source: draft-ietf-httpbis/latest/p1-messaging.xml @ 374

Last change on this file since 374 was 374, checked in by julian.reschke@…, 11 years ago

Resolve #34: update to current URI spec, get rid of discussion of URI history (closes #34)

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File size: 197.4 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypermedia
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets for
235   interaction and to identify other resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is also designed for use as a generic protocol for translating
243   communication to and from other Internet information systems, such as
244   USENET news services via NNTP <xref target="RFC3977"/>,
245   file services via FTP <xref target="RFC959"/>,
246   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
247   HTTP proxies and gateways provide access to alternative information
248   services by translating their diverse protocols into a hypermedia
249   format that can be viewed and manipulated by clients in the same way
250   as HTTP services.
251</t>
252<t>
253   This document is Part 1 of the seven-part specification of HTTP,
254   defining the protocol referred to as "HTTP/1.1" and obsoleting
255   <xref target="RFC2616"/>.
256   Part 1 defines how clients determine when to use HTTP, the URI schemes
257   specific to HTTP-based resources, overall network operation with
258   transport protocol connection management, and HTTP message framing.
259   Our goal is to define all of the mechanisms necessary for HTTP message
260   handling that are independent of message semantics, thereby defining the
261   complete set of requirements for an HTTP message relay or generic
262   message parser.
263</t>
264
265<section title="Requirements" anchor="intro.requirements">
266<t>
267   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
268   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
269   document are to be interpreted as described in <xref target="RFC2119"/>.
270</t>
271<t>
272   An implementation is not compliant if it fails to satisfy one or more
273   of the &MUST; or &REQUIRED; level requirements for the protocols it
274   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
275   level and all the &SHOULD; level requirements for its protocols is said
276   to be "unconditionally compliant"; one that satisfies all the &MUST;
277   level requirements but not all the &SHOULD; level requirements for its
278   protocols is said to be "conditionally compliant."
279</t>
280</section>
281
282<section title="Overall Operation" anchor="intro.overall.operation">
283<t>
284   HTTP is a request/response protocol. A client sends a
285   request to the server in the form of a request method, URI, and
286   protocol version, followed by a MIME-like message containing request
287   modifiers, client information, and possible body content over a
288   connection with a server. The server responds with a status line,
289   including the message's protocol version and a success or error code,
290   followed by a MIME-like message containing server information, entity
291   metainformation, and possible entity-body content. The relationship
292   between HTTP and MIME is described in &diff2045entity;.
293</t>
294<t>
295   Most HTTP communication is initiated by a user agent and consists of
296   a request to be applied to a resource on some origin server. In the
297   simplest case, this may be accomplished via a single connection (v)
298   between the user agent (UA) and the origin server (O).
299</t>
300<figure><artwork type="drawing">
301       request chain ------------------------&gt;
302    UA -------------------v------------------- O
303       &lt;----------------------- response chain
304</artwork></figure>
305<t>
306   A more complicated situation occurs when one or more intermediaries
307   are present in the request/response chain. There are three common
308   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
309   forwarding agent, receiving requests for a URI in its absolute form,
310   rewriting all or part of the message, and forwarding the reformatted
311   request toward the server identified by the URI. A gateway is a
312   receiving agent, acting as a layer above some other server(s) and, if
313   necessary, translating the requests to the underlying server's
314   protocol. A tunnel acts as a relay point between two connections
315   without changing the messages; tunnels are used when the
316   communication needs to pass through an intermediary (such as a
317   firewall) even when the intermediary cannot understand the contents
318   of the messages.
319</t>
320<figure><artwork type="drawing">
321       request chain --------------------------------------&gt;
322    UA -----v----- A -----v----- B -----v----- C -----v----- O
323       &lt;------------------------------------- response chain
324</artwork></figure>
325<t>
326   The figure above shows three intermediaries (A, B, and C) between the
327   user agent and origin server. A request or response message that
328   travels the whole chain will pass through four separate connections.
329   This distinction is important because some HTTP communication options
330   may apply only to the connection with the nearest, non-tunnel
331   neighbor, only to the end-points of the chain, or to all connections
332   along the chain. Although the diagram is linear, each participant may
333   be engaged in multiple, simultaneous communications. For example, B
334   may be receiving requests from many clients other than A, and/or
335   forwarding requests to servers other than C, at the same time that it
336   is handling A's request.
337</t>
338<t>
339   Any party to the communication which is not acting as a tunnel may
340   employ an internal cache for handling requests. The effect of a cache
341   is that the request/response chain is shortened if one of the
342   participants along the chain has a cached response applicable to that
343   request. The following illustrates the resulting chain if B has a
344   cached copy of an earlier response from O (via C) for a request which
345   has not been cached by UA or A.
346</t>
347<figure><artwork type="drawing">
348          request chain ----------&gt;
349       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
350          &lt;--------- response chain
351</artwork></figure>
352<t>
353   Not all responses are usefully cacheable, and some requests may
354   contain modifiers which place special requirements on cache behavior.
355   HTTP requirements for cache behavior and cacheable responses are
356   defined in &caching;.
357</t>
358<t>
359   In fact, there are a wide variety of architectures and configurations
360   of caches and proxies currently being experimented with or deployed
361   across the World Wide Web. These systems include national hierarchies
362   of proxy caches to save transoceanic bandwidth, systems that
363   broadcast or multicast cache entries, organizations that distribute
364   subsets of cached data via CD-ROM, and so on. HTTP systems are used
365   in corporate intranets over high-bandwidth links, and for access via
366   PDAs with low-power radio links and intermittent connectivity. The
367   goal of HTTP/1.1 is to support the wide diversity of configurations
368   already deployed while introducing protocol constructs that meet the
369   needs of those who build web applications that require high
370   reliability and, failing that, at least reliable indications of
371   failure.
372</t>
373<t>
374   HTTP communication usually takes place over TCP/IP connections. The
375   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
376   not preclude HTTP from being implemented on top of any other protocol
377   on the Internet, or on other networks. HTTP only presumes a reliable
378   transport; any protocol that provides such guarantees can be used;
379   the mapping of the HTTP/1.1 request and response structures onto the
380   transport data units of the protocol in question is outside the scope
381   of this specification.
382</t>
383<t>
384   In HTTP/1.0, most implementations used a new connection for each
385   request/response exchange. In HTTP/1.1, a connection may be used for
386   one or more request/response exchanges, although connections may be
387   closed for a variety of reasons (see <xref target="persistent.connections"/>).
388</t>
389</section>
390</section>
391
392<section title="Notational Conventions and Generic Grammar" anchor="notation">
393
394<section title="ABNF Extension: #rule" anchor="notation.abnf">
395  <t>
396    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
397    improve readability.
398  </t>
399  <t>
400    A construct "#" is defined, similar to "*", for defining lists of
401    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
402    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
403    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
404    form of lists very easy; a rule such as
405    <figure><artwork type="example">
406 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
407  </t>
408  <t>
409    can be shown as
410    <figure><artwork type="example">
411 1#element</artwork></figure>
412  </t>
413  <t>
414    Wherever this construct is used, null elements are allowed, but do
415    not contribute to the count of elements present. That is,
416    "(element), , (element) " is permitted, but counts as only two
417    elements. Therefore, where at least one element is required, at
418    least one non-null element &MUST; be present. Default values are 0
419    and infinity so that "#element" allows any number, including zero;
420    "1#element" requires at least one; and "1#2element" allows one or
421    two.
422  </t>
423</section>
424
425<section title="Basic Rules" anchor="basic.rules">
426<t anchor="core.rules">
427  <x:anchor-alias value="ALPHA"/>
428  <x:anchor-alias value="CHAR"/>
429  <x:anchor-alias value="CTL"/>
430  <x:anchor-alias value="CR"/>
431  <x:anchor-alias value="CRLF"/>
432  <x:anchor-alias value="DIGIT"/>
433  <x:anchor-alias value="DQUOTE"/>
434  <x:anchor-alias value="HEXDIG"/>
435  <x:anchor-alias value="HTAB"/>
436  <x:anchor-alias value="LF"/>
437  <x:anchor-alias value="OCTET"/>
438  <x:anchor-alias value="SP"/>
439  <x:anchor-alias value="WSP"/>
440   This specification uses the Augmented Backus-Naur Form (ABNF) notation
441   of <xref target="RFC5234"/>.  The following core rules are included by
442   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
443   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
444   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
445   DIGIT (decimal 0-9), DQUOTE (double quote),
446   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
447   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
448   and WSP (white space).
449</t>
450<t anchor="rule.CRLF">
451  <x:anchor-alias value="CRLF"/>
452   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
453   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
454   tolerant applications). The end-of-line marker within an entity-body
455   is defined by its associated media type, as described in &media-types;.
456</t>
457<t anchor="rule.LWS">
458   All linear white space (LWS) in header field-values has the same semantics as SP. A
459   recipient &MAY; replace any such linear white space with a single SP before
460   interpreting the field value or forwarding the message downstream.
461</t>
462<t>
463   Historically, HTTP/1.1 header field values allow linear white space folding across
464   multiple lines. However, this specification deprecates its use; senders &MUST-NOT; 
465   produce messages that include LWS folding (i.e., use the obs-fold rule), except
466   within the message/http media type (<xref target="internet.media.type.message.http"/>).
467   Receivers &SHOULD; still parse folded linear white space.
468</t>
469<t>
470   This specification uses three rules to denote the use of linear white space;
471   BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
472</t>
473<t>
474   "Bad" white space is allowed by the BNF, but senders &SHOULD-NOT; produce it in messages.
475   Receivers &MUST; accept it in incoming messages.
476</t>
477<t>
478   Required white space is used when at least one linear white space character
479   is required to separate field tokens. In all such cases, a single SP character
480   &SHOULD; be used.
481</t>
482<t anchor="rule.whitespace">
483  <x:anchor-alias value="BWS"/>
484  <x:anchor-alias value="OWS"/>
485  <x:anchor-alias value="RWS"/>
486  <x:anchor-alias value="obs-fold"/>
487</t>
488<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"/>
489  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
490                 ; "optional" white space
491  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
492                 ; "required" white space
493  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
494                 ; "bad" white space
495  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
496</artwork></figure>
497<t anchor="rule.TEXT">
498  <x:anchor-alias value="TEXT"/>
499   The TEXT rule is only used for descriptive field contents and values
500   that are not intended to be interpreted by the message parser. Words
501   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
502   <xref target="ISO-8859-1"/> only when encoded according to the rules of
503   <xref target="RFC2047"/>.
504</t>
505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
506  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>OWS</x:ref>
507                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>OWS</x:ref>
508</artwork></figure>
509<t>
510   A CRLF is allowed in the definition of TEXT only as part of a header
511   field continuation. It is expected that the folding LWS will be
512   replaced with a single SP before interpretation of the TEXT value.
513</t>
514<t anchor="rule.token.separators">
515  <x:anchor-alias value="tchar"/>
516  <x:anchor-alias value="token"/>
517   Many HTTP/1.1 header field values consist of words separated by LWS
518   or special characters. These special characters &MUST; be in a quoted
519   string to be used within a parameter value (as defined in
520   <xref target="transfer.codings"/>).
521</t>
522<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
523  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
524                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
525                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
526                 
527  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
528</artwork></figure>
529<t anchor="rule.comment">
530  <x:anchor-alias value="comment"/>
531  <x:anchor-alias value="ctext"/>
532   Comments can be included in some HTTP header fields by surrounding
533   the comment text with parentheses. Comments are only allowed in
534   fields containing "comment" as part of their field value definition.
535   In all other fields, parentheses are considered part of the field
536   value.
537</t>
538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
539  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
540  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
541</artwork></figure>
542<t anchor="rule.quoted-string">
543  <x:anchor-alias value="quoted-string"/>
544  <x:anchor-alias value="qdtext"/>
545   A string of text is parsed as a single word if it is quoted using
546   double-quote marks.
547</t>
548<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
549  <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> )
550  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
551</artwork></figure>
552<t anchor="rule.quoted-pair">
553  <x:anchor-alias value="quoted-pair"/>
554  <x:anchor-alias value="quoted-text"/>
555   The backslash character ("\") &MAY; be used as a single-character
556   quoting mechanism only within quoted-string and comment constructs.
557</t>
558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
559  <x:ref>quoted-text</x:ref>    = %x01-09 /
560                   %x0B-0C /
561                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
562  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
563</artwork></figure>
564</section>
565
566<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
567  <x:anchor-alias value="request-header"/>
568  <x:anchor-alias value="response-header"/>
569  <x:anchor-alias value="accept-params"/>
570  <x:anchor-alias value="entity-body"/>
571  <x:anchor-alias value="entity-header"/>
572  <x:anchor-alias value="Cache-Control"/>
573  <x:anchor-alias value="Pragma"/>
574  <x:anchor-alias value="Warning"/>
575<t>
576  The ABNF rules below are defined in other parts:
577</t>
578<figure><!-- Part2--><artwork type="abnf2616">
579  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
580  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
581</artwork></figure>
582<figure><!-- Part3--><artwork type="abnf2616">
583  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
584  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
585  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
586</artwork></figure>
587<figure><!-- Part6--><artwork type="abnf2616">
588  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
589  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
590  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
591</artwork></figure>
592</section>
593
594</section>
595
596<section title="Protocol Parameters" anchor="protocol.parameters">
597
598<section title="HTTP Version" anchor="http.version">
599  <x:anchor-alias value="HTTP-Version"/>
600  <x:anchor-alias value="HTTP-Prot-Name"/>
601<t>
602   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
603   of the protocol. The protocol versioning policy is intended to allow
604   the sender to indicate the format of a message and its capacity for
605   understanding further HTTP communication, rather than the features
606   obtained via that communication. No change is made to the version
607   number for the addition of message components which do not affect
608   communication behavior or which only add to extensible field values.
609   The &lt;minor&gt; number is incremented when the changes made to the
610   protocol add features which do not change the general message parsing
611   algorithm, but which may add to the message semantics and imply
612   additional capabilities of the sender. The &lt;major&gt; number is
613   incremented when the format of a message within the protocol is
614   changed. See <xref target="RFC2145"/> for a fuller explanation.
615</t>
616<t>
617   The version of an HTTP message is indicated by an HTTP-Version field
618   in the first line of the message. HTTP-Version is case-sensitive.
619</t>
620<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
621  <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>
622  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
623</artwork></figure>
624<t>
625   Note that the major and minor numbers &MUST; be treated as separate
626   integers and that each &MAY; be incremented higher than a single digit.
627   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
628   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
629   &MUST-NOT; be sent.
630</t>
631<t>
632   An application that sends a request or response message that includes
633   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
634   with this specification. Applications that are at least conditionally
635   compliant with this specification &SHOULD; use an HTTP-Version of
636   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
637   not compatible with HTTP/1.0. For more details on when to send
638   specific HTTP-Version values, see <xref target="RFC2145"/>.
639</t>
640<t>
641   The HTTP version of an application is the highest HTTP version for
642   which the application is at least conditionally compliant.
643</t>
644<t>
645   Proxy and gateway applications need to be careful when forwarding
646   messages in protocol versions different from that of the application.
647   Since the protocol version indicates the protocol capability of the
648   sender, a proxy/gateway &MUST-NOT; send a message with a version
649   indicator which is greater than its actual version. If a higher
650   version request is received, the proxy/gateway &MUST; either downgrade
651   the request version, or respond with an error, or switch to tunnel
652   behavior.
653</t>
654<t>
655   Due to interoperability problems with HTTP/1.0 proxies discovered
656   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
657   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
658   they support. The proxy/gateway's response to that request &MUST; be in
659   the same major version as the request.
660</t>
661<t>
662  <list>
663    <t>
664      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
665      of header fields required or forbidden by the versions involved.
666    </t>
667  </list>
668</t>
669</section>
670
671<section title="Uniform Resource Identifiers" anchor="uri">
672<t>
673   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
674   to indicate the target of a request and to identify additional resources related
675   to that resource, the request, or the response. Each protocol element in HTTP
676   that allows a URI reference will indicate in its ABNF whether the element allows
677   only a URI in absolute form, any relative reference, or some limited subset of
678   the URI-reference grammar. Unless otherwise indicated, relative URI references
679   are to be parsed relative to the URI corresponding to the request target
680   (the base URI).
681</t>
682  <x:anchor-alias value="URI-reference"/>
683  <x:anchor-alias value="absolute-URI"/>
684  <x:anchor-alias value="authority"/>
685  <x:anchor-alias value="fragment"/>
686  <x:anchor-alias value="path-abempty"/>
687  <x:anchor-alias value="path-absolute"/>
688  <x:anchor-alias value="port"/>
689  <x:anchor-alias value="query"/>
690  <x:anchor-alias value="relativeURI"/>
691  <x:anchor-alias value="relative-part"/>
692  <x:anchor-alias value="uri-host"/>
693<t>
694   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
695   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
696</t>
697<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><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="uri-host"/><iref primary="true" item="Grammar" subitem="relativeURI"/><iref primary="true" item="Grammar" subitem="relative-part"/>
698  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
699  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
700  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
701  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
702  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
703  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
704  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
705  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
706
707  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>>
708  <x:ref>relativeURI</x:ref>   = <x:ref>relative-part</x:ref> [ "?" <x:ref>query</x:ref> ]
709</artwork></figure>
710<t>
711   HTTP does not place an a priori limit on the length of
712   a URI. Servers &MUST; be able to handle the URI of any resource they
713   serve, and &SHOULD; be able to handle URIs of unbounded length if they
714   provide GET-based forms that could generate such URIs. A server
715   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
716   than the server can handle (see &status-414;).
717</t>
718<t>
719  <list>
720    <t>
721      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
722      above 255 bytes, because some older client or proxy
723      implementations might not properly support these lengths.
