source: draft-ietf-httpbis/latest/p1-messaging.xml @ 704

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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 "October">
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 within quoted-string constructs:
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> )
468   Producers &SHOULD-NOT; escape characters that do not require escaping
469   (i.e., other than DQUOTE and the backslash character).
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
482  The ABNF rules below are defined in other parts:
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
502<section title="HTTP architecture" anchor="architecture">
504   HTTP was created for the World Wide Web architecture
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
510<section title="Client/Server Operation" anchor="operation">
511<iref item="client"/>
512<iref item="server"/>
513<iref item="connection"/>
515   HTTP is a request/response protocol that operates by exchanging messages
516   across a reliable transport or session-layer connection. An HTTP client
517   is a program that establishes a connection to a server for the purpose
518   of sending one or more HTTP requests.  An HTTP server is a program that
519   accepts connections in order to service HTTP requests by sending HTTP
520   responses.
522<iref item="user agent"/>
523<iref item="origin server"/>
525   Note that the terms "client" and "server" refer only to the roles that
526   these programs perform for a particular connection.  The same program
527   may act as a client on some connections and a server on others.  We use
528   the term "user agent" to refer to the program that initiates a request,
529   such as a WWW browser, editor, or spider (web-traversing robot), and
530   the term "origin server" to refer to the program that can originate
531   authoritative responses to a request.
534   Most HTTP communication consists of a retrieval request (GET) for
535   a representation of some resource identified by a URI.  In the
536   simplest case, this may be accomplished via a single connection (v)
537   between the user agent (UA) and the origin server (O).
539<figure><artwork type="drawing">
540       request chain ------------------------&gt;
541    UA -------------------v------------------- O
542       &lt;----------------------- response chain
544<iref item="message"/>
545<iref item="request"/>
546<iref item="response"/>
548   A client sends an HTTP request to the server in the form of a request
549   message (<xref target="request"/>), beginning with a method, URI, and
550   protocol version, followed by MIME-like header fields containing
551   request modifiers, client information, and payload metadata, an empty
552   line to indicate the end of the header section, and finally the payload
553   body (if any).
556   A server responds to the client's request by sending an HTTP response
557   message (<xref target="response"/>), beginning with a status line that
558   includes the protocol version, a success or error code, and textual
559   reason phrase, followed by MIME-like header fields containing server
560   information, resource metadata, and payload metadata, an empty line to
561   indicate the end of the header section, and finally the payload body (if any).
564   The following example illustrates a typical message exchange for a
565   GET request on the URI "":
568client request:
569</preamble><artwork  type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
570GET /hello.txt HTTP/1.1
571User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
573Accept: */*
577server response:
578</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
579HTTP/1.1 200 OK
580Date: Mon, 27 Jul 2009 12:28:53 GMT
581Server: Apache
582Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
583ETag: "34aa387-d-1568eb00"
584Accept-Ranges: bytes
585Content-Length: <x:length-of target="exbody"/>
586Vary: Accept-Encoding
587Content-Type: text/plain
589<x:span anchor="exbody">Hello World!
593<section title="Intermediaries" anchor="intermediaries">
595   A more complicated situation occurs when one or more intermediaries
596   are present in the request/response chain. There are three common
597   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
598   a single intermediary may act as an origin server, proxy, gateway,
599   or tunnel, switching behavior based on the nature of each request.
601<figure><artwork type="drawing">
602       request chain --------------------------------------&gt;
603    UA -----v----- A -----v----- B -----v----- C -----v----- O
604       &lt;------------------------------------- response chain
607   The figure above shows three intermediaries (A, B, and C) between the
608   user agent and origin server. A request or response message that
609   travels the whole chain will pass through four separate connections.
610   Some HTTP communication options
611   may apply only to the connection with the nearest, non-tunnel
612   neighbor, only to the end-points of the chain, or to all connections
613   along the chain. Although the diagram is linear, each participant may
614   be engaged in multiple, simultaneous communications. For example, B
615   may be receiving requests from many clients other than A, and/or
616   forwarding requests to servers other than C, at the same time that it
617   is handling A's request.
620<iref item="upstream"/><iref item="downstream"/>
621<iref item="inbound"/><iref item="outbound"/>
622   We use the terms "upstream" and "downstream" to describe various
623   requirements in relation to the directional flow of a message:
624   all messages flow from upstream to downstream.
625   Likewise, we use the terms "inbound" and "outbound" to refer to
626   directions in relation to the request path: "inbound" means toward
627   the origin server and "outbound" means toward the user agent.
629<t><iref item="proxy"/>
630   A proxy is a message forwarding agent that is selected by the
631   client, usually via local configuration rules, to receive requests
632   for some type(s) of absolute URI and attempt to satisfy those
633   requests via translation through the HTTP interface.  Some translations
634   are minimal, such as for proxy requests for "http" URIs, whereas
635   other requests may require translation to and from entirely different
636   application-layer protocols. Proxies are often used to group an
637   organization's HTTP requests through a common intermediary for the
638   sake of security, annotation services, or shared caching.
640<t><iref item="gateway"/><iref item="reverse proxy"/>
641   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
642   as a layer above some other server(s) and translates the received
643   requests to the underlying server's protocol.  Gateways are often
644   used for load balancing or partitioning HTTP services across
645   multiple machines.
646   Unlike a proxy, a gateway receives requests as if it were the
647   origin server for the requested resource; the requesting client
648   will not be aware that it is communicating with a gateway.
649   A gateway communicates with the client as if the gateway is the
650   origin server and thus is subject to all of the requirements on
651   origin servers for that connection.  A gateway communicates
652   with inbound servers using any protocol it desires, including
653   private extensions to HTTP that are outside the scope of this
654   specification.
656<t><iref item="tunnel"/>
657   A tunnel acts as a blind relay between two connections
658   without changing the messages. Once active, a tunnel is not
659   considered a party to the HTTP communication, though the tunnel may
660   have been initiated by an HTTP request. A tunnel ceases to exist when
661   both ends of the relayed connection are closed. Tunnels are used to
662   extend a virtual connection through an intermediary, such as when
663   transport-layer security is used to establish private communication
664   through a shared firewall proxy.
668<section title="Caches" anchor="caches">
669<iref item="cache"/>
671   Any party to HTTP communication that is not acting as a tunnel may
672   employ an internal cache for handling requests.
673   A cache is a local store of previous response messages and the
674   subsystem that controls its message storage, retrieval, and deletion.
675   A cache stores cacheable responses in order to reduce the response
676   time and network bandwidth consumption on future, equivalent
677   requests. Any client or server may include a cache, though a cache
678   cannot be used by a server while it is acting as a tunnel.
681   The effect of a cache is that the request/response chain is shortened
682   if one of the participants along the chain has a cached response
683   applicable to that request. The following illustrates the resulting
684   chain if B has a cached copy of an earlier response from O (via C)
685   for a request which has not been cached by UA or A.
687<figure><artwork type="drawing">
688          request chain ----------&gt;
689       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
690          &lt;--------- response chain
692<t><iref item="cacheable"/>
693   A response is cacheable if a cache is allowed to store a copy of
694   the response message for use in answering subsequent requests.
695   Even when a response is cacheable, there may be additional
696   constraints placed by the client or by the origin server on when
697   that cached response can be used for a particular request. HTTP
698   requirements for cache behavior and cacheable responses are
699   defined in &caching-overview;. 
702   There are a wide variety of architectures and configurations
703   of caches and proxies deployed across the World Wide Web and
704   inside large organizations. These systems include national hierarchies
705   of proxy caches to save transoceanic bandwidth, systems that
706   broadcast or multicast cache entries, organizations that distribute
707   subsets of cached data via optical media, and so on.
711<section title="Transport Independence" anchor="transport-independence">
713  HTTP systems are used in a wide variety of environments, from
714  corporate intranets with high-bandwidth links to long-distance
715  communication over low-power radio links and intermittent connectivity.
718   HTTP communication usually takes place over TCP/IP connections. The
719   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
720   not preclude HTTP from being implemented on top of any other protocol
721   on the Internet, or on other networks. HTTP only presumes a reliable
722   transport; any protocol that provides such guarantees can be used;
723   the mapping of the HTTP/1.1 request and response structures onto the
724   transport data units of the protocol in question is outside the scope
725   of this specification.
728   In HTTP/1.0, most implementations used a new connection for each
729   request/response exchange. In HTTP/1.1, a connection may be used for
730   one or more request/response exchanges, although connections may be
731   closed for a variety of reasons (see <xref target="persistent.connections"/>).
735<section title="HTTP Version" anchor="http.version">
736  <x:anchor-alias value="HTTP-Version"/>
737  <x:anchor-alias value="HTTP-Prot-Name"/>
739   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
740   of the protocol. The protocol versioning policy is intended to allow
741   the sender to indicate the format of a message and its capacity for
742   understanding further HTTP communication, rather than the features
743   obtained via that communication. No change is made to the version
744   number for the addition of message components which do not affect
745   communication behavior or which only add to extensible field values.
746   The &lt;minor&gt; number is incremented when the changes made to the
747   protocol add features which do not change the general message parsing
748   algorithm, but which may add to the message semantics and imply
749   additional capabilities of the sender. The &lt;major&gt; number is
750   incremented when the format of a message within the protocol is
751   changed. See <xref target="RFC2145"/> for a fuller explanation.
754   The version of an HTTP message is indicated by an HTTP-Version field
755   in the first line of the message. HTTP-Version is case-sensitive.
757<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
758  <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>
759  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
762   Note that the major and minor numbers &MUST; be treated as separate
763   integers and that each &MAY; be incremented higher than a single digit.
764   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
765   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
766   &MUST-NOT; be sent.
769   An application that sends a request or response message that includes
770   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
771   with this specification. Applications that are at least conditionally
772   compliant with this specification &SHOULD; use an HTTP-Version of
773   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
774   not compatible with HTTP/1.0. For more details on when to send
775   specific HTTP-Version values, see <xref target="RFC2145"/>.
778   The HTTP version of an application is the highest HTTP version for
779   which the application is at least conditionally compliant.
782   Proxy and gateway applications need to be careful when forwarding
783   messages in protocol versions different from that of the application.
784   Since the protocol version indicates the protocol capability of the
785   sender, a proxy/gateway &MUST-NOT; send a message with a version
786   indicator which is greater than its actual version. If a higher
787   version request is received, the proxy/gateway &MUST; either downgrade
788   the request version, or respond with an error, or switch to tunnel
789   behavior.
792   Due to interoperability problems with HTTP/1.0 proxies discovered
793   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
794   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
795   they support. The proxy/gateway's response to that request &MUST; be in
796   the same major version as the request.
799  <t>
800    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
801    of header fields required or forbidden by the versions involved.
802  </t>
806<section title="Uniform Resource Identifiers" anchor="uri">
807<iref primary="true" item="resource"/>
809   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
810   throughout HTTP as the means for identifying resources. URI references
811   are used to target requests, indicate redirects, and define relationships.
812   HTTP does not limit what a resource may be; it merely defines an interface
813   that can be used to interact with a resource via HTTP. More information on
814   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
816  <x:anchor-alias value="URI"/>
817  <x:anchor-alias value="URI-reference"/>
818  <x:anchor-alias value="absolute-URI"/>
819  <x:anchor-alias value="relative-part"/>
820  <x:anchor-alias value="authority"/>
821  <x:anchor-alias value="path-abempty"/>
822  <x:anchor-alias value="path-absolute"/>
823  <x:anchor-alias value="port"/>
824  <x:anchor-alias value="query"/>
825  <x:anchor-alias value="uri-host"/>
826  <x:anchor-alias value="partial-URI"/>
828   This specification adopts the definitions of "URI-reference",
829   "absolute-URI", "relative-part", "port", "host",
830   "path-abempty", "path-absolute", "query", and "authority" from
831   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
832   protocol elements that allow a relative URI without a fragment.
834<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"/>
835  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
836  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
837  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
838  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
839  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
840  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
841  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
842  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
843  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
844  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
846  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
849   Each protocol element in HTTP that allows a URI reference will indicate in
850   its ABNF production whether the element allows only a URI in absolute form
851   (absolute-URI), any relative reference (relative-ref), or some other subset
852   of the URI-reference grammar. Unless otherwise indicated, URI references
853   are parsed relative to the request target (the default base URI for both
854   the request and its corresponding response).
857<section title="http URI scheme" anchor="http.uri">
858  <x:anchor-alias value="http-URI"/>
859  <iref item="http URI scheme" primary="true"/>
860  <iref item="URI scheme" subitem="http" primary="true"/>
862   The "http" URI scheme is hereby defined for the purpose of minting
863   identifiers according to their association with the hierarchical
864   namespace governed by a potential HTTP origin server listening for
865   TCP connections on a given port.
866   The HTTP server is identified via the generic syntax's
867   <x:ref>authority</x:ref> component, which includes a host
868   identifier and optional TCP port, and the remainder of the URI is
869   considered to be identifying data corresponding to a resource for
870   which that server might provide an HTTP interface.
872<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
873  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
876   The host identifier within an <x:ref>authority</x:ref> component is
877   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
878   provided as an IP literal or IPv4 address, then the HTTP server is any
879   listener on the indicated TCP port at that IP address. If host is a
880   registered name, then that name is considered an indirect identifier
881   and the recipient might use a name resolution service, such as DNS,
882   to find the address of a listener for that host.
883   The host &MUST-NOT; be empty; if an "http" URI is received with an
884   empty host, then it &MUST; be rejected as invalid.
885   If the port subcomponent is empty or not given, then TCP port 80 is
886   assumed (the default reserved port for WWW services).
889   Regardless of the form of host identifier, access to that host is not
890   implied by the mere presence of its name or address. The host may or may
891   not exist and, even when it does exist, may or may not be running an
892   HTTP server or listening to the indicated port. The "http" URI scheme
893   makes use of the delegated nature of Internet names and addresses to
894   establish a naming authority (whatever entity has the ability to place
895   an HTTP server at that Internet name or address) and allows that
896   authority to determine which names are valid and how they might be used.
899   When an "http" URI is used within a context that calls for access to the
900   indicated resource, a client &MAY; attempt access by resolving
901   the host to an IP address, establishing a TCP connection to that address
902   on the indicated port, and sending an HTTP request message to the server
903   containing the URI's identifying data as described in <xref target="request"/>.
904   If the server responds to that request with a non-interim HTTP response
905   message, as described in <xref target="response"/>, then that response
906   is considered an authoritative answer to the client's request.
909   Although HTTP is independent of the transport protocol, the "http"
910   scheme is specific to TCP-based services because the name delegation
911   process depends on TCP for establishing authority.
912   An HTTP service based on some other underlying connection protocol
913   would presumably be identified using a different URI scheme, just as
914   the "https" scheme (below) is used for servers that require an SSL/TLS
915   transport layer on a connection. Other protocols may also be used to
916   provide access to "http" identified resources --- it is only the
917   authoritative interface used for mapping the namespace that is
918   specific to TCP.
922<section title="https URI scheme" anchor="https.uri">
923   <x:anchor-alias value="https-URI"/>
924   <iref item="https URI scheme"/>
925   <iref item="URI scheme" subitem="https"/>
927   The "https" URI scheme is hereby defined for the purpose of minting
928   identifiers according to their association with the hierarchical
929   namespace governed by a potential HTTP origin server listening for
930   SSL/TLS-secured connections on a given TCP port.
931   The host and port are determined in the same way
932   as for the "http" scheme, except that a default TCP port of 443
933   is assumed if the port subcomponent is empty or not given.
935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
936  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
939   The primary difference between the "http" and "https" schemes is
940   that interaction with the latter is required to be secured for
941   privacy through the use of strong encryption. The URI cannot be
942   sent in a request until the connection is secure. Likewise, the
943   default for caching is that each response that would be considered
944   "public" under the "http" scheme is instead treated as "private"
945   and thus not eligible for shared caching.
948   The process for authoritative access to an "https" identified
949   resource is defined in <xref target="RFC2818"/>.
953<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
955   Since the "http" and "https" schemes conform to the URI generic syntax,
956   such URIs are normalized and compared according to the algorithm defined
957   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
958   described above for each scheme.
961   If the port is equal to the default port for a scheme, the normal
962   form is to elide the port subcomponent. Likewise, an empty path
963   component is equivalent to an absolute path of "/", so the normal
964   form is to provide a path of "/" instead. The scheme and host
965   are case-insensitive and normally provided in lowercase; all
966   other components are compared in a case-sensitive manner.
967   Characters other than those in the "reserved" set are equivalent
968   to their percent-encoded octets (see <xref target="RFC3986"
969   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
972   For example, the following three URIs are equivalent:
974<figure><artwork type="example">
980   <cref>[[This paragraph does not belong here. --Roy]]</cref>
981   If path-abempty is the empty string (i.e., there is no slash "/"
982   path separator following the authority), then the "http" URI
983   &MUST; be given as "/" when
984   used as a request-target (<xref target="request-target"/>). If a proxy
985   receives a host name which is not a fully qualified domain name, it
986   &MAY; add its domain to the host name it received. If a proxy receives
987   a fully qualified domain name, the proxy &MUST-NOT; change the host
988   name.
994<section title="HTTP Message" anchor="http.message">
995<x:anchor-alias value="generic-message"/>
996<x:anchor-alias value="message.types"/>
997<x:anchor-alias value="HTTP-message"/>
998<x:anchor-alias value="start-line"/>
999<iref item="header section"/>
1000<iref item="headers"/>
1001<iref item="header field"/>
1003   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1004   characters in a format similar to the Internet Message Format
1005   <xref target="RFC5322"/>: zero or more header fields (collectively
1006   referred to as the "headers" or the "header section"), an empty line
1007   indicating the end of the header section, and an optional message-body.
