source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1156

Last change on this file since 1156 was 1156, checked in by fielding@…, 11 years ago

Explicitly require that recipients fix duplicate received Content-Length
and correctly combine multiple Transfer-Encoding fields prior to
determining the message-body length. Require (MUST instead of SHOULD)
user agents to discard messages with framing errors that might indicate
response smuggling.

Addresses #95

  • Property svn:eol-style set to native
File size: 249.1 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 "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' 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-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</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">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.12"/>.
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 &diff-mime; 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 an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can 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 ought to be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients might 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", obsoleting
274   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
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 syntactic 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 other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
431   The OWS rule is used where zero or more linear whitespace characters might
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
456<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"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
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="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
499<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"/>
500  <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>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <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>
503  <x:ref>obs-text</x:ref>       = %x80-FF
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525  <x:anchor-alias value="MIME-Version"/>
527  The ABNF rules below are defined in other parts:
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&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-related 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 Messaging" anchor="operation">
555<iref primary="true" item="client"/>
556<iref primary="true" item="server"/>
557<iref primary="true" item="connection"/>
559   HTTP is a stateless request/response protocol that operates by exchanging
560   messages across a reliable transport or session-layer connection. An HTTP
561   "client" is a program that establishes a connection to a server for the
562   purpose of sending one or more HTTP requests.  An HTTP "server" is a
563   program that accepts connections in order to service HTTP requests by
564   sending HTTP responses.
566<iref primary="true" item="user agent"/>
567<iref primary="true" item="origin server"/>
568<iref primary="true" item="browser"/>
569<iref primary="true" item="spider"/>
571   Note that the terms client and server refer only to the roles that
572   these programs perform for a particular connection.  The same program
573   might act as a client on some connections and a server on others.  We use
574   the term "user agent" to refer to the program that initiates a request,
575   such as a WWW browser, editor, or spider (web-traversing robot), and
576   the term "origin server" to refer to the program that can originate
577   authoritative responses to a request.  For general requirements, we use
578   the term "sender" to refer to whichever component sent a given message
579   and the term "recipient" to refer to any component that receives the
580   message.
583   Most HTTP communication consists of a retrieval request (GET) for
584   a representation of some resource identified by a URI.  In the
585   simplest case, this might be accomplished via a single bidirectional
586   connection (===) between the user agent (UA) and the origin server (O).
588<figure><artwork type="drawing">
589         request   &gt;
590    UA ======================================= O
591                                &lt;   response
593<iref primary="true" item="message"/>
594<iref primary="true" item="request"/>
595<iref primary="true" item="response"/>
597   A client sends an HTTP request to the server in the form of a request
598   message (<xref target="request"/>), beginning with a method, URI, and
599   protocol version, followed by MIME-like header fields containing
600   request modifiers, client information, and payload metadata, an empty
601   line to indicate the end of the header section, and finally the payload
602   body (if any).
605   A server responds to the client's request by sending an HTTP response
606   message (<xref target="response"/>), beginning with a status line that
607   includes the protocol version, a success or error code, and textual
608   reason phrase, followed by MIME-like header fields containing server
609   information, resource metadata, and payload metadata, an empty line to
610   indicate the end of the header section, and finally the payload body (if any).
613   The following example illustrates a typical message exchange for a
614   GET request on the URI "":
617client request:
618</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
619GET /hello.txt HTTP/1.1
620User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
622Accept: */*
626server response:
627</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
628HTTP/1.1 200 OK
629Date: Mon, 27 Jul 2009 12:28:53 GMT
630Server: Apache
631Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
632ETag: "34aa387-d-1568eb00"
633Accept-Ranges: bytes
634Content-Length: <x:length-of target="exbody"/>
635Vary: Accept-Encoding
636Content-Type: text/plain
638<x:span anchor="exbody">Hello World!
642<section title="Connections and Transport Independence" anchor="transport-independence">
644   HTTP messaging is independent of the underlying transport or
645   session-layer connection protocol(s).  HTTP only presumes a reliable
646   transport with in-order delivery of requests and the corresponding
647   in-order delivery of responses.  The mapping of HTTP request and
648   response structures onto the data units of the underlying transport
649   protocol is outside the scope of this specification.
652   The specific connection protocols to be used for an interaction
653   are determined by client configuration and the identifier (if any)
654   provided for the request target.  For example, the "http" URI scheme
655   (<xref target="http.uri"/>) indicates a default connection of TCP
656   over IP, with a default TCP port of 80, but the client might be
657   configured to use a proxy via some other connection port or protocol
658   instead of using the defaults.
661   A connection might be used for multiple HTTP request/response exchanges,
662   as defined in <xref target="persistent.connections"/>.
666<section title="Intermediaries" anchor="intermediaries">
667<iref primary="true" item="intermediary"/>
669   HTTP enables the use of intermediaries to satisfy requests through
670   a chain of connections.  There are three common forms of HTTP
671   intermediary: proxy, gateway, and tunnel.  In some cases,
672   a single intermediary might act as an origin server, proxy, gateway,
673   or tunnel, switching behavior based on the nature of each request.
675<figure><artwork type="drawing">
676         &gt;             &gt;             &gt;             &gt;
677    UA =========== A =========== B =========== C =========== O
678               &lt;             &lt;             &lt;             &lt;
681   The figure above shows three intermediaries (A, B, and C) between the
682   user agent and origin server. A request or response message that
683   travels the whole chain will pass through four separate connections.
684   Some HTTP communication options
685   might apply only to the connection with the nearest, non-tunnel
686   neighbor, only to the end-points of the chain, or to all connections
687   along the chain. Although the diagram is linear, each participant might
688   be engaged in multiple, simultaneous communications. For example, B
689   might be receiving requests from many clients other than A, and/or
690   forwarding requests to servers other than C, at the same time that it
691   is handling A's request.
694<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
695<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
696   We use the terms "upstream" and "downstream" to describe various
697   requirements in relation to the directional flow of a message:
698   all messages flow from upstream to downstream.
699   Likewise, we use the terms "inbound" and "outbound" to refer to
700   directions in relation to the request path: "inbound" means toward
701   the origin server and "outbound" means toward the user agent.
703<t><iref primary="true" item="proxy"/>
704   A "proxy" is a message forwarding agent that is selected by the
705   client, usually via local configuration rules, to receive requests
706   for some type(s) of absolute URI and attempt to satisfy those
707   requests via translation through the HTTP interface.  Some translations
708   are minimal, such as for proxy requests for "http" URIs, whereas
709   other requests might require translation to and from entirely different
710   application-layer protocols. Proxies are often used to group an
711   organization's HTTP requests through a common intermediary for the
712   sake of security, annotation services, or shared caching.
715<iref primary="true" item="transforming proxy"/>
716<iref primary="true" item="non-transforming proxy"/>
717   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
718   or configured to modify request or response messages in a semantically
719   meaningful way (i.e., modifications, beyond those required by normal
720   HTTP processing, that change the message in a way that would be
721   significant to the original sender or potentially significant to
722   downstream recipients).  For example, a transforming proxy might be
723   acting as a shared annotation server (modifying responses to include
724   references to a local annotation database), a malware filter, a
725   format transcoder, or an intranet-to-Internet privacy filter.  Such
726   transformations are presumed to be desired by the client (or client
727   organization) that selected the proxy and are beyond the scope of
728   this specification.  However, when a proxy is not intended to transform
729   a given message, we use the term "non-transforming proxy" to target
730   requirements that preserve HTTP message semantics.
732<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
733   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
734   as a layer above some other server(s) and translates the received
735   requests to the underlying server's protocol.  Gateways are often
736   used for load balancing or partitioning HTTP services across
737   multiple machines.
738   Unlike a proxy, a gateway receives requests as if it were the
739   origin server for the target resource; the requesting client
740   will not be aware that it is communicating with a gateway.
741   A gateway communicates with the client as if the gateway is the
742   origin server and thus is subject to all of the requirements on
743   origin servers for that connection.  A gateway communicates
744   with inbound servers using any protocol it desires, including
745   private extensions to HTTP that are outside the scope of this
746   specification.
748<t><iref primary="true" item="tunnel"/>
749   A "tunnel" acts as a blind relay between two connections
750   without changing the messages. Once active, a tunnel is not
751   considered a party to the HTTP communication, though the tunnel might
752   have been initiated by an HTTP request. A tunnel ceases to exist when
753   both ends of the relayed connection are closed. Tunnels are used to
754   extend a virtual connection through an intermediary, such as when
755   transport-layer security is used to establish private communication
756   through a shared firewall proxy.
758<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
759   In addition, there may exist network intermediaries that are not
760   considered part of the HTTP communication but nevertheless act as
761   filters or redirecting agents (usually violating HTTP semantics,
762   causing security problems, and otherwise making a mess of things).
763   Such a network intermediary, referred to as an "interception proxy"
764   <xref target="RFC3040"/> or "transparent proxy" <xref target="RFC1919"/>,
765   differs from an HTTP proxy because it has not been selected by the client.
766   Instead, the network intermediary redirects outgoing TCP port 80 packets
767   (and occasionally other common port traffic) to an internal HTTP server.
768   Interception proxies are commonly found on public network access points
769   as a means of enforcing account subscription prior to allowing use of
770   non-local Internet services.  They are indistinguishable from a
771   man-in-the-middle attack.
775<section title="Caches" anchor="caches">
776<iref primary="true" item="cache"/>
778   A "cache" is a local store of previous response messages and the
779   subsystem that controls its message storage, retrieval, and deletion.
780   A cache stores cacheable responses in order to reduce the response
781   time and network bandwidth consumption on future, equivalent
782   requests. Any client or server &MAY; employ a cache, though a cache
783   cannot be used by a server while it is acting as a tunnel.
786   The effect of a cache is that the request/response chain is shortened
787   if one of the participants along the chain has a cached response
788   applicable to that request. The following illustrates the resulting
789   chain if B has a cached copy of an earlier response from O (via C)
790   for a request which has not been cached by UA or A.
792<figure><artwork type="drawing">
793            &gt;             &gt;
794       UA =========== A =========== B - - - - - - C - - - - - - O
795                  &lt;             &lt;
797<t><iref primary="true" item="cacheable"/>
798   A response is "cacheable" if a cache is allowed to store a copy of
799   the response message for use in answering subsequent requests.
800   Even when a response is cacheable, there might be additional
801   constraints placed by the client or by the origin server on when
802   that cached response can be used for a particular request. HTTP
803   requirements for cache behavior and cacheable responses are
804   defined in &caching-overview;. 
807   There are a wide variety of architectures and configurations
808   of caches and proxies deployed across the World Wide Web and
809   inside large organizations. These systems include national hierarchies
810   of proxy caches to save transoceanic bandwidth, systems that
811   broadcast or multicast cache entries, organizations that distribute
812   subsets of cached data via optical media, and so on.
816<section title="Protocol Versioning" anchor="http.version">
817  <x:anchor-alias value="HTTP-Version"/>
818  <x:anchor-alias value="HTTP-Prot-Name"/>
820   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
821   versions of the protocol. This specification defines version "1.1".
822   The protocol version as a whole indicates the sender's compliance
823   with the set of requirements laid out in that version's corresponding
824   specification of HTTP.
827   The version of an HTTP message is indicated by an HTTP-Version field
828   in the first line of the message. HTTP-Version is case-sensitive.
830<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
831  <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>
832  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
835   The HTTP version number consists of two non-negative decimal integers
836   separated by the "." (period or decimal point) character.  The first
837   number ("major version") indicates the HTTP messaging syntax, whereas
838   the second number ("minor version") indicates the highest minor
839   version to which the sender is at least conditionally compliant and
840   able to understand for future communication.  The minor version
841   advertises the sender's communication capabilities even when the
842   sender is only using a backwards-compatible subset of the protocol,
843   thereby letting the recipient know that more advanced features can
844   be used in response (by servers) or in future requests (by clients).
847   When comparing HTTP versions, the numbers &MUST; be compared
848   numerically rather than lexically.  For example, HTTP/2.4 is a lower
849   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
850   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
853   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
854   (or a recipient whose version is unknown), the HTTP/1.1 message is
855   constructed such that it will be interpreted as a valid HTTP/1.0
856   message even if all of the provided header fields not defined in
857   the HTTP/1.0 specification <xref target="RFC1945"/> are ignored.
858   This specification excludes incompatible message constructions by
859   imposing recipient-version requirements on new HTTP/1.1 features
860   that are not safely interpreted by earlier HTTP/1.0 recipients.
863   The interpretation of an HTTP message header field does not change
864   between minor versions of the same major version, though the default
865   behavior of a recipient in the absence of such a field can change.
866   Unless specified otherwise, header fields defined in HTTP/1.1 are
867   defined for all versions of HTTP/1.x.  The most popular example of
868   this is the Host header field, which was introduced during the
869   standardization process of HTTP/1.1 and widely deployed for HTTP/1.0
870   requests out of necessity.
873   Likewise, new header fields can be defined such that, when they are
874   understood by a recipient, they might override or enhance the
875   interpretation of previously defined header fields.  When an
876   implementation receives an unrecognized header field, the recipient
877   &MUST; ignore that header field for local processing regardless of
878   the message's HTTP version.  An unrecognized header field received
879   by a proxy &MUST; be forwarded downstream unless the header field's
880   field-name is listed in the message's Connection header-field
881   (see <xref target="header.connection"/>).
882   These requirements allow HTTP's functionality to be enhanced without
883   requiring prior update of all compliant intermediaries.
886   Intermediaries that process HTTP messages (i.e., all intermediaries
887   other than those acting as a tunnel) &MUST; send their own HTTP-Version
888   in forwarded messages.  In other words, they &MUST-NOT; blindly
889   forward the first line of an HTTP message without ensuring that the
890   protocol version matches what the intermediary understands, and
891   is at least conditionally compliant to, for both the receiving and
892   sending of messages.  Forwarding an HTTP message without rewriting
893   the HTTP-Version might result in communication errors when downstream
894   recipients use the message sender's version to determine what features
895   are safe to use for later communication with that sender.
898   An HTTP client &SHOULD; send a request version equal to the highest
899   version for which the client is at least conditionally compliant and
900   whose major version is no higher than the highest version supported
901   by the server, if this is known.  An HTTP client &MUST-NOT; send a
902   version for which it is not at least conditionally compliant.
905   An HTTP client &MAY; send a lower request version if it is known that
906   the server incorrectly implements the HTTP specification, but only
907   after the client has attempted at least one normal request and determined
908   from the response status or header fields (e.g., Server) that the
909   server improperly handles higher request versions.
912   An HTTP server &SHOULD; send a response version equal to the highest
913   version for which the server is at least conditionally compliant and
914   whose major version is less than or equal to the one received in the
915   request.  An HTTP server &MUST-NOT; send a version for which it is not
916   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
917   Version Not Supported) response if it cannot send a response using the
918   major version used in the client's request.
921   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
922   if it is known or suspected that the client incorrectly implements the
923   HTTP specification and is incapable of correctly processing later
924   version responses, such as when a client fails to parse the version
925   number correctly or when an intermediary is known to blindly forward
926   the HTTP-Version even when it doesn't comply with the given minor
927   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
928   performed unless triggered by specific client attributes, such as when
929   one or more of the request header fields (e.g., User-Agent) uniquely
930   match the values sent by a client known to be in error.
933   The intention of HTTP's versioning design is that the major number
934   will only be incremented if an incompatible message syntax is
935   introduced, and that the minor number will only be incremented when
936   changes made to the protocol have the effect of adding to the message
937   semantics or implying additional capabilities of the sender.  However,
938   the minor version was not incremented for the changes introduced in
939   <xref target="RFC2616"/>, and this revision is specifically avoiding
940   any such changes to the protocol.
944<section title="Uniform Resource Identifiers" anchor="uri">
945<iref primary="true" item="resource"/>
947   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
948   throughout HTTP as the means for identifying resources. URI references
949   are used to target requests, indicate redirects, and define relationships.
950   HTTP does not limit what a resource might be; it merely defines an interface
951   that can be used to interact with a resource via HTTP. More information on
952   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
954  <x:anchor-alias value="URI-reference"/>
955  <x:anchor-alias value="absolute-URI"/>
956  <x:anchor-alias value="relative-part"/>
957  <x:anchor-alias value="authority"/>
958  <x:anchor-alias value="path-abempty"/>
959  <x:anchor-alias value="path-absolute"/>
960  <x:anchor-alias value="port"/>
961  <x:anchor-alias value="query"/>
962  <x:anchor-alias value="uri-host"/>
963  <x:anchor-alias value="partial-URI"/>
965   This specification adopts the definitions of "URI-reference",
966   "absolute-URI", "relative-part", "port", "host",
967   "path-abempty", "path-absolute", "query", and "authority" from
968   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
969   protocol elements that allow a relative URI without a fragment.
971<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"/>
972  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
973  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
974  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
975  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
976  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
977  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
978  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
979  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
980  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
982  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
985   Each protocol element in HTTP that allows a URI reference will indicate in
986   its ABNF production whether the element allows only a URI in absolute form
987   (absolute-URI), any relative reference (relative-ref), or some other subset
988   of the URI-reference grammar. Unless otherwise indicated, URI references
989   are parsed relative to the request target (the default base URI for both
990   the request and its corresponding response).
993<section title="http URI scheme" anchor="http.uri">
994  <x:anchor-alias value="http-URI"/>
995  <iref item="http URI scheme" primary="true"/>
996  <iref item="URI scheme" subitem="http" primary="true"/>
998   The "http" URI scheme is hereby defined for the purpose of minting
999   identifiers according to their association with the hierarchical
1000   namespace governed by a potential HTTP origin server listening for
1001   TCP connections on a given port.
1002   The HTTP server is identified via the generic syntax's
1003   <x:ref>authority</x:ref> component, which includes a host
1004   identifier and optional TCP port, and the remainder of the URI is
1005   considered to be identifying data corresponding to a resource for
1006   which that server might provide an HTTP interface.
1008<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1009  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1012   The host identifier within an <x:ref>authority</x:ref> component is
1013   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
1014   provided as an IP literal or IPv4 address, then the HTTP server is any
1015   listener on the indicated TCP port at that IP address. If host is a
1016   registered name, then that name is considered an indirect identifier
1017   and the recipient might use a name resolution service, such as DNS,
1018   to find the address of a listener for that host.
1019   The host &MUST-NOT; be empty; if an "http" URI is received with an
1020   empty host, then it &MUST; be rejected as invalid.
1021   If the port subcomponent is empty or not given, then TCP port 80 is
1022   assumed (the default reserved port for WWW services).
1025   Regardless of the form of host identifier, access to that host is not
1026   implied by the mere presence of its name or address. The host might or might
1027   not exist and, even when it does exist, might or might not be running an
1028   HTTP server or listening to the indicated port. The "http" URI scheme
1029   makes use of the delegated nature of Internet names and addresses to
1030   establish a naming authority (whatever entity has the ability to place
1031   an HTTP server at that Internet name or address) and allows that
1032   authority to determine which names are valid and how they might be used.
1035   When an "http" URI is used within a context that calls for access to the
1036   indicated resource, a client &MAY; attempt access by resolving
1037   the host to an IP address, establishing a TCP connection to that address
1038   on the indicated port, and sending an HTTP request message to the server
1039   containing the URI's identifying data as described in <xref target="request"/>.
1040   If the server responds to that request with a non-interim HTTP response
1041   message, as described in <xref target="response"/>, then that response
1042   is considered an authoritative answer to the client's request.
