:">
3882    </t>
3883    <t hangText="Additional information:">
3884      <list style="hanging">
3885        <t hangText="Magic number(s):">none</t>
3886        <t hangText="File extension(s):">none</t>
3887        <t hangText="Macintosh file type code(s):">none</t>
3888      </list>
3889    </t>
3890    <t hangText="Person and email address to contact for further information:">
3891      See Authors Section.
3892    </t>
3893                <t hangText="Intended usage:">
3894                  COMMON
3895    </t>
3896                <t hangText="Restrictions on usage:">
3897                  none
3898    </t>
3899    <t hangText="Author/Change controller:">
3900      IESG
3901    </t>
3902  </list>
3905<section title="Internet Media Type application/http" anchor="">
3906<iref item="Media Type" subitem="application/http" primary="true"/>
3907<iref item="application/http Media Type" primary="true"/>
3909   The application/http type can be used to enclose a pipeline of one or more
3910   HTTP request or response messages (not intermixed).
3913  <list style="hanging" x:indent="12em">
3914    <t hangText="Type name:">
3915      application
3916    </t>
3917    <t hangText="Subtype name:">
3918      http
3919    </t>
3920    <t hangText="Required parameters:">
3921      none
3922    </t>
3923    <t hangText="Optional parameters:">
3924      version, msgtype
3925      <list style="hanging">
3926        <t hangText="version:">
3927          The HTTP-Version number of the enclosed messages
3928          (e.g., "1.1"). If not present, the version can be
3929          determined from the first line of the body.
3930        </t>
3931        <t hangText="msgtype:">
3932          The message type -- "request" or "response". If not
3933          present, the type can be determined from the first
3934          line of the body.
3935        </t>
3936      </list>
3937    </t>
3938    <t hangText="Encoding considerations:">
3939      HTTP messages enclosed by this type
3940      are in "binary" format; use of an appropriate
3941      Content-Transfer-Encoding is required when
3942      transmitted via E-mail.
3943    </t>
3944    <t hangText="Security considerations:">
3945      none
3946    </t>
3947    <t hangText="Interoperability considerations:">
3948      none
3949    </t>
3950    <t hangText="Published specification:">
3951      This specification (see <xref target=""/>).
3952    </t>
3953    <t hangText="Applications that use this media type:">
3954    </t>
3955    <t hangText="Additional information:">
3956      <list style="hanging">
3957        <t hangText="Magic number(s):">none</t>
3958        <t hangText="File extension(s):">none</t>
3959        <t hangText="Macintosh file type code(s):">none</t>
3960      </list>
3961    </t>
3962    <t hangText="Person and email address to contact for further information:">
3963      See Authors Section.
3964    </t>
3965                <t hangText="Intended usage:">
3966                  COMMON
3967    </t>
3968                <t hangText="Restrictions on usage:">
3969                  none
3970    </t>
3971    <t hangText="Author/Change controller:">
3972      IESG
3973    </t>
3974  </list>
3979<section title="Tolerant Applications" anchor="tolerant.applications">
3981   Although this document specifies the requirements for the generation
3982   of HTTP/1.1 messages, not all applications will be correct in their
3983   implementation. We therefore recommend that operational applications
3984   be tolerant of deviations whenever those deviations can be
3985   interpreted unambiguously.
3988   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3989   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3990   accept any amount of SP or HTAB characters between fields, even though
3991   only a single SP is required.
3994   The line terminator for message-header fields is the sequence CRLF.
3995   However, we recommend that applications, when parsing such headers,
3996   recognize a single LF as a line terminator and ignore the leading CR.
