source: draft-ietf-httpbis/latest/p1-messaging.xml @ 698

Last change on this file since 698 was 698, checked in by julian.reschke@…, 13 years ago

editorial: enhance readability of header introductions

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
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" updates="2817" 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   The backslash character ("\") can be used as a single-character
462   quoting mechanism only within quoted-string and comment constructs (<xref target="header.fields"/>).
464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
465  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
469<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
470  <x:anchor-alias value="request-header"/>
471  <x:anchor-alias value="response-header"/>
472  <x:anchor-alias value="entity-body"/>
473  <x:anchor-alias value="entity-header"/>
474  <x:anchor-alias value="Cache-Control"/>
475  <x:anchor-alias value="Pragma"/>
476  <x:anchor-alias value="Warning"/>
478  The ABNF rules below are defined in other parts:
480<figure><!-- Part2--><artwork type="abnf2616">
481  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
482  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
484<figure><!-- Part3--><artwork type="abnf2616">
485  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
486  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
488<figure><!-- Part6--><artwork type="abnf2616">
489  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
490  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
491  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
498<section title="HTTP architecture" anchor="architecture">
500   HTTP was created for the World Wide Web architecture
501   and has evolved over time to support the scalability needs of a worldwide
502   hypertext system. Much of that architecture is reflected in the terminology
503   and syntax productions used to define HTTP.
506<section title="Client/Server Operation" anchor="operation">
507<iref item="client"/>
508<iref item="server"/>
509<iref item="connection"/>
511   HTTP is a request/response protocol that operates by exchanging messages
512   across a reliable transport or session-layer connection. An HTTP client
513   is a program that establishes a connection to a server for the purpose
514   of sending one or more HTTP requests.  An HTTP server is a program that
515   accepts connections in order to service HTTP requests by sending HTTP
516   responses.
518<iref item="user agent"/>
519<iref item="origin server"/>
521   Note that the terms "client" and "server" refer only to the roles that
522   these programs perform for a particular connection.  The same program
523   may act as a client on some connections and a server on others.  We use
524   the term "user agent" to refer to the program that initiates a request,
525   such as a WWW browser, editor, or spider (web-traversing robot), and
526   the term "origin server" to refer to the program that can originate
527   authoritative responses to a request.
530   Most HTTP communication consists of a retrieval request (GET) for
531   a representation of some resource identified by a URI.  In the
532   simplest case, this may be accomplished via a single connection (v)
533   between the user agent (UA) and the origin server (O).
535<figure><artwork type="drawing">
536       request chain ------------------------&gt;
537    UA -------------------v------------------- O
538       &lt;----------------------- response chain
540<iref item="message"/>
541<iref item="request"/>
542<iref item="response"/>
544   A client sends an HTTP request to the server in the form of a request
545   message (<xref target="request"/>), beginning with a method, URI, and
546   protocol version, followed by MIME-like header fields containing
547   request modifiers, client information, and payload metadata, an empty
548   line to indicate the end of the header section, and finally the payload
549   body (if any).
552   A server responds to the client's request by sending an HTTP response
553   message (<xref target="response"/>), beginning with a status line that
554   includes 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, and payload metadata, an empty line to
557   indicate the end of the header section, and 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.
990<section title="HTTP Message" anchor="http.message">
991<x:anchor-alias value="generic-message"/>
992<x:anchor-alias value="message.types"/>
993<x:anchor-alias value="HTTP-message"/>
994<x:anchor-alias value="start-line"/>
995<iref item="header section"/>
996<iref item="headers"/>
997<iref item="header field"/>
999   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1000   characters in a format similar to the Internet Message Format
1001   <xref target="RFC5322"/>: zero or more header fields (collectively
1002   referred to as the "headers" or the "header section"), an empty line
1003   indicating the end of the header section, and an optional message-body.
1006   An HTTP message can either be a request from client to server or a
1007   response from server to client.  Syntactically, the two types of message
1008   differ only in the start-line, which is either a Request-Line (for requests)
1009   or a Status-Line (for responses), and in the algorithm for determining
1010   the length of the message-body (<xref target="message.length"/>).
1011   In theory, a client could receive requests and a server could receive
1012   responses, distinguishing them by their different start-line formats,
1013   but in practice servers are implemented to only expect a request
1014   (a response is interpreted as an unknown or invalid request method)
1015   and clients are implemented to only expect a response.
1017<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1018  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1019                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1020                    <x:ref>CRLF</x:ref>
1021                    [ <x:ref>message-body</x:ref> ]
1022  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1025   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1026   header field. The presence of whitespace might be an attempt to trick a
1027   noncompliant implementation of HTTP into ignoring that field or processing
1028   the next line as a new request, either of which may result in security
1029   issues when implementations within the request chain interpret the
1030   same message differently. HTTP/1.1 servers &MUST; reject such a message
1031   with a 400 (Bad Request) response.
1034<section title="Message Parsing Robustness" anchor="message.robustness">
1036   In the interest of robustness, servers &SHOULD; ignore at least one
1037   empty line received where a Request-Line is expected. In other words, if
1038   the server is reading the protocol stream at the beginning of a
1039   message and receives a CRLF first, it should ignore the CRLF.
1042   Some old HTTP/1.0 client implementations generate an extra CRLF
1043   after a POST request as a lame workaround for some early server
1044   applications that failed to read message-body content that was
1045   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1046   preface or follow a request with an extra CRLF.  If terminating
1047   the request message-body with a line-ending is desired, then the
1048   client &MUST; include the terminating CRLF octets as part of the
1049   message-body length.
1052   The normal procedure for parsing an HTTP message is to read the
1053   start-line into a structure, read each header field into a hash
1054   table by field name until the empty line, and then use the parsed
1055   data to determine if a message-body is expected.  If a message-body
1056   has been indicated, then it is read as a stream until an amount
1057   of OCTETs equal to the message-length is read or the connection
1058   is closed.  Care must be taken to parse an HTTP message as a sequence
1059   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1060   to parse HTTP as a stream of Unicode characters in a character encoding
1061   like UTF-16 may introduce security flaws due to the differing ways
1062   that such parsers interpret invalid characters.
1066<section title="Header Fields" anchor="header.fields">
1067  <x:anchor-alias value="header-field"/>
1068  <x:anchor-alias value="field-content"/>
1069  <x:anchor-alias value="field-name"/>
1070  <x:anchor-alias value="field-value"/>
1071  <x:anchor-alias value="OWS"/>
1073   Each HTTP header field consists of a case-insensitive field name
1074   followed by a colon (":"), optional whitespace, and the field value.
1076<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"/>
1077  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> [ <x:ref>field-value</x:ref> ] <x:ref>OWS</x:ref>
1078  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1079  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1080  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1083   No whitespace is allowed between the header field name and colon. For
1084   security reasons, any request message received containing such whitespace
1085   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1086   &MUST; remove any such whitespace from a response message before
1087   forwarding the message downstream.
1090   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1091   preferred. The field value does not include any leading or trailing white
1092   space: OWS occurring before the first non-whitespace character of the
1093   field value or after the last non-whitespace character of the field value
1094   is ignored and &SHOULD; be removed without changing the meaning of the header
1095   field.
1098   The order in which header fields with differing field names are
1099   received is not significant. However, it is "good practice" to send
1100   header fields that contain control data first, such as Host on
1101   requests and Date on responses, so that implementations can decide
1102   when not to handle a message as early as possible.  A server &MUST;
1103   wait until the entire header section is received before interpreting
1104   a request message, since later header fields might include conditionals,
1105   authentication credentials, or deliberately misleading duplicate
1106   header fields that would impact request processing.
1109   Multiple header fields with the same field name &MUST-NOT; be
1110   sent in a message unless the entire field value for that
1111   header field is defined as a comma-separated list [i.e., #(values)].
1112   Multiple header fields with the same field name can be combined into
1113   one "field-name: field-value" pair, without changing the semantics of the
1114   message, by appending each subsequent field value to the combined
1115   field value in order, separated by a comma. The order in which
1116   header fields with the same field name are received is therefore
1117   significant to the interpretation of the combined field value;
1118   a proxy &MUST-NOT; change the order of these field values when
1119   forwarding a message.
1122  <t>
1123   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1124   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1125   can occur multiple times, but does not use the list syntax, and thus cannot
1126   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1127   for details.) Also note that the Set-Cookie2 header specified in
1128   <xref target="RFC2965"/> does not share this problem.
1129  </t>
1132   Historically, HTTP header field values could be extended over multiple
1133   lines by preceding each extra line with at least one space or horizontal
1134   tab character (line folding). This specification deprecates such line
1135   folding except within the message/http media type
1136   (<xref target=""/>).
1137   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1138   (i.e., that contain any field-content that matches the obs-fold rule) unless
1139   the message is intended for packaging within the message/http media type.
1140   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1141   obs-fold whitespace with a single SP prior to interpreting the field value
1142   or forwarding the message downstream.
1145   Historically, HTTP has allowed field content with text in the ISO-8859-1
1146   <xref target="ISO-8859-1"/> character encoding and supported other
1147   character sets only through use of <xref target="RFC2047"/> encoding.
1148   In practice, most HTTP header field values use only a subset of the
1149   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1150   header fields &SHOULD; limit their field values to US-ASCII characters.
1151   Recipients &SHOULD; treat other (obs-text) octets in field content as
1152   opaque data.
1154<t anchor="rule.comment">
1155  <x:anchor-alias value="comment"/>
1156  <x:anchor-alias value="ctext"/>
1157   Comments can be included in some HTTP header fields by surrounding
1158   the comment text with parentheses. Comments are only allowed in
1159   fields containing "comment" as part of their field value definition.
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1162  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1163  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1164                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1169<section title="Message Body" anchor="message.body">
1170  <x:anchor-alias value="message-body"/>
1172   The message-body (if any) of an HTTP message is used to carry the
1173   entity-body associated with the request or response. The message-body
1174   differs from the entity-body only when a transfer-coding has been
1175   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1178  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1179               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1182   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1183   applied by an application to ensure safe and proper transfer of the
1184   message. Transfer-Encoding is a property of the message, not of the
1185   entity, and thus &MAY; be added or removed by any application along the
1186   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1187   when certain transfer-codings may be used.)
1190   The rules for when a message-body is allowed in a message differ for
1191   requests and responses.
1194   The presence of a message-body in a request is signaled by the
1195   inclusion of a Content-Length or Transfer-Encoding header field in
1196   the request's header fields.
1197   When a request message contains both a message-body of non-zero
1198   length and a method that does not define any semantics for that
1199   request message-body, then an origin server &SHOULD; either ignore
1200   the message-body or respond with an appropriate error message
1201   (e.g., 413).  A proxy or gateway, when presented the same request,
1202   &SHOULD; either forward the request inbound with the message-body or
1203   ignore the message-body when determining a response.
1206   For response messages, whether or not a message-body is included with
1207   a message is dependent on both the request method and the response
1208   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1209   &MUST-NOT; include a message-body, even though the presence of entity-header
1210   fields might lead one to believe they do. All 1xx
1211   (informational), 204 (No Content), and 304 (Not Modified) responses
1212   &MUST-NOT; include a message-body. All other responses do include a
1213   message-body, although it &MAY; be of zero length.
1217<section title="Message Length" anchor="message.length">
1219   The transfer-length of a message is the length of the message-body as
1220   it appears in the message; that is, after any transfer-codings have
1221   been applied. When a message-body is included with a message, the
1222   transfer-length of that body is determined by one of the following
1223   (in order of precedence):
1226  <list style="numbers">
1227    <x:lt><t>
1228     Any response message which "&MUST-NOT;" include a message-body (such
1229     as the 1xx, 204, and 304 responses and any response to a HEAD
1230     request) is always terminated by the first empty line after the
1231     header fields, regardless of the entity-header fields present in
1232     the message.
1233    </t></x:lt>
1234    <x:lt><t>
1235     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1236     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1237     is used, the transfer-length is defined by the use of this transfer-coding.
1238     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1239     is not present, the transfer-length is defined by the sender closing the connection.
1240    </t></x:lt>
1241    <x:lt><t>
1242     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1243     value in OCTETs represents both the entity-length and the
1244     transfer-length. The Content-Length header field &MUST-NOT; be sent
1245     if these two lengths are different (i.e., if a Transfer-Encoding
1246     header field is present). If a message is received with both a
1247     Transfer-Encoding header field and a Content-Length header field,
1248     the latter &MUST; be ignored.
1249    </t></x:lt>
1250    <x:lt><t>
1251     If the message uses the media type "multipart/byteranges", and the
1252     transfer-length is not otherwise specified, then this self-delimiting
1253     media type defines the transfer-length. This media type
1254     &MUST-NOT; be used unless the sender knows that the recipient can parse
1255     it; the presence in a request of a Range header with multiple byte-range
1256     specifiers from a 1.1 client implies that the client can parse
1257     multipart/byteranges responses.
1258    <list style="empty"><t>
1259       A range header might be forwarded by a 1.0 proxy that does not
1260       understand multipart/byteranges; in this case the server &MUST;
1261       delimit the message using methods defined in items 1, 3 or 5 of
1262       this section.
1263    </t></list>
1264    </t></x:lt>
1265    <x:lt><t>
1266     By the server closing the connection. (Closing the connection
1267     cannot be used to indicate the end of a request body, since that
1268     would leave no possibility for the server to send back a response.)
1269    </t></x:lt>
1270  </list>
1273   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1274   containing a message-body &MUST; include a valid Content-Length header
1275   field unless the server is known to be HTTP/1.1 compliant. If a
1276   request contains a message-body and a Content-Length is not given,
1277   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1278   determine the length of the message, or with 411 (Length Required) if
1279   it wishes to insist on receiving a valid Content-Length.
1282   All HTTP/1.1 applications that receive entities &MUST; accept the
1283   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1284   to be used for messages when the message length cannot be determined
1285   in advance.
1288   Messages &MUST-NOT; include both a Content-Length header field and a
1289   transfer-coding. If the message does include a
1290   transfer-coding, the Content-Length &MUST; be ignored.
1293   When a Content-Length is given in a message where a message-body is
1294   allowed, its field value &MUST; exactly match the number of OCTETs in
1295   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1296   invalid length is received and detected.
1300<section title="General Header Fields" anchor="general.header.fields">
1301  <x:anchor-alias value="general-header"/>
1303   There are a few header fields which have general applicability for
1304   both request and response messages, but which do not apply to the
1305   entity being transferred. These header fields apply only to the
1306   message being transmitted.
1308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1309  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1310                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1311                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1312                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1313                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1314                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1315                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1316                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1317                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1320   General-header field names can be extended reliably only in
1321   combination with a change in the protocol version. However, new or
1322   experimental header fields may be given the semantics of general
1323   header fields if all parties in the communication recognize them to
1324   be general-header fields. Unrecognized header fields are treated as
1325   entity-header fields.
1330<section title="Request" anchor="request">
1331  <x:anchor-alias value="Request"/>
1333   A request message from a client to a server includes, within the
1334   first line of that message, the method to be applied to the resource,
1335   the identifier of the resource, and the protocol version in use.
1337<!--                 Host                      ; should be moved here eventually -->
1338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1339  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1340                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1341                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1342                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1343                  <x:ref>CRLF</x:ref>
1344                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1347<section title="Request-Line" anchor="request-line">
1348  <x:anchor-alias value="Request-Line"/>
1350   The Request-Line begins with a method token, followed by the
1351   request-target and the protocol version, and ending with CRLF. The
1352   elements are separated by SP characters. No CR or LF is allowed
1353   except in the final CRLF sequence.
1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1356  <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>
1359<section title="Method" anchor="method">
1360  <x:anchor-alias value="Method"/>
1362   The Method  token indicates the method to be performed on the
1363   resource identified by the request-target. The method is case-sensitive.
