source: draft-ietf-httpbis/latest/p1-messaging.xml @ 581

Last change on this file since 581 was 581, checked in by julian.reschke@…, 13 years ago

editorial: use BAP's mode that adds comments for productions that contain printable characters

  • Property svn:eol-style set to native
File size: 211.7 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>     = s-Mon / s-Tue / s-Wed
889               / s-Thu / s-Fri / s-Sat / s-Sun
891  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
892  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
893  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
894  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
895  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
896  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
897  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
899  <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>
900               ; e.g., 02 Jun 1982
902  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
903  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
904               / s-May / s-Jun / s-Jul / s-Aug
905               / s-Sep / s-Oct / s-Nov / s-Dec
906  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
908  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
909  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
910  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
911  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
912  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
913  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
914  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
915  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
916  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
917  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
918  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
919  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
921  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
923  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
924                 ; 00:00:00 - 23:59:59
926  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
927  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
928  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
931  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
932  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
933  same as those defined in the RFC 5322 constructs
934  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
936<t anchor="">
937  <x:anchor-alias value="obs-date"/>
938  <x:anchor-alias value="rfc850-date"/>
939  <x:anchor-alias value="asctime-date"/>
940  <x:anchor-alias value="date1"/>
941  <x:anchor-alias value="date2"/>
942  <x:anchor-alias value="date3"/>
943  <x:anchor-alias value="rfc1123-date"/>
944  <x:anchor-alias value="day-name-l"/>
945  Obsolete formats:
947<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
948  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
950<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
951  <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>
952  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
953                 ; day-month-year (e.g., 02-Jun-82)
955  <x:ref>day-name-l</x:ref>   = l-Mon / l-Tue / l-Wed
956               / l-Thu / l-Fri / l-Sat / l-Sun
958  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
959  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
960  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
961  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
962  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
963  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
964  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
967  <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>
968  <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> ))
969                 ; month day (e.g., Jun  2)
972  <t>
973    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
974    accepting date values that may have been sent by non-HTTP
975    applications, as is sometimes the case when retrieving or posting
976    messages via proxies/gateways to SMTP or NNTP.
977  </t>
980  <t>
981    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
982    to their usage within the protocol stream. Clients and servers are
983    not required to use these formats for user presentation, request
984    logging, etc.
985  </t>
989<section title="Transfer Codings" anchor="transfer.codings">
990  <x:anchor-alias value="parameter"/>
991  <x:anchor-alias value="transfer-coding"/>
992  <x:anchor-alias value="transfer-extension"/>
994   Transfer-coding values are used to indicate an encoding
995   transformation that has been, can be, or may need to be applied to an
996   entity-body in order to ensure "safe transport" through the network.
997   This differs from a content coding in that the transfer-coding is a
998   property of the message, not of the original entity.
1000<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1001  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
1002  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
1004<t anchor="rule.parameter">
1005  <x:anchor-alias value="attribute"/>
1006  <x:anchor-alias value="parameter"/>
1007  <x:anchor-alias value="value"/>
1008   Parameters are in  the form of attribute/value pairs.
1010<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1011  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1012  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1013  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1016   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1017   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1018   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1021   Whenever a transfer-coding is applied to a message-body, the set of
1022   transfer-codings &MUST; include "chunked", unless the message indicates it
1023   is terminated by closing the connection. When the "chunked" transfer-coding
1024   is used, it &MUST; be the last transfer-coding applied to the
1025   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1026   than once to a message-body. These rules allow the recipient to
1027   determine the transfer-length of the message (<xref target="message.length"/>).
1030   Transfer-codings are analogous to the Content-Transfer-Encoding
1031   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1032   binary data over a 7-bit transport service. However, safe transport
1033   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1034   the only unsafe characteristic of message-bodies is the difficulty in
1035   determining the exact body length (<xref target="message.length"/>), or the desire to
1036   encrypt data over a shared transport.
1039   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1040   transfer-coding value tokens. Initially, the registry contains the
1041   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1042   "gzip", "compress", and "deflate" (&content-codings;).
1045   New transfer-coding value tokens &SHOULD; be registered in the same way
1046   as new content-coding value tokens (&content-codings;).
1049   A server which receives an entity-body with a transfer-coding it does
1050   not understand &SHOULD; return 501 (Not Implemented), and close the
1051   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1052   client.
1055<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1056  <x:anchor-alias value="chunk"/>
1057  <x:anchor-alias value="Chunked-Body"/>
1058  <x:anchor-alias value="chunk-data"/>
1059  <x:anchor-alias value="chunk-ext"/>
1060  <x:anchor-alias value="chunk-ext-name"/>
1061  <x:anchor-alias value="chunk-ext-val"/>
1062  <x:anchor-alias value="chunk-size"/>
1063  <x:anchor-alias value="last-chunk"/>
1064  <x:anchor-alias value="trailer-part"/>
1066   The chunked encoding modifies the body of a message in order to
1067   transfer it as a series of chunks, each with its own size indicator,
1068   followed by an &OPTIONAL; trailer containing entity-header fields. This
1069   allows dynamically produced content to be transferred along with the
1070   information necessary for the recipient to verify that it has
1071   received the full message.
1073<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"/>
1074  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1075                   <x:ref>last-chunk</x:ref>
1076                   <x:ref>trailer-part</x:ref>
1077                   <x:ref>CRLF</x:ref>
1079  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1080                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1081  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1082  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1084  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1085                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1086  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1087  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1088  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1089  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1092   The chunk-size field is a string of hex digits indicating the size of
1093   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1094   zero, followed by the trailer, which is terminated by an empty line.
1097   The trailer allows the sender to include additional HTTP header
1098   fields at the end of the message. The Trailer header field can be
1099   used to indicate which header fields are included in a trailer (see
1100   <xref target="header.trailer"/>).
1103   A server using chunked transfer-coding in a response &MUST-NOT; use the
1104   trailer for any header fields unless at least one of the following is
1105   true:
1106  <list style="numbers">
1107    <t>the request included a TE header field that indicates "trailers" is
1108     acceptable in the transfer-coding of the  response, as described in
1109     <xref target="header.te"/>; or,</t>
1111    <t>the server is the origin server for the response, the trailer
1112     fields consist entirely of optional metadata, and the recipient
1113     could use the message (in a manner acceptable to the origin server)
1114     without receiving this metadata.  In other words, the origin server
1115     is willing to accept the possibility that the trailer fields might
1116     be silently discarded along the path to the client.</t>
1117  </list>
1120   This requirement prevents an interoperability failure when the
1121   message is being received by an HTTP/1.1 (or later) proxy and
1122   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1123   compliance with the protocol would have necessitated a possibly
1124   infinite buffer on the proxy.
1127   A process for decoding the "chunked" transfer-coding
1128   can be represented in pseudo-code as:
1130<figure><artwork type="code">
1131  length := 0
1132  read chunk-size, chunk-ext (if any) and CRLF
1133  while (chunk-size &gt; 0) {
1134     read chunk-data and CRLF
1135     append chunk-data to entity-body
1136     length := length + chunk-size
1137     read chunk-size and CRLF
1138  }
1139  read entity-header
1140  while (entity-header not empty) {
1141     append entity-header to existing header fields
1142     read entity-header
1143  }
1144  Content-Length := length
1145  Remove "chunked" from Transfer-Encoding
1148   All HTTP/1.1 applications &MUST; be able to receive and decode the
1149   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1150   they do not understand.
1155<section title="Product Tokens" anchor="product.tokens">
1156  <x:anchor-alias value="product"/>
1157  <x:anchor-alias value="product-version"/>
1159   Product tokens are used to allow communicating applications to
1160   identify themselves by software name and version. Most fields using
1161   product tokens also allow sub-products which form a significant part
1162   of the application to be listed, separated by whitespace. By
1163   convention, the products are listed in order of their significance
1164   for identifying the application.
1166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1167  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1168  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1171   Examples:
1173<figure><artwork type="example">
1174  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1175  Server: Apache/0.8.4
1178   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1179   used for advertising or other non-essential information. Although any
1180   token character &MAY; appear in a product-version, this token &SHOULD;
1181   only be used for a version identifier (i.e., successive versions of
1182   the same product &SHOULD; only differ in the product-version portion of
1183   the product value).
1187<section title="Quality Values" anchor="quality.values">
1188  <x:anchor-alias value="qvalue"/>
1190   Both transfer codings (TE request header, <xref target="header.te"/>)
1191   and content negotiation (&content.negotiation;) use short "floating point"
1192   numbers to indicate the relative importance ("weight") of various
1193   negotiable parameters.  A weight is normalized to a real number in
1194   the range 0 through 1, where 0 is the minimum and 1 the maximum
1195   value. If a parameter has a quality value of 0, then content with
1196   this parameter is `not acceptable' for the client. HTTP/1.1
1197   applications &MUST-NOT; generate more than three digits after the
1198   decimal point. User configuration of these values &SHOULD; also be
1199   limited in this fashion.
1201<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1202  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1203                 / ( "1" [ "." 0*3("0") ] )
1206  <t>
1207     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1208     relative degradation in desired quality.
1209  </t>
1215<section title="HTTP Message" anchor="http.message">
1217<section title="Message Types" anchor="message.types">
1218  <x:anchor-alias value="generic-message"/>
1219  <x:anchor-alias value="HTTP-message"/>
1220  <x:anchor-alias value="start-line"/>
1222   HTTP messages consist of requests from client to server and responses
1223   from server to client.
1225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1226  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1229   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1230   message format of <xref target="RFC5322"/> for transferring entities (the payload
1231   of the message). Both types of message consist of a start-line, zero
1232   or more header fields (also known as "headers"), an empty line (i.e.,
1233   a line with nothing preceding the CRLF) indicating the end of the
1234   header fields, and possibly a message-body.
1236<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1237  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1238                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1239                    <x:ref>CRLF</x:ref>
1240                    [ <x:ref>message-body</x:ref> ]
1241  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1244   In the interest of robustness, servers &SHOULD; ignore any empty
1245   line(s) received where a Request-Line is expected. In other words, if
1246   the server is reading the protocol stream at the beginning of a
1247   message and receives a CRLF first, it should ignore the CRLF.
1250   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1251   after a POST request. To restate what is explicitly forbidden by the
1252   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1253   extra CRLF.
1256   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1257   header field. The presence of whitespace might be an attempt to trick a
1258   noncompliant implementation of HTTP into ignoring that field or processing
1259   the next line as a new request, either of which may result in security
1260   issues when implementations within the request chain interpret the
1261   same message differently. HTTP/1.1 servers &MUST; reject such a message
1262   with a 400 (Bad Request) response.
1266<section title="Message Headers" anchor="message.headers">
1267  <x:anchor-alias value="field-content"/>
1268  <x:anchor-alias value="field-name"/>
1269  <x:anchor-alias value="field-value"/>
1270  <x:anchor-alias value="message-header"/>
1272   HTTP header fields follow the same general format as Internet messages in
1273   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1274   of a name followed by a colon (":"), optional whitespace, and the field
1275   value. Field names are case-insensitive.
1277<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"/>
1278  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1279  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1280  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1281  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1284   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1285   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1286   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1287   header field-values use only a subset of the US-ASCII charset
1288   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1289   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1290   (obs-text) octets in field-content as opaque data.
1293   No whitespace is allowed between the header field-name and colon. For
1294   security reasons, any request message received containing such whitespace
1295   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1296   whitespace in a response message &MUST; be removed.
1299   The field value &MAY; be preceded by optional whitespace; a single SP is
1300   preferred. The field-value does not include any leading or trailing white
1301   space: OWS occurring before the first non-whitespace character of the
1302   field-value or after the last non-whitespace character of the field-value
1303   is ignored and &MAY; be removed without changing the meaning of the header
1304   field.
1307   Historically, HTTP header field values could be extended over multiple
1308   lines by preceding each extra line with at least one space or horizontal
1309   tab character (line folding). This specification deprecates such line
1310   folding except within the message/http media type
1311   (<xref target=""/>).
1312   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1313   (i.e., that contain any field-content that matches the obs-fold rule) unless
1314   the message is intended for packaging within the message/http media type.
1315   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1316   obs-fold whitespace with a single SP prior to interpreting the field value
1317   or forwarding the message downstream.
1319<t anchor="rule.comment">
1320  <x:anchor-alias value="comment"/>
1321  <x:anchor-alias value="ctext"/>
1322   Comments can be included in some HTTP header fields by surrounding
1323   the comment text with parentheses. Comments are only allowed in
1324   fields containing "comment" as part of their field value definition.
1325   In all other fields, parentheses are considered part of the field
1326   value.
1328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1329  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1330  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1331                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1334   The order in which header fields with differing field names are
1335   received is not significant. However, it is "good practice" to send
1336   general-header fields first, followed by request-header or response-header
1337   fields, and ending with the entity-header fields.
1340   Multiple message-header fields with the same field-name &MAY; be
1341   present in a message if and only if the entire field-value for that
1342   header field is defined as a comma-separated list [i.e., #(values)].
1343   It &MUST; be possible to combine the multiple header fields into one
1344   "field-name: field-value" pair, without changing the semantics of the
1345   message, by appending each subsequent field-value to the first, each
1346   separated by a comma. The order in which header fields with the same
1347   field-name are received is therefore significant to the
1348   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1349   change the order of these field values when a message is forwarded.
1352  <t>
1353   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1354   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1355   can occur multiple times, but does not use the list syntax, and thus cannot
1356   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1357   for details.) Also note that the Set-Cookie2 header specified in
1358   <xref target="RFC2965"/> does not share this problem.
1359  </t>
1364<section title="Message Body" anchor="message.body">
1365  <x:anchor-alias value="message-body"/>
1367   The message-body (if any) of an HTTP message is used to carry the
1368   entity-body associated with the request or response. The message-body
1369   differs from the entity-body only when a transfer-coding has been
1370   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1373  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1374               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1377   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1378   applied by an application to ensure safe and proper transfer of the
1379   message. Transfer-Encoding is a property of the message, not of the
1380   entity, and thus &MAY; be added or removed by any application along the
1381   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1382   when certain transfer-codings may be used.)
1385   The rules for when a message-body is allowed in a message differ for
1386   requests and responses.
1389   The presence of a message-body in a request is signaled by the
1390   inclusion of a Content-Length or Transfer-Encoding header field in
1391   the request's message-headers. A message-body &MUST-NOT; be included in
1392   a request if the specification of the request method (&method;)
1393   explicitly disallows an entity-body in requests.