1010   An HTTP message can either be a request from client to server or a
1011   response from server to client.  Syntactically, the two types of message
1012   differ only in the start-line, which is either a Request-Line (for requests)
1013   or a Status-Line (for responses), and in the algorithm for determining
1014   the length of the message-body (<xref target="message.length"/>).
1015   In theory, a client could receive requests and a server could receive
1016   responses, distinguishing them by their different start-line formats,
1017   but in practice servers are implemented to only expect a request
1018   (a response is interpreted as an unknown or invalid request method)
1019   and clients are implemented to only expect a response.
1021<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1022  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1023                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1024                    <x:ref>CRLF</x:ref>
1025                    [ <x:ref>message-body</x:ref> ]
1026  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1029   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1030   header field. The presence of whitespace might be an attempt to trick a
1031   noncompliant implementation of HTTP into ignoring that field or processing
1032   the next line as a new request, either of which may result in security
1033   issues when implementations within the request chain interpret the
1034   same message differently. HTTP/1.1 servers &MUST; reject such a message
1035   with a 400 (Bad Request) response.
1038<section title="Message Parsing Robustness" anchor="message.robustness">
1040   In the interest of robustness, servers &SHOULD; ignore at least one
1041   empty line received where a Request-Line is expected. In other words, if
1042   the server is reading the protocol stream at the beginning of a
1043   message and receives a CRLF first, it should ignore the CRLF.
1046   Some old HTTP/1.0 client implementations generate an extra CRLF
1047   after a POST request as a lame workaround for some early server
1048   applications that failed to read message-body content that was
1049   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1050   preface or follow a request with an extra CRLF.  If terminating
1051   the request message-body with a line-ending is desired, then the
1052   client &MUST; include the terminating CRLF octets as part of the
1053   message-body length.
1056   The normal procedure for parsing an HTTP message is to read the
1057   start-line into a structure, read each header field into a hash
1058   table by field name until the empty line, and then use the parsed
1059   data to determine if a message-body is expected.  If a message-body
1060   has been indicated, then it is read as a stream until an amount
1061   of OCTETs equal to the message-length is read or the connection
1062   is closed.  Care must be taken to parse an HTTP message as a sequence
1063   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1064   to parse HTTP as a stream of Unicode characters in a character encoding
1065   like UTF-16 may introduce security flaws due to the differing ways
1066   that such parsers interpret invalid characters.
1070<section title="Header Fields" anchor="header.fields">
1071  <x:anchor-alias value="header-field"/>
1072  <x:anchor-alias value="field-content"/>
1073  <x:anchor-alias value="field-name"/>
1074  <x:anchor-alias value="field-value"/>
1075  <x:anchor-alias value="OWS"/>
1077   Each HTTP header field consists of a case-insensitive field name
1078   followed by a colon (":"), optional whitespace, and the field value.
1080<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"/>
1081  <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>
1082  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1083  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1084  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1087   No whitespace is allowed between the header field name and colon. For
1088   security reasons, any request message received containing such whitespace
1089   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1090   &MUST; remove any such whitespace from a response message before
1091   forwarding the message downstream.
1094   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1095   preferred. The field value does not include any leading or trailing white
1096   space: OWS occurring before the first non-whitespace character of the
1097   field value or after the last non-whitespace character of the field value
1098   is ignored and &SHOULD; be removed without changing the meaning of the header
1099   field.
1102   The order in which header fields with differing field names are
1103   received is not significant. However, it is "good practice" to send
1104   header fields that contain control data first, such as Host on
1105   requests and Date on responses, so that implementations can decide
1106   when not to handle a message as early as possible.  A server &MUST;
1107   wait until the entire header section is received before interpreting
1108   a request message, since later header fields might include conditionals,
1109   authentication credentials, or deliberately misleading duplicate
1110   header fields that would impact request processing.
1113   Multiple header fields with the same field name &MUST-NOT; be
1114   sent in a message unless the entire field value for that
1115   header field is defined as a comma-separated list [i.e., #(values)].
1116   Multiple header fields with the same field name can be combined into
1117   one "field-name: field-value" pair, without changing the semantics of the
1118   message, by appending each subsequent field value to the combined
1119   field value in order, separated by a comma. The order in which
1120   header fields with the same field name are received is therefore
1121   significant to the interpretation of the combined field value;
1122   a proxy &MUST-NOT; change the order of these field values when
1123   forwarding a message.
1126  <t>
1127   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1128   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1129   can occur multiple times, but does not use the list syntax, and thus cannot
1130   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1131   for details.) Also note that the Set-Cookie2 header specified in
1132   <xref target="RFC2965"/> does not share this problem.
1133  </t>
1136   Historically, HTTP header field values could be extended over multiple
1137   lines by preceding each extra line with at least one space or horizontal
1138   tab character (line folding). This specification deprecates such line
1139   folding except within the message/http media type
1140   (<xref target=""/>).
1141   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1142   (i.e., that contain any field-content that matches the obs-fold rule) unless
1143   the message is intended for packaging within the message/http media type.
1144   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1145   obs-fold whitespace with a single SP prior to interpreting the field value
1146   or forwarding the message downstream.
1149   Historically, HTTP has allowed field content with text in the ISO-8859-1
1150   <xref target="ISO-8859-1"/> character encoding and supported other
1151   character sets only through use of <xref target="RFC2047"/> encoding.
1152   In practice, most HTTP header field values use only a subset of the
1153   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1154   header fields &SHOULD; limit their field values to US-ASCII characters.
1155   Recipients &SHOULD; treat other (obs-text) octets in field content as
1156   opaque data.
1158<t anchor="rule.comment">
1159  <x:anchor-alias value="comment"/>
1160  <x:anchor-alias value="ctext"/>
1161   Comments can be included in some HTTP header fields by surrounding
1162   the comment text with parentheses. Comments are only allowed in
1163   fields containing "comment" as part of their field value definition.
1165<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1166  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1167  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1168                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1170<t anchor="rule.quoted-cpair">
1171  <x:anchor-alias value="quoted-cpair"/>
1172   The backslash character ("\") can be used as a single-character
1173   quoting mechanism within comment constructs:
1175<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1176  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1179   Producers &SHOULD-NOT; escape characters that do not require escaping
1180   (i.e., other than the backslash character "\" and the parentheses "(" and
1181   ")").
1185<section title="Message Body" anchor="message.body">
1186  <x:anchor-alias value="message-body"/>
1188   The message-body (if any) of an HTTP message is used to carry the
1189   entity-body associated with the request or response. The message-body
1190   differs from the entity-body only when a transfer-coding has been
1191   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1194  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1195               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1198   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1199   applied by an application to ensure safe and proper transfer of the
1200   message. Transfer-Encoding is a property of the message, not of the
1201   entity, and thus &MAY; be added or removed by any application along the
1202   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1203   when certain transfer-codings may be used.)
1206   The rules for when a message-body is allowed in a message differ for
1207   requests and responses.
1210   The presence of a message-body in a request is signaled by the
1211   inclusion of a Content-Length or Transfer-Encoding header field in
1212   the request's header fields.
1213   When a request message contains both a message-body of non-zero
1214   length and a method that does not define any semantics for that
1215   request message-body, then an origin server &SHOULD; either ignore
1216   the message-body or respond with an appropriate error message
1217   (e.g., 413).  A proxy or gateway, when presented the same request,
1218   &SHOULD; either forward the request inbound with the message-body or
1219   ignore the message-body when determining a response.
1222   For response messages, whether or not a message-body is included with
1223   a message is dependent on both the request method and the response
1224   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1225   &MUST-NOT; include a message-body, even though the presence of entity-header
1226   fields might lead one to believe they do. All 1xx
1227   (informational), 204 (No Content), and 304 (Not Modified) responses
1228   &MUST-NOT; include a message-body. All other responses do include a
1229   message-body, although it &MAY; be of zero length.
1233<section title="Message Length" anchor="message.length">
1235   The transfer-length of a message is the length of the message-body as
1236   it appears in the message; that is, after any transfer-codings have
1237   been applied. When a message-body is included with a message, the
1238   transfer-length of that body is determined by one of the following
1239   (in order of precedence):
1242  <list style="numbers">
1243    <x:lt><t>
1244     Any response message which "&MUST-NOT;" include a message-body (such
1245     as the 1xx, 204, and 304 responses and any response to a HEAD
1246     request) is always terminated by the first empty line after the
1247     header fields, regardless of the entity-header fields present in
1248     the message.
1249    </t></x:lt>
1250    <x:lt><t>
1251     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1252     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1253     is used, the transfer-length is defined by the use of this transfer-coding.
1254     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1255     is not present, the transfer-length is defined by the sender closing the connection.
1256    </t></x:lt>
1257    <x:lt><t>
1258     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1259     value in OCTETs represents both the entity-length and the
1260     transfer-length. The Content-Length header field &MUST-NOT; be sent
1261     if these two lengths are different (i.e., if a Transfer-Encoding
1262     header field is present). If a message is received with both a
1263     Transfer-Encoding header field and a Content-Length header field,
1264     the latter &MUST; be ignored.
1265    </t></x:lt>
1266    <x:lt><t>
1267     If the message uses the media type "multipart/byteranges", and the
1268     transfer-length is not otherwise specified, then this self-delimiting
1269     media type defines the transfer-length. This media type
1270     &MUST-NOT; be used unless the sender knows that the recipient can parse
1271     it; the presence in a request of a Range header with multiple byte-range
1272     specifiers from a 1.1 client implies that the client can parse
1273     multipart/byteranges responses.
1274    <list style="empty"><t>
1275       A range header might be forwarded by a 1.0 proxy that does not
1276       understand multipart/byteranges; in this case the server &MUST;
1277       delimit the message using methods defined in items 1, 3 or 5 of
1278       this section.
1279    </t></list>
1280    </t></x:lt>
1281    <x:lt><t>
1282     By the server closing the connection. (Closing the connection
1283     cannot be used to indicate the end of a request body, since that
1284     would leave no possibility for the server to send back a response.)
1285    </t></x:lt>
1286  </list>
1289   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1290   containing a message-body &MUST; include a valid Content-Length header
1291   field unless the server is known to be HTTP/1.1 compliant. If a
1292   request contains a message-body and a Content-Length is not given,
1293   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1294   determine the length of the message, or with 411 (Length Required) if
1295   it wishes to insist on receiving a valid Content-Length.
1298   All HTTP/1.1 applications that receive entities &MUST; accept the
1299   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1300   to be used for messages when the message length cannot be determined
1301   in advance.
1304   Messages &MUST-NOT; include both a Content-Length header field and a
1305   transfer-coding. If the message does include a
1306   transfer-coding, the Content-Length &MUST; be ignored.
1309   When a Content-Length is given in a message where a message-body is
1310   allowed, its field value &MUST; exactly match the number of OCTETs in
1311   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1312   invalid length is received and detected.
1316<section title="General Header Fields" anchor="general.header.fields">
1317  <x:anchor-alias value="general-header"/>
1319   There are a few header fields which have general applicability for
1320   both request and response messages, but which do not apply to the
1321   entity being transferred. These header fields apply only to the
1322   message being transmitted.
1324<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1325  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1326                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1327                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1328                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1329                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1330                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1331                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1332                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1333                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1336   General-header field names can be extended reliably only in
1337   combination with a change in the protocol version. However, new or
1338   experimental header fields may be given the semantics of general
1339   header fields if all parties in the communication recognize them to
1340   be general-header fields. Unrecognized header fields are treated as
1341   entity-header fields.
1346<section title="Request" anchor="request">
1347  <x:anchor-alias value="Request"/>
1349   A request message from a client to a server includes, within the
1350   first line of that message, the method to be applied to the resource,
1351   the identifier of the resource, and the protocol version in use.
1353<!--                 Host                      ; should be moved here eventually -->
1354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1355  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1356                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1357                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1358                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1359                  <x:ref>CRLF</x:ref>
1360                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1363<section title="Request-Line" anchor="request-line">
1364  <x:anchor-alias value="Request-Line"/>
1366   The Request-Line begins with a method token, followed by the
1367   request-target and the protocol version, and ending with CRLF. The
1368   elements are separated by SP characters. No CR or LF is allowed
1369   except in the final CRLF sequence.
1371<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1372  <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>
1375<section title="Method" anchor="method">
1376  <x:anchor-alias value="Method"/>
1378   The Method  token indicates the method to be performed on the
1379   resource identified by the request-target. The method is case-sensitive.
1381<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1382  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1386<section title="request-target" anchor="request-target">
1387  <x:anchor-alias value="request-target"/>
1389   The request-target
1390   identifies the resource upon which to apply the request.
1392<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1393  <x:ref>request-target</x:ref> = "*"
1394                 / <x:ref>absolute-URI</x:ref>
1395                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1396                 / <x:ref>authority</x:ref>
1399   The four options for request-target are dependent on the nature of the
1400   request. The asterisk "*" means that the request does not apply to a
1401   particular resource, but to the server itself, and is only allowed
1402   when the method used does not necessarily apply to a resource. One
1403   example would be
1405<figure><artwork type="example">
1406  OPTIONS * HTTP/1.1
1409   The absolute-URI form is &REQUIRED; when the request is being made to a
1410   proxy. The proxy is requested to forward the request or service it
1411   from a valid cache, and return the response. Note that the proxy &MAY;
1412   forward the request on to another proxy or directly to the server
1413   specified by the absolute-URI. In order to avoid request loops, a
1414   proxy &MUST; be able to recognize all of its server names, including
1415   any aliases, local variations, and the numeric IP address. An example
1416   Request-Line would be:
1418<figure><artwork type="example">
1419  GET HTTP/1.1
1422   To allow for transition to absolute-URIs in all requests in future
1423   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1424   form in requests, even though HTTP/1.1 clients will only generate
1425   them in requests to proxies.
1428   The authority form is only used by the CONNECT method (&CONNECT;).
1431   The most common form of request-target is that used to identify a
1432   resource on an origin server or gateway. In this case the absolute
1433   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1434   the request-target, and the network location of the URI (authority) &MUST;
1435   be transmitted in a Host header field. For example, a client wishing
1436   to retrieve the resource above directly from the origin server would
1437   create a TCP connection to port 80 of the host "" and send
1438   the lines:
1440<figure><artwork type="example">
1441  GET /pub/WWW/TheProject.html HTTP/1.1
1442  Host:
1445   followed by the remainder of the Request. Note that the absolute path
1446   cannot be empty; if none is present in the original URI, it &MUST; be
1447   given as "/" (the server root).
1450   If a proxy receives a request without any path in the request-target and
1451   the method specified is capable of supporting the asterisk form of
1452   request-target, then the last proxy on the request chain &MUST; forward the
1453   request with "*" as the final request-target.
1456   For example, the request
1457</preamble><artwork type="example">
1458  OPTIONS HTTP/1.1
1461  would be forwarded by the proxy as
1462</preamble><artwork type="example">
1463  OPTIONS * HTTP/1.1
1464  Host:
1467   after connecting to port 8001 of host "".
1471   The request-target is transmitted in the format specified in
1472   <xref target="http.uri"/>. If the request-target is percent-encoded
1473   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1474   &MUST; decode the request-target in order to
1475   properly interpret the request. Servers &SHOULD; respond to invalid
1476   request-targets with an appropriate status code.
1479   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1480   received request-target when forwarding it to the next inbound server,
1481   except as noted above to replace a null path-absolute with "/".
1484  <t>
1485    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1486    meaning of the request when the origin server is improperly using
1487    a non-reserved URI character for a reserved purpose.  Implementors
1488    should be aware that some pre-HTTP/1.1 proxies have been known to
1489    rewrite the request-target.
1490  </t>
1493   HTTP does not place a pre-defined limit on the length of a request-target.
1494   A server &MUST; be prepared to receive URIs of unbounded length and
1495   respond with the 414 (URI Too Long) status if the received
1496   request-target would be longer than the server wishes to handle
1497   (see &status-414;).
1500   Various ad-hoc limitations on request-target length are found in practice.
1501   It is &RECOMMENDED; that all HTTP senders and recipients support
1502   request-target lengths of 8000 or more OCTETs.
1507<section title="The Resource Identified by a Request" anchor="">
1509   The exact resource identified by an Internet request is determined by
1510   examining both the request-target and the Host header field.
1513   An origin server that does not allow resources to differ by the
1514   requested host &MAY; ignore the Host header field value when
1515   determining the resource identified by an HTTP/1.1 request. (But see
1516   <xref target=""/>
1517   for other requirements on Host support in HTTP/1.1.)
1520   An origin server that does differentiate resources based on the host
1521   requested (sometimes referred to as virtual hosts or vanity host
1522   names) &MUST; use the following rules for determining the requested
1523   resource on an HTTP/1.1 request:
1524  <list style="numbers">
1525    <t>If request-target is an absolute-URI, the host is part of the
1526     request-target. Any Host header field value in the request &MUST; be
1527     ignored.</t>
1528    <t>If the request-target is not an absolute-URI, and the request includes
1529     a Host header field, the host is determined by the Host header
1530     field value.</t>
1531    <t>If the host as determined by rule 1 or 2 is not a valid host on
1532     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1533  </list>
1536   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1537   attempt to use heuristics (e.g., examination of the URI path for
1538   something unique to a particular host) in order to determine what
1539   exact resource is being requested.