1365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1366  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1370<section title="request-target" anchor="request-target">
1371  <x:anchor-alias value="request-target"/>
1373   The request-target
1374   identifies the resource upon which to apply the request.
1376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1377  <x:ref>request-target</x:ref> = "*"
1378                 / <x:ref>absolute-URI</x:ref>
1379                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1380                 / <x:ref>authority</x:ref>
1383   The four options for request-target are dependent on the nature of the
1384   request. The asterisk "*" means that the request does not apply to a
1385   particular resource, but to the server itself, and is only allowed
1386   when the method used does not necessarily apply to a resource. One
1387   example would be
1389<figure><artwork type="example">
1390  OPTIONS * HTTP/1.1
1393   The absolute-URI form is &REQUIRED; when the request is being made to a
1394   proxy. The proxy is requested to forward the request or service it
1395   from a valid cache, and return the response. Note that the proxy &MAY;
1396   forward the request on to another proxy or directly to the server
1397   specified by the absolute-URI. In order to avoid request loops, a
1398   proxy &MUST; be able to recognize all of its server names, including
1399   any aliases, local variations, and the numeric IP address. An example
1400   Request-Line would be:
1402<figure><artwork type="example">
1403  GET HTTP/1.1
1406   To allow for transition to absolute-URIs in all requests in future
1407   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1408   form in requests, even though HTTP/1.1 clients will only generate
1409   them in requests to proxies.
1412   The authority form is only used by the CONNECT method (&CONNECT;).
1415   The most common form of request-target is that used to identify a
1416   resource on an origin server or gateway. In this case the absolute
1417   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1418   the request-target, and the network location of the URI (authority) &MUST;
1419   be transmitted in a Host header field. For example, a client wishing
1420   to retrieve the resource above directly from the origin server would
1421   create a TCP connection to port 80 of the host "" and send
1422   the lines:
1424<figure><artwork type="example">
1425  GET /pub/WWW/TheProject.html HTTP/1.1
1426  Host:
1429   followed by the remainder of the Request. Note that the absolute path
1430   cannot be empty; if none is present in the original URI, it &MUST; be
1431   given as "/" (the server root).
1434   If a proxy receives a request without any path in the request-target and
1435   the method specified is capable of supporting the asterisk form of
1436   request-target, then the last proxy on the request chain &MUST; forward the
1437   request with "*" as the final request-target.
1440   For example, the request
1441</preamble><artwork type="example">
1442  OPTIONS HTTP/1.1
1445  would be forwarded by the proxy as
1446</preamble><artwork type="example">
1447  OPTIONS * HTTP/1.1
1448  Host:
1451   after connecting to port 8001 of host "".
1455   The request-target is transmitted in the format specified in
1456   <xref target="http.uri"/>. If the request-target is percent-encoded
1457   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1458   &MUST; decode the request-target in order to
1459   properly interpret the request. Servers &SHOULD; respond to invalid
1460   request-targets with an appropriate status code.
1463   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1464   received request-target when forwarding it to the next inbound server,
1465   except as noted above to replace a null path-absolute with "/".
1468  <t>
1469    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1470    meaning of the request when the origin server is improperly using
1471    a non-reserved URI character for a reserved purpose.  Implementors
1472    should be aware that some pre-HTTP/1.1 proxies have been known to
1473    rewrite the request-target.
1474  </t>
1477   HTTP does not place a pre-defined limit on the length of a request-target.
1478   A server &MUST; be prepared to receive URIs of unbounded length and
1479   respond with the 414 (URI Too Long) status if the received
1480   request-target would be longer than the server wishes to handle
1481   (see &status-414;).
1484   Various ad-hoc limitations on request-target length are found in practice.
1485   It is &RECOMMENDED; that all HTTP senders and recipients support
1486   request-target lengths of 8000 or more OCTETs.
1491<section title="The Resource Identified by a Request" anchor="">
1493   The exact resource identified by an Internet request is determined by
1494   examining both the request-target and the Host header field.
1497   An origin server that does not allow resources to differ by the
1498   requested host &MAY; ignore the Host header field value when
1499   determining the resource identified by an HTTP/1.1 request. (But see
1500   <xref target=""/>
1501   for other requirements on Host support in HTTP/1.1.)
1504   An origin server that does differentiate resources based on the host
1505   requested (sometimes referred to as virtual hosts or vanity host
1506   names) &MUST; use the following rules for determining the requested
1507   resource on an HTTP/1.1 request:
1508  <list style="numbers">
1509    <t>If request-target is an absolute-URI, the host is part of the
1510     request-target. Any Host header field value in the request &MUST; be
1511     ignored.</t>
1512    <t>If the request-target is not an absolute-URI, and the request includes
1513     a Host header field, the host is determined by the Host header
1514     field value.</t>
1515    <t>If the host as determined by rule 1 or 2 is not a valid host on
1516     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1517  </list>
1520   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1521   attempt to use heuristics (e.g., examination of the URI path for
1522   something unique to a particular host) in order to determine what
1523   exact resource is being requested.
1530<section title="Response" anchor="response">
1531  <x:anchor-alias value="Response"/>
1533   After receiving and interpreting a request message, a server responds
1534   with an HTTP response message.
1536<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1537  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1538                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1539                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1540                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1541                  <x:ref>CRLF</x:ref>
1542                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1545<section title="Status-Line" anchor="status-line">
1546  <x:anchor-alias value="Status-Line"/>
1548   The first line of a Response message is the Status-Line, consisting
1549   of the protocol version followed by a numeric status code and its
1550   associated textual phrase, with each element separated by SP
1551   characters. No CR or LF is allowed except in the final CRLF sequence.
1553<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1554  <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>
1557<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1558  <x:anchor-alias value="Reason-Phrase"/>
1559  <x:anchor-alias value="Status-Code"/>
1561   The Status-Code element is a 3-digit integer result code of the
1562   attempt to understand and satisfy the request. These codes are fully
1563   defined in &status-codes;.  The Reason Phrase exists for the sole
1564   purpose of providing a textual description associated with the numeric
1565   status code, out of deference to earlier Internet application protocols
1566   that were more frequently used with interactive text clients.
1567   A client &SHOULD; ignore the content of the Reason Phrase.
1570   The first digit of the Status-Code defines the class of response. The
1571   last two digits do not have any categorization role. There are 5
1572   values for the first digit:
1573  <list style="symbols">
1574    <t>
1575      1xx: Informational - Request received, continuing process
1576    </t>
1577    <t>
1578      2xx: Success - The action was successfully received,
1579        understood, and accepted
1580    </t>
1581    <t>
1582      3xx: Redirection - Further action must be taken in order to
1583        complete the request
1584    </t>
1585    <t>
1586      4xx: Client Error - The request contains bad syntax or cannot
1587        be fulfilled
1588    </t>
1589    <t>
1590      5xx: Server Error - The server failed to fulfill an apparently
1591        valid request
1592    </t>
1593  </list>
1595<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"/>
1596  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1597  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1605<section title="Protocol Parameters" anchor="protocol.parameters">
1607<section title="Date/Time Formats: Full Date" anchor="">
1608  <x:anchor-alias value="HTTP-date"/>
1610   HTTP applications have historically allowed three different formats
1611   for the representation of date/time stamps:
1613<figure><artwork type="example">
1614  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1615  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1616  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1619   The first format is preferred as an Internet standard and represents
1620   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1621   other formats are described here only for
1622   compatibility with obsolete implementations.
1623   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1624   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1625   only generate the RFC 1123 format for representing HTTP-date values
1626   in header fields. See <xref target="tolerant.applications"/> for further information.
1629   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1630   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1631   equal to UTC (Coordinated Universal Time). This is indicated in the
1632   first two formats by the inclusion of "GMT" as the three-letter
1633   abbreviation for time zone, and &MUST; be assumed when reading the
1634   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1635   additional whitespace beyond that specifically included as SP in the
1636   grammar.
1638<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1639  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1641<t anchor="">
1642  <x:anchor-alias value="rfc1123-date"/>
1643  <x:anchor-alias value="time-of-day"/>
1644  <x:anchor-alias value="hour"/>
1645  <x:anchor-alias value="minute"/>
1646  <x:anchor-alias value="second"/>
1647  <x:anchor-alias value="day-name"/>
1648  <x:anchor-alias value="day"/>
1649  <x:anchor-alias value="month"/>
1650  <x:anchor-alias value="year"/>
1651  <x:anchor-alias value="GMT"/>
1652  Preferred format:
1654<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"/>
1655  <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>
1657  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1658               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1659               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1660               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1661               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1662               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1663               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1665  <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>
1666               ; e.g., 02 Jun 1982
1668  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1669  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1670               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1671               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1672               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1673               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1674               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1675               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1676               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1677               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1678               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1679               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1680               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1681  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1683  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1685  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1686                 ; 00:00:00 - 23:59:59
1688  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1689  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1690  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1693  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1694  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1695  same as those defined for the RFC 5322 constructs
1696  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1698<t anchor="">
1699  <x:anchor-alias value="obs-date"/>
1700  <x:anchor-alias value="rfc850-date"/>
1701  <x:anchor-alias value="asctime-date"/>
1702  <x:anchor-alias value="date1"/>
1703  <x:anchor-alias value="date2"/>
1704  <x:anchor-alias value="date3"/>
1705  <x:anchor-alias value="rfc1123-date"/>
1706  <x:anchor-alias value="day-name-l"/>
1707  Obsolete formats:
1709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1710  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1712<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1713  <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>
1714  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1715                 ; day-month-year (e.g., 02-Jun-82)
1717  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1718         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1719         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1720         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1721         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1722         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1723         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1725<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1726  <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>
1727  <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> ))
1728                 ; month day (e.g., Jun  2)
1731  <t>
1732    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1733    accepting date values that may have been sent by non-HTTP
1734    applications, as is sometimes the case when retrieving or posting
1735    messages via proxies/gateways to SMTP or NNTP.
1736  </t>
1739  <t>
1740    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1741    to their usage within the protocol stream. Clients and servers are
1742    not required to use these formats for user presentation, request
1743    logging, etc.
1744  </t>
1748<section title="Transfer Codings" anchor="transfer.codings">
1749  <x:anchor-alias value="transfer-coding"/>
1750  <x:anchor-alias value="transfer-extension"/>
1752   Transfer-coding values are used to indicate an encoding
1753   transformation that has been, can be, or may need to be applied to an
1754   entity-body in order to ensure "safe transport" through the network.
1755   This differs from a content coding in that the transfer-coding is a
1756   property of the message, not of the original entity.
1758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1759  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1760                          / "compress" ; <xref target="compress.coding"/>
1761                          / "deflate" ; <xref target="deflate.coding"/>
1762                          / "gzip" ; <xref target="gzip.coding"/>
1763                          / <x:ref>transfer-extension</x:ref>
1764  <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> )
1766<t anchor="rule.parameter">
1767  <x:anchor-alias value="attribute"/>
1768  <x:anchor-alias value="transfer-parameter"/>
1769  <x:anchor-alias value="value"/>
1770   Parameters are in  the form of attribute/value pairs.
1772<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"/>
1773  <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>
1774  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1775  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1778   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1779   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1780   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1783   Whenever a transfer-coding is applied to a message-body, the set of
1784   transfer-codings &MUST; include "chunked", unless the message indicates it
1785   is terminated by closing the connection. When the "chunked" transfer-coding
1786   is used, it &MUST; be the last transfer-coding applied to the
1787   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1788   than once to a message-body. These rules allow the recipient to
1789   determine the transfer-length of the message (<xref target="message.length"/>).
1792   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1793   MIME, which were designed to enable safe transport of binary data over a
1794   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1795   However, safe transport
1796   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1797   the only unsafe characteristic of message-bodies is the difficulty in
1798   determining the exact body length (<xref target="message.length"/>), or the desire to
1799   encrypt data over a shared transport.
1802   A server which receives an entity-body with a transfer-coding it does
1803   not understand &SHOULD; return 501 (Not Implemented), and close the
1804   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1805   client.
1808<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1809  <iref item="chunked (Coding Format)"/>
1810  <iref item="Coding Format" subitem="chunked"/>
1811  <x:anchor-alias value="chunk"/>
1812  <x:anchor-alias value="Chunked-Body"/>
1813  <x:anchor-alias value="chunk-data"/>
1814  <x:anchor-alias value="chunk-ext"/>
1815  <x:anchor-alias value="chunk-ext-name"/>
1816  <x:anchor-alias value="chunk-ext-val"/>
1817  <x:anchor-alias value="chunk-size"/>
1818  <x:anchor-alias value="last-chunk"/>
1819  <x:anchor-alias value="trailer-part"/>
1821   The chunked encoding modifies the body of a message in order to
1822   transfer it as a series of chunks, each with its own size indicator,
1823   followed by an &OPTIONAL; trailer containing entity-header fields. This
1824   allows dynamically produced content to be transferred along with the
1825   information necessary for the recipient to verify that it has
1826   received the full message.
1828<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"/>
1829  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1830                   <x:ref>last-chunk</x:ref>
1831                   <x:ref>trailer-part</x:ref>
1832                   <x:ref>CRLF</x:ref>
1834  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1835                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1836  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1837  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1839  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1840                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1841  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1842  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1843  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1844  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1847   The chunk-size field is a string of hex digits indicating the size of
1848   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1849   zero, followed by the trailer, which is terminated by an empty line.
1852   The trailer allows the sender to include additional HTTP header
1853   fields at the end of the message. The Trailer header field can be
1854   used to indicate which header fields are included in a trailer (see
1855   <xref target="header.trailer"/>).
1858   A server using chunked transfer-coding in a response &MUST-NOT; use the
1859   trailer for any header fields unless at least one of the following is
1860   true:
1861  <list style="numbers">
1862    <t>the request included a TE header field that indicates "trailers" is
1863     acceptable in the transfer-coding of the  response, as described in
1864     <xref target="header.te"/>; or,</t>
1866    <t>the server is the origin server for the response, the trailer
1867     fields consist entirely of optional metadata, and the recipient
1868     could use the message (in a manner acceptable to the origin server)
1869     without receiving this metadata.  In other words, the origin server
1870     is willing to accept the possibility that the trailer fields might
1871     be silently discarded along the path to the client.</t>
1872  </list>
1875   This requirement prevents an interoperability failure when the
1876   message is being received by an HTTP/1.1 (or later) proxy and
1877   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1878   compliance with the protocol would have necessitated a possibly
1879   infinite buffer on the proxy.
1882   A process for decoding the "chunked" transfer-coding
1883   can be represented in pseudo-code as:
1885<figure><artwork type="code">
1886  length := 0
1887  read chunk-size, chunk-ext (if any) and CRLF
1888  while (chunk-size &gt; 0) {
1889     read chunk-data and CRLF
1890     append chunk-data to entity-body
1891     length := length + chunk-size
1892     read chunk-size and CRLF
1893  }
1894  read entity-header
1895  while (entity-header not empty) {
1896     append entity-header to existing header fields
1897     read entity-header
1898  }
1899  Content-Length := length
1900  Remove "chunked" from Transfer-Encoding
1903   All HTTP/1.1 applications &MUST; be able to receive and decode the
1904   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1905   they do not understand.
1909<section title="Compression Codings" anchor="compression.codings">
1911   The codings defined below can be used to compress the payload of a
1912   message.
1915   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1916   is not desirable and is discouraged for future encodings. Their
1917   use here is representative of historical practice, not good
1918   design.
1921   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1922   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1923   equivalent to "gzip" and "compress" respectively.
