source: draft-ietf-httpbis/latest/p1-messaging.xml @ 584

Last change on this file since 584 was 584, checked in by julian.reschke@…, 13 years ago

fix typo (related to #163)

  • Property svn:eol-style set to native
File size: 211.1 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "May">
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>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
458  <x:ref>obs-text</x:ref>       = %x80-FF
460<t anchor="rule.quoted-pair">
461  <x:anchor-alias value="quoted-pair"/>
462  <x:anchor-alias value="quoted-text"/>
463   The backslash character ("\") &MAY; be used as a single-character
464   quoting mechanism only within quoted-string and comment constructs.
466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
467  <x:ref>quoted-text</x:ref>    = %x01-09 /
468                   %x0B-0C /
469                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
470  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
474<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
475  <x:anchor-alias value="request-header"/>
476  <x:anchor-alias value="response-header"/>
477  <x:anchor-alias value="entity-body"/>
478  <x:anchor-alias value="entity-header"/>
479  <x:anchor-alias value="Cache-Control"/>
480  <x:anchor-alias value="Pragma"/>
481  <x:anchor-alias value="Warning"/>
483  The ABNF rules below are defined in other parts:
485<figure><!-- Part2--><artwork type="abnf2616">
486  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
487  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
489<figure><!-- Part3--><artwork type="abnf2616">
490  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
491  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
493<figure><!-- Part6--><artwork type="abnf2616">
494  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
495  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
496  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
503<section title="HTTP architecture" anchor="architecture">
505   HTTP was created with a specific architecture in mind, the World Wide Web,
506   and has evolved over time to support the scalability needs of a worldwide
507   hypertext system. Much of that architecture is reflected in the terminology
508   and syntax productions used to define HTTP.
511<section title="Uniform Resource Identifiers" anchor="uri">
513   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
514   throughout HTTP as the means for identifying resources. URI references
515   are used to target requests, redirect responses, and define relationships.
516   HTTP does not limit what a resource may be; it merely defines an interface
517   that can be used to interact with a resource via HTTP. More information on
518   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
520  <x:anchor-alias value="URI"/>
521  <x:anchor-alias value="URI-reference"/>
522  <x:anchor-alias value="absolute-URI"/>
523  <x:anchor-alias value="relative-part"/>
524  <x:anchor-alias value="authority"/>
525  <x:anchor-alias value="fragment"/>
526  <x:anchor-alias value="path-abempty"/>
527  <x:anchor-alias value="path-absolute"/>
528  <x:anchor-alias value="port"/>
529  <x:anchor-alias value="query"/>
530  <x:anchor-alias value="uri-host"/>
531  <x:anchor-alias value="partial-URI"/>
533   This specification adopts the definitions of "URI-reference",
534   "absolute-URI", "relative-part", "fragment", "port", "host",
535   "path-abempty", "path-absolute", "query", and "authority" from
536   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
537   protocol elements that allow a relative URI without a fragment.
539<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
540  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
541  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
542  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
543  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
544  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
545  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
546  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
549  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
550  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
552  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
555   Each protocol element in HTTP that allows a URI reference will indicate in
556   its ABNF production whether the element allows only a URI in absolute form
557   (absolute-URI), any relative reference (relative-ref), or some other subset
558   of the URI-reference grammar. Unless otherwise indicated, URI references
559   are parsed relative to the request target (the default base URI for both
560   the request and its corresponding response).
563<section title="http URI scheme" anchor="http.uri">
564  <x:anchor-alias value="http-URI"/>
565  <iref item="http URI scheme" primary="true"/>
566  <iref item="URI scheme" subitem="http" primary="true"/>
568   The "http" scheme is used to locate network resources via the HTTP
569   protocol.
571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
572  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
575   If the port is empty or not given, port 80 is assumed. The semantics
576   are that the identified resource is located at the server listening
577   for TCP connections on that port of that host, and the request-target
578   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
579   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
580   the path-absolute is not present in the URL, it &MUST; be given as "/" when
581   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
582   receives a host name which is not a fully qualified domain name, it
583   &MAY; add its domain to the host name it received. If a proxy receives
584   a fully qualified domain name, the proxy &MUST-NOT; change the host
585   name.
589<section title="https URI scheme" anchor="https.uri">
590   <iref item="https URI scheme"/>
591   <iref item="URI scheme" subitem="https"/>
593   <cref>TBD: Define and explain purpose of https scheme.</cref>
596  <t>
597    <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
598  </t>
602<section title="URI Comparison" anchor="uri.comparison">
604   When comparing two URIs to decide if they match or not, a client
605   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
606   URIs, with these exceptions:
607  <list style="symbols">
608    <t>A port that is empty or not given is equivalent to the default
609        port for that URI-reference;</t>
610    <t>Comparisons of host names &MUST; be case-insensitive;</t>
611    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
612    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
613    <t>Characters other than those in the "reserved" set are equivalent to their
614       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
615    </t>
616  </list>
619   For example, the following three URIs are equivalent:
621<figure><artwork type="example">
628<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
634<section title="Overall Operation" anchor="intro.overall.operation">
636   HTTP is a request/response protocol. A client sends a
637   request to the server in the form of a request method, URI, and
638   protocol version, followed by a MIME-like message containing request
639   modifiers, client information, and possible body content over a
640   connection with a server. The server responds with a status line,
641   including the message's protocol version and a success or error code,
642   followed by a MIME-like message containing server information, entity
643   metainformation, and possible entity-body content.
646   Most HTTP communication is initiated by a user agent and consists of
647   a request to be applied to a resource on some origin server. In the
648   simplest case, this may be accomplished via a single connection (v)
649   between the user agent (UA) and the origin server (O).
651<figure><artwork type="drawing">
652       request chain ------------------------&gt;
653    UA -------------------v------------------- O
654       &lt;----------------------- response chain
657   A more complicated situation occurs when one or more intermediaries
658   are present in the request/response chain. There are three common
659   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
660   forwarding agent, receiving requests for a URI in its absolute form,
661   rewriting all or part of the message, and forwarding the reformatted
662   request toward the server identified by the URI. A gateway is a
663   receiving agent, acting as a layer above some other server(s) and, if
664   necessary, translating the requests to the underlying server's
665   protocol. A tunnel acts as a relay point between two connections
666   without changing the messages; tunnels are used when the
667   communication needs to pass through an intermediary (such as a
668   firewall) even when the intermediary cannot understand the contents
669   of the messages.
671<figure><artwork type="drawing">
672       request chain --------------------------------------&gt;
673    UA -----v----- A -----v----- B -----v----- C -----v----- O
674       &lt;------------------------------------- response chain
677   The figure above shows three intermediaries (A, B, and C) between the
678   user agent and origin server. A request or response message that
679   travels the whole chain will pass through four separate connections.
680   This distinction is important because some HTTP communication options
681   may apply only to the connection with the nearest, non-tunnel
682   neighbor, only to the end-points of the chain, or to all connections
683   along the chain. Although the diagram is linear, each participant may
684   be engaged in multiple, simultaneous communications. For example, B
685   may be receiving requests from many clients other than A, and/or
686   forwarding requests to servers other than C, at the same time that it
687   is handling A's request.
690   Any party to the communication which is not acting as a tunnel may
691   employ an internal cache for handling requests. The effect of a cache
692   is that the request/response chain is shortened if one of the
693   participants along the chain has a cached response applicable to that
694   request. The following illustrates the resulting chain if B has a
695   cached copy of an earlier response from O (via C) for a request which
696   has not been cached by UA or A.
698<figure><artwork type="drawing">
699          request chain ----------&gt;
700       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
701          &lt;--------- response chain
704   Not all responses are usefully cacheable, and some requests may
705   contain modifiers which place special requirements on cache behavior.
706   HTTP requirements for cache behavior and cacheable responses are
707   defined in &caching;.
710   In fact, there are a wide variety of architectures and configurations
711   of caches and proxies currently being experimented with or deployed
712   across the World Wide Web. These systems include national hierarchies
713   of proxy caches to save transoceanic bandwidth, systems that
714   broadcast or multicast cache entries, organizations that distribute
715   subsets of cached data via CD-ROM, and so on. HTTP systems are used
716   in corporate intranets over high-bandwidth links, and for access via
717   PDAs with low-power radio links and intermittent connectivity. The
718   goal of HTTP/1.1 is to support the wide diversity of configurations
719   already deployed while introducing protocol constructs that meet the
720   needs of those who build web applications that require high
721   reliability and, failing that, at least reliable indications of
722   failure.
725   HTTP communication usually takes place over TCP/IP connections. The
726   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
727   not preclude HTTP from being implemented on top of any other protocol
728   on the Internet, or on other networks. HTTP only presumes a reliable
729   transport; any protocol that provides such guarantees can be used;
730   the mapping of the HTTP/1.1 request and response structures onto the
731   transport data units of the protocol in question is outside the scope
732   of this specification.
735   In HTTP/1.0, most implementations used a new connection for each
736   request/response exchange. In HTTP/1.1, a connection may be used for
737   one or more request/response exchanges, although connections may be
738   closed for a variety of reasons (see <xref target="persistent.connections"/>).
742<section title="Use of HTTP for proxy communication" anchor="http.proxy">
744   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
747<section title="Interception of HTTP for access control" anchor="http.intercept">
749   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
752<section title="Use of HTTP by other protocols" anchor="http.others">
754   <cref>TBD: Profiles of HTTP defined by other protocol.
755   Extensions of HTTP like WebDAV.</cref>
758<section title="Use of HTTP by media type specification" anchor="">
760   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
765<section title="Protocol Parameters" anchor="protocol.parameters">
767<section title="HTTP Version" anchor="http.version">
768  <x:anchor-alias value="HTTP-Version"/>
769  <x:anchor-alias value="HTTP-Prot-Name"/>
771   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
772   of the protocol. The protocol versioning policy is intended to allow
773   the sender to indicate the format of a message and its capacity for
774   understanding further HTTP communication, rather than the features
775   obtained via that communication. No change is made to the version
776   number for the addition of message components which do not affect
777   communication behavior or which only add to extensible field values.
778   The &lt;minor&gt; number is incremented when the changes made to the
779   protocol add features which do not change the general message parsing
780   algorithm, but which may add to the message semantics and imply
781   additional capabilities of the sender. The &lt;major&gt; number is
782   incremented when the format of a message within the protocol is
783   changed. See <xref target="RFC2145"/> for a fuller explanation.
786   The version of an HTTP message is indicated by an HTTP-Version field
787   in the first line of the message. HTTP-Version is case-sensitive.
789<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
790  <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>
791  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
794   Note that the major and minor numbers &MUST; be treated as separate
795   integers and that each &MAY; be incremented higher than a single digit.
796   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
797   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
798   &MUST-NOT; be sent.
801   An application that sends a request or response message that includes
802   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
803   with this specification. Applications that are at least conditionally
804   compliant with this specification &SHOULD; use an HTTP-Version of
805   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
806   not compatible with HTTP/1.0. For more details on when to send
807   specific HTTP-Version values, see <xref target="RFC2145"/>.
810   The HTTP version of an application is the highest HTTP version for
811   which the application is at least conditionally compliant.
814   Proxy and gateway applications need to be careful when forwarding
815   messages in protocol versions different from that of the application.
816   Since the protocol version indicates the protocol capability of the
817   sender, a proxy/gateway &MUST-NOT; send a message with a version
818   indicator which is greater than its actual version. If a higher
819   version request is received, the proxy/gateway &MUST; either downgrade
820   the request version, or respond with an error, or switch to tunnel
821   behavior.
824   Due to interoperability problems with HTTP/1.0 proxies discovered
825   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
826   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
827   they support. The proxy/gateway's response to that request &MUST; be in
828   the same major version as the request.
831  <t>
832    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
833    of header fields required or forbidden by the versions involved.
834  </t>
838<section title="Date/Time Formats: Full Date" anchor="">
839  <x:anchor-alias value="HTTP-date"/>
841   HTTP applications have historically allowed three different formats
842   for the representation of date/time stamps:
844<figure><artwork type="example">
845  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
846  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
847  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
850   The first format is preferred as an Internet standard and represents
851   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
852   other formats are described here only for
853   compatibility with obsolete implementations.
854   HTTP/1.1 clients and servers that parse the date value &MUST; accept
855   all three formats (for compatibility with HTTP/1.0), though they &MUST;
856   only generate the RFC 1123 format for representing HTTP-date values
857   in header fields. See <xref target="tolerant.applications"/> for further information.
860   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
861   (GMT), without exception. For the purposes of HTTP, GMT is exactly
862   equal to UTC (Coordinated Universal Time). This is indicated in the
863   first two formats by the inclusion of "GMT" as the three-letter
864   abbreviation for time zone, and &MUST; be assumed when reading the
865   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
866   additional whitespace beyond that specifically included as SP in the
867   grammar.
869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
870  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
872<t anchor="">
873  <x:anchor-alias value="rfc1123-date"/>
874  <x:anchor-alias value="time-of-day"/>
875  <x:anchor-alias value="hour"/>
876  <x:anchor-alias value="minute"/>
877  <x:anchor-alias value="second"/>
878  <x:anchor-alias value="day-name"/>
879  <x:anchor-alias value="day"/>
880  <x:anchor-alias value="month"/>
881  <x:anchor-alias value="year"/>
882  <x:anchor-alias value="GMT"/>
883  Preferred format:
885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
886  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
888  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
889               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
890               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
891               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
892               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
893               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
894               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
896  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
897               ; e.g., 02 Jun 1982
899  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
900  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
901               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
902               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
903               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
904               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
905               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
906               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
907               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
908               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
909               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
910               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
911               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
912  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
914  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
916  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
917                 ; 00:00:00 - 23:59:59
919  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
920  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
921  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
924  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
925  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
926  same as those defined for the RFC 5322 constructs
927  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
929<t anchor="">
930  <x:anchor-alias value="obs-date"/>
931  <x:anchor-alias value="rfc850-date"/>
932  <x:anchor-alias value="asctime-date"/>
933  <x:anchor-alias value="date1"/>
934  <x:anchor-alias value="date2"/>
935  <x:anchor-alias value="date3"/>
936  <x:anchor-alias value="rfc1123-date"/>
937  <x:anchor-alias value="day-name-l"/>
938  Obsolete formats:
940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
941  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
944  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
945  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
946                 ; day-month-year (e.g., 02-Jun-82)
948  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
949         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
950         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
951         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
952         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
953         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
954         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
956<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
957  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
958  <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> ))
959                 ; month day (e.g., Jun  2)
962  <t>
963    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
964    accepting date values that may have been sent by non-HTTP
965    applications, as is sometimes the case when retrieving or posting
966    messages via proxies/gateways to SMTP or NNTP.
967  </t>
970  <t>
971    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
972    to their usage within the protocol stream. Clients and servers are
973    not required to use these formats for user presentation, request
974    logging, etc.
975  </t>
979<section title="Transfer Codings" anchor="transfer.codings">
980  <x:anchor-alias value="transfer-coding"/>
981  <x:anchor-alias value="transfer-extension"/>
983   Transfer-coding values are used to indicate an encoding
984   transformation that has been, can be, or may need to be applied to an
985   entity-body in order to ensure "safe transport" through the network.
986   This differs from a content coding in that the transfer-coding is a
987   property of the message, not of the original entity.
989<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
990  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
991  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
993<t anchor="rule.parameter">
994  <x:anchor-alias value="attribute"/>
995  <x:anchor-alias value="transfer-parameter"/>
996  <x:anchor-alias value="value"/>
997   Parameters are in  the form of attribute/value pairs.
999<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1000  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1001  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1002  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1005   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1006   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1007   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1010   Whenever a transfer-coding is applied to a message-body, the set of
1011   transfer-codings &MUST; include "chunked", unless the message indicates it
1012   is terminated by closing the connection. When the "chunked" transfer-coding
1013   is used, it &MUST; be the last transfer-coding applied to the
1014   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1015   than once to a message-body. These rules allow the recipient to
1016   determine the transfer-length of the message (<xref target="message.length"/>).