1394   When a request message contains both a message-body of non-zero
1395   length and a method that does not define any semantics for that
1396   request message-body, then an origin server &SHOULD; either ignore
1397   the message-body or respond with an appropriate error message
1398   (e.g., 413).  A proxy or gateway, when presented the same request,
1399   &SHOULD; either forward the request inbound with the message-body or
1400   ignore the message-body when determining a response.
1403   For response messages, whether or not a message-body is included with
1404   a message is dependent on both the request method and the response
1405   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1406   &MUST-NOT; include a message-body, even though the presence of entity-header
1407   fields might lead one to believe they do. All 1xx
1408   (informational), 204 (No Content), and 304 (Not Modified) responses
1409   &MUST-NOT; include a message-body. All other responses do include a
1410   message-body, although it &MAY; be of zero length.
1414<section title="Message Length" anchor="message.length">
1416   The transfer-length of a message is the length of the message-body as
1417   it appears in the message; that is, after any transfer-codings have
1418   been applied. When a message-body is included with a message, the
1419   transfer-length of that body is determined by one of the following
1420   (in order of precedence):
1423  <list style="numbers">
1424    <x:lt><t>
1425     Any response message which "&MUST-NOT;" include a message-body (such
1426     as the 1xx, 204, and 304 responses and any response to a HEAD
1427     request) is always terminated by the first empty line after the
1428     header fields, regardless of the entity-header fields present in
1429     the message.
1430    </t></x:lt>
1431    <x:lt><t>
1432     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1433     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1434     is used, the transfer-length is defined by the use of this transfer-coding.
1435     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1436     is not present, the transfer-length is defined by the sender closing the connection.
1437    </t></x:lt>
1438    <x:lt><t>
1439     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1440     value in OCTETs represents both the entity-length and the
1441     transfer-length. The Content-Length header field &MUST-NOT; be sent
1442     if these two lengths are different (i.e., if a Transfer-Encoding
1443     header field is present). If a message is received with both a
1444     Transfer-Encoding header field and a Content-Length header field,
1445     the latter &MUST; be ignored.
1446    </t></x:lt>
1447    <x:lt><t>
1448     If the message uses the media type "multipart/byteranges", and the
1449     transfer-length is not otherwise specified, then this self-delimiting
1450     media type defines the transfer-length. This media type
1451     &MUST-NOT; be used unless the sender knows that the recipient can parse
1452     it; the presence in a request of a Range header with multiple byte-range
1453     specifiers from a 1.1 client implies that the client can parse
1454     multipart/byteranges responses.
1455    <list style="empty"><t>
1456       A range header might be forwarded by a 1.0 proxy that does not
1457       understand multipart/byteranges; in this case the server &MUST;
1458       delimit the message using methods defined in items 1, 3 or 5 of
1459       this section.
1460    </t></list>
1461    </t></x:lt>
1462    <x:lt><t>
1463     By the server closing the connection. (Closing the connection
1464     cannot be used to indicate the end of a request body, since that
1465     would leave no possibility for the server to send back a response.)
1466    </t></x:lt>
1467  </list>
1470   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1471   containing a message-body &MUST; include a valid Content-Length header
1472   field unless the server is known to be HTTP/1.1 compliant. If a
1473   request contains a message-body and a Content-Length is not given,
1474   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1475   determine the length of the message, or with 411 (Length Required) if
1476   it wishes to insist on receiving a valid Content-Length.
1479   All HTTP/1.1 applications that receive entities &MUST; accept the
1480   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1481   to be used for messages when the message length cannot be determined
1482   in advance.
1485   Messages &MUST-NOT; include both a Content-Length header field and a
1486   transfer-coding. If the message does include a
1487   transfer-coding, the Content-Length &MUST; be ignored.
1490   When a Content-Length is given in a message where a message-body is
1491   allowed, its field value &MUST; exactly match the number of OCTETs in
1492   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1493   invalid length is received and detected.
1497<section title="General Header Fields" anchor="general.header.fields">
1498  <x:anchor-alias value="general-header"/>
1500   There are a few header fields which have general applicability for
1501   both request and response messages, but which do not apply to the
1502   entity being transferred. These header fields apply only to the
1503   message being transmitted.
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1506  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1507                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1508                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1509                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1510                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1511                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1512                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1513                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1514                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1517   General-header field names can be extended reliably only in
1518   combination with a change in the protocol version. However, new or
1519   experimental header fields may be given the semantics of general
1520   header fields if all parties in the communication recognize them to
1521   be general-header fields. Unrecognized header fields are treated as
1522   entity-header fields.
1527<section title="Request" anchor="request">
1528  <x:anchor-alias value="Request"/>
1530   A request message from a client to a server includes, within the
1531   first line of that message, the method to be applied to the resource,
1532   the identifier of the resource, and the protocol version in use.
1534<!--                 Host                      ; should be moved here eventually -->
1535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1536  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1537                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1538                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1539                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1540                  <x:ref>CRLF</x:ref>
1541                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1544<section title="Request-Line" anchor="request-line">
1545  <x:anchor-alias value="Request-Line"/>
1547   The Request-Line begins with a method token, followed by the
1548   request-target and the protocol version, and ending with CRLF. The
1549   elements are separated by SP characters. No CR or LF is allowed
1550   except in the final CRLF sequence.
1552<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1553  <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>
1556<section title="Method" anchor="method">
1557  <x:anchor-alias value="Method"/>
1559   The Method  token indicates the method to be performed on the
1560   resource identified by the request-target. The method is case-sensitive.
1562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1563  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1567<section title="request-target" anchor="request-target">
1568  <x:anchor-alias value="request-target"/>
1570   The request-target
1571   identifies the resource upon which to apply the request.
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1574  <x:ref>request-target</x:ref> = "*"
1575                 / <x:ref>absolute-URI</x:ref>
1576                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1577                 / <x:ref>authority</x:ref>
1580   The four options for request-target are dependent on the nature of the
1581   request. The asterisk "*" means that the request does not apply to a
1582   particular resource, but to the server itself, and is only allowed
1583   when the method used does not necessarily apply to a resource. One
1584   example would be
1586<figure><artwork type="example">
1587  OPTIONS * HTTP/1.1
1590   The absolute-URI form is &REQUIRED; when the request is being made to a
1591   proxy. The proxy is requested to forward the request or service it
1592   from a valid cache, and return the response. Note that the proxy &MAY;
1593   forward the request on to another proxy or directly to the server
1594   specified by the absolute-URI. In order to avoid request loops, a
1595   proxy &MUST; be able to recognize all of its server names, including
1596   any aliases, local variations, and the numeric IP address. An example
1597   Request-Line would be:
1599<figure><artwork type="example">
1600  GET HTTP/1.1
1603   To allow for transition to absolute-URIs in all requests in future
1604   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1605   form in requests, even though HTTP/1.1 clients will only generate
1606   them in requests to proxies.
1609   The authority form is only used by the CONNECT method (&CONNECT;).
1612   The most common form of request-target is that used to identify a
1613   resource on an origin server or gateway. In this case the absolute
1614   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1615   the request-target, and the network location of the URI (authority) &MUST;
1616   be transmitted in a Host header field. For example, a client wishing
1617   to retrieve the resource above directly from the origin server would
1618   create a TCP connection to port 80 of the host "" and send
1619   the lines:
1621<figure><artwork type="example">
1622  GET /pub/WWW/TheProject.html HTTP/1.1
1623  Host:
1626   followed by the remainder of the Request. Note that the absolute path
1627   cannot be empty; if none is present in the original URI, it &MUST; be
1628   given as "/" (the server root).
1631   If a proxy receives a request without any path in the request-target and
1632   the method specified is capable of supporting the asterisk form of
1633   request-target, then the last proxy on the request chain &MUST; forward the
1634   request with "*" as the final request-target.
1637   For example, the request
1638</preamble><artwork type="example">
1639  OPTIONS HTTP/1.1
1642  would be forwarded by the proxy as
1643</preamble><artwork type="example">
1644  OPTIONS * HTTP/1.1
1645  Host:
1648   after connecting to port 8001 of host "".
1652   The request-target is transmitted in the format specified in
1653   <xref target="http.uri"/>. If the request-target is percent-encoded
1654   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1655   &MUST; decode the request-target in order to
1656   properly interpret the request. Servers &SHOULD; respond to invalid
1657   request-targets with an appropriate status code.
1660   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1661   received request-target when forwarding it to the next inbound server,
1662   except as noted above to replace a null path-absolute with "/".
1665  <t>
1666    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1667    meaning of the request when the origin server is improperly using
1668    a non-reserved URI character for a reserved purpose.  Implementors
1669    should be aware that some pre-HTTP/1.1 proxies have been known to
1670    rewrite the request-target.
1671  </t>
1674   HTTP does not place a pre-defined limit on the length of a request-target.
1675   A server &MUST; be prepared to receive URIs of unbounded length and
1676   respond with the 414 (URI Too Long) status if the received
1677   request-target would be longer than the server wishes to handle
1678   (see &status-414;).
1681   Various ad-hoc limitations on request-target length are found in practice.
1682   It is &RECOMMENDED; that all HTTP senders and recipients support
1683   request-target lengths of 8000 or more OCTETs.
1688<section title="The Resource Identified by a Request" anchor="">
1690   The exact resource identified by an Internet request is determined by
1691   examining both the request-target and the Host header field.
1694   An origin server that does not allow resources to differ by the
1695   requested host &MAY; ignore the Host header field value when
1696   determining the resource identified by an HTTP/1.1 request. (But see
1697   <xref target=""/>
1698   for other requirements on Host support in HTTP/1.1.)
1701   An origin server that does differentiate resources based on the host
1702   requested (sometimes referred to as virtual hosts or vanity host
1703   names) &MUST; use the following rules for determining the requested
1704   resource on an HTTP/1.1 request:
1705  <list style="numbers">
1706    <t>If request-target is an absolute-URI, the host is part of the
1707     request-target. Any Host header field value in the request &MUST; be
1708     ignored.</t>
1709    <t>If the request-target is not an absolute-URI, and the request includes
1710     a Host header field, the host is determined by the Host header
1711     field value.</t>
1712    <t>If the host as determined by rule 1 or 2 is not a valid host on
1713     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1714  </list>
1717   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1718   attempt to use heuristics (e.g., examination of the URI path for
1719   something unique to a particular host) in order to determine what
1720   exact resource is being requested.
1727<section title="Response" anchor="response">
1728  <x:anchor-alias value="Response"/>
1730   After receiving and interpreting a request message, a server responds
1731   with an HTTP response message.
1733<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1734  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1735                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1736                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1737                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1738                  <x:ref>CRLF</x:ref>
1739                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1742<section title="Status-Line" anchor="status-line">
1743  <x:anchor-alias value="Status-Line"/>
1745   The first line of a Response message is the Status-Line, consisting
1746   of the protocol version followed by a numeric status code and its
1747   associated textual phrase, with each element separated by SP
1748   characters. No CR or LF is allowed except in the final CRLF sequence.
1750<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1751  <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>
1754<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1755  <x:anchor-alias value="Reason-Phrase"/>
1756  <x:anchor-alias value="Status-Code"/>
1758   The Status-Code element is a 3-digit integer result code of the
1759   attempt to understand and satisfy the request. These codes are fully
1760   defined in &status-codes;.  The Reason Phrase exists for the sole
1761   purpose of providing a textual description associated with the numeric
1762   status code, out of deference to earlier Internet application protocols
1763   that were more frequently used with interactive text clients.
1764   A client &SHOULD; ignore the content of the Reason Phrase.
1767   The first digit of the Status-Code defines the class of response. The
1768   last two digits do not have any categorization role. There are 5
1769   values for the first digit:
1770  <list style="symbols">
1771    <t>
1772      1xx: Informational - Request received, continuing process
1773    </t>
1774    <t>
1775      2xx: Success - The action was successfully received,
1776        understood, and accepted
1777    </t>
1778    <t>
1779      3xx: Redirection - Further action must be taken in order to
1780        complete the request
1781    </t>
1782    <t>
1783      4xx: Client Error - The request contains bad syntax or cannot
1784        be fulfilled
1785    </t>
1786    <t>
1787      5xx: Server Error - The server failed to fulfill an apparently
1788        valid request
1789    </t>
1790  </list>
1792<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"/>
1793  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1794  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1802<section title="Connections" anchor="connections">
1804<section title="Persistent Connections" anchor="persistent.connections">
1806<section title="Purpose" anchor="persistent.purpose">
1808   Prior to persistent connections, a separate TCP connection was
1809   established to fetch each URL, increasing the load on HTTP servers
1810   and causing congestion on the Internet. The use of inline images and
1811   other associated data often require a client to make multiple
1812   requests of the same server in a short amount of time. Analysis of
1813   these performance problems and results from a prototype
1814   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1815   measurements of actual HTTP/1.1 implementations show good
1816   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1817   T/TCP <xref target="Tou1998"/>.
1820   Persistent HTTP connections have a number of advantages:
1821  <list style="symbols">
1822      <t>
1823        By opening and closing fewer TCP connections, CPU time is saved
1824        in routers and hosts (clients, servers, proxies, gateways,
1825        tunnels, or caches), and memory used for TCP protocol control
1826        blocks can be saved in hosts.
1827      </t>
1828      <t>
1829        HTTP requests and responses can be pipelined on a connection.
1830        Pipelining allows a client to make multiple requests without
1831        waiting for each response, allowing a single TCP connection to
1832        be used much more efficiently, with much lower elapsed time.
1833      </t>
1834      <t>
1835        Network congestion is reduced by reducing the number of packets
1836        caused by TCP opens, and by allowing TCP sufficient time to
1837        determine the congestion state of the network.
1838      </t>
1839      <t>
1840        Latency on subsequent requests is reduced since there is no time
1841        spent in TCP's connection opening handshake.
1842      </t>
1843      <t>
1844        HTTP can evolve more gracefully, since errors can be reported
1845        without the penalty of closing the TCP connection. Clients using
1846        future versions of HTTP might optimistically try a new feature,
1847        but if communicating with an older server, retry with old
1848        semantics after an error is reported.
1849      </t>
1850    </list>
1853   HTTP implementations &SHOULD; implement persistent connections.
1857<section title="Overall Operation" anchor="persistent.overall">
1859   A significant difference between HTTP/1.1 and earlier versions of
1860   HTTP is that persistent connections are the default behavior of any
1861   HTTP connection. That is, unless otherwise indicated, the client
1862   &SHOULD; assume that the server will maintain a persistent connection,
1863   even after error responses from the server.
1866   Persistent connections provide a mechanism by which a client and a
1867   server can signal the close of a TCP connection. This signaling takes
1868   place using the Connection header field (<xref target="header.connection"/>). Once a close
1869   has been signaled, the client &MUST-NOT; send any more requests on that
1870   connection.