1926<section title="Compress Coding" anchor="compress.coding">
1927<iref item="compress (Coding Format)"/>
1928<iref item="Coding Format" subitem="compress"/>
1930   The "compress" format is produced by the common UNIX file compression
1931   program "compress". This format is an adaptive Lempel-Ziv-Welch
1932   coding (LZW).
1936<section title="Deflate Coding" anchor="deflate.coding">
1937<iref item="deflate (Coding Format)"/>
1938<iref item="Coding Format" subitem="deflate"/>
1940   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
1941   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
1945<section title="Gzip Coding" anchor="gzip.coding">
1946<iref item="gzip (Coding Format)"/>
1947<iref item="Coding Format" subitem="gzip"/>
1949   The "gzip" format is produced by the file compression program
1950   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
1951   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
1957<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
1959   The HTTP Transfer Coding Registry defines the name space for the transfer
1960   coding names.
1963   Registrations &MUST; include the following fields:
1964   <list style="symbols">
1965     <t>Name</t>
1966     <t>Description</t>
1967     <t>Pointer to specification text</t>
1968   </list>
1971   Values to be added to this name space require expert review and a specification
1972   (see "Expert Review" and "Specification Required" in
1973   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
1974   conform to the purpose of transfer coding defined in this section.
1977   The registry itself is maintained at
1978   <eref target=""/>.
1983<section title="Product Tokens" anchor="product.tokens">
1984  <x:anchor-alias value="product"/>
1985  <x:anchor-alias value="product-version"/>
1987   Product tokens are used to allow communicating applications to
1988   identify themselves by software name and version. Most fields using
1989   product tokens also allow sub-products which form a significant part
1990   of the application to be listed, separated by whitespace. By
1991   convention, the products are listed in order of their significance
1992   for identifying the application.
1994<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1995  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1996  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1999   Examples:
2001<figure><artwork type="example">
2002  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2003  Server: Apache/0.8.4
2006   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2007   used for advertising or other non-essential information. Although any
2008   token character &MAY; appear in a product-version, this token &SHOULD;
2009   only be used for a version identifier (i.e., successive versions of
2010   the same product &SHOULD; only differ in the product-version portion of
2011   the product value).
2015<section title="Quality Values" anchor="quality.values">
2016  <x:anchor-alias value="qvalue"/>
2018   Both transfer codings (TE request header, <xref target="header.te"/>)
2019   and content negotiation (&content.negotiation;) use short "floating point"
2020   numbers to indicate the relative importance ("weight") of various
2021   negotiable parameters.  A weight is normalized to a real number in
2022   the range 0 through 1, where 0 is the minimum and 1 the maximum
2023   value. If a parameter has a quality value of 0, then content with
2024   this parameter is `not acceptable' for the client. HTTP/1.1
2025   applications &MUST-NOT; generate more than three digits after the
2026   decimal point. User configuration of these values &SHOULD; also be
2027   limited in this fashion.
2029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2030  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2031                 / ( "1" [ "." 0*3("0") ] )
2034  <t>
2035     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2036     relative degradation in desired quality.
2037  </t>
2043<section title="Connections" anchor="connections">
2045<section title="Persistent Connections" anchor="persistent.connections">
2047<section title="Purpose" anchor="persistent.purpose">
2049   Prior to persistent connections, a separate TCP connection was
2050   established to fetch each URL, increasing the load on HTTP servers
2051   and causing congestion on the Internet. The use of inline images and
2052   other associated data often require a client to make multiple
2053   requests of the same server in a short amount of time. Analysis of
2054   these performance problems and results from a prototype
2055   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2056   measurements of actual HTTP/1.1 implementations show good
2057   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2058   T/TCP <xref target="Tou1998"/>.
2061   Persistent HTTP connections have a number of advantages:
2062  <list style="symbols">
2063      <t>
2064        By opening and closing fewer TCP connections, CPU time is saved
2065        in routers and hosts (clients, servers, proxies, gateways,
2066        tunnels, or caches), and memory used for TCP protocol control
2067        blocks can be saved in hosts.
2068      </t>
2069      <t>
2070        HTTP requests and responses can be pipelined on a connection.
2071        Pipelining allows a client to make multiple requests without
2072        waiting for each response, allowing a single TCP connection to
2073        be used much more efficiently, with much lower elapsed time.
2074      </t>
2075      <t>
2076        Network congestion is reduced by reducing the number of packets
2077        caused by TCP opens, and by allowing TCP sufficient time to
2078        determine the congestion state of the network.
2079      </t>
2080      <t>
2081        Latency on subsequent requests is reduced since there is no time
2082        spent in TCP's connection opening handshake.
2083      </t>
2084      <t>
2085        HTTP can evolve more gracefully, since errors can be reported
2086        without the penalty of closing the TCP connection. Clients using
2087        future versions of HTTP might optimistically try a new feature,
2088        but if communicating with an older server, retry with old
2089        semantics after an error is reported.
2090      </t>
2091    </list>
2094   HTTP implementations &SHOULD; implement persistent connections.
2098<section title="Overall Operation" anchor="persistent.overall">
2100   A significant difference between HTTP/1.1 and earlier versions of
2101   HTTP is that persistent connections are the default behavior of any
2102   HTTP connection. That is, unless otherwise indicated, the client
2103   &SHOULD; assume that the server will maintain a persistent connection,
2104   even after error responses from the server.
2107   Persistent connections provide a mechanism by which a client and a
2108   server can signal the close of a TCP connection. This signaling takes
2109   place using the Connection header field (<xref target="header.connection"/>). Once a close
2110   has been signaled, the client &MUST-NOT; send any more requests on that
2111   connection.
2114<section title="Negotiation" anchor="persistent.negotiation">
2116   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2117   maintain a persistent connection unless a Connection header including
2118   the connection-token "close" was sent in the request. If the server
2119   chooses to close the connection immediately after sending the
2120   response, it &SHOULD; send a Connection header including the
2121   connection-token close.
2124   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2125   decide to keep it open based on whether the response from a server
2126   contains a Connection header with the connection-token close. In case
2127   the client does not want to maintain a connection for more than that
2128   request, it &SHOULD; send a Connection header including the
2129   connection-token close.
2132   If either the client or the server sends the close token in the
2133   Connection header, that request becomes the last one for the
2134   connection.
2137   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2138   maintained for HTTP versions less than 1.1 unless it is explicitly
2139   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2140   compatibility with HTTP/1.0 clients.
2143   In order to remain persistent, all messages on the connection &MUST;
2144   have a self-defined message length (i.e., one not defined by closure
2145   of the connection), as described in <xref target="message.length"/>.
2149<section title="Pipelining" anchor="pipelining">
2151   A client that supports persistent connections &MAY; "pipeline" its
2152   requests (i.e., send multiple requests without waiting for each
2153   response). A server &MUST; send its responses to those requests in the
2154   same order that the requests were received.
2157   Clients which assume persistent connections and pipeline immediately
2158   after connection establishment &SHOULD; be prepared to retry their
2159   connection if the first pipelined attempt fails. If a client does
2160   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2161   persistent. Clients &MUST; also be prepared to resend their requests if
2162   the server closes the connection before sending all of the
2163   corresponding responses.
2166   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2167   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2168   premature termination of the transport connection could lead to
2169   indeterminate results. A client wishing to send a non-idempotent
2170   request &SHOULD; wait to send that request until it has received the
2171   response status for the previous request.
2176<section title="Proxy Servers" anchor="persistent.proxy">
2178   It is especially important that proxies correctly implement the
2179   properties of the Connection header field as specified in <xref target="header.connection"/>.
2182   The proxy server &MUST; signal persistent connections separately with
2183   its clients and the origin servers (or other proxy servers) that it
2184   connects to. Each persistent connection applies to only one transport
2185   link.
2188   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2189   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2190   for information and discussion of the problems with the Keep-Alive header
2191   implemented by many HTTP/1.0 clients).
2195<section title="Practical Considerations" anchor="persistent.practical">
2197   Servers will usually have some time-out value beyond which they will
2198   no longer maintain an inactive connection. Proxy servers might make
2199   this a higher value since it is likely that the client will be making
2200   more connections through the same server. The use of persistent
2201   connections places no requirements on the length (or existence) of
2202   this time-out for either the client or the server.
2205   When a client or server wishes to time-out it &SHOULD; issue a graceful
2206   close on the transport connection. Clients and servers &SHOULD; both
2207   constantly watch for the other side of the transport close, and
2208   respond to it as appropriate. If a client or server does not detect
2209   the other side's close promptly it could cause unnecessary resource
2210   drain on the network.
2213   A client, server, or proxy &MAY; close the transport connection at any
2214   time. For example, a client might have started to send a new request
2215   at the same time that the server has decided to close the "idle"
2216   connection. From the server's point of view, the connection is being
2217   closed while it was idle, but from the client's point of view, a
2218   request is in progress.
2221   This means that clients, servers, and proxies &MUST; be able to recover
2222   from asynchronous close events. Client software &SHOULD; reopen the
2223   transport connection and retransmit the aborted sequence of requests
2224   without user interaction so long as the request sequence is
2225   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2226   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2227   human operator the choice of retrying the request(s). Confirmation by
2228   user-agent software with semantic understanding of the application
2229   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2230   be repeated if the second sequence of requests fails.
2233   Servers &SHOULD; always respond to at least one request per connection,
2234   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2235   middle of transmitting a response, unless a network or client failure
2236   is suspected.
2239   Clients that use persistent connections &SHOULD; limit the number of
2240   simultaneous connections that they maintain to a given server. A
2241   single-user client &SHOULD-NOT; maintain more than 2 connections with
2242   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2243   another server or proxy, where N is the number of simultaneously
2244   active users. These guidelines are intended to improve HTTP response
2245   times and avoid congestion.
2250<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2252<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2254   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2255   flow control mechanisms to resolve temporary overloads, rather than
2256   terminating connections with the expectation that clients will retry.
2257   The latter technique can exacerbate network congestion.
2261<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2263   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2264   the network connection for an error status while it is transmitting
2265   the request. If the client sees an error status, it &SHOULD;
2266   immediately cease transmitting the body. If the body is being sent
2267   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2268   empty trailer &MAY; be used to prematurely mark the end of the message.
2269   If the body was preceded by a Content-Length header, the client &MUST;
2270   close the connection.
2274<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2276   The purpose of the 100 (Continue) status (see &status-100;) is to
2277   allow a client that is sending a request message with a request body
2278   to determine if the origin server is willing to accept the request
2279   (based on the request headers) before the client sends the request
2280   body. In some cases, it might either be inappropriate or highly
2281   inefficient for the client to send the body if the server will reject
2282   the message without looking at the body.
2285   Requirements for HTTP/1.1 clients:
2286  <list style="symbols">
2287    <t>
2288        If a client will wait for a 100 (Continue) response before
2289        sending the request body, it &MUST; send an Expect request-header
2290        field (&header-expect;) with the "100-continue" expectation.
2291    </t>
2292    <t>
2293        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2294        with the "100-continue" expectation if it does not intend
2295        to send a request body.
2296    </t>
2297  </list>
2300   Because of the presence of older implementations, the protocol allows
2301   ambiguous situations in which a client may send "Expect: 100-continue"
2302   without receiving either a 417 (Expectation Failed) status
2303   or a 100 (Continue) status. Therefore, when a client sends this
2304   header field to an origin server (possibly via a proxy) from which it
2305   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2306   for an indefinite period before sending the request body.
2309   Requirements for HTTP/1.1 origin servers:
2310  <list style="symbols">
2311    <t> Upon receiving a request which includes an Expect request-header
2312        field with the "100-continue" expectation, an origin server &MUST;
2313        either respond with 100 (Continue) status and continue to read
2314        from the input stream, or respond with a final status code. The
2315        origin server &MUST-NOT; wait for the request body before sending
2316        the 100 (Continue) response. If it responds with a final status
2317        code, it &MAY; close the transport connection or it &MAY; continue
2318        to read and discard the rest of the request.  It &MUST-NOT;
2319        perform the requested method if it returns a final status code.
2320    </t>
2321    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2322        the request message does not include an Expect request-header
2323        field with the "100-continue" expectation, and &MUST-NOT; send a
2324        100 (Continue) response if such a request comes from an HTTP/1.0
2325        (or earlier) client. There is an exception to this rule: for
2326        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2327        status in response to an HTTP/1.1 PUT or POST request that does
2328        not include an Expect request-header field with the "100-continue"
2329        expectation. This exception, the purpose of which is
2330        to minimize any client processing delays associated with an
2331        undeclared wait for 100 (Continue) status, applies only to
2332        HTTP/1.1 requests, and not to requests with any other HTTP-version
2333        value.
2334    </t>
2335    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2336        already received some or all of the request body for the
2337        corresponding request.
2338    </t>
2339    <t> An origin server that sends a 100 (Continue) response &MUST;
2340    ultimately send a final status code, once the request body is
2341        received and processed, unless it terminates the transport
2342        connection prematurely.
2343    </t>
2344    <t> If an origin server receives a request that does not include an
2345        Expect request-header field with the "100-continue" expectation,
2346        the request includes a request body, and the server responds
2347        with a final status code before reading the entire request body
2348        from the transport connection, then the server &SHOULD-NOT;  close
2349        the transport connection until it has read the entire request,
2350        or until the client closes the connection. Otherwise, the client
2351        might not reliably receive the response message. However, this
2352        requirement is not be construed as preventing a server from
2353        defending itself against denial-of-service attacks, or from
2354        badly broken client implementations.
2355      </t>
2356    </list>
2359   Requirements for HTTP/1.1 proxies:
2360  <list style="symbols">
2361    <t> If a proxy receives a request that includes an Expect request-header
2362        field with the "100-continue" expectation, and the proxy
2363        either knows that the next-hop server complies with HTTP/1.1 or
2364        higher, or does not know the HTTP version of the next-hop
2365        server, it &MUST; forward the request, including the Expect header
2366        field.
2367    </t>
2368    <t> If the proxy knows that the version of the next-hop server is
2369        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2370        respond with a 417 (Expectation Failed) status.
2371    </t>
2372    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2373        numbers received from recently-referenced next-hop servers.
2374    </t>
2375    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2376        request message was received from an HTTP/1.0 (or earlier)
2377        client and did not include an Expect request-header field with
2378        the "100-continue" expectation. This requirement overrides the
2379        general rule for forwarding of 1xx responses (see &status-1xx;).
2380    </t>
2381  </list>
2385<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2387   If an HTTP/1.1 client sends a request which includes a request body,
2388   but which does not include an Expect request-header field with the
2389   "100-continue" expectation, and if the client is not directly
2390   connected to an HTTP/1.1 origin server, and if the client sees the
2391   connection close before receiving any status from the server, the
2392   client &SHOULD; retry the request.  If the client does retry this
2393   request, it &MAY; use the following "binary exponential backoff"
2394   algorithm to be assured of obtaining a reliable response:
2395  <list style="numbers">
2396    <t>
2397      Initiate a new connection to the server
2398    </t>
2399    <t>
2400      Transmit the request-headers
2401    </t>
2402    <t>
2403      Initialize a variable R to the estimated round-trip time to the
2404         server (e.g., based on the time it took to establish the
2405         connection), or to a constant value of 5 seconds if the round-trip
2406         time is not available.
2407    </t>
2408    <t>
2409       Compute T = R * (2**N), where N is the number of previous
2410         retries of this request.
2411    </t>
2412    <t>
2413       Wait either for an error response from the server, or for T
2414         seconds (whichever comes first)
2415    </t>
2416    <t>
2417       If no error response is received, after T seconds transmit the
2418         body of the request.
2419    </t>
2420    <t>
2421       If client sees that the connection is closed prematurely,
2422         repeat from step 1 until the request is accepted, an error
2423         response is received, or the user becomes impatient and
2424         terminates the retry process.
