source: draft-ietf-httpbis/06/p1-messaging.xml @ 547

Last change on this file since 547 was 547, checked in by julian.reschke@…, 14 years ago

Prepare submission of draft -06 on Monday, March 09.

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
15  <!ENTITY ID-MONTH "March">
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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x=''/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization>One Laptop per Child</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>   
189      <facsimile>+49 251 2807761</facsimile>   
190      <email></email>       
191      <uri></uri>     
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;" day="9"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.05"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as a generic protocol for translating
253   communication to and from other Internet information systems.
254   HTTP proxies and gateways provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions should be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients may act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP and defines the URI schemes specific to
277   HTTP-based resources, overall network operation, connection
278   management, and HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the &MUST; or &REQUIRED; level requirements for the protocols it
294   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
295   level and all the &SHOULD; level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the &MUST;
297   level requirements but not all the &SHOULD; level requirements for its
298   protocols is said to be "conditionally compliant."
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   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 ] ) ]
375  1#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="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
482  The ABNF rules below are defined in other parts:
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
502<section title="HTTP architecture" anchor="architecture">
504   HTTP was created with a specific architecture in mind, the World Wide Web,
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
510<section title="Uniform Resource Identifiers" anchor="uri">
512   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
513   throughout HTTP as the means for identifying resources. URI references
514   are used to target requests, redirect responses, and define relationships.
515   HTTP does not limit what a resource may be; it merely defines an interface
516   that can be used to interact with a resource via HTTP. More information on
517   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
519  <x:anchor-alias value="URI"/>
520  <x:anchor-alias value="URI-reference"/>
521  <x:anchor-alias value="absolute-URI"/>
522  <x:anchor-alias value="relative-part"/>
523  <x:anchor-alias value="authority"/>
524  <x:anchor-alias value="fragment"/>
525  <x:anchor-alias value="path-abempty"/>
526  <x:anchor-alias value="path-absolute"/>
527  <x:anchor-alias value="port"/>
528  <x:anchor-alias value="query"/>
529  <x:anchor-alias value="uri-host"/>
530  <x:anchor-alias value="partial-URI"/>
532   This specification adopts the definitions of "URI-reference",
533   "absolute-URI", "relative-part", "fragment", "port", "host",
534   "path-abempty", "path-absolute", "query", and "authority" from
535   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
536   protocol elements that allow a relative URI without a fragment.
538<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"/>
539  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
540  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
541  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
542  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
543  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
544  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
545  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
546  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
548  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
549  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
551  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
554   Each protocol element in HTTP that allows a URI reference will indicate in
555   its ABNF production whether the element allows only a URI in absolute form
556   (absolute-URI), any relative reference (relative-ref), or some other subset
557   of the URI-reference grammar. Unless otherwise indicated, URI references
558   are parsed relative to the request target (the default base URI for both
559   the request and its corresponding response).
562<section title="http URI scheme" anchor="http.uri">
563  <x:anchor-alias value="http-URI"/>
564  <iref item="http URI scheme" primary="true"/>
565  <iref item="URI scheme" subitem="http" primary="true"/>
567   The "http" scheme is used to locate network resources via the HTTP
568   protocol.
570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
571  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
574   If the port is empty or not given, port 80 is assumed. The semantics
575   are that the identified resource is located at the server listening
576   for TCP connections on that port of that host, and the request-target
577   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
578   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
579   the path-absolute is not present in the URL, it &MUST; be given as "/" when
580   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
581   receives a host name which is not a fully qualified domain name, it
582   &MAY; add its domain to the host name it received. If a proxy receives
583   a fully qualified domain name, the proxy &MUST-NOT; change the host
584   name.
588<section title="https URI scheme" anchor="https.uri">
589   <iref item="https URI scheme"/>
590   <iref item="URI scheme" subitem="https"/>
592   <cref>TBD: Define and explain purpose of https scheme.</cref>
595  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
599<section title="URI Comparison" anchor="uri.comparison">
601   When comparing two URIs to decide if they match or not, a client
602   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
603   URIs, with these exceptions:
604  <list style="symbols">
605    <t>A port that is empty or not given is equivalent to the default
606        port for that URI-reference;</t>
607    <t>Comparisons of host names &MUST; be case-insensitive;</t>
608    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
609    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
610    <t>Characters other than those in the "reserved" set are equivalent to their
611       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
612    </t>
613  </list>
616   For example, the following three URIs are equivalent:
618<figure><artwork type="example">
625<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
631<section title="Overall Operation" anchor="intro.overall.operation">
633   HTTP is a request/response protocol. A client sends a
634   request to the server in the form of a request method, URI, and
635   protocol version, followed by a MIME-like message containing request
636   modifiers, client information, and possible body content over a
637   connection with a server. The server responds with a status line,
638   including the message's protocol version and a success or error code,
639   followed by a MIME-like message containing server information, entity
640   metainformation, and possible entity-body content.
643   Most HTTP communication is initiated by a user agent and consists of
644   a request to be applied to a resource on some origin server. In the
645   simplest case, this may be accomplished via a single connection (v)
646   between the user agent (UA) and the origin server (O).
648<figure><artwork type="drawing">
649       request chain ------------------------&gt;
650    UA -------------------v------------------- O
651       &lt;----------------------- response chain
654   A more complicated situation occurs when one or more intermediaries
655   are present in the request/response chain. There are three common
656   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
657   forwarding agent, receiving requests for a URI in its absolute form,
658   rewriting all or part of the message, and forwarding the reformatted
659   request toward the server identified by the URI. A gateway is a
660   receiving agent, acting as a layer above some other server(s) and, if
661   necessary, translating the requests to the underlying server's
662   protocol. A tunnel acts as a relay point between two connections
663   without changing the messages; tunnels are used when the
664   communication needs to pass through an intermediary (such as a
665   firewall) even when the intermediary cannot understand the contents
666   of the messages.
668<figure><artwork type="drawing">
669       request chain --------------------------------------&gt;
670    UA -----v----- A -----v----- B -----v----- C -----v----- O
671       &lt;------------------------------------- response chain
674   The figure above shows three intermediaries (A, B, and C) between the
675   user agent and origin server. A request or response message that
676   travels the whole chain will pass through four separate connections.
677   This distinction is important because some HTTP communication options
678   may apply only to the connection with the nearest, non-tunnel
679   neighbor, only to the end-points of the chain, or to all connections
680   along the chain. Although the diagram is linear, each participant may
681   be engaged in multiple, simultaneous communications. For example, B
682   may be receiving requests from many clients other than A, and/or
683   forwarding requests to servers other than C, at the same time that it
684   is handling A's request.
687   Any party to the communication which is not acting as a tunnel may
688   employ an internal cache for handling requests. The effect of a cache
689   is that the request/response chain is shortened if one of the
690   participants along the chain has a cached response applicable to that
691   request. The following illustrates the resulting chain if B has a
692   cached copy of an earlier response from O (via C) for a request which
693   has not been cached by UA or A.
695<figure><artwork type="drawing">
696          request chain ----------&gt;
697       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
698          &lt;--------- response chain
701   Not all responses are usefully cacheable, and some requests may
702   contain modifiers which place special requirements on cache behavior.
703   HTTP requirements for cache behavior and cacheable responses are
704   defined in &caching;.
707   In fact, there are a wide variety of architectures and configurations
708   of caches and proxies currently being experimented with or deployed
709   across the World Wide Web. These systems include national hierarchies
710   of proxy caches to save transoceanic bandwidth, systems that
711   broadcast or multicast cache entries, organizations that distribute
712   subsets of cached data via CD-ROM, and so on. HTTP systems are used
713   in corporate intranets over high-bandwidth links, and for access via
714   PDAs with low-power radio links and intermittent connectivity. The
715   goal of HTTP/1.1 is to support the wide diversity of configurations
716   already deployed while introducing protocol constructs that meet the
717   needs of those who build web applications that require high
718   reliability and, failing that, at least reliable indications of
719   failure.
722   HTTP communication usually takes place over TCP/IP connections. The
723   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
724   not preclude HTTP from being implemented on top of any other protocol
725   on the Internet, or on other networks. HTTP only presumes a reliable
726   transport; any protocol that provides such guarantees can be used;
727   the mapping of the HTTP/1.1 request and response structures onto the
728   transport data units of the protocol in question is outside the scope
729   of this specification.
732   In HTTP/1.0, most implementations used a new connection for each
733   request/response exchange. In HTTP/1.1, a connection may be used for
734   one or more request/response exchanges, although connections may be
735   closed for a variety of reasons (see <xref target="persistent.connections"/>).
739<section title="Use of HTTP for proxy communication" anchor="http.proxy">
741   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
744<section title="Interception of HTTP for access control" anchor="http.intercept">
746   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
749<section title="Use of HTTP by other protocols" anchor="http.others">
751   <cref>TBD: Profiles of HTTP defined by other protocol.
752   Extensions of HTTP like WebDAV.</cref>
755<section title="Use of HTTP by media type specification" anchor="">
757   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
762<section title="Protocol Parameters" anchor="protocol.parameters">
764<section title="HTTP Version" anchor="http.version">
765  <x:anchor-alias value="HTTP-Version"/>
766  <x:anchor-alias value="HTTP-Prot-Name"/>
768   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
769   of the protocol. The protocol versioning policy is intended to allow
770   the sender to indicate the format of a message and its capacity for
771   understanding further HTTP communication, rather than the features
772   obtained via that communication. No change is made to the version
773   number for the addition of message components which do not affect
774   communication behavior or which only add to extensible field values.
775   The &lt;minor&gt; number is incremented when the changes made to the
776   protocol add features which do not change the general message parsing
777   algorithm, but which may add to the message semantics and imply
778   additional capabilities of the sender. The &lt;major&gt; number is
779   incremented when the format of a message within the protocol is
780   changed. See <xref target="RFC2145"/> for a fuller explanation.
783   The version of an HTTP message is indicated by an HTTP-Version field
784   in the first line of the message. HTTP-Version is case-sensitive.
786<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
787  <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>
788  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
791   Note that the major and minor numbers &MUST; be treated as separate
792   integers and that each &MAY; be incremented higher than a single digit.
793   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
794   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
795   &MUST-NOT; be sent.
798   An application that sends a request or response message that includes
799   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
800   with this specification. Applications that are at least conditionally
801   compliant with this specification &SHOULD; use an HTTP-Version of
802   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
803   not compatible with HTTP/1.0. For more details on when to send
804   specific HTTP-Version values, see <xref target="RFC2145"/>.
807   The HTTP version of an application is the highest HTTP version for
808   which the application is at least conditionally compliant.
811   Proxy and gateway applications need to be careful when forwarding
812   messages in protocol versions different from that of the application.
813   Since the protocol version indicates the protocol capability of the
814   sender, a proxy/gateway &MUST-NOT; send a message with a version
815   indicator which is greater than its actual version. If a higher
816   version request is received, the proxy/gateway &MUST; either downgrade
817   the request version, or respond with an error, or switch to tunnel
818   behavior.
821   Due to interoperability problems with HTTP/1.0 proxies discovered
822   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
823   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
824   they support. The proxy/gateway's response to that request &MUST; be in
825   the same major version as the request.
828  <list>
829    <t>
830      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
831      of header fields required or forbidden by the versions involved.
832    </t>
833  </list>
837<section title="Date/Time Formats" anchor="date.time.formats">
838<section title="Full Date" anchor="">
839  <x:anchor-alias value="HTTP-date"/>
840  <x:anchor-alias value="obsolete-date"/>
841  <x:anchor-alias value="rfc1123-date"/>
842  <x:anchor-alias value="rfc850-date"/>
843  <x:anchor-alias value="asctime-date"/>
844  <x:anchor-alias value="date1"/>
845  <x:anchor-alias value="date2"/>
846  <x:anchor-alias value="date3"/>
847  <x:anchor-alias value="rfc1123-date"/>
848  <x:anchor-alias value="time"/>
849  <x:anchor-alias value="wkday"/>
850  <x:anchor-alias value="weekday"/>
851  <x:anchor-alias value="month"/>
853   HTTP applications have historically allowed three different formats
854   for the representation of date/time stamps:
856<figure><artwork type="example">
857  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
858  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
859  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
862   The first format is preferred as an Internet standard and represents
863   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
864   other formats are described here only for
865   compatibility with obsolete implementations.
866   HTTP/1.1 clients and servers that parse the date value &MUST; accept
867   all three formats (for compatibility with HTTP/1.0), though they &MUST;
868   only generate the RFC 1123 format for representing HTTP-date values
869   in header fields. See <xref target="tolerant.applications"/> for further information.
872      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
873      accepting date values that may have been sent by non-HTTP
874      applications, as is sometimes the case when retrieving or posting
875      messages via proxies/gateways to SMTP or NNTP.
878   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
879   (GMT), without exception. For the purposes of HTTP, GMT is exactly
880   equal to UTC (Coordinated Universal Time). This is indicated in the
881   first two formats by the inclusion of "GMT" as the three-letter
882   abbreviation for time zone, and &MUST; be assumed when reading the
883   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
884   additional whitespace beyond that specifically included as SP in the
885   grammar.
887<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"/>
888  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
889  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
890  <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
891  <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
892  <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>
893  <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>
894                 ; day month year (e.g., 02 Jun 1982)
895  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
896                 ; day-month-year (e.g., 02-Jun-82)
897  <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> ))
898                 ; month day (e.g., Jun  2)
899  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
900                 ; 00:00:00 - 23:59:59
901  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
902               / s-Thu / s-Fri / s-Sat / s-Sun
903  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
904               / l-Thu / l-Fri / l-Sat / l-Sun
905  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
906               / s-May / s-Jun / s-Jul / s-Aug
907               / s-Sep / s-Oct / s-Nov / s-Dec
909  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
911  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
912  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
913  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
914  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
915  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
916  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
917  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
919  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
920  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
921  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
922  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
923  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
924  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
925  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
927  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
928  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
929  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
930  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
931  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
932  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
933  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
934  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
935  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
936  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
937  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
938  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
941      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
942      to their usage within the protocol stream. Clients and servers are
943      not required to use these formats for user presentation, request
944      logging, etc.
949<section title="Transfer Codings" anchor="transfer.codings">
950  <x:anchor-alias value="parameter"/>
951  <x:anchor-alias value="transfer-coding"/>
952  <x:anchor-alias value="transfer-extension"/>
954   Transfer-coding values are used to indicate an encoding
955   transformation that has been, can be, or may need to be applied to an
956   entity-body in order to ensure "safe transport" through the network.
957   This differs from a content coding in that the transfer-coding is a
958   property of the message, not of the original entity.
960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
961  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
962  <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> )
964<t anchor="rule.parameter">
965  <x:anchor-alias value="attribute"/>
966  <x:anchor-alias value="parameter"/>
967  <x:anchor-alias value="value"/>
968   Parameters are in  the form of attribute/value pairs.
970<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"/>
971  <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>
972  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
973  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
976   All transfer-coding values are case-insensitive. HTTP/1.1 uses
977   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
978   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
981   Whenever a transfer-coding is applied to a message-body, the set of
982   transfer-codings &MUST; include "chunked", unless the message indicates it
983   is terminated by closing the connection. When the "chunked" transfer-coding
984   is used, it &MUST; be the last transfer-coding applied to the
985   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
986   than once to a message-body. These rules allow the recipient to
987   determine the transfer-length of the message (<xref target="message.length"/>).
990   Transfer-codings are analogous to the Content-Transfer-Encoding
991   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
992   binary data over a 7-bit transport service. However, safe transport
993   has a different focus for an 8bit-clean transfer protocol. In HTTP,
994   the only unsafe characteristic of message-bodies is the difficulty in
995   determining the exact body length (<xref target="message.length"/>), or the desire to
996   encrypt data over a shared transport.
999   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1000   transfer-coding value tokens. Initially, the registry contains the
1001   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1002   "gzip", "compress", and "deflate" (&content-codings;).