1546<section title="Response" anchor="response">
1547  <x:anchor-alias value="Response"/>
1549   After receiving and interpreting a request message, a server responds
1550   with an HTTP response message.
1552<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1553  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1554                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1555                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1556                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1557                  <x:ref>CRLF</x:ref>
1558                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1561<section title="Status-Line" anchor="status-line">
1562  <x:anchor-alias value="Status-Line"/>
1564   The first line of a Response message is the Status-Line, consisting
1565   of the protocol version followed by a numeric status code and its
1566   associated textual phrase, with each element separated by SP
1567   characters. No CR or LF is allowed except in the final CRLF sequence.
1569<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1570  <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>
1573<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1574  <x:anchor-alias value="Reason-Phrase"/>
1575  <x:anchor-alias value="Status-Code"/>
1577   The Status-Code element is a 3-digit integer result code of the
1578   attempt to understand and satisfy the request. These codes are fully
1579   defined in &status-codes;.  The Reason Phrase exists for the sole
1580   purpose of providing a textual description associated with the numeric
1581   status code, out of deference to earlier Internet application protocols
1582   that were more frequently used with interactive text clients.
1583   A client &SHOULD; ignore the content of the Reason Phrase.
1586   The first digit of the Status-Code defines the class of response. The
1587   last two digits do not have any categorization role. There are 5
1588   values for the first digit:
1589  <list style="symbols">
1590    <t>
1591      1xx: Informational - Request received, continuing process
1592    </t>
1593    <t>
1594      2xx: Success - The action was successfully received,
1595        understood, and accepted
1596    </t>
1597    <t>
1598      3xx: Redirection - Further action must be taken in order to
1599        complete the request
1600    </t>
1601    <t>
1602      4xx: Client Error - The request contains bad syntax or cannot
1603        be fulfilled
1604    </t>
1605    <t>
1606      5xx: Server Error - The server failed to fulfill an apparently
1607        valid request
1608    </t>
1609  </list>
1611<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"/>
1612  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1613  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1621<section title="Protocol Parameters" anchor="protocol.parameters">
1623<section title="Date/Time Formats: Full Date" anchor="">
1624  <x:anchor-alias value="HTTP-date"/>
1626   HTTP applications have historically allowed three different formats
1627   for the representation of date/time stamps:
1629<figure><artwork type="example">
1630  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1631  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1632  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1635   The first format is preferred as an Internet standard and represents
1636   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1637   other formats are described here only for
1638   compatibility with obsolete implementations.
1639   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1640   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1641   only generate the RFC 1123 format for representing HTTP-date values
1642   in header fields. See <xref target="tolerant.applications"/> for further information.
1645   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1646   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1647   equal to UTC (Coordinated Universal Time). This is indicated in the
1648   first two formats by the inclusion of "GMT" as the three-letter
1649   abbreviation for time zone, and &MUST; be assumed when reading the
1650   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1651   additional whitespace beyond that specifically included as SP in the
1652   grammar.
1654<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1655  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1657<t anchor="">
1658  <x:anchor-alias value="rfc1123-date"/>
1659  <x:anchor-alias value="time-of-day"/>
1660  <x:anchor-alias value="hour"/>
1661  <x:anchor-alias value="minute"/>
1662  <x:anchor-alias value="second"/>
1663  <x:anchor-alias value="day-name"/>
1664  <x:anchor-alias value="day"/>
1665  <x:anchor-alias value="month"/>
1666  <x:anchor-alias value="year"/>
1667  <x:anchor-alias value="GMT"/>
1668  Preferred format:
1670<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"/>
1671  <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>
1673  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1674               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1675               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1676               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1677               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1678               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1679               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1681  <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>
1682               ; e.g., 02 Jun 1982
1684  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1685  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1686               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1687               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1688               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1689               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1690               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1691               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1692               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1693               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1694               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1695               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1696               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1697  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1699  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1701  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1702                 ; 00:00:00 - 23:59:59
1704  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1705  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1706  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1709  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1710  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1711  same as those defined for the RFC 5322 constructs
1712  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1714<t anchor="">
1715  <x:anchor-alias value="obs-date"/>
1716  <x:anchor-alias value="rfc850-date"/>
1717  <x:anchor-alias value="asctime-date"/>
1718  <x:anchor-alias value="date1"/>
1719  <x:anchor-alias value="date2"/>
1720  <x:anchor-alias value="date3"/>
1721  <x:anchor-alias value="rfc1123-date"/>
1722  <x:anchor-alias value="day-name-l"/>
1723  Obsolete formats:
1725<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1726  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1728<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1729  <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>
1730  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1731                 ; day-month-year (e.g., 02-Jun-82)
1733  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1734         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1735         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1736         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1737         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1738         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1739         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1741<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1742  <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>
1743  <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> ))
1744                 ; month day (e.g., Jun  2)
1747  <t>
1748    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1749    accepting date values that may have been sent by non-HTTP
1750    applications, as is sometimes the case when retrieving or posting
1751    messages via proxies/gateways to SMTP or NNTP.
1752  </t>
1755  <t>
1756    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1757    to their usage within the protocol stream. Clients and servers are
1758    not required to use these formats for user presentation, request
1759    logging, etc.
1760  </t>
1764<section title="Transfer Codings" anchor="transfer.codings">
1765  <x:anchor-alias value="transfer-coding"/>
1766  <x:anchor-alias value="transfer-extension"/>
1768   Transfer-coding values are used to indicate an encoding
1769   transformation that has been, can be, or may need to be applied to an
1770   entity-body in order to ensure "safe transport" through the network.
1771   This differs from a content coding in that the transfer-coding is a
1772   property of the message, not of the original entity.
1774<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1775  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1776                          / "compress" ; <xref target="compress.coding"/>
1777                          / "deflate" ; <xref target="deflate.coding"/>
1778                          / "gzip" ; <xref target="gzip.coding"/>
1779                          / <x:ref>transfer-extension</x:ref>
1780  <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> )
1782<t anchor="rule.parameter">
1783  <x:anchor-alias value="attribute"/>
1784  <x:anchor-alias value="transfer-parameter"/>
1785  <x:anchor-alias value="value"/>
1786   Parameters are in  the form of attribute/value pairs.
1788<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"/>
1789  <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>
1790  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1791  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1794   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1795   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1796   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1799   Whenever a transfer-coding is applied to a message-body, the set of
1800   transfer-codings &MUST; include "chunked", unless the message indicates it
1801   is terminated by closing the connection. When the "chunked" transfer-coding
1802   is used, it &MUST; be the last transfer-coding applied to the
1803   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1804   than once to a message-body. These rules allow the recipient to
1805   determine the transfer-length of the message (<xref target="message.length"/>).
1808   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1809   MIME, which were designed to enable safe transport of binary data over a
1810   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1811   However, safe transport
1812   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1813   the only unsafe characteristic of message-bodies is the difficulty in
1814   determining the exact body length (<xref target="message.length"/>), or the desire to
1815   encrypt data over a shared transport.
1818   A server which receives an entity-body with a transfer-coding it does
1819   not understand &SHOULD; return 501 (Not Implemented), and close the
1820   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1821   client.
1824<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1825  <iref item="chunked (Coding Format)"/>
1826  <iref item="Coding Format" subitem="chunked"/>
1827  <x:anchor-alias value="chunk"/>
1828  <x:anchor-alias value="Chunked-Body"/>
1829  <x:anchor-alias value="chunk-data"/>
1830  <x:anchor-alias value="chunk-ext"/>
1831  <x:anchor-alias value="chunk-ext-name"/>
1832  <x:anchor-alias value="chunk-ext-val"/>
1833  <x:anchor-alias value="chunk-size"/>
1834  <x:anchor-alias value="last-chunk"/>
1835  <x:anchor-alias value="trailer-part"/>
1837   The chunked encoding modifies the body of a message in order to
1838   transfer it as a series of chunks, each with its own size indicator,
1839   followed by an &OPTIONAL; trailer containing entity-header fields. This
1840   allows dynamically produced content to be transferred along with the
1841   information necessary for the recipient to verify that it has
1842   received the full message.
1844<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"/>
1845  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1846                   <x:ref>last-chunk</x:ref>
1847                   <x:ref>trailer-part</x:ref>
1848                   <x:ref>CRLF</x:ref>
1850  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1851                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1852  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1853  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1855  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1856                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1857  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1858  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1859  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1860  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1863   The chunk-size field is a string of hex digits indicating the size of
1864   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1865   zero, followed by the trailer, which is terminated by an empty line.
1868   The trailer allows the sender to include additional HTTP header
1869   fields at the end of the message. The Trailer header field can be
1870   used to indicate which header fields are included in a trailer (see
1871   <xref target="header.trailer"/>).
1874   A server using chunked transfer-coding in a response &MUST-NOT; use the
1875   trailer for any header fields unless at least one of the following is
1876   true:
1877  <list style="numbers">
1878    <t>the request included a TE header field that indicates "trailers" is
1879     acceptable in the transfer-coding of the  response, as described in
1880     <xref target="header.te"/>; or,</t>
1882    <t>the server is the origin server for the response, the trailer
1883     fields consist entirely of optional metadata, and the recipient
1884     could use the message (in a manner acceptable to the origin server)
1885     without receiving this metadata.  In other words, the origin server
1886     is willing to accept the possibility that the trailer fields might
1887     be silently discarded along the path to the client.</t>
1888  </list>
1891   This requirement prevents an interoperability failure when the
1892   message is being received by an HTTP/1.1 (or later) proxy and
1893   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1894   compliance with the protocol would have necessitated a possibly
1895   infinite buffer on the proxy.
1898   A process for decoding the "chunked" transfer-coding
1899   can be represented in pseudo-code as:
1901<figure><artwork type="code">
1902  length := 0
1903  read chunk-size, chunk-ext (if any) and CRLF
1904  while (chunk-size &gt; 0) {
1905     read chunk-data and CRLF
1906     append chunk-data to entity-body
1907     length := length + chunk-size
1908     read chunk-size and CRLF
1909  }
1910  read entity-header
1911  while (entity-header not empty) {
1912     append entity-header to existing header fields
1913     read entity-header
1914  }
1915  Content-Length := length
1916  Remove "chunked" from Transfer-Encoding
1919   All HTTP/1.1 applications &MUST; be able to receive and decode the
1920   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1921   they do not understand.
1925<section title="Compression Codings" anchor="compression.codings">
1927   The codings defined below can be used to compress the payload of a
1928   message.
1931   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1932   is not desirable and is discouraged for future encodings. Their
1933   use here is representative of historical practice, not good
1934   design.
1937   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1938   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1939   equivalent to "gzip" and "compress" respectively.
1942<section title="Compress Coding" anchor="compress.coding">
1943<iref item="compress (Coding Format)"/>
1944<iref item="Coding Format" subitem="compress"/>
1946   The "compress" format is produced by the common UNIX file compression
1947   program "compress". This format is an adaptive Lempel-Ziv-Welch
1948   coding (LZW).
1952<section title="Deflate Coding" anchor="deflate.coding">
1953<iref item="deflate (Coding Format)"/>
1954<iref item="Coding Format" subitem="deflate"/>
1956   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
1957   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
1961<section title="Gzip Coding" anchor="gzip.coding">
1962<iref item="gzip (Coding Format)"/>
1963<iref item="Coding Format" subitem="gzip"/>
1965   The "gzip" format is produced by the file compression program
1966   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
1967   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
1973<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
1975   The HTTP Transfer Coding Registry defines the name space for the transfer
1976   coding names.
1979   Registrations &MUST; include the following fields:
1980   <list style="symbols">
1981     <t>Name</t>
1982     <t>Description</t>
1983     <t>Pointer to specification text</t>
1984   </list>
1987   Values to be added to this name space require expert review and a specification
1988   (see "Expert Review" and "Specification Required" in
1989   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
1990   conform to the purpose of transfer coding defined in this section.
1993   The registry itself is maintained at
1994   <eref target=""/>.
1999<section title="Product Tokens" anchor="product.tokens">
2000  <x:anchor-alias value="product"/>
2001  <x:anchor-alias value="product-version"/>
2003   Product tokens are used to allow communicating applications to
2004   identify themselves by software name and version. Most fields using
2005   product tokens also allow sub-products which form a significant part
2006   of the application to be listed, separated by whitespace. By
2007   convention, the products are listed in order of their significance
2008   for identifying the application.
2010<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2011  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2012  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2015   Examples:
2017<figure><artwork type="example">
2018  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2019  Server: Apache/0.8.4
2022   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2023   used for advertising or other non-essential information. Although any
2024   token character &MAY; appear in a product-version, this token &SHOULD;
2025   only be used for a version identifier (i.e., successive versions of
2026   the same product &SHOULD; only differ in the product-version portion of
2027   the product value).
2031<section title="Quality Values" anchor="quality.values">
2032  <x:anchor-alias value="qvalue"/>
2034   Both transfer codings (TE request header, <xref target="header.te"/>)
2035   and content negotiation (&content.negotiation;) use short "floating point"
2036   numbers to indicate the relative importance ("weight") of various
2037   negotiable parameters.  A weight is normalized to a real number in
2038   the range 0 through 1, where 0 is the minimum and 1 the maximum
2039   value. If a parameter has a quality value of 0, then content with
2040   this parameter is `not acceptable' for the client. HTTP/1.1
2041   applications &MUST-NOT; generate more than three digits after the
2042   decimal point. User configuration of these values &SHOULD; also be
2043   limited in this fashion.
2045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2046  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2047                 / ( "1" [ "." 0*3("0") ] )
2050  <t>
2051     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2052     relative degradation in desired quality.
2053  </t>
2059<section title="Connections" anchor="connections">
2061<section title="Persistent Connections" anchor="persistent.connections">
2063<section title="Purpose" anchor="persistent.purpose">
2065   Prior to persistent connections, a separate TCP connection was
2066   established to fetch each URL, increasing the load on HTTP servers
2067   and causing congestion on the Internet. The use of inline images and
2068   other associated data often require a client to make multiple
2069   requests of the same server in a short amount of time. Analysis of
2070   these performance problems and results from a prototype
2071   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2072   measurements of actual HTTP/1.1 implementations show good
2073   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2074   T/TCP <xref target="Tou1998"/>.
2077   Persistent HTTP connections have a number of advantages:
2078  <list style="symbols">
2079      <t>
2080        By opening and closing fewer TCP connections, CPU time is saved
2081        in routers and hosts (clients, servers, proxies, gateways,
2082        tunnels, or caches), and memory used for TCP protocol control
2083        blocks can be saved in hosts.
2084      </t>
2085      <t>
2086        HTTP requests and responses can be pipelined on a connection.
2087        Pipelining allows a client to make multiple requests without
2088        waiting for each response, allowing a single TCP connection to
2089        be used much more efficiently, with much lower elapsed time.
2090      </t>
2091      <t>
2092        Network congestion is reduced by reducing the number of packets
2093        caused by TCP opens, and by allowing TCP sufficient time to
2094        determine the congestion state of the network.
2095      </t>
2096      <t>
2097        Latency on subsequent requests is reduced since there is no time
2098        spent in TCP's connection opening handshake.
2099      </t>
2100      <t>
2101        HTTP can evolve more gracefully, since errors can be reported
2102        without the penalty of closing the TCP connection. Clients using
2103        future versions of HTTP might optimistically try a new feature,
2104        but if communicating with an older server, retry with old
2105        semantics after an error is reported.
2106      </t>
2107    </list>
2110   HTTP implementations &SHOULD; implement persistent connections.
2114<section title="Overall Operation" anchor="persistent.overall">
2116   A significant difference between HTTP/1.1 and earlier versions of
2117   HTTP is that persistent connections are the default behavior of any
2118   HTTP connection. That is, unless otherwise indicated, the client
2119   &SHOULD; assume that the server will maintain a persistent connection,
2120   even after error responses from the server.
2123   Persistent connections provide a mechanism by which a client and a
2124   server can signal the close of a TCP connection. This signaling takes
2125   place using the Connection header field (<xref target="header.connection"/>). Once a close
2126   has been signaled, the client &MUST-NOT; send any more requests on that
2127   connection.
2130<section title="Negotiation" anchor="persistent.negotiation">
2132   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2133   maintain a persistent connection unless a Connection header including
2134   the connection-token "close" was sent in the request. If the server
2135   chooses to close the connection immediately after sending the
2136   response, it &SHOULD; send a Connection header including the
2137   connection-token close.
2140   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2141   decide to keep it open based on whether the response from a server
2142   contains a Connection header with the connection-token close. In case
2143   the client does not want to maintain a connection for more than that
2144   request, it &SHOULD; send a Connection header including the
2145   connection-token close.
2148   If either the client or the server sends the close token in the
2149   Connection header, that request becomes the last one for the
2150   connection.
2153   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2154   maintained for HTTP versions less than 1.1 unless it is explicitly
2155   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2156   compatibility with HTTP/1.0 clients.
2159   In order to remain persistent, all messages on the connection &MUST;
2160   have a self-defined message length (i.e., one not defined by closure
2161   of the connection), as described in <xref target="message.length"/>.
2165<section title="Pipelining" anchor="pipelining">
2167   A client that supports persistent connections &MAY; "pipeline" its
2168   requests (i.e., send multiple requests without waiting for each
2169   response). A server &MUST; send its responses to those requests in the
2170   same order that the requests were received.