724    </t>
725  </list>
726</t>
727
728<section title="http URI scheme" anchor="http.uri">
729  <x:anchor-alias value="http-URI"/>
730  <iref item="http URI scheme" primary="true"/>
731  <iref item="URI scheme" subitem="http" primary="true"/>
732<t>
733   The "http" scheme is used to locate network resources via the HTTP
734   protocol. This section defines the syntax and semantics for identifiers
735   using the http or https URI schemes.
736</t>
737<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
738  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
739</artwork></figure>
740<t>
741   If the port is empty or not given, port 80 is assumed. The semantics
742   are that the identified resource is located at the server listening
743   for TCP connections on that port of that host, and the Request-URI
744   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
745   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
746   the path-absolute is not present in the URL, it &MUST; be given as "/" when
747   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
748   receives a host name which is not a fully qualified domain name, it
749   &MAY; add its domain to the host name it received. If a proxy receives
750   a fully qualified domain name, the proxy &MUST-NOT; change the host
751   name.
752</t>
753<t><list><t>
754  <iref item="https URI scheme"/>
755  <iref item="URI scheme" subitem="https"/>
756  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
757</t></list></t>
758</section>
759
760<section title="URI Comparison" anchor="uri.comparison">
761<t>
762   When comparing two URIs to decide if they match or not, a client
763   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
764   URIs, with these exceptions:
765  <list style="symbols">
766    <t>A port that is empty or not given is equivalent to the default
767        port for that URI-reference;</t>
768    <t>Comparisons of host names &MUST; be case-insensitive;</t>
769    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
770    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
771  </list>
772</t>
773<t>
774   Characters other than those in the "reserved" set (see
775   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
776   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
777</t>
778<t>
779   For example, the following three URIs are equivalent:
780</t>
781<figure><artwork type="example">
782   http://example.com:80/~smith/home.html
783   http://EXAMPLE.com/%7Esmith/home.html
784   http://EXAMPLE.com:/%7esmith/home.html
785</artwork></figure>
786</section>
787</section>
788
789<section title="Date/Time Formats" anchor="date.time.formats">
790<section title="Full Date" anchor="full.date">
791  <x:anchor-alias value="HTTP-date"/>
792  <x:anchor-alias value="obsolete-date"/>
793  <x:anchor-alias value="rfc1123-date"/>
794  <x:anchor-alias value="rfc850-date"/>
795  <x:anchor-alias value="asctime-date"/>
796  <x:anchor-alias value="date1"/>
797  <x:anchor-alias value="date2"/>
798  <x:anchor-alias value="date3"/>
799  <x:anchor-alias value="rfc1123-date"/>
800  <x:anchor-alias value="time"/>
801  <x:anchor-alias value="wkday"/>
802  <x:anchor-alias value="weekday"/>
803  <x:anchor-alias value="month"/>
804<t>
805   HTTP applications have historically allowed three different formats
806   for the representation of date/time stamps:
807</t>
808<figure><artwork type="example">
809   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
810   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
811   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
812</artwork></figure>
813<t>
814   The first format is preferred as an Internet standard and represents
815   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
816   <xref target="RFC822"/>). The other formats are described here only for
817   compatibility with obsolete implementations.
818   HTTP/1.1 clients and servers that parse the date value &MUST; accept
819   all three formats (for compatibility with HTTP/1.0), though they &MUST;
820   only generate the RFC 1123 format for representing HTTP-date values
821   in header fields. See <xref target="tolerant.applications"/> for further information.
822</t>
823<t><list><t>
824      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
825      accepting date values that may have been sent by non-HTTP
826      applications, as is sometimes the case when retrieving or posting
827      messages via proxies/gateways to SMTP or NNTP.
828</t></list></t>
829<t>
830   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
831   (GMT), without exception. For the purposes of HTTP, GMT is exactly
832   equal to UTC (Coordinated Universal Time). This is indicated in the
833   first two formats by the inclusion of "GMT" as the three-letter
834   abbreviation for time zone, and &MUST; be assumed when reading the
835   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
836   additional LWS beyond that specifically included as SP in the
837   grammar.
838</t>
839<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"/>
840  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
841  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
842  <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
843  <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
844  <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>
845  <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>
846                 ; day month year (e.g., 02 Jun 1982)
847  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
848                 ; day-month-year (e.g., 02-Jun-82)
849  <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> ))
850                 ; month day (e.g., Jun  2)
851  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
852                 ; 00:00:00 - 23:59:59
853  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
854               / s-Thu / s-Fri / s-Sat / s-Sun
855  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
856               / l-Thu / l-Fri / l-Sat / l-Sun
857  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
858               / s-May / s-Jun / s-Jul / s-Aug
859               / s-Sep / s-Oct / s-Nov / s-Dec
860               
861  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
862
863  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
864  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
865  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
866  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
867  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
868  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
869  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
870
871  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
872  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
873  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
874  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
875  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
876  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
877  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
878
879  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
880  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
881  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
882  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
883  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
884  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
885  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
886  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
887  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
888  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
889  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
890  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
891</artwork></figure>
892<t>
893      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
894      to their usage within the protocol stream. Clients and servers are
895      not required to use these formats for user presentation, request
896      logging, etc.
897</t>
898</section>
899</section>
900
901<section title="Transfer Codings" anchor="transfer.codings">
902  <x:anchor-alias value="parameter"/>
903  <x:anchor-alias value="transfer-coding"/>
904  <x:anchor-alias value="transfer-extension"/>
905<t>
906   Transfer-coding values are used to indicate an encoding
907   transformation that has been, can be, or may need to be applied to an
908   entity-body in order to ensure "safe transport" through the network.
909   This differs from a content coding in that the transfer-coding is a
910   property of the message, not of the original entity.
911</t>
912<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
913  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
914  <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> )
915</artwork></figure>
916<t anchor="rule.parameter">
917  <x:anchor-alias value="attribute"/>
918  <x:anchor-alias value="parameter"/>
919  <x:anchor-alias value="value"/>
920   Parameters are in  the form of attribute/value pairs.
921</t>
922<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"/>
923  <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>
924  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
925  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
926</artwork></figure>
927<t>
928   All transfer-coding values are case-insensitive. HTTP/1.1 uses
929   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
930   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
931</t>
932<t>
933   Whenever a transfer-coding is applied to a message-body, the set of
934   transfer-codings &MUST; include "chunked", unless the message indicates it
935   is terminated by closing the connection. When the "chunked" transfer-coding
936   is used, it &MUST; be the last transfer-coding applied to the
937   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
938   than once to a message-body. These rules allow the recipient to
939   determine the transfer-length of the message (<xref target="message.length"/>).
940</t>
941<t>
942   Transfer-codings are analogous to the Content-Transfer-Encoding
943   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
944   binary data over a 7-bit transport service. However, safe transport
945   has a different focus for an 8bit-clean transfer protocol. In HTTP,
946   the only unsafe characteristic of message-bodies is the difficulty in
947   determining the exact body length (<xref target="message.length"/>), or the desire to
948   encrypt data over a shared transport.
949</t>
950<t>
951   The Internet Assigned Numbers Authority (IANA) acts as a registry for
952   transfer-coding value tokens. Initially, the registry contains the
953   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
954   "gzip", "compress", and "deflate" (&content-codings;).
955</t>
956<t>
957   New transfer-coding value tokens &SHOULD; be registered in the same way
958   as new content-coding value tokens (&content-codings;).
959</t>
960<t>
961   A server which receives an entity-body with a transfer-coding it does
962   not understand &SHOULD; return 501 (Not Implemented), and close the
963   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
964   client.
965</t>
966
967<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
968  <x:anchor-alias value="chunk"/>
969  <x:anchor-alias value="Chunked-Body"/>
970  <x:anchor-alias value="chunk-data"/>
971  <x:anchor-alias value="chunk-ext"/>
972  <x:anchor-alias value="chunk-ext-name"/>
973  <x:anchor-alias value="chunk-ext-val"/>
974  <x:anchor-alias value="chunk-size"/>
975  <x:anchor-alias value="last-chunk"/>
976  <x:anchor-alias value="trailer-part"/>
977<t>
978   The chunked encoding modifies the body of a message in order to
979   transfer it as a series of chunks, each with its own size indicator,
980   followed by an &OPTIONAL; trailer containing entity-header fields. This
981   allows dynamically produced content to be transferred along with the
982   information necessary for the recipient to verify that it has
983   received the full message.
984</t>
985<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"/>
986  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
987                   <x:ref>last-chunk</x:ref>
988                   <x:ref>trailer-part</x:ref>
989                   <x:ref>CRLF</x:ref>
990 
991  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
992                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
993  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
994  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
995 
996  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
997  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
998  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
999  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1000  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1001</artwork></figure>
1002<t>
1003   The chunk-size field is a string of hex digits indicating the size of
1004   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1005   zero, followed by the trailer, which is terminated by an empty line.
1006</t>
1007<t>
1008   The trailer allows the sender to include additional HTTP header
1009   fields at the end of the message. The Trailer header field can be
1010   used to indicate which header fields are included in a trailer (see
1011   <xref target="header.trailer"/>).
1012</t>
1013<t>
1014   A server using chunked transfer-coding in a response &MUST-NOT; use the
1015   trailer for any header fields unless at least one of the following is
1016   true:
1017  <list style="numbers">
1018    <t>the request included a TE header field that indicates "trailers" is
1019     acceptable in the transfer-coding of the  response, as described in
1020     <xref target="header.te"/>; or,</t>
1021
1022    <t>the server is the origin server for the response, the trailer
1023     fields consist entirely of optional metadata, and the recipient
1024     could use the message (in a manner acceptable to the origin server)
1025     without receiving this metadata.  In other words, the origin server
1026     is willing to accept the possibility that the trailer fields might
1027     be silently discarded along the path to the client.</t>
1028  </list>
1029</t>
1030<t>
1031   This requirement prevents an interoperability failure when the
1032   message is being received by an HTTP/1.1 (or later) proxy and
1033   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1034   compliance with the protocol would have necessitated a possibly
1035   infinite buffer on the proxy.
1036</t>
1037<t>
1038   A process for decoding the "chunked" transfer-coding
1039   can be represented in pseudo-code as:
1040</t>
1041<figure><artwork type="code">
1042  length := 0
1043  read chunk-size, chunk-ext (if any) and CRLF
1044  while (chunk-size &gt; 0) {
1045     read chunk-data and CRLF
1046     append chunk-data to entity-body
1047     length := length + chunk-size
1048     read chunk-size and CRLF
1049  }
1050  read entity-header
1051  while (entity-header not empty) {
1052     append entity-header to existing header fields
1053     read entity-header
1054  }
1055  Content-Length := length
1056  Remove "chunked" from Transfer-Encoding
1057</artwork></figure>
1058<t>
1059   All HTTP/1.1 applications &MUST; be able to receive and decode the
1060   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1061   they do not understand.
1062</t>
1063</section>
1064</section>
1065
1066<section title="Product Tokens" anchor="product.tokens">
1067  <x:anchor-alias value="product"/>
1068  <x:anchor-alias value="product-version"/>
1069<t>
1070   Product tokens are used to allow communicating applications to
1071   identify themselves by software name and version. Most fields using
1072   product tokens also allow sub-products which form a significant part
1073   of the application to be listed, separated by white space. By
1074   convention, the products are listed in order of their significance
1075   for identifying the application.
1076</t>
1077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1078  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1079  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1080</artwork></figure>
1081<t>
1082   Examples:
1083</t>
1084<figure><artwork type="example">
1085    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1086    Server: Apache/0.8.4
1087</artwork></figure>
1088<t>
1089   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1090   used for advertising or other non-essential information. Although any
1091   token character &MAY; appear in a product-version, this token &SHOULD;
1092   only be used for a version identifier (i.e., successive versions of
1093   the same product &SHOULD; only differ in the product-version portion of
1094   the product value).
1095</t>
1096</section>
1097
1098</section>
1099
1100<section title="HTTP Message" anchor="http.message">
1101
1102<section title="Message Types" anchor="message.types">
1103  <x:anchor-alias value="generic-message"/>
1104  <x:anchor-alias value="HTTP-message"/>
1105  <x:anchor-alias value="start-line"/>
1106<t>
1107   HTTP messages consist of requests from client to server and responses
1108   from server to client.
1109</t>
1110<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1111  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1112</artwork></figure>
1113<t>
1114   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1115   message format of <xref target="RFC5322"/> for transferring entities (the payload
1116   of the message). Both types of message consist of a start-line, zero
1117   or more header fields (also known as "headers"), an empty line (i.e.,
1118   a line with nothing preceding the CRLF) indicating the end of the
1119   header fields, and possibly a message-body.
1120</t>
1121<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1122  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1123                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1124                    <x:ref>CRLF</x:ref>
1125                    [ <x:ref>message-body</x:ref> ]
1126  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1127</artwork></figure>
1128<t>
1129   In the interest of robustness, servers &SHOULD; ignore any empty
1130   line(s) received where a Request-Line is expected. In other words, if
1131   the server is reading the protocol stream at the beginning of a
1132   message and receives a CRLF first, it should ignore the CRLF.
1133</t>
1134<t>
1135   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1136   after a POST request. To restate what is explicitly forbidden by the
1137   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1138   extra CRLF.
1139</t>
1140</section>
1141
1142<section title="Message Headers" anchor="message.headers">
1143  <x:anchor-alias value="field-content"/>
1144  <x:anchor-alias value="field-name"/>
1145  <x:anchor-alias value="field-value"/>
1146  <x:anchor-alias value="message-header"/>
1147<t>
1148   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1149   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1150   entity-header (&entity-header-fields;) fields, follow the same generic format as
1151   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1152   of a name followed by a colon (":") and the field value. Field names
1153   are case-insensitive. The field value &MAY; be preceded by any amount
1154   of LWS, though a single SP is preferred. Header fields can be
1155   extended over multiple lines by preceding each extra line with at
1156   least one SP or HTAB. Applications ought to follow "common form", where
1157   one is known or indicated, when generating HTTP constructs, since
1158   there might exist some implementations that fail to accept anything
1159   beyond the common forms.
1160</t>
1161<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"/>
1162  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1163  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1164  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1165  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1166</artwork></figure>
1167<t>
1168  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1169</t>
1170<t>
1171   The field-content does not include any leading or trailing LWS:
1172   linear white space occurring before the first non-whitespace
1173   character of the field-value or after the last non-whitespace
1174   character of the field-value. Such leading or trailing LWS &MAY; be
1175   removed without changing the semantics of the field value. Any LWS
1176   that occurs between field-content &MAY; be replaced with a single SP
1177   before interpreting the field value or forwarding the message
1178   downstream.
1179</t>
1180<t>
1181   The order in which header fields with differing field names are
1182   received is not significant. However, it is "good practice" to send
1183   general-header fields first, followed by request-header or response-header
1184   fields, and ending with the entity-header fields.
1185</t>
1186<t>
1187   Multiple message-header fields with the same field-name &MAY; be
1188   present in a message if and only if the entire field-value for that
1189   header field is defined as a comma-separated list [i.e., #(values)].
1190   It &MUST; be possible to combine the multiple header fields into one
1191   "field-name: field-value" pair, without changing the semantics of the
1192   message, by appending each subsequent field-value to the first, each
1193   separated by a comma. The order in which header fields with the same
1194   field-name are received is therefore significant to the
1195   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1196   change the order of these field values when a message is forwarded.
1197</t>
1198<t>
1199  <list><t>
1200   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1201   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1202   can occur multiple times, but does not use the list syntax, and thus cannot
1203   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1204   for details.) Also note that the Set-Cookie2 header specified in
1205   <xref target="RFC2965"/> does not share this problem.
1206  </t></list>
1207</t>
1208 
1209</section>
1210
1211<section title="Message Body" anchor="message.body">
1212  <x:anchor-alias value="message-body"/>
1213<t>
1214   The message-body (if any) of an HTTP message is used to carry the
1215   entity-body associated with the request or response. The message-body
1216   differs from the entity-body only when a transfer-coding has been
1217   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1218</t>
1219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1220  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1221               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1222</artwork></figure>
1223<t>
1224   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1225   applied by an application to ensure safe and proper transfer of the
1226   message. Transfer-Encoding is a property of the message, not of the
1227   entity, and thus &MAY; be added or removed by any application along the
1228   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1229   when certain transfer-codings may be used.)
1230</t>
1231<t>
1232   The rules for when a message-body is allowed in a message differ for
1233   requests and responses.
1234</t>
1235<t>
1236   The presence of a message-body in a request is signaled by the
1237   inclusion of a Content-Length or Transfer-Encoding header field in
1238   the request's message-headers. A message-body &MUST-NOT; be included in
1239   a request if the specification of the request method (&method;)
1240   explicitly disallows an entity-body in requests.
1241   When a request message contains both a message-body of non-zero
1242   length and a method that does not define any semantics for that
1243   request message-body, then an origin server &SHOULD; either ignore
1244   the message-body or respond with an appropriate error message
1245   (e.g., 413).  A proxy or gateway, when presented the same request,
1246   &SHOULD; either forward the request inbound with the message-body or
1247   ignore the message-body when determining a response.
1248</t>
1249<t>
1250   For response messages, whether or not a message-body is included with
1251   a message is dependent on both the request method and the response
1252   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1253   &MUST-NOT; include a message-body, even though the presence of entity-header
1254   fields might lead one to believe they do. All 1xx
1255   (informational), 204 (No Content), and 304 (Not Modified) responses
1256   &MUST-NOT; include a message-body. All other responses do include a
1257   message-body, although it &MAY; be of zero length.
