source: draft-ietf-httpbis/latest/p1-messaging.xml @ 785

Last change on this file since 785 was 785, checked in by julian.reschke@…, 12 years ago

Allow URI-reference instead of URI in Location; state that there are currently no defined precedence rules for fragment identifiers (relates to #43 and #185)

  • Property svn:eol-style set to native
File size: 234.4 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2010">
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 entity-length          "<xref target='Part3' x:rel='#entity.length' xmlns:x=''/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization>One Laptop per Child</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.09"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as a generic protocol for translating
253   communication to and from other Internet information systems.
254   HTTP proxies and gateways provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions should be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients may act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the &MUST; or &REQUIRED; level requirements for the protocols it
294   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
295   level and all the &SHOULD; level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the &MUST;
297   level requirements but not all the &SHOULD; level requirements for its
298   protocols is said to be "conditionally compliant."
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342   As a syntactical convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383  Note that empty elements do not contribute to the count of elements present,
384  though.
387  For example, given these ABNF productions:
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
404  But these values would be invalid, as at least one non-empty element is
405  required:
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
423   tolerant applications). The end-of-line marker within an entity-body
424   is defined by its associated media type, as described in &media-types;.
426<t anchor="rule.LWS">
427   This specification uses three rules to denote the use of linear
428   whitespace: OWS (optional whitespace), RWS (required whitespace), and
429   BWS ("bad" whitespace).
432   The OWS rule is used where zero or more linear whitespace characters may
433   appear. OWS &SHOULD; either not be produced or be produced as a single SP
434   character. Multiple OWS characters that occur within field-content &SHOULD;
435   be replaced with a single SP before interpreting the field value or
436   forwarding the message downstream.
439   RWS is used when at least one linear whitespace character is required to
440   separate field tokens. RWS &SHOULD; be produced as a single SP character.
441   Multiple RWS characters that occur within field-content &SHOULD; be
442   replaced with a single SP before interpreting the field value or
443   forwarding the message downstream.
446   BWS is used where the grammar allows optional whitespace for historical
447   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
448   recipients &MUST; accept such bad optional whitespace and remove it before
449   interpreting the field value or forwarding the message downstream.
451<t anchor="rule.whitespace">
452  <x:anchor-alias value="BWS"/>
453  <x:anchor-alias value="OWS"/>
454  <x:anchor-alias value="RWS"/>
455  <x:anchor-alias value="obs-fold"/>
457<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"/>
458  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
459                 ; "optional" whitespace
460  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
461                 ; "required" whitespace
462  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
463                 ; "bad" whitespace
464  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
465                 ; see <xref target="header.fields"/>
467<t anchor="rule.token.separators">
468  <x:anchor-alias value="tchar"/>
469  <x:anchor-alias value="token"/>
470  <x:anchor-alias value="special"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
479  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
480 -->
481  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
482                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
483                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
484                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
486  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
487                 / ";" / ":" / "\" / DQUOTE / "/" / "["
488                 / "]" / "?" / "=" / "{" / "}"
490<t anchor="rule.quoted-string">
491  <x:anchor-alias value="quoted-string"/>
492  <x:anchor-alias value="qdtext"/>
493  <x:anchor-alias value="obs-text"/>
494   A string of text is parsed as a single word if it is quoted using
495   double-quote marks.
497<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"/>
498  <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>
499  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
500                 ; <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>
501  <x:ref>obs-text</x:ref>       = %x80-FF
503<t anchor="rule.quoted-pair">
504  <x:anchor-alias value="quoted-pair"/>
505   The backslash character ("\") can be used as a single-character
506   quoting mechanism within quoted-string constructs:
508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
509  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
512   Producers &SHOULD-NOT; escape characters that do not require escaping
513   (i.e., other than DQUOTE and the backslash character).
517<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
518  <x:anchor-alias value="request-header"/>
519  <x:anchor-alias value="response-header"/>
520  <x:anchor-alias value="entity-body"/>
521  <x:anchor-alias value="entity-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
526  The ABNF rules below are defined in other parts:
528<figure><!-- Part2--><artwork type="abnf2616">
529  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
530  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
532<figure><!-- Part3--><artwork type="abnf2616">
533  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
534  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
546<section title="HTTP architecture" anchor="architecture">
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
554<section title="Client/Server Operation" anchor="operation">
555<iref item="client"/>
556<iref item="server"/>
557<iref item="connection"/>
559   HTTP is a request/response protocol that operates by exchanging messages
560   across a reliable transport or session-layer connection. An HTTP client
561   is a program that establishes a connection to a server for the purpose
562   of sending one or more HTTP requests.  An HTTP server is a program that
563   accepts connections in order to service HTTP requests by sending HTTP
564   responses.
566<iref item="user agent"/>
567<iref item="origin server"/>
569   Note that the terms "client" and "server" refer only to the roles that
570   these programs perform for a particular connection.  The same program
571   may act as a client on some connections and a server on others.  We use
572   the term "user agent" to refer to the program that initiates a request,
573   such as a WWW browser, editor, or spider (web-traversing robot), and
574   the term "origin server" to refer to the program that can originate
575   authoritative responses to a request.
578   Most HTTP communication consists of a retrieval request (GET) for
579   a representation of some resource identified by a URI.  In the
580   simplest case, this may be accomplished via a single connection (v)
581   between the user agent (UA) and the origin server (O).
583<figure><artwork type="drawing">
584       request chain ------------------------&gt;
585    UA -------------------v------------------- O
586       &lt;----------------------- response chain
588<iref item="message"/>
589<iref item="request"/>
590<iref item="response"/>
592   A client sends an HTTP request to the server in the form of a request
593   message (<xref target="request"/>), beginning with a method, URI, and
594   protocol version, followed by MIME-like header fields containing
595   request modifiers, client information, and payload metadata, an empty
596   line to indicate the end of the header section, and finally the payload
597   body (if any).
600   A server responds to the client's request by sending an HTTP response
601   message (<xref target="response"/>), beginning with a status line that
602   includes the protocol version, a success or error code, and textual
603   reason phrase, followed by MIME-like header fields containing server
604   information, resource metadata, and payload metadata, an empty line to
605   indicate the end of the header section, and finally the payload body (if any).
608   The following example illustrates a typical message exchange for a
609   GET request on the URI "":
612client request:
613</preamble><artwork  type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
614GET /hello.txt HTTP/1.1
615User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
617Accept: */*
621server response:
622</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
623HTTP/1.1 200 OK
624Date: Mon, 27 Jul 2009 12:28:53 GMT
625Server: Apache
626Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
627ETag: "34aa387-d-1568eb00"
628Accept-Ranges: bytes
629Content-Length: <x:length-of target="exbody"/>
630Vary: Accept-Encoding
631Content-Type: text/plain
633<x:span anchor="exbody">Hello World!
637<section title="Intermediaries" anchor="intermediaries">
639   A more complicated situation occurs when one or more intermediaries
640   are present in the request/response chain. There are three common
641   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
642   a single intermediary may act as an origin server, proxy, gateway,
643   or tunnel, switching behavior based on the nature of each request.
645<figure><artwork type="drawing">
646       request chain --------------------------------------&gt;
647    UA -----v----- A -----v----- B -----v----- C -----v----- O
648       &lt;------------------------------------- response chain
651   The figure above shows three intermediaries (A, B, and C) between the
652   user agent and origin server. A request or response message that
653   travels the whole chain will pass through four separate connections.
654   Some HTTP communication options
655   may apply only to the connection with the nearest, non-tunnel
656   neighbor, only to the end-points of the chain, or to all connections
657   along the chain. Although the diagram is linear, each participant may
658   be engaged in multiple, simultaneous communications. For example, B
659   may be receiving requests from many clients other than A, and/or
660   forwarding requests to servers other than C, at the same time that it
661   is handling A's request.
664<iref item="upstream"/><iref item="downstream"/>
665<iref item="inbound"/><iref item="outbound"/>
666   We use the terms "upstream" and "downstream" to describe various
667   requirements in relation to the directional flow of a message:
668   all messages flow from upstream to downstream.
669   Likewise, we use the terms "inbound" and "outbound" to refer to
670   directions in relation to the request path: "inbound" means toward
671   the origin server and "outbound" means toward the user agent.
673<t><iref item="proxy"/>
674   A proxy is a message forwarding agent that is selected by the
675   client, usually via local configuration rules, to receive requests
676   for some type(s) of absolute URI and attempt to satisfy those
677   requests via translation through the HTTP interface.  Some translations
678   are minimal, such as for proxy requests for "http" URIs, whereas
679   other requests may require translation to and from entirely different
680   application-layer protocols. Proxies are often used to group an
681   organization's HTTP requests through a common intermediary for the
682   sake of security, annotation services, or shared caching.
684<t><iref item="gateway"/><iref item="reverse proxy"/>
685   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
686   as a layer above some other server(s) and translates the received
687   requests to the underlying server's protocol.  Gateways are often
688   used for load balancing or partitioning HTTP services across
689   multiple machines.
690   Unlike a proxy, a gateway receives requests as if it were the
691   origin server for the requested resource; the requesting client
692   will not be aware that it is communicating with a gateway.
693   A gateway communicates with the client as if the gateway is the
694   origin server and thus is subject to all of the requirements on
695   origin servers for that connection.  A gateway communicates
696   with inbound servers using any protocol it desires, including
697   private extensions to HTTP that are outside the scope of this
698   specification.
700<t><iref item="tunnel"/>
701   A tunnel acts as a blind relay between two connections
702   without changing the messages. Once active, a tunnel is not
703   considered a party to the HTTP communication, though the tunnel may
704   have been initiated by an HTTP request. A tunnel ceases to exist when
705   both ends of the relayed connection are closed. Tunnels are used to
706   extend a virtual connection through an intermediary, such as when
707   transport-layer security is used to establish private communication
708   through a shared firewall proxy.
712<section title="Caches" anchor="caches">
713<iref item="cache"/>
715   Any party to HTTP communication that is not acting as a tunnel may
716   employ an internal cache for handling requests.
717   A cache is a local store of previous response messages and the
718   subsystem that controls its message storage, retrieval, and deletion.
719   A cache stores cacheable responses in order to reduce the response
720   time and network bandwidth consumption on future, equivalent
721   requests. Any client or server may include a cache, though a cache
722   cannot be used by a server while it is acting as a tunnel.
725   The effect of a cache is that the request/response chain is shortened
726   if one of the participants along the chain has a cached response
727   applicable to that request. The following illustrates the resulting
728   chain if B has a cached copy of an earlier response from O (via C)
729   for a request which has not been cached by UA or A.
731<figure><artwork type="drawing">
732          request chain ----------&gt;
733       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
734          &lt;--------- response chain
736<t><iref item="cacheable"/>
737   A response is cacheable if a cache is allowed to store a copy of
738   the response message for use in answering subsequent requests.
739   Even when a response is cacheable, there may be additional
740   constraints placed by the client or by the origin server on when
741   that cached response can be used for a particular request. HTTP
742   requirements for cache behavior and cacheable responses are
743   defined in &caching-overview;. 
746   There are a wide variety of architectures and configurations
747   of caches and proxies deployed across the World Wide Web and
748   inside large organizations. These systems include national hierarchies
749   of proxy caches to save transoceanic bandwidth, systems that
750   broadcast or multicast cache entries, organizations that distribute
751   subsets of cached data via optical media, and so on.
755<section title="Transport Independence" anchor="transport-independence">
757  HTTP systems are used in a wide variety of environments, from
758  corporate intranets with high-bandwidth links to long-distance
759  communication over low-power radio links and intermittent connectivity.
762   HTTP communication usually takes place over TCP/IP connections. The
763   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
764   not preclude HTTP from being implemented on top of any other protocol
765   on the Internet, or on other networks. HTTP only presumes a reliable
766   transport; any protocol that provides such guarantees can be used;
767   the mapping of the HTTP/1.1 request and response structures onto the
768   transport data units of the protocol in question is outside the scope
769   of this specification.
772   In HTTP/1.0, most implementations used a new connection for each
773   request/response exchange. In HTTP/1.1, a connection may be used for
774   one or more request/response exchanges, although connections may be
775   closed for a variety of reasons (see <xref target="persistent.connections"/>).
779<section title="HTTP Version" anchor="http.version">
780  <x:anchor-alias value="HTTP-Version"/>
781  <x:anchor-alias value="HTTP-Prot-Name"/>
783   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
784   of the protocol. The protocol versioning policy is intended to allow
785   the sender to indicate the format of a message and its capacity for
786   understanding further HTTP communication, rather than the features
787   obtained via that communication. No change is made to the version
788   number for the addition of message components which do not affect
789   communication behavior or which only add to extensible field values.
790   The &lt;minor&gt; number is incremented when the changes made to the
791   protocol add features which do not change the general message parsing
792   algorithm, but which may add to the message semantics and imply
793   additional capabilities of the sender. The &lt;major&gt; number is
794   incremented when the format of a message within the protocol is
795   changed. See <xref target="RFC2145"/> for a fuller explanation.
798   The version of an HTTP message is indicated by an HTTP-Version field
799   in the first line of the message. HTTP-Version is case-sensitive.
801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
802  <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>
803  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
806   Note that the major and minor numbers &MUST; be treated as separate
807   integers and that each &MAY; be incremented higher than a single digit.
808   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
809   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
810   &MUST-NOT; be sent.
813   An application that sends a request or response message that includes
814   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
815   with this specification. Applications that are at least conditionally
816   compliant with this specification &SHOULD; use an HTTP-Version of
817   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
818   not compatible with HTTP/1.0. For more details on when to send
819   specific HTTP-Version values, see <xref target="RFC2145"/>.
822   The HTTP version of an application is the highest HTTP version for
823   which the application is at least conditionally compliant.
826   Proxy and gateway applications need to be careful when forwarding
827   messages in protocol versions different from that of the application.
828   Since the protocol version indicates the protocol capability of the
829   sender, a proxy/gateway &MUST-NOT; send a message with a version
830   indicator which is greater than its actual version. If a higher
831   version request is received, the proxy/gateway &MUST; either downgrade
832   the request version, or respond with an error, or switch to tunnel
833   behavior.
836   Due to interoperability problems with HTTP/1.0 proxies discovered
837   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
838   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
839   they support. The proxy/gateway's response to that request &MUST; be in
840   the same major version as the request.
843  <t>
844    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
845    of header fields required or forbidden by the versions involved.
846  </t>
850<section title="Uniform Resource Identifiers" anchor="uri">
851<iref primary="true" item="resource"/>
853   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
854   throughout HTTP as the means for identifying resources. URI references
855   are used to target requests, indicate redirects, and define relationships.
856   HTTP does not limit what a resource may be; it merely defines an interface
857   that can be used to interact with a resource via HTTP. More information on
858   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
860  <x:anchor-alias value="URI-reference"/>
861  <x:anchor-alias value="absolute-URI"/>
862  <x:anchor-alias value="relative-part"/>
863  <x:anchor-alias value="authority"/>
864  <x:anchor-alias value="path-abempty"/>
865  <x:anchor-alias value="path-absolute"/>
866  <x:anchor-alias value="port"/>
867  <x:anchor-alias value="query"/>
868  <x:anchor-alias value="uri-host"/>
869  <x:anchor-alias value="partial-URI"/>
871   This specification adopts the definitions of "URI-reference",
872   "absolute-URI", "relative-part", "port", "host",
873   "path-abempty", "path-absolute", "query", and "authority" from
874   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
875   protocol elements that allow a relative URI without a fragment.
877<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"/>
878  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
879  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
880  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
881  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
882  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
883  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
885  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
886  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
888  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
891   Each protocol element in HTTP that allows a URI reference will indicate in
892   its ABNF production whether the element allows only a URI in absolute form
893   (absolute-URI), any relative reference (relative-ref), or some other subset
894   of the URI-reference grammar. Unless otherwise indicated, URI references
895   are parsed relative to the request target (the default base URI for both
896   the request and its corresponding response).
899<section title="http URI scheme" anchor="http.uri">
900  <x:anchor-alias value="http-URI"/>
901  <iref item="http URI scheme" primary="true"/>
902  <iref item="URI scheme" subitem="http" primary="true"/>
904   The "http" URI scheme is hereby defined for the purpose of minting
905   identifiers according to their association with the hierarchical
906   namespace governed by a potential HTTP origin server listening for
907   TCP connections on a given port.
908   The HTTP server is identified via the generic syntax's
909   <x:ref>authority</x:ref> component, which includes a host
910   identifier and optional TCP port, and the remainder of the URI is
911   considered to be identifying data corresponding to a resource for
912   which that server might provide an HTTP interface.
914<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
915  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
918   The host identifier within an <x:ref>authority</x:ref> component is
919   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
920   provided as an IP literal or IPv4 address, then the HTTP server is any
921   listener on the indicated TCP port at that IP address. If host is a
922   registered name, then that name is considered an indirect identifier
923   and the recipient might use a name resolution service, such as DNS,
924   to find the address of a listener for that host.
925   The host &MUST-NOT; be empty; if an "http" URI is received with an
926   empty host, then it &MUST; be rejected as invalid.
927   If the port subcomponent is empty or not given, then TCP port 80 is
928   assumed (the default reserved port for WWW services).
931   Regardless of the form of host identifier, access to that host is not
932   implied by the mere presence of its name or address. The host may or may
933   not exist and, even when it does exist, may or may not be running an
934   HTTP server or listening to the indicated port. The "http" URI scheme
935   makes use of the delegated nature of Internet names and addresses to
936   establish a naming authority (whatever entity has the ability to place
937   an HTTP server at that Internet name or address) and allows that
938   authority to determine which names are valid and how they might be used.
941   When an "http" URI is used within a context that calls for access to the
942   indicated resource, a client &MAY; attempt access by resolving
943   the host to an IP address, establishing a TCP connection to that address
944   on the indicated port, and sending an HTTP request message to the server
945   containing the URI's identifying data as described in <xref target="request"/>.
946   If the server responds to that request with a non-interim HTTP response
947   message, as described in <xref target="response"/>, then that response
948   is considered an authoritative answer to the client's request.
951   Although HTTP is independent of the transport protocol, the "http"
952   scheme is specific to TCP-based services because the name delegation
953   process depends on TCP for establishing authority.
