source: draft-ietf-httpbis/latest/p1-messaging.xml @ 433

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "December">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x=''/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x=''/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x=''/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x=''/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x=''/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
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=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
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></email>
73      <uri></uri>
74    </address>
75  </author>
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></email>
88      <uri></uri>
89    </address>
90  </author>
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></email>
104    </address>
105  </author>
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></email>
118    </address>
119  </author>
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></email>
132      <uri></uri>
133    </address>
134  </author>
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></email>
146    </address>
147  </author>
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></email>
162      <uri></uri>
163    </address>
164  </author>
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></email>
178      <uri></uri>
179    </address>
180  </author>
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></email>       
193      <uri></uri>     
194    </address>
195  </author>
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
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.
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 ( The current issues list is
218    at <eref target=""/>
219    and related documents (including fancy diffs) can be found at
220    <eref target=""/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.05"/>.
224  </t>
228<section title="Introduction" anchor="introduction">
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 hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets and
235   relationships between 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).
242   HTTP is a generic interface protocol for informations systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
253   HTTP is also designed for use as a generic protocol for translating
254   communication to and from other Internet information systems, such as
255   USENET news services via NNTP <xref target="RFC3977"/>,
256   file services via FTP <xref target="RFC959"/>,
257   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
258   HTTP proxies and gateways provide access to alternative information
259   services by translating their diverse protocols into a hypermedia
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
264   One consequence of HTTP flexibility is that we cannot define the protocol
265   in terms of how to implement it behind the interface. Instead, we are
266   limited to restricting the syntax of communication, defining the intent
267   of received communication, and the expected behavior of recipients. If
268   the communication is considered in isolation, then successful actions
269   should be reflected in the observable interface provided by servers.
270   However, since many clients are potentially acting in parallel and
271   perhaps at cross-purposes, it would be meaningless to require that such
272   behavior be observable.
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1" and obsoleting
277   <xref target="RFC2616"/>.
278   Part 1 defines the URI schemes specific to HTTP-based resources, overall
279   network operation, transport protocol connection management, and HTTP
280   message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for a message parser and transparent
284   message-forwarding intermediaries.
287<section title="Requirements" anchor="intro.requirements">
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
294   An implementation is not compliant if it fails to satisfy one or more
295   of the &MUST; or &REQUIRED; level requirements for the protocols it
296   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
297   level and all the &SHOULD; level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the &MUST;
299   level requirements but not all the &SHOULD; level requirements for its
300   protocols is said to be "conditionally compliant."
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CR"/>
307<iref primary="true" item="Grammar" subitem="CRLF"/>
308<iref primary="true" item="Grammar" subitem="CTL"/>
309<iref primary="true" item="Grammar" subitem="DIGIT"/>
310<iref primary="true" item="Grammar" subitem="DQUOTE"/>
311<iref primary="true" item="Grammar" subitem="HEXDIG"/>
312<iref primary="true" item="Grammar" subitem="LF"/>
313<iref primary="true" item="Grammar" subitem="OCTET"/>
314<iref primary="true" item="Grammar" subitem="SP"/>
315<iref primary="true" item="Grammar" subitem="VCHAR"/>
316<iref primary="true" item="Grammar" subitem="WSP"/>
317<t anchor="core.rules">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CTL"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="CRLF"/>
322  <x:anchor-alias value="DIGIT"/>
323  <x:anchor-alias value="DQUOTE"/>
324  <x:anchor-alias value="HEXDIG"/>
325  <x:anchor-alias value="LF"/>
326  <x:anchor-alias value="OCTET"/>
327  <x:anchor-alias value="SP"/>
328  <x:anchor-alias value="VCHAR"/>
329  <x:anchor-alias value="WSP"/>
330   This specification uses the Augmented Backus-Naur Form (ABNF) notation
331   of <xref target="RFC5234"/>.  The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372#element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
3741#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
421<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"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429                 ; see <xref target="message.headers"/>
431<t anchor="rule.token.separators">
432  <x:anchor-alias value="tchar"/>
433  <x:anchor-alias value="token"/>
434   Many HTTP/1.1 header field values consist of words separated by whitespace
435   or special characters. These special characters &MUST; be in a quoted
436   string to be used within a parameter value (as defined in
437   <xref target="transfer.codings"/>).
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
440  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
441                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
442                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
444  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
446<t anchor="rule.quoted-string">
447  <x:anchor-alias value="quoted-string"/>
448  <x:anchor-alias value="qdtext"/>
449  <x:anchor-alias value="obs-text"/>
450   A string of text is parsed as a single word if it is quoted using
451   double-quote marks.
453<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
454  <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>
455  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
456  <x:ref>obs-text</x:ref>       = %x80-FF
458<t anchor="rule.quoted-pair">
459  <x:anchor-alias value="quoted-pair"/>
460  <x:anchor-alias value="quoted-text"/>
461   The backslash character ("\") &MAY; be used as a single-character
462   quoting mechanism only within quoted-string and comment constructs.
464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
465  <x:ref>quoted-text</x:ref>    = %x01-09 /
466                   %x0B-0C /
467                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
468  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
472<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
473  <x:anchor-alias value="request-header"/>
474  <x:anchor-alias value="response-header"/>
475  <x:anchor-alias value="accept-params"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
482  The ABNF rules below are defined in other parts:
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
490  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
491  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
493<figure><!-- Part6--><artwork type="abnf2616">
494  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
495  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
496  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
503<section title="HTTP architecture" anchor="architecture">
505   HTTP was created with a specific architecture in mind, the World Wide Web,
506   and has evolved over time to support the scalability needs of a worldwide
507   hypertext system. Much of that architecture is reflected in the terminology
508   and syntax productions used to define HTTP.
511<section title="Uniform Resource Identifiers" anchor="uri">
513   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
514   throughout HTTP as the means for identifying resources. URI references
515   are used to target requests, redirect responses, and define relationships.
516   HTTP does not limit what a resource may be; it merely defines an interface
517   that can be used to interact with a resource via HTTP. More information on
518   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
520  <x:anchor-alias value="URI"/>
521  <x:anchor-alias value="URI-reference"/>
522  <x:anchor-alias value="absolute-URI"/>
523  <x:anchor-alias value="relative-part"/>
524  <x:anchor-alias value="authority"/>
525  <x:anchor-alias value="fragment"/>
526  <x:anchor-alias value="path-abempty"/>
527  <x:anchor-alias value="path-absolute"/>
528  <x:anchor-alias value="port"/>
529  <x:anchor-alias value="query"/>
530  <x:anchor-alias value="uri-host"/>
531  <x:anchor-alias value="partial-URI"/>
533   This specification adopts the definitions of "URI-reference",
534   "absolute-URI", "relative-part", "fragment", "port", "host",
535   "path-abempty", "path-absolute", "query", and "authority" from
536   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
537   protocol elements that allow a relative URI without a fragment.
539<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"/>
540  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
541  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
542  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
543  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
544  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
545  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
546  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
549  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
550  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
552  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
555   Each protocol element in HTTP that allows a URI reference will indicate in
556   its ABNF production whether the element allows only a URI in absolute form
557   (absolute-URI), any relative reference (relative-ref), or some other subset
558   of the URI-reference grammar. Unless otherwise indicated, URI references
559   are parsed relative to the request target (the default base URI for both
560   the request and its corresponding response).
563<section title="http URI scheme" anchor="http.uri">
564  <x:anchor-alias value="http-URI"/>
565  <iref item="http URI scheme" primary="true"/>
566  <iref item="URI scheme" subitem="http" primary="true"/>
568   The "http" scheme is used to locate network resources via the HTTP
569   protocol. This section defines the syntax and semantics for identifiers
570   using the http or https URI schemes.
572<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
573  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
576   If the port is empty or not given, port 80 is assumed. The semantics
577   are that the identified resource is located at the server listening
578   for TCP connections on that port of that host, and the request-target
579   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
580   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
581   the path-absolute is not present in the URL, it &MUST; be given as "/" when
582   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
583   receives a host name which is not a fully qualified domain name, it
584   &MAY; add its domain to the host name it received. If a proxy receives
585   a fully qualified domain name, the proxy &MUST-NOT; change the host
586   name.
589  <iref item="https URI scheme"/>
590  <iref item="URI scheme" subitem="https"/>
591  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
595<section title="URI Comparison" anchor="uri.comparison">
597   When comparing two URIs to decide if they match or not, a client
598   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
599   URIs, with these exceptions:
600  <list style="symbols">
601    <t>A port that is empty or not given is equivalent to the default
602        port for that URI-reference;</t>
603    <t>Comparisons of host names &MUST; be case-insensitive;</t>
604    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
605    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
606  </list>
609   Characters other than those in the "reserved" set (see
610   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
611   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
614   For example, the following three URIs are equivalent:
616<figure><artwork type="example">
623<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
629<section title="Overall Operation" anchor="intro.overall.operation">
631   HTTP is a request/response protocol. A client sends a
632   request to the server in the form of a request method, URI, and
633   protocol version, followed by a MIME-like message containing request
634   modifiers, client information, and possible body content over a
635   connection with a server. The server responds with a status line,
636   including the message's protocol version and a success or error code,
637   followed by a MIME-like message containing server information, entity
638   metainformation, and possible entity-body content.
641   Most HTTP communication is initiated by a user agent and consists of
642   a request to be applied to a resource on some origin server. In the
643   simplest case, this may be accomplished via a single connection (v)
644   between the user agent (UA) and the origin server (O).
646<figure><artwork type="drawing">
647       request chain ------------------------&gt;
648    UA -------------------v------------------- O
649       &lt;----------------------- response chain
652   A more complicated situation occurs when one or more intermediaries
653   are present in the request/response chain. There are three common
654   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
655   forwarding agent, receiving requests for a URI in its absolute form,
656   rewriting all or part of the message, and forwarding the reformatted
657   request toward the server identified by the URI. A gateway is a
658   receiving agent, acting as a layer above some other server(s) and, if
659   necessary, translating the requests to the underlying server's
660   protocol. A tunnel acts as a relay point between two connections
661   without changing the messages; tunnels are used when the
662   communication needs to pass through an intermediary (such as a
663   firewall) even when the intermediary cannot understand the contents
664   of the messages.
666<figure><artwork type="drawing">
667       request chain --------------------------------------&gt;
668    UA -----v----- A -----v----- B -----v----- C -----v----- O
669       &lt;------------------------------------- response chain
672   The figure above shows three intermediaries (A, B, and C) between the
673   user agent and origin server. A request or response message that
674   travels the whole chain will pass through four separate connections.
675   This distinction is important because some HTTP communication options
676   may apply only to the connection with the nearest, non-tunnel
677   neighbor, only to the end-points of the chain, or to all connections
678   along the chain. Although the diagram is linear, each participant may
679   be engaged in multiple, simultaneous communications. For example, B
680   may be receiving requests from many clients other than A, and/or
681   forwarding requests to servers other than C, at the same time that it
682   is handling A's request.
685   Any party to the communication which is not acting as a tunnel may
686   employ an internal cache for handling requests. The effect of a cache
687   is that the request/response chain is shortened if one of the
688   participants along the chain has a cached response applicable to that
689   request. The following illustrates the resulting chain if B has a
690   cached copy of an earlier response from O (via C) for a request which
691   has not been cached by UA or A.
693<figure><artwork type="drawing">
694          request chain ----------&gt;
695       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
696          &lt;--------- response chain
699   Not all responses are usefully cacheable, and some requests may
700   contain modifiers which place special requirements on cache behavior.
701   HTTP requirements for cache behavior and cacheable responses are
702   defined in &caching;.
705   In fact, there are a wide variety of architectures and configurations
706   of caches and proxies currently being experimented with or deployed
707   across the World Wide Web. These systems include national hierarchies
708   of proxy caches to save transoceanic bandwidth, systems that
709   broadcast or multicast cache entries, organizations that distribute
710   subsets of cached data via CD-ROM, and so on. HTTP systems are used
711   in corporate intranets over high-bandwidth links, and for access via
712   PDAs with low-power radio links and intermittent connectivity. The
713   goal of HTTP/1.1 is to support the wide diversity of configurations
714   already deployed while introducing protocol constructs that meet the
715   needs of those who build web applications that require high
716   reliability and, failing that, at least reliable indications of
717   failure.
720   HTTP communication usually takes place over TCP/IP connections. The
721   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
722   not preclude HTTP from being implemented on top of any other protocol
723   on the Internet, or on other networks. HTTP only presumes a reliable
724   transport; any protocol that provides such guarantees can be used;
725   the mapping of the HTTP/1.1 request and response structures onto the
726   transport data units of the protocol in question is outside the scope
727   of this specification.
730   In HTTP/1.0, most implementations used a new connection for each
731   request/response exchange. In HTTP/1.1, a connection may be used for
732   one or more request/response exchanges, although connections may be
733   closed for a variety of reasons (see <xref target="persistent.connections"/>).
737<section title="Use of HTTP for proxy communication" anchor="http.proxy">
739   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
742<section title="Interception of HTTP for access control" anchor="http.intercept">
744   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
747<section title="Use of HTTP by other protocols" anchor="http.others">
749   <cref>TBD: Profiles of HTTP defined by other protocol.
750   Extensions of HTTP like WebDAV.</cref>
753<section title="Use of HTTP by media type specification" anchor="">
755   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
760<section title="Protocol Parameters" anchor="protocol.parameters">
762<section title="HTTP Version" anchor="http.version">
763  <x:anchor-alias value="HTTP-Version"/>
764  <x:anchor-alias value="HTTP-Prot-Name"/>
766   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
767   of the protocol. The protocol versioning policy is intended to allow
768   the sender to indicate the format of a message and its capacity for
769   understanding further HTTP communication, rather than the features
770   obtained via that communication. No change is made to the version
771   number for the addition of message components which do not affect
772   communication behavior or which only add to extensible field values.
773   The &lt;minor&gt; number is incremented when the changes made to the
774   protocol add features which do not change the general message parsing
775   algorithm, but which may add to the message semantics and imply
776   additional capabilities of the sender. The &lt;major&gt; number is
777   incremented when the format of a message within the protocol is
778   changed. See <xref target="RFC2145"/> for a fuller explanation.
781   The version of an HTTP message is indicated by an HTTP-Version field
782   in the first line of the message. HTTP-Version is case-sensitive.
784<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
785  <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>
786  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
789   Note that the major and minor numbers &MUST; be treated as separate
790   integers and that each &MAY; be incremented higher than a single digit.
791   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
792   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
793   &MUST-NOT; be sent.
796   An application that sends a request or response message that includes
797   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
798   with this specification. Applications that are at least conditionally
799   compliant with this specification &SHOULD; use an HTTP-Version of
800   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
801   not compatible with HTTP/1.0. For more details on when to send
802   specific HTTP-Version values, see <xref target="RFC2145"/>.
805   The HTTP version of an application is the highest HTTP version for
806   which the application is at least conditionally compliant.
809   Proxy and gateway applications need to be careful when forwarding
810   messages in protocol versions different from that of the application.
811   Since the protocol version indicates the protocol capability of the
812   sender, a proxy/gateway &MUST-NOT; send a message with a version
813   indicator which is greater than its actual version. If a higher
814   version request is received, the proxy/gateway &MUST; either downgrade
815   the request version, or respond with an error, or switch to tunnel
816   behavior.
819   Due to interoperability problems with HTTP/1.0 proxies discovered
820   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
821   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
822   they support. The proxy/gateway's response to that request &MUST; be in
823   the same major version as the request.
826  <list>
827    <t>
828      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
829      of header fields required or forbidden by the versions involved.
830    </t>
831  </list>
835<section title="Date/Time Formats" anchor="date.time.formats">
836<section title="Full Date" anchor="">
837  <x:anchor-alias value="HTTP-date"/>
838  <x:anchor-alias value="obsolete-date"/>
839  <x:anchor-alias value="rfc1123-date"/>
840  <x:anchor-alias value="rfc850-date"/>
841  <x:anchor-alias value="asctime-date"/>
842  <x:anchor-alias value="date1"/>
843  <x:anchor-alias value="date2"/>
844  <x:anchor-alias value="date3"/>
845  <x:anchor-alias value="rfc1123-date"/>
846  <x:anchor-alias value="time"/>
847  <x:anchor-alias value="wkday"/>
848  <x:anchor-alias value="weekday"/>
849  <x:anchor-alias value="month"/>
851   HTTP applications have historically allowed three different formats
852   for the representation of date/time stamps:
854<figure><artwork type="example">
855   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
856   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
857   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
860   The first format is preferred as an Internet standard and represents
861   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
862   other formats are described here only for
863   compatibility with obsolete implementations.
