source: draft-ietf-httpbis/latest/p1-messaging.xml @ 349

Last change on this file since 349 was 349, checked in by julian.reschke@…, 11 years ago

only reference RFC 6234's core rules (related to #36)

  • Property svn:eol-style set to native
File size: 199.0 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
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='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
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>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
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>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
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>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
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>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
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>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
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>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
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>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
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>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
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>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
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.
211</t>
212</abstract>
213
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 (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
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.
246</t>
247<t>
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.
258</t>
259<t>
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"/>.
268</t>
269
270<section title="Purpose" anchor="intro.purpose">
271<t>
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"/>.
281</t>
282<t>
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.
288</t>
289</section>
290
291<section title="Requirements" anchor="intro.requirements">
292<t>
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"/>.
296</t>
297<t>
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."
305</t>
306</section>
307
308<section title="Overall Operation" anchor="intro.overall.operation">
309<t>
310   HTTP is a request/response protocol. A client sends a
311   request to the server in the form of a request method, URI, and
312   protocol version, followed by a MIME-like message containing request
313   modifiers, client information, and possible body content over a
314   connection with a server. The server responds with a status line,
315   including the message's protocol version and a success or error code,
316   followed by a MIME-like message containing server information, entity
317   metainformation, and possible entity-body content. The relationship
318   between HTTP and MIME is described in &diff2045entity;.
319</t>
320<t>
321   Most HTTP communication is initiated by a user agent and consists of
322   a request to be applied to a resource on some origin server. In the
323   simplest case, this may be accomplished via a single connection (v)
324   between the user agent (UA) and the origin server (O).
325</t>
326<figure><artwork type="drawing">
327       request chain ------------------------&gt;
328    UA -------------------v------------------- O
329       &lt;----------------------- response chain
330</artwork></figure>
331<t>
332   A more complicated situation occurs when one or more intermediaries
333   are present in the request/response chain. There are three common
334   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
335   forwarding agent, receiving requests for a URI in its absolute form,
336   rewriting all or part of the message, and forwarding the reformatted
337   request toward the server identified by the URI. A gateway is a
338   receiving agent, acting as a layer above some other server(s) and, if
339   necessary, translating the requests to the underlying server's
340   protocol. A tunnel acts as a relay point between two connections
341   without changing the messages; tunnels are used when the
342   communication needs to pass through an intermediary (such as a
343   firewall) even when the intermediary cannot understand the contents
344   of the messages.
345</t>
346<figure><artwork type="drawing">
347       request chain --------------------------------------&gt;
348    UA -----v----- A -----v----- B -----v----- C -----v----- O
349       &lt;------------------------------------- response chain
350</artwork></figure>
351<t>
352   The figure above shows three intermediaries (A, B, and C) between the
353   user agent and origin server. A request or response message that
354   travels the whole chain will pass through four separate connections.
355   This distinction is important because some HTTP communication options
356   may apply only to the connection with the nearest, non-tunnel
357   neighbor, only to the end-points of the chain, or to all connections
358   along the chain. Although the diagram is linear, each participant may
359   be engaged in multiple, simultaneous communications. For example, B
360   may be receiving requests from many clients other than A, and/or
361   forwarding requests to servers other than C, at the same time that it
362   is handling A's request.
363</t>
364<t>
365   Any party to the communication which is not acting as a tunnel may
366   employ an internal cache for handling requests. The effect of a cache
367   is that the request/response chain is shortened if one of the
368   participants along the chain has a cached response applicable to that
369   request. The following illustrates the resulting chain if B has a
370   cached copy of an earlier response from O (via C) for a request which
371   has not been cached by UA or A.
372</t>
373<figure><artwork type="drawing">
374          request chain ----------&gt;
375       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
376          &lt;--------- response chain
377</artwork></figure>
378<t>
379   Not all responses are usefully cacheable, and some requests may
380   contain modifiers which place special requirements on cache behavior.
381   HTTP requirements for cache behavior and cacheable responses are
382   defined in &caching;.
383</t>
384<t>
385   In fact, there are a wide variety of architectures and configurations
386   of caches and proxies currently being experimented with or deployed
387   across the World Wide Web. These systems include national hierarchies
388   of proxy caches to save transoceanic bandwidth, systems that
389   broadcast or multicast cache entries, organizations that distribute
390   subsets of cached data via CD-ROM, and so on. HTTP systems are used
391   in corporate intranets over high-bandwidth links, and for access via
392   PDAs with low-power radio links and intermittent connectivity. The
393   goal of HTTP/1.1 is to support the wide diversity of configurations
394   already deployed while introducing protocol constructs that meet the
395   needs of those who build web applications that require high
396   reliability and, failing that, at least reliable indications of
397   failure.
398</t>
399<t>
400   HTTP communication usually takes place over TCP/IP connections. The
401   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
402   not preclude HTTP from being implemented on top of any other protocol
403   on the Internet, or on other networks. HTTP only presumes a reliable
404   transport; any protocol that provides such guarantees can be used;
405   the mapping of the HTTP/1.1 request and response structures onto the
406   transport data units of the protocol in question is outside the scope
407   of this specification.
408</t>
409<t>
410   In HTTP/1.0, most implementations used a new connection for each
411   request/response exchange. In HTTP/1.1, a connection may be used for
412   one or more request/response exchanges, although connections may be
413   closed for a variety of reasons (see <xref target="persistent.connections"/>).
414</t>
415</section>
416</section>
417
418<section title="Notational Conventions and Generic Grammar" anchor="notation">
419
420<section title="ABNF Extensions" anchor="notation.abnf">
421<t>
422   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
423   improve readability.<cref>The current plan is to remove these extensions prior
424   to the last call draft.</cref>
425</t>
426
427<section title="#rule">
428  <t>
429    A construct "#" is defined, similar to "*", for defining lists of
430    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
431    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
432    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
433    form of lists very easy; a rule such as
434    <figure><artwork type="example">
435 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
436  </t>
437  <t>
438    can be shown as
439    <figure><artwork type="example">
440 1#element</artwork></figure>
441  </t>
442  <t>
443    Wherever this construct is used, null elements are allowed, but do
444    not contribute to the count of elements present. That is,
445    "(element), , (element) " is permitted, but counts as only two
446    elements. Therefore, where at least one element is required, at
447    least one non-null element &MUST; be present. Default values are 0
448    and infinity so that "#element" allows any number, including zero;
449    "1#element" requires at least one; and "1#2element" allows one or
450    two.
451  </t>
452</section>
453
454<section title="implied *LWS" anchor="implied.LWS">
455  <iref item="implied *LWS" primary="true"/>
456    <t>
457      The grammar described by this specification is word-based. Except
458      where noted otherwise, linear white space (LWS) can be included
459      between any two adjacent words (token or quoted-string), and
460      between adjacent words and separators, without changing the
461      interpretation of a field. At least one delimiter (LWS and/or
462      separators) &MUST; exist between any two tokens (for the definition
463      of "token" below), since they would otherwise be interpreted as a
464      single token.
465    </t>
466</section>
467</section>
468
469<section title="Basic Rules" anchor="basic.rules">
470<t anchor="core.rules">
471  <x:anchor-alias value="ALPHA"/>
472  <x:anchor-alias value="CHAR"/>
473  <x:anchor-alias value="CTL"/>
474  <x:anchor-alias value="CR"/>
475  <x:anchor-alias value="CRLF"/>
476  <x:anchor-alias value="DIGIT"/>
477  <x:anchor-alias value="DQUOTE"/>
478  <x:anchor-alias value="HEXDIG"/>
479  <x:anchor-alias value="HTAB"/>
480  <x:anchor-alias value="LF"/>
481  <x:anchor-alias value="OCTET"/>
482  <x:anchor-alias value="SP"/>
483  <x:anchor-alias value="WSP"/>
484   This specification uses the Augmented Backus-Naur Form (ABNF) notation
485   of <xref target="RFC5234"/>.  The following core rules are included by
486   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
487   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
488   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
489   DIGIT (decimal 0-9), DQUOTE (double quote),
490   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
491   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
492   and WSP (white space).
493</t>
494<t anchor="rule.CRLF">
495  <x:anchor-alias value="CRLF"/>
496   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
497   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
498   tolerant applications). The end-of-line marker within an entity-body
499   is defined by its associated media type, as described in &media-types;.
500</t>
501<t anchor="rule.LWS">
502  <x:anchor-alias value="LWS"/>
503   HTTP/1.1 header field values can be folded onto multiple lines if the
504   continuation line begins with a space or horizontal tab. All linear
505   white space, including folding, has the same semantics as SP. A
506   recipient &MAY; replace any linear white space with a single SP before
507   interpreting the field value or forwarding the message downstream.
508</t>
509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
510  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
511</artwork></figure>
512<t anchor="rule.TEXT">
513  <x:anchor-alias value="TEXT"/>
514   The TEXT rule is only used for descriptive field contents and values
515   that are not intended to be interpreted by the message parser. Words
516   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
517   <xref target="ISO-8859-1"/> only when encoded according to the rules of
518   <xref target="RFC2047"/>.
519</t>
520<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
521  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
522                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
523</artwork></figure>
524<t>
525   A CRLF is allowed in the definition of TEXT only as part of a header
526   field continuation. It is expected that the folding LWS will be
527   replaced with a single SP before interpretation of the TEXT value.
528</t>
529<t anchor="rule.token.separators">
530  <x:anchor-alias value="tchar"/>
531  <x:anchor-alias value="token"/>
532  <x:anchor-alias value="separators"/>
533   Many HTTP/1.1 header field values consist of words separated by LWS
534   or special characters. These special characters &MUST; be in a quoted
535   string to be used within a parameter value (as defined in
536   <xref target="transfer.codings"/>).
537</t>
538<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"/>
539  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
540                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
541                 / "/" / "[" / "]" / "?" / "="
542                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
543                 
544  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
545                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
546                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
547                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
548                 
549  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
550</artwork></figure>
551<t anchor="rule.comment">
552  <x:anchor-alias value="comment"/>
553  <x:anchor-alias value="ctext"/>
554   Comments can be included in some HTTP header fields by surrounding
555   the comment text with parentheses. Comments are only allowed in
556   fields containing "comment" as part of their field value definition.
557   In all other fields, parentheses are considered part of the field
558   value.
559</t>
560<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
561  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
562  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
563</artwork></figure>
564<t anchor="rule.quoted-string">
565  <x:anchor-alias value="quoted-string"/>
566  <x:anchor-alias value="qdtext"/>
567   A string of text is parsed as a single word if it is quoted using
568   double-quote marks.
569</t>
570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
571  <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> )
572  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
573</artwork></figure>
574<t anchor="rule.quoted-pair">
575  <x:anchor-alias value="quoted-pair"/>
576  <x:anchor-alias value="quoted-text"/>
577   The backslash character ("\") &MAY; be used as a single-character
578   quoting mechanism only within quoted-string and comment constructs.
579</t>
580<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
581  <x:ref>quoted-text</x:ref>    = %x01-09 /
582                   %x0B-0C /
583                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
584  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
585</artwork></figure>
586</section>
587
588<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
589  <x:anchor-alias value="request-header"/>
590  <x:anchor-alias value="response-header"/>
591  <x:anchor-alias value="accept-params"/>
592  <x:anchor-alias value="entity-body"/>
593  <x:anchor-alias value="entity-header"/>
594  <x:anchor-alias value="Cache-Control"/>
595  <x:anchor-alias value="Pragma"/>
596  <x:anchor-alias value="Warning"/>
597<t>
598  The ABNF rules below are defined in other parts:
599</t>
600<figure><!-- Part2--><artwork type="abnf2616">
601  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
602  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
603</artwork></figure>
604<figure><!-- Part3--><artwork type="abnf2616">
605  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
606  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
607  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
608</artwork></figure>
609<figure><!-- Part6--><artwork type="abnf2616">
610  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
611  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
612  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
613</artwork></figure>
614</section>
615
616</section>
617
618<section title="Protocol Parameters" anchor="protocol.parameters">
619
620<section title="HTTP Version" anchor="http.version">
621  <x:anchor-alias value="HTTP-Version"/>
622  <x:anchor-alias value="HTTP-Prot-Name"/>
623<t>
624   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
625   of the protocol. The protocol versioning policy is intended to allow
626   the sender to indicate the format of a message and its capacity for
627   understanding further HTTP communication, rather than the features
628   obtained via that communication. No change is made to the version
629   number for the addition of message components which do not affect
630   communication behavior or which only add to extensible field values.
631   The &lt;minor&gt; number is incremented when the changes made to the
632   protocol add features which do not change the general message parsing
633   algorithm, but which may add to the message semantics and imply
634   additional capabilities of the sender. The &lt;major&gt; number is
635   incremented when the format of a message within the protocol is
636   changed. See <xref target="RFC2145"/> for a fuller explanation.
637</t>
638<t>
639   The version of an HTTP message is indicated by an HTTP-Version field
640   in the first line of the message. HTTP-Version is case-sensitive.
641</t>
642<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
643  <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>
644  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
645</artwork></figure>
646<t>
647   Note that the major and minor numbers &MUST; be treated as separate
648   integers and that each &MAY; be incremented higher than a single digit.
649   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
650   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
651   &MUST-NOT; be sent.
652</t>
653<t>
654   An application that sends a request or response message that includes
655   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
656   with this specification. Applications that are at least conditionally
657   compliant with this specification &SHOULD; use an HTTP-Version of
658   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
659   not compatible with HTTP/1.0. For more details on when to send
660   specific HTTP-Version values, see <xref target="RFC2145"/>.
661</t>
662<t>
663   The HTTP version of an application is the highest HTTP version for
664   which the application is at least conditionally compliant.
665</t>
666<t>
667   Proxy and gateway applications need to be careful when forwarding
668   messages in protocol versions different from that of the application.
669   Since the protocol version indicates the protocol capability of the
670   sender, a proxy/gateway &MUST-NOT; send a message with a version
671   indicator which is greater than its actual version. If a higher
672   version request is received, the proxy/gateway &MUST; either downgrade
673   the request version, or respond with an error, or switch to tunnel
674   behavior.
675</t>
676<t>
677   Due to interoperability problems with HTTP/1.0 proxies discovered
678   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
679   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
680   they support. The proxy/gateway's response to that request &MUST; be in
681   the same major version as the request.
682</t>
683<t>
684  <list>
685    <t>
686      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
687      of header fields required or forbidden by the versions involved.
688    </t>
689  </list>
690</t>
691</section>
692
693<section title="Uniform Resource Identifiers" anchor="uri">
694<t>
695   URIs have been known by many names: WWW addresses, Universal Document
696   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
697   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
698   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
699   simply formatted strings which identify--via name, location, or any
700   other characteristic--a resource.
701</t>
702
703<section title="General Syntax" anchor="general.syntax">
704  <x:anchor-alias value="absoluteURI"/>
705  <x:anchor-alias value="authority"/>
706  <x:anchor-alias value="fragment"/>
707  <x:anchor-alias value="path-absolute"/>
708  <x:anchor-alias value="port"/>
709  <x:anchor-alias value="query"/>
710  <x:anchor-alias value="relativeURI"/>
711  <x:anchor-alias value="uri-host"/>
712<t>
713   URIs in HTTP can be represented in absolute form or relative to some
714   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
715   forms are differentiated by the fact that absolute URIs always begin
716   with a scheme name followed by a colon. For definitive information on
717   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
718   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
719   and <xref target="RFC1808"/>). This specification adopts the
720   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
721   "host", "abs_path", "query", and "authority" from that specification:
722</t>
723<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"/>
724  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
725  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
726  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
727  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
728  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
729  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
730  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
731  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
732</artwork></figure>
733<t>
734   HTTP does not place any a priori limit on the length of
735   a URI. Servers &MUST; be able to handle the URI of any resource they
736   serve, and &SHOULD; be able to handle URIs of unbounded length if they
737   provide GET-based forms that could generate such URIs. A server
738   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
739   than the server can handle (see &status-414;).
740</t>
741<t>
742  <list>
743    <t>
744      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
745      above 255 bytes, because some older client or proxy
746      implementations might not properly support these lengths.
747    </t>
748  </list>
749</t>
750</section>
751
752<section title="http URL" anchor="http.url">
753  <x:anchor-alias value="http-URL"/>
754  <iref item="http URI scheme" primary="true"/>
755  <iref item="URI scheme" subitem="http" primary="true"/>
756<t>
757   The "http" scheme is used to locate network resources via the HTTP
758   protocol. This section defines the scheme-specific syntax and
759   semantics for http URLs.
760</t>
761<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
762  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
763             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
764</artwork></figure>
765<t>
766   If the port is empty or not given, port 80 is assumed. The semantics
767   are that the identified resource is located at the server listening
768   for TCP connections on that port of that host, and the Request-URI
769   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
770   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
771   the path-absolute is not present in the URL, it &MUST; be given as "/" when
772   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
773   receives a host name which is not a fully qualified domain name, it
774   &MAY; add its domain to the host name it received. If a proxy receives
775   a fully qualified domain name, the proxy &MUST-NOT; change the host
776   name.
