source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 339

Last change on this file since 339 was 339, checked in by fielding@…, 14 years ago

Introduce notation early, split intro for overall operation

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
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" x:maturity-level="draft"
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    The changes in this draft are summarized in <xref target="changes.since.02"/>.
224  </t>
228<section title="Introduction" anchor="introduction">
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   protocol for distributed, collaborative, hypermedia information
232   systems. HTTP has been in use by the World-Wide Web global
233   information initiative since 1990. The first version of HTTP, commonly
234   referred to as HTTP/0.9, was a simple protocol for raw data transfer
235   across the Internet with only a single method and no metadata.
236   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
237   the protocol by allowing messages to be in the format of MIME-like
238   messages, containing metadata about the data transferred and
239   modifiers on the request/response semantics. However, HTTP/1.0 did
240   not sufficiently take into consideration the effects of hierarchical
241   proxies, caching, the need for persistent connections, or name-based
242   virtual hosts. In addition, the proliferation of incompletely-implemented
243   applications calling themselves "HTTP/1.0" necessitated a
244   protocol version change in order for two communicating applications
245   to determine each other's true capabilities.
248   This document is Part 1 of the seven-part specification that defines
249   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
250   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
251   requirements that enable reliable implementations and adding only
252   those new features that will either be safely ignored by an HTTP/1.0
253   recipient or only sent when communicating with a party advertising
254   compliance with HTTP/1.1.
255   Part 1 defines those aspects of HTTP/1.1 related to overall network
256   operation, message framing, interaction with transport protocols, and
257   URI schemes.
260   This document is currently disorganized in order to minimize the changes
261   between drafts and enable reviewers to see the smaller errata changes.
262   The next draft will reorganize the sections to better reflect the content.
263   In particular, the sections will be organized according to the typical
264   process of deciding when to use HTTP (URI schemes), overall network operation,
265   connection management, message framing, and generic message parsing.
266   The current mess reflects how widely dispersed these topics and associated
267   requirements had become in <xref target="RFC2616"/>.
270<section title="Purpose" anchor="intro.purpose">
272   Practical information systems require more functionality than simple
273   retrieval, including search, front-end update, and annotation. HTTP
274   allows an open-ended set of methods and headers that indicate the
275   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
276   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
277   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
278   method is to be applied. Messages are passed in a format similar to
279   that used by Internet mail <xref target="RFC5322"/> as defined by the Multipurpose
280   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
283   HTTP is also used as a generic protocol for communication between
284   user agents and proxies/gateways to other Internet systems, including
285   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
286   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
287   access to resources available from diverse applications.
291<section title="Requirements" anchor="intro.requirements">
293   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
294   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
295   document are to be interpreted as described in <xref target="RFC2119"/>.
298   An implementation is not compliant if it fails to satisfy one or more
299   of the &MUST; or &REQUIRED; level requirements for the protocols it
300   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
301   level and all the &SHOULD; level requirements for its protocols is said
302   to be "unconditionally compliant"; one that satisfies all the &MUST;
303   level requirements but not all the &SHOULD; level requirements for its
304   protocols is said to be "conditionally compliant."
308<section title="Syntax Notation" anchor="syntax.notation">
310   This specification uses the Augmented Backus-Naur Form (ABNF) notation
311   of <xref target="RFC5234"/>, including its core ABNF syntax rules:
312   ALPHA (letters), CR (carriage return), DIGIT (decimal digits),
313   DQUOTE (double quote), HEXDIG (hexadecimal digits), LF (line feed),
314   and SP (space).
319<section title="When to use HTTP" anchor="when">
321<section title="Overall Operation" anchor="intro.overall.operation">
323   HTTP is a request/response protocol. A client sends a
324   request to the server in the form of a request method, URI, and
325   protocol version, followed by a MIME-like message containing request
326   modifiers, client information, and possible body content over a
327   connection with a server. The server responds with a status line,
328   including the message's protocol version and a success or error code,
329   followed by a MIME-like message containing server information, entity
330   metainformation, and possible entity-body content. The relationship
331   between HTTP and MIME is described in &diff2045entity;.
334   Most HTTP communication is initiated by a user agent and consists of
335   a request to be applied to a resource on some origin server. In the
336   simplest case, this may be accomplished via a single connection (v)
337   between the user agent (UA) and the origin server (O).
339<figure><artwork type="drawing">
340       request chain ------------------------&gt;
341    UA -------------------v------------------- O
342       &lt;----------------------- response chain
345   A more complicated situation occurs when one or more intermediaries
346   are present in the request/response chain. There are three common
347   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
348   forwarding agent, receiving requests for a URI in its absolute form,
349   rewriting all or part of the message, and forwarding the reformatted
350   request toward the server identified by the URI. A gateway is a
351   receiving agent, acting as a layer above some other server(s) and, if
352   necessary, translating the requests to the underlying server's
353   protocol. A tunnel acts as a relay point between two connections
354   without changing the messages; tunnels are used when the
355   communication needs to pass through an intermediary (such as a
356   firewall) even when the intermediary cannot understand the contents
357   of the messages.
359<figure><artwork type="drawing">
360       request chain --------------------------------------&gt;
361    UA -----v----- A -----v----- B -----v----- C -----v----- O
362       &lt;------------------------------------- response chain
365   The figure above shows three intermediaries (A, B, and C) between the
366   user agent and origin server. A request or response message that
367   travels the whole chain will pass through four separate connections.
368   This distinction is important because some HTTP communication options
369   may apply only to the connection with the nearest, non-tunnel
370   neighbor, only to the end-points of the chain, or to all connections
371   along the chain. Although the diagram is linear, each participant may
372   be engaged in multiple, simultaneous communications. For example, B
373   may be receiving requests from many clients other than A, and/or
374   forwarding requests to servers other than C, at the same time that it
375   is handling A's request.
378   Any party to the communication which is not acting as a tunnel may
379   employ an internal cache for handling requests. The effect of a cache
380   is that the request/response chain is shortened if one of the
381   participants along the chain has a cached response applicable to that
382   request. The following illustrates the resulting chain if B has a
383   cached copy of an earlier response from O (via C) for a request which
384   has not been cached by UA or A.
386<figure><artwork type="drawing">
387          request chain ----------&gt;
388       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
389          &lt;--------- response chain
392   Not all responses are usefully cacheable, and some requests may
393   contain modifiers which place special requirements on cache behavior.
394   HTTP requirements for cache behavior and cacheable responses are
395   defined in &caching;.
398   In fact, there are a wide variety of architectures and configurations
399   of caches and proxies currently being experimented with or deployed
400   across the World Wide Web. These systems include national hierarchies
401   of proxy caches to save transoceanic bandwidth, systems that
402   broadcast or multicast cache entries, organizations that distribute
403   subsets of cached data via CD-ROM, and so on. HTTP systems are used
404   in corporate intranets over high-bandwidth links, and for access via
405   PDAs with low-power radio links and intermittent connectivity. The
406   goal of HTTP/1.1 is to support the wide diversity of configurations
407   already deployed while introducing protocol constructs that meet the
408   needs of those who build web applications that require high
409   reliability and, failing that, at least reliable indications of
410   failure.
413   HTTP communication usually takes place over TCP/IP connections. The
414   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
415   not preclude HTTP from being implemented on top of any other protocol
416   on the Internet, or on other networks. HTTP only presumes a reliable
417   transport; any protocol that provides such guarantees can be used;
418   the mapping of the HTTP/1.1 request and response structures onto the
419   transport data units of the protocol in question is outside the scope
420   of this specification.
423   In HTTP/1.0, most implementations used a new connection for each
424   request/response exchange. In HTTP/1.1, a connection may be used for
425   one or more request/response exchanges, although connections may be
426   closed for a variety of reasons (see <xref target="persistent.connections"/>).
431<section title="Notational Conventions and Generic Grammar" anchor="notation">
433<section title="Augmented BNF" anchor="notation.abnf">
435   All of the mechanisms specified in this document are described in
436   both prose and an augmented Backus-Naur Form (ABNF) based on that
437   defined in <xref target="RFC5234"/>. Implementors will need to be
438   familiar with the notation in order to understand this specification. The
439   extensions to ABNF used in this specification are described below.
442<section title="#rule">
443  <t>
444    A construct "#" is defined, similar to "*", for defining lists of
445    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
446    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
447    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
448    form of lists very easy; a rule such as
449    <figure><artwork type="example">
450 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
451  </t>
452  <t>
453    can be shown as
454    <figure><artwork type="example">
455 1#element</artwork></figure>
456  </t>
457  <t>
458    Wherever this construct is used, null elements are allowed, but do
459    not contribute to the count of elements present. That is,
460    "(element), , (element) " is permitted, but counts as only two
461    elements. Therefore, where at least one element is required, at
462    least one non-null element &MUST; be present. Default values are 0
463    and infinity so that "#element" allows any number, including zero;
464    "1#element" requires at least one; and "1#2element" allows one or
465    two.
466  </t>
469<section title="implied *LWS" anchor="implied.LWS">
470  <iref item="implied *LWS" primary="true"/>
471    <t>
472      The grammar described by this specification is word-based. Except
473      where noted otherwise, linear white space (LWS) can be included
474      between any two adjacent words (token or quoted-string), and
475      between adjacent words and separators, without changing the
476      interpretation of a field. At least one delimiter (LWS and/or
477      separators) &MUST; exist between any two tokens (for the definition
478      of "token" below), since they would otherwise be interpreted as a
479      single token.
480    </t>
484<section title="Basic Rules" anchor="basic.rules">
485<t anchor="core.rules">
486  <x:anchor-alias value="OCTET"/>
487  <x:anchor-alias value="CHAR"/>
488  <x:anchor-alias value="ALPHA"/>
489  <x:anchor-alias value="DIGIT"/>
490  <x:anchor-alias value="CTL"/>
491  <x:anchor-alias value="CR"/>
492  <x:anchor-alias value="LF"/>
493  <x:anchor-alias value="SP"/>
494  <x:anchor-alias value="HTAB"/>
495  <x:anchor-alias value="DQUOTE"/>
496   The following rules are used throughout this specification to
497   describe basic parsing constructs. The US-ASCII coded character set
498   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
500<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"/>
501  <x:ref>OCTET</x:ref>          = %x00-FF
502                   ; any 8-bit sequence of data
503  <x:ref>CHAR</x:ref>           = %x01-7F
504                   ; any US-ASCII character, excluding NUL
505  <x:ref>ALPHA</x:ref>          = %x41-5A / %x61-7A
506                   ; A-Z / a-z
507  <x:ref>DIGIT</x:ref>          = %x30-39
508                   ; any US-ASCII digit "0".."9"
509  <x:ref>CTL</x:ref>            = %x00-1F / %x7F
510                   ; (octets 0 - 31) and DEL (127)
511  <x:ref>CR</x:ref>             = %x0D
512                   ; US-ASCII CR, carriage return (13)
513  <x:ref>LF</x:ref>             = %x0A
514                   ; US-ASCII LF, linefeed (10)
515  <x:ref>SP</x:ref>             = %x20
516                   ; US-ASCII SP, space (32)
517  <x:ref>HTAB</x:ref>           = %x09
518                   ; US-ASCII HT, horizontal-tab (9)
519  <x:ref>DQUOTE</x:ref>         = %x22
520                   ; US-ASCII double-quote mark (34)
522<t anchor="rule.CRLF">
523  <x:anchor-alias value="CRLF"/>
524   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
525   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
526   tolerant applications). The end-of-line marker within an entity-body
527   is defined by its associated media type, as described in &media-types;.
529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
530  <x:ref>CRLF</x:ref>           = <x:ref>CR</x:ref> LF
532<t anchor="rule.LWS">
533  <x:anchor-alias value="LWS"/>
534   HTTP/1.1 header field values can be folded onto multiple lines if the
535   continuation line begins with a space or horizontal tab. All linear
536   white space, including folding, has the same semantics as SP. A
537   recipient &MAY; replace any linear white space with a single SP before
538   interpreting the field value or forwarding the message downstream.
540<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
541  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
543<t anchor="rule.TEXT">
544  <x:anchor-alias value="TEXT"/>
545   The TEXT rule is only used for descriptive field contents and values
546   that are not intended to be interpreted by the message parser. Words
547   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
548   <xref target="ISO-8859-1"/> only when encoded according to the rules of
549   <xref target="RFC2047"/>.
551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
552  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
553                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
556   A CRLF is allowed in the definition of TEXT only as part of a header
557   field continuation. It is expected that the folding LWS will be
558   replaced with a single SP before interpretation of the TEXT value.
560<t anchor="rule.HEXDIG">
561  <x:anchor-alias value="HEXDIG"/>
562   Hexadecimal numeric characters are used in several protocol elements.
564<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEXDIG"/>
565  <x:ref>HEXDIG</x:ref>         = "A" / "B" / "C" / "D" / "E" / "F"
566                 / "a" / "b" / "c" / "d" / "e" / "f" / <x:ref>DIGIT</x:ref>
568<t anchor="rule.token.separators">
569  <x:anchor-alias value="tchar"/>
570  <x:anchor-alias value="token"/>
571  <x:anchor-alias value="separators"/>
572   Many HTTP/1.1 header field values consist of words separated by LWS
573   or special characters. These special characters &MUST; be in a quoted
574   string to be used within a parameter value (as defined in
575   <xref target="transfer.codings"/>).
577<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"/>
578  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
579                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
580                 / "/" / "[" / "]" / "?" / "="
581                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
583  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
584                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
585                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
586                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
588  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
590<t anchor="rule.comment">
591  <x:anchor-alias value="comment"/>
592  <x:anchor-alias value="ctext"/>
593   Comments can be included in some HTTP header fields by surrounding
594   the comment text with parentheses. Comments are only allowed in
595   fields containing "comment" as part of their field value definition.
596   In all other fields, parentheses are considered part of the field
597   value.
599<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
600  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
601  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
603<t anchor="rule.quoted-string">
604  <x:anchor-alias value="quoted-string"/>
605  <x:anchor-alias value="qdtext"/>
606   A string of text is parsed as a single word if it is quoted using
607   double-quote marks.
609<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
610  <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> )
611  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
613<t anchor="rule.quoted-pair">
614  <x:anchor-alias value="quoted-pair"/>
615  <x:anchor-alias value="quoted-text"/>
616   The backslash character ("\") &MAY; be used as a single-character
617   quoting mechanism only within quoted-string and comment constructs.
619<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
620  <x:ref>quoted-text</x:ref>    = %x01-09 /
621                   %x0B-0C /
622                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
623  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
627<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
628  <x:anchor-alias value="request-header"/>
629  <x:anchor-alias value="response-header"/>
630  <x:anchor-alias value="accept-params"/>
631  <x:anchor-alias value="entity-body"/>
632  <x:anchor-alias value="entity-header"/>
633  <x:anchor-alias value="Cache-Control"/>
634  <x:anchor-alias value="Pragma"/>
635  <x:anchor-alias value="Warning"/>
637  The ABNF rules below are defined in other parts:
639<figure><!-- Part2--><artwork type="abnf2616">
640  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
641  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
643<figure><!-- Part3--><artwork type="abnf2616">
644  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
645  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
646  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
648<figure><!-- Part6--><artwork type="abnf2616">
649  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
650  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
651  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
657<section title="Protocol Parameters" anchor="protocol.parameters">
659<section title="HTTP Version" anchor="http.version">
660  <x:anchor-alias value="HTTP-Version"/>
661  <x:anchor-alias value="HTTP-Prot-Name"/>
663   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
664   of the protocol. The protocol versioning policy is intended to allow
665   the sender to indicate the format of a message and its capacity for
666   understanding further HTTP communication, rather than the features
667   obtained via that communication. No change is made to the version
668   number for the addition of message components which do not affect
669   communication behavior or which only add to extensible field values.
670   The &lt;minor&gt; number is incremented when the changes made to the
671   protocol add features which do not change the general message parsing
672   algorithm, but which may add to the message semantics and imply
673   additional capabilities of the sender. The &lt;major&gt; number is
674   incremented when the format of a message within the protocol is
675   changed. See <xref target="RFC2145"/> for a fuller explanation.