1019   Transfer-codings are analogous to the Content-Transfer-Encoding
1020   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1021   binary data over a 7-bit transport service. However, safe transport
1022   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1023   the only unsafe characteristic of message-bodies is the difficulty in
1024   determining the exact body length (<xref target="message.length"/>), or the desire to
1025   encrypt data over a shared transport.
1028   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1029   transfer-coding value tokens. Initially, the registry contains the
1030   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1031   "gzip", "compress", and "deflate" (&content-codings;).
1034   New transfer-coding value tokens &SHOULD; be registered in the same way
1035   as new content-coding value tokens (&content-codings;).
1038   A server which receives an entity-body with a transfer-coding it does
1039   not understand &SHOULD; return 501 (Not Implemented), and close the
1040   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1041   client.
1044<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1045  <x:anchor-alias value="chunk"/>
1046  <x:anchor-alias value="Chunked-Body"/>
1047  <x:anchor-alias value="chunk-data"/>
1048  <x:anchor-alias value="chunk-ext"/>
1049  <x:anchor-alias value="chunk-ext-name"/>
1050  <x:anchor-alias value="chunk-ext-val"/>
1051  <x:anchor-alias value="chunk-size"/>
1052  <x:anchor-alias value="last-chunk"/>
1053  <x:anchor-alias value="trailer-part"/>
1055   The chunked encoding modifies the body of a message in order to
1056   transfer it as a series of chunks, each with its own size indicator,
1057   followed by an &OPTIONAL; trailer containing entity-header fields. This
1058   allows dynamically produced content to be transferred along with the
1059   information necessary for the recipient to verify that it has
1060   received the full message.
1062<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"/>
1063  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1064                   <x:ref>last-chunk</x:ref>
1065                   <x:ref>trailer-part</x:ref>
1066                   <x:ref>CRLF</x:ref>
1068  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1069                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1070  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1071  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1073  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1074                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1075  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1076  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1077  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1078  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1081   The chunk-size field is a string of hex digits indicating the size of
1082   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1083   zero, followed by the trailer, which is terminated by an empty line.
1086   The trailer allows the sender to include additional HTTP header
1087   fields at the end of the message. The Trailer header field can be
1088   used to indicate which header fields are included in a trailer (see
1089   <xref target="header.trailer"/>).
1092   A server using chunked transfer-coding in a response &MUST-NOT; use the
1093   trailer for any header fields unless at least one of the following is
1094   true:
1095  <list style="numbers">
1096    <t>the request included a TE header field that indicates "trailers" is
1097     acceptable in the transfer-coding of the  response, as described in
1098     <xref target="header.te"/>; or,</t>
1100    <t>the server is the origin server for the response, the trailer
1101     fields consist entirely of optional metadata, and the recipient
1102     could use the message (in a manner acceptable to the origin server)
1103     without receiving this metadata.  In other words, the origin server
1104     is willing to accept the possibility that the trailer fields might
1105     be silently discarded along the path to the client.</t>
1106  </list>
1109   This requirement prevents an interoperability failure when the
1110   message is being received by an HTTP/1.1 (or later) proxy and
1111   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1112   compliance with the protocol would have necessitated a possibly
1113   infinite buffer on the proxy.
1116   A process for decoding the "chunked" transfer-coding
1117   can be represented in pseudo-code as:
1119<figure><artwork type="code">
1120  length := 0
1121  read chunk-size, chunk-ext (if any) and CRLF
1122  while (chunk-size &gt; 0) {
1123     read chunk-data and CRLF
1124     append chunk-data to entity-body
1125     length := length + chunk-size
1126     read chunk-size and CRLF
1127  }
1128  read entity-header
1129  while (entity-header not empty) {
1130     append entity-header to existing header fields
1131     read entity-header
1132  }
1133  Content-Length := length
1134  Remove "chunked" from Transfer-Encoding
1137   All HTTP/1.1 applications &MUST; be able to receive and decode the
1138   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1139   they do not understand.
1144<section title="Product Tokens" anchor="product.tokens">
1145  <x:anchor-alias value="product"/>
1146  <x:anchor-alias value="product-version"/>
1148   Product tokens are used to allow communicating applications to
1149   identify themselves by software name and version. Most fields using
1150   product tokens also allow sub-products which form a significant part
1151   of the application to be listed, separated by whitespace. By
1152   convention, the products are listed in order of their significance
1153   for identifying the application.
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1156  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1157  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1160   Examples:
1162<figure><artwork type="example">
1163  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1164  Server: Apache/0.8.4
1167   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1168   used for advertising or other non-essential information. Although any
1169   token character &MAY; appear in a product-version, this token &SHOULD;
1170   only be used for a version identifier (i.e., successive versions of
1171   the same product &SHOULD; only differ in the product-version portion of
1172   the product value).
1176<section title="Quality Values" anchor="quality.values">
1177  <x:anchor-alias value="qvalue"/>
1179   Both transfer codings (TE request header, <xref target="header.te"/>)
1180   and content negotiation (&content.negotiation;) use short "floating point"
1181   numbers to indicate the relative importance ("weight") of various
1182   negotiable parameters.  A weight is normalized to a real number in
1183   the range 0 through 1, where 0 is the minimum and 1 the maximum
1184   value. If a parameter has a quality value of 0, then content with
1185   this parameter is `not acceptable' for the client. HTTP/1.1
1186   applications &MUST-NOT; generate more than three digits after the
1187   decimal point. User configuration of these values &SHOULD; also be
1188   limited in this fashion.
1190<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1191  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1192                 / ( "1" [ "." 0*3("0") ] )
1195  <t>
1196     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1197     relative degradation in desired quality.
1198  </t>
1204<section title="HTTP Message" anchor="http.message">
1206<section title="Message Types" anchor="message.types">
1207  <x:anchor-alias value="generic-message"/>
1208  <x:anchor-alias value="HTTP-message"/>
1209  <x:anchor-alias value="start-line"/>
1211   HTTP messages consist of requests from client to server and responses
1212   from server to client.
1214<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1215  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1218   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1219   message format of <xref target="RFC5322"/> for transferring entities (the payload
1220   of the message). Both types of message consist of a start-line, zero
1221   or more header fields (also known as "headers"), an empty line (i.e.,
1222   a line with nothing preceding the CRLF) indicating the end of the
1223   header fields, and possibly a message-body.
1225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1226  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1227                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1228                    <x:ref>CRLF</x:ref>
1229                    [ <x:ref>message-body</x:ref> ]
1230  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1233   In the interest of robustness, servers &SHOULD; ignore any empty
1234   line(s) received where a Request-Line is expected. In other words, if
1235   the server is reading the protocol stream at the beginning of a
1236   message and receives a CRLF first, it should ignore the CRLF.
1239   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1240   after a POST request. To restate what is explicitly forbidden by the
1241   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1242   extra CRLF.
1245   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1246   header field. The presence of whitespace might be an attempt to trick a
1247   noncompliant implementation of HTTP into ignoring that field or processing
1248   the next line as a new request, either of which may result in security
1249   issues when implementations within the request chain interpret the
1250   same message differently. HTTP/1.1 servers &MUST; reject such a message
1251   with a 400 (Bad Request) response.
1255<section title="Message Headers" anchor="message.headers">
1256  <x:anchor-alias value="field-content"/>
1257  <x:anchor-alias value="field-name"/>
1258  <x:anchor-alias value="field-value"/>
1259  <x:anchor-alias value="message-header"/>
1261   HTTP header fields follow the same general format as Internet messages in
1262   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1263   of a name followed by a colon (":"), optional whitespace, and the field
1264   value. Field names are case-insensitive.
1266<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"/>
1267  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1268  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1269  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1270  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1273   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1274   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1275   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1276   header field-values use only a subset of the US-ASCII charset
1277   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1278   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1279   (obs-text) octets in field-content as opaque data.
1282   No whitespace is allowed between the header field-name and colon. For
1283   security reasons, any request message received containing such whitespace
1284   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1285   whitespace in a response message &MUST; be removed.
1288   The field value &MAY; be preceded by optional whitespace; a single SP is
1289   preferred. The field-value does not include any leading or trailing white
1290   space: OWS occurring before the first non-whitespace character of the
1291   field-value or after the last non-whitespace character of the field-value
1292   is ignored and &MAY; be removed without changing the meaning of the header
1293   field.
1296   Historically, HTTP header field values could be extended over multiple
1297   lines by preceding each extra line with at least one space or horizontal
1298   tab character (line folding). This specification deprecates such line
1299   folding except within the message/http media type
1300   (<xref target=""/>).
1301   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1302   (i.e., that contain any field-content that matches the obs-fold rule) unless
1303   the message is intended for packaging within the message/http media type.
1304   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1305   obs-fold whitespace with a single SP prior to interpreting the field value
1306   or forwarding the message downstream.
1308<t anchor="rule.comment">
1309  <x:anchor-alias value="comment"/>
1310  <x:anchor-alias value="ctext"/>
1311   Comments can be included in some HTTP header fields by surrounding
1312   the comment text with parentheses. Comments are only allowed in
1313   fields containing "comment" as part of their field value definition.
1314   In all other fields, parentheses are considered part of the field
1315   value.
1317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1318  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1319  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1320                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1323   The order in which header fields with differing field names are
1324   received is not significant. However, it is "good practice" to send
1325   general-header fields first, followed by request-header or response-header
1326   fields, and ending with the entity-header fields.
1329   Multiple message-header fields with the same field-name &MAY; be
1330   present in a message if and only if the entire field-value for that
1331   header field is defined as a comma-separated list [i.e., #(values)].
1332   It &MUST; be possible to combine the multiple header fields into one
1333   "field-name: field-value" pair, without changing the semantics of the
1334   message, by appending each subsequent field-value to the first, each
1335   separated by a comma. The order in which header fields with the same
1336   field-name are received is therefore significant to the
1337   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1338   change the order of these field values when a message is forwarded.
1341  <t>
1342   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1343   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1344   can occur multiple times, but does not use the list syntax, and thus cannot
1345   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1346   for details.) Also note that the Set-Cookie2 header specified in
1347   <xref target="RFC2965"/> does not share this problem.
1348  </t>
1353<section title="Message Body" anchor="message.body">
1354  <x:anchor-alias value="message-body"/>
1356   The message-body (if any) of an HTTP message is used to carry the
1357   entity-body associated with the request or response. The message-body
1358   differs from the entity-body only when a transfer-coding has been
1359   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1361<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1362  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1363               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1366   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1367   applied by an application to ensure safe and proper transfer of the
1368   message. Transfer-Encoding is a property of the message, not of the
1369   entity, and thus &MAY; be added or removed by any application along the
1370   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1371   when certain transfer-codings may be used.)
1374   The rules for when a message-body is allowed in a message differ for
1375   requests and responses.
1378   The presence of a message-body in a request is signaled by the
1379   inclusion of a Content-Length or Transfer-Encoding header field in
1380   the request's message-headers. A message-body &MUST-NOT; be included in
1381   a request if the specification of the request method (&method;)
1382   explicitly disallows an entity-body in requests.
1383   When a request message contains both a message-body of non-zero
1384   length and a method that does not define any semantics for that
1385   request message-body, then an origin server &SHOULD; either ignore
1386   the message-body or respond with an appropriate error message
1387   (e.g., 413).  A proxy or gateway, when presented the same request,
1388   &SHOULD; either forward the request inbound with the message-body or
1389   ignore the message-body when determining a response.
1392   For response messages, whether or not a message-body is included with
1393   a message is dependent on both the request method and the response
1394   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1395   &MUST-NOT; include a message-body, even though the presence of entity-header
1396   fields might lead one to believe they do. All 1xx
1397   (informational), 204 (No Content), and 304 (Not Modified) responses
1398   &MUST-NOT; include a message-body. All other responses do include a
1399   message-body, although it &MAY; be of zero length.
1403<section title="Message Length" anchor="message.length">
1405   The transfer-length of a message is the length of the message-body as
1406   it appears in the message; that is, after any transfer-codings have
1407   been applied. When a message-body is included with a message, the
1408   transfer-length of that body is determined by one of the following
1409   (in order of precedence):
1412  <list style="numbers">
1413    <x:lt><t>
1414     Any response message which "&MUST-NOT;" include a message-body (such
1415     as the 1xx, 204, and 304 responses and any response to a HEAD
1416     request) is always terminated by the first empty line after the
1417     header fields, regardless of the entity-header fields present in
1418     the message.
1419    </t></x:lt>
1420    <x:lt><t>
1421     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1422     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1423     is used, the transfer-length is defined by the use of this transfer-coding.
1424     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1425     is not present, the transfer-length is defined by the sender closing the connection.
1426    </t></x:lt>
1427    <x:lt><t>
1428     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1429     value in OCTETs represents both the entity-length and the
1430     transfer-length. The Content-Length header field &MUST-NOT; be sent
1431     if these two lengths are different (i.e., if a Transfer-Encoding
1432     header field is present). If a message is received with both a
1433     Transfer-Encoding header field and a Content-Length header field,
1434     the latter &MUST; be ignored.
1435    </t></x:lt>
1436    <x:lt><t>
1437     If the message uses the media type "multipart/byteranges", and the
1438     transfer-length is not otherwise specified, then this self-delimiting
1439     media type defines the transfer-length. This media type
1440     &MUST-NOT; be used unless the sender knows that the recipient can parse
1441     it; the presence in a request of a Range header with multiple byte-range
1442     specifiers from a 1.1 client implies that the client can parse
1443     multipart/byteranges responses.
1444    <list style="empty"><t>
1445       A range header might be forwarded by a 1.0 proxy that does not
1446       understand multipart/byteranges; in this case the server &MUST;
1447       delimit the message using methods defined in items 1, 3 or 5 of
1448       this section.
1449    </t></list>
1450    </t></x:lt>
1451    <x:lt><t>
1452     By the server closing the connection. (Closing the connection
1453     cannot be used to indicate the end of a request body, since that
1454     would leave no possibility for the server to send back a response.)
1455    </t></x:lt>
1456  </list>
1459   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1460   containing a message-body &MUST; include a valid Content-Length header
1461   field unless the server is known to be HTTP/1.1 compliant. If a
1462   request contains a message-body and a Content-Length is not given,
1463   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1464   determine the length of the message, or with 411 (Length Required) if
1465   it wishes to insist on receiving a valid Content-Length.
1468   All HTTP/1.1 applications that receive entities &MUST; accept the
1469   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1470   to be used for messages when the message length cannot be determined
1471   in advance.
1474   Messages &MUST-NOT; include both a Content-Length header field and a
1475   transfer-coding. If the message does include a
1476   transfer-coding, the Content-Length &MUST; be ignored.
1479   When a Content-Length is given in a message where a message-body is
1480   allowed, its field value &MUST; exactly match the number of OCTETs in
1481   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1482   invalid length is received and detected.
1486<section title="General Header Fields" anchor="general.header.fields">
1487  <x:anchor-alias value="general-header"/>
1489   There are a few header fields which have general applicability for
1490   both request and response messages, but which do not apply to the
1491   entity being transferred. These header fields apply only to the
1492   message being transmitted.
1494<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1495  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1496                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1497                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1498                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1499                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1500                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1501                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1502                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1503                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1506   General-header field names can be extended reliably only in
1507   combination with a change in the protocol version. However, new or
1508   experimental header fields may be given the semantics of general
1509   header fields if all parties in the communication recognize them to
1510   be general-header fields. Unrecognized header fields are treated as
1511   entity-header fields.
1516<section title="Request" anchor="request">
1517  <x:anchor-alias value="Request"/>
1519   A request message from a client to a server includes, within the
1520   first line of that message, the method to be applied to the resource,
1521   the identifier of the resource, and the protocol version in use.
1523<!--                 Host                      ; should be moved here eventually -->
1524<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1525  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1526                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1527                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1528                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1529                  <x:ref>CRLF</x:ref>
1530                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1533<section title="Request-Line" anchor="request-line">
1534  <x:anchor-alias value="Request-Line"/>
1536   The Request-Line begins with a method token, followed by the
1537   request-target and the protocol version, and ending with CRLF. The
1538   elements are separated by SP characters. No CR or LF is allowed
1539   except in the final CRLF sequence.
