source: draft-ietf-httpbis/latest/p1-messaging.xml @ 650

Last change on this file since 650 was 650, checked in by julian.reschke@…, 13 years ago

Add IANA considerations sub section for transfer codings (see #148)

  • Property svn:eol-style set to native
File size: 217.0 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 "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' 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 status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
52     xmlns:x=''>
55  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email></email>
70      <uri></uri>
71    </address>
72  </author>
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email></email>
85      <uri></uri>
86    </address>
87  </author>
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email></email>
101    </address>
102  </author>
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email></email>
115    </address>
116  </author>
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email></email>
129      <uri></uri>
130    </address>
131  </author>
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email></email>
143    </address>
144  </author>
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email></email>
159      <uri></uri>
160    </address>
161  </author>
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email></email>
175      <uri></uri>
176    </address>
177  </author>
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email></email>
190      <uri></uri>
191    </address>
192  </author>
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list ( The current issues list is
216    at <eref target=""/>
217    and related documents (including fancy diffs) can be found at
218    <eref target=""/>.
219  </t>
220  <t>
221    The changes in this draft are summarized in <xref target="changes.since.07"/>.
222  </t>
226<section title="Introduction" anchor="introduction">
228   The Hypertext Transfer Protocol (HTTP) is an application-level
229   request/response protocol that uses extensible semantics and MIME-like
230   message payloads for flexible interaction with network-based hypertext
231   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
232   standard <xref target="RFC3986"/> to indicate request targets and
233   relationships between resources.
234   Messages are passed in a format similar to that used by Internet mail
235   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
236   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
237   between HTTP and MIME messages).
240   HTTP is a generic interface protocol for information systems. It is
241   designed to hide the details of how a service is implemented by presenting
242   a uniform interface to clients that is independent of the types of
243   resources provided. Likewise, servers do not need to be aware of each
244   client's purpose: an HTTP request can be considered in isolation rather
245   than being associated with a specific type of client or a predetermined
246   sequence of application steps. The result is a protocol that can be used
247   effectively in many different contexts and for which implementations can
248   evolve independently over time.
251   HTTP is also designed for use as a generic protocol for translating
252   communication to and from other Internet information systems.
253   HTTP proxies and gateways provide access to alternative information
254   services by translating their diverse protocols into a hypertext
255   format that can be viewed and manipulated by clients in the same way
256   as HTTP services.
259   One consequence of HTTP flexibility is that the protocol cannot be
260   defined in terms of what occurs behind the interface. Instead, we
261   are limited to defining the syntax of communication, the intent
262   of received communication, and the expected behavior of recipients.
263   If the communication is considered in isolation, then successful
264   actions should be reflected in corresponding changes to the
265   observable interface provided by servers. However, since multiple
266   clients may act in parallel and perhaps at cross-purposes, we
267   cannot require that such changes be observable beyond the scope
268   of a single response.
271   This document is Part 1 of the seven-part specification of HTTP,
272   defining the protocol referred to as "HTTP/1.1" and obsoleting
273   <xref target="RFC2616"/>.
274   Part 1 describes the architectural elements that are used or
275   referred to in HTTP, defines the "http" and "https" URI schemes,
276   describes overall network operation and connection management,
277   and defines HTTP message framing and forwarding requirements.
278   Our goal is to define all of the mechanisms necessary for HTTP message
279   handling that are independent of message semantics, thereby defining the
280   complete set of requirements for message parsers and
281   message-forwarding intermediaries.
284<section title="Requirements" anchor="intro.requirements">
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
291   An implementation is not compliant if it fails to satisfy one or more
292   of the &MUST; or &REQUIRED; level requirements for the protocols it
293   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
294   level and all the &SHOULD; level requirements for its protocols is said
295   to be "unconditionally compliant"; one that satisfies all the &MUST;
296   level requirements but not all the &SHOULD; level requirements for its
297   protocols is said to be "conditionally compliant."
301<section title="Syntax Notation" anchor="notation">
302<iref primary="true" item="Grammar" subitem="ALPHA"/>
303<iref primary="true" item="Grammar" subitem="CR"/>
304<iref primary="true" item="Grammar" subitem="CRLF"/>
305<iref primary="true" item="Grammar" subitem="CTL"/>
306<iref primary="true" item="Grammar" subitem="DIGIT"/>
307<iref primary="true" item="Grammar" subitem="DQUOTE"/>
308<iref primary="true" item="Grammar" subitem="HEXDIG"/>
309<iref primary="true" item="Grammar" subitem="LF"/>
310<iref primary="true" item="Grammar" subitem="OCTET"/>
311<iref primary="true" item="Grammar" subitem="SP"/>
312<iref primary="true" item="Grammar" subitem="VCHAR"/>
313<iref primary="true" item="Grammar" subitem="WSP"/>
315   This specification uses the Augmented Backus-Naur Form (ABNF) notation
316   of <xref target="RFC5234"/>.
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
374  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
421<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"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429                 ; see <xref target="header.fields"/>
431<t anchor="rule.token.separators">
432  <x:anchor-alias value="tchar"/>
433  <x:anchor-alias value="token"/>
434   Many HTTP/1.1 header field values consist of words separated by whitespace
435   or special characters. These special characters &MUST; be in a quoted
436   string to be used within a parameter value (as defined in
437   <xref target="transfer.codings"/>).
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
440  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
441                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
442                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
444  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
446<t anchor="rule.quoted-string">
447  <x:anchor-alias value="quoted-string"/>
448  <x:anchor-alias value="qdtext"/>
449  <x:anchor-alias value="obs-text"/>
450   A string of text is parsed as a single word if it is quoted using
451   double-quote marks.
453<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"/>
454  <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>
455  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
456                 ; <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>
457  <x:ref>obs-text</x:ref>       = %x80-FF
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
482  The ABNF rules below are defined in other parts:
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
502<section title="HTTP architecture" anchor="architecture">
504   HTTP was created for the World Wide Web architecture
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
510<section title="Client/Server Operation" anchor="operation">
511<iref item="client"/>
512<iref item="server"/>
513<iref item="connection"/>
515   HTTP is a request/response protocol that operates by exchanging messages
516   across a reliable transport or session-layer connection. An HTTP client
517   is a program that establishes a connection to a server for the purpose
518   of sending one or more HTTP requests.  An HTTP server is a program that
519   accepts connections in order to service HTTP requests by sending HTTP
520   responses.
522<iref item="user agent"/>
523<iref item="origin server"/>
525   Note that the terms "client" and "server" refer only to the roles that
526   these programs perform for a particular connection.  The same program
527   may act as a client on some connections and a server on others.  We use
528   the term "user agent" to refer to the program that initiates a request,
529   such as a WWW browser, editor, or spider (web-traversing robot), and
530   the term "origin server" to refer to the program that can originate
531   authoritative responses to a request.
534   Most HTTP communication consists of a retrieval request (GET) for
535   a representation of some resource identified by a URI.  In the
536   simplest case, this may be accomplished via a single connection (v)
537   between the user agent (UA) and the origin server (O).
539<figure><artwork type="drawing">
540       request chain ------------------------&gt;
541    UA -------------------v------------------- O
542       &lt;----------------------- response chain
544<iref item="message"/>
545<iref item="request"/>
546<iref item="response"/>
548   A client sends an HTTP request to the server in the form of a request
549   message (<xref target="request"/>), beginning with a method, URI, and
550   protocol version, followed by MIME-like header fields containing
551   request modifiers, client information, and payload metadata, an empty
552   line, and finally the payload body (if any).
553   The server response (<xref target="response"/>) begins with a status line,
554   including the protocol version, a success or error code, and textual
555   reason phrase, followed by MIME-like header fields containing server
556   information, resource metadata, payload metadata, an empty line, and
557   finally the payload body (if any).
560   The following example illustrates a typical message exchange for a
561   GET request on the URI "":
564client request:
565</preamble><artwork  type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
566GET /hello.txt HTTP/1.1
567User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
569Accept: */*
573server response:
574</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
575HTTP/1.1 200 OK
576Date: Mon, 27 Jul 2009 12:28:53 GMT
577Server: Apache
578Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
579ETag: "34aa387-d-1568eb00"
580Accept-Ranges: bytes
581Content-Length: <x:length-of target="exbody"/>
582Vary: Accept-Encoding
583Content-Type: text/plain
585<x:span anchor="exbody">Hello World!
589<section title="Intermediaries" anchor="intermediaries">
591   A more complicated situation occurs when one or more intermediaries
592   are present in the request/response chain. There are three common
593   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
594   a single intermediary may act as an origin server, proxy, gateway,
595   or tunnel, switching behavior based on the nature of each request.
597<figure><artwork type="drawing">
598       request chain --------------------------------------&gt;
599    UA -----v----- A -----v----- B -----v----- C -----v----- O
600       &lt;------------------------------------- response chain
603   The figure above shows three intermediaries (A, B, and C) between the
604   user agent and origin server. A request or response message that
605   travels the whole chain will pass through four separate connections.
606   Some HTTP communication options
607   may apply only to the connection with the nearest, non-tunnel
608   neighbor, only to the end-points of the chain, or to all connections
609   along the chain. Although the diagram is linear, each participant may
610   be engaged in multiple, simultaneous communications. For example, B
611   may be receiving requests from many clients other than A, and/or
612   forwarding requests to servers other than C, at the same time that it
613   is handling A's request.
616<iref item="upstream"/><iref item="downstream"/>
617<iref item="inbound"/><iref item="outbound"/>
618   We use the terms "upstream" and "downstream" to describe various
619   requirements in relation to the directional flow of a message:
620   all messages flow from upstream to downstream.
621   Likewise, we use the terms "inbound" and "outbound" to refer to
622   directions in relation to the request path: "inbound" means toward
623   the origin server and "outbound" means toward the user agent.
625<t><iref item="proxy"/>
626   A proxy is a message forwarding agent that is selected by the
627   client, usually via local configuration rules, to receive requests
628   for some type(s) of absolute URI and attempt to satisfy those
629   requests via translation through the HTTP interface.  Some translations
630   are minimal, such as for proxy requests for "http" URIs, whereas
631   other requests may require translation to and from entirely different
632   application-layer protocols. Proxies are often used to group an
633   organization's HTTP requests through a common intermediary for the
634   sake of security, annotation services, or shared caching.
636<t><iref item="gateway"/><iref item="reverse proxy"/>
637   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
638   as a layer above some other server(s) and translates the received
639   requests to the underlying server's protocol.  Gateways are often
640   used for load balancing or partitioning HTTP services across
641   multiple machines.
642   Unlike a proxy, a gateway receives requests as if it were the
643   origin server for the requested resource; the requesting client
644   will not be aware that it is communicating with a gateway.
645   A gateway communicates with the client as if the gateway is the
646   origin server and thus is subject to all of the requirements on
647   origin servers for that connection.  A gateway communicates
648   with inbound servers using any protocol it desires, including
649   private extensions to HTTP that are outside the scope of this
650   specification.
652<t><iref item="tunnel"/>
653   A tunnel acts as a blind relay between two connections
654   without changing the messages. Once active, a tunnel is not
655   considered a party to the HTTP communication, though the tunnel may
656   have been initiated by an HTTP request. A tunnel ceases to exist when
657   both ends of the relayed connection are closed. Tunnels are used to
658   extend a virtual connection through an intermediary, such as when
659   transport-layer security is used to establish private communication
660   through a shared firewall proxy.
664<section title="Caches" anchor="caches">
665<iref item="cache"/>
667   Any party to HTTP communication that is not acting as a tunnel may
668   employ an internal cache for handling requests.
669   A cache is a local store of previous response messages and the
670   subsystem that controls its message storage, retrieval, and deletion.
671   A cache stores cacheable responses in order to reduce the response
672   time and network bandwidth consumption on future, equivalent
673   requests. Any client or server may include a cache, though a cache
674   cannot be used by a server while it is acting as a tunnel.
677   The effect of a cache is that the request/response chain is shortened
678   if one of the participants along the chain has a cached response
679   applicable to that request. The following illustrates the resulting
680   chain if B has a cached copy of an earlier response from O (via C)
681   for a request which has not been cached by UA or A.
683<figure><artwork type="drawing">
684          request chain ----------&gt;
685       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
686          &lt;--------- response chain
688<t><iref item="cacheable"/>
689   A response is cacheable if a cache is allowed to store a copy of
690   the response message for use in answering subsequent requests.
691   Even when a response is cacheable, there may be additional
692   constraints placed by the client or by the origin server on when
693   that cached response can be used for a particular request. HTTP
694   requirements for cache behavior and cacheable responses are
695   defined in &caching-overview;. 
698   There are a wide variety of architectures and configurations
699   of caches and proxies deployed across the World Wide Web and
700   inside large organizations. These systems include national hierarchies
701   of proxy caches to save transoceanic bandwidth, systems that
702   broadcast or multicast cache entries, organizations that distribute
703   subsets of cached data via optical media, and so on.
707<section title="Transport Independence" anchor="transport-independence">
709  HTTP systems are used in a wide variety of environments, from
710  corporate intranets with high-bandwidth links to long-distance
711  communication over low-power radio links and intermittent connectivity.
714   HTTP communication usually takes place over TCP/IP connections. The
715   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
716   not preclude HTTP from being implemented on top of any other protocol
717   on the Internet, or on other networks. HTTP only presumes a reliable
718   transport; any protocol that provides such guarantees can be used;
719   the mapping of the HTTP/1.1 request and response structures onto the
720   transport data units of the protocol in question is outside the scope
721   of this specification.
724   In HTTP/1.0, most implementations used a new connection for each
725   request/response exchange. In HTTP/1.1, a connection may be used for
726   one or more request/response exchanges, although connections may be
727   closed for a variety of reasons (see <xref target="persistent.connections"/>).
731<section title="HTTP Version" anchor="http.version">
732  <x:anchor-alias value="HTTP-Version"/>
733  <x:anchor-alias value="HTTP-Prot-Name"/>
735   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
736   of the protocol. The protocol versioning policy is intended to allow
737   the sender to indicate the format of a message and its capacity for
738   understanding further HTTP communication, rather than the features
739   obtained via that communication. No change is made to the version
740   number for the addition of message components which do not affect
741   communication behavior or which only add to extensible field values.
742   The &lt;minor&gt; number is incremented when the changes made to the
743   protocol add features which do not change the general message parsing
744   algorithm, but which may add to the message semantics and imply
745   additional capabilities of the sender. The &lt;major&gt; number is
746   incremented when the format of a message within the protocol is
747   changed. See <xref target="RFC2145"/> for a fuller explanation.
750   The version of an HTTP message is indicated by an HTTP-Version field
751   in the first line of the message. HTTP-Version is case-sensitive.
753<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
754  <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>
755  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
758   Note that the major and minor numbers &MUST; be treated as separate
759   integers and that each &MAY; be incremented higher than a single digit.
760   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
761   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
762   &MUST-NOT; be sent.
765   An application that sends a request or response message that includes
766   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
767   with this specification. Applications that are at least conditionally
768   compliant with this specification &SHOULD; use an HTTP-Version of
769   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
770   not compatible with HTTP/1.0. For more details on when to send
771   specific HTTP-Version values, see <xref target="RFC2145"/>.
774   The HTTP version of an application is the highest HTTP version for
775   which the application is at least conditionally compliant.
778   Proxy and gateway applications need to be careful when forwarding
779   messages in protocol versions different from that of the application.
780   Since the protocol version indicates the protocol capability of the
781   sender, a proxy/gateway &MUST-NOT; send a message with a version
782   indicator which is greater than its actual version. If a higher
783   version request is received, the proxy/gateway &MUST; either downgrade
784   the request version, or respond with an error, or switch to tunnel
785   behavior.
788   Due to interoperability problems with HTTP/1.0 proxies discovered
789   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
790   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
791   they support. The proxy/gateway's response to that request &MUST; be in
792   the same major version as the request.
795  <t>
796    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
797    of header fields required or forbidden by the versions involved.
798  </t>
802<section title="Uniform Resource Identifiers" anchor="uri">
803<iref primary="true" item="resource"/>
805   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
806   throughout HTTP as the means for identifying resources. URI references
807   are used to target requests, indicate redirects, and define relationships.
808   HTTP does not limit what a resource may be; it merely defines an interface
809   that can be used to interact with a resource via HTTP. More information on
810   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
812  <x:anchor-alias value="URI"/>
813  <x:anchor-alias value="URI-reference"/>
814  <x:anchor-alias value="absolute-URI"/>
815  <x:anchor-alias value="relative-part"/>
816  <x:anchor-alias value="authority"/>
817  <x:anchor-alias value="path-abempty"/>
818  <x:anchor-alias value="path-absolute"/>
819  <x:anchor-alias value="port"/>
820  <x:anchor-alias value="query"/>
821  <x:anchor-alias value="uri-host"/>
822  <x:anchor-alias value="partial-URI"/>
824   This specification adopts the definitions of "URI-reference",
825   "absolute-URI", "relative-part", "port", "host",
826   "path-abempty", "path-absolute", "query", and "authority" from
827   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
828   protocol elements that allow a relative URI without a fragment.