2173   Clients which assume persistent connections and pipeline immediately
2174   after connection establishment &SHOULD; be prepared to retry their
2175   connection if the first pipelined attempt fails. If a client does
2176   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2177   persistent. Clients &MUST; also be prepared to resend their requests if
2178   the server closes the connection before sending all of the
2179   corresponding responses.
2182   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2183   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2184   premature termination of the transport connection could lead to
2185   indeterminate results. A client wishing to send a non-idempotent
2186   request &SHOULD; wait to send that request until it has received the
2187   response status for the previous request.
2192<section title="Proxy Servers" anchor="persistent.proxy">
2194   It is especially important that proxies correctly implement the
2195   properties of the Connection header field as specified in <xref target="header.connection"/>.
2198   The proxy server &MUST; signal persistent connections separately with
2199   its clients and the origin servers (or other proxy servers) that it
2200   connects to. Each persistent connection applies to only one transport
2201   link.
2204   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2205   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2206   for information and discussion of the problems with the Keep-Alive header
2207   implemented by many HTTP/1.0 clients).
2211<section title="Practical Considerations" anchor="persistent.practical">
2213   Servers will usually have some time-out value beyond which they will
2214   no longer maintain an inactive connection. Proxy servers might make
2215   this a higher value since it is likely that the client will be making
2216   more connections through the same server. The use of persistent
2217   connections places no requirements on the length (or existence) of
2218   this time-out for either the client or the server.
2221   When a client or server wishes to time-out it &SHOULD; issue a graceful
2222   close on the transport connection. Clients and servers &SHOULD; both
2223   constantly watch for the other side of the transport close, and
2224   respond to it as appropriate. If a client or server does not detect
2225   the other side's close promptly it could cause unnecessary resource
2226   drain on the network.
2229   A client, server, or proxy &MAY; close the transport connection at any
2230   time. For example, a client might have started to send a new request
2231   at the same time that the server has decided to close the "idle"
2232   connection. From the server's point of view, the connection is being
2233   closed while it was idle, but from the client's point of view, a
2234   request is in progress.
2237   This means that clients, servers, and proxies &MUST; be able to recover
2238   from asynchronous close events. Client software &SHOULD; reopen the
2239   transport connection and retransmit the aborted sequence of requests
2240   without user interaction so long as the request sequence is
2241   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2242   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2243   human operator the choice of retrying the request(s). Confirmation by
2244   user-agent software with semantic understanding of the application
2245   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2246   be repeated if the second sequence of requests fails.
2249   Servers &SHOULD; always respond to at least one request per connection,
2250   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2251   middle of transmitting a response, unless a network or client failure
2252   is suspected.
2255   Clients that use persistent connections &SHOULD; limit the number of
2256   simultaneous connections that they maintain to a given server. A
2257   single-user client &SHOULD-NOT; maintain more than 2 connections with
2258   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2259   another server or proxy, where N is the number of simultaneously
2260   active users. These guidelines are intended to improve HTTP response
2261   times and avoid congestion.
2266<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2268<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2270   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2271   flow control mechanisms to resolve temporary overloads, rather than
2272   terminating connections with the expectation that clients will retry.
2273   The latter technique can exacerbate network congestion.
2277<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2279   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2280   the network connection for an error status while it is transmitting
2281   the request. If the client sees an error status, it &SHOULD;
2282   immediately cease transmitting the body. If the body is being sent
2283   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2284   empty trailer &MAY; be used to prematurely mark the end of the message.
2285   If the body was preceded by a Content-Length header, the client &MUST;
2286   close the connection.
2290<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2292   The purpose of the 100 (Continue) status (see &status-100;) is to
2293   allow a client that is sending a request message with a request body
2294   to determine if the origin server is willing to accept the request
2295   (based on the request headers) before the client sends the request
2296   body. In some cases, it might either be inappropriate or highly
2297   inefficient for the client to send the body if the server will reject
2298   the message without looking at the body.
2301   Requirements for HTTP/1.1 clients:
2302  <list style="symbols">
2303    <t>
2304        If a client will wait for a 100 (Continue) response before
2305        sending the request body, it &MUST; send an Expect request-header
2306        field (&header-expect;) with the "100-continue" expectation.
2307    </t>
2308    <t>
2309        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2310        with the "100-continue" expectation if it does not intend
2311        to send a request body.
2312    </t>
2313  </list>
2316   Because of the presence of older implementations, the protocol allows
2317   ambiguous situations in which a client may send "Expect: 100-continue"
2318   without receiving either a 417 (Expectation Failed) status
2319   or a 100 (Continue) status. Therefore, when a client sends this
2320   header field to an origin server (possibly via a proxy) from which it
2321   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2322   for an indefinite period before sending the request body.
2325   Requirements for HTTP/1.1 origin servers:
2326  <list style="symbols">
2327    <t> Upon receiving a request which includes an Expect request-header
2328        field with the "100-continue" expectation, an origin server &MUST;
2329        either respond with 100 (Continue) status and continue to read
2330        from the input stream, or respond with a final status code. The
2331        origin server &MUST-NOT; wait for the request body before sending
2332        the 100 (Continue) response. If it responds with a final status
2333        code, it &MAY; close the transport connection or it &MAY; continue
2334        to read and discard the rest of the request.  It &MUST-NOT;
2335        perform the requested method if it returns a final status code.
2336    </t>
2337    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2338        the request message does not include an Expect request-header
2339        field with the "100-continue" expectation, and &MUST-NOT; send a
2340        100 (Continue) response if such a request comes from an HTTP/1.0
2341        (or earlier) client. There is an exception to this rule: for
2342        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2343        status in response to an HTTP/1.1 PUT or POST request that does
2344        not include an Expect request-header field with the "100-continue"
2345        expectation. This exception, the purpose of which is
2346        to minimize any client processing delays associated with an
2347        undeclared wait for 100 (Continue) status, applies only to
2348        HTTP/1.1 requests, and not to requests with any other HTTP-version
2349        value.
2350    </t>
2351    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2352        already received some or all of the request body for the
2353        corresponding request.
2354    </t>
2355    <t> An origin server that sends a 100 (Continue) response &MUST;
2356    ultimately send a final status code, once the request body is
2357        received and processed, unless it terminates the transport
2358        connection prematurely.
2359    </t>
2360    <t> If an origin server receives a request that does not include an
2361        Expect request-header field with the "100-continue" expectation,
2362        the request includes a request body, and the server responds
2363        with a final status code before reading the entire request body
2364        from the transport connection, then the server &SHOULD-NOT;  close
2365        the transport connection until it has read the entire request,
2366        or until the client closes the connection. Otherwise, the client
2367        might not reliably receive the response message. However, this
2368        requirement is not be construed as preventing a server from
2369        defending itself against denial-of-service attacks, or from
2370        badly broken client implementations.
2371      </t>
2372    </list>
2375   Requirements for HTTP/1.1 proxies:
2376  <list style="symbols">
2377    <t> If a proxy receives a request that includes an Expect request-header
2378        field with the "100-continue" expectation, and the proxy
2379        either knows that the next-hop server complies with HTTP/1.1 or
2380        higher, or does not know the HTTP version of the next-hop
2381        server, it &MUST; forward the request, including the Expect header
2382        field.
2383    </t>
2384    <t> If the proxy knows that the version of the next-hop server is
2385        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2386        respond with a 417 (Expectation Failed) status.
2387    </t>
2388    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2389        numbers received from recently-referenced next-hop servers.
2390    </t>
2391    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2392        request message was received from an HTTP/1.0 (or earlier)
2393        client and did not include an Expect request-header field with
2394        the "100-continue" expectation. This requirement overrides the
2395        general rule for forwarding of 1xx responses (see &status-1xx;).
2396    </t>
2397  </list>
2401<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2403   If an HTTP/1.1 client sends a request which includes a request body,
2404   but which does not include an Expect request-header field with the
2405   "100-continue" expectation, and if the client is not directly
2406   connected to an HTTP/1.1 origin server, and if the client sees the
2407   connection close before receiving any status from the server, the
2408   client &SHOULD; retry the request.  If the client does retry this
2409   request, it &MAY; use the following "binary exponential backoff"
2410   algorithm to be assured of obtaining a reliable response:
2411  <list style="numbers">
2412    <t>
2413      Initiate a new connection to the server
2414    </t>
2415    <t>
2416      Transmit the request-headers
2417    </t>
2418    <t>
2419      Initialize a variable R to the estimated round-trip time to the
2420         server (e.g., based on the time it took to establish the
2421         connection), or to a constant value of 5 seconds if the round-trip
2422         time is not available.
2423    </t>
2424    <t>
2425       Compute T = R * (2**N), where N is the number of previous
2426         retries of this request.
2427    </t>
2428    <t>
2429       Wait either for an error response from the server, or for T
2430         seconds (whichever comes first)
2431    </t>
2432    <t>
2433       If no error response is received, after T seconds transmit the
2434         body of the request.
2435    </t>
2436    <t>
2437       If client sees that the connection is closed prematurely,
2438         repeat from step 1 until the request is accepted, an error
2439         response is received, or the user becomes impatient and
2440         terminates the retry process.
2441    </t>
2442  </list>
2445   If at any point an error status is received, the client
2446  <list style="symbols">
2447      <t>&SHOULD-NOT;  continue and</t>
2449      <t>&SHOULD; close the connection if it has not completed sending the
2450        request message.</t>
2451    </list>
2458<section title="Miscellaneous notes that may disappear" anchor="misc">
2459<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2461   <cref>TBS: describe why aliases like webcal are harmful.</cref>
2465<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2467   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
2471<section title="Interception of HTTP for access control" anchor="http.intercept">
2473   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
2477<section title="Use of HTTP by other protocols" anchor="http.others">
2479   <cref>TBD: Profiles of HTTP defined by other protocol.
2480   Extensions of HTTP like WebDAV.</cref>
2484<section title="Use of HTTP by media type specification" anchor="">
2486   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
2491<section title="Header Field Definitions" anchor="header.field.definitions">
2493   This section defines the syntax and semantics of HTTP/1.1 header fields
2494   related to message framing and transport protocols.
2497   For entity-header fields, both sender and recipient refer to either the
2498   client or the server, depending on who sends and who receives the entity.
2501<section title="Connection" anchor="header.connection">
2502  <iref primary="true" item="Connection header" x:for-anchor=""/>
2503  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2504  <x:anchor-alias value="Connection"/>
2505  <x:anchor-alias value="connection-token"/>
2506  <x:anchor-alias value="Connection-v"/>
2508   The "Connection" general-header field allows the sender to specify
2509   options that are desired for that particular connection and &MUST-NOT;
2510   be communicated by proxies over further connections.
2513   The Connection header's value has the following grammar:
2515<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"/>
2516  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2517  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2518  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2521   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2522   message is forwarded and, for each connection-token in this field,
2523   remove any header field(s) from the message with the same name as the
2524   connection-token. Connection options are signaled by the presence of
2525   a connection-token in the Connection header field, not by any
2526   corresponding additional header field(s), since the additional header
2527   field may not be sent if there are no parameters associated with that
2528   connection option.
2531   Message headers listed in the Connection header &MUST-NOT; include
2532   end-to-end headers, such as Cache-Control.
2535   HTTP/1.1 defines the "close" connection option for the sender to
2536   signal that the connection will be closed after completion of the
2537   response. For example,
2539<figure><artwork type="example">
2540  Connection: close
2543   in either the request or the response header fields indicates that
2544   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2545   after the current request/response is complete.
2548   An HTTP/1.1 client that does not support persistent connections &MUST;
2549   include the "close" connection option in every request message.
2552   An HTTP/1.1 server that does not support persistent connections &MUST;
2553   include the "close" connection option in every response message that
2554   does not have a 1xx (informational) status code.
2557   A system receiving an HTTP/1.0 (or lower-version) message that
2558   includes a Connection header &MUST;, for each connection-token in this
2559   field, remove and ignore any header field(s) from the message with
2560   the same name as the connection-token. This protects against mistaken
2561   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2565<section title="Content-Length" anchor="header.content-length">
2566  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2567  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2568  <x:anchor-alias value="Content-Length"/>
2569  <x:anchor-alias value="Content-Length-v"/>
2571   The "Content-Length" entity-header field indicates the size of the
2572   entity-body, in number of OCTETs. In the case of responses to the HEAD
2573   method, it indicates the size of the entity-body that would have been sent
2574   had the request been a GET.
2576<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2577  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2578  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2581   An example is
2583<figure><artwork type="example">
2584  Content-Length: 3495
2587   Applications &SHOULD; use this field to indicate the transfer-length of
2588   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2591   Any Content-Length greater than or equal to zero is a valid value.
2592   <xref target="message.length"/> describes how to determine the length of a message-body
2593   if a Content-Length is not given.
2596   Note that the meaning of this field is significantly different from
2597   the corresponding definition in MIME, where it is an optional field
2598   used within the "message/external-body" content-type. In HTTP, it
2599   &SHOULD; be sent whenever the message's length can be determined prior
2600   to being transferred, unless this is prohibited by the rules in
2601   <xref target="message.length"/>.
2605<section title="Date" anchor="">
2606  <iref primary="true" item="Date header" x:for-anchor=""/>
2607  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2608  <x:anchor-alias value="Date"/>
2609  <x:anchor-alias value="Date-v"/>
2611   The "Date" general-header field represents the date and time at which
2612   the message was originated, having the same semantics as orig-date in
2613   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2614   HTTP-date, as described in <xref target=""/>;
2615   it &MUST; be sent in rfc1123-date format.
2617<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2618  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2619  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2622   An example is
2624<figure><artwork type="example">
2625  Date: Tue, 15 Nov 1994 08:12:31 GMT
2628   Origin servers &MUST; include a Date header field in all responses,
2629   except in these cases:
2630  <list style="numbers">
2631      <t>If the response status code is 100 (Continue) or 101 (Switching
2632         Protocols), the response &MAY; include a Date header field, at
2633         the server's option.</t>
2635      <t>If the response status code conveys a server error, e.g. 500
2636         (Internal Server Error) or 503 (Service Unavailable), and it is
2637         inconvenient or impossible to generate a valid Date.</t>
2639      <t>If the server does not have a clock that can provide a
2640         reasonable approximation of the current time, its responses
2641         &MUST-NOT; include a Date header field. In this case, the rules
2642         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2643  </list>
2646   A received message that does not have a Date header field &MUST; be
2647   assigned one by the recipient if the message will be cached by that
2648   recipient or gatewayed via a protocol which requires a Date. An HTTP
2649   implementation without a clock &MUST-NOT; cache responses without
2650   revalidating them on every use. An HTTP cache, especially a shared
2651   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2652   clock with a reliable external standard.
2655   Clients &SHOULD; only send a Date header field in messages that include
2656   an entity-body, as in the case of the PUT and POST requests, and even
2657   then it is optional. A client without a clock &MUST-NOT; send a Date
2658   header field in a request.
2661   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2662   time subsequent to the generation of the message. It &SHOULD; represent
2663   the best available approximation of the date and time of message
2664   generation, unless the implementation has no means of generating a
2665   reasonably accurate date and time. In theory, the date ought to
2666   represent the moment just before the entity is generated. In
2667   practice, the date can be generated at any time during the message
2668   origination without affecting its semantic value.
2671<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2673   Some origin server implementations might not have a clock available.
2674   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2675   values to a response, unless these values were associated
2676   with the resource by a system or user with a reliable clock. It &MAY;
2677   assign an Expires value that is known, at or before server
2678   configuration time, to be in the past (this allows "pre-expiration"
2679   of responses without storing separate Expires values for each
2680   resource).
2685<section title="Host" anchor="">
2686  <iref primary="true" item="Host header" x:for-anchor=""/>
2687  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2688  <x:anchor-alias value="Host"/>
2689  <x:anchor-alias value="Host-v"/>
2691   The "Host" request-header field specifies the Internet host and port
2692   number of the resource being requested, allowing the origin server or
2693   gateway to differentiate between internally-ambiguous URLs, such as the root
2694   "/" URL of a server for multiple host names on a single IP address.
2697   The Host field value &MUST; represent the naming authority of the origin
2698   server or gateway given by the original URL obtained from the user or
2699   referring resource (generally an http URI, as described in
2700   <xref target="http.uri"/>).
2702<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2703  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2704  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2707   A "host" without any trailing port information implies the default
2708   port for the service requested (e.g., "80" for an HTTP URL). For
2709   example, a request on the origin server for
2710   &lt;; would properly include:
2712<figure><artwork type="example">
2713  GET /pub/WWW/ HTTP/1.1
2714  Host:
2717   A client &MUST; include a Host header field in all HTTP/1.1 request
2718   messages. If the requested URI does not include an Internet host
2719   name for the service being requested, then the Host header field &MUST;
2720   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2721   request message it forwards does contain an appropriate Host header
2722   field that identifies the service being requested by the proxy. All
2723   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2724   status code to any HTTP/1.1 request message which lacks a Host header
2725   field.
2728   See Sections <xref target="" format="counter"/>
2729   and <xref target="" format="counter"/>
2730   for other requirements relating to Host.
2734<section title="TE" anchor="header.te">
2735  <iref primary="true" item="TE header" x:for-anchor=""/>
2736  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2737  <x:anchor-alias value="TE"/>
2738  <x:anchor-alias value="TE-v"/>
2739  <x:anchor-alias value="t-codings"/>
2740  <x:anchor-alias value="te-params"/>
2741  <x:anchor-alias value="te-ext"/>
2743   The "TE" request-header field indicates what extension transfer-codings
2744   it is willing to accept in the response, and whether or not it is
2745   willing to accept trailer fields in a chunked transfer-coding.
