source: draft-ietf-httpbis/latest/p1-messaging.xml @ 369

Last change on this file since 369 was 369, checked in by julian.reschke@…, 13 years ago

Explain rationale for OWS/BWS/RWS, do not use LWS production anymore (related to #36)

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   protocol for distributed, collaborative, hypermedia information
232   systems. HTTP has been in use by the World-Wide Web global
233   information initiative since 1990. The first version of HTTP, commonly
234   referred to as HTTP/0.9, was a simple protocol for raw data transfer
235   across the Internet with only a single method and no metadata.
236   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
237   the protocol by allowing messages to be in the format of MIME-like
238   messages, containing metadata about the data transferred and
239   modifiers on the request/response semantics. However, HTTP/1.0 did
240   not sufficiently take into consideration the effects of hierarchical
241   proxies, caching, the need for persistent connections, or name-based
242   virtual hosts. In addition, the proliferation of incompletely-implemented
243   applications calling themselves "HTTP/1.0" necessitated a
244   protocol version change in order for two communicating applications
245   to determine each other's true capabilities.
246</t>
247<t>
248   This document is Part 1 of the seven-part specification that defines
249   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
250   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
251   requirements that enable reliable implementations and adding only
252   those new features that will either be safely ignored by an HTTP/1.0
253   recipient or only sent when communicating with a party advertising
254   compliance with HTTP/1.1.
255   Part 1 defines those aspects of HTTP/1.1 related to overall network
256   operation, message framing, interaction with transport protocols, and
257   URI schemes.
258</t>
259<t>
260   This document is currently disorganized in order to minimize the changes
261   between drafts and enable reviewers to see the smaller errata changes.
262   The next draft will reorganize the sections to better reflect the content.
263   In particular, the sections will be organized according to the typical
264   process of deciding when to use HTTP (URI schemes), overall network operation,
265   connection management, message framing, and generic message parsing.
266   The current mess reflects how widely dispersed these topics and associated
267   requirements had become in <xref target="RFC2616"/>.
268</t>
269
270<section title="Purpose" anchor="intro.purpose">
271<t>
272   Practical information systems require more functionality than simple
273   retrieval, including search, front-end update, and annotation. HTTP
274   allows an open-ended set of methods and headers that indicate the
275   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
276   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
277   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
278   method is to be applied. Messages are passed in a format similar to
279   that used by Internet mail <xref target="RFC5322"/> as defined by the Multipurpose
280   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
281</t>
282<t>
283   HTTP is also used as a generic protocol for communication between
284   user agents and proxies/gateways to other Internet systems, including
285   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
286   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
287   access to resources available from diverse applications.
288</t>
289</section>
290
291<section title="Requirements" anchor="intro.requirements">
292<t>
293   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
294   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
295   document are to be interpreted as described in <xref target="RFC2119"/>.
296</t>
297<t>
298   An implementation is not compliant if it fails to satisfy one or more
299   of the &MUST; or &REQUIRED; level requirements for the protocols it
300   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
301   level and all the &SHOULD; level requirements for its protocols is said
302   to be "unconditionally compliant"; one that satisfies all the &MUST;
303   level requirements but not all the &SHOULD; level requirements for its
304   protocols is said to be "conditionally compliant."
305</t>
306</section>
307
308<section title="Overall Operation" anchor="intro.overall.operation">
309<t>
310   HTTP is a request/response protocol. A client sends a
311   request to the server in the form of a request method, URI, and
312   protocol version, followed by a MIME-like message containing request
313   modifiers, client information, and possible body content over a
314   connection with a server. The server responds with a status line,
315   including the message's protocol version and a success or error code,
316   followed by a MIME-like message containing server information, entity
317   metainformation, and possible entity-body content. The relationship
318   between HTTP and MIME is described in &diff2045entity;.
319</t>
320<t>
321   Most HTTP communication is initiated by a user agent and consists of
322   a request to be applied to a resource on some origin server. In the
323   simplest case, this may be accomplished via a single connection (v)
324   between the user agent (UA) and the origin server (O).
325</t>
326<figure><artwork type="drawing">
327       request chain ------------------------&gt;
328    UA -------------------v------------------- O
329       &lt;----------------------- response chain
330</artwork></figure>
331<t>
332   A more complicated situation occurs when one or more intermediaries
333   are present in the request/response chain. There are three common
334   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
335   forwarding agent, receiving requests for a URI in its absolute form,
336   rewriting all or part of the message, and forwarding the reformatted
337   request toward the server identified by the URI. A gateway is a
338   receiving agent, acting as a layer above some other server(s) and, if
339   necessary, translating the requests to the underlying server's
340   protocol. A tunnel acts as a relay point between two connections
341   without changing the messages; tunnels are used when the
342   communication needs to pass through an intermediary (such as a
343   firewall) even when the intermediary cannot understand the contents
344   of the messages.
345</t>
346<figure><artwork type="drawing">
347       request chain --------------------------------------&gt;
348    UA -----v----- A -----v----- B -----v----- C -----v----- O
349       &lt;------------------------------------- response chain
350</artwork></figure>
351<t>
352   The figure above shows three intermediaries (A, B, and C) between the
353   user agent and origin server. A request or response message that
354   travels the whole chain will pass through four separate connections.
355   This distinction is important because some HTTP communication options
356   may apply only to the connection with the nearest, non-tunnel
357   neighbor, only to the end-points of the chain, or to all connections
358   along the chain. Although the diagram is linear, each participant may
359   be engaged in multiple, simultaneous communications. For example, B
360   may be receiving requests from many clients other than A, and/or
361   forwarding requests to servers other than C, at the same time that it
362   is handling A's request.
363</t>
364<t>
365   Any party to the communication which is not acting as a tunnel may
366   employ an internal cache for handling requests. The effect of a cache
367   is that the request/response chain is shortened if one of the
368   participants along the chain has a cached response applicable to that
369   request. The following illustrates the resulting chain if B has a
370   cached copy of an earlier response from O (via C) for a request which
371   has not been cached by UA or A.
372</t>
373<figure><artwork type="drawing">
374          request chain ----------&gt;
375       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
376          &lt;--------- response chain
377</artwork></figure>
378<t>
379   Not all responses are usefully cacheable, and some requests may
380   contain modifiers which place special requirements on cache behavior.
381   HTTP requirements for cache behavior and cacheable responses are
382   defined in &caching;.
383</t>
384<t>
385   In fact, there are a wide variety of architectures and configurations
386   of caches and proxies currently being experimented with or deployed
387   across the World Wide Web. These systems include national hierarchies
388   of proxy caches to save transoceanic bandwidth, systems that
389   broadcast or multicast cache entries, organizations that distribute
390   subsets of cached data via CD-ROM, and so on. HTTP systems are used
391   in corporate intranets over high-bandwidth links, and for access via
392   PDAs with low-power radio links and intermittent connectivity. The
393   goal of HTTP/1.1 is to support the wide diversity of configurations
394   already deployed while introducing protocol constructs that meet the
395   needs of those who build web applications that require high
396   reliability and, failing that, at least reliable indications of
397   failure.
398</t>
399<t>
400   HTTP communication usually takes place over TCP/IP connections. The
401   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
402   not preclude HTTP from being implemented on top of any other protocol
403   on the Internet, or on other networks. HTTP only presumes a reliable
404   transport; any protocol that provides such guarantees can be used;
405   the mapping of the HTTP/1.1 request and response structures onto the
406   transport data units of the protocol in question is outside the scope
407   of this specification.
408</t>
409<t>
410   In HTTP/1.0, most implementations used a new connection for each
411   request/response exchange. In HTTP/1.1, a connection may be used for
412   one or more request/response exchanges, although connections may be
413   closed for a variety of reasons (see <xref target="persistent.connections"/>).
414</t>
415</section>
416</section>
417
418<section title="Notational Conventions and Generic Grammar" anchor="notation">
419
420<section title="ABNF Extension: #rule" anchor="notation.abnf">
421  <t>
422    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
423    improve readability.
424  </t>
425  <t>
426    A construct "#" is defined, similar to "*", for defining lists of
427    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
428    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
429    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
430    form of lists very easy; a rule such as
431    <figure><artwork type="example">
432 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
433  </t>
434  <t>
435    can be shown as
436    <figure><artwork type="example">
437 1#element</artwork></figure>
438  </t>
439  <t>
440    Wherever this construct is used, null elements are allowed, but do
441    not contribute to the count of elements present. That is,
442    "(element), , (element) " is permitted, but counts as only two
443    elements. Therefore, where at least one element is required, at
444    least one non-null element &MUST; be present. Default values are 0
445    and infinity so that "#element" allows any number, including zero;
446    "1#element" requires at least one; and "1#2element" allows one or
447    two.
448  </t>
449</section>
450
451<section title="Basic Rules" anchor="basic.rules">
452<t anchor="core.rules">
453  <x:anchor-alias value="ALPHA"/>
454  <x:anchor-alias value="CHAR"/>
455  <x:anchor-alias value="CTL"/>
456  <x:anchor-alias value="CR"/>
457  <x:anchor-alias value="CRLF"/>
458  <x:anchor-alias value="DIGIT"/>
459  <x:anchor-alias value="DQUOTE"/>
460  <x:anchor-alias value="HEXDIG"/>
461  <x:anchor-alias value="HTAB"/>
462  <x:anchor-alias value="LF"/>
463  <x:anchor-alias value="OCTET"/>
464  <x:anchor-alias value="SP"/>
465  <x:anchor-alias value="WSP"/>
466   This specification uses the Augmented Backus-Naur Form (ABNF) notation
467   of <xref target="RFC5234"/>.  The following core rules are included by
468   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
469   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
470   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
471   DIGIT (decimal 0-9), DQUOTE (double quote),
472   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
473   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
474   and WSP (white space).
475</t>
476<t anchor="rule.CRLF">
477  <x:anchor-alias value="CRLF"/>
478   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
479   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
480   tolerant applications). The end-of-line marker within an entity-body
481   is defined by its associated media type, as described in &media-types;.
482</t>
483<t anchor="rule.LWS">
484   All linear white space (LWS) in header field-values has the same semantics as SP. A
485   recipient &MAY; replace any such linear white space with a single SP before
486   interpreting the field value or forwarding the message downstream.
487</t>
488<t>
489   Historically, HTTP/1.1 header field values allow linear white space folding across
490   multiple lines. However, this specification deprecates its use; senders &MUST-NOT;
491   produce messages that include LWS folding (i.e., use the obs-fold rule), except
492   within the message/http media type (<xref target="internet.media.type.message.http"/>).
493   Receivers &SHOULD; still parse folded linear white space.
494</t>
495<t>
496   This specification uses three rules to denote the use of linear white space;
497   BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
498</t>
499<t>
500   "Bad" white space is allowed by the BNF, but senders &SHOULD-NOT; produce it in messages.
501   Receivers &MUST; accept it in incoming messages.
502</t>
503<t>
504   Required white space is used when at least one linear white space character
505   is required to separate field tokens. In all such cases, a single SP character
506   &SHOULD; be used.
507</t>
508<t anchor="rule.whitespace">
509  <x:anchor-alias value="BWS"/>
510  <x:anchor-alias value="OWS"/>
511  <x:anchor-alias value="RWS"/>
512  <x:anchor-alias value="obs-fold"/>
513</t>
514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
515  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
516                 ; "optional" white space
517  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
518                 ; "required" white space
519  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
520                 ; "bad" white space
521  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
522</artwork></figure>
523<t anchor="rule.TEXT">
524  <x:anchor-alias value="TEXT"/>
525   The TEXT rule is only used for descriptive field contents and values
526   that are not intended to be interpreted by the message parser. Words
527   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
528   <xref target="ISO-8859-1"/> only when encoded according to the rules of
529   <xref target="RFC2047"/>.
530</t>
531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
532  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>OWS</x:ref>
533                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>OWS</x:ref>
534</artwork></figure>
535<t>
536   A CRLF is allowed in the definition of TEXT only as part of a header
537   field continuation. It is expected that the folding LWS will be
538   replaced with a single SP before interpretation of the TEXT value.
539</t>
540<t anchor="rule.token.separators">
541  <x:anchor-alias value="tchar"/>
542  <x:anchor-alias value="token"/>
543  <x:anchor-alias value="separators"/>
544   Many HTTP/1.1 header field values consist of words separated by LWS
545   or special characters. These special characters &MUST; be in a quoted
546   string to be used within a parameter value (as defined in
547   <xref target="transfer.codings"/>).
548</t>
549<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"/>
550  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
551                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
552                 / "/" / "[" / "]" / "?" / "="
553                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
554                 
555  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
556                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
557                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
558                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
559                 
560  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
561</artwork></figure>
562<t anchor="rule.comment">
563  <x:anchor-alias value="comment"/>
564  <x:anchor-alias value="ctext"/>
565   Comments can be included in some HTTP header fields by surrounding
566   the comment text with parentheses. Comments are only allowed in
567   fields containing "comment" as part of their field value definition.
568   In all other fields, parentheses are considered part of the field
569   value.
570</t>
571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
572  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
573  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
574</artwork></figure>
575<t anchor="rule.quoted-string">
576  <x:anchor-alias value="quoted-string"/>
577  <x:anchor-alias value="qdtext"/>
578   A string of text is parsed as a single word if it is quoted using
579   double-quote marks.
580</t>
581<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
582  <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> )
583  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
584</artwork></figure>
585<t anchor="rule.quoted-pair">
586  <x:anchor-alias value="quoted-pair"/>
587  <x:anchor-alias value="quoted-text"/>
588   The backslash character ("\") &MAY; be used as a single-character
589   quoting mechanism only within quoted-string and comment constructs.
590</t>
591<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
592  <x:ref>quoted-text</x:ref>    = %x01-09 /
593                   %x0B-0C /
594                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
595  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
596</artwork></figure>
597</section>
598
599<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
600  <x:anchor-alias value="request-header"/>
601  <x:anchor-alias value="response-header"/>
602  <x:anchor-alias value="accept-params"/>
603  <x:anchor-alias value="entity-body"/>
604  <x:anchor-alias value="entity-header"/>
605  <x:anchor-alias value="Cache-Control"/>
606  <x:anchor-alias value="Pragma"/>
607  <x:anchor-alias value="Warning"/>
608<t>
609  The ABNF rules below are defined in other parts:
610</t>
611<figure><!-- Part2--><artwork type="abnf2616">
612  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
613  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
614</artwork></figure>
615<figure><!-- Part3--><artwork type="abnf2616">
616  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
617  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
618  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
619</artwork></figure>
620<figure><!-- Part6--><artwork type="abnf2616">
621  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
622  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
623  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
624</artwork></figure>
625</section>
626
627</section>
628
629<section title="Protocol Parameters" anchor="protocol.parameters">
630
631<section title="HTTP Version" anchor="http.version">
632  <x:anchor-alias value="HTTP-Version"/>
633  <x:anchor-alias value="HTTP-Prot-Name"/>
634<t>
635   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
636   of the protocol. The protocol versioning policy is intended to allow
637   the sender to indicate the format of a message and its capacity for
638   understanding further HTTP communication, rather than the features
639   obtained via that communication. No change is made to the version
640   number for the addition of message components which do not affect
641   communication behavior or which only add to extensible field values.
642   The &lt;minor&gt; number is incremented when the changes made to the
643   protocol add features which do not change the general message parsing
644   algorithm, but which may add to the message semantics and imply
645   additional capabilities of the sender. The &lt;major&gt; number is
646   incremented when the format of a message within the protocol is
647   changed. See <xref target="RFC2145"/> for a fuller explanation.
648</t>
649<t>
650   The version of an HTTP message is indicated by an HTTP-Version field
651   in the first line of the message. HTTP-Version is case-sensitive.
652</t>
653<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
654  <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>
655  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
656</artwork></figure>
657<t>
658   Note that the major and minor numbers &MUST; be treated as separate
659   integers and that each &MAY; be incremented higher than a single digit.
660   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
661   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
662   &MUST-NOT; be sent.
663</t>
664<t>
665   An application that sends a request or response message that includes
666   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
667   with this specification. Applications that are at least conditionally
668   compliant with this specification &SHOULD; use an HTTP-Version of
669   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
670   not compatible with HTTP/1.0. For more details on when to send
671   specific HTTP-Version values, see <xref target="RFC2145"/>.
672</t>
673<t>
674   The HTTP version of an application is the highest HTTP version for
675   which the application is at least conditionally compliant.
676</t>
677<t>
678   Proxy and gateway applications need to be careful when forwarding
679   messages in protocol versions different from that of the application.
680   Since the protocol version indicates the protocol capability of the
681   sender, a proxy/gateway &MUST-NOT; send a message with a version
682   indicator which is greater than its actual version. If a higher
683   version request is received, the proxy/gateway &MUST; either downgrade
684   the request version, or respond with an error, or switch to tunnel
685   behavior.
686</t>
687<t>
688   Due to interoperability problems with HTTP/1.0 proxies discovered
689   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
690   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
691   they support. The proxy/gateway's response to that request &MUST; be in
692   the same major version as the request.
693</t>
694<t>
695  <list>
696    <t>
697      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
698      of header fields required or forbidden by the versions involved.
699    </t>
700  </list>
701</t>
702</section>
703
704<section title="Uniform Resource Identifiers" anchor="uri">
705<t>
706   URIs have been known by many names: WWW addresses, Universal Document
707   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
708   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
709   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
710   simply formatted strings which identify--via name, location, or any
711   other characteristic--a resource.
