source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1393

Last change on this file since 1393 was 1393, checked in by fielding@…, 11 years ago

Reorganize and clarify the sections on message header parsing.

  • Property svn:eol-style set to native
File size: 251.5 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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='#response.cacheability' 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
205   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
206   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
207   2068</xref>.
210   Part 1 provides an overview of HTTP and its associated terminology, defines
211   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
212   the generic message syntax and parsing requirements for HTTP message frames,
213   and describes general security concerns for implementations.
216   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
217   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
218   (on using CONNECT for TLS upgrades) and moves them to historic status.
222<note title="Editorial Note (To be removed by RFC Editor)">
223  <t>
224    Discussion of this draft should take place on the HTTPBIS working group
225    mailing list (, which is archived at
226    <eref target=""/>.
227  </t>
228  <t>
229    The current issues list is at
230    <eref target=""/> and related
231    documents (including fancy diffs) can be found at
232    <eref target=""/>.
233  </t>
234  <t>
235    The changes in this draft are summarized in <xref target="changes.since.15"/>.
236  </t>
240<section title="Introduction" anchor="introduction">
242   The Hypertext Transfer Protocol (HTTP) is an application-level
243   request/response protocol that uses extensible semantics and MIME-like
244   message payloads for flexible interaction with network-based hypertext
245   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
246   standard <xref target="RFC3986"/> to indicate the target resource and
247   relationships between resources.
248   Messages are passed in a format similar to that used by Internet mail
249   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
250   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
251   between HTTP and MIME messages).
254   HTTP is a generic interface protocol for information systems. It is
255   designed to hide the details of how a service is implemented by presenting
256   a uniform interface to clients that is independent of the types of
257   resources provided. Likewise, servers do not need to be aware of each
258   client's purpose: an HTTP request can be considered in isolation rather
259   than being associated with a specific type of client or a predetermined
260   sequence of application steps. The result is a protocol that can be used
261   effectively in many different contexts and for which implementations can
262   evolve independently over time.
265   HTTP is also designed for use as an intermediation protocol for translating
266   communication to and from non-HTTP information systems.
267   HTTP proxies and gateways can provide access to alternative information
268   services by translating their diverse protocols into a hypertext
269   format that can be viewed and manipulated by clients in the same way
270   as HTTP services.
273   One consequence of HTTP flexibility is that the protocol cannot be
274   defined in terms of what occurs behind the interface. Instead, we
275   are limited to defining the syntax of communication, the intent
276   of received communication, and the expected behavior of recipients.
277   If the communication is considered in isolation, then successful
278   actions ought to be reflected in corresponding changes to the
279   observable interface provided by servers. However, since multiple
280   clients might act in parallel and perhaps at cross-purposes, we
281   cannot require that such changes be observable beyond the scope
282   of a single response.
285   This document is Part 1 of the seven-part specification of HTTP,
286   defining the protocol referred to as "HTTP/1.1", obsoleting
287   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
288   Part 1 describes the architectural elements that are used or
289   referred to in HTTP, defines the "http" and "https" URI schemes,
290   describes overall network operation and connection management,
291   and defines HTTP message framing and forwarding requirements.
292   Our goal is to define all of the mechanisms necessary for HTTP message
293   handling that are independent of message semantics, thereby defining the
294   complete set of requirements for message parsers and
295   message-forwarding intermediaries.
298<section title="Requirements" anchor="intro.requirements">
300   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
301   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
302   document are to be interpreted as described in <xref target="RFC2119"/>.
305   An implementation is not compliant if it fails to satisfy one or more
306   of the "MUST" or "REQUIRED" level requirements for the protocols it
307   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
308   level and all the "SHOULD" level requirements for its protocols is said
309   to be "unconditionally compliant"; one that satisfies all the "MUST"
310   level requirements but not all the "SHOULD" level requirements for its
311   protocols is said to be "conditionally compliant".
315<section title="Syntax Notation" anchor="notation">
316<iref primary="true" item="Grammar" subitem="ALPHA"/>
317<iref primary="true" item="Grammar" subitem="CR"/>
318<iref primary="true" item="Grammar" subitem="CRLF"/>
319<iref primary="true" item="Grammar" subitem="CTL"/>
320<iref primary="true" item="Grammar" subitem="DIGIT"/>
321<iref primary="true" item="Grammar" subitem="DQUOTE"/>
322<iref primary="true" item="Grammar" subitem="HEXDIG"/>
323<iref primary="true" item="Grammar" subitem="LF"/>
324<iref primary="true" item="Grammar" subitem="OCTET"/>
325<iref primary="true" item="Grammar" subitem="SP"/>
326<iref primary="true" item="Grammar" subitem="VCHAR"/>
327<iref primary="true" item="Grammar" subitem="WSP"/>
329   This specification uses the Augmented Backus-Naur Form (ABNF) notation
330   of <xref target="RFC5234"/>.
332<t anchor="core.rules">
333  <x:anchor-alias value="ALPHA"/>
334  <x:anchor-alias value="CTL"/>
335  <x:anchor-alias value="CR"/>
336  <x:anchor-alias value="CRLF"/>
337  <x:anchor-alias value="DIGIT"/>
338  <x:anchor-alias value="DQUOTE"/>
339  <x:anchor-alias value="HEXDIG"/>
340  <x:anchor-alias value="LF"/>
341  <x:anchor-alias value="OCTET"/>
342  <x:anchor-alias value="SP"/>
343  <x:anchor-alias value="VCHAR"/>
344  <x:anchor-alias value="WSP"/>
345   The following core rules are included by
346   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
347   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
348   DIGIT (decimal 0-9), DQUOTE (double quote),
349   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
350   OCTET (any 8-bit sequence of data), SP (space),
351   VCHAR (any visible <xref target="USASCII"/> character),
352   and WSP (whitespace).
355   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
356   "obsolete" grammar rules that appear for historical reasons.
359<section title="ABNF Extension: #rule" anchor="notation.abnf">
361  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
362  improve readability.
365  A construct "#" is defined, similar to "*", for defining comma-delimited
366  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
367  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
368  comma (",") and optional whitespace (OWS,
369  <xref target="basic.rules"/>).   
372  Thus,
373</preamble><artwork type="example">
374  1#element =&gt; element *( OWS "," OWS element )
377  and:
378</preamble><artwork type="example">
379  #element =&gt; [ 1#element ]
382  and for n &gt;= 1 and m &gt; 1:
383</preamble><artwork type="example">
384  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
387  For compatibility with legacy list rules, recipients &SHOULD; accept empty
388  list elements. In other words, consumers would follow the list productions:
390<figure><artwork type="example">
391  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
393  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
396  Note that empty elements do not contribute to the count of elements present,
397  though.
400  For example, given these ABNF productions:
402<figure><artwork type="example">
403  example-list      = 1#example-list-elmt
404  example-list-elmt = token ; see <xref target="basic.rules"/>
407  Then these are valid values for example-list (not including the double
408  quotes, which are present for delimitation only):
410<figure><artwork type="example">
411  "foo,bar"
412  " foo ,bar,"
413  "  foo , ,bar,charlie   "
414  "foo ,bar,   charlie "
417  But these values would be invalid, as at least one non-empty element is
418  required:
420<figure><artwork type="example">
421  ""
422  ","
423  ",   ,"
426  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
427  expanded as explained above.
431<section title="Basic Rules" anchor="basic.rules">
432<t anchor="rule.LWS">
433   This specification uses three rules to denote the use of linear
434   whitespace: OWS (optional whitespace), RWS (required whitespace), and
435   BWS ("bad" whitespace).
437<t anchor="rule.OWS">
438   The OWS rule is used where zero or more linear whitespace octets might
439   appear. OWS &SHOULD; either not be produced or be produced as a single
440   SP. Multiple OWS octets that occur within field-content &SHOULD; either
441   be replaced with a single SP or transformed to all SP octets (each WSP
442   octet other than SP replaced with SP) before interpreting the field value
443   or forwarding the message downstream.
445<t anchor="rule.RWS">
446   RWS is used when at least one linear whitespace octet is required to
447   separate field tokens. RWS &SHOULD; be produced as a single SP.
448   Multiple RWS octets octets that occur within field-content &SHOULD; either
449   be replaced with a single SP or transformed to all SP octets (each WSP
450   octet other than SP replaced with SP) before interpreting the field value
451   or forwarding the message downstream.
453<t anchor="rule.BWS">
454   BWS is used where the grammar allows optional whitespace for historical
455   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
456   recipients &MUST; accept such bad optional whitespace and remove it before
457   interpreting the field value or forwarding the message downstream.
459<t anchor="rule.whitespace">
460  <x:anchor-alias value="BWS"/>
461  <x:anchor-alias value="OWS"/>
462  <x:anchor-alias value="RWS"/>
463  <x:anchor-alias value="obs-fold"/>
465<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"/>
466  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
467                 ; "optional" whitespace
468  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
469                 ; "required" whitespace
470  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
471                 ; "bad" whitespace
472  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
473                 ; see <xref target="header.fields"/>
479<section title="HTTP-related architecture" anchor="architecture">
481   HTTP was created for the World Wide Web architecture
482   and has evolved over time to support the scalability needs of a worldwide
483   hypertext system. Much of that architecture is reflected in the terminology
484   and syntax productions used to define HTTP.
487<section title="Client/Server Messaging" anchor="operation">
488<iref primary="true" item="client"/>
489<iref primary="true" item="server"/>
490<iref primary="true" item="connection"/>
492   HTTP is a stateless request/response protocol that operates by exchanging
493   messages across a reliable transport or session-layer
494   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
495   program that establishes a connection to a server for the purpose of
496   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
497   program that accepts connections in order to service HTTP requests by
498   sending HTTP responses.
500<iref primary="true" item="user agent"/>
501<iref primary="true" item="origin server"/>
502<iref primary="true" item="browser"/>
503<iref primary="true" item="spider"/>
504<iref primary="true" item="sender"/>
505<iref primary="true" item="recipient"/>
507   Note that the terms client and server refer only to the roles that
508   these programs perform for a particular connection.  The same program
509   might act as a client on some connections and a server on others.  We use
510   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
511   such as a WWW browser, editor, or spider (web-traversing robot), and
512   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
513   authoritative responses to a request.  For general requirements, we use
514   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
515   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
516   message.
519   Most HTTP communication consists of a retrieval request (GET) for
520   a representation of some resource identified by a URI.  In the
521   simplest case, this might be accomplished via a single bidirectional
522   connection (===) between the user agent (UA) and the origin server (O).
524<figure><artwork type="drawing">
525         request   &gt;
526    UA ======================================= O
527                                &lt;   response
529<iref primary="true" item="message"/>
530<iref primary="true" item="request"/>
531<iref primary="true" item="response"/>
533   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
534   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
535   protocol version, followed by MIME-like header fields containing
536   request modifiers, client information, and payload metadata, an empty
537   line to indicate the end of the header section, and finally the payload
538   body (if any).
541   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
542   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
543   includes the protocol version, a success or error code, and textual
544   reason phrase, followed by MIME-like header fields containing server
545   information, resource metadata, and payload metadata, an empty line to
546   indicate the end of the header section, and finally the payload body (if any).
549   The following example illustrates a typical message exchange for a
550   GET request on the URI "":
553client request:
554</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
555GET /hello.txt HTTP/1.1
556User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
558Accept: */*
562server response:
563</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
564HTTP/1.1 200 OK
565Date: Mon, 27 Jul 2009 12:28:53 GMT
566Server: Apache
567Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
568ETag: "34aa387-d-1568eb00"
569Accept-Ranges: bytes
570Content-Length: <x:length-of target="exbody"/>
571Vary: Accept-Encoding
572Content-Type: text/plain
574<x:span anchor="exbody">Hello World!
578<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
580   Fundamentally, HTTP is a message-based protocol. Although message bodies can
581   be chunked (<xref target="chunked.encoding"/>) and implementations often
582   make parts of a message available progressively, this is not required, and
583   some widely-used implementations only make a message available when it is
584   complete. Furthermore, while most proxies will progressively stream messages,
585   some amount of buffering will take place, and some proxies might buffer
586   messages to perform transformations, check content or provide other services.
589   Therefore, extensions to and uses of HTTP cannot rely on the availability of
590   a partial message, or assume that messages will not be buffered. There are
591   strategies that can be used to test for buffering in a given connection, but
592   it should be understood that behaviors can differ across connections, and
593   between requests and responses.
596   Recipients &MUST; consider every message in a connection in isolation;
597   because HTTP is a stateless protocol, it cannot be assumed that two requests
598   on the same connection are from the same client or share any other common
599   attributes. In particular, intermediaries might mix requests from different
600   clients into a single server connection. Note that some existing HTTP
601   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
602   potentially causing interoperability and security problems.
606<section title="Connections and Transport Independence" anchor="transport-independence">
608   HTTP messaging is independent of the underlying transport or
609   session-layer connection protocol(s).  HTTP only presumes a reliable
610   transport with in-order delivery of requests and the corresponding
611   in-order delivery of responses.  The mapping of HTTP request and
612   response structures onto the data units of the underlying transport
613   protocol is outside the scope of this specification.
616   The specific connection protocols to be used for an interaction
617   are determined by client configuration and the target resource's URI.
618   For example, the "http" URI scheme
619   (<xref target="http.uri"/>) indicates a default connection of TCP
620   over IP, with a default TCP port of 80, but the client might be
621   configured to use a proxy via some other connection port or protocol
622   instead of using the defaults.
625   A connection might be used for multiple HTTP request/response exchanges,
626   as defined in <xref target="persistent.connections"/>.
630<section title="Intermediaries" anchor="intermediaries">
631<iref primary="true" item="intermediary"/>
633   HTTP enables the use of intermediaries to satisfy requests through
634   a chain of connections.  There are three common forms of HTTP
635   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
636   a single intermediary might act as an origin server, proxy, gateway,
637   or tunnel, switching behavior based on the nature of each request.
639<figure><artwork type="drawing">
640         &gt;             &gt;             &gt;             &gt;
641    <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>
642               &lt;             &lt;             &lt;             &lt;
645   The figure above shows three intermediaries (A, B, and C) between the
646   user agent and origin server. A request or response message that
647   travels the whole chain will pass through four separate connections.
648   Some HTTP communication options
649   might apply only to the connection with the nearest, non-tunnel
650   neighbor, only to the end-points of the chain, or to all connections
651   along the chain. Although the diagram is linear, each participant might
652   be engaged in multiple, simultaneous communications. For example, B
653   might be receiving requests from many clients other than A, and/or
654   forwarding requests to servers other than C, at the same time that it
655   is handling A's request.
658<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
659<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
660   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
661   to describe various requirements in relation to the directional flow of a
662   message: all messages flow from upstream to downstream.
663   Likewise, we use the terms inbound and outbound to refer to
664   directions in relation to the request path:
665   "<x:dfn>inbound</x:dfn>" means toward the origin server and
666   "<x:dfn>outbound</x:dfn>" means toward the user agent.
668<t><iref primary="true" item="proxy"/>
669   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
670   client, usually via local configuration rules, to receive requests
671   for some type(s) of absolute URI and attempt to satisfy those
672   requests via translation through the HTTP interface.  Some translations
673   are minimal, such as for proxy requests for "http" URIs, whereas
674   other requests might require translation to and from entirely different
675   application-layer protocols. Proxies are often used to group an
676   organization's HTTP requests through a common intermediary for the
677   sake of security, annotation services, or shared caching.
680<iref primary="true" item="transforming proxy"/>
681<iref primary="true" item="non-transforming proxy"/>
682   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
683   or configured to modify request or response messages in a semantically
684   meaningful way (i.e., modifications, beyond those required by normal
685   HTTP processing, that change the message in a way that would be
686   significant to the original sender or potentially significant to
687   downstream recipients).  For example, a transforming proxy might be
688   acting as a shared annotation server (modifying responses to include
689   references to a local annotation database), a malware filter, a
690   format transcoder, or an intranet-to-Internet privacy filter.  Such
691   transformations are presumed to be desired by the client (or client
692   organization) that selected the proxy and are beyond the scope of
693   this specification.  However, when a proxy is not intended to transform
694   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
695   requirements that preserve HTTP message semantics. See &status-203; and
696   &header-warning; for status and warning codes related to transformations.
698<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
699<iref primary="true" item="accelerator"/>
700   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
701   is a receiving agent that acts
702   as a layer above some other server(s) and translates the received
703   requests to the underlying server's protocol.  Gateways are often
704   used to encapsulate legacy or untrusted information services, to
705   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
706   enable partitioning or load-balancing of HTTP services across
707   multiple machines.
710   A gateway behaves as an origin server on its outbound connection and
711   as a user agent on its inbound connection.
712   All HTTP requirements applicable to an origin server
713   also apply to the outbound communication of a gateway.
714   A gateway communicates with inbound servers using any protocol that
715   it desires, including private extensions to HTTP that are outside
716   the scope of this specification.  However, an HTTP-to-HTTP gateway
717   that wishes to interoperate with third-party HTTP servers &MUST;
718   comply with HTTP user agent requirements on the gateway's inbound
719   connection and &MUST; implement the Connection
720   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
721   header fields for both connections.
723<t><iref primary="true" item="tunnel"/>
724   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
725   without changing the messages. Once active, a tunnel is not
726   considered a party to the HTTP communication, though the tunnel might
727   have been initiated by an HTTP request. A tunnel ceases to exist when
728   both ends of the relayed connection are closed. Tunnels are used to
729   extend a virtual connection through an intermediary, such as when
730   transport-layer security is used to establish private communication
731   through a shared firewall proxy.
733<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
734<iref primary="true" item="captive portal"/>
735   In addition, there may exist network intermediaries that are not
736   considered part of the HTTP communication but nevertheless act as
737   filters or redirecting agents (usually violating HTTP semantics,
738   causing security problems, and otherwise making a mess of things).
739   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
740   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
741   or "<x:dfn>captive portal</x:dfn>",
742   differs from an HTTP proxy because it has not been selected by the client.
743   Instead, the network intermediary redirects outgoing TCP port 80 packets
744   (and occasionally other common port traffic) to an internal HTTP server.
745   Interception proxies are commonly found on public network access points,
746   as a means of enforcing account subscription prior to allowing use of
747   non-local Internet services, and within corporate firewalls to enforce
748   network usage policies.
749   They are indistinguishable from a man-in-the-middle attack.
753<section title="Caches" anchor="caches">
754<iref primary="true" item="cache"/>
756   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
757   subsystem that controls its message storage, retrieval, and deletion.
758   A cache stores cacheable responses in order to reduce the response
759   time and network bandwidth consumption on future, equivalent
760   requests. Any client or server &MAY; employ a cache, though a cache
761   cannot be used by a server while it is acting as a tunnel.
764   The effect of a cache is that the request/response chain is shortened
765   if one of the participants along the chain has a cached response
766   applicable to that request. The following illustrates the resulting
767   chain if B has a cached copy of an earlier response from O (via C)
768   for a request which has not been cached by UA or A.
770<figure><artwork type="drawing">
771            &gt;             &gt;
772       UA =========== A =========== B - - - - - - C - - - - - - O
773                  &lt;             &lt;
775<t><iref primary="true" item="cacheable"/>
776   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
777   the response message for use in answering subsequent requests.
778   Even when a response is cacheable, there might be additional
779   constraints placed by the client or by the origin server on when
780   that cached response can be used for a particular request. HTTP
781   requirements for cache behavior and cacheable responses are
782   defined in &caching-overview;. 
785   There are a wide variety of architectures and configurations
786   of caches and proxies deployed across the World Wide Web and
787   inside large organizations. These systems include national hierarchies
788   of proxy caches to save transoceanic bandwidth, systems that
789   broadcast or multicast cache entries, organizations that distribute
790   subsets of cached data via optical media, and so on.
794<section title="Protocol Versioning" anchor="http.version">
795  <x:anchor-alias value="HTTP-Version"/>
796  <x:anchor-alias value="HTTP-Prot-Name"/>
798   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
799   versions of the protocol. This specification defines version "1.1".
800   The protocol version as a whole indicates the sender's compliance
801   with the set of requirements laid out in that version's corresponding
802   specification of HTTP.
805   The version of an HTTP message is indicated by an HTTP-Version field
806   in the first line of the message. HTTP-Version is case-sensitive.
808<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
809  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
810  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
813   The HTTP version number consists of two decimal digits separated by a "."
814   (period or decimal point).  The first digit ("major version") indicates the
815   HTTP messaging syntax, whereas the second digit ("minor version") indicates
816   the highest minor version to which the sender is at least conditionally
817   compliant and able to understand for future communication.  The minor
818   version advertises the sender's communication capabilities even when the
819   sender is only using a backwards-compatible subset of the protocol,
820   thereby letting the recipient know that more advanced features can
821   be used in response (by servers) or in future requests (by clients).
824   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
825   <xref target="RFC1945"/> or a recipient whose version is unknown,
826   the HTTP/1.1 message is constructed such that it can be interpreted
827   as a valid HTTP/1.0 message if all of the newer features are ignored.
828   This specification places recipient-version requirements on some
829   new features so that a compliant sender will only use compatible
830   features until it has determined, through configuration or the
831   receipt of a message, that the recipient supports HTTP/1.1.