1258</t>
1259</section>
1260
1261<section title="Message Length" anchor="message.length">
1262<t>
1263   The transfer-length of a message is the length of the message-body as
1264   it appears in the message; that is, after any transfer-codings have
1265   been applied. When a message-body is included with a message, the
1266   transfer-length of that body is determined by one of the following
1267   (in order of precedence):
1268</t>
1269<t>
1270  <list style="numbers">
1271    <x:lt><t>
1272     Any response message which "&MUST-NOT;" include a message-body (such
1273     as the 1xx, 204, and 304 responses and any response to a HEAD
1274     request) is always terminated by the first empty line after the
1275     header fields, regardless of the entity-header fields present in
1276     the message.
1277    </t></x:lt>
1278    <x:lt><t>
1279     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1280     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1281     is used, the transfer-length is defined by the use of this transfer-coding.
1282     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1283     is not present, the transfer-length is defined by the sender closing the connection.
1284    </t></x:lt>
1285    <x:lt><t>
1286     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1287     decimal value in OCTETs represents both the entity-length and the
1288     transfer-length. The Content-Length header field &MUST-NOT; be sent
1289     if these two lengths are different (i.e., if a Transfer-Encoding
1290     header field is present). If a message is received with both a
1291     Transfer-Encoding header field and a Content-Length header field,
1292     the latter &MUST; be ignored.
1293    </t></x:lt>
1294    <x:lt><t>
1295     If the message uses the media type "multipart/byteranges", and the
1296     transfer-length is not otherwise specified, then this self-delimiting
1297     media type defines the transfer-length. This media type
1298     &MUST-NOT; be used unless the sender knows that the recipient can parse
1299     it; the presence in a request of a Range header with multiple byte-range
1300     specifiers from a 1.1 client implies that the client can parse
1301     multipart/byteranges responses.
1302    <list style="empty"><t>
1303       A range header might be forwarded by a 1.0 proxy that does not
1304       understand multipart/byteranges; in this case the server &MUST;
1305       delimit the message using methods defined in items 1, 3 or 5 of
1306       this section.
1307    </t></list>
1308    </t></x:lt>
1309    <x:lt><t>
1310     By the server closing the connection. (Closing the connection
1311     cannot be used to indicate the end of a request body, since that
1312     would leave no possibility for the server to send back a response.)
1313    </t></x:lt>
1314  </list>
1315</t>
1316<t>
1317   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1318   containing a message-body &MUST; include a valid Content-Length header
1319   field unless the server is known to be HTTP/1.1 compliant. If a
1320   request contains a message-body and a Content-Length is not given,
1321   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1322   determine the length of the message, or with 411 (Length Required) if
1323   it wishes to insist on receiving a valid Content-Length.
1324</t>
1325<t>
1326   All HTTP/1.1 applications that receive entities &MUST; accept the
1327   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1328   to be used for messages when the message length cannot be determined
1329   in advance.
1330</t>
1331<t>
1332   Messages &MUST-NOT; include both a Content-Length header field and a
1333   transfer-coding. If the message does include a
1334   transfer-coding, the Content-Length &MUST; be ignored.
1335</t>
1336<t>
1337   When a Content-Length is given in a message where a message-body is
1338   allowed, its field value &MUST; exactly match the number of OCTETs in
1339   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1340   invalid length is received and detected.
1341</t>
1342</section>
1343
1344<section title="General Header Fields" anchor="general.header.fields">
1345  <x:anchor-alias value="general-header"/>
1346<t>
1347   There are a few header fields which have general applicability for
1348   both request and response messages, but which do not apply to the
1349   entity being transferred. These header fields apply only to the
1350   message being transmitted.
1351</t>
1352<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1353  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1354                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1355                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1356                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1357                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1358                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1359                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1360                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1361                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1362</artwork></figure>
1363<t>
1364   General-header field names can be extended reliably only in
1365   combination with a change in the protocol version. However, new or
1366   experimental header fields may be given the semantics of general
1367   header fields if all parties in the communication recognize them to
1368   be general-header fields. Unrecognized header fields are treated as
1369   entity-header fields.
1370</t>
1371</section>
1372</section>
1373
1374<section title="Request" anchor="request">
1375  <x:anchor-alias value="Request"/>
1376<t>
1377   A request message from a client to a server includes, within the
1378   first line of that message, the method to be applied to the resource,
1379   the identifier of the resource, and the protocol version in use.
1380</t>
1381<!--                 Host                      ; should be moved here eventually -->
1382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1383  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1384                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1385                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1386                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1387                  <x:ref>CRLF</x:ref>
1388                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1389</artwork></figure>
1390
1391<section title="Request-Line" anchor="request-line">
1392  <x:anchor-alias value="Request-Line"/>
1393<t>
1394   The Request-Line begins with a method token, followed by the
1395   Request-URI and the protocol version, and ending with CRLF. The
1396   elements are separated by SP characters. No CR or LF is allowed
1397   except in the final CRLF sequence.
1398</t>
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1400  <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>
1401</artwork></figure>
1402
1403<section title="Method" anchor="method">
1404  <x:anchor-alias value="Method"/>
1405<t>
1406   The Method  token indicates the method to be performed on the
1407   resource identified by the Request-URI. The method is case-sensitive.
1408</t>
1409<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1410  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1411</artwork></figure>
1412</section>
1413
1414<section title="Request-URI" anchor="request-uri">
1415  <x:anchor-alias value="Request-URI"/>
1416<t>
1417   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1418   identifies the resource upon which to apply the request.
1419</t>
1420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1421  <x:ref>Request-URI</x:ref>    = "*"
1422                 / <x:ref>absolute-URI</x:ref>
1423                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1424                 / <x:ref>authority</x:ref>
1425</artwork></figure>
1426<t>
1427   The four options for Request-URI are dependent on the nature of the
1428   request. The asterisk "*" means that the request does not apply to a
1429   particular resource, but to the server itself, and is only allowed
1430   when the method used does not necessarily apply to a resource. One
1431   example would be
1432</t>
1433<figure><artwork type="example">
1434    OPTIONS * HTTP/1.1
1435</artwork></figure>
1436<t>
1437   The absolute-URI form is &REQUIRED; when the request is being made to a
1438   proxy. The proxy is requested to forward the request or service it
1439   from a valid cache, and return the response. Note that the proxy &MAY;
1440   forward the request on to another proxy or directly to the server
1441   specified by the absolute-URI. In order to avoid request loops, a
1442   proxy &MUST; be able to recognize all of its server names, including
1443   any aliases, local variations, and the numeric IP address. An example
1444   Request-Line would be:
1445</t>
1446<figure><artwork type="example">
1447    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1448</artwork></figure>
1449<t>
1450   To allow for transition to absolute-URIs in all requests in future
1451   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1452   form in requests, even though HTTP/1.1 clients will only generate
1453   them in requests to proxies.
1454</t>
1455<t>
1456   The authority form is only used by the CONNECT method (&CONNECT;).
1457</t>
1458<t>
1459   The most common form of Request-URI is that used to identify a
1460   resource on an origin server or gateway. In this case the absolute
1461   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1462   the Request-URI, and the network location of the URI (authority) &MUST;
1463   be transmitted in a Host header field. For example, a client wishing
1464   to retrieve the resource above directly from the origin server would
1465   create a TCP connection to port 80 of the host "www.example.org" and send
1466   the lines:
1467</t>
1468<figure><artwork type="example">
1469    GET /pub/WWW/TheProject.html HTTP/1.1
1470    Host: www.example.org
1471</artwork></figure>
1472<t>
1473   followed by the remainder of the Request. Note that the absolute path
1474   cannot be empty; if none is present in the original URI, it &MUST; be
1475   given as "/" (the server root).
1476</t>
1477<t>
1478   The Request-URI is transmitted in the format specified in
1479   <xref target="http.uri"/>. If the Request-URI is encoded using the
1480   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1481   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1482   &MUST; decode the Request-URI in order to
1483   properly interpret the request. Servers &SHOULD; respond to invalid
1484   Request-URIs with an appropriate status code.
1485</t>
1486<t>
1487   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1488   received Request-URI when forwarding it to the next inbound server,
1489   except as noted above to replace a null path-absolute with "/".
1490</t>
1491<t>
1492  <list><t>
1493      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1494      meaning of the request when the origin server is improperly using
1495      a non-reserved URI character for a reserved purpose.  Implementors
1496      should be aware that some pre-HTTP/1.1 proxies have been known to
1497      rewrite the Request-URI.
1498  </t></list>
1499</t>
1500</section>
1501</section>
1502
1503<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1504<t>
1505   The exact resource identified by an Internet request is determined by
1506   examining both the Request-URI and the Host header field.
1507</t>
1508<t>
1509   An origin server that does not allow resources to differ by the
1510   requested host &MAY; ignore the Host header field value when
1511   determining the resource identified by an HTTP/1.1 request. (But see
1512   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1513   for other requirements on Host support in HTTP/1.1.)
1514</t>
1515<t>
1516   An origin server that does differentiate resources based on the host
1517   requested (sometimes referred to as virtual hosts or vanity host
1518   names) &MUST; use the following rules for determining the requested
1519   resource on an HTTP/1.1 request:
1520  <list style="numbers">
1521    <t>If Request-URI is an absolute-URI, the host is part of the
1522     Request-URI. Any Host header field value in the request &MUST; be
1523     ignored.</t>
1524    <t>If the Request-URI is not an absolute-URI, and the request includes
1525     a Host header field, the host is determined by the Host header
1526     field value.</t>
1527    <t>If the host as determined by rule 1 or 2 is not a valid host on
1528     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1529  </list>
1530</t>
1531<t>
1532   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1533   attempt to use heuristics (e.g., examination of the URI path for
1534   something unique to a particular host) in order to determine what
1535   exact resource is being requested.
1536</t>
1537</section>
1538
1539</section>
1540
1541
1542<section title="Response" anchor="response">
1543  <x:anchor-alias value="Response"/>
1544<t>
1545   After receiving and interpreting a request message, a server responds
1546   with an HTTP response message.
1547</t>
1548<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1549  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1550                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1551                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1552                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1553                  <x:ref>CRLF</x:ref>
1554                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1555</artwork></figure>
1556
1557<section title="Status-Line" anchor="status-line">
1558  <x:anchor-alias value="Status-Line"/>
1559<t>
1560   The first line of a Response message is the Status-Line, consisting
1561   of the protocol version followed by a numeric status code and its
1562   associated textual phrase, with each element separated by SP
1563   characters. No CR or LF is allowed except in the final CRLF sequence.
1564</t>
1565<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1566  <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>
1567</artwork></figure>
1568
1569<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1570  <x:anchor-alias value="Reason-Phrase"/>
1571  <x:anchor-alias value="Status-Code"/>
1572<t>
1573   The Status-Code element is a 3-digit integer result code of the
1574   attempt to understand and satisfy the request. These codes are fully
1575   defined in &status-codes;.  The Reason Phrase exists for the sole
1576   purpose of providing a textual description associated with the numeric
1577   status code, out of deference to earlier Internet application protocols
1578   that were more frequently used with interactive text clients.
1579   A client &SHOULD; ignore the content of the Reason Phrase.
1580</t>
1581<t>
1582   The first digit of the Status-Code defines the class of response. The
1583   last two digits do not have any categorization role. There are 5
1584   values for the first digit:
1585  <list style="symbols">
1586    <t>
1587      1xx: Informational - Request received, continuing process
1588    </t>
1589    <t>
1590      2xx: Success - The action was successfully received,
1591        understood, and accepted
1592    </t>
1593    <t>
1594      3xx: Redirection - Further action must be taken in order to
1595        complete the request
1596    </t>
1597    <t>
1598      4xx: Client Error - The request contains bad syntax or cannot
1599        be fulfilled
1600    </t>
1601    <t>
1602      5xx: Server Error - The server failed to fulfill an apparently
1603        valid request
1604    </t>
1605  </list>
1606</t>
1607<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"/>
1608  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1609  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1610</artwork></figure>
1611</section>
1612</section>
1613
1614</section>
1615
1616
1617<section title="Connections" anchor="connections">
1618
1619<section title="Persistent Connections" anchor="persistent.connections">
1620
1621<section title="Purpose" anchor="persistent.purpose">
1622<t>
1623   Prior to persistent connections, a separate TCP connection was
1624   established to fetch each URL, increasing the load on HTTP servers
1625   and causing congestion on the Internet. The use of inline images and
1626   other associated data often require a client to make multiple
1627   requests of the same server in a short amount of time. Analysis of
1628   these performance problems and results from a prototype
1629   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1630   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1631   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1632   T/TCP <xref target="Tou1998"/>.
1633</t>
1634<t>
1635   Persistent HTTP connections have a number of advantages:
1636  <list style="symbols">
1637      <t>
1638        By opening and closing fewer TCP connections, CPU time is saved
1639        in routers and hosts (clients, servers, proxies, gateways,
1640        tunnels, or caches), and memory used for TCP protocol control
1641        blocks can be saved in hosts.
1642      </t>
1643      <t>
1644        HTTP requests and responses can be pipelined on a connection.
1645        Pipelining allows a client to make multiple requests without
1646        waiting for each response, allowing a single TCP connection to
1647        be used much more efficiently, with much lower elapsed time.
1648      </t>
1649      <t>
1650        Network congestion is reduced by reducing the number of packets
1651        caused by TCP opens, and by allowing TCP sufficient time to
1652        determine the congestion state of the network.
1653      </t>
1654      <t>
1655        Latency on subsequent requests is reduced since there is no time
1656        spent in TCP's connection opening handshake.
1657      </t>
1658      <t>
1659        HTTP can evolve more gracefully, since errors can be reported
1660        without the penalty of closing the TCP connection. Clients using
1661        future versions of HTTP might optimistically try a new feature,
1662        but if communicating with an older server, retry with old
1663        semantics after an error is reported.
1664      </t>
1665    </list>
1666</t>
1667<t>
1668   HTTP implementations &SHOULD; implement persistent connections.
1669</t>
1670</section>
1671
1672<section title="Overall Operation" anchor="persistent.overall">
1673<t>
1674   A significant difference between HTTP/1.1 and earlier versions of
1675   HTTP is that persistent connections are the default behavior of any
1676   HTTP connection. That is, unless otherwise indicated, the client
1677   &SHOULD; assume that the server will maintain a persistent connection,
1678   even after error responses from the server.
1679</t>
1680<t>
1681   Persistent connections provide a mechanism by which a client and a
1682   server can signal the close of a TCP connection. This signaling takes
1683   place using the Connection header field (<xref target="header.connection"/>). Once a close
1684   has been signaled, the client &MUST-NOT; send any more requests on that
1685   connection.
1686</t>
1687
1688<section title="Negotiation" anchor="persistent.negotiation">
1689<t>
1690   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1691   maintain a persistent connection unless a Connection header including
1692   the connection-token "close" was sent in the request. If the server
1693   chooses to close the connection immediately after sending the
1694   response, it &SHOULD; send a Connection header including the
1695   connection-token close.
1696</t>
1697<t>
1698   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1699   decide to keep it open based on whether the response from a server
1700   contains a Connection header with the connection-token close. In case
1701   the client does not want to maintain a connection for more than that
1702   request, it &SHOULD; send a Connection header including the
1703   connection-token close.
1704</t>
1705<t>
1706   If either the client or the server sends the close token in the
1707   Connection header, that request becomes the last one for the
1708   connection.
1709</t>
1710<t>
1711   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1712   maintained for HTTP versions less than 1.1 unless it is explicitly
1713   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1714   compatibility with HTTP/1.0 clients.
1715</t>
1716<t>
1717   In order to remain persistent, all messages on the connection &MUST;
1718   have a self-defined message length (i.e., one not defined by closure
1719   of the connection), as described in <xref target="message.length"/>.
1720</t>
1721</section>
1722
1723<section title="Pipelining" anchor="pipelining">
1724<t>
1725   A client that supports persistent connections &MAY; "pipeline" its
1726   requests (i.e., send multiple requests without waiting for each
1727   response). A server &MUST; send its responses to those requests in the
1728   same order that the requests were received.
1729</t>
1730<t>
1731   Clients which assume persistent connections and pipeline immediately
1732   after connection establishment &SHOULD; be prepared to retry their
1733   connection if the first pipelined attempt fails. If a client does
1734   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1735   persistent. Clients &MUST; also be prepared to resend their requests if
1736   the server closes the connection before sending all of the
1737   corresponding responses.
1738</t>
1739<t>
1740   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1741   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1742   premature termination of the transport connection could lead to
1743   indeterminate results. A client wishing to send a non-idempotent
1744   request &SHOULD; wait to send that request until it has received the
1745   response status for the previous request.
1746</t>
1747</section>
1748</section>
1749
1750<section title="Proxy Servers" anchor="persistent.proxy">
1751<t>
1752   It is especially important that proxies correctly implement the
1753   properties of the Connection header field as specified in <xref target="header.connection"/>.
1754</t>
1755<t>
1756   The proxy server &MUST; signal persistent connections separately with
1757   its clients and the origin servers (or other proxy servers) that it
1758   connects to. Each persistent connection applies to only one transport
1759   link.
1760</t>
1761<t>
1762   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1763   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1764   discussion of the problems with the Keep-Alive header implemented by
1765   many HTTP/1.0 clients).
1766</t>
1767</section>
1768
1769<section title="Practical Considerations" anchor="persistent.practical">
1770<t>
1771   Servers will usually have some time-out value beyond which they will
1772   no longer maintain an inactive connection. Proxy servers might make
1773   this a higher value since it is likely that the client will be making
1774   more connections through the same server. The use of persistent
1775   connections places no requirements on the length (or existence) of
1776   this time-out for either the client or the server.