1045   Although HTTP is independent of the transport protocol, the "http"
1046   scheme is specific to TCP-based services because the name delegation
1047   process depends on TCP for establishing authority.
1048   An HTTP service based on some other underlying connection protocol
1049   would presumably be identified using a different URI scheme, just as
1050   the "https" scheme (below) is used for servers that require an SSL/TLS
1051   transport layer on a connection. Other protocols might also be used to
1052   provide access to "http" identified resources &mdash; it is only the
1053   authoritative interface used for mapping the namespace that is
1054   specific to TCP.
1057   The URI generic syntax for authority also includes a deprecated
1058   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1059   for including user authentication information in the URI.  The userinfo
1060   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
1061   URI.  URI reference recipients &SHOULD; parse for the existence of
1062   userinfo and treat its presence as an error, likely indicating that
1063   the deprecated subcomponent is being used to obscure the authority
1064   for the sake of phishing attacks.
1068<section title="https URI scheme" anchor="https.uri">
1069   <x:anchor-alias value="https-URI"/>
1070   <iref item="https URI scheme"/>
1071   <iref item="URI scheme" subitem="https"/>
1073   The "https" URI scheme is hereby defined for the purpose of minting
1074   identifiers according to their association with the hierarchical
1075   namespace governed by a potential HTTP origin server listening for
1076   SSL/TLS-secured connections on a given TCP port.
1079   All of the requirements listed above for the "http" scheme are also
1080   requirements for the "https" scheme, except that a default TCP port
1081   of 443 is assumed if the port subcomponent is empty or not given,
1082   and the TCP connection &MUST; be secured for privacy through the
1083   use of strong encryption prior to sending the first HTTP request.
1085<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1086  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1089   Unlike the "http" scheme, responses to "https" identified requests
1090   are never "public" and thus are ineligible for shared caching.
1091   Their default is "private" and might be further constrained via use
1092   of the Cache-Control header field.
1095   Resources made available via the "https" scheme have no shared
1096   identity with the "http" scheme even if their resource identifiers
1097   only differ by the single "s" in the scheme name.  They are
1098   different services governed by different authorities.  However,
1099   some extensions to HTTP that apply to entire host domains, such
1100   as the Cookie protocol, do allow one service to effect communication
1101   with the other services based on host domain matching.
1104   The process for authoritative access to an "https" identified
1105   resource is defined in <xref target="RFC2818"/>.
1109<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1111   Since the "http" and "https" schemes conform to the URI generic syntax,
1112   such URIs are normalized and compared according to the algorithm defined
1113   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1114   described above for each scheme.
1117   If the port is equal to the default port for a scheme, the normal
1118   form is to elide the port subcomponent. Likewise, an empty path
1119   component is equivalent to an absolute path of "/", so the normal
1120   form is to provide a path of "/" instead. The scheme and host
1121   are case-insensitive and normally provided in lowercase; all
1122   other components are compared in a case-sensitive manner.
1123   Characters other than those in the "reserved" set are equivalent
1124   to their percent-encoded octets (see <xref target="RFC3986"
1125   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1128   For example, the following three URIs are equivalent:
1130<figure><artwork type="example">
1136   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1137   If path-abempty is the empty string (i.e., there is no slash "/"
1138   path separator following the authority), then the "http" URI
1139   &MUST; be given as "/" when
1140   used as a request-target (<xref target="request-target"/>). If a proxy
1141   receives a host name which is not a fully qualified domain name, it
1142   &MAY; add its domain to the host name it received. If a proxy receives
1143   a fully qualified domain name, the proxy &MUST-NOT; change the host
1144   name.
1150<section title="HTTP Message" anchor="http.message">
1151<x:anchor-alias value="generic-message"/>
1152<x:anchor-alias value="message.types"/>
1153<x:anchor-alias value="HTTP-message"/>
1154<x:anchor-alias value="start-line"/>
1155<iref item="header section"/>
1156<iref item="headers"/>
1157<iref item="header field"/>
1159   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1160   characters in a format similar to the Internet Message Format
1161   <xref target="RFC5322"/>: zero or more header fields (collectively
1162   referred to as the "headers" or the "header section"), an empty line
1163   indicating the end of the header section, and an optional message-body.
1166   An HTTP message can either be a request from client to server or a
1167   response from server to client.  Syntactically, the two types of message
1168   differ only in the start-line, which is either a Request-Line (for requests)
1169   or a Status-Line (for responses), and in the algorithm for determining
1170   the length of the message-body (<xref target="message.body"/>).
1171   In theory, a client could receive requests and a server could receive
1172   responses, distinguishing them by their different start-line formats,
1173   but in practice servers are implemented to only expect a request
1174   (a response is interpreted as an unknown or invalid request method)
1175   and clients are implemented to only expect a response.
1177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1178  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1179                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1180                    <x:ref>CRLF</x:ref>
1181                    [ <x:ref>message-body</x:ref> ]
1182  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1185   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1186   header field. The presence of whitespace might be an attempt to trick a
1187   noncompliant implementation of HTTP into ignoring that field or processing
1188   the next line as a new request, either of which might result in security
1189   issues when implementations within the request chain interpret the
1190   same message differently. HTTP/1.1 servers &MUST; reject such a message
1191   with a 400 (Bad Request) response.
1194<section title="Message Parsing Robustness" anchor="message.robustness">
1196   In the interest of robustness, servers &SHOULD; ignore at least one
1197   empty line received where a Request-Line is expected. In other words, if
1198   the server is reading the protocol stream at the beginning of a
1199   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1202   Some old HTTP/1.0 client implementations generate an extra CRLF
1203   after a POST request as a lame workaround for some early server
1204   applications that failed to read message-body content that was
1205   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1206   preface or follow a request with an extra CRLF.  If terminating
1207   the request message-body with a line-ending is desired, then the
1208   client &MUST; include the terminating CRLF octets as part of the
1209   message-body length.
1212   The normal procedure for parsing an HTTP message is to read the
1213   start-line into a structure, read each header field into a hash
1214   table by field name until the empty line, and then use the parsed
1215   data to determine if a message-body is expected.  If a message-body
1216   has been indicated, then it is read as a stream until an amount
1217   of octets equal to the message-body length is read or the connection
1218   is closed.  Care must be taken to parse an HTTP message as a sequence
1219   of octets in an encoding that is a superset of US-ASCII.  Attempting
1220   to parse HTTP as a stream of Unicode characters in a character encoding
1221   like UTF-16 might introduce security flaws due to the differing ways
1222   that such parsers interpret invalid characters.
1225   HTTP allows the set of defined header fields to be extended without
1226   changing the protocol version (see <xref target="header.field.registration"/>).
1227   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1228   proxy is specifically configured to block or otherwise transform such
1229   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1233<section title="Header Fields" anchor="header.fields">
1234  <x:anchor-alias value="header-field"/>
1235  <x:anchor-alias value="field-content"/>
1236  <x:anchor-alias value="field-name"/>
1237  <x:anchor-alias value="field-value"/>
1238  <x:anchor-alias value="OWS"/>
1240   Each HTTP header field consists of a case-insensitive field name
1241   followed by a colon (":"), optional whitespace, and the field value.
1243<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"/>
1244  <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>
1245  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1246  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1247  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1250   No whitespace is allowed between the header field name and colon. For
1251   security reasons, any request message received containing such whitespace
1252   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1253   &MUST; remove any such whitespace from a response message before
1254   forwarding the message downstream.
1257   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1258   preferred. The field value does not include any leading or trailing white
1259   space: OWS occurring before the first non-whitespace character of the
1260   field value or after the last non-whitespace character of the field value
1261   is ignored and &SHOULD; be removed before further processing (as this does
1262   not change the meaning of the header field).
1265   The order in which header fields with differing field names are
1266   received is not significant. However, it is "good practice" to send
1267   header fields that contain control data first, such as Host on
1268   requests and Date on responses, so that implementations can decide
1269   when not to handle a message as early as possible.  A server &MUST;
1270   wait until the entire header section is received before interpreting
1271   a request message, since later header fields might include conditionals,
1272   authentication credentials, or deliberately misleading duplicate
1273   header fields that would impact request processing.
1276   Multiple header fields with the same field name &MUST-NOT; be
1277   sent in a message unless the entire field value for that
1278   header field is defined as a comma-separated list [i.e., #(values)].
1279   Multiple header fields with the same field name can be combined into
1280   one "field-name: field-value" pair, without changing the semantics of the
1281   message, by appending each subsequent field value to the combined
1282   field value in order, separated by a comma. The order in which
1283   header fields with the same field name are received is therefore
1284   significant to the interpretation of the combined field value;
1285   a proxy &MUST-NOT; change the order of these field values when
1286   forwarding a message.
1289  <t>
1290   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1291   practice can occur multiple times, but does not use the list syntax, and
1292   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1293   for details.) Also note that the Set-Cookie2 header field specified in
1294   <xref target="RFC2965"/> does not share this problem.
1295  </t>
1298   Historically, HTTP header field values could be extended over multiple
1299   lines by preceding each extra line with at least one space or horizontal
1300   tab character (line folding). This specification deprecates such line
1301   folding except within the message/http media type
1302   (<xref target=""/>).
1303   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1304   (i.e., that contain any field-content that matches the obs-fold rule) unless
1305   the message is intended for packaging within the message/http media type.
1306   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1307   obs-fold whitespace with a single SP prior to interpreting the field value
1308   or forwarding the message downstream.
1311   Historically, HTTP has allowed field content with text in the ISO-8859-1
1312   <xref target="ISO-8859-1"/> character encoding and supported other
1313   character sets only through use of <xref target="RFC2047"/> encoding.
1314   In practice, most HTTP header field values use only a subset of the
1315   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1316   header fields &SHOULD; limit their field values to US-ASCII characters.
1317   Recipients &SHOULD; treat other (obs-text) octets in field content as
1318   opaque data.
1320<t anchor="rule.comment">
1321  <x:anchor-alias value="comment"/>
1322  <x:anchor-alias value="ctext"/>
1323   Comments can be included in some HTTP header fields by surrounding
1324   the comment text with parentheses. Comments are only allowed in
1325   fields containing "comment" as part of their field value definition.
1327<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1328  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1329  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1330                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1332<t anchor="rule.quoted-cpair">
1333  <x:anchor-alias value="quoted-cpair"/>
1334   The backslash character ("\") can be used as a single-character
1335   quoting mechanism within comment constructs:
1337<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1338  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1341   Producers &SHOULD-NOT; escape characters that do not require escaping
1342   (i.e., other than the backslash character "\" and the parentheses "(" and
1343   ")").
1347<section title="Message Body" anchor="message.body">
1348  <x:anchor-alias value="message-body"/>
1350   The message-body (if any) of an HTTP message is used to carry the
1351   payload body associated with the request or response.
1353<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1354  <x:ref>message-body</x:ref> = *OCTET
1357   The message-body differs from the payload body only when a transfer-coding
1358   has been applied, as indicated by the Transfer-Encoding header field
1359   (<xref target="header.transfer-encoding"/>).  If more than one
1360   Transfer-Encoding header field is present in a message, the multiple
1361   field-values &MUST; be combined into one field-value, according to the
1362   algorithm defined in <xref target="header.fields"/>, before determining
1363   the message-body length.
1366   When one or more transfer-codings are applied to a payload in order to
1367   form the message-body, the Transfer-Encoding header field &MUST; contain
1368   the list of transfer-codings applied. Transfer-Encoding is a property of
1369   the message, not of the payload, and thus &MAY; be added or removed by
1370   any implementation along the request/response chain under the constraints
1371   found in <xref target="transfer.codings"/>.
1374   If a message is received that has multiple Content-Length header fields
1375   (<xref target="header.content-length"/>) with field-values consisting
1376   of the same decimal value, or a single Content-Length header field with
1377   a field value containing a list of identical decimal values (e.g.,
1378   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1379   header fields have been generated or combined by an upstream message
1380   processor, then the recipient &MUST; replace the duplicated fields or
1381   field-values with a single valid Content-Length field containing that
1382   decimal value prior to determining the message-body length.
1385   The rules for when a message-body is allowed in a message differ for
1386   requests and responses.
1389   The presence of a message-body in a request is signaled by the
1390   inclusion of a Content-Length or Transfer-Encoding header field in
1391   the request's header fields, even if the request method does not
1392   define any use for a message-body.  This allows the request
1393   message framing algorithm to be independent of method semantics.
1396   For response messages, whether or not a message-body is included with
1397   a message is dependent on both the request method and the response
1398   status code (<xref target="status.code.and.reason.phrase"/>).
1399   Responses to the HEAD request method never include a message-body
1400   because the associated response header fields (e.g., Transfer-Encoding,
1401   Content-Length, etc.) only indicate what their values would have been
1402   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1403   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1404   All other responses do include a message-body, although the body
1405   &MAY; be of zero length.
1408   The length of the message-body is determined by one of the following
1409   (in order of precedence):
1412  <list style="numbers">
1413    <x:lt><t>
1414     Any response to a HEAD request and any response with a status
1415     code of 100-199, 204, or 304 is always terminated by the first
1416     empty line after the header fields, regardless of the header
1417     fields present in the message, and thus cannot contain a message-body.
1418    </t></x:lt>
1419    <x:lt><t>
1420     If a Transfer-Encoding header field is present
1421     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1422     is the final encoding, the message-body length is determined by reading
1423     and decoding the chunked data until the transfer-coding indicates the
1424     data is complete.
1425    </t>
1426    <t>
1427     If a Transfer-Encoding header field is present in a response and the
1428     "chunked" transfer-coding is not the final encoding, the message-body
1429     length is determined by reading the connection until it is closed by
1430     the server.
1431     If a Transfer-Encoding header field is present in a request and the
1432     "chunked" transfer-coding is not the final encoding, the message-body
1433     length cannot be determined reliably; the server &MUST; respond with
1434     the 400 (Bad Request) status code and then close the connection.
1435    </t>
1436    <t>
1437     If a message is received with both a Transfer-Encoding header field
1438     and a Content-Length header field, the Transfer-Encoding overrides
1439     the Content-Length.
1440     Such a message might indicate an attempt to perform request or response
1441     smuggling (bypass of security-related checks on message routing or content)
1442     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1443     be removed, prior to forwarding the message downstream, or replaced with
1444     the real message-body length after the transfer-coding is decoded.
1445    </t></x:lt>
1446    <x:lt><t>
1447     If a message is received without Transfer-Encoding and with either
1448     multiple Content-Length header fields having differing field-values or
1449     a single Content-Length header field having an invalid value, then the
1450     message framing is invalid and &MUST; be treated as an error to
1451     prevent request or response smuggling.
1452     If this is a request message, the server &MUST; respond with
1453     a 400 (Bad Request) status code and then close the connection.
1454     If this is a response message received by a proxy or gateway, the proxy
1455     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1456     status code as its downstream response, and then close the connection.
1457     If this is a response message received by a user-agent, it &MUST; be
1458     treated as an error by discarding the message and closing the connection.
1459    </t></x:lt>
1460    <x:lt><t>
1461     If a valid Content-Length header field
1462     is present without Transfer-Encoding, its decimal value defines the
1463     message-body length in octets.  If the actual number of octets sent in
1464     the message is less than the indicated Content-Length, the recipient
1465     &MUST; consider the message to be incomplete and treat the connection
1466     as no longer usable.
1467     If the actual number of octets sent in the message is more than the indicated
1468     Content-Length, the recipient &MUST; only process the message-body up to the
1469     field value's number of octets; the remainder of the message &MUST; either
1470     be discarded or treated as the next message in a pipeline.  For the sake of
1471     robustness, a user-agent &MAY; attempt to detect and correct such an error
1472     in message framing if it is parsing the response to the last request on
1473     on a connection and the connection has been closed by the server.
1474    </t></x:lt>
1475    <x:lt><t>
1476     If this is a request message and none of the above are true, then the
1477     message-body length is zero (no message-body is present).
1478    </t></x:lt>
1479    <x:lt><t>
1480     Otherwise, this is a response message without a declared message-body
1481     length, so the message-body length is determined by the number of octets
1482     received prior to the server closing the connection.
1483    </t></x:lt>
1484  </list>
1487   Since there is no way to distinguish a successfully completed,
1488   close-delimited message from a partially-received message interrupted
1489   by network failure, implementations &SHOULD; use encoding or
1490   length-delimited messages whenever possible.  The close-delimiting
1491   feature exists primarily for backwards compatibility with HTTP/1.0.
1494   A server &MAY; reject a request that contains a message-body but
1495   not a Content-Length by responding with 411 (Length Required).
1498   Unless a transfer-coding other than "chunked" has been applied,
1499   a client that sends a request containing a message-body &SHOULD;
1500   use a valid Content-Length header field if the message-body length
1501   is known in advance, rather than the "chunked" encoding, since some
1502   existing services respond to "chunked" with a 411 (Length Required)
1503   status code even though they understand the chunked encoding.  This
1504   is typically because such services are implemented via a gateway that
1505   requires a content-length in advance of being called and the server
1506   is unable or unwilling to buffer the entire request before processing.
1509   A client that sends a request containing a message-body &MUST; include a
1510   valid Content-Length header field if it does not know the server will
1511   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1512   of specific user configuration or by remembering the version of a prior
1513   received response.
1516   Request messages that are prematurely terminated, possibly due to a
1517   cancelled connection or a server-imposed time-out exception, &MUST;
1518   result in closure of the connection; sending an HTTP/1.1 error response
1519   prior to closing the connection is &OPTIONAL;.
1520   Response messages that are prematurely terminated, usually by closure
1521   of the connection prior to receiving the expected number of octets or by
1522   failure to decode a transfer-encoded message-body, &MUST; be recorded
1523   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1524   message-body as if it were complete (i.e., some indication must be given
1525   to the user that an error occurred).  Cache requirements for incomplete
1526   responses are defined in &cache-incomplete;.
1529   A server &MUST; read the entire request message-body or close
1530   the connection after sending its response, since otherwise the
1531   remaining data on a persistent connection would be misinterpreted
1532   as the next request.  Likewise,
1533   a client &MUST; read the entire response message-body if it intends
1534   to reuse the same connection for a subsequent request.  Pipelining
1535   multiple requests on a connection is described in <xref target="pipelining"/>.
1539<section title="General Header Fields" anchor="general.header.fields">
1540  <x:anchor-alias value="general-header"/>
1542   There are a few header fields which have general applicability for
1543   both request and response messages, but which do not apply to the
1544   payload being transferred. These header fields apply only to the
1545   message being transmitted.
1547<texttable align="left">
1548  <ttcol>Header Field Name</ttcol>
1549  <ttcol>Defined in...</ttcol>
1551  <c>Connection</c> <c><xref target="header.connection"/></c>
1552  <c>Date</c> <c><xref target=""/></c>
1553  <c>Pragma</c> <c>&header-pragma;</c>
1554  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1555  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1556  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1557  <c>Via</c> <c><xref target="header.via"/></c>
1558  <c>Warning</c> <c>&header-warning;</c>
1559  <c>MIME-Version</c> <c>&header-mime-version;</c>
1562   General-header field names can be extended reliably only in
1563   combination with a change in the protocol version. However, new or
1564   experimental header fields might be given the semantics of general
1565   header fields if all parties in the communication recognize them to
1566   be general-header fields.
1571<section title="Request" anchor="request">
1572  <x:anchor-alias value="Request"/>
1574   A request message from a client to a server includes, within the
1575   first line of that message, the method to be applied to the resource,
1576   the identifier of the resource, and the protocol version in use.