1541<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1542  <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>
1545<section title="Method" anchor="method">
1546  <x:anchor-alias value="Method"/>
1548   The Method  token indicates the method to be performed on the
1549   resource identified by the request-target. The method is case-sensitive.
1551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1552  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1556<section title="request-target" anchor="request-target">
1557  <x:anchor-alias value="request-target"/>
1559   The request-target
1560   identifies the resource upon which to apply the request.
1562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1563  <x:ref>request-target</x:ref> = "*"
1564                 / <x:ref>absolute-URI</x:ref>
1565                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1566                 / <x:ref>authority</x:ref>
1569   The four options for request-target are dependent on the nature of the
1570   request. The asterisk "*" means that the request does not apply to a
1571   particular resource, but to the server itself, and is only allowed
1572   when the method used does not necessarily apply to a resource. One
1573   example would be
1575<figure><artwork type="example">
1576  OPTIONS * HTTP/1.1
1579   The absolute-URI form is &REQUIRED; when the request is being made to a
1580   proxy. The proxy is requested to forward the request or service it
1581   from a valid cache, and return the response. Note that the proxy &MAY;
1582   forward the request on to another proxy or directly to the server
1583   specified by the absolute-URI. In order to avoid request loops, a
1584   proxy &MUST; be able to recognize all of its server names, including
1585   any aliases, local variations, and the numeric IP address. An example
1586   Request-Line would be:
1588<figure><artwork type="example">
1589  GET HTTP/1.1
1592   To allow for transition to absolute-URIs in all requests in future
1593   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1594   form in requests, even though HTTP/1.1 clients will only generate
1595   them in requests to proxies.
1598   The authority form is only used by the CONNECT method (&CONNECT;).
1601   The most common form of request-target is that used to identify a
1602   resource on an origin server or gateway. In this case the absolute
1603   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1604   the request-target, and the network location of the URI (authority) &MUST;
1605   be transmitted in a Host header field. For example, a client wishing
1606   to retrieve the resource above directly from the origin server would
1607   create a TCP connection to port 80 of the host "" and send
1608   the lines:
1610<figure><artwork type="example">
1611  GET /pub/WWW/TheProject.html HTTP/1.1
1612  Host:
1615   followed by the remainder of the Request. Note that the absolute path
1616   cannot be empty; if none is present in the original URI, it &MUST; be
1617   given as "/" (the server root).
1620   If a proxy receives a request without any path in the request-target and
1621   the method specified is capable of supporting the asterisk form of
1622   request-target, then the last proxy on the request chain &MUST; forward the
1623   request with "*" as the final request-target.
1626   For example, the request
1627</preamble><artwork type="example">
1628  OPTIONS HTTP/1.1
1631  would be forwarded by the proxy as
1632</preamble><artwork type="example">
1633  OPTIONS * HTTP/1.1
1634  Host:
1637   after connecting to port 8001 of host "".
1641   The request-target is transmitted in the format specified in
1642   <xref target="http.uri"/>. If the request-target is percent-encoded
1643   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1644   &MUST; decode the request-target in order to
1645   properly interpret the request. Servers &SHOULD; respond to invalid
1646   request-targets with an appropriate status code.
1649   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1650   received request-target when forwarding it to the next inbound server,
1651   except as noted above to replace a null path-absolute with "/".
1654  <t>
1655    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1656    meaning of the request when the origin server is improperly using
1657    a non-reserved URI character for a reserved purpose.  Implementors
1658    should be aware that some pre-HTTP/1.1 proxies have been known to
1659    rewrite the request-target.
1660  </t>
1663   HTTP does not place a pre-defined limit on the length of a request-target.
1664   A server &MUST; be prepared to receive URIs of unbounded length and
1665   respond with the 414 (URI Too Long) status if the received
1666   request-target would be longer than the server wishes to handle
1667   (see &status-414;).
1670   Various ad-hoc limitations on request-target length are found in practice.
1671   It is &RECOMMENDED; that all HTTP senders and recipients support
1672   request-target lengths of 8000 or more OCTETs.
1677<section title="The Resource Identified by a Request" anchor="">
1679   The exact resource identified by an Internet request is determined by
1680   examining both the request-target and the Host header field.
1683   An origin server that does not allow resources to differ by the
1684   requested host &MAY; ignore the Host header field value when
1685   determining the resource identified by an HTTP/1.1 request. (But see
1686   <xref target=""/>
1687   for other requirements on Host support in HTTP/1.1.)
1690   An origin server that does differentiate resources based on the host
1691   requested (sometimes referred to as virtual hosts or vanity host
1692   names) &MUST; use the following rules for determining the requested
1693   resource on an HTTP/1.1 request:
1694  <list style="numbers">
1695    <t>If request-target is an absolute-URI, the host is part of the
1696     request-target. Any Host header field value in the request &MUST; be
1697     ignored.</t>
1698    <t>If the request-target is not an absolute-URI, and the request includes
1699     a Host header field, the host is determined by the Host header
1700     field value.</t>
1701    <t>If the host as determined by rule 1 or 2 is not a valid host on
1702     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1703  </list>
1706   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1707   attempt to use heuristics (e.g., examination of the URI path for
1708   something unique to a particular host) in order to determine what
1709   exact resource is being requested.
1716<section title="Response" anchor="response">
1717  <x:anchor-alias value="Response"/>
1719   After receiving and interpreting a request message, a server responds
1720   with an HTTP response message.
1722<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1723  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1724                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1725                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1726                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1727                  <x:ref>CRLF</x:ref>
1728                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1731<section title="Status-Line" anchor="status-line">
1732  <x:anchor-alias value="Status-Line"/>
1734   The first line of a Response message is the Status-Line, consisting
1735   of the protocol version followed by a numeric status code and its
1736   associated textual phrase, with each element separated by SP
1737   characters. No CR or LF is allowed except in the final CRLF sequence.
1739<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1740  <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>
1743<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1744  <x:anchor-alias value="Reason-Phrase"/>
1745  <x:anchor-alias value="Status-Code"/>
1747   The Status-Code element is a 3-digit integer result code of the
1748   attempt to understand and satisfy the request. These codes are fully
1749   defined in &status-codes;.  The Reason Phrase exists for the sole
1750   purpose of providing a textual description associated with the numeric
1751   status code, out of deference to earlier Internet application protocols
1752   that were more frequently used with interactive text clients.
1753   A client &SHOULD; ignore the content of the Reason Phrase.
1756   The first digit of the Status-Code defines the class of response. The
1757   last two digits do not have any categorization role. There are 5
1758   values for the first digit:
1759  <list style="symbols">
1760    <t>
1761      1xx: Informational - Request received, continuing process
1762    </t>
1763    <t>
1764      2xx: Success - The action was successfully received,
1765        understood, and accepted
1766    </t>
1767    <t>
1768      3xx: Redirection - Further action must be taken in order to
1769        complete the request
1770    </t>
1771    <t>
1772      4xx: Client Error - The request contains bad syntax or cannot
1773        be fulfilled
1774    </t>
1775    <t>
1776      5xx: Server Error - The server failed to fulfill an apparently
1777        valid request
1778    </t>
1779  </list>
1781<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"/>
1782  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1783  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1791<section title="Connections" anchor="connections">
1793<section title="Persistent Connections" anchor="persistent.connections">
1795<section title="Purpose" anchor="persistent.purpose">
1797   Prior to persistent connections, a separate TCP connection was
1798   established to fetch each URL, increasing the load on HTTP servers
1799   and causing congestion on the Internet. The use of inline images and
1800   other associated data often require a client to make multiple
1801   requests of the same server in a short amount of time. Analysis of
1802   these performance problems and results from a prototype
1803   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1804   measurements of actual HTTP/1.1 implementations show good
1805   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1806   T/TCP <xref target="Tou1998"/>.
1809   Persistent HTTP connections have a number of advantages:
1810  <list style="symbols">
1811      <t>
1812        By opening and closing fewer TCP connections, CPU time is saved
1813        in routers and hosts (clients, servers, proxies, gateways,
1814        tunnels, or caches), and memory used for TCP protocol control
1815        blocks can be saved in hosts.
1816      </t>
1817      <t>
1818        HTTP requests and responses can be pipelined on a connection.
1819        Pipelining allows a client to make multiple requests without
1820        waiting for each response, allowing a single TCP connection to
1821        be used much more efficiently, with much lower elapsed time.
1822      </t>
1823      <t>
1824        Network congestion is reduced by reducing the number of packets
1825        caused by TCP opens, and by allowing TCP sufficient time to
1826        determine the congestion state of the network.
1827      </t>
1828      <t>
1829        Latency on subsequent requests is reduced since there is no time
1830        spent in TCP's connection opening handshake.
1831      </t>
1832      <t>
1833        HTTP can evolve more gracefully, since errors can be reported
1834        without the penalty of closing the TCP connection. Clients using
1835        future versions of HTTP might optimistically try a new feature,
1836        but if communicating with an older server, retry with old
1837        semantics after an error is reported.
1838      </t>
1839    </list>
1842   HTTP implementations &SHOULD; implement persistent connections.
1846<section title="Overall Operation" anchor="persistent.overall">
1848   A significant difference between HTTP/1.1 and earlier versions of
1849   HTTP is that persistent connections are the default behavior of any
1850   HTTP connection. That is, unless otherwise indicated, the client
1851   &SHOULD; assume that the server will maintain a persistent connection,
1852   even after error responses from the server.
1855   Persistent connections provide a mechanism by which a client and a
1856   server can signal the close of a TCP connection. This signaling takes
1857   place using the Connection header field (<xref target="header.connection"/>). Once a close
1858   has been signaled, the client &MUST-NOT; send any more requests on that
1859   connection.
1862<section title="Negotiation" anchor="persistent.negotiation">
1864   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1865   maintain a persistent connection unless a Connection header including
1866   the connection-token "close" was sent in the request. If the server
1867   chooses to close the connection immediately after sending the
1868   response, it &SHOULD; send a Connection header including the
1869   connection-token close.
1872   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1873   decide to keep it open based on whether the response from a server
1874   contains a Connection header with the connection-token close. In case
1875   the client does not want to maintain a connection for more than that
1876   request, it &SHOULD; send a Connection header including the
1877   connection-token close.
1880   If either the client or the server sends the close token in the
1881   Connection header, that request becomes the last one for the
1882   connection.
1885   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1886   maintained for HTTP versions less than 1.1 unless it is explicitly
1887   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1888   compatibility with HTTP/1.0 clients.
1891   In order to remain persistent, all messages on the connection &MUST;
1892   have a self-defined message length (i.e., one not defined by closure
1893   of the connection), as described in <xref target="message.length"/>.
1897<section title="Pipelining" anchor="pipelining">
1899   A client that supports persistent connections &MAY; "pipeline" its
1900   requests (i.e., send multiple requests without waiting for each
1901   response). A server &MUST; send its responses to those requests in the
1902   same order that the requests were received.
1905   Clients which assume persistent connections and pipeline immediately
1906   after connection establishment &SHOULD; be prepared to retry their
1907   connection if the first pipelined attempt fails. If a client does
1908   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1909   persistent. Clients &MUST; also be prepared to resend their requests if
1910   the server closes the connection before sending all of the
1911   corresponding responses.
1914   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1915   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1916   premature termination of the transport connection could lead to
1917   indeterminate results. A client wishing to send a non-idempotent
1918   request &SHOULD; wait to send that request until it has received the
1919   response status for the previous request.
1924<section title="Proxy Servers" anchor="persistent.proxy">
1926   It is especially important that proxies correctly implement the
1927   properties of the Connection header field as specified in <xref target="header.connection"/>.
1930   The proxy server &MUST; signal persistent connections separately with
1931   its clients and the origin servers (or other proxy servers) that it
1932   connects to. Each persistent connection applies to only one transport
1933   link.
1936   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1937   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
1938   for information and discussion of the problems with the Keep-Alive header
1939   implemented by many HTTP/1.0 clients).
1943<section title="Practical Considerations" anchor="persistent.practical">
1945   Servers will usually have some time-out value beyond which they will
1946   no longer maintain an inactive connection. Proxy servers might make
1947   this a higher value since it is likely that the client will be making
1948   more connections through the same server. The use of persistent
1949   connections places no requirements on the length (or existence) of
1950   this time-out for either the client or the server.
1953   When a client or server wishes to time-out it &SHOULD; issue a graceful
1954   close on the transport connection. Clients and servers &SHOULD; both
1955   constantly watch for the other side of the transport close, and
1956   respond to it as appropriate. If a client or server does not detect
1957   the other side's close promptly it could cause unnecessary resource
1958   drain on the network.
1961   A client, server, or proxy &MAY; close the transport connection at any
1962   time. For example, a client might have started to send a new request
1963   at the same time that the server has decided to close the "idle"
1964   connection. From the server's point of view, the connection is being
1965   closed while it was idle, but from the client's point of view, a
1966   request is in progress.
1969   This means that clients, servers, and proxies &MUST; be able to recover
1970   from asynchronous close events. Client software &SHOULD; reopen the
1971   transport connection and retransmit the aborted sequence of requests
1972   without user interaction so long as the request sequence is
1973   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1974   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1975   human operator the choice of retrying the request(s). Confirmation by
1976   user-agent software with semantic understanding of the application
1977   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1978   be repeated if the second sequence of requests fails.
1981   Servers &SHOULD; always respond to at least one request per connection,
1982   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1983   middle of transmitting a response, unless a network or client failure
1984   is suspected.
1987   Clients that use persistent connections &SHOULD; limit the number of
1988   simultaneous connections that they maintain to a given server. A
1989   single-user client &SHOULD-NOT; maintain more than 2 connections with
1990   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1991   another server or proxy, where N is the number of simultaneously
1992   active users. These guidelines are intended to improve HTTP response
1993   times and avoid congestion.
1998<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2000<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2002   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2003   flow control mechanisms to resolve temporary overloads, rather than
2004   terminating connections with the expectation that clients will retry.
2005   The latter technique can exacerbate network congestion.
2009<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2011   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2012   the network connection for an error status while it is transmitting
2013   the request. If the client sees an error status, it &SHOULD;
2014   immediately cease transmitting the body. If the body is being sent
2015   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2016   empty trailer &MAY; be used to prematurely mark the end of the message.
2017   If the body was preceded by a Content-Length header, the client &MUST;
2018   close the connection.
2022<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2024   The purpose of the 100 (Continue) status (see &status-100;) is to
2025   allow a client that is sending a request message with a request body
2026   to determine if the origin server is willing to accept the request
2027   (based on the request headers) before the client sends the request
2028   body. In some cases, it might either be inappropriate or highly
2029   inefficient for the client to send the body if the server will reject
2030   the message without looking at the body.
2033   Requirements for HTTP/1.1 clients:
2034  <list style="symbols">
2035    <t>
2036        If a client will wait for a 100 (Continue) response before
2037        sending the request body, it &MUST; send an Expect request-header
2038        field (&header-expect;) with the "100-continue" expectation.
2039    </t>
2040    <t>
2041        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2042        with the "100-continue" expectation if it does not intend
2043        to send a request body.
2044    </t>
2045  </list>
2048   Because of the presence of older implementations, the protocol allows
2049   ambiguous situations in which a client may send "Expect: 100-continue"
2050   without receiving either a 417 (Expectation Failed) status
2051   or a 100 (Continue) status. Therefore, when a client sends this
2052   header field to an origin server (possibly via a proxy) from which it
2053   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2054   for an indefinite period before sending the request body.
2057   Requirements for HTTP/1.1 origin servers:
2058  <list style="symbols">
2059    <t> Upon receiving a request which includes an Expect request-header
2060        field with the "100-continue" expectation, an origin server &MUST;
2061        either respond with 100 (Continue) status and continue to read
2062        from the input stream, or respond with a final status code. The
2063        origin server &MUST-NOT; wait for the request body before sending
2064        the 100 (Continue) response. If it responds with a final status
2065        code, it &MAY; close the transport connection or it &MAY; continue
2066        to read and discard the rest of the request.  It &MUST-NOT;
2067        perform the requested method if it returns a final status code.