2748   Its value may consist of the keyword "trailers" and/or a comma-separated
2749   list of extension transfer-coding names with optional accept
2750   parameters (as described in <xref target="transfer.codings"/>).
2752<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"/>
2753  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2754  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2755  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2756  <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> )
2757  <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> ) ]
2760   The presence of the keyword "trailers" indicates that the client is
2761   willing to accept trailer fields in a chunked transfer-coding, as
2762   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2763   transfer-coding values even though it does not itself represent a
2764   transfer-coding.
2767   Examples of its use are:
2769<figure><artwork type="example">
2770  TE: deflate
2771  TE:
2772  TE: trailers, deflate;q=0.5
2775   The TE header field only applies to the immediate connection.
2776   Therefore, the keyword &MUST; be supplied within a Connection header
2777   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2780   A server tests whether a transfer-coding is acceptable, according to
2781   a TE field, using these rules:
2782  <list style="numbers">
2783    <x:lt>
2784      <t>The "chunked" transfer-coding is always acceptable. If the
2785         keyword "trailers" is listed, the client indicates that it is
2786         willing to accept trailer fields in the chunked response on
2787         behalf of itself and any downstream clients. The implication is
2788         that, if given, the client is stating that either all
2789         downstream clients are willing to accept trailer fields in the
2790         forwarded response, or that it will attempt to buffer the
2791         response on behalf of downstream recipients.
2792      </t><t>
2793         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2794         chunked response such that a client can be assured of buffering
2795         the entire response.</t>
2796    </x:lt>
2797    <x:lt>
2798      <t>If the transfer-coding being tested is one of the transfer-codings
2799         listed in the TE field, then it is acceptable unless it
2800         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2801         qvalue of 0 means "not acceptable.")</t>
2802    </x:lt>
2803    <x:lt>
2804      <t>If multiple transfer-codings are acceptable, then the
2805         acceptable transfer-coding with the highest non-zero qvalue is
2806         preferred.  The "chunked" transfer-coding always has a qvalue
2807         of 1.</t>
2808    </x:lt>
2809  </list>
2812   If the TE field-value is empty or if no TE field is present, the only
2813   transfer-coding is "chunked". A message with no transfer-coding is
2814   always acceptable.
2818<section title="Trailer" anchor="header.trailer">
2819  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2820  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2821  <x:anchor-alias value="Trailer"/>
2822  <x:anchor-alias value="Trailer-v"/>
2824   The "Trailer" general-header field indicates that the given set of
2825   header fields is present in the trailer of a message encoded with
2826   chunked transfer-coding.
2828<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2829  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2830  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2833   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2834   message using chunked transfer-coding with a non-empty trailer. Doing
2835   so allows the recipient to know which header fields to expect in the
2836   trailer.
2839   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2840   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2841   trailer fields in a "chunked" transfer-coding.
2844   Message header fields listed in the Trailer header field &MUST-NOT;
2845   include the following header fields:
2846  <list style="symbols">
2847    <t>Transfer-Encoding</t>
2848    <t>Content-Length</t>
2849    <t>Trailer</t>
2850  </list>
2854<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2855  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2856  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2857  <x:anchor-alias value="Transfer-Encoding"/>
2858  <x:anchor-alias value="Transfer-Encoding-v"/>
2860   The "Transfer-Encoding" general-header field indicates what transfer-codings
2861   (if any) have been applied to the message body. It differs from
2862   Content-Encoding (&content-codings;) in that transfer-codings are a property
2863   of the message (and therefore are removed by intermediaries), whereas
2864   content-codings are not.
2866<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2867  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2868                        <x:ref>Transfer-Encoding-v</x:ref>
2869  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2872   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2874<figure><artwork type="example">
2875  Transfer-Encoding: chunked
2878   If multiple encodings have been applied to an entity, the transfer-codings
2879   &MUST; be listed in the order in which they were applied.
2880   Additional information about the encoding parameters &MAY; be provided
2881   by other entity-header fields not defined by this specification.
2884   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2885   header.
2889<section title="Upgrade" anchor="header.upgrade">
2890  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2891  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2892  <x:anchor-alias value="Upgrade"/>
2893  <x:anchor-alias value="Upgrade-v"/>
2895   The "Upgrade" general-header field allows the client to specify what
2896   additional communication protocols it would like to use, if the server
2897   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
2898   header field within a 101 (Switching Protocols) response to indicate which
2899   protocol(s) are being switched to.
2901<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2902  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2903  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2906   For example,
2908<figure><artwork type="example">
2909  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2912   The Upgrade header field is intended to provide a simple mechanism
2913   for transition from HTTP/1.1 to some other, incompatible protocol. It
2914   does so by allowing the client to advertise its desire to use another
2915   protocol, such as a later version of HTTP with a higher major version
2916   number, even though the current request has been made using HTTP/1.1.
2917   This eases the difficult transition between incompatible protocols by
2918   allowing the client to initiate a request in the more commonly
2919   supported protocol while indicating to the server that it would like
2920   to use a "better" protocol if available (where "better" is determined
2921   by the server, possibly according to the nature of the method and/or
2922   resource being requested).
2925   The Upgrade header field only applies to switching application-layer
2926   protocols upon the existing transport-layer connection. Upgrade
2927   cannot be used to insist on a protocol change; its acceptance and use
2928   by the server is optional. The capabilities and nature of the
2929   application-layer communication after the protocol change is entirely
2930   dependent upon the new protocol chosen, although the first action
2931   after changing the protocol &MUST; be a response to the initial HTTP
2932   request containing the Upgrade header field.
2935   The Upgrade header field only applies to the immediate connection.
2936   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2937   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2938   HTTP/1.1 message.
2941   The Upgrade header field cannot be used to indicate a switch to a
2942   protocol on a different connection. For that purpose, it is more
2943   appropriate to use a 301, 302, 303, or 305 redirection response.
2946   This specification only defines the protocol name "HTTP" for use by
2947   the family of Hypertext Transfer Protocols, as defined by the HTTP
2948   version rules of <xref target="http.version"/> and future updates to this
2949   specification. Additional tokens can be registered with IANA using the
2950   registration procedure defined below. 
2953<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
2955   The HTTP Upgrade Token Registry defines the name space for product
2956   tokens used to identify protocols in the Upgrade header field.
2957   Each registered token should be associated with one or a set of
2958   specifications, and with contact information.
2961   Registrations should be allowed on a First Come First Served basis as
2962   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
2963   specifications need not be IETF documents or be subject to IESG review, but
2964   should obey the following rules:
2965  <list style="numbers">
2966    <t>A token, once registered, stays registered forever.</t>
2967    <t>The registration &MUST; name a responsible party for the
2968       registration.</t>
2969    <t>The registration &MUST; name a point of contact.</t>
2970    <t>The registration &MAY; name the documentation required for the
2971       token.</t>
2972    <t>The responsible party &MAY; change the registration at any time.
2973       The IANA will keep a record of all such changes, and make them
2974       available upon request.</t>
2975    <t>The responsible party for the first registration of a "product"
2976       token &MUST; approve later registrations of a "version" token
2977       together with that "product" token before they can be registered.</t>
2978    <t>If absolutely required, the IESG &MAY; reassign the responsibility
2979       for a token. This will normally only be used in the case when a
2980       responsible party cannot be contacted.</t>
2981  </list>
2984   It is not required that specifications for upgrade tokens be made
2985   publicly available, but the contact information for the registration
2986   should be.
2993<section title="Via" anchor="header.via">
2994  <iref primary="true" item="Via header" x:for-anchor=""/>
2995  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2996  <x:anchor-alias value="protocol-name"/>
2997  <x:anchor-alias value="protocol-version"/>
2998  <x:anchor-alias value="pseudonym"/>
2999  <x:anchor-alias value="received-by"/>
3000  <x:anchor-alias value="received-protocol"/>
3001  <x:anchor-alias value="Via"/>
3002  <x:anchor-alias value="Via-v"/>
3004   The "Via" general-header field &MUST; be used by gateways and proxies to
3005   indicate the intermediate protocols and recipients between the user
3006   agent and the server on requests, and between the origin server and
3007   the client on responses. It is analogous to the "Received" field defined in
3008   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3009   avoiding request loops, and identifying the protocol capabilities of
3010   all senders along the request/response chain.
3012<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"/>
3013  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3014  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3015                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3016  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3017  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3018  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3019  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3020  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3023   The received-protocol indicates the protocol version of the message
3024   received by the server or client along each segment of the
3025   request/response chain. The received-protocol version is appended to
3026   the Via field value when the message is forwarded so that information
3027   about the protocol capabilities of upstream applications remains
3028   visible to all recipients.
3031   The protocol-name is optional if and only if it would be "HTTP". The
3032   received-by field is normally the host and optional port number of a
3033   recipient server or client that subsequently forwarded the message.
3034   However, if the real host is considered to be sensitive information,
3035   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3036   be assumed to be the default port of the received-protocol.
3039   Multiple Via field values represents each proxy or gateway that has
3040   forwarded the message. Each recipient &MUST; append its information
3041   such that the end result is ordered according to the sequence of
3042   forwarding applications.
3045   Comments &MAY; be used in the Via header field to identify the software
3046   of the recipient proxy or gateway, analogous to the User-Agent and
3047   Server header fields. However, all comments in the Via field are
3048   optional and &MAY; be removed by any recipient prior to forwarding the
3049   message.
3052   For example, a request message could be sent from an HTTP/1.0 user
3053   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3054   forward the request to a public proxy at, which completes
3055   the request by forwarding it to the origin server at
3056   The request received by would then have the following
3057   Via header field:
3059<figure><artwork type="example">
3060  Via: 1.0 fred, 1.1 (Apache/1.1)
3063   Proxies and gateways used as a portal through a network firewall
3064   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3065   the firewall region. This information &SHOULD; only be propagated if
3066   explicitly enabled. If not enabled, the received-by host of any host
3067   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3068   for that host.
3071   For organizations that have strong privacy requirements for hiding
3072   internal structures, a proxy &MAY; combine an ordered subsequence of
3073   Via header field entries with identical received-protocol values into
3074   a single such entry. For example,
3076<figure><artwork type="example">
3077  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3080        could be collapsed to
3082<figure><artwork type="example">
3083  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3086   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3087   under the same organizational control and the hosts have already been
3088   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3089   have different received-protocol values.
3095<section title="IANA Considerations" anchor="IANA.considerations">
3097<section title="Message Header Registration" anchor="message.header.registration">
3099   The Message Header Registry located at <eref target=""/> should be updated
3100   with the permanent registrations below (see <xref target="RFC3864"/>):
3102<?BEGININC p1-messaging.iana-headers ?>
3103<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3104<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3105   <ttcol>Header Field Name</ttcol>
3106   <ttcol>Protocol</ttcol>
3107   <ttcol>Status</ttcol>
3108   <ttcol>Reference</ttcol>
3110   <c>Connection</c>
3111   <c>http</c>
3112   <c>standard</c>
3113   <c>
3114      <xref target="header.connection"/>
3115   </c>
3116   <c>Content-Length</c>
3117   <c>http</c>
3118   <c>standard</c>
3119   <c>
3120      <xref target="header.content-length"/>
3121   </c>
3122   <c>Date</c>
3123   <c>http</c>
3124   <c>standard</c>
3125   <c>
3126      <xref target=""/>
3127   </c>
3128   <c>Host</c>
3129   <c>http</c>
3130   <c>standard</c>
3131   <c>
3132      <xref target=""/>
3133   </c>
3134   <c>TE</c>
3135   <c>http</c>
3136   <c>standard</c>
3137   <c>
3138      <xref target="header.te"/>
3139   </c>
3140   <c>Trailer</c>
3141   <c>http</c>
3142   <c>standard</c>
3143   <c>
3144      <xref target="header.trailer"/>
3145   </c>
3146   <c>Transfer-Encoding</c>
3147   <c>http</c>
3148   <c>standard</c>
3149   <c>
3150      <xref target="header.transfer-encoding"/>
3151   </c>
3152   <c>Upgrade</c>
3153   <c>http</c>
3154   <c>standard</c>
3155   <c>
3156      <xref target="header.upgrade"/>
3157   </c>
3158   <c>Via</c>
3159   <c>http</c>
3160   <c>standard</c>
3161   <c>
3162      <xref target="header.via"/>
3163   </c>
3166<?ENDINC p1-messaging.iana-headers ?>
3168   The change controller is: "IETF ( - Internet Engineering Task Force".
3172<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3174   The entries for the "http" and "https" URI Schemes in the registry located at
3175   <eref target=""/>
3176   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3177   and <xref target="https.uri" format="counter"/> of this document
3178   (see <xref target="RFC4395"/>).
3182<section title="Internet Media Type Registrations" anchor="">
3184   This document serves as the specification for the Internet media types
3185   "message/http" and "application/http". The following is to be registered with
3186   IANA (see <xref target="RFC4288"/>).
3188<section title="Internet Media Type message/http" anchor="">
3189<iref item="Media Type" subitem="message/http" primary="true"/>
3190<iref item="message/http Media Type" primary="true"/>
3192   The message/http type can be used to enclose a single HTTP request or
3193   response message, provided that it obeys the MIME restrictions for all
3194   "message" types regarding line length and encodings.
3197  <list style="hanging" x:indent="12em">
3198    <t hangText="Type name:">
3199      message
3200    </t>
3201    <t hangText="Subtype name:">
3202      http
3203    </t>
3204    <t hangText="Required parameters:">
3205      none
3206    </t>
3207    <t hangText="Optional parameters:">
3208      version, msgtype
3209      <list style="hanging">
3210        <t hangText="version:">
3211          The HTTP-Version number of the enclosed message
3212          (e.g., "1.1"). If not present, the version can be
3213          determined from the first line of the body.
3214        </t>
3215        <t hangText="msgtype:">
3216          The message type -- "request" or "response". If not
3217          present, the type can be determined from the first
3218          line of the body.
3219        </t>
3220      </list>
3221    </t>
3222    <t hangText="Encoding considerations:">
3223      only "7bit", "8bit", or "binary" are permitted
3224    </t>
3225    <t hangText="Security considerations:">
3226      none
3227    </t>
3228    <t hangText="Interoperability considerations:">
3229      none
3230    </t>
3231    <t hangText="Published specification:">
3232      This specification (see <xref target=""/>).
3233    </t>
3234    <t hangText="Applications that use this media type:">
3235    </t>
3236    <t hangText="Additional information:">
3237      <list style="hanging">
3238        <t hangText="Magic number(s):">none</t>
3239        <t hangText="File extension(s):">none</t>
3240        <t hangText="Macintosh file type code(s):">none</t>
3241      </list>
3242    </t>
3243    <t hangText="Person and email address to contact for further information:">
3244      See Authors Section.
3245    </t>
3246    <t hangText="Intended usage:">
3247      COMMON
3248    </t>
3249    <t hangText="Restrictions on usage:">
3250      none
3251    </t>
3252    <t hangText="Author/Change controller:">
3253      IESG
3254    </t>
3255  </list>
3258<section title="Internet Media Type application/http" anchor="">
3259<iref item="Media Type" subitem="application/http" primary="true"/>
3260<iref item="application/http Media Type" primary="true"/>
3262   The application/http type can be used to enclose a pipeline of one or more
3263   HTTP request or response messages (not intermixed).
3266  <list style="hanging" x:indent="12em">
3267    <t hangText="Type name:">
3268      application
3269    </t>
3270    <t hangText="Subtype name:">
3271      http
3272    </t>
3273    <t hangText="Required parameters:">
3274      none
3275    </t>
3276    <t hangText="Optional parameters:">
3277      version, msgtype
3278      <list style="hanging">
3279        <t hangText="version:">
3280          The HTTP-Version number of the enclosed messages
3281          (e.g., "1.1"). If not present, the version can be
3282          determined from the first line of the body.
3283        </t>
3284        <t hangText="msgtype:">
3285          The message type -- "request" or "response". If not
3286          present, the type can be determined from the first
3287          line of the body.
3288        </t>
3289      </list>
3290    </t>
3291    <t hangText="Encoding considerations:">
3292      HTTP messages enclosed by this type
3293      are in "binary" format; use of an appropriate
3294      Content-Transfer-Encoding is required when
3295      transmitted via E-mail.
3296    </t>
3297    <t hangText="Security considerations:">
3298      none
3299    </t>
3300    <t hangText="Interoperability considerations:">
3301      none
3302    </t>
3303    <t hangText="Published specification:">
3304      This specification (see <xref target=""/>).
3305    </t>
3306    <t hangText="Applications that use this media type:">
3307    </t>
3308    <t hangText="Additional information:">
3309      <list style="hanging">
3310        <t hangText="Magic number(s):">none</t>
3311        <t hangText="File extension(s):">none</t>
3312        <t hangText="Macintosh file type code(s):">none</t>
3313      </list>
3314    </t>
3315    <t hangText="Person and email address to contact for further information:">
3316      See Authors Section.
3317    </t>
3318    <t hangText="Intended usage:">
3319      COMMON
3320    </t>
3321    <t hangText="Restrictions on usage:">
3322      none
3323    </t>
3324    <t hangText="Author/Change controller:">
3325      IESG
3326    </t>
3327  </list>
3332<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3334   The registration procedure for HTTP Transfer Codings is now defined by
3335   <xref target="transfer.coding.registry"/> of this document.