3999   The character set of an entity-body &SHOULD; be labeled as the lowest
4000   common denominator of the character codes used within that body, with
4001   the exception that not labeling the entity is preferred over labeling
4002   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4005   Additional rules for requirements on parsing and encoding of dates
4006   and other potential problems with date encodings include:
4009  <list style="symbols">
4010     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4011        which appears to be more than 50 years in the future is in fact
4012        in the past (this helps solve the "year 2000" problem).</t>
4014     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4015        Expires date as earlier than the proper value, but &MUST-NOT;
4016        internally represent a parsed Expires date as later than the
4017        proper value.</t>
4019     <t>All expiration-related calculations &MUST; be done in GMT. The
4020        local time zone &MUST-NOT; influence the calculation or comparison
4021        of an age or expiration time.</t>
4023     <t>If an HTTP header incorrectly carries a date value with a time
4024        zone other than GMT, it &MUST; be converted into GMT using the
4025        most conservative possible conversion.</t>
4026  </list>
4030<section title="Conversion of Date Formats" anchor="">
4032   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
4033   simplify the process of date comparison. Proxies and gateways from
4034   other protocols &SHOULD; ensure that any Date header field present in a
4035   message conforms to one of the HTTP/1.1 formats and rewrite the date
4036   if necessary.
4040<section title="Compatibility with Previous Versions" anchor="compatibility">
4042   It is beyond the scope of a protocol specification to mandate
4043   compliance with previous versions. HTTP/1.1 was deliberately
4044   designed, however, to make supporting previous versions easy. It is
4045   worth noting that, at the time of composing this specification
4046   (1996), we would expect commercial HTTP/1.1 servers to:
4047  <list style="symbols">
4048     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4049        1.1 requests;</t>
4051     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4052        1.1;</t>
4054     <t>respond appropriately with a message in the same major version
4055        used by the client.</t>
4056  </list>
4059   And we would expect HTTP/1.1 clients to:
4060  <list style="symbols">
4061     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4062        responses;</t>
4064     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4065        1.1.</t>
4066  </list>
4069   For most implementations of HTTP/1.0, each connection is established
4070   by the client prior to the request and closed by the server after
4071   sending the response. Some implementations implement the Keep-Alive
4072   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4075<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4077   This section summarizes major differences between versions HTTP/1.0
4078   and HTTP/1.1.
4081<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4083   The requirements that clients and servers support the Host request-header,
4084   report an error if the Host request-header (<xref target=""/>) is
4085   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4086   are among the most important changes defined by this
4087   specification.
4090   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4091   addresses and servers; there was no other established mechanism for
4092   distinguishing the intended server of a request than the IP address
4093   to which that request was directed. The changes outlined above will
4094   allow the Internet, once older HTTP clients are no longer common, to
4095   support multiple Web sites from a single IP address, greatly
4096   simplifying large operational Web servers, where allocation of many
4097   IP addresses to a single host has created serious problems. The
4098   Internet will also be able to recover the IP addresses that have been
4099   allocated for the sole purpose of allowing special-purpose domain
4100   names to be used in root-level HTTP URLs. Given the rate of growth of
4101   the Web, and the number of servers already deployed, it is extremely
4102   important that all implementations of HTTP (including updates to
4103   existing HTTP/1.0 applications) correctly implement these
4104   requirements:
4105  <list style="symbols">
4106     <t>Both clients and servers &MUST; support the Host request-header.</t>
4108     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4110     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4111        request does not include a Host request-header.</t>
4113     <t>Servers &MUST; accept absolute URIs.</t>
4114  </list>
4119<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4121   Some clients and servers might wish to be compatible with some
4122   previous implementations of persistent connections in HTTP/1.0
4123   clients and servers. Persistent connections in HTTP/1.0 are
4124   explicitly negotiated as they are not the default behavior. HTTP/1.0
4125   experimental implementations of persistent connections are faulty,
4126   and the new facilities in HTTP/1.1 are designed to rectify these
4127   problems. The problem was that some existing 1.0 clients may be
4128   sending Keep-Alive to a proxy server that doesn't understand
4129   Connection, which would then erroneously forward it to the next
4130   inbound server, which would establish the Keep-Alive connection and
4131   result in a hung HTTP/1.0 proxy waiting for the close on the
4132   response. The result is that HTTP/1.0 clients must be prevented from
4133   using Keep-Alive when talking to proxies.
