source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1373

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "August">
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 status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
34  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
35  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
36  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
37  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
38  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' 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 protocol for
201   distributed, collaborative, hypertext information systems. HTTP has been in
202   use by the World Wide Web global information initiative since 1990. This
203   document is Part 1 of the seven-part specification that defines the protocol
204   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
207   Part 1 provides an overview of HTTP and its associated terminology, defines
208   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
209   the generic message syntax and parsing requirements for HTTP message frames,
210   and describes general security concerns for implementations.
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (, which is archived at
218    <eref target=""/>.
219  </t>
220  <t>
221    The current issues list is at
222    <eref target=""/> and related
223    documents (including fancy diffs) can be found at
224    <eref target=""/>.
225  </t>
226  <t>
227    The changes in this draft are summarized in <xref target="changes.since.15"/>.
228  </t>
232<section title="Introduction" anchor="introduction">
234   The Hypertext Transfer Protocol (HTTP) is an application-level
235   request/response protocol that uses extensible semantics and MIME-like
236   message payloads for flexible interaction with network-based hypertext
237   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
238   standard <xref target="RFC3986"/> to indicate the target resource and
239   relationships between resources.
240   Messages are passed in a format similar to that used by Internet mail
241   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
242   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
243   between HTTP and MIME messages).
246   HTTP is a generic interface protocol for information systems. It is
247   designed to hide the details of how a service is implemented by presenting
248   a uniform interface to clients that is independent of the types of
249   resources provided. Likewise, servers do not need to be aware of each
250   client's purpose: an HTTP request can be considered in isolation rather
251   than being associated with a specific type of client or a predetermined
252   sequence of application steps. The result is a protocol that can be used
253   effectively in many different contexts and for which implementations can
254   evolve independently over time.
257   HTTP is also designed for use as an intermediation protocol for translating
258   communication to and from non-HTTP information systems.
259   HTTP proxies and gateways can provide access to alternative information
260   services by translating their diverse protocols into a hypertext
261   format that can be viewed and manipulated by clients in the same way
262   as HTTP services.
265   One consequence of HTTP flexibility is that the protocol cannot be
266   defined in terms of what occurs behind the interface. Instead, we
267   are limited to defining the syntax of communication, the intent
268   of received communication, and the expected behavior of recipients.
269   If the communication is considered in isolation, then successful
270   actions ought to be reflected in corresponding changes to the
271   observable interface provided by servers. However, since multiple
272   clients might act in parallel and perhaps at cross-purposes, we
273   cannot require that such changes be observable beyond the scope
274   of a single response.
277   This document is Part 1 of the seven-part specification of HTTP,
278   defining the protocol referred to as "HTTP/1.1", obsoleting
279   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
280   Part 1 describes the architectural elements that are used or
281   referred to in HTTP, defines the "http" and "https" URI schemes,
282   describes overall network operation and connection management,
283   and defines HTTP message framing and forwarding requirements.
284   Our goal is to define all of the mechanisms necessary for HTTP message
285   handling that are independent of message semantics, thereby defining the
286   complete set of requirements for message parsers and
287   message-forwarding intermediaries.
290<section title="Requirements" anchor="intro.requirements">
292   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
293   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
294   document are to be interpreted as described in <xref target="RFC2119"/>.
297   An implementation is not compliant if it fails to satisfy one or more
298   of the "MUST" or "REQUIRED" level requirements for the protocols it
299   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
300   level and all the "SHOULD" level requirements for its protocols is said
301   to be "unconditionally compliant"; one that satisfies all the "MUST"
302   level requirements but not all the "SHOULD" level requirements for its
303   protocols is said to be "conditionally compliant".
307<section title="Syntax Notation" anchor="notation">
308<iref primary="true" item="Grammar" subitem="ALPHA"/>
309<iref primary="true" item="Grammar" subitem="CR"/>
310<iref primary="true" item="Grammar" subitem="CRLF"/>
311<iref primary="true" item="Grammar" subitem="CTL"/>
312<iref primary="true" item="Grammar" subitem="DIGIT"/>
313<iref primary="true" item="Grammar" subitem="DQUOTE"/>
314<iref primary="true" item="Grammar" subitem="HEXDIG"/>
315<iref primary="true" item="Grammar" subitem="LF"/>
316<iref primary="true" item="Grammar" subitem="OCTET"/>
317<iref primary="true" item="Grammar" subitem="SP"/>
318<iref primary="true" item="Grammar" subitem="VCHAR"/>
319<iref primary="true" item="Grammar" subitem="WSP"/>
321   This specification uses the Augmented Backus-Naur Form (ABNF) notation
322   of <xref target="RFC5234"/>.
324<t anchor="core.rules">
325  <x:anchor-alias value="ALPHA"/>
326  <x:anchor-alias value="CTL"/>
327  <x:anchor-alias value="CR"/>
328  <x:anchor-alias value="CRLF"/>
329  <x:anchor-alias value="DIGIT"/>
330  <x:anchor-alias value="DQUOTE"/>
331  <x:anchor-alias value="HEXDIG"/>
332  <x:anchor-alias value="LF"/>
333  <x:anchor-alias value="OCTET"/>
334  <x:anchor-alias value="SP"/>
335  <x:anchor-alias value="VCHAR"/>
336  <x:anchor-alias value="WSP"/>
337   The following core rules are included by
338   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
339   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
340   DIGIT (decimal 0-9), DQUOTE (double quote),
341   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
342   OCTET (any 8-bit sequence of data), SP (space),
343   VCHAR (any visible <xref target="USASCII"/> character),
344   and WSP (whitespace).
347   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
348   "obsolete" grammar rules that appear for historical reasons.
351<section title="ABNF Extension: #rule" anchor="notation.abnf">
353  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
354  improve readability.
357  A construct "#" is defined, similar to "*", for defining comma-delimited
358  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
359  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
360  comma (",") and optional whitespace (OWS,
361  <xref target="basic.rules"/>).   
364  Thus,
365</preamble><artwork type="example">
366  1#element =&gt; element *( OWS "," OWS element )
369  and:
370</preamble><artwork type="example">
371  #element =&gt; [ 1#element ]
374  and for n &gt;= 1 and m &gt; 1:
375</preamble><artwork type="example">
376  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
379  For compatibility with legacy list rules, recipients &SHOULD; accept empty
380  list elements. In other words, consumers would follow the list productions:
382<figure><artwork type="example">
383  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
385  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
388  Note that empty elements do not contribute to the count of elements present,
389  though.
392  For example, given these ABNF productions:
394<figure><artwork type="example">
395  example-list      = 1#example-list-elmt
396  example-list-elmt = token ; see <xref target="basic.rules"/>
399  Then these are valid values for example-list (not including the double
400  quotes, which are present for delimitation only):
402<figure><artwork type="example">
403  "foo,bar"
404  " foo ,bar,"
405  "  foo , ,bar,charlie   "
406  "foo ,bar,   charlie "
409  But these values would be invalid, as at least one non-empty element is
410  required:
412<figure><artwork type="example">
413  ""
414  ","
415  ",   ,"
418  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
419  expanded as explained above.
423<section title="Basic Rules" anchor="basic.rules">
424<t anchor="rule.CRLF">
425  <x:anchor-alias value="CRLF"/>
426   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
427   protocol elements other than the message-body
428   (see <xref target="tolerant.applications"/> for tolerant applications).
430<t anchor="rule.LWS">
431   This specification uses three rules to denote the use of linear
432   whitespace: OWS (optional whitespace), RWS (required whitespace), and
433   BWS ("bad" whitespace).
436   The OWS rule is used where zero or more linear whitespace octets might
437   appear. OWS &SHOULD; either not be produced or be produced as a single
438   SP. Multiple OWS octets that occur within field-content &SHOULD;
439   be replaced with a single SP before interpreting the field value or
440   forwarding the message downstream.
443   RWS is used when at least one linear whitespace octet is required to
444   separate field tokens. RWS &SHOULD; be produced as a single SP.
445   Multiple RWS octets that occur within field-content &SHOULD; be
446   replaced with a single SP before interpreting the field value or
447   forwarding the message downstream.
450   BWS is used where the grammar allows optional whitespace for historical
451   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
452   recipients &MUST; accept such bad optional whitespace and remove it before
453   interpreting the field value or forwarding the message downstream.
455<t anchor="rule.whitespace">
456  <x:anchor-alias value="BWS"/>
457  <x:anchor-alias value="OWS"/>
458  <x:anchor-alias value="RWS"/>
459  <x:anchor-alias value="obs-fold"/>
461<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"/>
462  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
463                 ; "optional" whitespace
464  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
465                 ; "required" whitespace
466  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
467                 ; "bad" whitespace
468  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
469                 ; see <xref target="header.fields"/>
471<t anchor="rule.token.separators">
472  <x:anchor-alias value="tchar"/>
473  <x:anchor-alias value="token"/>
474  <x:anchor-alias value="special"/>
475  <x:anchor-alias value="word"/>
476   Many HTTP/1.1 header field values consist of words (token or quoted-string)
477   separated by whitespace or special characters. These special characters
478   &MUST; be in a quoted string to be used within a parameter value (as defined
479   in <xref target="transfer.codings"/>).
481<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"/>
482  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
484  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
486  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
487 -->
488  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
489                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
490                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
491                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
493  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
494                 / ";" / ":" / "\" / DQUOTE / "/" / "["
495                 / "]" / "?" / "=" / "{" / "}"
497<t anchor="rule.quoted-string">
498  <x:anchor-alias value="quoted-string"/>
499  <x:anchor-alias value="qdtext"/>
500  <x:anchor-alias value="obs-text"/>
501   A string of text is parsed as a single word if it is quoted using
502   double-quote marks.
504<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"/>
505  <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>
506  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
507                 ; <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>
508  <x:ref>obs-text</x:ref>       = %x80-FF
510<t anchor="rule.quoted-pair">
511  <x:anchor-alias value="quoted-pair"/>
512   The backslash octet ("\") can be used as a single-octet
513   quoting mechanism within quoted-string constructs:
515<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
516  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
519   Recipients that process the value of the quoted-string &MUST; handle a
520   quoted-pair as if it were replaced by the octet following the backslash.
523   Senders &SHOULD-NOT; escape octets that do not require escaping
524   (i.e., other than DQUOTE and the backslash octet).
531<section title="HTTP-related architecture" anchor="architecture">
533   HTTP was created for the World Wide Web architecture
534   and has evolved over time to support the scalability needs of a worldwide
535   hypertext system. Much of that architecture is reflected in the terminology
536   and syntax productions used to define HTTP.
539<section title="Client/Server Messaging" anchor="operation">
540<iref primary="true" item="client"/>
541<iref primary="true" item="server"/>
542<iref primary="true" item="connection"/>
544   HTTP is a stateless request/response protocol that operates by exchanging
545   messages across a reliable transport or session-layer
546   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
547   program that establishes a connection to a server for the purpose of
548   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
549   program that accepts connections in order to service HTTP requests by
550   sending HTTP responses.
552<iref primary="true" item="user agent"/>
553<iref primary="true" item="origin server"/>
554<iref primary="true" item="browser"/>
555<iref primary="true" item="spider"/>
556<iref primary="true" item="sender"/>
557<iref primary="true" item="recipient"/>
559   Note that the terms client and server refer only to the roles that
560   these programs perform for a particular connection.  The same program
561   might act as a client on some connections and a server on others.  We use
562   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
563   such as a WWW browser, editor, or spider (web-traversing robot), and
564   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
565   authoritative responses to a request.  For general requirements, we use
566   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
567   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
568   message.
571   Most HTTP communication consists of a retrieval request (GET) for
572   a representation of some resource identified by a URI.  In the
573   simplest case, this might be accomplished via a single bidirectional
574   connection (===) between the user agent (UA) and the origin server (O).
576<figure><artwork type="drawing">
577         request   &gt;
578    UA ======================================= O
579                                &lt;   response
581<iref primary="true" item="message"/>
582<iref primary="true" item="request"/>
583<iref primary="true" item="response"/>
585   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
586   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
587   protocol version, followed by MIME-like header fields containing
588   request modifiers, client information, and payload metadata, an empty
589   line to indicate the end of the header section, and finally the payload
590   body (if any).
593   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
594   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
595   includes the protocol version, a success or error code, and textual
596   reason phrase, followed by MIME-like header fields containing server
597   information, resource metadata, and payload metadata, an empty line to
598   indicate the end of the header section, and finally the payload body (if any).
601   The following example illustrates a typical message exchange for a
602   GET request on the URI "":
605client request:
606</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
607GET /hello.txt HTTP/1.1
608User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
610Accept: */*
614server response:
615</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
616HTTP/1.1 200 OK
617Date: Mon, 27 Jul 2009 12:28:53 GMT
618Server: Apache
619Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
620ETag: "34aa387-d-1568eb00"
621Accept-Ranges: bytes
622Content-Length: <x:length-of target="exbody"/>
623Vary: Accept-Encoding
624Content-Type: text/plain
626<x:span anchor="exbody">Hello World!
630<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
632   Fundamentally, HTTP is a message-based protocol. Although message bodies can
633   be chunked (<xref target="chunked.encoding"/>) and implementations often
634   make parts of a message available progressively, this is not required, and
635   some widely-used implementations only make a message available when it is
636   complete. Furthermore, while most proxies will progressively stream messages,
637   some amount of buffering will take place, and some proxies might buffer
638   messages to perform transformations, check content or provide other services.
641   Therefore, extensions to and uses of HTTP cannot rely on the availability of
642   a partial message, or assume that messages will not be buffered. There are
643   strategies that can be used to test for buffering in a given connection, but
644   it should be understood that behaviors can differ across connections, and
645   between requests and responses.
648   Recipients &MUST; consider every message in a connection in isolation;
649   because HTTP is a stateless protocol, it cannot be assumed that two requests
650   on the same connection are from the same client or share any other common
651   attributes. In particular, intermediaries might mix requests from different
652   clients into a single server connection. Note that some existing HTTP
653   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
654   potentially causing interoperability and security problems.
658<section title="Connections and Transport Independence" anchor="transport-independence">
660   HTTP messaging is independent of the underlying transport or
661   session-layer connection protocol(s).  HTTP only presumes a reliable
662   transport with in-order delivery of requests and the corresponding
663   in-order delivery of responses.  The mapping of HTTP request and
664   response structures onto the data units of the underlying transport
665   protocol is outside the scope of this specification.
668   The specific connection protocols to be used for an interaction
669   are determined by client configuration and the target resource's URI.
670   For example, the "http" URI scheme
671   (<xref target="http.uri"/>) indicates a default connection of TCP
672   over IP, with a default TCP port of 80, but the client might be
673   configured to use a proxy via some other connection port or protocol
674   instead of using the defaults.
677   A connection might be used for multiple HTTP request/response exchanges,
678   as defined in <xref target="persistent.connections"/>.
682<section title="Intermediaries" anchor="intermediaries">
683<iref primary="true" item="intermediary"/>
685   HTTP enables the use of intermediaries to satisfy requests through
686   a chain of connections.  There are three common forms of HTTP
687   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
688   a single intermediary might act as an origin server, proxy, gateway,
689   or tunnel, switching behavior based on the nature of each request.
691<figure><artwork type="drawing">
692         &gt;             &gt;             &gt;             &gt;
693    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
694               &lt;             &lt;             &lt;             &lt;
697   The figure above shows three intermediaries (A, B, and C) between the
698   user agent and origin server. A request or response message that
699   travels the whole chain will pass through four separate connections.
700   Some HTTP communication options
701   might apply only to the connection with the nearest, non-tunnel
702   neighbor, only to the end-points of the chain, or to all connections
703   along the chain. Although the diagram is linear, each participant might
704   be engaged in multiple, simultaneous communications. For example, B
705   might be receiving requests from many clients other than A, and/or
706   forwarding requests to servers other than C, at the same time that it
707   is handling A's request.
710<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
711<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
712   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
713   to describe various requirements in relation to the directional flow of a
714   message: all messages flow from upstream to downstream.
715   Likewise, we use the terms inbound and outbound to refer to
716   directions in relation to the request path:
717   "<x:dfn>inbound</x:dfn>" means toward the origin server and
718   "<x:dfn>outbound</x:dfn>" means toward the user agent.
720<t><iref primary="true" item="proxy"/>
721   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
722   client, usually via local configuration rules, to receive requests
723   for some type(s) of absolute URI and attempt to satisfy those
724   requests via translation through the HTTP interface.  Some translations
725   are minimal, such as for proxy requests for "http" URIs, whereas
726   other requests might require translation to and from entirely different
727   application-layer protocols. Proxies are often used to group an
728   organization's HTTP requests through a common intermediary for the
729   sake of security, annotation services, or shared caching.
732<iref primary="true" item="transforming proxy"/>
733<iref primary="true" item="non-transforming proxy"/>
734   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
735   or configured to modify request or response messages in a semantically
736   meaningful way (i.e., modifications, beyond those required by normal
737   HTTP processing, that change the message in a way that would be
738   significant to the original sender or potentially significant to
739   downstream recipients).  For example, a transforming proxy might be
740   acting as a shared annotation server (modifying responses to include
741   references to a local annotation database), a malware filter, a
742   format transcoder, or an intranet-to-Internet privacy filter.  Such
743   transformations are presumed to be desired by the client (or client
744   organization) that selected the proxy and are beyond the scope of
745   this specification.  However, when a proxy is not intended to transform
746   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
747   requirements that preserve HTTP message semantics. See &status-203; and
748   &header-warning; for status and warning codes related to transformations.
750<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
751<iref primary="true" item="accelerator"/>
752   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
753   is a receiving agent that acts
754   as a layer above some other server(s) and translates the received
755   requests to the underlying server's protocol.  Gateways are often
756   used to encapsulate legacy or untrusted information services, to
757   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
758   enable partitioning or load-balancing of HTTP services across
759   multiple machines.
762   A gateway behaves as an origin server on its outbound connection and
763   as a user agent on its inbound connection.
764   All HTTP requirements applicable to an origin server
765   also apply to the outbound communication of a gateway.
766   A gateway communicates with inbound servers using any protocol that
767   it desires, including private extensions to HTTP that are outside
768   the scope of this specification.  However, an HTTP-to-HTTP gateway
769   that wishes to interoperate with third-party HTTP servers &MUST;
770   comply with HTTP user agent requirements on the gateway's inbound
771   connection and &MUST; implement the Connection
772   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
773   header fields for both connections.
775<t><iref primary="true" item="tunnel"/>
776   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
777   without changing the messages. Once active, a tunnel is not
778   considered a party to the HTTP communication, though the tunnel might
779   have been initiated by an HTTP request. A tunnel ceases to exist when
780   both ends of the relayed connection are closed. Tunnels are used to
781   extend a virtual connection through an intermediary, such as when
782   transport-layer security is used to establish private communication
783   through a shared firewall proxy.
785<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
786<iref primary="true" item="captive portal"/>
787   In addition, there may exist network intermediaries that are not
788   considered part of the HTTP communication but nevertheless act as
789   filters or redirecting agents (usually violating HTTP semantics,
790   causing security problems, and otherwise making a mess of things).
791   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
792   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
793   or "<x:dfn>captive portal</x:dfn>",
794   differs from an HTTP proxy because it has not been selected by the client.
795   Instead, the network intermediary redirects outgoing TCP port 80 packets
796   (and occasionally other common port traffic) to an internal HTTP server.
797   Interception proxies are commonly found on public network access points,
798   as a means of enforcing account subscription prior to allowing use of
799   non-local Internet services, and within corporate firewalls to enforce
800   network usage policies.
801   They are indistinguishable from a man-in-the-middle attack.
805<section title="Caches" anchor="caches">
806<iref primary="true" item="cache"/>
808   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
809   subsystem that controls its message storage, retrieval, and deletion.
810   A cache stores cacheable responses in order to reduce the response
811   time and network bandwidth consumption on future, equivalent
812   requests. Any client or server &MAY; employ a cache, though a cache
813   cannot be used by a server while it is acting as a tunnel.
816   The effect of a cache is that the request/response chain is shortened
817   if one of the participants along the chain has a cached response
818   applicable to that request. The following illustrates the resulting
819   chain if B has a cached copy of an earlier response from O (via C)
820   for a request which has not been cached by UA or A.
822<figure><artwork type="drawing">
823            &gt;             &gt;
824       UA =========== A =========== B - - - - - - C - - - - - - O
825                  &lt;             &lt;
827<t><iref primary="true" item="cacheable"/>
828   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
829   the response message for use in answering subsequent requests.
830   Even when a response is cacheable, there might be additional
831   constraints placed by the client or by the origin server on when
832   that cached response can be used for a particular request. HTTP
833   requirements for cache behavior and cacheable responses are
834   defined in &caching-overview;. 
837   There are a wide variety of architectures and configurations
838   of caches and proxies deployed across the World Wide Web and
839   inside large organizations. These systems include national hierarchies
840   of proxy caches to save transoceanic bandwidth, systems that
841   broadcast or multicast cache entries, organizations that distribute
842   subsets of cached data via optical media, and so on.