2068    </t>
2069    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2070        the request message does not include an Expect request-header
2071        field with the "100-continue" expectation, and &MUST-NOT; send a
2072        100 (Continue) response if such a request comes from an HTTP/1.0
2073        (or earlier) client. There is an exception to this rule: for
2074        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2075        status in response to an HTTP/1.1 PUT or POST request that does
2076        not include an Expect request-header field with the "100-continue"
2077        expectation. This exception, the purpose of which is
2078        to minimize any client processing delays associated with an
2079        undeclared wait for 100 (Continue) status, applies only to
2080        HTTP/1.1 requests, and not to requests with any other HTTP-version
2081        value.
2082    </t>
2083    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2084        already received some or all of the request body for the
2085        corresponding request.
2086    </t>
2087    <t> An origin server that sends a 100 (Continue) response &MUST;
2088    ultimately send a final status code, once the request body is
2089        received and processed, unless it terminates the transport
2090        connection prematurely.
2091    </t>
2092    <t> If an origin server receives a request that does not include an
2093        Expect request-header field with the "100-continue" expectation,
2094        the request includes a request body, and the server responds
2095        with a final status code before reading the entire request body
2096        from the transport connection, then the server &SHOULD-NOT;  close
2097        the transport connection until it has read the entire request,
2098        or until the client closes the connection. Otherwise, the client
2099        might not reliably receive the response message. However, this
2100        requirement is not be construed as preventing a server from
2101        defending itself against denial-of-service attacks, or from
2102        badly broken client implementations.
2103      </t>
2104    </list>
2107   Requirements for HTTP/1.1 proxies:
2108  <list style="symbols">
2109    <t> If a proxy receives a request that includes an Expect request-header
2110        field with the "100-continue" expectation, and the proxy
2111        either knows that the next-hop server complies with HTTP/1.1 or
2112        higher, or does not know the HTTP version of the next-hop
2113        server, it &MUST; forward the request, including the Expect header
2114        field.
2115    </t>
2116    <t> If the proxy knows that the version of the next-hop server is
2117        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2118        respond with a 417 (Expectation Failed) status.
2119    </t>
2120    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2121        numbers received from recently-referenced next-hop servers.
2122    </t>
2123    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2124        request message was received from an HTTP/1.0 (or earlier)
2125        client and did not include an Expect request-header field with
2126        the "100-continue" expectation. This requirement overrides the
2127        general rule for forwarding of 1xx responses (see &status-1xx;).
2128    </t>
2129  </list>
2133<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2135   If an HTTP/1.1 client sends a request which includes a request body,
2136   but which does not include an Expect request-header field with the
2137   "100-continue" expectation, and if the client is not directly
2138   connected to an HTTP/1.1 origin server, and if the client sees the
2139   connection close before receiving any status from the server, the
2140   client &SHOULD; retry the request.  If the client does retry this
2141   request, it &MAY; use the following "binary exponential backoff"
2142   algorithm to be assured of obtaining a reliable response:
2143  <list style="numbers">
2144    <t>
2145      Initiate a new connection to the server
2146    </t>
2147    <t>
2148      Transmit the request-headers
2149    </t>
2150    <t>
2151      Initialize a variable R to the estimated round-trip time to the
2152         server (e.g., based on the time it took to establish the
2153         connection), or to a constant value of 5 seconds if the round-trip
2154         time is not available.
2155    </t>
2156    <t>
2157       Compute T = R * (2**N), where N is the number of previous
2158         retries of this request.
2159    </t>
2160    <t>
2161       Wait either for an error response from the server, or for T
2162         seconds (whichever comes first)
2163    </t>
2164    <t>
2165       If no error response is received, after T seconds transmit the
2166         body of the request.
2167    </t>
2168    <t>
2169       If client sees that the connection is closed prematurely,
2170         repeat from step 1 until the request is accepted, an error
2171         response is received, or the user becomes impatient and
2172         terminates the retry process.
2173    </t>
2174  </list>
2177   If at any point an error status is received, the client
2178  <list style="symbols">
2179      <t>&SHOULD-NOT;  continue and</t>
2181      <t>&SHOULD; close the connection if it has not completed sending the
2182        request message.</t>
2183    </list>
2190<section title="Header Field Definitions" anchor="header.fields">
2192   This section defines the syntax and semantics of HTTP/1.1 header fields
2193   related to message framing and transport protocols.
2196   For entity-header fields, both sender and recipient refer to either the
2197   client or the server, depending on who sends and who receives the entity.
2200<section title="Connection" anchor="header.connection">
2201  <iref primary="true" item="Connection header" x:for-anchor=""/>
2202  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2203  <x:anchor-alias value="Connection"/>
2204  <x:anchor-alias value="connection-token"/>
2205  <x:anchor-alias value="Connection-v"/>
2207   The general-header field "Connection" allows the sender to specify
2208   options that are desired for that particular connection and &MUST-NOT;
2209   be communicated by proxies over further connections.
2212   The Connection header's value has the following grammar:
2214<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"/>
2215  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2216  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2217  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2220   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2221   message is forwarded and, for each connection-token in this field,
2222   remove any header field(s) from the message with the same name as the
2223   connection-token. Connection options are signaled by the presence of
2224   a connection-token in the Connection header field, not by any
2225   corresponding additional header field(s), since the additional header
2226   field may not be sent if there are no parameters associated with that
2227   connection option.
2230   Message headers listed in the Connection header &MUST-NOT; include
2231   end-to-end headers, such as Cache-Control.
2234   HTTP/1.1 defines the "close" connection option for the sender to
2235   signal that the connection will be closed after completion of the
2236   response. For example,
2238<figure><artwork type="example">
2239  Connection: close
2242   in either the request or the response header fields indicates that
2243   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2244   after the current request/response is complete.
2247   An HTTP/1.1 client that does not support persistent connections &MUST;
2248   include the "close" connection option in every request message.
2251   An HTTP/1.1 server that does not support persistent connections &MUST;
2252   include the "close" connection option in every response message that
2253   does not have a 1xx (informational) status code.
2256   A system receiving an HTTP/1.0 (or lower-version) message that
2257   includes a Connection header &MUST;, for each connection-token in this
2258   field, remove and ignore any header field(s) from the message with
2259   the same name as the connection-token. This protects against mistaken
2260   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2264<section title="Content-Length" anchor="header.content-length">
2265  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2266  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2267  <x:anchor-alias value="Content-Length"/>
2268  <x:anchor-alias value="Content-Length-v"/>
2270   The entity-header field "Content-Length" indicates the size of the
2271   entity-body, in number of OCTETs, sent to the recipient or,
2272   in the case of the HEAD method, the size of the entity-body that
2273   would have been sent had the request been a GET.
2275<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2276  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2277  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2280   An example is
2282<figure><artwork type="example">
2283  Content-Length: 3495
2286   Applications &SHOULD; use this field to indicate the transfer-length of
2287   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2290   Any Content-Length greater than or equal to zero is a valid value.
2291   <xref target="message.length"/> describes how to determine the length of a message-body
2292   if a Content-Length is not given.
2295   Note that the meaning of this field is significantly different from
2296   the corresponding definition in MIME, where it is an optional field
2297   used within the "message/external-body" content-type. In HTTP, it
2298   &SHOULD; be sent whenever the message's length can be determined prior
2299   to being transferred, unless this is prohibited by the rules in
2300   <xref target="message.length"/>.
2304<section title="Date" anchor="">
2305  <iref primary="true" item="Date header" x:for-anchor=""/>
2306  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2307  <x:anchor-alias value="Date"/>
2308  <x:anchor-alias value="Date-v"/>
2310   The general-header field "Date" represents the date and time at which
2311   the message was originated, having the same semantics as orig-date in
2312   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2313   HTTP-date, as described in <xref target=""/>;
2314   it &MUST; be sent in rfc1123-date format.
2316<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2317  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2318  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2321   An example is
2323<figure><artwork type="example">
2324  Date: Tue, 15 Nov 1994 08:12:31 GMT
2327   Origin servers &MUST; include a Date header field in all responses,
2328   except in these cases:
2329  <list style="numbers">
2330      <t>If the response status code is 100 (Continue) or 101 (Switching
2331         Protocols), the response &MAY; include a Date header field, at
2332         the server's option.</t>
2334      <t>If the response status code conveys a server error, e.g. 500
2335         (Internal Server Error) or 503 (Service Unavailable), and it is
2336         inconvenient or impossible to generate a valid Date.</t>
2338      <t>If the server does not have a clock that can provide a
2339         reasonable approximation of the current time, its responses
2340         &MUST-NOT; include a Date header field. In this case, the rules
2341         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2342  </list>
2345   A received message that does not have a Date header field &MUST; be
2346   assigned one by the recipient if the message will be cached by that
2347   recipient or gatewayed via a protocol which requires a Date. An HTTP
2348   implementation without a clock &MUST-NOT; cache responses without
2349   revalidating them on every use. An HTTP cache, especially a shared
2350   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2351   clock with a reliable external standard.
2354   Clients &SHOULD; only send a Date header field in messages that include
2355   an entity-body, as in the case of the PUT and POST requests, and even
2356   then it is optional. A client without a clock &MUST-NOT; send a Date
2357   header field in a request.
2360   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2361   time subsequent to the generation of the message. It &SHOULD; represent
2362   the best available approximation of the date and time of message
2363   generation, unless the implementation has no means of generating a
2364   reasonably accurate date and time. In theory, the date ought to
2365   represent the moment just before the entity is generated. In
2366   practice, the date can be generated at any time during the message
2367   origination without affecting its semantic value.
2370<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2372   Some origin server implementations might not have a clock available.
2373   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2374   values to a response, unless these values were associated
2375   with the resource by a system or user with a reliable clock. It &MAY;
2376   assign an Expires value that is known, at or before server
2377   configuration time, to be in the past (this allows "pre-expiration"
2378   of responses without storing separate Expires values for each
2379   resource).
2384<section title="Host" anchor="">
2385  <iref primary="true" item="Host header" x:for-anchor=""/>
2386  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2387  <x:anchor-alias value="Host"/>
2388  <x:anchor-alias value="Host-v"/>
2390   The request-header field "Host" specifies the Internet host and port
2391   number of the resource being requested, as obtained from the original
2392   URI given by the user or referring resource (generally an http URI,
2393   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2394   the naming authority of the origin server or gateway given by the
2395   original URL. This allows the origin server or gateway to
2396   differentiate between internally-ambiguous URLs, such as the root "/"
2397   URL of a server for multiple host names on a single IP address.
2399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2400  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2401  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2404   A "host" without any trailing port information implies the default
2405   port for the service requested (e.g., "80" for an HTTP URL). For
2406   example, a request on the origin server for
2407   &lt;; would properly include:
2409<figure><artwork type="example">
2410  GET /pub/WWW/ HTTP/1.1
2411  Host:
2414   A client &MUST; include a Host header field in all HTTP/1.1 request
2415   messages. If the requested URI does not include an Internet host
2416   name for the service being requested, then the Host header field &MUST;
2417   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2418   request message it forwards does contain an appropriate Host header
2419   field that identifies the service being requested by the proxy. All
2420   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2421   status code to any HTTP/1.1 request message which lacks a Host header
2422   field.
2425   See Sections <xref target="" format="counter"/>
2426   and <xref target="" format="counter"/>
2427   for other requirements relating to Host.
2431<section title="TE" anchor="header.te">
2432  <iref primary="true" item="TE header" x:for-anchor=""/>
2433  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2434  <x:anchor-alias value="TE"/>
2435  <x:anchor-alias value="TE-v"/>
2436  <x:anchor-alias value="t-codings"/>
2437  <x:anchor-alias value="te-params"/>
2438  <x:anchor-alias value="te-ext"/>
2440   The request-header field "TE" indicates what extension transfer-codings
2441   it is willing to accept in the response and whether or not it is
2442   willing to accept trailer fields in a chunked transfer-coding. Its
2443   value may consist of the keyword "trailers" and/or a comma-separated
2444   list of extension transfer-coding names with optional accept
2445   parameters (as described in <xref target="transfer.codings"/>).
2447<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"/>
2448  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2449  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2450  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2451  <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> )
2452  <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> ) ]
2455   The presence of the keyword "trailers" indicates that the client is
2456   willing to accept trailer fields in a chunked transfer-coding, as
2457   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2458   transfer-coding values even though it does not itself represent a
2459   transfer-coding.
2462   Examples of its use are:
2464<figure><artwork type="example">
2465  TE: deflate
2466  TE:
2467  TE: trailers, deflate;q=0.5
2470   The TE header field only applies to the immediate connection.
2471   Therefore, the keyword &MUST; be supplied within a Connection header
2472   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2475   A server tests whether a transfer-coding is acceptable, according to
2476   a TE field, using these rules:
2477  <list style="numbers">
2478    <x:lt>
2479      <t>The "chunked" transfer-coding is always acceptable. If the
2480         keyword "trailers" is listed, the client indicates that it is
2481         willing to accept trailer fields in the chunked response on
2482         behalf of itself and any downstream clients. The implication is
2483         that, if given, the client is stating that either all
2484         downstream clients are willing to accept trailer fields in the
2485         forwarded response, or that it will attempt to buffer the
2486         response on behalf of downstream recipients.
2487      </t><t>
2488         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2489         chunked response such that a client can be assured of buffering
2490         the entire response.</t>
2491    </x:lt>
2492    <x:lt>
2493      <t>If the transfer-coding being tested is one of the transfer-codings
2494         listed in the TE field, then it is acceptable unless it
2495         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2496         qvalue of 0 means "not acceptable.")</t>
2497    </x:lt>
2498    <x:lt>
2499      <t>If multiple transfer-codings are acceptable, then the
2500         acceptable transfer-coding with the highest non-zero qvalue is
2501         preferred.  The "chunked" transfer-coding always has a qvalue
2502         of 1.</t>
2503    </x:lt>
2504  </list>
2507   If the TE field-value is empty or if no TE field is present, the only
2508   transfer-coding is "chunked". A message with no transfer-coding is
2509   always acceptable.
2513<section title="Trailer" anchor="header.trailer">
2514  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2515  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2516  <x:anchor-alias value="Trailer"/>
2517  <x:anchor-alias value="Trailer-v"/>
2519   The general field "Trailer" indicates that the given set of
2520   header fields is present in the trailer of a message encoded with
2521   chunked transfer-coding.
2523<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2524  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2525  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2528   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2529   message using chunked transfer-coding with a non-empty trailer. Doing
2530   so allows the recipient to know which header fields to expect in the
2531   trailer.
2534   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2535   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2536   trailer fields in a "chunked" transfer-coding.
2539   Message header fields listed in the Trailer header field &MUST-NOT;
2540   include the following header fields:
2541  <list style="symbols">
2542    <t>Transfer-Encoding</t>
2543    <t>Content-Length</t>
2544    <t>Trailer</t>
2545  </list>
2549<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2550  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2551  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2552  <x:anchor-alias value="Transfer-Encoding"/>
2553  <x:anchor-alias value="Transfer-Encoding-v"/>
2555   The general-header "Transfer-Encoding" field indicates what (if any)
2556   type of transformation has been applied to the message body in order
2557   to safely transfer it between the sender and the recipient. This
2558   differs from the content-coding in that the transfer-coding is a
2559   property of the message, not of the entity.
2561<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2562  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2563                        <x:ref>Transfer-Encoding-v</x:ref>
2564  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2567   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2569<figure><artwork type="example">
2570  Transfer-Encoding: chunked
2573   If multiple encodings have been applied to an entity, the transfer-codings
2574   &MUST; be listed in the order in which they were applied.
2575   Additional information about the encoding parameters &MAY; be provided
2576   by other entity-header fields not defined by this specification.
2579   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2580   header.
2584<section title="Upgrade" anchor="header.upgrade">
2585  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2586  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2587  <x:anchor-alias value="Upgrade"/>
2588  <x:anchor-alias value="Upgrade-v"/>
2590   The general-header "Upgrade" allows the client to specify what
2591   additional communication protocols it supports and would like to use
2592   if the server finds it appropriate to switch protocols. The server
2593   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2594   response to indicate which protocol(s) are being switched.