954   An HTTP service based on some other underlying connection protocol
955   would presumably be identified using a different URI scheme, just as
956   the "https" scheme (below) is used for servers that require an SSL/TLS
957   transport layer on a connection. Other protocols may also be used to
958   provide access to "http" identified resources --- it is only the
959   authoritative interface used for mapping the namespace that is
960   specific to TCP.
964<section title="https URI scheme" anchor="https.uri">
965   <x:anchor-alias value="https-URI"/>
966   <iref item="https URI scheme"/>
967   <iref item="URI scheme" subitem="https"/>
969   The "https" URI scheme is hereby defined for the purpose of minting
970   identifiers according to their association with the hierarchical
971   namespace governed by a potential HTTP origin server listening for
972   SSL/TLS-secured connections on a given TCP port.
973   The host and port are determined in the same way
974   as for the "http" scheme, except that a default TCP port of 443
975   is assumed if the port subcomponent is empty or not given.
977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
978  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
981   The primary difference between the "http" and "https" schemes is
982   that interaction with the latter is required to be secured for
983   privacy through the use of strong encryption. The URI cannot be
984   sent in a request until the connection is secure. Likewise, the
985   default for caching is that each response that would be considered
986   "public" under the "http" scheme is instead treated as "private"
987   and thus not eligible for shared caching.
990   The process for authoritative access to an "https" identified
991   resource is defined in <xref target="RFC2818"/>.
995<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
997   Since the "http" and "https" schemes conform to the URI generic syntax,
998   such URIs are normalized and compared according to the algorithm defined
999   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1000   described above for each scheme.
1003   If the port is equal to the default port for a scheme, the normal
1004   form is to elide the port subcomponent. Likewise, an empty path
1005   component is equivalent to an absolute path of "/", so the normal
1006   form is to provide a path of "/" instead. The scheme and host
1007   are case-insensitive and normally provided in lowercase; all
1008   other components are compared in a case-sensitive manner.
1009   Characters other than those in the "reserved" set are equivalent
1010   to their percent-encoded octets (see <xref target="RFC3986"
1011   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1014   For example, the following three URIs are equivalent:
1016<figure><artwork type="example">
1022   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1023   If path-abempty is the empty string (i.e., there is no slash "/"
1024   path separator following the authority), then the "http" URI
1025   &MUST; be given as "/" when
1026   used as a request-target (<xref target="request-target"/>). If a proxy
1027   receives a host name which is not a fully qualified domain name, it
1028   &MAY; add its domain to the host name it received. If a proxy receives
1029   a fully qualified domain name, the proxy &MUST-NOT; change the host
1030   name.
1036<section title="HTTP Message" anchor="http.message">
1037<x:anchor-alias value="generic-message"/>
1038<x:anchor-alias value="message.types"/>
1039<x:anchor-alias value="HTTP-message"/>
1040<x:anchor-alias value="start-line"/>
1041<iref item="header section"/>
1042<iref item="headers"/>
1043<iref item="header field"/>
1045   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1046   characters in a format similar to the Internet Message Format
1047   <xref target="RFC5322"/>: zero or more header fields (collectively
1048   referred to as the "headers" or the "header section"), an empty line
1049   indicating the end of the header section, and an optional message-body.
1052   An HTTP message can either be a request from client to server or a
1053   response from server to client.  Syntactically, the two types of message
1054   differ only in the start-line, which is either a Request-Line (for requests)
1055   or a Status-Line (for responses), and in the algorithm for determining
1056   the length of the message-body (<xref target="message.length"/>).
1057   In theory, a client could receive requests and a server could receive
1058   responses, distinguishing them by their different start-line formats,
1059   but in practice servers are implemented to only expect a request
1060   (a response is interpreted as an unknown or invalid request method)
1061   and clients are implemented to only expect a response.
1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1064  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1065                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1066                    <x:ref>CRLF</x:ref>
1067                    [ <x:ref>message-body</x:ref> ]
1068  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1071   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1072   header field. The presence of whitespace might be an attempt to trick a
1073   noncompliant implementation of HTTP into ignoring that field or processing
1074   the next line as a new request, either of which may result in security
1075   issues when implementations within the request chain interpret the
1076   same message differently. HTTP/1.1 servers &MUST; reject such a message
1077   with a 400 (Bad Request) response.
1080<section title="Message Parsing Robustness" anchor="message.robustness">
1082   In the interest of robustness, servers &SHOULD; ignore at least one
1083   empty line received where a Request-Line is expected. In other words, if
1084   the server is reading the protocol stream at the beginning of a
1085   message and receives a CRLF first, it should ignore the CRLF.
1088   Some old HTTP/1.0 client implementations generate an extra CRLF
1089   after a POST request as a lame workaround for some early server
1090   applications that failed to read message-body content that was
1091   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1092   preface or follow a request with an extra CRLF.  If terminating
1093   the request message-body with a line-ending is desired, then the
1094   client &MUST; include the terminating CRLF octets as part of the
1095   message-body length.
1098   The normal procedure for parsing an HTTP message is to read the
1099   start-line into a structure, read each header field into a hash
1100   table by field name until the empty line, and then use the parsed
1101   data to determine if a message-body is expected.  If a message-body
1102   has been indicated, then it is read as a stream until an amount
1103   of OCTETs equal to the message-length is read or the connection
1104   is closed.  Care must be taken to parse an HTTP message as a sequence
1105   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1106   to parse HTTP as a stream of Unicode characters in a character encoding
1107   like UTF-16 may introduce security flaws due to the differing ways
1108   that such parsers interpret invalid characters.
1112<section title="Header Fields" anchor="header.fields">
1113  <x:anchor-alias value="header-field"/>
1114  <x:anchor-alias value="field-content"/>
1115  <x:anchor-alias value="field-name"/>
1116  <x:anchor-alias value="field-value"/>
1117  <x:anchor-alias value="OWS"/>
1119   Each HTTP header field consists of a case-insensitive field name
1120   followed by a colon (":"), optional whitespace, and the field value.
1122<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"/>
1123  <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>
1124  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1125  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1126  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1129   No whitespace is allowed between the header field name and colon. For
1130   security reasons, any request message received containing such whitespace
1131   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1132   &MUST; remove any such whitespace from a response message before
1133   forwarding the message downstream.
1136   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1137   preferred. The field value does not include any leading or trailing white
1138   space: OWS occurring before the first non-whitespace character of the
1139   field value or after the last non-whitespace character of the field value
1140   is ignored and &SHOULD; be removed before further processing (as this does
1141   not change the meaning of the header field).
1144   The order in which header fields with differing field names are
1145   received is not significant. However, it is "good practice" to send
1146   header fields that contain control data first, such as Host on
1147   requests and Date on responses, so that implementations can decide
1148   when not to handle a message as early as possible.  A server &MUST;
1149   wait until the entire header section is received before interpreting
1150   a request message, since later header fields might include conditionals,
1151   authentication credentials, or deliberately misleading duplicate
1152   header fields that would impact request processing.
1155   Multiple header fields with the same field name &MUST-NOT; be
1156   sent in a message unless the entire field value for that
1157   header field is defined as a comma-separated list [i.e., #(values)].
1158   Multiple header fields with the same field name can be combined into
1159   one "field-name: field-value" pair, without changing the semantics of the
1160   message, by appending each subsequent field value to the combined
1161   field value in order, separated by a comma. The order in which
1162   header fields with the same field name are received is therefore
1163   significant to the interpretation of the combined field value;
1164   a proxy &MUST-NOT; change the order of these field values when
1165   forwarding a message.
1168  <t>
1169   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1170   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1171   can occur multiple times, but does not use the list syntax, and thus cannot
1172   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1173   for details.) Also note that the Set-Cookie2 header specified in
1174   <xref target="RFC2965"/> does not share this problem.
1175  </t>
1178   Historically, HTTP header field values could be extended over multiple
1179   lines by preceding each extra line with at least one space or horizontal
1180   tab character (line folding). This specification deprecates such line
1181   folding except within the message/http media type
1182   (<xref target=""/>).
1183   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1184   (i.e., that contain any field-content that matches the obs-fold rule) unless
1185   the message is intended for packaging within the message/http media type.
1186   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1187   obs-fold whitespace with a single SP prior to interpreting the field value
1188   or forwarding the message downstream.
1191   Historically, HTTP has allowed field content with text in the ISO-8859-1
1192   <xref target="ISO-8859-1"/> character encoding and supported other
1193   character sets only through use of <xref target="RFC2047"/> encoding.
1194   In practice, most HTTP header field values use only a subset of the
1195   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1196   header fields &SHOULD; limit their field values to US-ASCII characters.
1197   Recipients &SHOULD; treat other (obs-text) octets in field content as
1198   opaque data.
1200<t anchor="rule.comment">
1201  <x:anchor-alias value="comment"/>
1202  <x:anchor-alias value="ctext"/>
1203   Comments can be included in some HTTP header fields by surrounding
1204   the comment text with parentheses. Comments are only allowed in
1205   fields containing "comment" as part of their field value definition.
1207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1208  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1209  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1210                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1212<t anchor="rule.quoted-cpair">
1213  <x:anchor-alias value="quoted-cpair"/>
1214   The backslash character ("\") can be used as a single-character
1215   quoting mechanism within comment constructs:
1217<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1218  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1221   Producers &SHOULD-NOT; escape characters that do not require escaping
1222   (i.e., other than the backslash character "\" and the parentheses "(" and
1223   ")").
1227<section title="Message Body" anchor="message.body">
1228  <x:anchor-alias value="message-body"/>
1230   The message-body (if any) of an HTTP message is used to carry the
1231   entity-body associated with the request or response. The message-body
1232   differs from the entity-body only when a transfer-coding has been
1233   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1235<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1236  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1237               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1240   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1241   applied by an application to ensure safe and proper transfer of the
1242   message. Transfer-Encoding is a property of the message, not of the
1243   entity, and thus &MAY; be added or removed by any application along the
1244   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1245   when certain transfer-codings may be used.)
1248   The rules for when a message-body is allowed in a message differ for
1249   requests and responses.
1252   The presence of a message-body in a request is signaled by the
1253   inclusion of a Content-Length or Transfer-Encoding header field in
1254   the request's header fields.
1255   When a request message contains both a message-body of non-zero
1256   length and a method that does not define any semantics for that
1257   request message-body, then an origin server &SHOULD; either ignore
1258   the message-body or respond with an appropriate error message
1259   (e.g., 413).  A proxy or gateway, when presented the same request,
1260   &SHOULD; either forward the request inbound with the message-body or
1261   ignore the message-body when determining a response.
1264   For response messages, whether or not a message-body is included with
1265   a message is dependent on both the request method and the response
1266   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1267   &MUST-NOT; include a message-body, even though the presence of entity-header
1268   fields might lead one to believe they do. All 1xx
1269   (Informational), 204 (No Content), and 304 (Not Modified) responses
1270   &MUST-NOT; include a message-body. All other responses do include a
1271   message-body, although it &MAY; be of zero length.
1275<section title="Message Length" anchor="message.length">
1277   The transfer-length of a message is the length of the message-body as
1278   it appears in the message; that is, after any transfer-codings have
1279   been applied. When a message-body is included with a message, the
1280   transfer-length of that body is determined by one of the following
1281   (in order of precedence):
1284  <list style="numbers">
1285    <x:lt><t>
1286     Any response message which "&MUST-NOT;" include a message-body (such
1287     as the 1xx, 204, and 304 responses and any response to a HEAD
1288     request) is always terminated by the first empty line after the
1289     header fields, regardless of the entity-header fields present in
1290     the message.
1291    </t></x:lt>
1292    <x:lt><t>
1293     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1294     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1295     is used, the transfer-length is defined by the use of this transfer-coding.
1296     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1297     is not present, the transfer-length is defined by the sender closing the connection.
1298    </t></x:lt>
1299    <x:lt><t>
1300     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1301     value in OCTETs represents both the entity-length and the
1302     transfer-length. The Content-Length header field &MUST-NOT; be sent
1303     if these two lengths are different (i.e., if a Transfer-Encoding
1304     header field is present). If a message is received with both a
1305     Transfer-Encoding header field and a Content-Length header field,
1306     the latter &MUST; be ignored.
1307    </t></x:lt>
1308    <x:lt><t>
1309     If the message uses the media type "multipart/byteranges", and the
1310     transfer-length is not otherwise specified, then this self-delimiting
1311     media type defines the transfer-length. This media type
1312     &MUST-NOT; be used unless the sender knows that the recipient can parse
1313     it; the presence in a request of a Range header with multiple byte-range
1314     specifiers from a HTTP/1.1 client implies that the client can parse
1315     multipart/byteranges responses.
1316    <list style="empty"><t>
1317       A range header might be forwarded by a HTTP/1.0 proxy that does not
1318       understand multipart/byteranges; in this case the server &MUST;
1319       delimit the message using methods defined in items 1, 3 or 5 of
1320       this section.
1321    </t></list>
1322    </t></x:lt>
1323    <x:lt><t>
1324     By the server closing the connection. (Closing the connection
1325     cannot be used to indicate the end of a request body, since that
1326     would leave no possibility for the server to send back a response.)
1327    </t></x:lt>
1328  </list>
1331   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1332   containing a message-body &MUST; include a valid Content-Length header
1333   field unless the server is known to be HTTP/1.1 compliant. If a
1334   request contains a message-body and a Content-Length is not given,
1335   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1336   determine the length of the message, or with 411 (Length Required) if
1337   it wishes to insist on receiving a valid Content-Length.
1340   All HTTP/1.1 applications that receive entities &MUST; accept the
1341   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1342   to be used for messages when the message length cannot be determined
1343   in advance.
1346   Messages &MUST-NOT; include both a Content-Length header field and a
1347   transfer-coding. If the message does include a
1348   transfer-coding, the Content-Length &MUST; be ignored.
1351   When a Content-Length is given in a message where a message-body is
1352   allowed, its field value &MUST; exactly match the number of OCTETs in
1353   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1354   invalid length is received and detected.
1358<section title="General Header Fields" anchor="general.header.fields">
1359  <x:anchor-alias value="general-header"/>
1361   There are a few header fields which have general applicability for
1362   both request and response messages, but which do not apply to the
1363   entity being transferred. These header fields apply only to the
1364   message being transmitted.
1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1367  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1368                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1369                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1370                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1371                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1372                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1373                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1374                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1375                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1378   General-header field names can be extended reliably only in
1379   combination with a change in the protocol version. However, new or
1380   experimental header fields may be given the semantics of general
1381   header fields if all parties in the communication recognize them to
1382   be general-header fields. Unrecognized header fields are treated as
1383   entity-header fields.
1388<section title="Request" anchor="request">
1389  <x:anchor-alias value="Request"/>
1391   A request message from a client to a server includes, within the
1392   first line of that message, the method to be applied to the resource,
1393   the identifier of the resource, and the protocol version in use.
1395<!--                 Host                      ; should be moved here eventually -->
1396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1397  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1398                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1399                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1400                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1401                  <x:ref>CRLF</x:ref>
1402                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1405<section title="Request-Line" anchor="request-line">
1406  <x:anchor-alias value="Request-Line"/>
1408   The Request-Line begins with a method token, followed by the
1409   request-target and the protocol version, and ending with CRLF. The
1410   elements are separated by SP characters. No CR or LF is allowed
1411   except in the final CRLF sequence.
1413<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1414  <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>
1417<section title="Method" anchor="method">
1418  <x:anchor-alias value="Method"/>
1420   The Method  token indicates the method to be performed on the
1421   resource identified by the request-target. The method is case-sensitive.
1423<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1424  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1428<section title="request-target" anchor="request-target">
1429  <x:anchor-alias value="request-target"/>
1431   The request-target
1432   identifies the resource upon which to apply the request.
1434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1435  <x:ref>request-target</x:ref> = "*"
1436                 / <x:ref>absolute-URI</x:ref>
1437                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1438                 / <x:ref>authority</x:ref>
1441   The four options for request-target are dependent on the nature of the
1442   request. The asterisk "*" means that the request does not apply to a
1443   particular resource, but to the server itself, and is only allowed
1444   when the method used does not necessarily apply to a resource. One
1445   example would be
1447<figure><artwork type="example">
1448  OPTIONS * HTTP/1.1
1451   The absolute-URI form is &REQUIRED; when the request is being made to a
1452   proxy. The proxy is requested to forward the request or service it
1453   from a valid cache, and return the response. Note that the proxy &MAY;
1454   forward the request on to another proxy or directly to the server
1455   specified by the absolute-URI. In order to avoid request loops, a
1456   proxy &MUST; be able to recognize all of its server names, including
1457   any aliases, local variations, and the numeric IP address. An example
1458   Request-Line would be:
1460<figure><artwork type="example">
1461  GET HTTP/1.1
1464   To allow for transition to absolute-URIs in all requests in future
1465   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1466   form in requests, even though HTTP/1.1 clients will only generate
1467   them in requests to proxies.
1470   The authority form is only used by the CONNECT method (&CONNECT;).
1473   The most common form of request-target is that used to identify a
1474   resource on an origin server or gateway. In this case the absolute
1475   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1476   the request-target, and the network location of the URI (authority) &MUST;
1477   be transmitted in a Host header field. For example, a client wishing
1478   to retrieve the resource above directly from the origin server would
1479   create a TCP connection to port 80 of the host "" and send
1480   the lines:
1482<figure><artwork type="example">
1483  GET /pub/WWW/TheProject.html HTTP/1.1
1484  Host:
1487   followed by the remainder of the Request. Note that the absolute path
1488   cannot be empty; if none is present in the original URI, it &MUST; be
1489   given as "/" (the server root).
1492   If a proxy receives a request without any path in the request-target and
1493   the method specified is capable of supporting the asterisk form of
1494   request-target, then the last proxy on the request chain &MUST; forward the
1495   request with "*" as the final request-target.
1498   For example, the request
1499</preamble><artwork type="example">
1500  OPTIONS HTTP/1.1
1503  would be forwarded by the proxy as
1504</preamble><artwork type="example">
1505  OPTIONS * HTTP/1.1
1506  Host:
1509   after connecting to port 8001 of host "".
1513   The request-target is transmitted in the format specified in
1514   <xref target="http.uri"/>. If the request-target is percent-encoded
1515   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1516   &MUST; decode the request-target in order to
1517   properly interpret the request. Servers &SHOULD; respond to invalid
1518   request-targets with an appropriate status code.
1521   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1522   received request-target when forwarding it to the next inbound server,
1523   except as noted above to replace a null path-absolute with "/".
