source: draft-ietf-httpbis/latest/p1-messaging.xml @ 852

Last change on this file since 852 was 852, checked in by fielding@…, 12 years ago

Changed message-body ABNF to be *OCTET. Specifying the actual
number of octets will have to be done in prose.

Moved mistitled "Message Length" section into the Message Body
section, since it only explains how many octets are in the body.
Deleted useless "Entity Length" section and transfer-length term.

Addresses #28: Connection closing

Removed redundant mention of terminating by connection close
and rewrote explanation so that it doesn't self-contradict.

Addresses #90: Delimiting messages with multipart/byteranges

Removed message-delimiting paragraphs of multipart/byteranges
from p1 and p3.

Addresses #95: Handling multiple Content-Length headers

Added requirements for what to do if multiple or invalid
Content-Length is received.

Rephrased requirements for Transfer-Encoding to only apply
when a transfer-coding is present. Clarify that Transfer-Encoding
overrides Content-Length and treat receiving both as an error.
Clarify that only the chunked transfer-coding can delimit a
message (the original design allowed other self-descriptive
encodings, but that was abandoned in 2616).

Addresses #109: Clarify entity / representation / variant terminology

Entity-body terminology changed to payload in order to clarify that
it is what gets packaged (as a message-body) into a message,
allowing us to (eventually) distinguish between messages containing
whole representations and messages containing only partial
representations. Reduce use of the same terms for other things
(e.g., in explanation of dates).

  • Property svn:eol-style set to native
File size: 241.5 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 "July">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
18  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
19  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
20  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
21  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
22  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
23  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
24  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
25  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x=''/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc rfcedstyle="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization 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 Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.10"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions should be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients may act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383  Note that empty elements do not contribute to the count of elements present,
384  though.
387  For example, given these ABNF productions:
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
404  But these values would be invalid, as at least one non-empty element is
405  required:
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
431   The OWS rule is used where zero or more linear whitespace characters may
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
500  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
503  <x:ref>obs-text</x:ref>       = %x80-FF
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="entity-header"/>
523  <x:anchor-alias value="Cache-Control"/>
524  <x:anchor-alias value="Pragma"/>
525  <x:anchor-alias value="Warning"/>
527  The ABNF rules below are defined in other parts:
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
546<section title="HTTP architecture" anchor="architecture">
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
554<section title="Client/Server Operation" anchor="operation">
555<iref item="client"/>
556<iref item="server"/>
557<iref item="connection"/>
559   HTTP is a request/response protocol that operates by exchanging messages
560   across a reliable transport or session-layer connection. An HTTP client
561   is a program that establishes a connection to a server for the purpose
562   of sending one or more HTTP requests.  An HTTP server is a program that
563   accepts connections in order to service HTTP requests by sending HTTP
564   responses.
566<iref item="user agent"/>
567<iref item="origin server"/>
569   Note that the terms "client" and "server" refer only to the roles that
570   these programs perform for a particular connection.  The same program
571   may act as a client on some connections and a server on others.  We use
572   the term "user agent" to refer to the program that initiates a request,
573   such as a WWW browser, editor, or spider (web-traversing robot), and
574   the term "origin server" to refer to the program that can originate
575   authoritative responses to a request.
578   Most HTTP communication consists of a retrieval request (GET) for
579   a representation of some resource identified by a URI.  In the
580   simplest case, this may be accomplished via a single connection (v)
581   between the user agent (UA) and the origin server (O).
583<figure><artwork type="drawing">
584       request chain ------------------------&gt;
585    UA -------------------v------------------- O
586       &lt;----------------------- response chain
588<iref item="message"/>
589<iref item="request"/>
590<iref item="response"/>
592   A client sends an HTTP request to the server in the form of a request
593   message (<xref target="request"/>), beginning with a method, URI, and
594   protocol version, followed by MIME-like header fields containing
595   request modifiers, client information, and payload metadata, an empty
596   line to indicate the end of the header section, and finally the payload
597   body (if any).
600   A server responds to the client's request by sending an HTTP response
601   message (<xref target="response"/>), beginning with a status line that
602   includes the protocol version, a success or error code, and textual
603   reason phrase, followed by MIME-like header fields containing server
604   information, resource metadata, and payload metadata, an empty line to
605   indicate the end of the header section, and finally the payload body (if any).
608   The following example illustrates a typical message exchange for a
609   GET request on the URI "":
612client request:
613</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
614GET /hello.txt HTTP/1.1
615User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
617Accept: */*
621server response:
622</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
623HTTP/1.1 200 OK
624Date: Mon, 27 Jul 2009 12:28:53 GMT
625Server: Apache
626Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
627ETag: "34aa387-d-1568eb00"
628Accept-Ranges: bytes
629Content-Length: <x:length-of target="exbody"/>
630Vary: Accept-Encoding
631Content-Type: text/plain
633<x:span anchor="exbody">Hello World!
637<section title="Intermediaries" anchor="intermediaries">
639   A more complicated situation occurs when one or more intermediaries
640   are present in the request/response chain. There are three common
641   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
642   a single intermediary may act as an origin server, proxy, gateway,
643   or tunnel, switching behavior based on the nature of each request.