678   The version of an HTTP message is indicated by an HTTP-Version field
679   in the first line of the message. HTTP-Version is case-sensitive.
681<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
682  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
683  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
686   Note that the major and minor numbers &MUST; be treated as separate
687   integers and that each &MAY; be incremented higher than a single digit.
688   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
689   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
690   &MUST-NOT; be sent.
693   An application that sends a request or response message that includes
694   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
695   with this specification. Applications that are at least conditionally
696   compliant with this specification &SHOULD; use an HTTP-Version of
697   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
698   not compatible with HTTP/1.0. For more details on when to send
699   specific HTTP-Version values, see <xref target="RFC2145"/>.
702   The HTTP version of an application is the highest HTTP version for
703   which the application is at least conditionally compliant.
706   Proxy and gateway applications need to be careful when forwarding
707   messages in protocol versions different from that of the application.
708   Since the protocol version indicates the protocol capability of the
709   sender, a proxy/gateway &MUST-NOT; send a message with a version
710   indicator which is greater than its actual version. If a higher
711   version request is received, the proxy/gateway &MUST; either downgrade
712   the request version, or respond with an error, or switch to tunnel
713   behavior.
716   Due to interoperability problems with HTTP/1.0 proxies discovered
717   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
718   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
719   they support. The proxy/gateway's response to that request &MUST; be in
720   the same major version as the request.
723  <list>
724    <t>
725      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
726      of header fields required or forbidden by the versions involved.
727    </t>
728  </list>
732<section title="Uniform Resource Identifiers" anchor="uri">
734   URIs have been known by many names: WWW addresses, Universal Document
735   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
736   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
737   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
738   simply formatted strings which identify--via name, location, or any
739   other characteristic--a resource.
742<section title="General Syntax" anchor="general.syntax">
743  <x:anchor-alias value="absoluteURI"/>
744  <x:anchor-alias value="authority"/>
745  <x:anchor-alias value="fragment"/>
746  <x:anchor-alias value="path-absolute"/>
747  <x:anchor-alias value="port"/>
748  <x:anchor-alias value="query"/>
749  <x:anchor-alias value="relativeURI"/>
750  <x:anchor-alias value="uri-host"/>
752   URIs in HTTP can be represented in absolute form or relative to some
753   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
754   forms are differentiated by the fact that absolute URIs always begin
755   with a scheme name followed by a colon. For definitive information on
756   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
757   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
758   and <xref target="RFC1808"/>). This specification adopts the
759   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
760   "host", "abs_path", "query", and "authority" from that specification:
762<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"/>
763  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
764  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
765  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
766  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
767  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
768  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
769  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
770  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
773   HTTP does not place any a priori limit on the length of
774   a URI. Servers &MUST; be able to handle the URI of any resource they
775   serve, and &SHOULD; be able to handle URIs of unbounded length if they
776   provide GET-based forms that could generate such URIs. A server
777   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
778   than the server can handle (see &status-414;).
781  <list>
782    <t>
783      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
784      above 255 bytes, because some older client or proxy
785      implementations might not properly support these lengths.
786    </t>
787  </list>
791<section title="http URL" anchor="http.url">
792  <x:anchor-alias value="http-URL"/>
793  <iref item="http URI scheme" primary="true"/>
794  <iref item="URI scheme" subitem="http" primary="true"/>
796   The "http" scheme is used to locate network resources via the HTTP
797   protocol. This section defines the scheme-specific syntax and
798   semantics for http URLs.
800<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
801  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
802             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
805   If the port is empty or not given, port 80 is assumed. The semantics
806   are that the identified resource is located at the server listening
807   for TCP connections on that port of that host, and the Request-URI
808   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
809   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
810   the path-absolute is not present in the URL, it &MUST; be given as "/" when
811   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
812   receives a host name which is not a fully qualified domain name, it
813   &MAY; add its domain to the host name it received. If a proxy receives
814   a fully qualified domain name, the proxy &MUST-NOT; change the host
815   name.
818  <iref item="https URI scheme"/>
819  <iref item="URI scheme" subitem="https"/>
820  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
824<section title="URI Comparison" anchor="uri.comparison">
826   When comparing two URIs to decide if they match or not, a client
827   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
828   URIs, with these exceptions:
829  <list style="symbols">
830    <t>A port that is empty or not given is equivalent to the default
831        port for that URI-reference;</t>
832    <t>Comparisons of host names &MUST; be case-insensitive;</t>
833    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
834    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
835  </list>
838   Characters other than those in the "reserved" set (see
839   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
840   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
843   For example, the following three URIs are equivalent:
845<figure><artwork type="example">
853<section title="Date/Time Formats" anchor="date.time.formats">
854<section title="Full Date" anchor="">
855  <x:anchor-alias value="HTTP-date"/>
856  <x:anchor-alias value="obsolete-date"/>
857  <x:anchor-alias value="rfc1123-date"/>
858  <x:anchor-alias value="rfc850-date"/>
859  <x:anchor-alias value="asctime-date"/>
860  <x:anchor-alias value="date1"/>
861  <x:anchor-alias value="date2"/>
862  <x:anchor-alias value="date3"/>
863  <x:anchor-alias value="rfc1123-date"/>
864  <x:anchor-alias value="time"/>
865  <x:anchor-alias value="wkday"/>
866  <x:anchor-alias value="weekday"/>
867  <x:anchor-alias value="month"/>
869   HTTP applications have historically allowed three different formats
870   for the representation of date/time stamps:
872<figure><artwork type="example">
873   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
874   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
875   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
878   The first format is preferred as an Internet standard and represents
879   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
880   <xref target="RFC822"/>). The other formats are described here only for
881   compatibility with obsolete implementations.
882   HTTP/1.1 clients and servers that parse the date value &MUST; accept
883   all three formats (for compatibility with HTTP/1.0), though they &MUST;
884   only generate the RFC 1123 format for representing HTTP-date values
885   in header fields. See <xref target="tolerant.applications"/> for further information.
888      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
889      accepting date values that may have been sent by non-HTTP
890      applications, as is sometimes the case when retrieving or posting
891      messages via proxies/gateways to SMTP or NNTP.
894   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
895   (GMT), without exception. For the purposes of HTTP, GMT is exactly
896   equal to UTC (Coordinated Universal Time). This is indicated in the
897   first two formats by the inclusion of "GMT" as the three-letter
898   abbreviation for time zone, and &MUST; be assumed when reading the
899   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
900   additional LWS beyond that specifically included as SP in the
901   grammar.
903<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"/>
904  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
905  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
906  <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
907  <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
908  <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>
909  <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>
910                 ; day month year (e.g., 02 Jun 1982)
911  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
912                 ; day-month-year (e.g., 02-Jun-82)
913  <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> ))
914                 ; month day (e.g., Jun  2)
915  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
916                 ; 00:00:00 - 23:59:59
917  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
918               / s-Thu / s-Fri / s-Sat / s-Sun
919  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
920               / l-Thu / l-Fri / l-Sat / l-Sun
921  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
922               / s-May / s-Jun / s-Jul / s-Aug
923               / s-Sep / s-Oct / s-Nov / s-Dec
925  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
927  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
928  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
929  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
930  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
931  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
932  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
933  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
935  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
936  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
937  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
938  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
939  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
940  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
941  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
943  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
944  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
945  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
946  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
947  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
948  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
949  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
950  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
951  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
952  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
953  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
954  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
957      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
958      to their usage within the protocol stream. Clients and servers are
959      not required to use these formats for user presentation, request
960      logging, etc.
965<section title="Transfer Codings" anchor="transfer.codings">
966  <x:anchor-alias value="parameter"/>
967  <x:anchor-alias value="transfer-coding"/>
968  <x:anchor-alias value="transfer-extension"/>
970   Transfer-coding values are used to indicate an encoding
971   transformation that has been, can be, or may need to be applied to an
972   entity-body in order to ensure "safe transport" through the network.
973   This differs from a content coding in that the transfer-coding is a
974   property of the message, not of the original entity.
976<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
977  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
978  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
980<t anchor="rule.parameter">
981  <x:anchor-alias value="attribute"/>
982  <x:anchor-alias value="parameter"/>
983  <x:anchor-alias value="value"/>
984   Parameters are in  the form of attribute/value pairs.
986<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"/>
987  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
988  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
989  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
992   All transfer-coding values are case-insensitive. HTTP/1.1 uses
993   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
994   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
997   Whenever a transfer-coding is applied to a message-body, the set of
998   transfer-codings &MUST; include "chunked", unless the message indicates it
999   is terminated by closing the connection. When the "chunked" transfer-coding
1000   is used, it &MUST; be the last transfer-coding applied to the
1001   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1002   than once to a message-body. These rules allow the recipient to
1003   determine the transfer-length of the message (<xref target="message.length"/>).
1006   Transfer-codings are analogous to the Content-Transfer-Encoding
1007   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1008   binary data over a 7-bit transport service. However, safe transport
1009   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1010   the only unsafe characteristic of message-bodies is the difficulty in
1011   determining the exact body length (<xref target="message.length"/>), or the desire to
1012   encrypt data over a shared transport.
1015   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1016   transfer-coding value tokens. Initially, the registry contains the
1017   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1018   "gzip", "compress", and "deflate" (&content-codings;).
1021   New transfer-coding value tokens &SHOULD; be registered in the same way
1022   as new content-coding value tokens (&content-codings;).
1025   A server which receives an entity-body with a transfer-coding it does
1026   not understand &SHOULD; return 501 (Not Implemented), and close the
1027   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1028   client.
1031<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1032  <x:anchor-alias value="chunk"/>
1033  <x:anchor-alias value="Chunked-Body"/>
1034  <x:anchor-alias value="chunk-data"/>
1035  <x:anchor-alias value="chunk-extension"/>
1036  <x:anchor-alias value="chunk-ext-name"/>
1037  <x:anchor-alias value="chunk-ext-val"/>
1038  <x:anchor-alias value="chunk-size"/>
1039  <x:anchor-alias value="last-chunk"/>
1040  <x:anchor-alias value="trailer-part"/>
1042   The chunked encoding modifies the body of a message in order to
1043   transfer it as a series of chunks, each with its own size indicator,
1044   followed by an &OPTIONAL; trailer containing entity-header fields. This
1045   allows dynamically produced content to be transferred along with the
1046   information necessary for the recipient to verify that it has
1047   received the full message.
1049<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"/>
1050  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1051                   <x:ref>last-chunk</x:ref>
1052                   <x:ref>trailer-part</x:ref>
1053                   <x:ref>CRLF</x:ref>
1055  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1056                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1057  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1058  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1060  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1061  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1062  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1063  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1064  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1067   The chunk-size field is a string of hex digits indicating the size of
1068   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1069   zero, followed by the trailer, which is terminated by an empty line.
1072   The trailer allows the sender to include additional HTTP header
1073   fields at the end of the message. The Trailer header field can be
1074   used to indicate which header fields are included in a trailer (see
1075   <xref target="header.trailer"/>).
1078   A server using chunked transfer-coding in a response &MUST-NOT; use the
1079   trailer for any header fields unless at least one of the following is
1080   true:
1081  <list style="numbers">
1082    <t>the request included a TE header field that indicates "trailers" is
1083     acceptable in the transfer-coding of the  response, as described in
1084     <xref target="header.te"/>; or,</t>
1086    <t>the server is the origin server for the response, the trailer
1087     fields consist entirely of optional metadata, and the recipient
1088     could use the message (in a manner acceptable to the origin server)
1089     without receiving this metadata.  In other words, the origin server
1090     is willing to accept the possibility that the trailer fields might
1091     be silently discarded along the path to the client.</t>
1092  </list>
1095   This requirement prevents an interoperability failure when the
1096   message is being received by an HTTP/1.1 (or later) proxy and
1097   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1098   compliance with the protocol would have necessitated a possibly
1099   infinite buffer on the proxy.
1102   A process for decoding the "chunked" transfer-coding
1103   can be represented in pseudo-code as:
1105<figure><artwork type="code">
1106    length := 0
1107    read chunk-size, chunk-extension (if any) and CRLF
1108    while (chunk-size &gt; 0) {
1109       read chunk-data and CRLF
1110       append chunk-data to entity-body
1111       length := length + chunk-size
1112       read chunk-size and CRLF
1113    }
1114    read entity-header
1115    while (entity-header not empty) {
1116       append entity-header to existing header fields
1117       read entity-header
1118    }
1119    Content-Length := length
1120    Remove "chunked" from Transfer-Encoding
1123   All HTTP/1.1 applications &MUST; be able to receive and decode the
1124   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1125   they do not understand.
1130<section title="Product Tokens" anchor="product.tokens">
1131  <x:anchor-alias value="product"/>
1132  <x:anchor-alias value="product-version"/>
1134   Product tokens are used to allow communicating applications to
1135   identify themselves by software name and version. Most fields using
1136   product tokens also allow sub-products which form a significant part
1137   of the application to be listed, separated by white space. By
1138   convention, the products are listed in order of their significance
1139   for identifying the application.
1141<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1142  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1143  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1146   Examples:
1148<figure><artwork type="example">
1149    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1150    Server: Apache/0.8.4
1153   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1154   used for advertising or other non-essential information. Although any
1155   token character &MAY; appear in a product-version, this token &SHOULD;
1156   only be used for a version identifier (i.e., successive versions of
1157   the same product &SHOULD; only differ in the product-version portion of
1158   the product value).
1164<section title="HTTP Message" anchor="http.message">
1166<section title="Message Types" anchor="message.types">
1167  <x:anchor-alias value="generic-message"/>
1168  <x:anchor-alias value="HTTP-message"/>
1169  <x:anchor-alias value="start-line"/>
1171   HTTP messages consist of requests from client to server and responses
1172   from server to client.
1174<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1175  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1178   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1179   message format of <xref target="RFC5322"/> for transferring entities (the payload
1180   of the message). Both types of message consist of a start-line, zero
1181   or more header fields (also known as "headers"), an empty line (i.e.,
1182   a line with nothing preceding the CRLF) indicating the end of the
1183   header fields, and possibly a message-body.
1185<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1186  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1187                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1188                    <x:ref>CRLF</x:ref>
1189                    [ <x:ref>message-body</x:ref> ]
1190  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1193   In the interest of robustness, servers &SHOULD; ignore any empty
1194   line(s) received where a Request-Line is expected. In other words, if
1195   the server is reading the protocol stream at the beginning of a
1196   message and receives a CRLF first, it should ignore the CRLF.
1199   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1200   after a POST request. To restate what is explicitly forbidden by the
1201   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1202   extra CRLF.
1206<section title="Message Headers" anchor="message.headers">
1207  <x:anchor-alias value="field-content"/>
1208  <x:anchor-alias value="field-name"/>
1209  <x:anchor-alias value="field-value"/>
1210  <x:anchor-alias value="message-header"/>
1212   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1213   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1214   entity-header (&entity-header-fields;) fields, follow the same generic format as
1215   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1216   of a name followed by a colon (":") and the field value. Field names
1217   are case-insensitive. The field value &MAY; be preceded by any amount
1218   of LWS, though a single SP is preferred. Header fields can be
1219   extended over multiple lines by preceding each extra line with at
1220   least one SP or HTAB. Applications ought to follow "common form", where
1221   one is known or indicated, when generating HTTP constructs, since
1222   there might exist some implementations that fail to accept anything
1223   beyond the common forms.
1225<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"/>
1226  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1227  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1228  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1229  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1230                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1231                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1232                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1235   The field-content does not include any leading or trailing LWS:
1236   linear white space occurring before the first non-whitespace
1237   character of the field-value or after the last non-whitespace
1238   character of the field-value. Such leading or trailing LWS &MAY; be
1239   removed without changing the semantics of the field value. Any LWS
1240   that occurs between field-content &MAY; be replaced with a single SP
1241   before interpreting the field value or forwarding the message
1242   downstream.