2596<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2597  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2598  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2601   For example,
2603<figure><artwork type="example">
2604  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2607   The Upgrade header field is intended to provide a simple mechanism
2608   for transition from HTTP/1.1 to some other, incompatible protocol. It
2609   does so by allowing the client to advertise its desire to use another
2610   protocol, such as a later version of HTTP with a higher major version
2611   number, even though the current request has been made using HTTP/1.1.
2612   This eases the difficult transition between incompatible protocols by
2613   allowing the client to initiate a request in the more commonly
2614   supported protocol while indicating to the server that it would like
2615   to use a "better" protocol if available (where "better" is determined
2616   by the server, possibly according to the nature of the method and/or
2617   resource being requested).
2620   The Upgrade header field only applies to switching application-layer
2621   protocols upon the existing transport-layer connection. Upgrade
2622   cannot be used to insist on a protocol change; its acceptance and use
2623   by the server is optional. The capabilities and nature of the
2624   application-layer communication after the protocol change is entirely
2625   dependent upon the new protocol chosen, although the first action
2626   after changing the protocol &MUST; be a response to the initial HTTP
2627   request containing the Upgrade header field.
2630   The Upgrade header field only applies to the immediate connection.
2631   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2632   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2633   HTTP/1.1 message.
2636   The Upgrade header field cannot be used to indicate a switch to a
2637   protocol on a different connection. For that purpose, it is more
2638   appropriate to use a 301, 302, 303, or 305 redirection response.
2641   This specification only defines the protocol name "HTTP" for use by
2642   the family of Hypertext Transfer Protocols, as defined by the HTTP
2643   version rules of <xref target="http.version"/> and future updates to this
2644   specification. Any token can be used as a protocol name; however, it
2645   will only be useful if both the client and server associate the name
2646   with the same protocol.
2650<section title="Via" anchor="header.via">
2651  <iref primary="true" item="Via header" x:for-anchor=""/>
2652  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2653  <x:anchor-alias value="protocol-name"/>
2654  <x:anchor-alias value="protocol-version"/>
2655  <x:anchor-alias value="pseudonym"/>
2656  <x:anchor-alias value="received-by"/>
2657  <x:anchor-alias value="received-protocol"/>
2658  <x:anchor-alias value="Via"/>
2659  <x:anchor-alias value="Via-v"/>
2661   The general-header field "Via" &MUST; be used by gateways and proxies to
2662   indicate the intermediate protocols and recipients between the user
2663   agent and the server on requests, and between the origin server and
2664   the client on responses. It is analogous to the "Received" field defined in
2665   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2666   avoiding request loops, and identifying the protocol capabilities of
2667   all senders along the request/response chain.
2669<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"/>
2670  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2671  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2672                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2673  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2674  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2675  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2676  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2677  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2680   The received-protocol indicates the protocol version of the message
2681   received by the server or client along each segment of the
2682   request/response chain. The received-protocol version is appended to
2683   the Via field value when the message is forwarded so that information
2684   about the protocol capabilities of upstream applications remains
2685   visible to all recipients.
2688   The protocol-name is optional if and only if it would be "HTTP". The
2689   received-by field is normally the host and optional port number of a
2690   recipient server or client that subsequently forwarded the message.
2691   However, if the real host is considered to be sensitive information,
2692   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2693   be assumed to be the default port of the received-protocol.
2696   Multiple Via field values represents each proxy or gateway that has
2697   forwarded the message. Each recipient &MUST; append its information
2698   such that the end result is ordered according to the sequence of
2699   forwarding applications.
2702   Comments &MAY; be used in the Via header field to identify the software
2703   of the recipient proxy or gateway, analogous to the User-Agent and
2704   Server header fields. However, all comments in the Via field are
2705   optional and &MAY; be removed by any recipient prior to forwarding the
2706   message.
2709   For example, a request message could be sent from an HTTP/1.0 user
2710   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2711   forward the request to a public proxy at, which completes
2712   the request by forwarding it to the origin server at
2713   The request received by would then have the following
2714   Via header field:
2716<figure><artwork type="example">
2717  Via: 1.0 fred, 1.1 (Apache/1.1)
2720   Proxies and gateways used as a portal through a network firewall
2721   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2722   the firewall region. This information &SHOULD; only be propagated if
2723   explicitly enabled. If not enabled, the received-by host of any host
2724   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2725   for that host.
2728   For organizations that have strong privacy requirements for hiding
2729   internal structures, a proxy &MAY; combine an ordered subsequence of
2730   Via header field entries with identical received-protocol values into
2731   a single such entry. For example,
2733<figure><artwork type="example">
2734  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2737        could be collapsed to
2739<figure><artwork type="example">
2740  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2743   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2744   under the same organizational control and the hosts have already been
2745   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2746   have different received-protocol values.
2752<section title="IANA Considerations" anchor="IANA.considerations">
2753<section title="Message Header Registration" anchor="message.header.registration">
2755   The Message Header Registry located at <eref target=""/> should be updated
2756   with the permanent registrations below (see <xref target="RFC3864"/>):
2758<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2759<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2760   <ttcol>Header Field Name</ttcol>
2761   <ttcol>Protocol</ttcol>
2762   <ttcol>Status</ttcol>
2763   <ttcol>Reference</ttcol>
2765   <c>Connection</c>
2766   <c>http</c>
2767   <c>standard</c>
2768   <c>
2769      <xref target="header.connection"/>
2770   </c>
2771   <c>Content-Length</c>
2772   <c>http</c>
2773   <c>standard</c>
2774   <c>
2775      <xref target="header.content-length"/>
2776   </c>
2777   <c>Date</c>
2778   <c>http</c>
2779   <c>standard</c>
2780   <c>
2781      <xref target=""/>
2782   </c>
2783   <c>Host</c>
2784   <c>http</c>
2785   <c>standard</c>
2786   <c>
2787      <xref target=""/>
2788   </c>
2789   <c>TE</c>
2790   <c>http</c>
2791   <c>standard</c>
2792   <c>
2793      <xref target="header.te"/>
2794   </c>
2795   <c>Trailer</c>
2796   <c>http</c>
2797   <c>standard</c>
2798   <c>
2799      <xref target="header.trailer"/>
2800   </c>
2801   <c>Transfer-Encoding</c>
2802   <c>http</c>
2803   <c>standard</c>
2804   <c>
2805      <xref target="header.transfer-encoding"/>
2806   </c>
2807   <c>Upgrade</c>
2808   <c>http</c>
2809   <c>standard</c>
2810   <c>
2811      <xref target="header.upgrade"/>
2812   </c>
2813   <c>Via</c>
2814   <c>http</c>
2815   <c>standard</c>
2816   <c>
2817      <xref target="header.via"/>
2818   </c>
2822   The change controller is: "IETF ( - Internet Engineering Task Force".
2826<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2828   The entry for the "http" URI Scheme in the registry located at
2829   <eref target=""/>
2830   should be updated to point to <xref target="http.uri"/> of this document
2831   (see <xref target="RFC4395"/>).
2835<section title="Internet Media Type Registrations" anchor="">
2837   This document serves as the specification for the Internet media types
2838   "message/http" and "application/http". The following is to be registered with
2839   IANA (see <xref target="RFC4288"/>).
2841<section title="Internet Media Type message/http" anchor="">
2842<iref item="Media Type" subitem="message/http" primary="true"/>
2843<iref item="message/http Media Type" primary="true"/>
2845   The message/http type can be used to enclose a single HTTP request or
2846   response message, provided that it obeys the MIME restrictions for all
2847   "message" types regarding line length and encodings.
2850  <list style="hanging" x:indent="12em">
2851    <t hangText="Type name:">
2852      message
2853    </t>
2854    <t hangText="Subtype name:">
2855      http
2856    </t>
2857    <t hangText="Required parameters:">
2858      none
2859    </t>
2860    <t hangText="Optional parameters:">
2861      version, msgtype
2862      <list style="hanging">
2863        <t hangText="version:">
2864          The HTTP-Version number of the enclosed message
2865          (e.g., "1.1"). If not present, the version can be
2866          determined from the first line of the body.
2867        </t>
2868        <t hangText="msgtype:">
2869          The message type -- "request" or "response". If not
2870          present, the type can be determined from the first
2871          line of the body.
2872        </t>
2873      </list>
2874    </t>
2875    <t hangText="Encoding considerations:">
2876      only "7bit", "8bit", or "binary" are permitted
2877    </t>
2878    <t hangText="Security considerations:">
2879      none
2880    </t>
2881    <t hangText="Interoperability considerations:">
2882      none
2883    </t>
2884    <t hangText="Published specification:">
2885      This specification (see <xref target=""/>).
2886    </t>
2887    <t hangText="Applications that use this media type:">
2888    </t>
2889    <t hangText="Additional information:">
2890      <list style="hanging">
2891        <t hangText="Magic number(s):">none</t>
2892        <t hangText="File extension(s):">none</t>
2893        <t hangText="Macintosh file type code(s):">none</t>
2894      </list>
2895    </t>
2896    <t hangText="Person and email address to contact for further information:">
2897      See Authors Section.
2898    </t>
2899                <t hangText="Intended usage:">
2900                  COMMON
2901    </t>
2902                <t hangText="Restrictions on usage:">
2903                  none
2904    </t>
2905    <t hangText="Author/Change controller:">
2906      IESG
2907    </t>
2908  </list>
2911<section title="Internet Media Type application/http" anchor="">
2912<iref item="Media Type" subitem="application/http" primary="true"/>
2913<iref item="application/http Media Type" primary="true"/>
2915   The application/http type can be used to enclose a pipeline of one or more
2916   HTTP request or response messages (not intermixed).
2919  <list style="hanging" x:indent="12em">
2920    <t hangText="Type name:">
2921      application
2922    </t>
2923    <t hangText="Subtype name:">
2924      http
2925    </t>
2926    <t hangText="Required parameters:">
2927      none
2928    </t>
2929    <t hangText="Optional parameters:">
2930      version, msgtype
2931      <list style="hanging">
2932        <t hangText="version:">
2933          The HTTP-Version number of the enclosed messages
2934          (e.g., "1.1"). If not present, the version can be
2935          determined from the first line of the body.
2936        </t>
2937        <t hangText="msgtype:">
2938          The message type -- "request" or "response". If not
2939          present, the type can be determined from the first
2940          line of the body.
2941        </t>
2942      </list>
2943    </t>
2944    <t hangText="Encoding considerations:">
2945      HTTP messages enclosed by this type
2946      are in "binary" format; use of an appropriate
2947      Content-Transfer-Encoding is required when
2948      transmitted via E-mail.
2949    </t>
2950    <t hangText="Security considerations:">
2951      none
2952    </t>
2953    <t hangText="Interoperability considerations:">
2954      none
2955    </t>
2956    <t hangText="Published specification:">
2957      This specification (see <xref target=""/>).
2958    </t>
2959    <t hangText="Applications that use this media type:">
2960    </t>
2961    <t hangText="Additional information:">
2962      <list style="hanging">
2963        <t hangText="Magic number(s):">none</t>
2964        <t hangText="File extension(s):">none</t>
2965        <t hangText="Macintosh file type code(s):">none</t>
2966      </list>
2967    </t>
2968    <t hangText="Person and email address to contact for further information:">
2969      See Authors Section.
2970    </t>
2971                <t hangText="Intended usage:">
2972                  COMMON
2973    </t>
2974                <t hangText="Restrictions on usage:">
2975                  none
2976    </t>
2977    <t hangText="Author/Change controller:">
2978      IESG
2979    </t>
2980  </list>
2987<section title="Security Considerations" anchor="security.considerations">
2989   This section is meant to inform application developers, information
2990   providers, and users of the security limitations in HTTP/1.1 as
2991   described by this document. The discussion does not include
2992   definitive solutions to the problems revealed, though it does make
2993   some suggestions for reducing security risks.
2996<section title="Personal Information" anchor="personal.information">
2998   HTTP clients are often privy to large amounts of personal information
2999   (e.g. the user's name, location, mail address, passwords, encryption
3000   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3001   leakage of this information.
3002   We very strongly recommend that a convenient interface be provided
3003   for the user to control dissemination of such information, and that
3004   designers and implementors be particularly careful in this area.
3005   History shows that errors in this area often create serious security
3006   and/or privacy problems and generate highly adverse publicity for the
3007   implementor's company.
3011<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3013   A server is in the position to save personal data about a user's
3014   requests which might identify their reading patterns or subjects of
3015   interest. This information is clearly confidential in nature and its
3016   handling can be constrained by law in certain countries. People using
3017   HTTP to provide data are responsible for ensuring that
3018   such material is not distributed without the permission of any
3019   individuals that are identifiable by the published results.
3023<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3025   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3026   the documents returned by HTTP requests to be only those that were
3027   intended by the server administrators. If an HTTP server translates
3028   HTTP URIs directly into file system calls, the server &MUST; take
3029   special care not to serve files that were not intended to be
3030   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3031   other operating systems use ".." as a path component to indicate a
3032   directory level above the current one. On such a system, an HTTP
3033   server &MUST; disallow any such construct in the request-target if it
3034   would otherwise allow access to a resource outside those intended to
3035   be accessible via the HTTP server. Similarly, files intended for
3036   reference only internally to the server (such as access control
3037   files, configuration files, and script code) &MUST; be protected from
3038   inappropriate retrieval, since they might contain sensitive
3039   information. Experience has shown that minor bugs in such HTTP server
3040   implementations have turned into security risks.
3044<section title="DNS Spoofing" anchor="dns.spoofing">
3046   Clients using HTTP rely heavily on the Domain Name Service, and are
3047   thus generally prone to security attacks based on the deliberate
3048   mis-association of IP addresses and DNS names. Clients need to be
3049   cautious in assuming the continuing validity of an IP number/DNS name
3050   association.
3053   In particular, HTTP clients &SHOULD; rely on their name resolver for
3054   confirmation of an IP number/DNS name association, rather than
3055   caching the result of previous host name lookups. Many platforms
3056   already can cache host name lookups locally when appropriate, and
3057   they &SHOULD; be configured to do so. It is proper for these lookups to
3058   be cached, however, only when the TTL (Time To Live) information
3059   reported by the name server makes it likely that the cached
3060   information will remain useful.
3063   If HTTP clients cache the results of host name lookups in order to
3064   achieve a performance improvement, they &MUST; observe the TTL
3065   information reported by DNS.
3068   If HTTP clients do not observe this rule, they could be spoofed when
3069   a previously-accessed server's IP address changes. As network
3070   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3071   possibility of this form of attack will grow. Observing this
3072   requirement thus reduces this potential security vulnerability.
3075   This requirement also improves the load-balancing behavior of clients
3076   for replicated servers using the same DNS name and reduces the
3077   likelihood of a user's experiencing failure in accessing sites which
3078   use that strategy.
3082<section title="Proxies and Caching" anchor="attack.proxies">
3084   By their very nature, HTTP proxies are men-in-the-middle, and
3085   represent an opportunity for man-in-the-middle attacks. Compromise of
3086   the systems on which the proxies run can result in serious security
3087   and privacy problems. Proxies have access to security-related
3088   information, personal information about individual users and
3089   organizations, and proprietary information belonging to users and
3090   content providers. A compromised proxy, or a proxy implemented or
3091   configured without regard to security and privacy considerations,
3092   might be used in the commission of a wide range of potential attacks.
3095   Proxy operators should protect the systems on which proxies run as
3096   they would protect any system that contains or transports sensitive
3097   information. In particular, log information gathered at proxies often
3098   contains highly sensitive personal information, and/or information
3099   about organizations. Log information should be carefully guarded, and
3100   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3103   Proxy implementors should consider the privacy and security
3104   implications of their design and coding decisions, and of the
3105   configuration options they provide to proxy operators (especially the
3106   default configuration).
3109   Users of a proxy need to be aware that they are no trustworthier than
3110   the people who run the proxy; HTTP itself cannot solve this problem.