645<figure><artwork type="drawing">
646       request chain --------------------------------------&gt;
647    UA -----v----- A -----v----- B -----v----- C -----v----- O
648       &lt;------------------------------------- response chain
651   The figure above shows three intermediaries (A, B, and C) between the
652   user agent and origin server. A request or response message that
653   travels the whole chain will pass through four separate connections.
654   Some HTTP communication options
655   may apply only to the connection with the nearest, non-tunnel
656   neighbor, only to the end-points of the chain, or to all connections
657   along the chain. Although the diagram is linear, each participant may
658   be engaged in multiple, simultaneous communications. For example, B
659   may be receiving requests from many clients other than A, and/or
660   forwarding requests to servers other than C, at the same time that it
661   is handling A's request.
664<iref item="upstream"/><iref item="downstream"/>
665<iref item="inbound"/><iref item="outbound"/>
666   We use the terms "upstream" and "downstream" to describe various
667   requirements in relation to the directional flow of a message:
668   all messages flow from upstream to downstream.
669   Likewise, we use the terms "inbound" and "outbound" to refer to
670   directions in relation to the request path: "inbound" means toward
671   the origin server and "outbound" means toward the user agent.
673<t><iref item="proxy"/>
674   A proxy is a message forwarding agent that is selected by the
675   client, usually via local configuration rules, to receive requests
676   for some type(s) of absolute URI and attempt to satisfy those
677   requests via translation through the HTTP interface.  Some translations
678   are minimal, such as for proxy requests for "http" URIs, whereas
679   other requests may require translation to and from entirely different
680   application-layer protocols. Proxies are often used to group an
681   organization's HTTP requests through a common intermediary for the
682   sake of security, annotation services, or shared caching.
684<t><iref item="gateway"/><iref item="reverse proxy"/>
685   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
686   as a layer above some other server(s) and translates the received
687   requests to the underlying server's protocol.  Gateways are often
688   used for load balancing or partitioning HTTP services across
689   multiple machines.
690   Unlike a proxy, a gateway receives requests as if it were the
691   origin server for the requested resource; the requesting client
692   will not be aware that it is communicating with a gateway.
693   A gateway communicates with the client as if the gateway is the
694   origin server and thus is subject to all of the requirements on
695   origin servers for that connection.  A gateway communicates
696   with inbound servers using any protocol it desires, including
697   private extensions to HTTP that are outside the scope of this
698   specification.
700<t><iref item="tunnel"/>
701   A tunnel acts as a blind relay between two connections
702   without changing the messages. Once active, a tunnel is not
703   considered a party to the HTTP communication, though the tunnel may
704   have been initiated by an HTTP request. A tunnel ceases to exist when
705   both ends of the relayed connection are closed. Tunnels are used to
706   extend a virtual connection through an intermediary, such as when
707   transport-layer security is used to establish private communication
708   through a shared firewall proxy.
712<section title="Caches" anchor="caches">
713<iref item="cache"/>
715   Any party to HTTP communication that is not acting as a tunnel may
716   employ an internal cache for handling requests.
717   A cache is a local store of previous response messages and the
718   subsystem that controls its message storage, retrieval, and deletion.
719   A cache stores cacheable responses in order to reduce the response
720   time and network bandwidth consumption on future, equivalent
721   requests. Any client or server may include a cache, though a cache
722   cannot be used by a server while it is acting as a tunnel.
725   The effect of a cache is that the request/response chain is shortened
726   if one of the participants along the chain has a cached response
727   applicable to that request. The following illustrates the resulting
728   chain if B has a cached copy of an earlier response from O (via C)
729   for a request which has not been cached by UA or A.
731<figure><artwork type="drawing">
732          request chain ----------&gt;
733       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
734          &lt;--------- response chain
736<t><iref item="cacheable"/>
737   A response is cacheable if a cache is allowed to store a copy of
738   the response message for use in answering subsequent requests.
739   Even when a response is cacheable, there may be additional
740   constraints placed by the client or by the origin server on when
741   that cached response can be used for a particular request. HTTP
742   requirements for cache behavior and cacheable responses are
743   defined in &caching-overview;. 
746   There are a wide variety of architectures and configurations
747   of caches and proxies deployed across the World Wide Web and
748   inside large organizations. These systems include national hierarchies
749   of proxy caches to save transoceanic bandwidth, systems that
750   broadcast or multicast cache entries, organizations that distribute
751   subsets of cached data via optical media, and so on.
755<section title="Transport Independence" anchor="transport-independence">
757  HTTP systems are used in a wide variety of environments, from
758  corporate intranets with high-bandwidth links to long-distance
759  communication over low-power radio links and intermittent connectivity.
762   HTTP communication usually takes place over TCP/IP connections. The
763   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
764   not preclude HTTP from being implemented on top of any other protocol
765   on the Internet, or on other networks. HTTP only presumes a reliable
766   transport; any protocol that provides such guarantees can be used;
767   the mapping of the HTTP/1.1 request and response structures onto the
768   transport data units of the protocol in question is outside the scope
769   of this specification.
