source: draft-ietf-httpbis/latest/p1-messaging.xml @ 351

Last change on this file since 351 was 351, checked in by julian.reschke@…, 11 years ago

introduce BWS, OWS, RWS, but do not use them yet (related to #36)

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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.whitespace">
513  <x:anchor-alias value="BWS"/>
514  <x:anchor-alias value="OWS"/>
515  <x:anchor-alias value="RWS"/>
516  <x:anchor-alias value="obs-fold"/>
517  <cref>Add prose introducing the different kinds of WS.</cref>
518<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
519  <x:ref>OWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
520                 ; "optional" white space
521  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
522                 ; "required" white space
523  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
524                 ; "bad" white space
525  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
526                 ; <cref>to be explained: do not produce</cref>
527</artwork></figure>
528</t>
529<t anchor="rule.TEXT">
530  <x:anchor-alias value="TEXT"/>
531   The TEXT rule is only used for descriptive field contents and values
532   that are not intended to be interpreted by the message parser. Words
533   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
534   <xref target="ISO-8859-1"/> only when encoded according to the rules of
535   <xref target="RFC2047"/>.
536</t>
537<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
538  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
539                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
540</artwork></figure>
541<t>
542   A CRLF is allowed in the definition of TEXT only as part of a header
543   field continuation. It is expected that the folding LWS will be
544   replaced with a single SP before interpretation of the TEXT value.
545</t>
546<t anchor="rule.token.separators">
547  <x:anchor-alias value="tchar"/>
548  <x:anchor-alias value="token"/>
549  <x:anchor-alias value="separators"/>
550   Many HTTP/1.1 header field values consist of words separated by LWS
551   or special characters. These special characters &MUST; be in a quoted
552   string to be used within a parameter value (as defined in
553   <xref target="transfer.codings"/>).
554</t>
555<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"/>
556  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
557                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
558                 / "/" / "[" / "]" / "?" / "="
559                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
560                 
561  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
562                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
563                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
564                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
565                 
566  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
567</artwork></figure>
568<t anchor="rule.comment">
569  <x:anchor-alias value="comment"/>
570  <x:anchor-alias value="ctext"/>
571   Comments can be included in some HTTP header fields by surrounding
572   the comment text with parentheses. Comments are only allowed in
573   fields containing "comment" as part of their field value definition.
574   In all other fields, parentheses are considered part of the field
575   value.
576</t>
577<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
578  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
579  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
580</artwork></figure>
581<t anchor="rule.quoted-string">
582  <x:anchor-alias value="quoted-string"/>
583  <x:anchor-alias value="qdtext"/>
584   A string of text is parsed as a single word if it is quoted using
585   double-quote marks.
586</t>
587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
588  <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> )
589  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
590</artwork></figure>
591<t anchor="rule.quoted-pair">
592  <x:anchor-alias value="quoted-pair"/>
593  <x:anchor-alias value="quoted-text"/>
594   The backslash character ("\") &MAY; be used as a single-character
595   quoting mechanism only within quoted-string and comment constructs.
596</t>
597<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
598  <x:ref>quoted-text</x:ref>    = %x01-09 /
599                   %x0B-0C /
600                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
601  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
602</artwork></figure>
603</section>
604
605<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
606  <x:anchor-alias value="request-header"/>
607  <x:anchor-alias value="response-header"/>
608  <x:anchor-alias value="accept-params"/>
609  <x:anchor-alias value="entity-body"/>
610  <x:anchor-alias value="entity-header"/>
611  <x:anchor-alias value="Cache-Control"/>
612  <x:anchor-alias value="Pragma"/>
613  <x:anchor-alias value="Warning"/>
614<t>
615  The ABNF rules below are defined in other parts:
616</t>
617<figure><!-- Part2--><artwork type="abnf2616">
618  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
619  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
620</artwork></figure>
621<figure><!-- Part3--><artwork type="abnf2616">
622  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
623  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
624  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
625</artwork></figure>
626<figure><!-- Part6--><artwork type="abnf2616">
627  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
628  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
629  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
630</artwork></figure>
631</section>
632
633</section>
634
635<section title="Protocol Parameters" anchor="protocol.parameters">
636
637<section title="HTTP Version" anchor="http.version">
638  <x:anchor-alias value="HTTP-Version"/>
639  <x:anchor-alias value="HTTP-Prot-Name"/>
640<t>
641   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
642   of the protocol. The protocol versioning policy is intended to allow
643   the sender to indicate the format of a message and its capacity for
644   understanding further HTTP communication, rather than the features
645   obtained via that communication. No change is made to the version
646   number for the addition of message components which do not affect
647   communication behavior or which only add to extensible field values.
648   The &lt;minor&gt; number is incremented when the changes made to the
649   protocol add features which do not change the general message parsing
650   algorithm, but which may add to the message semantics and imply
651   additional capabilities of the sender. The &lt;major&gt; number is
652   incremented when the format of a message within the protocol is
653   changed. See <xref target="RFC2145"/> for a fuller explanation.
654</t>
655<t>
656   The version of an HTTP message is indicated by an HTTP-Version field
657   in the first line of the message. HTTP-Version is case-sensitive.
658</t>
659<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
660  <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>
661  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
662</artwork></figure>
663<t>
664   Note that the major and minor numbers &MUST; be treated as separate
665   integers and that each &MAY; be incremented higher than a single digit.
666   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
667   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
668   &MUST-NOT; be sent.
669</t>
670<t>
671   An application that sends a request or response message that includes
672   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
673   with this specification. Applications that are at least conditionally
674   compliant with this specification &SHOULD; use an HTTP-Version of
675   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
676   not compatible with HTTP/1.0. For more details on when to send
677   specific HTTP-Version values, see <xref target="RFC2145"/>.
678</t>
679<t>
680   The HTTP version of an application is the highest HTTP version for
681   which the application is at least conditionally compliant.
682</t>
683<t>
684   Proxy and gateway applications need to be careful when forwarding
685   messages in protocol versions different from that of the application.
686   Since the protocol version indicates the protocol capability of the
687   sender, a proxy/gateway &MUST-NOT; send a message with a version
688   indicator which is greater than its actual version. If a higher
689   version request is received, the proxy/gateway &MUST; either downgrade
690   the request version, or respond with an error, or switch to tunnel
691   behavior.
692</t>
693<t>
694   Due to interoperability problems with HTTP/1.0 proxies discovered
695   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
696   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
697   they support. The proxy/gateway's response to that request &MUST; be in
698   the same major version as the request.
699</t>
700<t>
701  <list>
702    <t>
703      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
704      of header fields required or forbidden by the versions involved.
705    </t>
706  </list>
707</t>
708</section>
709
710<section title="Uniform Resource Identifiers" anchor="uri">
711<t>
712   URIs have been known by many names: WWW addresses, Universal Document
713   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
714   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
715   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
716   simply formatted strings which identify--via name, location, or any
717   other characteristic--a resource.
718</t>
719
720<section title="General Syntax" anchor="general.syntax">
721  <x:anchor-alias value="absoluteURI"/>
722  <x:anchor-alias value="authority"/>
723  <x:anchor-alias value="fragment"/>
724  <x:anchor-alias value="path-absolute"/>
725  <x:anchor-alias value="port"/>
726  <x:anchor-alias value="query"/>
727  <x:anchor-alias value="relativeURI"/>
728  <x:anchor-alias value="uri-host"/>
729<t>
730   URIs in HTTP can be represented in absolute form or relative to some
731   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
732   forms are differentiated by the fact that absolute URIs always begin
733   with a scheme name followed by a colon. For definitive information on
734   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
735   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
736   and <xref target="RFC1808"/>). This specification adopts the
737   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
738   "host", "abs_path", "query", and "authority" from that specification:
739</t>
740<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"/>
741  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
742  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
743  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
744  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
745  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
746  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
747  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
748  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
749</artwork></figure>
750<t>
751   HTTP does not place any a priori limit on the length of
752   a URI. Servers &MUST; be able to handle the URI of any resource they
753   serve, and &SHOULD; be able to handle URIs of unbounded length if they
754   provide GET-based forms that could generate such URIs. A server
755   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
756   than the server can handle (see &status-414;).
757</t>
758<t>
759  <list>
760    <t>
761      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
762      above 255 bytes, because some older client or proxy
763      implementations might not properly support these lengths.
764    </t>
765  </list>
766</t>
767</section>
768
769<section title="http URL" anchor="http.url">
770  <x:anchor-alias value="http-URL"/>
771  <iref item="http URI scheme" primary="true"/>
772  <iref item="URI scheme" subitem="http" primary="true"/>
773<t>
774   The "http" scheme is used to locate network resources via the HTTP
775   protocol. This section defines the scheme-specific syntax and
776   semantics for http URLs.
777</t>
778<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
779  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
780             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
781</artwork></figure>
782<t>
783   If the port is empty or not given, port 80 is assumed. The semantics
784   are that the identified resource is located at the server listening
785   for TCP connections on that port of that host, and the Request-URI
786   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
787   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
788   the path-absolute is not present in the URL, it &MUST; be given as "/" when
789   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
790   receives a host name which is not a fully qualified domain name, it
791   &MAY; add its domain to the host name it received. If a proxy receives
792   a fully qualified domain name, the proxy &MUST-NOT; change the host
793   name.
794</t>
795<t><list><t>
796  <iref item="https URI scheme"/>
797  <iref item="URI scheme" subitem="https"/>
798  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
799</t></list></t>
800</section>
801
802<section title="URI Comparison" anchor="uri.comparison">
803<t>
804   When comparing two URIs to decide if they match or not, a client
805   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
806   URIs, with these exceptions:
807  <list style="symbols">
808    <t>A port that is empty or not given is equivalent to the default
809        port for that URI-reference;</t>
810    <t>Comparisons of host names &MUST; be case-insensitive;</t>
811    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
812    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
813  </list>
814</t>
815<t>
816   Characters other than those in the "reserved" set (see
817   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
818   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
819</t>
820<t>
821   For example, the following three URIs are equivalent:
822</t>
823<figure><artwork type="example">
824   http://example.com:80/~smith/home.html
825   http://EXAMPLE.com/%7Esmith/home.html
826   http://EXAMPLE.com:/%7esmith/home.html
827</artwork></figure>
828</section>
829</section>
830
831<section title="Date/Time Formats" anchor="date.time.formats">
832<section title="Full Date" anchor="full.date">
833  <x:anchor-alias value="HTTP-date"/>
834  <x:anchor-alias value="obsolete-date"/>
835  <x:anchor-alias value="rfc1123-date"/>
836  <x:anchor-alias value="rfc850-date"/>
837  <x:anchor-alias value="asctime-date"/>
838  <x:anchor-alias value="date1"/>
839  <x:anchor-alias value="date2"/>
840  <x:anchor-alias value="date3"/>
841  <x:anchor-alias value="rfc1123-date"/>
842  <x:anchor-alias value="time"/>
843  <x:anchor-alias value="wkday"/>
844  <x:anchor-alias value="weekday"/>
845  <x:anchor-alias value="month"/>
846<t>
847   HTTP applications have historically allowed three different formats
848   for the representation of date/time stamps:
849</t>
850<figure><artwork type="example">
851   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
852   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
853   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
854</artwork></figure>
855<t>
856   The first format is preferred as an Internet standard and represents
857   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
858   <xref target="RFC822"/>). The other formats are described here only for
859   compatibility with obsolete implementations.
860   HTTP/1.1 clients and servers that parse the date value &MUST; accept
861   all three formats (for compatibility with HTTP/1.0), though they &MUST;
862   only generate the RFC 1123 format for representing HTTP-date values
863   in header fields. See <xref target="tolerant.applications"/> for further information.
864</t>
865<t><list><t>
866      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
867      accepting date values that may have been sent by non-HTTP
868      applications, as is sometimes the case when retrieving or posting
869      messages via proxies/gateways to SMTP or NNTP.
870</t></list></t>
871<t>
872   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
873   (GMT), without exception. For the purposes of HTTP, GMT is exactly
874   equal to UTC (Coordinated Universal Time). This is indicated in the
875   first two formats by the inclusion of "GMT" as the three-letter
876   abbreviation for time zone, and &MUST; be assumed when reading the
877   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
878   additional LWS beyond that specifically included as SP in the
879   grammar.
880</t>
881<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"/>
882  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
883  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
884  <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
885  <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
886  <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>
887  <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>
888                 ; day month year (e.g., 02 Jun 1982)
889  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
890                 ; day-month-year (e.g., 02-Jun-82)
891  <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> ))
892                 ; month day (e.g., Jun  2)
893  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
894                 ; 00:00:00 - 23:59:59
895  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
896               / s-Thu / s-Fri / s-Sat / s-Sun
897  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
898               / l-Thu / l-Fri / l-Sat / l-Sun
899  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
900               / s-May / s-Jun / s-Jul / s-Aug
901               / s-Sep / s-Oct / s-Nov / s-Dec
902               
903  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
904
905  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
906  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
907  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
908  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
909  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
910  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
911  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
912
913  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
914  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
915  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
916  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
917  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
918  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
919  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
920
921  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
922  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
923  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
924  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
925  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
926  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
927  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
928  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
929  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
930  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
931  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
932  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
933</artwork></figure>
934<t>
935      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
936      to their usage within the protocol stream. Clients and servers are
937      not required to use these formats for user presentation, request
938      logging, etc.
939</t>
940</section>
941</section>
942
943<section title="Transfer Codings" anchor="transfer.codings">
944  <x:anchor-alias value="parameter"/>
945  <x:anchor-alias value="transfer-coding"/>
946  <x:anchor-alias value="transfer-extension"/>
947<t>
948   Transfer-coding values are used to indicate an encoding
949   transformation that has been, can be, or may need to be applied to an
950   entity-body in order to ensure "safe transport" through the network.
951   This differs from a content coding in that the transfer-coding is a
952   property of the message, not of the original entity.
953</t>
954<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
955  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
956  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
957</artwork></figure>
958<t anchor="rule.parameter">
959  <x:anchor-alias value="attribute"/>
960  <x:anchor-alias value="parameter"/>
961  <x:anchor-alias value="value"/>
962   Parameters are in  the form of attribute/value pairs.
963</t>
964<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"/>
965  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
966  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
967  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
968</artwork></figure>
969<t>
970   All transfer-coding values are case-insensitive. HTTP/1.1 uses
971   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
972   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
973</t>
974<t>
975   Whenever a transfer-coding is applied to a message-body, the set of
976   transfer-codings &MUST; include "chunked", unless the message indicates it
977   is terminated by closing the connection. When the "chunked" transfer-coding
978   is used, it &MUST; be the last transfer-coding applied to the
979   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
980   than once to a message-body. These rules allow the recipient to
981   determine the transfer-length of the message (<xref target="message.length"/>).
982</t>
983<t>
984   Transfer-codings are analogous to the Content-Transfer-Encoding
985   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
986   binary data over a 7-bit transport service. However, safe transport
987   has a different focus for an 8bit-clean transfer protocol. In HTTP,
988   the only unsafe characteristic of message-bodies is the difficulty in
989   determining the exact body length (<xref target="message.length"/>), or the desire to
990   encrypt data over a shared transport.
991</t>
992<t>
993   The Internet Assigned Numbers Authority (IANA) acts as a registry for
994   transfer-coding value tokens. Initially, the registry contains the
995   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
996   "gzip", "compress", and "deflate" (&content-codings;).
997</t>
998<t>
999   New transfer-coding value tokens &SHOULD; be registered in the same way
1000   as new content-coding value tokens (&content-codings;).
1001</t>
1002<t>
1003   A server which receives an entity-body with a transfer-coding it does
1004   not understand &SHOULD; return 501 (Not Implemented), and close the
1005   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1006   client.
1007</t>
1008
1009<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1010  <x:anchor-alias value="chunk"/>
1011  <x:anchor-alias value="Chunked-Body"/>
1012  <x:anchor-alias value="chunk-data"/>
1013  <x:anchor-alias value="chunk-extension"/>
1014  <x:anchor-alias value="chunk-ext-name"/>
1015  <x:anchor-alias value="chunk-ext-val"/>
1016  <x:anchor-alias value="chunk-size"/>
1017  <x:anchor-alias value="last-chunk"/>
1018  <x:anchor-alias value="trailer-part"/>
1019<t>
1020   The chunked encoding modifies the body of a message in order to
1021   transfer it as a series of chunks, each with its own size indicator,
1022   followed by an &OPTIONAL; trailer containing entity-header fields. This
1023   allows dynamically produced content to be transferred along with the
1024   information necessary for the recipient to verify that it has
1025   received the full message.
