source: draft-ietf-httpbis/latest/p1-messaging.xml @ 372

Last change on this file since 372 was 372, checked in by julian.reschke@…, 11 years ago

Mention implied LWS change in the Changes section (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   Many HTTP/1.1 header field values consist of words separated by LWS
544   or special characters. These special characters &MUST; be in a quoted
545   string to be used within a parameter value (as defined in
546   <xref target="transfer.codings"/>).
547</t>
548<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
549  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
550                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
551                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
552                 
553  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
554</artwork></figure>
555<t anchor="rule.comment">
556  <x:anchor-alias value="comment"/>
557  <x:anchor-alias value="ctext"/>
558   Comments can be included in some HTTP header fields by surrounding
559   the comment text with parentheses. Comments are only allowed in
560   fields containing "comment" as part of their field value definition.
561   In all other fields, parentheses are considered part of the field
562   value.
563</t>
564<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
565  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
566  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
567</artwork></figure>
568<t anchor="rule.quoted-string">
569  <x:anchor-alias value="quoted-string"/>
570  <x:anchor-alias value="qdtext"/>
571   A string of text is parsed as a single word if it is quoted using
572   double-quote marks.
573</t>
574<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
575  <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> )
576  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
577</artwork></figure>
578<t anchor="rule.quoted-pair">
579  <x:anchor-alias value="quoted-pair"/>
580  <x:anchor-alias value="quoted-text"/>
581   The backslash character ("\") &MAY; be used as a single-character
582   quoting mechanism only within quoted-string and comment constructs.
583</t>
584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
585  <x:ref>quoted-text</x:ref>    = %x01-09 /
586                   %x0B-0C /
587                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
588  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
589</artwork></figure>
590</section>
591
592<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
593  <x:anchor-alias value="request-header"/>
594  <x:anchor-alias value="response-header"/>
595  <x:anchor-alias value="accept-params"/>
596  <x:anchor-alias value="entity-body"/>
597  <x:anchor-alias value="entity-header"/>
598  <x:anchor-alias value="Cache-Control"/>
599  <x:anchor-alias value="Pragma"/>
600  <x:anchor-alias value="Warning"/>
601<t>
602  The ABNF rules below are defined in other parts:
603</t>
604<figure><!-- Part2--><artwork type="abnf2616">
605  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
606  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
607</artwork></figure>
608<figure><!-- Part3--><artwork type="abnf2616">
609  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
610  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
611  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
612</artwork></figure>
613<figure><!-- Part6--><artwork type="abnf2616">
614  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
615  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
616  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
617</artwork></figure>
618</section>
619
620</section>
621
622<section title="Protocol Parameters" anchor="protocol.parameters">
623
624<section title="HTTP Version" anchor="http.version">
625  <x:anchor-alias value="HTTP-Version"/>
626  <x:anchor-alias value="HTTP-Prot-Name"/>
627<t>
628   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
629   of the protocol. The protocol versioning policy is intended to allow
630   the sender to indicate the format of a message and its capacity for
631   understanding further HTTP communication, rather than the features
632   obtained via that communication. No change is made to the version
633   number for the addition of message components which do not affect
634   communication behavior or which only add to extensible field values.
635   The &lt;minor&gt; number is incremented when the changes made to the
636   protocol add features which do not change the general message parsing
637   algorithm, but which may add to the message semantics and imply
638   additional capabilities of the sender. The &lt;major&gt; number is
639   incremented when the format of a message within the protocol is
640   changed. See <xref target="RFC2145"/> for a fuller explanation.
641</t>
642<t>
643   The version of an HTTP message is indicated by an HTTP-Version field
644   in the first line of the message. HTTP-Version is case-sensitive.
645</t>
646<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
647  <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>
648  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
649</artwork></figure>
650<t>
651   Note that the major and minor numbers &MUST; be treated as separate
652   integers and that each &MAY; be incremented higher than a single digit.
653   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
654   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
655   &MUST-NOT; be sent.
656</t>
657<t>
658   An application that sends a request or response message that includes
659   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
660   with this specification. Applications that are at least conditionally
661   compliant with this specification &SHOULD; use an HTTP-Version of
662   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
663   not compatible with HTTP/1.0. For more details on when to send
664   specific HTTP-Version values, see <xref target="RFC2145"/>.
665</t>
666<t>
667   The HTTP version of an application is the highest HTTP version for
668   which the application is at least conditionally compliant.
669</t>
670<t>
671   Proxy and gateway applications need to be careful when forwarding
672   messages in protocol versions different from that of the application.
673   Since the protocol version indicates the protocol capability of the
674   sender, a proxy/gateway &MUST-NOT; send a message with a version
675   indicator which is greater than its actual version. If a higher
676   version request is received, the proxy/gateway &MUST; either downgrade
677   the request version, or respond with an error, or switch to tunnel
678   behavior.
679</t>
680<t>
681   Due to interoperability problems with HTTP/1.0 proxies discovered
682   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
683   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
684   they support. The proxy/gateway's response to that request &MUST; be in
685   the same major version as the request.
686</t>
687<t>
688  <list>
689    <t>
690      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
691      of header fields required or forbidden by the versions involved.
692    </t>
693  </list>
694</t>
695</section>
696
697<section title="Uniform Resource Identifiers" anchor="uri">
698<t>
699   URIs have been known by many names: WWW addresses, Universal Document
700   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
701   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
702   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
703   simply formatted strings which identify--via name, location, or any
704   other characteristic--a resource.
705</t>
706
707<section title="General Syntax" anchor="general.syntax">
708  <x:anchor-alias value="absoluteURI"/>
709  <x:anchor-alias value="authority"/>
710  <x:anchor-alias value="fragment"/>
711  <x:anchor-alias value="path-absolute"/>
712  <x:anchor-alias value="port"/>
713  <x:anchor-alias value="query"/>
714  <x:anchor-alias value="relativeURI"/>
715  <x:anchor-alias value="uri-host"/>
716<t>
717   URIs in HTTP can be represented in absolute form or relative to some
718   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
719   forms are differentiated by the fact that absolute URIs always begin
720   with a scheme name followed by a colon. For definitive information on
721   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
722   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
723   and <xref target="RFC1808"/>). This specification adopts the
724   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
725   "host", "abs_path", "query", and "authority" from that specification:
726</t>
727<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"/>
728  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
729  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
730  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC2396" x:fmt="," x:sec="4.1"/>>
731  <x:ref>path-absolute</x:ref> = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
732  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
733  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
734  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
735  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
736</artwork></figure>
737<t>
738   HTTP does not place any a priori limit on the length of
739   a URI. Servers &MUST; be able to handle the URI of any resource they
740   serve, and &SHOULD; be able to handle URIs of unbounded length if they
741   provide GET-based forms that could generate such URIs. A server
742   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
743   than the server can handle (see &status-414;).
744</t>
745<t>
746  <list>
747    <t>
748      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
749      above 255 bytes, because some older client or proxy
750      implementations might not properly support these lengths.
751    </t>
752  </list>
753</t>
754</section>
755
756<section title="http URL" anchor="http.url">
757  <x:anchor-alias value="http-URL"/>
758  <iref item="http URI scheme" primary="true"/>
759  <iref item="URI scheme" subitem="http" primary="true"/>
760<t>
761   The "http" scheme is used to locate network resources via the HTTP
762   protocol. This section defines the scheme-specific syntax and
763   semantics for http URLs.
764</t>
765<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
766  <x:ref>http-URL</x:ref> = "http:" "//" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ]
767             [ <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]]
768</artwork></figure>
769<t>
770   If the port is empty or not given, port 80 is assumed. The semantics
771   are that the identified resource is located at the server listening
772   for TCP connections on that port of that host, and the Request-URI
773   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
774   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
775   the path-absolute is not present in the URL, it &MUST; be given as "/" when
776   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
777   receives a host name which is not a fully qualified domain name, it
778   &MAY; add its domain to the host name it received. If a proxy receives
779   a fully qualified domain name, the proxy &MUST-NOT; change the host
780   name.
781</t>
782<t><list><t>
783  <iref item="https URI scheme"/>
784  <iref item="URI scheme" subitem="https"/>
785  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
786</t></list></t>
787</section>
788
789<section title="URI Comparison" anchor="uri.comparison">
790<t>
791   When comparing two URIs to decide if they match or not, a client
792   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
793   URIs, with these exceptions:
794  <list style="symbols">
795    <t>A port that is empty or not given is equivalent to the default
796        port for that URI-reference;</t>
797    <t>Comparisons of host names &MUST; be case-insensitive;</t>
798    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
799    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
800  </list>
801</t>
802<t>
803   Characters other than those in the "reserved" set (see
804   <xref target="RFC2396" x:fmt="," x:sec="2.2"/>) are equivalent to their
805   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
806</t>
807<t>
808   For example, the following three URIs are equivalent:
809</t>
810<figure><artwork type="example">
811   http://example.com:80/~smith/home.html
812   http://EXAMPLE.com/%7Esmith/home.html
813   http://EXAMPLE.com:/%7esmith/home.html
814</artwork></figure>
815</section>
816</section>
817
818<section title="Date/Time Formats" anchor="date.time.formats">
819<section title="Full Date" anchor="full.date">
820  <x:anchor-alias value="HTTP-date"/>
821  <x:anchor-alias value="obsolete-date"/>
822  <x:anchor-alias value="rfc1123-date"/>
823  <x:anchor-alias value="rfc850-date"/>
824  <x:anchor-alias value="asctime-date"/>
825  <x:anchor-alias value="date1"/>
826  <x:anchor-alias value="date2"/>
827  <x:anchor-alias value="date3"/>
828  <x:anchor-alias value="rfc1123-date"/>
829  <x:anchor-alias value="time"/>
830  <x:anchor-alias value="wkday"/>
831  <x:anchor-alias value="weekday"/>
832  <x:anchor-alias value="month"/>
833<t>
834   HTTP applications have historically allowed three different formats
835   for the representation of date/time stamps:
836</t>
837<figure><artwork type="example">
838   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
839   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
840   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
841</artwork></figure>
842<t>
843   The first format is preferred as an Internet standard and represents
844   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
845   <xref target="RFC822"/>). The other formats are described here only for
846   compatibility with obsolete implementations.
847   HTTP/1.1 clients and servers that parse the date value &MUST; accept
848   all three formats (for compatibility with HTTP/1.0), though they &MUST;
849   only generate the RFC 1123 format for representing HTTP-date values
850   in header fields. See <xref target="tolerant.applications"/> for further information.
851</t>
852<t><list><t>
853      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
854      accepting date values that may have been sent by non-HTTP
855      applications, as is sometimes the case when retrieving or posting
856      messages via proxies/gateways to SMTP or NNTP.
857</t></list></t>
858<t>
859   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
860   (GMT), without exception. For the purposes of HTTP, GMT is exactly
861   equal to UTC (Coordinated Universal Time). This is indicated in the
862   first two formats by the inclusion of "GMT" as the three-letter
863   abbreviation for time zone, and &MUST; be assumed when reading the
864   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
865   additional LWS beyond that specifically included as SP in the
866   grammar.
867</t>
868<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"/>
869  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
870  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
871  <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
872  <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
873  <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>
874  <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>
875                 ; day month year (e.g., 02 Jun 1982)
876  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
877                 ; day-month-year (e.g., 02-Jun-82)
878  <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> ))
879                 ; month day (e.g., Jun  2)
880  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
881                 ; 00:00:00 - 23:59:59
882  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
883               / s-Thu / s-Fri / s-Sat / s-Sun
884  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
885               / l-Thu / l-Fri / l-Sat / l-Sun
886  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
887               / s-May / s-Jun / s-Jul / s-Aug
888               / s-Sep / s-Oct / s-Nov / s-Dec
889               
890  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
891
892  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
893  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
894  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
895  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
896  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
897  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
898  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
899
900  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
901  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
902  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
903  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
904  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
905  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
906  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
907
908  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
909  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
910  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
911  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
912  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
913  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
914  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
915  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
916  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
917  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
918  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
919  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
920</artwork></figure>
921<t>
922      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
923      to their usage within the protocol stream. Clients and servers are
924      not required to use these formats for user presentation, request
925      logging, etc.
926</t>
927</section>
928</section>
929
930<section title="Transfer Codings" anchor="transfer.codings">
931  <x:anchor-alias value="parameter"/>
932  <x:anchor-alias value="transfer-coding"/>
933  <x:anchor-alias value="transfer-extension"/>
934<t>
935   Transfer-coding values are used to indicate an encoding
936   transformation that has been, can be, or may need to be applied to an
937   entity-body in order to ensure "safe transport" through the network.
938   This differs from a content coding in that the transfer-coding is a
939   property of the message, not of the original entity.
940</t>
941<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
942  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
943  <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> )
944</artwork></figure>
945<t anchor="rule.parameter">
946  <x:anchor-alias value="attribute"/>
947  <x:anchor-alias value="parameter"/>
948  <x:anchor-alias value="value"/>
949   Parameters are in  the form of attribute/value pairs.
950</t>
951<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"/>
952  <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>
953  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
954  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
955</artwork></figure>
956<t>
957   All transfer-coding values are case-insensitive. HTTP/1.1 uses
958   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
959   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
960</t>
961<t>
962   Whenever a transfer-coding is applied to a message-body, the set of
963   transfer-codings &MUST; include "chunked", unless the message indicates it
964   is terminated by closing the connection. When the "chunked" transfer-coding
965   is used, it &MUST; be the last transfer-coding applied to the
966   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
967   than once to a message-body. These rules allow the recipient to
968   determine the transfer-length of the message (<xref target="message.length"/>).
969</t>
970<t>
971   Transfer-codings are analogous to the Content-Transfer-Encoding
972   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
973   binary data over a 7-bit transport service. However, safe transport
974   has a different focus for an 8bit-clean transfer protocol. In HTTP,
975   the only unsafe characteristic of message-bodies is the difficulty in
976   determining the exact body length (<xref target="message.length"/>), or the desire to
977   encrypt data over a shared transport.
978</t>
979<t>
980   The Internet Assigned Numbers Authority (IANA) acts as a registry for
981   transfer-coding value tokens. Initially, the registry contains the
982   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
983   "gzip", "compress", and "deflate" (&content-codings;).
984</t>
985<t>
986   New transfer-coding value tokens &SHOULD; be registered in the same way
987   as new content-coding value tokens (&content-codings;).
988</t>
989<t>
990   A server which receives an entity-body with a transfer-coding it does
991   not understand &SHOULD; return 501 (Not Implemented), and close the
992   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
993   client.
994</t>
995
996<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
997  <x:anchor-alias value="chunk"/>
998  <x:anchor-alias value="Chunked-Body"/>
999  <x:anchor-alias value="chunk-data"/>
1000  <x:anchor-alias value="chunk-ext"/>
1001  <x:anchor-alias value="chunk-ext-name"/>
1002  <x:anchor-alias value="chunk-ext-val"/>
1003  <x:anchor-alias value="chunk-size"/>
1004  <x:anchor-alias value="last-chunk"/>
1005  <x:anchor-alias value="trailer-part"/>
1006<t>
1007   The chunked encoding modifies the body of a message in order to
1008   transfer it as a series of chunks, each with its own size indicator,
1009   followed by an &OPTIONAL; trailer containing entity-header fields. This
1010   allows dynamically produced content to be transferred along with the
1011   information necessary for the recipient to verify that it has
1012   received the full message.
1013</t>
1014<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"/>
1015  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1016                   <x:ref>last-chunk</x:ref>
1017                   <x:ref>trailer-part</x:ref>
1018                   <x:ref>CRLF</x:ref>
1019 
1020  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1021                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1022  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1023  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1024 
1025  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1026  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1027  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1028  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1029  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1030</artwork></figure>
1031<t>
1032   The chunk-size field is a string of hex digits indicating the size of
1033   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1034   zero, followed by the trailer, which is terminated by an empty line.
1035</t>
1036<t>
1037   The trailer allows the sender to include additional HTTP header
1038   fields at the end of the message. The Trailer header field can be
1039   used to indicate which header fields are included in a trailer (see
1040   <xref target="header.trailer"/>).
