source: draft-ietf-httpbis/latest/p1-messaging.xml @ 454

Last change on this file since 454 was 454, checked in by julian.reschke@…, 14 years ago

fix line wrap in ABNF prose problem; update XSLT for collected ABNF to move diagnostics into separate figure

  • Property svn:eol-style set to native
File size: 211.3 KB
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 "February">
16  <!ENTITY ID-YEAR "2009">
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="pre5378Trust200902" 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;"/>
198  <workgroup>HTTPbis Working Group</workgroup>
202   The Hypertext Transfer Protocol (HTTP) is an application-level
203   protocol for distributed, collaborative, hypertext information
204   systems. HTTP has been in use by the World Wide Web global information
205   initiative since 1990. This document is Part 1 of the seven-part specification
206   that defines the protocol referred to as "HTTP/1.1" and, taken together,
207   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
208   its associated terminology, defines the "http" and "https" Uniform
209   Resource Identifier (URI) schemes, defines the generic message syntax
210   and parsing requirements for HTTP message frames, and describes
211   general security concerns for implementations.
215<note title="Editorial Note (To be removed by RFC Editor)">
216  <t>
217    Discussion of this draft should take place on the HTTPBIS working group
218    mailing list ( The current issues list is
219    at <eref target=""/>
220    and related documents (including fancy diffs) can be found at
221    <eref target=""/>.
222  </t>
223  <t>
224    The changes in this draft are summarized in <xref target="changes.since.05"/>.
225  </t>
229<section title="Introduction" anchor="introduction">
231   The Hypertext Transfer Protocol (HTTP) is an application-level
232   request/response protocol that uses extensible semantics and MIME-like
233   message payloads for flexible interaction with network-based hypertext
234   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
235   standard <xref target="RFC3986"/> to indicate resource targets and
236   relationships between resources.
237   Messages are passed in a format similar to that used by Internet mail
238   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
239   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
240   between HTTP and MIME messages).
243   HTTP is a generic interface protocol for informations systems. It is
244   designed to hide the details of how a service is implemented by presenting
245   a uniform interface to clients that is independent of the types of
246   resources provided. Likewise, servers do not need to be aware of each
247   client's purpose: an HTTP request can be considered in isolation rather
248   than being associated with a specific type of client or a predetermined
249   sequence of application steps. The result is a protocol that can be used
250   effectively in many different contexts and for which implementations can
251   evolve independently over time.
254   HTTP is also designed for use as a generic protocol for translating
255   communication to and from other Internet information systems, such as
256   USENET news services via NNTP <xref target="RFC3977"/>,
257   file services via FTP <xref target="RFC959"/>,
258   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
259   HTTP proxies and gateways provide access to alternative information
260   services by translating their diverse protocols into a hypertext
261   format that can be viewed and manipulated by clients in the same way
262   as HTTP services.
265   One consequence of HTTP flexibility is that the protocol cannot be defined
266   in terms of what occurs behind the interface. Instead, we are
267   limited to defining the syntax of communication, the intent
268   of received communication, and the expected behavior of recipients. If
269   the communication is considered in isolation, then successful actions
270   should be reflected in the observable interface provided by servers.
271   However, since many clients are potentially acting in parallel and
272   perhaps at cross-purposes, it would be meaningless to require that such
273   behavior be observable.
276   This document is Part 1 of the seven-part specification of HTTP,
277   defining the protocol referred to as "HTTP/1.1" and obsoleting
278   <xref target="RFC2616"/>.
279   Part 1 defines the URI schemes specific to HTTP-based resources, overall
280   network operation, transport protocol connection management, and HTTP
281   message framing and forwarding requirements.
282   Our goal is to define all of the mechanisms necessary for HTTP message
283   handling that are independent of message semantics, thereby defining the
284   complete set of requirements for a message parser and transparent
285   message-forwarding intermediaries.
288<section title="Requirements" anchor="intro.requirements">
290   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
291   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
292   document are to be interpreted as described in <xref target="RFC2119"/>.
295   An implementation is not compliant if it fails to satisfy one or more
296   of the &MUST; or &REQUIRED; level requirements for the protocols it
297   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
298   level and all the &SHOULD; level requirements for its protocols is said
299   to be "unconditionally compliant"; one that satisfies all the &MUST;
300   level requirements but not all the &SHOULD; level requirements for its
301   protocols is said to be "conditionally compliant."
305<section title="Syntax Notation" anchor="notation">
306<iref primary="true" item="Grammar" subitem="ALPHA"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="LF"/>
314<iref primary="true" item="Grammar" subitem="OCTET"/>
315<iref primary="true" item="Grammar" subitem="SP"/>
316<iref primary="true" item="Grammar" subitem="VCHAR"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   This specification uses the Augmented Backus-Naur Form (ABNF) notation
332   of <xref target="RFC5234"/>.  The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342<section title="ABNF Extension: #rule" anchor="notation.abnf">
343  <t>
344    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
345    improve readability.
346  </t>
347  <t>
348    A construct "#" is defined, similar to "*", for defining lists of
349    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
350    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
351    (",") and optional whitespace (OWS).   
352  </t>
353  <figure><preamble>
354    Thus,
355</preamble><artwork type="example">
356  1#element =&gt; element *( OWS "," OWS element )
358  <figure><preamble>
359    and:
360</preamble><artwork type="example">
361  #element =&gt; [ 1#element ]
363  <figure><preamble>
364    and for n &gt;= 1 and m &gt; 1:
365</preamble><artwork type="example">
366  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
368  <t>
369    For compatibility with legacy list rules, recipients &SHOULD; accept empty
370    list elements. In other words, consumers would follow the list productions:
371  </t>
372<figure><artwork type="example">
373#element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
3751#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
378  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
379  expanded as explained above.
383<section title="Basic Rules" anchor="basic.rules">
384<t anchor="rule.CRLF">
385  <x:anchor-alias value="CRLF"/>
386   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
387   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
388   tolerant applications). The end-of-line marker within an entity-body
389   is defined by its associated media type, as described in &media-types;.
391<t anchor="rule.LWS">
392   This specification uses three rules to denote the use of linear
393   whitespace: OWS (optional whitespace), RWS (required whitespace), and
394   BWS ("bad" whitespace).
397   The OWS rule is used where zero or more linear whitespace characters may
398   appear. OWS &SHOULD; either not be produced or be produced as a single SP
399   character. Multiple OWS characters that occur within field-content &SHOULD;
400   be replaced with a single SP before interpreting the field value or
401   forwarding the message downstream.
404   RWS is used when at least one linear whitespace character is required to
405   separate field tokens. RWS &SHOULD; be produced as a single SP character.
406   Multiple RWS characters that occur within field-content &SHOULD; be
407   replaced with a single SP before interpreting the field value or
408   forwarding the message downstream.
411   BWS is used where the grammar allows optional whitespace for historical
412   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
413   recipients &MUST; accept such bad optional whitespace and remove it before
414   interpreting the field value or forwarding the message downstream.
416<t anchor="rule.whitespace">
417  <x:anchor-alias value="BWS"/>
418  <x:anchor-alias value="OWS"/>
419  <x:anchor-alias value="RWS"/>
420  <x:anchor-alias value="obs-fold"/>
422<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"/>
423  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
424                 ; "optional" whitespace
425  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
426                 ; "required" whitespace
427  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
428                 ; "bad" whitespace
429  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
430                 ; see <xref target="message.headers"/>
432<t anchor="rule.token.separators">
433  <x:anchor-alias value="tchar"/>
434  <x:anchor-alias value="token"/>
435   Many HTTP/1.1 header field values consist of words separated by whitespace
436   or special characters. These special characters &MUST; be in a quoted
437   string to be used within a parameter value (as defined in
438   <xref target="transfer.codings"/>).
440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
441  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
442                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
443                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
445  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
447<t anchor="rule.quoted-string">
448  <x:anchor-alias value="quoted-string"/>
449  <x:anchor-alias value="qdtext"/>
450  <x:anchor-alias value="obs-text"/>
451   A string of text is parsed as a single word if it is quoted using
452   double-quote marks.
454<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"/>
455  <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>
456  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
457  <x:ref>obs-text</x:ref>       = %x80-FF
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="accept-params"/>
477  <x:anchor-alias value="entity-body"/>
478  <x:anchor-alias value="entity-header"/>
479  <x:anchor-alias value="Cache-Control"/>
480  <x:anchor-alias value="Pragma"/>
481  <x:anchor-alias value="Warning"/>
483  The ABNF rules below are defined in other parts:
485<figure><!-- Part2--><artwork type="abnf2616">
486  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
487  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
489<figure><!-- Part3--><artwork type="abnf2616">
490  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
491  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
492  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
494<figure><!-- Part6--><artwork type="abnf2616">
495  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
496  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
497  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
504<section title="HTTP architecture" anchor="architecture">
506   HTTP was created with a specific architecture in mind, the World Wide Web,
507   and has evolved over time to support the scalability needs of a worldwide
508   hypertext system. Much of that architecture is reflected in the terminology
509   and syntax productions used to define HTTP.
512<section title="Uniform Resource Identifiers" anchor="uri">
514   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
515   throughout HTTP as the means for identifying resources. URI references
516   are used to target requests, redirect responses, and define relationships.
517   HTTP does not limit what a resource may be; it merely defines an interface
518   that can be used to interact with a resource via HTTP. More information on
519   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
521  <x:anchor-alias value="URI"/>
522  <x:anchor-alias value="URI-reference"/>
523  <x:anchor-alias value="absolute-URI"/>
524  <x:anchor-alias value="relative-part"/>
525  <x:anchor-alias value="authority"/>
526  <x:anchor-alias value="fragment"/>
527  <x:anchor-alias value="path-abempty"/>
528  <x:anchor-alias value="path-absolute"/>
529  <x:anchor-alias value="port"/>
530  <x:anchor-alias value="query"/>
531  <x:anchor-alias value="uri-host"/>
532  <x:anchor-alias value="partial-URI"/>
534   This specification adopts the definitions of "URI-reference",
535   "absolute-URI", "relative-part", "fragment", "port", "host",
536   "path-abempty", "path-absolute", "query", and "authority" from
537   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
538   protocol elements that allow a relative URI without a fragment.
540<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"/>
541  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
542  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
543  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
544  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
545  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
546  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
547  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
549  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
550  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
551  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
553  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
556   Each protocol element in HTTP that allows a URI reference will indicate in
557   its ABNF production whether the element allows only a URI in absolute form
558   (absolute-URI), any relative reference (relative-ref), or some other subset
559   of the URI-reference grammar. Unless otherwise indicated, URI references
560   are parsed relative to the request target (the default base URI for both
561   the request and its corresponding response).
564<section title="http URI scheme" anchor="http.uri">
565  <x:anchor-alias value="http-URI"/>
566  <iref item="http URI scheme" primary="true"/>
567  <iref item="URI scheme" subitem="http" primary="true"/>
569   The "http" scheme is used to locate network resources via the HTTP
570   protocol.
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.
590<section title="https URI scheme" anchor="https.uri">
591   <iref item="https URI scheme"/>
592   <iref item="URI scheme" subitem="https"/>
594   <cref>TBD: Define and explain purpose of https scheme.</cref>
597  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
601<section title="URI Comparison" anchor="uri.comparison">
603   When comparing two URIs to decide if they match or not, a client
604   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
605   URIs, with these exceptions:
606  <list style="symbols">
607    <t>A port that is empty or not given is equivalent to the default
608        port for that URI-reference;</t>
609    <t>Comparisons of host names &MUST; be case-insensitive;</t>
610    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
611    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
612    <t>Characters other than those in the "reserved" set are equivalent to their
613       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
614    </t>
615  </list>
618   For example, the following three URIs are equivalent:
620<figure><artwork type="example">
627<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
633<section title="Overall Operation" anchor="intro.overall.operation">
635   HTTP is a request/response protocol. A client sends a
636   request to the server in the form of a request method, URI, and
637   protocol version, followed by a MIME-like message containing request
638   modifiers, client information, and possible body content over a
639   connection with a server. The server responds with a status line,
640   including the message's protocol version and a success or error code,
641   followed by a MIME-like message containing server information, entity
642   metainformation, and possible entity-body content.
645   Most HTTP communication is initiated by a user agent and consists of
646   a request to be applied to a resource on some origin server. In the
647   simplest case, this may be accomplished via a single connection (v)
648   between the user agent (UA) and the origin server (O).
650<figure><artwork type="drawing">
651       request chain ------------------------&gt;
652    UA -------------------v------------------- O
653       &lt;----------------------- response chain
656   A more complicated situation occurs when one or more intermediaries
657   are present in the request/response chain. There are three common
658   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
659   forwarding agent, receiving requests for a URI in its absolute form,
660   rewriting all or part of the message, and forwarding the reformatted
661   request toward the server identified by the URI. A gateway is a
662   receiving agent, acting as a layer above some other server(s) and, if
663   necessary, translating the requests to the underlying server's
664   protocol. A tunnel acts as a relay point between two connections
665   without changing the messages; tunnels are used when the
666   communication needs to pass through an intermediary (such as a
667   firewall) even when the intermediary cannot understand the contents
668   of the messages.
670<figure><artwork type="drawing">
671       request chain --------------------------------------&gt;
672    UA -----v----- A -----v----- B -----v----- C -----v----- O
673       &lt;------------------------------------- response chain
676   The figure above shows three intermediaries (A, B, and C) between the
677   user agent and origin server. A request or response message that
678   travels the whole chain will pass through four separate connections.
679   This distinction is important because some HTTP communication options
680   may apply only to the connection with the nearest, non-tunnel
681   neighbor, only to the end-points of the chain, or to all connections
682   along the chain. Although the diagram is linear, each participant may
683   be engaged in multiple, simultaneous communications. For example, B
684   may be receiving requests from many clients other than A, and/or
685   forwarding requests to servers other than C, at the same time that it
686   is handling A's request.
689   Any party to the communication which is not acting as a tunnel may
690   employ an internal cache for handling requests. The effect of a cache
691   is that the request/response chain is shortened if one of the
692   participants along the chain has a cached response applicable to that
693   request. The following illustrates the resulting chain if B has a
694   cached copy of an earlier response from O (via C) for a request which
695   has not been cached by UA or A.
697<figure><artwork type="drawing">
698          request chain ----------&gt;
699       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
700          &lt;--------- response chain
703   Not all responses are usefully cacheable, and some requests may
704   contain modifiers which place special requirements on cache behavior.
705   HTTP requirements for cache behavior and cacheable responses are
706   defined in &caching;.
709   In fact, there are a wide variety of architectures and configurations
710   of caches and proxies currently being experimented with or deployed
711   across the World Wide Web. These systems include national hierarchies
712   of proxy caches to save transoceanic bandwidth, systems that
713   broadcast or multicast cache entries, organizations that distribute
714   subsets of cached data via CD-ROM, and so on. HTTP systems are used
715   in corporate intranets over high-bandwidth links, and for access via
716   PDAs with low-power radio links and intermittent connectivity. The
717   goal of HTTP/1.1 is to support the wide diversity of configurations
718   already deployed while introducing protocol constructs that meet the
719   needs of those who build web applications that require high
720   reliability and, failing that, at least reliable indications of
721   failure.
724   HTTP communication usually takes place over TCP/IP connections. The
725   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
726   not preclude HTTP from being implemented on top of any other protocol
727   on the Internet, or on other networks. HTTP only presumes a reliable
728   transport; any protocol that provides such guarantees can be used;
729   the mapping of the HTTP/1.1 request and response structures onto the
730   transport data units of the protocol in question is outside the scope
731   of this specification.
734   In HTTP/1.0, most implementations used a new connection for each
735   request/response exchange. In HTTP/1.1, a connection may be used for
736   one or more request/response exchanges, although connections may be
737   closed for a variety of reasons (see <xref target="persistent.connections"/>).
741<section title="Use of HTTP for proxy communication" anchor="http.proxy">
743   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
746<section title="Interception of HTTP for access control" anchor="http.intercept">
748   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
751<section title="Use of HTTP by other protocols" anchor="http.others">
753   <cref>TBD: Profiles of HTTP defined by other protocol.
754   Extensions of HTTP like WebDAV.</cref>
757<section title="Use of HTTP by media type specification" anchor="">
759   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
764<section title="Protocol Parameters" anchor="protocol.parameters">
766<section title="HTTP Version" anchor="http.version">
767  <x:anchor-alias value="HTTP-Version"/>
768  <x:anchor-alias value="HTTP-Prot-Name"/>
770   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
771   of the protocol. The protocol versioning policy is intended to allow
772   the sender to indicate the format of a message and its capacity for
773   understanding further HTTP communication, rather than the features
774   obtained via that communication. No change is made to the version
775   number for the addition of message components which do not affect
776   communication behavior or which only add to extensible field values.
777   The &lt;minor&gt; number is incremented when the changes made to the
778   protocol add features which do not change the general message parsing
779   algorithm, but which may add to the message semantics and imply
780   additional capabilities of the sender. The &lt;major&gt; number is
781   incremented when the format of a message within the protocol is
782   changed. See <xref target="RFC2145"/> for a fuller explanation.