3338   The HTTP Transfer Codings Registry located at <eref target=""/>
3339   should be updated with the registrations below:
3341<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3342   <ttcol>Name</ttcol>
3343   <ttcol>Description</ttcol>
3344   <ttcol>Reference</ttcol>
3345   <c>chunked</c>
3346   <c>Transfer in a series of chunks</c>
3347   <c>
3348      <xref target="chunked.encoding"/>
3349   </c>
3350   <c>compress</c>
3351   <c>UNIX "compress" program method</c>
3352   <c>
3353      <xref target="compress.coding"/>
3354   </c>
3355   <c>deflate</c>
3356   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3357   <c>
3358      <xref target="deflate.coding"/>
3359   </c>
3360   <c>gzip</c>
3361   <c>Same as GNU zip <xref target="RFC1952"/></c>
3362   <c>
3363      <xref target="gzip.coding"/>
3364   </c>
3368<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3370   The registration procedure for HTTP Upgrade Tokens -- previously defined
3371   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3372   by <xref target="upgrade.token.registry"/> of this document.
3375   The HTTP Status Code Registry located at <eref target=""/>
3376   should be updated with the registration below:
3378<texttable align="left" suppress-title="true">
3379   <ttcol>Value</ttcol>
3380   <ttcol>Description</ttcol>
3381   <ttcol>Reference</ttcol>
3383   <c>HTTP</c>
3384   <c>Hypertext Transfer Protocol</c>
3385   <c><xref target="http.version"/> of this specification</c>
3386<!-- IANA should add this without our instructions; emailed on June 05, 2009
3387   <c>TLS/1.0</c>
3388   <c>Transport Layer Security</c>
3389   <c><xref target="RFC2817"/></c> -->
3396<section title="Security Considerations" anchor="security.considerations">
3398   This section is meant to inform application developers, information
3399   providers, and users of the security limitations in HTTP/1.1 as
3400   described by this document. The discussion does not include
3401   definitive solutions to the problems revealed, though it does make
3402   some suggestions for reducing security risks.
3405<section title="Personal Information" anchor="personal.information">
3407   HTTP clients are often privy to large amounts of personal information
3408   (e.g. the user's name, location, mail address, passwords, encryption
3409   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3410   leakage of this information.
3411   We very strongly recommend that a convenient interface be provided
3412   for the user to control dissemination of such information, and that
3413   designers and implementors be particularly careful in this area.
3414   History shows that errors in this area often create serious security
3415   and/or privacy problems and generate highly adverse publicity for the
3416   implementor's company.
3420<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3422   A server is in the position to save personal data about a user's
3423   requests which might identify their reading patterns or subjects of
3424   interest. This information is clearly confidential in nature and its
3425   handling can be constrained by law in certain countries. People using
3426   HTTP to provide data are responsible for ensuring that
3427   such material is not distributed without the permission of any
3428   individuals that are identifiable by the published results.
3432<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3434   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3435   the documents returned by HTTP requests to be only those that were
3436   intended by the server administrators. If an HTTP server translates
3437   HTTP URIs directly into file system calls, the server &MUST; take
3438   special care not to serve files that were not intended to be
3439   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3440   other operating systems use ".." as a path component to indicate a
3441   directory level above the current one. On such a system, an HTTP
3442   server &MUST; disallow any such construct in the request-target if it
3443   would otherwise allow access to a resource outside those intended to
3444   be accessible via the HTTP server. Similarly, files intended for
3445   reference only internally to the server (such as access control
3446   files, configuration files, and script code) &MUST; be protected from
3447   inappropriate retrieval, since they might contain sensitive
3448   information. Experience has shown that minor bugs in such HTTP server
3449   implementations have turned into security risks.
3453<section title="DNS Spoofing" anchor="dns.spoofing">
3455   Clients using HTTP rely heavily on the Domain Name Service, and are
3456   thus generally prone to security attacks based on the deliberate
3457   mis-association of IP addresses and DNS names. Clients need to be
3458   cautious in assuming the continuing validity of an IP number/DNS name
3459   association.
3462   In particular, HTTP clients &SHOULD; rely on their name resolver for
3463   confirmation of an IP number/DNS name association, rather than
3464   caching the result of previous host name lookups. Many platforms
3465   already can cache host name lookups locally when appropriate, and
3466   they &SHOULD; be configured to do so. It is proper for these lookups to
3467   be cached, however, only when the TTL (Time To Live) information
3468   reported by the name server makes it likely that the cached
3469   information will remain useful.
3472   If HTTP clients cache the results of host name lookups in order to
3473   achieve a performance improvement, they &MUST; observe the TTL
3474   information reported by DNS.
3477   If HTTP clients do not observe this rule, they could be spoofed when
3478   a previously-accessed server's IP address changes. As network
3479   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3480   possibility of this form of attack will grow. Observing this
3481   requirement thus reduces this potential security vulnerability.
3484   This requirement also improves the load-balancing behavior of clients
3485   for replicated servers using the same DNS name and reduces the
3486   likelihood of a user's experiencing failure in accessing sites which
3487   use that strategy.
3491<section title="Proxies and Caching" anchor="attack.proxies">
3493   By their very nature, HTTP proxies are men-in-the-middle, and
3494   represent an opportunity for man-in-the-middle attacks. Compromise of
3495   the systems on which the proxies run can result in serious security
3496   and privacy problems. Proxies have access to security-related
3497   information, personal information about individual users and
3498   organizations, and proprietary information belonging to users and
3499   content providers. A compromised proxy, or a proxy implemented or
3500   configured without regard to security and privacy considerations,
3501   might be used in the commission of a wide range of potential attacks.
3504   Proxy operators should protect the systems on which proxies run as
3505   they would protect any system that contains or transports sensitive
3506   information. In particular, log information gathered at proxies often
3507   contains highly sensitive personal information, and/or information
3508   about organizations. Log information should be carefully guarded, and
3509   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3512   Proxy implementors should consider the privacy and security
3513   implications of their design and coding decisions, and of the
3514   configuration options they provide to proxy operators (especially the
3515   default configuration).
3518   Users of a proxy need to be aware that they are no trustworthier than
3519   the people who run the proxy; HTTP itself cannot solve this problem.
3522   The judicious use of cryptography, when appropriate, may suffice to
3523   protect against a broad range of security and privacy attacks. Such
3524   cryptography is beyond the scope of the HTTP/1.1 specification.
3528<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3530   They exist. They are hard to defend against. Research continues.
3531   Beware.
3536<section title="Acknowledgments" anchor="ack">
3538   HTTP has evolved considerably over the years. It has
3539   benefited from a large and active developer community--the many
3540   people who have participated on the www-talk mailing list--and it is
3541   that community which has been most responsible for the success of
3542   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3543   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3544   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3545   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3546   VanHeyningen deserve special recognition for their efforts in
3547   defining early aspects of the protocol.
3550   This document has benefited greatly from the comments of all those
3551   participating in the HTTP-WG. In addition to those already mentioned,
3552   the following individuals have contributed to this specification:
3555   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3556   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3557   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3558   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3559   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3560   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3561   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3562   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3563   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3564   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3565   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3566   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3567   Josh Cohen.
3570   Thanks to the "cave men" of Palo Alto. You know who you are.
3573   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3574   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3575   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3576   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3577   Larry Masinter for their help. And thanks go particularly to Jeff
3578   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3581   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3582   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3583   discovery of many of the problems that this document attempts to
3584   rectify.
3587   This specification makes heavy use of the augmented BNF and generic
3588   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3589   reuses many of the definitions provided by Nathaniel Borenstein and
3590   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3591   specification will help reduce past confusion over the relationship
3592   between HTTP and Internet mail message formats.
3599<references title="Normative References">
3601<reference anchor="ISO-8859-1">
3602  <front>
3603    <title>
3604     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3605    </title>
3606    <author>
3607      <organization>International Organization for Standardization</organization>
3608    </author>
3609    <date year="1998"/>
3610  </front>
3611  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3614<reference anchor="Part2">
3615  <front>
3616    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3617    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3618      <organization abbrev="Day Software">Day Software</organization>
3619      <address><email></email></address>
3620    </author>
3621    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3622      <organization>One Laptop per Child</organization>
3623      <address><email></email></address>
3624    </author>
3625    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3626      <organization abbrev="HP">Hewlett-Packard Company</organization>
3627      <address><email></email></address>
3628    </author>
3629    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3630      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3631      <address><email></email></address>
3632    </author>
3633    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3634      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3635      <address><email></email></address>
3636    </author>
3637    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3638      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3639      <address><email></email></address>
3640    </author>
3641    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3642      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3643      <address><email></email></address>
3644    </author>
3645    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3646      <organization abbrev="W3C">World Wide Web Consortium</organization>
3647      <address><email></email></address>
3648    </author>
3649    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3650      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3651      <address><email></email></address>
3652    </author>
3653    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3654  </front>
3655  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3656  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3659<reference anchor="Part3">
3660  <front>
3661    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3662    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3663      <organization abbrev="Day Software">Day Software</organization>
3664      <address><email></email></address>
3665    </author>
3666    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3667      <organization>One Laptop per Child</organization>
3668      <address><email></email></address>
3669    </author>
3670    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3671      <organization abbrev="HP">Hewlett-Packard Company</organization>
3672      <address><email></email></address>
3673    </author>
3674    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3675      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3676      <address><email></email></address>
3677    </author>
3678    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3679      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3680      <address><email></email></address>
3681    </author>
3682    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3683      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3684      <address><email></email></address>
3685    </author>
3686    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3687      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3688      <address><email></email></address>
3689    </author>
3690    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3691      <organization abbrev="W3C">World Wide Web Consortium</organization>
3692      <address><email></email></address>
3693    </author>
3694    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3695      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3696      <address><email></email></address>
3697    </author>
3698    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3699  </front>
3700  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3701  <x:source href="p3-payload.xml" basename="p3-payload"/>
3704<reference anchor="Part5">
3705  <front>
3706    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3707    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3708      <organization abbrev="Day Software">Day Software</organization>
3709      <address><email></email></address>
3710    </author>
3711    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3712      <organization>One Laptop per Child</organization>
3713      <address><email></email></address>
3714    </author>
3715    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3716      <organization abbrev="HP">Hewlett-Packard Company</organization>
3717      <address><email></email></address>
3718    </author>
3719    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3720      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3721      <address><email></email></address>
3722    </author>
3723    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3724      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3725      <address><email></email></address>
3726    </author>
3727    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3728      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3729      <address><email></email></address>
3730    </author>
3731    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3732      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3733      <address><email></email></address>
3734    </author>
3735    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3736      <organization abbrev="W3C">World Wide Web Consortium</organization>
3737      <address><email></email></address>
3738    </author>
3739    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3740      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3741      <address><email></email></address>
3742    </author>
3743    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3744  </front>
3745  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3746  <x:source href="p5-range.xml" basename="p5-range"/>
3749<reference anchor="Part6">
3750  <front>
3751    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3752    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3753      <organization abbrev="Day Software">Day Software</organization>
3754      <address><email></email></address>
3755    </author>
3756    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3757      <organization>One Laptop per Child</organization>
3758      <address><email></email></address>
3759    </author>
3760    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3761      <organization abbrev="HP">Hewlett-Packard Company</organization>
3762      <address><email></email></address>
3763    </author>
3764    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3765      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3766      <address><email></email></address>
3767    </author>
3768    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3769      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3770      <address><email></email></address>
3771    </author>
3772    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3773      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3774      <address><email></email></address>
3775    </author>
3776    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3777      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3778      <address><email></email></address>
3779    </author>
3780    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3781      <organization abbrev="W3C">World Wide Web Consortium</organization>
3782      <address><email></email></address>
3783    </author>
3784    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3785      <organization />
3786      <address><email></email></address>
3787    </author>
3788    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3789      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3790      <address><email></email></address>
3791    </author>
3792    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3793  </front>
3794  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3795  <x:source href="p6-cache.xml" basename="p6-cache"/>
3798<reference anchor="RFC5234">
3799  <front>
3800    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3801    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3802      <organization>Brandenburg InternetWorking</organization>
3803      <address>
3804      <postal>
3805      <street>675 Spruce Dr.</street>
3806      <city>Sunnyvale</city>
3807      <region>CA</region>
3808      <code>94086</code>
3809      <country>US</country></postal>
3810      <phone>+1.408.246.8253</phone>
3811      <email></email></address> 
3812    </author>
3813    <author initials="P." surname="Overell" fullname="Paul Overell">
3814      <organization>THUS plc.</organization>
3815      <address>
3816      <postal>
3817      <street>1/2 Berkeley Square</street>
3818      <street>99 Berkely Street</street>
3819      <city>Glasgow</city>
3820      <code>G3 7HR</code>
3821      <country>UK</country></postal>
3822      <email></email></address>
3823    </author>
3824    <date month="January" year="2008"/>
3825  </front>
3826  <seriesInfo name="STD" value="68"/>
3827  <seriesInfo name="RFC" value="5234"/>
3830<reference anchor="RFC2119">
3831  <front>
3832    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3833    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3834      <organization>Harvard University</organization>
3835      <address><email></email></address>
3836    </author>
3837    <date month="March" year="1997"/>
3838  </front>
3839  <seriesInfo name="BCP" value="14"/>
3840  <seriesInfo name="RFC" value="2119"/>
3843<reference anchor="RFC3986">
3844 <front>
3845  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3846  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3847    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3848    <address>
3849       <email></email>
3850       <uri></uri>
3851    </address>
3852  </author>
3853  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3854    <organization abbrev="Day Software">Day Software</organization>
3855    <address>
3856      <email></email>
3857      <uri></uri>
3858    </address>
3859  </author>
3860  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3861    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3862    <address>
3863      <email></email>
3864      <uri></uri>
3865    </address>
3866  </author>
3867  <date month='January' year='2005'></date>
3868 </front>
3869 <seriesInfo name="RFC" value="3986"/>
3870 <seriesInfo name="STD" value="66"/>
3873<reference anchor="USASCII">
3874  <front>
3875    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3876    <author>
3877      <organization>American National Standards Institute</organization>
3878    </author>
3879    <date year="1986"/>
3880  </front>
3881  <seriesInfo name="ANSI" value="X3.4"/>
3884<reference anchor="RFC1950">
3885  <front>
3886    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3887    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3888      <organization>Aladdin Enterprises</organization>
3889      <address><email></email></address>
3890    </author>
3891    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3892      <organization/>
3893    </author>
3894    <date month="May" year="1996"/>
3895  </front>
3896  <seriesInfo name="RFC" value="1950"/>
3897  <annotation>
3898    RFC 1950 is an Informational RFC, thus it may be less stable than
3899    this specification. On the other hand, this downward reference was
3900    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3901    therefore it is unlikely to cause problems in practice. See also
3902    <xref target="BCP97"/>.
3903  </annotation>
3906<reference anchor="RFC1951">
3907  <front>
3908    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3909    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3910      <organization>Aladdin Enterprises</organization>
3911      <address><email></email></address>
3912    </author>
3913    <date month="May" year="1996"/>
3914  </front>
3915  <seriesInfo name="RFC" value="1951"/>
3916  <annotation>
3917    RFC 1951 is an Informational RFC, thus it may be less stable than
3918    this specification. On the other hand, this downward reference was
3919    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3920    therefore it is unlikely to cause problems in practice. See also
3921    <xref target="BCP97"/>.
3922  </annotation>
3925<reference anchor="RFC1952">
3926  <front>
3927    <title>GZIP file format specification version 4.3</title>
3928    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3929      <organization>Aladdin Enterprises</organization>
3930      <address><email></email></address>
3931    </author>
3932    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3933      <organization/>
3934      <address><email></email></address>
3935    </author>
3936    <author initials="M." surname="Adler" fullname="Mark Adler">
3937      <organization/>
3938      <address><email></email></address>
3939    </author>
3940    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3941      <organization/>
3942      <address><email></email></address>
3943    </author>
3944    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3945      <organization/>
3946      <address><email></email></address>
3947    </author>
3948    <date month="May" year="1996"/>
3949  </front>
3950  <seriesInfo name="RFC" value="1952"/>
3951  <annotation>
3952    RFC 1952 is an Informational RFC, thus it may be less stable than
3953    this specification. On the other hand, this downward reference was
3954    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3955    therefore it is unlikely to cause problems in practice. See also
3956    <xref target="BCP97"/>.