1041</t>
1042<t>
1043   A server using chunked transfer-coding in a response &MUST-NOT; use the
1044   trailer for any header fields unless at least one of the following is
1045   true:
1046  <list style="numbers">
1047    <t>the request included a TE header field that indicates "trailers" is
1048     acceptable in the transfer-coding of the  response, as described in
1049     <xref target="header.te"/>; or,</t>
1050
1051    <t>the server is the origin server for the response, the trailer
1052     fields consist entirely of optional metadata, and the recipient
1053     could use the message (in a manner acceptable to the origin server)
1054     without receiving this metadata.  In other words, the origin server
1055     is willing to accept the possibility that the trailer fields might
1056     be silently discarded along the path to the client.</t>
1057  </list>
1058</t>
1059<t>
1060   This requirement prevents an interoperability failure when the
1061   message is being received by an HTTP/1.1 (or later) proxy and
1062   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1063   compliance with the protocol would have necessitated a possibly
1064   infinite buffer on the proxy.
1065</t>
1066<t>
1067   A process for decoding the "chunked" transfer-coding
1068   can be represented in pseudo-code as:
1069</t>
1070<figure><artwork type="code">
1071  length := 0
1072  read chunk-size, chunk-ext (if any) and CRLF
1073  while (chunk-size &gt; 0) {
1074     read chunk-data and CRLF
1075     append chunk-data to entity-body
1076     length := length + chunk-size
1077     read chunk-size and CRLF
1078  }
1079  read entity-header
1080  while (entity-header not empty) {
1081     append entity-header to existing header fields
1082     read entity-header
1083  }
1084  Content-Length := length
1085  Remove "chunked" from Transfer-Encoding
1086</artwork></figure>
1087<t>
1088   All HTTP/1.1 applications &MUST; be able to receive and decode the
1089   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1090   they do not understand.
1091</t>
1092</section>
1093</section>
1094
1095<section title="Product Tokens" anchor="product.tokens">
1096  <x:anchor-alias value="product"/>
1097  <x:anchor-alias value="product-version"/>
1098<t>
1099   Product tokens are used to allow communicating applications to
1100   identify themselves by software name and version. Most fields using
1101   product tokens also allow sub-products which form a significant part
1102   of the application to be listed, separated by white space. By
1103   convention, the products are listed in order of their significance
1104   for identifying the application.
1105</t>
1106<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1107  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1108  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1109</artwork></figure>
1110<t>
1111   Examples:
1112</t>
1113<figure><artwork type="example">
1114    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1115    Server: Apache/0.8.4
1116</artwork></figure>
1117<t>
1118   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1119   used for advertising or other non-essential information. Although any
1120   token character &MAY; appear in a product-version, this token &SHOULD;
1121   only be used for a version identifier (i.e., successive versions of
1122   the same product &SHOULD; only differ in the product-version portion of
1123   the product value).
1124</t>
1125</section>
1126
1127</section>
1128
1129<section title="HTTP Message" anchor="http.message">
1130
1131<section title="Message Types" anchor="message.types">
1132  <x:anchor-alias value="generic-message"/>
1133  <x:anchor-alias value="HTTP-message"/>
1134  <x:anchor-alias value="start-line"/>
1135<t>
1136   HTTP messages consist of requests from client to server and responses
1137   from server to client.
1138</t>
1139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1140  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1141</artwork></figure>
1142<t>
1143   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1144   message format of <xref target="RFC5322"/> for transferring entities (the payload
1145   of the message). Both types of message consist of a start-line, zero
1146   or more header fields (also known as "headers"), an empty line (i.e.,
1147   a line with nothing preceding the CRLF) indicating the end of the
1148   header fields, and possibly a message-body.
1149</t>
1150<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1151  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1152                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1153                    <x:ref>CRLF</x:ref>
1154                    [ <x:ref>message-body</x:ref> ]
1155  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1156</artwork></figure>
1157<t>
1158   In the interest of robustness, servers &SHOULD; ignore any empty
1159   line(s) received where a Request-Line is expected. In other words, if
1160   the server is reading the protocol stream at the beginning of a
1161   message and receives a CRLF first, it should ignore the CRLF.
1162</t>
1163<t>
1164   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1165   after a POST request. To restate what is explicitly forbidden by the
1166   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1167   extra CRLF.
1168</t>
1169</section>
1170
1171<section title="Message Headers" anchor="message.headers">
1172  <x:anchor-alias value="field-content"/>
1173  <x:anchor-alias value="field-name"/>
1174  <x:anchor-alias value="field-value"/>
1175  <x:anchor-alias value="message-header"/>
1176<t>
1177   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1178   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1179   entity-header (&entity-header-fields;) fields, follow the same generic format as
1180   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1181   of a name followed by a colon (":") and the field value. Field names
1182   are case-insensitive. The field value &MAY; be preceded by any amount
1183   of LWS, though a single SP is preferred. Header fields can be
1184   extended over multiple lines by preceding each extra line with at
1185   least one SP or HTAB. Applications ought to follow "common form", where
1186   one is known or indicated, when generating HTTP constructs, since
1187   there might exist some implementations that fail to accept anything
1188   beyond the common forms.
1189</t>
1190<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"/>
1191  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1192  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1193  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1194  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1195</artwork></figure>
1196<t>
1197  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1198</t>
1199<t>
1200   The field-content does not include any leading or trailing LWS:
1201   linear white space occurring before the first non-whitespace
1202   character of the field-value or after the last non-whitespace
1203   character of the field-value. Such leading or trailing LWS &MAY; be
1204   removed without changing the semantics of the field value. Any LWS
1205   that occurs between field-content &MAY; be replaced with a single SP
1206   before interpreting the field value or forwarding the message
1207   downstream.
1208</t>
1209<t>
1210   The order in which header fields with differing field names are
1211   received is not significant. However, it is "good practice" to send
1212   general-header fields first, followed by request-header or response-header
1213   fields, and ending with the entity-header fields.
1214</t>
1215<t>
1216   Multiple message-header fields with the same field-name &MAY; be
1217   present in a message if and only if the entire field-value for that
1218   header field is defined as a comma-separated list [i.e., #(values)].
1219   It &MUST; be possible to combine the multiple header fields into one
1220   "field-name: field-value" pair, without changing the semantics of the
1221   message, by appending each subsequent field-value to the first, each
1222   separated by a comma. The order in which header fields with the same
1223   field-name are received is therefore significant to the
1224   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1225   change the order of these field values when a message is forwarded.
1226</t>
1227<t>
1228  <list><t>
1229   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1230   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1231   can occur multiple times, but does not use the list syntax, and thus cannot
1232   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1233   for details.) Also note that the Set-Cookie2 header specified in
1234   <xref target="RFC2965"/> does not share this problem.
1235  </t></list>
1236</t>
1237 
1238</section>
1239
1240<section title="Message Body" anchor="message.body">
1241  <x:anchor-alias value="message-body"/>
1242<t>
1243   The message-body (if any) of an HTTP message is used to carry the
1244   entity-body associated with the request or response. The message-body
1245   differs from the entity-body only when a transfer-coding has been
1246   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1247</t>
1248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1249  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1250               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1251</artwork></figure>
1252<t>
1253   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1254   applied by an application to ensure safe and proper transfer of the
1255   message. Transfer-Encoding is a property of the message, not of the
1256   entity, and thus &MAY; be added or removed by any application along the
1257   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1258   when certain transfer-codings may be used.)
1259</t>
1260<t>
1261   The rules for when a message-body is allowed in a message differ for
1262   requests and responses.
1263</t>
1264<t>
1265   The presence of a message-body in a request is signaled by the
1266   inclusion of a Content-Length or Transfer-Encoding header field in
1267   the request's message-headers. A message-body &MUST-NOT; be included in
1268   a request if the specification of the request method (&method;)
1269   explicitly disallows an entity-body in requests.
1270   When a request message contains both a message-body of non-zero
1271   length and a method that does not define any semantics for that
1272   request message-body, then an origin server &SHOULD; either ignore
1273   the message-body or respond with an appropriate error message
1274   (e.g., 413).  A proxy or gateway, when presented the same request,
1275   &SHOULD; either forward the request inbound with the message-body or
1276   ignore the message-body when determining a response.
1277</t>
1278<t>
1279   For response messages, whether or not a message-body is included with
1280   a message is dependent on both the request method and the response
1281   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1282   &MUST-NOT; include a message-body, even though the presence of entity-header
1283   fields might lead one to believe they do. All 1xx
1284   (informational), 204 (No Content), and 304 (Not Modified) responses
1285   &MUST-NOT; include a message-body. All other responses do include a
1286   message-body, although it &MAY; be of zero length.
1287</t>
1288</section>
1289
1290<section title="Message Length" anchor="message.length">
1291<t>
1292   The transfer-length of a message is the length of the message-body as
1293   it appears in the message; that is, after any transfer-codings have
1294   been applied. When a message-body is included with a message, the
1295   transfer-length of that body is determined by one of the following
1296   (in order of precedence):
1297</t>
1298<t>
1299  <list style="numbers">
1300    <x:lt><t>
1301     Any response message which "&MUST-NOT;" include a message-body (such
1302     as the 1xx, 204, and 304 responses and any response to a HEAD
1303     request) is always terminated by the first empty line after the
1304     header fields, regardless of the entity-header fields present in
1305     the message.
1306    </t></x:lt>
1307    <x:lt><t>
1308     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1309     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1310     is used, the transfer-length is defined by the use of this transfer-coding.
1311     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1312     is not present, the transfer-length is defined by the sender closing the connection.
1313    </t></x:lt>
1314    <x:lt><t>
1315     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1316     decimal value in OCTETs represents both the entity-length and the
1317     transfer-length. The Content-Length header field &MUST-NOT; be sent
1318     if these two lengths are different (i.e., if a Transfer-Encoding
1319     header field is present). If a message is received with both a
1320     Transfer-Encoding header field and a Content-Length header field,
1321     the latter &MUST; be ignored.
1322    </t></x:lt>
1323    <x:lt><t>
1324     If the message uses the media type "multipart/byteranges", and the
1325     transfer-length is not otherwise specified, then this self-delimiting
1326     media type defines the transfer-length. This media type
1327     &MUST-NOT; be used unless the sender knows that the recipient can parse
1328     it; the presence in a request of a Range header with multiple byte-range
1329     specifiers from a 1.1 client implies that the client can parse
1330     multipart/byteranges responses.
1331    <list style="empty"><t>
1332       A range header might be forwarded by a 1.0 proxy that does not
1333       understand multipart/byteranges; in this case the server &MUST;
1334       delimit the message using methods defined in items 1, 3 or 5 of
1335       this section.
1336    </t></list>
1337    </t></x:lt>
1338    <x:lt><t>
1339     By the server closing the connection. (Closing the connection
1340     cannot be used to indicate the end of a request body, since that
1341     would leave no possibility for the server to send back a response.)
1342    </t></x:lt>
1343  </list>
1344</t>
1345<t>
1346   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1347   containing a message-body &MUST; include a valid Content-Length header
1348   field unless the server is known to be HTTP/1.1 compliant. If a
1349   request contains a message-body and a Content-Length is not given,
1350   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1351   determine the length of the message, or with 411 (Length Required) if
1352   it wishes to insist on receiving a valid Content-Length.
1353</t>
1354<t>
1355   All HTTP/1.1 applications that receive entities &MUST; accept the
1356   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1357   to be used for messages when the message length cannot be determined
1358   in advance.
1359</t>
1360<t>
1361   Messages &MUST-NOT; include both a Content-Length header field and a
1362   transfer-coding. If the message does include a
1363   transfer-coding, the Content-Length &MUST; be ignored.
1364</t>
1365<t>
1366   When a Content-Length is given in a message where a message-body is
1367   allowed, its field value &MUST; exactly match the number of OCTETs in
1368   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1369   invalid length is received and detected.
1370</t>
1371</section>
1372
1373<section title="General Header Fields" anchor="general.header.fields">
1374  <x:anchor-alias value="general-header"/>
1375<t>
1376   There are a few header fields which have general applicability for
1377   both request and response messages, but which do not apply to the
1378   entity being transferred. These header fields apply only to the
1379   message being transmitted.
1380</t>
1381<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1382  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1383                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1384                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1385                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1386                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1387                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1388                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1389                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1390                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1391</artwork></figure>
1392<t>
1393   General-header field names can be extended reliably only in
1394   combination with a change in the protocol version. However, new or
1395   experimental header fields may be given the semantics of general
1396   header fields if all parties in the communication recognize them to
1397   be general-header fields. Unrecognized header fields are treated as
1398   entity-header fields.
1399</t>
1400</section>
1401</section>
1402
1403<section title="Request" anchor="request">
1404  <x:anchor-alias value="Request"/>
1405<t>
1406   A request message from a client to a server includes, within the
1407   first line of that message, the method to be applied to the resource,
1408   the identifier of the resource, and the protocol version in use.
1409</t>
1410<!--                 Host                      ; should be moved here eventually -->
1411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1412  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1413                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1414                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1415                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1416                  <x:ref>CRLF</x:ref>
1417                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1418</artwork></figure>
1419
1420<section title="Request-Line" anchor="request-line">
1421  <x:anchor-alias value="Request-Line"/>
1422<t>
1423   The Request-Line begins with a method token, followed by the
1424   Request-URI and the protocol version, and ending with CRLF. The
1425   elements are separated by SP characters. No CR or LF is allowed
1426   except in the final CRLF sequence.
1427</t>
1428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1429  <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>
1430</artwork></figure>
1431
1432<section title="Method" anchor="method">
1433  <x:anchor-alias value="Method"/>
1434<t>
1435   The Method  token indicates the method to be performed on the
1436   resource identified by the Request-URI. The method is case-sensitive.
1437</t>
1438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1439  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1440</artwork></figure>
1441</section>
1442
1443<section title="Request-URI" anchor="request-uri">
1444  <x:anchor-alias value="Request-URI"/>
1445<t>
1446   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1447   identifies the resource upon which to apply the request.
1448</t>
1449<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1450  <x:ref>Request-URI</x:ref>    = "*"
1451                 / <x:ref>absoluteURI</x:ref>
1452                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1453                 / <x:ref>authority</x:ref>
1454</artwork></figure>
1455<t>
1456   The four options for Request-URI are dependent on the nature of the
1457   request. The asterisk "*" means that the request does not apply to a
1458   particular resource, but to the server itself, and is only allowed
1459   when the method used does not necessarily apply to a resource. One
1460   example would be
1461</t>
1462<figure><artwork type="example">
1463    OPTIONS * HTTP/1.1
1464</artwork></figure>
1465<t>
1466   The absoluteURI form is &REQUIRED; when the request is being made to a
1467   proxy. The proxy is requested to forward the request or service it
1468   from a valid cache, and return the response. Note that the proxy &MAY;
1469   forward the request on to another proxy or directly to the server
1470   specified by the absoluteURI. In order to avoid request loops, a
1471   proxy &MUST; be able to recognize all of its server names, including
1472   any aliases, local variations, and the numeric IP address. An example
1473   Request-Line would be:
1474</t>
1475<figure><artwork type="example">
1476    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1477</artwork></figure>
1478<t>
1479   To allow for transition to absoluteURIs in all requests in future
1480   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1481   form in requests, even though HTTP/1.1 clients will only generate
1482   them in requests to proxies.
1483</t>
1484<t>
1485   The authority form is only used by the CONNECT method (&CONNECT;).
1486</t>
1487<t>
1488   The most common form of Request-URI is that used to identify a
1489   resource on an origin server or gateway. In this case the absolute
1490   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1491   the Request-URI, and the network location of the URI (authority) &MUST;
1492   be transmitted in a Host header field. For example, a client wishing
1493   to retrieve the resource above directly from the origin server would
1494   create a TCP connection to port 80 of the host "www.example.org" and send
1495   the lines:
1496</t>
1497<figure><artwork type="example">
1498    GET /pub/WWW/TheProject.html HTTP/1.1
1499    Host: www.example.org
1500</artwork></figure>
1501<t>
1502   followed by the remainder of the Request. Note that the absolute path
1503   cannot be empty; if none is present in the original URI, it &MUST; be
1504   given as "/" (the server root).
1505</t>
1506<t>
1507   The Request-URI is transmitted in the format specified in
1508   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1509   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1510   (<xref target="RFC2396" x:fmt="," x:sec="2.4.1"/>), the origin server
1511   &MUST; decode the Request-URI in order to
1512   properly interpret the request. Servers &SHOULD; respond to invalid
1513   Request-URIs with an appropriate status code.
1514</t>
1515<t>
1516   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1517   received Request-URI when forwarding it to the next inbound server,
1518   except as noted above to replace a null path-absolute with "/".
1519</t>
1520<t>
1521  <list><t>
1522      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1523      meaning of the request when the origin server is improperly using
1524      a non-reserved URI character for a reserved purpose.  Implementors
1525      should be aware that some pre-HTTP/1.1 proxies have been known to
1526      rewrite the Request-URI.