2425    </t>
2426  </list>
2429   If at any point an error status is received, the client
2430  <list style="symbols">
2431      <t>&SHOULD-NOT;  continue and</t>
2433      <t>&SHOULD; close the connection if it has not completed sending the
2434        request message.</t>
2435    </list>
2442<section title="Miscellaneous notes that may disappear" anchor="misc">
2443<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2445   <cref>TBS: describe why aliases like webcal are harmful.</cref>
2449<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2451   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
2455<section title="Interception of HTTP for access control" anchor="http.intercept">
2457   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
2461<section title="Use of HTTP by other protocols" anchor="http.others">
2463   <cref>TBD: Profiles of HTTP defined by other protocol.
2464   Extensions of HTTP like WebDAV.</cref>
2468<section title="Use of HTTP by media type specification" anchor="">
2470   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
2475<section title="Header Field Definitions" anchor="header.field.definitions">
2477   This section defines the syntax and semantics of HTTP/1.1 header fields
2478   related to message framing and transport protocols.
2481   For entity-header fields, both sender and recipient refer to either the
2482   client or the server, depending on who sends and who receives the entity.
2485<section title="Connection" anchor="header.connection">
2486  <iref primary="true" item="Connection header" x:for-anchor=""/>
2487  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2488  <x:anchor-alias value="Connection"/>
2489  <x:anchor-alias value="connection-token"/>
2490  <x:anchor-alias value="Connection-v"/>
2492   The "Connection" general-header field allows the sender to specify
2493   options that are desired for that particular connection and &MUST-NOT;
2494   be communicated by proxies over further connections.
2497   The Connection header's value has the following grammar:
2499<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"/>
2500  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2501  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2502  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2505   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2506   message is forwarded and, for each connection-token in this field,
2507   remove any header field(s) from the message with the same name as the
2508   connection-token. Connection options are signaled by the presence of
2509   a connection-token in the Connection header field, not by any
2510   corresponding additional header field(s), since the additional header
2511   field may not be sent if there are no parameters associated with that
2512   connection option.
2515   Message headers listed in the Connection header &MUST-NOT; include
2516   end-to-end headers, such as Cache-Control.
2519   HTTP/1.1 defines the "close" connection option for the sender to
2520   signal that the connection will be closed after completion of the
2521   response. For example,
2523<figure><artwork type="example">
2524  Connection: close
2527   in either the request or the response header fields indicates that
2528   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2529   after the current request/response is complete.
2532   An HTTP/1.1 client that does not support persistent connections &MUST;
2533   include the "close" connection option in every request message.
2536   An HTTP/1.1 server that does not support persistent connections &MUST;
2537   include the "close" connection option in every response message that
2538   does not have a 1xx (informational) status code.
2541   A system receiving an HTTP/1.0 (or lower-version) message that
2542   includes a Connection header &MUST;, for each connection-token in this
2543   field, remove and ignore any header field(s) from the message with
2544   the same name as the connection-token. This protects against mistaken
2545   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2549<section title="Content-Length" anchor="header.content-length">
2550  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2551  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2552  <x:anchor-alias value="Content-Length"/>
2553  <x:anchor-alias value="Content-Length-v"/>
2555   The "Content-Length" entity-header field indicates the size of the
2556   entity-body, in number of OCTETs. In the case of responses to the HEAD
2557   method, it indicates the size of the entity-body that would have been sent
2558   had the request been a GET.
2560<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2561  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2562  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2565   An example is
2567<figure><artwork type="example">
2568  Content-Length: 3495
2571   Applications &SHOULD; use this field to indicate the transfer-length of
2572   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2575   Any Content-Length greater than or equal to zero is a valid value.
2576   <xref target="message.length"/> describes how to determine the length of a message-body
2577   if a Content-Length is not given.
2580   Note that the meaning of this field is significantly different from
2581   the corresponding definition in MIME, where it is an optional field
2582   used within the "message/external-body" content-type. In HTTP, it
2583   &SHOULD; be sent whenever the message's length can be determined prior
2584   to being transferred, unless this is prohibited by the rules in
2585   <xref target="message.length"/>.
2589<section title="Date" anchor="">
2590  <iref primary="true" item="Date header" x:for-anchor=""/>
2591  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2592  <x:anchor-alias value="Date"/>
2593  <x:anchor-alias value="Date-v"/>
2595   The "Date" general-header field represents the date and time at which
2596   the message was originated, having the same semantics as orig-date in
2597   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2598   HTTP-date, as described in <xref target=""/>;
2599   it &MUST; be sent in rfc1123-date format.
2601<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2602  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2603  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2606   An example is
2608<figure><artwork type="example">
2609  Date: Tue, 15 Nov 1994 08:12:31 GMT
2612   Origin servers &MUST; include a Date header field in all responses,
2613   except in these cases:
2614  <list style="numbers">
2615      <t>If the response status code is 100 (Continue) or 101 (Switching
2616         Protocols), the response &MAY; include a Date header field, at
2617         the server's option.</t>
2619      <t>If the response status code conveys a server error, e.g. 500
2620         (Internal Server Error) or 503 (Service Unavailable), and it is
2621         inconvenient or impossible to generate a valid Date.</t>
2623      <t>If the server does not have a clock that can provide a
2624         reasonable approximation of the current time, its responses
2625         &MUST-NOT; include a Date header field. In this case, the rules
2626         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2627  </list>
2630   A received message that does not have a Date header field &MUST; be
2631   assigned one by the recipient if the message will be cached by that
2632   recipient or gatewayed via a protocol which requires a Date. An HTTP
2633   implementation without a clock &MUST-NOT; cache responses without
2634   revalidating them on every use. An HTTP cache, especially a shared
2635   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2636   clock with a reliable external standard.
2639   Clients &SHOULD; only send a Date header field in messages that include
2640   an entity-body, as in the case of the PUT and POST requests, and even
2641   then it is optional. A client without a clock &MUST-NOT; send a Date
2642   header field in a request.
2645   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2646   time subsequent to the generation of the message. It &SHOULD; represent
2647   the best available approximation of the date and time of message
2648   generation, unless the implementation has no means of generating a
2649   reasonably accurate date and time. In theory, the date ought to
2650   represent the moment just before the entity is generated. In
2651   practice, the date can be generated at any time during the message
2652   origination without affecting its semantic value.
2655<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2657   Some origin server implementations might not have a clock available.
2658   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2659   values to a response, unless these values were associated
2660   with the resource by a system or user with a reliable clock. It &MAY;
2661   assign an Expires value that is known, at or before server
2662   configuration time, to be in the past (this allows "pre-expiration"
2663   of responses without storing separate Expires values for each
2664   resource).
2669<section title="Host" anchor="">
2670  <iref primary="true" item="Host header" x:for-anchor=""/>
2671  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2672  <x:anchor-alias value="Host"/>
2673  <x:anchor-alias value="Host-v"/>
2675   The "Host" request-header field specifies the Internet host and port
2676   number of the resource being requested, allowing the origin server or
2677   gateway to differentiate between internally-ambiguous URLs, such as the root
2678   "/" URL of a server for multiple host names on a single IP address.
2681   The Host field value &MUST; represent the naming authority of the origin
2682   server or gateway given by the original URL obtained from the user or
2683   referring resource (generally an http URI, as described in
2684   <xref target="http.uri"/>).
2686<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2687  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2688  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2691   A "host" without any trailing port information implies the default
2692   port for the service requested (e.g., "80" for an HTTP URL). For
2693   example, a request on the origin server for
2694   &lt;; would properly include:
2696<figure><artwork type="example">
2697  GET /pub/WWW/ HTTP/1.1
2698  Host:
2701   A client &MUST; include a Host header field in all HTTP/1.1 request
2702   messages. If the requested URI does not include an Internet host
2703   name for the service being requested, then the Host header field &MUST;
2704   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2705   request message it forwards does contain an appropriate Host header
2706   field that identifies the service being requested by the proxy. All
2707   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2708   status code to any HTTP/1.1 request message which lacks a Host header
2709   field.
2712   See Sections <xref target="" format="counter"/>
2713   and <xref target="" format="counter"/>
2714   for other requirements relating to Host.
2718<section title="TE" anchor="header.te">
2719  <iref primary="true" item="TE header" x:for-anchor=""/>
2720  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2721  <x:anchor-alias value="TE"/>
2722  <x:anchor-alias value="TE-v"/>
2723  <x:anchor-alias value="t-codings"/>
2724  <x:anchor-alias value="te-params"/>
2725  <x:anchor-alias value="te-ext"/>
2727   The "TE" request-header field indicates what extension transfer-codings
2728   it is willing to accept in the response, and whether or not it is
2729   willing to accept trailer fields in a chunked transfer-coding.
2732   Its value may consist of the keyword "trailers" and/or a comma-separated
2733   list of extension transfer-coding names with optional accept
2734   parameters (as described in <xref target="transfer.codings"/>).
2736<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"/>
2737  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2738  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2739  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2740  <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> )
2741  <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> ) ]
2744   The presence of the keyword "trailers" indicates that the client is
2745   willing to accept trailer fields in a chunked transfer-coding, as
2746   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2747   transfer-coding values even though it does not itself represent a
2748   transfer-coding.
2751   Examples of its use are:
2753<figure><artwork type="example">
2754  TE: deflate
2755  TE:
2756  TE: trailers, deflate;q=0.5
2759   The TE header field only applies to the immediate connection.
2760   Therefore, the keyword &MUST; be supplied within a Connection header
2761   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2764   A server tests whether a transfer-coding is acceptable, according to
2765   a TE field, using these rules:
2766  <list style="numbers">
2767    <x:lt>
2768      <t>The "chunked" transfer-coding is always acceptable. If the
2769         keyword "trailers" is listed, the client indicates that it is
2770         willing to accept trailer fields in the chunked response on
2771         behalf of itself and any downstream clients. The implication is
2772         that, if given, the client is stating that either all
2773         downstream clients are willing to accept trailer fields in the
2774         forwarded response, or that it will attempt to buffer the
2775         response on behalf of downstream recipients.
2776      </t><t>
2777         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2778         chunked response such that a client can be assured of buffering
2779         the entire response.</t>
2780    </x:lt>
2781    <x:lt>
2782      <t>If the transfer-coding being tested is one of the transfer-codings
2783         listed in the TE field, then it is acceptable unless it
2784         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2785         qvalue of 0 means "not acceptable.")</t>
2786    </x:lt>
2787    <x:lt>
2788      <t>If multiple transfer-codings are acceptable, then the
2789         acceptable transfer-coding with the highest non-zero qvalue is
2790         preferred.  The "chunked" transfer-coding always has a qvalue
2791         of 1.</t>
2792    </x:lt>
2793  </list>
2796   If the TE field-value is empty or if no TE field is present, the only
2797   transfer-coding is "chunked". A message with no transfer-coding is
2798   always acceptable.
2802<section title="Trailer" anchor="header.trailer">
2803  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2804  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2805  <x:anchor-alias value="Trailer"/>
2806  <x:anchor-alias value="Trailer-v"/>
2808   The "Trailer" general-header field indicates that the given set of
2809   header fields is present in the trailer of a message encoded with
2810   chunked transfer-coding.
2812<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2813  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2814  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2817   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2818   message using chunked transfer-coding with a non-empty trailer. Doing
2819   so allows the recipient to know which header fields to expect in the
2820   trailer.
2823   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2824   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2825   trailer fields in a "chunked" transfer-coding.
2828   Message header fields listed in the Trailer header field &MUST-NOT;
2829   include the following header fields:
2830  <list style="symbols">
2831    <t>Transfer-Encoding</t>
2832    <t>Content-Length</t>
2833    <t>Trailer</t>
2834  </list>
2838<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2839  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2840  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2841  <x:anchor-alias value="Transfer-Encoding"/>
2842  <x:anchor-alias value="Transfer-Encoding-v"/>
2844   The "Transfer-Encoding" general-header field indicates what transfer-codings
2845   (if any) have been applied to the message body. It differs from
2846   Content-Encoding (&content-codings;) in that transfer-codings are a property
2847   of the message (and therefore are removed by intermediaries), whereas
2848   content-codings are not.
2850<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2851  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2852                        <x:ref>Transfer-Encoding-v</x:ref>
2853  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2856   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2858<figure><artwork type="example">
2859  Transfer-Encoding: chunked
2862   If multiple encodings have been applied to an entity, the transfer-codings
2863   &MUST; be listed in the order in which they were applied.
2864   Additional information about the encoding parameters &MAY; be provided
2865   by other entity-header fields not defined by this specification.
2868   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2869   header.
2873<section title="Upgrade" anchor="header.upgrade">
2874  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2875  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2876  <x:anchor-alias value="Upgrade"/>
2877  <x:anchor-alias value="Upgrade-v"/>
2879   The "Upgrade" general-header field allows the client to specify what
2880   additional communication protocols it would like to use, if the server
2881   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
2882   header field within a 101 (Switching Protocols) response to indicate which
2883   protocol(s) are being switched to.
2885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2886  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2887  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2890   For example,
2892<figure><artwork type="example">
2893  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2896   The Upgrade header field is intended to provide a simple mechanism
2897   for transition from HTTP/1.1 to some other, incompatible protocol. It
2898   does so by allowing the client to advertise its desire to use another
2899   protocol, such as a later version of HTTP with a higher major version
2900   number, even though the current request has been made using HTTP/1.1.
2901   This eases the difficult transition between incompatible protocols by
2902   allowing the client to initiate a request in the more commonly
2903   supported protocol while indicating to the server that it would like
2904   to use a "better" protocol if available (where "better" is determined
2905   by the server, possibly according to the nature of the method and/or
2906   resource being requested).
2909   The Upgrade header field only applies to switching application-layer
2910   protocols upon the existing transport-layer connection. Upgrade
2911   cannot be used to insist on a protocol change; its acceptance and use
2912   by the server is optional. The capabilities and nature of the
2913   application-layer communication after the protocol change is entirely
2914   dependent upon the new protocol chosen, although the first action
2915   after changing the protocol &MUST; be a response to the initial HTTP
2916   request containing the Upgrade header field.
2919   The Upgrade header field only applies to the immediate connection.
2920   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2921   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2922   HTTP/1.1 message.
2925   The Upgrade header field cannot be used to indicate a switch to a
2926   protocol on a different connection. For that purpose, it is more
2927   appropriate to use a 301, 302, 303, or 305 redirection response.
2930   This specification only defines the protocol name "HTTP" for use by
2931   the family of Hypertext Transfer Protocols, as defined by the HTTP
2932   version rules of <xref target="http.version"/> and future updates to this
2933   specification. Additional tokens can be registered with IANA using the
2934   registration procedure defined below. 
2937<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
2939   The HTTP Upgrade Token Registry defines the name space for product
2940   tokens used to identify protocols in the Upgrade header field.
2941   Each registered token should be associated with one or a set of
2942   specifications, and with contact information.
2945   Registrations should be allowed on a First Come First Served basis as
2946   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
2947   specifications need not be IETF documents or be subject to IESG review, but
2948   should obey the following rules:
2949  <list style="numbers">
2950    <t>A token, once registered, stays registered forever.</t>
2951    <t>The registration &MUST; name a responsible party for the
2952       registration.</t>
2953    <t>The registration &MUST; name a point of contact.</t>
2954    <t>The registration &MAY; name the documentation required for the
2955       token.</t>
2956    <t>The responsible party &MAY; change the registration at any time.