3957  </annotation>
3962<references title="Informative References">
3964<reference anchor="Nie1997" target="">
3965  <front>
3966    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3967    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3968      <organization/>
3969    </author>
3970    <author initials="J." surname="Gettys" fullname="J. Gettys">
3971      <organization/>
3972    </author>
3973    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3974      <organization/>
3975    </author>
3976    <author initials="H." surname="Lie" fullname="H. Lie">
3977      <organization/>
3978    </author>
3979    <author initials="C." surname="Lilley" fullname="C. Lilley">
3980      <organization/>
3981    </author>
3982    <date year="1997" month="September"/>
3983  </front>
3984  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3987<reference anchor="Pad1995" target="">
3988  <front>
3989    <title>Improving HTTP Latency</title>
3990    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3991      <organization/>
3992    </author>
3993    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3994      <organization/>
3995    </author>
3996    <date year="1995" month="December"/>
3997  </front>
3998  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4001<reference anchor="RFC1123">
4002  <front>
4003    <title>Requirements for Internet Hosts - Application and Support</title>
4004    <author initials="R." surname="Braden" fullname="Robert Braden">
4005      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4006      <address><email>Braden@ISI.EDU</email></address>
4007    </author>
4008    <date month="October" year="1989"/>
4009  </front>
4010  <seriesInfo name="STD" value="3"/>
4011  <seriesInfo name="RFC" value="1123"/>
4014<reference anchor="RFC1305">
4015  <front>
4016    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4017    <author initials="D." surname="Mills" fullname="David L. Mills">
4018      <organization>University of Delaware, Electrical Engineering Department</organization>
4019      <address><email></email></address>
4020    </author>
4021    <date month="March" year="1992"/>
4022  </front>
4023  <seriesInfo name="RFC" value="1305"/>
4026<reference anchor="RFC1900">
4027  <front>
4028    <title>Renumbering Needs Work</title>
4029    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4030      <organization>CERN, Computing and Networks Division</organization>
4031      <address><email></email></address>
4032    </author>
4033    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4034      <organization>cisco Systems</organization>
4035      <address><email></email></address>
4036    </author>
4037    <date month="February" year="1996"/>
4038  </front>
4039  <seriesInfo name="RFC" value="1900"/>
4042<reference anchor="RFC1945">
4043  <front>
4044    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4045    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4046      <organization>MIT, Laboratory for Computer Science</organization>
4047      <address><email></email></address>
4048    </author>
4049    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4050      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4051      <address><email></email></address>
4052    </author>
4053    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4054      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4055      <address><email></email></address>
4056    </author>
4057    <date month="May" year="1996"/>
4058  </front>
4059  <seriesInfo name="RFC" value="1945"/>
4062<reference anchor="RFC2045">
4063  <front>
4064    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4065    <author initials="N." surname="Freed" fullname="Ned Freed">
4066      <organization>Innosoft International, Inc.</organization>
4067      <address><email></email></address>
4068    </author>
4069    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4070      <organization>First Virtual Holdings</organization>
4071      <address><email></email></address>
4072    </author>
4073    <date month="November" year="1996"/>
4074  </front>
4075  <seriesInfo name="RFC" value="2045"/>
4078<reference anchor="RFC2047">
4079  <front>
4080    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4081    <author initials="K." surname="Moore" fullname="Keith Moore">
4082      <organization>University of Tennessee</organization>
4083      <address><email></email></address>
4084    </author>
4085    <date month="November" year="1996"/>
4086  </front>
4087  <seriesInfo name="RFC" value="2047"/>
4090<reference anchor="RFC2068">
4091  <front>
4092    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4093    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4094      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4095      <address><email></email></address>
4096    </author>
4097    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4098      <organization>MIT Laboratory for Computer Science</organization>
4099      <address><email></email></address>
4100    </author>
4101    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4102      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4103      <address><email></email></address>
4104    </author>
4105    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4106      <organization>MIT Laboratory for Computer Science</organization>
4107      <address><email></email></address>
4108    </author>
4109    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4110      <organization>MIT Laboratory for Computer Science</organization>
4111      <address><email></email></address>
4112    </author>
4113    <date month="January" year="1997"/>
4114  </front>
4115  <seriesInfo name="RFC" value="2068"/>
4118<reference anchor='RFC2109'>
4119  <front>
4120    <title>HTTP State Management Mechanism</title>
4121    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4122      <organization>Bell Laboratories, Lucent Technologies</organization>
4123      <address><email></email></address>
4124    </author>
4125    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4126      <organization>Netscape Communications Corp.</organization>
4127      <address><email></email></address>
4128    </author>
4129    <date year='1997' month='February' />
4130  </front>
4131  <seriesInfo name='RFC' value='2109' />
4134<reference anchor="RFC2145">
4135  <front>
4136    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4137    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4138      <organization>Western Research Laboratory</organization>
4139      <address><email></email></address>
4140    </author>
4141    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4142      <organization>Department of Information and Computer Science</organization>
4143      <address><email></email></address>
4144    </author>
4145    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4146      <organization>MIT Laboratory for Computer Science</organization>
4147      <address><email></email></address>
4148    </author>
4149    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4150      <organization>W3 Consortium</organization>
4151      <address><email></email></address>
4152    </author>
4153    <date month="May" year="1997"/>
4154  </front>
4155  <seriesInfo name="RFC" value="2145"/>
4158<reference anchor="RFC2616">
4159  <front>
4160    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4161    <author initials="R." surname="Fielding" fullname="R. Fielding">
4162      <organization>University of California, Irvine</organization>
4163      <address><email></email></address>
4164    </author>
4165    <author initials="J." surname="Gettys" fullname="J. Gettys">
4166      <organization>W3C</organization>
4167      <address><email></email></address>
4168    </author>
4169    <author initials="J." surname="Mogul" fullname="J. Mogul">
4170      <organization>Compaq Computer Corporation</organization>
4171      <address><email></email></address>
4172    </author>
4173    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4174      <organization>MIT Laboratory for Computer Science</organization>
4175      <address><email></email></address>
4176    </author>
4177    <author initials="L." surname="Masinter" fullname="L. Masinter">
4178      <organization>Xerox Corporation</organization>
4179      <address><email></email></address>
4180    </author>
4181    <author initials="P." surname="Leach" fullname="P. Leach">
4182      <organization>Microsoft Corporation</organization>
4183      <address><email></email></address>
4184    </author>
4185    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4186      <organization>W3C</organization>
4187      <address><email></email></address>
4188    </author>
4189    <date month="June" year="1999"/>
4190  </front>
4191  <seriesInfo name="RFC" value="2616"/>
4194<reference anchor='RFC2817'>
4195  <front>
4196    <title>Upgrading to TLS Within HTTP/1.1</title>
4197    <author initials='R.' surname='Khare' fullname='R. Khare'>
4198      <organization>4K Associates / UC Irvine</organization>
4199      <address><email></email></address>
4200    </author>
4201    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4202      <organization>Agranat Systems, Inc.</organization>
4203      <address><email></email></address>
4204    </author>
4205    <date year='2000' month='May' />
4206  </front>
4207  <seriesInfo name='RFC' value='2817' />
4210<reference anchor='RFC2818'>
4211  <front>
4212    <title>HTTP Over TLS</title>
4213    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4214      <organization>RTFM, Inc.</organization>
4215      <address><email></email></address>
4216    </author>
4217    <date year='2000' month='May' />
4218  </front>
4219  <seriesInfo name='RFC' value='2818' />
4222<reference anchor='RFC2965'>
4223  <front>
4224    <title>HTTP State Management Mechanism</title>
4225    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4226      <organization>Bell Laboratories, Lucent Technologies</organization>
4227      <address><email></email></address>
4228    </author>
4229    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4230      <organization>, Inc.</organization>
4231      <address><email></email></address>
4232    </author>
4233    <date year='2000' month='October' />
4234  </front>
4235  <seriesInfo name='RFC' value='2965' />
4238<reference anchor='RFC3864'>
4239  <front>
4240    <title>Registration Procedures for Message Header Fields</title>
4241    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4242      <organization>Nine by Nine</organization>
4243      <address><email></email></address>
4244    </author>
4245    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4246      <organization>BEA Systems</organization>
4247      <address><email></email></address>
4248    </author>
4249    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4250      <organization>HP Labs</organization>
4251      <address><email></email></address>
4252    </author>
4253    <date year='2004' month='September' />
4254  </front>
4255  <seriesInfo name='BCP' value='90' />
4256  <seriesInfo name='RFC' value='3864' />
4259<reference anchor="RFC4288">
4260  <front>
4261    <title>Media Type Specifications and Registration Procedures</title>
4262    <author initials="N." surname="Freed" fullname="N. Freed">
4263      <organization>Sun Microsystems</organization>
4264      <address>
4265        <email></email>
4266      </address>
4267    </author>
4268    <author initials="J." surname="Klensin" fullname="J. Klensin">
4269      <organization/>
4270      <address>
4271        <email></email>
4272      </address>
4273    </author>
4274    <date year="2005" month="December"/>
4275  </front>
4276  <seriesInfo name="BCP" value="13"/>
4277  <seriesInfo name="RFC" value="4288"/>
4280<reference anchor='RFC4395'>
4281  <front>
4282    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4283    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4284      <organization>AT&amp;T Laboratories</organization>
4285      <address>
4286        <email></email>
4287      </address>
4288    </author>
4289    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4290      <organization>Qualcomm, Inc.</organization>
4291      <address>
4292        <email></email>
4293      </address>
4294    </author>
4295    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4296      <organization>Adobe Systems</organization>
4297      <address>
4298        <email></email>
4299      </address>
4300    </author>
4301    <date year='2006' month='February' />
4302  </front>
4303  <seriesInfo name='BCP' value='115' />
4304  <seriesInfo name='RFC' value='4395' />
4307<reference anchor='RFC5226'>
4308  <front>
4309    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4310    <author initials='T.' surname='Narten' fullname='T. Narten'>
4311      <organization>IBM</organization>
4312      <address><email></email></address>
4313    </author>
4314    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4315      <organization>Google</organization>
4316      <address><email></email></address>
4317    </author>
4318    <date year='2008' month='May' />
4319  </front>
4320  <seriesInfo name='BCP' value='26' />
4321  <seriesInfo name='RFC' value='5226' />
4324<reference anchor="RFC5322">
4325  <front>
4326    <title>Internet Message Format</title>
4327    <author initials="P." surname="Resnick" fullname="P. Resnick">
4328      <organization>Qualcomm Incorporated</organization>
4329    </author>
4330    <date year="2008" month="October"/>
4331  </front>
4332  <seriesInfo name="RFC" value="5322"/>
4335<reference anchor='BCP97'>
4336  <front>
4337    <title>Handling Normative References to Standards-Track Documents</title>
4338    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4339      <organization />
4340      <address>
4341        <email></email>
4342      </address>
4343    </author>
4344    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4345      <organization>MIT</organization>
4346      <address>
4347        <email></email>
4348      </address>
4349    </author>
4350    <date year='2007' month='June' />
4351  </front>
4352  <seriesInfo name='BCP' value='97' />
4353  <seriesInfo name='RFC' value='4897' />
4356<reference anchor="Kri2001" target="">
4357  <front>
4358    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4359    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4360      <organization/>
4361    </author>
4362    <date year="2001" month="November"/>
4363  </front>
4364  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4367<reference anchor="Spe" target="">
4368  <front>
4369  <title>Analysis of HTTP Performance Problems</title>
4370  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4371    <organization/>
4372  </author>
4373  <date/>
4374  </front>
4377<reference anchor="Tou1998" target="">
4378  <front>
4379  <title>Analysis of HTTP Performance</title>
4380  <author initials="J." surname="Touch" fullname="Joe Touch">
4381    <organization>USC/Information Sciences Institute</organization>
4382    <address><email></email></address>
4383  </author>
4384  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4385    <organization>USC/Information Sciences Institute</organization>
4386    <address><email></email></address>
4387  </author>
4388  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4389    <organization>USC/Information Sciences Institute</organization>
4390    <address><email></email></address>
4391  </author>
4392  <date year="1998" month="Aug"/>
4393  </front>
4394  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4395  <annotation>(original report dated Aug. 1996)</annotation>
4401<section title="Tolerant Applications" anchor="tolerant.applications">
4403   Although this document specifies the requirements for the generation
4404   of HTTP/1.1 messages, not all applications will be correct in their
4405   implementation. We therefore recommend that operational applications
4406   be tolerant of deviations whenever those deviations can be
4407   interpreted unambiguously.
4410   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4411   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4412   accept any amount of WSP characters between fields, even though
4413   only a single SP is required.
4416   The line terminator for header fields is the sequence CRLF.
4417   However, we recommend that applications, when parsing such headers,
4418   recognize a single LF as a line terminator and ignore the leading CR.
4421   The character set of an entity-body &SHOULD; be labeled as the lowest
4422   common denominator of the character codes used within that body, with
4423   the exception that not labeling the entity is preferred over labeling
4424   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4427   Additional rules for requirements on parsing and encoding of dates
4428   and other potential problems with date encodings include:
4431  <list style="symbols">
4432     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4433        which appears to be more than 50 years in the future is in fact
4434        in the past (this helps solve the "year 2000" problem).</t>
4436     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4437        Expires date as earlier than the proper value, but &MUST-NOT;
4438        internally represent a parsed Expires date as later than the
4439        proper value.</t>
4441     <t>All expiration-related calculations &MUST; be done in GMT. The
4442        local time zone &MUST-NOT; influence the calculation or comparison
4443        of an age or expiration time.</t>
4445     <t>If an HTTP header incorrectly carries a date value with a time
4446        zone other than GMT, it &MUST; be converted into GMT using the
4447        most conservative possible conversion.</t>
4448  </list>
4452<section title="Compatibility with Previous Versions" anchor="compatibility">
4454   HTTP has been in use by the World-Wide Web global information initiative
4455   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4456   was a simple protocol for hypertext data transfer across the Internet
4457   with only a single method and no metadata.
4458   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4459   methods and MIME-like messaging that could include metadata about the data
4460   transferred and modifiers on the request/response semantics. However,
4461   HTTP/1.0 did not sufficiently take into consideration the effects of
4462   hierarchical proxies, caching, the need for persistent connections, or
4463   name-based virtual hosts. The proliferation of incompletely-implemented
4464   applications calling themselves "HTTP/1.0" further necessitated a
4465   protocol version change in order for two communicating applications
4466   to determine each other's true capabilities.
4469   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4470   requirements that enable reliable implementations, adding only
4471   those new features that will either be safely ignored by an HTTP/1.0
4472   recipient or only sent when communicating with a party advertising
4473   compliance with HTTP/1.1.
4476   It is beyond the scope of a protocol specification to mandate
4477   compliance with previous versions. HTTP/1.1 was deliberately
4478   designed, however, to make supporting previous versions easy. It is
4479   worth noting that, at the time of composing this specification, we would
4480   expect general-purpose HTTP/1.1 servers to:
4481  <list style="symbols">
4482     <t>understand any valid request in the format of HTTP/1.0 and
4483        1.1;</t>
4485     <t>respond appropriately with a message in the same major version
4486        used by the client.</t>
4487  </list>
4490   And we would expect HTTP/1.1 clients to:
4491  <list style="symbols">
4492     <t>understand any valid response in the format of HTTP/1.0 or
4493        1.1.</t>
4494  </list>
4497   For most implementations of HTTP/1.0, each connection is established
4498   by the client prior to the request and closed by the server after
4499   sending the response. Some implementations implement the Keep-Alive
4500   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4503<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4505   This section summarizes major differences between versions HTTP/1.0
4506   and HTTP/1.1.
4509<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4511   The requirements that clients and servers support the Host request-header,
4512   report an error if the Host request-header (<xref target=""/>) is
4513   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4514   are among the most important changes defined by this
4515   specification.
4518   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4519   addresses and servers; there was no other established mechanism for
4520   distinguishing the intended server of a request than the IP address
4521   to which that request was directed. The changes outlined above will
4522   allow the Internet, once older HTTP clients are no longer common, to
4523   support multiple Web sites from a single IP address, greatly
4524   simplifying large operational Web servers, where allocation of many
4525   IP addresses to a single host has created serious problems. The
4526   Internet will also be able to recover the IP addresses that have been
4527   allocated for the sole purpose of allowing special-purpose domain
4528   names to be used in root-level HTTP URLs. Given the rate of growth of
4529   the Web, and the number of servers already deployed, it is extremely
4530   important that all implementations of HTTP (including updates to
4531   existing HTTP/1.0 applications) correctly implement these
4532   requirements:
4533  <list style="symbols">
4534     <t>Both clients and servers &MUST; support the Host request-header.</t>
4536     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4538     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4539        request does not include a Host request-header.</t>
4541     <t>Servers &MUST; accept absolute URIs.</t>
4542  </list>
4547<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4549   Some clients and servers might wish to be compatible with some
4550   previous implementations of persistent connections in HTTP/1.0
4551   clients and servers. Persistent connections in HTTP/1.0 are
4552   explicitly negotiated as they are not the default behavior. HTTP/1.0
4553   experimental implementations of persistent connections are faulty,
4554   and the new facilities in HTTP/1.1 are designed to rectify these
4555   problems. The problem was that some existing 1.0 clients may be
4556   sending Keep-Alive to a proxy server that doesn't understand
4557   Connection, which would then erroneously forward it to the next
4558   inbound server, which would establish the Keep-Alive connection and
4559   result in a hung HTTP/1.0 proxy waiting for the close on the
4560   response. The result is that HTTP/1.0 clients must be prevented from
4561   using Keep-Alive when talking to proxies.
4564   However, talking to proxies is the most important use of persistent
4565   connections, so that prohibition is clearly unacceptable. Therefore,
4566   we need some other mechanism for indicating a persistent connection
4567   is desired, which is safe to use even when talking to an old proxy
4568   that ignores Connection. Persistent connections are the default for
4569   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4570   declaring non-persistence. See <xref target="header.connection"/>.
4573   The original HTTP/1.0 form of persistent connections (the Connection:
4574   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4578<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4580   This specification has been carefully audited to correct and
4581   disambiguate key word usage; RFC 2068 had many problems in respect to
4582   the conventions laid out in <xref target="RFC2119"/>.