1527  </t></list>
1528</t>
1529</section>
1530</section>
1531
1532<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1533<t>
1534   The exact resource identified by an Internet request is determined by
1535   examining both the Request-URI and the Host header field.
1536</t>
1537<t>
1538   An origin server that does not allow resources to differ by the
1539   requested host &MAY; ignore the Host header field value when
1540   determining the resource identified by an HTTP/1.1 request. (But see
1541   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1542   for other requirements on Host support in HTTP/1.1.)
1543</t>
1544<t>
1545   An origin server that does differentiate resources based on the host
1546   requested (sometimes referred to as virtual hosts or vanity host
1547   names) &MUST; use the following rules for determining the requested
1548   resource on an HTTP/1.1 request:
1549  <list style="numbers">
1550    <t>If Request-URI is an absoluteURI, the host is part of the
1551     Request-URI. Any Host header field value in the request &MUST; be
1552     ignored.</t>
1553    <t>If the Request-URI is not an absoluteURI, and the request includes
1554     a Host header field, the host is determined by the Host header
1555     field value.</t>
1556    <t>If the host as determined by rule 1 or 2 is not a valid host on
1557     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1558  </list>
1559</t>
1560<t>
1561   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1562   attempt to use heuristics (e.g., examination of the URI path for
1563   something unique to a particular host) in order to determine what
1564   exact resource is being requested.
1565</t>
1566</section>
1567
1568</section>
1569
1570
1571<section title="Response" anchor="response">
1572  <x:anchor-alias value="Response"/>
1573<t>
1574   After receiving and interpreting a request message, a server responds
1575   with an HTTP response message.
1576</t>
1577<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1578  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1579                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1580                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1581                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1582                  <x:ref>CRLF</x:ref>
1583                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1584</artwork></figure>
1585
1586<section title="Status-Line" anchor="status-line">
1587  <x:anchor-alias value="Status-Line"/>
1588<t>
1589   The first line of a Response message is the Status-Line, consisting
1590   of the protocol version followed by a numeric status code and its
1591   associated textual phrase, with each element separated by SP
1592   characters. No CR or LF is allowed except in the final CRLF sequence.
1593</t>
1594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1595  <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>
1596</artwork></figure>
1597
1598<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1599  <x:anchor-alias value="Reason-Phrase"/>
1600  <x:anchor-alias value="Status-Code"/>
1601<t>
1602   The Status-Code element is a 3-digit integer result code of the
1603   attempt to understand and satisfy the request. These codes are fully
1604   defined in &status-codes;.  The Reason Phrase exists for the sole
1605   purpose of providing a textual description associated with the numeric
1606   status code, out of deference to earlier Internet application protocols
1607   that were more frequently used with interactive text clients.
1608   A client &SHOULD; ignore the content of the Reason Phrase.
1609</t>
1610<t>
1611   The first digit of the Status-Code defines the class of response. The
1612   last two digits do not have any categorization role. There are 5
1613   values for the first digit:
1614  <list style="symbols">
1615    <t>
1616      1xx: Informational - Request received, continuing process
1617    </t>
1618    <t>
1619      2xx: Success - The action was successfully received,
1620        understood, and accepted
1621    </t>
1622    <t>
1623      3xx: Redirection - Further action must be taken in order to
1624        complete the request
1625    </t>
1626    <t>
1627      4xx: Client Error - The request contains bad syntax or cannot
1628        be fulfilled
1629    </t>
1630    <t>
1631      5xx: Server Error - The server failed to fulfill an apparently
1632        valid request
1633    </t>
1634  </list>
1635</t>
1636<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"/>
1637  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1638  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1639</artwork></figure>
1640</section>
1641</section>
1642
1643</section>
1644
1645
1646<section title="Connections" anchor="connections">
1647
1648<section title="Persistent Connections" anchor="persistent.connections">
1649
1650<section title="Purpose" anchor="persistent.purpose">
1651<t>
1652   Prior to persistent connections, a separate TCP connection was
1653   established to fetch each URL, increasing the load on HTTP servers
1654   and causing congestion on the Internet. The use of inline images and
1655   other associated data often require a client to make multiple
1656   requests of the same server in a short amount of time. Analysis of
1657   these performance problems and results from a prototype
1658   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1659   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1660   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1661   T/TCP <xref target="Tou1998"/>.
1662</t>
1663<t>
1664   Persistent HTTP connections have a number of advantages:
1665  <list style="symbols">
1666      <t>
1667        By opening and closing fewer TCP connections, CPU time is saved
1668        in routers and hosts (clients, servers, proxies, gateways,
1669        tunnels, or caches), and memory used for TCP protocol control
1670        blocks can be saved in hosts.
1671      </t>
1672      <t>
1673        HTTP requests and responses can be pipelined on a connection.
1674        Pipelining allows a client to make multiple requests without
1675        waiting for each response, allowing a single TCP connection to
1676        be used much more efficiently, with much lower elapsed time.
1677      </t>
1678      <t>
1679        Network congestion is reduced by reducing the number of packets
1680        caused by TCP opens, and by allowing TCP sufficient time to
1681        determine the congestion state of the network.
1682      </t>
1683      <t>
1684        Latency on subsequent requests is reduced since there is no time
1685        spent in TCP's connection opening handshake.
1686      </t>
1687      <t>
1688        HTTP can evolve more gracefully, since errors can be reported
1689        without the penalty of closing the TCP connection. Clients using
1690        future versions of HTTP might optimistically try a new feature,
1691        but if communicating with an older server, retry with old
1692        semantics after an error is reported.
1693      </t>
1694    </list>
1695</t>
1696<t>
1697   HTTP implementations &SHOULD; implement persistent connections.
1698</t>
1699</section>
1700
1701<section title="Overall Operation" anchor="persistent.overall">
1702<t>
1703   A significant difference between HTTP/1.1 and earlier versions of
1704   HTTP is that persistent connections are the default behavior of any
1705   HTTP connection. That is, unless otherwise indicated, the client
1706   &SHOULD; assume that the server will maintain a persistent connection,
1707   even after error responses from the server.
1708</t>
1709<t>
1710   Persistent connections provide a mechanism by which a client and a
1711   server can signal the close of a TCP connection. This signaling takes
1712   place using the Connection header field (<xref target="header.connection"/>). Once a close
1713   has been signaled, the client &MUST-NOT; send any more requests on that
1714   connection.
1715</t>
1716
1717<section title="Negotiation" anchor="persistent.negotiation">
1718<t>
1719   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1720   maintain a persistent connection unless a Connection header including
1721   the connection-token "close" was sent in the request. If the server
1722   chooses to close the connection immediately after sending the
1723   response, it &SHOULD; send a Connection header including the
1724   connection-token close.
1725</t>
1726<t>
1727   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1728   decide to keep it open based on whether the response from a server
1729   contains a Connection header with the connection-token close. In case
1730   the client does not want to maintain a connection for more than that
1731   request, it &SHOULD; send a Connection header including the
1732   connection-token close.
1733</t>
1734<t>
1735   If either the client or the server sends the close token in the
1736   Connection header, that request becomes the last one for the
1737   connection.
1738</t>
1739<t>
1740   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1741   maintained for HTTP versions less than 1.1 unless it is explicitly
1742   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1743   compatibility with HTTP/1.0 clients.
1744</t>
1745<t>
1746   In order to remain persistent, all messages on the connection &MUST;
1747   have a self-defined message length (i.e., one not defined by closure
1748   of the connection), as described in <xref target="message.length"/>.
1749</t>
1750</section>
1751
1752<section title="Pipelining" anchor="pipelining">
1753<t>
1754   A client that supports persistent connections &MAY; "pipeline" its
1755   requests (i.e., send multiple requests without waiting for each
1756   response). A server &MUST; send its responses to those requests in the
1757   same order that the requests were received.
1758</t>
1759<t>
1760   Clients which assume persistent connections and pipeline immediately
1761   after connection establishment &SHOULD; be prepared to retry their
1762   connection if the first pipelined attempt fails. If a client does
1763   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1764   persistent. Clients &MUST; also be prepared to resend their requests if
1765   the server closes the connection before sending all of the
1766   corresponding responses.
1767</t>
1768<t>
1769   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1770   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1771   premature termination of the transport connection could lead to
1772   indeterminate results. A client wishing to send a non-idempotent
1773   request &SHOULD; wait to send that request until it has received the
1774   response status for the previous request.
1775</t>
1776</section>
1777</section>
1778
1779<section title="Proxy Servers" anchor="persistent.proxy">
1780<t>
1781   It is especially important that proxies correctly implement the
1782   properties of the Connection header field as specified in <xref target="header.connection"/>.
1783</t>
1784<t>
1785   The proxy server &MUST; signal persistent connections separately with
1786   its clients and the origin servers (or other proxy servers) that it
1787   connects to. Each persistent connection applies to only one transport
1788   link.
1789</t>
1790<t>
1791   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1792   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1793   discussion of the problems with the Keep-Alive header implemented by
1794   many HTTP/1.0 clients).
1795</t>
1796</section>
1797
1798<section title="Practical Considerations" anchor="persistent.practical">
1799<t>
1800   Servers will usually have some time-out value beyond which they will
1801   no longer maintain an inactive connection. Proxy servers might make
1802   this a higher value since it is likely that the client will be making
1803   more connections through the same server. The use of persistent
1804   connections places no requirements on the length (or existence) of
1805   this time-out for either the client or the server.
1806</t>
1807<t>
1808   When a client or server wishes to time-out it &SHOULD; issue a graceful
1809   close on the transport connection. Clients and servers &SHOULD; both
1810   constantly watch for the other side of the transport close, and
1811   respond to it as appropriate. If a client or server does not detect
1812   the other side's close promptly it could cause unnecessary resource
1813   drain on the network.
1814</t>
1815<t>
1816   A client, server, or proxy &MAY; close the transport connection at any
1817   time. For example, a client might have started to send a new request
1818   at the same time that the server has decided to close the "idle"
1819   connection. From the server's point of view, the connection is being
1820   closed while it was idle, but from the client's point of view, a
1821   request is in progress.
1822</t>
1823<t>
1824   This means that clients, servers, and proxies &MUST; be able to recover
1825   from asynchronous close events. Client software &SHOULD; reopen the
1826   transport connection and retransmit the aborted sequence of requests
1827   without user interaction so long as the request sequence is
1828   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1829   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1830   human operator the choice of retrying the request(s). Confirmation by
1831   user-agent software with semantic understanding of the application
1832   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1833   be repeated if the second sequence of requests fails.
1834</t>
1835<t>
1836   Servers &SHOULD; always respond to at least one request per connection,
1837   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1838   middle of transmitting a response, unless a network or client failure
1839   is suspected.
1840</t>
1841<t>
1842   Clients that use persistent connections &SHOULD; limit the number of
1843   simultaneous connections that they maintain to a given server. A
1844   single-user client &SHOULD-NOT; maintain more than 2 connections with
1845   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1846   another server or proxy, where N is the number of simultaneously
1847   active users. These guidelines are intended to improve HTTP response
1848   times and avoid congestion.
1849</t>
1850</section>
1851</section>
1852
1853<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1854
1855<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1856<t>
1857   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1858   flow control mechanisms to resolve temporary overloads, rather than
1859   terminating connections with the expectation that clients will retry.
1860   The latter technique can exacerbate network congestion.
1861</t>
1862</section>
1863
1864<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1865<t>
1866   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1867   the network connection for an error status while it is transmitting
1868   the request. If the client sees an error status, it &SHOULD;
1869   immediately cease transmitting the body. If the body is being sent
1870   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1871   empty trailer &MAY; be used to prematurely mark the end of the message.
1872   If the body was preceded by a Content-Length header, the client &MUST;
1873   close the connection.
1874</t>
1875</section>
1876
1877<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1878<t>
1879   The purpose of the 100 (Continue) status (see &status-100;) is to
1880   allow a client that is sending a request message with a request body
1881   to determine if the origin server is willing to accept the request
1882   (based on the request headers) before the client sends the request
1883   body. In some cases, it might either be inappropriate or highly
1884   inefficient for the client to send the body if the server will reject
1885   the message without looking at the body.
1886</t>
1887<t>
1888   Requirements for HTTP/1.1 clients:
1889  <list style="symbols">
1890    <t>
1891        If a client will wait for a 100 (Continue) response before
1892        sending the request body, it &MUST; send an Expect request-header
1893        field (&header-expect;) with the "100-continue" expectation.
1894    </t>
1895    <t>
1896        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1897        with the "100-continue" expectation if it does not intend
1898        to send a request body.
1899    </t>
1900  </list>
1901</t>
1902<t>
1903   Because of the presence of older implementations, the protocol allows
1904   ambiguous situations in which a client may send "Expect: 100-continue"
1905   without receiving either a 417 (Expectation Failed) status
1906   or a 100 (Continue) status. Therefore, when a client sends this
1907   header field to an origin server (possibly via a proxy) from which it
1908   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1909   for an indefinite period before sending the request body.
1910</t>
1911<t>
1912   Requirements for HTTP/1.1 origin servers:
1913  <list style="symbols">
1914    <t> Upon receiving a request which includes an Expect request-header
1915        field with the "100-continue" expectation, an origin server &MUST;
1916        either respond with 100 (Continue) status and continue to read
1917        from the input stream, or respond with a final status code. The
1918        origin server &MUST-NOT; wait for the request body before sending
1919        the 100 (Continue) response. If it responds with a final status
1920        code, it &MAY; close the transport connection or it &MAY; continue
1921        to read and discard the rest of the request.  It &MUST-NOT;
1922        perform the requested method if it returns a final status code.
1923    </t>
1924    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1925        the request message does not include an Expect request-header
1926        field with the "100-continue" expectation, and &MUST-NOT; send a
1927        100 (Continue) response if such a request comes from an HTTP/1.0
1928        (or earlier) client. There is an exception to this rule: for
1929        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1930        status in response to an HTTP/1.1 PUT or POST request that does
1931        not include an Expect request-header field with the "100-continue"
1932        expectation. This exception, the purpose of which is
1933        to minimize any client processing delays associated with an
1934        undeclared wait for 100 (Continue) status, applies only to
1935        HTTP/1.1 requests, and not to requests with any other HTTP-version
1936        value.
1937    </t>
1938    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1939        already received some or all of the request body for the
1940        corresponding request.
1941    </t>
1942    <t> An origin server that sends a 100 (Continue) response &MUST;
1943    ultimately send a final status code, once the request body is
1944        received and processed, unless it terminates the transport
1945        connection prematurely.
1946    </t>
1947    <t> If an origin server receives a request that does not include an
1948        Expect request-header field with the "100-continue" expectation,
1949        the request includes a request body, and the server responds
1950        with a final status code before reading the entire request body
1951        from the transport connection, then the server &SHOULD-NOT;  close
1952        the transport connection until it has read the entire request,
1953        or until the client closes the connection. Otherwise, the client
1954        might not reliably receive the response message. However, this
1955        requirement is not be construed as preventing a server from
1956        defending itself against denial-of-service attacks, or from
1957        badly broken client implementations.
1958      </t>
1959    </list>
1960</t>
1961<t>
1962   Requirements for HTTP/1.1 proxies:
1963  <list style="symbols">
1964    <t> If a proxy receives a request that includes an Expect request-header
1965        field with the "100-continue" expectation, and the proxy
1966        either knows that the next-hop server complies with HTTP/1.1 or
1967        higher, or does not know the HTTP version of the next-hop
1968        server, it &MUST; forward the request, including the Expect header
1969        field.
1970    </t>
1971    <t> If the proxy knows that the version of the next-hop server is
1972        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1973        respond with a 417 (Expectation Failed) status.
1974    </t>
1975    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1976        numbers received from recently-referenced next-hop servers.
1977    </t>
1978    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1979        request message was received from an HTTP/1.0 (or earlier)
1980        client and did not include an Expect request-header field with
1981        the "100-continue" expectation. This requirement overrides the
1982        general rule for forwarding of 1xx responses (see &status-1xx;).
1983    </t>
1984  </list>
1985</t>
1986</section>
1987
1988<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1989<t>
1990   If an HTTP/1.1 client sends a request which includes a request body,
1991   but which does not include an Expect request-header field with the
1992   "100-continue" expectation, and if the client is not directly
1993   connected to an HTTP/1.1 origin server, and if the client sees the
1994   connection close before receiving any status from the server, the
1995   client &SHOULD; retry the request.  If the client does retry this
1996   request, it &MAY; use the following "binary exponential backoff"
1997   algorithm to be assured of obtaining a reliable response:
1998  <list style="numbers">
1999    <t>
2000      Initiate a new connection to the server
2001    </t>
2002    <t>
2003      Transmit the request-headers
2004    </t>
2005    <t>
2006      Initialize a variable R to the estimated round-trip time to the
2007         server (e.g., based on the time it took to establish the
2008         connection), or to a constant value of 5 seconds if the round-trip
2009         time is not available.