2957       The IANA will keep a record of all such changes, and make them
2958       available upon request.</t>
2959    <t>The responsible party for the first registration of a "product"
2960       token &MUST; approve later registrations of a "version" token
2961       together with that "product" token before they can be registered.</t>
2962    <t>If absolutely required, the IESG &MAY; reassign the responsibility
2963       for a token. This will normally only be used in the case when a
2964       responsible party cannot be contacted.</t>
2965  </list>
2968   It is not required that specifications for upgrade tokens be made
2969   publicly available, but the contact information for the registration
2970   should be.
2977<section title="Via" anchor="header.via">
2978  <iref primary="true" item="Via header" x:for-anchor=""/>
2979  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2980  <x:anchor-alias value="protocol-name"/>
2981  <x:anchor-alias value="protocol-version"/>
2982  <x:anchor-alias value="pseudonym"/>
2983  <x:anchor-alias value="received-by"/>
2984  <x:anchor-alias value="received-protocol"/>
2985  <x:anchor-alias value="Via"/>
2986  <x:anchor-alias value="Via-v"/>
2988   The "Via" general-header field &MUST; be used by gateways and proxies to
2989   indicate the intermediate protocols and recipients between the user
2990   agent and the server on requests, and between the origin server and
2991   the client on responses. It is analogous to the "Received" field defined in
2992   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2993   avoiding request loops, and identifying the protocol capabilities of
2994   all senders along the request/response chain.
2996<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"/>
2997  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2998  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2999                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3000  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3001  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3002  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3003  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3004  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3007   The received-protocol indicates the protocol version of the message
3008   received by the server or client along each segment of the
3009   request/response chain. The received-protocol version is appended to
3010   the Via field value when the message is forwarded so that information
3011   about the protocol capabilities of upstream applications remains
3012   visible to all recipients.
3015   The protocol-name is optional if and only if it would be "HTTP". The
3016   received-by field is normally the host and optional port number of a
3017   recipient server or client that subsequently forwarded the message.
3018   However, if the real host is considered to be sensitive information,
3019   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3020   be assumed to be the default port of the received-protocol.
3023   Multiple Via field values represents each proxy or gateway that has
3024   forwarded the message. Each recipient &MUST; append its information
3025   such that the end result is ordered according to the sequence of
3026   forwarding applications.
3029   Comments &MAY; be used in the Via header field to identify the software
3030   of the recipient proxy or gateway, analogous to the User-Agent and
3031   Server header fields. However, all comments in the Via field are
3032   optional and &MAY; be removed by any recipient prior to forwarding the
3033   message.
3036   For example, a request message could be sent from an HTTP/1.0 user
3037   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3038   forward the request to a public proxy at, which completes
3039   the request by forwarding it to the origin server at
3040   The request received by would then have the following
3041   Via header field:
3043<figure><artwork type="example">
3044  Via: 1.0 fred, 1.1 (Apache/1.1)
3047   Proxies and gateways used as a portal through a network firewall
3048   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3049   the firewall region. This information &SHOULD; only be propagated if
3050   explicitly enabled. If not enabled, the received-by host of any host
3051   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3052   for that host.
3055   For organizations that have strong privacy requirements for hiding
3056   internal structures, a proxy &MAY; combine an ordered subsequence of
3057   Via header field entries with identical received-protocol values into
3058   a single such entry. For example,
3060<figure><artwork type="example">
3061  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3064        could be collapsed to
3066<figure><artwork type="example">
3067  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3070   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3071   under the same organizational control and the hosts have already been
3072   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3073   have different received-protocol values.
3079<section title="IANA Considerations" anchor="IANA.considerations">
3081<section title="Message Header Registration" anchor="message.header.registration">
3083   The Message Header Registry located at <eref target=""/> should be updated
3084   with the permanent registrations below (see <xref target="RFC3864"/>):
3086<?BEGININC p1-messaging.iana-headers ?>
3087<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3088<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3089   <ttcol>Header Field Name</ttcol>
3090   <ttcol>Protocol</ttcol>
3091   <ttcol>Status</ttcol>
3092   <ttcol>Reference</ttcol>
3094   <c>Connection</c>
3095   <c>http</c>
3096   <c>standard</c>
3097   <c>
3098      <xref target="header.connection"/>
3099   </c>
3100   <c>Content-Length</c>
3101   <c>http</c>
3102   <c>standard</c>
3103   <c>
3104      <xref target="header.content-length"/>
3105   </c>
3106   <c>Date</c>
3107   <c>http</c>
3108   <c>standard</c>
3109   <c>
3110      <xref target=""/>
3111   </c>
3112   <c>Host</c>
3113   <c>http</c>
3114   <c>standard</c>
3115   <c>
3116      <xref target=""/>
3117   </c>
3118   <c>TE</c>
3119   <c>http</c>
3120   <c>standard</c>
3121   <c>
3122      <xref target="header.te"/>
3123   </c>
3124   <c>Trailer</c>
3125   <c>http</c>
3126   <c>standard</c>
3127   <c>
3128      <xref target="header.trailer"/>
3129   </c>
3130   <c>Transfer-Encoding</c>
3131   <c>http</c>
3132   <c>standard</c>
3133   <c>
3134      <xref target="header.transfer-encoding"/>
3135   </c>
3136   <c>Upgrade</c>
3137   <c>http</c>
3138   <c>standard</c>
3139   <c>
3140      <xref target="header.upgrade"/>
3141   </c>
3142   <c>Via</c>
3143   <c>http</c>
3144   <c>standard</c>
3145   <c>
3146      <xref target="header.via"/>
3147   </c>
3150<?ENDINC p1-messaging.iana-headers ?>
3152   The change controller is: "IETF ( - Internet Engineering Task Force".
3156<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3158   The entries for the "http" and "https" URI Schemes in the registry located at
3159   <eref target=""/>
3160   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3161   and <xref target="https.uri" format="counter"/> of this document
3162   (see <xref target="RFC4395"/>).
3166<section title="Internet Media Type Registrations" anchor="">
3168   This document serves as the specification for the Internet media types
3169   "message/http" and "application/http". The following is to be registered with
3170   IANA (see <xref target="RFC4288"/>).
3172<section title="Internet Media Type message/http" anchor="">
3173<iref item="Media Type" subitem="message/http" primary="true"/>
3174<iref item="message/http Media Type" primary="true"/>
3176   The message/http type can be used to enclose a single HTTP request or
3177   response message, provided that it obeys the MIME restrictions for all
3178   "message" types regarding line length and encodings.
3181  <list style="hanging" x:indent="12em">
3182    <t hangText="Type name:">
3183      message
3184    </t>
3185    <t hangText="Subtype name:">
3186      http
3187    </t>
3188    <t hangText="Required parameters:">
3189      none
3190    </t>
3191    <t hangText="Optional parameters:">
3192      version, msgtype
3193      <list style="hanging">
3194        <t hangText="version:">
3195          The HTTP-Version number of the enclosed message
3196          (e.g., "1.1"). If not present, the version can be
3197          determined from the first line of the body.
3198        </t>
3199        <t hangText="msgtype:">
3200          The message type -- "request" or "response". If not
3201          present, the type can be determined from the first
3202          line of the body.
3203        </t>
3204      </list>
3205    </t>
3206    <t hangText="Encoding considerations:">
3207      only "7bit", "8bit", or "binary" are permitted
3208    </t>
3209    <t hangText="Security considerations:">
3210      none
3211    </t>
3212    <t hangText="Interoperability considerations:">
3213      none
3214    </t>
3215    <t hangText="Published specification:">
3216      This specification (see <xref target=""/>).
3217    </t>
3218    <t hangText="Applications that use this media type:">
3219    </t>
3220    <t hangText="Additional information:">
3221      <list style="hanging">
3222        <t hangText="Magic number(s):">none</t>
3223        <t hangText="File extension(s):">none</t>
3224        <t hangText="Macintosh file type code(s):">none</t>
3225      </list>
3226    </t>
3227    <t hangText="Person and email address to contact for further information:">
3228      See Authors Section.
3229    </t>
3230    <t hangText="Intended usage:">
3231      COMMON
3232    </t>
3233    <t hangText="Restrictions on usage:">
3234      none
3235    </t>
3236    <t hangText="Author/Change controller:">
3237      IESG
3238    </t>
3239  </list>
3242<section title="Internet Media Type application/http" anchor="">
3243<iref item="Media Type" subitem="application/http" primary="true"/>
3244<iref item="application/http Media Type" primary="true"/>
3246   The application/http type can be used to enclose a pipeline of one or more
3247   HTTP request or response messages (not intermixed).
3250  <list style="hanging" x:indent="12em">
3251    <t hangText="Type name:">
3252      application
3253    </t>
3254    <t hangText="Subtype name:">
3255      http
3256    </t>
3257    <t hangText="Required parameters:">
3258      none
3259    </t>
3260    <t hangText="Optional parameters:">
3261      version, msgtype
3262      <list style="hanging">
3263        <t hangText="version:">
3264          The HTTP-Version number of the enclosed messages
3265          (e.g., "1.1"). If not present, the version can be
3266          determined from the first line of the body.
3267        </t>
3268        <t hangText="msgtype:">
3269          The message type -- "request" or "response". If not
3270          present, the type can be determined from the first
3271          line of the body.
3272        </t>
3273      </list>
3274    </t>
3275    <t hangText="Encoding considerations:">
3276      HTTP messages enclosed by this type
3277      are in "binary" format; use of an appropriate
3278      Content-Transfer-Encoding is required when
3279      transmitted via E-mail.
3280    </t>
3281    <t hangText="Security considerations:">
3282      none
3283    </t>
3284    <t hangText="Interoperability considerations:">
3285      none
3286    </t>
3287    <t hangText="Published specification:">
3288      This specification (see <xref target=""/>).
3289    </t>
3290    <t hangText="Applications that use this media type:">
3291    </t>
3292    <t hangText="Additional information:">
3293      <list style="hanging">
3294        <t hangText="Magic number(s):">none</t>
3295        <t hangText="File extension(s):">none</t>
3296        <t hangText="Macintosh file type code(s):">none</t>
3297      </list>
3298    </t>
3299    <t hangText="Person and email address to contact for further information:">
3300      See Authors Section.
3301    </t>
3302    <t hangText="Intended usage:">
3303      COMMON
3304    </t>
3305    <t hangText="Restrictions on usage:">
3306      none
3307    </t>
3308    <t hangText="Author/Change controller:">
3309      IESG
3310    </t>
3311  </list>
3316<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3318   The registration procedure for HTTP Transfer Codings is now defined by
3319   <xref target="transfer.coding.registry"/> of this document.
3322   The HTTP Transfer Codings Registry located at <eref target=""/>
3323   should be updated with the registrations below:
3325<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3326   <ttcol>Name</ttcol>
3327   <ttcol>Description</ttcol>
3328   <ttcol>Reference</ttcol>
3329   <c>chunked</c>
3330   <c>Transfer in a series of chunks</c>
3331   <c>
3332      <xref target="chunked.encoding"/>
3333   </c>
3334   <c>compress</c>
3335   <c>UNIX "compress" program method</c>
3336   <c>
3337      <xref target="compress.coding"/>
3338   </c>
3339   <c>deflate</c>
3340   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3341   <c>
3342      <xref target="deflate.coding"/>
3343   </c>
3344   <c>gzip</c>
3345   <c>Same as GNU zip <xref target="RFC1952"/></c>
3346   <c>
3347      <xref target="gzip.coding"/>
3348   </c>
3352<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3354   The registration procedure for HTTP Upgrade Tokens -- previously defined
3355   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3356   by <xref target="upgrade.token.registry"/> of this document.
3359   The HTTP Status Code Registry located at <eref target=""/>
3360   should be updated with the registration below:
3362<texttable align="left" suppress-title="true">
3363   <ttcol>Value</ttcol>
3364   <ttcol>Description</ttcol>
3365   <ttcol>Reference</ttcol>
3367   <c>HTTP</c>
3368   <c>Hypertext Transfer Protocol</c>
3369   <c><xref target="http.version"/> of this specification</c>
3370<!-- IANA should add this without our instructions; emailed on June 05, 2009
3371   <c>TLS/1.0</c>
3372   <c>Transport Layer Security</c>
3373   <c><xref target="RFC2817"/></c> -->
3380<section title="Security Considerations" anchor="security.considerations">
3382   This section is meant to inform application developers, information
3383   providers, and users of the security limitations in HTTP/1.1 as
3384   described by this document. The discussion does not include
3385   definitive solutions to the problems revealed, though it does make
3386   some suggestions for reducing security risks.
3389<section title="Personal Information" anchor="personal.information">
3391   HTTP clients are often privy to large amounts of personal information
3392   (e.g. the user's name, location, mail address, passwords, encryption
3393   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3394   leakage of this information.
3395   We very strongly recommend that a convenient interface be provided
3396   for the user to control dissemination of such information, and that
3397   designers and implementors be particularly careful in this area.
3398   History shows that errors in this area often create serious security
3399   and/or privacy problems and generate highly adverse publicity for the
3400   implementor's company.
3404<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3406   A server is in the position to save personal data about a user's
3407   requests which might identify their reading patterns or subjects of
3408   interest. This information is clearly confidential in nature and its
3409   handling can be constrained by law in certain countries. People using
3410   HTTP to provide data are responsible for ensuring that
3411   such material is not distributed without the permission of any
3412   individuals that are identifiable by the published results.
3416<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3418   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3419   the documents returned by HTTP requests to be only those that were
3420   intended by the server administrators. If an HTTP server translates
3421   HTTP URIs directly into file system calls, the server &MUST; take
3422   special care not to serve files that were not intended to be
3423   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3424   other operating systems use ".." as a path component to indicate a
3425   directory level above the current one. On such a system, an HTTP
3426   server &MUST; disallow any such construct in the request-target if it
3427   would otherwise allow access to a resource outside those intended to
3428   be accessible via the HTTP server. Similarly, files intended for
3429   reference only internally to the server (such as access control
3430   files, configuration files, and script code) &MUST; be protected from
3431   inappropriate retrieval, since they might contain sensitive
3432   information. Experience has shown that minor bugs in such HTTP server
3433   implementations have turned into security risks.
3437<section title="DNS Spoofing" anchor="dns.spoofing">
3439   Clients using HTTP rely heavily on the Domain Name Service, and are
3440   thus generally prone to security attacks based on the deliberate
3441   mis-association of IP addresses and DNS names. Clients need to be
3442   cautious in assuming the continuing validity of an IP number/DNS name
3443   association.
3446   In particular, HTTP clients &SHOULD; rely on their name resolver for
3447   confirmation of an IP number/DNS name association, rather than
3448   caching the result of previous host name lookups. Many platforms
3449   already can cache host name lookups locally when appropriate, and
3450   they &SHOULD; be configured to do so. It is proper for these lookups to
3451   be cached, however, only when the TTL (Time To Live) information
3452   reported by the name server makes it likely that the cached
3453   information will remain useful.
3456   If HTTP clients cache the results of host name lookups in order to
3457   achieve a performance improvement, they &MUST; observe the TTL
3458   information reported by DNS.
3461   If HTTP clients do not observe this rule, they could be spoofed when
3462   a previously-accessed server's IP address changes. As network
3463   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3464   possibility of this form of attack will grow. Observing this
3465   requirement thus reduces this potential security vulnerability.
3468   This requirement also improves the load-balancing behavior of clients
3469   for replicated servers using the same DNS name and reduces the
3470   likelihood of a user's experiencing failure in accessing sites which
3471   use that strategy.
3475<section title="Proxies and Caching" anchor="attack.proxies">
3477   By their very nature, HTTP proxies are men-in-the-middle, and
3478   represent an opportunity for man-in-the-middle attacks. Compromise of
3479   the systems on which the proxies run can result in serious security
3480   and privacy problems. Proxies have access to security-related
3481   information, personal information about individual users and
3482   organizations, and proprietary information belonging to users and
3483   content providers. A compromised proxy, or a proxy implemented or
3484   configured without regard to security and privacy considerations,
3485   might be used in the commission of a wide range of potential attacks.
