source: draft-ietf-httpbis/latest/p1-messaging.xml @ 563

Last change on this file since 563 was 563, checked in by julian.reschke@…, 13 years ago

replace <list> elements used for indentation by <x:note> elements

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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;"/>
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.06"/>.
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  <t>
596    <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
597  </t>
601<section title="URI Comparison" anchor="uri.comparison">
603   When comparing two URIs to decide if they match or not, a client
604   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
605   URIs, with these exceptions:
606  <list style="symbols">
607    <t>A port that is empty or not given is equivalent to the default
608        port for that URI-reference;</t>
609    <t>Comparisons of host names &MUST; be case-insensitive;</t>
610    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
611    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
612    <t>Characters other than those in the "reserved" set are equivalent to their
613       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
614    </t>
615  </list>
618   For example, the following three URIs are equivalent:
620<figure><artwork type="example">
627<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
633<section title="Overall Operation" anchor="intro.overall.operation">
635   HTTP is a request/response protocol. A client sends a
636   request to the server in the form of a request method, URI, and
637   protocol version, followed by a MIME-like message containing request
638   modifiers, client information, and possible body content over a
639   connection with a server. The server responds with a status line,
640   including the message's protocol version and a success or error code,
641   followed by a MIME-like message containing server information, entity
642   metainformation, and possible entity-body content.
645   Most HTTP communication is initiated by a user agent and consists of
646   a request to be applied to a resource on some origin server. In the
647   simplest case, this may be accomplished via a single connection (v)
648   between the user agent (UA) and the origin server (O).
650<figure><artwork type="drawing">
651       request chain ------------------------&gt;
652    UA -------------------v------------------- O
653       &lt;----------------------- response chain
656   A more complicated situation occurs when one or more intermediaries
657   are present in the request/response chain. There are three common
658   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
659   forwarding agent, receiving requests for a URI in its absolute form,
660   rewriting all or part of the message, and forwarding the reformatted
661   request toward the server identified by the URI. A gateway is a
662   receiving agent, acting as a layer above some other server(s) and, if
663   necessary, translating the requests to the underlying server's
664   protocol. A tunnel acts as a relay point between two connections
665   without changing the messages; tunnels are used when the
666   communication needs to pass through an intermediary (such as a
667   firewall) even when the intermediary cannot understand the contents
668   of the messages.
670<figure><artwork type="drawing">
671       request chain --------------------------------------&gt;
672    UA -----v----- A -----v----- B -----v----- C -----v----- O
673       &lt;------------------------------------- response chain
676   The figure above shows three intermediaries (A, B, and C) between the
677   user agent and origin server. A request or response message that
678   travels the whole chain will pass through four separate connections.
679   This distinction is important because some HTTP communication options
680   may apply only to the connection with the nearest, non-tunnel
681   neighbor, only to the end-points of the chain, or to all connections
682   along the chain. Although the diagram is linear, each participant may
683   be engaged in multiple, simultaneous communications. For example, B
684   may be receiving requests from many clients other than A, and/or
685   forwarding requests to servers other than C, at the same time that it
686   is handling A's request.
689   Any party to the communication which is not acting as a tunnel may
690   employ an internal cache for handling requests. The effect of a cache
691   is that the request/response chain is shortened if one of the
692   participants along the chain has a cached response applicable to that
693   request. The following illustrates the resulting chain if B has a
694   cached copy of an earlier response from O (via C) for a request which
695   has not been cached by UA or A.
697<figure><artwork type="drawing">
698          request chain ----------&gt;
699       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
700          &lt;--------- response chain
703   Not all responses are usefully cacheable, and some requests may
704   contain modifiers which place special requirements on cache behavior.
705   HTTP requirements for cache behavior and cacheable responses are
706   defined in &caching;.
709   In fact, there are a wide variety of architectures and configurations
710   of caches and proxies currently being experimented with or deployed
711   across the World Wide Web. These systems include national hierarchies
712   of proxy caches to save transoceanic bandwidth, systems that
713   broadcast or multicast cache entries, organizations that distribute
714   subsets of cached data via CD-ROM, and so on. HTTP systems are used
715   in corporate intranets over high-bandwidth links, and for access via
716   PDAs with low-power radio links and intermittent connectivity. The
717   goal of HTTP/1.1 is to support the wide diversity of configurations
718   already deployed while introducing protocol constructs that meet the
719   needs of those who build web applications that require high
720   reliability and, failing that, at least reliable indications of
721   failure.
724   HTTP communication usually takes place over TCP/IP connections. The
725   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
726   not preclude HTTP from being implemented on top of any other protocol
727   on the Internet, or on other networks. HTTP only presumes a reliable
728   transport; any protocol that provides such guarantees can be used;
729   the mapping of the HTTP/1.1 request and response structures onto the
730   transport data units of the protocol in question is outside the scope
731   of this specification.
734   In HTTP/1.0, most implementations used a new connection for each
735   request/response exchange. In HTTP/1.1, a connection may be used for
736   one or more request/response exchanges, although connections may be
737   closed for a variety of reasons (see <xref target="persistent.connections"/>).
741<section title="Use of HTTP for proxy communication" anchor="http.proxy">
743   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
746<section title="Interception of HTTP for access control" anchor="http.intercept">
748   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
751<section title="Use of HTTP by other protocols" anchor="http.others">
753   <cref>TBD: Profiles of HTTP defined by other protocol.
754   Extensions of HTTP like WebDAV.</cref>
757<section title="Use of HTTP by media type specification" anchor="">
759   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
764<section title="Protocol Parameters" anchor="protocol.parameters">
766<section title="HTTP Version" anchor="http.version">
767  <x:anchor-alias value="HTTP-Version"/>
768  <x:anchor-alias value="HTTP-Prot-Name"/>
770   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
771   of the protocol. The protocol versioning policy is intended to allow
772   the sender to indicate the format of a message and its capacity for
773   understanding further HTTP communication, rather than the features
774   obtained via that communication. No change is made to the version
775   number for the addition of message components which do not affect
776   communication behavior or which only add to extensible field values.
777   The &lt;minor&gt; number is incremented when the changes made to the
778   protocol add features which do not change the general message parsing
779   algorithm, but which may add to the message semantics and imply
780   additional capabilities of the sender. The &lt;major&gt; number is
781   incremented when the format of a message within the protocol is
782   changed. See <xref target="RFC2145"/> for a fuller explanation.
785   The version of an HTTP message is indicated by an HTTP-Version field
786   in the first line of the message. HTTP-Version is case-sensitive.
788<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
789  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
790  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
793   Note that the major and minor numbers &MUST; be treated as separate
794   integers and that each &MAY; be incremented higher than a single digit.
795   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
796   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
797   &MUST-NOT; be sent.
800   An application that sends a request or response message that includes
801   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
802   with this specification. Applications that are at least conditionally
803   compliant with this specification &SHOULD; use an HTTP-Version of
804   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
805   not compatible with HTTP/1.0. For more details on when to send
806   specific HTTP-Version values, see <xref target="RFC2145"/>.
809   The HTTP version of an application is the highest HTTP version for
810   which the application is at least conditionally compliant.
813   Proxy and gateway applications need to be careful when forwarding
814   messages in protocol versions different from that of the application.
815   Since the protocol version indicates the protocol capability of the
816   sender, a proxy/gateway &MUST-NOT; send a message with a version
817   indicator which is greater than its actual version. If a higher
818   version request is received, the proxy/gateway &MUST; either downgrade
819   the request version, or respond with an error, or switch to tunnel
820   behavior.
823   Due to interoperability problems with HTTP/1.0 proxies discovered
824   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
825   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
826   they support. The proxy/gateway's response to that request &MUST; be in
827   the same major version as the request.
830  <t>
831    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
832    of header fields required or forbidden by the versions involved.
833  </t>
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  <t>
873    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
874    accepting date values that may have been sent by non-HTTP
875    applications, as is sometimes the case when retrieving or posting
876    messages via proxies/gateways to SMTP or NNTP.
877  </t>
880   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
881   (GMT), without exception. For the purposes of HTTP, GMT is exactly
882   equal to UTC (Coordinated Universal Time). This is indicated in the
883   first two formats by the inclusion of "GMT" as the three-letter
884   abbreviation for time zone, and &MUST; be assumed when reading the
885   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
886   additional whitespace beyond that specifically included as SP in the
887   grammar.
889<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
890  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
891  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
892  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
893  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
894  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
895  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
896                 ; day month year (e.g., 02 Jun 1982)
897  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
898                 ; day-month-year (e.g., 02-Jun-82)
899  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
900                 ; month day (e.g., Jun  2)
901  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
902                 ; 00:00:00 - 23:59:59
903  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
904               / s-Thu / s-Fri / s-Sat / s-Sun
905  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
906               / l-Thu / l-Fri / l-Sat / l-Sun
907  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
908               / s-May / s-Jun / s-Jul / s-Aug
909               / s-Sep / s-Oct / s-Nov / s-Dec
911  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
913  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
914  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
915  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
916  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
917  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
918  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
919  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
921  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
922  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
923  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
924  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
925  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
926  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
927  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
929  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
930  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
931  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
932  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
933  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
934  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
935  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
936  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
937  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
938  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
939  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
940  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
943      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
944      to their usage within the protocol stream. Clients and servers are
945      not required to use these formats for user presentation, request
946      logging, etc.
951<section title="Transfer Codings" anchor="transfer.codings">
952  <x:anchor-alias value="parameter"/>
953  <x:anchor-alias value="transfer-coding"/>
954  <x:anchor-alias value="transfer-extension"/>
956   Transfer-coding values are used to indicate an encoding
957   transformation that has been, can be, or may need to be applied to an
958   entity-body in order to ensure "safe transport" through the network.
959   This differs from a content coding in that the transfer-coding is a
960   property of the message, not of the original entity.
962<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
963  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
964  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
966<t anchor="rule.parameter">
967  <x:anchor-alias value="attribute"/>
968  <x:anchor-alias value="parameter"/>
969  <x:anchor-alias value="value"/>
970   Parameters are in  the form of attribute/value pairs.
972<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
973  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
974  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
975  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
978   All transfer-coding values are case-insensitive. HTTP/1.1 uses
979   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
980   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
983   Whenever a transfer-coding is applied to a message-body, the set of
984   transfer-codings &MUST; include "chunked", unless the message indicates it
985   is terminated by closing the connection. When the "chunked" transfer-coding
986   is used, it &MUST; be the last transfer-coding applied to the
987   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
988   than once to a message-body. These rules allow the recipient to
989   determine the transfer-length of the message (<xref target="message.length"/>).
992   Transfer-codings are analogous to the Content-Transfer-Encoding
993   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
994   binary data over a 7-bit transport service. However, safe transport
995   has a different focus for an 8bit-clean transfer protocol. In HTTP,
996   the only unsafe characteristic of message-bodies is the difficulty in
997   determining the exact body length (<xref target="message.length"/>), or the desire to
998   encrypt data over a shared transport.
1001   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1002   transfer-coding value tokens. Initially, the registry contains the
1003   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1004   "gzip", "compress", and "deflate" (&content-codings;).
1007   New transfer-coding value tokens &SHOULD; be registered in the same way
1008   as new content-coding value tokens (&content-codings;).
1011   A server which receives an entity-body with a transfer-coding it does
1012   not understand &SHOULD; return 501 (Not Implemented), and close the
1013   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1014   client.
1017<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1018  <x:anchor-alias value="chunk"/>
1019  <x:anchor-alias value="Chunked-Body"/>
1020  <x:anchor-alias value="chunk-data"/>
1021  <x:anchor-alias value="chunk-ext"/>
1022  <x:anchor-alias value="chunk-ext-name"/>
1023  <x:anchor-alias value="chunk-ext-val"/>
1024  <x:anchor-alias value="chunk-size"/>
1025  <x:anchor-alias value="last-chunk"/>
1026  <x:anchor-alias value="trailer-part"/>
1028   The chunked encoding modifies the body of a message in order to
1029   transfer it as a series of chunks, each with its own size indicator,
1030   followed by an &OPTIONAL; trailer containing entity-header fields. This
1031   allows dynamically produced content to be transferred along with the
1032   information necessary for the recipient to verify that it has
1033   received the full message.
1035<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1036  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1037                   <x:ref>last-chunk</x:ref>
1038                   <x:ref>trailer-part</x:ref>
1039                   <x:ref>CRLF</x:ref>
1041  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1042                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1043  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1044  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1046  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1047                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1048  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1049  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1050  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1051  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1054   The chunk-size field is a string of hex digits indicating the size of
1055   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1056   zero, followed by the trailer, which is terminated by an empty line.
1059   The trailer allows the sender to include additional HTTP header
1060   fields at the end of the message. The Trailer header field can be
1061   used to indicate which header fields are included in a trailer (see
1062   <xref target="header.trailer"/>).
1065   A server using chunked transfer-coding in a response &MUST-NOT; use the
1066   trailer for any header fields unless at least one of the following is
1067   true:
1068  <list style="numbers">
1069    <t>the request included a TE header field that indicates "trailers" is
1070     acceptable in the transfer-coding of the  response, as described in
1071     <xref target="header.te"/>; or,</t>
1073    <t>the server is the origin server for the response, the trailer
1074     fields consist entirely of optional metadata, and the recipient
1075     could use the message (in a manner acceptable to the origin server)
1076     without receiving this metadata.  In other words, the origin server
1077     is willing to accept the possibility that the trailer fields might
1078     be silently discarded along the path to the client.</t>
1079  </list>
1082   This requirement prevents an interoperability failure when the
1083   message is being received by an HTTP/1.1 (or later) proxy and
1084   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1085   compliance with the protocol would have necessitated a possibly
1086   infinite buffer on the proxy.
1089   A process for decoding the "chunked" transfer-coding
1090   can be represented in pseudo-code as:
1092<figure><artwork type="code">
1093  length := 0
1094  read chunk-size, chunk-ext (if any) and CRLF
1095  while (chunk-size &gt; 0) {
1096     read chunk-data and CRLF
1097     append chunk-data to entity-body
1098     length := length + chunk-size
1099     read chunk-size and CRLF
1100  }
1101  read entity-header
1102  while (entity-header not empty) {
1103     append entity-header to existing header fields
1104     read entity-header
1105  }
1106  Content-Length := length
1107  Remove "chunked" from Transfer-Encoding
1110   All HTTP/1.1 applications &MUST; be able to receive and decode the
1111   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1112   they do not understand.
1117<section title="Product Tokens" anchor="product.tokens">
1118  <x:anchor-alias value="product"/>
1119  <x:anchor-alias value="product-version"/>
1121   Product tokens are used to allow communicating applications to
1122   identify themselves by software name and version. Most fields using
1123   product tokens also allow sub-products which form a significant part
1124   of the application to be listed, separated by whitespace. By
1125   convention, the products are listed in order of their significance
1126   for identifying the application.
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1129  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1130  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1133   Examples:
1135<figure><artwork type="example">
1136  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1137  Server: Apache/0.8.4
1140   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1141   used for advertising or other non-essential information. Although any
1142   token character &MAY; appear in a product-version, this token &SHOULD;
1143   only be used for a version identifier (i.e., successive versions of
1144   the same product &SHOULD; only differ in the product-version portion of
1145   the product value).