2010    </t>
2011    <t>
2012       Compute T = R * (2**N), where N is the number of previous
2013         retries of this request.
2014    </t>
2015    <t>
2016       Wait either for an error response from the server, or for T
2017         seconds (whichever comes first)
2018    </t>
2019    <t>
2020       If no error response is received, after T seconds transmit the
2021         body of the request.
2022    </t>
2023    <t>
2024       If client sees that the connection is closed prematurely,
2025         repeat from step 1 until the request is accepted, an error
2026         response is received, or the user becomes impatient and
2027         terminates the retry process.
2028    </t>
2029  </list>
2030</t>
2031<t>
2032   If at any point an error status is received, the client
2033  <list style="symbols">
2034      <t>&SHOULD-NOT;  continue and</t>
2035
2036      <t>&SHOULD; close the connection if it has not completed sending the
2037        request message.</t>
2038    </list>
2039</t>
2040</section>
2041</section>
2042</section>
2043
2044
2045<section title="Header Field Definitions" anchor="header.fields">
2046<t>
2047   This section defines the syntax and semantics of HTTP/1.1 header fields
2048   related to message framing and transport protocols.
2049</t>
2050<t>
2051   For entity-header fields, both sender and recipient refer to either the
2052   client or the server, depending on who sends and who receives the entity.
2053</t>
2054
2055<section title="Connection" anchor="header.connection">
2056  <iref primary="true" item="Connection header" x:for-anchor=""/>
2057  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2058  <x:anchor-alias value="Connection"/>
2059  <x:anchor-alias value="connection-token"/>
2060  <x:anchor-alias value="Connection-v"/>
2061<t>
2062   The general-header field "Connection" allows the sender to specify
2063   options that are desired for that particular connection and &MUST-NOT;
2064   be communicated by proxies over further connections.
2065</t>
2066<t>
2067   The Connection header's value has the following grammar:
2068</t>
2069<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"/>
2070  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2071  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2072  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2073</artwork></figure>
2074<t>
2075   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2076   message is forwarded and, for each connection-token in this field,
2077   remove any header field(s) from the message with the same name as the
2078   connection-token. Connection options are signaled by the presence of
2079   a connection-token in the Connection header field, not by any
2080   corresponding additional header field(s), since the additional header
2081   field may not be sent if there are no parameters associated with that
2082   connection option.
2083</t>
2084<t>
2085   Message headers listed in the Connection header &MUST-NOT; include
2086   end-to-end headers, such as Cache-Control.
2087</t>
2088<t>
2089   HTTP/1.1 defines the "close" connection option for the sender to
2090   signal that the connection will be closed after completion of the
2091   response. For example,
2092</t>
2093<figure><artwork type="example">
2094  Connection: close
2095</artwork></figure>
2096<t>
2097   in either the request or the response header fields indicates that
2098   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2099   after the current request/response is complete.
2100</t>
2101<t>
2102   An HTTP/1.1 client that does not support persistent connections &MUST;
2103   include the "close" connection option in every request message.
2104</t>
2105<t>
2106   An HTTP/1.1 server that does not support persistent connections &MUST;
2107   include the "close" connection option in every response message that
2108   does not have a 1xx (informational) status code.
2109</t>
2110<t>
2111   A system receiving an HTTP/1.0 (or lower-version) message that
2112   includes a Connection header &MUST;, for each connection-token in this
2113   field, remove and ignore any header field(s) from the message with
2114   the same name as the connection-token. This protects against mistaken
2115   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2116</t>
2117</section>
2118
2119<section title="Content-Length" anchor="header.content-length">
2120  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2121  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2122  <x:anchor-alias value="Content-Length"/>
2123  <x:anchor-alias value="Content-Length-v"/>
2124<t>
2125   The entity-header field "Content-Length" indicates the size of the
2126   entity-body, in decimal number of OCTETs, sent to the recipient or,
2127   in the case of the HEAD method, the size of the entity-body that
2128   would have been sent had the request been a GET.
2129</t>
2130<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2131  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2132  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2133</artwork></figure>
2134<t>
2135   An example is
2136</t>
2137<figure><artwork type="example">
2138  Content-Length: 3495
2139</artwork></figure>
2140<t>
2141   Applications &SHOULD; use this field to indicate the transfer-length of
2142   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2143</t>
2144<t>
2145   Any Content-Length greater than or equal to zero is a valid value.
2146   <xref target="message.length"/> describes how to determine the length of a message-body
2147   if a Content-Length is not given.
2148</t>
2149<t>
2150   Note that the meaning of this field is significantly different from
2151   the corresponding definition in MIME, where it is an optional field
2152   used within the "message/external-body" content-type. In HTTP, it
2153   &SHOULD; be sent whenever the message's length can be determined prior
2154   to being transferred, unless this is prohibited by the rules in
2155   <xref target="message.length"/>.
2156</t>
2157</section>
2158
2159<section title="Date" anchor="header.date">
2160  <iref primary="true" item="Date header" x:for-anchor=""/>
2161  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2162  <x:anchor-alias value="Date"/>
2163  <x:anchor-alias value="Date-v"/>
2164<t>
2165   The general-header field "Date" represents the date and time at which
2166   the message was originated, having the same semantics as orig-date in
2167   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2168   HTTP-date, as described in <xref target="full.date"/>;
2169   it &MUST; be sent in rfc1123-date format.
2170</t>
2171<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2172  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2173  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2174</artwork></figure>
2175<t>
2176   An example is
2177</t>
2178<figure><artwork type="example">
2179  Date: Tue, 15 Nov 1994 08:12:31 GMT
2180</artwork></figure>
2181<t>
2182   Origin servers &MUST; include a Date header field in all responses,
2183   except in these cases:
2184  <list style="numbers">
2185      <t>If the response status code is 100 (Continue) or 101 (Switching
2186         Protocols), the response &MAY; include a Date header field, at
2187         the server's option.</t>
2188
2189      <t>If the response status code conveys a server error, e.g. 500
2190         (Internal Server Error) or 503 (Service Unavailable), and it is
2191         inconvenient or impossible to generate a valid Date.</t>
2192
2193      <t>If the server does not have a clock that can provide a
2194         reasonable approximation of the current time, its responses
2195         &MUST-NOT; include a Date header field. In this case, the rules
2196         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2197  </list>
2198</t>
2199<t>
2200   A received message that does not have a Date header field &MUST; be
2201   assigned one by the recipient if the message will be cached by that
2202   recipient or gatewayed via a protocol which requires a Date. An HTTP
2203   implementation without a clock &MUST-NOT; cache responses without
2204   revalidating them on every use. An HTTP cache, especially a shared
2205   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2206   clock with a reliable external standard.
2207</t>
2208<t>
2209   Clients &SHOULD; only send a Date header field in messages that include
2210   an entity-body, as in the case of the PUT and POST requests, and even
2211   then it is optional. A client without a clock &MUST-NOT; send a Date
2212   header field in a request.
2213</t>
2214<t>
2215   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2216   time subsequent to the generation of the message. It &SHOULD; represent
2217   the best available approximation of the date and time of message
2218   generation, unless the implementation has no means of generating a
2219   reasonably accurate date and time. In theory, the date ought to
2220   represent the moment just before the entity is generated. In
2221   practice, the date can be generated at any time during the message
2222   origination without affecting its semantic value.
2223</t>
2224
2225<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2226<t>
2227   Some origin server implementations might not have a clock available.
2228   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2229   values to a response, unless these values were associated
2230   with the resource by a system or user with a reliable clock. It &MAY;
2231   assign an Expires value that is known, at or before server
2232   configuration time, to be in the past (this allows "pre-expiration"
2233   of responses without storing separate Expires values for each
2234   resource).
2235</t>
2236</section>
2237</section>
2238
2239<section title="Host" anchor="header.host">
2240  <iref primary="true" item="Host header" x:for-anchor=""/>
2241  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2242  <x:anchor-alias value="Host"/>
2243  <x:anchor-alias value="Host-v"/>
2244<t>
2245   The request-header field "Host" specifies the Internet host and port
2246   number of the resource being requested, as obtained from the original
2247   URI given by the user or referring resource (generally an HTTP URL,
2248   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2249   the naming authority of the origin server or gateway given by the
2250   original URL. This allows the origin server or gateway to
2251   differentiate between internally-ambiguous URLs, such as the root "/"
2252   URL of a server for multiple host names on a single IP address.
2253</t>
2254<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2255  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2256  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.url"/>
2257</artwork></figure>
2258<t>
2259   A "host" without any trailing port information implies the default
2260   port for the service requested (e.g., "80" for an HTTP URL). For
2261   example, a request on the origin server for
2262   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2263</t>
2264<figure><artwork type="example">
2265  GET /pub/WWW/ HTTP/1.1
2266  Host: www.example.org
2267</artwork></figure>
2268<t>
2269   A client &MUST; include a Host header field in all HTTP/1.1 request
2270   messages. If the requested URI does not include an Internet host
2271   name for the service being requested, then the Host header field &MUST;
2272   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2273   request message it forwards does contain an appropriate Host header
2274   field that identifies the service being requested by the proxy. All
2275   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2276   status code to any HTTP/1.1 request message which lacks a Host header
2277   field.
2278</t>
2279<t>
2280   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2281   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2282   for other requirements relating to Host.
2283</t>
2284</section>
2285
2286<section title="TE" anchor="header.te">
2287  <iref primary="true" item="TE header" x:for-anchor=""/>
2288  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2289  <x:anchor-alias value="TE"/>
2290  <x:anchor-alias value="TE-v"/>
2291  <x:anchor-alias value="t-codings"/>
2292<t>
2293   The request-header field "TE" indicates what extension transfer-codings
2294   it is willing to accept in the response and whether or not it is
2295   willing to accept trailer fields in a chunked transfer-coding. Its
2296   value may consist of the keyword "trailers" and/or a comma-separated
2297   list of extension transfer-coding names with optional accept
2298   parameters (as described in <xref target="transfer.codings"/>).
2299</t>
2300<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"/>
2301  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2302  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2303  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2304</artwork></figure>
2305<t>
2306   The presence of the keyword "trailers" indicates that the client is
2307   willing to accept trailer fields in a chunked transfer-coding, as
2308   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2309   transfer-coding values even though it does not itself represent a
2310   transfer-coding.
2311</t>
2312<t>
2313   Examples of its use are:
2314</t>
2315<figure><artwork type="example">
2316  TE: deflate
2317  TE:
2318  TE: trailers, deflate;q=0.5
2319</artwork></figure>
2320<t>
2321   The TE header field only applies to the immediate connection.
2322   Therefore, the keyword &MUST; be supplied within a Connection header
2323   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2324</t>
2325<t>
2326   A server tests whether a transfer-coding is acceptable, according to
2327   a TE field, using these rules:
2328  <list style="numbers">
2329    <x:lt>
2330      <t>The "chunked" transfer-coding is always acceptable. If the
2331         keyword "trailers" is listed, the client indicates that it is
2332         willing to accept trailer fields in the chunked response on
2333         behalf of itself and any downstream clients. The implication is
2334         that, if given, the client is stating that either all
2335         downstream clients are willing to accept trailer fields in the
2336         forwarded response, or that it will attempt to buffer the
2337         response on behalf of downstream recipients.
2338      </t><t>
2339         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2340         chunked response such that a client can be assured of buffering
2341         the entire response.</t>
2342    </x:lt>
2343    <x:lt>
2344      <t>If the transfer-coding being tested is one of the transfer-codings
2345         listed in the TE field, then it is acceptable unless it
2346         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2347         qvalue of 0 means "not acceptable.")</t>
2348    </x:lt>
2349    <x:lt>
2350      <t>If multiple transfer-codings are acceptable, then the
2351         acceptable transfer-coding with the highest non-zero qvalue is
2352         preferred.  The "chunked" transfer-coding always has a qvalue
2353         of 1.</t>
2354    </x:lt>
2355  </list>
2356</t>
2357<t>
2358   If the TE field-value is empty or if no TE field is present, the only
2359   transfer-coding  is "chunked". A message with no transfer-coding is
2360   always acceptable.
2361</t>
2362</section>
2363
2364<section title="Trailer" anchor="header.trailer">
2365  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2366  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2367  <x:anchor-alias value="Trailer"/>
2368  <x:anchor-alias value="Trailer-v"/>
2369<t>
2370   The general field "Trailer" indicates that the given set of
2371   header fields is present in the trailer of a message encoded with
2372   chunked transfer-coding.
2373</t>
2374<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2375  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2376  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2377</artwork></figure>
2378<t>
2379   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2380   message using chunked transfer-coding with a non-empty trailer. Doing
2381   so allows the recipient to know which header fields to expect in the
2382   trailer.
2383</t>
2384<t>
2385   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2386   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2387   trailer fields in a "chunked" transfer-coding.
2388</t>
2389<t>
2390   Message header fields listed in the Trailer header field &MUST-NOT;
2391   include the following header fields:
2392  <list style="symbols">
2393    <t>Transfer-Encoding</t>
2394    <t>Content-Length</t>
2395    <t>Trailer</t>
2396  </list>
2397</t>
2398</section>
2399
2400<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2401  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2402  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2403  <x:anchor-alias value="Transfer-Encoding"/>
2404  <x:anchor-alias value="Transfer-Encoding-v"/>
2405<t>
2406   The general-header "Transfer-Encoding" field indicates what (if any)
2407   type of transformation has been applied to the message body in order
2408   to safely transfer it between the sender and the recipient. This
2409   differs from the content-coding in that the transfer-coding is a
2410   property of the message, not of the entity.
2411</t>
2412<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2413  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Transfer-Encoding-v</x:ref>
2414  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2415</artwork></figure>
2416<t>
2417   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2418</t>
2419<figure><artwork type="example">
2420  Transfer-Encoding: chunked
2421</artwork></figure>
2422<t>
2423   If multiple encodings have been applied to an entity, the transfer-codings
2424   &MUST; be listed in the order in which they were applied.
2425   Additional information about the encoding parameters &MAY; be provided
2426   by other entity-header fields not defined by this specification.
2427</t>
2428<t>
2429   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2430   header.
2431</t>
2432</section>
2433
2434<section title="Upgrade" anchor="header.upgrade">
2435  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2436  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2437  <x:anchor-alias value="Upgrade"/>
2438  <x:anchor-alias value="Upgrade-v"/>
2439<t>
2440   The general-header "Upgrade" allows the client to specify what
2441   additional communication protocols it supports and would like to use
2442   if the server finds it appropriate to switch protocols. The server
2443   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2444   response to indicate which protocol(s) are being switched.
2445</t>
2446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2447  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2448  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2449</artwork></figure>
2450<t>
2451   For example,
2452</t>
2453<figure><artwork type="example">
2454  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2455</artwork></figure>
2456<t>
2457   The Upgrade header field is intended to provide a simple mechanism
2458   for transition from HTTP/1.1 to some other, incompatible protocol. It
2459   does so by allowing the client to advertise its desire to use another
2460   protocol, such as a later version of HTTP with a higher major version
2461   number, even though the current request has been made using HTTP/1.1.
2462   This eases the difficult transition between incompatible protocols by
2463   allowing the client to initiate a request in the more commonly
2464   supported protocol while indicating to the server that it would like
2465   to use a "better" protocol if available (where "better" is determined
2466   by the server, possibly according to the nature of the method and/or
2467   resource being requested).
2468</t>
2469<t>
2470   The Upgrade header field only applies to switching application-layer
2471   protocols upon the existing transport-layer connection. Upgrade
2472   cannot be used to insist on a protocol change; its acceptance and use
2473   by the server is optional. The capabilities and nature of the
2474   application-layer communication after the protocol change is entirely
2475   dependent upon the new protocol chosen, although the first action
2476   after changing the protocol &MUST; be a response to the initial HTTP
2477   request containing the Upgrade header field.
2478</t>
2479<t>
2480   The Upgrade header field only applies to the immediate connection.
2481   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2482   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2483   HTTP/1.1 message.
2484</t>
2485<t>
2486   The Upgrade header field cannot be used to indicate a switch to a
2487   protocol on a different connection. For that purpose, it is more
2488   appropriate to use a 301, 302, 303, or 305 redirection response.
