source: draft-ietf-httpbis/latest/p1-messaging.xml @ 376

Last change on this file since 376 was 376, checked in by julian.reschke@…, 11 years ago

fix width problems in ABNF (related to #36)

  • Property svn:eol-style set to native
File size: 197.5 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   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>
997                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
998  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
999  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1000  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1001  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1002</artwork></figure>
1003<t>
1004   The chunk-size field is a string of hex digits indicating the size of
1005   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1006   zero, followed by the trailer, which is terminated by an empty line.
1007</t>
1008<t>
1009   The trailer allows the sender to include additional HTTP header
1010   fields at the end of the message. The Trailer header field can be
1011   used to indicate which header fields are included in a trailer (see
1012   <xref target="header.trailer"/>).
1013</t>
1014<t>
1015   A server using chunked transfer-coding in a response &MUST-NOT; use the
1016   trailer for any header fields unless at least one of the following is
1017   true:
1018  <list style="numbers">
1019    <t>the request included a TE header field that indicates "trailers" is
1020     acceptable in the transfer-coding of the  response, as described in
1021     <xref target="header.te"/>; or,</t>
1022
1023    <t>the server is the origin server for the response, the trailer
1024     fields consist entirely of optional metadata, and the recipient
1025     could use the message (in a manner acceptable to the origin server)
1026     without receiving this metadata.  In other words, the origin server
1027     is willing to accept the possibility that the trailer fields might
1028     be silently discarded along the path to the client.</t>
1029  </list>
1030</t>
1031<t>
1032   This requirement prevents an interoperability failure when the
1033   message is being received by an HTTP/1.1 (or later) proxy and
1034   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1035   compliance with the protocol would have necessitated a possibly
1036   infinite buffer on the proxy.
1037</t>
1038<t>
1039   A process for decoding the "chunked" transfer-coding
1040   can be represented in pseudo-code as:
1041</t>
1042<figure><artwork type="code">
1043  length := 0
1044  read chunk-size, chunk-ext (if any) and CRLF
1045  while (chunk-size &gt; 0) {
1046     read chunk-data and CRLF
1047     append chunk-data to entity-body
1048     length := length + chunk-size
1049     read chunk-size and CRLF
1050  }
1051  read entity-header
1052  while (entity-header not empty) {
1053     append entity-header to existing header fields
1054     read entity-header
1055  }
1056  Content-Length := length
1057  Remove "chunked" from Transfer-Encoding
1058</artwork></figure>
1059<t>
1060   All HTTP/1.1 applications &MUST; be able to receive and decode the
1061   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1062   they do not understand.
1063</t>
1064</section>
1065</section>
1066
1067<section title="Product Tokens" anchor="product.tokens">
1068  <x:anchor-alias value="product"/>
1069  <x:anchor-alias value="product-version"/>
1070<t>
1071   Product tokens are used to allow communicating applications to
1072   identify themselves by software name and version. Most fields using
1073   product tokens also allow sub-products which form a significant part
1074   of the application to be listed, separated by white space. By
1075   convention, the products are listed in order of their significance
1076   for identifying the application.
1077</t>
1078<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1079  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1080  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1081</artwork></figure>
1082<t>
1083   Examples:
1084</t>
1085<figure><artwork type="example">
1086    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1087    Server: Apache/0.8.4
1088</artwork></figure>
1089<t>
1090   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1091   used for advertising or other non-essential information. Although any
1092   token character &MAY; appear in a product-version, this token &SHOULD;
1093   only be used for a version identifier (i.e., successive versions of
1094   the same product &SHOULD; only differ in the product-version portion of
1095   the product value).
1096</t>
1097</section>
1098
1099</section>
1100
1101<section title="HTTP Message" anchor="http.message">
1102
1103<section title="Message Types" anchor="message.types">
1104  <x:anchor-alias value="generic-message"/>
1105  <x:anchor-alias value="HTTP-message"/>
1106  <x:anchor-alias value="start-line"/>
1107<t>
1108   HTTP messages consist of requests from client to server and responses
1109   from server to client.
1110</t>
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1112  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1113</artwork></figure>
1114<t>
1115   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1116   message format of <xref target="RFC5322"/> for transferring entities (the payload
1117   of the message). Both types of message consist of a start-line, zero
1118   or more header fields (also known as "headers"), an empty line (i.e.,
1119   a line with nothing preceding the CRLF) indicating the end of the
1120   header fields, and possibly a message-body.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1123  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1124                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1125                    <x:ref>CRLF</x:ref>
1126                    [ <x:ref>message-body</x:ref> ]
1127  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1128</artwork></figure>
1129<t>
1130   In the interest of robustness, servers &SHOULD; ignore any empty
1131   line(s) received where a Request-Line is expected. In other words, if
1132   the server is reading the protocol stream at the beginning of a
1133   message and receives a CRLF first, it should ignore the CRLF.
1134</t>
1135<t>
1136   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1137   after a POST request. To restate what is explicitly forbidden by the
1138   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1139   extra CRLF.
1140</t>
1141</section>
1142
1143<section title="Message Headers" anchor="message.headers">
1144  <x:anchor-alias value="field-content"/>
1145  <x:anchor-alias value="field-name"/>
1146  <x:anchor-alias value="field-value"/>
1147  <x:anchor-alias value="message-header"/>
1148<t>
1149   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1150   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1151   entity-header (&entity-header-fields;) fields, follow the same generic format as
1152   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1153   of a name followed by a colon (":") and the field value. Field names
1154   are case-insensitive. The field value &MAY; be preceded by any amount
1155   of LWS, though a single SP is preferred. Header fields can be
1156   extended over multiple lines by preceding each extra line with at
1157   least one SP or HTAB. Applications ought to follow "common form", where
1158   one is known or indicated, when generating HTTP constructs, since
1159   there might exist some implementations that fail to accept anything
1160   beyond the common forms.
1161</t>
1162<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"/>
1163  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1164  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1165  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1166  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1167</artwork></figure>
1168<t>
1169  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1170</t>
1171<t>
1172   The field-content does not include any leading or trailing LWS:
1173   linear white space occurring before the first non-whitespace
1174   character of the field-value or after the last non-whitespace
1175   character of the field-value. Such leading or trailing LWS &MAY; be
1176   removed without changing the semantics of the field value. Any LWS
1177   that occurs between field-content &MAY; be replaced with a single SP
1178   before interpreting the field value or forwarding the message
1179   downstream.
1180</t>
1181<t>
1182   The order in which header fields with differing field names are
1183   received is not significant. However, it is "good practice" to send
1184   general-header fields first, followed by request-header or response-header
1185   fields, and ending with the entity-header fields.
1186</t>
1187<t>
1188   Multiple message-header fields with the same field-name &MAY; be
1189   present in a message if and only if the entire field-value for that
1190   header field is defined as a comma-separated list [i.e., #(values)].
1191   It &MUST; be possible to combine the multiple header fields into one
1192   "field-name: field-value" pair, without changing the semantics of the
1193   message, by appending each subsequent field-value to the first, each
1194   separated by a comma. The order in which header fields with the same
1195   field-name are received is therefore significant to the
1196   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1197   change the order of these field values when a message is forwarded.
1198</t>
1199<t>
1200  <list><t>
1201   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1202   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1203   can occur multiple times, but does not use the list syntax, and thus cannot
1204   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1205   for details.) Also note that the Set-Cookie2 header specified in
1206   <xref target="RFC2965"/> does not share this problem.
1207  </t></list>
1208</t>
1209 
1210</section>
1211
1212<section title="Message Body" anchor="message.body">
1213  <x:anchor-alias value="message-body"/>
1214<t>
1215   The message-body (if any) of an HTTP message is used to carry the
1216   entity-body associated with the request or response. The message-body
1217   differs from the entity-body only when a transfer-coding has been
1218   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1219</t>
1220<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1221  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1222               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1223</artwork></figure>
1224<t>
1225   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1226   applied by an application to ensure safe and proper transfer of the
1227   message. Transfer-Encoding is a property of the message, not of the
1228   entity, and thus &MAY; be added or removed by any application along the
1229   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1230   when certain transfer-codings may be used.)
1231</t>
1232<t>
1233   The rules for when a message-body is allowed in a message differ for
1234   requests and responses.
1235</t>
1236<t>
1237   The presence of a message-body in a request is signaled by the
1238   inclusion of a Content-Length or Transfer-Encoding header field in
1239   the request's message-headers. A message-body &MUST-NOT; be included in
1240   a request if the specification of the request method (&method;)
1241   explicitly disallows an entity-body in requests.
1242   When a request message contains both a message-body of non-zero
1243   length and a method that does not define any semantics for that
1244   request message-body, then an origin server &SHOULD; either ignore
1245   the message-body or respond with an appropriate error message
1246   (e.g., 413).  A proxy or gateway, when presented the same request,
1247   &SHOULD; either forward the request inbound with the message-body or
1248   ignore the message-body when determining a response.
1249</t>
1250<t>
1251   For response messages, whether or not a message-body is included with
1252   a message is dependent on both the request method and the response
1253   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1254   &MUST-NOT; include a message-body, even though the presence of entity-header
1255   fields might lead one to believe they do. All 1xx
1256   (informational), 204 (No Content), and 304 (Not Modified) responses
1257   &MUST-NOT; include a message-body. All other responses do include a
1258   message-body, although it &MAY; be of zero length.
1259</t>
1260</section>
1261
1262<section title="Message Length" anchor="message.length">
1263<t>
1264   The transfer-length of a message is the length of the message-body as
1265   it appears in the message; that is, after any transfer-codings have
1266   been applied. When a message-body is included with a message, the
1267   transfer-length of that body is determined by one of the following
1268   (in order of precedence):
1269</t>
1270<t>
1271  <list style="numbers">
1272    <x:lt><t>
1273     Any response message which "&MUST-NOT;" include a message-body (such
1274     as the 1xx, 204, and 304 responses and any response to a HEAD
1275     request) is always terminated by the first empty line after the
1276     header fields, regardless of the entity-header fields present in
1277     the message.
1278    </t></x:lt>
1279    <x:lt><t>
1280     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1281     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1282     is used, the transfer-length is defined by the use of this transfer-coding.
1283     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1284     is not present, the transfer-length is defined by the sender closing the connection.
1285    </t></x:lt>
1286    <x:lt><t>
1287     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1288     decimal value in OCTETs represents both the entity-length and the
1289     transfer-length. The Content-Length header field &MUST-NOT; be sent
1290     if these two lengths are different (i.e., if a Transfer-Encoding
1291     header field is present). If a message is received with both a
1292     Transfer-Encoding header field and a Content-Length header field,
1293     the latter &MUST; be ignored.
1294    </t></x:lt>
1295    <x:lt><t>
1296     If the message uses the media type "multipart/byteranges", and the
1297     transfer-length is not otherwise specified, then this self-delimiting
1298     media type defines the transfer-length. This media type
1299     &MUST-NOT; be used unless the sender knows that the recipient can parse
1300     it; the presence in a request of a Range header with multiple byte-range
1301     specifiers from a 1.1 client implies that the client can parse
1302     multipart/byteranges responses.
1303    <list style="empty"><t>
1304       A range header might be forwarded by a 1.0 proxy that does not
1305       understand multipart/byteranges; in this case the server &MUST;
1306       delimit the message using methods defined in items 1, 3 or 5 of
1307       this section.
1308    </t></list>
1309    </t></x:lt>
1310    <x:lt><t>
1311     By the server closing the connection. (Closing the connection
1312     cannot be used to indicate the end of a request body, since that
1313     would leave no possibility for the server to send back a response.)
1314    </t></x:lt>
1315  </list>
1316</t>
1317<t>
1318   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1319   containing a message-body &MUST; include a valid Content-Length header
1320   field unless the server is known to be HTTP/1.1 compliant. If a
1321   request contains a message-body and a Content-Length is not given,
1322   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1323   determine the length of the message, or with 411 (Length Required) if
1324   it wishes to insist on receiving a valid Content-Length.
1325</t>
1326<t>
1327   All HTTP/1.1 applications that receive entities &MUST; accept the
1328   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1329   to be used for messages when the message length cannot be determined
1330   in advance.
1331</t>
1332<t>
1333   Messages &MUST-NOT; include both a Content-Length header field and a
1334   transfer-coding. If the message does include a
1335   transfer-coding, the Content-Length &MUST; be ignored.
1336</t>
1337<t>
1338   When a Content-Length is given in a message where a message-body is
1339   allowed, its field value &MUST; exactly match the number of OCTETs in
1340   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1341   invalid length is received and detected.
1342</t>
1343</section>
1344
1345<section title="General Header Fields" anchor="general.header.fields">
1346  <x:anchor-alias value="general-header"/>
1347<t>
1348   There are a few header fields which have general applicability for
1349   both request and response messages, but which do not apply to the
1350   entity being transferred. These header fields apply only to the
1351   message being transmitted.
1352</t>
1353<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1354  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1355                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1356                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1357                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1358                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1359                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1360                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1361                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1362                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1363</artwork></figure>
1364<t>
1365   General-header field names can be extended reliably only in
1366   combination with a change in the protocol version. However, new or
1367   experimental header fields may be given the semantics of general
1368   header fields if all parties in the communication recognize them to
1369   be general-header fields. Unrecognized header fields are treated as
1370   entity-header fields.
1371</t>
1372</section>
1373</section>
1374
1375<section title="Request" anchor="request">
1376  <x:anchor-alias value="Request"/>
1377<t>
1378   A request message from a client to a server includes, within the
1379   first line of that message, the method to be applied to the resource,
1380   the identifier of the resource, and the protocol version in use.
1381</t>
1382<!--                 Host                      ; should be moved here eventually -->
1383<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1384  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1385                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1386                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1387                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1388                  <x:ref>CRLF</x:ref>
1389                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1390</artwork></figure>
1391
1392<section title="Request-Line" anchor="request-line">
1393  <x:anchor-alias value="Request-Line"/>
1394<t>
1395   The Request-Line begins with a method token, followed by the
1396   Request-URI and the protocol version, and ending with CRLF. The
1397   elements are separated by SP characters. No CR or LF is allowed
1398   except in the final CRLF sequence.
1399</t>
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1401  <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>
1402</artwork></figure>
1403
1404<section title="Method" anchor="method">
1405  <x:anchor-alias value="Method"/>
1406<t>
1407   The Method  token indicates the method to be performed on the
1408   resource identified by the Request-URI. The method is case-sensitive.