1578<!--                 Host                      ; should be moved here eventually -->
1579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1580  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1581                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1582                  <x:ref>CRLF</x:ref>
1583                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1586<section title="Request-Line" anchor="request-line">
1587  <x:anchor-alias value="Request-Line"/>
1589   The Request-Line begins with a method token, followed by the
1590   request-target and the protocol version, and ending with CRLF. The
1591   elements are separated by SP characters. No CR or LF is allowed
1592   except in the final CRLF sequence.
1594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1595  <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>
1598<section title="Method" anchor="method">
1599  <x:anchor-alias value="Method"/>
1601   The Method  token indicates the method to be performed on the
1602   resource identified by the request-target. The method is case-sensitive.
1604<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1605  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1609<section title="request-target" anchor="request-target">
1610  <x:anchor-alias value="request-target"/>
1612   The request-target identifies the resource upon which to apply the request.
1614<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1615  <x:ref>request-target</x:ref> = "*"
1616                 / <x:ref>absolute-URI</x:ref>
1617                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1618                 / <x:ref>authority</x:ref>
1621   The four options for request-target are dependent on the nature of the
1622   request.
1624<t><iref item="asterisk form (of request-target)"/>
1625   The asterisk "*" ("asterisk form") means that the request does not apply to a
1626   particular resource, but to the server itself. This is only allowed for the
1627   OPTIONS method. Thus, the only valid example is
1629<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1630OPTIONS * HTTP/1.1
1632<t><iref item="absolute-URI form (of request-target)"/>
1633   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1634   proxy. The proxy is requested to forward the request or service it
1635   from a valid cache, and return the response. Note that the proxy &MAY;
1636   forward the request on to another proxy or directly to the server
1637   specified by the absolute-URI. In order to avoid request loops, a
1638   proxy &MUST; be able to recognize all of its server names, including
1639   any aliases, local variations, and the numeric IP address. An example
1640   Request-Line would be:
1642<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1643GET HTTP/1.1
1646   To allow for transition to absolute-URIs in all requests in future
1647   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1648   form in requests, even though HTTP/1.1 clients will only generate
1649   them in requests to proxies.
1651<t><iref item="authority form (of request-target)"/>
1652   The "authority form" is only used by the CONNECT method (&CONNECT;).
1654<t><iref item="path-absolute form (of request-target)"/>
1655   The most common form of request-target is that used to identify a
1656   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1657   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1658   the request-target, and the network location of the URI (authority) &MUST;
1659   be transmitted in a Host header field. For example, a client wishing
1660   to retrieve the resource above directly from the origin server would
1661   create a TCP connection to port 80 of the host "" and send
1662   the lines:
1664<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1665GET /pub/WWW/TheProject.html HTTP/1.1
1669   followed by the remainder of the Request. Note that the absolute path
1670   cannot be empty; if none is present in the original URI, it &MUST; be
1671   given as "/" (the server root).
1674   If a proxy receives a request without any path in the request-target and
1675   the method specified is capable of supporting the asterisk form of
1676   request-target, then the last proxy on the request chain &MUST; forward the
1677   request with "*" as the final request-target.
1680   For example, the request
1681</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1685  would be forwarded by the proxy as
1686</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1687OPTIONS * HTTP/1.1
1691   after connecting to port 8001 of host "".
1695   The request-target is transmitted in the format specified in
1696   <xref target="http.uri"/>. If the request-target is percent-encoded
1697   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1698   &MUST; decode the request-target in order to
1699   properly interpret the request. Servers &SHOULD; respond to invalid
1700   request-targets with an appropriate status code.
1703   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1704   received request-target when forwarding it to the next inbound server,
1705   except as noted above to replace a null path-absolute with "/" or "*".
1708  <t>
1709    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1710    meaning of the request when the origin server is improperly using
1711    a non-reserved URI character for a reserved purpose.  Implementors
1712    need to be aware that some pre-HTTP/1.1 proxies have been known to
1713    rewrite the request-target.
1714  </t>
1717   HTTP does not place a pre-defined limit on the length of a request-target.
1718   A server &MUST; be prepared to receive URIs of unbounded length and
1719   respond with the 414 (URI Too Long) status code if the received
1720   request-target would be longer than the server wishes to handle
1721   (see &status-414;).
1724   Various ad-hoc limitations on request-target length are found in practice.
1725   It is &RECOMMENDED; that all HTTP senders and recipients support
1726   request-target lengths of 8000 or more octets.
1729  <t>
1730    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1731    are not part of the request-target and thus will not be transmitted
1732    in an HTTP request.
1733  </t>
1738<section title="The Resource Identified by a Request" anchor="">
1740   The exact resource identified by an Internet request is determined by
1741   examining both the request-target and the Host header field.
1744   An origin server that does not allow resources to differ by the
1745   requested host &MAY; ignore the Host header field value when
1746   determining the resource identified by an HTTP/1.1 request. (But see
1747   <xref target=""/>
1748   for other requirements on Host support in HTTP/1.1.)
1751   An origin server that does differentiate resources based on the host
1752   requested (sometimes referred to as virtual hosts or vanity host
1753   names) &MUST; use the following rules for determining the requested
1754   resource on an HTTP/1.1 request:
1755  <list style="numbers">
1756    <t>If request-target is an absolute-URI, the host is part of the
1757     request-target. Any Host header field value in the request &MUST; be
1758     ignored.</t>
1759    <t>If the request-target is not an absolute-URI, and the request includes
1760     a Host header field, the host is determined by the Host header
1761     field value.</t>
1762    <t>If the host as determined by rule 1 or 2 is not a valid host on
1763     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1764  </list>
1767   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1768   attempt to use heuristics (e.g., examination of the URI path for
1769   something unique to a particular host) in order to determine what
1770   exact resource is being requested.
1774<section title="Effective Request URI" anchor="effective.request.uri">
1775  <iref primary="true" item="effective request URI"/>
1776  <iref primary="true" item="target resource"/>
1778   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1779   for the target resource; instead, the URI needs to be inferred from the
1780   request-target, Host header field, and connection context. The result of
1781   this process is called the "effective request URI".  The "target resource"
1782   is the resource identified by the effective request URI.
1785   If the request-target is an absolute-URI, then the effective request URI is
1786   the request-target.
1789   If the request-target uses the path-absolute form or the asterisk form,
1790   and the Host header field is present, then the effective request URI is
1791   constructed by concatenating
1794  <list style="symbols">
1795    <t>
1796      the scheme name: "http" if the request was received over an insecure
1797      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1798      connection,
1799    </t>
1800    <t>
1801      the character sequence "://",
1802    </t>
1803    <t>
1804      the authority component, as specified in the Host header field
1805      (<xref target=""/>), and
1806    </t>
1807    <t>
1808      the request-target obtained from the Request-Line, unless the
1809      request-target is just the asterisk "*".
1810    </t>
1811  </list>
1814   If the request-target uses the path-absolute form or the asterisk form,
1815   and the Host header field is not present, then the effective request URI is
1816   undefined.
1819   Otherwise, when request-target uses the authority form, the effective
1820   request URI is undefined.
1824   Example 1: the effective request URI for the message
1826<artwork type="example" x:indent-with="  ">
1827GET /pub/WWW/TheProject.html HTTP/1.1
1831  (received over an insecure TCP connection) is "http", plus "://", plus the
1832  authority component "", plus the request-target
1833  "/pub/WWW/TheProject.html", thus
1834  "".
1839   Example 2: the effective request URI for the message
1841<artwork type="example" x:indent-with="  ">
1842GET * HTTP/1.1
1846  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1847  authority component "", thus "".
1851   Effective request URIs are compared using the rules described in
1852   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1853   be treated as equivalent to an absolute path of "/".
1860<section title="Response" anchor="response">
1861  <x:anchor-alias value="Response"/>
1863   After receiving and interpreting a request message, a server responds
1864   with an HTTP response message.
1866<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1867  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1868                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1869                  <x:ref>CRLF</x:ref>
1870                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1873<section title="Status-Line" anchor="status-line">
1874  <x:anchor-alias value="Status-Line"/>
1876   The first line of a Response message is the Status-Line, consisting
1877   of the protocol version followed by a numeric status code and its
1878   associated textual phrase, with each element separated by SP
1879   characters. No CR or LF is allowed except in the final CRLF sequence.
1881<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1882  <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>
1885<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1886  <x:anchor-alias value="Reason-Phrase"/>
1887  <x:anchor-alias value="Status-Code"/>
1889   The Status-Code element is a 3-digit integer result code of the
1890   attempt to understand and satisfy the request. These codes are fully
1891   defined in &status-codes;.  The Reason Phrase exists for the sole
1892   purpose of providing a textual description associated with the numeric
1893   status code, out of deference to earlier Internet application protocols
1894   that were more frequently used with interactive text clients.
1895   A client &SHOULD; ignore the content of the Reason Phrase.
1898   The first digit of the Status-Code defines the class of response. The
1899   last two digits do not have any categorization role. There are 5
1900   values for the first digit:
1901  <list style="symbols">
1902    <t>
1903      1xx: Informational - Request received, continuing process
1904    </t>
1905    <t>
1906      2xx: Success - The action was successfully received,
1907        understood, and accepted
1908    </t>
1909    <t>
1910      3xx: Redirection - Further action must be taken in order to
1911        complete the request
1912    </t>
1913    <t>
1914      4xx: Client Error - The request contains bad syntax or cannot
1915        be fulfilled
1916    </t>
1917    <t>
1918      5xx: Server Error - The server failed to fulfill an apparently
1919        valid request
1920    </t>
1921  </list>
1923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1924  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1925  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1933<section title="Protocol Parameters" anchor="protocol.parameters">
1935<section title="Date/Time Formats: Full Date" anchor="">
1936  <x:anchor-alias value="HTTP-date"/>
1938   HTTP applications have historically allowed three different formats
1939   for date/time stamps. However, the preferred format is a fixed-length subset
1940   of that defined by <xref target="RFC1123"/>:
1942<figure><artwork type="example" x:indent-with="  ">
1943Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1946   The other formats are described here only for compatibility with obsolete
1947   implementations.
1949<figure><artwork type="example" x:indent-with="  ">
1950Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1951Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1954   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1955   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1956   only generate the RFC 1123 format for representing HTTP-date values
1957   in header fields. See <xref target="tolerant.applications"/> for further information.
1960   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1961   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1962   equal to UTC (Coordinated Universal Time). This is indicated in the
1963   first two formats by the inclusion of "GMT" as the three-letter
1964   abbreviation for time zone, and &MUST; be assumed when reading the
1965   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1966   additional whitespace beyond that specifically included as SP in the
1967   grammar.
1969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1970  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1972<t anchor="">
1973  <x:anchor-alias value="rfc1123-date"/>
1974  <x:anchor-alias value="time-of-day"/>
1975  <x:anchor-alias value="hour"/>
1976  <x:anchor-alias value="minute"/>
1977  <x:anchor-alias value="second"/>
1978  <x:anchor-alias value="day-name"/>
1979  <x:anchor-alias value="day"/>
1980  <x:anchor-alias value="month"/>
1981  <x:anchor-alias value="year"/>
1982  <x:anchor-alias value="GMT"/>
1983  Preferred format:
1985<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"/>
1986  <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>
1987  ; fixed length subset of the format defined in
1988  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1990  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1991               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1992               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1993               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1994               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1995               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1996               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1998  <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>
1999               ; e.g., 02 Jun 1982
2001  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2002  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2003               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2004               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2005               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2006               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2007               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2008               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2009               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2010               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2011               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2012               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2013               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2014  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2016  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2018  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2019                 ; 00:00:00 - 23:59:59
2021  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2022  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2023  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2026  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2027  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2028  same as those defined for the RFC 5322 constructs
2029  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2031<t anchor="">
2032  <x:anchor-alias value="obs-date"/>
2033  <x:anchor-alias value="rfc850-date"/>
2034  <x:anchor-alias value="asctime-date"/>
2035  <x:anchor-alias value="date1"/>
2036  <x:anchor-alias value="date2"/>
2037  <x:anchor-alias value="date3"/>
2038  <x:anchor-alias value="rfc1123-date"/>
2039  <x:anchor-alias value="day-name-l"/>
2040  Obsolete formats:
2042<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2043  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2046  <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>
2047  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2048                 ; day-month-year (e.g., 02-Jun-82)
2050  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2051         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2052         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2053         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2054         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2055         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2056         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2058<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2059  <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>
2060  <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> ))
2061                 ; month day (e.g., Jun  2)
2064  <t>
2065    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2066    accepting date values that might have been sent by non-HTTP
2067    applications, as is sometimes the case when retrieving or posting
2068    messages via proxies/gateways to SMTP or NNTP.
2069  </t>
2072  <t>
2073    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2074    to their usage within the protocol stream. Clients and servers are
2075    not required to use these formats for user presentation, request
2076    logging, etc.
2077  </t>
2081<section title="Transfer Codings" anchor="transfer.codings">
2082  <x:anchor-alias value="transfer-coding"/>
2083  <x:anchor-alias value="transfer-extension"/>
2085   Transfer-coding values are used to indicate an encoding
2086   transformation that has been, can be, or might need to be applied to a
2087   payload body in order to ensure "safe transport" through the network.
2088   This differs from a content coding in that the transfer-coding is a
2089   property of the message rather than a property of the representation
2090   that is being transferred.
2092<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2093  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2094                          / "compress" ; <xref target="compress.coding"/>
2095                          / "deflate" ; <xref target="deflate.coding"/>
2096                          / "gzip" ; <xref target="gzip.coding"/>
2097                          / <x:ref>transfer-extension</x:ref>
2098  <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> )
2100<t anchor="rule.parameter">
2101  <x:anchor-alias value="attribute"/>
2102  <x:anchor-alias value="transfer-parameter"/>
2103  <x:anchor-alias value="value"/>
2104   Parameters are in the form of attribute/value pairs.
2106<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"/>
2107  <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>
2108  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2109  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2112   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2113   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2114   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2117   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2118   MIME, which were designed to enable safe transport of binary data over a
2119   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2120   However, safe transport
2121   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2122   the only unsafe characteristic of message-bodies is the difficulty in
2123   determining the exact message body length (<xref target="message.body"/>),
2124   or the desire to encrypt data over a shared transport.
2127   A server that receives a request message with a transfer-coding it does
2128   not understand &SHOULD; respond with 501 (Not Implemented) and then
2129   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2130   client.
2133<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2134  <iref item="chunked (Coding Format)"/>
2135  <iref item="Coding Format" subitem="chunked"/>
2136  <x:anchor-alias value="chunk"/>
2137  <x:anchor-alias value="Chunked-Body"/>
2138  <x:anchor-alias value="chunk-data"/>
2139  <x:anchor-alias value="chunk-ext"/>
2140  <x:anchor-alias value="chunk-ext-name"/>
2141  <x:anchor-alias value="chunk-ext-val"/>
2142  <x:anchor-alias value="chunk-size"/>
2143  <x:anchor-alias value="last-chunk"/>
2144  <x:anchor-alias value="trailer-part"/>
2145  <x:anchor-alias value="quoted-str-nf"/>
2146  <x:anchor-alias value="qdtext-nf"/>
2148   The chunked encoding modifies the body of a message in order to
2149   transfer it as a series of chunks, each with its own size indicator,
2150   followed by an &OPTIONAL; trailer containing header fields. This
2151   allows dynamically produced content to be transferred along with the
2152   information necessary for the recipient to verify that it has
2153   received the full message.
2155<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"/>
2156  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2157                   <x:ref>last-chunk</x:ref>
2158                   <x:ref>trailer-part</x:ref>
2159                   <x:ref>CRLF</x:ref>
2161  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2162                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2163  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2164  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2166  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2167                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2168  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2169  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2170  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2171  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2173  <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>
2174                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2175  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2176                 ; <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>
2179   The chunk-size field is a string of hex digits indicating the size of
2180   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2181   zero, followed by the trailer, which is terminated by an empty line.
2184   The trailer allows the sender to include additional HTTP header
2185   fields at the end of the message. The Trailer header field can be
2186   used to indicate which header fields are included in a trailer (see
2187   <xref target="header.trailer"/>).
2190   A server using chunked transfer-coding in a response &MUST-NOT; use the
2191   trailer for any header fields unless at least one of the following is
2192   true:
2193  <list style="numbers">
2194    <t>the request included a TE header field that indicates "trailers" is
2195     acceptable in the transfer-coding of the  response, as described in
2196     <xref target="header.te"/>; or,</t>
2198    <t>the trailer fields consist entirely of optional metadata, and the
2199    recipient could use the message (in a manner acceptable to the server where
2200    the field originated) without receiving it. In other words, the server that
2201    generated the header (often but not always the origin server) is willing to
2202    accept the possibility that the trailer fields might be silently discarded
2203    along the path to the client.</t>
2204  </list>
2207   This requirement prevents an interoperability failure when the
2208   message is being received by an HTTP/1.1 (or later) proxy and
2209   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2210   compliance with the protocol would have necessitated a possibly
2211   infinite buffer on the proxy.
2214   A process for decoding the "chunked" transfer-coding
2215   can be represented in pseudo-code as:
2217<figure><artwork type="code">
2218  length := 0
2219  read chunk-size, chunk-ext (if any) and CRLF
2220  while (chunk-size &gt; 0) {
2221     read chunk-data and CRLF
2222     append chunk-data to decoded-body
2223     length := length + chunk-size
2224     read chunk-size and CRLF
2225  }
2226  read header-field
2227  while (header-field not empty) {
2228     append header-field to existing header fields
2229     read header-field
2230  }
2231  Content-Length := length
2232  Remove "chunked" from Transfer-Encoding
2235   All HTTP/1.1 applications &MUST; be able to receive and decode the
2236   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2237   they do not understand.
2240   Since "chunked" is the only transfer-coding required to be understood
2241   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2242   on a persistent connection.  Whenever a transfer-coding is applied to
2243   a payload body in a request, the final transfer-coding applied &MUST;
2244   be "chunked".  If a transfer-coding is applied to a response payload
2245   body, then either the final transfer-coding applied &MUST; be "chunked"
2246   or the message &MUST; be terminated by closing the connection. When the
2247   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2248   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2249   be applied more than once in a message-body.
2253<section title="Compression Codings" anchor="compression.codings">
2255   The codings defined below can be used to compress the payload of a
2256   message.
2259   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2260   is not desirable and is discouraged for future encodings. Their
2261   use here is representative of historical practice, not good
2262   design.
2265   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2266   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2267   equivalent to "gzip" and "compress" respectively.
2270<section title="Compress Coding" anchor="compress.coding">
2271<iref item="compress (Coding Format)"/>
2272<iref item="Coding Format" subitem="compress"/>
2274   The "compress" format is produced by the common UNIX file compression
2275   program "compress". This format is an adaptive Lempel-Ziv-Welch
2276   coding (LZW).
2280<section title="Deflate Coding" anchor="deflate.coding">
2281<iref item="deflate (Coding Format)"/>
2282<iref item="Coding Format" subitem="deflate"/>
2284   The "deflate" format is defined as the "deflate" compression mechanism
2285   (described in <xref target="RFC1951"/>) used inside the "zlib"
2286   data format (<xref target="RFC1950"/>).
2289  <t>
2290    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2291    compressed data without the zlib wrapper.