834   The interpretation of an HTTP header field does not change
835   between minor versions of the same major version, though the default
836   behavior of a recipient in the absence of such a field can change.
837   Unless specified otherwise, header fields defined in HTTP/1.1 are
838   defined for all versions of HTTP/1.x.  In particular, the Host and
839   Connection header fields ought to be implemented by all HTTP/1.x
840   implementations whether or not they advertise compliance with HTTP/1.1.
843   New header fields can be defined such that, when they are
844   understood by a recipient, they might override or enhance the
845   interpretation of previously defined header fields.  When an
846   implementation receives an unrecognized header field, the recipient
847   &MUST; ignore that header field for local processing regardless of
848   the message's HTTP version.  An unrecognized header field received
849   by a proxy &MUST; be forwarded downstream unless the header field's
850   field-name is listed in the message's Connection header-field
851   (see <xref target="header.connection"/>).
852   These requirements allow HTTP's functionality to be enhanced without
853   requiring prior update of all compliant intermediaries.
856   Intermediaries that process HTTP messages (i.e., all intermediaries
857   other than those acting as a tunnel) &MUST; send their own HTTP-Version
858   in forwarded messages.  In other words, they &MUST-NOT; blindly
859   forward the first line of an HTTP message without ensuring that the
860   protocol version matches what the intermediary understands, and
861   is at least conditionally compliant to, for both the receiving and
862   sending of messages.  Forwarding an HTTP message without rewriting
863   the HTTP-Version might result in communication errors when downstream
864   recipients use the message sender's version to determine what features
865   are safe to use for later communication with that sender.
868   An HTTP client &SHOULD; send a request version equal to the highest
869   version for which the client is at least conditionally compliant and
870   whose major version is no higher than the highest version supported
871   by the server, if this is known.  An HTTP client &MUST-NOT; send a
872   version for which it is not at least conditionally compliant.
875   An HTTP client &MAY; send a lower request version if it is known that
876   the server incorrectly implements the HTTP specification, but only
877   after the client has attempted at least one normal request and determined
878   from the response status or header fields (e.g., Server) that the
879   server improperly handles higher request versions.
882   An HTTP server &SHOULD; send a response version equal to the highest
883   version for which the server is at least conditionally compliant and
884   whose major version is less than or equal to the one received in the
885   request.  An HTTP server &MUST-NOT; send a version for which it is not
886   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
887   Version Not Supported) response if it cannot send a response using the
888   major version used in the client's request.
891   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
892   if it is known or suspected that the client incorrectly implements the
893   HTTP specification and is incapable of correctly processing later
894   version responses, such as when a client fails to parse the version
895   number correctly or when an intermediary is known to blindly forward
896   the HTTP-Version even when it doesn't comply with the given minor
897   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
898   performed unless triggered by specific client attributes, such as when
899   one or more of the request header fields (e.g., User-Agent) uniquely
900   match the values sent by a client known to be in error.
903   The intention of HTTP's versioning design is that the major number
904   will only be incremented if an incompatible message syntax is
905   introduced, and that the minor number will only be incremented when
906   changes made to the protocol have the effect of adding to the message
907   semantics or implying additional capabilities of the sender.  However,
908   the minor version was not incremented for the changes introduced between
909   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
910   is specifically avoiding any such changes to the protocol.
914<section title="Uniform Resource Identifiers" anchor="uri">
915<iref primary="true" item="resource"/>
917   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
918   throughout HTTP as the means for identifying resources. URI references
919   are used to target requests, indicate redirects, and define relationships.
920   HTTP does not limit what a resource might be; it merely defines an interface
921   that can be used to interact with a resource via HTTP. More information on
922   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
924  <x:anchor-alias value="URI-reference"/>
925  <x:anchor-alias value="absolute-URI"/>
926  <x:anchor-alias value="relative-part"/>
927  <x:anchor-alias value="authority"/>
928  <x:anchor-alias value="path-abempty"/>
929  <x:anchor-alias value="path-absolute"/>
930  <x:anchor-alias value="port"/>
931  <x:anchor-alias value="query"/>
932  <x:anchor-alias value="uri-host"/>
933  <x:anchor-alias value="partial-URI"/>
935   This specification adopts the definitions of "URI-reference",
936   "absolute-URI", "relative-part", "port", "host",
937   "path-abempty", "path-absolute", "query", and "authority" from the
938   URI generic syntax <xref target="RFC3986"/>.
939   In addition, we define a partial-URI rule for protocol elements
940   that allow a relative URI but not a fragment.
942<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"/>
943  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
944  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
945  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
946  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
947  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
948  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
949  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
950  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
951  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
953  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
956   Each protocol element in HTTP that allows a URI reference will indicate
957   in its ABNF production whether the element allows any form of reference
958   (URI-reference), only a URI in absolute form (absolute-URI), only the
959   path and optional query components, or some combination of the above.
960   Unless otherwise indicated, URI references are parsed relative to the
961   effective request URI, which defines the default base URI for references
962   in both the request and its corresponding response.
965<section title="http URI scheme" anchor="http.uri">
966  <x:anchor-alias value="http-URI"/>
967  <iref item="http URI scheme" primary="true"/>
968  <iref item="URI scheme" subitem="http" primary="true"/>
970   The "http" URI scheme is hereby defined for the purpose of minting
971   identifiers according to their association with the hierarchical
972   namespace governed by a potential HTTP origin server listening for
973   TCP connections on a given port.
975<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
976  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
979   The HTTP origin server is identified by the generic syntax's
980   <x:ref>authority</x:ref> component, which includes a host identifier
981   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
982   The remainder of the URI, consisting of both the hierarchical path
983   component and optional query component, serves as an identifier for
984   a potential resource within that origin server's name space.
987   If the host identifier is provided as an IP literal or IPv4 address,
988   then the origin server is any listener on the indicated TCP port at
989   that IP address. If host is a registered name, then that name is
990   considered an indirect identifier and the recipient might use a name
991   resolution service, such as DNS, to find the address of a listener
992   for that host.
993   The host &MUST-NOT; be empty; if an "http" URI is received with an
994   empty host, then it &MUST; be rejected as invalid.
995   If the port subcomponent is empty or not given, then TCP port 80 is
996   assumed (the default reserved port for WWW services).
999   Regardless of the form of host identifier, access to that host is not
1000   implied by the mere presence of its name or address. The host might or might
1001   not exist and, even when it does exist, might or might not be running an
1002   HTTP server or listening to the indicated port. The "http" URI scheme
1003   makes use of the delegated nature of Internet names and addresses to
1004   establish a naming authority (whatever entity has the ability to place
1005   an HTTP server at that Internet name or address) and allows that
1006   authority to determine which names are valid and how they might be used.
1009   When an "http" URI is used within a context that calls for access to the
1010   indicated resource, a client &MAY; attempt access by resolving
1011   the host to an IP address, establishing a TCP connection to that address
1012   on the indicated port, and sending an HTTP request message to the server
1013   containing the URI's identifying data as described in <xref target="request"/>.
1014   If the server responds to that request with a non-interim HTTP response
1015   message, as described in <xref target="response"/>, then that response
1016   is considered an authoritative answer to the client's request.
1019   Although HTTP is independent of the transport protocol, the "http"
1020   scheme is specific to TCP-based services because the name delegation
1021   process depends on TCP for establishing authority.
1022   An HTTP service based on some other underlying connection protocol
1023   would presumably be identified using a different URI scheme, just as
1024   the "https" scheme (below) is used for servers that require an SSL/TLS
1025   transport layer on a connection. Other protocols might also be used to
1026   provide access to "http" identified resources &mdash; it is only the
1027   authoritative interface used for mapping the namespace that is
1028   specific to TCP.
1031   The URI generic syntax for authority also includes a deprecated
1032   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1033   for including user authentication information in the URI.  Some
1034   implementations make use of the userinfo component for internal
1035   configuration of authentication information, such as within command
1036   invocation options, configuration files, or bookmark lists, even
1037   though such usage might expose a user identifier or password.
1038   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1039   delimiter) when transmitting an "http" URI in a message.  Recipients
1040   of HTTP messages that contain a URI reference &SHOULD; parse for the
1041   existence of userinfo and treat its presence as an error, likely
1042   indicating that the deprecated subcomponent is being used to obscure
1043   the authority for the sake of phishing attacks.
1047<section title="https URI scheme" anchor="https.uri">
1048   <x:anchor-alias value="https-URI"/>
1049   <iref item="https URI scheme"/>
1050   <iref item="URI scheme" subitem="https"/>
1052   The "https" URI scheme is hereby defined for the purpose of minting
1053   identifiers according to their association with the hierarchical
1054   namespace governed by a potential HTTP origin server listening for
1055   SSL/TLS-secured connections on a given TCP port.
1058   All of the requirements listed above for the "http" scheme are also
1059   requirements for the "https" scheme, except that a default TCP port
1060   of 443 is assumed if the port subcomponent is empty or not given,
1061   and the TCP connection &MUST; be secured for privacy through the
1062   use of strong encryption prior to sending the first HTTP request.
1064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1065  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1068   Unlike the "http" scheme, responses to "https" identified requests
1069   are never "public" and thus &MUST-NOT; be reused for shared caching.
1070   They can, however, be reused in a private cache if the message is
1071   cacheable by default in HTTP or specifically indicated as such by
1072   the Cache-Control header field (&header-cache-control;).
1075   Resources made available via the "https" scheme have no shared
1076   identity with the "http" scheme even if their resource identifiers
1077   indicate the same authority (the same host listening to the same
1078   TCP port).  They are distinct name spaces and are considered to be
1079   distinct origin servers.  However, an extension to HTTP that is
1080   defined to apply to entire host domains, such as the Cookie protocol
1081   <xref target="RFC6265"/>, can allow information
1082   set by one service to impact communication with other services
1083   within a matching group of host domains.
1086   The process for authoritative access to an "https" identified
1087   resource is defined in <xref target="RFC2818"/>.
1091<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1093   Since the "http" and "https" schemes conform to the URI generic syntax,
1094   such URIs are normalized and compared according to the algorithm defined
1095   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1096   described above for each scheme.
1099   If the port is equal to the default port for a scheme, the normal
1100   form is to elide the port subcomponent. Likewise, an empty path
1101   component is equivalent to an absolute path of "/", so the normal
1102   form is to provide a path of "/" instead. The scheme and host
1103   are case-insensitive and normally provided in lowercase; all
1104   other components are compared in a case-sensitive manner.
1105   Characters other than those in the "reserved" set are equivalent
1106   to their percent-encoded octets (see <xref target="RFC3986"
1107   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1110   For example, the following three URIs are equivalent:
1112<figure><artwork type="example">
1121<section title="Message Format" anchor="http.message">
1122<x:anchor-alias value="generic-message"/>
1123<x:anchor-alias value="message.types"/>
1124<x:anchor-alias value="HTTP-message"/>
1125<x:anchor-alias value="start-line"/>
1126<iref item="header section"/>
1127<iref item="headers"/>
1128<iref item="header field"/>
1130   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1131   octets in a format similar to the Internet Message Format
1132   <xref target="RFC5322"/>: zero or more header fields (collectively
1133   referred to as the "headers" or the "header section"), an empty line
1134   indicating the end of the header section, and an optional message-body.
1137   An HTTP message can either be a request from client to server or a
1138   response from server to client.  Syntactically, the two types of message
1139   differ only in the start-line, which is either a Request-Line (for requests)
1140   or a Status-Line (for responses), and in the algorithm for determining
1141   the length of the message-body (<xref target="message.body"/>).
1142   In theory, a client could receive requests and a server could receive
1143   responses, distinguishing them by their different start-line formats,
1144   but in practice servers are implemented to only expect a request
1145   (a response is interpreted as an unknown or invalid request method)
1146   and clients are implemented to only expect a response.
1148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1149  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1150                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1151                    <x:ref>CRLF</x:ref>
1152                    [ <x:ref>message-body</x:ref> ]
1153  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1156   Implementations &MUST-NOT; send whitespace between the start-line and
1157   the first header field. The presence of such whitespace in a request
1158   might be an attempt to trick a server into ignoring that field or
1159   processing the line after it as a new request, either of which might
1160   result in a security vulnerability if other implementations within
1161   the request chain interpret the same message differently.
1162   Likewise, the presence of such whitespace in a response might be
1163   ignored by some clients or cause others to cease parsing.
1166<section title="Message Parsing and Robustness" anchor="message.robustness">
1168   The normal procedure for parsing an HTTP message is to read the
1169   start-line into a structure, read each header field into a hash
1170   table by field name until the empty line, and then use the parsed
1171   data to determine if a message-body is expected.  If a message-body
1172   has been indicated, then it is read as a stream until an amount
1173   of octets equal to the message-body length is read or the connection
1174   is closed.
1177   Care must be taken to parse an HTTP message as a sequence
1178   of octets in an encoding that is a superset of US-ASCII.  Attempting
1179   to parse HTTP as a stream of Unicode characters in a character encoding
1180   like UTF-16 might introduce security flaws due to the differing ways
1181   that such parsers interpret invalid characters.
1184   Older HTTP/1.0 client implementations might send an extra CRLF
1185   after a POST request as a lame workaround for some early server
1186   applications that failed to read message-body content that was
1187   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1188   preface or follow a request with an extra CRLF.  If terminating
1189   the request message-body with a line-ending is desired, then the
1190   client &MUST; include the terminating CRLF octets as part of the
1191   message-body length.
1194   In the interest of robustness, servers &SHOULD; ignore at least one
1195   empty line received where a Request-Line is expected. In other words, if
1196   the server is reading the protocol stream at the beginning of a
1197   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1198   Likewise, although the line terminator for the start-line and header
1199   fields is the sequence CRLF, we recommend that recipients recognize a
1200   single LF as a line terminator and ignore any CR.
1203   When a server listening only for HTTP request messages, or processing
1204   what appears from the start-line to be an HTTP request message,
1205   receives a sequence of octets that does not match the HTTP-message
1206   grammar aside from the robustness exceptions listed above, the
1207   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1211<section title="Header Fields" anchor="header.fields">
1212  <x:anchor-alias value="header-field"/>
1213  <x:anchor-alias value="field-content"/>
1214  <x:anchor-alias value="field-name"/>
1215  <x:anchor-alias value="field-value"/>
1216  <x:anchor-alias value="OWS"/>
1218   Each HTTP header field consists of a case-insensitive field name
1219   followed by a colon (":"), optional whitespace, and the field value.
1221<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"/>
1222  <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>
1223  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1224  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1225  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1228   The field-name token labels the corresponding field-value as having the
1229   semantics defined by that header field.  For example, the Date header field
1230   is defined in <xref target=""/> as containing the origination
1231   timestamp for the message in which it appears.
1234   HTTP header fields are fully extensible: there is no limit on the
1235   introduction of new field names, each presumably defining new semantics,
1236   or on the number of header fields used in a given message.  Existing
1237   fields are defined in each part of this specification and in many other
1238   specifications outside the standards process.
1239   New header fields can be introduced without changing the protocol version
1240   if their defined semantics allow them to be safely ignored by recipients
1241   that do not recognize them.
1244   New HTTP header fields &SHOULD; be registered with IANA according
1245   to the procedures in <xref target="header.field.registration"/>.
1246   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1247   field-name is listed in the Connection header field
1248   (<xref target="header.connection"/>) or the proxy is specifically
1249   configured to block or otherwise transform such fields.
1250   Unrecognized header fields &SHOULD; be ignored by other recipients.
1253   The order in which header fields with differing field names are
1254   received is not significant. However, it is "good practice" to send
1255   header fields that contain control data first, such as Host on
1256   requests and Date on responses, so that implementations can decide
1257   when not to handle a message as early as possible.  A server &MUST;
1258   wait until the entire header section is received before interpreting
1259   a request message, since later header fields might include conditionals,
1260   authentication credentials, or deliberately misleading duplicate
1261   header fields that would impact request processing.
1264   Multiple header fields with the same field name &MUST-NOT; be
1265   sent in a message unless the entire field value for that
1266   header field is defined as a comma-separated list [i.e., #(values)].
1267   Multiple header fields with the same field name can be combined into
1268   one "field-name: field-value" pair, without changing the semantics of the
1269   message, by appending each subsequent field value to the combined
1270   field value in order, separated by a comma. The order in which
1271   header fields with the same field name are received is therefore
1272   significant to the interpretation of the combined field value;
1273   a proxy &MUST-NOT; change the order of these field values when
1274   forwarding a message.
1277  <t>
1278   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1279   practice can occur multiple times, but does not use the list syntax, and
1280   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1281   for details.) Also note that the Set-Cookie2 header field specified in
1282   <xref target="RFC2965"/> does not share this problem.
1283  </t>
1286<section title="Field Parsing" anchor="field.parsing">
1288   No whitespace is allowed between the header field-name and colon.
1289   In the past, differences in the handling of such whitespace have led to
1290   security vulnerabilities in request routing and response handling.
1291   Any received request message that contains whitespace between a header
1292   field-name and colon &MUST; be rejected with a response code of 400
1293   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1294   message before forwarding the message downstream.
1297   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1298   preferred. The field value does not include any leading or trailing white
1299   space: OWS occurring before the first non-whitespace octet of the
1300   field value or after the last non-whitespace octet of the field value
1301   is ignored and &SHOULD; be removed before further processing (as this does
1302   not change the meaning of the header field).
1305   Historically, HTTP header field values could be extended over multiple
1306   lines by preceding each extra line with at least one space or horizontal
1307   tab octet (line folding). This specification deprecates such line
1308   folding except within the message/http media type
1309   (<xref target=""/>).
1310   HTTP senders &MUST-NOT; produce messages that include line folding
1311   (i.e., that contain any field-content that matches the obs-fold rule) unless
1312   the message is intended for packaging within the message/http media type.
1313   HTTP recipients &SHOULD; accept line folding and replace any embedded
1314   obs-fold whitespace with either a single SP or a matching number of SP
1315   octets (to avoid buffer copying) prior to interpreting the field value or
1316   forwarding the message downstream.
1319   Historically, HTTP has allowed field content with text in the ISO-8859-1
1320   <xref target="ISO-8859-1"/> character encoding and supported other
1321   character sets only through use of <xref target="RFC2047"/> encoding.
1322   In practice, most HTTP header field values use only a subset of the
1323   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1324   header fields &SHOULD; limit their field values to US-ASCII octets.
1325   Recipients &SHOULD; treat other (obs-text) octets in field content as
1326   opaque data.
1330<section title="Field Length" anchor="field.length">
1332   HTTP does not place a pre-defined limit on the length of header fields,
1333   either in isolation or as a set. A server &MUST; be prepared to receive
1334   request header fields of unbounded length and respond with a 4xx status
1335   code if the received header field(s) would be longer than the server wishes
1336   to handle.
1339   A client that receives response headers that are longer than it wishes to
1340   handle can only treat it as a server error.
1343   Various ad-hoc limitations on header length are found in practice. It is
1344   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1345   combined header fields have 4000 or more octets.
1349<section title="Common Field ABNF Rules" anchor="field.rules">
1350<t anchor="rule.token.separators">
1351  <x:anchor-alias value="tchar"/>
1352  <x:anchor-alias value="token"/>
1353  <x:anchor-alias value="special"/>
1354  <x:anchor-alias value="word"/>
1355   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1356   separated by whitespace or special characters. These special characters
1357   &MUST; be in a quoted string to be used within a parameter value (as defined
1358   in <xref target="transfer.codings"/>).
1360<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"/>
1361  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1363  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1365  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1366 -->
1367  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1368                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1369                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1370                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1372  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1373                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1374                 / "]" / "?" / "=" / "{" / "}"
1376<t anchor="rule.quoted-string">
1377  <x:anchor-alias value="quoted-string"/>
1378  <x:anchor-alias value="qdtext"/>
1379  <x:anchor-alias value="obs-text"/>
1380   A string of text is parsed as a single word if it is quoted using
1381   double-quote marks.
1383<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"/>
1384  <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>
1385  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1386  <x:ref>obs-text</x:ref>       = %x80-FF
1388<t anchor="rule.quoted-pair">
1389  <x:anchor-alias value="quoted-pair"/>
1390   The backslash octet ("\") can be used as a single-octet
1391   quoting mechanism within quoted-string constructs:
1393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1394  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1397   Recipients that process the value of the quoted-string &MUST; handle a
1398   quoted-pair as if it were replaced by the octet following the backslash.
1401   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1402   escaping (i.e., other than DQUOTE and the backslash octet).
1404<t anchor="rule.comment">
1405  <x:anchor-alias value="comment"/>
1406  <x:anchor-alias value="ctext"/>
1407   Comments can be included in some HTTP header fields by surrounding
1408   the comment text with parentheses. Comments are only allowed in
1409   fields containing "comment" as part of their field value definition.
1411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1412  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1413  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1415<t anchor="rule.quoted-cpair">
1416  <x:anchor-alias value="quoted-cpair"/>
1417   The backslash octet ("\") can be used as a single-octet
1418   quoting mechanism within comment constructs:
1420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1421  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1424   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1425   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1430<section title="Message Body" anchor="message.body">
1431  <x:anchor-alias value="message-body"/>
1433   The message-body (if any) of an HTTP message is used to carry the
1434   payload body associated with the request or response.