785   The version of an HTTP message is indicated by an HTTP-Version field
786   in the first line of the message. HTTP-Version is case-sensitive.
788<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
789  <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>
790  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
793   Note that the major and minor numbers &MUST; be treated as separate
794   integers and that each &MAY; be incremented higher than a single digit.
795   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
796   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
797   &MUST-NOT; be sent.
800   An application that sends a request or response message that includes
801   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
802   with this specification. Applications that are at least conditionally
803   compliant with this specification &SHOULD; use an HTTP-Version of
804   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
805   not compatible with HTTP/1.0. For more details on when to send
806   specific HTTP-Version values, see <xref target="RFC2145"/>.
809   The HTTP version of an application is the highest HTTP version for
810   which the application is at least conditionally compliant.
813   Proxy and gateway applications need to be careful when forwarding
814   messages in protocol versions different from that of the application.
815   Since the protocol version indicates the protocol capability of the
816   sender, a proxy/gateway &MUST-NOT; send a message with a version
817   indicator which is greater than its actual version. If a higher
818   version request is received, the proxy/gateway &MUST; either downgrade
819   the request version, or respond with an error, or switch to tunnel
820   behavior.
823   Due to interoperability problems with HTTP/1.0 proxies discovered
824   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
825   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
826   they support. The proxy/gateway's response to that request &MUST; be in
827   the same major version as the request.
830  <list>
831    <t>
832      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
833      of header fields required or forbidden by the versions involved.
834    </t>
835  </list>
839<section title="Date/Time Formats" anchor="date.time.formats">
840<section title="Full Date" anchor="">
841  <x:anchor-alias value="HTTP-date"/>
842  <x:anchor-alias value="obsolete-date"/>
843  <x:anchor-alias value="rfc1123-date"/>
844  <x:anchor-alias value="rfc850-date"/>
845  <x:anchor-alias value="asctime-date"/>
846  <x:anchor-alias value="date1"/>
847  <x:anchor-alias value="date2"/>
848  <x:anchor-alias value="date3"/>
849  <x:anchor-alias value="rfc1123-date"/>
850  <x:anchor-alias value="time"/>
851  <x:anchor-alias value="wkday"/>
852  <x:anchor-alias value="weekday"/>
853  <x:anchor-alias value="month"/>
855   HTTP applications have historically allowed three different formats
856   for the representation of date/time stamps:
858<figure><artwork type="example">
859   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
860   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
861   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
864   The first format is preferred as an Internet standard and represents
865   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
866   other formats are described here only for
867   compatibility with obsolete implementations.
868   HTTP/1.1 clients and servers that parse the date value &MUST; accept
869   all three formats (for compatibility with HTTP/1.0), though they &MUST;
870   only generate the RFC 1123 format for representing HTTP-date values
871   in header fields. See <xref target="tolerant.applications"/> for further information.
874      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
875      accepting date values that may have been sent by non-HTTP
876      applications, as is sometimes the case when retrieving or posting
877      messages via proxies/gateways to SMTP or NNTP.
880   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
881   (GMT), without exception. For the purposes of HTTP, GMT is exactly
882   equal to UTC (Coordinated Universal Time). This is indicated in the
883   first two formats by the inclusion of "GMT" as the three-letter
884   abbreviation for time zone, and &MUST; be assumed when reading the
885   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
886   additional whitespace beyond that specifically included as SP in the
887   grammar.
889<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"/>
890  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
891  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
892  <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
893  <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
894  <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>
895  <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>
896                 ; day month year (e.g., 02 Jun 1982)
897  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
898                 ; day-month-year (e.g., 02-Jun-82)
899  <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> ))
900                 ; month day (e.g., Jun  2)
901  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
902                 ; 00:00:00 - 23:59:59
903  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
904               / s-Thu / s-Fri / s-Sat / s-Sun
905  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
906               / l-Thu / l-Fri / l-Sat / l-Sun
907  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
908               / s-May / s-Jun / s-Jul / s-Aug
909               / s-Sep / s-Oct / s-Nov / s-Dec
911  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
913  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
914  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
915  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
916  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
917  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
918  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
919  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
921  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
922  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
923  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
924  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
925  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
926  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
927  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
929  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
930  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
931  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
932  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
933  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
934  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
935  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
936  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
937  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
938  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
939  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
940  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
943      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
944      to their usage within the protocol stream. Clients and servers are
945      not required to use these formats for user presentation, request
946      logging, etc.
951<section title="Transfer Codings" anchor="transfer.codings">
952  <x:anchor-alias value="parameter"/>
953  <x:anchor-alias value="transfer-coding"/>
954  <x:anchor-alias value="transfer-extension"/>
956   Transfer-coding values are used to indicate an encoding
957   transformation that has been, can be, or may need to be applied to an
958   entity-body in order to ensure "safe transport" through the network.
959   This differs from a content coding in that the transfer-coding is a
960   property of the message, not of the original entity.
962<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
963  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
964  <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> )
966<t anchor="rule.parameter">
967  <x:anchor-alias value="attribute"/>
968  <x:anchor-alias value="parameter"/>
969  <x:anchor-alias value="value"/>
970   Parameters are in  the form of attribute/value pairs.
972<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"/>
973  <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>
974  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
975  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
978   All transfer-coding values are case-insensitive. HTTP/1.1 uses
979   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
980   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
983   Whenever a transfer-coding is applied to a message-body, the set of
984   transfer-codings &MUST; include "chunked", unless the message indicates it
985   is terminated by closing the connection. When the "chunked" transfer-coding
986   is used, it &MUST; be the last transfer-coding applied to the
987   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
988   than once to a message-body. These rules allow the recipient to
989   determine the transfer-length of the message (<xref target="message.length"/>).
992   Transfer-codings are analogous to the Content-Transfer-Encoding
993   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
994   binary data over a 7-bit transport service. However, safe transport
995   has a different focus for an 8bit-clean transfer protocol. In HTTP,
996   the only unsafe characteristic of message-bodies is the difficulty in
997   determining the exact body length (<xref target="message.length"/>), or the desire to
998   encrypt data over a shared transport.
1001   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1002   transfer-coding value tokens. Initially, the registry contains the
1003   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1004   "gzip", "compress", and "deflate" (&content-codings;).
1007   New transfer-coding value tokens &SHOULD; be registered in the same way
1008   as new content-coding value tokens (&content-codings;).
1011   A server which receives an entity-body with a transfer-coding it does
1012   not understand &SHOULD; return 501 (Not Implemented), and close the
1013   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1014   client.
1017<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1018  <x:anchor-alias value="chunk"/>
1019  <x:anchor-alias value="Chunked-Body"/>
1020  <x:anchor-alias value="chunk-data"/>
1021  <x:anchor-alias value="chunk-ext"/>
1022  <x:anchor-alias value="chunk-ext-name"/>
1023  <x:anchor-alias value="chunk-ext-val"/>
1024  <x:anchor-alias value="chunk-size"/>
1025  <x:anchor-alias value="last-chunk"/>
1026  <x:anchor-alias value="trailer-part"/>
1028   The chunked encoding modifies the body of a message in order to
1029   transfer it as a series of chunks, each with its own size indicator,
1030   followed by an &OPTIONAL; trailer containing entity-header fields. This
1031   allows dynamically produced content to be transferred along with the
1032   information necessary for the recipient to verify that it has
1033   received the full message.
1035<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"/>
1036  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1037                   <x:ref>last-chunk</x:ref>
1038                   <x:ref>trailer-part</x:ref>
1039                   <x:ref>CRLF</x:ref>
1041  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1042                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1043  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1044  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1046  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1047                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1048  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1049  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1050  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1051  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1054   The chunk-size field is a string of hex digits indicating the size of
1055   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1056   zero, followed by the trailer, which is terminated by an empty line.
1059   The trailer allows the sender to include additional HTTP header
1060   fields at the end of the message. The Trailer header field can be
1061   used to indicate which header fields are included in a trailer (see
1062   <xref target="header.trailer"/>).
1065   A server using chunked transfer-coding in a response &MUST-NOT; use the
1066   trailer for any header fields unless at least one of the following is
1067   true:
1068  <list style="numbers">
1069    <t>the request included a TE header field that indicates "trailers" is
1070     acceptable in the transfer-coding of the  response, as described in
1071     <xref target="header.te"/>; or,</t>
1073    <t>the server is the origin server for the response, the trailer
1074     fields consist entirely of optional metadata, and the recipient
1075     could use the message (in a manner acceptable to the origin server)
1076     without receiving this metadata.  In other words, the origin server
1077     is willing to accept the possibility that the trailer fields might
1078     be silently discarded along the path to the client.</t>
1079  </list>
1082   This requirement prevents an interoperability failure when the
1083   message is being received by an HTTP/1.1 (or later) proxy and
1084   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1085   compliance with the protocol would have necessitated a possibly
1086   infinite buffer on the proxy.
1089   A process for decoding the "chunked" transfer-coding
1090   can be represented in pseudo-code as:
1092<figure><artwork type="code">
1093  length := 0
1094  read chunk-size, chunk-ext (if any) and CRLF
1095  while (chunk-size &gt; 0) {
1096     read chunk-data and CRLF
1097     append chunk-data to entity-body
1098     length := length + chunk-size
1099     read chunk-size and CRLF
1100  }
1101  read entity-header
1102  while (entity-header not empty) {
1103     append entity-header to existing header fields
1104     read entity-header
1105  }
1106  Content-Length := length
1107  Remove "chunked" from Transfer-Encoding
1110   All HTTP/1.1 applications &MUST; be able to receive and decode the
1111   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1112   they do not understand.
1117<section title="Product Tokens" anchor="product.tokens">
1118  <x:anchor-alias value="product"/>
1119  <x:anchor-alias value="product-version"/>
1121   Product tokens are used to allow communicating applications to
1122   identify themselves by software name and version. Most fields using
1123   product tokens also allow sub-products which form a significant part
1124   of the application to be listed, separated by whitespace. By
1125   convention, the products are listed in order of their significance
1126   for identifying the application.
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1129  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1130  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1133   Examples:
1135<figure><artwork type="example">
1136    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1137    Server: Apache/0.8.4
1140   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1141   used for advertising or other non-essential information. Although any
1142   token character &MAY; appear in a product-version, this token &SHOULD;
1143   only be used for a version identifier (i.e., successive versions of
1144   the same product &SHOULD; only differ in the product-version portion of
1145   the product value).
1151<section title="HTTP Message" anchor="http.message">
1153<section title="Message Types" anchor="message.types">
1154  <x:anchor-alias value="generic-message"/>
1155  <x:anchor-alias value="HTTP-message"/>
1156  <x:anchor-alias value="start-line"/>
1158   HTTP messages consist of requests from client to server and responses
1159   from server to client.
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1162  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1165   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1166   message format of <xref target="RFC5322"/> for transferring entities (the payload
1167   of the message). Both types of message consist of a start-line, zero
1168   or more header fields (also known as "headers"), an empty line (i.e.,
1169   a line with nothing preceding the CRLF) indicating the end of the
1170   header fields, and possibly a message-body.
1172<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1173  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1174                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1175                    <x:ref>CRLF</x:ref>
1176                    [ <x:ref>message-body</x:ref> ]
1177  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1180   In the interest of robustness, servers &SHOULD; ignore any empty
1181   line(s) received where a Request-Line is expected. In other words, if
1182   the server is reading the protocol stream at the beginning of a
1183   message and receives a CRLF first, it should ignore the CRLF.
1186   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1187   after a POST request. To restate what is explicitly forbidden by the
1188   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1189   extra CRLF.
1192   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1193   header field. The presence of whitespace might be an attempt to trick a
1194   noncompliant implementation of HTTP into ignoring that field or processing
1195   the next line as a new request, either of which may result in security
1196   issues when implementations within the request chain interpret the
1197   same message differently. HTTP/1.1 servers &MUST; reject such a message
1198   with a 400 (Bad Request) response.
1202<section title="Message Headers" anchor="message.headers">
1203  <x:anchor-alias value="field-content"/>
1204  <x:anchor-alias value="field-name"/>
1205  <x:anchor-alias value="field-value"/>
1206  <x:anchor-alias value="message-header"/>
1208   HTTP header fields follow the same general format as Internet messages in
1209   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1210   of a name followed by a colon (":"), optional whitespace, and the field
1211   value. Field names are case-insensitive.
1213<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"/>
1214  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1215  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1216  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1217  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1220   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1221   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1222   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1223   header field-values use only a subset of the US-ASCII charset
1224   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1225   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1226   (obs-text) octets in field-content as opaque data.
1229   No whitespace is allowed between the header field-name and colon. For
1230   security reasons, any request message received containing such whitespace
1231   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1232   whitespace in a response message &MUST; be removed.
1235   The field value &MAY; be preceded by optional whitespace; a single SP is
1236   preferred. The field-value does not include any leading or trailing white
1237   space: OWS occurring before the first non-whitespace character of the
1238   field-value or after the last non-whitespace character of the field-value
1239   is ignored and &MAY; be removed without changing the meaning of the header
1240   field.
1243   Historically, HTTP header field values could be extended over multiple
1244   lines by preceding each extra line with at least one space or horizontal
1245   tab character (line folding). This specification deprecates such line
1246   folding except within the message/http media type
1247   (<xref target=""/>).
1248   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1249   (i.e., that contain any field-content that matches the obs-fold rule) unless
1250   the message is intended for packaging within the message/http media type.
1251   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1252   obs-fold whitespace with a single SP prior to interpreting the field value
1253   or forwarding the message downstream.
1255<t anchor="rule.comment">
1256  <x:anchor-alias value="comment"/>
1257  <x:anchor-alias value="ctext"/>
1258   Comments can be included in some HTTP header fields by surrounding
1259   the comment text with parentheses. Comments are only allowed in
1260   fields containing "comment" as part of their field value definition.
1261   In all other fields, parentheses are considered part of the field
1262   value.
1264<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1265  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1266  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1269   The order in which header fields with differing field names are
1270   received is not significant. However, it is "good practice" to send
1271   general-header fields first, followed by request-header or response-header
1272   fields, and ending with the entity-header fields.
1275   Multiple message-header fields with the same field-name &MAY; be
1276   present in a message if and only if the entire field-value for that
1277   header field is defined as a comma-separated list [i.e., #(values)].
1278   It &MUST; be possible to combine the multiple header fields into one
1279   "field-name: field-value" pair, without changing the semantics of the
1280   message, by appending each subsequent field-value to the first, each
1281   separated by a comma. The order in which header fields with the same
1282   field-name are received is therefore significant to the
1283   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1284   change the order of these field values when a message is forwarded.
1287  <list><t>
1288   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1289   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1290   can occur multiple times, but does not use the list syntax, and thus cannot
1291   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1292   for details.) Also note that the Set-Cookie2 header specified in
1293   <xref target="RFC2965"/> does not share this problem.
1294  </t></list>
1299<section title="Message Body" anchor="message.body">
1300  <x:anchor-alias value="message-body"/>
1302   The message-body (if any) of an HTTP message is used to carry the
1303   entity-body associated with the request or response. The message-body
1304   differs from the entity-body only when a transfer-coding has been
1305   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1307<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1308  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1309               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1312   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1313   applied by an application to ensure safe and proper transfer of the
1314   message. Transfer-Encoding is a property of the message, not of the
1315   entity, and thus &MAY; be added or removed by any application along the
1316   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1317   when certain transfer-codings may be used.)
1320   The rules for when a message-body is allowed in a message differ for
1321   requests and responses.
1324   The presence of a message-body in a request is signaled by the
1325   inclusion of a Content-Length or Transfer-Encoding header field in
1326   the request's message-headers. A message-body &MUST-NOT; be included in
1327   a request if the specification of the request method (&method;)
1328   explicitly disallows an entity-body in requests.
1329   When a request message contains both a message-body of non-zero
1330   length and a method that does not define any semantics for that
1331   request message-body, then an origin server &SHOULD; either ignore
1332   the message-body or respond with an appropriate error message
1333   (e.g., 413).  A proxy or gateway, when presented the same request,
1334   &SHOULD; either forward the request inbound with the message-body or
1335   ignore the message-body when determining a response.
1338   For response messages, whether or not a message-body is included with
1339   a message is dependent on both the request method and the response
1340   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1341   &MUST-NOT; include a message-body, even though the presence of entity-header
1342   fields might lead one to believe they do. All 1xx
1343   (informational), 204 (No Content), and 304 (Not Modified) responses
1344   &MUST-NOT; include a message-body. All other responses do include a
1345   message-body, although it &MAY; be of zero length.
1349<section title="Message Length" anchor="message.length">
1351   The transfer-length of a message is the length of the message-body as
1352   it appears in the message; that is, after any transfer-codings have
1353   been applied. When a message-body is included with a message, the
1354   transfer-length of that body is determined by one of the following
1355   (in order of precedence):
1358  <list style="numbers">
1359    <x:lt><t>
1360     Any response message which "&MUST-NOT;" include a message-body (such
1361     as the 1xx, 204, and 304 responses and any response to a HEAD
1362     request) is always terminated by the first empty line after the
1363     header fields, regardless of the entity-header fields present in
1364     the message.
