source: draft-ietf-httpbis/latest/p1-messaging.xml @ 346

Last change on this file since 346 was 346, checked in by julian.reschke@…, 11 years ago

Move Terminology Section to the back.

  • Property svn:eol-style set to native
File size: 200.6 KB
Line 
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="Augmented BNF" anchor="notation.abnf">
421<t>
422   All of the mechanisms specified in this document are described in
423   both prose and an augmented Backus-Naur Form (ABNF) based on that
424   defined in <xref target="RFC5234"/>. Implementors will need to be
425   familiar with the notation in order to understand this specification. The
426   extensions to ABNF used in this specification are described below.
427</t>
428
429<section title="#rule">
430  <t>
431    A construct "#" is defined, similar to "*", for defining lists of
432    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
433    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
434    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
435    form of lists very easy; a rule such as
436    <figure><artwork type="example">
437 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
438  </t>
439  <t>
440    can be shown as
441    <figure><artwork type="example">
442 1#element</artwork></figure>
443  </t>
444  <t>
445    Wherever this construct is used, null elements are allowed, but do
446    not contribute to the count of elements present. That is,
447    "(element), , (element) " is permitted, but counts as only two
448    elements. Therefore, where at least one element is required, at
449    least one non-null element &MUST; be present. Default values are 0
450    and infinity so that "#element" allows any number, including zero;
451    "1#element" requires at least one; and "1#2element" allows one or
452    two.
453  </t>
454</section>
455
456<section title="implied *LWS" anchor="implied.LWS">
457  <iref item="implied *LWS" primary="true"/>
458    <t>
459      The grammar described by this specification is word-based. Except
460      where noted otherwise, linear white space (LWS) can be included
461      between any two adjacent words (token or quoted-string), and
462      between adjacent words and separators, without changing the
463      interpretation of a field. At least one delimiter (LWS and/or
464      separators) &MUST; exist between any two tokens (for the definition
465      of "token" below), since they would otherwise be interpreted as a
466      single token.
467    </t>
468</section>
469</section>
470
471<section title="Basic Rules" anchor="basic.rules">
472<t anchor="core.rules">
473  <x:anchor-alias value="OCTET"/>
474  <x:anchor-alias value="CHAR"/>
475  <x:anchor-alias value="ALPHA"/>
476  <x:anchor-alias value="DIGIT"/>
477  <x:anchor-alias value="CTL"/>
478  <x:anchor-alias value="CR"/>
479  <x:anchor-alias value="LF"/>
480  <x:anchor-alias value="SP"/>
481  <x:anchor-alias value="HTAB"/>
482  <x:anchor-alias value="DQUOTE"/>
483   The following rules are used throughout this specification to
484   describe basic parsing constructs. The US-ASCII coded character set
485   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
486</t>
487<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="ALPHA"/><iref primary="true" item="Grammar" subitem="DIGIT"/><iref primary="true" item="Grammar" subitem="CTL"/><iref primary="true" item="Grammar" subitem="CR"/><iref primary="true" item="Grammar" subitem="LF"/><iref primary="true" item="Grammar" subitem="SP"/><iref primary="true" item="Grammar" subitem="HTAB"/><iref primary="true" item="Grammar" subitem="DQUOTE"/>
488  <x:ref>OCTET</x:ref>          = %x00-FF
489                   ; any 8-bit sequence of data
490  <x:ref>CHAR</x:ref>           = %x01-7F
491                   ; any US-ASCII character, excluding NUL
492  <x:ref>ALPHA</x:ref>          = %x41-5A / %x61-7A
493                   ; A-Z / a-z
494  <x:ref>DIGIT</x:ref>          = %x30-39
495                   ; any US-ASCII digit "0".."9"
496  <x:ref>CTL</x:ref>            = %x00-1F / %x7F
497                   ; (octets 0 - 31) and DEL (127)
498  <x:ref>CR</x:ref>             = %x0D
499                   ; US-ASCII CR, carriage return (13)
500  <x:ref>LF</x:ref>             = %x0A
501                   ; US-ASCII LF, linefeed (10)
502  <x:ref>SP</x:ref>             = %x20
503                   ; US-ASCII SP, space (32)
504  <x:ref>HTAB</x:ref>           = %x09
505                   ; US-ASCII HT, horizontal-tab (9)
506  <x:ref>DQUOTE</x:ref>         = %x22
507                   ; US-ASCII double-quote mark (34)
508</artwork></figure>
509<t anchor="rule.CRLF">
510  <x:anchor-alias value="CRLF"/>
511   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
512   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
513   tolerant applications). The end-of-line marker within an entity-body
514   is defined by its associated media type, as described in &media-types;.
515</t>
516<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
517  <x:ref>CRLF</x:ref>           = <x:ref>CR</x:ref> LF
518</artwork></figure>
519<t anchor="rule.LWS">
520  <x:anchor-alias value="LWS"/>
521   HTTP/1.1 header field values can be folded onto multiple lines if the
522   continuation line begins with a space or horizontal tab. All linear
523   white space, including folding, has the same semantics as SP. A
524   recipient &MAY; replace any linear white space with a single SP before
525   interpreting the field value or forwarding the message downstream.
526</t>
527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
528  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
529</artwork></figure>
530<t anchor="rule.TEXT">
531  <x:anchor-alias value="TEXT"/>
532   The TEXT rule is only used for descriptive field contents and values
533   that are not intended to be interpreted by the message parser. Words
534   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
535   <xref target="ISO-8859-1"/> only when encoded according to the rules of
536   <xref target="RFC2047"/>.
537</t>
538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
539  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
540                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
541</artwork></figure>
542<t>
543   A CRLF is allowed in the definition of TEXT only as part of a header
544   field continuation. It is expected that the folding LWS will be
545   replaced with a single SP before interpretation of the TEXT value.
546</t>
547<t anchor="rule.HEXDIG">
548  <x:anchor-alias value="HEXDIG"/>
549   Hexadecimal numeric characters are used in several protocol elements.
550</t>
551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEXDIG"/>
552  <x:ref>HEXDIG</x:ref>         = "A" / "B" / "C" / "D" / "E" / "F"
553                 / "a" / "b" / "c" / "d" / "e" / "f" / <x:ref>DIGIT</x:ref>
554</artwork></figure>
555<t anchor="rule.token.separators">
556  <x:anchor-alias value="tchar"/>
557  <x:anchor-alias value="token"/>
558  <x:anchor-alias value="separators"/>
559   Many HTTP/1.1 header field values consist of words separated by LWS
560   or special characters. These special characters &MUST; be in a quoted
561   string to be used within a parameter value (as defined in
562   <xref target="transfer.codings"/>).
563</t>
564<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"/>
565  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
566                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
567                 / "/" / "[" / "]" / "?" / "="
568                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
569                 
570  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
571                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
572                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
573                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
574                 
575  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
576</artwork></figure>
577<t anchor="rule.comment">
578  <x:anchor-alias value="comment"/>
579  <x:anchor-alias value="ctext"/>
580   Comments can be included in some HTTP header fields by surrounding
581   the comment text with parentheses. Comments are only allowed in
582   fields containing "comment" as part of their field value definition.
583   In all other fields, parentheses are considered part of the field
584   value.
585</t>
586<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
587  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
588  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
589</artwork></figure>
590<t anchor="rule.quoted-string">
591  <x:anchor-alias value="quoted-string"/>
592  <x:anchor-alias value="qdtext"/>
593   A string of text is parsed as a single word if it is quoted using
594   double-quote marks.
595</t>
596<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
597  <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> )
598  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
599</artwork></figure>
600<t anchor="rule.quoted-pair">
601  <x:anchor-alias value="quoted-pair"/>
602  <x:anchor-alias value="quoted-text"/>
603   The backslash character ("\") &MAY; be used as a single-character
604   quoting mechanism only within quoted-string and comment constructs.
605</t>
606<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
607  <x:ref>quoted-text</x:ref>    = %x01-09 /
608                   %x0B-0C /
609                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
610  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
611</artwork></figure>
612</section>
613
614<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
615  <x:anchor-alias value="request-header"/>
616  <x:anchor-alias value="response-header"/>
617  <x:anchor-alias value="accept-params"/>
618  <x:anchor-alias value="entity-body"/>
619  <x:anchor-alias value="entity-header"/>
620  <x:anchor-alias value="Cache-Control"/>
621  <x:anchor-alias value="Pragma"/>
622  <x:anchor-alias value="Warning"/>
623<t>
624  The ABNF rules below are defined in other parts:
625</t>
626<figure><!-- Part2--><artwork type="abnf2616">
627  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
628  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
629</artwork></figure>
630<figure><!-- Part3--><artwork type="abnf2616">
631  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
632  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
633  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
634</artwork></figure>
635<figure><!-- Part6--><artwork type="abnf2616">
636  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
637  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
638  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
639</artwork></figure>
640</section>
641
642</section>
643
644<section title="Protocol Parameters" anchor="protocol.parameters">
645
646<section title="HTTP Version" anchor="http.version">
647  <x:anchor-alias value="HTTP-Version"/>
648  <x:anchor-alias value="HTTP-Prot-Name"/>
649<t>
650   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
651   of the protocol. The protocol versioning policy is intended to allow
652   the sender to indicate the format of a message and its capacity for
653   understanding further HTTP communication, rather than the features
654   obtained via that communication. No change is made to the version
655   number for the addition of message components which do not affect
656   communication behavior or which only add to extensible field values.
657   The &lt;minor&gt; number is incremented when the changes made to the
658   protocol add features which do not change the general message parsing
659   algorithm, but which may add to the message semantics and imply
660   additional capabilities of the sender. The &lt;major&gt; number is
661   incremented when the format of a message within the protocol is
662   changed. See <xref target="RFC2145"/> for a fuller explanation.
663</t>
664<t>
665   The version of an HTTP message is indicated by an HTTP-Version field
666   in the first line of the message. HTTP-Version is case-sensitive.
667</t>
668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
669  <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>
670  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
671</artwork></figure>
672<t>
673   Note that the major and minor numbers &MUST; be treated as separate
674   integers and that each &MAY; be incremented higher than a single digit.
675   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
676   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
677   &MUST-NOT; be sent.
678</t>
679<t>
680   An application that sends a request or response message that includes
681   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
682   with this specification. Applications that are at least conditionally
683   compliant with this specification &SHOULD; use an HTTP-Version of
684   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
685   not compatible with HTTP/1.0. For more details on when to send
686   specific HTTP-Version values, see <xref target="RFC2145"/>.
687</t>
688<t>
689   The HTTP version of an application is the highest HTTP version for
690   which the application is at least conditionally compliant.
691</t>
692<t>
693   Proxy and gateway applications need to be careful when forwarding
694   messages in protocol versions different from that of the application.
695   Since the protocol version indicates the protocol capability of the
696   sender, a proxy/gateway &MUST-NOT; send a message with a version
697   indicator which is greater than its actual version. If a higher
698   version request is received, the proxy/gateway &MUST; either downgrade
699   the request version, or respond with an error, or switch to tunnel
700   behavior.
701</t>
702<t>
703   Due to interoperability problems with HTTP/1.0 proxies discovered
704   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
705   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
706   they support. The proxy/gateway's response to that request &MUST; be in
707   the same major version as the request.
708</t>
709<t>
710  <list>
711    <t>
712      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
713      of header fields required or forbidden by the versions involved.
714    </t>
715  </list>
716</t>
717</section>
718
719<section title="Uniform Resource Identifiers" anchor="uri">
720<t>
721   URIs have been known by many names: WWW addresses, Universal Document
722   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
723   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
724   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
725   simply formatted strings which identify--via name, location, or any
726   other characteristic--a resource.
727</t>
728
729<section title="General Syntax" anchor="general.syntax">
730  <x:anchor-alias value="absoluteURI"/>
731  <x:anchor-alias value="authority"/>
732  <x:anchor-alias value="fragment"/>
733  <x:anchor-alias value="path-absolute"/>
734  <x:anchor-alias value="port"/>
735  <x:anchor-alias value="query"/>
736  <x:anchor-alias value="relativeURI"/>
737  <x:anchor-alias value="uri-host"/>
738<t>
739   URIs in HTTP can be represented in absolute form or relative to some
740   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
741   forms are differentiated by the fact that absolute URIs always begin
742   with a scheme name followed by a colon. For definitive information on
743   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
744   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
745   and <xref target="RFC1808"/>). This specification adopts the
746   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
747   "host", "abs_path", "query", and "authority" from that specification:
748</t>
749<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"/>
750  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
751  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
752  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
753  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
754  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
755  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
756  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
757  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
758</artwork></figure>
759<t>
760   HTTP does not place any a priori limit on the length of
761   a URI. Servers &MUST; be able to handle the URI of any resource they
762   serve, and &SHOULD; be able to handle URIs of unbounded length if they
763   provide GET-based forms that could generate such URIs. A server
764   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
765   than the server can handle (see &status-414;).
766</t>
767<t>
768  <list>
769    <t>
770      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
771      above 255 bytes, because some older client or proxy
772      implementations might not properly support these lengths.
773    </t>
774  </list>
775</t>
776</section>
777
778<section title="http URL" anchor="http.url">
779  <x:anchor-alias value="http-URL"/>
780  <iref item="http URI scheme" primary="true"/>
781  <iref item="URI scheme" subitem="http" primary="true"/>
782<t>
783   The "http" scheme is used to locate network resources via the HTTP
784   protocol. This section defines the scheme-specific syntax and
785   semantics for http URLs.
786</t>
787<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
788  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
789             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
790</artwork></figure>
791<t>
792   If the port is empty or not given, port 80 is assumed. The semantics
793   are that the identified resource is located at the server listening
794   for TCP connections on that port of that host, and the Request-URI
795   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
796   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
797   the path-absolute is not present in the URL, it &MUST; be given as "/" when
798   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
799   receives a host name which is not a fully qualified domain name, it
800   &MAY; add its domain to the host name it received. If a proxy receives
801   a fully qualified domain name, the proxy &MUST-NOT; change the host
802   name.
803</t>
804<t><list><t>
805  <iref item="https URI scheme"/>
806  <iref item="URI scheme" subitem="https"/>
807  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
808</t></list></t>
809</section>
810
811<section title="URI Comparison" anchor="uri.comparison">
812<t>
813   When comparing two URIs to decide if they match or not, a client
814   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
815   URIs, with these exceptions:
816  <list style="symbols">
817    <t>A port that is empty or not given is equivalent to the default
818        port for that URI-reference;</t>
819    <t>Comparisons of host names &MUST; be case-insensitive;</t>
820    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
821    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
822  </list>
823</t>
824<t>
825   Characters other than those in the "reserved" set (see
826   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
827   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
828</t>
829<t>
830   For example, the following three URIs are equivalent:
831</t>
832<figure><artwork type="example">
833   http://example.com:80/~smith/home.html
834   http://EXAMPLE.com/%7Esmith/home.html
835   http://EXAMPLE.com:/%7esmith/home.html
836</artwork></figure>
837</section>
838</section>
839
840<section title="Date/Time Formats" anchor="date.time.formats">
841<section title="Full Date" anchor="full.date">
842  <x:anchor-alias value="HTTP-date"/>
843  <x:anchor-alias value="obsolete-date"/>
844  <x:anchor-alias value="rfc1123-date"/>
845  <x:anchor-alias value="rfc850-date"/>
846  <x:anchor-alias value="asctime-date"/>
847  <x:anchor-alias value="date1"/>
848  <x:anchor-alias value="date2"/>
849  <x:anchor-alias value="date3"/>
850  <x:anchor-alias value="rfc1123-date"/>
851  <x:anchor-alias value="time"/>
852  <x:anchor-alias value="wkday"/>
853  <x:anchor-alias value="weekday"/>
854  <x:anchor-alias value="month"/>
855<t>
856   HTTP applications have historically allowed three different formats
857   for the representation of date/time stamps:
858</t>
859<figure><artwork type="example">
860   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
861   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
862   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
863</artwork></figure>
864<t>
865   The first format is preferred as an Internet standard and represents
866   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
867   <xref target="RFC822"/>). The other formats are described here only for
868   compatibility with obsolete implementations.
869   HTTP/1.1 clients and servers that parse the date value &MUST; accept
870   all three formats (for compatibility with HTTP/1.0), though they &MUST;
871   only generate the RFC 1123 format for representing HTTP-date values
872   in header fields. See <xref target="tolerant.applications"/> for further information.
873</t>
874<t><list><t>
875      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
876      accepting date values that may have been sent by non-HTTP
877      applications, as is sometimes the case when retrieving or posting
878      messages via proxies/gateways to SMTP or NNTP.
879</t></list></t>
880<t>
881   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
882   (GMT), without exception. For the purposes of HTTP, GMT is exactly
883   equal to UTC (Coordinated Universal Time). This is indicated in the
884   first two formats by the inclusion of "GMT" as the three-letter
885   abbreviation for time zone, and &MUST; be assumed when reading the
886   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
887   additional LWS beyond that specifically included as SP in the
888   grammar.