864   HTTP/1.1 clients and servers that parse the date value &MUST; accept
865   all three formats (for compatibility with HTTP/1.0), though they &MUST;
866   only generate the RFC 1123 format for representing HTTP-date values
867   in header fields. See <xref target="tolerant.applications"/> for further information.
870      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
871      accepting date values that may have been sent by non-HTTP
872      applications, as is sometimes the case when retrieving or posting
873      messages via proxies/gateways to SMTP or NNTP.
876   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
877   (GMT), without exception. For the purposes of HTTP, GMT is exactly
878   equal to UTC (Coordinated Universal Time). This is indicated in the
879   first two formats by the inclusion of "GMT" as the three-letter
880   abbreviation for time zone, and &MUST; be assumed when reading the
881   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
882   additional whitespace beyond that specifically included as SP in the
883   grammar.
885<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"/>
886  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
887  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
888  <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
889  <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
890  <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>
891  <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>
892                 ; day month year (e.g., 02 Jun 1982)
893  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
894                 ; day-month-year (e.g., 02-Jun-82)
895  <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> ))
896                 ; month day (e.g., Jun  2)
897  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
898                 ; 00:00:00 - 23:59:59
899  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
900               / s-Thu / s-Fri / s-Sat / s-Sun
901  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
902               / l-Thu / l-Fri / l-Sat / l-Sun
903  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
904               / s-May / s-Jun / s-Jul / s-Aug
905               / s-Sep / s-Oct / s-Nov / s-Dec
907  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
909  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
910  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
911  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
912  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
913  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
914  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
915  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
917  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
918  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
919  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
920  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
921  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
922  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
923  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
925  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
926  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
927  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
928  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
929  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
930  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
931  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
932  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
933  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
934  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
935  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
936  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
939      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
940      to their usage within the protocol stream. Clients and servers are
941      not required to use these formats for user presentation, request
942      logging, etc.
947<section title="Transfer Codings" anchor="transfer.codings">
948  <x:anchor-alias value="parameter"/>
949  <x:anchor-alias value="transfer-coding"/>
950  <x:anchor-alias value="transfer-extension"/>
952   Transfer-coding values are used to indicate an encoding
953   transformation that has been, can be, or may need to be applied to an
954   entity-body in order to ensure "safe transport" through the network.
955   This differs from a content coding in that the transfer-coding is a
956   property of the message, not of the original entity.
958<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
959  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
960  <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> )
962<t anchor="rule.parameter">
963  <x:anchor-alias value="attribute"/>
964  <x:anchor-alias value="parameter"/>
965  <x:anchor-alias value="value"/>
966   Parameters are in  the form of attribute/value pairs.
968<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"/>
969  <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>
970  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
971  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
974   All transfer-coding values are case-insensitive. HTTP/1.1 uses
975   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
976   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
979   Whenever a transfer-coding is applied to a message-body, the set of
980   transfer-codings &MUST; include "chunked", unless the message indicates it
981   is terminated by closing the connection. When the "chunked" transfer-coding
982   is used, it &MUST; be the last transfer-coding applied to the
983   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
984   than once to a message-body. These rules allow the recipient to
985   determine the transfer-length of the message (<xref target="message.length"/>).
988   Transfer-codings are analogous to the Content-Transfer-Encoding
989   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
990   binary data over a 7-bit transport service. However, safe transport
991   has a different focus for an 8bit-clean transfer protocol. In HTTP,
992   the only unsafe characteristic of message-bodies is the difficulty in
993   determining the exact body length (<xref target="message.length"/>), or the desire to
994   encrypt data over a shared transport.
997   The Internet Assigned Numbers Authority (IANA) acts as a registry for
998   transfer-coding value tokens. Initially, the registry contains the
999   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1000   "gzip", "compress", and "deflate" (&content-codings;).
1003   New transfer-coding value tokens &SHOULD; be registered in the same way
1004   as new content-coding value tokens (&content-codings;).
1007   A server which receives an entity-body with a transfer-coding it does
1008   not understand &SHOULD; return 501 (Not Implemented), and close the
1009   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1010   client.
1013<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1014  <x:anchor-alias value="chunk"/>
1015  <x:anchor-alias value="Chunked-Body"/>
1016  <x:anchor-alias value="chunk-data"/>
1017  <x:anchor-alias value="chunk-ext"/>
1018  <x:anchor-alias value="chunk-ext-name"/>
1019  <x:anchor-alias value="chunk-ext-val"/>
1020  <x:anchor-alias value="chunk-size"/>
1021  <x:anchor-alias value="last-chunk"/>
1022  <x:anchor-alias value="trailer-part"/>
1024   The chunked encoding modifies the body of a message in order to
1025   transfer it as a series of chunks, each with its own size indicator,
1026   followed by an &OPTIONAL; trailer containing entity-header fields. This
1027   allows dynamically produced content to be transferred along with the
1028   information necessary for the recipient to verify that it has
1029   received the full message.
1031<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"/>
1032  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1033                   <x:ref>last-chunk</x:ref>
1034                   <x:ref>trailer-part</x:ref>
1035                   <x:ref>CRLF</x:ref>
1037  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1038                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1039  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1040  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1042  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1043                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1044  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1045  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1046  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1047  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1050   The chunk-size field is a string of hex digits indicating the size of
1051   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1052   zero, followed by the trailer, which is terminated by an empty line.
1055   The trailer allows the sender to include additional HTTP header
1056   fields at the end of the message. The Trailer header field can be
1057   used to indicate which header fields are included in a trailer (see
1058   <xref target="header.trailer"/>).
1061   A server using chunked transfer-coding in a response &MUST-NOT; use the
1062   trailer for any header fields unless at least one of the following is
1063   true:
1064  <list style="numbers">
1065    <t>the request included a TE header field that indicates "trailers" is
1066     acceptable in the transfer-coding of the  response, as described in
1067     <xref target="header.te"/>; or,</t>
1069    <t>the server is the origin server for the response, the trailer
1070     fields consist entirely of optional metadata, and the recipient
1071     could use the message (in a manner acceptable to the origin server)
1072     without receiving this metadata.  In other words, the origin server
1073     is willing to accept the possibility that the trailer fields might
1074     be silently discarded along the path to the client.</t>
1075  </list>
1078   This requirement prevents an interoperability failure when the
1079   message is being received by an HTTP/1.1 (or later) proxy and
1080   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1081   compliance with the protocol would have necessitated a possibly
1082   infinite buffer on the proxy.
1085   A process for decoding the "chunked" transfer-coding
1086   can be represented in pseudo-code as:
1088<figure><artwork type="code">
1089  length := 0
1090  read chunk-size, chunk-ext (if any) and CRLF
1091  while (chunk-size &gt; 0) {
1092     read chunk-data and CRLF
1093     append chunk-data to entity-body
1094     length := length + chunk-size
1095     read chunk-size and CRLF
1096  }
1097  read entity-header
1098  while (entity-header not empty) {
1099     append entity-header to existing header fields
1100     read entity-header
1101  }
1102  Content-Length := length
1103  Remove "chunked" from Transfer-Encoding
1106   All HTTP/1.1 applications &MUST; be able to receive and decode the
1107   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1108   they do not understand.
1113<section title="Product Tokens" anchor="product.tokens">
1114  <x:anchor-alias value="product"/>
1115  <x:anchor-alias value="product-version"/>
1117   Product tokens are used to allow communicating applications to
1118   identify themselves by software name and version. Most fields using
1119   product tokens also allow sub-products which form a significant part
1120   of the application to be listed, separated by whitespace. By
1121   convention, the products are listed in order of their significance
1122   for identifying the application.
1124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1125  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1126  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1129   Examples:
1131<figure><artwork type="example">
1132    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1133    Server: Apache/0.8.4
1136   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1137   used for advertising or other non-essential information. Although any
1138   token character &MAY; appear in a product-version, this token &SHOULD;
1139   only be used for a version identifier (i.e., successive versions of
1140   the same product &SHOULD; only differ in the product-version portion of
1141   the product value).
1147<section title="HTTP Message" anchor="http.message">
1149<section title="Message Types" anchor="message.types">
1150  <x:anchor-alias value="generic-message"/>
1151  <x:anchor-alias value="HTTP-message"/>
1152  <x:anchor-alias value="start-line"/>
1154   HTTP messages consist of requests from client to server and responses
1155   from server to client.
1157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1158  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1161   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1162   message format of <xref target="RFC5322"/> for transferring entities (the payload
1163   of the message). Both types of message consist of a start-line, zero
1164   or more header fields (also known as "headers"), an empty line (i.e.,
1165   a line with nothing preceding the CRLF) indicating the end of the
1166   header fields, and possibly a message-body.
1168<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1169  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1170                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1171                    <x:ref>CRLF</x:ref>
1172                    [ <x:ref>message-body</x:ref> ]
1173  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1176   In the interest of robustness, servers &SHOULD; ignore any empty
1177   line(s) received where a Request-Line is expected. In other words, if
1178   the server is reading the protocol stream at the beginning of a
1179   message and receives a CRLF first, it should ignore the CRLF.
1182   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1183   after a POST request. To restate what is explicitly forbidden by the
1184   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1185   extra CRLF.
1188   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1189   header field. The presence of whitespace might be an attempt to trick a
1190   noncompliant implementation of HTTP into ignoring that field or processing
1191   the next line as a new request, either of which may result in security
1192   issues when implementations within the request chain interpret the
1193   same message differently. HTTP/1.1 servers &MUST; reject such a message
1194   with a 400 (Bad Request) response.
1198<section title="Message Headers" anchor="message.headers">
1199  <x:anchor-alias value="field-content"/>
1200  <x:anchor-alias value="field-name"/>
1201  <x:anchor-alias value="field-value"/>
1202  <x:anchor-alias value="message-header"/>
1204   HTTP header fields follow the same general format as Internet messages in
1205   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1206   of a name followed by a colon (":"), optional whitespace, and the field
1207   value. Field names are case-insensitive.
1209<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"/>
1210  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1211  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1212  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1213  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1216   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1217   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1218   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1219   header field-values use only a subset of the US-ASCII charset
1220   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1221   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1222   (obs-text) octets in field-content as opaque data.
1225   No whitespace is allowed between the header field-name and colon. For
1226   security reasons, any request message received containing such whitespace
1227   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1228   whitespace in a response message &MUST; be removed.
1231   The field value &MAY; be preceded by optional whitespace; a single SP is
1232   preferred. The field-value does not include any leading or trailing white
1233   space: OWS occurring before the first non-whitespace character of the
1234   field-value or after the last non-whitespace character of the field-value
1235   is ignored and &MAY; be removed without changing the meaning of the header
1236   field.
1239   Historically, HTTP header field values could be extended over multiple
1240   lines by preceding each extra line with at least one space or horizontal
1241   tab character (line folding). This specification deprecates such line
1242   folding except within the message/http media type
1243   (<xref target=""/>).
1244   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1245   (i.e., that contain any field-content that matches the obs-fold rule) unless
1246   the message is intended for packaging within the message/http media type.
1247   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1248   obs-fold whitespace with a single SP prior to interpreting the field value
1249   or forwarding the message downstream.
1251<t anchor="rule.comment">
1252  <x:anchor-alias value="comment"/>
1253  <x:anchor-alias value="ctext"/>
1254   Comments can be included in some HTTP header fields by surrounding
1255   the comment text with parentheses. Comments are only allowed in
1256   fields containing "comment" as part of their field value definition.
1257   In all other fields, parentheses are considered part of the field
1258   value.
1260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1261  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1262  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1265   The order in which header fields with differing field names are
1266   received is not significant. However, it is "good practice" to send
1267   general-header fields first, followed by request-header or response-header
1268   fields, and ending with the entity-header fields.
1271   Multiple message-header fields with the same field-name &MAY; be
1272   present in a message if and only if the entire field-value for that
1273   header field is defined as a comma-separated list [i.e., #(values)].
1274   It &MUST; be possible to combine the multiple header fields into one
1275   "field-name: field-value" pair, without changing the semantics of the
1276   message, by appending each subsequent field-value to the first, each
1277   separated by a comma. The order in which header fields with the same
1278   field-name are received is therefore significant to the
1279   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1280   change the order of these field values when a message is forwarded.
1283  <list><t>
1284   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1285   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1286   can occur multiple times, but does not use the list syntax, and thus cannot
1287   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1288   for details.) Also note that the Set-Cookie2 header specified in
1289   <xref target="RFC2965"/> does not share this problem.
1290  </t></list>
1295<section title="Message Body" anchor="message.body">
1296  <x:anchor-alias value="message-body"/>
1298   The message-body (if any) of an HTTP message is used to carry the
1299   entity-body associated with the request or response. The message-body
1300   differs from the entity-body only when a transfer-coding has been
1301   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1303<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1304  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1305               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1308   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1309   applied by an application to ensure safe and proper transfer of the
1310   message. Transfer-Encoding is a property of the message, not of the
1311   entity, and thus &MAY; be added or removed by any application along the
1312   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1313   when certain transfer-codings may be used.)
1316   The rules for when a message-body is allowed in a message differ for
1317   requests and responses.
1320   The presence of a message-body in a request is signaled by the
1321   inclusion of a Content-Length or Transfer-Encoding header field in
1322   the request's message-headers. A message-body &MUST-NOT; be included in
1323   a request if the specification of the request method (&method;)
1324   explicitly disallows an entity-body in requests.
1325   When a request message contains both a message-body of non-zero
1326   length and a method that does not define any semantics for that
1327   request message-body, then an origin server &SHOULD; either ignore
1328   the message-body or respond with an appropriate error message
1329   (e.g., 413).  A proxy or gateway, when presented the same request,
1330   &SHOULD; either forward the request inbound with the message-body or
1331   ignore the message-body when determining a response.
1334   For response messages, whether or not a message-body is included with
1335   a message is dependent on both the request method and the response
1336   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1337   &MUST-NOT; include a message-body, even though the presence of entity-header
1338   fields might lead one to believe they do. All 1xx
1339   (informational), 204 (No Content), and 304 (Not Modified) responses
1340   &MUST-NOT; include a message-body. All other responses do include a
1341   message-body, although it &MAY; be of zero length.
1345<section title="Message Length" anchor="message.length">
1347   The transfer-length of a message is the length of the message-body as
1348   it appears in the message; that is, after any transfer-codings have
1349   been applied. When a message-body is included with a message, the
1350   transfer-length of that body is determined by one of the following
1351   (in order of precedence):
1354  <list style="numbers">
1355    <x:lt><t>
1356     Any response message which "&MUST-NOT;" include a message-body (such
1357     as the 1xx, 204, and 304 responses and any response to a HEAD
1358     request) is always terminated by the first empty line after the
1359     header fields, regardless of the entity-header fields present in
1360     the message.
1361    </t></x:lt>
1362    <x:lt><t>
1363     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1364     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1365     is used, the transfer-length is defined by the use of this transfer-coding.
1366     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1367     is not present, the transfer-length is defined by the sender closing the connection.
1368    </t></x:lt>
1369    <x:lt><t>
1370     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1371     decimal value in OCTETs represents both the entity-length and the
1372     transfer-length. The Content-Length header field &MUST-NOT; be sent
1373     if these two lengths are different (i.e., if a Transfer-Encoding
1374     header field is present). If a message is received with both a
1375     Transfer-Encoding header field and a Content-Length header field,
1376     the latter &MUST; be ignored.
1377    </t></x:lt>
1378    <x:lt><t>
1379     If the message uses the media type "multipart/byteranges", and the
1380     transfer-length is not otherwise specified, then this self-delimiting
1381     media type defines the transfer-length. This media type
1382     &MUST-NOT; be used unless the sender knows that the recipient can parse
1383     it; the presence in a request of a Range header with multiple byte-range
1384     specifiers from a 1.1 client implies that the client can parse
1385     multipart/byteranges responses.
1386    <list style="empty"><t>
1387       A range header might be forwarded by a 1.0 proxy that does not
1388       understand multipart/byteranges; in this case the server &MUST;
1389       delimit the message using methods defined in items 1, 3 or 5 of
1390       this section.
1391    </t></list>
1392    </t></x:lt>
1393    <x:lt><t>
1394     By the server closing the connection. (Closing the connection
1395     cannot be used to indicate the end of a request body, since that
1396     would leave no possibility for the server to send back a response.)
1397    </t></x:lt>
1398  </list>
1401   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1402   containing a message-body &MUST; include a valid Content-Length header
1403   field unless the server is known to be HTTP/1.1 compliant. If a
1404   request contains a message-body and a Content-Length is not given,
1405   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1406   determine the length of the message, or with 411 (Length Required) if
1407   it wishes to insist on receiving a valid Content-Length.