1149<section title="Quality Values" anchor="quality.values">
1150  <x:anchor-alias value="qvalue"/>
1152   Both transfer codings (TE request header, <xref target="header.te"/>)
1153   and content negotiation (&content.negotiation;) use short "floating point"
1154   numbers to indicate the relative importance ("weight") of various
1155   negotiable parameters.  A weight is normalized to a real number in
1156   the range 0 through 1, where 0 is the minimum and 1 the maximum
1157   value. If a parameter has a quality value of 0, then content with
1158   this parameter is `not acceptable' for the client. HTTP/1.1
1159   applications &MUST-NOT; generate more than three digits after the
1160   decimal point. User configuration of these values &SHOULD; also be
1161   limited in this fashion.
1163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1164  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1165                 / ( "1" [ "." 0*3("0") ] )
1168  <t>
1169     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1170     relative degradation in desired quality.
1171  </t>
1177<section title="HTTP Message" anchor="http.message">
1179<section title="Message Types" anchor="message.types">
1180  <x:anchor-alias value="generic-message"/>
1181  <x:anchor-alias value="HTTP-message"/>
1182  <x:anchor-alias value="start-line"/>
1184   HTTP messages consist of requests from client to server and responses
1185   from server to client.
1187<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1188  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1191   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1192   message format of <xref target="RFC5322"/> for transferring entities (the payload
1193   of the message). Both types of message consist of a start-line, zero
1194   or more header fields (also known as "headers"), an empty line (i.e.,
1195   a line with nothing preceding the CRLF) indicating the end of the
1196   header fields, and possibly a message-body.
1198<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1199  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1200                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1201                    <x:ref>CRLF</x:ref>
1202                    [ <x:ref>message-body</x:ref> ]
1203  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1206   In the interest of robustness, servers &SHOULD; ignore any empty
1207   line(s) received where a Request-Line is expected. In other words, if
1208   the server is reading the protocol stream at the beginning of a
1209   message and receives a CRLF first, it should ignore the CRLF.
1212   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1213   after a POST request. To restate what is explicitly forbidden by the
1214   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1215   extra CRLF.
1218   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1219   header field. The presence of whitespace might be an attempt to trick a
1220   noncompliant implementation of HTTP into ignoring that field or processing
1221   the next line as a new request, either of which may result in security
1222   issues when implementations within the request chain interpret the
1223   same message differently. HTTP/1.1 servers &MUST; reject such a message
1224   with a 400 (Bad Request) response.
1228<section title="Message Headers" anchor="message.headers">
1229  <x:anchor-alias value="field-content"/>
1230  <x:anchor-alias value="field-name"/>
1231  <x:anchor-alias value="field-value"/>
1232  <x:anchor-alias value="message-header"/>
1234   HTTP header fields follow the same general format as Internet messages in
1235   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1236   of a name followed by a colon (":"), optional whitespace, and the field
1237   value. Field names are case-insensitive.
1239<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"/>
1240  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1241  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1242  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1243  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1246   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1247   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1248   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1249   header field-values use only a subset of the US-ASCII charset
1250   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1251   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1252   (obs-text) octets in field-content as opaque data.
1255   No whitespace is allowed between the header field-name and colon. For
1256   security reasons, any request message received containing such whitespace
1257   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1258   whitespace in a response message &MUST; be removed.
1261   The field value &MAY; be preceded by optional whitespace; a single SP is
1262   preferred. The field-value does not include any leading or trailing white
1263   space: OWS occurring before the first non-whitespace character of the
1264   field-value or after the last non-whitespace character of the field-value
1265   is ignored and &MAY; be removed without changing the meaning of the header
1266   field.
1269   Historically, HTTP header field values could be extended over multiple
1270   lines by preceding each extra line with at least one space or horizontal
1271   tab character (line folding). This specification deprecates such line
1272   folding except within the message/http media type
1273   (<xref target=""/>).
1274   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1275   (i.e., that contain any field-content that matches the obs-fold rule) unless
1276   the message is intended for packaging within the message/http media type.
1277   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1278   obs-fold whitespace with a single SP prior to interpreting the field value
1279   or forwarding the message downstream.
1281<t anchor="rule.comment">
1282  <x:anchor-alias value="comment"/>
1283  <x:anchor-alias value="ctext"/>
1284   Comments can be included in some HTTP header fields by surrounding
1285   the comment text with parentheses. Comments are only allowed in
1286   fields containing "comment" as part of their field value definition.
1287   In all other fields, parentheses are considered part of the field
1288   value.
1290<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1291  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1292  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1295   The order in which header fields with differing field names are
1296   received is not significant. However, it is "good practice" to send
1297   general-header fields first, followed by request-header or response-header
1298   fields, and ending with the entity-header fields.
1301   Multiple message-header fields with the same field-name &MAY; be
1302   present in a message if and only if the entire field-value for that
1303   header field is defined as a comma-separated list [i.e., #(values)].
1304   It &MUST; be possible to combine the multiple header fields into one
1305   "field-name: field-value" pair, without changing the semantics of the
1306   message, by appending each subsequent field-value to the first, each
1307   separated by a comma. The order in which header fields with the same
1308   field-name are received is therefore significant to the
1309   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1310   change the order of these field values when a message is forwarded.
1313  <t>
1314   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1315   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1316   can occur multiple times, but does not use the list syntax, and thus cannot
1317   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1318   for details.) Also note that the Set-Cookie2 header specified in
1319   <xref target="RFC2965"/> does not share this problem.
1320  </t>
1325<section title="Message Body" anchor="message.body">
1326  <x:anchor-alias value="message-body"/>
1328   The message-body (if any) of an HTTP message is used to carry the
1329   entity-body associated with the request or response. The message-body
1330   differs from the entity-body only when a transfer-coding has been
1331   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1333<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1334  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1335               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1338   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1339   applied by an application to ensure safe and proper transfer of the
1340   message. Transfer-Encoding is a property of the message, not of the
1341   entity, and thus &MAY; be added or removed by any application along the
1342   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1343   when certain transfer-codings may be used.)
1346   The rules for when a message-body is allowed in a message differ for
1347   requests and responses.
1350   The presence of a message-body in a request is signaled by the
1351   inclusion of a Content-Length or Transfer-Encoding header field in
1352   the request's message-headers. A message-body &MUST-NOT; be included in
1353   a request if the specification of the request method (&method;)
1354   explicitly disallows an entity-body in requests.
1355   When a request message contains both a message-body of non-zero
1356   length and a method that does not define any semantics for that
1357   request message-body, then an origin server &SHOULD; either ignore
1358   the message-body or respond with an appropriate error message
1359   (e.g., 413).  A proxy or gateway, when presented the same request,
1360   &SHOULD; either forward the request inbound with the message-body or
1361   ignore the message-body when determining a response.
1364   For response messages, whether or not a message-body is included with
1365   a message is dependent on both the request method and the response
1366   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1367   &MUST-NOT; include a message-body, even though the presence of entity-header
1368   fields might lead one to believe they do. All 1xx
1369   (informational), 204 (No Content), and 304 (Not Modified) responses
1370   &MUST-NOT; include a message-body. All other responses do include a
1371   message-body, although it &MAY; be of zero length.
1375<section title="Message Length" anchor="message.length">
1377   The transfer-length of a message is the length of the message-body as
1378   it appears in the message; that is, after any transfer-codings have
1379   been applied. When a message-body is included with a message, the
1380   transfer-length of that body is determined by one of the following
1381   (in order of precedence):
1384  <list style="numbers">
1385    <x:lt><t>
1386     Any response message which "&MUST-NOT;" include a message-body (such
1387     as the 1xx, 204, and 304 responses and any response to a HEAD
1388     request) is always terminated by the first empty line after the
1389     header fields, regardless of the entity-header fields present in
1390     the message.
1391    </t></x:lt>
1392    <x:lt><t>
1393     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1394     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1395     is used, the transfer-length is defined by the use of this transfer-coding.
1396     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1397     is not present, the transfer-length is defined by the sender closing the connection.
1398    </t></x:lt>
1399    <x:lt><t>
1400     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1401     decimal value in OCTETs represents both the entity-length and the
1402     transfer-length. The Content-Length header field &MUST-NOT; be sent
1403     if these two lengths are different (i.e., if a Transfer-Encoding
1404     header field is present). If a message is received with both a
1405     Transfer-Encoding header field and a Content-Length header field,
1406     the latter &MUST; be ignored.
1407    </t></x:lt>
1408    <x:lt><t>
1409     If the message uses the media type "multipart/byteranges", and the
1410     transfer-length is not otherwise specified, then this self-delimiting
1411     media type defines the transfer-length. This media type
1412     &MUST-NOT; be used unless the sender knows that the recipient can parse
1413     it; the presence in a request of a Range header with multiple byte-range
1414     specifiers from a 1.1 client implies that the client can parse
1415     multipart/byteranges responses.
1416    <list style="empty"><t>
1417       A range header might be forwarded by a 1.0 proxy that does not
1418       understand multipart/byteranges; in this case the server &MUST;
1419       delimit the message using methods defined in items 1, 3 or 5 of
1420       this section.
1421    </t></list>
1422    </t></x:lt>
1423    <x:lt><t>
1424     By the server closing the connection. (Closing the connection
1425     cannot be used to indicate the end of a request body, since that
1426     would leave no possibility for the server to send back a response.)
1427    </t></x:lt>
1428  </list>
1431   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1432   containing a message-body &MUST; include a valid Content-Length header
1433   field unless the server is known to be HTTP/1.1 compliant. If a
1434   request contains a message-body and a Content-Length is not given,
1435   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1436   determine the length of the message, or with 411 (Length Required) if
1437   it wishes to insist on receiving a valid Content-Length.
1440   All HTTP/1.1 applications that receive entities &MUST; accept the
1441   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1442   to be used for messages when the message length cannot be determined
1443   in advance.
1446   Messages &MUST-NOT; include both a Content-Length header field and a
1447   transfer-coding. If the message does include a
1448   transfer-coding, the Content-Length &MUST; be ignored.
1451   When a Content-Length is given in a message where a message-body is
1452   allowed, its field value &MUST; exactly match the number of OCTETs in
1453   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1454   invalid length is received and detected.
1458<section title="General Header Fields" anchor="general.header.fields">
1459  <x:anchor-alias value="general-header"/>
1461   There are a few header fields which have general applicability for
1462   both request and response messages, but which do not apply to the
1463   entity being transferred. These header fields apply only to the
1464   message being transmitted.
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1467  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1468                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1469                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1470                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1471                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1472                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1473                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1474                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1475                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1478   General-header field names can be extended reliably only in
1479   combination with a change in the protocol version. However, new or
1480   experimental header fields may be given the semantics of general
1481   header fields if all parties in the communication recognize them to
1482   be general-header fields. Unrecognized header fields are treated as
1483   entity-header fields.
1488<section title="Request" anchor="request">
1489  <x:anchor-alias value="Request"/>
1491   A request message from a client to a server includes, within the
1492   first line of that message, the method to be applied to the resource,
1493   the identifier of the resource, and the protocol version in use.
1495<!--                 Host                      ; should be moved here eventually -->
1496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1497  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1498                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1499                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1500                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1501                  <x:ref>CRLF</x:ref>
1502                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1505<section title="Request-Line" anchor="request-line">
1506  <x:anchor-alias value="Request-Line"/>
1508   The Request-Line begins with a method token, followed by the
1509   request-target and the protocol version, and ending with CRLF. The
1510   elements are separated by SP characters. No CR or LF is allowed
1511   except in the final CRLF sequence.
1513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1514  <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>
1517<section title="Method" anchor="method">
1518  <x:anchor-alias value="Method"/>
1520   The Method  token indicates the method to be performed on the
1521   resource identified by the request-target. The method is case-sensitive.
1523<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1524  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1528<section title="request-target" anchor="request-target">
1529  <x:anchor-alias value="request-target"/>
1531   The request-target
1532   identifies the resource upon which to apply the request.
1534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1535  <x:ref>request-target</x:ref> = "*"
1536                 / <x:ref>absolute-URI</x:ref>
1537                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1538                 / <x:ref>authority</x:ref>
1541   The four options for request-target are dependent on the nature of the
1542   request. The asterisk "*" means that the request does not apply to a
1543   particular resource, but to the server itself, and is only allowed
1544   when the method used does not necessarily apply to a resource. One
1545   example would be
1547<figure><artwork type="example">
1548  OPTIONS * HTTP/1.1
1551   The absolute-URI form is &REQUIRED; when the request is being made to a
1552   proxy. The proxy is requested to forward the request or service it
1553   from a valid cache, and return the response. Note that the proxy &MAY;
1554   forward the request on to another proxy or directly to the server
1555   specified by the absolute-URI. In order to avoid request loops, a
1556   proxy &MUST; be able to recognize all of its server names, including
1557   any aliases, local variations, and the numeric IP address. An example
1558   Request-Line would be:
1560<figure><artwork type="example">
1561  GET HTTP/1.1
1564   To allow for transition to absolute-URIs in all requests in future
1565   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1566   form in requests, even though HTTP/1.1 clients will only generate
1567   them in requests to proxies.
1570   The authority form is only used by the CONNECT method (&CONNECT;).
1573   The most common form of request-target is that used to identify a
1574   resource on an origin server or gateway. In this case the absolute
1575   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1576   the request-target, and the network location of the URI (authority) &MUST;
1577   be transmitted in a Host header field. For example, a client wishing
1578   to retrieve the resource above directly from the origin server would
1579   create a TCP connection to port 80 of the host "" and send
1580   the lines:
1582<figure><artwork type="example">
1583  GET /pub/WWW/TheProject.html HTTP/1.1
1584  Host:
1587   followed by the remainder of the Request. Note that the absolute path
1588   cannot be empty; if none is present in the original URI, it &MUST; be
1589   given as "/" (the server root).
1592   If a proxy receives a request without any path in the request-target and
1593   the method specified is capable of supporting the asterisk form of
1594   request-target, then the last proxy on the request chain &MUST; forward the
1595   request with "*" as the final request-target.
1598   For example, the request
1599</preamble><artwork type="example">
1600  OPTIONS HTTP/1.1
1603  would be forwarded by the proxy as
1604</preamble><artwork type="example">
1605  OPTIONS * HTTP/1.1
1606  Host:
1609   after connecting to port 8001 of host "".
1613   The request-target is transmitted in the format specified in
1614   <xref target="http.uri"/>. If the request-target is percent-encoded
1615   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1616   &MUST; decode the request-target in order to
1617   properly interpret the request. Servers &SHOULD; respond to invalid
1618   request-targets with an appropriate status code.
1621   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1622   received request-target when forwarding it to the next inbound server,
1623   except as noted above to replace a null path-absolute with "/".
1626  <t>
1627    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1628    meaning of the request when the origin server is improperly using
1629    a non-reserved URI character for a reserved purpose.  Implementors
1630    should be aware that some pre-HTTP/1.1 proxies have been known to
1631    rewrite the request-target.
1632  </t>
1635   HTTP does not place a pre-defined limit on the length of a request-target.
1636   A server &MUST; be prepared to receive URIs of unbounded length and
1637   respond with the 414 (URI Too Long) status if the received
1638   request-target would be longer than the server wishes to handle
1639   (see &status-414;).