3113   The judicious use of cryptography, when appropriate, may suffice to
3114   protect against a broad range of security and privacy attacks. Such
3115   cryptography is beyond the scope of the HTTP/1.1 specification.
3119<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3121   They exist. They are hard to defend against. Research continues.
3122   Beware.
3127<section title="Acknowledgments" anchor="ack">
3129   HTTP has evolved considerably over the years. It has
3130   benefited from a large and active developer community--the many
3131   people who have participated on the www-talk mailing list--and it is
3132   that community which has been most responsible for the success of
3133   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3134   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3135   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3136   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3137   VanHeyningen deserve special recognition for their efforts in
3138   defining early aspects of the protocol.
3141   This document has benefited greatly from the comments of all those
3142   participating in the HTTP-WG. In addition to those already mentioned,
3143   the following individuals have contributed to this specification:
3146   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3147   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3148   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3149   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3150   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3151   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3152   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3153   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3154   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3155   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3156   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3157   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3158   Josh Cohen.
3161   Thanks to the "cave men" of Palo Alto. You know who you are.
3164   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3165   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3166   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3167   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3168   Larry Masinter for their help. And thanks go particularly to Jeff
3169   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3172   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3173   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3174   discovery of many of the problems that this document attempts to
3175   rectify.
3178   This specification makes heavy use of the augmented BNF and generic
3179   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3180   reuses many of the definitions provided by Nathaniel Borenstein and
3181   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3182   specification will help reduce past confusion over the relationship
3183   between HTTP and Internet mail message formats.
3190<references title="Normative References">
3192<reference anchor="ISO-8859-1">
3193  <front>
3194    <title>
3195     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3196    </title>
3197    <author>
3198      <organization>International Organization for Standardization</organization>
3199    </author>
3200    <date year="1998"/>
3201  </front>
3202  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3205<reference anchor="Part2">
3206  <front>
3207    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3208    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3209      <organization abbrev="Day Software">Day Software</organization>
3210      <address><email></email></address>
3211    </author>
3212    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3213      <organization>One Laptop per Child</organization>
3214      <address><email></email></address>
3215    </author>
3216    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3217      <organization abbrev="HP">Hewlett-Packard Company</organization>
3218      <address><email></email></address>
3219    </author>
3220    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3221      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3222      <address><email></email></address>
3223    </author>
3224    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3225      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3226      <address><email></email></address>
3227    </author>
3228    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3229      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3230      <address><email></email></address>
3231    </author>
3232    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3233      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3234      <address><email></email></address>
3235    </author>
3236    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3237      <organization abbrev="W3C">World Wide Web Consortium</organization>
3238      <address><email></email></address>
3239    </author>
3240    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3241      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3242      <address><email></email></address>
3243    </author>
3244    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3245  </front>
3246  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3247  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3250<reference anchor="Part3">
3251  <front>
3252    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3253    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3254      <organization abbrev="Day Software">Day Software</organization>
3255      <address><email></email></address>
3256    </author>
3257    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3258      <organization>One Laptop per Child</organization>
3259      <address><email></email></address>
3260    </author>
3261    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3262      <organization abbrev="HP">Hewlett-Packard Company</organization>
3263      <address><email></email></address>
3264    </author>
3265    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3266      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3267      <address><email></email></address>
3268    </author>
3269    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3270      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3271      <address><email></email></address>
3272    </author>
3273    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3274      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3275      <address><email></email></address>
3276    </author>
3277    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3278      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3279      <address><email></email></address>
3280    </author>
3281    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3282      <organization abbrev="W3C">World Wide Web Consortium</organization>
3283      <address><email></email></address>
3284    </author>
3285    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3286      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3287      <address><email></email></address>
3288    </author>
3289    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3290  </front>
3291  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3292  <x:source href="p3-payload.xml" basename="p3-payload"/>
3295<reference anchor="Part5">
3296  <front>
3297    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3298    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3299      <organization abbrev="Day Software">Day Software</organization>
3300      <address><email></email></address>
3301    </author>
3302    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3303      <organization>One Laptop per Child</organization>
3304      <address><email></email></address>
3305    </author>
3306    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3307      <organization abbrev="HP">Hewlett-Packard Company</organization>
3308      <address><email></email></address>
3309    </author>
3310    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3311      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3312      <address><email></email></address>
3313    </author>
3314    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3315      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3316      <address><email></email></address>
3317    </author>
3318    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3319      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3320      <address><email></email></address>
3321    </author>
3322    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3323      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3324      <address><email></email></address>
3325    </author>
3326    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3327      <organization abbrev="W3C">World Wide Web Consortium</organization>
3328      <address><email></email></address>
3329    </author>
3330    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3331      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3332      <address><email></email></address>
3333    </author>
3334    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3335  </front>
3336  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3337  <x:source href="p5-range.xml" basename="p5-range"/>
3340<reference anchor="Part6">
3341  <front>
3342    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3343    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3344      <organization abbrev="Day Software">Day Software</organization>
3345      <address><email></email></address>
3346    </author>
3347    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3348      <organization>One Laptop per Child</organization>
3349      <address><email></email></address>
3350    </author>
3351    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3352      <organization abbrev="HP">Hewlett-Packard Company</organization>
3353      <address><email></email></address>
3354    </author>
3355    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3356      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3357      <address><email></email></address>
3358    </author>
3359    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3360      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3361      <address><email></email></address>
3362    </author>
3363    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3364      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3365      <address><email></email></address>
3366    </author>
3367    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3368      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3369      <address><email></email></address>
3370    </author>
3371    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3372      <organization abbrev="W3C">World Wide Web Consortium</organization>
3373      <address><email></email></address>
3374    </author>
3375    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3376      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3377      <address><email></email></address>
3378    </author>
3379    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3380  </front>
3381  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3382  <x:source href="p6-cache.xml" basename="p6-cache"/>
3385<reference anchor="RFC5234">
3386  <front>
3387    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3388    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3389      <organization>Brandenburg InternetWorking</organization>
3390      <address>
3391      <postal>
3392      <street>675 Spruce Dr.</street>
3393      <city>Sunnyvale</city>
3394      <region>CA</region>
3395      <code>94086</code>
3396      <country>US</country></postal>
3397      <phone>+1.408.246.8253</phone>
3398      <email></email></address> 
3399    </author>
3400    <author initials="P." surname="Overell" fullname="Paul Overell">
3401      <organization>THUS plc.</organization>
3402      <address>
3403      <postal>
3404      <street>1/2 Berkeley Square</street>
3405      <street>99 Berkely Street</street>
3406      <city>Glasgow</city>
3407      <code>G3 7HR</code>
3408      <country>UK</country></postal>
3409      <email></email></address>
3410    </author>
3411    <date month="January" year="2008"/>
3412  </front>
3413  <seriesInfo name="STD" value="68"/>
3414  <seriesInfo name="RFC" value="5234"/>
3417<reference anchor="RFC2119">
3418  <front>
3419    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3420    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3421      <organization>Harvard University</organization>
3422      <address><email></email></address>
3423    </author>
3424    <date month="March" year="1997"/>
3425  </front>
3426  <seriesInfo name="BCP" value="14"/>
3427  <seriesInfo name="RFC" value="2119"/>
3430<reference anchor="RFC3986">
3431 <front>
3432  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3433  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3434    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3435    <address>
3436       <email></email>
3437       <uri></uri>
3438    </address>
3439  </author>
3440  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3441    <organization abbrev="Day Software">Day Software</organization>
3442    <address>
3443      <email></email>
3444      <uri></uri>
3445    </address>
3446  </author>
3447  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3448    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3449    <address>
3450      <email></email>
3451      <uri></uri>
3452    </address>
3453  </author>
3454  <date month='January' year='2005'></date>
3455 </front>
3456 <seriesInfo name="RFC" value="3986"/>
3457 <seriesInfo name="STD" value="66"/>
3460<reference anchor="USASCII">
3461  <front>
3462    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3463    <author>
3464      <organization>American National Standards Institute</organization>
3465    </author>
3466    <date year="1986"/>
3467  </front>
3468  <seriesInfo name="ANSI" value="X3.4"/>
3473<references title="Informative References">
3475<reference anchor="Nie1997" target="">
3476  <front>
3477    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3478    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3479      <organization/>
3480    </author>
3481    <author initials="J." surname="Gettys" fullname="J. Gettys">
3482      <organization/>
3483    </author>
3484    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3485      <organization/>
3486    </author>
3487    <author initials="H." surname="Lie" fullname="H. Lie">
3488      <organization/>
3489    </author>
3490    <author initials="C." surname="Lilley" fullname="C. Lilley">
3491      <organization/>
3492    </author>
3493    <date year="1997" month="September"/>
3494  </front>
3495  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3498<reference anchor="Pad1995" target="">
3499  <front>
3500    <title>Improving HTTP Latency</title>
3501    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3502      <organization/>
3503    </author>
3504    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3505      <organization/>
3506    </author>
3507    <date year="1995" month="December"/>
3508  </front>
3509  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3512<reference anchor="RFC1123">
3513  <front>
3514    <title>Requirements for Internet Hosts - Application and Support</title>
3515    <author initials="R." surname="Braden" fullname="Robert Braden">
3516      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3517      <address><email>Braden@ISI.EDU</email></address>
3518    </author>
3519    <date month="October" year="1989"/>
3520  </front>
3521  <seriesInfo name="STD" value="3"/>
3522  <seriesInfo name="RFC" value="1123"/>
3525<reference anchor="RFC1305">
3526  <front>
3527    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3528    <author initials="D." surname="Mills" fullname="David L. Mills">
3529      <organization>University of Delaware, Electrical Engineering Department</organization>
3530      <address><email></email></address>
3531    </author>
3532    <date month="March" year="1992"/>
3533  </front>
3534  <seriesInfo name="RFC" value="1305"/>
3537<reference anchor="RFC1900">
3538  <front>
3539    <title>Renumbering Needs Work</title>
3540    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3541      <organization>CERN, Computing and Networks Division</organization>
3542      <address><email></email></address>
3543    </author>
3544    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3545      <organization>cisco Systems</organization>
3546      <address><email></email></address>
3547    </author>
3548    <date month="February" year="1996"/>
3549  </front>
3550  <seriesInfo name="RFC" value="1900"/>
3553<reference anchor="RFC1945">
3554  <front>
3555    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3556    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3557      <organization>MIT, Laboratory for Computer Science</organization>
3558      <address><email></email></address>
3559    </author>
3560    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3561      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3562      <address><email></email></address>
3563    </author>
3564    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3565      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3566      <address><email></email></address>
3567    </author>
3568    <date month="May" year="1996"/>
3569  </front>
3570  <seriesInfo name="RFC" value="1945"/>
3573<reference anchor="RFC2045">
3574  <front>
3575    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3576    <author initials="N." surname="Freed" fullname="Ned Freed">
3577      <organization>Innosoft International, Inc.</organization>
3578      <address><email></email></address>
3579    </author>
3580    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3581      <organization>First Virtual Holdings</organization>
3582      <address><email></email></address>
3583    </author>
3584    <date month="November" year="1996"/>
3585  </front>
3586  <seriesInfo name="RFC" value="2045"/>
3589<reference anchor="RFC2047">
3590  <front>
3591    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3592    <author initials="K." surname="Moore" fullname="Keith Moore">
3593      <organization>University of Tennessee</organization>
3594      <address><email></email></address>
3595    </author>
3596    <date month="November" year="1996"/>
3597  </front>
3598  <seriesInfo name="RFC" value="2047"/>
3601<reference anchor="RFC2068">
3602  <front>
3603    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3604    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3605      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3606      <address><email></email></address>
3607    </author>
3608    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3609      <organization>MIT Laboratory for Computer Science</organization>
3610      <address><email></email></address>
3611    </author>
3612    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3613      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3614      <address><email></email></address>
3615    </author>
3616    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3617      <organization>MIT Laboratory for Computer Science</organization>
3618      <address><email></email></address>
3619    </author>
3620    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3621      <organization>MIT Laboratory for Computer Science</organization>
3622      <address><email></email></address>
3623    </author>
3624    <date month="January" year="1997"/>
3625  </front>
3626  <seriesInfo name="RFC" value="2068"/>
3629<reference anchor='RFC2109'>
3630  <front>
3631    <title>HTTP State Management Mechanism</title>
3632    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3633      <organization>Bell Laboratories, Lucent Technologies</organization>
3634      <address><email></email></address>
3635    </author>
3636    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3637      <organization>Netscape Communications Corp.</organization>
3638      <address><email></email></address>
3639    </author>
3640    <date year='1997' month='February' />
3641  </front>
3642  <seriesInfo name='RFC' value='2109' />
3645<reference anchor="RFC2145">
3646  <front>
3647    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3648    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3649      <organization>Western Research Laboratory</organization>
3650      <address><email></email></address>
3651    </author>
3652    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3653      <organization>Department of Information and Computer Science</organization>
3654      <address><email></email></address>
3655    </author>
3656    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3657      <organization>MIT Laboratory for Computer Science</organization>
3658      <address><email></email></address>
3659    </author>
3660    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3661      <organization>W3 Consortium</organization>
3662      <address><email></email></address>
3663    </author>
3664    <date month="May" year="1997"/>
3665  </front>
3666  <seriesInfo name="RFC" value="2145"/>
3669<reference anchor="RFC2616">
3670  <front>
3671    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3672    <author initials="R." surname="Fielding" fullname="R. Fielding">
3673      <organization>University of California, Irvine</organization>
3674      <address><email></email></address>
3675    </author>
3676    <author initials="J." surname="Gettys" fullname="J. Gettys">
3677      <organization>W3C</organization>
3678      <address><email></email></address>
3679    </author>
3680    <author initials="J." surname="Mogul" fullname="J. Mogul">
3681      <organization>Compaq Computer Corporation</organization>
3682      <address><email></email></address>
3683    </author>
3684    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3685      <organization>MIT Laboratory for Computer Science</organization>
3686      <address><email></email></address>
3687    </author>
3688    <author initials="L." surname="Masinter" fullname="L. Masinter">
3689      <organization>Xerox Corporation</organization>
3690      <address><email></email></address>
3691    </author>
3692    <author initials="P." surname="Leach" fullname="P. Leach">
3693      <organization>Microsoft Corporation</organization>
3694      <address><email></email></address>
3695    </author>
3696    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3697      <organization>W3C</organization>
3698      <address><email></email></address>
3699    </author>
3700    <date month="June" year="1999"/>
3701  </front>
3702  <seriesInfo name="RFC" value="2616"/>
3705<reference anchor='RFC2818'>
3706  <front>
3707    <title>HTTP Over TLS</title>
3708    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3709      <organization>RTFM, Inc.</organization>
3710      <address><email></email></address>
3711    </author>
3712    <date year='2000' month='May' />
3713  </front>
3714  <seriesInfo name='RFC' value='2818' />
3717<reference anchor='RFC2965'>
3718  <front>
3719    <title>HTTP State Management Mechanism</title>
3720    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3721      <organization>Bell Laboratories, Lucent Technologies</organization>
3722      <address><email></email></address>
3723    </author>
3724    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3725      <organization>, Inc.</organization>
3726      <address><email></email></address>
3727    </author>
3728    <date year='2000' month='October' />
3729  </front>
3730  <seriesInfo name='RFC' value='2965' />
3733<reference anchor='RFC3864'>
3734  <front>
3735    <title>Registration Procedures for Message Header Fields</title>
3736    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3737      <organization>Nine by Nine</organization>
3738      <address><email></email></address>
3739    </author>
3740    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3741      <organization>BEA Systems</organization>
3742      <address><email></email></address>
3743    </author>
3744    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3745      <organization>HP Labs</organization>
3746      <address><email></email></address>
3747    </author>
3748    <date year='2004' month='September' />
3749  </front>
3750  <seriesInfo name='BCP' value='90' />
3751  <seriesInfo name='RFC' value='3864' />
3754<reference anchor="RFC4288">
3755  <front>
3756    <title>Media Type Specifications and Registration Procedures</title>
3757    <author initials="N." surname="Freed" fullname="N. Freed">
3758      <organization>Sun Microsystems</organization>
3759      <address>
3760        <email></email>
3761      </address>
3762    </author>
3763    <author initials="J." surname="Klensin" fullname="J. Klensin">
3764      <organization/>
3765      <address>
3766        <email></email>
3767      </address>
3768    </author>
3769    <date year="2005" month="December"/>
3770  </front>
3771  <seriesInfo name="BCP" value="13"/>
3772  <seriesInfo name="RFC" value="4288"/>
3775<reference anchor='RFC4395'>
3776  <front>
3777    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3778    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3779      <organization>AT&amp;T Laboratories</organization>
3780      <address>
3781        <email></email>
3782      </address>
3783    </author>
3784    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3785      <organization>Qualcomm, Inc.</organization>
3786      <address>
3787        <email></email>
3788      </address>
3789    </author>
3790    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3791      <organization>Adobe Systems</organization>
3792      <address>
3793        <email></email>
3794      </address>
3795    </author>
3796    <date year='2006' month='February' />
3797  </front>
3798  <seriesInfo name='BCP' value='115' />
3799  <seriesInfo name='RFC' value='4395' />
3802<reference anchor="RFC5322">
3803  <front>
3804    <title>Internet Message Format</title>
3805    <author initials="P." surname="Resnick" fullname="P. Resnick">
3806      <organization>Qualcomm Incorporated</organization>
3807    </author>
3808    <date year="2008" month="October"/>
3809  </front>
3810  <seriesInfo name="RFC" value="5322"/>
3813<reference anchor="Kri2001" target="">
3814  <front>
3815    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3816    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3817      <organization/>
3818    </author>
3819    <date year="2001" month="November"/>
3820  </front>
3821  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3824<reference anchor="Spe" target="">
3825  <front>
3826  <title>Analysis of HTTP Performance Problems</title>
3827  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3828    <organization/>
3829  </author>
3830  <date/>
3831  </front>
3834<reference anchor="Tou1998" target="">
3835  <front>
3836  <title>Analysis of HTTP Performance</title>
3837  <author initials="J." surname="Touch" fullname="Joe Touch">
3838    <organization>USC/Information Sciences Institute</organization>
3839    <address><email></email></address>
3840  </author>
3841  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3842    <organization>USC/Information Sciences Institute</organization>
3843    <address><email></email></address>
3844  </author>
3845  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3846    <organization>USC/Information Sciences Institute</organization>
3847    <address><email></email></address>
3848  </author>
3849  <date year="1998" month="Aug"/>
3850  </front>
3851  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3852  <annotation>(original report dated Aug. 1996)</annotation>
3858<section title="Tolerant Applications" anchor="tolerant.applications">
3860   Although this document specifies the requirements for the generation
3861   of HTTP/1.1 messages, not all applications will be correct in their
3862   implementation. We therefore recommend that operational applications
3863   be tolerant of deviations whenever those deviations can be
3864   interpreted unambiguously.