846<section title="Protocol Versioning" anchor="http.version">
847  <x:anchor-alias value="HTTP-Version"/>
848  <x:anchor-alias value="HTTP-Prot-Name"/>
850   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
851   versions of the protocol. This specification defines version "1.1".
852   The protocol version as a whole indicates the sender's compliance
853   with the set of requirements laid out in that version's corresponding
854   specification of HTTP.
857   The version of an HTTP message is indicated by an HTTP-Version field
858   in the first line of the message. HTTP-Version is case-sensitive.
860<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
861  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
862  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
865   The HTTP version number consists of two decimal digits separated by a "."
866   (period or decimal point).  The first digit ("major version") indicates the
867   HTTP messaging syntax, whereas the second digit ("minor version") indicates
868   the highest minor version to which the sender is at least conditionally
869   compliant and able to understand for future communication.  The minor
870   version advertises the sender's communication capabilities even when the
871   sender is only using a backwards-compatible subset of the protocol,
872   thereby letting the recipient know that more advanced features can
873   be used in response (by servers) or in future requests (by clients).
876   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
877   <xref target="RFC1945"/> or a recipient whose version is unknown,
878   the HTTP/1.1 message is constructed such that it can be interpreted
879   as a valid HTTP/1.0 message if all of the newer features are ignored.
880   This specification places recipient-version requirements on some
881   new features so that a compliant sender will only use compatible
882   features until it has determined, through configuration or the
883   receipt of a message, that the recipient supports HTTP/1.1.
886   The interpretation of an HTTP header field does not change
887   between minor versions of the same major version, though the default
888   behavior of a recipient in the absence of such a field can change.
889   Unless specified otherwise, header fields defined in HTTP/1.1 are
890   defined for all versions of HTTP/1.x.  In particular, the Host and
891   Connection header fields ought to be implemented by all HTTP/1.x
892   implementations whether or not they advertise compliance with HTTP/1.1.
895   New header fields can be defined such that, when they are
896   understood by a recipient, they might override or enhance the
897   interpretation of previously defined header fields.  When an
898   implementation receives an unrecognized header field, the recipient
899   &MUST; ignore that header field for local processing regardless of
900   the message's HTTP version.  An unrecognized header field received
901   by a proxy &MUST; be forwarded downstream unless the header field's
902   field-name is listed in the message's Connection header-field
903   (see <xref target="header.connection"/>).
904   These requirements allow HTTP's functionality to be enhanced without
905   requiring prior update of all compliant intermediaries.
908   Intermediaries that process HTTP messages (i.e., all intermediaries
909   other than those acting as a tunnel) &MUST; send their own HTTP-Version
910   in forwarded messages.  In other words, they &MUST-NOT; blindly
911   forward the first line of an HTTP message without ensuring that the
912   protocol version matches what the intermediary understands, and
913   is at least conditionally compliant to, for both the receiving and
914   sending of messages.  Forwarding an HTTP message without rewriting
915   the HTTP-Version might result in communication errors when downstream
916   recipients use the message sender's version to determine what features
917   are safe to use for later communication with that sender.
920   An HTTP client &SHOULD; send a request version equal to the highest
921   version for which the client is at least conditionally compliant and
922   whose major version is no higher than the highest version supported
923   by the server, if this is known.  An HTTP client &MUST-NOT; send a
924   version for which it is not at least conditionally compliant.
927   An HTTP client &MAY; send a lower request version if it is known that
928   the server incorrectly implements the HTTP specification, but only
929   after the client has attempted at least one normal request and determined
930   from the response status or header fields (e.g., Server) that the
931   server improperly handles higher request versions.
934   An HTTP server &SHOULD; send a response version equal to the highest
935   version for which the server is at least conditionally compliant and
936   whose major version is less than or equal to the one received in the
937   request.  An HTTP server &MUST-NOT; send a version for which it is not
938   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
939   Version Not Supported) response if it cannot send a response using the
940   major version used in the client's request.
943   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
944   if it is known or suspected that the client incorrectly implements the
945   HTTP specification and is incapable of correctly processing later
946   version responses, such as when a client fails to parse the version
947   number correctly or when an intermediary is known to blindly forward
948   the HTTP-Version even when it doesn't comply with the given minor
949   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
950   performed unless triggered by specific client attributes, such as when
951   one or more of the request header fields (e.g., User-Agent) uniquely
952   match the values sent by a client known to be in error.
955   The intention of HTTP's versioning design is that the major number
956   will only be incremented if an incompatible message syntax is
957   introduced, and that the minor number will only be incremented when
958   changes made to the protocol have the effect of adding to the message
959   semantics or implying additional capabilities of the sender.  However,
960   the minor version was not incremented for the changes introduced between
961   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
962   is specifically avoiding any such changes to the protocol.
966<section title="Uniform Resource Identifiers" anchor="uri">
967<iref primary="true" item="resource"/>
969   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
970   throughout HTTP as the means for identifying resources. URI references
971   are used to target requests, indicate redirects, and define relationships.
972   HTTP does not limit what a resource might be; it merely defines an interface
973   that can be used to interact with a resource via HTTP. More information on
974   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
976  <x:anchor-alias value="URI-reference"/>
977  <x:anchor-alias value="absolute-URI"/>
978  <x:anchor-alias value="relative-part"/>
979  <x:anchor-alias value="authority"/>
980  <x:anchor-alias value="path-abempty"/>
981  <x:anchor-alias value="path-absolute"/>
982  <x:anchor-alias value="port"/>
983  <x:anchor-alias value="query"/>
984  <x:anchor-alias value="uri-host"/>
985  <x:anchor-alias value="partial-URI"/>
987   This specification adopts the definitions of "URI-reference",
988   "absolute-URI", "relative-part", "port", "host",
989   "path-abempty", "path-absolute", "query", and "authority" from the
990   URI generic syntax <xref target="RFC3986"/>.
991   In addition, we define a partial-URI rule for protocol elements
992   that allow a relative URI but not a fragment.
994<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"/>
995  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
996  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
997  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
998  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
999  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1000  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1001  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
1002  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
1003  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
1005  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
1008   Each protocol element in HTTP that allows a URI reference will indicate
1009   in its ABNF production whether the element allows any form of reference
1010   (URI-reference), only a URI in absolute form (absolute-URI), only the
1011   path and optional query components, or some combination of the above.
1012   Unless otherwise indicated, URI references are parsed relative to the
1013   effective request URI, which defines the default base URI for references
1014   in both the request and its corresponding response.
1017<section title="http URI scheme" anchor="http.uri">
1018  <x:anchor-alias value="http-URI"/>
1019  <iref item="http URI scheme" primary="true"/>
1020  <iref item="URI scheme" subitem="http" primary="true"/>
1022   The "http" URI scheme is hereby defined for the purpose of minting
1023   identifiers according to their association with the hierarchical
1024   namespace governed by a potential HTTP origin server listening for
1025   TCP connections on a given port.
1027<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1028  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1031   The HTTP origin server is identified by the generic syntax's
1032   <x:ref>authority</x:ref> component, which includes a host identifier
1033   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1034   The remainder of the URI, consisting of both the hierarchical path
1035   component and optional query component, serves as an identifier for
1036   a potential resource within that origin server's name space.
1039   If the host identifier is provided as an IP literal or IPv4 address,
1040   then the origin server is any listener on the indicated TCP port at
1041   that IP address. If host is a registered name, then that name is
1042   considered an indirect identifier and the recipient might use a name
1043   resolution service, such as DNS, to find the address of a listener
1044   for that host.
1045   The host &MUST-NOT; be empty; if an "http" URI is received with an
1046   empty host, then it &MUST; be rejected as invalid.
1047   If the port subcomponent is empty or not given, then TCP port 80 is
1048   assumed (the default reserved port for WWW services).
1051   Regardless of the form of host identifier, access to that host is not
1052   implied by the mere presence of its name or address. The host might or might
1053   not exist and, even when it does exist, might or might not be running an
1054   HTTP server or listening to the indicated port. The "http" URI scheme
1055   makes use of the delegated nature of Internet names and addresses to
1056   establish a naming authority (whatever entity has the ability to place
1057   an HTTP server at that Internet name or address) and allows that
1058   authority to determine which names are valid and how they might be used.
1061   When an "http" URI is used within a context that calls for access to the
1062   indicated resource, a client &MAY; attempt access by resolving
1063   the host to an IP address, establishing a TCP connection to that address
1064   on the indicated port, and sending an HTTP request message to the server
1065   containing the URI's identifying data as described in <xref target="request"/>.
1066   If the server responds to that request with a non-interim HTTP response
1067   message, as described in <xref target="response"/>, then that response
1068   is considered an authoritative answer to the client's request.
1071   Although HTTP is independent of the transport protocol, the "http"
1072   scheme is specific to TCP-based services because the name delegation
1073   process depends on TCP for establishing authority.
1074   An HTTP service based on some other underlying connection protocol
1075   would presumably be identified using a different URI scheme, just as
1076   the "https" scheme (below) is used for servers that require an SSL/TLS
1077   transport layer on a connection. Other protocols might also be used to
1078   provide access to "http" identified resources &mdash; it is only the
1079   authoritative interface used for mapping the namespace that is
1080   specific to TCP.
1083   The URI generic syntax for authority also includes a deprecated
1084   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1085   for including user authentication information in the URI.  Some
1086   implementations make use of the userinfo component for internal
1087   configuration of authentication information, such as within command
1088   invocation options, configuration files, or bookmark lists, even
1089   though such usage might expose a user identifier or password.
1090   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1091   delimiter) when transmitting an "http" URI in a message.  Recipients
1092   of HTTP messages that contain a URI reference &SHOULD; parse for the
1093   existence of userinfo and treat its presence as an error, likely
1094   indicating that the deprecated subcomponent is being used to obscure
1095   the authority for the sake of phishing attacks.
1099<section title="https URI scheme" anchor="https.uri">
1100   <x:anchor-alias value="https-URI"/>
1101   <iref item="https URI scheme"/>
1102   <iref item="URI scheme" subitem="https"/>
1104   The "https" URI scheme is hereby defined for the purpose of minting
1105   identifiers according to their association with the hierarchical
1106   namespace governed by a potential HTTP origin server listening for
1107   SSL/TLS-secured connections on a given TCP port.
1110   All of the requirements listed above for the "http" scheme are also
1111   requirements for the "https" scheme, except that a default TCP port
1112   of 443 is assumed if the port subcomponent is empty or not given,
1113   and the TCP connection &MUST; be secured for privacy through the
1114   use of strong encryption prior to sending the first HTTP request.
1116<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1117  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1120   Unlike the "http" scheme, responses to "https" identified requests
1121   are never "public" and thus &MUST-NOT; be reused for shared caching.
1122   They can, however, be reused in a private cache if the message is
1123   cacheable by default in HTTP or specifically indicated as such by
1124   the Cache-Control header field (&header-cache-control;).
1127   Resources made available via the "https" scheme have no shared
1128   identity with the "http" scheme even if their resource identifiers
1129   indicate the same authority (the same host listening to the same
1130   TCP port).  They are distinct name spaces and are considered to be
1131   distinct origin servers.  However, an extension to HTTP that is
1132   defined to apply to entire host domains, such as the Cookie protocol
1133   <xref target="RFC6265"/>, can allow information
1134   set by one service to impact communication with other services
1135   within a matching group of host domains.
1138   The process for authoritative access to an "https" identified
1139   resource is defined in <xref target="RFC2818"/>.
1143<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1145   Since the "http" and "https" schemes conform to the URI generic syntax,
1146   such URIs are normalized and compared according to the algorithm defined
1147   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1148   described above for each scheme.
1151   If the port is equal to the default port for a scheme, the normal
1152   form is to elide the port subcomponent. Likewise, an empty path
1153   component is equivalent to an absolute path of "/", so the normal
1154   form is to provide a path of "/" instead. The scheme and host
1155   are case-insensitive and normally provided in lowercase; all
1156   other components are compared in a case-sensitive manner.
1157   Characters other than those in the "reserved" set are equivalent
1158   to their percent-encoded octets (see <xref target="RFC3986"
1159   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1162   For example, the following three URIs are equivalent:
1164<figure><artwork type="example">
1173<section title="Message Format" anchor="http.message">
1174<x:anchor-alias value="generic-message"/>
1175<x:anchor-alias value="message.types"/>
1176<x:anchor-alias value="HTTP-message"/>
1177<x:anchor-alias value="start-line"/>
1178<iref item="header section"/>
1179<iref item="headers"/>
1180<iref item="header field"/>
1182   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1183   octets in a format similar to the Internet Message Format
1184   <xref target="RFC5322"/>: zero or more header fields (collectively
1185   referred to as the "headers" or the "header section"), an empty line
1186   indicating the end of the header section, and an optional message-body.
1189   An HTTP message can either be a request from client to server or a
1190   response from server to client.  Syntactically, the two types of message
1191   differ only in the start-line, which is either a Request-Line (for requests)
1192   or a Status-Line (for responses), and in the algorithm for determining
1193   the length of the message-body (<xref target="message.body"/>).
1194   In theory, a client could receive requests and a server could receive
1195   responses, distinguishing them by their different start-line formats,
1196   but in practice servers are implemented to only expect a request
1197   (a response is interpreted as an unknown or invalid request method)
1198   and clients are implemented to only expect a response.
1200<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1201  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1202                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1203                    <x:ref>CRLF</x:ref>
1204                    [ <x:ref>message-body</x:ref> ]
1205  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1208   Implementations &MUST-NOT; send whitespace between the start-line and
1209   the first header field. The presence of such whitespace in a request
1210   might be an attempt to trick a server into ignoring that field or
1211   processing the line after it as a new request, either of which might
1212   result in a security vulnerability if other implementations within
1213   the request chain interpret the same message differently.
1214   Likewise, the presence of such whitespace in a response might be
1215   ignored by some clients or cause others to cease parsing.
1218<section title="Message Parsing Robustness" anchor="message.robustness">
1220   In the interest of robustness, servers &SHOULD; ignore at least one
1221   empty line received where a Request-Line is expected. In other words, if
1222   the server is reading the protocol stream at the beginning of a
1223   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1226   Some old HTTP/1.0 client implementations send an extra CRLF
1227   after a POST request as a lame workaround for some early server
1228   applications that failed to read message-body content that was
1229   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1230   preface or follow a request with an extra CRLF.  If terminating
1231   the request message-body with a line-ending is desired, then the
1232   client &MUST; include the terminating CRLF octets as part of the
1233   message-body length.
1236   When a server listening only for HTTP request messages, or processing
1237   what appears from the start-line to be an HTTP request message,
1238   receives a sequence of octets that does not match the HTTP-message
1239   grammar aside from the robustness exceptions listed above, the
1240   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1243   The normal procedure for parsing an HTTP message is to read the
1244   start-line into a structure, read each header field into a hash
1245   table by field name until the empty line, and then use the parsed
1246   data to determine if a message-body is expected.  If a message-body
1247   has been indicated, then it is read as a stream until an amount
1248   of octets equal to the message-body length is read or the connection
1249   is closed.  Care must be taken to parse an HTTP message as a sequence
1250   of octets in an encoding that is a superset of US-ASCII.  Attempting
1251   to parse HTTP as a stream of Unicode characters in a character encoding
1252   like UTF-16 might introduce security flaws due to the differing ways
1253   that such parsers interpret invalid characters.
1256   HTTP allows the set of defined header fields to be extended without
1257   changing the protocol version (see <xref target="header.field.registration"/>).
1258   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1259   proxy is specifically configured to block or otherwise transform such
1260   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1264<section title="Header Fields" anchor="header.fields">
1265  <x:anchor-alias value="header-field"/>
1266  <x:anchor-alias value="field-content"/>
1267  <x:anchor-alias value="field-name"/>
1268  <x:anchor-alias value="field-value"/>
1269  <x:anchor-alias value="OWS"/>
1271   Each HTTP header field consists of a case-insensitive field name
1272   followed by a colon (":"), optional whitespace, and the field value.
1274<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"/>
1275  <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>
1276  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1277  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1278  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1281   No whitespace is allowed between the header field name and colon. For
1282   security reasons, any request message received containing such whitespace
1283   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1284   &MUST; remove any such whitespace from a response message before
1285   forwarding the message downstream.
1288   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1289   preferred. The field value does not include any leading or trailing white
1290   space: OWS occurring before the first non-whitespace octet of the
1291   field value or after the last non-whitespace octet of the field value
1292   is ignored and &SHOULD; be removed before further processing (as this does
1293   not change the meaning of the header field).
1296   The order in which header fields with differing field names are
1297   received is not significant. However, it is "good practice" to send
1298   header fields that contain control data first, such as Host on
1299   requests and Date on responses, so that implementations can decide
1300   when not to handle a message as early as possible.  A server &MUST;
1301   wait until the entire header section is received before interpreting
1302   a request message, since later header fields might include conditionals,
1303   authentication credentials, or deliberately misleading duplicate
1304   header fields that would impact request processing.
1307   Multiple header fields with the same field name &MUST-NOT; be
1308   sent in a message unless the entire field value for that
1309   header field is defined as a comma-separated list [i.e., #(values)].
1310   Multiple header fields with the same field name can be combined into
1311   one "field-name: field-value" pair, without changing the semantics of the
1312   message, by appending each subsequent field value to the combined
1313   field value in order, separated by a comma. The order in which
1314   header fields with the same field name are received is therefore
1315   significant to the interpretation of the combined field value;
1316   a proxy &MUST-NOT; change the order of these field values when
1317   forwarding a message.
1320  <t>
1321   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1322   practice can occur multiple times, but does not use the list syntax, and
1323   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1324   for details.) Also note that the Set-Cookie2 header field specified in
1325   <xref target="RFC2965"/> does not share this problem.
1326  </t>
1329   Historically, HTTP header field values could be extended over multiple
1330   lines by preceding each extra line with at least one space or horizontal
1331   tab octet (line folding). This specification deprecates such line
1332   folding except within the message/http media type
1333   (<xref target=""/>).
1334   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1335   (i.e., that contain any field-content that matches the obs-fold rule) unless
1336   the message is intended for packaging within the message/http media type.
1337   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1338   obs-fold whitespace with a single SP prior to interpreting the field value
1339   or forwarding the message downstream.
1342   Historically, HTTP has allowed field content with text in the ISO-8859-1
1343   <xref target="ISO-8859-1"/> character encoding and supported other
1344   character sets only through use of <xref target="RFC2047"/> encoding.
1345   In practice, most HTTP header field values use only a subset of the
1346   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1347   header fields &SHOULD; limit their field values to US-ASCII octets.
1348   Recipients &SHOULD; treat other (obs-text) octets in field content as
1349   opaque data.
1351<t anchor="rule.comment">
1352  <x:anchor-alias value="comment"/>
1353  <x:anchor-alias value="ctext"/>
1354   Comments can be included in some HTTP header fields by surrounding
1355   the comment text with parentheses. Comments are only allowed in
1356   fields containing "comment" as part of their field value definition.
1358<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1359  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1360  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1361                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1363<t anchor="rule.quoted-cpair">
1364  <x:anchor-alias value="quoted-cpair"/>
1365   The backslash octet ("\") can be used as a single-octet
1366   quoting mechanism within comment constructs:
1368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1369  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1372   Senders &SHOULD-NOT; escape octets that do not require escaping
1373   (i.e., other than the backslash octet "\" and the parentheses "(" and
1374   ")").
1377   HTTP does not place a pre-defined limit on the length of header fields,
1378   either in isolation or as a set. A server &MUST; be prepared to receive
1379   request header fields of unbounded length and respond with a 4xx status
1380   code if the received header field(s) would be longer than the server wishes
1381   to handle.
1384   A client that receives response headers that are longer than it wishes to
1385   handle can only treat it as a server error.
1388   Various ad-hoc limitations on header length are found in practice. It is
1389   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1390   combined header fields have 4000 or more octets.
1394<section title="Message Body" anchor="message.body">
1395  <x:anchor-alias value="message-body"/>
1397   The message-body (if any) of an HTTP message is used to carry the
1398   payload body associated with the request or response.
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1401  <x:ref>message-body</x:ref> = *OCTET
1404   The message-body differs from the payload body only when a transfer-coding
1405   has been applied, as indicated by the Transfer-Encoding header field
1406   (<xref target="header.transfer-encoding"/>).  If more than one
1407   Transfer-Encoding header field is present in a message, the multiple
1408   field-values &MUST; be combined into one field-value, according to the
1409   algorithm defined in <xref target="header.fields"/>, before determining
1410   the message-body length.
1413   When one or more transfer-codings are applied to a payload in order to
1414   form the message-body, the Transfer-Encoding header field &MUST; contain
1415   the list of transfer-codings applied. Transfer-Encoding is a property of
1416   the message, not of the payload, and thus &MAY; be added or removed by
1417   any implementation along the request/response chain under the constraints
1418   found in <xref target="transfer.codings"/>.
1421   If a message is received that has multiple Content-Length header fields
1422   (<xref target="header.content-length"/>) with field-values consisting
1423   of the same decimal value, or a single Content-Length header field with
1424   a field value containing a list of identical decimal values (e.g.,
1425   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1426   header fields have been generated or combined by an upstream message
1427   processor, then the recipient &MUST; either reject the message as invalid
1428   or replace the duplicated field-values with a single valid Content-Length
1429   field containing that decimal value prior to determining the message-body
1430   length.