4136   However, talking to proxies is the most important use of persistent
4137   connections, so that prohibition is clearly unacceptable. Therefore,
4138   we need some other mechanism for indicating a persistent connection
4139   is desired, which is safe to use even when talking to an old proxy
4140   that ignores Connection. Persistent connections are the default for
4141   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4142   declaring non-persistence. See <xref target="header.connection"/>.
4145   The original HTTP/1.0 form of persistent connections (the Connection:
4146   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4150<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4152   This specification has been carefully audited to correct and
4153   disambiguate key word usage; RFC 2068 had many problems in respect to
4154   the conventions laid out in <xref target="RFC2119"/>.
4157   Transfer-coding and message lengths all interact in ways that
4158   required fixing exactly when chunked encoding is used (to allow for
4159   transfer encoding that may not be self delimiting); it was important
4160   to straighten out exactly how message lengths are computed. (Sections
4161   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4162   <xref target="header.content-length" format="counter"/>,
4163   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4166   The use and interpretation of HTTP version numbers has been clarified
4167   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4168   version they support to deal with problems discovered in HTTP/1.0
4169   implementations (<xref target="http.version"/>)
4172   Transfer-coding had significant problems, particularly with
4173   interactions with chunked encoding. The solution is that transfer-codings
4174   become as full fledged as content-codings. This involves
4175   adding an IANA registry for transfer-codings (separate from content
4176   codings), a new header field (TE) and enabling trailer headers in the
4177   future. Transfer encoding is a major performance benefit, so it was
4178   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4179   interoperability problem that could have occurred due to interactions
4180   between authentication trailers, chunked encoding and HTTP/1.0
4181   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4182   and <xref target="header.te" format="counter"/>)
4186<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4188  The CHAR rule does not allow the NUL character anymore (this affects
4189  the comment and quoted-string rules).  Furthermore, the quoted-pair
4190  rule does not allow escaping NUL, CR or LF anymore.
4191  (<xref target="basic.rules"/>)
4194  Clarify that HTTP-Version is case sensitive.
4195  (<xref target="http.version"/>)
4198  Remove reference to non-existant identity transfer-coding value tokens.
4199  (Sections <xref format="counter" target="transfer.codings"/> and
4200  <xref format="counter" target="message.length"/>)
4203  Clarification that the chunk length does not include
4204  the count of the octets in the chunk header and trailer.
4205  (<xref target="chunked.transfer.encoding"/>)
4208  Fix BNF to add query, as the abs_path production in
4209  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4210  (<xref target="request-uri"/>)
4213  Clarify exactly when close connection options must be sent.
4214  (<xref target="header.connection"/>)
4219<section title="Change Log (to be removed by RFC Editor before publication)">