3867   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3868   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3869   accept any amount of WSP characters between fields, even though
3870   only a single SP is required.
3873   The line terminator for message-header fields is the sequence CRLF.
3874   However, we recommend that applications, when parsing such headers,
3875   recognize a single LF as a line terminator and ignore the leading CR.
3878   The character set of an entity-body &SHOULD; be labeled as the lowest
3879   common denominator of the character codes used within that body, with
3880   the exception that not labeling the entity is preferred over labeling
3881   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3884   Additional rules for requirements on parsing and encoding of dates
3885   and other potential problems with date encodings include:
3888  <list style="symbols">
3889     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3890        which appears to be more than 50 years in the future is in fact
3891        in the past (this helps solve the "year 2000" problem).</t>
3893     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3894        Expires date as earlier than the proper value, but &MUST-NOT;
3895        internally represent a parsed Expires date as later than the
3896        proper value.</t>
3898     <t>All expiration-related calculations &MUST; be done in GMT. The
3899        local time zone &MUST-NOT; influence the calculation or comparison
3900        of an age or expiration time.</t>
3902     <t>If an HTTP header incorrectly carries a date value with a time
3903        zone other than GMT, it &MUST; be converted into GMT using the
3904        most conservative possible conversion.</t>
3905  </list>
3909<section title="Compatibility with Previous Versions" anchor="compatibility">
3911   HTTP has been in use by the World-Wide Web global information initiative
3912   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3913   was a simple protocol for hypertext data transfer across the Internet
3914   with only a single method and no metadata.
3915   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3916   methods and MIME-like messaging that could include metadata about the data
3917   transferred and modifiers on the request/response semantics. However,
3918   HTTP/1.0 did not sufficiently take into consideration the effects of
3919   hierarchical proxies, caching, the need for persistent connections, or
3920   name-based virtual hosts. The proliferation of incompletely-implemented
3921   applications calling themselves "HTTP/1.0" further necessitated a
3922   protocol version change in order for two communicating applications
3923   to determine each other's true capabilities.
3926   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3927   requirements that enable reliable implementations, adding only
3928   those new features that will either be safely ignored by an HTTP/1.0
3929   recipient or only sent when communicating with a party advertising
3930   compliance with HTTP/1.1.
3933   It is beyond the scope of a protocol specification to mandate
3934   compliance with previous versions. HTTP/1.1 was deliberately
3935   designed, however, to make supporting previous versions easy. It is
3936   worth noting that, at the time of composing this specification
3937   (1996), we would expect commercial HTTP/1.1 servers to:
3938  <list style="symbols">
3939     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3940        1.1 requests;</t>
3942     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3943        1.1;</t>
3945     <t>respond appropriately with a message in the same major version
3946        used by the client.</t>
3947  </list>
3950   And we would expect HTTP/1.1 clients to:
3951  <list style="symbols">
3952     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3953        responses;</t>
3955     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3956        1.1.</t>
3957  </list>
3960   For most implementations of HTTP/1.0, each connection is established
3961   by the client prior to the request and closed by the server after
3962   sending the response. Some implementations implement the Keep-Alive
3963   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3966<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3968   This section summarizes major differences between versions HTTP/1.0
3969   and HTTP/1.1.
3972<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3974   The requirements that clients and servers support the Host request-header,
3975   report an error if the Host request-header (<xref target=""/>) is
3976   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3977   are among the most important changes defined by this
3978   specification.
3981   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3982   addresses and servers; there was no other established mechanism for
3983   distinguishing the intended server of a request than the IP address
3984   to which that request was directed. The changes outlined above will
3985   allow the Internet, once older HTTP clients are no longer common, to
3986   support multiple Web sites from a single IP address, greatly
3987   simplifying large operational Web servers, where allocation of many
3988   IP addresses to a single host has created serious problems. The
3989   Internet will also be able to recover the IP addresses that have been
3990   allocated for the sole purpose of allowing special-purpose domain
3991   names to be used in root-level HTTP URLs. Given the rate of growth of
3992   the Web, and the number of servers already deployed, it is extremely
3993   important that all implementations of HTTP (including updates to
3994   existing HTTP/1.0 applications) correctly implement these
3995   requirements:
3996  <list style="symbols">
3997     <t>Both clients and servers &MUST; support the Host request-header.</t>
3999     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4001     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4002        request does not include a Host request-header.</t>
4004     <t>Servers &MUST; accept absolute URIs.</t>
4005  </list>
4010<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4012   Some clients and servers might wish to be compatible with some
4013   previous implementations of persistent connections in HTTP/1.0
4014   clients and servers. Persistent connections in HTTP/1.0 are
4015   explicitly negotiated as they are not the default behavior. HTTP/1.0
4016   experimental implementations of persistent connections are faulty,
4017   and the new facilities in HTTP/1.1 are designed to rectify these
4018   problems. The problem was that some existing 1.0 clients may be
4019   sending Keep-Alive to a proxy server that doesn't understand
4020   Connection, which would then erroneously forward it to the next
4021   inbound server, which would establish the Keep-Alive connection and
4022   result in a hung HTTP/1.0 proxy waiting for the close on the
4023   response. The result is that HTTP/1.0 clients must be prevented from
4024   using Keep-Alive when talking to proxies.
4027   However, talking to proxies is the most important use of persistent
4028   connections, so that prohibition is clearly unacceptable. Therefore,
4029   we need some other mechanism for indicating a persistent connection
4030   is desired, which is safe to use even when talking to an old proxy
4031   that ignores Connection. Persistent connections are the default for
4032   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4033   declaring non-persistence. See <xref target="header.connection"/>.
4036   The original HTTP/1.0 form of persistent connections (the Connection:
4037   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4041<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4043   This specification has been carefully audited to correct and
4044   disambiguate key word usage; RFC 2068 had many problems in respect to
4045   the conventions laid out in <xref target="RFC2119"/>.
4048   Transfer-coding and message lengths all interact in ways that
4049   required fixing exactly when chunked encoding is used (to allow for
4050   transfer encoding that may not be self delimiting); it was important
4051   to straighten out exactly how message lengths are computed. (Sections
4052   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4053   <xref target="header.content-length" format="counter"/>,
4054   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4057   The use and interpretation of HTTP version numbers has been clarified
4058   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4059   version they support to deal with problems discovered in HTTP/1.0
4060   implementations (<xref target="http.version"/>)
4063   Quality Values of zero should indicate that "I don't want something"
4064   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4067   Transfer-coding had significant problems, particularly with
4068   interactions with chunked encoding. The solution is that transfer-codings
4069   become as full fledged as content-codings. This involves
4070   adding an IANA registry for transfer-codings (separate from content
4071   codings), a new header field (TE) and enabling trailer headers in the
4072   future. Transfer encoding is a major performance benefit, so it was
4073   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4074   interoperability problem that could have occurred due to interactions
4075   between authentication trailers, chunked encoding and HTTP/1.0
4076   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4077   and <xref target="header.te" format="counter"/>)
4081<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4083  Empty list elements in list productions have been deprecated.
4084  (<xref target="notation.abnf"/>)
4087  Rules about implicit linear whitespace between certain grammar productions
4088  have been removed; now it's only allowed when specifically pointed out
4089  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4090  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4091  Non-ASCII content in header fields and reason phrase has been obsoleted and
4092  made opaque (the TEXT rule was removed)
4093  (<xref target="basic.rules"/>)
4096  Clarify that HTTP-Version is case sensitive.
4097  (<xref target="http.version"/>)
4100  Remove reference to non-existant identity transfer-coding value tokens.
4101  (Sections <xref format="counter" target="transfer.codings"/> and
4102  <xref format="counter" target="message.length"/>)
4105  Clarification that the chunk length does not include
4106  the count of the octets in the chunk header and trailer.
4107  (<xref target="chunked.transfer.encoding"/>)
4110  Require that invalid whitespace around field-names be rejected.
4111  (<xref target="message.headers"/>)
4114  Update use of abs_path production from RFC1808 to the path-absolute + query
4115  components of RFC3986.
4116  (<xref target="request-target"/>)
4119  Clarify exactly when close connection options must be sent.
4120  (<xref target="header.connection"/>)
4125<section title="Terminology" anchor="terminology">
4127   This specification uses a number of terms to refer to the roles
4128   played by participants in, and objects of, the HTTP communication.
4131  <iref item="cache"/>
4132  <x:dfn>cache</x:dfn>
4133  <list>
4134    <t>
4135      A program's local store of response messages and the subsystem
4136      that controls its message storage, retrieval, and deletion. A
4137      cache stores cacheable responses in order to reduce the response
4138      time and network bandwidth consumption on future, equivalent
4139      requests. Any client or server may include a cache, though a cache
4140      cannot be used by a server that is acting as a tunnel.
4141    </t>
4142  </list>
4145  <iref item="cacheable"/>
4146  <x:dfn>cacheable</x:dfn>
4147  <list>
4148    <t>
4149      A response is cacheable if a cache is allowed to store a copy of
4150      the response message for use in answering subsequent requests. The
4151      rules for determining the cacheability of HTTP responses are
4152      defined in &caching;. Even if a resource is cacheable, there may
4153      be additional constraints on whether a cache can use the cached
4154      copy for a particular request.
4155    </t>
4156  </list>
4159  <iref item="client"/>
4160  <x:dfn>client</x:dfn>
4161  <list>
4162    <t>
4163      A program that establishes connections for the purpose of sending
4164      requests.
4165    </t>
4166  </list>
4169  <iref item="connection"/>
4170  <x:dfn>connection</x:dfn>
4171  <list>
4172    <t>
4173      A transport layer virtual circuit established between two programs
4174      for the purpose of communication.
4175    </t>
4176  </list>
4179  <iref item="content negotiation"/>
4180  <x:dfn>content negotiation</x:dfn>
4181  <list>
4182    <t>
4183      The mechanism for selecting the appropriate representation when
4184      servicing a request, as described in &content.negotiation;. The
4185      representation of entities in any response can be negotiated
4186      (including error responses).
4187    </t>
4188  </list>
4191  <iref item="entity"/>
4192  <x:dfn>entity</x:dfn>
4193  <list>
4194    <t>
4195      The information transferred as the payload of a request or
4196      response. An entity consists of metainformation in the form of
4197      entity-header fields and content in the form of an entity-body, as
4198      described in &entity;.
4199    </t>
4200  </list>
4203  <iref item="gateway"/>
4204  <x:dfn>gateway</x:dfn>
4205  <list>
4206    <t>
4207      A server which acts as an intermediary for some other server.
4208      Unlike a proxy, a gateway receives requests as if it were the
4209      origin server for the requested resource; the requesting client
4210      may not be aware that it is communicating with a gateway.
4211    </t>
4212  </list>
4215  <iref item="inbound"/>
4216  <iref item="outbound"/>
4217  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4218  <list>
4219    <t>
4220      Inbound and outbound refer to the request and response paths for
4221      messages: "inbound" means "traveling toward the origin server",
4222      and "outbound" means "traveling toward the user agent"
4223    </t>
4224  </list>
4227  <iref item="message"/>
4228  <x:dfn>message</x:dfn>
4229  <list>
4230    <t>
4231      The basic unit of HTTP communication, consisting of a structured
4232      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4233      transmitted via the connection.
4234    </t>
4235  </list>
4238  <iref item="origin server"/>
4239  <x:dfn>origin server</x:dfn>
4240  <list>
4241    <t>
4242      The server on which a given resource resides or is to be created.
4243    </t>
4244  </list>
4247  <iref item="proxy"/>
4248  <x:dfn>proxy</x:dfn>
4249  <list>
4250    <t>
4251      An intermediary program which acts as both a server and a client
4252      for the purpose of making requests on behalf of other clients.
4253      Requests are serviced internally or by passing them on, with
4254      possible translation, to other servers. A proxy &MUST; implement
4255      both the client and server requirements of this specification. A
4256      "transparent proxy" is a proxy that does not modify the request or
4257      response beyond what is required for proxy authentication and
4258      identification. A "non-transparent proxy" is a proxy that modifies
4259      the request or response in order to provide some added service to
4260      the user agent, such as group annotation services, media type
4261      transformation, protocol reduction, or anonymity filtering. Except
4262      where either transparent or non-transparent behavior is explicitly
4263      stated, the HTTP proxy requirements apply to both types of
4264      proxies.
4265    </t>
4266  </list>
4269  <iref item="request"/>
4270  <x:dfn>request</x:dfn>
4271  <list>
4272    <t>
4273      An HTTP request message, as defined in <xref target="request"/>.
4274    </t>
4275  </list>
4278  <iref item="resource"/>
4279  <x:dfn>resource</x:dfn>
4280  <list>
4281    <t>
4282      A network data object or service that can be identified by a URI,
4283      as defined in <xref target="uri"/>. Resources may be available in multiple
4284      representations (e.g. multiple languages, data formats, size, and
4285      resolutions) or vary in other ways.
4286    </t>
4287  </list>
4290  <iref item="response"/>
4291  <x:dfn>response</x:dfn>
4292  <list>
4293    <t>
4294      An HTTP response message, as defined in <xref target="response"/>.
4295    </t>
4296  </list>
4299  <iref item="representation"/>
4300  <x:dfn>representation</x:dfn>
4301  <list>
4302    <t>
4303      An entity included with a response that is subject to content
4304      negotiation, as described in &content.negotiation;. There may exist multiple
4305      representations associated with a particular response status.