1642   Various ad-hoc limitations on request-target length are found in practice.
1643   It is &RECOMMENDED; that all HTTP senders and recipients support
1644   request-target lengths of 8000 or more OCTETs.
1649<section title="The Resource Identified by a Request" anchor="">
1651   The exact resource identified by an Internet request is determined by
1652   examining both the request-target and the Host header field.
1655   An origin server that does not allow resources to differ by the
1656   requested host &MAY; ignore the Host header field value when
1657   determining the resource identified by an HTTP/1.1 request. (But see
1658   <xref target=""/>
1659   for other requirements on Host support in HTTP/1.1.)
1662   An origin server that does differentiate resources based on the host
1663   requested (sometimes referred to as virtual hosts or vanity host
1664   names) &MUST; use the following rules for determining the requested
1665   resource on an HTTP/1.1 request:
1666  <list style="numbers">
1667    <t>If request-target is an absolute-URI, the host is part of the
1668     request-target. Any Host header field value in the request &MUST; be
1669     ignored.</t>
1670    <t>If the request-target is not an absolute-URI, and the request includes
1671     a Host header field, the host is determined by the Host header
1672     field value.</t>
1673    <t>If the host as determined by rule 1 or 2 is not a valid host on
1674     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1675  </list>
1678   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1679   attempt to use heuristics (e.g., examination of the URI path for
1680   something unique to a particular host) in order to determine what
1681   exact resource is being requested.
1688<section title="Response" anchor="response">
1689  <x:anchor-alias value="Response"/>
1691   After receiving and interpreting a request message, a server responds
1692   with an HTTP response message.
1694<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1695  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1696                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1697                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1698                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1699                  <x:ref>CRLF</x:ref>
1700                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1703<section title="Status-Line" anchor="status-line">
1704  <x:anchor-alias value="Status-Line"/>
1706   The first line of a Response message is the Status-Line, consisting
1707   of the protocol version followed by a numeric status code and its
1708   associated textual phrase, with each element separated by SP
1709   characters. No CR or LF is allowed except in the final CRLF sequence.
1711<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1712  <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>
1715<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1716  <x:anchor-alias value="Reason-Phrase"/>
1717  <x:anchor-alias value="Status-Code"/>
1719   The Status-Code element is a 3-digit integer result code of the
1720   attempt to understand and satisfy the request. These codes are fully
1721   defined in &status-codes;.  The Reason Phrase exists for the sole
1722   purpose of providing a textual description associated with the numeric
1723   status code, out of deference to earlier Internet application protocols
1724   that were more frequently used with interactive text clients.
1725   A client &SHOULD; ignore the content of the Reason Phrase.
1728   The first digit of the Status-Code defines the class of response. The
1729   last two digits do not have any categorization role. There are 5
1730   values for the first digit:
1731  <list style="symbols">
1732    <t>
1733      1xx: Informational - Request received, continuing process
1734    </t>
1735    <t>
1736      2xx: Success - The action was successfully received,
1737        understood, and accepted
1738    </t>
1739    <t>
1740      3xx: Redirection - Further action must be taken in order to
1741        complete the request
1742    </t>
1743    <t>
1744      4xx: Client Error - The request contains bad syntax or cannot
1745        be fulfilled
1746    </t>
1747    <t>
1748      5xx: Server Error - The server failed to fulfill an apparently
1749        valid request
1750    </t>
1751  </list>
1753<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"/>
1754  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1755  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1763<section title="Connections" anchor="connections">
1765<section title="Persistent Connections" anchor="persistent.connections">
1767<section title="Purpose" anchor="persistent.purpose">
1769   Prior to persistent connections, a separate TCP connection was
1770   established to fetch each URL, increasing the load on HTTP servers
1771   and causing congestion on the Internet. The use of inline images and
1772   other associated data often require a client to make multiple
1773   requests of the same server in a short amount of time. Analysis of
1774   these performance problems and results from a prototype
1775   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1776   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1777   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1778   T/TCP <xref target="Tou1998"/>.
1781   Persistent HTTP connections have a number of advantages:
1782  <list style="symbols">
1783      <t>
1784        By opening and closing fewer TCP connections, CPU time is saved
1785        in routers and hosts (clients, servers, proxies, gateways,
1786        tunnels, or caches), and memory used for TCP protocol control
1787        blocks can be saved in hosts.
1788      </t>
1789      <t>
1790        HTTP requests and responses can be pipelined on a connection.
1791        Pipelining allows a client to make multiple requests without
1792        waiting for each response, allowing a single TCP connection to
1793        be used much more efficiently, with much lower elapsed time.
1794      </t>
1795      <t>
1796        Network congestion is reduced by reducing the number of packets
1797        caused by TCP opens, and by allowing TCP sufficient time to
1798        determine the congestion state of the network.
1799      </t>
1800      <t>
1801        Latency on subsequent requests is reduced since there is no time
1802        spent in TCP's connection opening handshake.
1803      </t>
1804      <t>
1805        HTTP can evolve more gracefully, since errors can be reported
1806        without the penalty of closing the TCP connection. Clients using
1807        future versions of HTTP might optimistically try a new feature,
1808        but if communicating with an older server, retry with old
1809        semantics after an error is reported.
1810      </t>
1811    </list>
1814   HTTP implementations &SHOULD; implement persistent connections.
1818<section title="Overall Operation" anchor="persistent.overall">
1820   A significant difference between HTTP/1.1 and earlier versions of
1821   HTTP is that persistent connections are the default behavior of any
1822   HTTP connection. That is, unless otherwise indicated, the client
1823   &SHOULD; assume that the server will maintain a persistent connection,
1824   even after error responses from the server.
1827   Persistent connections provide a mechanism by which a client and a
1828   server can signal the close of a TCP connection. This signaling takes
1829   place using the Connection header field (<xref target="header.connection"/>). Once a close
1830   has been signaled, the client &MUST-NOT; send any more requests on that
1831   connection.
1834<section title="Negotiation" anchor="persistent.negotiation">
1836   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1837   maintain a persistent connection unless a Connection header including
1838   the connection-token "close" was sent in the request. If the server
1839   chooses to close the connection immediately after sending the
1840   response, it &SHOULD; send a Connection header including the
1841   connection-token close.
1844   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1845   decide to keep it open based on whether the response from a server
1846   contains a Connection header with the connection-token close. In case
1847   the client does not want to maintain a connection for more than that
1848   request, it &SHOULD; send a Connection header including the
1849   connection-token close.
1852   If either the client or the server sends the close token in the
1853   Connection header, that request becomes the last one for the
1854   connection.
1857   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1858   maintained for HTTP versions less than 1.1 unless it is explicitly
1859   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1860   compatibility with HTTP/1.0 clients.
1863   In order to remain persistent, all messages on the connection &MUST;
1864   have a self-defined message length (i.e., one not defined by closure
1865   of the connection), as described in <xref target="message.length"/>.
1869<section title="Pipelining" anchor="pipelining">
1871   A client that supports persistent connections &MAY; "pipeline" its
1872   requests (i.e., send multiple requests without waiting for each
1873   response). A server &MUST; send its responses to those requests in the
1874   same order that the requests were received.
1877   Clients which assume persistent connections and pipeline immediately
1878   after connection establishment &SHOULD; be prepared to retry their
1879   connection if the first pipelined attempt fails. If a client does
1880   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1881   persistent. Clients &MUST; also be prepared to resend their requests if
1882   the server closes the connection before sending all of the
1883   corresponding responses.
1886   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1887   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1888   premature termination of the transport connection could lead to
1889   indeterminate results. A client wishing to send a non-idempotent
1890   request &SHOULD; wait to send that request until it has received the
1891   response status for the previous request.
1896<section title="Proxy Servers" anchor="persistent.proxy">
1898   It is especially important that proxies correctly implement the
1899   properties of the Connection header field as specified in <xref target="header.connection"/>.
1902   The proxy server &MUST; signal persistent connections separately with
1903   its clients and the origin servers (or other proxy servers) that it
1904   connects to. Each persistent connection applies to only one transport
1905   link.
1908   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1909   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1910   discussion of the problems with the Keep-Alive header implemented by
1911   many HTTP/1.0 clients).
1915<section title="Practical Considerations" anchor="persistent.practical">
1917   Servers will usually have some time-out value beyond which they will
1918   no longer maintain an inactive connection. Proxy servers might make
1919   this a higher value since it is likely that the client will be making
1920   more connections through the same server. The use of persistent
1921   connections places no requirements on the length (or existence) of
1922   this time-out for either the client or the server.
1925   When a client or server wishes to time-out it &SHOULD; issue a graceful
1926   close on the transport connection. Clients and servers &SHOULD; both
1927   constantly watch for the other side of the transport close, and
1928   respond to it as appropriate. If a client or server does not detect
1929   the other side's close promptly it could cause unnecessary resource
1930   drain on the network.
1933   A client, server, or proxy &MAY; close the transport connection at any
1934   time. For example, a client might have started to send a new request
1935   at the same time that the server has decided to close the "idle"
1936   connection. From the server's point of view, the connection is being
1937   closed while it was idle, but from the client's point of view, a
1938   request is in progress.
1941   This means that clients, servers, and proxies &MUST; be able to recover
1942   from asynchronous close events. Client software &SHOULD; reopen the
1943   transport connection and retransmit the aborted sequence of requests
1944   without user interaction so long as the request sequence is
1945   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1946   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1947   human operator the choice of retrying the request(s). Confirmation by
1948   user-agent software with semantic understanding of the application
1949   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1950   be repeated if the second sequence of requests fails.
1953   Servers &SHOULD; always respond to at least one request per connection,
1954   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1955   middle of transmitting a response, unless a network or client failure
1956   is suspected.
1959   Clients that use persistent connections &SHOULD; limit the number of
1960   simultaneous connections that they maintain to a given server. A
1961   single-user client &SHOULD-NOT; maintain more than 2 connections with
1962   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1963   another server or proxy, where N is the number of simultaneously
1964   active users. These guidelines are intended to improve HTTP response
1965   times and avoid congestion.
1970<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1972<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1974   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1975   flow control mechanisms to resolve temporary overloads, rather than
1976   terminating connections with the expectation that clients will retry.
1977   The latter technique can exacerbate network congestion.
1981<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1983   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1984   the network connection for an error status while it is transmitting
1985   the request. If the client sees an error status, it &SHOULD;
1986   immediately cease transmitting the body. If the body is being sent
1987   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1988   empty trailer &MAY; be used to prematurely mark the end of the message.
1989   If the body was preceded by a Content-Length header, the client &MUST;
1990   close the connection.
1994<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1996   The purpose of the 100 (Continue) status (see &status-100;) is to
1997   allow a client that is sending a request message with a request body
1998   to determine if the origin server is willing to accept the request
1999   (based on the request headers) before the client sends the request
2000   body. In some cases, it might either be inappropriate or highly
2001   inefficient for the client to send the body if the server will reject
2002   the message without looking at the body.
2005   Requirements for HTTP/1.1 clients:
2006  <list style="symbols">
2007    <t>
2008        If a client will wait for a 100 (Continue) response before
2009        sending the request body, it &MUST; send an Expect request-header
2010        field (&header-expect;) with the "100-continue" expectation.
2011    </t>
2012    <t>
2013        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2014        with the "100-continue" expectation if it does not intend
2015        to send a request body.
2016    </t>
2017  </list>
2020   Because of the presence of older implementations, the protocol allows
2021   ambiguous situations in which a client may send "Expect: 100-continue"
2022   without receiving either a 417 (Expectation Failed) status
2023   or a 100 (Continue) status. Therefore, when a client sends this
2024   header field to an origin server (possibly via a proxy) from which it
2025   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2026   for an indefinite period before sending the request body.
2029   Requirements for HTTP/1.1 origin servers:
2030  <list style="symbols">
2031    <t> Upon receiving a request which includes an Expect request-header
2032        field with the "100-continue" expectation, an origin server &MUST;
2033        either respond with 100 (Continue) status and continue to read
2034        from the input stream, or respond with a final status code. The
2035        origin server &MUST-NOT; wait for the request body before sending
2036        the 100 (Continue) response. If it responds with a final status
2037        code, it &MAY; close the transport connection or it &MAY; continue
2038        to read and discard the rest of the request.  It &MUST-NOT;
2039        perform the requested method if it returns a final status code.
2040    </t>
2041    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2042        the request message does not include an Expect request-header
2043        field with the "100-continue" expectation, and &MUST-NOT; send a
2044        100 (Continue) response if such a request comes from an HTTP/1.0
2045        (or earlier) client. There is an exception to this rule: for
2046        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2047        status in response to an HTTP/1.1 PUT or POST request that does
2048        not include an Expect request-header field with the "100-continue"
2049        expectation. This exception, the purpose of which is
2050        to minimize any client processing delays associated with an
2051        undeclared wait for 100 (Continue) status, applies only to
2052        HTTP/1.1 requests, and not to requests with any other HTTP-version
2053        value.
2054    </t>
2055    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2056        already received some or all of the request body for the
2057        corresponding request.
2058    </t>
2059    <t> An origin server that sends a 100 (Continue) response &MUST;
2060    ultimately send a final status code, once the request body is
2061        received and processed, unless it terminates the transport
2062        connection prematurely.
2063    </t>
2064    <t> If an origin server receives a request that does not include an
2065        Expect request-header field with the "100-continue" expectation,
2066        the request includes a request body, and the server responds
2067        with a final status code before reading the entire request body
2068        from the transport connection, then the server &SHOULD-NOT;  close
2069        the transport connection until it has read the entire request,
2070        or until the client closes the connection. Otherwise, the client
2071        might not reliably receive the response message. However, this
2072        requirement is not be construed as preventing a server from
2073        defending itself against denial-of-service attacks, or from
2074        badly broken client implementations.
2075      </t>
2076    </list>
2079   Requirements for HTTP/1.1 proxies:
2080  <list style="symbols">
2081    <t> If a proxy receives a request that includes an Expect request-header
2082        field with the "100-continue" expectation, and the proxy
2083        either knows that the next-hop server complies with HTTP/1.1 or
2084        higher, or does not know the HTTP version of the next-hop
2085        server, it &MUST; forward the request, including the Expect header
2086        field.
2087    </t>
2088    <t> If the proxy knows that the version of the next-hop server is
2089        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2090        respond with a 417 (Expectation Failed) status.
2091    </t>
2092    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2093        numbers received from recently-referenced next-hop servers.
2094    </t>
2095    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2096        request message was received from an HTTP/1.0 (or earlier)
2097        client and did not include an Expect request-header field with
2098        the "100-continue" expectation. This requirement overrides the
2099        general rule for forwarding of 1xx responses (see &status-1xx;).
2100    </t>
2101  </list>
2105<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2107   If an HTTP/1.1 client sends a request which includes a request body,
2108   but which does not include an Expect request-header field with the
2109   "100-continue" expectation, and if the client is not directly
2110   connected to an HTTP/1.1 origin server, and if the client sees the
2111   connection close before receiving any status from the server, the
2112   client &SHOULD; retry the request.  If the client does retry this
2113   request, it &MAY; use the following "binary exponential backoff"
2114   algorithm to be assured of obtaining a reliable response:
2115  <list style="numbers">
2116    <t>
2117      Initiate a new connection to the server
2118    </t>
2119    <t>
2120      Transmit the request-headers
2121    </t>
2122    <t>
2123      Initialize a variable R to the estimated round-trip time to the
2124         server (e.g., based on the time it took to establish the
2125         connection), or to a constant value of 5 seconds if the round-trip
2126         time is not available.