1433   The rules for when a message-body is allowed in a message differ for
1434   requests and responses.
1437   The presence of a message-body in a request is signaled by the
1438   inclusion of a Content-Length or Transfer-Encoding header field in
1439   the request's header fields, even if the request method does not
1440   define any use for a message-body.  This allows the request
1441   message framing algorithm to be independent of method semantics.
1444   For response messages, whether or not a message-body is included with
1445   a message is dependent on both the request method and the response
1446   status code (<xref target="status.code.and.reason.phrase"/>).
1447   Responses to the HEAD request method never include a message-body
1448   because the associated response header fields (e.g., Transfer-Encoding,
1449   Content-Length, etc.) only indicate what their values would have been
1450   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1451   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1452   All other responses do include a message-body, although the body
1453   &MAY; be of zero length.
1456   The length of the message-body is determined by one of the following
1457   (in order of precedence):
1460  <list style="numbers">
1461    <x:lt><t>
1462     Any response to a HEAD request and any response with a status
1463     code of 100-199, 204, or 304 is always terminated by the first
1464     empty line after the header fields, regardless of the header
1465     fields present in the message, and thus cannot contain a message-body.
1466    </t></x:lt>
1467    <x:lt><t>
1468     If a Transfer-Encoding header field is present
1469     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1470     is the final encoding, the message-body length is determined by reading
1471     and decoding the chunked data until the transfer-coding indicates the
1472     data is complete.
1473    </t>
1474    <t>
1475     If a Transfer-Encoding header field is present in a response and the
1476     "chunked" transfer-coding is not the final encoding, the message-body
1477     length is determined by reading the connection until it is closed by
1478     the server.
1479     If a Transfer-Encoding header field is present in a request and the
1480     "chunked" transfer-coding is not the final encoding, the message-body
1481     length cannot be determined reliably; the server &MUST; respond with
1482     the 400 (Bad Request) status code and then close the connection.
1483    </t>
1484    <t>
1485     If a message is received with both a Transfer-Encoding header field
1486     and a Content-Length header field, the Transfer-Encoding overrides
1487     the Content-Length.
1488     Such a message might indicate an attempt to perform request or response
1489     smuggling (bypass of security-related checks on message routing or content)
1490     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1491     be removed, prior to forwarding the message downstream, or replaced with
1492     the real message-body length after the transfer-coding is decoded.
1493    </t></x:lt>
1494    <x:lt><t>
1495     If a message is received without Transfer-Encoding and with either
1496     multiple Content-Length header fields having differing field-values or
1497     a single Content-Length header field having an invalid value, then the
1498     message framing is invalid and &MUST; be treated as an error to
1499     prevent request or response smuggling.
1500     If this is a request message, the server &MUST; respond with
1501     a 400 (Bad Request) status code and then close the connection.
1502     If this is a response message received by a proxy, the proxy
1503     &MUST; discard the received response, send a 502 (Bad Gateway)
1504     status code as its downstream response, and then close the connection.
1505     If this is a response message received by a user-agent, it &MUST; be
1506     treated as an error by discarding the message and closing the connection.
1507    </t></x:lt>
1508    <x:lt><t>
1509     If a valid Content-Length header field
1510     is present without Transfer-Encoding, its decimal value defines the
1511     message-body length in octets.  If the actual number of octets sent in
1512     the message is less than the indicated Content-Length, the recipient
1513     &MUST; consider the message to be incomplete and treat the connection
1514     as no longer usable.
1515     If the actual number of octets sent in the message is more than the indicated
1516     Content-Length, the recipient &MUST; only process the message-body up to the
1517     field value's number of octets; the remainder of the message &MUST; either
1518     be discarded or treated as the next message in a pipeline.  For the sake of
1519     robustness, a user-agent &MAY; attempt to detect and correct such an error
1520     in message framing if it is parsing the response to the last request on
1521     a connection and the connection has been closed by the server.
1522    </t></x:lt>
1523    <x:lt><t>
1524     If this is a request message and none of the above are true, then the
1525     message-body length is zero (no message-body is present).
1526    </t></x:lt>
1527    <x:lt><t>
1528     Otherwise, this is a response message without a declared message-body
1529     length, so the message-body length is determined by the number of octets
1530     received prior to the server closing the connection.
1531    </t></x:lt>
1532  </list>
1535   Since there is no way to distinguish a successfully completed,
1536   close-delimited message from a partially-received message interrupted
1537   by network failure, implementations &SHOULD; use encoding or
1538   length-delimited messages whenever possible.  The close-delimiting
1539   feature exists primarily for backwards compatibility with HTTP/1.0.
1542   A server &MAY; reject a request that contains a message-body but
1543   not a Content-Length by responding with 411 (Length Required).
1546   Unless a transfer-coding other than "chunked" has been applied,
1547   a client that sends a request containing a message-body &SHOULD;
1548   use a valid Content-Length header field if the message-body length
1549   is known in advance, rather than the "chunked" encoding, since some
1550   existing services respond to "chunked" with a 411 (Length Required)
1551   status code even though they understand the chunked encoding.  This
1552   is typically because such services are implemented via a gateway that
1553   requires a content-length in advance of being called and the server
1554   is unable or unwilling to buffer the entire request before processing.
1557   A client that sends a request containing a message-body &MUST; include a
1558   valid Content-Length header field if it does not know the server will
1559   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1560   of specific user configuration or by remembering the version of a prior
1561   received response.
1564   Request messages that are prematurely terminated, possibly due to a
1565   cancelled connection or a server-imposed time-out exception, &MUST;
1566   result in closure of the connection; sending an HTTP/1.1 error response
1567   prior to closing the connection is &OPTIONAL;.
1568   Response messages that are prematurely terminated, usually by closure
1569   of the connection prior to receiving the expected number of octets or by
1570   failure to decode a transfer-encoded message-body, &MUST; be recorded
1571   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1572   message-body as if it were complete (i.e., some indication must be given
1573   to the user that an error occurred).  Cache requirements for incomplete
1574   responses are defined in &cache-incomplete;.
1577   A server &MUST; read the entire request message-body or close
1578   the connection after sending its response, since otherwise the
1579   remaining data on a persistent connection would be misinterpreted
1580   as the next request.  Likewise,
1581   a client &MUST; read the entire response message-body if it intends
1582   to reuse the same connection for a subsequent request.  Pipelining
1583   multiple requests on a connection is described in <xref target="pipelining"/>.
1587<section title="General Header Fields" anchor="general.header.fields">
1588  <x:anchor-alias value="general-header"/>
1590   There are a few header fields which have general applicability for
1591   both request and response messages, but which do not apply to the
1592   payload being transferred. These header fields apply only to the
1593   message being transmitted.
1595<texttable align="left">
1596  <ttcol>Header Field Name</ttcol>
1597  <ttcol>Defined in...</ttcol>
1599  <c>Connection</c> <c><xref target="header.connection"/></c>
1600  <c>Date</c> <c><xref target=""/></c>
1601  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1602  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1603  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1604  <c>Via</c> <c><xref target="header.via"/></c>
1609<section title="Request" anchor="request">
1610  <x:anchor-alias value="Request"/>
1612   A request message from a client to a server begins with a
1613   Request-Line, followed by zero or more header fields, an empty
1614   line signifying the end of the header block, and an optional
1615   message body.
1617<!--                 Host                      ; should be moved here eventually -->
1618<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1619  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1620                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1621                  <x:ref>CRLF</x:ref>
1622                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1625<section title="Request-Line" anchor="request-line">
1626  <x:anchor-alias value="Request-Line"/>
1628   The Request-Line begins with a method token, followed by a single
1629   space (SP), the request-target, another single space (SP), the
1630   protocol version, and ending with CRLF.
1632<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1633  <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>
1636<section title="Method" anchor="method">
1637  <x:anchor-alias value="Method"/>
1639   The Method token indicates the request method to be performed on the
1640   target resource. The request method is case-sensitive.
1642<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1643  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1647<section title="request-target" anchor="request-target">
1648  <x:anchor-alias value="request-target"/>
1650   The request-target identifies the target resource upon which to apply
1651   the request.  In most cases, the user agent is provided a URI reference
1652   from which it determines an absolute URI for identifying the target
1653   resource.  When a request to the resource is initiated, all or part
1654   of that URI is used to construct the HTTP request-target.
1656<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1657  <x:ref>request-target</x:ref> = "*"
1658                 / <x:ref>absolute-URI</x:ref>
1659                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1660                 / <x:ref>authority</x:ref>
1663   The four options for request-target are dependent on the nature of the
1664   request.
1666<t><iref item="asterisk form (of request-target)"/>
1667   The asterisk "*" form of request-target, which &MUST-NOT; be used
1668   with any request method other than OPTIONS, means that the request
1669   applies to the server as a whole (the listening process) rather than
1670   to a specific named resource at that server.  For example,
1672<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1673OPTIONS * HTTP/1.1
1675<t><iref item="absolute-URI form (of request-target)"/>
1676   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1677   proxy. The proxy is requested to either forward the request or service it
1678   from a valid cache, and then return the response. Note that the proxy &MAY;
1679   forward the request on to another proxy or directly to the server
1680   specified by the absolute-URI. In order to avoid request loops, a
1681   proxy that forwards requests to other proxies &MUST; be able to
1682   recognize and exclude all of its own server names, including
1683   any aliases, local variations, and the numeric IP address. An example
1684   Request-Line would be:
1686<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1687GET HTTP/1.1
1690   To allow for transition to absolute-URIs in all requests in future
1691   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1692   form in requests, even though HTTP/1.1 clients will only generate
1693   them in requests to proxies.
1696   If a proxy receives a host name that is not a fully qualified domain
1697   name, it &MAY; add its domain to the host name it received. If a proxy
1698   receives a fully qualified domain name, the proxy &MUST-NOT; change
1699   the host name.
1701<t><iref item="authority form (of request-target)"/>
1702   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1704<t><iref item="origin form (of request-target)"/>
1705   The most common form of request-target is that used when making
1706   a request to an origin server ("origin form").
1707   In this case, the absolute path and query components of the URI
1708   &MUST; be transmitted as the request-target, and the authority component
1709   &MUST; be transmitted in a Host header field. For example, a client wishing
1710   to retrieve a representation of the resource, as identified above,
1711   directly from the origin server would open (or reuse) a TCP connection
1712   to port 80 of the host "" and send the lines:
1714<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1715GET /pub/WWW/TheProject.html HTTP/1.1
1719   followed by the remainder of the Request. Note that the origin form
1720   of request-target always starts with an absolute path; if the target
1721   resource's URI path is empty, then an absolute path of "/" &MUST; be
1722   provided in the request-target.
1725   If a proxy receives an OPTIONS request with an absolute-URI form of
1726   request-target in which the URI has an empty path and no query component,
1727   then the last proxy on the request chain &MUST; use a request-target
1728   of "*" when it forwards the request to the indicated origin server.
1731   For example, the request
1732</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1736  would be forwarded by the final proxy as
1737</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1738OPTIONS * HTTP/1.1
1742   after connecting to port 8001 of host "".
1746   The request-target is transmitted in the format specified in
1747   <xref target="http.uri"/>. If the request-target is percent-encoded
1748   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1749   &MUST; decode the request-target in order to
1750   properly interpret the request. Servers &SHOULD; respond to invalid
1751   request-targets with an appropriate status code.
1754   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1755   received request-target when forwarding it to the next inbound server,
1756   except as noted above to replace a null path-absolute with "/" or "*".
1759  <t>
1760    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1761    meaning of the request when the origin server is improperly using
1762    a non-reserved URI character for a reserved purpose.  Implementors
1763    need to be aware that some pre-HTTP/1.1 proxies have been known to
1764    rewrite the request-target.
1765  </t>
1768   HTTP does not place a pre-defined limit on the length of a request-target.
1769   A server &MUST; be prepared to receive URIs of unbounded length and
1770   respond with the 414 (URI Too Long) status code if the received
1771   request-target would be longer than the server wishes to handle
1772   (see &status-414;).
1775   Various ad-hoc limitations on request-target length are found in practice.
1776   It is &RECOMMENDED; that all HTTP senders and recipients support
1777   request-target lengths of 8000 or more octets.
1780  <t>
1781    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1782    are not part of the request-target and thus will not be transmitted
1783    in an HTTP request.
1784  </t>
1789<section title="The Resource Identified by a Request" anchor="">
1791   The exact resource identified by an Internet request is determined by
1792   examining both the request-target and the Host header field.
1795   An origin server that does not allow resources to differ by the
1796   requested host &MAY; ignore the Host header field value when
1797   determining the resource identified by an HTTP/1.1 request. (But see
1798   <xref target=""/>
1799   for other requirements on Host support in HTTP/1.1.)
1802   An origin server that does differentiate resources based on the host
1803   requested (sometimes referred to as virtual hosts or vanity host
1804   names) &MUST; use the following rules for determining the requested
1805   resource on an HTTP/1.1 request:
1806  <list style="numbers">
1807    <t>If request-target is an absolute-URI, the host is part of the
1808     request-target. Any Host header field value in the request &MUST; be
1809     ignored.</t>
1810    <t>If the request-target is not an absolute-URI, and the request includes
1811     a Host header field, the host is determined by the Host header
1812     field value.</t>
1813    <t>If the host as determined by rule 1 or 2 is not a valid host on
1814     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1815  </list>
1818   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1819   attempt to use heuristics (e.g., examination of the URI path for
1820   something unique to a particular host) in order to determine what
1821   exact resource is being requested.
1825<section title="Effective Request URI" anchor="effective.request.uri">
1826  <iref primary="true" item="effective request URI"/>
1827  <iref primary="true" item="target resource"/>
1829   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1830   for the target resource; instead, the URI needs to be inferred from the
1831   request-target, Host header field, and connection context. The result of
1832   this process is called the "effective request URI".  The "target resource"
1833   is the resource identified by the effective request URI.
1836   If the request-target is an absolute-URI, then the effective request URI is
1837   the request-target.
1840   If the request-target uses the path-absolute form or the asterisk form,
1841   and the Host header field is present, then the effective request URI is
1842   constructed by concatenating
1845  <list style="symbols">
1846    <t>
1847      the scheme name: "http" if the request was received over an insecure
1848      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1849      connection,
1850    </t>
1851    <t>
1852      the octet sequence "://",
1853    </t>
1854    <t>
1855      the authority component, as specified in the Host header field
1856      (<xref target=""/>), and
1857    </t>
1858    <t>
1859      the request-target obtained from the Request-Line, unless the
1860      request-target is just the asterisk "*".
1861    </t>
1862  </list>
1865   If the request-target uses the path-absolute form or the asterisk form,
1866   and the Host header field is not present, then the effective request URI is
1867   undefined.
1870   Otherwise, when request-target uses the authority form, the effective
1871   request URI is undefined.
1875   Example 1: the effective request URI for the message
1877<artwork type="example" x:indent-with="  ">
1878GET /pub/WWW/TheProject.html HTTP/1.1
1882  (received over an insecure TCP connection) is "http", plus "://", plus the
1883  authority component "", plus the request-target
1884  "/pub/WWW/TheProject.html", thus
1885  "".
1890   Example 2: the effective request URI for the message
1892<artwork type="example" x:indent-with="  ">
1893OPTIONS * HTTP/1.1
1897  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1898  authority component "", thus "".
1902   Effective request URIs are compared using the rules described in
1903   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1904   be treated as equivalent to an absolute path of "/".
1911<section title="Response" anchor="response">
1912  <x:anchor-alias value="Response"/>
1914   After receiving and interpreting a request message, a server responds
1915   with an HTTP response message.
1917<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1918  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1919                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1920                  <x:ref>CRLF</x:ref>
1921                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1924<section title="Status-Line" anchor="status-line">
1925  <x:anchor-alias value="Status-Line"/>
1927   The first line of a Response message is the Status-Line, consisting
1928   of the protocol version, a space (SP), the status code, another space,
1929   a possibly-empty textual phrase describing the status code, and
1930   ending with CRLF.
1932<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1933  <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>
1936<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1937  <x:anchor-alias value="Reason-Phrase"/>
1938  <x:anchor-alias value="Status-Code"/>
1940   The Status-Code element is a 3-digit integer result code of the
1941   attempt to understand and satisfy the request. These codes are fully
1942   defined in &status-codes;.  The Reason Phrase exists for the sole
1943   purpose of providing a textual description associated with the numeric
1944   status code, out of deference to earlier Internet application protocols
1945   that were more frequently used with interactive text clients.
1946   A client &SHOULD; ignore the content of the Reason Phrase.
1949   The first digit of the Status-Code defines the class of response. The
1950   last two digits do not have any categorization role. There are 5
1951   values for the first digit:
1952  <list style="symbols">
1953    <t>
1954      1xx: Informational - Request received, continuing process
1955    </t>
1956    <t>
1957      2xx: Success - The action was successfully received,
1958        understood, and accepted
1959    </t>
1960    <t>
1961      3xx: Redirection - Further action must be taken in order to
1962        complete the request
1963    </t>
1964    <t>
1965      4xx: Client Error - The request contains bad syntax or cannot
1966        be fulfilled
1967    </t>
1968    <t>
1969      5xx: Server Error - The server failed to fulfill an apparently
1970        valid request
1971    </t>
1972  </list>
1974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1975  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1976  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1984<section title="Protocol Parameters" anchor="protocol.parameters">
1986<section title="Date/Time Formats: Full Date" anchor="">
1987  <x:anchor-alias value="HTTP-date"/>
1989   HTTP applications have historically allowed three different formats
1990   for date/time stamps. However, the preferred format is a fixed-length subset
1991   of that defined by <xref target="RFC1123"/>:
1993<figure><artwork type="example" x:indent-with="  ">
1994Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1997   The other formats are described here only for compatibility with obsolete
1998   implementations.
2000<figure><artwork type="example" x:indent-with="  ">
2001Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2002Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2005   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2006   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2007   only generate the RFC 1123 format for representing HTTP-date values
2008   in header fields. See <xref target="tolerant.applications"/> for further information.
2011   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2012   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2013   equal to UTC (Coordinated Universal Time). This is indicated in the
2014   first two formats by the inclusion of "GMT" as the three-letter
2015   abbreviation for time zone, and &MUST; be assumed when reading the
2016   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2017   additional whitespace beyond that specifically included as SP in the
2018   grammar.
2020<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2021  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2023<t anchor="">
2024  <x:anchor-alias value="rfc1123-date"/>
2025  <x:anchor-alias value="time-of-day"/>
2026  <x:anchor-alias value="hour"/>
2027  <x:anchor-alias value="minute"/>
2028  <x:anchor-alias value="second"/>
2029  <x:anchor-alias value="day-name"/>
2030  <x:anchor-alias value="day"/>
2031  <x:anchor-alias value="month"/>
2032  <x:anchor-alias value="year"/>
2033  <x:anchor-alias value="GMT"/>
2034  Preferred format:
2036<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"/>
2037  <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>
2038  ; fixed length subset of the format defined in
2039  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2041  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2042               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2043               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2044               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2045               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2046               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2047               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2049  <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>
2050               ; e.g., 02 Jun 1982
2052  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2053  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2054               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2055               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2056               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2057               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2058               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2059               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2060               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2061               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2062               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2063               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2064               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2065  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2067  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2069  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2070                 ; 00:00:00 - 23:59:59
2072  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2073  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2074  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2077  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2078  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2079  same as those defined for the RFC 5322 constructs
2080  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2082<t anchor="">
2083  <x:anchor-alias value="obs-date"/>
2084  <x:anchor-alias value="rfc850-date"/>
2085  <x:anchor-alias value="asctime-date"/>
2086  <x:anchor-alias value="date1"/>
2087  <x:anchor-alias value="date2"/>
2088  <x:anchor-alias value="date3"/>
2089  <x:anchor-alias value="rfc1123-date"/>
2090  <x:anchor-alias value="day-name-l"/>
2091  Obsolete formats:
2093<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2094  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2096<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2097  <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>
2098  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2099                 ; day-month-year (e.g., 02-Jun-82)
2101  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2102         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2103         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2104         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2105         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2106         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2107         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2109<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2110  <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>
2111  <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> ))
2112                 ; month day (e.g., Jun  2)
2115  <t>
2116    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2117    accepting date values that might have been sent by non-HTTP
2118    applications, as is sometimes the case when retrieving or posting
2119    messages via proxies/gateways to SMTP or NNTP.
2120  </t>
2123  <t>
2124    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2125    to their usage within the protocol stream. Clients and servers are
2126    not required to use these formats for user presentation, request
2127    logging, etc.
2128  </t>
2132<section title="Transfer Codings" anchor="transfer.codings">
2133  <x:anchor-alias value="transfer-coding"/>
2134  <x:anchor-alias value="transfer-extension"/>
2136   Transfer-coding values are used to indicate an encoding
2137   transformation that has been, can be, or might need to be applied to a
2138   payload body in order to ensure "safe transport" through the network.