3488   Proxy operators should protect the systems on which proxies run as
3489   they would protect any system that contains or transports sensitive
3490   information. In particular, log information gathered at proxies often
3491   contains highly sensitive personal information, and/or information
3492   about organizations. Log information should be carefully guarded, and
3493   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3496   Proxy implementors should consider the privacy and security
3497   implications of their design and coding decisions, and of the
3498   configuration options they provide to proxy operators (especially the
3499   default configuration).
3502   Users of a proxy need to be aware that they are no trustworthier than
3503   the people who run the proxy; HTTP itself cannot solve this problem.
3506   The judicious use of cryptography, when appropriate, may suffice to
3507   protect against a broad range of security and privacy attacks. Such
3508   cryptography is beyond the scope of the HTTP/1.1 specification.
3512<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3514   They exist. They are hard to defend against. Research continues.
3515   Beware.
3520<section title="Acknowledgments" anchor="ack">
3522   HTTP has evolved considerably over the years. It has
3523   benefited from a large and active developer community--the many
3524   people who have participated on the www-talk mailing list--and it is
3525   that community which has been most responsible for the success of
3526   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3527   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3528   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3529   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3530   VanHeyningen deserve special recognition for their efforts in
3531   defining early aspects of the protocol.
3534   This document has benefited greatly from the comments of all those
3535   participating in the HTTP-WG. In addition to those already mentioned,
3536   the following individuals have contributed to this specification:
3539   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3540   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3541   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3542   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3543   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3544   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3545   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3546   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3547   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3548   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3549   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3550   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3551   Josh Cohen.
3554   Thanks to the "cave men" of Palo Alto. You know who you are.
3557   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3558   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3559   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3560   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3561   Larry Masinter for their help. And thanks go particularly to Jeff
3562   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3565   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3566   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3567   discovery of many of the problems that this document attempts to
3568   rectify.
3571   This specification makes heavy use of the augmented BNF and generic
3572   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3573   reuses many of the definitions provided by Nathaniel Borenstein and
3574   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3575   specification will help reduce past confusion over the relationship
3576   between HTTP and Internet mail message formats.
3583<references title="Normative References">
3585<reference anchor="ISO-8859-1">
3586  <front>
3587    <title>
3588     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3589    </title>
3590    <author>
3591      <organization>International Organization for Standardization</organization>
3592    </author>
3593    <date year="1998"/>
3594  </front>
3595  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3598<reference anchor="Part2">
3599  <front>
3600    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3601    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3602      <organization abbrev="Day Software">Day Software</organization>
3603      <address><email></email></address>
3604    </author>
3605    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3606      <organization>One Laptop per Child</organization>
3607      <address><email></email></address>
3608    </author>
3609    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3610      <organization abbrev="HP">Hewlett-Packard Company</organization>
3611      <address><email></email></address>
3612    </author>
3613    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3614      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3615      <address><email></email></address>
3616    </author>
3617    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3618      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3619      <address><email></email></address>
3620    </author>
3621    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3622      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3623      <address><email></email></address>
3624    </author>
3625    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3626      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3627      <address><email></email></address>
3628    </author>
3629    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3630      <organization abbrev="W3C">World Wide Web Consortium</organization>
3631      <address><email></email></address>
3632    </author>
3633    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3634      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3635      <address><email></email></address>
3636    </author>
3637    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3638  </front>
3639  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3640  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3643<reference anchor="Part3">
3644  <front>
3645    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3646    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3647      <organization abbrev="Day Software">Day Software</organization>
3648      <address><email></email></address>
3649    </author>
3650    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3651      <organization>One Laptop per Child</organization>
3652      <address><email></email></address>
3653    </author>
3654    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3655      <organization abbrev="HP">Hewlett-Packard Company</organization>
3656      <address><email></email></address>
3657    </author>
3658    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3659      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3660      <address><email></email></address>
3661    </author>
3662    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3663      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3664      <address><email></email></address>
3665    </author>
3666    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3667      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3668      <address><email></email></address>
3669    </author>
3670    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3671      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3672      <address><email></email></address>
3673    </author>
3674    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3675      <organization abbrev="W3C">World Wide Web Consortium</organization>
3676      <address><email></email></address>
3677    </author>
3678    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3679      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3680      <address><email></email></address>
3681    </author>
3682    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3683  </front>
3684  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3685  <x:source href="p3-payload.xml" basename="p3-payload"/>
3688<reference anchor="Part5">
3689  <front>
3690    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3691    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3692      <organization abbrev="Day Software">Day Software</organization>
3693      <address><email></email></address>
3694    </author>
3695    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3696      <organization>One Laptop per Child</organization>
3697      <address><email></email></address>
3698    </author>
3699    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3700      <organization abbrev="HP">Hewlett-Packard Company</organization>
3701      <address><email></email></address>
3702    </author>
3703    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3704      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3705      <address><email></email></address>
3706    </author>
3707    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3708      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3709      <address><email></email></address>
3710    </author>
3711    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3712      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3713      <address><email></email></address>
3714    </author>
3715    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3716      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3717      <address><email></email></address>
3718    </author>
3719    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3720      <organization abbrev="W3C">World Wide Web Consortium</organization>
3721      <address><email></email></address>
3722    </author>
3723    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3724      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3725      <address><email></email></address>
3726    </author>
3727    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3728  </front>
3729  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3730  <x:source href="p5-range.xml" basename="p5-range"/>
3733<reference anchor="Part6">
3734  <front>
3735    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3736    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3737      <organization abbrev="Day Software">Day Software</organization>
3738      <address><email></email></address>
3739    </author>
3740    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3741      <organization>One Laptop per Child</organization>
3742      <address><email></email></address>
3743    </author>
3744    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3745      <organization abbrev="HP">Hewlett-Packard Company</organization>
3746      <address><email></email></address>
3747    </author>
3748    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3749      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3750      <address><email></email></address>
3751    </author>
3752    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3753      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3754      <address><email></email></address>
3755    </author>
3756    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3757      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3758      <address><email></email></address>
3759    </author>
3760    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3761      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3762      <address><email></email></address>
3763    </author>
3764    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3765      <organization abbrev="W3C">World Wide Web Consortium</organization>
3766      <address><email></email></address>
3767    </author>
3768    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3769      <organization />
3770      <address><email></email></address>
3771    </author>
3772    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3773      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3774      <address><email></email></address>
3775    </author>
3776    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3777  </front>
3778  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3779  <x:source href="p6-cache.xml" basename="p6-cache"/>
3782<reference anchor="RFC5234">
3783  <front>
3784    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3785    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3786      <organization>Brandenburg InternetWorking</organization>
3787      <address>
3788      <postal>
3789      <street>675 Spruce Dr.</street>
3790      <city>Sunnyvale</city>
3791      <region>CA</region>
3792      <code>94086</code>
3793      <country>US</country></postal>
3794      <phone>+1.408.246.8253</phone>
3795      <email></email></address> 
3796    </author>
3797    <author initials="P." surname="Overell" fullname="Paul Overell">
3798      <organization>THUS plc.</organization>
3799      <address>
3800      <postal>
3801      <street>1/2 Berkeley Square</street>
3802      <street>99 Berkely Street</street>
3803      <city>Glasgow</city>
3804      <code>G3 7HR</code>
3805      <country>UK</country></postal>
3806      <email></email></address>
3807    </author>
3808    <date month="January" year="2008"/>
3809  </front>
3810  <seriesInfo name="STD" value="68"/>
3811  <seriesInfo name="RFC" value="5234"/>
3814<reference anchor="RFC2119">
3815  <front>
3816    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3817    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3818      <organization>Harvard University</organization>
3819      <address><email></email></address>
3820    </author>
3821    <date month="March" year="1997"/>
3822  </front>
3823  <seriesInfo name="BCP" value="14"/>
3824  <seriesInfo name="RFC" value="2119"/>
3827<reference anchor="RFC3986">
3828 <front>
3829  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3830  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3831    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3832    <address>
3833       <email></email>
3834       <uri></uri>
3835    </address>
3836  </author>
3837  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3838    <organization abbrev="Day Software">Day Software</organization>
3839    <address>
3840      <email></email>
3841      <uri></uri>
3842    </address>
3843  </author>
3844  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3845    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3846    <address>
3847      <email></email>
3848      <uri></uri>
3849    </address>
3850  </author>
3851  <date month='January' year='2005'></date>
3852 </front>
3853 <seriesInfo name="RFC" value="3986"/>
3854 <seriesInfo name="STD" value="66"/>
3857<reference anchor="USASCII">
3858  <front>
3859    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3860    <author>
3861      <organization>American National Standards Institute</organization>
3862    </author>
3863    <date year="1986"/>
3864  </front>
3865  <seriesInfo name="ANSI" value="X3.4"/>
3868<reference anchor="RFC1950">
3869  <front>
3870    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3871    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3872      <organization>Aladdin Enterprises</organization>
3873      <address><email></email></address>
3874    </author>
3875    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3876      <organization/>
3877    </author>
3878    <date month="May" year="1996"/>
3879  </front>
3880  <seriesInfo name="RFC" value="1950"/>
3881  <annotation>
3882    RFC 1950 is an Informational RFC, thus it may be less stable than
3883    this specification. On the other hand, this downward reference was
3884    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3885    therefore it is unlikely to cause problems in practice. See also
3886    <xref target="BCP97"/>.
3887  </annotation>
3890<reference anchor="RFC1951">
3891  <front>
3892    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3893    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3894      <organization>Aladdin Enterprises</organization>
3895      <address><email></email></address>
3896    </author>
3897    <date month="May" year="1996"/>
3898  </front>
3899  <seriesInfo name="RFC" value="1951"/>
3900  <annotation>
3901    RFC 1951 is an Informational RFC, thus it may be less stable than
3902    this specification. On the other hand, this downward reference was
3903    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3904    therefore it is unlikely to cause problems in practice. See also
3905    <xref target="BCP97"/>.
3906  </annotation>
3909<reference anchor="RFC1952">
3910  <front>
3911    <title>GZIP file format specification version 4.3</title>
3912    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3913      <organization>Aladdin Enterprises</organization>
3914      <address><email></email></address>
3915    </author>
3916    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3917      <organization/>
3918      <address><email></email></address>
3919    </author>
3920    <author initials="M." surname="Adler" fullname="Mark Adler">
3921      <organization/>
3922      <address><email></email></address>
3923    </author>
3924    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3925      <organization/>
3926      <address><email></email></address>
3927    </author>
3928    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3929      <organization/>
3930      <address><email></email></address>
3931    </author>
3932    <date month="May" year="1996"/>
3933  </front>
3934  <seriesInfo name="RFC" value="1952"/>
3935  <annotation>
3936    RFC 1952 is an Informational RFC, thus it may be less stable than
3937    this specification. On the other hand, this downward reference was
3938    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3939    therefore it is unlikely to cause problems in practice. See also
3940    <xref target="BCP97"/>.