1873<section title="Negotiation" anchor="persistent.negotiation">
1875   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1876   maintain a persistent connection unless a Connection header including
1877   the connection-token "close" was sent in the request. If the server
1878   chooses to close the connection immediately after sending the
1879   response, it &SHOULD; send a Connection header including the
1880   connection-token close.
1883   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1884   decide to keep it open based on whether the response from a server
1885   contains a Connection header with the connection-token close. In case
1886   the client does not want to maintain a connection for more than that
1887   request, it &SHOULD; send a Connection header including the
1888   connection-token close.
1891   If either the client or the server sends the close token in the
1892   Connection header, that request becomes the last one for the
1893   connection.
1896   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1897   maintained for HTTP versions less than 1.1 unless it is explicitly
1898   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1899   compatibility with HTTP/1.0 clients.
1902   In order to remain persistent, all messages on the connection &MUST;
1903   have a self-defined message length (i.e., one not defined by closure
1904   of the connection), as described in <xref target="message.length"/>.
1908<section title="Pipelining" anchor="pipelining">
1910   A client that supports persistent connections &MAY; "pipeline" its
1911   requests (i.e., send multiple requests without waiting for each
1912   response). A server &MUST; send its responses to those requests in the
1913   same order that the requests were received.
1916   Clients which assume persistent connections and pipeline immediately
1917   after connection establishment &SHOULD; be prepared to retry their
1918   connection if the first pipelined attempt fails. If a client does
1919   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1920   persistent. Clients &MUST; also be prepared to resend their requests if
1921   the server closes the connection before sending all of the
1922   corresponding responses.
1925   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1926   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1927   premature termination of the transport connection could lead to
1928   indeterminate results. A client wishing to send a non-idempotent
1929   request &SHOULD; wait to send that request until it has received the
1930   response status for the previous request.
1935<section title="Proxy Servers" anchor="persistent.proxy">
1937   It is especially important that proxies correctly implement the
1938   properties of the Connection header field as specified in <xref target="header.connection"/>.
1941   The proxy server &MUST; signal persistent connections separately with
1942   its clients and the origin servers (or other proxy servers) that it
1943   connects to. Each persistent connection applies to only one transport
1944   link.
1947   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1948   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
1949   for information and discussion of the problems with the Keep-Alive header
1950   implemented by many HTTP/1.0 clients).
1954<section title="Practical Considerations" anchor="persistent.practical">
1956   Servers will usually have some time-out value beyond which they will
1957   no longer maintain an inactive connection. Proxy servers might make
1958   this a higher value since it is likely that the client will be making
1959   more connections through the same server. The use of persistent
1960   connections places no requirements on the length (or existence) of
1961   this time-out for either the client or the server.
1964   When a client or server wishes to time-out it &SHOULD; issue a graceful
1965   close on the transport connection. Clients and servers &SHOULD; both
1966   constantly watch for the other side of the transport close, and
1967   respond to it as appropriate. If a client or server does not detect
1968   the other side's close promptly it could cause unnecessary resource
1969   drain on the network.
1972   A client, server, or proxy &MAY; close the transport connection at any
1973   time. For example, a client might have started to send a new request
1974   at the same time that the server has decided to close the "idle"
1975   connection. From the server's point of view, the connection is being
1976   closed while it was idle, but from the client's point of view, a
1977   request is in progress.
1980   This means that clients, servers, and proxies &MUST; be able to recover
1981   from asynchronous close events. Client software &SHOULD; reopen the
1982   transport connection and retransmit the aborted sequence of requests
1983   without user interaction so long as the request sequence is
1984   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1985   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1986   human operator the choice of retrying the request(s). Confirmation by
1987   user-agent software with semantic understanding of the application
1988   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1989   be repeated if the second sequence of requests fails.
1992   Servers &SHOULD; always respond to at least one request per connection,
1993   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1994   middle of transmitting a response, unless a network or client failure
1995   is suspected.
1998   Clients that use persistent connections &SHOULD; limit the number of
1999   simultaneous connections that they maintain to a given server. A
2000   single-user client &SHOULD-NOT; maintain more than 2 connections with
2001   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2002   another server or proxy, where N is the number of simultaneously
2003   active users. These guidelines are intended to improve HTTP response
2004   times and avoid congestion.
2009<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2011<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2013   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2014   flow control mechanisms to resolve temporary overloads, rather than
2015   terminating connections with the expectation that clients will retry.
2016   The latter technique can exacerbate network congestion.
2020<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2022   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2023   the network connection for an error status while it is transmitting
2024   the request. If the client sees an error status, it &SHOULD;
2025   immediately cease transmitting the body. If the body is being sent
2026   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2027   empty trailer &MAY; be used to prematurely mark the end of the message.
2028   If the body was preceded by a Content-Length header, the client &MUST;
2029   close the connection.
2033<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2035   The purpose of the 100 (Continue) status (see &status-100;) is to
2036   allow a client that is sending a request message with a request body
2037   to determine if the origin server is willing to accept the request
2038   (based on the request headers) before the client sends the request
2039   body. In some cases, it might either be inappropriate or highly
2040   inefficient for the client to send the body if the server will reject
2041   the message without looking at the body.
2044   Requirements for HTTP/1.1 clients:
2045  <list style="symbols">
2046    <t>
2047        If a client will wait for a 100 (Continue) response before
2048        sending the request body, it &MUST; send an Expect request-header
2049        field (&header-expect;) with the "100-continue" expectation.
2050    </t>
2051    <t>
2052        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2053        with the "100-continue" expectation if it does not intend
2054        to send a request body.
2055    </t>
2056  </list>
2059   Because of the presence of older implementations, the protocol allows
2060   ambiguous situations in which a client may send "Expect: 100-continue"
2061   without receiving either a 417 (Expectation Failed) status
2062   or a 100 (Continue) status. Therefore, when a client sends this
2063   header field to an origin server (possibly via a proxy) from which it
2064   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2065   for an indefinite period before sending the request body.
2068   Requirements for HTTP/1.1 origin servers:
2069  <list style="symbols">
2070    <t> Upon receiving a request which includes an Expect request-header
2071        field with the "100-continue" expectation, an origin server &MUST;
2072        either respond with 100 (Continue) status and continue to read
2073        from the input stream, or respond with a final status code. The
2074        origin server &MUST-NOT; wait for the request body before sending
2075        the 100 (Continue) response. If it responds with a final status
2076        code, it &MAY; close the transport connection or it &MAY; continue
2077        to read and discard the rest of the request.  It &MUST-NOT;
2078        perform the requested method if it returns a final status code.
2079    </t>
2080    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2081        the request message does not include an Expect request-header
2082        field with the "100-continue" expectation, and &MUST-NOT; send a
2083        100 (Continue) response if such a request comes from an HTTP/1.0
2084        (or earlier) client. There is an exception to this rule: for
2085        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2086        status in response to an HTTP/1.1 PUT or POST request that does
2087        not include an Expect request-header field with the "100-continue"
2088        expectation. This exception, the purpose of which is
2089        to minimize any client processing delays associated with an
2090        undeclared wait for 100 (Continue) status, applies only to
2091        HTTP/1.1 requests, and not to requests with any other HTTP-version
2092        value.
2093    </t>
2094    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2095        already received some or all of the request body for the
2096        corresponding request.
2097    </t>
2098    <t> An origin server that sends a 100 (Continue) response &MUST;
2099    ultimately send a final status code, once the request body is
2100        received and processed, unless it terminates the transport
2101        connection prematurely.
2102    </t>
2103    <t> If an origin server receives a request that does not include an
2104        Expect request-header field with the "100-continue" expectation,
2105        the request includes a request body, and the server responds
2106        with a final status code before reading the entire request body
2107        from the transport connection, then the server &SHOULD-NOT;  close
2108        the transport connection until it has read the entire request,
2109        or until the client closes the connection. Otherwise, the client
2110        might not reliably receive the response message. However, this
2111        requirement is not be construed as preventing a server from
2112        defending itself against denial-of-service attacks, or from
2113        badly broken client implementations.
2114      </t>
2115    </list>
2118   Requirements for HTTP/1.1 proxies:
2119  <list style="symbols">
2120    <t> If a proxy receives a request that includes an Expect request-header
2121        field with the "100-continue" expectation, and the proxy
2122        either knows that the next-hop server complies with HTTP/1.1 or
2123        higher, or does not know the HTTP version of the next-hop
2124        server, it &MUST; forward the request, including the Expect header
2125        field.
2126    </t>
2127    <t> If the proxy knows that the version of the next-hop server is
2128        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2129        respond with a 417 (Expectation Failed) status.
2130    </t>
2131    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2132        numbers received from recently-referenced next-hop servers.
2133    </t>
2134    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2135        request message was received from an HTTP/1.0 (or earlier)
2136        client and did not include an Expect request-header field with
2137        the "100-continue" expectation. This requirement overrides the
2138        general rule for forwarding of 1xx responses (see &status-1xx;).
2139    </t>
2140  </list>
2144<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2146   If an HTTP/1.1 client sends a request which includes a request body,
2147   but which does not include an Expect request-header field with the
2148   "100-continue" expectation, and if the client is not directly
2149   connected to an HTTP/1.1 origin server, and if the client sees the
2150   connection close before receiving any status from the server, the
2151   client &SHOULD; retry the request.  If the client does retry this
2152   request, it &MAY; use the following "binary exponential backoff"
2153   algorithm to be assured of obtaining a reliable response:
2154  <list style="numbers">
2155    <t>
2156      Initiate a new connection to the server
2157    </t>
2158    <t>
2159      Transmit the request-headers
2160    </t>
2161    <t>
2162      Initialize a variable R to the estimated round-trip time to the
2163         server (e.g., based on the time it took to establish the
2164         connection), or to a constant value of 5 seconds if the round-trip
2165         time is not available.
2166    </t>
2167    <t>
2168       Compute T = R * (2**N), where N is the number of previous
2169         retries of this request.
2170    </t>
2171    <t>
2172       Wait either for an error response from the server, or for T
2173         seconds (whichever comes first)
2174    </t>
2175    <t>
2176       If no error response is received, after T seconds transmit the
2177         body of the request.
2178    </t>
2179    <t>
2180       If client sees that the connection is closed prematurely,
2181         repeat from step 1 until the request is accepted, an error
2182         response is received, or the user becomes impatient and
2183         terminates the retry process.
2184    </t>
2185  </list>
2188   If at any point an error status is received, the client
2189  <list style="symbols">
2190      <t>&SHOULD-NOT;  continue and</t>
2192      <t>&SHOULD; close the connection if it has not completed sending the
2193        request message.</t>
2194    </list>
2201<section title="Header Field Definitions" anchor="header.fields">
2203   This section defines the syntax and semantics of HTTP/1.1 header fields
2204   related to message framing and transport protocols.
2207   For entity-header fields, both sender and recipient refer to either the
2208   client or the server, depending on who sends and who receives the entity.
2211<section title="Connection" anchor="header.connection">
2212  <iref primary="true" item="Connection header" x:for-anchor=""/>
2213  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2214  <x:anchor-alias value="Connection"/>
2215  <x:anchor-alias value="connection-token"/>
2216  <x:anchor-alias value="Connection-v"/>
2218   The general-header field "Connection" allows the sender to specify
2219   options that are desired for that particular connection and &MUST-NOT;
2220   be communicated by proxies over further connections.
2223   The Connection header's value has the following grammar:
2225<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"/>
2226  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2227  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2228  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2231   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2232   message is forwarded and, for each connection-token in this field,
2233   remove any header field(s) from the message with the same name as the
2234   connection-token. Connection options are signaled by the presence of
2235   a connection-token in the Connection header field, not by any
2236   corresponding additional header field(s), since the additional header
2237   field may not be sent if there are no parameters associated with that
2238   connection option.
2241   Message headers listed in the Connection header &MUST-NOT; include
2242   end-to-end headers, such as Cache-Control.
2245   HTTP/1.1 defines the "close" connection option for the sender to
2246   signal that the connection will be closed after completion of the
2247   response. For example,
2249<figure><artwork type="example">
2250  Connection: close
2253   in either the request or the response header fields indicates that
2254   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2255   after the current request/response is complete.
2258   An HTTP/1.1 client that does not support persistent connections &MUST;
2259   include the "close" connection option in every request message.
2262   An HTTP/1.1 server that does not support persistent connections &MUST;
2263   include the "close" connection option in every response message that
2264   does not have a 1xx (informational) status code.
2267   A system receiving an HTTP/1.0 (or lower-version) message that
2268   includes a Connection header &MUST;, for each connection-token in this
2269   field, remove and ignore any header field(s) from the message with
2270   the same name as the connection-token. This protects against mistaken
2271   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2275<section title="Content-Length" anchor="header.content-length">
2276  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2277  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2278  <x:anchor-alias value="Content-Length"/>
2279  <x:anchor-alias value="Content-Length-v"/>
2281   The entity-header field "Content-Length" indicates the size of the
2282   entity-body, in number of OCTETs, sent to the recipient or,
2283   in the case of the HEAD method, the size of the entity-body that
2284   would have been sent had the request been a GET.
2286<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2287  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2288  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2291   An example is
2293<figure><artwork type="example">
2294  Content-Length: 3495
2297   Applications &SHOULD; use this field to indicate the transfer-length of
2298   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2301   Any Content-Length greater than or equal to zero is a valid value.
2302   <xref target="message.length"/> describes how to determine the length of a message-body
2303   if a Content-Length is not given.
2306   Note that the meaning of this field is significantly different from
2307   the corresponding definition in MIME, where it is an optional field
2308   used within the "message/external-body" content-type. In HTTP, it
2309   &SHOULD; be sent whenever the message's length can be determined prior
2310   to being transferred, unless this is prohibited by the rules in
2311   <xref target="message.length"/>.
2315<section title="Date" anchor="">
2316  <iref primary="true" item="Date header" x:for-anchor=""/>
2317  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2318  <x:anchor-alias value="Date"/>
2319  <x:anchor-alias value="Date-v"/>
2321   The general-header field "Date" represents the date and time at which
2322   the message was originated, having the same semantics as orig-date in
2323   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2324   HTTP-date, as described in <xref target=""/>;
2325   it &MUST; be sent in rfc1123-date format.