1005   New transfer-coding value tokens &SHOULD; be registered in the same way
1006   as new content-coding value tokens (&content-codings;).
1009   A server which receives an entity-body with a transfer-coding it does
1010   not understand &SHOULD; return 501 (Not Implemented), and close the
1011   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1012   client.
1015<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1016  <x:anchor-alias value="chunk"/>
1017  <x:anchor-alias value="Chunked-Body"/>
1018  <x:anchor-alias value="chunk-data"/>
1019  <x:anchor-alias value="chunk-ext"/>
1020  <x:anchor-alias value="chunk-ext-name"/>
1021  <x:anchor-alias value="chunk-ext-val"/>
1022  <x:anchor-alias value="chunk-size"/>
1023  <x:anchor-alias value="last-chunk"/>
1024  <x:anchor-alias value="trailer-part"/>
1026   The chunked encoding modifies the body of a message in order to
1027   transfer it as a series of chunks, each with its own size indicator,
1028   followed by an &OPTIONAL; trailer containing entity-header fields. This
1029   allows dynamically produced content to be transferred along with the
1030   information necessary for the recipient to verify that it has
1031   received the full message.
1033<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"/>
1034  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1035                   <x:ref>last-chunk</x:ref>
1036                   <x:ref>trailer-part</x:ref>
1037                   <x:ref>CRLF</x:ref>
1039  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1040                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1041  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1042  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1044  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1045                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1046  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1047  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1048  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1049  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1052   The chunk-size field is a string of hex digits indicating the size of
1053   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1054   zero, followed by the trailer, which is terminated by an empty line.
1057   The trailer allows the sender to include additional HTTP header
1058   fields at the end of the message. The Trailer header field can be
1059   used to indicate which header fields are included in a trailer (see
1060   <xref target="header.trailer"/>).
1063   A server using chunked transfer-coding in a response &MUST-NOT; use the
1064   trailer for any header fields unless at least one of the following is
1065   true:
1066  <list style="numbers">
1067    <t>the request included a TE header field that indicates "trailers" is
1068     acceptable in the transfer-coding of the  response, as described in
1069     <xref target="header.te"/>; or,</t>
1071    <t>the server is the origin server for the response, the trailer
1072     fields consist entirely of optional metadata, and the recipient
1073     could use the message (in a manner acceptable to the origin server)
1074     without receiving this metadata.  In other words, the origin server
1075     is willing to accept the possibility that the trailer fields might
1076     be silently discarded along the path to the client.</t>
1077  </list>
1080   This requirement prevents an interoperability failure when the
1081   message is being received by an HTTP/1.1 (or later) proxy and
1082   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1083   compliance with the protocol would have necessitated a possibly
1084   infinite buffer on the proxy.
1087   A process for decoding the "chunked" transfer-coding
1088   can be represented in pseudo-code as:
1090<figure><artwork type="code">
1091  length := 0
1092  read chunk-size, chunk-ext (if any) and CRLF
1093  while (chunk-size &gt; 0) {
1094     read chunk-data and CRLF
1095     append chunk-data to entity-body
1096     length := length + chunk-size
1097     read chunk-size and CRLF
1098  }
1099  read entity-header
1100  while (entity-header not empty) {
1101     append entity-header to existing header fields
1102     read entity-header
1103  }
1104  Content-Length := length
1105  Remove "chunked" from Transfer-Encoding
1108   All HTTP/1.1 applications &MUST; be able to receive and decode the
1109   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1110   they do not understand.
1115<section title="Product Tokens" anchor="product.tokens">
1116  <x:anchor-alias value="product"/>
1117  <x:anchor-alias value="product-version"/>
1119   Product tokens are used to allow communicating applications to
1120   identify themselves by software name and version. Most fields using
1121   product tokens also allow sub-products which form a significant part
1122   of the application to be listed, separated by whitespace. By
1123   convention, the products are listed in order of their significance
1124   for identifying the application.
1126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1127  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1128  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1131   Examples:
1133<figure><artwork type="example">
1134  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1135  Server: Apache/0.8.4
1138   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1139   used for advertising or other non-essential information. Although any
1140   token character &MAY; appear in a product-version, this token &SHOULD;
1141   only be used for a version identifier (i.e., successive versions of
1142   the same product &SHOULD; only differ in the product-version portion of
1143   the product value).
1147<section title="Quality Values" anchor="quality.values">
1148  <x:anchor-alias value="qvalue"/>
1150   Both transfer codings (TE request header, <xref target="header.te"/>)
1151   and content negotiation (&content.negotiation;) use short "floating point"
1152   numbers to indicate the relative importance ("weight") of various
1153   negotiable parameters.  A weight is normalized to a real number in
1154   the range 0 through 1, where 0 is the minimum and 1 the maximum
1155   value. If a parameter has a quality value of 0, then content with
1156   this parameter is `not acceptable' for the client. HTTP/1.1
1157   applications &MUST-NOT; generate more than three digits after the
1158   decimal point. User configuration of these values &SHOULD; also be
1159   limited in this fashion.
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1162  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1163                 / ( "1" [ "." 0*3("0") ] )
1166  <t>
1167     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1168     relative degradation in desired quality.
1169  </t>
1175<section title="HTTP Message" anchor="http.message">
1177<section title="Message Types" anchor="message.types">
1178  <x:anchor-alias value="generic-message"/>
1179  <x:anchor-alias value="HTTP-message"/>
1180  <x:anchor-alias value="start-line"/>
1182   HTTP messages consist of requests from client to server and responses
1183   from server to client.
1185<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1186  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1189   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1190   message format of <xref target="RFC5322"/> for transferring entities (the payload
1191   of the message). Both types of message consist of a start-line, zero
1192   or more header fields (also known as "headers"), an empty line (i.e.,
1193   a line with nothing preceding the CRLF) indicating the end of the
1194   header fields, and possibly a message-body.
1196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1197  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1198                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1199                    <x:ref>CRLF</x:ref>
1200                    [ <x:ref>message-body</x:ref> ]
1201  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1204   In the interest of robustness, servers &SHOULD; ignore any empty
1205   line(s) received where a Request-Line is expected. In other words, if
1206   the server is reading the protocol stream at the beginning of a
1207   message and receives a CRLF first, it should ignore the CRLF.
1210   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1211   after a POST request. To restate what is explicitly forbidden by the
1212   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1213   extra CRLF.
1216   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1217   header field. The presence of whitespace might be an attempt to trick a
1218   noncompliant implementation of HTTP into ignoring that field or processing
1219   the next line as a new request, either of which may result in security
1220   issues when implementations within the request chain interpret the
1221   same message differently. HTTP/1.1 servers &MUST; reject such a message
1222   with a 400 (Bad Request) response.
1226<section title="Message Headers" anchor="message.headers">
1227  <x:anchor-alias value="field-content"/>
1228  <x:anchor-alias value="field-name"/>
1229  <x:anchor-alias value="field-value"/>
1230  <x:anchor-alias value="message-header"/>
1232   HTTP header fields follow the same general format as Internet messages in
1233   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1234   of a name followed by a colon (":"), optional whitespace, and the field
1235   value. Field names are case-insensitive.
1237<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"/>
1238  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1239  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1240  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1241  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1244   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1245   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1246   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1247   header field-values use only a subset of the US-ASCII charset
1248   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1249   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1250   (obs-text) octets in field-content as opaque data.
1253   No whitespace is allowed between the header field-name and colon. For
1254   security reasons, any request message received containing such whitespace
1255   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1256   whitespace in a response message &MUST; be removed.
1259   The field value &MAY; be preceded by optional whitespace; a single SP is
1260   preferred. The field-value does not include any leading or trailing white
1261   space: OWS occurring before the first non-whitespace character of the
1262   field-value or after the last non-whitespace character of the field-value
1263   is ignored and &MAY; be removed without changing the meaning of the header
1264   field.
1267   Historically, HTTP header field values could be extended over multiple
1268   lines by preceding each extra line with at least one space or horizontal
1269   tab character (line folding). This specification deprecates such line
1270   folding except within the message/http media type
1271   (<xref target=""/>).
1272   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1273   (i.e., that contain any field-content that matches the obs-fold rule) unless
1274   the message is intended for packaging within the message/http media type.
1275   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1276   obs-fold whitespace with a single SP prior to interpreting the field value
1277   or forwarding the message downstream.
1279<t anchor="rule.comment">
1280  <x:anchor-alias value="comment"/>
1281  <x:anchor-alias value="ctext"/>
1282   Comments can be included in some HTTP header fields by surrounding
1283   the comment text with parentheses. Comments are only allowed in
1284   fields containing "comment" as part of their field value definition.
1285   In all other fields, parentheses are considered part of the field
1286   value.
1288<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1289  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1290  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1293   The order in which header fields with differing field names are
1294   received is not significant. However, it is "good practice" to send
1295   general-header fields first, followed by request-header or response-header
1296   fields, and ending with the entity-header fields.
1299   Multiple message-header fields with the same field-name &MAY; be
1300   present in a message if and only if the entire field-value for that
1301   header field is defined as a comma-separated list [i.e., #(values)].
1302   It &MUST; be possible to combine the multiple header fields into one
1303   "field-name: field-value" pair, without changing the semantics of the
1304   message, by appending each subsequent field-value to the first, each
1305   separated by a comma. The order in which header fields with the same
1306   field-name are received is therefore significant to the
1307   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1308   change the order of these field values when a message is forwarded.
1311  <list><t>
1312   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1313   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1314   can occur multiple times, but does not use the list syntax, and thus cannot
1315   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1316   for details.) Also note that the Set-Cookie2 header specified in
1317   <xref target="RFC2965"/> does not share this problem.
1318  </t></list>
1323<section title="Message Body" anchor="message.body">
1324  <x:anchor-alias value="message-body"/>
1326   The message-body (if any) of an HTTP message is used to carry the
1327   entity-body associated with the request or response. The message-body
1328   differs from the entity-body only when a transfer-coding has been
1329   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1331<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1332  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1333               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1336   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1337   applied by an application to ensure safe and proper transfer of the
1338   message. Transfer-Encoding is a property of the message, not of the
1339   entity, and thus &MAY; be added or removed by any application along the
1340   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1341   when certain transfer-codings may be used.)
1344   The rules for when a message-body is allowed in a message differ for
1345   requests and responses.
1348   The presence of a message-body in a request is signaled by the
1349   inclusion of a Content-Length or Transfer-Encoding header field in
1350   the request's message-headers. A message-body &MUST-NOT; be included in
1351   a request if the specification of the request method (&method;)
1352   explicitly disallows an entity-body in requests.
1353   When a request message contains both a message-body of non-zero
1354   length and a method that does not define any semantics for that
1355   request message-body, then an origin server &SHOULD; either ignore
1356   the message-body or respond with an appropriate error message
1357   (e.g., 413).  A proxy or gateway, when presented the same request,
1358   &SHOULD; either forward the request inbound with the message-body or
1359   ignore the message-body when determining a response.
1362   For response messages, whether or not a message-body is included with
1363   a message is dependent on both the request method and the response
1364   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1365   &MUST-NOT; include a message-body, even though the presence of entity-header
1366   fields might lead one to believe they do. All 1xx
1367   (informational), 204 (No Content), and 304 (Not Modified) responses
1368   &MUST-NOT; include a message-body. All other responses do include a
1369   message-body, although it &MAY; be of zero length.
1373<section title="Message Length" anchor="message.length">
1375   The transfer-length of a message is the length of the message-body as
1376   it appears in the message; that is, after any transfer-codings have
1377   been applied. When a message-body is included with a message, the
1378   transfer-length of that body is determined by one of the following
1379   (in order of precedence):
1382  <list style="numbers">
1383    <x:lt><t>
1384     Any response message which "&MUST-NOT;" include a message-body (such
1385     as the 1xx, 204, and 304 responses and any response to a HEAD
1386     request) is always terminated by the first empty line after the
1387     header fields, regardless of the entity-header fields present in
1388     the message.
1389    </t></x:lt>
1390    <x:lt><t>
1391     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1392     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1393     is used, the transfer-length is defined by the use of this transfer-coding.
1394     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1395     is not present, the transfer-length is defined by the sender closing the connection.
1396    </t></x:lt>
1397    <x:lt><t>
1398     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1399     decimal value in OCTETs represents both the entity-length and the
1400     transfer-length. The Content-Length header field &MUST-NOT; be sent
1401     if these two lengths are different (i.e., if a Transfer-Encoding
1402     header field is present). If a message is received with both a
1403     Transfer-Encoding header field and a Content-Length header field,
1404     the latter &MUST; be ignored.
1405    </t></x:lt>
1406    <x:lt><t>
1407     If the message uses the media type "multipart/byteranges", and the
1408     transfer-length is not otherwise specified, then this self-delimiting
1409     media type defines the transfer-length. This media type
1410     &MUST-NOT; be used unless the sender knows that the recipient can parse
1411     it; the presence in a request of a Range header with multiple byte-range
1412     specifiers from a 1.1 client implies that the client can parse
1413     multipart/byteranges responses.
1414    <list style="empty"><t>
1415       A range header might be forwarded by a 1.0 proxy that does not
1416       understand multipart/byteranges; in this case the server &MUST;
1417       delimit the message using methods defined in items 1, 3 or 5 of
1418       this section.
1419    </t></list>
1420    </t></x:lt>
1421    <x:lt><t>
1422     By the server closing the connection. (Closing the connection
1423     cannot be used to indicate the end of a request body, since that
1424     would leave no possibility for the server to send back a response.)
1425    </t></x:lt>
1426  </list>
1429   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1430   containing a message-body &MUST; include a valid Content-Length header
1431   field unless the server is known to be HTTP/1.1 compliant. If a
1432   request contains a message-body and a Content-Length is not given,
1433   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1434   determine the length of the message, or with 411 (Length Required) if
1435   it wishes to insist on receiving a valid Content-Length.
1438   All HTTP/1.1 applications that receive entities &MUST; accept the
1439   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1440   to be used for messages when the message length cannot be determined
1441   in advance.
1444   Messages &MUST-NOT; include both a Content-Length header field and a
1445   transfer-coding. If the message does include a
1446   transfer-coding, the Content-Length &MUST; be ignored.
1449   When a Content-Length is given in a message where a message-body is
1450   allowed, its field value &MUST; exactly match the number of OCTETs in
1451   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1452   invalid length is received and detected.
1456<section title="General Header Fields" anchor="general.header.fields">
1457  <x:anchor-alias value="general-header"/>
1459   There are a few header fields which have general applicability for
1460   both request and response messages, but which do not apply to the
1461   entity being transferred. These header fields apply only to the
1462   message being transmitted.
1464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1465  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1466                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1467                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1468                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1469                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1470                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1471                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1472                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1473                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1476   General-header field names can be extended reliably only in
1477   combination with a change in the protocol version. However, new or
1478   experimental header fields may be given the semantics of general
1479   header fields if all parties in the communication recognize them to
1480   be general-header fields. Unrecognized header fields are treated as
1481   entity-header fields.
1486<section title="Request" anchor="request">
1487  <x:anchor-alias value="Request"/>
1489   A request message from a client to a server includes, within the
1490   first line of that message, the method to be applied to the resource,
1491   the identifier of the resource, and the protocol version in use.
1493<!--                 Host                      ; should be moved here eventually -->
1494<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1495  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1496                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1497                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1498                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1499                  <x:ref>CRLF</x:ref>
1500                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1503<section title="Request-Line" anchor="request-line">
1504  <x:anchor-alias value="Request-Line"/>
1506   The Request-Line begins with a method token, followed by the
1507   request-target and the protocol version, and ending with CRLF. The
1508   elements are separated by SP characters. No CR or LF is allowed
1509   except in the final CRLF sequence.
1511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1512  <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>
1515<section title="Method" anchor="method">
1516  <x:anchor-alias value="Method"/>
1518   The Method  token indicates the method to be performed on the
1519   resource identified by the request-target. The method is case-sensitive.