1526  <t>
1527    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1528    meaning of the request when the origin server is improperly using
1529    a non-reserved URI character for a reserved purpose.  Implementors
1530    should be aware that some pre-HTTP/1.1 proxies have been known to
1531    rewrite the request-target.
1532  </t>
1535   HTTP does not place a pre-defined limit on the length of a request-target.
1536   A server &MUST; be prepared to receive URIs of unbounded length and
1537   respond with the 414 (URI Too Long) status if the received
1538   request-target would be longer than the server wishes to handle
1539   (see &status-414;).
1542   Various ad-hoc limitations on request-target length are found in practice.
1543   It is &RECOMMENDED; that all HTTP senders and recipients support
1544   request-target lengths of 8000 or more OCTETs.
1549<section title="The Resource Identified by a Request" anchor="">
1551   The exact resource identified by an Internet request is determined by
1552   examining both the request-target and the Host header field.
1555   An origin server that does not allow resources to differ by the
1556   requested host &MAY; ignore the Host header field value when
1557   determining the resource identified by an HTTP/1.1 request. (But see
1558   <xref target=""/>
1559   for other requirements on Host support in HTTP/1.1.)
1562   An origin server that does differentiate resources based on the host
1563   requested (sometimes referred to as virtual hosts or vanity host
1564   names) &MUST; use the following rules for determining the requested
1565   resource on an HTTP/1.1 request:
1566  <list style="numbers">
1567    <t>If request-target is an absolute-URI, the host is part of the
1568     request-target. Any Host header field value in the request &MUST; be
1569     ignored.</t>
1570    <t>If the request-target is not an absolute-URI, and the request includes
1571     a Host header field, the host is determined by the Host header
1572     field value.</t>
1573    <t>If the host as determined by rule 1 or 2 is not a valid host on
1574     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1575  </list>
1578   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1579   attempt to use heuristics (e.g., examination of the URI path for
1580   something unique to a particular host) in order to determine what
1581   exact resource is being requested.
1588<section title="Response" anchor="response">
1589  <x:anchor-alias value="Response"/>
1591   After receiving and interpreting a request message, a server responds
1592   with an HTTP response message.
1594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1595  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1596                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1597                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1598                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1599                  <x:ref>CRLF</x:ref>
1600                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1603<section title="Status-Line" anchor="status-line">
1604  <x:anchor-alias value="Status-Line"/>
1606   The first line of a Response message is the Status-Line, consisting
1607   of the protocol version followed by a numeric status code and its
1608   associated textual phrase, with each element separated by SP
1609   characters. No CR or LF is allowed except in the final CRLF sequence.
1611<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1612  <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>
1615<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1616  <x:anchor-alias value="Reason-Phrase"/>
1617  <x:anchor-alias value="Status-Code"/>
1619   The Status-Code element is a 3-digit integer result code of the
1620   attempt to understand and satisfy the request. These codes are fully
1621   defined in &status-codes;.  The Reason Phrase exists for the sole
1622   purpose of providing a textual description associated with the numeric
1623   status code, out of deference to earlier Internet application protocols
1624   that were more frequently used with interactive text clients.
1625   A client &SHOULD; ignore the content of the Reason Phrase.
1628   The first digit of the Status-Code defines the class of response. The
1629   last two digits do not have any categorization role. There are 5
1630   values for the first digit:
1631  <list style="symbols">
1632    <t>
1633      1xx: Informational - Request received, continuing process
1634    </t>
1635    <t>
1636      2xx: Success - The action was successfully received,
1637        understood, and accepted
1638    </t>
1639    <t>
1640      3xx: Redirection - Further action must be taken in order to
1641        complete the request
1642    </t>
1643    <t>
1644      4xx: Client Error - The request contains bad syntax or cannot
1645        be fulfilled
1646    </t>
1647    <t>
1648      5xx: Server Error - The server failed to fulfill an apparently
1649        valid request
1650    </t>
1651  </list>
1653<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"/>
1654  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1655  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1663<section title="Protocol Parameters" anchor="protocol.parameters">
1665<section title="Date/Time Formats: Full Date" anchor="">
1666  <x:anchor-alias value="HTTP-date"/>
1668   HTTP applications have historically allowed three different formats
1669   for the representation of date/time stamps:
1671<figure><artwork type="example">
1672  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1673  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1674  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1677   The first format is preferred as an Internet standard and represents
1678   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1679   other formats are described here only for
1680   compatibility with obsolete implementations.
1681   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1682   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1683   only generate the RFC 1123 format for representing HTTP-date values
1684   in header fields. See <xref target="tolerant.applications"/> for further information.
1687   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1688   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1689   equal to UTC (Coordinated Universal Time). This is indicated in the
1690   first two formats by the inclusion of "GMT" as the three-letter
1691   abbreviation for time zone, and &MUST; be assumed when reading the
1692   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1693   additional whitespace beyond that specifically included as SP in the
1694   grammar.
1696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1697  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1699<t anchor="">
1700  <x:anchor-alias value="rfc1123-date"/>
1701  <x:anchor-alias value="time-of-day"/>
1702  <x:anchor-alias value="hour"/>
1703  <x:anchor-alias value="minute"/>
1704  <x:anchor-alias value="second"/>
1705  <x:anchor-alias value="day-name"/>
1706  <x:anchor-alias value="day"/>
1707  <x:anchor-alias value="month"/>
1708  <x:anchor-alias value="year"/>
1709  <x:anchor-alias value="GMT"/>
1710  Preferred format:
1712<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"/>
1713  <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>
1715  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1716               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1717               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1718               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1719               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1720               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1721               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1723  <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>
1724               ; e.g., 02 Jun 1982
1726  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1727  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1728               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1729               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1730               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1731               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1732               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1733               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1734               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1735               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1736               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1737               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1738               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1739  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1741  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1743  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1744                 ; 00:00:00 - 23:59:59
1746  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1747  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1748  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1751  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1752  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1753  same as those defined for the RFC 5322 constructs
1754  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1756<t anchor="">
1757  <x:anchor-alias value="obs-date"/>
1758  <x:anchor-alias value="rfc850-date"/>
1759  <x:anchor-alias value="asctime-date"/>
1760  <x:anchor-alias value="date1"/>
1761  <x:anchor-alias value="date2"/>
1762  <x:anchor-alias value="date3"/>
1763  <x:anchor-alias value="rfc1123-date"/>
1764  <x:anchor-alias value="day-name-l"/>
1765  Obsolete formats:
1767<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1768  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1770<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1771  <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>
1772  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1773                 ; day-month-year (e.g., 02-Jun-82)
1775  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1776         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1777         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1778         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1779         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1780         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1781         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1783<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1784  <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>
1785  <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> ))
1786                 ; month day (e.g., Jun  2)
1789  <t>
1790    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1791    accepting date values that may have been sent by non-HTTP
1792    applications, as is sometimes the case when retrieving or posting
1793    messages via proxies/gateways to SMTP or NNTP.
1794  </t>
1797  <t>
1798    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1799    to their usage within the protocol stream. Clients and servers are
1800    not required to use these formats for user presentation, request
1801    logging, etc.
1802  </t>
1806<section title="Transfer Codings" anchor="transfer.codings">
1807  <x:anchor-alias value="transfer-coding"/>
1808  <x:anchor-alias value="transfer-extension"/>
1810   Transfer-coding values are used to indicate an encoding
1811   transformation that has been, can be, or may need to be applied to an
1812   entity-body in order to ensure "safe transport" through the network.
1813   This differs from a content coding in that the transfer-coding is a
1814   property of the message, not of the original entity.
1816<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1817  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1818                          / "compress" ; <xref target="compress.coding"/>
1819                          / "deflate" ; <xref target="deflate.coding"/>
1820                          / "gzip" ; <xref target="gzip.coding"/>
1821                          / <x:ref>transfer-extension</x:ref>
1822  <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> )
1824<t anchor="rule.parameter">
1825  <x:anchor-alias value="attribute"/>
1826  <x:anchor-alias value="transfer-parameter"/>
1827  <x:anchor-alias value="value"/>
1828   Parameters are in  the form of attribute/value pairs.
1830<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"/>
1831  <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>
1832  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1833  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1836   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1837   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1838   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1841   Whenever a transfer-coding is applied to a message-body, the set of
1842   transfer-codings &MUST; include "chunked", unless the message indicates it
1843   is terminated by closing the connection. When the "chunked" transfer-coding
1844   is used, it &MUST; be the last transfer-coding applied to the
1845   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1846   than once to a message-body. These rules allow the recipient to
1847   determine the transfer-length of the message (<xref target="message.length"/>).
1850   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1851   MIME, which were designed to enable safe transport of binary data over a
1852   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1853   However, safe transport
1854   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1855   the only unsafe characteristic of message-bodies is the difficulty in
1856   determining the exact body length (<xref target="message.length"/>), or the desire to
1857   encrypt data over a shared transport.
1860   A server which receives an entity-body with a transfer-coding it does
1861   not understand &SHOULD; return 501 (Not Implemented), and close the
1862   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1863   client.
1866<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1867  <iref item="chunked (Coding Format)"/>
1868  <iref item="Coding Format" subitem="chunked"/>
1869  <x:anchor-alias value="chunk"/>
1870  <x:anchor-alias value="Chunked-Body"/>
1871  <x:anchor-alias value="chunk-data"/>
1872  <x:anchor-alias value="chunk-ext"/>
1873  <x:anchor-alias value="chunk-ext-name"/>
1874  <x:anchor-alias value="chunk-ext-val"/>
1875  <x:anchor-alias value="chunk-size"/>
1876  <x:anchor-alias value="last-chunk"/>
1877  <x:anchor-alias value="trailer-part"/>
1878  <x:anchor-alias value="quoted-str-nf"/>
1879  <x:anchor-alias value="qdtext-nf"/>
1881   The chunked encoding modifies the body of a message in order to
1882   transfer it as a series of chunks, each with its own size indicator,
1883   followed by an &OPTIONAL; trailer containing entity-header fields. This
1884   allows dynamically produced content to be transferred along with the
1885   information necessary for the recipient to verify that it has
1886   received the full message.
1888<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"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1889  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1890                   <x:ref>last-chunk</x:ref>
1891                   <x:ref>trailer-part</x:ref>
1892                   <x:ref>CRLF</x:ref>
1894  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1895                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1896  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1897  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1899  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1900                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1901  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1902  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1903  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1904  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1906  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1907                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1908  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1909                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
1912   The chunk-size field is a string of hex digits indicating the size of
1913   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1914   zero, followed by the trailer, which is terminated by an empty line.
1917   The trailer allows the sender to include additional HTTP header
1918   fields at the end of the message. The Trailer header field can be
1919   used to indicate which header fields are included in a trailer (see
1920   <xref target="header.trailer"/>).
1923   A server using chunked transfer-coding in a response &MUST-NOT; use the
1924   trailer for any header fields unless at least one of the following is
1925   true:
1926  <list style="numbers">
1927    <t>the request included a TE header field that indicates "trailers" is
1928     acceptable in the transfer-coding of the  response, as described in
1929     <xref target="header.te"/>; or,</t>
1931    <t>the server is the origin server for the response, the trailer
1932     fields consist entirely of optional metadata, and the recipient
1933     could use the message (in a manner acceptable to the origin server)
1934     without receiving this metadata.  In other words, the origin server
1935     is willing to accept the possibility that the trailer fields might
1936     be silently discarded along the path to the client.</t>
1937  </list>
1940   This requirement prevents an interoperability failure when the
1941   message is being received by an HTTP/1.1 (or later) proxy and
1942   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1943   compliance with the protocol would have necessitated a possibly
1944   infinite buffer on the proxy.
1947   A process for decoding the "chunked" transfer-coding
1948   can be represented in pseudo-code as:
1950<figure><artwork type="code">
1951  length := 0
1952  read chunk-size, chunk-ext (if any) and CRLF
1953  while (chunk-size &gt; 0) {
1954     read chunk-data and CRLF
1955     append chunk-data to entity-body
1956     length := length + chunk-size
1957     read chunk-size and CRLF
1958  }
1959  read entity-header
1960  while (entity-header not empty) {
1961     append entity-header to existing header fields
1962     read entity-header
1963  }
1964  Content-Length := length
1965  Remove "chunked" from Transfer-Encoding
1968   All HTTP/1.1 applications &MUST; be able to receive and decode the
1969   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1970   they do not understand.
1974<section title="Compression Codings" anchor="compression.codings">
1976   The codings defined below can be used to compress the payload of a
1977   message.
1980   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1981   is not desirable and is discouraged for future encodings. Their
1982   use here is representative of historical practice, not good
1983   design.
1986   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1987   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1988   equivalent to "gzip" and "compress" respectively.
1991<section title="Compress Coding" anchor="compress.coding">
1992<iref item="compress (Coding Format)"/>
1993<iref item="Coding Format" subitem="compress"/>
1995   The "compress" format is produced by the common UNIX file compression
1996   program "compress". This format is an adaptive Lempel-Ziv-Welch
1997   coding (LZW).
2001<section title="Deflate Coding" anchor="deflate.coding">
2002<iref item="deflate (Coding Format)"/>
2003<iref item="Coding Format" subitem="deflate"/>
2005   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
2006   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
2010<section title="Gzip Coding" anchor="gzip.coding">
2011<iref item="gzip (Coding Format)"/>
2012<iref item="Coding Format" subitem="gzip"/>
2014   The "gzip" format is produced by the file compression program
2015   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2016   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2022<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2024   The HTTP Transfer Coding Registry defines the name space for the transfer
2025   coding names.
2028   Registrations &MUST; include the following fields:
2029   <list style="symbols">
2030     <t>Name</t>
2031     <t>Description</t>
2032     <t>Pointer to specification text</t>
2033   </list>
2036   Values to be added to this name space require expert review and a specification
2037   (see "Expert Review" and "Specification Required" in
2038   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2039   conform to the purpose of transfer coding defined in this section.
2042   The registry itself is maintained at
2043   <eref target=""/>.
2048<section title="Product Tokens" anchor="product.tokens">
2049  <x:anchor-alias value="product"/>
2050  <x:anchor-alias value="product-version"/>
2052   Product tokens are used to allow communicating applications to
2053   identify themselves by software name and version. Most fields using
2054   product tokens also allow sub-products which form a significant part
2055   of the application to be listed, separated by whitespace. By
2056   convention, the products are listed in order of their significance
2057   for identifying the application.
2059<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2060  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2061  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2064   Examples:
2066<figure><artwork type="example">
2067  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2068  Server: Apache/0.8.4
2071   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2072   used for advertising or other non-essential information. Although any
2073   token character &MAY; appear in a product-version, this token &SHOULD;
2074   only be used for a version identifier (i.e., successive versions of
2075   the same product &SHOULD; only differ in the product-version portion of
2076   the product value).
2080<section title="Quality Values" anchor="quality.values">
2081  <x:anchor-alias value="qvalue"/>
2083   Both transfer codings (TE request header, <xref target="header.te"/>)
2084   and content negotiation (&content.negotiation;) use short "floating point"
2085   numbers to indicate the relative importance ("weight") of various
2086   negotiable parameters.  A weight is normalized to a real number in
2087   the range 0 through 1, where 0 is the minimum and 1 the maximum
2088   value. If a parameter has a quality value of 0, then content with
2089   this parameter is "not acceptable" for the client. HTTP/1.1
2090   applications &MUST-NOT; generate more than three digits after the
2091   decimal point. User configuration of these values &SHOULD; also be
2092   limited in this fashion.
2094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2095  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2096                 / ( "1" [ "." 0*3("0") ] )
2099  <t>
2100     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2101     relative degradation in desired quality.
2102  </t>
2108<section title="Connections" anchor="connections">
2110<section title="Persistent Connections" anchor="persistent.connections">
2112<section title="Purpose" anchor="persistent.purpose">
2114   Prior to persistent connections, a separate TCP connection was
2115   established to fetch each URL, increasing the load on HTTP servers
2116   and causing congestion on the Internet. The use of inline images and
2117   other associated data often requires a client to make multiple
2118   requests of the same server in a short amount of time. Analysis of
2119   these performance problems and results from a prototype
2120   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2121   measurements of actual HTTP/1.1 implementations show good
2122   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2123   T/TCP <xref target="Tou1998"/>.
2126   Persistent HTTP connections have a number of advantages:
2127  <list style="symbols">
2128      <t>
2129        By opening and closing fewer TCP connections, CPU time is saved
2130        in routers and hosts (clients, servers, proxies, gateways,
2131        tunnels, or caches), and memory used for TCP protocol control
2132        blocks can be saved in hosts.
2133      </t>
2134      <t>
2135        HTTP requests and responses can be pipelined on a connection.
2136        Pipelining allows a client to make multiple requests without
2137        waiting for each response, allowing a single TCP connection to
2138        be used much more efficiently, with much lower elapsed time.
2139      </t>
2140      <t>
2141        Network congestion is reduced by reducing the number of packets
2142        caused by TCP opens, and by allowing TCP sufficient time to
2143        determine the congestion state of the network.
2144      </t>
2145      <t>
2146        Latency on subsequent requests is reduced since there is no time
2147        spent in TCP's connection opening handshake.
2148      </t>
2149      <t>
2150        HTTP can evolve more gracefully, since errors can be reported
2151        without the penalty of closing the TCP connection. Clients using
2152        future versions of HTTP might optimistically try a new feature,
2153        but if communicating with an older server, retry with old
2154        semantics after an error is reported.
2155      </t>
2156    </list>
2159   HTTP implementations &SHOULD; implement persistent connections.
2163<section title="Overall Operation" anchor="persistent.overall">
2165   A significant difference between HTTP/1.1 and earlier versions of
2166   HTTP is that persistent connections are the default behavior of any
2167   HTTP connection. That is, unless otherwise indicated, the client
2168   &SHOULD; assume that the server will maintain a persistent connection,
2169   even after error responses from the server.
2172   Persistent connections provide a mechanism by which a client and a
2173   server can signal the close of a TCP connection. This signaling takes
2174   place using the Connection header field (<xref target="header.connection"/>). Once a close
2175   has been signaled, the client &MUST-NOT; send any more requests on that
2176   connection.
2179<section title="Negotiation" anchor="persistent.negotiation">
2181   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2182   maintain a persistent connection unless a Connection header including
2183   the connection-token "close" was sent in the request. If the server
2184   chooses to close the connection immediately after sending the
2185   response, it &SHOULD; send a Connection header including the
2186   connection-token "close".