2327<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2328  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2329  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2332   An example is
2334<figure><artwork type="example">
2335  Date: Tue, 15 Nov 1994 08:12:31 GMT
2338   Origin servers &MUST; include a Date header field in all responses,
2339   except in these cases:
2340  <list style="numbers">
2341      <t>If the response status code is 100 (Continue) or 101 (Switching
2342         Protocols), the response &MAY; include a Date header field, at
2343         the server's option.</t>
2345      <t>If the response status code conveys a server error, e.g. 500
2346         (Internal Server Error) or 503 (Service Unavailable), and it is
2347         inconvenient or impossible to generate a valid Date.</t>
2349      <t>If the server does not have a clock that can provide a
2350         reasonable approximation of the current time, its responses
2351         &MUST-NOT; include a Date header field. In this case, the rules
2352         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2353  </list>
2356   A received message that does not have a Date header field &MUST; be
2357   assigned one by the recipient if the message will be cached by that
2358   recipient or gatewayed via a protocol which requires a Date. An HTTP
2359   implementation without a clock &MUST-NOT; cache responses without
2360   revalidating them on every use. An HTTP cache, especially a shared
2361   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2362   clock with a reliable external standard.
2365   Clients &SHOULD; only send a Date header field in messages that include
2366   an entity-body, as in the case of the PUT and POST requests, and even
2367   then it is optional. A client without a clock &MUST-NOT; send a Date
2368   header field in a request.
2371   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2372   time subsequent to the generation of the message. It &SHOULD; represent
2373   the best available approximation of the date and time of message
2374   generation, unless the implementation has no means of generating a
2375   reasonably accurate date and time. In theory, the date ought to
2376   represent the moment just before the entity is generated. In
2377   practice, the date can be generated at any time during the message
2378   origination without affecting its semantic value.
2381<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2383   Some origin server implementations might not have a clock available.
2384   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2385   values to a response, unless these values were associated
2386   with the resource by a system or user with a reliable clock. It &MAY;
2387   assign an Expires value that is known, at or before server
2388   configuration time, to be in the past (this allows "pre-expiration"
2389   of responses without storing separate Expires values for each
2390   resource).
2395<section title="Host" anchor="">
2396  <iref primary="true" item="Host header" x:for-anchor=""/>
2397  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2398  <x:anchor-alias value="Host"/>
2399  <x:anchor-alias value="Host-v"/>
2401   The request-header field "Host" specifies the Internet host and port
2402   number of the resource being requested, as obtained from the original
2403   URI given by the user or referring resource (generally an http URI,
2404   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2405   the naming authority of the origin server or gateway given by the
2406   original URL. This allows the origin server or gateway to
2407   differentiate between internally-ambiguous URLs, such as the root "/"
2408   URL of a server for multiple host names on a single IP address.
2410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2411  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2412  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2415   A "host" without any trailing port information implies the default
2416   port for the service requested (e.g., "80" for an HTTP URL). For
2417   example, a request on the origin server for
2418   &lt;; would properly include:
2420<figure><artwork type="example">
2421  GET /pub/WWW/ HTTP/1.1
2422  Host:
2425   A client &MUST; include a Host header field in all HTTP/1.1 request
2426   messages. If the requested URI does not include an Internet host
2427   name for the service being requested, then the Host header field &MUST;
2428   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2429   request message it forwards does contain an appropriate Host header
2430   field that identifies the service being requested by the proxy. All
2431   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2432   status code to any HTTP/1.1 request message which lacks a Host header
2433   field.
2436   See Sections <xref target="" format="counter"/>
2437   and <xref target="" format="counter"/>
2438   for other requirements relating to Host.
2442<section title="TE" anchor="header.te">
2443  <iref primary="true" item="TE header" x:for-anchor=""/>
2444  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2445  <x:anchor-alias value="TE"/>
2446  <x:anchor-alias value="TE-v"/>
2447  <x:anchor-alias value="t-codings"/>
2448  <x:anchor-alias value="te-params"/>
2449  <x:anchor-alias value="te-ext"/>
2451   The request-header field "TE" indicates what extension transfer-codings
2452   it is willing to accept in the response and whether or not it is
2453   willing to accept trailer fields in a chunked transfer-coding. Its
2454   value may consist of the keyword "trailers" and/or a comma-separated
2455   list of extension transfer-coding names with optional accept
2456   parameters (as described in <xref target="transfer.codings"/>).
2458<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"/>
2459  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2460  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2461  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2462  <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> )
2463  <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> ) ]
2466   The presence of the keyword "trailers" indicates that the client is
2467   willing to accept trailer fields in a chunked transfer-coding, as
2468   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2469   transfer-coding values even though it does not itself represent a
2470   transfer-coding.
2473   Examples of its use are:
2475<figure><artwork type="example">
2476  TE: deflate
2477  TE:
2478  TE: trailers, deflate;q=0.5
2481   The TE header field only applies to the immediate connection.
2482   Therefore, the keyword &MUST; be supplied within a Connection header
2483   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2486   A server tests whether a transfer-coding is acceptable, according to
2487   a TE field, using these rules:
2488  <list style="numbers">
2489    <x:lt>
2490      <t>The "chunked" transfer-coding is always acceptable. If the
2491         keyword "trailers" is listed, the client indicates that it is
2492         willing to accept trailer fields in the chunked response on
2493         behalf of itself and any downstream clients. The implication is
2494         that, if given, the client is stating that either all
2495         downstream clients are willing to accept trailer fields in the
2496         forwarded response, or that it will attempt to buffer the
2497         response on behalf of downstream recipients.
2498      </t><t>
2499         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2500         chunked response such that a client can be assured of buffering
2501         the entire response.</t>
2502    </x:lt>
2503    <x:lt>
2504      <t>If the transfer-coding being tested is one of the transfer-codings
2505         listed in the TE field, then it is acceptable unless it
2506         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2507         qvalue of 0 means "not acceptable.")</t>
2508    </x:lt>
2509    <x:lt>
2510      <t>If multiple transfer-codings are acceptable, then the
2511         acceptable transfer-coding with the highest non-zero qvalue is
2512         preferred.  The "chunked" transfer-coding always has a qvalue
2513         of 1.</t>
2514    </x:lt>
2515  </list>
2518   If the TE field-value is empty or if no TE field is present, the only
2519   transfer-coding is "chunked". A message with no transfer-coding is
2520   always acceptable.
2524<section title="Trailer" anchor="header.trailer">
2525  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2526  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2527  <x:anchor-alias value="Trailer"/>
2528  <x:anchor-alias value="Trailer-v"/>
2530   The general field "Trailer" indicates that the given set of
2531   header fields is present in the trailer of a message encoded with
2532   chunked transfer-coding.
2534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2535  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2536  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2539   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2540   message using chunked transfer-coding with a non-empty trailer. Doing
2541   so allows the recipient to know which header fields to expect in the
2542   trailer.
2545   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2546   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2547   trailer fields in a "chunked" transfer-coding.
2550   Message header fields listed in the Trailer header field &MUST-NOT;
2551   include the following header fields:
2552  <list style="symbols">
2553    <t>Transfer-Encoding</t>
2554    <t>Content-Length</t>
2555    <t>Trailer</t>
2556  </list>
2560<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2561  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2562  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2563  <x:anchor-alias value="Transfer-Encoding"/>
2564  <x:anchor-alias value="Transfer-Encoding-v"/>
2566   The general-header "Transfer-Encoding" field indicates what (if any)
2567   type of transformation has been applied to the message body in order
2568   to safely transfer it between the sender and the recipient. This
2569   differs from the content-coding in that the transfer-coding is a
2570   property of the message, not of the entity.
2572<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2573  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2574                        <x:ref>Transfer-Encoding-v</x:ref>
2575  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2578   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2580<figure><artwork type="example">
2581  Transfer-Encoding: chunked
2584   If multiple encodings have been applied to an entity, the transfer-codings
2585   &MUST; be listed in the order in which they were applied.
2586   Additional information about the encoding parameters &MAY; be provided
2587   by other entity-header fields not defined by this specification.
2590   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2591   header.
2595<section title="Upgrade" anchor="header.upgrade">
2596  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2597  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2598  <x:anchor-alias value="Upgrade"/>
2599  <x:anchor-alias value="Upgrade-v"/>
2601   The general-header "Upgrade" allows the client to specify what
2602   additional communication protocols it supports and would like to use
2603   if the server finds it appropriate to switch protocols. The server
2604   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2605   response to indicate which protocol(s) are being switched.
2607<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2608  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2609  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2612   For example,
2614<figure><artwork type="example">
2615  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2618   The Upgrade header field is intended to provide a simple mechanism
2619   for transition from HTTP/1.1 to some other, incompatible protocol. It
2620   does so by allowing the client to advertise its desire to use another
2621   protocol, such as a later version of HTTP with a higher major version
2622   number, even though the current request has been made using HTTP/1.1.
2623   This eases the difficult transition between incompatible protocols by
2624   allowing the client to initiate a request in the more commonly
2625   supported protocol while indicating to the server that it would like
2626   to use a "better" protocol if available (where "better" is determined
2627   by the server, possibly according to the nature of the method and/or
2628   resource being requested).
2631   The Upgrade header field only applies to switching application-layer
2632   protocols upon the existing transport-layer connection. Upgrade
2633   cannot be used to insist on a protocol change; its acceptance and use
2634   by the server is optional. The capabilities and nature of the
2635   application-layer communication after the protocol change is entirely
2636   dependent upon the new protocol chosen, although the first action
2637   after changing the protocol &MUST; be a response to the initial HTTP
2638   request containing the Upgrade header field.
2641   The Upgrade header field only applies to the immediate connection.
2642   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2643   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2644   HTTP/1.1 message.
2647   The Upgrade header field cannot be used to indicate a switch to a
2648   protocol on a different connection. For that purpose, it is more
2649   appropriate to use a 301, 302, 303, or 305 redirection response.
2652   This specification only defines the protocol name "HTTP" for use by
2653   the family of Hypertext Transfer Protocols, as defined by the HTTP
2654   version rules of <xref target="http.version"/> and future updates to this
2655   specification. Any token can be used as a protocol name; however, it
2656   will only be useful if both the client and server associate the name
2657   with the same protocol.
2661<section title="Via" anchor="header.via">
2662  <iref primary="true" item="Via header" x:for-anchor=""/>
2663  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2664  <x:anchor-alias value="protocol-name"/>
2665  <x:anchor-alias value="protocol-version"/>
2666  <x:anchor-alias value="pseudonym"/>
2667  <x:anchor-alias value="received-by"/>
2668  <x:anchor-alias value="received-protocol"/>
2669  <x:anchor-alias value="Via"/>
2670  <x:anchor-alias value="Via-v"/>
2672   The general-header field "Via" &MUST; be used by gateways and proxies to
2673   indicate the intermediate protocols and recipients between the user
2674   agent and the server on requests, and between the origin server and
2675   the client on responses. It is analogous to the "Received" field defined in
2676   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2677   avoiding request loops, and identifying the protocol capabilities of
2678   all senders along the request/response chain.
2680<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"/>
2681  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2682  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2683                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2684  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2685  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2686  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2687  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2688  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2691   The received-protocol indicates the protocol version of the message
2692   received by the server or client along each segment of the
2693   request/response chain. The received-protocol version is appended to
2694   the Via field value when the message is forwarded so that information
2695   about the protocol capabilities of upstream applications remains
2696   visible to all recipients.
2699   The protocol-name is optional if and only if it would be "HTTP". The
2700   received-by field is normally the host and optional port number of a
2701   recipient server or client that subsequently forwarded the message.
2702   However, if the real host is considered to be sensitive information,
2703   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2704   be assumed to be the default port of the received-protocol.
2707   Multiple Via field values represents each proxy or gateway that has
2708   forwarded the message. Each recipient &MUST; append its information
2709   such that the end result is ordered according to the sequence of
2710   forwarding applications.
2713   Comments &MAY; be used in the Via header field to identify the software
2714   of the recipient proxy or gateway, analogous to the User-Agent and
2715   Server header fields. However, all comments in the Via field are
2716   optional and &MAY; be removed by any recipient prior to forwarding the
2717   message.
2720   For example, a request message could be sent from an HTTP/1.0 user
2721   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2722   forward the request to a public proxy at, which completes
2723   the request by forwarding it to the origin server at
2724   The request received by would then have the following
2725   Via header field:
2727<figure><artwork type="example">
2728  Via: 1.0 fred, 1.1 (Apache/1.1)
2731   Proxies and gateways used as a portal through a network firewall
2732   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2733   the firewall region. This information &SHOULD; only be propagated if
2734   explicitly enabled. If not enabled, the received-by host of any host
2735   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2736   for that host.
2739   For organizations that have strong privacy requirements for hiding
2740   internal structures, a proxy &MAY; combine an ordered subsequence of
2741   Via header field entries with identical received-protocol values into
2742   a single such entry. For example,
2744<figure><artwork type="example">
2745  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2748        could be collapsed to
2750<figure><artwork type="example">
2751  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2754   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2755   under the same organizational control and the hosts have already been
2756   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2757   have different received-protocol values.
2763<section title="IANA Considerations" anchor="IANA.considerations">
2764<section title="Message Header Registration" anchor="message.header.registration">
2766   The Message Header Registry located at <eref target=""/> should be updated
2767   with the permanent registrations below (see <xref target="RFC3864"/>):
2769<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2770<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2771   <ttcol>Header Field Name</ttcol>
2772   <ttcol>Protocol</ttcol>
2773   <ttcol>Status</ttcol>
2774   <ttcol>Reference</ttcol>
2776   <c>Connection</c>
2777   <c>http</c>
2778   <c>standard</c>
2779   <c>
2780      <xref target="header.connection"/>
2781   </c>
2782   <c>Content-Length</c>
2783   <c>http</c>
2784   <c>standard</c>
2785   <c>
2786      <xref target="header.content-length"/>
2787   </c>
2788   <c>Date</c>
2789   <c>http</c>
2790   <c>standard</c>
2791   <c>
2792      <xref target=""/>
2793   </c>
2794   <c>Host</c>
2795   <c>http</c>
2796   <c>standard</c>
2797   <c>
2798      <xref target=""/>
2799   </c>
2800   <c>TE</c>
2801   <c>http</c>
2802   <c>standard</c>
2803   <c>
2804      <xref target="header.te"/>
2805   </c>
2806   <c>Trailer</c>
2807   <c>http</c>
2808   <c>standard</c>
2809   <c>
2810      <xref target="header.trailer"/>
2811   </c>
2812   <c>Transfer-Encoding</c>
2813   <c>http</c>
2814   <c>standard</c>
2815   <c>
2816      <xref target="header.transfer-encoding"/>
2817   </c>
2818   <c>Upgrade</c>
2819   <c>http</c>
2820   <c>standard</c>
2821   <c>
2822      <xref target="header.upgrade"/>
2823   </c>
2824   <c>Via</c>
2825   <c>http</c>
2826   <c>standard</c>
2827   <c>
2828      <xref target="header.via"/>
2829   </c>
2833   The change controller is: "IETF ( - Internet Engineering Task Force".
2837<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2839   The entry for the "http" URI Scheme in the registry located at
2840   <eref target=""/>
2841   should be updated to point to <xref target="http.uri"/> of this document
2842   (see <xref target="RFC4395"/>).