1777</t>
1778<t>
1779   When a client or server wishes to time-out it &SHOULD; issue a graceful
1780   close on the transport connection. Clients and servers &SHOULD; both
1781   constantly watch for the other side of the transport close, and
1782   respond to it as appropriate. If a client or server does not detect
1783   the other side's close promptly it could cause unnecessary resource
1784   drain on the network.
1785</t>
1786<t>
1787   A client, server, or proxy &MAY; close the transport connection at any
1788   time. For example, a client might have started to send a new request
1789   at the same time that the server has decided to close the "idle"
1790   connection. From the server's point of view, the connection is being
1791   closed while it was idle, but from the client's point of view, a
1792   request is in progress.
1793</t>
1794<t>
1795   This means that clients, servers, and proxies &MUST; be able to recover
1796   from asynchronous close events. Client software &SHOULD; reopen the
1797   transport connection and retransmit the aborted sequence of requests
1798   without user interaction so long as the request sequence is
1799   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1800   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1801   human operator the choice of retrying the request(s). Confirmation by
1802   user-agent software with semantic understanding of the application
1803   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1804   be repeated if the second sequence of requests fails.
1805</t>
1806<t>
1807   Servers &SHOULD; always respond to at least one request per connection,
1808   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1809   middle of transmitting a response, unless a network or client failure
1810   is suspected.
1811</t>
1812<t>
1813   Clients that use persistent connections &SHOULD; limit the number of
1814   simultaneous connections that they maintain to a given server. A
1815   single-user client &SHOULD-NOT; maintain more than 2 connections with
1816   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1817   another server or proxy, where N is the number of simultaneously
1818   active users. These guidelines are intended to improve HTTP response
1819   times and avoid congestion.
1820</t>
1821</section>
1822</section>
1823
1824<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1825
1826<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1827<t>
1828   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1829   flow control mechanisms to resolve temporary overloads, rather than
1830   terminating connections with the expectation that clients will retry.
1831   The latter technique can exacerbate network congestion.
1832</t>
1833</section>
1834
1835<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1836<t>
1837   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1838   the network connection for an error status while it is transmitting
1839   the request. If the client sees an error status, it &SHOULD;
1840   immediately cease transmitting the body. If the body is being sent
1841   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1842   empty trailer &MAY; be used to prematurely mark the end of the message.
1843   If the body was preceded by a Content-Length header, the client &MUST;
1844   close the connection.
1845</t>
1846</section>
1847
1848<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1849<t>
1850   The purpose of the 100 (Continue) status (see &status-100;) is to
1851   allow a client that is sending a request message with a request body
1852   to determine if the origin server is willing to accept the request
1853   (based on the request headers) before the client sends the request
1854   body. In some cases, it might either be inappropriate or highly
1855   inefficient for the client to send the body if the server will reject
1856   the message without looking at the body.
1857</t>
1858<t>
1859   Requirements for HTTP/1.1 clients:
1860  <list style="symbols">
1861    <t>
1862        If a client will wait for a 100 (Continue) response before
1863        sending the request body, it &MUST; send an Expect request-header
1864        field (&header-expect;) with the "100-continue" expectation.
1865    </t>
1866    <t>
1867        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1868        with the "100-continue" expectation if it does not intend
1869        to send a request body.
1870    </t>
1871  </list>
1872</t>
1873<t>
1874   Because of the presence of older implementations, the protocol allows
1875   ambiguous situations in which a client may send "Expect: 100-continue"
1876   without receiving either a 417 (Expectation Failed) status
1877   or a 100 (Continue) status. Therefore, when a client sends this
1878   header field to an origin server (possibly via a proxy) from which it
1879   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1880   for an indefinite period before sending the request body.
1881</t>
1882<t>
1883   Requirements for HTTP/1.1 origin servers:
1884  <list style="symbols">
1885    <t> Upon receiving a request which includes an Expect request-header
1886        field with the "100-continue" expectation, an origin server &MUST;
1887        either respond with 100 (Continue) status and continue to read
1888        from the input stream, or respond with a final status code. The
1889        origin server &MUST-NOT; wait for the request body before sending
1890        the 100 (Continue) response. If it responds with a final status
1891        code, it &MAY; close the transport connection or it &MAY; continue
1892        to read and discard the rest of the request.  It &MUST-NOT;
1893        perform the requested method if it returns a final status code.
1894    </t>
1895    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1896        the request message does not include an Expect request-header
1897        field with the "100-continue" expectation, and &MUST-NOT; send a
1898        100 (Continue) response if such a request comes from an HTTP/1.0
1899        (or earlier) client. There is an exception to this rule: for
1900        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1901        status in response to an HTTP/1.1 PUT or POST request that does
1902        not include an Expect request-header field with the "100-continue"
1903        expectation. This exception, the purpose of which is
1904        to minimize any client processing delays associated with an
1905        undeclared wait for 100 (Continue) status, applies only to
1906        HTTP/1.1 requests, and not to requests with any other HTTP-version
1907        value.
1908    </t>
1909    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1910        already received some or all of the request body for the
1911        corresponding request.
1912    </t>
1913    <t> An origin server that sends a 100 (Continue) response &MUST;
1914    ultimately send a final status code, once the request body is
1915        received and processed, unless it terminates the transport
1916        connection prematurely.
1917    </t>
1918    <t> If an origin server receives a request that does not include an
1919        Expect request-header field with the "100-continue" expectation,
1920        the request includes a request body, and the server responds
1921        with a final status code before reading the entire request body
1922        from the transport connection, then the server &SHOULD-NOT;  close
1923        the transport connection until it has read the entire request,
1924        or until the client closes the connection. Otherwise, the client
1925        might not reliably receive the response message. However, this
1926        requirement is not be construed as preventing a server from
1927        defending itself against denial-of-service attacks, or from
1928        badly broken client implementations.
1929      </t>
1930    </list>
1931</t>
1932<t>
1933   Requirements for HTTP/1.1 proxies:
1934  <list style="symbols">
1935    <t> If a proxy receives a request that includes an Expect request-header
1936        field with the "100-continue" expectation, and the proxy
1937        either knows that the next-hop server complies with HTTP/1.1 or
1938        higher, or does not know the HTTP version of the next-hop
1939        server, it &MUST; forward the request, including the Expect header
1940        field.
1941    </t>
1942    <t> If the proxy knows that the version of the next-hop server is
1943        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1944        respond with a 417 (Expectation Failed) status.
1945    </t>
1946    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1947        numbers received from recently-referenced next-hop servers.
1948    </t>
1949    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1950        request message was received from an HTTP/1.0 (or earlier)
1951        client and did not include an Expect request-header field with
1952        the "100-continue" expectation. This requirement overrides the
1953        general rule for forwarding of 1xx responses (see &status-1xx;).
1954    </t>
1955  </list>
1956</t>
1957</section>
1958
1959<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1960<t>
1961   If an HTTP/1.1 client sends a request which includes a request body,
1962   but which does not include an Expect request-header field with the
1963   "100-continue" expectation, and if the client is not directly
1964   connected to an HTTP/1.1 origin server, and if the client sees the
1965   connection close before receiving any status from the server, the
1966   client &SHOULD; retry the request.  If the client does retry this
1967   request, it &MAY; use the following "binary exponential backoff"
1968   algorithm to be assured of obtaining a reliable response:
1969  <list style="numbers">
1970    <t>
1971      Initiate a new connection to the server
1972    </t>
1973    <t>
1974      Transmit the request-headers
1975    </t>
1976    <t>
1977      Initialize a variable R to the estimated round-trip time to the
1978         server (e.g., based on the time it took to establish the
1979         connection), or to a constant value of 5 seconds if the round-trip
1980         time is not available.
1981    </t>
1982    <t>
1983       Compute T = R * (2**N), where N is the number of previous
1984         retries of this request.
1985    </t>
1986    <t>
1987       Wait either for an error response from the server, or for T
1988         seconds (whichever comes first)
1989    </t>
1990    <t>
1991       If no error response is received, after T seconds transmit the
1992         body of the request.
1993    </t>
1994    <t>
1995       If client sees that the connection is closed prematurely,
1996         repeat from step 1 until the request is accepted, an error
1997         response is received, or the user becomes impatient and
1998         terminates the retry process.
1999    </t>
2000  </list>
2001</t>
2002<t>
2003   If at any point an error status is received, the client
2004  <list style="symbols">
2005      <t>&SHOULD-NOT;  continue and</t>
2006
2007      <t>&SHOULD; close the connection if it has not completed sending the
2008        request message.</t>
2009    </list>
2010</t>
2011</section>
2012</section>
2013</section>
2014
2015
2016<section title="Header Field Definitions" anchor="header.fields">
2017<t>
2018   This section defines the syntax and semantics of HTTP/1.1 header fields
2019   related to message framing and transport protocols.
2020</t>
2021<t>
2022   For entity-header fields, both sender and recipient refer to either the
2023   client or the server, depending on who sends and who receives the entity.
2024</t>
2025
2026<section title="Connection" anchor="header.connection">
2027  <iref primary="true" item="Connection header" x:for-anchor=""/>
2028  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2029  <x:anchor-alias value="Connection"/>
2030  <x:anchor-alias value="connection-token"/>
2031  <x:anchor-alias value="Connection-v"/>
2032<t>
2033   The general-header field "Connection" allows the sender to specify
2034   options that are desired for that particular connection and &MUST-NOT;
2035   be communicated by proxies over further connections.
2036</t>
2037<t>
2038   The Connection header's value has the following grammar:
2039</t>
2040<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"/>
2041  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2042  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2043  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2044</artwork></figure>
2045<t>
2046   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2047   message is forwarded and, for each connection-token in this field,
2048   remove any header field(s) from the message with the same name as the
2049   connection-token. Connection options are signaled by the presence of
2050   a connection-token in the Connection header field, not by any
2051   corresponding additional header field(s), since the additional header
2052   field may not be sent if there are no parameters associated with that
2053   connection option.
2054</t>
2055<t>
2056   Message headers listed in the Connection header &MUST-NOT; include
2057   end-to-end headers, such as Cache-Control.
2058</t>
2059<t>
2060   HTTP/1.1 defines the "close" connection option for the sender to
2061   signal that the connection will be closed after completion of the
2062   response. For example,
2063</t>
2064<figure><artwork type="example">
2065  Connection: close
2066</artwork></figure>
2067<t>
2068   in either the request or the response header fields indicates that
2069   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2070   after the current request/response is complete.
2071</t>
2072<t>
2073   An HTTP/1.1 client that does not support persistent connections &MUST;
2074   include the "close" connection option in every request message.
2075</t>
2076<t>
2077   An HTTP/1.1 server that does not support persistent connections &MUST;
2078   include the "close" connection option in every response message that
2079   does not have a 1xx (informational) status code.
2080</t>
2081<t>
2082   A system receiving an HTTP/1.0 (or lower-version) message that
2083   includes a Connection header &MUST;, for each connection-token in this
2084   field, remove and ignore any header field(s) from the message with
2085   the same name as the connection-token. This protects against mistaken
2086   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2087</t>
2088</section>
2089
2090<section title="Content-Length" anchor="header.content-length">
2091  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2092  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2093  <x:anchor-alias value="Content-Length"/>
2094  <x:anchor-alias value="Content-Length-v"/>
2095<t>
2096   The entity-header field "Content-Length" indicates the size of the
2097   entity-body, in decimal number of OCTETs, sent to the recipient or,
2098   in the case of the HEAD method, the size of the entity-body that
2099   would have been sent had the request been a GET.
2100</t>
2101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2102  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2103  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2104</artwork></figure>
2105<t>
2106   An example is
2107</t>
2108<figure><artwork type="example">
2109  Content-Length: 3495
2110</artwork></figure>
2111<t>
2112   Applications &SHOULD; use this field to indicate the transfer-length of
2113   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2114</t>
2115<t>
2116   Any Content-Length greater than or equal to zero is a valid value.
2117   <xref target="message.length"/> describes how to determine the length of a message-body
2118   if a Content-Length is not given.
2119</t>
2120<t>
2121   Note that the meaning of this field is significantly different from
2122   the corresponding definition in MIME, where it is an optional field
2123   used within the "message/external-body" content-type. In HTTP, it
2124   &SHOULD; be sent whenever the message's length can be determined prior
2125   to being transferred, unless this is prohibited by the rules in
2126   <xref target="message.length"/>.
2127</t>
2128</section>
2129
2130<section title="Date" anchor="header.date">
2131  <iref primary="true" item="Date header" x:for-anchor=""/>
2132  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2133  <x:anchor-alias value="Date"/>
2134  <x:anchor-alias value="Date-v"/>
2135<t>
2136   The general-header field "Date" represents the date and time at which
2137   the message was originated, having the same semantics as orig-date in
2138   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2139   HTTP-date, as described in <xref target="full.date"/>;
2140   it &MUST; be sent in rfc1123-date format.
2141</t>
2142<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2143  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2144  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2145</artwork></figure>
2146<t>
2147   An example is
2148</t>
2149<figure><artwork type="example">
2150  Date: Tue, 15 Nov 1994 08:12:31 GMT
2151</artwork></figure>
2152<t>
2153   Origin servers &MUST; include a Date header field in all responses,
2154   except in these cases:
2155  <list style="numbers">
2156      <t>If the response status code is 100 (Continue) or 101 (Switching
2157         Protocols), the response &MAY; include a Date header field, at
2158         the server's option.</t>
2159
2160      <t>If the response status code conveys a server error, e.g. 500
2161         (Internal Server Error) or 503 (Service Unavailable), and it is
2162         inconvenient or impossible to generate a valid Date.</t>
2163
2164      <t>If the server does not have a clock that can provide a
2165         reasonable approximation of the current time, its responses
2166         &MUST-NOT; include a Date header field. In this case, the rules
2167         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2168  </list>
2169</t>
2170<t>
2171   A received message that does not have a Date header field &MUST; be
2172   assigned one by the recipient if the message will be cached by that
2173   recipient or gatewayed via a protocol which requires a Date. An HTTP
2174   implementation without a clock &MUST-NOT; cache responses without
2175   revalidating them on every use. An HTTP cache, especially a shared
2176   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2177   clock with a reliable external standard.
2178</t>
2179<t>
2180   Clients &SHOULD; only send a Date header field in messages that include
2181   an entity-body, as in the case of the PUT and POST requests, and even
2182   then it is optional. A client without a clock &MUST-NOT; send a Date
2183   header field in a request.
2184</t>
2185<t>
2186   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2187   time subsequent to the generation of the message. It &SHOULD; represent
2188   the best available approximation of the date and time of message
2189   generation, unless the implementation has no means of generating a
2190   reasonably accurate date and time. In theory, the date ought to
2191   represent the moment just before the entity is generated. In
2192   practice, the date can be generated at any time during the message
2193   origination without affecting its semantic value.
2194</t>
2195
2196<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2197<t>
2198   Some origin server implementations might not have a clock available.
2199   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2200   values to a response, unless these values were associated
2201   with the resource by a system or user with a reliable clock. It &MAY;
2202   assign an Expires value that is known, at or before server
2203   configuration time, to be in the past (this allows "pre-expiration"
2204   of responses without storing separate Expires values for each
2205   resource).
2206</t>
2207</section>
2208</section>
2209
2210<section title="Host" anchor="header.host">
2211  <iref primary="true" item="Host header" x:for-anchor=""/>
2212  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2213  <x:anchor-alias value="Host"/>
2214  <x:anchor-alias value="Host-v"/>
2215<t>
2216   The request-header field "Host" specifies the Internet host and port
2217   number of the resource being requested, as obtained from the original
2218   URI given by the user or referring resource (generally an HTTP URL,
2219   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2220   the naming authority of the origin server or gateway given by the
2221   original URL. This allows the origin server or gateway to
2222   differentiate between internally-ambiguous URLs, such as the root "/"
2223   URL of a server for multiple host names on a single IP address.
2224</t>
2225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2226  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2227  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2228</artwork></figure>
2229<t>
2230   A "host" without any trailing port information implies the default
2231   port for the service requested (e.g., "80" for an HTTP URL). For
2232   example, a request on the origin server for
2233   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2234</t>
2235<figure><artwork type="example">
2236  GET /pub/WWW/ HTTP/1.1
2237  Host: www.example.org
2238</artwork></figure>
2239<t>
2240   A client &MUST; include a Host header field in all HTTP/1.1 request
2241   messages. If the requested URI does not include an Internet host
2242   name for the service being requested, then the Host header field &MUST;
2243   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2244   request message it forwards does contain an appropriate Host header
2245   field that identifies the service being requested by the proxy. All
2246   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2247   status code to any HTTP/1.1 request message which lacks a Host header
2248   field.
2249</t>
2250<t>
2251   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2252   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2253   for other requirements relating to Host.
2254</t>
2255</section>
2256
2257<section title="TE" anchor="header.te">
2258  <iref primary="true" item="TE header" x:for-anchor=""/>
2259  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2260  <x:anchor-alias value="TE"/>
2261  <x:anchor-alias value="TE-v"/>
2262  <x:anchor-alias value="t-codings"/>
2263<t>
2264   The request-header field "TE" indicates what extension transfer-codings
2265   it is willing to accept in the response and whether or not it is
2266   willing to accept trailer fields in a chunked transfer-coding. Its
2267   value may consist of the keyword "trailers" and/or a comma-separated
2268   list of extension transfer-coding names with optional accept
2269   parameters (as described in <xref target="transfer.codings"/>).
2270</t>
2271<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"/>
2272  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2273  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2274  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2275</artwork></figure>
2276<t>
2277   The presence of the keyword "trailers" indicates that the client is
2278   willing to accept trailer fields in a chunked transfer-coding, as
2279   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2280   transfer-coding values even though it does not itself represent a
2281   transfer-coding.