1521<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1522  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1526<section title="request-target" anchor="request-target">
1527  <x:anchor-alias value="request-target"/>
1529   The request-target
1530   identifies the resource upon which to apply the request.
1532<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1533  <x:ref>request-target</x:ref> = "*"
1534                 / <x:ref>absolute-URI</x:ref>
1535                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1536                 / <x:ref>authority</x:ref>
1539   The four options for request-target are dependent on the nature of the
1540   request. The asterisk "*" means that the request does not apply to a
1541   particular resource, but to the server itself, and is only allowed
1542   when the method used does not necessarily apply to a resource. One
1543   example would be
1545<figure><artwork type="example">
1546  OPTIONS * HTTP/1.1
1549   The absolute-URI form is &REQUIRED; when the request is being made to a
1550   proxy. The proxy is requested to forward the request or service it
1551   from a valid cache, and return the response. Note that the proxy &MAY;
1552   forward the request on to another proxy or directly to the server
1553   specified by the absolute-URI. In order to avoid request loops, a
1554   proxy &MUST; be able to recognize all of its server names, including
1555   any aliases, local variations, and the numeric IP address. An example
1556   Request-Line would be:
1558<figure><artwork type="example">
1559  GET HTTP/1.1
1562   To allow for transition to absolute-URIs in all requests in future
1563   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1564   form in requests, even though HTTP/1.1 clients will only generate
1565   them in requests to proxies.
1568   The authority form is only used by the CONNECT method (&CONNECT;).
1571   The most common form of request-target is that used to identify a
1572   resource on an origin server or gateway. In this case the absolute
1573   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1574   the request-target, and the network location of the URI (authority) &MUST;
1575   be transmitted in a Host header field. For example, a client wishing
1576   to retrieve the resource above directly from the origin server would
1577   create a TCP connection to port 80 of the host "" and send
1578   the lines:
1580<figure><artwork type="example">
1581  GET /pub/WWW/TheProject.html HTTP/1.1
1582  Host:
1585   followed by the remainder of the Request. Note that the absolute path
1586   cannot be empty; if none is present in the original URI, it &MUST; be
1587   given as "/" (the server root).
1590   If a proxy receives a request without any path in the request-target and
1591   the method specified is capable of supporting the asterisk form of
1592   request-target, then the last proxy on the request chain &MUST; forward the
1593   request with "*" as the final request-target.
1596   For example, the request
1597</preamble><artwork type="example">
1598  OPTIONS HTTP/1.1
1601  would be forwarded by the proxy as
1602</preamble><artwork type="example">
1603  OPTIONS * HTTP/1.1
1604  Host:
1607   after connecting to port 8001 of host "".
1611   The request-target is transmitted in the format specified in
1612   <xref target="http.uri"/>. If the request-target is percent-encoded
1613   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1614   &MUST; decode the request-target in order to
1615   properly interpret the request. Servers &SHOULD; respond to invalid
1616   request-targets with an appropriate status code.
1619   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1620   received request-target when forwarding it to the next inbound server,
1621   except as noted above to replace a null path-absolute with "/".
1624  <list><t>
1625      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1626      meaning of the request when the origin server is improperly using
1627      a non-reserved URI character for a reserved purpose.  Implementors
1628      should be aware that some pre-HTTP/1.1 proxies have been known to
1629      rewrite the request-target.
1630  </t></list>
1633   HTTP does not place a pre-defined limit on the length of a request-target.
1634   A server &MUST; be prepared to receive URIs of unbounded length and
1635   respond with the 414 (URI Too Long) status if the received
1636   request-target would be longer than the server wishes to handle
1637   (see &status-414;).
1640   Various ad-hoc limitations on request-target length are found in practice.
1641   It is &RECOMMENDED; that all HTTP senders and recipients support
1642   request-target lengths of 8000 or more OCTETs.
1647<section title="The Resource Identified by a Request" anchor="">
1649   The exact resource identified by an Internet request is determined by
1650   examining both the request-target and the Host header field.
1653   An origin server that does not allow resources to differ by the
1654   requested host &MAY; ignore the Host header field value when
1655   determining the resource identified by an HTTP/1.1 request. (But see
1656   <xref target=""/>
1657   for other requirements on Host support in HTTP/1.1.)
1660   An origin server that does differentiate resources based on the host
1661   requested (sometimes referred to as virtual hosts or vanity host
1662   names) &MUST; use the following rules for determining the requested
1663   resource on an HTTP/1.1 request:
1664  <list style="numbers">
1665    <t>If request-target is an absolute-URI, the host is part of the
1666     request-target. Any Host header field value in the request &MUST; be
1667     ignored.</t>
1668    <t>If the request-target is not an absolute-URI, and the request includes
1669     a Host header field, the host is determined by the Host header
1670     field value.</t>
1671    <t>If the host as determined by rule 1 or 2 is not a valid host on
1672     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1673  </list>
1676   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1677   attempt to use heuristics (e.g., examination of the URI path for
1678   something unique to a particular host) in order to determine what
1679   exact resource is being requested.
1686<section title="Response" anchor="response">
1687  <x:anchor-alias value="Response"/>
1689   After receiving and interpreting a request message, a server responds
1690   with an HTTP response message.
1692<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1693  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1694                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1695                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1696                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1697                  <x:ref>CRLF</x:ref>
1698                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1701<section title="Status-Line" anchor="status-line">
1702  <x:anchor-alias value="Status-Line"/>
1704   The first line of a Response message is the Status-Line, consisting
1705   of the protocol version followed by a numeric status code and its
1706   associated textual phrase, with each element separated by SP
1707   characters. No CR or LF is allowed except in the final CRLF sequence.
1709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1710  <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>
1713<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1714  <x:anchor-alias value="Reason-Phrase"/>
1715  <x:anchor-alias value="Status-Code"/>
1717   The Status-Code element is a 3-digit integer result code of the
1718   attempt to understand and satisfy the request. These codes are fully
1719   defined in &status-codes;.  The Reason Phrase exists for the sole
1720   purpose of providing a textual description associated with the numeric
1721   status code, out of deference to earlier Internet application protocols
1722   that were more frequently used with interactive text clients.
1723   A client &SHOULD; ignore the content of the Reason Phrase.
1726   The first digit of the Status-Code defines the class of response. The
1727   last two digits do not have any categorization role. There are 5
1728   values for the first digit:
1729  <list style="symbols">
1730    <t>
1731      1xx: Informational - Request received, continuing process
1732    </t>
1733    <t>
1734      2xx: Success - The action was successfully received,
1735        understood, and accepted
1736    </t>
1737    <t>
1738      3xx: Redirection - Further action must be taken in order to
1739        complete the request
1740    </t>
1741    <t>
1742      4xx: Client Error - The request contains bad syntax or cannot
1743        be fulfilled
1744    </t>
1745    <t>
1746      5xx: Server Error - The server failed to fulfill an apparently
1747        valid request
1748    </t>
1749  </list>
1751<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"/>
1752  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1753  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1761<section title="Connections" anchor="connections">
1763<section title="Persistent Connections" anchor="persistent.connections">
1765<section title="Purpose" anchor="persistent.purpose">
1767   Prior to persistent connections, a separate TCP connection was
1768   established to fetch each URL, increasing the load on HTTP servers
1769   and causing congestion on the Internet. The use of inline images and
1770   other associated data often require a client to make multiple
1771   requests of the same server in a short amount of time. Analysis of
1772   these performance problems and results from a prototype
1773   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1774   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1775   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1776   T/TCP <xref target="Tou1998"/>.
1779   Persistent HTTP connections have a number of advantages:
1780  <list style="symbols">
1781      <t>
1782        By opening and closing fewer TCP connections, CPU time is saved
1783        in routers and hosts (clients, servers, proxies, gateways,
1784        tunnels, or caches), and memory used for TCP protocol control
1785        blocks can be saved in hosts.
1786      </t>
1787      <t>
1788        HTTP requests and responses can be pipelined on a connection.
1789        Pipelining allows a client to make multiple requests without
1790        waiting for each response, allowing a single TCP connection to
1791        be used much more efficiently, with much lower elapsed time.
1792      </t>
1793      <t>
1794        Network congestion is reduced by reducing the number of packets
1795        caused by TCP opens, and by allowing TCP sufficient time to
1796        determine the congestion state of the network.
1797      </t>
1798      <t>
1799        Latency on subsequent requests is reduced since there is no time
1800        spent in TCP's connection opening handshake.
1801      </t>
1802      <t>
1803        HTTP can evolve more gracefully, since errors can be reported
1804        without the penalty of closing the TCP connection. Clients using
1805        future versions of HTTP might optimistically try a new feature,
1806        but if communicating with an older server, retry with old
1807        semantics after an error is reported.
1808      </t>
1809    </list>
1812   HTTP implementations &SHOULD; implement persistent connections.
1816<section title="Overall Operation" anchor="persistent.overall">
1818   A significant difference between HTTP/1.1 and earlier versions of
1819   HTTP is that persistent connections are the default behavior of any
1820   HTTP connection. That is, unless otherwise indicated, the client
1821   &SHOULD; assume that the server will maintain a persistent connection,
1822   even after error responses from the server.
1825   Persistent connections provide a mechanism by which a client and a
1826   server can signal the close of a TCP connection. This signaling takes
1827   place using the Connection header field (<xref target="header.connection"/>). Once a close
1828   has been signaled, the client &MUST-NOT; send any more requests on that
1829   connection.
1832<section title="Negotiation" anchor="persistent.negotiation">
1834   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1835   maintain a persistent connection unless a Connection header including
1836   the connection-token "close" was sent in the request. If the server
1837   chooses to close the connection immediately after sending the
1838   response, it &SHOULD; send a Connection header including the
1839   connection-token close.
1842   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1843   decide to keep it open based on whether the response from a server
1844   contains a Connection header with the connection-token close. In case
1845   the client does not want to maintain a connection for more than that
1846   request, it &SHOULD; send a Connection header including the
1847   connection-token close.
1850   If either the client or the server sends the close token in the
1851   Connection header, that request becomes the last one for the
1852   connection.
1855   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1856   maintained for HTTP versions less than 1.1 unless it is explicitly
1857   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1858   compatibility with HTTP/1.0 clients.
1861   In order to remain persistent, all messages on the connection &MUST;
1862   have a self-defined message length (i.e., one not defined by closure
1863   of the connection), as described in <xref target="message.length"/>.
1867<section title="Pipelining" anchor="pipelining">
1869   A client that supports persistent connections &MAY; "pipeline" its
1870   requests (i.e., send multiple requests without waiting for each
1871   response). A server &MUST; send its responses to those requests in the
1872   same order that the requests were received.
1875   Clients which assume persistent connections and pipeline immediately
1876   after connection establishment &SHOULD; be prepared to retry their
1877   connection if the first pipelined attempt fails. If a client does
1878   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1879   persistent. Clients &MUST; also be prepared to resend their requests if
1880   the server closes the connection before sending all of the
1881   corresponding responses.
1884   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1885   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1886   premature termination of the transport connection could lead to
1887   indeterminate results. A client wishing to send a non-idempotent
1888   request &SHOULD; wait to send that request until it has received the
1889   response status for the previous request.
1894<section title="Proxy Servers" anchor="persistent.proxy">
1896   It is especially important that proxies correctly implement the
1897   properties of the Connection header field as specified in <xref target="header.connection"/>.
1900   The proxy server &MUST; signal persistent connections separately with
1901   its clients and the origin servers (or other proxy servers) that it
1902   connects to. Each persistent connection applies to only one transport
1903   link.
1906   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1907   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1908   discussion of the problems with the Keep-Alive header implemented by
1909   many HTTP/1.0 clients).
1913<section title="Practical Considerations" anchor="persistent.practical">
1915   Servers will usually have some time-out value beyond which they will
1916   no longer maintain an inactive connection. Proxy servers might make
1917   this a higher value since it is likely that the client will be making
1918   more connections through the same server. The use of persistent
1919   connections places no requirements on the length (or existence) of
1920   this time-out for either the client or the server.
1923   When a client or server wishes to time-out it &SHOULD; issue a graceful
1924   close on the transport connection. Clients and servers &SHOULD; both
1925   constantly watch for the other side of the transport close, and
1926   respond to it as appropriate. If a client or server does not detect
1927   the other side's close promptly it could cause unnecessary resource
1928   drain on the network.
1931   A client, server, or proxy &MAY; close the transport connection at any
1932   time. For example, a client might have started to send a new request
1933   at the same time that the server has decided to close the "idle"
1934   connection. From the server's point of view, the connection is being
1935   closed while it was idle, but from the client's point of view, a
1936   request is in progress.
1939   This means that clients, servers, and proxies &MUST; be able to recover
1940   from asynchronous close events. Client software &SHOULD; reopen the
1941   transport connection and retransmit the aborted sequence of requests
1942   without user interaction so long as the request sequence is
1943   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1944   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1945   human operator the choice of retrying the request(s). Confirmation by
1946   user-agent software with semantic understanding of the application
1947   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1948   be repeated if the second sequence of requests fails.
1951   Servers &SHOULD; always respond to at least one request per connection,
1952   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1953   middle of transmitting a response, unless a network or client failure
1954   is suspected.
1957   Clients that use persistent connections &SHOULD; limit the number of
1958   simultaneous connections that they maintain to a given server. A
1959   single-user client &SHOULD-NOT; maintain more than 2 connections with
1960   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1961   another server or proxy, where N is the number of simultaneously
1962   active users. These guidelines are intended to improve HTTP response
1963   times and avoid congestion.
1968<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1970<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1972   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1973   flow control mechanisms to resolve temporary overloads, rather than
1974   terminating connections with the expectation that clients will retry.
1975   The latter technique can exacerbate network congestion.
1979<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1981   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1982   the network connection for an error status while it is transmitting
1983   the request. If the client sees an error status, it &SHOULD;
1984   immediately cease transmitting the body. If the body is being sent
1985   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1986   empty trailer &MAY; be used to prematurely mark the end of the message.
1987   If the body was preceded by a Content-Length header, the client &MUST;
1988   close the connection.
1992<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1994   The purpose of the 100 (Continue) status (see &status-100;) is to
1995   allow a client that is sending a request message with a request body
1996   to determine if the origin server is willing to accept the request
1997   (based on the request headers) before the client sends the request
1998   body. In some cases, it might either be inappropriate or highly
1999   inefficient for the client to send the body if the server will reject
2000   the message without looking at the body.
2003   Requirements for HTTP/1.1 clients:
2004  <list style="symbols">
2005    <t>
2006        If a client will wait for a 100 (Continue) response before
2007        sending the request body, it &MUST; send an Expect request-header
2008        field (&header-expect;) with the "100-continue" expectation.
2009    </t>
2010    <t>
2011        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2012        with the "100-continue" expectation if it does not intend
2013        to send a request body.
2014    </t>
2015  </list>
2018   Because of the presence of older implementations, the protocol allows
2019   ambiguous situations in which a client may send "Expect: 100-continue"
2020   without receiving either a 417 (Expectation Failed) status
2021   or a 100 (Continue) status. Therefore, when a client sends this
2022   header field to an origin server (possibly via a proxy) from which it
2023   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2024   for an indefinite period before sending the request body.
2027   Requirements for HTTP/1.1 origin servers:
2028  <list style="symbols">
2029    <t> Upon receiving a request which includes an Expect request-header
2030        field with the "100-continue" expectation, an origin server &MUST;
2031        either respond with 100 (Continue) status and continue to read
2032        from the input stream, or respond with a final status code. The
2033        origin server &MUST-NOT; wait for the request body before sending
2034        the 100 (Continue) response. If it responds with a final status
2035        code, it &MAY; close the transport connection or it &MAY; continue
2036        to read and discard the rest of the request.  It &MUST-NOT;
2037        perform the requested method if it returns a final status code.