772   In HTTP/1.0, most implementations used a new connection for each
773   request/response exchange. In HTTP/1.1, a connection may be used for
774   one or more request/response exchanges, although connections may be
775   closed for a variety of reasons (see <xref target="persistent.connections"/>).
779<section title="HTTP Version" anchor="http.version">
780  <x:anchor-alias value="HTTP-Version"/>
781  <x:anchor-alias value="HTTP-Prot-Name"/>
783   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
784   of the protocol. The protocol versioning policy is intended to allow
785   the sender to indicate the format of a message and its capacity for
786   understanding further HTTP communication, rather than the features
787   obtained via that communication. No change is made to the version
788   number for the addition of message components which do not affect
789   communication behavior or which only add to extensible field values.
790   The &lt;minor&gt; number is incremented when the changes made to the
791   protocol add features which do not change the general message parsing
792   algorithm, but which may add to the message semantics and imply
793   additional capabilities of the sender. The &lt;major&gt; number is
794   incremented when the format of a message within the protocol is
795   changed. See <xref target="RFC2145"/> for a fuller explanation.
798   The version of an HTTP message is indicated by an HTTP-Version field
799   in the first line of the message. HTTP-Version is case-sensitive.
801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
802  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
803  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
806   Note that the major and minor numbers &MUST; be treated as separate
807   integers and that each &MAY; be incremented higher than a single digit.
808   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
809   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
810   &MUST-NOT; be sent.
813   An application that sends a request or response message that includes
814   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
815   with this specification. Applications that are at least conditionally
816   compliant with this specification &SHOULD; use an HTTP-Version of
817   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
818   not compatible with HTTP/1.0. For more details on when to send
819   specific HTTP-Version values, see <xref target="RFC2145"/>.
822   The HTTP version of an application is the highest HTTP version for
823   which the application is at least conditionally compliant.
826   Proxy and gateway applications need to be careful when forwarding
827   messages in protocol versions different from that of the application.
828   Since the protocol version indicates the protocol capability of the
829   sender, a proxy/gateway &MUST-NOT; send a message with a version
830   indicator which is greater than its actual version. If a higher
831   version request is received, the proxy/gateway &MUST; either downgrade
832   the request version, or respond with an error, or switch to tunnel
833   behavior.
836   Due to interoperability problems with HTTP/1.0 proxies discovered
837   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
838   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
839   they support. The proxy/gateway's response to that request &MUST; be in
840   the same major version as the request.
843  <t>
844    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
845    of header fields required or forbidden by the versions involved.
846  </t>
850<section title="Uniform Resource Identifiers" anchor="uri">
851<iref primary="true" item="resource"/>
853   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
854   throughout HTTP as the means for identifying resources. URI references
855   are used to target requests, indicate redirects, and define relationships.
856   HTTP does not limit what a resource may be; it merely defines an interface
857   that can be used to interact with a resource via HTTP. More information on
858   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
860  <x:anchor-alias value="URI-reference"/>
861  <x:anchor-alias value="absolute-URI"/>
862  <x:anchor-alias value="relative-part"/>
863  <x:anchor-alias value="authority"/>
864  <x:anchor-alias value="path-abempty"/>
865  <x:anchor-alias value="path-absolute"/>
866  <x:anchor-alias value="port"/>
867  <x:anchor-alias value="query"/>
868  <x:anchor-alias value="uri-host"/>
869  <x:anchor-alias value="partial-URI"/>
871   This specification adopts the definitions of "URI-reference",
872   "absolute-URI", "relative-part", "port", "host",
873   "path-abempty", "path-absolute", "query", and "authority" from
874   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
875   protocol elements that allow a relative URI without a fragment.
877<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
878  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
879  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
880  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
881  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
882  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
883  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
885  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
886  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
888  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
891   Each protocol element in HTTP that allows a URI reference will indicate in
892   its ABNF production whether the element allows only a URI in absolute form
893   (absolute-URI), any relative reference (relative-ref), or some other subset
894   of the URI-reference grammar. Unless otherwise indicated, URI references
895   are parsed relative to the request target (the default base URI for both
896   the request and its corresponding response).
899<section title="http URI scheme" anchor="http.uri">
900  <x:anchor-alias value="http-URI"/>
901  <iref item="http URI scheme" primary="true"/>
902  <iref item="URI scheme" subitem="http" primary="true"/>
904   The "http" URI scheme is hereby defined for the purpose of minting
905   identifiers according to their association with the hierarchical
906   namespace governed by a potential HTTP origin server listening for
907   TCP connections on a given port.
908   The HTTP server is identified via the generic syntax's
909   <x:ref>authority</x:ref> component, which includes a host
910   identifier and optional TCP port, and the remainder of the URI is
911   considered to be identifying data corresponding to a resource for
912   which that server might provide an HTTP interface.
914<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
915  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
918   The host identifier within an <x:ref>authority</x:ref> component is
919   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
920   provided as an IP literal or IPv4 address, then the HTTP server is any
921   listener on the indicated TCP port at that IP address. If host is a
922   registered name, then that name is considered an indirect identifier
923   and the recipient might use a name resolution service, such as DNS,
924   to find the address of a listener for that host.