777</t>
778<t><list><t>
779  <iref item="https URI scheme"/>
780  <iref item="URI scheme" subitem="https"/>
781  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
782</t></list></t>
783</section>
784
785<section title="URI Comparison" anchor="uri.comparison">
786<t>
787   When comparing two URIs to decide if they match or not, a client
788   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
789   URIs, with these exceptions:
790  <list style="symbols">
791    <t>A port that is empty or not given is equivalent to the default
792        port for that URI-reference;</t>
793    <t>Comparisons of host names &MUST; be case-insensitive;</t>
794    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
795    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
796  </list>
797</t>
798<t>
799   Characters other than those in the "reserved" set (see
800   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
801   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
802</t>
803<t>
804   For example, the following three URIs are equivalent:
805</t>
806<figure><artwork type="example">
807   http://example.com:80/~smith/home.html
808   http://EXAMPLE.com/%7Esmith/home.html
809   http://EXAMPLE.com:/%7esmith/home.html
810</artwork></figure>
811</section>
812</section>
813
814<section title="Date/Time Formats" anchor="date.time.formats">
815<section title="Full Date" anchor="full.date">
816  <x:anchor-alias value="HTTP-date"/>
817  <x:anchor-alias value="obsolete-date"/>
818  <x:anchor-alias value="rfc1123-date"/>
819  <x:anchor-alias value="rfc850-date"/>
820  <x:anchor-alias value="asctime-date"/>
821  <x:anchor-alias value="date1"/>
822  <x:anchor-alias value="date2"/>
823  <x:anchor-alias value="date3"/>
824  <x:anchor-alias value="rfc1123-date"/>
825  <x:anchor-alias value="time"/>
826  <x:anchor-alias value="wkday"/>
827  <x:anchor-alias value="weekday"/>
828  <x:anchor-alias value="month"/>
829<t>
830   HTTP applications have historically allowed three different formats
831   for the representation of date/time stamps:
832</t>
833<figure><artwork type="example">
834   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
835   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
836   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
837</artwork></figure>
838<t>
839   The first format is preferred as an Internet standard and represents
840   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
841   <xref target="RFC822"/>). The other formats are described here only for
842   compatibility with obsolete implementations.
843   HTTP/1.1 clients and servers that parse the date value &MUST; accept
844   all three formats (for compatibility with HTTP/1.0), though they &MUST;
845   only generate the RFC 1123 format for representing HTTP-date values
846   in header fields. See <xref target="tolerant.applications"/> for further information.
847</t>
848<t><list><t>
849      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
850      accepting date values that may have been sent by non-HTTP
851      applications, as is sometimes the case when retrieving or posting
852      messages via proxies/gateways to SMTP or NNTP.
853</t></list></t>
854<t>
855   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
856   (GMT), without exception. For the purposes of HTTP, GMT is exactly
857   equal to UTC (Coordinated Universal Time). This is indicated in the
858   first two formats by the inclusion of "GMT" as the three-letter
859   abbreviation for time zone, and &MUST; be assumed when reading the
860   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
861   additional LWS beyond that specifically included as SP in the
862   grammar.
863</t>
864<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"/>
865  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
866  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
867  <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
868  <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
869  <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>
870  <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>
871                 ; day month year (e.g., 02 Jun 1982)
872  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
873                 ; day-month-year (e.g., 02-Jun-82)
874  <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> ))
875                 ; month day (e.g., Jun  2)
876  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
877                 ; 00:00:00 - 23:59:59
878  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
879               / s-Thu / s-Fri / s-Sat / s-Sun
880  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
881               / l-Thu / l-Fri / l-Sat / l-Sun
882  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
883               / s-May / s-Jun / s-Jul / s-Aug
884               / s-Sep / s-Oct / s-Nov / s-Dec
885               
886  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
887
888  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
889  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
890  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
891  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
892  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
893  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
894  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
895
896  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
897  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
898  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
899  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
900  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
901  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
902  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
903
904  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
905  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
906  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
907  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
908  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
909  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
910  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
911  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
912  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
913  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
914  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
915  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
916</artwork></figure>
917<t>
918      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
919      to their usage within the protocol stream. Clients and servers are
920      not required to use these formats for user presentation, request
921      logging, etc.
922</t>
923</section>
924</section>
925
926<section title="Transfer Codings" anchor="transfer.codings">
927  <x:anchor-alias value="parameter"/>
928  <x:anchor-alias value="transfer-coding"/>
929  <x:anchor-alias value="transfer-extension"/>
930<t>
931   Transfer-coding values are used to indicate an encoding
932   transformation that has been, can be, or may need to be applied to an
933   entity-body in order to ensure "safe transport" through the network.
934   This differs from a content coding in that the transfer-coding is a
935   property of the message, not of the original entity.
936</t>
937<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
938  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
939  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
940</artwork></figure>
941<t anchor="rule.parameter">
942  <x:anchor-alias value="attribute"/>
943  <x:anchor-alias value="parameter"/>
944  <x:anchor-alias value="value"/>
945   Parameters are in  the form of attribute/value pairs.
946</t>
947<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"/>
948  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
949  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
950  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
951</artwork></figure>
952<t>
953   All transfer-coding values are case-insensitive. HTTP/1.1 uses
954   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
955   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
956</t>
957<t>
958   Whenever a transfer-coding is applied to a message-body, the set of
959   transfer-codings &MUST; include "chunked", unless the message indicates it
960   is terminated by closing the connection. When the "chunked" transfer-coding
961   is used, it &MUST; be the last transfer-coding applied to the
962   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
963   than once to a message-body. These rules allow the recipient to
964   determine the transfer-length of the message (<xref target="message.length"/>).
965</t>
966<t>
967   Transfer-codings are analogous to the Content-Transfer-Encoding
968   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
969   binary data over a 7-bit transport service. However, safe transport
970   has a different focus for an 8bit-clean transfer protocol. In HTTP,
971   the only unsafe characteristic of message-bodies is the difficulty in
972   determining the exact body length (<xref target="message.length"/>), or the desire to
973   encrypt data over a shared transport.
974</t>
975<t>
976   The Internet Assigned Numbers Authority (IANA) acts as a registry for
977   transfer-coding value tokens. Initially, the registry contains the
978   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
979   "gzip", "compress", and "deflate" (&content-codings;).
980</t>
981<t>
982   New transfer-coding value tokens &SHOULD; be registered in the same way
983   as new content-coding value tokens (&content-codings;).
984</t>
985<t>
986   A server which receives an entity-body with a transfer-coding it does
987   not understand &SHOULD; return 501 (Not Implemented), and close the
988   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
989   client.
990</t>
991
992<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
993  <x:anchor-alias value="chunk"/>
994  <x:anchor-alias value="Chunked-Body"/>
995  <x:anchor-alias value="chunk-data"/>
996  <x:anchor-alias value="chunk-extension"/>
997  <x:anchor-alias value="chunk-ext-name"/>
998  <x:anchor-alias value="chunk-ext-val"/>
999  <x:anchor-alias value="chunk-size"/>
1000  <x:anchor-alias value="last-chunk"/>
1001  <x:anchor-alias value="trailer-part"/>
1002<t>
1003   The chunked encoding modifies the body of a message in order to
1004   transfer it as a series of chunks, each with its own size indicator,
1005   followed by an &OPTIONAL; trailer containing entity-header fields. This
1006   allows dynamically produced content to be transferred along with the
1007   information necessary for the recipient to verify that it has
1008   received the full message.
1009</t>
1010<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"/>
1011  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1012                   <x:ref>last-chunk</x:ref>
1013                   <x:ref>trailer-part</x:ref>
1014                   <x:ref>CRLF</x:ref>
1015 
1016  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1017                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1018  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1019  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1020 
1021  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1022  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1023  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1024  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1025  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1026</artwork></figure>
1027<t>
1028   The chunk-size field is a string of hex digits indicating the size of
1029   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1030   zero, followed by the trailer, which is terminated by an empty line.
1031</t>
1032<t>
1033   The trailer allows the sender to include additional HTTP header
1034   fields at the end of the message. The Trailer header field can be
1035   used to indicate which header fields are included in a trailer (see
1036   <xref target="header.trailer"/>).
1037</t>
1038<t>
1039   A server using chunked transfer-coding in a response &MUST-NOT; use the
1040   trailer for any header fields unless at least one of the following is
1041   true:
1042  <list style="numbers">
1043    <t>the request included a TE header field that indicates "trailers" is
1044     acceptable in the transfer-coding of the  response, as described in
1045     <xref target="header.te"/>; or,</t>
1046
1047    <t>the server is the origin server for the response, the trailer
1048     fields consist entirely of optional metadata, and the recipient
1049     could use the message (in a manner acceptable to the origin server)
1050     without receiving this metadata.  In other words, the origin server
1051     is willing to accept the possibility that the trailer fields might
1052     be silently discarded along the path to the client.</t>
1053  </list>
1054</t>
1055<t>
1056   This requirement prevents an interoperability failure when the
1057   message is being received by an HTTP/1.1 (or later) proxy and
1058   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1059   compliance with the protocol would have necessitated a possibly
1060   infinite buffer on the proxy.
1061</t>
1062<t>
1063   A process for decoding the "chunked" transfer-coding
1064   can be represented in pseudo-code as:
1065</t>
1066<figure><artwork type="code">
1067    length := 0
1068    read chunk-size, chunk-extension (if any) and CRLF
1069    while (chunk-size &gt; 0) {
1070       read chunk-data and CRLF
1071       append chunk-data to entity-body
1072       length := length + chunk-size
1073       read chunk-size and CRLF
1074    }
1075    read entity-header
1076    while (entity-header not empty) {
1077       append entity-header to existing header fields
1078       read entity-header
1079    }
1080    Content-Length := length
1081    Remove "chunked" from Transfer-Encoding
1082</artwork></figure>
1083<t>
1084   All HTTP/1.1 applications &MUST; be able to receive and decode the
1085   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1086   they do not understand.
1087</t>
1088</section>
1089</section>
1090
1091<section title="Product Tokens" anchor="product.tokens">
1092  <x:anchor-alias value="product"/>
1093  <x:anchor-alias value="product-version"/>
1094<t>
1095   Product tokens are used to allow communicating applications to
1096   identify themselves by software name and version. Most fields using
1097   product tokens also allow sub-products which form a significant part
1098   of the application to be listed, separated by white space. By
1099   convention, the products are listed in order of their significance
1100   for identifying the application.
1101</t>
1102<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1103  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1104  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1105</artwork></figure>
1106<t>
1107   Examples:
1108</t>
1109<figure><artwork type="example">
1110    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1111    Server: Apache/0.8.4
1112</artwork></figure>
1113<t>
1114   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1115   used for advertising or other non-essential information. Although any
1116   token character &MAY; appear in a product-version, this token &SHOULD;
1117   only be used for a version identifier (i.e., successive versions of
1118   the same product &SHOULD; only differ in the product-version portion of
1119   the product value).
1120</t>
1121</section>
1122
1123</section>
1124
1125<section title="HTTP Message" anchor="http.message">
1126
1127<section title="Message Types" anchor="message.types">
1128  <x:anchor-alias value="generic-message"/>
1129  <x:anchor-alias value="HTTP-message"/>
1130  <x:anchor-alias value="start-line"/>
1131<t>
1132   HTTP messages consist of requests from client to server and responses
1133   from server to client.
1134</t>
1135<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1136  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1137</artwork></figure>
1138<t>
1139   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1140   message format of <xref target="RFC5322"/> for transferring entities (the payload
1141   of the message). Both types of message consist of a start-line, zero
1142   or more header fields (also known as "headers"), an empty line (i.e.,
1143   a line with nothing preceding the CRLF) indicating the end of the
1144   header fields, and possibly a message-body.
1145</t>
1146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1147  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1148                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1149                    <x:ref>CRLF</x:ref>
1150                    [ <x:ref>message-body</x:ref> ]
1151  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1152</artwork></figure>
1153<t>
1154   In the interest of robustness, servers &SHOULD; ignore any empty
1155   line(s) received where a Request-Line is expected. In other words, if
1156   the server is reading the protocol stream at the beginning of a
1157   message and receives a CRLF first, it should ignore the CRLF.
1158</t>
1159<t>
1160   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1161   after a POST request. To restate what is explicitly forbidden by the
1162   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1163   extra CRLF.
1164</t>
1165</section>
1166
1167<section title="Message Headers" anchor="message.headers">
1168  <x:anchor-alias value="field-content"/>
1169  <x:anchor-alias value="field-name"/>
1170  <x:anchor-alias value="field-value"/>
1171  <x:anchor-alias value="message-header"/>
1172<t>
1173   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1174   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1175   entity-header (&entity-header-fields;) fields, follow the same generic format as
1176   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1177   of a name followed by a colon (":") and the field value. Field names
1178   are case-insensitive. The field value &MAY; be preceded by any amount
1179   of LWS, though a single SP is preferred. Header fields can be
1180   extended over multiple lines by preceding each extra line with at
1181   least one SP or HTAB. Applications ought to follow "common form", where
1182   one is known or indicated, when generating HTTP constructs, since
1183   there might exist some implementations that fail to accept anything
1184   beyond the common forms.
1185</t>
1186<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"/>
1187  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1188  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1189  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1190  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1191                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1192                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1193                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1194</artwork></figure>
1195<t>
1196   The field-content does not include any leading or trailing LWS:
1197   linear white space occurring before the first non-whitespace
1198   character of the field-value or after the last non-whitespace
1199   character of the field-value. Such leading or trailing LWS &MAY; be
1200   removed without changing the semantics of the field value. Any LWS
1201   that occurs between field-content &MAY; be replaced with a single SP
1202   before interpreting the field value or forwarding the message
1203   downstream.
1204</t>
1205<t>
1206   The order in which header fields with differing field names are
1207   received is not significant. However, it is "good practice" to send
1208   general-header fields first, followed by request-header or response-header
1209   fields, and ending with the entity-header fields.
1210</t>
1211<t>
1212   Multiple message-header fields with the same field-name &MAY; be
1213   present in a message if and only if the entire field-value for that
1214   header field is defined as a comma-separated list [i.e., #(values)].
1215   It &MUST; be possible to combine the multiple header fields into one
1216   "field-name: field-value" pair, without changing the semantics of the
1217   message, by appending each subsequent field-value to the first, each
1218   separated by a comma. The order in which header fields with the same
1219   field-name are received is therefore significant to the
1220   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1221   change the order of these field values when a message is forwarded.
1222</t>
1223<t>
1224  <list><t>
1225   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1226   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1227   can occur multiple times, but does not use the list syntax, and thus cannot
1228   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1229   for details.) Also note that the Set-Cookie2 header specified in
1230   <xref target="RFC2965"/> does not share this problem.
1231  </t></list>
1232</t>
1233 
1234</section>
1235
1236<section title="Message Body" anchor="message.body">
1237  <x:anchor-alias value="message-body"/>
1238<t>
1239   The message-body (if any) of an HTTP message is used to carry the
1240   entity-body associated with the request or response. The message-body
1241   differs from the entity-body only when a transfer-coding has been
1242   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1243</t>
1244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1245  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1246               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1247</artwork></figure>
1248<t>
1249   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1250   applied by an application to ensure safe and proper transfer of the
1251   message. Transfer-Encoding is a property of the message, not of the
1252   entity, and thus &MAY; be added or removed by any application along the
1253   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1254   when certain transfer-codings may be used.)
1255</t>
1256<t>
1257   The rules for when a message-body is allowed in a message differ for
1258   requests and responses.
1259</t>
1260<t>
1261   The presence of a message-body in a request is signaled by the
1262   inclusion of a Content-Length or Transfer-Encoding header field in
1263   the request's message-headers. A message-body &MUST-NOT; be included in
1264   a request if the specification of the request method (&method;)
1265   explicitly disallows an entity-body in requests.
1266   When a request message contains both a message-body of non-zero
1267   length and a method that does not define any semantics for that
1268   request message-body, then an origin server &SHOULD; either ignore
1269   the message-body or respond with an appropriate error message
1270   (e.g., 413).  A proxy or gateway, when presented the same request,
1271   &SHOULD; either forward the request inbound with the message-body or
1272   ignore the message-body when determining a response.
1273</t>
1274<t>
1275   For response messages, whether or not a message-body is included with
1276   a message is dependent on both the request method and the response
1277   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1278   &MUST-NOT; include a message-body, even though the presence of entity-header
1279   fields might lead one to believe they do. All 1xx
1280   (informational), 204 (No Content), and 304 (Not Modified) responses
1281   &MUST-NOT; include a message-body. All other responses do include a
1282   message-body, although it &MAY; be of zero length.
1283</t>
1284</section>
1285
1286<section title="Message Length" anchor="message.length">
1287<t>
1288   The transfer-length of a message is the length of the message-body as
1289   it appears in the message; that is, after any transfer-codings have
1290   been applied. When a message-body is included with a message, the
1291   transfer-length of that body is determined by one of the following
1292   (in order of precedence):
1293</t>
1294<t>
1295  <list style="numbers">
1296    <x:lt><t>
1297     Any response message which "&MUST-NOT;" include a message-body (such
1298     as the 1xx, 204, and 304 responses and any response to a HEAD
1299     request) is always terminated by the first empty line after the
1300     header fields, regardless of the entity-header fields present in
1301     the message.
1302    </t></x:lt>
1303    <x:lt><t>
1304     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1305     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1306     is used, the transfer-length is defined by the use of this transfer-coding.
1307     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1308     is not present, the transfer-length is defined by the sender closing the connection.
1309    </t></x:lt>
1310    <x:lt><t>
1311     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1312     decimal value in OCTETs represents both the entity-length and the
1313     transfer-length. The Content-Length header field &MUST-NOT; be sent
1314     if these two lengths are different (i.e., if a Transfer-Encoding
1315     header field is present). If a message is received with both a
1316     Transfer-Encoding header field and a Content-Length header field,
1317     the latter &MUST; be ignored.