1409</t>
1410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1411  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1412</artwork></figure>
1413</section>
1414
1415<section title="Request-URI" anchor="request-uri">
1416  <x:anchor-alias value="Request-URI"/>
1417<t>
1418   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1419   identifies the resource upon which to apply the request.
1420</t>
1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1422  <x:ref>Request-URI</x:ref>    = "*"
1423                 / <x:ref>absolute-URI</x:ref>
1424                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1425                 / <x:ref>authority</x:ref>
1426</artwork></figure>
1427<t>
1428   The four options for Request-URI are dependent on the nature of the
1429   request. The asterisk "*" means that the request does not apply to a
1430   particular resource, but to the server itself, and is only allowed
1431   when the method used does not necessarily apply to a resource. One
1432   example would be
1433</t>
1434<figure><artwork type="example">
1435    OPTIONS * HTTP/1.1
1436</artwork></figure>
1437<t>
1438   The absolute-URI form is &REQUIRED; when the request is being made to a
1439   proxy. The proxy is requested to forward the request or service it
1440   from a valid cache, and return the response. Note that the proxy &MAY;
1441   forward the request on to another proxy or directly to the server
1442   specified by the absolute-URI. In order to avoid request loops, a
1443   proxy &MUST; be able to recognize all of its server names, including
1444   any aliases, local variations, and the numeric IP address. An example
1445   Request-Line would be:
1446</t>
1447<figure><artwork type="example">
1448    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1449</artwork></figure>
1450<t>
1451   To allow for transition to absolute-URIs in all requests in future
1452   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1453   form in requests, even though HTTP/1.1 clients will only generate
1454   them in requests to proxies.
1455</t>
1456<t>
1457   The authority form is only used by the CONNECT method (&CONNECT;).
1458</t>
1459<t>
1460   The most common form of Request-URI is that used to identify a
1461   resource on an origin server or gateway. In this case the absolute
1462   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1463   the Request-URI, and the network location of the URI (authority) &MUST;
1464   be transmitted in a Host header field. For example, a client wishing
1465   to retrieve the resource above directly from the origin server would
1466   create a TCP connection to port 80 of the host "www.example.org" and send
1467   the lines:
1468</t>
1469<figure><artwork type="example">
1470    GET /pub/WWW/TheProject.html HTTP/1.1
1471    Host: www.example.org
1472</artwork></figure>
1473<t>
1474   followed by the remainder of the Request. Note that the absolute path
1475   cannot be empty; if none is present in the original URI, it &MUST; be
1476   given as "/" (the server root).
1477</t>
1478<t>
1479   The Request-URI is transmitted in the format specified in
1480   <xref target="http.uri"/>. If the Request-URI is encoded using the
1481   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1482   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1483   &MUST; decode the Request-URI in order to
1484   properly interpret the request. Servers &SHOULD; respond to invalid
1485   Request-URIs with an appropriate status code.
1486</t>
1487<t>
1488   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1489   received Request-URI when forwarding it to the next inbound server,
1490   except as noted above to replace a null path-absolute with "/".
1491</t>
1492<t>
1493  <list><t>
1494      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1495      meaning of the request when the origin server is improperly using
1496      a non-reserved URI character for a reserved purpose.  Implementors
1497      should be aware that some pre-HTTP/1.1 proxies have been known to
1498      rewrite the Request-URI.
1499  </t></list>
1500</t>
1501</section>
1502</section>
1503
1504<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1505<t>
1506   The exact resource identified by an Internet request is determined by
1507   examining both the Request-URI and the Host header field.
1508</t>
1509<t>
1510   An origin server that does not allow resources to differ by the
1511   requested host &MAY; ignore the Host header field value when
1512   determining the resource identified by an HTTP/1.1 request. (But see
1513   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1514   for other requirements on Host support in HTTP/1.1.)
1515</t>
1516<t>
1517   An origin server that does differentiate resources based on the host
1518   requested (sometimes referred to as virtual hosts or vanity host
1519   names) &MUST; use the following rules for determining the requested
1520   resource on an HTTP/1.1 request:
1521  <list style="numbers">
1522    <t>If Request-URI is an absolute-URI, the host is part of the
1523     Request-URI. Any Host header field value in the request &MUST; be
1524     ignored.</t>
1525    <t>If the Request-URI is not an absolute-URI, and the request includes
1526     a Host header field, the host is determined by the Host header
1527     field value.</t>
1528    <t>If the host as determined by rule 1 or 2 is not a valid host on
1529     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1530  </list>
1531</t>
1532<t>
1533   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1534   attempt to use heuristics (e.g., examination of the URI path for
1535   something unique to a particular host) in order to determine what
1536   exact resource is being requested.
1537</t>
1538</section>
1539
1540</section>
1541
1542
1543<section title="Response" anchor="response">
1544  <x:anchor-alias value="Response"/>
1545<t>
1546   After receiving and interpreting a request message, a server responds
1547   with an HTTP response message.
1548</t>
1549<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1550  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1551                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1552                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1553                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1554                  <x:ref>CRLF</x:ref>
1555                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1556</artwork></figure>
1557
1558<section title="Status-Line" anchor="status-line">
1559  <x:anchor-alias value="Status-Line"/>
1560<t>
1561   The first line of a Response message is the Status-Line, consisting
1562   of the protocol version followed by a numeric status code and its
1563   associated textual phrase, with each element separated by SP
1564   characters. No CR or LF is allowed except in the final CRLF sequence.
1565</t>
1566<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1567  <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>
1568</artwork></figure>
1569
1570<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1571  <x:anchor-alias value="Reason-Phrase"/>
1572  <x:anchor-alias value="Status-Code"/>
1573<t>
1574   The Status-Code element is a 3-digit integer result code of the
1575   attempt to understand and satisfy the request. These codes are fully
1576   defined in &status-codes;.  The Reason Phrase exists for the sole
1577   purpose of providing a textual description associated with the numeric
1578   status code, out of deference to earlier Internet application protocols
1579   that were more frequently used with interactive text clients.
1580   A client &SHOULD; ignore the content of the Reason Phrase.
1581</t>
1582<t>
1583   The first digit of the Status-Code defines the class of response. The
1584   last two digits do not have any categorization role. There are 5
1585   values for the first digit:
1586  <list style="symbols">
1587    <t>
1588      1xx: Informational - Request received, continuing process
1589    </t>
1590    <t>
1591      2xx: Success - The action was successfully received,
1592        understood, and accepted
1593    </t>
1594    <t>
1595      3xx: Redirection - Further action must be taken in order to
1596        complete the request
1597    </t>
1598    <t>
1599      4xx: Client Error - The request contains bad syntax or cannot
1600        be fulfilled
1601    </t>
1602    <t>
1603      5xx: Server Error - The server failed to fulfill an apparently
1604        valid request
1605    </t>
1606  </list>
1607</t>
1608<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"/>
1609  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1610  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1611</artwork></figure>
1612</section>
1613</section>
1614
1615</section>
1616
1617
1618<section title="Connections" anchor="connections">
1619
1620<section title="Persistent Connections" anchor="persistent.connections">
1621
1622<section title="Purpose" anchor="persistent.purpose">
1623<t>
1624   Prior to persistent connections, a separate TCP connection was
1625   established to fetch each URL, increasing the load on HTTP servers
1626   and causing congestion on the Internet. The use of inline images and
1627   other associated data often require a client to make multiple
1628   requests of the same server in a short amount of time. Analysis of
1629   these performance problems and results from a prototype
1630   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1631   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1632   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1633   T/TCP <xref target="Tou1998"/>.
1634</t>
1635<t>
1636   Persistent HTTP connections have a number of advantages:
1637  <list style="symbols">
1638      <t>
1639        By opening and closing fewer TCP connections, CPU time is saved
1640        in routers and hosts (clients, servers, proxies, gateways,
1641        tunnels, or caches), and memory used for TCP protocol control
1642        blocks can be saved in hosts.
1643      </t>
1644      <t>
1645        HTTP requests and responses can be pipelined on a connection.
1646        Pipelining allows a client to make multiple requests without
1647        waiting for each response, allowing a single TCP connection to
1648        be used much more efficiently, with much lower elapsed time.
1649      </t>
1650      <t>
1651        Network congestion is reduced by reducing the number of packets
1652        caused by TCP opens, and by allowing TCP sufficient time to
1653        determine the congestion state of the network.
1654      </t>
1655      <t>
1656        Latency on subsequent requests is reduced since there is no time
1657        spent in TCP's connection opening handshake.
1658      </t>
1659      <t>
1660        HTTP can evolve more gracefully, since errors can be reported
1661        without the penalty of closing the TCP connection. Clients using
1662        future versions of HTTP might optimistically try a new feature,
1663        but if communicating with an older server, retry with old
1664        semantics after an error is reported.
1665      </t>
1666    </list>
1667</t>
1668<t>
1669   HTTP implementations &SHOULD; implement persistent connections.
1670</t>
1671</section>
1672
1673<section title="Overall Operation" anchor="persistent.overall">
1674<t>
1675   A significant difference between HTTP/1.1 and earlier versions of
1676   HTTP is that persistent connections are the default behavior of any
1677   HTTP connection. That is, unless otherwise indicated, the client
1678   &SHOULD; assume that the server will maintain a persistent connection,
1679   even after error responses from the server.
1680</t>
1681<t>
1682   Persistent connections provide a mechanism by which a client and a
1683   server can signal the close of a TCP connection. This signaling takes
1684   place using the Connection header field (<xref target="header.connection"/>). Once a close
1685   has been signaled, the client &MUST-NOT; send any more requests on that
1686   connection.
1687</t>
1688
1689<section title="Negotiation" anchor="persistent.negotiation">
1690<t>
1691   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1692   maintain a persistent connection unless a Connection header including
1693   the connection-token "close" was sent in the request. If the server
1694   chooses to close the connection immediately after sending the
1695   response, it &SHOULD; send a Connection header including the
1696   connection-token close.
1697</t>
1698<t>
1699   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1700   decide to keep it open based on whether the response from a server
1701   contains a Connection header with the connection-token close. In case
1702   the client does not want to maintain a connection for more than that
1703   request, it &SHOULD; send a Connection header including the
1704   connection-token close.
1705</t>
1706<t>
1707   If either the client or the server sends the close token in the
1708   Connection header, that request becomes the last one for the
1709   connection.
1710</t>
1711<t>
1712   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1713   maintained for HTTP versions less than 1.1 unless it is explicitly
1714   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1715   compatibility with HTTP/1.0 clients.
1716</t>
1717<t>
1718   In order to remain persistent, all messages on the connection &MUST;
1719   have a self-defined message length (i.e., one not defined by closure
1720   of the connection), as described in <xref target="message.length"/>.
1721</t>
1722</section>
1723
1724<section title="Pipelining" anchor="pipelining">
1725<t>
1726   A client that supports persistent connections &MAY; "pipeline" its
1727   requests (i.e., send multiple requests without waiting for each
1728   response). A server &MUST; send its responses to those requests in the
1729   same order that the requests were received.
1730</t>
1731<t>
1732   Clients which assume persistent connections and pipeline immediately
1733   after connection establishment &SHOULD; be prepared to retry their
1734   connection if the first pipelined attempt fails. If a client does
1735   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1736   persistent. Clients &MUST; also be prepared to resend their requests if
1737   the server closes the connection before sending all of the
1738   corresponding responses.
1739</t>
1740<t>
1741   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1742   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1743   premature termination of the transport connection could lead to
1744   indeterminate results. A client wishing to send a non-idempotent
1745   request &SHOULD; wait to send that request until it has received the
1746   response status for the previous request.
1747</t>
1748</section>
1749</section>
1750
1751<section title="Proxy Servers" anchor="persistent.proxy">
1752<t>
1753   It is especially important that proxies correctly implement the
1754   properties of the Connection header field as specified in <xref target="header.connection"/>.
1755</t>
1756<t>
1757   The proxy server &MUST; signal persistent connections separately with
1758   its clients and the origin servers (or other proxy servers) that it
1759   connects to. Each persistent connection applies to only one transport
1760   link.
1761</t>
1762<t>
1763   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1764   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1765   discussion of the problems with the Keep-Alive header implemented by
1766   many HTTP/1.0 clients).
1767</t>
1768</section>
1769
1770<section title="Practical Considerations" anchor="persistent.practical">
1771<t>
1772   Servers will usually have some time-out value beyond which they will
1773   no longer maintain an inactive connection. Proxy servers might make
1774   this a higher value since it is likely that the client will be making
1775   more connections through the same server. The use of persistent
1776   connections places no requirements on the length (or existence) of
1777   this time-out for either the client or the server.
1778</t>
1779<t>
1780   When a client or server wishes to time-out it &SHOULD; issue a graceful
1781   close on the transport connection. Clients and servers &SHOULD; both
1782   constantly watch for the other side of the transport close, and
1783   respond to it as appropriate. If a client or server does not detect
1784   the other side's close promptly it could cause unnecessary resource
1785   drain on the network.
1786</t>
1787<t>
1788   A client, server, or proxy &MAY; close the transport connection at any
1789   time. For example, a client might have started to send a new request
1790   at the same time that the server has decided to close the "idle"
1791   connection. From the server's point of view, the connection is being
1792   closed while it was idle, but from the client's point of view, a
1793   request is in progress.
1794</t>
1795<t>
1796   This means that clients, servers, and proxies &MUST; be able to recover
1797   from asynchronous close events. Client software &SHOULD; reopen the
1798   transport connection and retransmit the aborted sequence of requests
1799   without user interaction so long as the request sequence is
1800   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1801   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1802   human operator the choice of retrying the request(s). Confirmation by
1803   user-agent software with semantic understanding of the application
1804   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1805   be repeated if the second sequence of requests fails.
1806</t>
1807<t>
1808   Servers &SHOULD; always respond to at least one request per connection,
1809   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1810   middle of transmitting a response, unless a network or client failure
1811   is suspected.
1812</t>
1813<t>
1814   Clients that use persistent connections &SHOULD; limit the number of
1815   simultaneous connections that they maintain to a given server. A
1816   single-user client &SHOULD-NOT; maintain more than 2 connections with
1817   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1818   another server or proxy, where N is the number of simultaneously
1819   active users. These guidelines are intended to improve HTTP response
1820   times and avoid congestion.
1821</t>
1822</section>
1823</section>
1824
1825<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1826
1827<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1828<t>
1829   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1830   flow control mechanisms to resolve temporary overloads, rather than
1831   terminating connections with the expectation that clients will retry.