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1437  <x:ref>message-body</x:ref> = *OCTET
1440   The message-body differs from the payload body only when a transfer-coding
1441   has been applied, as indicated by the Transfer-Encoding header field
1442   (<xref target="header.transfer-encoding"/>).  If more than one
1443   Transfer-Encoding header field is present in a message, the multiple
1444   field-values &MUST; be combined into one field-value, according to the
1445   algorithm defined in <xref target="header.fields"/>, before determining
1446   the message-body length.
1449   When one or more transfer-codings are applied to a payload in order to
1450   form the message-body, the Transfer-Encoding header field &MUST; contain
1451   the list of transfer-codings applied. Transfer-Encoding is a property of
1452   the message, not of the payload, and thus &MAY; be added or removed by
1453   any implementation along the request/response chain under the constraints
1454   found in <xref target="transfer.codings"/>.
1457   If a message is received that has multiple Content-Length header fields
1458   (<xref target="header.content-length"/>) with field-values consisting
1459   of the same decimal value, or a single Content-Length header field with
1460   a field value containing a list of identical decimal values (e.g.,
1461   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1462   header fields have been generated or combined by an upstream message
1463   processor, then the recipient &MUST; either reject the message as invalid
1464   or replace the duplicated field-values with a single valid Content-Length
1465   field containing that decimal value prior to determining the message-body
1466   length.
1469   The rules for when a message-body is allowed in a message differ for
1470   requests and responses.
1473   The presence of a message-body in a request is signaled by the
1474   inclusion of a Content-Length or Transfer-Encoding header field in
1475   the request's header fields, even if the request method does not
1476   define any use for a message-body.  This allows the request
1477   message framing algorithm to be independent of method semantics.
1480   For response messages, whether or not a message-body is included with
1481   a message is dependent on both the request method and the response
1482   status code (<xref target="status.code.and.reason.phrase"/>).
1483   Responses to the HEAD request method never include a message-body
1484   because the associated response header fields (e.g., Transfer-Encoding,
1485   Content-Length, etc.) only indicate what their values would have been
1486   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1487   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1488   All other responses do include a message-body, although the body
1489   &MAY; be of zero length.
1492   The length of the message-body is determined by one of the following
1493   (in order of precedence):
1496  <list style="numbers">
1497    <x:lt><t>
1498     Any response to a HEAD request and any response with a status
1499     code of 100-199, 204, or 304 is always terminated by the first
1500     empty line after the header fields, regardless of the header
1501     fields present in the message, and thus cannot contain a message-body.
1502    </t></x:lt>
1503    <x:lt><t>
1504     If a Transfer-Encoding header field is present
1505     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1506     is the final encoding, the message-body length is determined by reading
1507     and decoding the chunked data until the transfer-coding indicates the
1508     data is complete.
1509    </t>
1510    <t>
1511     If a Transfer-Encoding header field is present in a response and the
1512     "chunked" transfer-coding is not the final encoding, the message-body
1513     length is determined by reading the connection until it is closed by
1514     the server.
1515     If a Transfer-Encoding header field is present in a request and the
1516     "chunked" transfer-coding is not the final encoding, the message-body
1517     length cannot be determined reliably; the server &MUST; respond with
1518     the 400 (Bad Request) status code and then close the connection.
1519    </t>
1520    <t>
1521     If a message is received with both a Transfer-Encoding header field
1522     and a Content-Length header field, the Transfer-Encoding overrides
1523     the Content-Length.
1524     Such a message might indicate an attempt to perform request or response
1525     smuggling (bypass of security-related checks on message routing or content)
1526     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1527     be removed, prior to forwarding the message downstream, or replaced with
1528     the real message-body length after the transfer-coding is decoded.
1529    </t></x:lt>
1530    <x:lt><t>
1531     If a message is received without Transfer-Encoding and with either
1532     multiple Content-Length header fields having differing field-values or
1533     a single Content-Length header field having an invalid value, then the
1534     message framing is invalid and &MUST; be treated as an error to
1535     prevent request or response smuggling.
1536     If this is a request message, the server &MUST; respond with
1537     a 400 (Bad Request) status code and then close the connection.
1538     If this is a response message received by a proxy, the proxy
1539     &MUST; discard the received response, send a 502 (Bad Gateway)
1540     status code as its downstream response, and then close the connection.
1541     If this is a response message received by a user-agent, it &MUST; be
1542     treated as an error by discarding the message and closing the connection.
1543    </t></x:lt>
1544    <x:lt><t>
1545     If a valid Content-Length header field
1546     is present without Transfer-Encoding, its decimal value defines the
1547     message-body length in octets.  If the actual number of octets sent in
1548     the message is less than the indicated Content-Length, the recipient
1549     &MUST; consider the message to be incomplete and treat the connection
1550     as no longer usable.
1551     If the actual number of octets sent in the message is more than the indicated
1552     Content-Length, the recipient &MUST; only process the message-body up to the
1553     field value's number of octets; the remainder of the message &MUST; either
1554     be discarded or treated as the next message in a pipeline.  For the sake of
1555     robustness, a user-agent &MAY; attempt to detect and correct such an error
1556     in message framing if it is parsing the response to the last request on
1557     a connection and the connection has been closed by the server.
1558    </t></x:lt>
1559    <x:lt><t>
1560     If this is a request message and none of the above are true, then the
1561     message-body length is zero (no message-body is present).
1562    </t></x:lt>
1563    <x:lt><t>
1564     Otherwise, this is a response message without a declared message-body
1565     length, so the message-body length is determined by the number of octets
1566     received prior to the server closing the connection.
1567    </t></x:lt>
1568  </list>
1571   Since there is no way to distinguish a successfully completed,
1572   close-delimited message from a partially-received message interrupted
1573   by network failure, implementations &SHOULD; use encoding or
1574   length-delimited messages whenever possible.  The close-delimiting
1575   feature exists primarily for backwards compatibility with HTTP/1.0.
1578   A server &MAY; reject a request that contains a message-body but
1579   not a Content-Length by responding with 411 (Length Required).
1582   Unless a transfer-coding other than "chunked" has been applied,
1583   a client that sends a request containing a message-body &SHOULD;
1584   use a valid Content-Length header field if the message-body length
1585   is known in advance, rather than the "chunked" encoding, since some
1586   existing services respond to "chunked" with a 411 (Length Required)
1587   status code even though they understand the chunked encoding.  This
1588   is typically because such services are implemented via a gateway that
1589   requires a content-length in advance of being called and the server
1590   is unable or unwilling to buffer the entire request before processing.
1593   A client that sends a request containing a message-body &MUST; include a
1594   valid Content-Length header field if it does not know the server will
1595   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1596   of specific user configuration or by remembering the version of a prior
1597   received response.
1601<section anchor="incomplete.messages" title="Incomplete Messages">
1603   Request messages that are prematurely terminated, possibly due to a
1604   cancelled connection or a server-imposed time-out exception, &MUST;
1605   result in closure of the connection; sending an HTTP/1.1 error response
1606   prior to closing the connection is &OPTIONAL;.
1609   Response messages that are prematurely terminated, usually by closure
1610   of the connection prior to receiving the expected number of octets or by
1611   failure to decode a transfer-encoded message-body, &MUST; be recorded
1612   as incomplete.  A response that terminates in the middle of the header
1613   block (before the empty line is received) cannot be assumed to convey the
1614   full semantics of the response and &MUST; be treated as an error.
1617   A message-body that uses the chunked transfer encoding is
1618   incomplete if the zero-sized chunk that terminates the encoding has not
1619   been received.  A message that uses a valid Content-Length is incomplete
1620   if the size of the message-body received (in octets) is less than the
1621   value given by Content-Length.  A response that has neither chunked
1622   transfer encoding nor Content-Length is terminated by closure of the
1623   connection, and thus is considered complete regardless of the number of
1624   message-body octets received, provided that the header block was received
1625   intact.
1628   A user agent &MUST-NOT; render an incomplete response message-body as if
1629   it were complete (i.e., some indication must be given to the user that an
1630   error occurred).  Cache requirements for incomplete responses are defined
1631   in &cache-incomplete;.
1634   A server &MUST; read the entire request message-body or close
1635   the connection after sending its response, since otherwise the
1636   remaining data on a persistent connection would be misinterpreted
1637   as the next request.  Likewise,
1638   a client &MUST; read the entire response message-body if it intends
1639   to reuse the same connection for a subsequent request.  Pipelining
1640   multiple requests on a connection is described in <xref target="pipelining"/>.
1644<section title="General Header Fields" anchor="general.header.fields">
1645  <x:anchor-alias value="general-header"/>
1647   There are a few header fields which have general applicability for
1648   both request and response messages, but which do not apply to the
1649   payload being transferred. These header fields apply only to the
1650   message being transmitted.
1652<texttable align="left">
1653  <ttcol>Header Field Name</ttcol>
1654  <ttcol>Defined in...</ttcol>
1656  <c>Connection</c> <c><xref target="header.connection"/></c>
1657  <c>Date</c> <c><xref target=""/></c>
1658  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1659  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1660  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1661  <c>Via</c> <c><xref target="header.via"/></c>
1666<section title="Request" anchor="request">
1667  <x:anchor-alias value="Request"/>
1669   A request message from a client to a server begins with a
1670   Request-Line, followed by zero or more header fields, an empty
1671   line signifying the end of the header block, and an optional
1672   message body.
1674<!--                 Host                      ; should be moved here eventually -->
1675<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1676  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1677                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1678                  <x:ref>CRLF</x:ref>
1679                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1682<section title="Request-Line" anchor="request-line">
1683  <x:anchor-alias value="Request-Line"/>
1685   The Request-Line begins with a method token, followed by a single
1686   space (SP), the request-target, another single space (SP), the
1687   protocol version, and ending with CRLF.
1689<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1690  <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>
1693<section title="Method" anchor="method">
1694  <x:anchor-alias value="Method"/>
1696   The Method token indicates the request method to be performed on the
1697   target resource. The request method is case-sensitive.
1699<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1700  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1704<section title="request-target" anchor="request-target">
1705  <x:anchor-alias value="request-target"/>
1707   The request-target identifies the target resource upon which to apply
1708   the request.  In most cases, the user agent is provided a URI reference
1709   from which it determines an absolute URI for identifying the target
1710   resource.  When a request to the resource is initiated, all or part
1711   of that URI is used to construct the HTTP request-target.
1713<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1714  <x:ref>request-target</x:ref> = "*"
1715                 / <x:ref>absolute-URI</x:ref>
1716                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1717                 / <x:ref>authority</x:ref>
1720   The four options for request-target are dependent on the nature of the
1721   request.
1723<t><iref item="asterisk form (of request-target)"/>
1724   The asterisk "*" form of request-target, which &MUST-NOT; be used
1725   with any request method other than OPTIONS, means that the request
1726   applies to the server as a whole (the listening process) rather than
1727   to a specific named resource at that server.  For example,
1729<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1730OPTIONS * HTTP/1.1
1732<t><iref item="absolute-URI form (of request-target)"/>
1733   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1734   proxy. The proxy is requested to either forward the request or service it
1735   from a valid cache, and then return the response. Note that the proxy &MAY;
1736   forward the request on to another proxy or directly to the server
1737   specified by the absolute-URI. In order to avoid request loops, a
1738   proxy that forwards requests to other proxies &MUST; be able to
1739   recognize and exclude all of its own server names, including
1740   any aliases, local variations, and the numeric IP address. An example
1741   Request-Line would be:
1743<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1744GET HTTP/1.1
1747   To allow for transition to absolute-URIs in all requests in future
1748   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1749   form in requests, even though HTTP/1.1 clients will only generate
1750   them in requests to proxies.
1753   If a proxy receives a host name that is not a fully qualified domain
1754   name, it &MAY; add its domain to the host name it received. If a proxy
1755   receives a fully qualified domain name, the proxy &MUST-NOT; change
1756   the host name.
1758<t><iref item="authority form (of request-target)"/>
1759   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1761<t><iref item="origin form (of request-target)"/>
1762   The most common form of request-target is that used when making
1763   a request to an origin server ("origin form").
1764   In this case, the absolute path and query components of the URI
1765   &MUST; be transmitted as the request-target, and the authority component
1766   &MUST; be transmitted in a Host header field. For example, a client wishing
1767   to retrieve a representation of the resource, as identified above,
1768   directly from the origin server would open (or reuse) a TCP connection
1769   to port 80 of the host "" and send the lines:
1771<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1772GET /pub/WWW/TheProject.html HTTP/1.1
1776   followed by the remainder of the Request. Note that the origin form
1777   of request-target always starts with an absolute path; if the target
1778   resource's URI path is empty, then an absolute path of "/" &MUST; be
1779   provided in the request-target.
1782   If a proxy receives an OPTIONS request with an absolute-URI form of
1783   request-target in which the URI has an empty path and no query component,
1784   then the last proxy on the request chain &MUST; use a request-target
1785   of "*" when it forwards the request to the indicated origin server.
1788   For example, the request
1789</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1793  would be forwarded by the final proxy as
1794</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1795OPTIONS * HTTP/1.1
1799   after connecting to port 8001 of host "".
1803   The request-target is transmitted in the format specified in
1804   <xref target="http.uri"/>. If the request-target is percent-encoded
1805   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1806   &MUST; decode the request-target in order to
1807   properly interpret the request. Servers &SHOULD; respond to invalid
1808   request-targets with an appropriate status code.
1811   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1812   received request-target when forwarding it to the next inbound server,
1813   except as noted above to replace a null path-absolute with "/" or "*".
1816  <t>
1817    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1818    meaning of the request when the origin server is improperly using
1819    a non-reserved URI character for a reserved purpose.  Implementors
1820    need to be aware that some pre-HTTP/1.1 proxies have been known to
1821    rewrite the request-target.
1822  </t>
1825   HTTP does not place a pre-defined limit on the length of a request-target.
1826   A server &MUST; be prepared to receive URIs of unbounded length and
1827   respond with the 414 (URI Too Long) status code if the received
1828   request-target would be longer than the server wishes to handle
1829   (see &status-414;).
1832   Various ad-hoc limitations on request-target length are found in practice.
1833   It is &RECOMMENDED; that all HTTP senders and recipients support
1834   request-target lengths of 8000 or more octets.
1837  <t>
1838    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1839    are not part of the request-target and thus will not be transmitted
1840    in an HTTP request.
1841  </t>
1846<section title="The Resource Identified by a Request" anchor="">
1848   The exact resource identified by an Internet request is determined by
1849   examining both the request-target and the Host header field.
1852   An origin server that does not allow resources to differ by the
1853   requested host &MAY; ignore the Host header field value when
1854   determining the resource identified by an HTTP/1.1 request. (But see
1855   <xref target=""/>
1856   for other requirements on Host support in HTTP/1.1.)
1859   An origin server that does differentiate resources based on the host
1860   requested (sometimes referred to as virtual hosts or vanity host
1861   names) &MUST; use the following rules for determining the requested
1862   resource on an HTTP/1.1 request:
1863  <list style="numbers">
1864    <t>If request-target is an absolute-URI, the host is part of the
1865     request-target. Any Host header field value in the request &MUST; be
1866     ignored.</t>
1867    <t>If the request-target is not an absolute-URI, and the request includes
1868     a Host header field, the host is determined by the Host header
1869     field value.</t>
1870    <t>If the host as determined by rule 1 or 2 is not a valid host on
1871     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1872  </list>
1875   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1876   attempt to use heuristics (e.g., examination of the URI path for
1877   something unique to a particular host) in order to determine what
1878   exact resource is being requested.
1882<section title="Effective Request URI" anchor="effective.request.uri">
1883  <iref primary="true" item="effective request URI"/>
1884  <iref primary="true" item="target resource"/>
1886   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1887   for the target resource; instead, the URI needs to be inferred from the
1888   request-target, Host header field, and connection context. The result of
1889   this process is called the "effective request URI".  The "target resource"
1890   is the resource identified by the effective request URI.
1893   If the request-target is an absolute-URI, then the effective request URI is
1894   the request-target.
1897   If the request-target uses the path-absolute form or the asterisk form,
1898   and the Host header field is present, then the effective request URI is
1899   constructed by concatenating
1902  <list style="symbols">
1903    <t>
1904      the scheme name: "http" if the request was received over an insecure
1905      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1906      connection,
1907    </t>
1908    <t>
1909      the octet sequence "://",
1910    </t>
1911    <t>
1912      the authority component, as specified in the Host header field
1913      (<xref target=""/>), and
1914    </t>
1915    <t>
1916      the request-target obtained from the Request-Line, unless the
1917      request-target is just the asterisk "*".
1918    </t>
1919  </list>
1922   If the request-target uses the path-absolute form or the asterisk form,
1923   and the Host header field is not present, then the effective request URI is
1924   undefined.
1927   Otherwise, when request-target uses the authority form, the effective
1928   request URI is undefined.
1932   Example 1: the effective request URI for the message
1934<artwork type="example" x:indent-with="  ">
1935GET /pub/WWW/TheProject.html HTTP/1.1
1939  (received over an insecure TCP connection) is "http", plus "://", plus the
1940  authority component "", plus the request-target
1941  "/pub/WWW/TheProject.html", thus
1942  "".
1947   Example 2: the effective request URI for the message
1949<artwork type="example" x:indent-with="  ">
1950OPTIONS * HTTP/1.1
1954  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1955  authority component "", thus "".
1959   Effective request URIs are compared using the rules described in
1960   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1961   be treated as equivalent to an absolute path of "/".
1968<section title="Response" anchor="response">
1969  <x:anchor-alias value="Response"/>
1971   After receiving and interpreting a request message, a server responds
1972   with an HTTP response message.
1974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1975  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1976                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1977                  <x:ref>CRLF</x:ref>
1978                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1981<section title="Status-Line" anchor="status-line">
1982  <x:anchor-alias value="Status-Line"/>
1984   The first line of a Response message is the Status-Line, consisting
1985   of the protocol version, a space (SP), the status code, another space,
1986   a possibly-empty textual phrase describing the status code, and
1987   ending with CRLF.
1989<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1990  <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>
1993<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1994  <x:anchor-alias value="Reason-Phrase"/>
1995  <x:anchor-alias value="Status-Code"/>
1997   The Status-Code element is a 3-digit integer result code of the
1998   attempt to understand and satisfy the request. These codes are fully
1999   defined in &status-codes;.  The Reason Phrase exists for the sole
2000   purpose of providing a textual description associated with the numeric
2001   status code, out of deference to earlier Internet application protocols
2002   that were more frequently used with interactive text clients.
2003   A client &SHOULD; ignore the content of the Reason Phrase.
2006   The first digit of the Status-Code defines the class of response. The
2007   last two digits do not have any categorization role. There are 5
2008   values for the first digit:
2009  <list style="symbols">
2010    <t>
2011      1xx: Informational - Request received, continuing process
2012    </t>
2013    <t>
2014      2xx: Success - The action was successfully received,
2015        understood, and accepted
2016    </t>
2017    <t>
2018      3xx: Redirection - Further action must be taken in order to
2019        complete the request
2020    </t>
2021    <t>
2022      4xx: Client Error - The request contains bad syntax or cannot
2023        be fulfilled
2024    </t>
2025    <t>
2026      5xx: Server Error - The server failed to fulfill an apparently
2027        valid request
2028    </t>
2029  </list>
2031<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
2032  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
2033  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
2041<section title="Protocol Parameters" anchor="protocol.parameters">
2043<section title="Date/Time Formats: Full Date" anchor="">
2044  <x:anchor-alias value="HTTP-date"/>
2046   HTTP applications have historically allowed three different formats
2047   for date/time stamps. However, the preferred format is a fixed-length subset
2048   of that defined by <xref target="RFC1123"/>:
2050<figure><artwork type="example" x:indent-with="  ">
2051Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2054   The other formats are described here only for compatibility with obsolete
2055   implementations.
2057<figure><artwork type="example" x:indent-with="  ">
2058Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2059Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2062   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2063   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2064   only generate the RFC 1123 format for representing HTTP-date values
2065   in header fields.
2068   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2069   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2070   equal to UTC (Coordinated Universal Time). This is indicated in the
2071   first two formats by the inclusion of "GMT" as the three-letter
2072   abbreviation for time zone, and &MUST; be assumed when reading the
2073   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2074   additional whitespace beyond that specifically included as SP in the
2075   grammar.