712</t>
713
714<section title="General Syntax" anchor="general.syntax">
715  <x:anchor-alias value="absoluteURI"/>
716  <x:anchor-alias value="authority"/>
717  <x:anchor-alias value="fragment"/>
718  <x:anchor-alias value="path-absolute"/>
719  <x:anchor-alias value="port"/>
720  <x:anchor-alias value="query"/>
721  <x:anchor-alias value="relativeURI"/>
722  <x:anchor-alias value="uri-host"/>
723<t>
724   URIs in HTTP can be represented in absolute form or relative to some
725   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
726   forms are differentiated by the fact that absolute URIs always begin
727   with a scheme name followed by a colon. For definitive information on
728   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
729   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
730   and <xref target="RFC1808"/>). This specification adopts the
731   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
732   "host", "abs_path", "query", and "authority" from that specification:
733</t>
734<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"/>
735  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
736  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
737  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
738  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
739  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
740  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
741  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
742  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
743</artwork></figure>
744<t>
745   HTTP does not place any a priori limit on the length of
746   a URI. Servers &MUST; be able to handle the URI of any resource they
747   serve, and &SHOULD; be able to handle URIs of unbounded length if they
748   provide GET-based forms that could generate such URIs. A server
749   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
750   than the server can handle (see &status-414;).
751</t>
752<t>
753  <list>
754    <t>
755      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
756      above 255 bytes, because some older client or proxy
757      implementations might not properly support these lengths.
758    </t>
759  </list>
760</t>
761</section>
762
763<section title="http URL" anchor="http.url">
764  <x:anchor-alias value="http-URL"/>
765  <iref item="http URI scheme" primary="true"/>
766  <iref item="URI scheme" subitem="http" primary="true"/>
767<t>
768   The "http" scheme is used to locate network resources via the HTTP
769   protocol. This section defines the scheme-specific syntax and
770   semantics for http URLs.
771</t>
772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
773  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
774             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
775</artwork></figure>
776<t>
777   If the port is empty or not given, port 80 is assumed. The semantics
778   are that the identified resource is located at the server listening
779   for TCP connections on that port of that host, and the Request-URI
780   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
781   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
782   the path-absolute is not present in the URL, it &MUST; be given as "/" when
783   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
784   receives a host name which is not a fully qualified domain name, it
785   &MAY; add its domain to the host name it received. If a proxy receives
786   a fully qualified domain name, the proxy &MUST-NOT; change the host
787   name.
788</t>
789<t><list><t>
790  <iref item="https URI scheme"/>
791  <iref item="URI scheme" subitem="https"/>
792  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
793</t></list></t>
794</section>
795
796<section title="URI Comparison" anchor="uri.comparison">
797<t>
798   When comparing two URIs to decide if they match or not, a client
799   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
800   URIs, with these exceptions:
801  <list style="symbols">
802    <t>A port that is empty or not given is equivalent to the default
803        port for that URI-reference;</t>
804    <t>Comparisons of host names &MUST; be case-insensitive;</t>
805    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
806    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
807  </list>
808</t>
809<t>
810   Characters other than those in the "reserved" set (see
811   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
812   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
813</t>
814<t>
815   For example, the following three URIs are equivalent:
816</t>
817<figure><artwork type="example">
818   http://example.com:80/~smith/home.html
819   http://EXAMPLE.com/%7Esmith/home.html
820   http://EXAMPLE.com:/%7esmith/home.html
821</artwork></figure>
822</section>
823</section>
824
825<section title="Date/Time Formats" anchor="date.time.formats">
826<section title="Full Date" anchor="full.date">
827  <x:anchor-alias value="HTTP-date"/>
828  <x:anchor-alias value="obsolete-date"/>
829  <x:anchor-alias value="rfc1123-date"/>
830  <x:anchor-alias value="rfc850-date"/>
831  <x:anchor-alias value="asctime-date"/>
832  <x:anchor-alias value="date1"/>
833  <x:anchor-alias value="date2"/>
834  <x:anchor-alias value="date3"/>
835  <x:anchor-alias value="rfc1123-date"/>
836  <x:anchor-alias value="time"/>
837  <x:anchor-alias value="wkday"/>
838  <x:anchor-alias value="weekday"/>
839  <x:anchor-alias value="month"/>
840<t>
841   HTTP applications have historically allowed three different formats
842   for the representation of date/time stamps:
843</t>
844<figure><artwork type="example">
845   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
846   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
847   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
848</artwork></figure>
849<t>
850   The first format is preferred as an Internet standard and represents
851   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
852   <xref target="RFC822"/>). The other formats are described here only for
853   compatibility with obsolete implementations.
854   HTTP/1.1 clients and servers that parse the date value &MUST; accept
855   all three formats (for compatibility with HTTP/1.0), though they &MUST;
856   only generate the RFC 1123 format for representing HTTP-date values
857   in header fields. See <xref target="tolerant.applications"/> for further information.
858</t>
859<t><list><t>
860      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
861      accepting date values that may have been sent by non-HTTP
862      applications, as is sometimes the case when retrieving or posting
863      messages via proxies/gateways to SMTP or NNTP.
864</t></list></t>
865<t>
866   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
867   (GMT), without exception. For the purposes of HTTP, GMT is exactly
868   equal to UTC (Coordinated Universal Time). This is indicated in the
869   first two formats by the inclusion of "GMT" as the three-letter
870   abbreviation for time zone, and &MUST; be assumed when reading the
871   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
872   additional LWS beyond that specifically included as SP in the
873   grammar.
874</t>
875<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"/>
876  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
877  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
878  <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
879  <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
880  <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>
881  <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>
882                 ; day month year (e.g., 02 Jun 1982)
883  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
884                 ; day-month-year (e.g., 02-Jun-82)
885  <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> ))
886                 ; month day (e.g., Jun  2)
887  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
888                 ; 00:00:00 - 23:59:59
889  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
890               / s-Thu / s-Fri / s-Sat / s-Sun
891  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
892               / l-Thu / l-Fri / l-Sat / l-Sun
893  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
894               / s-May / s-Jun / s-Jul / s-Aug
895               / s-Sep / s-Oct / s-Nov / s-Dec
896               
897  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
898
899  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
900  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
901  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
902  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
903  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
904  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
905  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
906
907  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
908  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
909  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
910  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
911  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
912  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
913  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
914
915  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
916  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
917  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
918  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
919  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
920  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
921  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
922  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
923  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
924  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
925  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
926  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
927</artwork></figure>
928<t>
929      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
930      to their usage within the protocol stream. Clients and servers are
931      not required to use these formats for user presentation, request
932      logging, etc.
933</t>
934</section>
935</section>
936
937<section title="Transfer Codings" anchor="transfer.codings">
938  <x:anchor-alias value="parameter"/>
939  <x:anchor-alias value="transfer-coding"/>
940  <x:anchor-alias value="transfer-extension"/>
941<t>
942   Transfer-coding values are used to indicate an encoding
943   transformation that has been, can be, or may need to be applied to an
944   entity-body in order to ensure "safe transport" through the network.
945   This differs from a content coding in that the transfer-coding is a
946   property of the message, not of the original entity.
947</t>
948<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
949  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
950  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
951</artwork></figure>
952<t anchor="rule.parameter">
953  <x:anchor-alias value="attribute"/>
954  <x:anchor-alias value="parameter"/>
955  <x:anchor-alias value="value"/>
956   Parameters are in  the form of attribute/value pairs.
957</t>
958<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"/>
959  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
960  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
961  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
962</artwork></figure>
963<t>
964   All transfer-coding values are case-insensitive. HTTP/1.1 uses
965   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
966   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
967</t>
968<t>
969   Whenever a transfer-coding is applied to a message-body, the set of
970   transfer-codings &MUST; include "chunked", unless the message indicates it
971   is terminated by closing the connection. When the "chunked" transfer-coding
972   is used, it &MUST; be the last transfer-coding applied to the
973   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
974   than once to a message-body. These rules allow the recipient to
975   determine the transfer-length of the message (<xref target="message.length"/>).
976</t>
977<t>
978   Transfer-codings are analogous to the Content-Transfer-Encoding
979   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
980   binary data over a 7-bit transport service. However, safe transport
981   has a different focus for an 8bit-clean transfer protocol. In HTTP,
982   the only unsafe characteristic of message-bodies is the difficulty in
983   determining the exact body length (<xref target="message.length"/>), or the desire to
984   encrypt data over a shared transport.
985</t>
986<t>
987   The Internet Assigned Numbers Authority (IANA) acts as a registry for
988   transfer-coding value tokens. Initially, the registry contains the
989   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
990   "gzip", "compress", and "deflate" (&content-codings;).
991</t>
992<t>
993   New transfer-coding value tokens &SHOULD; be registered in the same way
994   as new content-coding value tokens (&content-codings;).
995</t>
996<t>
997   A server which receives an entity-body with a transfer-coding it does
998   not understand &SHOULD; return 501 (Not Implemented), and close the
999   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1000   client.
1001</t>
1002
1003<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1004  <x:anchor-alias value="chunk"/>
1005  <x:anchor-alias value="Chunked-Body"/>
1006  <x:anchor-alias value="chunk-data"/>
1007  <x:anchor-alias value="chunk-ext"/>
1008  <x:anchor-alias value="chunk-ext-name"/>
1009  <x:anchor-alias value="chunk-ext-val"/>
1010  <x:anchor-alias value="chunk-size"/>
1011  <x:anchor-alias value="last-chunk"/>
1012  <x:anchor-alias value="trailer-part"/>
1013<t>
1014   The chunked encoding modifies the body of a message in order to
1015   transfer it as a series of chunks, each with its own size indicator,
1016   followed by an &OPTIONAL; trailer containing entity-header fields. This
1017   allows dynamically produced content to be transferred along with the
1018   information necessary for the recipient to verify that it has
1019   received the full message.
1020</t>
1021<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-ext"/><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"/>
1022  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1023                   <x:ref>last-chunk</x:ref>
1024                   <x:ref>trailer-part</x:ref>
1025                   <x:ref>CRLF</x:ref>
1026 
1027  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1028                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1029  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1030  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1031 
1032  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1033  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1034  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1035  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1036  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1037</artwork></figure>
1038<t>
1039   The chunk-size field is a string of hex digits indicating the size of
1040   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1041   zero, followed by the trailer, which is terminated by an empty line.
1042</t>
1043<t>
1044   The trailer allows the sender to include additional HTTP header
1045   fields at the end of the message. The Trailer header field can be
1046   used to indicate which header fields are included in a trailer (see
1047   <xref target="header.trailer"/>).
1048</t>
1049<t>
1050   A server using chunked transfer-coding in a response &MUST-NOT; use the
1051   trailer for any header fields unless at least one of the following is
1052   true:
1053  <list style="numbers">
1054    <t>the request included a TE header field that indicates "trailers" is
1055     acceptable in the transfer-coding of the  response, as described in
1056     <xref target="header.te"/>; or,</t>
1057
1058    <t>the server is the origin server for the response, the trailer
1059     fields consist entirely of optional metadata, and the recipient
1060     could use the message (in a manner acceptable to the origin server)
1061     without receiving this metadata.  In other words, the origin server
1062     is willing to accept the possibility that the trailer fields might
1063     be silently discarded along the path to the client.</t>
1064  </list>
1065</t>
1066<t>
1067   This requirement prevents an interoperability failure when the
1068   message is being received by an HTTP/1.1 (or later) proxy and
1069   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1070   compliance with the protocol would have necessitated a possibly
1071   infinite buffer on the proxy.
1072</t>
1073<t>
1074   A process for decoding the "chunked" transfer-coding
1075   can be represented in pseudo-code as:
1076</t>
1077<figure><artwork type="code">
1078  length := 0
1079  read chunk-size, chunk-ext (if any) and CRLF
1080  while (chunk-size &gt; 0) {
1081     read chunk-data and CRLF
1082     append chunk-data to entity-body
1083     length := length + chunk-size
1084     read chunk-size and CRLF
1085  }
1086  read entity-header
1087  while (entity-header not empty) {
1088     append entity-header to existing header fields
1089     read entity-header
1090  }
1091  Content-Length := length
1092  Remove "chunked" from Transfer-Encoding
1093</artwork></figure>
1094<t>
1095   All HTTP/1.1 applications &MUST; be able to receive and decode the
1096   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1097   they do not understand.
1098</t>
1099</section>
1100</section>
1101
1102<section title="Product Tokens" anchor="product.tokens">
1103  <x:anchor-alias value="product"/>
1104  <x:anchor-alias value="product-version"/>
1105<t>
1106   Product tokens are used to allow communicating applications to
1107   identify themselves by software name and version. Most fields using
1108   product tokens also allow sub-products which form a significant part
1109   of the application to be listed, separated by white space. By
1110   convention, the products are listed in order of their significance
1111   for identifying the application.
1112</t>
1113<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1114  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1115  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1116</artwork></figure>
1117<t>
1118   Examples:
1119</t>
1120<figure><artwork type="example">
1121    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1122    Server: Apache/0.8.4
1123</artwork></figure>
1124<t>
1125   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1126   used for advertising or other non-essential information. Although any
1127   token character &MAY; appear in a product-version, this token &SHOULD;
1128   only be used for a version identifier (i.e., successive versions of
1129   the same product &SHOULD; only differ in the product-version portion of
1130   the product value).
1131</t>
1132</section>
1133
1134</section>
1135
1136<section title="HTTP Message" anchor="http.message">
1137
1138<section title="Message Types" anchor="message.types">
1139  <x:anchor-alias value="generic-message"/>
1140  <x:anchor-alias value="HTTP-message"/>
1141  <x:anchor-alias value="start-line"/>
1142<t>
1143   HTTP messages consist of requests from client to server and responses
1144   from server to client.
1145</t>
1146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1147  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1148</artwork></figure>
1149<t>
1150   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1151   message format of <xref target="RFC5322"/> for transferring entities (the payload
1152   of the message). Both types of message consist of a start-line, zero
1153   or more header fields (also known as "headers"), an empty line (i.e.,
1154   a line with nothing preceding the CRLF) indicating the end of the
1155   header fields, and possibly a message-body.
1156</t>
1157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1158  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1159                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1160                    <x:ref>CRLF</x:ref>
1161                    [ <x:ref>message-body</x:ref> ]
1162  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1163</artwork></figure>
1164<t>
1165   In the interest of robustness, servers &SHOULD; ignore any empty
1166   line(s) received where a Request-Line is expected. In other words, if
1167   the server is reading the protocol stream at the beginning of a
1168   message and receives a CRLF first, it should ignore the CRLF.
1169</t>
1170<t>
1171   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1172   after a POST request. To restate what is explicitly forbidden by the
1173   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1174   extra CRLF.
1175</t>
1176</section>
1177
1178<section title="Message Headers" anchor="message.headers">
1179  <x:anchor-alias value="field-content"/>
1180  <x:anchor-alias value="field-name"/>
1181  <x:anchor-alias value="field-value"/>
1182  <x:anchor-alias value="message-header"/>
1183<t>
1184   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1185   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1186   entity-header (&entity-header-fields;) fields, follow the same generic format as
1187   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1188   of a name followed by a colon (":") and the field value. Field names
1189   are case-insensitive. The field value &MAY; be preceded by any amount
1190   of LWS, though a single SP is preferred. Header fields can be
1191   extended over multiple lines by preceding each extra line with at
1192   least one SP or HTAB. Applications ought to follow "common form", where
1193   one is known or indicated, when generating HTTP constructs, since
1194   there might exist some implementations that fail to accept anything
1195   beyond the common forms.
1196</t>
1197<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"/>
1198  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1199  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1200  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1201  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1202                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1203                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1204                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1205</artwork></figure>
1206<t>
1207  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1208</t>
1209<t>
1210   The field-content does not include any leading or trailing LWS:
1211   linear white space occurring before the first non-whitespace
1212   character of the field-value or after the last non-whitespace
1213   character of the field-value. Such leading or trailing LWS &MAY; be
1214   removed without changing the semantics of the field value. Any LWS
1215   that occurs between field-content &MAY; be replaced with a single SP
1216   before interpreting the field value or forwarding the message
1217   downstream.
1218</t>
1219<t>
1220   The order in which header fields with differing field names are
1221   received is not significant. However, it is "good practice" to send
1222   general-header fields first, followed by request-header or response-header
1223   fields, and ending with the entity-header fields.
1224</t>
1225<t>
1226   Multiple message-header fields with the same field-name &MAY; be
1227   present in a message if and only if the entire field-value for that
1228   header field is defined as a comma-separated list [i.e., #(values)].
1229   It &MUST; be possible to combine the multiple header fields into one
1230   "field-name: field-value" pair, without changing the semantics of the
1231   message, by appending each subsequent field-value to the first, each
1232   separated by a comma. The order in which header fields with the same
1233   field-name are received is therefore significant to the
1234   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1235   change the order of these field values when a message is forwarded.
1236</t>
1237<t>
1238  <list><t>
1239   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1240   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1241   can occur multiple times, but does not use the list syntax, and thus cannot
1242   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1243   for details.) Also note that the Set-Cookie2 header specified in
1244   <xref target="RFC2965"/> does not share this problem.
1245  </t></list>
1246</t>
1247 
1248</section>
1249
1250<section title="Message Body" anchor="message.body">
1251  <x:anchor-alias value="message-body"/>
1252<t>
1253   The message-body (if any) of an HTTP message is used to carry the
1254   entity-body associated with the request or response. The message-body
1255   differs from the entity-body only when a transfer-coding has been
1256   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1257</t>
1258<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1259  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1260               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1261</artwork></figure>
1262<t>
1263   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1264   applied by an application to ensure safe and proper transfer of the
1265   message. Transfer-Encoding is a property of the message, not of the
1266   entity, and thus &MAY; be added or removed by any application along the
1267   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1268   when certain transfer-codings may be used.)
1269</t>
1270<t>
1271   The rules for when a message-body is allowed in a message differ for
1272   requests and responses.
1273</t>
1274<t>
1275   The presence of a message-body in a request is signaled by the
1276   inclusion of a Content-Length or Transfer-Encoding header field in
1277   the request's message-headers. A message-body &MUST-NOT; be included in
1278   a request if the specification of the request method (&method;)
1279   explicitly disallows an entity-body in requests.