1026</t>
1027<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"/>
1028  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1029                   <x:ref>last-chunk</x:ref>
1030                   <x:ref>trailer-part</x:ref>
1031                   <x:ref>CRLF</x:ref>
1032 
1033  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1034                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1035  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1036  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1037 
1038  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1039  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1040  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1041  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1042  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1043</artwork></figure>
1044<t>
1045   The chunk-size field is a string of hex digits indicating the size of
1046   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1047   zero, followed by the trailer, which is terminated by an empty line.
1048</t>
1049<t>
1050   The trailer allows the sender to include additional HTTP header
1051   fields at the end of the message. The Trailer header field can be
1052   used to indicate which header fields are included in a trailer (see
1053   <xref target="header.trailer"/>).
1054</t>
1055<t>
1056   A server using chunked transfer-coding in a response &MUST-NOT; use the
1057   trailer for any header fields unless at least one of the following is
1058   true:
1059  <list style="numbers">
1060    <t>the request included a TE header field that indicates "trailers" is
1061     acceptable in the transfer-coding of the  response, as described in
1062     <xref target="header.te"/>; or,</t>
1063
1064    <t>the server is the origin server for the response, the trailer
1065     fields consist entirely of optional metadata, and the recipient
1066     could use the message (in a manner acceptable to the origin server)
1067     without receiving this metadata.  In other words, the origin server
1068     is willing to accept the possibility that the trailer fields might
1069     be silently discarded along the path to the client.</t>
1070  </list>
1071</t>
1072<t>
1073   This requirement prevents an interoperability failure when the
1074   message is being received by an HTTP/1.1 (or later) proxy and
1075   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1076   compliance with the protocol would have necessitated a possibly
1077   infinite buffer on the proxy.
1078</t>
1079<t>
1080   A process for decoding the "chunked" transfer-coding
1081   can be represented in pseudo-code as:
1082</t>
1083<figure><artwork type="code">
1084    length := 0
1085    read chunk-size, chunk-extension (if any) and CRLF
1086    while (chunk-size &gt; 0) {
1087       read chunk-data and CRLF
1088       append chunk-data to entity-body
1089       length := length + chunk-size
1090       read chunk-size and CRLF
1091    }
1092    read entity-header
1093    while (entity-header not empty) {
1094       append entity-header to existing header fields
1095       read entity-header
1096    }
1097    Content-Length := length
1098    Remove "chunked" from Transfer-Encoding
1099</artwork></figure>
1100<t>
1101   All HTTP/1.1 applications &MUST; be able to receive and decode the
1102   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1103   they do not understand.
1104</t>
1105</section>
1106</section>
1107
1108<section title="Product Tokens" anchor="product.tokens">
1109  <x:anchor-alias value="product"/>
1110  <x:anchor-alias value="product-version"/>
1111<t>
1112   Product tokens are used to allow communicating applications to
1113   identify themselves by software name and version. Most fields using
1114   product tokens also allow sub-products which form a significant part
1115   of the application to be listed, separated by white space. By
1116   convention, the products are listed in order of their significance
1117   for identifying the application.
1118</t>
1119<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1120  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1121  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1122</artwork></figure>
1123<t>
1124   Examples:
1125</t>
1126<figure><artwork type="example">
1127    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1128    Server: Apache/0.8.4
1129</artwork></figure>
1130<t>
1131   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1132   used for advertising or other non-essential information. Although any
1133   token character &MAY; appear in a product-version, this token &SHOULD;
1134   only be used for a version identifier (i.e., successive versions of
1135   the same product &SHOULD; only differ in the product-version portion of
1136   the product value).
1137</t>
1138</section>
1139
1140</section>
1141
1142<section title="HTTP Message" anchor="http.message">
1143
1144<section title="Message Types" anchor="message.types">
1145  <x:anchor-alias value="generic-message"/>
1146  <x:anchor-alias value="HTTP-message"/>
1147  <x:anchor-alias value="start-line"/>
1148<t>
1149   HTTP messages consist of requests from client to server and responses
1150   from server to client.
1151</t>
1152<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1153  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1154</artwork></figure>
1155<t>
1156   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1157   message format of <xref target="RFC5322"/> for transferring entities (the payload
1158   of the message). Both types of message consist of a start-line, zero
1159   or more header fields (also known as "headers"), an empty line (i.e.,
1160   a line with nothing preceding the CRLF) indicating the end of the
1161   header fields, and possibly a message-body.
1162</t>
1163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1164  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1165                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1166                    <x:ref>CRLF</x:ref>
1167                    [ <x:ref>message-body</x:ref> ]
1168  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1169</artwork></figure>
1170<t>
1171   In the interest of robustness, servers &SHOULD; ignore any empty
1172   line(s) received where a Request-Line is expected. In other words, if
1173   the server is reading the protocol stream at the beginning of a
1174   message and receives a CRLF first, it should ignore the CRLF.
1175</t>
1176<t>
1177   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1178   after a POST request. To restate what is explicitly forbidden by the
1179   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1180   extra CRLF.
1181</t>
1182</section>
1183
1184<section title="Message Headers" anchor="message.headers">
1185  <x:anchor-alias value="field-content"/>
1186  <x:anchor-alias value="field-name"/>
1187  <x:anchor-alias value="field-value"/>
1188  <x:anchor-alias value="message-header"/>
1189<t>
1190   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1191   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1192   entity-header (&entity-header-fields;) fields, follow the same generic format as
1193   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1194   of a name followed by a colon (":") and the field value. Field names
1195   are case-insensitive. The field value &MAY; be preceded by any amount
1196   of LWS, though a single SP is preferred. Header fields can be
1197   extended over multiple lines by preceding each extra line with at
1198   least one SP or HTAB. Applications ought to follow "common form", where
1199   one is known or indicated, when generating HTTP constructs, since
1200   there might exist some implementations that fail to accept anything
1201   beyond the common forms.
1202</t>
1203<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"/>
1204  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1205  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1206  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1207  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1208                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1209                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1210                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1211</artwork></figure>
1212<t>
1213   The field-content does not include any leading or trailing LWS:
1214   linear white space occurring before the first non-whitespace
1215   character of the field-value or after the last non-whitespace
1216   character of the field-value. Such leading or trailing LWS &MAY; be
1217   removed without changing the semantics of the field value. Any LWS
1218   that occurs between field-content &MAY; be replaced with a single SP
1219   before interpreting the field value or forwarding the message
1220   downstream.
1221</t>
1222<t>
1223   The order in which header fields with differing field names are
1224   received is not significant. However, it is "good practice" to send
1225   general-header fields first, followed by request-header or response-header
1226   fields, and ending with the entity-header fields.
1227</t>
1228<t>
1229   Multiple message-header fields with the same field-name &MAY; be
1230   present in a message if and only if the entire field-value for that
1231   header field is defined as a comma-separated list [i.e., #(values)].
1232   It &MUST; be possible to combine the multiple header fields into one
1233   "field-name: field-value" pair, without changing the semantics of the
1234   message, by appending each subsequent field-value to the first, each
1235   separated by a comma. The order in which header fields with the same
1236   field-name are received is therefore significant to the
1237   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1238   change the order of these field values when a message is forwarded.
1239</t>
1240<t>
1241  <list><t>
1242   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1243   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1244   can occur multiple times, but does not use the list syntax, and thus cannot
1245   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1246   for details.) Also note that the Set-Cookie2 header specified in
1247   <xref target="RFC2965"/> does not share this problem.
1248  </t></list>
1249</t>
1250 
1251</section>
1252
1253<section title="Message Body" anchor="message.body">
1254  <x:anchor-alias value="message-body"/>
1255<t>
1256   The message-body (if any) of an HTTP message is used to carry the
1257   entity-body associated with the request or response. The message-body
1258   differs from the entity-body only when a transfer-coding has been
1259   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1260</t>
1261<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1262  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1263               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1264</artwork></figure>
1265<t>
1266   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1267   applied by an application to ensure safe and proper transfer of the
1268   message. Transfer-Encoding is a property of the message, not of the
1269   entity, and thus &MAY; be added or removed by any application along the
1270   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1271   when certain transfer-codings may be used.)
1272</t>
1273<t>
1274   The rules for when a message-body is allowed in a message differ for
1275   requests and responses.
1276</t>
1277<t>
1278   The presence of a message-body in a request is signaled by the
1279   inclusion of a Content-Length or Transfer-Encoding header field in
1280   the request's message-headers. A message-body &MUST-NOT; be included in
1281   a request if the specification of the request method (&method;)
1282   explicitly disallows an entity-body in requests.
1283   When a request message contains both a message-body of non-zero
1284   length and a method that does not define any semantics for that
1285   request message-body, then an origin server &SHOULD; either ignore
1286   the message-body or respond with an appropriate error message
1287   (e.g., 413).  A proxy or gateway, when presented the same request,
1288   &SHOULD; either forward the request inbound with the message-body or
1289   ignore the message-body when determining a response.
1290</t>
1291<t>
1292   For response messages, whether or not a message-body is included with
1293   a message is dependent on both the request method and the response
1294   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1295   &MUST-NOT; include a message-body, even though the presence of entity-header
1296   fields might lead one to believe they do. All 1xx
1297   (informational), 204 (No Content), and 304 (Not Modified) responses
1298   &MUST-NOT; include a message-body. All other responses do include a
1299   message-body, although it &MAY; be of zero length.
1300</t>
1301</section>
1302
1303<section title="Message Length" anchor="message.length">
1304<t>
1305   The transfer-length of a message is the length of the message-body as
1306   it appears in the message; that is, after any transfer-codings have
1307   been applied. When a message-body is included with a message, the
1308   transfer-length of that body is determined by one of the following
1309   (in order of precedence):
1310</t>
1311<t>
1312  <list style="numbers">
1313    <x:lt><t>
1314     Any response message which "&MUST-NOT;" include a message-body (such
1315     as the 1xx, 204, and 304 responses and any response to a HEAD
1316     request) is always terminated by the first empty line after the
1317     header fields, regardless of the entity-header fields present in
1318     the message.
1319    </t></x:lt>
1320    <x:lt><t>
1321     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1322     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1323     is used, the transfer-length is defined by the use of this transfer-coding.
1324     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1325     is not present, the transfer-length is defined by the sender closing the connection.
1326    </t></x:lt>
1327    <x:lt><t>
1328     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1329     decimal value in OCTETs represents both the entity-length and the
1330     transfer-length. The Content-Length header field &MUST-NOT; be sent
1331     if these two lengths are different (i.e., if a Transfer-Encoding
1332     header field is present). If a message is received with both a
1333     Transfer-Encoding header field and a Content-Length header field,
1334     the latter &MUST; be ignored.
1335    </t></x:lt>
1336    <x:lt><t>
1337     If the message uses the media type "multipart/byteranges", and the
1338     transfer-length is not otherwise specified, then this self-delimiting
1339     media type defines the transfer-length. This media type
1340     &MUST-NOT; be used unless the sender knows that the recipient can parse
1341     it; the presence in a request of a Range header with multiple byte-range
1342     specifiers from a 1.1 client implies that the client can parse
1343     multipart/byteranges responses.
1344    <list style="empty"><t>
1345       A range header might be forwarded by a 1.0 proxy that does not
1346       understand multipart/byteranges; in this case the server &MUST;
1347       delimit the message using methods defined in items 1, 3 or 5 of
1348       this section.
1349    </t></list>
1350    </t></x:lt>
1351    <x:lt><t>
1352     By the server closing the connection. (Closing the connection
1353     cannot be used to indicate the end of a request body, since that
1354     would leave no possibility for the server to send back a response.)
1355    </t></x:lt>
1356  </list>
1357</t>
1358<t>
1359   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1360   containing a message-body &MUST; include a valid Content-Length header
1361   field unless the server is known to be HTTP/1.1 compliant. If a
1362   request contains a message-body and a Content-Length is not given,
1363   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1364   determine the length of the message, or with 411 (Length Required) if
1365   it wishes to insist on receiving a valid Content-Length.
1366</t>
1367<t>
1368   All HTTP/1.1 applications that receive entities &MUST; accept the
1369   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1370   to be used for messages when the message length cannot be determined
1371   in advance.
1372</t>
1373<t>
1374   Messages &MUST-NOT; include both a Content-Length header field and a
1375   transfer-coding. If the message does include a
1376   transfer-coding, the Content-Length &MUST; be ignored.
1377</t>
1378<t>
1379   When a Content-Length is given in a message where a message-body is
1380   allowed, its field value &MUST; exactly match the number of OCTETs in
1381   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1382   invalid length is received and detected.
1383</t>
1384</section>
1385
1386<section title="General Header Fields" anchor="general.header.fields">
1387  <x:anchor-alias value="general-header"/>
1388<t>
1389   There are a few header fields which have general applicability for
1390   both request and response messages, but which do not apply to the
1391   entity being transferred. These header fields apply only to the
1392   message being transmitted.
1393</t>
1394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1395  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1396                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1397                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1398                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1399                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1400                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1401                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1402                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1403                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1404</artwork></figure>
1405<t>
1406   General-header field names can be extended reliably only in
1407   combination with a change in the protocol version. However, new or
1408   experimental header fields may be given the semantics of general
1409   header fields if all parties in the communication recognize them to
1410   be general-header fields. Unrecognized header fields are treated as
1411   entity-header fields.
1412</t>
1413</section>
1414</section>
1415
1416<section title="Request" anchor="request">
1417  <x:anchor-alias value="Request"/>
1418<t>
1419   A request message from a client to a server includes, within the
1420   first line of that message, the method to be applied to the resource,
1421   the identifier of the resource, and the protocol version in use.
1422</t>
1423<!--                 Host                      ; should be moved here eventually -->
1424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1425  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1426                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1427                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1428                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1429                  <x:ref>CRLF</x:ref>
1430                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1431</artwork></figure>
1432
1433<section title="Request-Line" anchor="request-line">
1434  <x:anchor-alias value="Request-Line"/>
1435<t>
1436   The Request-Line begins with a method token, followed by the
1437   Request-URI and the protocol version, and ending with CRLF. The
1438   elements are separated by SP characters. No CR or LF is allowed
1439   except in the final CRLF sequence.
1440</t>
1441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1442  <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>
1443</artwork></figure>
1444
1445<section title="Method" anchor="method">
1446  <x:anchor-alias value="Method"/>
1447<t>
1448   The Method  token indicates the method to be performed on the
1449   resource identified by the Request-URI. The method is case-sensitive.
1450</t>
1451<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1452  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1453</artwork></figure>
1454</section>
1455
1456<section title="Request-URI" anchor="request-uri">
1457  <x:anchor-alias value="Request-URI"/>
1458<t>
1459   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1460   identifies the resource upon which to apply the request.
1461</t>
1462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1463  <x:ref>Request-URI</x:ref>    = "*"
1464                 / <x:ref>absoluteURI</x:ref>
1465                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1466                 / <x:ref>authority</x:ref>
1467</artwork></figure>
1468<t>
1469   The four options for Request-URI are dependent on the nature of the
1470   request. The asterisk "*" means that the request does not apply to a
1471   particular resource, but to the server itself, and is only allowed
1472   when the method used does not necessarily apply to a resource. One
1473   example would be
1474</t>
1475<figure><artwork type="example">
1476    OPTIONS * HTTP/1.1
1477</artwork></figure>
1478<t>
1479   The absoluteURI form is &REQUIRED; when the request is being made to a
1480   proxy. The proxy is requested to forward the request or service it
1481   from a valid cache, and return the response. Note that the proxy &MAY;
1482   forward the request on to another proxy or directly to the server
1483   specified by the absoluteURI. In order to avoid request loops, a
1484   proxy &MUST; be able to recognize all of its server names, including
1485   any aliases, local variations, and the numeric IP address. An example
1486   Request-Line would be:
1487</t>
1488<figure><artwork type="example">
1489    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1490</artwork></figure>
1491<t>
1492   To allow for transition to absoluteURIs in all requests in future
1493   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1494   form in requests, even though HTTP/1.1 clients will only generate
1495   them in requests to proxies.
1496</t>
1497<t>
1498   The authority form is only used by the CONNECT method (&CONNECT;).
1499</t>
1500<t>
1501   The most common form of Request-URI is that used to identify a
1502   resource on an origin server or gateway. In this case the absolute
1503   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1504   the Request-URI, and the network location of the URI (authority) &MUST;
1505   be transmitted in a Host header field. For example, a client wishing
1506   to retrieve the resource above directly from the origin server would
1507   create a TCP connection to port 80 of the host "www.example.org" and send
1508   the lines:
1509</t>
1510<figure><artwork type="example">
1511    GET /pub/WWW/TheProject.html HTTP/1.1
1512    Host: www.example.org
1513</artwork></figure>
1514<t>
1515   followed by the remainder of the Request. Note that the absolute path
1516   cannot be empty; if none is present in the original URI, it &MUST; be
1517   given as "/" (the server root).