2077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2078  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2080<t anchor="">
2081  <x:anchor-alias value="rfc1123-date"/>
2082  <x:anchor-alias value="time-of-day"/>
2083  <x:anchor-alias value="hour"/>
2084  <x:anchor-alias value="minute"/>
2085  <x:anchor-alias value="second"/>
2086  <x:anchor-alias value="day-name"/>
2087  <x:anchor-alias value="day"/>
2088  <x:anchor-alias value="month"/>
2089  <x:anchor-alias value="year"/>
2090  <x:anchor-alias value="GMT"/>
2091  Preferred format:
2093<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"/>
2094  <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>
2095  ; fixed length subset of the format defined in
2096  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2098  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2099               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2100               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2101               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2102               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2103               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2104               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2106  <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>
2107               ; e.g., 02 Jun 1982
2109  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2110  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2111               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2112               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2113               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2114               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2115               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2116               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2117               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2118               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2119               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2120               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2121               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2122  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2124  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2126  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2127                 ; 00:00:00 - 23:59:59
2129  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2130  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2131  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2134  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2135  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2136  same as those defined for the RFC 5322 constructs
2137  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2139<t anchor="">
2140  <x:anchor-alias value="obs-date"/>
2141  <x:anchor-alias value="rfc850-date"/>
2142  <x:anchor-alias value="asctime-date"/>
2143  <x:anchor-alias value="date1"/>
2144  <x:anchor-alias value="date2"/>
2145  <x:anchor-alias value="date3"/>
2146  <x:anchor-alias value="rfc1123-date"/>
2147  <x:anchor-alias value="day-name-l"/>
2148  Obsolete formats:
2150<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2151  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2153<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2154  <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>
2155  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2156                 ; day-month-year (e.g., 02-Jun-82)
2158  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2159         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2160         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2161         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2162         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2163         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2164         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2167  <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>
2168  <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> ))
2169                 ; month day (e.g., Jun  2)
2172  <t>
2173    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2174    accepting date values that might have been sent by non-HTTP
2175    applications, as is sometimes the case when retrieving or posting
2176    messages via proxies/gateways to SMTP or NNTP.
2177  </t>
2180  <t>
2181    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2182    to their usage within the protocol stream. Clients and servers are
2183    not required to use these formats for user presentation, request
2184    logging, etc.
2185  </t>
2189<section title="Transfer Codings" anchor="transfer.codings">
2190  <x:anchor-alias value="transfer-coding"/>
2191  <x:anchor-alias value="transfer-extension"/>
2193   Transfer-coding values are used to indicate an encoding
2194   transformation that has been, can be, or might need to be applied to a
2195   payload body in order to ensure "safe transport" through the network.
2196   This differs from a content coding in that the transfer-coding is a
2197   property of the message rather than a property of the representation
2198   that is being transferred.
2200<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2201  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2202                          / "compress" ; <xref target="compress.coding"/>
2203                          / "deflate" ; <xref target="deflate.coding"/>
2204                          / "gzip" ; <xref target="gzip.coding"/>
2205                          / <x:ref>transfer-extension</x:ref>
2206  <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> )
2208<t anchor="rule.parameter">
2209  <x:anchor-alias value="attribute"/>
2210  <x:anchor-alias value="transfer-parameter"/>
2211  <x:anchor-alias value="value"/>
2212   Parameters are in the form of attribute/value pairs.
2214<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"/>
2215  <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>
2216  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2217  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2220   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2221   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2222   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2225   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2226   MIME, which were designed to enable safe transport of binary data over a
2227   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2228   However, safe transport
2229   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2230   the only unsafe characteristic of message-bodies is the difficulty in
2231   determining the exact message body length (<xref target="message.body"/>),
2232   or the desire to encrypt data over a shared transport.
2235   A server that receives a request message with a transfer-coding it does
2236   not understand &SHOULD; respond with 501 (Not Implemented) and then
2237   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2238   client.
2241<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2242  <iref item="chunked (Coding Format)"/>
2243  <iref item="Coding Format" subitem="chunked"/>
2244  <x:anchor-alias value="chunk"/>
2245  <x:anchor-alias value="Chunked-Body"/>
2246  <x:anchor-alias value="chunk-data"/>
2247  <x:anchor-alias value="chunk-ext"/>
2248  <x:anchor-alias value="chunk-ext-name"/>
2249  <x:anchor-alias value="chunk-ext-val"/>
2250  <x:anchor-alias value="chunk-size"/>
2251  <x:anchor-alias value="last-chunk"/>
2252  <x:anchor-alias value="trailer-part"/>
2253  <x:anchor-alias value="quoted-str-nf"/>
2254  <x:anchor-alias value="qdtext-nf"/>
2256   The chunked encoding modifies the body of a message in order to
2257   transfer it as a series of chunks, each with its own size indicator,
2258   followed by an &OPTIONAL; trailer containing header fields. This
2259   allows dynamically produced content to be transferred along with the
2260   information necessary for the recipient to verify that it has
2261   received the full message.
2263<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"/>
2264  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2265                   <x:ref>last-chunk</x:ref>
2266                   <x:ref>trailer-part</x:ref>
2267                   <x:ref>CRLF</x:ref>
2269  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2270                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2271  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2272  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2274  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2275                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2276  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2277  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2278  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2279  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2281  <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>
2282                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2283  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2284                 ; <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>
2287   The chunk-size field is a string of hex digits indicating the size of
2288   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2289   zero, followed by the trailer, which is terminated by an empty line.
2292   The trailer allows the sender to include additional HTTP header
2293   fields at the end of the message. The Trailer header field can be
2294   used to indicate which header fields are included in a trailer (see
2295   <xref target="header.trailer"/>).
2298   A server using chunked transfer-coding in a response &MUST-NOT; use the
2299   trailer for any header fields unless at least one of the following is
2300   true:
2301  <list style="numbers">
2302    <t>the request included a TE header field that indicates "trailers" is
2303     acceptable in the transfer-coding of the  response, as described in
2304     <xref target="header.te"/>; or,</t>
2306    <t>the trailer fields consist entirely of optional metadata, and the
2307    recipient could use the message (in a manner acceptable to the server where
2308    the field originated) without receiving it. In other words, the server that
2309    generated the header (often but not always the origin server) is willing to
2310    accept the possibility that the trailer fields might be silently discarded
2311    along the path to the client.</t>
2312  </list>
2315   This requirement prevents an interoperability failure when the
2316   message is being received by an HTTP/1.1 (or later) proxy and
2317   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2318   compliance with the protocol would have necessitated a possibly
2319   infinite buffer on the proxy.
2322   A process for decoding the "chunked" transfer-coding
2323   can be represented in pseudo-code as:
2325<figure><artwork type="code">
2326  length := 0
2327  read chunk-size, chunk-ext (if any) and CRLF
2328  while (chunk-size &gt; 0) {
2329     read chunk-data and CRLF
2330     append chunk-data to decoded-body
2331     length := length + chunk-size
2332     read chunk-size and CRLF
2333  }
2334  read header-field
2335  while (header-field not empty) {
2336     append header-field to existing header fields
2337     read header-field
2338  }
2339  Content-Length := length
2340  Remove "chunked" from Transfer-Encoding
2343   All HTTP/1.1 applications &MUST; be able to receive and decode the
2344   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2345   they do not understand.
2348   Since "chunked" is the only transfer-coding required to be understood
2349   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2350   on a persistent connection.  Whenever a transfer-coding is applied to
2351   a payload body in a request, the final transfer-coding applied &MUST;
2352   be "chunked".  If a transfer-coding is applied to a response payload
2353   body, then either the final transfer-coding applied &MUST; be "chunked"
2354   or the message &MUST; be terminated by closing the connection. When the
2355   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2356   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2357   be applied more than once in a message-body.
2361<section title="Compression Codings" anchor="compression.codings">
2363   The codings defined below can be used to compress the payload of a
2364   message.
2367   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2368   is not desirable and is discouraged for future encodings. Their
2369   use here is representative of historical practice, not good
2370   design.
2373   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2374   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2375   equivalent to "gzip" and "compress" respectively.
2378<section title="Compress Coding" anchor="compress.coding">
2379<iref item="compress (Coding Format)"/>
2380<iref item="Coding Format" subitem="compress"/>
2382   The "compress" format is produced by the common UNIX file compression
2383   program "compress". This format is an adaptive Lempel-Ziv-Welch
2384   coding (LZW).
2388<section title="Deflate Coding" anchor="deflate.coding">
2389<iref item="deflate (Coding Format)"/>
2390<iref item="Coding Format" subitem="deflate"/>
2392   The "deflate" format is defined as the "deflate" compression mechanism
2393   (described in <xref target="RFC1951"/>) used inside the "zlib"
2394   data format (<xref target="RFC1950"/>).
2397  <t>
2398    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2399    compressed data without the zlib wrapper.
2400   </t>
2404<section title="Gzip Coding" anchor="gzip.coding">
2405<iref item="gzip (Coding Format)"/>
2406<iref item="Coding Format" subitem="gzip"/>
2408   The "gzip" format is produced by the file compression program
2409   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2410   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2416<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2418   The HTTP Transfer Coding Registry defines the name space for the transfer
2419   coding names.
2422   Registrations &MUST; include the following fields:
2423   <list style="symbols">
2424     <t>Name</t>
2425     <t>Description</t>
2426     <t>Pointer to specification text</t>
2427   </list>
2430   Names of transfer codings &MUST-NOT; overlap with names of content codings
2431   (&content-codings;), unless the encoding transformation is identical (as it
2432   is the case for the compression codings defined in
2433   <xref target="compression.codings"/>).
2436   Values to be added to this name space require a specification
2437   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2438   conform to the purpose of transfer coding defined in this section.
2441   The registry itself is maintained at
2442   <eref target=""/>.
2447<section title="Product Tokens" anchor="product.tokens">
2448  <x:anchor-alias value="product"/>
2449  <x:anchor-alias value="product-version"/>
2451   Product tokens are used to allow communicating applications to
2452   identify themselves by software name and version. Most fields using
2453   product tokens also allow sub-products which form a significant part
2454   of the application to be listed, separated by whitespace. By
2455   convention, the products are listed in order of their significance
2456   for identifying the application.
2458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2459  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2460  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2463   Examples:
2465<figure><artwork type="example">
2466  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2467  Server: Apache/0.8.4
2470   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2471   used for advertising or other non-essential information. Although any
2472   token octet &MAY; appear in a product-version, this token &SHOULD;
2473   only be used for a version identifier (i.e., successive versions of
2474   the same product &SHOULD; only differ in the product-version portion of
2475   the product value).
2479<section title="Quality Values" anchor="quality.values">
2480  <x:anchor-alias value="qvalue"/>
2482   Both transfer codings (TE request header field, <xref target="header.te"/>)
2483   and content negotiation (&content.negotiation;) use short "floating point"
2484   numbers to indicate the relative importance ("weight") of various
2485   negotiable parameters.  A weight is normalized to a real number in
2486   the range 0 through 1, where 0 is the minimum and 1 the maximum
2487   value. If a parameter has a quality value of 0, then content with
2488   this parameter is "not acceptable" for the client. HTTP/1.1
2489   applications &MUST-NOT; generate more than three digits after the
2490   decimal point. User configuration of these values &SHOULD; also be
2491   limited in this fashion.
2493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2494  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2495                 / ( "1" [ "." 0*3("0") ] )
2498  <t>
2499     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2500     relative degradation in desired quality.
2501  </t>
2507<section title="Connections" anchor="connections">
2509<section title="Persistent Connections" anchor="persistent.connections">
2511<section title="Purpose" anchor="persistent.purpose">
2513   Prior to persistent connections, a separate TCP connection was
2514   established for each request, increasing the load on HTTP servers
2515   and causing congestion on the Internet. The use of inline images and
2516   other associated data often requires a client to make multiple
2517   requests of the same server in a short amount of time. Analysis of
2518   these performance problems and results from a prototype
2519   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2520   measurements of actual HTTP/1.1 implementations show good
2521   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2522   T/TCP <xref target="Tou1998"/>.
2525   Persistent HTTP connections have a number of advantages:
2526  <list style="symbols">
2527      <t>
2528        By opening and closing fewer TCP connections, CPU time is saved
2529        in routers and hosts (clients, servers, proxies, gateways,
2530        tunnels, or caches), and memory used for TCP protocol control
2531        blocks can be saved in hosts.
2532      </t>
2533      <t>
2534        HTTP requests and responses can be pipelined on a connection.
2535        Pipelining allows a client to make multiple requests without
2536        waiting for each response, allowing a single TCP connection to
2537        be used much more efficiently, with much lower elapsed time.
2538      </t>
2539      <t>
2540        Network congestion is reduced by reducing the number of packets
2541        caused by TCP opens, and by allowing TCP sufficient time to
2542        determine the congestion state of the network.
2543      </t>
2544      <t>
2545        Latency on subsequent requests is reduced since there is no time
2546        spent in TCP's connection opening handshake.
2547      </t>
2548      <t>
2549        HTTP can evolve more gracefully, since errors can be reported
2550        without the penalty of closing the TCP connection. Clients using
2551        future versions of HTTP might optimistically try a new feature,
2552        but if communicating with an older server, retry with old
2553        semantics after an error is reported.
2554      </t>
2555    </list>
2558   HTTP implementations &SHOULD; implement persistent connections.
2562<section title="Overall Operation" anchor="persistent.overall">
2564   A significant difference between HTTP/1.1 and earlier versions of
2565   HTTP is that persistent connections are the default behavior of any
2566   HTTP connection. That is, unless otherwise indicated, the client
2567   &SHOULD; assume that the server will maintain a persistent connection,
2568   even after error responses from the server.
2571   Persistent connections provide a mechanism by which a client and a
2572   server can signal the close of a TCP connection. This signaling takes
2573   place using the Connection header field (<xref target="header.connection"/>). Once a close
2574   has been signaled, the client &MUST-NOT; send any more requests on that
2575   connection.
2578<section title="Negotiation" anchor="persistent.negotiation">
2580   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2581   maintain a persistent connection unless a Connection header field including
2582   the connection-token "close" was sent in the request. If the server
2583   chooses to close the connection immediately after sending the
2584   response, it &SHOULD; send a Connection header field including the
2585   connection-token "close".
2588   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2589   decide to keep it open based on whether the response from a server
2590   contains a Connection header field with the connection-token close. In case
2591   the client does not want to maintain a connection for more than that
2592   request, it &SHOULD; send a Connection header field including the
2593   connection-token close.
2596   If either the client or the server sends the close token in the
2597   Connection header field, that request becomes the last one for the
2598   connection.
2601   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2602   maintained for HTTP versions less than 1.1 unless it is explicitly
2603   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2604   compatibility with HTTP/1.0 clients.
2607   In order to remain persistent, all messages on the connection &MUST;
2608   have a self-defined message length (i.e., one not defined by closure
2609   of the connection), as described in <xref target="message.body"/>.
2613<section title="Pipelining" anchor="pipelining">
2615   A client that supports persistent connections &MAY; "pipeline" its
2616   requests (i.e., send multiple requests without waiting for each
2617   response). A server &MUST; send its responses to those requests in the
2618   same order that the requests were received.
2621   Clients which assume persistent connections and pipeline immediately
2622   after connection establishment &SHOULD; be prepared to retry their
2623   connection if the first pipelined attempt fails. If a client does
2624   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2625   persistent. Clients &MUST; also be prepared to resend their requests if
2626   the server closes the connection before sending all of the
2627   corresponding responses.
2630   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2631   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2632   premature termination of the transport connection could lead to
2633   indeterminate results. A client wishing to send a non-idempotent
2634   request &SHOULD; wait to send that request until it has received the
2635   response status line for the previous request.
2640<section title="Proxy Servers" anchor="persistent.proxy">
2642   It is especially important that proxies correctly implement the
2643   properties of the Connection header field as specified in <xref target="header.connection"/>.
2646   The proxy server &MUST; signal persistent connections separately with
2647   its clients and the origin servers (or other proxy servers) that it
2648   connects to. Each persistent connection applies to only one transport
2649   link.
2652   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2653   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2654   for information and discussion of the problems with the Keep-Alive header field
2655   implemented by many HTTP/1.0 clients).
2658<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2660  <cref anchor="TODO-end-to-end" source="jre">
2661    Restored from <eref target=""/>.
2662    See also <eref target=""/>.
2663  </cref>
2666   For the purpose of defining the behavior of caches and non-caching
2667   proxies, we divide HTTP header fields into two categories:
2668  <list style="symbols">
2669      <t>End-to-end header fields, which are  transmitted to the ultimate
2670        recipient of a request or response. End-to-end header fields in
2671        responses MUST be stored as part of a cache entry and &MUST; be
2672        transmitted in any response formed from a cache entry.</t>
2674      <t>Hop-by-hop header fields, which are meaningful only for a single
2675        transport-level connection, and are not stored by caches or
2676        forwarded by proxies.</t>
2677  </list>
2680   The following HTTP/1.1 header fields are hop-by-hop header fields:
2681  <list style="symbols">
2682      <t>Connection</t>
2683      <t>Keep-Alive</t>
2684      <t>Proxy-Authenticate</t>
2685      <t>Proxy-Authorization</t>
2686      <t>TE</t>
2687      <t>Trailer</t>
2688      <t>Transfer-Encoding</t>
2689      <t>Upgrade</t>
2690  </list>
2693   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2696   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2697   (<xref target="header.connection"/>).
2701<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2703  <cref anchor="TODO-non-mod-headers" source="jre">
2704    Restored from <eref target=""/>.
2705    See also <eref target=""/>.
2706  </cref>
2709   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2710   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2711   modify an end-to-end header field unless the definition of that header field requires
2712   or specifically allows that.
2715   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2716   request or response, and it &MUST-NOT; add any of these fields if not
2717   already present:
2718  <list style="symbols">
2719    <t>Allow</t>
2720    <t>Content-Location</t>
2721    <t>Content-MD5</t>
2722    <t>ETag</t>
2723    <t>Last-Modified</t>
2724    <t>Server</t>
2725  </list>
2728   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2729   response:
2730  <list style="symbols">
2731    <t>Expires</t>
2732  </list>
2735   but it &MAY; add any of these fields if not already present. If an
2736   Expires header field is added, it &MUST; be given a field-value identical to
2737   that of the Date header field in that response.
2740   A proxy &MUST-NOT; modify or add any of the following fields in a
2741   message that contains the no-transform cache-control directive, or in
2742   any request:
2743  <list style="symbols">
2744    <t>Content-Encoding</t>
2745    <t>Content-Range</t>
2746    <t>Content-Type</t>
2747  </list>
2750   A transforming proxy &MAY; modify or add these fields to a message
2751   that does not include no-transform, but if it does so, it &MUST; add a
2752   Warning 214 (Transformation applied) if one does not already appear
2753   in the message (see &header-warning;).
2756  <t>
2757    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2758    cause authentication failures if stronger authentication
2759    mechanisms are introduced in later versions of HTTP. Such
2760    authentication mechanisms &MAY; rely on the values of header fields
2761    not listed here.
2762  </t>
2765   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2766   though it &MAY; change the message-body through application or removal
2767   of a transfer-coding (<xref target="transfer.codings"/>).
2773<section title="Practical Considerations" anchor="persistent.practical">
2775   Servers will usually have some time-out value beyond which they will
2776   no longer maintain an inactive connection. Proxy servers might make
2777   this a higher value since it is likely that the client will be making
2778   more connections through the same server. The use of persistent
2779   connections places no requirements on the length (or existence) of
2780   this time-out for either the client or the server.
2783   When a client or server wishes to time-out it &SHOULD; issue a graceful
2784   close on the transport connection. Clients and servers &SHOULD; both
2785   constantly watch for the other side of the transport close, and
2786   respond to it as appropriate. If a client or server does not detect
2787   the other side's close promptly it could cause unnecessary resource
2788   drain on the network.
2791   A client, server, or proxy &MAY; close the transport connection at any
2792   time. For example, a client might have started to send a new request
2793   at the same time that the server has decided to close the "idle"
2794   connection. From the server's point of view, the connection is being
2795   closed while it was idle, but from the client's point of view, a
2796   request is in progress.
2799   This means that clients, servers, and proxies &MUST; be able to recover
2800   from asynchronous close events. Client software &SHOULD; reopen the
2801   transport connection and retransmit the aborted sequence of requests
2802   without user interaction so long as the request sequence is
2803   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2804   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2805   human operator the choice of retrying the request(s). Confirmation by
2806   user-agent software with semantic understanding of the application
2807   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2808   be repeated if the second sequence of requests fails.
2811   Servers &SHOULD; always respond to at least one request per connection,
2812   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2813   middle of transmitting a response, unless a network or client failure
2814   is suspected.
2817   Clients (including proxies) &SHOULD; limit the number of simultaneous
2818   connections that they maintain to a given server (including proxies).
2821   Previous revisions of HTTP gave a specific number of connections as a
2822   ceiling, but this was found to be impractical for many applications. As a
2823   result, this specification does not mandate a particular maximum number of
2824   connections, but instead encourages clients to be conservative when opening
2825   multiple connections.
2828   In particular, while using multiple connections avoids the "head-of-line
2829   blocking" problem (whereby a request that takes significant server-side
2830   processing and/or has a large payload can block subsequent requests on the
2831   same connection), each connection used consumes server resources (sometimes
2832   significantly), and furthermore using multiple connections can cause
2833   undesirable side effects in congested networks.
2836   Note that servers might reject traffic that they deem abusive, including an
2837   excessive number of connections from a client.
2842<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2844<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2846   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2847   flow control mechanisms to resolve temporary overloads, rather than
2848   terminating connections with the expectation that clients will retry.
2849   The latter technique can exacerbate network congestion.
2853<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2855   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2856   the network connection for an error status code while it is transmitting
2857   the request. If the client sees an error status code, it &SHOULD;
2858   immediately cease transmitting the body. If the body is being sent
2859   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2860   empty trailer &MAY; be used to prematurely mark the end of the message.
2861   If the body was preceded by a Content-Length header field, the client &MUST;
2862   close the connection.