830<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"/>
831  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
832  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
833  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
834  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
835  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
836  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
837  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
838  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
839  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
840  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
842  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
845   Each protocol element in HTTP that allows a URI reference will indicate in
846   its ABNF production whether the element allows only a URI in absolute form
847   (absolute-URI), any relative reference (relative-ref), or some other subset
848   of the URI-reference grammar. Unless otherwise indicated, URI references
849   are parsed relative to the request target (the default base URI for both
850   the request and its corresponding response).
853<section title="http URI scheme" anchor="http.uri">
854  <x:anchor-alias value="http-URI"/>
855  <iref item="http URI scheme" primary="true"/>
856  <iref item="URI scheme" subitem="http" primary="true"/>
858   The "http" URI scheme is hereby defined for the purpose of minting
859   identifiers according to their association with the hierarchical
860   namespace governed by a potential HTTP origin server listening for
861   TCP connections on a given port.
862   The HTTP server is identified via the generic syntax's
863   <x:ref>authority</x:ref> component, which includes a host
864   identifier and optional TCP port, and the remainder of the URI is
865   considered to be identifying data corresponding to a resource for
866   which that server might provide an HTTP interface.
868<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
869  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
872   The host identifier within an <x:ref>authority</x:ref> component is
873   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
874   provided as an IP literal or IPv4 address, then the HTTP server is any
875   listener on the indicated TCP port at that IP address. If host is a
876   registered name, then that name is considered an indirect identifier
877   and the recipient might use a name resolution service, such as DNS,
878   to find the address of a listener for that host.
879   The host &MUST-NOT; be empty; if an "http" URI is received with an
880   empty host, then it &MUST; be rejected as invalid.
881   If the port subcomponent is empty or not given, then TCP port 80 is
882   assumed (the default reserved port for WWW services).
885   Regardless of the form of host identifier, access to that host is not
886   implied by the mere presence of its name or address. The host may or may
887   not exist and, even when it does exist, may or may not be running an
888   HTTP server or listening to the indicated port. The "http" URI scheme
889   makes use of the delegated nature of Internet names and addresses to
890   establish a naming authority (whatever entity has the ability to place
891   an HTTP server at that Internet name or address) and allows that
892   authority to determine which names are valid and how they might be used.
895   When an "http" URI is used within a context that calls for access to the
896   indicated resource, a client &MAY; attempt access by resolving
897   the host to an IP address, establishing a TCP connection to that address
898   on the indicated port, and sending an HTTP request message to the server
899   containing the URI's identifying data as described in <xref target="request"/>.
900   If the server responds to that request with a non-interim HTTP response
901   message, as described in <xref target="response"/>, then that response
902   is considered an authoritative answer to the client's request.
905   Although HTTP is independent of the transport protocol, the "http"
906   scheme is specific to TCP-based services because the name delegation
907   process depends on TCP for establishing authority.
908   An HTTP service based on some other underlying connection protocol
909   would presumably be identified using a different URI scheme, just as
910   the "https" scheme (below) is used for servers that require an SSL/TLS
911   transport layer on a connection. Other protocols may also be used to
912   provide access to "http" identified resources --- it is only the
913   authoritative interface used for mapping the namespace that is
914   specific to TCP.
918<section title="https URI scheme" anchor="https.uri">
919   <x:anchor-alias value="https-URI"/>
920   <iref item="https URI scheme"/>
921   <iref item="URI scheme" subitem="https"/>
923   The "https" URI scheme is hereby defined for the purpose of minting
924   identifiers according to their association with the hierarchical
925   namespace governed by a potential HTTP origin server listening for
926   SSL/TLS-secured connections on a given TCP port.
927   The host and port are determined in the same way
928   as for the "http" scheme, except that a default TCP port of 443
929   is assumed if the port subcomponent is empty or not given.
931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
932  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
935   The primary difference between the "http" and "https" schemes is
936   that interaction with the latter is required to be secured for
937   privacy through the use of strong encryption. The URI cannot be
938   sent in a request until the connection is secure. Likewise, the
939   default for caching is that each response that would be considered
940   "public" under the "http" scheme is instead treated as "private"
941   and thus not eligible for shared caching.
944   The process for authoritative access to an "https" identified
945   resource is defined in <xref target="RFC2818"/>.
949<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
951   Since the "http" and "https" schemes conform to the URI generic syntax,
952   such URIs are normalized and compared according to the algorithm defined
953   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
954   described above for each scheme.
957   If the port is equal to the default port for a scheme, the normal
958   form is to elide the port subcomponent. Likewise, an empty path
959   component is equivalent to an absolute path of "/", so the normal
960   form is to provide a path of "/" instead. The scheme and host
961   are case-insensitive and normally provided in lowercase; all
962   other components are compared in a case-sensitive manner.
963   Characters other than those in the "reserved" set are equivalent
964   to their percent-encoded octets (see <xref target="RFC3986"
965   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
968   For example, the following three URIs are equivalent:
970<figure><artwork type="example">
976   <cref>[[This paragraph does not belong here. --Roy]]</cref>
977   If path-abempty is the empty string (i.e., there is no slash "/"
978   path separator following the authority), then the "http" URI
979   &MUST; be given as "/" when
980   used as a request-target (<xref target="request-target"/>). If a proxy
981   receives a host name which is not a fully qualified domain name, it
982   &MAY; add its domain to the host name it received. If a proxy receives
983   a fully qualified domain name, the proxy &MUST-NOT; change the host
984   name.
988<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
990   <cref>TBS: describe why aliases like webcal are harmful.</cref>
995<section title="Use of HTTP for proxy communication" anchor="http.proxy">
997   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
1000<section title="Interception of HTTP for access control" anchor="http.intercept">
1002   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
1005<section title="Use of HTTP by other protocols" anchor="http.others">
1007   <cref>TBD: Profiles of HTTP defined by other protocol.
1008   Extensions of HTTP like WebDAV.</cref>
1011<section title="Use of HTTP by media type specification" anchor="">
1013   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
1018<section title="HTTP Message" anchor="http.message">
1019<x:anchor-alias value="generic-message"/>
1020<x:anchor-alias value="message.types"/>
1021<x:anchor-alias value="HTTP-message"/>
1022<x:anchor-alias value="start-line"/>
1023<iref item="header section"/>
1024<iref item="headers"/>
1025<iref item="header field"/>
1027   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1028   characters in a format similar to the Internet Message Format
1029   <xref target="RFC5322"/>: zero or more header fields (collectively
1030   referred to as the "headers" or the "header section"), an empty line
1031   indicating the end of the header section, and an optional message-body.
1034   An HTTP message can either be a request from client to server or a
1035   response from server to client.  Syntactically, the two types of message
1036   differ only in the start-line, which is either a Request-Line (for requests)
1037   or a Status-Line (for responses), and in the algorithm for determining
1038   the length of the message-body (<xref target="message.length"/>).
1039   In theory, a client could receive requests and a server could receive
1040   responses, distinguishing them by their different start-line formats,
1041   but in practice servers are implemented to only expect a request
1042   (a response is interpreted as an unknown or invalid request method)
1043   and clients are implemented to only expect a response.
1045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1046  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1047                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1048                    <x:ref>CRLF</x:ref>
1049                    [ <x:ref>message-body</x:ref> ]
1050  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1053   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1054   header field. The presence of whitespace might be an attempt to trick a
1055   noncompliant implementation of HTTP into ignoring that field or processing
1056   the next line as a new request, either of which may result in security
1057   issues when implementations within the request chain interpret the
1058   same message differently. HTTP/1.1 servers &MUST; reject such a message
1059   with a 400 (Bad Request) response.
1062<section title="Message Parsing Robustness" anchor="message.robustness">
1064   In the interest of robustness, servers &SHOULD; ignore at least one
1065   empty line received where a Request-Line is expected. In other words, if
1066   the server is reading the protocol stream at the beginning of a
1067   message and receives a CRLF first, it should ignore the CRLF.
1070   Some old HTTP/1.0 client implementations generate an extra CRLF
1071   after a POST request as a lame workaround for some early server
1072   applications that failed to read message-body content that was
1073   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1074   preface or follow a request with an extra CRLF.  If terminating
1075   the request message-body with a line-ending is desired, then the
1076   client &MUST; include the terminating CRLF octets as part of the
1077   message-body length.
1080   The normal procedure for parsing an HTTP message is to read the
1081   start-line into a structure, read each header field into a hash
1082   table by field name until the empty line, and then use the parsed
1083   data to determine if a message-body is expected.  If a message-body
1084   has been indicated, then it is read as a stream until an amount
1085   of OCTETs equal to the message-length is read or the connection
1086   is closed.  Care must be taken to parse an HTTP message as a sequence
1087   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1088   to parse HTTP as a stream of Unicode characters in a character encoding
1089   like UTF-16 may introduce security flaws due to the differing ways
1090   that such parsers interpret invalid characters.
1094<section title="Header Fields" anchor="header.fields">
1095  <x:anchor-alias value="header-field"/>
1096  <x:anchor-alias value="field-content"/>
1097  <x:anchor-alias value="field-name"/>
1098  <x:anchor-alias value="field-value"/>
1099  <x:anchor-alias value="OWS"/>
1101   Each HTTP header field consists of a case-insensitive field name
1102   followed by a colon (":"), optional whitespace, and the field value.
1104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1105  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1106  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1107  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1108  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1111   No whitespace is allowed between the header field name and colon. For
1112   security reasons, any request message received containing such whitespace
1113   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1114   &MUST; remove any such whitespace from a response message before
1115   forwarding the message downstream.
1118   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1119   preferred. The field value does not include any leading or trailing white
1120   space: OWS occurring before the first non-whitespace character of the
1121   field value or after the last non-whitespace character of the field value
1122   is ignored and &SHOULD; be removed without changing the meaning of the header
1123   field.
1126   The order in which header fields with differing field names are
1127   received is not significant. However, it is "good practice" to send
1128   header fields that contain control data first, such as Host on
1129   requests and Date on responses, so that implementations can decide
1130   when not to handle a message as early as possible.  A server &MUST;
1131   wait until the entire header section is received before interpreting
1132   a request message, since later header fields might include conditionals,
1133   authentication credentials, or deliberately misleading duplicate
1134   header fields that would impact request processing.
1137   Multiple header fields with the same field name &MAY; be
1138   sent in a message if and only if the entire field value for that
1139   header field is defined as a comma-separated list [i.e., #(values)].
1140   Multiple header fields with the same field name can be combined into
1141   one "field-name: field-value" pair, without changing the semantics of the
1142   message, by appending each subsequent field value to the combined
1143   field value in order, separated by a comma. The order in which
1144   header fields with the same field name are received is therefore
1145   significant to the interpretation of the combined field value;
1146   a proxy &MUST-NOT; change the order of these field values when
1147   forwarding a message.
1150  <t>
1151   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1152   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1153   can occur multiple times, but does not use the list syntax, and thus cannot
1154   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1155   for details.) Also note that the Set-Cookie2 header specified in
1156   <xref target="RFC2965"/> does not share this problem.
1157  </t>
1160   Historically, HTTP header field values could be extended over multiple
1161   lines by preceding each extra line with at least one space or horizontal
1162   tab character (line folding). This specification deprecates such line
1163   folding except within the message/http media type
1164   (<xref target=""/>).
1165   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1166   (i.e., that contain any field-content that matches the obs-fold rule) unless
1167   the message is intended for packaging within the message/http media type.
1168   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1169   obs-fold whitespace with a single SP prior to interpreting the field value
1170   or forwarding the message downstream.
1173   Historically, HTTP has allowed field content with text in the ISO-8859-1
1174   <xref target="ISO-8859-1"/> character encoding and supported other
1175   character sets only through use of <xref target="RFC2047"/> encoding.
1176   In practice, most HTTP header field values use only a subset of the
1177   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1178   header fields &SHOULD; limit their field values to US-ASCII characters.
1179   Recipients &SHOULD; treat other (obs-text) octets in field content as
1180   opaque data.
1182<t anchor="rule.comment">
1183  <x:anchor-alias value="comment"/>
1184  <x:anchor-alias value="ctext"/>
1185   Comments can be included in some HTTP header fields by surrounding
1186   the comment text with parentheses. Comments are only allowed in
1187   fields containing "comment" as part of their field value definition.
1189<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1190  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1191  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1192                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1197<section title="Message Body" anchor="message.body">
1198  <x:anchor-alias value="message-body"/>
1200   The message-body (if any) of an HTTP message is used to carry the
1201   entity-body associated with the request or response. The message-body
1202   differs from the entity-body only when a transfer-coding has been
1203   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1205<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1206  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1207               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1210   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1211   applied by an application to ensure safe and proper transfer of the
1212   message. Transfer-Encoding is a property of the message, not of the
1213   entity, and thus &MAY; be added or removed by any application along the
1214   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1215   when certain transfer-codings may be used.)
1218   The rules for when a message-body is allowed in a message differ for
1219   requests and responses.
1222   The presence of a message-body in a request is signaled by the
1223   inclusion of a Content-Length or Transfer-Encoding header field in
1224   the request's header fields.
1225   When a request message contains both a message-body of non-zero
1226   length and a method that does not define any semantics for that
1227   request message-body, then an origin server &SHOULD; either ignore
1228   the message-body or respond with an appropriate error message
1229   (e.g., 413).  A proxy or gateway, when presented the same request,
1230   &SHOULD; either forward the request inbound with the message-body or
1231   ignore the message-body when determining a response.
1234   For response messages, whether or not a message-body is included with
1235   a message is dependent on both the request method and the response
1236   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1237   &MUST-NOT; include a message-body, even though the presence of entity-header
1238   fields might lead one to believe they do. All 1xx
1239   (informational), 204 (No Content), and 304 (Not Modified) responses
1240   &MUST-NOT; include a message-body. All other responses do include a
1241   message-body, although it &MAY; be of zero length.
1245<section title="Message Length" anchor="message.length">
1247   The transfer-length of a message is the length of the message-body as
1248   it appears in the message; that is, after any transfer-codings have
1249   been applied. When a message-body is included with a message, the
1250   transfer-length of that body is determined by one of the following
1251   (in order of precedence):
1254  <list style="numbers">
1255    <x:lt><t>
1256     Any response message which "&MUST-NOT;" include a message-body (such
1257     as the 1xx, 204, and 304 responses and any response to a HEAD
1258     request) is always terminated by the first empty line after the
1259     header fields, regardless of the entity-header fields present in
1260     the message.
1261    </t></x:lt>
1262    <x:lt><t>
1263     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1264     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1265     is used, the transfer-length is defined by the use of this transfer-coding.
1266     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1267     is not present, the transfer-length is defined by the sender closing the connection.
1268    </t></x:lt>
1269    <x:lt><t>
1270     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1271     value in OCTETs represents both the entity-length and the
1272     transfer-length. The Content-Length header field &MUST-NOT; be sent
1273     if these two lengths are different (i.e., if a Transfer-Encoding
1274     header field is present). If a message is received with both a
1275     Transfer-Encoding header field and a Content-Length header field,
1276     the latter &MUST; be ignored.
1277    </t></x:lt>
1278    <x:lt><t>
1279     If the message uses the media type "multipart/byteranges", and the
1280     transfer-length is not otherwise specified, then this self-delimiting
1281     media type defines the transfer-length. This media type
1282     &MUST-NOT; be used unless the sender knows that the recipient can parse
1283     it; the presence in a request of a Range header with multiple byte-range
1284     specifiers from a 1.1 client implies that the client can parse
1285     multipart/byteranges responses.
1286    <list style="empty"><t>
1287       A range header might be forwarded by a 1.0 proxy that does not
1288       understand multipart/byteranges; in this case the server &MUST;
1289       delimit the message using methods defined in items 1, 3 or 5 of
1290       this section.
1291    </t></list>
1292    </t></x:lt>
1293    <x:lt><t>
1294     By the server closing the connection. (Closing the connection
1295     cannot be used to indicate the end of a request body, since that
1296     would leave no possibility for the server to send back a response.)
1297    </t></x:lt>
1298  </list>
1301   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1302   containing a message-body &MUST; include a valid Content-Length header
1303   field unless the server is known to be HTTP/1.1 compliant. If a
1304   request contains a message-body and a Content-Length is not given,
1305   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1306   determine the length of the message, or with 411 (Length Required) if
1307   it wishes to insist on receiving a valid Content-Length.
1310   All HTTP/1.1 applications that receive entities &MUST; accept the
1311   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1312   to be used for messages when the message length cannot be determined
1313   in advance.
1316   Messages &MUST-NOT; include both a Content-Length header field and a
1317   transfer-coding. If the message does include a
1318   transfer-coding, the Content-Length &MUST; be ignored.
1321   When a Content-Length is given in a message where a message-body is
1322   allowed, its field value &MUST; exactly match the number of OCTETs in
1323   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1324   invalid length is received and detected.
1328<section title="General Header Fields" anchor="general.header.fields">
1329  <x:anchor-alias value="general-header"/>
1331   There are a few header fields which have general applicability for
1332   both request and response messages, but which do not apply to the
1333   entity being transferred. These header fields apply only to the
1334   message being transmitted.