2292   </t>
2296<section title="Gzip Coding" anchor="gzip.coding">
2297<iref item="gzip (Coding Format)"/>
2298<iref item="Coding Format" subitem="gzip"/>
2300   The "gzip" format is produced by the file compression program
2301   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2302   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2308<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2310   The HTTP Transfer Coding Registry defines the name space for the transfer
2311   coding names.
2314   Registrations &MUST; include the following fields:
2315   <list style="symbols">
2316     <t>Name</t>
2317     <t>Description</t>
2318     <t>Pointer to specification text</t>
2319   </list>
2322   Names of transfer codings &MUST-NOT; overlap with names of content codings
2323   (&content-codings;), unless the encoding transformation is identical (as it
2324   is the case for the compression codings defined in
2325   <xref target="compression.codings"/>).
2328   Values to be added to this name space require a specification
2329   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2330   conform to the purpose of transfer coding defined in this section.
2333   The registry itself is maintained at
2334   <eref target=""/>.
2339<section title="Product Tokens" anchor="product.tokens">
2340  <x:anchor-alias value="product"/>
2341  <x:anchor-alias value="product-version"/>
2343   Product tokens are used to allow communicating applications to
2344   identify themselves by software name and version. Most fields using
2345   product tokens also allow sub-products which form a significant part
2346   of the application to be listed, separated by whitespace. By
2347   convention, the products are listed in order of their significance
2348   for identifying the application.
2350<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2351  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2352  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2355   Examples:
2357<figure><artwork type="example">
2358  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2359  Server: Apache/0.8.4
2362   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2363   used for advertising or other non-essential information. Although any
2364   token character &MAY; appear in a product-version, this token &SHOULD;
2365   only be used for a version identifier (i.e., successive versions of
2366   the same product &SHOULD; only differ in the product-version portion of
2367   the product value).
2371<section title="Quality Values" anchor="quality.values">
2372  <x:anchor-alias value="qvalue"/>
2374   Both transfer codings (TE request header field, <xref target="header.te"/>)
2375   and content negotiation (&content.negotiation;) use short "floating point"
2376   numbers to indicate the relative importance ("weight") of various
2377   negotiable parameters.  A weight is normalized to a real number in
2378   the range 0 through 1, where 0 is the minimum and 1 the maximum
2379   value. If a parameter has a quality value of 0, then content with
2380   this parameter is "not acceptable" for the client. HTTP/1.1
2381   applications &MUST-NOT; generate more than three digits after the
2382   decimal point. User configuration of these values &SHOULD; also be
2383   limited in this fashion.
2385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2386  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2387                 / ( "1" [ "." 0*3("0") ] )
2390  <t>
2391     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2392     relative degradation in desired quality.
2393  </t>
2399<section title="Connections" anchor="connections">
2401<section title="Persistent Connections" anchor="persistent.connections">
2403<section title="Purpose" anchor="persistent.purpose">
2405   Prior to persistent connections, a separate TCP connection was
2406   established to fetch each URL, increasing the load on HTTP servers
2407   and causing congestion on the Internet. The use of inline images and
2408   other associated data often requires a client to make multiple
2409   requests of the same server in a short amount of time. Analysis of
2410   these performance problems and results from a prototype
2411   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2412   measurements of actual HTTP/1.1 implementations show good
2413   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2414   T/TCP <xref target="Tou1998"/>.
2417   Persistent HTTP connections have a number of advantages:
2418  <list style="symbols">
2419      <t>
2420        By opening and closing fewer TCP connections, CPU time is saved
2421        in routers and hosts (clients, servers, proxies, gateways,
2422        tunnels, or caches), and memory used for TCP protocol control
2423        blocks can be saved in hosts.
2424      </t>
2425      <t>
2426        HTTP requests and responses can be pipelined on a connection.
2427        Pipelining allows a client to make multiple requests without
2428        waiting for each response, allowing a single TCP connection to
2429        be used much more efficiently, with much lower elapsed time.
2430      </t>
2431      <t>
2432        Network congestion is reduced by reducing the number of packets
2433        caused by TCP opens, and by allowing TCP sufficient time to
2434        determine the congestion state of the network.
2435      </t>
2436      <t>
2437        Latency on subsequent requests is reduced since there is no time
2438        spent in TCP's connection opening handshake.
2439      </t>
2440      <t>
2441        HTTP can evolve more gracefully, since errors can be reported
2442        without the penalty of closing the TCP connection. Clients using
2443        future versions of HTTP might optimistically try a new feature,
2444        but if communicating with an older server, retry with old
2445        semantics after an error is reported.
2446      </t>
2447    </list>
2450   HTTP implementations &SHOULD; implement persistent connections.
2454<section title="Overall Operation" anchor="persistent.overall">
2456   A significant difference between HTTP/1.1 and earlier versions of
2457   HTTP is that persistent connections are the default behavior of any
2458   HTTP connection. That is, unless otherwise indicated, the client
2459   &SHOULD; assume that the server will maintain a persistent connection,
2460   even after error responses from the server.
2463   Persistent connections provide a mechanism by which a client and a
2464   server can signal the close of a TCP connection. This signaling takes
2465   place using the Connection header field (<xref target="header.connection"/>). Once a close
2466   has been signaled, the client &MUST-NOT; send any more requests on that
2467   connection.
2470<section title="Negotiation" anchor="persistent.negotiation">
2472   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2473   maintain a persistent connection unless a Connection header field including
2474   the connection-token "close" was sent in the request. If the server
2475   chooses to close the connection immediately after sending the
2476   response, it &SHOULD; send a Connection header field including the
2477   connection-token "close".
2480   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2481   decide to keep it open based on whether the response from a server
2482   contains a Connection header field with the connection-token close. In case
2483   the client does not want to maintain a connection for more than that
2484   request, it &SHOULD; send a Connection header field including the
2485   connection-token close.
2488   If either the client or the server sends the close token in the
2489   Connection header field, that request becomes the last one for the
2490   connection.
2493   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2494   maintained for HTTP versions less than 1.1 unless it is explicitly
2495   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2496   compatibility with HTTP/1.0 clients.
2499   In order to remain persistent, all messages on the connection &MUST;
2500   have a self-defined message length (i.e., one not defined by closure
2501   of the connection), as described in <xref target="message.body"/>.
2505<section title="Pipelining" anchor="pipelining">
2507   A client that supports persistent connections &MAY; "pipeline" its
2508   requests (i.e., send multiple requests without waiting for each
2509   response). A server &MUST; send its responses to those requests in the
2510   same order that the requests were received.
2513   Clients which assume persistent connections and pipeline immediately
2514   after connection establishment &SHOULD; be prepared to retry their
2515   connection if the first pipelined attempt fails. If a client does
2516   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2517   persistent. Clients &MUST; also be prepared to resend their requests if
2518   the server closes the connection before sending all of the
2519   corresponding responses.
2522   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2523   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2524   premature termination of the transport connection could lead to
2525   indeterminate results. A client wishing to send a non-idempotent
2526   request &SHOULD; wait to send that request until it has received the
2527   response status line for the previous request.
2532<section title="Proxy Servers" anchor="persistent.proxy">
2534   It is especially important that proxies correctly implement the
2535   properties of the Connection header field as specified in <xref target="header.connection"/>.
2538   The proxy server &MUST; signal persistent connections separately with
2539   its clients and the origin servers (or other proxy servers) that it
2540   connects to. Each persistent connection applies to only one transport
2541   link.
2544   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2545   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2546   for information and discussion of the problems with the Keep-Alive header field
2547   implemented by many HTTP/1.0 clients).
2550<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2552  <cref anchor="TODO-end-to-end" source="jre">
2553    Restored from <eref target=""/>.
2554    See also <eref target=""/>.
2555  </cref>
2558   For the purpose of defining the behavior of caches and non-caching
2559   proxies, we divide HTTP header fields into two categories:
2560  <list style="symbols">
2561      <t>End-to-end header fields, which are  transmitted to the ultimate
2562        recipient of a request or response. End-to-end header fields in
2563        responses MUST be stored as part of a cache entry and &MUST; be
2564        transmitted in any response formed from a cache entry.</t>
2566      <t>Hop-by-hop header fields, which are meaningful only for a single
2567        transport-level connection, and are not stored by caches or
2568        forwarded by proxies.</t>
2569  </list>
2572   The following HTTP/1.1 header fields are hop-by-hop header fields:
2573  <list style="symbols">
2574      <t>Connection</t>
2575      <t>Keep-Alive</t>
2576      <t>Proxy-Authenticate</t>
2577      <t>Proxy-Authorization</t>
2578      <t>TE</t>
2579      <t>Trailer</t>
2580      <t>Transfer-Encoding</t>
2581      <t>Upgrade</t>
2582  </list>
2585   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2588   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2589   (<xref target="header.connection"/>).
2593<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2595  <cref anchor="TODO-non-mod-headers" source="jre">
2596    Restored from <eref target=""/>.
2597    See also <eref target=""/>.
2598  </cref>
2601   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2602   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2603   modify an end-to-end header field unless the definition of that header field requires
2604   or specifically allows that.
2607   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2608   request or response, and it &MUST-NOT; add any of these fields if not
2609   already present:
2610  <list style="symbols">
2611      <t>Content-Location</t>
2612      <t>Content-MD5</t>
2613      <t>ETag</t>
2614      <t>Last-Modified</t>
2615  </list>
2618   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2619   response:
2620  <list style="symbols">
2621    <t>Expires</t>
2622  </list>
2625   but it &MAY; add any of these fields if not already present. If an
2626   Expires header field is added, it &MUST; be given a field-value identical to
2627   that of the Date header field in that response.
2630   A proxy &MUST-NOT; modify or add any of the following fields in a
2631   message that contains the no-transform cache-control directive, or in
2632   any request:
2633  <list style="symbols">
2634    <t>Content-Encoding</t>
2635    <t>Content-Range</t>
2636    <t>Content-Type</t>
2637  </list>
2640   A transforming proxy &MAY; modify or add these fields to a message
2641   that does not include no-transform, but if it does so, it &MUST; add a
2642   Warning 214 (Transformation applied) if one does not already appear
2643   in the message (see &header-warning;).
2646  <t>
2647    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2648    cause authentication failures if stronger authentication
2649    mechanisms are introduced in later versions of HTTP. Such
2650    authentication mechanisms &MAY; rely on the values of header fields
2651    not listed here.
2652  </t>
2655   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2656   though it &MAY; change the message-body through application or removal
2657   of a transfer-coding (<xref target="transfer.codings"/>).
2663<section title="Practical Considerations" anchor="persistent.practical">
2665   Servers will usually have some time-out value beyond which they will
2666   no longer maintain an inactive connection. Proxy servers might make
2667   this a higher value since it is likely that the client will be making
2668   more connections through the same server. The use of persistent
2669   connections places no requirements on the length (or existence) of
2670   this time-out for either the client or the server.
2673   When a client or server wishes to time-out it &SHOULD; issue a graceful
2674   close on the transport connection. Clients and servers &SHOULD; both
2675   constantly watch for the other side of the transport close, and
2676   respond to it as appropriate. If a client or server does not detect
2677   the other side's close promptly it could cause unnecessary resource
2678   drain on the network.
2681   A client, server, or proxy &MAY; close the transport connection at any
2682   time. For example, a client might have started to send a new request
2683   at the same time that the server has decided to close the "idle"
2684   connection. From the server's point of view, the connection is being
2685   closed while it was idle, but from the client's point of view, a
2686   request is in progress.
2689   This means that clients, servers, and proxies &MUST; be able to recover
2690   from asynchronous close events. Client software &SHOULD; reopen the
2691   transport connection and retransmit the aborted sequence of requests
2692   without user interaction so long as the request sequence is
2693   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2694   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2695   human operator the choice of retrying the request(s). Confirmation by
2696   user-agent software with semantic understanding of the application
2697   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2698   be repeated if the second sequence of requests fails.
2701   Servers &SHOULD; always respond to at least one request per connection,
2702   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2703   middle of transmitting a response, unless a network or client failure
2704   is suspected.
2707   Clients (including proxies) &SHOULD; limit the number of simultaneous
2708   connections that they maintain to a given server (including proxies).
2711   Previous revisions of HTTP gave a specific number of connections as a
2712   ceiling, but this was found to be impractical for many applications. As a
2713   result, this specification does not mandate a particular maximum number of
2714   connections, but instead encourages clients to be conservative when opening
2715   multiple connections.
2718   In particular, while using multiple connections avoids the "head-of-line
2719   blocking" problem (whereby a request that takes significant server-side
2720   processing and/or has a large payload can block subsequent requests on the
2721   same connection), each connection used consumes server resources (sometimes
2722   significantly), and furthermore using multiple connections can cause
2723   undesirable side effects in congested networks.
2726   Note that servers might reject traffic that they deem abusive, including an
2727   excessive number of connections from a client.
2732<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2734<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2736   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2737   flow control mechanisms to resolve temporary overloads, rather than
2738   terminating connections with the expectation that clients will retry.
2739   The latter technique can exacerbate network congestion.
2743<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2745   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2746   the network connection for an error status code while it is transmitting
2747   the request. If the client sees an error status code, it &SHOULD;
2748   immediately cease transmitting the body. If the body is being sent
2749   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2750   empty trailer &MAY; be used to prematurely mark the end of the message.
2751   If the body was preceded by a Content-Length header field, the client &MUST;
2752   close the connection.
2756<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2758   The purpose of the 100 (Continue) status code (see &status-100;) is to
2759   allow a client that is sending a request message with a request body
2760   to determine if the origin server is willing to accept the request
2761   (based on the request header fields) before the client sends the request
2762   body. In some cases, it might either be inappropriate or highly
2763   inefficient for the client to send the body if the server will reject
2764   the message without looking at the body.
2767   Requirements for HTTP/1.1 clients:
2768  <list style="symbols">
2769    <t>
2770        If a client will wait for a 100 (Continue) response before
2771        sending the request body, it &MUST; send an Expect request-header
2772        field (&header-expect;) with the "100-continue" expectation.
2773    </t>
2774    <t>
2775        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2776        with the "100-continue" expectation if it does not intend
2777        to send a request body.
2778    </t>
2779  </list>
2782   Because of the presence of older implementations, the protocol allows
2783   ambiguous situations in which a client might send "Expect: 100-continue"
2784   without receiving either a 417 (Expectation Failed)
2785   or a 100 (Continue) status code. Therefore, when a client sends this
2786   header field to an origin server (possibly via a proxy) from which it
2787   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2788   wait for an indefinite period before sending the request body.
2791   Requirements for HTTP/1.1 origin servers:
2792  <list style="symbols">
2793    <t> Upon receiving a request which includes an Expect request-header
2794        field with the "100-continue" expectation, an origin server &MUST;
2795        either respond with 100 (Continue) status code and continue to read
2796        from the input stream, or respond with a final status code. The
2797        origin server &MUST-NOT; wait for the request body before sending
2798        the 100 (Continue) response. If it responds with a final status
2799        code, it &MAY; close the transport connection or it &MAY; continue
2800        to read and discard the rest of the request.  It &MUST-NOT;
2801        perform the requested method if it returns a final status code.
2802    </t>
2803    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2804        the request message does not include an Expect request-header
2805        field with the "100-continue" expectation, and &MUST-NOT; send a
2806        100 (Continue) response if such a request comes from an HTTP/1.0
2807        (or earlier) client. There is an exception to this rule: for
2808        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2809        status code in response to an HTTP/1.1 PUT or POST request that does
2810        not include an Expect request-header field with the "100-continue"
2811        expectation. This exception, the purpose of which is
2812        to minimize any client processing delays associated with an
2813        undeclared wait for 100 (Continue) status code, applies only to
2814        HTTP/1.1 requests, and not to requests with any other HTTP-version
2815        value.
2816    </t>
2817    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2818        already received some or all of the request body for the
2819        corresponding request.
2820    </t>
2821    <t> An origin server that sends a 100 (Continue) response &MUST;
2822    ultimately send a final status code, once the request body is
2823        received and processed, unless it terminates the transport
2824        connection prematurely.
2825    </t>
2826    <t> If an origin server receives a request that does not include an
2827        Expect request-header field with the "100-continue" expectation,
2828        the request includes a request body, and the server responds
2829        with a final status code before reading the entire request body
2830        from the transport connection, then the server &SHOULD-NOT;  close
2831        the transport connection until it has read the entire request,
2832        or until the client closes the connection. Otherwise, the client
2833        might not reliably receive the response message. However, this
2834        requirement is not be construed as preventing a server from
2835        defending itself against denial-of-service attacks, or from
2836        badly broken client implementations.
2837      </t>
2838    </list>
2841   Requirements for HTTP/1.1 proxies:
2842  <list style="symbols">
2843    <t> If a proxy receives a request that includes an Expect request-header
2844        field with the "100-continue" expectation, and the proxy
2845        either knows that the next-hop server complies with HTTP/1.1 or
2846        higher, or does not know the HTTP version of the next-hop
2847        server, it &MUST; forward the request, including the Expect header
2848        field.
2849    </t>
2850    <t> If the proxy knows that the version of the next-hop server is
2851        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2852        respond with a 417 (Expectation Failed) status code.
2853    </t>
2854    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2855        numbers received from recently-referenced next-hop servers.
2856    </t>
2857    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2858        request message was received from an HTTP/1.0 (or earlier)
2859        client and did not include an Expect request-header field with
2860        the "100-continue" expectation. This requirement overrides the
2861        general rule for forwarding of 1xx responses (see &status-1xx;).
2862    </t>
2863  </list>
2867<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2869   If an HTTP/1.1 client sends a request which includes a request body,
2870   but which does not include an Expect request-header field with the
2871   "100-continue" expectation, and if the client is not directly
2872   connected to an HTTP/1.1 origin server, and if the client sees the
2873   connection close before receiving a status line from the server, the
2874   client &SHOULD; retry the request.  If the client does retry this
2875   request, it &MAY; use the following "binary exponential backoff"
2876   algorithm to be assured of obtaining a reliable response:
2877  <list style="numbers">
2878    <t>
2879      Initiate a new connection to the server
2880    </t>
2881    <t>
2882      Transmit the request-header fields
2883    </t>
2884    <t>
2885      Initialize a variable R to the estimated round-trip time to the
2886         server (e.g., based on the time it took to establish the
2887         connection), or to a constant value of 5 seconds if the round-trip
2888         time is not available.
2889    </t>
2890    <t>
2891       Compute T = R * (2**N), where N is the number of previous
2892         retries of this request.
2893    </t>
2894    <t>
2895       Wait either for an error response from the server, or for T
2896         seconds (whichever comes first)
2897    </t>
2898    <t>
2899       If no error response is received, after T seconds transmit the
2900         body of the request.
2901    </t>
2902    <t>
2903       If client sees that the connection is closed prematurely,
2904         repeat from step 1 until the request is accepted, an error
2905         response is received, or the user becomes impatient and
2906         terminates the retry process.
2907    </t>
2908  </list>
2911   If at any point an error status code is received, the client
2912  <list style="symbols">
2913      <t>&SHOULD-NOT;  continue and</t>
2915      <t>&SHOULD; close the connection if it has not completed sending the
2916        request message.</t>
2917    </list>
2924<section title="Miscellaneous notes that might disappear" anchor="misc">
2925<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2927   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2931<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2933   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2937<section title="Interception of HTTP for access control" anchor="http.intercept">
2939   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2943<section title="Use of HTTP by other protocols" anchor="http.others">
2945   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2946   Extensions of HTTP like WebDAV.</cref>
2950<section title="Use of HTTP by media type specification" anchor="">
2952   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2957<section title="Header Field Definitions" anchor="header.field.definitions">
2959   This section defines the syntax and semantics of HTTP/1.1 header fields
2960   related to message framing and transport protocols.