925   The host &MUST-NOT; be empty; if an "http" URI is received with an
926   empty host, then it &MUST; be rejected as invalid.
927   If the port subcomponent is empty or not given, then TCP port 80 is
928   assumed (the default reserved port for WWW services).
931   Regardless of the form of host identifier, access to that host is not
932   implied by the mere presence of its name or address. The host may or may
933   not exist and, even when it does exist, may or may not be running an
934   HTTP server or listening to the indicated port. The "http" URI scheme
935   makes use of the delegated nature of Internet names and addresses to
936   establish a naming authority (whatever entity has the ability to place
937   an HTTP server at that Internet name or address) and allows that
938   authority to determine which names are valid and how they might be used.
941   When an "http" URI is used within a context that calls for access to the
942   indicated resource, a client &MAY; attempt access by resolving
943   the host to an IP address, establishing a TCP connection to that address
944   on the indicated port, and sending an HTTP request message to the server
945   containing the URI's identifying data as described in <xref target="request"/>.
946   If the server responds to that request with a non-interim HTTP response
947   message, as described in <xref target="response"/>, then that response
948   is considered an authoritative answer to the client's request.
951   Although HTTP is independent of the transport protocol, the "http"
952   scheme is specific to TCP-based services because the name delegation
953   process depends on TCP for establishing authority.
954   An HTTP service based on some other underlying connection protocol
955   would presumably be identified using a different URI scheme, just as
956   the "https" scheme (below) is used for servers that require an SSL/TLS
957   transport layer on a connection. Other protocols may also be used to
958   provide access to "http" identified resources --- it is only the
959   authoritative interface used for mapping the namespace that is
960   specific to TCP.
964<section title="https URI scheme" anchor="https.uri">
965   <x:anchor-alias value="https-URI"/>
966   <iref item="https URI scheme"/>
967   <iref item="URI scheme" subitem="https"/>
969   The "https" URI scheme is hereby defined for the purpose of minting
970   identifiers according to their association with the hierarchical
971   namespace governed by a potential HTTP origin server listening for
972   SSL/TLS-secured connections on a given TCP port.
973   The host and port are determined in the same way
974   as for the "http" scheme, except that a default TCP port of 443
975   is assumed if the port subcomponent is empty or not given.
977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
978  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
981   The primary difference between the "http" and "https" schemes is
982   that interaction with the latter is required to be secured for
983   privacy through the use of strong encryption. The URI cannot be
984   sent in a request until the connection is secure. Likewise, the
985   default for caching is that each response that would be considered
986   "public" under the "http" scheme is instead treated as "private"
987   and thus not eligible for shared caching.
990   The process for authoritative access to an "https" identified
991   resource is defined in <xref target="RFC2818"/>.
995<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
997   Since the "http" and "https" schemes conform to the URI generic syntax,
998   such URIs are normalized and compared according to the algorithm defined
999   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1000   described above for each scheme.
1003   If the port is equal to the default port for a scheme, the normal
1004   form is to elide the port subcomponent. Likewise, an empty path
1005   component is equivalent to an absolute path of "/", so the normal
1006   form is to provide a path of "/" instead. The scheme and host
1007   are case-insensitive and normally provided in lowercase; all
1008   other components are compared in a case-sensitive manner.
1009   Characters other than those in the "reserved" set are equivalent
1010   to their percent-encoded octets (see <xref target="RFC3986"
1011   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1014   For example, the following three URIs are equivalent:
1016<figure><artwork type="example">
1022   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1023   If path-abempty is the empty string (i.e., there is no slash "/"
1024   path separator following the authority), then the "http" URI
1025   &MUST; be given as "/" when
1026   used as a request-target (<xref target="request-target"/>). If a proxy
1027   receives a host name which is not a fully qualified domain name, it
1028   &MAY; add its domain to the host name it received. If a proxy receives
1029   a fully qualified domain name, the proxy &MUST-NOT; change the host
1030   name.
1036<section title="HTTP Message" anchor="http.message">
1037<x:anchor-alias value="generic-message"/>
1038<x:anchor-alias value="message.types"/>
1039<x:anchor-alias value="HTTP-message"/>
1040<x:anchor-alias value="start-line"/>
1041<iref item="header section"/>
1042<iref item="headers"/>
1043<iref item="header field"/>
1045   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1046   characters in a format similar to the Internet Message Format
1047   <xref target="RFC5322"/>: zero or more header fields (collectively
1048   referred to as the "headers" or the "header section"), an empty line
1049   indicating the end of the header section, and an optional message-body.
1052   An HTTP message can either be a request from client to server or a
1053   response from server to client.  Syntactically, the two types of message
1054   differ only in the start-line, which is either a Request-Line (for requests)
1055   or a Status-Line (for responses), and in the algorithm for determining
1056   the length of the message-body (<xref target="message.body.length"/>).
1057   In theory, a client could receive requests and a server could receive
1058   responses, distinguishing them by their different start-line formats,
1059   but in practice servers are implemented to only expect a request
1060   (a response is interpreted as an unknown or invalid request method)
1061   and clients are implemented to only expect a response.