2139   This differs from a content coding in that the transfer-coding is a
2140   property of the message rather than a property of the representation
2141   that is being transferred.
2143<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2144  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2145                          / "compress" ; <xref target="compress.coding"/>
2146                          / "deflate" ; <xref target="deflate.coding"/>
2147                          / "gzip" ; <xref target="gzip.coding"/>
2148                          / <x:ref>transfer-extension</x:ref>
2149  <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> )
2151<t anchor="rule.parameter">
2152  <x:anchor-alias value="attribute"/>
2153  <x:anchor-alias value="transfer-parameter"/>
2154  <x:anchor-alias value="value"/>
2155   Parameters are in the form of attribute/value pairs.
2157<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"/>
2158  <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>
2159  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2160  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2163   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2164   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2165   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2168   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2169   MIME, which were designed to enable safe transport of binary data over a
2170   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2171   However, safe transport
2172   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2173   the only unsafe characteristic of message-bodies is the difficulty in
2174   determining the exact message body length (<xref target="message.body"/>),
2175   or the desire to encrypt data over a shared transport.
2178   A server that receives a request message with a transfer-coding it does
2179   not understand &SHOULD; respond with 501 (Not Implemented) and then
2180   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2181   client.
2184<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2185  <iref item="chunked (Coding Format)"/>
2186  <iref item="Coding Format" subitem="chunked"/>
2187  <x:anchor-alias value="chunk"/>
2188  <x:anchor-alias value="Chunked-Body"/>
2189  <x:anchor-alias value="chunk-data"/>
2190  <x:anchor-alias value="chunk-ext"/>
2191  <x:anchor-alias value="chunk-ext-name"/>
2192  <x:anchor-alias value="chunk-ext-val"/>
2193  <x:anchor-alias value="chunk-size"/>
2194  <x:anchor-alias value="last-chunk"/>
2195  <x:anchor-alias value="trailer-part"/>
2196  <x:anchor-alias value="quoted-str-nf"/>
2197  <x:anchor-alias value="qdtext-nf"/>
2199   The chunked encoding modifies the body of a message in order to
2200   transfer it as a series of chunks, each with its own size indicator,
2201   followed by an &OPTIONAL; trailer containing header fields. This
2202   allows dynamically produced content to be transferred along with the
2203   information necessary for the recipient to verify that it has
2204   received the full message.
2206<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"/>
2207  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2208                   <x:ref>last-chunk</x:ref>
2209                   <x:ref>trailer-part</x:ref>
2210                   <x:ref>CRLF</x:ref>
2212  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2213                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2214  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2215  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2217  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2218                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2219  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2220  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2221  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2222  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2224  <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>
2225                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2226  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2227                 ; <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>
2230   The chunk-size field is a string of hex digits indicating the size of
2231   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2232   zero, followed by the trailer, which is terminated by an empty line.
2235   The trailer allows the sender to include additional HTTP header
2236   fields at the end of the message. The Trailer header field can be
2237   used to indicate which header fields are included in a trailer (see
2238   <xref target="header.trailer"/>).
2241   A server using chunked transfer-coding in a response &MUST-NOT; use the
2242   trailer for any header fields unless at least one of the following is
2243   true:
2244  <list style="numbers">
2245    <t>the request included a TE header field that indicates "trailers" is
2246     acceptable in the transfer-coding of the  response, as described in
2247     <xref target="header.te"/>; or,</t>
2249    <t>the trailer fields consist entirely of optional metadata, and the
2250    recipient could use the message (in a manner acceptable to the server where
2251    the field originated) without receiving it. In other words, the server that
2252    generated the header (often but not always the origin server) is willing to
2253    accept the possibility that the trailer fields might be silently discarded
2254    along the path to the client.</t>
2255  </list>
2258   This requirement prevents an interoperability failure when the
2259   message is being received by an HTTP/1.1 (or later) proxy and
2260   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2261   compliance with the protocol would have necessitated a possibly
2262   infinite buffer on the proxy.
2265   A process for decoding the "chunked" transfer-coding
2266   can be represented in pseudo-code as:
2268<figure><artwork type="code">
2269  length := 0
2270  read chunk-size, chunk-ext (if any) and CRLF
2271  while (chunk-size &gt; 0) {
2272     read chunk-data and CRLF
2273     append chunk-data to decoded-body
2274     length := length + chunk-size
2275     read chunk-size and CRLF
2276  }
2277  read header-field
2278  while (header-field not empty) {
2279     append header-field to existing header fields
2280     read header-field
2281  }
2282  Content-Length := length
2283  Remove "chunked" from Transfer-Encoding
2286   All HTTP/1.1 applications &MUST; be able to receive and decode the
2287   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2288   they do not understand.
2291   Since "chunked" is the only transfer-coding required to be understood
2292   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2293   on a persistent connection.  Whenever a transfer-coding is applied to
2294   a payload body in a request, the final transfer-coding applied &MUST;
2295   be "chunked".  If a transfer-coding is applied to a response payload
2296   body, then either the final transfer-coding applied &MUST; be "chunked"
2297   or the message &MUST; be terminated by closing the connection. When the
2298   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2299   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2300   be applied more than once in a message-body.
2304<section title="Compression Codings" anchor="compression.codings">
2306   The codings defined below can be used to compress the payload of a
2307   message.
2310   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2311   is not desirable and is discouraged for future encodings. Their
2312   use here is representative of historical practice, not good
2313   design.
2316   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2317   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2318   equivalent to "gzip" and "compress" respectively.
2321<section title="Compress Coding" anchor="compress.coding">
2322<iref item="compress (Coding Format)"/>
2323<iref item="Coding Format" subitem="compress"/>
2325   The "compress" format is produced by the common UNIX file compression
2326   program "compress". This format is an adaptive Lempel-Ziv-Welch
2327   coding (LZW).
2331<section title="Deflate Coding" anchor="deflate.coding">
2332<iref item="deflate (Coding Format)"/>
2333<iref item="Coding Format" subitem="deflate"/>
2335   The "deflate" format is defined as the "deflate" compression mechanism
2336   (described in <xref target="RFC1951"/>) used inside the "zlib"
2337   data format (<xref target="RFC1950"/>).
2340  <t>
2341    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2342    compressed data without the zlib wrapper.
2343   </t>
2347<section title="Gzip Coding" anchor="gzip.coding">
2348<iref item="gzip (Coding Format)"/>
2349<iref item="Coding Format" subitem="gzip"/>
2351   The "gzip" format is produced by the file compression program
2352   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2353   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2359<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2361   The HTTP Transfer Coding Registry defines the name space for the transfer
2362   coding names.
2365   Registrations &MUST; include the following fields:
2366   <list style="symbols">
2367     <t>Name</t>
2368     <t>Description</t>
2369     <t>Pointer to specification text</t>
2370   </list>
2373   Names of transfer codings &MUST-NOT; overlap with names of content codings
2374   (&content-codings;), unless the encoding transformation is identical (as it
2375   is the case for the compression codings defined in
2376   <xref target="compression.codings"/>).
2379   Values to be added to this name space require a specification
2380   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2381   conform to the purpose of transfer coding defined in this section.
2384   The registry itself is maintained at
2385   <eref target=""/>.
2390<section title="Product Tokens" anchor="product.tokens">
2391  <x:anchor-alias value="product"/>
2392  <x:anchor-alias value="product-version"/>
2394   Product tokens are used to allow communicating applications to
2395   identify themselves by software name and version. Most fields using
2396   product tokens also allow sub-products which form a significant part
2397   of the application to be listed, separated by whitespace. By
2398   convention, the products are listed in order of their significance
2399   for identifying the application.
2401<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2402  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2403  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2406   Examples:
2408<figure><artwork type="example">
2409  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2410  Server: Apache/0.8.4
2413   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2414   used for advertising or other non-essential information. Although any
2415   token octet &MAY; appear in a product-version, this token &SHOULD;
2416   only be used for a version identifier (i.e., successive versions of
2417   the same product &SHOULD; only differ in the product-version portion of
2418   the product value).
2422<section title="Quality Values" anchor="quality.values">
2423  <x:anchor-alias value="qvalue"/>
2425   Both transfer codings (TE request header field, <xref target="header.te"/>)
2426   and content negotiation (&content.negotiation;) use short "floating point"
2427   numbers to indicate the relative importance ("weight") of various
2428   negotiable parameters.  A weight is normalized to a real number in
2429   the range 0 through 1, where 0 is the minimum and 1 the maximum
2430   value. If a parameter has a quality value of 0, then content with
2431   this parameter is "not acceptable" for the client. HTTP/1.1
2432   applications &MUST-NOT; generate more than three digits after the
2433   decimal point. User configuration of these values &SHOULD; also be
2434   limited in this fashion.
2436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2437  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2438                 / ( "1" [ "." 0*3("0") ] )
2441  <t>
2442     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2443     relative degradation in desired quality.
2444  </t>
2450<section title="Connections" anchor="connections">
2452<section title="Persistent Connections" anchor="persistent.connections">
2454<section title="Purpose" anchor="persistent.purpose">
2456   Prior to persistent connections, a separate TCP connection was
2457   established for each request, increasing the load on HTTP servers
2458   and causing congestion on the Internet. The use of inline images and
2459   other associated data often requires a client to make multiple
2460   requests of the same server in a short amount of time. Analysis of
2461   these performance problems and results from a prototype
2462   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2463   measurements of actual HTTP/1.1 implementations show good
2464   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2465   T/TCP <xref target="Tou1998"/>.
2468   Persistent HTTP connections have a number of advantages:
2469  <list style="symbols">
2470      <t>
2471        By opening and closing fewer TCP connections, CPU time is saved
2472        in routers and hosts (clients, servers, proxies, gateways,
2473        tunnels, or caches), and memory used for TCP protocol control
2474        blocks can be saved in hosts.
2475      </t>
2476      <t>
2477        HTTP requests and responses can be pipelined on a connection.
2478        Pipelining allows a client to make multiple requests without
2479        waiting for each response, allowing a single TCP connection to
2480        be used much more efficiently, with much lower elapsed time.
2481      </t>
2482      <t>
2483        Network congestion is reduced by reducing the number of packets
2484        caused by TCP opens, and by allowing TCP sufficient time to
2485        determine the congestion state of the network.
2486      </t>
2487      <t>
2488        Latency on subsequent requests is reduced since there is no time
2489        spent in TCP's connection opening handshake.
2490      </t>
2491      <t>
2492        HTTP can evolve more gracefully, since errors can be reported
2493        without the penalty of closing the TCP connection. Clients using
2494        future versions of HTTP might optimistically try a new feature,
2495        but if communicating with an older server, retry with old
2496        semantics after an error is reported.
2497      </t>
2498    </list>
2501   HTTP implementations &SHOULD; implement persistent connections.
2505<section title="Overall Operation" anchor="persistent.overall">
2507   A significant difference between HTTP/1.1 and earlier versions of
2508   HTTP is that persistent connections are the default behavior of any
2509   HTTP connection. That is, unless otherwise indicated, the client
2510   &SHOULD; assume that the server will maintain a persistent connection,
2511   even after error responses from the server.
2514   Persistent connections provide a mechanism by which a client and a
2515   server can signal the close of a TCP connection. This signaling takes
2516   place using the Connection header field (<xref target="header.connection"/>). Once a close
2517   has been signaled, the client &MUST-NOT; send any more requests on that
2518   connection.
2521<section title="Negotiation" anchor="persistent.negotiation">
2523   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2524   maintain a persistent connection unless a Connection header field including
2525   the connection-token "close" was sent in the request. If the server
2526   chooses to close the connection immediately after sending the
2527   response, it &SHOULD; send a Connection header field including the
2528   connection-token "close".
2531   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2532   decide to keep it open based on whether the response from a server
2533   contains a Connection header field with the connection-token close. In case
2534   the client does not want to maintain a connection for more than that
2535   request, it &SHOULD; send a Connection header field including the
2536   connection-token close.
2539   If either the client or the server sends the close token in the
2540   Connection header field, that request becomes the last one for the
2541   connection.
2544   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2545   maintained for HTTP versions less than 1.1 unless it is explicitly
2546   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2547   compatibility with HTTP/1.0 clients.
2550   In order to remain persistent, all messages on the connection &MUST;
2551   have a self-defined message length (i.e., one not defined by closure
2552   of the connection), as described in <xref target="message.body"/>.
2556<section title="Pipelining" anchor="pipelining">
2558   A client that supports persistent connections &MAY; "pipeline" its
2559   requests (i.e., send multiple requests without waiting for each
2560   response). A server &MUST; send its responses to those requests in the
2561   same order that the requests were received.
2564   Clients which assume persistent connections and pipeline immediately
2565   after connection establishment &SHOULD; be prepared to retry their
2566   connection if the first pipelined attempt fails. If a client does
2567   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2568   persistent. Clients &MUST; also be prepared to resend their requests if
2569   the server closes the connection before sending all of the
2570   corresponding responses.
2573   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2574   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2575   premature termination of the transport connection could lead to
2576   indeterminate results. A client wishing to send a non-idempotent
2577   request &SHOULD; wait to send that request until it has received the
2578   response status line for the previous request.
2583<section title="Proxy Servers" anchor="persistent.proxy">
2585   It is especially important that proxies correctly implement the
2586   properties of the Connection header field as specified in <xref target="header.connection"/>.
2589   The proxy server &MUST; signal persistent connections separately with
2590   its clients and the origin servers (or other proxy servers) that it
2591   connects to. Each persistent connection applies to only one transport
2592   link.
2595   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2596   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2597   for information and discussion of the problems with the Keep-Alive header field
2598   implemented by many HTTP/1.0 clients).
2601<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2603  <cref anchor="TODO-end-to-end" source="jre">
2604    Restored from <eref target=""/>.
2605    See also <eref target=""/>.
2606  </cref>
2609   For the purpose of defining the behavior of caches and non-caching
2610   proxies, we divide HTTP header fields into two categories:
2611  <list style="symbols">
2612      <t>End-to-end header fields, which are  transmitted to the ultimate
2613        recipient of a request or response. End-to-end header fields in
2614        responses MUST be stored as part of a cache entry and &MUST; be
2615        transmitted in any response formed from a cache entry.</t>
2617      <t>Hop-by-hop header fields, which are meaningful only for a single
2618        transport-level connection, and are not stored by caches or
2619        forwarded by proxies.</t>
2620  </list>
2623   The following HTTP/1.1 header fields are hop-by-hop header fields:
2624  <list style="symbols">
2625      <t>Connection</t>
2626      <t>Keep-Alive</t>
2627      <t>Proxy-Authenticate</t>
2628      <t>Proxy-Authorization</t>
2629      <t>TE</t>
2630      <t>Trailer</t>
2631      <t>Transfer-Encoding</t>
2632      <t>Upgrade</t>
2633  </list>
2636   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2639   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2640   (<xref target="header.connection"/>).
2644<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2646  <cref anchor="TODO-non-mod-headers" source="jre">
2647    Restored from <eref target=""/>.
2648    See also <eref target=""/>.
2649  </cref>
2652   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2653   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2654   modify an end-to-end header field unless the definition of that header field requires
2655   or specifically allows that.
2658   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2659   request or response, and it &MUST-NOT; add any of these fields if not
2660   already present:
2661  <list style="symbols">
2662    <t>Allow</t>
2663    <t>Content-Location</t>
2664    <t>Content-MD5</t>
2665    <t>ETag</t>
2666    <t>Last-Modified</t>
2667    <t>Server</t>
2668  </list>
2671   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2672   response:
2673  <list style="symbols">
2674    <t>Expires</t>
2675  </list>
2678   but it &MAY; add any of these fields if not already present. If an
2679   Expires header field is added, it &MUST; be given a field-value identical to
2680   that of the Date header field in that response.
2683   A proxy &MUST-NOT; modify or add any of the following fields in a
2684   message that contains the no-transform cache-control directive, or in
2685   any request:
2686  <list style="symbols">
2687    <t>Content-Encoding</t>
2688    <t>Content-Range</t>
2689    <t>Content-Type</t>
2690  </list>
2693   A transforming proxy &MAY; modify or add these fields to a message
2694   that does not include no-transform, but if it does so, it &MUST; add a
2695   Warning 214 (Transformation applied) if one does not already appear
2696   in the message (see &header-warning;).
2699  <t>
2700    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2701    cause authentication failures if stronger authentication
2702    mechanisms are introduced in later versions of HTTP. Such
2703    authentication mechanisms &MAY; rely on the values of header fields
2704    not listed here.
2705  </t>
2708   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2709   though it &MAY; change the message-body through application or removal
2710   of a transfer-coding (<xref target="transfer.codings"/>).
2716<section title="Practical Considerations" anchor="persistent.practical">
2718   Servers will usually have some time-out value beyond which they will
2719   no longer maintain an inactive connection. Proxy servers might make
2720   this a higher value since it is likely that the client will be making
2721   more connections through the same server. The use of persistent
2722   connections places no requirements on the length (or existence) of
2723   this time-out for either the client or the server.
2726   When a client or server wishes to time-out it &SHOULD; issue a graceful
2727   close on the transport connection. Clients and servers &SHOULD; both
2728   constantly watch for the other side of the transport close, and
2729   respond to it as appropriate. If a client or server does not detect
2730   the other side's close promptly it could cause unnecessary resource
2731   drain on the network.
2734   A client, server, or proxy &MAY; close the transport connection at any
2735   time. For example, a client might have started to send a new request
2736   at the same time that the server has decided to close the "idle"
2737   connection. From the server's point of view, the connection is being
2738   closed while it was idle, but from the client's point of view, a
2739   request is in progress.
2742   This means that clients, servers, and proxies &MUST; be able to recover
2743   from asynchronous close events. Client software &SHOULD; reopen the
2744   transport connection and retransmit the aborted sequence of requests
2745   without user interaction so long as the request sequence is
2746   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2747   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2748   human operator the choice of retrying the request(s). Confirmation by
2749   user-agent software with semantic understanding of the application
2750   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2751   be repeated if the second sequence of requests fails.
2754   Servers &SHOULD; always respond to at least one request per connection,
2755   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2756   middle of transmitting a response, unless a network or client failure
2757   is suspected.
2760   Clients (including proxies) &SHOULD; limit the number of simultaneous
2761   connections that they maintain to a given server (including proxies).
2764   Previous revisions of HTTP gave a specific number of connections as a
2765   ceiling, but this was found to be impractical for many applications. As a
2766   result, this specification does not mandate a particular maximum number of
2767   connections, but instead encourages clients to be conservative when opening
2768   multiple connections.
2771   In particular, while using multiple connections avoids the "head-of-line
2772   blocking" problem (whereby a request that takes significant server-side
2773   processing and/or has a large payload can block subsequent requests on the
2774   same connection), each connection used consumes server resources (sometimes
2775   significantly), and furthermore using multiple connections can cause
2776   undesirable side effects in congested networks.
2779   Note that servers might reject traffic that they deem abusive, including an
2780   excessive number of connections from a client.
2785<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2787<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2789   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2790   flow control mechanisms to resolve temporary overloads, rather than
2791   terminating connections with the expectation that clients will retry.
2792   The latter technique can exacerbate network congestion.
2796<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2798   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2799   the network connection for an error status code while it is transmitting
2800   the request. If the client sees an error status code, it &SHOULD;
2801   immediately cease transmitting the body. If the body is being sent
2802   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2803   empty trailer &MAY; be used to prematurely mark the end of the message.
2804   If the body was preceded by a Content-Length header field, the client &MUST;
2805   close the connection.
2809<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2811   The purpose of the 100 (Continue) status code (see &status-100;) is to
2812   allow a client that is sending a request message with a request body
2813   to determine if the origin server is willing to accept the request
2814   (based on the request header fields) before the client sends the request
2815   body. In some cases, it might either be inappropriate or highly
2816   inefficient for the client to send the body if the server will reject
2817   the message without looking at the body.
2820   Requirements for HTTP/1.1 clients:
2821  <list style="symbols">
2822    <t>
2823        If a client will wait for a 100 (Continue) response before
2824        sending the request body, it &MUST; send an Expect header
2825        field (&header-expect;) with the "100-continue" expectation.
2826    </t>
2827    <t>
2828        A client &MUST-NOT; send an Expect header field (&header-expect;)
2829        with the "100-continue" expectation if it does not intend
2830        to send a request body.
2831    </t>
2832  </list>
2835   Because of the presence of older implementations, the protocol allows
2836   ambiguous situations in which a client might send "Expect: 100-continue"
2837   without receiving either a 417 (Expectation Failed)
2838   or a 100 (Continue) status code. Therefore, when a client sends this
2839   header field to an origin server (possibly via a proxy) from which it
2840   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2841   wait for an indefinite period before sending the request body.
2844   Requirements for HTTP/1.1 origin servers:
2845  <list style="symbols">
2846    <t> Upon receiving a request which includes an Expect header
2847        field with the "100-continue" expectation, an origin server &MUST;
2848        either respond with 100 (Continue) status code and continue to read
2849        from the input stream, or respond with a final status code. The
2850        origin server &MUST-NOT; wait for the request body before sending
2851        the 100 (Continue) response. If it responds with a final status
2852        code, it &MAY; close the transport connection or it &MAY; continue
2853        to read and discard the rest of the request.  It &MUST-NOT;
2854        perform the request method if it returns a final status code.