889</t>
890<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"/>
891  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
892  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
893  <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
894  <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
895  <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>
896  <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>
897                 ; day month year (e.g., 02 Jun 1982)
898  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
899                 ; day-month-year (e.g., 02-Jun-82)
900  <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> ))
901                 ; month day (e.g., Jun  2)
902  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
903                 ; 00:00:00 - 23:59:59
904  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
905               / s-Thu / s-Fri / s-Sat / s-Sun
906  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
907               / l-Thu / l-Fri / l-Sat / l-Sun
908  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
909               / s-May / s-Jun / s-Jul / s-Aug
910               / s-Sep / s-Oct / s-Nov / s-Dec
911               
912  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
913
914  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
915  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
916  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
917  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
918  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
919  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
920  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
921
922  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
923  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
924  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
925  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
926  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
927  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
928  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
929
930  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
931  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
932  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
933  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
934  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
935  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
936  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
937  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
938  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
939  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
940  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
941  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
942</artwork></figure>
943<t>
944      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
945      to their usage within the protocol stream. Clients and servers are
946      not required to use these formats for user presentation, request
947      logging, etc.
948</t>
949</section>
950</section>
951
952<section title="Transfer Codings" anchor="transfer.codings">
953  <x:anchor-alias value="parameter"/>
954  <x:anchor-alias value="transfer-coding"/>
955  <x:anchor-alias value="transfer-extension"/>
956<t>
957   Transfer-coding values are used to indicate an encoding
958   transformation that has been, can be, or may need to be applied to an
959   entity-body in order to ensure "safe transport" through the network.
960   This differs from a content coding in that the transfer-coding is a
961   property of the message, not of the original entity.
962</t>
963<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
964  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
965  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
966</artwork></figure>
967<t anchor="rule.parameter">
968  <x:anchor-alias value="attribute"/>
969  <x:anchor-alias value="parameter"/>
970  <x:anchor-alias value="value"/>
971   Parameters are in  the form of attribute/value pairs.
972</t>
973<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"/>
974  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
975  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
976  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
977</artwork></figure>
978<t>
979   All transfer-coding values are case-insensitive. HTTP/1.1 uses
980   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
981   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
982</t>
983<t>
984   Whenever a transfer-coding is applied to a message-body, the set of
985   transfer-codings &MUST; include "chunked", unless the message indicates it
986   is terminated by closing the connection. When the "chunked" transfer-coding
987   is used, it &MUST; be the last transfer-coding applied to the
988   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
989   than once to a message-body. These rules allow the recipient to
990   determine the transfer-length of the message (<xref target="message.length"/>).
991</t>
992<t>
993   Transfer-codings are analogous to the Content-Transfer-Encoding
994   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
995   binary data over a 7-bit transport service. However, safe transport
996   has a different focus for an 8bit-clean transfer protocol. In HTTP,
997   the only unsafe characteristic of message-bodies is the difficulty in
998   determining the exact body length (<xref target="message.length"/>), or the desire to
999   encrypt data over a shared transport.
1000</t>
1001<t>
1002   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1003   transfer-coding value tokens. Initially, the registry contains the
1004   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1005   "gzip", "compress", and "deflate" (&content-codings;).
1006</t>
1007<t>
1008   New transfer-coding value tokens &SHOULD; be registered in the same way
1009   as new content-coding value tokens (&content-codings;).
1010</t>
1011<t>
1012   A server which receives an entity-body with a transfer-coding it does
1013   not understand &SHOULD; return 501 (Not Implemented), and close the
1014   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1015   client.
1016</t>
1017
1018<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1019  <x:anchor-alias value="chunk"/>
1020  <x:anchor-alias value="Chunked-Body"/>
1021  <x:anchor-alias value="chunk-data"/>
1022  <x:anchor-alias value="chunk-extension"/>
1023  <x:anchor-alias value="chunk-ext-name"/>
1024  <x:anchor-alias value="chunk-ext-val"/>
1025  <x:anchor-alias value="chunk-size"/>
1026  <x:anchor-alias value="last-chunk"/>
1027  <x:anchor-alias value="trailer-part"/>
1028<t>
1029   The chunked encoding modifies the body of a message in order to
1030   transfer it as a series of chunks, each with its own size indicator,
1031   followed by an &OPTIONAL; trailer containing entity-header fields. This
1032   allows dynamically produced content to be transferred along with the
1033   information necessary for the recipient to verify that it has
1034   received the full message.
1035</t>
1036<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"/>
1037  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1038                   <x:ref>last-chunk</x:ref>
1039                   <x:ref>trailer-part</x:ref>
1040                   <x:ref>CRLF</x:ref>
1041 
1042  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1043                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1044  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1045  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1046 
1047  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1048  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1049  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1050  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1051  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1052</artwork></figure>
1053<t>
1054   The chunk-size field is a string of hex digits indicating the size of
1055   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1056   zero, followed by the trailer, which is terminated by an empty line.
1057</t>
1058<t>
1059   The trailer allows the sender to include additional HTTP header
1060   fields at the end of the message. The Trailer header field can be
1061   used to indicate which header fields are included in a trailer (see
1062   <xref target="header.trailer"/>).
1063</t>
1064<t>
1065   A server using chunked transfer-coding in a response &MUST-NOT; use the
1066   trailer for any header fields unless at least one of the following is
1067   true:
1068  <list style="numbers">
1069    <t>the request included a TE header field that indicates "trailers" is
1070     acceptable in the transfer-coding of the  response, as described in
1071     <xref target="header.te"/>; or,</t>
1072
1073    <t>the server is the origin server for the response, the trailer
1074     fields consist entirely of optional metadata, and the recipient
1075     could use the message (in a manner acceptable to the origin server)
1076     without receiving this metadata.  In other words, the origin server
1077     is willing to accept the possibility that the trailer fields might
1078     be silently discarded along the path to the client.</t>
1079  </list>
1080</t>
1081<t>
1082   This requirement prevents an interoperability failure when the
1083   message is being received by an HTTP/1.1 (or later) proxy and
1084   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1085   compliance with the protocol would have necessitated a possibly
1086   infinite buffer on the proxy.
1087</t>
1088<t>
1089   A process for decoding the "chunked" transfer-coding
1090   can be represented in pseudo-code as:
1091</t>
1092<figure><artwork type="code">
1093    length := 0
1094    read chunk-size, chunk-extension (if any) and CRLF
1095    while (chunk-size &gt; 0) {
1096       read chunk-data and CRLF
1097       append chunk-data to entity-body
1098       length := length + chunk-size
1099       read chunk-size and CRLF
1100    }
1101    read entity-header
1102    while (entity-header not empty) {
1103       append entity-header to existing header fields
1104       read entity-header
1105    }
1106    Content-Length := length
1107    Remove "chunked" from Transfer-Encoding
1108</artwork></figure>
1109<t>
1110   All HTTP/1.1 applications &MUST; be able to receive and decode the
1111   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1112   they do not understand.
1113</t>
1114</section>
1115</section>
1116
1117<section title="Product Tokens" anchor="product.tokens">
1118  <x:anchor-alias value="product"/>
1119  <x:anchor-alias value="product-version"/>
1120<t>
1121   Product tokens are used to allow communicating applications to
1122   identify themselves by software name and version. Most fields using
1123   product tokens also allow sub-products which form a significant part
1124   of the application to be listed, separated by white space. By
1125   convention, the products are listed in order of their significance
1126   for identifying the application.
1127</t>
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1129  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1130  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1131</artwork></figure>
1132<t>
1133   Examples:
1134</t>
1135<figure><artwork type="example">
1136    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1137    Server: Apache/0.8.4
1138</artwork></figure>
1139<t>
1140   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1141   used for advertising or other non-essential information. Although any
1142   token character &MAY; appear in a product-version, this token &SHOULD;
1143   only be used for a version identifier (i.e., successive versions of
1144   the same product &SHOULD; only differ in the product-version portion of
1145   the product value).
1146</t>
1147</section>
1148
1149</section>
1150
1151<section title="HTTP Message" anchor="http.message">
1152
1153<section title="Message Types" anchor="message.types">
1154  <x:anchor-alias value="generic-message"/>
1155  <x:anchor-alias value="HTTP-message"/>
1156  <x:anchor-alias value="start-line"/>
1157<t>
1158   HTTP messages consist of requests from client to server and responses
1159   from server to client.
1160</t>
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1162  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1163</artwork></figure>
1164<t>
1165   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1166   message format of <xref target="RFC5322"/> for transferring entities (the payload
1167   of the message). Both types of message consist of a start-line, zero
1168   or more header fields (also known as "headers"), an empty line (i.e.,
1169   a line with nothing preceding the CRLF) indicating the end of the
1170   header fields, and possibly a message-body.
1171</t>
1172<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1173  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1174                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1175                    <x:ref>CRLF</x:ref>
1176                    [ <x:ref>message-body</x:ref> ]
1177  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1178</artwork></figure>
1179<t>
1180   In the interest of robustness, servers &SHOULD; ignore any empty
1181   line(s) received where a Request-Line is expected. In other words, if
1182   the server is reading the protocol stream at the beginning of a
1183   message and receives a CRLF first, it should ignore the CRLF.
1184</t>
1185<t>
1186   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1187   after a POST request. To restate what is explicitly forbidden by the
1188   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1189   extra CRLF.
1190</t>
1191</section>
1192
1193<section title="Message Headers" anchor="message.headers">
1194  <x:anchor-alias value="field-content"/>
1195  <x:anchor-alias value="field-name"/>
1196  <x:anchor-alias value="field-value"/>
1197  <x:anchor-alias value="message-header"/>
1198<t>
1199   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1200   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1201   entity-header (&entity-header-fields;) fields, follow the same generic format as
1202   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1203   of a name followed by a colon (":") and the field value. Field names
1204   are case-insensitive. The field value &MAY; be preceded by any amount
1205   of LWS, though a single SP is preferred. Header fields can be
1206   extended over multiple lines by preceding each extra line with at
1207   least one SP or HTAB. Applications ought to follow "common form", where
1208   one is known or indicated, when generating HTTP constructs, since
1209   there might exist some implementations that fail to accept anything
1210   beyond the common forms.
1211</t>
1212<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"/>
1213  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1214  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1215  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1216  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1217                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1218                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1219                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1220</artwork></figure>
1221<t>
1222   The field-content does not include any leading or trailing LWS:
1223   linear white space occurring before the first non-whitespace
1224   character of the field-value or after the last non-whitespace
1225   character of the field-value. Such leading or trailing LWS &MAY; be
1226   removed without changing the semantics of the field value. Any LWS
1227   that occurs between field-content &MAY; be replaced with a single SP
1228   before interpreting the field value or forwarding the message
1229   downstream.
1230</t>
1231<t>
1232   The order in which header fields with differing field names are
1233   received is not significant. However, it is "good practice" to send
1234   general-header fields first, followed by request-header or response-header
1235   fields, and ending with the entity-header fields.
1236</t>
1237<t>
1238   Multiple message-header fields with the same field-name &MAY; be
1239   present in a message if and only if the entire field-value for that
1240   header field is defined as a comma-separated list [i.e., #(values)].
1241   It &MUST; be possible to combine the multiple header fields into one
1242   "field-name: field-value" pair, without changing the semantics of the
1243   message, by appending each subsequent field-value to the first, each
1244   separated by a comma. The order in which header fields with the same
1245   field-name are received is therefore significant to the
1246   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1247   change the order of these field values when a message is forwarded.
1248</t>
1249<t>
1250  <list><t>
1251   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1252   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1253   can occur multiple times, but does not use the list syntax, and thus cannot
1254   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1255   for details.) Also note that the Set-Cookie2 header specified in
1256   <xref target="RFC2965"/> does not share this problem.
1257  </t></list>
1258</t>
1259 
1260</section>
1261
1262<section title="Message Body" anchor="message.body">
1263  <x:anchor-alias value="message-body"/>
1264<t>
1265   The message-body (if any) of an HTTP message is used to carry the
1266   entity-body associated with the request or response. The message-body
1267   differs from the entity-body only when a transfer-coding has been
1268   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1269</t>
1270<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1271  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1272               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1273</artwork></figure>
1274<t>
1275   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1276   applied by an application to ensure safe and proper transfer of the
1277   message. Transfer-Encoding is a property of the message, not of the
1278   entity, and thus &MAY; be added or removed by any application along the
1279   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1280   when certain transfer-codings may be used.)
1281</t>
1282<t>
1283   The rules for when a message-body is allowed in a message differ for
1284   requests and responses.
1285</t>
1286<t>
1287   The presence of a message-body in a request is signaled by the
1288   inclusion of a Content-Length or Transfer-Encoding header field in
1289   the request's message-headers. A message-body &MUST-NOT; be included in
1290   a request if the specification of the request method (&method;)
1291   explicitly disallows an entity-body in requests.
1292   When a request message contains both a message-body of non-zero
1293   length and a method that does not define any semantics for that
1294   request message-body, then an origin server &SHOULD; either ignore
1295   the message-body or respond with an appropriate error message
1296   (e.g., 413).  A proxy or gateway, when presented the same request,
1297   &SHOULD; either forward the request inbound with the message-body or
1298   ignore the message-body when determining a response.
1299</t>
1300<t>
1301   For response messages, whether or not a message-body is included with
1302   a message is dependent on both the request method and the response
1303   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1304   &MUST-NOT; include a message-body, even though the presence of entity-header
1305   fields might lead one to believe they do. All 1xx
1306   (informational), 204 (No Content), and 304 (Not Modified) responses
1307   &MUST-NOT; include a message-body. All other responses do include a
1308   message-body, although it &MAY; be of zero length.
1309</t>
1310</section>
1311
1312<section title="Message Length" anchor="message.length">
1313<t>
1314   The transfer-length of a message is the length of the message-body as
1315   it appears in the message; that is, after any transfer-codings have
1316   been applied. When a message-body is included with a message, the
1317   transfer-length of that body is determined by one of the following
1318   (in order of precedence):
1319</t>
1320<t>
1321  <list style="numbers">
1322    <x:lt><t>
1323     Any response message which "&MUST-NOT;" include a message-body (such
1324     as the 1xx, 204, and 304 responses and any response to a HEAD
1325     request) is always terminated by the first empty line after the
1326     header fields, regardless of the entity-header fields present in
1327     the message.
1328    </t></x:lt>
1329    <x:lt><t>
1330     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1331     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1332     is used, the transfer-length is defined by the use of this transfer-coding.
1333     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1334     is not present, the transfer-length is defined by the sender closing the connection.
1335    </t></x:lt>
1336    <x:lt><t>
1337     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1338     decimal value in OCTETs represents both the entity-length and the
1339     transfer-length. The Content-Length header field &MUST-NOT; be sent
1340     if these two lengths are different (i.e., if a Transfer-Encoding
1341     header field is present). If a message is received with both a
1342     Transfer-Encoding header field and a Content-Length header field,
1343     the latter &MUST; be ignored.
1344    </t></x:lt>
1345    <x:lt><t>
1346     If the message uses the media type "multipart/byteranges", and the
1347     transfer-length is not otherwise specified, then this self-delimiting
1348     media type defines the transfer-length. This media type
1349     &MUST-NOT; be used unless the sender knows that the recipient can parse
1350     it; the presence in a request of a Range header with multiple byte-range
1351     specifiers from a 1.1 client implies that the client can parse
1352     multipart/byteranges responses.
1353    <list style="empty"><t>
1354       A range header might be forwarded by a 1.0 proxy that does not
1355       understand multipart/byteranges; in this case the server &MUST;
1356       delimit the message using methods defined in items 1, 3 or 5 of
1357       this section.
1358    </t></list>
1359    </t></x:lt>
1360    <x:lt><t>
1361     By the server closing the connection. (Closing the connection
1362     cannot be used to indicate the end of a request body, since that
1363     would leave no possibility for the server to send back a response.)
1364    </t></x:lt>
1365  </list>
1366</t>
1367<t>
1368   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1369   containing a message-body &MUST; include a valid Content-Length header
1370   field unless the server is known to be HTTP/1.1 compliant. If a
1371   request contains a message-body and a Content-Length is not given,
1372   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1373   determine the length of the message, or with 411 (Length Required) if
1374   it wishes to insist on receiving a valid Content-Length.
1375</t>
1376<t>
1377   All HTTP/1.1 applications that receive entities &MUST; accept the
1378   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1379   to be used for messages when the message length cannot be determined
1380   in advance.
1381</t>
1382<t>
1383   Messages &MUST-NOT; include both a Content-Length header field and a
1384   transfer-coding. If the message does include a
1385   transfer-coding, the Content-Length &MUST; be ignored.
1386</t>
1387<t>
1388   When a Content-Length is given in a message where a message-body is
1389   allowed, its field value &MUST; exactly match the number of OCTETs in
1390   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1391   invalid length is received and detected.
1392</t>
1393</section>
1394
1395<section title="General Header Fields" anchor="general.header.fields">
1396  <x:anchor-alias value="general-header"/>
1397<t>
1398   There are a few header fields which have general applicability for
1399   both request and response messages, but which do not apply to the
1400   entity being transferred. These header fields apply only to the
1401   message being transmitted.