2127    </t>
2128    <t>
2129       Compute T = R * (2**N), where N is the number of previous
2130         retries of this request.
2131    </t>
2132    <t>
2133       Wait either for an error response from the server, or for T
2134         seconds (whichever comes first)
2135    </t>
2136    <t>
2137       If no error response is received, after T seconds transmit the
2138         body of the request.
2139    </t>
2140    <t>
2141       If client sees that the connection is closed prematurely,
2142         repeat from step 1 until the request is accepted, an error
2143         response is received, or the user becomes impatient and
2144         terminates the retry process.
2145    </t>
2146  </list>
2149   If at any point an error status is received, the client
2150  <list style="symbols">
2151      <t>&SHOULD-NOT;  continue and</t>
2153      <t>&SHOULD; close the connection if it has not completed sending the
2154        request message.</t>
2155    </list>
2162<section title="Header Field Definitions" anchor="header.fields">
2164   This section defines the syntax and semantics of HTTP/1.1 header fields
2165   related to message framing and transport protocols.
2168   For entity-header fields, both sender and recipient refer to either the
2169   client or the server, depending on who sends and who receives the entity.
2172<section title="Connection" anchor="header.connection">
2173  <iref primary="true" item="Connection header" x:for-anchor=""/>
2174  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2175  <x:anchor-alias value="Connection"/>
2176  <x:anchor-alias value="connection-token"/>
2177  <x:anchor-alias value="Connection-v"/>
2179   The general-header field "Connection" allows the sender to specify
2180   options that are desired for that particular connection and &MUST-NOT;
2181   be communicated by proxies over further connections.
2184   The Connection header's value has the following grammar:
2186<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"/>
2187  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2188  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2189  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2192   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2193   message is forwarded and, for each connection-token in this field,
2194   remove any header field(s) from the message with the same name as the
2195   connection-token. Connection options are signaled by the presence of
2196   a connection-token in the Connection header field, not by any
2197   corresponding additional header field(s), since the additional header
2198   field may not be sent if there are no parameters associated with that
2199   connection option.
2202   Message headers listed in the Connection header &MUST-NOT; include
2203   end-to-end headers, such as Cache-Control.
2206   HTTP/1.1 defines the "close" connection option for the sender to
2207   signal that the connection will be closed after completion of the
2208   response. For example,
2210<figure><artwork type="example">
2211  Connection: close
2214   in either the request or the response header fields indicates that
2215   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2216   after the current request/response is complete.
2219   An HTTP/1.1 client that does not support persistent connections &MUST;
2220   include the "close" connection option in every request message.
2223   An HTTP/1.1 server that does not support persistent connections &MUST;
2224   include the "close" connection option in every response message that
2225   does not have a 1xx (informational) status code.
2228   A system receiving an HTTP/1.0 (or lower-version) message that
2229   includes a Connection header &MUST;, for each connection-token in this
2230   field, remove and ignore any header field(s) from the message with
2231   the same name as the connection-token. This protects against mistaken
2232   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2236<section title="Content-Length" anchor="header.content-length">
2237  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2238  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2239  <x:anchor-alias value="Content-Length"/>
2240  <x:anchor-alias value="Content-Length-v"/>
2242   The entity-header field "Content-Length" indicates the size of the
2243   entity-body, in decimal number of OCTETs, sent to the recipient or,
2244   in the case of the HEAD method, the size of the entity-body that
2245   would have been sent had the request been a GET.
2247<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2248  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2249  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2252   An example is
2254<figure><artwork type="example">
2255  Content-Length: 3495
2258   Applications &SHOULD; use this field to indicate the transfer-length of
2259   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2262   Any Content-Length greater than or equal to zero is a valid value.
2263   <xref target="message.length"/> describes how to determine the length of a message-body
2264   if a Content-Length is not given.
2267   Note that the meaning of this field is significantly different from
2268   the corresponding definition in MIME, where it is an optional field
2269   used within the "message/external-body" content-type. In HTTP, it
2270   &SHOULD; be sent whenever the message's length can be determined prior
2271   to being transferred, unless this is prohibited by the rules in
2272   <xref target="message.length"/>.
2276<section title="Date" anchor="">
2277  <iref primary="true" item="Date header" x:for-anchor=""/>
2278  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2279  <x:anchor-alias value="Date"/>
2280  <x:anchor-alias value="Date-v"/>
2282   The general-header field "Date" represents the date and time at which
2283   the message was originated, having the same semantics as orig-date in
2284   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2285   HTTP-date, as described in <xref target=""/>;
2286   it &MUST; be sent in rfc1123-date format.
2288<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2289  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2290  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2293   An example is
2295<figure><artwork type="example">
2296  Date: Tue, 15 Nov 1994 08:12:31 GMT
2299   Origin servers &MUST; include a Date header field in all responses,
2300   except in these cases:
2301  <list style="numbers">
2302      <t>If the response status code is 100 (Continue) or 101 (Switching
2303         Protocols), the response &MAY; include a Date header field, at
2304         the server's option.</t>
2306      <t>If the response status code conveys a server error, e.g. 500
2307         (Internal Server Error) or 503 (Service Unavailable), and it is
2308         inconvenient or impossible to generate a valid Date.</t>
2310      <t>If the server does not have a clock that can provide a
2311         reasonable approximation of the current time, its responses
2312         &MUST-NOT; include a Date header field. In this case, the rules
2313         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2314  </list>
2317   A received message that does not have a Date header field &MUST; be
2318   assigned one by the recipient if the message will be cached by that
2319   recipient or gatewayed via a protocol which requires a Date. An HTTP
2320   implementation without a clock &MUST-NOT; cache responses without
2321   revalidating them on every use. An HTTP cache, especially a shared
2322   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2323   clock with a reliable external standard.
2326   Clients &SHOULD; only send a Date header field in messages that include
2327   an entity-body, as in the case of the PUT and POST requests, and even
2328   then it is optional. A client without a clock &MUST-NOT; send a Date
2329   header field in a request.
2332   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2333   time subsequent to the generation of the message. It &SHOULD; represent
2334   the best available approximation of the date and time of message
2335   generation, unless the implementation has no means of generating a
2336   reasonably accurate date and time. In theory, the date ought to
2337   represent the moment just before the entity is generated. In
2338   practice, the date can be generated at any time during the message
2339   origination without affecting its semantic value.
2342<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2344   Some origin server implementations might not have a clock available.
2345   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2346   values to a response, unless these values were associated
2347   with the resource by a system or user with a reliable clock. It &MAY;
2348   assign an Expires value that is known, at or before server
2349   configuration time, to be in the past (this allows "pre-expiration"
2350   of responses without storing separate Expires values for each
2351   resource).
2356<section title="Host" anchor="">
2357  <iref primary="true" item="Host header" x:for-anchor=""/>
2358  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2359  <x:anchor-alias value="Host"/>
2360  <x:anchor-alias value="Host-v"/>
2362   The request-header field "Host" specifies the Internet host and port
2363   number of the resource being requested, as obtained from the original
2364   URI given by the user or referring resource (generally an http URI,
2365   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2366   the naming authority of the origin server or gateway given by the
2367   original URL. This allows the origin server or gateway to
2368   differentiate between internally-ambiguous URLs, such as the root "/"
2369   URL of a server for multiple host names on a single IP address.
2371<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2372  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2373  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2376   A "host" without any trailing port information implies the default
2377   port for the service requested (e.g., "80" for an HTTP URL). For
2378   example, a request on the origin server for
2379   &lt;; would properly include:
2381<figure><artwork type="example">
2382  GET /pub/WWW/ HTTP/1.1
2383  Host:
2386   A client &MUST; include a Host header field in all HTTP/1.1 request
2387   messages. If the requested URI does not include an Internet host
2388   name for the service being requested, then the Host header field &MUST;
2389   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2390   request message it forwards does contain an appropriate Host header
2391   field that identifies the service being requested by the proxy. All
2392   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2393   status code to any HTTP/1.1 request message which lacks a Host header
2394   field.
2397   See Sections <xref target="" format="counter"/>
2398   and <xref target="" format="counter"/>
2399   for other requirements relating to Host.
2403<section title="TE" anchor="header.te">
2404  <iref primary="true" item="TE header" x:for-anchor=""/>
2405  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2406  <x:anchor-alias value="TE"/>
2407  <x:anchor-alias value="TE-v"/>
2408  <x:anchor-alias value="t-codings"/>
2409  <x:anchor-alias value="te-params"/>
2410  <x:anchor-alias value="te-ext"/>
2412   The request-header field "TE" indicates what extension transfer-codings
2413   it is willing to accept in the response and whether or not it is
2414   willing to accept trailer fields in a chunked transfer-coding. Its
2415   value may consist of the keyword "trailers" and/or a comma-separated
2416   list of extension transfer-coding names with optional accept
2417   parameters (as described in <xref target="transfer.codings"/>).
2419<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"/>
2420  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2421  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2422  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2423  <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> )
2424  <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> ) ]
2427   The presence of the keyword "trailers" indicates that the client is
2428   willing to accept trailer fields in a chunked transfer-coding, as
2429   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2430   transfer-coding values even though it does not itself represent a
2431   transfer-coding.
2434   Examples of its use are:
2436<figure><artwork type="example">
2437  TE: deflate
2438  TE:
2439  TE: trailers, deflate;q=0.5
2442   The TE header field only applies to the immediate connection.
2443   Therefore, the keyword &MUST; be supplied within a Connection header
2444   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2447   A server tests whether a transfer-coding is acceptable, according to
2448   a TE field, using these rules:
2449  <list style="numbers">
2450    <x:lt>
2451      <t>The "chunked" transfer-coding is always acceptable. If the
2452         keyword "trailers" is listed, the client indicates that it is
2453         willing to accept trailer fields in the chunked response on
2454         behalf of itself and any downstream clients. The implication is
2455         that, if given, the client is stating that either all
2456         downstream clients are willing to accept trailer fields in the
2457         forwarded response, or that it will attempt to buffer the
2458         response on behalf of downstream recipients.
2459      </t><t>
2460         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2461         chunked response such that a client can be assured of buffering
2462         the entire response.</t>
2463    </x:lt>
2464    <x:lt>
2465      <t>If the transfer-coding being tested is one of the transfer-codings
2466         listed in the TE field, then it is acceptable unless it
2467         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2468         qvalue of 0 means "not acceptable.")</t>
2469    </x:lt>
2470    <x:lt>
2471      <t>If multiple transfer-codings are acceptable, then the
2472         acceptable transfer-coding with the highest non-zero qvalue is
2473         preferred.  The "chunked" transfer-coding always has a qvalue
2474         of 1.</t>
2475    </x:lt>
2476  </list>
2479   If the TE field-value is empty or if no TE field is present, the only
2480   transfer-coding is "chunked". A message with no transfer-coding is
2481   always acceptable.
2485<section title="Trailer" anchor="header.trailer">
2486  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2487  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2488  <x:anchor-alias value="Trailer"/>
2489  <x:anchor-alias value="Trailer-v"/>
2491   The general field "Trailer" indicates that the given set of
2492   header fields is present in the trailer of a message encoded with
2493   chunked transfer-coding.
2495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2496  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2497  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2500   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2501   message using chunked transfer-coding with a non-empty trailer. Doing
2502   so allows the recipient to know which header fields to expect in the
2503   trailer.
2506   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2507   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2508   trailer fields in a "chunked" transfer-coding.
2511   Message header fields listed in the Trailer header field &MUST-NOT;
2512   include the following header fields:
2513  <list style="symbols">
2514    <t>Transfer-Encoding</t>
2515    <t>Content-Length</t>
2516    <t>Trailer</t>
2517  </list>
2521<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2522  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2523  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2524  <x:anchor-alias value="Transfer-Encoding"/>
2525  <x:anchor-alias value="Transfer-Encoding-v"/>
2527   The general-header "Transfer-Encoding" field indicates what (if any)
2528   type of transformation has been applied to the message body in order
2529   to safely transfer it between the sender and the recipient. This
2530   differs from the content-coding in that the transfer-coding is a
2531   property of the message, not of the entity.
2533<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2534  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2535                        <x:ref>Transfer-Encoding-v</x:ref>
2536  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2539   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2541<figure><artwork type="example">
2542  Transfer-Encoding: chunked
2545   If multiple encodings have been applied to an entity, the transfer-codings
2546   &MUST; be listed in the order in which they were applied.
2547   Additional information about the encoding parameters &MAY; be provided
2548   by other entity-header fields not defined by this specification.
2551   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2552   header.
2556<section title="Upgrade" anchor="header.upgrade">
2557  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2558  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2559  <x:anchor-alias value="Upgrade"/>
2560  <x:anchor-alias value="Upgrade-v"/>
2562   The general-header "Upgrade" allows the client to specify what
2563   additional communication protocols it supports and would like to use
2564   if the server finds it appropriate to switch protocols. The server
2565   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2566   response to indicate which protocol(s) are being switched.
2568<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2569  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2570  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2573   For example,
2575<figure><artwork type="example">
2576  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2579   The Upgrade header field is intended to provide a simple mechanism
2580   for transition from HTTP/1.1 to some other, incompatible protocol. It
2581   does so by allowing the client to advertise its desire to use another
2582   protocol, such as a later version of HTTP with a higher major version
2583   number, even though the current request has been made using HTTP/1.1.
2584   This eases the difficult transition between incompatible protocols by
2585   allowing the client to initiate a request in the more commonly
2586   supported protocol while indicating to the server that it would like
2587   to use a "better" protocol if available (where "better" is determined
2588   by the server, possibly according to the nature of the method and/or
2589   resource being requested).
2592   The Upgrade header field only applies to switching application-layer
2593   protocols upon the existing transport-layer connection. Upgrade
2594   cannot be used to insist on a protocol change; its acceptance and use
2595   by the server is optional. The capabilities and nature of the
2596   application-layer communication after the protocol change is entirely
2597   dependent upon the new protocol chosen, although the first action
2598   after changing the protocol &MUST; be a response to the initial HTTP
2599   request containing the Upgrade header field.
2602   The Upgrade header field only applies to the immediate connection.
2603   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2604   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2605   HTTP/1.1 message.
2608   The Upgrade header field cannot be used to indicate a switch to a
2609   protocol on a different connection. For that purpose, it is more
2610   appropriate to use a 301, 302, 303, or 305 redirection response.
2613   This specification only defines the protocol name "HTTP" for use by
2614   the family of Hypertext Transfer Protocols, as defined by the HTTP
2615   version rules of <xref target="http.version"/> and future updates to this
2616   specification. Any token can be used as a protocol name; however, it
2617   will only be useful if both the client and server associate the name
2618   with the same protocol.
2622<section title="Via" anchor="header.via">
2623  <iref primary="true" item="Via header" x:for-anchor=""/>
2624  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2625  <x:anchor-alias value="protocol-name"/>
2626  <x:anchor-alias value="protocol-version"/>
2627  <x:anchor-alias value="pseudonym"/>
2628  <x:anchor-alias value="received-by"/>
2629  <x:anchor-alias value="received-protocol"/>
2630  <x:anchor-alias value="Via"/>
2631  <x:anchor-alias value="Via-v"/>
2633   The general-header field "Via" &MUST; be used by gateways and proxies to
2634   indicate the intermediate protocols and recipients between the user
2635   agent and the server on requests, and between the origin server and
2636   the client on responses. It is analogous to the "Received" field defined in
2637   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2638   avoiding request loops, and identifying the protocol capabilities of
2639   all senders along the request/response chain.