1410   All HTTP/1.1 applications that receive entities &MUST; accept the
1411   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1412   to be used for messages when the message length cannot be determined
1413   in advance.
1416   Messages &MUST-NOT; include both a Content-Length header field and a
1417   transfer-coding. If the message does include a
1418   transfer-coding, the Content-Length &MUST; be ignored.
1421   When a Content-Length is given in a message where a message-body is
1422   allowed, its field value &MUST; exactly match the number of OCTETs in
1423   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1424   invalid length is received and detected.
1428<section title="General Header Fields" anchor="general.header.fields">
1429  <x:anchor-alias value="general-header"/>
1431   There are a few header fields which have general applicability for
1432   both request and response messages, but which do not apply to the
1433   entity being transferred. These header fields apply only to the
1434   message being transmitted.
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1437  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1438                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1439                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1440                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1441                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1442                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1443                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1444                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1445                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1448   General-header field names can be extended reliably only in
1449   combination with a change in the protocol version. However, new or
1450   experimental header fields may be given the semantics of general
1451   header fields if all parties in the communication recognize them to
1452   be general-header fields. Unrecognized header fields are treated as
1453   entity-header fields.
1458<section title="Request" anchor="request">
1459  <x:anchor-alias value="Request"/>
1461   A request message from a client to a server includes, within the
1462   first line of that message, the method to be applied to the resource,
1463   the identifier of the resource, and the protocol version in use.
1465<!--                 Host                      ; should be moved here eventually -->
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1467  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1468                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1469                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1470                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1471                  <x:ref>CRLF</x:ref>
1472                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1475<section title="Request-Line" anchor="request-line">
1476  <x:anchor-alias value="Request-Line"/>
1478   The Request-Line begins with a method token, followed by the
1479   request-target and the protocol version, and ending with CRLF. The
1480   elements are separated by SP characters. No CR or LF is allowed
1481   except in the final CRLF sequence.
1483<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1484  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1487<section title="Method" anchor="method">
1488  <x:anchor-alias value="Method"/>
1490   The Method  token indicates the method to be performed on the
1491   resource identified by the request-target. The method is case-sensitive.
1493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1494  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1498<section title="request-target" anchor="request-target">
1499  <x:anchor-alias value="request-target"/>
1501   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1502   identifies the resource upon which to apply the request.
1504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1505  <x:ref>request-target</x:ref> = "*"
1506                 / <x:ref>absolute-URI</x:ref>
1507                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1508                 / <x:ref>authority</x:ref>
1511   The four options for request-target are dependent on the nature of the
1512   request. The asterisk "*" means that the request does not apply to a
1513   particular resource, but to the server itself, and is only allowed
1514   when the method used does not necessarily apply to a resource. One
1515   example would be
1517<figure><artwork type="example">
1518  OPTIONS * HTTP/1.1
1521   The absolute-URI form is &REQUIRED; when the request is being made to a
1522   proxy. The proxy is requested to forward the request or service it
1523   from a valid cache, and return the response. Note that the proxy &MAY;
1524   forward the request on to another proxy or directly to the server
1525   specified by the absolute-URI. In order to avoid request loops, a
1526   proxy &MUST; be able to recognize all of its server names, including
1527   any aliases, local variations, and the numeric IP address. An example
1528   Request-Line would be:
1530<figure><artwork type="example">
1531  GET HTTP/1.1
1534   To allow for transition to absolute-URIs in all requests in future
1535   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1536   form in requests, even though HTTP/1.1 clients will only generate
1537   them in requests to proxies.
1540   The authority form is only used by the CONNECT method (&CONNECT;).
1543   The most common form of request-target is that used to identify a
1544   resource on an origin server or gateway. In this case the absolute
1545   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1546   the request-target, and the network location of the URI (authority) &MUST;
1547   be transmitted in a Host header field. For example, a client wishing
1548   to retrieve the resource above directly from the origin server would
1549   create a TCP connection to port 80 of the host "" and send
1550   the lines:
1552<figure><artwork type="example">
1553  GET /pub/WWW/TheProject.html HTTP/1.1
1554  Host:
1557   followed by the remainder of the Request. Note that the absolute path
1558   cannot be empty; if none is present in the original URI, it &MUST; be
1559   given as "/" (the server root).
1562   If a proxy receives a request without any path in the request-target and
1563   the method specified is capable of supporting the asterisk form of
1564   request-target, then the last proxy on the request chain &MUST; forward the
1565   request with "*" as the final request-target.
1568   For example, the request
1569</preamble><artwork type="example">
1570  OPTIONS HTTP/1.1
1573  would be forwarded by the proxy as
1574</preamble><artwork type="example">
1575  OPTIONS * HTTP/1.1
1576  Host:
1579   after connecting to port 8001 of host "".
1583   The request-target is transmitted in the format specified in
1584   <xref target="http.uri"/>. If the request-target is encoded using the
1585   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1586   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1587   &MUST; decode the request-target in order to
1588   properly interpret the request. Servers &SHOULD; respond to invalid
1589   request-targets with an appropriate status code.
1592   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1593   received request-target when forwarding it to the next inbound server,
1594   except as noted above to replace a null path-absolute with "/".
1597  <list><t>
1598      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1599      meaning of the request when the origin server is improperly using
1600      a non-reserved URI character for a reserved purpose.  Implementors
1601      should be aware that some pre-HTTP/1.1 proxies have been known to
1602      rewrite the request-target.
1603  </t></list>
1606   HTTP does not place a pre-defined limit on the length of a request-target.
1607   A server &MUST; be prepared to receive URIs of unbounded length and
1608   respond with the 414 (Request-target too Long) status if the received
1609   request-target would be longer than the server wishes to handle
1610   (see &status-414;).
1613   Various ad-hoc limitations on request-target length are found in practice.
1614   It is &RECOMMENDED; that all HTTP senders and recipients support
1615   request-target lengths of 8000 or more OCTETs.
1620<section title="The Resource Identified by a Request" anchor="">
1622   The exact resource identified by an Internet request is determined by
1623   examining both the request-target and the Host header field.
1626   An origin server that does not allow resources to differ by the
1627   requested host &MAY; ignore the Host header field value when
1628   determining the resource identified by an HTTP/1.1 request. (But see
1629   <xref target=""/>
1630   for other requirements on Host support in HTTP/1.1.)
1633   An origin server that does differentiate resources based on the host
1634   requested (sometimes referred to as virtual hosts or vanity host
1635   names) &MUST; use the following rules for determining the requested
1636   resource on an HTTP/1.1 request:
1637  <list style="numbers">
1638    <t>If request-target is an absolute-URI, the host is part of the
1639     request-target. Any Host header field value in the request &MUST; be
1640     ignored.</t>
1641    <t>If the request-target is not an absolute-URI, and the request includes
1642     a Host header field, the host is determined by the Host header
1643     field value.</t>
1644    <t>If the host as determined by rule 1 or 2 is not a valid host on
1645     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1646  </list>
1649   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1650   attempt to use heuristics (e.g., examination of the URI path for
1651   something unique to a particular host) in order to determine what
1652   exact resource is being requested.
1659<section title="Response" anchor="response">
1660  <x:anchor-alias value="Response"/>
1662   After receiving and interpreting a request message, a server responds
1663   with an HTTP response message.
1665<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1666  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1667                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1668                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1669                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1670                  <x:ref>CRLF</x:ref>
1671                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1674<section title="Status-Line" anchor="status-line">
1675  <x:anchor-alias value="Status-Line"/>
1677   The first line of a Response message is the Status-Line, consisting
1678   of the protocol version followed by a numeric status code and its
1679   associated textual phrase, with each element separated by SP
1680   characters. No CR or LF is allowed except in the final CRLF sequence.
1682<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1683  <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>
1686<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1687  <x:anchor-alias value="Reason-Phrase"/>
1688  <x:anchor-alias value="Status-Code"/>
1690   The Status-Code element is a 3-digit integer result code of the
1691   attempt to understand and satisfy the request. These codes are fully
1692   defined in &status-codes;.  The Reason Phrase exists for the sole
1693   purpose of providing a textual description associated with the numeric
1694   status code, out of deference to earlier Internet application protocols
1695   that were more frequently used with interactive text clients.
1696   A client &SHOULD; ignore the content of the Reason Phrase.
1699   The first digit of the Status-Code defines the class of response. The
1700   last two digits do not have any categorization role. There are 5
1701   values for the first digit:
1702  <list style="symbols">
1703    <t>
1704      1xx: Informational - Request received, continuing process
1705    </t>
1706    <t>
1707      2xx: Success - The action was successfully received,
1708        understood, and accepted
1709    </t>
1710    <t>
1711      3xx: Redirection - Further action must be taken in order to
1712        complete the request
1713    </t>
1714    <t>
1715      4xx: Client Error - The request contains bad syntax or cannot
1716        be fulfilled
1717    </t>
1718    <t>
1719      5xx: Server Error - The server failed to fulfill an apparently
1720        valid request
1721    </t>
1722  </list>
1724<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"/>
1725  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1726  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1734<section title="Connections" anchor="connections">
1736<section title="Persistent Connections" anchor="persistent.connections">
1738<section title="Purpose" anchor="persistent.purpose">
1740   Prior to persistent connections, a separate TCP connection was
1741   established to fetch each URL, increasing the load on HTTP servers
1742   and causing congestion on the Internet. The use of inline images and
1743   other associated data often require a client to make multiple
1744   requests of the same server in a short amount of time. Analysis of
1745   these performance problems and results from a prototype
1746   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1747   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1748   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1749   T/TCP <xref target="Tou1998"/>.
1752   Persistent HTTP connections have a number of advantages:
1753  <list style="symbols">
1754      <t>
1755        By opening and closing fewer TCP connections, CPU time is saved
1756        in routers and hosts (clients, servers, proxies, gateways,
1757        tunnels, or caches), and memory used for TCP protocol control
1758        blocks can be saved in hosts.
1759      </t>
1760      <t>
1761        HTTP requests and responses can be pipelined on a connection.
1762        Pipelining allows a client to make multiple requests without
1763        waiting for each response, allowing a single TCP connection to
1764        be used much more efficiently, with much lower elapsed time.
1765      </t>
1766      <t>
1767        Network congestion is reduced by reducing the number of packets
1768        caused by TCP opens, and by allowing TCP sufficient time to
1769        determine the congestion state of the network.
1770      </t>
1771      <t>
1772        Latency on subsequent requests is reduced since there is no time
1773        spent in TCP's connection opening handshake.
1774      </t>
1775      <t>
1776        HTTP can evolve more gracefully, since errors can be reported
1777        without the penalty of closing the TCP connection. Clients using
1778        future versions of HTTP might optimistically try a new feature,
1779        but if communicating with an older server, retry with old
1780        semantics after an error is reported.
1781      </t>
1782    </list>
1785   HTTP implementations &SHOULD; implement persistent connections.
1789<section title="Overall Operation" anchor="persistent.overall">
1791   A significant difference between HTTP/1.1 and earlier versions of
1792   HTTP is that persistent connections are the default behavior of any
1793   HTTP connection. That is, unless otherwise indicated, the client
1794   &SHOULD; assume that the server will maintain a persistent connection,
1795   even after error responses from the server.
1798   Persistent connections provide a mechanism by which a client and a
1799   server can signal the close of a TCP connection. This signaling takes
1800   place using the Connection header field (<xref target="header.connection"/>). Once a close
1801   has been signaled, the client &MUST-NOT; send any more requests on that
1802   connection.
1805<section title="Negotiation" anchor="persistent.negotiation">
1807   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1808   maintain a persistent connection unless a Connection header including
1809   the connection-token "close" was sent in the request. If the server
1810   chooses to close the connection immediately after sending the
1811   response, it &SHOULD; send a Connection header including the
1812   connection-token close.
1815   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1816   decide to keep it open based on whether the response from a server
1817   contains a Connection header with the connection-token close. In case
1818   the client does not want to maintain a connection for more than that
1819   request, it &SHOULD; send a Connection header including the
1820   connection-token close.
1823   If either the client or the server sends the close token in the
1824   Connection header, that request becomes the last one for the
1825   connection.
1828   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1829   maintained for HTTP versions less than 1.1 unless it is explicitly
1830   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1831   compatibility with HTTP/1.0 clients.
1834   In order to remain persistent, all messages on the connection &MUST;
1835   have a self-defined message length (i.e., one not defined by closure
1836   of the connection), as described in <xref target="message.length"/>.
1840<section title="Pipelining" anchor="pipelining">
1842   A client that supports persistent connections &MAY; "pipeline" its
1843   requests (i.e., send multiple requests without waiting for each
1844   response). A server &MUST; send its responses to those requests in the
1845   same order that the requests were received.
1848   Clients which assume persistent connections and pipeline immediately
1849   after connection establishment &SHOULD; be prepared to retry their
1850   connection if the first pipelined attempt fails. If a client does
1851   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1852   persistent. Clients &MUST; also be prepared to resend their requests if
1853   the server closes the connection before sending all of the
1854   corresponding responses.
1857   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1858   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1859   premature termination of the transport connection could lead to
1860   indeterminate results. A client wishing to send a non-idempotent
1861   request &SHOULD; wait to send that request until it has received the
1862   response status for the previous request.
1867<section title="Proxy Servers" anchor="persistent.proxy">
1869   It is especially important that proxies correctly implement the
1870   properties of the Connection header field as specified in <xref target="header.connection"/>.
1873   The proxy server &MUST; signal persistent connections separately with
1874   its clients and the origin servers (or other proxy servers) that it
1875   connects to. Each persistent connection applies to only one transport
1876   link.
1879   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1880   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1881   discussion of the problems with the Keep-Alive header implemented by
1882   many HTTP/1.0 clients).
1886<section title="Practical Considerations" anchor="persistent.practical">
1888   Servers will usually have some time-out value beyond which they will
1889   no longer maintain an inactive connection. Proxy servers might make
1890   this a higher value since it is likely that the client will be making
1891   more connections through the same server. The use of persistent
1892   connections places no requirements on the length (or existence) of
1893   this time-out for either the client or the server.
1896   When a client or server wishes to time-out it &SHOULD; issue a graceful
1897   close on the transport connection. Clients and servers &SHOULD; both
1898   constantly watch for the other side of the transport close, and
1899   respond to it as appropriate. If a client or server does not detect
1900   the other side's close promptly it could cause unnecessary resource
1901   drain on the network.
1904   A client, server, or proxy &MAY; close the transport connection at any
1905   time. For example, a client might have started to send a new request
1906   at the same time that the server has decided to close the "idle"
1907   connection. From the server's point of view, the connection is being
1908   closed while it was idle, but from the client's point of view, a
1909   request is in progress.
1912   This means that clients, servers, and proxies &MUST; be able to recover
1913   from asynchronous close events. Client software &SHOULD; reopen the
1914   transport connection and retransmit the aborted sequence of requests
1915   without user interaction so long as the request sequence is
1916   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1917   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1918   human operator the choice of retrying the request(s). Confirmation by
1919   user-agent software with semantic understanding of the application
1920   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1921   be repeated if the second sequence of requests fails.
1924   Servers &SHOULD; always respond to at least one request per connection,
1925   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1926   middle of transmitting a response, unless a network or client failure
1927   is suspected.
1930   Clients that use persistent connections &SHOULD; limit the number of
1931   simultaneous connections that they maintain to a given server. A
1932   single-user client &SHOULD-NOT; maintain more than 2 connections with
1933   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1934   another server or proxy, where N is the number of simultaneously
1935   active users. These guidelines are intended to improve HTTP response
1936   times and avoid congestion.
1941<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1943<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1945   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1946   flow control mechanisms to resolve temporary overloads, rather than
1947   terminating connections with the expectation that clients will retry.
1948   The latter technique can exacerbate network congestion.
1952<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1954   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1955   the network connection for an error status while it is transmitting
1956   the request. If the client sees an error status, it &SHOULD;
1957   immediately cease transmitting the body. If the body is being sent
1958   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1959   empty trailer &MAY; be used to prematurely mark the end of the message.
1960   If the body was preceded by a Content-Length header, the client &MUST;
1961   close the connection.
1965<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1967   The purpose of the 100 (Continue) status (see &status-100;) is to
1968   allow a client that is sending a request message with a request body
1969   to determine if the origin server is willing to accept the request
1970   (based on the request headers) before the client sends the request
1971   body. In some cases, it might either be inappropriate or highly
1972   inefficient for the client to send the body if the server will reject
1973   the message without looking at the body.
1976   Requirements for HTTP/1.1 clients:
1977  <list style="symbols">
1978    <t>
1979        If a client will wait for a 100 (Continue) response before
1980        sending the request body, it &MUST; send an Expect request-header
1981        field (&header-expect;) with the "100-continue" expectation.