1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1064  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1065                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1066                    <x:ref>CRLF</x:ref>
1067                    [ <x:ref>message-body</x:ref> ]
1068  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1071   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1072   header field. The presence of whitespace might be an attempt to trick a
1073   noncompliant implementation of HTTP into ignoring that field or processing
1074   the next line as a new request, either of which may result in security
1075   issues when implementations within the request chain interpret the
1076   same message differently. HTTP/1.1 servers &MUST; reject such a message
1077   with a 400 (Bad Request) response.
1080<section title="Message Parsing Robustness" anchor="message.robustness">
1082   In the interest of robustness, servers &SHOULD; ignore at least one
1083   empty line received where a Request-Line is expected. In other words, if
1084   the server is reading the protocol stream at the beginning of a
1085   message and receives a CRLF first, it should ignore the CRLF.
1088   Some old HTTP/1.0 client implementations generate an extra CRLF
1089   after a POST request as a lame workaround for some early server
1090   applications that failed to read message-body content that was
1091   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1092   preface or follow a request with an extra CRLF.  If terminating
1093   the request message-body with a line-ending is desired, then the
1094   client &MUST; include the terminating CRLF octets as part of the
1095   message-body length.
1098   The normal procedure for parsing an HTTP message is to read the
1099   start-line into a structure, read each header field into a hash
1100   table by field name until the empty line, and then use the parsed
1101   data to determine if a message-body is expected.  If a message-body
1102   has been indicated, then it is read as a stream until an amount
1103   of octets equal to the message-body length is read or the connection
1104   is closed.  Care must be taken to parse an HTTP message as a sequence
1105   of octets in an encoding that is a superset of US-ASCII.  Attempting
1106   to parse HTTP as a stream of Unicode characters in a character encoding
1107   like UTF-16 may introduce security flaws due to the differing ways
1108   that such parsers interpret invalid characters.
1112<section title="Header Fields" anchor="header.fields">
1113  <x:anchor-alias value="header-field"/>
1114  <x:anchor-alias value="field-content"/>
1115  <x:anchor-alias value="field-name"/>
1116  <x:anchor-alias value="field-value"/>
1117  <x:anchor-alias value="OWS"/>
1119   Each HTTP header field consists of a case-insensitive field name
1120   followed by a colon (":"), optional whitespace, and the field value.
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1123  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> [ <x:ref>field-value</x:ref> ] <x:ref>OWS</x:ref>
1124  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1125  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1126  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1129   No whitespace is allowed between the header field name and colon. For
1130   security reasons, any request message received containing such whitespace
1131   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1132   &MUST; remove any such whitespace from a response message before
1133   forwarding the message downstream.
1136   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1137   preferred. The field value does not include any leading or trailing white
1138   space: OWS occurring before the first non-whitespace character of the
1139   field value or after the last non-whitespace character of the field value
1140   is ignored and &SHOULD; be removed before further processing (as this does
1141   not change the meaning of the header field).
1144   The order in which header fields with differing field names are
1145   received is not significant. However, it is "good practice" to send
1146   header fields that contain control data first, such as Host on
1147   requests and Date on responses, so that implementations can decide
1148   when not to handle a message as early as possible.  A server &MUST;
1149   wait until the entire header section is received before interpreting
1150   a request message, since later header fields might include conditionals,
1151   authentication credentials, or deliberately misleading duplicate
1152   header fields that would impact request processing.
1155   Multiple header fields with the same field name &MUST-NOT; be
1156   sent in a message unless the entire field value for that
1157   header field is defined as a comma-separated list [i.e., #(values)].
1158   Multiple header fields with the same field name can be combined into
1159   one "field-name: field-value" pair, without changing the semantics of the
1160   message, by appending each subsequent field value to the combined
1161   field value in order, separated by a comma. The order in which
1162   header fields with the same field name are received is therefore
1163   significant to the interpretation of the combined field value;
1164   a proxy &MUST-NOT; change the order of these field values when
1165   forwarding a message.
1168  <t>
1169   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1170   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1171   can occur multiple times, but does not use the list syntax, and thus cannot
1172   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1173   for details.) Also note that the Set-Cookie2 header specified in
1174   <xref target="RFC2965"/> does not share this problem.
1175  </t>
1178   Historically, HTTP header field values could be extended over multiple
1179   lines by preceding each extra line with at least one space or horizontal
1180   tab character (line folding). This specification deprecates such line
1181   folding except within the message/http media type
1182   (<xref target=""/>).
1183   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1184   (i.e., that contain any field-content that matches the obs-fold rule) unless
1185   the message is intended for packaging within the message/http media type.
1186   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1187   obs-fold whitespace with a single SP prior to interpreting the field value
1188   or forwarding the message downstream.
1191   Historically, HTTP has allowed field content with text in the ISO-8859-1
1192   <xref target="ISO-8859-1"/> character encoding and supported other
1193   character sets only through use of <xref target="RFC2047"/> encoding.
1194   In practice, most HTTP header field values use only a subset of the
1195   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1196   header fields &SHOULD; limit their field values to US-ASCII characters.