2846<section title="Internet Media Type Registrations" anchor="">
2848   This document serves as the specification for the Internet media types
2849   "message/http" and "application/http". The following is to be registered with
2850   IANA (see <xref target="RFC4288"/>).
2852<section title="Internet Media Type message/http" anchor="">
2853<iref item="Media Type" subitem="message/http" primary="true"/>
2854<iref item="message/http Media Type" primary="true"/>
2856   The message/http type can be used to enclose a single HTTP request or
2857   response message, provided that it obeys the MIME restrictions for all
2858   "message" types regarding line length and encodings.
2861  <list style="hanging" x:indent="12em">
2862    <t hangText="Type name:">
2863      message
2864    </t>
2865    <t hangText="Subtype name:">
2866      http
2867    </t>
2868    <t hangText="Required parameters:">
2869      none
2870    </t>
2871    <t hangText="Optional parameters:">
2872      version, msgtype
2873      <list style="hanging">
2874        <t hangText="version:">
2875          The HTTP-Version number of the enclosed message
2876          (e.g., "1.1"). If not present, the version can be
2877          determined from the first line of the body.
2878        </t>
2879        <t hangText="msgtype:">
2880          The message type -- "request" or "response". If not
2881          present, the type can be determined from the first
2882          line of the body.
2883        </t>
2884      </list>
2885    </t>
2886    <t hangText="Encoding considerations:">
2887      only "7bit", "8bit", or "binary" are permitted
2888    </t>
2889    <t hangText="Security considerations:">
2890      none
2891    </t>
2892    <t hangText="Interoperability considerations:">
2893      none
2894    </t>
2895    <t hangText="Published specification:">
2896      This specification (see <xref target=""/>).
2897    </t>
2898    <t hangText="Applications that use this media type:">
2899    </t>
2900    <t hangText="Additional information:">
2901      <list style="hanging">
2902        <t hangText="Magic number(s):">none</t>
2903        <t hangText="File extension(s):">none</t>
2904        <t hangText="Macintosh file type code(s):">none</t>
2905      </list>
2906    </t>
2907    <t hangText="Person and email address to contact for further information:">
2908      See Authors Section.
2909    </t>
2910                <t hangText="Intended usage:">
2911                  COMMON
2912    </t>
2913                <t hangText="Restrictions on usage:">
2914                  none
2915    </t>
2916    <t hangText="Author/Change controller:">
2917      IESG
2918    </t>
2919  </list>
2922<section title="Internet Media Type application/http" anchor="">
2923<iref item="Media Type" subitem="application/http" primary="true"/>
2924<iref item="application/http Media Type" primary="true"/>
2926   The application/http type can be used to enclose a pipeline of one or more
2927   HTTP request or response messages (not intermixed).
2930  <list style="hanging" x:indent="12em">
2931    <t hangText="Type name:">
2932      application
2933    </t>
2934    <t hangText="Subtype name:">
2935      http
2936    </t>
2937    <t hangText="Required parameters:">
2938      none
2939    </t>
2940    <t hangText="Optional parameters:">
2941      version, msgtype
2942      <list style="hanging">
2943        <t hangText="version:">
2944          The HTTP-Version number of the enclosed messages
2945          (e.g., "1.1"). If not present, the version can be
2946          determined from the first line of the body.
2947        </t>
2948        <t hangText="msgtype:">
2949          The message type -- "request" or "response". If not
2950          present, the type can be determined from the first
2951          line of the body.
2952        </t>
2953      </list>
2954    </t>
2955    <t hangText="Encoding considerations:">
2956      HTTP messages enclosed by this type
2957      are in "binary" format; use of an appropriate
2958      Content-Transfer-Encoding is required when
2959      transmitted via E-mail.
2960    </t>
2961    <t hangText="Security considerations:">
2962      none
2963    </t>
2964    <t hangText="Interoperability considerations:">
2965      none
2966    </t>
2967    <t hangText="Published specification:">
2968      This specification (see <xref target=""/>).
2969    </t>
2970    <t hangText="Applications that use this media type:">
2971    </t>
2972    <t hangText="Additional information:">
2973      <list style="hanging">
2974        <t hangText="Magic number(s):">none</t>
2975        <t hangText="File extension(s):">none</t>
2976        <t hangText="Macintosh file type code(s):">none</t>
2977      </list>
2978    </t>
2979    <t hangText="Person and email address to contact for further information:">
2980      See Authors Section.
2981    </t>
2982                <t hangText="Intended usage:">
2983                  COMMON
2984    </t>
2985                <t hangText="Restrictions on usage:">
2986                  none
2987    </t>
2988    <t hangText="Author/Change controller:">
2989      IESG
2990    </t>
2991  </list>
2998<section title="Security Considerations" anchor="security.considerations">
3000   This section is meant to inform application developers, information
3001   providers, and users of the security limitations in HTTP/1.1 as
3002   described by this document. The discussion does not include
3003   definitive solutions to the problems revealed, though it does make
3004   some suggestions for reducing security risks.
3007<section title="Personal Information" anchor="personal.information">
3009   HTTP clients are often privy to large amounts of personal information
3010   (e.g. the user's name, location, mail address, passwords, encryption
3011   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3012   leakage of this information.
3013   We very strongly recommend that a convenient interface be provided
3014   for the user to control dissemination of such information, and that
3015   designers and implementors be particularly careful in this area.
3016   History shows that errors in this area often create serious security
3017   and/or privacy problems and generate highly adverse publicity for the
3018   implementor's company.
3022<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3024   A server is in the position to save personal data about a user's
3025   requests which might identify their reading patterns or subjects of
3026   interest. This information is clearly confidential in nature and its
3027   handling can be constrained by law in certain countries. People using
3028   HTTP to provide data are responsible for ensuring that
3029   such material is not distributed without the permission of any
3030   individuals that are identifiable by the published results.
3034<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3036   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3037   the documents returned by HTTP requests to be only those that were
3038   intended by the server administrators. If an HTTP server translates
3039   HTTP URIs directly into file system calls, the server &MUST; take
3040   special care not to serve files that were not intended to be
3041   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3042   other operating systems use ".." as a path component to indicate a
3043   directory level above the current one. On such a system, an HTTP
3044   server &MUST; disallow any such construct in the request-target if it
3045   would otherwise allow access to a resource outside those intended to
3046   be accessible via the HTTP server. Similarly, files intended for
3047   reference only internally to the server (such as access control
3048   files, configuration files, and script code) &MUST; be protected from
3049   inappropriate retrieval, since they might contain sensitive
3050   information. Experience has shown that minor bugs in such HTTP server
3051   implementations have turned into security risks.
3055<section title="DNS Spoofing" anchor="dns.spoofing">
3057   Clients using HTTP rely heavily on the Domain Name Service, and are
3058   thus generally prone to security attacks based on the deliberate
3059   mis-association of IP addresses and DNS names. Clients need to be
3060   cautious in assuming the continuing validity of an IP number/DNS name
3061   association.
3064   In particular, HTTP clients &SHOULD; rely on their name resolver for
3065   confirmation of an IP number/DNS name association, rather than
3066   caching the result of previous host name lookups. Many platforms
3067   already can cache host name lookups locally when appropriate, and
3068   they &SHOULD; be configured to do so. It is proper for these lookups to
3069   be cached, however, only when the TTL (Time To Live) information
3070   reported by the name server makes it likely that the cached
3071   information will remain useful.
3074   If HTTP clients cache the results of host name lookups in order to
3075   achieve a performance improvement, they &MUST; observe the TTL
3076   information reported by DNS.
3079   If HTTP clients do not observe this rule, they could be spoofed when
3080   a previously-accessed server's IP address changes. As network
3081   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3082   possibility of this form of attack will grow. Observing this
3083   requirement thus reduces this potential security vulnerability.
3086   This requirement also improves the load-balancing behavior of clients
3087   for replicated servers using the same DNS name and reduces the
3088   likelihood of a user's experiencing failure in accessing sites which
3089   use that strategy.
3093<section title="Proxies and Caching" anchor="attack.proxies">
3095   By their very nature, HTTP proxies are men-in-the-middle, and
3096   represent an opportunity for man-in-the-middle attacks. Compromise of
3097   the systems on which the proxies run can result in serious security
3098   and privacy problems. Proxies have access to security-related
3099   information, personal information about individual users and
3100   organizations, and proprietary information belonging to users and
3101   content providers. A compromised proxy, or a proxy implemented or
3102   configured without regard to security and privacy considerations,
3103   might be used in the commission of a wide range of potential attacks.
3106   Proxy operators should protect the systems on which proxies run as
3107   they would protect any system that contains or transports sensitive
3108   information. In particular, log information gathered at proxies often
3109   contains highly sensitive personal information, and/or information
3110   about organizations. Log information should be carefully guarded, and
3111   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3114   Proxy implementors should consider the privacy and security
3115   implications of their design and coding decisions, and of the
3116   configuration options they provide to proxy operators (especially the
3117   default configuration).
3120   Users of a proxy need to be aware that they are no trustworthier than
3121   the people who run the proxy; HTTP itself cannot solve this problem.
3124   The judicious use of cryptography, when appropriate, may suffice to
3125   protect against a broad range of security and privacy attacks. Such
3126   cryptography is beyond the scope of the HTTP/1.1 specification.
3130<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3132   They exist. They are hard to defend against. Research continues.
3133   Beware.
3138<section title="Acknowledgments" anchor="ack">
3140   HTTP has evolved considerably over the years. It has
3141   benefited from a large and active developer community--the many
3142   people who have participated on the www-talk mailing list--and it is
3143   that community which has been most responsible for the success of
3144   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3145   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3146   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3147   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3148   VanHeyningen deserve special recognition for their efforts in
3149   defining early aspects of the protocol.
3152   This document has benefited greatly from the comments of all those
3153   participating in the HTTP-WG. In addition to those already mentioned,
3154   the following individuals have contributed to this specification:
3157   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3158   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3159   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3160   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3161   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3162   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3163   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3164   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3165   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3166   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3167   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3168   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3169   Josh Cohen.
3172   Thanks to the "cave men" of Palo Alto. You know who you are.
3175   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3176   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3177   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3178   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3179   Larry Masinter for their help. And thanks go particularly to Jeff
3180   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3183   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3184   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3185   discovery of many of the problems that this document attempts to
3186   rectify.
3189   This specification makes heavy use of the augmented BNF and generic
3190   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3191   reuses many of the definitions provided by Nathaniel Borenstein and
3192   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3193   specification will help reduce past confusion over the relationship
3194   between HTTP and Internet mail message formats.