1336<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1337  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1338                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1339                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1340                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1341                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1342                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1343                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1344                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1345                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1348   General-header field names can be extended reliably only in
1349   combination with a change in the protocol version. However, new or
1350   experimental header fields may be given the semantics of general
1351   header fields if all parties in the communication recognize them to
1352   be general-header fields. Unrecognized header fields are treated as
1353   entity-header fields.
1358<section title="Request" anchor="request">
1359  <x:anchor-alias value="Request"/>
1361   A request message from a client to a server includes, within the
1362   first line of that message, the method to be applied to the resource,
1363   the identifier of the resource, and the protocol version in use.
1365<!--                 Host                      ; should be moved here eventually -->
1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1367  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1368                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1369                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1370                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1371                  <x:ref>CRLF</x:ref>
1372                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1375<section title="Request-Line" anchor="request-line">
1376  <x:anchor-alias value="Request-Line"/>
1378   The Request-Line begins with a method token, followed by the
1379   request-target and the protocol version, and ending with CRLF. The
1380   elements are separated by SP characters. No CR or LF is allowed
1381   except in the final CRLF sequence.
1383<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1384  <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>
1387<section title="Method" anchor="method">
1388  <x:anchor-alias value="Method"/>
1390   The Method  token indicates the method to be performed on the
1391   resource identified by the request-target. The method is case-sensitive.
1393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1394  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1398<section title="request-target" anchor="request-target">
1399  <x:anchor-alias value="request-target"/>
1401   The request-target
1402   identifies the resource upon which to apply the request.
1404<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1405  <x:ref>request-target</x:ref> = "*"
1406                 / <x:ref>absolute-URI</x:ref>
1407                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1408                 / <x:ref>authority</x:ref>
1411   The four options for request-target are dependent on the nature of the
1412   request. The asterisk "*" means that the request does not apply to a
1413   particular resource, but to the server itself, and is only allowed
1414   when the method used does not necessarily apply to a resource. One
1415   example would be
1417<figure><artwork type="example">
1418  OPTIONS * HTTP/1.1
1421   The absolute-URI form is &REQUIRED; when the request is being made to a
1422   proxy. The proxy is requested to forward the request or service it
1423   from a valid cache, and return the response. Note that the proxy &MAY;
1424   forward the request on to another proxy or directly to the server
1425   specified by the absolute-URI. In order to avoid request loops, a
1426   proxy &MUST; be able to recognize all of its server names, including
1427   any aliases, local variations, and the numeric IP address. An example
1428   Request-Line would be:
1430<figure><artwork type="example">
1431  GET HTTP/1.1
1434   To allow for transition to absolute-URIs in all requests in future
1435   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1436   form in requests, even though HTTP/1.1 clients will only generate
1437   them in requests to proxies.
1440   The authority form is only used by the CONNECT method (&CONNECT;).
1443   The most common form of request-target is that used to identify a
1444   resource on an origin server or gateway. In this case the absolute
1445   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1446   the request-target, and the network location of the URI (authority) &MUST;
1447   be transmitted in a Host header field. For example, a client wishing
1448   to retrieve the resource above directly from the origin server would
1449   create a TCP connection to port 80 of the host "" and send
1450   the lines:
1452<figure><artwork type="example">
1453  GET /pub/WWW/TheProject.html HTTP/1.1
1454  Host:
1457   followed by the remainder of the Request. Note that the absolute path
1458   cannot be empty; if none is present in the original URI, it &MUST; be
1459   given as "/" (the server root).
1462   If a proxy receives a request without any path in the request-target and
1463   the method specified is capable of supporting the asterisk form of
1464   request-target, then the last proxy on the request chain &MUST; forward the
1465   request with "*" as the final request-target.
1468   For example, the request
1469</preamble><artwork type="example">
1470  OPTIONS HTTP/1.1
1473  would be forwarded by the proxy as
1474</preamble><artwork type="example">
1475  OPTIONS * HTTP/1.1
1476  Host:
1479   after connecting to port 8001 of host "".
1483   The request-target is transmitted in the format specified in
1484   <xref target="http.uri"/>. If the request-target is percent-encoded
1485   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1486   &MUST; decode the request-target in order to
1487   properly interpret the request. Servers &SHOULD; respond to invalid
1488   request-targets with an appropriate status code.
1491   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1492   received request-target when forwarding it to the next inbound server,
1493   except as noted above to replace a null path-absolute with "/".
1496  <t>
1497    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1498    meaning of the request when the origin server is improperly using
1499    a non-reserved URI character for a reserved purpose.  Implementors
1500    should be aware that some pre-HTTP/1.1 proxies have been known to
1501    rewrite the request-target.
1502  </t>
1505   HTTP does not place a pre-defined limit on the length of a request-target.
1506   A server &MUST; be prepared to receive URIs of unbounded length and
1507   respond with the 414 (URI Too Long) status if the received
1508   request-target would be longer than the server wishes to handle
1509   (see &status-414;).
1512   Various ad-hoc limitations on request-target length are found in practice.
1513   It is &RECOMMENDED; that all HTTP senders and recipients support
1514   request-target lengths of 8000 or more OCTETs.
1519<section title="The Resource Identified by a Request" anchor="">
1521   The exact resource identified by an Internet request is determined by
1522   examining both the request-target and the Host header field.
1525   An origin server that does not allow resources to differ by the
1526   requested host &MAY; ignore the Host header field value when
1527   determining the resource identified by an HTTP/1.1 request. (But see
1528   <xref target=""/>
1529   for other requirements on Host support in HTTP/1.1.)
1532   An origin server that does differentiate resources based on the host
1533   requested (sometimes referred to as virtual hosts or vanity host
1534   names) &MUST; use the following rules for determining the requested
1535   resource on an HTTP/1.1 request:
1536  <list style="numbers">
1537    <t>If request-target is an absolute-URI, the host is part of the
1538     request-target. Any Host header field value in the request &MUST; be
1539     ignored.</t>
1540    <t>If the request-target is not an absolute-URI, and the request includes
1541     a Host header field, the host is determined by the Host header
1542     field value.</t>
1543    <t>If the host as determined by rule 1 or 2 is not a valid host on
1544     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1545  </list>
1548   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1549   attempt to use heuristics (e.g., examination of the URI path for
1550   something unique to a particular host) in order to determine what
1551   exact resource is being requested.
1558<section title="Response" anchor="response">
1559  <x:anchor-alias value="Response"/>
1561   After receiving and interpreting a request message, a server responds
1562   with an HTTP response message.
1564<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1565  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1566                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1567                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1568                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1569                  <x:ref>CRLF</x:ref>
1570                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1573<section title="Status-Line" anchor="status-line">
1574  <x:anchor-alias value="Status-Line"/>
1576   The first line of a Response message is the Status-Line, consisting
1577   of the protocol version followed by a numeric status code and its
1578   associated textual phrase, with each element separated by SP
1579   characters. No CR or LF is allowed except in the final CRLF sequence.
1581<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1582  <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>
1585<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1586  <x:anchor-alias value="Reason-Phrase"/>
1587  <x:anchor-alias value="Status-Code"/>
1589   The Status-Code element is a 3-digit integer result code of the
1590   attempt to understand and satisfy the request. These codes are fully
1591   defined in &status-codes;.  The Reason Phrase exists for the sole
1592   purpose of providing a textual description associated with the numeric
1593   status code, out of deference to earlier Internet application protocols
1594   that were more frequently used with interactive text clients.
1595   A client &SHOULD; ignore the content of the Reason Phrase.
1598   The first digit of the Status-Code defines the class of response. The
1599   last two digits do not have any categorization role. There are 5
1600   values for the first digit:
1601  <list style="symbols">
1602    <t>
1603      1xx: Informational - Request received, continuing process
1604    </t>
1605    <t>
1606      2xx: Success - The action was successfully received,
1607        understood, and accepted
1608    </t>
1609    <t>
1610      3xx: Redirection - Further action must be taken in order to
1611        complete the request
1612    </t>
1613    <t>
1614      4xx: Client Error - The request contains bad syntax or cannot
1615        be fulfilled
1616    </t>
1617    <t>
1618      5xx: Server Error - The server failed to fulfill an apparently
1619        valid request
1620    </t>
1621  </list>
1623<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"/>
1624  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1625  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1633<section title="Protocol Parameters" anchor="protocol.parameters">
1635<section title="Date/Time Formats: Full Date" anchor="">
1636  <x:anchor-alias value="HTTP-date"/>
1638   HTTP applications have historically allowed three different formats
1639   for the representation of date/time stamps:
1641<figure><artwork type="example">
1642  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1643  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1644  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1647   The first format is preferred as an Internet standard and represents
1648   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1649   other formats are described here only for
1650   compatibility with obsolete implementations.
1651   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1652   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1653   only generate the RFC 1123 format for representing HTTP-date values
1654   in header fields. See <xref target="tolerant.applications"/> for further information.
1657   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1658   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1659   equal to UTC (Coordinated Universal Time). This is indicated in the
1660   first two formats by the inclusion of "GMT" as the three-letter
1661   abbreviation for time zone, and &MUST; be assumed when reading the
1662   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1663   additional whitespace beyond that specifically included as SP in the
1664   grammar.
1666<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1667  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1669<t anchor="">
1670  <x:anchor-alias value="rfc1123-date"/>
1671  <x:anchor-alias value="time-of-day"/>
1672  <x:anchor-alias value="hour"/>
1673  <x:anchor-alias value="minute"/>
1674  <x:anchor-alias value="second"/>
1675  <x:anchor-alias value="day-name"/>
1676  <x:anchor-alias value="day"/>
1677  <x:anchor-alias value="month"/>
1678  <x:anchor-alias value="year"/>
1679  <x:anchor-alias value="GMT"/>
1680  Preferred format:
1682<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"/>
1683  <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>
1685  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1686               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1687               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1688               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1689               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1690               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1691               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1693  <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>
1694               ; e.g., 02 Jun 1982
1696  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1697  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1698               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1699               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1700               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1701               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1702               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1703               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1704               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1705               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1706               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1707               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1708               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1709  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1711  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1713  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1714                 ; 00:00:00 - 23:59:59
1716  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1717  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1718  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1721  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1722  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1723  same as those defined for the RFC 5322 constructs
1724  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1726<t anchor="">
1727  <x:anchor-alias value="obs-date"/>
1728  <x:anchor-alias value="rfc850-date"/>
1729  <x:anchor-alias value="asctime-date"/>
1730  <x:anchor-alias value="date1"/>
1731  <x:anchor-alias value="date2"/>
1732  <x:anchor-alias value="date3"/>
1733  <x:anchor-alias value="rfc1123-date"/>
1734  <x:anchor-alias value="day-name-l"/>
1735  Obsolete formats:
1737<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1738  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1741  <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>
1742  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1743                 ; day-month-year (e.g., 02-Jun-82)
1745  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1746         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1747         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1748         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1749         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1750         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1751         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1753<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1754  <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>
1755  <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> ))
1756                 ; month day (e.g., Jun  2)
1759  <t>
1760    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1761    accepting date values that may have been sent by non-HTTP
1762    applications, as is sometimes the case when retrieving or posting
1763    messages via proxies/gateways to SMTP or NNTP.
1764  </t>
1767  <t>
1768    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1769    to their usage within the protocol stream. Clients and servers are
1770    not required to use these formats for user presentation, request
1771    logging, etc.
1772  </t>
1776<section title="Transfer Codings" anchor="transfer.codings">
1777  <x:anchor-alias value="transfer-coding"/>
1778  <x:anchor-alias value="transfer-extension"/>
1780   Transfer-coding values are used to indicate an encoding
1781   transformation that has been, can be, or may need to be applied to an
1782   entity-body in order to ensure "safe transport" through the network.
1783   This differs from a content coding in that the transfer-coding is a
1784   property of the message, not of the original entity.
1786<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1787  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
1788  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1790<t anchor="rule.parameter">
1791  <x:anchor-alias value="attribute"/>
1792  <x:anchor-alias value="transfer-parameter"/>
1793  <x:anchor-alias value="value"/>
1794   Parameters are in  the form of attribute/value pairs.
1796<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1797  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1798  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1799  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1802   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1803   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1804   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1807   Whenever a transfer-coding is applied to a message-body, the set of
1808   transfer-codings &MUST; include "chunked", unless the message indicates it
1809   is terminated by closing the connection. When the "chunked" transfer-coding
1810   is used, it &MUST; be the last transfer-coding applied to the
1811   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1812   than once to a message-body. These rules allow the recipient to
1813   determine the transfer-length of the message (<xref target="message.length"/>).
1816   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1817   MIME, which were designed to enable safe transport of binary data over a
1818   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1819   However, safe transport
1820   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1821   the only unsafe characteristic of message-bodies is the difficulty in
1822   determining the exact body length (<xref target="message.length"/>), or the desire to
1823   encrypt data over a shared transport.
1826   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1827   transfer-coding value tokens. Initially, the registry contains the
1828   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1829   "gzip", "compress", and "deflate" (&content-codings;).
1832   New transfer-coding value tokens &SHOULD; be registered in the same way
1833   as new content-coding value tokens (&content-codings;).
1836   A server which receives an entity-body with a transfer-coding it does
1837   not understand &SHOULD; return 501 (Not Implemented), and close the
1838   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1839   client.
1842<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1843  <x:anchor-alias value="chunk"/>
1844  <x:anchor-alias value="Chunked-Body"/>
1845  <x:anchor-alias value="chunk-data"/>
1846  <x:anchor-alias value="chunk-ext"/>
1847  <x:anchor-alias value="chunk-ext-name"/>
1848  <x:anchor-alias value="chunk-ext-val"/>
1849  <x:anchor-alias value="chunk-size"/>
1850  <x:anchor-alias value="last-chunk"/>
1851  <x:anchor-alias value="trailer-part"/>
1853   The chunked encoding modifies the body of a message in order to
1854   transfer it as a series of chunks, each with its own size indicator,
1855   followed by an &OPTIONAL; trailer containing entity-header fields. This
1856   allows dynamically produced content to be transferred along with the
1857   information necessary for the recipient to verify that it has
1858   received the full message.
1860<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"/>
1861  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1862                   <x:ref>last-chunk</x:ref>
1863                   <x:ref>trailer-part</x:ref>
1864                   <x:ref>CRLF</x:ref>
1866  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1867                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1868  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1869  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1871  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1872                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1873  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1874  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1875  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1876  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1879   The chunk-size field is a string of hex digits indicating the size of
1880   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1881   zero, followed by the trailer, which is terminated by an empty line.
1884   The trailer allows the sender to include additional HTTP header
1885   fields at the end of the message. The Trailer header field can be
1886   used to indicate which header fields are included in a trailer (see
1887   <xref target="header.trailer"/>).
1890   A server using chunked transfer-coding in a response &MUST-NOT; use the
1891   trailer for any header fields unless at least one of the following is
1892   true:
1893  <list style="numbers">
1894    <t>the request included a TE header field that indicates "trailers" is
1895     acceptable in the transfer-coding of the  response, as described in
1896     <xref target="header.te"/>; or,</t>
1898    <t>the server is the origin server for the response, the trailer
1899     fields consist entirely of optional metadata, and the recipient
1900     could use the message (in a manner acceptable to the origin server)
1901     without receiving this metadata.  In other words, the origin server
1902     is willing to accept the possibility that the trailer fields might
1903     be silently discarded along the path to the client.</t>
1904  </list>
1907   This requirement prevents an interoperability failure when the
1908   message is being received by an HTTP/1.1 (or later) proxy and
1909   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1910   compliance with the protocol would have necessitated a possibly
1911   infinite buffer on the proxy.
1914   A process for decoding the "chunked" transfer-coding
1915   can be represented in pseudo-code as:
1917<figure><artwork type="code">
1918  length := 0
1919  read chunk-size, chunk-ext (if any) and CRLF
1920  while (chunk-size &gt; 0) {
1921     read chunk-data and CRLF
1922     append chunk-data to entity-body
1923     length := length + chunk-size
1924     read chunk-size and CRLF
1925  }
1926  read entity-header
1927  while (entity-header not empty) {
1928     append entity-header to existing header fields
1929     read entity-header
1930  }
1931  Content-Length := length
1932  Remove "chunked" from Transfer-Encoding
1935   All HTTP/1.1 applications &MUST; be able to receive and decode the
1936   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1937   they do not understand.
1942<section title="Product Tokens" anchor="product.tokens">
1943  <x:anchor-alias value="product"/>
1944  <x:anchor-alias value="product-version"/>
1946   Product tokens are used to allow communicating applications to
1947   identify themselves by software name and version. Most fields using
1948   product tokens also allow sub-products which form a significant part
1949   of the application to be listed, separated by whitespace. By
1950   convention, the products are listed in order of their significance
1951   for identifying the application.
1953<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1954  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1955  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1958   Examples:
1960<figure><artwork type="example">
1961  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1962  Server: Apache/0.8.4
1965   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1966   used for advertising or other non-essential information. Although any
1967   token character &MAY; appear in a product-version, this token &SHOULD;
1968   only be used for a version identifier (i.e., successive versions of
1969   the same product &SHOULD; only differ in the product-version portion of
1970   the product value).