1197   Recipients &SHOULD; treat other (obs-text) octets in field content as
1198   opaque data.
1200<t anchor="rule.comment">
1201  <x:anchor-alias value="comment"/>
1202  <x:anchor-alias value="ctext"/>
1203   Comments can be included in some HTTP header fields by surrounding
1204   the comment text with parentheses. Comments are only allowed in
1205   fields containing "comment" as part of their field value definition.
1207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1208  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1209  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1210                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1212<t anchor="rule.quoted-cpair">
1213  <x:anchor-alias value="quoted-cpair"/>
1214   The backslash character ("\") can be used as a single-character
1215   quoting mechanism within comment constructs:
1217<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1218  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1221   Producers &SHOULD-NOT; escape characters that do not require escaping
1222   (i.e., other than the backslash character "\" and the parentheses "(" and
1223   ")").
1227<section title="Message Body" anchor="message.body">
1228  <x:anchor-alias value="message-body"/>
1230   The message-body (if any) of an HTTP message is used to carry the
1231   payload body associated with the request or response. The message-body
1232   differs from the payload body only when a transfer-coding has been
1233   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1235<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1236  <x:ref>message-body</x:ref> = *OCTET
1239   When one or more transfer-codings are applied to a payload body,
1240   usually for the sake of stream-delimiting or data compression, the
1241   Transfer-Encoding header field &MUST; be provided with the list of
1242   transfer-codings applied. Transfer-Encoding is a property of the message,
1243   not of the payload, and thus &MAY; be added or removed by any implementation
1244   along the request/response chain under the constraints found in
1245   <xref target="transfer.codings"/>.
1248   The rules for when a message-body is allowed in a message differ for
1249   requests and responses.
1252   The presence of a message-body in a request is signaled by the
1253   inclusion of a Content-Length or Transfer-Encoding header field in
1254   the request's header fields, even if the request method does not
1255   define any use for a message-body.  This allows the request
1256   message framing algorithm to be independent of method semantics.
1257   A server &MUST; read the entire request message-body or close
1258   the connection after sending its response.
1261   For response messages, whether or not a message-body is included with
1262   a message is dependent on both the request method and the response
1263   status code (<xref target="status.code.and.reason.phrase"/>).
1264   Responses to the HEAD request method never include a message-body
1265   because the associated response header fields (e.g., Transfer-Encoding,
1266   Content-Length, etc.) only indicate what their values would have been
1267   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1268   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1269   All other responses do include a message-body, although the body
1270   &MAY; be of zero length.
1272<t anchor="message.body.length">
1273   The length of the message-body is determined by one of the following
1274   (in order of precedence):
1277  <list style="numbers">
1278    <x:lt><t>
1279     Any response to a HEAD request and any response with a status
1280     code of 100-199, 204, or 304 is always terminated by the first
1281     empty line after the header fields, regardless of the header
1282     fields present in the message, and thus cannot contain a message-body.
1283    </t></x:lt>
1284    <x:lt><t>
1285     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1286     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1287     is used, the message-body length is determined by reading and decoding the
1288     chunked data until the transfer-coding indicates the data is complete.
1289    </t>
1290    <t>
1291     If a message is received with both a Transfer-Encoding header field and a
1292     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1293     Such a message may indicate an attempt to perform request or response
1294     smuggling (bypass of security-related checks on message routing or content)
1295     and thus should be handled as an error.  The provided Content-Length &MUST;
1296     be removed, prior to forwarding the message downstream, or replaced with
1297     the real message-body length after the transfer-coding is decoded.
1298    </t>
1299    <t>
1300     If a Transfer-Encoding header field is present in a response and the
1301     "chunked" transfer-coding is not present, the message-body length is
1302     determined by reading the connection until it is closed.
1303     If a Transfer-Encoding header field is present in a request and the
1304     "chunked" transfer-coding is not present, the message-body length cannot
1305     be determined reliably; the server &MUST; respond with 400 (Bad Request)
1306     and then close the connection.
1307    </t></x:lt>
1308    <x:lt><t>
1309     If a valid Content-Length header field (<xref target="header.content-length"/>)
1310     is present without Transfer-Encoding, its decimal value in octets defines
1311     the message-body length.  If the actual number of octets sent in the message
1312     is less than the indicated Content-Length, the recipient &MUST; consider
1313     the message to be incomplete and treat the connection as no longer usable.
1314     If the actual number of octets sent in the message is less than the indicated
1315     Content-Length, the recipient &MUST; only process the message-body up to the
1316     field value's number of octets; the remainder of the message &MUST; either
1317     be discarded or treated as the next message in a pipeline.  For the sake of
1318     robustness, a user-agent &MAY; attempt to detect and correct such an error
1319     in message framing if it is parsing the response to the last request on
1320     on a connection and the connection has been closed by the server.
1321    </t>
1322    <t>
1323     If a message is received with multiple Content-Length header fields or a
1324     Content-Length header field with an invalid value, the message framing
1325     is invalid and &MUST; be treated as an error to prevent request or
1326     response smuggling.
1327     If this is a request message, the server &MUST; respond with
1328     a 400 (Bad Request) status and then close the connection.