1245   The order in which header fields with differing field names are
1246   received is not significant. However, it is "good practice" to send
1247   general-header fields first, followed by request-header or response-header
1248   fields, and ending with the entity-header fields.
1251   Multiple message-header fields with the same field-name &MAY; be
1252   present in a message if and only if the entire field-value for that
1253   header field is defined as a comma-separated list [i.e., #(values)].
1254   It &MUST; be possible to combine the multiple header fields into one
1255   "field-name: field-value" pair, without changing the semantics of the
1256   message, by appending each subsequent field-value to the first, each
1257   separated by a comma. The order in which header fields with the same
1258   field-name are received is therefore significant to the
1259   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1260   change the order of these field values when a message is forwarded.
1263  <list><t>
1264   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1265   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1266   can occur multiple times, but does not use the list syntax, and thus cannot
1267   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1268   for details.) Also note that the Set-Cookie2 header specified in
1269   <xref target="RFC2965"/> does not share this problem.
1270  </t></list>
1275<section title="Message Body" anchor="message.body">
1276  <x:anchor-alias value="message-body"/>
1278   The message-body (if any) of an HTTP message is used to carry the
1279   entity-body associated with the request or response. The message-body
1280   differs from the entity-body only when a transfer-coding has been
1281   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1283<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1284  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1285               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1288   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1289   applied by an application to ensure safe and proper transfer of the
1290   message. Transfer-Encoding is a property of the message, not of the
1291   entity, and thus &MAY; be added or removed by any application along the
1292   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1293   when certain transfer-codings may be used.)
1296   The rules for when a message-body is allowed in a message differ for
1297   requests and responses.
1300   The presence of a message-body in a request is signaled by the
1301   inclusion of a Content-Length or Transfer-Encoding header field in
1302   the request's message-headers. A message-body &MUST-NOT; be included in
1303   a request if the specification of the request method (&method;)
1304   explicitly disallows an entity-body in requests.
1305   When a request message contains both a message-body of non-zero
1306   length and a method that does not define any semantics for that
1307   request message-body, then an origin server &SHOULD; either ignore
1308   the message-body or respond with an appropriate error message
1309   (e.g., 413).  A proxy or gateway, when presented the same request,
1310   &SHOULD; either forward the request inbound with the message-body or
1311   ignore the message-body when determining a response.
1314   For response messages, whether or not a message-body is included with
1315   a message is dependent on both the request method and the response
1316   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1317   &MUST-NOT; include a message-body, even though the presence of entity-header
1318   fields might lead one to believe they do. All 1xx
1319   (informational), 204 (No Content), and 304 (Not Modified) responses
1320   &MUST-NOT; include a message-body. All other responses do include a
1321   message-body, although it &MAY; be of zero length.
1325<section title="Message Length" anchor="message.length">
1327   The transfer-length of a message is the length of the message-body as
1328   it appears in the message; that is, after any transfer-codings have
1329   been applied. When a message-body is included with a message, the
1330   transfer-length of that body is determined by one of the following
1331   (in order of precedence):
1334  <list style="numbers">
1335    <x:lt><t>
1336     Any response message which "&MUST-NOT;" include a message-body (such
1337     as the 1xx, 204, and 304 responses and any response to a HEAD
1338     request) is always terminated by the first empty line after the
1339     header fields, regardless of the entity-header fields present in
1340     the message.
1341    </t></x:lt>
1342    <x:lt><t>
1343     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1344     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1345     is used, the transfer-length is defined by the use of this transfer-coding.
1346     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1347     is not present, the transfer-length is defined by the sender closing the connection.
1348    </t></x:lt>
1349    <x:lt><t>
1350     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1351     decimal value in OCTETs represents both the entity-length and the
1352     transfer-length. The Content-Length header field &MUST-NOT; be sent
1353     if these two lengths are different (i.e., if a Transfer-Encoding
1354     header field is present). If a message is received with both a
1355     Transfer-Encoding header field and a Content-Length header field,
1356     the latter &MUST; be ignored.
1357    </t></x:lt>
1358    <x:lt><t>
1359     If the message uses the media type "multipart/byteranges", and the
1360     transfer-length is not otherwise specified, then this self-delimiting
1361     media type defines the transfer-length. This media type
1362     &MUST-NOT; be used unless the sender knows that the recipient can parse
1363     it; the presence in a request of a Range header with multiple byte-range
1364     specifiers from a 1.1 client implies that the client can parse
1365     multipart/byteranges responses.
1366    <list style="empty"><t>
1367       A range header might be forwarded by a 1.0 proxy that does not
1368       understand multipart/byteranges; in this case the server &MUST;
1369       delimit the message using methods defined in items 1, 3 or 5 of
1370       this section.
1371    </t></list>
1372    </t></x:lt>
1373    <x:lt><t>
1374     By the server closing the connection. (Closing the connection
1375     cannot be used to indicate the end of a request body, since that
1376     would leave no possibility for the server to send back a response.)
1377    </t></x:lt>
1378  </list>
1381   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1382   containing a message-body &MUST; include a valid Content-Length header
1383   field unless the server is known to be HTTP/1.1 compliant. If a
1384   request contains a message-body and a Content-Length is not given,
1385   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1386   determine the length of the message, or with 411 (Length Required) if
1387   it wishes to insist on receiving a valid Content-Length.
1390   All HTTP/1.1 applications that receive entities &MUST; accept the
1391   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1392   to be used for messages when the message length cannot be determined
1393   in advance.
1396   Messages &MUST-NOT; include both a Content-Length header field and a
1397   transfer-coding. If the message does include a
1398   transfer-coding, the Content-Length &MUST; be ignored.
1401   When a Content-Length is given in a message where a message-body is
1402   allowed, its field value &MUST; exactly match the number of OCTETs in
1403   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1404   invalid length is received and detected.
1408<section title="General Header Fields" anchor="general.header.fields">
1409  <x:anchor-alias value="general-header"/>
1411   There are a few header fields which have general applicability for
1412   both request and response messages, but which do not apply to the
1413   entity being transferred. These header fields apply only to the
1414   message being transmitted.
1416<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1417  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1418                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1419                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1420                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1421                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1422                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1423                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1424                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1425                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1428   General-header field names can be extended reliably only in
1429   combination with a change in the protocol version. However, new or
1430   experimental header fields may be given the semantics of general
1431   header fields if all parties in the communication recognize them to
1432   be general-header fields. Unrecognized header fields are treated as
1433   entity-header fields.
1438<section title="Request" anchor="request">
1439  <x:anchor-alias value="Request"/>
1441   A request message from a client to a server includes, within the
1442   first line of that message, the method to be applied to the resource,
1443   the identifier of the resource, and the protocol version in use.
1445<!--                 Host                      ; should be moved here eventually -->
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1447  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1448                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1449                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1450                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1451                  <x:ref>CRLF</x:ref>
1452                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1455<section title="Request-Line" anchor="request-line">
1456  <x:anchor-alias value="Request-Line"/>
1458   The Request-Line begins with a method token, followed by the
1459   Request-URI and the protocol version, and ending with CRLF. The
1460   elements are separated by SP characters. No CR or LF is allowed
1461   except in the final CRLF sequence.
1463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1464  <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>
1467<section title="Method" anchor="method">
1468  <x:anchor-alias value="Method"/>
1470   The Method  token indicates the method to be performed on the
1471   resource identified by the Request-URI. The method is case-sensitive.
1473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1474  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1478<section title="Request-URI" anchor="request-uri">
1479  <x:anchor-alias value="Request-URI"/>
1481   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1482   identifies the resource upon which to apply the request.
1484<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1485  <x:ref>Request-URI</x:ref>    = "*"
1486                 / <x:ref>absoluteURI</x:ref>
1487                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1488                 / <x:ref>authority</x:ref>
1491   The four options for Request-URI are dependent on the nature of the
1492   request. The asterisk "*" means that the request does not apply to a
1493   particular resource, but to the server itself, and is only allowed
1494   when the method used does not necessarily apply to a resource. One
1495   example would be
1497<figure><artwork type="example">
1498    OPTIONS * HTTP/1.1
1501   The absoluteURI form is &REQUIRED; when the request is being made to a
1502   proxy. The proxy is requested to forward the request or service it
1503   from a valid cache, and return the response. Note that the proxy &MAY;
1504   forward the request on to another proxy or directly to the server
1505   specified by the absoluteURI. In order to avoid request loops, a
1506   proxy &MUST; be able to recognize all of its server names, including
1507   any aliases, local variations, and the numeric IP address. An example
1508   Request-Line would be:
1510<figure><artwork type="example">
1511    GET HTTP/1.1
1514   To allow for transition to absoluteURIs in all requests in future
1515   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1516   form in requests, even though HTTP/1.1 clients will only generate
1517   them in requests to proxies.
1520   The authority form is only used by the CONNECT method (&CONNECT;).
1523   The most common form of Request-URI is that used to identify a
1524   resource on an origin server or gateway. In this case the absolute
1525   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1526   the Request-URI, and the network location of the URI (authority) &MUST;
1527   be transmitted in a Host header field. For example, a client wishing
1528   to retrieve the resource above directly from the origin server would
1529   create a TCP connection to port 80 of the host "" and send
1530   the lines:
1532<figure><artwork type="example">
1533    GET /pub/WWW/TheProject.html HTTP/1.1
1534    Host:
1537   followed by the remainder of the Request. Note that the absolute path
1538   cannot be empty; if none is present in the original URI, it &MUST; be
1539   given as "/" (the server root).
1542   The Request-URI is transmitted in the format specified in
1543   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1544   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1545   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1546   &MUST; decode the Request-URI in order to
1547   properly interpret the request. Servers &SHOULD; respond to invalid
1548   Request-URIs with an appropriate status code.
1551   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1552   received Request-URI when forwarding it to the next inbound server,
1553   except as noted above to replace a null path-absolute with "/".
1556  <list><t>
1557      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1558      meaning of the request when the origin server is improperly using
1559      a non-reserved URI character for a reserved purpose.  Implementors
1560      should be aware that some pre-HTTP/1.1 proxies have been known to
1561      rewrite the Request-URI.
1562  </t></list>
1567<section title="The Resource Identified by a Request" anchor="">
1569   The exact resource identified by an Internet request is determined by
1570   examining both the Request-URI and the Host header field.
1573   An origin server that does not allow resources to differ by the
1574   requested host &MAY; ignore the Host header field value when
1575   determining the resource identified by an HTTP/1.1 request. (But see
1576   <xref target=""/>
1577   for other requirements on Host support in HTTP/1.1.)
1580   An origin server that does differentiate resources based on the host
1581   requested (sometimes referred to as virtual hosts or vanity host
1582   names) &MUST; use the following rules for determining the requested
1583   resource on an HTTP/1.1 request:
1584  <list style="numbers">
1585    <t>If Request-URI is an absoluteURI, the host is part of the
1586     Request-URI. Any Host header field value in the request &MUST; be
1587     ignored.</t>
1588    <t>If the Request-URI is not an absoluteURI, and the request includes
1589     a Host header field, the host is determined by the Host header
1590     field value.</t>
1591    <t>If the host as determined by rule 1 or 2 is not a valid host on
1592     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1593  </list>
1596   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1597   attempt to use heuristics (e.g., examination of the URI path for
1598   something unique to a particular host) in order to determine what
1599   exact resource is being requested.
1606<section title="Response" anchor="response">
1607  <x:anchor-alias value="Response"/>
1609   After receiving and interpreting a request message, a server responds
1610   with an HTTP response message.
1612<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1613  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1614                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1615                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1616                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1617                  <x:ref>CRLF</x:ref>
1618                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1621<section title="Status-Line" anchor="status-line">
1622  <x:anchor-alias value="Status-Line"/>
1624   The first line of a Response message is the Status-Line, consisting
1625   of the protocol version followed by a numeric status code and its
1626   associated textual phrase, with each element separated by SP
1627   characters. No CR or LF is allowed except in the final CRLF sequence.
1629<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1630  <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>
1633<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1634  <x:anchor-alias value="Reason-Phrase"/>
1635  <x:anchor-alias value="Status-Code"/>
1637   The Status-Code element is a 3-digit integer result code of the
1638   attempt to understand and satisfy the request. These codes are fully
1639   defined in &status-codes;.  The Reason Phrase exists for the sole
1640   purpose of providing a textual description associated with the numeric
1641   status code, out of deference to earlier Internet application protocols
1642   that were more frequently used with interactive text clients.
1643   A client &SHOULD; ignore the content of the Reason Phrase.
1646   The first digit of the Status-Code defines the class of response. The
1647   last two digits do not have any categorization role. There are 5
1648   values for the first digit:
1649  <list style="symbols">
1650    <t>
1651      1xx: Informational - Request received, continuing process
1652    </t>
1653    <t>
1654      2xx: Success - The action was successfully received,
1655        understood, and accepted
1656    </t>
1657    <t>
1658      3xx: Redirection - Further action must be taken in order to
1659        complete the request
1660    </t>
1661    <t>
1662      4xx: Client Error - The request contains bad syntax or cannot
1663        be fulfilled
1664    </t>
1665    <t>
1666      5xx: Server Error - The server failed to fulfill an apparently
1667        valid request
1668    </t>
1669  </list>
1671<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"/>
1672  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1673  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1681<section title="Connections" anchor="connections">
1683<section title="Persistent Connections" anchor="persistent.connections">
1685<section title="Purpose" anchor="persistent.purpose">
1687   Prior to persistent connections, a separate TCP connection was
1688   established to fetch each URL, increasing the load on HTTP servers
1689   and causing congestion on the Internet. The use of inline images and
1690   other associated data often require a client to make multiple
1691   requests of the same server in a short amount of time. Analysis of
1692   these performance problems and results from a prototype
1693   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1694   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1695   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1696   T/TCP <xref target="Tou1998"/>.
1699   Persistent HTTP connections have a number of advantages:
1700  <list style="symbols">
1701      <t>
1702        By opening and closing fewer TCP connections, CPU time is saved
1703        in routers and hosts (clients, servers, proxies, gateways,
1704        tunnels, or caches), and memory used for TCP protocol control
1705        blocks can be saved in hosts.
1706      </t>
1707      <t>
1708        HTTP requests and responses can be pipelined on a connection.
1709        Pipelining allows a client to make multiple requests without
1710        waiting for each response, allowing a single TCP connection to
1711        be used much more efficiently, with much lower elapsed time.
1712      </t>
1713      <t>
1714        Network congestion is reduced by reducing the number of packets
1715        caused by TCP opens, and by allowing TCP sufficient time to
1716        determine the congestion state of the network.
1717      </t>
1718      <t>
1719        Latency on subsequent requests is reduced since there is no time
1720        spent in TCP's connection opening handshake.
1721      </t>
1722      <t>
1723        HTTP can evolve more gracefully, since errors can be reported
1724        without the penalty of closing the TCP connection. Clients using
1725        future versions of HTTP might optimistically try a new feature,
1726        but if communicating with an older server, retry with old
1727        semantics after an error is reported.
1728      </t>
1729    </list>
1732   HTTP implementations &SHOULD; implement persistent connections.
1736<section title="Overall Operation" anchor="persistent.overall">
1738   A significant difference between HTTP/1.1 and earlier versions of
1739   HTTP is that persistent connections are the default behavior of any
1740   HTTP connection. That is, unless otherwise indicated, the client
1741   &SHOULD; assume that the server will maintain a persistent connection,
1742   even after error responses from the server.
1745   Persistent connections provide a mechanism by which a client and a
1746   server can signal the close of a TCP connection. This signaling takes
1747   place using the Connection header field (<xref target="header.connection"/>). Once a close
1748   has been signaled, the client &MUST-NOT; send any more requests on that
1749   connection.
1752<section title="Negotiation" anchor="persistent.negotiation">
1754   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1755   maintain a persistent connection unless a Connection header including
1756   the connection-token "close" was sent in the request. If the server
1757   chooses to close the connection immediately after sending the
1758   response, it &SHOULD; send a Connection header including the
1759   connection-token close.