1318    </t></x:lt>
1319    <x:lt><t>
1320     If the message uses the media type "multipart/byteranges", and the
1321     transfer-length is not otherwise specified, then this self-delimiting
1322     media type defines the transfer-length. This media type
1323     &MUST-NOT; be used unless the sender knows that the recipient can parse
1324     it; the presence in a request of a Range header with multiple byte-range
1325     specifiers from a 1.1 client implies that the client can parse
1326     multipart/byteranges responses.
1327    <list style="empty"><t>
1328       A range header might be forwarded by a 1.0 proxy that does not
1329       understand multipart/byteranges; in this case the server &MUST;
1330       delimit the message using methods defined in items 1, 3 or 5 of
1331       this section.
1332    </t></list>
1333    </t></x:lt>
1334    <x:lt><t>
1335     By the server closing the connection. (Closing the connection
1336     cannot be used to indicate the end of a request body, since that
1337     would leave no possibility for the server to send back a response.)
1338    </t></x:lt>
1339  </list>
1340</t>
1341<t>
1342   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1343   containing a message-body &MUST; include a valid Content-Length header
1344   field unless the server is known to be HTTP/1.1 compliant. If a
1345   request contains a message-body and a Content-Length is not given,
1346   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1347   determine the length of the message, or with 411 (Length Required) if
1348   it wishes to insist on receiving a valid Content-Length.
1349</t>
1350<t>
1351   All HTTP/1.1 applications that receive entities &MUST; accept the
1352   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1353   to be used for messages when the message length cannot be determined
1354   in advance.
1355</t>
1356<t>
1357   Messages &MUST-NOT; include both a Content-Length header field and a
1358   transfer-coding. If the message does include a
1359   transfer-coding, the Content-Length &MUST; be ignored.
1360</t>
1361<t>
1362   When a Content-Length is given in a message where a message-body is
1363   allowed, its field value &MUST; exactly match the number of OCTETs in
1364   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1365   invalid length is received and detected.
1366</t>
1367</section>
1368
1369<section title="General Header Fields" anchor="general.header.fields">
1370  <x:anchor-alias value="general-header"/>
1371<t>
1372   There are a few header fields which have general applicability for
1373   both request and response messages, but which do not apply to the
1374   entity being transferred. These header fields apply only to the
1375   message being transmitted.
1376</t>
1377<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1378  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1379                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1380                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1381                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1382                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1383                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1384                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1385                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1386                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1387</artwork></figure>
1388<t>
1389   General-header field names can be extended reliably only in
1390   combination with a change in the protocol version. However, new or
1391   experimental header fields may be given the semantics of general
1392   header fields if all parties in the communication recognize them to
1393   be general-header fields. Unrecognized header fields are treated as
1394   entity-header fields.
1395</t>
1396</section>
1397</section>
1398
1399<section title="Request" anchor="request">
1400  <x:anchor-alias value="Request"/>
1401<t>
1402   A request message from a client to a server includes, within the
1403   first line of that message, the method to be applied to the resource,
1404   the identifier of the resource, and the protocol version in use.
1405</t>
1406<!--                 Host                      ; should be moved here eventually -->
1407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1408  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1409                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1410                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1411                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1412                  <x:ref>CRLF</x:ref>
1413                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1414</artwork></figure>
1415
1416<section title="Request-Line" anchor="request-line">
1417  <x:anchor-alias value="Request-Line"/>
1418<t>
1419   The Request-Line begins with a method token, followed by the
1420   Request-URI and the protocol version, and ending with CRLF. The
1421   elements are separated by SP characters. No CR or LF is allowed
1422   except in the final CRLF sequence.
1423</t>
1424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1425  <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>
1426</artwork></figure>
1427
1428<section title="Method" anchor="method">
1429  <x:anchor-alias value="Method"/>
1430<t>
1431   The Method  token indicates the method to be performed on the
1432   resource identified by the Request-URI. The method is case-sensitive.
1433</t>
1434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1435  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1436</artwork></figure>
1437</section>
1438
1439<section title="Request-URI" anchor="request-uri">
1440  <x:anchor-alias value="Request-URI"/>
1441<t>
1442   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1443   identifies the resource upon which to apply the request.
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1446  <x:ref>Request-URI</x:ref>    = "*"
1447                 / <x:ref>absoluteURI</x:ref>
1448                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1449                 / <x:ref>authority</x:ref>
1450</artwork></figure>
1451<t>
1452   The four options for Request-URI are dependent on the nature of the
1453   request. The asterisk "*" means that the request does not apply to a
1454   particular resource, but to the server itself, and is only allowed
1455   when the method used does not necessarily apply to a resource. One
1456   example would be
1457</t>
1458<figure><artwork type="example">
1459    OPTIONS * HTTP/1.1
1460</artwork></figure>
1461<t>
1462   The absoluteURI form is &REQUIRED; when the request is being made to a
1463   proxy. The proxy is requested to forward the request or service it
1464   from a valid cache, and return the response. Note that the proxy &MAY;
1465   forward the request on to another proxy or directly to the server
1466   specified by the absoluteURI. In order to avoid request loops, a
1467   proxy &MUST; be able to recognize all of its server names, including
1468   any aliases, local variations, and the numeric IP address. An example
1469   Request-Line would be:
1470</t>
1471<figure><artwork type="example">
1472    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1473</artwork></figure>
1474<t>
1475   To allow for transition to absoluteURIs in all requests in future
1476   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1477   form in requests, even though HTTP/1.1 clients will only generate
1478   them in requests to proxies.
1479</t>
1480<t>
1481   The authority form is only used by the CONNECT method (&CONNECT;).
1482</t>
1483<t>
1484   The most common form of Request-URI is that used to identify a
1485   resource on an origin server or gateway. In this case the absolute
1486   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1487   the Request-URI, and the network location of the URI (authority) &MUST;
1488   be transmitted in a Host header field. For example, a client wishing
1489   to retrieve the resource above directly from the origin server would
1490   create a TCP connection to port 80 of the host "www.example.org" and send
1491   the lines:
1492</t>
1493<figure><artwork type="example">
1494    GET /pub/WWW/TheProject.html HTTP/1.1
1495    Host: www.example.org
1496</artwork></figure>
1497<t>
1498   followed by the remainder of the Request. Note that the absolute path
1499   cannot be empty; if none is present in the original URI, it &MUST; be
1500   given as "/" (the server root).
1501</t>
1502<t>
1503   The Request-URI is transmitted in the format specified in
1504   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1505   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1506   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1507   &MUST; decode the Request-URI in order to
1508   properly interpret the request. Servers &SHOULD; respond to invalid
1509   Request-URIs with an appropriate status code.
1510</t>
1511<t>
1512   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1513   received Request-URI when forwarding it to the next inbound server,
1514   except as noted above to replace a null path-absolute with "/".
1515</t>
1516<t>
1517  <list><t>
1518      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1519      meaning of the request when the origin server is improperly using
1520      a non-reserved URI character for a reserved purpose.  Implementors
1521      should be aware that some pre-HTTP/1.1 proxies have been known to
1522      rewrite the Request-URI.
1523  </t></list>
1524</t>
1525</section>
1526</section>
1527
1528<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1529<t>
1530   The exact resource identified by an Internet request is determined by
1531   examining both the Request-URI and the Host header field.
1532</t>
1533<t>
1534   An origin server that does not allow resources to differ by the
1535   requested host &MAY; ignore the Host header field value when
1536   determining the resource identified by an HTTP/1.1 request. (But see
1537   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1538   for other requirements on Host support in HTTP/1.1.)
1539</t>
1540<t>
1541   An origin server that does differentiate resources based on the host
1542   requested (sometimes referred to as virtual hosts or vanity host
1543   names) &MUST; use the following rules for determining the requested
1544   resource on an HTTP/1.1 request:
1545  <list style="numbers">
1546    <t>If Request-URI is an absoluteURI, the host is part of the
1547     Request-URI. Any Host header field value in the request &MUST; be
1548     ignored.</t>
1549    <t>If the Request-URI is not an absoluteURI, and the request includes
1550     a Host header field, the host is determined by the Host header
1551     field value.</t>
1552    <t>If the host as determined by rule 1 or 2 is not a valid host on
1553     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1554  </list>
1555</t>
1556<t>
1557   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1558   attempt to use heuristics (e.g., examination of the URI path for
1559   something unique to a particular host) in order to determine what
1560   exact resource is being requested.
1561</t>
1562</section>
1563
1564</section>
1565
1566
1567<section title="Response" anchor="response">
1568  <x:anchor-alias value="Response"/>
1569<t>
1570   After receiving and interpreting a request message, a server responds
1571   with an HTTP response message.
1572</t>
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1574  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1575                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1576                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1577                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1578                  <x:ref>CRLF</x:ref>
1579                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1580</artwork></figure>
1581
1582<section title="Status-Line" anchor="status-line">
1583  <x:anchor-alias value="Status-Line"/>
1584<t>
1585   The first line of a Response message is the Status-Line, consisting
1586   of the protocol version followed by a numeric status code and its
1587   associated textual phrase, with each element separated by SP
1588   characters. No CR or LF is allowed except in the final CRLF sequence.
1589</t>
1590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1591  <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>
1592</artwork></figure>
1593
1594<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1595  <x:anchor-alias value="Reason-Phrase"/>
1596  <x:anchor-alias value="Status-Code"/>
1597<t>
1598   The Status-Code element is a 3-digit integer result code of the
1599   attempt to understand and satisfy the request. These codes are fully
1600   defined in &status-codes;.  The Reason Phrase exists for the sole
1601   purpose of providing a textual description associated with the numeric
1602   status code, out of deference to earlier Internet application protocols
1603   that were more frequently used with interactive text clients.
1604   A client &SHOULD; ignore the content of the Reason Phrase.
1605</t>
1606<t>
1607   The first digit of the Status-Code defines the class of response. The
1608   last two digits do not have any categorization role. There are 5
1609   values for the first digit:
1610  <list style="symbols">
1611    <t>
1612      1xx: Informational - Request received, continuing process
1613    </t>
1614    <t>
1615      2xx: Success - The action was successfully received,
1616        understood, and accepted
1617    </t>
1618    <t>
1619      3xx: Redirection - Further action must be taken in order to
1620        complete the request
1621    </t>
1622    <t>
1623      4xx: Client Error - The request contains bad syntax or cannot
1624        be fulfilled
1625    </t>
1626    <t>
1627      5xx: Server Error - The server failed to fulfill an apparently
1628        valid request
1629    </t>
1630  </list>
1631</t>
1632<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"/>
1633  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1634  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1635</artwork></figure>
1636</section>
1637</section>
1638
1639</section>
1640
1641
1642<section title="Connections" anchor="connections">
1643
1644<section title="Persistent Connections" anchor="persistent.connections">
1645
1646<section title="Purpose" anchor="persistent.purpose">
1647<t>
1648   Prior to persistent connections, a separate TCP connection was
1649   established to fetch each URL, increasing the load on HTTP servers
1650   and causing congestion on the Internet. The use of inline images and
1651   other associated data often require a client to make multiple
1652   requests of the same server in a short amount of time. Analysis of
1653   these performance problems and results from a prototype
1654   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1655   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1656   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1657   T/TCP <xref target="Tou1998"/>.
1658</t>
1659<t>
1660   Persistent HTTP connections have a number of advantages:
1661  <list style="symbols">
1662      <t>
1663        By opening and closing fewer TCP connections, CPU time is saved
1664        in routers and hosts (clients, servers, proxies, gateways,
1665        tunnels, or caches), and memory used for TCP protocol control
1666        blocks can be saved in hosts.
1667      </t>
1668      <t>
1669        HTTP requests and responses can be pipelined on a connection.
1670        Pipelining allows a client to make multiple requests without
1671        waiting for each response, allowing a single TCP connection to
1672        be used much more efficiently, with much lower elapsed time.
1673      </t>
1674      <t>
1675        Network congestion is reduced by reducing the number of packets
1676        caused by TCP opens, and by allowing TCP sufficient time to
1677        determine the congestion state of the network.
1678      </t>
1679      <t>
1680        Latency on subsequent requests is reduced since there is no time
1681        spent in TCP's connection opening handshake.
1682      </t>
1683      <t>
1684        HTTP can evolve more gracefully, since errors can be reported
1685        without the penalty of closing the TCP connection. Clients using
1686        future versions of HTTP might optimistically try a new feature,
1687        but if communicating with an older server, retry with old
1688        semantics after an error is reported.
1689      </t>
1690    </list>
1691</t>
1692<t>
1693   HTTP implementations &SHOULD; implement persistent connections.
1694</t>
1695</section>
1696
1697<section title="Overall Operation" anchor="persistent.overall">
1698<t>
1699   A significant difference between HTTP/1.1 and earlier versions of
1700   HTTP is that persistent connections are the default behavior of any
1701   HTTP connection. That is, unless otherwise indicated, the client
1702   &SHOULD; assume that the server will maintain a persistent connection,
1703   even after error responses from the server.
1704</t>
1705<t>
1706   Persistent connections provide a mechanism by which a client and a
1707   server can signal the close of a TCP connection. This signaling takes
1708   place using the Connection header field (<xref target="header.connection"/>). Once a close
1709   has been signaled, the client &MUST-NOT; send any more requests on that
1710   connection.
1711</t>
1712
1713<section title="Negotiation" anchor="persistent.negotiation">
1714<t>
1715   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1716   maintain a persistent connection unless a Connection header including
1717   the connection-token "close" was sent in the request. If the server
1718   chooses to close the connection immediately after sending the
1719   response, it &SHOULD; send a Connection header including the
1720   connection-token close.
1721</t>
1722<t>
1723   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1724   decide to keep it open based on whether the response from a server
1725   contains a Connection header with the connection-token close. In case
1726   the client does not want to maintain a connection for more than that
1727   request, it &SHOULD; send a Connection header including the
1728   connection-token close.
1729</t>
1730<t>
1731   If either the client or the server sends the close token in the
1732   Connection header, that request becomes the last one for the
1733   connection.
1734</t>
1735<t>
1736   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1737   maintained for HTTP versions less than 1.1 unless it is explicitly
1738   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1739   compatibility with HTTP/1.0 clients.
1740</t>
1741<t>
1742   In order to remain persistent, all messages on the connection &MUST;
1743   have a self-defined message length (i.e., one not defined by closure
1744   of the connection), as described in <xref target="message.length"/>.
1745</t>
1746</section>
1747
1748<section title="Pipelining" anchor="pipelining">
1749<t>
1750   A client that supports persistent connections &MAY; "pipeline" its
1751   requests (i.e., send multiple requests without waiting for each
1752   response). A server &MUST; send its responses to those requests in the
1753   same order that the requests were received.
1754</t>
1755<t>
1756   Clients which assume persistent connections and pipeline immediately
1757   after connection establishment &SHOULD; be prepared to retry their
1758   connection if the first pipelined attempt fails. If a client does
1759   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1760   persistent. Clients &MUST; also be prepared to resend their requests if
1761   the server closes the connection before sending all of the
1762   corresponding responses.
1763</t>
1764<t>
1765   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1766   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1767   premature termination of the transport connection could lead to
1768   indeterminate results. A client wishing to send a non-idempotent
1769   request &SHOULD; wait to send that request until it has received the
1770   response status for the previous request.
1771</t>
1772</section>
1773</section>
1774
1775<section title="Proxy Servers" anchor="persistent.proxy">
1776<t>
1777   It is especially important that proxies correctly implement the
1778   properties of the Connection header field as specified in <xref target="header.connection"/>.
1779</t>
1780<t>
1781   The proxy server &MUST; signal persistent connections separately with
1782   its clients and the origin servers (or other proxy servers) that it
1783   connects to. Each persistent connection applies to only one transport
1784   link.
1785</t>
1786<t>
1787   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1788   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1789   discussion of the problems with the Keep-Alive header implemented by
1790   many HTTP/1.0 clients).
1791</t>
1792</section>
1793
1794<section title="Practical Considerations" anchor="persistent.practical">
1795<t>
1796   Servers will usually have some time-out value beyond which they will
1797   no longer maintain an inactive connection. Proxy servers might make
1798   this a higher value since it is likely that the client will be making
1799   more connections through the same server. The use of persistent
1800   connections places no requirements on the length (or existence) of
1801   this time-out for either the client or the server.
1802</t>
1803<t>
1804   When a client or server wishes to time-out it &SHOULD; issue a graceful
1805   close on the transport connection. Clients and servers &SHOULD; both
1806   constantly watch for the other side of the transport close, and
1807   respond to it as appropriate. If a client or server does not detect
1808   the other side's close promptly it could cause unnecessary resource
1809   drain on the network.
1810</t>
1811<t>
1812   A client, server, or proxy &MAY; close the transport connection at any
1813   time. For example, a client might have started to send a new request
1814   at the same time that the server has decided to close the "idle"
1815   connection. From the server's point of view, the connection is being
1816   closed while it was idle, but from the client's point of view, a
1817   request is in progress.
1818</t>
1819<t>
1820   This means that clients, servers, and proxies &MUST; be able to recover
1821   from asynchronous close events. Client software &SHOULD; reopen the
1822   transport connection and retransmit the aborted sequence of requests
1823   without user interaction so long as the request sequence is
1824   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1825   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1826   human operator the choice of retrying the request(s). Confirmation by
1827   user-agent software with semantic understanding of the application
1828   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1829   be repeated if the second sequence of requests fails.