2038    </t>
2039    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2040        the request message does not include an Expect request-header
2041        field with the "100-continue" expectation, and &MUST-NOT; send a
2042        100 (Continue) response if such a request comes from an HTTP/1.0
2043        (or earlier) client. There is an exception to this rule: for
2044        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2045        status in response to an HTTP/1.1 PUT or POST request that does
2046        not include an Expect request-header field with the "100-continue"
2047        expectation. This exception, the purpose of which is
2048        to minimize any client processing delays associated with an
2049        undeclared wait for 100 (Continue) status, applies only to
2050        HTTP/1.1 requests, and not to requests with any other HTTP-version
2051        value.
2052    </t>
2053    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2054        already received some or all of the request body for the
2055        corresponding request.
2056    </t>
2057    <t> An origin server that sends a 100 (Continue) response &MUST;
2058    ultimately send a final status code, once the request body is
2059        received and processed, unless it terminates the transport
2060        connection prematurely.
2061    </t>
2062    <t> If an origin server receives a request that does not include an
2063        Expect request-header field with the "100-continue" expectation,
2064        the request includes a request body, and the server responds
2065        with a final status code before reading the entire request body
2066        from the transport connection, then the server &SHOULD-NOT;  close
2067        the transport connection until it has read the entire request,
2068        or until the client closes the connection. Otherwise, the client
2069        might not reliably receive the response message. However, this
2070        requirement is not be construed as preventing a server from
2071        defending itself against denial-of-service attacks, or from
2072        badly broken client implementations.
2073      </t>
2074    </list>
2077   Requirements for HTTP/1.1 proxies:
2078  <list style="symbols">
2079    <t> If a proxy receives a request that includes an Expect request-header
2080        field with the "100-continue" expectation, and the proxy
2081        either knows that the next-hop server complies with HTTP/1.1 or
2082        higher, or does not know the HTTP version of the next-hop
2083        server, it &MUST; forward the request, including the Expect header
2084        field.
2085    </t>
2086    <t> If the proxy knows that the version of the next-hop server is
2087        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2088        respond with a 417 (Expectation Failed) status.
2089    </t>
2090    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2091        numbers received from recently-referenced next-hop servers.
2092    </t>
2093    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2094        request message was received from an HTTP/1.0 (or earlier)
2095        client and did not include an Expect request-header field with
2096        the "100-continue" expectation. This requirement overrides the
2097        general rule for forwarding of 1xx responses (see &status-1xx;).
2098    </t>
2099  </list>
2103<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2105   If an HTTP/1.1 client sends a request which includes a request body,
2106   but which does not include an Expect request-header field with the
2107   "100-continue" expectation, and if the client is not directly
2108   connected to an HTTP/1.1 origin server, and if the client sees the
2109   connection close before receiving any status from the server, the
2110   client &SHOULD; retry the request.  If the client does retry this
2111   request, it &MAY; use the following "binary exponential backoff"
2112   algorithm to be assured of obtaining a reliable response:
2113  <list style="numbers">
2114    <t>
2115      Initiate a new connection to the server
2116    </t>
2117    <t>
2118      Transmit the request-headers
2119    </t>
2120    <t>
2121      Initialize a variable R to the estimated round-trip time to the
2122         server (e.g., based on the time it took to establish the
2123         connection), or to a constant value of 5 seconds if the round-trip
2124         time is not available.
2125    </t>
2126    <t>
2127       Compute T = R * (2**N), where N is the number of previous
2128         retries of this request.
2129    </t>
2130    <t>
2131       Wait either for an error response from the server, or for T
2132         seconds (whichever comes first)
2133    </t>
2134    <t>
2135       If no error response is received, after T seconds transmit the
2136         body of the request.
2137    </t>
2138    <t>
2139       If client sees that the connection is closed prematurely,
2140         repeat from step 1 until the request is accepted, an error
2141         response is received, or the user becomes impatient and
2142         terminates the retry process.
2143    </t>
2144  </list>
2147   If at any point an error status is received, the client
2148  <list style="symbols">
2149      <t>&SHOULD-NOT;  continue and</t>
2151      <t>&SHOULD; close the connection if it has not completed sending the
2152        request message.</t>
2153    </list>
2160<section title="Header Field Definitions" anchor="header.fields">
2162   This section defines the syntax and semantics of HTTP/1.1 header fields
2163   related to message framing and transport protocols.
2166   For entity-header fields, both sender and recipient refer to either the
2167   client or the server, depending on who sends and who receives the entity.
2170<section title="Connection" anchor="header.connection">
2171  <iref primary="true" item="Connection header" x:for-anchor=""/>
2172  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2173  <x:anchor-alias value="Connection"/>
2174  <x:anchor-alias value="connection-token"/>
2175  <x:anchor-alias value="Connection-v"/>
2177   The general-header field "Connection" allows the sender to specify
2178   options that are desired for that particular connection and &MUST-NOT;
2179   be communicated by proxies over further connections.
2182   The Connection header's value has the following grammar:
2184<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"/>
2185  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2186  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2187  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2190   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2191   message is forwarded and, for each connection-token in this field,
2192   remove any header field(s) from the message with the same name as the
2193   connection-token. Connection options are signaled by the presence of
2194   a connection-token in the Connection header field, not by any
2195   corresponding additional header field(s), since the additional header
2196   field may not be sent if there are no parameters associated with that
2197   connection option.
2200   Message headers listed in the Connection header &MUST-NOT; include
2201   end-to-end headers, such as Cache-Control.
2204   HTTP/1.1 defines the "close" connection option for the sender to
2205   signal that the connection will be closed after completion of the
2206   response. For example,
2208<figure><artwork type="example">
2209  Connection: close
2212   in either the request or the response header fields indicates that
2213   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2214   after the current request/response is complete.
2217   An HTTP/1.1 client that does not support persistent connections &MUST;
2218   include the "close" connection option in every request message.
2221   An HTTP/1.1 server that does not support persistent connections &MUST;
2222   include the "close" connection option in every response message that
2223   does not have a 1xx (informational) status code.
2226   A system receiving an HTTP/1.0 (or lower-version) message that
2227   includes a Connection header &MUST;, for each connection-token in this
2228   field, remove and ignore any header field(s) from the message with
2229   the same name as the connection-token. This protects against mistaken
2230   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2234<section title="Content-Length" anchor="header.content-length">
2235  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2236  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2237  <x:anchor-alias value="Content-Length"/>
2238  <x:anchor-alias value="Content-Length-v"/>
2240   The entity-header field "Content-Length" indicates the size of the
2241   entity-body, in decimal number of OCTETs, sent to the recipient or,
2242   in the case of the HEAD method, the size of the entity-body that
2243   would have been sent had the request been a GET.
2245<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2246  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2247  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2250   An example is
2252<figure><artwork type="example">
2253  Content-Length: 3495
2256   Applications &SHOULD; use this field to indicate the transfer-length of
2257   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2260   Any Content-Length greater than or equal to zero is a valid value.
2261   <xref target="message.length"/> describes how to determine the length of a message-body
2262   if a Content-Length is not given.
2265   Note that the meaning of this field is significantly different from
2266   the corresponding definition in MIME, where it is an optional field
2267   used within the "message/external-body" content-type. In HTTP, it
2268   &SHOULD; be sent whenever the message's length can be determined prior
2269   to being transferred, unless this is prohibited by the rules in
2270   <xref target="message.length"/>.
2274<section title="Date" anchor="">
2275  <iref primary="true" item="Date header" x:for-anchor=""/>
2276  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2277  <x:anchor-alias value="Date"/>
2278  <x:anchor-alias value="Date-v"/>
2280   The general-header field "Date" represents the date and time at which
2281   the message was originated, having the same semantics as orig-date in
2282   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2283   HTTP-date, as described in <xref target=""/>;
2284   it &MUST; be sent in rfc1123-date format.
2286<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2287  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2288  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2291   An example is
2293<figure><artwork type="example">
2294  Date: Tue, 15 Nov 1994 08:12:31 GMT
2297   Origin servers &MUST; include a Date header field in all responses,
2298   except in these cases:
2299  <list style="numbers">
2300      <t>If the response status code is 100 (Continue) or 101 (Switching
2301         Protocols), the response &MAY; include a Date header field, at
2302         the server's option.</t>
2304      <t>If the response status code conveys a server error, e.g. 500
2305         (Internal Server Error) or 503 (Service Unavailable), and it is
2306         inconvenient or impossible to generate a valid Date.</t>
2308      <t>If the server does not have a clock that can provide a
2309         reasonable approximation of the current time, its responses
2310         &MUST-NOT; include a Date header field. In this case, the rules
2311         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2312  </list>
2315   A received message that does not have a Date header field &MUST; be
2316   assigned one by the recipient if the message will be cached by that
2317   recipient or gatewayed via a protocol which requires a Date. An HTTP
2318   implementation without a clock &MUST-NOT; cache responses without
2319   revalidating them on every use. An HTTP cache, especially a shared
2320   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2321   clock with a reliable external standard.
2324   Clients &SHOULD; only send a Date header field in messages that include
2325   an entity-body, as in the case of the PUT and POST requests, and even
2326   then it is optional. A client without a clock &MUST-NOT; send a Date
2327   header field in a request.
2330   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2331   time subsequent to the generation of the message. It &SHOULD; represent
2332   the best available approximation of the date and time of message
2333   generation, unless the implementation has no means of generating a
2334   reasonably accurate date and time. In theory, the date ought to
2335   represent the moment just before the entity is generated. In
2336   practice, the date can be generated at any time during the message
2337   origination without affecting its semantic value.
2340<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2342   Some origin server implementations might not have a clock available.
2343   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2344   values to a response, unless these values were associated
2345   with the resource by a system or user with a reliable clock. It &MAY;
2346   assign an Expires value that is known, at or before server
2347   configuration time, to be in the past (this allows "pre-expiration"
2348   of responses without storing separate Expires values for each
2349   resource).
2354<section title="Host" anchor="">
2355  <iref primary="true" item="Host header" x:for-anchor=""/>
2356  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2357  <x:anchor-alias value="Host"/>
2358  <x:anchor-alias value="Host-v"/>
2360   The request-header field "Host" specifies the Internet host and port
2361   number of the resource being requested, as obtained from the original
2362   URI given by the user or referring resource (generally an http URI,
2363   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2364   the naming authority of the origin server or gateway given by the
2365   original URL. This allows the origin server or gateway to
2366   differentiate between internally-ambiguous URLs, such as the root "/"
2367   URL of a server for multiple host names on a single IP address.
2369<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2370  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2371  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2374   A "host" without any trailing port information implies the default
2375   port for the service requested (e.g., "80" for an HTTP URL). For
2376   example, a request on the origin server for
2377   &lt;; would properly include:
2379<figure><artwork type="example">
2380  GET /pub/WWW/ HTTP/1.1
2381  Host:
2384   A client &MUST; include a Host header field in all HTTP/1.1 request
2385   messages. If the requested URI does not include an Internet host
2386   name for the service being requested, then the Host header field &MUST;
2387   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2388   request message it forwards does contain an appropriate Host header
2389   field that identifies the service being requested by the proxy. All
2390   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2391   status code to any HTTP/1.1 request message which lacks a Host header
2392   field.
2395   See Sections <xref target="" format="counter"/>
2396   and <xref target="" format="counter"/>
2397   for other requirements relating to Host.
2401<section title="TE" anchor="header.te">
2402  <iref primary="true" item="TE header" x:for-anchor=""/>
2403  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2404  <x:anchor-alias value="TE"/>
2405  <x:anchor-alias value="TE-v"/>
2406  <x:anchor-alias value="t-codings"/>
2407  <x:anchor-alias value="te-params"/>
2408  <x:anchor-alias value="te-ext"/>
2410   The request-header field "TE" indicates what extension transfer-codings
2411   it is willing to accept in the response and whether or not it is
2412   willing to accept trailer fields in a chunked transfer-coding. Its
2413   value may consist of the keyword "trailers" and/or a comma-separated
2414   list of extension transfer-coding names with optional accept
2415   parameters (as described in <xref target="transfer.codings"/>).
2417<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"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2418  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2419  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2420  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2421  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2422  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2425   The presence of the keyword "trailers" indicates that the client is
2426   willing to accept trailer fields in a chunked transfer-coding, as
2427   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2428   transfer-coding values even though it does not itself represent a
2429   transfer-coding.
2432   Examples of its use are:
2434<figure><artwork type="example">
2435  TE: deflate
2436  TE:
2437  TE: trailers, deflate;q=0.5
2440   The TE header field only applies to the immediate connection.
2441   Therefore, the keyword &MUST; be supplied within a Connection header
2442   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2445   A server tests whether a transfer-coding is acceptable, according to
2446   a TE field, using these rules:
2447  <list style="numbers">
2448    <x:lt>
2449      <t>The "chunked" transfer-coding is always acceptable. If the
2450         keyword "trailers" is listed, the client indicates that it is
2451         willing to accept trailer fields in the chunked response on
2452         behalf of itself and any downstream clients. The implication is
2453         that, if given, the client is stating that either all
2454         downstream clients are willing to accept trailer fields in the
2455         forwarded response, or that it will attempt to buffer the
2456         response on behalf of downstream recipients.
2457      </t><t>
2458         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2459         chunked response such that a client can be assured of buffering
2460         the entire response.</t>
2461    </x:lt>
2462    <x:lt>
2463      <t>If the transfer-coding being tested is one of the transfer-codings
2464         listed in the TE field, then it is acceptable unless it
2465         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2466         qvalue of 0 means "not acceptable.")</t>
2467    </x:lt>
2468    <x:lt>
2469      <t>If multiple transfer-codings are acceptable, then the
2470         acceptable transfer-coding with the highest non-zero qvalue is
2471         preferred.  The "chunked" transfer-coding always has a qvalue
2472         of 1.</t>
2473    </x:lt>
2474  </list>
2477   If the TE field-value is empty or if no TE field is present, the only
2478   transfer-coding is "chunked". A message with no transfer-coding is
2479   always acceptable.
2483<section title="Trailer" anchor="header.trailer">
2484  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2485  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2486  <x:anchor-alias value="Trailer"/>
2487  <x:anchor-alias value="Trailer-v"/>
2489   The general field "Trailer" indicates that the given set of
2490   header fields is present in the trailer of a message encoded with
2491   chunked transfer-coding.
2493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2494  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2495  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2498   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2499   message using chunked transfer-coding with a non-empty trailer. Doing
2500   so allows the recipient to know which header fields to expect in the
2501   trailer.
2504   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2505   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2506   trailer fields in a "chunked" transfer-coding.
2509   Message header fields listed in the Trailer header field &MUST-NOT;
2510   include the following header fields:
2511  <list style="symbols">
2512    <t>Transfer-Encoding</t>
2513    <t>Content-Length</t>
2514    <t>Trailer</t>
2515  </list>
2519<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2520  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2521  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2522  <x:anchor-alias value="Transfer-Encoding"/>
2523  <x:anchor-alias value="Transfer-Encoding-v"/>
2525   The general-header "Transfer-Encoding" field indicates what (if any)
2526   type of transformation has been applied to the message body in order
2527   to safely transfer it between the sender and the recipient. This
2528   differs from the content-coding in that the transfer-coding is a
2529   property of the message, not of the entity.
2531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2532  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2533                        <x:ref>Transfer-Encoding-v</x:ref>
2534  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2537   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2539<figure><artwork type="example">
2540  Transfer-Encoding: chunked
2543   If multiple encodings have been applied to an entity, the transfer-codings
2544   &MUST; be listed in the order in which they were applied.
2545   Additional information about the encoding parameters &MAY; be provided
2546   by other entity-header fields not defined by this specification.
2549   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2550   header.