1402</t>
1403<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1404  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1405                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1406                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1407                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1408                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1409                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1410                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1411                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1412                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1413</artwork></figure>
1414<t>
1415   General-header field names can be extended reliably only in
1416   combination with a change in the protocol version. However, new or
1417   experimental header fields may be given the semantics of general
1418   header fields if all parties in the communication recognize them to
1419   be general-header fields. Unrecognized header fields are treated as
1420   entity-header fields.
1421</t>
1422</section>
1423</section>
1424
1425<section title="Request" anchor="request">
1426  <x:anchor-alias value="Request"/>
1427<t>
1428   A request message from a client to a server includes, within the
1429   first line of that message, the method to be applied to the resource,
1430   the identifier of the resource, and the protocol version in use.
1431</t>
1432<!--                 Host                      ; should be moved here eventually -->
1433<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1434  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1435                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1436                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1437                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1438                  <x:ref>CRLF</x:ref>
1439                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1440</artwork></figure>
1441
1442<section title="Request-Line" anchor="request-line">
1443  <x:anchor-alias value="Request-Line"/>
1444<t>
1445   The Request-Line begins with a method token, followed by the
1446   Request-URI and the protocol version, and ending with CRLF. The
1447   elements are separated by SP characters. No CR or LF is allowed
1448   except in the final CRLF sequence.
1449</t>
1450<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1451  <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>
1452</artwork></figure>
1453
1454<section title="Method" anchor="method">
1455  <x:anchor-alias value="Method"/>
1456<t>
1457   The Method  token indicates the method to be performed on the
1458   resource identified by the Request-URI. The method is case-sensitive.
1459</t>
1460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1461  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1462</artwork></figure>
1463</section>
1464
1465<section title="Request-URI" anchor="request-uri">
1466  <x:anchor-alias value="Request-URI"/>
1467<t>
1468   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1469   identifies the resource upon which to apply the request.
1470</t>
1471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1472  <x:ref>Request-URI</x:ref>    = "*"
1473                 / <x:ref>absoluteURI</x:ref>
1474                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1475                 / <x:ref>authority</x:ref>
1476</artwork></figure>
1477<t>
1478   The four options for Request-URI are dependent on the nature of the
1479   request. The asterisk "*" means that the request does not apply to a
1480   particular resource, but to the server itself, and is only allowed
1481   when the method used does not necessarily apply to a resource. One
1482   example would be
1483</t>
1484<figure><artwork type="example">
1485    OPTIONS * HTTP/1.1
1486</artwork></figure>
1487<t>
1488   The absoluteURI form is &REQUIRED; when the request is being made to a
1489   proxy. The proxy is requested to forward the request or service it
1490   from a valid cache, and return the response. Note that the proxy &MAY;
1491   forward the request on to another proxy or directly to the server
1492   specified by the absoluteURI. In order to avoid request loops, a
1493   proxy &MUST; be able to recognize all of its server names, including
1494   any aliases, local variations, and the numeric IP address. An example
1495   Request-Line would be:
1496</t>
1497<figure><artwork type="example">
1498    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1499</artwork></figure>
1500<t>
1501   To allow for transition to absoluteURIs in all requests in future
1502   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1503   form in requests, even though HTTP/1.1 clients will only generate
1504   them in requests to proxies.
1505</t>
1506<t>
1507   The authority form is only used by the CONNECT method (&CONNECT;).
1508</t>
1509<t>
1510   The most common form of Request-URI is that used to identify a
1511   resource on an origin server or gateway. In this case the absolute
1512   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1513   the Request-URI, and the network location of the URI (authority) &MUST;
1514   be transmitted in a Host header field. For example, a client wishing
1515   to retrieve the resource above directly from the origin server would
1516   create a TCP connection to port 80 of the host "www.example.org" and send
1517   the lines:
1518</t>
1519<figure><artwork type="example">
1520    GET /pub/WWW/TheProject.html HTTP/1.1
1521    Host: www.example.org
1522</artwork></figure>
1523<t>
1524   followed by the remainder of the Request. Note that the absolute path
1525   cannot be empty; if none is present in the original URI, it &MUST; be
1526   given as "/" (the server root).
1527</t>
1528<t>
1529   The Request-URI is transmitted in the format specified in
1530   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1531   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1532   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1533   &MUST; decode the Request-URI in order to
1534   properly interpret the request. Servers &SHOULD; respond to invalid
1535   Request-URIs with an appropriate status code.
1536</t>
1537<t>
1538   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1539   received Request-URI when forwarding it to the next inbound server,
1540   except as noted above to replace a null path-absolute with "/".
1541</t>
1542<t>
1543  <list><t>
1544      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1545      meaning of the request when the origin server is improperly using
1546      a non-reserved URI character for a reserved purpose.  Implementors
1547      should be aware that some pre-HTTP/1.1 proxies have been known to
1548      rewrite the Request-URI.
1549  </t></list>
1550</t>
1551</section>
1552</section>
1553
1554<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1555<t>
1556   The exact resource identified by an Internet request is determined by
1557   examining both the Request-URI and the Host header field.
1558</t>
1559<t>
1560   An origin server that does not allow resources to differ by the
1561   requested host &MAY; ignore the Host header field value when
1562   determining the resource identified by an HTTP/1.1 request. (But see
1563   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1564   for other requirements on Host support in HTTP/1.1.)
1565</t>
1566<t>
1567   An origin server that does differentiate resources based on the host
1568   requested (sometimes referred to as virtual hosts or vanity host
1569   names) &MUST; use the following rules for determining the requested
1570   resource on an HTTP/1.1 request:
1571  <list style="numbers">
1572    <t>If Request-URI is an absoluteURI, the host is part of the
1573     Request-URI. Any Host header field value in the request &MUST; be
1574     ignored.</t>
1575    <t>If the Request-URI is not an absoluteURI, and the request includes
1576     a Host header field, the host is determined by the Host header
1577     field value.</t>
1578    <t>If the host as determined by rule 1 or 2 is not a valid host on
1579     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1580  </list>
1581</t>
1582<t>
1583   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1584   attempt to use heuristics (e.g., examination of the URI path for
1585   something unique to a particular host) in order to determine what
1586   exact resource is being requested.
1587</t>
1588</section>
1589
1590</section>
1591
1592
1593<section title="Response" anchor="response">
1594  <x:anchor-alias value="Response"/>
1595<t>
1596   After receiving and interpreting a request message, a server responds
1597   with an HTTP response message.
1598</t>
1599<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1600  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1601                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1602                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1603                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1604                  <x:ref>CRLF</x:ref>
1605                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1606</artwork></figure>
1607
1608<section title="Status-Line" anchor="status-line">
1609  <x:anchor-alias value="Status-Line"/>
1610<t>
1611   The first line of a Response message is the Status-Line, consisting
1612   of the protocol version followed by a numeric status code and its
1613   associated textual phrase, with each element separated by SP
1614   characters. No CR or LF is allowed except in the final CRLF sequence.
1615</t>
1616<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1617  <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>
1618</artwork></figure>
1619
1620<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1621  <x:anchor-alias value="Reason-Phrase"/>
1622  <x:anchor-alias value="Status-Code"/>
1623<t>
1624   The Status-Code element is a 3-digit integer result code of the
1625   attempt to understand and satisfy the request. These codes are fully
1626   defined in &status-codes;.  The Reason Phrase exists for the sole
1627   purpose of providing a textual description associated with the numeric
1628   status code, out of deference to earlier Internet application protocols
1629   that were more frequently used with interactive text clients.
1630   A client &SHOULD; ignore the content of the Reason Phrase.
1631</t>
1632<t>
1633   The first digit of the Status-Code defines the class of response. The
1634   last two digits do not have any categorization role. There are 5
1635   values for the first digit:
1636  <list style="symbols">
1637    <t>
1638      1xx: Informational - Request received, continuing process
1639    </t>
1640    <t>
1641      2xx: Success - The action was successfully received,
1642        understood, and accepted
1643    </t>
1644    <t>
1645      3xx: Redirection - Further action must be taken in order to
1646        complete the request
1647    </t>
1648    <t>
1649      4xx: Client Error - The request contains bad syntax or cannot
1650        be fulfilled
1651    </t>
1652    <t>
1653      5xx: Server Error - The server failed to fulfill an apparently
1654        valid request
1655    </t>
1656  </list>
1657</t>
1658<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"/>
1659  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1660  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1661</artwork></figure>
1662</section>
1663</section>
1664
1665</section>
1666
1667
1668<section title="Connections" anchor="connections">
1669
1670<section title="Persistent Connections" anchor="persistent.connections">
1671
1672<section title="Purpose" anchor="persistent.purpose">
1673<t>
1674   Prior to persistent connections, a separate TCP connection was
1675   established to fetch each URL, increasing the load on HTTP servers
1676   and causing congestion on the Internet. The use of inline images and
1677   other associated data often require a client to make multiple
1678   requests of the same server in a short amount of time. Analysis of
1679   these performance problems and results from a prototype
1680   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1681   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1682   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1683   T/TCP <xref target="Tou1998"/>.
1684</t>
1685<t>
1686   Persistent HTTP connections have a number of advantages:
1687  <list style="symbols">
1688      <t>
1689        By opening and closing fewer TCP connections, CPU time is saved
1690        in routers and hosts (clients, servers, proxies, gateways,
1691        tunnels, or caches), and memory used for TCP protocol control
1692        blocks can be saved in hosts.
1693      </t>
1694      <t>
1695        HTTP requests and responses can be pipelined on a connection.
1696        Pipelining allows a client to make multiple requests without
1697        waiting for each response, allowing a single TCP connection to
1698        be used much more efficiently, with much lower elapsed time.
1699      </t>
1700      <t>
1701        Network congestion is reduced by reducing the number of packets
1702        caused by TCP opens, and by allowing TCP sufficient time to
1703        determine the congestion state of the network.
1704      </t>
1705      <t>
1706        Latency on subsequent requests is reduced since there is no time
1707        spent in TCP's connection opening handshake.
1708      </t>
1709      <t>
1710        HTTP can evolve more gracefully, since errors can be reported
1711        without the penalty of closing the TCP connection. Clients using
1712        future versions of HTTP might optimistically try a new feature,
1713        but if communicating with an older server, retry with old
1714        semantics after an error is reported.
1715      </t>
1716    </list>
1717</t>
1718<t>
1719   HTTP implementations &SHOULD; implement persistent connections.
1720</t>
1721</section>
1722
1723<section title="Overall Operation" anchor="persistent.overall">
1724<t>
1725   A significant difference between HTTP/1.1 and earlier versions of
1726   HTTP is that persistent connections are the default behavior of any
1727   HTTP connection. That is, unless otherwise indicated, the client
1728   &SHOULD; assume that the server will maintain a persistent connection,
1729   even after error responses from the server.
1730</t>
1731<t>
1732   Persistent connections provide a mechanism by which a client and a
1733   server can signal the close of a TCP connection. This signaling takes
1734   place using the Connection header field (<xref target="header.connection"/>). Once a close
1735   has been signaled, the client &MUST-NOT; send any more requests on that
1736   connection.
1737</t>
1738
1739<section title="Negotiation" anchor="persistent.negotiation">
1740<t>
1741   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1742   maintain a persistent connection unless a Connection header including
1743   the connection-token "close" was sent in the request. If the server
1744   chooses to close the connection immediately after sending the
1745   response, it &SHOULD; send a Connection header including the
1746   connection-token close.
1747</t>
1748<t>
1749   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1750   decide to keep it open based on whether the response from a server
1751   contains a Connection header with the connection-token close. In case
1752   the client does not want to maintain a connection for more than that
1753   request, it &SHOULD; send a Connection header including the
1754   connection-token close.
1755</t>
1756<t>
1757   If either the client or the server sends the close token in the
1758   Connection header, that request becomes the last one for the
1759   connection.
1760</t>
1761<t>
1762   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1763   maintained for HTTP versions less than 1.1 unless it is explicitly
1764   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1765   compatibility with HTTP/1.0 clients.
1766</t>
1767<t>
1768   In order to remain persistent, all messages on the connection &MUST;
1769   have a self-defined message length (i.e., one not defined by closure
1770   of the connection), as described in <xref target="message.length"/>.
1771</t>
1772</section>
1773
1774<section title="Pipelining" anchor="pipelining">
1775<t>
1776   A client that supports persistent connections &MAY; "pipeline" its
1777   requests (i.e., send multiple requests without waiting for each
1778   response). A server &MUST; send its responses to those requests in the
1779   same order that the requests were received.
1780</t>
1781<t>
1782   Clients which assume persistent connections and pipeline immediately
1783   after connection establishment &SHOULD; be prepared to retry their
1784   connection if the first pipelined attempt fails. If a client does
1785   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1786   persistent. Clients &MUST; also be prepared to resend their requests if
1787   the server closes the connection before sending all of the
1788   corresponding responses.
1789</t>
1790<t>
1791   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1792   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1793   premature termination of the transport connection could lead to
1794   indeterminate results. A client wishing to send a non-idempotent
1795   request &SHOULD; wait to send that request until it has received the
1796   response status for the previous request.
1797</t>
1798</section>
1799</section>
1800
1801<section title="Proxy Servers" anchor="persistent.proxy">
1802<t>
1803   It is especially important that proxies correctly implement the
1804   properties of the Connection header field as specified in <xref target="header.connection"/>.
1805</t>
1806<t>
1807   The proxy server &MUST; signal persistent connections separately with
1808   its clients and the origin servers (or other proxy servers) that it
1809   connects to. Each persistent connection applies to only one transport
1810   link.
1811</t>
1812<t>
1813   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1814   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1815   discussion of the problems with the Keep-Alive header implemented by
1816   many HTTP/1.0 clients).
1817</t>
1818</section>
1819
1820<section title="Practical Considerations" anchor="persistent.practical">
1821<t>
1822   Servers will usually have some time-out value beyond which they will
1823   no longer maintain an inactive connection. Proxy servers might make
1824   this a higher value since it is likely that the client will be making
1825   more connections through the same server. The use of persistent
1826   connections places no requirements on the length (or existence) of
1827   this time-out for either the client or the server.
1828</t>
1829<t>
1830   When a client or server wishes to time-out it &SHOULD; issue a graceful
1831   close on the transport connection. Clients and servers &SHOULD; both
1832   constantly watch for the other side of the transport close, and
1833   respond to it as appropriate. If a client or server does not detect
1834   the other side's close promptly it could cause unnecessary resource
1835   drain on the network.
1836</t>
1837<t>
1838   A client, server, or proxy &MAY; close the transport connection at any
1839   time. For example, a client might have started to send a new request
1840   at the same time that the server has decided to close the "idle"
1841   connection. From the server's point of view, the connection is being
1842   closed while it was idle, but from the client's point of view, a
1843   request is in progress.
1844</t>
1845<t>
1846   This means that clients, servers, and proxies &MUST; be able to recover
1847   from asynchronous close events. Client software &SHOULD; reopen the
1848   transport connection and retransmit the aborted sequence of requests
1849   without user interaction so long as the request sequence is
1850   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1851   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1852   human operator the choice of retrying the request(s). Confirmation by
1853   user-agent software with semantic understanding of the application
1854   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1855   be repeated if the second sequence of requests fails.
1856</t>
1857<t>
1858   Servers &SHOULD; always respond to at least one request per connection,
1859   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1860   middle of transmitting a response, unless a network or client failure
1861   is suspected.
1862</t>
1863<t>
1864   Clients that use persistent connections &SHOULD; limit the number of
1865   simultaneous connections that they maintain to a given server. A
1866   single-user client &SHOULD-NOT; maintain more than 2 connections with
1867   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1868   another server or proxy, where N is the number of simultaneously
1869   active users. These guidelines are intended to improve HTTP response
1870   times and avoid congestion.
1871</t>
1872</section>
1873</section>
1874
1875<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1876
1877<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1878<t>
1879   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1880   flow control mechanisms to resolve temporary overloads, rather than
1881   terminating connections with the expectation that clients will retry.
1882   The latter technique can exacerbate network congestion.
1883</t>
1884</section>
1885
1886<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1887<t>
1888   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1889   the network connection for an error status while it is transmitting
1890   the request. If the client sees an error status, it &SHOULD;
1891   immediately cease transmitting the body. If the body is being sent
1892   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1893   empty trailer &MAY; be used to prematurely mark the end of the message.
1894   If the body was preceded by a Content-Length header, the client &MUST;
1895   close the connection.
1896</t>
1897</section>
1898
1899<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1900<t>
1901   The purpose of the 100 (Continue) status (see &status-100;) is to
1902   allow a client that is sending a request message with a request body
1903   to determine if the origin server is willing to accept the request
1904   (based on the request headers) before the client sends the request
1905   body. In some cases, it might either be inappropriate or highly
1906   inefficient for the client to send the body if the server will reject
1907   the message without looking at the body.
1908</t>
1909<t>
1910   Requirements for HTTP/1.1 clients:
1911  <list style="symbols">
1912    <t>
1913        If a client will wait for a 100 (Continue) response before
1914        sending the request body, it &MUST; send an Expect request-header
1915        field (&header-expect;) with the "100-continue" expectation.
1916    </t>
1917    <t>
1918        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1919        with the "100-continue" expectation if it does not intend
1920        to send a request body.