2855    </t>
2856    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2857        the request message does not include an Expect header
2858        field with the "100-continue" expectation, and &MUST-NOT; send a
2859        100 (Continue) response if such a request comes from an HTTP/1.0
2860        (or earlier) client. There is an exception to this rule: for
2861        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2862        status code in response to an HTTP/1.1 PUT or POST request that does
2863        not include an Expect header field with the "100-continue"
2864        expectation. This exception, the purpose of which is
2865        to minimize any client processing delays associated with an
2866        undeclared wait for 100 (Continue) status code, applies only to
2867        HTTP/1.1 requests, and not to requests with any other HTTP-version
2868        value.
2869    </t>
2870    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2871        already received some or all of the request body for the
2872        corresponding request.
2873    </t>
2874    <t> An origin server that sends a 100 (Continue) response &MUST;
2875    ultimately send a final status code, once the request body is
2876        received and processed, unless it terminates the transport
2877        connection prematurely.
2878    </t>
2879    <t> If an origin server receives a request that does not include an
2880        Expect header field with the "100-continue" expectation,
2881        the request includes a request body, and the server responds
2882        with a final status code before reading the entire request body
2883        from the transport connection, then the server &SHOULD-NOT;  close
2884        the transport connection until it has read the entire request,
2885        or until the client closes the connection. Otherwise, the client
2886        might not reliably receive the response message. However, this
2887        requirement is not be construed as preventing a server from
2888        defending itself against denial-of-service attacks, or from
2889        badly broken client implementations.
2890      </t>
2891    </list>
2894   Requirements for HTTP/1.1 proxies:
2895  <list style="symbols">
2896    <t> If a proxy receives a request that includes an Expect header
2897        field with the "100-continue" expectation, and the proxy
2898        either knows that the next-hop server complies with HTTP/1.1 or
2899        higher, or does not know the HTTP version of the next-hop
2900        server, it &MUST; forward the request, including the Expect header
2901        field.
2902    </t>
2903    <t> If the proxy knows that the version of the next-hop server is
2904        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2905        respond with a 417 (Expectation Failed) status code.
2906    </t>
2907    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2908        numbers received from recently-referenced next-hop servers.
2909    </t>
2910    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2911        request message was received from an HTTP/1.0 (or earlier)
2912        client and did not include an Expect header field with
2913        the "100-continue" expectation. This requirement overrides the
2914        general rule for forwarding of 1xx responses (see &status-1xx;).
2915    </t>
2916  </list>
2920<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2922   If an HTTP/1.1 client sends a request which includes a request body,
2923   but which does not include an Expect header field with the
2924   "100-continue" expectation, and if the client is not directly
2925   connected to an HTTP/1.1 origin server, and if the client sees the
2926   connection close before receiving a status line from the server, the
2927   client &SHOULD; retry the request.  If the client does retry this
2928   request, it &MAY; use the following "binary exponential backoff"
2929   algorithm to be assured of obtaining a reliable response:
2930  <list style="numbers">
2931    <t>
2932      Initiate a new connection to the server
2933    </t>
2934    <t>
2935      Transmit the request-line, header fields, and the CRLF that
2936      indicates the end of header fields.
2937    </t>
2938    <t>
2939      Initialize a variable R to the estimated round-trip time to the
2940         server (e.g., based on the time it took to establish the
2941         connection), or to a constant value of 5 seconds if the round-trip
2942         time is not available.
2943    </t>
2944    <t>
2945       Compute T = R * (2**N), where N is the number of previous
2946         retries of this request.
2947    </t>
2948    <t>
2949       Wait either for an error response from the server, or for T
2950         seconds (whichever comes first)
2951    </t>
2952    <t>
2953       If no error response is received, after T seconds transmit the
2954         body of the request.
2955    </t>
2956    <t>
2957       If client sees that the connection is closed prematurely,
2958         repeat from step 1 until the request is accepted, an error
2959         response is received, or the user becomes impatient and
2960         terminates the retry process.
2961    </t>
2962  </list>
2965   If at any point an error status code is received, the client
2966  <list style="symbols">
2967      <t>&SHOULD-NOT;  continue and</t>
2969      <t>&SHOULD; close the connection if it has not completed sending the
2970        request message.</t>
2971    </list>
2978<section title="Miscellaneous notes that might disappear" anchor="misc">
2979<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2981   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2985<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2987   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2991<section title="Interception of HTTP for access control" anchor="http.intercept">
2993   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2997<section title="Use of HTTP by other protocols" anchor="http.others">
2999   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3000   Extensions of HTTP like WebDAV.</cref>
3004<section title="Use of HTTP by media type specification" anchor="">
3006   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3011<section title="Header Field Definitions" anchor="header.field.definitions">
3013   This section defines the syntax and semantics of HTTP header fields
3014   related to message framing and transport protocols.
3017<section title="Connection" anchor="header.connection">
3018  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3019  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3020  <x:anchor-alias value="Connection"/>
3021  <x:anchor-alias value="connection-token"/>
3023   The "Connection" header field allows the sender to specify
3024   options that are desired only for that particular connection.
3025   Such connection options &MUST; be removed or replaced before the
3026   message can be forwarded downstream by a proxy or gateway.
3027   This mechanism also allows the sender to indicate which HTTP
3028   header fields used in the message are only intended for the
3029   immediate recipient ("hop-by-hop"), as opposed to all recipients
3030   on the chain ("end-to-end"), enabling the message to be
3031   self-descriptive and allowing future connection-specific extensions
3032   to be deployed in HTTP without fear that they will be blindly
3033   forwarded by previously deployed intermediaries.
3036   The Connection header field's value has the following grammar:
3038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3039  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3040  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3043   A proxy or gateway &MUST; parse a received Connection
3044   header field before a message is forwarded and, for each
3045   connection-token in this field, remove any header field(s) from
3046   the message with the same name as the connection-token, and then
3047   remove the Connection header field itself or replace it with the
3048   sender's own connection options for the forwarded message.
3051   A sender &MUST-NOT; include field-names in the Connection header
3052   field-value for fields that are defined as expressing constraints
3053   for all recipients in the request or response chain, such as the
3054   Cache-Control header field (&header-cache-control;).
3057   The connection options do not have to correspond to a header field
3058   present in the message, since a connection-specific header field
3059   might not be needed if there are no parameters associated with that
3060   connection option.  Recipients that trigger certain connection
3061   behavior based on the presence of connection options &MUST; do so
3062   based on the presence of the connection-token rather than only the
3063   presence of the optional header field.  In other words, if the
3064   connection option is received as a header field but not indicated
3065   within the Connection field-value, then the recipient &MUST; ignore
3066   the connection-specific header field because it has likely been
3067   forwarded by an intermediary that is only partially compliant.
3070   When defining new connection options, specifications ought to
3071   carefully consider existing deployed header fields and ensure
3072   that the new connection-token does not share the same name as
3073   an unrelated header field that might already be deployed.
3074   Defining a new connection-token essentially reserves that potential
3075   field-name for carrying additional information related to the
3076   connection option, since it would be unwise for senders to use
3077   that field-name for anything else.
3080   HTTP/1.1 defines the "close" connection option for the sender to
3081   signal that the connection will be closed after completion of the
3082   response. For example,
3084<figure><artwork type="example">
3085  Connection: close
3088   in either the request or the response header fields indicates that
3089   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3090   after the current request/response is complete.
3093   An HTTP/1.1 client that does not support persistent connections &MUST;
3094   include the "close" connection option in every request message.
3097   An HTTP/1.1 server that does not support persistent connections &MUST;
3098   include the "close" connection option in every response message that
3099   does not have a 1xx (Informational) status code.
3103<section title="Content-Length" anchor="header.content-length">
3104  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3105  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3106  <x:anchor-alias value="Content-Length"/>
3108   The "Content-Length" header field indicates the size of the
3109   message-body, in decimal number of octets, for any message other than
3110   a response to a HEAD request or a response with a status code of 304.
3111   In the case of a response to a HEAD request, Content-Length indicates
3112   the size of the payload body (not including any potential transfer-coding)
3113   that would have been sent had the request been a GET.
3114   In the case of a 304 (Not Modified) response to a GET request,
3115   Content-Length indicates the size of the payload body (not including
3116   any potential transfer-coding) that would have been sent in a 200 (OK)
3117   response.
3119<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3120  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3123   An example is
3125<figure><artwork type="example">
3126  Content-Length: 3495
3129   Implementations &SHOULD; use this field to indicate the message-body
3130   length when no transfer-coding is being applied and the
3131   payload's body length can be determined prior to being transferred.
3132   <xref target="message.body"/> describes how recipients determine the length
3133   of a message-body.
3136   Any Content-Length greater than or equal to zero is a valid value.
3139   Note that the use of this field in HTTP is significantly different from
3140   the corresponding definition in MIME, where it is an optional field
3141   used within the "message/external-body" content-type.
3145<section title="Date" anchor="">
3146  <iref primary="true" item="Date header field" x:for-anchor=""/>
3147  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3148  <x:anchor-alias value="Date"/>
3150   The "Date" header field represents the date and time at which
3151   the message was originated, having the same semantics as the Origination
3152   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3153   The field value is an HTTP-date, as described in <xref target=""/>;
3154   it &MUST; be sent in rfc1123-date format.
3156<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3157  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3160   An example is
3162<figure><artwork type="example">
3163  Date: Tue, 15 Nov 1994 08:12:31 GMT
3166   Origin servers &MUST; include a Date header field in all responses,
3167   except in these cases:
3168  <list style="numbers">
3169      <t>If the response status code is 100 (Continue) or 101 (Switching
3170         Protocols), the response &MAY; include a Date header field, at
3171         the server's option.</t>
3173      <t>If the response status code conveys a server error, e.g., 500
3174         (Internal Server Error) or 503 (Service Unavailable), and it is
3175         inconvenient or impossible to generate a valid Date.</t>
3177      <t>If the server does not have a clock that can provide a
3178         reasonable approximation of the current time, its responses
3179         &MUST-NOT; include a Date header field. In this case, the rules
3180         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3181  </list>
3184   A received message that does not have a Date header field &MUST; be
3185   assigned one by the recipient if the message will be cached by that
3186   recipient.
3189   Clients can use the Date header field as well; in order to keep request
3190   messages small, they are advised not to include it when it doesn't convey
3191   any useful information (as it is usually the case for requests that do not
3192   contain a payload).
3195   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3196   time subsequent to the generation of the message. It &SHOULD; represent
3197   the best available approximation of the date and time of message
3198   generation, unless the implementation has no means of generating a
3199   reasonably accurate date and time. In theory, the date ought to
3200   represent the moment just before the payload is generated. In
3201   practice, the date can be generated at any time during the message
3202   origination without affecting its semantic value.
3205<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3207   Some origin server implementations might not have a clock available.
3208   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3209   values to a response, unless these values were associated
3210   with the resource by a system or user with a reliable clock. It &MAY;
3211   assign an Expires value that is known, at or before server
3212   configuration time, to be in the past (this allows "pre-expiration"
3213   of responses without storing separate Expires values for each
3214   resource).
3219<section title="Host" anchor="">
3220  <iref primary="true" item="Host header field" x:for-anchor=""/>
3221  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3222  <x:anchor-alias value="Host"/>
3224   The "Host" header field in a request provides the host and port
3225   information from the target resource's URI, enabling the origin
3226   server to distinguish between resources while servicing requests
3227   for multiple host names on a single IP address.  Since the Host
3228   field-value is critical information for handling a request, it
3229   &SHOULD; be sent as the first header field following the Request-Line.
3231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3232  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3235   A client &MUST; send a Host header field in all HTTP/1.1 request
3236   messages.  If the target resource's URI includes an authority
3237   component, then the Host field-value &MUST; be identical to that
3238   authority component after excluding any userinfo (<xref target="http.uri"/>).
3239   If the authority component is missing or undefined for the target
3240   resource's URI, then the Host header field &MUST; be sent with an
3241   empty field-value.
3244   For example, a GET request to the origin server for
3245   &lt;; would begin with:
3247<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3248GET /pub/WWW/ HTTP/1.1
3252   The Host header field &MUST; be sent in an HTTP/1.1 request even
3253   if the request-target is in the form of an absolute-URI, since this
3254   allows the Host information to be forwarded through ancient HTTP/1.0
3255   proxies that might not have implemented Host.
3258   When an HTTP/1.1 proxy receives a request with a request-target in
3259   the form of an absolute-URI, the proxy &MUST; ignore the received
3260   Host header field (if any) and instead replace it with the host
3261   information of the request-target.  When a proxy forwards a request,
3262   it &MUST; generate the Host header field based on the received
3263   absolute-URI rather than the received Host.
3266   Since the Host header field acts as an application-level routing
3267   mechanism, it is a frequent target for malware seeking to poison
3268   a shared cache or redirect a request to an unintended server.
3269   An interception proxy is particularly vulnerable if it relies on
3270   the Host header field value for redirecting requests to internal
3271   servers, or for use as a cache key in a shared cache, without
3272   first verifying that the intercepted connection is targeting a
3273   valid IP address for that host.
3276   A server &MUST; respond with a 400 (Bad Request) status code to
3277   any HTTP/1.1 request message that lacks a Host header field and
3278   to any request message that contains more than one Host header field
3279   or a Host header field with an invalid field-value.
3282   See Sections <xref target="" format="counter"/>
3283   and <xref target="" format="counter"/>
3284   for other requirements relating to Host.
3288<section title="TE" anchor="header.te">
3289  <iref primary="true" item="TE header field" x:for-anchor=""/>
3290  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3291  <x:anchor-alias value="TE"/>
3292  <x:anchor-alias value="t-codings"/>
3293  <x:anchor-alias value="te-params"/>
3294  <x:anchor-alias value="te-ext"/>
3296   The "TE" header field indicates what extension transfer-codings
3297   it is willing to accept in the response, and whether or not it is
3298   willing to accept trailer fields in a chunked transfer-coding.
3301   Its value consists of the keyword "trailers" and/or a comma-separated
3302   list of extension transfer-coding names with optional accept
3303   parameters (as described in <xref target="transfer.codings"/>).
3305<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3306  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3307  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3308  <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> )
3309  <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> ]
3312   The presence of the keyword "trailers" indicates that the client is
3313   willing to accept trailer fields in a chunked transfer-coding, as
3314   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3315   transfer-coding values even though it does not itself represent a
3316   transfer-coding.
3319   Examples of its use are:
3321<figure><artwork type="example">
3322  TE: deflate
3323  TE:
3324  TE: trailers, deflate;q=0.5
3327   The TE header field only applies to the immediate connection.
3328   Therefore, the keyword &MUST; be supplied within a Connection header
3329   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3332   A server tests whether a transfer-coding is acceptable, according to
3333   a TE field, using these rules:
3334  <list style="numbers">
3335    <x:lt>
3336      <t>The "chunked" transfer-coding is always acceptable. If the
3337         keyword "trailers" is listed, the client indicates that it is
3338         willing to accept trailer fields in the chunked response on
3339         behalf of itself and any downstream clients. The implication is
3340         that, if given, the client is stating that either all
3341         downstream clients are willing to accept trailer fields in the
3342         forwarded response, or that it will attempt to buffer the
3343         response on behalf of downstream recipients.
3344      </t><t>
3345         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3346         chunked response such that a client can be assured of buffering
3347         the entire response.</t>
3348    </x:lt>
3349    <x:lt>
3350      <t>If the transfer-coding being tested is one of the transfer-codings
3351         listed in the TE field, then it is acceptable unless it
3352         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3353         qvalue of 0 means "not acceptable".)</t>
3354    </x:lt>
3355    <x:lt>
3356      <t>If multiple transfer-codings are acceptable, then the
3357         acceptable transfer-coding with the highest non-zero qvalue is
3358         preferred.  The "chunked" transfer-coding always has a qvalue
3359         of 1.</t>
3360    </x:lt>
3361  </list>
3364   If the TE field-value is empty or if no TE field is present, the only
3365   transfer-coding is "chunked". A message with no transfer-coding is
3366   always acceptable.
3370<section title="Trailer" anchor="header.trailer">
3371  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3372  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3373  <x:anchor-alias value="Trailer"/>
3375   The "Trailer" header field indicates that the given set of
3376   header fields is present in the trailer of a message encoded with
3377   chunked transfer-coding.
3379<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3380  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3383   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3384   message using chunked transfer-coding with a non-empty trailer. Doing
3385   so allows the recipient to know which header fields to expect in the
3386   trailer.
3389   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3390   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3391   trailer fields in a "chunked" transfer-coding.
3394   Message header fields listed in the Trailer header field &MUST-NOT;
3395   include the following header fields:
3396  <list style="symbols">
3397    <t>Transfer-Encoding</t>
3398    <t>Content-Length</t>
3399    <t>Trailer</t>
3400  </list>
3404<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3405  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3406  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3407  <x:anchor-alias value="Transfer-Encoding"/>
3409   The "Transfer-Encoding" header field indicates what transfer-codings
3410   (if any) have been applied to the message body. It differs from
3411   Content-Encoding (&content-codings;) in that transfer-codings are a property
3412   of the message (and therefore are removed by intermediaries), whereas
3413   content-codings are not.
3415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3416  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3419   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3421<figure><artwork type="example">
3422  Transfer-Encoding: chunked
3425   If multiple encodings have been applied to a representation, the transfer-codings
3426   &MUST; be listed in the order in which they were applied.
3427   Additional information about the encoding parameters &MAY; be provided
3428   by other header fields not defined by this specification.
3431   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3432   header field.
3436<section title="Upgrade" anchor="header.upgrade">
3437  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3438  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3439  <x:anchor-alias value="Upgrade"/>
3441   The "Upgrade" header field allows the client to specify what
3442   additional communication protocols it would like to use, if the server
3443   chooses to switch protocols. Servers can use it to indicate what protocols
3444   they are willing to switch to.
3446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3447  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3450   For example,
3452<figure><artwork type="example">
3453  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3456   The Upgrade header field is intended to provide a simple mechanism
3457   for transition from HTTP/1.1 to some other, incompatible protocol. It
3458   does so by allowing the client to advertise its desire to use another
3459   protocol, such as a later version of HTTP with a higher major version
3460   number, even though the current request has been made using HTTP/1.1.
3461   This eases the difficult transition between incompatible protocols by
3462   allowing the client to initiate a request in the more commonly
3463   supported protocol while indicating to the server that it would like
3464   to use a "better" protocol if available (where "better" is determined
3465   by the server, possibly according to the nature of the request method
3466   or target resource).
3469   The Upgrade header field only applies to switching application-layer
3470   protocols upon the existing transport-layer connection. Upgrade
3471   cannot be used to insist on a protocol change; its acceptance and use
3472   by the server is optional. The capabilities and nature of the
3473   application-layer communication after the protocol change is entirely
3474   dependent upon the new protocol chosen, although the first action
3475   after changing the protocol &MUST; be a response to the initial HTTP
3476   request containing the Upgrade header field.
3479   The Upgrade header field only applies to the immediate connection.
3480   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3481   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3482   HTTP/1.1 message.
3485   The Upgrade header field cannot be used to indicate a switch to a
3486   protocol on a different connection. For that purpose, it is more
3487   appropriate to use a 3xx redirection response (&status-3xx;).
3490   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3491   Protocols) responses to indicate which protocol(s) are being switched to,
3492   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3493   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3494   response to indicate that they are willing to upgrade to one of the
3495   specified protocols.
3498   This specification only defines the protocol name "HTTP" for use by
3499   the family of Hypertext Transfer Protocols, as defined by the HTTP
3500   version rules of <xref target="http.version"/> and future updates to this
3501   specification. Additional tokens can be registered with IANA using the
3502   registration procedure defined below. 
3505<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3507   The HTTP Upgrade Token Registry defines the name space for product
3508   tokens used to identify protocols in the Upgrade header field.
3509   Each registered token is associated with contact information and
3510   an optional set of specifications that details how the connection
3511   will be processed after it has been upgraded.
3514   Registrations are allowed on a First Come First Served basis as
3515   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3516   specifications need not be IETF documents or be subject to IESG review.
3517   Registrations are subject to the following rules:
3518  <list style="numbers">
3519    <t>A token, once registered, stays registered forever.</t>
3520    <t>The registration &MUST; name a responsible party for the
3521       registration.</t>
3522    <t>The registration &MUST; name a point of contact.</t>
3523    <t>The registration &MAY; name a set of specifications associated with that
3524       token. Such specifications need not be publicly available.</t>
3525    <t>The responsible party &MAY; change the registration at any time.