1832   The latter technique can exacerbate network congestion.
1833</t>
1834</section>
1835
1836<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1837<t>
1838   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1839   the network connection for an error status while it is transmitting
1840   the request. If the client sees an error status, it &SHOULD;
1841   immediately cease transmitting the body. If the body is being sent
1842   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1843   empty trailer &MAY; be used to prematurely mark the end of the message.
1844   If the body was preceded by a Content-Length header, the client &MUST;
1845   close the connection.
1846</t>
1847</section>
1848
1849<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1850<t>
1851   The purpose of the 100 (Continue) status (see &status-100;) is to
1852   allow a client that is sending a request message with a request body
1853   to determine if the origin server is willing to accept the request
1854   (based on the request headers) before the client sends the request
1855   body. In some cases, it might either be inappropriate or highly
1856   inefficient for the client to send the body if the server will reject
1857   the message without looking at the body.
1858</t>
1859<t>
1860   Requirements for HTTP/1.1 clients:
1861  <list style="symbols">
1862    <t>
1863        If a client will wait for a 100 (Continue) response before
1864        sending the request body, it &MUST; send an Expect request-header
1865        field (&header-expect;) with the "100-continue" expectation.
1866    </t>
1867    <t>
1868        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1869        with the "100-continue" expectation if it does not intend
1870        to send a request body.
1871    </t>
1872  </list>
1873</t>
1874<t>
1875   Because of the presence of older implementations, the protocol allows
1876   ambiguous situations in which a client may send "Expect: 100-continue"
1877   without receiving either a 417 (Expectation Failed) status
1878   or a 100 (Continue) status. Therefore, when a client sends this
1879   header field to an origin server (possibly via a proxy) from which it
1880   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1881   for an indefinite period before sending the request body.
1882</t>
1883<t>
1884   Requirements for HTTP/1.1 origin servers:
1885  <list style="symbols">
1886    <t> Upon receiving a request which includes an Expect request-header
1887        field with the "100-continue" expectation, an origin server &MUST;
1888        either respond with 100 (Continue) status and continue to read
1889        from the input stream, or respond with a final status code. The
1890        origin server &MUST-NOT; wait for the request body before sending
1891        the 100 (Continue) response. If it responds with a final status
1892        code, it &MAY; close the transport connection or it &MAY; continue
1893        to read and discard the rest of the request.  It &MUST-NOT;
1894        perform the requested method if it returns a final status code.
1895    </t>
1896    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1897        the request message does not include an Expect request-header
1898        field with the "100-continue" expectation, and &MUST-NOT; send a
1899        100 (Continue) response if such a request comes from an HTTP/1.0
1900        (or earlier) client. There is an exception to this rule: for
1901        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1902        status in response to an HTTP/1.1 PUT or POST request that does
1903        not include an Expect request-header field with the "100-continue"
1904        expectation. This exception, the purpose of which is
1905        to minimize any client processing delays associated with an
1906        undeclared wait for 100 (Continue) status, applies only to
1907        HTTP/1.1 requests, and not to requests with any other HTTP-version
1908        value.
1909    </t>
1910    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1911        already received some or all of the request body for the
1912        corresponding request.
1913    </t>
1914    <t> An origin server that sends a 100 (Continue) response &MUST;
1915    ultimately send a final status code, once the request body is
1916        received and processed, unless it terminates the transport
1917        connection prematurely.
1918    </t>
1919    <t> If an origin server receives a request that does not include an
1920        Expect request-header field with the "100-continue" expectation,
1921        the request includes a request body, and the server responds
1922        with a final status code before reading the entire request body
1923        from the transport connection, then the server &SHOULD-NOT;  close
1924        the transport connection until it has read the entire request,
1925        or until the client closes the connection. Otherwise, the client
1926        might not reliably receive the response message. However, this
1927        requirement is not be construed as preventing a server from
1928        defending itself against denial-of-service attacks, or from
1929        badly broken client implementations.
1930      </t>
1931    </list>
1932</t>
1933<t>
1934   Requirements for HTTP/1.1 proxies:
1935  <list style="symbols">
1936    <t> If a proxy receives a request that includes an Expect request-header
1937        field with the "100-continue" expectation, and the proxy
1938        either knows that the next-hop server complies with HTTP/1.1 or
1939        higher, or does not know the HTTP version of the next-hop
1940        server, it &MUST; forward the request, including the Expect header
1941        field.
1942    </t>
1943    <t> If the proxy knows that the version of the next-hop server is
1944        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1945        respond with a 417 (Expectation Failed) status.
1946    </t>
1947    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1948        numbers received from recently-referenced next-hop servers.
1949    </t>
1950    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1951        request message was received from an HTTP/1.0 (or earlier)
1952        client and did not include an Expect request-header field with
1953        the "100-continue" expectation. This requirement overrides the
1954        general rule for forwarding of 1xx responses (see &status-1xx;).
1955    </t>
1956  </list>
1957</t>
1958</section>
1959
1960<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1961<t>
1962   If an HTTP/1.1 client sends a request which includes a request body,
1963   but which does not include an Expect request-header field with the
1964   "100-continue" expectation, and if the client is not directly
1965   connected to an HTTP/1.1 origin server, and if the client sees the
1966   connection close before receiving any status from the server, the
1967   client &SHOULD; retry the request.  If the client does retry this
1968   request, it &MAY; use the following "binary exponential backoff"
1969   algorithm to be assured of obtaining a reliable response:
1970  <list style="numbers">
1971    <t>
1972      Initiate a new connection to the server
1973    </t>
1974    <t>
1975      Transmit the request-headers
1976    </t>
1977    <t>
1978      Initialize a variable R to the estimated round-trip time to the
1979         server (e.g., based on the time it took to establish the
1980         connection), or to a constant value of 5 seconds if the round-trip
1981         time is not available.
1982    </t>
1983    <t>
1984       Compute T = R * (2**N), where N is the number of previous
1985         retries of this request.
1986    </t>
1987    <t>
1988       Wait either for an error response from the server, or for T
1989         seconds (whichever comes first)
1990    </t>
1991    <t>
1992       If no error response is received, after T seconds transmit the
1993         body of the request.
1994    </t>
1995    <t>
1996       If client sees that the connection is closed prematurely,
1997         repeat from step 1 until the request is accepted, an error
1998         response is received, or the user becomes impatient and
1999         terminates the retry process.
2000    </t>
2001  </list>
2002</t>
2003<t>
2004   If at any point an error status is received, the client
2005  <list style="symbols">
2006      <t>&SHOULD-NOT;  continue and</t>
2007
2008      <t>&SHOULD; close the connection if it has not completed sending the
2009        request message.</t>
2010    </list>
2011</t>
2012</section>
2013</section>
2014</section>
2015
2016
2017<section title="Header Field Definitions" anchor="header.fields">
2018<t>
2019   This section defines the syntax and semantics of HTTP/1.1 header fields
2020   related to message framing and transport protocols.
2021</t>
2022<t>
2023   For entity-header fields, both sender and recipient refer to either the
2024   client or the server, depending on who sends and who receives the entity.
2025</t>
2026
2027<section title="Connection" anchor="header.connection">
2028  <iref primary="true" item="Connection header" x:for-anchor=""/>
2029  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2030  <x:anchor-alias value="Connection"/>
2031  <x:anchor-alias value="connection-token"/>
2032  <x:anchor-alias value="Connection-v"/>
2033<t>
2034   The general-header field "Connection" allows the sender to specify
2035   options that are desired for that particular connection and &MUST-NOT;
2036   be communicated by proxies over further connections.
2037</t>
2038<t>
2039   The Connection header's value has the following grammar:
2040</t>
2041<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"/>
2042  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2043  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2044  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2045</artwork></figure>
2046<t>
2047   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2048   message is forwarded and, for each connection-token in this field,
2049   remove any header field(s) from the message with the same name as the
2050   connection-token. Connection options are signaled by the presence of
2051   a connection-token in the Connection header field, not by any
2052   corresponding additional header field(s), since the additional header
2053   field may not be sent if there are no parameters associated with that
2054   connection option.
2055</t>
2056<t>
2057   Message headers listed in the Connection header &MUST-NOT; include
2058   end-to-end headers, such as Cache-Control.
2059</t>
2060<t>
2061   HTTP/1.1 defines the "close" connection option for the sender to
2062   signal that the connection will be closed after completion of the
2063   response. For example,
2064</t>
2065<figure><artwork type="example">
2066  Connection: close
2067</artwork></figure>
2068<t>
2069   in either the request or the response header fields indicates that
2070   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2071   after the current request/response is complete.
2072</t>
2073<t>
2074   An HTTP/1.1 client that does not support persistent connections &MUST;
2075   include the "close" connection option in every request message.
2076</t>
2077<t>
2078   An HTTP/1.1 server that does not support persistent connections &MUST;
2079   include the "close" connection option in every response message that
2080   does not have a 1xx (informational) status code.
2081</t>
2082<t>
2083   A system receiving an HTTP/1.0 (or lower-version) message that
2084   includes a Connection header &MUST;, for each connection-token in this
2085   field, remove and ignore any header field(s) from the message with
2086   the same name as the connection-token. This protects against mistaken
2087   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2088</t>
2089</section>
2090
2091<section title="Content-Length" anchor="header.content-length">
2092  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2093  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2094  <x:anchor-alias value="Content-Length"/>
2095  <x:anchor-alias value="Content-Length-v"/>
2096<t>
2097   The entity-header field "Content-Length" indicates the size of the
2098   entity-body, in decimal number of OCTETs, sent to the recipient or,
2099   in the case of the HEAD method, the size of the entity-body that
2100   would have been sent had the request been a GET.
2101</t>
2102<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2103  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2104  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2105</artwork></figure>
2106<t>
2107   An example is
2108</t>
2109<figure><artwork type="example">
2110  Content-Length: 3495
2111</artwork></figure>
2112<t>
2113   Applications &SHOULD; use this field to indicate the transfer-length of
2114   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2115</t>
2116<t>
2117   Any Content-Length greater than or equal to zero is a valid value.
2118   <xref target="message.length"/> describes how to determine the length of a message-body
2119   if a Content-Length is not given.
2120</t>
2121<t>
2122   Note that the meaning of this field is significantly different from
2123   the corresponding definition in MIME, where it is an optional field
2124   used within the "message/external-body" content-type. In HTTP, it
2125   &SHOULD; be sent whenever the message's length can be determined prior
2126   to being transferred, unless this is prohibited by the rules in
2127   <xref target="message.length"/>.
2128</t>
2129</section>
2130
2131<section title="Date" anchor="header.date">
2132  <iref primary="true" item="Date header" x:for-anchor=""/>
2133  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2134  <x:anchor-alias value="Date"/>
2135  <x:anchor-alias value="Date-v"/>
2136<t>
2137   The general-header field "Date" represents the date and time at which
2138   the message was originated, having the same semantics as orig-date in
2139   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2140   HTTP-date, as described in <xref target="full.date"/>;
2141   it &MUST; be sent in rfc1123-date format.
2142</t>
2143<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2144  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2145  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2146</artwork></figure>
2147<t>
2148   An example is
2149</t>
2150<figure><artwork type="example">
2151  Date: Tue, 15 Nov 1994 08:12:31 GMT
2152</artwork></figure>
2153<t>
2154   Origin servers &MUST; include a Date header field in all responses,
2155   except in these cases:
2156  <list style="numbers">
2157      <t>If the response status code is 100 (Continue) or 101 (Switching
2158         Protocols), the response &MAY; include a Date header field, at
2159         the server's option.</t>
2160
2161      <t>If the response status code conveys a server error, e.g. 500
2162         (Internal Server Error) or 503 (Service Unavailable), and it is
2163         inconvenient or impossible to generate a valid Date.</t>
2164
2165      <t>If the server does not have a clock that can provide a
2166         reasonable approximation of the current time, its responses
2167         &MUST-NOT; include a Date header field. In this case, the rules
2168         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2169  </list>
2170</t>
2171<t>
2172   A received message that does not have a Date header field &MUST; be
2173   assigned one by the recipient if the message will be cached by that
2174   recipient or gatewayed via a protocol which requires a Date. An HTTP
2175   implementation without a clock &MUST-NOT; cache responses without
2176   revalidating them on every use. An HTTP cache, especially a shared
2177   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2178   clock with a reliable external standard.
2179</t>
2180<t>
2181   Clients &SHOULD; only send a Date header field in messages that include
2182   an entity-body, as in the case of the PUT and POST requests, and even
2183   then it is optional. A client without a clock &MUST-NOT; send a Date
2184   header field in a request.
2185</t>
2186<t>
2187   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2188   time subsequent to the generation of the message. It &SHOULD; represent
2189   the best available approximation of the date and time of message
2190   generation, unless the implementation has no means of generating a
2191   reasonably accurate date and time. In theory, the date ought to
2192   represent the moment just before the entity is generated. In
2193   practice, the date can be generated at any time during the message
2194   origination without affecting its semantic value.
2195</t>
2196
2197<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2198<t>
2199   Some origin server implementations might not have a clock available.
2200   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2201   values to a response, unless these values were associated
2202   with the resource by a system or user with a reliable clock. It &MAY;
2203   assign an Expires value that is known, at or before server
2204   configuration time, to be in the past (this allows "pre-expiration"
2205   of responses without storing separate Expires values for each
2206   resource).
2207</t>
2208</section>
2209</section>
2210
2211<section title="Host" anchor="header.host">
2212  <iref primary="true" item="Host header" x:for-anchor=""/>
2213  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2214  <x:anchor-alias value="Host"/>
2215  <x:anchor-alias value="Host-v"/>
2216<t>
2217   The request-header field "Host" specifies the Internet host and port
2218   number of the resource being requested, as obtained from the original
2219   URI given by the user or referring resource (generally an HTTP URL,
2220   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2221   the naming authority of the origin server or gateway given by the
2222   original URL. This allows the origin server or gateway to
2223   differentiate between internally-ambiguous URLs, such as the root "/"
2224   URL of a server for multiple host names on a single IP address.
2225</t>
2226<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2227  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2228  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2229</artwork></figure>
2230<t>
2231   A "host" without any trailing port information implies the default
2232   port for the service requested (e.g., "80" for an HTTP URL). For
2233   example, a request on the origin server for
2234   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2235</t>
2236<figure><artwork type="example">
2237  GET /pub/WWW/ HTTP/1.1
2238  Host: www.example.org
2239</artwork></figure>
2240<t>
2241   A client &MUST; include a Host header field in all HTTP/1.1 request
2242   messages. If the requested URI does not include an Internet host
2243   name for the service being requested, then the Host header field &MUST;
2244   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2245   request message it forwards does contain an appropriate Host header
2246   field that identifies the service being requested by the proxy. All
2247   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2248   status code to any HTTP/1.1 request message which lacks a Host header
2249   field.