1830</t>
1831<t>
1832   Servers &SHOULD; always respond to at least one request per connection,
1833   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1834   middle of transmitting a response, unless a network or client failure
1835   is suspected.
1836</t>
1837<t>
1838   Clients that use persistent connections &SHOULD; limit the number of
1839   simultaneous connections that they maintain to a given server. A
1840   single-user client &SHOULD-NOT; maintain more than 2 connections with
1841   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1842   another server or proxy, where N is the number of simultaneously
1843   active users. These guidelines are intended to improve HTTP response
1844   times and avoid congestion.
1845</t>
1846</section>
1847</section>
1848
1849<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1850
1851<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1852<t>
1853   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1854   flow control mechanisms to resolve temporary overloads, rather than
1855   terminating connections with the expectation that clients will retry.
1856   The latter technique can exacerbate network congestion.
1857</t>
1858</section>
1859
1860<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1861<t>
1862   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1863   the network connection for an error status while it is transmitting
1864   the request. If the client sees an error status, it &SHOULD;
1865   immediately cease transmitting the body. If the body is being sent
1866   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1867   empty trailer &MAY; be used to prematurely mark the end of the message.
1868   If the body was preceded by a Content-Length header, the client &MUST;
1869   close the connection.
1870</t>
1871</section>
1872
1873<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1874<t>
1875   The purpose of the 100 (Continue) status (see &status-100;) is to
1876   allow a client that is sending a request message with a request body
1877   to determine if the origin server is willing to accept the request
1878   (based on the request headers) before the client sends the request
1879   body. In some cases, it might either be inappropriate or highly
1880   inefficient for the client to send the body if the server will reject
1881   the message without looking at the body.
1882</t>
1883<t>
1884   Requirements for HTTP/1.1 clients:
1885  <list style="symbols">
1886    <t>
1887        If a client will wait for a 100 (Continue) response before
1888        sending the request body, it &MUST; send an Expect request-header
1889        field (&header-expect;) with the "100-continue" expectation.
1890    </t>
1891    <t>
1892        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1893        with the "100-continue" expectation if it does not intend
1894        to send a request body.
1895    </t>
1896  </list>
1897</t>
1898<t>
1899   Because of the presence of older implementations, the protocol allows
1900   ambiguous situations in which a client may send "Expect: 100-continue"
1901   without receiving either a 417 (Expectation Failed) status
1902   or a 100 (Continue) status. Therefore, when a client sends this
1903   header field to an origin server (possibly via a proxy) from which it
1904   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1905   for an indefinite period before sending the request body.
1906</t>
1907<t>
1908   Requirements for HTTP/1.1 origin servers:
1909  <list style="symbols">
1910    <t> Upon receiving a request which includes an Expect request-header
1911        field with the "100-continue" expectation, an origin server &MUST;
1912        either respond with 100 (Continue) status and continue to read
1913        from the input stream, or respond with a final status code. The
1914        origin server &MUST-NOT; wait for the request body before sending
1915        the 100 (Continue) response. If it responds with a final status
1916        code, it &MAY; close the transport connection or it &MAY; continue
1917        to read and discard the rest of the request.  It &MUST-NOT;
1918        perform the requested method if it returns a final status code.
1919    </t>
1920    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1921        the request message does not include an Expect request-header
1922        field with the "100-continue" expectation, and &MUST-NOT; send a
1923        100 (Continue) response if such a request comes from an HTTP/1.0
1924        (or earlier) client. There is an exception to this rule: for
1925        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1926        status in response to an HTTP/1.1 PUT or POST request that does
1927        not include an Expect request-header field with the "100-continue"
1928        expectation. This exception, the purpose of which is
1929        to minimize any client processing delays associated with an
1930        undeclared wait for 100 (Continue) status, applies only to
1931        HTTP/1.1 requests, and not to requests with any other HTTP-version
1932        value.
1933    </t>
1934    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1935        already received some or all of the request body for the
1936        corresponding request.
1937    </t>
1938    <t> An origin server that sends a 100 (Continue) response &MUST;
1939    ultimately send a final status code, once the request body is
1940        received and processed, unless it terminates the transport
1941        connection prematurely.
1942    </t>
1943    <t> If an origin server receives a request that does not include an
1944        Expect request-header field with the "100-continue" expectation,
1945        the request includes a request body, and the server responds
1946        with a final status code before reading the entire request body
1947        from the transport connection, then the server &SHOULD-NOT;  close
1948        the transport connection until it has read the entire request,
1949        or until the client closes the connection. Otherwise, the client
1950        might not reliably receive the response message. However, this
1951        requirement is not be construed as preventing a server from
1952        defending itself against denial-of-service attacks, or from
1953        badly broken client implementations.
1954      </t>
1955    </list>
1956</t>
1957<t>
1958   Requirements for HTTP/1.1 proxies:
1959  <list style="symbols">
1960    <t> If a proxy receives a request that includes an Expect request-header
1961        field with the "100-continue" expectation, and the proxy
1962        either knows that the next-hop server complies with HTTP/1.1 or
1963        higher, or does not know the HTTP version of the next-hop
1964        server, it &MUST; forward the request, including the Expect header
1965        field.
1966    </t>
1967    <t> If the proxy knows that the version of the next-hop server is
1968        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1969        respond with a 417 (Expectation Failed) status.
1970    </t>
1971    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1972        numbers received from recently-referenced next-hop servers.
1973    </t>
1974    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1975        request message was received from an HTTP/1.0 (or earlier)
1976        client and did not include an Expect request-header field with
1977        the "100-continue" expectation. This requirement overrides the
1978        general rule for forwarding of 1xx responses (see &status-1xx;).
1979    </t>
1980  </list>
1981</t>
1982</section>
1983
1984<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1985<t>
1986   If an HTTP/1.1 client sends a request which includes a request body,
1987   but which does not include an Expect request-header field with the
1988   "100-continue" expectation, and if the client is not directly
1989   connected to an HTTP/1.1 origin server, and if the client sees the
1990   connection close before receiving any status from the server, the
1991   client &SHOULD; retry the request.  If the client does retry this
1992   request, it &MAY; use the following "binary exponential backoff"
1993   algorithm to be assured of obtaining a reliable response:
1994  <list style="numbers">
1995    <t>
1996      Initiate a new connection to the server
1997    </t>
1998    <t>
1999      Transmit the request-headers
2000    </t>
2001    <t>
2002      Initialize a variable R to the estimated round-trip time to the
2003         server (e.g., based on the time it took to establish the
2004         connection), or to a constant value of 5 seconds if the round-trip
2005         time is not available.
2006    </t>
2007    <t>
2008       Compute T = R * (2**N), where N is the number of previous
2009         retries of this request.
2010    </t>
2011    <t>
2012       Wait either for an error response from the server, or for T
2013         seconds (whichever comes first)
2014    </t>
2015    <t>
2016       If no error response is received, after T seconds transmit the
2017         body of the request.
2018    </t>
2019    <t>
2020       If client sees that the connection is closed prematurely,
2021         repeat from step 1 until the request is accepted, an error
2022         response is received, or the user becomes impatient and
2023         terminates the retry process.
2024    </t>
2025  </list>
2026</t>
2027<t>
2028   If at any point an error status is received, the client
2029  <list style="symbols">
2030      <t>&SHOULD-NOT;  continue and</t>
2031
2032      <t>&SHOULD; close the connection if it has not completed sending the
2033        request message.</t>
2034    </list>
2035</t>
2036</section>
2037</section>
2038</section>
2039
2040
2041<section title="Header Field Definitions" anchor="header.fields">
2042<t>
2043   This section defines the syntax and semantics of HTTP/1.1 header fields
2044   related to message framing and transport protocols.
2045</t>
2046<t>
2047   For entity-header fields, both sender and recipient refer to either the
2048   client or the server, depending on who sends and who receives the entity.
2049</t>
2050
2051<section title="Connection" anchor="header.connection">
2052  <iref primary="true" item="Connection header" x:for-anchor=""/>
2053  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2054  <x:anchor-alias value="Connection"/>
2055  <x:anchor-alias value="connection-token"/>
2056<t>
2057   The Connection general-header field allows the sender to specify
2058   options that are desired for that particular connection and &MUST-NOT;
2059   be communicated by proxies over further connections.
2060</t>
2061<t>
2062   The Connection header has the following grammar:
2063</t>
2064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2065  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2066  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2067</artwork></figure>
2068<t>
2069   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2070   message is forwarded and, for each connection-token in this field,
2071   remove any header field(s) from the message with the same name as the
2072   connection-token. Connection options are signaled by the presence of
2073   a connection-token in the Connection header field, not by any
2074   corresponding additional header field(s), since the additional header
2075   field may not be sent if there are no parameters associated with that
2076   connection option.
2077</t>
2078<t>
2079   Message headers listed in the Connection header &MUST-NOT; include
2080   end-to-end headers, such as Cache-Control.
2081</t>
2082<t>
2083   HTTP/1.1 defines the "close" connection option for the sender to
2084   signal that the connection will be closed after completion of the
2085   response. For example,
2086</t>
2087<figure><artwork type="example">
2088    Connection: close
2089</artwork></figure>
2090<t>
2091   in either the request or the response header fields indicates that
2092   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2093   after the current request/response is complete.
2094</t>
2095<t>
2096   An HTTP/1.1 client that does not support persistent connections &MUST;
2097   include the "close" connection option in every request message.
2098</t>
2099<t>
2100   An HTTP/1.1 server that does not support persistent connections &MUST;
2101   include the "close" connection option in every response message that
2102   does not have a 1xx (informational) status code.
2103</t>
2104<t>
2105   A system receiving an HTTP/1.0 (or lower-version) message that
2106   includes a Connection header &MUST;, for each connection-token in this
2107   field, remove and ignore any header field(s) from the message with
2108   the same name as the connection-token. This protects against mistaken
2109   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2110</t>
2111</section>
2112
2113<section title="Content-Length" anchor="header.content-length">
2114  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2115  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2116  <x:anchor-alias value="Content-Length"/>
2117<t>
2118   The Content-Length entity-header field indicates the size of the
2119   entity-body, in decimal number of OCTETs, sent to the recipient or,
2120   in the case of the HEAD method, the size of the entity-body that
2121   would have been sent had the request been a GET.
2122</t>
2123<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2124  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2125</artwork></figure>
2126<t>
2127   An example is
2128</t>
2129<figure><artwork type="example">
2130    Content-Length: 3495
2131</artwork></figure>
2132<t>
2133   Applications &SHOULD; use this field to indicate the transfer-length of
2134   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2135</t>
2136<t>
2137   Any Content-Length greater than or equal to zero is a valid value.
2138   <xref target="message.length"/> describes how to determine the length of a message-body
2139   if a Content-Length is not given.
2140</t>
2141<t>
2142   Note that the meaning of this field is significantly different from
2143   the corresponding definition in MIME, where it is an optional field
2144   used within the "message/external-body" content-type. In HTTP, it
2145   &SHOULD; be sent whenever the message's length can be determined prior
2146   to being transferred, unless this is prohibited by the rules in
2147   <xref target="message.length"/>.
2148</t>
2149</section>
2150
2151<section title="Date" anchor="header.date">
2152  <iref primary="true" item="Date header" x:for-anchor=""/>
2153  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2154  <x:anchor-alias value="Date"/>
2155<t>
2156   The Date general-header field represents the date and time at which
2157   the message was originated, having the same semantics as orig-date in
2158   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2159   HTTP-date, as described in <xref target="full.date"/>;
2160   it &MUST; be sent in rfc1123-date format.
2161</t>
2162<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2163  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2164</artwork></figure>
2165<t>
2166   An example is
2167</t>
2168<figure><artwork type="example">
2169    Date: Tue, 15 Nov 1994 08:12:31 GMT
2170</artwork></figure>
2171<t>
2172   Origin servers &MUST; include a Date header field in all responses,
2173   except in these cases:
2174  <list style="numbers">
2175      <t>If the response status code is 100 (Continue) or 101 (Switching
2176         Protocols), the response &MAY; include a Date header field, at
2177         the server's option.</t>
2178
2179      <t>If the response status code conveys a server error, e.g. 500
2180         (Internal Server Error) or 503 (Service Unavailable), and it is
2181         inconvenient or impossible to generate a valid Date.</t>
2182
2183      <t>If the server does not have a clock that can provide a
2184         reasonable approximation of the current time, its responses
2185         &MUST-NOT; include a Date header field. In this case, the rules
2186         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2187  </list>
2188</t>
2189<t>
2190   A received message that does not have a Date header field &MUST; be
2191   assigned one by the recipient if the message will be cached by that
2192   recipient or gatewayed via a protocol which requires a Date. An HTTP
2193   implementation without a clock &MUST-NOT; cache responses without
2194   revalidating them on every use. An HTTP cache, especially a shared
2195   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2196   clock with a reliable external standard.
2197</t>
2198<t>
2199   Clients &SHOULD; only send a Date header field in messages that include
2200   an entity-body, as in the case of the PUT and POST requests, and even
2201   then it is optional. A client without a clock &MUST-NOT; send a Date
2202   header field in a request.
2203</t>
2204<t>
2205   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2206   time subsequent to the generation of the message. It &SHOULD; represent
2207   the best available approximation of the date and time of message
2208   generation, unless the implementation has no means of generating a
2209   reasonably accurate date and time. In theory, the date ought to
2210   represent the moment just before the entity is generated. In
2211   practice, the date can be generated at any time during the message
2212   origination without affecting its semantic value.
2213</t>
2214
2215<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2216<t>
2217   Some origin server implementations might not have a clock available.
2218   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2219   values to a response, unless these values were associated
2220   with the resource by a system or user with a reliable clock. It &MAY;
2221   assign an Expires value that is known, at or before server
2222   configuration time, to be in the past (this allows "pre-expiration"
2223   of responses without storing separate Expires values for each
2224   resource).
2225</t>
2226</section>
2227</section>
2228
2229<section title="Host" anchor="header.host">
2230  <iref primary="true" item="Host header" x:for-anchor=""/>
2231  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2232  <x:anchor-alias value="Host"/>
2233<t>
2234   The Host request-header field specifies the Internet host and port
2235   number of the resource being requested, as obtained from the original
2236   URI given by the user or referring resource (generally an HTTP URL,
2237   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2238   the naming authority of the origin server or gateway given by the
2239   original URL. This allows the origin server or gateway to
2240   differentiate between internally-ambiguous URLs, such as the root "/"
2241   URL of a server for multiple host names on a single IP address.
2242</t>
2243<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2244  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2245</artwork></figure>
2246<t>
2247   A "host" without any trailing port information implies the default
2248   port for the service requested (e.g., "80" for an HTTP URL). For
2249   example, a request on the origin server for
2250   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2251</t>
2252<figure><artwork type="example">
2253    GET /pub/WWW/ HTTP/1.1
2254    Host: www.example.org
2255</artwork></figure>
2256<t>
2257   A client &MUST; include a Host header field in all HTTP/1.1 request
2258   messages. If the requested URI does not include an Internet host
2259   name for the service being requested, then the Host header field &MUST;
2260   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2261   request message it forwards does contain an appropriate Host header
2262   field that identifies the service being requested by the proxy. All
2263   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2264   status code to any HTTP/1.1 request message which lacks a Host header
2265   field.
2266</t>
2267<t>
2268   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2269   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2270   for other requirements relating to Host.
2271</t>
2272</section>
2273
2274<section title="TE" anchor="header.te">
2275  <iref primary="true" item="TE header" x:for-anchor=""/>
2276  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2277  <x:anchor-alias value="TE"/>
2278  <x:anchor-alias value="t-codings"/>
2279<t>
2280   The TE request-header field indicates what extension transfer-codings
2281   it is willing to accept in the response and whether or not it is
2282   willing to accept trailer fields in a chunked transfer-coding. Its
2283   value may consist of the keyword "trailers" and/or a comma-separated
2284   list of extension transfer-coding names with optional accept
2285   parameters (as described in <xref target="transfer.codings"/>).
2286</t>
2287<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2288  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2289  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2290</artwork></figure>
2291<t>
2292   The presence of the keyword "trailers" indicates that the client is
2293   willing to accept trailer fields in a chunked transfer-coding, as
2294   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2295   transfer-coding values even though it does not itself represent a
2296   transfer-coding.
2297</t>
2298<t>
2299   Examples of its use are:
2300</t>
2301<figure><artwork type="example">
2302    TE: deflate
2303    TE:
2304    TE: trailers, deflate;q=0.5
2305</artwork></figure>
2306<t>
2307   The TE header field only applies to the immediate connection.
2308   Therefore, the keyword &MUST; be supplied within a Connection header
2309   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2310</t>
2311<t>
2312   A server tests whether a transfer-coding is acceptable, according to
2313   a TE field, using these rules:
2314  <list style="numbers">
2315    <x:lt>
2316      <t>The "chunked" transfer-coding is always acceptable. If the
2317         keyword "trailers" is listed, the client indicates that it is
2318         willing to accept trailer fields in the chunked response on
2319         behalf of itself and any downstream clients. The implication is
2320         that, if given, the client is stating that either all
2321         downstream clients are willing to accept trailer fields in the
2322         forwarded response, or that it will attempt to buffer the
2323         response on behalf of downstream recipients.