1365    </t></x:lt>
1366    <x:lt><t>
1367     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1368     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1369     is used, the transfer-length is defined by the use of this transfer-coding.
1370     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1371     is not present, the transfer-length is defined by the sender closing the connection.
1372    </t></x:lt>
1373    <x:lt><t>
1374     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1375     decimal value in OCTETs represents both the entity-length and the
1376     transfer-length. The Content-Length header field &MUST-NOT; be sent
1377     if these two lengths are different (i.e., if a Transfer-Encoding
1378     header field is present). If a message is received with both a
1379     Transfer-Encoding header field and a Content-Length header field,
1380     the latter &MUST; be ignored.
1381    </t></x:lt>
1382    <x:lt><t>
1383     If the message uses the media type "multipart/byteranges", and the
1384     transfer-length is not otherwise specified, then this self-delimiting
1385     media type defines the transfer-length. This media type
1386     &MUST-NOT; be used unless the sender knows that the recipient can parse
1387     it; the presence in a request of a Range header with multiple byte-range
1388     specifiers from a 1.1 client implies that the client can parse
1389     multipart/byteranges responses.
1390    <list style="empty"><t>
1391       A range header might be forwarded by a 1.0 proxy that does not
1392       understand multipart/byteranges; in this case the server &MUST;
1393       delimit the message using methods defined in items 1, 3 or 5 of
1394       this section.
1395    </t></list>
1396    </t></x:lt>
1397    <x:lt><t>
1398     By the server closing the connection. (Closing the connection
1399     cannot be used to indicate the end of a request body, since that
1400     would leave no possibility for the server to send back a response.)
1401    </t></x:lt>
1402  </list>
1405   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1406   containing a message-body &MUST; include a valid Content-Length header
1407   field unless the server is known to be HTTP/1.1 compliant. If a
1408   request contains a message-body and a Content-Length is not given,
1409   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1410   determine the length of the message, or with 411 (Length Required) if
1411   it wishes to insist on receiving a valid Content-Length.
1414   All HTTP/1.1 applications that receive entities &MUST; accept the
1415   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1416   to be used for messages when the message length cannot be determined
1417   in advance.
1420   Messages &MUST-NOT; include both a Content-Length header field and a
1421   transfer-coding. If the message does include a
1422   transfer-coding, the Content-Length &MUST; be ignored.
1425   When a Content-Length is given in a message where a message-body is
1426   allowed, its field value &MUST; exactly match the number of OCTETs in
1427   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1428   invalid length is received and detected.
1432<section title="General Header Fields" anchor="general.header.fields">
1433  <x:anchor-alias value="general-header"/>
1435   There are a few header fields which have general applicability for
1436   both request and response messages, but which do not apply to the
1437   entity being transferred. These header fields apply only to the
1438   message being transmitted.
1440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1441  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1442                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1443                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1444                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1445                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1446                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1447                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1448                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1449                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1452   General-header field names can be extended reliably only in
1453   combination with a change in the protocol version. However, new or
1454   experimental header fields may be given the semantics of general
1455   header fields if all parties in the communication recognize them to
1456   be general-header fields. Unrecognized header fields are treated as
1457   entity-header fields.
1462<section title="Request" anchor="request">
1463  <x:anchor-alias value="Request"/>
1465   A request message from a client to a server includes, within the
1466   first line of that message, the method to be applied to the resource,
1467   the identifier of the resource, and the protocol version in use.
1469<!--                 Host                      ; should be moved here eventually -->
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1471  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1472                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1473                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1474                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1475                  <x:ref>CRLF</x:ref>
1476                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1479<section title="Request-Line" anchor="request-line">
1480  <x:anchor-alias value="Request-Line"/>
1482   The Request-Line begins with a method token, followed by the
1483   request-target and the protocol version, and ending with CRLF. The
1484   elements are separated by SP characters. No CR or LF is allowed
1485   except in the final CRLF sequence.
1487<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1488  <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>
1491<section title="Method" anchor="method">
1492  <x:anchor-alias value="Method"/>
1494   The Method  token indicates the method to be performed on the
1495   resource identified by the request-target. The method is case-sensitive.
1497<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1498  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1502<section title="request-target" anchor="request-target">
1503  <x:anchor-alias value="request-target"/>
1505   The request-target
1506   identifies the resource upon which to apply the request.
1508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1509  <x:ref>request-target</x:ref> = "*"
1510                 / <x:ref>absolute-URI</x:ref>
1511                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1512                 / <x:ref>authority</x:ref>
1515   The four options for request-target are dependent on the nature of the
1516   request. The asterisk "*" means that the request does not apply to a
1517   particular resource, but to the server itself, and is only allowed
1518   when the method used does not necessarily apply to a resource. One
1519   example would be
1521<figure><artwork type="example">
1522  OPTIONS * HTTP/1.1
1525   The absolute-URI form is &REQUIRED; when the request is being made to a
1526   proxy. The proxy is requested to forward the request or service it
1527   from a valid cache, and return the response. Note that the proxy &MAY;
1528   forward the request on to another proxy or directly to the server
1529   specified by the absolute-URI. In order to avoid request loops, a
1530   proxy &MUST; be able to recognize all of its server names, including
1531   any aliases, local variations, and the numeric IP address. An example
1532   Request-Line would be:
1534<figure><artwork type="example">
1535  GET HTTP/1.1
1538   To allow for transition to absolute-URIs in all requests in future
1539   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1540   form in requests, even though HTTP/1.1 clients will only generate
1541   them in requests to proxies.
1544   The authority form is only used by the CONNECT method (&CONNECT;).
1547   The most common form of request-target is that used to identify a
1548   resource on an origin server or gateway. In this case the absolute
1549   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1550   the request-target, and the network location of the URI (authority) &MUST;
1551   be transmitted in a Host header field. For example, a client wishing
1552   to retrieve the resource above directly from the origin server would
1553   create a TCP connection to port 80 of the host "" and send
1554   the lines:
1556<figure><artwork type="example">
1557  GET /pub/WWW/TheProject.html HTTP/1.1
1558  Host:
1561   followed by the remainder of the Request. Note that the absolute path
1562   cannot be empty; if none is present in the original URI, it &MUST; be
1563   given as "/" (the server root).
1566   If a proxy receives a request without any path in the request-target and
1567   the method specified is capable of supporting the asterisk form of
1568   request-target, then the last proxy on the request chain &MUST; forward the
1569   request with "*" as the final request-target.
1572   For example, the request
1573</preamble><artwork type="example">
1574  OPTIONS HTTP/1.1
1577  would be forwarded by the proxy as
1578</preamble><artwork type="example">
1579  OPTIONS * HTTP/1.1
1580  Host:
1583   after connecting to port 8001 of host "".
1587   The request-target is transmitted in the format specified in
1588   <xref target="http.uri"/>. If the request-target is percent-encoded
1589   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1590   &MUST; decode the request-target in order to
1591   properly interpret the request. Servers &SHOULD; respond to invalid
1592   request-targets with an appropriate status code.
1595   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1596   received request-target when forwarding it to the next inbound server,
1597   except as noted above to replace a null path-absolute with "/".
1600  <list><t>
1601      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1602      meaning of the request when the origin server is improperly using
1603      a non-reserved URI character for a reserved purpose.  Implementors
1604      should be aware that some pre-HTTP/1.1 proxies have been known to
1605      rewrite the request-target.
1606  </t></list>
1609   HTTP does not place a pre-defined limit on the length of a request-target.
1610   A server &MUST; be prepared to receive URIs of unbounded length and
1611   respond with the 414 (URI Too Long) status if the received
1612   request-target would be longer than the server wishes to handle
1613   (see &status-414;).
1616   Various ad-hoc limitations on request-target length are found in practice.
1617   It is &RECOMMENDED; that all HTTP senders and recipients support
1618   request-target lengths of 8000 or more OCTETs.
1623<section title="The Resource Identified by a Request" anchor="">
1625   The exact resource identified by an Internet request is determined by
1626   examining both the request-target and the Host header field.
1629   An origin server that does not allow resources to differ by the
1630   requested host &MAY; ignore the Host header field value when
1631   determining the resource identified by an HTTP/1.1 request. (But see
1632   <xref target=""/>
1633   for other requirements on Host support in HTTP/1.1.)
1636   An origin server that does differentiate resources based on the host
1637   requested (sometimes referred to as virtual hosts or vanity host
1638   names) &MUST; use the following rules for determining the requested
1639   resource on an HTTP/1.1 request:
1640  <list style="numbers">
1641    <t>If request-target is an absolute-URI, the host is part of the
1642     request-target. Any Host header field value in the request &MUST; be
1643     ignored.</t>
1644    <t>If the request-target is not an absolute-URI, and the request includes
1645     a Host header field, the host is determined by the Host header
1646     field value.</t>
1647    <t>If the host as determined by rule 1 or 2 is not a valid host on
1648     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1649  </list>
1652   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1653   attempt to use heuristics (e.g., examination of the URI path for
1654   something unique to a particular host) in order to determine what
1655   exact resource is being requested.
1662<section title="Response" anchor="response">
1663  <x:anchor-alias value="Response"/>
1665   After receiving and interpreting a request message, a server responds
1666   with an HTTP response message.
1668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1669  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1670                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1671                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1672                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1673                  <x:ref>CRLF</x:ref>
1674                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1677<section title="Status-Line" anchor="status-line">
1678  <x:anchor-alias value="Status-Line"/>
1680   The first line of a Response message is the Status-Line, consisting
1681   of the protocol version followed by a numeric status code and its
1682   associated textual phrase, with each element separated by SP
1683   characters. No CR or LF is allowed except in the final CRLF sequence.
1685<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1686  <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>
1689<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1690  <x:anchor-alias value="Reason-Phrase"/>
1691  <x:anchor-alias value="Status-Code"/>
1693   The Status-Code element is a 3-digit integer result code of the
1694   attempt to understand and satisfy the request. These codes are fully
1695   defined in &status-codes;.  The Reason Phrase exists for the sole
1696   purpose of providing a textual description associated with the numeric
1697   status code, out of deference to earlier Internet application protocols
1698   that were more frequently used with interactive text clients.
1699   A client &SHOULD; ignore the content of the Reason Phrase.
1702   The first digit of the Status-Code defines the class of response. The
1703   last two digits do not have any categorization role. There are 5
1704   values for the first digit:
1705  <list style="symbols">
1706    <t>
1707      1xx: Informational - Request received, continuing process
1708    </t>
1709    <t>
1710      2xx: Success - The action was successfully received,
1711        understood, and accepted
1712    </t>
1713    <t>
1714      3xx: Redirection - Further action must be taken in order to
1715        complete the request
1716    </t>
1717    <t>
1718      4xx: Client Error - The request contains bad syntax or cannot
1719        be fulfilled
1720    </t>
1721    <t>
1722      5xx: Server Error - The server failed to fulfill an apparently
1723        valid request
1724    </t>
1725  </list>
1727<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"/>
1728  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1729  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1737<section title="Connections" anchor="connections">
1739<section title="Persistent Connections" anchor="persistent.connections">
1741<section title="Purpose" anchor="persistent.purpose">
1743   Prior to persistent connections, a separate TCP connection was
1744   established to fetch each URL, increasing the load on HTTP servers
1745   and causing congestion on the Internet. The use of inline images and
1746   other associated data often require a client to make multiple
1747   requests of the same server in a short amount of time. Analysis of
1748   these performance problems and results from a prototype
1749   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1750   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1751   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1752   T/TCP <xref target="Tou1998"/>.
1755   Persistent HTTP connections have a number of advantages:
1756  <list style="symbols">
1757      <t>
1758        By opening and closing fewer TCP connections, CPU time is saved
1759        in routers and hosts (clients, servers, proxies, gateways,
1760        tunnels, or caches), and memory used for TCP protocol control
1761        blocks can be saved in hosts.
1762      </t>
1763      <t>
1764        HTTP requests and responses can be pipelined on a connection.
1765        Pipelining allows a client to make multiple requests without
1766        waiting for each response, allowing a single TCP connection to
1767        be used much more efficiently, with much lower elapsed time.
1768      </t>
1769      <t>
1770        Network congestion is reduced by reducing the number of packets
1771        caused by TCP opens, and by allowing TCP sufficient time to
1772        determine the congestion state of the network.
1773      </t>
1774      <t>
1775        Latency on subsequent requests is reduced since there is no time
1776        spent in TCP's connection opening handshake.
1777      </t>
1778      <t>
1779        HTTP can evolve more gracefully, since errors can be reported
1780        without the penalty of closing the TCP connection. Clients using
1781        future versions of HTTP might optimistically try a new feature,
1782        but if communicating with an older server, retry with old
1783        semantics after an error is reported.
1784      </t>
1785    </list>
1788   HTTP implementations &SHOULD; implement persistent connections.
1792<section title="Overall Operation" anchor="persistent.overall">
1794   A significant difference between HTTP/1.1 and earlier versions of
1795   HTTP is that persistent connections are the default behavior of any
1796   HTTP connection. That is, unless otherwise indicated, the client
1797   &SHOULD; assume that the server will maintain a persistent connection,
1798   even after error responses from the server.
1801   Persistent connections provide a mechanism by which a client and a
1802   server can signal the close of a TCP connection. This signaling takes
1803   place using the Connection header field (<xref target="header.connection"/>). Once a close
1804   has been signaled, the client &MUST-NOT; send any more requests on that
1805   connection.
1808<section title="Negotiation" anchor="persistent.negotiation">
1810   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1811   maintain a persistent connection unless a Connection header including
1812   the connection-token "close" was sent in the request. If the server
1813   chooses to close the connection immediately after sending the
1814   response, it &SHOULD; send a Connection header including the
1815   connection-token close.
1818   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1819   decide to keep it open based on whether the response from a server
1820   contains a Connection header with the connection-token close. In case
1821   the client does not want to maintain a connection for more than that
1822   request, it &SHOULD; send a Connection header including the
1823   connection-token close.
1826   If either the client or the server sends the close token in the
1827   Connection header, that request becomes the last one for the
1828   connection.
1831   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1832   maintained for HTTP versions less than 1.1 unless it is explicitly
1833   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1834   compatibility with HTTP/1.0 clients.
1837   In order to remain persistent, all messages on the connection &MUST;
1838   have a self-defined message length (i.e., one not defined by closure
1839   of the connection), as described in <xref target="message.length"/>.
1843<section title="Pipelining" anchor="pipelining">
1845   A client that supports persistent connections &MAY; "pipeline" its
1846   requests (i.e., send multiple requests without waiting for each
1847   response). A server &MUST; send its responses to those requests in the
1848   same order that the requests were received.
1851   Clients which assume persistent connections and pipeline immediately
1852   after connection establishment &SHOULD; be prepared to retry their
1853   connection if the first pipelined attempt fails. If a client does
1854   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1855   persistent. Clients &MUST; also be prepared to resend their requests if
1856   the server closes the connection before sending all of the
1857   corresponding responses.
1860   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1861   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1862   premature termination of the transport connection could lead to
1863   indeterminate results. A client wishing to send a non-idempotent
1864   request &SHOULD; wait to send that request until it has received the
1865   response status for the previous request.
1870<section title="Proxy Servers" anchor="persistent.proxy">
1872   It is especially important that proxies correctly implement the
1873   properties of the Connection header field as specified in <xref target="header.connection"/>.
1876   The proxy server &MUST; signal persistent connections separately with
1877   its clients and the origin servers (or other proxy servers) that it
1878   connects to. Each persistent connection applies to only one transport
1879   link.
1882   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1883   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1884   discussion of the problems with the Keep-Alive header implemented by
1885   many HTTP/1.0 clients).
1889<section title="Practical Considerations" anchor="persistent.practical">
1891   Servers will usually have some time-out value beyond which they will
1892   no longer maintain an inactive connection. Proxy servers might make
1893   this a higher value since it is likely that the client will be making
1894   more connections through the same server. The use of persistent
1895   connections places no requirements on the length (or existence) of
1896   this time-out for either the client or the server.
1899   When a client or server wishes to time-out it &SHOULD; issue a graceful
1900   close on the transport connection. Clients and servers &SHOULD; both
1901   constantly watch for the other side of the transport close, and
1902   respond to it as appropriate. If a client or server does not detect
1903   the other side's close promptly it could cause unnecessary resource
1904   drain on the network.
1907   A client, server, or proxy &MAY; close the transport connection at any
1908   time. For example, a client might have started to send a new request
1909   at the same time that the server has decided to close the "idle"
1910   connection. From the server's point of view, the connection is being
1911   closed while it was idle, but from the client's point of view, a
1912   request is in progress.
1915   This means that clients, servers, and proxies &MUST; be able to recover
1916   from asynchronous close events. Client software &SHOULD; reopen the
1917   transport connection and retransmit the aborted sequence of requests
1918   without user interaction so long as the request sequence is
1919   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1920   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1921   human operator the choice of retrying the request(s). Confirmation by
1922   user-agent software with semantic understanding of the application
1923   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1924   be repeated if the second sequence of requests fails.