1974<section title="Quality Values" anchor="quality.values">
1975  <x:anchor-alias value="qvalue"/>
1977   Both transfer codings (TE request header, <xref target="header.te"/>)
1978   and content negotiation (&content.negotiation;) use short "floating point"
1979   numbers to indicate the relative importance ("weight") of various
1980   negotiable parameters.  A weight is normalized to a real number in
1981   the range 0 through 1, where 0 is the minimum and 1 the maximum
1982   value. If a parameter has a quality value of 0, then content with
1983   this parameter is `not acceptable' for the client. HTTP/1.1
1984   applications &MUST-NOT; generate more than three digits after the
1985   decimal point. User configuration of these values &SHOULD; also be
1986   limited in this fashion.
1988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1989  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1990                 / ( "1" [ "." 0*3("0") ] )
1993  <t>
1994     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1995     relative degradation in desired quality.
1996  </t>
2002<section title="Connections" anchor="connections">
2004<section title="Persistent Connections" anchor="persistent.connections">
2006<section title="Purpose" anchor="persistent.purpose">
2008   Prior to persistent connections, a separate TCP connection was
2009   established to fetch each URL, increasing the load on HTTP servers
2010   and causing congestion on the Internet. The use of inline images and
2011   other associated data often require a client to make multiple
2012   requests of the same server in a short amount of time. Analysis of
2013   these performance problems and results from a prototype
2014   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2015   measurements of actual HTTP/1.1 implementations show good
2016   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2017   T/TCP <xref target="Tou1998"/>.
2020   Persistent HTTP connections have a number of advantages:
2021  <list style="symbols">
2022      <t>
2023        By opening and closing fewer TCP connections, CPU time is saved
2024        in routers and hosts (clients, servers, proxies, gateways,
2025        tunnels, or caches), and memory used for TCP protocol control
2026        blocks can be saved in hosts.
2027      </t>
2028      <t>
2029        HTTP requests and responses can be pipelined on a connection.
2030        Pipelining allows a client to make multiple requests without
2031        waiting for each response, allowing a single TCP connection to
2032        be used much more efficiently, with much lower elapsed time.
2033      </t>
2034      <t>
2035        Network congestion is reduced by reducing the number of packets
2036        caused by TCP opens, and by allowing TCP sufficient time to
2037        determine the congestion state of the network.
2038      </t>
2039      <t>
2040        Latency on subsequent requests is reduced since there is no time
2041        spent in TCP's connection opening handshake.
2042      </t>
2043      <t>
2044        HTTP can evolve more gracefully, since errors can be reported
2045        without the penalty of closing the TCP connection. Clients using
2046        future versions of HTTP might optimistically try a new feature,
2047        but if communicating with an older server, retry with old
2048        semantics after an error is reported.
2049      </t>
2050    </list>
2053   HTTP implementations &SHOULD; implement persistent connections.
2057<section title="Overall Operation" anchor="persistent.overall">
2059   A significant difference between HTTP/1.1 and earlier versions of
2060   HTTP is that persistent connections are the default behavior of any
2061   HTTP connection. That is, unless otherwise indicated, the client
2062   &SHOULD; assume that the server will maintain a persistent connection,
2063   even after error responses from the server.
2066   Persistent connections provide a mechanism by which a client and a
2067   server can signal the close of a TCP connection. This signaling takes
2068   place using the Connection header field (<xref target="header.connection"/>). Once a close
2069   has been signaled, the client &MUST-NOT; send any more requests on that
2070   connection.
2073<section title="Negotiation" anchor="persistent.negotiation">
2075   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2076   maintain a persistent connection unless a Connection header including
2077   the connection-token "close" was sent in the request. If the server
2078   chooses to close the connection immediately after sending the
2079   response, it &SHOULD; send a Connection header including the
2080   connection-token close.
2083   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2084   decide to keep it open based on whether the response from a server
2085   contains a Connection header with the connection-token close. In case
2086   the client does not want to maintain a connection for more than that
2087   request, it &SHOULD; send a Connection header including the
2088   connection-token close.
2091   If either the client or the server sends the close token in the
2092   Connection header, that request becomes the last one for the
2093   connection.
2096   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2097   maintained for HTTP versions less than 1.1 unless it is explicitly
2098   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2099   compatibility with HTTP/1.0 clients.
2102   In order to remain persistent, all messages on the connection &MUST;
2103   have a self-defined message length (i.e., one not defined by closure
2104   of the connection), as described in <xref target="message.length"/>.
2108<section title="Pipelining" anchor="pipelining">
2110   A client that supports persistent connections &MAY; "pipeline" its
2111   requests (i.e., send multiple requests without waiting for each
2112   response). A server &MUST; send its responses to those requests in the
2113   same order that the requests were received.
2116   Clients which assume persistent connections and pipeline immediately
2117   after connection establishment &SHOULD; be prepared to retry their
2118   connection if the first pipelined attempt fails. If a client does
2119   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2120   persistent. Clients &MUST; also be prepared to resend their requests if
2121   the server closes the connection before sending all of the
2122   corresponding responses.
2125   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2126   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2127   premature termination of the transport connection could lead to
2128   indeterminate results. A client wishing to send a non-idempotent
2129   request &SHOULD; wait to send that request until it has received the
2130   response status for the previous request.
2135<section title="Proxy Servers" anchor="persistent.proxy">
2137   It is especially important that proxies correctly implement the
2138   properties of the Connection header field as specified in <xref target="header.connection"/>.
2141   The proxy server &MUST; signal persistent connections separately with
2142   its clients and the origin servers (or other proxy servers) that it
2143   connects to. Each persistent connection applies to only one transport
2144   link.
2147   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2148   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2149   for information and discussion of the problems with the Keep-Alive header
2150   implemented by many HTTP/1.0 clients).
2154<section title="Practical Considerations" anchor="persistent.practical">
2156   Servers will usually have some time-out value beyond which they will
2157   no longer maintain an inactive connection. Proxy servers might make
2158   this a higher value since it is likely that the client will be making
2159   more connections through the same server. The use of persistent
2160   connections places no requirements on the length (or existence) of
2161   this time-out for either the client or the server.
2164   When a client or server wishes to time-out it &SHOULD; issue a graceful
2165   close on the transport connection. Clients and servers &SHOULD; both
2166   constantly watch for the other side of the transport close, and
2167   respond to it as appropriate. If a client or server does not detect
2168   the other side's close promptly it could cause unnecessary resource
2169   drain on the network.
2172   A client, server, or proxy &MAY; close the transport connection at any
2173   time. For example, a client might have started to send a new request
2174   at the same time that the server has decided to close the "idle"
2175   connection. From the server's point of view, the connection is being
2176   closed while it was idle, but from the client's point of view, a
2177   request is in progress.
2180   This means that clients, servers, and proxies &MUST; be able to recover
2181   from asynchronous close events. Client software &SHOULD; reopen the
2182   transport connection and retransmit the aborted sequence of requests
2183   without user interaction so long as the request sequence is
2184   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2185   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2186   human operator the choice of retrying the request(s). Confirmation by
2187   user-agent software with semantic understanding of the application
2188   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2189   be repeated if the second sequence of requests fails.
2192   Servers &SHOULD; always respond to at least one request per connection,
2193   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2194   middle of transmitting a response, unless a network or client failure
2195   is suspected.
2198   Clients that use persistent connections &SHOULD; limit the number of
2199   simultaneous connections that they maintain to a given server. A
2200   single-user client &SHOULD-NOT; maintain more than 2 connections with
2201   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2202   another server or proxy, where N is the number of simultaneously
2203   active users. These guidelines are intended to improve HTTP response
2204   times and avoid congestion.
2209<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2211<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2213   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2214   flow control mechanisms to resolve temporary overloads, rather than
2215   terminating connections with the expectation that clients will retry.
2216   The latter technique can exacerbate network congestion.
2220<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2222   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2223   the network connection for an error status while it is transmitting
2224   the request. If the client sees an error status, it &SHOULD;
2225   immediately cease transmitting the body. If the body is being sent
2226   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2227   empty trailer &MAY; be used to prematurely mark the end of the message.
2228   If the body was preceded by a Content-Length header, the client &MUST;
2229   close the connection.
2233<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2235   The purpose of the 100 (Continue) status (see &status-100;) is to
2236   allow a client that is sending a request message with a request body
2237   to determine if the origin server is willing to accept the request
2238   (based on the request headers) before the client sends the request
2239   body. In some cases, it might either be inappropriate or highly
2240   inefficient for the client to send the body if the server will reject
2241   the message without looking at the body.
2244   Requirements for HTTP/1.1 clients:
2245  <list style="symbols">
2246    <t>
2247        If a client will wait for a 100 (Continue) response before
2248        sending the request body, it &MUST; send an Expect request-header
2249        field (&header-expect;) with the "100-continue" expectation.
2250    </t>
2251    <t>
2252        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2253        with the "100-continue" expectation if it does not intend
2254        to send a request body.
2255    </t>
2256  </list>
2259   Because of the presence of older implementations, the protocol allows
2260   ambiguous situations in which a client may send "Expect: 100-continue"
2261   without receiving either a 417 (Expectation Failed) status
2262   or a 100 (Continue) status. Therefore, when a client sends this
2263   header field to an origin server (possibly via a proxy) from which it
2264   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2265   for an indefinite period before sending the request body.
2268   Requirements for HTTP/1.1 origin servers:
2269  <list style="symbols">
2270    <t> Upon receiving a request which includes an Expect request-header
2271        field with the "100-continue" expectation, an origin server &MUST;
2272        either respond with 100 (Continue) status and continue to read
2273        from the input stream, or respond with a final status code. The
2274        origin server &MUST-NOT; wait for the request body before sending
2275        the 100 (Continue) response. If it responds with a final status
2276        code, it &MAY; close the transport connection or it &MAY; continue
2277        to read and discard the rest of the request.  It &MUST-NOT;
2278        perform the requested method if it returns a final status code.
2279    </t>
2280    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2281        the request message does not include an Expect request-header
2282        field with the "100-continue" expectation, and &MUST-NOT; send a
2283        100 (Continue) response if such a request comes from an HTTP/1.0
2284        (or earlier) client. There is an exception to this rule: for
2285        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2286        status in response to an HTTP/1.1 PUT or POST request that does
2287        not include an Expect request-header field with the "100-continue"
2288        expectation. This exception, the purpose of which is
2289        to minimize any client processing delays associated with an
2290        undeclared wait for 100 (Continue) status, applies only to
2291        HTTP/1.1 requests, and not to requests with any other HTTP-version
2292        value.
2293    </t>
2294    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2295        already received some or all of the request body for the
2296        corresponding request.
2297    </t>
2298    <t> An origin server that sends a 100 (Continue) response &MUST;
2299    ultimately send a final status code, once the request body is
2300        received and processed, unless it terminates the transport
2301        connection prematurely.
2302    </t>
2303    <t> If an origin server receives a request that does not include an
2304        Expect request-header field with the "100-continue" expectation,
2305        the request includes a request body, and the server responds
2306        with a final status code before reading the entire request body
2307        from the transport connection, then the server &SHOULD-NOT;  close
2308        the transport connection until it has read the entire request,
2309        or until the client closes the connection. Otherwise, the client
2310        might not reliably receive the response message. However, this
2311        requirement is not be construed as preventing a server from
2312        defending itself against denial-of-service attacks, or from
2313        badly broken client implementations.
2314      </t>
2315    </list>
2318   Requirements for HTTP/1.1 proxies:
2319  <list style="symbols">
2320    <t> If a proxy receives a request that includes an Expect request-header
2321        field with the "100-continue" expectation, and the proxy
2322        either knows that the next-hop server complies with HTTP/1.1 or
2323        higher, or does not know the HTTP version of the next-hop
2324        server, it &MUST; forward the request, including the Expect header
2325        field.
2326    </t>
2327    <t> If the proxy knows that the version of the next-hop server is
2328        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2329        respond with a 417 (Expectation Failed) status.
2330    </t>
2331    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2332        numbers received from recently-referenced next-hop servers.
2333    </t>
2334    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2335        request message was received from an HTTP/1.0 (or earlier)
2336        client and did not include an Expect request-header field with
2337        the "100-continue" expectation. This requirement overrides the
2338        general rule for forwarding of 1xx responses (see &status-1xx;).
2339    </t>
2340  </list>
2344<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2346   If an HTTP/1.1 client sends a request which includes a request body,
2347   but which does not include an Expect request-header field with the
2348   "100-continue" expectation, and if the client is not directly
2349   connected to an HTTP/1.1 origin server, and if the client sees the
2350   connection close before receiving any status from the server, the
2351   client &SHOULD; retry the request.  If the client does retry this
2352   request, it &MAY; use the following "binary exponential backoff"
2353   algorithm to be assured of obtaining a reliable response:
2354  <list style="numbers">
2355    <t>
2356      Initiate a new connection to the server
2357    </t>
2358    <t>
2359      Transmit the request-headers
2360    </t>
2361    <t>
2362      Initialize a variable R to the estimated round-trip time to the
2363         server (e.g., based on the time it took to establish the
2364         connection), or to a constant value of 5 seconds if the round-trip
2365         time is not available.
2366    </t>
2367    <t>
2368       Compute T = R * (2**N), where N is the number of previous
2369         retries of this request.
2370    </t>
2371    <t>
2372       Wait either for an error response from the server, or for T
2373         seconds (whichever comes first)
2374    </t>
2375    <t>
2376       If no error response is received, after T seconds transmit the
2377         body of the request.
2378    </t>
2379    <t>
2380       If client sees that the connection is closed prematurely,
2381         repeat from step 1 until the request is accepted, an error
2382         response is received, or the user becomes impatient and
2383         terminates the retry process.
2384    </t>
2385  </list>
2388   If at any point an error status is received, the client
2389  <list style="symbols">
2390      <t>&SHOULD-NOT;  continue and</t>
2392      <t>&SHOULD; close the connection if it has not completed sending the
2393        request message.</t>
2394    </list>
2401<section title="Header Field Definitions" anchor="header.field.definitions">
2403   This section defines the syntax and semantics of HTTP/1.1 header fields
2404   related to message framing and transport protocols.
2407   For entity-header fields, both sender and recipient refer to either the
2408   client or the server, depending on who sends and who receives the entity.
2411<section title="Connection" anchor="header.connection">
2412  <iref primary="true" item="Connection header" x:for-anchor=""/>
2413  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2414  <x:anchor-alias value="Connection"/>
2415  <x:anchor-alias value="connection-token"/>
2416  <x:anchor-alias value="Connection-v"/>
2418   The general-header field "Connection" allows the sender to specify
2419   options that are desired for that particular connection and &MUST-NOT;
2420   be communicated by proxies over further connections.
2423   The Connection header's value has the following grammar:
2425<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"/>
2426  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2427  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2428  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2431   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2432   message is forwarded and, for each connection-token in this field,
2433   remove any header field(s) from the message with the same name as the
2434   connection-token. Connection options are signaled by the presence of
2435   a connection-token in the Connection header field, not by any
2436   corresponding additional header field(s), since the additional header
2437   field may not be sent if there are no parameters associated with that
2438   connection option.
2441   Message headers listed in the Connection header &MUST-NOT; include
2442   end-to-end headers, such as Cache-Control.
2445   HTTP/1.1 defines the "close" connection option for the sender to
2446   signal that the connection will be closed after completion of the
2447   response. For example,
2449<figure><artwork type="example">
2450  Connection: close
2453   in either the request or the response header fields indicates that
2454   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2455   after the current request/response is complete.
2458   An HTTP/1.1 client that does not support persistent connections &MUST;
2459   include the "close" connection option in every request message.
2462   An HTTP/1.1 server that does not support persistent connections &MUST;
2463   include the "close" connection option in every response message that
2464   does not have a 1xx (informational) status code.
2467   A system receiving an HTTP/1.0 (or lower-version) message that
2468   includes a Connection header &MUST;, for each connection-token in this
2469   field, remove and ignore any header field(s) from the message with
2470   the same name as the connection-token. This protects against mistaken
2471   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2475<section title="Content-Length" anchor="header.content-length">
2476  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2477  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2478  <x:anchor-alias value="Content-Length"/>
2479  <x:anchor-alias value="Content-Length-v"/>
2481   The entity-header field "Content-Length" indicates the size of the
2482   entity-body, in number of OCTETs, sent to the recipient or,
2483   in the case of the HEAD method, the size of the entity-body that
2484   would have been sent had the request been a GET.
2486<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2487  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2488  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2491   An example is
2493<figure><artwork type="example">
2494  Content-Length: 3495
2497   Applications &SHOULD; use this field to indicate the transfer-length of
2498   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2501   Any Content-Length greater than or equal to zero is a valid value.
2502   <xref target="message.length"/> describes how to determine the length of a message-body
2503   if a Content-Length is not given.
2506   Note that the meaning of this field is significantly different from
2507   the corresponding definition in MIME, where it is an optional field
2508   used within the "message/external-body" content-type. In HTTP, it
2509   &SHOULD; be sent whenever the message's length can be determined prior
2510   to being transferred, unless this is prohibited by the rules in
2511   <xref target="message.length"/>.