2324      </t><t>
2325         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2326         chunked response such that a client can be assured of buffering
2327         the entire response.</t>
2328    </x:lt>
2329    <x:lt>
2330      <t>If the transfer-coding being tested is one of the transfer-codings
2331         listed in the TE field, then it is acceptable unless it
2332         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2333         qvalue of 0 means "not acceptable.")</t>
2334    </x:lt>
2335    <x:lt>
2336      <t>If multiple transfer-codings are acceptable, then the
2337         acceptable transfer-coding with the highest non-zero qvalue is
2338         preferred.  The "chunked" transfer-coding always has a qvalue
2339         of 1.</t>
2340    </x:lt>
2341  </list>
2342</t>
2343<t>
2344   If the TE field-value is empty or if no TE field is present, the only
2345   transfer-coding  is "chunked". A message with no transfer-coding is
2346   always acceptable.
2347</t>
2348</section>
2349
2350<section title="Trailer" anchor="header.trailer">
2351  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2352  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2353  <x:anchor-alias value="Trailer"/>
2354<t>
2355   The Trailer general field value indicates that the given set of
2356   header fields is present in the trailer of a message encoded with
2357   chunked transfer-coding.
2358</t>
2359<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2360  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2361</artwork></figure>
2362<t>
2363   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2364   message using chunked transfer-coding with a non-empty trailer. Doing
2365   so allows the recipient to know which header fields to expect in the
2366   trailer.
2367</t>
2368<t>
2369   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2370   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2371   trailer fields in a "chunked" transfer-coding.
2372</t>
2373<t>
2374   Message header fields listed in the Trailer header field &MUST-NOT;
2375   include the following header fields:
2376  <list style="symbols">
2377    <t>Transfer-Encoding</t>
2378    <t>Content-Length</t>
2379    <t>Trailer</t>
2380  </list>
2381</t>
2382</section>
2383
2384<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2385  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2386  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2387  <x:anchor-alias value="Transfer-Encoding"/>
2388<t>
2389   The Transfer-Encoding general-header field indicates what (if any)
2390   type of transformation has been applied to the message body in order
2391   to safely transfer it between the sender and the recipient. This
2392   differs from the content-coding in that the transfer-coding is a
2393   property of the message, not of the entity.
2394</t>
2395<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2396  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2397</artwork></figure>
2398<t>
2399   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2400</t>
2401<figure><artwork type="example">
2402  Transfer-Encoding: chunked
2403</artwork></figure>
2404<t>
2405   If multiple encodings have been applied to an entity, the transfer-codings
2406   &MUST; be listed in the order in which they were applied.
2407   Additional information about the encoding parameters &MAY; be provided
2408   by other entity-header fields not defined by this specification.
2409</t>
2410<t>
2411   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2412   header.
2413</t>
2414</section>
2415
2416<section title="Upgrade" anchor="header.upgrade">
2417  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2418  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2419  <x:anchor-alias value="Upgrade"/>
2420<t>
2421   The Upgrade general-header allows the client to specify what
2422   additional communication protocols it supports and would like to use
2423   if the server finds it appropriate to switch protocols. The server
2424   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2425   response to indicate which protocol(s) are being switched.
2426</t>
2427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2428  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2429</artwork></figure>
2430<t>
2431   For example,
2432</t>
2433<figure><artwork type="example">
2434    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2435</artwork></figure>
2436<t>
2437   The Upgrade header field is intended to provide a simple mechanism
2438   for transition from HTTP/1.1 to some other, incompatible protocol. It
2439   does so by allowing the client to advertise its desire to use another
2440   protocol, such as a later version of HTTP with a higher major version
2441   number, even though the current request has been made using HTTP/1.1.
2442   This eases the difficult transition between incompatible protocols by
2443   allowing the client to initiate a request in the more commonly
2444   supported protocol while indicating to the server that it would like
2445   to use a "better" protocol if available (where "better" is determined
2446   by the server, possibly according to the nature of the method and/or
2447   resource being requested).
2448</t>
2449<t>
2450   The Upgrade header field only applies to switching application-layer
2451   protocols upon the existing transport-layer connection. Upgrade
2452   cannot be used to insist on a protocol change; its acceptance and use
2453   by the server is optional. The capabilities and nature of the
2454   application-layer communication after the protocol change is entirely
2455   dependent upon the new protocol chosen, although the first action
2456   after changing the protocol &MUST; be a response to the initial HTTP
2457   request containing the Upgrade header field.
2458</t>
2459<t>
2460   The Upgrade header field only applies to the immediate connection.
2461   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2462   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2463   HTTP/1.1 message.
2464</t>
2465<t>
2466   The Upgrade header field cannot be used to indicate a switch to a
2467   protocol on a different connection. For that purpose, it is more
2468   appropriate to use a 301, 302, 303, or 305 redirection response.
2469</t>
2470<t>
2471   This specification only defines the protocol name "HTTP" for use by
2472   the family of Hypertext Transfer Protocols, as defined by the HTTP
2473   version rules of <xref target="http.version"/> and future updates to this
2474   specification. Any token can be used as a protocol name; however, it
2475   will only be useful if both the client and server associate the name
2476   with the same protocol.
2477</t>
2478</section>
2479
2480<section title="Via" anchor="header.via">
2481  <iref primary="true" item="Via header" x:for-anchor=""/>
2482  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2483  <x:anchor-alias value="protocol-name"/>
2484  <x:anchor-alias value="protocol-version"/>
2485  <x:anchor-alias value="pseudonym"/>
2486  <x:anchor-alias value="received-by"/>
2487  <x:anchor-alias value="received-protocol"/>
2488  <x:anchor-alias value="Via"/>
2489<t>
2490   The Via general-header field &MUST; be used by gateways and proxies to
2491   indicate the intermediate protocols and recipients between the user
2492   agent and the server on requests, and between the origin server and
2493   the client on responses. It is analogous to the "Received" field defined in
2494   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2495   avoiding request loops, and identifying the protocol capabilities of
2496   all senders along the request/response chain.
2497</t>
2498<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"/>
2499  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2500  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2501  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2502  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2503  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2504  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2505</artwork></figure>
2506<t>
2507   The received-protocol indicates the protocol version of the message
2508   received by the server or client along each segment of the
2509   request/response chain. The received-protocol version is appended to
2510   the Via field value when the message is forwarded so that information
2511   about the protocol capabilities of upstream applications remains
2512   visible to all recipients.
2513</t>
2514<t>
2515   The protocol-name is optional if and only if it would be "HTTP". The
2516   received-by field is normally the host and optional port number of a
2517   recipient server or client that subsequently forwarded the message.
2518   However, if the real host is considered to be sensitive information,
2519   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2520   be assumed to be the default port of the received-protocol.
2521</t>
2522<t>
2523   Multiple Via field values represents each proxy or gateway that has
2524   forwarded the message. Each recipient &MUST; append its information
2525   such that the end result is ordered according to the sequence of
2526   forwarding applications.
2527</t>
2528<t>
2529   Comments &MAY; be used in the Via header field to identify the software
2530   of the recipient proxy or gateway, analogous to the User-Agent and
2531   Server header fields. However, all comments in the Via field are
2532   optional and &MAY; be removed by any recipient prior to forwarding the
2533   message.
2534</t>
2535<t>
2536   For example, a request message could be sent from an HTTP/1.0 user
2537   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2538   forward the request to a public proxy at p.example.net, which completes
2539   the request by forwarding it to the origin server at www.example.com.
2540   The request received by www.example.com would then have the following
2541   Via header field:
2542</t>
2543<figure><artwork type="example">
2544    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2545</artwork></figure>
2546<t>
2547   Proxies and gateways used as a portal through a network firewall
2548   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2549   the firewall region. This information &SHOULD; only be propagated if
2550   explicitly enabled. If not enabled, the received-by host of any host
2551   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2552   for that host.
2553</t>
2554<t>
2555   For organizations that have strong privacy requirements for hiding
2556   internal structures, a proxy &MAY; combine an ordered subsequence of
2557   Via header field entries with identical received-protocol values into
2558   a single such entry. For example,
2559</t>
2560<figure><artwork type="example">
2561    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2562</artwork></figure>
2563<t>
2564        could be collapsed to
2565</t>
2566<figure><artwork type="example">
2567    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2568</artwork></figure>
2569<t>
2570   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2571   under the same organizational control and the hosts have already been
2572   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2573   have different received-protocol values.
2574</t>
2575</section>
2576
2577</section>
2578
2579<section title="IANA Considerations" anchor="IANA.considerations">
2580<section title="Message Header Registration" anchor="message.header.registration">
2581<t>
2582   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2583   with the permanent registrations below (see <xref target="RFC3864"/>):
2584</t>
2585<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2586<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2587   <ttcol>Header Field Name</ttcol>
2588   <ttcol>Protocol</ttcol>
2589   <ttcol>Status</ttcol>
2590   <ttcol>Reference</ttcol>
2591
2592   <c>Connection</c>
2593   <c>http</c>
2594   <c>standard</c>
2595   <c>
2596      <xref target="header.connection"/>
2597   </c>
2598   <c>Content-Length</c>
2599   <c>http</c>
2600   <c>standard</c>
2601   <c>
2602      <xref target="header.content-length"/>
2603   </c>
2604   <c>Date</c>
2605   <c>http</c>
2606   <c>standard</c>
2607   <c>
2608      <xref target="header.date"/>
2609   </c>
2610   <c>Host</c>
2611   <c>http</c>
2612   <c>standard</c>
2613   <c>
2614      <xref target="header.host"/>
2615   </c>
2616   <c>TE</c>
2617   <c>http</c>
2618   <c>standard</c>
2619   <c>
2620      <xref target="header.te"/>
2621   </c>
2622   <c>Trailer</c>
2623   <c>http</c>
2624   <c>standard</c>
2625   <c>
2626      <xref target="header.trailer"/>
2627   </c>
2628   <c>Transfer-Encoding</c>
2629   <c>http</c>
2630   <c>standard</c>
2631   <c>
2632      <xref target="header.transfer-encoding"/>
2633   </c>
2634   <c>Upgrade</c>
2635   <c>http</c>
2636   <c>standard</c>
2637   <c>
2638      <xref target="header.upgrade"/>
2639   </c>
2640   <c>Via</c>
2641   <c>http</c>
2642   <c>standard</c>
2643   <c>
2644      <xref target="header.via"/>
2645   </c>
2646</texttable>
2647<!--(END)-->
2648<t>
2649   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2650</t>
2651</section>
2652
2653<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2654<t>
2655   The entry for the "http" URI Scheme in the registry located at
2656   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2657   should be updated to point to <xref target="http.url"/> of this document
2658   (see <xref target="RFC4395"/>).
2659</t>
2660</section>
2661
2662<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2663<t>
2664   This document serves as the specification for the Internet media types
2665   "message/http" and "application/http". The following is to be registered with
2666   IANA (see <xref target="RFC4288"/>).
2667</t>
2668<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2669<iref item="Media Type" subitem="message/http" primary="true"/>
2670<iref item="message/http Media Type" primary="true"/>
2671<t>
2672   The message/http type can be used to enclose a single HTTP request or
2673   response message, provided that it obeys the MIME restrictions for all
2674   "message" types regarding line length and encodings.
2675</t>
2676<t>
2677  <list style="hanging" x:indent="12em">
2678    <t hangText="Type name:">
2679      message
2680    </t>
2681    <t hangText="Subtype name:">
2682      http
2683    </t>
2684    <t hangText="Required parameters:">
2685      none
2686    </t>
2687    <t hangText="Optional parameters:">
2688      version, msgtype
2689      <list style="hanging">
2690        <t hangText="version:">
2691          The HTTP-Version number of the enclosed message
2692          (e.g., "1.1"). If not present, the version can be
2693          determined from the first line of the body.
2694        </t>
2695        <t hangText="msgtype:">
2696          The message type -- "request" or "response". If not
2697          present, the type can be determined from the first
2698          line of the body.
2699        </t>
2700      </list>
2701    </t>
2702    <t hangText="Encoding considerations:">
2703      only "7bit", "8bit", or "binary" are permitted
2704    </t>
2705    <t hangText="Security considerations:">
2706      none
2707    </t>
2708    <t hangText="Interoperability considerations:">
2709      none
2710    </t>
2711    <t hangText="Published specification:">
2712      This specification (see <xref target="internet.media.type.message.http"/>).
2713    </t>
2714    <t hangText="Applications that use this media type:">
2715    </t>
2716    <t hangText="Additional information:">
2717      <list style="hanging">
2718        <t hangText="Magic number(s):">none</t>
2719        <t hangText="File extension(s):">none</t>
2720        <t hangText="Macintosh file type code(s):">none</t>
2721      </list>
2722    </t>
2723    <t hangText="Person and email address to contact for further information:">
2724      See Authors Section.
2725    </t>
2726                <t hangText="Intended usage:">
2727                  COMMON
2728    </t>
2729                <t hangText="Restrictions on usage:">
2730                  none
2731    </t>
2732    <t hangText="Author/Change controller:">
2733      IESG
2734    </t>
2735  </list>
2736</t>
2737</section>
2738<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2739<iref item="Media Type" subitem="application/http" primary="true"/>
2740<iref item="application/http Media Type" primary="true"/>
2741<t>
2742   The application/http type can be used to enclose a pipeline of one or more
2743   HTTP request or response messages (not intermixed).
2744</t>
2745<t>
2746  <list style="hanging" x:indent="12em">
2747    <t hangText="Type name:">
2748      application
2749    </t>
2750    <t hangText="Subtype name:">
2751      http
2752    </t>
2753    <t hangText="Required parameters:">
2754      none
2755    </t>
2756    <t hangText="Optional parameters:">
2757      version, msgtype
2758      <list style="hanging">
2759        <t hangText="version:">
2760          The HTTP-Version number of the enclosed messages
2761          (e.g., "1.1"). If not present, the version can be
2762          determined from the first line of the body.
2763        </t>
2764        <t hangText="msgtype:">
2765          The message type -- "request" or "response". If not
2766          present, the type can be determined from the first
2767          line of the body.
2768        </t>
2769      </list>
2770    </t>
2771    <t hangText="Encoding considerations:">
2772      HTTP messages enclosed by this type
2773      are in "binary" format; use of an appropriate
2774      Content-Transfer-Encoding is required when
2775      transmitted via E-mail.
2776    </t>
2777    <t hangText="Security considerations:">
2778      none
2779    </t>
2780    <t hangText="Interoperability considerations:">
2781      none
2782    </t>
2783    <t hangText="Published specification:">
2784      This specification (see <xref target="internet.media.type.application.http"/>).
2785    </t>
2786    <t hangText="Applications that use this media type:">
2787    </t>
2788    <t hangText="Additional information:">
2789      <list style="hanging">
2790        <t hangText="Magic number(s):">none</t>
2791        <t hangText="File extension(s):">none</t>
2792        <t hangText="Macintosh file type code(s):">none</t>
2793      </list>
2794    </t>
2795    <t hangText="Person and email address to contact for further information:">
2796      See Authors Section.
2797    </t>
2798                <t hangText="Intended usage:">
2799                  COMMON
2800    </t>
2801                <t hangText="Restrictions on usage:">
2802                  none
2803    </t>
2804    <t hangText="Author/Change controller:">
2805      IESG
2806    </t>
2807  </list>
2808</t>
2809</section>
2810</section>
2811
2812</section>
2813
2814<section title="Security Considerations" anchor="security.considerations">
2815<t>
2816   This section is meant to inform application developers, information
2817   providers, and users of the security limitations in HTTP/1.1 as
2818   described by this document. The discussion does not include
2819   definitive solutions to the problems revealed, though it does make
2820   some suggestions for reducing security risks.
2821</t>
2822
2823<section title="Personal Information" anchor="personal.information">
2824<t>
2825   HTTP clients are often privy to large amounts of personal information
2826   (e.g. the user's name, location, mail address, passwords, encryption
2827   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2828   leakage of this information.
2829   We very strongly recommend that a convenient interface be provided
2830   for the user to control dissemination of such information, and that
2831   designers and implementors be particularly careful in this area.
2832   History shows that errors in this area often create serious security
2833   and/or privacy problems and generate highly adverse publicity for the
2834   implementor's company.
2835</t>
2836</section>
2837
2838<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2839<t>
2840   A server is in the position to save personal data about a user's
2841   requests which might identify their reading patterns or subjects of
2842   interest. This information is clearly confidential in nature and its
2843   handling can be constrained by law in certain countries. People using
2844   HTTP to provide data are responsible for ensuring that
2845   such material is not distributed without the permission of any
2846   individuals that are identifiable by the published results.
2847</t>
2848</section>
2849
2850<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2851<t>
2852   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2853   the documents returned by HTTP requests to be only those that were
2854   intended by the server administrators. If an HTTP server translates
2855   HTTP URIs directly into file system calls, the server &MUST; take
2856   special care not to serve files that were not intended to be
2857   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2858   other operating systems use ".." as a path component to indicate a
2859   directory level above the current one. On such a system, an HTTP
2860   server &MUST; disallow any such construct in the Request-URI if it
2861   would otherwise allow access to a resource outside those intended to
2862   be accessible via the HTTP server. Similarly, files intended for
2863   reference only internally to the server (such as access control
2864   files, configuration files, and script code) &MUST; be protected from
2865   inappropriate retrieval, since they might contain sensitive
2866   information. Experience has shown that minor bugs in such HTTP server
2867   implementations have turned into security risks.
2868</t>
2869</section>
2870
2871<section title="DNS Spoofing" anchor="dns.spoofing">
2872<t>
2873   Clients using HTTP rely heavily on the Domain Name Service, and are
2874   thus generally prone to security attacks based on the deliberate
2875   mis-association of IP addresses and DNS names. Clients need to be
2876   cautious in assuming the continuing validity of an IP number/DNS name
2877   association.