2866<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2868   The purpose of the 100 (Continue) status code (see &status-100;) is to
2869   allow a client that is sending a request message with a request body
2870   to determine if the origin server is willing to accept the request
2871   (based on the request header fields) before the client sends the request
2872   body. In some cases, it might either be inappropriate or highly
2873   inefficient for the client to send the body if the server will reject
2874   the message without looking at the body.
2877   Requirements for HTTP/1.1 clients:
2878  <list style="symbols">
2879    <t>
2880        If a client will wait for a 100 (Continue) response before
2881        sending the request body, it &MUST; send an Expect header
2882        field (&header-expect;) with the "100-continue" expectation.
2883    </t>
2884    <t>
2885        A client &MUST-NOT; send an Expect header field (&header-expect;)
2886        with the "100-continue" expectation if it does not intend
2887        to send a request body.
2888    </t>
2889  </list>
2892   Because of the presence of older implementations, the protocol allows
2893   ambiguous situations in which a client might send "Expect: 100-continue"
2894   without receiving either a 417 (Expectation Failed)
2895   or a 100 (Continue) status code. Therefore, when a client sends this
2896   header field to an origin server (possibly via a proxy) from which it
2897   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2898   wait for an indefinite period before sending the request body.
2901   Requirements for HTTP/1.1 origin servers:
2902  <list style="symbols">
2903    <t> Upon receiving a request which includes an Expect header
2904        field with the "100-continue" expectation, an origin server &MUST;
2905        either respond with 100 (Continue) status code and continue to read
2906        from the input stream, or respond with a final status code. The
2907        origin server &MUST-NOT; wait for the request body before sending
2908        the 100 (Continue) response. If it responds with a final status
2909        code, it &MAY; close the transport connection or it &MAY; continue
2910        to read and discard the rest of the request.  It &MUST-NOT;
2911        perform the request method if it returns a final status code.
2912    </t>
2913    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2914        the request message does not include an Expect header
2915        field with the "100-continue" expectation, and &MUST-NOT; send a
2916        100 (Continue) response if such a request comes from an HTTP/1.0
2917        (or earlier) client. There is an exception to this rule: for
2918        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2919        status code in response to an HTTP/1.1 PUT or POST request that does
2920        not include an Expect header field with the "100-continue"
2921        expectation. This exception, the purpose of which is
2922        to minimize any client processing delays associated with an
2923        undeclared wait for 100 (Continue) status code, applies only to
2924        HTTP/1.1 requests, and not to requests with any other HTTP-version
2925        value.
2926    </t>
2927    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2928        already received some or all of the request body for the
2929        corresponding request.
2930    </t>
2931    <t> An origin server that sends a 100 (Continue) response &MUST;
2932    ultimately send a final status code, once the request body is
2933        received and processed, unless it terminates the transport
2934        connection prematurely.
2935    </t>
2936    <t> If an origin server receives a request that does not include an
2937        Expect header field with the "100-continue" expectation,
2938        the request includes a request body, and the server responds
2939        with a final status code before reading the entire request body
2940        from the transport connection, then the server &SHOULD-NOT;  close
2941        the transport connection until it has read the entire request,
2942        or until the client closes the connection. Otherwise, the client
2943        might not reliably receive the response message. However, this
2944        requirement is not be construed as preventing a server from
2945        defending itself against denial-of-service attacks, or from
2946        badly broken client implementations.
2947      </t>
2948    </list>
2951   Requirements for HTTP/1.1 proxies:
2952  <list style="symbols">
2953    <t> If a proxy receives a request that includes an Expect header
2954        field with the "100-continue" expectation, and the proxy
2955        either knows that the next-hop server complies with HTTP/1.1 or
2956        higher, or does not know the HTTP version of the next-hop
2957        server, it &MUST; forward the request, including the Expect header
2958        field.
2959    </t>
2960    <t> If the proxy knows that the version of the next-hop server is
2961        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2962        respond with a 417 (Expectation Failed) status code.
2963    </t>
2964    <t> Proxies &SHOULD; maintain a record of the HTTP version
2965        numbers received from recently-referenced next-hop servers.
2966    </t>
2967    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2968        request message was received from an HTTP/1.0 (or earlier)
2969        client and did not include an Expect header field with
2970        the "100-continue" expectation. This requirement overrides the
2971        general rule for forwarding of 1xx responses (see &status-1xx;).
2972    </t>
2973  </list>
2977<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2979   If an HTTP/1.1 client sends a request which includes a request body,
2980   but which does not include an Expect header field with the
2981   "100-continue" expectation, and if the client is not directly
2982   connected to an HTTP/1.1 origin server, and if the client sees the
2983   connection close before receiving a status line from the server, the
2984   client &SHOULD; retry the request.  If the client does retry this
2985   request, it &MAY; use the following "binary exponential backoff"
2986   algorithm to be assured of obtaining a reliable response:
2987  <list style="numbers">
2988    <t>
2989      Initiate a new connection to the server
2990    </t>
2991    <t>
2992      Transmit the request-line, header fields, and the CRLF that
2993      indicates the end of header fields.
2994    </t>
2995    <t>
2996      Initialize a variable R to the estimated round-trip time to the
2997         server (e.g., based on the time it took to establish the
2998         connection), or to a constant value of 5 seconds if the round-trip
2999         time is not available.
3000    </t>
3001    <t>
3002       Compute T = R * (2**N), where N is the number of previous
3003         retries of this request.
3004    </t>
3005    <t>
3006       Wait either for an error response from the server, or for T
3007         seconds (whichever comes first)
3008    </t>
3009    <t>
3010       If no error response is received, after T seconds transmit the
3011         body of the request.
3012    </t>
3013    <t>
3014       If client sees that the connection is closed prematurely,
3015         repeat from step 1 until the request is accepted, an error
3016         response is received, or the user becomes impatient and
3017         terminates the retry process.
3018    </t>
3019  </list>
3022   If at any point an error status code is received, the client
3023  <list style="symbols">
3024      <t>&SHOULD-NOT;  continue and</t>
3026      <t>&SHOULD; close the connection if it has not completed sending the
3027        request message.</t>
3028    </list>
3035<section title="Miscellaneous notes that might disappear" anchor="misc">
3036<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3038   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3042<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3044   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3048<section title="Interception of HTTP for access control" anchor="http.intercept">
3050   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3054<section title="Use of HTTP by other protocols" anchor="http.others">
3056   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3057   Extensions of HTTP like WebDAV.</cref>
3061<section title="Use of HTTP by media type specification" anchor="">
3063   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3068<section title="Header Field Definitions" anchor="header.field.definitions">
3070   This section defines the syntax and semantics of HTTP header fields
3071   related to message framing and transport protocols.
3074<section title="Connection" anchor="header.connection">
3075  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3076  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3077  <x:anchor-alias value="Connection"/>
3078  <x:anchor-alias value="connection-token"/>
3080   The "Connection" header field allows the sender to specify
3081   options that are desired only for that particular connection.
3082   Such connection options &MUST; be removed or replaced before the
3083   message can be forwarded downstream by a proxy or gateway.
3084   This mechanism also allows the sender to indicate which HTTP
3085   header fields used in the message are only intended for the
3086   immediate recipient ("hop-by-hop"), as opposed to all recipients
3087   on the chain ("end-to-end"), enabling the message to be
3088   self-descriptive and allowing future connection-specific extensions
3089   to be deployed in HTTP without fear that they will be blindly
3090   forwarded by previously deployed intermediaries.
3093   The Connection header field's value has the following grammar:
3095<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3096  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3097  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3100   A proxy or gateway &MUST; parse a received Connection
3101   header field before a message is forwarded and, for each
3102   connection-token in this field, remove any header field(s) from
3103   the message with the same name as the connection-token, and then
3104   remove the Connection header field itself or replace it with the
3105   sender's own connection options for the forwarded message.
3108   A sender &MUST-NOT; include field-names in the Connection header
3109   field-value for fields that are defined as expressing constraints
3110   for all recipients in the request or response chain, such as the
3111   Cache-Control header field (&header-cache-control;).
3114   The connection options do not have to correspond to a header field
3115   present in the message, since a connection-specific header field
3116   might not be needed if there are no parameters associated with that
3117   connection option.  Recipients that trigger certain connection
3118   behavior based on the presence of connection options &MUST; do so
3119   based on the presence of the connection-token rather than only the
3120   presence of the optional header field.  In other words, if the
3121   connection option is received as a header field but not indicated
3122   within the Connection field-value, then the recipient &MUST; ignore
3123   the connection-specific header field because it has likely been
3124   forwarded by an intermediary that is only partially compliant.
3127   When defining new connection options, specifications ought to
3128   carefully consider existing deployed header fields and ensure
3129   that the new connection-token does not share the same name as
3130   an unrelated header field that might already be deployed.
3131   Defining a new connection-token essentially reserves that potential
3132   field-name for carrying additional information related to the
3133   connection option, since it would be unwise for senders to use
3134   that field-name for anything else.
3137   HTTP/1.1 defines the "close" connection option for the sender to
3138   signal that the connection will be closed after completion of the
3139   response. For example,
3141<figure><artwork type="example">
3142  Connection: close
3145   in either the request or the response header fields indicates that
3146   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3147   after the current request/response is complete.
3150   An HTTP/1.1 client that does not support persistent connections &MUST;
3151   include the "close" connection option in every request message.
3154   An HTTP/1.1 server that does not support persistent connections &MUST;
3155   include the "close" connection option in every response message that
3156   does not have a 1xx (Informational) status code.
3160<section title="Content-Length" anchor="header.content-length">
3161  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3162  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3163  <x:anchor-alias value="Content-Length"/>
3165   The "Content-Length" header field indicates the size of the
3166   message-body, in decimal number of octets, for any message other than
3167   a response to a HEAD request or a response with a status code of 304.
3168   In the case of a response to a HEAD request, Content-Length indicates
3169   the size of the payload body (not including any potential transfer-coding)
3170   that would have been sent had the request been a GET.
3171   In the case of a 304 (Not Modified) response to a GET request,
3172   Content-Length indicates the size of the payload body (not including
3173   any potential transfer-coding) that would have been sent in a 200 (OK)
3174   response.
3176<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3177  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3180   An example is
3182<figure><artwork type="example">
3183  Content-Length: 3495
3186   Implementations &SHOULD; use this field to indicate the message-body
3187   length when no transfer-coding is being applied and the
3188   payload's body length can be determined prior to being transferred.
3189   <xref target="message.body"/> describes how recipients determine the length
3190   of a message-body.
3193   Any Content-Length greater than or equal to zero is a valid value.
3196   Note that the use of this field in HTTP is significantly different from
3197   the corresponding definition in MIME, where it is an optional field
3198   used within the "message/external-body" content-type.
3202<section title="Date" anchor="">
3203  <iref primary="true" item="Date header field" x:for-anchor=""/>
3204  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3205  <x:anchor-alias value="Date"/>
3207   The "Date" header field represents the date and time at which
3208   the message was originated, having the same semantics as the Origination
3209   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3210   The field value is an HTTP-date, as described in <xref target=""/>;
3211   it &MUST; be sent in rfc1123-date format.
3213<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3214  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3217   An example is
3219<figure><artwork type="example">
3220  Date: Tue, 15 Nov 1994 08:12:31 GMT
3223   Origin servers &MUST; include a Date header field in all responses,
3224   except in these cases:
3225  <list style="numbers">
3226      <t>If the response status code is 100 (Continue) or 101 (Switching
3227         Protocols), the response &MAY; include a Date header field, at
3228         the server's option.</t>
3230      <t>If the response status code conveys a server error, e.g., 500
3231         (Internal Server Error) or 503 (Service Unavailable), and it is
3232         inconvenient or impossible to generate a valid Date.</t>
3234      <t>If the server does not have a clock that can provide a
3235         reasonable approximation of the current time, its responses
3236         &MUST-NOT; include a Date header field. In this case, the rules
3237         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3238  </list>
3241   A received message that does not have a Date header field &MUST; be
3242   assigned one by the recipient if the message will be cached by that
3243   recipient.
3246   Clients can use the Date header field as well; in order to keep request
3247   messages small, they are advised not to include it when it doesn't convey
3248   any useful information (as it is usually the case for requests that do not
3249   contain a payload).
3252   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3253   time subsequent to the generation of the message. It &SHOULD; represent
3254   the best available approximation of the date and time of message
3255   generation, unless the implementation has no means of generating a
3256   reasonably accurate date and time. In theory, the date ought to
3257   represent the moment just before the payload is generated. In
3258   practice, the date can be generated at any time during the message
3259   origination without affecting its semantic value.
3262<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3264   Some origin server implementations might not have a clock available.
3265   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3266   values to a response, unless these values were associated
3267   with the resource by a system or user with a reliable clock. It &MAY;
3268   assign an Expires value that is known, at or before server
3269   configuration time, to be in the past (this allows "pre-expiration"
3270   of responses without storing separate Expires values for each
3271   resource).
3276<section title="Host" anchor="">
3277  <iref primary="true" item="Host header field" x:for-anchor=""/>
3278  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3279  <x:anchor-alias value="Host"/>
3281   The "Host" header field in a request provides the host and port
3282   information from the target resource's URI, enabling the origin
3283   server to distinguish between resources while servicing requests
3284   for multiple host names on a single IP address.  Since the Host
3285   field-value is critical information for handling a request, it
3286   &SHOULD; be sent as the first header field following the Request-Line.
3288<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3289  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3292   A client &MUST; send a Host header field in all HTTP/1.1 request
3293   messages.  If the target resource's URI includes an authority
3294   component, then the Host field-value &MUST; be identical to that
3295   authority component after excluding any userinfo (<xref target="http.uri"/>).
3296   If the authority component is missing or undefined for the target
3297   resource's URI, then the Host header field &MUST; be sent with an
3298   empty field-value.
3301   For example, a GET request to the origin server for
3302   &lt;; would begin with:
3304<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3305GET /pub/WWW/ HTTP/1.1
3309   The Host header field &MUST; be sent in an HTTP/1.1 request even
3310   if the request-target is in the form of an absolute-URI, since this
3311   allows the Host information to be forwarded through ancient HTTP/1.0
3312   proxies that might not have implemented Host.
3315   When an HTTP/1.1 proxy receives a request with a request-target in
3316   the form of an absolute-URI, the proxy &MUST; ignore the received
3317   Host header field (if any) and instead replace it with the host
3318   information of the request-target.  When a proxy forwards a request,
3319   it &MUST; generate the Host header field based on the received
3320   absolute-URI rather than the received Host.
3323   Since the Host header field acts as an application-level routing
3324   mechanism, it is a frequent target for malware seeking to poison
3325   a shared cache or redirect a request to an unintended server.
3326   An interception proxy is particularly vulnerable if it relies on
3327   the Host header field value for redirecting requests to internal
3328   servers, or for use as a cache key in a shared cache, without
3329   first verifying that the intercepted connection is targeting a
3330   valid IP address for that host.
3333   A server &MUST; respond with a 400 (Bad Request) status code to
3334   any HTTP/1.1 request message that lacks a Host header field and
3335   to any request message that contains more than one Host header field
3336   or a Host header field with an invalid field-value.
3339   See Sections <xref target="" format="counter"/>
3340   and <xref target="" format="counter"/>
3341   for other requirements relating to Host.
3345<section title="TE" anchor="header.te">
3346  <iref primary="true" item="TE header field" x:for-anchor=""/>
3347  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3348  <x:anchor-alias value="TE"/>
3349  <x:anchor-alias value="t-codings"/>
3350  <x:anchor-alias value="te-params"/>
3351  <x:anchor-alias value="te-ext"/>
3353   The "TE" header field indicates what extension transfer-codings
3354   it is willing to accept in the response, and whether or not it is
3355   willing to accept trailer fields in a chunked transfer-coding.
3358   Its value consists of the keyword "trailers" and/or a comma-separated
3359   list of extension transfer-coding names with optional accept
3360   parameters (as described in <xref target="transfer.codings"/>).
3362<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"/>
3363  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3364  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3365  <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> )
3366  <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> ]
3369   The presence of the keyword "trailers" indicates that the client is
3370   willing to accept trailer fields in a chunked transfer-coding, as
3371   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3372   transfer-coding values even though it does not itself represent a
3373   transfer-coding.
3376   Examples of its use are:
3378<figure><artwork type="example">
3379  TE: deflate
3380  TE:
3381  TE: trailers, deflate;q=0.5
3384   The TE header field only applies to the immediate connection.
3385   Therefore, the keyword &MUST; be supplied within a Connection header
3386   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3389   A server tests whether a transfer-coding is acceptable, according to
3390   a TE field, using these rules:
3391  <list style="numbers">
3392    <x:lt>
3393      <t>The "chunked" transfer-coding is always acceptable. If the
3394         keyword "trailers" is listed, the client indicates that it is
3395         willing to accept trailer fields in the chunked response on
3396         behalf of itself and any downstream clients. The implication is
3397         that, if given, the client is stating that either all
3398         downstream clients are willing to accept trailer fields in the
3399         forwarded response, or that it will attempt to buffer the
3400         response on behalf of downstream recipients.
3401      </t><t>
3402         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3403         chunked response such that a client can be assured of buffering
3404         the entire response.</t>
3405    </x:lt>
3406    <x:lt>
3407      <t>If the transfer-coding being tested is one of the transfer-codings
3408         listed in the TE field, then it is acceptable unless it
3409         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3410         qvalue of 0 means "not acceptable".)</t>
3411    </x:lt>
3412    <x:lt>
3413      <t>If multiple transfer-codings are acceptable, then the
3414         acceptable transfer-coding with the highest non-zero qvalue is
3415         preferred.  The "chunked" transfer-coding always has a qvalue
3416         of 1.</t>
3417    </x:lt>
3418  </list>
3421   If the TE field-value is empty or if no TE field is present, the only
3422   transfer-coding is "chunked". A message with no transfer-coding is
3423   always acceptable.
3427<section title="Trailer" anchor="header.trailer">
3428  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3429  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3430  <x:anchor-alias value="Trailer"/>
3432   The "Trailer" header field indicates that the given set of
3433   header fields is present in the trailer of a message encoded with
3434   chunked transfer-coding.
3436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3437  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3440   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3441   message using chunked transfer-coding with a non-empty trailer. Doing
3442   so allows the recipient to know which header fields to expect in the
3443   trailer.
3446   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3447   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3448   trailer fields in a "chunked" transfer-coding.
3451   Message header fields listed in the Trailer header field &MUST-NOT;
3452   include the following header fields:
3453  <list style="symbols">
3454    <t>Transfer-Encoding</t>
3455    <t>Content-Length</t>
3456    <t>Trailer</t>
3457  </list>
3461<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3462  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3463  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3464  <x:anchor-alias value="Transfer-Encoding"/>
3466   The "Transfer-Encoding" header field indicates what transfer-codings
3467   (if any) have been applied to the message body. It differs from
3468   Content-Encoding (&content-codings;) in that transfer-codings are a property
3469   of the message (and therefore are removed by intermediaries), whereas
3470   content-codings are not.
3472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3473  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3476   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3478<figure><artwork type="example">
3479  Transfer-Encoding: chunked
3482   If multiple encodings have been applied to a representation, the transfer-codings
3483   &MUST; be listed in the order in which they were applied.
3484   Additional information about the encoding parameters &MAY; be provided
3485   by other header fields not defined by this specification.
3488   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3489   header field.
3493<section title="Upgrade" anchor="header.upgrade">
3494  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3495  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3496  <x:anchor-alias value="Upgrade"/>
3498   The "Upgrade" header field allows the client to specify what
3499   additional communication protocols it would like to use, if the server
3500   chooses to switch protocols. Servers can use it to indicate what protocols
3501   they are willing to switch to.
3503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3504  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3507   For example,
3509<figure><artwork type="example">
3510  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3513   The Upgrade header field is intended to provide a simple mechanism
3514   for transition from HTTP/1.1 to some other, incompatible protocol. It
3515   does so by allowing the client to advertise its desire to use another
3516   protocol, such as a later version of HTTP with a higher major version
3517   number, even though the current request has been made using HTTP/1.1.
3518   This eases the difficult transition between incompatible protocols by
3519   allowing the client to initiate a request in the more commonly
3520   supported protocol while indicating to the server that it would like
3521   to use a "better" protocol if available (where "better" is determined
3522   by the server, possibly according to the nature of the request method
3523   or target resource).
3526   The Upgrade header field only applies to switching application-layer
3527   protocols upon the existing transport-layer connection. Upgrade
3528   cannot be used to insist on a protocol change; its acceptance and use
3529   by the server is optional. The capabilities and nature of the
3530   application-layer communication after the protocol change is entirely
3531   dependent upon the new protocol chosen, although the first action
3532   after changing the protocol &MUST; be a response to the initial HTTP
3533   request containing the Upgrade header field.
3536   The Upgrade header field only applies to the immediate connection.
3537   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3538   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3539   HTTP/1.1 message.
3542   The Upgrade header field cannot be used to indicate a switch to a
3543   protocol on a different connection. For that purpose, it is more
3544   appropriate to use a 3xx redirection response (&status-3xx;).
3547   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3548   Protocols) responses to indicate which protocol(s) are being switched to,
3549   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3550   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3551   response to indicate that they are willing to upgrade to one of the
3552   specified protocols.