2641<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"/>
2642  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2643  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2644                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2645  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2646  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2647  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2648  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2649  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2652   The received-protocol indicates the protocol version of the message
2653   received by the server or client along each segment of the
2654   request/response chain. The received-protocol version is appended to
2655   the Via field value when the message is forwarded so that information
2656   about the protocol capabilities of upstream applications remains
2657   visible to all recipients.
2660   The protocol-name is optional if and only if it would be "HTTP". The
2661   received-by field is normally the host and optional port number of a
2662   recipient server or client that subsequently forwarded the message.
2663   However, if the real host is considered to be sensitive information,
2664   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2665   be assumed to be the default port of the received-protocol.
2668   Multiple Via field values represents each proxy or gateway that has
2669   forwarded the message. Each recipient &MUST; append its information
2670   such that the end result is ordered according to the sequence of
2671   forwarding applications.
2674   Comments &MAY; be used in the Via header field to identify the software
2675   of the recipient proxy or gateway, analogous to the User-Agent and
2676   Server header fields. However, all comments in the Via field are
2677   optional and &MAY; be removed by any recipient prior to forwarding the
2678   message.
2681   For example, a request message could be sent from an HTTP/1.0 user
2682   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2683   forward the request to a public proxy at, which completes
2684   the request by forwarding it to the origin server at
2685   The request received by would then have the following
2686   Via header field:
2688<figure><artwork type="example">
2689  Via: 1.0 fred, 1.1 (Apache/1.1)
2692   Proxies and gateways used as a portal through a network firewall
2693   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2694   the firewall region. This information &SHOULD; only be propagated if
2695   explicitly enabled. If not enabled, the received-by host of any host
2696   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2697   for that host.
2700   For organizations that have strong privacy requirements for hiding
2701   internal structures, a proxy &MAY; combine an ordered subsequence of
2702   Via header field entries with identical received-protocol values into
2703   a single such entry. For example,
2705<figure><artwork type="example">
2706  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2709        could be collapsed to
2711<figure><artwork type="example">
2712  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2715   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2716   under the same organizational control and the hosts have already been
2717   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2718   have different received-protocol values.
2724<section title="IANA Considerations" anchor="IANA.considerations">
2725<section title="Message Header Registration" anchor="message.header.registration">
2727   The Message Header Registry located at <eref target=""/> should be updated
2728   with the permanent registrations below (see <xref target="RFC3864"/>):
2730<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2731<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2732   <ttcol>Header Field Name</ttcol>
2733   <ttcol>Protocol</ttcol>
2734   <ttcol>Status</ttcol>
2735   <ttcol>Reference</ttcol>
2737   <c>Connection</c>
2738   <c>http</c>
2739   <c>standard</c>
2740   <c>
2741      <xref target="header.connection"/>
2742   </c>
2743   <c>Content-Length</c>
2744   <c>http</c>
2745   <c>standard</c>
2746   <c>
2747      <xref target="header.content-length"/>
2748   </c>
2749   <c>Date</c>
2750   <c>http</c>
2751   <c>standard</c>
2752   <c>
2753      <xref target=""/>
2754   </c>
2755   <c>Host</c>
2756   <c>http</c>
2757   <c>standard</c>
2758   <c>
2759      <xref target=""/>
2760   </c>
2761   <c>TE</c>
2762   <c>http</c>
2763   <c>standard</c>
2764   <c>
2765      <xref target="header.te"/>
2766   </c>
2767   <c>Trailer</c>
2768   <c>http</c>
2769   <c>standard</c>
2770   <c>
2771      <xref target="header.trailer"/>
2772   </c>
2773   <c>Transfer-Encoding</c>
2774   <c>http</c>
2775   <c>standard</c>
2776   <c>
2777      <xref target="header.transfer-encoding"/>
2778   </c>
2779   <c>Upgrade</c>
2780   <c>http</c>
2781   <c>standard</c>
2782   <c>
2783      <xref target="header.upgrade"/>
2784   </c>
2785   <c>Via</c>
2786   <c>http</c>
2787   <c>standard</c>
2788   <c>
2789      <xref target="header.via"/>
2790   </c>
2794   The change controller is: "IETF ( - Internet Engineering Task Force".
2798<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2800   The entry for the "http" URI Scheme in the registry located at
2801   <eref target=""/>
2802   should be updated to point to <xref target="http.uri"/> of this document
2803   (see <xref target="RFC4395"/>).
2807<section title="Internet Media Type Registrations" anchor="">
2809   This document serves as the specification for the Internet media types
2810   "message/http" and "application/http". The following is to be registered with
2811   IANA (see <xref target="RFC4288"/>).
2813<section title="Internet Media Type message/http" anchor="">
2814<iref item="Media Type" subitem="message/http" primary="true"/>
2815<iref item="message/http Media Type" primary="true"/>
2817   The message/http type can be used to enclose a single HTTP request or
2818   response message, provided that it obeys the MIME restrictions for all
2819   "message" types regarding line length and encodings.
2822  <list style="hanging" x:indent="12em">
2823    <t hangText="Type name:">
2824      message
2825    </t>
2826    <t hangText="Subtype name:">
2827      http
2828    </t>
2829    <t hangText="Required parameters:">
2830      none
2831    </t>
2832    <t hangText="Optional parameters:">
2833      version, msgtype
2834      <list style="hanging">
2835        <t hangText="version:">
2836          The HTTP-Version number of the enclosed message
2837          (e.g., "1.1"). If not present, the version can be
2838          determined from the first line of the body.
2839        </t>
2840        <t hangText="msgtype:">
2841          The message type -- "request" or "response". If not
2842          present, the type can be determined from the first
2843          line of the body.
2844        </t>
2845      </list>
2846    </t>
2847    <t hangText="Encoding considerations:">
2848      only "7bit", "8bit", or "binary" are permitted
2849    </t>
2850    <t hangText="Security considerations:">
2851      none
2852    </t>
2853    <t hangText="Interoperability considerations:">
2854      none
2855    </t>
2856    <t hangText="Published specification:">
2857      This specification (see <xref target=""/>).
2858    </t>
2859    <t hangText="Applications that use this media type:">
2860    </t>
2861    <t hangText="Additional information:">
2862      <list style="hanging">
2863        <t hangText="Magic number(s):">none</t>
2864        <t hangText="File extension(s):">none</t>
2865        <t hangText="Macintosh file type code(s):">none</t>
2866      </list>
2867    </t>
2868    <t hangText="Person and email address to contact for further information:">
2869      See Authors Section.
2870    </t>
2871                <t hangText="Intended usage:">
2872                  COMMON
2873    </t>
2874                <t hangText="Restrictions on usage:">
2875                  none
2876    </t>
2877    <t hangText="Author/Change controller:">
2878      IESG
2879    </t>
2880  </list>
2883<section title="Internet Media Type application/http" anchor="">
2884<iref item="Media Type" subitem="application/http" primary="true"/>
2885<iref item="application/http Media Type" primary="true"/>
2887   The application/http type can be used to enclose a pipeline of one or more
2888   HTTP request or response messages (not intermixed).
2891  <list style="hanging" x:indent="12em">
2892    <t hangText="Type name:">
2893      application
2894    </t>
2895    <t hangText="Subtype name:">
2896      http
2897    </t>
2898    <t hangText="Required parameters:">
2899      none
2900    </t>
2901    <t hangText="Optional parameters:">
2902      version, msgtype
2903      <list style="hanging">
2904        <t hangText="version:">
2905          The HTTP-Version number of the enclosed messages
2906          (e.g., "1.1"). If not present, the version can be
2907          determined from the first line of the body.
2908        </t>
2909        <t hangText="msgtype:">
2910          The message type -- "request" or "response". If not
2911          present, the type can be determined from the first
2912          line of the body.
2913        </t>
2914      </list>
2915    </t>
2916    <t hangText="Encoding considerations:">
2917      HTTP messages enclosed by this type
2918      are in "binary" format; use of an appropriate
2919      Content-Transfer-Encoding is required when
2920      transmitted via E-mail.
2921    </t>
2922    <t hangText="Security considerations:">
2923      none
2924    </t>
2925    <t hangText="Interoperability considerations:">
2926      none
2927    </t>
2928    <t hangText="Published specification:">
2929      This specification (see <xref target=""/>).
2930    </t>
2931    <t hangText="Applications that use this media type:">
2932    </t>
2933    <t hangText="Additional information:">
2934      <list style="hanging">
2935        <t hangText="Magic number(s):">none</t>
2936        <t hangText="File extension(s):">none</t>
2937        <t hangText="Macintosh file type code(s):">none</t>
2938      </list>
2939    </t>
2940    <t hangText="Person and email address to contact for further information:">
2941      See Authors Section.
2942    </t>
2943                <t hangText="Intended usage:">
2944                  COMMON
2945    </t>
2946                <t hangText="Restrictions on usage:">
2947                  none
2948    </t>
2949    <t hangText="Author/Change controller:">
2950      IESG
2951    </t>
2952  </list>
2959<section title="Security Considerations" anchor="security.considerations">
2961   This section is meant to inform application developers, information
2962   providers, and users of the security limitations in HTTP/1.1 as
2963   described by this document. The discussion does not include
2964   definitive solutions to the problems revealed, though it does make
2965   some suggestions for reducing security risks.
2968<section title="Personal Information" anchor="personal.information">
2970   HTTP clients are often privy to large amounts of personal information
2971   (e.g. the user's name, location, mail address, passwords, encryption
2972   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2973   leakage of this information.
2974   We very strongly recommend that a convenient interface be provided
2975   for the user to control dissemination of such information, and that
2976   designers and implementors be particularly careful in this area.
2977   History shows that errors in this area often create serious security
2978   and/or privacy problems and generate highly adverse publicity for the
2979   implementor's company.
2983<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2985   A server is in the position to save personal data about a user's
2986   requests which might identify their reading patterns or subjects of
2987   interest. This information is clearly confidential in nature and its
2988   handling can be constrained by law in certain countries. People using
2989   HTTP to provide data are responsible for ensuring that
2990   such material is not distributed without the permission of any
2991   individuals that are identifiable by the published results.
2995<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2997   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2998   the documents returned by HTTP requests to be only those that were
2999   intended by the server administrators. If an HTTP server translates
3000   HTTP URIs directly into file system calls, the server &MUST; take
3001   special care not to serve files that were not intended to be
3002   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3003   other operating systems use ".." as a path component to indicate a
3004   directory level above the current one. On such a system, an HTTP
3005   server &MUST; disallow any such construct in the request-target if it
3006   would otherwise allow access to a resource outside those intended to
3007   be accessible via the HTTP server. Similarly, files intended for
3008   reference only internally to the server (such as access control
3009   files, configuration files, and script code) &MUST; be protected from
3010   inappropriate retrieval, since they might contain sensitive
3011   information. Experience has shown that minor bugs in such HTTP server
3012   implementations have turned into security risks.
3016<section title="DNS Spoofing" anchor="dns.spoofing">
3018   Clients using HTTP rely heavily on the Domain Name Service, and are
3019   thus generally prone to security attacks based on the deliberate
3020   mis-association of IP addresses and DNS names. Clients need to be
3021   cautious in assuming the continuing validity of an IP number/DNS name
3022   association.
3025   In particular, HTTP clients &SHOULD; rely on their name resolver for
3026   confirmation of an IP number/DNS name association, rather than
3027   caching the result of previous host name lookups. Many platforms
3028   already can cache host name lookups locally when appropriate, and
3029   they &SHOULD; be configured to do so. It is proper for these lookups to
3030   be cached, however, only when the TTL (Time To Live) information
3031   reported by the name server makes it likely that the cached
3032   information will remain useful.
3035   If HTTP clients cache the results of host name lookups in order to
3036   achieve a performance improvement, they &MUST; observe the TTL
3037   information reported by DNS.
3040   If HTTP clients do not observe this rule, they could be spoofed when
3041   a previously-accessed server's IP address changes. As network
3042   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3043   possibility of this form of attack will grow. Observing this
3044   requirement thus reduces this potential security vulnerability.
3047   This requirement also improves the load-balancing behavior of clients
3048   for replicated servers using the same DNS name and reduces the
3049   likelihood of a user's experiencing failure in accessing sites which
3050   use that strategy.
3054<section title="Proxies and Caching" anchor="attack.proxies">
3056   By their very nature, HTTP proxies are men-in-the-middle, and
3057   represent an opportunity for man-in-the-middle attacks. Compromise of
3058   the systems on which the proxies run can result in serious security
3059   and privacy problems. Proxies have access to security-related
3060   information, personal information about individual users and
3061   organizations, and proprietary information belonging to users and
3062   content providers. A compromised proxy, or a proxy implemented or
3063   configured without regard to security and privacy considerations,
3064   might be used in the commission of a wide range of potential attacks.
3067   Proxy operators should protect the systems on which proxies run as
3068   they would protect any system that contains or transports sensitive
3069   information. In particular, log information gathered at proxies often
3070   contains highly sensitive personal information, and/or information
3071   about organizations. Log information should be carefully guarded, and
3072   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3075   Proxy implementors should consider the privacy and security
3076   implications of their design and coding decisions, and of the
3077   configuration options they provide to proxy operators (especially the
3078   default configuration).
3081   Users of a proxy need to be aware that they are no trustworthier than
3082   the people who run the proxy; HTTP itself cannot solve this problem.
3085   The judicious use of cryptography, when appropriate, may suffice to
3086   protect against a broad range of security and privacy attacks. Such
3087   cryptography is beyond the scope of the HTTP/1.1 specification.
3091<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3093   They exist. They are hard to defend against. Research continues.
3094   Beware.
3099<section title="Acknowledgments" anchor="ack">
3101   HTTP has evolved considerably over the years. It has
3102   benefited from a large and active developer community--the many
3103   people who have participated on the www-talk mailing list--and it is
3104   that community which has been most responsible for the success of
3105   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3106   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3107   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3108   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3109   VanHeyningen deserve special recognition for their efforts in
3110   defining early aspects of the protocol.
3113   This document has benefited greatly from the comments of all those
3114   participating in the HTTP-WG. In addition to those already mentioned,
3115   the following individuals have contributed to this specification:
3118   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3119   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3120   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3121   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3122   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3123   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3124   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3125   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3126   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3127   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3128   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3129   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3130   Josh Cohen.
3133   Thanks to the "cave men" of Palo Alto. You know who you are.
3136   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3137   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3138   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3139   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3140   Larry Masinter for their help. And thanks go particularly to Jeff
3141   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3144   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3145   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3146   discovery of many of the problems that this document attempts to
3147   rectify.
3150   This specification makes heavy use of the augmented BNF and generic
3151   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3152   reuses many of the definitions provided by Nathaniel Borenstein and
3153   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3154   specification will help reduce past confusion over the relationship
3155   between HTTP and Internet mail message formats.