2489</t>
2490<t>
2491   This specification only defines the protocol name "HTTP" for use by
2492   the family of Hypertext Transfer Protocols, as defined by the HTTP
2493   version rules of <xref target="http.version"/> and future updates to this
2494   specification. Any token can be used as a protocol name; however, it
2495   will only be useful if both the client and server associate the name
2496   with the same protocol.
2497</t>
2498</section>
2499
2500<section title="Via" anchor="header.via">
2501  <iref primary="true" item="Via header" x:for-anchor=""/>
2502  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2503  <x:anchor-alias value="protocol-name"/>
2504  <x:anchor-alias value="protocol-version"/>
2505  <x:anchor-alias value="pseudonym"/>
2506  <x:anchor-alias value="received-by"/>
2507  <x:anchor-alias value="received-protocol"/>
2508  <x:anchor-alias value="Via"/>
2509  <x:anchor-alias value="Via-v"/>
2510<t>
2511   The general-header field "Via" &MUST; be used by gateways and proxies to
2512   indicate the intermediate protocols and recipients between the user
2513   agent and the server on requests, and between the origin server and
2514   the client on responses. It is analogous to the "Received" field defined in
2515   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2516   avoiding request loops, and identifying the protocol capabilities of
2517   all senders along the request/response chain.
2518</t>
2519<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"/>
2520  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2521  <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> ] )
2522  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2523  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2524  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2525  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2526  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2527</artwork></figure>
2528<t>
2529   The received-protocol indicates the protocol version of the message
2530   received by the server or client along each segment of the
2531   request/response chain. The received-protocol version is appended to
2532   the Via field value when the message is forwarded so that information
2533   about the protocol capabilities of upstream applications remains
2534   visible to all recipients.
2535</t>
2536<t>
2537   The protocol-name is optional if and only if it would be "HTTP". The
2538   received-by field is normally the host and optional port number of a
2539   recipient server or client that subsequently forwarded the message.
2540   However, if the real host is considered to be sensitive information,
2541   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2542   be assumed to be the default port of the received-protocol.
2543</t>
2544<t>
2545   Multiple Via field values represents each proxy or gateway that has
2546   forwarded the message. Each recipient &MUST; append its information
2547   such that the end result is ordered according to the sequence of
2548   forwarding applications.
2549</t>
2550<t>
2551   Comments &MAY; be used in the Via header field to identify the software
2552   of the recipient proxy or gateway, analogous to the User-Agent and
2553   Server header fields. However, all comments in the Via field are
2554   optional and &MAY; be removed by any recipient prior to forwarding the
2555   message.
2556</t>
2557<t>
2558   For example, a request message could be sent from an HTTP/1.0 user
2559   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2560   forward the request to a public proxy at p.example.net, which completes
2561   the request by forwarding it to the origin server at www.example.com.
2562   The request received by www.example.com would then have the following
2563   Via header field:
2564</t>
2565<figure><artwork type="example">
2566  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2567</artwork></figure>
2568<t>
2569   Proxies and gateways used as a portal through a network firewall
2570   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2571   the firewall region. This information &SHOULD; only be propagated if
2572   explicitly enabled. If not enabled, the received-by host of any host
2573   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2574   for that host.
2575</t>
2576<t>
2577   For organizations that have strong privacy requirements for hiding
2578   internal structures, a proxy &MAY; combine an ordered subsequence of
2579   Via header field entries with identical received-protocol values into
2580   a single such entry. For example,
2581</t>
2582<figure><artwork type="example">
2583  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2584</artwork></figure>
2585<t>
2586        could be collapsed to
2587</t>
2588<figure><artwork type="example">
2589  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2590</artwork></figure>
2591<t>
2592   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2593   under the same organizational control and the hosts have already been
2594   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2595   have different received-protocol values.
2596</t>
2597</section>
2598
2599</section>
2600
2601<section title="IANA Considerations" anchor="IANA.considerations">
2602<section title="Message Header Registration" anchor="message.header.registration">
2603<t>
2604   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2605   with the permanent registrations below (see <xref target="RFC3864"/>):
2606</t>
2607<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2608<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2609   <ttcol>Header Field Name</ttcol>
2610   <ttcol>Protocol</ttcol>
2611   <ttcol>Status</ttcol>
2612   <ttcol>Reference</ttcol>
2613
2614   <c>Connection</c>
2615   <c>http</c>
2616   <c>standard</c>
2617   <c>
2618      <xref target="header.connection"/>
2619   </c>
2620   <c>Content-Length</c>
2621   <c>http</c>
2622   <c>standard</c>
2623   <c>
2624      <xref target="header.content-length"/>
2625   </c>
2626   <c>Date</c>
2627   <c>http</c>
2628   <c>standard</c>
2629   <c>
2630      <xref target="header.date"/>
2631   </c>
2632   <c>Host</c>
2633   <c>http</c>
2634   <c>standard</c>
2635   <c>
2636      <xref target="header.host"/>
2637   </c>
2638   <c>TE</c>
2639   <c>http</c>
2640   <c>standard</c>
2641   <c>
2642      <xref target="header.te"/>
2643   </c>
2644   <c>Trailer</c>
2645   <c>http</c>
2646   <c>standard</c>
2647   <c>
2648      <xref target="header.trailer"/>
2649   </c>
2650   <c>Transfer-Encoding</c>
2651   <c>http</c>
2652   <c>standard</c>
2653   <c>
2654      <xref target="header.transfer-encoding"/>
2655   </c>
2656   <c>Upgrade</c>
2657   <c>http</c>
2658   <c>standard</c>
2659   <c>
2660      <xref target="header.upgrade"/>
2661   </c>
2662   <c>Via</c>
2663   <c>http</c>
2664   <c>standard</c>
2665   <c>
2666      <xref target="header.via"/>
2667   </c>
2668</texttable>
2669<!--(END)-->
2670<t>
2671   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2672</t>
2673</section>
2674
2675<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2676<t>
2677   The entry for the "http" URI Scheme in the registry located at
2678   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2679   should be updated to point to <xref target="http.url"/> of this document
2680   (see <xref target="RFC4395"/>).
2681</t>
2682</section>
2683
2684<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2685<t>
2686   This document serves as the specification for the Internet media types
2687   "message/http" and "application/http". The following is to be registered with
2688   IANA (see <xref target="RFC4288"/>).
2689</t>
2690<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2691<iref item="Media Type" subitem="message/http" primary="true"/>
2692<iref item="message/http Media Type" primary="true"/>
2693<t>
2694   The message/http type can be used to enclose a single HTTP request or
2695   response message, provided that it obeys the MIME restrictions for all
2696   "message" types regarding line length and encodings.
2697</t>
2698<t>
2699  <list style="hanging" x:indent="12em">
2700    <t hangText="Type name:">
2701      message
2702    </t>
2703    <t hangText="Subtype name:">
2704      http
2705    </t>
2706    <t hangText="Required parameters:">
2707      none
2708    </t>
2709    <t hangText="Optional parameters:">
2710      version, msgtype
2711      <list style="hanging">
2712        <t hangText="version:">
2713          The HTTP-Version number of the enclosed message
2714          (e.g., "1.1"). If not present, the version can be
2715          determined from the first line of the body.
2716        </t>
2717        <t hangText="msgtype:">
2718          The message type -- "request" or "response". If not
2719          present, the type can be determined from the first
2720          line of the body.
2721        </t>
2722      </list>
2723    </t>
2724    <t hangText="Encoding considerations:">
2725      only "7bit", "8bit", or "binary" are permitted
2726    </t>
2727    <t hangText="Security considerations:">
2728      none
2729    </t>
2730    <t hangText="Interoperability considerations:">
2731      none
2732    </t>
2733    <t hangText="Published specification:">
2734      This specification (see <xref target="internet.media.type.message.http"/>).
2735    </t>
2736    <t hangText="Applications that use this media type:">
2737    </t>
2738    <t hangText="Additional information:">
2739      <list style="hanging">
2740        <t hangText="Magic number(s):">none</t>
2741        <t hangText="File extension(s):">none</t>
2742        <t hangText="Macintosh file type code(s):">none</t>
2743      </list>
2744    </t>
2745    <t hangText="Person and email address to contact for further information:">
2746      See Authors Section.
2747    </t>
2748                <t hangText="Intended usage:">
2749                  COMMON
2750    </t>
2751                <t hangText="Restrictions on usage:">
2752                  none
2753    </t>
2754    <t hangText="Author/Change controller:">
2755      IESG
2756    </t>
2757  </list>
2758</t>
2759</section>
2760<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2761<iref item="Media Type" subitem="application/http" primary="true"/>
2762<iref item="application/http Media Type" primary="true"/>
2763<t>
2764   The application/http type can be used to enclose a pipeline of one or more
2765   HTTP request or response messages (not intermixed).
2766</t>
2767<t>
2768  <list style="hanging" x:indent="12em">
2769    <t hangText="Type name:">
2770      application
2771    </t>
2772    <t hangText="Subtype name:">
2773      http
2774    </t>
2775    <t hangText="Required parameters:">
2776      none
2777    </t>
2778    <t hangText="Optional parameters:">
2779      version, msgtype
2780      <list style="hanging">
2781        <t hangText="version:">
2782          The HTTP-Version number of the enclosed messages
2783          (e.g., "1.1"). If not present, the version can be
2784          determined from the first line of the body.
2785        </t>
2786        <t hangText="msgtype:">
2787          The message type -- "request" or "response". If not
2788          present, the type can be determined from the first
2789          line of the body.
2790        </t>
2791      </list>
2792    </t>
2793    <t hangText="Encoding considerations:">
2794      HTTP messages enclosed by this type
2795      are in "binary" format; use of an appropriate
2796      Content-Transfer-Encoding is required when
2797      transmitted via E-mail.
2798    </t>
2799    <t hangText="Security considerations:">
2800      none
2801    </t>
2802    <t hangText="Interoperability considerations:">
2803      none
2804    </t>
2805    <t hangText="Published specification:">
2806      This specification (see <xref target="internet.media.type.application.http"/>).
2807    </t>
2808    <t hangText="Applications that use this media type:">
2809    </t>
2810    <t hangText="Additional information:">
2811      <list style="hanging">
2812        <t hangText="Magic number(s):">none</t>
2813        <t hangText="File extension(s):">none</t>
2814        <t hangText="Macintosh file type code(s):">none</t>
2815      </list>
2816    </t>
2817    <t hangText="Person and email address to contact for further information:">
2818      See Authors Section.
2819    </t>
2820                <t hangText="Intended usage:">
2821                  COMMON
2822    </t>
2823                <t hangText="Restrictions on usage:">
2824                  none
2825    </t>
2826    <t hangText="Author/Change controller:">
2827      IESG
2828    </t>
2829  </list>
2830</t>
2831</section>
2832</section>
2833
2834</section>
2835
2836<section title="Security Considerations" anchor="security.considerations">
2837<t>
2838   This section is meant to inform application developers, information
2839   providers, and users of the security limitations in HTTP/1.1 as
2840   described by this document. The discussion does not include
2841   definitive solutions to the problems revealed, though it does make
2842   some suggestions for reducing security risks.
2843</t>
2844
2845<section title="Personal Information" anchor="personal.information">
2846<t>
2847   HTTP clients are often privy to large amounts of personal information
2848   (e.g. the user's name, location, mail address, passwords, encryption
2849   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2850   leakage of this information.
2851   We very strongly recommend that a convenient interface be provided
2852   for the user to control dissemination of such information, and that
2853   designers and implementors be particularly careful in this area.
2854   History shows that errors in this area often create serious security
2855   and/or privacy problems and generate highly adverse publicity for the
2856   implementor's company.
2857</t>
2858</section>
2859
2860<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2861<t>
2862   A server is in the position to save personal data about a user's
2863   requests which might identify their reading patterns or subjects of
2864   interest. This information is clearly confidential in nature and its
2865   handling can be constrained by law in certain countries. People using
2866   HTTP to provide data are responsible for ensuring that
2867   such material is not distributed without the permission of any
2868   individuals that are identifiable by the published results.
2869</t>
2870</section>
2871
2872<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2873<t>
2874   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2875   the documents returned by HTTP requests to be only those that were
2876   intended by the server administrators. If an HTTP server translates
2877   HTTP URIs directly into file system calls, the server &MUST; take
2878   special care not to serve files that were not intended to be
2879   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2880   other operating systems use ".." as a path component to indicate a
2881   directory level above the current one. On such a system, an HTTP
2882   server &MUST; disallow any such construct in the Request-URI if it
2883   would otherwise allow access to a resource outside those intended to
2884   be accessible via the HTTP server. Similarly, files intended for
2885   reference only internally to the server (such as access control
2886   files, configuration files, and script code) &MUST; be protected from
2887   inappropriate retrieval, since they might contain sensitive
2888   information. Experience has shown that minor bugs in such HTTP server
2889   implementations have turned into security risks.
2890</t>
2891</section>
2892
2893<section title="DNS Spoofing" anchor="dns.spoofing">
2894<t>
2895   Clients using HTTP rely heavily on the Domain Name Service, and are
2896   thus generally prone to security attacks based on the deliberate
2897   mis-association of IP addresses and DNS names. Clients need to be
2898   cautious in assuming the continuing validity of an IP number/DNS name
2899   association.
2900</t>
2901<t>
2902   In particular, HTTP clients &SHOULD; rely on their name resolver for
2903   confirmation of an IP number/DNS name association, rather than
2904   caching the result of previous host name lookups. Many platforms
2905   already can cache host name lookups locally when appropriate, and
2906   they &SHOULD; be configured to do so. It is proper for these lookups to
2907   be cached, however, only when the TTL (Time To Live) information
2908   reported by the name server makes it likely that the cached
2909   information will remain useful.
2910</t>
2911<t>
2912   If HTTP clients cache the results of host name lookups in order to
2913   achieve a performance improvement, they &MUST; observe the TTL
2914   information reported by DNS.
2915</t>
2916<t>
2917   If HTTP clients do not observe this rule, they could be spoofed when
2918   a previously-accessed server's IP address changes. As network
2919   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2920   possibility of this form of attack will grow. Observing this
2921   requirement thus reduces this potential security vulnerability.
2922</t>
2923<t>
2924   This requirement also improves the load-balancing behavior of clients
2925   for replicated servers using the same DNS name and reduces the
2926   likelihood of a user's experiencing failure in accessing sites which
2927   use that strategy.
2928</t>
2929</section>
2930
2931<section title="Proxies and Caching" anchor="attack.proxies">
2932<t>
2933   By their very nature, HTTP proxies are men-in-the-middle, and
2934   represent an opportunity for man-in-the-middle attacks. Compromise of
2935   the systems on which the proxies run can result in serious security
2936   and privacy problems. Proxies have access to security-related
2937   information, personal information about individual users and
2938   organizations, and proprietary information belonging to users and
2939   content providers. A compromised proxy, or a proxy implemented or
2940   configured without regard to security and privacy considerations,
2941   might be used in the commission of a wide range of potential attacks.
2942</t>
2943<t>
2944   Proxy operators should protect the systems on which proxies run as
2945   they would protect any system that contains or transports sensitive
2946   information. In particular, log information gathered at proxies often
2947   contains highly sensitive personal information, and/or information
2948   about organizations. Log information should be carefully guarded, and
2949   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2950</t>
2951<t>
2952   Proxy implementors should consider the privacy and security
2953   implications of their design and coding decisions, and of the
2954   configuration options they provide to proxy operators (especially the
2955   default configuration).
2956</t>
2957<t>
2958   Users of a proxy need to be aware that they are no trustworthier than
2959   the people who run the proxy; HTTP itself cannot solve this problem.
2960</t>
2961<t>
2962   The judicious use of cryptography, when appropriate, may suffice to
2963   protect against a broad range of security and privacy attacks. Such
2964   cryptography is beyond the scope of the HTTP/1.1 specification.
2965</t>
2966</section>
2967
2968<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2969<t>
2970   They exist. They are hard to defend against. Research continues.
2971   Beware.
2972</t>
2973</section>
2974</section>
2975
2976<section title="Acknowledgments" anchor="ack">
2977<t>
2978   This specification makes heavy use of the augmented BNF and generic
2979   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2980   reuses many of the definitions provided by Nathaniel Borenstein and
2981   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2982   specification will help reduce past confusion over the relationship
2983   between HTTP and Internet mail message formats.
2984</t>
2985<t>
2986   HTTP has evolved considerably over the years. It has
2987   benefited from a large and active developer community--the many
2988   people who have participated on the www-talk mailing list--and it is
2989   that community which has been most responsible for the success of
2990   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2991   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2992   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2993   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2994   VanHeyningen deserve special recognition for their efforts in
2995   defining early aspects of the protocol.