2250</t>
2251<t>
2252   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2253   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2254   for other requirements relating to Host.
2255</t>
2256</section>
2257
2258<section title="TE" anchor="header.te">
2259  <iref primary="true" item="TE header" x:for-anchor=""/>
2260  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2261  <x:anchor-alias value="TE"/>
2262  <x:anchor-alias value="TE-v"/>
2263  <x:anchor-alias value="t-codings"/>
2264<t>
2265   The request-header field "TE" indicates what extension transfer-codings
2266   it is willing to accept in the response and whether or not it is
2267   willing to accept trailer fields in a chunked transfer-coding. Its
2268   value may consist of the keyword "trailers" and/or a comma-separated
2269   list of extension transfer-coding names with optional accept
2270   parameters (as described in <xref target="transfer.codings"/>).
2271</t>
2272<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"/>
2273  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2274  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2275  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2276</artwork></figure>
2277<t>
2278   The presence of the keyword "trailers" indicates that the client is
2279   willing to accept trailer fields in a chunked transfer-coding, as
2280   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2281   transfer-coding values even though it does not itself represent a
2282   transfer-coding.
2283</t>
2284<t>
2285   Examples of its use are:
2286</t>
2287<figure><artwork type="example">
2288  TE: deflate
2289  TE:
2290  TE: trailers, deflate;q=0.5
2291</artwork></figure>
2292<t>
2293   The TE header field only applies to the immediate connection.
2294   Therefore, the keyword &MUST; be supplied within a Connection header
2295   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2296</t>
2297<t>
2298   A server tests whether a transfer-coding is acceptable, according to
2299   a TE field, using these rules:
2300  <list style="numbers">
2301    <x:lt>
2302      <t>The "chunked" transfer-coding is always acceptable. If the
2303         keyword "trailers" is listed, the client indicates that it is
2304         willing to accept trailer fields in the chunked response on
2305         behalf of itself and any downstream clients. The implication is
2306         that, if given, the client is stating that either all
2307         downstream clients are willing to accept trailer fields in the
2308         forwarded response, or that it will attempt to buffer the
2309         response on behalf of downstream recipients.
2310      </t><t>
2311         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2312         chunked response such that a client can be assured of buffering
2313         the entire response.</t>
2314    </x:lt>
2315    <x:lt>
2316      <t>If the transfer-coding being tested is one of the transfer-codings
2317         listed in the TE field, then it is acceptable unless it
2318         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2319         qvalue of 0 means "not acceptable.")</t>
2320    </x:lt>
2321    <x:lt>
2322      <t>If multiple transfer-codings are acceptable, then the
2323         acceptable transfer-coding with the highest non-zero qvalue is
2324         preferred.  The "chunked" transfer-coding always has a qvalue
2325         of 1.</t>
2326    </x:lt>
2327  </list>
2328</t>
2329<t>
2330   If the TE field-value is empty or if no TE field is present, the only
2331   transfer-coding  is "chunked". A message with no transfer-coding is
2332   always acceptable.
2333</t>
2334</section>
2335
2336<section title="Trailer" anchor="header.trailer">
2337  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2338  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2339  <x:anchor-alias value="Trailer"/>
2340  <x:anchor-alias value="Trailer-v"/>
2341<t>
2342   The general field "Trailer" indicates that the given set of
2343   header fields is present in the trailer of a message encoded with
2344   chunked transfer-coding.
2345</t>
2346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2347  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2348  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2349</artwork></figure>
2350<t>
2351   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2352   message using chunked transfer-coding with a non-empty trailer. Doing
2353   so allows the recipient to know which header fields to expect in the
2354   trailer.
2355</t>
2356<t>
2357   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2358   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2359   trailer fields in a "chunked" transfer-coding.
2360</t>
2361<t>
2362   Message header fields listed in the Trailer header field &MUST-NOT;
2363   include the following header fields:
2364  <list style="symbols">
2365    <t>Transfer-Encoding</t>
2366    <t>Content-Length</t>
2367    <t>Trailer</t>
2368  </list>
2369</t>
2370</section>
2371
2372<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2373  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2374  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2375  <x:anchor-alias value="Transfer-Encoding"/>
2376  <x:anchor-alias value="Transfer-Encoding-v"/>
2377<t>
2378   The general-header "Transfer-Encoding" field indicates what (if any)
2379   type of transformation has been applied to the message body in order
2380   to safely transfer it between the sender and the recipient. This
2381   differs from the content-coding in that the transfer-coding is a
2382   property of the message, not of the entity.
2383</t>
2384<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2385  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2386                        <x:ref>Transfer-Encoding-v</x:ref>
2387  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2388</artwork></figure>
2389<t>
2390   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2391</t>
2392<figure><artwork type="example">
2393  Transfer-Encoding: chunked
2394</artwork></figure>
2395<t>
2396   If multiple encodings have been applied to an entity, the transfer-codings
2397   &MUST; be listed in the order in which they were applied.
2398   Additional information about the encoding parameters &MAY; be provided
2399   by other entity-header fields not defined by this specification.
2400</t>
2401<t>
2402   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2403   header.
2404</t>
2405</section>
2406
2407<section title="Upgrade" anchor="header.upgrade">
2408  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2409  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2410  <x:anchor-alias value="Upgrade"/>
2411  <x:anchor-alias value="Upgrade-v"/>
2412<t>
2413   The general-header "Upgrade" allows the client to specify what
2414   additional communication protocols it supports and would like to use
2415   if the server finds it appropriate to switch protocols. The server
2416   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2417   response to indicate which protocol(s) are being switched.
2418</t>
2419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2420  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2421  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2422</artwork></figure>
2423<t>
2424   For example,
2425</t>
2426<figure><artwork type="example">
2427  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2428</artwork></figure>
2429<t>
2430   The Upgrade header field is intended to provide a simple mechanism
2431   for transition from HTTP/1.1 to some other, incompatible protocol. It
2432   does so by allowing the client to advertise its desire to use another
2433   protocol, such as a later version of HTTP with a higher major version
2434   number, even though the current request has been made using HTTP/1.1.
2435   This eases the difficult transition between incompatible protocols by
2436   allowing the client to initiate a request in the more commonly
2437   supported protocol while indicating to the server that it would like
2438   to use a "better" protocol if available (where "better" is determined
2439   by the server, possibly according to the nature of the method and/or
2440   resource being requested).
2441</t>
2442<t>
2443   The Upgrade header field only applies to switching application-layer
2444   protocols upon the existing transport-layer connection. Upgrade
2445   cannot be used to insist on a protocol change; its acceptance and use
2446   by the server is optional. The capabilities and nature of the
2447   application-layer communication after the protocol change is entirely
2448   dependent upon the new protocol chosen, although the first action
2449   after changing the protocol &MUST; be a response to the initial HTTP
2450   request containing the Upgrade header field.
2451</t>
2452<t>
2453   The Upgrade header field only applies to the immediate connection.
2454   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2455   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2456   HTTP/1.1 message.
2457</t>
2458<t>
2459   The Upgrade header field cannot be used to indicate a switch to a
2460   protocol on a different connection. For that purpose, it is more
2461   appropriate to use a 301, 302, 303, or 305 redirection response.
2462</t>
2463<t>
2464   This specification only defines the protocol name "HTTP" for use by
2465   the family of Hypertext Transfer Protocols, as defined by the HTTP
2466   version rules of <xref target="http.version"/> and future updates to this
2467   specification. Any token can be used as a protocol name; however, it
2468   will only be useful if both the client and server associate the name
2469   with the same protocol.
2470</t>
2471</section>
2472
2473<section title="Via" anchor="header.via">
2474  <iref primary="true" item="Via header" x:for-anchor=""/>
2475  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2476  <x:anchor-alias value="protocol-name"/>
2477  <x:anchor-alias value="protocol-version"/>
2478  <x:anchor-alias value="pseudonym"/>
2479  <x:anchor-alias value="received-by"/>
2480  <x:anchor-alias value="received-protocol"/>
2481  <x:anchor-alias value="Via"/>
2482  <x:anchor-alias value="Via-v"/>
2483<t>
2484   The general-header field "Via" &MUST; be used by gateways and proxies to
2485   indicate the intermediate protocols and recipients between the user
2486   agent and the server on requests, and between the origin server and
2487   the client on responses. It is analogous to the "Received" field defined in
2488   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2489   avoiding request loops, and identifying the protocol capabilities of
2490   all senders along the request/response chain.
2491</t>
2492<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"/>
2493  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2494  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2495                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2496  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2497  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2498  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2499  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2500  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2501</artwork></figure>
2502<t>
2503   The received-protocol indicates the protocol version of the message
2504   received by the server or client along each segment of the
2505   request/response chain. The received-protocol version is appended to
2506   the Via field value when the message is forwarded so that information
2507   about the protocol capabilities of upstream applications remains
2508   visible to all recipients.
2509</t>
2510<t>
2511   The protocol-name is optional if and only if it would be "HTTP". The
2512   received-by field is normally the host and optional port number of a
2513   recipient server or client that subsequently forwarded the message.
2514   However, if the real host is considered to be sensitive information,
2515   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2516   be assumed to be the default port of the received-protocol.
2517</t>
2518<t>
2519   Multiple Via field values represents each proxy or gateway that has
2520   forwarded the message. Each recipient &MUST; append its information
2521   such that the end result is ordered according to the sequence of
2522   forwarding applications.
2523</t>
2524<t>
2525   Comments &MAY; be used in the Via header field to identify the software
2526   of the recipient proxy or gateway, analogous to the User-Agent and
2527   Server header fields. However, all comments in the Via field are
2528   optional and &MAY; be removed by any recipient prior to forwarding the
2529   message.
2530</t>
2531<t>
2532   For example, a request message could be sent from an HTTP/1.0 user
2533   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2534   forward the request to a public proxy at p.example.net, which completes
2535   the request by forwarding it to the origin server at www.example.com.
2536   The request received by www.example.com would then have the following
2537   Via header field:
2538</t>
2539<figure><artwork type="example">
2540  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2541</artwork></figure>
2542<t>
2543   Proxies and gateways used as a portal through a network firewall
2544   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2545   the firewall region. This information &SHOULD; only be propagated if
2546   explicitly enabled. If not enabled, the received-by host of any host
2547   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2548   for that host.
2549</t>
2550<t>
2551   For organizations that have strong privacy requirements for hiding
2552   internal structures, a proxy &MAY; combine an ordered subsequence of
2553   Via header field entries with identical received-protocol values into
2554   a single such entry. For example,
2555</t>
2556<figure><artwork type="example">
2557  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2558</artwork></figure>
2559<t>
2560        could be collapsed to
2561</t>
2562<figure><artwork type="example">
2563  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2564</artwork></figure>
2565<t>
2566   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2567   under the same organizational control and the hosts have already been
2568   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2569   have different received-protocol values.
2570</t>
2571</section>
2572
2573</section>
2574
2575<section title="IANA Considerations" anchor="IANA.considerations">
2576<section title="Message Header Registration" anchor="message.header.registration">
2577<t>
2578   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2579   with the permanent registrations below (see <xref target="RFC3864"/>):
2580</t>
2581<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2582<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2583   <ttcol>Header Field Name</ttcol>
2584   <ttcol>Protocol</ttcol>
2585   <ttcol>Status</ttcol>
2586   <ttcol>Reference</ttcol>
2587
2588   <c>Connection</c>
2589   <c>http</c>
2590   <c>standard</c>
2591   <c>
2592      <xref target="header.connection"/>
2593   </c>
2594   <c>Content-Length</c>
2595   <c>http</c>
2596   <c>standard</c>
2597   <c>
2598      <xref target="header.content-length"/>
2599   </c>
2600   <c>Date</c>
2601   <c>http</c>
2602   <c>standard</c>
2603   <c>
2604      <xref target="header.date"/>
2605   </c>
2606   <c>Host</c>
2607   <c>http</c>
2608   <c>standard</c>
2609   <c>
2610      <xref target="header.host"/>
2611   </c>
2612   <c>TE</c>
2613   <c>http</c>
2614   <c>standard</c>
2615   <c>
2616      <xref target="header.te"/>
2617   </c>
2618   <c>Trailer</c>
2619   <c>http</c>
2620   <c>standard</c>
2621   <c>
2622      <xref target="header.trailer"/>
2623   </c>
2624   <c>Transfer-Encoding</c>
2625   <c>http</c>
2626   <c>standard</c>
2627   <c>
2628      <xref target="header.transfer-encoding"/>
2629   </c>
2630   <c>Upgrade</c>
2631   <c>http</c>
2632   <c>standard</c>
2633   <c>
2634      <xref target="header.upgrade"/>
2635   </c>
2636   <c>Via</c>
2637   <c>http</c>
2638   <c>standard</c>
2639   <c>
2640      <xref target="header.via"/>
2641   </c>
2642</texttable>
2643<!--(END)-->
2644<t>
2645   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2646</t>
2647</section>
2648
2649<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2650<t>
2651   The entry for the "http" URI Scheme in the registry located at
2652   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2653   should be updated to point to <xref target="http.uri"/> of this document
2654   (see <xref target="RFC4395"/>).
2655</t>
2656</section>
2657
2658<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2659<t>
2660   This document serves as the specification for the Internet media types
2661   "message/http" and "application/http". The following is to be registered with
2662   IANA (see <xref target="RFC4288"/>).
2663</t>
2664<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2665<iref item="Media Type" subitem="message/http" primary="true"/>
2666<iref item="message/http Media Type" primary="true"/>
2667<t>
2668   The message/http type can be used to enclose a single HTTP request or
2669   response message, provided that it obeys the MIME restrictions for all
2670   "message" types regarding line length and encodings.
2671</t>
2672<t>
2673  <list style="hanging" x:indent="12em">
2674    <t hangText="Type name:">
2675      message
2676    </t>
2677    <t hangText="Subtype name:">
2678      http
2679    </t>
2680    <t hangText="Required parameters:">
2681      none
2682    </t>
2683    <t hangText="Optional parameters:">
2684      version, msgtype
2685      <list style="hanging">
2686        <t hangText="version:">
2687          The HTTP-Version number of the enclosed message
2688          (e.g., "1.1"). If not present, the version can be
2689          determined from the first line of the body.