3162<references title="Normative References">
3164<reference anchor="ISO-8859-1">
3165  <front>
3166    <title>
3167     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3168    </title>
3169    <author>
3170      <organization>International Organization for Standardization</organization>
3171    </author>
3172    <date year="1998"/>
3173  </front>
3174  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3177<reference anchor="Part2">
3178  <front>
3179    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3180    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3181      <organization abbrev="Day Software">Day Software</organization>
3182      <address><email></email></address>
3183    </author>
3184    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3185      <organization>One Laptop per Child</organization>
3186      <address><email></email></address>
3187    </author>
3188    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3189      <organization abbrev="HP">Hewlett-Packard Company</organization>
3190      <address><email></email></address>
3191    </author>
3192    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3193      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3194      <address><email></email></address>
3195    </author>
3196    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3197      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3198      <address><email></email></address>
3199    </author>
3200    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3201      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3202      <address><email></email></address>
3203    </author>
3204    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3205      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3206      <address><email></email></address>
3207    </author>
3208    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3209      <organization abbrev="W3C">World Wide Web Consortium</organization>
3210      <address><email></email></address>
3211    </author>
3212    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3213      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3214      <address><email></email></address>
3215    </author>
3216    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3217  </front>
3218  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3219  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3222<reference anchor="Part3">
3223  <front>
3224    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3225    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3226      <organization abbrev="Day Software">Day Software</organization>
3227      <address><email></email></address>
3228    </author>
3229    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3230      <organization>One Laptop per Child</organization>
3231      <address><email></email></address>
3232    </author>
3233    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3234      <organization abbrev="HP">Hewlett-Packard Company</organization>
3235      <address><email></email></address>
3236    </author>
3237    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3238      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3239      <address><email></email></address>
3240    </author>
3241    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3242      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3243      <address><email></email></address>
3244    </author>
3245    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3246      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3247      <address><email></email></address>
3248    </author>
3249    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3250      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3251      <address><email></email></address>
3252    </author>
3253    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3254      <organization abbrev="W3C">World Wide Web Consortium</organization>
3255      <address><email></email></address>
3256    </author>
3257    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3258      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3259      <address><email></email></address>
3260    </author>
3261    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3262  </front>
3263  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3264  <x:source href="p3-payload.xml" basename="p3-payload"/>
3267<reference anchor="Part5">
3268  <front>
3269    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3270    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3271      <organization abbrev="Day Software">Day Software</organization>
3272      <address><email></email></address>
3273    </author>
3274    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3275      <organization>One Laptop per Child</organization>
3276      <address><email></email></address>
3277    </author>
3278    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3279      <organization abbrev="HP">Hewlett-Packard Company</organization>
3280      <address><email></email></address>
3281    </author>
3282    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3283      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3284      <address><email></email></address>
3285    </author>
3286    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3287      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3288      <address><email></email></address>
3289    </author>
3290    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3291      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3292      <address><email></email></address>
3293    </author>
3294    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3295      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3296      <address><email></email></address>
3297    </author>
3298    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3299      <organization abbrev="W3C">World Wide Web Consortium</organization>
3300      <address><email></email></address>
3301    </author>
3302    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3303      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3304      <address><email></email></address>
3305    </author>
3306    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3307  </front>
3308  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3309  <x:source href="p5-range.xml" basename="p5-range"/>
3312<reference anchor="Part6">
3313  <front>
3314    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3315    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3316      <organization abbrev="Day Software">Day Software</organization>
3317      <address><email></email></address>
3318    </author>
3319    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3320      <organization>One Laptop per Child</organization>
3321      <address><email></email></address>
3322    </author>
3323    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3324      <organization abbrev="HP">Hewlett-Packard Company</organization>
3325      <address><email></email></address>
3326    </author>
3327    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3328      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3329      <address><email></email></address>
3330    </author>
3331    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3332      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3333      <address><email></email></address>
3334    </author>
3335    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3336      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3337      <address><email></email></address>
3338    </author>
3339    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3340      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3341      <address><email></email></address>
3342    </author>
3343    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3344      <organization abbrev="W3C">World Wide Web Consortium</organization>
3345      <address><email></email></address>
3346    </author>
3347    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3348      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3349      <address><email></email></address>
3350    </author>
3351    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3352  </front>
3353  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3354  <x:source href="p6-cache.xml" basename="p6-cache"/>
3357<reference anchor="RFC5234">
3358  <front>
3359    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3360    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3361      <organization>Brandenburg InternetWorking</organization>
3362      <address>
3363      <postal>
3364      <street>675 Spruce Dr.</street>
3365      <city>Sunnyvale</city>
3366      <region>CA</region>
3367      <code>94086</code>
3368      <country>US</country></postal>
3369      <phone>+1.408.246.8253</phone>
3370      <email></email></address> 
3371    </author>
3372    <author initials="P." surname="Overell" fullname="Paul Overell">
3373      <organization>THUS plc.</organization>
3374      <address>
3375      <postal>
3376      <street>1/2 Berkeley Square</street>
3377      <street>99 Berkely Street</street>
3378      <city>Glasgow</city>
3379      <code>G3 7HR</code>
3380      <country>UK</country></postal>
3381      <email></email></address>
3382    </author>
3383    <date month="January" year="2008"/>
3384  </front>
3385  <seriesInfo name="STD" value="68"/>
3386  <seriesInfo name="RFC" value="5234"/>
3389<reference anchor="RFC2119">
3390  <front>
3391    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3392    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3393      <organization>Harvard University</organization>
3394      <address><email></email></address>
3395    </author>
3396    <date month="March" year="1997"/>
3397  </front>
3398  <seriesInfo name="BCP" value="14"/>
3399  <seriesInfo name="RFC" value="2119"/>
3402<reference anchor="RFC3986">
3403 <front>
3404  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3405  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3406    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3407    <address>
3408       <email></email>
3409       <uri></uri>
3410    </address>
3411  </author>
3412  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3413    <organization abbrev="Day Software">Day Software</organization>
3414    <address>
3415      <email></email>
3416      <uri></uri>
3417    </address>
3418  </author>
3419  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3420    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3421    <address>
3422      <email></email>
3423      <uri></uri>
3424    </address>
3425  </author>
3426  <date month='January' year='2005'></date>
3427 </front>
3428 <seriesInfo name="RFC" value="3986"/>
3429 <seriesInfo name="STD" value="66"/>
3432<reference anchor="USASCII">
3433  <front>
3434    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3435    <author>
3436      <organization>American National Standards Institute</organization>
3437    </author>
3438    <date year="1986"/>
3439  </front>
3440  <seriesInfo name="ANSI" value="X3.4"/>
3445<references title="Informative References">
3447<reference anchor="Nie1997" target="">
3448  <front>
3449    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3450    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3451      <organization/>
3452    </author>
3453    <author initials="J." surname="Gettys" fullname="J. Gettys">
3454      <organization/>
3455    </author>
3456    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3457      <organization/>
3458    </author>
3459    <author initials="H." surname="Lie" fullname="H. Lie">
3460      <organization/>
3461    </author>
3462    <author initials="C." surname="Lilley" fullname="C. Lilley">
3463      <organization/>
3464    </author>
3465    <date year="1997" month="September"/>
3466  </front>
3467  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3470<reference anchor="Pad1995" target="">
3471  <front>
3472    <title>Improving HTTP Latency</title>
3473    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3474      <organization/>
3475    </author>
3476    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3477      <organization/>
3478    </author>
3479    <date year="1995" month="December"/>
3480  </front>
3481  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3484<reference anchor="RFC1123">
3485  <front>
3486    <title>Requirements for Internet Hosts - Application and Support</title>
3487    <author initials="R." surname="Braden" fullname="Robert Braden">
3488      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3489      <address><email>Braden@ISI.EDU</email></address>
3490    </author>
3491    <date month="October" year="1989"/>
3492  </front>
3493  <seriesInfo name="STD" value="3"/>
3494  <seriesInfo name="RFC" value="1123"/>
3497<reference anchor="RFC1305">
3498  <front>
3499    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3500    <author initials="D." surname="Mills" fullname="David L. Mills">
3501      <organization>University of Delaware, Electrical Engineering Department</organization>
3502      <address><email></email></address>
3503    </author>
3504    <date month="March" year="1992"/>
3505  </front>
3506  <seriesInfo name="RFC" value="1305"/>
3509<reference anchor="RFC1900">
3510  <front>
3511    <title>Renumbering Needs Work</title>
3512    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3513      <organization>CERN, Computing and Networks Division</organization>
3514      <address><email></email></address>
3515    </author>
3516    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3517      <organization>cisco Systems</organization>
3518      <address><email></email></address>
3519    </author>
3520    <date month="February" year="1996"/>
3521  </front>
3522  <seriesInfo name="RFC" value="1900"/>
3525<reference anchor="RFC1945">
3526  <front>
3527    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3528    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3529      <organization>MIT, Laboratory for Computer Science</organization>
3530      <address><email></email></address>
3531    </author>
3532    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3533      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3534      <address><email></email></address>
3535    </author>
3536    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3537      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3538      <address><email></email></address>
3539    </author>
3540    <date month="May" year="1996"/>
3541  </front>
3542  <seriesInfo name="RFC" value="1945"/>
3545<reference anchor="RFC2045">
3546  <front>
3547    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3548    <author initials="N." surname="Freed" fullname="Ned Freed">
3549      <organization>Innosoft International, Inc.</organization>
3550      <address><email></email></address>
3551    </author>
3552    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3553      <organization>First Virtual Holdings</organization>
3554      <address><email></email></address>
3555    </author>
3556    <date month="November" year="1996"/>
3557  </front>
3558  <seriesInfo name="RFC" value="2045"/>
3561<reference anchor="RFC2047">
3562  <front>
3563    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3564    <author initials="K." surname="Moore" fullname="Keith Moore">
3565      <organization>University of Tennessee</organization>
3566      <address><email></email></address>
3567    </author>
3568    <date month="November" year="1996"/>
3569  </front>
3570  <seriesInfo name="RFC" value="2047"/>
3573<reference anchor="RFC2068">
3574  <front>
3575    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3576    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3577      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3578      <address><email></email></address>
3579    </author>
3580    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3581      <organization>MIT Laboratory for Computer Science</organization>
3582      <address><email></email></address>
3583    </author>
3584    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3585      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3586      <address><email></email></address>
3587    </author>
3588    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3589      <organization>MIT Laboratory for Computer Science</organization>
3590      <address><email></email></address>
3591    </author>
3592    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3593      <organization>MIT Laboratory for Computer Science</organization>
3594      <address><email></email></address>
3595    </author>
3596    <date month="January" year="1997"/>
3597  </front>
3598  <seriesInfo name="RFC" value="2068"/>
3601<reference anchor='RFC2109'>
3602  <front>
3603    <title>HTTP State Management Mechanism</title>
3604    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3605      <organization>Bell Laboratories, Lucent Technologies</organization>
3606      <address><email></email></address>
3607    </author>
3608    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3609      <organization>Netscape Communications Corp.</organization>
3610      <address><email></email></address>
3611    </author>
3612    <date year='1997' month='February' />
3613  </front>
3614  <seriesInfo name='RFC' value='2109' />
3617<reference anchor="RFC2145">
3618  <front>
3619    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3620    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3621      <organization>Western Research Laboratory</organization>
3622      <address><email></email></address>
3623    </author>
3624    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3625      <organization>Department of Information and Computer Science</organization>
3626      <address><email></email></address>
3627    </author>
3628    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3629      <organization>MIT Laboratory for Computer Science</organization>
3630      <address><email></email></address>
3631    </author>
3632    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3633      <organization>W3 Consortium</organization>
3634      <address><email></email></address>
3635    </author>
3636    <date month="May" year="1997"/>
3637  </front>
3638  <seriesInfo name="RFC" value="2145"/>
3641<reference anchor="RFC2616">
3642  <front>
3643    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3644    <author initials="R." surname="Fielding" fullname="R. Fielding">
3645      <organization>University of California, Irvine</organization>
3646      <address><email></email></address>
3647    </author>
3648    <author initials="J." surname="Gettys" fullname="J. Gettys">
3649      <organization>W3C</organization>
3650      <address><email></email></address>
3651    </author>
3652    <author initials="J." surname="Mogul" fullname="J. Mogul">
3653      <organization>Compaq Computer Corporation</organization>
3654      <address><email></email></address>
3655    </author>
3656    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3657      <organization>MIT Laboratory for Computer Science</organization>
3658      <address><email></email></address>
3659    </author>
3660    <author initials="L." surname="Masinter" fullname="L. Masinter">
3661      <organization>Xerox Corporation</organization>
3662      <address><email></email></address>
3663    </author>
3664    <author initials="P." surname="Leach" fullname="P. Leach">
3665      <organization>Microsoft Corporation</organization>
3666      <address><email></email></address>
3667    </author>
3668    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3669      <organization>W3C</organization>
3670      <address><email></email></address>
3671    </author>
3672    <date month="June" year="1999"/>
3673  </front>
3674  <seriesInfo name="RFC" value="2616"/>
3677<reference anchor='RFC2818'>
3678  <front>
3679    <title>HTTP Over TLS</title>
3680    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3681      <organization>RTFM, Inc.</organization>
3682      <address><email></email></address>
3683    </author>
3684    <date year='2000' month='May' />
3685  </front>
3686  <seriesInfo name='RFC' value='2818' />
3689<reference anchor='RFC2965'>
3690  <front>
3691    <title>HTTP State Management Mechanism</title>
3692    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3693      <organization>Bell Laboratories, Lucent Technologies</organization>
3694      <address><email></email></address>
3695    </author>
3696    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3697      <organization>, Inc.</organization>
3698      <address><email></email></address>
3699    </author>
3700    <date year='2000' month='October' />
3701  </front>
3702  <seriesInfo name='RFC' value='2965' />
3705<reference anchor='RFC3864'>
3706  <front>
3707    <title>Registration Procedures for Message Header Fields</title>
3708    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3709      <organization>Nine by Nine</organization>
3710      <address><email></email></address>
3711    </author>
3712    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3713      <organization>BEA Systems</organization>
3714      <address><email></email></address>
3715    </author>
3716    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3717      <organization>HP Labs</organization>
3718      <address><email></email></address>
3719    </author>
3720    <date year='2004' month='September' />
3721  </front>
3722  <seriesInfo name='BCP' value='90' />
3723  <seriesInfo name='RFC' value='3864' />
3726<reference anchor="RFC4288">
3727  <front>
3728    <title>Media Type Specifications and Registration Procedures</title>
3729    <author initials="N." surname="Freed" fullname="N. Freed">
3730      <organization>Sun Microsystems</organization>
3731      <address>
3732        <email></email>
3733      </address>
3734    </author>
3735    <author initials="J." surname="Klensin" fullname="J. Klensin">
3736      <organization/>
3737      <address>
3738        <email></email>
3739      </address>
3740    </author>
3741    <date year="2005" month="December"/>
3742  </front>
3743  <seriesInfo name="BCP" value="13"/>
3744  <seriesInfo name="RFC" value="4288"/>
3747<reference anchor='RFC4395'>
3748  <front>
3749    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3750    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3751      <organization>AT&amp;T Laboratories</organization>
3752      <address>
3753        <email></email>
3754      </address>
3755    </author>
3756    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3757      <organization>Qualcomm, Inc.</organization>
3758      <address>
3759        <email></email>
3760      </address>
3761    </author>
3762    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3763      <organization>Adobe Systems</organization>
3764      <address>
3765        <email></email>
3766      </address>
3767    </author>
3768    <date year='2006' month='February' />
3769  </front>
3770  <seriesInfo name='BCP' value='115' />
3771  <seriesInfo name='RFC' value='4395' />
3774<reference anchor="RFC5322">
3775  <front>
3776    <title>Internet Message Format</title>
3777    <author initials="P." surname="Resnick" fullname="P. Resnick">
3778      <organization>Qualcomm Incorporated</organization>
3779    </author>
3780    <date year="2008" month="October"/>
3781  </front>
3782  <seriesInfo name="RFC" value="5322"/>
3785<reference anchor="Kri2001" target="">
3786  <front>
3787    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3788    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3789      <organization/>
3790    </author>
3791    <date year="2001" month="November"/>
3792  </front>
3793  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3796<reference anchor="Spe" target="">
3797  <front>
3798  <title>Analysis of HTTP Performance Problems</title>
3799  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3800    <organization/>
3801  </author>
3802  <date/>
3803  </front>
3806<reference anchor="Tou1998" target="">
3807  <front>
3808  <title>Analysis of HTTP Performance</title>
3809  <author initials="J." surname="Touch" fullname="Joe Touch">
3810    <organization>USC/Information Sciences Institute</organization>
3811    <address><email></email></address>
3812  </author>
3813  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3814    <organization>USC/Information Sciences Institute</organization>
3815    <address><email></email></address>
3816  </author>
3817  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3818    <organization>USC/Information Sciences Institute</organization>
3819    <address><email></email></address>
3820  </author>
3821  <date year="1998" month="Aug"/>
3822  </front>
3823  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3824  <annotation>(original report dated Aug. 1996)</annotation>
3830<section title="Tolerant Applications" anchor="tolerant.applications">
3832   Although this document specifies the requirements for the generation
3833   of HTTP/1.1 messages, not all applications will be correct in their
3834   implementation. We therefore recommend that operational applications
3835   be tolerant of deviations whenever those deviations can be
3836   interpreted unambiguously.