1921    </t>
1922  </list>
1923</t>
1924<t>
1925   Because of the presence of older implementations, the protocol allows
1926   ambiguous situations in which a client may send "Expect: 100-continue"
1927   without receiving either a 417 (Expectation Failed) status
1928   or a 100 (Continue) status. Therefore, when a client sends this
1929   header field to an origin server (possibly via a proxy) from which it
1930   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1931   for an indefinite period before sending the request body.
1932</t>
1933<t>
1934   Requirements for HTTP/1.1 origin servers:
1935  <list style="symbols">
1936    <t> Upon receiving a request which includes an Expect request-header
1937        field with the "100-continue" expectation, an origin server &MUST;
1938        either respond with 100 (Continue) status and continue to read
1939        from the input stream, or respond with a final status code. The
1940        origin server &MUST-NOT; wait for the request body before sending
1941        the 100 (Continue) response. If it responds with a final status
1942        code, it &MAY; close the transport connection or it &MAY; continue
1943        to read and discard the rest of the request.  It &MUST-NOT;
1944        perform the requested method if it returns a final status code.
1945    </t>
1946    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1947        the request message does not include an Expect request-header
1948        field with the "100-continue" expectation, and &MUST-NOT; send a
1949        100 (Continue) response if such a request comes from an HTTP/1.0
1950        (or earlier) client. There is an exception to this rule: for
1951        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1952        status in response to an HTTP/1.1 PUT or POST request that does
1953        not include an Expect request-header field with the "100-continue"
1954        expectation. This exception, the purpose of which is
1955        to minimize any client processing delays associated with an
1956        undeclared wait for 100 (Continue) status, applies only to
1957        HTTP/1.1 requests, and not to requests with any other HTTP-version
1958        value.
1959    </t>
1960    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1961        already received some or all of the request body for the
1962        corresponding request.
1963    </t>
1964    <t> An origin server that sends a 100 (Continue) response &MUST;
1965    ultimately send a final status code, once the request body is
1966        received and processed, unless it terminates the transport
1967        connection prematurely.
1968    </t>
1969    <t> If an origin server receives a request that does not include an
1970        Expect request-header field with the "100-continue" expectation,
1971        the request includes a request body, and the server responds
1972        with a final status code before reading the entire request body
1973        from the transport connection, then the server &SHOULD-NOT;  close
1974        the transport connection until it has read the entire request,
1975        or until the client closes the connection. Otherwise, the client
1976        might not reliably receive the response message. However, this
1977        requirement is not be construed as preventing a server from
1978        defending itself against denial-of-service attacks, or from
1979        badly broken client implementations.
1980      </t>
1981    </list>
1982</t>
1983<t>
1984   Requirements for HTTP/1.1 proxies:
1985  <list style="symbols">
1986    <t> If a proxy receives a request that includes an Expect request-header
1987        field with the "100-continue" expectation, and the proxy
1988        either knows that the next-hop server complies with HTTP/1.1 or
1989        higher, or does not know the HTTP version of the next-hop
1990        server, it &MUST; forward the request, including the Expect header
1991        field.
1992    </t>
1993    <t> If the proxy knows that the version of the next-hop server is
1994        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1995        respond with a 417 (Expectation Failed) status.
1996    </t>
1997    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1998        numbers received from recently-referenced next-hop servers.
1999    </t>
2000    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2001        request message was received from an HTTP/1.0 (or earlier)
2002        client and did not include an Expect request-header field with
2003        the "100-continue" expectation. This requirement overrides the
2004        general rule for forwarding of 1xx responses (see &status-1xx;).
2005    </t>
2006  </list>
2007</t>
2008</section>
2009
2010<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2011<t>
2012   If an HTTP/1.1 client sends a request which includes a request body,
2013   but which does not include an Expect request-header field with the
2014   "100-continue" expectation, and if the client is not directly
2015   connected to an HTTP/1.1 origin server, and if the client sees the
2016   connection close before receiving any status from the server, the
2017   client &SHOULD; retry the request.  If the client does retry this
2018   request, it &MAY; use the following "binary exponential backoff"
2019   algorithm to be assured of obtaining a reliable response:
2020  <list style="numbers">
2021    <t>
2022      Initiate a new connection to the server
2023    </t>
2024    <t>
2025      Transmit the request-headers
2026    </t>
2027    <t>
2028      Initialize a variable R to the estimated round-trip time to the
2029         server (e.g., based on the time it took to establish the
2030         connection), or to a constant value of 5 seconds if the round-trip
2031         time is not available.
2032    </t>
2033    <t>
2034       Compute T = R * (2**N), where N is the number of previous
2035         retries of this request.
2036    </t>
2037    <t>
2038       Wait either for an error response from the server, or for T
2039         seconds (whichever comes first)
2040    </t>
2041    <t>
2042       If no error response is received, after T seconds transmit the
2043         body of the request.
2044    </t>
2045    <t>
2046       If client sees that the connection is closed prematurely,
2047         repeat from step 1 until the request is accepted, an error
2048         response is received, or the user becomes impatient and
2049         terminates the retry process.
2050    </t>
2051  </list>
2052</t>
2053<t>
2054   If at any point an error status is received, the client
2055  <list style="symbols">
2056      <t>&SHOULD-NOT;  continue and</t>
2057
2058      <t>&SHOULD; close the connection if it has not completed sending the
2059        request message.</t>
2060    </list>
2061</t>
2062</section>
2063</section>
2064</section>
2065
2066
2067<section title="Header Field Definitions" anchor="header.fields">
2068<t>
2069   This section defines the syntax and semantics of HTTP/1.1 header fields
2070   related to message framing and transport protocols.
2071</t>
2072<t>
2073   For entity-header fields, both sender and recipient refer to either the
2074   client or the server, depending on who sends and who receives the entity.
2075</t>
2076
2077<section title="Connection" anchor="header.connection">
2078  <iref primary="true" item="Connection header" x:for-anchor=""/>
2079  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2080  <x:anchor-alias value="Connection"/>
2081  <x:anchor-alias value="connection-token"/>
2082<t>
2083   The Connection general-header field allows the sender to specify
2084   options that are desired for that particular connection and &MUST-NOT;
2085   be communicated by proxies over further connections.
2086</t>
2087<t>
2088   The Connection header has the following grammar:
2089</t>
2090<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2091  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2092  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2093</artwork></figure>
2094<t>
2095   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2096   message is forwarded and, for each connection-token in this field,
2097   remove any header field(s) from the message with the same name as the
2098   connection-token. Connection options are signaled by the presence of
2099   a connection-token in the Connection header field, not by any
2100   corresponding additional header field(s), since the additional header
2101   field may not be sent if there are no parameters associated with that
2102   connection option.
2103</t>
2104<t>
2105   Message headers listed in the Connection header &MUST-NOT; include
2106   end-to-end headers, such as Cache-Control.
2107</t>
2108<t>
2109   HTTP/1.1 defines the "close" connection option for the sender to
2110   signal that the connection will be closed after completion of the
2111   response. For example,
2112</t>
2113<figure><artwork type="example">
2114    Connection: close
2115</artwork></figure>
2116<t>
2117   in either the request or the response header fields indicates that
2118   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2119   after the current request/response is complete.
2120</t>
2121<t>
2122   An HTTP/1.1 client that does not support persistent connections &MUST;
2123   include the "close" connection option in every request message.
2124</t>
2125<t>
2126   An HTTP/1.1 server that does not support persistent connections &MUST;
2127   include the "close" connection option in every response message that
2128   does not have a 1xx (informational) status code.
2129</t>
2130<t>
2131   A system receiving an HTTP/1.0 (or lower-version) message that
2132   includes a Connection header &MUST;, for each connection-token in this
2133   field, remove and ignore any header field(s) from the message with
2134   the same name as the connection-token. This protects against mistaken
2135   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2136</t>
2137</section>
2138
2139<section title="Content-Length" anchor="header.content-length">
2140  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2141  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2142  <x:anchor-alias value="Content-Length"/>
2143<t>
2144   The Content-Length entity-header field indicates the size of the
2145   entity-body, in decimal number of OCTETs, sent to the recipient or,
2146   in the case of the HEAD method, the size of the entity-body that
2147   would have been sent had the request been a GET.
2148</t>
2149<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2150  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2151</artwork></figure>
2152<t>
2153   An example is
2154</t>
2155<figure><artwork type="example">
2156    Content-Length: 3495
2157</artwork></figure>
2158<t>
2159   Applications &SHOULD; use this field to indicate the transfer-length of
2160   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2161</t>
2162<t>
2163   Any Content-Length greater than or equal to zero is a valid value.
2164   <xref target="message.length"/> describes how to determine the length of a message-body
2165   if a Content-Length is not given.
2166</t>
2167<t>
2168   Note that the meaning of this field is significantly different from
2169   the corresponding definition in MIME, where it is an optional field
2170   used within the "message/external-body" content-type. In HTTP, it
2171   &SHOULD; be sent whenever the message's length can be determined prior
2172   to being transferred, unless this is prohibited by the rules in
2173   <xref target="message.length"/>.
2174</t>
2175</section>
2176
2177<section title="Date" anchor="header.date">
2178  <iref primary="true" item="Date header" x:for-anchor=""/>
2179  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2180  <x:anchor-alias value="Date"/>
2181<t>
2182   The Date general-header field represents the date and time at which
2183   the message was originated, having the same semantics as orig-date in
2184   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2185   HTTP-date, as described in <xref target="full.date"/>;
2186   it &MUST; be sent in rfc1123-date format.
2187</t>
2188<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2189  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2190</artwork></figure>
2191<t>
2192   An example is
2193</t>
2194<figure><artwork type="example">
2195    Date: Tue, 15 Nov 1994 08:12:31 GMT
2196</artwork></figure>
2197<t>
2198   Origin servers &MUST; include a Date header field in all responses,
2199   except in these cases:
2200  <list style="numbers">
2201      <t>If the response status code is 100 (Continue) or 101 (Switching
2202         Protocols), the response &MAY; include a Date header field, at
2203         the server's option.</t>
2204
2205      <t>If the response status code conveys a server error, e.g. 500
2206         (Internal Server Error) or 503 (Service Unavailable), and it is
2207         inconvenient or impossible to generate a valid Date.</t>
2208
2209      <t>If the server does not have a clock that can provide a
2210         reasonable approximation of the current time, its responses
2211         &MUST-NOT; include a Date header field. In this case, the rules
2212         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2213  </list>
2214</t>
2215<t>
2216   A received message that does not have a Date header field &MUST; be
2217   assigned one by the recipient if the message will be cached by that
2218   recipient or gatewayed via a protocol which requires a Date. An HTTP
2219   implementation without a clock &MUST-NOT; cache responses without
2220   revalidating them on every use. An HTTP cache, especially a shared
2221   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2222   clock with a reliable external standard.
2223</t>
2224<t>
2225   Clients &SHOULD; only send a Date header field in messages that include
2226   an entity-body, as in the case of the PUT and POST requests, and even
2227   then it is optional. A client without a clock &MUST-NOT; send a Date
2228   header field in a request.
2229</t>
2230<t>
2231   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2232   time subsequent to the generation of the message. It &SHOULD; represent
2233   the best available approximation of the date and time of message
2234   generation, unless the implementation has no means of generating a
2235   reasonably accurate date and time. In theory, the date ought to
2236   represent the moment just before the entity is generated. In
2237   practice, the date can be generated at any time during the message
2238   origination without affecting its semantic value.
2239</t>
2240
2241<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2242<t>
2243   Some origin server implementations might not have a clock available.
2244   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2245   values to a response, unless these values were associated
2246   with the resource by a system or user with a reliable clock. It &MAY;
2247   assign an Expires value that is known, at or before server
2248   configuration time, to be in the past (this allows "pre-expiration"
2249   of responses without storing separate Expires values for each
2250   resource).
2251</t>
2252</section>
2253</section>
2254
2255<section title="Host" anchor="header.host">
2256  <iref primary="true" item="Host header" x:for-anchor=""/>
2257  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2258  <x:anchor-alias value="Host"/>
2259<t>
2260   The Host request-header field specifies the Internet host and port
2261   number of the resource being requested, as obtained from the original
2262   URI given by the user or referring resource (generally an HTTP URL,
2263   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2264   the naming authority of the origin server or gateway given by the
2265   original URL. This allows the origin server or gateway to
2266   differentiate between internally-ambiguous URLs, such as the root "/"
2267   URL of a server for multiple host names on a single IP address.
2268</t>
2269<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2270  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2271</artwork></figure>
2272<t>
2273   A "host" without any trailing port information implies the default
2274   port for the service requested (e.g., "80" for an HTTP URL). For
2275   example, a request on the origin server for
2276   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2277</t>
2278<figure><artwork type="example">
2279    GET /pub/WWW/ HTTP/1.1
2280    Host: www.example.org
2281</artwork></figure>
2282<t>
2283   A client &MUST; include a Host header field in all HTTP/1.1 request
2284   messages. If the requested URI does not include an Internet host
2285   name for the service being requested, then the Host header field &MUST;
2286   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2287   request message it forwards does contain an appropriate Host header
2288   field that identifies the service being requested by the proxy. All
2289   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2290   status code to any HTTP/1.1 request message which lacks a Host header
2291   field.
2292</t>
2293<t>
2294   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2295   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2296   for other requirements relating to Host.
2297</t>
2298</section>
2299
2300<section title="TE" anchor="header.te">
2301  <iref primary="true" item="TE header" x:for-anchor=""/>
2302  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2303  <x:anchor-alias value="TE"/>
2304  <x:anchor-alias value="t-codings"/>
2305<t>
2306   The TE request-header field indicates what extension transfer-codings
2307   it is willing to accept in the response and whether or not it is
2308   willing to accept trailer fields in a chunked transfer-coding. Its
2309   value may consist of the keyword "trailers" and/or a comma-separated
2310   list of extension transfer-coding names with optional accept
2311   parameters (as described in <xref target="transfer.codings"/>).
2312</t>
2313<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2314  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2315  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2316</artwork></figure>
2317<t>
2318   The presence of the keyword "trailers" indicates that the client is
2319   willing to accept trailer fields in a chunked transfer-coding, as
2320   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2321   transfer-coding values even though it does not itself represent a
2322   transfer-coding.
2323</t>
2324<t>
2325   Examples of its use are:
2326</t>
2327<figure><artwork type="example">
2328    TE: deflate
2329    TE:
2330    TE: trailers, deflate;q=0.5
2331</artwork></figure>
2332<t>
2333   The TE header field only applies to the immediate connection.
2334   Therefore, the keyword &MUST; be supplied within a Connection header
2335   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2336</t>
2337<t>
2338   A server tests whether a transfer-coding is acceptable, according to
2339   a TE field, using these rules:
2340  <list style="numbers">
2341    <x:lt>
2342      <t>The "chunked" transfer-coding is always acceptable. If the
2343         keyword "trailers" is listed, the client indicates that it is
2344         willing to accept trailer fields in the chunked response on
2345         behalf of itself and any downstream clients. The implication is
2346         that, if given, the client is stating that either all
2347         downstream clients are willing to accept trailer fields in the
2348         forwarded response, or that it will attempt to buffer the
2349         response on behalf of downstream recipients.
2350      </t><t>
2351         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2352         chunked response such that a client can be assured of buffering
2353         the entire response.</t>
2354    </x:lt>
2355    <x:lt>
2356      <t>If the transfer-coding being tested is one of the transfer-codings
2357         listed in the TE field, then it is acceptable unless it
2358         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2359         qvalue of 0 means "not acceptable.")</t>
2360    </x:lt>
2361    <x:lt>
2362      <t>If multiple transfer-codings are acceptable, then the
2363         acceptable transfer-coding with the highest non-zero qvalue is
2364         preferred.  The "chunked" transfer-coding always has a qvalue
2365         of 1.</t>
2366    </x:lt>
2367  </list>
2368</t>
2369<t>
2370   If the TE field-value is empty or if no TE field is present, the only
2371   transfer-coding  is "chunked". A message with no transfer-coding is
2372   always acceptable.
2373</t>
2374</section>
2375
2376<section title="Trailer" anchor="header.trailer">
2377  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2378  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2379  <x:anchor-alias value="Trailer"/>
2380<t>
2381   The Trailer general field value indicates that the given set of
2382   header fields is present in the trailer of a message encoded with
2383   chunked transfer-coding.
2384</t>
2385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2386  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2387</artwork></figure>
2388<t>
2389   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2390   message using chunked transfer-coding with a non-empty trailer. Doing
2391   so allows the recipient to know which header fields to expect in the
2392   trailer.
2393</t>
2394<t>
2395   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2396   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2397   trailer fields in a "chunked" transfer-coding.
2398</t>
2399<t>
2400   Message header fields listed in the Trailer header field &MUST-NOT;
2401   include the following header fields:
2402  <list style="symbols">
2403    <t>Transfer-Encoding</t>
2404    <t>Content-Length</t>
2405    <t>Trailer</t>
2406  </list>
2407</t>
2408</section>
2409
2410<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2411  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2412  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2413  <x:anchor-alias value="Transfer-Encoding"/>
2414<t>
2415   The Transfer-Encoding general-header field indicates what (if any)
2416   type of transformation has been applied to the message body in order
2417   to safely transfer it between the sender and the recipient. This
2418   differs from the content-coding in that the transfer-coding is a
2419   property of the message, not of the entity.