2963<section title="Connection" anchor="header.connection">
2964  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2965  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2966  <x:anchor-alias value="Connection"/>
2967  <x:anchor-alias value="connection-token"/>
2968  <x:anchor-alias value="Connection-v"/>
2970   The "Connection" general-header field allows the sender to specify
2971   options that are desired for that particular connection and &MUST-NOT;
2972   be communicated by proxies over further connections.
2975   The Connection header field's value has the following grammar:
2977<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"/>
2978  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2979  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2980  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2983   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2984   message is forwarded and, for each connection-token in this field,
2985   remove any header field(s) from the message with the same name as the
2986   connection-token. Connection options are signaled by the presence of
2987   a connection-token in the Connection header field, not by any
2988   corresponding additional header field(s), since the additional header
2989   field might not be sent if there are no parameters associated with that
2990   connection option.
2993   Message header fields listed in the Connection header field &MUST-NOT; include
2994   end-to-end header fields, such as Cache-Control.
2997   HTTP/1.1 defines the "close" connection option for the sender to
2998   signal that the connection will be closed after completion of the
2999   response. For example,
3001<figure><artwork type="example">
3002  Connection: close
3005   in either the request or the response header fields indicates that
3006   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3007   after the current request/response is complete.
3010   An HTTP/1.1 client that does not support persistent connections &MUST;
3011   include the "close" connection option in every request message.
3014   An HTTP/1.1 server that does not support persistent connections &MUST;
3015   include the "close" connection option in every response message that
3016   does not have a 1xx (Informational) status code.
3019   A system receiving an HTTP/1.0 (or lower-version) message that
3020   includes a Connection header field &MUST;, for each connection-token in this
3021   field, remove and ignore any header field(s) from the message with
3022   the same name as the connection-token. This protects against mistaken
3023   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
3027<section title="Content-Length" anchor="header.content-length">
3028  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3029  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3030  <x:anchor-alias value="Content-Length"/>
3031  <x:anchor-alias value="Content-Length-v"/>
3033   The "Content-Length" header field indicates the size of the
3034   message-body, in decimal number of octets, for any message other than
3035   a response to the HEAD method or a response with a status code of 304.
3036   In the case of responses to the HEAD method, it indicates the size of
3037   the payload body (not including any potential transfer-coding) that
3038   would have been sent had the request been a GET.
3039   In the case of the 304 (Not Modified) response, it indicates the size of
3040   the payload body (not including any potential transfer-coding) that
3041   would have been sent in a 200 (OK) response.
3043<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3044  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3045  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3048   An example is
3050<figure><artwork type="example">
3051  Content-Length: 3495
3054   Implementations &SHOULD; use this field to indicate the message-body
3055   length when no transfer-coding is being applied and the
3056   payload's body length can be determined prior to being transferred.
3057   <xref target="message.body"/> describes how recipients determine the length
3058   of a message-body.
3061   Any Content-Length greater than or equal to zero is a valid value.
3064   Note that the use of this field in HTTP is significantly different from
3065   the corresponding definition in MIME, where it is an optional field
3066   used within the "message/external-body" content-type.
3070<section title="Date" anchor="">
3071  <iref primary="true" item="Date header field" x:for-anchor=""/>
3072  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3073  <x:anchor-alias value="Date"/>
3074  <x:anchor-alias value="Date-v"/>
3076   The "Date" general-header field represents the date and time at which
3077   the message was originated, having the same semantics as the Origination
3078   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3079   The field value is an HTTP-date, as described in <xref target=""/>;
3080   it &MUST; be sent in rfc1123-date format.
3082<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3083  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3084  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3087   An example is
3089<figure><artwork type="example">
3090  Date: Tue, 15 Nov 1994 08:12:31 GMT
3093   Origin servers &MUST; include a Date header field in all responses,
3094   except in these cases:
3095  <list style="numbers">
3096      <t>If the response status code is 100 (Continue) or 101 (Switching
3097         Protocols), the response &MAY; include a Date header field, at
3098         the server's option.</t>
3100      <t>If the response status code conveys a server error, e.g., 500
3101         (Internal Server Error) or 503 (Service Unavailable), and it is
3102         inconvenient or impossible to generate a valid Date.</t>
3104      <t>If the server does not have a clock that can provide a
3105         reasonable approximation of the current time, its responses
3106         &MUST-NOT; include a Date header field. In this case, the rules
3107         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3108  </list>
3111   A received message that does not have a Date header field &MUST; be
3112   assigned one by the recipient if the message will be cached by that
3113   recipient or gatewayed via a protocol which requires a Date.
3116   Clients can use the Date header field as well; in order to keep request
3117   messages small, they are advised not to include it when it doesn't convey
3118   any useful information (as it is usually the case for requests that do not
3119   contain a payload).
3122   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3123   time subsequent to the generation of the message. It &SHOULD; represent
3124   the best available approximation of the date and time of message
3125   generation, unless the implementation has no means of generating a
3126   reasonably accurate date and time. In theory, the date ought to
3127   represent the moment just before the payload is generated. In
3128   practice, the date can be generated at any time during the message
3129   origination without affecting its semantic value.
3132<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3134   Some origin server implementations might not have a clock available.
3135   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3136   values to a response, unless these values were associated
3137   with the resource by a system or user with a reliable clock. It &MAY;
3138   assign an Expires value that is known, at or before server
3139   configuration time, to be in the past (this allows "pre-expiration"
3140   of responses without storing separate Expires values for each
3141   resource).
3146<section title="Host" anchor="">
3147  <iref primary="true" item="Host header field" x:for-anchor=""/>
3148  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3149  <x:anchor-alias value="Host"/>
3150  <x:anchor-alias value="Host-v"/>
3152   The "Host" request-header field specifies the Internet host and port
3153   number of the resource being requested, allowing the origin server or
3154   gateway to differentiate between internally-ambiguous URLs, such as the root
3155   "/" URL of a server for multiple host names on a single IP address.
3158   The Host field value &MUST; represent the naming authority of the origin
3159   server or gateway given by the original URL obtained from the user or
3160   referring resource (generally an http URI, as described in
3161   <xref target="http.uri"/>).
3163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3164  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3165  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3168   A "host" without any trailing port information implies the default
3169   port for the service requested (e.g., "80" for an HTTP URL). For
3170   example, a request on the origin server for
3171   &lt;; would properly include:
3173<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3174GET /pub/WWW/ HTTP/1.1
3178   A client &MUST; include a Host header field in all HTTP/1.1 request
3179   messages. If the requested URI does not include an Internet host
3180   name for the service being requested, then the Host header field &MUST;
3181   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3182   request message it forwards does contain an appropriate Host header
3183   field that identifies the service being requested by the proxy. All
3184   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3185   status code to any HTTP/1.1 request message which lacks a Host header
3186   field.
3189   See Sections <xref target="" format="counter"/>
3190   and <xref target="" format="counter"/>
3191   for other requirements relating to Host.
3195<section title="TE" anchor="header.te">
3196  <iref primary="true" item="TE header field" x:for-anchor=""/>
3197  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3198  <x:anchor-alias value="TE"/>
3199  <x:anchor-alias value="TE-v"/>
3200  <x:anchor-alias value="t-codings"/>
3201  <x:anchor-alias value="te-params"/>
3202  <x:anchor-alias value="te-ext"/>
3204   The "TE" request-header field indicates what extension transfer-codings
3205   it is willing to accept in the response, and whether or not it is
3206   willing to accept trailer fields in a chunked transfer-coding.
3209   Its value consists of the keyword "trailers" and/or a comma-separated
3210   list of extension transfer-coding names with optional accept
3211   parameters (as described in <xref target="transfer.codings"/>).
3213<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"/>
3214  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3215  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3216  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3217  <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> )
3218  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3221   The presence of the keyword "trailers" indicates that the client is
3222   willing to accept trailer fields in a chunked transfer-coding, as
3223   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3224   transfer-coding values even though it does not itself represent a
3225   transfer-coding.
3228   Examples of its use are:
3230<figure><artwork type="example">
3231  TE: deflate
3232  TE:
3233  TE: trailers, deflate;q=0.5
3236   The TE header field only applies to the immediate connection.
3237   Therefore, the keyword &MUST; be supplied within a Connection header
3238   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3241   A server tests whether a transfer-coding is acceptable, according to
3242   a TE field, using these rules:
3243  <list style="numbers">
3244    <x:lt>
3245      <t>The "chunked" transfer-coding is always acceptable. If the
3246         keyword "trailers" is listed, the client indicates that it is
3247         willing to accept trailer fields in the chunked response on
3248         behalf of itself and any downstream clients. The implication is
3249         that, if given, the client is stating that either all
3250         downstream clients are willing to accept trailer fields in the
3251         forwarded response, or that it will attempt to buffer the
3252         response on behalf of downstream recipients.
3253      </t><t>
3254         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3255         chunked response such that a client can be assured of buffering
3256         the entire response.</t>
3257    </x:lt>
3258    <x:lt>
3259      <t>If the transfer-coding being tested is one of the transfer-codings
3260         listed in the TE field, then it is acceptable unless it
3261         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3262         qvalue of 0 means "not acceptable".)</t>
3263    </x:lt>
3264    <x:lt>
3265      <t>If multiple transfer-codings are acceptable, then the
3266         acceptable transfer-coding with the highest non-zero qvalue is
3267         preferred.  The "chunked" transfer-coding always has a qvalue
3268         of 1.</t>
3269    </x:lt>
3270  </list>
3273   If the TE field-value is empty or if no TE field is present, the only
3274   transfer-coding is "chunked". A message with no transfer-coding is
3275   always acceptable.
3279<section title="Trailer" anchor="header.trailer">
3280  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3281  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3282  <x:anchor-alias value="Trailer"/>
3283  <x:anchor-alias value="Trailer-v"/>
3285   The "Trailer" general-header field indicates that the given set of
3286   header fields is present in the trailer of a message encoded with
3287   chunked transfer-coding.
3289<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3290  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3291  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3294   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3295   message using chunked transfer-coding with a non-empty trailer. Doing
3296   so allows the recipient to know which header fields to expect in the
3297   trailer.
3300   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3301   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3302   trailer fields in a "chunked" transfer-coding.
3305   Message header fields listed in the Trailer header field &MUST-NOT;
3306   include the following header fields:
3307  <list style="symbols">
3308    <t>Transfer-Encoding</t>
3309    <t>Content-Length</t>
3310    <t>Trailer</t>
3311  </list>
3315<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3316  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3317  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3318  <x:anchor-alias value="Transfer-Encoding"/>
3319  <x:anchor-alias value="Transfer-Encoding-v"/>
3321   The "Transfer-Encoding" general-header field indicates what transfer-codings
3322   (if any) have been applied to the message body. It differs from
3323   Content-Encoding (&content-codings;) in that transfer-codings are a property
3324   of the message (and therefore are removed by intermediaries), whereas
3325   content-codings are not.
3327<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3328  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3329                        <x:ref>Transfer-Encoding-v</x:ref>
3330  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3333   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3335<figure><artwork type="example">
3336  Transfer-Encoding: chunked
3339   If multiple encodings have been applied to a representation, the transfer-codings
3340   &MUST; be listed in the order in which they were applied.
3341   Additional information about the encoding parameters &MAY; be provided
3342   by other header fields not defined by this specification.
3345   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3346   header field.
3350<section title="Upgrade" anchor="header.upgrade">
3351  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3352  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3353  <x:anchor-alias value="Upgrade"/>
3354  <x:anchor-alias value="Upgrade-v"/>
3356   The "Upgrade" general-header field allows the client to specify what
3357   additional communication protocols it would like to use, if the server
3358   chooses to switch protocols. Servers can use it to indicate what protocols
3359   they are willing to switch to.
3361<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3362  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3363  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3366   For example,
3368<figure><artwork type="example">
3369  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3372   The Upgrade header field is intended to provide a simple mechanism
3373   for transition from HTTP/1.1 to some other, incompatible protocol. It
3374   does so by allowing the client to advertise its desire to use another
3375   protocol, such as a later version of HTTP with a higher major version
3376   number, even though the current request has been made using HTTP/1.1.
3377   This eases the difficult transition between incompatible protocols by
3378   allowing the client to initiate a request in the more commonly
3379   supported protocol while indicating to the server that it would like
3380   to use a "better" protocol if available (where "better" is determined
3381   by the server, possibly according to the nature of the method and/or
3382   resource being requested).
3385   The Upgrade header field only applies to switching application-layer
3386   protocols upon the existing transport-layer connection. Upgrade
3387   cannot be used to insist on a protocol change; its acceptance and use
3388   by the server is optional. The capabilities and nature of the
3389   application-layer communication after the protocol change is entirely
3390   dependent upon the new protocol chosen, although the first action
3391   after changing the protocol &MUST; be a response to the initial HTTP
3392   request containing the Upgrade header field.
3395   The Upgrade header field only applies to the immediate connection.
3396   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3397   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3398   HTTP/1.1 message.
3401   The Upgrade header field cannot be used to indicate a switch to a
3402   protocol on a different connection. For that purpose, it is more
3403   appropriate to use a 3xx redirection response (&status-3xx;).
3406   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3407   Protocols) responses to indicate which protocol(s) are being switched to,
3408   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3409   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3410   response to indicate that they are willing to upgrade to one of the
3411   specified protocols.
3414   This specification only defines the protocol name "HTTP" for use by
3415   the family of Hypertext Transfer Protocols, as defined by the HTTP
3416   version rules of <xref target="http.version"/> and future updates to this
3417   specification. Additional tokens can be registered with IANA using the
3418   registration procedure defined below. 
3421<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3423   The HTTP Upgrade Token Registry defines the name space for product
3424   tokens used to identify protocols in the Upgrade header field.
3425   Each registered token is associated with contact information and
3426   an optional set of specifications that details how the connection
3427   will be processed after it has been upgraded.
3430   Registrations are allowed on a First Come First Served basis as
3431   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3432   specifications need not be IETF documents or be subject to IESG review.
3433   Registrations are subject to the following rules:
3434  <list style="numbers">
3435    <t>A token, once registered, stays registered forever.</t>
3436    <t>The registration &MUST; name a responsible party for the
3437       registration.</t>
3438    <t>The registration &MUST; name a point of contact.</t>
3439    <t>The registration &MAY; name a set of specifications associated with that
3440       token. Such specifications need not be publicly available.</t>
3441    <t>The responsible party &MAY; change the registration at any time.
3442       The IANA will keep a record of all such changes, and make them
3443       available upon request.</t>
3444    <t>The responsible party for the first registration of a "product"
3445       token &MUST; approve later registrations of a "version" token
3446       together with that "product" token before they can be registered.</t>
3447    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3448       for a token. This will normally only be used in the case when a
3449       responsible party cannot be contacted.</t>
3450  </list>
3457<section title="Via" anchor="header.via">
3458  <iref primary="true" item="Via header field" x:for-anchor=""/>
3459  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3460  <x:anchor-alias value="protocol-name"/>
3461  <x:anchor-alias value="protocol-version"/>
3462  <x:anchor-alias value="pseudonym"/>
3463  <x:anchor-alias value="received-by"/>
3464  <x:anchor-alias value="received-protocol"/>
3465  <x:anchor-alias value="Via"/>
3466  <x:anchor-alias value="Via-v"/>
3468   The "Via" general-header field &MUST; be used by gateways and proxies to
3469   indicate the intermediate protocols and recipients between the user
3470   agent and the server on requests, and between the origin server and
3471   the client on responses. It is analogous to the "Received" field defined in
3472   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3473   avoiding request loops, and identifying the protocol capabilities of
3474   all senders along the request/response chain.
3476<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"/>
3477  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3478  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3479                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3480  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3481  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3482  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3483  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3484  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3487   The received-protocol indicates the protocol version of the message
3488   received by the server or client along each segment of the
3489   request/response chain. The received-protocol version is appended to
3490   the Via field value when the message is forwarded so that information
3491   about the protocol capabilities of upstream applications remains
3492   visible to all recipients.
3495   The protocol-name is optional if and only if it would be "HTTP". The
3496   received-by field is normally the host and optional port number of a
3497   recipient server or client that subsequently forwarded the message.
3498   However, if the real host is considered to be sensitive information,
3499   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3500   be assumed to be the default port of the received-protocol.
3503   Multiple Via field values represent each proxy or gateway that has
3504   forwarded the message. Each recipient &MUST; append its information
3505   such that the end result is ordered according to the sequence of
3506   forwarding applications.
3509   Comments &MAY; be used in the Via header field to identify the software
3510   of the recipient proxy or gateway, analogous to the User-Agent and
3511   Server header fields. However, all comments in the Via field are
3512   optional and &MAY; be removed by any recipient prior to forwarding the
3513   message.
3516   For example, a request message could be sent from an HTTP/1.0 user
3517   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3518   forward the request to a public proxy at, which completes
3519   the request by forwarding it to the origin server at
3520   The request received by would then have the following
3521   Via header field:
3523<figure><artwork type="example">
3524  Via: 1.0 fred, 1.1 (Apache/1.1)
3527   Proxies and gateways used as a portal through a network firewall
3528   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3529   the firewall region. This information &SHOULD; only be propagated if
3530   explicitly enabled. If not enabled, the received-by host of any host
3531   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3532   for that host.
3535   For organizations that have strong privacy requirements for hiding
3536   internal structures, a proxy &MAY; combine an ordered subsequence of
3537   Via header field entries with identical received-protocol values into
3538   a single such entry. For example,
3540<figure><artwork type="example">
3541  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3544  could be collapsed to
3546<figure><artwork type="example">
3547  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3550   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3551   under the same organizational control and the hosts have already been
3552   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3553   have different received-protocol values.
3559<section title="IANA Considerations" anchor="IANA.considerations">
3561<section title="Header Field Registration" anchor="header.field.registration">
3563   The Message Header Field Registry located at <eref target=""/> shall be updated
3564   with the permanent registrations below (see <xref target="RFC3864"/>):
3566<?BEGININC p1-messaging.iana-headers ?>
3567<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3568<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3569   <ttcol>Header Field Name</ttcol>
3570   <ttcol>Protocol</ttcol>
3571   <ttcol>Status</ttcol>
3572   <ttcol>Reference</ttcol>
3574   <c>Connection</c>
3575   <c>http</c>
3576   <c>standard</c>
3577   <c>
3578      <xref target="header.connection"/>
3579   </c>
3580   <c>Content-Length</c>
3581   <c>http</c>
3582   <c>standard</c>
3583   <c>
3584      <xref target="header.content-length"/>
3585   </c>
3586   <c>Date</c>
3587   <c>http</c>
3588   <c>standard</c>
3589   <c>
3590      <xref target=""/>
3591   </c>
3592   <c>Host</c>
3593   <c>http</c>
3594   <c>standard</c>
3595   <c>
3596      <xref target=""/>
3597   </c>
3598   <c>TE</c>
3599   <c>http</c>
3600   <c>standard</c>
3601   <c>
3602      <xref target="header.te"/>
3603   </c>
3604   <c>Trailer</c>
3605   <c>http</c>
3606   <c>standard</c>
3607   <c>
3608      <xref target="header.trailer"/>
3609   </c>
3610   <c>Transfer-Encoding</c>
3611   <c>http</c>
3612   <c>standard</c>
3613   <c>
3614      <xref target="header.transfer-encoding"/>
3615   </c>
3616   <c>Upgrade</c>
3617   <c>http</c>
3618   <c>standard</c>
3619   <c>
3620      <xref target="header.upgrade"/>
3621   </c>
3622   <c>Via</c>
3623   <c>http</c>
3624   <c>standard</c>
3625   <c>
3626      <xref target="header.via"/>
3627   </c>
3630<?ENDINC p1-messaging.iana-headers ?>
3632   The change controller is: "IETF ( - Internet Engineering Task Force".
3636<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3638   The entries for the "http" and "https" URI Schemes in the registry located at
3639   <eref target=""/>
3640   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3641   and <xref target="https.uri" format="counter"/> of this document
3642   (see <xref target="RFC4395"/>).