1762   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1763   decide to keep it open based on whether the response from a server
1764   contains a Connection header with the connection-token close. In case
1765   the client does not want to maintain a connection for more than that
1766   request, it &SHOULD; send a Connection header including the
1767   connection-token close.
1770   If either the client or the server sends the close token in the
1771   Connection header, that request becomes the last one for the
1772   connection.
1775   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1776   maintained for HTTP versions less than 1.1 unless it is explicitly
1777   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1778   compatibility with HTTP/1.0 clients.
1781   In order to remain persistent, all messages on the connection &MUST;
1782   have a self-defined message length (i.e., one not defined by closure
1783   of the connection), as described in <xref target="message.length"/>.
1787<section title="Pipelining" anchor="pipelining">
1789   A client that supports persistent connections &MAY; "pipeline" its
1790   requests (i.e., send multiple requests without waiting for each
1791   response). A server &MUST; send its responses to those requests in the
1792   same order that the requests were received.
1795   Clients which assume persistent connections and pipeline immediately
1796   after connection establishment &SHOULD; be prepared to retry their
1797   connection if the first pipelined attempt fails. If a client does
1798   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1799   persistent. Clients &MUST; also be prepared to resend their requests if
1800   the server closes the connection before sending all of the
1801   corresponding responses.
1804   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1805   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1806   premature termination of the transport connection could lead to
1807   indeterminate results. A client wishing to send a non-idempotent
1808   request &SHOULD; wait to send that request until it has received the
1809   response status for the previous request.
1814<section title="Proxy Servers" anchor="persistent.proxy">
1816   It is especially important that proxies correctly implement the
1817   properties of the Connection header field as specified in <xref target="header.connection"/>.
1820   The proxy server &MUST; signal persistent connections separately with
1821   its clients and the origin servers (or other proxy servers) that it
1822   connects to. Each persistent connection applies to only one transport
1823   link.
1826   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1827   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1828   discussion of the problems with the Keep-Alive header implemented by
1829   many HTTP/1.0 clients).
1833<section title="Practical Considerations" anchor="persistent.practical">
1835   Servers will usually have some time-out value beyond which they will
1836   no longer maintain an inactive connection. Proxy servers might make
1837   this a higher value since it is likely that the client will be making
1838   more connections through the same server. The use of persistent
1839   connections places no requirements on the length (or existence) of
1840   this time-out for either the client or the server.
1843   When a client or server wishes to time-out it &SHOULD; issue a graceful
1844   close on the transport connection. Clients and servers &SHOULD; both
1845   constantly watch for the other side of the transport close, and
1846   respond to it as appropriate. If a client or server does not detect
1847   the other side's close promptly it could cause unnecessary resource
1848   drain on the network.
1851   A client, server, or proxy &MAY; close the transport connection at any
1852   time. For example, a client might have started to send a new request
1853   at the same time that the server has decided to close the "idle"
1854   connection. From the server's point of view, the connection is being
1855   closed while it was idle, but from the client's point of view, a
1856   request is in progress.
1859   This means that clients, servers, and proxies &MUST; be able to recover
1860   from asynchronous close events. Client software &SHOULD; reopen the
1861   transport connection and retransmit the aborted sequence of requests
1862   without user interaction so long as the request sequence is
1863   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1864   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1865   human operator the choice of retrying the request(s). Confirmation by
1866   user-agent software with semantic understanding of the application
1867   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1868   be repeated if the second sequence of requests fails.
1871   Servers &SHOULD; always respond to at least one request per connection,
1872   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1873   middle of transmitting a response, unless a network or client failure
1874   is suspected.
1877   Clients that use persistent connections &SHOULD; limit the number of
1878   simultaneous connections that they maintain to a given server. A
1879   single-user client &SHOULD-NOT; maintain more than 2 connections with
1880   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1881   another server or proxy, where N is the number of simultaneously
1882   active users. These guidelines are intended to improve HTTP response
1883   times and avoid congestion.
1888<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1890<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1892   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1893   flow control mechanisms to resolve temporary overloads, rather than
1894   terminating connections with the expectation that clients will retry.
1895   The latter technique can exacerbate network congestion.
1899<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1901   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1902   the network connection for an error status while it is transmitting
1903   the request. If the client sees an error status, it &SHOULD;
1904   immediately cease transmitting the body. If the body is being sent
1905   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1906   empty trailer &MAY; be used to prematurely mark the end of the message.
1907   If the body was preceded by a Content-Length header, the client &MUST;
1908   close the connection.
1912<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1914   The purpose of the 100 (Continue) status (see &status-100;) is to
1915   allow a client that is sending a request message with a request body
1916   to determine if the origin server is willing to accept the request
1917   (based on the request headers) before the client sends the request
1918   body. In some cases, it might either be inappropriate or highly
1919   inefficient for the client to send the body if the server will reject
1920   the message without looking at the body.
1923   Requirements for HTTP/1.1 clients:
1924  <list style="symbols">
1925    <t>
1926        If a client will wait for a 100 (Continue) response before
1927        sending the request body, it &MUST; send an Expect request-header
1928        field (&header-expect;) with the "100-continue" expectation.
1929    </t>
1930    <t>
1931        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1932        with the "100-continue" expectation if it does not intend
1933        to send a request body.
1934    </t>
1935  </list>
1938   Because of the presence of older implementations, the protocol allows
1939   ambiguous situations in which a client may send "Expect: 100-continue"
1940   without receiving either a 417 (Expectation Failed) status
1941   or a 100 (Continue) status. Therefore, when a client sends this
1942   header field to an origin server (possibly via a proxy) from which it
1943   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1944   for an indefinite period before sending the request body.
1947   Requirements for HTTP/1.1 origin servers:
1948  <list style="symbols">
1949    <t> Upon receiving a request which includes an Expect request-header
1950        field with the "100-continue" expectation, an origin server &MUST;
1951        either respond with 100 (Continue) status and continue to read
1952        from the input stream, or respond with a final status code. The
1953        origin server &MUST-NOT; wait for the request body before sending
1954        the 100 (Continue) response. If it responds with a final status
1955        code, it &MAY; close the transport connection or it &MAY; continue
1956        to read and discard the rest of the request.  It &MUST-NOT;
1957        perform the requested method if it returns a final status code.
1958    </t>
1959    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1960        the request message does not include an Expect request-header
1961        field with the "100-continue" expectation, and &MUST-NOT; send a
1962        100 (Continue) response if such a request comes from an HTTP/1.0
1963        (or earlier) client. There is an exception to this rule: for
1964        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1965        status in response to an HTTP/1.1 PUT or POST request that does
1966        not include an Expect request-header field with the "100-continue"
1967        expectation. This exception, the purpose of which is
1968        to minimize any client processing delays associated with an
1969        undeclared wait for 100 (Continue) status, applies only to
1970        HTTP/1.1 requests, and not to requests with any other HTTP-version
1971        value.
1972    </t>
1973    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1974        already received some or all of the request body for the
1975        corresponding request.
1976    </t>
1977    <t> An origin server that sends a 100 (Continue) response &MUST;
1978    ultimately send a final status code, once the request body is
1979        received and processed, unless it terminates the transport
1980        connection prematurely.
1981    </t>
1982    <t> If an origin server receives a request that does not include an
1983        Expect request-header field with the "100-continue" expectation,
1984        the request includes a request body, and the server responds
1985        with a final status code before reading the entire request body
1986        from the transport connection, then the server &SHOULD-NOT;  close
1987        the transport connection until it has read the entire request,
1988        or until the client closes the connection. Otherwise, the client
1989        might not reliably receive the response message. However, this
1990        requirement is not be construed as preventing a server from
1991        defending itself against denial-of-service attacks, or from
1992        badly broken client implementations.
1993      </t>
1994    </list>
1997   Requirements for HTTP/1.1 proxies:
1998  <list style="symbols">
1999    <t> If a proxy receives a request that includes an Expect request-header
2000        field with the "100-continue" expectation, and the proxy
2001        either knows that the next-hop server complies with HTTP/1.1 or
2002        higher, or does not know the HTTP version of the next-hop
2003        server, it &MUST; forward the request, including the Expect header
2004        field.
2005    </t>
2006    <t> If the proxy knows that the version of the next-hop server is
2007        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2008        respond with a 417 (Expectation Failed) status.
2009    </t>
2010    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2011        numbers received from recently-referenced next-hop servers.
2012    </t>
2013    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2014        request message was received from an HTTP/1.0 (or earlier)
2015        client and did not include an Expect request-header field with
2016        the "100-continue" expectation. This requirement overrides the
2017        general rule for forwarding of 1xx responses (see &status-1xx;).
2018    </t>
2019  </list>
2023<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2025   If an HTTP/1.1 client sends a request which includes a request body,
2026   but which does not include an Expect request-header field with the
2027   "100-continue" expectation, and if the client is not directly
2028   connected to an HTTP/1.1 origin server, and if the client sees the
2029   connection close before receiving any status from the server, the
2030   client &SHOULD; retry the request.  If the client does retry this
2031   request, it &MAY; use the following "binary exponential backoff"
2032   algorithm to be assured of obtaining a reliable response:
2033  <list style="numbers">
2034    <t>
2035      Initiate a new connection to the server
2036    </t>
2037    <t>
2038      Transmit the request-headers
2039    </t>
2040    <t>
2041      Initialize a variable R to the estimated round-trip time to the
2042         server (e.g., based on the time it took to establish the
2043         connection), or to a constant value of 5 seconds if the round-trip
2044         time is not available.
2045    </t>
2046    <t>
2047       Compute T = R * (2**N), where N is the number of previous
2048         retries of this request.
2049    </t>
2050    <t>
2051       Wait either for an error response from the server, or for T
2052         seconds (whichever comes first)
2053    </t>
2054    <t>
2055       If no error response is received, after T seconds transmit the
2056         body of the request.
2057    </t>
2058    <t>
2059       If client sees that the connection is closed prematurely,
2060         repeat from step 1 until the request is accepted, an error
2061         response is received, or the user becomes impatient and
2062         terminates the retry process.
2063    </t>
2064  </list>
2067   If at any point an error status is received, the client
2068  <list style="symbols">
2069      <t>&SHOULD-NOT;  continue and</t>
2071      <t>&SHOULD; close the connection if it has not completed sending the
2072        request message.</t>
2073    </list>
2080<section title="Header Field Definitions" anchor="header.fields">
2082   This section defines the syntax and semantics of HTTP/1.1 header fields
2083   related to message framing and transport protocols.
2086   For entity-header fields, both sender and recipient refer to either the
2087   client or the server, depending on who sends and who receives the entity.
2090<section title="Connection" anchor="header.connection">
2091  <iref primary="true" item="Connection header" x:for-anchor=""/>
2092  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2093  <x:anchor-alias value="Connection"/>
2094  <x:anchor-alias value="connection-token"/>
2096   The Connection general-header field allows the sender to specify
2097   options that are desired for that particular connection and &MUST-NOT;
2098   be communicated by proxies over further connections.
2101   The Connection header has the following grammar:
2103<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2104  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2105  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2108   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2109   message is forwarded and, for each connection-token in this field,
2110   remove any header field(s) from the message with the same name as the
2111   connection-token. Connection options are signaled by the presence of
2112   a connection-token in the Connection header field, not by any
2113   corresponding additional header field(s), since the additional header
2114   field may not be sent if there are no parameters associated with that
2115   connection option.
2118   Message headers listed in the Connection header &MUST-NOT; include
2119   end-to-end headers, such as Cache-Control.
2122   HTTP/1.1 defines the "close" connection option for the sender to
2123   signal that the connection will be closed after completion of the
2124   response. For example,
2126<figure><artwork type="example">
2127    Connection: close
2130   in either the request or the response header fields indicates that
2131   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2132   after the current request/response is complete.
2135   An HTTP/1.1 client that does not support persistent connections &MUST;
2136   include the "close" connection option in every request message.
2139   An HTTP/1.1 server that does not support persistent connections &MUST;
2140   include the "close" connection option in every response message that
2141   does not have a 1xx (informational) status code.
2144   A system receiving an HTTP/1.0 (or lower-version) message that
2145   includes a Connection header &MUST;, for each connection-token in this
2146   field, remove and ignore any header field(s) from the message with
2147   the same name as the connection-token. This protects against mistaken
2148   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2152<section title="Content-Length" anchor="header.content-length">
2153  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2154  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2155  <x:anchor-alias value="Content-Length"/>
2157   The Content-Length entity-header field indicates the size of the
2158   entity-body, in decimal number of OCTETs, sent to the recipient or,
2159   in the case of the HEAD method, the size of the entity-body that
2160   would have been sent had the request been a GET.
2162<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2163  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2166   An example is
2168<figure><artwork type="example">
2169    Content-Length: 3495
2172   Applications &SHOULD; use this field to indicate the transfer-length of
2173   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2176   Any Content-Length greater than or equal to zero is a valid value.
2177   <xref target="message.length"/> describes how to determine the length of a message-body
2178   if a Content-Length is not given.
2181   Note that the meaning of this field is significantly different from
2182   the corresponding definition in MIME, where it is an optional field
2183   used within the "message/external-body" content-type. In HTTP, it
2184   &SHOULD; be sent whenever the message's length can be determined prior
2185   to being transferred, unless this is prohibited by the rules in
2186   <xref target="message.length"/>.
2190<section title="Date" anchor="">
2191  <iref primary="true" item="Date header" x:for-anchor=""/>
2192  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2193  <x:anchor-alias value="Date"/>
2195   The Date general-header field represents the date and time at which
2196   the message was originated, having the same semantics as orig-date in
2197   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2198   HTTP-date, as described in <xref target=""/>;
2199   it &MUST; be sent in rfc1123-date format.
2201<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2202  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2205   An example is
2207<figure><artwork type="example">
2208    Date: Tue, 15 Nov 1994 08:12:31 GMT
2211   Origin servers &MUST; include a Date header field in all responses,
2212   except in these cases:
2213  <list style="numbers">
2214      <t>If the response status code is 100 (Continue) or 101 (Switching
2215         Protocols), the response &MAY; include a Date header field, at
2216         the server's option.</t>
2218      <t>If the response status code conveys a server error, e.g. 500
2219         (Internal Server Error) or 503 (Service Unavailable), and it is
2220         inconvenient or impossible to generate a valid Date.</t>
2222      <t>If the server does not have a clock that can provide a
2223         reasonable approximation of the current time, its responses
2224         &MUST-NOT; include a Date header field. In this case, the rules
2225         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2226  </list>
2229   A received message that does not have a Date header field &MUST; be
2230   assigned one by the recipient if the message will be cached by that
2231   recipient or gatewayed via a protocol which requires a Date. An HTTP
2232   implementation without a clock &MUST-NOT; cache responses without
2233   revalidating them on every use. An HTTP cache, especially a shared
2234   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2235   clock with a reliable external standard.
2238   Clients &SHOULD; only send a Date header field in messages that include
2239   an entity-body, as in the case of the PUT and POST requests, and even
2240   then it is optional. A client without a clock &MUST-NOT; send a Date
2241   header field in a request.
2244   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2245   time subsequent to the generation of the message. It &SHOULD; represent
2246   the best available approximation of the date and time of message
2247   generation, unless the implementation has no means of generating a
2248   reasonably accurate date and time. In theory, the date ought to
2249   represent the moment just before the entity is generated. In
2250   practice, the date can be generated at any time during the message
2251   origination without affecting its semantic value.
2254<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2256   Some origin server implementations might not have a clock available.
2257   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2258   values to a response, unless these values were associated
2259   with the resource by a system or user with a reliable clock. It &MAY;
2260   assign an Expires value that is known, at or before server
2261   configuration time, to be in the past (this allows "pre-expiration"
2262   of responses without storing separate Expires values for each
2263   resource).