2690        </t>
2691        <t hangText="msgtype:">
2692          The message type -- "request" or "response". If not
2693          present, the type can be determined from the first
2694          line of the body.
2695        </t>
2696      </list>
2697    </t>
2698    <t hangText="Encoding considerations:">
2699      only "7bit", "8bit", or "binary" are permitted
2700    </t>
2701    <t hangText="Security considerations:">
2702      none
2703    </t>
2704    <t hangText="Interoperability considerations:">
2705      none
2706    </t>
2707    <t hangText="Published specification:">
2708      This specification (see <xref target="internet.media.type.message.http"/>).
2709    </t>
2710    <t hangText="Applications that use this media type:">
2711    </t>
2712    <t hangText="Additional information:">
2713      <list style="hanging">
2714        <t hangText="Magic number(s):">none</t>
2715        <t hangText="File extension(s):">none</t>
2716        <t hangText="Macintosh file type code(s):">none</t>
2717      </list>
2718    </t>
2719    <t hangText="Person and email address to contact for further information:">
2720      See Authors Section.
2721    </t>
2722                <t hangText="Intended usage:">
2723                  COMMON
2724    </t>
2725                <t hangText="Restrictions on usage:">
2726                  none
2727    </t>
2728    <t hangText="Author/Change controller:">
2729      IESG
2730    </t>
2731  </list>
2732</t>
2733</section>
2734<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2735<iref item="Media Type" subitem="application/http" primary="true"/>
2736<iref item="application/http Media Type" primary="true"/>
2737<t>
2738   The application/http type can be used to enclose a pipeline of one or more
2739   HTTP request or response messages (not intermixed).
2740</t>
2741<t>
2742  <list style="hanging" x:indent="12em">
2743    <t hangText="Type name:">
2744      application
2745    </t>
2746    <t hangText="Subtype name:">
2747      http
2748    </t>
2749    <t hangText="Required parameters:">
2750      none
2751    </t>
2752    <t hangText="Optional parameters:">
2753      version, msgtype
2754      <list style="hanging">
2755        <t hangText="version:">
2756          The HTTP-Version number of the enclosed messages
2757          (e.g., "1.1"). If not present, the version can be
2758          determined from the first line of the body.
2759        </t>
2760        <t hangText="msgtype:">
2761          The message type -- "request" or "response". If not
2762          present, the type can be determined from the first
2763          line of the body.
2764        </t>
2765      </list>
2766    </t>
2767    <t hangText="Encoding considerations:">
2768      HTTP messages enclosed by this type
2769      are in "binary" format; use of an appropriate
2770      Content-Transfer-Encoding is required when
2771      transmitted via E-mail.
2772    </t>
2773    <t hangText="Security considerations:">
2774      none
2775    </t>
2776    <t hangText="Interoperability considerations:">
2777      none
2778    </t>
2779    <t hangText="Published specification:">
2780      This specification (see <xref target="internet.media.type.application.http"/>).
2781    </t>
2782    <t hangText="Applications that use this media type:">
2783    </t>
2784    <t hangText="Additional information:">
2785      <list style="hanging">
2786        <t hangText="Magic number(s):">none</t>
2787        <t hangText="File extension(s):">none</t>
2788        <t hangText="Macintosh file type code(s):">none</t>
2789      </list>
2790    </t>
2791    <t hangText="Person and email address to contact for further information:">
2792      See Authors Section.
2793    </t>
2794                <t hangText="Intended usage:">
2795                  COMMON
2796    </t>
2797                <t hangText="Restrictions on usage:">
2798                  none
2799    </t>
2800    <t hangText="Author/Change controller:">
2801      IESG
2802    </t>
2803  </list>
2804</t>
2805</section>
2806</section>
2807
2808</section>
2809
2810<section title="Security Considerations" anchor="security.considerations">
2811<t>
2812   This section is meant to inform application developers, information
2813   providers, and users of the security limitations in HTTP/1.1 as
2814   described by this document. The discussion does not include
2815   definitive solutions to the problems revealed, though it does make
2816   some suggestions for reducing security risks.
2817</t>
2818
2819<section title="Personal Information" anchor="personal.information">
2820<t>
2821   HTTP clients are often privy to large amounts of personal information
2822   (e.g. the user's name, location, mail address, passwords, encryption
2823   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2824   leakage of this information.
2825   We very strongly recommend that a convenient interface be provided
2826   for the user to control dissemination of such information, and that
2827   designers and implementors be particularly careful in this area.
2828   History shows that errors in this area often create serious security
2829   and/or privacy problems and generate highly adverse publicity for the
2830   implementor's company.
2831</t>
2832</section>
2833
2834<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2835<t>
2836   A server is in the position to save personal data about a user's
2837   requests which might identify their reading patterns or subjects of
2838   interest. This information is clearly confidential in nature and its
2839   handling can be constrained by law in certain countries. People using
2840   HTTP to provide data are responsible for ensuring that
2841   such material is not distributed without the permission of any
2842   individuals that are identifiable by the published results.
2843</t>
2844</section>
2845
2846<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2847<t>
2848   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2849   the documents returned by HTTP requests to be only those that were
2850   intended by the server administrators. If an HTTP server translates
2851   HTTP URIs directly into file system calls, the server &MUST; take
2852   special care not to serve files that were not intended to be
2853   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2854   other operating systems use ".." as a path component to indicate a
2855   directory level above the current one. On such a system, an HTTP
2856   server &MUST; disallow any such construct in the Request-URI if it
2857   would otherwise allow access to a resource outside those intended to
2858   be accessible via the HTTP server. Similarly, files intended for
2859   reference only internally to the server (such as access control
2860   files, configuration files, and script code) &MUST; be protected from
2861   inappropriate retrieval, since they might contain sensitive
2862   information. Experience has shown that minor bugs in such HTTP server
2863   implementations have turned into security risks.
2864</t>
2865</section>
2866
2867<section title="DNS Spoofing" anchor="dns.spoofing">
2868<t>
2869   Clients using HTTP rely heavily on the Domain Name Service, and are
2870   thus generally prone to security attacks based on the deliberate
2871   mis-association of IP addresses and DNS names. Clients need to be
2872   cautious in assuming the continuing validity of an IP number/DNS name
2873   association.
2874</t>
2875<t>
2876   In particular, HTTP clients &SHOULD; rely on their name resolver for
2877   confirmation of an IP number/DNS name association, rather than
2878   caching the result of previous host name lookups. Many platforms
2879   already can cache host name lookups locally when appropriate, and
2880   they &SHOULD; be configured to do so. It is proper for these lookups to
2881   be cached, however, only when the TTL (Time To Live) information
2882   reported by the name server makes it likely that the cached
2883   information will remain useful.
2884</t>
2885<t>
2886   If HTTP clients cache the results of host name lookups in order to
2887   achieve a performance improvement, they &MUST; observe the TTL
2888   information reported by DNS.
2889</t>
2890<t>
2891   If HTTP clients do not observe this rule, they could be spoofed when
2892   a previously-accessed server's IP address changes. As network
2893   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2894   possibility of this form of attack will grow. Observing this
2895   requirement thus reduces this potential security vulnerability.
2896</t>
2897<t>
2898   This requirement also improves the load-balancing behavior of clients
2899   for replicated servers using the same DNS name and reduces the
2900   likelihood of a user's experiencing failure in accessing sites which
2901   use that strategy.
2902</t>
2903</section>
2904
2905<section title="Proxies and Caching" anchor="attack.proxies">
2906<t>
2907   By their very nature, HTTP proxies are men-in-the-middle, and
2908   represent an opportunity for man-in-the-middle attacks. Compromise of
2909   the systems on which the proxies run can result in serious security
2910   and privacy problems. Proxies have access to security-related
2911   information, personal information about individual users and
2912   organizations, and proprietary information belonging to users and
2913   content providers. A compromised proxy, or a proxy implemented or
2914   configured without regard to security and privacy considerations,
2915   might be used in the commission of a wide range of potential attacks.
2916</t>
2917<t>
2918   Proxy operators should protect the systems on which proxies run as
2919   they would protect any system that contains or transports sensitive
2920   information. In particular, log information gathered at proxies often
2921   contains highly sensitive personal information, and/or information
2922   about organizations. Log information should be carefully guarded, and
2923   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2924</t>
2925<t>
2926   Proxy implementors should consider the privacy and security
2927   implications of their design and coding decisions, and of the
2928   configuration options they provide to proxy operators (especially the
2929   default configuration).
2930</t>
2931<t>
2932   Users of a proxy need to be aware that they are no trustworthier than
2933   the people who run the proxy; HTTP itself cannot solve this problem.
2934</t>
2935<t>
2936   The judicious use of cryptography, when appropriate, may suffice to
2937   protect against a broad range of security and privacy attacks. Such
2938   cryptography is beyond the scope of the HTTP/1.1 specification.
2939</t>
2940</section>
2941
2942<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2943<t>
2944   They exist. They are hard to defend against. Research continues.
2945   Beware.
2946</t>
2947</section>
2948</section>
2949
2950<section title="Acknowledgments" anchor="ack">
2951<t>
2952   HTTP has evolved considerably over the years. It has
2953   benefited from a large and active developer community--the many
2954   people who have participated on the www-talk mailing list--and it is
2955   that community which has been most responsible for the success of
2956   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2957   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2958   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2959   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2960   VanHeyningen deserve special recognition for their efforts in
2961   defining early aspects of the protocol.
2962</t>
2963<t>
2964   This document has benefited greatly from the comments of all those
2965   participating in the HTTP-WG. In addition to those already mentioned,
2966   the following individuals have contributed to this specification:
2967</t>
2968<t>
2969   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2970   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2971   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2972   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2973   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2974   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2975   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2976   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2977   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2978   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2979   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2980   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2981   Josh Cohen.
2982</t>
2983<t>
2984   Thanks to the "cave men" of Palo Alto. You know who you are.
2985</t>
2986<t>
2987   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2988   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2989   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2990   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2991   Larry Masinter for their help. And thanks go particularly to Jeff
2992   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2993</t>
2994<t>
2995   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2996   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2997   discovery of many of the problems that this document attempts to
2998   rectify.
2999</t>
3000<t>
3001   This specification makes heavy use of the augmented BNF and generic
3002   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3003   reuses many of the definitions provided by Nathaniel Borenstein and
3004   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3005   specification will help reduce past confusion over the relationship
3006   between HTTP and Internet mail message formats.