1982    </t>
1983    <t>
1984        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1985        with the "100-continue" expectation if it does not intend
1986        to send a request body.
1987    </t>
1988  </list>
1991   Because of the presence of older implementations, the protocol allows
1992   ambiguous situations in which a client may send "Expect: 100-continue"
1993   without receiving either a 417 (Expectation Failed) status
1994   or a 100 (Continue) status. Therefore, when a client sends this
1995   header field to an origin server (possibly via a proxy) from which it
1996   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1997   for an indefinite period before sending the request body.
2000   Requirements for HTTP/1.1 origin servers:
2001  <list style="symbols">
2002    <t> Upon receiving a request which includes an Expect request-header
2003        field with the "100-continue" expectation, an origin server &MUST;
2004        either respond with 100 (Continue) status and continue to read
2005        from the input stream, or respond with a final status code. The
2006        origin server &MUST-NOT; wait for the request body before sending
2007        the 100 (Continue) response. If it responds with a final status
2008        code, it &MAY; close the transport connection or it &MAY; continue
2009        to read and discard the rest of the request.  It &MUST-NOT;
2010        perform the requested method if it returns a final status code.
2011    </t>
2012    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2013        the request message does not include an Expect request-header
2014        field with the "100-continue" expectation, and &MUST-NOT; send a
2015        100 (Continue) response if such a request comes from an HTTP/1.0
2016        (or earlier) client. There is an exception to this rule: for
2017        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2018        status in response to an HTTP/1.1 PUT or POST request that does
2019        not include an Expect request-header field with the "100-continue"
2020        expectation. This exception, the purpose of which is
2021        to minimize any client processing delays associated with an
2022        undeclared wait for 100 (Continue) status, applies only to
2023        HTTP/1.1 requests, and not to requests with any other HTTP-version
2024        value.
2025    </t>
2026    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2027        already received some or all of the request body for the
2028        corresponding request.
2029    </t>
2030    <t> An origin server that sends a 100 (Continue) response &MUST;
2031    ultimately send a final status code, once the request body is
2032        received and processed, unless it terminates the transport
2033        connection prematurely.
2034    </t>
2035    <t> If an origin server receives a request that does not include an
2036        Expect request-header field with the "100-continue" expectation,
2037        the request includes a request body, and the server responds
2038        with a final status code before reading the entire request body
2039        from the transport connection, then the server &SHOULD-NOT;  close
2040        the transport connection until it has read the entire request,
2041        or until the client closes the connection. Otherwise, the client
2042        might not reliably receive the response message. However, this
2043        requirement is not be construed as preventing a server from
2044        defending itself against denial-of-service attacks, or from
2045        badly broken client implementations.
2046      </t>
2047    </list>
2050   Requirements for HTTP/1.1 proxies:
2051  <list style="symbols">
2052    <t> If a proxy receives a request that includes an Expect request-header
2053        field with the "100-continue" expectation, and the proxy
2054        either knows that the next-hop server complies with HTTP/1.1 or
2055        higher, or does not know the HTTP version of the next-hop
2056        server, it &MUST; forward the request, including the Expect header
2057        field.
2058    </t>
2059    <t> If the proxy knows that the version of the next-hop server is
2060        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2061        respond with a 417 (Expectation Failed) status.
2062    </t>
2063    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2064        numbers received from recently-referenced next-hop servers.
2065    </t>
2066    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2067        request message was received from an HTTP/1.0 (or earlier)
2068        client and did not include an Expect request-header field with
2069        the "100-continue" expectation. This requirement overrides the
2070        general rule for forwarding of 1xx responses (see &status-1xx;).
2071    </t>
2072  </list>
2076<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2078   If an HTTP/1.1 client sends a request which includes a request body,
2079   but which does not include an Expect request-header field with the
2080   "100-continue" expectation, and if the client is not directly
2081   connected to an HTTP/1.1 origin server, and if the client sees the
2082   connection close before receiving any status from the server, the
2083   client &SHOULD; retry the request.  If the client does retry this
2084   request, it &MAY; use the following "binary exponential backoff"
2085   algorithm to be assured of obtaining a reliable response:
2086  <list style="numbers">
2087    <t>
2088      Initiate a new connection to the server
2089    </t>
2090    <t>
2091      Transmit the request-headers
2092    </t>
2093    <t>
2094      Initialize a variable R to the estimated round-trip time to the
2095         server (e.g., based on the time it took to establish the
2096         connection), or to a constant value of 5 seconds if the round-trip
2097         time is not available.
2098    </t>
2099    <t>
2100       Compute T = R * (2**N), where N is the number of previous
2101         retries of this request.
2102    </t>
2103    <t>
2104       Wait either for an error response from the server, or for T
2105         seconds (whichever comes first)
2106    </t>
2107    <t>
2108       If no error response is received, after T seconds transmit the
2109         body of the request.
2110    </t>
2111    <t>
2112       If client sees that the connection is closed prematurely,
2113         repeat from step 1 until the request is accepted, an error
2114         response is received, or the user becomes impatient and
2115         terminates the retry process.
2116    </t>
2117  </list>
2120   If at any point an error status is received, the client
2121  <list style="symbols">
2122      <t>&SHOULD-NOT;  continue and</t>
2124      <t>&SHOULD; close the connection if it has not completed sending the
2125        request message.</t>
2126    </list>
2133<section title="Header Field Definitions" anchor="header.fields">
2135   This section defines the syntax and semantics of HTTP/1.1 header fields
2136   related to message framing and transport protocols.
2139   For entity-header fields, both sender and recipient refer to either the
2140   client or the server, depending on who sends and who receives the entity.
2143<section title="Connection" anchor="header.connection">
2144  <iref primary="true" item="Connection header" x:for-anchor=""/>
2145  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2146  <x:anchor-alias value="Connection"/>
2147  <x:anchor-alias value="connection-token"/>
2148  <x:anchor-alias value="Connection-v"/>
2150   The general-header field "Connection" allows the sender to specify
2151   options that are desired for that particular connection and &MUST-NOT;
2152   be communicated by proxies over further connections.
2155   The Connection header's value has the following grammar:
2157<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"/>
2158  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2159  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2160  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2163   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2164   message is forwarded and, for each connection-token in this field,
2165   remove any header field(s) from the message with the same name as the
2166   connection-token. Connection options are signaled by the presence of
2167   a connection-token in the Connection header field, not by any
2168   corresponding additional header field(s), since the additional header
2169   field may not be sent if there are no parameters associated with that
2170   connection option.
2173   Message headers listed in the Connection header &MUST-NOT; include
2174   end-to-end headers, such as Cache-Control.
2177   HTTP/1.1 defines the "close" connection option for the sender to
2178   signal that the connection will be closed after completion of the
2179   response. For example,
2181<figure><artwork type="example">
2182  Connection: close
2185   in either the request or the response header fields indicates that
2186   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2187   after the current request/response is complete.
2190   An HTTP/1.1 client that does not support persistent connections &MUST;
2191   include the "close" connection option in every request message.
2194   An HTTP/1.1 server that does not support persistent connections &MUST;
2195   include the "close" connection option in every response message that
2196   does not have a 1xx (informational) status code.
2199   A system receiving an HTTP/1.0 (or lower-version) message that
2200   includes a Connection header &MUST;, for each connection-token in this
2201   field, remove and ignore any header field(s) from the message with
2202   the same name as the connection-token. This protects against mistaken
2203   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2207<section title="Content-Length" anchor="header.content-length">
2208  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2209  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2210  <x:anchor-alias value="Content-Length"/>
2211  <x:anchor-alias value="Content-Length-v"/>
2213   The entity-header field "Content-Length" indicates the size of the
2214   entity-body, in decimal number of OCTETs, sent to the recipient or,
2215   in the case of the HEAD method, the size of the entity-body that
2216   would have been sent had the request been a GET.
2218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2219  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2220  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2223   An example is
2225<figure><artwork type="example">
2226  Content-Length: 3495
2229   Applications &SHOULD; use this field to indicate the transfer-length of
2230   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2233   Any Content-Length greater than or equal to zero is a valid value.
2234   <xref target="message.length"/> describes how to determine the length of a message-body
2235   if a Content-Length is not given.
2238   Note that the meaning of this field is significantly different from
2239   the corresponding definition in MIME, where it is an optional field
2240   used within the "message/external-body" content-type. In HTTP, it
2241   &SHOULD; be sent whenever the message's length can be determined prior
2242   to being transferred, unless this is prohibited by the rules in
2243   <xref target="message.length"/>.
2247<section title="Date" anchor="">
2248  <iref primary="true" item="Date header" x:for-anchor=""/>
2249  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2250  <x:anchor-alias value="Date"/>
2251  <x:anchor-alias value="Date-v"/>
2253   The general-header field "Date" represents the date and time at which
2254   the message was originated, having the same semantics as orig-date in
2255   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2256   HTTP-date, as described in <xref target=""/>;
2257   it &MUST; be sent in rfc1123-date format.
2259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2260  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2261  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2264   An example is
2266<figure><artwork type="example">
2267  Date: Tue, 15 Nov 1994 08:12:31 GMT
2270   Origin servers &MUST; include a Date header field in all responses,
2271   except in these cases:
2272  <list style="numbers">
2273      <t>If the response status code is 100 (Continue) or 101 (Switching
2274         Protocols), the response &MAY; include a Date header field, at
2275         the server's option.</t>
2277      <t>If the response status code conveys a server error, e.g. 500
2278         (Internal Server Error) or 503 (Service Unavailable), and it is
2279         inconvenient or impossible to generate a valid Date.</t>
2281      <t>If the server does not have a clock that can provide a
2282         reasonable approximation of the current time, its responses
2283         &MUST-NOT; include a Date header field. In this case, the rules
2284         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2285  </list>
2288   A received message that does not have a Date header field &MUST; be
2289   assigned one by the recipient if the message will be cached by that
2290   recipient or gatewayed via a protocol which requires a Date. An HTTP
2291   implementation without a clock &MUST-NOT; cache responses without
2292   revalidating them on every use. An HTTP cache, especially a shared
2293   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2294   clock with a reliable external standard.
2297   Clients &SHOULD; only send a Date header field in messages that include
2298   an entity-body, as in the case of the PUT and POST requests, and even
2299   then it is optional. A client without a clock &MUST-NOT; send a Date
2300   header field in a request.
2303   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2304   time subsequent to the generation of the message. It &SHOULD; represent
2305   the best available approximation of the date and time of message
2306   generation, unless the implementation has no means of generating a
2307   reasonably accurate date and time. In theory, the date ought to
2308   represent the moment just before the entity is generated. In
2309   practice, the date can be generated at any time during the message
2310   origination without affecting its semantic value.
2313<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2315   Some origin server implementations might not have a clock available.
2316   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2317   values to a response, unless these values were associated
2318   with the resource by a system or user with a reliable clock. It &MAY;
2319   assign an Expires value that is known, at or before server
2320   configuration time, to be in the past (this allows "pre-expiration"
2321   of responses without storing separate Expires values for each
2322   resource).
2327<section title="Host" anchor="">
2328  <iref primary="true" item="Host header" x:for-anchor=""/>
2329  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2330  <x:anchor-alias value="Host"/>
2331  <x:anchor-alias value="Host-v"/>
2333   The request-header field "Host" specifies the Internet host and port
2334   number of the resource being requested, as obtained from the original
2335   URI given by the user or referring resource (generally an http URI,
2336   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2337   the naming authority of the origin server or gateway given by the
2338   original URL. This allows the origin server or gateway to
2339   differentiate between internally-ambiguous URLs, such as the root "/"
2340   URL of a server for multiple host names on a single IP address.
2342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2343  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2344  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2347   A "host" without any trailing port information implies the default
2348   port for the service requested (e.g., "80" for an HTTP URL). For
2349   example, a request on the origin server for
2350   &lt;; would properly include:
2352<figure><artwork type="example">
2353  GET /pub/WWW/ HTTP/1.1
2354  Host:
2357   A client &MUST; include a Host header field in all HTTP/1.1 request
2358   messages. If the requested URI does not include an Internet host
2359   name for the service being requested, then the Host header field &MUST;
2360   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2361   request message it forwards does contain an appropriate Host header
2362   field that identifies the service being requested by the proxy. All
2363   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2364   status code to any HTTP/1.1 request message which lacks a Host header
2365   field.
2368   See Sections <xref target="" format="counter"/>
2369   and <xref target="" format="counter"/>
2370   for other requirements relating to Host.
2374<section title="TE" anchor="header.te">
2375  <iref primary="true" item="TE header" x:for-anchor=""/>
2376  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2377  <x:anchor-alias value="TE"/>
2378  <x:anchor-alias value="TE-v"/>
2379  <x:anchor-alias value="t-codings"/>
2381   The request-header field "TE" indicates what extension transfer-codings
2382   it is willing to accept in the response and whether or not it is
2383   willing to accept trailer fields in a chunked transfer-coding. Its
2384   value may consist of the keyword "trailers" and/or a comma-separated
2385   list of extension transfer-coding names with optional accept
2386   parameters (as described in <xref target="transfer.codings"/>).
2388<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"/>
2389  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2390  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2391  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2394   The presence of the keyword "trailers" indicates that the client is
2395   willing to accept trailer fields in a chunked transfer-coding, as
2396   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2397   transfer-coding values even though it does not itself represent a
2398   transfer-coding.
2401   Examples of its use are:
2403<figure><artwork type="example">
2404  TE: deflate
2405  TE:
2406  TE: trailers, deflate;q=0.5
2409   The TE header field only applies to the immediate connection.
2410   Therefore, the keyword &MUST; be supplied within a Connection header
2411   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2414   A server tests whether a transfer-coding is acceptable, according to
2415   a TE field, using these rules:
2416  <list style="numbers">
2417    <x:lt>
2418      <t>The "chunked" transfer-coding is always acceptable. If the
2419         keyword "trailers" is listed, the client indicates that it is
2420         willing to accept trailer fields in the chunked response on
2421         behalf of itself and any downstream clients. The implication is
2422         that, if given, the client is stating that either all
2423         downstream clients are willing to accept trailer fields in the
2424         forwarded response, or that it will attempt to buffer the
2425         response on behalf of downstream recipients.
2426      </t><t>
2427         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2428         chunked response such that a client can be assured of buffering
2429         the entire response.</t>
2430    </x:lt>
2431    <x:lt>
2432      <t>If the transfer-coding being tested is one of the transfer-codings
2433         listed in the TE field, then it is acceptable unless it
2434         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2435         qvalue of 0 means "not acceptable.")</t>
2436    </x:lt>
2437    <x:lt>
2438      <t>If multiple transfer-codings are acceptable, then the
2439         acceptable transfer-coding with the highest non-zero qvalue is
2440         preferred.  The "chunked" transfer-coding always has a qvalue
2441         of 1.</t>
2442    </x:lt>
2443  </list>
2446   If the TE field-value is empty or if no TE field is present, the only
2447   transfer-coding  is "chunked". A message with no transfer-coding is
2448   always acceptable.
2452<section title="Trailer" anchor="header.trailer">
2453  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2454  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2455  <x:anchor-alias value="Trailer"/>
2456  <x:anchor-alias value="Trailer-v"/>
2458   The general field "Trailer" indicates that the given set of
2459   header fields is present in the trailer of a message encoded with
2460   chunked transfer-coding.
2462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2463  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2464  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2467   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2468   message using chunked transfer-coding with a non-empty trailer. Doing
2469   so allows the recipient to know which header fields to expect in the
2470   trailer.
2473   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2474   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2475   trailer fields in a "chunked" transfer-coding.
2478   Message header fields listed in the Trailer header field &MUST-NOT;
2479   include the following header fields:
2480  <list style="symbols">
2481    <t>Transfer-Encoding</t>
2482    <t>Content-Length</t>
2483    <t>Trailer</t>
2484  </list>
2488<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2489  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2490  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2491  <x:anchor-alias value="Transfer-Encoding"/>
2492  <x:anchor-alias value="Transfer-Encoding-v"/>
2494   The general-header "Transfer-Encoding" field indicates what (if any)
2495   type of transformation has been applied to the message body in order
2496   to safely transfer it between the sender and the recipient. This
2497   differs from the content-coding in that the transfer-coding is a
2498   property of the message, not of the entity.
2500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2501  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2502                        <x:ref>Transfer-Encoding-v</x:ref>
2503  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2506   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2508<figure><artwork type="example">
2509  Transfer-Encoding: chunked
2512   If multiple encodings have been applied to an entity, the transfer-codings
2513   &MUST; be listed in the order in which they were applied.
2514   Additional information about the encoding parameters &MAY; be provided
2515   by other entity-header fields not defined by this specification.