2268<section title="Host" anchor="">
2269  <iref primary="true" item="Host header" x:for-anchor=""/>
2270  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2271  <x:anchor-alias value="Host"/>
2273   The Host request-header field specifies the Internet host and port
2274   number of the resource being requested, as obtained from the original
2275   URI given by the user or referring resource (generally an HTTP URL,
2276   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2277   the naming authority of the origin server or gateway given by the
2278   original URL. This allows the origin server or gateway to
2279   differentiate between internally-ambiguous URLs, such as the root "/"
2280   URL of a server for multiple host names on a single IP address.
2282<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2283  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2286   A "host" without any trailing port information implies the default
2287   port for the service requested (e.g., "80" for an HTTP URL). For
2288   example, a request on the origin server for
2289   &lt;; would properly include:
2291<figure><artwork type="example">
2292    GET /pub/WWW/ HTTP/1.1
2293    Host:
2296   A client &MUST; include a Host header field in all HTTP/1.1 request
2297   messages. If the requested URI does not include an Internet host
2298   name for the service being requested, then the Host header field &MUST;
2299   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2300   request message it forwards does contain an appropriate Host header
2301   field that identifies the service being requested by the proxy. All
2302   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2303   status code to any HTTP/1.1 request message which lacks a Host header
2304   field.
2307   See Sections <xref target="" format="counter"/>
2308   and <xref target="" format="counter"/>
2309   for other requirements relating to Host.
2313<section title="TE" anchor="header.te">
2314  <iref primary="true" item="TE header" x:for-anchor=""/>
2315  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2316  <x:anchor-alias value="TE"/>
2317  <x:anchor-alias value="t-codings"/>
2319   The TE request-header field indicates what extension transfer-codings
2320   it is willing to accept in the response and whether or not it is
2321   willing to accept trailer fields in a chunked transfer-coding. Its
2322   value may consist of the keyword "trailers" and/or a comma-separated
2323   list of extension transfer-coding names with optional accept
2324   parameters (as described in <xref target="transfer.codings"/>).
2326<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2327  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2328  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2331   The presence of the keyword "trailers" indicates that the client is
2332   willing to accept trailer fields in a chunked transfer-coding, as
2333   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2334   transfer-coding values even though it does not itself represent a
2335   transfer-coding.
2338   Examples of its use are:
2340<figure><artwork type="example">
2341    TE: deflate
2342    TE:
2343    TE: trailers, deflate;q=0.5
2346   The TE header field only applies to the immediate connection.
2347   Therefore, the keyword &MUST; be supplied within a Connection header
2348   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2351   A server tests whether a transfer-coding is acceptable, according to
2352   a TE field, using these rules:
2353  <list style="numbers">
2354    <x:lt>
2355      <t>The "chunked" transfer-coding is always acceptable. If the
2356         keyword "trailers" is listed, the client indicates that it is
2357         willing to accept trailer fields in the chunked response on
2358         behalf of itself and any downstream clients. The implication is
2359         that, if given, the client is stating that either all
2360         downstream clients are willing to accept trailer fields in the
2361         forwarded response, or that it will attempt to buffer the
2362         response on behalf of downstream recipients.
2363      </t><t>
2364         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2365         chunked response such that a client can be assured of buffering
2366         the entire response.</t>
2367    </x:lt>
2368    <x:lt>
2369      <t>If the transfer-coding being tested is one of the transfer-codings
2370         listed in the TE field, then it is acceptable unless it
2371         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2372         qvalue of 0 means "not acceptable.")</t>
2373    </x:lt>
2374    <x:lt>
2375      <t>If multiple transfer-codings are acceptable, then the
2376         acceptable transfer-coding with the highest non-zero qvalue is
2377         preferred.  The "chunked" transfer-coding always has a qvalue
2378         of 1.</t>
2379    </x:lt>
2380  </list>
2383   If the TE field-value is empty or if no TE field is present, the only
2384   transfer-coding  is "chunked". A message with no transfer-coding is
2385   always acceptable.
2389<section title="Trailer" anchor="header.trailer">
2390  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2391  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2392  <x:anchor-alias value="Trailer"/>
2394   The Trailer general field value indicates that the given set of
2395   header fields is present in the trailer of a message encoded with
2396   chunked transfer-coding.
2398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2399  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2402   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2403   message using chunked transfer-coding with a non-empty trailer. Doing
2404   so allows the recipient to know which header fields to expect in the
2405   trailer.
2408   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2409   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2410   trailer fields in a "chunked" transfer-coding.
2413   Message header fields listed in the Trailer header field &MUST-NOT;
2414   include the following header fields:
2415  <list style="symbols">
2416    <t>Transfer-Encoding</t>
2417    <t>Content-Length</t>
2418    <t>Trailer</t>
2419  </list>
2423<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2424  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2425  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2426  <x:anchor-alias value="Transfer-Encoding"/>
2428   The Transfer-Encoding general-header field indicates what (if any)
2429   type of transformation has been applied to the message body in order
2430   to safely transfer it between the sender and the recipient. This
2431   differs from the content-coding in that the transfer-coding is a
2432   property of the message, not of the entity.
2434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2435  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2438   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2440<figure><artwork type="example">
2441  Transfer-Encoding: chunked
2444   If multiple encodings have been applied to an entity, the transfer-codings
2445   &MUST; be listed in the order in which they were applied.
2446   Additional information about the encoding parameters &MAY; be provided
2447   by other entity-header fields not defined by this specification.
2450   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2451   header.
2455<section title="Upgrade" anchor="header.upgrade">
2456  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2457  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2458  <x:anchor-alias value="Upgrade"/>
2460   The Upgrade general-header allows the client to specify what
2461   additional communication protocols it supports and would like to use
2462   if the server finds it appropriate to switch protocols. The server
2463   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2464   response to indicate which protocol(s) are being switched.
2466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2467  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2470   For example,
2472<figure><artwork type="example">
2473    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2476   The Upgrade header field is intended to provide a simple mechanism
2477   for transition from HTTP/1.1 to some other, incompatible protocol. It
2478   does so by allowing the client to advertise its desire to use another
2479   protocol, such as a later version of HTTP with a higher major version
2480   number, even though the current request has been made using HTTP/1.1.
2481   This eases the difficult transition between incompatible protocols by
2482   allowing the client to initiate a request in the more commonly
2483   supported protocol while indicating to the server that it would like
2484   to use a "better" protocol if available (where "better" is determined
2485   by the server, possibly according to the nature of the method and/or
2486   resource being requested).
2489   The Upgrade header field only applies to switching application-layer
2490   protocols upon the existing transport-layer connection. Upgrade
2491   cannot be used to insist on a protocol change; its acceptance and use
2492   by the server is optional. The capabilities and nature of the
2493   application-layer communication after the protocol change is entirely
2494   dependent upon the new protocol chosen, although the first action
2495   after changing the protocol &MUST; be a response to the initial HTTP
2496   request containing the Upgrade header field.
2499   The Upgrade header field only applies to the immediate connection.
2500   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2501   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2502   HTTP/1.1 message.
2505   The Upgrade header field cannot be used to indicate a switch to a
2506   protocol on a different connection. For that purpose, it is more
2507   appropriate to use a 301, 302, 303, or 305 redirection response.
2510   This specification only defines the protocol name "HTTP" for use by
2511   the family of Hypertext Transfer Protocols, as defined by the HTTP
2512   version rules of <xref target="http.version"/> and future updates to this
2513   specification. Any token can be used as a protocol name; however, it
2514   will only be useful if both the client and server associate the name
2515   with the same protocol.
2519<section title="Via" anchor="header.via">
2520  <iref primary="true" item="Via header" x:for-anchor=""/>
2521  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2522  <x:anchor-alias value="protocol-name"/>
2523  <x:anchor-alias value="protocol-version"/>
2524  <x:anchor-alias value="pseudonym"/>
2525  <x:anchor-alias value="received-by"/>
2526  <x:anchor-alias value="received-protocol"/>
2527  <x:anchor-alias value="Via"/>
2529   The Via general-header field &MUST; be used by gateways and proxies to
2530   indicate the intermediate protocols and recipients between the user
2531   agent and the server on requests, and between the origin server and
2532   the client on responses. It is analogous to the "Received" field defined in
2533   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2534   avoiding request loops, and identifying the protocol capabilities of
2535   all senders along the request/response chain.
2537<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"/>
2538  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2539  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2540  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2541  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2542  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2543  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2546   The received-protocol indicates the protocol version of the message
2547   received by the server or client along each segment of the
2548   request/response chain. The received-protocol version is appended to
2549   the Via field value when the message is forwarded so that information
2550   about the protocol capabilities of upstream applications remains
2551   visible to all recipients.
2554   The protocol-name is optional if and only if it would be "HTTP". The
2555   received-by field is normally the host and optional port number of a
2556   recipient server or client that subsequently forwarded the message.
2557   However, if the real host is considered to be sensitive information,
2558   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2559   be assumed to be the default port of the received-protocol.
2562   Multiple Via field values represents each proxy or gateway that has
2563   forwarded the message. Each recipient &MUST; append its information
2564   such that the end result is ordered according to the sequence of
2565   forwarding applications.
2568   Comments &MAY; be used in the Via header field to identify the software
2569   of the recipient proxy or gateway, analogous to the User-Agent and
2570   Server header fields. However, all comments in the Via field are
2571   optional and &MAY; be removed by any recipient prior to forwarding the
2572   message.
2575   For example, a request message could be sent from an HTTP/1.0 user
2576   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2577   forward the request to a public proxy at, which completes
2578   the request by forwarding it to the origin server at
2579   The request received by would then have the following
2580   Via header field:
2582<figure><artwork type="example">
2583    Via: 1.0 fred, 1.1 (Apache/1.1)
2586   Proxies and gateways used as a portal through a network firewall
2587   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2588   the firewall region. This information &SHOULD; only be propagated if
2589   explicitly enabled. If not enabled, the received-by host of any host
2590   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2591   for that host.
2594   For organizations that have strong privacy requirements for hiding
2595   internal structures, a proxy &MAY; combine an ordered subsequence of
2596   Via header field entries with identical received-protocol values into
2597   a single such entry. For example,
2599<figure><artwork type="example">
2600    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2603        could be collapsed to
2605<figure><artwork type="example">
2606    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2609   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2610   under the same organizational control and the hosts have already been
2611   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2612   have different received-protocol values.
2618<section title="IANA Considerations" anchor="IANA.considerations">
2619<section title="Message Header Registration" anchor="message.header.registration">
2621   The Message Header Registry located at <eref target=""/> should be updated
2622   with the permanent registrations below (see <xref target="RFC3864"/>):
2624<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2625<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2626   <ttcol>Header Field Name</ttcol>
2627   <ttcol>Protocol</ttcol>
2628   <ttcol>Status</ttcol>
2629   <ttcol>Reference</ttcol>
2631   <c>Connection</c>
2632   <c>http</c>
2633   <c>standard</c>
2634   <c>
2635      <xref target="header.connection"/>
2636   </c>
2637   <c>Content-Length</c>
2638   <c>http</c>
2639   <c>standard</c>
2640   <c>
2641      <xref target="header.content-length"/>
2642   </c>
2643   <c>Date</c>
2644   <c>http</c>
2645   <c>standard</c>
2646   <c>
2647      <xref target=""/>
2648   </c>
2649   <c>Host</c>
2650   <c>http</c>
2651   <c>standard</c>
2652   <c>
2653      <xref target=""/>
2654   </c>
2655   <c>TE</c>
2656   <c>http</c>
2657   <c>standard</c>
2658   <c>
2659      <xref target="header.te"/>
2660   </c>
2661   <c>Trailer</c>
2662   <c>http</c>
2663   <c>standard</c>
2664   <c>
2665      <xref target="header.trailer"/>
2666   </c>
2667   <c>Transfer-Encoding</c>
2668   <c>http</c>
2669   <c>standard</c>
2670   <c>
2671      <xref target="header.transfer-encoding"/>
2672   </c>
2673   <c>Upgrade</c>
2674   <c>http</c>
2675   <c>standard</c>
2676   <c>
2677      <xref target="header.upgrade"/>
2678   </c>
2679   <c>Via</c>
2680   <c>http</c>
2681   <c>standard</c>
2682   <c>
2683      <xref target="header.via"/>
2684   </c>
2688   The change controller is: "IETF ( - Internet Engineering Task Force".
2692<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2694   The entry for the "http" URI Scheme in the registry located at
2695   <eref target=""/>
2696   should be updated to point to <xref target="http.url"/> of this document
2697   (see <xref target="RFC4395"/>).
2701<section title="Internet Media Type Registrations" anchor="">
2703   This document serves as the specification for the Internet media types
2704   "message/http" and "application/http". The following is to be registered with
2705   IANA (see <xref target="RFC4288"/>).
2707<section title="Internet Media Type message/http" anchor="">
2708<iref item="Media Type" subitem="message/http" primary="true"/>
2709<iref item="message/http Media Type" primary="true"/>
2711   The message/http type can be used to enclose a single HTTP request or
2712   response message, provided that it obeys the MIME restrictions for all
2713   "message" types regarding line length and encodings.
2716  <list style="hanging" x:indent="12em">
2717    <t hangText="Type name:">
2718      message
2719    </t>
2720    <t hangText="Subtype name:">
2721      http
2722    </t>
2723    <t hangText="Required parameters:">
2724      none
2725    </t>
2726    <t hangText="Optional parameters:">
2727      version, msgtype
2728      <list style="hanging">
2729        <t hangText="version:">
2730          The HTTP-Version number of the enclosed message
2731          (e.g., "1.1"). If not present, the version can be
2732          determined from the first line of the body.
2733        </t>
2734        <t hangText="msgtype:">
2735          The message type -- "request" or "response". If not
2736          present, the type can be determined from the first
2737          line of the body.
2738        </t>
2739      </list>
2740    </t>
2741    <t hangText="Encoding considerations:">
2742      only "7bit", "8bit", or "binary" are permitted
2743    </t>
2744    <t hangText="Security considerations:">
2745      none
2746    </t>
2747    <t hangText="Interoperability considerations:">
2748      none
2749    </t>
2750    <t hangText="Published specification:">
2751      This specification (see <xref target=""/>).
2752    </t>
2753    <t hangText="Applications that use this media type:">
2754    </t>
2755    <t hangText="Additional information:">
2756      <list style="hanging">
2757        <t hangText="Magic number(s):">none</t>
2758        <t hangText="File extension(s):">none</t>
2759        <t hangText="Macintosh file type code(s):">none</t>
2760      </list>
2761    </t>
2762    <t hangText="Person and email address to contact for further information:">
2763      See Authors Section.
2764    </t>
2765                <t hangText="Intended usage:">
2766                  COMMON
2767    </t>
2768                <t hangText="Restrictions on usage:">
2769                  none
2770    </t>
2771    <t hangText="Author/Change controller:">
2772      IESG
2773    </t>
2774  </list>
2777<section title="Internet Media Type application/http" anchor="">
2778<iref item="Media Type" subitem="application/http" primary="true"/>
2779<iref item="application/http Media Type" primary="true"/>
2781   The application/http type can be used to enclose a pipeline of one or more
2782   HTTP request or response messages (not intermixed).
2785  <list style="hanging" x:indent="12em">
2786    <t hangText="Type name:">
2787      application
2788    </t>
2789    <t hangText="Subtype name:">
2790      http
2791    </t>
2792    <t hangText="Required parameters:">
2793      none
2794    </t>
2795    <t hangText="Optional parameters:">
2796      version, msgtype
2797      <list style="hanging">
2798        <t hangText="version:">
2799          The HTTP-Version number of the enclosed messages
2800          (e.g., "1.1"). If not present, the version can be
2801          determined from the first line of the body.
2802        </t>
2803        <t hangText="msgtype:">
2804          The message type -- "request" or "response". If not
2805          present, the type can be determined from the first
2806          line of the body.
2807        </t>
2808      </list>
2809    </t>
2810    <t hangText="Encoding considerations:">
2811      HTTP messages enclosed by this type
2812      are in "binary" format; use of an appropriate
2813      Content-Transfer-Encoding is required when
2814      transmitted via E-mail.