3007</t>
3008</section>
3009
3010</middle>
3011<back>
3012
3013<references title="Normative References">
3014
3015<reference anchor="ISO-8859-1">
3016  <front>
3017    <title>
3018     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3019    </title>
3020    <author>
3021      <organization>International Organization for Standardization</organization>
3022    </author>
3023    <date year="1998"/>
3024  </front>
3025  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3026</reference>
3027
3028<reference anchor="Part2">
3029  <front>
3030    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3031    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3032      <organization abbrev="Day Software">Day Software</organization>
3033      <address><email>fielding@gbiv.com</email></address>
3034    </author>
3035    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3036      <organization>One Laptop per Child</organization>
3037      <address><email>jg@laptop.org</email></address>
3038    </author>
3039    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3040      <organization abbrev="HP">Hewlett-Packard Company</organization>
3041      <address><email>JeffMogul@acm.org</email></address>
3042    </author>
3043    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3044      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3045      <address><email>henrikn@microsoft.com</email></address>
3046    </author>
3047    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3048      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3049      <address><email>LMM@acm.org</email></address>
3050    </author>
3051    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3052      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3053      <address><email>paulle@microsoft.com</email></address>
3054    </author>
3055    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3056      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3057      <address><email>timbl@w3.org</email></address>
3058    </author>
3059    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3060      <organization abbrev="W3C">World Wide Web Consortium</organization>
3061      <address><email>ylafon@w3.org</email></address>
3062    </author>
3063    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3064      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3065      <address><email>julian.reschke@greenbytes.de</email></address>
3066    </author>
3067    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3068  </front>
3069  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3070  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3071</reference>
3072
3073<reference anchor="Part3">
3074  <front>
3075    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3076    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3077      <organization abbrev="Day Software">Day Software</organization>
3078      <address><email>fielding@gbiv.com</email></address>
3079    </author>
3080    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3081      <organization>One Laptop per Child</organization>
3082      <address><email>jg@laptop.org</email></address>
3083    </author>
3084    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3085      <organization abbrev="HP">Hewlett-Packard Company</organization>
3086      <address><email>JeffMogul@acm.org</email></address>
3087    </author>
3088    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3089      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3090      <address><email>henrikn@microsoft.com</email></address>
3091    </author>
3092    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3093      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3094      <address><email>LMM@acm.org</email></address>
3095    </author>
3096    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3097      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3098      <address><email>paulle@microsoft.com</email></address>
3099    </author>
3100    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3101      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3102      <address><email>timbl@w3.org</email></address>
3103    </author>
3104    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3105      <organization abbrev="W3C">World Wide Web Consortium</organization>
3106      <address><email>ylafon@w3.org</email></address>
3107    </author>
3108    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3109      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3110      <address><email>julian.reschke@greenbytes.de</email></address>
3111    </author>
3112    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3113  </front>
3114  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3115  <x:source href="p3-payload.xml" basename="p3-payload"/>
3116</reference>
3117
3118<reference anchor="Part5">
3119  <front>
3120    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3121    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3122      <organization abbrev="Day Software">Day Software</organization>
3123      <address><email>fielding@gbiv.com</email></address>
3124    </author>
3125    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3126      <organization>One Laptop per Child</organization>
3127      <address><email>jg@laptop.org</email></address>
3128    </author>
3129    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3130      <organization abbrev="HP">Hewlett-Packard Company</organization>
3131      <address><email>JeffMogul@acm.org</email></address>
3132    </author>
3133    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3134      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3135      <address><email>henrikn@microsoft.com</email></address>
3136    </author>
3137    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3138      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3139      <address><email>LMM@acm.org</email></address>
3140    </author>
3141    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3142      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3143      <address><email>paulle@microsoft.com</email></address>
3144    </author>
3145    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3146      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3147      <address><email>timbl@w3.org</email></address>
3148    </author>
3149    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3150      <organization abbrev="W3C">World Wide Web Consortium</organization>
3151      <address><email>ylafon@w3.org</email></address>
3152    </author>
3153    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3154      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3155      <address><email>julian.reschke@greenbytes.de</email></address>
3156    </author>
3157    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3158  </front>
3159  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3160  <x:source href="p5-range.xml" basename="p5-range"/>
3161</reference>
3162
3163<reference anchor="Part6">
3164  <front>
3165    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3166    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3167      <organization abbrev="Day Software">Day Software</organization>
3168      <address><email>fielding@gbiv.com</email></address>
3169    </author>
3170    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3171      <organization>One Laptop per Child</organization>
3172      <address><email>jg@laptop.org</email></address>
3173    </author>
3174    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3175      <organization abbrev="HP">Hewlett-Packard Company</organization>
3176      <address><email>JeffMogul@acm.org</email></address>
3177    </author>
3178    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3179      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3180      <address><email>henrikn@microsoft.com</email></address>
3181    </author>
3182    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3183      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3184      <address><email>LMM@acm.org</email></address>
3185    </author>
3186    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3187      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3188      <address><email>paulle@microsoft.com</email></address>
3189    </author>
3190    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3191      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3192      <address><email>timbl@w3.org</email></address>
3193    </author>
3194    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3195      <organization abbrev="W3C">World Wide Web Consortium</organization>
3196      <address><email>ylafon@w3.org</email></address>
3197    </author>
3198    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3199      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3200      <address><email>julian.reschke@greenbytes.de</email></address>
3201    </author>
3202    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3203  </front>
3204  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3205  <x:source href="p6-cache.xml" basename="p6-cache"/>
3206</reference>
3207
3208<reference anchor="RFC5234">
3209  <front>
3210    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3211    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3212      <organization>Brandenburg InternetWorking</organization>
3213      <address>
3214      <postal>
3215      <street>675 Spruce Dr.</street>
3216      <city>Sunnyvale</city>
3217      <region>CA</region>
3218      <code>94086</code>
3219      <country>US</country></postal>
3220      <phone>+1.408.246.8253</phone>
3221      <email>dcrocker@bbiw.net</email></address> 
3222    </author>
3223    <author initials="P." surname="Overell" fullname="Paul Overell">
3224      <organization>THUS plc.</organization>
3225      <address>
3226      <postal>
3227      <street>1/2 Berkeley Square</street>
3228      <street>99 Berkely Street</street>
3229      <city>Glasgow</city>
3230      <code>G3 7HR</code>
3231      <country>UK</country></postal>
3232      <email>paul.overell@thus.net</email></address>
3233    </author>
3234    <date month="January" year="2008"/>
3235  </front>
3236  <seriesInfo name="STD" value="68"/>
3237  <seriesInfo name="RFC" value="5234"/>
3238</reference>
3239
3240<reference anchor="RFC2045">
3241  <front>
3242    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3243    <author initials="N." surname="Freed" fullname="Ned Freed">
3244      <organization>Innosoft International, Inc.</organization>
3245      <address><email>ned@innosoft.com</email></address>
3246    </author>
3247    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3248      <organization>First Virtual Holdings</organization>
3249      <address><email>nsb@nsb.fv.com</email></address>
3250    </author>
3251    <date month="November" year="1996"/>
3252  </front>
3253  <seriesInfo name="RFC" value="2045"/>
3254</reference>
3255
3256<reference anchor="RFC2047">
3257  <front>
3258    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3259    <author initials="K." surname="Moore" fullname="Keith Moore">
3260      <organization>University of Tennessee</organization>
3261      <address><email>moore@cs.utk.edu</email></address>
3262    </author>
3263    <date month="November" year="1996"/>
3264  </front>
3265  <seriesInfo name="RFC" value="2047"/>
3266</reference>
3267
3268<reference anchor="RFC2119">
3269  <front>
3270    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3271    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3272      <organization>Harvard University</organization>
3273      <address><email>sob@harvard.edu</email></address>
3274    </author>
3275    <date month="March" year="1997"/>
3276  </front>
3277  <seriesInfo name="BCP" value="14"/>
3278  <seriesInfo name="RFC" value="2119"/>
3279</reference>
3280
3281<reference anchor="RFC3986">
3282 <front>
3283  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3284  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3285    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3286    <address>
3287       <email>timbl@w3.org</email>
3288       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3289    </address>
3290  </author>
3291  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3292    <organization abbrev="Day Software">Day Software</organization>
3293    <address>
3294      <email>fielding@gbiv.com</email>
3295      <uri>http://roy.gbiv.com/</uri>
3296    </address>
3297  </author>
3298  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3299    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3300    <address>
3301      <email>LMM@acm.org</email>
3302      <uri>http://larry.masinter.net/</uri>
3303    </address>
3304  </author>
3305  <date month='January' year='2005'></date>
3306 </front>
3307 <seriesInfo name="RFC" value="3986"/>
3308 <seriesInfo name="STD" value="66"/>
3309</reference>
3310
3311<reference anchor="USASCII">
3312  <front>
3313    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3314    <author>
3315      <organization>American National Standards Institute</organization>
3316    </author>
3317    <date year="1986"/>
3318  </front>
3319  <seriesInfo name="ANSI" value="X3.4"/>
3320</reference>
3321
3322</references>
3323
3324<references title="Informative References">
3325
3326<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3327  <front>
3328    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3329    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3330      <organization/>
3331    </author>
3332    <author initials="J." surname="Gettys" fullname="J. Gettys">
3333      <organization/>
3334    </author>
3335    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3336      <organization/>
3337    </author>
3338    <author initials="H." surname="Lie" fullname="H. Lie">
3339      <organization/>
3340    </author>
3341    <author initials="C." surname="Lilley" fullname="C. Lilley">
3342      <organization/>
3343    </author>
3344    <date year="1997" month="September"/>
3345  </front>
3346  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3347</reference>
3348
3349<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3350  <front>
3351    <title>Improving HTTP Latency</title>
3352    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3353      <organization/>
3354    </author>
3355    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3356      <organization/>
3357    </author>
3358    <date year="1995" month="December"/>
3359  </front>
3360  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3361</reference>
3362
3363<reference anchor="RFC822">
3364  <front>
3365    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3366    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3367      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3368      <address><email>DCrocker@UDel-Relay</email></address>
3369    </author>
3370    <date month="August" day="13" year="1982"/>
3371  </front>
3372  <seriesInfo name="STD" value="11"/>
3373  <seriesInfo name="RFC" value="822"/>
3374</reference>
3375
3376<reference anchor="RFC959">
3377  <front>
3378    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3379    <author initials="J." surname="Postel" fullname="J. Postel">
3380      <organization>Information Sciences Institute (ISI)</organization>
3381    </author>
3382    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3383      <organization/>
3384    </author>
3385    <date month="October" year="1985"/>
3386  </front>
3387  <seriesInfo name="STD" value="9"/>
3388  <seriesInfo name="RFC" value="959"/>
3389</reference>
3390
3391<reference anchor="RFC1123">
3392  <front>
3393    <title>Requirements for Internet Hosts - Application and Support</title>
3394    <author initials="R." surname="Braden" fullname="Robert Braden">
3395      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3396      <address><email>Braden@ISI.EDU</email></address>
3397    </author>
3398    <date month="October" year="1989"/>
3399  </front>
3400  <seriesInfo name="STD" value="3"/>
3401  <seriesInfo name="RFC" value="1123"/>
3402</reference>
3403
3404<reference anchor="RFC1305">
3405  <front>
3406    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3407    <author initials="D." surname="Mills" fullname="David L. Mills">
3408      <organization>University of Delaware, Electrical Engineering Department</organization>
3409      <address><email>mills@udel.edu</email></address>
3410    </author>
3411    <date month="March" year="1992"/>
3412  </front>
3413  <seriesInfo name="RFC" value="1305"/>
3414</reference>
3415
3416<reference anchor="RFC1436">
3417  <front>
3418    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3419    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3420      <organization>University of Minnesota, Computer and Information Services</organization>
3421      <address><email>fxa@boombox.micro.umn.edu</email></address>
3422    </author>
3423    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3424      <organization>University of Minnesota, Computer and Information Services</organization>
3425      <address><email>mpm@boombox.micro.umn.edu</email></address>
3426    </author>
3427    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3428      <organization>University of Minnesota, Computer and Information Services</organization>
3429      <address><email>lindner@boombox.micro.umn.edu</email></address>
3430    </author>
3431    <author initials="D." surname="Johnson" fullname="David Johnson">
3432      <organization>University of Minnesota, Computer and Information Services</organization>
3433      <address><email>dmj@boombox.micro.umn.edu</email></address>
3434    </author>
3435    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3436      <organization>University of Minnesota, Computer and Information Services</organization>
3437      <address><email>daniel@boombox.micro.umn.edu</email></address>
3438    </author>
3439    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3440      <organization>University of Minnesota, Computer and Information Services</organization>
3441      <address><email>alberti@boombox.micro.umn.edu</email></address>
3442    </author>
3443    <date month="March" year="1993"/>
3444  </front>
3445  <seriesInfo name="RFC" value="1436"/>
3446</reference>
3447
3448<reference anchor="RFC1900">
3449  <front>
3450    <title>Renumbering Needs Work</title>
3451    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3452      <organization>CERN, Computing and Networks Division</organization>
3453      <address><email>brian@dxcoms.cern.ch</email></address>
3454    </author>
3455    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3456      <organization>cisco Systems</organization>
3457      <address><email>yakov@cisco.com</email></address>
3458    </author>
3459    <date month="February" year="1996"/>
3460  </front>
3461  <seriesInfo name="RFC" value="1900"/>
3462</reference>
3463
3464<reference anchor="RFC1945">
3465  <front>
3466    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3467    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3468      <organization>MIT, Laboratory for Computer Science</organization>
3469      <address><email>timbl@w3.org</email></address>
3470    </author>
3471    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3472      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3473      <address><email>fielding@ics.uci.edu</email></address>
3474    </author>
3475    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3476      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3477      <address><email>frystyk@w3.org</email></address>
3478    </author>
3479    <date month="May" year="1996"/>
3480  </front>
3481  <seriesInfo name="RFC" value="1945"/>
3482</reference>
3483
3484<reference anchor="RFC2068">
3485  <front>
3486    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3487    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3488      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3489      <address><email>fielding@ics.uci.edu</email></address>
3490    </author>
3491    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3492      <organization>MIT Laboratory for Computer Science</organization>
3493      <address><email>jg@w3.org</email></address>
3494    </author>
3495    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3496      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3497      <address><email>mogul@wrl.dec.com</email></address>
3498    </author>
3499    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3500      <organization>MIT Laboratory for Computer Science</organization>
3501      <address><email>frystyk@w3.org</email></address>
3502    </author>
3503    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3504      <organization>MIT Laboratory for Computer Science</organization>
3505      <address><email>timbl@w3.org</email></address>
3506    </author>
3507    <date month="January" year="1997"/>
3508  </front>
3509  <seriesInfo name="RFC" value="2068"/>
3510</reference>
3511
3512<reference anchor='RFC2109'>
3513  <front>
3514    <title>HTTP State Management Mechanism</title>
3515    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3516      <organization>Bell Laboratories, Lucent Technologies</organization>
3517      <address><email>dmk@bell-labs.com</email></address>
3518    </author>
3519    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3520      <organization>Netscape Communications Corp.</organization>
3521      <address><email>montulli@netscape.com</email></address>
3522    </author>
3523    <date year='1997' month='February' />
3524  </front>
3525  <seriesInfo name='RFC' value='2109' />
3526</reference>
3527
3528<reference anchor="RFC2145">
3529  <front>