3839   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3840   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3841   accept any amount of WSP characters between fields, even though
3842   only a single SP is required.
3845   The line terminator for message-header fields is the sequence CRLF.
3846   However, we recommend that applications, when parsing such headers,
3847   recognize a single LF as a line terminator and ignore the leading CR.
3850   The character set of an entity-body &SHOULD; be labeled as the lowest
3851   common denominator of the character codes used within that body, with
3852   the exception that not labeling the entity is preferred over labeling
3853   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3856   Additional rules for requirements on parsing and encoding of dates
3857   and other potential problems with date encodings include:
3860  <list style="symbols">
3861     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3862        which appears to be more than 50 years in the future is in fact
3863        in the past (this helps solve the "year 2000" problem).</t>
3865     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3866        Expires date as earlier than the proper value, but &MUST-NOT;
3867        internally represent a parsed Expires date as later than the
3868        proper value.</t>
3870     <t>All expiration-related calculations &MUST; be done in GMT. The
3871        local time zone &MUST-NOT; influence the calculation or comparison
3872        of an age or expiration time.</t>
3874     <t>If an HTTP header incorrectly carries a date value with a time
3875        zone other than GMT, it &MUST; be converted into GMT using the
3876        most conservative possible conversion.</t>
3877  </list>
3881<section title="Compatibility with Previous Versions" anchor="compatibility">
3883   HTTP has been in use by the World-Wide Web global information initiative
3884   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3885   was a simple protocol for hypertext data transfer across the Internet
3886   with only a single method and no metadata.
3887   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3888   methods and MIME-like messaging that could include metadata about the data
3889   transferred and modifiers on the request/response semantics. However,
3890   HTTP/1.0 did not sufficiently take into consideration the effects of
3891   hierarchical proxies, caching, the need for persistent connections, or
3892   name-based virtual hosts. The proliferation of incompletely-implemented
3893   applications calling themselves "HTTP/1.0" further necessitated a
3894   protocol version change in order for two communicating applications
3895   to determine each other's true capabilities.
3898   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3899   requirements that enable reliable implementations, adding only
3900   those new features that will either be safely ignored by an HTTP/1.0
3901   recipient or only sent when communicating with a party advertising
3902   compliance with HTTP/1.1.
3905   It is beyond the scope of a protocol specification to mandate
3906   compliance with previous versions. HTTP/1.1 was deliberately
3907   designed, however, to make supporting previous versions easy. It is
3908   worth noting that, at the time of composing this specification
3909   (1996), we would expect commercial HTTP/1.1 servers to:
3910  <list style="symbols">
3911     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3912        1.1 requests;</t>
3914     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3915        1.1;</t>
3917     <t>respond appropriately with a message in the same major version
3918        used by the client.</t>
3919  </list>
3922   And we would expect HTTP/1.1 clients to:
3923  <list style="symbols">
3924     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3925        responses;</t>
3927     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3928        1.1.</t>
3929  </list>
3932   For most implementations of HTTP/1.0, each connection is established
3933   by the client prior to the request and closed by the server after
3934   sending the response. Some implementations implement the Keep-Alive
3935   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3938<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3940   This section summarizes major differences between versions HTTP/1.0
3941   and HTTP/1.1.
3944<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3946   The requirements that clients and servers support the Host request-header,
3947   report an error if the Host request-header (<xref target=""/>) is
3948   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3949   are among the most important changes defined by this
3950   specification.
3953   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3954   addresses and servers; there was no other established mechanism for
3955   distinguishing the intended server of a request than the IP address
3956   to which that request was directed. The changes outlined above will
3957   allow the Internet, once older HTTP clients are no longer common, to
3958   support multiple Web sites from a single IP address, greatly
3959   simplifying large operational Web servers, where allocation of many
3960   IP addresses to a single host has created serious problems. The
3961   Internet will also be able to recover the IP addresses that have been
3962   allocated for the sole purpose of allowing special-purpose domain
3963   names to be used in root-level HTTP URLs. Given the rate of growth of
3964   the Web, and the number of servers already deployed, it is extremely
3965   important that all implementations of HTTP (including updates to
3966   existing HTTP/1.0 applications) correctly implement these
3967   requirements:
3968  <list style="symbols">
3969     <t>Both clients and servers &MUST; support the Host request-header.</t>
3971     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3973     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3974        request does not include a Host request-header.</t>
3976     <t>Servers &MUST; accept absolute URIs.</t>
3977  </list>
3982<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3984   Some clients and servers might wish to be compatible with some
3985   previous implementations of persistent connections in HTTP/1.0
3986   clients and servers. Persistent connections in HTTP/1.0 are
3987   explicitly negotiated as they are not the default behavior. HTTP/1.0
3988   experimental implementations of persistent connections are faulty,
3989   and the new facilities in HTTP/1.1 are designed to rectify these
3990   problems. The problem was that some existing 1.0 clients may be
3991   sending Keep-Alive to a proxy server that doesn't understand
3992   Connection, which would then erroneously forward it to the next
3993   inbound server, which would establish the Keep-Alive connection and
3994   result in a hung HTTP/1.0 proxy waiting for the close on the
3995   response. The result is that HTTP/1.0 clients must be prevented from
3996   using Keep-Alive when talking to proxies.
3999   However, talking to proxies is the most important use of persistent
4000   connections, so that prohibition is clearly unacceptable. Therefore,
4001   we need some other mechanism for indicating a persistent connection
4002   is desired, which is safe to use even when talking to an old proxy
4003   that ignores Connection. Persistent connections are the default for
4004   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4005   declaring non-persistence. See <xref target="header.connection"/>.
4008   The original HTTP/1.0 form of persistent connections (the Connection:
4009   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4013<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4015   This specification has been carefully audited to correct and
4016   disambiguate key word usage; RFC 2068 had many problems in respect to
4017   the conventions laid out in <xref target="RFC2119"/>.
4020   Transfer-coding and message lengths all interact in ways that
4021   required fixing exactly when chunked encoding is used (to allow for
4022   transfer encoding that may not be self delimiting); it was important
4023   to straighten out exactly how message lengths are computed. (Sections
4024   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4025   <xref target="header.content-length" format="counter"/>,
4026   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4029   The use and interpretation of HTTP version numbers has been clarified
4030   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4031   version they support to deal with problems discovered in HTTP/1.0
4032   implementations (<xref target="http.version"/>)
4035   Quality Values of zero should indicate that "I don't want something"
4036   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4039   Transfer-coding had significant problems, particularly with
4040   interactions with chunked encoding. The solution is that transfer-codings
4041   become as full fledged as content-codings. This involves
4042   adding an IANA registry for transfer-codings (separate from content
4043   codings), a new header field (TE) and enabling trailer headers in the
4044   future. Transfer encoding is a major performance benefit, so it was
4045   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4046   interoperability problem that could have occurred due to interactions
4047   between authentication trailers, chunked encoding and HTTP/1.0
4048   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4049   and <xref target="header.te" format="counter"/>)
4053<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4055  Empty list elements in list productions have been deprecated.
4056  (<xref target="notation.abnf"/>)
4059  Rules about implicit linear whitespace between certain grammar productions
4060  have been removed; now it's only allowed when specifically pointed out
4061  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4062  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4063  Non-ASCII content in header fields and reason phrase has been obsoleted and
4064  made opaque (the TEXT rule was removed)
4065  (<xref target="basic.rules"/>)
4068  Clarify that HTTP-Version is case sensitive.
4069  (<xref target="http.version"/>)
4072  Remove reference to non-existant identity transfer-coding value tokens.
4073  (Sections <xref format="counter" target="transfer.codings"/> and
4074  <xref format="counter" target="message.length"/>)
4077  Clarification that the chunk length does not include
4078  the count of the octets in the chunk header and trailer.
4079  (<xref target="chunked.transfer.encoding"/>)
4082  Require that invalid whitespace around field-names be rejected.
4083  (<xref target="message.headers"/>)
4086  Update use of abs_path production from RFC1808 to the path-absolute + query
4087  components of RFC3986.
4088  (<xref target="request-target"/>)
4091  Clarify exactly when close connection options must be sent.
4092  (<xref target="header.connection"/>)
4097<section title="Terminology" anchor="terminology">
4099   This specification uses a number of terms to refer to the roles
4100   played by participants in, and objects of, the HTTP communication.
4103  <iref item="cache"/>
4104  <x:dfn>cache</x:dfn>
4105  <list>
4106    <t>
4107      A program's local store of response messages and the subsystem
4108      that controls its message storage, retrieval, and deletion. A
4109      cache stores cacheable responses in order to reduce the response
4110      time and network bandwidth consumption on future, equivalent
4111      requests. Any client or server may include a cache, though a cache
4112      cannot be used by a server that is acting as a tunnel.
4113    </t>
4114  </list>
4117  <iref item="cacheable"/>
4118  <x:dfn>cacheable</x:dfn>
4119  <list>
4120    <t>
4121      A response is cacheable if a cache is allowed to store a copy of
4122      the response message for use in answering subsequent requests. The
4123      rules for determining the cacheability of HTTP responses are
4124      defined in &caching;. Even if a resource is cacheable, there may
4125      be additional constraints on whether a cache can use the cached
4126      copy for a particular request.
4127    </t>
4128  </list>
4131  <iref item="client"/>
4132  <x:dfn>client</x:dfn>
4133  <list>
4134    <t>
4135      A program that establishes connections for the purpose of sending
4136      requests.
4137    </t>
4138  </list>
4141  <iref item="connection"/>
4142  <x:dfn>connection</x:dfn>
4143  <list>
4144    <t>
4145      A transport layer virtual circuit established between two programs
4146      for the purpose of communication.
4147    </t>
4148  </list>
4151  <iref item="content negotiation"/>
4152  <x:dfn>content negotiation</x:dfn>
4153  <list>
4154    <t>
4155      The mechanism for selecting the appropriate representation when
4156      servicing a request, as described in &content.negotiation;. The
4157      representation of entities in any response can be negotiated
4158      (including error responses).
4159    </t>
4160  </list>
4163  <iref item="entity"/>
4164  <x:dfn>entity</x:dfn>
4165  <list>
4166    <t>
4167      The information transferred as the payload of a request or
4168      response. An entity consists of metainformation in the form of
4169      entity-header fields and content in the form of an entity-body, as
4170      described in &entity;.
4171    </t>
4172  </list>
4175  <iref item="gateway"/>
4176  <x:dfn>gateway</x:dfn>
4177  <list>
4178    <t>
4179      A server which acts as an intermediary for some other server.
4180      Unlike a proxy, a gateway receives requests as if it were the
4181      origin server for the requested resource; the requesting client
4182      may not be aware that it is communicating with a gateway.
4183    </t>
4184  </list>
4187  <iref item="inbound"/>
4188  <iref item="outbound"/>
4189  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4190  <list>
4191    <t>
4192      Inbound and outbound refer to the request and response paths for
4193      messages: "inbound" means "traveling toward the origin server",
4194      and "outbound" means "traveling toward the user agent"
4195    </t>
4196  </list>
4199  <iref item="message"/>
4200  <x:dfn>message</x:dfn>
4201  <list>
4202    <t>
4203      The basic unit of HTTP communication, consisting of a structured
4204      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4205      transmitted via the connection.
4206    </t>
4207  </list>
4210  <iref item="origin server"/>
4211  <x:dfn>origin server</x:dfn>
4212  <list>
4213    <t>
4214      The server on which a given resource resides or is to be created.
4215    </t>
4216  </list>
4219  <iref item="proxy"/>
4220  <x:dfn>proxy</x:dfn>
4221  <list>
4222    <t>
4223      An intermediary program which acts as both a server and a client
4224      for the purpose of making requests on behalf of other clients.
4225      Requests are serviced internally or by passing them on, with
4226      possible translation, to other servers. A proxy &MUST; implement
4227      both the client and server requirements of this specification. A
4228      "transparent proxy" is a proxy that does not modify the request or
4229      response beyond what is required for proxy authentication and
4230      identification. A "non-transparent proxy" is a proxy that modifies
4231      the request or response in order to provide some added service to
4232      the user agent, such as group annotation services, media type
4233      transformation, protocol reduction, or anonymity filtering. Except
4234      where either transparent or non-transparent behavior is explicitly
4235      stated, the HTTP proxy requirements apply to both types of
4236      proxies.
4237    </t>
4238  </list>
4241  <iref item="request"/>
4242  <x:dfn>request</x:dfn>
4243  <list>
4244    <t>
4245      An HTTP request message, as defined in <xref target="request"/>.
4246    </t>
4247  </list>
4250  <iref item="resource"/>
4251  <x:dfn>resource</x:dfn>
4252  <list>
4253    <t>
4254      A network data object or service that can be identified by a URI,
4255      as defined in <xref target="uri"/>. Resources may be available in multiple
4256      representations (e.g. multiple languages, data formats, size, and
4257      resolutions) or vary in other ways.
4258    </t>
4259  </list>
4262  <iref item="response"/>
4263  <x:dfn>response</x:dfn>
4264  <list>
4265    <t>
4266      An HTTP response message, as defined in <xref target="response"/>.
4267    </t>
4268  </list>
4271  <iref item="representation"/>
4272  <x:dfn>representation</x:dfn>
4273  <list>
4274    <t>
4275      An entity included with a response that is subject to content
4276      negotiation, as described in &content.negotiation;. There may exist multiple
4277      representations associated with a particular response status.