2815    </t>
2816    <t hangText="Security considerations:">
2817      none
2818    </t>
2819    <t hangText="Interoperability considerations:">
2820      none
2821    </t>
2822    <t hangText="Published specification:">
2823      This specification (see <xref target=""/>).
2824    </t>
2825    <t hangText="Applications that use this media type:">
2826    </t>
2827    <t hangText="Additional information:">
2828      <list style="hanging">
2829        <t hangText="Magic number(s):">none</t>
2830        <t hangText="File extension(s):">none</t>
2831        <t hangText="Macintosh file type code(s):">none</t>
2832      </list>
2833    </t>
2834    <t hangText="Person and email address to contact for further information:">
2835      See Authors Section.
2836    </t>
2837                <t hangText="Intended usage:">
2838                  COMMON
2839    </t>
2840                <t hangText="Restrictions on usage:">
2841                  none
2842    </t>
2843    <t hangText="Author/Change controller:">
2844      IESG
2845    </t>
2846  </list>
2853<section title="Security Considerations" anchor="security.considerations">
2855   This section is meant to inform application developers, information
2856   providers, and users of the security limitations in HTTP/1.1 as
2857   described by this document. The discussion does not include
2858   definitive solutions to the problems revealed, though it does make
2859   some suggestions for reducing security risks.
2862<section title="Personal Information" anchor="personal.information">
2864   HTTP clients are often privy to large amounts of personal information
2865   (e.g. the user's name, location, mail address, passwords, encryption
2866   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2867   leakage of this information.
2868   We very strongly recommend that a convenient interface be provided
2869   for the user to control dissemination of such information, and that
2870   designers and implementors be particularly careful in this area.
2871   History shows that errors in this area often create serious security
2872   and/or privacy problems and generate highly adverse publicity for the
2873   implementor's company.
2877<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2879   A server is in the position to save personal data about a user's
2880   requests which might identify their reading patterns or subjects of
2881   interest. This information is clearly confidential in nature and its
2882   handling can be constrained by law in certain countries. People using
2883   HTTP to provide data are responsible for ensuring that
2884   such material is not distributed without the permission of any
2885   individuals that are identifiable by the published results.
2889<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2891   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2892   the documents returned by HTTP requests to be only those that were
2893   intended by the server administrators. If an HTTP server translates
2894   HTTP URIs directly into file system calls, the server &MUST; take
2895   special care not to serve files that were not intended to be
2896   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2897   other operating systems use ".." as a path component to indicate a
2898   directory level above the current one. On such a system, an HTTP
2899   server &MUST; disallow any such construct in the Request-URI if it
2900   would otherwise allow access to a resource outside those intended to
2901   be accessible via the HTTP server. Similarly, files intended for
2902   reference only internally to the server (such as access control
2903   files, configuration files, and script code) &MUST; be protected from
2904   inappropriate retrieval, since they might contain sensitive
2905   information. Experience has shown that minor bugs in such HTTP server
2906   implementations have turned into security risks.
2910<section title="DNS Spoofing" anchor="dns.spoofing">
2912   Clients using HTTP rely heavily on the Domain Name Service, and are
2913   thus generally prone to security attacks based on the deliberate
2914   mis-association of IP addresses and DNS names. Clients need to be
2915   cautious in assuming the continuing validity of an IP number/DNS name
2916   association.
2919   In particular, HTTP clients &SHOULD; rely on their name resolver for
2920   confirmation of an IP number/DNS name association, rather than
2921   caching the result of previous host name lookups. Many platforms
2922   already can cache host name lookups locally when appropriate, and
2923   they &SHOULD; be configured to do so. It is proper for these lookups to
2924   be cached, however, only when the TTL (Time To Live) information
2925   reported by the name server makes it likely that the cached
2926   information will remain useful.
2929   If HTTP clients cache the results of host name lookups in order to
2930   achieve a performance improvement, they &MUST; observe the TTL
2931   information reported by DNS.
2934   If HTTP clients do not observe this rule, they could be spoofed when
2935   a previously-accessed server's IP address changes. As network
2936   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2937   possibility of this form of attack will grow. Observing this
2938   requirement thus reduces this potential security vulnerability.
2941   This requirement also improves the load-balancing behavior of clients
2942   for replicated servers using the same DNS name and reduces the
2943   likelihood of a user's experiencing failure in accessing sites which
2944   use that strategy.
2948<section title="Proxies and Caching" anchor="attack.proxies">
2950   By their very nature, HTTP proxies are men-in-the-middle, and
2951   represent an opportunity for man-in-the-middle attacks. Compromise of
2952   the systems on which the proxies run can result in serious security
2953   and privacy problems. Proxies have access to security-related
2954   information, personal information about individual users and
2955   organizations, and proprietary information belonging to users and
2956   content providers. A compromised proxy, or a proxy implemented or
2957   configured without regard to security and privacy considerations,
2958   might be used in the commission of a wide range of potential attacks.
2961   Proxy operators should protect the systems on which proxies run as
2962   they would protect any system that contains or transports sensitive
2963   information. In particular, log information gathered at proxies often
2964   contains highly sensitive personal information, and/or information
2965   about organizations. Log information should be carefully guarded, and
2966   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2969   Proxy implementors should consider the privacy and security
2970   implications of their design and coding decisions, and of the
2971   configuration options they provide to proxy operators (especially the
2972   default configuration).
2975   Users of a proxy need to be aware that they are no trustworthier than
2976   the people who run the proxy; HTTP itself cannot solve this problem.
2979   The judicious use of cryptography, when appropriate, may suffice to
2980   protect against a broad range of security and privacy attacks. Such
2981   cryptography is beyond the scope of the HTTP/1.1 specification.
2985<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2987   They exist. They are hard to defend against. Research continues.
2988   Beware.
2993<section title="Acknowledgments" anchor="ack">
2995   This specification makes heavy use of the augmented BNF and generic
2996   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2997   reuses many of the definitions provided by Nathaniel Borenstein and
2998   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2999   specification will help reduce past confusion over the relationship
3000   between HTTP and Internet mail message formats.
3003   HTTP has evolved considerably over the years. It has
3004   benefited from a large and active developer community--the many
3005   people who have participated on the www-talk mailing list--and it is
3006   that community which has been most responsible for the success of
3007   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3008   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3009   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3010   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3011   VanHeyningen deserve special recognition for their efforts in
3012   defining early aspects of the protocol.
3015   This document has benefited greatly from the comments of all those
3016   participating in the HTTP-WG. In addition to those already mentioned,
3017   the following individuals have contributed to this specification:
3020   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3021   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3022   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3023   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3024   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3025   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3026   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3027   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3028   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3029   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3030   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3031   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3032   Josh Cohen.
3035   Thanks to the "cave men" of Palo Alto. You know who you are.
3038   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3039   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3040   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3041   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3042   Larry Masinter for their help. And thanks go particularly to Jeff
3043   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3046   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3047   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3048   discovery of many of the problems that this document attempts to
3049   rectify.
3056<references title="Normative References">
3058<reference anchor="ISO-8859-1">
3059  <front>
3060    <title>
3061     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3062    </title>
3063    <author>
3064      <organization>International Organization for Standardization</organization>
3065    </author>
3066    <date year="1998"/>
3067  </front>
3068  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3071<reference anchor="Part2">
3072  <front>
3073    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3074    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3075      <organization abbrev="Day Software">Day Software</organization>
3076      <address><email></email></address>
3077    </author>
3078    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3079      <organization>One Laptop per Child</organization>
3080      <address><email></email></address>
3081    </author>
3082    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3083      <organization abbrev="HP">Hewlett-Packard Company</organization>
3084      <address><email></email></address>
3085    </author>
3086    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3087      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3088      <address><email></email></address>
3089    </author>
3090    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3091      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3092      <address><email></email></address>
3093    </author>
3094    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3095      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3096      <address><email></email></address>
3097    </author>
3098    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3099      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3100      <address><email></email></address>
3101    </author>
3102    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3103      <organization abbrev="W3C">World Wide Web Consortium</organization>
3104      <address><email></email></address>
3105    </author>
3106    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3107      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3108      <address><email></email></address>
3109    </author>
3110    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3111  </front>
3112  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3113  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3116<reference anchor="Part3">
3117  <front>
3118    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</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-p3-payload-&ID-VERSION;"/>
3158  <x:source href="p3-payload.xml" basename="p3-payload"/>
3161<reference anchor="Part5">
3162  <front>
3163    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</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-p5-range-&ID-VERSION;"/>
3203  <x:source href="p5-range.xml" basename="p5-range"/>
3206<reference anchor="Part6">
3207  <front>
3208    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</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-p6-cache-&ID-VERSION;"/>
3248  <x:source href="p6-cache.xml" basename="p6-cache"/>
3251<reference anchor="RFC5234">
3252  <front>
3253    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3254    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3255      <organization>Brandenburg InternetWorking</organization>
3256      <address>
3257      <postal>
3258      <street>675 Spruce Dr.</street>
3259      <city>Sunnyvale</city>
3260      <region>CA</region>
3261      <code>94086</code>
3262      <country>US</country></postal>
3263      <phone>+1.408.246.8253</phone>
3264      <email></email></address> 
3265    </author>
3266    <author initials="P." surname="Overell" fullname="Paul Overell">
3267      <organization>THUS plc.</organization>
3268      <address>
3269      <postal>
3270      <street>1/2 Berkeley Square</street>
3271      <street>99 Berkely Street</street>
3272      <city>Glasgow</city>
3273      <code>G3 7HR</code>
3274      <country>UK</country></postal>
3275      <email></email></address>
3276    </author>
3277    <date month="January" year="2008"/>
3278  </front>
3279  <seriesInfo name="STD" value="68"/>
3280  <seriesInfo name="RFC" value="5234"/>
3283<reference anchor="RFC2045">
3284  <front>
3285    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3286    <author initials="N." surname="Freed" fullname="Ned Freed">
3287      <organization>Innosoft International, Inc.</organization>
3288      <address><email></email></address>
3289    </author>
3290    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3291      <organization>First Virtual Holdings</organization>
3292      <address><email></email></address>
3293    </author>
3294    <date month="November" year="1996"/>
3295  </front>
3296  <seriesInfo name="RFC" value="2045"/>
3299<reference anchor="RFC2047">
3300  <front>
3301    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3302    <author initials="K." surname="Moore" fullname="Keith Moore">
3303      <organization>University of Tennessee</organization>
3304      <address><email></email></address>
3305    </author>
3306    <date month="November" year="1996"/>
3307  </front>
3308  <seriesInfo name="RFC" value="2047"/>
3311<reference anchor="RFC2119">
3312  <front>
3313    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3314    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3315      <organization>Harvard University</organization>
3316      <address><email></email></address>
3317    </author>
3318    <date month="March" year="1997"/>
3319  </front>
3320  <seriesInfo name="BCP" value="14"/>
3321  <seriesInfo name="RFC" value="2119"/>
3324<reference anchor="RFC2396">
3325  <front>
3326    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3327    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3328      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3329      <address><email></email></address>
3330    </author>
3331    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3332      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3333      <address><email></email></address>
3334    </author>
3335    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3336      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3337      <address><email></email></address>
3338    </author>
3339    <date month="August" year="1998"/>
3340  </front>
3341  <seriesInfo name="RFC" value="2396"/>
3344<reference anchor="USASCII">
3345  <front>
3346    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3347    <author>
3348      <organization>American National Standards Institute</organization>
3349    </author>
3350    <date year="1986"/>
3351  </front>
3352  <seriesInfo name="ANSI" value="X3.4"/>
3357<references title="Informative References">
3359<reference anchor="Nie1997" target="">
3360  <front>
3361    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3362    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3363      <organization/>
3364    </author>
3365    <author initials="J." surname="Gettys" fullname="J. Gettys">
3366      <organization/>
3367    </author>
3368    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3369      <organization/>
3370    </author>
3371    <author initials="H." surname="Lie" fullname="H. Lie">
3372      <organization/>
3373    </author>
3374    <author initials="C." surname="Lilley" fullname="C. Lilley">
3375      <organization/>
3376    </author>
3377    <date year="1997" month="September"/>
3378  </front>
3379  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3382<reference anchor="Pad1995" target="">
3383  <front>
3384    <title>Improving HTTP Latency</title>
3385    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3386      <organization/>
3387    </author>
3388    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3389      <organization/>
3390    </author>
3391    <date year="1995" month="December"/>
3392  </front>
3393  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3396<reference anchor="RFC822">
3397  <front>
3398    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3399    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3400      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3401      <address><email>DCrocker@UDel-Relay</email></address>
3402    </author>
3403    <date month="August" day="13" year="1982"/>
3404  </front>
3405  <seriesInfo name="STD" value="11"/>
3406  <seriesInfo name="RFC" value="822"/>
3409<reference anchor="RFC959">
3410  <front>
3411    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3412    <author initials="J." surname="Postel" fullname="J. Postel">
3413      <organization>Information Sciences Institute (ISI)</organization>
3414    </author>
3415    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3416      <organization/>
3417    </author>
3418    <date month="October" year="1985"/>
3419  </front>
3420  <seriesInfo name="STD" value="9"/>
3421  <seriesInfo name="RFC" value="959"/>
3424<reference anchor="RFC1123">
3425  <front>
3426    <title>Requirements for Internet Hosts - Application and Support</title>
3427    <author initials="R." surname="Braden" fullname="Robert Braden">
3428      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3429      <address><email>Braden@ISI.EDU</email></address>
3430    </author>
3431    <date month="October" year="1989"/>
3432  </front>
3433  <seriesInfo name="STD" value="3"/>
3434  <seriesInfo name="RFC" value="1123"/>
3437<reference anchor="RFC1305">
3438  <front>
3439    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3440    <author initials="D." surname="Mills" fullname="David L. Mills">
3441      <organization>University of Delaware, Electrical Engineering Department</organization>
3442      <address><email></email></address>
3443    </author>
3444    <date month="March" year="1992"/>
3445  </front>
3446  <seriesInfo name="RFC" value="1305"/>
3449<reference anchor="RFC1436">
3450  <front>
3451    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3452    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3453      <organization>University of Minnesota, Computer and Information Services</organization>
3454      <address><email></email></address>
3455    </author>
3456    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3457      <organization>University of Minnesota, Computer and Information Services</organization>
3458      <address><email></email></address>
3459    </author>
3460    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3461      <organization>University of Minnesota, Computer and Information Services</organization>
3462      <address><email></email></address>
3463    </author>
3464    <author initials="D." surname="Johnson" fullname="David Johnson">
3465      <organization>University of Minnesota, Computer and Information Services</organization>
3466      <address><email></email></address>
3467    </author>
3468    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3469      <organization>University of Minnesota, Computer and Information Services</organization>
3470      <address><email></email></address>
3471    </author>
3472    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3473      <organization>University of Minnesota, Computer and Information Services</organization>
3474      <address><email></email></address>
3475    </author>
3476    <date month="March" year="1993"/>
3477  </front>
3478  <seriesInfo name="RFC" value="1436"/>
3481<reference anchor="RFC1630">
3482  <front>
3483    <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>
3484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3485      <organization>CERN, World-Wide Web project</organization>
3486      <address><email></email></address>
3487    </author>
3488    <date month="June" year="1994"/>
3489  </front>
3490  <seriesInfo name="RFC" value="1630"/>
3493<reference anchor="RFC1737">
3494  <front>