3201<references title="Normative References">
3203<reference anchor="ISO-8859-1">
3204  <front>
3205    <title>
3206     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3207    </title>
3208    <author>
3209      <organization>International Organization for Standardization</organization>
3210    </author>
3211    <date year="1998"/>
3212  </front>
3213  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3216<reference anchor="Part2">
3217  <front>
3218    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3219    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3220      <organization abbrev="Day Software">Day Software</organization>
3221      <address><email></email></address>
3222    </author>
3223    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3224      <organization>One Laptop per Child</organization>
3225      <address><email></email></address>
3226    </author>
3227    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3228      <organization abbrev="HP">Hewlett-Packard Company</organization>
3229      <address><email></email></address>
3230    </author>
3231    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3232      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3233      <address><email></email></address>
3234    </author>
3235    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3236      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3237      <address><email></email></address>
3238    </author>
3239    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3240      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3241      <address><email></email></address>
3242    </author>
3243    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3244      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3245      <address><email></email></address>
3246    </author>
3247    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3248      <organization abbrev="W3C">World Wide Web Consortium</organization>
3249      <address><email></email></address>
3250    </author>
3251    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3252      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3253      <address><email></email></address>
3254    </author>
3255    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3256  </front>
3257  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3258  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3261<reference anchor="Part3">
3262  <front>
3263    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3264    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3265      <organization abbrev="Day Software">Day Software</organization>
3266      <address><email></email></address>
3267    </author>
3268    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3269      <organization>One Laptop per Child</organization>
3270      <address><email></email></address>
3271    </author>
3272    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3273      <organization abbrev="HP">Hewlett-Packard Company</organization>
3274      <address><email></email></address>
3275    </author>
3276    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3277      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3278      <address><email></email></address>
3279    </author>
3280    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3281      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3282      <address><email></email></address>
3283    </author>
3284    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3285      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3286      <address><email></email></address>
3287    </author>
3288    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3289      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3290      <address><email></email></address>
3291    </author>
3292    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3293      <organization abbrev="W3C">World Wide Web Consortium</organization>
3294      <address><email></email></address>
3295    </author>
3296    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3297      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3298      <address><email></email></address>
3299    </author>
3300    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3301  </front>
3302  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3303  <x:source href="p3-payload.xml" basename="p3-payload"/>
3306<reference anchor="Part5">
3307  <front>
3308    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3309    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3310      <organization abbrev="Day Software">Day Software</organization>
3311      <address><email></email></address>
3312    </author>
3313    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3314      <organization>One Laptop per Child</organization>
3315      <address><email></email></address>
3316    </author>
3317    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3318      <organization abbrev="HP">Hewlett-Packard Company</organization>
3319      <address><email></email></address>
3320    </author>
3321    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3322      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3323      <address><email></email></address>
3324    </author>
3325    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3326      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3327      <address><email></email></address>
3328    </author>
3329    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3330      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3331      <address><email></email></address>
3332    </author>
3333    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3334      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3335      <address><email></email></address>
3336    </author>
3337    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3338      <organization abbrev="W3C">World Wide Web Consortium</organization>
3339      <address><email></email></address>
3340    </author>
3341    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3342      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3343      <address><email></email></address>
3344    </author>
3345    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3346  </front>
3347  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3348  <x:source href="p5-range.xml" basename="p5-range"/>
3351<reference anchor="Part6">
3352  <front>
3353    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3354    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3355      <organization abbrev="Day Software">Day Software</organization>
3356      <address><email></email></address>
3357    </author>
3358    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3359      <organization>One Laptop per Child</organization>
3360      <address><email></email></address>
3361    </author>
3362    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3363      <organization abbrev="HP">Hewlett-Packard Company</organization>
3364      <address><email></email></address>
3365    </author>
3366    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3367      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3368      <address><email></email></address>
3369    </author>
3370    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3371      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3372      <address><email></email></address>
3373    </author>
3374    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3375      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3376      <address><email></email></address>
3377    </author>
3378    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3379      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3380      <address><email></email></address>
3381    </author>
3382    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3383      <organization abbrev="W3C">World Wide Web Consortium</organization>
3384      <address><email></email></address>
3385    </author>
3386    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3387      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3388      <address><email></email></address>
3389    </author>
3390    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3391  </front>
3392  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3393  <x:source href="p6-cache.xml" basename="p6-cache"/>
3396<reference anchor="RFC5234">
3397  <front>
3398    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3399    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3400      <organization>Brandenburg InternetWorking</organization>
3401      <address>
3402      <postal>
3403      <street>675 Spruce Dr.</street>
3404      <city>Sunnyvale</city>
3405      <region>CA</region>
3406      <code>94086</code>
3407      <country>US</country></postal>
3408      <phone>+1.408.246.8253</phone>
3409      <email></email></address> 
3410    </author>
3411    <author initials="P." surname="Overell" fullname="Paul Overell">
3412      <organization>THUS plc.</organization>
3413      <address>
3414      <postal>
3415      <street>1/2 Berkeley Square</street>
3416      <street>99 Berkely Street</street>
3417      <city>Glasgow</city>
3418      <code>G3 7HR</code>
3419      <country>UK</country></postal>
3420      <email></email></address>
3421    </author>
3422    <date month="January" year="2008"/>
3423  </front>
3424  <seriesInfo name="STD" value="68"/>
3425  <seriesInfo name="RFC" value="5234"/>
3428<reference anchor="RFC2119">
3429  <front>
3430    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3431    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3432      <organization>Harvard University</organization>
3433      <address><email></email></address>
3434    </author>
3435    <date month="March" year="1997"/>
3436  </front>
3437  <seriesInfo name="BCP" value="14"/>
3438  <seriesInfo name="RFC" value="2119"/>
3441<reference anchor="RFC3986">
3442 <front>
3443  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3444  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3445    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3446    <address>
3447       <email></email>
3448       <uri></uri>
3449    </address>
3450  </author>
3451  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3452    <organization abbrev="Day Software">Day Software</organization>
3453    <address>
3454      <email></email>
3455      <uri></uri>
3456    </address>
3457  </author>
3458  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3459    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3460    <address>
3461      <email></email>
3462      <uri></uri>
3463    </address>
3464  </author>
3465  <date month='January' year='2005'></date>
3466 </front>
3467 <seriesInfo name="RFC" value="3986"/>
3468 <seriesInfo name="STD" value="66"/>
3471<reference anchor="USASCII">
3472  <front>
3473    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3474    <author>
3475      <organization>American National Standards Institute</organization>
3476    </author>
3477    <date year="1986"/>
3478  </front>
3479  <seriesInfo name="ANSI" value="X3.4"/>
3484<references title="Informative References">
3486<reference anchor="Nie1997" target="">
3487  <front>
3488    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3489    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3490      <organization/>
3491    </author>
3492    <author initials="J." surname="Gettys" fullname="J. Gettys">
3493      <organization/>
3494    </author>
3495    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3496      <organization/>
3497    </author>
3498    <author initials="H." surname="Lie" fullname="H. Lie">
3499      <organization/>
3500    </author>
3501    <author initials="C." surname="Lilley" fullname="C. Lilley">
3502      <organization/>
3503    </author>
3504    <date year="1997" month="September"/>
3505  </front>
3506  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3509<reference anchor="Pad1995" target="">
3510  <front>
3511    <title>Improving HTTP Latency</title>
3512    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3513      <organization/>
3514    </author>
3515    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3516      <organization/>
3517    </author>
3518    <date year="1995" month="December"/>
3519  </front>
3520  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3523<reference anchor="RFC1123">
3524  <front>
3525    <title>Requirements for Internet Hosts - Application and Support</title>
3526    <author initials="R." surname="Braden" fullname="Robert Braden">
3527      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3528      <address><email>Braden@ISI.EDU</email></address>
3529    </author>
3530    <date month="October" year="1989"/>
3531  </front>
3532  <seriesInfo name="STD" value="3"/>
3533  <seriesInfo name="RFC" value="1123"/>
3536<reference anchor="RFC1305">
3537  <front>
3538    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3539    <author initials="D." surname="Mills" fullname="David L. Mills">
3540      <organization>University of Delaware, Electrical Engineering Department</organization>
3541      <address><email></email></address>
3542    </author>
3543    <date month="March" year="1992"/>
3544  </front>
3545  <seriesInfo name="RFC" value="1305"/>
3548<reference anchor="RFC1900">
3549  <front>
3550    <title>Renumbering Needs Work</title>
3551    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3552      <organization>CERN, Computing and Networks Division</organization>
3553      <address><email></email></address>
3554    </author>
3555    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3556      <organization>cisco Systems</organization>
3557      <address><email></email></address>
3558    </author>
3559    <date month="February" year="1996"/>
3560  </front>
3561  <seriesInfo name="RFC" value="1900"/>
3564<reference anchor="RFC1945">
3565  <front>
3566    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3567    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3568      <organization>MIT, Laboratory for Computer Science</organization>
3569      <address><email></email></address>
3570    </author>
3571    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3572      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3573      <address><email></email></address>
3574    </author>
3575    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3576      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3577      <address><email></email></address>
3578    </author>
3579    <date month="May" year="1996"/>
3580  </front>
3581  <seriesInfo name="RFC" value="1945"/>
3584<reference anchor="RFC2045">
3585  <front>
3586    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3587    <author initials="N." surname="Freed" fullname="Ned Freed">
3588      <organization>Innosoft International, Inc.</organization>
3589      <address><email></email></address>
3590    </author>
3591    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3592      <organization>First Virtual Holdings</organization>
3593      <address><email></email></address>
3594    </author>
3595    <date month="November" year="1996"/>
3596  </front>
3597  <seriesInfo name="RFC" value="2045"/>
3600<reference anchor="RFC2047">
3601  <front>
3602    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3603    <author initials="K." surname="Moore" fullname="Keith Moore">
3604      <organization>University of Tennessee</organization>
3605      <address><email></email></address>
3606    </author>
3607    <date month="November" year="1996"/>
3608  </front>
3609  <seriesInfo name="RFC" value="2047"/>
3612<reference anchor="RFC2068">
3613  <front>
3614    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3615    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3616      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3617      <address><email></email></address>
3618    </author>
3619    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3620      <organization>MIT Laboratory for Computer Science</organization>
3621      <address><email></email></address>
3622    </author>
3623    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3624      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3625      <address><email></email></address>
3626    </author>
3627    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3628      <organization>MIT Laboratory for Computer Science</organization>
3629      <address><email></email></address>
3630    </author>
3631    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3632      <organization>MIT Laboratory for Computer Science</organization>
3633      <address><email></email></address>
3634    </author>
3635    <date month="January" year="1997"/>
3636  </front>
3637  <seriesInfo name="RFC" value="2068"/>
3640<reference anchor='RFC2109'>
3641  <front>
3642    <title>HTTP State Management Mechanism</title>
3643    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3644      <organization>Bell Laboratories, Lucent Technologies</organization>
3645      <address><email></email></address>
3646    </author>
3647    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3648      <organization>Netscape Communications Corp.</organization>
3649      <address><email></email></address>
3650    </author>
3651    <date year='1997' month='February' />
3652  </front>
3653  <seriesInfo name='RFC' value='2109' />
3656<reference anchor="RFC2145">
3657  <front>
3658    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3659    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3660      <organization>Western Research Laboratory</organization>
3661      <address><email></email></address>
3662    </author>
3663    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3664      <organization>Department of Information and Computer Science</organization>
3665      <address><email></email></address>
3666    </author>
3667    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3668      <organization>MIT Laboratory for Computer Science</organization>
3669      <address><email></email></address>
3670    </author>
3671    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3672      <organization>W3 Consortium</organization>
3673      <address><email></email></address>
3674    </author>
3675    <date month="May" year="1997"/>
3676  </front>
3677  <seriesInfo name="RFC" value="2145"/>
3680<reference anchor="RFC2616">
3681  <front>
3682    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3683    <author initials="R." surname="Fielding" fullname="R. Fielding">
3684      <organization>University of California, Irvine</organization>
3685      <address><email></email></address>
3686    </author>
3687    <author initials="J." surname="Gettys" fullname="J. Gettys">
3688      <organization>W3C</organization>
3689      <address><email></email></address>
3690    </author>
3691    <author initials="J." surname="Mogul" fullname="J. Mogul">
3692      <organization>Compaq Computer Corporation</organization>
3693      <address><email></email></address>
3694    </author>
3695    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3696      <organization>MIT Laboratory for Computer Science</organization>
3697      <address><email></email></address>
3698    </author>
3699    <author initials="L." surname="Masinter" fullname="L. Masinter">
3700      <organization>Xerox Corporation</organization>
3701      <address><email></email></address>
3702    </author>
3703    <author initials="P." surname="Leach" fullname="P. Leach">
3704      <organization>Microsoft Corporation</organization>
3705      <address><email></email></address>
3706    </author>
3707    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3708      <organization>W3C</organization>
3709      <address><email></email></address>
3710    </author>
3711    <date month="June" year="1999"/>
3712  </front>
3713  <seriesInfo name="RFC" value="2616"/>
3716<reference anchor='RFC2818'>
3717  <front>
3718    <title>HTTP Over TLS</title>
3719    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3720      <organization>RTFM, Inc.</organization>
3721      <address><email></email></address>
3722    </author>
3723    <date year='2000' month='May' />
3724  </front>
3725  <seriesInfo name='RFC' value='2818' />
3728<reference anchor='RFC2965'>
3729  <front>
3730    <title>HTTP State Management Mechanism</title>
3731    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3732      <organization>Bell Laboratories, Lucent Technologies</organization>
3733      <address><email></email></address>
3734    </author>
3735    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3736      <organization>, Inc.</organization>
3737      <address><email></email></address>
3738    </author>
3739    <date year='2000' month='October' />
3740  </front>
3741  <seriesInfo name='RFC' value='2965' />
3744<reference anchor='RFC3864'>
3745  <front>
3746    <title>Registration Procedures for Message Header Fields</title>
3747    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3748      <organization>Nine by Nine</organization>
3749      <address><email></email></address>
3750    </author>
3751    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3752      <organization>BEA Systems</organization>
3753      <address><email></email></address>
3754    </author>
3755    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3756      <organization>HP Labs</organization>
3757      <address><email></email></address>
3758    </author>
3759    <date year='2004' month='September' />
3760  </front>
3761  <seriesInfo name='BCP' value='90' />
3762  <seriesInfo name='RFC' value='3864' />
3765<reference anchor="RFC4288">
3766  <front>
3767    <title>Media Type Specifications and Registration Procedures</title>
3768    <author initials="N." surname="Freed" fullname="N. Freed">
3769      <organization>Sun Microsystems</organization>
3770      <address>
3771        <email></email>
3772      </address>
3773    </author>
3774    <author initials="J." surname="Klensin" fullname="J. Klensin">
3775      <organization/>
3776      <address>
3777        <email></email>
3778      </address>
3779    </author>
3780    <date year="2005" month="December"/>
3781  </front>
3782  <seriesInfo name="BCP" value="13"/>
3783  <seriesInfo name="RFC" value="4288"/>
3786<reference anchor='RFC4395'>
3787  <front>
3788    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3789    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3790      <organization>AT&amp;T Laboratories</organization>
3791      <address>
3792        <email></email>
3793      </address>
3794    </author>
3795    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3796      <organization>Qualcomm, Inc.</organization>
3797      <address>
3798        <email></email>
3799      </address>
3800    </author>
3801    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3802      <organization>Adobe Systems</organization>
3803      <address>
3804        <email></email>
3805      </address>
3806    </author>
3807    <date year='2006' month='February' />
3808  </front>
3809  <seriesInfo name='BCP' value='115' />
3810  <seriesInfo name='RFC' value='4395' />
3813<reference anchor="RFC5322">
3814  <front>
3815    <title>Internet Message Format</title>
3816    <author initials="P." surname="Resnick" fullname="P. Resnick">
3817      <organization>Qualcomm Incorporated</organization>
3818    </author>
3819    <date year="2008" month="October"/>
3820  </front>
3821  <seriesInfo name="RFC" value="5322"/>
3824<reference anchor="Kri2001" target="">
3825  <front>
3826    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3827    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3828      <organization/>
3829    </author>
3830    <date year="2001" month="November"/>
3831  </front>
3832  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3835<reference anchor="Spe" target="">
3836  <front>
3837  <title>Analysis of HTTP Performance Problems</title>
3838  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3839    <organization/>
3840  </author>
3841  <date/>
3842  </front>
3845<reference anchor="Tou1998" target="">
3846  <front>
3847  <title>Analysis of HTTP Performance</title>
3848  <author initials="J." surname="Touch" fullname="Joe Touch">
3849    <organization>USC/Information Sciences Institute</organization>
3850    <address><email></email></address>
3851  </author>
3852  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3853    <organization>USC/Information Sciences Institute</organization>
3854    <address><email></email></address>
3855  </author>
3856  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3857    <organization>USC/Information Sciences Institute</organization>
3858    <address><email></email></address>
3859  </author>
3860  <date year="1998" month="Aug"/>
3861  </front>
3862  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3863  <annotation>(original report dated Aug. 1996)</annotation>
3869<section title="Tolerant Applications" anchor="tolerant.applications">
3871   Although this document specifies the requirements for the generation
3872   of HTTP/1.1 messages, not all applications will be correct in their
3873   implementation. We therefore recommend that operational applications
3874   be tolerant of deviations whenever those deviations can be
3875   interpreted unambiguously.
3878   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3879   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3880   accept any amount of WSP characters between fields, even though
3881   only a single SP is required.
3884   The line terminator for message-header fields is the sequence CRLF.
3885   However, we recommend that applications, when parsing such headers,
3886   recognize a single LF as a line terminator and ignore the leading CR.