3941  </annotation>
3946<references title="Informative References">
3948<reference anchor="Nie1997" target="">
3949  <front>
3950    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3951    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3952      <organization/>
3953    </author>
3954    <author initials="J." surname="Gettys" fullname="J. Gettys">
3955      <organization/>
3956    </author>
3957    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3958      <organization/>
3959    </author>
3960    <author initials="H." surname="Lie" fullname="H. Lie">
3961      <organization/>
3962    </author>
3963    <author initials="C." surname="Lilley" fullname="C. Lilley">
3964      <organization/>
3965    </author>
3966    <date year="1997" month="September"/>
3967  </front>
3968  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3971<reference anchor="Pad1995" target="">
3972  <front>
3973    <title>Improving HTTP Latency</title>
3974    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3975      <organization/>
3976    </author>
3977    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3978      <organization/>
3979    </author>
3980    <date year="1995" month="December"/>
3981  </front>
3982  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3985<reference anchor="RFC1123">
3986  <front>
3987    <title>Requirements for Internet Hosts - Application and Support</title>
3988    <author initials="R." surname="Braden" fullname="Robert Braden">
3989      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3990      <address><email>Braden@ISI.EDU</email></address>
3991    </author>
3992    <date month="October" year="1989"/>
3993  </front>
3994  <seriesInfo name="STD" value="3"/>
3995  <seriesInfo name="RFC" value="1123"/>
3998<reference anchor="RFC1305">
3999  <front>
4000    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4001    <author initials="D." surname="Mills" fullname="David L. Mills">
4002      <organization>University of Delaware, Electrical Engineering Department</organization>
4003      <address><email></email></address>
4004    </author>
4005    <date month="March" year="1992"/>
4006  </front>
4007  <seriesInfo name="RFC" value="1305"/>
4010<reference anchor="RFC1900">
4011  <front>
4012    <title>Renumbering Needs Work</title>
4013    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4014      <organization>CERN, Computing and Networks Division</organization>
4015      <address><email></email></address>
4016    </author>
4017    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4018      <organization>cisco Systems</organization>
4019      <address><email></email></address>
4020    </author>
4021    <date month="February" year="1996"/>
4022  </front>
4023  <seriesInfo name="RFC" value="1900"/>
4026<reference anchor="RFC1945">
4027  <front>
4028    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4029    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4030      <organization>MIT, Laboratory for Computer Science</organization>
4031      <address><email></email></address>
4032    </author>
4033    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4034      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4035      <address><email></email></address>
4036    </author>
4037    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4038      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4039      <address><email></email></address>
4040    </author>
4041    <date month="May" year="1996"/>
4042  </front>
4043  <seriesInfo name="RFC" value="1945"/>
4046<reference anchor="RFC2045">
4047  <front>
4048    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4049    <author initials="N." surname="Freed" fullname="Ned Freed">
4050      <organization>Innosoft International, Inc.</organization>
4051      <address><email></email></address>
4052    </author>
4053    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4054      <organization>First Virtual Holdings</organization>
4055      <address><email></email></address>
4056    </author>
4057    <date month="November" year="1996"/>
4058  </front>
4059  <seriesInfo name="RFC" value="2045"/>
4062<reference anchor="RFC2047">
4063  <front>
4064    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4065    <author initials="K." surname="Moore" fullname="Keith Moore">
4066      <organization>University of Tennessee</organization>
4067      <address><email></email></address>
4068    </author>
4069    <date month="November" year="1996"/>
4070  </front>
4071  <seriesInfo name="RFC" value="2047"/>
4074<reference anchor="RFC2068">
4075  <front>
4076    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4077    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4078      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4079      <address><email></email></address>
4080    </author>
4081    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4082      <organization>MIT Laboratory for Computer Science</organization>
4083      <address><email></email></address>
4084    </author>
4085    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4086      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4087      <address><email></email></address>
4088    </author>
4089    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4090      <organization>MIT Laboratory for Computer Science</organization>
4091      <address><email></email></address>
4092    </author>
4093    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4094      <organization>MIT Laboratory for Computer Science</organization>
4095      <address><email></email></address>
4096    </author>
4097    <date month="January" year="1997"/>
4098  </front>
4099  <seriesInfo name="RFC" value="2068"/>
4102<reference anchor='RFC2109'>
4103  <front>
4104    <title>HTTP State Management Mechanism</title>
4105    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4106      <organization>Bell Laboratories, Lucent Technologies</organization>
4107      <address><email></email></address>
4108    </author>
4109    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4110      <organization>Netscape Communications Corp.</organization>
4111      <address><email></email></address>
4112    </author>
4113    <date year='1997' month='February' />
4114  </front>
4115  <seriesInfo name='RFC' value='2109' />
4118<reference anchor="RFC2145">
4119  <front>
4120    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4121    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4122      <organization>Western Research Laboratory</organization>
4123      <address><email></email></address>
4124    </author>
4125    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4126      <organization>Department of Information and Computer Science</organization>
4127      <address><email></email></address>
4128    </author>
4129    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4130      <organization>MIT Laboratory for Computer Science</organization>
4131      <address><email></email></address>
4132    </author>
4133    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4134      <organization>W3 Consortium</organization>
4135      <address><email></email></address>
4136    </author>
4137    <date month="May" year="1997"/>
4138  </front>
4139  <seriesInfo name="RFC" value="2145"/>
4142<reference anchor="RFC2616">
4143  <front>
4144    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4145    <author initials="R." surname="Fielding" fullname="R. Fielding">
4146      <organization>University of California, Irvine</organization>
4147      <address><email></email></address>
4148    </author>
4149    <author initials="J." surname="Gettys" fullname="J. Gettys">
4150      <organization>W3C</organization>
4151      <address><email></email></address>
4152    </author>
4153    <author initials="J." surname="Mogul" fullname="J. Mogul">
4154      <organization>Compaq Computer Corporation</organization>
4155      <address><email></email></address>
4156    </author>
4157    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4158      <organization>MIT Laboratory for Computer Science</organization>
4159      <address><email></email></address>
4160    </author>
4161    <author initials="L." surname="Masinter" fullname="L. Masinter">
4162      <organization>Xerox Corporation</organization>
4163      <address><email></email></address>
4164    </author>
4165    <author initials="P." surname="Leach" fullname="P. Leach">
4166      <organization>Microsoft Corporation</organization>
4167      <address><email></email></address>
4168    </author>
4169    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4170      <organization>W3C</organization>
4171      <address><email></email></address>
4172    </author>
4173    <date month="June" year="1999"/>
4174  </front>
4175  <seriesInfo name="RFC" value="2616"/>
4178<reference anchor='RFC2817'>
4179  <front>
4180    <title>Upgrading to TLS Within HTTP/1.1</title>
4181    <author initials='R.' surname='Khare' fullname='R. Khare'>
4182      <organization>4K Associates / UC Irvine</organization>
4183      <address><email></email></address>
4184    </author>
4185    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4186      <organization>Agranat Systems, Inc.</organization>
4187      <address><email></email></address>
4188    </author>
4189    <date year='2000' month='May' />
4190  </front>
4191  <seriesInfo name='RFC' value='2817' />
4194<reference anchor='RFC2818'>
4195  <front>
4196    <title>HTTP Over TLS</title>
4197    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4198      <organization>RTFM, Inc.</organization>
4199      <address><email></email></address>
4200    </author>
4201    <date year='2000' month='May' />
4202  </front>
4203  <seriesInfo name='RFC' value='2818' />
4206<reference anchor='RFC2965'>
4207  <front>
4208    <title>HTTP State Management Mechanism</title>
4209    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4210      <organization>Bell Laboratories, Lucent Technologies</organization>
4211      <address><email></email></address>
4212    </author>
4213    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4214      <organization>, Inc.</organization>
4215      <address><email></email></address>
4216    </author>
4217    <date year='2000' month='October' />
4218  </front>
4219  <seriesInfo name='RFC' value='2965' />
4222<reference anchor='RFC3864'>
4223  <front>
4224    <title>Registration Procedures for Message Header Fields</title>
4225    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4226      <organization>Nine by Nine</organization>
4227      <address><email></email></address>
4228    </author>
4229    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4230      <organization>BEA Systems</organization>
4231      <address><email></email></address>
4232    </author>
4233    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4234      <organization>HP Labs</organization>
4235      <address><email></email></address>
4236    </author>
4237    <date year='2004' month='September' />
4238  </front>
4239  <seriesInfo name='BCP' value='90' />
4240  <seriesInfo name='RFC' value='3864' />
4243<reference anchor="RFC4288">
4244  <front>
4245    <title>Media Type Specifications and Registration Procedures</title>
4246    <author initials="N." surname="Freed" fullname="N. Freed">
4247      <organization>Sun Microsystems</organization>
4248      <address>
4249        <email></email>
4250      </address>
4251    </author>
4252    <author initials="J." surname="Klensin" fullname="J. Klensin">
4253      <organization/>
4254      <address>
4255        <email></email>
4256      </address>
4257    </author>
4258    <date year="2005" month="December"/>
4259  </front>
4260  <seriesInfo name="BCP" value="13"/>
4261  <seriesInfo name="RFC" value="4288"/>
4264<reference anchor='RFC4395'>
4265  <front>
4266    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4267    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4268      <organization>AT&amp;T Laboratories</organization>
4269      <address>
4270        <email></email>
4271      </address>
4272    </author>
4273    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4274      <organization>Qualcomm, Inc.</organization>
4275      <address>
4276        <email></email>
4277      </address>
4278    </author>
4279    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4280      <organization>Adobe Systems</organization>
4281      <address>
4282        <email></email>
4283      </address>
4284    </author>
4285    <date year='2006' month='February' />
4286  </front>
4287  <seriesInfo name='BCP' value='115' />
4288  <seriesInfo name='RFC' value='4395' />
4291<reference anchor='RFC5226'>
4292  <front>
4293    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4294    <author initials='T.' surname='Narten' fullname='T. Narten'>
4295      <organization>IBM</organization>
4296      <address><email></email></address>
4297    </author>
4298    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4299      <organization>Google</organization>
4300      <address><email></email></address>
4301    </author>
4302    <date year='2008' month='May' />
4303  </front>
4304  <seriesInfo name='BCP' value='26' />
4305  <seriesInfo name='RFC' value='5226' />
4308<reference anchor="RFC5322">
4309  <front>
4310    <title>Internet Message Format</title>
4311    <author initials="P." surname="Resnick" fullname="P. Resnick">
4312      <organization>Qualcomm Incorporated</organization>
4313    </author>
4314    <date year="2008" month="October"/>
4315  </front>
4316  <seriesInfo name="RFC" value="5322"/>
4319<reference anchor='BCP97'>
4320  <front>
4321    <title>Handling Normative References to Standards-Track Documents</title>
4322    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4323      <organization />
4324      <address>
4325        <email></email>
4326      </address>
4327    </author>
4328    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4329      <organization>MIT</organization>
4330      <address>
4331        <email></email>
4332      </address>
4333    </author>
4334    <date year='2007' month='June' />
4335  </front>
4336  <seriesInfo name='BCP' value='97' />
4337  <seriesInfo name='RFC' value='4897' />
4340<reference anchor="Kri2001" target="">
4341  <front>
4342    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4343    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4344      <organization/>
4345    </author>
4346    <date year="2001" month="November"/>
4347  </front>
4348  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4351<reference anchor="Spe" target="">
4352  <front>
4353  <title>Analysis of HTTP Performance Problems</title>
4354  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4355    <organization/>
4356  </author>
4357  <date/>
4358  </front>
4361<reference anchor="Tou1998" target="">
4362  <front>
4363  <title>Analysis of HTTP Performance</title>
4364  <author initials="J." surname="Touch" fullname="Joe Touch">
4365    <organization>USC/Information Sciences Institute</organization>
4366    <address><email></email></address>
4367  </author>
4368  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4369    <organization>USC/Information Sciences Institute</organization>
4370    <address><email></email></address>
4371  </author>
4372  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4373    <organization>USC/Information Sciences Institute</organization>
4374    <address><email></email></address>
4375  </author>
4376  <date year="1998" month="Aug"/>
4377  </front>
4378  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4379  <annotation>(original report dated Aug. 1996)</annotation>
4385<section title="Tolerant Applications" anchor="tolerant.applications">
4387   Although this document specifies the requirements for the generation
4388   of HTTP/1.1 messages, not all applications will be correct in their
4389   implementation. We therefore recommend that operational applications
4390   be tolerant of deviations whenever those deviations can be
4391   interpreted unambiguously.
4394   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4395   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4396   accept any amount of WSP characters between fields, even though
4397   only a single SP is required.
4400   The line terminator for header fields is the sequence CRLF.
4401   However, we recommend that applications, when parsing such headers,
4402   recognize a single LF as a line terminator and ignore the leading CR.
4405   The character set of an entity-body &SHOULD; be labeled as the lowest
4406   common denominator of the character codes used within that body, with
4407   the exception that not labeling the entity is preferred over labeling
4408   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4411   Additional rules for requirements on parsing and encoding of dates
4412   and other potential problems with date encodings include:
4415  <list style="symbols">
4416     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4417        which appears to be more than 50 years in the future is in fact
4418        in the past (this helps solve the "year 2000" problem).</t>
4420     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4421        Expires date as earlier than the proper value, but &MUST-NOT;
4422        internally represent a parsed Expires date as later than the
4423        proper value.</t>
4425     <t>All expiration-related calculations &MUST; be done in GMT. The
4426        local time zone &MUST-NOT; influence the calculation or comparison
4427        of an age or expiration time.</t>
4429     <t>If an HTTP header incorrectly carries a date value with a time
4430        zone other than GMT, it &MUST; be converted into GMT using the
4431        most conservative possible conversion.</t>
4432  </list>
4436<section title="Compatibility with Previous Versions" anchor="compatibility">
4438   HTTP has been in use by the World-Wide Web global information initiative
4439   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4440   was a simple protocol for hypertext data transfer across the Internet
4441   with only a single method and no metadata.
4442   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4443   methods and MIME-like messaging that could include metadata about the data
4444   transferred and modifiers on the request/response semantics. However,
4445   HTTP/1.0 did not sufficiently take into consideration the effects of
4446   hierarchical proxies, caching, the need for persistent connections, or
4447   name-based virtual hosts. The proliferation of incompletely-implemented
4448   applications calling themselves "HTTP/1.0" further necessitated a
4449   protocol version change in order for two communicating applications
4450   to determine each other's true capabilities.
4453   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4454   requirements that enable reliable implementations, adding only
4455   those new features that will either be safely ignored by an HTTP/1.0
4456   recipient or only sent when communicating with a party advertising
4457   compliance with HTTP/1.1.
4460   It is beyond the scope of a protocol specification to mandate
4461   compliance with previous versions. HTTP/1.1 was deliberately
4462   designed, however, to make supporting previous versions easy. It is
4463   worth noting that, at the time of composing this specification, we would
4464   expect general-purpose HTTP/1.1 servers to:
4465  <list style="symbols">
4466     <t>understand any valid request in the format of HTTP/1.0 and
4467        1.1;</t>
4469     <t>respond appropriately with a message in the same major version
4470        used by the client.</t>
4471  </list>
4474   And we would expect HTTP/1.1 clients to:
4475  <list style="symbols">
4476     <t>understand any valid response in the format of HTTP/1.0 or
4477        1.1.</t>
4478  </list>
4481   For most implementations of HTTP/1.0, each connection is established
4482   by the client prior to the request and closed by the server after
4483   sending the response. Some implementations implement the Keep-Alive
4484   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4487<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4489   This section summarizes major differences between versions HTTP/1.0
4490   and HTTP/1.1.
4493<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4495   The requirements that clients and servers support the Host request-header,
4496   report an error if the Host request-header (<xref target=""/>) is
4497   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4498   are among the most important changes defined by this
4499   specification.
4502   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4503   addresses and servers; there was no other established mechanism for
4504   distinguishing the intended server of a request than the IP address
4505   to which that request was directed. The changes outlined above will
4506   allow the Internet, once older HTTP clients are no longer common, to
4507   support multiple Web sites from a single IP address, greatly
4508   simplifying large operational Web servers, where allocation of many
4509   IP addresses to a single host has created serious problems. The
4510   Internet will also be able to recover the IP addresses that have been
4511   allocated for the sole purpose of allowing special-purpose domain
4512   names to be used in root-level HTTP URLs. Given the rate of growth of
4513   the Web, and the number of servers already deployed, it is extremely
4514   important that all implementations of HTTP (including updates to
4515   existing HTTP/1.0 applications) correctly implement these
4516   requirements:
4517  <list style="symbols">
4518     <t>Both clients and servers &MUST; support the Host request-header.</t>
4520     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4522     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4523        request does not include a Host request-header.</t>
4525     <t>Servers &MUST; accept absolute URIs.</t>
4526  </list>
4531<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4533   Some clients and servers might wish to be compatible with some
4534   previous implementations of persistent connections in HTTP/1.0
4535   clients and servers. Persistent connections in HTTP/1.0 are
4536   explicitly negotiated as they are not the default behavior. HTTP/1.0
4537   experimental implementations of persistent connections are faulty,
4538   and the new facilities in HTTP/1.1 are designed to rectify these
4539   problems. The problem was that some existing 1.0 clients may be
4540   sending Keep-Alive to a proxy server that doesn't understand
4541   Connection, which would then erroneously forward it to the next
4542   inbound server, which would establish the Keep-Alive connection and
4543   result in a hung HTTP/1.0 proxy waiting for the close on the
4544   response. The result is that HTTP/1.0 clients must be prevented from
4545   using Keep-Alive when talking to proxies.
4548   However, talking to proxies is the most important use of persistent
4549   connections, so that prohibition is clearly unacceptable. Therefore,
4550   we need some other mechanism for indicating a persistent connection
4551   is desired, which is safe to use even when talking to an old proxy
4552   that ignores Connection. Persistent connections are the default for
4553   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4554   declaring non-persistence. See <xref target="header.connection"/>.
4557   The original HTTP/1.0 form of persistent connections (the Connection:
4558   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4562<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4564   This specification has been carefully audited to correct and
4565   disambiguate key word usage; RFC 2068 had many problems in respect to
4566   the conventions laid out in <xref target="RFC2119"/>.
4569   Transfer-coding and message lengths all interact in ways that
4570   required fixing exactly when chunked encoding is used (to allow for
4571   transfer encoding that may not be self delimiting); it was important
4572   to straighten out exactly how message lengths are computed. (Sections
4573   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4574   <xref target="header.content-length" format="counter"/>,
4575   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4578   The use and interpretation of HTTP version numbers has been clarified
4579   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4580   version they support to deal with problems discovered in HTTP/1.0
4581   implementations (<xref target="http.version"/>)
4584   Quality Values of zero should indicate that "I don't want something"
4585   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4588   Transfer-coding had significant problems, particularly with
4589   interactions with chunked encoding. The solution is that transfer-codings
4590   become as full fledged as content-codings. This involves
4591   adding an IANA registry for transfer-codings (separate from content
4592   codings), a new header field (TE) and enabling trailer headers in the
4593   future. Transfer encoding is a major performance benefit, so it was
4594   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4595   interoperability problem that could have occurred due to interactions
4596   between authentication trailers, chunked encoding and HTTP/1.0
4597   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.encoding" format="counter"/>,
4598   and <xref target="header.te" format="counter"/>)
4602<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4604  Empty list elements in list productions have been deprecated.
4605  (<xref target="notation.abnf"/>)
4608  Rules about implicit linear whitespace between certain grammar productions
4609  have been removed; now it's only allowed when specifically pointed out
4610  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4611  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4612  Non-ASCII content in header fields and reason phrase has been obsoleted and
4613  made opaque (the TEXT rule was removed)
4614  (<xref target="basic.rules"/>)
4617  Clarify that HTTP-Version is case sensitive.
4618  (<xref target="http.version"/>)
4621  Remove reference to non-existant identity transfer-coding value tokens.
4622  (Sections <xref format="counter" target="transfer.codings"/> and
4623  <xref format="counter" target="message.length"/>)
4626  Clarification that the chunk length does not include
4627  the count of the octets in the chunk header and trailer.
4628  (<xref target="chunked.encoding"/>)
4631  Require that invalid whitespace around field-names be rejected.
4632  (<xref target="header.fields"/>)
4635  Update use of abs_path production from RFC1808 to the path-absolute + query
4636  components of RFC3986.