2420</t>
2421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2422  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2423</artwork></figure>
2424<t>
2425   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2426</t>
2427<figure><artwork type="example">
2428  Transfer-Encoding: chunked
2429</artwork></figure>
2430<t>
2431   If multiple encodings have been applied to an entity, the transfer-codings
2432   &MUST; be listed in the order in which they were applied.
2433   Additional information about the encoding parameters &MAY; be provided
2434   by other entity-header fields not defined by this specification.
2435</t>
2436<t>
2437   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2438   header.
2439</t>
2440</section>
2441
2442<section title="Upgrade" anchor="header.upgrade">
2443  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2444  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2445  <x:anchor-alias value="Upgrade"/>
2446<t>
2447   The Upgrade general-header allows the client to specify what
2448   additional communication protocols it supports and would like to use
2449   if the server finds it appropriate to switch protocols. The server
2450   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2451   response to indicate which protocol(s) are being switched.
2452</t>
2453<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2454  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2455</artwork></figure>
2456<t>
2457   For example,
2458</t>
2459<figure><artwork type="example">
2460    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2461</artwork></figure>
2462<t>
2463   The Upgrade header field is intended to provide a simple mechanism
2464   for transition from HTTP/1.1 to some other, incompatible protocol. It
2465   does so by allowing the client to advertise its desire to use another
2466   protocol, such as a later version of HTTP with a higher major version
2467   number, even though the current request has been made using HTTP/1.1.
2468   This eases the difficult transition between incompatible protocols by
2469   allowing the client to initiate a request in the more commonly
2470   supported protocol while indicating to the server that it would like
2471   to use a "better" protocol if available (where "better" is determined
2472   by the server, possibly according to the nature of the method and/or
2473   resource being requested).
2474</t>
2475<t>
2476   The Upgrade header field only applies to switching application-layer
2477   protocols upon the existing transport-layer connection. Upgrade
2478   cannot be used to insist on a protocol change; its acceptance and use
2479   by the server is optional. The capabilities and nature of the
2480   application-layer communication after the protocol change is entirely
2481   dependent upon the new protocol chosen, although the first action
2482   after changing the protocol &MUST; be a response to the initial HTTP
2483   request containing the Upgrade header field.
2484</t>
2485<t>
2486   The Upgrade header field only applies to the immediate connection.
2487   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2488   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2489   HTTP/1.1 message.
2490</t>
2491<t>
2492   The Upgrade header field cannot be used to indicate a switch to a
2493   protocol on a different connection. For that purpose, it is more
2494   appropriate to use a 301, 302, 303, or 305 redirection response.
2495</t>
2496<t>
2497   This specification only defines the protocol name "HTTP" for use by
2498   the family of Hypertext Transfer Protocols, as defined by the HTTP
2499   version rules of <xref target="http.version"/> and future updates to this
2500   specification. Any token can be used as a protocol name; however, it
2501   will only be useful if both the client and server associate the name
2502   with the same protocol.
2503</t>
2504</section>
2505
2506<section title="Via" anchor="header.via">
2507  <iref primary="true" item="Via header" x:for-anchor=""/>
2508  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2509  <x:anchor-alias value="protocol-name"/>
2510  <x:anchor-alias value="protocol-version"/>
2511  <x:anchor-alias value="pseudonym"/>
2512  <x:anchor-alias value="received-by"/>
2513  <x:anchor-alias value="received-protocol"/>
2514  <x:anchor-alias value="Via"/>
2515<t>
2516   The Via general-header field &MUST; be used by gateways and proxies to
2517   indicate the intermediate protocols and recipients between the user
2518   agent and the server on requests, and between the origin server and
2519   the client on responses. It is analogous to the "Received" field defined in
2520   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2521   avoiding request loops, and identifying the protocol capabilities of
2522   all senders along the request/response chain.
2523</t>
2524<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"/>
2525  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2526  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2527  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2528  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2529  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2530  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2531</artwork></figure>
2532<t>
2533   The received-protocol indicates the protocol version of the message
2534   received by the server or client along each segment of the
2535   request/response chain. The received-protocol version is appended to
2536   the Via field value when the message is forwarded so that information
2537   about the protocol capabilities of upstream applications remains
2538   visible to all recipients.
2539</t>
2540<t>
2541   The protocol-name is optional if and only if it would be "HTTP". The
2542   received-by field is normally the host and optional port number of a
2543   recipient server or client that subsequently forwarded the message.
2544   However, if the real host is considered to be sensitive information,
2545   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2546   be assumed to be the default port of the received-protocol.
2547</t>
2548<t>
2549   Multiple Via field values represents each proxy or gateway that has
2550   forwarded the message. Each recipient &MUST; append its information
2551   such that the end result is ordered according to the sequence of
2552   forwarding applications.
2553</t>
2554<t>
2555   Comments &MAY; be used in the Via header field to identify the software
2556   of the recipient proxy or gateway, analogous to the User-Agent and
2557   Server header fields. However, all comments in the Via field are
2558   optional and &MAY; be removed by any recipient prior to forwarding the
2559   message.
2560</t>
2561<t>
2562   For example, a request message could be sent from an HTTP/1.0 user
2563   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2564   forward the request to a public proxy at p.example.net, which completes
2565   the request by forwarding it to the origin server at www.example.com.
2566   The request received by www.example.com would then have the following
2567   Via header field:
2568</t>
2569<figure><artwork type="example">
2570    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2571</artwork></figure>
2572<t>
2573   Proxies and gateways used as a portal through a network firewall
2574   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2575   the firewall region. This information &SHOULD; only be propagated if
2576   explicitly enabled. If not enabled, the received-by host of any host
2577   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2578   for that host.
2579</t>
2580<t>
2581   For organizations that have strong privacy requirements for hiding
2582   internal structures, a proxy &MAY; combine an ordered subsequence of
2583   Via header field entries with identical received-protocol values into
2584   a single such entry. For example,
2585</t>
2586<figure><artwork type="example">
2587    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2588</artwork></figure>
2589<t>
2590        could be collapsed to
2591</t>
2592<figure><artwork type="example">
2593    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2594</artwork></figure>
2595<t>
2596   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2597   under the same organizational control and the hosts have already been
2598   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2599   have different received-protocol values.
2600</t>
2601</section>
2602
2603</section>
2604
2605<section title="IANA Considerations" anchor="IANA.considerations">
2606<section title="Message Header Registration" anchor="message.header.registration">
2607<t>
2608   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2609   with the permanent registrations below (see <xref target="RFC3864"/>):
2610</t>
2611<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2612<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2613   <ttcol>Header Field Name</ttcol>
2614   <ttcol>Protocol</ttcol>
2615   <ttcol>Status</ttcol>
2616   <ttcol>Reference</ttcol>
2617
2618   <c>Connection</c>
2619   <c>http</c>
2620   <c>standard</c>
2621   <c>
2622      <xref target="header.connection"/>
2623   </c>
2624   <c>Content-Length</c>
2625   <c>http</c>
2626   <c>standard</c>
2627   <c>
2628      <xref target="header.content-length"/>
2629   </c>
2630   <c>Date</c>
2631   <c>http</c>
2632   <c>standard</c>
2633   <c>
2634      <xref target="header.date"/>
2635   </c>
2636   <c>Host</c>
2637   <c>http</c>
2638   <c>standard</c>
2639   <c>
2640      <xref target="header.host"/>
2641   </c>
2642   <c>TE</c>
2643   <c>http</c>
2644   <c>standard</c>
2645   <c>
2646      <xref target="header.te"/>
2647   </c>
2648   <c>Trailer</c>
2649   <c>http</c>
2650   <c>standard</c>
2651   <c>
2652      <xref target="header.trailer"/>
2653   </c>
2654   <c>Transfer-Encoding</c>
2655   <c>http</c>
2656   <c>standard</c>
2657   <c>
2658      <xref target="header.transfer-encoding"/>
2659   </c>
2660   <c>Upgrade</c>
2661   <c>http</c>
2662   <c>standard</c>
2663   <c>
2664      <xref target="header.upgrade"/>
2665   </c>
2666   <c>Via</c>
2667   <c>http</c>
2668   <c>standard</c>
2669   <c>
2670      <xref target="header.via"/>
2671   </c>
2672</texttable>
2673<!--(END)-->
2674<t>
2675   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2676</t>
2677</section>
2678
2679<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2680<t>
2681   The entry for the "http" URI Scheme in the registry located at
2682   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2683   should be updated to point to <xref target="http.url"/> of this document
2684   (see <xref target="RFC4395"/>).
2685</t>
2686</section>
2687
2688<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2689<t>
2690   This document serves as the specification for the Internet media types
2691   "message/http" and "application/http". The following is to be registered with
2692   IANA (see <xref target="RFC4288"/>).
2693</t>
2694<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2695<iref item="Media Type" subitem="message/http" primary="true"/>
2696<iref item="message/http Media Type" primary="true"/>
2697<t>
2698   The message/http type can be used to enclose a single HTTP request or
2699   response message, provided that it obeys the MIME restrictions for all
2700   "message" types regarding line length and encodings.
2701</t>
2702<t>
2703  <list style="hanging" x:indent="12em">
2704    <t hangText="Type name:">
2705      message
2706    </t>
2707    <t hangText="Subtype name:">
2708      http
2709    </t>
2710    <t hangText="Required parameters:">
2711      none
2712    </t>
2713    <t hangText="Optional parameters:">
2714      version, msgtype
2715      <list style="hanging">
2716        <t hangText="version:">
2717          The HTTP-Version number of the enclosed message
2718          (e.g., "1.1"). If not present, the version can be
2719          determined from the first line of the body.
2720        </t>
2721        <t hangText="msgtype:">
2722          The message type -- "request" or "response". If not
2723          present, the type can be determined from the first
2724          line of the body.
2725        </t>
2726      </list>
2727    </t>
2728    <t hangText="Encoding considerations:">
2729      only "7bit", "8bit", or "binary" are permitted
2730    </t>
2731    <t hangText="Security considerations:">
2732      none
2733    </t>
2734    <t hangText="Interoperability considerations:">
2735      none
2736    </t>
2737    <t hangText="Published specification:">
2738      This specification (see <xref target="internet.media.type.message.http"/>).
2739    </t>
2740    <t hangText="Applications that use this media type:">
2741    </t>
2742    <t hangText="Additional information:">
2743      <list style="hanging">
2744        <t hangText="Magic number(s):">none</t>
2745        <t hangText="File extension(s):">none</t>
2746        <t hangText="Macintosh file type code(s):">none</t>
2747      </list>
2748    </t>
2749    <t hangText="Person and email address to contact for further information:">
2750      See Authors Section.
2751    </t>
2752                <t hangText="Intended usage:">
2753                  COMMON
2754    </t>
2755                <t hangText="Restrictions on usage:">
2756                  none
2757    </t>
2758    <t hangText="Author/Change controller:">
2759      IESG
2760    </t>
2761  </list>
2762</t>
2763</section>
2764<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2765<iref item="Media Type" subitem="application/http" primary="true"/>
2766<iref item="application/http Media Type" primary="true"/>
2767<t>
2768   The application/http type can be used to enclose a pipeline of one or more
2769   HTTP request or response messages (not intermixed).
2770</t>
2771<t>
2772  <list style="hanging" x:indent="12em">
2773    <t hangText="Type name:">
2774      application
2775    </t>
2776    <t hangText="Subtype name:">
2777      http
2778    </t>
2779    <t hangText="Required parameters:">
2780      none
2781    </t>
2782    <t hangText="Optional parameters:">
2783      version, msgtype
2784      <list style="hanging">
2785        <t hangText="version:">
2786          The HTTP-Version number of the enclosed messages
2787          (e.g., "1.1"). If not present, the version can be
2788          determined from the first line of the body.
2789        </t>
2790        <t hangText="msgtype:">
2791          The message type -- "request" or "response". If not
2792          present, the type can be determined from the first
2793          line of the body.
2794        </t>
2795      </list>
2796    </t>
2797    <t hangText="Encoding considerations:">
2798      HTTP messages enclosed by this type
2799      are in "binary" format; use of an appropriate
2800      Content-Transfer-Encoding is required when
2801      transmitted via E-mail.
2802    </t>
2803    <t hangText="Security considerations:">
2804      none
2805    </t>
2806    <t hangText="Interoperability considerations:">
2807      none
2808    </t>
2809    <t hangText="Published specification:">
2810      This specification (see <xref target="internet.media.type.application.http"/>).
2811    </t>
2812    <t hangText="Applications that use this media type:">
2813    </t>
2814    <t hangText="Additional information:">
2815      <list style="hanging">
2816        <t hangText="Magic number(s):">none</t>
2817        <t hangText="File extension(s):">none</t>
2818        <t hangText="Macintosh file type code(s):">none</t>
2819      </list>
2820    </t>
2821    <t hangText="Person and email address to contact for further information:">
2822      See Authors Section.
2823    </t>
2824                <t hangText="Intended usage:">
2825                  COMMON
2826    </t>
2827                <t hangText="Restrictions on usage:">
2828                  none
2829    </t>
2830    <t hangText="Author/Change controller:">
2831      IESG
2832    </t>
2833  </list>
2834</t>
2835</section>
2836</section>
2837
2838</section>
2839
2840<section title="Security Considerations" anchor="security.considerations">
2841<t>
2842   This section is meant to inform application developers, information
2843   providers, and users of the security limitations in HTTP/1.1 as
2844   described by this document. The discussion does not include
2845   definitive solutions to the problems revealed, though it does make
2846   some suggestions for reducing security risks.
2847</t>
2848
2849<section title="Personal Information" anchor="personal.information">
2850<t>
2851   HTTP clients are often privy to large amounts of personal information
2852   (e.g. the user's name, location, mail address, passwords, encryption
2853   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2854   leakage of this information.
2855   We very strongly recommend that a convenient interface be provided
2856   for the user to control dissemination of such information, and that
2857   designers and implementors be particularly careful in this area.
2858   History shows that errors in this area often create serious security
2859   and/or privacy problems and generate highly adverse publicity for the
2860   implementor's company.
2861</t>
2862</section>
2863
2864<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2865<t>
2866   A server is in the position to save personal data about a user's
2867   requests which might identify their reading patterns or subjects of
2868   interest. This information is clearly confidential in nature and its
2869   handling can be constrained by law in certain countries. People using
2870   HTTP to provide data are responsible for ensuring that
2871   such material is not distributed without the permission of any
2872   individuals that are identifiable by the published results.
2873</t>
2874</section>
2875
2876<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2877<t>
2878   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2879   the documents returned by HTTP requests to be only those that were
2880   intended by the server administrators. If an HTTP server translates
2881   HTTP URIs directly into file system calls, the server &MUST; take
2882   special care not to serve files that were not intended to be
2883   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2884   other operating systems use ".." as a path component to indicate a
2885   directory level above the current one. On such a system, an HTTP
2886   server &MUST; disallow any such construct in the Request-URI if it
2887   would otherwise allow access to a resource outside those intended to
2888   be accessible via the HTTP server. Similarly, files intended for
2889   reference only internally to the server (such as access control
2890   files, configuration files, and script code) &MUST; be protected from
2891   inappropriate retrieval, since they might contain sensitive
2892   information. Experience has shown that minor bugs in such HTTP server
2893   implementations have turned into security risks.
2894</t>
2895</section>
2896
2897<section title="DNS Spoofing" anchor="dns.spoofing">
2898<t>
2899   Clients using HTTP rely heavily on the Domain Name Service, and are
2900   thus generally prone to security attacks based on the deliberate
2901   mis-association of IP addresses and DNS names. Clients need to be
2902   cautious in assuming the continuing validity of an IP number/DNS name
2903   association.
2904</t>
2905<t>
2906   In particular, HTTP clients &SHOULD; rely on their name resolver for
2907   confirmation of an IP number/DNS name association, rather than
2908   caching the result of previous host name lookups. Many platforms
2909   already can cache host name lookups locally when appropriate, and
2910   they &SHOULD; be configured to do so. It is proper for these lookups to
2911   be cached, however, only when the TTL (Time To Live) information
2912   reported by the name server makes it likely that the cached
2913   information will remain useful.
2914</t>
2915<t>
2916   If HTTP clients cache the results of host name lookups in order to
2917   achieve a performance improvement, they &MUST; observe the TTL
2918   information reported by DNS.
2919</t>
2920<t>
2921   If HTTP clients do not observe this rule, they could be spoofed when
2922   a previously-accessed server's IP address changes. As network
2923   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2924   possibility of this form of attack will grow. Observing this
2925   requirement thus reduces this potential security vulnerability.
2926</t>
2927<t>
2928   This requirement also improves the load-balancing behavior of clients
2929   for replicated servers using the same DNS name and reduces the
2930   likelihood of a user's experiencing failure in accessing sites which
2931   use that strategy.