3555   This specification only defines the protocol name "HTTP" for use by
3556   the family of Hypertext Transfer Protocols, as defined by the HTTP
3557   version rules of <xref target="http.version"/> and future updates to this
3558   specification. Additional tokens can be registered with IANA using the
3559   registration procedure defined below. 
3562<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3564   The HTTP Upgrade Token Registry defines the name space for product
3565   tokens used to identify protocols in the Upgrade header field.
3566   Each registered token is associated with contact information and
3567   an optional set of specifications that details how the connection
3568   will be processed after it has been upgraded.
3571   Registrations are allowed on a First Come First Served basis as
3572   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3573   specifications need not be IETF documents or be subject to IESG review.
3574   Registrations are subject to the following rules:
3575  <list style="numbers">
3576    <t>A token, once registered, stays registered forever.</t>
3577    <t>The registration &MUST; name a responsible party for the
3578       registration.</t>
3579    <t>The registration &MUST; name a point of contact.</t>
3580    <t>The registration &MAY; name a set of specifications associated with that
3581       token. Such specifications need not be publicly available.</t>
3582    <t>The responsible party &MAY; change the registration at any time.
3583       The IANA will keep a record of all such changes, and make them
3584       available upon request.</t>
3585    <t>The responsible party for the first registration of a "product"
3586       token &MUST; approve later registrations of a "version" token
3587       together with that "product" token before they can be registered.</t>
3588    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3589       for a token. This will normally only be used in the case when a
3590       responsible party cannot be contacted.</t>
3591  </list>
3598<section title="Via" anchor="header.via">
3599  <iref primary="true" item="Via header field" x:for-anchor=""/>
3600  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3601  <x:anchor-alias value="protocol-name"/>
3602  <x:anchor-alias value="protocol-version"/>
3603  <x:anchor-alias value="pseudonym"/>
3604  <x:anchor-alias value="received-by"/>
3605  <x:anchor-alias value="received-protocol"/>
3606  <x:anchor-alias value="Via"/>
3608   The "Via" header field &MUST; be sent by a proxy or gateway to
3609   indicate the intermediate protocols and recipients between the user
3610   agent and the server on requests, and between the origin server and
3611   the client on responses. It is analogous to the "Received" field
3612   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3613   and is intended to be used for tracking message forwards,
3614   avoiding request loops, and identifying the protocol capabilities of
3615   all senders along the request/response chain.
3617<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"/>
3618  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3619                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3620  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3621  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3622  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3623  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3624  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3627   The received-protocol indicates the protocol version of the message
3628   received by the server or client along each segment of the
3629   request/response chain. The received-protocol version is appended to
3630   the Via field value when the message is forwarded so that information
3631   about the protocol capabilities of upstream applications remains
3632   visible to all recipients.
3635   The protocol-name is excluded if and only if it would be "HTTP". The
3636   received-by field is normally the host and optional port number of a
3637   recipient server or client that subsequently forwarded the message.
3638   However, if the real host is considered to be sensitive information,
3639   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3640   be assumed to be the default port of the received-protocol.
3643   Multiple Via field values represent each proxy or gateway that has
3644   forwarded the message. Each recipient &MUST; append its information
3645   such that the end result is ordered according to the sequence of
3646   forwarding applications.
3649   Comments &MAY; be used in the Via header field to identify the software
3650   of each recipient, analogous to the User-Agent and Server header fields.
3651   However, all comments in the Via field are optional and &MAY; be removed
3652   by any recipient prior to forwarding the message.
3655   For example, a request message could be sent from an HTTP/1.0 user
3656   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3657   forward the request to a public proxy at, which completes
3658   the request by forwarding it to the origin server at
3659   The request received by would then have the following
3660   Via header field:
3662<figure><artwork type="example">
3663  Via: 1.0 fred, 1.1 (Apache/1.1)
3666   A proxy or gateway used as a portal through a network firewall
3667   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3668   region unless it is explicitly enabled to do so. If not enabled, the
3669   received-by host of any host behind the firewall &SHOULD; be replaced
3670   by an appropriate pseudonym for that host.
3673   For organizations that have strong privacy requirements for hiding
3674   internal structures, a proxy or gateway &MAY; combine an ordered
3675   subsequence of Via header field entries with identical received-protocol
3676   values into a single such entry. For example,
3678<figure><artwork type="example">
3679  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3682  could be collapsed to
3684<figure><artwork type="example">
3685  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3688   Senders &SHOULD-NOT; combine multiple entries unless they are all
3689   under the same organizational control and the hosts have already been
3690   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3691   have different received-protocol values.
3697<section title="IANA Considerations" anchor="IANA.considerations">
3699<section title="Header Field Registration" anchor="header.field.registration">
3701   The Message Header Field Registry located at <eref target=""/> shall be updated
3702   with the permanent registrations below (see <xref target="RFC3864"/>):
3704<?BEGININC p1-messaging.iana-headers ?>
3705<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3706<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3707   <ttcol>Header Field Name</ttcol>
3708   <ttcol>Protocol</ttcol>
3709   <ttcol>Status</ttcol>
3710   <ttcol>Reference</ttcol>
3712   <c>Connection</c>
3713   <c>http</c>
3714   <c>standard</c>
3715   <c>
3716      <xref target="header.connection"/>
3717   </c>
3718   <c>Content-Length</c>
3719   <c>http</c>
3720   <c>standard</c>
3721   <c>
3722      <xref target="header.content-length"/>
3723   </c>
3724   <c>Date</c>
3725   <c>http</c>
3726   <c>standard</c>
3727   <c>
3728      <xref target=""/>
3729   </c>
3730   <c>Host</c>
3731   <c>http</c>
3732   <c>standard</c>
3733   <c>
3734      <xref target=""/>
3735   </c>
3736   <c>TE</c>
3737   <c>http</c>
3738   <c>standard</c>
3739   <c>
3740      <xref target="header.te"/>
3741   </c>
3742   <c>Trailer</c>
3743   <c>http</c>
3744   <c>standard</c>
3745   <c>
3746      <xref target="header.trailer"/>
3747   </c>
3748   <c>Transfer-Encoding</c>
3749   <c>http</c>
3750   <c>standard</c>
3751   <c>
3752      <xref target="header.transfer-encoding"/>
3753   </c>
3754   <c>Upgrade</c>
3755   <c>http</c>
3756   <c>standard</c>
3757   <c>
3758      <xref target="header.upgrade"/>
3759   </c>
3760   <c>Via</c>
3761   <c>http</c>
3762   <c>standard</c>
3763   <c>
3764      <xref target="header.via"/>
3765   </c>
3768<?ENDINC p1-messaging.iana-headers ?>
3770   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3771   HTTP header field would be in conflict with the use of the "close" connection
3772   option for the "Connection" header field (<xref target="header.connection"/>).
3774<texttable align="left" suppress-title="true">
3775   <ttcol>Header Field Name</ttcol>
3776   <ttcol>Protocol</ttcol>
3777   <ttcol>Status</ttcol>
3778   <ttcol>Reference</ttcol>
3780   <c>Close</c>
3781   <c>http</c>
3782   <c>reserved</c>
3783   <c>
3784      <xref target="header.field.registration"/>
3785   </c>
3788   The change controller is: "IETF ( - Internet Engineering Task Force".
3792<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3794   The entries for the "http" and "https" URI Schemes in the registry located at
3795   <eref target=""/>
3796   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3797   and <xref target="https.uri" format="counter"/> of this document
3798   (see <xref target="RFC4395"/>).
3802<section title="Internet Media Type Registrations" anchor="">
3804   This document serves as the specification for the Internet media types
3805   "message/http" and "application/http". The following is to be registered with
3806   IANA (see <xref target="RFC4288"/>).
3808<section title="Internet Media Type message/http" anchor="">
3809<iref item="Media Type" subitem="message/http" primary="true"/>
3810<iref item="message/http Media Type" primary="true"/>
3812   The message/http type can be used to enclose a single HTTP request or
3813   response message, provided that it obeys the MIME restrictions for all
3814   "message" types regarding line length and encodings.
3817  <list style="hanging" x:indent="12em">
3818    <t hangText="Type name:">
3819      message
3820    </t>
3821    <t hangText="Subtype name:">
3822      http
3823    </t>
3824    <t hangText="Required parameters:">
3825      none
3826    </t>
3827    <t hangText="Optional parameters:">
3828      version, msgtype
3829      <list style="hanging">
3830        <t hangText="version:">
3831          The HTTP-Version number of the enclosed message
3832          (e.g., "1.1"). If not present, the version can be
3833          determined from the first line of the body.
3834        </t>
3835        <t hangText="msgtype:">
3836          The message type &mdash; "request" or "response". If not
3837          present, the type can be determined from the first
3838          line of the body.
3839        </t>
3840      </list>
3841    </t>
3842    <t hangText="Encoding considerations:">
3843      only "7bit", "8bit", or "binary" are permitted
3844    </t>
3845    <t hangText="Security considerations:">
3846      none
3847    </t>
3848    <t hangText="Interoperability considerations:">
3849      none
3850    </t>
3851    <t hangText="Published specification:">
3852      This specification (see <xref target=""/>).
3853    </t>
3854    <t hangText="Applications that use this media type:">
3855    </t>
3856    <t hangText="Additional information:">
3857      <list style="hanging">
3858        <t hangText="Magic number(s):">none</t>
3859        <t hangText="File extension(s):">none</t>
3860        <t hangText="Macintosh file type code(s):">none</t>
3861      </list>
3862    </t>
3863    <t hangText="Person and email address to contact for further information:">
3864      See Authors Section.
3865    </t>
3866    <t hangText="Intended usage:">
3867      COMMON
3868    </t>
3869    <t hangText="Restrictions on usage:">
3870      none
3871    </t>
3872    <t hangText="Author/Change controller:">
3873      IESG
3874    </t>
3875  </list>
3878<section title="Internet Media Type application/http" anchor="">
3879<iref item="Media Type" subitem="application/http" primary="true"/>
3880<iref item="application/http Media Type" primary="true"/>
3882   The application/http type can be used to enclose a pipeline of one or more
3883   HTTP request or response messages (not intermixed).
3886  <list style="hanging" x:indent="12em">
3887    <t hangText="Type name:">
3888      application
3889    </t>
3890    <t hangText="Subtype name:">
3891      http
3892    </t>
3893    <t hangText="Required parameters:">
3894      none
3895    </t>
3896    <t hangText="Optional parameters:">
3897      version, msgtype
3898      <list style="hanging">
3899        <t hangText="version:">
3900          The HTTP-Version number of the enclosed messages
3901          (e.g., "1.1"). If not present, the version can be
3902          determined from the first line of the body.
3903        </t>
3904        <t hangText="msgtype:">
3905          The message type &mdash; "request" or "response". If not
3906          present, the type can be determined from the first
3907          line of the body.
3908        </t>
3909      </list>
3910    </t>
3911    <t hangText="Encoding considerations:">
3912      HTTP messages enclosed by this type
3913      are in "binary" format; use of an appropriate
3914      Content-Transfer-Encoding is required when
3915      transmitted via E-mail.
3916    </t>
3917    <t hangText="Security considerations:">
3918      none
3919    </t>
3920    <t hangText="Interoperability considerations:">
3921      none
3922    </t>
3923    <t hangText="Published specification:">
3924      This specification (see <xref target=""/>).
3925    </t>
3926    <t hangText="Applications that use this media type:">
3927    </t>
3928    <t hangText="Additional information:">
3929      <list style="hanging">
3930        <t hangText="Magic number(s):">none</t>
3931        <t hangText="File extension(s):">none</t>
3932        <t hangText="Macintosh file type code(s):">none</t>
3933      </list>
3934    </t>
3935    <t hangText="Person and email address to contact for further information:">
3936      See Authors Section.
3937    </t>
3938    <t hangText="Intended usage:">
3939      COMMON
3940    </t>
3941    <t hangText="Restrictions on usage:">
3942      none
3943    </t>
3944    <t hangText="Author/Change controller:">
3945      IESG
3946    </t>
3947  </list>
3952<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3954   The registration procedure for HTTP Transfer Codings is now defined by
3955   <xref target="transfer.coding.registry"/> of this document.
3958   The HTTP Transfer Codings Registry located at <eref target=""/>
3959   shall be updated with the registrations below:
3961<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3962   <ttcol>Name</ttcol>
3963   <ttcol>Description</ttcol>
3964   <ttcol>Reference</ttcol>
3965   <c>chunked</c>
3966   <c>Transfer in a series of chunks</c>
3967   <c>
3968      <xref target="chunked.encoding"/>
3969   </c>
3970   <c>compress</c>
3971   <c>UNIX "compress" program method</c>
3972   <c>
3973      <xref target="compress.coding"/>
3974   </c>
3975   <c>deflate</c>
3976   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3977   the "zlib" data format (<xref target="RFC1950"/>)
3978   </c>
3979   <c>
3980      <xref target="deflate.coding"/>
3981   </c>
3982   <c>gzip</c>
3983   <c>Same as GNU zip <xref target="RFC1952"/></c>
3984   <c>
3985      <xref target="gzip.coding"/>
3986   </c>
3990<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3992   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3993   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3994   by <xref target="upgrade.token.registry"/> of this document.
3997   The HTTP Status Code Registry located at <eref target=""/>
3998   shall be updated with the registration below:
4000<texttable align="left" suppress-title="true">
4001   <ttcol>Value</ttcol>
4002   <ttcol>Description</ttcol>
4003   <ttcol>Reference</ttcol>
4005   <c>HTTP</c>
4006   <c>Hypertext Transfer Protocol</c>
4007   <c><xref target="http.version"/> of this specification</c>
4014<section title="Security Considerations" anchor="security.considerations">
4016   This section is meant to inform application developers, information
4017   providers, and users of the security limitations in HTTP/1.1 as
4018   described by this document. The discussion does not include
4019   definitive solutions to the problems revealed, though it does make
4020   some suggestions for reducing security risks.
4023<section title="Personal Information" anchor="personal.information">
4025   HTTP clients are often privy to large amounts of personal information
4026   (e.g., the user's name, location, mail address, passwords, encryption
4027   keys, etc.), and &SHOULD; be very careful to prevent unintentional
4028   leakage of this information.
4029   We very strongly recommend that a convenient interface be provided
4030   for the user to control dissemination of such information, and that
4031   designers and implementors be particularly careful in this area.
4032   History shows that errors in this area often create serious security
4033   and/or privacy problems and generate highly adverse publicity for the
4034   implementor's company.
4038<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
4040   A server is in the position to save personal data about a user's
4041   requests which might identify their reading patterns or subjects of
4042   interest. This information is clearly confidential in nature and its
4043   handling can be constrained by law in certain countries. People using
4044   HTTP to provide data are responsible for ensuring that
4045   such material is not distributed without the permission of any
4046   individuals that are identifiable by the published results.
4050<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4052   Implementations of HTTP origin servers &SHOULD; be careful to restrict
4053   the documents returned by HTTP requests to be only those that were
4054   intended by the server administrators. If an HTTP server translates
4055   HTTP URIs directly into file system calls, the server &MUST; take
4056   special care not to serve files that were not intended to be
4057   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4058   other operating systems use ".." as a path component to indicate a
4059   directory level above the current one. On such a system, an HTTP
4060   server &MUST; disallow any such construct in the request-target if it
4061   would otherwise allow access to a resource outside those intended to
4062   be accessible via the HTTP server. Similarly, files intended for
4063   reference only internally to the server (such as access control
4064   files, configuration files, and script code) &MUST; be protected from
4065   inappropriate retrieval, since they might contain sensitive
4066   information. Experience has shown that minor bugs in such HTTP server
4067   implementations have turned into security risks.
4071<section title="DNS-related Attacks" anchor="dns.related.attacks">
4073   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4074   generally prone to security attacks based on the deliberate misassociation
4075   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4076   cautious in assuming the validity of an IP number/DNS name association unless
4077   the response is protected by DNSSec (<xref target="RFC4033"/>).
4081<section title="Proxies and Caching" anchor="attack.proxies">
4083   By their very nature, HTTP proxies are men-in-the-middle, and
4084   represent an opportunity for man-in-the-middle attacks. Compromise of
4085   the systems on which the proxies run can result in serious security
4086   and privacy problems. Proxies have access to security-related
4087   information, personal information about individual users and
4088   organizations, and proprietary information belonging to users and
4089   content providers. A compromised proxy, or a proxy implemented or
4090   configured without regard to security and privacy considerations,
4091   might be used in the commission of a wide range of potential attacks.
4094   Proxy operators need to protect the systems on which proxies run as
4095   they would protect any system that contains or transports sensitive
4096   information. In particular, log information gathered at proxies often
4097   contains highly sensitive personal information, and/or information
4098   about organizations. Log information needs to be carefully guarded, and
4099   appropriate guidelines for use need to be developed and followed.
4100   (<xref target="abuse.of.server.log.information"/>).
4103   Proxy implementors need to consider the privacy and security
4104   implications of their design and coding decisions, and of the
4105   configuration options they provide to proxy operators (especially the
4106   default configuration).
4109   Users of a proxy need to be aware that proxies are no trustworthier than
4110   the people who run them; HTTP itself cannot solve this problem.
4113   The judicious use of cryptography, when appropriate, might suffice to
4114   protect against a broad range of security and privacy attacks. Such
4115   cryptography is beyond the scope of the HTTP/1.1 specification.
4119<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4121   Because HTTP uses mostly textual, character-delimited fields, attackers can
4122   overflow buffers in implementations, and/or perform a Denial of Service
4123   against implementations that accept fields with unlimited lengths.
4126   To promote interoperability, this specification makes specific
4127   recommendations for size limits on request-targets (<xref target="request-target"/>)
4128   and blocks of header fields (<xref target="header.fields"/>). These are
4129   minimum recommendations, chosen to be supportable even by implementations
4130   with limited resources; it is expected that most implementations will choose
4131   substantially higher limits.
4134   This specification also provides a way for servers to reject messages that
4135   have request-targets that are too long (&status-414;) or request entities
4136   that are too large (&status-4xx;).
4139   Other fields (including but not limited to request methods, response status
4140   phrases, header field-names, and body chunks) &SHOULD; be limited by
4141   implementations carefully, so as to not impede interoperability.
4145<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4147   They exist. They are hard to defend against. Research continues.
4148   Beware.
4153<section title="Acknowledgments" anchor="acks">
4155   This document revision builds on the work that went into
4156   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4157   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4158   acknowledgements.