3526       The IANA will keep a record of all such changes, and make them
3527       available upon request.</t>
3528    <t>The responsible party for the first registration of a "product"
3529       token &MUST; approve later registrations of a "version" token
3530       together with that "product" token before they can be registered.</t>
3531    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3532       for a token. This will normally only be used in the case when a
3533       responsible party cannot be contacted.</t>
3534  </list>
3541<section title="Via" anchor="header.via">
3542  <iref primary="true" item="Via header field" x:for-anchor=""/>
3543  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3544  <x:anchor-alias value="protocol-name"/>
3545  <x:anchor-alias value="protocol-version"/>
3546  <x:anchor-alias value="pseudonym"/>
3547  <x:anchor-alias value="received-by"/>
3548  <x:anchor-alias value="received-protocol"/>
3549  <x:anchor-alias value="Via"/>
3551   The "Via" header field &MUST; be sent by a proxy or gateway to
3552   indicate the intermediate protocols and recipients between the user
3553   agent and the server on requests, and between the origin server and
3554   the client on responses. It is analogous to the "Received" field
3555   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3556   and is intended to be used for tracking message forwards,
3557   avoiding request loops, and identifying the protocol capabilities of
3558   all senders along the request/response chain.
3560<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><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"/>
3561  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3562                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3563  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3564  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3565  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3566  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3567  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3570   The received-protocol indicates the protocol version of the message
3571   received by the server or client along each segment of the
3572   request/response chain. The received-protocol version is appended to
3573   the Via field value when the message is forwarded so that information
3574   about the protocol capabilities of upstream applications remains
3575   visible to all recipients.
3578   The protocol-name is excluded if and only if it would be "HTTP". The
3579   received-by field is normally the host and optional port number of a
3580   recipient server or client that subsequently forwarded the message.
3581   However, if the real host is considered to be sensitive information,
3582   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3583   be assumed to be the default port of the received-protocol.
3586   Multiple Via field values represent each proxy or gateway that has
3587   forwarded the message. Each recipient &MUST; append its information
3588   such that the end result is ordered according to the sequence of
3589   forwarding applications.
3592   Comments &MAY; be used in the Via header field to identify the software
3593   of each recipient, analogous to the User-Agent and Server header fields.
3594   However, all comments in the Via field are optional and &MAY; be removed
3595   by any recipient prior to forwarding the message.
3598   For example, a request message could be sent from an HTTP/1.0 user
3599   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3600   forward the request to a public proxy at, which completes
3601   the request by forwarding it to the origin server at
3602   The request received by would then have the following
3603   Via header field:
3605<figure><artwork type="example">
3606  Via: 1.0 fred, 1.1 (Apache/1.1)
3609   A proxy or gateway used as a portal through a network firewall
3610   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3611   region unless it is explicitly enabled to do so. If not enabled, the
3612   received-by host of any host behind the firewall &SHOULD; be replaced
3613   by an appropriate pseudonym for that host.
3616   For organizations that have strong privacy requirements for hiding
3617   internal structures, a proxy or gateway &MAY; combine an ordered
3618   subsequence of Via header field entries with identical received-protocol
3619   values into a single such entry. For example,
3621<figure><artwork type="example">
3622  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3625  could be collapsed to
3627<figure><artwork type="example">
3628  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3631   Senders &SHOULD-NOT; combine multiple entries unless they are all
3632   under the same organizational control and the hosts have already been
3633   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3634   have different received-protocol values.
3640<section title="IANA Considerations" anchor="IANA.considerations">
3642<section title="Header Field Registration" anchor="header.field.registration">
3644   The Message Header Field Registry located at <eref target=""/> shall be updated
3645   with the permanent registrations below (see <xref target="RFC3864"/>):
3647<?BEGININC p1-messaging.iana-headers ?>
3648<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3649<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3650   <ttcol>Header Field Name</ttcol>
3651   <ttcol>Protocol</ttcol>
3652   <ttcol>Status</ttcol>
3653   <ttcol>Reference</ttcol>
3655   <c>Connection</c>
3656   <c>http</c>
3657   <c>standard</c>
3658   <c>
3659      <xref target="header.connection"/>
3660   </c>
3661   <c>Content-Length</c>
3662   <c>http</c>
3663   <c>standard</c>
3664   <c>
3665      <xref target="header.content-length"/>
3666   </c>
3667   <c>Date</c>
3668   <c>http</c>
3669   <c>standard</c>
3670   <c>
3671      <xref target=""/>
3672   </c>
3673   <c>Host</c>
3674   <c>http</c>
3675   <c>standard</c>
3676   <c>
3677      <xref target=""/>
3678   </c>
3679   <c>TE</c>
3680   <c>http</c>
3681   <c>standard</c>
3682   <c>
3683      <xref target="header.te"/>
3684   </c>
3685   <c>Trailer</c>
3686   <c>http</c>
3687   <c>standard</c>
3688   <c>
3689      <xref target="header.trailer"/>
3690   </c>
3691   <c>Transfer-Encoding</c>
3692   <c>http</c>
3693   <c>standard</c>
3694   <c>
3695      <xref target="header.transfer-encoding"/>
3696   </c>
3697   <c>Upgrade</c>
3698   <c>http</c>
3699   <c>standard</c>
3700   <c>
3701      <xref target="header.upgrade"/>
3702   </c>
3703   <c>Via</c>
3704   <c>http</c>
3705   <c>standard</c>
3706   <c>
3707      <xref target="header.via"/>
3708   </c>
3711<?ENDINC p1-messaging.iana-headers ?>
3713   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3714   HTTP header field would be in conflict with the use of the "close" connection
3715   option for the "Connection" header field (<xref target="header.connection"/>).
3717<texttable align="left" suppress-title="true">
3718   <ttcol>Header Field Name</ttcol>
3719   <ttcol>Protocol</ttcol>
3720   <ttcol>Status</ttcol>
3721   <ttcol>Reference</ttcol>
3723   <c>Close</c>
3724   <c>http</c>
3725   <c>reserved</c>
3726   <c>
3727      <xref target="header.field.registration"/>
3728   </c>
3731   The change controller is: "IETF ( - Internet Engineering Task Force".
3735<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3737   The entries for the "http" and "https" URI Schemes in the registry located at
3738   <eref target=""/>
3739   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3740   and <xref target="https.uri" format="counter"/> of this document
3741   (see <xref target="RFC4395"/>).
3745<section title="Internet Media Type Registrations" anchor="">
3747   This document serves as the specification for the Internet media types
3748   "message/http" and "application/http". The following is to be registered with
3749   IANA (see <xref target="RFC4288"/>).
3751<section title="Internet Media Type message/http" anchor="">
3752<iref item="Media Type" subitem="message/http" primary="true"/>
3753<iref item="message/http Media Type" primary="true"/>
3755   The message/http type can be used to enclose a single HTTP request or
3756   response message, provided that it obeys the MIME restrictions for all
3757   "message" types regarding line length and encodings.
3760  <list style="hanging" x:indent="12em">
3761    <t hangText="Type name:">
3762      message
3763    </t>
3764    <t hangText="Subtype name:">
3765      http
3766    </t>
3767    <t hangText="Required parameters:">
3768      none
3769    </t>
3770    <t hangText="Optional parameters:">
3771      version, msgtype
3772      <list style="hanging">
3773        <t hangText="version:">
3774          The HTTP-Version number of the enclosed message
3775          (e.g., "1.1"). If not present, the version can be
3776          determined from the first line of the body.
3777        </t>
3778        <t hangText="msgtype:">
3779          The message type &mdash; "request" or "response". If not
3780          present, the type can be determined from the first
3781          line of the body.
3782        </t>
3783      </list>
3784    </t>
3785    <t hangText="Encoding considerations:">
3786      only "7bit", "8bit", or "binary" are permitted
3787    </t>
3788    <t hangText="Security considerations:">
3789      none
3790    </t>
3791    <t hangText="Interoperability considerations:">
3792      none
3793    </t>
3794    <t hangText="Published specification:">
3795      This specification (see <xref target=""/>).
3796    </t>
3797    <t hangText="Applications that use this media type:">
3798    </t>
3799    <t hangText="Additional information:">
3800      <list style="hanging">
3801        <t hangText="Magic number(s):">none</t>
3802        <t hangText="File extension(s):">none</t>
3803        <t hangText="Macintosh file type code(s):">none</t>
3804      </list>
3805    </t>
3806    <t hangText="Person and email address to contact for further information:">
3807      See Authors Section.
3808    </t>
3809    <t hangText="Intended usage:">
3810      COMMON
3811    </t>
3812    <t hangText="Restrictions on usage:">
3813      none
3814    </t>
3815    <t hangText="Author/Change controller:">
3816      IESG
3817    </t>
3818  </list>
3821<section title="Internet Media Type application/http" anchor="">
3822<iref item="Media Type" subitem="application/http" primary="true"/>
3823<iref item="application/http Media Type" primary="true"/>
3825   The application/http type can be used to enclose a pipeline of one or more
3826   HTTP request or response messages (not intermixed).
3829  <list style="hanging" x:indent="12em">
3830    <t hangText="Type name:">
3831      application
3832    </t>
3833    <t hangText="Subtype name:">
3834      http
3835    </t>
3836    <t hangText="Required parameters:">
3837      none
3838    </t>
3839    <t hangText="Optional parameters:">
3840      version, msgtype
3841      <list style="hanging">
3842        <t hangText="version:">
3843          The HTTP-Version number of the enclosed messages
3844          (e.g., "1.1"). If not present, the version can be
3845          determined from the first line of the body.
3846        </t>
3847        <t hangText="msgtype:">
3848          The message type &mdash; "request" or "response". If not
3849          present, the type can be determined from the first
3850          line of the body.
3851        </t>
3852      </list>
3853    </t>
3854    <t hangText="Encoding considerations:">
3855      HTTP messages enclosed by this type
3856      are in "binary" format; use of an appropriate
3857      Content-Transfer-Encoding is required when
3858      transmitted via E-mail.
3859    </t>
3860    <t hangText="Security considerations:">
3861      none
3862    </t>
3863    <t hangText="Interoperability considerations:">
3864      none
3865    </t>
3866    <t hangText="Published specification:">
3867      This specification (see <xref target=""/>).
3868    </t>
3869    <t hangText="Applications that use this media type:">
3870    </t>
3871    <t hangText="Additional information:">
3872      <list style="hanging">
3873        <t hangText="Magic number(s):">none</t>
3874        <t hangText="File extension(s):">none</t>
3875        <t hangText="Macintosh file type code(s):">none</t>
3876      </list>
3877    </t>
3878    <t hangText="Person and email address to contact for further information:">
3879      See Authors Section.
3880    </t>
3881    <t hangText="Intended usage:">
3882      COMMON
3883    </t>
3884    <t hangText="Restrictions on usage:">
3885      none
3886    </t>
3887    <t hangText="Author/Change controller:">
3888      IESG
3889    </t>
3890  </list>
3895<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3897   The registration procedure for HTTP Transfer Codings is now defined by
3898   <xref target="transfer.coding.registry"/> of this document.
3901   The HTTP Transfer Codings Registry located at <eref target=""/>
3902   shall be updated with the registrations below:
3904<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3905   <ttcol>Name</ttcol>
3906   <ttcol>Description</ttcol>
3907   <ttcol>Reference</ttcol>
3908   <c>chunked</c>
3909   <c>Transfer in a series of chunks</c>
3910   <c>
3911      <xref target="chunked.encoding"/>
3912   </c>
3913   <c>compress</c>
3914   <c>UNIX "compress" program method</c>
3915   <c>
3916      <xref target="compress.coding"/>
3917   </c>
3918   <c>deflate</c>
3919   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3920   the "zlib" data format (<xref target="RFC1950"/>)
3921   </c>
3922   <c>
3923      <xref target="deflate.coding"/>
3924   </c>
3925   <c>gzip</c>
3926   <c>Same as GNU zip <xref target="RFC1952"/></c>
3927   <c>
3928      <xref target="gzip.coding"/>
3929   </c>
3933<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3935   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3936   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3937   by <xref target="upgrade.token.registry"/> of this document.
3940   The HTTP Status Code Registry located at <eref target=""/>
3941   shall be updated with the registration below:
3943<texttable align="left" suppress-title="true">
3944   <ttcol>Value</ttcol>
3945   <ttcol>Description</ttcol>
3946   <ttcol>Reference</ttcol>
3948   <c>HTTP</c>
3949   <c>Hypertext Transfer Protocol</c>
3950   <c><xref target="http.version"/> of this specification</c>
3957<section title="Security Considerations" anchor="security.considerations">
3959   This section is meant to inform application developers, information
3960   providers, and users of the security limitations in HTTP/1.1 as
3961   described by this document. The discussion does not include
3962   definitive solutions to the problems revealed, though it does make
3963   some suggestions for reducing security risks.
3966<section title="Personal Information" anchor="personal.information">
3968   HTTP clients are often privy to large amounts of personal information
3969   (e.g., the user's name, location, mail address, passwords, encryption
3970   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3971   leakage of this information.
3972   We very strongly recommend that a convenient interface be provided
3973   for the user to control dissemination of such information, and that
3974   designers and implementors be particularly careful in this area.
3975   History shows that errors in this area often create serious security
3976   and/or privacy problems and generate highly adverse publicity for the
3977   implementor's company.
3981<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3983   A server is in the position to save personal data about a user's
3984   requests which might identify their reading patterns or subjects of
3985   interest. This information is clearly confidential in nature and its
3986   handling can be constrained by law in certain countries. People using
3987   HTTP to provide data are responsible for ensuring that
3988   such material is not distributed without the permission of any
3989   individuals that are identifiable by the published results.
3993<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3995   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3996   the documents returned by HTTP requests to be only those that were
3997   intended by the server administrators. If an HTTP server translates
3998   HTTP URIs directly into file system calls, the server &MUST; take
3999   special care not to serve files that were not intended to be
4000   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4001   other operating systems use ".." as a path component to indicate a
4002   directory level above the current one. On such a system, an HTTP
4003   server &MUST; disallow any such construct in the request-target if it
4004   would otherwise allow access to a resource outside those intended to
4005   be accessible via the HTTP server. Similarly, files intended for
4006   reference only internally to the server (such as access control
4007   files, configuration files, and script code) &MUST; be protected from
4008   inappropriate retrieval, since they might contain sensitive
4009   information. Experience has shown that minor bugs in such HTTP server
4010   implementations have turned into security risks.
4014<section title="DNS-related Attacks" anchor="dns.related.attacks">
4016   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4017   generally prone to security attacks based on the deliberate misassociation
4018   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4019   cautious in assuming the validity of an IP number/DNS name association unless
4020   the response is protected by DNSSec (<xref target="RFC4033"/>).
4024<section title="Proxies and Caching" anchor="attack.proxies">
4026   By their very nature, HTTP proxies are men-in-the-middle, and
4027   represent an opportunity for man-in-the-middle attacks. Compromise of
4028   the systems on which the proxies run can result in serious security
4029   and privacy problems. Proxies have access to security-related
4030   information, personal information about individual users and
4031   organizations, and proprietary information belonging to users and
4032   content providers. A compromised proxy, or a proxy implemented or
4033   configured without regard to security and privacy considerations,
4034   might be used in the commission of a wide range of potential attacks.
4037   Proxy operators need to protect the systems on which proxies run as
4038   they would protect any system that contains or transports sensitive
4039   information. In particular, log information gathered at proxies often
4040   contains highly sensitive personal information, and/or information
4041   about organizations. Log information needs to be carefully guarded, and
4042   appropriate guidelines for use need to be developed and followed.
4043   (<xref target="abuse.of.server.log.information"/>).
4046   Proxy implementors need to consider the privacy and security
4047   implications of their design and coding decisions, and of the
4048   configuration options they provide to proxy operators (especially the
4049   default configuration).
4052   Users of a proxy need to be aware that proxies are no trustworthier than
4053   the people who run them; HTTP itself cannot solve this problem.
4056   The judicious use of cryptography, when appropriate, might suffice to
4057   protect against a broad range of security and privacy attacks. Such
4058   cryptography is beyond the scope of the HTTP/1.1 specification.
4062<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4064   Because HTTP uses mostly textual, character-delimited fields, attackers can
4065   overflow buffers in implementations, and/or perform a Denial of Service
4066   against implementations that accept fields with unlimited lengths.
4069   To promote interoperability, this specification makes specific
4070   recommendations for size limits on request-targets (<xref target="request-target"/>)
4071   and blocks of header fields (<xref target="header.fields"/>). These are
4072   minimum recommendations, chosen to be supportable even by implementations
4073   with limited resources; it is expected that most implementations will choose
4074   substantially higher limits.
4077   This specification also provides a way for servers to reject messages that
4078   have request-targets that are too long (&status-414;) or request entities
4079   that are too large (&status-4xx;).
4082   Other fields (including but not limited to request methods, response status
4083   phrases, header field-names, and body chunks) &SHOULD; be limited by
4084   implementations carefully, so as to not impede interoperability.
4088<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4090   They exist. They are hard to defend against. Research continues.
4091   Beware.
4096<section title="Acknowledgments" anchor="acks">
4098   This document revision builds on the work that went into
4099   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4100   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4101   acknowledgements.
4104  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4108Acknowledgements TODO list
4110- Jeff Hodges ("effective request URI")
4118<references title="Normative References">
4120<reference anchor="ISO-8859-1">
4121  <front>
4122    <title>
4123     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4124    </title>
4125    <author>
4126      <organization>International Organization for Standardization</organization>
4127    </author>
4128    <date year="1998"/>
4129  </front>
4130  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4133<reference anchor="Part2">
4134  <front>
4135    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4136    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4137      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4138      <address><email></email></address>
4139    </author>
4140    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4141      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4142      <address><email></email></address>
4143    </author>
4144    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4145      <organization abbrev="HP">Hewlett-Packard Company</organization>
4146      <address><email></email></address>
4147    </author>
4148    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4149      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4150      <address><email></email></address>
4151    </author>
4152    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4153      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4154      <address><email></email></address>
4155    </author>
4156    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4157      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4158      <address><email></email></address>
4159    </author>
4160    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4161      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4162      <address><email></email></address>
4163    </author>
4164    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4165      <organization abbrev="W3C">World Wide Web Consortium</organization>
4166      <address><email></email></address>
4167    </author>
4168    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4169      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4170      <address><email></email></address>
4171    </author>
4172    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4173  </front>
4174  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4175  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4178<reference anchor="Part3">
4179  <front>
4180    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4181    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4182      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4183      <address><email></email></address>
4184    </author>
4185    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4186      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4187      <address><email></email></address>
4188    </author>
4189    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4190      <organization abbrev="HP">Hewlett-Packard Company</organization>
4191      <address><email></email></address>
4192    </author>
4193    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4194      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4195      <address><email></email></address>
4196    </author>
4197    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4198      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4199      <address><email></email></address>
4200    </author>
4201    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4202      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4203      <address><email></email></address>
4204    </author>
4205    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4206      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4207      <address><email></email></address>
4208    </author>
4209    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4210      <organization abbrev="W3C">World Wide Web Consortium</organization>
4211      <address><email></email></address>
4212    </author>
4213    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4214      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4215      <address><email></email></address>
4216    </author>
4217    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4218  </front>
4219  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4220  <x:source href="p3-payload.xml" basename="p3-payload"/>
4223<reference anchor="Part6">
4224  <front>
4225    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4226    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4227      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4228      <address><email></email></address>
4229    </author>
4230    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4231      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4232      <address><email></email></address>
4233    </author>
4234    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4235      <organization abbrev="HP">Hewlett-Packard Company</organization>
4236      <address><email></email></address>
4237    </author>
4238    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4239      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4243      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4244      <address><email></email></address>
4245    </author>
4246    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4247      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4248      <address><email></email></address>
4249    </author>
4250    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4251      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4252      <address><email></email></address>
4253    </author>
4254    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4255      <organization abbrev="W3C">World Wide Web Consortium</organization>
4256      <address><email></email></address>
4257    </author>
4258    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4259      <address><email></email></address>
4260    </author>
4261    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4262      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4263      <address><email></email></address>
4264    </author>
4265    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4266  </front>
4267  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4268  <x:source href="p6-cache.xml" basename="p6-cache"/>
4271<reference anchor="RFC5234">
4272  <front>
4273    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4274    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4275      <organization>Brandenburg InternetWorking</organization>
4276      <address>
4277        <email></email>
4278      </address> 
4279    </author>
4280    <author initials="P." surname="Overell" fullname="Paul Overell">
4281      <organization>THUS plc.</organization>
4282      <address>
4283        <email></email>
4284      </address>
4285    </author>
4286    <date month="January" year="2008"/>
4287  </front>
4288  <seriesInfo name="STD" value="68"/>
4289  <seriesInfo name="RFC" value="5234"/>
4292<reference anchor="RFC2119">
4293  <front>
4294    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4295    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4296      <organization>Harvard University</organization>
4297      <address><email></email></address>
4298    </author>
4299    <date month="March" year="1997"/>
4300  </front>
4301  <seriesInfo name="BCP" value="14"/>
4302  <seriesInfo name="RFC" value="2119"/>
4305<reference anchor="RFC3986">
4306 <front>
4307  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4308  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4309    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4310    <address>
4311       <email></email>
4312       <uri></uri>
4313    </address>
4314  </author>
4315  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4316    <organization abbrev="Day Software">Day Software</organization>
4317    <address>
4318      <email></email>
4319      <uri></uri>
4320    </address>
4321  </author>
4322  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4323    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4324    <address>
4325      <email></email>
4326      <uri></uri>
4327    </address>
4328  </author>
4329  <date month='January' year='2005'></date>
4330 </front>
4331 <seriesInfo name="STD" value="66"/>
4332 <seriesInfo name="RFC" value="3986"/>
4335<reference anchor="USASCII">
4336  <front>
4337    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4338    <author>
4339      <organization>American National Standards Institute</organization>
4340    </author>
4341    <date year="1986"/>
4342  </front>
4343  <seriesInfo name="ANSI" value="X3.4"/>
4346<reference anchor="RFC1950">
4347  <front>
4348    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4349    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4350      <organization>Aladdin Enterprises</organization>
4351      <address><email></email></address>
4352    </author>
4353    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4354    <date month="May" year="1996"/>
4355  </front>
4356  <seriesInfo name="RFC" value="1950"/>
4357  <annotation>
4358    RFC 1950 is an Informational RFC, thus it might be less stable than
4359    this specification. On the other hand, this downward reference was
4360    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4361    therefore it is unlikely to cause problems in practice. See also
4362    <xref target="BCP97"/>.