3889   The character set of an entity-body &SHOULD; be labeled as the lowest
3890   common denominator of the character codes used within that body, with
3891   the exception that not labeling the entity is preferred over labeling
3892   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3895   Additional rules for requirements on parsing and encoding of dates
3896   and other potential problems with date encodings include:
3899  <list style="symbols">
3900     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3901        which appears to be more than 50 years in the future is in fact
3902        in the past (this helps solve the "year 2000" problem).</t>
3904     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3905        Expires date as earlier than the proper value, but &MUST-NOT;
3906        internally represent a parsed Expires date as later than the
3907        proper value.</t>
3909     <t>All expiration-related calculations &MUST; be done in GMT. The
3910        local time zone &MUST-NOT; influence the calculation or comparison
3911        of an age or expiration time.</t>
3913     <t>If an HTTP header incorrectly carries a date value with a time
3914        zone other than GMT, it &MUST; be converted into GMT using the
3915        most conservative possible conversion.</t>
3916  </list>
3920<section title="Compatibility with Previous Versions" anchor="compatibility">
3922   HTTP has been in use by the World-Wide Web global information initiative
3923   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3924   was a simple protocol for hypertext data transfer across the Internet
3925   with only a single method and no metadata.
3926   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3927   methods and MIME-like messaging that could include metadata about the data
3928   transferred and modifiers on the request/response semantics. However,
3929   HTTP/1.0 did not sufficiently take into consideration the effects of
3930   hierarchical proxies, caching, the need for persistent connections, or
3931   name-based virtual hosts. The proliferation of incompletely-implemented
3932   applications calling themselves "HTTP/1.0" further necessitated a
3933   protocol version change in order for two communicating applications
3934   to determine each other's true capabilities.
3937   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3938   requirements that enable reliable implementations, adding only
3939   those new features that will either be safely ignored by an HTTP/1.0
3940   recipient or only sent when communicating with a party advertising
3941   compliance with HTTP/1.1.
3944   It is beyond the scope of a protocol specification to mandate
3945   compliance with previous versions. HTTP/1.1 was deliberately
3946   designed, however, to make supporting previous versions easy. It is
3947   worth noting that, at the time of composing this specification
3948   (1996), we would expect commercial HTTP/1.1 servers to:
3949  <list style="symbols">
3950     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3951        1.1 requests;</t>
3953     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3954        1.1;</t>
3956     <t>respond appropriately with a message in the same major version
3957        used by the client.</t>
3958  </list>
3961   And we would expect HTTP/1.1 clients to:
3962  <list style="symbols">
3963     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3964        responses;</t>
3966     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3967        1.1.</t>
3968  </list>
3971   For most implementations of HTTP/1.0, each connection is established
3972   by the client prior to the request and closed by the server after
3973   sending the response. Some implementations implement the Keep-Alive
3974   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3977<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3979   This section summarizes major differences between versions HTTP/1.0
3980   and HTTP/1.1.
3983<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3985   The requirements that clients and servers support the Host request-header,
3986   report an error if the Host request-header (<xref target=""/>) is
3987   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3988   are among the most important changes defined by this
3989   specification.
3992   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3993   addresses and servers; there was no other established mechanism for
3994   distinguishing the intended server of a request than the IP address
3995   to which that request was directed. The changes outlined above will
3996   allow the Internet, once older HTTP clients are no longer common, to
3997   support multiple Web sites from a single IP address, greatly
3998   simplifying large operational Web servers, where allocation of many
3999   IP addresses to a single host has created serious problems. The
4000   Internet will also be able to recover the IP addresses that have been
4001   allocated for the sole purpose of allowing special-purpose domain
4002   names to be used in root-level HTTP URLs. Given the rate of growth of
4003   the Web, and the number of servers already deployed, it is extremely
4004   important that all implementations of HTTP (including updates to
4005   existing HTTP/1.0 applications) correctly implement these
4006   requirements:
4007  <list style="symbols">
4008     <t>Both clients and servers &MUST; support the Host request-header.</t>
4010     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4012     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4013        request does not include a Host request-header.</t>
4015     <t>Servers &MUST; accept absolute URIs.</t>
4016  </list>
4021<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4023   Some clients and servers might wish to be compatible with some
4024   previous implementations of persistent connections in HTTP/1.0
4025   clients and servers. Persistent connections in HTTP/1.0 are
4026   explicitly negotiated as they are not the default behavior. HTTP/1.0
4027   experimental implementations of persistent connections are faulty,
4028   and the new facilities in HTTP/1.1 are designed to rectify these
4029   problems. The problem was that some existing 1.0 clients may be
4030   sending Keep-Alive to a proxy server that doesn't understand
4031   Connection, which would then erroneously forward it to the next
4032   inbound server, which would establish the Keep-Alive connection and
4033   result in a hung HTTP/1.0 proxy waiting for the close on the
4034   response. The result is that HTTP/1.0 clients must be prevented from
4035   using Keep-Alive when talking to proxies.
4038   However, talking to proxies is the most important use of persistent
4039   connections, so that prohibition is clearly unacceptable. Therefore,
4040   we need some other mechanism for indicating a persistent connection
4041   is desired, which is safe to use even when talking to an old proxy
4042   that ignores Connection. Persistent connections are the default for
4043   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4044   declaring non-persistence. See <xref target="header.connection"/>.
4047   The original HTTP/1.0 form of persistent connections (the Connection:
4048   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4052<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4054   This specification has been carefully audited to correct and
4055   disambiguate key word usage; RFC 2068 had many problems in respect to
4056   the conventions laid out in <xref target="RFC2119"/>.
4059   Transfer-coding and message lengths all interact in ways that
4060   required fixing exactly when chunked encoding is used (to allow for
4061   transfer encoding that may not be self delimiting); it was important
4062   to straighten out exactly how message lengths are computed. (Sections
4063   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4064   <xref target="header.content-length" format="counter"/>,
4065   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4068   The use and interpretation of HTTP version numbers has been clarified
4069   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4070   version they support to deal with problems discovered in HTTP/1.0
4071   implementations (<xref target="http.version"/>)
4074   Quality Values of zero should indicate that "I don't want something"
4075   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4078   Transfer-coding had significant problems, particularly with
4079   interactions with chunked encoding. The solution is that transfer-codings
4080   become as full fledged as content-codings. This involves
4081   adding an IANA registry for transfer-codings (separate from content
4082   codings), a new header field (TE) and enabling trailer headers in the
4083   future. Transfer encoding is a major performance benefit, so it was
4084   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4085   interoperability problem that could have occurred due to interactions
4086   between authentication trailers, chunked encoding and HTTP/1.0
4087   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4088   and <xref target="header.te" format="counter"/>)
4092<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4094  Empty list elements in list productions have been deprecated.
4095  (<xref target="notation.abnf"/>)
4098  Rules about implicit linear whitespace between certain grammar productions
4099  have been removed; now it's only allowed when specifically pointed out
4100  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4101  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4102  Non-ASCII content in header fields and reason phrase has been obsoleted and
4103  made opaque (the TEXT rule was removed)
4104  (<xref target="basic.rules"/>)
4107  Clarify that HTTP-Version is case sensitive.
4108  (<xref target="http.version"/>)
4111  Remove reference to non-existant identity transfer-coding value tokens.
4112  (Sections <xref format="counter" target="transfer.codings"/> and
4113  <xref format="counter" target="message.length"/>)
4116  Clarification that the chunk length does not include
4117  the count of the octets in the chunk header and trailer.
4118  (<xref target="chunked.transfer.encoding"/>)
4121  Require that invalid whitespace around field-names be rejected.
4122  (<xref target="message.headers"/>)
4125  Update use of abs_path production from RFC1808 to the path-absolute + query
4126  components of RFC3986.
4127  (<xref target="request-target"/>)
4130  Clarify exactly when close connection options must be sent.
4131  (<xref target="header.connection"/>)
4136<section title="Terminology" anchor="terminology">
4138   This specification uses a number of terms to refer to the roles
4139   played by participants in, and objects of, the HTTP communication.
4142  <iref item="cache"/>
4143  <x:dfn>cache</x:dfn>
4144  <list>
4145    <t>
4146      A program's local store of response messages and the subsystem
4147      that controls its message storage, retrieval, and deletion. A
4148      cache stores cacheable responses in order to reduce the response
4149      time and network bandwidth consumption on future, equivalent
4150      requests. Any client or server may include a cache, though a cache
4151      cannot be used by a server that is acting as a tunnel.
4152    </t>
4153  </list>
4156  <iref item="cacheable"/>
4157  <x:dfn>cacheable</x:dfn>
4158  <list>
4159    <t>
4160      A response is cacheable if a cache is allowed to store a copy of
4161      the response message for use in answering subsequent requests. The
4162      rules for determining the cacheability of HTTP responses are
4163      defined in &caching;. Even if a resource is cacheable, there may
4164      be additional constraints on whether a cache can use the cached
4165      copy for a particular request.
4166    </t>
4167  </list>
4170  <iref item="client"/>
4171  <x:dfn>client</x:dfn>
4172  <list>
4173    <t>
4174      A program that establishes connections for the purpose of sending
4175      requests.
4176    </t>
4177  </list>
4180  <iref item="connection"/>
4181  <x:dfn>connection</x:dfn>
4182  <list>
4183    <t>
4184      A transport layer virtual circuit established between two programs
4185      for the purpose of communication.
4186    </t>
4187  </list>
4190  <iref item="content negotiation"/>
4191  <x:dfn>content negotiation</x:dfn>
4192  <list>
4193    <t>
4194      The mechanism for selecting the appropriate representation when
4195      servicing a request, as described in &content.negotiation;. The
4196      representation of entities in any response can be negotiated
4197      (including error responses).
4198    </t>
4199  </list>
4202  <iref item="entity"/>
4203  <x:dfn>entity</x:dfn>
4204  <list>
4205    <t>
4206      The information transferred as the payload of a request or
4207      response. An entity consists of metainformation in the form of
4208      entity-header fields and content in the form of an entity-body, as
4209      described in &entity;.
4210    </t>
4211  </list>
4214  <iref item="gateway"/>
4215  <x:dfn>gateway</x:dfn>
4216  <list>
4217    <t>
4218      A server which acts as an intermediary for some other server.
4219      Unlike a proxy, a gateway receives requests as if it were the
4220      origin server for the requested resource; the requesting client
4221      may not be aware that it is communicating with a gateway.
4222    </t>
4223  </list>
4226  <iref item="inbound"/>
4227  <iref item="outbound"/>
4228  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4229  <list>
4230    <t>
4231      Inbound and outbound refer to the request and response paths for
4232      messages: "inbound" means "traveling toward the origin server",
4233      and "outbound" means "traveling toward the user agent"
4234    </t>
4235  </list>
4238  <iref item="message"/>
4239  <x:dfn>message</x:dfn>
4240  <list>
4241    <t>
4242      The basic unit of HTTP communication, consisting of a structured
4243      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4244      transmitted via the connection.
4245    </t>
4246  </list>
4249  <iref item="origin server"/>
4250  <x:dfn>origin server</x:dfn>
4251  <list>
4252    <t>
4253      The server on which a given resource resides or is to be created.
4254    </t>
4255  </list>
4258  <iref item="proxy"/>
4259  <x:dfn>proxy</x:dfn>
4260  <list>
4261    <t>
4262      An intermediary program which acts as both a server and a client
4263      for the purpose of making requests on behalf of other clients.
4264      Requests are serviced internally or by passing them on, with
4265      possible translation, to other servers. A proxy &MUST; implement
4266      both the client and server requirements of this specification. A
4267      "transparent proxy" is a proxy that does not modify the request or
4268      response beyond what is required for proxy authentication and
4269      identification. A "non-transparent proxy" is a proxy that modifies
4270      the request or response in order to provide some added service to
4271      the user agent, such as group annotation services, media type
4272      transformation, protocol reduction, or anonymity filtering. Except
4273      where either transparent or non-transparent behavior is explicitly
4274      stated, the HTTP proxy requirements apply to both types of
4275      proxies.
4276    </t>
4277  </list>
4280  <iref item="request"/>
4281  <x:dfn>request</x:dfn>
4282  <list>
4283    <t>
4284      An HTTP request message, as defined in <xref target="request"/>.
4285    </t>
4286  </list>
4289  <iref item="resource"/>
4290  <x:dfn>resource</x:dfn>
4291  <list>
4292    <t>
4293      A network data object or service that can be identified by a URI,
4294      as defined in <xref target="uri"/>. Resources may be available in multiple
4295      representations (e.g. multiple languages, data formats, size, and
4296      resolutions) or vary in other ways.
4297    </t>
4298  </list>
4301  <iref item="response"/>
4302  <x:dfn>response</x:dfn>
4303  <list>
4304    <t>
4305      An HTTP response message, as defined in <xref target="response"/>.
4306    </t>
4307  </list>
4310  <iref item="representation"/>
4311  <x:dfn>representation</x:dfn>
4312  <list>
4313    <t>
4314      An entity included with a response that is subject to content
4315      negotiation, as described in &content.negotiation;. There may exist multiple
4316      representations associated with a particular response status.
4317    </t>
4318  </list>
4321  <iref item="server"/>
4322  <x:dfn>server</x:dfn>
4323  <list>
4324    <t>
4325      An application program that accepts connections in order to
4326      service requests by sending back responses. Any given program may
4327      be capable of being both a client and a server; our use of these
4328      terms refers only to the role being performed by the program for a
4329      particular connection, rather than to the program's capabilities
4330      in general. Likewise, any server may act as an origin server,
4331      proxy, gateway, or tunnel, switching behavior based on the nature
4332      of each request.
4333    </t>
4334  </list>
4337  <iref item="tunnel"/>
4338  <x:dfn>tunnel</x:dfn>
4339  <list>
4340    <t>
4341      An intermediary program which is acting as a blind relay between
4342      two connections. Once active, a tunnel is not considered a party
4343      to the HTTP communication, though the tunnel may have been
4344      initiated by an HTTP request. The tunnel ceases to exist when both
4345      ends of the relayed connections are closed.
4346    </t>
4347  </list>
4350  <iref item="upstream"/>
4351  <iref item="downstream"/>
4352  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4353  <list>
4354    <t>
4355      Upstream and downstream describe the flow of a message: all
4356      messages flow from upstream to downstream.
4357    </t>
4358  </list>
4361  <iref item="user agent"/>
4362  <x:dfn>user agent</x:dfn>
4363  <list>
4364    <t>
4365      The client which initiates a request. These are often browsers,
4366      editors, spiders (web-traversing robots), or other end user tools.
4367    </t>
4368  </list>
4371  <iref item="variant"/>
4372  <x:dfn>variant</x:dfn>
4373  <list>
4374    <t>
4375      A resource may have one, or more than one, representation(s)
4376      associated with it at any given instant. Each of these
4377      representations is termed a `variant'.  Use of the term `variant'
4378      does not necessarily imply that the resource is subject to content
4379      negotiation.