2189   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2190   decide to keep it open based on whether the response from a server
2191   contains a Connection header with the connection-token close. In case
2192   the client does not want to maintain a connection for more than that
2193   request, it &SHOULD; send a Connection header including the
2194   connection-token close.
2197   If either the client or the server sends the close token in the
2198   Connection header, that request becomes the last one for the
2199   connection.
2202   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2203   maintained for HTTP versions less than 1.1 unless it is explicitly
2204   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2205   compatibility with HTTP/1.0 clients.
2208   In order to remain persistent, all messages on the connection &MUST;
2209   have a self-defined message length (i.e., one not defined by closure
2210   of the connection), as described in <xref target="message.length"/>.
2214<section title="Pipelining" anchor="pipelining">
2216   A client that supports persistent connections &MAY; "pipeline" its
2217   requests (i.e., send multiple requests without waiting for each
2218   response). A server &MUST; send its responses to those requests in the
2219   same order that the requests were received.
2222   Clients which assume persistent connections and pipeline immediately
2223   after connection establishment &SHOULD; be prepared to retry their
2224   connection if the first pipelined attempt fails. If a client does
2225   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2226   persistent. Clients &MUST; also be prepared to resend their requests if
2227   the server closes the connection before sending all of the
2228   corresponding responses.
2231   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2232   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2233   premature termination of the transport connection could lead to
2234   indeterminate results. A client wishing to send a non-idempotent
2235   request &SHOULD; wait to send that request until it has received the
2236   response status for the previous request.
2241<section title="Proxy Servers" anchor="persistent.proxy">
2243   It is especially important that proxies correctly implement the
2244   properties of the Connection header field as specified in <xref target="header.connection"/>.
2247   The proxy server &MUST; signal persistent connections separately with
2248   its clients and the origin servers (or other proxy servers) that it
2249   connects to. Each persistent connection applies to only one transport
2250   link.
2253   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2254   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2255   for information and discussion of the problems with the Keep-Alive header
2256   implemented by many HTTP/1.0 clients).
2259<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2261  <cref anchor="TODO-end-to-end" source="jre">
2262    Restored from <eref target=""/>.
2263    See also <eref target=""/>.
2264  </cref>
2267   For the purpose of defining the behavior of caches and non-caching
2268   proxies, we divide HTTP headers into two categories:
2269  <list style="symbols">
2270      <t>End-to-end headers, which are  transmitted to the ultimate
2271        recipient of a request or response. End-to-end headers in
2272        responses MUST be stored as part of a cache entry and &MUST; be
2273        transmitted in any response formed from a cache entry.</t>
2275      <t>Hop-by-hop headers, which are meaningful only for a single
2276        transport-level connection, and are not stored by caches or
2277        forwarded by proxies.</t>
2278  </list>
2281   The following HTTP/1.1 headers are hop-by-hop headers:
2282  <list style="symbols">
2283      <t>Connection</t>
2284      <t>Keep-Alive</t>
2285      <t>Proxy-Authenticate</t>
2286      <t>Proxy-Authorization</t>
2287      <t>TE</t>
2288      <t>Trailer</t>
2289      <t>Transfer-Encoding</t>
2290      <t>Upgrade</t>
2291  </list>
2294   All other headers defined by HTTP/1.1 are end-to-end headers.
2297   Other hop-by-hop headers &MUST; be listed in a Connection header
2298   (<xref target="header.connection"/>).
2302<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2304  <cref anchor="TODO-non-mod-headers" source="jre">
2305    Restored from <eref target=""/>.
2306    See also <eref target=""/>.
2307  </cref>
2310   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2311   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2312   modify an end-to-end header unless the definition of that header requires
2313   or specifically allows that.
2316   A transparent proxy &MUST-NOT; modify any of the following fields in a
2317   request or response, and it &MUST-NOT; add any of these fields if not
2318   already present:
2319  <list style="symbols">
2320      <t>Content-Location</t>
2321      <t>Content-MD5</t>
2322      <t>ETag</t>
2323      <t>Last-Modified</t>
2324  </list>
2327   A transparent proxy &MUST-NOT; modify any of the following fields in a
2328   response:
2329  <list style="symbols">
2330    <t>Expires</t>
2331  </list>
2334   but it &MAY; add any of these fields if not already present. If an
2335   Expires header is added, it &MUST; be given a field-value identical to
2336   that of the Date header in that response.
2339   A proxy &MUST-NOT; modify or add any of the following fields in a
2340   message that contains the no-transform cache-control directive, or in
2341   any request:
2342  <list style="symbols">
2343    <t>Content-Encoding</t>
2344    <t>Content-Range</t>
2345    <t>Content-Type</t>
2346  </list>
2349   A non-transparent proxy &MAY; modify or add these fields to a message
2350   that does not include no-transform, but if it does so, it &MUST; add a
2351   Warning 214 (Transformation applied) if one does not already appear
2352   in the message (see &header-warning;).
2355  <t>
2356    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2357    cause authentication failures if stronger authentication
2358    mechanisms are introduced in later versions of HTTP. Such
2359    authentication mechanisms &MAY; rely on the values of header fields
2360    not listed here.
2361  </t>
2364   The Content-Length field of a request or response is added or deleted
2365   according to the rules in <xref target="message.length"/>. A transparent proxy &MUST;
2366   preserve the entity-length (&entity-length;) of the entity-body,
2367   although it &MAY; change the transfer-length (<xref target="message.length"/>).
2373<section title="Practical Considerations" anchor="persistent.practical">
2375   Servers will usually have some time-out value beyond which they will
2376   no longer maintain an inactive connection. Proxy servers might make
2377   this a higher value since it is likely that the client will be making
2378   more connections through the same server. The use of persistent
2379   connections places no requirements on the length (or existence) of
2380   this time-out for either the client or the server.
2383   When a client or server wishes to time-out it &SHOULD; issue a graceful
2384   close on the transport connection. Clients and servers &SHOULD; both
2385   constantly watch for the other side of the transport close, and
2386   respond to it as appropriate. If a client or server does not detect
2387   the other side's close promptly it could cause unnecessary resource
2388   drain on the network.
2391   A client, server, or proxy &MAY; close the transport connection at any
2392   time. For example, a client might have started to send a new request
2393   at the same time that the server has decided to close the "idle"
2394   connection. From the server's point of view, the connection is being
2395   closed while it was idle, but from the client's point of view, a
2396   request is in progress.
2399   This means that clients, servers, and proxies &MUST; be able to recover
2400   from asynchronous close events. Client software &SHOULD; reopen the
2401   transport connection and retransmit the aborted sequence of requests
2402   without user interaction so long as the request sequence is
2403   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2404   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2405   human operator the choice of retrying the request(s). Confirmation by
2406   user-agent software with semantic understanding of the application
2407   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2408   be repeated if the second sequence of requests fails.
2411   Servers &SHOULD; always respond to at least one request per connection,
2412   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2413   middle of transmitting a response, unless a network or client failure
2414   is suspected.
2417   Clients (including proxies) &SHOULD; limit the number of simultaneous
2418   connections that they maintain to a given server (including proxies).
2421   Previous revisions of HTTP gave a specific number of connections as a
2422   ceiling, but this was found to be impractical for many applications. As a
2423   result, this specification does not mandate a particular maximum number of
2424   connections, but instead encourages clients to be conservative when opening
2425   multiple connections.
2428   In particular, while using multiple connections avoids the "head-of-line
2429   blocking" problem (whereby a request that takes significant server-side
2430   processing and/or has a large payload can block subsequent requests on the
2431   same connection), each connection used consumes server resources (sometimes
2432   significantly), and furthermore using multiple connections can cause
2433   undesirable side effects in congested networks.
2436   Note that servers might reject traffic that they deem abusive, including an
2437   excessive number of connections from a client.
2442<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2444<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2446   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2447   flow control mechanisms to resolve temporary overloads, rather than
2448   terminating connections with the expectation that clients will retry.
2449   The latter technique can exacerbate network congestion.
2453<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2455   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2456   the network connection for an error status while it is transmitting
2457   the request. If the client sees an error status, it &SHOULD;
2458   immediately cease transmitting the body. If the body is being sent
2459   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2460   empty trailer &MAY; be used to prematurely mark the end of the message.
2461   If the body was preceded by a Content-Length header, the client &MUST;
2462   close the connection.
2466<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2468   The purpose of the 100 (Continue) status (see &status-100;) is to
2469   allow a client that is sending a request message with a request body
2470   to determine if the origin server is willing to accept the request
2471   (based on the request headers) before the client sends the request
2472   body. In some cases, it might either be inappropriate or highly
2473   inefficient for the client to send the body if the server will reject
2474   the message without looking at the body.
2477   Requirements for HTTP/1.1 clients:
2478  <list style="symbols">
2479    <t>
2480        If a client will wait for a 100 (Continue) response before
2481        sending the request body, it &MUST; send an Expect request-header
2482        field (&header-expect;) with the "100-continue" expectation.
2483    </t>
2484    <t>
2485        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2486        with the "100-continue" expectation if it does not intend
2487        to send a request body.
2488    </t>
2489  </list>
2492   Because of the presence of older implementations, the protocol allows
2493   ambiguous situations in which a client may send "Expect: 100-continue"
2494   without receiving either a 417 (Expectation Failed) status
2495   or a 100 (Continue) status. Therefore, when a client sends this
2496   header field to an origin server (possibly via a proxy) from which it
2497   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2498   for an indefinite period before sending the request body.
2501   Requirements for HTTP/1.1 origin servers:
2502  <list style="symbols">
2503    <t> Upon receiving a request which includes an Expect request-header
2504        field with the "100-continue" expectation, an origin server &MUST;
2505        either respond with 100 (Continue) status and continue to read
2506        from the input stream, or respond with a final status code. The
2507        origin server &MUST-NOT; wait for the request body before sending
2508        the 100 (Continue) response. If it responds with a final status
2509        code, it &MAY; close the transport connection or it &MAY; continue
2510        to read and discard the rest of the request.  It &MUST-NOT;
2511        perform the requested method if it returns a final status code.
2512    </t>
2513    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2514        the request message does not include an Expect request-header
2515        field with the "100-continue" expectation, and &MUST-NOT; send a
2516        100 (Continue) response if such a request comes from an HTTP/1.0
2517        (or earlier) client. There is an exception to this rule: for
2518        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2519        status in response to an HTTP/1.1 PUT or POST request that does
2520        not include an Expect request-header field with the "100-continue"
2521        expectation. This exception, the purpose of which is
2522        to minimize any client processing delays associated with an
2523        undeclared wait for 100 (Continue) status, applies only to
2524        HTTP/1.1 requests, and not to requests with any other HTTP-version
2525        value.
2526    </t>
2527    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2528        already received some or all of the request body for the
2529        corresponding request.
2530    </t>
2531    <t> An origin server that sends a 100 (Continue) response &MUST;
2532    ultimately send a final status code, once the request body is
2533        received and processed, unless it terminates the transport
2534        connection prematurely.
2535    </t>
2536    <t> If an origin server receives a request that does not include an
2537        Expect request-header field with the "100-continue" expectation,
2538        the request includes a request body, and the server responds
2539        with a final status code before reading the entire request body
2540        from the transport connection, then the server &SHOULD-NOT;  close
2541        the transport connection until it has read the entire request,
2542        or until the client closes the connection. Otherwise, the client
2543        might not reliably receive the response message. However, this
2544        requirement is not be construed as preventing a server from
2545        defending itself against denial-of-service attacks, or from
2546        badly broken client implementations.
2547      </t>
2548    </list>
2551   Requirements for HTTP/1.1 proxies:
2552  <list style="symbols">
2553    <t> If a proxy receives a request that includes an Expect request-header
2554        field with the "100-continue" expectation, and the proxy
2555        either knows that the next-hop server complies with HTTP/1.1 or
2556        higher, or does not know the HTTP version of the next-hop
2557        server, it &MUST; forward the request, including the Expect header
2558        field.
2559    </t>
2560    <t> If the proxy knows that the version of the next-hop server is
2561        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2562        respond with a 417 (Expectation Failed) status.
2563    </t>
2564    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2565        numbers received from recently-referenced next-hop servers.
2566    </t>
2567    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2568        request message was received from an HTTP/1.0 (or earlier)
2569        client and did not include an Expect request-header field with
2570        the "100-continue" expectation. This requirement overrides the
2571        general rule for forwarding of 1xx responses (see &status-1xx;).
2572    </t>
2573  </list>
2577<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2579   If an HTTP/1.1 client sends a request which includes a request body,
2580   but which does not include an Expect request-header field with the
2581   "100-continue" expectation, and if the client is not directly
2582   connected to an HTTP/1.1 origin server, and if the client sees the
2583   connection close before receiving any status from the server, the
2584   client &SHOULD; retry the request.  If the client does retry this
2585   request, it &MAY; use the following "binary exponential backoff"
2586   algorithm to be assured of obtaining a reliable response:
2587  <list style="numbers">
2588    <t>
2589      Initiate a new connection to the server
2590    </t>
2591    <t>
2592      Transmit the request-headers
2593    </t>
2594    <t>
2595      Initialize a variable R to the estimated round-trip time to the
2596         server (e.g., based on the time it took to establish the
2597         connection), or to a constant value of 5 seconds if the round-trip
2598         time is not available.
2599    </t>
2600    <t>
2601       Compute T = R * (2**N), where N is the number of previous
2602         retries of this request.
2603    </t>
2604    <t>
2605       Wait either for an error response from the server, or for T
2606         seconds (whichever comes first)
2607    </t>
2608    <t>
2609       If no error response is received, after T seconds transmit the
2610         body of the request.
2611    </t>
2612    <t>
2613       If client sees that the connection is closed prematurely,
2614         repeat from step 1 until the request is accepted, an error
2615         response is received, or the user becomes impatient and
2616         terminates the retry process.
2617    </t>
2618  </list>
2621   If at any point an error status is received, the client
2622  <list style="symbols">
2623      <t>&SHOULD-NOT;  continue and</t>
2625      <t>&SHOULD; close the connection if it has not completed sending the
2626        request message.</t>
2627    </list>
2634<section title="Miscellaneous notes that may disappear" anchor="misc">
2635<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2637   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2641<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2643   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2647<section title="Interception of HTTP for access control" anchor="http.intercept">
2649   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2653<section title="Use of HTTP by other protocols" anchor="http.others">
2655   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2656   Extensions of HTTP like WebDAV.</cref>
2660<section title="Use of HTTP by media type specification" anchor="">
2662   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2667<section title="Header Field Definitions" anchor="header.field.definitions">
2669   This section defines the syntax and semantics of HTTP/1.1 header fields
2670   related to message framing and transport protocols.
2673   For entity-header fields, both sender and recipient refer to either the
2674   client or the server, depending on who sends and who receives the entity.
2677<section title="Connection" anchor="header.connection">
2678  <iref primary="true" item="Connection header" x:for-anchor=""/>
2679  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2680  <x:anchor-alias value="Connection"/>
2681  <x:anchor-alias value="connection-token"/>
2682  <x:anchor-alias value="Connection-v"/>
2684   The "Connection" general-header field allows the sender to specify
2685   options that are desired for that particular connection and &MUST-NOT;
2686   be communicated by proxies over further connections.
2689   The Connection header's value has the following grammar:
2691<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"/>
2692  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2693  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2694  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2697   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2698   message is forwarded and, for each connection-token in this field,
2699   remove any header field(s) from the message with the same name as the
2700   connection-token. Connection options are signaled by the presence of
2701   a connection-token in the Connection header field, not by any
2702   corresponding additional header field(s), since the additional header
2703   field may not be sent if there are no parameters associated with that
2704   connection option.
2707   Message headers listed in the Connection header &MUST-NOT; include
2708   end-to-end headers, such as Cache-Control.
2711   HTTP/1.1 defines the "close" connection option for the sender to
2712   signal that the connection will be closed after completion of the
2713   response. For example,
2715<figure><artwork type="example">
2716  Connection: close
2719   in either the request or the response header fields indicates that
2720   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2721   after the current request/response is complete.
2724   An HTTP/1.1 client that does not support persistent connections &MUST;
2725   include the "close" connection option in every request message.
2728   An HTTP/1.1 server that does not support persistent connections &MUST;
2729   include the "close" connection option in every response message that
2730   does not have a 1xx (Informational) status code.
2733   A system receiving an HTTP/1.0 (or lower-version) message that
2734   includes a Connection header &MUST;, for each connection-token in this
2735   field, remove and ignore any header field(s) from the message with
2736   the same name as the connection-token. This protects against mistaken
2737   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2741<section title="Content-Length" anchor="header.content-length">
2742  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2743  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2744  <x:anchor-alias value="Content-Length"/>
2745  <x:anchor-alias value="Content-Length-v"/>
2747   The "Content-Length" entity-header field indicates the size of the
2748   entity-body, in number of OCTETs. In the case of responses to the HEAD
2749   method, it indicates the size of the entity-body that would have been sent
2750   had the request been a GET.
2752<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2753  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2754  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2757   An example is
2759<figure><artwork type="example">
2760  Content-Length: 3495
2763   Applications &SHOULD; use this field to indicate the transfer-length of
2764   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2767   Any Content-Length greater than or equal to zero is a valid value.
2768   <xref target="message.length"/> describes how to determine the length of a message-body
2769   if a Content-Length is not given.
2772   Note that the meaning of this field is significantly different from
2773   the corresponding definition in MIME, where it is an optional field
2774   used within the "message/external-body" content-type. In HTTP, it
2775   &SHOULD; be sent whenever the message's length can be determined prior
2776   to being transferred, unless this is prohibited by the rules in
2777   <xref target="message.length"/>.
2781<section title="Date" anchor="">
2782  <iref primary="true" item="Date header" x:for-anchor=""/>
2783  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2784  <x:anchor-alias value="Date"/>
2785  <x:anchor-alias value="Date-v"/>
2787   The "Date" general-header field represents the date and time at which
2788   the message was originated, having the same semantics as the Origination
2789   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2790   The field value is an HTTP-date, as described in <xref target=""/>;
2791   it &MUST; be sent in rfc1123-date format.