1329     If this is a response message received by a proxy or gateway, the proxy
1330     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1331     status as its downstream response, and then close the connection.
1332     If this is a response message received by a user-agent, the message-body
1333     length is determined by reading the connection until it is closed;
1334     an error &SHOULD; be indicated to the user.
1335    </t></x:lt>
1336    <x:lt><t>
1337     If this is a request message and none of the above are true, then the
1338     message-body length is zero (no message-body is present).
1339    </t></x:lt>
1340    <x:lt><t>
1341     Otherwise, this is a response message without a declared message-body
1342     length, so the message-body length is determined by the number of octets
1343     received prior to the server closing the connection.
1344    </t></x:lt>
1345  </list>
1348   Since there is no way to distinguish a successfully completed,
1349   close-delimited message from a partially-received message interrupted
1350   by network failure, implementations &SHOULD; use encoding or
1351   length-delimited messages whenever possible.  The close-delimiting
1352   feature exists primarily for backwards compatibility with HTTP/1.0.
1355   A server &MAY; reject a request that contains a message-body but
1356   not a Content-Length by responding with 411 (Length Required).
1359   A client that sends a request containing a message-body &SHOULD;
1360   include a valid Content-Length header field if the message-body length
1361   is known in advance, since many existing services will otherwise respond
1362   with a 411 (Length Required) status code though they can handle the
1363   chunked encoding.  This is typically because such services are
1364   implemented via a gateway that requires a content-length in
1365   advance of being called and the server is unable or unwilling
1366   to buffer the entire request before processing.
1369   A client that sends a request containing a message-body &MUST; include a
1370   valid Content-Length header field if it does not know the server will
1371   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1372   of specific user configuration or by remembering the version of a prior
1373   received response.
1376   Request messages that are prematurely terminated, possibly due to a
1377   cancelled connection or a server-imposed time-out exception, &MUST;
1378   result in closure of the connection; sending an HTTP/1.1 error response
1379   prior to closing the connection is &OPTIONAL;.
1380   Response messages that are prematurely terminated, usually by closure
1381   of the connection prior to receiving the given number of octets or by
1382   failure to decode a transfer-encoded message-body, &MUST; be recorded
1383   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1384   message-body as if it were complete (i.e., some indication must be given
1385   to the user that an error occurred).  Cache requirements for incomplete
1386   responses are defined in &cache-incomplete;.
1390<section title="General Header Fields" anchor="general.header.fields">
1391  <x:anchor-alias value="general-header"/>
1393   There are a few header fields which have general applicability for
1394   both request and response messages, but which do not apply to the
1395   payload being transferred. These header fields apply only to the
1396   message being transmitted.
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1399  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1400                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1401                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1402                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1403                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1404                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1405                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1406                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1407                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1410   General-header field names can be extended reliably only in
1411   combination with a change in the protocol version. However, new or
1412   experimental header fields may be given the semantics of general
1413   header fields if all parties in the communication recognize them to
1414   be general-header fields. Unrecognized header fields are treated as
1415   entity-header fields.
1420<section title="Request" anchor="request">
1421  <x:anchor-alias value="Request"/>
1423   A request message from a client to a server includes, within the
1424   first line of that message, the method to be applied to the resource,
1425   the identifier of the resource, and the protocol version in use.
1427<!--                 Host                      ; should be moved here eventually -->
1428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1429  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1430                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1431                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1432                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1433                  <x:ref>CRLF</x:ref>
1434                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1437<section title="Request-Line" anchor="request-line">
1438  <x:anchor-alias value="Request-Line"/>
1440   The Request-Line begins with a method token, followed by the
1441   request-target and the protocol version, and ending with CRLF. The
1442   elements are separated by SP characters. No CR or LF is allowed
1443   except in the final CRLF sequence.
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1446  <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>
1449<section title="Method" anchor="method">
1450  <x:anchor-alias value="Method"/>
1452   The Method  token indicates the method to be performed on the
1453   resource identified by the request-target. The method is case-sensitive.
1455<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1456  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1460<section title="request-target" anchor="request-target">
1461  <x:anchor-alias value="request-target"/>
1463   The request-target
1464   identifies the resource upon which to apply the request.
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1467  <x:ref>request-target</x:ref> = "*"
1468                 / <x:ref>absolute-URI</x:ref>
1469                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1470                 / <x:ref>authority</x:ref>
1473   The four options for request-target are dependent on the nature of the
1474   request.
1477   The asterisk "*" means that the request does not apply to a
1478   particular resource, but to the server itself, and is only allowed
1479   when the method used does not necessarily apply to a resource. One
1480   example would be
1482<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1483OPTIONS * HTTP/1.1
1486   The absolute-URI form is &REQUIRED; when the request is being made to a
1487   proxy. The proxy is requested to forward the request or service it
1488   from a valid cache, and return the response. Note that the proxy &MAY;
1489   forward the request on to another proxy or directly to the server
1490   specified by the absolute-URI. In order to avoid request loops, a
1491   proxy &MUST; be able to recognize all of its server names, including
1492   any aliases, local variations, and the numeric IP address. An example
1493   Request-Line would be:
1495<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1496GET HTTP/1.1
1499   To allow for transition to absolute-URIs in all requests in future
1500   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1501   form in requests, even though HTTP/1.1 clients will only generate
1502   them in requests to proxies.