1518</t>
1519<t>
1520   The Request-URI is transmitted in the format specified in
1521   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1522   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1523   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1524   &MUST; decode the Request-URI in order to
1525   properly interpret the request. Servers &SHOULD; respond to invalid
1526   Request-URIs with an appropriate status code.
1527</t>
1528<t>
1529   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1530   received Request-URI when forwarding it to the next inbound server,
1531   except as noted above to replace a null path-absolute with "/".
1532</t>
1533<t>
1534  <list><t>
1535      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1536      meaning of the request when the origin server is improperly using
1537      a non-reserved URI character for a reserved purpose.  Implementors
1538      should be aware that some pre-HTTP/1.1 proxies have been known to
1539      rewrite the Request-URI.
1540  </t></list>
1541</t>
1542</section>
1543</section>
1544
1545<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1546<t>
1547   The exact resource identified by an Internet request is determined by
1548   examining both the Request-URI and the Host header field.
1549</t>
1550<t>
1551   An origin server that does not allow resources to differ by the
1552   requested host &MAY; ignore the Host header field value when
1553   determining the resource identified by an HTTP/1.1 request. (But see
1554   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1555   for other requirements on Host support in HTTP/1.1.)
1556</t>
1557<t>
1558   An origin server that does differentiate resources based on the host
1559   requested (sometimes referred to as virtual hosts or vanity host
1560   names) &MUST; use the following rules for determining the requested
1561   resource on an HTTP/1.1 request:
1562  <list style="numbers">
1563    <t>If Request-URI is an absoluteURI, the host is part of the
1564     Request-URI. Any Host header field value in the request &MUST; be
1565     ignored.</t>
1566    <t>If the Request-URI is not an absoluteURI, and the request includes
1567     a Host header field, the host is determined by the Host header
1568     field value.</t>
1569    <t>If the host as determined by rule 1 or 2 is not a valid host on
1570     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1571  </list>
1572</t>
1573<t>
1574   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1575   attempt to use heuristics (e.g., examination of the URI path for
1576   something unique to a particular host) in order to determine what
1577   exact resource is being requested.
1578</t>
1579</section>
1580
1581</section>
1582
1583
1584<section title="Response" anchor="response">
1585  <x:anchor-alias value="Response"/>
1586<t>
1587   After receiving and interpreting a request message, a server responds
1588   with an HTTP response message.
1589</t>
1590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1591  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1592                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1593                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1594                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1595                  <x:ref>CRLF</x:ref>
1596                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1597</artwork></figure>
1598
1599<section title="Status-Line" anchor="status-line">
1600  <x:anchor-alias value="Status-Line"/>
1601<t>
1602   The first line of a Response message is the Status-Line, consisting
1603   of the protocol version followed by a numeric status code and its
1604   associated textual phrase, with each element separated by SP
1605   characters. No CR or LF is allowed except in the final CRLF sequence.
1606</t>
1607<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1608  <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>
1609</artwork></figure>
1610
1611<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1612  <x:anchor-alias value="Reason-Phrase"/>
1613  <x:anchor-alias value="Status-Code"/>
1614<t>
1615   The Status-Code element is a 3-digit integer result code of the
1616   attempt to understand and satisfy the request. These codes are fully
1617   defined in &status-codes;.  The Reason Phrase exists for the sole
1618   purpose of providing a textual description associated with the numeric
1619   status code, out of deference to earlier Internet application protocols
1620   that were more frequently used with interactive text clients.
1621   A client &SHOULD; ignore the content of the Reason Phrase.
1622</t>
1623<t>
1624   The first digit of the Status-Code defines the class of response. The
1625   last two digits do not have any categorization role. There are 5
1626   values for the first digit:
1627  <list style="symbols">
1628    <t>
1629      1xx: Informational - Request received, continuing process
1630    </t>
1631    <t>
1632      2xx: Success - The action was successfully received,
1633        understood, and accepted
1634    </t>
1635    <t>
1636      3xx: Redirection - Further action must be taken in order to
1637        complete the request
1638    </t>
1639    <t>
1640      4xx: Client Error - The request contains bad syntax or cannot
1641        be fulfilled
1642    </t>
1643    <t>
1644      5xx: Server Error - The server failed to fulfill an apparently
1645        valid request
1646    </t>
1647  </list>
1648</t>
1649<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"/>
1650  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1651  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1652</artwork></figure>
1653</section>
1654</section>
1655
1656</section>
1657
1658
1659<section title="Connections" anchor="connections">
1660
1661<section title="Persistent Connections" anchor="persistent.connections">
1662
1663<section title="Purpose" anchor="persistent.purpose">
1664<t>
1665   Prior to persistent connections, a separate TCP connection was
1666   established to fetch each URL, increasing the load on HTTP servers
1667   and causing congestion on the Internet. The use of inline images and
1668   other associated data often require a client to make multiple
1669   requests of the same server in a short amount of time. Analysis of
1670   these performance problems and results from a prototype
1671   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1672   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1673   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1674   T/TCP <xref target="Tou1998"/>.
1675</t>
1676<t>
1677   Persistent HTTP connections have a number of advantages:
1678  <list style="symbols">
1679      <t>
1680        By opening and closing fewer TCP connections, CPU time is saved
1681        in routers and hosts (clients, servers, proxies, gateways,
1682        tunnels, or caches), and memory used for TCP protocol control
1683        blocks can be saved in hosts.
1684      </t>
1685      <t>
1686        HTTP requests and responses can be pipelined on a connection.
1687        Pipelining allows a client to make multiple requests without
1688        waiting for each response, allowing a single TCP connection to
1689        be used much more efficiently, with much lower elapsed time.
1690      </t>
1691      <t>
1692        Network congestion is reduced by reducing the number of packets
1693        caused by TCP opens, and by allowing TCP sufficient time to
1694        determine the congestion state of the network.
1695      </t>
1696      <t>
1697        Latency on subsequent requests is reduced since there is no time
1698        spent in TCP's connection opening handshake.
1699      </t>
1700      <t>
1701        HTTP can evolve more gracefully, since errors can be reported
1702        without the penalty of closing the TCP connection. Clients using
1703        future versions of HTTP might optimistically try a new feature,
1704        but if communicating with an older server, retry with old
1705        semantics after an error is reported.
1706      </t>
1707    </list>
1708</t>
1709<t>
1710   HTTP implementations &SHOULD; implement persistent connections.
1711</t>
1712</section>
1713
1714<section title="Overall Operation" anchor="persistent.overall">
1715<t>
1716   A significant difference between HTTP/1.1 and earlier versions of
1717   HTTP is that persistent connections are the default behavior of any
1718   HTTP connection. That is, unless otherwise indicated, the client
1719   &SHOULD; assume that the server will maintain a persistent connection,
1720   even after error responses from the server.
1721</t>
1722<t>
1723   Persistent connections provide a mechanism by which a client and a
1724   server can signal the close of a TCP connection. This signaling takes
1725   place using the Connection header field (<xref target="header.connection"/>). Once a close
1726   has been signaled, the client &MUST-NOT; send any more requests on that
1727   connection.
1728</t>
1729
1730<section title="Negotiation" anchor="persistent.negotiation">
1731<t>
1732   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1733   maintain a persistent connection unless a Connection header including
1734   the connection-token "close" was sent in the request. If the server
1735   chooses to close the connection immediately after sending the
1736   response, it &SHOULD; send a Connection header including the
1737   connection-token close.
1738</t>
1739<t>
1740   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1741   decide to keep it open based on whether the response from a server
1742   contains a Connection header with the connection-token close. In case
1743   the client does not want to maintain a connection for more than that
1744   request, it &SHOULD; send a Connection header including the
1745   connection-token close.
1746</t>
1747<t>
1748   If either the client or the server sends the close token in the
1749   Connection header, that request becomes the last one for the
1750   connection.
1751</t>
1752<t>
1753   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1754   maintained for HTTP versions less than 1.1 unless it is explicitly
1755   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1756   compatibility with HTTP/1.0 clients.
1757</t>
1758<t>
1759   In order to remain persistent, all messages on the connection &MUST;
1760   have a self-defined message length (i.e., one not defined by closure
1761   of the connection), as described in <xref target="message.length"/>.
1762</t>
1763</section>
1764
1765<section title="Pipelining" anchor="pipelining">
1766<t>
1767   A client that supports persistent connections &MAY; "pipeline" its
1768   requests (i.e., send multiple requests without waiting for each
1769   response). A server &MUST; send its responses to those requests in the
1770   same order that the requests were received.
1771</t>
1772<t>
1773   Clients which assume persistent connections and pipeline immediately
1774   after connection establishment &SHOULD; be prepared to retry their
1775   connection if the first pipelined attempt fails. If a client does
1776   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1777   persistent. Clients &MUST; also be prepared to resend their requests if
1778   the server closes the connection before sending all of the
1779   corresponding responses.
1780</t>
1781<t>
1782   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1783   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1784   premature termination of the transport connection could lead to
1785   indeterminate results. A client wishing to send a non-idempotent
1786   request &SHOULD; wait to send that request until it has received the
1787   response status for the previous request.
1788</t>
1789</section>
1790</section>
1791
1792<section title="Proxy Servers" anchor="persistent.proxy">
1793<t>
1794   It is especially important that proxies correctly implement the
1795   properties of the Connection header field as specified in <xref target="header.connection"/>.
1796</t>
1797<t>
1798   The proxy server &MUST; signal persistent connections separately with
1799   its clients and the origin servers (or other proxy servers) that it
1800   connects to. Each persistent connection applies to only one transport
1801   link.
1802</t>
1803<t>
1804   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1805   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1806   discussion of the problems with the Keep-Alive header implemented by
1807   many HTTP/1.0 clients).
1808</t>
1809</section>
1810
1811<section title="Practical Considerations" anchor="persistent.practical">
1812<t>
1813   Servers will usually have some time-out value beyond which they will
1814   no longer maintain an inactive connection. Proxy servers might make
1815   this a higher value since it is likely that the client will be making
1816   more connections through the same server. The use of persistent
1817   connections places no requirements on the length (or existence) of
1818   this time-out for either the client or the server.
1819</t>
1820<t>
1821   When a client or server wishes to time-out it &SHOULD; issue a graceful
1822   close on the transport connection. Clients and servers &SHOULD; both
1823   constantly watch for the other side of the transport close, and
1824   respond to it as appropriate. If a client or server does not detect
1825   the other side's close promptly it could cause unnecessary resource
1826   drain on the network.
1827</t>
1828<t>
1829   A client, server, or proxy &MAY; close the transport connection at any
1830   time. For example, a client might have started to send a new request
1831   at the same time that the server has decided to close the "idle"
1832   connection. From the server's point of view, the connection is being
1833   closed while it was idle, but from the client's point of view, a
1834   request is in progress.
1835</t>
1836<t>
1837   This means that clients, servers, and proxies &MUST; be able to recover
1838   from asynchronous close events. Client software &SHOULD; reopen the
1839   transport connection and retransmit the aborted sequence of requests
1840   without user interaction so long as the request sequence is
1841   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1842   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1843   human operator the choice of retrying the request(s). Confirmation by
1844   user-agent software with semantic understanding of the application
1845   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1846   be repeated if the second sequence of requests fails.
1847</t>
1848<t>
1849   Servers &SHOULD; always respond to at least one request per connection,
1850   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1851   middle of transmitting a response, unless a network or client failure
1852   is suspected.
1853</t>
1854<t>
1855   Clients that use persistent connections &SHOULD; limit the number of
1856   simultaneous connections that they maintain to a given server. A
1857   single-user client &SHOULD-NOT; maintain more than 2 connections with
1858   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1859   another server or proxy, where N is the number of simultaneously
1860   active users. These guidelines are intended to improve HTTP response
1861   times and avoid congestion.
1862</t>
1863</section>
1864</section>
1865
1866<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1867
1868<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1869<t>
1870   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1871   flow control mechanisms to resolve temporary overloads, rather than
1872   terminating connections with the expectation that clients will retry.
1873   The latter technique can exacerbate network congestion.
1874</t>
1875</section>
1876
1877<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1878<t>
1879   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1880   the network connection for an error status while it is transmitting
1881   the request. If the client sees an error status, it &SHOULD;
1882   immediately cease transmitting the body. If the body is being sent
1883   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1884   empty trailer &MAY; be used to prematurely mark the end of the message.
1885   If the body was preceded by a Content-Length header, the client &MUST;
1886   close the connection.
1887</t>
1888</section>
1889
1890<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1891<t>
1892   The purpose of the 100 (Continue) status (see &status-100;) is to
1893   allow a client that is sending a request message with a request body
1894   to determine if the origin server is willing to accept the request
1895   (based on the request headers) before the client sends the request
1896   body. In some cases, it might either be inappropriate or highly
1897   inefficient for the client to send the body if the server will reject
1898   the message without looking at the body.
1899</t>
1900<t>
1901   Requirements for HTTP/1.1 clients:
1902  <list style="symbols">
1903    <t>
1904        If a client will wait for a 100 (Continue) response before
1905        sending the request body, it &MUST; send an Expect request-header
1906        field (&header-expect;) with the "100-continue" expectation.
1907    </t>
1908    <t>
1909        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1910        with the "100-continue" expectation if it does not intend
1911        to send a request body.
1912    </t>
1913  </list>
1914</t>
1915<t>
1916   Because of the presence of older implementations, the protocol allows
1917   ambiguous situations in which a client may send "Expect: 100-continue"
1918   without receiving either a 417 (Expectation Failed) status
1919   or a 100 (Continue) status. Therefore, when a client sends this
1920   header field to an origin server (possibly via a proxy) from which it
1921   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1922   for an indefinite period before sending the request body.
1923</t>
1924<t>
1925   Requirements for HTTP/1.1 origin servers:
1926  <list style="symbols">
1927    <t> Upon receiving a request which includes an Expect request-header
1928        field with the "100-continue" expectation, an origin server &MUST;
1929        either respond with 100 (Continue) status and continue to read
1930        from the input stream, or respond with a final status code. The
1931        origin server &MUST-NOT; wait for the request body before sending
1932        the 100 (Continue) response. If it responds with a final status
1933        code, it &MAY; close the transport connection or it &MAY; continue
1934        to read and discard the rest of the request.  It &MUST-NOT;
1935        perform the requested method if it returns a final status code.
1936    </t>
1937    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1938        the request message does not include an Expect request-header
1939        field with the "100-continue" expectation, and &MUST-NOT; send a
1940        100 (Continue) response if such a request comes from an HTTP/1.0
1941        (or earlier) client. There is an exception to this rule: for
1942        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1943        status in response to an HTTP/1.1 PUT or POST request that does
1944        not include an Expect request-header field with the "100-continue"
1945        expectation. This exception, the purpose of which is
1946        to minimize any client processing delays associated with an
1947        undeclared wait for 100 (Continue) status, applies only to
1948        HTTP/1.1 requests, and not to requests with any other HTTP-version
1949        value.
1950    </t>
1951    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1952        already received some or all of the request body for the
1953        corresponding request.
1954    </t>
1955    <t> An origin server that sends a 100 (Continue) response &MUST;
1956    ultimately send a final status code, once the request body is
1957        received and processed, unless it terminates the transport
1958        connection prematurely.
1959    </t>
1960    <t> If an origin server receives a request that does not include an
1961        Expect request-header field with the "100-continue" expectation,
1962        the request includes a request body, and the server responds
1963        with a final status code before reading the entire request body
1964        from the transport connection, then the server &SHOULD-NOT;  close
1965        the transport connection until it has read the entire request,
1966        or until the client closes the connection. Otherwise, the client
1967        might not reliably receive the response message. However, this
1968        requirement is not be construed as preventing a server from
1969        defending itself against denial-of-service attacks, or from
1970        badly broken client implementations.
1971      </t>
1972    </list>
1973</t>
1974<t>
1975   Requirements for HTTP/1.1 proxies:
1976  <list style="symbols">
1977    <t> If a proxy receives a request that includes an Expect request-header
1978        field with the "100-continue" expectation, and the proxy
1979        either knows that the next-hop server complies with HTTP/1.1 or
1980        higher, or does not know the HTTP version of the next-hop
1981        server, it &MUST; forward the request, including the Expect header
1982        field.