2518   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2519   header.
2523<section title="Upgrade" anchor="header.upgrade">
2524  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2525  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2526  <x:anchor-alias value="Upgrade"/>
2527  <x:anchor-alias value="Upgrade-v"/>
2529   The general-header "Upgrade" allows the client to specify what
2530   additional communication protocols it supports and would like to use
2531   if the server finds it appropriate to switch protocols. The server
2532   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2533   response to indicate which protocol(s) are being switched.
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2536  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2537  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2540   For example,
2542<figure><artwork type="example">
2543  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2546   The Upgrade header field is intended to provide a simple mechanism
2547   for transition from HTTP/1.1 to some other, incompatible protocol. It
2548   does so by allowing the client to advertise its desire to use another
2549   protocol, such as a later version of HTTP with a higher major version
2550   number, even though the current request has been made using HTTP/1.1.
2551   This eases the difficult transition between incompatible protocols by
2552   allowing the client to initiate a request in the more commonly
2553   supported protocol while indicating to the server that it would like
2554   to use a "better" protocol if available (where "better" is determined
2555   by the server, possibly according to the nature of the method and/or
2556   resource being requested).
2559   The Upgrade header field only applies to switching application-layer
2560   protocols upon the existing transport-layer connection. Upgrade
2561   cannot be used to insist on a protocol change; its acceptance and use
2562   by the server is optional. The capabilities and nature of the
2563   application-layer communication after the protocol change is entirely
2564   dependent upon the new protocol chosen, although the first action
2565   after changing the protocol &MUST; be a response to the initial HTTP
2566   request containing the Upgrade header field.
2569   The Upgrade header field only applies to the immediate connection.
2570   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2571   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2572   HTTP/1.1 message.
2575   The Upgrade header field cannot be used to indicate a switch to a
2576   protocol on a different connection. For that purpose, it is more
2577   appropriate to use a 301, 302, 303, or 305 redirection response.
2580   This specification only defines the protocol name "HTTP" for use by
2581   the family of Hypertext Transfer Protocols, as defined by the HTTP
2582   version rules of <xref target="http.version"/> and future updates to this
2583   specification. Any token can be used as a protocol name; however, it
2584   will only be useful if both the client and server associate the name
2585   with the same protocol.
2589<section title="Via" anchor="header.via">
2590  <iref primary="true" item="Via header" x:for-anchor=""/>
2591  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2592  <x:anchor-alias value="protocol-name"/>
2593  <x:anchor-alias value="protocol-version"/>
2594  <x:anchor-alias value="pseudonym"/>
2595  <x:anchor-alias value="received-by"/>
2596  <x:anchor-alias value="received-protocol"/>
2597  <x:anchor-alias value="Via"/>
2598  <x:anchor-alias value="Via-v"/>
2600   The general-header field "Via" &MUST; be used by gateways and proxies to
2601   indicate the intermediate protocols and recipients between the user
2602   agent and the server on requests, and between the origin server and
2603   the client on responses. It is analogous to the "Received" field defined in
2604   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2605   avoiding request loops, and identifying the protocol capabilities of
2606   all senders along the request/response chain.
2608<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"/>
2609  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2610  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2611                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2612  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2613  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2614  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2615  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2616  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2619   The received-protocol indicates the protocol version of the message
2620   received by the server or client along each segment of the
2621   request/response chain. The received-protocol version is appended to
2622   the Via field value when the message is forwarded so that information
2623   about the protocol capabilities of upstream applications remains
2624   visible to all recipients.
2627   The protocol-name is optional if and only if it would be "HTTP". The
2628   received-by field is normally the host and optional port number of a
2629   recipient server or client that subsequently forwarded the message.
2630   However, if the real host is considered to be sensitive information,
2631   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2632   be assumed to be the default port of the received-protocol.
2635   Multiple Via field values represents each proxy or gateway that has
2636   forwarded the message. Each recipient &MUST; append its information
2637   such that the end result is ordered according to the sequence of
2638   forwarding applications.
2641   Comments &MAY; be used in the Via header field to identify the software
2642   of the recipient proxy or gateway, analogous to the User-Agent and
2643   Server header fields. However, all comments in the Via field are
2644   optional and &MAY; be removed by any recipient prior to forwarding the
2645   message.
2648   For example, a request message could be sent from an HTTP/1.0 user
2649   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2650   forward the request to a public proxy at, which completes
2651   the request by forwarding it to the origin server at
2652   The request received by would then have the following
2653   Via header field:
2655<figure><artwork type="example">
2656  Via: 1.0 fred, 1.1 (Apache/1.1)
2659   Proxies and gateways used as a portal through a network firewall
2660   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2661   the firewall region. This information &SHOULD; only be propagated if
2662   explicitly enabled. If not enabled, the received-by host of any host
2663   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2664   for that host.
2667   For organizations that have strong privacy requirements for hiding
2668   internal structures, a proxy &MAY; combine an ordered subsequence of
2669   Via header field entries with identical received-protocol values into
2670   a single such entry. For example,
2672<figure><artwork type="example">
2673  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2676        could be collapsed to
2678<figure><artwork type="example">
2679  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2682   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2683   under the same organizational control and the hosts have already been
2684   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2685   have different received-protocol values.
2691<section title="IANA Considerations" anchor="IANA.considerations">
2692<section title="Message Header Registration" anchor="message.header.registration">
2694   The Message Header Registry located at <eref target=""/> should be updated
2695   with the permanent registrations below (see <xref target="RFC3864"/>):
2697<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2698<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2699   <ttcol>Header Field Name</ttcol>
2700   <ttcol>Protocol</ttcol>
2701   <ttcol>Status</ttcol>
2702   <ttcol>Reference</ttcol>
2704   <c>Connection</c>
2705   <c>http</c>
2706   <c>standard</c>
2707   <c>
2708      <xref target="header.connection"/>
2709   </c>
2710   <c>Content-Length</c>
2711   <c>http</c>
2712   <c>standard</c>
2713   <c>
2714      <xref target="header.content-length"/>
2715   </c>
2716   <c>Date</c>
2717   <c>http</c>
2718   <c>standard</c>
2719   <c>
2720      <xref target=""/>
2721   </c>
2722   <c>Host</c>
2723   <c>http</c>
2724   <c>standard</c>
2725   <c>
2726      <xref target=""/>
2727   </c>
2728   <c>TE</c>
2729   <c>http</c>
2730   <c>standard</c>
2731   <c>
2732      <xref target="header.te"/>
2733   </c>
2734   <c>Trailer</c>
2735   <c>http</c>
2736   <c>standard</c>
2737   <c>
2738      <xref target="header.trailer"/>
2739   </c>
2740   <c>Transfer-Encoding</c>
2741   <c>http</c>
2742   <c>standard</c>
2743   <c>
2744      <xref target="header.transfer-encoding"/>
2745   </c>
2746   <c>Upgrade</c>
2747   <c>http</c>
2748   <c>standard</c>
2749   <c>
2750      <xref target="header.upgrade"/>
2751   </c>
2752   <c>Via</c>
2753   <c>http</c>
2754   <c>standard</c>
2755   <c>
2756      <xref target="header.via"/>
2757   </c>
2761   The change controller is: "IETF ( - Internet Engineering Task Force".
2765<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2767   The entry for the "http" URI Scheme in the registry located at
2768   <eref target=""/>
2769   should be updated to point to <xref target="http.uri"/> of this document
2770   (see <xref target="RFC4395"/>).
2774<section title="Internet Media Type Registrations" anchor="">
2776   This document serves as the specification for the Internet media types
2777   "message/http" and "application/http". The following is to be registered with
2778   IANA (see <xref target="RFC4288"/>).
2780<section title="Internet Media Type message/http" anchor="">
2781<iref item="Media Type" subitem="message/http" primary="true"/>
2782<iref item="message/http Media Type" primary="true"/>
2784   The message/http type can be used to enclose a single HTTP request or
2785   response message, provided that it obeys the MIME restrictions for all
2786   "message" types regarding line length and encodings.
2789  <list style="hanging" x:indent="12em">
2790    <t hangText="Type name:">
2791      message
2792    </t>
2793    <t hangText="Subtype name:">
2794      http
2795    </t>
2796    <t hangText="Required parameters:">
2797      none
2798    </t>
2799    <t hangText="Optional parameters:">
2800      version, msgtype
2801      <list style="hanging">
2802        <t hangText="version:">
2803          The HTTP-Version number of the enclosed message
2804          (e.g., "1.1"). If not present, the version can be
2805          determined from the first line of the body.
2806        </t>
2807        <t hangText="msgtype:">
2808          The message type -- "request" or "response". If not
2809          present, the type can be determined from the first
2810          line of the body.
2811        </t>
2812      </list>
2813    </t>
2814    <t hangText="Encoding considerations:">
2815      only "7bit", "8bit", or "binary" are permitted
2816    </t>
2817    <t hangText="Security considerations:">
2818      none
2819    </t>
2820    <t hangText="Interoperability considerations:">
2821      none
2822    </t>
2823    <t hangText="Published specification:">
2824      This specification (see <xref target=""/>).
2825    </t>
2826    <t hangText="Applications that use this media type:">
2827    </t>
2828    <t hangText="Additional information:">
2829      <list style="hanging">
2830        <t hangText="Magic number(s):">none</t>
2831        <t hangText="File extension(s):">none</t>
2832        <t hangText="Macintosh file type code(s):">none</t>
2833      </list>
2834    </t>
2835    <t hangText="Person and email address to contact for further information:">
2836      See Authors Section.
2837    </t>
2838                <t hangText="Intended usage:">
2839                  COMMON
2840    </t>
2841                <t hangText="Restrictions on usage:">
2842                  none
2843    </t>
2844    <t hangText="Author/Change controller:">
2845      IESG
2846    </t>
2847  </list>
2850<section title="Internet Media Type application/http" anchor="">
2851<iref item="Media Type" subitem="application/http" primary="true"/>
2852<iref item="application/http Media Type" primary="true"/>
2854   The application/http type can be used to enclose a pipeline of one or more
2855   HTTP request or response messages (not intermixed).
2858  <list style="hanging" x:indent="12em">
2859    <t hangText="Type name:">
2860      application
2861    </t>
2862    <t hangText="Subtype name:">
2863      http
2864    </t>
2865    <t hangText="Required parameters:">
2866      none
2867    </t>
2868    <t hangText="Optional parameters:">
2869      version, msgtype
2870      <list style="hanging">
2871        <t hangText="version:">
2872          The HTTP-Version number of the enclosed messages
2873          (e.g., "1.1"). If not present, the version can be
2874          determined from the first line of the body.
2875        </t>
2876        <t hangText="msgtype:">
2877          The message type -- "request" or "response". If not
2878          present, the type can be determined from the first
2879          line of the body.
2880        </t>
2881      </list>
2882    </t>
2883    <t hangText="Encoding considerations:">
2884      HTTP messages enclosed by this type
2885      are in "binary" format; use of an appropriate
2886      Content-Transfer-Encoding is required when
2887      transmitted via E-mail.
2888    </t>
2889    <t hangText="Security considerations:">
2890      none
2891    </t>
2892    <t hangText="Interoperability considerations:">
2893      none
2894    </t>
2895    <t hangText="Published specification:">
2896      This specification (see <xref target=""/>).
2897    </t>
2898    <t hangText="Applications that use this media type:">
2899    </t>
2900    <t hangText="Additional information:">
2901      <list style="hanging">
2902        <t hangText="Magic number(s):">none</t>
2903        <t hangText="File extension(s):">none</t>
2904        <t hangText="Macintosh file type code(s):">none</t>
2905      </list>
2906    </t>
2907    <t hangText="Person and email address to contact for further information:">
2908      See Authors Section.
2909    </t>
2910                <t hangText="Intended usage:">
2911                  COMMON
2912    </t>
2913                <t hangText="Restrictions on usage:">
2914                  none
2915    </t>
2916    <t hangText="Author/Change controller:">
2917      IESG
2918    </t>
2919  </list>
2926<section title="Security Considerations" anchor="security.considerations">
2928   This section is meant to inform application developers, information
2929   providers, and users of the security limitations in HTTP/1.1 as
2930   described by this document. The discussion does not include
2931   definitive solutions to the problems revealed, though it does make
2932   some suggestions for reducing security risks.
2935<section title="Personal Information" anchor="personal.information">
2937   HTTP clients are often privy to large amounts of personal information
2938   (e.g. the user's name, location, mail address, passwords, encryption
2939   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2940   leakage of this information.
2941   We very strongly recommend that a convenient interface be provided
2942   for the user to control dissemination of such information, and that
2943   designers and implementors be particularly careful in this area.
2944   History shows that errors in this area often create serious security
2945   and/or privacy problems and generate highly adverse publicity for the
2946   implementor's company.
2950<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2952   A server is in the position to save personal data about a user's
2953   requests which might identify their reading patterns or subjects of
2954   interest. This information is clearly confidential in nature and its
2955   handling can be constrained by law in certain countries. People using
2956   HTTP to provide data are responsible for ensuring that
2957   such material is not distributed without the permission of any
2958   individuals that are identifiable by the published results.
2962<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2964   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2965   the documents returned by HTTP requests to be only those that were
2966   intended by the server administrators. If an HTTP server translates
2967   HTTP URIs directly into file system calls, the server &MUST; take
2968   special care not to serve files that were not intended to be
2969   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2970   other operating systems use ".." as a path component to indicate a
2971   directory level above the current one. On such a system, an HTTP
2972   server &MUST; disallow any such construct in the request-target if it
2973   would otherwise allow access to a resource outside those intended to
2974   be accessible via the HTTP server. Similarly, files intended for
2975   reference only internally to the server (such as access control
2976   files, configuration files, and script code) &MUST; be protected from
2977   inappropriate retrieval, since they might contain sensitive
2978   information. Experience has shown that minor bugs in such HTTP server
2979   implementations have turned into security risks.
2983<section title="DNS Spoofing" anchor="dns.spoofing">
2985   Clients using HTTP rely heavily on the Domain Name Service, and are
2986   thus generally prone to security attacks based on the deliberate
2987   mis-association of IP addresses and DNS names. Clients need to be
2988   cautious in assuming the continuing validity of an IP number/DNS name
2989   association.
2992   In particular, HTTP clients &SHOULD; rely on their name resolver for
2993   confirmation of an IP number/DNS name association, rather than
2994   caching the result of previous host name lookups. Many platforms
2995   already can cache host name lookups locally when appropriate, and
2996   they &SHOULD; be configured to do so. It is proper for these lookups to
2997   be cached, however, only when the TTL (Time To Live) information
2998   reported by the name server makes it likely that the cached
2999   information will remain useful.
3002   If HTTP clients cache the results of host name lookups in order to
3003   achieve a performance improvement, they &MUST; observe the TTL
3004   information reported by DNS.
3007   If HTTP clients do not observe this rule, they could be spoofed when
3008   a previously-accessed server's IP address changes. As network
3009   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3010   possibility of this form of attack will grow. Observing this
3011   requirement thus reduces this potential security vulnerability.
3014   This requirement also improves the load-balancing behavior of clients
3015   for replicated servers using the same DNS name and reduces the
3016   likelihood of a user's experiencing failure in accessing sites which
3017   use that strategy.
3021<section title="Proxies and Caching" anchor="attack.proxies">
3023   By their very nature, HTTP proxies are men-in-the-middle, and
3024   represent an opportunity for man-in-the-middle attacks. Compromise of
3025   the systems on which the proxies run can result in serious security
3026   and privacy problems. Proxies have access to security-related
3027   information, personal information about individual users and
3028   organizations, and proprietary information belonging to users and
3029   content providers. A compromised proxy, or a proxy implemented or
3030   configured without regard to security and privacy considerations,
3031   might be used in the commission of a wide range of potential attacks.
3034   Proxy operators should protect the systems on which proxies run as
3035   they would protect any system that contains or transports sensitive
3036   information. In particular, log information gathered at proxies often
3037   contains highly sensitive personal information, and/or information
3038   about organizations. Log information should be carefully guarded, and
3039   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3042   Proxy implementors should consider the privacy and security
3043   implications of their design and coding decisions, and of the
3044   configuration options they provide to proxy operators (especially the
3045   default configuration).
3048   Users of a proxy need to be aware that they are no trustworthier than
3049   the people who run the proxy; HTTP itself cannot solve this problem.
3052   The judicious use of cryptography, when appropriate, may suffice to
3053   protect against a broad range of security and privacy attacks. Such
3054   cryptography is beyond the scope of the HTTP/1.1 specification.
3058<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3060   They exist. They are hard to defend against. Research continues.