2996</t>
2997<t>
2998   This document has benefited greatly from the comments of all those
2999   participating in the HTTP-WG. In addition to those already mentioned,
3000   the following individuals have contributed to this specification:
3001</t>
3002<t>
3003   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3004   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3005   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3006   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3007   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3008   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3009   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3010   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3011   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3012   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3013   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3014   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3015   Josh Cohen.
3016</t>
3017<t>
3018   Thanks to the "cave men" of Palo Alto. You know who you are.
3019</t>
3020<t>
3021   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3022   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3023   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3024   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3025   Larry Masinter for their help. And thanks go particularly to Jeff
3026   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3027</t>
3028<t>
3029   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3030   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3031   discovery of many of the problems that this document attempts to
3032   rectify.
3033</t>
3034</section>
3035
3036</middle>
3037<back>
3038
3039<references title="Normative References">
3040
3041<reference anchor="ISO-8859-1">
3042  <front>
3043    <title>
3044     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3045    </title>
3046    <author>
3047      <organization>International Organization for Standardization</organization>
3048    </author>
3049    <date year="1998"/>
3050  </front>
3051  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3052</reference>
3053
3054<reference anchor="Part2">
3055  <front>
3056    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3057    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3058      <organization abbrev="Day Software">Day Software</organization>
3059      <address><email>fielding@gbiv.com</email></address>
3060    </author>
3061    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3062      <organization>One Laptop per Child</organization>
3063      <address><email>jg@laptop.org</email></address>
3064    </author>
3065    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3066      <organization abbrev="HP">Hewlett-Packard Company</organization>
3067      <address><email>JeffMogul@acm.org</email></address>
3068    </author>
3069    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3070      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3071      <address><email>henrikn@microsoft.com</email></address>
3072    </author>
3073    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3074      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3075      <address><email>LMM@acm.org</email></address>
3076    </author>
3077    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3078      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3079      <address><email>paulle@microsoft.com</email></address>
3080    </author>
3081    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3082      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3083      <address><email>timbl@w3.org</email></address>
3084    </author>
3085    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3086      <organization abbrev="W3C">World Wide Web Consortium</organization>
3087      <address><email>ylafon@w3.org</email></address>
3088    </author>
3089    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3090      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3091      <address><email>julian.reschke@greenbytes.de</email></address>
3092    </author>
3093    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3094  </front>
3095  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3096  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3097</reference>
3098
3099<reference anchor="Part3">
3100  <front>
3101    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3102    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3103      <organization abbrev="Day Software">Day Software</organization>
3104      <address><email>fielding@gbiv.com</email></address>
3105    </author>
3106    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3107      <organization>One Laptop per Child</organization>
3108      <address><email>jg@laptop.org</email></address>
3109    </author>
3110    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3111      <organization abbrev="HP">Hewlett-Packard Company</organization>
3112      <address><email>JeffMogul@acm.org</email></address>
3113    </author>
3114    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3115      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3116      <address><email>henrikn@microsoft.com</email></address>
3117    </author>
3118    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3119      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3120      <address><email>LMM@acm.org</email></address>
3121    </author>
3122    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3123      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3124      <address><email>paulle@microsoft.com</email></address>
3125    </author>
3126    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3127      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3128      <address><email>timbl@w3.org</email></address>
3129    </author>
3130    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3131      <organization abbrev="W3C">World Wide Web Consortium</organization>
3132      <address><email>ylafon@w3.org</email></address>
3133    </author>
3134    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3135      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3136      <address><email>julian.reschke@greenbytes.de</email></address>
3137    </author>
3138    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3139  </front>
3140  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3141  <x:source href="p3-payload.xml" basename="p3-payload"/>
3142</reference>
3143
3144<reference anchor="Part5">
3145  <front>
3146    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3147    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3148      <organization abbrev="Day Software">Day Software</organization>
3149      <address><email>fielding@gbiv.com</email></address>
3150    </author>
3151    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3152      <organization>One Laptop per Child</organization>
3153      <address><email>jg@laptop.org</email></address>
3154    </author>
3155    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3156      <organization abbrev="HP">Hewlett-Packard Company</organization>
3157      <address><email>JeffMogul@acm.org</email></address>
3158    </author>
3159    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3160      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3161      <address><email>henrikn@microsoft.com</email></address>
3162    </author>
3163    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3164      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3165      <address><email>LMM@acm.org</email></address>
3166    </author>
3167    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3168      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3169      <address><email>paulle@microsoft.com</email></address>
3170    </author>
3171    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3172      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3173      <address><email>timbl@w3.org</email></address>
3174    </author>
3175    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3176      <organization abbrev="W3C">World Wide Web Consortium</organization>
3177      <address><email>ylafon@w3.org</email></address>
3178    </author>
3179    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3180      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3181      <address><email>julian.reschke@greenbytes.de</email></address>
3182    </author>
3183    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3184  </front>
3185  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3186  <x:source href="p5-range.xml" basename="p5-range"/>
3187</reference>
3188
3189<reference anchor="Part6">
3190  <front>
3191    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3192    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3193      <organization abbrev="Day Software">Day Software</organization>
3194      <address><email>fielding@gbiv.com</email></address>
3195    </author>
3196    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3197      <organization>One Laptop per Child</organization>
3198      <address><email>jg@laptop.org</email></address>
3199    </author>
3200    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3201      <organization abbrev="HP">Hewlett-Packard Company</organization>
3202      <address><email>JeffMogul@acm.org</email></address>
3203    </author>
3204    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3206      <address><email>henrikn@microsoft.com</email></address>
3207    </author>
3208    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3209      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3210      <address><email>LMM@acm.org</email></address>
3211    </author>
3212    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3214      <address><email>paulle@microsoft.com</email></address>
3215    </author>
3216    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3217      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3218      <address><email>timbl@w3.org</email></address>
3219    </author>
3220    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3221      <organization abbrev="W3C">World Wide Web Consortium</organization>
3222      <address><email>ylafon@w3.org</email></address>
3223    </author>
3224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3226      <address><email>julian.reschke@greenbytes.de</email></address>
3227    </author>
3228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3229  </front>
3230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3231  <x:source href="p6-cache.xml" basename="p6-cache"/>
3232</reference>
3233
3234<reference anchor="RFC5234">
3235  <front>
3236    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3237    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3238      <organization>Brandenburg InternetWorking</organization>
3239      <address>
3240      <postal>
3241      <street>675 Spruce Dr.</street>
3242      <city>Sunnyvale</city>
3243      <region>CA</region>
3244      <code>94086</code>
3245      <country>US</country></postal>
3246      <phone>+1.408.246.8253</phone>
3247      <email>dcrocker@bbiw.net</email></address> 
3248    </author>
3249    <author initials="P." surname="Overell" fullname="Paul Overell">
3250      <organization>THUS plc.</organization>
3251      <address>
3252      <postal>
3253      <street>1/2 Berkeley Square</street>
3254      <street>99 Berkely Street</street>
3255      <city>Glasgow</city>
3256      <code>G3 7HR</code>
3257      <country>UK</country></postal>
3258      <email>paul.overell@thus.net</email></address>
3259    </author>
3260    <date month="January" year="2008"/>
3261  </front>
3262  <seriesInfo name="STD" value="68"/>
3263  <seriesInfo name="RFC" value="5234"/>
3264</reference>
3265
3266<reference anchor="RFC2045">
3267  <front>
3268    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3269    <author initials="N." surname="Freed" fullname="Ned Freed">
3270      <organization>Innosoft International, Inc.</organization>
3271      <address><email>ned@innosoft.com</email></address>
3272    </author>
3273    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3274      <organization>First Virtual Holdings</organization>
3275      <address><email>nsb@nsb.fv.com</email></address>
3276    </author>
3277    <date month="November" year="1996"/>
3278  </front>
3279  <seriesInfo name="RFC" value="2045"/>
3280</reference>
3281
3282<reference anchor="RFC2047">
3283  <front>
3284    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3285    <author initials="K." surname="Moore" fullname="Keith Moore">
3286      <organization>University of Tennessee</organization>
3287      <address><email>moore@cs.utk.edu</email></address>
3288    </author>
3289    <date month="November" year="1996"/>
3290  </front>
3291  <seriesInfo name="RFC" value="2047"/>
3292</reference>
3293
3294<reference anchor="RFC2119">
3295  <front>
3296    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3297    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3298      <organization>Harvard University</organization>
3299      <address><email>sob@harvard.edu</email></address>
3300    </author>
3301    <date month="March" year="1997"/>
3302  </front>
3303  <seriesInfo name="BCP" value="14"/>
3304  <seriesInfo name="RFC" value="2119"/>
3305</reference>
3306
3307<reference anchor="RFC2396">
3308  <front>
3309    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3310    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3311      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3312      <address><email>timbl@w3.org</email></address>
3313    </author>
3314    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3315      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3316      <address><email>fielding@ics.uci.edu</email></address>
3317    </author>
3318    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3319      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3320      <address><email>masinter@parc.xerox.com</email></address>
3321    </author>
3322    <date month="August" year="1998"/>
3323  </front>
3324  <seriesInfo name="RFC" value="2396"/>
3325</reference>
3326
3327<reference anchor="USASCII">
3328  <front>
3329    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3330    <author>
3331      <organization>American National Standards Institute</organization>
3332    </author>
3333    <date year="1986"/>
3334  </front>
3335  <seriesInfo name="ANSI" value="X3.4"/>
3336</reference>
3337
3338</references>
3339
3340<references title="Informative References">
3341
3342<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3343  <front>
3344    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3345    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3346      <organization/>
3347    </author>
3348    <author initials="J." surname="Gettys" fullname="J. Gettys">
3349      <organization/>
3350    </author>
3351    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3352      <organization/>
3353    </author>
3354    <author initials="H." surname="Lie" fullname="H. Lie">
3355      <organization/>
3356    </author>
3357    <author initials="C." surname="Lilley" fullname="C. Lilley">
3358      <organization/>
3359    </author>
3360    <date year="1997" month="September"/>
3361  </front>
3362  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3363</reference>
3364
3365<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3366  <front>
3367    <title>Improving HTTP Latency</title>
3368    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3369      <organization/>
3370    </author>
3371    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3372      <organization/>
3373    </author>
3374    <date year="1995" month="December"/>
3375  </front>
3376  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3377</reference>
3378
3379<reference anchor="RFC822">
3380  <front>
3381    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3382    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3383      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3384      <address><email>DCrocker@UDel-Relay</email></address>
3385    </author>
3386    <date month="August" day="13" year="1982"/>
3387  </front>
3388  <seriesInfo name="STD" value="11"/>
3389  <seriesInfo name="RFC" value="822"/>
3390</reference>
3391
3392<reference anchor="RFC959">
3393  <front>
3394    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3395    <author initials="J." surname="Postel" fullname="J. Postel">
3396      <organization>Information Sciences Institute (ISI)</organization>
3397    </author>
3398    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3399      <organization/>
3400    </author>
3401    <date month="October" year="1985"/>
3402  </front>
3403  <seriesInfo name="STD" value="9"/>
3404  <seriesInfo name="RFC" value="959"/>
3405</reference>
3406
3407<reference anchor="RFC1123">
3408  <front>
3409    <title>Requirements for Internet Hosts - Application and Support</title>
3410    <author initials="R." surname="Braden" fullname="Robert Braden">
3411      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3412      <address><email>Braden@ISI.EDU</email></address>
3413    </author>
3414    <date month="October" year="1989"/>
3415  </front>
3416  <seriesInfo name="STD" value="3"/>
3417  <seriesInfo name="RFC" value="1123"/>
3418</reference>
3419
3420<reference anchor="RFC1305">
3421  <front>
3422    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3423    <author initials="D." surname="Mills" fullname="David L. Mills">
3424      <organization>University of Delaware, Electrical Engineering Department</organization>
3425      <address><email>mills@udel.edu</email></address>
3426    </author>
3427    <date month="March" year="1992"/>
3428  </front>
3429  <seriesInfo name="RFC" value="1305"/>
3430</reference>
3431
3432<reference anchor="RFC1436">
3433  <front>
3434    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3435    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3436      <organization>University of Minnesota, Computer and Information Services</organization>
3437      <address><email>fxa@boombox.micro.umn.edu</email></address>
3438    </author>
3439    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3440      <organization>University of Minnesota, Computer and Information Services</organization>
3441      <address><email>mpm@boombox.micro.umn.edu</email></address>
3442    </author>
3443    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3444      <organization>University of Minnesota, Computer and Information Services</organization>
3445      <address><email>lindner@boombox.micro.umn.edu</email></address>
3446    </author>
3447    <author initials="D." surname="Johnson" fullname="David Johnson">
3448      <organization>University of Minnesota, Computer and Information Services</organization>
3449      <address><email>dmj@boombox.micro.umn.edu</email></address>
3450    </author>
3451    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3452      <organization>University of Minnesota, Computer and Information Services</organization>
3453      <address><email>daniel@boombox.micro.umn.edu</email></address>
3454    </author>
3455    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3456      <organization>University of Minnesota, Computer and Information Services</organization>
3457      <address><email>alberti@boombox.micro.umn.edu</email></address>
3458    </author>
3459    <date month="March" year="1993"/>
3460  </front>
3461  <seriesInfo name="RFC" value="1436"/>
3462</reference>
3463
3464<reference anchor="RFC1630">
3465  <front>
3466    <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>
3467    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3468      <organization>CERN, World-Wide Web project</organization>
3469      <address><email>timbl@info.cern.ch</email></address>
3470    </author>
3471    <date month="June" year="1994"/>
3472  </front>
3473  <seriesInfo name="RFC" value="1630"/>
3474</reference>
3475
3476<reference anchor="RFC1737">
3477  <front>
3478    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3479    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3480      <organization>Xerox Palo Alto Research Center</organization>
3481      <address><email>masinter@parc.xerox.com</email></address>
3482    </author>
3483    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3484      <organization>MIT Laboratory for Computer Science</organization>
3485      <address><email>sollins@lcs.mit.edu</email></address>
3486    </author>
3487    <date month="December" year="1994"/>
3488  </front>
3489  <seriesInfo name="RFC" value="1737"/>
3490</reference>
3491
3492<reference anchor="RFC1738">
3493  <front>
3494    <title>Uniform Resource Locators (URL)</title>
3495    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3496      <organization>CERN, World-Wide Web project</organization>
3497      <address><email>timbl@info.cern.ch</email></address>
3498    </author>
3499    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3500      <organization>Xerox PARC</organization>
3501      <address><email>masinter@parc.xerox.com</email></address>
3502    </author>
3503    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3504      <organization>University of Minnesota, Computer and Information Services</organization>
3505      <address><email>mpm@boombox.micro.umn.edu</email></address>
3506    </author>
3507    <date month="December" year="1994"/>
3508  </front>
3509  <seriesInfo name="RFC" value="1738"/>
3510</reference>
3511
3512<reference anchor="RFC1808">
3513  <front>
3514    <title>Relative Uniform Resource Locators</title>
3515    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3516      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3517      <address><email>fielding@ics.uci.edu</email></address>
3518    </author>
3519    <date month="June" year="1995"/>
3520  </front>
3521  <seriesInfo name="RFC" value="1808"/>