1983    </t>
1984    <t> If the proxy knows that the version of the next-hop server is
1985        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1986        respond with a 417 (Expectation Failed) status.
1987    </t>
1988    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1989        numbers received from recently-referenced next-hop servers.
1990    </t>
1991    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1992        request message was received from an HTTP/1.0 (or earlier)
1993        client and did not include an Expect request-header field with
1994        the "100-continue" expectation. This requirement overrides the
1995        general rule for forwarding of 1xx responses (see &status-1xx;).
1996    </t>
1997  </list>
1998</t>
1999</section>
2000
2001<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2002<t>
2003   If an HTTP/1.1 client sends a request which includes a request body,
2004   but which does not include an Expect request-header field with the
2005   "100-continue" expectation, and if the client is not directly
2006   connected to an HTTP/1.1 origin server, and if the client sees the
2007   connection close before receiving any status from the server, the
2008   client &SHOULD; retry the request.  If the client does retry this
2009   request, it &MAY; use the following "binary exponential backoff"
2010   algorithm to be assured of obtaining a reliable response:
2011  <list style="numbers">
2012    <t>
2013      Initiate a new connection to the server
2014    </t>
2015    <t>
2016      Transmit the request-headers
2017    </t>
2018    <t>
2019      Initialize a variable R to the estimated round-trip time to the
2020         server (e.g., based on the time it took to establish the
2021         connection), or to a constant value of 5 seconds if the round-trip
2022         time is not available.
2023    </t>
2024    <t>
2025       Compute T = R * (2**N), where N is the number of previous
2026         retries of this request.
2027    </t>
2028    <t>
2029       Wait either for an error response from the server, or for T
2030         seconds (whichever comes first)
2031    </t>
2032    <t>
2033       If no error response is received, after T seconds transmit the
2034         body of the request.
2035    </t>
2036    <t>
2037       If client sees that the connection is closed prematurely,
2038         repeat from step 1 until the request is accepted, an error
2039         response is received, or the user becomes impatient and
2040         terminates the retry process.
2041    </t>
2042  </list>
2043</t>
2044<t>
2045   If at any point an error status is received, the client
2046  <list style="symbols">
2047      <t>&SHOULD-NOT;  continue and</t>
2048
2049      <t>&SHOULD; close the connection if it has not completed sending the
2050        request message.</t>
2051    </list>
2052</t>
2053</section>
2054</section>
2055</section>
2056
2057
2058<section title="Header Field Definitions" anchor="header.fields">
2059<t>
2060   This section defines the syntax and semantics of HTTP/1.1 header fields
2061   related to message framing and transport protocols.
2062</t>
2063<t>
2064   For entity-header fields, both sender and recipient refer to either the
2065   client or the server, depending on who sends and who receives the entity.
2066</t>
2067
2068<section title="Connection" anchor="header.connection">
2069  <iref primary="true" item="Connection header" x:for-anchor=""/>
2070  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2071  <x:anchor-alias value="Connection"/>
2072  <x:anchor-alias value="connection-token"/>
2073<t>
2074   The Connection general-header field allows the sender to specify
2075   options that are desired for that particular connection and &MUST-NOT;
2076   be communicated by proxies over further connections.
2077</t>
2078<t>
2079   The Connection header has the following grammar:
2080</t>
2081<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2082  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2083  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2084</artwork></figure>
2085<t>
2086   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2087   message is forwarded and, for each connection-token in this field,
2088   remove any header field(s) from the message with the same name as the
2089   connection-token. Connection options are signaled by the presence of
2090   a connection-token in the Connection header field, not by any
2091   corresponding additional header field(s), since the additional header
2092   field may not be sent if there are no parameters associated with that
2093   connection option.
2094</t>
2095<t>
2096   Message headers listed in the Connection header &MUST-NOT; include
2097   end-to-end headers, such as Cache-Control.
2098</t>
2099<t>
2100   HTTP/1.1 defines the "close" connection option for the sender to
2101   signal that the connection will be closed after completion of the
2102   response. For example,
2103</t>
2104<figure><artwork type="example">
2105    Connection: close
2106</artwork></figure>
2107<t>
2108   in either the request or the response header fields indicates that
2109   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2110   after the current request/response is complete.
2111</t>
2112<t>
2113   An HTTP/1.1 client that does not support persistent connections &MUST;
2114   include the "close" connection option in every request message.
2115</t>
2116<t>
2117   An HTTP/1.1 server that does not support persistent connections &MUST;
2118   include the "close" connection option in every response message that
2119   does not have a 1xx (informational) status code.
2120</t>
2121<t>
2122   A system receiving an HTTP/1.0 (or lower-version) message that
2123   includes a Connection header &MUST;, for each connection-token in this
2124   field, remove and ignore any header field(s) from the message with
2125   the same name as the connection-token. This protects against mistaken
2126   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2127</t>
2128</section>
2129
2130<section title="Content-Length" anchor="header.content-length">
2131  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2132  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2133  <x:anchor-alias value="Content-Length"/>
2134<t>
2135   The Content-Length entity-header field indicates the size of the
2136   entity-body, in decimal number of OCTETs, sent to the recipient or,
2137   in the case of the HEAD method, the size of the entity-body that
2138   would have been sent had the request been a GET.
2139</t>
2140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2141  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2142</artwork></figure>
2143<t>
2144   An example is
2145</t>
2146<figure><artwork type="example">
2147    Content-Length: 3495
2148</artwork></figure>
2149<t>
2150   Applications &SHOULD; use this field to indicate the transfer-length of
2151   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2152</t>
2153<t>
2154   Any Content-Length greater than or equal to zero is a valid value.
2155   <xref target="message.length"/> describes how to determine the length of a message-body
2156   if a Content-Length is not given.
2157</t>
2158<t>
2159   Note that the meaning of this field is significantly different from
2160   the corresponding definition in MIME, where it is an optional field
2161   used within the "message/external-body" content-type. In HTTP, it
2162   &SHOULD; be sent whenever the message's length can be determined prior
2163   to being transferred, unless this is prohibited by the rules in
2164   <xref target="message.length"/>.
2165</t>
2166</section>
2167
2168<section title="Date" anchor="header.date">
2169  <iref primary="true" item="Date header" x:for-anchor=""/>
2170  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2171  <x:anchor-alias value="Date"/>
2172<t>
2173   The Date general-header field represents the date and time at which
2174   the message was originated, having the same semantics as orig-date in
2175   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2176   HTTP-date, as described in <xref target="full.date"/>;
2177   it &MUST; be sent in rfc1123-date format.
2178</t>
2179<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2180  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2181</artwork></figure>
2182<t>
2183   An example is
2184</t>
2185<figure><artwork type="example">
2186    Date: Tue, 15 Nov 1994 08:12:31 GMT
2187</artwork></figure>
2188<t>
2189   Origin servers &MUST; include a Date header field in all responses,
2190   except in these cases:
2191  <list style="numbers">
2192      <t>If the response status code is 100 (Continue) or 101 (Switching
2193         Protocols), the response &MAY; include a Date header field, at
2194         the server's option.</t>
2195
2196      <t>If the response status code conveys a server error, e.g. 500
2197         (Internal Server Error) or 503 (Service Unavailable), and it is
2198         inconvenient or impossible to generate a valid Date.</t>
2199
2200      <t>If the server does not have a clock that can provide a
2201         reasonable approximation of the current time, its responses
2202         &MUST-NOT; include a Date header field. In this case, the rules
2203         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2204  </list>
2205</t>
2206<t>
2207   A received message that does not have a Date header field &MUST; be
2208   assigned one by the recipient if the message will be cached by that
2209   recipient or gatewayed via a protocol which requires a Date. An HTTP
2210   implementation without a clock &MUST-NOT; cache responses without
2211   revalidating them on every use. An HTTP cache, especially a shared
2212   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2213   clock with a reliable external standard.
2214</t>
2215<t>
2216   Clients &SHOULD; only send a Date header field in messages that include
2217   an entity-body, as in the case of the PUT and POST requests, and even
2218   then it is optional. A client without a clock &MUST-NOT; send a Date
2219   header field in a request.
2220</t>
2221<t>
2222   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2223   time subsequent to the generation of the message. It &SHOULD; represent
2224   the best available approximation of the date and time of message
2225   generation, unless the implementation has no means of generating a
2226   reasonably accurate date and time. In theory, the date ought to
2227   represent the moment just before the entity is generated. In
2228   practice, the date can be generated at any time during the message
2229   origination without affecting its semantic value.
2230</t>
2231
2232<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2233<t>
2234   Some origin server implementations might not have a clock available.
2235   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2236   values to a response, unless these values were associated
2237   with the resource by a system or user with a reliable clock. It &MAY;
2238   assign an Expires value that is known, at or before server
2239   configuration time, to be in the past (this allows "pre-expiration"
2240   of responses without storing separate Expires values for each
2241   resource).
2242</t>
2243</section>
2244</section>
2245
2246<section title="Host" anchor="header.host">
2247  <iref primary="true" item="Host header" x:for-anchor=""/>
2248  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2249  <x:anchor-alias value="Host"/>
2250<t>
2251   The Host request-header field specifies the Internet host and port
2252   number of the resource being requested, as obtained from the original
2253   URI given by the user or referring resource (generally an HTTP URL,
2254   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2255   the naming authority of the origin server or gateway given by the
2256   original URL. This allows the origin server or gateway to
2257   differentiate between internally-ambiguous URLs, such as the root "/"
2258   URL of a server for multiple host names on a single IP address.
2259</t>
2260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2261  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2262</artwork></figure>
2263<t>
2264   A "host" without any trailing port information implies the default
2265   port for the service requested (e.g., "80" for an HTTP URL). For
2266   example, a request on the origin server for
2267   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2268</t>
2269<figure><artwork type="example">
2270    GET /pub/WWW/ HTTP/1.1
2271    Host: www.example.org
2272</artwork></figure>
2273<t>
2274   A client &MUST; include a Host header field in all HTTP/1.1 request
2275   messages. If the requested URI does not include an Internet host
2276   name for the service being requested, then the Host header field &MUST;
2277   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2278   request message it forwards does contain an appropriate Host header
2279   field that identifies the service being requested by the proxy. All
2280   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2281   status code to any HTTP/1.1 request message which lacks a Host header
2282   field.
2283</t>
2284<t>
2285   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2286   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2287   for other requirements relating to Host.
2288</t>
2289</section>
2290
2291<section title="TE" anchor="header.te">
2292  <iref primary="true" item="TE header" x:for-anchor=""/>
2293  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2294  <x:anchor-alias value="TE"/>
2295  <x:anchor-alias value="t-codings"/>
2296<t>
2297   The TE request-header field indicates what extension transfer-codings
2298   it is willing to accept in the response and whether or not it is
2299   willing to accept trailer fields in a chunked transfer-coding. Its
2300   value may consist of the keyword "trailers" and/or a comma-separated
2301   list of extension transfer-coding names with optional accept
2302   parameters (as described in <xref target="transfer.codings"/>).
2303</t>
2304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2305  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2306  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2307</artwork></figure>
2308<t>
2309   The presence of the keyword "trailers" indicates that the client is
2310   willing to accept trailer fields in a chunked transfer-coding, as
2311   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2312   transfer-coding values even though it does not itself represent a
2313   transfer-coding.
2314</t>
2315<t>
2316   Examples of its use are:
2317</t>
2318<figure><artwork type="example">
2319    TE: deflate
2320    TE:
2321    TE: trailers, deflate;q=0.5
2322</artwork></figure>
2323<t>
2324   The TE header field only applies to the immediate connection.
2325   Therefore, the keyword &MUST; be supplied within a Connection header
2326   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2327</t>
2328<t>
2329   A server tests whether a transfer-coding is acceptable, according to
2330   a TE field, using these rules:
2331  <list style="numbers">
2332    <x:lt>
2333      <t>The "chunked" transfer-coding is always acceptable. If the
2334         keyword "trailers" is listed, the client indicates that it is
2335         willing to accept trailer fields in the chunked response on
2336         behalf of itself and any downstream clients. The implication is
2337         that, if given, the client is stating that either all
2338         downstream clients are willing to accept trailer fields in the
2339         forwarded response, or that it will attempt to buffer the
2340         response on behalf of downstream recipients.
2341      </t><t>
2342         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2343         chunked response such that a client can be assured of buffering
2344         the entire response.</t>
2345    </x:lt>
2346    <x:lt>
2347      <t>If the transfer-coding being tested is one of the transfer-codings
2348         listed in the TE field, then it is acceptable unless it
2349         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2350         qvalue of 0 means "not acceptable.")</t>
2351    </x:lt>
2352    <x:lt>
2353      <t>If multiple transfer-codings are acceptable, then the
2354         acceptable transfer-coding with the highest non-zero qvalue is
2355         preferred.  The "chunked" transfer-coding always has a qvalue
2356         of 1.</t>
2357    </x:lt>
2358  </list>
2359</t>
2360<t>
2361   If the TE field-value is empty or if no TE field is present, the only
2362   transfer-coding  is "chunked". A message with no transfer-coding is
2363   always acceptable.
2364</t>
2365</section>
2366
2367<section title="Trailer" anchor="header.trailer">
2368  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2369  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2370  <x:anchor-alias value="Trailer"/>
2371<t>
2372   The Trailer general field value indicates that the given set of
2373   header fields is present in the trailer of a message encoded with
2374   chunked transfer-coding.
2375</t>
2376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2377  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2378</artwork></figure>
2379<t>
2380   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2381   message using chunked transfer-coding with a non-empty trailer. Doing
2382   so allows the recipient to know which header fields to expect in the
2383   trailer.
2384</t>
2385<t>
2386   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2387   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2388   trailer fields in a "chunked" transfer-coding.
2389</t>
2390<t>
2391   Message header fields listed in the Trailer header field &MUST-NOT;
2392   include the following header fields:
2393  <list style="symbols">
2394    <t>Transfer-Encoding</t>
2395    <t>Content-Length</t>
2396    <t>Trailer</t>
2397  </list>
2398</t>
2399</section>
2400
2401<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2402  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2403  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2404  <x:anchor-alias value="Transfer-Encoding"/>
2405<t>
2406   The Transfer-Encoding general-header field indicates what (if any)
2407   type of transformation has been applied to the message body in order
2408   to safely transfer it between the sender and the recipient. This
2409   differs from the content-coding in that the transfer-coding is a
2410   property of the message, not of the entity.
2411</t>
2412<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2413  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2414</artwork></figure>
2415<t>
2416   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2417</t>
2418<figure><artwork type="example">
2419  Transfer-Encoding: chunked
2420</artwork></figure>
2421<t>
2422   If multiple encodings have been applied to an entity, the transfer-codings
2423   &MUST; be listed in the order in which they were applied.
2424   Additional information about the encoding parameters &MAY; be provided
2425   by other entity-header fields not defined by this specification.
2426</t>
2427<t>
2428   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2429   header.
2430</t>
2431</section>
2432
2433<section title="Upgrade" anchor="header.upgrade">
2434  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2435  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2436  <x:anchor-alias value="Upgrade"/>
2437<t>
2438   The Upgrade general-header allows the client to specify what
2439   additional communication protocols it supports and would like to use
2440   if the server finds it appropriate to switch protocols. The server
2441   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2442   response to indicate which protocol(s) are being switched.
2443</t>
2444<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2445  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2446</artwork></figure>
2447<t>
2448   For example,
2449</t>
2450<figure><artwork type="example">
2451    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2452</artwork></figure>
2453<t>
2454   The Upgrade header field is intended to provide a simple mechanism
2455   for transition from HTTP/1.1 to some other, incompatible protocol. It
2456   does so by allowing the client to advertise its desire to use another
2457   protocol, such as a later version of HTTP with a higher major version
2458   number, even though the current request has been made using HTTP/1.1.
2459   This eases the difficult transition between incompatible protocols by
2460   allowing the client to initiate a request in the more commonly
2461   supported protocol while indicating to the server that it would like
2462   to use a "better" protocol if available (where "better" is determined
2463   by the server, possibly according to the nature of the method and/or
2464   resource being requested).
2465</t>
2466<t>
2467   The Upgrade header field only applies to switching application-layer
2468   protocols upon the existing transport-layer connection. Upgrade
2469   cannot be used to insist on a protocol change; its acceptance and use
2470   by the server is optional. The capabilities and nature of the
2471   application-layer communication after the protocol change is entirely
2472   dependent upon the new protocol chosen, although the first action
2473   after changing the protocol &MUST; be a response to the initial HTTP
2474   request containing the Upgrade header field.