1280   When a request message contains both a message-body of non-zero
1281   length and a method that does not define any semantics for that
1282   request message-body, then an origin server &SHOULD; either ignore
1283   the message-body or respond with an appropriate error message
1284   (e.g., 413).  A proxy or gateway, when presented the same request,
1285   &SHOULD; either forward the request inbound with the message-body or
1286   ignore the message-body when determining a response.
1287</t>
1288<t>
1289   For response messages, whether or not a message-body is included with
1290   a message is dependent on both the request method and the response
1291   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1292   &MUST-NOT; include a message-body, even though the presence of entity-header
1293   fields might lead one to believe they do. All 1xx
1294   (informational), 204 (No Content), and 304 (Not Modified) responses
1295   &MUST-NOT; include a message-body. All other responses do include a
1296   message-body, although it &MAY; be of zero length.
1297</t>
1298</section>
1299
1300<section title="Message Length" anchor="message.length">
1301<t>
1302   The transfer-length of a message is the length of the message-body as
1303   it appears in the message; that is, after any transfer-codings have
1304   been applied. When a message-body is included with a message, the
1305   transfer-length of that body is determined by one of the following
1306   (in order of precedence):
1307</t>
1308<t>
1309  <list style="numbers">
1310    <x:lt><t>
1311     Any response message which "&MUST-NOT;" include a message-body (such
1312     as the 1xx, 204, and 304 responses and any response to a HEAD
1313     request) is always terminated by the first empty line after the
1314     header fields, regardless of the entity-header fields present in
1315     the message.
1316    </t></x:lt>
1317    <x:lt><t>
1318     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1319     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1320     is used, the transfer-length is defined by the use of this transfer-coding.
1321     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1322     is not present, the transfer-length is defined by the sender closing the connection.
1323    </t></x:lt>
1324    <x:lt><t>
1325     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1326     decimal value in OCTETs represents both the entity-length and the
1327     transfer-length. The Content-Length header field &MUST-NOT; be sent
1328     if these two lengths are different (i.e., if a Transfer-Encoding
1329     header field is present). If a message is received with both a
1330     Transfer-Encoding header field and a Content-Length header field,
1331     the latter &MUST; be ignored.
1332    </t></x:lt>
1333    <x:lt><t>
1334     If the message uses the media type "multipart/byteranges", and the
1335     transfer-length is not otherwise specified, then this self-delimiting
1336     media type defines the transfer-length. This media type
1337     &MUST-NOT; be used unless the sender knows that the recipient can parse
1338     it; the presence in a request of a Range header with multiple byte-range
1339     specifiers from a 1.1 client implies that the client can parse
1340     multipart/byteranges responses.
1341    <list style="empty"><t>
1342       A range header might be forwarded by a 1.0 proxy that does not
1343       understand multipart/byteranges; in this case the server &MUST;
1344       delimit the message using methods defined in items 1, 3 or 5 of
1345       this section.
1346    </t></list>
1347    </t></x:lt>
1348    <x:lt><t>
1349     By the server closing the connection. (Closing the connection
1350     cannot be used to indicate the end of a request body, since that
1351     would leave no possibility for the server to send back a response.)
1352    </t></x:lt>
1353  </list>
1354</t>
1355<t>
1356   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1357   containing a message-body &MUST; include a valid Content-Length header
1358   field unless the server is known to be HTTP/1.1 compliant. If a
1359   request contains a message-body and a Content-Length is not given,
1360   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1361   determine the length of the message, or with 411 (Length Required) if
1362   it wishes to insist on receiving a valid Content-Length.
1363</t>
1364<t>
1365   All HTTP/1.1 applications that receive entities &MUST; accept the
1366   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1367   to be used for messages when the message length cannot be determined
1368   in advance.
1369</t>
1370<t>
1371   Messages &MUST-NOT; include both a Content-Length header field and a
1372   transfer-coding. If the message does include a
1373   transfer-coding, the Content-Length &MUST; be ignored.
1374</t>
1375<t>
1376   When a Content-Length is given in a message where a message-body is
1377   allowed, its field value &MUST; exactly match the number of OCTETs in
1378   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1379   invalid length is received and detected.
1380</t>
1381</section>
1382
1383<section title="General Header Fields" anchor="general.header.fields">
1384  <x:anchor-alias value="general-header"/>
1385<t>
1386   There are a few header fields which have general applicability for
1387   both request and response messages, but which do not apply to the
1388   entity being transferred. These header fields apply only to the
1389   message being transmitted.
1390</t>
1391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1392  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1393                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1394                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1395                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1396                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1397                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1398                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1399                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1400                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1401</artwork></figure>
1402<t>
1403   General-header field names can be extended reliably only in
1404   combination with a change in the protocol version. However, new or
1405   experimental header fields may be given the semantics of general
1406   header fields if all parties in the communication recognize them to
1407   be general-header fields. Unrecognized header fields are treated as
1408   entity-header fields.
1409</t>
1410</section>
1411</section>
1412
1413<section title="Request" anchor="request">
1414  <x:anchor-alias value="Request"/>
1415<t>
1416   A request message from a client to a server includes, within the
1417   first line of that message, the method to be applied to the resource,
1418   the identifier of the resource, and the protocol version in use.
1419</t>
1420<!--                 Host                      ; should be moved here eventually -->
1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1422  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1423                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1424                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1425                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1426                  <x:ref>CRLF</x:ref>
1427                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1428</artwork></figure>
1429
1430<section title="Request-Line" anchor="request-line">
1431  <x:anchor-alias value="Request-Line"/>
1432<t>
1433   The Request-Line begins with a method token, followed by the
1434   Request-URI and the protocol version, and ending with CRLF. The
1435   elements are separated by SP characters. No CR or LF is allowed
1436   except in the final CRLF sequence.
1437</t>
1438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1439  <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>
1440</artwork></figure>
1441
1442<section title="Method" anchor="method">
1443  <x:anchor-alias value="Method"/>
1444<t>
1445   The Method  token indicates the method to be performed on the
1446   resource identified by the Request-URI. The method is case-sensitive.
1447</t>
1448<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1449  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1450</artwork></figure>
1451</section>
1452
1453<section title="Request-URI" anchor="request-uri">
1454  <x:anchor-alias value="Request-URI"/>
1455<t>
1456   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1457   identifies the resource upon which to apply the request.
1458</t>
1459<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1460  <x:ref>Request-URI</x:ref>    = "*"
1461                 / <x:ref>absoluteURI</x:ref>
1462                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1463                 / <x:ref>authority</x:ref>
1464</artwork></figure>
1465<t>
1466   The four options for Request-URI are dependent on the nature of the
1467   request. The asterisk "*" means that the request does not apply to a
1468   particular resource, but to the server itself, and is only allowed
1469   when the method used does not necessarily apply to a resource. One
1470   example would be
1471</t>
1472<figure><artwork type="example">
1473    OPTIONS * HTTP/1.1
1474</artwork></figure>
1475<t>
1476   The absoluteURI form is &REQUIRED; when the request is being made to a
1477   proxy. The proxy is requested to forward the request or service it
1478   from a valid cache, and return the response. Note that the proxy &MAY;
1479   forward the request on to another proxy or directly to the server
1480   specified by the absoluteURI. In order to avoid request loops, a
1481   proxy &MUST; be able to recognize all of its server names, including
1482   any aliases, local variations, and the numeric IP address. An example
1483   Request-Line would be:
1484</t>
1485<figure><artwork type="example">
1486    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1487</artwork></figure>
1488<t>
1489   To allow for transition to absoluteURIs in all requests in future
1490   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1491   form in requests, even though HTTP/1.1 clients will only generate
1492   them in requests to proxies.
1493</t>
1494<t>
1495   The authority form is only used by the CONNECT method (&CONNECT;).
1496</t>
1497<t>
1498   The most common form of Request-URI is that used to identify a
1499   resource on an origin server or gateway. In this case the absolute
1500   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1501   the Request-URI, and the network location of the URI (authority) &MUST;
1502   be transmitted in a Host header field. For example, a client wishing
1503   to retrieve the resource above directly from the origin server would
1504   create a TCP connection to port 80 of the host "www.example.org" and send
1505   the lines:
1506</t>
1507<figure><artwork type="example">
1508    GET /pub/WWW/TheProject.html HTTP/1.1
1509    Host: www.example.org
1510</artwork></figure>
1511<t>
1512   followed by the remainder of the Request. Note that the absolute path
1513   cannot be empty; if none is present in the original URI, it &MUST; be
1514   given as "/" (the server root).
1515</t>
1516<t>
1517   The Request-URI is transmitted in the format specified in
1518   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1519   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1520   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1521   &MUST; decode the Request-URI in order to
1522   properly interpret the request. Servers &SHOULD; respond to invalid
1523   Request-URIs with an appropriate status code.
1524</t>
1525<t>
1526   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1527   received Request-URI when forwarding it to the next inbound server,
1528   except as noted above to replace a null path-absolute with "/".
1529</t>
1530<t>
1531  <list><t>
1532      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1533      meaning of the request when the origin server is improperly using
1534      a non-reserved URI character for a reserved purpose.  Implementors
1535      should be aware that some pre-HTTP/1.1 proxies have been known to
1536      rewrite the Request-URI.
1537  </t></list>
1538</t>
1539</section>
1540</section>
1541
1542<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1543<t>
1544   The exact resource identified by an Internet request is determined by
1545   examining both the Request-URI and the Host header field.
1546</t>
1547<t>
1548   An origin server that does not allow resources to differ by the
1549   requested host &MAY; ignore the Host header field value when
1550   determining the resource identified by an HTTP/1.1 request. (But see
1551   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1552   for other requirements on Host support in HTTP/1.1.)
1553</t>
1554<t>
1555   An origin server that does differentiate resources based on the host
1556   requested (sometimes referred to as virtual hosts or vanity host
1557   names) &MUST; use the following rules for determining the requested
1558   resource on an HTTP/1.1 request:
1559  <list style="numbers">
1560    <t>If Request-URI is an absoluteURI, the host is part of the
1561     Request-URI. Any Host header field value in the request &MUST; be
1562     ignored.</t>
1563    <t>If the Request-URI is not an absoluteURI, and the request includes
1564     a Host header field, the host is determined by the Host header
1565     field value.</t>
1566    <t>If the host as determined by rule 1 or 2 is not a valid host on
1567     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1568  </list>
1569</t>
1570<t>
1571   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1572   attempt to use heuristics (e.g., examination of the URI path for
1573   something unique to a particular host) in order to determine what
1574   exact resource is being requested.
1575</t>
1576</section>
1577
1578</section>
1579
1580
1581<section title="Response" anchor="response">
1582  <x:anchor-alias value="Response"/>
1583<t>
1584   After receiving and interpreting a request message, a server responds
1585   with an HTTP response message.
1586</t>
1587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1588  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1589                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1590                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1591                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1592                  <x:ref>CRLF</x:ref>
1593                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1594</artwork></figure>
1595
1596<section title="Status-Line" anchor="status-line">
1597  <x:anchor-alias value="Status-Line"/>
1598<t>
1599   The first line of a Response message is the Status-Line, consisting
1600   of the protocol version followed by a numeric status code and its
1601   associated textual phrase, with each element separated by SP
1602   characters. No CR or LF is allowed except in the final CRLF sequence.
1603</t>
1604<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1605  <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>
1606</artwork></figure>
1607
1608<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1609  <x:anchor-alias value="Reason-Phrase"/>
1610  <x:anchor-alias value="Status-Code"/>
1611<t>
1612   The Status-Code element is a 3-digit integer result code of the
1613   attempt to understand and satisfy the request. These codes are fully
1614   defined in &status-codes;.  The Reason Phrase exists for the sole
1615   purpose of providing a textual description associated with the numeric
1616   status code, out of deference to earlier Internet application protocols
1617   that were more frequently used with interactive text clients.
1618   A client &SHOULD; ignore the content of the Reason Phrase.
1619</t>
1620<t>
1621   The first digit of the Status-Code defines the class of response. The
1622   last two digits do not have any categorization role. There are 5
1623   values for the first digit:
1624  <list style="symbols">
1625    <t>
1626      1xx: Informational - Request received, continuing process
1627    </t>
1628    <t>
1629      2xx: Success - The action was successfully received,
1630        understood, and accepted
1631    </t>
1632    <t>
1633      3xx: Redirection - Further action must be taken in order to
1634        complete the request
1635    </t>
1636    <t>
1637      4xx: Client Error - The request contains bad syntax or cannot
1638        be fulfilled
1639    </t>
1640    <t>
1641      5xx: Server Error - The server failed to fulfill an apparently
1642        valid request
1643    </t>
1644  </list>
1645</t>
1646<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"/>
1647  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1648  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1649</artwork></figure>
1650</section>
1651</section>
1652
1653</section>
1654
1655
1656<section title="Connections" anchor="connections">
1657
1658<section title="Persistent Connections" anchor="persistent.connections">
1659
1660<section title="Purpose" anchor="persistent.purpose">
1661<t>
1662   Prior to persistent connections, a separate TCP connection was
1663   established to fetch each URL, increasing the load on HTTP servers
1664   and causing congestion on the Internet. The use of inline images and
1665   other associated data often require a client to make multiple
1666   requests of the same server in a short amount of time. Analysis of
1667   these performance problems and results from a prototype
1668   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1669   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1670   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1671   T/TCP <xref target="Tou1998"/>.
1672</t>
1673<t>
1674   Persistent HTTP connections have a number of advantages:
1675  <list style="symbols">
1676      <t>
1677        By opening and closing fewer TCP connections, CPU time is saved
1678        in routers and hosts (clients, servers, proxies, gateways,
1679        tunnels, or caches), and memory used for TCP protocol control
1680        blocks can be saved in hosts.
1681      </t>
1682      <t>
1683        HTTP requests and responses can be pipelined on a connection.
1684        Pipelining allows a client to make multiple requests without
1685        waiting for each response, allowing a single TCP connection to
1686        be used much more efficiently, with much lower elapsed time.
1687      </t>
1688      <t>
1689        Network congestion is reduced by reducing the number of packets
1690        caused by TCP opens, and by allowing TCP sufficient time to
1691        determine the congestion state of the network.
1692      </t>
1693      <t>
1694        Latency on subsequent requests is reduced since there is no time
1695        spent in TCP's connection opening handshake.
1696      </t>
1697      <t>
1698        HTTP can evolve more gracefully, since errors can be reported
1699        without the penalty of closing the TCP connection. Clients using
1700        future versions of HTTP might optimistically try a new feature,
1701        but if communicating with an older server, retry with old
1702        semantics after an error is reported.
1703      </t>
1704    </list>
1705</t>
1706<t>
1707   HTTP implementations &SHOULD; implement persistent connections.
1708</t>
1709</section>
1710
1711<section title="Overall Operation" anchor="persistent.overall">
1712<t>
1713   A significant difference between HTTP/1.1 and earlier versions of
1714   HTTP is that persistent connections are the default behavior of any
1715   HTTP connection. That is, unless otherwise indicated, the client
1716   &SHOULD; assume that the server will maintain a persistent connection,
1717   even after error responses from the server.
1718</t>
1719<t>
1720   Persistent connections provide a mechanism by which a client and a
1721   server can signal the close of a TCP connection. This signaling takes
1722   place using the Connection header field (<xref target="header.connection"/>). Once a close
1723   has been signaled, the client &MUST-NOT; send any more requests on that
1724   connection.
1725</t>
1726
1727<section title="Negotiation" anchor="persistent.negotiation">
1728<t>
1729   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1730   maintain a persistent connection unless a Connection header including
1731   the connection-token "close" was sent in the request. If the server
1732   chooses to close the connection immediately after sending the
1733   response, it &SHOULD; send a Connection header including the
1734   connection-token close.
1735</t>
1736<t>
1737   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1738   decide to keep it open based on whether the response from a server
1739   contains a Connection header with the connection-token close. In case
1740   the client does not want to maintain a connection for more than that
1741   request, it &SHOULD; send a Connection header including the
1742   connection-token close.
1743</t>
1744<t>
1745   If either the client or the server sends the close token in the
1746   Connection header, that request becomes the last one for the
1747   connection.
1748</t>
1749<t>
1750   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1751   maintained for HTTP versions less than 1.1 unless it is explicitly
1752   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1753   compatibility with HTTP/1.0 clients.
1754</t>
1755<t>
1756   In order to remain persistent, all messages on the connection &MUST;
1757   have a self-defined message length (i.e., one not defined by closure
1758   of the connection), as described in <xref target="message.length"/>.
1759</t>
1760</section>
1761
1762<section title="Pipelining" anchor="pipelining">
1763<t>
1764   A client that supports persistent connections &MAY; "pipeline" its
1765   requests (i.e., send multiple requests without waiting for each
1766   response). A server &MUST; send its responses to those requests in the
1767   same order that the requests were received.
1768</t>
1769<t>
1770   Clients which assume persistent connections and pipeline immediately
1771   after connection establishment &SHOULD; be prepared to retry their
1772   connection if the first pipelined attempt fails. If a client does
1773   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1774   persistent. Clients &MUST; also be prepared to resend their requests if
1775   the server closes the connection before sending all of the
1776   corresponding responses.
1777</t>
1778<t>
1779   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1780   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1781   premature termination of the transport connection could lead to
1782   indeterminate results. A client wishing to send a non-idempotent
1783   request &SHOULD; wait to send that request until it has received the
1784   response status for the previous request.
1785</t>
1786</section>
1787</section>
1788
1789<section title="Proxy Servers" anchor="persistent.proxy">
1790<t>
1791   It is especially important that proxies correctly implement the
1792   properties of the Connection header field as specified in <xref target="header.connection"/>.
1793</t>
1794<t>
1795   The proxy server &MUST; signal persistent connections separately with
1796   its clients and the origin servers (or other proxy servers) that it
1797   connects to. Each persistent connection applies to only one transport
1798   link.