3495    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3496    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3497      <organization>Xerox Palo Alto Research Center</organization>
3498      <address><email></email></address>
3499    </author>
3500    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3501      <organization>MIT Laboratory for Computer Science</organization>
3502      <address><email></email></address>
3503    </author>
3504    <date month="December" year="1994"/>
3505  </front>
3506  <seriesInfo name="RFC" value="1737"/>
3509<reference anchor="RFC1738">
3510  <front>
3511    <title>Uniform Resource Locators (URL)</title>
3512    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3513      <organization>CERN, World-Wide Web project</organization>
3514      <address><email></email></address>
3515    </author>
3516    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3517      <organization>Xerox PARC</organization>
3518      <address><email></email></address>
3519    </author>
3520    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3521      <organization>University of Minnesota, Computer and Information Services</organization>
3522      <address><email></email></address>
3523    </author>
3524    <date month="December" year="1994"/>
3525  </front>
3526  <seriesInfo name="RFC" value="1738"/>
3529<reference anchor="RFC1808">
3530  <front>
3531    <title>Relative Uniform Resource Locators</title>
3532    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3533      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3534      <address><email></email></address>
3535    </author>
3536    <date month="June" year="1995"/>
3537  </front>
3538  <seriesInfo name="RFC" value="1808"/>
3541<reference anchor="RFC1900">
3542  <front>
3543    <title>Renumbering Needs Work</title>
3544    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3545      <organization>CERN, Computing and Networks Division</organization>
3546      <address><email></email></address>
3547    </author>
3548    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3549      <organization>cisco Systems</organization>
3550      <address><email></email></address>
3551    </author>
3552    <date month="February" year="1996"/>
3553  </front>
3554  <seriesInfo name="RFC" value="1900"/>
3557<reference anchor="RFC1945">
3558  <front>
3559    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3560    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3561      <organization>MIT, Laboratory for Computer Science</organization>
3562      <address><email></email></address>
3563    </author>
3564    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3565      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3566      <address><email></email></address>
3567    </author>
3568    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3569      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3570      <address><email></email></address>
3571    </author>
3572    <date month="May" year="1996"/>
3573  </front>
3574  <seriesInfo name="RFC" value="1945"/>
3577<reference anchor="RFC2068">
3578  <front>
3579    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3580    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3581      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3582      <address><email></email></address>
3583    </author>
3584    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3585      <organization>MIT Laboratory for Computer Science</organization>
3586      <address><email></email></address>
3587    </author>
3588    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3589      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3590      <address><email></email></address>
3591    </author>
3592    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3593      <organization>MIT Laboratory for Computer Science</organization>
3594      <address><email></email></address>
3595    </author>
3596    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3597      <organization>MIT Laboratory for Computer Science</organization>
3598      <address><email></email></address>
3599    </author>
3600    <date month="January" year="1997"/>
3601  </front>
3602  <seriesInfo name="RFC" value="2068"/>
3605<reference anchor='RFC2109'>
3606  <front>
3607    <title>HTTP State Management Mechanism</title>
3608    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3609      <organization>Bell Laboratories, Lucent Technologies</organization>
3610      <address><email></email></address>
3611    </author>
3612    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3613      <organization>Netscape Communications Corp.</organization>
3614      <address><email></email></address>
3615    </author>
3616    <date year='1997' month='February' />
3617  </front>
3618  <seriesInfo name='RFC' value='2109' />
3621<reference anchor="RFC2145">
3622  <front>
3623    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3624    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3625      <organization>Western Research Laboratory</organization>
3626      <address><email></email></address>
3627    </author>
3628    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3629      <organization>Department of Information and Computer Science</organization>
3630      <address><email></email></address>
3631    </author>
3632    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3633      <organization>MIT Laboratory for Computer Science</organization>
3634      <address><email></email></address>
3635    </author>
3636    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3637      <organization>W3 Consortium</organization>
3638      <address><email></email></address>
3639    </author>
3640    <date month="May" year="1997"/>
3641  </front>
3642  <seriesInfo name="RFC" value="2145"/>
3645<reference anchor="RFC2324">
3646  <front>
3647    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3648    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3649      <organization>Xerox Palo Alto Research Center</organization>
3650      <address><email></email></address>
3651    </author>
3652    <date month="April" day="1" year="1998"/>
3653  </front>
3654  <seriesInfo name="RFC" value="2324"/>
3657<reference anchor="RFC2616">
3658  <front>
3659    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3660    <author initials="R." surname="Fielding" fullname="R. Fielding">
3661      <organization>University of California, Irvine</organization>
3662      <address><email></email></address>
3663    </author>
3664    <author initials="J." surname="Gettys" fullname="J. Gettys">
3665      <organization>W3C</organization>
3666      <address><email></email></address>
3667    </author>
3668    <author initials="J." surname="Mogul" fullname="J. Mogul">
3669      <organization>Compaq Computer Corporation</organization>
3670      <address><email></email></address>
3671    </author>
3672    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3673      <organization>MIT Laboratory for Computer Science</organization>
3674      <address><email></email></address>
3675    </author>
3676    <author initials="L." surname="Masinter" fullname="L. Masinter">
3677      <organization>Xerox Corporation</organization>
3678      <address><email></email></address>
3679    </author>
3680    <author initials="P." surname="Leach" fullname="P. Leach">
3681      <organization>Microsoft Corporation</organization>
3682      <address><email></email></address>
3683    </author>
3684    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3685      <organization>W3C</organization>
3686      <address><email></email></address>
3687    </author>
3688    <date month="June" year="1999"/>
3689  </front>
3690  <seriesInfo name="RFC" value="2616"/>
3693<reference anchor='RFC2818'>
3694  <front>
3695    <title>HTTP Over TLS</title>
3696    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3697      <organization>RTFM, Inc.</organization>
3698      <address><email></email></address>
3699    </author>
3700    <date year='2000' month='May' />
3701  </front>
3702  <seriesInfo name='RFC' value='2818' />
3705<reference anchor="RFC2821">
3706  <front>
3707    <title>Simple Mail Transfer Protocol</title>
3708    <author initials="J." surname="Klensin" fullname="J. Klensin">
3709      <organization>AT&amp;T Laboratories</organization>
3710      <address><email></email></address>
3711    </author>
3712    <date year="2001" month="April"/>
3713  </front>
3714  <seriesInfo name="RFC" value="2821"/>
3717<reference anchor='RFC2965'>
3718  <front>
3719    <title>HTTP State Management Mechanism</title>
3720    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3721      <organization>Bell Laboratories, Lucent Technologies</organization>
3722      <address><email></email></address>
3723    </author>
3724    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3725      <organization>, Inc.</organization>
3726      <address><email></email></address>
3727    </author>
3728    <date year='2000' month='October' />
3729  </front>
3730  <seriesInfo name='RFC' value='2965' />
3733<reference anchor='RFC3864'>
3734  <front>
3735    <title>Registration Procedures for Message Header Fields</title>
3736    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3737      <organization>Nine by Nine</organization>
3738      <address><email></email></address>
3739    </author>
3740    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3741      <organization>BEA Systems</organization>
3742      <address><email></email></address>
3743    </author>
3744    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3745      <organization>HP Labs</organization>
3746      <address><email></email></address>
3747    </author>
3748    <date year='2004' month='September' />
3749  </front>
3750  <seriesInfo name='BCP' value='90' />
3751  <seriesInfo name='RFC' value='3864' />
3754<reference anchor='RFC3977'>
3755  <front>
3756    <title>Network News Transfer Protocol (NNTP)</title>
3757    <author initials='C.' surname='Feather' fullname='C. Feather'>
3758      <organization>THUS plc</organization>
3759      <address><email></email></address>
3760    </author>
3761    <date year='2006' month='October' />
3762  </front>
3763  <seriesInfo name="RFC" value="3977"/>
3766<reference anchor="RFC4288">
3767  <front>
3768    <title>Media Type Specifications and Registration Procedures</title>
3769    <author initials="N." surname="Freed" fullname="N. Freed">
3770      <organization>Sun Microsystems</organization>
3771      <address>
3772        <email></email>
3773      </address>
3774    </author>
3775    <author initials="J." surname="Klensin" fullname="J. Klensin">
3776      <organization/>
3777      <address>
3778        <email></email>
3779      </address>
3780    </author>
3781    <date year="2005" month="December"/>
3782  </front>
3783  <seriesInfo name="BCP" value="13"/>
3784  <seriesInfo name="RFC" value="4288"/>
3787<reference anchor='RFC4395'>
3788  <front>
3789    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3790    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3791      <organization>AT&amp;T Laboratories</organization>
3792      <address>
3793        <email></email>
3794      </address>
3795    </author>
3796    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3797      <organization>Qualcomm, Inc.</organization>
3798      <address>
3799        <email></email>
3800      </address>
3801    </author>
3802    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3803      <organization>Adobe Systems</organization>
3804      <address>
3805        <email></email>
3806      </address>
3807    </author>
3808    <date year='2006' month='February' />
3809  </front>
3810  <seriesInfo name='BCP' value='115' />
3811  <seriesInfo name='RFC' value='4395' />
3814<reference anchor="RFC5322">
3815  <front>
3816    <title>Internet Message Format</title>
3817    <author initials="P." surname="Resnick" fullname="P. Resnick">
3818      <organization>Qualcomm Incorporated</organization>
3819    </author>
3820    <date year="2008" month="October"/>
3821  </front>
3822  <seriesInfo name="RFC" value="5322"/>
3825<reference anchor="Kri2001" target="">
3826  <front>
3827    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3828    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3829      <organization/>
3830    </author>
3831    <date year="2001" month="November"/>
3832  </front>
3833  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3836<reference anchor="Spe" target="">
3837  <front>
3838  <title>Analysis of HTTP Performance Problems</title>
3839  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3840    <organization/>
3841  </author>
3842  <date/>
3843  </front>
3846<reference anchor="Tou1998" target="">
3847  <front>
3848  <title>Analysis of HTTP Performance</title>
3849  <author initials="J." surname="Touch" fullname="Joe Touch">
3850    <organization>USC/Information Sciences Institute</organization>
3851    <address><email></email></address>
3852  </author>
3853  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3854    <organization>USC/Information Sciences Institute</organization>
3855    <address><email></email></address>
3856  </author>
3857  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3858    <organization>USC/Information Sciences Institute</organization>
3859    <address><email></email></address>
3860  </author>
3861  <date year="1998" month="Aug"/>
3862  </front>
3863  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3864  <annotation>(original report dated Aug. 1996)</annotation>
3867<reference anchor="WAIS">
3868  <front>
3869    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3870    <author initials="F." surname="Davis" fullname="F. Davis">
3871      <organization>Thinking Machines Corporation</organization>
3872    </author>
3873    <author initials="B." surname="Kahle" fullname="B. Kahle">
3874      <organization>Thinking Machines Corporation</organization>
3875    </author>
3876    <author initials="H." surname="Morris" fullname="H. Morris">
3877      <organization>Thinking Machines Corporation</organization>
3878    </author>
3879    <author initials="J." surname="Salem" fullname="J. Salem">
3880      <organization>Thinking Machines Corporation</organization>
3881    </author>
3882    <author initials="T." surname="Shen" fullname="T. Shen">
3883      <organization>Thinking Machines Corporation</organization>
3884    </author>
3885    <author initials="R." surname="Wang" fullname="R. Wang">
3886      <organization>Thinking Machines Corporation</organization>
3887    </author>
3888    <author initials="J." surname="Sui" fullname="J. Sui">
3889      <organization>Thinking Machines Corporation</organization>
3890    </author>
3891    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3892      <organization>Thinking Machines Corporation</organization>
3893    </author>
3894    <date month="April" year="1990"/>
3895  </front>
3896  <seriesInfo name="Thinking Machines Corporation" value=""/>
3902<section title="Tolerant Applications" anchor="tolerant.applications">
3904   Although this document specifies the requirements for the generation
3905   of HTTP/1.1 messages, not all applications will be correct in their
3906   implementation. We therefore recommend that operational applications
3907   be tolerant of deviations whenever those deviations can be
3908   interpreted unambiguously.
3911   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3912   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3913   accept any amount of SP or HTAB characters between fields, even though
3914   only a single SP is required.
3917   The line terminator for message-header fields is the sequence CRLF.
3918   However, we recommend that applications, when parsing such headers,
3919   recognize a single LF as a line terminator and ignore the leading CR.
3922   The character set of an entity-body &SHOULD; be labeled as the lowest
3923   common denominator of the character codes used within that body, with
3924   the exception that not labeling the entity is preferred over labeling
3925   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3928   Additional rules for requirements on parsing and encoding of dates
3929   and other potential problems with date encodings include:
3932  <list style="symbols">
3933     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3934        which appears to be more than 50 years in the future is in fact
3935        in the past (this helps solve the "year 2000" problem).</t>
3937     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3938        Expires date as earlier than the proper value, but &MUST-NOT;
3939        internally represent a parsed Expires date as later than the
3940        proper value.</t>
3942     <t>All expiration-related calculations &MUST; be done in GMT. The
3943        local time zone &MUST-NOT; influence the calculation or comparison
3944        of an age or expiration time.</t>
3946     <t>If an HTTP header incorrectly carries a date value with a time
3947        zone other than GMT, it &MUST; be converted into GMT using the
3948        most conservative possible conversion.</t>
3949  </list>
3953<section title="Conversion of Date Formats" anchor="">
3955   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
3956   simplify the process of date comparison. Proxies and gateways from
3957   other protocols &SHOULD; ensure that any Date header field present in a
3958   message conforms to one of the HTTP/1.1 formats and rewrite the date
3959   if necessary.
3963<section title="Compatibility with Previous Versions" anchor="compatibility">
3965   It is beyond the scope of a protocol specification to mandate
3966   compliance with previous versions. HTTP/1.1 was deliberately
3967   designed, however, to make supporting previous versions easy. It is
3968   worth noting that, at the time of composing this specification
3969   (1996), we would expect commercial HTTP/1.1 servers to:
3970  <list style="symbols">
3971     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3972        1.1 requests;</t>
3974     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3975        1.1;</t>
3977     <t>respond appropriately with a message in the same major version
3978        used by the client.</t>
3979  </list>
3982   And we would expect HTTP/1.1 clients to:
3983  <list style="symbols">
3984     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3985        responses;</t>
3987     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3988        1.1.</t>
3989  </list>
3992   For most implementations of HTTP/1.0, each connection is established
3993   by the client prior to the request and closed by the server after
3994   sending the response. Some implementations implement the Keep-Alive
3995   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3998<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4000   This section summarizes major differences between versions HTTP/1.0
4001   and HTTP/1.1.
4004<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4006   The requirements that clients and servers support the Host request-header,
4007   report an error if the Host request-header (<xref target=""/>) is
4008   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4009   are among the most important changes defined by this
4010   specification.
4013   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4014   addresses and servers; there was no other established mechanism for
4015   distinguishing the intended server of a request than the IP address
4016   to which that request was directed. The changes outlined above will
4017   allow the Internet, once older HTTP clients are no longer common, to
4018   support multiple Web sites from a single IP address, greatly
4019   simplifying large operational Web servers, where allocation of many
4020   IP addresses to a single host has created serious problems. The
4021   Internet will also be able to recover the IP addresses that have been
4022   allocated for the sole purpose of allowing special-purpose domain
4023   names to be used in root-level HTTP URLs. Given the rate of growth of
4024   the Web, and the number of servers already deployed, it is extremely
4025   important that all implementations of HTTP (including updates to
4026   existing HTTP/1.0 applications) correctly implement these
4027   requirements:
4028  <list style="symbols">
4029     <t>Both clients and servers &MUST; support the Host request-header.</t>
4031     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4033     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4034        request does not include a Host request-header.</t>
4036     <t>Servers &MUST; accept absolute URIs.</t>
4037  </list>
4042<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4044   Some clients and servers might wish to be compatible with some
4045   previous implementations of persistent connections in HTTP/1.0
4046   clients and servers. Persistent connections in HTTP/1.0 are
4047   explicitly negotiated as they are not the default behavior. HTTP/1.0
4048   experimental implementations of persistent connections are faulty,
4049   and the new facilities in HTTP/1.1 are designed to rectify these
4050   problems. The problem was that some existing 1.0 clients may be
4051   sending Keep-Alive to a proxy server that doesn't understand
4052   Connection, which would then erroneously forward it to the next
4053   inbound server, which would establish the Keep-Alive connection and
4054   result in a hung HTTP/1.0 proxy waiting for the close on the
4055   response. The result is that HTTP/1.0 clients must be prevented from
4056   using Keep-Alive when talking to proxies.
4059   However, talking to proxies is the most important use of persistent
4060   connections, so that prohibition is clearly unacceptable. Therefore,
4061   we need some other mechanism for indicating a persistent connection
4062   is desired, which is safe to use even when talking to an old proxy
4063   that ignores Connection. Persistent connections are the default for
4064   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4065   declaring non-persistence. See <xref target="header.connection"/>.