2475</t>
2476<t>
2477   The Upgrade header field only applies to the immediate connection.
2478   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2479   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2480   HTTP/1.1 message.
2481</t>
2482<t>
2483   The Upgrade header field cannot be used to indicate a switch to a
2484   protocol on a different connection. For that purpose, it is more
2485   appropriate to use a 301, 302, 303, or 305 redirection response.
2486</t>
2487<t>
2488   This specification only defines the protocol name "HTTP" for use by
2489   the family of Hypertext Transfer Protocols, as defined by the HTTP
2490   version rules of <xref target="http.version"/> and future updates to this
2491   specification. Any token can be used as a protocol name; however, it
2492   will only be useful if both the client and server associate the name
2493   with the same protocol.
2494</t>
2495</section>
2496
2497<section title="Via" anchor="header.via">
2498  <iref primary="true" item="Via header" x:for-anchor=""/>
2499  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2500  <x:anchor-alias value="protocol-name"/>
2501  <x:anchor-alias value="protocol-version"/>
2502  <x:anchor-alias value="pseudonym"/>
2503  <x:anchor-alias value="received-by"/>
2504  <x:anchor-alias value="received-protocol"/>
2505  <x:anchor-alias value="Via"/>
2506<t>
2507   The Via general-header field &MUST; be used by gateways and proxies to
2508   indicate the intermediate protocols and recipients between the user
2509   agent and the server on requests, and between the origin server and
2510   the client on responses. It is analogous to the "Received" field defined in
2511   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2512   avoiding request loops, and identifying the protocol capabilities of
2513   all senders along the request/response chain.
2514</t>
2515<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"/>
2516  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2517  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2518  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2519  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2520  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2521  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2522</artwork></figure>
2523<t>
2524   The received-protocol indicates the protocol version of the message
2525   received by the server or client along each segment of the
2526   request/response chain. The received-protocol version is appended to
2527   the Via field value when the message is forwarded so that information
2528   about the protocol capabilities of upstream applications remains
2529   visible to all recipients.
2530</t>
2531<t>
2532   The protocol-name is optional if and only if it would be "HTTP". The
2533   received-by field is normally the host and optional port number of a
2534   recipient server or client that subsequently forwarded the message.
2535   However, if the real host is considered to be sensitive information,
2536   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2537   be assumed to be the default port of the received-protocol.
2538</t>
2539<t>
2540   Multiple Via field values represents each proxy or gateway that has
2541   forwarded the message. Each recipient &MUST; append its information
2542   such that the end result is ordered according to the sequence of
2543   forwarding applications.
2544</t>
2545<t>
2546   Comments &MAY; be used in the Via header field to identify the software
2547   of the recipient proxy or gateway, analogous to the User-Agent and
2548   Server header fields. However, all comments in the Via field are
2549   optional and &MAY; be removed by any recipient prior to forwarding the
2550   message.
2551</t>
2552<t>
2553   For example, a request message could be sent from an HTTP/1.0 user
2554   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2555   forward the request to a public proxy at p.example.net, which completes
2556   the request by forwarding it to the origin server at www.example.com.
2557   The request received by www.example.com would then have the following
2558   Via header field:
2559</t>
2560<figure><artwork type="example">
2561    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2562</artwork></figure>
2563<t>
2564   Proxies and gateways used as a portal through a network firewall
2565   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2566   the firewall region. This information &SHOULD; only be propagated if
2567   explicitly enabled. If not enabled, the received-by host of any host
2568   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2569   for that host.
2570</t>
2571<t>
2572   For organizations that have strong privacy requirements for hiding
2573   internal structures, a proxy &MAY; combine an ordered subsequence of
2574   Via header field entries with identical received-protocol values into
2575   a single such entry. For example,
2576</t>
2577<figure><artwork type="example">
2578    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2579</artwork></figure>
2580<t>
2581        could be collapsed to
2582</t>
2583<figure><artwork type="example">
2584    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2585</artwork></figure>
2586<t>
2587   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2588   under the same organizational control and the hosts have already been
2589   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2590   have different received-protocol values.
2591</t>
2592</section>
2593
2594</section>
2595
2596<section title="IANA Considerations" anchor="IANA.considerations">
2597<section title="Message Header Registration" anchor="message.header.registration">
2598<t>
2599   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2600   with the permanent registrations below (see <xref target="RFC3864"/>):
2601</t>
2602<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2603<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2604   <ttcol>Header Field Name</ttcol>
2605   <ttcol>Protocol</ttcol>
2606   <ttcol>Status</ttcol>
2607   <ttcol>Reference</ttcol>
2608
2609   <c>Connection</c>
2610   <c>http</c>
2611   <c>standard</c>
2612   <c>
2613      <xref target="header.connection"/>
2614   </c>
2615   <c>Content-Length</c>
2616   <c>http</c>
2617   <c>standard</c>
2618   <c>
2619      <xref target="header.content-length"/>
2620   </c>
2621   <c>Date</c>
2622   <c>http</c>
2623   <c>standard</c>
2624   <c>
2625      <xref target="header.date"/>
2626   </c>
2627   <c>Host</c>
2628   <c>http</c>
2629   <c>standard</c>
2630   <c>
2631      <xref target="header.host"/>
2632   </c>
2633   <c>TE</c>
2634   <c>http</c>
2635   <c>standard</c>
2636   <c>
2637      <xref target="header.te"/>
2638   </c>
2639   <c>Trailer</c>
2640   <c>http</c>
2641   <c>standard</c>
2642   <c>
2643      <xref target="header.trailer"/>
2644   </c>
2645   <c>Transfer-Encoding</c>
2646   <c>http</c>
2647   <c>standard</c>
2648   <c>
2649      <xref target="header.transfer-encoding"/>
2650   </c>
2651   <c>Upgrade</c>
2652   <c>http</c>
2653   <c>standard</c>
2654   <c>
2655      <xref target="header.upgrade"/>
2656   </c>
2657   <c>Via</c>
2658   <c>http</c>
2659   <c>standard</c>
2660   <c>
2661      <xref target="header.via"/>
2662   </c>
2663</texttable>
2664<!--(END)-->
2665<t>
2666   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2667</t>
2668</section>
2669
2670<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2671<t>
2672   The entry for the "http" URI Scheme in the registry located at
2673   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2674   should be updated to point to <xref target="http.url"/> of this document
2675   (see <xref target="RFC4395"/>).
2676</t>
2677</section>
2678
2679<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2680<t>
2681   This document serves as the specification for the Internet media types
2682   "message/http" and "application/http". The following is to be registered with
2683   IANA (see <xref target="RFC4288"/>).
2684</t>
2685<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2686<iref item="Media Type" subitem="message/http" primary="true"/>
2687<iref item="message/http Media Type" primary="true"/>
2688<t>
2689   The message/http type can be used to enclose a single HTTP request or
2690   response message, provided that it obeys the MIME restrictions for all
2691   "message" types regarding line length and encodings.
2692</t>
2693<t>
2694  <list style="hanging" x:indent="12em">
2695    <t hangText="Type name:">
2696      message
2697    </t>
2698    <t hangText="Subtype name:">
2699      http
2700    </t>
2701    <t hangText="Required parameters:">
2702      none
2703    </t>
2704    <t hangText="Optional parameters:">
2705      version, msgtype
2706      <list style="hanging">
2707        <t hangText="version:">
2708          The HTTP-Version number of the enclosed message
2709          (e.g., "1.1"). If not present, the version can be
2710          determined from the first line of the body.
2711        </t>
2712        <t hangText="msgtype:">
2713          The message type -- "request" or "response". If not
2714          present, the type can be determined from the first
2715          line of the body.
2716        </t>
2717      </list>
2718    </t>
2719    <t hangText="Encoding considerations:">
2720      only "7bit", "8bit", or "binary" are permitted
2721    </t>
2722    <t hangText="Security considerations:">
2723      none
2724    </t>
2725    <t hangText="Interoperability considerations:">
2726      none
2727    </t>
2728    <t hangText="Published specification:">
2729      This specification (see <xref target="internet.media.type.message.http"/>).
2730    </t>
2731    <t hangText="Applications that use this media type:">
2732    </t>
2733    <t hangText="Additional information:">
2734      <list style="hanging">
2735        <t hangText="Magic number(s):">none</t>
2736        <t hangText="File extension(s):">none</t>
2737        <t hangText="Macintosh file type code(s):">none</t>
2738      </list>
2739    </t>
2740    <t hangText="Person and email address to contact for further information:">
2741      See Authors Section.
2742    </t>
2743                <t hangText="Intended usage:">
2744                  COMMON
2745    </t>
2746                <t hangText="Restrictions on usage:">
2747                  none
2748    </t>
2749    <t hangText="Author/Change controller:">
2750      IESG
2751    </t>
2752  </list>
2753</t>
2754</section>
2755<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2756<iref item="Media Type" subitem="application/http" primary="true"/>
2757<iref item="application/http Media Type" primary="true"/>
2758<t>
2759   The application/http type can be used to enclose a pipeline of one or more
2760   HTTP request or response messages (not intermixed).
2761</t>
2762<t>
2763  <list style="hanging" x:indent="12em">
2764    <t hangText="Type name:">
2765      application
2766    </t>
2767    <t hangText="Subtype name:">
2768      http
2769    </t>
2770    <t hangText="Required parameters:">
2771      none
2772    </t>
2773    <t hangText="Optional parameters:">
2774      version, msgtype
2775      <list style="hanging">
2776        <t hangText="version:">
2777          The HTTP-Version number of the enclosed messages
2778          (e.g., "1.1"). If not present, the version can be
2779          determined from the first line of the body.
2780        </t>
2781        <t hangText="msgtype:">
2782          The message type -- "request" or "response". If not
2783          present, the type can be determined from the first
2784          line of the body.
2785        </t>
2786      </list>
2787    </t>
2788    <t hangText="Encoding considerations:">
2789      HTTP messages enclosed by this type
2790      are in "binary" format; use of an appropriate
2791      Content-Transfer-Encoding is required when
2792      transmitted via E-mail.
2793    </t>
2794    <t hangText="Security considerations:">
2795      none
2796    </t>
2797    <t hangText="Interoperability considerations:">
2798      none
2799    </t>
2800    <t hangText="Published specification:">
2801      This specification (see <xref target="internet.media.type.application.http"/>).
2802    </t>
2803    <t hangText="Applications that use this media type:">
2804    </t>
2805    <t hangText="Additional information:">
2806      <list style="hanging">
2807        <t hangText="Magic number(s):">none</t>
2808        <t hangText="File extension(s):">none</t>
2809        <t hangText="Macintosh file type code(s):">none</t>
2810      </list>
2811    </t>
2812    <t hangText="Person and email address to contact for further information:">
2813      See Authors Section.
2814    </t>
2815                <t hangText="Intended usage:">
2816                  COMMON
2817    </t>
2818                <t hangText="Restrictions on usage:">
2819                  none
2820    </t>
2821    <t hangText="Author/Change controller:">
2822      IESG
2823    </t>
2824  </list>
2825</t>
2826</section>
2827</section>
2828
2829</section>
2830
2831<section title="Security Considerations" anchor="security.considerations">
2832<t>
2833   This section is meant to inform application developers, information
2834   providers, and users of the security limitations in HTTP/1.1 as
2835   described by this document. The discussion does not include
2836   definitive solutions to the problems revealed, though it does make
2837   some suggestions for reducing security risks.
2838</t>
2839
2840<section title="Personal Information" anchor="personal.information">
2841<t>
2842   HTTP clients are often privy to large amounts of personal information
2843   (e.g. the user's name, location, mail address, passwords, encryption
2844   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2845   leakage of this information.
2846   We very strongly recommend that a convenient interface be provided
2847   for the user to control dissemination of such information, and that
2848   designers and implementors be particularly careful in this area.
2849   History shows that errors in this area often create serious security
2850   and/or privacy problems and generate highly adverse publicity for the
2851   implementor's company.
2852</t>
2853</section>
2854
2855<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2856<t>
2857   A server is in the position to save personal data about a user's
2858   requests which might identify their reading patterns or subjects of
2859   interest. This information is clearly confidential in nature and its
2860   handling can be constrained by law in certain countries. People using
2861   HTTP to provide data are responsible for ensuring that
2862   such material is not distributed without the permission of any
2863   individuals that are identifiable by the published results.
2864</t>
2865</section>
2866
2867<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2868<t>
2869   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2870   the documents returned by HTTP requests to be only those that were
2871   intended by the server administrators. If an HTTP server translates
2872   HTTP URIs directly into file system calls, the server &MUST; take
2873   special care not to serve files that were not intended to be
2874   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2875   other operating systems use ".." as a path component to indicate a
2876   directory level above the current one. On such a system, an HTTP
2877   server &MUST; disallow any such construct in the Request-URI if it
2878   would otherwise allow access to a resource outside those intended to
2879   be accessible via the HTTP server. Similarly, files intended for
2880   reference only internally to the server (such as access control
2881   files, configuration files, and script code) &MUST; be protected from
2882   inappropriate retrieval, since they might contain sensitive
2883   information. Experience has shown that minor bugs in such HTTP server
2884   implementations have turned into security risks.
2885</t>
2886</section>
2887
2888<section title="DNS Spoofing" anchor="dns.spoofing">
2889<t>
2890   Clients using HTTP rely heavily on the Domain Name Service, and are
2891   thus generally prone to security attacks based on the deliberate
2892   mis-association of IP addresses and DNS names. Clients need to be
2893   cautious in assuming the continuing validity of an IP number/DNS name
2894   association.
2895</t>
2896<t>
2897   In particular, HTTP clients &SHOULD; rely on their name resolver for
2898   confirmation of an IP number/DNS name association, rather than
2899   caching the result of previous host name lookups. Many platforms
2900   already can cache host name lookups locally when appropriate, and
2901   they &SHOULD; be configured to do so. It is proper for these lookups to
2902   be cached, however, only when the TTL (Time To Live) information
2903   reported by the name server makes it likely that the cached
2904   information will remain useful.
2905</t>
2906<t>
2907   If HTTP clients cache the results of host name lookups in order to
2908   achieve a performance improvement, they &MUST; observe the TTL
2909   information reported by DNS.
2910</t>
2911<t>
2912   If HTTP clients do not observe this rule, they could be spoofed when
2913   a previously-accessed server's IP address changes. As network
2914   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2915   possibility of this form of attack will grow. Observing this
2916   requirement thus reduces this potential security vulnerability.
2917</t>
2918<t>
2919   This requirement also improves the load-balancing behavior of clients
2920   for replicated servers using the same DNS name and reduces the
2921   likelihood of a user's experiencing failure in accessing sites which
2922   use that strategy.
2923</t>
2924</section>
2925
2926<section title="Proxies and Caching" anchor="attack.proxies">
2927<t>
2928   By their very nature, HTTP proxies are men-in-the-middle, and
2929   represent an opportunity for man-in-the-middle attacks. Compromise of
2930   the systems on which the proxies run can result in serious security
2931   and privacy problems. Proxies have access to security-related
2932   information, personal information about individual users and
2933   organizations, and proprietary information belonging to users and
2934   content providers. A compromised proxy, or a proxy implemented or
2935   configured without regard to security and privacy considerations,
2936   might be used in the commission of a wide range of potential attacks.
2937</t>
2938<t>
2939   Proxy operators should protect the systems on which proxies run as
2940   they would protect any system that contains or transports sensitive
2941   information. In particular, log information gathered at proxies often
2942   contains highly sensitive personal information, and/or information
2943   about organizations. Log information should be carefully guarded, and
2944   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2945</t>
2946<t>
2947   Proxy implementors should consider the privacy and security
2948   implications of their design and coding decisions, and of the
2949   configuration options they provide to proxy operators (especially the
2950   default configuration).
2951</t>
2952<t>
2953   Users of a proxy need to be aware that they are no trustworthier than
2954   the people who run the proxy; HTTP itself cannot solve this problem.
2955</t>
2956<t>
2957   The judicious use of cryptography, when appropriate, may suffice to
2958   protect against a broad range of security and privacy attacks. Such
2959   cryptography is beyond the scope of the HTTP/1.1 specification.
2960</t>
2961</section>
2962
2963<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2964<t>
2965   They exist. They are hard to defend against. Research continues.
2966   Beware.
2967</t>
2968</section>
2969</section>
2970
2971<section title="Acknowledgments" anchor="ack">
2972<t>
2973   This specification makes heavy use of the augmented BNF and generic
2974   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2975   reuses many of the definitions provided by Nathaniel Borenstein and
2976   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2977   specification will help reduce past confusion over the relationship
2978   between HTTP and Internet mail message formats.