1799</t>
1800<t>
1801   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1802   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1803   discussion of the problems with the Keep-Alive header implemented by
1804   many HTTP/1.0 clients).
1805</t>
1806</section>
1807
1808<section title="Practical Considerations" anchor="persistent.practical">
1809<t>
1810   Servers will usually have some time-out value beyond which they will
1811   no longer maintain an inactive connection. Proxy servers might make
1812   this a higher value since it is likely that the client will be making
1813   more connections through the same server. The use of persistent
1814   connections places no requirements on the length (or existence) of
1815   this time-out for either the client or the server.
1816</t>
1817<t>
1818   When a client or server wishes to time-out it &SHOULD; issue a graceful
1819   close on the transport connection. Clients and servers &SHOULD; both
1820   constantly watch for the other side of the transport close, and
1821   respond to it as appropriate. If a client or server does not detect
1822   the other side's close promptly it could cause unnecessary resource
1823   drain on the network.
1824</t>
1825<t>
1826   A client, server, or proxy &MAY; close the transport connection at any
1827   time. For example, a client might have started to send a new request
1828   at the same time that the server has decided to close the "idle"
1829   connection. From the server's point of view, the connection is being
1830   closed while it was idle, but from the client's point of view, a
1831   request is in progress.
1832</t>
1833<t>
1834   This means that clients, servers, and proxies &MUST; be able to recover
1835   from asynchronous close events. Client software &SHOULD; reopen the
1836   transport connection and retransmit the aborted sequence of requests
1837   without user interaction so long as the request sequence is
1838   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1839   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1840   human operator the choice of retrying the request(s). Confirmation by
1841   user-agent software with semantic understanding of the application
1842   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1843   be repeated if the second sequence of requests fails.
1844</t>
1845<t>
1846   Servers &SHOULD; always respond to at least one request per connection,
1847   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1848   middle of transmitting a response, unless a network or client failure
1849   is suspected.
1850</t>
1851<t>
1852   Clients that use persistent connections &SHOULD; limit the number of
1853   simultaneous connections that they maintain to a given server. A
1854   single-user client &SHOULD-NOT; maintain more than 2 connections with
1855   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1856   another server or proxy, where N is the number of simultaneously
1857   active users. These guidelines are intended to improve HTTP response
1858   times and avoid congestion.
1859</t>
1860</section>
1861</section>
1862
1863<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1864
1865<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1866<t>
1867   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1868   flow control mechanisms to resolve temporary overloads, rather than
1869   terminating connections with the expectation that clients will retry.
1870   The latter technique can exacerbate network congestion.
1871</t>
1872</section>
1873
1874<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1875<t>
1876   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1877   the network connection for an error status while it is transmitting
1878   the request. If the client sees an error status, it &SHOULD;
1879   immediately cease transmitting the body. If the body is being sent
1880   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1881   empty trailer &MAY; be used to prematurely mark the end of the message.
1882   If the body was preceded by a Content-Length header, the client &MUST;
1883   close the connection.
1884</t>
1885</section>
1886
1887<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1888<t>
1889   The purpose of the 100 (Continue) status (see &status-100;) is to
1890   allow a client that is sending a request message with a request body
1891   to determine if the origin server is willing to accept the request
1892   (based on the request headers) before the client sends the request
1893   body. In some cases, it might either be inappropriate or highly
1894   inefficient for the client to send the body if the server will reject
1895   the message without looking at the body.
1896</t>
1897<t>
1898   Requirements for HTTP/1.1 clients:
1899  <list style="symbols">
1900    <t>
1901        If a client will wait for a 100 (Continue) response before
1902        sending the request body, it &MUST; send an Expect request-header
1903        field (&header-expect;) with the "100-continue" expectation.
1904    </t>
1905    <t>
1906        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1907        with the "100-continue" expectation if it does not intend
1908        to send a request body.
1909    </t>
1910  </list>
1911</t>
1912<t>
1913   Because of the presence of older implementations, the protocol allows
1914   ambiguous situations in which a client may send "Expect: 100-continue"
1915   without receiving either a 417 (Expectation Failed) status
1916   or a 100 (Continue) status. Therefore, when a client sends this
1917   header field to an origin server (possibly via a proxy) from which it
1918   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1919   for an indefinite period before sending the request body.
1920</t>
1921<t>
1922   Requirements for HTTP/1.1 origin servers:
1923  <list style="symbols">
1924    <t> Upon receiving a request which includes an Expect request-header
1925        field with the "100-continue" expectation, an origin server &MUST;
1926        either respond with 100 (Continue) status and continue to read
1927        from the input stream, or respond with a final status code. The
1928        origin server &MUST-NOT; wait for the request body before sending
1929        the 100 (Continue) response. If it responds with a final status
1930        code, it &MAY; close the transport connection or it &MAY; continue
1931        to read and discard the rest of the request.  It &MUST-NOT;
1932        perform the requested method if it returns a final status code.
1933    </t>
1934    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1935        the request message does not include an Expect request-header
1936        field with the "100-continue" expectation, and &MUST-NOT; send a
1937        100 (Continue) response if such a request comes from an HTTP/1.0
1938        (or earlier) client. There is an exception to this rule: for
1939        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1940        status in response to an HTTP/1.1 PUT or POST request that does
1941        not include an Expect request-header field with the "100-continue"
1942        expectation. This exception, the purpose of which is
1943        to minimize any client processing delays associated with an
1944        undeclared wait for 100 (Continue) status, applies only to
1945        HTTP/1.1 requests, and not to requests with any other HTTP-version
1946        value.
1947    </t>
1948    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1949        already received some or all of the request body for the
1950        corresponding request.
1951    </t>
1952    <t> An origin server that sends a 100 (Continue) response &MUST;
1953    ultimately send a final status code, once the request body is
1954        received and processed, unless it terminates the transport
1955        connection prematurely.
1956    </t>
1957    <t> If an origin server receives a request that does not include an
1958        Expect request-header field with the "100-continue" expectation,
1959        the request includes a request body, and the server responds
1960        with a final status code before reading the entire request body
1961        from the transport connection, then the server &SHOULD-NOT;  close
1962        the transport connection until it has read the entire request,
1963        or until the client closes the connection. Otherwise, the client
1964        might not reliably receive the response message. However, this
1965        requirement is not be construed as preventing a server from
1966        defending itself against denial-of-service attacks, or from
1967        badly broken client implementations.
1968      </t>
1969    </list>
1970</t>
1971<t>
1972   Requirements for HTTP/1.1 proxies:
1973  <list style="symbols">
1974    <t> If a proxy receives a request that includes an Expect request-header
1975        field with the "100-continue" expectation, and the proxy
1976        either knows that the next-hop server complies with HTTP/1.1 or
1977        higher, or does not know the HTTP version of the next-hop
1978        server, it &MUST; forward the request, including the Expect header
1979        field.
1980    </t>
1981    <t> If the proxy knows that the version of the next-hop server is
1982        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1983        respond with a 417 (Expectation Failed) status.
1984    </t>
1985    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1986        numbers received from recently-referenced next-hop servers.
1987    </t>
1988    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1989        request message was received from an HTTP/1.0 (or earlier)
1990        client and did not include an Expect request-header field with
1991        the "100-continue" expectation. This requirement overrides the
1992        general rule for forwarding of 1xx responses (see &status-1xx;).
1993    </t>
1994  </list>
1995</t>
1996</section>
1997
1998<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1999<t>
2000   If an HTTP/1.1 client sends a request which includes a request body,
2001   but which does not include an Expect request-header field with the
2002   "100-continue" expectation, and if the client is not directly
2003   connected to an HTTP/1.1 origin server, and if the client sees the
2004   connection close before receiving any status from the server, the
2005   client &SHOULD; retry the request.  If the client does retry this
2006   request, it &MAY; use the following "binary exponential backoff"
2007   algorithm to be assured of obtaining a reliable response:
2008  <list style="numbers">
2009    <t>
2010      Initiate a new connection to the server
2011    </t>
2012    <t>
2013      Transmit the request-headers
2014    </t>
2015    <t>
2016      Initialize a variable R to the estimated round-trip time to the
2017         server (e.g., based on the time it took to establish the
2018         connection), or to a constant value of 5 seconds if the round-trip
2019         time is not available.
2020    </t>
2021    <t>
2022       Compute T = R * (2**N), where N is the number of previous
2023         retries of this request.
2024    </t>
2025    <t>
2026       Wait either for an error response from the server, or for T
2027         seconds (whichever comes first)
2028    </t>
2029    <t>
2030       If no error response is received, after T seconds transmit the
2031         body of the request.
2032    </t>
2033    <t>
2034       If client sees that the connection is closed prematurely,
2035         repeat from step 1 until the request is accepted, an error
2036         response is received, or the user becomes impatient and
2037         terminates the retry process.
2038    </t>
2039  </list>
2040</t>
2041<t>
2042   If at any point an error status is received, the client
2043  <list style="symbols">
2044      <t>&SHOULD-NOT;  continue and</t>
2045
2046      <t>&SHOULD; close the connection if it has not completed sending the
2047        request message.</t>
2048    </list>
2049</t>
2050</section>
2051</section>
2052</section>
2053
2054
2055<section title="Header Field Definitions" anchor="header.fields">
2056<t>
2057   This section defines the syntax and semantics of HTTP/1.1 header fields
2058   related to message framing and transport protocols.
2059</t>
2060<t>
2061   For entity-header fields, both sender and recipient refer to either the
2062   client or the server, depending on who sends and who receives the entity.
2063</t>
2064
2065<section title="Connection" anchor="header.connection">
2066  <iref primary="true" item="Connection header" x:for-anchor=""/>
2067  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2068  <x:anchor-alias value="Connection"/>
2069  <x:anchor-alias value="connection-token"/>
2070  <x:anchor-alias value="Connection-v"/>
2071<t>
2072   The general-header field "Connection" allows the sender to specify
2073   options that are desired for that particular connection and &MUST-NOT;
2074   be communicated by proxies over further connections.
2075</t>
2076<t>
2077   The Connection header's value has the following grammar:
2078</t>
2079<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2080  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2081  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2082  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2083</artwork></figure>
2084<t>
2085   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2086   message is forwarded and, for each connection-token in this field,
2087   remove any header field(s) from the message with the same name as the
2088   connection-token. Connection options are signaled by the presence of
2089   a connection-token in the Connection header field, not by any
2090   corresponding additional header field(s), since the additional header
2091   field may not be sent if there are no parameters associated with that
2092   connection option.
2093</t>
2094<t>
2095   Message headers listed in the Connection header &MUST-NOT; include
2096   end-to-end headers, such as Cache-Control.
2097</t>
2098<t>
2099   HTTP/1.1 defines the "close" connection option for the sender to
2100   signal that the connection will be closed after completion of the
2101   response. For example,
2102</t>
2103<figure><artwork type="example">
2104  Connection: close
2105</artwork></figure>
2106<t>
2107   in either the request or the response header fields indicates that
2108   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2109   after the current request/response is complete.
2110</t>
2111<t>
2112   An HTTP/1.1 client that does not support persistent connections &MUST;
2113   include the "close" connection option in every request message.
2114</t>
2115<t>
2116   An HTTP/1.1 server that does not support persistent connections &MUST;
2117   include the "close" connection option in every response message that
2118   does not have a 1xx (informational) status code.
2119</t>
2120<t>
2121   A system receiving an HTTP/1.0 (or lower-version) message that
2122   includes a Connection header &MUST;, for each connection-token in this
2123   field, remove and ignore any header field(s) from the message with
2124   the same name as the connection-token. This protects against mistaken
2125   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2126</t>
2127</section>
2128
2129<section title="Content-Length" anchor="header.content-length">
2130  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2131  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2132  <x:anchor-alias value="Content-Length"/>
2133  <x:anchor-alias value="Content-Length-v"/>
2134<t>
2135   The entity-header field "Content-Length" indicates the size of the
2136   entity-body, in decimal number of OCTETs, sent to the recipient or,
2137   in the case of the HEAD method, the size of the entity-body that
2138   would have been sent had the request been a GET.
2139</t>
2140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2141  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2142  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2143</artwork></figure>
2144<t>
2145   An example is
2146</t>
2147<figure><artwork type="example">
2148  Content-Length: 3495
2149</artwork></figure>
2150<t>
2151   Applications &SHOULD; use this field to indicate the transfer-length of
2152   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2153</t>
2154<t>
2155   Any Content-Length greater than or equal to zero is a valid value.
2156   <xref target="message.length"/> describes how to determine the length of a message-body
2157   if a Content-Length is not given.
2158</t>
2159<t>
2160   Note that the meaning of this field is significantly different from
2161   the corresponding definition in MIME, where it is an optional field
2162   used within the "message/external-body" content-type. In HTTP, it
2163   &SHOULD; be sent whenever the message's length can be determined prior
2164   to being transferred, unless this is prohibited by the rules in
2165   <xref target="message.length"/>.
2166</t>
2167</section>
2168
2169<section title="Date" anchor="header.date">
2170  <iref primary="true" item="Date header" x:for-anchor=""/>
2171  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2172  <x:anchor-alias value="Date"/>
2173  <x:anchor-alias value="Date-v"/>
2174<t>
2175   The general-header field "Date" represents the date and time at which
2176   the message was originated, having the same semantics as orig-date in
2177   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2178   HTTP-date, as described in <xref target="full.date"/>;
2179   it &MUST; be sent in rfc1123-date format.
2180</t>
2181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2182  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2183  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2184</artwork></figure>
2185<t>
2186   An example is
2187</t>
2188<figure><artwork type="example">
2189  Date: Tue, 15 Nov 1994 08:12:31 GMT
2190</artwork></figure>
2191<t>
2192   Origin servers &MUST; include a Date header field in all responses,
2193   except in these cases:
2194  <list style="numbers">
2195      <t>If the response status code is 100 (Continue) or 101 (Switching
2196         Protocols), the response &MAY; include a Date header field, at
2197         the server's option.</t>
2198
2199      <t>If the response status code conveys a server error, e.g. 500
2200         (Internal Server Error) or 503 (Service Unavailable), and it is
2201         inconvenient or impossible to generate a valid Date.</t>
2202
2203      <t>If the server does not have a clock that can provide a
2204         reasonable approximation of the current time, its responses
2205         &MUST-NOT; include a Date header field. In this case, the rules
2206         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2207  </list>
2208</t>
2209<t>
2210   A received message that does not have a Date header field &MUST; be
2211   assigned one by the recipient if the message will be cached by that
2212   recipient or gatewayed via a protocol which requires a Date. An HTTP
2213   implementation without a clock &MUST-NOT; cache responses without
2214   revalidating them on every use. An HTTP cache, especially a shared
2215   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2216   clock with a reliable external standard.
2217</t>
2218<t>
2219   Clients &SHOULD; only send a Date header field in messages that include
2220   an entity-body, as in the case of the PUT and POST requests, and even
2221   then it is optional. A client without a clock &MUST-NOT; send a Date
2222   header field in a request.
2223</t>
2224<t>
2225   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2226   time subsequent to the generation of the message. It &SHOULD; represent
2227   the best available approximation of the date and time of message
2228   generation, unless the implementation has no means of generating a
2229   reasonably accurate date and time. In theory, the date ought to
2230   represent the moment just before the entity is generated. In
2231   practice, the date can be generated at any time during the message
2232   origination without affecting its semantic value.
2233</t>
2234
2235<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2236<t>
2237   Some origin server implementations might not have a clock available.
2238   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2239   values to a response, unless these values were associated
2240   with the resource by a system or user with a reliable clock. It &MAY;
2241   assign an Expires value that is known, at or before server
2242   configuration time, to be in the past (this allows "pre-expiration"
2243   of responses without storing separate Expires values for each
2244   resource).
2245</t>
2246</section>
2247</section>
2248
2249<section title="Host" anchor="header.host">
2250  <iref primary="true" item="Host header" x:for-anchor=""/>
2251  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2252  <x:anchor-alias value="Host"/>
2253  <x:anchor-alias value="Host-v"/>
2254<t>
2255   The request-header field "Host" specifies the Internet host and port
2256   number of the resource being requested, as obtained from the original
2257   URI given by the user or referring resource (generally an HTTP URL,
2258   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2259   the naming authority of the origin server or gateway given by the
2260   original URL. This allows the origin server or gateway to
2261   differentiate between internally-ambiguous URLs, such as the root "/"
2262   URL of a server for multiple host names on a single IP address.
2263</t>
2264<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2265  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2266  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2267</artwork></figure>
2268<t>
2269   A "host" without any trailing port information implies the default
2270   port for the service requested (e.g., "80" for an HTTP URL). For
2271   example, a request on the origin server for
2272   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2273</t>
2274<figure><artwork type="example">
2275  GET /pub/WWW/ HTTP/1.1
2276  Host: www.example.org
2277</artwork></figure>
2278<t>
2279   A client &MUST; include a Host header field in all HTTP/1.1 request
2280   messages. If the requested URI does not include an Internet host
2281   name for the service being requested, then the Host header field &MUST;
2282   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2283   request message it forwards does contain an appropriate Host header
2284   field that identifies the service being requested by the proxy. All
2285   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2286   status code to any HTTP/1.1 request message which lacks a Host header
2287   field.
2288</t>
2289<t>
2290   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2291   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2292   for other requirements relating to Host.
2293</t>
2294</section>
2295
2296<section title="TE" anchor="header.te">
2297  <iref primary="true" item="TE header" x:for-anchor=""/>
2298  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2299  <x:anchor-alias value="TE"/>
2300  <x:anchor-alias value="TE-v"/>
2301  <x:anchor-alias value="t-codings"/>
2302<t>
2303   The request-header field "TE" indicates what extension transfer-codings
2304   it is willing to accept in the response and whether or not it is
2305   willing to accept trailer fields in a chunked transfer-coding. Its
2306   value may consist of the keyword "trailers" and/or a comma-separated
2307   list of extension transfer-coding names with optional accept
2308   parameters (as described in <xref target="transfer.codings"/>).