2515<section title="Date" anchor="">
2516  <iref primary="true" item="Date header" x:for-anchor=""/>
2517  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2518  <x:anchor-alias value="Date"/>
2519  <x:anchor-alias value="Date-v"/>
2521   The general-header field "Date" represents the date and time at which
2522   the message was originated, having the same semantics as orig-date in
2523   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2524   HTTP-date, as described in <xref target=""/>;
2525   it &MUST; be sent in rfc1123-date format.
2527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2528  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2529  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2532   An example is
2534<figure><artwork type="example">
2535  Date: Tue, 15 Nov 1994 08:12:31 GMT
2538   Origin servers &MUST; include a Date header field in all responses,
2539   except in these cases:
2540  <list style="numbers">
2541      <t>If the response status code is 100 (Continue) or 101 (Switching
2542         Protocols), the response &MAY; include a Date header field, at
2543         the server's option.</t>
2545      <t>If the response status code conveys a server error, e.g. 500
2546         (Internal Server Error) or 503 (Service Unavailable), and it is
2547         inconvenient or impossible to generate a valid Date.</t>
2549      <t>If the server does not have a clock that can provide a
2550         reasonable approximation of the current time, its responses
2551         &MUST-NOT; include a Date header field. In this case, the rules
2552         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2553  </list>
2556   A received message that does not have a Date header field &MUST; be
2557   assigned one by the recipient if the message will be cached by that
2558   recipient or gatewayed via a protocol which requires a Date. An HTTP
2559   implementation without a clock &MUST-NOT; cache responses without
2560   revalidating them on every use. An HTTP cache, especially a shared
2561   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2562   clock with a reliable external standard.
2565   Clients &SHOULD; only send a Date header field in messages that include
2566   an entity-body, as in the case of the PUT and POST requests, and even
2567   then it is optional. A client without a clock &MUST-NOT; send a Date
2568   header field in a request.
2571   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2572   time subsequent to the generation of the message. It &SHOULD; represent
2573   the best available approximation of the date and time of message
2574   generation, unless the implementation has no means of generating a
2575   reasonably accurate date and time. In theory, the date ought to
2576   represent the moment just before the entity is generated. In
2577   practice, the date can be generated at any time during the message
2578   origination without affecting its semantic value.
2581<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2583   Some origin server implementations might not have a clock available.
2584   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2585   values to a response, unless these values were associated
2586   with the resource by a system or user with a reliable clock. It &MAY;
2587   assign an Expires value that is known, at or before server
2588   configuration time, to be in the past (this allows "pre-expiration"
2589   of responses without storing separate Expires values for each
2590   resource).
2595<section title="Host" anchor="">
2596  <iref primary="true" item="Host header" x:for-anchor=""/>
2597  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2598  <x:anchor-alias value="Host"/>
2599  <x:anchor-alias value="Host-v"/>
2601   The request-header field "Host" specifies the Internet host and port
2602   number of the resource being requested, as obtained from the original
2603   URI given by the user or referring resource (generally an http URI,
2604   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2605   the naming authority of the origin server or gateway given by the
2606   original URL. This allows the origin server or gateway to
2607   differentiate between internally-ambiguous URLs, such as the root "/"
2608   URL of a server for multiple host names on a single IP address.
2610<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2611  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2612  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2615   A "host" without any trailing port information implies the default
2616   port for the service requested (e.g., "80" for an HTTP URL). For
2617   example, a request on the origin server for
2618   &lt;; would properly include:
2620<figure><artwork type="example">
2621  GET /pub/WWW/ HTTP/1.1
2622  Host:
2625   A client &MUST; include a Host header field in all HTTP/1.1 request
2626   messages. If the requested URI does not include an Internet host
2627   name for the service being requested, then the Host header field &MUST;
2628   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2629   request message it forwards does contain an appropriate Host header
2630   field that identifies the service being requested by the proxy. All
2631   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2632   status code to any HTTP/1.1 request message which lacks a Host header
2633   field.
2636   See Sections <xref target="" format="counter"/>
2637   and <xref target="" format="counter"/>
2638   for other requirements relating to Host.
2642<section title="TE" anchor="header.te">
2643  <iref primary="true" item="TE header" x:for-anchor=""/>
2644  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2645  <x:anchor-alias value="TE"/>
2646  <x:anchor-alias value="TE-v"/>
2647  <x:anchor-alias value="t-codings"/>
2648  <x:anchor-alias value="te-params"/>
2649  <x:anchor-alias value="te-ext"/>
2651   The request-header field "TE" indicates what extension transfer-codings
2652   it is willing to accept in the response and whether or not it is
2653   willing to accept trailer fields in a chunked transfer-coding. Its
2654   value may consist of the keyword "trailers" and/or a comma-separated
2655   list of extension transfer-coding names with optional accept
2656   parameters (as described in <xref target="transfer.codings"/>).
2658<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"/>
2659  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2660  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2661  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2662  <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> )
2663  <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> ) ]
2666   The presence of the keyword "trailers" indicates that the client is
2667   willing to accept trailer fields in a chunked transfer-coding, as
2668   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2669   transfer-coding values even though it does not itself represent a
2670   transfer-coding.
2673   Examples of its use are:
2675<figure><artwork type="example">
2676  TE: deflate
2677  TE:
2678  TE: trailers, deflate;q=0.5
2681   The TE header field only applies to the immediate connection.
2682   Therefore, the keyword &MUST; be supplied within a Connection header
2683   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2686   A server tests whether a transfer-coding is acceptable, according to
2687   a TE field, using these rules:
2688  <list style="numbers">
2689    <x:lt>
2690      <t>The "chunked" transfer-coding is always acceptable. If the
2691         keyword "trailers" is listed, the client indicates that it is
2692         willing to accept trailer fields in the chunked response on
2693         behalf of itself and any downstream clients. The implication is
2694         that, if given, the client is stating that either all
2695         downstream clients are willing to accept trailer fields in the
2696         forwarded response, or that it will attempt to buffer the
2697         response on behalf of downstream recipients.
2698      </t><t>
2699         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2700         chunked response such that a client can be assured of buffering
2701         the entire response.</t>
2702    </x:lt>
2703    <x:lt>
2704      <t>If the transfer-coding being tested is one of the transfer-codings
2705         listed in the TE field, then it is acceptable unless it
2706         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2707         qvalue of 0 means "not acceptable.")</t>
2708    </x:lt>
2709    <x:lt>
2710      <t>If multiple transfer-codings are acceptable, then the
2711         acceptable transfer-coding with the highest non-zero qvalue is
2712         preferred.  The "chunked" transfer-coding always has a qvalue
2713         of 1.</t>
2714    </x:lt>
2715  </list>
2718   If the TE field-value is empty or if no TE field is present, the only
2719   transfer-coding is "chunked". A message with no transfer-coding is
2720   always acceptable.
2724<section title="Trailer" anchor="header.trailer">
2725  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2726  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2727  <x:anchor-alias value="Trailer"/>
2728  <x:anchor-alias value="Trailer-v"/>
2730   The general field "Trailer" indicates that the given set of
2731   header fields is present in the trailer of a message encoded with
2732   chunked transfer-coding.
2734<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2735  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2736  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2739   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2740   message using chunked transfer-coding with a non-empty trailer. Doing
2741   so allows the recipient to know which header fields to expect in the
2742   trailer.
2745   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2746   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2747   trailer fields in a "chunked" transfer-coding.
2750   Message header fields listed in the Trailer header field &MUST-NOT;
2751   include the following header fields:
2752  <list style="symbols">
2753    <t>Transfer-Encoding</t>
2754    <t>Content-Length</t>
2755    <t>Trailer</t>
2756  </list>
2760<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2761  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2762  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2763  <x:anchor-alias value="Transfer-Encoding"/>
2764  <x:anchor-alias value="Transfer-Encoding-v"/>
2766   The general-header "Transfer-Encoding" field indicates what (if any)
2767   type of transformation has been applied to the message body in order
2768   to safely transfer it between the sender and the recipient. This
2769   differs from the content-coding in that the transfer-coding is a
2770   property of the message, not of the entity.
2772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2773  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2774                        <x:ref>Transfer-Encoding-v</x:ref>
2775  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2778   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2780<figure><artwork type="example">
2781  Transfer-Encoding: chunked
2784   If multiple encodings have been applied to an entity, the transfer-codings
2785   &MUST; be listed in the order in which they were applied.
2786   Additional information about the encoding parameters &MAY; be provided
2787   by other entity-header fields not defined by this specification.
2790   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2791   header.
2795<section title="Upgrade" anchor="header.upgrade">
2796  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2797  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2798  <x:anchor-alias value="Upgrade"/>
2799  <x:anchor-alias value="Upgrade-v"/>
2801   The general-header "Upgrade" allows the client to specify what
2802   additional communication protocols it supports and would like to use
2803   if the server finds it appropriate to switch protocols. The server
2804   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2805   response to indicate which protocol(s) are being switched.
2807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2808  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2809  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2812   For example,
2814<figure><artwork type="example">
2815  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2818   The Upgrade header field is intended to provide a simple mechanism
2819   for transition from HTTP/1.1 to some other, incompatible protocol. It
2820   does so by allowing the client to advertise its desire to use another
2821   protocol, such as a later version of HTTP with a higher major version
2822   number, even though the current request has been made using HTTP/1.1.
2823   This eases the difficult transition between incompatible protocols by
2824   allowing the client to initiate a request in the more commonly
2825   supported protocol while indicating to the server that it would like
2826   to use a "better" protocol if available (where "better" is determined
2827   by the server, possibly according to the nature of the method and/or
2828   resource being requested).
2831   The Upgrade header field only applies to switching application-layer
2832   protocols upon the existing transport-layer connection. Upgrade
2833   cannot be used to insist on a protocol change; its acceptance and use
2834   by the server is optional. The capabilities and nature of the
2835   application-layer communication after the protocol change is entirely
2836   dependent upon the new protocol chosen, although the first action
2837   after changing the protocol &MUST; be a response to the initial HTTP
2838   request containing the Upgrade header field.
2841   The Upgrade header field only applies to the immediate connection.
2842   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2843   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2844   HTTP/1.1 message.
2847   The Upgrade header field cannot be used to indicate a switch to a
2848   protocol on a different connection. For that purpose, it is more
2849   appropriate to use a 301, 302, 303, or 305 redirection response.
2852   This specification only defines the protocol name "HTTP" for use by
2853   the family of Hypertext Transfer Protocols, as defined by the HTTP
2854   version rules of <xref target="http.version"/> and future updates to this
2855   specification. Any token can be used as a protocol name; however, it
2856   will only be useful if both the client and server associate the name
2857   with the same protocol.
2861<section title="Via" anchor="header.via">
2862  <iref primary="true" item="Via header" x:for-anchor=""/>
2863  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2864  <x:anchor-alias value="protocol-name"/>
2865  <x:anchor-alias value="protocol-version"/>
2866  <x:anchor-alias value="pseudonym"/>
2867  <x:anchor-alias value="received-by"/>
2868  <x:anchor-alias value="received-protocol"/>
2869  <x:anchor-alias value="Via"/>
2870  <x:anchor-alias value="Via-v"/>
2872   The general-header field "Via" &MUST; be used by gateways and proxies to
2873   indicate the intermediate protocols and recipients between the user
2874   agent and the server on requests, and between the origin server and
2875   the client on responses. It is analogous to the "Received" field defined in
2876   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2877   avoiding request loops, and identifying the protocol capabilities of
2878   all senders along the request/response chain.
2880<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"/>
2881  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2882  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2883                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2884  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2885  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2886  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2887  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2888  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2891   The received-protocol indicates the protocol version of the message
2892   received by the server or client along each segment of the
2893   request/response chain. The received-protocol version is appended to
2894   the Via field value when the message is forwarded so that information
2895   about the protocol capabilities of upstream applications remains
2896   visible to all recipients.
2899   The protocol-name is optional if and only if it would be "HTTP". The
2900   received-by field is normally the host and optional port number of a
2901   recipient server or client that subsequently forwarded the message.
2902   However, if the real host is considered to be sensitive information,
2903   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2904   be assumed to be the default port of the received-protocol.
2907   Multiple Via field values represents each proxy or gateway that has
2908   forwarded the message. Each recipient &MUST; append its information
2909   such that the end result is ordered according to the sequence of
2910   forwarding applications.
2913   Comments &MAY; be used in the Via header field to identify the software
2914   of the recipient proxy or gateway, analogous to the User-Agent and
2915   Server header fields. However, all comments in the Via field are
2916   optional and &MAY; be removed by any recipient prior to forwarding the
2917   message.
2920   For example, a request message could be sent from an HTTP/1.0 user
2921   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2922   forward the request to a public proxy at, which completes
2923   the request by forwarding it to the origin server at
2924   The request received by would then have the following
2925   Via header field:
2927<figure><artwork type="example">
2928  Via: 1.0 fred, 1.1 (Apache/1.1)
2931   Proxies and gateways used as a portal through a network firewall
2932   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2933   the firewall region. This information &SHOULD; only be propagated if
2934   explicitly enabled. If not enabled, the received-by host of any host
2935   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2936   for that host.
2939   For organizations that have strong privacy requirements for hiding
2940   internal structures, a proxy &MAY; combine an ordered subsequence of
2941   Via header field entries with identical received-protocol values into
2942   a single such entry. For example,
2944<figure><artwork type="example">
2945  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2948        could be collapsed to
2950<figure><artwork type="example">
2951  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2954   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2955   under the same organizational control and the hosts have already been
2956   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2957   have different received-protocol values.
2963<section title="IANA Considerations" anchor="IANA.considerations">
2964<section title="Message Header Registration" anchor="message.header.registration">
2966   The Message Header Registry located at <eref target=""/> should be updated
2967   with the permanent registrations below (see <xref target="RFC3864"/>):
2969<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2970<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2971   <ttcol>Header Field Name</ttcol>
2972   <ttcol>Protocol</ttcol>
2973   <ttcol>Status</ttcol>
2974   <ttcol>Reference</ttcol>
2976   <c>Connection</c>
2977   <c>http</c>
2978   <c>standard</c>
2979   <c>
2980      <xref target="header.connection"/>
2981   </c>
2982   <c>Content-Length</c>
2983   <c>http</c>
2984   <c>standard</c>
2985   <c>
2986      <xref target="header.content-length"/>
2987   </c>
2988   <c>Date</c>
2989   <c>http</c>
2990   <c>standard</c>
2991   <c>
2992      <xref target=""/>
2993   </c>
2994   <c>Host</c>
2995   <c>http</c>
2996   <c>standard</c>
2997   <c>
2998      <xref target=""/>
2999   </c>
3000   <c>TE</c>
3001   <c>http</c>
3002   <c>standard</c>
3003   <c>
3004      <xref target="header.te"/>
3005   </c>
3006   <c>Trailer</c>
3007   <c>http</c>
3008   <c>standard</c>
3009   <c>
3010      <xref target="header.trailer"/>
3011   </c>
3012   <c>Transfer-Encoding</c>
3013   <c>http</c>
3014   <c>standard</c>
3015   <c>
3016      <xref target="header.transfer-encoding"/>
3017   </c>
3018   <c>Upgrade</c>
3019   <c>http</c>
3020   <c>standard</c>
3021   <c>
3022      <xref target="header.upgrade"/>
3023   </c>
3024   <c>Via</c>
3025   <c>http</c>
3026   <c>standard</c>
3027   <c>
3028      <xref target="header.via"/>
3029   </c>
3033   The change controller is: "IETF ( - Internet Engineering Task Force".
3037<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3039   The entries for the "http" and "https" URI Schemes in the registry located at
3040   <eref target=""/>
3041   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3042   and <xref target="https.uri" format="counter"/> of this document
3043   (see <xref target="RFC4395"/>).
3047<section title="Internet Media Type Registrations" anchor="">
3049   This document serves as the specification for the Internet media types
3050   "message/http" and "application/http". The following is to be registered with
3051   IANA (see <xref target="RFC4288"/>).
3053<section title="Internet Media Type message/http" anchor="">
3054<iref item="Media Type" subitem="message/http" primary="true"/>
3055<iref item="message/http Media Type" primary="true"/>
3057   The message/http type can be used to enclose a single HTTP request or
3058   response message, provided that it obeys the MIME restrictions for all
3059   "message" types regarding line length and encodings.
3062  <list style="hanging" x:indent="12em">
3063    <t hangText="Type name:">
3064      message
3065    </t>
3066    <t hangText="Subtype name:">
3067      http
3068    </t>
3069    <t hangText="Required parameters:">
3070      none
3071    </t>
3072    <t hangText="Optional parameters:">
3073      version, msgtype
3074      <list style="hanging">
3075        <t hangText="version:">
3076          The HTTP-Version number of the enclosed message
3077          (e.g., "1.1"). If not present, the version can be
3078          determined from the first line of the body.
3079        </t>
3080        <t hangText="msgtype:">
3081          The message type -- "request" or "response". If not
3082          present, the type can be determined from the first
3083          line of the body.