2979</t>
2980<t>
2981   HTTP has evolved considerably over the years. It has
2982   benefited from a large and active developer community--the many
2983   people who have participated on the www-talk mailing list--and it is
2984   that community which has been most responsible for the success of
2985   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2986   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2987   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2988   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2989   VanHeyningen deserve special recognition for their efforts in
2990   defining early aspects of the protocol.
2991</t>
2992<t>
2993   This document has benefited greatly from the comments of all those
2994   participating in the HTTP-WG. In addition to those already mentioned,
2995   the following individuals have contributed to this specification:
2996</t>
2997<t>
2998   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2999   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3000   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3001   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3002   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3003   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3004   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3005   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3006   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3007   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3008   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3009   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3010   Josh Cohen.
3011</t>
3012<t>
3013   Thanks to the "cave men" of Palo Alto. You know who you are.
3014</t>
3015<t>
3016   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3017   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3018   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3019   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3020   Larry Masinter for their help. And thanks go particularly to Jeff
3021   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3022</t>
3023<t>
3024   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3025   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3026   discovery of many of the problems that this document attempts to
3027   rectify.
3028</t>
3029</section>
3030
3031</middle>
3032<back>
3033
3034<references title="Normative References">
3035
3036<reference anchor="ISO-8859-1">
3037  <front>
3038    <title>
3039     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3040    </title>
3041    <author>
3042      <organization>International Organization for Standardization</organization>
3043    </author>
3044    <date year="1998"/>
3045  </front>
3046  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3047</reference>
3048
3049<reference anchor="Part2">
3050  <front>
3051    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3053      <organization abbrev="Day Software">Day Software</organization>
3054      <address><email>fielding@gbiv.com</email></address>
3055    </author>
3056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3057      <organization>One Laptop per Child</organization>
3058      <address><email>jg@laptop.org</email></address>
3059    </author>
3060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3061      <organization abbrev="HP">Hewlett-Packard Company</organization>
3062      <address><email>JeffMogul@acm.org</email></address>
3063    </author>
3064    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3065      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3066      <address><email>henrikn@microsoft.com</email></address>
3067    </author>
3068    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3069      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3070      <address><email>LMM@acm.org</email></address>
3071    </author>
3072    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3074      <address><email>paulle@microsoft.com</email></address>
3075    </author>
3076    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3077      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3078      <address><email>timbl@w3.org</email></address>
3079    </author>
3080    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3081      <organization abbrev="W3C">World Wide Web Consortium</organization>
3082      <address><email>ylafon@w3.org</email></address>
3083    </author>
3084    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3085      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3086      <address><email>julian.reschke@greenbytes.de</email></address>
3087    </author>
3088    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3089  </front>
3090  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3091  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3092</reference>
3093
3094<reference anchor="Part3">
3095  <front>
3096    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3097    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3098      <organization abbrev="Day Software">Day Software</organization>
3099      <address><email>fielding@gbiv.com</email></address>
3100    </author>
3101    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3102      <organization>One Laptop per Child</organization>
3103      <address><email>jg@laptop.org</email></address>
3104    </author>
3105    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3106      <organization abbrev="HP">Hewlett-Packard Company</organization>
3107      <address><email>JeffMogul@acm.org</email></address>
3108    </author>
3109    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3110      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3111      <address><email>henrikn@microsoft.com</email></address>
3112    </author>
3113    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3114      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3115      <address><email>LMM@acm.org</email></address>
3116    </author>
3117    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3119      <address><email>paulle@microsoft.com</email></address>
3120    </author>
3121    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3122      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3123      <address><email>timbl@w3.org</email></address>
3124    </author>
3125    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3126      <organization abbrev="W3C">World Wide Web Consortium</organization>
3127      <address><email>ylafon@w3.org</email></address>
3128    </author>
3129    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3130      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3131      <address><email>julian.reschke@greenbytes.de</email></address>
3132    </author>
3133    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3134  </front>
3135  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3136  <x:source href="p3-payload.xml" basename="p3-payload"/>
3137</reference>
3138
3139<reference anchor="Part5">
3140  <front>
3141    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3142    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3143      <organization abbrev="Day Software">Day Software</organization>
3144      <address><email>fielding@gbiv.com</email></address>
3145    </author>
3146    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3147      <organization>One Laptop per Child</organization>
3148      <address><email>jg@laptop.org</email></address>
3149    </author>
3150    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3151      <organization abbrev="HP">Hewlett-Packard Company</organization>
3152      <address><email>JeffMogul@acm.org</email></address>
3153    </author>
3154    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3155      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3156      <address><email>henrikn@microsoft.com</email></address>
3157    </author>
3158    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3159      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3160      <address><email>LMM@acm.org</email></address>
3161    </author>
3162    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3164      <address><email>paulle@microsoft.com</email></address>
3165    </author>
3166    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3167      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3168      <address><email>timbl@w3.org</email></address>
3169    </author>
3170    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3171      <organization abbrev="W3C">World Wide Web Consortium</organization>
3172      <address><email>ylafon@w3.org</email></address>
3173    </author>
3174    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3175      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3176      <address><email>julian.reschke@greenbytes.de</email></address>
3177    </author>
3178    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3179  </front>
3180  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3181  <x:source href="p5-range.xml" basename="p5-range"/>
3182</reference>
3183
3184<reference anchor="Part6">
3185  <front>
3186    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3187    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3188      <organization abbrev="Day Software">Day Software</organization>
3189      <address><email>fielding@gbiv.com</email></address>
3190    </author>
3191    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3192      <organization>One Laptop per Child</organization>
3193      <address><email>jg@laptop.org</email></address>
3194    </author>
3195    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3196      <organization abbrev="HP">Hewlett-Packard Company</organization>
3197      <address><email>JeffMogul@acm.org</email></address>
3198    </author>
3199    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3200      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3201      <address><email>henrikn@microsoft.com</email></address>
3202    </author>
3203    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3204      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3205      <address><email>LMM@acm.org</email></address>
3206    </author>
3207    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3208      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3209      <address><email>paulle@microsoft.com</email></address>
3210    </author>
3211    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3212      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3213      <address><email>timbl@w3.org</email></address>
3214    </author>
3215    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3216      <organization abbrev="W3C">World Wide Web Consortium</organization>
3217      <address><email>ylafon@w3.org</email></address>
3218    </author>
3219    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3220      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3221      <address><email>julian.reschke@greenbytes.de</email></address>
3222    </author>
3223    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3224  </front>
3225  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3226  <x:source href="p6-cache.xml" basename="p6-cache"/>
3227</reference>
3228
3229<reference anchor="RFC5234">
3230  <front>
3231    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3232    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3233      <organization>Brandenburg InternetWorking</organization>
3234      <address>
3235      <postal>
3236      <street>675 Spruce Dr.</street>
3237      <city>Sunnyvale</city>
3238      <region>CA</region>
3239      <code>94086</code>
3240      <country>US</country></postal>
3241      <phone>+1.408.246.8253</phone>
3242      <email>dcrocker@bbiw.net</email></address> 
3243    </author>
3244    <author initials="P." surname="Overell" fullname="Paul Overell">
3245      <organization>THUS plc.</organization>
3246      <address>
3247      <postal>
3248      <street>1/2 Berkeley Square</street>
3249      <street>99 Berkely Street</street>
3250      <city>Glasgow</city>
3251      <code>G3 7HR</code>
3252      <country>UK</country></postal>
3253      <email>paul.overell@thus.net</email></address>
3254    </author>
3255    <date month="January" year="2008"/>
3256  </front>
3257  <seriesInfo name="STD" value="68"/>
3258  <seriesInfo name="RFC" value="5234"/>
3259</reference>
3260
3261<reference anchor="RFC2045">
3262  <front>
3263    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3264    <author initials="N." surname="Freed" fullname="Ned Freed">
3265      <organization>Innosoft International, Inc.</organization>
3266      <address><email>ned@innosoft.com</email></address>
3267    </author>
3268    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3269      <organization>First Virtual Holdings</organization>
3270      <address><email>nsb@nsb.fv.com</email></address>
3271    </author>
3272    <date month="November" year="1996"/>
3273  </front>
3274  <seriesInfo name="RFC" value="2045"/>
3275</reference>
3276
3277<reference anchor="RFC2047">
3278  <front>
3279    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3280    <author initials="K." surname="Moore" fullname="Keith Moore">
3281      <organization>University of Tennessee</organization>
3282      <address><email>moore@cs.utk.edu</email></address>
3283    </author>
3284    <date month="November" year="1996"/>
3285  </front>
3286  <seriesInfo name="RFC" value="2047"/>
3287</reference>
3288
3289<reference anchor="RFC2119">
3290  <front>
3291    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3292    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3293      <organization>Harvard University</organization>
3294      <address><email>sob@harvard.edu</email></address>
3295    </author>
3296    <date month="March" year="1997"/>
3297  </front>
3298  <seriesInfo name="BCP" value="14"/>
3299  <seriesInfo name="RFC" value="2119"/>
3300</reference>
3301
3302<reference anchor="RFC2396">
3303  <front>
3304    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3305    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3306      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3307      <address><email>timbl@w3.org</email></address>
3308    </author>
3309    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3310      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3311      <address><email>fielding@ics.uci.edu</email></address>
3312    </author>
3313    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3314      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3315      <address><email>masinter@parc.xerox.com</email></address>
3316    </author>
3317    <date month="August" year="1998"/>
3318  </front>
3319  <seriesInfo name="RFC" value="2396"/>
3320</reference>
3321
3322<reference anchor="USASCII">
3323  <front>
3324    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3325    <author>
3326      <organization>American National Standards Institute</organization>
3327    </author>
3328    <date year="1986"/>
3329  </front>
3330  <seriesInfo name="ANSI" value="X3.4"/>
3331</reference>
3332
3333</references>
3334
3335<references title="Informative References">
3336
3337<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3338  <front>
3339    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3340    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3341      <organization/>
3342    </author>
3343    <author initials="J." surname="Gettys" fullname="J. Gettys">
3344      <organization/>
3345    </author>
3346    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3347      <organization/>
3348    </author>
3349    <author initials="H." surname="Lie" fullname="H. Lie">
3350      <organization/>
3351    </author>
3352    <author initials="C." surname="Lilley" fullname="C. Lilley">
3353      <organization/>
3354    </author>
3355    <date year="1997" month="September"/>
3356  </front>
3357  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3358</reference>
3359
3360<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3361  <front>
3362    <title>Improving HTTP Latency</title>
3363    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3364      <organization/>
3365    </author>
3366    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3367      <organization/>
3368    </author>
3369    <date year="1995" month="December"/>
3370  </front>
3371  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3372</reference>
3373
3374<reference anchor="RFC822">
3375  <front>
3376    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3377    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3378      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3379      <address><email>DCrocker@UDel-Relay</email></address>
3380    </author>
3381    <date month="August" day="13" year="1982"/>
3382  </front>
3383  <seriesInfo name="STD" value="11"/>
3384  <seriesInfo name="RFC" value="822"/>
3385</reference>
3386
3387<reference anchor="RFC959">
3388  <front>
3389    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3390    <author initials="J." surname="Postel" fullname="J. Postel">
3391      <organization>Information Sciences Institute (ISI)</organization>
3392    </author>
3393    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3394      <organization/>
3395    </author>
3396    <date month="October" year="1985"/>
3397  </front>
3398  <seriesInfo name="STD" value="9"/>
3399  <seriesInfo name="RFC" value="959"/>
3400</reference>
3401
3402<reference anchor="RFC1123">
3403  <front>
3404    <title>Requirements for Internet Hosts - Application and Support</title>
3405    <author initials="R." surname="Braden" fullname="Robert Braden">
3406      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3407      <address><email>Braden@ISI.EDU</email></address>
3408    </author>
3409    <date month="October" year="1989"/>
3410  </front>
3411  <seriesInfo name="STD" value="3"/>
3412  <seriesInfo name="RFC" value="1123"/>
3413</reference>
3414
3415<reference anchor="RFC1305">
3416  <front>
3417    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3418    <author initials="D." surname="Mills" fullname="David L. Mills">
3419      <organization>University of Delaware, Electrical Engineering Department</organization>
3420      <address><email>mills@udel.edu</email></address>
3421    </author>
3422    <date month="March" year="1992"/>
3423  </front>
3424  <seriesInfo name="RFC" value="1305"/>
3425</reference>
3426
3427<reference anchor="RFC1436">
3428  <front>
3429    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3430    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3431      <organization>University of Minnesota, Computer and Information Services</organization>
3432      <address><email>fxa@boombox.micro.umn.edu</email></address>
3433    </author>
3434    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3435      <organization>University of Minnesota, Computer and Information Services</organization>
3436      <address><email>mpm@boombox.micro.umn.edu</email></address>
3437    </author>
3438    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3439      <organization>University of Minnesota, Computer and Information Services</organization>
3440      <address><email>lindner@boombox.micro.umn.edu</email></address>
3441    </author>
3442    <author initials="D." surname="Johnson" fullname="David Johnson">
3443      <organization>University of Minnesota, Computer and Information Services</organization>
3444      <address><email>dmj@boombox.micro.umn.edu</email></address>
3445    </author>
3446    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3447      <organization>University of Minnesota, Computer and Information Services</organization>
3448      <address><email>daniel@boombox.micro.umn.edu</email></address>
3449    </author>
3450    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3451      <organization>University of Minnesota, Computer and Information Services</organization>
3452      <address><email>alberti@boombox.micro.umn.edu</email></address>
3453    </author>
3454    <date month="March" year="1993"/>
3455  </front>
3456  <seriesInfo name="RFC" value="1436"/>
3457</reference>
3458
3459<reference anchor="RFC1630">
3460  <front>
3461    <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>
3462    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3463      <organization>CERN, World-Wide Web project</organization>
3464      <address><email>timbl@info.cern.ch</email></address>
3465    </author>
3466    <date month="June" year="1994"/>
3467  </front>
3468  <seriesInfo name="RFC" value="1630"/>
3469</reference>
3470
3471<reference anchor="RFC1737">
3472  <front>
3473    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3474    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3475      <organization>Xerox Palo Alto Research Center</organization>
3476      <address><email>masinter@parc.xerox.com</email></address>
3477    </author>
3478    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3479      <organization>MIT Laboratory for Computer Science</organization>
3480      <address><email>sollins@lcs.mit.edu</email></address>
3481    </author>
3482    <date month="December" year="1994"/>
3483  </front>
3484  <seriesInfo name="RFC" value="1737"/>
3485</reference>
3486
3487<reference anchor="RFC1738">
3488  <front>
3489    <title>Uniform Resource Locators (URL)</title>
3490    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3491      <organization>CERN, World-Wide Web project</organization>
3492      <address><email>timbl@info.cern.ch</email></address>
3493    </author>
3494    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3495      <organization>Xerox PARC</organization>
3496      <address><email>masinter@parc.xerox.com</email></address>
3497    </author>
3498    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3499      <organization>University of Minnesota, Computer and Information Services</organization>
3500      <address><email>mpm@boombox.micro.umn.edu</email></address>