2309</t>
2310<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2311  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2312  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2313  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2314</artwork></figure>
2315<t>
2316   The presence of the keyword "trailers" indicates that the client is
2317   willing to accept trailer fields in a chunked transfer-coding, as
2318   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2319   transfer-coding values even though it does not itself represent a
2320   transfer-coding.
2321</t>
2322<t>
2323   Examples of its use are:
2324</t>
2325<figure><artwork type="example">
2326  TE: deflate
2327  TE:
2328  TE: trailers, deflate;q=0.5
2329</artwork></figure>
2330<t>
2331   The TE header field only applies to the immediate connection.
2332   Therefore, the keyword &MUST; be supplied within a Connection header
2333   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2334</t>
2335<t>
2336   A server tests whether a transfer-coding is acceptable, according to
2337   a TE field, using these rules:
2338  <list style="numbers">
2339    <x:lt>
2340      <t>The "chunked" transfer-coding is always acceptable. If the
2341         keyword "trailers" is listed, the client indicates that it is
2342         willing to accept trailer fields in the chunked response on
2343         behalf of itself and any downstream clients. The implication is
2344         that, if given, the client is stating that either all
2345         downstream clients are willing to accept trailer fields in the
2346         forwarded response, or that it will attempt to buffer the
2347         response on behalf of downstream recipients.
2348      </t><t>
2349         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2350         chunked response such that a client can be assured of buffering
2351         the entire response.</t>
2352    </x:lt>
2353    <x:lt>
2354      <t>If the transfer-coding being tested is one of the transfer-codings
2355         listed in the TE field, then it is acceptable unless it
2356         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2357         qvalue of 0 means "not acceptable.")</t>
2358    </x:lt>
2359    <x:lt>
2360      <t>If multiple transfer-codings are acceptable, then the
2361         acceptable transfer-coding with the highest non-zero qvalue is
2362         preferred.  The "chunked" transfer-coding always has a qvalue
2363         of 1.</t>
2364    </x:lt>
2365  </list>
2366</t>
2367<t>
2368   If the TE field-value is empty or if no TE field is present, the only
2369   transfer-coding  is "chunked". A message with no transfer-coding is
2370   always acceptable.
2371</t>
2372</section>
2373
2374<section title="Trailer" anchor="header.trailer">
2375  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2376  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2377  <x:anchor-alias value="Trailer"/>
2378  <x:anchor-alias value="Trailer-v"/>
2379<t>
2380   The general field "Trailer" indicates that the given set of
2381   header fields is present in the trailer of a message encoded with
2382   chunked transfer-coding.
2383</t>
2384<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2385  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2386  <x:ref>Trailer-v</x:ref> = 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  <x:anchor-alias value="Transfer-Encoding-v"/>
2415<t>
2416   The general-header "Transfer-Encoding" field indicates what (if any)
2417   type of transformation has been applied to the message body in order
2418   to safely transfer it between the sender and the recipient. This
2419   differs from the content-coding in that the transfer-coding is a
2420   property of the message, not of the entity.
2421</t>
2422<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2423  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Transfer-Encoding-v</x:ref>
2424  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2425</artwork></figure>
2426<t>
2427   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2428</t>
2429<figure><artwork type="example">
2430  Transfer-Encoding: chunked
2431</artwork></figure>
2432<t>
2433   If multiple encodings have been applied to an entity, the transfer-codings
2434   &MUST; be listed in the order in which they were applied.
2435   Additional information about the encoding parameters &MAY; be provided
2436   by other entity-header fields not defined by this specification.
2437</t>
2438<t>
2439   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2440   header.
2441</t>
2442</section>
2443
2444<section title="Upgrade" anchor="header.upgrade">
2445  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2446  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2447  <x:anchor-alias value="Upgrade"/>
2448  <x:anchor-alias value="Upgrade-v"/>
2449<t>
2450   The general-header "Upgrade" allows the client to specify what
2451   additional communication protocols it supports and would like to use
2452   if the server finds it appropriate to switch protocols. The server
2453   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2454   response to indicate which protocol(s) are being switched.
2455</t>
2456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2457  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2458  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2459</artwork></figure>
2460<t>
2461   For example,
2462</t>
2463<figure><artwork type="example">
2464  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2465</artwork></figure>
2466<t>
2467   The Upgrade header field is intended to provide a simple mechanism
2468   for transition from HTTP/1.1 to some other, incompatible protocol. It
2469   does so by allowing the client to advertise its desire to use another
2470   protocol, such as a later version of HTTP with a higher major version
2471   number, even though the current request has been made using HTTP/1.1.
2472   This eases the difficult transition between incompatible protocols by
2473   allowing the client to initiate a request in the more commonly
2474   supported protocol while indicating to the server that it would like
2475   to use a "better" protocol if available (where "better" is determined
2476   by the server, possibly according to the nature of the method and/or
2477   resource being requested).
2478</t>
2479<t>
2480   The Upgrade header field only applies to switching application-layer
2481   protocols upon the existing transport-layer connection. Upgrade
2482   cannot be used to insist on a protocol change; its acceptance and use
2483   by the server is optional. The capabilities and nature of the
2484   application-layer communication after the protocol change is entirely
2485   dependent upon the new protocol chosen, although the first action
2486   after changing the protocol &MUST; be a response to the initial HTTP
2487   request containing the Upgrade header field.
2488</t>
2489<t>
2490   The Upgrade header field only applies to the immediate connection.
2491   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2492   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2493   HTTP/1.1 message.
2494</t>
2495<t>
2496   The Upgrade header field cannot be used to indicate a switch to a
2497   protocol on a different connection. For that purpose, it is more
2498   appropriate to use a 301, 302, 303, or 305 redirection response.
2499</t>
2500<t>
2501   This specification only defines the protocol name "HTTP" for use by
2502   the family of Hypertext Transfer Protocols, as defined by the HTTP
2503   version rules of <xref target="http.version"/> and future updates to this
2504   specification. Any token can be used as a protocol name; however, it
2505   will only be useful if both the client and server associate the name
2506   with the same protocol.
2507</t>
2508</section>
2509
2510<section title="Via" anchor="header.via">
2511  <iref primary="true" item="Via header" x:for-anchor=""/>
2512  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2513  <x:anchor-alias value="protocol-name"/>
2514  <x:anchor-alias value="protocol-version"/>
2515  <x:anchor-alias value="pseudonym"/>
2516  <x:anchor-alias value="received-by"/>
2517  <x:anchor-alias value="received-protocol"/>
2518  <x:anchor-alias value="Via"/>
2519  <x:anchor-alias value="Via-v"/>
2520<t>
2521   The general-header field "Via" &MUST; be used by gateways and proxies to
2522   indicate the intermediate protocols and recipients between the user
2523   agent and the server on requests, and between the origin server and
2524   the client on responses. It is analogous to the "Received" field defined in
2525   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2526   avoiding request loops, and identifying the protocol capabilities of
2527   all senders along the request/response chain.
2528</t>
2529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><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"/>
2530  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2531  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref> [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2532  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2533  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2534  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2535  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2536  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2537</artwork></figure>
2538<t>
2539   The received-protocol indicates the protocol version of the message
2540   received by the server or client along each segment of the
2541   request/response chain. The received-protocol version is appended to
2542   the Via field value when the message is forwarded so that information
2543   about the protocol capabilities of upstream applications remains
2544   visible to all recipients.
2545</t>
2546<t>
2547   The protocol-name is optional if and only if it would be "HTTP". The
2548   received-by field is normally the host and optional port number of a
2549   recipient server or client that subsequently forwarded the message.
2550   However, if the real host is considered to be sensitive information,
2551   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2552   be assumed to be the default port of the received-protocol.
2553</t>
2554<t>
2555   Multiple Via field values represents each proxy or gateway that has
2556   forwarded the message. Each recipient &MUST; append its information
2557   such that the end result is ordered according to the sequence of
2558   forwarding applications.
2559</t>
2560<t>
2561   Comments &MAY; be used in the Via header field to identify the software
2562   of the recipient proxy or gateway, analogous to the User-Agent and
2563   Server header fields. However, all comments in the Via field are
2564   optional and &MAY; be removed by any recipient prior to forwarding the
2565   message.
2566</t>
2567<t>
2568   For example, a request message could be sent from an HTTP/1.0 user
2569   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2570   forward the request to a public proxy at p.example.net, which completes
2571   the request by forwarding it to the origin server at www.example.com.
2572   The request received by www.example.com would then have the following
2573   Via header field:
2574</t>
2575<figure><artwork type="example">
2576  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2577</artwork></figure>
2578<t>
2579   Proxies and gateways used as a portal through a network firewall
2580   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2581   the firewall region. This information &SHOULD; only be propagated if
2582   explicitly enabled. If not enabled, the received-by host of any host
2583   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2584   for that host.
2585</t>
2586<t>
2587   For organizations that have strong privacy requirements for hiding
2588   internal structures, a proxy &MAY; combine an ordered subsequence of
2589   Via header field entries with identical received-protocol values into
2590   a single such entry. For example,
2591</t>
2592<figure><artwork type="example">
2593  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2594</artwork></figure>
2595<t>
2596        could be collapsed to
2597</t>
2598<figure><artwork type="example">
2599  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2600</artwork></figure>
2601<t>
2602   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2603   under the same organizational control and the hosts have already been
2604   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2605   have different received-protocol values.
2606</t>
2607</section>
2608
2609</section>
2610
2611<section title="IANA Considerations" anchor="IANA.considerations">
2612<section title="Message Header Registration" anchor="message.header.registration">
2613<t>
2614   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2615   with the permanent registrations below (see <xref target="RFC3864"/>):
2616</t>
2617<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2618<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2619   <ttcol>Header Field Name</ttcol>
2620   <ttcol>Protocol</ttcol>
2621   <ttcol>Status</ttcol>
2622   <ttcol>Reference</ttcol>
2623
2624   <c>Connection</c>
2625   <c>http</c>
2626   <c>standard</c>
2627   <c>
2628      <xref target="header.connection"/>
2629   </c>
2630   <c>Content-Length</c>
2631   <c>http</c>
2632   <c>standard</c>
2633   <c>
2634      <xref target="header.content-length"/>
2635   </c>
2636   <c>Date</c>
2637   <c>http</c>
2638   <c>standard</c>
2639   <c>
2640      <xref target="header.date"/>
2641   </c>
2642   <c>Host</c>
2643   <c>http</c>
2644   <c>standard</c>
2645   <c>
2646      <xref target="header.host"/>
2647   </c>
2648   <c>TE</c>
2649   <c>http</c>
2650   <c>standard</c>
2651   <c>
2652      <xref target="header.te"/>
2653   </c>
2654   <c>Trailer</c>
2655   <c>http</c>
2656   <c>standard</c>
2657   <c>
2658      <xref target="header.trailer"/>
2659   </c>
2660   <c>Transfer-Encoding</c>
2661   <c>http</c>
2662   <c>standard</c>
2663   <c>
2664      <xref target="header.transfer-encoding"/>
2665   </c>
2666   <c>Upgrade</c>
2667   <c>http</c>
2668   <c>standard</c>
2669   <c>
2670      <xref target="header.upgrade"/>
2671   </c>
2672   <c>Via</c>
2673   <c>http</c>
2674   <c>standard</c>
2675   <c>
2676      <xref target="header.via"/>
2677   </c>
2678</texttable>
2679<!--(END)-->
2680<t>
2681   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2682</t>
2683</section>
2684
2685<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2686<t>
2687   The entry for the "http" URI Scheme in the registry located at
2688   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2689   should be updated to point to <xref target="http.url"/> of this document
2690   (see <xref target="RFC4395"/>).
2691</t>
2692</section>
2693
2694<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2695<t>
2696   This document serves as the specification for the Internet media types
2697   "message/http" and "application/http". The following is to be registered with
2698   IANA (see <xref target="RFC4288"/>).
2699</t>
2700<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2701<iref item="Media Type" subitem="message/http" primary="true"/>
2702<iref item="message/http Media Type" primary="true"/>
2703<t>
2704   The message/http type can be used to enclose a single HTTP request or
2705   response message, provided that it obeys the MIME restrictions for all
2706   "message" types regarding line length and encodings.
2707</t>
2708<t>
2709  <list style="hanging" x:indent="12em">
2710    <t hangText="Type name:">
2711      message
2712    </t>
2713    <t hangText="Subtype name:">
2714      http
2715    </t>
2716    <t hangText="Required parameters:">
2717      none
2718    </t>
2719    <t hangText="Optional parameters:">
2720      version, msgtype
2721      <list style="hanging">
2722        <t hangText="version:">
2723          The HTTP-Version number of the enclosed message
2724          (e.g., "1.1"). If not present, the version can be
2725          determined from the first line of the body.
2726        </t>
2727        <t hangText="msgtype:">
2728          The message type -- "request" or "response". If not
2729          present, the type can be determined from the first
2730          line of the body.
2731        </t>
2732      </list>
2733    </t>
2734    <t hangText="Encoding considerations:">
2735      only "7bit", "8bit", or "binary" are permitted
2736    </t>
2737    <t hangText="Security considerations:">
2738      none
2739    </t>
2740    <t hangText="Interoperability considerations:">
2741      none
2742    </t>
2743    <t hangText="Published specification:">
2744      This specification (see <xref target="internet.media.type.message.http"/>).
2745    </t>
2746    <t hangText="Applications that use this media type:">
2747    </t>
2748    <t hangText="Additional information:">
2749      <list style="hanging">
2750        <t hangText="Magic number(s):">none</t>
2751        <t hangText="File extension(s):">none</t>
2752        <t hangText="Macintosh file type code(s):">none</t>
2753      </list>
2754    </t>
2755    <t hangText="Person and email address to contact for further information:">
2756      See Authors Section.
2757    </t>
2758                <t hangText="Intended usage:">
2759                  COMMON
2760    </t>
2761                <t hangText="Restrictions on usage:">
2762                  none
2763    </t>
2764    <t hangText="Author/Change controller:">
2765      IESG
2766    </t>
2767  </list>
2768</t>
2769</section>
2770<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2771<iref item="Media Type" subitem="application/http" primary="true"/>
2772<iref item="application/http Media Type" primary="true"/>
2773<t>
2774   The application/http type can be used to enclose a pipeline of one or more
2775   HTTP request or response messages (not intermixed).
2776</t>
2777<t>
2778  <list style="hanging" x:indent="12em">
2779    <t hangText="Type name:">
2780      application
2781    </t>
2782    <t hangText="Subtype name:">
2783      http
2784    </t>
2785    <t hangText="Required parameters:">
2786      none
2787    </t>
2788    <t hangText="Optional parameters:">
2789      version, msgtype
2790      <list style="hanging">
2791        <t hangText="version:">
2792          The HTTP-Version number of the enclosed messages
2793          (e.g., "1.1"). If not present, the version can be
2794          determined from the first line of the body.
2795        </t>
2796        <t hangText="msgtype:">
2797          The message type -- "request" or "response". If not
2798          present, the type can be determined from the first
2799          line of the body.
2800        </t>
2801      </list>
2802    </t>
2803    <t hangText="Encoding considerations:">
2804      HTTP messages enclosed by this type
2805      are in "binary" format; use of an appropriate
2806      Content-Transfer-Encoding is required when
2807      transmitted via E-mail.
2808    </t>
2809    <t hangText="Security considerations:">
2810      none
2811    </t>
2812    <t hangText="Interoperability considerations:">
2813      none
2814    </t>
2815    <t hangText="Published specification:">
2816      This specification (see <xref target="internet.media.type.application.http"/>).
2817    </t>
2818    <t hangText="Applications that use this media type:">
2819    </t>
2820    <t hangText="Additional information:">
2821      <list style="hanging">
2822        <t hangText="Magic number(s):">none</t>
2823        <t hangText="File extension(s):">none</t>
2824        <t hangText="Macintosh file type code(s):">none</t>
2825      </list>
2826    </t>
2827    <t hangText="Person and email address to contact for further information:">
2828      See Authors Section.
2829    </t>
2830                <t hangText="Intended usage:">
2831                  COMMON
2832    </t>
2833                <t hangText="Restrictions on usage:">
2834                  none
2835    </t>
2836    <t hangText="Author/Change controller:">
2837      IESG
2838    </t>
2839  </list>
2840</t>
2841</section>
2842</section>
2843
2844</section>
2845
2846<section title="Security Considerations" anchor="security.considerations">
2847<t>
2848   This section is meant to inform application developers, information
2849   providers, and users of the security limitations in HTTP/1.1 as
2850   described by this document. The discussion does not include
2851   definitive solutions to the problems revealed, though it does make
2852   some suggestions for reducing security risks.
2853</t>
2854
2855<section title="Personal Information" anchor="personal.information">
2856<t>
2857   HTTP clients are often privy to large amounts of personal information
2858   (e.g. the user's name, location, mail address, passwords, encryption
2859   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2860   leakage of this information.
2861   We very strongly recommend that a convenient interface be provided
2862   for the user to control dissemination of such information, and that
2863   designers and implementors be particularly careful in this area.
2864   History shows that errors in this area often create serious security
2865   and/or privacy problems and generate highly adverse publicity for the
2866   implementor's company.
2867</t>
2868</section>
2869
2870<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2871<t>
2872   A server is in the position to save personal data about a user's
2873   requests which might identify their reading patterns or subjects of
2874   interest. This information is clearly confidential in nature and its
2875   handling can be constrained by law in certain countries. People using
2876   HTTP to provide data are responsible for ensuring that
2877   such material is not distributed without the permission of any
2878   individuals that are identifiable by the published results.