4637  (<xref target="request-target"/>)
4640  Clarify exactly when close connection options must be sent.
4641  (<xref target="header.connection"/>)
4646<?BEGININC p1-messaging.abnf-appendix ?>
4647<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4649<artwork type="abnf" name="p1-messaging.parsed-abnf">
4650<x:ref>BWS</x:ref> = OWS
4652<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4653<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4654<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4655<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4656 connection-token ] )
4657<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4658<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4660<x:ref>Date</x:ref> = "Date:" OWS Date-v
4661<x:ref>Date-v</x:ref> = HTTP-date
4663<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4665<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4666<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4667<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4668<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4669 ]
4670<x:ref>Host</x:ref> = "Host:" OWS Host-v
4671<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4673<x:ref>Method</x:ref> = token
4675<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4677<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4679<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4680<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4681<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4682 entity-header ) CRLF ) CRLF [ message-body ]
4683<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4684<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4685 entity-header ) CRLF ) CRLF [ message-body ]
4687<x:ref>Status-Code</x:ref> = 3DIGIT
4688<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4690<x:ref>TE</x:ref> = "TE:" OWS TE-v
4691<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4692<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4693<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4694<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4695<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4696 transfer-coding ] )
4698<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4699<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4700<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4701<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4703<x:ref>Via</x:ref> = "Via:" OWS Via-v
4704<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4705 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4706 ] )
4708<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4710<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4711<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4712<x:ref>attribute</x:ref> = token
4713<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4715<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4716<x:ref>chunk-data</x:ref> = 1*OCTET
4717<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4718<x:ref>chunk-ext-name</x:ref> = token
4719<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4720<x:ref>chunk-size</x:ref> = 1*HEXDIG
4721<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4722<x:ref>connection-token</x:ref> = token
4723<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4724 / %x2A-5B ; '*'-'['
4725 / %x5D-7E ; ']'-'~'
4726 / obs-text
4728<x:ref>date1</x:ref> = day SP month SP year
4729<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4730<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4731<x:ref>day</x:ref> = 2DIGIT
4732<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4733 / %x54.75.65 ; Tue
4734 / %x57.65.64 ; Wed
4735 / %x54.68.75 ; Thu
4736 / %x46.72.69 ; Fri
4737 / %x53.61.74 ; Sat
4738 / %x53.75.6E ; Sun
4739<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4740 / %x54. ; Tuesday
4741 / %x57.65.64.6E. ; Wednesday
4742 / %x54. ; Thursday
4743 / %x46. ; Friday
4744 / %x53. ; Saturday
4745 / %x53.75.6E.64.61.79 ; Sunday
4747<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4748<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4750<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4751<x:ref>field-name</x:ref> = token
4752<x:ref>field-value</x:ref> = *( field-content / OWS )
4754<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4755 / Transfer-Encoding / Upgrade / Via / Warning
4757<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4758<x:ref>hour</x:ref> = 2DIGIT
4759<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4760<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4762<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4764<x:ref>message-body</x:ref> = entity-body /
4765 &lt;entity-body encoded as per Transfer-Encoding&gt;
4766<x:ref>minute</x:ref> = 2DIGIT
4767<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4768 / %x46.65.62 ; Feb
4769 / %x4D.61.72 ; Mar
4770 / %x41.70.72 ; Apr
4771 / %x4D.61.79 ; May
4772 / %x4A.75.6E ; Jun
4773 / %x4A.75.6C ; Jul
4774 / %x41.75.67 ; Aug
4775 / %x53.65.70 ; Sep
4776 / %x4F.63.74 ; Oct
4777 / %x4E.6F.76 ; Nov
4778 / %x44.65.63 ; Dec
4780<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4781<x:ref>obs-fold</x:ref> = CRLF
4782<x:ref>obs-text</x:ref> = %x80-FF
4784<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4785<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4786<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4787<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4788<x:ref>product</x:ref> = token [ "/" product-version ]
4789<x:ref>product-version</x:ref> = token
4790<x:ref>protocol-name</x:ref> = token
4791<x:ref>protocol-version</x:ref> = token
4792<x:ref>pseudonym</x:ref> = token
4794<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4795 / %x5D-7E ; ']'-'~'
4796 / obs-text
4797<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4798<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4799<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4800<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4802<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4803<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4804<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4805<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4806<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4807 / authority
4808<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4809<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4810<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4812<x:ref>second</x:ref> = 2DIGIT
4813<x:ref>start-line</x:ref> = Request-Line / Status-Line
4815<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4816<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4817 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4818<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4819<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4820<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4821<x:ref>token</x:ref> = 1*tchar
4822<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4823<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
4824 transfer-extension
4825<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4826<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4828<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4830<x:ref>value</x:ref> = token / quoted-string
4832<x:ref>year</x:ref> = 4DIGIT
4835<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4836; Chunked-Body defined but not used
4837; Content-Length defined but not used
4838; HTTP-message defined but not used
4839; Host defined but not used
4840; Request defined but not used
4841; Response defined but not used
4842; TE defined but not used
4843; URI defined but not used
4844; URI-reference defined but not used
4845; http-URI defined but not used
4846; https-URI defined but not used
4847; partial-URI defined but not used
4849<?ENDINC p1-messaging.abnf-appendix ?>
4851<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4853<section title="Since RFC2616">
4855  Extracted relevant partitions from <xref target="RFC2616"/>.
4859<section title="Since draft-ietf-httpbis-p1-messaging-00">
4861  Closed issues:
4862  <list style="symbols">
4863    <t>
4864      <eref target=""/>:
4865      "HTTP Version should be case sensitive"
4866      (<eref target=""/>)
4867    </t>
4868    <t>
4869      <eref target=""/>:
4870      "'unsafe' characters"
4871      (<eref target=""/>)
4872    </t>
4873    <t>
4874      <eref target=""/>:
4875      "Chunk Size Definition"
4876      (<eref target=""/>)
4877    </t>
4878    <t>
4879      <eref target=""/>:
4880      "Message Length"
4881      (<eref target=""/>)
4882    </t>
4883    <t>
4884      <eref target=""/>:
4885      "Media Type Registrations"
4886      (<eref target=""/>)
4887    </t>
4888    <t>
4889      <eref target=""/>:
4890      "URI includes query"
4891      (<eref target=""/>)
4892    </t>
4893    <t>
4894      <eref target=""/>:
4895      "No close on 1xx responses"
4896      (<eref target=""/>)
4897    </t>
4898    <t>
4899      <eref target=""/>:
4900      "Remove 'identity' token references"
4901      (<eref target=""/>)
4902    </t>
4903    <t>
4904      <eref target=""/>:
4905      "Import query BNF"
4906    </t>
4907    <t>
4908      <eref target=""/>:
4909      "qdtext BNF"
4910    </t>
4911    <t>
4912      <eref target=""/>:
4913      "Normative and Informative references"
4914    </t>
4915    <t>
4916      <eref target=""/>:
4917      "RFC2606 Compliance"
4918    </t>
4919    <t>
4920      <eref target=""/>:
4921      "RFC977 reference"
4922    </t>
4923    <t>
4924      <eref target=""/>:
4925      "RFC1700 references"
4926    </t>
4927    <t>
4928      <eref target=""/>:
4929      "inconsistency in date format explanation"
4930    </t>
4931    <t>
4932      <eref target=""/>:
4933      "Date reference typo"
4934    </t>
4935    <t>
4936      <eref target=""/>:
4937      "Informative references"
4938    </t>
4939    <t>
4940      <eref target=""/>:
4941      "ISO-8859-1 Reference"
4942    </t>
4943    <t>
4944      <eref target=""/>:
4945      "Normative up-to-date references"
4946    </t>
4947  </list>
4950  Other changes:
4951  <list style="symbols">
4952    <t>
4953      Update media type registrations to use RFC4288 template.
4954    </t>
4955    <t>
4956      Use names of RFC4234 core rules DQUOTE and WSP,
4957      fix broken ABNF for chunk-data
4958      (work in progress on <eref target=""/>)
4959    </t>
4960  </list>
4964<section title="Since draft-ietf-httpbis-p1-messaging-01">
4966  Closed issues:
4967  <list style="symbols">
4968    <t>
4969      <eref target=""/>:
4970      "Bodies on GET (and other) requests"
4971    </t>
4972    <t>
4973      <eref target=""/>:
4974      "Updating to RFC4288"
4975    </t>
4976    <t>
4977      <eref target=""/>:
4978      "Status Code and Reason Phrase"
4979    </t>
4980    <t>
4981      <eref target=""/>:
4982      "rel_path not used"
4983    </t>
4984  </list>
4987  Ongoing work on ABNF conversion (<eref target=""/>):
4988  <list style="symbols">
4989    <t>
4990      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4991      "trailer-part").
4992    </t>
4993    <t>
4994      Avoid underscore character in rule names ("http_URL" ->
4995      "http-URL", "abs_path" -> "path-absolute").
4996    </t>
4997    <t>
4998      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4999      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5000      have to be updated when switching over to RFC3986.
5001    </t>
5002    <t>
5003      Synchronize core rules with RFC5234.
5004    </t>
5005    <t>
5006      Get rid of prose rules that span multiple lines.
5007    </t>
5008    <t>
5009      Get rid of unused rules LOALPHA and UPALPHA.
5010    </t>
5011    <t>
5012      Move "Product Tokens" section (back) into Part 1, as "token" is used
5013      in the definition of the Upgrade header.
5014    </t>
5015    <t>
5016      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5017    </t>
5018    <t>
5019      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5020    </t>
5021  </list>
5025<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5027  Closed issues:
5028  <list style="symbols">
5029    <t>
5030      <eref target=""/>:
5031      "HTTP-date vs. rfc1123-date"
5032    </t>
5033    <t>
5034      <eref target=""/>:
5035      "WS in quoted-pair"
5036    </t>
5037  </list>
5040  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5041  <list style="symbols">
5042    <t>
5043      Reference RFC 3984, and update header registrations for headers defined
5044      in this document.
5045    </t>
5046  </list>
5049  Ongoing work on ABNF conversion (<eref target=""/>):
5050  <list style="symbols">
5051    <t>
5052      Replace string literals when the string really is case-sensitive (HTTP-Version).
5053    </t>
5054  </list>
5058<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5060  Closed issues:
5061  <list style="symbols">
5062    <t>
5063      <eref target=""/>:
5064      "Connection closing"
5065    </t>
5066    <t>
5067      <eref target=""/>:
5068      "Move registrations and registry information to IANA Considerations"
5069    </t>
5070    <t>
5071      <eref target=""/>:
5072      "need new URL for PAD1995 reference"
5073    </t>
5074    <t>
5075      <eref target=""/>:
5076      "IANA Considerations: update HTTP URI scheme registration"
5077    </t>
5078    <t>
5079      <eref target=""/>:
5080      "Cite HTTPS URI scheme definition"
5081    </t>
5082    <t>
5083      <eref target=""/>:
5084      "List-type headers vs Set-Cookie"
5085    </t>
5086  </list>
5089  Ongoing work on ABNF conversion (<eref target=""/>):
5090  <list style="symbols">
5091    <t>
5092      Replace string literals when the string really is case-sensitive (HTTP-Date).
5093    </t>
5094    <t>
5095      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5096    </t>
5097  </list>
5101<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5103  Closed issues:
5104  <list style="symbols">
5105    <t>
5106      <eref target=""/>:
5107      "Out-of-date reference for URIs"
5108    </t>
5109    <t>
5110      <eref target=""/>:
5111      "RFC 2822 is updated by RFC 5322"
5112    </t>
5113  </list>
5116  Ongoing work on ABNF conversion (<eref target=""/>):
5117  <list style="symbols">
5118    <t>
5119      Use "/" instead of "|" for alternatives.
5120    </t>
5121    <t>
5122      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5123    </t>
5124    <t>
5125      Only reference RFC 5234's core rules.
5126    </t>
5127    <t>
5128      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5129      whitespace ("OWS") and required whitespace ("RWS").
5130    </t>
5131    <t>
5132      Rewrite ABNFs to spell out whitespace rules, factor out
5133      header value format definitions.
5134    </t>
5135  </list>
5139<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5141  Closed issues:
5142  <list style="symbols">
5143    <t>
5144      <eref target=""/>:
5145      "Header LWS"
5146    </t>
5147    <t>
5148      <eref target=""/>:
5149      "Sort 1.3 Terminology"
5150    </t>
5151    <t>
5152      <eref target=""/>:
5153      "RFC2047 encoded words"
5154    </t>
5155    <t>
5156      <eref target=""/>:
5157      "Character Encodings in TEXT"
5158    </t>
5159    <t>
5160      <eref target=""/>:
5161      "Line Folding"
5162    </t>
5163    <t>
5164      <eref target=""/>:
5165      "OPTIONS * and proxies"
5166    </t>
5167    <t>
5168      <eref target=""/>:
5169      "Reason-Phrase BNF"
5170    </t>
5171    <t>
5172      <eref target=""/>:
5173      "Use of TEXT"
5174    </t>
5175    <t>
5176      <eref target=""/>:
5177      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5178    </t>
5179    <t>
5180      <eref target=""/>:
5181      "RFC822 reference left in discussion of date formats"
5182    </t>
5183  </list>
5186  Final work on ABNF conversion (<eref target=""/>):
5187  <list style="symbols">
5188    <t>
5189      Rewrite definition of list rules, deprecate empty list elements.
5190    </t>
5191    <t>
5192      Add appendix containing collected and expanded ABNF.
5193    </t>
5194  </list>
5197  Other changes:
5198  <list style="symbols">
5199    <t>
5200      Rewrite introduction; add mostly new Architecture Section.
5201    </t>
5202    <t>
5203      Move definition of quality values from Part 3 into Part 1;
5204      make TE request header grammar independent of accept-params (defined in Part 3).
5205    </t>
5206  </list>
5210<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5212  Closed issues:
5213  <list style="symbols">
5214    <t>
5215      <eref target=""/>:
5216      "base for numeric protocol elements"
5217    </t>
5218    <t>
5219      <eref target=""/>:
5220      "comment ABNF"
5221    </t>
5222  </list>
5225  Partly resolved issues:
5226  <list style="symbols">
5227    <t>
5228      <eref target=""/>:
5229      "205 Bodies" (took out language that implied that there may be
5230      methods for which a request body MUST NOT be included)
5231    </t>
5232    <t>
5233      <eref target=""/>:
5234      "editorial improvements around HTTP-date"
5235    </t>
5236  </list>
5240<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5242  Closed issues:
5243  <list style="symbols">
5244    <t>
5245      <eref target=""/>:
5246      "Repeating single-value headers"
5247    </t>
5248    <t>
5249      <eref target=""/>:
5250      "IP addresses in URLs"
5251    </t>
5252    <t>
5253      <eref target=""/>:
5254      "take over HTTP Upgrade Token Registry"
5255    </t>
5256    <t>
5257      <eref target=""/>:
5258      "HTTP/0.9 support"
5259    </t>
5260    <t>
5261      <eref target=""/>:
5262      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5263    </t>
5264    <t>
5265      <eref target=""/>:
5266      "move definitions of gzip/deflate/compress to part 1"
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "disallow control characters in quoted-pair"
5271    </t>
5272  </list>
5275  Partly resolved issues:
5276  <list style="symbols">
5277    <t>
5278      <eref target=""/>:
5279      "update IANA requirements wrt Transfer-Coding values" (add the
5280      IANA Considerations subsection)
5281    </t>
5282    <t>
5283      <eref target=""/>:
5284      "disallow control characters in quoted-pair"
5285    </t>
5286  </list>
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