3646<section title="Internet Media Type Registrations" anchor="">
3648   This document serves as the specification for the Internet media types
3649   "message/http" and "application/http". The following is to be registered with
3650   IANA (see <xref target="RFC4288"/>).
3652<section title="Internet Media Type message/http" anchor="">
3653<iref item="Media Type" subitem="message/http" primary="true"/>
3654<iref item="message/http Media Type" primary="true"/>
3656   The message/http type can be used to enclose a single HTTP request or
3657   response message, provided that it obeys the MIME restrictions for all
3658   "message" types regarding line length and encodings.
3661  <list style="hanging" x:indent="12em">
3662    <t hangText="Type name:">
3663      message
3664    </t>
3665    <t hangText="Subtype name:">
3666      http
3667    </t>
3668    <t hangText="Required parameters:">
3669      none
3670    </t>
3671    <t hangText="Optional parameters:">
3672      version, msgtype
3673      <list style="hanging">
3674        <t hangText="version:">
3675          The HTTP-Version number of the enclosed message
3676          (e.g., "1.1"). If not present, the version can be
3677          determined from the first line of the body.
3678        </t>
3679        <t hangText="msgtype:">
3680          The message type &mdash; "request" or "response". If not
3681          present, the type can be determined from the first
3682          line of the body.
3683        </t>
3684      </list>
3685    </t>
3686    <t hangText="Encoding considerations:">
3687      only "7bit", "8bit", or "binary" are permitted
3688    </t>
3689    <t hangText="Security considerations:">
3690      none
3691    </t>
3692    <t hangText="Interoperability considerations:">
3693      none
3694    </t>
3695    <t hangText="Published specification:">
3696      This specification (see <xref target=""/>).
3697    </t>
3698    <t hangText="Applications that use this media type:">
3699    </t>
3700    <t hangText="Additional information:">
3701      <list style="hanging">
3702        <t hangText="Magic number(s):">none</t>
3703        <t hangText="File extension(s):">none</t>
3704        <t hangText="Macintosh file type code(s):">none</t>
3705      </list>
3706    </t>
3707    <t hangText="Person and email address to contact for further information:">
3708      See Authors Section.
3709    </t>
3710    <t hangText="Intended usage:">
3711      COMMON
3712    </t>
3713    <t hangText="Restrictions on usage:">
3714      none
3715    </t>
3716    <t hangText="Author/Change controller:">
3717      IESG
3718    </t>
3719  </list>
3722<section title="Internet Media Type application/http" anchor="">
3723<iref item="Media Type" subitem="application/http" primary="true"/>
3724<iref item="application/http Media Type" primary="true"/>
3726   The application/http type can be used to enclose a pipeline of one or more
3727   HTTP request or response messages (not intermixed).
3730  <list style="hanging" x:indent="12em">
3731    <t hangText="Type name:">
3732      application
3733    </t>
3734    <t hangText="Subtype name:">
3735      http
3736    </t>
3737    <t hangText="Required parameters:">
3738      none
3739    </t>
3740    <t hangText="Optional parameters:">
3741      version, msgtype
3742      <list style="hanging">
3743        <t hangText="version:">
3744          The HTTP-Version number of the enclosed messages
3745          (e.g., "1.1"). If not present, the version can be
3746          determined from the first line of the body.
3747        </t>
3748        <t hangText="msgtype:">
3749          The message type &mdash; "request" or "response". If not
3750          present, the type can be determined from the first
3751          line of the body.
3752        </t>
3753      </list>
3754    </t>
3755    <t hangText="Encoding considerations:">
3756      HTTP messages enclosed by this type
3757      are in "binary" format; use of an appropriate
3758      Content-Transfer-Encoding is required when
3759      transmitted via E-mail.
3760    </t>
3761    <t hangText="Security considerations:">
3762      none
3763    </t>
3764    <t hangText="Interoperability considerations:">
3765      none
3766    </t>
3767    <t hangText="Published specification:">
3768      This specification (see <xref target=""/>).
3769    </t>
3770    <t hangText="Applications that use this media type:">
3771    </t>
3772    <t hangText="Additional information:">
3773      <list style="hanging">
3774        <t hangText="Magic number(s):">none</t>
3775        <t hangText="File extension(s):">none</t>
3776        <t hangText="Macintosh file type code(s):">none</t>
3777      </list>
3778    </t>
3779    <t hangText="Person and email address to contact for further information:">
3780      See Authors Section.
3781    </t>
3782    <t hangText="Intended usage:">
3783      COMMON
3784    </t>
3785    <t hangText="Restrictions on usage:">
3786      none
3787    </t>
3788    <t hangText="Author/Change controller:">
3789      IESG
3790    </t>
3791  </list>
3796<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3798   The registration procedure for HTTP Transfer Codings is now defined by
3799   <xref target="transfer.coding.registry"/> of this document.
3802   The HTTP Transfer Codings Registry located at <eref target=""/>
3803   shall be updated with the registrations below:
3805<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3806   <ttcol>Name</ttcol>
3807   <ttcol>Description</ttcol>
3808   <ttcol>Reference</ttcol>
3809   <c>chunked</c>
3810   <c>Transfer in a series of chunks</c>
3811   <c>
3812      <xref target="chunked.encoding"/>
3813   </c>
3814   <c>compress</c>
3815   <c>UNIX "compress" program method</c>
3816   <c>
3817      <xref target="compress.coding"/>
3818   </c>
3819   <c>deflate</c>
3820   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3821   the "zlib" data format (<xref target="RFC1950"/>)
3822   </c>
3823   <c>
3824      <xref target="deflate.coding"/>
3825   </c>
3826   <c>gzip</c>
3827   <c>Same as GNU zip <xref target="RFC1952"/></c>
3828   <c>
3829      <xref target="gzip.coding"/>
3830   </c>
3834<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3836   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3837   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3838   by <xref target="upgrade.token.registry"/> of this document.
3841   The HTTP Status Code Registry located at <eref target=""/>
3842   shall be updated with the registration below:
3844<texttable align="left" suppress-title="true">
3845   <ttcol>Value</ttcol>
3846   <ttcol>Description</ttcol>
3847   <ttcol>Reference</ttcol>
3849   <c>HTTP</c>
3850   <c>Hypertext Transfer Protocol</c>
3851   <c><xref target="http.version"/> of this specification</c>
3852<!-- IANA should add this without our instructions; emailed on June 05, 2009
3853   <c>TLS/1.0</c>
3854   <c>Transport Layer Security</c>
3855   <c><xref target="RFC2817"/></c> -->
3862<section title="Security Considerations" anchor="security.considerations">
3864   This section is meant to inform application developers, information
3865   providers, and users of the security limitations in HTTP/1.1 as
3866   described by this document. The discussion does not include
3867   definitive solutions to the problems revealed, though it does make
3868   some suggestions for reducing security risks.
3871<section title="Personal Information" anchor="personal.information">
3873   HTTP clients are often privy to large amounts of personal information
3874   (e.g., the user's name, location, mail address, passwords, encryption
3875   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3876   leakage of this information.
3877   We very strongly recommend that a convenient interface be provided
3878   for the user to control dissemination of such information, and that
3879   designers and implementors be particularly careful in this area.
3880   History shows that errors in this area often create serious security
3881   and/or privacy problems and generate highly adverse publicity for the
3882   implementor's company.
3886<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3888   A server is in the position to save personal data about a user's
3889   requests which might identify their reading patterns or subjects of
3890   interest. This information is clearly confidential in nature and its
3891   handling can be constrained by law in certain countries. People using
3892   HTTP to provide data are responsible for ensuring that
3893   such material is not distributed without the permission of any
3894   individuals that are identifiable by the published results.
3898<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3900   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3901   the documents returned by HTTP requests to be only those that were
3902   intended by the server administrators. If an HTTP server translates
3903   HTTP URIs directly into file system calls, the server &MUST; take
3904   special care not to serve files that were not intended to be
3905   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3906   other operating systems use ".." as a path component to indicate a
3907   directory level above the current one. On such a system, an HTTP
3908   server &MUST; disallow any such construct in the request-target if it
3909   would otherwise allow access to a resource outside those intended to
3910   be accessible via the HTTP server. Similarly, files intended for
3911   reference only internally to the server (such as access control
3912   files, configuration files, and script code) &MUST; be protected from
3913   inappropriate retrieval, since they might contain sensitive
3914   information. Experience has shown that minor bugs in such HTTP server
3915   implementations have turned into security risks.
3919<section title="DNS Spoofing" anchor="dns.spoofing">
3921   Clients using HTTP rely heavily on the Domain Name Service, and are
3922   thus generally prone to security attacks based on the deliberate
3923   mis-association of IP addresses and DNS names. Clients need to be
3924   cautious in assuming the continuing validity of an IP number/DNS name
3925   association.
3928   In particular, HTTP clients &SHOULD; rely on their name resolver for
3929   confirmation of an IP number/DNS name association, rather than
3930   caching the result of previous host name lookups. Many platforms
3931   already can cache host name lookups locally when appropriate, and
3932   they &SHOULD; be configured to do so. It is proper for these lookups to
3933   be cached, however, only when the TTL (Time To Live) information
3934   reported by the name server makes it likely that the cached
3935   information will remain useful.
3938   If HTTP clients cache the results of host name lookups in order to
3939   achieve a performance improvement, they &MUST; observe the TTL
3940   information reported by DNS.
3943   If HTTP clients do not observe this rule, they could be spoofed when
3944   a previously-accessed server's IP address changes. As network
3945   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3946   possibility of this form of attack will grow. Observing this
3947   requirement thus reduces this potential security vulnerability.
3950   This requirement also improves the load-balancing behavior of clients
3951   for replicated servers using the same DNS name and reduces the
3952   likelihood of a user's experiencing failure in accessing sites which
3953   use that strategy.
3957<section title="Proxies and Caching" anchor="attack.proxies">
3959   By their very nature, HTTP proxies are men-in-the-middle, and
3960   represent an opportunity for man-in-the-middle attacks. Compromise of
3961   the systems on which the proxies run can result in serious security
3962   and privacy problems. Proxies have access to security-related
3963   information, personal information about individual users and
3964   organizations, and proprietary information belonging to users and
3965   content providers. A compromised proxy, or a proxy implemented or
3966   configured without regard to security and privacy considerations,
3967   might be used in the commission of a wide range of potential attacks.
3970   Proxy operators need to protect the systems on which proxies run as
3971   they would protect any system that contains or transports sensitive
3972   information. In particular, log information gathered at proxies often
3973   contains highly sensitive personal information, and/or information
3974   about organizations. Log information needs to be carefully guarded, and
3975   appropriate guidelines for use need to be developed and followed.
3976   (<xref target="abuse.of.server.log.information"/>).
3979   Proxy implementors need to consider the privacy and security
3980   implications of their design and coding decisions, and of the
3981   configuration options they provide to proxy operators (especially the
3982   default configuration).
3985   Users of a proxy need to be aware that proxies are no trustworthier than
3986   the people who run them; HTTP itself cannot solve this problem.
3989   The judicious use of cryptography, when appropriate, might suffice to
3990   protect against a broad range of security and privacy attacks. Such
3991   cryptography is beyond the scope of the HTTP/1.1 specification.
3995<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3997   They exist. They are hard to defend against. Research continues.
3998   Beware.
4003<section title="Acknowledgments" anchor="ack">
4005   HTTP has evolved considerably over the years. It has
4006   benefited from a large and active developer community &mdash; the many
4007   people who have participated on the www-talk mailing list &mdash; and it is
4008   that community which has been most responsible for the success of
4009   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4010   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4011   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4012   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4013   VanHeyningen deserve special recognition for their efforts in
4014   defining early aspects of the protocol.
4017   This document has benefited greatly from the comments of all those
4018   participating in the HTTP-WG. In addition to those already mentioned,
4019   the following individuals have contributed to this specification:
4022   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4023   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4024   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4025   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4026   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4027   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4028   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4029   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4030   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4031   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4032   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4033   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4036   Thanks to the "cave men" of Palo Alto. You know who you are.
4039   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4040   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4041   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4042   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4043   Larry Masinter for their help. And thanks go particularly to Jeff
4044   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4047   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4048   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4049   discovery of many of the problems that this document attempts to
4050   rectify.
4053   This specification makes heavy use of the augmented BNF and generic
4054   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4055   reuses many of the definitions provided by Nathaniel Borenstein and
4056   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4057   specification will help reduce past confusion over the relationship
4058   between HTTP and Internet mail message formats.
4062Acknowledgements TODO list
4064- Jeff Hodges ("effective request URI")
4072<references title="Normative References">
4074<reference anchor="ISO-8859-1">
4075  <front>
4076    <title>
4077     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4078    </title>
4079    <author>
4080      <organization>International Organization for Standardization</organization>
4081    </author>
4082    <date year="1998"/>
4083  </front>
4084  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4087<reference anchor="Part2">
4088  <front>
4089    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4090    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4091      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4092      <address><email></email></address>
4093    </author>
4094    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4095      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4096      <address><email></email></address>
4097    </author>
4098    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4099      <organization abbrev="HP">Hewlett-Packard Company</organization>
4100      <address><email></email></address>
4101    </author>
4102    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4103      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4104      <address><email></email></address>
4105    </author>
4106    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4107      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4108      <address><email></email></address>
4109    </author>
4110    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4111      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4112      <address><email></email></address>
4113    </author>
4114    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4115      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4116      <address><email></email></address>
4117    </author>
4118    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4119      <organization abbrev="W3C">World Wide Web Consortium</organization>
4120      <address><email></email></address>
4121    </author>
4122    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4123      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4124      <address><email></email></address>
4125    </author>
4126    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4127  </front>
4128  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4129  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4132<reference anchor="Part3">
4133  <front>
4134    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4135    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4136      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4137      <address><email></email></address>
4138    </author>
4139    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4140      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4141      <address><email></email></address>
4142    </author>
4143    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4144      <organization abbrev="HP">Hewlett-Packard Company</organization>
4145      <address><email></email></address>
4146    </author>
4147    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4148      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4149      <address><email></email></address>
4150    </author>
4151    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4152      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4153      <address><email></email></address>
4154    </author>
4155    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4156      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4157      <address><email></email></address>
4158    </author>
4159    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4160      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4161      <address><email></email></address>
4162    </author>
4163    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4164      <organization abbrev="W3C">World Wide Web Consortium</organization>
4165      <address><email></email></address>
4166    </author>
4167    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4168      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4169      <address><email></email></address>
4170    </author>
4171    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4172  </front>
4173  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4174  <x:source href="p3-payload.xml" basename="p3-payload"/>
4177<reference anchor="Part6">
4178  <front>
4179    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4180    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4181      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4182      <address><email></email></address>
4183    </author>
4184    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4185      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4186      <address><email></email></address>
4187    </author>
4188    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4189      <organization abbrev="HP">Hewlett-Packard Company</organization>
4190      <address><email></email></address>
4191    </author>
4192    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4193      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4197      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4198      <address><email></email></address>
4199    </author>
4200    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4201      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4202      <address><email></email></address>
4203    </author>
4204    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4205      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4206      <address><email></email></address>
4207    </author>
4208    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4209      <organization abbrev="W3C">World Wide Web Consortium</organization>
4210      <address><email></email></address>
4211    </author>
4212    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4213      <address><email></email></address>
4214    </author>
4215    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4216      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4217      <address><email></email></address>
4218    </author>
4219    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4220  </front>
4221  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4222  <x:source href="p6-cache.xml" basename="p6-cache"/>
4225<reference anchor="RFC5234">
4226  <front>
4227    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4228    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4229      <organization>Brandenburg InternetWorking</organization>
4230      <address>
4231        <email></email>
4232      </address> 
4233    </author>
4234    <author initials="P." surname="Overell" fullname="Paul Overell">
4235      <organization>THUS plc.</organization>
4236      <address>
4237        <email></email>
4238      </address>
4239    </author>
4240    <date month="January" year="2008"/>
4241  </front>
4242  <seriesInfo name="STD" value="68"/>
4243  <seriesInfo name="RFC" value="5234"/>
4246<reference anchor="RFC2119">
4247  <front>
4248    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4249    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4250      <organization>Harvard University</organization>
4251      <address><email></email></address>
4252    </author>
4253    <date month="March" year="1997"/>
4254  </front>
4255  <seriesInfo name="BCP" value="14"/>
4256  <seriesInfo name="RFC" value="2119"/>
4259<reference anchor="RFC3986">
4260 <front>
4261  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4262  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4263    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4264    <address>
4265       <email></email>
4266       <uri></uri>
4267    </address>
4268  </author>
4269  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4270    <organization abbrev="Day Software">Day Software</organization>
4271    <address>
4272      <email></email>
4273      <uri></uri>
4274    </address>
4275  </author>
4276  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4277    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4278    <address>
4279      <email></email>
4280      <uri></uri>
4281    </address>
4282  </author>
4283  <date month='January' year='2005'></date>
4284 </front>
4285 <seriesInfo name="STD" value="66"/>
4286 <seriesInfo name="RFC" value="3986"/>
4289<reference anchor="USASCII">
4290  <front>
4291    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4292    <author>
4293      <organization>American National Standards Institute</organization>
4294    </author>
4295    <date year="1986"/>
4296  </front>
4297  <seriesInfo name="ANSI" value="X3.4"/>
4300<reference anchor="RFC1950">
4301  <front>
4302    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4303    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4304      <organization>Aladdin Enterprises</organization>
4305      <address><email></email></address>
4306    </author>
4307    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4308    <date month="May" year="1996"/>
4309  </front>
4310  <seriesInfo name="RFC" value="1950"/>
4311  <annotation>
4312    RFC 1950 is an Informational RFC, thus it might be less stable than
4313    this specification. On the other hand, this downward reference was
4314    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4315    therefore it is unlikely to cause problems in practice. See also
4316    <xref target="BCP97"/>.
4317  </annotation>
4320<reference anchor="RFC1951">
4321  <front>
4322    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4323    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4324      <organization>Aladdin Enterprises</organization>
4325      <address><email></email></address>
4326    </author>
4327    <date month="May" year="1996"/>
4328  </front>
4329  <seriesInfo name="RFC" value="1951"/>
4330  <annotation>
4331    RFC 1951 is an Informational RFC, thus it might be less stable than
4332    this specification. On the other hand, this downward reference was
4333    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4334    therefore it is unlikely to cause problems in practice. See also
4335    <xref target="BCP97"/>.