2282</t>
2283<t>
2284   Examples of its use are:
2285</t>
2286<figure><artwork type="example">
2287  TE: deflate
2288  TE:
2289  TE: trailers, deflate;q=0.5
2290</artwork></figure>
2291<t>
2292   The TE header field only applies to the immediate connection.
2293   Therefore, the keyword &MUST; be supplied within a Connection header
2294   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2295</t>
2296<t>
2297   A server tests whether a transfer-coding is acceptable, according to
2298   a TE field, using these rules:
2299  <list style="numbers">
2300    <x:lt>
2301      <t>The "chunked" transfer-coding is always acceptable. If the
2302         keyword "trailers" is listed, the client indicates that it is
2303         willing to accept trailer fields in the chunked response on
2304         behalf of itself and any downstream clients. The implication is
2305         that, if given, the client is stating that either all
2306         downstream clients are willing to accept trailer fields in the
2307         forwarded response, or that it will attempt to buffer the
2308         response on behalf of downstream recipients.
2309      </t><t>
2310         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2311         chunked response such that a client can be assured of buffering
2312         the entire response.</t>
2313    </x:lt>
2314    <x:lt>
2315      <t>If the transfer-coding being tested is one of the transfer-codings
2316         listed in the TE field, then it is acceptable unless it
2317         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2318         qvalue of 0 means "not acceptable.")</t>
2319    </x:lt>
2320    <x:lt>
2321      <t>If multiple transfer-codings are acceptable, then the
2322         acceptable transfer-coding with the highest non-zero qvalue is
2323         preferred.  The "chunked" transfer-coding always has a qvalue
2324         of 1.</t>
2325    </x:lt>
2326  </list>
2327</t>
2328<t>
2329   If the TE field-value is empty or if no TE field is present, the only
2330   transfer-coding  is "chunked". A message with no transfer-coding is
2331   always acceptable.
2332</t>
2333</section>
2334
2335<section title="Trailer" anchor="header.trailer">
2336  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2337  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2338  <x:anchor-alias value="Trailer"/>
2339  <x:anchor-alias value="Trailer-v"/>
2340<t>
2341   The general field "Trailer" indicates that the given set of
2342   header fields is present in the trailer of a message encoded with
2343   chunked transfer-coding.
2344</t>
2345<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2346  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2347  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2348</artwork></figure>
2349<t>
2350   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2351   message using chunked transfer-coding with a non-empty trailer. Doing
2352   so allows the recipient to know which header fields to expect in the
2353   trailer.
2354</t>
2355<t>
2356   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2357   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2358   trailer fields in a "chunked" transfer-coding.
2359</t>
2360<t>
2361   Message header fields listed in the Trailer header field &MUST-NOT;
2362   include the following header fields:
2363  <list style="symbols">
2364    <t>Transfer-Encoding</t>
2365    <t>Content-Length</t>
2366    <t>Trailer</t>
2367  </list>
2368</t>
2369</section>
2370
2371<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2372  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2373  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2374  <x:anchor-alias value="Transfer-Encoding"/>
2375  <x:anchor-alias value="Transfer-Encoding-v"/>
2376<t>
2377   The general-header "Transfer-Encoding" field indicates what (if any)
2378   type of transformation has been applied to the message body in order
2379   to safely transfer it between the sender and the recipient. This
2380   differs from the content-coding in that the transfer-coding is a
2381   property of the message, not of the entity.
2382</t>
2383<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2384  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Transfer-Encoding-v</x:ref>
2385  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2386</artwork></figure>
2387<t>
2388   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2389</t>
2390<figure><artwork type="example">
2391  Transfer-Encoding: chunked
2392</artwork></figure>
2393<t>
2394   If multiple encodings have been applied to an entity, the transfer-codings
2395   &MUST; be listed in the order in which they were applied.
2396   Additional information about the encoding parameters &MAY; be provided
2397   by other entity-header fields not defined by this specification.
2398</t>
2399<t>
2400   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2401   header.
2402</t>
2403</section>
2404
2405<section title="Upgrade" anchor="header.upgrade">
2406  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2407  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2408  <x:anchor-alias value="Upgrade"/>
2409  <x:anchor-alias value="Upgrade-v"/>
2410<t>
2411   The general-header "Upgrade" allows the client to specify what
2412   additional communication protocols it supports and would like to use
2413   if the server finds it appropriate to switch protocols. The server
2414   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2415   response to indicate which protocol(s) are being switched.
2416</t>
2417<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2418  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2419  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2420</artwork></figure>
2421<t>
2422   For example,
2423</t>
2424<figure><artwork type="example">
2425  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2426</artwork></figure>
2427<t>
2428   The Upgrade header field is intended to provide a simple mechanism
2429   for transition from HTTP/1.1 to some other, incompatible protocol. It
2430   does so by allowing the client to advertise its desire to use another
2431   protocol, such as a later version of HTTP with a higher major version
2432   number, even though the current request has been made using HTTP/1.1.
2433   This eases the difficult transition between incompatible protocols by
2434   allowing the client to initiate a request in the more commonly
2435   supported protocol while indicating to the server that it would like
2436   to use a "better" protocol if available (where "better" is determined
2437   by the server, possibly according to the nature of the method and/or
2438   resource being requested).
2439</t>
2440<t>
2441   The Upgrade header field only applies to switching application-layer
2442   protocols upon the existing transport-layer connection. Upgrade
2443   cannot be used to insist on a protocol change; its acceptance and use
2444   by the server is optional. The capabilities and nature of the
2445   application-layer communication after the protocol change is entirely
2446   dependent upon the new protocol chosen, although the first action
2447   after changing the protocol &MUST; be a response to the initial HTTP
2448   request containing the Upgrade header field.
2449</t>
2450<t>
2451   The Upgrade header field only applies to the immediate connection.
2452   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2453   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2454   HTTP/1.1 message.
2455</t>
2456<t>
2457   The Upgrade header field cannot be used to indicate a switch to a
2458   protocol on a different connection. For that purpose, it is more
2459   appropriate to use a 301, 302, 303, or 305 redirection response.
2460</t>
2461<t>
2462   This specification only defines the protocol name "HTTP" for use by
2463   the family of Hypertext Transfer Protocols, as defined by the HTTP
2464   version rules of <xref target="http.version"/> and future updates to this
2465   specification. Any token can be used as a protocol name; however, it
2466   will only be useful if both the client and server associate the name
2467   with the same protocol.
2468</t>
2469</section>
2470
2471<section title="Via" anchor="header.via">
2472  <iref primary="true" item="Via header" x:for-anchor=""/>
2473  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2474  <x:anchor-alias value="protocol-name"/>
2475  <x:anchor-alias value="protocol-version"/>
2476  <x:anchor-alias value="pseudonym"/>
2477  <x:anchor-alias value="received-by"/>
2478  <x:anchor-alias value="received-protocol"/>
2479  <x:anchor-alias value="Via"/>
2480  <x:anchor-alias value="Via-v"/>
2481<t>
2482   The general-header field "Via" &MUST; be used by gateways and proxies to
2483   indicate the intermediate protocols and recipients between the user
2484   agent and the server on requests, and between the origin server and
2485   the client on responses. It is analogous to the "Received" field defined in
2486   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2487   avoiding request loops, and identifying the protocol capabilities of
2488   all senders along the request/response chain.
2489</t>
2490<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"/>
2491  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2492  <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> ] )
2493  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2494  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2495  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2496  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2497  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2498</artwork></figure>
2499<t>
2500   The received-protocol indicates the protocol version of the message
2501   received by the server or client along each segment of the
2502   request/response chain. The received-protocol version is appended to
2503   the Via field value when the message is forwarded so that information
2504   about the protocol capabilities of upstream applications remains
2505   visible to all recipients.
2506</t>
2507<t>
2508   The protocol-name is optional if and only if it would be "HTTP". The
2509   received-by field is normally the host and optional port number of a
2510   recipient server or client that subsequently forwarded the message.
2511   However, if the real host is considered to be sensitive information,
2512   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2513   be assumed to be the default port of the received-protocol.
2514</t>
2515<t>
2516   Multiple Via field values represents each proxy or gateway that has
2517   forwarded the message. Each recipient &MUST; append its information
2518   such that the end result is ordered according to the sequence of
2519   forwarding applications.
2520</t>
2521<t>
2522   Comments &MAY; be used in the Via header field to identify the software
2523   of the recipient proxy or gateway, analogous to the User-Agent and
2524   Server header fields. However, all comments in the Via field are
2525   optional and &MAY; be removed by any recipient prior to forwarding the
2526   message.
2527</t>
2528<t>
2529   For example, a request message could be sent from an HTTP/1.0 user
2530   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2531   forward the request to a public proxy at p.example.net, which completes
2532   the request by forwarding it to the origin server at www.example.com.
2533   The request received by www.example.com would then have the following
2534   Via header field:
2535</t>
2536<figure><artwork type="example">
2537  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2538</artwork></figure>
2539<t>
2540   Proxies and gateways used as a portal through a network firewall
2541   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2542   the firewall region. This information &SHOULD; only be propagated if
2543   explicitly enabled. If not enabled, the received-by host of any host
2544   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2545   for that host.
2546</t>
2547<t>
2548   For organizations that have strong privacy requirements for hiding
2549   internal structures, a proxy &MAY; combine an ordered subsequence of
2550   Via header field entries with identical received-protocol values into
2551   a single such entry. For example,
2552</t>
2553<figure><artwork type="example">
2554  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2555</artwork></figure>
2556<t>
2557        could be collapsed to
2558</t>
2559<figure><artwork type="example">
2560  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2561</artwork></figure>
2562<t>
2563   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2564   under the same organizational control and the hosts have already been
2565   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2566   have different received-protocol values.
2567</t>
2568</section>
2569
2570</section>
2571
2572<section title="IANA Considerations" anchor="IANA.considerations">
2573<section title="Message Header Registration" anchor="message.header.registration">
2574<t>
2575   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2576   with the permanent registrations below (see <xref target="RFC3864"/>):
2577</t>
2578<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2579<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2580   <ttcol>Header Field Name</ttcol>
2581   <ttcol>Protocol</ttcol>
2582   <ttcol>Status</ttcol>
2583   <ttcol>Reference</ttcol>
2584
2585   <c>Connection</c>
2586   <c>http</c>
2587   <c>standard</c>
2588   <c>
2589      <xref target="header.connection"/>
2590   </c>
2591   <c>Content-Length</c>
2592   <c>http</c>
2593   <c>standard</c>
2594   <c>
2595      <xref target="header.content-length"/>
2596   </c>
2597   <c>Date</c>
2598   <c>http</c>
2599   <c>standard</c>
2600   <c>
2601      <xref target="header.date"/>
2602   </c>
2603   <c>Host</c>
2604   <c>http</c>
2605   <c>standard</c>
2606   <c>
2607      <xref target="header.host"/>
2608   </c>
2609   <c>TE</c>
2610   <c>http</c>
2611   <c>standard</c>
2612   <c>
2613      <xref target="header.te"/>
2614   </c>
2615   <c>Trailer</c>
2616   <c>http</c>
2617   <c>standard</c>
2618   <c>
2619      <xref target="header.trailer"/>
2620   </c>
2621   <c>Transfer-Encoding</c>
2622   <c>http</c>
2623   <c>standard</c>
2624   <c>
2625      <xref target="header.transfer-encoding"/>
2626   </c>
2627   <c>Upgrade</c>
2628   <c>http</c>
2629   <c>standard</c>
2630   <c>
2631      <xref target="header.upgrade"/>
2632   </c>
2633   <c>Via</c>
2634   <c>http</c>
2635   <c>standard</c>
2636   <c>
2637      <xref target="header.via"/>
2638   </c>
2639</texttable>
2640<!--(END)-->
2641<t>
2642   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2643</t>
2644</section>
2645
2646<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2647<t>
2648   The entry for the "http" URI Scheme in the registry located at
2649   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2650   should be updated to point to <xref target="http.uri"/> of this document
2651   (see <xref target="RFC4395"/>).
2652</t>
2653</section>
2654
2655<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2656<t>
2657   This document serves as the specification for the Internet media types
2658   "message/http" and "application/http". The following is to be registered with
2659   IANA (see <xref target="RFC4288"/>).
2660</t>
2661<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2662<iref item="Media Type" subitem="message/http" primary="true"/>
2663<iref item="message/http Media Type" primary="true"/>
2664<t>
2665   The message/http type can be used to enclose a single HTTP request or
2666   response message, provided that it obeys the MIME restrictions for all
2667   "message" types regarding line length and encodings.
2668</t>
2669<t>
2670  <list style="hanging" x:indent="12em">
2671    <t hangText="Type name:">
2672      message
2673    </t>
2674    <t hangText="Subtype name:">
2675      http
2676    </t>
2677    <t hangText="Required parameters:">
2678      none
2679    </t>
2680    <t hangText="Optional parameters:">
2681      version, msgtype
2682      <list style="hanging">
2683        <t hangText="version:">
2684          The HTTP-Version number of the enclosed message
2685          (e.g., "1.1"). If not present, the version can be
2686          determined from the first line of the body.
2687        </t>
2688        <t hangText="msgtype:">
2689          The message type -- "request" or "response". If not
2690          present, the type can be determined from the first
2691          line of the body.
2692        </t>
2693      </list>
2694    </t>
2695    <t hangText="Encoding considerations:">
2696      only "7bit", "8bit", or "binary" are permitted
2697    </t>
2698    <t hangText="Security considerations:">
2699      none
2700    </t>
2701    <t hangText="Interoperability considerations:">
2702      none
2703    </t>
2704    <t hangText="Published specification:">
2705      This specification (see <xref target="internet.media.type.message.http"/>).
2706    </t>
2707    <t hangText="Applications that use this media type:">
2708    </t>
2709    <t hangText="Additional information:">
2710      <list style="hanging">
2711        <t hangText="Magic number(s):">none</t>
2712        <t hangText="File extension(s):">none</t>
2713        <t hangText="Macintosh file type code(s):">none</t>
2714      </list>
2715    </t>
2716    <t hangText="Person and email address to contact for further information:">
2717      See Authors Section.
2718    </t>
2719                <t hangText="Intended usage:">
2720                  COMMON
2721    </t>
2722                <t hangText="Restrictions on usage:">
2723                  none
2724    </t>
2725    <t hangText="Author/Change controller:">
2726      IESG
2727    </t>
2728  </list>
2729</t>
2730</section>
2731<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2732<iref item="Media Type" subitem="application/http" primary="true"/>
2733<iref item="application/http Media Type" primary="true"/>
2734<t>
2735   The application/http type can be used to enclose a pipeline of one or more
2736   HTTP request or response messages (not intermixed).
2737</t>
2738<t>
2739  <list style="hanging" x:indent="12em">
2740    <t hangText="Type name:">
2741      application
2742    </t>
2743    <t hangText="Subtype name:">
2744      http
2745    </t>
2746    <t hangText="Required parameters:">
2747      none
2748    </t>
2749    <t hangText="Optional parameters:">
2750      version, msgtype
2751      <list style="hanging">
2752        <t hangText="version:">
2753          The HTTP-Version number of the enclosed messages
2754          (e.g., "1.1"). If not present, the version can be
2755          determined from the first line of the body.
2756        </t>
2757        <t hangText="msgtype:">
2758          The message type -- "request" or "response". If not
2759          present, the type can be determined from the first
2760          line of the body.
2761        </t>
2762      </list>
2763    </t>
2764    <t hangText="Encoding considerations:">
2765      HTTP messages enclosed by this type
2766      are in "binary" format; use of an appropriate
2767      Content-Transfer-Encoding is required when
2768      transmitted via E-mail.
2769    </t>
2770    <t hangText="Security considerations:">
2771      none
2772    </t>
2773    <t hangText="Interoperability considerations:">
2774      none
2775    </t>
2776    <t hangText="Published specification:">
2777      This specification (see <xref target="internet.media.type.application.http"/>).
2778    </t>
2779    <t hangText="Applications that use this media type:">
2780    </t>
2781    <t hangText="Additional information:">
2782      <list style="hanging">
2783        <t hangText="Magic number(s):">none</t>
2784        <t hangText="File extension(s):">none</t>
2785        <t hangText="Macintosh file type code(s):">none</t>
2786      </list>
2787    </t>
2788    <t hangText="Person and email address to contact for further information:">
2789      See Authors Section.
2790    </t>
2791                <t hangText="Intended usage:">
2792                  COMMON
2793    </t>
2794                <t hangText="Restrictions on usage:">
2795                  none
2796    </t>
2797    <t hangText="Author/Change controller:">
2798      IESG
2799    </t>
2800  </list>
2801</t>
2802</section>
2803</section>
2804
2805</section>
2806
2807<section title="Security Considerations" anchor="security.considerations">
2808<t>
2809   This section is meant to inform application developers, information
2810   providers, and users of the security limitations in HTTP/1.1 as
2811   described by this document. The discussion does not include
2812   definitive solutions to the problems revealed, though it does make
2813   some suggestions for reducing security risks.
2814</t>
2815
2816<section title="Personal Information" anchor="personal.information">
2817<t>
2818   HTTP clients are often privy to large amounts of personal information
2819   (e.g. the user's name, location, mail address, passwords, encryption
2820   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2821   leakage of this information.
2822   We very strongly recommend that a convenient interface be provided
2823   for the user to control dissemination of such information, and that
2824   designers and implementors be particularly careful in this area.
2825   History shows that errors in this area often create serious security
2826   and/or privacy problems and generate highly adverse publicity for the
2827   implementor's company.