3084        </t>
3085      </list>
3086    </t>
3087    <t hangText="Encoding considerations:">
3088      only "7bit", "8bit", or "binary" are permitted
3089    </t>
3090    <t hangText="Security considerations:">
3091      none
3092    </t>
3093    <t hangText="Interoperability considerations:">
3094      none
3095    </t>
3096    <t hangText="Published specification:">
3097      This specification (see <xref target=""/>).
3098    </t>
3099    <t hangText="Applications that use this media type:">
3100    </t>
3101    <t hangText="Additional information:">
3102      <list style="hanging">
3103        <t hangText="Magic number(s):">none</t>
3104        <t hangText="File extension(s):">none</t>
3105        <t hangText="Macintosh file type code(s):">none</t>
3106      </list>
3107    </t>
3108    <t hangText="Person and email address to contact for further information:">
3109      See Authors Section.
3110    </t>
3111    <t hangText="Intended usage:">
3112      COMMON
3113    </t>
3114    <t hangText="Restrictions on usage:">
3115      none
3116    </t>
3117    <t hangText="Author/Change controller:">
3118      IESG
3119    </t>
3120  </list>
3123<section title="Internet Media Type application/http" anchor="">
3124<iref item="Media Type" subitem="application/http" primary="true"/>
3125<iref item="application/http Media Type" primary="true"/>
3127   The application/http type can be used to enclose a pipeline of one or more
3128   HTTP request or response messages (not intermixed).
3131  <list style="hanging" x:indent="12em">
3132    <t hangText="Type name:">
3133      application
3134    </t>
3135    <t hangText="Subtype name:">
3136      http
3137    </t>
3138    <t hangText="Required parameters:">
3139      none
3140    </t>
3141    <t hangText="Optional parameters:">
3142      version, msgtype
3143      <list style="hanging">
3144        <t hangText="version:">
3145          The HTTP-Version number of the enclosed messages
3146          (e.g., "1.1"). If not present, the version can be
3147          determined from the first line of the body.
3148        </t>
3149        <t hangText="msgtype:">
3150          The message type -- "request" or "response". If not
3151          present, the type can be determined from the first
3152          line of the body.
3153        </t>
3154      </list>
3155    </t>
3156    <t hangText="Encoding considerations:">
3157      HTTP messages enclosed by this type
3158      are in "binary" format; use of an appropriate
3159      Content-Transfer-Encoding is required when
3160      transmitted via E-mail.
3161    </t>
3162    <t hangText="Security considerations:">
3163      none
3164    </t>
3165    <t hangText="Interoperability considerations:">
3166      none
3167    </t>
3168    <t hangText="Published specification:">
3169      This specification (see <xref target=""/>).
3170    </t>
3171    <t hangText="Applications that use this media type:">
3172    </t>
3173    <t hangText="Additional information:">
3174      <list style="hanging">
3175        <t hangText="Magic number(s):">none</t>
3176        <t hangText="File extension(s):">none</t>
3177        <t hangText="Macintosh file type code(s):">none</t>
3178      </list>
3179    </t>
3180    <t hangText="Person and email address to contact for further information:">
3181      See Authors Section.
3182    </t>
3183    <t hangText="Intended usage:">
3184      COMMON
3185    </t>
3186    <t hangText="Restrictions on usage:">
3187      none
3188    </t>
3189    <t hangText="Author/Change controller:">
3190      IESG
3191    </t>
3192  </list>
3197<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3199   The registration procedure for HTTP Transfer Codings is now defined
3200   by <xref target="transfer.codings"/> of this document.
3203   The HTTP Transfer Codings Registry located at <eref target=""/>
3204   should be updated with the registration below:
3206<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3207   <ttcol>Registry Name</ttcol>
3208   <ttcol>Description</ttcol>
3209   <ttcol>Reference</ttcol>
3210   <c>Chunked</c>
3211   <c>Transfer in a series of chunks</c>
3212   <c>
3213      <xref target="chunked.transfer.encoding"/>
3214   </c>
3220<section title="Security Considerations" anchor="security.considerations">
3222   This section is meant to inform application developers, information
3223   providers, and users of the security limitations in HTTP/1.1 as
3224   described by this document. The discussion does not include
3225   definitive solutions to the problems revealed, though it does make
3226   some suggestions for reducing security risks.
3229<section title="Personal Information" anchor="personal.information">
3231   HTTP clients are often privy to large amounts of personal information
3232   (e.g. the user's name, location, mail address, passwords, encryption
3233   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3234   leakage of this information.
3235   We very strongly recommend that a convenient interface be provided
3236   for the user to control dissemination of such information, and that
3237   designers and implementors be particularly careful in this area.
3238   History shows that errors in this area often create serious security
3239   and/or privacy problems and generate highly adverse publicity for the
3240   implementor's company.
3244<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3246   A server is in the position to save personal data about a user's
3247   requests which might identify their reading patterns or subjects of
3248   interest. This information is clearly confidential in nature and its
3249   handling can be constrained by law in certain countries. People using
3250   HTTP to provide data are responsible for ensuring that
3251   such material is not distributed without the permission of any
3252   individuals that are identifiable by the published results.
3256<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3258   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3259   the documents returned by HTTP requests to be only those that were
3260   intended by the server administrators. If an HTTP server translates
3261   HTTP URIs directly into file system calls, the server &MUST; take
3262   special care not to serve files that were not intended to be
3263   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3264   other operating systems use ".." as a path component to indicate a
3265   directory level above the current one. On such a system, an HTTP
3266   server &MUST; disallow any such construct in the request-target if it
3267   would otherwise allow access to a resource outside those intended to
3268   be accessible via the HTTP server. Similarly, files intended for
3269   reference only internally to the server (such as access control
3270   files, configuration files, and script code) &MUST; be protected from
3271   inappropriate retrieval, since they might contain sensitive
3272   information. Experience has shown that minor bugs in such HTTP server
3273   implementations have turned into security risks.
3277<section title="DNS Spoofing" anchor="dns.spoofing">
3279   Clients using HTTP rely heavily on the Domain Name Service, and are
3280   thus generally prone to security attacks based on the deliberate
3281   mis-association of IP addresses and DNS names. Clients need to be
3282   cautious in assuming the continuing validity of an IP number/DNS name
3283   association.
3286   In particular, HTTP clients &SHOULD; rely on their name resolver for
3287   confirmation of an IP number/DNS name association, rather than
3288   caching the result of previous host name lookups. Many platforms
3289   already can cache host name lookups locally when appropriate, and
3290   they &SHOULD; be configured to do so. It is proper for these lookups to
3291   be cached, however, only when the TTL (Time To Live) information
3292   reported by the name server makes it likely that the cached
3293   information will remain useful.
3296   If HTTP clients cache the results of host name lookups in order to
3297   achieve a performance improvement, they &MUST; observe the TTL
3298   information reported by DNS.
3301   If HTTP clients do not observe this rule, they could be spoofed when
3302   a previously-accessed server's IP address changes. As network
3303   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3304   possibility of this form of attack will grow. Observing this
3305   requirement thus reduces this potential security vulnerability.
3308   This requirement also improves the load-balancing behavior of clients
3309   for replicated servers using the same DNS name and reduces the
3310   likelihood of a user's experiencing failure in accessing sites which
3311   use that strategy.
3315<section title="Proxies and Caching" anchor="attack.proxies">
3317   By their very nature, HTTP proxies are men-in-the-middle, and
3318   represent an opportunity for man-in-the-middle attacks. Compromise of
3319   the systems on which the proxies run can result in serious security
3320   and privacy problems. Proxies have access to security-related
3321   information, personal information about individual users and
3322   organizations, and proprietary information belonging to users and
3323   content providers. A compromised proxy, or a proxy implemented or
3324   configured without regard to security and privacy considerations,
3325   might be used in the commission of a wide range of potential attacks.
3328   Proxy operators should protect the systems on which proxies run as
3329   they would protect any system that contains or transports sensitive
3330   information. In particular, log information gathered at proxies often
3331   contains highly sensitive personal information, and/or information
3332   about organizations. Log information should be carefully guarded, and
3333   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3336   Proxy implementors should consider the privacy and security
3337   implications of their design and coding decisions, and of the
3338   configuration options they provide to proxy operators (especially the
3339   default configuration).
3342   Users of a proxy need to be aware that they are no trustworthier than
3343   the people who run the proxy; HTTP itself cannot solve this problem.
3346   The judicious use of cryptography, when appropriate, may suffice to
3347   protect against a broad range of security and privacy attacks. Such
3348   cryptography is beyond the scope of the HTTP/1.1 specification.
3352<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3354   They exist. They are hard to defend against. Research continues.
3355   Beware.
3360<section title="Acknowledgments" anchor="ack">
3362   HTTP has evolved considerably over the years. It has
3363   benefited from a large and active developer community--the many
3364   people who have participated on the www-talk mailing list--and it is
3365   that community which has been most responsible for the success of
3366   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3367   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3368   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3369   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3370   VanHeyningen deserve special recognition for their efforts in
3371   defining early aspects of the protocol.
3374   This document has benefited greatly from the comments of all those
3375   participating in the HTTP-WG. In addition to those already mentioned,
3376   the following individuals have contributed to this specification:
3379   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3380   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3381   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3382   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3383   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3384   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3385   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3386   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3387   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3388   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3389   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3390   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3391   Josh Cohen.
3394   Thanks to the "cave men" of Palo Alto. You know who you are.
3397   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3398   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3399   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3400   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3401   Larry Masinter for their help. And thanks go particularly to Jeff
3402   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3405   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3406   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3407   discovery of many of the problems that this document attempts to
3408   rectify.
3411   This specification makes heavy use of the augmented BNF and generic
3412   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3413   reuses many of the definitions provided by Nathaniel Borenstein and
3414   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3415   specification will help reduce past confusion over the relationship
3416   between HTTP and Internet mail message formats.
3423<references title="Normative References">
3425<reference anchor="ISO-8859-1">
3426  <front>
3427    <title>
3428     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3429    </title>
3430    <author>
3431      <organization>International Organization for Standardization</organization>
3432    </author>
3433    <date year="1998"/>
3434  </front>
3435  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3438<reference anchor="Part2">
3439  <front>
3440    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3441    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3442      <organization abbrev="Day Software">Day Software</organization>
3443      <address><email></email></address>
3444    </author>
3445    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3446      <organization>One Laptop per Child</organization>
3447      <address><email></email></address>
3448    </author>
3449    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3450      <organization abbrev="HP">Hewlett-Packard Company</organization>
3451      <address><email></email></address>
3452    </author>
3453    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3454      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3455      <address><email></email></address>
3456    </author>
3457    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3458      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3459      <address><email></email></address>
3460    </author>
3461    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3462      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3463      <address><email></email></address>
3464    </author>
3465    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3466      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3467      <address><email></email></address>
3468    </author>
3469    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3470      <organization abbrev="W3C">World Wide Web Consortium</organization>
3471      <address><email></email></address>
3472    </author>
3473    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3474      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3475      <address><email></email></address>
3476    </author>
3477    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3478  </front>
3479  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3480  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3483<reference anchor="Part3">
3484  <front>
3485    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3486    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3487      <organization abbrev="Day Software">Day Software</organization>
3488      <address><email></email></address>
3489    </author>
3490    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3491      <organization>One Laptop per Child</organization>
3492      <address><email></email></address>
3493    </author>
3494    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3495      <organization abbrev="HP">Hewlett-Packard Company</organization>
3496      <address><email></email></address>
3497    </author>
3498    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3499      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3500      <address><email></email></address>
3501    </author>
3502    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3503      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3504      <address><email></email></address>
3505    </author>
3506    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3507      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3508      <address><email></email></address>
3509    </author>
3510    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3511      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3512      <address><email></email></address>
3513    </author>
3514    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3515      <organization abbrev="W3C">World Wide Web Consortium</organization>
3516      <address><email></email></address>
3517    </author>
3518    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3519      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3520      <address><email></email></address>
3521    </author>
3522    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3523  </front>
3524  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3525  <x:source href="p3-payload.xml" basename="p3-payload"/>
3528<reference anchor="Part5">
3529  <front>
3530    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3531    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3532      <organization abbrev="Day Software">Day Software</organization>
3533      <address><email></email></address>
3534    </author>
3535    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3536      <organization>One Laptop per Child</organization>
3537      <address><email></email></address>
3538    </author>
3539    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3540      <organization abbrev="HP">Hewlett-Packard Company</organization>
3541      <address><email></email></address>
3542    </author>
3543    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3544      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3545      <address><email></email></address>
3546    </author>
3547    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3548      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3549      <address><email></email></address>
3550    </author>
3551    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3552      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3553      <address><email></email></address>
3554    </author>
3555    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3556      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3557      <address><email></email></address>
3558    </author>
3559    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3560      <organization abbrev="W3C">World Wide Web Consortium</organization>
3561      <address><email></email></address>
3562    </author>
3563    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3564      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3565      <address><email></email></address>
3566    </author>
3567    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3568  </front>
3569  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3570  <x:source href="p5-range.xml" basename="p5-range"/>
3573<reference anchor="Part6">
3574  <front>
3575    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3576    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3577      <organization abbrev="Day Software">Day Software</organization>
3578      <address><email></email></address>
3579    </author>
3580    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3581      <organization>One Laptop per Child</organization>
3582      <address><email></email></address>
3583    </author>
3584    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3585      <organization abbrev="HP">Hewlett-Packard Company</organization>
3586      <address><email></email></address>
3587    </author>
3588    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3589      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3590      <address><email></email></address>
3591    </author>
3592    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3593      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3594      <address><email></email></address>
3595    </author>
3596    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3597      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3598      <address><email></email></address>
3599    </author>
3600    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3601      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3602      <address><email></email></address>
3603    </author>
3604    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3605      <organization abbrev="W3C">World Wide Web Consortium</organization>
3606      <address><email></email></address>
3607    </author>
3608    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3609      <organization />
3610      <address><email></email></address>
3611    </author>
3612    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3613      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3614      <address><email></email></address>
3615    </author>
3616    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3617  </front>
3618  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3619  <x:source href="p6-cache.xml" basename="p6-cache"/>
3622<reference anchor="RFC5234">
3623  <front>
3624    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3625    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3626      <organization>Brandenburg InternetWorking</organization>
3627      <address>
3628      <postal>
3629      <street>675 Spruce Dr.</street>
3630      <city>Sunnyvale</city>
3631      <region>CA</region>
3632      <code>94086</code>
3633      <country>US</country></postal>
3634      <phone>+1.408.246.8253</phone>
3635      <email></email></address> 
3636    </author>
3637    <author initials="P." surname="Overell" fullname="Paul Overell">
3638      <organization>THUS plc.</organization>
3639      <address>
3640      <postal>
3641      <street>1/2 Berkeley Square</street>
3642      <street>99 Berkely Street</street>
3643      <city>Glasgow</city>
3644      <code>G3 7HR</code>
3645      <country>UK</country></postal>
3646      <email></email></address>
3647    </author>
3648    <date month="January" year="2008"/>
3649  </front>
3650  <seriesInfo name="STD" value="68"/>
3651  <seriesInfo name="RFC" value="5234"/>
3654<reference anchor="RFC2119">
3655  <front>
3656    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3657    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3658      <organization>Harvard University</organization>
3659      <address><email></email></address>
3660    </author>
3661    <date month="March" year="1997"/>
3662  </front>
3663  <seriesInfo name="BCP" value="14"/>
3664  <seriesInfo name="RFC" value="2119"/>
3667<reference anchor="RFC3986">
3668 <front>
3669  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3670  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3671    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3672    <address>
3673       <email></email>
3674       <uri></uri>
3675    </address>
3676  </author>
3677  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3678    <organization abbrev="Day Software">Day Software</organization>
3679    <address>
3680      <email></email>
3681      <uri></uri>
3682    </address>
3683  </author>
3684  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3685    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3686    <address>
3687      <email></email>
3688      <uri></uri>
3689    </address>
3690  </author>
3691  <date month='January' year='2005'></date>
3692 </front>
3693 <seriesInfo name="RFC" value="3986"/>
3694 <seriesInfo name="STD" value="66"/>