3061   Beware.
3066<section title="Acknowledgments" anchor="ack">
3068   HTTP has evolved considerably over the years. It has
3069   benefited from a large and active developer community--the many
3070   people who have participated on the www-talk mailing list--and it is
3071   that community which has been most responsible for the success of
3072   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3073   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3074   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3075   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3076   VanHeyningen deserve special recognition for their efforts in
3077   defining early aspects of the protocol.
3080   This document has benefited greatly from the comments of all those
3081   participating in the HTTP-WG. In addition to those already mentioned,
3082   the following individuals have contributed to this specification:
3085   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3086   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3087   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3088   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3089   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3090   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3091   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3092   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3093   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3094   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3095   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3096   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3097   Josh Cohen.
3100   Thanks to the "cave men" of Palo Alto. You know who you are.
3103   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3104   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3105   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3106   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3107   Larry Masinter for their help. And thanks go particularly to Jeff
3108   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3111   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3112   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3113   discovery of many of the problems that this document attempts to
3114   rectify.
3117   This specification makes heavy use of the augmented BNF and generic
3118   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3119   reuses many of the definitions provided by Nathaniel Borenstein and
3120   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3121   specification will help reduce past confusion over the relationship
3122   between HTTP and Internet mail message formats.
3129<references title="Normative References">
3131<reference anchor="ISO-8859-1">
3132  <front>
3133    <title>
3134     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3135    </title>
3136    <author>
3137      <organization>International Organization for Standardization</organization>
3138    </author>
3139    <date year="1998"/>
3140  </front>
3141  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3144<reference anchor="Part2">
3145  <front>
3146    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3147    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3148      <organization abbrev="Day Software">Day Software</organization>
3149      <address><email></email></address>
3150    </author>
3151    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3152      <organization>One Laptop per Child</organization>
3153      <address><email></email></address>
3154    </author>
3155    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3156      <organization abbrev="HP">Hewlett-Packard Company</organization>
3157      <address><email></email></address>
3158    </author>
3159    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3160      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3161      <address><email></email></address>
3162    </author>
3163    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3164      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3165      <address><email></email></address>
3166    </author>
3167    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3168      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3169      <address><email></email></address>
3170    </author>
3171    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3172      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3173      <address><email></email></address>
3174    </author>
3175    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3176      <organization abbrev="W3C">World Wide Web Consortium</organization>
3177      <address><email></email></address>
3178    </author>
3179    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3180      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3181      <address><email></email></address>
3182    </author>
3183    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3184  </front>
3185  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3186  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3189<reference anchor="Part3">
3190  <front>
3191    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3192    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3193      <organization abbrev="Day Software">Day Software</organization>
3194      <address><email></email></address>
3195    </author>
3196    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3197      <organization>One Laptop per Child</organization>
3198      <address><email></email></address>
3199    </author>
3200    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3201      <organization abbrev="HP">Hewlett-Packard Company</organization>
3202      <address><email></email></address>
3203    </author>
3204    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3206      <address><email></email></address>
3207    </author>
3208    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3209      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3210      <address><email></email></address>
3211    </author>
3212    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3214      <address><email></email></address>
3215    </author>
3216    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3217      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3218      <address><email></email></address>
3219    </author>
3220    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3221      <organization abbrev="W3C">World Wide Web Consortium</organization>
3222      <address><email></email></address>
3223    </author>
3224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3226      <address><email></email></address>
3227    </author>
3228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3229  </front>
3230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3231  <x:source href="p3-payload.xml" basename="p3-payload"/>
3234<reference anchor="Part5">
3235  <front>
3236    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3237    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3238      <organization abbrev="Day Software">Day Software</organization>
3239      <address><email></email></address>
3240    </author>
3241    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3242      <organization>One Laptop per Child</organization>
3243      <address><email></email></address>
3244    </author>
3245    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3246      <organization abbrev="HP">Hewlett-Packard Company</organization>
3247      <address><email></email></address>
3248    </author>
3249    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3251      <address><email></email></address>
3252    </author>
3253    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3254      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3255      <address><email></email></address>
3256    </author>
3257    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3258      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3259      <address><email></email></address>
3260    </author>
3261    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3262      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3263      <address><email></email></address>
3264    </author>
3265    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3266      <organization abbrev="W3C">World Wide Web Consortium</organization>
3267      <address><email></email></address>
3268    </author>
3269    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3270      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3271      <address><email></email></address>
3272    </author>
3273    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3274  </front>
3275  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3276  <x:source href="p5-range.xml" basename="p5-range"/>
3279<reference anchor="Part6">
3280  <front>
3281    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3282    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3283      <organization abbrev="Day Software">Day Software</organization>
3284      <address><email></email></address>
3285    </author>
3286    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3287      <organization>One Laptop per Child</organization>
3288      <address><email></email></address>
3289    </author>
3290    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3291      <organization abbrev="HP">Hewlett-Packard Company</organization>
3292      <address><email></email></address>
3293    </author>
3294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3296      <address><email></email></address>
3297    </author>
3298    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3299      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3300      <address><email></email></address>
3301    </author>
3302    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3303      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3304      <address><email></email></address>
3305    </author>
3306    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3307      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3308      <address><email></email></address>
3309    </author>
3310    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3311      <organization abbrev="W3C">World Wide Web Consortium</organization>
3312      <address><email></email></address>
3313    </author>
3314    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3315      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3316      <address><email></email></address>
3317    </author>
3318    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3319  </front>
3320  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3321  <x:source href="p6-cache.xml" basename="p6-cache"/>
3324<reference anchor="RFC5234">
3325  <front>
3326    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3327    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3328      <organization>Brandenburg InternetWorking</organization>
3329      <address>
3330      <postal>
3331      <street>675 Spruce Dr.</street>
3332      <city>Sunnyvale</city>
3333      <region>CA</region>
3334      <code>94086</code>
3335      <country>US</country></postal>
3336      <phone>+1.408.246.8253</phone>
3337      <email></email></address> 
3338    </author>
3339    <author initials="P." surname="Overell" fullname="Paul Overell">
3340      <organization>THUS plc.</organization>
3341      <address>
3342      <postal>
3343      <street>1/2 Berkeley Square</street>
3344      <street>99 Berkely Street</street>
3345      <city>Glasgow</city>
3346      <code>G3 7HR</code>
3347      <country>UK</country></postal>
3348      <email></email></address>
3349    </author>
3350    <date month="January" year="2008"/>
3351  </front>
3352  <seriesInfo name="STD" value="68"/>
3353  <seriesInfo name="RFC" value="5234"/>
3356<reference anchor="RFC2045">
3357  <front>
3358    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3359    <author initials="N." surname="Freed" fullname="Ned Freed">
3360      <organization>Innosoft International, Inc.</organization>
3361      <address><email></email></address>
3362    </author>
3363    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3364      <organization>First Virtual Holdings</organization>
3365      <address><email></email></address>
3366    </author>
3367    <date month="November" year="1996"/>
3368  </front>
3369  <seriesInfo name="RFC" value="2045"/>
3372<reference anchor="RFC2119">
3373  <front>
3374    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3375    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3376      <organization>Harvard University</organization>
3377      <address><email></email></address>
3378    </author>
3379    <date month="March" year="1997"/>
3380  </front>
3381  <seriesInfo name="BCP" value="14"/>
3382  <seriesInfo name="RFC" value="2119"/>
3385<reference anchor="RFC3986">
3386 <front>
3387  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3388  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3389    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3390    <address>
3391       <email></email>
3392       <uri></uri>
3393    </address>
3394  </author>
3395  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3396    <organization abbrev="Day Software">Day Software</organization>
3397    <address>
3398      <email></email>
3399      <uri></uri>
3400    </address>
3401  </author>
3402  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3403    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3404    <address>
3405      <email></email>
3406      <uri></uri>
3407    </address>
3408  </author>
3409  <date month='January' year='2005'></date>
3410 </front>
3411 <seriesInfo name="RFC" value="3986"/>
3412 <seriesInfo name="STD" value="66"/>
3415<reference anchor="USASCII">
3416  <front>
3417    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3418    <author>
3419      <organization>American National Standards Institute</organization>
3420    </author>
3421    <date year="1986"/>
3422  </front>
3423  <seriesInfo name="ANSI" value="X3.4"/>
3428<references title="Informative References">
3430<reference anchor="Nie1997" target="">
3431  <front>
3432    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3433    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3434      <organization/>
3435    </author>
3436    <author initials="J." surname="Gettys" fullname="J. Gettys">
3437      <organization/>
3438    </author>
3439    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3440      <organization/>
3441    </author>
3442    <author initials="H." surname="Lie" fullname="H. Lie">
3443      <organization/>
3444    </author>
3445    <author initials="C." surname="Lilley" fullname="C. Lilley">
3446      <organization/>
3447    </author>
3448    <date year="1997" month="September"/>
3449  </front>
3450  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3453<reference anchor="Pad1995" target="">
3454  <front>
3455    <title>Improving HTTP Latency</title>
3456    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3457      <organization/>
3458    </author>
3459    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3460      <organization/>
3461    </author>
3462    <date year="1995" month="December"/>
3463  </front>
3464  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3467<reference anchor="RFC959">
3468  <front>
3469    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3470    <author initials="J." surname="Postel" fullname="J. Postel">
3471      <organization>Information Sciences Institute (ISI)</organization>
3472    </author>
3473    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3474      <organization/>
3475    </author>
3476    <date month="October" year="1985"/>
3477  </front>
3478  <seriesInfo name="STD" value="9"/>
3479  <seriesInfo name="RFC" value="959"/>
3482<reference anchor="RFC1123">
3483  <front>
3484    <title>Requirements for Internet Hosts - Application and Support</title>
3485    <author initials="R." surname="Braden" fullname="Robert Braden">
3486      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3487      <address><email>Braden@ISI.EDU</email></address>
3488    </author>
3489    <date month="October" year="1989"/>
3490  </front>
3491  <seriesInfo name="STD" value="3"/>
3492  <seriesInfo name="RFC" value="1123"/>
3495<reference anchor="RFC1305">
3496  <front>
3497    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3498    <author initials="D." surname="Mills" fullname="David L. Mills">
3499      <organization>University of Delaware, Electrical Engineering Department</organization>
3500      <address><email></email></address>
3501    </author>
3502    <date month="March" year="1992"/>
3503  </front>
3504  <seriesInfo name="RFC" value="1305"/>
3507<reference anchor="RFC1436">
3508  <front>
3509    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3510    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3511      <organization>University of Minnesota, Computer and Information Services</organization>
3512      <address><email></email></address>
3513    </author>
3514    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3515      <organization>University of Minnesota, Computer and Information Services</organization>
3516      <address><email></email></address>
3517    </author>
3518    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3519      <organization>University of Minnesota, Computer and Information Services</organization>
3520      <address><email></email></address>
3521    </author>
3522    <author initials="D." surname="Johnson" fullname="David Johnson">
3523      <organization>University of Minnesota, Computer and Information Services</organization>
3524      <address><email></email></address>
3525    </author>
3526    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3527      <organization>University of Minnesota, Computer and Information Services</organization>
3528      <address><email></email></address>
3529    </author>
3530    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3531      <organization>University of Minnesota, Computer and Information Services</organization>
3532      <address><email></email></address>
3533    </author>
3534    <date month="March" year="1993"/>
3535  </front>
3536  <seriesInfo name="RFC" value="1436"/>
3539<reference anchor="RFC1900">
3540  <front>
3541    <title>Renumbering Needs Work</title>
3542    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3543      <organization>CERN, Computing and Networks Division</organization>
3544      <address><email></email></address>
3545    </author>
3546    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3547      <organization>cisco Systems</organization>
3548      <address><email></email></address>
3549    </author>
3550    <date month="February" year="1996"/>
3551  </front>
3552  <seriesInfo name="RFC" value="1900"/>
3555<reference anchor="RFC1945">
3556  <front>
3557    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3558    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3559      <organization>MIT, Laboratory for Computer Science</organization>
3560      <address><email></email></address>
3561    </author>
3562    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3563      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3564      <address><email></email></address>
3565    </author>
3566    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3567      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3568      <address><email></email></address>
3569    </author>
3570    <date month="May" year="1996"/>
3571  </front>
3572  <seriesInfo name="RFC" value="1945"/>
3575<reference anchor="RFC2047">
3576  <front>
3577    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3578    <author initials="K." surname="Moore" fullname="Keith Moore">
3579      <organization>University of Tennessee</organization>
3580      <address><email></email></address>
3581    </author>
3582    <date month="November" year="1996"/>
3583  </front>
3584  <seriesInfo name="RFC" value="2047"/>
3587<reference anchor="RFC2068">
3588  <front>
3589    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3590    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3591      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3592      <address><email></email></address>
3593    </author>
3594    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3595      <organization>MIT Laboratory for Computer Science</organization>
3596      <address><email></email></address>
3597    </author>
3598    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3599      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3600      <address><email></email></address>
3601    </author>
3602    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3603      <organization>MIT Laboratory for Computer Science</organization>
3604      <address><email></email></address>
3605    </author>
3606    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3607      <organization>MIT Laboratory for Computer Science</organization>
3608      <address><email></email></address>
3609    </author>
3610    <date month="January" year="1997"/>
3611  </front>
3612  <seriesInfo name="RFC" value="2068"/>
3615<reference anchor='RFC2109'>
3616  <front>
3617    <title>HTTP State Management Mechanism</title>
3618    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3619      <organization>Bell Laboratories, Lucent Technologies</organization>
3620      <address><email></email></address>
3621    </author>
3622    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3623      <organization>Netscape Communications Corp.</organization>
3624      <address><email></email></address>
3625    </author>
3626    <date year='1997' month='February' />
3627  </front>
3628  <seriesInfo name='RFC' value='2109' />
3631<reference anchor="RFC2145">
3632  <front>
3633    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3634    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3635      <organization>Western Research Laboratory</organization>
3636      <address><email></email></address>
3637    </author>
3638    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3639      <organization>Department of Information and Computer Science</organization>
3640      <address><email></email></address>
3641    </author>
3642    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3643      <organization>MIT Laboratory for Computer Science</organization>
3644      <address><email></email></address>
3645    </author>
3646    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3647      <organization>W3 Consortium</organization>
3648      <address><email></email></address>
3649    </author>
3650    <date month="May" year="1997"/>
3651  </front>
3652  <seriesInfo name="RFC" value="2145"/>
3655<reference anchor="RFC2616">
3656  <front>
3657    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3658    <author initials="R." surname="Fielding" fullname="R. Fielding">
3659      <organization>University of California, Irvine</organization>
3660      <address><email></email></address>
3661    </author>
3662    <author initials="J." surname="Gettys" fullname="J. Gettys">
3663      <organization>W3C</organization>
3664      <address><email></email></address>
3665    </author>
3666    <author initials="J." surname="Mogul" fullname="J. Mogul">
3667      <organization>Compaq Computer Corporation</organization>
3668      <address><email></email></address>
3669    </author>
3670    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3671      <organization>MIT Laboratory for Computer Science</organization>
3672      <address><email></email></address>
3673    </author>
3674    <author initials="L." surname="Masinter" fullname="L. Masinter">
3675      <organization>Xerox Corporation</organization>
3676      <address><email></email></address>
3677    </author>
3678    <author initials="P." surname="Leach" fullname="P. Leach">
3679      <organization>Microsoft Corporation</organization>
3680      <address><email></email></address>
3681    </author>
3682    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3683      <organization>W3C</organization>
3684      <address><email></email></address>
3685    </author>
3686    <date month="June" year="1999"/>
3687  </front>
3688  <seriesInfo name="RFC" value="2616"/>
3691<reference anchor='RFC2818'>
3692  <front>
3693    <title>HTTP Over TLS</title>
3694    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3695      <organization>RTFM, Inc.</organization>
3696      <address><email></email></address>
3697    </author>
3698    <date year='2000' month='May' />
3699  </front>
3700  <seriesInfo name='RFC' value='2818' />
3703<reference anchor='RFC2965'>
3704  <front>
3705    <title>HTTP State Management Mechanism</title>
3706    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3707      <organization>Bell Laboratories, Lucent Technologies</organization>
3708      <address><email></email></address>
3709    </author>
3710    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3711      <organization>, Inc.</organization>
3712      <address><email></email></address>
3713    </author>
3714    <date year='2000' month='October' />
3715  </front>
3716  <seriesInfo name='RFC' value='2965' />
3719<reference anchor='RFC3864'>
3720  <front>
3721    <title>Registration Procedures for Message Header Fields</title>
3722    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3723      <organization>Nine by Nine</organization>
3724      <address><email></email></address>
3725    </author>
3726    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3727      <organization>BEA Systems</organization>
3728      <address><email></email></address>
3729    </author>
3730    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3731      <organization>HP Labs</organization>
3732      <address><email></email></address>
3733    </author>
3734    <date year='2004' month='September' />
3735  </front>
3736  <seriesInfo name='BCP' value='90' />
3737  <seriesInfo name='RFC' value='3864' />
3740<reference anchor='RFC3977'>
3741  <front>
3742    <title>Network News Transfer Protocol (NNTP)</title>
3743    <author initials='C.' surname='Feather' fullname='C. Feather'>
3744      <organization>THUS plc</organization>
3745      <address><email></email></address>
3746    </author>
3747    <date year='2006' month='October' />
3748  </front>
3749  <seriesInfo name="RFC" value="3977"/>
3752<reference anchor="RFC4288">
3753  <front>
3754    <title>Media Type Specifications and Registration Procedures</title>
3755    <author initials="N." surname="Freed" fullname="N. Freed">
3756      <organization>Sun Microsystems</organization>
3757      <address>
3758        <email></email>
3759      </address>
3760    </author>
3761    <author initials="J." surname="Klensin" fullname="J. Klensin">
3762      <organization/>
3763      <address>
3764        <email></email>
3765      </address>
3766    </author>
3767    <date year="2005" month="December"/>
3768  </front>
3769  <seriesInfo name="BCP" value="13"/>
3770  <seriesInfo name="RFC" value="4288"/>
3773<reference anchor='RFC4395'>
3774  <front>
3775    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3776    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3777      <organization>AT&amp;T Laboratories</organization>
3778      <address>
3779        <email></email>
3780      </address>
3781    </author>
3782    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3783      <organization>Qualcomm, Inc.</organization>
3784      <address>
3785        <email></email>
3786      </address>
3787    </author>
3788    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3789      <organization>Adobe Systems</organization>
3790      <address>
3791        <email></email>
3792      </address>
3793    </author>
3794    <date year='2006' month='February' />
3795  </front>
3796  <seriesInfo name='BCP' value='115' />
3797  <seriesInfo name='RFC' value='4395' />
3800<reference anchor="RFC5322">
3801  <front>
3802    <title>Internet Message Format</title>
3803    <author initials="P." surname="Resnick" fullname="P. Resnick">
3804      <organization>Qualcomm Incorporated</organization>
3805    </author>
3806    <date year="2008" month="October"/>
3807  </front>
3808  <seriesInfo name="RFC" value="5322"/>
3811<reference anchor="Kri2001" target="">
3812  <front>
3813    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3814    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3815      <organization/>
3816    </author>
3817    <date year="2001" month="November"/>
3818  </front>
3819  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3822<reference anchor="Spe" target="">
3823  <front>
3824  <title>Analysis of HTTP Performance Problems</title>
3825  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3826    <organization/>
3827  </author>
3828  <date/>
3829  </front>
3832<reference anchor="Tou1998" target="">
3833  <front>
3834  <title>Analysis of HTTP Performance</title>
3835  <author initials="J." surname="Touch" fullname="Joe Touch">
3836    <organization>USC/Information Sciences Institute</organization>
3837    <address><email></email></address>
3838  </author>
3839  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3840    <organization>USC/Information Sciences Institute</organization>
3841    <address><email></email></address>
3842  </author>
3843  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3844    <organization>USC/Information Sciences Institute</organization>
3845    <address><email></email></address>
3846  </author>
3847  <date year="1998" month="Aug"/>
3848  </front>
3849  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3850  <annotation>(original report dated Aug. 1996)</annotation>
3853<reference anchor="WAIS">
3854  <front>
3855    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3856    <author initials="F." surname="Davis" fullname="F. Davis">
3857      <organization>Thinking Machines Corporation</organization>
3858    </author>
3859    <author initials="B." surname="Kahle" fullname="B. Kahle">
3860      <organization>Thinking Machines Corporation</organization>
3861    </author>
3862    <author initials="H." surname="Morris" fullname="H. Morris">
3863      <organization>Thinking Machines Corporation</organization>
3864    </author>
3865    <author initials="J." surname="Salem" fullname="J. Salem">
3866      <organization>Thinking Machines Corporation</organization>
3867    </author>
3868    <author initials="T." surname="Shen" fullname="T. Shen">
3869      <organization>Thinking Machines Corporation</organization>
3870    </author>
3871    <author initials="R." surname="Wang" fullname="R. Wang">
3872      <organization>Thinking Machines Corporation</organization>
3873    </author>
3874    <author initials="J." surname="Sui" fullname="J. Sui">
3875      <organization>Thinking Machines Corporation</organization>
3876    </author>
3877    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3878      <organization>Thinking Machines Corporation</organization>
3879    </author>
3880    <date month="April" year="1990"/>
3881  </front>
3882  <seriesInfo name="Thinking Machines Corporation" value=""/>
3888<section title="Tolerant Applications" anchor="tolerant.applications">
3890   Although this document specifies the requirements for the generation
3891   of HTTP/1.1 messages, not all applications will be correct in their
3892   implementation. We therefore recommend that operational applications
3893   be tolerant of deviations whenever those deviations can be
3894   interpreted unambiguously.