4161  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4165Acknowledgements TODO list
4167- Jeff Hodges ("effective request URI")
4175<references title="Normative References">
4177<reference anchor="ISO-8859-1">
4178  <front>
4179    <title>
4180     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4181    </title>
4182    <author>
4183      <organization>International Organization for Standardization</organization>
4184    </author>
4185    <date year="1998"/>
4186  </front>
4187  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4190<reference anchor="Part2">
4191  <front>
4192    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4193    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4194      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4195      <address><email></email></address>
4196    </author>
4197    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4198      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4199      <address><email></email></address>
4200    </author>
4201    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4202      <organization abbrev="HP">Hewlett-Packard Company</organization>
4203      <address><email></email></address>
4204    </author>
4205    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4206      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4207      <address><email></email></address>
4208    </author>
4209    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4210      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4211      <address><email></email></address>
4212    </author>
4213    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4214      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4215      <address><email></email></address>
4216    </author>
4217    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4218      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4219      <address><email></email></address>
4220    </author>
4221    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4222      <organization abbrev="W3C">World Wide Web Consortium</organization>
4223      <address><email></email></address>
4224    </author>
4225    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4226      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4227      <address><email></email></address>
4228    </author>
4229    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4230  </front>
4231  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4232  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4235<reference anchor="Part3">
4236  <front>
4237    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4239      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4243      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4244      <address><email></email></address>
4245    </author>
4246    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4247      <organization abbrev="HP">Hewlett-Packard Company</organization>
4248      <address><email></email></address>
4249    </author>
4250    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4251      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4252      <address><email></email></address>
4253    </author>
4254    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4255      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4256      <address><email></email></address>
4257    </author>
4258    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4259      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4260      <address><email></email></address>
4261    </author>
4262    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4263      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4264      <address><email></email></address>
4265    </author>
4266    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4267      <organization abbrev="W3C">World Wide Web Consortium</organization>
4268      <address><email></email></address>
4269    </author>
4270    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4271      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4272      <address><email></email></address>
4273    </author>
4274    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4275  </front>
4276  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4277  <x:source href="p3-payload.xml" basename="p3-payload"/>
4280<reference anchor="Part6">
4281  <front>
4282    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4283    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4284      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4285      <address><email></email></address>
4286    </author>
4287    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4288      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4289      <address><email></email></address>
4290    </author>
4291    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4292      <organization abbrev="HP">Hewlett-Packard Company</organization>
4293      <address><email></email></address>
4294    </author>
4295    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4296      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4297      <address><email></email></address>
4298    </author>
4299    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4300      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4301      <address><email></email></address>
4302    </author>
4303    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4304      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4305      <address><email></email></address>
4306    </author>
4307    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4308      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4309      <address><email></email></address>
4310    </author>
4311    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4312      <organization abbrev="W3C">World Wide Web Consortium</organization>
4313      <address><email></email></address>
4314    </author>
4315    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4316      <address><email></email></address>
4317    </author>
4318    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4319      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4320      <address><email></email></address>
4321    </author>
4322    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4323  </front>
4324  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4325  <x:source href="p6-cache.xml" basename="p6-cache"/>
4328<reference anchor="RFC5234">
4329  <front>
4330    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4331    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4332      <organization>Brandenburg InternetWorking</organization>
4333      <address>
4334        <email></email>
4335      </address> 
4336    </author>
4337    <author initials="P." surname="Overell" fullname="Paul Overell">
4338      <organization>THUS plc.</organization>
4339      <address>
4340        <email></email>
4341      </address>
4342    </author>
4343    <date month="January" year="2008"/>
4344  </front>
4345  <seriesInfo name="STD" value="68"/>
4346  <seriesInfo name="RFC" value="5234"/>
4349<reference anchor="RFC2119">
4350  <front>
4351    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4352    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4353      <organization>Harvard University</organization>
4354      <address><email></email></address>
4355    </author>
4356    <date month="March" year="1997"/>
4357  </front>
4358  <seriesInfo name="BCP" value="14"/>
4359  <seriesInfo name="RFC" value="2119"/>
4362<reference anchor="RFC3986">
4363 <front>
4364  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4365  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4366    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4367    <address>
4368       <email></email>
4369       <uri></uri>
4370    </address>
4371  </author>
4372  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4373    <organization abbrev="Day Software">Day Software</organization>
4374    <address>
4375      <email></email>
4376      <uri></uri>
4377    </address>
4378  </author>
4379  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4380    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4381    <address>
4382      <email></email>
4383      <uri></uri>
4384    </address>
4385  </author>
4386  <date month='January' year='2005'></date>
4387 </front>
4388 <seriesInfo name="STD" value="66"/>
4389 <seriesInfo name="RFC" value="3986"/>
4392<reference anchor="USASCII">
4393  <front>
4394    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4395    <author>
4396      <organization>American National Standards Institute</organization>
4397    </author>
4398    <date year="1986"/>
4399  </front>
4400  <seriesInfo name="ANSI" value="X3.4"/>
4403<reference anchor="RFC1950">
4404  <front>
4405    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4406    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4407      <organization>Aladdin Enterprises</organization>
4408      <address><email></email></address>
4409    </author>
4410    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4411    <date month="May" year="1996"/>
4412  </front>
4413  <seriesInfo name="RFC" value="1950"/>
4414  <annotation>
4415    RFC 1950 is an Informational RFC, thus it might be less stable than
4416    this specification. On the other hand, this downward reference was
4417    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4418    therefore it is unlikely to cause problems in practice. See also
4419    <xref target="BCP97"/>.
4420  </annotation>
4423<reference anchor="RFC1951">
4424  <front>
4425    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4426    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4427      <organization>Aladdin Enterprises</organization>
4428      <address><email></email></address>
4429    </author>
4430    <date month="May" year="1996"/>
4431  </front>
4432  <seriesInfo name="RFC" value="1951"/>
4433  <annotation>
4434    RFC 1951 is an Informational RFC, thus it might be less stable than
4435    this specification. On the other hand, this downward reference was
4436    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4437    therefore it is unlikely to cause problems in practice. See also
4438    <xref target="BCP97"/>.
4439  </annotation>
4442<reference anchor="RFC1952">
4443  <front>
4444    <title>GZIP file format specification version 4.3</title>
4445    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4446      <organization>Aladdin Enterprises</organization>
4447      <address><email></email></address>
4448    </author>
4449    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4450      <address><email></email></address>
4451    </author>
4452    <author initials="M." surname="Adler" fullname="Mark Adler">
4453      <address><email></email></address>
4454    </author>
4455    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4456      <address><email></email></address>
4457    </author>
4458    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4459      <address><email></email></address>
4460    </author>
4461    <date month="May" year="1996"/>
4462  </front>
4463  <seriesInfo name="RFC" value="1952"/>
4464  <annotation>
4465    RFC 1952 is an Informational RFC, thus it might be less stable than
4466    this specification. On the other hand, this downward reference was
4467    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4468    therefore it is unlikely to cause problems in practice. See also
4469    <xref target="BCP97"/>.
4470  </annotation>
4475<references title="Informative References">
4477<reference anchor="Nie1997" target="">
4478  <front>
4479    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4480    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4481    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4482    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4483    <author initials="H." surname="Lie" fullname="H. Lie"/>
4484    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4485    <date year="1997" month="September"/>
4486  </front>
4487  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4490<reference anchor="Pad1995" target="">
4491  <front>
4492    <title>Improving HTTP Latency</title>
4493    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4494    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4495    <date year="1995" month="December"/>
4496  </front>
4497  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4500<reference anchor="RFC1123">
4501  <front>
4502    <title>Requirements for Internet Hosts - Application and Support</title>
4503    <author initials="R." surname="Braden" fullname="Robert Braden">
4504      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4505      <address><email>Braden@ISI.EDU</email></address>
4506    </author>
4507    <date month="October" year="1989"/>
4508  </front>
4509  <seriesInfo name="STD" value="3"/>
4510  <seriesInfo name="RFC" value="1123"/>
4513<reference anchor='RFC1919'>
4514  <front>
4515    <title>Classical versus Transparent IP Proxies</title>
4516    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4517      <address><email></email></address>
4518    </author>
4519    <date year='1996' month='March' />
4520  </front>
4521  <seriesInfo name='RFC' value='1919' />
4524<reference anchor="RFC1945">
4525  <front>
4526    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4527    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4528      <organization>MIT, Laboratory for Computer Science</organization>
4529      <address><email></email></address>
4530    </author>
4531    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4532      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4533      <address><email></email></address>
4534    </author>
4535    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4536      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4537      <address><email></email></address>
4538    </author>
4539    <date month="May" year="1996"/>
4540  </front>
4541  <seriesInfo name="RFC" value="1945"/>
4544<reference anchor="RFC2045">
4545  <front>
4546    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4547    <author initials="N." surname="Freed" fullname="Ned Freed">
4548      <organization>Innosoft International, Inc.</organization>
4549      <address><email></email></address>
4550    </author>
4551    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4552      <organization>First Virtual Holdings</organization>
4553      <address><email></email></address>
4554    </author>
4555    <date month="November" year="1996"/>
4556  </front>
4557  <seriesInfo name="RFC" value="2045"/>
4560<reference anchor="RFC2047">
4561  <front>
4562    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4563    <author initials="K." surname="Moore" fullname="Keith Moore">
4564      <organization>University of Tennessee</organization>
4565      <address><email></email></address>
4566    </author>
4567    <date month="November" year="1996"/>
4568  </front>
4569  <seriesInfo name="RFC" value="2047"/>
4572<reference anchor="RFC2068">
4573  <front>
4574    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4575    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4576      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4577      <address><email></email></address>
4578    </author>
4579    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4580      <organization>MIT Laboratory for Computer Science</organization>
4581      <address><email></email></address>
4582    </author>
4583    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4584      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4585      <address><email></email></address>
4586    </author>
4587    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4588      <organization>MIT Laboratory for Computer Science</organization>
4589      <address><email></email></address>
4590    </author>
4591    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4592      <organization>MIT Laboratory for Computer Science</organization>
4593      <address><email></email></address>
4594    </author>
4595    <date month="January" year="1997"/>
4596  </front>
4597  <seriesInfo name="RFC" value="2068"/>
4600<reference anchor="RFC2145">
4601  <front>
4602    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4603    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4604      <organization>Western Research Laboratory</organization>
4605      <address><email></email></address>
4606    </author>
4607    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4608      <organization>Department of Information and Computer Science</organization>
4609      <address><email></email></address>
4610    </author>
4611    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4612      <organization>MIT Laboratory for Computer Science</organization>
4613      <address><email></email></address>
4614    </author>
4615    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4616      <organization>W3 Consortium</organization>
4617      <address><email></email></address>
4618    </author>
4619    <date month="May" year="1997"/>
4620  </front>
4621  <seriesInfo name="RFC" value="2145"/>
4624<reference anchor="RFC2616">
4625  <front>
4626    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4627    <author initials="R." surname="Fielding" fullname="R. Fielding">
4628      <organization>University of California, Irvine</organization>
4629      <address><email></email></address>
4630    </author>
4631    <author initials="J." surname="Gettys" fullname="J. Gettys">
4632      <organization>W3C</organization>
4633      <address><email></email></address>
4634    </author>
4635    <author initials="J." surname="Mogul" fullname="J. Mogul">
4636      <organization>Compaq Computer Corporation</organization>
4637      <address><email></email></address>
4638    </author>
4639    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4640      <organization>MIT Laboratory for Computer Science</organization>
4641      <address><email></email></address>
4642    </author>
4643    <author initials="L." surname="Masinter" fullname="L. Masinter">
4644      <organization>Xerox Corporation</organization>
4645      <address><email></email></address>
4646    </author>
4647    <author initials="P." surname="Leach" fullname="P. Leach">
4648      <organization>Microsoft Corporation</organization>
4649      <address><email></email></address>
4650    </author>
4651    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4652      <organization>W3C</organization>
4653      <address><email></email></address>
4654    </author>
4655    <date month="June" year="1999"/>
4656  </front>
4657  <seriesInfo name="RFC" value="2616"/>
4660<reference anchor='RFC2817'>
4661  <front>
4662    <title>Upgrading to TLS Within HTTP/1.1</title>
4663    <author initials='R.' surname='Khare' fullname='R. Khare'>
4664      <organization>4K Associates / UC Irvine</organization>
4665      <address><email></email></address>
4666    </author>
4667    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4668      <organization>Agranat Systems, Inc.</organization>
4669      <address><email></email></address>
4670    </author>
4671    <date year='2000' month='May' />
4672  </front>
4673  <seriesInfo name='RFC' value='2817' />
4676<reference anchor='RFC2818'>
4677  <front>
4678    <title>HTTP Over TLS</title>
4679    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4680      <organization>RTFM, Inc.</organization>
4681      <address><email></email></address>
4682    </author>
4683    <date year='2000' month='May' />
4684  </front>
4685  <seriesInfo name='RFC' value='2818' />
4688<reference anchor='RFC2965'>
4689  <front>
4690    <title>HTTP State Management Mechanism</title>
4691    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4692      <organization>Bell Laboratories, Lucent Technologies</organization>
4693      <address><email></email></address>
4694    </author>
4695    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4696      <organization>, Inc.</organization>
4697      <address><email></email></address>
4698    </author>
4699    <date year='2000' month='October' />
4700  </front>
4701  <seriesInfo name='RFC' value='2965' />
4704<reference anchor='RFC3040'>
4705  <front>
4706    <title>Internet Web Replication and Caching Taxonomy</title>
4707    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4708      <organization>Equinix, Inc.</organization>
4709    </author>
4710    <author initials='I.' surname='Melve' fullname='I. Melve'>
4711      <organization>UNINETT</organization>
4712    </author>
4713    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4714      <organization>CacheFlow Inc.</organization>
4715    </author>
4716    <date year='2001' month='January' />
4717  </front>
4718  <seriesInfo name='RFC' value='3040' />
4721<reference anchor='RFC3864'>
4722  <front>
4723    <title>Registration Procedures for Message Header Fields</title>
4724    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4725      <organization>Nine by Nine</organization>
4726      <address><email></email></address>
4727    </author>
4728    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4729      <organization>BEA Systems</organization>
4730      <address><email></email></address>
4731    </author>
4732    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4733      <organization>HP Labs</organization>
4734      <address><email></email></address>
4735    </author>
4736    <date year='2004' month='September' />
4737  </front>
4738  <seriesInfo name='BCP' value='90' />
4739  <seriesInfo name='RFC' value='3864' />
4742<reference anchor='RFC4033'>
4743  <front>
4744    <title>DNS Security Introduction and Requirements</title>
4745    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4746    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4747    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4748    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4749    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4750    <date year='2005' month='March' />
4751  </front>
4752  <seriesInfo name='RFC' value='4033' />
4755<reference anchor="RFC4288">
4756  <front>
4757    <title>Media Type Specifications and Registration Procedures</title>
4758    <author initials="N." surname="Freed" fullname="N. Freed">
4759      <organization>Sun Microsystems</organization>
4760      <address>
4761        <email></email>
4762      </address>
4763    </author>
4764    <author initials="J." surname="Klensin" fullname="J. Klensin">
4765      <address>
4766        <email></email>
4767      </address>
4768    </author>
4769    <date year="2005" month="December"/>
4770  </front>
4771  <seriesInfo name="BCP" value="13"/>
4772  <seriesInfo name="RFC" value="4288"/>
4775<reference anchor='RFC4395'>
4776  <front>
4777    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4778    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4779      <organization>AT&amp;T Laboratories</organization>
4780      <address>
4781        <email></email>
4782      </address>
4783    </author>
4784    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4785      <organization>Qualcomm, Inc.</organization>
4786      <address>
4787        <email></email>
4788      </address>
4789    </author>
4790    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4791      <organization>Adobe Systems</organization>
4792      <address>
4793        <email></email>
4794      </address>
4795    </author>
4796    <date year='2006' month='February' />
4797  </front>
4798  <seriesInfo name='BCP' value='115' />
4799  <seriesInfo name='RFC' value='4395' />
4802<reference anchor='RFC4559'>
4803  <front>
4804    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4805    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4806    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4807    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4808    <date year='2006' month='June' />
4809  </front>
4810  <seriesInfo name='RFC' value='4559' />
4813<reference anchor='RFC5226'>
4814  <front>
4815    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4816    <author initials='T.' surname='Narten' fullname='T. Narten'>
4817      <organization>IBM</organization>
4818      <address><email></email></address>
4819    </author>
4820    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4821      <organization>Google</organization>
4822      <address><email></email></address>
4823    </author>
4824    <date year='2008' month='May' />
4825  </front>
4826  <seriesInfo name='BCP' value='26' />
4827  <seriesInfo name='RFC' value='5226' />
4830<reference anchor="RFC5322">
4831  <front>
4832    <title>Internet Message Format</title>
4833    <author initials="P." surname="Resnick" fullname="P. Resnick">
4834      <organization>Qualcomm Incorporated</organization>
4835    </author>
4836    <date year="2008" month="October"/>
4837  </front>
4838  <seriesInfo name="RFC" value="5322"/>
4841<reference anchor="RFC6265">
4842  <front>
4843    <title>HTTP State Management Mechanism</title>
4844    <author initials="A." surname="Barth" fullname="Adam Barth">
4845      <organization abbrev="U.C. Berkeley">
4846        University of California, Berkeley
4847      </organization>
4848      <address><email></email></address>
4849    </author>
4850    <date year="2011" month="April" />
4851  </front>
4852  <seriesInfo name="RFC" value="6265"/>
4855<reference anchor='BCP97'>
4856  <front>
4857    <title>Handling Normative References to Standards-Track Documents</title>
4858    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4859      <address>
4860        <email></email>
4861      </address>
4862    </author>
4863    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4864      <organization>MIT</organization>
4865      <address>
4866        <email></email>
4867      </address>
4868    </author>
4869    <date year='2007' month='June' />
4870  </front>
4871  <seriesInfo name='BCP' value='97' />
4872  <seriesInfo name='RFC' value='4897' />
4875<reference anchor="Kri2001" target="">
4876  <front>
4877    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4878    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4879    <date year="2001" month="November"/>
4880  </front>
4881  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4884<reference anchor="Spe" target="">
4885  <front>
4886    <title>Analysis of HTTP Performance Problems</title>
4887    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4888    <date/>
4889  </front>
4892<reference anchor="Tou1998" target="">
4893  <front>
4894  <title>Analysis of HTTP Performance</title>
4895  <author initials="J." surname="Touch" fullname="Joe Touch">
4896    <organization>USC/Information Sciences Institute</organization>
4897    <address><email></email></address>
4898  </author>
4899  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4900    <organization>USC/Information Sciences Institute</organization>
4901    <address><email></email></address>
4902  </author>
4903  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4904    <organization>USC/Information Sciences Institute</organization>
4905    <address><email></email></address>
4906  </author>
4907  <date year="1998" month="Aug"/>
4908  </front>
4909  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4910  <annotation>(original report dated Aug. 1996)</annotation>
4916<section title="HTTP Version History" anchor="compatibility">
4918   HTTP has been in use by the World-Wide Web global information initiative
4919   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4920   was a simple protocol for hypertext data transfer across the Internet
4921   with only a single request method (GET) and no metadata.
4922   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4923   methods and MIME-like messaging that could include metadata about the data
4924   transferred and modifiers on the request/response semantics. However,
4925   HTTP/1.0 did not sufficiently take into consideration the effects of
4926   hierarchical proxies, caching, the need for persistent connections, or
4927   name-based virtual hosts. The proliferation of incompletely-implemented
4928   applications calling themselves "HTTP/1.0" further necessitated a
4929   protocol version change in order for two communicating applications
4930   to determine each other's true capabilities.
4933   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4934   requirements that enable reliable implementations, adding only
4935   those new features that will either be safely ignored by an HTTP/1.0
4936   recipient or only sent when communicating with a party advertising
4937   compliance with HTTP/1.1.
4940   It is beyond the scope of a protocol specification to mandate
4941   compliance with previous versions. HTTP/1.1 was deliberately
4942   designed, however, to make supporting previous versions easy.
4943   We would expect a general-purpose HTTP/1.1 server to understand
4944   any valid request in the format of HTTP/1.0 and respond appropriately
4945   with an HTTP/1.1 message that only uses features understood (or
4946   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4947   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4950   Since HTTP/0.9 did not support header fields in a request,
4951   there is no mechanism for it to support name-based virtual
4952   hosts (selection of resource by inspection of the Host header
4953   field).  Any server that implements name-based virtual hosts
4954   ought to disable support for HTTP/0.9.  Most requests that
4955   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4956   requests wherein a buggy client failed to properly encode
4957   linear whitespace found in a URI reference and placed in
4958   the request-target.
4961<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4963   This section summarizes major differences between versions HTTP/1.0
4964   and HTTP/1.1.
4967<section title="Multi-homed Web Servers" anchor="">
4969   The requirements that clients and servers support the Host header
4970   field (<xref target=""/>), report an error if it is
4971   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4972   are among the most important changes defined by HTTP/1.1.
4975   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4976   addresses and servers; there was no other established mechanism for
4977   distinguishing the intended server of a request than the IP address
4978   to which that request was directed. The Host header field was
4979   introduced during the development of HTTP/1.1 and, though it was
4980   quickly implemented by most HTTP/1.0 browsers, additional requirements
4981   were placed on all HTTP/1.1 requests in order to ensure complete
4982   adoption.  At the time of this writing, most HTTP-based services
4983   are dependent upon the Host header field for targeting requests.
4987<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4989   For most implementations of HTTP/1.0, each connection is established
4990   by the client prior to the request and closed by the server after
4991   sending the response. However, some implementations implement the
4992   Keep-Alive version of persistent connections described in
4993   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4996   Some clients and servers might wish to be compatible with some
4997   previous implementations of persistent connections in HTTP/1.0
4998   clients and servers. Persistent connections in HTTP/1.0 are
4999   explicitly negotiated as they are not the default behavior. HTTP/1.0
5000   experimental implementations of persistent connections are faulty,
5001   and the new facilities in HTTP/1.1 are designed to rectify these
5002   problems. The problem was that some existing HTTP/1.0 clients might
5003   send Keep-Alive to a proxy server that doesn't understand
5004   Connection, which would then erroneously forward it to the next
5005   inbound server, which would establish the Keep-Alive connection and
5006   result in a hung HTTP/1.0 proxy waiting for the close on the
5007   response. The result is that HTTP/1.0 clients must be prevented from
5008   using Keep-Alive when talking to proxies.
5011   However, talking to proxies is the most important use of persistent
5012   connections, so that prohibition is clearly unacceptable. Therefore,
5013   we need some other mechanism for indicating a persistent connection
5014   is desired, which is safe to use even when talking to an old proxy
5015   that ignores Connection. Persistent connections are the default for
5016   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5017   declaring non-persistence. See <xref target="header.connection"/>.
5022<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5024  Empty list elements in list productions have been deprecated.
5025  (<xref target="notation.abnf"/>)
5028  Rules about implicit linear whitespace between certain grammar productions
5029  have been removed; now it's only allowed when specifically pointed out
5030  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5031  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5032  Non-ASCII content in header fields and reason phrase has been obsoleted and
5033  made opaque (the TEXT rule was removed)
5034  (<xref target="basic.rules"/>)
5037  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5038  sensitive. Restrict the version numbers to be single digits due to the fact
5039  that implementations are known to handle multi-digit version numbers
5040  incorrectly.
5041  (<xref target="http.version"/>)
5044  Require that invalid whitespace around field-names be rejected.
5045  (<xref target="header.fields"/>)
5048  Require recipients to handle bogus Content-Length header fields as errors.
5049  (<xref target="message.body"/>)
5052  Remove reference to non-existent identity transfer-coding value tokens.
5053  (Sections <xref format="counter" target="message.body"/> and
5054  <xref format="counter" target="transfer.codings"/>)
5057  Update use of abs_path production from RFC 1808 to the path-absolute + query
5058  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5059  request method only.