2932</t>
2933</section>
2934
2935<section title="Proxies and Caching" anchor="attack.proxies">
2936<t>
2937   By their very nature, HTTP proxies are men-in-the-middle, and
2938   represent an opportunity for man-in-the-middle attacks. Compromise of
2939   the systems on which the proxies run can result in serious security
2940   and privacy problems. Proxies have access to security-related
2941   information, personal information about individual users and
2942   organizations, and proprietary information belonging to users and
2943   content providers. A compromised proxy, or a proxy implemented or
2944   configured without regard to security and privacy considerations,
2945   might be used in the commission of a wide range of potential attacks.
2946</t>
2947<t>
2948   Proxy operators should protect the systems on which proxies run as
2949   they would protect any system that contains or transports sensitive
2950   information. In particular, log information gathered at proxies often
2951   contains highly sensitive personal information, and/or information
2952   about organizations. Log information should be carefully guarded, and
2953   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2954</t>
2955<t>
2956   Proxy implementors should consider the privacy and security
2957   implications of their design and coding decisions, and of the
2958   configuration options they provide to proxy operators (especially the
2959   default configuration).
2960</t>
2961<t>
2962   Users of a proxy need to be aware that they are no trustworthier than
2963   the people who run the proxy; HTTP itself cannot solve this problem.
2964</t>
2965<t>
2966   The judicious use of cryptography, when appropriate, may suffice to
2967   protect against a broad range of security and privacy attacks. Such
2968   cryptography is beyond the scope of the HTTP/1.1 specification.
2969</t>
2970</section>
2971
2972<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2973<t>
2974   They exist. They are hard to defend against. Research continues.
2975   Beware.
2976</t>
2977</section>
2978</section>
2979
2980<section title="Acknowledgments" anchor="ack">
2981<t>
2982   This specification makes heavy use of the augmented BNF and generic
2983   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2984   reuses many of the definitions provided by Nathaniel Borenstein and
2985   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2986   specification will help reduce past confusion over the relationship
2987   between HTTP and Internet mail message formats.
2988</t>
2989<t>
2990   HTTP has evolved considerably over the years. It has
2991   benefited from a large and active developer community--the many
2992   people who have participated on the www-talk mailing list--and it is
2993   that community which has been most responsible for the success of
2994   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2995   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2996   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2997   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2998   VanHeyningen deserve special recognition for their efforts in
2999   defining early aspects of the protocol.
3000</t>
3001<t>
3002   This document has benefited greatly from the comments of all those
3003   participating in the HTTP-WG. In addition to those already mentioned,
3004   the following individuals have contributed to this specification:
3005</t>
3006<t>
3007   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3008   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3009   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3010   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3011   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3012   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3013   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3014   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3015   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3016   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3017   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3018   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3019   Josh Cohen.
3020</t>
3021<t>
3022   Thanks to the "cave men" of Palo Alto. You know who you are.
3023</t>
3024<t>
3025   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3026   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3027   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3028   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3029   Larry Masinter for their help. And thanks go particularly to Jeff
3030   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3031</t>
3032<t>
3033   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3034   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3035   discovery of many of the problems that this document attempts to
3036   rectify.
3037</t>
3038</section>
3039
3040</middle>
3041<back>
3042
3043<references title="Normative References">
3044
3045<reference anchor="ISO-8859-1">
3046  <front>
3047    <title>
3048     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3049    </title>
3050    <author>
3051      <organization>International Organization for Standardization</organization>
3052    </author>
3053    <date year="1998"/>
3054  </front>
3055  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3056</reference>
3057
3058<reference anchor="Part2">
3059  <front>
3060    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3061    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3062      <organization abbrev="Day Software">Day Software</organization>
3063      <address><email>fielding@gbiv.com</email></address>
3064    </author>
3065    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3066      <organization>One Laptop per Child</organization>
3067      <address><email>jg@laptop.org</email></address>
3068    </author>
3069    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3070      <organization abbrev="HP">Hewlett-Packard Company</organization>
3071      <address><email>JeffMogul@acm.org</email></address>
3072    </author>
3073    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3074      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3075      <address><email>henrikn@microsoft.com</email></address>
3076    </author>
3077    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3078      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3079      <address><email>LMM@acm.org</email></address>
3080    </author>
3081    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3082      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3083      <address><email>paulle@microsoft.com</email></address>
3084    </author>
3085    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3086      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3087      <address><email>timbl@w3.org</email></address>
3088    </author>
3089    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3090      <organization abbrev="W3C">World Wide Web Consortium</organization>
3091      <address><email>ylafon@w3.org</email></address>
3092    </author>
3093    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3094      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3095      <address><email>julian.reschke@greenbytes.de</email></address>
3096    </author>
3097    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3098  </front>
3099  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3100  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3101</reference>
3102
3103<reference anchor="Part3">
3104  <front>
3105    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3106    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3107      <organization abbrev="Day Software">Day Software</organization>
3108      <address><email>fielding@gbiv.com</email></address>
3109    </author>
3110    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3111      <organization>One Laptop per Child</organization>
3112      <address><email>jg@laptop.org</email></address>
3113    </author>
3114    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3115      <organization abbrev="HP">Hewlett-Packard Company</organization>
3116      <address><email>JeffMogul@acm.org</email></address>
3117    </author>
3118    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3119      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3120      <address><email>henrikn@microsoft.com</email></address>
3121    </author>
3122    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3123      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3124      <address><email>LMM@acm.org</email></address>
3125    </author>
3126    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3127      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3128      <address><email>paulle@microsoft.com</email></address>
3129    </author>
3130    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3131      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3132      <address><email>timbl@w3.org</email></address>
3133    </author>
3134    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3135      <organization abbrev="W3C">World Wide Web Consortium</organization>
3136      <address><email>ylafon@w3.org</email></address>
3137    </author>
3138    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3139      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3140      <address><email>julian.reschke@greenbytes.de</email></address>
3141    </author>
3142    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3143  </front>
3144  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3145  <x:source href="p3-payload.xml" basename="p3-payload"/>
3146</reference>
3147
3148<reference anchor="Part5">
3149  <front>
3150    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3151    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3152      <organization abbrev="Day Software">Day Software</organization>
3153      <address><email>fielding@gbiv.com</email></address>
3154    </author>
3155    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3156      <organization>One Laptop per Child</organization>
3157      <address><email>jg@laptop.org</email></address>
3158    </author>
3159    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3160      <organization abbrev="HP">Hewlett-Packard Company</organization>
3161      <address><email>JeffMogul@acm.org</email></address>
3162    </author>
3163    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3164      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3165      <address><email>henrikn@microsoft.com</email></address>
3166    </author>
3167    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3168      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3169      <address><email>LMM@acm.org</email></address>
3170    </author>
3171    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3172      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3173      <address><email>paulle@microsoft.com</email></address>
3174    </author>
3175    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3176      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3177      <address><email>timbl@w3.org</email></address>
3178    </author>
3179    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3180      <organization abbrev="W3C">World Wide Web Consortium</organization>
3181      <address><email>ylafon@w3.org</email></address>
3182    </author>
3183    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3184      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3185      <address><email>julian.reschke@greenbytes.de</email></address>
3186    </author>
3187    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3188  </front>
3189  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3190  <x:source href="p5-range.xml" basename="p5-range"/>
3191</reference>
3192
3193<reference anchor="Part6">
3194  <front>
3195    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3196    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3197      <organization abbrev="Day Software">Day Software</organization>
3198      <address><email>fielding@gbiv.com</email></address>
3199    </author>
3200    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3201      <organization>One Laptop per Child</organization>
3202      <address><email>jg@laptop.org</email></address>
3203    </author>
3204    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3205      <organization abbrev="HP">Hewlett-Packard Company</organization>
3206      <address><email>JeffMogul@acm.org</email></address>
3207    </author>
3208    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3209      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3210      <address><email>henrikn@microsoft.com</email></address>
3211    </author>
3212    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3213      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3214      <address><email>LMM@acm.org</email></address>
3215    </author>
3216    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3217      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3218      <address><email>paulle@microsoft.com</email></address>
3219    </author>
3220    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3221      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3222      <address><email>timbl@w3.org</email></address>
3223    </author>
3224    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3225      <organization abbrev="W3C">World Wide Web Consortium</organization>
3226      <address><email>ylafon@w3.org</email></address>
3227    </author>
3228    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3229      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3230      <address><email>julian.reschke@greenbytes.de</email></address>
3231    </author>
3232    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3233  </front>
3234  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3235  <x:source href="p6-cache.xml" basename="p6-cache"/>
3236</reference>
3237
3238<reference anchor="RFC5234">
3239  <front>
3240    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3241    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3242      <organization>Brandenburg InternetWorking</organization>
3243      <address>
3244      <postal>
3245      <street>675 Spruce Dr.</street>
3246      <city>Sunnyvale</city>
3247      <region>CA</region>
3248      <code>94086</code>
3249      <country>US</country></postal>
3250      <phone>+1.408.246.8253</phone>
3251      <email>dcrocker@bbiw.net</email></address> 
3252    </author>
3253    <author initials="P." surname="Overell" fullname="Paul Overell">
3254      <organization>THUS plc.</organization>
3255      <address>
3256      <postal>
3257      <street>1/2 Berkeley Square</street>
3258      <street>99 Berkely Street</street>
3259      <city>Glasgow</city>
3260      <code>G3 7HR</code>
3261      <country>UK</country></postal>
3262      <email>paul.overell@thus.net</email></address>
3263    </author>
3264    <date month="January" year="2008"/>
3265  </front>
3266  <seriesInfo name="STD" value="68"/>
3267  <seriesInfo name="RFC" value="5234"/>
3268</reference>
3269
3270<reference anchor="RFC2045">
3271  <front>
3272    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3273    <author initials="N." surname="Freed" fullname="Ned Freed">
3274      <organization>Innosoft International, Inc.</organization>
3275      <address><email>ned@innosoft.com</email></address>
3276    </author>
3277    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3278      <organization>First Virtual Holdings</organization>
3279      <address><email>nsb@nsb.fv.com</email></address>
3280    </author>
3281    <date month="November" year="1996"/>
3282  </front>
3283  <seriesInfo name="RFC" value="2045"/>
3284</reference>
3285
3286<reference anchor="RFC2047">
3287  <front>
3288    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3289    <author initials="K." surname="Moore" fullname="Keith Moore">
3290      <organization>University of Tennessee</organization>
3291      <address><email>moore@cs.utk.edu</email></address>
3292    </author>
3293    <date month="November" year="1996"/>
3294  </front>
3295  <seriesInfo name="RFC" value="2047"/>
3296</reference>
3297
3298<reference anchor="RFC2119">
3299  <front>
3300    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3301    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3302      <organization>Harvard University</organization>
3303      <address><email>sob@harvard.edu</email></address>
3304    </author>
3305    <date month="March" year="1997"/>
3306  </front>
3307  <seriesInfo name="BCP" value="14"/>
3308  <seriesInfo name="RFC" value="2119"/>
3309</reference>
3310
3311<reference anchor="RFC2396">
3312  <front>
3313    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3314    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3315      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3316      <address><email>timbl@w3.org</email></address>
3317    </author>
3318    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3319      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3320      <address><email>fielding@ics.uci.edu</email></address>
3321    </author>
3322    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3323      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3324      <address><email>masinter@parc.xerox.com</email></address>
3325    </author>
3326    <date month="August" year="1998"/>
3327  </front>
3328  <seriesInfo name="RFC" value="2396"/>
3329</reference>
3330
3331<reference anchor="USASCII">
3332  <front>
3333    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3334    <author>
3335      <organization>American National Standards Institute</organization>
3336    </author>
3337    <date year="1986"/>
3338  </front>
3339  <seriesInfo name="ANSI" value="X3.4"/>
3340</reference>
3341
3342</references>
3343
3344<references title="Informative References">
3345
3346<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3347  <front>
3348    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3349    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3350      <organization/>
3351    </author>
3352    <author initials="J." surname="Gettys" fullname="J. Gettys">
3353      <organization/>
3354    </author>
3355    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3356      <organization/>
3357    </author>
3358    <author initials="H." surname="Lie" fullname="H. Lie">
3359      <organization/>
3360    </author>
3361    <author initials="C." surname="Lilley" fullname="C. Lilley">
3362      <organization/>
3363    </author>
3364    <date year="1997" month="September"/>
3365  </front>
3366  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3367</reference>
3368
3369<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3370  <front>
3371    <title>Improving HTTP Latency</title>
3372    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3373      <organization/>
3374    </author>
3375    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3376      <organization/>
3377    </author>
3378    <date year="1995" month="December"/>
3379  </front>
3380  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3381</reference>
3382
3383<reference anchor="RFC822">
3384  <front>
3385    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3386    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3387      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3388      <address><email>DCrocker@UDel-Relay</email></address>
3389    </author>
3390    <date month="August" day="13" year="1982"/>
3391  </front>
3392  <seriesInfo name="STD" value="11"/>
3393  <seriesInfo name="RFC" value="822"/>
3394</reference>
3395
3396<reference anchor="RFC959">
3397  <front>
3398    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3399    <author initials="J." surname="Postel" fullname="J. Postel">
3400      <organization>Information Sciences Institute (ISI)</organization>
3401    </author>
3402    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3403      <organization/>
3404    </author>
3405    <date month="October" year="1985"/>
3406  </front>
3407  <seriesInfo name="STD" value="9"/>
3408  <seriesInfo name="RFC" value="959"/>
3409</reference>
3410
3411<reference anchor="RFC1123">
3412  <front>
3413    <title>Requirements for Internet Hosts - Application and Support</title>
3414    <author initials="R." surname="Braden" fullname="Robert Braden">
3415      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3416      <address><email>Braden@ISI.EDU</email></address>
3417    </author>
3418    <date month="October" year="1989"/>
3419  </front>
3420  <seriesInfo name="STD" value="3"/>
3421  <seriesInfo name="RFC" value="1123"/>
3422</reference>
3423
3424<reference anchor="RFC1305">
3425  <front>
3426    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3427    <author initials="D." surname="Mills" fullname="David L. Mills">
3428      <organization>University of Delaware, Electrical Engineering Department</organization>
3429      <address><email>mills@udel.edu</email></address>
3430    </author>
3431    <date month="March" year="1992"/>
3432  </front>
3433  <seriesInfo name="RFC" value="1305"/>
3434</reference>
3435
3436<reference anchor="RFC1436">
3437  <front>
3438    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3439    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3440      <organization>University of Minnesota, Computer and Information Services</organization>
3441      <address><email>fxa@boombox.micro.umn.edu</email></address>
3442    </author>
3443    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3444      <organization>University of Minnesota, Computer and Information Services</organization>
3445      <address><email>mpm@boombox.micro.umn.edu</email></address>
3446    </author>
3447    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3448      <organization>University of Minnesota, Computer and Information Services</organization>
3449      <address><email>lindner@boombox.micro.umn.edu</email></address>
3450    </author>
3451    <author initials="D." surname="Johnson" fullname="David Johnson">
3452      <organization>University of Minnesota, Computer and Information Services</organization>
3453      <address><email>dmj@boombox.micro.umn.edu</email></address>
3454    </author>
3455    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3456      <organization>University of Minnesota, Computer and Information Services</organization>
3457      <address><email>daniel@boombox.micro.umn.edu</email></address>
3458    </author>
3459    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3460      <organization>University of Minnesota, Computer and Information Services</organization>
3461      <address><email>alberti@boombox.micro.umn.edu</email></address>
3462    </author>
3463    <date month="March" year="1993"/>
3464  </front>
3465  <seriesInfo name="RFC" value="1436"/>
3466</reference>
3467
3468<reference anchor="RFC1630">
3469  <front>
3470    <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>
3471    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3472      <organization>CERN, World-Wide Web project</organization>
3473      <address><email>timbl@info.cern.ch</email></address>
3474    </author>
3475    <date month="June" year="1994"/>
3476  </front>
3477  <seriesInfo name="RFC" value="1630"/>
3478</reference>
3479