4585   Transfer-coding and message lengths all interact in ways that
4586   required fixing exactly when chunked encoding is used (to allow for
4587   transfer encoding that may not be self delimiting); it was important
4588   to straighten out exactly how message lengths are computed. (Sections
4589   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4590   <xref target="header.content-length" format="counter"/>,
4591   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4594   The use and interpretation of HTTP version numbers has been clarified
4595   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4596   version they support to deal with problems discovered in HTTP/1.0
4597   implementations (<xref target="http.version"/>)
4600   Quality Values of zero should indicate that "I don't want something"
4601   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4604   Transfer-coding had significant problems, particularly with
4605   interactions with chunked encoding. The solution is that transfer-codings
4606   become as full fledged as content-codings. This involves
4607   adding an IANA registry for transfer-codings (separate from content
4608   codings), a new header field (TE) and enabling trailer headers in the
4609   future. Transfer encoding is a major performance benefit, so it was
4610   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4611   interoperability problem that could have occurred due to interactions
4612   between authentication trailers, chunked encoding and HTTP/1.0
4613   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.encoding" format="counter"/>,
4614   and <xref target="header.te" format="counter"/>)
4618<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4620  Empty list elements in list productions have been deprecated.
4621  (<xref target="notation.abnf"/>)
4624  Rules about implicit linear whitespace between certain grammar productions
4625  have been removed; now it's only allowed when specifically pointed out
4626  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4627  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4628  Non-ASCII content in header fields and reason phrase has been obsoleted and
4629  made opaque (the TEXT rule was removed)
4630  (<xref target="basic.rules"/>)
4633  Clarify that HTTP-Version is case sensitive.
4634  (<xref target="http.version"/>)
4637  Remove reference to non-existant identity transfer-coding value tokens.
4638  (Sections <xref format="counter" target="transfer.codings"/> and
4639  <xref format="counter" target="message.length"/>)
4642  Clarification that the chunk length does not include
4643  the count of the octets in the chunk header and trailer.
4644  (<xref target="chunked.encoding"/>)
4647  Require that invalid whitespace around field-names be rejected.
4648  (<xref target="header.fields"/>)
4651  Update use of abs_path production from RFC1808 to the path-absolute + query
4652  components of RFC3986.
4653  (<xref target="request-target"/>)
4656  Clarify exactly when close connection options must be sent.
4657  (<xref target="header.connection"/>)
4662<?BEGININC p1-messaging.abnf-appendix ?>
4663<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4665<artwork type="abnf" name="p1-messaging.parsed-abnf">
4666<x:ref>BWS</x:ref> = OWS
4668<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4669<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4670<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4671<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4672 connection-token ] )
4673<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4674<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4676<x:ref>Date</x:ref> = "Date:" OWS Date-v
4677<x:ref>Date-v</x:ref> = HTTP-date
4679<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4681<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4682<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4683<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4684<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4685 ]
4686<x:ref>Host</x:ref> = "Host:" OWS Host-v
4687<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4689<x:ref>Method</x:ref> = token
4691<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4693<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4695<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4696<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4697<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4698 entity-header ) CRLF ) CRLF [ message-body ]
4699<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4700<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4701 entity-header ) CRLF ) CRLF [ message-body ]
4703<x:ref>Status-Code</x:ref> = 3DIGIT
4704<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4706<x:ref>TE</x:ref> = "TE:" OWS TE-v
4707<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4708<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4709<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4710<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4711<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4712 transfer-coding ] )
4714<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4715<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4716<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4717<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4719<x:ref>Via</x:ref> = "Via:" OWS Via-v
4720<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4721 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4722 ] )
4724<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4726<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4727<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4728<x:ref>attribute</x:ref> = token
4729<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4731<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4732<x:ref>chunk-data</x:ref> = 1*OCTET
4733<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4734<x:ref>chunk-ext-name</x:ref> = token
4735<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4736<x:ref>chunk-size</x:ref> = 1*HEXDIG
4737<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4738<x:ref>connection-token</x:ref> = token
4739<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4740 / %x2A-5B ; '*'-'['
4741 / %x5D-7E ; ']'-'~'
4742 / obs-text
4744<x:ref>date1</x:ref> = day SP month SP year
4745<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4746<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4747<x:ref>day</x:ref> = 2DIGIT
4748<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4749 / %x54.75.65 ; Tue
4750 / %x57.65.64 ; Wed
4751 / %x54.68.75 ; Thu
4752 / %x46.72.69 ; Fri
4753 / %x53.61.74 ; Sat
4754 / %x53.75.6E ; Sun
4755<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4756 / %x54. ; Tuesday
4757 / %x57.65.64.6E. ; Wednesday
4758 / %x54. ; Thursday
4759 / %x46. ; Friday
4760 / %x53. ; Saturday
4761 / %x53.75.6E.64.61.79 ; Sunday
4763<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4764<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4766<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4767<x:ref>field-name</x:ref> = token
4768<x:ref>field-value</x:ref> = *( field-content / OWS )
4770<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4771 / Transfer-Encoding / Upgrade / Via / Warning
4773<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4774<x:ref>hour</x:ref> = 2DIGIT
4775<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4776<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4778<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4780<x:ref>message-body</x:ref> = entity-body /
4781 &lt;entity-body encoded as per Transfer-Encoding&gt;
4782<x:ref>minute</x:ref> = 2DIGIT
4783<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4784 / %x46.65.62 ; Feb
4785 / %x4D.61.72 ; Mar
4786 / %x41.70.72 ; Apr
4787 / %x4D.61.79 ; May
4788 / %x4A.75.6E ; Jun
4789 / %x4A.75.6C ; Jul
4790 / %x41.75.67 ; Aug
4791 / %x53.65.70 ; Sep
4792 / %x4F.63.74 ; Oct
4793 / %x4E.6F.76 ; Nov
4794 / %x44.65.63 ; Dec
4796<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4797<x:ref>obs-fold</x:ref> = CRLF
4798<x:ref>obs-text</x:ref> = %x80-FF
4800<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4801<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4802<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4803<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4804<x:ref>product</x:ref> = token [ "/" product-version ]
4805<x:ref>product-version</x:ref> = token
4806<x:ref>protocol-name</x:ref> = token
4807<x:ref>protocol-version</x:ref> = token
4808<x:ref>pseudonym</x:ref> = token
4810<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4811 / %x5D-7E ; ']'-'~'
4812 / obs-text
4813<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4814<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4815<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4816<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4818<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4819<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4820<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4821<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4822<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4823 / authority
4824<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4825<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4826<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4828<x:ref>second</x:ref> = 2DIGIT
4829<x:ref>start-line</x:ref> = Request-Line / Status-Line
4831<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4832<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4833 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4834<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4835<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4836<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4837<x:ref>token</x:ref> = 1*tchar
4838<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4839<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
4840 transfer-extension
4841<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4842<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4844<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4846<x:ref>value</x:ref> = token / quoted-string
4848<x:ref>year</x:ref> = 4DIGIT
4851<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4852; Chunked-Body defined but not used
4853; Content-Length defined but not used
4854; HTTP-message defined but not used
4855; Host defined but not used
4856; Request defined but not used
4857; Response defined but not used
4858; TE defined but not used
4859; URI defined but not used
4860; URI-reference defined but not used
4861; http-URI defined but not used
4862; https-URI defined but not used
4863; partial-URI defined but not used
4865<?ENDINC p1-messaging.abnf-appendix ?>
4867<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4869<section title="Since RFC2616">
4871  Extracted relevant partitions from <xref target="RFC2616"/>.
4875<section title="Since draft-ietf-httpbis-p1-messaging-00">
4877  Closed issues:
4878  <list style="symbols">
4879    <t>
4880      <eref target=""/>:
4881      "HTTP Version should be case sensitive"
4882      (<eref target=""/>)
4883    </t>
4884    <t>
4885      <eref target=""/>:
4886      "'unsafe' characters"
4887      (<eref target=""/>)
4888    </t>
4889    <t>
4890      <eref target=""/>:
4891      "Chunk Size Definition"
4892      (<eref target=""/>)
4893    </t>
4894    <t>
4895      <eref target=""/>:
4896      "Message Length"
4897      (<eref target=""/>)
4898    </t>
4899    <t>
4900      <eref target=""/>:
4901      "Media Type Registrations"
4902      (<eref target=""/>)
4903    </t>
4904    <t>
4905      <eref target=""/>:
4906      "URI includes query"
4907      (<eref target=""/>)
4908    </t>
4909    <t>
4910      <eref target=""/>:
4911      "No close on 1xx responses"
4912      (<eref target=""/>)
4913    </t>
4914    <t>
4915      <eref target=""/>:
4916      "Remove 'identity' token references"
4917      (<eref target=""/>)
4918    </t>
4919    <t>
4920      <eref target=""/>:
4921      "Import query BNF"
4922    </t>
4923    <t>
4924      <eref target=""/>:
4925      "qdtext BNF"
4926    </t>
4927    <t>
4928      <eref target=""/>:
4929      "Normative and Informative references"
4930    </t>
4931    <t>
4932      <eref target=""/>:
4933      "RFC2606 Compliance"
4934    </t>
4935    <t>
4936      <eref target=""/>:
4937      "RFC977 reference"
4938    </t>
4939    <t>
4940      <eref target=""/>:
4941      "RFC1700 references"
4942    </t>
4943    <t>
4944      <eref target=""/>:
4945      "inconsistency in date format explanation"
4946    </t>
4947    <t>
4948      <eref target=""/>:
4949      "Date reference typo"
4950    </t>
4951    <t>
4952      <eref target=""/>:
4953      "Informative references"
4954    </t>
4955    <t>
4956      <eref target=""/>:
4957      "ISO-8859-1 Reference"
4958    </t>
4959    <t>
4960      <eref target=""/>:
4961      "Normative up-to-date references"
4962    </t>
4963  </list>
4966  Other changes:
4967  <list style="symbols">
4968    <t>
4969      Update media type registrations to use RFC4288 template.
4970    </t>
4971    <t>
4972      Use names of RFC4234 core rules DQUOTE and WSP,
4973      fix broken ABNF for chunk-data
4974      (work in progress on <eref target=""/>)
4975    </t>
4976  </list>
4980<section title="Since draft-ietf-httpbis-p1-messaging-01">
4982  Closed issues:
4983  <list style="symbols">
4984    <t>
4985      <eref target=""/>:
4986      "Bodies on GET (and other) requests"
4987    </t>
4988    <t>
4989      <eref target=""/>:
4990      "Updating to RFC4288"
4991    </t>
4992    <t>
4993      <eref target=""/>:
4994      "Status Code and Reason Phrase"
4995    </t>
4996    <t>
4997      <eref target=""/>:
4998      "rel_path not used"
4999    </t>
5000  </list>
5003  Ongoing work on ABNF conversion (<eref target=""/>):
5004  <list style="symbols">
5005    <t>
5006      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5007      "trailer-part").
5008    </t>
5009    <t>
5010      Avoid underscore character in rule names ("http_URL" ->
5011      "http-URL", "abs_path" -> "path-absolute").
5012    </t>
5013    <t>
5014      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5015      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5016      have to be updated when switching over to RFC3986.
5017    </t>
5018    <t>
5019      Synchronize core rules with RFC5234.
5020    </t>
5021    <t>
5022      Get rid of prose rules that span multiple lines.
5023    </t>
5024    <t>
5025      Get rid of unused rules LOALPHA and UPALPHA.
5026    </t>
5027    <t>
5028      Move "Product Tokens" section (back) into Part 1, as "token" is used
5029      in the definition of the Upgrade header.
5030    </t>
5031    <t>
5032      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5033    </t>
5034    <t>
5035      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5036    </t>
5037  </list>
5041<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5043  Closed issues:
5044  <list style="symbols">
5045    <t>
5046      <eref target=""/>:
5047      "HTTP-date vs. rfc1123-date"
5048    </t>
5049    <t>
5050      <eref target=""/>:
5051      "WS in quoted-pair"
5052    </t>
5053  </list>
5056  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5057  <list style="symbols">
5058    <t>
5059      Reference RFC 3984, and update header registrations for headers defined
5060      in this document.
5061    </t>
5062  </list>
5065  Ongoing work on ABNF conversion (<eref target=""/>):
5066  <list style="symbols">
5067    <t>
5068      Replace string literals when the string really is case-sensitive (HTTP-Version).
5069    </t>
5070  </list>
5074<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5076  Closed issues:
5077  <list style="symbols">
5078    <t>
5079      <eref target=""/>:
5080      "Connection closing"
5081    </t>
5082    <t>
5083      <eref target=""/>:
5084      "Move registrations and registry information to IANA Considerations"
5085    </t>
5086    <t>
5087      <eref target=""/>:
5088      "need new URL for PAD1995 reference"
5089    </t>
5090    <t>
5091      <eref target=""/>:
5092      "IANA Considerations: update HTTP URI scheme registration"
5093    </t>
5094    <t>
5095      <eref target=""/>:
5096      "Cite HTTPS URI scheme definition"
5097    </t>
5098    <t>
5099      <eref target=""/>:
5100      "List-type headers vs Set-Cookie"
5101    </t>
5102  </list>
5105  Ongoing work on ABNF conversion (<eref target=""/>):
5106  <list style="symbols">
5107    <t>
5108      Replace string literals when the string really is case-sensitive (HTTP-Date).
5109    </t>
5110    <t>
5111      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5112    </t>
5113  </list>
5117<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5119  Closed issues:
5120  <list style="symbols">
5121    <t>
5122      <eref target=""/>:
5123      "Out-of-date reference for URIs"
5124    </t>
5125    <t>
5126      <eref target=""/>:
5127      "RFC 2822 is updated by RFC 5322"
5128    </t>
5129  </list>
5132  Ongoing work on ABNF conversion (<eref target=""/>):
5133  <list style="symbols">
5134    <t>
5135      Use "/" instead of "|" for alternatives.
5136    </t>
5137    <t>
5138      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5139    </t>
5140    <t>
5141      Only reference RFC 5234's core rules.
5142    </t>
5143    <t>
5144      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5145      whitespace ("OWS") and required whitespace ("RWS").
5146    </t>
5147    <t>
5148      Rewrite ABNFs to spell out whitespace rules, factor out
5149      header value format definitions.
5150    </t>
5151  </list>
5155<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5157  Closed issues:
5158  <list style="symbols">
5159    <t>
5160      <eref target=""/>:
5161      "Header LWS"
5162    </t>
5163    <t>
5164      <eref target=""/>:
5165      "Sort 1.3 Terminology"
5166    </t>
5167    <t>
5168      <eref target=""/>:
5169      "RFC2047 encoded words"
5170    </t>
5171    <t>
5172      <eref target=""/>:
5173      "Character Encodings in TEXT"
5174    </t>
5175    <t>
5176      <eref target=""/>:
5177      "Line Folding"
5178    </t>
5179    <t>
5180      <eref target=""/>:
5181      "OPTIONS * and proxies"
5182    </t>
5183    <t>
5184      <eref target=""/>:
5185      "Reason-Phrase BNF"
5186    </t>
5187    <t>
5188      <eref target=""/>:
5189      "Use of TEXT"
5190    </t>
5191    <t>
5192      <eref target=""/>:
5193      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5194    </t>
5195    <t>
5196      <eref target=""/>:
5197      "RFC822 reference left in discussion of date formats"
5198    </t>
5199  </list>
5202  Final work on ABNF conversion (<eref target=""/>):
5203  <list style="symbols">
5204    <t>
5205      Rewrite definition of list rules, deprecate empty list elements.
5206    </t>
5207    <t>
5208      Add appendix containing collected and expanded ABNF.
5209    </t>
5210  </list>
5213  Other changes:
5214  <list style="symbols">
5215    <t>
5216      Rewrite introduction; add mostly new Architecture Section.
5217    </t>
5218    <t>
5219      Move definition of quality values from Part 3 into Part 1;
5220      make TE request header grammar independent of accept-params (defined in Part 3).
5221    </t>
5222  </list>
5226<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5228  Closed issues:
5229  <list style="symbols">
5230    <t>
5231      <eref target=""/>:
5232      "base for numeric protocol elements"
5233    </t>
5234    <t>
5235      <eref target=""/>:
5236      "comment ABNF"
5237    </t>
5238  </list>
5241  Partly resolved issues:
5242  <list style="symbols">
5243    <t>
5244      <eref target=""/>:
5245      "205 Bodies" (took out language that implied that there may be
5246      methods for which a request body MUST NOT be included)
5247    </t>
5248    <t>
5249      <eref target=""/>:
5250      "editorial improvements around HTTP-date"
5251    </t>
5252  </list>
5256<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5258  Closed issues:
5259  <list style="symbols">
5260    <t>
5261      <eref target=""/>:
5262      "Repeating single-value headers"
5263    </t>
5264    <t>
5265      <eref target=""/>:
5266      "IP addresses in URLs"
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "take over HTTP Upgrade Token Registry"
5271    </t>
5272    <t>
5273      <eref target=""/>:
5274      "HTTP/0.9 support"
5275    </t>
5276    <t>
5277      <eref target=""/>:
5278      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5279    </t>
5280    <t>
5281      <eref target=""/>:
5282      "move definitions of gzip/deflate/compress to part 1"
5283    </t>
5284    <t>
5285      <eref target=""/>:
5286      "disallow control characters in quoted-pair"
5287    </t>
5288  </list>
5291  Partly resolved issues:
5292  <list style="symbols">
5293    <t>
5294      <eref target=""/>:
5295      "update IANA requirements wrt Transfer-Coding values" (add the
5296      IANA Considerations subsection)
5297    </t>
5298    <t>
5299      <eref target=""/>:
5300      "disallow control characters in quoted-pair"
5301    </t>
5302  </list>
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