4363  </annotation>
4366<reference anchor="RFC1951">
4367  <front>
4368    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4369    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4370      <organization>Aladdin Enterprises</organization>
4371      <address><email></email></address>
4372    </author>
4373    <date month="May" year="1996"/>
4374  </front>
4375  <seriesInfo name="RFC" value="1951"/>
4376  <annotation>
4377    RFC 1951 is an Informational RFC, thus it might be less stable than
4378    this specification. On the other hand, this downward reference was
4379    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4380    therefore it is unlikely to cause problems in practice. See also
4381    <xref target="BCP97"/>.
4382  </annotation>
4385<reference anchor="RFC1952">
4386  <front>
4387    <title>GZIP file format specification version 4.3</title>
4388    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4389      <organization>Aladdin Enterprises</organization>
4390      <address><email></email></address>
4391    </author>
4392    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4393      <address><email></email></address>
4394    </author>
4395    <author initials="M." surname="Adler" fullname="Mark Adler">
4396      <address><email></email></address>
4397    </author>
4398    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4399      <address><email></email></address>
4400    </author>
4401    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4402      <address><email></email></address>
4403    </author>
4404    <date month="May" year="1996"/>
4405  </front>
4406  <seriesInfo name="RFC" value="1952"/>
4407  <annotation>
4408    RFC 1952 is an Informational RFC, thus it might be less stable than
4409    this specification. On the other hand, this downward reference was
4410    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4411    therefore it is unlikely to cause problems in practice. See also
4412    <xref target="BCP97"/>.
4413  </annotation>
4418<references title="Informative References">
4420<reference anchor="Nie1997" target="">
4421  <front>
4422    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4423    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4424    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4425    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4426    <author initials="H." surname="Lie" fullname="H. Lie"/>
4427    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4428    <date year="1997" month="September"/>
4429  </front>
4430  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4433<reference anchor="Pad1995" target="">
4434  <front>
4435    <title>Improving HTTP Latency</title>
4436    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4437    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4438    <date year="1995" month="December"/>
4439  </front>
4440  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4443<reference anchor="RFC1123">
4444  <front>
4445    <title>Requirements for Internet Hosts - Application and Support</title>
4446    <author initials="R." surname="Braden" fullname="Robert Braden">
4447      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4448      <address><email>Braden@ISI.EDU</email></address>
4449    </author>
4450    <date month="October" year="1989"/>
4451  </front>
4452  <seriesInfo name="STD" value="3"/>
4453  <seriesInfo name="RFC" value="1123"/>
4456<reference anchor='RFC1919'>
4457  <front>
4458    <title>Classical versus Transparent IP Proxies</title>
4459    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4460      <address><email></email></address>
4461    </author>
4462    <date year='1996' month='March' />
4463  </front>
4464  <seriesInfo name='RFC' value='1919' />
4467<reference anchor="RFC1945">
4468  <front>
4469    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4470    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4471      <organization>MIT, Laboratory for Computer Science</organization>
4472      <address><email></email></address>
4473    </author>
4474    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4475      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4476      <address><email></email></address>
4477    </author>
4478    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4479      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4480      <address><email></email></address>
4481    </author>
4482    <date month="May" year="1996"/>
4483  </front>
4484  <seriesInfo name="RFC" value="1945"/>
4487<reference anchor="RFC2045">
4488  <front>
4489    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4490    <author initials="N." surname="Freed" fullname="Ned Freed">
4491      <organization>Innosoft International, Inc.</organization>
4492      <address><email></email></address>
4493    </author>
4494    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4495      <organization>First Virtual Holdings</organization>
4496      <address><email></email></address>
4497    </author>
4498    <date month="November" year="1996"/>
4499  </front>
4500  <seriesInfo name="RFC" value="2045"/>
4503<reference anchor="RFC2047">
4504  <front>
4505    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4506    <author initials="K." surname="Moore" fullname="Keith Moore">
4507      <organization>University of Tennessee</organization>
4508      <address><email></email></address>
4509    </author>
4510    <date month="November" year="1996"/>
4511  </front>
4512  <seriesInfo name="RFC" value="2047"/>
4515<reference anchor="RFC2068">
4516  <front>
4517    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4518    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4519      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4520      <address><email></email></address>
4521    </author>
4522    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4523      <organization>MIT Laboratory for Computer Science</organization>
4524      <address><email></email></address>
4525    </author>
4526    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4527      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4528      <address><email></email></address>
4529    </author>
4530    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4531      <organization>MIT Laboratory for Computer Science</organization>
4532      <address><email></email></address>
4533    </author>
4534    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4535      <organization>MIT Laboratory for Computer Science</organization>
4536      <address><email></email></address>
4537    </author>
4538    <date month="January" year="1997"/>
4539  </front>
4540  <seriesInfo name="RFC" value="2068"/>
4543<reference anchor="RFC2145">
4544  <front>
4545    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4546    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4547      <organization>Western Research Laboratory</organization>
4548      <address><email></email></address>
4549    </author>
4550    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4551      <organization>Department of Information and Computer Science</organization>
4552      <address><email></email></address>
4553    </author>
4554    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4555      <organization>MIT Laboratory for Computer Science</organization>
4556      <address><email></email></address>
4557    </author>
4558    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4559      <organization>W3 Consortium</organization>
4560      <address><email></email></address>
4561    </author>
4562    <date month="May" year="1997"/>
4563  </front>
4564  <seriesInfo name="RFC" value="2145"/>
4567<reference anchor="RFC2616">
4568  <front>
4569    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4570    <author initials="R." surname="Fielding" fullname="R. Fielding">
4571      <organization>University of California, Irvine</organization>
4572      <address><email></email></address>
4573    </author>
4574    <author initials="J." surname="Gettys" fullname="J. Gettys">
4575      <organization>W3C</organization>
4576      <address><email></email></address>
4577    </author>
4578    <author initials="J." surname="Mogul" fullname="J. Mogul">
4579      <organization>Compaq Computer Corporation</organization>
4580      <address><email></email></address>
4581    </author>
4582    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4583      <organization>MIT Laboratory for Computer Science</organization>
4584      <address><email></email></address>
4585    </author>
4586    <author initials="L." surname="Masinter" fullname="L. Masinter">
4587      <organization>Xerox Corporation</organization>
4588      <address><email></email></address>
4589    </author>
4590    <author initials="P." surname="Leach" fullname="P. Leach">
4591      <organization>Microsoft Corporation</organization>
4592      <address><email></email></address>
4593    </author>
4594    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4595      <organization>W3C</organization>
4596      <address><email></email></address>
4597    </author>
4598    <date month="June" year="1999"/>
4599  </front>
4600  <seriesInfo name="RFC" value="2616"/>
4603<reference anchor='RFC2817'>
4604  <front>
4605    <title>Upgrading to TLS Within HTTP/1.1</title>
4606    <author initials='R.' surname='Khare' fullname='R. Khare'>
4607      <organization>4K Associates / UC Irvine</organization>
4608      <address><email></email></address>
4609    </author>
4610    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4611      <organization>Agranat Systems, Inc.</organization>
4612      <address><email></email></address>
4613    </author>
4614    <date year='2000' month='May' />
4615  </front>
4616  <seriesInfo name='RFC' value='2817' />
4619<reference anchor='RFC2818'>
4620  <front>
4621    <title>HTTP Over TLS</title>
4622    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4623      <organization>RTFM, Inc.</organization>
4624      <address><email></email></address>
4625    </author>
4626    <date year='2000' month='May' />
4627  </front>
4628  <seriesInfo name='RFC' value='2818' />
4631<reference anchor='RFC2965'>
4632  <front>
4633    <title>HTTP State Management Mechanism</title>
4634    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4635      <organization>Bell Laboratories, Lucent Technologies</organization>
4636      <address><email></email></address>
4637    </author>
4638    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4639      <organization>, Inc.</organization>
4640      <address><email></email></address>
4641    </author>
4642    <date year='2000' month='October' />
4643  </front>
4644  <seriesInfo name='RFC' value='2965' />
4647<reference anchor='RFC3040'>
4648  <front>
4649    <title>Internet Web Replication and Caching Taxonomy</title>
4650    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4651      <organization>Equinix, Inc.</organization>
4652    </author>
4653    <author initials='I.' surname='Melve' fullname='I. Melve'>
4654      <organization>UNINETT</organization>
4655    </author>
4656    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4657      <organization>CacheFlow Inc.</organization>
4658    </author>
4659    <date year='2001' month='January' />
4660  </front>
4661  <seriesInfo name='RFC' value='3040' />
4664<reference anchor='RFC3864'>
4665  <front>
4666    <title>Registration Procedures for Message Header Fields</title>
4667    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4668      <organization>Nine by Nine</organization>
4669      <address><email></email></address>
4670    </author>
4671    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4672      <organization>BEA Systems</organization>
4673      <address><email></email></address>
4674    </author>
4675    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4676      <organization>HP Labs</organization>
4677      <address><email></email></address>
4678    </author>
4679    <date year='2004' month='September' />
4680  </front>
4681  <seriesInfo name='BCP' value='90' />
4682  <seriesInfo name='RFC' value='3864' />
4685<reference anchor='RFC4033'>
4686  <front>
4687    <title>DNS Security Introduction and Requirements</title>
4688    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4689    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4690    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4691    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4692    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4693    <date year='2005' month='March' />
4694  </front>
4695  <seriesInfo name='RFC' value='4033' />
4698<reference anchor="RFC4288">
4699  <front>
4700    <title>Media Type Specifications and Registration Procedures</title>
4701    <author initials="N." surname="Freed" fullname="N. Freed">
4702      <organization>Sun Microsystems</organization>
4703      <address>
4704        <email></email>
4705      </address>
4706    </author>
4707    <author initials="J." surname="Klensin" fullname="J. Klensin">
4708      <address>
4709        <email></email>
4710      </address>
4711    </author>
4712    <date year="2005" month="December"/>
4713  </front>
4714  <seriesInfo name="BCP" value="13"/>
4715  <seriesInfo name="RFC" value="4288"/>
4718<reference anchor='RFC4395'>
4719  <front>
4720    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4721    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4722      <organization>AT&amp;T Laboratories</organization>
4723      <address>
4724        <email></email>
4725      </address>
4726    </author>
4727    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4728      <organization>Qualcomm, Inc.</organization>
4729      <address>
4730        <email></email>
4731      </address>
4732    </author>
4733    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4734      <organization>Adobe Systems</organization>
4735      <address>
4736        <email></email>
4737      </address>
4738    </author>
4739    <date year='2006' month='February' />
4740  </front>
4741  <seriesInfo name='BCP' value='115' />
4742  <seriesInfo name='RFC' value='4395' />
4745<reference anchor='RFC4559'>
4746  <front>
4747    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4748    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4749    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4750    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4751    <date year='2006' month='June' />
4752  </front>
4753  <seriesInfo name='RFC' value='4559' />
4756<reference anchor='RFC5226'>
4757  <front>
4758    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4759    <author initials='T.' surname='Narten' fullname='T. Narten'>
4760      <organization>IBM</organization>
4761      <address><email></email></address>
4762    </author>
4763    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4764      <organization>Google</organization>
4765      <address><email></email></address>
4766    </author>
4767    <date year='2008' month='May' />
4768  </front>
4769  <seriesInfo name='BCP' value='26' />
4770  <seriesInfo name='RFC' value='5226' />
4773<reference anchor="RFC5322">
4774  <front>
4775    <title>Internet Message Format</title>
4776    <author initials="P." surname="Resnick" fullname="P. Resnick">
4777      <organization>Qualcomm Incorporated</organization>
4778    </author>
4779    <date year="2008" month="October"/>
4780  </front>
4781  <seriesInfo name="RFC" value="5322"/>
4784<reference anchor="RFC6265">
4785  <front>
4786    <title>HTTP State Management Mechanism</title>
4787    <author initials="A." surname="Barth" fullname="Adam Barth">
4788      <organization abbrev="U.C. Berkeley">
4789        University of California, Berkeley
4790      </organization>
4791      <address><email></email></address>
4792    </author>
4793    <date year="2011" month="April" />
4794  </front>
4795  <seriesInfo name="RFC" value="6265"/>
4798<reference anchor='BCP97'>
4799  <front>
4800    <title>Handling Normative References to Standards-Track Documents</title>
4801    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4802      <address>
4803        <email></email>
4804      </address>
4805    </author>
4806    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4807      <organization>MIT</organization>
4808      <address>
4809        <email></email>
4810      </address>
4811    </author>
4812    <date year='2007' month='June' />
4813  </front>
4814  <seriesInfo name='BCP' value='97' />
4815  <seriesInfo name='RFC' value='4897' />
4818<reference anchor="Kri2001" target="">
4819  <front>
4820    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4821    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4822    <date year="2001" month="November"/>
4823  </front>
4824  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4827<reference anchor="Spe" target="">
4828  <front>
4829    <title>Analysis of HTTP Performance Problems</title>
4830    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4831    <date/>
4832  </front>
4835<reference anchor="Tou1998" target="">
4836  <front>
4837  <title>Analysis of HTTP Performance</title>
4838  <author initials="J." surname="Touch" fullname="Joe Touch">
4839    <organization>USC/Information Sciences Institute</organization>
4840    <address><email></email></address>
4841  </author>
4842  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4843    <organization>USC/Information Sciences Institute</organization>
4844    <address><email></email></address>
4845  </author>
4846  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4847    <organization>USC/Information Sciences Institute</organization>
4848    <address><email></email></address>
4849  </author>
4850  <date year="1998" month="Aug"/>
4851  </front>
4852  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4853  <annotation>(original report dated Aug. 1996)</annotation>
4859<section title="Tolerant Applications" anchor="tolerant.applications">
4861   Although this document specifies the requirements for the generation
4862   of HTTP/1.1 messages, not all applications will be correct in their
4863   implementation. We therefore recommend that operational applications
4864   be tolerant of deviations whenever those deviations can be
4865   interpreted unambiguously.
4868   The line terminator for header fields is the sequence CRLF.
4869   However, we recommend that applications, when parsing such headers fields,
4870   recognize a single LF as a line terminator and ignore the leading CR.
4873   The character encoding of a representation &SHOULD; be labeled as the lowest
4874   common denominator of the character codes used within that representation, with
4875   the exception that not labeling the representation is preferred over labeling
4876   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4879   Additional rules for requirements on parsing and encoding of dates
4880   and other potential problems with date encodings include:
4883  <list style="symbols">
4884     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4885        which appears to be more than 50 years in the future is in fact
4886        in the past (this helps solve the "year 2000" problem).</t>
4888     <t>Although all date formats are specified to be case-sensitive,
4889        recipients &SHOULD; match day, week and timezone names
4890        case-insensitively.</t>
4892     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4893        Expires date as earlier than the proper value, but &MUST-NOT;
4894        internally represent a parsed Expires date as later than the
4895        proper value.</t>
4897     <t>All expiration-related calculations &MUST; be done in GMT. The
4898        local time zone &MUST-NOT; influence the calculation or comparison
4899        of an age or expiration time.</t>
4901     <t>If an HTTP header field incorrectly carries a date value with a time
4902        zone other than GMT, it &MUST; be converted into GMT using the
4903        most conservative possible conversion.</t>
4904  </list>
4908<section title="HTTP Version History" anchor="compatibility">
4910   HTTP has been in use by the World-Wide Web global information initiative
4911   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4912   was a simple protocol for hypertext data transfer across the Internet
4913   with only a single request method (GET) and no metadata.
4914   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4915   methods and MIME-like messaging that could include metadata about the data
4916   transferred and modifiers on the request/response semantics. However,
4917   HTTP/1.0 did not sufficiently take into consideration the effects of
4918   hierarchical proxies, caching, the need for persistent connections, or
4919   name-based virtual hosts. The proliferation of incompletely-implemented
4920   applications calling themselves "HTTP/1.0" further necessitated a
4921   protocol version change in order for two communicating applications
4922   to determine each other's true capabilities.
4925   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4926   requirements that enable reliable implementations, adding only
4927   those new features that will either be safely ignored by an HTTP/1.0
4928   recipient or only sent when communicating with a party advertising
4929   compliance with HTTP/1.1.
4932   It is beyond the scope of a protocol specification to mandate
4933   compliance with previous versions. HTTP/1.1 was deliberately
4934   designed, however, to make supporting previous versions easy.
4935   We would expect a general-purpose HTTP/1.1 server to understand
4936   any valid request in the format of HTTP/1.0 and respond appropriately
4937   with an HTTP/1.1 message that only uses features understood (or
4938   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4939   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4942   Since HTTP/0.9 did not support header fields in a request,
4943   there is no mechanism for it to support name-based virtual
4944   hosts (selection of resource by inspection of the Host header
4945   field).  Any server that implements name-based virtual hosts
4946   ought to disable support for HTTP/0.9.  Most requests that
4947   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4948   requests wherein a buggy client failed to properly encode
4949   linear whitespace found in a URI reference and placed in
4950   the request-target.
4953<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4955   This section summarizes major differences between versions HTTP/1.0
4956   and HTTP/1.1.
4959<section title="Multi-homed Web Servers" anchor="">
4961   The requirements that clients and servers support the Host header
4962   field (<xref target=""/>), report an error if it is
4963   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4964   are among the most important changes defined by HTTP/1.1.
4967   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4968   addresses and servers; there was no other established mechanism for
4969   distinguishing the intended server of a request than the IP address
4970   to which that request was directed. The Host header field was
4971   introduced during the development of HTTP/1.1 and, though it was
4972   quickly implemented by most HTTP/1.0 browsers, additional requirements
4973   were placed on all HTTP/1.1 requests in order to ensure complete
4974   adoption.  At the time of this writing, most HTTP-based services
4975   are dependent upon the Host header field for targeting requests.
4979<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4981   For most implementations of HTTP/1.0, each connection is established
4982   by the client prior to the request and closed by the server after
4983   sending the response. However, some implementations implement the
4984   Keep-Alive version of persistent connections described in
4985   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4988   Some clients and servers might wish to be compatible with some
4989   previous implementations of persistent connections in HTTP/1.0
4990   clients and servers. Persistent connections in HTTP/1.0 are
4991   explicitly negotiated as they are not the default behavior. HTTP/1.0
4992   experimental implementations of persistent connections are faulty,
4993   and the new facilities in HTTP/1.1 are designed to rectify these
4994   problems. The problem was that some existing HTTP/1.0 clients might
4995   send Keep-Alive to a proxy server that doesn't understand
4996   Connection, which would then erroneously forward it to the next
4997   inbound server, which would establish the Keep-Alive connection and
4998   result in a hung HTTP/1.0 proxy waiting for the close on the
4999   response. The result is that HTTP/1.0 clients must be prevented from
5000   using Keep-Alive when talking to proxies.
5003   However, talking to proxies is the most important use of persistent
5004   connections, so that prohibition is clearly unacceptable. Therefore,
5005   we need some other mechanism for indicating a persistent connection
5006   is desired, which is safe to use even when talking to an old proxy
5007   that ignores Connection. Persistent connections are the default for
5008   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5009   declaring non-persistence. See <xref target="header.connection"/>.
5014<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5016  Empty list elements in list productions have been deprecated.
5017  (<xref target="notation.abnf"/>)
5020  Rules about implicit linear whitespace between certain grammar productions
5021  have been removed; now it's only allowed when specifically pointed out
5022  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5023  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5024  Non-ASCII content in header fields and reason phrase has been obsoleted and
5025  made opaque (the TEXT rule was removed)
5026  (<xref target="basic.rules"/>)
5029  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5030  sensitive. Restrict the version numbers to be single digits due to the fact
5031  that implementations are known to handle multi-digit version numbers
5032  incorrectly.
5033  (<xref target="http.version"/>)
5036  Require that invalid whitespace around field-names be rejected.
5037  (<xref target="header.fields"/>)
5040  Require recipients to handle bogus Content-Length header fields as errors.
5041  (<xref target="message.body"/>)
5044  Remove reference to non-existent identity transfer-coding value tokens.
5045  (Sections <xref format="counter" target="message.body"/> and
5046  <xref format="counter" target="transfer.codings"/>)
5049  Update use of abs_path production from RFC 1808 to the path-absolute + query
5050  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5051  request method only.