1927   Servers &SHOULD; always respond to at least one request per connection,
1928   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1929   middle of transmitting a response, unless a network or client failure
1930   is suspected.
1933   Clients that use persistent connections &SHOULD; limit the number of
1934   simultaneous connections that they maintain to a given server. A
1935   single-user client &SHOULD-NOT; maintain more than 2 connections with
1936   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1937   another server or proxy, where N is the number of simultaneously
1938   active users. These guidelines are intended to improve HTTP response
1939   times and avoid congestion.
1944<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1946<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1948   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1949   flow control mechanisms to resolve temporary overloads, rather than
1950   terminating connections with the expectation that clients will retry.
1951   The latter technique can exacerbate network congestion.
1955<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1957   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1958   the network connection for an error status while it is transmitting
1959   the request. If the client sees an error status, it &SHOULD;
1960   immediately cease transmitting the body. If the body is being sent
1961   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1962   empty trailer &MAY; be used to prematurely mark the end of the message.
1963   If the body was preceded by a Content-Length header, the client &MUST;
1964   close the connection.
1968<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1970   The purpose of the 100 (Continue) status (see &status-100;) is to
1971   allow a client that is sending a request message with a request body
1972   to determine if the origin server is willing to accept the request
1973   (based on the request headers) before the client sends the request
1974   body. In some cases, it might either be inappropriate or highly
1975   inefficient for the client to send the body if the server will reject
1976   the message without looking at the body.
1979   Requirements for HTTP/1.1 clients:
1980  <list style="symbols">
1981    <t>
1982        If a client will wait for a 100 (Continue) response before
1983        sending the request body, it &MUST; send an Expect request-header
1984        field (&header-expect;) with the "100-continue" expectation.
1985    </t>
1986    <t>
1987        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1988        with the "100-continue" expectation if it does not intend
1989        to send a request body.
1990    </t>
1991  </list>
1994   Because of the presence of older implementations, the protocol allows
1995   ambiguous situations in which a client may send "Expect: 100-continue"
1996   without receiving either a 417 (Expectation Failed) status
1997   or a 100 (Continue) status. Therefore, when a client sends this
1998   header field to an origin server (possibly via a proxy) from which it
1999   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2000   for an indefinite period before sending the request body.
2003   Requirements for HTTP/1.1 origin servers:
2004  <list style="symbols">
2005    <t> Upon receiving a request which includes an Expect request-header
2006        field with the "100-continue" expectation, an origin server &MUST;
2007        either respond with 100 (Continue) status and continue to read
2008        from the input stream, or respond with a final status code. The
2009        origin server &MUST-NOT; wait for the request body before sending
2010        the 100 (Continue) response. If it responds with a final status
2011        code, it &MAY; close the transport connection or it &MAY; continue
2012        to read and discard the rest of the request.  It &MUST-NOT;
2013        perform the requested method if it returns a final status code.
2014    </t>
2015    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2016        the request message does not include an Expect request-header
2017        field with the "100-continue" expectation, and &MUST-NOT; send a
2018        100 (Continue) response if such a request comes from an HTTP/1.0
2019        (or earlier) client. There is an exception to this rule: for
2020        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2021        status in response to an HTTP/1.1 PUT or POST request that does
2022        not include an Expect request-header field with the "100-continue"
2023        expectation. This exception, the purpose of which is
2024        to minimize any client processing delays associated with an
2025        undeclared wait for 100 (Continue) status, applies only to
2026        HTTP/1.1 requests, and not to requests with any other HTTP-version
2027        value.
2028    </t>
2029    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2030        already received some or all of the request body for the
2031        corresponding request.
2032    </t>
2033    <t> An origin server that sends a 100 (Continue) response &MUST;
2034    ultimately send a final status code, once the request body is
2035        received and processed, unless it terminates the transport
2036        connection prematurely.
2037    </t>
2038    <t> If an origin server receives a request that does not include an
2039        Expect request-header field with the "100-continue" expectation,
2040        the request includes a request body, and the server responds
2041        with a final status code before reading the entire request body
2042        from the transport connection, then the server &SHOULD-NOT;  close
2043        the transport connection until it has read the entire request,
2044        or until the client closes the connection. Otherwise, the client
2045        might not reliably receive the response message. However, this
2046        requirement is not be construed as preventing a server from
2047        defending itself against denial-of-service attacks, or from
2048        badly broken client implementations.
2049      </t>
2050    </list>
2053   Requirements for HTTP/1.1 proxies:
2054  <list style="symbols">
2055    <t> If a proxy receives a request that includes an Expect request-header
2056        field with the "100-continue" expectation, and the proxy
2057        either knows that the next-hop server complies with HTTP/1.1 or
2058        higher, or does not know the HTTP version of the next-hop
2059        server, it &MUST; forward the request, including the Expect header
2060        field.
2061    </t>
2062    <t> If the proxy knows that the version of the next-hop server is
2063        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2064        respond with a 417 (Expectation Failed) status.
2065    </t>
2066    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2067        numbers received from recently-referenced next-hop servers.
2068    </t>
2069    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2070        request message was received from an HTTP/1.0 (or earlier)
2071        client and did not include an Expect request-header field with
2072        the "100-continue" expectation. This requirement overrides the
2073        general rule for forwarding of 1xx responses (see &status-1xx;).
2074    </t>
2075  </list>
2079<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2081   If an HTTP/1.1 client sends a request which includes a request body,
2082   but which does not include an Expect request-header field with the
2083   "100-continue" expectation, and if the client is not directly
2084   connected to an HTTP/1.1 origin server, and if the client sees the
2085   connection close before receiving any status from the server, the
2086   client &SHOULD; retry the request.  If the client does retry this
2087   request, it &MAY; use the following "binary exponential backoff"
2088   algorithm to be assured of obtaining a reliable response:
2089  <list style="numbers">
2090    <t>
2091      Initiate a new connection to the server
2092    </t>
2093    <t>
2094      Transmit the request-headers
2095    </t>
2096    <t>
2097      Initialize a variable R to the estimated round-trip time to the
2098         server (e.g., based on the time it took to establish the
2099         connection), or to a constant value of 5 seconds if the round-trip
2100         time is not available.
2101    </t>
2102    <t>
2103       Compute T = R * (2**N), where N is the number of previous
2104         retries of this request.
2105    </t>
2106    <t>
2107       Wait either for an error response from the server, or for T
2108         seconds (whichever comes first)
2109    </t>
2110    <t>
2111       If no error response is received, after T seconds transmit the
2112         body of the request.
2113    </t>
2114    <t>
2115       If client sees that the connection is closed prematurely,
2116         repeat from step 1 until the request is accepted, an error
2117         response is received, or the user becomes impatient and
2118         terminates the retry process.
2119    </t>
2120  </list>
2123   If at any point an error status is received, the client
2124  <list style="symbols">
2125      <t>&SHOULD-NOT;  continue and</t>
2127      <t>&SHOULD; close the connection if it has not completed sending the
2128        request message.</t>
2129    </list>
2136<section title="Header Field Definitions" anchor="header.fields">
2138   This section defines the syntax and semantics of HTTP/1.1 header fields
2139   related to message framing and transport protocols.
2142   For entity-header fields, both sender and recipient refer to either the
2143   client or the server, depending on who sends and who receives the entity.
2146<section title="Connection" anchor="header.connection">
2147  <iref primary="true" item="Connection header" x:for-anchor=""/>
2148  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2149  <x:anchor-alias value="Connection"/>
2150  <x:anchor-alias value="connection-token"/>
2151  <x:anchor-alias value="Connection-v"/>
2153   The general-header field "Connection" allows the sender to specify
2154   options that are desired for that particular connection and &MUST-NOT;
2155   be communicated by proxies over further connections.
2158   The Connection header's value has the following grammar:
2160<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"/>
2161  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2162  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2163  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2166   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2167   message is forwarded and, for each connection-token in this field,
2168   remove any header field(s) from the message with the same name as the
2169   connection-token. Connection options are signaled by the presence of
2170   a connection-token in the Connection header field, not by any
2171   corresponding additional header field(s), since the additional header
2172   field may not be sent if there are no parameters associated with that
2173   connection option.
2176   Message headers listed in the Connection header &MUST-NOT; include
2177   end-to-end headers, such as Cache-Control.
2180   HTTP/1.1 defines the "close" connection option for the sender to
2181   signal that the connection will be closed after completion of the
2182   response. For example,
2184<figure><artwork type="example">
2185  Connection: close
2188   in either the request or the response header fields indicates that
2189   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2190   after the current request/response is complete.
2193   An HTTP/1.1 client that does not support persistent connections &MUST;
2194   include the "close" connection option in every request message.
2197   An HTTP/1.1 server that does not support persistent connections &MUST;
2198   include the "close" connection option in every response message that
2199   does not have a 1xx (informational) status code.
2202   A system receiving an HTTP/1.0 (or lower-version) message that
2203   includes a Connection header &MUST;, for each connection-token in this
2204   field, remove and ignore any header field(s) from the message with
2205   the same name as the connection-token. This protects against mistaken
2206   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2210<section title="Content-Length" anchor="header.content-length">
2211  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2212  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2213  <x:anchor-alias value="Content-Length"/>
2214  <x:anchor-alias value="Content-Length-v"/>
2216   The entity-header field "Content-Length" indicates the size of the
2217   entity-body, in decimal number of OCTETs, sent to the recipient or,
2218   in the case of the HEAD method, the size of the entity-body that
2219   would have been sent had the request been a GET.
2221<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2222  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2223  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2226   An example is
2228<figure><artwork type="example">
2229  Content-Length: 3495
2232   Applications &SHOULD; use this field to indicate the transfer-length of
2233   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2236   Any Content-Length greater than or equal to zero is a valid value.
2237   <xref target="message.length"/> describes how to determine the length of a message-body
2238   if a Content-Length is not given.
2241   Note that the meaning of this field is significantly different from
2242   the corresponding definition in MIME, where it is an optional field
2243   used within the "message/external-body" content-type. In HTTP, it
2244   &SHOULD; be sent whenever the message's length can be determined prior
2245   to being transferred, unless this is prohibited by the rules in
2246   <xref target="message.length"/>.
2250<section title="Date" anchor="">
2251  <iref primary="true" item="Date header" x:for-anchor=""/>
2252  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2253  <x:anchor-alias value="Date"/>
2254  <x:anchor-alias value="Date-v"/>
2256   The general-header field "Date" represents the date and time at which
2257   the message was originated, having the same semantics as orig-date in
2258   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2259   HTTP-date, as described in <xref target=""/>;
2260   it &MUST; be sent in rfc1123-date format.
2262<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2263  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2264  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2267   An example is
2269<figure><artwork type="example">
2270  Date: Tue, 15 Nov 1994 08:12:31 GMT
2273   Origin servers &MUST; include a Date header field in all responses,
2274   except in these cases:
2275  <list style="numbers">
2276      <t>If the response status code is 100 (Continue) or 101 (Switching
2277         Protocols), the response &MAY; include a Date header field, at
2278         the server's option.</t>
2280      <t>If the response status code conveys a server error, e.g. 500
2281         (Internal Server Error) or 503 (Service Unavailable), and it is
2282         inconvenient or impossible to generate a valid Date.</t>
2284      <t>If the server does not have a clock that can provide a
2285         reasonable approximation of the current time, its responses
2286         &MUST-NOT; include a Date header field. In this case, the rules
2287         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2288  </list>
2291   A received message that does not have a Date header field &MUST; be
2292   assigned one by the recipient if the message will be cached by that
2293   recipient or gatewayed via a protocol which requires a Date. An HTTP
2294   implementation without a clock &MUST-NOT; cache responses without
2295   revalidating them on every use. An HTTP cache, especially a shared
2296   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2297   clock with a reliable external standard.
2300   Clients &SHOULD; only send a Date header field in messages that include
2301   an entity-body, as in the case of the PUT and POST requests, and even
2302   then it is optional. A client without a clock &MUST-NOT; send a Date
2303   header field in a request.
2306   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2307   time subsequent to the generation of the message. It &SHOULD; represent
2308   the best available approximation of the date and time of message
2309   generation, unless the implementation has no means of generating a
2310   reasonably accurate date and time. In theory, the date ought to
2311   represent the moment just before the entity is generated. In
2312   practice, the date can be generated at any time during the message
2313   origination without affecting its semantic value.
2316<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2318   Some origin server implementations might not have a clock available.
2319   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2320   values to a response, unless these values were associated
2321   with the resource by a system or user with a reliable clock. It &MAY;
2322   assign an Expires value that is known, at or before server
2323   configuration time, to be in the past (this allows "pre-expiration"
2324   of responses without storing separate Expires values for each
2325   resource).
2330<section title="Host" anchor="">
2331  <iref primary="true" item="Host header" x:for-anchor=""/>
2332  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2333  <x:anchor-alias value="Host"/>
2334  <x:anchor-alias value="Host-v"/>
2336   The request-header field "Host" specifies the Internet host and port
2337   number of the resource being requested, as obtained from the original
2338   URI given by the user or referring resource (generally an http URI,
2339   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2340   the naming authority of the origin server or gateway given by the
2341   original URL. This allows the origin server or gateway to
2342   differentiate between internally-ambiguous URLs, such as the root "/"
2343   URL of a server for multiple host names on a single IP address.
2345<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2346  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2347  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2350   A "host" without any trailing port information implies the default
2351   port for the service requested (e.g., "80" for an HTTP URL). For
2352   example, a request on the origin server for
2353   &lt;; would properly include:
2355<figure><artwork type="example">
2356  GET /pub/WWW/ HTTP/1.1
2357  Host:
2360   A client &MUST; include a Host header field in all HTTP/1.1 request
2361   messages. If the requested URI does not include an Internet host
2362   name for the service being requested, then the Host header field &MUST;
2363   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2364   request message it forwards does contain an appropriate Host header
2365   field that identifies the service being requested by the proxy. All
2366   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2367   status code to any HTTP/1.1 request message which lacks a Host header
2368   field.
2371   See Sections <xref target="" format="counter"/>
2372   and <xref target="" format="counter"/>
2373   for other requirements relating to Host.
2377<section title="TE" anchor="header.te">
2378  <iref primary="true" item="TE header" x:for-anchor=""/>
2379  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2380  <x:anchor-alias value="TE"/>
2381  <x:anchor-alias value="TE-v"/>
2382  <x:anchor-alias value="t-codings"/>
2384   The request-header field "TE" indicates what extension transfer-codings
2385   it is willing to accept in the response and whether or not it is
2386   willing to accept trailer fields in a chunked transfer-coding. Its
2387   value may consist of the keyword "trailers" and/or a comma-separated
2388   list of extension transfer-coding names with optional accept
2389   parameters (as described in <xref target="transfer.codings"/>).
2391<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"/>
2392  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2393  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2394  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2397   The presence of the keyword "trailers" indicates that the client is
2398   willing to accept trailer fields in a chunked transfer-coding, as
2399   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2400   transfer-coding values even though it does not itself represent a
2401   transfer-coding.
2404   Examples of its use are:
2406<figure><artwork type="example">
2407  TE: deflate
2408  TE:
2409  TE: trailers, deflate;q=0.5
2412   The TE header field only applies to the immediate connection.
2413   Therefore, the keyword &MUST; be supplied within a Connection header
2414   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2417   A server tests whether a transfer-coding is acceptable, according to
2418   a TE field, using these rules:
2419  <list style="numbers">
2420    <x:lt>
2421      <t>The "chunked" transfer-coding is always acceptable. If the
2422         keyword "trailers" is listed, the client indicates that it is
2423         willing to accept trailer fields in the chunked response on
2424         behalf of itself and any downstream clients. The implication is
2425         that, if given, the client is stating that either all
2426         downstream clients are willing to accept trailer fields in the
2427         forwarded response, or that it will attempt to buffer the
2428         response on behalf of downstream recipients.
2429      </t><t>
2430         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2431         chunked response such that a client can be assured of buffering
2432         the entire response.</t>
2433    </x:lt>
2434    <x:lt>
2435      <t>If the transfer-coding being tested is one of the transfer-codings
2436         listed in the TE field, then it is acceptable unless it
2437         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2438         qvalue of 0 means "not acceptable.")</t>
2439    </x:lt>
2440    <x:lt>
2441      <t>If multiple transfer-codings are acceptable, then the
2442         acceptable transfer-coding with the highest non-zero qvalue is
2443         preferred.  The "chunked" transfer-coding always has a qvalue
2444         of 1.</t>
2445    </x:lt>
2446  </list>
2449   If the TE field-value is empty or if no TE field is present, the only
2450   transfer-coding  is "chunked". A message with no transfer-coding is
2451   always acceptable.
2455<section title="Trailer" anchor="header.trailer">
2456  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2457  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2458  <x:anchor-alias value="Trailer"/>
2459  <x:anchor-alias value="Trailer-v"/>
2461   The general field "Trailer" indicates that the given set of
2462   header fields is present in the trailer of a message encoded with
2463   chunked transfer-coding.