3480<reference anchor="RFC1737">
3481  <front>
3482    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3483    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3484      <organization>Xerox Palo Alto Research Center</organization>
3485      <address><email>masinter@parc.xerox.com</email></address>
3486    </author>
3487    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3488      <organization>MIT Laboratory for Computer Science</organization>
3489      <address><email>sollins@lcs.mit.edu</email></address>
3490    </author>
3491    <date month="December" year="1994"/>
3492  </front>
3493  <seriesInfo name="RFC" value="1737"/>
3494</reference>
3495
3496<reference anchor="RFC1738">
3497  <front>
3498    <title>Uniform Resource Locators (URL)</title>
3499    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3500      <organization>CERN, World-Wide Web project</organization>
3501      <address><email>timbl@info.cern.ch</email></address>
3502    </author>
3503    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3504      <organization>Xerox PARC</organization>
3505      <address><email>masinter@parc.xerox.com</email></address>
3506    </author>
3507    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3508      <organization>University of Minnesota, Computer and Information Services</organization>
3509      <address><email>mpm@boombox.micro.umn.edu</email></address>
3510    </author>
3511    <date month="December" year="1994"/>
3512  </front>
3513  <seriesInfo name="RFC" value="1738"/>
3514</reference>
3515
3516<reference anchor="RFC1808">
3517  <front>
3518    <title>Relative Uniform Resource Locators</title>
3519    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3520      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3521      <address><email>fielding@ics.uci.edu</email></address>
3522    </author>
3523    <date month="June" year="1995"/>
3524  </front>
3525  <seriesInfo name="RFC" value="1808"/>
3526</reference>
3527
3528<reference anchor="RFC1900">
3529  <front>
3530    <title>Renumbering Needs Work</title>
3531    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3532      <organization>CERN, Computing and Networks Division</organization>
3533      <address><email>brian@dxcoms.cern.ch</email></address>
3534    </author>
3535    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3536      <organization>cisco Systems</organization>
3537      <address><email>yakov@cisco.com</email></address>
3538    </author>
3539    <date month="February" year="1996"/>
3540  </front>
3541  <seriesInfo name="RFC" value="1900"/>
3542</reference>
3543
3544<reference anchor="RFC1945">
3545  <front>
3546    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3547    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3548      <organization>MIT, Laboratory for Computer Science</organization>
3549      <address><email>timbl@w3.org</email></address>
3550    </author>
3551    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3552      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3553      <address><email>fielding@ics.uci.edu</email></address>
3554    </author>
3555    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3556      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3557      <address><email>frystyk@w3.org</email></address>
3558    </author>
3559    <date month="May" year="1996"/>
3560  </front>
3561  <seriesInfo name="RFC" value="1945"/>
3562</reference>
3563
3564<reference anchor="RFC2068">
3565  <front>
3566    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3567    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3568      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3569      <address><email>fielding@ics.uci.edu</email></address>
3570    </author>
3571    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3572      <organization>MIT Laboratory for Computer Science</organization>
3573      <address><email>jg@w3.org</email></address>
3574    </author>
3575    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3576      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3577      <address><email>mogul@wrl.dec.com</email></address>
3578    </author>
3579    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3580      <organization>MIT Laboratory for Computer Science</organization>
3581      <address><email>frystyk@w3.org</email></address>
3582    </author>
3583    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3584      <organization>MIT Laboratory for Computer Science</organization>
3585      <address><email>timbl@w3.org</email></address>
3586    </author>
3587    <date month="January" year="1997"/>
3588  </front>
3589  <seriesInfo name="RFC" value="2068"/>
3590</reference>
3591
3592<reference anchor='RFC2109'>
3593  <front>
3594    <title>HTTP State Management Mechanism</title>
3595    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3596      <organization>Bell Laboratories, Lucent Technologies</organization>
3597      <address><email>dmk@bell-labs.com</email></address>
3598    </author>
3599    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3600      <organization>Netscape Communications Corp.</organization>
3601      <address><email>montulli@netscape.com</email></address>
3602    </author>
3603    <date year='1997' month='February' />
3604  </front>
3605  <seriesInfo name='RFC' value='2109' />
3606</reference>
3607
3608<reference anchor="RFC2145">
3609  <front>
3610    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3611    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3612      <organization>Western Research Laboratory</organization>
3613      <address><email>mogul@wrl.dec.com</email></address>
3614    </author>
3615    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3616      <organization>Department of Information and Computer Science</organization>
3617      <address><email>fielding@ics.uci.edu</email></address>
3618    </author>
3619    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3620      <organization>MIT Laboratory for Computer Science</organization>
3621      <address><email>jg@w3.org</email></address>
3622    </author>
3623    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3624      <organization>W3 Consortium</organization>
3625      <address><email>frystyk@w3.org</email></address>
3626    </author>
3627    <date month="May" year="1997"/>
3628  </front>
3629  <seriesInfo name="RFC" value="2145"/>
3630</reference>
3631
3632<reference anchor="RFC2324">
3633  <front>
3634    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3635    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3636      <organization>Xerox Palo Alto Research Center</organization>
3637      <address><email>masinter@parc.xerox.com</email></address>
3638    </author>
3639    <date month="April" day="1" year="1998"/>
3640  </front>
3641  <seriesInfo name="RFC" value="2324"/>
3642</reference>
3643
3644<reference anchor="RFC2616">
3645  <front>
3646    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3647    <author initials="R." surname="Fielding" fullname="R. Fielding">
3648      <organization>University of California, Irvine</organization>
3649      <address><email>fielding@ics.uci.edu</email></address>
3650    </author>
3651    <author initials="J." surname="Gettys" fullname="J. Gettys">
3652      <organization>W3C</organization>
3653      <address><email>jg@w3.org</email></address>
3654    </author>
3655    <author initials="J." surname="Mogul" fullname="J. Mogul">
3656      <organization>Compaq Computer Corporation</organization>
3657      <address><email>mogul@wrl.dec.com</email></address>
3658    </author>
3659    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3660      <organization>MIT Laboratory for Computer Science</organization>
3661      <address><email>frystyk@w3.org</email></address>
3662    </author>
3663    <author initials="L." surname="Masinter" fullname="L. Masinter">
3664      <organization>Xerox Corporation</organization>
3665      <address><email>masinter@parc.xerox.com</email></address>
3666    </author>
3667    <author initials="P." surname="Leach" fullname="P. Leach">
3668      <organization>Microsoft Corporation</organization>
3669      <address><email>paulle@microsoft.com</email></address>
3670    </author>
3671    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3672      <organization>W3C</organization>
3673      <address><email>timbl@w3.org</email></address>
3674    </author>
3675    <date month="June" year="1999"/>
3676  </front>
3677  <seriesInfo name="RFC" value="2616"/>
3678</reference>
3679
3680<reference anchor='RFC2818'>
3681  <front>
3682    <title>HTTP Over TLS</title>
3683    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3684      <organization>RTFM, Inc.</organization>
3685      <address><email>ekr@rtfm.com</email></address>
3686    </author>
3687    <date year='2000' month='May' />
3688  </front>
3689  <seriesInfo name='RFC' value='2818' />
3690</reference>
3691
3692<reference anchor="RFC2821">
3693  <front>
3694    <title>Simple Mail Transfer Protocol</title>
3695    <author initials="J." surname="Klensin" fullname="J. Klensin">
3696      <organization>AT&amp;T Laboratories</organization>
3697      <address><email>klensin@research.att.com</email></address>
3698    </author>
3699    <date year="2001" month="April"/>
3700  </front>
3701  <seriesInfo name="RFC" value="2821"/>
3702</reference>
3703
3704<reference anchor='RFC2965'>
3705  <front>
3706    <title>HTTP State Management Mechanism</title>
3707    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3708      <organization>Bell Laboratories, Lucent Technologies</organization>
3709      <address><email>dmk@bell-labs.com</email></address>
3710    </author>
3711    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3712      <organization>Epinions.com, Inc.</organization>
3713      <address><email>lou@montulli.org</email></address>
3714    </author>
3715    <date year='2000' month='October' />
3716  </front>
3717  <seriesInfo name='RFC' value='2965' />
3718</reference>
3719
3720<reference anchor='RFC3864'>
3721  <front>
3722    <title>Registration Procedures for Message Header Fields</title>
3723    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3724      <organization>Nine by Nine</organization>
3725      <address><email>GK-IETF@ninebynine.org</email></address>
3726    </author>
3727    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3728      <organization>BEA Systems</organization>
3729      <address><email>mnot@pobox.com</email></address>
3730    </author>
3731    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3732      <organization>HP Labs</organization>
3733      <address><email>JeffMogul@acm.org</email></address>
3734    </author>
3735    <date year='2004' month='September' />
3736  </front>
3737  <seriesInfo name='BCP' value='90' />
3738  <seriesInfo name='RFC' value='3864' />
3739</reference>
3740
3741<reference anchor='RFC3977'>
3742  <front>
3743    <title>Network News Transfer Protocol (NNTP)</title>
3744    <author initials='C.' surname='Feather' fullname='C. Feather'>
3745      <organization>THUS plc</organization>
3746      <address><email>clive@demon.net</email></address>
3747    </author>
3748    <date year='2006' month='October' />
3749  </front>
3750  <seriesInfo name="RFC" value="3977"/>
3751</reference>
3752
3753<reference anchor="RFC4288">
3754  <front>
3755    <title>Media Type Specifications and Registration Procedures</title>
3756    <author initials="N." surname="Freed" fullname="N. Freed">
3757      <organization>Sun Microsystems</organization>
3758      <address>
3759        <email>ned.freed@mrochek.com</email>
3760      </address>
3761    </author>
3762    <author initials="J." surname="Klensin" fullname="J. Klensin">
3763      <organization/>
3764      <address>
3765        <email>klensin+ietf@jck.com</email>
3766      </address>
3767    </author>
3768    <date year="2005" month="December"/>
3769  </front>
3770  <seriesInfo name="BCP" value="13"/>
3771  <seriesInfo name="RFC" value="4288"/>
3772</reference>
3773
3774<reference anchor='RFC4395'>
3775  <front>
3776    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3777    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3778      <organization>AT&amp;T Laboratories</organization>
3779      <address>
3780        <email>tony+urireg@maillennium.att.com</email>
3781      </address>
3782    </author>
3783    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3784      <organization>Qualcomm, Inc.</organization>
3785      <address>
3786        <email>hardie@qualcomm.com</email>
3787      </address>
3788    </author>
3789    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3790      <organization>Adobe Systems</organization>
3791      <address>
3792        <email>LMM@acm.org</email>
3793      </address>
3794    </author>
3795    <date year='2006' month='February' />
3796  </front>
3797  <seriesInfo name='BCP' value='115' />
3798  <seriesInfo name='RFC' value='4395' />
3799</reference>
3800
3801<reference anchor="RFC5322">
3802  <front>
3803    <title>Internet Message Format</title>
3804    <author initials="P." surname="Resnick" fullname="P. Resnick">
3805      <organization>Qualcomm Incorporated</organization>
3806    </author>
3807    <date year="2008" month="October"/>
3808  </front> 
3809  <seriesInfo name="RFC" value="5322"/>
3810</reference>
3811
3812<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3813  <front>
3814    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3815    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3816      <organization/>
3817    </author>
3818    <date year="2001" month="November"/>
3819  </front>
3820  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3821</reference>
3822
3823<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3824  <front>
3825  <title>Analysis of HTTP Performance Problems</title>
3826  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3827    <organization/>
3828  </author>
3829  <date/>
3830  </front>
3831</reference>
3832
3833<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3834  <front>
3835  <title>Analysis of HTTP Performance</title>
3836  <author initials="J." surname="Touch" fullname="Joe Touch">
3837    <organization>USC/Information Sciences Institute</organization>
3838    <address><email>touch@isi.edu</email></address>
3839  </author>
3840  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3841    <organization>USC/Information Sciences Institute</organization>
3842    <address><email>johnh@isi.edu</email></address>
3843  </author>
3844  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3845    <organization>USC/Information Sciences Institute</organization>
3846    <address><email>katia@isi.edu</email></address>
3847  </author>
3848  <date year="1998" month="Aug"/>
3849  </front>
3850  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3851  <annotation>(original report dated Aug. 1996)</annotation>
3852</reference>
3853
3854<reference anchor="WAIS">
3855  <front>
3856    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3857    <author initials="F." surname="Davis" fullname="F. Davis">
3858      <organization>Thinking Machines Corporation</organization>
3859    </author>
3860    <author initials="B." surname="Kahle" fullname="B. Kahle">
3861      <organization>Thinking Machines Corporation</organization>
3862    </author>
3863    <author initials="H." surname="Morris" fullname="H. Morris">
3864      <organization>Thinking Machines Corporation</organization>
3865    </author>
3866    <author initials="J." surname="Salem" fullname="J. Salem">
3867      <organization>Thinking Machines Corporation</organization>
3868    </author>
3869    <author initials="T." surname="Shen" fullname="T. Shen">
3870      <organization>Thinking Machines Corporation</organization>
3871    </author>
3872    <author initials="R." surname="Wang" fullname="R. Wang">
3873      <organization>Thinking Machines Corporation</organization>
3874    </author>
3875    <author initials="J." surname="Sui" fullname="J. Sui">
3876      <organization>Thinking Machines Corporation</organization>
3877    </author>
3878    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3879      <organization>Thinking Machines Corporation</organization>
3880    </author>
3881    <date month="April" year="1990"/>
3882  </front>
3883  <seriesInfo name="Thinking Machines Corporation" value=""/>
3884</reference>
3885
3886</references>
3887
3888
3889<section title="Tolerant Applications" anchor="tolerant.applications">
3890<t>
3891   Although this document specifies the requirements for the generation
3892   of HTTP/1.1 messages, not all applications will be correct in their
3893   implementation. We therefore recommend that operational applications
3894   be tolerant of deviations whenever those deviations can be
3895   interpreted unambiguously.
3896</t>
3897<t>
3898   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3899   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3900   accept any amount of SP or HTAB characters between fields, even though
3901   only a single SP is required.
3902</t>
3903<t>
3904   The line terminator for message-header fields is the sequence CRLF.
3905   However, we recommend that applications, when parsing such headers,
3906   recognize a single LF as a line terminator and ignore the leading CR.
3907</t>
3908<t>
3909   The character set of an entity-body &SHOULD; be labeled as the lowest
3910   common denominator of the character codes used within that body, with
3911   the exception that not labeling the entity is preferred over labeling
3912   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3913</t>
3914<t>
3915   Additional rules for requirements on parsing and encoding of dates
3916   and other potential problems with date encodings include:
3917</t>
3918<t>
3919  <list style="symbols">
3920     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3921        which appears to be more than 50 years in the future is in fact
3922        in the past (this helps solve the "year 2000" problem).</t>
3923
3924     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3925        Expires date as earlier than the proper value, but &MUST-NOT;
3926        internally represent a parsed Expires date as later than the
3927        proper value.</t>
3928
3929     <t>All expiration-related calculations &MUST; be done in GMT. The
3930        local time zone &MUST-NOT; influence the calculation or comparison
3931        of an age or expiration time.</t>
3932
3933     <t>If an HTTP header incorrectly carries a date value with a time
3934        zone other than GMT, it &MUST; be converted into GMT using the
3935        most conservative possible conversion.</t>
3936  </list>
3937</t>
3938</section>
3939
3940<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3941<t>
3942   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3943   simplify the process of date comparison. Proxies and gateways from
3944   other protocols &SHOULD; ensure that any Date header field present in a
3945   message conforms to one of the HTTP/1.1 formats and rewrite the date
3946   if necessary.
3947</t>
3948</section>
3949
3950<section title="Compatibility with Previous Versions" anchor="compatibility">
3951<t>
3952   It is beyond the scope of a protocol specification to mandate
3953   compliance with previous versions. HTTP/1.1 was deliberately
3954   designed, however, to make supporting previous versions easy. It is
3955   worth noting that, at the time of composing this specification
3956   (1996), we would expect commercial HTTP/1.1 servers to:
3957  <list style="symbols">
3958     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3959        1.1 requests;</t>
3960
3961     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3962        1.1;</t>
3963
3964     <t>respond appropriately with a message in the same major version
3965        used by the client.</t>
3966  </list>
3967</t>
3968<t>
3969   And we would expect HTTP/1.1 clients to:
3970  <list style="symbols">
3971     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3972        responses;</t>
3973
3974     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3975        1.1.</t>
3976  </list>
3977</t>
3978<t>
3979   For most implementations of HTTP/1.0, each connection is established
3980   by the client prior to the request and closed by the server after
3981   sending the response. Some implementations implement the Keep-Alive
3982   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3983</t>
3984
3985<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3986<t>
3987   This section summarizes major differences between versions HTTP/1.0
3988   and HTTP/1.1.
3989</t>
3990
3991<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">
3992<t>
3993   The requirements that clients and servers support the Host request-header,
3994   report an error if the Host request-header (<xref target="header.host"/>) is
3995   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3996   are among the most important changes defined by this
3997   specification.
3998</t>
3999<t>
4000   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4001   addresses and servers; there was no other established mechanism for
4002   distinguishing the intended server of a request than the IP address
4003   to which that request was directed. The changes outlined above will
4004   allow the Internet, once older HTTP clients are no longer common, to
4005   support multiple Web sites from a single IP address, greatly
4006   simplifying large operational Web servers, where allocation of many
4007   IP addresses to a single host has created serious problems. The
4008   Internet will also be able to recover the IP addresses that have been
4009   allocated for the sole purpose of allowing special-purpose domain
4010   names to be used in root-level HTTP URLs. Given the rate of growth of
4011   the Web, and the number of servers already deployed, it is extremely
4012   important that all implementations of HTTP (including updates to
4013   existing HTTP/1.0 applications) correctly implement these
4014   requirements:
4015  <list style="symbols">
4016     <t>Both clients and servers &MUST; support the Host request-header.</t>
4017
4018     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4019
4020     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4021        request does not include a Host request-header.</t>
4022
4023     <t>Servers &MUST; accept absolute URIs.</t>
4024  </list>
4025</t>
4026</section>
4027</section>
4028
4029<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4030<t>
4031   Some clients and servers might wish to be compatible with some
4032   previous implementations of persistent connections in HTTP/1.0
4033   clients and servers. Persistent connections in HTTP/1.0 are
4034   explicitly negotiated as they are not the default behavior. HTTP/1.0
4035   experimental implementations of persistent connections are faulty,
4036   and the new facilities in HTTP/1.1 are designed to rectify these
4037   problems. The problem was that some existing 1.0 clients may be
4038   sending Keep-Alive to a proxy server that doesn't understand
4039   Connection, which would then erroneously forward it to the next
4040   inbound server, which would establish the Keep-Alive connection and
4041   result in a hung HTTP/1.0 proxy waiting for the close on the
4042   response. The result is that HTTP/1.0 clients must be prevented from
4043   using Keep-Alive when talking to proxies.