2878</t>
2879<t>
2880   In particular, HTTP clients &SHOULD; rely on their name resolver for
2881   confirmation of an IP number/DNS name association, rather than
2882   caching the result of previous host name lookups. Many platforms
2883   already can cache host name lookups locally when appropriate, and
2884   they &SHOULD; be configured to do so. It is proper for these lookups to
2885   be cached, however, only when the TTL (Time To Live) information
2886   reported by the name server makes it likely that the cached
2887   information will remain useful.
2888</t>
2889<t>
2890   If HTTP clients cache the results of host name lookups in order to
2891   achieve a performance improvement, they &MUST; observe the TTL
2892   information reported by DNS.
2893</t>
2894<t>
2895   If HTTP clients do not observe this rule, they could be spoofed when
2896   a previously-accessed server's IP address changes. As network
2897   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2898   possibility of this form of attack will grow. Observing this
2899   requirement thus reduces this potential security vulnerability.
2900</t>
2901<t>
2902   This requirement also improves the load-balancing behavior of clients
2903   for replicated servers using the same DNS name and reduces the
2904   likelihood of a user's experiencing failure in accessing sites which
2905   use that strategy.
2906</t>
2907</section>
2908
2909<section title="Proxies and Caching" anchor="attack.proxies">
2910<t>
2911   By their very nature, HTTP proxies are men-in-the-middle, and
2912   represent an opportunity for man-in-the-middle attacks. Compromise of
2913   the systems on which the proxies run can result in serious security
2914   and privacy problems. Proxies have access to security-related
2915   information, personal information about individual users and
2916   organizations, and proprietary information belonging to users and
2917   content providers. A compromised proxy, or a proxy implemented or
2918   configured without regard to security and privacy considerations,
2919   might be used in the commission of a wide range of potential attacks.
2920</t>
2921<t>
2922   Proxy operators should protect the systems on which proxies run as
2923   they would protect any system that contains or transports sensitive
2924   information. In particular, log information gathered at proxies often
2925   contains highly sensitive personal information, and/or information
2926   about organizations. Log information should be carefully guarded, and
2927   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2928</t>
2929<t>
2930   Proxy implementors should consider the privacy and security
2931   implications of their design and coding decisions, and of the
2932   configuration options they provide to proxy operators (especially the
2933   default configuration).
2934</t>
2935<t>
2936   Users of a proxy need to be aware that they are no trustworthier than
2937   the people who run the proxy; HTTP itself cannot solve this problem.
2938</t>
2939<t>
2940   The judicious use of cryptography, when appropriate, may suffice to
2941   protect against a broad range of security and privacy attacks. Such
2942   cryptography is beyond the scope of the HTTP/1.1 specification.
2943</t>
2944</section>
2945
2946<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2947<t>
2948   They exist. They are hard to defend against. Research continues.
2949   Beware.
2950</t>
2951</section>
2952</section>
2953
2954<section title="Acknowledgments" anchor="ack">
2955<t>
2956   This specification makes heavy use of the augmented BNF and generic
2957   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2958   reuses many of the definitions provided by Nathaniel Borenstein and
2959   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2960   specification will help reduce past confusion over the relationship
2961   between HTTP and Internet mail message formats.
2962</t>
2963<t>
2964   HTTP has evolved considerably over the years. It has
2965   benefited from a large and active developer community--the many
2966   people who have participated on the www-talk mailing list--and it is
2967   that community which has been most responsible for the success of
2968   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2969   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2970   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2971   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2972   VanHeyningen deserve special recognition for their efforts in
2973   defining early aspects of the protocol.
2974</t>
2975<t>
2976   This document has benefited greatly from the comments of all those
2977   participating in the HTTP-WG. In addition to those already mentioned,
2978   the following individuals have contributed to this specification:
2979</t>
2980<t>
2981   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2982   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2983   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2984   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2985   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2986   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2987   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2988   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2989   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2990   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2991   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2992   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2993   Josh Cohen.
2994</t>
2995<t>
2996   Thanks to the "cave men" of Palo Alto. You know who you are.
2997</t>
2998<t>
2999   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3000   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3001   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3002   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3003   Larry Masinter for their help. And thanks go particularly to Jeff
3004   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3005</t>
3006<t>
3007   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3008   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3009   discovery of many of the problems that this document attempts to
3010   rectify.
3011</t>
3012</section>
3013
3014</middle>
3015<back>
3016
3017<references title="Normative References">
3018
3019<reference anchor="ISO-8859-1">
3020  <front>
3021    <title>
3022     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3023    </title>
3024    <author>
3025      <organization>International Organization for Standardization</organization>
3026    </author>
3027    <date year="1998"/>
3028  </front>
3029  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3030</reference>
3031
3032<reference anchor="Part2">
3033  <front>
3034    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3035    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3036      <organization abbrev="Day Software">Day Software</organization>
3037      <address><email>fielding@gbiv.com</email></address>
3038    </author>
3039    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3040      <organization>One Laptop per Child</organization>
3041      <address><email>jg@laptop.org</email></address>
3042    </author>
3043    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3044      <organization abbrev="HP">Hewlett-Packard Company</organization>
3045      <address><email>JeffMogul@acm.org</email></address>
3046    </author>
3047    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3048      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3049      <address><email>henrikn@microsoft.com</email></address>
3050    </author>
3051    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3052      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3053      <address><email>LMM@acm.org</email></address>
3054    </author>
3055    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3056      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3057      <address><email>paulle@microsoft.com</email></address>
3058    </author>
3059    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3060      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3061      <address><email>timbl@w3.org</email></address>
3062    </author>
3063    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3064      <organization abbrev="W3C">World Wide Web Consortium</organization>
3065      <address><email>ylafon@w3.org</email></address>
3066    </author>
3067    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3068      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3069      <address><email>julian.reschke@greenbytes.de</email></address>
3070    </author>
3071    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3072  </front>
3073  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3074  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3075</reference>
3076
3077<reference anchor="Part3">
3078  <front>
3079    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3080    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3081      <organization abbrev="Day Software">Day Software</organization>
3082      <address><email>fielding@gbiv.com</email></address>
3083    </author>
3084    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3085      <organization>One Laptop per Child</organization>
3086      <address><email>jg@laptop.org</email></address>
3087    </author>
3088    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3089      <organization abbrev="HP">Hewlett-Packard Company</organization>
3090      <address><email>JeffMogul@acm.org</email></address>
3091    </author>
3092    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3093      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3094      <address><email>henrikn@microsoft.com</email></address>
3095    </author>
3096    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3097      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3098      <address><email>LMM@acm.org</email></address>
3099    </author>
3100    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3101      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3102      <address><email>paulle@microsoft.com</email></address>
3103    </author>
3104    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3105      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3106      <address><email>timbl@w3.org</email></address>
3107    </author>
3108    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3109      <organization abbrev="W3C">World Wide Web Consortium</organization>
3110      <address><email>ylafon@w3.org</email></address>
3111    </author>
3112    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3113      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3114      <address><email>julian.reschke@greenbytes.de</email></address>
3115    </author>
3116    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3117  </front>
3118  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3119  <x:source href="p3-payload.xml" basename="p3-payload"/>
3120</reference>
3121
3122<reference anchor="Part5">
3123  <front>
3124    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3125    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3126      <organization abbrev="Day Software">Day Software</organization>
3127      <address><email>fielding@gbiv.com</email></address>
3128    </author>
3129    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3130      <organization>One Laptop per Child</organization>
3131      <address><email>jg@laptop.org</email></address>
3132    </author>
3133    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3134      <organization abbrev="HP">Hewlett-Packard Company</organization>
3135      <address><email>JeffMogul@acm.org</email></address>
3136    </author>
3137    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3138      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3139      <address><email>henrikn@microsoft.com</email></address>
3140    </author>
3141    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3142      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3143      <address><email>LMM@acm.org</email></address>
3144    </author>
3145    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3146      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3147      <address><email>paulle@microsoft.com</email></address>
3148    </author>
3149    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3150      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3151      <address><email>timbl@w3.org</email></address>
3152    </author>
3153    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3154      <organization abbrev="W3C">World Wide Web Consortium</organization>
3155      <address><email>ylafon@w3.org</email></address>
3156    </author>
3157    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3158      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3159      <address><email>julian.reschke@greenbytes.de</email></address>
3160    </author>
3161    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3162  </front>
3163  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3164  <x:source href="p5-range.xml" basename="p5-range"/>
3165</reference>
3166
3167<reference anchor="Part6">
3168  <front>
3169    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3170    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3171      <organization abbrev="Day Software">Day Software</organization>
3172      <address><email>fielding@gbiv.com</email></address>
3173    </author>
3174    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3175      <organization>One Laptop per Child</organization>
3176      <address><email>jg@laptop.org</email></address>
3177    </author>
3178    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3179      <organization abbrev="HP">Hewlett-Packard Company</organization>
3180      <address><email>JeffMogul@acm.org</email></address>
3181    </author>
3182    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3184      <address><email>henrikn@microsoft.com</email></address>
3185    </author>
3186    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3187      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3188      <address><email>LMM@acm.org</email></address>
3189    </author>
3190    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3191      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3192      <address><email>paulle@microsoft.com</email></address>
3193    </author>
3194    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3195      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3196      <address><email>timbl@w3.org</email></address>
3197    </author>
3198    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3199      <organization abbrev="W3C">World Wide Web Consortium</organization>
3200      <address><email>ylafon@w3.org</email></address>
3201    </author>
3202    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3203      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3204      <address><email>julian.reschke@greenbytes.de</email></address>
3205    </author>
3206    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3207  </front>
3208  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3209  <x:source href="p6-cache.xml" basename="p6-cache"/>
3210</reference>
3211
3212<reference anchor="RFC5234">
3213  <front>
3214    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3215    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3216      <organization>Brandenburg InternetWorking</organization>
3217      <address>
3218      <postal>
3219      <street>675 Spruce Dr.</street>
3220      <city>Sunnyvale</city>
3221      <region>CA</region>
3222      <code>94086</code>
3223      <country>US</country></postal>
3224      <phone>+1.408.246.8253</phone>
3225      <email>dcrocker@bbiw.net</email></address> 
3226    </author>
3227    <author initials="P." surname="Overell" fullname="Paul Overell">
3228      <organization>THUS plc.</organization>
3229      <address>
3230      <postal>
3231      <street>1/2 Berkeley Square</street>
3232      <street>99 Berkely Street</street>
3233      <city>Glasgow</city>
3234      <code>G3 7HR</code>
3235      <country>UK</country></postal>
3236      <email>paul.overell@thus.net</email></address>
3237    </author>
3238    <date month="January" year="2008"/>
3239  </front>
3240  <seriesInfo name="STD" value="68"/>
3241  <seriesInfo name="RFC" value="5234"/>
3242</reference>
3243
3244<reference anchor="RFC2045">
3245  <front>
3246    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3247    <author initials="N." surname="Freed" fullname="Ned Freed">
3248      <organization>Innosoft International, Inc.</organization>
3249      <address><email>ned@innosoft.com</email></address>
3250    </author>
3251    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3252      <organization>First Virtual Holdings</organization>
3253      <address><email>nsb@nsb.fv.com</email></address>
3254    </author>
3255    <date month="November" year="1996"/>
3256  </front>
3257  <seriesInfo name="RFC" value="2045"/>
3258</reference>
3259
3260<reference anchor="RFC2047">
3261  <front>
3262    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3263    <author initials="K." surname="Moore" fullname="Keith Moore">
3264      <organization>University of Tennessee</organization>
3265      <address><email>moore@cs.utk.edu</email></address>
3266    </author>
3267    <date month="November" year="1996"/>
3268  </front>
3269  <seriesInfo name="RFC" value="2047"/>
3270</reference>
3271
3272<reference anchor="RFC2119">
3273  <front>
3274    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3275    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3276      <organization>Harvard University</organization>
3277      <address><email>sob@harvard.edu</email></address>
3278    </author>
3279    <date month="March" year="1997"/>
3280  </front>
3281  <seriesInfo name="BCP" value="14"/>
3282  <seriesInfo name="RFC" value="2119"/>
3283</reference>
3284
3285<reference anchor="RFC2396">
3286  <front>
3287    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3288    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3289      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3290      <address><email>timbl@w3.org</email></address>
3291    </author>
3292    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3293      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3294      <address><email>fielding@ics.uci.edu</email></address>
3295    </author>
3296    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3297      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3298      <address><email>masinter@parc.xerox.com</email></address>
3299    </author>
3300    <date month="August" year="1998"/>
3301  </front>
3302  <seriesInfo name="RFC" value="2396"/>
3303</reference>
3304
3305<reference anchor="USASCII">
3306  <front>
3307    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3308    <author>
3309      <organization>American National Standards Institute</organization>
3310    </author>
3311    <date year="1986"/>
3312  </front>
3313  <seriesInfo name="ANSI" value="X3.4"/>
3314</reference>
3315
3316</references>
3317
3318<references title="Informative References">
3319
3320<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3321  <front>
3322    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3323    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3324      <organization/>
3325    </author>
3326    <author initials="J." surname="Gettys" fullname="J. Gettys">
3327      <organization/>
3328    </author>
3329    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3330      <organization/>
3331    </author>
3332    <author initials="H." surname="Lie" fullname="H. Lie">
3333      <organization/>
3334    </author>
3335    <author initials="C." surname="Lilley" fullname="C. Lilley">
3336      <organization/>
3337    </author>
3338    <date year="1997" month="September"/>
3339  </front>
3340  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3341</reference>
3342
3343<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3344  <front>
3345    <title>Improving HTTP Latency</title>
3346    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3347      <organization/>
3348    </author>
3349    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3350      <organization/>
3351    </author>
3352    <date year="1995" month="December"/>
3353  </front>
3354  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3355</reference>
3356
3357<reference anchor="RFC822">
3358  <front>
3359    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3360    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3361      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3362      <address><email>DCrocker@UDel-Relay</email></address>
3363    </author>
3364    <date month="August" day="13" year="1982"/>
3365  </front>
3366  <seriesInfo name="STD" value="11"/>
3367  <seriesInfo name="RFC" value="822"/>
3368</reference>
3369
3370<reference anchor="RFC959">
3371  <front>
3372    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3373    <author initials="J." surname="Postel" fullname="J. Postel">
3374      <organization>Information Sciences Institute (ISI)</organization>
3375    </author>
3376    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3377      <organization/>
3378    </author>
3379    <date month="October" year="1985"/>
3380  </front>
3381  <seriesInfo name="STD" value="9"/>
3382  <seriesInfo name="RFC" value="959"/>
3383</reference>
3384
3385<reference anchor="RFC1123">
3386  <front>
3387    <title>Requirements for Internet Hosts - Application and Support</title>
3388    <author initials="R." surname="Braden" fullname="Robert Braden">
3389      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3390      <address><email>Braden@ISI.EDU</email></address>
3391    </author>
3392    <date month="October" year="1989"/>
3393  </front>
3394  <seriesInfo name="STD" value="3"/>
3395  <seriesInfo name="RFC" value="1123"/>
3396</reference>
3397
3398<reference anchor="RFC1305">
3399  <front>
3400    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3401    <author initials="D." surname="Mills" fullname="David L. Mills">
3402      <organization>University of Delaware, Electrical Engineering Department</organization>
3403      <address><email>mills@udel.edu</email></address>
3404    </author>
3405    <date month="March" year="1992"/>
3406  </front>
3407  <seriesInfo name="RFC" value="1305"/>
3408</reference>
3409
3410<reference anchor="RFC1436">
3411  <front>
3412    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3413    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3414      <organization>University of Minnesota, Computer and Information Services</organization>