2879</t>
2880</section>
2881
2882<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2883<t>
2884   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2885   the documents returned by HTTP requests to be only those that were
2886   intended by the server administrators. If an HTTP server translates
2887   HTTP URIs directly into file system calls, the server &MUST; take
2888   special care not to serve files that were not intended to be
2889   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2890   other operating systems use ".." as a path component to indicate a
2891   directory level above the current one. On such a system, an HTTP
2892   server &MUST; disallow any such construct in the Request-URI if it
2893   would otherwise allow access to a resource outside those intended to
2894   be accessible via the HTTP server. Similarly, files intended for
2895   reference only internally to the server (such as access control
2896   files, configuration files, and script code) &MUST; be protected from
2897   inappropriate retrieval, since they might contain sensitive
2898   information. Experience has shown that minor bugs in such HTTP server
2899   implementations have turned into security risks.
2900</t>
2901</section>
2902
2903<section title="DNS Spoofing" anchor="dns.spoofing">
2904<t>
2905   Clients using HTTP rely heavily on the Domain Name Service, and are
2906   thus generally prone to security attacks based on the deliberate
2907   mis-association of IP addresses and DNS names. Clients need to be
2908   cautious in assuming the continuing validity of an IP number/DNS name
2909   association.
2910</t>
2911<t>
2912   In particular, HTTP clients &SHOULD; rely on their name resolver for
2913   confirmation of an IP number/DNS name association, rather than
2914   caching the result of previous host name lookups. Many platforms
2915   already can cache host name lookups locally when appropriate, and
2916   they &SHOULD; be configured to do so. It is proper for these lookups to
2917   be cached, however, only when the TTL (Time To Live) information
2918   reported by the name server makes it likely that the cached
2919   information will remain useful.
2920</t>
2921<t>
2922   If HTTP clients cache the results of host name lookups in order to
2923   achieve a performance improvement, they &MUST; observe the TTL
2924   information reported by DNS.
2925</t>
2926<t>
2927   If HTTP clients do not observe this rule, they could be spoofed when
2928   a previously-accessed server's IP address changes. As network
2929   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2930   possibility of this form of attack will grow. Observing this
2931   requirement thus reduces this potential security vulnerability.
2932</t>
2933<t>
2934   This requirement also improves the load-balancing behavior of clients
2935   for replicated servers using the same DNS name and reduces the
2936   likelihood of a user's experiencing failure in accessing sites which
2937   use that strategy.
2938</t>
2939</section>
2940
2941<section title="Proxies and Caching" anchor="attack.proxies">
2942<t>
2943   By their very nature, HTTP proxies are men-in-the-middle, and
2944   represent an opportunity for man-in-the-middle attacks. Compromise of
2945   the systems on which the proxies run can result in serious security
2946   and privacy problems. Proxies have access to security-related
2947   information, personal information about individual users and
2948   organizations, and proprietary information belonging to users and
2949   content providers. A compromised proxy, or a proxy implemented or
2950   configured without regard to security and privacy considerations,
2951   might be used in the commission of a wide range of potential attacks.
2952</t>
2953<t>
2954   Proxy operators should protect the systems on which proxies run as
2955   they would protect any system that contains or transports sensitive
2956   information. In particular, log information gathered at proxies often
2957   contains highly sensitive personal information, and/or information
2958   about organizations. Log information should be carefully guarded, and
2959   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2960</t>
2961<t>
2962   Proxy implementors should consider the privacy and security
2963   implications of their design and coding decisions, and of the
2964   configuration options they provide to proxy operators (especially the
2965   default configuration).
2966</t>
2967<t>
2968   Users of a proxy need to be aware that they are no trustworthier than
2969   the people who run the proxy; HTTP itself cannot solve this problem.
2970</t>
2971<t>
2972   The judicious use of cryptography, when appropriate, may suffice to
2973   protect against a broad range of security and privacy attacks. Such
2974   cryptography is beyond the scope of the HTTP/1.1 specification.
2975</t>
2976</section>
2977
2978<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2979<t>
2980   They exist. They are hard to defend against. Research continues.
2981   Beware.
2982</t>
2983</section>
2984</section>
2985
2986<section title="Acknowledgments" anchor="ack">
2987<t>
2988   This specification makes heavy use of the augmented BNF and generic
2989   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2990   reuses many of the definitions provided by Nathaniel Borenstein and
2991   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2992   specification will help reduce past confusion over the relationship
2993   between HTTP and Internet mail message formats.
2994</t>
2995<t>
2996   HTTP has evolved considerably over the years. It has
2997   benefited from a large and active developer community--the many
2998   people who have participated on the www-talk mailing list--and it is
2999   that community which has been most responsible for the success of
3000   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3001   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3002   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3003   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3004   VanHeyningen deserve special recognition for their efforts in
3005   defining early aspects of the protocol.
3006</t>
3007<t>
3008   This document has benefited greatly from the comments of all those
3009   participating in the HTTP-WG. In addition to those already mentioned,
3010   the following individuals have contributed to this specification:
3011</t>
3012<t>
3013   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3014   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3015   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3016   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3017   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3018   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3019   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3020   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3021   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3022   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3023   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3024   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3025   Josh Cohen.
3026</t>
3027<t>
3028   Thanks to the "cave men" of Palo Alto. You know who you are.
3029</t>
3030<t>
3031   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3032   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3033   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3034   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3035   Larry Masinter for their help. And thanks go particularly to Jeff
3036   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3037</t>
3038<t>
3039   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3040   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3041   discovery of many of the problems that this document attempts to
3042   rectify.
3043</t>
3044</section>
3045
3046</middle>
3047<back>
3048
3049<references title="Normative References">
3050
3051<reference anchor="ISO-8859-1">
3052  <front>
3053    <title>
3054     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3055    </title>
3056    <author>
3057      <organization>International Organization for Standardization</organization>
3058    </author>
3059    <date year="1998"/>
3060  </front>
3061  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3062</reference>
3063
3064<reference anchor="Part2">
3065  <front>
3066    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3067    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3068      <organization abbrev="Day Software">Day Software</organization>
3069      <address><email>fielding@gbiv.com</email></address>
3070    </author>
3071    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3072      <organization>One Laptop per Child</organization>
3073      <address><email>jg@laptop.org</email></address>
3074    </author>
3075    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3076      <organization abbrev="HP">Hewlett-Packard Company</organization>
3077      <address><email>JeffMogul@acm.org</email></address>
3078    </author>
3079    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3080      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3081      <address><email>henrikn@microsoft.com</email></address>
3082    </author>
3083    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3084      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3085      <address><email>LMM@acm.org</email></address>
3086    </author>
3087    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3088      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3089      <address><email>paulle@microsoft.com</email></address>
3090    </author>
3091    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3092      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3093      <address><email>timbl@w3.org</email></address>
3094    </author>
3095    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3096      <organization abbrev="W3C">World Wide Web Consortium</organization>
3097      <address><email>ylafon@w3.org</email></address>
3098    </author>
3099    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3100      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3101      <address><email>julian.reschke@greenbytes.de</email></address>
3102    </author>
3103    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3104  </front>
3105  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3106  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3107</reference>
3108
3109<reference anchor="Part3">
3110  <front>
3111    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3112    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3113      <organization abbrev="Day Software">Day Software</organization>
3114      <address><email>fielding@gbiv.com</email></address>
3115    </author>
3116    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3117      <organization>One Laptop per Child</organization>
3118      <address><email>jg@laptop.org</email></address>
3119    </author>
3120    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3121      <organization abbrev="HP">Hewlett-Packard Company</organization>
3122      <address><email>JeffMogul@acm.org</email></address>
3123    </author>
3124    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3125      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3126      <address><email>henrikn@microsoft.com</email></address>
3127    </author>
3128    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3129      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3130      <address><email>LMM@acm.org</email></address>
3131    </author>
3132    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3133      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3134      <address><email>paulle@microsoft.com</email></address>
3135    </author>
3136    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3137      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3138      <address><email>timbl@w3.org</email></address>
3139    </author>
3140    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3141      <organization abbrev="W3C">World Wide Web Consortium</organization>
3142      <address><email>ylafon@w3.org</email></address>
3143    </author>
3144    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3145      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3146      <address><email>julian.reschke@greenbytes.de</email></address>
3147    </author>
3148    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3149  </front>
3150  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3151  <x:source href="p3-payload.xml" basename="p3-payload"/>
3152</reference>
3153
3154<reference anchor="Part5">
3155  <front>
3156    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3157    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3158      <organization abbrev="Day Software">Day Software</organization>
3159      <address><email>fielding@gbiv.com</email></address>
3160    </author>
3161    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3162      <organization>One Laptop per Child</organization>
3163      <address><email>jg@laptop.org</email></address>
3164    </author>
3165    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3166      <organization abbrev="HP">Hewlett-Packard Company</organization>
3167      <address><email>JeffMogul@acm.org</email></address>
3168    </author>
3169    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3170      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3171      <address><email>henrikn@microsoft.com</email></address>
3172    </author>
3173    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3174      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3175      <address><email>LMM@acm.org</email></address>
3176    </author>
3177    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3178      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3179      <address><email>paulle@microsoft.com</email></address>
3180    </author>
3181    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3182      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3183      <address><email>timbl@w3.org</email></address>
3184    </author>
3185    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3186      <organization abbrev="W3C">World Wide Web Consortium</organization>
3187      <address><email>ylafon@w3.org</email></address>
3188    </author>
3189    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3190      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3191      <address><email>julian.reschke@greenbytes.de</email></address>
3192    </author>
3193    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3194  </front>
3195  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3196  <x:source href="p5-range.xml" basename="p5-range"/>
3197</reference>
3198
3199<reference anchor="Part6">
3200  <front>
3201    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3202    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3203      <organization abbrev="Day Software">Day Software</organization>
3204      <address><email>fielding@gbiv.com</email></address>
3205    </author>
3206    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3207      <organization>One Laptop per Child</organization>
3208      <address><email>jg@laptop.org</email></address>
3209    </author>
3210    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3211      <organization abbrev="HP">Hewlett-Packard Company</organization>
3212      <address><email>JeffMogul@acm.org</email></address>
3213    </author>
3214    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3215      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3216      <address><email>henrikn@microsoft.com</email></address>
3217    </author>
3218    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3219      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3220      <address><email>LMM@acm.org</email></address>
3221    </author>
3222    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3223      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3224      <address><email>paulle@microsoft.com</email></address>
3225    </author>
3226    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3227      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3228      <address><email>timbl@w3.org</email></address>
3229    </author>
3230    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3231      <organization abbrev="W3C">World Wide Web Consortium</organization>
3232      <address><email>ylafon@w3.org</email></address>
3233    </author>
3234    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3235      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3236      <address><email>julian.reschke@greenbytes.de</email></address>
3237    </author>
3238    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3239  </front>
3240  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3241  <x:source href="p6-cache.xml" basename="p6-cache"/>
3242</reference>
3243
3244<reference anchor="RFC5234">
3245  <front>
3246    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3247    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3248      <organization>Brandenburg InternetWorking</organization>
3249      <address>
3250      <postal>
3251      <street>675 Spruce Dr.</street>
3252      <city>Sunnyvale</city>
3253      <region>CA</region>
3254      <code>94086</code>
3255      <country>US</country></postal>
3256      <phone>+1.408.246.8253</phone>
3257      <email>dcrocker@bbiw.net</email></address> 
3258    </author>
3259    <author initials="P." surname="Overell" fullname="Paul Overell">
3260      <organization>THUS plc.</organization>
3261      <address>
3262      <postal>
3263      <street>1/2 Berkeley Square</street>
3264      <street>99 Berkely Street</street>
3265      <city>Glasgow</city>
3266      <code>G3 7HR</code>
3267      <country>UK</country></postal>
3268      <email>paul.overell@thus.net</email></address>
3269    </author>
3270    <date month="January" year="2008"/>
3271  </front>
3272  <seriesInfo name="STD" value="68"/>
3273  <seriesInfo name="RFC" value="5234"/>
3274</reference>
3275
3276<reference anchor="RFC2045">
3277  <front>
3278    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3279    <author initials="N." surname="Freed" fullname="Ned Freed">
3280      <organization>Innosoft International, Inc.</organization>
3281      <address><email>ned@innosoft.com</email></address>
3282    </author>
3283    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3284      <organization>First Virtual Holdings</organization>
3285      <address><email>nsb@nsb.fv.com</email></address>
3286    </author>
3287    <date month="November" year="1996"/>
3288  </front>
3289  <seriesInfo name="RFC" value="2045"/>
3290</reference>
3291
3292<reference anchor="RFC2047">
3293  <front>
3294    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3295    <author initials="K." surname="Moore" fullname="Keith Moore">
3296      <organization>University of Tennessee</organization>
3297      <address><email>moore@cs.utk.edu</email></address>
3298    </author>
3299    <date month="November" year="1996"/>
3300  </front>
3301  <seriesInfo name="RFC" value="2047"/>
3302</reference>
3303
3304<reference anchor="RFC2119">
3305  <front>
3306    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3307    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3308      <organization>Harvard University</organization>
3309      <address><email>sob@harvard.edu</email></address>
3310    </author>
3311    <date month="March" year="1997"/>
3312  </front>
3313  <seriesInfo name="BCP" value="14"/>
3314  <seriesInfo name="RFC" value="2119"/>
3315</reference>
3316
3317<reference anchor="RFC2396">
3318  <front>
3319    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3320    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3321      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3322      <address><email>timbl@w3.org</email></address>
3323    </author>
3324    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3325      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3326      <address><email>fielding@ics.uci.edu</email></address>
3327    </author>
3328    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3329      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3330      <address><email>masinter@parc.xerox.com</email></address>
3331    </author>
3332    <date month="August" year="1998"/>
3333  </front>
3334  <seriesInfo name="RFC" value="2396"/>
3335</reference>
3336
3337<reference anchor="USASCII">
3338  <front>
3339    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3340    <author>
3341      <organization>American National Standards Institute</organization>
3342    </author>
3343    <date year="1986"/>
3344  </front>
3345  <seriesInfo name="ANSI" value="X3.4"/>
3346</reference>
3347
3348</references>
3349
3350<references title="Informative References">
3351
3352<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3353  <front>
3354    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3355    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3356      <organization/>
3357    </author>
3358    <author initials="J." surname="Gettys" fullname="J. Gettys">
3359      <organization/>
3360    </author>
3361    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3362      <organization/>
3363    </author>
3364    <author initials="H." surname="Lie" fullname="H. Lie">
3365      <organization/>
3366    </author>
3367    <author initials="C." surname="Lilley" fullname="C. Lilley">
3368      <organization/>
3369    </author>
3370    <date year="1997" month="September"/>
3371  </front>
3372  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3373</reference>
3374
3375<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3376  <front>
3377    <title>Improving HTTP Latency</title>
3378    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3379      <organization/>
3380    </author>
3381    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3382      <organization/>
3383    </author>
3384    <date year="1995" month="December"/>
3385  </front>
3386  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3387</reference>
3388
3389<reference anchor="RFC822">
3390  <front>
3391    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3392    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3393      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3394      <address><email>DCrocker@UDel-Relay</email></address>
3395    </author>
3396    <date month="August" day="13" year="1982"/>
3397  </front>
3398  <seriesInfo name="STD" value="11"/>
3399  <seriesInfo name="RFC" value="822"/>
3400</reference>
3401
3402<reference anchor="RFC959">
3403  <front>
3404    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3405    <author initials="J." surname="Postel" fullname="J. Postel">
3406      <organization>Information Sciences Institute (ISI)</organization>
3407    </author>
3408    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3409      <organization/>
3410    </author>
3411    <date month="October" year="1985"/>
3412  </front>
3413  <seriesInfo name="STD" value="9"/>
3414  <seriesInfo name="RFC" value="959"/>
3415</reference>
3416
3417<reference anchor="RFC1123">
3418  <front>
3419    <title>Requirements for Internet Hosts - Application and Support</title>
3420    <author initials="R." surname="Braden" fullname="Robert Braden">
3421      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3422      <address><email>Braden@ISI.EDU</email></address>
3423    </author>
3424    <date month="October" year="1989"/>
3425  </front>
3426  <seriesInfo name="STD" value="3"/>