4336  </annotation>
4339<reference anchor="RFC1952">
4340  <front>
4341    <title>GZIP file format specification version 4.3</title>
4342    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4343      <organization>Aladdin Enterprises</organization>
4344      <address><email></email></address>
4345    </author>
4346    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4347      <address><email></email></address>
4348    </author>
4349    <author initials="M." surname="Adler" fullname="Mark Adler">
4350      <address><email></email></address>
4351    </author>
4352    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4353      <address><email></email></address>
4354    </author>
4355    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4356      <address><email></email></address>
4357    </author>
4358    <date month="May" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="1952"/>
4361  <annotation>
4362    RFC 1952 is an Informational RFC, thus it might be less stable than
4363    this specification. On the other hand, this downward reference was
4364    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4365    therefore it is unlikely to cause problems in practice. See also
4366    <xref target="BCP97"/>.
4367  </annotation>
4372<references title="Informative References">
4374<reference anchor="Nie1997" target="">
4375  <front>
4376    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4377    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4378    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4379    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4380    <author initials="H." surname="Lie" fullname="H. Lie"/>
4381    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4382    <date year="1997" month="September"/>
4383  </front>
4384  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4387<reference anchor="Pad1995" target="">
4388  <front>
4389    <title>Improving HTTP Latency</title>
4390    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4391    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4392    <date year="1995" month="December"/>
4393  </front>
4394  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4397<reference anchor="RFC1123">
4398  <front>
4399    <title>Requirements for Internet Hosts - Application and Support</title>
4400    <author initials="R." surname="Braden" fullname="Robert Braden">
4401      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4402      <address><email>Braden@ISI.EDU</email></address>
4403    </author>
4404    <date month="October" year="1989"/>
4405  </front>
4406  <seriesInfo name="STD" value="3"/>
4407  <seriesInfo name="RFC" value="1123"/>
4410<reference anchor="RFC1900">
4411  <front>
4412    <title>Renumbering Needs Work</title>
4413    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4414      <organization>CERN, Computing and Networks Division</organization>
4415      <address><email></email></address>
4416    </author>
4417    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4418      <organization>cisco Systems</organization>
4419      <address><email></email></address>
4420    </author>
4421    <date month="February" year="1996"/>
4422  </front>
4423  <seriesInfo name="RFC" value="1900"/>
4426<reference anchor='RFC1919'>
4427  <front>
4428    <title>Classical versus Transparent IP Proxies</title>
4429    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4430      <address><email></email></address>
4431    </author>
4432    <date year='1996' month='March' />
4433  </front>
4434  <seriesInfo name='RFC' value='1919' />
4437<reference anchor="RFC1945">
4438  <front>
4439    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4440    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4441      <organization>MIT, Laboratory for Computer Science</organization>
4442      <address><email></email></address>
4443    </author>
4444    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4445      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4446      <address><email></email></address>
4447    </author>
4448    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4449      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4450      <address><email></email></address>
4451    </author>
4452    <date month="May" year="1996"/>
4453  </front>
4454  <seriesInfo name="RFC" value="1945"/>
4457<reference anchor="RFC2045">
4458  <front>
4459    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4460    <author initials="N." surname="Freed" fullname="Ned Freed">
4461      <organization>Innosoft International, Inc.</organization>
4462      <address><email></email></address>
4463    </author>
4464    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4465      <organization>First Virtual Holdings</organization>
4466      <address><email></email></address>
4467    </author>
4468    <date month="November" year="1996"/>
4469  </front>
4470  <seriesInfo name="RFC" value="2045"/>
4473<reference anchor="RFC2047">
4474  <front>
4475    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4476    <author initials="K." surname="Moore" fullname="Keith Moore">
4477      <organization>University of Tennessee</organization>
4478      <address><email></email></address>
4479    </author>
4480    <date month="November" year="1996"/>
4481  </front>
4482  <seriesInfo name="RFC" value="2047"/>
4485<reference anchor="RFC2068">
4486  <front>
4487    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4488    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4489      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4490      <address><email></email></address>
4491    </author>
4492    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4493      <organization>MIT Laboratory for Computer Science</organization>
4494      <address><email></email></address>
4495    </author>
4496    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4497      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4498      <address><email></email></address>
4499    </author>
4500    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4501      <organization>MIT Laboratory for Computer Science</organization>
4502      <address><email></email></address>
4503    </author>
4504    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4505      <organization>MIT Laboratory for Computer Science</organization>
4506      <address><email></email></address>
4507    </author>
4508    <date month="January" year="1997"/>
4509  </front>
4510  <seriesInfo name="RFC" value="2068"/>
4513<reference anchor="RFC2145">
4514  <front>
4515    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4516    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4517      <organization>Western Research Laboratory</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4521      <organization>Department of Information and Computer Science</organization>
4522      <address><email></email></address>
4523    </author>
4524    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4525      <organization>MIT Laboratory for Computer Science</organization>
4526      <address><email></email></address>
4527    </author>
4528    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4529      <organization>W3 Consortium</organization>
4530      <address><email></email></address>
4531    </author>
4532    <date month="May" year="1997"/>
4533  </front>
4534  <seriesInfo name="RFC" value="2145"/>
4537<reference anchor="RFC2616">
4538  <front>
4539    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4540    <author initials="R." surname="Fielding" fullname="R. Fielding">
4541      <organization>University of California, Irvine</organization>
4542      <address><email></email></address>
4543    </author>
4544    <author initials="J." surname="Gettys" fullname="J. Gettys">
4545      <organization>W3C</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials="J." surname="Mogul" fullname="J. Mogul">
4549      <organization>Compaq Computer Corporation</organization>
4550      <address><email></email></address>
4551    </author>
4552    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4553      <organization>MIT Laboratory for Computer Science</organization>
4554      <address><email></email></address>
4555    </author>
4556    <author initials="L." surname="Masinter" fullname="L. Masinter">
4557      <organization>Xerox Corporation</organization>
4558      <address><email></email></address>
4559    </author>
4560    <author initials="P." surname="Leach" fullname="P. Leach">
4561      <organization>Microsoft Corporation</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4565      <organization>W3C</organization>
4566      <address><email></email></address>
4567    </author>
4568    <date month="June" year="1999"/>
4569  </front>
4570  <seriesInfo name="RFC" value="2616"/>
4573<reference anchor='RFC2817'>
4574  <front>
4575    <title>Upgrading to TLS Within HTTP/1.1</title>
4576    <author initials='R.' surname='Khare' fullname='R. Khare'>
4577      <organization>4K Associates / UC Irvine</organization>
4578      <address><email></email></address>
4579    </author>
4580    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4581      <organization>Agranat Systems, Inc.</organization>
4582      <address><email></email></address>
4583    </author>
4584    <date year='2000' month='May' />
4585  </front>
4586  <seriesInfo name='RFC' value='2817' />
4589<reference anchor='RFC2818'>
4590  <front>
4591    <title>HTTP Over TLS</title>
4592    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4593      <organization>RTFM, Inc.</organization>
4594      <address><email></email></address>
4595    </author>
4596    <date year='2000' month='May' />
4597  </front>
4598  <seriesInfo name='RFC' value='2818' />
4601<reference anchor='RFC2965'>
4602  <front>
4603    <title>HTTP State Management Mechanism</title>
4604    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4605      <organization>Bell Laboratories, Lucent Technologies</organization>
4606      <address><email></email></address>
4607    </author>
4608    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4609      <organization>, Inc.</organization>
4610      <address><email></email></address>
4611    </author>
4612    <date year='2000' month='October' />
4613  </front>
4614  <seriesInfo name='RFC' value='2965' />
4617<reference anchor='RFC3040'>
4618  <front>
4619    <title>Internet Web Replication and Caching Taxonomy</title>
4620    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4621      <organization>Equinix, Inc.</organization>
4622    </author>
4623    <author initials='I.' surname='Melve' fullname='I. Melve'>
4624      <organization>UNINETT</organization>
4625    </author>
4626    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4627      <organization>CacheFlow Inc.</organization>
4628    </author>
4629    <date year='2001' month='January' />
4630  </front>
4631  <seriesInfo name='RFC' value='3040' />
4634<reference anchor='RFC3864'>
4635  <front>
4636    <title>Registration Procedures for Message Header Fields</title>
4637    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4638      <organization>Nine by Nine</organization>
4639      <address><email></email></address>
4640    </author>
4641    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4642      <organization>BEA Systems</organization>
4643      <address><email></email></address>
4644    </author>
4645    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4646      <organization>HP Labs</organization>
4647      <address><email></email></address>
4648    </author>
4649    <date year='2004' month='September' />
4650  </front>
4651  <seriesInfo name='BCP' value='90' />
4652  <seriesInfo name='RFC' value='3864' />
4655<reference anchor="RFC4288">
4656  <front>
4657    <title>Media Type Specifications and Registration Procedures</title>
4658    <author initials="N." surname="Freed" fullname="N. Freed">
4659      <organization>Sun Microsystems</organization>
4660      <address>
4661        <email></email>
4662      </address>
4663    </author>
4664    <author initials="J." surname="Klensin" fullname="J. Klensin">
4665      <address>
4666        <email></email>
4667      </address>
4668    </author>
4669    <date year="2005" month="December"/>
4670  </front>
4671  <seriesInfo name="BCP" value="13"/>
4672  <seriesInfo name="RFC" value="4288"/>
4675<reference anchor='RFC4395'>
4676  <front>
4677    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4678    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4679      <organization>AT&amp;T Laboratories</organization>
4680      <address>
4681        <email></email>
4682      </address>
4683    </author>
4684    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4685      <organization>Qualcomm, Inc.</organization>
4686      <address>
4687        <email></email>
4688      </address>
4689    </author>
4690    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4691      <organization>Adobe Systems</organization>
4692      <address>
4693        <email></email>
4694      </address>
4695    </author>
4696    <date year='2006' month='February' />
4697  </front>
4698  <seriesInfo name='BCP' value='115' />
4699  <seriesInfo name='RFC' value='4395' />
4702<reference anchor='RFC5226'>
4703  <front>
4704    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4705    <author initials='T.' surname='Narten' fullname='T. Narten'>
4706      <organization>IBM</organization>
4707      <address><email></email></address>
4708    </author>
4709    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4710      <organization>Google</organization>
4711      <address><email></email></address>
4712    </author>
4713    <date year='2008' month='May' />
4714  </front>
4715  <seriesInfo name='BCP' value='26' />
4716  <seriesInfo name='RFC' value='5226' />
4719<reference anchor="RFC5322">
4720  <front>
4721    <title>Internet Message Format</title>
4722    <author initials="P." surname="Resnick" fullname="P. Resnick">
4723      <organization>Qualcomm Incorporated</organization>
4724    </author>
4725    <date year="2008" month="October"/>
4726  </front>
4727  <seriesInfo name="RFC" value="5322"/>
4730<reference anchor='draft-ietf-httpstate-cookie'>
4731  <front>
4732    <title>HTTP State Management Mechanism</title>
4733    <author initials="A." surname="Barth" fullname="Adam Barth">
4734      <organization abbrev="U.C. Berkeley">
4735        University of California, Berkeley
4736      </organization>
4737      <address><email></email></address>
4738    </author>
4739    <date year='2011' month='March' />
4740  </front>
4741  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4744<reference anchor='BCP97'>
4745  <front>
4746    <title>Handling Normative References to Standards-Track Documents</title>
4747    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4748      <address>
4749        <email></email>
4750      </address>
4751    </author>
4752    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4753      <organization>MIT</organization>
4754      <address>
4755        <email></email>
4756      </address>
4757    </author>
4758    <date year='2007' month='June' />
4759  </front>
4760  <seriesInfo name='BCP' value='97' />
4761  <seriesInfo name='RFC' value='4897' />
4764<reference anchor="Kri2001" target="">
4765  <front>
4766    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4767    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4768    <date year="2001" month="November"/>
4769  </front>
4770  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4773<reference anchor="Spe" target="">
4774  <front>
4775    <title>Analysis of HTTP Performance Problems</title>
4776    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4777    <date/>
4778  </front>
4781<reference anchor="Tou1998" target="">
4782  <front>
4783  <title>Analysis of HTTP Performance</title>
4784  <author initials="J." surname="Touch" fullname="Joe Touch">
4785    <organization>USC/Information Sciences Institute</organization>
4786    <address><email></email></address>
4787  </author>
4788  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4789    <organization>USC/Information Sciences Institute</organization>
4790    <address><email></email></address>
4791  </author>
4792  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4793    <organization>USC/Information Sciences Institute</organization>
4794    <address><email></email></address>
4795  </author>
4796  <date year="1998" month="Aug"/>
4797  </front>
4798  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4799  <annotation>(original report dated Aug. 1996)</annotation>
4805<section title="Tolerant Applications" anchor="tolerant.applications">
4807   Although this document specifies the requirements for the generation
4808   of HTTP/1.1 messages, not all applications will be correct in their
4809   implementation. We therefore recommend that operational applications
4810   be tolerant of deviations whenever those deviations can be
4811   interpreted unambiguously.
4814   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4815   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4816   &SHOULD; accept any amount of WSP characters between fields, even though
4817   only a single SP is required.
4820   The line terminator for header fields is the sequence CRLF.
4821   However, we recommend that applications, when parsing such headers fields,
4822   recognize a single LF as a line terminator and ignore the leading CR.
4825   The character set of a representation &SHOULD; be labeled as the lowest
4826   common denominator of the character codes used within that representation, with
4827   the exception that not labeling the representation is preferred over labeling
4828   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4831   Additional rules for requirements on parsing and encoding of dates
4832   and other potential problems with date encodings include:
4835  <list style="symbols">
4836     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4837        which appears to be more than 50 years in the future is in fact
4838        in the past (this helps solve the "year 2000" problem).</t>
4840     <t>Although all date formats are specified to be case-sensitive,
4841        recipients &SHOULD; match day, week and timezone names
4842        case-insensitively.</t>
4844     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4845        Expires date as earlier than the proper value, but &MUST-NOT;
4846        internally represent a parsed Expires date as later than the
4847        proper value.</t>
4849     <t>All expiration-related calculations &MUST; be done in GMT. The
4850        local time zone &MUST-NOT; influence the calculation or comparison
4851        of an age or expiration time.</t>
4853     <t>If an HTTP header field incorrectly carries a date value with a time
4854        zone other than GMT, it &MUST; be converted into GMT using the
4855        most conservative possible conversion.</t>
4856  </list>
4860<section title="Compatibility with Previous Versions" anchor="compatibility">
4862   HTTP has been in use by the World-Wide Web global information initiative
4863   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4864   was a simple protocol for hypertext data transfer across the Internet
4865   with only a single method and no metadata.
4866   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4867   methods and MIME-like messaging that could include metadata about the data
4868   transferred and modifiers on the request/response semantics. However,
4869   HTTP/1.0 did not sufficiently take into consideration the effects of
4870   hierarchical proxies, caching, the need for persistent connections, or
4871   name-based virtual hosts. The proliferation of incompletely-implemented
4872   applications calling themselves "HTTP/1.0" further necessitated a
4873   protocol version change in order for two communicating applications
4874   to determine each other's true capabilities.
4877   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4878   requirements that enable reliable implementations, adding only
4879   those new features that will either be safely ignored by an HTTP/1.0
4880   recipient or only sent when communicating with a party advertising
4881   compliance with HTTP/1.1.
4884   It is beyond the scope of a protocol specification to mandate
4885   compliance with previous versions. HTTP/1.1 was deliberately
4886   designed, however, to make supporting previous versions easy. It is
4887   worth noting that, at the time of composing this specification, we would
4888   expect general-purpose HTTP/1.1 servers to:
4889  <list style="symbols">
4890     <t>understand any valid request in the format of HTTP/1.0 and
4891        1.1;</t>
4893     <t>respond appropriately with a message in the same major version
4894        used by the client.</t>
4895  </list>
4898   And we would expect HTTP/1.1 clients to:
4899  <list style="symbols">
4900     <t>understand any valid response in the format of HTTP/1.0 or
4901        1.1.</t>
4902  </list>
4905   For most implementations of HTTP/1.0, each connection is established
4906   by the client prior to the request and closed by the server after
4907   sending the response. Some implementations implement the Keep-Alive
4908   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4911<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4913   This section summarizes major differences between versions HTTP/1.0
4914   and HTTP/1.1.
4917<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4919   The requirements that clients and servers support the Host request-header
4920   field (<xref target=""/>), report an error if it is
4921   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4922   are among the most important changes defined by this
4923   specification.
4926   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4927   addresses and servers; there was no other established mechanism for
4928   distinguishing the intended server of a request than the IP address
4929   to which that request was directed. The changes outlined above will
4930   allow the Internet, once older HTTP clients are no longer common, to
4931   support multiple Web sites from a single IP address, greatly
4932   simplifying large operational Web servers, where allocation of many
4933   IP addresses to a single host has created serious problems. The
4934   Internet will also be able to recover the IP addresses that have been
4935   allocated for the sole purpose of allowing special-purpose domain
4936   names to be used in root-level HTTP URLs. Given the rate of growth of
4937   the Web, and the number of servers already deployed, it is extremely
4938   important that all implementations of HTTP (including updates to
4939   existing HTTP/1.0 applications) correctly implement these
4940   requirements:
4941  <list style="symbols">
4942     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4944     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4946     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4947        request does not include a Host request-header field.</t>
4949     <t>Servers &MUST; accept absolute URIs.</t>
4950  </list>
4955<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4957   Some clients and servers might wish to be compatible with some
4958   previous implementations of persistent connections in HTTP/1.0
4959   clients and servers. Persistent connections in HTTP/1.0 are
4960   explicitly negotiated as they are not the default behavior. HTTP/1.0
4961   experimental implementations of persistent connections are faulty,
4962   and the new facilities in HTTP/1.1 are designed to rectify these
4963   problems. The problem was that some existing HTTP/1.0 clients might
4964   send Keep-Alive to a proxy server that doesn't understand
4965   Connection, which would then erroneously forward it to the next
4966   inbound server, which would establish the Keep-Alive connection and
4967   result in a hung HTTP/1.0 proxy waiting for the close on the
4968   response. The result is that HTTP/1.0 clients must be prevented from
4969   using Keep-Alive when talking to proxies.
4972   However, talking to proxies is the most important use of persistent
4973   connections, so that prohibition is clearly unacceptable. Therefore,
4974   we need some other mechanism for indicating a persistent connection
4975   is desired, which is safe to use even when talking to an old proxy
4976   that ignores Connection. Persistent connections are the default for
4977   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4978   declaring non-persistence. See <xref target="header.connection"/>.
4981   The original HTTP/1.0 form of persistent connections (the Connection:
4982   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4986<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4988  Empty list elements in list productions have been deprecated.
4989  (<xref target="notation.abnf"/>)
4992  Rules about implicit linear whitespace between certain grammar productions
4993  have been removed; now it's only allowed when specifically pointed out
4994  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4995  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4996  Non-ASCII content in header fields and reason phrase has been obsoleted and
4997  made opaque (the TEXT rule was removed)
4998  (<xref target="basic.rules"/>)
5001  Clarify that HTTP-Version is case sensitive.
5002  (<xref target="http.version"/>)
5005  Require that invalid whitespace around field-names be rejected.
5006  (<xref target="header.fields"/>)
5009  Require recipients to handle bogus Content-Length header fields as errors.
5010  (<xref target="message.body"/>)
5013  Remove reference to non-existent identity transfer-coding value tokens.
5014  (Sections <xref format="counter" target="message.body"/> and
5015  <xref format="counter" target="transfer.codings"/>)
5018  Update use of abs_path production from RFC 1808 to the path-absolute + query
5019  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5020  method only.
5021  (<xref target="request-target"/>)
5024  Clarification that the chunk length does not include the count of the octets
5025  in the chunk header and trailer. Furthermore disallowed line folding
5026  in chunk extensions.