3501    </author>
3502    <date month="December" year="1994"/>
3503  </front>
3504  <seriesInfo name="RFC" value="1738"/>
3505</reference>
3506
3507<reference anchor="RFC1808">
3508  <front>
3509    <title>Relative Uniform Resource Locators</title>
3510    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3511      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3512      <address><email>fielding@ics.uci.edu</email></address>
3513    </author>
3514    <date month="June" year="1995"/>
3515  </front>
3516  <seriesInfo name="RFC" value="1808"/>
3517</reference>
3518
3519<reference anchor="RFC1900">
3520  <front>
3521    <title>Renumbering Needs Work</title>
3522    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3523      <organization>CERN, Computing and Networks Division</organization>
3524      <address><email>brian@dxcoms.cern.ch</email></address>
3525    </author>
3526    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3527      <organization>cisco Systems</organization>
3528      <address><email>yakov@cisco.com</email></address>
3529    </author>
3530    <date month="February" year="1996"/>
3531  </front>
3532  <seriesInfo name="RFC" value="1900"/>
3533</reference>
3534
3535<reference anchor="RFC1945">
3536  <front>
3537    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3538    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3539      <organization>MIT, Laboratory for Computer Science</organization>
3540      <address><email>timbl@w3.org</email></address>
3541    </author>
3542    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3543      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3544      <address><email>fielding@ics.uci.edu</email></address>
3545    </author>
3546    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3547      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3548      <address><email>frystyk@w3.org</email></address>
3549    </author>
3550    <date month="May" year="1996"/>
3551  </front>
3552  <seriesInfo name="RFC" value="1945"/>
3553</reference>
3554
3555<reference anchor="RFC2068">
3556  <front>
3557    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3558    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3559      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3560      <address><email>fielding@ics.uci.edu</email></address>
3561    </author>
3562    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3563      <organization>MIT Laboratory for Computer Science</organization>
3564      <address><email>jg@w3.org</email></address>
3565    </author>
3566    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3567      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3568      <address><email>mogul@wrl.dec.com</email></address>
3569    </author>
3570    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3571      <organization>MIT Laboratory for Computer Science</organization>
3572      <address><email>frystyk@w3.org</email></address>
3573    </author>
3574    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3575      <organization>MIT Laboratory for Computer Science</organization>
3576      <address><email>timbl@w3.org</email></address>
3577    </author>
3578    <date month="January" year="1997"/>
3579  </front>
3580  <seriesInfo name="RFC" value="2068"/>
3581</reference>
3582
3583<reference anchor='RFC2109'>
3584  <front>
3585    <title>HTTP State Management Mechanism</title>
3586    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3587      <organization>Bell Laboratories, Lucent Technologies</organization>
3588      <address><email>dmk@bell-labs.com</email></address>
3589    </author>
3590    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3591      <organization>Netscape Communications Corp.</organization>
3592      <address><email>montulli@netscape.com</email></address>
3593    </author>
3594    <date year='1997' month='February' />
3595  </front>
3596  <seriesInfo name='RFC' value='2109' />
3597</reference>
3598
3599<reference anchor="RFC2145">
3600  <front>
3601    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3602    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3603      <organization>Western Research Laboratory</organization>
3604      <address><email>mogul@wrl.dec.com</email></address>
3605    </author>
3606    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3607      <organization>Department of Information and Computer Science</organization>
3608      <address><email>fielding@ics.uci.edu</email></address>
3609    </author>
3610    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3611      <organization>MIT Laboratory for Computer Science</organization>
3612      <address><email>jg@w3.org</email></address>
3613    </author>
3614    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3615      <organization>W3 Consortium</organization>
3616      <address><email>frystyk@w3.org</email></address>
3617    </author>
3618    <date month="May" year="1997"/>
3619  </front>
3620  <seriesInfo name="RFC" value="2145"/>
3621</reference>
3622
3623<reference anchor="RFC2324">
3624  <front>
3625    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3626    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3627      <organization>Xerox Palo Alto Research Center</organization>
3628      <address><email>masinter@parc.xerox.com</email></address>
3629    </author>
3630    <date month="April" day="1" year="1998"/>
3631  </front>
3632  <seriesInfo name="RFC" value="2324"/>
3633</reference>
3634
3635<reference anchor="RFC2616">
3636  <front>
3637    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3638    <author initials="R." surname="Fielding" fullname="R. Fielding">
3639      <organization>University of California, Irvine</organization>
3640      <address><email>fielding@ics.uci.edu</email></address>
3641    </author>
3642    <author initials="J." surname="Gettys" fullname="J. Gettys">
3643      <organization>W3C</organization>
3644      <address><email>jg@w3.org</email></address>
3645    </author>
3646    <author initials="J." surname="Mogul" fullname="J. Mogul">
3647      <organization>Compaq Computer Corporation</organization>
3648      <address><email>mogul@wrl.dec.com</email></address>
3649    </author>
3650    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3651      <organization>MIT Laboratory for Computer Science</organization>
3652      <address><email>frystyk@w3.org</email></address>
3653    </author>
3654    <author initials="L." surname="Masinter" fullname="L. Masinter">
3655      <organization>Xerox Corporation</organization>
3656      <address><email>masinter@parc.xerox.com</email></address>
3657    </author>
3658    <author initials="P." surname="Leach" fullname="P. Leach">
3659      <organization>Microsoft Corporation</organization>
3660      <address><email>paulle@microsoft.com</email></address>
3661    </author>
3662    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3663      <organization>W3C</organization>
3664      <address><email>timbl@w3.org</email></address>
3665    </author>
3666    <date month="June" year="1999"/>
3667  </front>
3668  <seriesInfo name="RFC" value="2616"/>
3669</reference>
3670
3671<reference anchor='RFC2818'>
3672  <front>
3673    <title>HTTP Over TLS</title>
3674    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3675      <organization>RTFM, Inc.</organization>
3676      <address><email>ekr@rtfm.com</email></address>
3677    </author>
3678    <date year='2000' month='May' />
3679  </front>
3680  <seriesInfo name='RFC' value='2818' />
3681</reference>
3682
3683<reference anchor="RFC2821">
3684  <front>
3685    <title>Simple Mail Transfer Protocol</title>
3686    <author initials="J." surname="Klensin" fullname="J. Klensin">
3687      <organization>AT&amp;T Laboratories</organization>
3688      <address><email>klensin@research.att.com</email></address>
3689    </author>
3690    <date year="2001" month="April"/>
3691  </front>
3692  <seriesInfo name="RFC" value="2821"/>
3693</reference>
3694
3695<reference anchor='RFC2965'>
3696  <front>
3697    <title>HTTP State Management Mechanism</title>
3698    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3699      <organization>Bell Laboratories, Lucent Technologies</organization>
3700      <address><email>dmk@bell-labs.com</email></address>
3701    </author>
3702    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3703      <organization>Epinions.com, Inc.</organization>
3704      <address><email>lou@montulli.org</email></address>
3705    </author>
3706    <date year='2000' month='October' />
3707  </front>
3708  <seriesInfo name='RFC' value='2965' />
3709</reference>
3710
3711<reference anchor='RFC3864'>
3712  <front>
3713    <title>Registration Procedures for Message Header Fields</title>
3714    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3715      <organization>Nine by Nine</organization>
3716      <address><email>GK-IETF@ninebynine.org</email></address>
3717    </author>
3718    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3719      <organization>BEA Systems</organization>
3720      <address><email>mnot@pobox.com</email></address>
3721    </author>
3722    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3723      <organization>HP Labs</organization>
3724      <address><email>JeffMogul@acm.org</email></address>
3725    </author>
3726    <date year='2004' month='September' />
3727  </front>
3728  <seriesInfo name='BCP' value='90' />
3729  <seriesInfo name='RFC' value='3864' />
3730</reference>
3731
3732<reference anchor='RFC3977'>
3733  <front>
3734    <title>Network News Transfer Protocol (NNTP)</title>
3735    <author initials='C.' surname='Feather' fullname='C. Feather'>
3736      <organization>THUS plc</organization>
3737      <address><email>clive@demon.net</email></address>
3738    </author>
3739    <date year='2006' month='October' />
3740  </front>
3741  <seriesInfo name="RFC" value="3977"/>
3742</reference>
3743
3744<reference anchor="RFC4288">
3745  <front>
3746    <title>Media Type Specifications and Registration Procedures</title>
3747    <author initials="N." surname="Freed" fullname="N. Freed">
3748      <organization>Sun Microsystems</organization>
3749      <address>
3750        <email>ned.freed@mrochek.com</email>
3751      </address>
3752    </author>
3753    <author initials="J." surname="Klensin" fullname="J. Klensin">
3754      <organization/>
3755      <address>
3756        <email>klensin+ietf@jck.com</email>
3757      </address>
3758    </author>
3759    <date year="2005" month="December"/>
3760  </front>
3761  <seriesInfo name="BCP" value="13"/>
3762  <seriesInfo name="RFC" value="4288"/>
3763</reference>
3764
3765<reference anchor='RFC4395'>
3766  <front>
3767    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3768    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3769      <organization>AT&amp;T Laboratories</organization>
3770      <address>
3771        <email>tony+urireg@maillennium.att.com</email>
3772      </address>
3773    </author>
3774    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3775      <organization>Qualcomm, Inc.</organization>
3776      <address>
3777        <email>hardie@qualcomm.com</email>
3778      </address>
3779    </author>
3780    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3781      <organization>Adobe Systems</organization>
3782      <address>
3783        <email>LMM@acm.org</email>
3784      </address>
3785    </author>
3786    <date year='2006' month='February' />
3787  </front>
3788  <seriesInfo name='BCP' value='115' />
3789  <seriesInfo name='RFC' value='4395' />
3790</reference>
3791
3792<reference anchor="RFC5322">
3793  <front>
3794    <title>Internet Message Format</title>
3795    <author initials="P." surname="Resnick" fullname="P. Resnick">
3796      <organization>Qualcomm Incorporated</organization>
3797    </author>
3798    <date year="2008" month="October"/>
3799  </front> 
3800  <seriesInfo name="RFC" value="5322"/>
3801</reference>
3802
3803<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3804  <front>
3805    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3806    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3807      <organization/>
3808    </author>
3809    <date year="2001" month="November"/>
3810  </front>
3811  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3812</reference>
3813
3814<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3815  <front>
3816  <title>Analysis of HTTP Performance Problems</title>
3817  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3818    <organization/>
3819  </author>
3820  <date/>
3821  </front>
3822</reference>
3823
3824<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3825  <front>
3826  <title>Analysis of HTTP Performance</title>
3827  <author initials="J." surname="Touch" fullname="Joe Touch">
3828    <organization>USC/Information Sciences Institute</organization>
3829    <address><email>touch@isi.edu</email></address>
3830  </author>
3831  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3832    <organization>USC/Information Sciences Institute</organization>
3833    <address><email>johnh@isi.edu</email></address>
3834  </author>
3835  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3836    <organization>USC/Information Sciences Institute</organization>
3837    <address><email>katia@isi.edu</email></address>
3838  </author>
3839  <date year="1998" month="Aug"/>
3840  </front>
3841  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3842  <annotation>(original report dated Aug. 1996)</annotation>
3843</reference>
3844
3845<reference anchor="WAIS">
3846  <front>
3847    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3848    <author initials="F." surname="Davis" fullname="F. Davis">
3849      <organization>Thinking Machines Corporation</organization>
3850    </author>
3851    <author initials="B." surname="Kahle" fullname="B. Kahle">
3852      <organization>Thinking Machines Corporation</organization>
3853    </author>
3854    <author initials="H." surname="Morris" fullname="H. Morris">
3855      <organization>Thinking Machines Corporation</organization>
3856    </author>
3857    <author initials="J." surname="Salem" fullname="J. Salem">
3858      <organization>Thinking Machines Corporation</organization>
3859    </author>
3860    <author initials="T." surname="Shen" fullname="T. Shen">
3861      <organization>Thinking Machines Corporation</organization>
3862    </author>
3863    <author initials="R." surname="Wang" fullname="R. Wang">
3864      <organization>Thinking Machines Corporation</organization>
3865    </author>
3866    <author initials="J." surname="Sui" fullname="J. Sui">
3867      <organization>Thinking Machines Corporation</organization>
3868    </author>
3869    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3870      <organization>Thinking Machines Corporation</organization>
3871    </author>
3872    <date month="April" year="1990"/>
3873  </front>
3874  <seriesInfo name="Thinking Machines Corporation" value=""/>
3875</reference>
3876
3877</references>
3878
3879
3880<section title="Tolerant Applications" anchor="tolerant.applications">
3881<t>
3882   Although this document specifies the requirements for the generation
3883   of HTTP/1.1 messages, not all applications will be correct in their
3884   implementation. We therefore recommend that operational applications
3885   be tolerant of deviations whenever those deviations can be
3886   interpreted unambiguously.
3887</t>
3888<t>
3889   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3890   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3891   accept any amount of SP or HTAB characters between fields, even though
3892   only a single SP is required.
3893</t>
3894<t>
3895   The line terminator for message-header fields is the sequence CRLF.
3896   However, we recommend that applications, when parsing such headers,
3897   recognize a single LF as a line terminator and ignore the leading CR.
3898</t>
3899<t>
3900   The character set of an entity-body &SHOULD; be labeled as the lowest
3901   common denominator of the character codes used within that body, with
3902   the exception that not labeling the entity is preferred over labeling
3903   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3904</t>
3905<t>
3906   Additional rules for requirements on parsing and encoding of dates
3907   and other potential problems with date encodings include:
3908</t>
3909<t>
3910  <list style="symbols">
3911     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3912        which appears to be more than 50 years in the future is in fact
3913        in the past (this helps solve the "year 2000" problem).</t>
3914
3915     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3916        Expires date as earlier than the proper value, but &MUST-NOT;
3917        internally represent a parsed Expires date as later than the
3918        proper value.</t>
3919
3920     <t>All expiration-related calculations &MUST; be done in GMT. The
3921        local time zone &MUST-NOT; influence the calculation or comparison
3922        of an age or expiration time.</t>
3923
3924     <t>If an HTTP header incorrectly carries a date value with a time
3925        zone other than GMT, it &MUST; be converted into GMT using the
3926        most conservative possible conversion.</t>
3927  </list>
3928</t>
3929</section>
3930
3931<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3932<t>
3933   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3934   simplify the process of date comparison. Proxies and gateways from
3935   other protocols &SHOULD; ensure that any Date header field present in a
3936   message conforms to one of the HTTP/1.1 formats and rewrite the date
3937   if necessary.
3938</t>
3939</section>
3940
3941<section title="Compatibility with Previous Versions" anchor="compatibility">
3942<t>
3943   It is beyond the scope of a protocol specification to mandate
3944   compliance with previous versions. HTTP/1.1 was deliberately
3945   designed, however, to make supporting previous versions easy. It is
3946   worth noting that, at the time of composing this specification
3947   (1996), we would expect commercial HTTP/1.1 servers to:
3948  <list style="symbols">
3949     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3950        1.1 requests;</t>
3951
3952     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3953        1.1;</t>
3954
3955     <t>respond appropriately with a message in the same major version
3956        used by the client.</t>
3957  </list>
3958</t>
3959<t>
3960   And we would expect HTTP/1.1 clients to:
3961  <list style="symbols">
3962     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3963        responses;</t>
3964
3965     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3966        1.1.</t>
3967  </list>
3968</t>
3969<t>
3970   For most implementations of HTTP/1.0, each connection is established
3971   by the client prior to the request and closed by the server after
3972   sending the response. Some implementations implement the Keep-Alive
3973   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3974</t>
3975
3976<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3977<t>
3978   This section summarizes major differences between versions HTTP/1.0
3979   and HTTP/1.1.
3980</t>
3981
3982<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">
3983<t>
3984   The requirements that clients and servers support the Host request-header,
3985   report an error if the Host request-header (<xref target="header.host"/>) is
3986   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3987   are among the most important changes defined by this
3988   specification.
3989</t>
3990<t>
3991   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3992   addresses and servers; there was no other established mechanism for
3993   distinguishing the intended server of a request than the IP address
3994   to which that request was directed. The changes outlined above will
3995   allow the Internet, once older HTTP clients are no longer common, to
3996   support multiple Web sites from a single IP address, greatly
3997   simplifying large operational Web servers, where allocation of many
3998   IP addresses to a single host has created serious problems. The
3999   Internet will also be able to recover the IP addresses that have been
4000   allocated for the sole purpose of allowing special-purpose domain
4001   names to be used in root-level HTTP URLs. Given the rate of growth of
4002   the Web, and the number of servers already deployed, it is extremely
4003   important that all implementations of HTTP (including updates to
4004   existing HTTP/1.0 applications) correctly implement these
4005   requirements:
4006  <list style="symbols">
4007     <t>Both clients and servers &MUST; support the Host request-header.</t>
4008
4009     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4010
4011     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4012        request does not include a Host request-header.</t>
4013
4014     <t>Servers &MUST; accept absolute URIs.</t>
4015  </list>
4016</t>
4017</section>
4018</section>
4019
4020<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4021<t>
4022   Some clients and servers might wish to be compatible with some
4023   previous implementations of persistent connections in HTTP/1.0
4024   clients and servers. Persistent connections in HTTP/1.0 are
4025   explicitly negotiated as they are not the default behavior. HTTP/1.0
4026   experimental implementations of persistent connections are faulty,
4027   and the new facilities in HTTP/1.1 are designed to rectify these
4028   problems. The problem was that some existing 1.0 clients may be
4029   sending Keep-Alive to a proxy server that doesn't understand
4030   Connection, which would then erroneously forward it to the next
4031   inbound server, which would establish the Keep-Alive connection and
4032   result in a hung HTTP/1.0 proxy waiting for the close on the
4033   response. The result is that HTTP/1.0 clients must be prevented from
4034   using Keep-Alive when talking to proxies.