3427  <seriesInfo name="RFC" value="1123"/>
3428</reference>
3429
3430<reference anchor="RFC1305">
3431  <front>
3432    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3433    <author initials="D." surname="Mills" fullname="David L. Mills">
3434      <organization>University of Delaware, Electrical Engineering Department</organization>
3435      <address><email>mills@udel.edu</email></address>
3436    </author>
3437    <date month="March" year="1992"/>
3438  </front>
3439  <seriesInfo name="RFC" value="1305"/>
3440</reference>
3441
3442<reference anchor="RFC1436">
3443  <front>
3444    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3445    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3446      <organization>University of Minnesota, Computer and Information Services</organization>
3447      <address><email>fxa@boombox.micro.umn.edu</email></address>
3448    </author>
3449    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3450      <organization>University of Minnesota, Computer and Information Services</organization>
3451      <address><email>mpm@boombox.micro.umn.edu</email></address>
3452    </author>
3453    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3454      <organization>University of Minnesota, Computer and Information Services</organization>
3455      <address><email>lindner@boombox.micro.umn.edu</email></address>
3456    </author>
3457    <author initials="D." surname="Johnson" fullname="David Johnson">
3458      <organization>University of Minnesota, Computer and Information Services</organization>
3459      <address><email>dmj@boombox.micro.umn.edu</email></address>
3460    </author>
3461    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3462      <organization>University of Minnesota, Computer and Information Services</organization>
3463      <address><email>daniel@boombox.micro.umn.edu</email></address>
3464    </author>
3465    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3466      <organization>University of Minnesota, Computer and Information Services</organization>
3467      <address><email>alberti@boombox.micro.umn.edu</email></address>
3468    </author>
3469    <date month="March" year="1993"/>
3470  </front>
3471  <seriesInfo name="RFC" value="1436"/>
3472</reference>
3473
3474<reference anchor="RFC1630">
3475  <front>
3476    <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>
3477    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3478      <organization>CERN, World-Wide Web project</organization>
3479      <address><email>timbl@info.cern.ch</email></address>
3480    </author>
3481    <date month="June" year="1994"/>
3482  </front>
3483  <seriesInfo name="RFC" value="1630"/>
3484</reference>
3485
3486<reference anchor="RFC1737">
3487  <front>
3488    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3489    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3490      <organization>Xerox Palo Alto Research Center</organization>
3491      <address><email>masinter@parc.xerox.com</email></address>
3492    </author>
3493    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3494      <organization>MIT Laboratory for Computer Science</organization>
3495      <address><email>sollins@lcs.mit.edu</email></address>
3496    </author>
3497    <date month="December" year="1994"/>
3498  </front>
3499  <seriesInfo name="RFC" value="1737"/>
3500</reference>
3501
3502<reference anchor="RFC1738">
3503  <front>
3504    <title>Uniform Resource Locators (URL)</title>
3505    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3506      <organization>CERN, World-Wide Web project</organization>
3507      <address><email>timbl@info.cern.ch</email></address>
3508    </author>
3509    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3510      <organization>Xerox PARC</organization>
3511      <address><email>masinter@parc.xerox.com</email></address>
3512    </author>
3513    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3514      <organization>University of Minnesota, Computer and Information Services</organization>
3515      <address><email>mpm@boombox.micro.umn.edu</email></address>
3516    </author>
3517    <date month="December" year="1994"/>
3518  </front>
3519  <seriesInfo name="RFC" value="1738"/>
3520</reference>
3521
3522<reference anchor="RFC1808">
3523  <front>
3524    <title>Relative Uniform Resource Locators</title>
3525    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3526      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3527      <address><email>fielding@ics.uci.edu</email></address>
3528    </author>
3529    <date month="June" year="1995"/>
3530  </front>
3531  <seriesInfo name="RFC" value="1808"/>
3532</reference>
3533
3534<reference anchor="RFC1900">
3535  <front>
3536    <title>Renumbering Needs Work</title>
3537    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3538      <organization>CERN, Computing and Networks Division</organization>
3539      <address><email>brian@dxcoms.cern.ch</email></address>
3540    </author>
3541    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3542      <organization>cisco Systems</organization>
3543      <address><email>yakov@cisco.com</email></address>
3544    </author>
3545    <date month="February" year="1996"/>
3546  </front>
3547  <seriesInfo name="RFC" value="1900"/>
3548</reference>
3549
3550<reference anchor="RFC1945">
3551  <front>
3552    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3553    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3554      <organization>MIT, Laboratory for Computer Science</organization>
3555      <address><email>timbl@w3.org</email></address>
3556    </author>
3557    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3558      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3559      <address><email>fielding@ics.uci.edu</email></address>
3560    </author>
3561    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3562      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3563      <address><email>frystyk@w3.org</email></address>
3564    </author>
3565    <date month="May" year="1996"/>
3566  </front>
3567  <seriesInfo name="RFC" value="1945"/>
3568</reference>
3569
3570<reference anchor="RFC2068">
3571  <front>
3572    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3573    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3574      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3575      <address><email>fielding@ics.uci.edu</email></address>
3576    </author>
3577    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3578      <organization>MIT Laboratory for Computer Science</organization>
3579      <address><email>jg@w3.org</email></address>
3580    </author>
3581    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3582      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3583      <address><email>mogul@wrl.dec.com</email></address>
3584    </author>
3585    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3586      <organization>MIT Laboratory for Computer Science</organization>
3587      <address><email>frystyk@w3.org</email></address>
3588    </author>
3589    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3590      <organization>MIT Laboratory for Computer Science</organization>
3591      <address><email>timbl@w3.org</email></address>
3592    </author>
3593    <date month="January" year="1997"/>
3594  </front>
3595  <seriesInfo name="RFC" value="2068"/>
3596</reference>
3597
3598<reference anchor='RFC2109'>
3599  <front>
3600    <title>HTTP State Management Mechanism</title>
3601    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3602      <organization>Bell Laboratories, Lucent Technologies</organization>
3603      <address><email>dmk@bell-labs.com</email></address>
3604    </author>
3605    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3606      <organization>Netscape Communications Corp.</organization>
3607      <address><email>montulli@netscape.com</email></address>
3608    </author>
3609    <date year='1997' month='February' />
3610  </front>
3611  <seriesInfo name='RFC' value='2109' />
3612</reference>
3613
3614<reference anchor="RFC2145">
3615  <front>
3616    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3617    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3618      <organization>Western Research Laboratory</organization>
3619      <address><email>mogul@wrl.dec.com</email></address>
3620    </author>
3621    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3622      <organization>Department of Information and Computer Science</organization>
3623      <address><email>fielding@ics.uci.edu</email></address>
3624    </author>
3625    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3626      <organization>MIT Laboratory for Computer Science</organization>
3627      <address><email>jg@w3.org</email></address>
3628    </author>
3629    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3630      <organization>W3 Consortium</organization>
3631      <address><email>frystyk@w3.org</email></address>
3632    </author>
3633    <date month="May" year="1997"/>
3634  </front>
3635  <seriesInfo name="RFC" value="2145"/>
3636</reference>
3637
3638<reference anchor="RFC2324">
3639  <front>
3640    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3641    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3642      <organization>Xerox Palo Alto Research Center</organization>
3643      <address><email>masinter@parc.xerox.com</email></address>
3644    </author>
3645    <date month="April" day="1" year="1998"/>
3646  </front>
3647  <seriesInfo name="RFC" value="2324"/>
3648</reference>
3649
3650<reference anchor="RFC2616">
3651  <front>
3652    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3653    <author initials="R." surname="Fielding" fullname="R. Fielding">
3654      <organization>University of California, Irvine</organization>
3655      <address><email>fielding@ics.uci.edu</email></address>
3656    </author>
3657    <author initials="J." surname="Gettys" fullname="J. Gettys">
3658      <organization>W3C</organization>
3659      <address><email>jg@w3.org</email></address>
3660    </author>
3661    <author initials="J." surname="Mogul" fullname="J. Mogul">
3662      <organization>Compaq Computer Corporation</organization>
3663      <address><email>mogul@wrl.dec.com</email></address>
3664    </author>
3665    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3666      <organization>MIT Laboratory for Computer Science</organization>
3667      <address><email>frystyk@w3.org</email></address>
3668    </author>
3669    <author initials="L." surname="Masinter" fullname="L. Masinter">
3670      <organization>Xerox Corporation</organization>
3671      <address><email>masinter@parc.xerox.com</email></address>
3672    </author>
3673    <author initials="P." surname="Leach" fullname="P. Leach">
3674      <organization>Microsoft Corporation</organization>
3675      <address><email>paulle@microsoft.com</email></address>
3676    </author>
3677    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3678      <organization>W3C</organization>
3679      <address><email>timbl@w3.org</email></address>
3680    </author>
3681    <date month="June" year="1999"/>
3682  </front>
3683  <seriesInfo name="RFC" value="2616"/>
3684</reference>
3685
3686<reference anchor='RFC2818'>
3687  <front>
3688    <title>HTTP Over TLS</title>
3689    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3690      <organization>RTFM, Inc.</organization>
3691      <address><email>ekr@rtfm.com</email></address>
3692    </author>
3693    <date year='2000' month='May' />
3694  </front>
3695  <seriesInfo name='RFC' value='2818' />
3696</reference>
3697
3698<reference anchor="RFC2821">
3699  <front>
3700    <title>Simple Mail Transfer Protocol</title>
3701    <author initials="J." surname="Klensin" fullname="J. Klensin">
3702      <organization>AT&amp;T Laboratories</organization>
3703      <address><email>klensin@research.att.com</email></address>
3704    </author>
3705    <date year="2001" month="April"/>
3706  </front>
3707  <seriesInfo name="RFC" value="2821"/>
3708</reference>
3709
3710<reference anchor='RFC2965'>
3711  <front>
3712    <title>HTTP State Management Mechanism</title>
3713    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3714      <organization>Bell Laboratories, Lucent Technologies</organization>
3715      <address><email>dmk@bell-labs.com</email></address>
3716    </author>
3717    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3718      <organization>Epinions.com, Inc.</organization>
3719      <address><email>lou@montulli.org</email></address>
3720    </author>
3721    <date year='2000' month='October' />
3722  </front>
3723  <seriesInfo name='RFC' value='2965' />
3724</reference>
3725
3726<reference anchor='RFC3864'>
3727  <front>
3728    <title>Registration Procedures for Message Header Fields</title>
3729    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3730      <organization>Nine by Nine</organization>
3731      <address><email>GK-IETF@ninebynine.org</email></address>
3732    </author>
3733    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3734      <organization>BEA Systems</organization>
3735      <address><email>mnot@pobox.com</email></address>
3736    </author>
3737    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3738      <organization>HP Labs</organization>
3739      <address><email>JeffMogul@acm.org</email></address>
3740    </author>
3741    <date year='2004' month='September' />
3742  </front>
3743  <seriesInfo name='BCP' value='90' />
3744  <seriesInfo name='RFC' value='3864' />
3745</reference>
3746
3747<reference anchor='RFC3977'>
3748  <front>
3749    <title>Network News Transfer Protocol (NNTP)</title>
3750    <author initials='C.' surname='Feather' fullname='C. Feather'>
3751      <organization>THUS plc</organization>
3752      <address><email>clive@demon.net</email></address>
3753    </author>
3754    <date year='2006' month='October' />
3755  </front>
3756  <seriesInfo name="RFC" value="3977"/>
3757</reference>
3758
3759<reference anchor="RFC4288">
3760  <front>
3761    <title>Media Type Specifications and Registration Procedures</title>
3762    <author initials="N." surname="Freed" fullname="N. Freed">
3763      <organization>Sun Microsystems</organization>
3764      <address>
3765        <email>ned.freed@mrochek.com</email>
3766      </address>
3767    </author>
3768    <author initials="J." surname="Klensin" fullname="J. Klensin">
3769      <organization/>
3770      <address>
3771        <email>klensin+ietf@jck.com</email>
3772      </address>
3773    </author>
3774    <date year="2005" month="December"/>
3775  </front>
3776  <seriesInfo name="BCP" value="13"/>
3777  <seriesInfo name="RFC" value="4288"/>
3778</reference>
3779
3780<reference anchor='RFC4395'>
3781  <front>
3782    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3783    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3784      <organization>AT&amp;T Laboratories</organization>
3785      <address>
3786        <email>tony+urireg@maillennium.att.com</email>
3787      </address>
3788    </author>
3789    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3790      <organization>Qualcomm, Inc.</organization>
3791      <address>
3792        <email>hardie@qualcomm.com</email>
3793      </address>
3794    </author>
3795    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3796      <organization>Adobe Systems</organization>
3797      <address>
3798        <email>LMM@acm.org</email>
3799      </address>
3800    </author>
3801    <date year='2006' month='February' />
3802  </front>
3803  <seriesInfo name='BCP' value='115' />
3804  <seriesInfo name='RFC' value='4395' />
3805</reference>
3806
3807<reference anchor="RFC5322">
3808  <front>
3809    <title>Internet Message Format</title>
3810    <author initials="P." surname="Resnick" fullname="P. Resnick">
3811      <organization>Qualcomm Incorporated</organization>
3812    </author>
3813    <date year="2008" month="October"/>
3814  </front>
3815  <seriesInfo name="RFC" value="5322"/>
3816</reference>
3817
3818<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3819  <front>
3820    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3821    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3822      <organization/>
3823    </author>
3824    <date year="2001" month="November"/>
3825  </front>
3826  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3827</reference>
3828
3829<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3830  <front>
3831  <title>Analysis of HTTP Performance Problems</title>
3832  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3833    <organization/>
3834  </author>
3835  <date/>
3836  </front>
3837</reference>
3838
3839<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3840  <front>
3841  <title>Analysis of HTTP Performance</title>
3842  <author initials="J." surname="Touch" fullname="Joe Touch">
3843    <organization>USC/Information Sciences Institute</organization>
3844    <address><email>touch@isi.edu</email></address>
3845  </author>
3846  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3847    <organization>USC/Information Sciences Institute</organization>
3848    <address><email>johnh@isi.edu</email></address>
3849  </author>
3850  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3851    <organization>USC/Information Sciences Institute</organization>
3852    <address><email>katia@isi.edu</email></address>
3853  </author>
3854  <date year="1998" month="Aug"/>
3855  </front>
3856  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3857  <annotation>(original report dated Aug. 1996)</annotation>
3858</reference>
3859
3860<reference anchor="WAIS">
3861  <front>
3862    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3863    <author initials="F." surname="Davis" fullname="F. Davis">
3864      <organization>Thinking Machines Corporation</organization>
3865    </author>
3866    <author initials="B." surname="Kahle" fullname="B. Kahle">
3867      <organization>Thinking Machines Corporation</organization>
3868    </author>
3869    <author initials="H." surname="Morris" fullname="H. Morris">
3870      <organization>Thinking Machines Corporation</organization>
3871    </author>
3872    <author initials="J." surname="Salem" fullname="J. Salem">
3873      <organization>Thinking Machines Corporation</organization>
3874    </author>
3875    <author initials="T." surname="Shen" fullname="T. Shen">
3876      <organization>Thinking Machines Corporation</organization>
3877    </author>
3878    <author initials="R." surname="Wang" fullname="R. Wang">
3879      <organization>Thinking Machines Corporation</organization>
3880    </author>
3881    <author initials="J." surname="Sui" fullname="J. Sui">
3882      <organization>Thinking Machines Corporation</organization>
3883    </author>
3884    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3885      <organization>Thinking Machines Corporation</organization>
3886    </author>
3887    <date month="April" year="1990"/>
3888  </front>
3889  <seriesInfo name="Thinking Machines Corporation" value=""/>
3890</reference>
3891
3892</references>
3893
3894
3895<section title="Tolerant Applications" anchor="tolerant.applications">
3896<t>
3897   Although this document specifies the requirements for the generation
3898   of HTTP/1.1 messages, not all applications will be correct in their
3899   implementation. We therefore recommend that operational applications
3900   be tolerant of deviations whenever those deviations can be
3901   interpreted unambiguously.
3902</t>
3903<t>
3904   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3905   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3906   accept any amount of SP or HTAB characters between fields, even though
3907   only a single SP is required.
3908</t>
3909<t>
3910   The line terminator for message-header fields is the sequence CRLF.
3911   However, we recommend that applications, when parsing such headers,
3912   recognize a single LF as a line terminator and ignore the leading CR.
3913</t>
3914<t>
3915   The character set of an entity-body &SHOULD; be labeled as the lowest
3916   common denominator of the character codes used within that body, with
3917   the exception that not labeling the entity is preferred over labeling
3918   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3919</t>
3920<t>
3921   Additional rules for requirements on parsing and encoding of dates
3922   and other potential problems with date encodings include:
3923</t>
3924<t>
3925  <list style="symbols">
3926     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3927        which appears to be more than 50 years in the future is in fact
3928        in the past (this helps solve the "year 2000" problem).</t>
3929
3930     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3931        Expires date as earlier than the proper value, but &MUST-NOT;
3932        internally represent a parsed Expires date as later than the
3933        proper value.</t>
3934
3935     <t>All expiration-related calculations &MUST; be done in GMT. The
3936        local time zone &MUST-NOT; influence the calculation or comparison
3937        of an age or expiration time.</t>
3938
3939     <t>If an HTTP header incorrectly carries a date value with a time
3940        zone other than GMT, it &MUST; be converted into GMT using the
3941        most conservative possible conversion.</t>
3942  </list>
3943</t>
3944</section>
3945
3946<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3947<t>
3948   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3949   simplify the process of date comparison. Proxies and gateways from
3950   other protocols &SHOULD; ensure that any Date header field present in a
3951   message conforms to one of the HTTP/1.1 formats and rewrite the date
3952   if necessary.
3953</t>
3954</section>
3955
3956<section title="Compatibility with Previous Versions" anchor="compatibility">
3957<t>
3958   It is beyond the scope of a protocol specification to mandate
3959   compliance with previous versions. HTTP/1.1 was deliberately
3960   designed, however, to make supporting previous versions easy. It is
3961   worth noting that, at the time of composing this specification
3962   (1996), we would expect commercial HTTP/1.1 servers to:
3963  <list style="symbols">
3964     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3965        1.1 requests;</t>
3966
3967     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3968        1.1;</t>
3969
3970     <t>respond appropriately with a message in the same major version
3971        used by the client.</t>
3972  </list>
3973</t>
3974<t>
3975   And we would expect HTTP/1.1 clients to:
3976  <list style="symbols">
3977     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3978        responses;</t>
3979
3980     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3981        1.1.</t>
3982  </list>
3983</t>
3984<t>
3985   For most implementations of HTTP/1.0, each connection is established
3986   by the client prior to the request and closed by the server after
3987   sending the response. Some implementations implement the Keep-Alive
3988   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3989</t>
3990
3991<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3992<t>
3993   This section summarizes major differences between versions HTTP/1.0
3994   and HTTP/1.1.
3995</t>
3996
3997<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">
3998<t>
3999   The requirements that clients and servers support the Host request-header,
4000   report an error if the Host request-header (<xref target="header.host"/>) is
4001   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4002   are among the most important changes defined by this
4003   specification.