4306    </t>
4307  </list>
4310  <iref item="server"/>
4311  <x:dfn>server</x:dfn>
4312  <list>
4313    <t>
4314      An application program that accepts connections in order to
4315      service requests by sending back responses. Any given program may
4316      be capable of being both a client and a server; our use of these
4317      terms refers only to the role being performed by the program for a
4318      particular connection, rather than to the program's capabilities
4319      in general. Likewise, any server may act as an origin server,
4320      proxy, gateway, or tunnel, switching behavior based on the nature
4321      of each request.
4322    </t>
4323  </list>
4326  <iref item="tunnel"/>
4327  <x:dfn>tunnel</x:dfn>
4328  <list>
4329    <t>
4330      An intermediary program which is acting as a blind relay between
4331      two connections. Once active, a tunnel is not considered a party
4332      to the HTTP communication, though the tunnel may have been
4333      initiated by an HTTP request. The tunnel ceases to exist when both
4334      ends of the relayed connections are closed.
4335    </t>
4336  </list>
4339  <iref item="upstream"/>
4340  <iref item="downstream"/>
4341  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4342  <list>
4343    <t>
4344      Upstream and downstream describe the flow of a message: all
4345      messages flow from upstream to downstream.
4346    </t>
4347  </list>
4350  <iref item="user agent"/>
4351  <x:dfn>user agent</x:dfn>
4352  <list>
4353    <t>
4354      The client which initiates a request. These are often browsers,
4355      editors, spiders (web-traversing robots), or other end user tools.
4356    </t>
4357  </list>
4360  <iref item="variant"/>
4361  <x:dfn>variant</x:dfn>
4362  <list>
4363    <t>
4364      A resource may have one, or more than one, representation(s)
4365      associated with it at any given instant. Each of these
4366      representations is termed a `variant'.  Use of the term `variant'
4367      does not necessarily imply that the resource is subject to content
4368      negotiation.
4369    </t>
4370  </list>
4374<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4376<artwork type="abnf" name="p1-messaging.parsed-abnf">
4377<x:ref>BWS</x:ref> = OWS
4379<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4380<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4381<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4382<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4383 connection-token ] )
4384<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4385<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4387<x:ref>Date</x:ref> = "Date:" OWS Date-v
4388<x:ref>Date-v</x:ref> = HTTP-date
4390<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4392<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4393<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4394<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4395<x:ref>HTTP-message</x:ref> = Request / Response
4396<x:ref>Host</x:ref> = "Host:" OWS Host-v
4397<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4399<x:ref>Method</x:ref> = token
4401<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4403<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4405<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4406<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4407<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4408 entity-header ) CRLF ) CRLF [ message-body ]
4409<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4410<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4411 entity-header ) CRLF ) CRLF [ message-body ]
4413<x:ref>Status-Code</x:ref> = 3DIGIT
4414<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4416<x:ref>TE</x:ref> = "TE:" OWS TE-v
4417<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4418<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4419<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4420<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4421<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4422 transfer-coding ] )
4424<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4425<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4426<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4427<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4429<x:ref>Via</x:ref> = "Via:" OWS Via-v
4430<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4431 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4432 ] )
4434<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4436<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4437<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4438<x:ref>attribute</x:ref> = token
4439<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4441<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4442<x:ref>chunk-data</x:ref> = 1*OCTET
4443<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4444<x:ref>chunk-ext-name</x:ref> = token
4445<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4446<x:ref>chunk-size</x:ref> = 1*HEXDIG
4447<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4448<x:ref>connection-token</x:ref> = token
4449<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4450 / %x2A-5B ; '*'-'['
4451 / %x5D-7E ; ']'-'~'
4452 / obs-text
4454<x:ref>date1</x:ref> = day SP month SP year
4455<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4456<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4457<x:ref>day</x:ref> = 2DIGIT
4458<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4459 / %x54.75.65 ; Tue
4460 / %x57.65.64 ; Wed
4461 / %x54.68.75 ; Thu
4462 / %x46.72.69 ; Fri
4463 / %x53.61.74 ; Sat
4464 / %x53.75.6E ; Sun
4465<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4466 / %x54. ; Tuesday
4467 / %x57.65.64.6E. ; Wednesday
4468 / %x54. ; Thursday
4469 / %x46. ; Friday
4470 / %x53. ; Saturday
4471 / %x53.75.6E.64.61.79 ; Sunday
4473<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4474<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4476<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4477<x:ref>field-name</x:ref> = token
4478<x:ref>field-value</x:ref> = *( field-content / OWS )
4479<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4481<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4482 / Transfer-Encoding / Upgrade / Via / Warning
4483<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4484 message-body ]
4486<x:ref>hour</x:ref> = 2DIGIT
4487<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4489<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4491<x:ref>message-body</x:ref> = entity-body /
4492 &lt;entity-body encoded as per Transfer-Encoding&gt;
4493<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4494<x:ref>minute</x:ref> = 2DIGIT
4495<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4496 / %x46.65.62 ; Feb
4497 / %x4D.61.72 ; Mar
4498 / %x41.70.72 ; Apr
4499 / %x4D.61.79 ; May
4500 / %x4A.75.6E ; Jun
4501 / %x4A.75.6C ; Jul
4502 / %x41.75.67 ; Aug
4503 / %x53.65.70 ; Sep
4504 / %x4F.63.74 ; Oct
4505 / %x4E.6F.76 ; Nov
4506 / %x44.65.63 ; Dec
4508<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4509<x:ref>obs-fold</x:ref> = CRLF
4510<x:ref>obs-text</x:ref> = %x80-FF
4512<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4513<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4514<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4515<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4516<x:ref>product</x:ref> = token [ "/" product-version ]
4517<x:ref>product-version</x:ref> = token
4518<x:ref>protocol-name</x:ref> = token
4519<x:ref>protocol-version</x:ref> = token
4520<x:ref>pseudonym</x:ref> = token
4522<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4523 / %x5D-7E ; ']'-'~'
4524 / obs-text
4525<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4526<x:ref>quoted-pair</x:ref> = "\" quoted-text
4527<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4528<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4529<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4531<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4532<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4533<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4534<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4535<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4536 / authority
4537<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4538<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4539<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4541<x:ref>second</x:ref> = 2DIGIT
4542<x:ref>start-line</x:ref> = Request-Line / Status-Line
4544<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4545<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4546 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4547<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4548<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4549<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4550<x:ref>token</x:ref> = 1*tchar
4551<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4552<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4553<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4554<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4556<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4558<x:ref>value</x:ref> = token / quoted-string
4560<x:ref>year</x:ref> = 4DIGIT
4563<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4564; Chunked-Body defined but not used
4565; Content-Length defined but not used
4566; HTTP-message defined but not used
4567; Host defined but not used
4568; TE defined but not used
4569; URI defined but not used
4570; URI-reference defined but not used
4571; fragment defined but not used
4572; generic-message defined but not used
4573; http-URI defined but not used
4574; partial-URI defined but not used
4577<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4579<section title="Since RFC2616">
4581  Extracted relevant partitions from <xref target="RFC2616"/>.
4585<section title="Since draft-ietf-httpbis-p1-messaging-00">
4587  Closed issues:
4588  <list style="symbols">
4589    <t>
4590      <eref target=""/>:
4591      "HTTP Version should be case sensitive"
4592      (<eref target=""/>)
4593    </t>
4594    <t>
4595      <eref target=""/>:
4596      "'unsafe' characters"
4597      (<eref target=""/>)
4598    </t>
4599    <t>
4600      <eref target=""/>:
4601      "Chunk Size Definition"
4602      (<eref target=""/>)
4603    </t>
4604    <t>
4605      <eref target=""/>:
4606      "Message Length"
4607      (<eref target=""/>)
4608    </t>
4609    <t>
4610      <eref target=""/>:
4611      "Media Type Registrations"
4612      (<eref target=""/>)
4613    </t>
4614    <t>
4615      <eref target=""/>:
4616      "URI includes query"
4617      (<eref target=""/>)
4618    </t>
4619    <t>
4620      <eref target=""/>:
4621      "No close on 1xx responses"
4622      (<eref target=""/>)
4623    </t>
4624    <t>
4625      <eref target=""/>:
4626      "Remove 'identity' token references"
4627      (<eref target=""/>)
4628    </t>
4629    <t>
4630      <eref target=""/>:
4631      "Import query BNF"
4632    </t>
4633    <t>
4634      <eref target=""/>:
4635      "qdtext BNF"
4636    </t>
4637    <t>
4638      <eref target=""/>:
4639      "Normative and Informative references"
4640    </t>
4641    <t>
4642      <eref target=""/>:
4643      "RFC2606 Compliance"
4644    </t>
4645    <t>
4646      <eref target=""/>:
4647      "RFC977 reference"
4648    </t>
4649    <t>
4650      <eref target=""/>:
4651      "RFC1700 references"
4652    </t>
4653    <t>
4654      <eref target=""/>:
4655      "inconsistency in date format explanation"
4656    </t>
4657    <t>
4658      <eref target=""/>:
4659      "Date reference typo"
4660    </t>
4661    <t>
4662      <eref target=""/>:
4663      "Informative references"
4664    </t>
4665    <t>
4666      <eref target=""/>:
4667      "ISO-8859-1 Reference"
4668    </t>
4669    <t>
4670      <eref target=""/>:
4671      "Normative up-to-date references"
4672    </t>
4673  </list>
4676  Other changes:
4677  <list style="symbols">
4678    <t>
4679      Update media type registrations to use RFC4288 template.
4680    </t>
4681    <t>
4682      Use names of RFC4234 core rules DQUOTE and WSP,
4683      fix broken ABNF for chunk-data
4684      (work in progress on <eref target=""/>)
4685    </t>
4686  </list>
4690<section title="Since draft-ietf-httpbis-p1-messaging-01">
4692  Closed issues:
4693  <list style="symbols">
4694    <t>
4695      <eref target=""/>:
4696      "Bodies on GET (and other) requests"
4697    </t>
4698    <t>
4699      <eref target=""/>:
4700      "Updating to RFC4288"
4701    </t>
4702    <t>
4703      <eref target=""/>:
4704      "Status Code and Reason Phrase"
4705    </t>
4706    <t>
4707      <eref target=""/>:
4708      "rel_path not used"
4709    </t>
4710  </list>
4713  Ongoing work on ABNF conversion (<eref target=""/>):
4714  <list style="symbols">
4715    <t>
4716      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4717      "trailer-part").
4718    </t>
4719    <t>
4720      Avoid underscore character in rule names ("http_URL" ->
4721      "http-URL", "abs_path" -> "path-absolute").
4722    </t>
4723    <t>
4724      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4725      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4726      have to be updated when switching over to RFC3986.
4727    </t>
4728    <t>
4729      Synchronize core rules with RFC5234.
4730    </t>
4731    <t>
4732      Get rid of prose rules that span multiple lines.
4733    </t>
4734    <t>
4735      Get rid of unused rules LOALPHA and UPALPHA.
4736    </t>
4737    <t>
4738      Move "Product Tokens" section (back) into Part 1, as "token" is used
4739      in the definition of the Upgrade header.
4740    </t>
4741    <t>
4742      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4743    </t>
4744    <t>
4745      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4746    </t>
4747  </list>
4751<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4753  Closed issues:
4754  <list style="symbols">
4755    <t>
4756      <eref target=""/>:
4757      "HTTP-date vs. rfc1123-date"
4758    </t>
4759    <t>
4760      <eref target=""/>:
4761      "WS in quoted-pair"
4762    </t>
4763  </list>
4766  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4767  <list style="symbols">
4768    <t>
4769      Reference RFC 3984, and update header registrations for headers defined
4770      in this document.
4771    </t>
4772  </list>
4775  Ongoing work on ABNF conversion (<eref target=""/>):
4776  <list style="symbols">
4777    <t>
4778      Replace string literals when the string really is case-sensitive (HTTP-Version).
4779    </t>
4780  </list>
4784<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4786  Closed issues:
4787  <list style="symbols">
4788    <t>
4789      <eref target=""/>:
4790      "Connection closing"
4791    </t>
4792    <t>
4793      <eref target=""/>:
4794      "Move registrations and registry information to IANA Considerations"
4795    </t>
4796    <t>
4797      <eref target=""/>:
4798      "need new URL for PAD1995 reference"
4799    </t>
4800    <t>
4801      <eref target=""/>:
4802      "IANA Considerations: update HTTP URI scheme registration"
4803    </t>
4804    <t>
4805      <eref target=""/>:
4806      "Cite HTTPS URI scheme definition"
4807    </t>
4808    <t>
4809      <eref target=""/>:
4810      "List-type headers vs Set-Cookie"
4811    </t>
4812  </list>
4815  Ongoing work on ABNF conversion (<eref target=""/>):
4816  <list style="symbols">
4817    <t>
4818      Replace string literals when the string really is case-sensitive (HTTP-Date).
4819    </t>
4820    <t>
4821      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4822    </t>
4823  </list>
4827<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4829  Closed issues:
4830  <list style="symbols">
4831    <t>
4832      <eref target=""/>:
4833      "Out-of-date reference for URIs"
4834    </t>
4835    <t>
4836      <eref target=""/>:
4837      "RFC 2822 is updated by RFC 5322"
4838    </t>
4839  </list>
4842  Ongoing work on ABNF conversion (<eref target=""/>):
4843  <list style="symbols">
4844    <t>
4845      Use "/" instead of "|" for alternatives.
4846    </t>
4847    <t>
4848      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4849    </t>
4850    <t>
4851      Only reference RFC 5234's core rules.
4852    </t>
4853    <t>
4854      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4855      whitespace ("OWS") and required whitespace ("RWS").
4856    </t>
4857    <t>
4858      Rewrite ABNFs to spell out whitespace rules, factor out
4859      header value format definitions.
4860    </t>
4861  </list>
4865<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4867  Closed issues:
4868  <list style="symbols">
4869    <t>
4870      <eref target=""/>:
4871      "Header LWS"
4872    </t>
4873    <t>
4874      <eref target=""/>:
4875      "Sort 1.3 Terminology"
4876    </t>
4877    <t>
4878      <eref target=""/>:
4879      "RFC2047 encoded words"
4880    </t>
4881    <t>
4882      <eref target=""/>:
4883      "Character Encodings in TEXT"
4884    </t>
4885    <t>
4886      <eref target=""/>:
4887      "Line Folding"
4888    </t>
4889    <t>
4890      <eref target=""/>:
4891      "OPTIONS * and proxies"
4892    </t>
4893    <t>
4894      <eref target=""/>:
4895      "Reason-Phrase BNF"
4896    </t>
4897    <t>
4898      <eref target=""/>:
4899      "Use of TEXT"
4900    </t>
4901    <t>
4902      <eref target=""/>:
4903      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4904    </t>
4905    <t>
4906      <eref target=""/>:
4907      "RFC822 reference left in discussion of date formats"
4908    </t>
4909  </list>
4912  Final work on ABNF conversion (<eref target=""/>):
4913  <list style="symbols">
4914    <t>
4915      Rewrite definition of list rules, deprecate empty list elements.
4916    </t>
4917    <t>
4918      Add appendix containing collected and expanded ABNF.
4919    </t>
4920  </list>
4923  Other changes:
4924  <list style="symbols">
4925    <t>
4926      Rewrite introduction; add mostly new Architecture Section.
4927    </t>
4928    <t>
4929      Move definition of quality values from Part 3 into Part 1;
4930      make TE request header grammar independent of accept-params (defined in Part 3).
4931    </t>
4932  </list>
4936<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4938  Closed issues:
4939  <list style="symbols">
4940    <t>
4941      <eref target=""/>:
4942      "base for numeric protocol elements"
4943    </t>
4944    <t>
4945      <eref target=""/>:
4946      "comment ABNF"
4947    </t>
4948  </list>
4951  Partly resolved issues:
4952  <list style="symbols">
4953    <t>
4954      <eref target=""/>:
4955      "editorial improvements around HTTP-date"
4956    </t>
4957  </list>
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