3530    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3531    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3532      <organization>Western Research Laboratory</organization>
3533      <address><email>mogul@wrl.dec.com</email></address>
3534    </author>
3535    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3536      <organization>Department of Information and Computer Science</organization>
3537      <address><email>fielding@ics.uci.edu</email></address>
3538    </author>
3539    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3540      <organization>MIT Laboratory for Computer Science</organization>
3541      <address><email>jg@w3.org</email></address>
3542    </author>
3543    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3544      <organization>W3 Consortium</organization>
3545      <address><email>frystyk@w3.org</email></address>
3546    </author>
3547    <date month="May" year="1997"/>
3548  </front>
3549  <seriesInfo name="RFC" value="2145"/>
3550</reference>
3551
3552<reference anchor="RFC2616">
3553  <front>
3554    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3555    <author initials="R." surname="Fielding" fullname="R. Fielding">
3556      <organization>University of California, Irvine</organization>
3557      <address><email>fielding@ics.uci.edu</email></address>
3558    </author>
3559    <author initials="J." surname="Gettys" fullname="J. Gettys">
3560      <organization>W3C</organization>
3561      <address><email>jg@w3.org</email></address>
3562    </author>
3563    <author initials="J." surname="Mogul" fullname="J. Mogul">
3564      <organization>Compaq Computer Corporation</organization>
3565      <address><email>mogul@wrl.dec.com</email></address>
3566    </author>
3567    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3568      <organization>MIT Laboratory for Computer Science</organization>
3569      <address><email>frystyk@w3.org</email></address>
3570    </author>
3571    <author initials="L." surname="Masinter" fullname="L. Masinter">
3572      <organization>Xerox Corporation</organization>
3573      <address><email>masinter@parc.xerox.com</email></address>
3574    </author>
3575    <author initials="P." surname="Leach" fullname="P. Leach">
3576      <organization>Microsoft Corporation</organization>
3577      <address><email>paulle@microsoft.com</email></address>
3578    </author>
3579    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3580      <organization>W3C</organization>
3581      <address><email>timbl@w3.org</email></address>
3582    </author>
3583    <date month="June" year="1999"/>
3584  </front>
3585  <seriesInfo name="RFC" value="2616"/>
3586</reference>
3587
3588<reference anchor='RFC2818'>
3589  <front>
3590    <title>HTTP Over TLS</title>
3591    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3592      <organization>RTFM, Inc.</organization>
3593      <address><email>ekr@rtfm.com</email></address>
3594    </author>
3595    <date year='2000' month='May' />
3596  </front>
3597  <seriesInfo name='RFC' value='2818' />
3598</reference>
3599
3600<reference anchor='RFC2965'>
3601  <front>
3602    <title>HTTP State Management Mechanism</title>
3603    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3604      <organization>Bell Laboratories, Lucent Technologies</organization>
3605      <address><email>dmk@bell-labs.com</email></address>
3606    </author>
3607    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3608      <organization>Epinions.com, Inc.</organization>
3609      <address><email>lou@montulli.org</email></address>
3610    </author>
3611    <date year='2000' month='October' />
3612  </front>
3613  <seriesInfo name='RFC' value='2965' />
3614</reference>
3615
3616<reference anchor='RFC3864'>
3617  <front>
3618    <title>Registration Procedures for Message Header Fields</title>
3619    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3620      <organization>Nine by Nine</organization>
3621      <address><email>GK-IETF@ninebynine.org</email></address>
3622    </author>
3623    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3624      <organization>BEA Systems</organization>
3625      <address><email>mnot@pobox.com</email></address>
3626    </author>
3627    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3628      <organization>HP Labs</organization>
3629      <address><email>JeffMogul@acm.org</email></address>
3630    </author>
3631    <date year='2004' month='September' />
3632  </front>
3633  <seriesInfo name='BCP' value='90' />
3634  <seriesInfo name='RFC' value='3864' />
3635</reference>
3636
3637<reference anchor='RFC3977'>
3638  <front>
3639    <title>Network News Transfer Protocol (NNTP)</title>
3640    <author initials='C.' surname='Feather' fullname='C. Feather'>
3641      <organization>THUS plc</organization>
3642      <address><email>clive@demon.net</email></address>
3643    </author>
3644    <date year='2006' month='October' />
3645  </front>
3646  <seriesInfo name="RFC" value="3977"/>
3647</reference>
3648
3649<reference anchor="RFC4288">
3650  <front>
3651    <title>Media Type Specifications and Registration Procedures</title>
3652    <author initials="N." surname="Freed" fullname="N. Freed">
3653      <organization>Sun Microsystems</organization>
3654      <address>
3655        <email>ned.freed@mrochek.com</email>
3656      </address>
3657    </author>
3658    <author initials="J." surname="Klensin" fullname="J. Klensin">
3659      <organization/>
3660      <address>
3661        <email>klensin+ietf@jck.com</email>
3662      </address>
3663    </author>
3664    <date year="2005" month="December"/>
3665  </front>
3666  <seriesInfo name="BCP" value="13"/>
3667  <seriesInfo name="RFC" value="4288"/>
3668</reference>
3669
3670<reference anchor='RFC4395'>
3671  <front>
3672    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3673    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3674      <organization>AT&amp;T Laboratories</organization>
3675      <address>
3676        <email>tony+urireg@maillennium.att.com</email>
3677      </address>
3678    </author>
3679    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3680      <organization>Qualcomm, Inc.</organization>
3681      <address>
3682        <email>hardie@qualcomm.com</email>
3683      </address>
3684    </author>
3685    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3686      <organization>Adobe Systems</organization>
3687      <address>
3688        <email>LMM@acm.org</email>
3689      </address>
3690    </author>
3691    <date year='2006' month='February' />
3692  </front>
3693  <seriesInfo name='BCP' value='115' />
3694  <seriesInfo name='RFC' value='4395' />
3695</reference>
3696
3697<reference anchor="RFC5322">
3698  <front>
3699    <title>Internet Message Format</title>
3700    <author initials="P." surname="Resnick" fullname="P. Resnick">
3701      <organization>Qualcomm Incorporated</organization>
3702    </author>
3703    <date year="2008" month="October"/>
3704  </front> 
3705  <seriesInfo name="RFC" value="5322"/>
3706</reference>
3707
3708<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3709  <front>
3710    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3711    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3712      <organization/>
3713    </author>
3714    <date year="2001" month="November"/>
3715  </front>
3716  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3717</reference>
3718
3719<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3720  <front>
3721  <title>Analysis of HTTP Performance Problems</title>
3722  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3723    <organization/>
3724  </author>
3725  <date/>
3726  </front>
3727</reference>
3728
3729<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3730  <front>
3731  <title>Analysis of HTTP Performance</title>
3732  <author initials="J." surname="Touch" fullname="Joe Touch">
3733    <organization>USC/Information Sciences Institute</organization>
3734    <address><email>touch@isi.edu</email></address>
3735  </author>
3736  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3737    <organization>USC/Information Sciences Institute</organization>
3738    <address><email>johnh@isi.edu</email></address>
3739  </author>
3740  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3741    <organization>USC/Information Sciences Institute</organization>
3742    <address><email>katia@isi.edu</email></address>
3743  </author>
3744  <date year="1998" month="Aug"/>
3745  </front>
3746  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3747  <annotation>(original report dated Aug. 1996)</annotation>
3748</reference>
3749
3750<reference anchor="WAIS">
3751  <front>
3752    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3753    <author initials="F." surname="Davis" fullname="F. Davis">
3754      <organization>Thinking Machines Corporation</organization>
3755    </author>
3756    <author initials="B." surname="Kahle" fullname="B. Kahle">
3757      <organization>Thinking Machines Corporation</organization>
3758    </author>
3759    <author initials="H." surname="Morris" fullname="H. Morris">
3760      <organization>Thinking Machines Corporation</organization>
3761    </author>
3762    <author initials="J." surname="Salem" fullname="J. Salem">
3763      <organization>Thinking Machines Corporation</organization>
3764    </author>
3765    <author initials="T." surname="Shen" fullname="T. Shen">
3766      <organization>Thinking Machines Corporation</organization>
3767    </author>
3768    <author initials="R." surname="Wang" fullname="R. Wang">
3769      <organization>Thinking Machines Corporation</organization>
3770    </author>
3771    <author initials="J." surname="Sui" fullname="J. Sui">
3772      <organization>Thinking Machines Corporation</organization>
3773    </author>
3774    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3775      <organization>Thinking Machines Corporation</organization>
3776    </author>
3777    <date month="April" year="1990"/>
3778  </front>
3779  <seriesInfo name="Thinking Machines Corporation" value=""/>
3780</reference>
3781
3782</references>
3783
3784
3785<section title="Tolerant Applications" anchor="tolerant.applications">
3786<t>
3787   Although this document specifies the requirements for the generation
3788   of HTTP/1.1 messages, not all applications will be correct in their
3789   implementation. We therefore recommend that operational applications
3790   be tolerant of deviations whenever those deviations can be
3791   interpreted unambiguously.
3792</t>
3793<t>
3794   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3795   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3796   accept any amount of SP or HTAB characters between fields, even though
3797   only a single SP is required.
3798</t>
3799<t>
3800   The line terminator for message-header fields is the sequence CRLF.
3801   However, we recommend that applications, when parsing such headers,
3802   recognize a single LF as a line terminator and ignore the leading CR.
3803</t>
3804<t>
3805   The character set of an entity-body &SHOULD; be labeled as the lowest
3806   common denominator of the character codes used within that body, with
3807   the exception that not labeling the entity is preferred over labeling
3808   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3809</t>
3810<t>
3811   Additional rules for requirements on parsing and encoding of dates
3812   and other potential problems with date encodings include:
3813</t>
3814<t>
3815  <list style="symbols">
3816     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3817        which appears to be more than 50 years in the future is in fact
3818        in the past (this helps solve the "year 2000" problem).</t>
3819
3820     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3821        Expires date as earlier than the proper value, but &MUST-NOT;
3822        internally represent a parsed Expires date as later than the
3823        proper value.</t>
3824
3825     <t>All expiration-related calculations &MUST; be done in GMT. The
3826        local time zone &MUST-NOT; influence the calculation or comparison
3827        of an age or expiration time.</t>
3828
3829     <t>If an HTTP header incorrectly carries a date value with a time
3830        zone other than GMT, it &MUST; be converted into GMT using the
3831        most conservative possible conversion.</t>
3832  </list>
3833</t>
3834</section>
3835
3836<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3837<t>
3838   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3839   simplify the process of date comparison. Proxies and gateways from
3840   other protocols &SHOULD; ensure that any Date header field present in a
3841   message conforms to one of the HTTP/1.1 formats and rewrite the date
3842   if necessary.
3843</t>
3844</section>
3845
3846<section title="Compatibility with Previous Versions" anchor="compatibility">
3847<t>
3848   HTTP has been in use by the World-Wide Web global information initiative
3849   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3850   was a simple protocol for hypertext data transfer across the Internet
3851   with only a single method and no metadata.
3852   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3853   methods and MIME-like messaging that could include metadata about the data
3854   transferred and modifiers on the request/response semantics. However,
3855   HTTP/1.0 did not sufficiently take into consideration the effects of
3856   hierarchical proxies, caching, the need for persistent connections, or
3857   name-based virtual hosts. The proliferation of incompletely-implemented
3858   applications calling themselves "HTTP/1.0" further necessitated a
3859   protocol version change in order for two communicating applications
3860   to determine each other's true capabilities.
3861</t>
3862<t>
3863   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3864   requirements that enable reliable implementations, adding only
3865   those new features that will either be safely ignored by an HTTP/1.0
3866   recipient or only sent when communicating with a party advertising
3867   compliance with HTTP/1.1.
3868</t>
3869<t>
3870   It is beyond the scope of a protocol specification to mandate
3871   compliance with previous versions. HTTP/1.1 was deliberately
3872   designed, however, to make supporting previous versions easy. It is
3873   worth noting that, at the time of composing this specification
3874   (1996), we would expect commercial HTTP/1.1 servers to:
3875  <list style="symbols">
3876     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3877        1.1 requests;</t>
3878
3879     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3880        1.1;</t>
3881
3882     <t>respond appropriately with a message in the same major version
3883        used by the client.</t>
3884  </list>
3885</t>
3886<t>
3887   And we would expect HTTP/1.1 clients to:
3888  <list style="symbols">
3889     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3890        responses;</t>
3891
3892     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3893        1.1.</t>
3894  </list>
3895</t>
3896<t>
3897   For most implementations of HTTP/1.0, each connection is established
3898   by the client prior to the request and closed by the server after
3899   sending the response. Some implementations implement the Keep-Alive
3900   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3901</t>
3902
3903<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3904<t>
3905   This section summarizes major differences between versions HTTP/1.0
3906   and HTTP/1.1.
3907</t>
3908
3909<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">
3910<t>
3911   The requirements that clients and servers support the Host request-header,
3912   report an error if the Host request-header (<xref target="header.host"/>) is
3913   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3914   are among the most important changes defined by this
3915   specification.
3916</t>
3917<t>
3918   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3919   addresses and servers; there was no other established mechanism for
3920   distinguishing the intended server of a request than the IP address
3921   to which that request was directed. The changes outlined above will
3922   allow the Internet, once older HTTP clients are no longer common, to
3923   support multiple Web sites from a single IP address, greatly
3924   simplifying large operational Web servers, where allocation of many
3925   IP addresses to a single host has created serious problems. The
3926   Internet will also be able to recover the IP addresses that have been
3927   allocated for the sole purpose of allowing special-purpose domain
3928   names to be used in root-level HTTP URLs. Given the rate of growth of
3929   the Web, and the number of servers already deployed, it is extremely
3930   important that all implementations of HTTP (including updates to
3931   existing HTTP/1.0 applications) correctly implement these
3932   requirements:
3933  <list style="symbols">
3934     <t>Both clients and servers &MUST; support the Host request-header.</t>
3935
3936     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3937
3938     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3939        request does not include a Host request-header.</t>
3940
3941     <t>Servers &MUST; accept absolute URIs.</t>
3942  </list>
3943</t>
3944</section>
3945</section>
3946
3947<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3948<t>
3949   Some clients and servers might wish to be compatible with some
3950   previous implementations of persistent connections in HTTP/1.0
3951   clients and servers. Persistent connections in HTTP/1.0 are
3952   explicitly negotiated as they are not the default behavior. HTTP/1.0
3953   experimental implementations of persistent connections are faulty,
3954   and the new facilities in HTTP/1.1 are designed to rectify these
3955   problems. The problem was that some existing 1.0 clients may be
3956   sending Keep-Alive to a proxy server that doesn't understand
3957   Connection, which would then erroneously forward it to the next
3958   inbound server, which would establish the Keep-Alive connection and
3959   result in a hung HTTP/1.0 proxy waiting for the close on the
3960   response. The result is that HTTP/1.0 clients must be prevented from
3961   using Keep-Alive when talking to proxies.
3962</t>
3963<t>
3964   However, talking to proxies is the most important use of persistent
3965   connections, so that prohibition is clearly unacceptable. Therefore,
3966   we need some other mechanism for indicating a persistent connection
3967   is desired, which is safe to use even when talking to an old proxy
3968   that ignores Connection. Persistent connections are the default for
3969   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3970   declaring non-persistence. See <xref target="header.connection"/>.
3971</t>
3972<t>
3973   The original HTTP/1.0 form of persistent connections (the Connection:
3974   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3975</t>
3976</section>
3977
3978<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3979<t>
3980   This specification has been carefully audited to correct and
3981   disambiguate key word usage; RFC 2068 had many problems in respect to
3982   the conventions laid out in <xref target="RFC2119"/>.
3983</t>
3984<t>
3985   Transfer-coding and message lengths all interact in ways that
3986   required fixing exactly when chunked encoding is used (to allow for
3987   transfer encoding that may not be self delimiting); it was important
3988   to straighten out exactly how message lengths are computed. (Sections
3989   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3990   <xref target="header.content-length" format="counter"/>,
3991   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3992</t>
3993<t>
3994   The use and interpretation of HTTP version numbers has been clarified
3995   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3996   version they support to deal with problems discovered in HTTP/1.0
3997   implementations (<xref target="http.version"/>)
3998</t>
3999<t>
4000   Transfer-coding had significant problems, particularly with
4001   interactions with chunked encoding. The solution is that transfer-codings
4002   become as full fledged as content-codings. This involves
4003   adding an IANA registry for transfer-codings (separate from content
4004   codings), a new header field (TE) and enabling trailer headers in the
4005   future. Transfer encoding is a major performance benefit, so it was
4006   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4007   interoperability problem that could have occurred due to interactions
4008   between authentication trailers, chunked encoding and HTTP/1.0
4009   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4010   and <xref target="header.te" format="counter"/>)
4011</t>
4012</section>
4013
4014<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4015<t>
4016  Rules about implicit linear white space between certain grammar productions
4017  have been removed; now it's only allowed when specifically pointed out
4018  in the ABNF.
4019  The CHAR rule does not allow the NUL character anymore (this affects
4020  the comment and quoted-string rules).  Furthermore, the quoted-pair
4021  rule does not allow escaping NUL, CR or LF anymore.
4022  (<xref target="basic.rules"/>)
4023</t>
4024<t>
4025  Clarify that HTTP-Version is case sensitive.
4026  (<xref target="http.version"/>)
4027</t>
4028<t>
4029  Remove reference to non-existant identity transfer-coding value tokens.
4030  (Sections <xref format="counter" target="transfer.codings"/> and
4031  <xref format="counter" target="message.length"/>)
4032</t>
4033<t>
4034  Clarification that the chunk length does not include
4035  the count of the octets in the chunk header and trailer.