2793<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2794  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2795  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2798   An example is
2800<figure><artwork type="example">
2801  Date: Tue, 15 Nov 1994 08:12:31 GMT
2804   Origin servers &MUST; include a Date header field in all responses,
2805   except in these cases:
2806  <list style="numbers">
2807      <t>If the response status code is 100 (Continue) or 101 (Switching
2808         Protocols), the response &MAY; include a Date header field, at
2809         the server's option.</t>
2811      <t>If the response status code conveys a server error, e.g., 500
2812         (Internal Server Error) or 503 (Service Unavailable), and it is
2813         inconvenient or impossible to generate a valid Date.</t>
2815      <t>If the server does not have a clock that can provide a
2816         reasonable approximation of the current time, its responses
2817         &MUST-NOT; include a Date header field. In this case, the rules
2818         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2819  </list>
2822   A received message that does not have a Date header field &MUST; be
2823   assigned one by the recipient if the message will be cached by that
2824   recipient or gatewayed via a protocol which requires a Date. An HTTP
2825   implementation without a clock &MUST-NOT; cache responses without
2826   revalidating them on every use. An HTTP cache, especially a shared
2827   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2828   clock with a reliable external standard.
2831   Clients &SHOULD; only send a Date header field in messages that include
2832   an entity-body, as in the case of the PUT and POST requests, and even
2833   then it is optional. A client without a clock &MUST-NOT; send a Date
2834   header field in a request.
2837   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2838   time subsequent to the generation of the message. It &SHOULD; represent
2839   the best available approximation of the date and time of message
2840   generation, unless the implementation has no means of generating a
2841   reasonably accurate date and time. In theory, the date ought to
2842   represent the moment just before the entity is generated. In
2843   practice, the date can be generated at any time during the message
2844   origination without affecting its semantic value.
2847<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2849   Some origin server implementations might not have a clock available.
2850   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2851   values to a response, unless these values were associated
2852   with the resource by a system or user with a reliable clock. It &MAY;
2853   assign an Expires value that is known, at or before server
2854   configuration time, to be in the past (this allows "pre-expiration"
2855   of responses without storing separate Expires values for each
2856   resource).
2861<section title="Host" anchor="">
2862  <iref primary="true" item="Host header" x:for-anchor=""/>
2863  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2864  <x:anchor-alias value="Host"/>
2865  <x:anchor-alias value="Host-v"/>
2867   The "Host" request-header field specifies the Internet host and port
2868   number of the resource being requested, allowing the origin server or
2869   gateway to differentiate between internally-ambiguous URLs, such as the root
2870   "/" URL of a server for multiple host names on a single IP address.
2873   The Host field value &MUST; represent the naming authority of the origin
2874   server or gateway given by the original URL obtained from the user or
2875   referring resource (generally an http URI, as described in
2876   <xref target="http.uri"/>).
2878<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2879  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2880  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2883   A "host" without any trailing port information implies the default
2884   port for the service requested (e.g., "80" for an HTTP URL). For
2885   example, a request on the origin server for
2886   &lt;; would properly include:
2888<figure><artwork type="example">
2889  GET /pub/WWW/ HTTP/1.1
2890  Host:
2893   A client &MUST; include a Host header field in all HTTP/1.1 request
2894   messages. If the requested URI does not include an Internet host
2895   name for the service being requested, then the Host header field &MUST;
2896   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2897   request message it forwards does contain an appropriate Host header
2898   field that identifies the service being requested by the proxy. All
2899   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2900   status code to any HTTP/1.1 request message which lacks a Host header
2901   field.
2904   See Sections <xref target="" format="counter"/>
2905   and <xref target="" format="counter"/>
2906   for other requirements relating to Host.
2910<section title="TE" anchor="header.te">
2911  <iref primary="true" item="TE header" x:for-anchor=""/>
2912  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2913  <x:anchor-alias value="TE"/>
2914  <x:anchor-alias value="TE-v"/>
2915  <x:anchor-alias value="t-codings"/>
2916  <x:anchor-alias value="te-params"/>
2917  <x:anchor-alias value="te-ext"/>
2919   The "TE" request-header field indicates what extension transfer-codings
2920   it is willing to accept in the response, and whether or not it is
2921   willing to accept trailer fields in a chunked transfer-coding.
2924   Its value may consist of the keyword "trailers" and/or a comma-separated
2925   list of extension transfer-coding names with optional accept
2926   parameters (as described in <xref target="transfer.codings"/>).
2928<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"/>
2929  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2930  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2931  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2932  <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> )
2933  <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> ) ]
2936   The presence of the keyword "trailers" indicates that the client is
2937   willing to accept trailer fields in a chunked transfer-coding, as
2938   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2939   transfer-coding values even though it does not itself represent a
2940   transfer-coding.
2943   Examples of its use are:
2945<figure><artwork type="example">
2946  TE: deflate
2947  TE:
2948  TE: trailers, deflate;q=0.5
2951   The TE header field only applies to the immediate connection.
2952   Therefore, the keyword &MUST; be supplied within a Connection header
2953   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2956   A server tests whether a transfer-coding is acceptable, according to
2957   a TE field, using these rules:
2958  <list style="numbers">
2959    <x:lt>
2960      <t>The "chunked" transfer-coding is always acceptable. If the
2961         keyword "trailers" is listed, the client indicates that it is
2962         willing to accept trailer fields in the chunked response on
2963         behalf of itself and any downstream clients. The implication is
2964         that, if given, the client is stating that either all
2965         downstream clients are willing to accept trailer fields in the
2966         forwarded response, or that it will attempt to buffer the
2967         response on behalf of downstream recipients.
2968      </t><t>
2969         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2970         chunked response such that a client can be assured of buffering
2971         the entire response.</t>
2972    </x:lt>
2973    <x:lt>
2974      <t>If the transfer-coding being tested is one of the transfer-codings
2975         listed in the TE field, then it is acceptable unless it
2976         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2977         qvalue of 0 means "not acceptable.")</t>
2978    </x:lt>
2979    <x:lt>
2980      <t>If multiple transfer-codings are acceptable, then the
2981         acceptable transfer-coding with the highest non-zero qvalue is
2982         preferred.  The "chunked" transfer-coding always has a qvalue
2983         of 1.</t>
2984    </x:lt>
2985  </list>
2988   If the TE field-value is empty or if no TE field is present, the only
2989   transfer-coding is "chunked". A message with no transfer-coding is
2990   always acceptable.
2994<section title="Trailer" anchor="header.trailer">
2995  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2996  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2997  <x:anchor-alias value="Trailer"/>
2998  <x:anchor-alias value="Trailer-v"/>
3000   The "Trailer" general-header field indicates that the given set of
3001   header fields is present in the trailer of a message encoded with
3002   chunked transfer-coding.
3004<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3005  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3006  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3009   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3010   message using chunked transfer-coding with a non-empty trailer. Doing
3011   so allows the recipient to know which header fields to expect in the
3012   trailer.
3015   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3016   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3017   trailer fields in a "chunked" transfer-coding.
3020   Message header fields listed in the Trailer header field &MUST-NOT;
3021   include the following header fields:
3022  <list style="symbols">
3023    <t>Transfer-Encoding</t>
3024    <t>Content-Length</t>
3025    <t>Trailer</t>
3026  </list>
3030<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3031  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3032  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3033  <x:anchor-alias value="Transfer-Encoding"/>
3034  <x:anchor-alias value="Transfer-Encoding-v"/>
3036   The "Transfer-Encoding" general-header field indicates what transfer-codings
3037   (if any) have been applied to the message body. It differs from
3038   Content-Encoding (&content-codings;) in that transfer-codings are a property
3039   of the message (and therefore are removed by intermediaries), whereas
3040   content-codings are not.
3042<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3043  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3044                        <x:ref>Transfer-Encoding-v</x:ref>
3045  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3048   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3050<figure><artwork type="example">
3051  Transfer-Encoding: chunked
3054   If multiple encodings have been applied to an entity, the transfer-codings
3055   &MUST; be listed in the order in which they were applied.
3056   Additional information about the encoding parameters &MAY; be provided
3057   by other entity-header fields not defined by this specification.
3060   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3061   header.
3065<section title="Upgrade" anchor="header.upgrade">
3066  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3067  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3068  <x:anchor-alias value="Upgrade"/>
3069  <x:anchor-alias value="Upgrade-v"/>
3071   The "Upgrade" general-header field allows the client to specify what
3072   additional communication protocols it would like to use, if the server
3073   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3074   header field within a 101 (Switching Protocols) response to indicate which
3075   protocol(s) are being switched to.
3077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3078  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3079  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3082   For example,
3084<figure><artwork type="example">
3085  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3088   The Upgrade header field is intended to provide a simple mechanism
3089   for transition from HTTP/1.1 to some other, incompatible protocol. It
3090   does so by allowing the client to advertise its desire to use another
3091   protocol, such as a later version of HTTP with a higher major version
3092   number, even though the current request has been made using HTTP/1.1.
3093   This eases the difficult transition between incompatible protocols by
3094   allowing the client to initiate a request in the more commonly
3095   supported protocol while indicating to the server that it would like
3096   to use a "better" protocol if available (where "better" is determined
3097   by the server, possibly according to the nature of the method and/or
3098   resource being requested).
3101   The Upgrade header field only applies to switching application-layer
3102   protocols upon the existing transport-layer connection. Upgrade
3103   cannot be used to insist on a protocol change; its acceptance and use
3104   by the server is optional. The capabilities and nature of the
3105   application-layer communication after the protocol change is entirely
3106   dependent upon the new protocol chosen, although the first action
3107   after changing the protocol &MUST; be a response to the initial HTTP
3108   request containing the Upgrade header field.
3111   The Upgrade header field only applies to the immediate connection.
3112   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3113   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3114   HTTP/1.1 message.
3117   The Upgrade header field cannot be used to indicate a switch to a
3118   protocol on a different connection. For that purpose, it is more
3119   appropriate to use a 301, 302, 303, or 305 redirection response.
3122   This specification only defines the protocol name "HTTP" for use by
3123   the family of Hypertext Transfer Protocols, as defined by the HTTP
3124   version rules of <xref target="http.version"/> and future updates to this
3125   specification. Additional tokens can be registered with IANA using the
3126   registration procedure defined below. 
3129<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3131   The HTTP Upgrade Token Registry defines the name space for product
3132   tokens used to identify protocols in the Upgrade header field.
3133   Each registered token should be associated with one or a set of
3134   specifications, and with contact information.
3137   Registrations should be allowed on a First Come First Served basis as
3138   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3139   specifications need not be IETF documents or be subject to IESG review, but
3140   should obey the following rules:
3141  <list style="numbers">
3142    <t>A token, once registered, stays registered forever.</t>
3143    <t>The registration &MUST; name a responsible party for the
3144       registration.</t>
3145    <t>The registration &MUST; name a point of contact.</t>
3146    <t>The registration &MAY; name the documentation required for the
3147       token.</t>
3148    <t>The responsible party &MAY; change the registration at any time.
3149       The IANA will keep a record of all such changes, and make them
3150       available upon request.</t>
3151    <t>The responsible party for the first registration of a "product"
3152       token &MUST; approve later registrations of a "version" token
3153       together with that "product" token before they can be registered.</t>
3154    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3155       for a token. This will normally only be used in the case when a
3156       responsible party cannot be contacted.</t>
3157  </list>
3160   It is not required that specifications for upgrade tokens be made
3161   publicly available, but the contact information for the registration
3162   should be.
3169<section title="Via" anchor="header.via">
3170  <iref primary="true" item="Via header" x:for-anchor=""/>
3171  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3172  <x:anchor-alias value="protocol-name"/>
3173  <x:anchor-alias value="protocol-version"/>
3174  <x:anchor-alias value="pseudonym"/>
3175  <x:anchor-alias value="received-by"/>
3176  <x:anchor-alias value="received-protocol"/>
3177  <x:anchor-alias value="Via"/>
3178  <x:anchor-alias value="Via-v"/>
3180   The "Via" general-header field &MUST; be used by gateways and proxies to
3181   indicate the intermediate protocols and recipients between the user
3182   agent and the server on requests, and between the origin server and
3183   the client on responses. It is analogous to the "Received" field defined in
3184   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3185   avoiding request loops, and identifying the protocol capabilities of
3186   all senders along the request/response chain.
3188<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"/>
3189  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3190  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3191                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3192  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3193  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3194  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3195  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3196  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3199   The received-protocol indicates the protocol version of the message
3200   received by the server or client along each segment of the
3201   request/response chain. The received-protocol version is appended to
3202   the Via field value when the message is forwarded so that information
3203   about the protocol capabilities of upstream applications remains
3204   visible to all recipients.
3207   The protocol-name is optional if and only if it would be "HTTP". The
3208   received-by field is normally the host and optional port number of a
3209   recipient server or client that subsequently forwarded the message.
3210   However, if the real host is considered to be sensitive information,
3211   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3212   be assumed to be the default port of the received-protocol.
3215   Multiple Via field values represent each proxy or gateway that has
3216   forwarded the message. Each recipient &MUST; append its information
3217   such that the end result is ordered according to the sequence of
3218   forwarding applications.
3221   Comments &MAY; be used in the Via header field to identify the software
3222   of the recipient proxy or gateway, analogous to the User-Agent and
3223   Server header fields. However, all comments in the Via field are
3224   optional and &MAY; be removed by any recipient prior to forwarding the
3225   message.
3228   For example, a request message could be sent from an HTTP/1.0 user
3229   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3230   forward the request to a public proxy at, which completes
3231   the request by forwarding it to the origin server at
3232   The request received by would then have the following
3233   Via header field:
3235<figure><artwork type="example">
3236  Via: 1.0 fred, 1.1 (Apache/1.1)
3239   Proxies and gateways used as a portal through a network firewall
3240   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3241   the firewall region. This information &SHOULD; only be propagated if
3242   explicitly enabled. If not enabled, the received-by host of any host
3243   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3244   for that host.
3247   For organizations that have strong privacy requirements for hiding
3248   internal structures, a proxy &MAY; combine an ordered subsequence of
3249   Via header field entries with identical received-protocol values into
3250   a single such entry. For example,
3252<figure><artwork type="example">
3253  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3256        could be collapsed to
3258<figure><artwork type="example">
3259  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3262   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3263   under the same organizational control and the hosts have already been
3264   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3265   have different received-protocol values.
3271<section title="IANA Considerations" anchor="IANA.considerations">
3273<section title="Message Header Registration" anchor="message.header.registration">
3275   The Message Header Registry located at <eref target=""/> should be updated
3276   with the permanent registrations below (see <xref target="RFC3864"/>):
3278<?BEGININC p1-messaging.iana-headers ?>
3279<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3280<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3281   <ttcol>Header Field Name</ttcol>
3282   <ttcol>Protocol</ttcol>
3283   <ttcol>Status</ttcol>
3284   <ttcol>Reference</ttcol>
3286   <c>Connection</c>
3287   <c>http</c>
3288   <c>standard</c>
3289   <c>
3290      <xref target="header.connection"/>
3291   </c>
3292   <c>Content-Length</c>
3293   <c>http</c>
3294   <c>standard</c>
3295   <c>
3296      <xref target="header.content-length"/>
3297   </c>
3298   <c>Date</c>
3299   <c>http</c>
3300   <c>standard</c>
3301   <c>
3302      <xref target=""/>
3303   </c>
3304   <c>Host</c>
3305   <c>http</c>
3306   <c>standard</c>
3307   <c>
3308      <xref target=""/>
3309   </c>
3310   <c>TE</c>
3311   <c>http</c>
3312   <c>standard</c>
3313   <c>
3314      <xref target="header.te"/>
3315   </c>
3316   <c>Trailer</c>
3317   <c>http</c>
3318   <c>standard</c>
3319   <c>
3320      <xref target="header.trailer"/>
3321   </c>
3322   <c>Transfer-Encoding</c>
3323   <c>http</c>
3324   <c>standard</c>
3325   <c>
3326      <xref target="header.transfer-encoding"/>
3327   </c>
3328   <c>Upgrade</c>
3329   <c>http</c>
3330   <c>standard</c>
3331   <c>
3332      <xref target="header.upgrade"/>
3333   </c>
3334   <c>Via</c>
3335   <c>http</c>
3336   <c>standard</c>
3337   <c>
3338      <xref target="header.via"/>
3339   </c>
3342<?ENDINC p1-messaging.iana-headers ?>
3344   The change controller is: "IETF ( - Internet Engineering Task Force".
3348<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3350   The entries for the "http" and "https" URI Schemes in the registry located at
3351   <eref target=""/>
3352   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3353   and <xref target="https.uri" format="counter"/> of this document
3354   (see <xref target="RFC4395"/>).
3358<section title="Internet Media Type Registrations" anchor="">
3360   This document serves as the specification for the Internet media types
3361   "message/http" and "application/http". The following is to be registered with
3362   IANA (see <xref target="RFC4288"/>).
3364<section title="Internet Media Type message/http" anchor="">
3365<iref item="Media Type" subitem="message/http" primary="true"/>
3366<iref item="message/http Media Type" primary="true"/>
3368   The message/http type can be used to enclose a single HTTP request or
3369   response message, provided that it obeys the MIME restrictions for all
3370   "message" types regarding line length and encodings.
3373  <list style="hanging" x:indent="12em">
3374    <t hangText="Type name:">
3375      message
3376    </t>
3377    <t hangText="Subtype name:">
3378      http
3379    </t>
3380    <t hangText="Required parameters:">
3381      none
3382    </t>
3383    <t hangText="Optional parameters:">
3384      version, msgtype
3385      <list style="hanging">
3386        <t hangText="version:">
3387          The HTTP-Version number of the enclosed message
3388          (e.g., "1.1"). If not present, the version can be
3389          determined from the first line of the body.
3390        </t>
3391        <t hangText="msgtype:">
3392          The message type -- "request" or "response". If not
3393          present, the type can be determined from the first
3394          line of the body.