2465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2466  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2467  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2470   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2471   message using chunked transfer-coding with a non-empty trailer. Doing
2472   so allows the recipient to know which header fields to expect in the
2473   trailer.
2476   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2477   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2478   trailer fields in a "chunked" transfer-coding.
2481   Message header fields listed in the Trailer header field &MUST-NOT;
2482   include the following header fields:
2483  <list style="symbols">
2484    <t>Transfer-Encoding</t>
2485    <t>Content-Length</t>
2486    <t>Trailer</t>
2487  </list>
2491<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2492  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2493  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2494  <x:anchor-alias value="Transfer-Encoding"/>
2495  <x:anchor-alias value="Transfer-Encoding-v"/>
2497   The general-header "Transfer-Encoding" field indicates what (if any)
2498   type of transformation has been applied to the message body in order
2499   to safely transfer it between the sender and the recipient. This
2500   differs from the content-coding in that the transfer-coding is a
2501   property of the message, not of the entity.
2503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2504  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2505                        <x:ref>Transfer-Encoding-v</x:ref>
2506  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2509   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2511<figure><artwork type="example">
2512  Transfer-Encoding: chunked
2515   If multiple encodings have been applied to an entity, the transfer-codings
2516   &MUST; be listed in the order in which they were applied.
2517   Additional information about the encoding parameters &MAY; be provided
2518   by other entity-header fields not defined by this specification.
2521   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2522   header.
2526<section title="Upgrade" anchor="header.upgrade">
2527  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2528  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2529  <x:anchor-alias value="Upgrade"/>
2530  <x:anchor-alias value="Upgrade-v"/>
2532   The general-header "Upgrade" allows the client to specify what
2533   additional communication protocols it supports and would like to use
2534   if the server finds it appropriate to switch protocols. The server
2535   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2536   response to indicate which protocol(s) are being switched.
2538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2539  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2540  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2543   For example,
2545<figure><artwork type="example">
2546  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2549   The Upgrade header field is intended to provide a simple mechanism
2550   for transition from HTTP/1.1 to some other, incompatible protocol. It
2551   does so by allowing the client to advertise its desire to use another
2552   protocol, such as a later version of HTTP with a higher major version
2553   number, even though the current request has been made using HTTP/1.1.
2554   This eases the difficult transition between incompatible protocols by
2555   allowing the client to initiate a request in the more commonly
2556   supported protocol while indicating to the server that it would like
2557   to use a "better" protocol if available (where "better" is determined
2558   by the server, possibly according to the nature of the method and/or
2559   resource being requested).
2562   The Upgrade header field only applies to switching application-layer
2563   protocols upon the existing transport-layer connection. Upgrade
2564   cannot be used to insist on a protocol change; its acceptance and use
2565   by the server is optional. The capabilities and nature of the
2566   application-layer communication after the protocol change is entirely
2567   dependent upon the new protocol chosen, although the first action
2568   after changing the protocol &MUST; be a response to the initial HTTP
2569   request containing the Upgrade header field.
2572   The Upgrade header field only applies to the immediate connection.
2573   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2574   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2575   HTTP/1.1 message.
2578   The Upgrade header field cannot be used to indicate a switch to a
2579   protocol on a different connection. For that purpose, it is more
2580   appropriate to use a 301, 302, 303, or 305 redirection response.
2583   This specification only defines the protocol name "HTTP" for use by
2584   the family of Hypertext Transfer Protocols, as defined by the HTTP
2585   version rules of <xref target="http.version"/> and future updates to this
2586   specification. Any token can be used as a protocol name; however, it
2587   will only be useful if both the client and server associate the name
2588   with the same protocol.
2592<section title="Via" anchor="header.via">
2593  <iref primary="true" item="Via header" x:for-anchor=""/>
2594  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2595  <x:anchor-alias value="protocol-name"/>
2596  <x:anchor-alias value="protocol-version"/>
2597  <x:anchor-alias value="pseudonym"/>
2598  <x:anchor-alias value="received-by"/>
2599  <x:anchor-alias value="received-protocol"/>
2600  <x:anchor-alias value="Via"/>
2601  <x:anchor-alias value="Via-v"/>
2603   The general-header field "Via" &MUST; be used by gateways and proxies to
2604   indicate the intermediate protocols and recipients between the user
2605   agent and the server on requests, and between the origin server and
2606   the client on responses. It is analogous to the "Received" field defined in
2607   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2608   avoiding request loops, and identifying the protocol capabilities of
2609   all senders along the request/response chain.
2611<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"/>
2612  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2613  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2614                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2615  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2616  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2617  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2618  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2619  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2622   The received-protocol indicates the protocol version of the message
2623   received by the server or client along each segment of the
2624   request/response chain. The received-protocol version is appended to
2625   the Via field value when the message is forwarded so that information
2626   about the protocol capabilities of upstream applications remains
2627   visible to all recipients.
2630   The protocol-name is optional if and only if it would be "HTTP". The
2631   received-by field is normally the host and optional port number of a
2632   recipient server or client that subsequently forwarded the message.
2633   However, if the real host is considered to be sensitive information,
2634   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2635   be assumed to be the default port of the received-protocol.
2638   Multiple Via field values represents each proxy or gateway that has
2639   forwarded the message. Each recipient &MUST; append its information
2640   such that the end result is ordered according to the sequence of
2641   forwarding applications.
2644   Comments &MAY; be used in the Via header field to identify the software
2645   of the recipient proxy or gateway, analogous to the User-Agent and
2646   Server header fields. However, all comments in the Via field are
2647   optional and &MAY; be removed by any recipient prior to forwarding the
2648   message.
2651   For example, a request message could be sent from an HTTP/1.0 user
2652   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2653   forward the request to a public proxy at, which completes
2654   the request by forwarding it to the origin server at
2655   The request received by would then have the following
2656   Via header field:
2658<figure><artwork type="example">
2659  Via: 1.0 fred, 1.1 (Apache/1.1)
2662   Proxies and gateways used as a portal through a network firewall
2663   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2664   the firewall region. This information &SHOULD; only be propagated if
2665   explicitly enabled. If not enabled, the received-by host of any host
2666   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2667   for that host.
2670   For organizations that have strong privacy requirements for hiding
2671   internal structures, a proxy &MAY; combine an ordered subsequence of
2672   Via header field entries with identical received-protocol values into
2673   a single such entry. For example,
2675<figure><artwork type="example">
2676  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2679        could be collapsed to
2681<figure><artwork type="example">
2682  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2685   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2686   under the same organizational control and the hosts have already been
2687   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2688   have different received-protocol values.
2694<section title="IANA Considerations" anchor="IANA.considerations">
2695<section title="Message Header Registration" anchor="message.header.registration">
2697   The Message Header Registry located at <eref target=""/> should be updated
2698   with the permanent registrations below (see <xref target="RFC3864"/>):
2700<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2701<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2702   <ttcol>Header Field Name</ttcol>
2703   <ttcol>Protocol</ttcol>
2704   <ttcol>Status</ttcol>
2705   <ttcol>Reference</ttcol>
2707   <c>Connection</c>
2708   <c>http</c>
2709   <c>standard</c>
2710   <c>
2711      <xref target="header.connection"/>
2712   </c>
2713   <c>Content-Length</c>
2714   <c>http</c>
2715   <c>standard</c>
2716   <c>
2717      <xref target="header.content-length"/>
2718   </c>
2719   <c>Date</c>
2720   <c>http</c>
2721   <c>standard</c>
2722   <c>
2723      <xref target=""/>
2724   </c>
2725   <c>Host</c>
2726   <c>http</c>
2727   <c>standard</c>
2728   <c>
2729      <xref target=""/>
2730   </c>
2731   <c>TE</c>
2732   <c>http</c>
2733   <c>standard</c>
2734   <c>
2735      <xref target="header.te"/>
2736   </c>
2737   <c>Trailer</c>
2738   <c>http</c>
2739   <c>standard</c>
2740   <c>
2741      <xref target="header.trailer"/>
2742   </c>
2743   <c>Transfer-Encoding</c>
2744   <c>http</c>
2745   <c>standard</c>
2746   <c>
2747      <xref target="header.transfer-encoding"/>
2748   </c>
2749   <c>Upgrade</c>
2750   <c>http</c>
2751   <c>standard</c>
2752   <c>
2753      <xref target="header.upgrade"/>
2754   </c>
2755   <c>Via</c>
2756   <c>http</c>
2757   <c>standard</c>
2758   <c>
2759      <xref target="header.via"/>
2760   </c>
2764   The change controller is: "IETF ( - Internet Engineering Task Force".
2768<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2770   The entry for the "http" URI Scheme in the registry located at
2771   <eref target=""/>
2772   should be updated to point to <xref target="http.uri"/> of this document
2773   (see <xref target="RFC4395"/>).
2777<section title="Internet Media Type Registrations" anchor="">
2779   This document serves as the specification for the Internet media types
2780   "message/http" and "application/http". The following is to be registered with
2781   IANA (see <xref target="RFC4288"/>).
2783<section title="Internet Media Type message/http" anchor="">
2784<iref item="Media Type" subitem="message/http" primary="true"/>
2785<iref item="message/http Media Type" primary="true"/>
2787   The message/http type can be used to enclose a single HTTP request or
2788   response message, provided that it obeys the MIME restrictions for all
2789   "message" types regarding line length and encodings.
2792  <list style="hanging" x:indent="12em">
2793    <t hangText="Type name:">
2794      message
2795    </t>
2796    <t hangText="Subtype name:">
2797      http
2798    </t>
2799    <t hangText="Required parameters:">
2800      none
2801    </t>
2802    <t hangText="Optional parameters:">
2803      version, msgtype
2804      <list style="hanging">
2805        <t hangText="version:">
2806          The HTTP-Version number of the enclosed message
2807          (e.g., "1.1"). If not present, the version can be
2808          determined from the first line of the body.
2809        </t>
2810        <t hangText="msgtype:">
2811          The message type -- "request" or "response". If not
2812          present, the type can be determined from the first
2813          line of the body.
2814        </t>
2815      </list>
2816    </t>
2817    <t hangText="Encoding considerations:">
2818      only "7bit", "8bit", or "binary" are permitted
2819    </t>
2820    <t hangText="Security considerations:">
2821      none
2822    </t>
2823    <t hangText="Interoperability considerations:">
2824      none
2825    </t>
2826    <t hangText="Published specification:">
2827      This specification (see <xref target=""/>).
2828    </t>
2829    <t hangText="Applications that use this media type:">
2830    </t>
2831    <t hangText="Additional information:">
2832      <list style="hanging">
2833        <t hangText="Magic number(s):">none</t>
2834        <t hangText="File extension(s):">none</t>
2835        <t hangText="Macintosh file type code(s):">none</t>
2836      </list>
2837    </t>
2838    <t hangText="Person and email address to contact for further information:">
2839      See Authors Section.
2840    </t>
2841                <t hangText="Intended usage:">
2842                  COMMON
2843    </t>
2844                <t hangText="Restrictions on usage:">
2845                  none
2846    </t>
2847    <t hangText="Author/Change controller:">
2848      IESG
2849    </t>
2850  </list>
2853<section title="Internet Media Type application/http" anchor="">
2854<iref item="Media Type" subitem="application/http" primary="true"/>
2855<iref item="application/http Media Type" primary="true"/>
2857   The application/http type can be used to enclose a pipeline of one or more
2858   HTTP request or response messages (not intermixed).
2861  <list style="hanging" x:indent="12em">
2862    <t hangText="Type name:">
2863      application
2864    </t>
2865    <t hangText="Subtype name:">
2866      http
2867    </t>
2868    <t hangText="Required parameters:">
2869      none
2870    </t>
2871    <t hangText="Optional parameters:">
2872      version, msgtype
2873      <list style="hanging">
2874        <t hangText="version:">
2875          The HTTP-Version number of the enclosed messages
2876          (e.g., "1.1"). If not present, the version can be
2877          determined from the first line of the body.
2878        </t>
2879        <t hangText="msgtype:">
2880          The message type -- "request" or "response". If not
2881          present, the type can be determined from the first
2882          line of the body.
2883        </t>
2884      </list>
2885    </t>
2886    <t hangText="Encoding considerations:">
2887      HTTP messages enclosed by this type
2888      are in "binary" format; use of an appropriate
2889      Content-Transfer-Encoding is required when
2890      transmitted via E-mail.
2891    </t>
2892    <t hangText="Security considerations:">
2893      none
2894    </t>
2895    <t hangText="Interoperability considerations:">
2896      none
2897    </t>
2898    <t hangText="Published specification:">
2899      This specification (see <xref target=""/>).
2900    </t>
2901    <t hangText="Applications that use this media type:">
2902    </t>
2903    <t hangText="Additional information:">
2904      <list style="hanging">
2905        <t hangText="Magic number(s):">none</t>
2906        <t hangText="File extension(s):">none</t>
2907        <t hangText="Macintosh file type code(s):">none</t>
2908      </list>
2909    </t>
2910    <t hangText="Person and email address to contact for further information:">
2911      See Authors Section.
2912    </t>
2913                <t hangText="Intended usage:">
2914                  COMMON
2915    </t>
2916                <t hangText="Restrictions on usage:">
2917                  none
2918    </t>
2919    <t hangText="Author/Change controller:">
2920      IESG
2921    </t>
2922  </list>
2929<section title="Security Considerations" anchor="security.considerations">
2931   This section is meant to inform application developers, information
2932   providers, and users of the security limitations in HTTP/1.1 as
2933   described by this document. The discussion does not include
2934   definitive solutions to the problems revealed, though it does make
2935   some suggestions for reducing security risks.
2938<section title="Personal Information" anchor="personal.information">
2940   HTTP clients are often privy to large amounts of personal information
2941   (e.g. the user's name, location, mail address, passwords, encryption
2942   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2943   leakage of this information.
2944   We very strongly recommend that a convenient interface be provided
2945   for the user to control dissemination of such information, and that
2946   designers and implementors be particularly careful in this area.
2947   History shows that errors in this area often create serious security
2948   and/or privacy problems and generate highly adverse publicity for the
2949   implementor's company.
2953<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2955   A server is in the position to save personal data about a user's
2956   requests which might identify their reading patterns or subjects of
2957   interest. This information is clearly confidential in nature and its
2958   handling can be constrained by law in certain countries. People using
2959   HTTP to provide data are responsible for ensuring that
2960   such material is not distributed without the permission of any
2961   individuals that are identifiable by the published results.
2965<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2967   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2968   the documents returned by HTTP requests to be only those that were
2969   intended by the server administrators. If an HTTP server translates
2970   HTTP URIs directly into file system calls, the server &MUST; take
2971   special care not to serve files that were not intended to be
2972   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2973   other operating systems use ".." as a path component to indicate a
2974   directory level above the current one. On such a system, an HTTP
2975   server &MUST; disallow any such construct in the request-target if it
2976   would otherwise allow access to a resource outside those intended to
2977   be accessible via the HTTP server. Similarly, files intended for
2978   reference only internally to the server (such as access control
2979   files, configuration files, and script code) &MUST; be protected from
2980   inappropriate retrieval, since they might contain sensitive
2981   information. Experience has shown that minor bugs in such HTTP server
2982   implementations have turned into security risks.
2986<section title="DNS Spoofing" anchor="dns.spoofing">
2988   Clients using HTTP rely heavily on the Domain Name Service, and are
2989   thus generally prone to security attacks based on the deliberate
2990   mis-association of IP addresses and DNS names. Clients need to be
2991   cautious in assuming the continuing validity of an IP number/DNS name
2992   association.
2995   In particular, HTTP clients &SHOULD; rely on their name resolver for
2996   confirmation of an IP number/DNS name association, rather than
2997   caching the result of previous host name lookups. Many platforms
2998   already can cache host name lookups locally when appropriate, and
2999   they &SHOULD; be configured to do so. It is proper for these lookups to
3000   be cached, however, only when the TTL (Time To Live) information
3001   reported by the name server makes it likely that the cached
3002   information will remain useful.
3005   If HTTP clients cache the results of host name lookups in order to
3006   achieve a performance improvement, they &MUST; observe the TTL
3007   information reported by DNS.
3010   If HTTP clients do not observe this rule, they could be spoofed when
3011   a previously-accessed server's IP address changes. As network
3012   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3013   possibility of this form of attack will grow. Observing this
3014   requirement thus reduces this potential security vulnerability.
3017   This requirement also improves the load-balancing behavior of clients
3018   for replicated servers using the same DNS name and reduces the
3019   likelihood of a user's experiencing failure in accessing sites which
3020   use that strategy.
3024<section title="Proxies and Caching" anchor="attack.proxies">
3026   By their very nature, HTTP proxies are men-in-the-middle, and
3027   represent an opportunity for man-in-the-middle attacks. Compromise of
3028   the systems on which the proxies run can result in serious security
3029   and privacy problems. Proxies have access to security-related
3030   information, personal information about individual users and
3031   organizations, and proprietary information belonging to users and
3032   content providers. A compromised proxy, or a proxy implemented or
3033   configured without regard to security and privacy considerations,
3034   might be used in the commission of a wide range of potential attacks.