3697<reference anchor="USASCII">
3698  <front>
3699    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3700    <author>
3701      <organization>American National Standards Institute</organization>
3702    </author>
3703    <date year="1986"/>
3704  </front>
3705  <seriesInfo name="ANSI" value="X3.4"/>
3710<references title="Informative References">
3712<reference anchor="Nie1997" target="">
3713  <front>
3714    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3715    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3716      <organization/>
3717    </author>
3718    <author initials="J." surname="Gettys" fullname="J. Gettys">
3719      <organization/>
3720    </author>
3721    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3722      <organization/>
3723    </author>
3724    <author initials="H." surname="Lie" fullname="H. Lie">
3725      <organization/>
3726    </author>
3727    <author initials="C." surname="Lilley" fullname="C. Lilley">
3728      <organization/>
3729    </author>
3730    <date year="1997" month="September"/>
3731  </front>
3732  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3735<reference anchor="Pad1995" target="">
3736  <front>
3737    <title>Improving HTTP Latency</title>
3738    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3739      <organization/>
3740    </author>
3741    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3742      <organization/>
3743    </author>
3744    <date year="1995" month="December"/>
3745  </front>
3746  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3749<reference anchor="RFC1123">
3750  <front>
3751    <title>Requirements for Internet Hosts - Application and Support</title>
3752    <author initials="R." surname="Braden" fullname="Robert Braden">
3753      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3754      <address><email>Braden@ISI.EDU</email></address>
3755    </author>
3756    <date month="October" year="1989"/>
3757  </front>
3758  <seriesInfo name="STD" value="3"/>
3759  <seriesInfo name="RFC" value="1123"/>
3762<reference anchor="RFC1305">
3763  <front>
3764    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3765    <author initials="D." surname="Mills" fullname="David L. Mills">
3766      <organization>University of Delaware, Electrical Engineering Department</organization>
3767      <address><email></email></address>
3768    </author>
3769    <date month="March" year="1992"/>
3770  </front>
3771  <seriesInfo name="RFC" value="1305"/>
3774<reference anchor="RFC1900">
3775  <front>
3776    <title>Renumbering Needs Work</title>
3777    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3778      <organization>CERN, Computing and Networks Division</organization>
3779      <address><email></email></address>
3780    </author>
3781    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3782      <organization>cisco Systems</organization>
3783      <address><email></email></address>
3784    </author>
3785    <date month="February" year="1996"/>
3786  </front>
3787  <seriesInfo name="RFC" value="1900"/>
3790<reference anchor="RFC1945">
3791  <front>
3792    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3793    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3794      <organization>MIT, Laboratory for Computer Science</organization>
3795      <address><email></email></address>
3796    </author>
3797    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3798      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3799      <address><email></email></address>
3800    </author>
3801    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3802      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3803      <address><email></email></address>
3804    </author>
3805    <date month="May" year="1996"/>
3806  </front>
3807  <seriesInfo name="RFC" value="1945"/>
3810<reference anchor="RFC2045">
3811  <front>
3812    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3813    <author initials="N." surname="Freed" fullname="Ned Freed">
3814      <organization>Innosoft International, Inc.</organization>
3815      <address><email></email></address>
3816    </author>
3817    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3818      <organization>First Virtual Holdings</organization>
3819      <address><email></email></address>
3820    </author>
3821    <date month="November" year="1996"/>
3822  </front>
3823  <seriesInfo name="RFC" value="2045"/>
3826<reference anchor="RFC2047">
3827  <front>
3828    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3829    <author initials="K." surname="Moore" fullname="Keith Moore">
3830      <organization>University of Tennessee</organization>
3831      <address><email></email></address>
3832    </author>
3833    <date month="November" year="1996"/>
3834  </front>
3835  <seriesInfo name="RFC" value="2047"/>
3838<reference anchor="RFC2068">
3839  <front>
3840    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3841    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3842      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3843      <address><email></email></address>
3844    </author>
3845    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3846      <organization>MIT Laboratory for Computer Science</organization>
3847      <address><email></email></address>
3848    </author>
3849    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3850      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3851      <address><email></email></address>
3852    </author>
3853    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3854      <organization>MIT Laboratory for Computer Science</organization>
3855      <address><email></email></address>
3856    </author>
3857    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3858      <organization>MIT Laboratory for Computer Science</organization>
3859      <address><email></email></address>
3860    </author>
3861    <date month="January" year="1997"/>
3862  </front>
3863  <seriesInfo name="RFC" value="2068"/>
3866<reference anchor='RFC2109'>
3867  <front>
3868    <title>HTTP State Management Mechanism</title>
3869    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3870      <organization>Bell Laboratories, Lucent Technologies</organization>
3871      <address><email></email></address>
3872    </author>
3873    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3874      <organization>Netscape Communications Corp.</organization>
3875      <address><email></email></address>
3876    </author>
3877    <date year='1997' month='February' />
3878  </front>
3879  <seriesInfo name='RFC' value='2109' />
3882<reference anchor="RFC2145">
3883  <front>
3884    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3885    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3886      <organization>Western Research Laboratory</organization>
3887      <address><email></email></address>
3888    </author>
3889    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3890      <organization>Department of Information and Computer Science</organization>
3891      <address><email></email></address>
3892    </author>
3893    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3894      <organization>MIT Laboratory for Computer Science</organization>
3895      <address><email></email></address>
3896    </author>
3897    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3898      <organization>W3 Consortium</organization>
3899      <address><email></email></address>
3900    </author>
3901    <date month="May" year="1997"/>
3902  </front>
3903  <seriesInfo name="RFC" value="2145"/>
3906<reference anchor="RFC2616">
3907  <front>
3908    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3909    <author initials="R." surname="Fielding" fullname="R. Fielding">
3910      <organization>University of California, Irvine</organization>
3911      <address><email></email></address>
3912    </author>
3913    <author initials="J." surname="Gettys" fullname="J. Gettys">
3914      <organization>W3C</organization>
3915      <address><email></email></address>
3916    </author>
3917    <author initials="J." surname="Mogul" fullname="J. Mogul">
3918      <organization>Compaq Computer Corporation</organization>
3919      <address><email></email></address>
3920    </author>
3921    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3922      <organization>MIT Laboratory for Computer Science</organization>
3923      <address><email></email></address>
3924    </author>
3925    <author initials="L." surname="Masinter" fullname="L. Masinter">
3926      <organization>Xerox Corporation</organization>
3927      <address><email></email></address>
3928    </author>
3929    <author initials="P." surname="Leach" fullname="P. Leach">
3930      <organization>Microsoft Corporation</organization>
3931      <address><email></email></address>
3932    </author>
3933    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3934      <organization>W3C</organization>
3935      <address><email></email></address>
3936    </author>
3937    <date month="June" year="1999"/>
3938  </front>
3939  <seriesInfo name="RFC" value="2616"/>
3942<reference anchor='RFC2818'>
3943  <front>
3944    <title>HTTP Over TLS</title>
3945    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3946      <organization>RTFM, Inc.</organization>
3947      <address><email></email></address>
3948    </author>
3949    <date year='2000' month='May' />
3950  </front>
3951  <seriesInfo name='RFC' value='2818' />
3954<reference anchor='RFC2965'>
3955  <front>
3956    <title>HTTP State Management Mechanism</title>
3957    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3958      <organization>Bell Laboratories, Lucent Technologies</organization>
3959      <address><email></email></address>
3960    </author>
3961    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3962      <organization>, Inc.</organization>
3963      <address><email></email></address>
3964    </author>
3965    <date year='2000' month='October' />
3966  </front>
3967  <seriesInfo name='RFC' value='2965' />
3970<reference anchor='RFC3864'>
3971  <front>
3972    <title>Registration Procedures for Message Header Fields</title>
3973    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3974      <organization>Nine by Nine</organization>
3975      <address><email></email></address>
3976    </author>
3977    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3978      <organization>BEA Systems</organization>
3979      <address><email></email></address>
3980    </author>
3981    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3982      <organization>HP Labs</organization>
3983      <address><email></email></address>
3984    </author>
3985    <date year='2004' month='September' />
3986  </front>
3987  <seriesInfo name='BCP' value='90' />
3988  <seriesInfo name='RFC' value='3864' />
3991<reference anchor="RFC4288">
3992  <front>
3993    <title>Media Type Specifications and Registration Procedures</title>
3994    <author initials="N." surname="Freed" fullname="N. Freed">
3995      <organization>Sun Microsystems</organization>
3996      <address>
3997        <email></email>
3998      </address>
3999    </author>
4000    <author initials="J." surname="Klensin" fullname="J. Klensin">
4001      <organization/>
4002      <address>
4003        <email></email>
4004      </address>
4005    </author>
4006    <date year="2005" month="December"/>
4007  </front>
4008  <seriesInfo name="BCP" value="13"/>
4009  <seriesInfo name="RFC" value="4288"/>
4012<reference anchor='RFC4395'>
4013  <front>
4014    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4015    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4016      <organization>AT&amp;T Laboratories</organization>
4017      <address>
4018        <email></email>
4019      </address>
4020    </author>
4021    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4022      <organization>Qualcomm, Inc.</organization>
4023      <address>
4024        <email></email>
4025      </address>
4026    </author>
4027    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4028      <organization>Adobe Systems</organization>
4029      <address>
4030        <email></email>
4031      </address>
4032    </author>
4033    <date year='2006' month='February' />
4034  </front>
4035  <seriesInfo name='BCP' value='115' />
4036  <seriesInfo name='RFC' value='4395' />
4039<reference anchor="RFC5322">
4040  <front>
4041    <title>Internet Message Format</title>
4042    <author initials="P." surname="Resnick" fullname="P. Resnick">
4043      <organization>Qualcomm Incorporated</organization>
4044    </author>
4045    <date year="2008" month="October"/>
4046  </front>
4047  <seriesInfo name="RFC" value="5322"/>
4050<reference anchor="Kri2001" target="">
4051  <front>
4052    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4053    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4054      <organization/>
4055    </author>
4056    <date year="2001" month="November"/>
4057  </front>
4058  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4061<reference anchor="Spe" target="">
4062  <front>
4063  <title>Analysis of HTTP Performance Problems</title>
4064  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4065    <organization/>
4066  </author>
4067  <date/>
4068  </front>
4071<reference anchor="Tou1998" target="">
4072  <front>
4073  <title>Analysis of HTTP Performance</title>
4074  <author initials="J." surname="Touch" fullname="Joe Touch">
4075    <organization>USC/Information Sciences Institute</organization>
4076    <address><email></email></address>
4077  </author>
4078  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4079    <organization>USC/Information Sciences Institute</organization>
4080    <address><email></email></address>
4081  </author>
4082  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4083    <organization>USC/Information Sciences Institute</organization>
4084    <address><email></email></address>
4085  </author>
4086  <date year="1998" month="Aug"/>
4087  </front>
4088  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4089  <annotation>(original report dated Aug. 1996)</annotation>
4095<section title="Tolerant Applications" anchor="tolerant.applications">
4097   Although this document specifies the requirements for the generation
4098   of HTTP/1.1 messages, not all applications will be correct in their
4099   implementation. We therefore recommend that operational applications
4100   be tolerant of deviations whenever those deviations can be
4101   interpreted unambiguously.
4104   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4105   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4106   accept any amount of WSP characters between fields, even though
4107   only a single SP is required.
4110   The line terminator for header fields is the sequence CRLF.
4111   However, we recommend that applications, when parsing such headers,
4112   recognize a single LF as a line terminator and ignore the leading CR.
4115   The character set of an entity-body &SHOULD; be labeled as the lowest
4116   common denominator of the character codes used within that body, with
4117   the exception that not labeling the entity is preferred over labeling
4118   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4121   Additional rules for requirements on parsing and encoding of dates
4122   and other potential problems with date encodings include:
4125  <list style="symbols">
4126     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4127        which appears to be more than 50 years in the future is in fact
4128        in the past (this helps solve the "year 2000" problem).</t>
4130     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4131        Expires date as earlier than the proper value, but &MUST-NOT;
4132        internally represent a parsed Expires date as later than the
4133        proper value.</t>
4135     <t>All expiration-related calculations &MUST; be done in GMT. The
4136        local time zone &MUST-NOT; influence the calculation or comparison
4137        of an age or expiration time.</t>
4139     <t>If an HTTP header incorrectly carries a date value with a time
4140        zone other than GMT, it &MUST; be converted into GMT using the
4141        most conservative possible conversion.</t>
4142  </list>
4146<section title="Compatibility with Previous Versions" anchor="compatibility">
4148   HTTP has been in use by the World-Wide Web global information initiative
4149   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4150   was a simple protocol for hypertext data transfer across the Internet
4151   with only a single method and no metadata.
4152   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4153   methods and MIME-like messaging that could include metadata about the data
4154   transferred and modifiers on the request/response semantics. However,
4155   HTTP/1.0 did not sufficiently take into consideration the effects of
4156   hierarchical proxies, caching, the need for persistent connections, or
4157   name-based virtual hosts. The proliferation of incompletely-implemented
4158   applications calling themselves "HTTP/1.0" further necessitated a
4159   protocol version change in order for two communicating applications
4160   to determine each other's true capabilities.
4163   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4164   requirements that enable reliable implementations, adding only
4165   those new features that will either be safely ignored by an HTTP/1.0
4166   recipient or only sent when communicating with a party advertising
4167   compliance with HTTP/1.1.
4170   It is beyond the scope of a protocol specification to mandate
4171   compliance with previous versions. HTTP/1.1 was deliberately
4172   designed, however, to make supporting previous versions easy. It is
4173   worth noting that, at the time of composing this specification
4174   (1996), we would expect commercial HTTP/1.1 servers to:
4175  <list style="symbols">
4176     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4177        1.1 requests;</t>
4179     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4180        1.1;</t>
4182     <t>respond appropriately with a message in the same major version
4183        used by the client.</t>
4184  </list>
4187   And we would expect HTTP/1.1 clients to:
4188  <list style="symbols">
4189     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4190        responses;</t>
4192     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4193        1.1.</t>
4194  </list>
4197   For most implementations of HTTP/1.0, each connection is established
4198   by the client prior to the request and closed by the server after
4199   sending the response. Some implementations implement the Keep-Alive
4200   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4203<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4205   This section summarizes major differences between versions HTTP/1.0
4206   and HTTP/1.1.
4209<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4211   The requirements that clients and servers support the Host request-header,
4212   report an error if the Host request-header (<xref target=""/>) is
4213   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4214   are among the most important changes defined by this
4215   specification.
4218   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4219   addresses and servers; there was no other established mechanism for
4220   distinguishing the intended server of a request than the IP address
4221   to which that request was directed. The changes outlined above will
4222   allow the Internet, once older HTTP clients are no longer common, to
4223   support multiple Web sites from a single IP address, greatly
4224   simplifying large operational Web servers, where allocation of many
4225   IP addresses to a single host has created serious problems. The
4226   Internet will also be able to recover the IP addresses that have been
4227   allocated for the sole purpose of allowing special-purpose domain
4228   names to be used in root-level HTTP URLs. Given the rate of growth of
4229   the Web, and the number of servers already deployed, it is extremely
4230   important that all implementations of HTTP (including updates to
4231   existing HTTP/1.0 applications) correctly implement these
4232   requirements:
4233  <list style="symbols">
4234     <t>Both clients and servers &MUST; support the Host request-header.</t>
4236     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4238     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4239        request does not include a Host request-header.</t>
4241     <t>Servers &MUST; accept absolute URIs.</t>
4242  </list>
4247<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4249   Some clients and servers might wish to be compatible with some
4250   previous implementations of persistent connections in HTTP/1.0
4251   clients and servers. Persistent connections in HTTP/1.0 are
4252   explicitly negotiated as they are not the default behavior. HTTP/1.0
4253   experimental implementations of persistent connections are faulty,
4254   and the new facilities in HTTP/1.1 are designed to rectify these
4255   problems. The problem was that some existing 1.0 clients may be
4256   sending Keep-Alive to a proxy server that doesn't understand
4257   Connection, which would then erroneously forward it to the next
4258   inbound server, which would establish the Keep-Alive connection and
4259   result in a hung HTTP/1.0 proxy waiting for the close on the
4260   response. The result is that HTTP/1.0 clients must be prevented from
4261   using Keep-Alive when talking to proxies.
4264   However, talking to proxies is the most important use of persistent
4265   connections, so that prohibition is clearly unacceptable. Therefore,
4266   we need some other mechanism for indicating a persistent connection
4267   is desired, which is safe to use even when talking to an old proxy
4268   that ignores Connection. Persistent connections are the default for
4269   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4270   declaring non-persistence. See <xref target="header.connection"/>.
4273   The original HTTP/1.0 form of persistent connections (the Connection:
4274   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4278<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4280   This specification has been carefully audited to correct and
4281   disambiguate key word usage; RFC 2068 had many problems in respect to
4282   the conventions laid out in <xref target="RFC2119"/>.
4285   Transfer-coding and message lengths all interact in ways that
4286   required fixing exactly when chunked encoding is used (to allow for
4287   transfer encoding that may not be self delimiting); it was important
4288   to straighten out exactly how message lengths are computed. (Sections
4289   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4290   <xref target="header.content-length" format="counter"/>,
4291   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4294   The use and interpretation of HTTP version numbers has been clarified
4295   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4296   version they support to deal with problems discovered in HTTP/1.0
4297   implementations (<xref target="http.version"/>)
4300   Quality Values of zero should indicate that "I don't want something"
4301   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4304   Transfer-coding had significant problems, particularly with
4305   interactions with chunked encoding. The solution is that transfer-codings
4306   become as full fledged as content-codings. This involves
4307   adding an IANA registry for transfer-codings (separate from content
4308   codings), a new header field (TE) and enabling trailer headers in the
4309   future. Transfer encoding is a major performance benefit, so it was
4310   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4311   interoperability problem that could have occurred due to interactions
4312   between authentication trailers, chunked encoding and HTTP/1.0
4313   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4314   and <xref target="header.te" format="counter"/>)
4318<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4320  Empty list elements in list productions have been deprecated.