5060  (<xref target="request-target"/>)
5063  Clarification that the chunk length does not include the count of the octets
5064  in the chunk header and trailer. Furthermore disallowed line folding
5065  in chunk extensions.
5066  (<xref target="chunked.encoding"/>)
5069  Remove hard limit of two connections per server.
5070  (<xref target="persistent.practical"/>)
5073  Change ABNF productions for header fields to only define the field value.
5074  (<xref target="header.field.definitions"/>)
5077  Clarify exactly when close connection options must be sent.
5078  (<xref target="header.connection"/>)
5081  Define the semantics of the "Upgrade" header field in responses other than
5082  101 (this was incorporated from <xref target="RFC2817"/>).
5083  (<xref target="header.upgrade"/>)
5088<?BEGININC p1-messaging.abnf-appendix ?>
5089<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5091<artwork type="abnf" name="p1-messaging.parsed-abnf">
5092<x:ref>BWS</x:ref> = OWS
5094<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5095<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5096 connection-token ] )
5097<x:ref>Content-Length</x:ref> = 1*DIGIT
5099<x:ref>Date</x:ref> = HTTP-date
5101<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5103<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5104<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5105<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5106<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5107 ]
5108<x:ref>Host</x:ref> = uri-host [ ":" port ]
5110<x:ref>Method</x:ref> = token
5112<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5114<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5115<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5116<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5117<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5118<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5120<x:ref>Status-Code</x:ref> = 3DIGIT
5121<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5123<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5124<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5125<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5126 transfer-coding ] )
5128<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5129<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5131<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5132 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5133 )
5135<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5136<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5137<x:ref>attribute</x:ref> = token
5138<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5140<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5141<x:ref>chunk-data</x:ref> = 1*OCTET
5142<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5143<x:ref>chunk-ext-name</x:ref> = token
5144<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5145<x:ref>chunk-size</x:ref> = 1*HEXDIG
5146<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5147<x:ref>connection-token</x:ref> = token
5148<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5149 / %x2A-5B ; '*'-'['
5150 / %x5D-7E ; ']'-'~'
5151 / obs-text
5153<x:ref>date1</x:ref> = day SP month SP year
5154<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5155<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5156<x:ref>day</x:ref> = 2DIGIT
5157<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5158 / %x54.75.65 ; Tue
5159 / %x57.65.64 ; Wed
5160 / %x54.68.75 ; Thu
5161 / %x46.72.69 ; Fri
5162 / %x53.61.74 ; Sat
5163 / %x53.75.6E ; Sun
5164<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5165 / %x54. ; Tuesday
5166 / %x57.65.64.6E. ; Wednesday
5167 / %x54. ; Thursday
5168 / %x46. ; Friday
5169 / %x53. ; Saturday
5170 / %x53.75.6E.64.61.79 ; Sunday
5172<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5173<x:ref>field-name</x:ref> = token
5174<x:ref>field-value</x:ref> = *( field-content / OWS )
5176<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5177<x:ref>hour</x:ref> = 2DIGIT
5178<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5179<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5181<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5183<x:ref>message-body</x:ref> = *OCTET
5184<x:ref>minute</x:ref> = 2DIGIT
5185<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5186 / %x46.65.62 ; Feb
5187 / %x4D.61.72 ; Mar
5188 / %x41.70.72 ; Apr
5189 / %x4D.61.79 ; May
5190 / %x4A.75.6E ; Jun
5191 / %x4A.75.6C ; Jul
5192 / %x41.75.67 ; Aug
5193 / %x53.65.70 ; Sep
5194 / %x4F.63.74 ; Oct
5195 / %x4E.6F.76 ; Nov
5196 / %x44.65.63 ; Dec
5198<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5199<x:ref>obs-fold</x:ref> = CRLF
5200<x:ref>obs-text</x:ref> = %x80-FF
5202<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5203<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5204<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5205<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5206<x:ref>product</x:ref> = token [ "/" product-version ]
5207<x:ref>product-version</x:ref> = token
5208<x:ref>protocol-name</x:ref> = token
5209<x:ref>protocol-version</x:ref> = token
5210<x:ref>pseudonym</x:ref> = token
5212<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5213 / %x5D-7E ; ']'-'~'
5214 / obs-text
5215<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5216 / %x5D-7E ; ']'-'~'
5217 / obs-text
5218<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5219<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5220<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5221<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5222<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5223<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5225<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5226<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5227<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5228<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5229 / authority
5230<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5231<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5233<x:ref>second</x:ref> = 2DIGIT
5234<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5235 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5236<x:ref>start-line</x:ref> = Request-Line / Status-Line
5238<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5239<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5240 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5241<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5242<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5243<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5244<x:ref>token</x:ref> = 1*tchar
5245<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5246<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5247 transfer-extension
5248<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5249<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5251<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5253<x:ref>value</x:ref> = word
5255<x:ref>word</x:ref> = token / quoted-string
5257<x:ref>year</x:ref> = 4DIGIT
5260<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5261; Chunked-Body defined but not used
5262; Connection defined but not used
5263; Content-Length defined but not used
5264; Date defined but not used
5265; HTTP-message defined but not used
5266; Host defined but not used
5267; Request defined but not used
5268; Response defined but not used
5269; TE defined but not used
5270; Trailer defined but not used
5271; Transfer-Encoding defined but not used
5272; URI-reference defined but not used
5273; Upgrade defined but not used
5274; Via defined but not used
5275; http-URI defined but not used
5276; https-URI defined but not used
5277; partial-URI defined but not used
5278; special defined but not used
5280<?ENDINC p1-messaging.abnf-appendix ?>
5282<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5284<section title="Since RFC 2616">
5286  Extracted relevant partitions from <xref target="RFC2616"/>.
5290<section title="Since draft-ietf-httpbis-p1-messaging-00">
5292  Closed issues:
5293  <list style="symbols">
5294    <t>
5295      <eref target=""/>:
5296      "HTTP Version should be case sensitive"
5297      (<eref target=""/>)
5298    </t>
5299    <t>
5300      <eref target=""/>:
5301      "'unsafe' characters"
5302      (<eref target=""/>)
5303    </t>
5304    <t>
5305      <eref target=""/>:
5306      "Chunk Size Definition"
5307      (<eref target=""/>)
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "Message Length"
5312      (<eref target=""/>)
5313    </t>
5314    <t>
5315      <eref target=""/>:
5316      "Media Type Registrations"
5317      (<eref target=""/>)
5318    </t>
5319    <t>
5320      <eref target=""/>:
5321      "URI includes query"
5322      (<eref target=""/>)
5323    </t>
5324    <t>
5325      <eref target=""/>:
5326      "No close on 1xx responses"
5327      (<eref target=""/>)
5328    </t>
5329    <t>
5330      <eref target=""/>:
5331      "Remove 'identity' token references"
5332      (<eref target=""/>)
5333    </t>
5334    <t>
5335      <eref target=""/>:
5336      "Import query BNF"
5337    </t>
5338    <t>
5339      <eref target=""/>:
5340      "qdtext BNF"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "Normative and Informative references"
5345    </t>
5346    <t>
5347      <eref target=""/>:
5348      "RFC2606 Compliance"
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "RFC977 reference"
5353    </t>
5354    <t>
5355      <eref target=""/>:
5356      "RFC1700 references"
5357    </t>
5358    <t>
5359      <eref target=""/>:
5360      "inconsistency in date format explanation"
5361    </t>
5362    <t>
5363      <eref target=""/>:
5364      "Date reference typo"
5365    </t>
5366    <t>
5367      <eref target=""/>:
5368      "Informative references"
5369    </t>
5370    <t>
5371      <eref target=""/>:
5372      "ISO-8859-1 Reference"
5373    </t>
5374    <t>
5375      <eref target=""/>:
5376      "Normative up-to-date references"
5377    </t>
5378  </list>
5381  Other changes:
5382  <list style="symbols">
5383    <t>
5384      Update media type registrations to use RFC4288 template.
5385    </t>
5386    <t>
5387      Use names of RFC4234 core rules DQUOTE and WSP,
5388      fix broken ABNF for chunk-data
5389      (work in progress on <eref target=""/>)
5390    </t>
5391  </list>
5395<section title="Since draft-ietf-httpbis-p1-messaging-01">
5397  Closed issues:
5398  <list style="symbols">
5399    <t>
5400      <eref target=""/>:
5401      "Bodies on GET (and other) requests"
5402    </t>
5403    <t>
5404      <eref target=""/>:
5405      "Updating to RFC4288"
5406    </t>
5407    <t>
5408      <eref target=""/>:
5409      "Status Code and Reason Phrase"
5410    </t>
5411    <t>
5412      <eref target=""/>:
5413      "rel_path not used"
5414    </t>
5415  </list>
5418  Ongoing work on ABNF conversion (<eref target=""/>):
5419  <list style="symbols">
5420    <t>
5421      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5422      "trailer-part").
5423    </t>
5424    <t>
5425      Avoid underscore character in rule names ("http_URL" ->
5426      "http-URL", "abs_path" -> "path-absolute").
5427    </t>
5428    <t>
5429      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5430      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5431      have to be updated when switching over to RFC3986.
5432    </t>
5433    <t>
5434      Synchronize core rules with RFC5234.
5435    </t>
5436    <t>
5437      Get rid of prose rules that span multiple lines.
5438    </t>
5439    <t>
5440      Get rid of unused rules LOALPHA and UPALPHA.
5441    </t>
5442    <t>
5443      Move "Product Tokens" section (back) into Part 1, as "token" is used
5444      in the definition of the Upgrade header field.
5445    </t>
5446    <t>
5447      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5448    </t>
5449    <t>
5450      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5451    </t>
5452  </list>
5456<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5458  Closed issues:
5459  <list style="symbols">
5460    <t>
5461      <eref target=""/>:
5462      "HTTP-date vs. rfc1123-date"
5463    </t>
5464    <t>
5465      <eref target=""/>:
5466      "WS in quoted-pair"
5467    </t>
5468  </list>
5471  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5472  <list style="symbols">
5473    <t>
5474      Reference RFC 3984, and update header field registrations for headers defined
5475      in this document.
5476    </t>
5477  </list>
5480  Ongoing work on ABNF conversion (<eref target=""/>):
5481  <list style="symbols">
5482    <t>
5483      Replace string literals when the string really is case-sensitive (HTTP-Version).
5484    </t>
5485  </list>
5489<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5491  Closed issues:
5492  <list style="symbols">
5493    <t>
5494      <eref target=""/>:
5495      "Connection closing"
5496    </t>
5497    <t>
5498      <eref target=""/>:
5499      "Move registrations and registry information to IANA Considerations"
5500    </t>
5501    <t>
5502      <eref target=""/>:
5503      "need new URL for PAD1995 reference"
5504    </t>
5505    <t>
5506      <eref target=""/>:
5507      "IANA Considerations: update HTTP URI scheme registration"
5508    </t>
5509    <t>
5510      <eref target=""/>:
5511      "Cite HTTPS URI scheme definition"
5512    </t>
5513    <t>
5514      <eref target=""/>:
5515      "List-type headers vs Set-Cookie"
5516    </t>
5517  </list>
5520  Ongoing work on ABNF conversion (<eref target=""/>):
5521  <list style="symbols">
5522    <t>
5523      Replace string literals when the string really is case-sensitive (HTTP-Date).
5524    </t>
5525    <t>
5526      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5527    </t>
5528  </list>
5532<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5534  Closed issues:
5535  <list style="symbols">
5536    <t>
5537      <eref target=""/>:
5538      "Out-of-date reference for URIs"
5539    </t>
5540    <t>
5541      <eref target=""/>:
5542      "RFC 2822 is updated by RFC 5322"
5543    </t>
5544  </list>
5547  Ongoing work on ABNF conversion (<eref target=""/>):
5548  <list style="symbols">
5549    <t>
5550      Use "/" instead of "|" for alternatives.
5551    </t>
5552    <t>
5553      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5554    </t>
5555    <t>
5556      Only reference RFC 5234's core rules.
5557    </t>
5558    <t>
5559      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5560      whitespace ("OWS") and required whitespace ("RWS").
5561    </t>
5562    <t>
5563      Rewrite ABNFs to spell out whitespace rules, factor out
5564      header field value format definitions.
5565    </t>
5566  </list>
5570<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5572  Closed issues:
5573  <list style="symbols">
5574    <t>
5575      <eref target=""/>:
5576      "Header LWS"
5577    </t>
5578    <t>
5579      <eref target=""/>:
5580      "Sort 1.3 Terminology"
5581    </t>
5582    <t>
5583      <eref target=""/>:
5584      "RFC2047 encoded words"
5585    </t>
5586    <t>
5587      <eref target=""/>:
5588      "Character Encodings in TEXT"
5589    </t>
5590    <t>
5591      <eref target=""/>:
5592      "Line Folding"
5593    </t>
5594    <t>
5595      <eref target=""/>:
5596      "OPTIONS * and proxies"
5597    </t>
5598    <t>
5599      <eref target=""/>:
5600      "Reason-Phrase BNF"
5601    </t>
5602    <t>
5603      <eref target=""/>:
5604      "Use of TEXT"
5605    </t>
5606    <t>
5607      <eref target=""/>:
5608      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5609    </t>
5610    <t>
5611      <eref target=""/>:
5612      "RFC822 reference left in discussion of date formats"
5613    </t>
5614  </list>
5617  Final work on ABNF conversion (<eref target=""/>):
5618  <list style="symbols">
5619    <t>
5620      Rewrite definition of list rules, deprecate empty list elements.
5621    </t>
5622    <t>
5623      Add appendix containing collected and expanded ABNF.
5624    </t>
5625  </list>
5628  Other changes:
5629  <list style="symbols">
5630    <t>
5631      Rewrite introduction; add mostly new Architecture Section.
5632    </t>
5633    <t>
5634      Move definition of quality values from Part 3 into Part 1;
5635      make TE request header field grammar independent of accept-params (defined in Part 3).
5636    </t>
5637  </list>
5641<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5643  Closed issues:
5644  <list style="symbols">
5645    <t>
5646      <eref target=""/>:
5647      "base for numeric protocol elements"
5648    </t>
5649    <t>
5650      <eref target=""/>:
5651      "comment ABNF"
5652    </t>
5653  </list>
5656  Partly resolved issues:
5657  <list style="symbols">
5658    <t>
5659      <eref target=""/>:
5660      "205 Bodies" (took out language that implied that there might be
5661      methods for which a request body MUST NOT be included)
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "editorial improvements around HTTP-date"
5666    </t>
5667  </list>
5671<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5673  Closed issues:
5674  <list style="symbols">
5675    <t>
5676      <eref target=""/>:
5677      "Repeating single-value headers"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "increase connection limit"
5682    </t>
5683    <t>
5684      <eref target=""/>:
5685      "IP addresses in URLs"
5686    </t>
5687    <t>
5688      <eref target=""/>:
5689      "take over HTTP Upgrade Token Registry"
5690    </t>
5691    <t>
5692      <eref target=""/>:
5693      "CR and LF in chunk extension values"
5694    </t>
5695    <t>
5696      <eref target=""/>:
5697      "HTTP/0.9 support"
5698    </t>
5699    <t>
5700      <eref target=""/>:
5701      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5702    </t>
5703    <t>
5704      <eref target=""/>:
5705      "move definitions of gzip/deflate/compress to part 1"
5706    </t>
5707    <t>
5708      <eref target=""/>:
5709      "disallow control characters in quoted-pair"
5710    </t>
5711  </list>
5714  Partly resolved issues:
5715  <list style="symbols">
5716    <t>
5717      <eref target=""/>:
5718      "update IANA requirements wrt Transfer-Coding values" (add the
5719      IANA Considerations subsection)
5720    </t>
5721  </list>
5725<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5727  Closed issues:
5728  <list style="symbols">
5729    <t>
5730      <eref target=""/>:
5731      "header parsing, treatment of leading and trailing OWS"
5732    </t>
5733  </list>
5736  Partly resolved issues:
5737  <list style="symbols">
5738    <t>
5739      <eref target=""/>:
5740      "Placement of 13.5.1 and 13.5.2"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "use of term "word" when talking about header structure"
5745    </t>
5746  </list>
5750<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5752  Closed issues:
5753  <list style="symbols">
5754    <t>
5755      <eref target=""/>:
5756      "Clarification of the term 'deflate'"
5757    </t>
5758    <t>
5759      <eref target=""/>:
5760      "OPTIONS * and proxies"
5761    </t>
5762    <t>
5763      <eref target=""/>:
5764      "MIME-Version not listed in P1, general header fields"
5765    </t>
5766    <t>
5767      <eref target=""/>:
5768      "IANA registry for content/transfer encodings"
5769    </t>
5770    <t>
5771      <eref target=""/>:
5772      "Case-sensitivity of HTTP-date"
5773    </t>
5774    <t>
5775      <eref target=""/>:
5776      "use of term "word" when talking about header structure"
5777    </t>
5778  </list>
5781  Partly resolved issues:
5782  <list style="symbols">
5783    <t>
5784      <eref target=""/>:
5785      "Term for the requested resource's URI"
5786    </t>
5787  </list>
5791<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5793  Closed issues:
5794  <list style="symbols">
5795    <t>
5796      <eref target=""/>:
5797      "Connection Closing"
5798    </t>
5799    <t>
5800      <eref target=""/>:
5801      "Delimiting messages with multipart/byteranges"
5802    </t>
5803    <t>
5804      <eref target=""/>:
5805      "Handling multiple Content-Length headers"
5806    </t>
5807    <t>
5808      <eref target=""/>:
5809      "Clarify entity / representation / variant terminology"
5810    </t>
5811    <t>
5812      <eref target=""/>:
5813      "consider removing the 'changes from 2068' sections"
5814    </t>
5815  </list>
5818  Partly resolved issues:
5819  <list style="symbols">
5820    <t>
5821      <eref target=""/>:
5822      "HTTP(s) URI scheme definitions"
5823    </t>
5824  </list>
5828<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5830  Closed issues:
5831  <list style="symbols">
5832    <t>
5833      <eref target=""/>:
5834      "Trailer requirements"
5835    </t>
5836    <t>
5837      <eref target=""/>:
5838      "Text about clock requirement for caches belongs in p6"
5839    </t>
5840    <t>
5841      <eref target=""/>:
5842      "effective request URI: handling of missing host in HTTP/1.0"
5843    </t>
5844    <t>
5845      <eref target=""/>:
5846      "confusing Date requirements for clients"
5847    </t>
5848  </list>
5851  Partly resolved issues:
5852  <list style="symbols">
5853    <t>
5854      <eref target=""/>:
5855      "Handling multiple Content-Length headers"
5856    </t>
5857  </list>
5861<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5863  Closed issues:
5864  <list style="symbols">
5865    <t>
5866      <eref target=""/>:
5867      "RFC2145 Normative"
5868    </t>
5869    <t>
5870      <eref target=""/>:
5871      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5872    </t>
5873    <t>
5874      <eref target=""/>:
5875      "define 'transparent' proxy"
5876    </t>
5877    <t>
5878      <eref target=""/>:
5879      "Header Classification"
5880    </t>
5881    <t>
5882      <eref target=""/>:
5883      "Is * usable as a request-uri for new methods?"
5884    </t>
5885    <t>
5886      <eref target=""/>:
5887      "Migrate Upgrade details from RFC2817"
5888    </t>
5889    <t>
5890      <eref target=""/>:
5891      "untangle ABNFs for header fields"
5892    </t>
5893    <t>
5894      <eref target=""/>:
5895      "update RFC 2109 reference"
5896    </t>
5897  </list>
5901<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5903  Closed issues:
5904  <list style="symbols">
5905    <t>
5906      <eref target=""/>:
5907      "Allow is not in 13.5.2"
5908    </t>
5909    <t>
5910      <eref target=""/>:
5911      "Handling multiple Content-Length headers"
5912    </t>
5913    <t>
5914      <eref target=""/>:
5915      "untangle ABNFs for header fields"
5916    </t>
5917    <t>
5918      <eref target=""/>:
5919      "Content-Length ABNF broken"
5920    </t>
5921  </list>
5925<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5927  Closed issues:
5928  <list style="symbols">
5929    <t>
5930      <eref target=""/>:
5931      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5932    </t>
5933    <t>
5934      <eref target=""/>:
5935      "Recommend minimum sizes for protocol elements"
5936    </t>
5937    <t>
5938      <eref target=""/>:
5939      "Set expectations around buffering"
5940    </t>
5941    <t>
5942      <eref target=""/>:
5943      "Considering messages in isolation"
5944    </t>
5945  </list>
5949<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5951  Closed issues:
5952  <list style="symbols">
5953    <t>
5954      <eref target=""/>:
5955      "DNS Spoofing / DNS Binding advice"
5956    </t>
5957    <t>
5958      <eref target=""/>:
5959      "move RFCs 2145, 2616, 2817 to Historic status"
5960    </t>
5961    <t>
5962      <eref target=""/>:
5963      "\-escaping in quoted strings"
5964    </t>
5965    <t>
5966      <eref target=""/>:
5967      "'Close' should be reserved in the HTTP header field registry"
5968    </t>
5969  </list>
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