2554<section title="Upgrade" anchor="header.upgrade">
2555  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2556  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2557  <x:anchor-alias value="Upgrade"/>
2558  <x:anchor-alias value="Upgrade-v"/>
2560   The general-header "Upgrade" allows the client to specify what
2561   additional communication protocols it supports and would like to use
2562   if the server finds it appropriate to switch protocols. The server
2563   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2564   response to indicate which protocol(s) are being switched.
2566<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2567  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2568  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2571   For example,
2573<figure><artwork type="example">
2574  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2577   The Upgrade header field is intended to provide a simple mechanism
2578   for transition from HTTP/1.1 to some other, incompatible protocol. It
2579   does so by allowing the client to advertise its desire to use another
2580   protocol, such as a later version of HTTP with a higher major version
2581   number, even though the current request has been made using HTTP/1.1.
2582   This eases the difficult transition between incompatible protocols by
2583   allowing the client to initiate a request in the more commonly
2584   supported protocol while indicating to the server that it would like
2585   to use a "better" protocol if available (where "better" is determined
2586   by the server, possibly according to the nature of the method and/or
2587   resource being requested).
2590   The Upgrade header field only applies to switching application-layer
2591   protocols upon the existing transport-layer connection. Upgrade
2592   cannot be used to insist on a protocol change; its acceptance and use
2593   by the server is optional. The capabilities and nature of the
2594   application-layer communication after the protocol change is entirely
2595   dependent upon the new protocol chosen, although the first action
2596   after changing the protocol &MUST; be a response to the initial HTTP
2597   request containing the Upgrade header field.
2600   The Upgrade header field only applies to the immediate connection.
2601   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2602   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2603   HTTP/1.1 message.
2606   The Upgrade header field cannot be used to indicate a switch to a
2607   protocol on a different connection. For that purpose, it is more
2608   appropriate to use a 301, 302, 303, or 305 redirection response.
2611   This specification only defines the protocol name "HTTP" for use by
2612   the family of Hypertext Transfer Protocols, as defined by the HTTP
2613   version rules of <xref target="http.version"/> and future updates to this
2614   specification. Any token can be used as a protocol name; however, it
2615   will only be useful if both the client and server associate the name
2616   with the same protocol.
2620<section title="Via" anchor="header.via">
2621  <iref primary="true" item="Via header" x:for-anchor=""/>
2622  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2623  <x:anchor-alias value="protocol-name"/>
2624  <x:anchor-alias value="protocol-version"/>
2625  <x:anchor-alias value="pseudonym"/>
2626  <x:anchor-alias value="received-by"/>
2627  <x:anchor-alias value="received-protocol"/>
2628  <x:anchor-alias value="Via"/>
2629  <x:anchor-alias value="Via-v"/>
2631   The general-header field "Via" &MUST; be used by gateways and proxies to
2632   indicate the intermediate protocols and recipients between the user
2633   agent and the server on requests, and between the origin server and
2634   the client on responses. It is analogous to the "Received" field defined in
2635   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2636   avoiding request loops, and identifying the protocol capabilities of
2637   all senders along the request/response chain.
2639<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"/>
2640  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2641  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2642                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2643  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2644  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2645  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2646  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2647  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2650   The received-protocol indicates the protocol version of the message
2651   received by the server or client along each segment of the
2652   request/response chain. The received-protocol version is appended to
2653   the Via field value when the message is forwarded so that information
2654   about the protocol capabilities of upstream applications remains
2655   visible to all recipients.
2658   The protocol-name is optional if and only if it would be "HTTP". The
2659   received-by field is normally the host and optional port number of a
2660   recipient server or client that subsequently forwarded the message.
2661   However, if the real host is considered to be sensitive information,
2662   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2663   be assumed to be the default port of the received-protocol.
2666   Multiple Via field values represents each proxy or gateway that has
2667   forwarded the message. Each recipient &MUST; append its information
2668   such that the end result is ordered according to the sequence of
2669   forwarding applications.
2672   Comments &MAY; be used in the Via header field to identify the software
2673   of the recipient proxy or gateway, analogous to the User-Agent and
2674   Server header fields. However, all comments in the Via field are
2675   optional and &MAY; be removed by any recipient prior to forwarding the
2676   message.
2679   For example, a request message could be sent from an HTTP/1.0 user
2680   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2681   forward the request to a public proxy at, which completes
2682   the request by forwarding it to the origin server at
2683   The request received by would then have the following
2684   Via header field:
2686<figure><artwork type="example">
2687  Via: 1.0 fred, 1.1 (Apache/1.1)
2690   Proxies and gateways used as a portal through a network firewall
2691   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2692   the firewall region. This information &SHOULD; only be propagated if
2693   explicitly enabled. If not enabled, the received-by host of any host
2694   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2695   for that host.
2698   For organizations that have strong privacy requirements for hiding
2699   internal structures, a proxy &MAY; combine an ordered subsequence of
2700   Via header field entries with identical received-protocol values into
2701   a single such entry. For example,
2703<figure><artwork type="example">
2704  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2707        could be collapsed to
2709<figure><artwork type="example">
2710  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2713   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2714   under the same organizational control and the hosts have already been
2715   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2716   have different received-protocol values.
2722<section title="IANA Considerations" anchor="IANA.considerations">
2723<section title="Message Header Registration" anchor="message.header.registration">
2725   The Message Header Registry located at <eref target=""/> should be updated
2726   with the permanent registrations below (see <xref target="RFC3864"/>):
2728<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2729<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2730   <ttcol>Header Field Name</ttcol>
2731   <ttcol>Protocol</ttcol>
2732   <ttcol>Status</ttcol>
2733   <ttcol>Reference</ttcol>
2735   <c>Connection</c>
2736   <c>http</c>
2737   <c>standard</c>
2738   <c>
2739      <xref target="header.connection"/>
2740   </c>
2741   <c>Content-Length</c>
2742   <c>http</c>
2743   <c>standard</c>
2744   <c>
2745      <xref target="header.content-length"/>
2746   </c>
2747   <c>Date</c>
2748   <c>http</c>
2749   <c>standard</c>
2750   <c>
2751      <xref target=""/>
2752   </c>
2753   <c>Host</c>
2754   <c>http</c>
2755   <c>standard</c>
2756   <c>
2757      <xref target=""/>
2758   </c>
2759   <c>TE</c>
2760   <c>http</c>
2761   <c>standard</c>
2762   <c>
2763      <xref target="header.te"/>
2764   </c>
2765   <c>Trailer</c>
2766   <c>http</c>
2767   <c>standard</c>
2768   <c>
2769      <xref target="header.trailer"/>
2770   </c>
2771   <c>Transfer-Encoding</c>
2772   <c>http</c>
2773   <c>standard</c>
2774   <c>
2775      <xref target="header.transfer-encoding"/>
2776   </c>
2777   <c>Upgrade</c>
2778   <c>http</c>
2779   <c>standard</c>
2780   <c>
2781      <xref target="header.upgrade"/>
2782   </c>
2783   <c>Via</c>
2784   <c>http</c>
2785   <c>standard</c>
2786   <c>
2787      <xref target="header.via"/>
2788   </c>
2792   The change controller is: "IETF ( - Internet Engineering Task Force".
2796<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2798   The entry for the "http" URI Scheme in the registry located at
2799   <eref target=""/>
2800   should be updated to point to <xref target="http.uri"/> of this document
2801   (see <xref target="RFC4395"/>).
2805<section title="Internet Media Type Registrations" anchor="">
2807   This document serves as the specification for the Internet media types
2808   "message/http" and "application/http". The following is to be registered with
2809   IANA (see <xref target="RFC4288"/>).
2811<section title="Internet Media Type message/http" anchor="">
2812<iref item="Media Type" subitem="message/http" primary="true"/>
2813<iref item="message/http Media Type" primary="true"/>
2815   The message/http type can be used to enclose a single HTTP request or
2816   response message, provided that it obeys the MIME restrictions for all
2817   "message" types regarding line length and encodings.
2820  <list style="hanging" x:indent="12em">
2821    <t hangText="Type name:">
2822      message
2823    </t>
2824    <t hangText="Subtype name:">
2825      http
2826    </t>
2827    <t hangText="Required parameters:">
2828      none
2829    </t>
2830    <t hangText="Optional parameters:">
2831      version, msgtype
2832      <list style="hanging">
2833        <t hangText="version:">
2834          The HTTP-Version number of the enclosed message
2835          (e.g., "1.1"). If not present, the version can be
2836          determined from the first line of the body.
2837        </t>
2838        <t hangText="msgtype:">
2839          The message type -- "request" or "response". If not
2840          present, the type can be determined from the first
2841          line of the body.
2842        </t>
2843      </list>
2844    </t>
2845    <t hangText="Encoding considerations:">
2846      only "7bit", "8bit", or "binary" are permitted
2847    </t>
2848    <t hangText="Security considerations:">
2849      none
2850    </t>
2851    <t hangText="Interoperability considerations:">
2852      none
2853    </t>
2854    <t hangText="Published specification:">
2855      This specification (see <xref target=""/>).
2856    </t>
2857    <t hangText="Applications that use this media type:">
2858    </t>
2859    <t hangText="Additional information:">
2860      <list style="hanging">
2861        <t hangText="Magic number(s):">none</t>
2862        <t hangText="File extension(s):">none</t>
2863        <t hangText="Macintosh file type code(s):">none</t>
2864      </list>
2865    </t>
2866    <t hangText="Person and email address to contact for further information:">
2867      See Authors Section.
2868    </t>
2869                <t hangText="Intended usage:">
2870                  COMMON
2871    </t>
2872                <t hangText="Restrictions on usage:">
2873                  none
2874    </t>
2875    <t hangText="Author/Change controller:">
2876      IESG
2877    </t>
2878  </list>
2881<section title="Internet Media Type application/http" anchor="">
2882<iref item="Media Type" subitem="application/http" primary="true"/>
2883<iref item="application/http Media Type" primary="true"/>
2885   The application/http type can be used to enclose a pipeline of one or more
2886   HTTP request or response messages (not intermixed).
2889  <list style="hanging" x:indent="12em">
2890    <t hangText="Type name:">
2891      application
2892    </t>
2893    <t hangText="Subtype name:">
2894      http
2895    </t>
2896    <t hangText="Required parameters:">
2897      none
2898    </t>
2899    <t hangText="Optional parameters:">
2900      version, msgtype
2901      <list style="hanging">
2902        <t hangText="version:">
2903          The HTTP-Version number of the enclosed messages
2904          (e.g., "1.1"). If not present, the version can be
2905          determined from the first line of the body.
2906        </t>
2907        <t hangText="msgtype:">
2908          The message type -- "request" or "response". If not
2909          present, the type can be determined from the first
2910          line of the body.
2911        </t>
2912      </list>
2913    </t>
2914    <t hangText="Encoding considerations:">
2915      HTTP messages enclosed by this type
2916      are in "binary" format; use of an appropriate
2917      Content-Transfer-Encoding is required when
2918      transmitted via E-mail.
2919    </t>
2920    <t hangText="Security considerations:">
2921      none
2922    </t>
2923    <t hangText="Interoperability considerations:">
2924      none
2925    </t>
2926    <t hangText="Published specification:">
2927      This specification (see <xref target=""/>).
2928    </t>
2929    <t hangText="Applications that use this media type:">
2930    </t>
2931    <t hangText="Additional information:">
2932      <list style="hanging">
2933        <t hangText="Magic number(s):">none</t>
2934        <t hangText="File extension(s):">none</t>
2935        <t hangText="Macintosh file type code(s):">none</t>
2936      </list>
2937    </t>
2938    <t hangText="Person and email address to contact for further information:">
2939      See Authors Section.
2940    </t>
2941                <t hangText="Intended usage:">
2942                  COMMON
2943    </t>
2944                <t hangText="Restrictions on usage:">
2945                  none
2946    </t>
2947    <t hangText="Author/Change controller:">
2948      IESG
2949    </t>
2950  </list>
2957<section title="Security Considerations" anchor="security.considerations">
2959   This section is meant to inform application developers, information
2960   providers, and users of the security limitations in HTTP/1.1 as
2961   described by this document. The discussion does not include
2962   definitive solutions to the problems revealed, though it does make
2963   some suggestions for reducing security risks.
2966<section title="Personal Information" anchor="personal.information">
2968   HTTP clients are often privy to large amounts of personal information
2969   (e.g. the user's name, location, mail address, passwords, encryption
2970   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2971   leakage of this information.
2972   We very strongly recommend that a convenient interface be provided
2973   for the user to control dissemination of such information, and that
2974   designers and implementors be particularly careful in this area.
2975   History shows that errors in this area often create serious security
2976   and/or privacy problems and generate highly adverse publicity for the
2977   implementor's company.
2981<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2983   A server is in the position to save personal data about a user's
2984   requests which might identify their reading patterns or subjects of
2985   interest. This information is clearly confidential in nature and its
2986   handling can be constrained by law in certain countries. People using
2987   HTTP to provide data are responsible for ensuring that
2988   such material is not distributed without the permission of any
2989   individuals that are identifiable by the published results.
2993<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2995   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2996   the documents returned by HTTP requests to be only those that were
2997   intended by the server administrators. If an HTTP server translates
2998   HTTP URIs directly into file system calls, the server &MUST; take
2999   special care not to serve files that were not intended to be
3000   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3001   other operating systems use ".." as a path component to indicate a
3002   directory level above the current one. On such a system, an HTTP
3003   server &MUST; disallow any such construct in the request-target if it
3004   would otherwise allow access to a resource outside those intended to
3005   be accessible via the HTTP server. Similarly, files intended for
3006   reference only internally to the server (such as access control
3007   files, configuration files, and script code) &MUST; be protected from
3008   inappropriate retrieval, since they might contain sensitive
3009   information. Experience has shown that minor bugs in such HTTP server
3010   implementations have turned into security risks.
3014<section title="DNS Spoofing" anchor="dns.spoofing">
3016   Clients using HTTP rely heavily on the Domain Name Service, and are
3017   thus generally prone to security attacks based on the deliberate
3018   mis-association of IP addresses and DNS names. Clients need to be
3019   cautious in assuming the continuing validity of an IP number/DNS name
3020   association.
3023   In particular, HTTP clients &SHOULD; rely on their name resolver for
3024   confirmation of an IP number/DNS name association, rather than
3025   caching the result of previous host name lookups. Many platforms
3026   already can cache host name lookups locally when appropriate, and
3027   they &SHOULD; be configured to do so. It is proper for these lookups to
3028   be cached, however, only when the TTL (Time To Live) information
3029   reported by the name server makes it likely that the cached
3030   information will remain useful.
3033   If HTTP clients cache the results of host name lookups in order to
3034   achieve a performance improvement, they &MUST; observe the TTL
3035   information reported by DNS.
3038   If HTTP clients do not observe this rule, they could be spoofed when
3039   a previously-accessed server's IP address changes. As network
3040   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3041   possibility of this form of attack will grow. Observing this
3042   requirement thus reduces this potential security vulnerability.
3045   This requirement also improves the load-balancing behavior of clients
3046   for replicated servers using the same DNS name and reduces the
3047   likelihood of a user's experiencing failure in accessing sites which
3048   use that strategy.
3052<section title="Proxies and Caching" anchor="attack.proxies">
3054   By their very nature, HTTP proxies are men-in-the-middle, and
3055   represent an opportunity for man-in-the-middle attacks. Compromise of
3056   the systems on which the proxies run can result in serious security
3057   and privacy problems. Proxies have access to security-related
3058   information, personal information about individual users and
3059   organizations, and proprietary information belonging to users and
3060   content providers. A compromised proxy, or a proxy implemented or
3061   configured without regard to security and privacy considerations,
3062   might be used in the commission of a wide range of potential attacks.
3065   Proxy operators should protect the systems on which proxies run as
3066   they would protect any system that contains or transports sensitive
3067   information. In particular, log information gathered at proxies often
3068   contains highly sensitive personal information, and/or information
3069   about organizations. Log information should be carefully guarded, and
3070   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3073   Proxy implementors should consider the privacy and security
3074   implications of their design and coding decisions, and of the
3075   configuration options they provide to proxy operators (especially the
3076   default configuration).