3522</reference>
3523
3524<reference anchor="RFC1900">
3525  <front>
3526    <title>Renumbering Needs Work</title>
3527    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3528      <organization>CERN, Computing and Networks Division</organization>
3529      <address><email>brian@dxcoms.cern.ch</email></address>
3530    </author>
3531    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3532      <organization>cisco Systems</organization>
3533      <address><email>yakov@cisco.com</email></address>
3534    </author>
3535    <date month="February" year="1996"/>
3536  </front>
3537  <seriesInfo name="RFC" value="1900"/>
3538</reference>
3539
3540<reference anchor="RFC1945">
3541  <front>
3542    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3543    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3544      <organization>MIT, Laboratory for Computer Science</organization>
3545      <address><email>timbl@w3.org</email></address>
3546    </author>
3547    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3548      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3549      <address><email>fielding@ics.uci.edu</email></address>
3550    </author>
3551    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3552      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3553      <address><email>frystyk@w3.org</email></address>
3554    </author>
3555    <date month="May" year="1996"/>
3556  </front>
3557  <seriesInfo name="RFC" value="1945"/>
3558</reference>
3559
3560<reference anchor="RFC2068">
3561  <front>
3562    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3563    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3564      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3565      <address><email>fielding@ics.uci.edu</email></address>
3566    </author>
3567    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3568      <organization>MIT Laboratory for Computer Science</organization>
3569      <address><email>jg@w3.org</email></address>
3570    </author>
3571    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3572      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3573      <address><email>mogul@wrl.dec.com</email></address>
3574    </author>
3575    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3576      <organization>MIT Laboratory for Computer Science</organization>
3577      <address><email>frystyk@w3.org</email></address>
3578    </author>
3579    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3580      <organization>MIT Laboratory for Computer Science</organization>
3581      <address><email>timbl@w3.org</email></address>
3582    </author>
3583    <date month="January" year="1997"/>
3584  </front>
3585  <seriesInfo name="RFC" value="2068"/>
3586</reference>
3587
3588<reference anchor='RFC2109'>
3589  <front>
3590    <title>HTTP State Management Mechanism</title>
3591    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3592      <organization>Bell Laboratories, Lucent Technologies</organization>
3593      <address><email>dmk@bell-labs.com</email></address>
3594    </author>
3595    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3596      <organization>Netscape Communications Corp.</organization>
3597      <address><email>montulli@netscape.com</email></address>
3598    </author>
3599    <date year='1997' month='February' />
3600  </front>
3601  <seriesInfo name='RFC' value='2109' />
3602</reference>
3603
3604<reference anchor="RFC2145">
3605  <front>
3606    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3607    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3608      <organization>Western Research Laboratory</organization>
3609      <address><email>mogul@wrl.dec.com</email></address>
3610    </author>
3611    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3612      <organization>Department of Information and Computer Science</organization>
3613      <address><email>fielding@ics.uci.edu</email></address>
3614    </author>
3615    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3616      <organization>MIT Laboratory for Computer Science</organization>
3617      <address><email>jg@w3.org</email></address>
3618    </author>
3619    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3620      <organization>W3 Consortium</organization>
3621      <address><email>frystyk@w3.org</email></address>
3622    </author>
3623    <date month="May" year="1997"/>
3624  </front>
3625  <seriesInfo name="RFC" value="2145"/>
3626</reference>
3627
3628<reference anchor="RFC2324">
3629  <front>
3630    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3631    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3632      <organization>Xerox Palo Alto Research Center</organization>
3633      <address><email>masinter@parc.xerox.com</email></address>
3634    </author>
3635    <date month="April" day="1" year="1998"/>
3636  </front>
3637  <seriesInfo name="RFC" value="2324"/>
3638</reference>
3639
3640<reference anchor="RFC2616">
3641  <front>
3642    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3643    <author initials="R." surname="Fielding" fullname="R. Fielding">
3644      <organization>University of California, Irvine</organization>
3645      <address><email>fielding@ics.uci.edu</email></address>
3646    </author>
3647    <author initials="J." surname="Gettys" fullname="J. Gettys">
3648      <organization>W3C</organization>
3649      <address><email>jg@w3.org</email></address>
3650    </author>
3651    <author initials="J." surname="Mogul" fullname="J. Mogul">
3652      <organization>Compaq Computer Corporation</organization>
3653      <address><email>mogul@wrl.dec.com</email></address>
3654    </author>
3655    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3656      <organization>MIT Laboratory for Computer Science</organization>
3657      <address><email>frystyk@w3.org</email></address>
3658    </author>
3659    <author initials="L." surname="Masinter" fullname="L. Masinter">
3660      <organization>Xerox Corporation</organization>
3661      <address><email>masinter@parc.xerox.com</email></address>
3662    </author>
3663    <author initials="P." surname="Leach" fullname="P. Leach">
3664      <organization>Microsoft Corporation</organization>
3665      <address><email>paulle@microsoft.com</email></address>
3666    </author>
3667    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3668      <organization>W3C</organization>
3669      <address><email>timbl@w3.org</email></address>
3670    </author>
3671    <date month="June" year="1999"/>
3672  </front>
3673  <seriesInfo name="RFC" value="2616"/>
3674</reference>
3675
3676<reference anchor='RFC2818'>
3677  <front>
3678    <title>HTTP Over TLS</title>
3679    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3680      <organization>RTFM, Inc.</organization>
3681      <address><email>ekr@rtfm.com</email></address>
3682    </author>
3683    <date year='2000' month='May' />
3684  </front>
3685  <seriesInfo name='RFC' value='2818' />
3686</reference>
3687
3688<reference anchor="RFC2821">
3689  <front>
3690    <title>Simple Mail Transfer Protocol</title>
3691    <author initials="J." surname="Klensin" fullname="J. Klensin">
3692      <organization>AT&amp;T Laboratories</organization>
3693      <address><email>klensin@research.att.com</email></address>
3694    </author>
3695    <date year="2001" month="April"/>
3696  </front>
3697  <seriesInfo name="RFC" value="2821"/>
3698</reference>
3699
3700<reference anchor='RFC2965'>
3701  <front>
3702    <title>HTTP State Management Mechanism</title>
3703    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3704      <organization>Bell Laboratories, Lucent Technologies</organization>
3705      <address><email>dmk@bell-labs.com</email></address>
3706    </author>
3707    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3708      <organization>Epinions.com, Inc.</organization>
3709      <address><email>lou@montulli.org</email></address>
3710    </author>
3711    <date year='2000' month='October' />
3712  </front>
3713  <seriesInfo name='RFC' value='2965' />
3714</reference>
3715
3716<reference anchor='RFC3864'>
3717  <front>
3718    <title>Registration Procedures for Message Header Fields</title>
3719    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3720      <organization>Nine by Nine</organization>
3721      <address><email>GK-IETF@ninebynine.org</email></address>
3722    </author>
3723    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3724      <organization>BEA Systems</organization>
3725      <address><email>mnot@pobox.com</email></address>
3726    </author>
3727    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3728      <organization>HP Labs</organization>
3729      <address><email>JeffMogul@acm.org</email></address>
3730    </author>
3731    <date year='2004' month='September' />
3732  </front>
3733  <seriesInfo name='BCP' value='90' />
3734  <seriesInfo name='RFC' value='3864' />
3735</reference>
3736
3737<reference anchor='RFC3977'>
3738  <front>
3739    <title>Network News Transfer Protocol (NNTP)</title>
3740    <author initials='C.' surname='Feather' fullname='C. Feather'>
3741      <organization>THUS plc</organization>
3742      <address><email>clive@demon.net</email></address>
3743    </author>
3744    <date year='2006' month='October' />
3745  </front>
3746  <seriesInfo name="RFC" value="3977"/>
3747</reference>
3748
3749<reference anchor="RFC4288">
3750  <front>
3751    <title>Media Type Specifications and Registration Procedures</title>
3752    <author initials="N." surname="Freed" fullname="N. Freed">
3753      <organization>Sun Microsystems</organization>
3754      <address>
3755        <email>ned.freed@mrochek.com</email>
3756      </address>
3757    </author>
3758    <author initials="J." surname="Klensin" fullname="J. Klensin">
3759      <organization/>
3760      <address>
3761        <email>klensin+ietf@jck.com</email>
3762      </address>
3763    </author>
3764    <date year="2005" month="December"/>
3765  </front>
3766  <seriesInfo name="BCP" value="13"/>
3767  <seriesInfo name="RFC" value="4288"/>
3768</reference>
3769
3770<reference anchor='RFC4395'>
3771  <front>
3772    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3773    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3774      <organization>AT&amp;T Laboratories</organization>
3775      <address>
3776        <email>tony+urireg@maillennium.att.com</email>
3777      </address>
3778    </author>
3779    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3780      <organization>Qualcomm, Inc.</organization>
3781      <address>
3782        <email>hardie@qualcomm.com</email>
3783      </address>
3784    </author>
3785    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3786      <organization>Adobe Systems</organization>
3787      <address>
3788        <email>LMM@acm.org</email>
3789      </address>
3790    </author>
3791    <date year='2006' month='February' />
3792  </front>
3793  <seriesInfo name='BCP' value='115' />
3794  <seriesInfo name='RFC' value='4395' />
3795</reference>
3796
3797<reference anchor="RFC5322">
3798  <front>
3799    <title>Internet Message Format</title>
3800    <author initials="P." surname="Resnick" fullname="P. Resnick">
3801      <organization>Qualcomm Incorporated</organization>
3802    </author>
3803    <date year="2008" month="October"/>
3804  </front> 
3805  <seriesInfo name="RFC" value="5322"/>
3806</reference>
3807
3808<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3809  <front>
3810    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3811    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3812      <organization/>
3813    </author>
3814    <date year="2001" month="November"/>
3815  </front>
3816  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3817</reference>
3818
3819<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3820  <front>
3821  <title>Analysis of HTTP Performance Problems</title>
3822  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3823    <organization/>
3824  </author>
3825  <date/>
3826  </front>
3827</reference>
3828
3829<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3830  <front>
3831  <title>Analysis of HTTP Performance</title>
3832  <author initials="J." surname="Touch" fullname="Joe Touch">
3833    <organization>USC/Information Sciences Institute</organization>
3834    <address><email>touch@isi.edu</email></address>
3835  </author>
3836  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3837    <organization>USC/Information Sciences Institute</organization>
3838    <address><email>johnh@isi.edu</email></address>
3839  </author>
3840  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3841    <organization>USC/Information Sciences Institute</organization>
3842    <address><email>katia@isi.edu</email></address>
3843  </author>
3844  <date year="1998" month="Aug"/>
3845  </front>
3846  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3847  <annotation>(original report dated Aug. 1996)</annotation>
3848</reference>
3849
3850<reference anchor="WAIS">
3851  <front>
3852    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3853    <author initials="F." surname="Davis" fullname="F. Davis">
3854      <organization>Thinking Machines Corporation</organization>
3855    </author>
3856    <author initials="B." surname="Kahle" fullname="B. Kahle">
3857      <organization>Thinking Machines Corporation</organization>
3858    </author>
3859    <author initials="H." surname="Morris" fullname="H. Morris">
3860      <organization>Thinking Machines Corporation</organization>
3861    </author>
3862    <author initials="J." surname="Salem" fullname="J. Salem">
3863      <organization>Thinking Machines Corporation</organization>
3864    </author>
3865    <author initials="T." surname="Shen" fullname="T. Shen">
3866      <organization>Thinking Machines Corporation</organization>
3867    </author>
3868    <author initials="R." surname="Wang" fullname="R. Wang">
3869      <organization>Thinking Machines Corporation</organization>
3870    </author>
3871    <author initials="J." surname="Sui" fullname="J. Sui">
3872      <organization>Thinking Machines Corporation</organization>
3873    </author>
3874    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3875      <organization>Thinking Machines Corporation</organization>
3876    </author>
3877    <date month="April" year="1990"/>
3878  </front>
3879  <seriesInfo name="Thinking Machines Corporation" value=""/>
3880</reference>
3881
3882</references>
3883
3884
3885<section title="Tolerant Applications" anchor="tolerant.applications">
3886<t>
3887   Although this document specifies the requirements for the generation
3888   of HTTP/1.1 messages, not all applications will be correct in their
3889   implementation. We therefore recommend that operational applications
3890   be tolerant of deviations whenever those deviations can be
3891   interpreted unambiguously.
3892</t>
3893<t>
3894   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3895   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3896   accept any amount of SP or HTAB characters between fields, even though
3897   only a single SP is required.
3898</t>
3899<t>
3900   The line terminator for message-header fields is the sequence CRLF.
3901   However, we recommend that applications, when parsing such headers,
3902   recognize a single LF as a line terminator and ignore the leading CR.
3903</t>
3904<t>
3905   The character set of an entity-body &SHOULD; be labeled as the lowest
3906   common denominator of the character codes used within that body, with
3907   the exception that not labeling the entity is preferred over labeling
3908   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3909</t>
3910<t>
3911   Additional rules for requirements on parsing and encoding of dates
3912   and other potential problems with date encodings include:
3913</t>
3914<t>
3915  <list style="symbols">
3916     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3917        which appears to be more than 50 years in the future is in fact
3918        in the past (this helps solve the "year 2000" problem).</t>
3919
3920     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3921        Expires date as earlier than the proper value, but &MUST-NOT;
3922        internally represent a parsed Expires date as later than the
3923        proper value.</t>
3924
3925     <t>All expiration-related calculations &MUST; be done in GMT. The
3926        local time zone &MUST-NOT; influence the calculation or comparison
3927        of an age or expiration time.</t>
3928
3929     <t>If an HTTP header incorrectly carries a date value with a time
3930        zone other than GMT, it &MUST; be converted into GMT using the
3931        most conservative possible conversion.</t>
3932  </list>
3933</t>
3934</section>
3935
3936<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3937<t>
3938   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3939   simplify the process of date comparison. Proxies and gateways from
3940   other protocols &SHOULD; ensure that any Date header field present in a
3941   message conforms to one of the HTTP/1.1 formats and rewrite the date
3942   if necessary.
3943</t>
3944</section>
3945
3946<section title="Compatibility with Previous Versions" anchor="compatibility">
3947<t>
3948   It is beyond the scope of a protocol specification to mandate
3949   compliance with previous versions. HTTP/1.1 was deliberately
3950   designed, however, to make supporting previous versions easy. It is
3951   worth noting that, at the time of composing this specification
3952   (1996), we would expect commercial HTTP/1.1 servers to:
3953  <list style="symbols">
3954     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3955        1.1 requests;</t>
3956
3957     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3958        1.1;</t>
3959
3960     <t>respond appropriately with a message in the same major version
3961        used by the client.</t>
3962  </list>
3963</t>
3964<t>
3965   And we would expect HTTP/1.1 clients to:
3966  <list style="symbols">
3967     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3968        responses;</t>
3969
3970     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3971        1.1.</t>
3972  </list>
3973</t>
3974<t>
3975   For most implementations of HTTP/1.0, each connection is established
3976   by the client prior to the request and closed by the server after
3977   sending the response. Some implementations implement the Keep-Alive
3978   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3979</t>
3980
3981<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3982<t>
3983   This section summarizes major differences between versions HTTP/1.0
3984   and HTTP/1.1.
3985</t>
3986
3987<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">
3988<t>
3989   The requirements that clients and servers support the Host request-header,
3990   report an error if the Host request-header (<xref target="header.host"/>) is
3991   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3992   are among the most important changes defined by this
3993   specification.
3994</t>
3995<t>
3996   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3997   addresses and servers; there was no other established mechanism for
3998   distinguishing the intended server of a request than the IP address
3999   to which that request was directed. The changes outlined above will
4000   allow the Internet, once older HTTP clients are no longer common, to
4001   support multiple Web sites from a single IP address, greatly
4002   simplifying large operational Web servers, where allocation of many
4003   IP addresses to a single host has created serious problems. The
4004   Internet will also be able to recover the IP addresses that have been
4005   allocated for the sole purpose of allowing special-purpose domain
4006   names to be used in root-level HTTP URLs. Given the rate of growth of
4007   the Web, and the number of servers already deployed, it is extremely
4008   important that all implementations of HTTP (including updates to
4009   existing HTTP/1.0 applications) correctly implement these
4010   requirements:
4011  <list style="symbols">
4012     <t>Both clients and servers &MUST; support the Host request-header.</t>
4013
4014     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4015
4016     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4017        request does not include a Host request-header.</t>
4018
4019     <t>Servers &MUST; accept absolute URIs.</t>
4020  </list>
4021</t>
4022</section>
4023</section>
4024
4025<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4026<t>
4027   Some clients and servers might wish to be compatible with some
4028   previous implementations of persistent connections in HTTP/1.0
4029   clients and servers. Persistent connections in HTTP/1.0 are
4030   explicitly negotiated as they are not the default behavior. HTTP/1.0
4031   experimental implementations of persistent connections are faulty,
4032   and the new facilities in HTTP/1.1 are designed to rectify these
4033   problems. The problem was that some existing 1.0 clients may be
4034   sending Keep-Alive to a proxy server that doesn't understand
4035   Connection, which would then erroneously forward it to the next
4036   inbound server, which would establish the Keep-Alive connection and
4037   result in a hung HTTP/1.0 proxy waiting for the close on the
4038   response. The result is that HTTP/1.0 clients must be prevented from
4039   using Keep-Alive when talking to proxies.
4040</t>
4041<t>
4042   However, talking to proxies is the most important use of persistent
4043   connections, so that prohibition is clearly unacceptable. Therefore,
4044   we need some other mechanism for indicating a persistent connection
4045   is desired, which is safe to use even when talking to an old proxy
4046   that ignores Connection. Persistent connections are the default for
4047   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4048   declaring non-persistence. See <xref target="header.connection"/>.