5027  (<xref target="chunked.encoding"/>)
5030  Remove hard limit of two connections per server.
5031  (<xref target="persistent.practical"/>)
5034  Clarify exactly when close connection options must be sent.
5035  (<xref target="header.connection"/>)
5038  Define the semantics of the "Upgrade" header field in responses other than
5039  101 (this was incorporated from <xref target="RFC2817"/>).
5040  (<xref target="header.upgrade"/>)
5045<?BEGININC p1-messaging.abnf-appendix ?>
5046<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5048<artwork type="abnf" name="p1-messaging.parsed-abnf">
5049<x:ref>BWS</x:ref> = OWS
5051<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
5052<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5053<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5054<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5055 connection-token ] )
5056<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5057<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5059<x:ref>Date</x:ref> = "Date:" OWS Date-v
5060<x:ref>Date-v</x:ref> = HTTP-date
5062<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5064<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5065<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5066<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5067<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5068 ]
5069<x:ref>Host</x:ref> = "Host:" OWS Host-v
5070<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5072<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
5073<x:ref>Method</x:ref> = token
5075<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5077<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
5079<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5080<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5081<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5082<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5083<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5085<x:ref>Status-Code</x:ref> = 3DIGIT
5086<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5088<x:ref>TE</x:ref> = "TE:" OWS TE-v
5089<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5090<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5091<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5092<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5093<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5094 transfer-coding ] )
5096<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5097<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5098<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5100<x:ref>Via</x:ref> = "Via:" OWS Via-v
5101<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5102 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5103 ] )
5105<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5107<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5108<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5109<x:ref>attribute</x:ref> = token
5110<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5112<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5113<x:ref>chunk-data</x:ref> = 1*OCTET
5114<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5115<x:ref>chunk-ext-name</x:ref> = token
5116<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5117<x:ref>chunk-size</x:ref> = 1*HEXDIG
5118<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5119<x:ref>connection-token</x:ref> = token
5120<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5121 / %x2A-5B ; '*'-'['
5122 / %x5D-7E ; ']'-'~'
5123 / obs-text
5125<x:ref>date1</x:ref> = day SP month SP year
5126<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5127<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5128<x:ref>day</x:ref> = 2DIGIT
5129<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5130 / %x54.75.65 ; Tue
5131 / %x57.65.64 ; Wed
5132 / %x54.68.75 ; Thu
5133 / %x46.72.69 ; Fri
5134 / %x53.61.74 ; Sat
5135 / %x53.75.6E ; Sun
5136<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5137 / %x54. ; Tuesday
5138 / %x57.65.64.6E. ; Wednesday
5139 / %x54. ; Thursday
5140 / %x46. ; Friday
5141 / %x53. ; Saturday
5142 / %x53.75.6E.64.61.79 ; Sunday
5144<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5145<x:ref>field-name</x:ref> = token
5146<x:ref>field-value</x:ref> = *( field-content / OWS )
5148<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5149<x:ref>hour</x:ref> = 2DIGIT
5150<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5151<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5153<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5155<x:ref>message-body</x:ref> = *OCTET
5156<x:ref>minute</x:ref> = 2DIGIT
5157<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5158 / %x46.65.62 ; Feb
5159 / %x4D.61.72 ; Mar
5160 / %x41.70.72 ; Apr
5161 / %x4D.61.79 ; May
5162 / %x4A.75.6E ; Jun
5163 / %x4A.75.6C ; Jul
5164 / %x41.75.67 ; Aug
5165 / %x53.65.70 ; Sep
5166 / %x4F.63.74 ; Oct
5167 / %x4E.6F.76 ; Nov
5168 / %x44.65.63 ; Dec
5170<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5171<x:ref>obs-fold</x:ref> = CRLF
5172<x:ref>obs-text</x:ref> = %x80-FF
5174<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5175<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5176<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5177<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5178<x:ref>product</x:ref> = token [ "/" product-version ]
5179<x:ref>product-version</x:ref> = token
5180<x:ref>protocol-name</x:ref> = token
5181<x:ref>protocol-version</x:ref> = token
5182<x:ref>pseudonym</x:ref> = token
5184<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5185 / %x5D-7E ; ']'-'~'
5186 / obs-text
5187<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5188 / %x5D-7E ; ']'-'~'
5189 / obs-text
5190<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5191<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5192<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5193<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5194<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5195<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5197<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5198<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5199<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5200<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5201<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5202 / authority
5203<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5204<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5205<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5207<x:ref>second</x:ref> = 2DIGIT
5208<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5209 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5210<x:ref>start-line</x:ref> = Request-Line / Status-Line
5212<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5213<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5214 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5215<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5216<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5217<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5218<x:ref>token</x:ref> = 1*tchar
5219<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5220<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5221 transfer-extension
5222<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5223<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5225<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5227<x:ref>value</x:ref> = word
5229<x:ref>word</x:ref> = token / quoted-string
5231<x:ref>year</x:ref> = 4DIGIT
5234<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5235; Cache-Control defined but not used
5236; Chunked-Body defined but not used
5237; Connection defined but not used
5238; Content-Length defined but not used
5239; Date defined but not used
5240; HTTP-message defined but not used
5241; Host defined but not used
5242; MIME-Version defined but not used
5243; Pragma defined but not used
5244; Request defined but not used
5245; Response defined but not used
5246; TE defined but not used
5247; Trailer defined but not used
5248; Transfer-Encoding defined but not used
5249; URI-reference defined but not used
5250; Upgrade defined but not used
5251; Via defined but not used
5252; Warning defined but not used
5253; http-URI defined but not used
5254; https-URI defined but not used
5255; partial-URI defined but not used
5256; request-header defined but not used
5257; response-header defined but not used
5258; special defined but not used
5260<?ENDINC p1-messaging.abnf-appendix ?>
5262<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5264<section title="Since RFC 2616">
5266  Extracted relevant partitions from <xref target="RFC2616"/>.
5270<section title="Since draft-ietf-httpbis-p1-messaging-00">
5272  Closed issues:
5273  <list style="symbols">
5274    <t>
5275      <eref target=""/>:
5276      "HTTP Version should be case sensitive"
5277      (<eref target=""/>)
5278    </t>
5279    <t>
5280      <eref target=""/>:
5281      "'unsafe' characters"
5282      (<eref target=""/>)
5283    </t>
5284    <t>
5285      <eref target=""/>:
5286      "Chunk Size Definition"
5287      (<eref target=""/>)
5288    </t>
5289    <t>
5290      <eref target=""/>:
5291      "Message Length"
5292      (<eref target=""/>)
5293    </t>
5294    <t>
5295      <eref target=""/>:
5296      "Media Type Registrations"
5297      (<eref target=""/>)
5298    </t>
5299    <t>
5300      <eref target=""/>:
5301      "URI includes query"
5302      (<eref target=""/>)
5303    </t>
5304    <t>
5305      <eref target=""/>:
5306      "No close on 1xx responses"
5307      (<eref target=""/>)
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "Remove 'identity' token references"
5312      (<eref target=""/>)
5313    </t>
5314    <t>
5315      <eref target=""/>:
5316      "Import query BNF"
5317    </t>
5318    <t>
5319      <eref target=""/>:
5320      "qdtext BNF"
5321    </t>
5322    <t>
5323      <eref target=""/>:
5324      "Normative and Informative references"
5325    </t>
5326    <t>
5327      <eref target=""/>:
5328      "RFC2606 Compliance"
5329    </t>
5330    <t>
5331      <eref target=""/>:
5332      "RFC977 reference"
5333    </t>
5334    <t>
5335      <eref target=""/>:
5336      "RFC1700 references"
5337    </t>
5338    <t>
5339      <eref target=""/>:
5340      "inconsistency in date format explanation"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "Date reference typo"
5345    </t>
5346    <t>
5347      <eref target=""/>:
5348      "Informative references"
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "ISO-8859-1 Reference"
5353    </t>
5354    <t>
5355      <eref target=""/>:
5356      "Normative up-to-date references"
5357    </t>
5358  </list>
5361  Other changes:
5362  <list style="symbols">
5363    <t>
5364      Update media type registrations to use RFC4288 template.
5365    </t>
5366    <t>
5367      Use names of RFC4234 core rules DQUOTE and WSP,
5368      fix broken ABNF for chunk-data
5369      (work in progress on <eref target=""/>)
5370    </t>
5371  </list>
5375<section title="Since draft-ietf-httpbis-p1-messaging-01">
5377  Closed issues:
5378  <list style="symbols">
5379    <t>
5380      <eref target=""/>:
5381      "Bodies on GET (and other) requests"
5382    </t>
5383    <t>
5384      <eref target=""/>:
5385      "Updating to RFC4288"
5386    </t>
5387    <t>
5388      <eref target=""/>:
5389      "Status Code and Reason Phrase"
5390    </t>
5391    <t>
5392      <eref target=""/>:
5393      "rel_path not used"
5394    </t>
5395  </list>
5398  Ongoing work on ABNF conversion (<eref target=""/>):
5399  <list style="symbols">
5400    <t>
5401      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5402      "trailer-part").
5403    </t>
5404    <t>
5405      Avoid underscore character in rule names ("http_URL" ->
5406      "http-URL", "abs_path" -> "path-absolute").
5407    </t>
5408    <t>
5409      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5410      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5411      have to be updated when switching over to RFC3986.
5412    </t>
5413    <t>
5414      Synchronize core rules with RFC5234.
5415    </t>
5416    <t>
5417      Get rid of prose rules that span multiple lines.
5418    </t>
5419    <t>
5420      Get rid of unused rules LOALPHA and UPALPHA.
5421    </t>
5422    <t>
5423      Move "Product Tokens" section (back) into Part 1, as "token" is used
5424      in the definition of the Upgrade header field.
5425    </t>
5426    <t>
5427      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5428    </t>
5429    <t>
5430      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5431    </t>
5432  </list>
5436<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5438  Closed issues:
5439  <list style="symbols">
5440    <t>
5441      <eref target=""/>:
5442      "HTTP-date vs. rfc1123-date"
5443    </t>
5444    <t>
5445      <eref target=""/>:
5446      "WS in quoted-pair"
5447    </t>
5448  </list>
5451  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5452  <list style="symbols">
5453    <t>
5454      Reference RFC 3984, and update header field registrations for headers defined
5455      in this document.
5456    </t>
5457  </list>
5460  Ongoing work on ABNF conversion (<eref target=""/>):
5461  <list style="symbols">
5462    <t>
5463      Replace string literals when the string really is case-sensitive (HTTP-Version).
5464    </t>
5465  </list>
5469<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5471  Closed issues:
5472  <list style="symbols">
5473    <t>
5474      <eref target=""/>:
5475      "Connection closing"
5476    </t>
5477    <t>
5478      <eref target=""/>:
5479      "Move registrations and registry information to IANA Considerations"
5480    </t>
5481    <t>
5482      <eref target=""/>:
5483      "need new URL for PAD1995 reference"
5484    </t>
5485    <t>
5486      <eref target=""/>:
5487      "IANA Considerations: update HTTP URI scheme registration"
5488    </t>
5489    <t>
5490      <eref target=""/>:
5491      "Cite HTTPS URI scheme definition"
5492    </t>
5493    <t>
5494      <eref target=""/>:
5495      "List-type headers vs Set-Cookie"
5496    </t>
5497  </list>
5500  Ongoing work on ABNF conversion (<eref target=""/>):
5501  <list style="symbols">
5502    <t>
5503      Replace string literals when the string really is case-sensitive (HTTP-Date).
5504    </t>
5505    <t>
5506      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5507    </t>
5508  </list>
5512<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5514  Closed issues:
5515  <list style="symbols">
5516    <t>
5517      <eref target=""/>:
5518      "Out-of-date reference for URIs"
5519    </t>
5520    <t>
5521      <eref target=""/>:
5522      "RFC 2822 is updated by RFC 5322"
5523    </t>
5524  </list>
5527  Ongoing work on ABNF conversion (<eref target=""/>):
5528  <list style="symbols">
5529    <t>
5530      Use "/" instead of "|" for alternatives.
5531    </t>
5532    <t>
5533      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5534    </t>
5535    <t>
5536      Only reference RFC 5234's core rules.
5537    </t>
5538    <t>
5539      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5540      whitespace ("OWS") and required whitespace ("RWS").
5541    </t>
5542    <t>
5543      Rewrite ABNFs to spell out whitespace rules, factor out
5544      header field value format definitions.
5545    </t>
5546  </list>
5550<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5552  Closed issues:
5553  <list style="symbols">
5554    <t>
5555      <eref target=""/>:
5556      "Header LWS"
5557    </t>
5558    <t>
5559      <eref target=""/>:
5560      "Sort 1.3 Terminology"
5561    </t>
5562    <t>
5563      <eref target=""/>:
5564      "RFC2047 encoded words"
5565    </t>
5566    <t>
5567      <eref target=""/>:
5568      "Character Encodings in TEXT"
5569    </t>
5570    <t>
5571      <eref target=""/>:
5572      "Line Folding"
5573    </t>
5574    <t>
5575      <eref target=""/>:
5576      "OPTIONS * and proxies"
5577    </t>
5578    <t>
5579      <eref target=""/>:
5580      "Reason-Phrase BNF"
5581    </t>
5582    <t>
5583      <eref target=""/>:
5584      "Use of TEXT"
5585    </t>
5586    <t>
5587      <eref target=""/>:
5588      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5589    </t>
5590    <t>
5591      <eref target=""/>:
5592      "RFC822 reference left in discussion of date formats"
5593    </t>
5594  </list>
5597  Final work on ABNF conversion (<eref target=""/>):
5598  <list style="symbols">
5599    <t>
5600      Rewrite definition of list rules, deprecate empty list elements.
5601    </t>
5602    <t>
5603      Add appendix containing collected and expanded ABNF.
5604    </t>
5605  </list>
5608  Other changes:
5609  <list style="symbols">
5610    <t>
5611      Rewrite introduction; add mostly new Architecture Section.
5612    </t>
5613    <t>
5614      Move definition of quality values from Part 3 into Part 1;
5615      make TE request header field grammar independent of accept-params (defined in Part 3).
5616    </t>
5617  </list>
5621<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5623  Closed issues:
5624  <list style="symbols">
5625    <t>
5626      <eref target=""/>:
5627      "base for numeric protocol elements"
5628    </t>
5629    <t>
5630      <eref target=""/>:
5631      "comment ABNF"
5632    </t>
5633  </list>
5636  Partly resolved issues:
5637  <list style="symbols">
5638    <t>
5639      <eref target=""/>:
5640      "205 Bodies" (took out language that implied that there might be
5641      methods for which a request body MUST NOT be included)
5642    </t>
5643    <t>
5644      <eref target=""/>:
5645      "editorial improvements around HTTP-date"
5646    </t>
5647  </list>
5651<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5653  Closed issues:
5654  <list style="symbols">
5655    <t>
5656      <eref target=""/>:
5657      "Repeating single-value headers"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "increase connection limit"
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "IP addresses in URLs"
5666    </t>
5667    <t>
5668      <eref target=""/>:
5669      "take over HTTP Upgrade Token Registry"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "CR and LF in chunk extension values"
5674    </t>
5675    <t>
5676      <eref target=""/>:
5677      "HTTP/0.9 support"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5682    </t>
5683    <t>
5684      <eref target=""/>:
5685      "move definitions of gzip/deflate/compress to part 1"
5686    </t>
5687    <t>
5688      <eref target=""/>:
5689      "disallow control characters in quoted-pair"
5690    </t>
5691  </list>
5694  Partly resolved issues:
5695  <list style="symbols">
5696    <t>
5697      <eref target=""/>:
5698      "update IANA requirements wrt Transfer-Coding values" (add the
5699      IANA Considerations subsection)
5700    </t>
5701  </list>
5705<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5707  Closed issues:
5708  <list style="symbols">
5709    <t>
5710      <eref target=""/>:
5711      "header parsing, treatment of leading and trailing OWS"
5712    </t>
5713  </list>
5716  Partly resolved issues:
5717  <list style="symbols">
5718    <t>
5719      <eref target=""/>:
5720      "Placement of 13.5.1 and 13.5.2"
5721    </t>
5722    <t>
5723      <eref target=""/>:
5724      "use of term "word" when talking about header structure"
5725    </t>
5726  </list>
5730<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5732  Closed issues:
5733  <list style="symbols">
5734    <t>
5735      <eref target=""/>:
5736      "Clarification of the term 'deflate'"
5737    </t>
5738    <t>
5739      <eref target=""/>:
5740      "OPTIONS * and proxies"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "MIME-Version not listed in P1, general header fields"
5745    </t>
5746    <t>
5747      <eref target=""/>:
5748      "IANA registry for content/transfer encodings"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "Case-sensitivity of HTTP-date"
5753    </t>
5754    <t>
5755      <eref target=""/>:
5756      "use of term "word" when talking about header structure"
5757    </t>
5758  </list>
5761  Partly resolved issues:
5762  <list style="symbols">
5763    <t>
5764      <eref target=""/>:
5765      "Term for the requested resource's URI"
5766    </t>
5767  </list>
5771<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5773  Closed issues:
5774  <list style="symbols">
5775    <t>
5776      <eref target=""/>:
5777      "Connection Closing"
5778    </t>
5779    <t>
5780      <eref target=""/>:
5781      "Delimiting messages with multipart/byteranges"
5782    </t>
5783    <t>
5784      <eref target=""/>:
5785      "Handling multiple Content-Length headers"
5786    </t>
5787    <t>
5788      <eref target=""/>:
5789      "Clarify entity / representation / variant terminology"
5790    </t>
5791    <t>
5792      <eref target=""/>:
5793      "consider removing the 'changes from 2068' sections"
5794    </t>
5795  </list>
5798  Partly resolved issues:
5799  <list style="symbols">
5800    <t>
5801      <eref target=""/>:
5802      "HTTP(s) URI scheme definitions"
5803    </t>
5804  </list>
5808<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5810  Closed issues:
5811  <list style="symbols">
5812    <t>
5813      <eref target=""/>:
5814      "Trailer requirements"
5815    </t>
5816    <t>
5817      <eref target=""/>:
5818      "Text about clock requirement for caches belongs in p6"
5819    </t>
5820    <t>
5821      <eref target=""/>:
5822      "effective request URI: handling of missing host in HTTP/1.0"
5823    </t>
5824    <t>
5825      <eref target=""/>:
5826      "confusing Date requirements for clients"
5827    </t>
5828  </list>
5831  Partly resolved issues:
5832  <list style="symbols">
5833    <t>
5834      <eref target=""/>:
5835      "Handling multiple Content-Length headers"
5836    </t>
5837  </list>
5841<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5843  Closed issues:
5844  <list style="symbols">
5845    <t>
5846      <eref target=""/>:
5847      "RFC2145 Normative"
5848    </t>
5849    <t>
5850      <eref target=""/>:
5851      "define 'transparent' proxy"
5852    </t>
5853    <t>
5854      <eref target=""/>:
5855      "Is * usable as a request-uri for new methods?"
5856    </t>
5857    <t>
5858      <eref target=""/>:
5859      "Migrate Upgrade details from RFC2817"
5860    </t>
5861    <t>
5862      <eref target=""/>:
5863      "untangle ABNFs for header fields"
5864    </t>
5865    <t>
5866      <eref target=""/>:
5867      "update RFC 2109 reference"
5868    </t>
5869  </list>
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