3079   Users of a proxy need to be aware that they are no trustworthier than
3080   the people who run the proxy; HTTP itself cannot solve this problem.
3083   The judicious use of cryptography, when appropriate, may suffice to
3084   protect against a broad range of security and privacy attacks. Such
3085   cryptography is beyond the scope of the HTTP/1.1 specification.
3089<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3091   They exist. They are hard to defend against. Research continues.
3092   Beware.
3097<section title="Acknowledgments" anchor="ack">
3099   HTTP has evolved considerably over the years. It has
3100   benefited from a large and active developer community--the many
3101   people who have participated on the www-talk mailing list--and it is
3102   that community which has been most responsible for the success of
3103   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3104   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3105   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3106   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3107   VanHeyningen deserve special recognition for their efforts in
3108   defining early aspects of the protocol.
3111   This document has benefited greatly from the comments of all those
3112   participating in the HTTP-WG. In addition to those already mentioned,
3113   the following individuals have contributed to this specification:
3116   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3117   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3118   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3119   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3120   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3121   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3122   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3123   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3124   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3125   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3126   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3127   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3128   Josh Cohen.
3131   Thanks to the "cave men" of Palo Alto. You know who you are.
3134   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3135   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3136   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3137   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3138   Larry Masinter for their help. And thanks go particularly to Jeff
3139   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3142   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3143   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3144   discovery of many of the problems that this document attempts to
3145   rectify.
3148   This specification makes heavy use of the augmented BNF and generic
3149   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3150   reuses many of the definitions provided by Nathaniel Borenstein and
3151   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3152   specification will help reduce past confusion over the relationship
3153   between HTTP and Internet mail message formats.
3160<references title="Normative References">
3162<reference anchor="ISO-8859-1">
3163  <front>
3164    <title>
3165     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3166    </title>
3167    <author>
3168      <organization>International Organization for Standardization</organization>
3169    </author>
3170    <date year="1998"/>
3171  </front>
3172  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3175<reference anchor="Part2">
3176  <front>
3177    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3178    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3179      <organization abbrev="Day Software">Day Software</organization>
3180      <address><email></email></address>
3181    </author>
3182    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3183      <organization>One Laptop per Child</organization>
3184      <address><email></email></address>
3185    </author>
3186    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3187      <organization abbrev="HP">Hewlett-Packard Company</organization>
3188      <address><email></email></address>
3189    </author>
3190    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3191      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3192      <address><email></email></address>
3193    </author>
3194    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3195      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3196      <address><email></email></address>
3197    </author>
3198    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3199      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3200      <address><email></email></address>
3201    </author>
3202    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3203      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3204      <address><email></email></address>
3205    </author>
3206    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3207      <organization abbrev="W3C">World Wide Web Consortium</organization>
3208      <address><email></email></address>
3209    </author>
3210    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3211      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3212      <address><email></email></address>
3213    </author>
3214    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3215  </front>
3216  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3217  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3220<reference anchor="Part3">
3221  <front>
3222    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3223    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3224      <organization abbrev="Day Software">Day Software</organization>
3225      <address><email></email></address>
3226    </author>
3227    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3228      <organization>One Laptop per Child</organization>
3229      <address><email></email></address>
3230    </author>
3231    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3232      <organization abbrev="HP">Hewlett-Packard Company</organization>
3233      <address><email></email></address>
3234    </author>
3235    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3236      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3237      <address><email></email></address>
3238    </author>
3239    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3240      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3241      <address><email></email></address>
3242    </author>
3243    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3244      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3245      <address><email></email></address>
3246    </author>
3247    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3248      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3249      <address><email></email></address>
3250    </author>
3251    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3252      <organization abbrev="W3C">World Wide Web Consortium</organization>
3253      <address><email></email></address>
3254    </author>
3255    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3256      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3257      <address><email></email></address>
3258    </author>
3259    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3260  </front>
3261  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3262  <x:source href="p3-payload.xml" basename="p3-payload"/>
3265<reference anchor="Part5">
3266  <front>
3267    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3268    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3269      <organization abbrev="Day Software">Day Software</organization>
3270      <address><email></email></address>
3271    </author>
3272    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3273      <organization>One Laptop per Child</organization>
3274      <address><email></email></address>
3275    </author>
3276    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3277      <organization abbrev="HP">Hewlett-Packard Company</organization>
3278      <address><email></email></address>
3279    </author>
3280    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3281      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3282      <address><email></email></address>
3283    </author>
3284    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3285      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3286      <address><email></email></address>
3287    </author>
3288    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3289      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3290      <address><email></email></address>
3291    </author>
3292    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3293      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3294      <address><email></email></address>
3295    </author>
3296    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3297      <organization abbrev="W3C">World Wide Web Consortium</organization>
3298      <address><email></email></address>
3299    </author>
3300    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3301      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3302      <address><email></email></address>
3303    </author>
3304    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3305  </front>
3306  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3307  <x:source href="p5-range.xml" basename="p5-range"/>
3310<reference anchor="Part6">
3311  <front>
3312    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3313    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3314      <organization abbrev="Day Software">Day Software</organization>
3315      <address><email></email></address>
3316    </author>
3317    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3318      <organization>One Laptop per Child</organization>
3319      <address><email></email></address>
3320    </author>
3321    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3322      <organization abbrev="HP">Hewlett-Packard Company</organization>
3323      <address><email></email></address>
3324    </author>
3325    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3326      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3327      <address><email></email></address>
3328    </author>
3329    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3330      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3331      <address><email></email></address>
3332    </author>
3333    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3334      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3335      <address><email></email></address>
3336    </author>
3337    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3338      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3339      <address><email></email></address>
3340    </author>
3341    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3342      <organization abbrev="W3C">World Wide Web Consortium</organization>
3343      <address><email></email></address>
3344    </author>
3345    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3346      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3347      <address><email></email></address>
3348    </author>
3349    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3350  </front>
3351  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3352  <x:source href="p6-cache.xml" basename="p6-cache"/>
3355<reference anchor="RFC5234">
3356  <front>
3357    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3358    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3359      <organization>Brandenburg InternetWorking</organization>
3360      <address>
3361      <postal>
3362      <street>675 Spruce Dr.</street>
3363      <city>Sunnyvale</city>
3364      <region>CA</region>
3365      <code>94086</code>
3366      <country>US</country></postal>
3367      <phone>+1.408.246.8253</phone>
3368      <email></email></address> 
3369    </author>
3370    <author initials="P." surname="Overell" fullname="Paul Overell">
3371      <organization>THUS plc.</organization>
3372      <address>
3373      <postal>
3374      <street>1/2 Berkeley Square</street>
3375      <street>99 Berkely Street</street>
3376      <city>Glasgow</city>
3377      <code>G3 7HR</code>
3378      <country>UK</country></postal>
3379      <email></email></address>
3380    </author>
3381    <date month="January" year="2008"/>
3382  </front>
3383  <seriesInfo name="STD" value="68"/>
3384  <seriesInfo name="RFC" value="5234"/>
3387<reference anchor="RFC2119">
3388  <front>
3389    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3390    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3391      <organization>Harvard University</organization>
3392      <address><email></email></address>
3393    </author>
3394    <date month="March" year="1997"/>
3395  </front>
3396  <seriesInfo name="BCP" value="14"/>
3397  <seriesInfo name="RFC" value="2119"/>
3400<reference anchor="RFC3986">
3401 <front>
3402  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3403  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3404    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3405    <address>
3406       <email></email>
3407       <uri></uri>
3408    </address>
3409  </author>
3410  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3411    <organization abbrev="Day Software">Day Software</organization>
3412    <address>
3413      <email></email>
3414      <uri></uri>
3415    </address>
3416  </author>
3417  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3418    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3419    <address>
3420      <email></email>
3421      <uri></uri>
3422    </address>
3423  </author>
3424  <date month='January' year='2005'></date>
3425 </front>
3426 <seriesInfo name="RFC" value="3986"/>
3427 <seriesInfo name="STD" value="66"/>
3430<reference anchor="USASCII">
3431  <front>
3432    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3433    <author>
3434      <organization>American National Standards Institute</organization>
3435    </author>
3436    <date year="1986"/>
3437  </front>
3438  <seriesInfo name="ANSI" value="X3.4"/>
3443<references title="Informative References">
3445<reference anchor="Nie1997" target="">
3446  <front>
3447    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3448    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3449      <organization/>
3450    </author>
3451    <author initials="J." surname="Gettys" fullname="J. Gettys">
3452      <organization/>
3453    </author>
3454    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3455      <organization/>
3456    </author>
3457    <author initials="H." surname="Lie" fullname="H. Lie">
3458      <organization/>
3459    </author>
3460    <author initials="C." surname="Lilley" fullname="C. Lilley">
3461      <organization/>
3462    </author>
3463    <date year="1997" month="September"/>
3464  </front>
3465  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3468<reference anchor="Pad1995" target="">
3469  <front>
3470    <title>Improving HTTP Latency</title>
3471    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3472      <organization/>
3473    </author>
3474    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3475      <organization/>
3476    </author>
3477    <date year="1995" month="December"/>
3478  </front>
3479  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3482<reference anchor="RFC1123">
3483  <front>
3484    <title>Requirements for Internet Hosts - Application and Support</title>
3485    <author initials="R." surname="Braden" fullname="Robert Braden">
3486      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3487      <address><email>Braden@ISI.EDU</email></address>
3488    </author>
3489    <date month="October" year="1989"/>
3490  </front>
3491  <seriesInfo name="STD" value="3"/>
3492  <seriesInfo name="RFC" value="1123"/>
3495<reference anchor="RFC1305">
3496  <front>
3497    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3498    <author initials="D." surname="Mills" fullname="David L. Mills">
3499      <organization>University of Delaware, Electrical Engineering Department</organization>
3500      <address><email></email></address>
3501    </author>
3502    <date month="March" year="1992"/>
3503  </front>
3504  <seriesInfo name="RFC" value="1305"/>
3507<reference anchor="RFC1900">
3508  <front>
3509    <title>Renumbering Needs Work</title>
3510    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3511      <organization>CERN, Computing and Networks Division</organization>
3512      <address><email></email></address>
3513    </author>
3514    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3515      <organization>cisco Systems</organization>
3516      <address><email></email></address>
3517    </author>
3518    <date month="February" year="1996"/>
3519  </front>
3520  <seriesInfo name="RFC" value="1900"/>
3523<reference anchor="RFC1945">
3524  <front>
3525    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3526    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3527      <organization>MIT, Laboratory for Computer Science</organization>
3528      <address><email></email></address>
3529    </author>
3530    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3531      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3532      <address><email></email></address>
3533    </author>
3534    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3535      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3536      <address><email></email></address>
3537    </author>
3538    <date month="May" year="1996"/>
3539  </front>
3540  <seriesInfo name="RFC" value="1945"/>
3543<reference anchor="RFC2045">
3544  <front>
3545    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3546    <author initials="N." surname="Freed" fullname="Ned Freed">
3547      <organization>Innosoft International, Inc.</organization>
3548      <address><email></email></address>
3549    </author>
3550    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3551      <organization>First Virtual Holdings</organization>
3552      <address><email></email></address>
3553    </author>
3554    <date month="November" year="1996"/>
3555  </front>
3556  <seriesInfo name="RFC" value="2045"/>
3559<reference anchor="RFC2047">
3560  <front>
3561    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3562    <author initials="K." surname="Moore" fullname="Keith Moore">
3563      <organization>University of Tennessee</organization>
3564      <address><email></email></address>
3565    </author>
3566    <date month="November" year="1996"/>
3567  </front>
3568  <seriesInfo name="RFC" value="2047"/>
3571<reference anchor="RFC2068">
3572  <front>
3573    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3574    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3575      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3576      <address><email></email></address>
3577    </author>
3578    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3579      <organization>MIT Laboratory for Computer Science</organization>
3580      <address><email></email></address>
3581    </author>
3582    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3583      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3584      <address><email></email></address>
3585    </author>
3586    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3587      <organization>MIT Laboratory for Computer Science</organization>
3588      <address><email></email></address>
3589    </author>
3590    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3591      <organization>MIT Laboratory for Computer Science</organization>
3592      <address><email></email></address>
3593    </author>
3594    <date month="January" year="1997"/>
3595  </front>
3596  <seriesInfo name="RFC" value="2068"/>
3599<reference anchor='RFC2109'>
3600  <front>
3601    <title>HTTP State Management Mechanism</title>
3602    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3603      <organization>Bell Laboratories, Lucent Technologies</organization>
3604      <address><email></email></address>
3605    </author>
3606    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3607      <organization>Netscape Communications Corp.</organization>
3608      <address><email></email></address>
3609    </author>
3610    <date year='1997' month='February' />
3611  </front>
3612  <seriesInfo name='RFC' value='2109' />
3615<reference anchor="RFC2145">
3616  <front>
3617    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3618    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3619      <organization>Western Research Laboratory</organization>
3620      <address><email></email></address>
3621    </author>
3622    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3623      <organization>Department of Information and Computer Science</organization>
3624      <address><email></email></address>
3625    </author>
3626    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3627      <organization>MIT Laboratory for Computer Science</organization>
3628      <address><email></email></address>
3629    </author>
3630    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3631      <organization>W3 Consortium</organization>
3632      <address><email></email></address>
3633    </author>
3634    <date month="May" year="1997"/>
3635  </front>
3636  <seriesInfo name="RFC" value="2145"/>
3639<reference anchor="RFC2616">
3640  <front>
3641    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3642    <author initials="R." surname="Fielding" fullname="R. Fielding">
3643      <organization>University of California, Irvine</organization>
3644      <address><email></email></address>
3645    </author>
3646    <author initials="J." surname="Gettys" fullname="J. Gettys">
3647      <organization>W3C</organization>
3648      <address><email></email></address>
3649    </author>
3650    <author initials="J." surname="Mogul" fullname="J. Mogul">
3651      <organization>Compaq Computer Corporation</organization>
3652      <address><email></email></address>
3653    </author>
3654    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3655      <organization>MIT Laboratory for Computer Science</organization>
3656      <address><email></email></address>
3657    </author>
3658    <author initials="L." surname="Masinter" fullname="L. Masinter">
3659      <organization>Xerox Corporation</organization>
3660      <address><email></email></address>
3661    </author>
3662    <author initials="P." surname="Leach" fullname="P. Leach">
3663      <organization>Microsoft Corporation</organization>
3664      <address><email></email></address>
3665    </author>
3666    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3667      <organization>W3C</organization>
3668      <address><email></email></address>
3669    </author>
3670    <date month="June" year="1999"/>
3671  </front>
3672  <seriesInfo name="RFC" value="2616"/>
3675<reference anchor='RFC2818'>
3676  <front>
3677    <title>HTTP Over TLS</title>
3678    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3679      <organization>RTFM, Inc.</organization>
3680      <address><email></email></address>
3681    </author>
3682    <date year='2000' month='May' />
3683  </front>
3684  <seriesInfo name='RFC' value='2818' />
3687<reference anchor='RFC2965'>
3688  <front>
3689    <title>HTTP State Management Mechanism</title>
3690    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3691      <organization>Bell Laboratories, Lucent Technologies</organization>
3692      <address><email></email></address>
3693    </author>
3694    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3695      <organization>, Inc.</organization>
3696      <address><email></email></address>
3697    </author>
3698    <date year='2000' month='October' />
3699  </front>
3700  <seriesInfo name='RFC' value='2965' />
3703<reference anchor='RFC3864'>
3704  <front>
3705    <title>Registration Procedures for Message Header Fields</title>
3706    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3707      <organization>Nine by Nine</organization>
3708      <address><email></email></address>
3709    </author>
3710    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3711      <organization>BEA Systems</organization>
3712      <address><email></email></address>
3713    </author>
3714    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3715      <organization>HP Labs</organization>
3716      <address><email></email></address>
3717    </author>
3718    <date year='2004' month='September' />
3719  </front>
3720  <seriesInfo name='BCP' value='90' />
3721  <seriesInfo name='RFC' value='3864' />
3724<reference anchor="RFC4288">
3725  <front>
3726    <title>Media Type Specifications and Registration Procedures</title>
3727    <author initials="N." surname="Freed" fullname="N. Freed">
3728      <organization>Sun Microsystems</organization>
3729      <address>
3730        <email></email>
3731      </address>
3732    </author>
3733    <author initials="J." surname="Klensin" fullname="J. Klensin">
3734      <organization/>
3735      <address>
3736        <email></email>
3737      </address>
3738    </author>
3739    <date year="2005" month="December"/>
3740  </front>
3741  <seriesInfo name="BCP" value="13"/>
3742  <seriesInfo name="RFC" value="4288"/>
3745<reference anchor='RFC4395'>
3746  <front>
3747    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3748    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3749      <organization>AT&amp;T Laboratories</organization>
3750      <address>
3751        <email></email>
3752      </address>
3753    </author>
3754    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3755      <organization>Qualcomm, Inc.</organization>
3756      <address>
3757        <email></email>
3758      </address>
3759    </author>
3760    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3761      <organization>Adobe Systems</organization>
3762      <address>
3763        <email></email>
3764      </address>
3765    </author>
3766    <date year='2006' month='February' />
3767  </front>
3768  <seriesInfo name='BCP' value='115' />
3769  <seriesInfo name='RFC' value='4395' />
3772<reference anchor="RFC5322">
3773  <front>
3774    <title>Internet Message Format</title>
3775    <author initials="P." surname="Resnick" fullname="P. Resnick">
3776      <organization>Qualcomm Incorporated</organization>
3777    </author>
3778    <date year="2008" month="October"/>
3779  </front>
3780  <seriesInfo name="RFC" value="5322"/>
3783<reference anchor="Kri2001" target="">
3784  <front>
3785    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3786    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3787      <organization/>
3788    </author>
3789    <date year="2001" month="November"/>
3790  </front>
3791  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3794<reference anchor="Spe" target="">
3795  <front>
3796  <title>Analysis of HTTP Performance Problems</title>
3797  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3798    <organization/>
3799  </author>
3800  <date/>
3801  </front>
3804<reference anchor="Tou1998" target="">
3805  <front>
3806  <title>Analysis of HTTP Performance</title>
3807  <author initials="J." surname="Touch" fullname="Joe Touch">
3808    <organization>USC/Information Sciences Institute</organization>
3809    <address><email></email></address>
3810  </author>
3811  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3812    <organization>USC/Information Sciences Institute</organization>
3813    <address><email></email></address>
3814  </author>
3815  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3816    <organization>USC/Information Sciences Institute</organization>
3817    <address><email></email></address>
3818  </author>
3819  <date year="1998" month="Aug"/>
3820  </front>
3821  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3822  <annotation>(original report dated Aug. 1996)</annotation>
3828<section title="Tolerant Applications" anchor="tolerant.applications">
3830   Although this document specifies the requirements for the generation
3831   of HTTP/1.1 messages, not all applications will be correct in their
3832   implementation. We therefore recommend that operational applications
3833   be tolerant of deviations whenever those deviations can be
3834   interpreted unambiguously.