4380    </t>
4381  </list>
4385<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4387<artwork type="abnf" name="p1-messaging.parsed-abnf">
4388<x:ref>BWS</x:ref> = OWS
4390<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4391<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4392<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4393<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4394 connection-token ] )
4395<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4396<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4398<x:ref>Date</x:ref> = "Date:" OWS Date-v
4399<x:ref>Date-v</x:ref> = HTTP-date
4401<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4403<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4404<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4405<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4406<x:ref>HTTP-message</x:ref> = Request / Response
4407<x:ref>Host</x:ref> = "Host:" OWS Host-v
4408<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4410<x:ref>Method</x:ref> = token
4412<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4414<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4416<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4417<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4418<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4419 entity-header ) CRLF ) CRLF [ message-body ]
4420<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4421<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4422 entity-header ) CRLF ) CRLF [ message-body ]
4424<x:ref>Status-Code</x:ref> = 3DIGIT
4425<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4427<x:ref>TE</x:ref> = "TE:" OWS TE-v
4428<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4429<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4430<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4431<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4432<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4433 transfer-coding ] )
4435<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4436<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4437<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4438<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4440<x:ref>Via</x:ref> = "Via:" OWS Via-v
4441<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4442 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4443 ] )
4445<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4447<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4448<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4449<x:ref>attribute</x:ref> = token
4450<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4452<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4453<x:ref>chunk-data</x:ref> = 1*OCTET
4454<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4455<x:ref>chunk-ext-name</x:ref> = token
4456<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4457<x:ref>chunk-size</x:ref> = 1*HEXDIG
4458<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4459<x:ref>connection-token</x:ref> = token
4460<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4461 / %x2A-5B ; '*'-'['
4462 / %x5D-7E ; ']'-'~'
4463 / obs-text
4465<x:ref>date1</x:ref> = day SP month SP year
4466<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4467<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4468<x:ref>day</x:ref> = 2DIGIT
4469<x:ref>day-name</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4470<x:ref>day-name-l</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4472<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4473<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4475<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4476<x:ref>field-name</x:ref> = token
4477<x:ref>field-value</x:ref> = *( field-content / OWS )
4478<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4480<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4481 / Transfer-Encoding / Upgrade / Via / Warning
4482<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4483 message-body ]
4485<x:ref>hour</x:ref> = 2DIGIT
4486<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4488l-Fri = %x46. ; Friday
4489l-Mon = %x4D.6F.6E.64.61.79 ; Monday
4490l-Sat = %x53. ; Saturday
4491l-Sun = %x53.75.6E.64.61.79 ; Sunday
4492l-Thu = %x54. ; Thursday
4493l-Tue = %x54. ; Tuesday
4494l-Wed = %x57.65.64.6E. ; Wednesday
4495<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4497<x:ref>message-body</x:ref> = entity-body /
4498 &lt;entity-body encoded as per Transfer-Encoding&gt;
4499<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4500<x:ref>minute</x:ref> = 2DIGIT
4501<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4502 / s-Sep / s-Oct / s-Nov / s-Dec
4504<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4505<x:ref>obs-fold</x:ref> = CRLF
4506<x:ref>obs-text</x:ref> = %x80-FF
4508<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4509<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4510<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4511<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4512<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4513<x:ref>product</x:ref> = token [ "/" product-version ]
4514<x:ref>product-version</x:ref> = token
4515<x:ref>protocol-name</x:ref> = token
4516<x:ref>protocol-version</x:ref> = token
4517<x:ref>pseudonym</x:ref> = token
4519<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4520 / %x5D-7E ; ']'-'~'
4521 / obs-text
4522<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4523<x:ref>quoted-pair</x:ref> = "\" quoted-text
4524<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4525<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4526<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4528<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4529<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4530<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4531<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4532<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4533 / authority
4534<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4535<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4536<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4538s-Apr = %x41.70.72 ; Apr
4539s-Aug = %x41.75.67 ; Aug
4540s-Dec = %x44.65.63 ; Dec
4541s-Feb = %x46.65.62 ; Feb
4542s-Fri = %x46.72.69 ; Fri
4543s-Jan = %x4A.61.6E ; Jan
4544s-Jul = %x4A.75.6C ; Jul
4545s-Jun = %x4A.75.6E ; Jun
4546s-Mar = %x4D.61.72 ; Mar
4547s-May = %x4D.61.79 ; May
4548s-Mon = %x4D.6F.6E ; Mon
4549s-Nov = %x4E.6F.76 ; Nov
4550s-Oct = %x4F.63.74 ; Oct
4551s-Sat = %x53.61.74 ; Sat
4552s-Sep = %x53.65.70 ; Sep
4553s-Sun = %x53.75.6E ; Sun
4554s-Thu = %x54.68.75 ; Thu
4555s-Tue = %x54.75.65 ; Tue
4556s-Wed = %x57.65.64 ; Wed
4557<x:ref>second</x:ref> = 2DIGIT
4558<x:ref>start-line</x:ref> = Request-Line / Status-Line
4560<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4561<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4562 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4563<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4564<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4565<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4566<x:ref>token</x:ref> = 1*tchar
4567<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4568<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4569<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4571<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4573<x:ref>value</x:ref> = token / quoted-string
4575<x:ref>year</x:ref> = 4DIGIT
4578<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4579; Chunked-Body defined but not used
4580; Content-Length defined but not used
4581; HTTP-message defined but not used
4582; Host defined but not used
4583; TE defined but not used
4584; URI defined but not used
4585; URI-reference defined but not used
4586; fragment defined but not used
4587; generic-message defined but not used
4588; http-URI defined but not used
4589; partial-URI defined but not used
4592<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4594<section title="Since RFC2616">
4596  Extracted relevant partitions from <xref target="RFC2616"/>.
4600<section title="Since draft-ietf-httpbis-p1-messaging-00">
4602  Closed issues:
4603  <list style="symbols">
4604    <t>
4605      <eref target=""/>:
4606      "HTTP Version should be case sensitive"
4607      (<eref target=""/>)
4608    </t>
4609    <t>
4610      <eref target=""/>:
4611      "'unsafe' characters"
4612      (<eref target=""/>)
4613    </t>
4614    <t>
4615      <eref target=""/>:
4616      "Chunk Size Definition"
4617      (<eref target=""/>)
4618    </t>
4619    <t>
4620      <eref target=""/>:
4621      "Message Length"
4622      (<eref target=""/>)
4623    </t>
4624    <t>
4625      <eref target=""/>:
4626      "Media Type Registrations"
4627      (<eref target=""/>)
4628    </t>
4629    <t>
4630      <eref target=""/>:
4631      "URI includes query"
4632      (<eref target=""/>)
4633    </t>
4634    <t>
4635      <eref target=""/>:
4636      "No close on 1xx responses"
4637      (<eref target=""/>)
4638    </t>
4639    <t>
4640      <eref target=""/>:
4641      "Remove 'identity' token references"
4642      (<eref target=""/>)
4643    </t>
4644    <t>
4645      <eref target=""/>:
4646      "Import query BNF"
4647    </t>
4648    <t>
4649      <eref target=""/>:
4650      "qdtext BNF"
4651    </t>
4652    <t>
4653      <eref target=""/>:
4654      "Normative and Informative references"
4655    </t>
4656    <t>
4657      <eref target=""/>:
4658      "RFC2606 Compliance"
4659    </t>
4660    <t>
4661      <eref target=""/>:
4662      "RFC977 reference"
4663    </t>
4664    <t>
4665      <eref target=""/>:
4666      "RFC1700 references"
4667    </t>
4668    <t>
4669      <eref target=""/>:
4670      "inconsistency in date format explanation"
4671    </t>
4672    <t>
4673      <eref target=""/>:
4674      "Date reference typo"
4675    </t>
4676    <t>
4677      <eref target=""/>:
4678      "Informative references"
4679    </t>
4680    <t>
4681      <eref target=""/>:
4682      "ISO-8859-1 Reference"
4683    </t>
4684    <t>
4685      <eref target=""/>:
4686      "Normative up-to-date references"
4687    </t>
4688  </list>
4691  Other changes:
4692  <list style="symbols">
4693    <t>
4694      Update media type registrations to use RFC4288 template.
4695    </t>
4696    <t>
4697      Use names of RFC4234 core rules DQUOTE and WSP,
4698      fix broken ABNF for chunk-data
4699      (work in progress on <eref target=""/>)
4700    </t>
4701  </list>
4705<section title="Since draft-ietf-httpbis-p1-messaging-01">
4707  Closed issues:
4708  <list style="symbols">
4709    <t>
4710      <eref target=""/>:
4711      "Bodies on GET (and other) requests"
4712    </t>
4713    <t>
4714      <eref target=""/>:
4715      "Updating to RFC4288"
4716    </t>
4717    <t>
4718      <eref target=""/>:
4719      "Status Code and Reason Phrase"
4720    </t>
4721    <t>
4722      <eref target=""/>:
4723      "rel_path not used"
4724    </t>
4725  </list>
4728  Ongoing work on ABNF conversion (<eref target=""/>):
4729  <list style="symbols">
4730    <t>
4731      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4732      "trailer-part").
4733    </t>
4734    <t>
4735      Avoid underscore character in rule names ("http_URL" ->
4736      "http-URL", "abs_path" -> "path-absolute").
4737    </t>
4738    <t>
4739      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4740      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4741      have to be updated when switching over to RFC3986.
4742    </t>
4743    <t>
4744      Synchronize core rules with RFC5234.
4745    </t>
4746    <t>
4747      Get rid of prose rules that span multiple lines.
4748    </t>
4749    <t>
4750      Get rid of unused rules LOALPHA and UPALPHA.
4751    </t>
4752    <t>
4753      Move "Product Tokens" section (back) into Part 1, as "token" is used
4754      in the definition of the Upgrade header.
4755    </t>
4756    <t>
4757      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4758    </t>
4759    <t>
4760      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4761    </t>
4762  </list>
4766<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4768  Closed issues:
4769  <list style="symbols">
4770    <t>
4771      <eref target=""/>:
4772      "HTTP-date vs. rfc1123-date"
4773    </t>
4774    <t>
4775      <eref target=""/>:
4776      "WS in quoted-pair"
4777    </t>
4778  </list>
4781  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4782  <list style="symbols">
4783    <t>
4784      Reference RFC 3984, and update header registrations for headers defined
4785      in this document.
4786    </t>
4787  </list>
4790  Ongoing work on ABNF conversion (<eref target=""/>):
4791  <list style="symbols">
4792    <t>
4793      Replace string literals when the string really is case-sensitive (HTTP-Version).
4794    </t>
4795  </list>
4799<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4801  Closed issues:
4802  <list style="symbols">
4803    <t>
4804      <eref target=""/>:
4805      "Connection closing"
4806    </t>
4807    <t>
4808      <eref target=""/>:
4809      "Move registrations and registry information to IANA Considerations"
4810    </t>
4811    <t>
4812      <eref target=""/>:
4813      "need new URL for PAD1995 reference"
4814    </t>
4815    <t>
4816      <eref target=""/>:
4817      "IANA Considerations: update HTTP URI scheme registration"
4818    </t>
4819    <t>
4820      <eref target=""/>:
4821      "Cite HTTPS URI scheme definition"
4822    </t>
4823    <t>
4824      <eref target=""/>:
4825      "List-type headers vs Set-Cookie"
4826    </t>
4827  </list>
4830  Ongoing work on ABNF conversion (<eref target=""/>):
4831  <list style="symbols">
4832    <t>
4833      Replace string literals when the string really is case-sensitive (HTTP-Date).
4834    </t>
4835    <t>
4836      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4837    </t>
4838  </list>
4842<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4844  Closed issues:
4845  <list style="symbols">
4846    <t>
4847      <eref target=""/>:
4848      "Out-of-date reference for URIs"
4849    </t>
4850    <t>
4851      <eref target=""/>:
4852      "RFC 2822 is updated by RFC 5322"
4853    </t>
4854  </list>
4857  Ongoing work on ABNF conversion (<eref target=""/>):
4858  <list style="symbols">
4859    <t>
4860      Use "/" instead of "|" for alternatives.
4861    </t>
4862    <t>
4863      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4864    </t>
4865    <t>
4866      Only reference RFC 5234's core rules.
4867    </t>
4868    <t>
4869      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4870      whitespace ("OWS") and required whitespace ("RWS").
4871    </t>
4872    <t>
4873      Rewrite ABNFs to spell out whitespace rules, factor out
4874      header value format definitions.
4875    </t>
4876  </list>
4880<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4882  Closed issues:
4883  <list style="symbols">
4884    <t>
4885      <eref target=""/>:
4886      "Header LWS"
4887    </t>
4888    <t>
4889      <eref target=""/>:
4890      "Sort 1.3 Terminology"
4891    </t>
4892    <t>
4893      <eref target=""/>:
4894      "RFC2047 encoded words"
4895    </t>
4896    <t>
4897      <eref target=""/>:
4898      "Character Encodings in TEXT"
4899    </t>
4900    <t>
4901      <eref target=""/>:
4902      "Line Folding"
4903    </t>
4904    <t>
4905      <eref target=""/>:
4906      "OPTIONS * and proxies"
4907    </t>
4908    <t>
4909      <eref target=""/>:
4910      "Reason-Phrase BNF"
4911    </t>
4912    <t>
4913      <eref target=""/>:
4914      "Use of TEXT"
4915    </t>
4916    <t>
4917      <eref target=""/>:
4918      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4919    </t>
4920    <t>
4921      <eref target=""/>:
4922      "RFC822 reference left in discussion of date formats"
4923    </t>
4924  </list>
4927  Final work on ABNF conversion (<eref target=""/>):
4928  <list style="symbols">
4929    <t>
4930      Rewrite definition of list rules, deprecate empty list elements.
4931    </t>
4932    <t>
4933      Add appendix containing collected and expanded ABNF.
4934    </t>
4935  </list>
4938  Other changes:
4939  <list style="symbols">
4940    <t>
4941      Rewrite introduction; add mostly new Architecture Section.
4942    </t>
4943    <t>
4944      Move definition of quality values from Part 3 into Part 1;
4945      make TE request header grammar independent of accept-params (defined in Part 3).
4946    </t>
4947  </list>
4951<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4953  Closed issues:
4954  <list style="symbols">
4955    <t>
4956      <eref target=""/>:
4957      "base for numeric protocol elements"
4958    </t>
4959    <t>
4960      <eref target=""/>:
4961      "comment ABNF"
4962    </t>
4963  </list>
4966  Partly resolved issues:
4967  <list style="symbols">
4968    <t>
4969      <eref target=""/>:
4970      "editorial improvements around HTTP-date"
4971    </t>
4972  </list>
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