5052  (<xref target="request-target"/>)
5055  Clarification that the chunk length does not include the count of the octets
5056  in the chunk header and trailer. Furthermore disallowed line folding
5057  in chunk extensions.
5058  (<xref target="chunked.encoding"/>)
5061  Remove hard limit of two connections per server.
5062  (<xref target="persistent.practical"/>)
5065  Change ABNF productions for header fields to only define the field value.
5066  (<xref target="header.field.definitions"/>)
5069  Clarify exactly when close connection options must be sent.
5070  (<xref target="header.connection"/>)
5073  Define the semantics of the "Upgrade" header field in responses other than
5074  101 (this was incorporated from <xref target="RFC2817"/>).
5075  (<xref target="header.upgrade"/>)
5080<?BEGININC p1-messaging.abnf-appendix ?>
5081<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5083<artwork type="abnf" name="p1-messaging.parsed-abnf">
5084<x:ref>BWS</x:ref> = OWS
5086<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5087<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5088 connection-token ] )
5089<x:ref>Content-Length</x:ref> = 1*DIGIT
5091<x:ref>Date</x:ref> = HTTP-date
5093<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5095<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5096<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5097<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5098<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5099 ]
5100<x:ref>Host</x:ref> = uri-host [ ":" port ]
5102<x:ref>Method</x:ref> = token
5104<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5106<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5107<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5108<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5109<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5110<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5112<x:ref>Status-Code</x:ref> = 3DIGIT
5113<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5115<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5116<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5117<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5118 transfer-coding ] )
5120<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5121<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5123<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5124 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5125 )
5127<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5128<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5129<x:ref>attribute</x:ref> = token
5130<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5132<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5133<x:ref>chunk-data</x:ref> = 1*OCTET
5134<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5135<x:ref>chunk-ext-name</x:ref> = token
5136<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5137<x:ref>chunk-size</x:ref> = 1*HEXDIG
5138<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5139<x:ref>connection-token</x:ref> = token
5140<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5141 / %x2A-5B ; '*'-'['
5142 / %x5D-7E ; ']'-'~'
5143 / obs-text
5145<x:ref>date1</x:ref> = day SP month SP year
5146<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5147<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5148<x:ref>day</x:ref> = 2DIGIT
5149<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5150 / %x54.75.65 ; Tue
5151 / %x57.65.64 ; Wed
5152 / %x54.68.75 ; Thu
5153 / %x46.72.69 ; Fri
5154 / %x53.61.74 ; Sat
5155 / %x53.75.6E ; Sun
5156<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5157 / %x54. ; Tuesday
5158 / %x57.65.64.6E. ; Wednesday
5159 / %x54. ; Thursday
5160 / %x46. ; Friday
5161 / %x53. ; Saturday
5162 / %x53.75.6E.64.61.79 ; Sunday
5164<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5165<x:ref>field-name</x:ref> = token
5166<x:ref>field-value</x:ref> = *( field-content / OWS )
5168<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5169<x:ref>hour</x:ref> = 2DIGIT
5170<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5171<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5173<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5175<x:ref>message-body</x:ref> = *OCTET
5176<x:ref>minute</x:ref> = 2DIGIT
5177<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5178 / %x46.65.62 ; Feb
5179 / %x4D.61.72 ; Mar
5180 / %x41.70.72 ; Apr
5181 / %x4D.61.79 ; May
5182 / %x4A.75.6E ; Jun
5183 / %x4A.75.6C ; Jul
5184 / %x41.75.67 ; Aug
5185 / %x53.65.70 ; Sep
5186 / %x4F.63.74 ; Oct
5187 / %x4E.6F.76 ; Nov
5188 / %x44.65.63 ; Dec
5190<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5191<x:ref>obs-fold</x:ref> = CRLF
5192<x:ref>obs-text</x:ref> = %x80-FF
5194<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5195<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5196<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5197<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5198<x:ref>product</x:ref> = token [ "/" product-version ]
5199<x:ref>product-version</x:ref> = token
5200<x:ref>protocol-name</x:ref> = token
5201<x:ref>protocol-version</x:ref> = token
5202<x:ref>pseudonym</x:ref> = token
5204<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5205 / %x5D-7E ; ']'-'~'
5206 / obs-text
5207<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5208 / %x5D-7E ; ']'-'~'
5209 / obs-text
5210<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5211<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5212<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5213<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5214<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5215<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5217<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5218<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5219<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5220<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5221 / authority
5222<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5223<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5225<x:ref>second</x:ref> = 2DIGIT
5226<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5227 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5228<x:ref>start-line</x:ref> = Request-Line / Status-Line
5230<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5231<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5232 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5233<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5234<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5235<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5236<x:ref>token</x:ref> = 1*tchar
5237<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5238<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5239 transfer-extension
5240<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5241<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5243<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5245<x:ref>value</x:ref> = word
5247<x:ref>word</x:ref> = token / quoted-string
5249<x:ref>year</x:ref> = 4DIGIT
5252<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5253; Chunked-Body defined but not used
5254; Connection defined but not used
5255; Content-Length defined but not used
5256; Date defined but not used
5257; HTTP-message defined but not used
5258; Host defined but not used
5259; Request defined but not used
5260; Response defined but not used
5261; TE defined but not used
5262; Trailer defined but not used
5263; Transfer-Encoding defined but not used
5264; URI-reference defined but not used
5265; Upgrade defined but not used
5266; Via defined but not used
5267; http-URI defined but not used
5268; https-URI defined but not used
5269; partial-URI defined but not used
5270; special defined but not used
5272<?ENDINC p1-messaging.abnf-appendix ?>
5274<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5276<section title="Since RFC 2616">
5278  Extracted relevant partitions from <xref target="RFC2616"/>.
5282<section title="Since draft-ietf-httpbis-p1-messaging-00">
5284  Closed issues:
5285  <list style="symbols">
5286    <t>
5287      <eref target=""/>:
5288      "HTTP Version should be case sensitive"
5289      (<eref target=""/>)
5290    </t>
5291    <t>
5292      <eref target=""/>:
5293      "'unsafe' characters"
5294      (<eref target=""/>)
5295    </t>
5296    <t>
5297      <eref target=""/>:
5298      "Chunk Size Definition"
5299      (<eref target=""/>)
5300    </t>
5301    <t>
5302      <eref target=""/>:
5303      "Message Length"
5304      (<eref target=""/>)
5305    </t>
5306    <t>
5307      <eref target=""/>:
5308      "Media Type Registrations"
5309      (<eref target=""/>)
5310    </t>
5311    <t>
5312      <eref target=""/>:
5313      "URI includes query"
5314      (<eref target=""/>)
5315    </t>
5316    <t>
5317      <eref target=""/>:
5318      "No close on 1xx responses"
5319      (<eref target=""/>)
5320    </t>
5321    <t>
5322      <eref target=""/>:
5323      "Remove 'identity' token references"
5324      (<eref target=""/>)
5325    </t>
5326    <t>
5327      <eref target=""/>:
5328      "Import query BNF"
5329    </t>
5330    <t>
5331      <eref target=""/>:
5332      "qdtext BNF"
5333    </t>
5334    <t>
5335      <eref target=""/>:
5336      "Normative and Informative references"
5337    </t>
5338    <t>
5339      <eref target=""/>:
5340      "RFC2606 Compliance"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "RFC977 reference"
5345    </t>
5346    <t>
5347      <eref target=""/>:
5348      "RFC1700 references"
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "inconsistency in date format explanation"
5353    </t>
5354    <t>
5355      <eref target=""/>:
5356      "Date reference typo"
5357    </t>
5358    <t>
5359      <eref target=""/>:
5360      "Informative references"
5361    </t>
5362    <t>
5363      <eref target=""/>:
5364      "ISO-8859-1 Reference"
5365    </t>
5366    <t>
5367      <eref target=""/>:
5368      "Normative up-to-date references"
5369    </t>
5370  </list>
5373  Other changes:
5374  <list style="symbols">
5375    <t>
5376      Update media type registrations to use RFC4288 template.
5377    </t>
5378    <t>
5379      Use names of RFC4234 core rules DQUOTE and WSP,
5380      fix broken ABNF for chunk-data
5381      (work in progress on <eref target=""/>)
5382    </t>
5383  </list>
5387<section title="Since draft-ietf-httpbis-p1-messaging-01">
5389  Closed issues:
5390  <list style="symbols">
5391    <t>
5392      <eref target=""/>:
5393      "Bodies on GET (and other) requests"
5394    </t>
5395    <t>
5396      <eref target=""/>:
5397      "Updating to RFC4288"
5398    </t>
5399    <t>
5400      <eref target=""/>:
5401      "Status Code and Reason Phrase"
5402    </t>
5403    <t>
5404      <eref target=""/>:
5405      "rel_path not used"
5406    </t>
5407  </list>
5410  Ongoing work on ABNF conversion (<eref target=""/>):
5411  <list style="symbols">
5412    <t>
5413      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5414      "trailer-part").
5415    </t>
5416    <t>
5417      Avoid underscore character in rule names ("http_URL" ->
5418      "http-URL", "abs_path" -> "path-absolute").
5419    </t>
5420    <t>
5421      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5422      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5423      have to be updated when switching over to RFC3986.
5424    </t>
5425    <t>
5426      Synchronize core rules with RFC5234.
5427    </t>
5428    <t>
5429      Get rid of prose rules that span multiple lines.
5430    </t>
5431    <t>
5432      Get rid of unused rules LOALPHA and UPALPHA.
5433    </t>
5434    <t>
5435      Move "Product Tokens" section (back) into Part 1, as "token" is used
5436      in the definition of the Upgrade header field.
5437    </t>
5438    <t>
5439      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5440    </t>
5441    <t>
5442      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5443    </t>
5444  </list>
5448<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5450  Closed issues:
5451  <list style="symbols">
5452    <t>
5453      <eref target=""/>:
5454      "HTTP-date vs. rfc1123-date"
5455    </t>
5456    <t>
5457      <eref target=""/>:
5458      "WS in quoted-pair"
5459    </t>
5460  </list>
5463  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5464  <list style="symbols">
5465    <t>
5466      Reference RFC 3984, and update header field registrations for headers defined
5467      in this document.
5468    </t>
5469  </list>
5472  Ongoing work on ABNF conversion (<eref target=""/>):
5473  <list style="symbols">
5474    <t>
5475      Replace string literals when the string really is case-sensitive (HTTP-Version).
5476    </t>
5477  </list>
5481<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5483  Closed issues:
5484  <list style="symbols">
5485    <t>
5486      <eref target=""/>:
5487      "Connection closing"
5488    </t>
5489    <t>
5490      <eref target=""/>:
5491      "Move registrations and registry information to IANA Considerations"
5492    </t>
5493    <t>
5494      <eref target=""/>:
5495      "need new URL for PAD1995 reference"
5496    </t>
5497    <t>
5498      <eref target=""/>:
5499      "IANA Considerations: update HTTP URI scheme registration"
5500    </t>
5501    <t>
5502      <eref target=""/>:
5503      "Cite HTTPS URI scheme definition"
5504    </t>
5505    <t>
5506      <eref target=""/>:
5507      "List-type headers vs Set-Cookie"
5508    </t>
5509  </list>
5512  Ongoing work on ABNF conversion (<eref target=""/>):
5513  <list style="symbols">
5514    <t>
5515      Replace string literals when the string really is case-sensitive (HTTP-Date).
5516    </t>
5517    <t>
5518      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5519    </t>
5520  </list>
5524<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5526  Closed issues:
5527  <list style="symbols">
5528    <t>
5529      <eref target=""/>:
5530      "Out-of-date reference for URIs"
5531    </t>
5532    <t>
5533      <eref target=""/>:
5534      "RFC 2822 is updated by RFC 5322"
5535    </t>
5536  </list>
5539  Ongoing work on ABNF conversion (<eref target=""/>):
5540  <list style="symbols">
5541    <t>
5542      Use "/" instead of "|" for alternatives.
5543    </t>
5544    <t>
5545      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5546    </t>
5547    <t>
5548      Only reference RFC 5234's core rules.
5549    </t>
5550    <t>
5551      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5552      whitespace ("OWS") and required whitespace ("RWS").
5553    </t>
5554    <t>
5555      Rewrite ABNFs to spell out whitespace rules, factor out
5556      header field value format definitions.
5557    </t>
5558  </list>
5562<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5564  Closed issues:
5565  <list style="symbols">
5566    <t>
5567      <eref target=""/>:
5568      "Header LWS"
5569    </t>
5570    <t>
5571      <eref target=""/>:
5572      "Sort 1.3 Terminology"
5573    </t>
5574    <t>
5575      <eref target=""/>:
5576      "RFC2047 encoded words"
5577    </t>
5578    <t>
5579      <eref target=""/>:
5580      "Character Encodings in TEXT"
5581    </t>
5582    <t>
5583      <eref target=""/>:
5584      "Line Folding"
5585    </t>
5586    <t>
5587      <eref target=""/>:
5588      "OPTIONS * and proxies"
5589    </t>
5590    <t>
5591      <eref target=""/>:
5592      "Reason-Phrase BNF"
5593    </t>
5594    <t>
5595      <eref target=""/>:
5596      "Use of TEXT"
5597    </t>
5598    <t>
5599      <eref target=""/>:
5600      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5601    </t>
5602    <t>
5603      <eref target=""/>:
5604      "RFC822 reference left in discussion of date formats"
5605    </t>
5606  </list>
5609  Final work on ABNF conversion (<eref target=""/>):
5610  <list style="symbols">
5611    <t>
5612      Rewrite definition of list rules, deprecate empty list elements.
5613    </t>
5614    <t>
5615      Add appendix containing collected and expanded ABNF.
5616    </t>
5617  </list>
5620  Other changes:
5621  <list style="symbols">
5622    <t>
5623      Rewrite introduction; add mostly new Architecture Section.
5624    </t>
5625    <t>
5626      Move definition of quality values from Part 3 into Part 1;
5627      make TE request header field grammar independent of accept-params (defined in Part 3).
5628    </t>
5629  </list>
5633<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5635  Closed issues:
5636  <list style="symbols">
5637    <t>
5638      <eref target=""/>:
5639      "base for numeric protocol elements"
5640    </t>
5641    <t>
5642      <eref target=""/>:
5643      "comment ABNF"
5644    </t>
5645  </list>
5648  Partly resolved issues:
5649  <list style="symbols">
5650    <t>
5651      <eref target=""/>:
5652      "205 Bodies" (took out language that implied that there might be
5653      methods for which a request body MUST NOT be included)
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "editorial improvements around HTTP-date"
5658    </t>
5659  </list>
5663<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5665  Closed issues:
5666  <list style="symbols">
5667    <t>
5668      <eref target=""/>:
5669      "Repeating single-value headers"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "increase connection limit"
5674    </t>
5675    <t>
5676      <eref target=""/>:
5677      "IP addresses in URLs"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "take over HTTP Upgrade Token Registry"
5682    </t>
5683    <t>
5684      <eref target=""/>:
5685      "CR and LF in chunk extension values"
5686    </t>
5687    <t>
5688      <eref target=""/>:
5689      "HTTP/0.9 support"
5690    </t>
5691    <t>
5692      <eref target=""/>:
5693      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5694    </t>
5695    <t>
5696      <eref target=""/>:
5697      "move definitions of gzip/deflate/compress to part 1"
5698    </t>
5699    <t>
5700      <eref target=""/>:
5701      "disallow control characters in quoted-pair"
5702    </t>
5703  </list>
5706  Partly resolved issues:
5707  <list style="symbols">
5708    <t>
5709      <eref target=""/>:
5710      "update IANA requirements wrt Transfer-Coding values" (add the
5711      IANA Considerations subsection)
5712    </t>
5713  </list>
5717<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5719  Closed issues:
5720  <list style="symbols">
5721    <t>
5722      <eref target=""/>:
5723      "header parsing, treatment of leading and trailing OWS"
5724    </t>
5725  </list>
5728  Partly resolved issues:
5729  <list style="symbols">
5730    <t>
5731      <eref target=""/>:
5732      "Placement of 13.5.1 and 13.5.2"
5733    </t>
5734    <t>
5735      <eref target=""/>:
5736      "use of term "word" when talking about header structure"
5737    </t>
5738  </list>
5742<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5744  Closed issues:
5745  <list style="symbols">
5746    <t>
5747      <eref target=""/>:
5748      "Clarification of the term 'deflate'"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "OPTIONS * and proxies"
5753    </t>
5754    <t>
5755      <eref target=""/>:
5756      "MIME-Version not listed in P1, general header fields"
5757    </t>
5758    <t>
5759      <eref target=""/>:
5760      "IANA registry for content/transfer encodings"
5761    </t>
5762    <t>
5763      <eref target=""/>:
5764      "Case-sensitivity of HTTP-date"
5765    </t>
5766    <t>
5767      <eref target=""/>:
5768      "use of term "word" when talking about header structure"
5769    </t>
5770  </list>
5773  Partly resolved issues:
5774  <list style="symbols">
5775    <t>
5776      <eref target=""/>:
5777      "Term for the requested resource's URI"
5778    </t>
5779  </list>
5783<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5785  Closed issues:
5786  <list style="symbols">
5787    <t>
5788      <eref target=""/>:
5789      "Connection Closing"
5790    </t>
5791    <t>
5792      <eref target=""/>:
5793      "Delimiting messages with multipart/byteranges"
5794    </t>
5795    <t>
5796      <eref target=""/>:
5797      "Handling multiple Content-Length headers"
5798    </t>
5799    <t>
5800      <eref target=""/>:
5801      "Clarify entity / representation / variant terminology"
5802    </t>
5803    <t>
5804      <eref target=""/>:
5805      "consider removing the 'changes from 2068' sections"
5806    </t>
5807  </list>
5810  Partly resolved issues:
5811  <list style="symbols">
5812    <t>
5813      <eref target=""/>:
5814      "HTTP(s) URI scheme definitions"
5815    </t>
5816  </list>
5820<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5822  Closed issues:
5823  <list style="symbols">
5824    <t>
5825      <eref target=""/>:
5826      "Trailer requirements"
5827    </t>
5828    <t>
5829      <eref target=""/>:
5830      "Text about clock requirement for caches belongs in p6"
5831    </t>
5832    <t>
5833      <eref target=""/>:
5834      "effective request URI: handling of missing host in HTTP/1.0"
5835    </t>
5836    <t>
5837      <eref target=""/>:
5838      "confusing Date requirements for clients"
5839    </t>
5840  </list>
5843  Partly resolved issues:
5844  <list style="symbols">
5845    <t>
5846      <eref target=""/>:
5847      "Handling multiple Content-Length headers"
5848    </t>
5849  </list>
5853<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5855  Closed issues:
5856  <list style="symbols">
5857    <t>
5858      <eref target=""/>:
5859      "RFC2145 Normative"
5860    </t>
5861    <t>
5862      <eref target=""/>:
5863      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5864    </t>
5865    <t>
5866      <eref target=""/>:
5867      "define 'transparent' proxy"
5868    </t>
5869    <t>
5870      <eref target=""/>:
5871      "Header Classification"
5872    </t>
5873    <t>
5874      <eref target=""/>:
5875      "Is * usable as a request-uri for new methods?"
5876    </t>
5877    <t>
5878      <eref target=""/>:
5879      "Migrate Upgrade details from RFC2817"
5880    </t>
5881    <t>
5882      <eref target=""/>:
5883      "untangle ABNFs for header fields"
5884    </t>
5885    <t>
5886      <eref target=""/>:
5887      "update RFC 2109 reference"
5888    </t>
5889  </list>
5893<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5895  Closed issues:
5896  <list style="symbols">
5897    <t>
5898      <eref target=""/>:
5899      "Allow is not in 13.5.2"
5900    </t>
5901    <t>
5902      <eref target=""/>:
5903      "Handling multiple Content-Length headers"
5904    </t>
5905    <t>
5906      <eref target=""/>:
5907      "untangle ABNFs for header fields"
5908    </t>
5909    <t>
5910      <eref target=""/>:
5911      "Content-Length ABNF broken"
5912    </t>
5913  </list>
5917<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5919  Closed issues:
5920  <list style="symbols">
5921    <t>
5922      <eref target=""/>:
5923      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5924    </t>
5925    <t>
5926      <eref target=""/>:
5927      "Recommend minimum sizes for protocol elements"
5928    </t>
5929    <t>
5930      <eref target=""/>:
5931      "Set expectations around buffering"
5932    </t>
5933    <t>
5934      <eref target=""/>:
5935      "Considering messages in isolation"
5936    </t>
5937  </list>
5941<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5943  Closed issues:
5944  <list style="symbols">
5945    <t>
5946      <eref target=""/>:
5947      "DNS Spoofing / DNS Binding advice"
5948    </t>
5949    <t>
5950      <eref target=""/>:
5951      "\-escaping in quoted strings"
5952    </t>
5953    <t>
5954      <eref target=""/>:
5955      "'Close' should be reserved in the HTTP header field registry"
5956    </t>
5957  </list>
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