3837   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3838   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3839   accept any amount of WSP characters between fields, even though
3840   only a single SP is required.
3843   The line terminator for message-header fields is the sequence CRLF.
3844   However, we recommend that applications, when parsing such headers,
3845   recognize a single LF as a line terminator and ignore the leading CR.
3848   The character set of an entity-body &SHOULD; be labeled as the lowest
3849   common denominator of the character codes used within that body, with
3850   the exception that not labeling the entity is preferred over labeling
3851   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3854   Additional rules for requirements on parsing and encoding of dates
3855   and other potential problems with date encodings include:
3858  <list style="symbols">
3859     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3860        which appears to be more than 50 years in the future is in fact
3861        in the past (this helps solve the "year 2000" problem).</t>
3863     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3864        Expires date as earlier than the proper value, but &MUST-NOT;
3865        internally represent a parsed Expires date as later than the
3866        proper value.</t>
3868     <t>All expiration-related calculations &MUST; be done in GMT. The
3869        local time zone &MUST-NOT; influence the calculation or comparison
3870        of an age or expiration time.</t>
3872     <t>If an HTTP header incorrectly carries a date value with a time
3873        zone other than GMT, it &MUST; be converted into GMT using the
3874        most conservative possible conversion.</t>
3875  </list>
3879<section title="Compatibility with Previous Versions" anchor="compatibility">
3881   HTTP has been in use by the World-Wide Web global information initiative
3882   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3883   was a simple protocol for hypertext data transfer across the Internet
3884   with only a single method and no metadata.
3885   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3886   methods and MIME-like messaging that could include metadata about the data
3887   transferred and modifiers on the request/response semantics. However,
3888   HTTP/1.0 did not sufficiently take into consideration the effects of
3889   hierarchical proxies, caching, the need for persistent connections, or
3890   name-based virtual hosts. The proliferation of incompletely-implemented
3891   applications calling themselves "HTTP/1.0" further necessitated a
3892   protocol version change in order for two communicating applications
3893   to determine each other's true capabilities.
3896   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3897   requirements that enable reliable implementations, adding only
3898   those new features that will either be safely ignored by an HTTP/1.0
3899   recipient or only sent when communicating with a party advertising
3900   compliance with HTTP/1.1.
3903   It is beyond the scope of a protocol specification to mandate
3904   compliance with previous versions. HTTP/1.1 was deliberately
3905   designed, however, to make supporting previous versions easy. It is
3906   worth noting that, at the time of composing this specification
3907   (1996), we would expect commercial HTTP/1.1 servers to:
3908  <list style="symbols">
3909     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3910        1.1 requests;</t>
3912     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3913        1.1;</t>
3915     <t>respond appropriately with a message in the same major version
3916        used by the client.</t>
3917  </list>
3920   And we would expect HTTP/1.1 clients to:
3921  <list style="symbols">
3922     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3923        responses;</t>
3925     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3926        1.1.</t>
3927  </list>
3930   For most implementations of HTTP/1.0, each connection is established
3931   by the client prior to the request and closed by the server after
3932   sending the response. Some implementations implement the Keep-Alive
3933   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3936<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3938   This section summarizes major differences between versions HTTP/1.0
3939   and HTTP/1.1.
3942<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3944   The requirements that clients and servers support the Host request-header,
3945   report an error if the Host request-header (<xref target=""/>) is
3946   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3947   are among the most important changes defined by this
3948   specification.
3951   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3952   addresses and servers; there was no other established mechanism for
3953   distinguishing the intended server of a request than the IP address
3954   to which that request was directed. The changes outlined above will
3955   allow the Internet, once older HTTP clients are no longer common, to
3956   support multiple Web sites from a single IP address, greatly
3957   simplifying large operational Web servers, where allocation of many
3958   IP addresses to a single host has created serious problems. The
3959   Internet will also be able to recover the IP addresses that have been
3960   allocated for the sole purpose of allowing special-purpose domain
3961   names to be used in root-level HTTP URLs. Given the rate of growth of
3962   the Web, and the number of servers already deployed, it is extremely
3963   important that all implementations of HTTP (including updates to
3964   existing HTTP/1.0 applications) correctly implement these
3965   requirements:
3966  <list style="symbols">
3967     <t>Both clients and servers &MUST; support the Host request-header.</t>
3969     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3971     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3972        request does not include a Host request-header.</t>
3974     <t>Servers &MUST; accept absolute URIs.</t>
3975  </list>
3980<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3982   Some clients and servers might wish to be compatible with some
3983   previous implementations of persistent connections in HTTP/1.0
3984   clients and servers. Persistent connections in HTTP/1.0 are
3985   explicitly negotiated as they are not the default behavior. HTTP/1.0
3986   experimental implementations of persistent connections are faulty,
3987   and the new facilities in HTTP/1.1 are designed to rectify these
3988   problems. The problem was that some existing 1.0 clients may be
3989   sending Keep-Alive to a proxy server that doesn't understand
3990   Connection, which would then erroneously forward it to the next
3991   inbound server, which would establish the Keep-Alive connection and
3992   result in a hung HTTP/1.0 proxy waiting for the close on the
3993   response. The result is that HTTP/1.0 clients must be prevented from
3994   using Keep-Alive when talking to proxies.
3997   However, talking to proxies is the most important use of persistent
3998   connections, so that prohibition is clearly unacceptable. Therefore,
3999   we need some other mechanism for indicating a persistent connection
4000   is desired, which is safe to use even when talking to an old proxy
4001   that ignores Connection. Persistent connections are the default for
4002   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4003   declaring non-persistence. See <xref target="header.connection"/>.
4006   The original HTTP/1.0 form of persistent connections (the Connection:
4007   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4011<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4013   This specification has been carefully audited to correct and
4014   disambiguate key word usage; RFC 2068 had many problems in respect to
4015   the conventions laid out in <xref target="RFC2119"/>.
4018   Transfer-coding and message lengths all interact in ways that
4019   required fixing exactly when chunked encoding is used (to allow for
4020   transfer encoding that may not be self delimiting); it was important
4021   to straighten out exactly how message lengths are computed. (Sections
4022   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4023   <xref target="header.content-length" format="counter"/>,
4024   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4027   The use and interpretation of HTTP version numbers has been clarified
4028   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4029   version they support to deal with problems discovered in HTTP/1.0
4030   implementations (<xref target="http.version"/>)
4033   Quality Values of zero should indicate that "I don't want something"
4034   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4037   Transfer-coding had significant problems, particularly with
4038   interactions with chunked encoding. The solution is that transfer-codings
4039   become as full fledged as content-codings. This involves
4040   adding an IANA registry for transfer-codings (separate from content
4041   codings), a new header field (TE) and enabling trailer headers in the
4042   future. Transfer encoding is a major performance benefit, so it was
4043   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4044   interoperability problem that could have occurred due to interactions
4045   between authentication trailers, chunked encoding and HTTP/1.0
4046   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4047   and <xref target="header.te" format="counter"/>)
4051<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4053  Empty list elements in list productions have been deprecated.
4054  (<xref target="notation.abnf"/>)
4057  Rules about implicit linear whitespace between certain grammar productions
4058  have been removed; now it's only allowed when specifically pointed out
4059  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4060  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4061  Non-ASCII content in header fields and reason phrase has been obsoleted and
4062  made opaque (the TEXT rule was removed)
4063  (<xref target="basic.rules"/>)
4066  Clarify that HTTP-Version is case sensitive.
4067  (<xref target="http.version"/>)
4070  Remove reference to non-existant identity transfer-coding value tokens.
4071  (Sections <xref format="counter" target="transfer.codings"/> and
4072  <xref format="counter" target="message.length"/>)
4075  Clarification that the chunk length does not include
4076  the count of the octets in the chunk header and trailer.
4077  (<xref target="chunked.transfer.encoding"/>)
4080  Require that invalid whitespace around field-names be rejected.
4081  (<xref target="message.headers"/>)
4084  Update use of abs_path production from RFC1808 to the path-absolute + query
4085  components of RFC3986.
4086  (<xref target="request-target"/>)
4089  Clarify exactly when close connection options must be sent.
4090  (<xref target="header.connection"/>)
4095<section title="Terminology" anchor="terminology">
4097   This specification uses a number of terms to refer to the roles
4098   played by participants in, and objects of, the HTTP communication.
4101  <iref item="cache"/>
4102  <x:dfn>cache</x:dfn>
4103  <list>
4104    <t>
4105      A program's local store of response messages and the subsystem
4106      that controls its message storage, retrieval, and deletion. A
4107      cache stores cacheable responses in order to reduce the response
4108      time and network bandwidth consumption on future, equivalent
4109      requests. Any client or server may include a cache, though a cache
4110      cannot be used by a server that is acting as a tunnel.
4111    </t>
4112  </list>
4115  <iref item="cacheable"/>
4116  <x:dfn>cacheable</x:dfn>
4117  <list>
4118    <t>
4119      A response is cacheable if a cache is allowed to store a copy of
4120      the response message for use in answering subsequent requests. The
4121      rules for determining the cacheability of HTTP responses are
4122      defined in &caching;. Even if a resource is cacheable, there may
4123      be additional constraints on whether a cache can use the cached
4124      copy for a particular request.
4125    </t>
4126  </list>
4129  <iref item="client"/>
4130  <x:dfn>client</x:dfn>
4131  <list>
4132    <t>
4133      A program that establishes connections for the purpose of sending
4134      requests.
4135    </t>
4136  </list>
4139  <iref item="connection"/>
4140  <x:dfn>connection</x:dfn>
4141  <list>
4142    <t>
4143      A transport layer virtual circuit established between two programs
4144      for the purpose of communication.
4145    </t>
4146  </list>
4149  <iref item="content negotiation"/>
4150  <x:dfn>content negotiation</x:dfn>
4151  <list>
4152    <t>
4153      The mechanism for selecting the appropriate representation when
4154      servicing a request, as described in &content.negotiation;. The
4155      representation of entities in any response can be negotiated
4156      (including error responses).
4157    </t>
4158  </list>
4161  <iref item="entity"/>
4162  <x:dfn>entity</x:dfn>
4163  <list>
4164    <t>
4165      The information transferred as the payload of a request or
4166      response. An entity consists of metainformation in the form of
4167      entity-header fields and content in the form of an entity-body, as
4168      described in &entity;.
4169    </t>
4170  </list>
4173  <iref item="gateway"/>
4174  <x:dfn>gateway</x:dfn>
4175  <list>
4176    <t>
4177      A server which acts as an intermediary for some other server.
4178      Unlike a proxy, a gateway receives requests as if it were the
4179      origin server for the requested resource; the requesting client
4180      may not be aware that it is communicating with a gateway.
4181    </t>
4182  </list>
4185  <iref item="inbound"/>
4186  <iref item="outbound"/>
4187  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4188  <list>
4189    <t>
4190      Inbound and outbound refer to the request and response paths for
4191      messages: "inbound" means "traveling toward the origin server",
4192      and "outbound" means "traveling toward the user agent"
4193    </t>
4194  </list>
4197  <iref item="message"/>
4198  <x:dfn>message</x:dfn>
4199  <list>
4200    <t>
4201      The basic unit of HTTP communication, consisting of a structured
4202      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4203      transmitted via the connection.
4204    </t>
4205  </list>
4208  <iref item="origin server"/>
4209  <x:dfn>origin server</x:dfn>
4210  <list>
4211    <t>
4212      The server on which a given resource resides or is to be created.
4213    </t>
4214  </list>
4217  <iref item="proxy"/>
4218  <x:dfn>proxy</x:dfn>
4219  <list>
4220    <t>
4221      An intermediary program which acts as both a server and a client
4222      for the purpose of making requests on behalf of other clients.
4223      Requests are serviced internally or by passing them on, with
4224      possible translation, to other servers. A proxy &MUST; implement
4225      both the client and server requirements of this specification. A
4226      "transparent proxy" is a proxy that does not modify the request or
4227      response beyond what is required for proxy authentication and
4228      identification. A "non-transparent proxy" is a proxy that modifies
4229      the request or response in order to provide some added service to
4230      the user agent, such as group annotation services, media type
4231      transformation, protocol reduction, or anonymity filtering. Except
4232      where either transparent or non-transparent behavior is explicitly
4233      stated, the HTTP proxy requirements apply to both types of
4234      proxies.
4235    </t>
4236  </list>
4239  <iref item="request"/>
4240  <x:dfn>request</x:dfn>
4241  <list>
4242    <t>
4243      An HTTP request message, as defined in <xref target="request"/>.
4244    </t>
4245  </list>
4248  <iref item="resource"/>
4249  <x:dfn>resource</x:dfn>
4250  <list>
4251    <t>
4252      A network data object or service that can be identified by a URI,
4253      as defined in <xref target="uri"/>. Resources may be available in multiple
4254      representations (e.g. multiple languages, data formats, size, and
4255      resolutions) or vary in other ways.