4049</t>
4050<t>
4051   The original HTTP/1.0 form of persistent connections (the Connection:
4052   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4053</t>
4054</section>
4055
4056<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4057<t>
4058   This specification has been carefully audited to correct and
4059   disambiguate key word usage; RFC 2068 had many problems in respect to
4060   the conventions laid out in <xref target="RFC2119"/>.
4061</t>
4062<t>
4063   Transfer-coding and message lengths all interact in ways that
4064   required fixing exactly when chunked encoding is used (to allow for
4065   transfer encoding that may not be self delimiting); it was important
4066   to straighten out exactly how message lengths are computed. (Sections
4067   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4068   <xref target="header.content-length" format="counter"/>,
4069   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4070</t>
4071<t>
4072   The use and interpretation of HTTP version numbers has been clarified
4073   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4074   version they support to deal with problems discovered in HTTP/1.0
4075   implementations (<xref target="http.version"/>)
4076</t>
4077<t>
4078   Transfer-coding had significant problems, particularly with
4079   interactions with chunked encoding. The solution is that transfer-codings
4080   become as full fledged as content-codings. This involves
4081   adding an IANA registry for transfer-codings (separate from content
4082   codings), a new header field (TE) and enabling trailer headers in the
4083   future. Transfer encoding is a major performance benefit, so it was
4084   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4085   interoperability problem that could have occurred due to interactions
4086   between authentication trailers, chunked encoding and HTTP/1.0
4087   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4088   and <xref target="header.te" format="counter"/>)
4089</t>
4090</section>
4091
4092<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4093<t>
4094  Rules about implicit linear white space between certain grammar productions
4095  have been removed; now it's only allowed when specifically pointed out
4096  in the ABNF.
4097  The CHAR rule does not allow the NUL character anymore (this affects
4098  the comment and quoted-string rules).  Furthermore, the quoted-pair
4099  rule does not allow escaping NUL, CR or LF anymore.
4100  (<xref target="basic.rules"/>)
4101</t>
4102<t>
4103  Clarify that HTTP-Version is case sensitive.
4104  (<xref target="http.version"/>)
4105</t>
4106<t>
4107  Remove reference to non-existant identity transfer-coding value tokens.
4108  (Sections <xref format="counter" target="transfer.codings"/> and
4109  <xref format="counter" target="message.length"/>)
4110</t>
4111<t>
4112  Clarification that the chunk length does not include
4113  the count of the octets in the chunk header and trailer.
4114  (<xref target="chunked.transfer.encoding"/>)
4115</t>
4116<t>
4117  Fix BNF to add query, as the abs_path production in
4118  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4119  (<xref target="request-uri"/>)
4120</t>
4121<t>
4122  Clarify exactly when close connection options must be sent.
4123  (<xref target="header.connection"/>)
4124</t>
4125</section>
4126</section>
4127
4128<section title="Terminology" anchor="terminology">
4129<t>
4130   This specification uses a number of terms to refer to the roles
4131   played by participants in, and objects of, the HTTP communication.
4132</t>
4133<t>
4134  <iref item="connection"/>
4135  <x:dfn>connection</x:dfn>
4136  <list>
4137    <t>
4138      A transport layer virtual circuit established between two programs
4139      for the purpose of communication.
4140    </t>
4141  </list>
4142</t>
4143<t>
4144  <iref item="message"/>
4145  <x:dfn>message</x:dfn>
4146  <list>
4147    <t>
4148      The basic unit of HTTP communication, consisting of a structured
4149      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4150      transmitted via the connection.
4151    </t>
4152  </list>
4153</t>
4154<t>
4155  <iref item="request"/>
4156  <x:dfn>request</x:dfn>
4157  <list>
4158    <t>
4159      An HTTP request message, as defined in <xref target="request"/>.
4160    </t>
4161  </list>
4162</t>
4163<t>
4164  <iref item="response"/>
4165  <x:dfn>response</x:dfn>
4166  <list>
4167    <t>
4168      An HTTP response message, as defined in <xref target="response"/>.
4169    </t>
4170  </list>
4171</t>
4172<t>
4173  <iref item="resource"/>
4174  <x:dfn>resource</x:dfn>
4175  <list>
4176    <t>
4177      A network data object or service that can be identified by a URI,
4178      as defined in <xref target="uri"/>. Resources may be available in multiple
4179      representations (e.g. multiple languages, data formats, size, and
4180      resolutions) or vary in other ways.
4181    </t>
4182  </list>
4183</t>
4184<t>
4185  <iref item="entity"/>
4186  <x:dfn>entity</x:dfn>
4187  <list>
4188    <t>
4189      The information transferred as the payload of a request or
4190      response. An entity consists of metainformation in the form of
4191      entity-header fields and content in the form of an entity-body, as
4192      described in &entity;.
4193    </t>
4194  </list>
4195</t>
4196<t>
4197  <iref item="representation"/>
4198  <x:dfn>representation</x:dfn>
4199  <list>
4200    <t>
4201      An entity included with a response that is subject to content
4202      negotiation, as described in &content.negotiation;. There may exist multiple
4203      representations associated with a particular response status.
4204    </t>
4205  </list>
4206</t>
4207<t>
4208  <iref item="content negotiation"/>
4209  <x:dfn>content negotiation</x:dfn>
4210  <list>
4211    <t>
4212      The mechanism for selecting the appropriate representation when
4213      servicing a request, as described in &content.negotiation;. The
4214      representation of entities in any response can be negotiated
4215      (including error responses).
4216    </t>
4217  </list>
4218</t>
4219<t>
4220  <iref item="variant"/>
4221  <x:dfn>variant</x:dfn>
4222  <list>
4223    <t>
4224      A resource may have one, or more than one, representation(s)
4225      associated with it at any given instant. Each of these
4226      representations is termed a `variant'.  Use of the term `variant'
4227      does not necessarily imply that the resource is subject to content
4228      negotiation.
4229    </t>
4230  </list>
4231</t>
4232<t>
4233  <iref item="client"/>
4234  <x:dfn>client</x:dfn>
4235  <list>
4236    <t>
4237      A program that establishes connections for the purpose of sending
4238      requests.
4239    </t>
4240  </list>
4241</t>
4242<t>
4243  <iref item="user agent"/>
4244  <x:dfn>user agent</x:dfn>
4245  <list>
4246    <t>
4247      The client which initiates a request. These are often browsers,
4248      editors, spiders (web-traversing robots), or other end user tools.
4249    </t>
4250  </list>
4251</t>
4252<t>
4253  <iref item="server"/>
4254  <x:dfn>server</x:dfn>
4255  <list>
4256    <t>
4257      An application program that accepts connections in order to
4258      service requests by sending back responses. Any given program may
4259      be capable of being both a client and a server; our use of these
4260      terms refers only to the role being performed by the program for a
4261      particular connection, rather than to the program's capabilities
4262      in general. Likewise, any server may act as an origin server,
4263      proxy, gateway, or tunnel, switching behavior based on the nature
4264      of each request.
4265    </t>
4266  </list>
4267</t>
4268<t>
4269  <iref item="origin server"/>
4270  <x:dfn>origin server</x:dfn>
4271  <list>
4272    <t>
4273      The server on which a given resource resides or is to be created.
4274    </t>
4275  </list>
4276</t>
4277<t>
4278  <iref item="proxy"/>
4279  <x:dfn>proxy</x:dfn>
4280  <list>
4281    <t>
4282      An intermediary program which acts as both a server and a client
4283      for the purpose of making requests on behalf of other clients.
4284      Requests are serviced internally or by passing them on, with
4285      possible translation, to other servers. A proxy &MUST; implement
4286      both the client and server requirements of this specification. A
4287      "transparent proxy" is a proxy that does not modify the request or
4288      response beyond what is required for proxy authentication and
4289      identification. A "non-transparent proxy" is a proxy that modifies
4290      the request or response in order to provide some added service to
4291      the user agent, such as group annotation services, media type
4292      transformation, protocol reduction, or anonymity filtering. Except
4293      where either transparent or non-transparent behavior is explicitly
4294      stated, the HTTP proxy requirements apply to both types of
4295      proxies.
4296    </t>
4297  </list>
4298</t>
4299<t>
4300  <iref item="gateway"/>
4301  <x:dfn>gateway</x:dfn>
4302  <list>
4303    <t>
4304      A server which acts as an intermediary for some other server.
4305      Unlike a proxy, a gateway receives requests as if it were the
4306      origin server for the requested resource; the requesting client
4307      may not be aware that it is communicating with a gateway.
4308    </t>
4309  </list>
4310</t>
4311<t>
4312  <iref item="tunnel"/>
4313  <x:dfn>tunnel</x:dfn>
4314  <list>
4315    <t>
4316      An intermediary program which is acting as a blind relay between
4317      two connections. Once active, a tunnel is not considered a party
4318      to the HTTP communication, though the tunnel may have been
4319      initiated by an HTTP request. The tunnel ceases to exist when both
4320      ends of the relayed connections are closed.
4321    </t>
4322  </list>
4323</t>
4324<t>
4325  <iref item="cache"/>
4326  <x:dfn>cache</x:dfn>
4327  <list>
4328    <t>
4329      A program's local store of response messages and the subsystem
4330      that controls its message storage, retrieval, and deletion. A
4331      cache stores cacheable responses in order to reduce the response
4332      time and network bandwidth consumption on future, equivalent
4333      requests. Any client or server may include a cache, though a cache
4334      cannot be used by a server that is acting as a tunnel.
4335    </t>
4336  </list>
4337</t>
4338<t>
4339  <iref item="cacheable"/>
4340  <x:dfn>cacheable</x:dfn>
4341  <list>
4342    <t>
4343      A response is cacheable if a cache is allowed to store a copy of
4344      the response message for use in answering subsequent requests. The
4345      rules for determining the cacheability of HTTP responses are
4346      defined in &caching;. Even if a resource is cacheable, there may
4347      be additional constraints on whether a cache can use the cached
4348      copy for a particular request.
4349    </t>
4350  </list>
4351</t>
4352<t>
4353  <iref item="upstream"/>
4354  <iref item="downstream"/>
4355  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4356  <list>
4357    <t>
4358      Upstream and downstream describe the flow of a message: all
4359      messages flow from upstream to downstream.
4360    </t>
4361  </list>
4362</t>
4363<t>
4364  <iref item="inbound"/>
4365  <iref item="outbound"/>
4366  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4367  <list>
4368    <t>
4369      Inbound and outbound refer to the request and response paths for
4370      messages: "inbound" means "traveling toward the origin server",
4371      and "outbound" means "traveling toward the user agent"
4372    </t>
4373  </list>
4374</t>
4375</section>
4376
4377<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4378
4379<section title="Since RFC2616">
4380<t>
4381  Extracted relevant partitions from <xref target="RFC2616"/>.
4382</t>
4383</section>
4384
4385<section title="Since draft-ietf-httpbis-p1-messaging-00">
4386<t>
4387  Closed issues:
4388  <list style="symbols"> 
4389    <t>
4390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4391      "HTTP Version should be case sensitive"
4392      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4396      "'unsafe' characters"
4397      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4398    </t>
4399    <t>
4400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4401      "Chunk Size Definition"
4402      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4403    </t>
4404    <t>
4405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4406      "Message Length"
4407      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4411      "Media Type Registrations"
4412      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4413    </t>
4414    <t>
4415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4416      "URI includes query"
4417      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4418    </t>
4419    <t>
4420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4421      "No close on 1xx responses"
4422      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4426      "Remove 'identity' token references"
4427      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4428    </t>
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4431      "Import query BNF"
4432    </t>
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4435      "qdtext BNF"
4436    </t>
4437    <t>
4438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4439      "Normative and Informative references"
4440    </t>
4441    <t>
4442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4443      "RFC2606 Compliance"
4444    </t>
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4447      "RFC977 reference"
4448    </t>
4449    <t>
4450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4451      "RFC1700 references"
4452    </t>
4453    <t>
4454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4455      "inconsistency in date format explanation"
4456    </t>
4457    <t>
4458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4459      "Date reference typo"
4460    </t>
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4463      "Informative references"
4464    </t>
4465    <t>
4466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4467      "ISO-8859-1 Reference"
4468    </t>
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4471      "Normative up-to-date references"
4472    </t>
4473  </list>
4474</t>
4475<t>
4476  Other changes:
4477  <list style="symbols"> 
4478    <t>
4479      Update media type registrations to use RFC4288 template.
4480    </t>
4481    <t>
4482      Use names of RFC4234 core rules DQUOTE and HTAB,
4483      fix broken ABNF for chunk-data
4484      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4485    </t>
4486  </list>
4487</t>
4488</section>
4489
4490<section title="Since draft-ietf-httpbis-p1-messaging-01">
4491<t>
4492  Closed issues:
4493  <list style="symbols"> 
4494    <t>
4495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4496      "Bodies on GET (and other) requests"
4497    </t>
4498    <t>
4499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4500      "Updating to RFC4288"
4501    </t>
4502    <t>
4503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4504      "Status Code and Reason Phrase"
4505    </t>
4506    <t>
4507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4508      "rel_path not used"
4509    </t>
4510  </list>
4511</t>
4512<t>
4513  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4514  <list style="symbols"> 
4515    <t>
4516      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4517      "trailer-part").
4518    </t>
4519    <t>
4520      Avoid underscore character in rule names ("http_URL" ->
4521      "http-URL", "abs_path" -> "path-absolute").
4522    </t>
4523    <t>
4524      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4525      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4526      have to be updated when switching over to RFC3986.
4527    </t>
4528    <t>
4529      Synchronize core rules with RFC5234 (this includes a change to CHAR
4530      which now excludes NUL).
4531    </t>
4532    <t>
4533      Get rid of prose rules that span multiple lines.
4534    </t>
4535    <t>
4536      Get rid of unused rules LOALPHA and UPALPHA.
4537    </t>
4538    <t>
4539      Move "Product Tokens" section (back) into Part 1, as "token" is used
4540      in the definition of the Upgrade header.
4541    </t>
4542    <t>
4543      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4544    </t>
4545    <t>
4546      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4547    </t>
4548  </list>
4549</t>
4550</section>
4551
4552<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4553<t>
4554  Closed issues:
4555  <list style="symbols"> 
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4558      "HTTP-date vs. rfc1123-date"
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4562      "WS in quoted-pair"
4563    </t>
4564  </list>
4565</t>
4566<t>
4567  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4568  <list style="symbols"> 
4569    <t>
4570      Reference RFC 3984, and update header registrations for headers defined
4571      in this document.
4572    </t>
4573  </list>
4574</t>
4575<t>
4576  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4577  <list style="symbols"> 
4578    <t>
4579      Replace string literals when the string really is case-sensitive (HTTP-Version).
4580    </t>
4581  </list>
4582</t>
4583</section>
4584
4585<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4586<t>
4587  Closed issues:
4588  <list style="symbols"> 
4589    <t>
4590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4591      "Connection closing"
4592    </t>
4593    <t>
4594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4595      "Move registrations and registry information to IANA Considerations"
4596    </t>
4597    <t>
4598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4599      "need new URL for PAD1995 reference"
4600    </t>
4601    <t>
4602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4603      "IANA Considerations: update HTTP URI scheme registration"
4604    </t>
4605    <t>
4606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4607      "Cite HTTPS URI scheme definition"
4608    </t>
4609    <t>
4610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4611      "List-type headers vs Set-Cookie"
4612    </t>
4613  </list>
4614</t>
4615<t>
4616  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4617  <list style="symbols"> 
4618    <t>
4619      Replace string literals when the string really is case-sensitive (HTTP-Date).
4620    </t>
4621    <t>
4622      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4623    </t>
4624  </list>
4625</t>
4626</section>
4627
4628<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4629<t>
4630  Closed issues:
4631  <list style="symbols"> 
4632    <t>
4633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4634      "RFC 2822 is updated by RFC 5322"
4635    </t>
4636  </list>
4637</t>
4638<t>
4639  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4640  <list style="symbols"> 
4641    <t>
4642      Use "/" instead of "|" for alternatives.
4643    </t>
4644    <t>
4645      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4646    </t>
4647    <t>
4648      Only reference RFC 5234's core rules.
4649    </t>
4650    <t>
4651      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4652      whitespace ("OWS") and required whitespace ("RWS").
4653    </t>
4654    <t>
4655      Rewrite ABNFs to spell out whitespace rules, factor out
4656      header value format definitions.
4657    </t>
4658  </list>
4659</t>
4660</section>
4661
4662</section>
4663
4664</back>
4665</rfc>
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