3395        </t>
3396      </list>
3397    </t>
3398    <t hangText="Encoding considerations:">
3399      only "7bit", "8bit", or "binary" are permitted
3400    </t>
3401    <t hangText="Security considerations:">
3402      none
3403    </t>
3404    <t hangText="Interoperability considerations:">
3405      none
3406    </t>
3407    <t hangText="Published specification:">
3408      This specification (see <xref target=""/>).
3409    </t>
3410    <t hangText="Applications that use this media type:">
3411    </t>
3412    <t hangText="Additional information:">
3413      <list style="hanging">
3414        <t hangText="Magic number(s):">none</t>
3415        <t hangText="File extension(s):">none</t>
3416        <t hangText="Macintosh file type code(s):">none</t>
3417      </list>
3418    </t>
3419    <t hangText="Person and email address to contact for further information:">
3420      See Authors Section.
3421    </t>
3422    <t hangText="Intended usage:">
3423      COMMON
3424    </t>
3425    <t hangText="Restrictions on usage:">
3426      none
3427    </t>
3428    <t hangText="Author/Change controller:">
3429      IESG
3430    </t>
3431  </list>
3434<section title="Internet Media Type application/http" anchor="">
3435<iref item="Media Type" subitem="application/http" primary="true"/>
3436<iref item="application/http Media Type" primary="true"/>
3438   The application/http type can be used to enclose a pipeline of one or more
3439   HTTP request or response messages (not intermixed).
3442  <list style="hanging" x:indent="12em">
3443    <t hangText="Type name:">
3444      application
3445    </t>
3446    <t hangText="Subtype name:">
3447      http
3448    </t>
3449    <t hangText="Required parameters:">
3450      none
3451    </t>
3452    <t hangText="Optional parameters:">
3453      version, msgtype
3454      <list style="hanging">
3455        <t hangText="version:">
3456          The HTTP-Version number of the enclosed messages
3457          (e.g., "1.1"). If not present, the version can be
3458          determined from the first line of the body.
3459        </t>
3460        <t hangText="msgtype:">
3461          The message type -- "request" or "response". If not
3462          present, the type can be determined from the first
3463          line of the body.
3464        </t>
3465      </list>
3466    </t>
3467    <t hangText="Encoding considerations:">
3468      HTTP messages enclosed by this type
3469      are in "binary" format; use of an appropriate
3470      Content-Transfer-Encoding is required when
3471      transmitted via E-mail.
3472    </t>
3473    <t hangText="Security considerations:">
3474      none
3475    </t>
3476    <t hangText="Interoperability considerations:">
3477      none
3478    </t>
3479    <t hangText="Published specification:">
3480      This specification (see <xref target=""/>).
3481    </t>
3482    <t hangText="Applications that use this media type:">
3483    </t>
3484    <t hangText="Additional information:">
3485      <list style="hanging">
3486        <t hangText="Magic number(s):">none</t>
3487        <t hangText="File extension(s):">none</t>
3488        <t hangText="Macintosh file type code(s):">none</t>
3489      </list>
3490    </t>
3491    <t hangText="Person and email address to contact for further information:">
3492      See Authors Section.
3493    </t>
3494    <t hangText="Intended usage:">
3495      COMMON
3496    </t>
3497    <t hangText="Restrictions on usage:">
3498      none
3499    </t>
3500    <t hangText="Author/Change controller:">
3501      IESG
3502    </t>
3503  </list>
3508<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3510   The registration procedure for HTTP Transfer Codings is now defined by
3511   <xref target="transfer.coding.registry"/> of this document.
3514   The HTTP Transfer Codings Registry located at <eref target=""/>
3515   should be updated with the registrations below:
3517<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3518   <ttcol>Name</ttcol>
3519   <ttcol>Description</ttcol>
3520   <ttcol>Reference</ttcol>
3521   <c>chunked</c>
3522   <c>Transfer in a series of chunks</c>
3523   <c>
3524      <xref target="chunked.encoding"/>
3525   </c>
3526   <c>compress</c>
3527   <c>UNIX "compress" program method</c>
3528   <c>
3529      <xref target="compress.coding"/>
3530   </c>
3531   <c>deflate</c>
3532   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3533   <c>
3534      <xref target="deflate.coding"/>
3535   </c>
3536   <c>gzip</c>
3537   <c>Same as GNU zip <xref target="RFC1952"/></c>
3538   <c>
3539      <xref target="gzip.coding"/>
3540   </c>
3544<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3546   The registration procedure for HTTP Upgrade Tokens -- previously defined
3547   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3548   by <xref target="upgrade.token.registry"/> of this document.
3551   The HTTP Status Code Registry located at <eref target=""/>
3552   should be updated with the registration below:
3554<texttable align="left" suppress-title="true">
3555   <ttcol>Value</ttcol>
3556   <ttcol>Description</ttcol>
3557   <ttcol>Reference</ttcol>
3559   <c>HTTP</c>
3560   <c>Hypertext Transfer Protocol</c>
3561   <c><xref target="http.version"/> of this specification</c>
3562<!-- IANA should add this without our instructions; emailed on June 05, 2009
3563   <c>TLS/1.0</c>
3564   <c>Transport Layer Security</c>
3565   <c><xref target="RFC2817"/></c> -->
3572<section title="Security Considerations" anchor="security.considerations">
3574   This section is meant to inform application developers, information
3575   providers, and users of the security limitations in HTTP/1.1 as
3576   described by this document. The discussion does not include
3577   definitive solutions to the problems revealed, though it does make
3578   some suggestions for reducing security risks.
3581<section title="Personal Information" anchor="personal.information">
3583   HTTP clients are often privy to large amounts of personal information
3584   (e.g., the user's name, location, mail address, passwords, encryption
3585   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3586   leakage of this information.
3587   We very strongly recommend that a convenient interface be provided
3588   for the user to control dissemination of such information, and that
3589   designers and implementors be particularly careful in this area.
3590   History shows that errors in this area often create serious security
3591   and/or privacy problems and generate highly adverse publicity for the
3592   implementor's company.
3596<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3598   A server is in the position to save personal data about a user's
3599   requests which might identify their reading patterns or subjects of
3600   interest. This information is clearly confidential in nature and its
3601   handling can be constrained by law in certain countries. People using
3602   HTTP to provide data are responsible for ensuring that
3603   such material is not distributed without the permission of any
3604   individuals that are identifiable by the published results.
3608<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3610   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3611   the documents returned by HTTP requests to be only those that were
3612   intended by the server administrators. If an HTTP server translates
3613   HTTP URIs directly into file system calls, the server &MUST; take
3614   special care not to serve files that were not intended to be
3615   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3616   other operating systems use ".." as a path component to indicate a
3617   directory level above the current one. On such a system, an HTTP
3618   server &MUST; disallow any such construct in the request-target if it
3619   would otherwise allow access to a resource outside those intended to
3620   be accessible via the HTTP server. Similarly, files intended for
3621   reference only internally to the server (such as access control
3622   files, configuration files, and script code) &MUST; be protected from
3623   inappropriate retrieval, since they might contain sensitive
3624   information. Experience has shown that minor bugs in such HTTP server
3625   implementations have turned into security risks.
3629<section title="DNS Spoofing" anchor="dns.spoofing">
3631   Clients using HTTP rely heavily on the Domain Name Service, and are
3632   thus generally prone to security attacks based on the deliberate
3633   mis-association of IP addresses and DNS names. Clients need to be
3634   cautious in assuming the continuing validity of an IP number/DNS name
3635   association.
3638   In particular, HTTP clients &SHOULD; rely on their name resolver for
3639   confirmation of an IP number/DNS name association, rather than
3640   caching the result of previous host name lookups. Many platforms
3641   already can cache host name lookups locally when appropriate, and
3642   they &SHOULD; be configured to do so. It is proper for these lookups to
3643   be cached, however, only when the TTL (Time To Live) information
3644   reported by the name server makes it likely that the cached
3645   information will remain useful.
3648   If HTTP clients cache the results of host name lookups in order to
3649   achieve a performance improvement, they &MUST; observe the TTL
3650   information reported by DNS.
3653   If HTTP clients do not observe this rule, they could be spoofed when
3654   a previously-accessed server's IP address changes. As network
3655   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3656   possibility of this form of attack will grow. Observing this
3657   requirement thus reduces this potential security vulnerability.
3660   This requirement also improves the load-balancing behavior of clients
3661   for replicated servers using the same DNS name and reduces the
3662   likelihood of a user's experiencing failure in accessing sites which
3663   use that strategy.
3667<section title="Proxies and Caching" anchor="attack.proxies">
3669   By their very nature, HTTP proxies are men-in-the-middle, and
3670   represent an opportunity for man-in-the-middle attacks. Compromise of
3671   the systems on which the proxies run can result in serious security
3672   and privacy problems. Proxies have access to security-related
3673   information, personal information about individual users and
3674   organizations, and proprietary information belonging to users and
3675   content providers. A compromised proxy, or a proxy implemented or
3676   configured without regard to security and privacy considerations,
3677   might be used in the commission of a wide range of potential attacks.
3680   Proxy operators should protect the systems on which proxies run as
3681   they would protect any system that contains or transports sensitive
3682   information. In particular, log information gathered at proxies often
3683   contains highly sensitive personal information, and/or information
3684   about organizations. Log information should be carefully guarded, and
3685   appropriate guidelines for use should be developed and followed.
3686   (<xref target="abuse.of.server.log.information"/>).
3689   Proxy implementors should consider the privacy and security
3690   implications of their design and coding decisions, and of the
3691   configuration options they provide to proxy operators (especially the
3692   default configuration).
3695   Users of a proxy need to be aware that proxies are no trustworthier than
3696   the people who run them; HTTP itself cannot solve this problem.
3699   The judicious use of cryptography, when appropriate, may suffice to
3700   protect against a broad range of security and privacy attacks. Such
3701   cryptography is beyond the scope of the HTTP/1.1 specification.
3705<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3707   They exist. They are hard to defend against. Research continues.
3708   Beware.
3713<section title="Acknowledgments" anchor="ack">
3715   HTTP has evolved considerably over the years. It has
3716   benefited from a large and active developer community--the many
3717   people who have participated on the www-talk mailing list--and it is
3718   that community which has been most responsible for the success of
3719   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3720   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3721   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3722   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3723   VanHeyningen deserve special recognition for their efforts in
3724   defining early aspects of the protocol.
3727   This document has benefited greatly from the comments of all those
3728   participating in the HTTP-WG. In addition to those already mentioned,
3729   the following individuals have contributed to this specification:
3732   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3733   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3734   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3735   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3736   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3737   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3738   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3739   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3740   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3741   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3742   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3743   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3744   Josh Cohen.
3747   Thanks to the "cave men" of Palo Alto. You know who you are.
3750   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3751   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3752   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3753   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3754   Larry Masinter for their help. And thanks go particularly to Jeff
3755   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3758   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3759   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3760   discovery of many of the problems that this document attempts to
3761   rectify.
3764   This specification makes heavy use of the augmented BNF and generic
3765   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3766   reuses many of the definitions provided by Nathaniel Borenstein and
3767   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3768   specification will help reduce past confusion over the relationship
3769   between HTTP and Internet mail message formats.
3776<references title="Normative References">
3778<reference anchor="ISO-8859-1">
3779  <front>
3780    <title>
3781     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3782    </title>
3783    <author>
3784      <organization>International Organization for Standardization</organization>
3785    </author>
3786    <date year="1998"/>
3787  </front>
3788  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3791<reference anchor="Part2">
3792  <front>
3793    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3794    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3795      <organization abbrev="Day Software">Day Software</organization>
3796      <address><email></email></address>
3797    </author>
3798    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3799      <organization>One Laptop per Child</organization>
3800      <address><email></email></address>
3801    </author>
3802    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3803      <organization abbrev="HP">Hewlett-Packard Company</organization>
3804      <address><email></email></address>
3805    </author>
3806    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3807      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3808      <address><email></email></address>
3809    </author>
3810    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3811      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3812      <address><email></email></address>
3813    </author>
3814    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3815      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3816      <address><email></email></address>
3817    </author>
3818    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3819      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3820      <address><email></email></address>
3821    </author>
3822    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3823      <organization abbrev="W3C">World Wide Web Consortium</organization>
3824      <address><email></email></address>
3825    </author>
3826    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3827      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3828      <address><email></email></address>
3829    </author>
3830    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3831  </front>
3832  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3833  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3836<reference anchor="Part3">
3837  <front>
3838    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3839    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3840      <organization abbrev="Day Software">Day Software</organization>
3841      <address><email></email></address>
3842    </author>
3843    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3844      <organization>One Laptop per Child</organization>
3845      <address><email></email></address>
3846    </author>
3847    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3848      <organization abbrev="HP">Hewlett-Packard Company</organization>
3849      <address><email></email></address>
3850    </author>
3851    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3852      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3853      <address><email></email></address>
3854    </author>
3855    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3856      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3857      <address><email></email></address>
3858    </author>
3859    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3860      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3861      <address><email></email></address>
3862    </author>
3863    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3864      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3865      <address><email></email></address>
3866    </author>
3867    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3868      <organization abbrev="W3C">World Wide Web Consortium</organization>
3869      <address><email></email></address>
3870    </author>
3871    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3872      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3873      <address><email></email></address>
3874    </author>
3875    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3876  </front>
3877  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3878  <x:source href="p3-payload.xml" basename="p3-payload"/>
3881<reference anchor="Part5">
3882  <front>
3883    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3884    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3885      <organization abbrev="Day Software">Day Software</organization>
3886      <address><email></email></address>
3887    </author>
3888    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3889      <organization>One Laptop per Child</organization>
3890      <address><email></email></address>
3891    </author>
3892    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3893      <organization abbrev="HP">Hewlett-Packard Company</organization>
3894      <address><email></email></address>
3895    </author>
3896    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3897      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3898      <address><email></email></address>
3899    </author>
3900    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3901      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3902      <address><email></email></address>
3903    </author>
3904    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3905      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3906      <address><email></email></address>
3907    </author>
3908    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3909      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3910      <address><email></email></address>
3911    </author>
3912    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3913      <organization abbrev="W3C">World Wide Web Consortium</organization>
3914      <address><email></email></address>
3915    </author>
3916    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3917      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3918      <address><email></email></address>
3919    </author>
3920    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3921  </front>
3922  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3923  <x:source href="p5-range.xml" basename="p5-range"/>
3926<reference anchor="Part6">
3927  <front>
3928    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3929    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3930      <organization abbrev="Day Software">Day Software</organization>
3931      <address><email></email></address>
3932    </author>
3933    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3934      <organization>One Laptop per Child</organization>
3935      <address><email></email></address>
3936    </author>
3937    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3938      <organization abbrev="HP">Hewlett-Packard Company</organization>
3939      <address><email></email></address>
3940    </author>
3941    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3942      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3943      <address><email></email></address>
3944    </author>
3945    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3946      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3947      <address><email></email></address>
3948    </author>
3949    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3950      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3951      <address><email></email></address>
3952    </author>
3953    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3954      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3955      <address><email></email></address>
3956    </author>
3957    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3958      <organization abbrev="W3C">World Wide Web Consortium</organization>
3959      <address><email></email></address>
3960    </author>
3961    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3962      <address><email></email></address>
3963    </author>
3964    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3965      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3966      <address><email></email></address>
3967    </author>
3968    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3969  </front>
3970  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3971  <x:source href="p6-cache.xml" basename="p6-cache"/>
3974<reference anchor="RFC5234">
3975  <front>
3976    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3977    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3978      <organization>Brandenburg InternetWorking</organization>
3979      <address>
3980        <email></email>
3981      </address> 
3982    </author>
3983    <author initials="P." surname="Overell" fullname="Paul Overell">
3984      <organization>THUS plc.</organization>
3985      <address>
3986        <email></email>
3987      </address>
3988    </author>
3989    <date month="January" year="2008"/>
3990  </front>
3991  <seriesInfo name="STD" value="68"/>
3992  <seriesInfo name="RFC" value="5234"/>
3995<reference anchor="RFC2119">
3996  <front>
3997    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3998    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3999      <organization>Harvard University</organization>
4000      <address><email></email></address>
4001    </author>
4002    <date month="March" year="1997"/>
4003  </front>
4004  <seriesInfo name="BCP" value="14"/>
4005  <seriesInfo name="RFC" value="2119"/>
4008<reference anchor="RFC3986">
4009 <front>
4010  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4011  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4012    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4013    <address>
4014       <email></email>
4015       <uri></uri>
4016    </address>
4017  </author>
4018  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4019    <organization abbrev="Day Software">Day Software</organization>
4020    <address>
4021      <email></email>
4022      <uri></uri>
4023    </address>
4024  </author>
4025  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4026    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4027    <address>
4028      <email></email>
4029      <uri></uri>
4030    </address>
4031  </author>
4032  <date month='January' year='2005'></date>
4033 </front>
4034 <seriesInfo name="RFC" value="3986"/>
4035 <seriesInfo name="STD" value="66"/>
4038<reference anchor="USASCII">
4039  <front>
4040    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4041    <author>
4042      <organization>American National Standards Institute</organization>
4043    </author>
4044    <date year="1986"/>
4045  </front>
4046  <seriesInfo name="ANSI" value="X3.4"/>
4049<reference anchor="RFC1950">
4050  <front>
4051    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4052    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4053      <organization>Aladdin Enterprises</organization>
4054      <address><email></email></address>
4055    </author>
4056    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4057    <date month="May" year="1996"/>
4058  </front>
4059  <seriesInfo name="RFC" value="1950"/>
4060  <annotation>
4061    RFC 1950 is an Informational RFC, thus it may be less stable than
4062    this specification. On the other hand, this downward reference was
4063    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4064    therefore it is unlikely to cause problems in practice. See also
4065    <xref target="BCP97"/>.
4066  </annotation>
4069<reference anchor="RFC1951">
4070  <front>
4071    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4072    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4073      <organization>Aladdin Enterprises</organization>
4074      <address><email></email></address>
4075    </author>
4076    <date month="May" year="1996"/>
4077  </front>
4078  <seriesInfo name="RFC" value="1951"/>
4079  <annotation>
4080    RFC 1951 is an Informational RFC, thus it may be less stable than
4081    this specification. On the other hand, this downward reference was
4082    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4083    therefore it is unlikely to cause problems in practice. See also
4084    <xref target="BCP97"/>.
4085  </annotation>
4088<reference anchor="RFC1952">
4089  <front>
4090    <title>GZIP file format specification version 4.3</title>
4091    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4092      <organization>Aladdin Enterprises</organization>
4093      <address><email></email></address>
4094    </author>
4095    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4096      <address><email></email></address>
4097    </author>
4098    <author initials="M." surname="Adler" fullname="Mark Adler">
4099      <address><email></email></address>
4100    </author>
4101    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4102      <address><email></email></address>
4103    </author>
4104    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4105      <address><email></email></address>
4106    </author>
4107    <date month="May" year="1996"/>
4108  </front>
4109  <seriesInfo name="RFC" value="1952"/>
4110  <annotation>
4111    RFC 1952 is an Informational RFC, thus it may be less stable than
4112    this specification. On the other hand, this downward reference was
4113    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4114    therefore it is unlikely to cause problems in practice. See also
4115    <xref target="BCP97"/>.