3897   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3898   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3899   accept any amount of WSP characters between fields, even though
3900   only a single SP is required.
3903   The line terminator for message-header fields is the sequence CRLF.
3904   However, we recommend that applications, when parsing such headers,
3905   recognize a single LF as a line terminator and ignore the leading CR.
3908   The character set of an entity-body &SHOULD; be labeled as the lowest
3909   common denominator of the character codes used within that body, with
3910   the exception that not labeling the entity is preferred over labeling
3911   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3914   Additional rules for requirements on parsing and encoding of dates
3915   and other potential problems with date encodings include:
3918  <list style="symbols">
3919     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3920        which appears to be more than 50 years in the future is in fact
3921        in the past (this helps solve the "year 2000" problem).</t>
3923     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3924        Expires date as earlier than the proper value, but &MUST-NOT;
3925        internally represent a parsed Expires date as later than the
3926        proper value.</t>
3928     <t>All expiration-related calculations &MUST; be done in GMT. The
3929        local time zone &MUST-NOT; influence the calculation or comparison
3930        of an age or expiration time.</t>
3932     <t>If an HTTP header incorrectly carries a date value with a time
3933        zone other than GMT, it &MUST; be converted into GMT using the
3934        most conservative possible conversion.</t>
3935  </list>
3939<section title="Compatibility with Previous Versions" anchor="compatibility">
3941   HTTP has been in use by the World-Wide Web global information initiative
3942   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3943   was a simple protocol for hypertext data transfer across the Internet
3944   with only a single method and no metadata.
3945   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3946   methods and MIME-like messaging that could include metadata about the data
3947   transferred and modifiers on the request/response semantics. However,
3948   HTTP/1.0 did not sufficiently take into consideration the effects of
3949   hierarchical proxies, caching, the need for persistent connections, or
3950   name-based virtual hosts. The proliferation of incompletely-implemented
3951   applications calling themselves "HTTP/1.0" further necessitated a
3952   protocol version change in order for two communicating applications
3953   to determine each other's true capabilities.
3956   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3957   requirements that enable reliable implementations, adding only
3958   those new features that will either be safely ignored by an HTTP/1.0
3959   recipient or only sent when communicating with a party advertising
3960   compliance with HTTP/1.1.
3963   It is beyond the scope of a protocol specification to mandate
3964   compliance with previous versions. HTTP/1.1 was deliberately
3965   designed, however, to make supporting previous versions easy. It is
3966   worth noting that, at the time of composing this specification
3967   (1996), we would expect commercial HTTP/1.1 servers to:
3968  <list style="symbols">
3969     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3970        1.1 requests;</t>
3972     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3973        1.1;</t>
3975     <t>respond appropriately with a message in the same major version
3976        used by the client.</t>
3977  </list>
3980   And we would expect HTTP/1.1 clients to:
3981  <list style="symbols">
3982     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3983        responses;</t>
3985     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3986        1.1.</t>
3987  </list>
3990   For most implementations of HTTP/1.0, each connection is established
3991   by the client prior to the request and closed by the server after
3992   sending the response. Some implementations implement the Keep-Alive
3993   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3996<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3998   This section summarizes major differences between versions HTTP/1.0
3999   and HTTP/1.1.
4002<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4004   The requirements that clients and servers support the Host request-header,
4005   report an error if the Host request-header (<xref target=""/>) is
4006   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4007   are among the most important changes defined by this
4008   specification.
4011   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4012   addresses and servers; there was no other established mechanism for
4013   distinguishing the intended server of a request than the IP address
4014   to which that request was directed. The changes outlined above will
4015   allow the Internet, once older HTTP clients are no longer common, to
4016   support multiple Web sites from a single IP address, greatly
4017   simplifying large operational Web servers, where allocation of many
4018   IP addresses to a single host has created serious problems. The
4019   Internet will also be able to recover the IP addresses that have been
4020   allocated for the sole purpose of allowing special-purpose domain
4021   names to be used in root-level HTTP URLs. Given the rate of growth of
4022   the Web, and the number of servers already deployed, it is extremely
4023   important that all implementations of HTTP (including updates to
4024   existing HTTP/1.0 applications) correctly implement these
4025   requirements:
4026  <list style="symbols">
4027     <t>Both clients and servers &MUST; support the Host request-header.</t>
4029     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4031     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4032        request does not include a Host request-header.</t>
4034     <t>Servers &MUST; accept absolute URIs.</t>
4035  </list>
4040<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4042   Some clients and servers might wish to be compatible with some
4043   previous implementations of persistent connections in HTTP/1.0
4044   clients and servers. Persistent connections in HTTP/1.0 are
4045   explicitly negotiated as they are not the default behavior. HTTP/1.0
4046   experimental implementations of persistent connections are faulty,
4047   and the new facilities in HTTP/1.1 are designed to rectify these
4048   problems. The problem was that some existing 1.0 clients may be
4049   sending Keep-Alive to a proxy server that doesn't understand
4050   Connection, which would then erroneously forward it to the next
4051   inbound server, which would establish the Keep-Alive connection and
4052   result in a hung HTTP/1.0 proxy waiting for the close on the
4053   response. The result is that HTTP/1.0 clients must be prevented from
4054   using Keep-Alive when talking to proxies.
4057   However, talking to proxies is the most important use of persistent
4058   connections, so that prohibition is clearly unacceptable. Therefore,
4059   we need some other mechanism for indicating a persistent connection
4060   is desired, which is safe to use even when talking to an old proxy
4061   that ignores Connection. Persistent connections are the default for
4062   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4063   declaring non-persistence. See <xref target="header.connection"/>.
4066   The original HTTP/1.0 form of persistent connections (the Connection:
4067   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4071<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4073   This specification has been carefully audited to correct and
4074   disambiguate key word usage; RFC 2068 had many problems in respect to
4075   the conventions laid out in <xref target="RFC2119"/>.
4078   Transfer-coding and message lengths all interact in ways that
4079   required fixing exactly when chunked encoding is used (to allow for
4080   transfer encoding that may not be self delimiting); it was important
4081   to straighten out exactly how message lengths are computed. (Sections
4082   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4083   <xref target="header.content-length" format="counter"/>,
4084   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4087   The use and interpretation of HTTP version numbers has been clarified
4088   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4089   version they support to deal with problems discovered in HTTP/1.0
4090   implementations (<xref target="http.version"/>)
4093   Transfer-coding had significant problems, particularly with
4094   interactions with chunked encoding. The solution is that transfer-codings
4095   become as full fledged as content-codings. This involves
4096   adding an IANA registry for transfer-codings (separate from content
4097   codings), a new header field (TE) and enabling trailer headers in the
4098   future. Transfer encoding is a major performance benefit, so it was
4099   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4100   interoperability problem that could have occurred due to interactions
4101   between authentication trailers, chunked encoding and HTTP/1.0
4102   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4103   and <xref target="header.te" format="counter"/>)
4107<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4109  Empty list elements in list productions have been deprecated.
4110  (<xref target="notation.abnf"/>)
4113  Rules about implicit linear whitespace between certain grammar productions
4114  have been removed; now it's only allowed when specifically pointed out
4115  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4116  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4117  Non-ASCII content in header fields and reason phrase has been obsoleted and
4118  made opaque (the TEXT rule was removed)
4119  (<xref target="basic.rules"/>)
4122  Clarify that HTTP-Version is case sensitive.
4123  (<xref target="http.version"/>)
4126  Remove reference to non-existant identity transfer-coding value tokens.
4127  (Sections <xref format="counter" target="transfer.codings"/> and
4128  <xref format="counter" target="message.length"/>)
4131  Clarification that the chunk length does not include
4132  the count of the octets in the chunk header and trailer.
4133  (<xref target="chunked.transfer.encoding"/>)
4136  Require that invalid whitespace around field-names be rejected.
4137  (<xref target="message.headers"/>)
4140  Update use of abs_path production from RFC1808 to the path-absolute + query
4141  components of RFC3986.
4142  (<xref target="request-target"/>)
4145  Clarify exactly when close connection options must be sent.
4146  (<xref target="header.connection"/>)
4151<section title="Terminology" anchor="terminology">
4153   This specification uses a number of terms to refer to the roles
4154   played by participants in, and objects of, the HTTP communication.
4157  <iref item="cache"/>
4158  <x:dfn>cache</x:dfn>
4159  <list>
4160    <t>
4161      A program's local store of response messages and the subsystem
4162      that controls its message storage, retrieval, and deletion. A
4163      cache stores cacheable responses in order to reduce the response
4164      time and network bandwidth consumption on future, equivalent
4165      requests. Any client or server may include a cache, though a cache
4166      cannot be used by a server that is acting as a tunnel.
4167    </t>
4168  </list>
4171  <iref item="cacheable"/>
4172  <x:dfn>cacheable</x:dfn>
4173  <list>
4174    <t>
4175      A response is cacheable if a cache is allowed to store a copy of
4176      the response message for use in answering subsequent requests. The
4177      rules for determining the cacheability of HTTP responses are
4178      defined in &caching;. Even if a resource is cacheable, there may
4179      be additional constraints on whether a cache can use the cached
4180      copy for a particular request.
4181    </t>
4182  </list>
4185  <iref item="client"/>
4186  <x:dfn>client</x:dfn>
4187  <list>
4188    <t>
4189      A program that establishes connections for the purpose of sending
4190      requests.
4191    </t>
4192  </list>
4195  <iref item="connection"/>
4196  <x:dfn>connection</x:dfn>
4197  <list>
4198    <t>
4199      A transport layer virtual circuit established between two programs
4200      for the purpose of communication.
4201    </t>
4202  </list>
4205  <iref item="content negotiation"/>
4206  <x:dfn>content negotiation</x:dfn>
4207  <list>
4208    <t>
4209      The mechanism for selecting the appropriate representation when
4210      servicing a request, as described in &content.negotiation;. The
4211      representation of entities in any response can be negotiated
4212      (including error responses).
4213    </t>
4214  </list>
4217  <iref item="entity"/>
4218  <x:dfn>entity</x:dfn>
4219  <list>
4220    <t>
4221      The information transferred as the payload of a request or
4222      response. An entity consists of metainformation in the form of
4223      entity-header fields and content in the form of an entity-body, as
4224      described in &entity;.
4225    </t>
4226  </list>
4229  <iref item="gateway"/>
4230  <x:dfn>gateway</x:dfn>
4231  <list>
4232    <t>
4233      A server which acts as an intermediary for some other server.
4234      Unlike a proxy, a gateway receives requests as if it were the
4235      origin server for the requested resource; the requesting client
4236      may not be aware that it is communicating with a gateway.
4237    </t>
4238  </list>
4241  <iref item="inbound"/>
4242  <iref item="outbound"/>
4243  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4244  <list>
4245    <t>
4246      Inbound and outbound refer to the request and response paths for
4247      messages: "inbound" means "traveling toward the origin server",
4248      and "outbound" means "traveling toward the user agent"
4249    </t>
4250  </list>
4253  <iref item="message"/>
4254  <x:dfn>message</x:dfn>
4255  <list>
4256    <t>
4257      The basic unit of HTTP communication, consisting of a structured
4258      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4259      transmitted via the connection.
4260    </t>
4261  </list>
4264  <iref item="origin server"/>
4265  <x:dfn>origin server</x:dfn>
4266  <list>
4267    <t>
4268      The server on which a given resource resides or is to be created.
4269    </t>
4270  </list>
4273  <iref item="proxy"/>
4274  <x:dfn>proxy</x:dfn>
4275  <list>
4276    <t>
4277      An intermediary program which acts as both a server and a client
4278      for the purpose of making requests on behalf of other clients.