4278    </t>
4279  </list>
4282  <iref item="server"/>
4283  <x:dfn>server</x:dfn>
4284  <list>
4285    <t>
4286      An application program that accepts connections in order to
4287      service requests by sending back responses. Any given program may
4288      be capable of being both a client and a server; our use of these
4289      terms refers only to the role being performed by the program for a
4290      particular connection, rather than to the program's capabilities
4291      in general. Likewise, any server may act as an origin server,
4292      proxy, gateway, or tunnel, switching behavior based on the nature
4293      of each request.
4294    </t>
4295  </list>
4298  <iref item="tunnel"/>
4299  <x:dfn>tunnel</x:dfn>
4300  <list>
4301    <t>
4302      An intermediary program which is acting as a blind relay between
4303      two connections. Once active, a tunnel is not considered a party
4304      to the HTTP communication, though the tunnel may have been
4305      initiated by an HTTP request. The tunnel ceases to exist when both
4306      ends of the relayed connections are closed.
4307    </t>
4308  </list>
4311  <iref item="upstream"/>
4312  <iref item="downstream"/>
4313  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4314  <list>
4315    <t>
4316      Upstream and downstream describe the flow of a message: all
4317      messages flow from upstream to downstream.
4318    </t>
4319  </list>
4322  <iref item="user agent"/>
4323  <x:dfn>user agent</x:dfn>
4324  <list>
4325    <t>
4326      The client which initiates a request. These are often browsers,
4327      editors, spiders (web-traversing robots), or other end user tools.
4328    </t>
4329  </list>
4332  <iref item="variant"/>
4333  <x:dfn>variant</x:dfn>
4334  <list>
4335    <t>
4336      A resource may have one, or more than one, representation(s)
4337      associated with it at any given instant. Each of these
4338      representations is termed a `variant'.  Use of the term `variant'
4339      does not necessarily imply that the resource is subject to content
4340      negotiation.
4341    </t>
4342  </list>
4346<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4348<artwork type="abnf" name="p1-messaging.parsed-abnf">
4349<x:ref>BWS</x:ref> = OWS
4351<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4352<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4353<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4354<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4355 connection-token ] )
4356<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4357<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4359<x:ref>Date</x:ref> = "Date:" OWS Date-v
4360<x:ref>Date-v</x:ref> = HTTP-date
4362GMT = %x47.4D.54
4364<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4365<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4366<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4367<x:ref>HTTP-message</x:ref> = Request / Response
4368<x:ref>Host</x:ref> = "Host:" OWS Host-v
4369<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4371<x:ref>Method</x:ref> = token
4373<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4375<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4377<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4378<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4379<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4380 entity-header ) CRLF ) CRLF [ message-body ]
4381<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4382<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4383 entity-header ) CRLF ) CRLF [ message-body ]
4385<x:ref>Status-Code</x:ref> = 3DIGIT
4386<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4388<x:ref>TE</x:ref> = "TE:" OWS TE-v
4389<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4390<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4391<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4392<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4393<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4394 transfer-coding ] )
4396<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4397<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4398<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4399<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4401<x:ref>Via</x:ref> = "Via:" OWS Via-v
4402<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4403 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4404 ] )
4406<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4408<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4409<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4410<x:ref>attribute</x:ref> = token
4411<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4413<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4414<x:ref>chunk-data</x:ref> = 1*OCTET
4415<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4416<x:ref>chunk-ext-name</x:ref> = token
4417<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4418<x:ref>chunk-size</x:ref> = 1*HEXDIG
4419<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4420<x:ref>connection-token</x:ref> = token
4421<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4423<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4424<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4425<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4427<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4428<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4430<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4431<x:ref>field-name</x:ref> = token
4432<x:ref>field-value</x:ref> = *( field-content / OWS )
4433<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4435<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4436 / Transfer-Encoding / Upgrade / Via / Warning
4437<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4438 message-body ]
4440<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4442l-Fri = %x46.
4443l-Mon = %x4D.6F.6E.64.61.79
4444l-Sat = %x53.
4445l-Sun = %x53.75.6E.64.61.79
4446l-Thu = %x54.
4447l-Tue = %x54.
4448l-Wed = %x57.65.64.6E.
4449<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4451<x:ref>message-body</x:ref> = entity-body /
4452 &lt;entity-body encoded as per Transfer-Encoding&gt;
4453<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4454<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4455 / s-Sep / s-Oct / s-Nov / s-Dec
4457<x:ref>obs-fold</x:ref> = CRLF
4458<x:ref>obs-text</x:ref> = %x80-FF
4459<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4461<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4462<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4463<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4464<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4465<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4466<x:ref>product</x:ref> = token [ "/" product-version ]
4467<x:ref>product-version</x:ref> = token
4468<x:ref>protocol-name</x:ref> = token
4469<x:ref>protocol-version</x:ref> = token
4470<x:ref>pseudonym</x:ref> = token
4472<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4473<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4474<x:ref>quoted-pair</x:ref> = "\" quoted-text
4475<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4476<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4477<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4479<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4480<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4481<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4482<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4483<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4484 / authority
4485<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4486<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4487<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4489s-Apr = %x41.70.72
4490s-Aug = %x41.75.67
4491s-Dec = %x44.65.63
4492s-Feb = %x46.65.62
4493s-Fri = %x46.72.69
4494s-Jan = %x4A.61.6E
4495s-Jul = %x4A.75.6C
4496s-Jun = %x4A.75.6E
4497s-Mar = %x4D.61.72
4498s-May = %x4D.61.79
4499s-Mon = %x4D.6F.6E
4500s-Nov = %x4E.6F.76
4501s-Oct = %x4F.63.74
4502s-Sat = %x53.61.74
4503s-Sep = %x53.65.70
4504s-Sun = %x53.75.6E
4505s-Thu = %x54.68.75
4506s-Tue = %x54.75.65
4507s-Wed = %x57.65.64
4508<x:ref>start-line</x:ref> = Request-Line / Status-Line
4510<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4511<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4512 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4513<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4514<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4515<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4516<x:ref>token</x:ref> = 1*tchar
4517<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4518<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4519<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4521<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4523<x:ref>value</x:ref> = token / quoted-string
4525<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4526<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4531<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4532; Chunked-Body defined but not used
4533; Content-Length defined but not used
4534; HTTP-message defined but not used
4535; Host defined but not used
4536; TE defined but not used
4537; URI defined but not used
4538; URI-reference defined but not used
4539; fragment defined but not used
4540; generic-message defined but not used
4541; http-URI defined but not used
4542; partial-URI defined but not used
4545<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4547<section title="Since RFC2616">
4549  Extracted relevant partitions from <xref target="RFC2616"/>.
4553<section title="Since draft-ietf-httpbis-p1-messaging-00">
4555  Closed issues:
4556  <list style="symbols">
4557    <t>
4558      <eref target=""/>:
4559      "HTTP Version should be case sensitive"
4560      (<eref target=""/>)
4561    </t>
4562    <t>
4563      <eref target=""/>:
4564      "'unsafe' characters"
4565      (<eref target=""/>)
4566    </t>
4567    <t>
4568      <eref target=""/>:
4569      "Chunk Size Definition"
4570      (<eref target=""/>)
4571    </t>
4572    <t>
4573      <eref target=""/>:
4574      "Message Length"
4575      (<eref target=""/>)
4576    </t>
4577    <t>
4578      <eref target=""/>:
4579      "Media Type Registrations"
4580      (<eref target=""/>)
4581    </t>
4582    <t>
4583      <eref target=""/>:
4584      "URI includes query"
4585      (<eref target=""/>)
4586    </t>
4587    <t>
4588      <eref target=""/>:
4589      "No close on 1xx responses"
4590      (<eref target=""/>)
4591    </t>
4592    <t>
4593      <eref target=""/>:
4594      "Remove 'identity' token references"
4595      (<eref target=""/>)
4596    </t>
4597    <t>
4598      <eref target=""/>:
4599      "Import query BNF"
4600    </t>
4601    <t>
4602      <eref target=""/>:
4603      "qdtext BNF"
4604    </t>
4605    <t>
4606      <eref target=""/>:
4607      "Normative and Informative references"
4608    </t>
4609    <t>
4610      <eref target=""/>:
4611      "RFC2606 Compliance"
4612    </t>
4613    <t>
4614      <eref target=""/>:
4615      "RFC977 reference"
4616    </t>
4617    <t>
4618      <eref target=""/>:
4619      "RFC1700 references"
4620    </t>
4621    <t>
4622      <eref target=""/>:
4623      "inconsistency in date format explanation"
4624    </t>
4625    <t>
4626      <eref target=""/>:
4627      "Date reference typo"
4628    </t>
4629    <t>
4630      <eref target=""/>:
4631      "Informative references"
4632    </t>
4633    <t>
4634      <eref target=""/>:
4635      "ISO-8859-1 Reference"
4636    </t>
4637    <t>
4638      <eref target=""/>:
4639      "Normative up-to-date references"
4640    </t>
4641  </list>
4644  Other changes:
4645  <list style="symbols">
4646    <t>
4647      Update media type registrations to use RFC4288 template.
4648    </t>
4649    <t>
4650      Use names of RFC4234 core rules DQUOTE and WSP,
4651      fix broken ABNF for chunk-data
4652      (work in progress on <eref target=""/>)
4653    </t>
4654  </list>
4658<section title="Since draft-ietf-httpbis-p1-messaging-01">
4660  Closed issues:
4661  <list style="symbols">
4662    <t>
4663      <eref target=""/>:
4664      "Bodies on GET (and other) requests"
4665    </t>
4666    <t>
4667      <eref target=""/>:
4668      "Updating to RFC4288"
4669    </t>
4670    <t>
4671      <eref target=""/>:
4672      "Status Code and Reason Phrase"
4673    </t>
4674    <t>
4675      <eref target=""/>:
4676      "rel_path not used"
4677    </t>
4678  </list>
4681  Ongoing work on ABNF conversion (<eref target=""/>):
4682  <list style="symbols">
4683    <t>
4684      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4685      "trailer-part").
4686    </t>
4687    <t>
4688      Avoid underscore character in rule names ("http_URL" ->
4689      "http-URL", "abs_path" -> "path-absolute").
4690    </t>
4691    <t>
4692      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4693      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4694      have to be updated when switching over to RFC3986.
4695    </t>
4696    <t>
4697      Synchronize core rules with RFC5234.
4698    </t>
4699    <t>
4700      Get rid of prose rules that span multiple lines.
4701    </t>
4702    <t>
4703      Get rid of unused rules LOALPHA and UPALPHA.
4704    </t>
4705    <t>
4706      Move "Product Tokens" section (back) into Part 1, as "token" is used
4707      in the definition of the Upgrade header.
4708    </t>
4709    <t>
4710      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4711    </t>
4712    <t>
4713      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4714    </t>
4715  </list>
4719<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4721  Closed issues:
4722  <list style="symbols">
4723    <t>
4724      <eref target=""/>:
4725      "HTTP-date vs. rfc1123-date"
4726    </t>
4727    <t>
4728      <eref target=""/>:
4729      "WS in quoted-pair"
4730    </t>
4731  </list>
4734  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4735  <list style="symbols">
4736    <t>
4737      Reference RFC 3984, and update header registrations for headers defined
4738      in this document.
4739    </t>
4740  </list>
4743  Ongoing work on ABNF conversion (<eref target=""/>):
4744  <list style="symbols">
4745    <t>
4746      Replace string literals when the string really is case-sensitive (HTTP-Version).
4747    </t>
4748  </list>
4752<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4754  Closed issues:
4755  <list style="symbols">
4756    <t>
4757      <eref target=""/>:
4758      "Connection closing"
4759    </t>
4760    <t>
4761      <eref target=""/>:
4762      "Move registrations and registry information to IANA Considerations"
4763    </t>
4764    <t>
4765      <eref target=""/>:
4766      "need new URL for PAD1995 reference"
4767    </t>
4768    <t>
4769      <eref target=""/>:
4770      "IANA Considerations: update HTTP URI scheme registration"
4771    </t>
4772    <t>
4773      <eref target=""/>:
4774      "Cite HTTPS URI scheme definition"
4775    </t>
4776    <t>
4777      <eref target=""/>:
4778      "List-type headers vs Set-Cookie"
4779    </t>
4780  </list>
4783  Ongoing work on ABNF conversion (<eref target=""/>):
4784  <list style="symbols">
4785    <t>
4786      Replace string literals when the string really is case-sensitive (HTTP-Date).
4787    </t>
4788    <t>
4789      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4790    </t>
4791  </list>
4795<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4797  Closed issues:
4798  <list style="symbols">
4799    <t>
4800      <eref target=""/>:
4801      "Out-of-date reference for URIs"
4802    </t>
4803    <t>
4804      <eref target=""/>:
4805      "RFC 2822 is updated by RFC 5322"
4806    </t>
4807  </list>
4810  Ongoing work on ABNF conversion (<eref target=""/>):
4811  <list style="symbols">
4812    <t>
4813      Use "/" instead of "|" for alternatives.
4814    </t>
4815    <t>
4816      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4817    </t>
4818    <t>
4819      Only reference RFC 5234's core rules.
4820    </t>
4821    <t>
4822      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4823      whitespace ("OWS") and required whitespace ("RWS").
4824    </t>
4825    <t>
4826      Rewrite ABNFs to spell out whitespace rules, factor out
4827      header value format definitions.
4828    </t>
4829  </list>
4833<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4835  Closed issues:
4836  <list style="symbols">
4837    <t>
4838      <eref target=""/>:
4839      "Header LWS"
4840    </t>
4841    <t>
4842      <eref target=""/>:
4843      "Sort 1.3 Terminology"
4844    </t>
4845    <t>
4846      <eref target=""/>:
4847      "RFC2047 encoded words"
4848    </t>
4849    <t>
4850      <eref target=""/>:
4851      "Character Encodings in TEXT"
4852    </t>
4853    <t>
4854      <eref target=""/>:
4855      "Line Folding"
4856    </t>
4857    <t>
4858      <eref target=""/>:
4859      "OPTIONS * and proxies"
4860    </t>
4861    <t>
4862      <eref target=""/>:
4863      "Reason-Phrase BNF"
4864    </t>
4865    <t>
4866      <eref target=""/>:
4867      "Use of TEXT"
4868    </t>
4869    <t>
4870      <eref target=""/>:
4871      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4872    </t>
4873    <t>
4874      <eref target=""/>:
4875      "RFC822 reference left in discussion of date formats"
4876    </t>
4877  </list>
4880  Final work on ABNF conversion (<eref target=""/>):
4881  <list style="symbols">
4882    <t>
4883      Rewrite definition of list rules, deprecate empty list elements.
4884    </t>
4885    <t>
4886      Add appendix containing collected and expanded ABNF.
4887    </t>
4888  </list>
4891  Other changes:
4892  <list style="symbols">
4893    <t>
4894      Rewrite introduction; add mostly new Architecture Section.
4895    </t>
4896    <t>
4897      Move definition of quality values from Part 3 into Part 1;
4898      make TE request header grammar independent of accept-params (defined in Part 3).
4899    </t>
4900  </list>
4904<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
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