4321  (<xref target="notation.abnf"/>)
4324  Rules about implicit linear whitespace between certain grammar productions
4325  have been removed; now it's only allowed when specifically pointed out
4326  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4327  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4328  Non-ASCII content in header fields and reason phrase has been obsoleted and
4329  made opaque (the TEXT rule was removed)
4330  (<xref target="basic.rules"/>)
4333  Clarify that HTTP-Version is case sensitive.
4334  (<xref target="http.version"/>)
4337  Remove reference to non-existant identity transfer-coding value tokens.
4338  (Sections <xref format="counter" target="transfer.codings"/> and
4339  <xref format="counter" target="message.length"/>)
4342  Clarification that the chunk length does not include
4343  the count of the octets in the chunk header and trailer.
4344  (<xref target="chunked.transfer.encoding"/>)
4347  Require that invalid whitespace around field-names be rejected.
4348  (<xref target="header.fields"/>)
4351  Update use of abs_path production from RFC1808 to the path-absolute + query
4352  components of RFC3986.
4353  (<xref target="request-target"/>)
4356  Clarify exactly when close connection options must be sent.
4357  (<xref target="header.connection"/>)
4362<section title="Terminology" anchor="terminology">
4364   This specification uses a number of terms to refer to the roles
4365   played by participants in, and objects of, the HTTP communication.
4368  <iref item="content negotiation"/>
4369  <x:dfn>content negotiation</x:dfn>
4370  <list>
4371    <t>
4372      The mechanism for selecting the appropriate representation when
4373      servicing a request, as described in &content.negotiation;. The
4374      representation of entities in any response can be negotiated
4375      (including error responses).
4376    </t>
4377  </list>
4380  <iref item="entity"/>
4381  <x:dfn>entity</x:dfn>
4382  <list>
4383    <t>
4384      The information transferred as the payload of a request or
4385      response. An entity consists of metadata in the form of
4386      entity-header fields and content in the form of an entity-body, as
4387      described in &entity;.
4388    </t>
4389  </list>
4392  <iref item="representation"/>
4393  <x:dfn>representation</x:dfn>
4394  <list>
4395    <t>
4396      An entity included with a response that is subject to content
4397      negotiation, as described in &content.negotiation;. There may exist multiple
4398      representations associated with a particular response status.
4399    </t>
4400  </list>
4403  <iref item="variant"/>
4404  <x:dfn>variant</x:dfn>
4405  <list>
4406    <t>
4407      A resource may have one, or more than one, representation(s)
4408      associated with it at any given instant. Each of these
4409      representations is termed a `variant'.  Use of the term `variant'
4410      does not necessarily imply that the resource is subject to content
4411      negotiation.
4412    </t>
4413  </list>
4417<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4419<artwork type="abnf" name="p1-messaging.parsed-abnf">
4420<x:ref>BWS</x:ref> = OWS
4422<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4423<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4424<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4425<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4426 connection-token ] )
4427<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4428<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4430<x:ref>Date</x:ref> = "Date:" OWS Date-v
4431<x:ref>Date-v</x:ref> = HTTP-date
4433<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4435<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4436<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4437<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4438<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4439 ]
4440<x:ref>Host</x:ref> = "Host:" OWS Host-v
4441<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4443<x:ref>Method</x:ref> = token
4445<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4447<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4449<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4450<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4451<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4452 entity-header ) CRLF ) CRLF [ message-body ]
4453<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4454<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4455 entity-header ) CRLF ) CRLF [ message-body ]
4457<x:ref>Status-Code</x:ref> = 3DIGIT
4458<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4460<x:ref>TE</x:ref> = "TE:" OWS TE-v
4461<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4462<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4463<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4464<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4465<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4466 transfer-coding ] )
4468<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4469<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4470<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4471<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4473<x:ref>Via</x:ref> = "Via:" OWS Via-v
4474<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4475 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4476 ] )
4478<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4480<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4481<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4482<x:ref>attribute</x:ref> = token
4483<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4485<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4486<x:ref>chunk-data</x:ref> = 1*OCTET
4487<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4488<x:ref>chunk-ext-name</x:ref> = token
4489<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4490<x:ref>chunk-size</x:ref> = 1*HEXDIG
4491<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4492<x:ref>connection-token</x:ref> = token
4493<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4494 / %x2A-5B ; '*'-'['
4495 / %x5D-7E ; ']'-'~'
4496 / obs-text
4498<x:ref>date1</x:ref> = day SP month SP year
4499<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4500<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4501<x:ref>day</x:ref> = 2DIGIT
4502<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4503 / %x54.75.65 ; Tue
4504 / %x57.65.64 ; Wed
4505 / %x54.68.75 ; Thu
4506 / %x46.72.69 ; Fri
4507 / %x53.61.74 ; Sat
4508 / %x53.75.6E ; Sun
4509<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4510 / %x54. ; Tuesday
4511 / %x57.65.64.6E. ; Wednesday
4512 / %x54. ; Thursday
4513 / %x46. ; Friday
4514 / %x53. ; Saturday
4515 / %x53.75.6E.64.61.79 ; Sunday
4517<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4518<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4520<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4521<x:ref>field-name</x:ref> = token
4522<x:ref>field-value</x:ref> = *( field-content / OWS )
4524<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4525 / Transfer-Encoding / Upgrade / Via / Warning
4527<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4528<x:ref>hour</x:ref> = 2DIGIT
4529<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4530<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4532<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4534<x:ref>message-body</x:ref> = entity-body /
4535 &lt;entity-body encoded as per Transfer-Encoding&gt;
4536<x:ref>minute</x:ref> = 2DIGIT
4537<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4538 / %x46.65.62 ; Feb
4539 / %x4D.61.72 ; Mar
4540 / %x41.70.72 ; Apr
4541 / %x4D.61.79 ; May
4542 / %x4A.75.6E ; Jun
4543 / %x4A.75.6C ; Jul
4544 / %x41.75.67 ; Aug
4545 / %x53.65.70 ; Sep
4546 / %x4F.63.74 ; Oct
4547 / %x4E.6F.76 ; Nov
4548 / %x44.65.63 ; Dec
4550<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4551<x:ref>obs-fold</x:ref> = CRLF
4552<x:ref>obs-text</x:ref> = %x80-FF
4554<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4555<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4556<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4557<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4558<x:ref>product</x:ref> = token [ "/" product-version ]
4559<x:ref>product-version</x:ref> = token
4560<x:ref>protocol-name</x:ref> = token
4561<x:ref>protocol-version</x:ref> = token
4562<x:ref>pseudonym</x:ref> = token
4564<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4565 / %x5D-7E ; ']'-'~'
4566 / obs-text
4567<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4568<x:ref>quoted-pair</x:ref> = "\" quoted-text
4569<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4570<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4571<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4573<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4574<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4575<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4576<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4577<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4578 / authority
4579<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4580<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4581<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4583<x:ref>second</x:ref> = 2DIGIT
4584<x:ref>start-line</x:ref> = Request-Line / Status-Line
4586<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4587<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4588 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4589<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4590<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4591<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4592<x:ref>token</x:ref> = 1*tchar
4593<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4594<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4595<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4596<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4598<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4600<x:ref>value</x:ref> = token / quoted-string
4602<x:ref>year</x:ref> = 4DIGIT
4605<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4606; Chunked-Body defined but not used
4607; Content-Length defined but not used
4608; HTTP-message defined but not used
4609; Host defined but not used
4610; Request defined but not used
4611; Response defined but not used
4612; TE defined but not used
4613; URI defined but not used
4614; URI-reference defined but not used
4615; http-URI defined but not used
4616; https-URI defined but not used
4617; partial-URI defined but not used
4620<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4622<section title="Since RFC2616">
4624  Extracted relevant partitions from <xref target="RFC2616"/>.
4628<section title="Since draft-ietf-httpbis-p1-messaging-00">
4630  Closed issues:
4631  <list style="symbols">
4632    <t>
4633      <eref target=""/>:
4634      "HTTP Version should be case sensitive"
4635      (<eref target=""/>)
4636    </t>
4637    <t>
4638      <eref target=""/>:
4639      "'unsafe' characters"
4640      (<eref target=""/>)
4641    </t>
4642    <t>
4643      <eref target=""/>:
4644      "Chunk Size Definition"
4645      (<eref target=""/>)
4646    </t>
4647    <t>
4648      <eref target=""/>:
4649      "Message Length"
4650      (<eref target=""/>)
4651    </t>
4652    <t>
4653      <eref target=""/>:
4654      "Media Type Registrations"
4655      (<eref target=""/>)
4656    </t>
4657    <t>
4658      <eref target=""/>:
4659      "URI includes query"
4660      (<eref target=""/>)
4661    </t>
4662    <t>
4663      <eref target=""/>:
4664      "No close on 1xx responses"
4665      (<eref target=""/>)
4666    </t>
4667    <t>
4668      <eref target=""/>:
4669      "Remove 'identity' token references"
4670      (<eref target=""/>)
4671    </t>
4672    <t>
4673      <eref target=""/>:
4674      "Import query BNF"
4675    </t>
4676    <t>
4677      <eref target=""/>:
4678      "qdtext BNF"
4679    </t>
4680    <t>
4681      <eref target=""/>:
4682      "Normative and Informative references"
4683    </t>
4684    <t>
4685      <eref target=""/>:
4686      "RFC2606 Compliance"
4687    </t>
4688    <t>
4689      <eref target=""/>:
4690      "RFC977 reference"
4691    </t>
4692    <t>
4693      <eref target=""/>:
4694      "RFC1700 references"
4695    </t>
4696    <t>
4697      <eref target=""/>:
4698      "inconsistency in date format explanation"
4699    </t>
4700    <t>
4701      <eref target=""/>:
4702      "Date reference typo"
4703    </t>
4704    <t>
4705      <eref target=""/>:
4706      "Informative references"
4707    </t>
4708    <t>
4709      <eref target=""/>:
4710      "ISO-8859-1 Reference"
4711    </t>
4712    <t>
4713      <eref target=""/>:
4714      "Normative up-to-date references"
4715    </t>
4716  </list>
4719  Other changes:
4720  <list style="symbols">
4721    <t>
4722      Update media type registrations to use RFC4288 template.
4723    </t>
4724    <t>
4725      Use names of RFC4234 core rules DQUOTE and WSP,
4726      fix broken ABNF for chunk-data
4727      (work in progress on <eref target=""/>)
4728    </t>
4729  </list>
4733<section title="Since draft-ietf-httpbis-p1-messaging-01">
4735  Closed issues:
4736  <list style="symbols">
4737    <t>
4738      <eref target=""/>:
4739      "Bodies on GET (and other) requests"
4740    </t>
4741    <t>
4742      <eref target=""/>:
4743      "Updating to RFC4288"
4744    </t>
4745    <t>
4746      <eref target=""/>:
4747      "Status Code and Reason Phrase"
4748    </t>
4749    <t>
4750      <eref target=""/>:
4751      "rel_path not used"
4752    </t>
4753  </list>
4756  Ongoing work on ABNF conversion (<eref target=""/>):
4757  <list style="symbols">
4758    <t>
4759      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4760      "trailer-part").
4761    </t>
4762    <t>
4763      Avoid underscore character in rule names ("http_URL" ->
4764      "http-URL", "abs_path" -> "path-absolute").
4765    </t>
4766    <t>
4767      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4768      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4769      have to be updated when switching over to RFC3986.
4770    </t>
4771    <t>
4772      Synchronize core rules with RFC5234.
4773    </t>
4774    <t>
4775      Get rid of prose rules that span multiple lines.
4776    </t>
4777    <t>
4778      Get rid of unused rules LOALPHA and UPALPHA.
4779    </t>
4780    <t>
4781      Move "Product Tokens" section (back) into Part 1, as "token" is used
4782      in the definition of the Upgrade header.
4783    </t>
4784    <t>
4785      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4786    </t>
4787    <t>
4788      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4789    </t>
4790  </list>
4794<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4796  Closed issues:
4797  <list style="symbols">
4798    <t>
4799      <eref target=""/>:
4800      "HTTP-date vs. rfc1123-date"
4801    </t>
4802    <t>
4803      <eref target=""/>:
4804      "WS in quoted-pair"
4805    </t>
4806  </list>
4809  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4810  <list style="symbols">
4811    <t>
4812      Reference RFC 3984, and update header registrations for headers defined
4813      in this document.
4814    </t>
4815  </list>
4818  Ongoing work on ABNF conversion (<eref target=""/>):
4819  <list style="symbols">
4820    <t>
4821      Replace string literals when the string really is case-sensitive (HTTP-Version).
4822    </t>
4823  </list>
4827<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4829  Closed issues:
4830  <list style="symbols">
4831    <t>
4832      <eref target=""/>:
4833      "Connection closing"
4834    </t>
4835    <t>
4836      <eref target=""/>:
4837      "Move registrations and registry information to IANA Considerations"
4838    </t>
4839    <t>
4840      <eref target=""/>:
4841      "need new URL for PAD1995 reference"
4842    </t>
4843    <t>
4844      <eref target=""/>:
4845      "IANA Considerations: update HTTP URI scheme registration"
4846    </t>
4847    <t>
4848      <eref target=""/>:
4849      "Cite HTTPS URI scheme definition"
4850    </t>
4851    <t>
4852      <eref target=""/>:
4853      "List-type headers vs Set-Cookie"
4854    </t>
4855  </list>
4858  Ongoing work on ABNF conversion (<eref target=""/>):
4859  <list style="symbols">
4860    <t>
4861      Replace string literals when the string really is case-sensitive (HTTP-Date).
4862    </t>
4863    <t>
4864      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4865    </t>
4866  </list>
4870<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4872  Closed issues:
4873  <list style="symbols">
4874    <t>
4875      <eref target=""/>:
4876      "Out-of-date reference for URIs"
4877    </t>
4878    <t>
4879      <eref target=""/>:
4880      "RFC 2822 is updated by RFC 5322"
4881    </t>
4882  </list>
4885  Ongoing work on ABNF conversion (<eref target=""/>):
4886  <list style="symbols">
4887    <t>
4888      Use "/" instead of "|" for alternatives.
4889    </t>
4890    <t>
4891      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4892    </t>
4893    <t>
4894      Only reference RFC 5234's core rules.
4895    </t>
4896    <t>
4897      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4898      whitespace ("OWS") and required whitespace ("RWS").
4899    </t>
4900    <t>
4901      Rewrite ABNFs to spell out whitespace rules, factor out
4902      header value format definitions.
4903    </t>
4904  </list>
4908<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4910  Closed issues:
4911  <list style="symbols">
4912    <t>
4913      <eref target=""/>:
4914      "Header LWS"
4915    </t>
4916    <t>
4917      <eref target=""/>:
4918      "Sort 1.3 Terminology"
4919    </t>
4920    <t>
4921      <eref target=""/>:
4922      "RFC2047 encoded words"
4923    </t>
4924    <t>
4925      <eref target=""/>:
4926      "Character Encodings in TEXT"
4927    </t>
4928    <t>
4929      <eref target=""/>:
4930      "Line Folding"
4931    </t>
4932    <t>
4933      <eref target=""/>:
4934      "OPTIONS * and proxies"
4935    </t>
4936    <t>
4937      <eref target=""/>:
4938      "Reason-Phrase BNF"
4939    </t>
4940    <t>
4941      <eref target=""/>:
4942      "Use of TEXT"
4943    </t>
4944    <t>
4945      <eref target=""/>:
4946      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4947    </t>
4948    <t>
4949      <eref target=""/>:
4950      "RFC822 reference left in discussion of date formats"
4951    </t>
4952  </list>
4955  Final work on ABNF conversion (<eref target=""/>):
4956  <list style="symbols">
4957    <t>
4958      Rewrite definition of list rules, deprecate empty list elements.
4959    </t>
4960    <t>
4961      Add appendix containing collected and expanded ABNF.
4962    </t>
4963  </list>
4966  Other changes:
4967  <list style="symbols">
4968    <t>
4969      Rewrite introduction; add mostly new Architecture Section.
4970    </t>
4971    <t>
4972      Move definition of quality values from Part 3 into Part 1;
4973      make TE request header grammar independent of accept-params (defined in Part 3).
4974    </t>
4975  </list>
4979<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4981  Closed issues:
4982  <list style="symbols">
4983    <t>
4984      <eref target=""/>:
4985      "base for numeric protocol elements"
4986    </t>
4987    <t>
4988      <eref target=""/>:
4989      "comment ABNF"
4990    </t>
4991  </list>
4994  Partly resolved issues:
4995  <list style="symbols">
4996    <t>
4997      <eref target=""/>:
4998      "205 Bodies" (took out language that implied that there may be
4999      methods for which a request body MUST NOT be included)
5000    </t>
5001    <t>
5002      <eref target=""/>:
5003      "editorial improvements around HTTP-date"
5004    </t>
5005  </list>
5009<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5011  Closed issues:
5012  <list style="symbols">
5013    <t>
5014      <eref target=""/>:
5015      "IP addresses in URLs"
5016    </t>
5017  </list>
5020  Partly resolved issues:
5021  <list style="symbols">
5022    <t>
5023      <eref target=""/>:
5024      "update IANA requirements wrt Transfer-Coding values" (add the
5025      IANA Considerations subsection)
5026    </t>
5027  </list>
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