4035</t>
4036<t>
4037   However, talking to proxies is the most important use of persistent
4038   connections, so that prohibition is clearly unacceptable. Therefore,
4039   we need some other mechanism for indicating a persistent connection
4040   is desired, which is safe to use even when talking to an old proxy
4041   that ignores Connection. Persistent connections are the default for
4042   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4043   declaring non-persistence. See <xref target="header.connection"/>.
4044</t>
4045<t>
4046   The original HTTP/1.0 form of persistent connections (the Connection:
4047   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4048</t>
4049</section>
4050
4051<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4052<t>
4053   This specification has been carefully audited to correct and
4054   disambiguate key word usage; RFC 2068 had many problems in respect to
4055   the conventions laid out in <xref target="RFC2119"/>.
4056</t>
4057<t>
4058   Transfer-coding and message lengths all interact in ways that
4059   required fixing exactly when chunked encoding is used (to allow for
4060   transfer encoding that may not be self delimiting); it was important
4061   to straighten out exactly how message lengths are computed. (Sections
4062   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4063   <xref target="header.content-length" format="counter"/>,
4064   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4065</t>
4066<t>
4067   The use and interpretation of HTTP version numbers has been clarified
4068   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4069   version they support to deal with problems discovered in HTTP/1.0
4070   implementations (<xref target="http.version"/>)
4071</t>
4072<t>
4073   Transfer-coding had significant problems, particularly with
4074   interactions with chunked encoding. The solution is that transfer-codings
4075   become as full fledged as content-codings. This involves
4076   adding an IANA registry for transfer-codings (separate from content
4077   codings), a new header field (TE) and enabling trailer headers in the
4078   future. Transfer encoding is a major performance benefit, so it was
4079   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4080   interoperability problem that could have occurred due to interactions
4081   between authentication trailers, chunked encoding and HTTP/1.0
4082   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4083   and <xref target="header.te" format="counter"/>)
4084</t>
4085</section>
4086
4087<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4088<t>
4089  The CHAR rule does not allow the NUL character anymore (this affects
4090  the comment and quoted-string rules).  Furthermore, the quoted-pair
4091  rule does not allow escaping NUL, CR or LF anymore.
4092  (<xref target="basic.rules"/>)
4093</t>
4094<t>
4095  Clarify that HTTP-Version is case sensitive.
4096  (<xref target="http.version"/>)
4097</t>
4098<t>
4099  Remove reference to non-existant identity transfer-coding value tokens.
4100  (Sections <xref format="counter" target="transfer.codings"/> and
4101  <xref format="counter" target="message.length"/>)
4102</t>
4103<t>
4104  Clarification that the chunk length does not include
4105  the count of the octets in the chunk header and trailer.
4106  (<xref target="chunked.transfer.encoding"/>)
4107</t>
4108<t>
4109  Fix BNF to add query, as the abs_path production in
4110  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4111  (<xref target="request-uri"/>)
4112</t>
4113<t>
4114  Clarify exactly when close connection options must be sent.
4115  (<xref target="header.connection"/>)
4116</t>
4117</section>
4118</section>
4119
4120<section title="Terminology" anchor="terminology">
4121<t>
4122   This specification uses a number of terms to refer to the roles
4123   played by participants in, and objects of, the HTTP communication.
4124</t>
4125<t>
4126  <iref item="connection"/>
4127  <x:dfn>connection</x:dfn>
4128  <list>
4129    <t>
4130      A transport layer virtual circuit established between two programs
4131      for the purpose of communication.
4132    </t>
4133  </list>
4134</t>
4135<t>
4136  <iref item="message"/>
4137  <x:dfn>message</x:dfn>
4138  <list>
4139    <t>
4140      The basic unit of HTTP communication, consisting of a structured
4141      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4142      transmitted via the connection.
4143    </t>
4144  </list>
4145</t>
4146<t>
4147  <iref item="request"/>
4148  <x:dfn>request</x:dfn>
4149  <list>
4150    <t>
4151      An HTTP request message, as defined in <xref target="request"/>.
4152    </t>
4153  </list>
4154</t>
4155<t>
4156  <iref item="response"/>
4157  <x:dfn>response</x:dfn>
4158  <list>
4159    <t>
4160      An HTTP response message, as defined in <xref target="response"/>.
4161    </t>
4162  </list>
4163</t>
4164<t>
4165  <iref item="resource"/>
4166  <x:dfn>resource</x:dfn>
4167  <list>
4168    <t>
4169      A network data object or service that can be identified by a URI,
4170      as defined in <xref target="uri"/>. Resources may be available in multiple
4171      representations (e.g. multiple languages, data formats, size, and
4172      resolutions) or vary in other ways.
4173    </t>
4174  </list>
4175</t>
4176<t>
4177  <iref item="entity"/>
4178  <x:dfn>entity</x:dfn>
4179  <list>
4180    <t>
4181      The information transferred as the payload of a request or
4182      response. An entity consists of metainformation in the form of
4183      entity-header fields and content in the form of an entity-body, as
4184      described in &entity;.
4185    </t>
4186  </list>
4187</t>
4188<t>
4189  <iref item="representation"/>
4190  <x:dfn>representation</x:dfn>
4191  <list>
4192    <t>
4193      An entity included with a response that is subject to content
4194      negotiation, as described in &content.negotiation;. There may exist multiple
4195      representations associated with a particular response status.
4196    </t>
4197  </list>
4198</t>
4199<t>
4200  <iref item="content negotiation"/>
4201  <x:dfn>content negotiation</x:dfn>
4202  <list>
4203    <t>
4204      The mechanism for selecting the appropriate representation when
4205      servicing a request, as described in &content.negotiation;. The
4206      representation of entities in any response can be negotiated
4207      (including error responses).
4208    </t>
4209  </list>
4210</t>
4211<t>
4212  <iref item="variant"/>
4213  <x:dfn>variant</x:dfn>
4214  <list>
4215    <t>
4216      A resource may have one, or more than one, representation(s)
4217      associated with it at any given instant. Each of these
4218      representations is termed a `variant'.  Use of the term `variant'
4219      does not necessarily imply that the resource is subject to content
4220      negotiation.
4221    </t>
4222  </list>
4223</t>
4224<t>
4225  <iref item="client"/>
4226  <x:dfn>client</x:dfn>
4227  <list>
4228    <t>
4229      A program that establishes connections for the purpose of sending
4230      requests.
4231    </t>
4232  </list>
4233</t>
4234<t>
4235  <iref item="user agent"/>
4236  <x:dfn>user agent</x:dfn>
4237  <list>
4238    <t>
4239      The client which initiates a request. These are often browsers,
4240      editors, spiders (web-traversing robots), or other end user tools.
4241    </t>
4242  </list>
4243</t>
4244<t>
4245  <iref item="server"/>
4246  <x:dfn>server</x:dfn>
4247  <list>
4248    <t>
4249      An application program that accepts connections in order to
4250      service requests by sending back responses. Any given program may
4251      be capable of being both a client and a server; our use of these
4252      terms refers only to the role being performed by the program for a
4253      particular connection, rather than to the program's capabilities
4254      in general. Likewise, any server may act as an origin server,
4255      proxy, gateway, or tunnel, switching behavior based on the nature
4256      of each request.
4257    </t>
4258  </list>
4259</t>
4260<t>
4261  <iref item="origin server"/>
4262  <x:dfn>origin server</x:dfn>
4263  <list>
4264    <t>
4265      The server on which a given resource resides or is to be created.
4266    </t>
4267  </list>
4268</t>
4269<t>
4270  <iref item="proxy"/>
4271  <x:dfn>proxy</x:dfn>
4272  <list>
4273    <t>
4274      An intermediary program which acts as both a server and a client
4275      for the purpose of making requests on behalf of other clients.
4276      Requests are serviced internally or by passing them on, with
4277      possible translation, to other servers. A proxy &MUST; implement
4278      both the client and server requirements of this specification. A
4279      "transparent proxy" is a proxy that does not modify the request or
4280      response beyond what is required for proxy authentication and
4281      identification. A "non-transparent proxy" is a proxy that modifies
4282      the request or response in order to provide some added service to
4283      the user agent, such as group annotation services, media type
4284      transformation, protocol reduction, or anonymity filtering. Except
4285      where either transparent or non-transparent behavior is explicitly
4286      stated, the HTTP proxy requirements apply to both types of
4287      proxies.
4288    </t>
4289  </list>
4290</t>
4291<t>
4292  <iref item="gateway"/>
4293  <x:dfn>gateway</x:dfn>
4294  <list>
4295    <t>
4296      A server which acts as an intermediary for some other server.
4297      Unlike a proxy, a gateway receives requests as if it were the
4298      origin server for the requested resource; the requesting client
4299      may not be aware that it is communicating with a gateway.
4300    </t>
4301  </list>
4302</t>
4303<t>
4304  <iref item="tunnel"/>
4305  <x:dfn>tunnel</x:dfn>
4306  <list>
4307    <t>
4308      An intermediary program which is acting as a blind relay between
4309      two connections. Once active, a tunnel is not considered a party
4310      to the HTTP communication, though the tunnel may have been
4311      initiated by an HTTP request. The tunnel ceases to exist when both
4312      ends of the relayed connections are closed.
4313    </t>
4314  </list>
4315</t>
4316<t>
4317  <iref item="cache"/>
4318  <x:dfn>cache</x:dfn>
4319  <list>
4320    <t>
4321      A program's local store of response messages and the subsystem
4322      that controls its message storage, retrieval, and deletion. A
4323      cache stores cacheable responses in order to reduce the response
4324      time and network bandwidth consumption on future, equivalent
4325      requests. Any client or server may include a cache, though a cache
4326      cannot be used by a server that is acting as a tunnel.
4327    </t>
4328  </list>
4329</t>
4330<t>
4331  <iref item="cacheable"/>
4332  <x:dfn>cacheable</x:dfn>
4333  <list>
4334    <t>
4335      A response is cacheable if a cache is allowed to store a copy of
4336      the response message for use in answering subsequent requests. The
4337      rules for determining the cacheability of HTTP responses are
4338      defined in &caching;. Even if a resource is cacheable, there may
4339      be additional constraints on whether a cache can use the cached
4340      copy for a particular request.
4341    </t>
4342  </list>
4343</t>
4344<t>
4345  <iref item="upstream"/>
4346  <iref item="downstream"/>
4347  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4348  <list>
4349    <t>
4350      Upstream and downstream describe the flow of a message: all
4351      messages flow from upstream to downstream.
4352    </t>
4353  </list>
4354</t>
4355<t>
4356  <iref item="inbound"/>
4357  <iref item="outbound"/>
4358  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4359  <list>
4360    <t>
4361      Inbound and outbound refer to the request and response paths for
4362      messages: "inbound" means "traveling toward the origin server",
4363      and "outbound" means "traveling toward the user agent"
4364    </t>
4365  </list>
4366</t>
4367</section>
4368
4369<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4370
4371<section title="Since RFC2616">
4372<t>
4373  Extracted relevant partitions from <xref target="RFC2616"/>.
4374</t>
4375</section>
4376
4377<section title="Since draft-ietf-httpbis-p1-messaging-00">
4378<t>
4379  Closed issues:
4380  <list style="symbols"> 
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4383      "HTTP Version should be case sensitive"
4384      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4385    </t>
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4388      "'unsafe' characters"
4389      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4390    </t>
4391    <t>
4392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4393      "Chunk Size Definition"
4394      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4395    </t>
4396    <t>
4397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4398      "Message Length"
4399      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4403      "Media Type Registrations"
4404      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4408      "URI includes query"
4409      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4410    </t>
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4413      "No close on 1xx responses"
4414      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4415    </t>
4416    <t>
4417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4418      "Remove 'identity' token references"
4419      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4420    </t>
4421    <t>
4422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4423      "Import query BNF"
4424    </t>
4425    <t>
4426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4427      "qdtext BNF"
4428    </t>
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4431      "Normative and Informative references"
4432    </t>
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4435      "RFC2606 Compliance"
4436    </t>
4437    <t>
4438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4439      "RFC977 reference"
4440    </t>
4441    <t>
4442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4443      "RFC1700 references"
4444    </t>
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4447      "inconsistency in date format explanation"
4448    </t>
4449    <t>
4450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4451      "Date reference typo"
4452    </t>
4453    <t>
4454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4455      "Informative references"
4456    </t>
4457    <t>
4458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4459      "ISO-8859-1 Reference"
4460    </t>
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4463      "Normative up-to-date references"
4464    </t>
4465  </list>
4466</t>
4467<t>
4468  Other changes:
4469  <list style="symbols"> 
4470    <t>
4471      Update media type registrations to use RFC4288 template.
4472    </t>
4473    <t>
4474      Use names of RFC4234 core rules DQUOTE and HTAB,
4475      fix broken ABNF for chunk-data
4476      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4477    </t>
4478  </list>
4479</t>
4480</section>
4481
4482<section title="Since draft-ietf-httpbis-p1-messaging-01">
4483<t>
4484  Closed issues:
4485  <list style="symbols"> 
4486    <t>
4487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4488      "Bodies on GET (and other) requests"
4489    </t>
4490    <t>
4491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4492      "Updating to RFC4288"
4493    </t>
4494    <t>
4495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4496      "Status Code and Reason Phrase"
4497    </t>
4498    <t>
4499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4500      "rel_path not used"
4501    </t>
4502  </list>
4503</t>
4504<t>
4505  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4506  <list style="symbols"> 
4507    <t>
4508      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4509      "trailer-part").
4510    </t>
4511    <t>
4512      Avoid underscore character in rule names ("http_URL" ->
4513      "http-URL", "abs_path" -> "path-absolute").
4514    </t>
4515    <t>
4516      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4517      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4518      have to be updated when switching over to RFC3986.
4519    </t>
4520    <t>
4521      Synchronize core rules with RFC5234 (this includes a change to CHAR
4522      which now excludes NUL).
4523    </t>
4524    <t>
4525      Get rid of prose rules that span multiple lines.
4526    </t>
4527    <t>
4528      Get rid of unused rules LOALPHA and UPALPHA.
4529    </t>
4530    <t>
4531      Move "Product Tokens" section (back) into Part 1, as "token" is used
4532      in the definition of the Upgrade header.
4533    </t>
4534    <t>
4535      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4536    </t>
4537    <t>
4538      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4539    </t>
4540  </list>
4541</t>
4542</section>
4543
4544<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4545<t>
4546  Closed issues:
4547  <list style="symbols"> 
4548    <t>
4549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4550      "HTTP-date vs. rfc1123-date"
4551    </t>
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4554      "WS in quoted-pair"
4555    </t>
4556  </list>
4557</t>
4558<t>
4559  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4560  <list style="symbols"> 
4561    <t>
4562      Reference RFC 3984, and update header registrations for headers defined
4563      in this document.
4564    </t>
4565  </list>
4566</t>
4567<t>
4568  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4569  <list style="symbols"> 
4570    <t>
4571      Replace string literals when the string really is case-sensitive (HTTP-Version).
4572    </t>
4573  </list>
4574</t>
4575</section>
4576
4577<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4578<t>
4579  Closed issues:
4580  <list style="symbols"> 
4581    <t>
4582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4583      "Connection closing"
4584    </t>
4585    <t>
4586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4587      "Move registrations and registry information to IANA Considerations"
4588    </t>
4589    <t>
4590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4591      "need new URL for PAD1995 reference"
4592    </t>
4593    <t>
4594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4595      "IANA Considerations: update HTTP URI scheme registration"
4596    </t>
4597    <t>
4598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4599      "Cite HTTPS URI scheme definition"
4600    </t>
4601    <t>
4602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4603      "List-type headers vs Set-Cookie"
4604    </t>
4605  </list>
4606</t>
4607<t>
4608  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4609  <list style="symbols"> 
4610    <t>
4611      Replace string literals when the string really is case-sensitive (HTTP-Date).
4612    </t>
4613    <t>
4614      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4615    </t>
4616  </list>
4617</t>
4618</section>
4619
4620<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4621<t>
4622  Closed issues:
4623  <list style="symbols"> 
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4626      "RFC 2822 is updated by RFC 5322"
4627    </t>
4628  </list>
4629</t>
4630<t>
4631  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4632  <list style="symbols"> 
4633    <t>
4634      Use "/" instead of "|" for alternatives.
4635    </t>
4636    <t>
4637      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4638    </t>
4639    <t>
4640      Only reference RFC 5234's core rules.
4641    </t>
4642    <t>
4643      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4644      whitespace ("OWS") and required whitespace ("RWS"), but do not use
4645      them yet.
4646    </t>
4647  </list>
4648</t>
4649</section>
4650
4651</section>
4652
4653</back>
4654</rfc>
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