4256    </t>
4257  </list>
4260  <iref item="response"/>
4261  <x:dfn>response</x:dfn>
4262  <list>
4263    <t>
4264      An HTTP response message, as defined in <xref target="response"/>.
4265    </t>
4266  </list>
4269  <iref item="representation"/>
4270  <x:dfn>representation</x:dfn>
4271  <list>
4272    <t>
4273      An entity included with a response that is subject to content
4274      negotiation, as described in &content.negotiation;. There may exist multiple
4275      representations associated with a particular response status.
4276    </t>
4277  </list>
4280  <iref item="server"/>
4281  <x:dfn>server</x:dfn>
4282  <list>
4283    <t>
4284      An application program that accepts connections in order to
4285      service requests by sending back responses. Any given program may
4286      be capable of being both a client and a server; our use of these
4287      terms refers only to the role being performed by the program for a
4288      particular connection, rather than to the program's capabilities
4289      in general. Likewise, any server may act as an origin server,
4290      proxy, gateway, or tunnel, switching behavior based on the nature
4291      of each request.
4292    </t>
4293  </list>
4296  <iref item="tunnel"/>
4297  <x:dfn>tunnel</x:dfn>
4298  <list>
4299    <t>
4300      An intermediary program which is acting as a blind relay between
4301      two connections. Once active, a tunnel is not considered a party
4302      to the HTTP communication, though the tunnel may have been
4303      initiated by an HTTP request. The tunnel ceases to exist when both
4304      ends of the relayed connections are closed.
4305    </t>
4306  </list>
4309  <iref item="upstream"/>
4310  <iref item="downstream"/>
4311  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4312  <list>
4313    <t>
4314      Upstream and downstream describe the flow of a message: all
4315      messages flow from upstream to downstream.
4316    </t>
4317  </list>
4320  <iref item="user agent"/>
4321  <x:dfn>user agent</x:dfn>
4322  <list>
4323    <t>
4324      The client which initiates a request. These are often browsers,
4325      editors, spiders (web-traversing robots), or other end user tools.
4326    </t>
4327  </list>
4330  <iref item="variant"/>
4331  <x:dfn>variant</x:dfn>
4332  <list>
4333    <t>
4334      A resource may have one, or more than one, representation(s)
4335      associated with it at any given instant. Each of these
4336      representations is termed a `variant'.  Use of the term `variant'
4337      does not necessarily imply that the resource is subject to content
4338      negotiation.
4339    </t>
4340  </list>
4344<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4346<artwork type="abnf" name="p1-messaging.parsed-abnf">
4347<x:ref>BWS</x:ref> = OWS
4349<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4350<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4351<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4352<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4353 connection-token ] )
4354<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4355<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4357<x:ref>Date</x:ref> = "Date:" OWS Date-v
4358<x:ref>Date-v</x:ref> = HTTP-date
4360GMT = %x47.4D.54
4362<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4363<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4364<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4365<x:ref>HTTP-message</x:ref> = Request / Response
4366<x:ref>Host</x:ref> = "Host:" OWS Host-v
4367<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4369<x:ref>Method</x:ref> = token
4371<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4373<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4375<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4376<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4377<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4378 entity-header ) CRLF ) CRLF [ message-body ]
4379<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4380<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4381 entity-header ) CRLF ) CRLF [ message-body ]
4383<x:ref>Status-Code</x:ref> = 3DIGIT
4384<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4386<x:ref>TE</x:ref> = "TE:" OWS TE-v
4387<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4388<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4389<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4390<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4391<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4392 transfer-coding ] )
4394<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4395<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4396<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4397<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4399<x:ref>Via</x:ref> = "Via:" OWS Via-v
4400<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4401 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4402 ] )
4404<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4406<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4407<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4408<x:ref>attribute</x:ref> = token
4409<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4411<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4412<x:ref>chunk-data</x:ref> = 1*OCTET
4413<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4414<x:ref>chunk-ext-name</x:ref> = token
4415<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4416<x:ref>chunk-size</x:ref> = 1*HEXDIG
4417<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4418<x:ref>connection-token</x:ref> = token
4419<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4421<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4422<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4423<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4425<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4426<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4428<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4429<x:ref>field-name</x:ref> = token
4430<x:ref>field-value</x:ref> = *( field-content / OWS )
4431<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4433<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4434 / Transfer-Encoding / Upgrade / Via / Warning
4435<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4436 message-body ]
4438<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4440l-Fri = %x46.
4441l-Mon = %x4D.6F.6E.64.61.79
4442l-Sat = %x53.
4443l-Sun = %x53.75.6E.64.61.79
4444l-Thu = %x54.
4445l-Tue = %x54.
4446l-Wed = %x57.65.64.6E.
4447<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4449<x:ref>message-body</x:ref> = entity-body /
4450 &lt;entity-body encoded as per Transfer-Encoding&gt;
4451<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4452<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4453 / s-Sep / s-Oct / s-Nov / s-Dec
4455<x:ref>obs-fold</x:ref> = CRLF
4456<x:ref>obs-text</x:ref> = %x80-FF
4457<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4459<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4460<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4461<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4462<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4463<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4464<x:ref>product</x:ref> = token [ "/" product-version ]
4465<x:ref>product-version</x:ref> = token
4466<x:ref>protocol-name</x:ref> = token
4467<x:ref>protocol-version</x:ref> = token
4468<x:ref>pseudonym</x:ref> = token
4470<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4471<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4472<x:ref>quoted-pair</x:ref> = "\" quoted-text
4473<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4474<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4475<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4477<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4478<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4479<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4480<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4481<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4482 / authority
4483<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4484<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4485<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4487s-Apr = %x41.70.72
4488s-Aug = %x41.75.67
4489s-Dec = %x44.65.63
4490s-Feb = %x46.65.62
4491s-Fri = %x46.72.69
4492s-Jan = %x4A.61.6E
4493s-Jul = %x4A.75.6C
4494s-Jun = %x4A.75.6E
4495s-Mar = %x4D.61.72
4496s-May = %x4D.61.79
4497s-Mon = %x4D.6F.6E
4498s-Nov = %x4E.6F.76
4499s-Oct = %x4F.63.74
4500s-Sat = %x53.61.74
4501s-Sep = %x53.65.70
4502s-Sun = %x53.75.6E
4503s-Thu = %x54.68.75
4504s-Tue = %x54.75.65
4505s-Wed = %x57.65.64
4506<x:ref>start-line</x:ref> = Request-Line / Status-Line
4508<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4509<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4510 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4511<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4512<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4513<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4514<x:ref>token</x:ref> = 1*tchar
4515<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4516<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4517<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4519<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4521<x:ref>value</x:ref> = token / quoted-string
4523<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4524<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4529<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4530; Chunked-Body defined but not used
4531; Content-Length defined but not used
4532; HTTP-message defined but not used
4533; Host defined but not used
4534; TE defined but not used
4535; URI defined but not used
4536; URI-reference defined but not used
4537; fragment defined but not used
4538; generic-message defined but not used
4539; http-URI defined but not used
4540; partial-URI defined but not used
4543<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4545<section title="Since RFC2616">
4547  Extracted relevant partitions from <xref target="RFC2616"/>.
4551<section title="Since draft-ietf-httpbis-p1-messaging-00">
4553  Closed issues:
4554  <list style="symbols">
4555    <t>
4556      <eref target=""/>:
4557      "HTTP Version should be case sensitive"
4558      (<eref target=""/>)
4559    </t>
4560    <t>
4561      <eref target=""/>:
4562      "'unsafe' characters"
4563      (<eref target=""/>)
4564    </t>
4565    <t>
4566      <eref target=""/>:
4567      "Chunk Size Definition"
4568      (<eref target=""/>)
4569    </t>
4570    <t>
4571      <eref target=""/>:
4572      "Message Length"
4573      (<eref target=""/>)
4574    </t>
4575    <t>
4576      <eref target=""/>:
4577      "Media Type Registrations"
4578      (<eref target=""/>)
4579    </t>
4580    <t>
4581      <eref target=""/>:
4582      "URI includes query"
4583      (<eref target=""/>)
4584    </t>
4585    <t>
4586      <eref target=""/>:
4587      "No close on 1xx responses"
4588      (<eref target=""/>)
4589    </t>
4590    <t>
4591      <eref target=""/>:
4592      "Remove 'identity' token references"
4593      (<eref target=""/>)
4594    </t>
4595    <t>
4596      <eref target=""/>:
4597      "Import query BNF"
4598    </t>
4599    <t>
4600      <eref target=""/>:
4601      "qdtext BNF"
4602    </t>
4603    <t>
4604      <eref target=""/>:
4605      "Normative and Informative references"
4606    </t>
4607    <t>
4608      <eref target=""/>:
4609      "RFC2606 Compliance"
4610    </t>
4611    <t>
4612      <eref target=""/>:
4613      "RFC977 reference"
4614    </t>
4615    <t>
4616      <eref target=""/>:
4617      "RFC1700 references"
4618    </t>
4619    <t>
4620      <eref target=""/>:
4621      "inconsistency in date format explanation"
4622    </t>
4623    <t>
4624      <eref target=""/>:
4625      "Date reference typo"
4626    </t>
4627    <t>
4628      <eref target=""/>:
4629      "Informative references"
4630    </t>
4631    <t>
4632      <eref target=""/>:
4633      "ISO-8859-1 Reference"
4634    </t>
4635    <t>
4636      <eref target=""/>:
4637      "Normative up-to-date references"
4638    </t>
4639  </list>
4642  Other changes:
4643  <list style="symbols">
4644    <t>
4645      Update media type registrations to use RFC4288 template.
4646    </t>
4647    <t>
4648      Use names of RFC4234 core rules DQUOTE and WSP,
4649      fix broken ABNF for chunk-data
4650      (work in progress on <eref target=""/>)
4651    </t>
4652  </list>
4656<section title="Since draft-ietf-httpbis-p1-messaging-01">
4658  Closed issues:
4659  <list style="symbols">
4660    <t>
4661      <eref target=""/>:
4662      "Bodies on GET (and other) requests"
4663    </t>
4664    <t>
4665      <eref target=""/>:
4666      "Updating to RFC4288"
4667    </t>
4668    <t>
4669      <eref target=""/>:
4670      "Status Code and Reason Phrase"
4671    </t>
4672    <t>
4673      <eref target=""/>:
4674      "rel_path not used"
4675    </t>
4676  </list>
4679  Ongoing work on ABNF conversion (<eref target=""/>):
4680  <list style="symbols">
4681    <t>
4682      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4683      "trailer-part").
4684    </t>
4685    <t>
4686      Avoid underscore character in rule names ("http_URL" ->
4687      "http-URL", "abs_path" -> "path-absolute").
4688    </t>
4689    <t>
4690      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4691      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4692      have to be updated when switching over to RFC3986.
4693    </t>
4694    <t>
4695      Synchronize core rules with RFC5234.
4696    </t>
4697    <t>
4698      Get rid of prose rules that span multiple lines.
4699    </t>
4700    <t>
4701      Get rid of unused rules LOALPHA and UPALPHA.
4702    </t>
4703    <t>
4704      Move "Product Tokens" section (back) into Part 1, as "token" is used
4705      in the definition of the Upgrade header.
4706    </t>
4707    <t>
4708      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4709    </t>
4710    <t>
4711      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4712    </t>
4713  </list>
4717<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4719  Closed issues:
4720  <list style="symbols">
4721    <t>
4722      <eref target=""/>:
4723      "HTTP-date vs. rfc1123-date"
4724    </t>
4725    <t>
4726      <eref target=""/>:
4727      "WS in quoted-pair"
4728    </t>
4729  </list>
4732  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4733  <list style="symbols">
4734    <t>
4735      Reference RFC 3984, and update header registrations for headers defined
4736      in this document.
4737    </t>
4738  </list>
4741  Ongoing work on ABNF conversion (<eref target=""/>):
4742  <list style="symbols">
4743    <t>
4744      Replace string literals when the string really is case-sensitive (HTTP-Version).
4745    </t>
4746  </list>
4750<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4752  Closed issues:
4753  <list style="symbols">
4754    <t>
4755      <eref target=""/>:
4756      "Connection closing"
4757    </t>
4758    <t>
4759      <eref target=""/>:
4760      "Move registrations and registry information to IANA Considerations"
4761    </t>
4762    <t>
4763      <eref target=""/>:
4764      "need new URL for PAD1995 reference"
4765    </t>
4766    <t>
4767      <eref target=""/>:
4768      "IANA Considerations: update HTTP URI scheme registration"
4769    </t>
4770    <t>
4771      <eref target=""/>:
4772      "Cite HTTPS URI scheme definition"
4773    </t>
4774    <t>
4775      <eref target=""/>:
4776      "List-type headers vs Set-Cookie"
4777    </t>
4778  </list>
4781  Ongoing work on ABNF conversion (<eref target=""/>):
4782  <list style="symbols">
4783    <t>
4784      Replace string literals when the string really is case-sensitive (HTTP-Date).
4785    </t>
4786    <t>
4787      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4788    </t>
4789  </list>
4793<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4795  Closed issues:
4796  <list style="symbols">
4797    <t>
4798      <eref target=""/>:
4799      "Out-of-date reference for URIs"
4800    </t>
4801    <t>
4802      <eref target=""/>:
4803      "RFC 2822 is updated by RFC 5322"
4804    </t>
4805  </list>
4808  Ongoing work on ABNF conversion (<eref target=""/>):
4809  <list style="symbols">
4810    <t>
4811      Use "/" instead of "|" for alternatives.
4812    </t>
4813    <t>
4814      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4815    </t>
4816    <t>
4817      Only reference RFC 5234's core rules.
4818    </t>
4819    <t>
4820      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4821      whitespace ("OWS") and required whitespace ("RWS").
4822    </t>
4823    <t>
4824      Rewrite ABNFs to spell out whitespace rules, factor out
4825      header value format definitions.
4826    </t>
4827  </list>
4831<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4833  Closed issues:
4834  <list style="symbols">
4835    <t>
4836      <eref target=""/>:
4837      "Header LWS"
4838    </t>
4839    <t>
4840      <eref target=""/>:
4841      "Sort 1.3 Terminology"
4842    </t>
4843    <t>
4844      <eref target=""/>:
4845      "RFC2047 encoded words"
4846    </t>
4847    <t>
4848      <eref target=""/>:
4849      "Character Encodings in TEXT"
4850    </t>
4851    <t>
4852      <eref target=""/>:
4853      "Line Folding"
4854    </t>
4855    <t>
4856      <eref target=""/>:
4857      "OPTIONS * and proxies"
4858    </t>
4859    <t>
4860      <eref target=""/>:
4861      "Reason-Phrase BNF"
4862    </t>
4863    <t>
4864      <eref target=""/>:
4865      "Use of TEXT"
4866    </t>
4867    <t>
4868      <eref target=""/>:
4869      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4870    </t>
4871    <t>
4872      <eref target=""/>:
4873      "RFC822 reference left in discussion of date formats"
4874    </t>
4875  </list>
4878  Final work on ABNF conversion (<eref target=""/>):
4879  <list style="symbols">
4880    <t>
4881      Rewrite definition of list rules, deprecate empty list elements.
4882    </t>
4883    <t>
4884      Add appendix containing collected and expanded ABNF.
4885    </t>
4886  </list>
4889  Other changes:
4890  <list style="symbols">
4891    <t>
4892      Rewrite introduction; add mostly new Architecture Section.
4893    </t>
4894    <t>
4895      Move definition of quality values from Part 3 into Part 1;
4896      make TE request header grammar independent of accept-params (defined in Part 3).
4897    </t>
4898  </list>
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