4004</t>
4005<t>
4006   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4007   addresses and servers; there was no other established mechanism for
4008   distinguishing the intended server of a request than the IP address
4009   to which that request was directed. The changes outlined above will
4010   allow the Internet, once older HTTP clients are no longer common, to
4011   support multiple Web sites from a single IP address, greatly
4012   simplifying large operational Web servers, where allocation of many
4013   IP addresses to a single host has created serious problems. The
4014   Internet will also be able to recover the IP addresses that have been
4015   allocated for the sole purpose of allowing special-purpose domain
4016   names to be used in root-level HTTP URLs. Given the rate of growth of
4017   the Web, and the number of servers already deployed, it is extremely
4018   important that all implementations of HTTP (including updates to
4019   existing HTTP/1.0 applications) correctly implement these
4020   requirements:
4021  <list style="symbols">
4022     <t>Both clients and servers &MUST; support the Host request-header.</t>
4023
4024     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4025
4026     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4027        request does not include a Host request-header.</t>
4028
4029     <t>Servers &MUST; accept absolute URIs.</t>
4030  </list>
4031</t>
4032</section>
4033</section>
4034
4035<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4036<t>
4037   Some clients and servers might wish to be compatible with some
4038   previous implementations of persistent connections in HTTP/1.0
4039   clients and servers. Persistent connections in HTTP/1.0 are
4040   explicitly negotiated as they are not the default behavior. HTTP/1.0
4041   experimental implementations of persistent connections are faulty,
4042   and the new facilities in HTTP/1.1 are designed to rectify these
4043   problems. The problem was that some existing 1.0 clients may be
4044   sending Keep-Alive to a proxy server that doesn't understand
4045   Connection, which would then erroneously forward it to the next
4046   inbound server, which would establish the Keep-Alive connection and
4047   result in a hung HTTP/1.0 proxy waiting for the close on the
4048   response. The result is that HTTP/1.0 clients must be prevented from
4049   using Keep-Alive when talking to proxies.
4050</t>
4051<t>
4052   However, talking to proxies is the most important use of persistent
4053   connections, so that prohibition is clearly unacceptable. Therefore,
4054   we need some other mechanism for indicating a persistent connection
4055   is desired, which is safe to use even when talking to an old proxy
4056   that ignores Connection. Persistent connections are the default for
4057   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4058   declaring non-persistence. See <xref target="header.connection"/>.
4059</t>
4060<t>
4061   The original HTTP/1.0 form of persistent connections (the Connection:
4062   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4063</t>
4064</section>
4065
4066<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4067<t>
4068   This specification has been carefully audited to correct and
4069   disambiguate key word usage; RFC 2068 had many problems in respect to
4070   the conventions laid out in <xref target="RFC2119"/>.
4071</t>
4072<t>
4073   Transfer-coding and message lengths all interact in ways that
4074   required fixing exactly when chunked encoding is used (to allow for
4075   transfer encoding that may not be self delimiting); it was important
4076   to straighten out exactly how message lengths are computed. (Sections
4077   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4078   <xref target="header.content-length" format="counter"/>,
4079   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4080</t>
4081<t>
4082   The use and interpretation of HTTP version numbers has been clarified
4083   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4084   version they support to deal with problems discovered in HTTP/1.0
4085   implementations (<xref target="http.version"/>)
4086</t>
4087<t>
4088   Transfer-coding had significant problems, particularly with
4089   interactions with chunked encoding. The solution is that transfer-codings
4090   become as full fledged as content-codings. This involves
4091   adding an IANA registry for transfer-codings (separate from content
4092   codings), a new header field (TE) and enabling trailer headers in the
4093   future. Transfer encoding is a major performance benefit, so it was
4094   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4095   interoperability problem that could have occurred due to interactions
4096   between authentication trailers, chunked encoding and HTTP/1.0
4097   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4098   and <xref target="header.te" format="counter"/>)
4099</t>
4100</section>
4101
4102<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4103<t>
4104  The CHAR rule does not allow the NUL character anymore (this affects
4105  the comment and quoted-string rules).  Furthermore, the quoted-pair
4106  rule does not allow escaping NUL, CR or LF anymore.
4107  (<xref target="basic.rules"/>)
4108</t>
4109<t>
4110  Clarify that HTTP-Version is case sensitive.
4111  (<xref target="http.version"/>)
4112</t>
4113<t>
4114  Remove reference to non-existant identity transfer-coding value tokens.
4115  (Sections <xref format="counter" target="transfer.codings"/> and
4116  <xref format="counter" target="message.length"/>)
4117</t>
4118<t>
4119  Clarification that the chunk length does not include
4120  the count of the octets in the chunk header and trailer.
4121  (<xref target="chunked.transfer.encoding"/>)
4122</t>
4123<t>
4124  Fix BNF to add query, as the abs_path production in
4125  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4126  (<xref target="request-uri"/>)
4127</t>
4128<t>
4129  Clarify exactly when close connection options must be sent.
4130  (<xref target="header.connection"/>)
4131</t>
4132</section>
4133</section>
4134
4135<section title="Terminology" anchor="terminology">
4136<t>
4137   This specification uses a number of terms to refer to the roles
4138   played by participants in, and objects of, the HTTP communication.
4139</t>
4140<t>
4141  <iref item="connection"/>
4142  <x:dfn>connection</x:dfn>
4143  <list>
4144    <t>
4145      A transport layer virtual circuit established between two programs
4146      for the purpose of communication.
4147    </t>
4148  </list>
4149</t>
4150<t>
4151  <iref item="message"/>
4152  <x:dfn>message</x:dfn>
4153  <list>
4154    <t>
4155      The basic unit of HTTP communication, consisting of a structured
4156      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4157      transmitted via the connection.
4158    </t>
4159  </list>
4160</t>
4161<t>
4162  <iref item="request"/>
4163  <x:dfn>request</x:dfn>
4164  <list>
4165    <t>
4166      An HTTP request message, as defined in <xref target="request"/>.
4167    </t>
4168  </list>
4169</t>
4170<t>
4171  <iref item="response"/>
4172  <x:dfn>response</x:dfn>
4173  <list>
4174    <t>
4175      An HTTP response message, as defined in <xref target="response"/>.
4176    </t>
4177  </list>
4178</t>
4179<t>
4180  <iref item="resource"/>
4181  <x:dfn>resource</x:dfn>
4182  <list>
4183    <t>
4184      A network data object or service that can be identified by a URI,
4185      as defined in <xref target="uri"/>. Resources may be available in multiple
4186      representations (e.g. multiple languages, data formats, size, and
4187      resolutions) or vary in other ways.
4188    </t>
4189  </list>
4190</t>
4191<t>
4192  <iref item="entity"/>
4193  <x:dfn>entity</x:dfn>
4194  <list>
4195    <t>
4196      The information transferred as the payload of a request or
4197      response. An entity consists of metainformation in the form of
4198      entity-header fields and content in the form of an entity-body, as
4199      described in &entity;.
4200    </t>
4201  </list>
4202</t>
4203<t>
4204  <iref item="representation"/>
4205  <x:dfn>representation</x:dfn>
4206  <list>
4207    <t>
4208      An entity included with a response that is subject to content
4209      negotiation, as described in &content.negotiation;. There may exist multiple
4210      representations associated with a particular response status.
4211    </t>
4212  </list>
4213</t>
4214<t>
4215  <iref item="content negotiation"/>
4216  <x:dfn>content negotiation</x:dfn>
4217  <list>
4218    <t>
4219      The mechanism for selecting the appropriate representation when
4220      servicing a request, as described in &content.negotiation;. The
4221      representation of entities in any response can be negotiated
4222      (including error responses).
4223    </t>
4224  </list>
4225</t>
4226<t>
4227  <iref item="variant"/>
4228  <x:dfn>variant</x:dfn>
4229  <list>
4230    <t>
4231      A resource may have one, or more than one, representation(s)
4232      associated with it at any given instant. Each of these
4233      representations is termed a `variant'.  Use of the term `variant'
4234      does not necessarily imply that the resource is subject to content
4235      negotiation.
4236    </t>
4237  </list>
4238</t>
4239<t>
4240  <iref item="client"/>
4241  <x:dfn>client</x:dfn>
4242  <list>
4243    <t>
4244      A program that establishes connections for the purpose of sending
4245      requests.
4246    </t>
4247  </list>
4248</t>
4249<t>
4250  <iref item="user agent"/>
4251  <x:dfn>user agent</x:dfn>
4252  <list>
4253    <t>
4254      The client which initiates a request. These are often browsers,
4255      editors, spiders (web-traversing robots), or other end user tools.
4256    </t>
4257  </list>
4258</t>
4259<t>
4260  <iref item="server"/>
4261  <x:dfn>server</x:dfn>
4262  <list>
4263    <t>
4264      An application program that accepts connections in order to
4265      service requests by sending back responses. Any given program may
4266      be capable of being both a client and a server; our use of these
4267      terms refers only to the role being performed by the program for a
4268      particular connection, rather than to the program's capabilities
4269      in general. Likewise, any server may act as an origin server,
4270      proxy, gateway, or tunnel, switching behavior based on the nature
4271      of each request.
4272    </t>
4273  </list>
4274</t>
4275<t>
4276  <iref item="origin server"/>
4277  <x:dfn>origin server</x:dfn>
4278  <list>
4279    <t>
4280      The server on which a given resource resides or is to be created.
4281    </t>
4282  </list>
4283</t>
4284<t>
4285  <iref item="proxy"/>
4286  <x:dfn>proxy</x:dfn>
4287  <list>
4288    <t>
4289      An intermediary program which acts as both a server and a client
4290      for the purpose of making requests on behalf of other clients.
4291      Requests are serviced internally or by passing them on, with
4292      possible translation, to other servers. A proxy &MUST; implement
4293      both the client and server requirements of this specification. A
4294      "transparent proxy" is a proxy that does not modify the request or
4295      response beyond what is required for proxy authentication and
4296      identification. A "non-transparent proxy" is a proxy that modifies
4297      the request or response in order to provide some added service to
4298      the user agent, such as group annotation services, media type
4299      transformation, protocol reduction, or anonymity filtering. Except
4300      where either transparent or non-transparent behavior is explicitly
4301      stated, the HTTP proxy requirements apply to both types of
4302      proxies.
4303    </t>
4304  </list>
4305</t>
4306<t>
4307  <iref item="gateway"/>
4308  <x:dfn>gateway</x:dfn>
4309  <list>
4310    <t>
4311      A server which acts as an intermediary for some other server.
4312      Unlike a proxy, a gateway receives requests as if it were the
4313      origin server for the requested resource; the requesting client
4314      may not be aware that it is communicating with a gateway.
4315    </t>
4316  </list>
4317</t>
4318<t>
4319  <iref item="tunnel"/>
4320  <x:dfn>tunnel</x:dfn>
4321  <list>
4322    <t>
4323      An intermediary program which is acting as a blind relay between
4324      two connections. Once active, a tunnel is not considered a party
4325      to the HTTP communication, though the tunnel may have been
4326      initiated by an HTTP request. The tunnel ceases to exist when both
4327      ends of the relayed connections are closed.
4328    </t>
4329  </list>
4330</t>
4331<t>
4332  <iref item="cache"/>
4333  <x:dfn>cache</x:dfn>
4334  <list>
4335    <t>
4336      A program's local store of response messages and the subsystem
4337      that controls its message storage, retrieval, and deletion. A
4338      cache stores cacheable responses in order to reduce the response
4339      time and network bandwidth consumption on future, equivalent
4340      requests. Any client or server may include a cache, though a cache
4341      cannot be used by a server that is acting as a tunnel.
4342    </t>
4343  </list>
4344</t>
4345<t>
4346  <iref item="cacheable"/>
4347  <x:dfn>cacheable</x:dfn>
4348  <list>
4349    <t>
4350      A response is cacheable if a cache is allowed to store a copy of
4351      the response message for use in answering subsequent requests. The
4352      rules for determining the cacheability of HTTP responses are
4353      defined in &caching;. Even if a resource is cacheable, there may
4354      be additional constraints on whether a cache can use the cached
4355      copy for a particular request.
4356    </t>
4357  </list>
4358</t>
4359<t>
4360  <iref item="upstream"/>
4361  <iref item="downstream"/>
4362  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4363  <list>
4364    <t>
4365      Upstream and downstream describe the flow of a message: all
4366      messages flow from upstream to downstream.
4367    </t>
4368  </list>
4369</t>
4370<t>
4371  <iref item="inbound"/>
4372  <iref item="outbound"/>
4373  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4374  <list>
4375    <t>
4376      Inbound and outbound refer to the request and response paths for
4377      messages: "inbound" means "traveling toward the origin server",
4378      and "outbound" means "traveling toward the user agent"
4379    </t>
4380  </list>
4381</t>
4382</section>
4383
4384<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4385
4386<section title="Since RFC2616">
4387<t>
4388  Extracted relevant partitions from <xref target="RFC2616"/>.
4389</t>
4390</section>
4391
4392<section title="Since draft-ietf-httpbis-p1-messaging-00">
4393<t>
4394  Closed issues:
4395  <list style="symbols">
4396    <t>
4397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4398      "HTTP Version should be case sensitive"
4399      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4403      "'unsafe' characters"
4404      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4408      "Chunk Size Definition"
4409      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4410    </t>
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4413      "Message Length"
4414      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4415    </t>
4416    <t>
4417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4418      "Media Type Registrations"
4419      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4420    </t>
4421    <t>
4422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4423      "URI includes query"
4424      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4425    </t>
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4428      "No close on 1xx responses"
4429      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4433      "Remove 'identity' token references"
4434      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4435    </t>
4436    <t>
4437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4438      "Import query BNF"
4439    </t>
4440    <t>
4441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4442      "qdtext BNF"
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4446      "Normative and Informative references"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4450      "RFC2606 Compliance"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4454      "RFC977 reference"
4455    </t>
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4458      "RFC1700 references"
4459    </t>
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4462      "inconsistency in date format explanation"
4463    </t>
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4466      "Date reference typo"
4467    </t>
4468    <t>
4469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4470      "Informative references"
4471    </t>
4472    <t>
4473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4474      "ISO-8859-1 Reference"
4475    </t>
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4478      "Normative up-to-date references"
4479    </t>
4480  </list>
4481</t>
4482<t>
4483  Other changes:
4484  <list style="symbols">
4485    <t>
4486      Update media type registrations to use RFC4288 template.
4487    </t>
4488    <t>
4489      Use names of RFC4234 core rules DQUOTE and HTAB,
4490      fix broken ABNF for chunk-data
4491      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4492    </t>
4493  </list>
4494</t>
4495</section>
4496
4497<section title="Since draft-ietf-httpbis-p1-messaging-01">
4498<t>
4499  Closed issues:
4500  <list style="symbols">
4501    <t>
4502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4503      "Bodies on GET (and other) requests"
4504    </t>
4505    <t>
4506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4507      "Updating to RFC4288"
4508    </t>
4509    <t>
4510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4511      "Status Code and Reason Phrase"
4512    </t>
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4515      "rel_path not used"
4516    </t>
4517  </list>
4518</t>
4519<t>
4520  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4521  <list style="symbols">
4522    <t>
4523      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4524      "trailer-part").
4525    </t>
4526    <t>
4527      Avoid underscore character in rule names ("http_URL" ->
4528      "http-URL", "abs_path" -> "path-absolute").
4529    </t>
4530    <t>
4531      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4532      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4533      have to be updated when switching over to RFC3986.
4534    </t>
4535    <t>
4536      Synchronize core rules with RFC5234 (this includes a change to CHAR
4537      which now excludes NUL).
4538    </t>
4539    <t>
4540      Get rid of prose rules that span multiple lines.
4541    </t>
4542    <t>
4543      Get rid of unused rules LOALPHA and UPALPHA.
4544    </t>
4545    <t>
4546      Move "Product Tokens" section (back) into Part 1, as "token" is used
4547      in the definition of the Upgrade header.
4548    </t>
4549    <t>
4550      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4551    </t>
4552    <t>
4553      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4554    </t>
4555  </list>
4556</t>
4557</section>
4558
4559<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4560<t>
4561  Closed issues:
4562  <list style="symbols">
4563    <t>
4564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4565      "HTTP-date vs. rfc1123-date"
4566    </t>
4567    <t>
4568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4569      "WS in quoted-pair"
4570    </t>
4571  </list>
4572</t>
4573<t>
4574  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4575  <list style="symbols">
4576    <t>
4577      Reference RFC 3984, and update header registrations for headers defined
4578      in this document.
4579    </t>
4580  </list>
4581</t>
4582<t>
4583  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4584  <list style="symbols">
4585    <t>
4586      Replace string literals when the string really is case-sensitive (HTTP-Version).
4587    </t>
4588  </list>
4589</t>
4590</section>
4591
4592<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4593<t>
4594  Closed issues:
4595  <list style="symbols">
4596    <t>
4597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4598      "Connection closing"
4599    </t>
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4602      "Move registrations and registry information to IANA Considerations"
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4606      "need new URL for PAD1995 reference"
4607    </t>
4608    <t>
4609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4610      "IANA Considerations: update HTTP URI scheme registration"
4611    </t>
4612    <t>
4613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4614      "Cite HTTPS URI scheme definition"
4615    </t>
4616    <t>
4617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4618      "List-type headers vs Set-Cookie"
4619    </t>
4620  </list>
4621</t>
4622<t>
4623  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4624  <list style="symbols">
4625    <t>
4626      Replace string literals when the string really is case-sensitive (HTTP-Date).
4627    </t>
4628    <t>
4629      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4630    </t>
4631  </list>
4632</t>
4633</section>
4634
4635<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4636<t>
4637  Closed issues:
4638  <list style="symbols">
4639    <t>
4640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4641      "RFC 2822 is updated by RFC 5322"
4642    </t>
4643  </list>
4644</t>
4645<t>
4646  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4647  <list style="symbols">
4648    <t>
4649      Use "/" instead of "|" for alternatives.
4650    </t>
4651    <t>
4652      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4653    </t>
4654    <t>
4655      Only reference RFC 5234's core rules.
4656    </t>
4657    <t>
4658      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4659      whitespace ("OWS") and required whitespace ("RWS").
4660    </t>
4661    <t>
4662      Rewrite ABNFs to spell out whitespace rules, factor out
4663      header value format definitions.
4664    </t>
4665  </list>
4666</t>
4667</section>
4668
4669</section>
4670
4671</back>
4672</rfc>
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