2828</t>
2829</section>
2830
2831<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2832<t>
2833   A server is in the position to save personal data about a user's
2834   requests which might identify their reading patterns or subjects of
2835   interest. This information is clearly confidential in nature and its
2836   handling can be constrained by law in certain countries. People using
2837   HTTP to provide data are responsible for ensuring that
2838   such material is not distributed without the permission of any
2839   individuals that are identifiable by the published results.
2840</t>
2841</section>
2842
2843<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2844<t>
2845   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2846   the documents returned by HTTP requests to be only those that were
2847   intended by the server administrators. If an HTTP server translates
2848   HTTP URIs directly into file system calls, the server &MUST; take
2849   special care not to serve files that were not intended to be
2850   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2851   other operating systems use ".." as a path component to indicate a
2852   directory level above the current one. On such a system, an HTTP
2853   server &MUST; disallow any such construct in the Request-URI if it
2854   would otherwise allow access to a resource outside those intended to
2855   be accessible via the HTTP server. Similarly, files intended for
2856   reference only internally to the server (such as access control
2857   files, configuration files, and script code) &MUST; be protected from
2858   inappropriate retrieval, since they might contain sensitive
2859   information. Experience has shown that minor bugs in such HTTP server
2860   implementations have turned into security risks.
2861</t>
2862</section>
2863
2864<section title="DNS Spoofing" anchor="dns.spoofing">
2865<t>
2866   Clients using HTTP rely heavily on the Domain Name Service, and are
2867   thus generally prone to security attacks based on the deliberate
2868   mis-association of IP addresses and DNS names. Clients need to be
2869   cautious in assuming the continuing validity of an IP number/DNS name
2870   association.
2871</t>
2872<t>
2873   In particular, HTTP clients &SHOULD; rely on their name resolver for
2874   confirmation of an IP number/DNS name association, rather than
2875   caching the result of previous host name lookups. Many platforms
2876   already can cache host name lookups locally when appropriate, and
2877   they &SHOULD; be configured to do so. It is proper for these lookups to
2878   be cached, however, only when the TTL (Time To Live) information
2879   reported by the name server makes it likely that the cached
2880   information will remain useful.
2881</t>
2882<t>
2883   If HTTP clients cache the results of host name lookups in order to
2884   achieve a performance improvement, they &MUST; observe the TTL
2885   information reported by DNS.
2886</t>
2887<t>
2888   If HTTP clients do not observe this rule, they could be spoofed when
2889   a previously-accessed server's IP address changes. As network
2890   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2891   possibility of this form of attack will grow. Observing this
2892   requirement thus reduces this potential security vulnerability.
2893</t>
2894<t>
2895   This requirement also improves the load-balancing behavior of clients
2896   for replicated servers using the same DNS name and reduces the
2897   likelihood of a user's experiencing failure in accessing sites which
2898   use that strategy.
2899</t>
2900</section>
2901
2902<section title="Proxies and Caching" anchor="attack.proxies">
2903<t>
2904   By their very nature, HTTP proxies are men-in-the-middle, and
2905   represent an opportunity for man-in-the-middle attacks. Compromise of
2906   the systems on which the proxies run can result in serious security
2907   and privacy problems. Proxies have access to security-related
2908   information, personal information about individual users and
2909   organizations, and proprietary information belonging to users and
2910   content providers. A compromised proxy, or a proxy implemented or
2911   configured without regard to security and privacy considerations,
2912   might be used in the commission of a wide range of potential attacks.
2913</t>
2914<t>
2915   Proxy operators should protect the systems on which proxies run as
2916   they would protect any system that contains or transports sensitive
2917   information. In particular, log information gathered at proxies often
2918   contains highly sensitive personal information, and/or information
2919   about organizations. Log information should be carefully guarded, and
2920   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2921</t>
2922<t>
2923   Proxy implementors should consider the privacy and security
2924   implications of their design and coding decisions, and of the
2925   configuration options they provide to proxy operators (especially the
2926   default configuration).
2927</t>
2928<t>
2929   Users of a proxy need to be aware that they are no trustworthier than
2930   the people who run the proxy; HTTP itself cannot solve this problem.
2931</t>
2932<t>
2933   The judicious use of cryptography, when appropriate, may suffice to
2934   protect against a broad range of security and privacy attacks. Such
2935   cryptography is beyond the scope of the HTTP/1.1 specification.
2936</t>
2937</section>
2938
2939<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2940<t>
2941   They exist. They are hard to defend against. Research continues.
2942   Beware.
2943</t>
2944</section>
2945</section>
2946
2947<section title="Acknowledgments" anchor="ack">
2948<t>
2949   HTTP has evolved considerably over the years. It has
2950   benefited from a large and active developer community--the many
2951   people who have participated on the www-talk mailing list--and it is
2952   that community which has been most responsible for the success of
2953   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2954   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2955   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2956   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2957   VanHeyningen deserve special recognition for their efforts in
2958   defining early aspects of the protocol.
2959</t>
2960<t>
2961   This document has benefited greatly from the comments of all those
2962   participating in the HTTP-WG. In addition to those already mentioned,
2963   the following individuals have contributed to this specification:
2964</t>
2965<t>
2966   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2967   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2968   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2969   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2970   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2971   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2972   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2973   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2974   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2975   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2976   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2977   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2978   Josh Cohen.
2979</t>
2980<t>
2981   Thanks to the "cave men" of Palo Alto. You know who you are.
2982</t>
2983<t>
2984   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2985   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2986   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2987   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2988   Larry Masinter for their help. And thanks go particularly to Jeff
2989   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2990</t>
2991<t>
2992   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2993   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2994   discovery of many of the problems that this document attempts to
2995   rectify.
2996</t>
2997<t>
2998   This specification makes heavy use of the augmented BNF and generic
2999   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3000   reuses many of the definitions provided by Nathaniel Borenstein and
3001   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3002   specification will help reduce past confusion over the relationship
3003   between HTTP and Internet mail message formats.
3004</t>
3005</section>
3006
3007</middle>
3008<back>
3009
3010<references title="Normative References">
3011
3012<reference anchor="ISO-8859-1">
3013  <front>
3014    <title>
3015     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3016    </title>
3017    <author>
3018      <organization>International Organization for Standardization</organization>
3019    </author>
3020    <date year="1998"/>
3021  </front>
3022  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3023</reference>
3024
3025<reference anchor="Part2">
3026  <front>
3027    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3028    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3029      <organization abbrev="Day Software">Day Software</organization>
3030      <address><email>fielding@gbiv.com</email></address>
3031    </author>
3032    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3033      <organization>One Laptop per Child</organization>
3034      <address><email>jg@laptop.org</email></address>
3035    </author>
3036    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3037      <organization abbrev="HP">Hewlett-Packard Company</organization>
3038      <address><email>JeffMogul@acm.org</email></address>
3039    </author>
3040    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3041      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3042      <address><email>henrikn@microsoft.com</email></address>
3043    </author>
3044    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3045      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3046      <address><email>LMM@acm.org</email></address>
3047    </author>
3048    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3049      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3050      <address><email>paulle@microsoft.com</email></address>
3051    </author>
3052    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3053      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3054      <address><email>timbl@w3.org</email></address>
3055    </author>
3056    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3057      <organization abbrev="W3C">World Wide Web Consortium</organization>
3058      <address><email>ylafon@w3.org</email></address>
3059    </author>
3060    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3061      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3062      <address><email>julian.reschke@greenbytes.de</email></address>
3063    </author>
3064    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3065  </front>
3066  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3067  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3068</reference>
3069
3070<reference anchor="Part3">
3071  <front>
3072    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3073    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3074      <organization abbrev="Day Software">Day Software</organization>
3075      <address><email>fielding@gbiv.com</email></address>
3076    </author>
3077    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3078      <organization>One Laptop per Child</organization>
3079      <address><email>jg@laptop.org</email></address>
3080    </author>
3081    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3082      <organization abbrev="HP">Hewlett-Packard Company</organization>
3083      <address><email>JeffMogul@acm.org</email></address>
3084    </author>
3085    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3086      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3087      <address><email>henrikn@microsoft.com</email></address>
3088    </author>
3089    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3090      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3091      <address><email>LMM@acm.org</email></address>
3092    </author>
3093    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3094      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3095      <address><email>paulle@microsoft.com</email></address>
3096    </author>
3097    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3098      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3099      <address><email>timbl@w3.org</email></address>
3100    </author>
3101    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3102      <organization abbrev="W3C">World Wide Web Consortium</organization>
3103      <address><email>ylafon@w3.org</email></address>
3104    </author>
3105    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3106      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3107      <address><email>julian.reschke@greenbytes.de</email></address>
3108    </author>
3109    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3110  </front>
3111  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3112  <x:source href="p3-payload.xml" basename="p3-payload"/>
3113</reference>
3114
3115<reference anchor="Part5">
3116  <front>
3117    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3118    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3119      <organization abbrev="Day Software">Day Software</organization>
3120      <address><email>fielding@gbiv.com</email></address>
3121    </author>
3122    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3123      <organization>One Laptop per Child</organization>
3124      <address><email>jg@laptop.org</email></address>
3125    </author>
3126    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3127      <organization abbrev="HP">Hewlett-Packard Company</organization>
3128      <address><email>JeffMogul@acm.org</email></address>
3129    </author>
3130    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3131      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3132      <address><email>henrikn@microsoft.com</email></address>
3133    </author>
3134    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3135      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3136      <address><email>LMM@acm.org</email></address>
3137    </author>
3138    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3140      <address><email>paulle@microsoft.com</email></address>
3141    </author>
3142    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3143      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3144      <address><email>timbl@w3.org</email></address>
3145    </author>
3146    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3147      <organization abbrev="W3C">World Wide Web Consortium</organization>
3148      <address><email>ylafon@w3.org</email></address>
3149    </author>
3150    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3151      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3152      <address><email>julian.reschke@greenbytes.de</email></address>
3153    </author>
3154    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3155  </front>
3156  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3157  <x:source href="p5-range.xml" basename="p5-range"/>
3158</reference>
3159
3160<reference anchor="Part6">
3161  <front>
3162    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3163    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3164      <organization abbrev="Day Software">Day Software</organization>
3165      <address><email>fielding@gbiv.com</email></address>
3166    </author>
3167    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3168      <organization>One Laptop per Child</organization>
3169      <address><email>jg@laptop.org</email></address>
3170    </author>
3171    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3172      <organization abbrev="HP">Hewlett-Packard Company</organization>
3173      <address><email>JeffMogul@acm.org</email></address>
3174    </author>
3175    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3176      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3177      <address><email>henrikn@microsoft.com</email></address>
3178    </author>
3179    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3180      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3181      <address><email>LMM@acm.org</email></address>
3182    </author>
3183    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3185      <address><email>paulle@microsoft.com</email></address>
3186    </author>
3187    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3188      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3189      <address><email>timbl@w3.org</email></address>
3190    </author>
3191    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3192      <organization abbrev="W3C">World Wide Web Consortium</organization>
3193      <address><email>ylafon@w3.org</email></address>
3194    </author>
3195    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3196      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3197      <address><email>julian.reschke@greenbytes.de</email></address>
3198    </author>
3199    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3200  </front>
3201  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3202  <x:source href="p6-cache.xml" basename="p6-cache"/>
3203</reference>
3204
3205<reference anchor="RFC5234">
3206  <front>
3207    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3208    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3209      <organization>Brandenburg InternetWorking</organization>
3210      <address>
3211      <postal>
3212      <street>675 Spruce Dr.</street>
3213      <city>Sunnyvale</city>
3214      <region>CA</region>
3215      <code>94086</code>
3216      <country>US</country></postal>
3217      <phone>+1.408.246.8253</phone>
3218      <email>dcrocker@bbiw.net</email></address> 
3219    </author>
3220    <author initials="P." surname="Overell" fullname="Paul Overell">
3221      <organization>THUS plc.</organization>
3222      <address>
3223      <postal>
3224      <street>1/2 Berkeley Square</street>
3225      <street>99 Berkely Street</street>
3226      <city>Glasgow</city>
3227      <code>G3 7HR</code>
3228      <country>UK</country></postal>
3229      <email>paul.overell@thus.net</email></address>
3230    </author>
3231    <date month="January" year="2008"/>
3232  </front>
3233  <seriesInfo name="STD" value="68"/>
3234  <seriesInfo name="RFC" value="5234"/>
3235</reference>
3236
3237<reference anchor="RFC2045">
3238  <front>
3239    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3240    <author initials="N." surname="Freed" fullname="Ned Freed">
3241      <organization>Innosoft International, Inc.</organization>
3242      <address><email>ned@innosoft.com</email></address>
3243    </author>
3244    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3245      <organization>First Virtual Holdings</organization>
3246      <address><email>nsb@nsb.fv.com</email></address>
3247    </author>
3248    <date month="November" year="1996"/>
3249  </front>
3250  <seriesInfo name="RFC" value="2045"/>
3251</reference>
3252
3253<reference anchor="RFC2047">
3254  <front>
3255    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3256    <author initials="K." surname="Moore" fullname="Keith Moore">
3257      <organization>University of Tennessee</organization>
3258      <address><email>moore@cs.utk.edu</email></address>
3259    </author>
3260    <date month="November" year="1996"/>
3261  </front>
3262  <seriesInfo name="RFC" value="2047"/>
3263</reference>
3264
3265<reference anchor="RFC2119">
3266  <front>
3267    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3268    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3269      <organization>Harvard University</organization>
3270      <address><email>sob@harvard.edu</email></address>
3271    </author>
3272    <date month="March" year="1997"/>
3273  </front>
3274  <seriesInfo name="BCP" value="14"/>
3275  <seriesInfo name="RFC" value="2119"/>
3276</reference>
3277
3278<reference anchor="RFC3986">
3279 <front>
3280  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3281  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3282    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3283    <address>
3284       <email>timbl@w3.org</email>
3285       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3286    </address>
3287  </author>
3288  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3289    <organization abbrev="Day Software">Day Software</organization>
3290    <address>
3291      <email>fielding@gbiv.com</email>
3292      <uri>http://roy.gbiv.com/</uri>
3293    </address>
3294  </author>
3295  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3296    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3297    <address>
3298      <email>LMM@acm.org</email>
3299      <uri>http://larry.masinter.net/</uri>
3300    </address>
3301  </author>
3302  <date month='January' year='2005'></date>
3303 </front>
3304 <seriesInfo name="RFC" value="3986"/>
3305 <seriesInfo name="STD" value="66"/>
3306</reference>
3307
3308<reference anchor="USASCII">
3309  <front>
3310    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3311    <author>
3312      <organization>American National Standards Institute</organization>
3313    </author>
3314    <date year="1986"/>
3315  </front>
3316  <seriesInfo name="ANSI" value="X3.4"/>
3317</reference>
3318
3319</references>
3320
3321<references title="Informative References">
3322
3323<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3324  <front>
3325    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3326    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3327      <organization/>
3328    </author>
3329    <author initials="J." surname="Gettys" fullname="J. Gettys">
3330      <organization/>
3331    </author>
3332    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3333      <organization/>
3334    </author>
3335    <author initials="H." surname="Lie" fullname="H. Lie">
3336      <organization/>
3337    </author>
3338    <author initials="C." surname="Lilley" fullname="C. Lilley">
3339      <organization/>
3340    </author>
3341    <date year="1997" month="September"/>
3342  </front>
3343  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3344</reference>
3345
3346<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3347  <front>
3348    <title>Improving HTTP Latency</title>
3349    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3350      <organization/>
3351    </author>
3352    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3353      <organization/>
3354    </author>
3355    <date year="1995" month="December"/>
3356  </front>
3357  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3358</reference>
3359
3360<reference anchor="RFC822">
3361  <front>
3362    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3363    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3364      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3365      <address><email>DCrocker@UDel-Relay</email></address>
3366    </author>
3367    <date month="August" day="13" year="1982"/>
3368  </front>
3369  <seriesInfo name="STD" value="11"/>
3370  <seriesInfo name="RFC" value="822"/>
3371</reference>
3372
3373<reference anchor="RFC959">
3374  <front>
3375    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3376    <author initials="J." surname="Postel" fullname="J. Postel">
3377      <organization>Information Sciences Institute (ISI)</organization>
3378    </author>
3379    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3380      <organization/>
3381    </author>
3382    <date month="October" year="1985"/>
3383  </front>
3384  <seriesInfo name="STD" value="9"/>
3385  <seriesInfo name="RFC" value="959"/>
3386</reference>
3387
3388<reference anchor="RFC1123">
3389  <front>
3390    <title>Requirements for Internet Hosts - Application and Support</title>
3391    <author initials="R." surname="Braden" fullname="Robert Braden">
3392      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3393      <address><email>Braden@ISI.EDU</email></address>