4221<section title="Since RFC2616">
4223  Extracted relevant partitions from <xref target="RFC2616"/>.
4227<section title="Since draft-ietf-httpbis-p1-messaging-00">
4229  Closed issues:
4230  <list style="symbols">
4231    <t>
4232      <eref target=""/>:
4233      "HTTP Version should be case sensitive"
4234      (<eref target=""/>)
4235    </t>
4236    <t>
4237      <eref target=""/>:
4238      "'unsafe' characters"
4239      (<eref target=""/>)
4240    </t>
4241    <t>
4242      <eref target=""/>:
4243      "Chunk Size Definition"
4244      (<eref target=""/>)
4245    </t>
4246    <t>
4247      <eref target=""/>:
4248      "Message Length"
4249      (<eref target=""/>)
4250    </t>
4251    <t>
4252      <eref target=""/>:
4253      "Media Type Registrations"
4254      (<eref target=""/>)
4255    </t>
4256    <t>
4257      <eref target=""/>:
4258      "URI includes query"
4259      (<eref target=""/>)
4260    </t>
4261    <t>
4262      <eref target=""/>:
4263      "No close on 1xx responses"
4264      (<eref target=""/>)
4265    </t>
4266    <t>
4267      <eref target=""/>:
4268      "Remove 'identity' token references"
4269      (<eref target=""/>)
4270    </t>
4271    <t>
4272      <eref target=""/>:
4273      "Import query BNF"
4274    </t>
4275    <t>
4276      <eref target=""/>:
4277      "qdtext BNF"
4278    </t>
4279    <t>
4280      <eref target=""/>:
4281      "Normative and Informative references"
4282    </t>
4283    <t>
4284      <eref target=""/>:
4285      "RFC2606 Compliance"
4286    </t>
4287    <t>
4288      <eref target=""/>:
4289      "RFC977 reference"
4290    </t>
4291    <t>
4292      <eref target=""/>:
4293      "RFC1700 references"
4294    </t>
4295    <t>
4296      <eref target=""/>:
4297      "inconsistency in date format explanation"
4298    </t>
4299    <t>
4300      <eref target=""/>:
4301      "Date reference typo"
4302    </t>
4303    <t>
4304      <eref target=""/>:
4305      "Informative references"
4306    </t>
4307    <t>
4308      <eref target=""/>:
4309      "ISO-8859-1 Reference"
4310    </t>
4311    <t>
4312      <eref target=""/>:
4313      "Normative up-to-date references"
4314    </t>
4315  </list>
4318  Other changes:
4319  <list style="symbols">
4320    <t>
4321      Update media type registrations to use RFC4288 template.
4322    </t>
4323    <t>
4324      Use names of RFC4234 core rules DQUOTE and HTAB,
4325      fix broken ABNF for chunk-data
4326      (work in progress on <eref target=""/>)
4327    </t>
4328  </list>
4332<section title="Since draft-ietf-httpbis-p1-messaging-01">
4334  Closed issues:
4335  <list style="symbols">
4336    <t>
4337      <eref target=""/>:
4338      "Bodies on GET (and other) requests"
4339    </t>
4340    <t>
4341      <eref target=""/>:
4342      "Updating to RFC4288"
4343    </t>
4344    <t>
4345      <eref target=""/>:
4346      "Status Code and Reason Phrase"
4347    </t>
4348    <t>
4349      <eref target=""/>:
4350      "rel_path not used"
4351    </t>
4352  </list>
4355  Ongoing work on ABNF conversion (<eref target=""/>):
4356  <list style="symbols">
4357    <t>
4358      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4359      "trailer-part").
4360    </t>
4361    <t>
4362      Avoid underscore character in rule names ("http_URL" ->
4363      "http-URL", "abs_path" -> "path-absolute").
4364    </t>
4365    <t>
4366      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4367      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4368      have to be updated when switching over to RFC3986.
4369    </t>
4370    <t>
4371      Synchronize core rules with RFC5234 (this includes a change to CHAR
4372      which now excludes NUL).
4373    </t>
4374    <t>
4375      Get rid of prose rules that span multiple lines.
4376    </t>
4377    <t>
4378      Get rid of unused rules LOALPHA and UPALPHA.
4379    </t>
4380    <t>
4381      Move "Product Tokens" section (back) into Part 1, as "token" is used
4382      in the definition of the Upgrade header.
4383    </t>
4384    <t>
4385      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4386    </t>
4387    <t>
4388      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4389    </t>
4390  </list>
4394<section title="Since draft-ietf-httpbis-p1-messaging-02">
4396  Closed issues:
4397  <list style="symbols">
4398    <t>
4399      <eref target=""/>:
4400      "HTTP-date vs. rfc1123-date"
4401    </t>
4402    <t>
4403      <eref target=""/>:
4404      "WS in quoted-pair"
4405    </t>
4406  </list>
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