4116  </annotation>
4121<references title="Informative References">
4123<reference anchor="Nie1997" target="">
4124  <front>
4125    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4126    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4127    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4128    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4129    <author initials="H." surname="Lie" fullname="H. Lie"/>
4130    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4131    <date year="1997" month="September"/>
4132  </front>
4133  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4136<reference anchor="Pad1995" target="">
4137  <front>
4138    <title>Improving HTTP Latency</title>
4139    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4140    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4141    <date year="1995" month="December"/>
4142  </front>
4143  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4146<reference anchor="RFC1123">
4147  <front>
4148    <title>Requirements for Internet Hosts - Application and Support</title>
4149    <author initials="R." surname="Braden" fullname="Robert Braden">
4150      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4151      <address><email>Braden@ISI.EDU</email></address>
4152    </author>
4153    <date month="October" year="1989"/>
4154  </front>
4155  <seriesInfo name="STD" value="3"/>
4156  <seriesInfo name="RFC" value="1123"/>
4159<reference anchor="RFC1305">
4160  <front>
4161    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4162    <author initials="D." surname="Mills" fullname="David L. Mills">
4163      <organization>University of Delaware, Electrical Engineering Department</organization>
4164      <address><email></email></address>
4165    </author>
4166    <date month="March" year="1992"/>
4167  </front>
4168  <seriesInfo name="RFC" value="1305"/>
4171<reference anchor="RFC1900">
4172  <front>
4173    <title>Renumbering Needs Work</title>
4174    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4175      <organization>CERN, Computing and Networks Division</organization>
4176      <address><email></email></address>
4177    </author>
4178    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4179      <organization>cisco Systems</organization>
4180      <address><email></email></address>
4181    </author>
4182    <date month="February" year="1996"/>
4183  </front>
4184  <seriesInfo name="RFC" value="1900"/>
4187<reference anchor="RFC1945">
4188  <front>
4189    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4190    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4191      <organization>MIT, Laboratory for Computer Science</organization>
4192      <address><email></email></address>
4193    </author>
4194    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4195      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4196      <address><email></email></address>
4197    </author>
4198    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4199      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4200      <address><email></email></address>
4201    </author>
4202    <date month="May" year="1996"/>
4203  </front>
4204  <seriesInfo name="RFC" value="1945"/>
4207<reference anchor="RFC2045">
4208  <front>
4209    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4210    <author initials="N." surname="Freed" fullname="Ned Freed">
4211      <organization>Innosoft International, Inc.</organization>
4212      <address><email></email></address>
4213    </author>
4214    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4215      <organization>First Virtual Holdings</organization>
4216      <address><email></email></address>
4217    </author>
4218    <date month="November" year="1996"/>
4219  </front>
4220  <seriesInfo name="RFC" value="2045"/>
4223<reference anchor="RFC2047">
4224  <front>
4225    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4226    <author initials="K." surname="Moore" fullname="Keith Moore">
4227      <organization>University of Tennessee</organization>
4228      <address><email></email></address>
4229    </author>
4230    <date month="November" year="1996"/>
4231  </front>
4232  <seriesInfo name="RFC" value="2047"/>
4235<reference anchor="RFC2068">
4236  <front>
4237    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4239      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4243      <organization>MIT Laboratory for Computer Science</organization>
4244      <address><email></email></address>
4245    </author>
4246    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4247      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4248      <address><email></email></address>
4249    </author>
4250    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4251      <organization>MIT Laboratory for Computer Science</organization>
4252      <address><email></email></address>
4253    </author>
4254    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4255      <organization>MIT Laboratory for Computer Science</organization>
4256      <address><email></email></address>
4257    </author>
4258    <date month="January" year="1997"/>
4259  </front>
4260  <seriesInfo name="RFC" value="2068"/>
4263<reference anchor='RFC2109'>
4264  <front>
4265    <title>HTTP State Management Mechanism</title>
4266    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4267      <organization>Bell Laboratories, Lucent Technologies</organization>
4268      <address><email></email></address>
4269    </author>
4270    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4271      <organization>Netscape Communications Corp.</organization>
4272      <address><email></email></address>
4273    </author>
4274    <date year='1997' month='February' />
4275  </front>
4276  <seriesInfo name='RFC' value='2109' />
4279<reference anchor="RFC2145">
4280  <front>
4281    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4282    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4283      <organization>Western Research Laboratory</organization>
4284      <address><email></email></address>
4285    </author>
4286    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4287      <organization>Department of Information and Computer Science</organization>
4288      <address><email></email></address>
4289    </author>
4290    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4291      <organization>MIT Laboratory for Computer Science</organization>
4292      <address><email></email></address>
4293    </author>
4294    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4295      <organization>W3 Consortium</organization>
4296      <address><email></email></address>
4297    </author>
4298    <date month="May" year="1997"/>
4299  </front>
4300  <seriesInfo name="RFC" value="2145"/>
4303<reference anchor="RFC2616">
4304  <front>
4305    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4306    <author initials="R." surname="Fielding" fullname="R. Fielding">
4307      <organization>University of California, Irvine</organization>
4308      <address><email></email></address>
4309    </author>
4310    <author initials="J." surname="Gettys" fullname="J. Gettys">
4311      <organization>W3C</organization>
4312      <address><email></email></address>
4313    </author>
4314    <author initials="J." surname="Mogul" fullname="J. Mogul">
4315      <organization>Compaq Computer Corporation</organization>
4316      <address><email></email></address>
4317    </author>
4318    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4319      <organization>MIT Laboratory for Computer Science</organization>
4320      <address><email></email></address>
4321    </author>
4322    <author initials="L." surname="Masinter" fullname="L. Masinter">
4323      <organization>Xerox Corporation</organization>
4324      <address><email></email></address>
4325    </author>
4326    <author initials="P." surname="Leach" fullname="P. Leach">
4327      <organization>Microsoft Corporation</organization>
4328      <address><email></email></address>
4329    </author>
4330    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4331      <organization>W3C</organization>
4332      <address><email></email></address>
4333    </author>
4334    <date month="June" year="1999"/>
4335  </front>
4336  <seriesInfo name="RFC" value="2616"/>
4339<reference anchor='RFC2817'>
4340  <front>
4341    <title>Upgrading to TLS Within HTTP/1.1</title>
4342    <author initials='R.' surname='Khare' fullname='R. Khare'>
4343      <organization>4K Associates / UC Irvine</organization>
4344      <address><email></email></address>
4345    </author>
4346    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4347      <organization>Agranat Systems, Inc.</organization>
4348      <address><email></email></address>
4349    </author>
4350    <date year='2000' month='May' />
4351  </front>
4352  <seriesInfo name='RFC' value='2817' />
4355<reference anchor='RFC2818'>
4356  <front>
4357    <title>HTTP Over TLS</title>
4358    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4359      <organization>RTFM, Inc.</organization>
4360      <address><email></email></address>
4361    </author>
4362    <date year='2000' month='May' />
4363  </front>
4364  <seriesInfo name='RFC' value='2818' />
4367<reference anchor='RFC2965'>
4368  <front>
4369    <title>HTTP State Management Mechanism</title>
4370    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4371      <organization>Bell Laboratories, Lucent Technologies</organization>
4372      <address><email></email></address>
4373    </author>
4374    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4375      <organization>, Inc.</organization>
4376      <address><email></email></address>
4377    </author>
4378    <date year='2000' month='October' />
4379  </front>
4380  <seriesInfo name='RFC' value='2965' />
4383<reference anchor='RFC3864'>
4384  <front>
4385    <title>Registration Procedures for Message Header Fields</title>
4386    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4387      <organization>Nine by Nine</organization>
4388      <address><email></email></address>
4389    </author>
4390    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4391      <organization>BEA Systems</organization>
4392      <address><email></email></address>
4393    </author>
4394    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4395      <organization>HP Labs</organization>
4396      <address><email></email></address>
4397    </author>
4398    <date year='2004' month='September' />
4399  </front>
4400  <seriesInfo name='BCP' value='90' />
4401  <seriesInfo name='RFC' value='3864' />
4404<reference anchor="RFC4288">
4405  <front>
4406    <title>Media Type Specifications and Registration Procedures</title>
4407    <author initials="N." surname="Freed" fullname="N. Freed">
4408      <organization>Sun Microsystems</organization>
4409      <address>
4410        <email></email>
4411      </address>
4412    </author>
4413    <author initials="J." surname="Klensin" fullname="J. Klensin">
4414      <address>
4415        <email></email>
4416      </address>
4417    </author>
4418    <date year="2005" month="December"/>
4419  </front>
4420  <seriesInfo name="BCP" value="13"/>
4421  <seriesInfo name="RFC" value="4288"/>
4424<reference anchor='RFC4395'>
4425  <front>
4426    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4427    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4428      <organization>AT&amp;T Laboratories</organization>
4429      <address>
4430        <email></email>
4431      </address>
4432    </author>
4433    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4434      <organization>Qualcomm, Inc.</organization>
4435      <address>
4436        <email></email>
4437      </address>
4438    </author>
4439    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4440      <organization>Adobe Systems</organization>
4441      <address>
4442        <email></email>
4443      </address>
4444    </author>
4445    <date year='2006' month='February' />
4446  </front>
4447  <seriesInfo name='BCP' value='115' />
4448  <seriesInfo name='RFC' value='4395' />
4451<reference anchor='RFC5226'>
4452  <front>
4453    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4454    <author initials='T.' surname='Narten' fullname='T. Narten'>
4455      <organization>IBM</organization>
4456      <address><email></email></address>
4457    </author>
4458    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4459      <organization>Google</organization>
4460      <address><email></email></address>
4461    </author>
4462    <date year='2008' month='May' />
4463  </front>
4464  <seriesInfo name='BCP' value='26' />
4465  <seriesInfo name='RFC' value='5226' />
4468<reference anchor="RFC5322">
4469  <front>
4470    <title>Internet Message Format</title>
4471    <author initials="P." surname="Resnick" fullname="P. Resnick">
4472      <organization>Qualcomm Incorporated</organization>
4473    </author>
4474    <date year="2008" month="October"/>
4475  </front>
4476  <seriesInfo name="RFC" value="5322"/>
4479<reference anchor='BCP97'>
4480  <front>
4481    <title>Handling Normative References to Standards-Track Documents</title>
4482    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4483      <address>
4484        <email></email>
4485      </address>
4486    </author>
4487    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4488      <organization>MIT</organization>
4489      <address>
4490        <email></email>
4491      </address>
4492    </author>
4493    <date year='2007' month='June' />
4494  </front>
4495  <seriesInfo name='BCP' value='97' />
4496  <seriesInfo name='RFC' value='4897' />
4499<reference anchor="Kri2001" target="">
4500  <front>
4501    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4502    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4503    <date year="2001" month="November"/>
4504  </front>
4505  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4508<reference anchor="Spe" target="">
4509  <front>
4510    <title>Analysis of HTTP Performance Problems</title>
4511    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4512    <date/>
4513  </front>
4516<reference anchor="Tou1998" target="">
4517  <front>
4518  <title>Analysis of HTTP Performance</title>
4519  <author initials="J." surname="Touch" fullname="Joe Touch">
4520    <organization>USC/Information Sciences Institute</organization>
4521    <address><email></email></address>
4522  </author>
4523  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4524    <organization>USC/Information Sciences Institute</organization>
4525    <address><email></email></address>
4526  </author>
4527  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4528    <organization>USC/Information Sciences Institute</organization>
4529    <address><email></email></address>
4530  </author>
4531  <date year="1998" month="Aug"/>
4532  </front>
4533  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4534  <annotation>(original report dated Aug. 1996)</annotation>
4540<section title="Tolerant Applications" anchor="tolerant.applications">
4542   Although this document specifies the requirements for the generation
4543   of HTTP/1.1 messages, not all applications will be correct in their
4544   implementation. We therefore recommend that operational applications
4545   be tolerant of deviations whenever those deviations can be
4546   interpreted unambiguously.
4549   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4550   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4551   &SHOULD; accept any amount of WSP characters between fields, even though
4552   only a single SP is required.
4555   The line terminator for header fields is the sequence CRLF.
4556   However, we recommend that applications, when parsing such headers,
4557   recognize a single LF as a line terminator and ignore the leading CR.
4560   The character set of an entity-body &SHOULD; be labeled as the lowest
4561   common denominator of the character codes used within that body, with
4562   the exception that not labeling the entity is preferred over labeling
4563   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4566   Additional rules for requirements on parsing and encoding of dates
4567   and other potential problems with date encodings include:
4570  <list style="symbols">
4571     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4572        which appears to be more than 50 years in the future is in fact
4573        in the past (this helps solve the "year 2000" problem).</t>
4575     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4576        Expires date as earlier than the proper value, but &MUST-NOT;
4577        internally represent a parsed Expires date as later than the
4578        proper value.</t>
4580     <t>All expiration-related calculations &MUST; be done in GMT. The
4581        local time zone &MUST-NOT; influence the calculation or comparison
4582        of an age or expiration time.</t>
4584     <t>If an HTTP header incorrectly carries a date value with a time
4585        zone other than GMT, it &MUST; be converted into GMT using the
4586        most conservative possible conversion.</t>
4587  </list>
4591<section title="Compatibility with Previous Versions" anchor="compatibility">
4593   HTTP has been in use by the World-Wide Web global information initiative
4594   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4595   was a simple protocol for hypertext data transfer across the Internet
4596   with only a single method and no metadata.
4597   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4598   methods and MIME-like messaging that could include metadata about the data
4599   transferred and modifiers on the request/response semantics. However,
4600   HTTP/1.0 did not sufficiently take into consideration the effects of
4601   hierarchical proxies, caching, the need for persistent connections, or
4602   name-based virtual hosts. The proliferation of incompletely-implemented
4603   applications calling themselves "HTTP/1.0" further necessitated a
4604   protocol version change in order for two communicating applications
4605   to determine each other's true capabilities.
4608   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4609   requirements that enable reliable implementations, adding only
4610   those new features that will either be safely ignored by an HTTP/1.0
4611   recipient or only sent when communicating with a party advertising
4612   compliance with HTTP/1.1.
4615   It is beyond the scope of a protocol specification to mandate
4616   compliance with previous versions. HTTP/1.1 was deliberately
4617   designed, however, to make supporting previous versions easy. It is
4618   worth noting that, at the time of composing this specification, we would
4619   expect general-purpose HTTP/1.1 servers to:
4620  <list style="symbols">
4621     <t>understand any valid request in the format of HTTP/1.0 and
4622        1.1;</t>
4624     <t>respond appropriately with a message in the same major version
4625        used by the client.</t>
4626  </list>
4629   And we would expect HTTP/1.1 clients to:
4630  <list style="symbols">
4631     <t>understand any valid response in the format of HTTP/1.0 or
4632        1.1.</t>
4633  </list>
4636   For most implementations of HTTP/1.0, each connection is established
4637   by the client prior to the request and closed by the server after
4638   sending the response. Some implementations implement the Keep-Alive
4639   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4642<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4644   This section summarizes major differences between versions HTTP/1.0
4645   and HTTP/1.1.
4648<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4650   The requirements that clients and servers support the Host request-header,
4651   report an error if the Host request-header (<xref target=""/>) is
4652   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4653   are among the most important changes defined by this
4654   specification.
4657   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4658   addresses and servers; there was no other established mechanism for
4659   distinguishing the intended server of a request than the IP address
4660   to which that request was directed. The changes outlined above will
4661   allow the Internet, once older HTTP clients are no longer common, to
4662   support multiple Web sites from a single IP address, greatly
4663   simplifying large operational Web servers, where allocation of many
4664   IP addresses to a single host has created serious problems. The
4665   Internet will also be able to recover the IP addresses that have been
4666   allocated for the sole purpose of allowing special-purpose domain
4667   names to be used in root-level HTTP URLs. Given the rate of growth of
4668   the Web, and the number of servers already deployed, it is extremely
4669   important that all implementations of HTTP (including updates to
4670   existing HTTP/1.0 applications) correctly implement these
4671   requirements:
4672  <list style="symbols">
4673     <t>Both clients and servers &MUST; support the Host request-header.</t>
4675     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4677     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4678        request does not include a Host request-header.</t>
4680     <t>Servers &MUST; accept absolute URIs.</t>
4681  </list>
4686<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4688   Some clients and servers might wish to be compatible with some
4689   previous implementations of persistent connections in HTTP/1.0
4690   clients and servers. Persistent connections in HTTP/1.0 are
4691   explicitly negotiated as they are not the default behavior. HTTP/1.0
4692   experimental implementations of persistent connections are faulty,
4693   and the new facilities in HTTP/1.1 are designed to rectify these
4694   problems. The problem was that some existing HTTP/1.0 clients may be
4695   sending Keep-Alive to a proxy server that doesn't understand
4696   Connection, which would then erroneously forward it to the next
4697   inbound server, which would establish the Keep-Alive connection and
4698   result in a hung HTTP/1.0 proxy waiting for the close on the
4699   response. The result is that HTTP/1.0 clients must be prevented from
4700   using Keep-Alive when talking to proxies.
4703   However, talking to proxies is the most important use of persistent
4704   connections, so that prohibition is clearly unacceptable. Therefore,
4705   we need some other mechanism for indicating a persistent connection
4706   is desired, which is safe to use even when talking to an old proxy
4707   that ignores Connection. Persistent connections are the default for
4708   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4709   declaring non-persistence. See <xref target="header.connection"/>.
4712   The original HTTP/1.0 form of persistent connections (the Connection:
4713   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4717<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4719   This specification has been carefully audited to correct and
4720   disambiguate key word usage; RFC 2068 had many problems in respect to
4721   the conventions laid out in <xref target="RFC2119"/>.