3394    </author>
3395    <date month="October" year="1989"/>
3396  </front>
3397  <seriesInfo name="STD" value="3"/>
3398  <seriesInfo name="RFC" value="1123"/>
3399</reference>
3400
3401<reference anchor="RFC1305">
3402  <front>
3403    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3404    <author initials="D." surname="Mills" fullname="David L. Mills">
3405      <organization>University of Delaware, Electrical Engineering Department</organization>
3406      <address><email>mills@udel.edu</email></address>
3407    </author>
3408    <date month="March" year="1992"/>
3409  </front>
3410  <seriesInfo name="RFC" value="1305"/>
3411</reference>
3412
3413<reference anchor="RFC1436">
3414  <front>
3415    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3416    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3417      <organization>University of Minnesota, Computer and Information Services</organization>
3418      <address><email>fxa@boombox.micro.umn.edu</email></address>
3419    </author>
3420    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3421      <organization>University of Minnesota, Computer and Information Services</organization>
3422      <address><email>mpm@boombox.micro.umn.edu</email></address>
3423    </author>
3424    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3425      <organization>University of Minnesota, Computer and Information Services</organization>
3426      <address><email>lindner@boombox.micro.umn.edu</email></address>
3427    </author>
3428    <author initials="D." surname="Johnson" fullname="David Johnson">
3429      <organization>University of Minnesota, Computer and Information Services</organization>
3430      <address><email>dmj@boombox.micro.umn.edu</email></address>
3431    </author>
3432    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3433      <organization>University of Minnesota, Computer and Information Services</organization>
3434      <address><email>daniel@boombox.micro.umn.edu</email></address>
3435    </author>
3436    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3437      <organization>University of Minnesota, Computer and Information Services</organization>
3438      <address><email>alberti@boombox.micro.umn.edu</email></address>
3439    </author>
3440    <date month="March" year="1993"/>
3441  </front>
3442  <seriesInfo name="RFC" value="1436"/>
3443</reference>
3444
3445<reference anchor="RFC1900">
3446  <front>
3447    <title>Renumbering Needs Work</title>
3448    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3449      <organization>CERN, Computing and Networks Division</organization>
3450      <address><email>brian@dxcoms.cern.ch</email></address>
3451    </author>
3452    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3453      <organization>cisco Systems</organization>
3454      <address><email>yakov@cisco.com</email></address>
3455    </author>
3456    <date month="February" year="1996"/>
3457  </front>
3458  <seriesInfo name="RFC" value="1900"/>
3459</reference>
3460
3461<reference anchor="RFC1945">
3462  <front>
3463    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3464    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3465      <organization>MIT, Laboratory for Computer Science</organization>
3466      <address><email>timbl@w3.org</email></address>
3467    </author>
3468    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3469      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3470      <address><email>fielding@ics.uci.edu</email></address>
3471    </author>
3472    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3473      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3474      <address><email>frystyk@w3.org</email></address>
3475    </author>
3476    <date month="May" year="1996"/>
3477  </front>
3478  <seriesInfo name="RFC" value="1945"/>
3479</reference>
3480
3481<reference anchor="RFC2068">
3482  <front>
3483    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3484    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3485      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3486      <address><email>fielding@ics.uci.edu</email></address>
3487    </author>
3488    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3489      <organization>MIT Laboratory for Computer Science</organization>
3490      <address><email>jg@w3.org</email></address>
3491    </author>
3492    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3493      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3494      <address><email>mogul@wrl.dec.com</email></address>
3495    </author>
3496    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3497      <organization>MIT Laboratory for Computer Science</organization>
3498      <address><email>frystyk@w3.org</email></address>
3499    </author>
3500    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3501      <organization>MIT Laboratory for Computer Science</organization>
3502      <address><email>timbl@w3.org</email></address>
3503    </author>
3504    <date month="January" year="1997"/>
3505  </front>
3506  <seriesInfo name="RFC" value="2068"/>
3507</reference>
3508
3509<reference anchor='RFC2109'>
3510  <front>
3511    <title>HTTP State Management Mechanism</title>
3512    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3513      <organization>Bell Laboratories, Lucent Technologies</organization>
3514      <address><email>dmk@bell-labs.com</email></address>
3515    </author>
3516    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3517      <organization>Netscape Communications Corp.</organization>
3518      <address><email>montulli@netscape.com</email></address>
3519    </author>
3520    <date year='1997' month='February' />
3521  </front>
3522  <seriesInfo name='RFC' value='2109' />
3523</reference>
3524
3525<reference anchor="RFC2145">
3526  <front>
3527    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3528    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3529      <organization>Western Research Laboratory</organization>
3530      <address><email>mogul@wrl.dec.com</email></address>
3531    </author>
3532    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3533      <organization>Department of Information and Computer Science</organization>
3534      <address><email>fielding@ics.uci.edu</email></address>
3535    </author>
3536    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3537      <organization>MIT Laboratory for Computer Science</organization>
3538      <address><email>jg@w3.org</email></address>
3539    </author>
3540    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3541      <organization>W3 Consortium</organization>
3542      <address><email>frystyk@w3.org</email></address>
3543    </author>
3544    <date month="May" year="1997"/>
3545  </front>
3546  <seriesInfo name="RFC" value="2145"/>
3547</reference>
3548
3549<reference anchor="RFC2616">
3550  <front>
3551    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3552    <author initials="R." surname="Fielding" fullname="R. Fielding">
3553      <organization>University of California, Irvine</organization>
3554      <address><email>fielding@ics.uci.edu</email></address>
3555    </author>
3556    <author initials="J." surname="Gettys" fullname="J. Gettys">
3557      <organization>W3C</organization>
3558      <address><email>jg@w3.org</email></address>
3559    </author>
3560    <author initials="J." surname="Mogul" fullname="J. Mogul">
3561      <organization>Compaq Computer Corporation</organization>
3562      <address><email>mogul@wrl.dec.com</email></address>
3563    </author>
3564    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3565      <organization>MIT Laboratory for Computer Science</organization>
3566      <address><email>frystyk@w3.org</email></address>
3567    </author>
3568    <author initials="L." surname="Masinter" fullname="L. Masinter">
3569      <organization>Xerox Corporation</organization>
3570      <address><email>masinter@parc.xerox.com</email></address>
3571    </author>
3572    <author initials="P." surname="Leach" fullname="P. Leach">
3573      <organization>Microsoft Corporation</organization>
3574      <address><email>paulle@microsoft.com</email></address>
3575    </author>
3576    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3577      <organization>W3C</organization>
3578      <address><email>timbl@w3.org</email></address>
3579    </author>
3580    <date month="June" year="1999"/>
3581  </front>
3582  <seriesInfo name="RFC" value="2616"/>
3583</reference>
3584
3585<reference anchor='RFC2818'>
3586  <front>
3587    <title>HTTP Over TLS</title>
3588    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3589      <organization>RTFM, Inc.</organization>
3590      <address><email>ekr@rtfm.com</email></address>
3591    </author>
3592    <date year='2000' month='May' />
3593  </front>
3594  <seriesInfo name='RFC' value='2818' />
3595</reference>
3596
3597<reference anchor='RFC2965'>
3598  <front>
3599    <title>HTTP State Management Mechanism</title>
3600    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3601      <organization>Bell Laboratories, Lucent Technologies</organization>
3602      <address><email>dmk@bell-labs.com</email></address>
3603    </author>
3604    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3605      <organization>Epinions.com, Inc.</organization>
3606      <address><email>lou@montulli.org</email></address>
3607    </author>
3608    <date year='2000' month='October' />
3609  </front>
3610  <seriesInfo name='RFC' value='2965' />
3611</reference>
3612
3613<reference anchor='RFC3864'>
3614  <front>
3615    <title>Registration Procedures for Message Header Fields</title>
3616    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3617      <organization>Nine by Nine</organization>
3618      <address><email>GK-IETF@ninebynine.org</email></address>
3619    </author>
3620    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3621      <organization>BEA Systems</organization>
3622      <address><email>mnot@pobox.com</email></address>
3623    </author>
3624    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3625      <organization>HP Labs</organization>
3626      <address><email>JeffMogul@acm.org</email></address>
3627    </author>
3628    <date year='2004' month='September' />
3629  </front>
3630  <seriesInfo name='BCP' value='90' />
3631  <seriesInfo name='RFC' value='3864' />
3632</reference>
3633
3634<reference anchor='RFC3977'>
3635  <front>
3636    <title>Network News Transfer Protocol (NNTP)</title>
3637    <author initials='C.' surname='Feather' fullname='C. Feather'>
3638      <organization>THUS plc</organization>
3639      <address><email>clive@demon.net</email></address>
3640    </author>
3641    <date year='2006' month='October' />
3642  </front>
3643  <seriesInfo name="RFC" value="3977"/>
3644</reference>
3645
3646<reference anchor="RFC4288">
3647  <front>
3648    <title>Media Type Specifications and Registration Procedures</title>
3649    <author initials="N." surname="Freed" fullname="N. Freed">
3650      <organization>Sun Microsystems</organization>
3651      <address>
3652        <email>ned.freed@mrochek.com</email>
3653      </address>
3654    </author>
3655    <author initials="J." surname="Klensin" fullname="J. Klensin">
3656      <organization/>
3657      <address>
3658        <email>klensin+ietf@jck.com</email>
3659      </address>
3660    </author>
3661    <date year="2005" month="December"/>
3662  </front>
3663  <seriesInfo name="BCP" value="13"/>
3664  <seriesInfo name="RFC" value="4288"/>
3665</reference>
3666
3667<reference anchor='RFC4395'>
3668  <front>
3669    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3670    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3671      <organization>AT&amp;T Laboratories</organization>
3672      <address>
3673        <email>tony+urireg@maillennium.att.com</email>
3674      </address>
3675    </author>
3676    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3677      <organization>Qualcomm, Inc.</organization>
3678      <address>
3679        <email>hardie@qualcomm.com</email>
3680      </address>
3681    </author>
3682    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3683      <organization>Adobe Systems</organization>
3684      <address>
3685        <email>LMM@acm.org</email>
3686      </address>
3687    </author>
3688    <date year='2006' month='February' />
3689  </front>
3690  <seriesInfo name='BCP' value='115' />
3691  <seriesInfo name='RFC' value='4395' />
3692</reference>
3693
3694<reference anchor="RFC5322">
3695  <front>
3696    <title>Internet Message Format</title>
3697    <author initials="P." surname="Resnick" fullname="P. Resnick">
3698      <organization>Qualcomm Incorporated</organization>
3699    </author>
3700    <date year="2008" month="October"/>
3701  </front> 
3702  <seriesInfo name="RFC" value="5322"/>
3703</reference>
3704
3705<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3706  <front>
3707    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3708    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3709      <organization/>
3710    </author>
3711    <date year="2001" month="November"/>
3712  </front>
3713  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3714</reference>
3715
3716<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3717  <front>
3718  <title>Analysis of HTTP Performance Problems</title>
3719  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3720    <organization/>
3721  </author>
3722  <date/>
3723  </front>
3724</reference>
3725
3726<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3727  <front>
3728  <title>Analysis of HTTP Performance</title>
3729  <author initials="J." surname="Touch" fullname="Joe Touch">
3730    <organization>USC/Information Sciences Institute</organization>
3731    <address><email>touch@isi.edu</email></address>
3732  </author>
3733  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3734    <organization>USC/Information Sciences Institute</organization>
3735    <address><email>johnh@isi.edu</email></address>
3736  </author>
3737  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3738    <organization>USC/Information Sciences Institute</organization>
3739    <address><email>katia@isi.edu</email></address>
3740  </author>
3741  <date year="1998" month="Aug"/>
3742  </front>
3743  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3744  <annotation>(original report dated Aug. 1996)</annotation>
3745</reference>
3746
3747<reference anchor="WAIS">
3748  <front>
3749    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3750    <author initials="F." surname="Davis" fullname="F. Davis">
3751      <organization>Thinking Machines Corporation</organization>
3752    </author>
3753    <author initials="B." surname="Kahle" fullname="B. Kahle">
3754      <organization>Thinking Machines Corporation</organization>
3755    </author>
3756    <author initials="H." surname="Morris" fullname="H. Morris">
3757      <organization>Thinking Machines Corporation</organization>
3758    </author>
3759    <author initials="J." surname="Salem" fullname="J. Salem">
3760      <organization>Thinking Machines Corporation</organization>
3761    </author>
3762    <author initials="T." surname="Shen" fullname="T. Shen">
3763      <organization>Thinking Machines Corporation</organization>
3764    </author>
3765    <author initials="R." surname="Wang" fullname="R. Wang">
3766      <organization>Thinking Machines Corporation</organization>
3767    </author>
3768    <author initials="J." surname="Sui" fullname="J. Sui">
3769      <organization>Thinking Machines Corporation</organization>
3770    </author>
3771    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3772      <organization>Thinking Machines Corporation</organization>
3773    </author>
3774    <date month="April" year="1990"/>
3775  </front>
3776  <seriesInfo name="Thinking Machines Corporation" value=""/>
3777</reference>
3778
3779</references>
3780
3781
3782<section title="Tolerant Applications" anchor="tolerant.applications">
3783<t>
3784   Although this document specifies the requirements for the generation
3785   of HTTP/1.1 messages, not all applications will be correct in their
3786   implementation. We therefore recommend that operational applications
3787   be tolerant of deviations whenever those deviations can be
3788   interpreted unambiguously.
3789</t>
3790<t>
3791   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3792   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3793   accept any amount of SP or HTAB characters between fields, even though
3794   only a single SP is required.
3795</t>
3796<t>
3797   The line terminator for message-header fields is the sequence CRLF.
3798   However, we recommend that applications, when parsing such headers,
3799   recognize a single LF as a line terminator and ignore the leading CR.
3800</t>
3801<t>
3802   The character set of an entity-body &SHOULD; be labeled as the lowest
3803   common denominator of the character codes used within that body, with
3804   the exception that not labeling the entity is preferred over labeling
3805   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3806</t>
3807<t>
3808   Additional rules for requirements on parsing and encoding of dates
3809   and other potential problems with date encodings include:
3810</t>
3811<t>
3812  <list style="symbols">
3813     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3814        which appears to be more than 50 years in the future is in fact
3815        in the past (this helps solve the "year 2000" problem).</t>
3816
3817     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3818        Expires date as earlier than the proper value, but &MUST-NOT;
3819        internally represent a parsed Expires date as later than the
3820        proper value.</t>
3821
3822     <t>All expiration-related calculations &MUST; be done in GMT. The
3823        local time zone &MUST-NOT; influence the calculation or comparison
3824        of an age or expiration time.</t>
3825
3826     <t>If an HTTP header incorrectly carries a date value with a time
3827        zone other than GMT, it &MUST; be converted into GMT using the
3828        most conservative possible conversion.</t>
3829  </list>
3830</t>
3831</section>
3832
3833<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3834<t>
3835   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3836   simplify the process of date comparison. Proxies and gateways from
3837   other protocols &SHOULD; ensure that any Date header field present in a
3838   message conforms to one of the HTTP/1.1 formats and rewrite the date
3839   if necessary.
3840</t>
3841</section>
3842
3843<section title="Compatibility with Previous Versions" anchor="compatibility">
3844<t>
3845   HTTP has been in use by the World-Wide Web global information initiative
3846   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3847   was a simple protocol for hypertext data transfer across the Internet
3848   with only a single method and no metadata.
3849   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3850   methods and MIME-like messaging that could include metadata about the data
3851   transferred and modifiers on the request/response semantics. However,
3852   HTTP/1.0 did not sufficiently take into consideration the effects of
3853   hierarchical proxies, caching, the need for persistent connections, or
3854   name-based virtual hosts. The proliferation of incompletely-implemented
3855   applications calling themselves "HTTP/1.0" further necessitated a
3856   protocol version change in order for two communicating applications
3857   to determine each other's true capabilities.
3858</t>
3859<t>
3860   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3861   requirements that enable reliable implementations, adding only
3862   those new features that will either be safely ignored by an HTTP/1.0
3863   recipient or only sent when communicating with a party advertising
3864   compliance with HTTP/1.1.
3865</t>
3866<t>
3867   It is beyond the scope of a protocol specification to mandate
3868   compliance with previous versions. HTTP/1.1 was deliberately
3869   designed, however, to make supporting previous versions easy. It is
3870   worth noting that, at the time of composing this specification
3871   (1996), we would expect commercial HTTP/1.1 servers to:
3872  <list style="symbols">
3873     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3874        1.1 requests;</t>
3875
3876     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3877        1.1;</t>
3878
3879     <t>respond appropriately with a message in the same major version
3880        used by the client.</t>
3881  </list>
3882</t>
3883<t>
3884   And we would expect HTTP/1.1 clients to:
3885  <list style="symbols">
3886     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3887        responses;</t>
3888
3889     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3890        1.1.</t>
3891  </list>
3892</t>
3893<t>
3894   For most implementations of HTTP/1.0, each connection is established
3895   by the client prior to the request and closed by the server after
3896   sending the response. Some implementations implement the Keep-Alive
3897   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3898</t>
3899
3900<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3901<t>
3902   This section summarizes major differences between versions HTTP/1.0
3903   and HTTP/1.1.
3904</t>
3905
3906<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">
3907<t>
3908   The requirements that clients and servers support the Host request-header,
3909   report an error if the Host request-header (<xref target="header.host"/>) is
3910   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3911   are among the most important changes defined by this
3912   specification.
3913</t>
3914<t>
3915   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3916   addresses and servers; there was no other established mechanism for
3917   distinguishing the intended server of a request than the IP address
3918   to which that request was directed. The changes outlined above will
3919   allow the Internet, once older HTTP clients are no longer common, to
3920   support multiple Web sites from a single IP address, greatly
3921   simplifying large operational Web servers, where allocation of many
3922   IP addresses to a single host has created serious problems. The
3923   Internet will also be able to recover the IP addresses that have been
3924   allocated for the sole purpose of allowing special-purpose domain
3925   names to be used in root-level HTTP URLs. Given the rate of growth of
3926   the Web, and the number of servers already deployed, it is extremely
3927   important that all implementations of HTTP (including updates to
3928   existing HTTP/1.0 applications) correctly implement these
3929   requirements:
3930  <list style="symbols">
3931     <t>Both clients and servers &MUST; support the Host request-header.</t>
3932
3933     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3934
3935     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3936        request does not include a Host request-header.</t>
3937
3938     <t>Servers &MUST; accept absolute URIs.</t>
3939  </list>
3940</t>
3941</section>
3942</section>
3943
3944<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3945<t>
3946   Some clients and servers might wish to be compatible with some
3947   previous implementations of persistent connections in HTTP/1.0
3948   clients and servers. Persistent connections in HTTP/1.0 are
3949   explicitly negotiated as they are not the default behavior. HTTP/1.0
3950   experimental implementations of persistent connections are faulty,
3951   and the new facilities in HTTP/1.1 are designed to rectify these
3952   problems. The problem was that some existing 1.0 clients may be
3953   sending Keep-Alive to a proxy server that doesn't understand
3954   Connection, which would then erroneously forward it to the next
3955   inbound server, which would establish the Keep-Alive connection and
3956   result in a hung HTTP/1.0 proxy waiting for the close on the
3957   response. The result is that HTTP/1.0 clients must be prevented from
3958   using Keep-Alive when talking to proxies.