3037   Proxy operators should protect the systems on which proxies run as
3038   they would protect any system that contains or transports sensitive
3039   information. In particular, log information gathered at proxies often
3040   contains highly sensitive personal information, and/or information
3041   about organizations. Log information should be carefully guarded, and
3042   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3045   Proxy implementors should consider the privacy and security
3046   implications of their design and coding decisions, and of the
3047   configuration options they provide to proxy operators (especially the
3048   default configuration).
3051   Users of a proxy need to be aware that they are no trustworthier than
3052   the people who run the proxy; HTTP itself cannot solve this problem.
3055   The judicious use of cryptography, when appropriate, may suffice to
3056   protect against a broad range of security and privacy attacks. Such
3057   cryptography is beyond the scope of the HTTP/1.1 specification.
3061<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3063   They exist. They are hard to defend against. Research continues.
3064   Beware.
3069<section title="Acknowledgments" anchor="ack">
3071   HTTP has evolved considerably over the years. It has
3072   benefited from a large and active developer community--the many
3073   people who have participated on the www-talk mailing list--and it is
3074   that community which has been most responsible for the success of
3075   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3076   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3077   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3078   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3079   VanHeyningen deserve special recognition for their efforts in
3080   defining early aspects of the protocol.
3083   This document has benefited greatly from the comments of all those
3084   participating in the HTTP-WG. In addition to those already mentioned,
3085   the following individuals have contributed to this specification:
3088   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3089   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3090   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3091   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3092   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3093   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3094   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3095   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3096   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3097   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3098   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3099   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3100   Josh Cohen.
3103   Thanks to the "cave men" of Palo Alto. You know who you are.
3106   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3107   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3108   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3109   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3110   Larry Masinter for their help. And thanks go particularly to Jeff
3111   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3114   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3115   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3116   discovery of many of the problems that this document attempts to
3117   rectify.
3120   This specification makes heavy use of the augmented BNF and generic
3121   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3122   reuses many of the definitions provided by Nathaniel Borenstein and
3123   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3124   specification will help reduce past confusion over the relationship
3125   between HTTP and Internet mail message formats.
3132<references title="Normative References">
3134<reference anchor="ISO-8859-1">
3135  <front>
3136    <title>
3137     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3138    </title>
3139    <author>
3140      <organization>International Organization for Standardization</organization>
3141    </author>
3142    <date year="1998"/>
3143  </front>
3144  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3147<reference anchor="Part2">
3148  <front>
3149    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3150    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3151      <organization abbrev="Day Software">Day Software</organization>
3152      <address><email></email></address>
3153    </author>
3154    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3155      <organization>One Laptop per Child</organization>
3156      <address><email></email></address>
3157    </author>
3158    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3159      <organization abbrev="HP">Hewlett-Packard Company</organization>
3160      <address><email></email></address>
3161    </author>
3162    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3164      <address><email></email></address>
3165    </author>
3166    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3167      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3168      <address><email></email></address>
3169    </author>
3170    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3171      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3172      <address><email></email></address>
3173    </author>
3174    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3175      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3176      <address><email></email></address>
3177    </author>
3178    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3179      <organization abbrev="W3C">World Wide Web Consortium</organization>
3180      <address><email></email></address>
3181    </author>
3182    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3183      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3184      <address><email></email></address>
3185    </author>
3186    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3187  </front>
3188  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3189  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3192<reference anchor="Part3">
3193  <front>
3194    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3195    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3196      <organization abbrev="Day Software">Day Software</organization>
3197      <address><email></email></address>
3198    </author>
3199    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3200      <organization>One Laptop per Child</organization>
3201      <address><email></email></address>
3202    </author>
3203    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3204      <organization abbrev="HP">Hewlett-Packard Company</organization>
3205      <address><email></email></address>
3206    </author>
3207    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3208      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3209      <address><email></email></address>
3210    </author>
3211    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3212      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3213      <address><email></email></address>
3214    </author>
3215    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3216      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3217      <address><email></email></address>
3218    </author>
3219    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3220      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3221      <address><email></email></address>
3222    </author>
3223    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3224      <organization abbrev="W3C">World Wide Web Consortium</organization>
3225      <address><email></email></address>
3226    </author>
3227    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3228      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3229      <address><email></email></address>
3230    </author>
3231    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3232  </front>
3233  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3234  <x:source href="p3-payload.xml" basename="p3-payload"/>
3237<reference anchor="Part5">
3238  <front>
3239    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3240    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3241      <organization abbrev="Day Software">Day Software</organization>
3242      <address><email></email></address>
3243    </author>
3244    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3245      <organization>One Laptop per Child</organization>
3246      <address><email></email></address>
3247    </author>
3248    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3249      <organization abbrev="HP">Hewlett-Packard Company</organization>
3250      <address><email></email></address>
3251    </author>
3252    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3253      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3254      <address><email></email></address>
3255    </author>
3256    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3257      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3258      <address><email></email></address>
3259    </author>
3260    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3261      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3262      <address><email></email></address>
3263    </author>
3264    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3265      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3266      <address><email></email></address>
3267    </author>
3268    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3269      <organization abbrev="W3C">World Wide Web Consortium</organization>
3270      <address><email></email></address>
3271    </author>
3272    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3273      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3274      <address><email></email></address>
3275    </author>
3276    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3277  </front>
3278  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3279  <x:source href="p5-range.xml" basename="p5-range"/>
3282<reference anchor="Part6">
3283  <front>
3284    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3285    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3286      <organization abbrev="Day Software">Day Software</organization>
3287      <address><email></email></address>
3288    </author>
3289    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3290      <organization>One Laptop per Child</organization>
3291      <address><email></email></address>
3292    </author>
3293    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3294      <organization abbrev="HP">Hewlett-Packard Company</organization>
3295      <address><email></email></address>
3296    </author>
3297    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3298      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3299      <address><email></email></address>
3300    </author>
3301    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3302      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3303      <address><email></email></address>
3304    </author>
3305    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3306      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3307      <address><email></email></address>
3308    </author>
3309    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3310      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3311      <address><email></email></address>
3312    </author>
3313    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3314      <organization abbrev="W3C">World Wide Web Consortium</organization>
3315      <address><email></email></address>
3316    </author>
3317    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3318      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3319      <address><email></email></address>
3320    </author>
3321    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3322  </front>
3323  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3324  <x:source href="p6-cache.xml" basename="p6-cache"/>
3327<reference anchor="RFC5234">
3328  <front>
3329    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3330    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3331      <organization>Brandenburg InternetWorking</organization>
3332      <address>
3333      <postal>
3334      <street>675 Spruce Dr.</street>
3335      <city>Sunnyvale</city>
3336      <region>CA</region>
3337      <code>94086</code>
3338      <country>US</country></postal>
3339      <phone>+1.408.246.8253</phone>
3340      <email></email></address> 
3341    </author>
3342    <author initials="P." surname="Overell" fullname="Paul Overell">
3343      <organization>THUS plc.</organization>
3344      <address>
3345      <postal>
3346      <street>1/2 Berkeley Square</street>
3347      <street>99 Berkely Street</street>
3348      <city>Glasgow</city>
3349      <code>G3 7HR</code>
3350      <country>UK</country></postal>
3351      <email></email></address>
3352    </author>
3353    <date month="January" year="2008"/>
3354  </front>
3355  <seriesInfo name="STD" value="68"/>
3356  <seriesInfo name="RFC" value="5234"/>
3359<reference anchor="RFC2119">
3360  <front>
3361    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3362    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3363      <organization>Harvard University</organization>
3364      <address><email></email></address>
3365    </author>
3366    <date month="March" year="1997"/>
3367  </front>
3368  <seriesInfo name="BCP" value="14"/>
3369  <seriesInfo name="RFC" value="2119"/>
3372<reference anchor="RFC3986">
3373 <front>
3374  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3375  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3376    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3377    <address>
3378       <email></email>
3379       <uri></uri>
3380    </address>
3381  </author>
3382  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3383    <organization abbrev="Day Software">Day Software</organization>
3384    <address>
3385      <email></email>
3386      <uri></uri>
3387    </address>
3388  </author>
3389  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3390    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3391    <address>
3392      <email></email>
3393      <uri></uri>
3394    </address>
3395  </author>
3396  <date month='January' year='2005'></date>
3397 </front>
3398 <seriesInfo name="RFC" value="3986"/>
3399 <seriesInfo name="STD" value="66"/>
3402<reference anchor="USASCII">
3403  <front>
3404    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3405    <author>
3406      <organization>American National Standards Institute</organization>
3407    </author>
3408    <date year="1986"/>
3409  </front>
3410  <seriesInfo name="ANSI" value="X3.4"/>
3415<references title="Informative References">
3417<reference anchor="Nie1997" target="">
3418  <front>
3419    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3420    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3421      <organization/>
3422    </author>
3423    <author initials="J." surname="Gettys" fullname="J. Gettys">
3424      <organization/>
3425    </author>
3426    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3427      <organization/>
3428    </author>
3429    <author initials="H." surname="Lie" fullname="H. Lie">
3430      <organization/>
3431    </author>
3432    <author initials="C." surname="Lilley" fullname="C. Lilley">
3433      <organization/>
3434    </author>
3435    <date year="1997" month="September"/>
3436  </front>
3437  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3440<reference anchor="Pad1995" target="">
3441  <front>
3442    <title>Improving HTTP Latency</title>
3443    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3444      <organization/>
3445    </author>
3446    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3447      <organization/>
3448    </author>
3449    <date year="1995" month="December"/>
3450  </front>
3451  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3454<reference anchor="RFC959">
3455  <front>
3456    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3457    <author initials="J." surname="Postel" fullname="J. Postel">
3458      <organization>Information Sciences Institute (ISI)</organization>
3459    </author>
3460    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3461      <organization/>
3462    </author>
3463    <date month="October" year="1985"/>
3464  </front>
3465  <seriesInfo name="STD" value="9"/>
3466  <seriesInfo name="RFC" value="959"/>
3469<reference anchor="RFC1123">
3470  <front>
3471    <title>Requirements for Internet Hosts - Application and Support</title>
3472    <author initials="R." surname="Braden" fullname="Robert Braden">
3473      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3474      <address><email>Braden@ISI.EDU</email></address>
3475    </author>
3476    <date month="October" year="1989"/>
3477  </front>
3478  <seriesInfo name="STD" value="3"/>
3479  <seriesInfo name="RFC" value="1123"/>
3482<reference anchor="RFC1305">
3483  <front>
3484    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3485    <author initials="D." surname="Mills" fullname="David L. Mills">
3486      <organization>University of Delaware, Electrical Engineering Department</organization>
3487      <address><email></email></address>
3488    </author>
3489    <date month="March" year="1992"/>
3490  </front>
3491  <seriesInfo name="RFC" value="1305"/>
3494<reference anchor="RFC1436">
3495  <front>
3496    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3497    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3498      <organization>University of Minnesota, Computer and Information Services</organization>
3499      <address><email></email></address>
3500    </author>
3501    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3502      <organization>University of Minnesota, Computer and Information Services</organization>
3503      <address><email></email></address>
3504    </author>
3505    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3506      <organization>University of Minnesota, Computer and Information Services</organization>
3507      <address><email></email></address>
3508    </author>
3509    <author initials="D." surname="Johnson" fullname="David Johnson">
3510      <organization>University of Minnesota, Computer and Information Services</organization>
3511      <address><email></email></address>
3512    </author>
3513    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3514      <organization>University of Minnesota, Computer and Information Services</organization>
3515      <address><email></email></address>
3516    </author>
3517    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3518      <organization>University of Minnesota, Computer and Information Services</organization>
3519      <address><email></email></address>
3520    </author>
3521    <date month="March" year="1993"/>
3522  </front>
3523  <seriesInfo name="RFC" value="1436"/>
3526<reference anchor="RFC1900">
3527  <front>
3528    <title>Renumbering Needs Work</title>
3529    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3530      <organization>CERN, Computing and Networks Division</organization>
3531      <address><email></email></address>
3532    </author>
3533    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3534      <organization>cisco Systems</organization>
3535      <address><email></email></address>
3536    </author>
3537    <date month="February" year="1996"/>
3538  </front>
3539  <seriesInfo name="RFC" value="1900"/>
3542<reference anchor="RFC1945">
3543  <front>
3544    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3545    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3546      <organization>MIT, Laboratory for Computer Science</organization>
3547      <address><email></email></address>
3548    </author>
3549    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3550      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3551      <address><email></email></address>
3552    </author>
3553    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3554      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3555      <address><email></email></address>
3556    </author>
3557    <date month="May" year="1996"/>
3558  </front>
3559  <seriesInfo name="RFC" value="1945"/>
3562<reference anchor="RFC2045">
3563  <front>
3564    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3565    <author initials="N." surname="Freed" fullname="Ned Freed">
3566      <organization>Innosoft International, Inc.</organization>
3567      <address><email></email></address>
3568    </author>
3569    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3570      <organization>First Virtual Holdings</organization>
3571      <address><email></email></address>
3572    </author>
3573    <date month="November" year="1996"/>
3574  </front>
3575  <seriesInfo name="RFC" value="2045"/>
3578<reference anchor="RFC2047">
3579  <front>
3580    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3581    <author initials="K." surname="Moore" fullname="Keith Moore">
3582      <organization>University of Tennessee</organization>
3583      <address><email></email></address>
3584    </author>
3585    <date month="November" year="1996"/>
3586  </front>
3587  <seriesInfo name="RFC" value="2047"/>
3590<reference anchor="RFC2068">
3591  <front>
3592    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3593    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3594      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3595      <address><email></email></address>
3596    </author>
3597    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3598      <organization>MIT Laboratory for Computer Science</organization>
3599      <address><email></email></address>
3600    </author>
3601    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3602      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3603      <address><email></email></address>
3604    </author>
3605    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3606      <organization>MIT Laboratory for Computer Science</organization>
3607      <address><email></email></address>
3608    </author>
3609    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3610      <organization>MIT Laboratory for Computer Science</organization>
3611      <address><email></email></address>
3612    </author>
3613    <date month="January" year="1997"/>
3614  </front>
3615  <seriesInfo name="RFC" value="2068"/>
3618<reference anchor='RFC2109'>
3619  <front>
3620    <title>HTTP State Management Mechanism</title>
3621    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3622      <organization>Bell Laboratories, Lucent Technologies</organization>
3623      <address><email></email></address>
3624    </author>
3625    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3626      <organization>Netscape Communications Corp.</organization>
3627      <address><email></email></address>
3628    </author>
3629    <date year='1997' month='February' />
3630  </front>
3631  <seriesInfo name='RFC' value='2109' />
3634<reference anchor="RFC2145">
3635  <front>
3636    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3637    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3638      <organization>Western Research Laboratory</organization>
3639      <address><email></email></address>
3640    </author>
3641    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3642      <organization>Department of Information and Computer Science</organization>
3643      <address><email></email></address>
3644    </author>
3645    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3646      <organization>MIT Laboratory for Computer Science</organization>