4044</t>
4045<t>
4046   However, talking to proxies is the most important use of persistent
4047   connections, so that prohibition is clearly unacceptable. Therefore,
4048   we need some other mechanism for indicating a persistent connection
4049   is desired, which is safe to use even when talking to an old proxy
4050   that ignores Connection. Persistent connections are the default for
4051   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4052   declaring non-persistence. See <xref target="header.connection"/>.
4053</t>
4054<t>
4055   The original HTTP/1.0 form of persistent connections (the Connection:
4056   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4057</t>
4058</section>
4059
4060<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4061<t>
4062   This specification has been carefully audited to correct and
4063   disambiguate key word usage; RFC 2068 had many problems in respect to
4064   the conventions laid out in <xref target="RFC2119"/>.
4065</t>
4066<t>
4067   Transfer-coding and message lengths all interact in ways that
4068   required fixing exactly when chunked encoding is used (to allow for
4069   transfer encoding that may not be self delimiting); it was important
4070   to straighten out exactly how message lengths are computed. (Sections
4071   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4072   <xref target="header.content-length" format="counter"/>,
4073   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4074</t>
4075<t>
4076   The use and interpretation of HTTP version numbers has been clarified
4077   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4078   version they support to deal with problems discovered in HTTP/1.0
4079   implementations (<xref target="http.version"/>)
4080</t>
4081<t>
4082   Transfer-coding had significant problems, particularly with
4083   interactions with chunked encoding. The solution is that transfer-codings
4084   become as full fledged as content-codings. This involves
4085   adding an IANA registry for transfer-codings (separate from content
4086   codings), a new header field (TE) and enabling trailer headers in the
4087   future. Transfer encoding is a major performance benefit, so it was
4088   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4089   interoperability problem that could have occurred due to interactions
4090   between authentication trailers, chunked encoding and HTTP/1.0
4091   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4092   and <xref target="header.te" format="counter"/>)
4093</t>
4094</section>
4095
4096<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4097<t>
4098  The CHAR rule does not allow the NUL character anymore (this affects
4099  the comment and quoted-string rules).  Furthermore, the quoted-pair
4100  rule does not allow escaping NUL, CR or LF anymore.
4101  (<xref target="basic.rules"/>)
4102</t>
4103<t>
4104  Clarify that HTTP-Version is case sensitive.
4105  (<xref target="http.version"/>)
4106</t>
4107<t>
4108  Remove reference to non-existant identity transfer-coding value tokens.
4109  (Sections <xref format="counter" target="transfer.codings"/> and
4110  <xref format="counter" target="message.length"/>)
4111</t>
4112<t>
4113  Clarification that the chunk length does not include
4114  the count of the octets in the chunk header and trailer.
4115  (<xref target="chunked.transfer.encoding"/>)
4116</t>
4117<t>
4118  Fix BNF to add query, as the abs_path production in
4119  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4120  (<xref target="request-uri"/>)
4121</t>
4122<t>
4123  Clarify exactly when close connection options must be sent.
4124  (<xref target="header.connection"/>)
4125</t>
4126</section>
4127</section>
4128
4129<section title="Terminology" anchor="terminology">
4130<t>
4131   This specification uses a number of terms to refer to the roles
4132   played by participants in, and objects of, the HTTP communication.
4133</t>
4134<t>
4135  <iref item="connection"/>
4136  <x:dfn>connection</x:dfn>
4137  <list>
4138    <t>
4139      A transport layer virtual circuit established between two programs
4140      for the purpose of communication.
4141    </t>
4142  </list>
4143</t>
4144<t>
4145  <iref item="message"/>
4146  <x:dfn>message</x:dfn>
4147  <list>
4148    <t>
4149      The basic unit of HTTP communication, consisting of a structured
4150      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4151      transmitted via the connection.
4152    </t>
4153  </list>
4154</t>
4155<t>
4156  <iref item="request"/>
4157  <x:dfn>request</x:dfn>
4158  <list>
4159    <t>
4160      An HTTP request message, as defined in <xref target="request"/>.
4161    </t>
4162  </list>
4163</t>
4164<t>
4165  <iref item="response"/>
4166  <x:dfn>response</x:dfn>
4167  <list>
4168    <t>
4169      An HTTP response message, as defined in <xref target="response"/>.
4170    </t>
4171  </list>
4172</t>
4173<t>
4174  <iref item="resource"/>
4175  <x:dfn>resource</x:dfn>
4176  <list>
4177    <t>
4178      A network data object or service that can be identified by a URI,
4179      as defined in <xref target="uri"/>. Resources may be available in multiple
4180      representations (e.g. multiple languages, data formats, size, and
4181      resolutions) or vary in other ways.
4182    </t>
4183  </list>
4184</t>
4185<t>
4186  <iref item="entity"/>
4187  <x:dfn>entity</x:dfn>
4188  <list>
4189    <t>
4190      The information transferred as the payload of a request or
4191      response. An entity consists of metainformation in the form of
4192      entity-header fields and content in the form of an entity-body, as
4193      described in &entity;.
4194    </t>
4195  </list>
4196</t>
4197<t>
4198  <iref item="representation"/>
4199  <x:dfn>representation</x:dfn>
4200  <list>
4201    <t>
4202      An entity included with a response that is subject to content
4203      negotiation, as described in &content.negotiation;. There may exist multiple
4204      representations associated with a particular response status.
4205    </t>
4206  </list>
4207</t>
4208<t>
4209  <iref item="content negotiation"/>
4210  <x:dfn>content negotiation</x:dfn>
4211  <list>
4212    <t>
4213      The mechanism for selecting the appropriate representation when
4214      servicing a request, as described in &content.negotiation;. The
4215      representation of entities in any response can be negotiated
4216      (including error responses).
4217    </t>
4218  </list>
4219</t>
4220<t>
4221  <iref item="variant"/>
4222  <x:dfn>variant</x:dfn>
4223  <list>
4224    <t>
4225      A resource may have one, or more than one, representation(s)
4226      associated with it at any given instant. Each of these
4227      representations is termed a `variant'.  Use of the term `variant'
4228      does not necessarily imply that the resource is subject to content
4229      negotiation.
4230    </t>
4231  </list>
4232</t>
4233<t>
4234  <iref item="client"/>
4235  <x:dfn>client</x:dfn>
4236  <list>
4237    <t>
4238      A program that establishes connections for the purpose of sending
4239      requests.
4240    </t>
4241  </list>
4242</t>
4243<t>
4244  <iref item="user agent"/>
4245  <x:dfn>user agent</x:dfn>
4246  <list>
4247    <t>
4248      The client which initiates a request. These are often browsers,
4249      editors, spiders (web-traversing robots), or other end user tools.
4250    </t>
4251  </list>
4252</t>
4253<t>
4254  <iref item="server"/>
4255  <x:dfn>server</x:dfn>
4256  <list>
4257    <t>
4258      An application program that accepts connections in order to
4259      service requests by sending back responses. Any given program may
4260      be capable of being both a client and a server; our use of these
4261      terms refers only to the role being performed by the program for a
4262      particular connection, rather than to the program's capabilities
4263      in general. Likewise, any server may act as an origin server,
4264      proxy, gateway, or tunnel, switching behavior based on the nature
4265      of each request.
4266    </t>
4267  </list>
4268</t>
4269<t>
4270  <iref item="origin server"/>
4271  <x:dfn>origin server</x:dfn>
4272  <list>
4273    <t>
4274      The server on which a given resource resides or is to be created.
4275    </t>
4276  </list>
4277</t>
4278<t>
4279  <iref item="proxy"/>
4280  <x:dfn>proxy</x:dfn>
4281  <list>
4282    <t>
4283      An intermediary program which acts as both a server and a client
4284      for the purpose of making requests on behalf of other clients.
4285      Requests are serviced internally or by passing them on, with
4286      possible translation, to other servers. A proxy &MUST; implement
4287      both the client and server requirements of this specification. A
4288      "transparent proxy" is a proxy that does not modify the request or
4289      response beyond what is required for proxy authentication and
4290      identification. A "non-transparent proxy" is a proxy that modifies
4291      the request or response in order to provide some added service to
4292      the user agent, such as group annotation services, media type
4293      transformation, protocol reduction, or anonymity filtering. Except
4294      where either transparent or non-transparent behavior is explicitly
4295      stated, the HTTP proxy requirements apply to both types of
4296      proxies.
4297    </t>
4298  </list>
4299</t>
4300<t>
4301  <iref item="gateway"/>
4302  <x:dfn>gateway</x:dfn>
4303  <list>
4304    <t>
4305      A server which acts as an intermediary for some other server.
4306      Unlike a proxy, a gateway receives requests as if it were the
4307      origin server for the requested resource; the requesting client
4308      may not be aware that it is communicating with a gateway.
4309    </t>
4310  </list>
4311</t>
4312<t>
4313  <iref item="tunnel"/>
4314  <x:dfn>tunnel</x:dfn>
4315  <list>
4316    <t>
4317      An intermediary program which is acting as a blind relay between
4318      two connections. Once active, a tunnel is not considered a party
4319      to the HTTP communication, though the tunnel may have been
4320      initiated by an HTTP request. The tunnel ceases to exist when both
4321      ends of the relayed connections are closed.
4322    </t>
4323  </list>
4324</t>
4325<t>
4326  <iref item="cache"/>
4327  <x:dfn>cache</x:dfn>
4328  <list>
4329    <t>
4330      A program's local store of response messages and the subsystem
4331      that controls its message storage, retrieval, and deletion. A
4332      cache stores cacheable responses in order to reduce the response
4333      time and network bandwidth consumption on future, equivalent
4334      requests. Any client or server may include a cache, though a cache
4335      cannot be used by a server that is acting as a tunnel.
4336    </t>
4337  </list>
4338</t>
4339<t>
4340  <iref item="cacheable"/>
4341  <x:dfn>cacheable</x:dfn>
4342  <list>
4343    <t>
4344      A response is cacheable if a cache is allowed to store a copy of
4345      the response message for use in answering subsequent requests. The
4346      rules for determining the cacheability of HTTP responses are
4347      defined in &caching;. Even if a resource is cacheable, there may
4348      be additional constraints on whether a cache can use the cached
4349      copy for a particular request.
4350    </t>
4351  </list>
4352</t>
4353<t>
4354  <iref item="upstream"/>
4355  <iref item="downstream"/>
4356  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4357  <list>
4358    <t>
4359      Upstream and downstream describe the flow of a message: all
4360      messages flow from upstream to downstream.
4361    </t>
4362  </list>
4363</t>
4364<t>
4365  <iref item="inbound"/>
4366  <iref item="outbound"/>
4367  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4368  <list>
4369    <t>
4370      Inbound and outbound refer to the request and response paths for
4371      messages: "inbound" means "traveling toward the origin server",
4372      and "outbound" means "traveling toward the user agent"
4373    </t>
4374  </list>
4375</t>
4376</section>
4377
4378<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4379
4380<section title="Since RFC2616">
4381<t>
4382  Extracted relevant partitions from <xref target="RFC2616"/>.
4383</t>
4384</section>
4385
4386<section title="Since draft-ietf-httpbis-p1-messaging-00">
4387<t>
4388  Closed issues:
4389  <list style="symbols"> 
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4392      "HTTP Version should be case sensitive"
4393      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4394    </t>
4395    <t>
4396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4397      "'unsafe' characters"
4398      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4399    </t>
4400    <t>
4401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4402      "Chunk Size Definition"
4403      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4407      "Message Length"
4408      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4409    </t>
4410    <t>
4411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4412      "Media Type Registrations"
4413      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4414    </t>
4415    <t>
4416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4417      "URI includes query"
4418      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4419    </t>
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4422      "No close on 1xx responses"
4423      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4424    </t>
4425    <t>
4426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4427      "Remove 'identity' token references"
4428      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4429    </t>
4430    <t>
4431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4432      "Import query BNF"
4433    </t>
4434    <t>
4435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4436      "qdtext BNF"
4437    </t>
4438    <t>
4439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4440      "Normative and Informative references"
4441    </t>
4442    <t>
4443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4444      "RFC2606 Compliance"
4445    </t>
4446    <t>
4447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4448      "RFC977 reference"
4449    </t>
4450    <t>
4451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4452      "RFC1700 references"
4453    </t>
4454    <t>
4455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4456      "inconsistency in date format explanation"
4457    </t>
4458    <t>
4459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4460      "Date reference typo"
4461    </t>
4462    <t>
4463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4464      "Informative references"
4465    </t>
4466    <t>
4467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4468      "ISO-8859-1 Reference"
4469    </t>
4470    <t>
4471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4472      "Normative up-to-date references"
4473    </t>
4474  </list>
4475</t>
4476<t>
4477  Other changes:
4478  <list style="symbols"> 
4479    <t>
4480      Update media type registrations to use RFC4288 template.
4481    </t>
4482    <t>
4483      Use names of RFC4234 core rules DQUOTE and HTAB,
4484      fix broken ABNF for chunk-data
4485      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4486    </t>
4487  </list>
4488</t>
4489</section>
4490
4491<section title="Since draft-ietf-httpbis-p1-messaging-01">
4492<t>
4493  Closed issues:
4494  <list style="symbols"> 
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4497      "Bodies on GET (and other) requests"
4498    </t>
4499    <t>
4500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4501      "Updating to RFC4288"
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4505      "Status Code and Reason Phrase"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4509      "rel_path not used"
4510    </t>
4511  </list>
4512</t>
4513<t>
4514  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4515  <list style="symbols"> 
4516    <t>
4517      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4518      "trailer-part").
4519    </t>
4520    <t>
4521      Avoid underscore character in rule names ("http_URL" ->
4522      "http-URL", "abs_path" -> "path-absolute").
4523    </t>
4524    <t>
4525      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4526      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4527      have to be updated when switching over to RFC3986.
4528    </t>
4529    <t>
4530      Synchronize core rules with RFC5234 (this includes a change to CHAR
4531      which now excludes NUL).
4532    </t>
4533    <t>
4534      Get rid of prose rules that span multiple lines.
4535    </t>
4536    <t>
4537      Get rid of unused rules LOALPHA and UPALPHA.
4538    </t>
4539    <t>
4540      Move "Product Tokens" section (back) into Part 1, as "token" is used
4541      in the definition of the Upgrade header.
4542    </t>
4543    <t>
4544      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4545    </t>
4546    <t>
4547      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4548    </t>
4549  </list>
4550</t>
4551</section>
4552
4553<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4554<t>
4555  Closed issues:
4556  <list style="symbols"> 
4557    <t>
4558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4559      "HTTP-date vs. rfc1123-date"
4560    </t>
4561    <t>
4562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4563      "WS in quoted-pair"
4564    </t>
4565  </list>
4566</t>
4567<t>
4568  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4569  <list style="symbols"> 
4570    <t>
4571      Reference RFC 3984, and update header registrations for headers defined
4572      in this document.
4573    </t>
4574  </list>
4575</t>
4576<t>
4577  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4578  <list style="symbols"> 
4579    <t>
4580      Replace string literals when the string really is case-sensitive (HTTP-Version).
4581    </t>
4582  </list>
4583</t>
4584</section>
4585
4586<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4587<t>
4588  Closed issues:
4589  <list style="symbols"> 
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4592      "Connection closing"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4596      "Move registrations and registry information to IANA Considerations"
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4600      "need new URL for PAD1995 reference"
4601    </t>
4602    <t>
4603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4604      "IANA Considerations: update HTTP URI scheme registration"
4605    </t>
4606    <t>
4607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4608      "Cite HTTPS URI scheme definition"
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4612      "List-type headers vs Set-Cookie"
4613    </t>
4614  </list>
4615</t>
4616<t>
4617  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4618  <list style="symbols"> 
4619    <t>
4620      Replace string literals when the string really is case-sensitive (HTTP-Date).
4621    </t>
4622    <t>
4623      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4624    </t>
4625  </list>
4626</t>
4627</section>
4628
4629<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4630<t>
4631  Closed issues:
4632  <list style="symbols"> 
4633    <t>
4634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4635      "RFC 2822 is updated by RFC 5322"
4636    </t>
4637  </list>
4638</t>
4639<t>
4640  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4641  <list style="symbols"> 
4642    <t>
4643      Use "/" instead of "|" for alternatives.
4644    </t>
4645    <t>
4646      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4647    </t>
4648  </list>
4649</t>
4650</section>
4651
4652</section>
4653
4654</back>
4655</rfc>
Note: See TracBrowser for help on using the repository browser.