3959</t>
3960<t>
3961   However, talking to proxies is the most important use of persistent
3962   connections, so that prohibition is clearly unacceptable. Therefore,
3963   we need some other mechanism for indicating a persistent connection
3964   is desired, which is safe to use even when talking to an old proxy
3965   that ignores Connection. Persistent connections are the default for
3966   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3967   declaring non-persistence. See <xref target="header.connection"/>.
3968</t>
3969<t>
3970   The original HTTP/1.0 form of persistent connections (the Connection:
3971   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3972</t>
3973</section>
3974
3975<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3976<t>
3977   This specification has been carefully audited to correct and
3978   disambiguate key word usage; RFC 2068 had many problems in respect to
3979   the conventions laid out in <xref target="RFC2119"/>.
3980</t>
3981<t>
3982   Transfer-coding and message lengths all interact in ways that
3983   required fixing exactly when chunked encoding is used (to allow for
3984   transfer encoding that may not be self delimiting); it was important
3985   to straighten out exactly how message lengths are computed. (Sections
3986   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3987   <xref target="header.content-length" format="counter"/>,
3988   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3989</t>
3990<t>
3991   The use and interpretation of HTTP version numbers has been clarified
3992   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3993   version they support to deal with problems discovered in HTTP/1.0
3994   implementations (<xref target="http.version"/>)
3995</t>
3996<t>
3997   Transfer-coding had significant problems, particularly with
3998   interactions with chunked encoding. The solution is that transfer-codings
3999   become as full fledged as content-codings. This involves
4000   adding an IANA registry for transfer-codings (separate from content
4001   codings), a new header field (TE) and enabling trailer headers in the
4002   future. Transfer encoding is a major performance benefit, so it was
4003   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4004   interoperability problem that could have occurred due to interactions
4005   between authentication trailers, chunked encoding and HTTP/1.0
4006   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4007   and <xref target="header.te" format="counter"/>)
4008</t>
4009</section>
4010
4011<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4012<t>
4013  Rules about implicit linear white space between certain grammar productions
4014  have been removed; now it's only allowed when specifically pointed out
4015  in the ABNF.
4016  The CHAR rule does not allow the NUL character anymore (this affects
4017  the comment and quoted-string rules).  Furthermore, the quoted-pair
4018  rule does not allow escaping NUL, CR or LF anymore.
4019  (<xref target="basic.rules"/>)
4020</t>
4021<t>
4022  Clarify that HTTP-Version is case sensitive.
4023  (<xref target="http.version"/>)
4024</t>
4025<t>
4026  Remove reference to non-existant identity transfer-coding value tokens.
4027  (Sections <xref format="counter" target="transfer.codings"/> and
4028  <xref format="counter" target="message.length"/>)
4029</t>
4030<t>
4031  Clarification that the chunk length does not include
4032  the count of the octets in the chunk header and trailer.
4033  (<xref target="chunked.transfer.encoding"/>)
4034</t>
4035<t>
4036  Update use of abs_path production from RFC1808 to the path-absolute + query
4037  components of RFC3986.
4038  (<xref target="request-uri"/>)
4039</t>
4040<t>
4041  Clarify exactly when close connection options must be sent.
4042  (<xref target="header.connection"/>)
4043</t>
4044</section>
4045</section>
4046
4047<section title="Terminology" anchor="terminology">
4048<t>
4049   This specification uses a number of terms to refer to the roles
4050   played by participants in, and objects of, the HTTP communication.
4051</t>
4052<t>
4053  <iref item="connection"/>
4054  <x:dfn>connection</x:dfn>
4055  <list>
4056    <t>
4057      A transport layer virtual circuit established between two programs
4058      for the purpose of communication.
4059    </t>
4060  </list>
4061</t>
4062<t>
4063  <iref item="message"/>
4064  <x:dfn>message</x:dfn>
4065  <list>
4066    <t>
4067      The basic unit of HTTP communication, consisting of a structured
4068      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4069      transmitted via the connection.
4070    </t>
4071  </list>
4072</t>
4073<t>
4074  <iref item="request"/>
4075  <x:dfn>request</x:dfn>
4076  <list>
4077    <t>
4078      An HTTP request message, as defined in <xref target="request"/>.
4079    </t>
4080  </list>
4081</t>
4082<t>
4083  <iref item="response"/>
4084  <x:dfn>response</x:dfn>
4085  <list>
4086    <t>
4087      An HTTP response message, as defined in <xref target="response"/>.
4088    </t>
4089  </list>
4090</t>
4091<t>
4092  <iref item="resource"/>
4093  <x:dfn>resource</x:dfn>
4094  <list>
4095    <t>
4096      A network data object or service that can be identified by a URI,
4097      as defined in <xref target="uri"/>. Resources may be available in multiple
4098      representations (e.g. multiple languages, data formats, size, and
4099      resolutions) or vary in other ways.
4100    </t>
4101  </list>
4102</t>
4103<t>
4104  <iref item="entity"/>
4105  <x:dfn>entity</x:dfn>
4106  <list>
4107    <t>
4108      The information transferred as the payload of a request or
4109      response. An entity consists of metainformation in the form of
4110      entity-header fields and content in the form of an entity-body, as
4111      described in &entity;.
4112    </t>
4113  </list>
4114</t>
4115<t>
4116  <iref item="representation"/>
4117  <x:dfn>representation</x:dfn>
4118  <list>
4119    <t>
4120      An entity included with a response that is subject to content
4121      negotiation, as described in &content.negotiation;. There may exist multiple
4122      representations associated with a particular response status.
4123    </t>
4124  </list>
4125</t>
4126<t>
4127  <iref item="content negotiation"/>
4128  <x:dfn>content negotiation</x:dfn>
4129  <list>
4130    <t>
4131      The mechanism for selecting the appropriate representation when
4132      servicing a request, as described in &content.negotiation;. The
4133      representation of entities in any response can be negotiated
4134      (including error responses).
4135    </t>
4136  </list>
4137</t>
4138<t>
4139  <iref item="variant"/>
4140  <x:dfn>variant</x:dfn>
4141  <list>
4142    <t>
4143      A resource may have one, or more than one, representation(s)
4144      associated with it at any given instant. Each of these
4145      representations is termed a `variant'.  Use of the term `variant'
4146      does not necessarily imply that the resource is subject to content
4147      negotiation.
4148    </t>
4149  </list>
4150</t>
4151<t>
4152  <iref item="client"/>
4153  <x:dfn>client</x:dfn>
4154  <list>
4155    <t>
4156      A program that establishes connections for the purpose of sending
4157      requests.
4158    </t>
4159  </list>
4160</t>
4161<t>
4162  <iref item="user agent"/>
4163  <x:dfn>user agent</x:dfn>
4164  <list>
4165    <t>
4166      The client which initiates a request. These are often browsers,
4167      editors, spiders (web-traversing robots), or other end user tools.
4168    </t>
4169  </list>
4170</t>
4171<t>
4172  <iref item="server"/>
4173  <x:dfn>server</x:dfn>
4174  <list>
4175    <t>
4176      An application program that accepts connections in order to
4177      service requests by sending back responses. Any given program may
4178      be capable of being both a client and a server; our use of these
4179      terms refers only to the role being performed by the program for a
4180      particular connection, rather than to the program's capabilities
4181      in general. Likewise, any server may act as an origin server,
4182      proxy, gateway, or tunnel, switching behavior based on the nature
4183      of each request.
4184    </t>
4185  </list>
4186</t>
4187<t>
4188  <iref item="origin server"/>
4189  <x:dfn>origin server</x:dfn>
4190  <list>
4191    <t>
4192      The server on which a given resource resides or is to be created.
4193    </t>
4194  </list>
4195</t>
4196<t>
4197  <iref item="proxy"/>
4198  <x:dfn>proxy</x:dfn>
4199  <list>
4200    <t>
4201      An intermediary program which acts as both a server and a client
4202      for the purpose of making requests on behalf of other clients.
4203      Requests are serviced internally or by passing them on, with
4204      possible translation, to other servers. A proxy &MUST; implement
4205      both the client and server requirements of this specification. A
4206      "transparent proxy" is a proxy that does not modify the request or
4207      response beyond what is required for proxy authentication and
4208      identification. A "non-transparent proxy" is a proxy that modifies
4209      the request or response in order to provide some added service to
4210      the user agent, such as group annotation services, media type
4211      transformation, protocol reduction, or anonymity filtering. Except
4212      where either transparent or non-transparent behavior is explicitly
4213      stated, the HTTP proxy requirements apply to both types of
4214      proxies.
4215    </t>
4216  </list>
4217</t>
4218<t>
4219  <iref item="gateway"/>
4220  <x:dfn>gateway</x:dfn>
4221  <list>
4222    <t>
4223      A server which acts as an intermediary for some other server.
4224      Unlike a proxy, a gateway receives requests as if it were the
4225      origin server for the requested resource; the requesting client
4226      may not be aware that it is communicating with a gateway.
4227    </t>
4228  </list>
4229</t>
4230<t>
4231  <iref item="tunnel"/>
4232  <x:dfn>tunnel</x:dfn>
4233  <list>
4234    <t>
4235      An intermediary program which is acting as a blind relay between
4236      two connections. Once active, a tunnel is not considered a party
4237      to the HTTP communication, though the tunnel may have been
4238      initiated by an HTTP request. The tunnel ceases to exist when both
4239      ends of the relayed connections are closed.
4240    </t>
4241  </list>
4242</t>
4243<t>
4244  <iref item="cache"/>
4245  <x:dfn>cache</x:dfn>
4246  <list>
4247    <t>
4248      A program's local store of response messages and the subsystem
4249      that controls its message storage, retrieval, and deletion. A
4250      cache stores cacheable responses in order to reduce the response
4251      time and network bandwidth consumption on future, equivalent
4252      requests. Any client or server may include a cache, though a cache
4253      cannot be used by a server that is acting as a tunnel.
4254    </t>
4255  </list>
4256</t>
4257<t>
4258  <iref item="cacheable"/>
4259  <x:dfn>cacheable</x:dfn>
4260  <list>
4261    <t>
4262      A response is cacheable if a cache is allowed to store a copy of
4263      the response message for use in answering subsequent requests. The
4264      rules for determining the cacheability of HTTP responses are
4265      defined in &caching;. Even if a resource is cacheable, there may
4266      be additional constraints on whether a cache can use the cached
4267      copy for a particular request.
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  <iref item="upstream"/>
4273  <iref item="downstream"/>
4274  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4275  <list>
4276    <t>
4277      Upstream and downstream describe the flow of a message: all
4278      messages flow from upstream to downstream.
4279    </t>
4280  </list>
4281</t>
4282<t>
4283  <iref item="inbound"/>
4284  <iref item="outbound"/>
4285  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4286  <list>
4287    <t>
4288      Inbound and outbound refer to the request and response paths for
4289      messages: "inbound" means "traveling toward the origin server",
4290      and "outbound" means "traveling toward the user agent"
4291    </t>
4292  </list>
4293</t>
4294</section>
4295
4296<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4297
4298<section title="Since RFC2616">
4299<t>
4300  Extracted relevant partitions from <xref target="RFC2616"/>.
4301</t>
4302</section>
4303
4304<section title="Since draft-ietf-httpbis-p1-messaging-00">
4305<t>
4306  Closed issues:
4307  <list style="symbols"> 
4308    <t>
4309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4310      "HTTP Version should be case sensitive"
4311      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4312    </t>
4313    <t>
4314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4315      "'unsafe' characters"
4316      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4317    </t>
4318    <t>
4319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4320      "Chunk Size Definition"
4321      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4322    </t>
4323    <t>
4324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4325      "Message Length"
4326      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4327    </t>
4328    <t>
4329      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4330      "Media Type Registrations"
4331      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4332    </t>
4333    <t>
4334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4335      "URI includes query"
4336      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4337    </t>
4338    <t>
4339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4340      "No close on 1xx responses"
4341      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4342    </t>
4343    <t>
4344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4345      "Remove 'identity' token references"
4346      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4347    </t>
4348    <t>
4349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4350      "Import query BNF"
4351    </t>
4352    <t>
4353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4354      "qdtext BNF"
4355    </t>
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4358      "Normative and Informative references"
4359    </t>
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4362      "RFC2606 Compliance"
4363    </t>
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4366      "RFC977 reference"
4367    </t>
4368    <t>
4369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4370      "RFC1700 references"
4371    </t>
4372    <t>
4373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4374      "inconsistency in date format explanation"
4375    </t>
4376    <t>
4377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4378      "Date reference typo"
4379    </t>
4380    <t>
4381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4382      "Informative references"
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4386      "ISO-8859-1 Reference"
4387    </t>
4388    <t>
4389      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4390      "Normative up-to-date references"
4391    </t>
4392  </list>
4393</t>
4394<t>
4395  Other changes:
4396  <list style="symbols"> 
4397    <t>
4398      Update media type registrations to use RFC4288 template.
4399    </t>
4400    <t>
4401      Use names of RFC4234 core rules DQUOTE and HTAB,
4402      fix broken ABNF for chunk-data
4403      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4404    </t>
4405  </list>
4406</t>
4407</section>
4408
4409<section title="Since draft-ietf-httpbis-p1-messaging-01">
4410<t>
4411  Closed issues:
4412  <list style="symbols"> 
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4415      "Bodies on GET (and other) requests"
4416    </t>
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4419      "Updating to RFC4288"
4420    </t>
4421    <t>
4422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4423      "Status Code and Reason Phrase"
4424    </t>
4425    <t>
4426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4427      "rel_path not used"
4428    </t>
4429  </list>
4430</t>
4431<t>
4432  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4433  <list style="symbols"> 
4434    <t>
4435      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4436      "trailer-part").
4437    </t>
4438    <t>
4439      Avoid underscore character in rule names ("http_URL" ->
4440      "http-URL", "abs_path" -> "path-absolute").
4441    </t>
4442    <t>
4443      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4444      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4445      have to be updated when switching over to RFC3986.
4446    </t>
4447    <t>
4448      Synchronize core rules with RFC5234 (this includes a change to CHAR
4449      which now excludes NUL).
4450    </t>
4451    <t>
4452      Get rid of prose rules that span multiple lines.
4453    </t>
4454    <t>
4455      Get rid of unused rules LOALPHA and UPALPHA.
4456    </t>
4457    <t>
4458      Move "Product Tokens" section (back) into Part 1, as "token" is used
4459      in the definition of the Upgrade header.
4460    </t>
4461    <t>
4462      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4463    </t>
4464    <t>
4465      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4466    </t>
4467  </list>
4468</t>
4469</section>
4470
4471<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4472<t>
4473  Closed issues:
4474  <list style="symbols"> 
4475    <t>
4476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4477      "HTTP-date vs. rfc1123-date"
4478    </t>
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4481      "WS in quoted-pair"
4482    </t>
4483  </list>
4484</t>
4485<t>
4486  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4487  <list style="symbols"> 
4488    <t>
4489      Reference RFC 3984, and update header registrations for headers defined
4490      in this document.
4491    </t>
4492  </list>
4493</t>
4494<t>
4495  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4496  <list style="symbols"> 
4497    <t>
4498      Replace string literals when the string really is case-sensitive (HTTP-Version).
4499    </t>
4500  </list>
4501</t>
4502</section>
4503
4504<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4505<t>
4506  Closed issues:
4507  <list style="symbols"> 
4508    <t>
4509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4510      "Connection closing"
4511    </t>
4512    <t>
4513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4514      "Move registrations and registry information to IANA Considerations"
4515    </t>
4516    <t>
4517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4518      "need new URL for PAD1995 reference"
4519    </t>
4520    <t>
4521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4522      "IANA Considerations: update HTTP URI scheme registration"
4523    </t>
4524    <t>
4525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4526      "Cite HTTPS URI scheme definition"
4527    </t>
4528    <t>
4529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4530      "List-type headers vs Set-Cookie"
4531    </t>
4532  </list>
4533</t>
4534<t>
4535  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4536  <list style="symbols"> 
4537    <t>
4538      Replace string literals when the string really is case-sensitive (HTTP-Date).
4539    </t>
4540    <t>
4541      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4542    </t>
4543  </list>
4544</t>
4545</section>
4546
4547<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4548<t>
4549  Closed issues:
4550  <list style="symbols"> 
4551    <t>
4552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4553      "Out-of-date reference for URIs"
4554    </t>
4555    <t>
4556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4557      "RFC 2822 is updated by RFC 5322"
4558    </t>
4559  </list>
4560</t>
4561<t>
4562  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4563  <list style="symbols"> 
4564    <t>
4565      Use "/" instead of "|" for alternatives.
4566    </t>
4567    <t>
4568      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4569    </t>
4570    <t>
4571      Only reference RFC 5234's core rules.
4572    </t>
4573    <t>
4574      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4575      whitespace ("OWS") and required whitespace ("RWS").
4576    </t>
4577    <t>
4578      Rewrite ABNFs to spell out whitespace rules, factor out
4579      header value format definitions.
4580    </t>
4581  </list>
4582</t>
4583</section>
4584
4585</section>
4586
4587</back>
4588</rfc>
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