3647      <address><email></email></address>
3648    </author>
3649    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3650      <organization>W3 Consortium</organization>
3651      <address><email></email></address>
3652    </author>
3653    <date month="May" year="1997"/>
3654  </front>
3655  <seriesInfo name="RFC" value="2145"/>
3658<reference anchor="RFC2616">
3659  <front>
3660    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3661    <author initials="R." surname="Fielding" fullname="R. Fielding">
3662      <organization>University of California, Irvine</organization>
3663      <address><email></email></address>
3664    </author>
3665    <author initials="J." surname="Gettys" fullname="J. Gettys">
3666      <organization>W3C</organization>
3667      <address><email></email></address>
3668    </author>
3669    <author initials="J." surname="Mogul" fullname="J. Mogul">
3670      <organization>Compaq Computer Corporation</organization>
3671      <address><email></email></address>
3672    </author>
3673    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3674      <organization>MIT Laboratory for Computer Science</organization>
3675      <address><email></email></address>
3676    </author>
3677    <author initials="L." surname="Masinter" fullname="L. Masinter">
3678      <organization>Xerox Corporation</organization>
3679      <address><email></email></address>
3680    </author>
3681    <author initials="P." surname="Leach" fullname="P. Leach">
3682      <organization>Microsoft Corporation</organization>
3683      <address><email></email></address>
3684    </author>
3685    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3686      <organization>W3C</organization>
3687      <address><email></email></address>
3688    </author>
3689    <date month="June" year="1999"/>
3690  </front>
3691  <seriesInfo name="RFC" value="2616"/>
3694<reference anchor='RFC2818'>
3695  <front>
3696    <title>HTTP Over TLS</title>
3697    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3698      <organization>RTFM, Inc.</organization>
3699      <address><email></email></address>
3700    </author>
3701    <date year='2000' month='May' />
3702  </front>
3703  <seriesInfo name='RFC' value='2818' />
3706<reference anchor='RFC2965'>
3707  <front>
3708    <title>HTTP State Management Mechanism</title>
3709    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3710      <organization>Bell Laboratories, Lucent Technologies</organization>
3711      <address><email></email></address>
3712    </author>
3713    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3714      <organization>, Inc.</organization>
3715      <address><email></email></address>
3716    </author>
3717    <date year='2000' month='October' />
3718  </front>
3719  <seriesInfo name='RFC' value='2965' />
3722<reference anchor='RFC3864'>
3723  <front>
3724    <title>Registration Procedures for Message Header Fields</title>
3725    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3726      <organization>Nine by Nine</organization>
3727      <address><email></email></address>
3728    </author>
3729    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3730      <organization>BEA Systems</organization>
3731      <address><email></email></address>
3732    </author>
3733    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3734      <organization>HP Labs</organization>
3735      <address><email></email></address>
3736    </author>
3737    <date year='2004' month='September' />
3738  </front>
3739  <seriesInfo name='BCP' value='90' />
3740  <seriesInfo name='RFC' value='3864' />
3743<reference anchor='RFC3977'>
3744  <front>
3745    <title>Network News Transfer Protocol (NNTP)</title>
3746    <author initials='C.' surname='Feather' fullname='C. Feather'>
3747      <organization>THUS plc</organization>
3748      <address><email></email></address>
3749    </author>
3750    <date year='2006' month='October' />
3751  </front>
3752  <seriesInfo name="RFC" value="3977"/>
3755<reference anchor="RFC4288">
3756  <front>
3757    <title>Media Type Specifications and Registration Procedures</title>
3758    <author initials="N." surname="Freed" fullname="N. Freed">
3759      <organization>Sun Microsystems</organization>
3760      <address>
3761        <email></email>
3762      </address>
3763    </author>
3764    <author initials="J." surname="Klensin" fullname="J. Klensin">
3765      <organization/>
3766      <address>
3767        <email></email>
3768      </address>
3769    </author>
3770    <date year="2005" month="December"/>
3771  </front>
3772  <seriesInfo name="BCP" value="13"/>
3773  <seriesInfo name="RFC" value="4288"/>
3776<reference anchor='RFC4395'>
3777  <front>
3778    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3779    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3780      <organization>AT&amp;T Laboratories</organization>
3781      <address>
3782        <email></email>
3783      </address>
3784    </author>
3785    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3786      <organization>Qualcomm, Inc.</organization>
3787      <address>
3788        <email></email>
3789      </address>
3790    </author>
3791    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3792      <organization>Adobe Systems</organization>
3793      <address>
3794        <email></email>
3795      </address>
3796    </author>
3797    <date year='2006' month='February' />
3798  </front>
3799  <seriesInfo name='BCP' value='115' />
3800  <seriesInfo name='RFC' value='4395' />
3803<reference anchor="RFC5322">
3804  <front>
3805    <title>Internet Message Format</title>
3806    <author initials="P." surname="Resnick" fullname="P. Resnick">
3807      <organization>Qualcomm Incorporated</organization>
3808    </author>
3809    <date year="2008" month="October"/>
3810  </front>
3811  <seriesInfo name="RFC" value="5322"/>
3814<reference anchor="Kri2001" target="">
3815  <front>
3816    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3817    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3818      <organization/>
3819    </author>
3820    <date year="2001" month="November"/>
3821  </front>
3822  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3825<reference anchor="Spe" target="">
3826  <front>
3827  <title>Analysis of HTTP Performance Problems</title>
3828  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3829    <organization/>
3830  </author>
3831  <date/>
3832  </front>
3835<reference anchor="Tou1998" target="">
3836  <front>
3837  <title>Analysis of HTTP Performance</title>
3838  <author initials="J." surname="Touch" fullname="Joe Touch">
3839    <organization>USC/Information Sciences Institute</organization>
3840    <address><email></email></address>
3841  </author>
3842  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3843    <organization>USC/Information Sciences Institute</organization>
3844    <address><email></email></address>
3845  </author>
3846  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3847    <organization>USC/Information Sciences Institute</organization>
3848    <address><email></email></address>
3849  </author>
3850  <date year="1998" month="Aug"/>
3851  </front>
3852  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3853  <annotation>(original report dated Aug. 1996)</annotation>
3856<reference anchor="WAIS">
3857  <front>
3858    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3859    <author initials="F." surname="Davis" fullname="F. Davis">
3860      <organization>Thinking Machines Corporation</organization>
3861    </author>
3862    <author initials="B." surname="Kahle" fullname="B. Kahle">
3863      <organization>Thinking Machines Corporation</organization>
3864    </author>
3865    <author initials="H." surname="Morris" fullname="H. Morris">
3866      <organization>Thinking Machines Corporation</organization>
3867    </author>
3868    <author initials="J." surname="Salem" fullname="J. Salem">
3869      <organization>Thinking Machines Corporation</organization>
3870    </author>
3871    <author initials="T." surname="Shen" fullname="T. Shen">
3872      <organization>Thinking Machines Corporation</organization>
3873    </author>
3874    <author initials="R." surname="Wang" fullname="R. Wang">
3875      <organization>Thinking Machines Corporation</organization>
3876    </author>
3877    <author initials="J." surname="Sui" fullname="J. Sui">
3878      <organization>Thinking Machines Corporation</organization>
3879    </author>
3880    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3881      <organization>Thinking Machines Corporation</organization>
3882    </author>
3883    <date month="April" year="1990"/>
3884  </front>
3885  <seriesInfo name="Thinking Machines Corporation" value=""/>
3891<section title="Tolerant Applications" anchor="tolerant.applications">
3893   Although this document specifies the requirements for the generation
3894   of HTTP/1.1 messages, not all applications will be correct in their
3895   implementation. We therefore recommend that operational applications
3896   be tolerant of deviations whenever those deviations can be
3897   interpreted unambiguously.
3900   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3901   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3902   accept any amount of WSP characters between fields, even though
3903   only a single SP is required.
3906   The line terminator for message-header fields is the sequence CRLF.
3907   However, we recommend that applications, when parsing such headers,
3908   recognize a single LF as a line terminator and ignore the leading CR.
3911   The character set of an entity-body &SHOULD; be labeled as the lowest
3912   common denominator of the character codes used within that body, with
3913   the exception that not labeling the entity is preferred over labeling
3914   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3917   Additional rules for requirements on parsing and encoding of dates
3918   and other potential problems with date encodings include:
3921  <list style="symbols">
3922     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3923        which appears to be more than 50 years in the future is in fact
3924        in the past (this helps solve the "year 2000" problem).</t>
3926     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3927        Expires date as earlier than the proper value, but &MUST-NOT;
3928        internally represent a parsed Expires date as later than the
3929        proper value.</t>
3931     <t>All expiration-related calculations &MUST; be done in GMT. The
3932        local time zone &MUST-NOT; influence the calculation or comparison
3933        of an age or expiration time.</t>
3935     <t>If an HTTP header incorrectly carries a date value with a time
3936        zone other than GMT, it &MUST; be converted into GMT using the
3937        most conservative possible conversion.</t>
3938  </list>
3942<section title="Compatibility with Previous Versions" anchor="compatibility">
3944   HTTP has been in use by the World-Wide Web global information initiative
3945   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3946   was a simple protocol for hypertext data transfer across the Internet
3947   with only a single method and no metadata.
3948   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3949   methods and MIME-like messaging that could include metadata about the data
3950   transferred and modifiers on the request/response semantics. However,
3951   HTTP/1.0 did not sufficiently take into consideration the effects of
3952   hierarchical proxies, caching, the need for persistent connections, or
3953   name-based virtual hosts. The proliferation of incompletely-implemented
3954   applications calling themselves "HTTP/1.0" further necessitated a
3955   protocol version change in order for two communicating applications
3956   to determine each other's true capabilities.
3959   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3960   requirements that enable reliable implementations, adding only
3961   those new features that will either be safely ignored by an HTTP/1.0
3962   recipient or only sent when communicating with a party advertising
3963   compliance with HTTP/1.1.
3966   It is beyond the scope of a protocol specification to mandate
3967   compliance with previous versions. HTTP/1.1 was deliberately
3968   designed, however, to make supporting previous versions easy. It is
3969   worth noting that, at the time of composing this specification
3970   (1996), we would expect commercial HTTP/1.1 servers to:
3971  <list style="symbols">
3972     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3973        1.1 requests;</t>
3975     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3976        1.1;</t>
3978     <t>respond appropriately with a message in the same major version
3979        used by the client.</t>
3980  </list>
3983   And we would expect HTTP/1.1 clients to:
3984  <list style="symbols">
3985     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3986        responses;</t>
3988     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3989        1.1.</t>
3990  </list>
3993   For most implementations of HTTP/1.0, each connection is established
3994   by the client prior to the request and closed by the server after
3995   sending the response. Some implementations implement the Keep-Alive
3996   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3999<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4001   This section summarizes major differences between versions HTTP/1.0
4002   and HTTP/1.1.
4005<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4007   The requirements that clients and servers support the Host request-header,
4008   report an error if the Host request-header (<xref target=""/>) is
4009   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4010   are among the most important changes defined by this
4011   specification.
4014   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4015   addresses and servers; there was no other established mechanism for
4016   distinguishing the intended server of a request than the IP address
4017   to which that request was directed. The changes outlined above will
4018   allow the Internet, once older HTTP clients are no longer common, to
4019   support multiple Web sites from a single IP address, greatly
4020   simplifying large operational Web servers, where allocation of many
4021   IP addresses to a single host has created serious problems. The
4022   Internet will also be able to recover the IP addresses that have been
4023   allocated for the sole purpose of allowing special-purpose domain
4024   names to be used in root-level HTTP URLs. Given the rate of growth of
4025   the Web, and the number of servers already deployed, it is extremely
4026   important that all implementations of HTTP (including updates to
4027   existing HTTP/1.0 applications) correctly implement these
4028   requirements:
4029  <list style="symbols">
4030     <t>Both clients and servers &MUST; support the Host request-header.</t>
4032     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4034     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4035        request does not include a Host request-header.</t>
4037     <t>Servers &MUST; accept absolute URIs.</t>
4038  </list>
4043<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4045   Some clients and servers might wish to be compatible with some
4046   previous implementations of persistent connections in HTTP/1.0
4047   clients and servers. Persistent connections in HTTP/1.0 are
4048   explicitly negotiated as they are not the default behavior. HTTP/1.0
4049   experimental implementations of persistent connections are faulty,
4050   and the new facilities in HTTP/1.1 are designed to rectify these
4051   problems. The problem was that some existing 1.0 clients may be
4052   sending Keep-Alive to a proxy server that doesn't understand
4053   Connection, which would then erroneously forward it to the next
4054   inbound server, which would establish the Keep-Alive connection and
4055   result in a hung HTTP/1.0 proxy waiting for the close on the
4056   response. The result is that HTTP/1.0 clients must be prevented from
4057   using Keep-Alive when talking to proxies.
4060   However, talking to proxies is the most important use of persistent
4061   connections, so that prohibition is clearly unacceptable. Therefore,
4062   we need some other mechanism for indicating a persistent connection
4063   is desired, which is safe to use even when talking to an old proxy
4064   that ignores Connection. Persistent connections are the default for
4065   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4066   declaring non-persistence. See <xref target="header.connection"/>.
4069   The original HTTP/1.0 form of persistent connections (the Connection:
4070   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4074<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4076   This specification has been carefully audited to correct and
4077   disambiguate key word usage; RFC 2068 had many problems in respect to
4078   the conventions laid out in <xref target="RFC2119"/>.
4081   Transfer-coding and message lengths all interact in ways that
4082   required fixing exactly when chunked encoding is used (to allow for
4083   transfer encoding that may not be self delimiting); it was important
4084   to straighten out exactly how message lengths are computed. (Sections
4085   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4086   <xref target="header.content-length" format="counter"/>,
4087   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4090   The use and interpretation of HTTP version numbers has been clarified
4091   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4092   version they support to deal with problems discovered in HTTP/1.0
4093   implementations (<xref target="http.version"/>)
4096   Transfer-coding had significant problems, particularly with
4097   interactions with chunked encoding. The solution is that transfer-codings
4098   become as full fledged as content-codings. This involves
4099   adding an IANA registry for transfer-codings (separate from content
4100   codings), a new header field (TE) and enabling trailer headers in the
4101   future. Transfer encoding is a major performance benefit, so it was
4102   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4103   interoperability problem that could have occurred due to interactions
4104   between authentication trailers, chunked encoding and HTTP/1.0
4105   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4106   and <xref target="header.te" format="counter"/>)
4110<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4112  Empty list elements in list productions have been deprecated.
4113  (<xref target="notation.abnf"/>)
4116  Rules about implicit linear whitespace between certain grammar productions
4117  have been removed; now it's only allowed when specifically pointed out
4118  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4119  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4120  Non-ASCII content in header fields and reason phrase has been obsoleted and
4121  made opaque (the TEXT rule was removed)
4122  (<xref target="basic.rules"/>)
4125  Clarify that HTTP-Version is case sensitive.
4126  (<xref target="http.version"/>)
4129  Remove reference to non-existant identity transfer-coding value tokens.
4130  (Sections <xref format="counter" target="transfer.codings"/> and
4131  <xref format="counter" target="message.length"/>)
4134  Clarification that the chunk length does not include
4135  the count of the octets in the chunk header and trailer.
4136  (<xref target="chunked.transfer.encoding"/>)
4139  Require that invalid whitespace around field-names be rejected.
4140  (<xref target="message.headers"/>)
4143  Update use of abs_path production from RFC1808 to the path-absolute + query
4144  components of RFC3986.
4145  (<xref target="request-target"/>)
4148  Clarify exactly when close connection options must be sent.
4149  (<xref target="header.connection"/>)
4154<section title="Terminology" anchor="terminology">
4156   This specification uses a number of terms to refer to the roles
4157   played by participants in, and objects of, the HTTP communication.
4160  <iref item="cache"/>
4161  <x:dfn>cache</x:dfn>
4162  <list>
4163    <t>
4164      A program's local store of response messages and the subsystem
4165      that controls its message storage, retrieval, and deletion. A
4166      cache stores cacheable responses in order to reduce the response
4167      time and network bandwidth consumption on future, equivalent
4168      requests. Any client or server may include a cache, though a cache
4169      cannot be used by a server that is acting as a tunnel.
4170    </t>
4171  </list>
4174  <iref item="cacheable"/>
4175  <x:dfn>cacheable</x:dfn>
4176  <list>
4177    <t>
4178      A response is cacheable if a cache is allowed to store a copy of
4179      the response message for use in answering subsequent requests. The
4180      rules for determining the cacheability of HTTP responses are
4181      defined in &caching;. Even if a resource is cacheable, there may
4182      be additional constraints on whether a cache can use the cached
4183      copy for a particular request.
4184    </t>
4185  </list>
4188  <iref item="client"/>
4189  <x:dfn>client</x:dfn>
4190  <list>
4191    <t>
4192      A program that establishes connections for the purpose of sending
4193      requests.
4194    </t>
4195  </list>
4198  <iref item="connection"/>
4199  <x:dfn>connection</x:dfn>
4200  <list>
4201    <t>
4202      A transport layer virtual circuit established between two programs
4203      for the purpose of communication.
4204    </t>
4205  </list>
4208  <iref item="content negotiation"/>
4209  <x:dfn>content negotiation</x:dfn>
4210  <list>
4211    <t>
4212      The mechanism for selecting the appropriate representation when
4213      servicing a request, as described in &content.negotiation;. The
4214      representation of entities in any response can be negotiated
4215      (including error responses).
4216    </t>
4217  </list>
4220  <iref item="entity"/>
4221  <x:dfn>entity</x:dfn>
4222  <list>
4223    <t>
4224      The information transferred as the payload of a request or
4225      response. An entity consists of metainformation in the form of
4226      entity-header fields and content in the form of an entity-body, as
4227      described in &entity;.
4228    </t>
4229  </list>
4232  <iref item="gateway"/>
4233  <x:dfn>gateway</x:dfn>
4234  <list>
4235    <t>
4236      A server which acts as an intermediary for some other server.
4237      Unlike a proxy, a gateway receives requests as if it were the
4238      origin server for the requested resource; the requesting client
4239      may not be aware that it is communicating with a gateway.
4240    </t>
4241  </list>
4244  <iref item="inbound"/>
4245  <iref item="outbound"/>
4246  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4247  <list>
4248    <t>
4249      Inbound and outbound refer to the request and response paths for
4250      messages: "inbound" means "traveling toward the origin server",
4251      and "outbound" means "traveling toward the user agent"
4252    </t>
4253  </list>
4256  <iref item="message"/>
4257  <x:dfn>message</x:dfn>
4258  <list>
4259    <t>
4260      The basic unit of HTTP communication, consisting of a structured
4261      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4262      transmitted via the connection.
4263    </t>
4264  </list>
4267  <iref item="origin server"/>
4268  <x:dfn>origin server</x:dfn>
4269  <list>
4270    <t>
4271      The server on which a given resource resides or is to be created.
4272    </t>
4273  </list>
4276  <iref item="proxy"/>
4277  <x:dfn>proxy</x:dfn>
4278  <list>
4279    <t>
4280      An intermediary program which acts as both a server and a client
4281      for the purpose of making requests on behalf of other clients.