4279      Requests are serviced internally or by passing them on, with
4280      possible translation, to other servers. A proxy &MUST; implement
4281      both the client and server requirements of this specification. A
4282      "transparent proxy" is a proxy that does not modify the request or
4283      response beyond what is required for proxy authentication and
4284      identification. A "non-transparent proxy" is a proxy that modifies
4285      the request or response in order to provide some added service to
4286      the user agent, such as group annotation services, media type
4287      transformation, protocol reduction, or anonymity filtering. Except
4288      where either transparent or non-transparent behavior is explicitly
4289      stated, the HTTP proxy requirements apply to both types of
4290      proxies.
4291    </t>
4292  </list>
4295  <iref item="request"/>
4296  <x:dfn>request</x:dfn>
4297  <list>
4298    <t>
4299      An HTTP request message, as defined in <xref target="request"/>.
4300    </t>
4301  </list>
4304  <iref item="resource"/>
4305  <x:dfn>resource</x:dfn>
4306  <list>
4307    <t>
4308      A network data object or service that can be identified by a URI,
4309      as defined in <xref target="uri"/>. Resources may be available in multiple
4310      representations (e.g. multiple languages, data formats, size, and
4311      resolutions) or vary in other ways.
4312    </t>
4313  </list>
4316  <iref item="response"/>
4317  <x:dfn>response</x:dfn>
4318  <list>
4319    <t>
4320      An HTTP response message, as defined in <xref target="response"/>.
4321    </t>
4322  </list>
4325  <iref item="representation"/>
4326  <x:dfn>representation</x:dfn>
4327  <list>
4328    <t>
4329      An entity included with a response that is subject to content
4330      negotiation, as described in &content.negotiation;. There may exist multiple
4331      representations associated with a particular response status.
4332    </t>
4333  </list>
4336  <iref item="server"/>
4337  <x:dfn>server</x:dfn>
4338  <list>
4339    <t>
4340      An application program that accepts connections in order to
4341      service requests by sending back responses. Any given program may
4342      be capable of being both a client and a server; our use of these
4343      terms refers only to the role being performed by the program for a
4344      particular connection, rather than to the program's capabilities
4345      in general. Likewise, any server may act as an origin server,
4346      proxy, gateway, or tunnel, switching behavior based on the nature
4347      of each request.
4348    </t>
4349  </list>
4352  <iref item="tunnel"/>
4353  <x:dfn>tunnel</x:dfn>
4354  <list>
4355    <t>
4356      An intermediary program which is acting as a blind relay between
4357      two connections. Once active, a tunnel is not considered a party
4358      to the HTTP communication, though the tunnel may have been
4359      initiated by an HTTP request. The tunnel ceases to exist when both
4360      ends of the relayed connections are closed.
4361    </t>
4362  </list>
4365  <iref item="upstream"/>
4366  <iref item="downstream"/>
4367  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4368  <list>
4369    <t>
4370      Upstream and downstream describe the flow of a message: all
4371      messages flow from upstream to downstream.
4372    </t>
4373  </list>
4376  <iref item="user agent"/>
4377  <x:dfn>user agent</x:dfn>
4378  <list>
4379    <t>
4380      The client which initiates a request. These are often browsers,
4381      editors, spiders (web-traversing robots), or other end user tools.
4382    </t>
4383  </list>
4386  <iref item="variant"/>
4387  <x:dfn>variant</x:dfn>
4388  <list>
4389    <t>
4390      A resource may have one, or more than one, representation(s)
4391      associated with it at any given instant. Each of these
4392      representations is termed a `variant'.  Use of the term `variant'
4393      does not necessarily imply that the resource is subject to content
4394      negotiation.
4395    </t>
4396  </list>
4400<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4402<artwork type="abnf" name="p1-messaging.parsed-abnf">
4403<x:ref>BWS</x:ref> = OWS
4405<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 15.4&gt;
4406<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4407<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4408<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4409 connection-token ] )
4410<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4411<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4413<x:ref>Date</x:ref> = "Date:" OWS Date-v
4414<x:ref>Date-v</x:ref> = HTTP-date
4416GMT = %x47.4D.54
4418<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4419<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4420<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4421<x:ref>HTTP-message</x:ref> = Request / Response
4422<x:ref>Host</x:ref> = "Host:" OWS Host-v
4423<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4425<x:ref>Method</x:ref> = token
4427<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4429<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 15.4&gt;
4431<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4432<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4433<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4434 entity-header ) CRLF ) CRLF [ message-body ]
4435<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4436<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4437 entity-header ) CRLF ) CRLF [ message-body ]
4439<x:ref>Status-Code</x:ref> = 3DIGIT
4440<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4442<x:ref>TE</x:ref> = "TE:" OWS TE-v
4443<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4444<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4445<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4446<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4447<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4448 transfer-coding ] )
4450<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4451<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4452<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4453<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4455<x:ref>Via</x:ref> = "Via:" OWS Via-v
4456<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4457 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4458 ] )
4460<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 15.6&gt;
4462<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4463<x:ref>accept-params</x:ref> = &lt;accept-params, defined in [Part3], Section 5.1&gt;
4464<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4465<x:ref>attribute</x:ref> = token
4466<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4468<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4469<x:ref>chunk-data</x:ref> = 1*OCTET
4470<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4471<x:ref>chunk-ext-name</x:ref> = token
4472<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4473<x:ref>chunk-size</x:ref> = 1*HEXDIG
4474<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4475<x:ref>connection-token</x:ref> = token
4476<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4478<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4479<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4480<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4482<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4483<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4485<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4486<x:ref>field-name</x:ref> = token
4487<x:ref>field-value</x:ref> = *( field-content / OWS )
4488<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4490<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4491 / Transfer-Encoding / Upgrade / Via / Warning
4492<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4493 message-body ]
4495<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4497l-Fri = %x46.
4498l-Mon = %x4D.6F.6E.64.61.79
4499l-Sat = %x53.
4500l-Sun = %x53.75.6E.64.61.79
4501l-Thu = %x54.
4502l-Tue = %x54.
4503l-Wed = %x57.65.64.6E.
4504<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4506<x:ref>message-body</x:ref> = entity-body / &lt;entity-body encoded as per
4507 Transfer-Encoding&gt;
4508<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4509<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4510 / s-Sep / s-Oct / s-Nov / s-Dec
4512<x:ref>obs-fold</x:ref> = CRLF
4513<x:ref>obs-text</x:ref> = %x80-FF
4514<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4516<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4517<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4518<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4519<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4520<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4521<x:ref>product</x:ref> = token [ "/" product-version ]
4522<x:ref>product-version</x:ref> = token
4523<x:ref>protocol-name</x:ref> = token
4524<x:ref>protocol-version</x:ref> = token
4525<x:ref>pseudonym</x:ref> = token
4527<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4528<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4529<x:ref>quoted-pair</x:ref> = "\" quoted-text
4530<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4531<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4533<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4534<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4535<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4536<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4537<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4538 / authority
4539<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4540<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4541<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4543s-Apr = %x41.70.72
4544s-Aug = %x41.75.67
4545s-Dec = %x44.65.63
4546s-Feb = %x46.65.62
4547s-Fri = %x46.72.69
4548s-Jan = %x4A.61.6E
4549s-Jul = %x4A.75.6C
4550s-Jun = %x4A.75.6E
4551s-Mar = %x4D.61.72
4552s-May = %x4D.61.79
4553s-Mon = %x4D.6F.6E
4554s-Nov = %x4E.6F.76
4555s-Oct = %x4F.63.74
4556s-Sat = %x53.61.74
4557s-Sep = %x53.65.70
4558s-Sun = %x53.75.6E
4559s-Thu = %x54.68.75
4560s-Tue = %x54.75.65
4561s-Wed = %x57.65.64
4562<x:ref>start-line</x:ref> = Request-Line / Status-Line
4564<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ accept-params ] )
4565<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4566 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4567<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4568<x:ref>token</x:ref> = 1*tchar
4569<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4570<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4571<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4573<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4575<x:ref>value</x:ref> = token / quoted-string
4577<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4578<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4580; Chunked-Body defined but not used
4581; Content-Length defined but not used
4582; HTTP-message defined but not used
4583; Host defined but not used
4584; TE defined but not used
4585; URI defined but not used
4586; URI-reference defined but not used
4587; fragment defined but not used
4588; generic-message defined but not used
4589; http-URI defined but not used
4590; partial-URI defined but not used
4597<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4599<section title="Since RFC2616">
4601  Extracted relevant partitions from <xref target="RFC2616"/>.
4605<section title="Since draft-ietf-httpbis-p1-messaging-00">
4607  Closed issues:
4608  <list style="symbols">
4609    <t>
4610      <eref target=""/>:
4611      "HTTP Version should be case sensitive"
4612      (<eref target=""/>)
4613    </t>
4614    <t>
4615      <eref target=""/>:
4616      "'unsafe' characters"
4617      (<eref target=""/>)
4618    </t>
4619    <t>
4620      <eref target=""/>:
4621      "Chunk Size Definition"
4622      (<eref target=""/>)
4623    </t>
4624    <t>
4625      <eref target=""/>:
4626      "Message Length"
4627      (<eref target=""/>)
4628    </t>
4629    <t>
4630      <eref target=""/>:
4631      "Media Type Registrations"
4632      (<eref target=""/>)
4633    </t>
4634    <t>
4635      <eref target=""/>:
4636      "URI includes query"
4637      (<eref target=""/>)
4638    </t>
4639    <t>
4640      <eref target=""/>:
4641      "No close on 1xx responses"
4642      (<eref target=""/>)
4643    </t>
4644    <t>
4645      <eref target=""/>:
4646      "Remove 'identity' token references"
4647      (<eref target=""/>)
4648    </t>
4649    <t>
4650      <eref target=""/>:
4651      "Import query BNF"
4652    </t>
4653    <t>
4654      <eref target=""/>:
4655      "qdtext BNF"
4656    </t>
4657    <t>
4658      <eref target=""/>:
4659      "Normative and Informative references"
4660    </t>
4661    <t>
4662      <eref target=""/>:
4663      "RFC2606 Compliance"
4664    </t>
4665    <t>
4666      <eref target=""/>:
4667      "RFC977 reference"
4668    </t>
4669    <t>
4670      <eref target=""/>:
4671      "RFC1700 references"
4672    </t>
4673    <t>
4674      <eref target=""/>:
4675      "inconsistency in date format explanation"
4676    </t>
4677    <t>
4678      <eref target=""/>:
4679      "Date reference typo"
4680    </t>
4681    <t>
4682      <eref target=""/>:
4683      "Informative references"
4684    </t>
4685    <t>
4686      <eref target=""/>:
4687      "ISO-8859-1 Reference"
4688    </t>
4689    <t>
4690      <eref target=""/>:
4691      "Normative up-to-date references"
4692    </t>
4693  </list>
4696  Other changes:
4697  <list style="symbols">
4698    <t>
4699      Update media type registrations to use RFC4288 template.
4700    </t>
4701    <t>
4702      Use names of RFC4234 core rules DQUOTE and WSP,
4703      fix broken ABNF for chunk-data
4704      (work in progress on <eref target=""/>)
4705    </t>
4706  </list>
4710<section title="Since draft-ietf-httpbis-p1-messaging-01">
4712  Closed issues:
4713  <list style="symbols">
4714    <t>
4715      <eref target=""/>:
4716      "Bodies on GET (and other) requests"
4717    </t>
4718    <t>
4719      <eref target=""/>:
4720      "Updating to RFC4288"
4721    </t>
4722    <t>
4723      <eref target=""/>:
4724      "Status Code and Reason Phrase"
4725    </t>
4726    <t>
4727      <eref target=""/>:
4728      "rel_path not used"
4729    </t>
4730  </list>
4733  Ongoing work on ABNF conversion (<eref target=""/>):
4734  <list style="symbols">
4735    <t>
4736      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4737      "trailer-part").
4738    </t>
4739    <t>
4740      Avoid underscore character in rule names ("http_URL" ->
4741      "http-URL", "abs_path" -> "path-absolute").
4742    </t>
4743    <t>
4744      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4745      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4746      have to be updated when switching over to RFC3986.
4747    </t>
4748    <t>
4749      Synchronize core rules with RFC5234.
4750    </t>
4751    <t>
4752      Get rid of prose rules that span multiple lines.
4753    </t>
4754    <t>
4755      Get rid of unused rules LOALPHA and UPALPHA.
4756    </t>
4757    <t>
4758      Move "Product Tokens" section (back) into Part 1, as "token" is used
4759      in the definition of the Upgrade header.
4760    </t>
4761    <t>
4762      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4763    </t>
4764    <t>
4765      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4766    </t>
4767  </list>
4771<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4773  Closed issues:
4774  <list style="symbols">
4775    <t>
4776      <eref target=""/>:
4777      "HTTP-date vs. rfc1123-date"
4778    </t>
4779    <t>
4780      <eref target=""/>:
4781      "WS in quoted-pair"
4782    </t>
4783  </list>
4786  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4787  <list style="symbols">
4788    <t>
4789      Reference RFC 3984, and update header registrations for headers defined
4790      in this document.
4791    </t>
4792  </list>
4795  Ongoing work on ABNF conversion (<eref target=""/>):
4796  <list style="symbols">
4797    <t>
4798      Replace string literals when the string really is case-sensitive (HTTP-Version).
4799    </t>
4800  </list>
4804<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4806  Closed issues:
4807  <list style="symbols">
4808    <t>
4809      <eref target=""/>:
4810      "Connection closing"
4811    </t>
4812    <t>
4813      <eref target=""/>:
4814      "Move registrations and registry information to IANA Considerations"
4815    </t>
4816    <t>
4817      <eref target=""/>:
4818      "need new URL for PAD1995 reference"
4819    </t>
4820    <t>
4821      <eref target=""/>:
4822      "IANA Considerations: update HTTP URI scheme registration"
4823    </t>
4824    <t>
4825      <eref target=""/>:
4826      "Cite HTTPS URI scheme definition"
4827    </t>
4828    <t>
4829      <eref target=""/>:
4830      "List-type headers vs Set-Cookie"
4831    </t>
4832  </list>
4835  Ongoing work on ABNF conversion (<eref target=""/>):
4836  <list style="symbols">
4837    <t>
4838      Replace string literals when the string really is case-sensitive (HTTP-Date).
4839    </t>
4840    <t>
4841      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4842    </t>
4843  </list>
4847<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4849  Closed issues:
4850  <list style="symbols">
4851    <t>
4852      <eref target=""/>:
4853      "Out-of-date reference for URIs"
4854    </t>
4855    <t>
4856      <eref target=""/>:
4857      "RFC 2822 is updated by RFC 5322"
4858    </t>
4859  </list>
4862  Ongoing work on ABNF conversion (<eref target=""/>):
4863  <list style="symbols">
4864    <t>
4865      Use "/" instead of "|" for alternatives.
4866    </t>
4867    <t>
4868      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4869    </t>
4870    <t>
4871      Only reference RFC 5234's core rules.
4872    </t>
4873    <t>
4874      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4875      whitespace ("OWS") and required whitespace ("RWS").
4876    </t>
4877    <t>
4878      Rewrite ABNFs to spell out whitespace rules, factor out
4879      header value format definitions.
4880    </t>
4881  </list>
4885<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4887  Closed issues:
4888  <list style="symbols">
4889    <t>
4890      <eref target=""/>:
4891      "Header LWS"
4892    </t>
4893    <t>
4894      <eref target=""/>:
4895      "Sort 1.3 Terminology"
4896    </t>
4897    <t>
4898      <eref target=""/>:
4899      "RFC2047 encoded words"
4900    </t>
4901    <t>
4902      <eref target=""/>:
4903      "Character Encodings in TEXT"
4904    </t>
4905    <t>
4906      <eref target=""/>:
4907      "Line Folding"
4908    </t>
4909    <t>
4910      <eref target=""/>:
4911      "OPTIONS * and proxies"
4912    </t>
4913    <t>
4914      <eref target=""/>:
4915      "Reason-Phrase BNF"
4916    </t>
4917    <t>
4918      <eref target=""/>:
4919      "Use of TEXT"
4920    </t>
4921    <t>
4922      <eref target=""/>:
4923      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4924    </t>
4925    <t>
4926      <eref target=""/>:
4927      "RFC822 reference left in discussion of date formats"
4928    </t>
4929  </list>
4932  Ongoing work on ABNF conversion (<eref target=""/>):
4933  <list style="symbols">
4934    <t>
4935      Rewrite definition of list rules, deprecate empty list elements.
4936    </t>
4937    <t>
4938      Add appendix containing collected and expanded ABNF.
4939    </t>
4940  </list>
4943  Other changes:
4944  <list style="symbols">
4945    <t>
4946      Rewrite introduction; add mostly new Architecture Section.
4947    </t>
4948  </list>
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