4068   The original HTTP/1.0 form of persistent connections (the Connection:
4069   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4073<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4075   This specification has been carefully audited to correct and
4076   disambiguate key word usage; RFC 2068 had many problems in respect to
4077   the conventions laid out in <xref target="RFC2119"/>.
4080   Transfer-coding and message lengths all interact in ways that
4081   required fixing exactly when chunked encoding is used (to allow for
4082   transfer encoding that may not be self delimiting); it was important
4083   to straighten out exactly how message lengths are computed. (Sections
4084   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4085   <xref target="header.content-length" format="counter"/>,
4086   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4089   The use and interpretation of HTTP version numbers has been clarified
4090   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4091   version they support to deal with problems discovered in HTTP/1.0
4092   implementations (<xref target="http.version"/>)
4095   Transfer-coding had significant problems, particularly with
4096   interactions with chunked encoding. The solution is that transfer-codings
4097   become as full fledged as content-codings. This involves
4098   adding an IANA registry for transfer-codings (separate from content
4099   codings), a new header field (TE) and enabling trailer headers in the
4100   future. Transfer encoding is a major performance benefit, so it was
4101   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4102   interoperability problem that could have occurred due to interactions
4103   between authentication trailers, chunked encoding and HTTP/1.0
4104   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4105   and <xref target="header.te" format="counter"/>)
4109<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4111  The CHAR rule does not allow the NUL character anymore (this affects
4112  the comment and quoted-string rules).  Furthermore, the quoted-pair
4113  rule does not allow escaping NUL, CR or LF anymore.
4114  (<xref target="basic.rules"/>)
4117  Clarify that HTTP-Version is case sensitive.
4118  (<xref target="http.version"/>)
4121  Remove reference to non-existant identity transfer-coding value tokens.
4122  (Sections <xref format="counter" target="transfer.codings"/> and
4123  <xref format="counter" target="message.length"/>)
4126  Clarification that the chunk length does not include
4127  the count of the octets in the chunk header and trailer.
4128  (<xref target="chunked.transfer.encoding"/>)
4131  Fix BNF to add query, as the abs_path production in
4132  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4133  (<xref target="request-uri"/>)
4136  Clarify exactly when close connection options must be sent.
4137  (<xref target="header.connection"/>)
4142<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4144<section title="Since RFC2616">
4146  Extracted relevant partitions from <xref target="RFC2616"/>.
4150<section title="Since draft-ietf-httpbis-p1-messaging-00">
4152  Closed issues:
4153  <list style="symbols">
4154    <t>
4155      <eref target=""/>:
4156      "HTTP Version should be case sensitive"
4157      (<eref target=""/>)
4158    </t>
4159    <t>
4160      <eref target=""/>:
4161      "'unsafe' characters"
4162      (<eref target=""/>)
4163    </t>
4164    <t>
4165      <eref target=""/>:
4166      "Chunk Size Definition"
4167      (<eref target=""/>)
4168    </t>
4169    <t>
4170      <eref target=""/>:
4171      "Message Length"
4172      (<eref target=""/>)
4173    </t>
4174    <t>
4175      <eref target=""/>:
4176      "Media Type Registrations"
4177      (<eref target=""/>)
4178    </t>
4179    <t>
4180      <eref target=""/>:
4181      "URI includes query"
4182      (<eref target=""/>)
4183    </t>
4184    <t>
4185      <eref target=""/>:
4186      "No close on 1xx responses"
4187      (<eref target=""/>)
4188    </t>
4189    <t>
4190      <eref target=""/>:
4191      "Remove 'identity' token references"
4192      (<eref target=""/>)
4193    </t>
4194    <t>
4195      <eref target=""/>:
4196      "Import query BNF"
4197    </t>
4198    <t>
4199      <eref target=""/>:
4200      "qdtext BNF"
4201    </t>
4202    <t>
4203      <eref target=""/>:
4204      "Normative and Informative references"
4205    </t>
4206    <t>
4207      <eref target=""/>:
4208      "RFC2606 Compliance"
4209    </t>
4210    <t>
4211      <eref target=""/>:
4212      "RFC977 reference"
4213    </t>
4214    <t>
4215      <eref target=""/>:
4216      "RFC1700 references"
4217    </t>
4218    <t>
4219      <eref target=""/>:
4220      "inconsistency in date format explanation"
4221    </t>
4222    <t>
4223      <eref target=""/>:
4224      "Date reference typo"
4225    </t>
4226    <t>
4227      <eref target=""/>:
4228      "Informative references"
4229    </t>
4230    <t>
4231      <eref target=""/>:
4232      "ISO-8859-1 Reference"
4233    </t>
4234    <t>
4235      <eref target=""/>:
4236      "Normative up-to-date references"
4237    </t>
4238  </list>
4241  Other changes:
4242  <list style="symbols">
4243    <t>
4244      Update media type registrations to use RFC4288 template.
4245    </t>
4246    <t>
4247      Use names of RFC4234 core rules DQUOTE and HTAB,
4248      fix broken ABNF for chunk-data
4249      (work in progress on <eref target=""/>)
4250    </t>
4251  </list>
4255<section title="Since draft-ietf-httpbis-p1-messaging-01">
4257  Closed issues:
4258  <list style="symbols">
4259    <t>
4260      <eref target=""/>:
4261      "Bodies on GET (and other) requests"
4262    </t>
4263    <t>
4264      <eref target=""/>:
4265      "Updating to RFC4288"
4266    </t>
4267    <t>
4268      <eref target=""/>:
4269      "Status Code and Reason Phrase"
4270    </t>
4271    <t>
4272      <eref target=""/>:
4273      "rel_path not used"
4274    </t>
4275  </list>
4278  Ongoing work on ABNF conversion (<eref target=""/>):
4279  <list style="symbols">
4280    <t>
4281      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4282      "trailer-part").
4283    </t>
4284    <t>
4285      Avoid underscore character in rule names ("http_URL" ->
4286      "http-URL", "abs_path" -> "path-absolute").
4287    </t>
4288    <t>
4289      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4290      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4291      have to be updated when switching over to RFC3986.
4292    </t>
4293    <t>
4294      Synchronize core rules with RFC5234 (this includes a change to CHAR
4295      which now excludes NUL).
4296    </t>
4297    <t>
4298      Get rid of prose rules that span multiple lines.
4299    </t>
4300    <t>
4301      Get rid of unused rules LOALPHA and UPALPHA.
4302    </t>
4303    <t>
4304      Move "Product Tokens" section (back) into Part 1, as "token" is used
4305      in the definition of the Upgrade header.
4306    </t>
4307    <t>
4308      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4309    </t>
4310    <t>
4311      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4312    </t>
4313  </list>
4317<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4319  Closed issues:
4320  <list style="symbols">
4321    <t>
4322      <eref target=""/>:
4323      "HTTP-date vs. rfc1123-date"
4324    </t>
4325    <t>
4326      <eref target=""/>:
4327      "WS in quoted-pair"
4328    </t>
4329  </list>
4332  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4333  <list style="symbols">
4334    <t>
4335      Reference RFC 3984, and update header registrations for headers defined
4336      in this document.
4337    </t>
4338  </list>
4341  Ongoing work on ABNF conversion (<eref target=""/>):
4342  <list style="symbols">
4343    <t>
4344      Replace string literals when the string really is case-sensitive (HTTP-Version).
4345    </t>
4346  </list>
4350<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4352  Closed issues:
4353  <list style="symbols">
4354    <t>
4355      <eref target=""/>:
4356      "Connection closing"
4357    </t>
4358    <t>
4359      <eref target=""/>:
4360      "Move registrations and registry information to IANA Considerations"
4361    </t>
4362    <t>
4363      <eref target=""/>:
4364      "need new URL for PAD1995 reference"
4365    </t>
4366    <t>
4367      <eref target=""/>:
4368      "IANA Considerations: update HTTP URI scheme registration"
4369    </t>
4370    <t>
4371      <eref target=""/>:
4372      "Cite HTTPS URI scheme definition"
4373    </t>
4374    <t>
4375      <eref target=""/>:
4376      "List-type headers vs Set-Cookie"
4377    </t>
4378  </list>
4381  Ongoing work on ABNF conversion (<eref target=""/>):
4382  <list style="symbols">
4383    <t>
4384      Replace string literals when the string really is case-sensitive (HTTP-Date).
4385    </t>
4386    <t>
4387      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4388    </t>
4389  </list>
4393<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4395  Closed issues:
4396  <list style="symbols">
4397    <t>
4398      <eref target=""/>:
4399      "RFC 2822 is updated by RFC 5322"
4400    </t>
4401  </list>
4404  Ongoing work on ABNF conversion (<eref target=""/>):
4405  <list style="symbols">
4406    <t>
4407      Use "/" instead of "|" for alternatives.
4408    </t>
4409    <t>
4410      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4411    </t>
4412  </list>
4418<section title="Terminology" anchor="intro.terminology">
4420   This specification uses a number of terms to refer to the roles
4421   played by participants in, and objects of, the HTTP communication.
4424  <iref item="connection"/>
4425  <x:dfn>connection</x:dfn>
4426  <list>
4427    <t>
4428      A transport layer virtual circuit established between two programs
4429      for the purpose of communication.
4430    </t>
4431  </list>
4434  <iref item="message"/>
4435  <x:dfn>message</x:dfn>
4436  <list>
4437    <t>
4438      The basic unit of HTTP communication, consisting of a structured
4439      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4440      transmitted via the connection.
4441    </t>
4442  </list>
4445  <iref item="request"/>
4446  <x:dfn>request</x:dfn>
4447  <list>
4448    <t>
4449      An HTTP request message, as defined in <xref target="request"/>.
4450    </t>
4451  </list>
4454  <iref item="response"/>
4455  <x:dfn>response</x:dfn>
4456  <list>
4457    <t>
4458      An HTTP response message, as defined in <xref target="response"/>.
4459    </t>
4460  </list>
4463  <iref item="resource"/>
4464  <x:dfn>resource</x:dfn>
4465  <list>
4466    <t>
4467      A network data object or service that can be identified by a URI,
4468      as defined in <xref target="uri"/>. Resources may be available in multiple
4469      representations (e.g. multiple languages, data formats, size, and
4470      resolutions) or vary in other ways.
4471    </t>
4472  </list>
4475  <iref item="entity"/>
4476  <x:dfn>entity</x:dfn>
4477  <list>
4478    <t>
4479      The information transferred as the payload of a request or
4480      response. An entity consists of metainformation in the form of
4481      entity-header fields and content in the form of an entity-body, as
4482      described in &entity;.
4483    </t>
4484  </list>
4487  <iref item="representation"/>
4488  <x:dfn>representation</x:dfn>
4489  <list>
4490    <t>
4491      An entity included with a response that is subject to content
4492      negotiation, as described in &content.negotiation;. There may exist multiple
4493      representations associated with a particular response status.
4494    </t>
4495  </list>
4498  <iref item="content negotiation"/>
4499  <x:dfn>content negotiation</x:dfn>
4500  <list>
4501    <t>
4502      The mechanism for selecting the appropriate representation when
4503      servicing a request, as described in &content.negotiation;. The
4504      representation of entities in any response can be negotiated
4505      (including error responses).
4506    </t>
4507  </list>
4510  <iref item="variant"/>
4511  <x:dfn>variant</x:dfn>
4512  <list>
4513    <t>
4514      A resource may have one, or more than one, representation(s)
4515      associated with it at any given instant. Each of these
4516      representations is termed a `variant'.  Use of the term `variant'
4517      does not necessarily imply that the resource is subject to content
4518      negotiation.
4519    </t>
4520  </list>
4523  <iref item="client"/>
4524  <x:dfn>client</x:dfn>
4525  <list>
4526    <t>
4527      A program that establishes connections for the purpose of sending
4528      requests.
4529    </t>
4530  </list>
4533  <iref item="user agent"/>
4534  <x:dfn>user agent</x:dfn>
4535  <list>
4536    <t>
4537      The client which initiates a request. These are often browsers,
4538      editors, spiders (web-traversing robots), or other end user tools.
4539    </t>
4540  </list>
4543  <iref item="server"/>
4544  <x:dfn>server</x:dfn>
4545  <list>
4546    <t>
4547      An application program that accepts connections in order to
4548      service requests by sending back responses. Any given program may
4549      be capable of being both a client and a server; our use of these
4550      terms refers only to the role being performed by the program for a
4551      particular connection, rather than to the program's capabilities
4552      in general. Likewise, any server may act as an origin server,
4553      proxy, gateway, or tunnel, switching behavior based on the nature
4554      of each request.
4555    </t>
4556  </list>
4559  <iref item="origin server"/>
4560  <x:dfn>origin server</x:dfn>
4561  <list>
4562    <t>
4563      The server on which a given resource resides or is to be created.
4564    </t>
4565  </list>
4568  <iref item="proxy"/>
4569  <x:dfn>proxy</x:dfn>
4570  <list>
4571    <t>
4572      An intermediary program which acts as both a server and a client
4573      for the purpose of making requests on behalf of other clients.
4574      Requests are serviced internally or by passing them on, with
4575      possible translation, to other servers. A proxy &MUST; implement
4576      both the client and server requirements of this specification. A
4577      "transparent proxy" is a proxy that does not modify the request or
4578      response beyond what is required for proxy authentication and
4579      identification. A "non-transparent proxy" is a proxy that modifies
4580      the request or response in order to provide some added service to
4581      the user agent, such as group annotation services, media type
4582      transformation, protocol reduction, or anonymity filtering. Except
4583      where either transparent or non-transparent behavior is explicitly
4584      stated, the HTTP proxy requirements apply to both types of
4585      proxies.
4586    </t>
4587  </list>
4590  <iref item="gateway"/>
4591  <x:dfn>gateway</x:dfn>
4592  <list>
4593    <t>
4594      A server which acts as an intermediary for some other server.
4595      Unlike a proxy, a gateway receives requests as if it were the
4596      origin server for the requested resource; the requesting client
4597      may not be aware that it is communicating with a gateway.
4598    </t>
4599  </list>
4602  <iref item="tunnel"/>
4603  <x:dfn>tunnel</x:dfn>
4604  <list>
4605    <t>
4606      An intermediary program which is acting as a blind relay between
4607      two connections. Once active, a tunnel is not considered a party
4608      to the HTTP communication, though the tunnel may have been
4609      initiated by an HTTP request. The tunnel ceases to exist when both
4610      ends of the relayed connections are closed.
4611    </t>
4612  </list>
4615  <iref item="cache"/>
4616  <x:dfn>cache</x:dfn>
4617  <list>
4618    <t>
4619      A program's local store of response messages and the subsystem
4620      that controls its message storage, retrieval, and deletion. A
4621      cache stores cacheable responses in order to reduce the response
4622      time and network bandwidth consumption on future, equivalent
4623      requests. Any client or server may include a cache, though a cache
4624      cannot be used by a server that is acting as a tunnel.
4625    </t>
4626  </list>
4629  <iref item="cacheable"/>
4630  <x:dfn>cacheable</x:dfn>
4631  <list>
4632    <t>
4633      A response is cacheable if a cache is allowed to store a copy of
4634      the response message for use in answering subsequent requests. The
4635      rules for determining the cacheability of HTTP responses are
4636      defined in &caching;. Even if a resource is cacheable, there may
4637      be additional constraints on whether a cache can use the cached
4638      copy for a particular request.
4639    </t>
4640  </list>
4643  <iref item="upstream"/>
4644  <iref item="downstream"/>
4645  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4646  <list>
4647    <t>
4648      Upstream and downstream describe the flow of a message: all
4649      messages flow from upstream to downstream.
4650    </t>
4651  </list>
4654  <iref item="inbound"/>
4655  <iref item="outbound"/>
4656  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4657  <list>
4658    <t>
4659      Inbound and outbound refer to the request and response paths for
4660      messages: "inbound" means "traveling toward the origin server",
4661      and "outbound" means "traveling toward the user agent"
4662    </t>
4663  </list>
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