4282      Requests are serviced internally or by passing them on, with
4283      possible translation, to other servers. A proxy &MUST; implement
4284      both the client and server requirements of this specification. A
4285      "transparent proxy" is a proxy that does not modify the request or
4286      response beyond what is required for proxy authentication and
4287      identification. A "non-transparent proxy" is a proxy that modifies
4288      the request or response in order to provide some added service to
4289      the user agent, such as group annotation services, media type
4290      transformation, protocol reduction, or anonymity filtering. Except
4291      where either transparent or non-transparent behavior is explicitly
4292      stated, the HTTP proxy requirements apply to both types of
4293      proxies.
4294    </t>
4295  </list>
4298  <iref item="request"/>
4299  <x:dfn>request</x:dfn>
4300  <list>
4301    <t>
4302      An HTTP request message, as defined in <xref target="request"/>.
4303    </t>
4304  </list>
4307  <iref item="resource"/>
4308  <x:dfn>resource</x:dfn>
4309  <list>
4310    <t>
4311      A network data object or service that can be identified by a URI,
4312      as defined in <xref target="uri"/>. Resources may be available in multiple
4313      representations (e.g. multiple languages, data formats, size, and
4314      resolutions) or vary in other ways.
4315    </t>
4316  </list>
4319  <iref item="response"/>
4320  <x:dfn>response</x:dfn>
4321  <list>
4322    <t>
4323      An HTTP response message, as defined in <xref target="response"/>.
4324    </t>
4325  </list>
4328  <iref item="representation"/>
4329  <x:dfn>representation</x:dfn>
4330  <list>
4331    <t>
4332      An entity included with a response that is subject to content
4333      negotiation, as described in &content.negotiation;. There may exist multiple
4334      representations associated with a particular response status.
4335    </t>
4336  </list>
4339  <iref item="server"/>
4340  <x:dfn>server</x:dfn>
4341  <list>
4342    <t>
4343      An application program that accepts connections in order to
4344      service requests by sending back responses. Any given program may
4345      be capable of being both a client and a server; our use of these
4346      terms refers only to the role being performed by the program for a
4347      particular connection, rather than to the program's capabilities
4348      in general. Likewise, any server may act as an origin server,
4349      proxy, gateway, or tunnel, switching behavior based on the nature
4350      of each request.
4351    </t>
4352  </list>
4355  <iref item="tunnel"/>
4356  <x:dfn>tunnel</x:dfn>
4357  <list>
4358    <t>
4359      An intermediary program which is acting as a blind relay between
4360      two connections. Once active, a tunnel is not considered a party
4361      to the HTTP communication, though the tunnel may have been
4362      initiated by an HTTP request. The tunnel ceases to exist when both
4363      ends of the relayed connections are closed.
4364    </t>
4365  </list>
4368  <iref item="upstream"/>
4369  <iref item="downstream"/>
4370  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4371  <list>
4372    <t>
4373      Upstream and downstream describe the flow of a message: all
4374      messages flow from upstream to downstream.
4375    </t>
4376  </list>
4379  <iref item="user agent"/>
4380  <x:dfn>user agent</x:dfn>
4381  <list>
4382    <t>
4383      The client which initiates a request. These are often browsers,
4384      editors, spiders (web-traversing robots), or other end user tools.
4385    </t>
4386  </list>
4389  <iref item="variant"/>
4390  <x:dfn>variant</x:dfn>
4391  <list>
4392    <t>
4393      A resource may have one, or more than one, representation(s)
4394      associated with it at any given instant. Each of these
4395      representations is termed a `variant'.  Use of the term `variant'
4396      does not necessarily imply that the resource is subject to content
4397      negotiation.
4398    </t>
4399  </list>
4403<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4405<artwork type="abnf" name="p1-messaging.parsed-abnf">
4406<x:ref>BWS</x:ref> = OWS
4408<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 15.4&gt;
4409<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4410<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4411<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4412 connection-token ] )
4413<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4414<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4416<x:ref>Date</x:ref> = "Date:" OWS Date-v
4417<x:ref>Date-v</x:ref> = HTTP-date
4419GMT = %x47.4D.54
4421<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4422<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4423<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4424<x:ref>HTTP-message</x:ref> = Request / Response
4425<x:ref>Host</x:ref> = "Host:" OWS Host-v
4426<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4428<x:ref>Method</x:ref> = token
4430<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4432<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 15.4&gt;
4434<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4435<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4436<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4437 entity-header ) CRLF ) CRLF [ message-body ]
4438<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4439<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4440 entity-header ) CRLF ) CRLF [ message-body ]
4442<x:ref>Status-Code</x:ref> = 3DIGIT
4443<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4445<x:ref>TE</x:ref> = "TE:" OWS TE-v
4446<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4447<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4448<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4449<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4450<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4451 transfer-coding ] )
4453<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4454<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4455<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4456<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4458<x:ref>Via</x:ref> = "Via:" OWS Via-v
4459<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4460 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4461 ] )
4463<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 15.6&gt;
4465<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4466<x:ref>accept-params</x:ref> = &lt;accept-params, defined in [Part3], Section 5.1&gt;
4467<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4468<x:ref>attribute</x:ref> = token
4469<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4471<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4472<x:ref>chunk-data</x:ref> = 1*OCTET
4473<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4474<x:ref>chunk-ext-name</x:ref> = token
4475<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4476<x:ref>chunk-size</x:ref> = 1*HEXDIG
4477<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4478<x:ref>connection-token</x:ref> = token
4479<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4481<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4482<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4483<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4485<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4486<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4488<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4489<x:ref>field-name</x:ref> = token
4490<x:ref>field-value</x:ref> = *( field-content / OWS )
4491<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4493<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4494 / Transfer-Encoding / Upgrade / Via / Warning
4495<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4496 message-body ]
4498<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4500l-Fri = %x46.
4501l-Mon = %x4D.6F.6E.64.61.79
4502l-Sat = %x53.
4503l-Sun = %x53.75.6E.64.61.79
4504l-Thu = %x54.
4505l-Tue = %x54.
4506l-Wed = %x57.65.64.6E.
4507<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4509<x:ref>message-body</x:ref> = entity-body /
4510 &lt;entity-body encoded as per Transfer-Encoding&gt;
4511<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4512<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4513 / s-Sep / s-Oct / s-Nov / s-Dec
4515<x:ref>obs-fold</x:ref> = CRLF
4516<x:ref>obs-text</x:ref> = %x80-FF
4517<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4519<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4520<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4521<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4522<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4523<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4524<x:ref>product</x:ref> = token [ "/" product-version ]
4525<x:ref>product-version</x:ref> = token
4526<x:ref>protocol-name</x:ref> = token
4527<x:ref>protocol-version</x:ref> = token
4528<x:ref>pseudonym</x:ref> = token
4530<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4531<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4532<x:ref>quoted-pair</x:ref> = "\" quoted-text
4533<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4534<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4536<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4537<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4538<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4539<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4540<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4541 / authority
4542<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4543<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4544<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4546s-Apr = %x41.70.72
4547s-Aug = %x41.75.67
4548s-Dec = %x44.65.63
4549s-Feb = %x46.65.62
4550s-Fri = %x46.72.69
4551s-Jan = %x4A.61.6E
4552s-Jul = %x4A.75.6C
4553s-Jun = %x4A.75.6E
4554s-Mar = %x4D.61.72
4555s-May = %x4D.61.79
4556s-Mon = %x4D.6F.6E
4557s-Nov = %x4E.6F.76
4558s-Oct = %x4F.63.74
4559s-Sat = %x53.61.74
4560s-Sep = %x53.65.70
4561s-Sun = %x53.75.6E
4562s-Thu = %x54.68.75
4563s-Tue = %x54.75.65
4564s-Wed = %x57.65.64
4565<x:ref>start-line</x:ref> = Request-Line / Status-Line
4567<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ accept-params ] )
4568<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4569 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4570<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4571<x:ref>token</x:ref> = 1*tchar
4572<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4573<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4574<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4576<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4578<x:ref>value</x:ref> = token / quoted-string
4580<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4581<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4586<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">; Chunked-Body defined but not used
4587; Content-Length defined but not used
4588; HTTP-message defined but not used
4589; Host defined but not used
4590; TE defined but not used
4591; URI defined but not used
4592; URI-reference defined but not used
4593; fragment defined but not used
4594; generic-message defined but not used
4595; http-URI defined but not used
4596; partial-URI defined but not used
4599<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4601<section title="Since RFC2616">
4603  Extracted relevant partitions from <xref target="RFC2616"/>.
4607<section title="Since draft-ietf-httpbis-p1-messaging-00">
4609  Closed issues:
4610  <list style="symbols">
4611    <t>
4612      <eref target=""/>:
4613      "HTTP Version should be case sensitive"
4614      (<eref target=""/>)
4615    </t>
4616    <t>
4617      <eref target=""/>:
4618      "'unsafe' characters"
4619      (<eref target=""/>)
4620    </t>
4621    <t>
4622      <eref target=""/>:
4623      "Chunk Size Definition"
4624      (<eref target=""/>)
4625    </t>
4626    <t>
4627      <eref target=""/>:
4628      "Message Length"
4629      (<eref target=""/>)
4630    </t>
4631    <t>
4632      <eref target=""/>:
4633      "Media Type Registrations"
4634      (<eref target=""/>)
4635    </t>
4636    <t>
4637      <eref target=""/>:
4638      "URI includes query"
4639      (<eref target=""/>)
4640    </t>
4641    <t>
4642      <eref target=""/>:
4643      "No close on 1xx responses"
4644      (<eref target=""/>)
4645    </t>
4646    <t>
4647      <eref target=""/>:
4648      "Remove 'identity' token references"
4649      (<eref target=""/>)
4650    </t>
4651    <t>
4652      <eref target=""/>:
4653      "Import query BNF"
4654    </t>
4655    <t>
4656      <eref target=""/>:
4657      "qdtext BNF"
4658    </t>
4659    <t>
4660      <eref target=""/>:
4661      "Normative and Informative references"
4662    </t>
4663    <t>
4664      <eref target=""/>:
4665      "RFC2606 Compliance"
4666    </t>
4667    <t>
4668      <eref target=""/>:
4669      "RFC977 reference"
4670    </t>
4671    <t>
4672      <eref target=""/>:
4673      "RFC1700 references"
4674    </t>
4675    <t>
4676      <eref target=""/>:
4677      "inconsistency in date format explanation"
4678    </t>
4679    <t>
4680      <eref target=""/>:
4681      "Date reference typo"
4682    </t>
4683    <t>
4684      <eref target=""/>:
4685      "Informative references"
4686    </t>
4687    <t>
4688      <eref target=""/>:
4689      "ISO-8859-1 Reference"
4690    </t>
4691    <t>
4692      <eref target=""/>:
4693      "Normative up-to-date references"
4694    </t>
4695  </list>
4698  Other changes:
4699  <list style="symbols">
4700    <t>
4701      Update media type registrations to use RFC4288 template.
4702    </t>
4703    <t>
4704      Use names of RFC4234 core rules DQUOTE and WSP,
4705      fix broken ABNF for chunk-data
4706      (work in progress on <eref target=""/>)
4707    </t>
4708  </list>
4712<section title="Since draft-ietf-httpbis-p1-messaging-01">
4714  Closed issues:
4715  <list style="symbols">
4716    <t>
4717      <eref target=""/>:
4718      "Bodies on GET (and other) requests"
4719    </t>
4720    <t>
4721      <eref target=""/>:
4722      "Updating to RFC4288"
4723    </t>
4724    <t>
4725      <eref target=""/>:
4726      "Status Code and Reason Phrase"
4727    </t>
4728    <t>
4729      <eref target=""/>:
4730      "rel_path not used"
4731    </t>
4732  </list>
4735  Ongoing work on ABNF conversion (<eref target=""/>):
4736  <list style="symbols">
4737    <t>
4738      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4739      "trailer-part").
4740    </t>
4741    <t>
4742      Avoid underscore character in rule names ("http_URL" ->
4743      "http-URL", "abs_path" -> "path-absolute").
4744    </t>
4745    <t>
4746      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4747      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4748      have to be updated when switching over to RFC3986.
4749    </t>
4750    <t>
4751      Synchronize core rules with RFC5234.
4752    </t>
4753    <t>
4754      Get rid of prose rules that span multiple lines.
4755    </t>
4756    <t>
4757      Get rid of unused rules LOALPHA and UPALPHA.
4758    </t>
4759    <t>
4760      Move "Product Tokens" section (back) into Part 1, as "token" is used
4761      in the definition of the Upgrade header.
4762    </t>
4763    <t>
4764      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4765    </t>
4766    <t>
4767      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4768    </t>
4769  </list>
4773<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4775  Closed issues:
4776  <list style="symbols">
4777    <t>
4778      <eref target=""/>:
4779      "HTTP-date vs. rfc1123-date"
4780    </t>
4781    <t>
4782      <eref target=""/>:
4783      "WS in quoted-pair"
4784    </t>
4785  </list>
4788  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4789  <list style="symbols">
4790    <t>
4791      Reference RFC 3984, and update header registrations for headers defined
4792      in this document.
4793    </t>
4794  </list>
4797  Ongoing work on ABNF conversion (<eref target=""/>):
4798  <list style="symbols">
4799    <t>
4800      Replace string literals when the string really is case-sensitive (HTTP-Version).
4801    </t>
4802  </list>
4806<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4808  Closed issues:
4809  <list style="symbols">
4810    <t>
4811      <eref target=""/>:
4812      "Connection closing"
4813    </t>
4814    <t>
4815      <eref target=""/>:
4816      "Move registrations and registry information to IANA Considerations"
4817    </t>
4818    <t>
4819      <eref target=""/>:
4820      "need new URL for PAD1995 reference"
4821    </t>
4822    <t>
4823      <eref target=""/>:
4824      "IANA Considerations: update HTTP URI scheme registration"
4825    </t>
4826    <t>
4827      <eref target=""/>:
4828      "Cite HTTPS URI scheme definition"
4829    </t>
4830    <t>
4831      <eref target=""/>:
4832      "List-type headers vs Set-Cookie"
4833    </t>
4834  </list>
4837  Ongoing work on ABNF conversion (<eref target=""/>):
4838  <list style="symbols">
4839    <t>
4840      Replace string literals when the string really is case-sensitive (HTTP-Date).
4841    </t>
4842    <t>
4843      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4844    </t>
4845  </list>
4849<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4851  Closed issues:
4852  <list style="symbols">
4853    <t>
4854      <eref target=""/>:
4855      "Out-of-date reference for URIs"
4856    </t>
4857    <t>
4858      <eref target=""/>:
4859      "RFC 2822 is updated by RFC 5322"
4860    </t>
4861  </list>
4864  Ongoing work on ABNF conversion (<eref target=""/>):
4865  <list style="symbols">
4866    <t>
4867      Use "/" instead of "|" for alternatives.
4868    </t>
4869    <t>
4870      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4871    </t>
4872    <t>
4873      Only reference RFC 5234's core rules.
4874    </t>
4875    <t>
4876      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4877      whitespace ("OWS") and required whitespace ("RWS").
4878    </t>
4879    <t>
4880      Rewrite ABNFs to spell out whitespace rules, factor out
4881      header value format definitions.
4882    </t>
4883  </list>
4887<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4889  Closed issues:
4890  <list style="symbols">
4891    <t>
4892      <eref target=""/>:
4893      "Header LWS"
4894    </t>
4895    <t>
4896      <eref target=""/>:
4897      "Sort 1.3 Terminology"
4898    </t>
4899    <t>
4900      <eref target=""/>:
4901      "RFC2047 encoded words"
4902    </t>
4903    <t>
4904      <eref target=""/>:
4905      "Character Encodings in TEXT"
4906    </t>
4907    <t>
4908      <eref target=""/>:
4909      "Line Folding"
4910    </t>
4911    <t>
4912      <eref target=""/>:
4913      "OPTIONS * and proxies"
4914    </t>
4915    <t>
4916      <eref target=""/>:
4917      "Reason-Phrase BNF"
4918    </t>
4919    <t>
4920      <eref target=""/>:
4921      "Use of TEXT"
4922    </t>
4923    <t>
4924      <eref target=""/>:
4925      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4926    </t>
4927    <t>
4928      <eref target=""/>:
4929      "RFC822 reference left in discussion of date formats"
4930    </t>
4931  </list>
4934  Ongoing work on ABNF conversion (<eref target=""/>):
4935  <list style="symbols">
4936    <t>
4937      Rewrite definition of list rules, deprecate empty list elements.
4938    </t>
4939    <t>
4940      Add appendix containing collected and expanded ABNF.
4941    </t>
4942  </list>
4945  Other changes:
4946  <list style="symbols">
4947    <t>
4948      Rewrite introduction; add mostly new Architecture Section.
4949    </t>
4950  </list>
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