3415      <address><email>fxa@boombox.micro.umn.edu</email></address>
3416    </author>
3417    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3418      <organization>University of Minnesota, Computer and Information Services</organization>
3419      <address><email>mpm@boombox.micro.umn.edu</email></address>
3420    </author>
3421    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3422      <organization>University of Minnesota, Computer and Information Services</organization>
3423      <address><email>lindner@boombox.micro.umn.edu</email></address>
3424    </author>
3425    <author initials="D." surname="Johnson" fullname="David Johnson">
3426      <organization>University of Minnesota, Computer and Information Services</organization>
3427      <address><email>dmj@boombox.micro.umn.edu</email></address>
3428    </author>
3429    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3430      <organization>University of Minnesota, Computer and Information Services</organization>
3431      <address><email>daniel@boombox.micro.umn.edu</email></address>
3432    </author>
3433    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3434      <organization>University of Minnesota, Computer and Information Services</organization>
3435      <address><email>alberti@boombox.micro.umn.edu</email></address>
3436    </author>
3437    <date month="March" year="1993"/>
3438  </front>
3439  <seriesInfo name="RFC" value="1436"/>
3440</reference>
3441
3442<reference anchor="RFC1630">
3443  <front>
3444    <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>
3445    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3446      <organization>CERN, World-Wide Web project</organization>
3447      <address><email>timbl@info.cern.ch</email></address>
3448    </author>
3449    <date month="June" year="1994"/>
3450  </front>
3451  <seriesInfo name="RFC" value="1630"/>
3452</reference>
3453
3454<reference anchor="RFC1737">
3455  <front>
3456    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3457    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3458      <organization>Xerox Palo Alto Research Center</organization>
3459      <address><email>masinter@parc.xerox.com</email></address>
3460    </author>
3461    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3462      <organization>MIT Laboratory for Computer Science</organization>
3463      <address><email>sollins@lcs.mit.edu</email></address>
3464    </author>
3465    <date month="December" year="1994"/>
3466  </front>
3467  <seriesInfo name="RFC" value="1737"/>
3468</reference>
3469
3470<reference anchor="RFC1738">
3471  <front>
3472    <title>Uniform Resource Locators (URL)</title>
3473    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3474      <organization>CERN, World-Wide Web project</organization>
3475      <address><email>timbl@info.cern.ch</email></address>
3476    </author>
3477    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3478      <organization>Xerox PARC</organization>
3479      <address><email>masinter@parc.xerox.com</email></address>
3480    </author>
3481    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3482      <organization>University of Minnesota, Computer and Information Services</organization>
3483      <address><email>mpm@boombox.micro.umn.edu</email></address>
3484    </author>
3485    <date month="December" year="1994"/>
3486  </front>
3487  <seriesInfo name="RFC" value="1738"/>
3488</reference>
3489
3490<reference anchor="RFC1808">
3491  <front>
3492    <title>Relative Uniform Resource Locators</title>
3493    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3494      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3495      <address><email>fielding@ics.uci.edu</email></address>
3496    </author>
3497    <date month="June" year="1995"/>
3498  </front>
3499  <seriesInfo name="RFC" value="1808"/>
3500</reference>
3501
3502<reference anchor="RFC1900">
3503  <front>
3504    <title>Renumbering Needs Work</title>
3505    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3506      <organization>CERN, Computing and Networks Division</organization>
3507      <address><email>brian@dxcoms.cern.ch</email></address>
3508    </author>
3509    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3510      <organization>cisco Systems</organization>
3511      <address><email>yakov@cisco.com</email></address>
3512    </author>
3513    <date month="February" year="1996"/>
3514  </front>
3515  <seriesInfo name="RFC" value="1900"/>
3516</reference>
3517
3518<reference anchor="RFC1945">
3519  <front>
3520    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3521    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3522      <organization>MIT, Laboratory for Computer Science</organization>
3523      <address><email>timbl@w3.org</email></address>
3524    </author>
3525    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3526      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3527      <address><email>fielding@ics.uci.edu</email></address>
3528    </author>
3529    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3530      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3531      <address><email>frystyk@w3.org</email></address>
3532    </author>
3533    <date month="May" year="1996"/>
3534  </front>
3535  <seriesInfo name="RFC" value="1945"/>
3536</reference>
3537
3538<reference anchor="RFC2068">
3539  <front>
3540    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3541    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3542      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3543      <address><email>fielding@ics.uci.edu</email></address>
3544    </author>
3545    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3546      <organization>MIT Laboratory for Computer Science</organization>
3547      <address><email>jg@w3.org</email></address>
3548    </author>
3549    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3550      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3551      <address><email>mogul@wrl.dec.com</email></address>
3552    </author>
3553    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3554      <organization>MIT Laboratory for Computer Science</organization>
3555      <address><email>frystyk@w3.org</email></address>
3556    </author>
3557    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3558      <organization>MIT Laboratory for Computer Science</organization>
3559      <address><email>timbl@w3.org</email></address>
3560    </author>
3561    <date month="January" year="1997"/>
3562  </front>
3563  <seriesInfo name="RFC" value="2068"/>
3564</reference>
3565
3566<reference anchor='RFC2109'>
3567  <front>
3568    <title>HTTP State Management Mechanism</title>
3569    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3570      <organization>Bell Laboratories, Lucent Technologies</organization>
3571      <address><email>dmk@bell-labs.com</email></address>
3572    </author>
3573    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3574      <organization>Netscape Communications Corp.</organization>
3575      <address><email>montulli@netscape.com</email></address>
3576    </author>
3577    <date year='1997' month='February' />
3578  </front>
3579  <seriesInfo name='RFC' value='2109' />
3580</reference>
3581
3582<reference anchor="RFC2145">
3583  <front>
3584    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3585    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3586      <organization>Western Research Laboratory</organization>
3587      <address><email>mogul@wrl.dec.com</email></address>
3588    </author>
3589    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3590      <organization>Department of Information and Computer Science</organization>
3591      <address><email>fielding@ics.uci.edu</email></address>
3592    </author>
3593    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3594      <organization>MIT Laboratory for Computer Science</organization>
3595      <address><email>jg@w3.org</email></address>
3596    </author>
3597    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3598      <organization>W3 Consortium</organization>
3599      <address><email>frystyk@w3.org</email></address>
3600    </author>
3601    <date month="May" year="1997"/>
3602  </front>
3603  <seriesInfo name="RFC" value="2145"/>
3604</reference>
3605
3606<reference anchor="RFC2324">
3607  <front>
3608    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3609    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3610      <organization>Xerox Palo Alto Research Center</organization>
3611      <address><email>masinter@parc.xerox.com</email></address>
3612    </author>
3613    <date month="April" day="1" year="1998"/>
3614  </front>
3615  <seriesInfo name="RFC" value="2324"/>
3616</reference>
3617
3618<reference anchor="RFC2616">
3619  <front>
3620    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3621    <author initials="R." surname="Fielding" fullname="R. Fielding">
3622      <organization>University of California, Irvine</organization>
3623      <address><email>fielding@ics.uci.edu</email></address>
3624    </author>
3625    <author initials="J." surname="Gettys" fullname="J. Gettys">
3626      <organization>W3C</organization>
3627      <address><email>jg@w3.org</email></address>
3628    </author>
3629    <author initials="J." surname="Mogul" fullname="J. Mogul">
3630      <organization>Compaq Computer Corporation</organization>
3631      <address><email>mogul@wrl.dec.com</email></address>
3632    </author>
3633    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3634      <organization>MIT Laboratory for Computer Science</organization>
3635      <address><email>frystyk@w3.org</email></address>
3636    </author>
3637    <author initials="L." surname="Masinter" fullname="L. Masinter">
3638      <organization>Xerox Corporation</organization>
3639      <address><email>masinter@parc.xerox.com</email></address>
3640    </author>
3641    <author initials="P." surname="Leach" fullname="P. Leach">
3642      <organization>Microsoft Corporation</organization>
3643      <address><email>paulle@microsoft.com</email></address>
3644    </author>
3645    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3646      <organization>W3C</organization>
3647      <address><email>timbl@w3.org</email></address>
3648    </author>
3649    <date month="June" year="1999"/>
3650  </front>
3651  <seriesInfo name="RFC" value="2616"/>
3652</reference>
3653
3654<reference anchor='RFC2818'>
3655  <front>
3656    <title>HTTP Over TLS</title>
3657    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3658      <organization>RTFM, Inc.</organization>
3659      <address><email>ekr@rtfm.com</email></address>
3660    </author>
3661    <date year='2000' month='May' />
3662  </front>
3663  <seriesInfo name='RFC' value='2818' />
3664</reference>
3665
3666<reference anchor="RFC2821">
3667  <front>
3668    <title>Simple Mail Transfer Protocol</title>
3669    <author initials="J." surname="Klensin" fullname="J. Klensin">
3670      <organization>AT&amp;T Laboratories</organization>
3671      <address><email>klensin@research.att.com</email></address>
3672    </author>
3673    <date year="2001" month="April"/>
3674  </front>
3675  <seriesInfo name="RFC" value="2821"/>
3676</reference>
3677
3678<reference anchor='RFC2965'>
3679  <front>
3680    <title>HTTP State Management Mechanism</title>
3681    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3682      <organization>Bell Laboratories, Lucent Technologies</organization>
3683      <address><email>dmk@bell-labs.com</email></address>
3684    </author>
3685    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3686      <organization>Epinions.com, Inc.</organization>
3687      <address><email>lou@montulli.org</email></address>
3688    </author>
3689    <date year='2000' month='October' />
3690  </front>
3691  <seriesInfo name='RFC' value='2965' />
3692</reference>
3693
3694<reference anchor='RFC3864'>
3695  <front>
3696    <title>Registration Procedures for Message Header Fields</title>
3697    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3698      <organization>Nine by Nine</organization>
3699      <address><email>GK-IETF@ninebynine.org</email></address>
3700    </author>
3701    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3702      <organization>BEA Systems</organization>
3703      <address><email>mnot@pobox.com</email></address>
3704    </author>
3705    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3706      <organization>HP Labs</organization>
3707      <address><email>JeffMogul@acm.org</email></address>
3708    </author>
3709    <date year='2004' month='September' />
3710  </front>
3711  <seriesInfo name='BCP' value='90' />
3712  <seriesInfo name='RFC' value='3864' />
3713</reference>
3714
3715<reference anchor='RFC3977'>
3716  <front>
3717    <title>Network News Transfer Protocol (NNTP)</title>
3718    <author initials='C.' surname='Feather' fullname='C. Feather'>
3719      <organization>THUS plc</organization>
3720      <address><email>clive@demon.net</email></address>
3721    </author>
3722    <date year='2006' month='October' />
3723  </front>
3724  <seriesInfo name="RFC" value="3977"/>
3725</reference>
3726
3727<reference anchor="RFC4288">
3728  <front>
3729    <title>Media Type Specifications and Registration Procedures</title>
3730    <author initials="N." surname="Freed" fullname="N. Freed">
3731      <organization>Sun Microsystems</organization>
3732      <address>
3733        <email>ned.freed@mrochek.com</email>
3734      </address>
3735    </author>
3736    <author initials="J." surname="Klensin" fullname="J. Klensin">
3737      <organization/>
3738      <address>
3739        <email>klensin+ietf@jck.com</email>
3740      </address>
3741    </author>
3742    <date year="2005" month="December"/>
3743  </front>
3744  <seriesInfo name="BCP" value="13"/>
3745  <seriesInfo name="RFC" value="4288"/>
3746</reference>
3747
3748<reference anchor='RFC4395'>
3749  <front>
3750    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3751    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3752      <organization>AT&amp;T Laboratories</organization>
3753      <address>
3754        <email>tony+urireg@maillennium.att.com</email>
3755      </address>
3756    </author>
3757    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3758      <organization>Qualcomm, Inc.</organization>
3759      <address>
3760        <email>hardie@qualcomm.com</email>
3761      </address>
3762    </author>
3763    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3764      <organization>Adobe Systems</organization>
3765      <address>
3766        <email>LMM@acm.org</email>
3767      </address>
3768    </author>
3769    <date year='2006' month='February' />
3770  </front>
3771  <seriesInfo name='BCP' value='115' />
3772  <seriesInfo name='RFC' value='4395' />
3773</reference>
3774
3775<reference anchor="RFC5322">
3776  <front>
3777    <title>Internet Message Format</title>
3778    <author initials="P." surname="Resnick" fullname="P. Resnick">
3779      <organization>Qualcomm Incorporated</organization>
3780    </author>
3781    <date year="2008" month="October"/>
3782  </front> 
3783  <seriesInfo name="RFC" value="5322"/>
3784</reference>
3785
3786<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3787  <front>
3788    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3789    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3790      <organization/>
3791    </author>
3792    <date year="2001" month="November"/>
3793  </front>
3794  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3795</reference>
3796
3797<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3798  <front>
3799  <title>Analysis of HTTP Performance Problems</title>
3800  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3801    <organization/>
3802  </author>
3803  <date/>
3804  </front>
3805</reference>
3806
3807<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3808  <front>
3809  <title>Analysis of HTTP Performance</title>
3810  <author initials="J." surname="Touch" fullname="Joe Touch">
3811    <organization>USC/Information Sciences Institute</organization>
3812    <address><email>touch@isi.edu</email></address>
3813  </author>
3814  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3815    <organization>USC/Information Sciences Institute</organization>
3816    <address><email>johnh@isi.edu</email></address>
3817  </author>
3818  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3819    <organization>USC/Information Sciences Institute</organization>
3820    <address><email>katia@isi.edu</email></address>
3821  </author>
3822  <date year="1998" month="Aug"/>
3823  </front>
3824  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3825  <annotation>(original report dated Aug. 1996)</annotation>
3826</reference>
3827
3828<reference anchor="WAIS">
3829  <front>
3830    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3831    <author initials="F." surname="Davis" fullname="F. Davis">
3832      <organization>Thinking Machines Corporation</organization>
3833    </author>
3834    <author initials="B." surname="Kahle" fullname="B. Kahle">
3835      <organization>Thinking Machines Corporation</organization>
3836    </author>
3837    <author initials="H." surname="Morris" fullname="H. Morris">
3838      <organization>Thinking Machines Corporation</organization>
3839    </author>
3840    <author initials="J." surname="Salem" fullname="J. Salem">
3841      <organization>Thinking Machines Corporation</organization>
3842    </author>
3843    <author initials="T." surname="Shen" fullname="T. Shen">
3844      <organization>Thinking Machines Corporation</organization>
3845    </author>
3846    <author initials="R." surname="Wang" fullname="R. Wang">
3847      <organization>Thinking Machines Corporation</organization>
3848    </author>
3849    <author initials="J." surname="Sui" fullname="J. Sui">
3850      <organization>Thinking Machines Corporation</organization>
3851    </author>
3852    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3853      <organization>Thinking Machines Corporation</organization>
3854    </author>
3855    <date month="April" year="1990"/>
3856  </front>
3857  <seriesInfo name="Thinking Machines Corporation" value=""/>
3858</reference>
3859
3860</references>
3861
3862
3863<section title="Tolerant Applications" anchor="tolerant.applications">
3864<t>
3865   Although this document specifies the requirements for the generation
3866   of HTTP/1.1 messages, not all applications will be correct in their
3867   implementation. We therefore recommend that operational applications
3868   be tolerant of deviations whenever those deviations can be
3869   interpreted unambiguously.
3870</t>
3871<t>
3872   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3873   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3874   accept any amount of SP or HTAB characters between fields, even though
3875   only a single SP is required.
3876</t>
3877<t>
3878   The line terminator for message-header fields is the sequence CRLF.
3879   However, we recommend that applications, when parsing such headers,
3880   recognize a single LF as a line terminator and ignore the leading CR.
3881</t>
3882<t>
3883   The character set of an entity-body &SHOULD; be labeled as the lowest
3884   common denominator of the character codes used within that body, with
3885   the exception that not labeling the entity is preferred over labeling
3886   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3887</t>
3888<t>
3889   Additional rules for requirements on parsing and encoding of dates
3890   and other potential problems with date encodings include:
3891</t>
3892<t>
3893  <list style="symbols">
3894     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3895        which appears to be more than 50 years in the future is in fact
3896        in the past (this helps solve the "year 2000" problem).</t>
3897
3898     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3899        Expires date as earlier than the proper value, but &MUST-NOT;
3900        internally represent a parsed Expires date as later than the
3901        proper value.</t>
3902
3903     <t>All expiration-related calculations &MUST; be done in GMT. The
3904        local time zone &MUST-NOT; influence the calculation or comparison
3905        of an age or expiration time.</t>
3906
3907     <t>If an HTTP header incorrectly carries a date value with a time
3908        zone other than GMT, it &MUST; be converted into GMT using the
3909        most conservative possible conversion.</t>
3910  </list>
3911</t>
3912</section>
3913
3914<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3915<t>
3916   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3917   simplify the process of date comparison. Proxies and gateways from
3918   other protocols &SHOULD; ensure that any Date header field present in a
3919   message conforms to one of the HTTP/1.1 formats and rewrite the date
3920   if necessary.
3921</t>
3922</section>
3923
3924<section title="Compatibility with Previous Versions" anchor="compatibility">
3925<t>
3926   It is beyond the scope of a protocol specification to mandate
3927   compliance with previous versions. HTTP/1.1 was deliberately
3928   designed, however, to make supporting previous versions easy. It is
3929   worth noting that, at the time of composing this specification
3930   (1996), we would expect commercial HTTP/1.1 servers to:
3931  <list style="symbols">
3932     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3933        1.1 requests;</t>
3934
3935     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3936        1.1;</t>
3937
3938     <t>respond appropriately with a message in the same major version
3939        used by the client.</t>
3940  </list>
3941</t>
3942<t>
3943   And we would expect HTTP/1.1 clients to:
3944  <list style="symbols">
3945     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3946        responses;</t>
3947
3948     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3949        1.1.</t>
3950  </list>
3951</t>
3952<t>
3953   For most implementations of HTTP/1.0, each connection is established
3954   by the client prior to the request and closed by the server after
3955   sending the response. Some implementations implement the Keep-Alive
3956   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3957</t>
3958
3959<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3960<t>
3961   This section summarizes major differences between versions HTTP/1.0
3962   and HTTP/1.1.
3963</t>
3964
3965<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
3966<t>
3967   The requirements that clients and servers support the Host request-header,
3968   report an error if the Host request-header (<xref target="header.host"/>) is
3969   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3970   are among the most important changes defined by this
3971   specification.