4724   Transfer-coding and message lengths all interact in ways that
4725   required fixing exactly when chunked encoding is used (to allow for
4726   transfer encoding that may not be self delimiting); it was important
4727   to straighten out exactly how message lengths are computed. (Sections
4728   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4729   <xref target="header.content-length" format="counter"/>,
4730   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4733   The use and interpretation of HTTP version numbers has been clarified
4734   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4735   version they support to deal with problems discovered in HTTP/1.0
4736   implementations (<xref target="http.version"/>)
4739   Quality Values of zero should indicate that "I don't want something"
4740   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4743   Transfer-coding had significant problems, particularly with
4744   interactions with chunked encoding. The solution is that transfer-codings
4745   become as full fledged as content-codings. This involves
4746   adding an IANA registry for transfer-codings (separate from content
4747   codings), a new header field (TE) and enabling trailer headers in the
4748   future. Transfer encoding is a major performance benefit, so it was
4749   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4750   interoperability problem that could have occurred due to interactions
4751   between authentication trailers, chunked encoding and HTTP/1.0
4752   clients.(Section
4753   <xref target="transfer.codings" format="counter"/>,
4754   <xref target="chunked.encoding" format="counter"/>,
4755   <xref target="non-modifiable.headers" format="counter"/>,
4756   and <xref target="header.te" format="counter"/>)
4759  Proxies should be able to add Content-Length when appropriate.
4760  (<xref target="non-modifiable.headers"/>)
4764<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4766  Empty list elements in list productions have been deprecated.
4767  (<xref target="notation.abnf"/>)
4770  Rules about implicit linear whitespace between certain grammar productions
4771  have been removed; now it's only allowed when specifically pointed out
4772  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4773  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4774  Non-ASCII content in header fields and reason phrase has been obsoleted and
4775  made opaque (the TEXT rule was removed)
4776  (<xref target="basic.rules"/>)
4779  Clarify that HTTP-Version is case sensitive.
4780  (<xref target="http.version"/>)
4783  Remove reference to non-existent identity transfer-coding value tokens.
4784  (Sections <xref format="counter" target="transfer.codings"/> and
4785  <xref format="counter" target="message.length"/>)
4788  Require that invalid whitespace around field-names be rejected.
4789  (<xref target="header.fields"/>)
4792  Update use of abs_path production from RFC1808 to the path-absolute + query
4793  components of RFC3986.
4794  (<xref target="request-target"/>)
4797  Clarification that the chunk length does not include the count of the octets
4798  in the chunk header and trailer. Furthermore disallowed line folding
4799  in chunk extensions.
4800  (<xref target="chunked.encoding"/>)
4803  Remove hard limit of two connections per server.
4804  (<xref target="persistent.practical"/>)
4807  Clarify exactly when close connection options must be sent.
4808  (<xref target="header.connection"/>)
4813<?BEGININC p1-messaging.abnf-appendix ?>
4814<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4816<artwork type="abnf" name="p1-messaging.parsed-abnf">
4817<x:ref>BWS</x:ref> = OWS
4819<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4820<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4821<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4822<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4823 connection-token ] )
4824<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4825<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4827<x:ref>Date</x:ref> = "Date:" OWS Date-v
4828<x:ref>Date-v</x:ref> = HTTP-date
4830<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4832<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4833<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4834<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4835<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4836 ]
4837<x:ref>Host</x:ref> = "Host:" OWS Host-v
4838<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4840<x:ref>Method</x:ref> = token
4842<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4844<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4846<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4847<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4848<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4849 entity-header ) CRLF ) CRLF [ message-body ]
4850<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4851<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4852 entity-header ) CRLF ) CRLF [ message-body ]
4854<x:ref>Status-Code</x:ref> = 3DIGIT
4855<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4857<x:ref>TE</x:ref> = "TE:" OWS TE-v
4858<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4859<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4860<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4861<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4862<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4863 transfer-coding ] )
4865<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4866<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4867<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4869<x:ref>Via</x:ref> = "Via:" OWS Via-v
4870<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4871 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4872 ] )
4874<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4876<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4877<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4878<x:ref>attribute</x:ref> = token
4879<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4881<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4882<x:ref>chunk-data</x:ref> = 1*OCTET
4883<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4884<x:ref>chunk-ext-name</x:ref> = token
4885<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4886<x:ref>chunk-size</x:ref> = 1*HEXDIG
4887<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4888<x:ref>connection-token</x:ref> = token
4889<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4890 / %x2A-5B ; '*'-'['
4891 / %x5D-7E ; ']'-'~'
4892 / obs-text
4894<x:ref>date1</x:ref> = day SP month SP year
4895<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4896<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4897<x:ref>day</x:ref> = 2DIGIT
4898<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4899 / %x54.75.65 ; Tue
4900 / %x57.65.64 ; Wed
4901 / %x54.68.75 ; Thu
4902 / %x46.72.69 ; Fri
4903 / %x53.61.74 ; Sat
4904 / %x53.75.6E ; Sun
4905<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4906 / %x54. ; Tuesday
4907 / %x57.65.64.6E. ; Wednesday
4908 / %x54. ; Thursday
4909 / %x46. ; Friday
4910 / %x53. ; Saturday
4911 / %x53.75.6E.64.61.79 ; Sunday
4913<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4914<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4916<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4917<x:ref>field-name</x:ref> = token
4918<x:ref>field-value</x:ref> = *( field-content / OWS )
4920<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4921 / Transfer-Encoding / Upgrade / Via / Warning
4923<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4924<x:ref>hour</x:ref> = 2DIGIT
4925<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4926<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4928<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4930<x:ref>message-body</x:ref> = entity-body /
4931 &lt;entity-body encoded as per Transfer-Encoding&gt;
4932<x:ref>minute</x:ref> = 2DIGIT
4933<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4934 / %x46.65.62 ; Feb
4935 / %x4D.61.72 ; Mar
4936 / %x41.70.72 ; Apr
4937 / %x4D.61.79 ; May
4938 / %x4A.75.6E ; Jun
4939 / %x4A.75.6C ; Jul
4940 / %x41.75.67 ; Aug
4941 / %x53.65.70 ; Sep
4942 / %x4F.63.74 ; Oct
4943 / %x4E.6F.76 ; Nov
4944 / %x44.65.63 ; Dec
4946<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4947<x:ref>obs-fold</x:ref> = CRLF
4948<x:ref>obs-text</x:ref> = %x80-FF
4950<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4951<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4952<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4953<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4954<x:ref>product</x:ref> = token [ "/" product-version ]
4955<x:ref>product-version</x:ref> = token
4956<x:ref>protocol-name</x:ref> = token
4957<x:ref>protocol-version</x:ref> = token
4958<x:ref>pseudonym</x:ref> = token
4960<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4961 / %x5D-7E ; ']'-'~'
4962 / obs-text
4963<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
4964 / %x5D-7E ; ']'-'~'
4965 / obs-text
4966<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4967<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4968<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4969<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4970<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4971<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4973<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4974<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4975<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4976<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4977<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4978 / authority
4979<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4980<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4981<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4983<x:ref>second</x:ref> = 2DIGIT
4984<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4985 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4986<x:ref>start-line</x:ref> = Request-Line / Status-Line
4988<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4989<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4990 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4991<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4992<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4993<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4994<x:ref>token</x:ref> = 1*tchar
4995<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4996<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
4997 transfer-extension
4998<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4999<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5001<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5003<x:ref>value</x:ref> = token / quoted-string
5005<x:ref>year</x:ref> = 4DIGIT
5008<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5009; Chunked-Body defined but not used
5010; Content-Length defined but not used
5011; HTTP-message defined but not used
5012; Host defined but not used
5013; Request defined but not used
5014; Response defined but not used
5015; TE defined but not used
5016; URI-reference defined but not used
5017; http-URI defined but not used
5018; https-URI defined but not used
5019; partial-URI defined but not used
5020; special defined but not used
5022<?ENDINC p1-messaging.abnf-appendix ?>
5024<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5026<section title="Since RFC2616">
5028  Extracted relevant partitions from <xref target="RFC2616"/>.
5032<section title="Since draft-ietf-httpbis-p1-messaging-00">
5034  Closed issues:
5035  <list style="symbols">
5036    <t>
5037      <eref target=""/>:
5038      "HTTP Version should be case sensitive"
5039      (<eref target=""/>)
5040    </t>
5041    <t>
5042      <eref target=""/>:
5043      "'unsafe' characters"
5044      (<eref target=""/>)
5045    </t>
5046    <t>
5047      <eref target=""/>:
5048      "Chunk Size Definition"
5049      (<eref target=""/>)
5050    </t>
5051    <t>
5052      <eref target=""/>:
5053      "Message Length"
5054      (<eref target=""/>)
5055    </t>
5056    <t>
5057      <eref target=""/>:
5058      "Media Type Registrations"
5059      (<eref target=""/>)
5060    </t>
5061    <t>
5062      <eref target=""/>:
5063      "URI includes query"
5064      (<eref target=""/>)
5065    </t>
5066    <t>
5067      <eref target=""/>:
5068      "No close on 1xx responses"
5069      (<eref target=""/>)
5070    </t>
5071    <t>
5072      <eref target=""/>:
5073      "Remove 'identity' token references"
5074      (<eref target=""/>)
5075    </t>
5076    <t>
5077      <eref target=""/>:
5078      "Import query BNF"
5079    </t>
5080    <t>
5081      <eref target=""/>:
5082      "qdtext BNF"
5083    </t>
5084    <t>
5085      <eref target=""/>:
5086      "Normative and Informative references"
5087    </t>
5088    <t>
5089      <eref target=""/>:
5090      "RFC2606 Compliance"
5091    </t>
5092    <t>
5093      <eref target=""/>:
5094      "RFC977 reference"
5095    </t>
5096    <t>
5097      <eref target=""/>:
5098      "RFC1700 references"
5099    </t>
5100    <t>
5101      <eref target=""/>:
5102      "inconsistency in date format explanation"
5103    </t>
5104    <t>
5105      <eref target=""/>:
5106      "Date reference typo"
5107    </t>
5108    <t>
5109      <eref target=""/>:
5110      "Informative references"
5111    </t>
5112    <t>
5113      <eref target=""/>:
5114      "ISO-8859-1 Reference"
5115    </t>
5116    <t>
5117      <eref target=""/>:
5118      "Normative up-to-date references"
5119    </t>
5120  </list>
5123  Other changes:
5124  <list style="symbols">
5125    <t>
5126      Update media type registrations to use RFC4288 template.
5127    </t>
5128    <t>
5129      Use names of RFC4234 core rules DQUOTE and WSP,
5130      fix broken ABNF for chunk-data
5131      (work in progress on <eref target=""/>)
5132    </t>
5133  </list>
5137<section title="Since draft-ietf-httpbis-p1-messaging-01">
5139  Closed issues:
5140  <list style="symbols">
5141    <t>
5142      <eref target=""/>:
5143      "Bodies on GET (and other) requests"
5144    </t>
5145    <t>
5146      <eref target=""/>:
5147      "Updating to RFC4288"
5148    </t>
5149    <t>
5150      <eref target=""/>:
5151      "Status Code and Reason Phrase"
5152    </t>
5153    <t>
5154      <eref target=""/>:
5155      "rel_path not used"
5156    </t>
5157  </list>
5160  Ongoing work on ABNF conversion (<eref target=""/>):
5161  <list style="symbols">
5162    <t>
5163      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5164      "trailer-part").
5165    </t>
5166    <t>
5167      Avoid underscore character in rule names ("http_URL" ->
5168      "http-URL", "abs_path" -> "path-absolute").
5169    </t>
5170    <t>
5171      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5172      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5173      have to be updated when switching over to RFC3986.
5174    </t>
5175    <t>
5176      Synchronize core rules with RFC5234.
5177    </t>
5178    <t>
5179      Get rid of prose rules that span multiple lines.
5180    </t>
5181    <t>
5182      Get rid of unused rules LOALPHA and UPALPHA.
5183    </t>
5184    <t>
5185      Move "Product Tokens" section (back) into Part 1, as "token" is used
5186      in the definition of the Upgrade header.
5187    </t>
5188    <t>
5189      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5190    </t>
5191    <t>
5192      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5193    </t>
5194  </list>
5198<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5200  Closed issues:
5201  <list style="symbols">
5202    <t>
5203      <eref target=""/>:
5204      "HTTP-date vs. rfc1123-date"
5205    </t>
5206    <t>
5207      <eref target=""/>:
5208      "WS in quoted-pair"
5209    </t>
5210  </list>
5213  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5214  <list style="symbols">
5215    <t>
5216      Reference RFC 3984, and update header registrations for headers defined
5217      in this document.
5218    </t>
5219  </list>
5222  Ongoing work on ABNF conversion (<eref target=""/>):
5223  <list style="symbols">
5224    <t>
5225      Replace string literals when the string really is case-sensitive (HTTP-Version).
5226    </t>
5227  </list>
5231<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5233  Closed issues:
5234  <list style="symbols">
5235    <t>
5236      <eref target=""/>:
5237      "Connection closing"
5238    </t>
5239    <t>
5240      <eref target=""/>:
5241      "Move registrations and registry information to IANA Considerations"
5242    </t>
5243    <t>
5244      <eref target=""/>:
5245      "need new URL for PAD1995 reference"
5246    </t>
5247    <t>
5248      <eref target=""/>:
5249      "IANA Considerations: update HTTP URI scheme registration"
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "Cite HTTPS URI scheme definition"
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "List-type headers vs Set-Cookie"
5258    </t>
5259  </list>
5262  Ongoing work on ABNF conversion (<eref target=""/>):
5263  <list style="symbols">
5264    <t>
5265      Replace string literals when the string really is case-sensitive (HTTP-Date).
5266    </t>
5267    <t>
5268      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5269    </t>
5270  </list>
5274<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5276  Closed issues:
5277  <list style="symbols">
5278    <t>
5279      <eref target=""/>:
5280      "Out-of-date reference for URIs"
5281    </t>
5282    <t>
5283      <eref target=""/>:
5284      "RFC 2822 is updated by RFC 5322"
5285    </t>
5286  </list>
5289  Ongoing work on ABNF conversion (<eref target=""/>):
5290  <list style="symbols">
5291    <t>
5292      Use "/" instead of "|" for alternatives.
5293    </t>
5294    <t>
5295      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5296    </t>
5297    <t>
5298      Only reference RFC 5234's core rules.
5299    </t>
5300    <t>
5301      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5302      whitespace ("OWS") and required whitespace ("RWS").
5303    </t>
5304    <t>
5305      Rewrite ABNFs to spell out whitespace rules, factor out
5306      header value format definitions.
5307    </t>
5308  </list>
5312<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5314  Closed issues:
5315  <list style="symbols">
5316    <t>
5317      <eref target=""/>:
5318      "Header LWS"
5319    </t>
5320    <t>
5321      <eref target=""/>:
5322      "Sort 1.3 Terminology"
5323    </t>
5324    <t>
5325      <eref target=""/>:
5326      "RFC2047 encoded words"
5327    </t>
5328    <t>
5329      <eref target=""/>:
5330      "Character Encodings in TEXT"
5331    </t>
5332    <t>
5333      <eref target=""/>:
5334      "Line Folding"
5335    </t>
5336    <t>
5337      <eref target=""/>:
5338      "OPTIONS * and proxies"
5339    </t>
5340    <t>
5341      <eref target=""/>:
5342      "Reason-Phrase BNF"
5343    </t>
5344    <t>
5345      <eref target=""/>:
5346      "Use of TEXT"
5347    </t>
5348    <t>
5349      <eref target=""/>:
5350      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5351    </t>
5352    <t>
5353      <eref target=""/>:
5354      "RFC822 reference left in discussion of date formats"
5355    </t>
5356  </list>
5359  Final work on ABNF conversion (<eref target=""/>):
5360  <list style="symbols">
5361    <t>
5362      Rewrite definition of list rules, deprecate empty list elements.
5363    </t>
5364    <t>
5365      Add appendix containing collected and expanded ABNF.
5366    </t>
5367  </list>
5370  Other changes:
5371  <list style="symbols">
5372    <t>
5373      Rewrite introduction; add mostly new Architecture Section.
5374    </t>
5375    <t>
5376      Move definition of quality values from Part 3 into Part 1;
5377      make TE request header grammar independent of accept-params (defined in Part 3).
5378    </t>
5379  </list>
5383<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5385  Closed issues:
5386  <list style="symbols">
5387    <t>
5388      <eref target=""/>:
5389      "base for numeric protocol elements"
5390    </t>
5391    <t>
5392      <eref target=""/>:
5393      "comment ABNF"
5394    </t>
5395  </list>
5398  Partly resolved issues:
5399  <list style="symbols">
5400    <t>
5401      <eref target=""/>:
5402      "205 Bodies" (took out language that implied that there may be
5403      methods for which a request body MUST NOT be included)
5404    </t>
5405    <t>
5406      <eref target=""/>:
5407      "editorial improvements around HTTP-date"
5408    </t>
5409  </list>
5413<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5415  Closed issues:
5416  <list style="symbols">
5417    <t>
5418      <eref target=""/>:
5419      "Repeating single-value headers"
5420    </t>
5421    <t>
5422      <eref target=""/>:
5423      "increase connection limit"
5424    </t>
5425    <t>
5426      <eref target=""/>:
5427      "IP addresses in URLs"
5428    </t>
5429    <t>
5430      <eref target=""/>:
5431      "take over HTTP Upgrade Token Registry"
5432    </t>
5433    <t>
5434      <eref target=""/>:
5435      "CR and LF in chunk extension values"
5436    </t>
5437    <t>
5438      <eref target=""/>:
5439      "HTTP/0.9 support"
5440    </t>
5441    <t>
5442      <eref target=""/>:
5443      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5444    </t>
5445    <t>
5446      <eref target=""/>:
5447      "move definitions of gzip/deflate/compress to part 1"
5448    </t>
5449    <t>
5450      <eref target=""/>:
5451      "disallow control characters in quoted-pair"
5452    </t>
5453  </list>
5456  Partly resolved issues:
5457  <list style="symbols">
5458    <t>
5459      <eref target=""/>:
5460      "update IANA requirements wrt Transfer-Coding values" (add the
5461      IANA Considerations subsection)
5462    </t>
5463  </list>
5467<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5469  Closed issues:
5470  <list style="symbols">
5471    <t>
5472      <eref target=""/>:
5473      "header parsing, treatment of leading and trailing OWS"
5474    </t>
5475  </list>
5478  Partly resolved issues:
5479  <list style="symbols">
5480    <t>
5481      <eref target=""/>:
5482      "Placement of 13.5.1 and 13.5.2"
5483    </t>
5484    <t>
5485      <eref target=""/>:
5486      "use of term "word" when talking about header structure"
5487    </t>
5488  </list>
5492<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5494  None yet.
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