4036  (<xref target="chunked.transfer.encoding"/>)
4037</t>
4038<t>
4039  Update use of abs_path production from RFC1808 to the path-absolute + query
4040  components of RFC3986.
4041  (<xref target="request-uri"/>)
4042</t>
4043<t>
4044  Clarify exactly when close connection options must be sent.
4045  (<xref target="header.connection"/>)
4046</t>
4047</section>
4048</section>
4049
4050<section title="Terminology" anchor="terminology">
4051<t>
4052   This specification uses a number of terms to refer to the roles
4053   played by participants in, and objects of, the HTTP communication.
4054</t>
4055<t>
4056  <iref item="connection"/>
4057  <x:dfn>connection</x:dfn>
4058  <list>
4059    <t>
4060      A transport layer virtual circuit established between two programs
4061      for the purpose of communication.
4062    </t>
4063  </list>
4064</t>
4065<t>
4066  <iref item="message"/>
4067  <x:dfn>message</x:dfn>
4068  <list>
4069    <t>
4070      The basic unit of HTTP communication, consisting of a structured
4071      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4072      transmitted via the connection.
4073    </t>
4074  </list>
4075</t>
4076<t>
4077  <iref item="request"/>
4078  <x:dfn>request</x:dfn>
4079  <list>
4080    <t>
4081      An HTTP request message, as defined in <xref target="request"/>.
4082    </t>
4083  </list>
4084</t>
4085<t>
4086  <iref item="response"/>
4087  <x:dfn>response</x:dfn>
4088  <list>
4089    <t>
4090      An HTTP response message, as defined in <xref target="response"/>.
4091    </t>
4092  </list>
4093</t>
4094<t>
4095  <iref item="resource"/>
4096  <x:dfn>resource</x:dfn>
4097  <list>
4098    <t>
4099      A network data object or service that can be identified by a URI,
4100      as defined in <xref target="uri"/>. Resources may be available in multiple
4101      representations (e.g. multiple languages, data formats, size, and
4102      resolutions) or vary in other ways.
4103    </t>
4104  </list>
4105</t>
4106<t>
4107  <iref item="entity"/>
4108  <x:dfn>entity</x:dfn>
4109  <list>
4110    <t>
4111      The information transferred as the payload of a request or
4112      response. An entity consists of metainformation in the form of
4113      entity-header fields and content in the form of an entity-body, as
4114      described in &entity;.
4115    </t>
4116  </list>
4117</t>
4118<t>
4119  <iref item="representation"/>
4120  <x:dfn>representation</x:dfn>
4121  <list>
4122    <t>
4123      An entity included with a response that is subject to content
4124      negotiation, as described in &content.negotiation;. There may exist multiple
4125      representations associated with a particular response status.
4126    </t>
4127  </list>
4128</t>
4129<t>
4130  <iref item="content negotiation"/>
4131  <x:dfn>content negotiation</x:dfn>
4132  <list>
4133    <t>
4134      The mechanism for selecting the appropriate representation when
4135      servicing a request, as described in &content.negotiation;. The
4136      representation of entities in any response can be negotiated
4137      (including error responses).
4138    </t>
4139  </list>
4140</t>
4141<t>
4142  <iref item="variant"/>
4143  <x:dfn>variant</x:dfn>
4144  <list>
4145    <t>
4146      A resource may have one, or more than one, representation(s)
4147      associated with it at any given instant. Each of these
4148      representations is termed a `variant'.  Use of the term `variant'
4149      does not necessarily imply that the resource is subject to content
4150      negotiation.
4151    </t>
4152  </list>
4153</t>
4154<t>
4155  <iref item="client"/>
4156  <x:dfn>client</x:dfn>
4157  <list>
4158    <t>
4159      A program that establishes connections for the purpose of sending
4160      requests.
4161    </t>
4162  </list>
4163</t>
4164<t>
4165  <iref item="user agent"/>
4166  <x:dfn>user agent</x:dfn>
4167  <list>
4168    <t>
4169      The client which initiates a request. These are often browsers,
4170      editors, spiders (web-traversing robots), or other end user tools.
4171    </t>
4172  </list>
4173</t>
4174<t>
4175  <iref item="server"/>
4176  <x:dfn>server</x:dfn>
4177  <list>
4178    <t>
4179      An application program that accepts connections in order to
4180      service requests by sending back responses. Any given program may
4181      be capable of being both a client and a server; our use of these
4182      terms refers only to the role being performed by the program for a
4183      particular connection, rather than to the program's capabilities
4184      in general. Likewise, any server may act as an origin server,
4185      proxy, gateway, or tunnel, switching behavior based on the nature
4186      of each request.
4187    </t>
4188  </list>
4189</t>
4190<t>
4191  <iref item="origin server"/>
4192  <x:dfn>origin server</x:dfn>
4193  <list>
4194    <t>
4195      The server on which a given resource resides or is to be created.
4196    </t>
4197  </list>
4198</t>
4199<t>
4200  <iref item="proxy"/>
4201  <x:dfn>proxy</x:dfn>
4202  <list>
4203    <t>
4204      An intermediary program which acts as both a server and a client
4205      for the purpose of making requests on behalf of other clients.
4206      Requests are serviced internally or by passing them on, with
4207      possible translation, to other servers. A proxy &MUST; implement
4208      both the client and server requirements of this specification. A
4209      "transparent proxy" is a proxy that does not modify the request or
4210      response beyond what is required for proxy authentication and
4211      identification. A "non-transparent proxy" is a proxy that modifies
4212      the request or response in order to provide some added service to
4213      the user agent, such as group annotation services, media type
4214      transformation, protocol reduction, or anonymity filtering. Except
4215      where either transparent or non-transparent behavior is explicitly
4216      stated, the HTTP proxy requirements apply to both types of
4217      proxies.
4218    </t>
4219  </list>
4220</t>
4221<t>
4222  <iref item="gateway"/>
4223  <x:dfn>gateway</x:dfn>
4224  <list>
4225    <t>
4226      A server which acts as an intermediary for some other server.
4227      Unlike a proxy, a gateway receives requests as if it were the
4228      origin server for the requested resource; the requesting client
4229      may not be aware that it is communicating with a gateway.
4230    </t>
4231  </list>
4232</t>
4233<t>
4234  <iref item="tunnel"/>
4235  <x:dfn>tunnel</x:dfn>
4236  <list>
4237    <t>
4238      An intermediary program which is acting as a blind relay between
4239      two connections. Once active, a tunnel is not considered a party
4240      to the HTTP communication, though the tunnel may have been
4241      initiated by an HTTP request. The tunnel ceases to exist when both
4242      ends of the relayed connections are closed.
4243    </t>
4244  </list>
4245</t>
4246<t>
4247  <iref item="cache"/>
4248  <x:dfn>cache</x:dfn>
4249  <list>
4250    <t>
4251      A program's local store of response messages and the subsystem
4252      that controls its message storage, retrieval, and deletion. A
4253      cache stores cacheable responses in order to reduce the response
4254      time and network bandwidth consumption on future, equivalent
4255      requests. Any client or server may include a cache, though a cache
4256      cannot be used by a server that is acting as a tunnel.
4257    </t>
4258  </list>
4259</t>
4260<t>
4261  <iref item="cacheable"/>
4262  <x:dfn>cacheable</x:dfn>
4263  <list>
4264    <t>
4265      A response is cacheable if a cache is allowed to store a copy of
4266      the response message for use in answering subsequent requests. The
4267      rules for determining the cacheability of HTTP responses are
4268      defined in &caching;. Even if a resource is cacheable, there may
4269      be additional constraints on whether a cache can use the cached
4270      copy for a particular request.
4271    </t>
4272  </list>
4273</t>
4274<t>
4275  <iref item="upstream"/>
4276  <iref item="downstream"/>
4277  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4278  <list>
4279    <t>
4280      Upstream and downstream describe the flow of a message: all
4281      messages flow from upstream to downstream.
4282    </t>
4283  </list>
4284</t>
4285<t>
4286  <iref item="inbound"/>
4287  <iref item="outbound"/>
4288  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4289  <list>
4290    <t>
4291      Inbound and outbound refer to the request and response paths for
4292      messages: "inbound" means "traveling toward the origin server",
4293      and "outbound" means "traveling toward the user agent"
4294    </t>
4295  </list>
4296</t>
4297</section>
4298
4299<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4300
4301<section title="Since RFC2616">
4302<t>
4303  Extracted relevant partitions from <xref target="RFC2616"/>.
4304</t>
4305</section>
4306
4307<section title="Since draft-ietf-httpbis-p1-messaging-00">
4308<t>
4309  Closed issues:
4310  <list style="symbols"> 
4311    <t>
4312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4313      "HTTP Version should be case sensitive"
4314      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4315    </t>
4316    <t>
4317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4318      "'unsafe' characters"
4319      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4320    </t>
4321    <t>
4322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4323      "Chunk Size Definition"
4324      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4328      "Message Length"
4329      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4330    </t>
4331    <t>
4332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4333      "Media Type Registrations"
4334      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4335    </t>
4336    <t>
4337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4338      "URI includes query"
4339      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4340    </t>
4341    <t>
4342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4343      "No close on 1xx responses"
4344      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4345    </t>
4346    <t>
4347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4348      "Remove 'identity' token references"
4349      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4350    </t>
4351    <t>
4352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4353      "Import query BNF"
4354    </t>
4355    <t>
4356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4357      "qdtext BNF"
4358    </t>
4359    <t>
4360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4361      "Normative and Informative references"
4362    </t>
4363    <t>
4364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4365      "RFC2606 Compliance"
4366    </t>
4367    <t>
4368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4369      "RFC977 reference"
4370    </t>
4371    <t>
4372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4373      "RFC1700 references"
4374    </t>
4375    <t>
4376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4377      "inconsistency in date format explanation"
4378    </t>
4379    <t>
4380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4381      "Date reference typo"
4382    </t>
4383    <t>
4384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4385      "Informative references"
4386    </t>
4387    <t>
4388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4389      "ISO-8859-1 Reference"
4390    </t>
4391    <t>
4392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4393      "Normative up-to-date references"
4394    </t>
4395  </list>
4396</t>
4397<t>
4398  Other changes:
4399  <list style="symbols"> 
4400    <t>
4401      Update media type registrations to use RFC4288 template.
4402    </t>
4403    <t>
4404      Use names of RFC4234 core rules DQUOTE and HTAB,
4405      fix broken ABNF for chunk-data
4406      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4407    </t>
4408  </list>
4409</t>
4410</section>
4411
4412<section title="Since draft-ietf-httpbis-p1-messaging-01">
4413<t>
4414  Closed issues:
4415  <list style="symbols"> 
4416    <t>
4417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4418      "Bodies on GET (and other) requests"
4419    </t>
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4422      "Updating to RFC4288"
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4426      "Status Code and Reason Phrase"
4427    </t>
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4430      "rel_path not used"
4431    </t>
4432  </list>
4433</t>
4434<t>
4435  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4436  <list style="symbols"> 
4437    <t>
4438      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4439      "trailer-part").
4440    </t>
4441    <t>
4442      Avoid underscore character in rule names ("http_URL" ->
4443      "http-URL", "abs_path" -> "path-absolute").
4444    </t>
4445    <t>
4446      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4447      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4448      have to be updated when switching over to RFC3986.
4449    </t>
4450    <t>
4451      Synchronize core rules with RFC5234 (this includes a change to CHAR
4452      which now excludes NUL).
4453    </t>
4454    <t>
4455      Get rid of prose rules that span multiple lines.
4456    </t>
4457    <t>
4458      Get rid of unused rules LOALPHA and UPALPHA.
4459    </t>
4460    <t>
4461      Move "Product Tokens" section (back) into Part 1, as "token" is used
4462      in the definition of the Upgrade header.
4463    </t>
4464    <t>
4465      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4466    </t>
4467    <t>
4468      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4469    </t>
4470  </list>
4471</t>
4472</section>
4473
4474<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4475<t>
4476  Closed issues:
4477  <list style="symbols"> 
4478    <t>
4479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4480      "HTTP-date vs. rfc1123-date"
4481    </t>
4482    <t>
4483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4484      "WS in quoted-pair"
4485    </t>
4486  </list>
4487</t>
4488<t>
4489  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4490  <list style="symbols"> 
4491    <t>
4492      Reference RFC 3984, and update header registrations for headers defined
4493      in this document.
4494    </t>
4495  </list>
4496</t>
4497<t>
4498  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4499  <list style="symbols"> 
4500    <t>
4501      Replace string literals when the string really is case-sensitive (HTTP-Version).
4502    </t>
4503  </list>
4504</t>
4505</section>
4506
4507<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4508<t>
4509  Closed issues:
4510  <list style="symbols"> 
4511    <t>
4512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4513      "Connection closing"
4514    </t>
4515    <t>
4516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4517      "Move registrations and registry information to IANA Considerations"
4518    </t>
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4521      "need new URL for PAD1995 reference"
4522    </t>
4523    <t>
4524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4525      "IANA Considerations: update HTTP URI scheme registration"
4526    </t>
4527    <t>
4528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4529      "Cite HTTPS URI scheme definition"
4530    </t>
4531    <t>
4532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4533      "List-type headers vs Set-Cookie"
4534    </t>
4535  </list>
4536</t>
4537<t>
4538  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4539  <list style="symbols"> 
4540    <t>
4541      Replace string literals when the string really is case-sensitive (HTTP-Date).
4542    </t>
4543    <t>
4544      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4545    </t>
4546  </list>
4547</t>
4548</section>
4549
4550<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4551<t>
4552  Closed issues:
4553  <list style="symbols"> 
4554    <t>
4555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4556      "Out-of-date reference for URIs"
4557    </t>
4558    <t>
4559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4560      "RFC 2822 is updated by RFC 5322"
4561    </t>
4562  </list>
4563</t>
4564<t>
4565  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4566  <list style="symbols"> 
4567    <t>
4568      Use "/" instead of "|" for alternatives.
4569    </t>
4570    <t>
4571      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4572    </t>
4573    <t>
4574      Only reference RFC 5234's core rules.
4575    </t>
4576    <t>
4577      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4578      whitespace ("OWS") and required whitespace ("RWS").
4579    </t>
4580    <t>
4581      Rewrite ABNFs to spell out whitespace rules, factor out
4582      header value format definitions.
4583    </t>
4584  </list>
4585</t>
4586</section>
4587
4588</section>
4589
4590</back>
4591</rfc>
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