3972</t>
3973<t>
3974   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3975   addresses and servers; there was no other established mechanism for
3976   distinguishing the intended server of a request than the IP address
3977   to which that request was directed. The changes outlined above will
3978   allow the Internet, once older HTTP clients are no longer common, to
3979   support multiple Web sites from a single IP address, greatly
3980   simplifying large operational Web servers, where allocation of many
3981   IP addresses to a single host has created serious problems. The
3982   Internet will also be able to recover the IP addresses that have been
3983   allocated for the sole purpose of allowing special-purpose domain
3984   names to be used in root-level HTTP URLs. Given the rate of growth of
3985   the Web, and the number of servers already deployed, it is extremely
3986   important that all implementations of HTTP (including updates to
3987   existing HTTP/1.0 applications) correctly implement these
3988   requirements:
3989  <list style="symbols">
3990     <t>Both clients and servers &MUST; support the Host request-header.</t>
3991
3992     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3993
3994     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3995        request does not include a Host request-header.</t>
3996
3997     <t>Servers &MUST; accept absolute URIs.</t>
3998  </list>
3999</t>
4000</section>
4001</section>
4002
4003<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4004<t>
4005   Some clients and servers might wish to be compatible with some
4006   previous implementations of persistent connections in HTTP/1.0
4007   clients and servers. Persistent connections in HTTP/1.0 are
4008   explicitly negotiated as they are not the default behavior. HTTP/1.0
4009   experimental implementations of persistent connections are faulty,
4010   and the new facilities in HTTP/1.1 are designed to rectify these
4011   problems. The problem was that some existing 1.0 clients may be
4012   sending Keep-Alive to a proxy server that doesn't understand
4013   Connection, which would then erroneously forward it to the next
4014   inbound server, which would establish the Keep-Alive connection and
4015   result in a hung HTTP/1.0 proxy waiting for the close on the
4016   response. The result is that HTTP/1.0 clients must be prevented from
4017   using Keep-Alive when talking to proxies.
4018</t>
4019<t>
4020   However, talking to proxies is the most important use of persistent
4021   connections, so that prohibition is clearly unacceptable. Therefore,
4022   we need some other mechanism for indicating a persistent connection
4023   is desired, which is safe to use even when talking to an old proxy
4024   that ignores Connection. Persistent connections are the default for
4025   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4026   declaring non-persistence. See <xref target="header.connection"/>.
4027</t>
4028<t>
4029   The original HTTP/1.0 form of persistent connections (the Connection:
4030   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4031</t>
4032</section>
4033
4034<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4035<t>
4036   This specification has been carefully audited to correct and
4037   disambiguate key word usage; RFC 2068 had many problems in respect to
4038   the conventions laid out in <xref target="RFC2119"/>.
4039</t>
4040<t>
4041   Transfer-coding and message lengths all interact in ways that
4042   required fixing exactly when chunked encoding is used (to allow for
4043   transfer encoding that may not be self delimiting); it was important
4044   to straighten out exactly how message lengths are computed. (Sections
4045   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4046   <xref target="header.content-length" format="counter"/>,
4047   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4048</t>
4049<t>
4050   The use and interpretation of HTTP version numbers has been clarified
4051   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4052   version they support to deal with problems discovered in HTTP/1.0
4053   implementations (<xref target="http.version"/>)
4054</t>
4055<t>
4056   Transfer-coding had significant problems, particularly with
4057   interactions with chunked encoding. The solution is that transfer-codings
4058   become as full fledged as content-codings. This involves
4059   adding an IANA registry for transfer-codings (separate from content
4060   codings), a new header field (TE) and enabling trailer headers in the
4061   future. Transfer encoding is a major performance benefit, so it was
4062   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4063   interoperability problem that could have occurred due to interactions
4064   between authentication trailers, chunked encoding and HTTP/1.0
4065   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4066   and <xref target="header.te" format="counter"/>)
4067</t>
4068</section>
4069
4070<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4071<t>
4072  The CHAR rule does not allow the NUL character anymore (this affects
4073  the comment and quoted-string rules).  Furthermore, the quoted-pair
4074  rule does not allow escaping NUL, CR or LF anymore.
4075  (<xref target="basic.rules"/>)
4076</t>
4077<t>
4078  Clarify that HTTP-Version is case sensitive.
4079  (<xref target="http.version"/>)
4080</t>
4081<t>
4082  Remove reference to non-existant identity transfer-coding value tokens.
4083  (Sections <xref format="counter" target="transfer.codings"/> and
4084  <xref format="counter" target="message.length"/>)
4085</t>
4086<t>
4087  Clarification that the chunk length does not include
4088  the count of the octets in the chunk header and trailer.
4089  (<xref target="chunked.transfer.encoding"/>)
4090</t>
4091<t>
4092  Fix BNF to add query, as the abs_path production in
4093  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4094  (<xref target="request-uri"/>)
4095</t>
4096<t>
4097  Clarify exactly when close connection options must be sent.
4098  (<xref target="header.connection"/>)
4099</t>
4100</section>
4101</section>
4102
4103<section title="Terminology" anchor="terminology">
4104<t>
4105   This specification uses a number of terms to refer to the roles
4106   played by participants in, and objects of, the HTTP communication.
4107</t>
4108<t>
4109  <iref item="connection"/>
4110  <x:dfn>connection</x:dfn>
4111  <list>
4112    <t>
4113      A transport layer virtual circuit established between two programs
4114      for the purpose of communication.
4115    </t>
4116  </list>
4117</t>
4118<t>
4119  <iref item="message"/>
4120  <x:dfn>message</x:dfn>
4121  <list>
4122    <t>
4123      The basic unit of HTTP communication, consisting of a structured
4124      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4125      transmitted via the connection.
4126    </t>
4127  </list>
4128</t>
4129<t>
4130  <iref item="request"/>
4131  <x:dfn>request</x:dfn>
4132  <list>
4133    <t>
4134      An HTTP request message, as defined in <xref target="request"/>.
4135    </t>
4136  </list>
4137</t>
4138<t>
4139  <iref item="response"/>
4140  <x:dfn>response</x:dfn>
4141  <list>
4142    <t>
4143      An HTTP response message, as defined in <xref target="response"/>.
4144    </t>
4145  </list>
4146</t>
4147<t>
4148  <iref item="resource"/>
4149  <x:dfn>resource</x:dfn>
4150  <list>
4151    <t>
4152      A network data object or service that can be identified by a URI,
4153      as defined in <xref target="uri"/>. Resources may be available in multiple
4154      representations (e.g. multiple languages, data formats, size, and
4155      resolutions) or vary in other ways.
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  <iref item="entity"/>
4161  <x:dfn>entity</x:dfn>
4162  <list>
4163    <t>
4164      The information transferred as the payload of a request or
4165      response. An entity consists of metainformation in the form of
4166      entity-header fields and content in the form of an entity-body, as
4167      described in &entity;.
4168    </t>
4169  </list>
4170</t>
4171<t>
4172  <iref item="representation"/>
4173  <x:dfn>representation</x:dfn>
4174  <list>
4175    <t>
4176      An entity included with a response that is subject to content
4177      negotiation, as described in &content.negotiation;. There may exist multiple
4178      representations associated with a particular response status.
4179    </t>
4180  </list>
4181</t>
4182<t>
4183  <iref item="content negotiation"/>
4184  <x:dfn>content negotiation</x:dfn>
4185  <list>
4186    <t>
4187      The mechanism for selecting the appropriate representation when
4188      servicing a request, as described in &content.negotiation;. The
4189      representation of entities in any response can be negotiated
4190      (including error responses).
4191    </t>
4192  </list>
4193</t>
4194<t>
4195  <iref item="variant"/>
4196  <x:dfn>variant</x:dfn>
4197  <list>
4198    <t>
4199      A resource may have one, or more than one, representation(s)
4200      associated with it at any given instant. Each of these
4201      representations is termed a `variant'.  Use of the term `variant'
4202      does not necessarily imply that the resource is subject to content
4203      negotiation.
4204    </t>
4205  </list>
4206</t>
4207<t>
4208  <iref item="client"/>
4209  <x:dfn>client</x:dfn>
4210  <list>
4211    <t>
4212      A program that establishes connections for the purpose of sending
4213      requests.
4214    </t>
4215  </list>
4216</t>
4217<t>
4218  <iref item="user agent"/>
4219  <x:dfn>user agent</x:dfn>
4220  <list>
4221    <t>
4222      The client which initiates a request. These are often browsers,
4223      editors, spiders (web-traversing robots), or other end user tools.
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="server"/>
4229  <x:dfn>server</x:dfn>
4230  <list>
4231    <t>
4232      An application program that accepts connections in order to
4233      service requests by sending back responses. Any given program may
4234      be capable of being both a client and a server; our use of these
4235      terms refers only to the role being performed by the program for a
4236      particular connection, rather than to the program's capabilities
4237      in general. Likewise, any server may act as an origin server,
4238      proxy, gateway, or tunnel, switching behavior based on the nature
4239      of each request.
4240    </t>
4241  </list>
4242</t>
4243<t>
4244  <iref item="origin server"/>
4245  <x:dfn>origin server</x:dfn>
4246  <list>
4247    <t>
4248      The server on which a given resource resides or is to be created.
4249    </t>
4250  </list>
4251</t>
4252<t>
4253  <iref item="proxy"/>
4254  <x:dfn>proxy</x:dfn>
4255  <list>
4256    <t>
4257      An intermediary program which acts as both a server and a client
4258      for the purpose of making requests on behalf of other clients.
4259      Requests are serviced internally or by passing them on, with
4260      possible translation, to other servers. A proxy &MUST; implement
4261      both the client and server requirements of this specification. A
4262      "transparent proxy" is a proxy that does not modify the request or
4263      response beyond what is required for proxy authentication and
4264      identification. A "non-transparent proxy" is a proxy that modifies
4265      the request or response in order to provide some added service to
4266      the user agent, such as group annotation services, media type
4267      transformation, protocol reduction, or anonymity filtering. Except
4268      where either transparent or non-transparent behavior is explicitly
4269      stated, the HTTP proxy requirements apply to both types of
4270      proxies.
4271    </t>
4272  </list>
4273</t>
4274<t>
4275  <iref item="gateway"/>
4276  <x:dfn>gateway</x:dfn>
4277  <list>
4278    <t>
4279      A server which acts as an intermediary for some other server.
4280      Unlike a proxy, a gateway receives requests as if it were the
4281      origin server for the requested resource; the requesting client
4282      may not be aware that it is communicating with a gateway.
4283    </t>
4284  </list>
4285</t>
4286<t>
4287  <iref item="tunnel"/>
4288  <x:dfn>tunnel</x:dfn>
4289  <list>
4290    <t>
4291      An intermediary program which is acting as a blind relay between
4292      two connections. Once active, a tunnel is not considered a party
4293      to the HTTP communication, though the tunnel may have been
4294      initiated by an HTTP request. The tunnel ceases to exist when both
4295      ends of the relayed connections are closed.
4296    </t>
4297  </list>
4298</t>
4299<t>
4300  <iref item="cache"/>
4301  <x:dfn>cache</x:dfn>
4302  <list>
4303    <t>
4304      A program's local store of response messages and the subsystem
4305      that controls its message storage, retrieval, and deletion. A
4306      cache stores cacheable responses in order to reduce the response
4307      time and network bandwidth consumption on future, equivalent
4308      requests. Any client or server may include a cache, though a cache
4309      cannot be used by a server that is acting as a tunnel.
4310    </t>
4311  </list>
4312</t>
4313<t>
4314  <iref item="cacheable"/>
4315  <x:dfn>cacheable</x:dfn>
4316  <list>
4317    <t>
4318      A response is cacheable if a cache is allowed to store a copy of
4319      the response message for use in answering subsequent requests. The
4320      rules for determining the cacheability of HTTP responses are
4321      defined in &caching;. Even if a resource is cacheable, there may
4322      be additional constraints on whether a cache can use the cached
4323      copy for a particular request.
4324    </t>
4325  </list>
4326</t>
4327<t>
4328  <iref item="upstream"/>
4329  <iref item="downstream"/>
4330  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4331  <list>
4332    <t>
4333      Upstream and downstream describe the flow of a message: all
4334      messages flow from upstream to downstream.
4335    </t>
4336  </list>
4337</t>
4338<t>
4339  <iref item="inbound"/>
4340  <iref item="outbound"/>
4341  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4342  <list>
4343    <t>
4344      Inbound and outbound refer to the request and response paths for
4345      messages: "inbound" means "traveling toward the origin server",
4346      and "outbound" means "traveling toward the user agent"
4347    </t>
4348  </list>
4349</t>
4350</section>
4351
4352<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4353
4354<section title="Since RFC2616">
4355<t>
4356  Extracted relevant partitions from <xref target="RFC2616"/>.
4357</t>
4358</section>
4359
4360<section title="Since draft-ietf-httpbis-p1-messaging-00">
4361<t>
4362  Closed issues:
4363  <list style="symbols"> 
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4366      "HTTP Version should be case sensitive"
4367      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4368    </t>
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4371      "'unsafe' characters"
4372      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4373    </t>
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4376      "Chunk Size Definition"
4377      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4378    </t>
4379    <t>
4380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4381      "Message Length"
4382      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4386      "Media Type Registrations"
4387      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4388    </t>
4389    <t>
4390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4391      "URI includes query"
4392      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4396      "No close on 1xx responses"
4397      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4398    </t>
4399    <t>
4400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4401      "Remove 'identity' token references"
4402      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4403    </t>
4404    <t>
4405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4406      "Import query BNF"
4407    </t>
4408    <t>
4409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4410      "qdtext BNF"
4411    </t>
4412    <t>
4413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4414      "Normative and Informative references"
4415    </t>
4416    <t>
4417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4418      "RFC2606 Compliance"
4419    </t>
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4422      "RFC977 reference"
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4426      "RFC1700 references"
4427    </t>
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4430      "inconsistency in date format explanation"
4431    </t>
4432    <t>
4433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4434      "Date reference typo"
4435    </t>
4436    <t>
4437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4438      "Informative references"
4439    </t>
4440    <t>
4441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4442      "ISO-8859-1 Reference"
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4446      "Normative up-to-date references"
4447    </t>
4448  </list>
4449</t>
4450<t>
4451  Other changes:
4452  <list style="symbols"> 
4453    <t>
4454      Update media type registrations to use RFC4288 template.
4455    </t>
4456    <t>
4457      Use names of RFC4234 core rules DQUOTE and HTAB,
4458      fix broken ABNF for chunk-data
4459      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4460    </t>
4461  </list>
4462</t>
4463</section>
4464
4465<section title="Since draft-ietf-httpbis-p1-messaging-01">
4466<t>
4467  Closed issues:
4468  <list style="symbols"> 
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4471      "Bodies on GET (and other) requests"
4472    </t>
4473    <t>
4474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4475      "Updating to RFC4288"
4476    </t>
4477    <t>
4478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4479      "Status Code and Reason Phrase"
4480    </t>
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4483      "rel_path not used"
4484    </t>
4485  </list>
4486</t>
4487<t>
4488  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4489  <list style="symbols"> 
4490    <t>
4491      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4492      "trailer-part").
4493    </t>
4494    <t>
4495      Avoid underscore character in rule names ("http_URL" ->
4496      "http-URL", "abs_path" -> "path-absolute").
4497    </t>
4498    <t>
4499      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4500      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4501      have to be updated when switching over to RFC3986.
4502    </t>
4503    <t>
4504      Synchronize core rules with RFC5234 (this includes a change to CHAR
4505      which now excludes NUL).
4506    </t>
4507    <t>
4508      Get rid of prose rules that span multiple lines.
4509    </t>
4510    <t>
4511      Get rid of unused rules LOALPHA and UPALPHA.
4512    </t>
4513    <t>
4514      Move "Product Tokens" section (back) into Part 1, as "token" is used
4515      in the definition of the Upgrade header.
4516    </t>
4517    <t>
4518      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4519    </t>
4520    <t>
4521      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4522    </t>
4523  </list>
4524</t>
4525</section>
4526
4527<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4528<t>
4529  Closed issues:
4530  <list style="symbols"> 
4531    <t>
4532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4533      "HTTP-date vs. rfc1123-date"
4534    </t>
4535    <t>
4536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4537      "WS in quoted-pair"
4538    </t>
4539  </list>
4540</t>
4541<t>
4542  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4543  <list style="symbols"> 
4544    <t>
4545      Reference RFC 3984, and update header registrations for headers defined
4546      in this document.
4547    </t>
4548  </list>
4549</t>
4550<t>
4551  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4552  <list style="symbols"> 
4553    <t>
4554      Replace string literals when the string really is case-sensitive (HTTP-Version).
4555    </t>
4556  </list>
4557</t>
4558</section>
4559
4560<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4561<t>
4562  Closed issues:
4563  <list style="symbols"> 
4564    <t>
4565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4566      "Connection closing"
4567    </t>
4568    <t>
4569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4570      "Move registrations and registry information to IANA Considerations"
4571    </t>
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4574      "need new URL for PAD1995 reference"
4575    </t>
4576    <t>
4577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4578      "IANA Considerations: update HTTP URI scheme registration"
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4582      "Cite HTTPS URI scheme definition"
4583    </t>
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4586      "List-type headers vs Set-Cookie"
4587    </t>
4588  </list>
4589</t>
4590<t>
4591  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4592  <list style="symbols"> 
4593    <t>
4594      Replace string literals when the string really is case-sensitive (HTTP-Date).
4595    </t>
4596    <t>
4597      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4598    </t>
4599  </list>
4600</t>
4601</section>
4602
4603<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4604<t>
4605  Closed issues:
4606  <list style="symbols"> 
4607    <t>
4608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4609      "RFC 2822 is updated by RFC 5322"
4610    </t>
4611  </list>
4612</t>
4613<t>
4614  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4615  <list style="symbols"> 
4616    <t>
4617      Use "/" instead of "|" for alternatives.
4618    </t>
4619    <t>
4620      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4621    </t>
4622    <t>
4623      Only reference RFC 5234's core rules.
4624    </t>
4625  </list>
4626</t>
4627</section>
4628
4629</section>
4630
4631</back>
4632</rfc>
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