1505   The authority form is only used by the CONNECT method (&CONNECT;).
1508   The most common form of request-target is that used to identify a
1509   resource on an origin server or gateway. In this case the absolute
1510   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1511   the request-target, and the network location of the URI (authority) &MUST;
1512   be transmitted in a Host header field. For example, a client wishing
1513   to retrieve the resource above directly from the origin server would
1514   create a TCP connection to port 80 of the host "" and send
1515   the lines:
1517<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1518GET /pub/WWW/TheProject.html HTTP/1.1
1522   followed by the remainder of the Request. Note that the absolute path
1523   cannot be empty; if none is present in the original URI, it &MUST; be
1524   given as "/" (the server root).
1527   If a proxy receives a request without any path in the request-target and
1528   the method specified is capable of supporting the asterisk form of
1529   request-target, then the last proxy on the request chain &MUST; forward the
1530   request with "*" as the final request-target.
1533   For example, the request
1534</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1538  would be forwarded by the proxy as
1539</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1540OPTIONS * HTTP/1.1
1544   after connecting to port 8001 of host "".
1548   The request-target is transmitted in the format specified in
1549   <xref target="http.uri"/>. If the request-target is percent-encoded
1550   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1551   &MUST; decode the request-target in order to
1552   properly interpret the request. Servers &SHOULD; respond to invalid
1553   request-targets with an appropriate status code.
1556   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1557   received request-target when forwarding it to the next inbound server,
1558   except as noted above to replace a null path-absolute with "/" or "*".
1561  <t>
1562    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1563    meaning of the request when the origin server is improperly using
1564    a non-reserved URI character for a reserved purpose.  Implementors
1565    should be aware that some pre-HTTP/1.1 proxies have been known to
1566    rewrite the request-target.
1567  </t>
1570   HTTP does not place a pre-defined limit on the length of a request-target.
1571   A server &MUST; be prepared to receive URIs of unbounded length and
1572   respond with the 414 (URI Too Long) status if the received
1573   request-target would be longer than the server wishes to handle
1574   (see &status-414;).
1577   Various ad-hoc limitations on request-target length are found in practice.
1578   It is &RECOMMENDED; that all HTTP senders and recipients support
1579   request-target lengths of 8000 or more octets.
1582  <t>
1583    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1584    are not part of the request-target and thus will not be transmitted
1585    in an HTTP request.
1586  </t>
1591<section title="The Resource Identified by a Request" anchor="">
1593   The exact resource identified by an Internet request is determined by
1594   examining both the request-target and the Host header field.
1597   An origin server that does not allow resources to differ by the
1598   requested host &MAY; ignore the Host header field value when
1599   determining the resource identified by an HTTP/1.1 request. (But see
1600   <xref target=""/>
1601   for other requirements on Host support in HTTP/1.1.)
1604   An origin server that does differentiate resources based on the host
1605   requested (sometimes referred to as virtual hosts or vanity host
1606   names) &MUST; use the following rules for determining the requested
1607   resource on an HTTP/1.1 request:
1608  <list style="numbers">
1609    <t>If request-target is an absolute-URI, the host is part of the
1610     request-target. Any Host header field value in the request &MUST; be
1611     ignored.</t>
1612    <t>If the request-target is not an absolute-URI, and the request includes
1613     a Host header field, the host is determined by the Host header
1614     field value.</t>
1615    <t>If the host as determined by rule 1 or 2 is not a valid host on
1616     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1617  </list>
1620   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1621   attempt to use heuristics (e.g., examination of the URI path for
1622   something unique to a particular host) in order to determine what
1623   exact resource is being requested.
1627<section title="Effective Request URI" anchor="effective.request.uri">
1628  <iref primary="true" item="Effective Request URI"/>
1630   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1631   for the resource they are intended for; instead, the value needs to be inferred from the
1632   request-target, Host header and other context. The result of this process is
1633   the "Effective Request URI".
1636   If the request-target is an absolute-URI, then the Effective Request URI is
1637   the request-target.
1640   If the request-target uses the path-absolute (plus optional query) syntax
1641   or if it is just the asterisk "*", then the Effective Request URI is
1642   constructed by concatenating
1645  <list style="symbols">
1646    <t>
1647      the scheme name: "http" if the request was received over an insecure
1648      TCP connection, or "https" when received over SSL/TLS-secured TCP
1649      connection,
1650    </t>
1651    <t>
1652      the character sequence "://",
1653    </t>
1654    <t>
1655      the authority component, as specified in the Host header
1656      (<xref target=""/>) and determined by the rules in
1657      <xref target=""/>,
1658      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1659      described in <xref target=""/>?</cref>
1660      and
1661    </t>
1662    <t>
1663      the request-target obtained from the Request-Line, unless the
1664      request-target is just the asterisk "*".
1665    </t>
1666  </list>
1669   Otherwise, when request-target uses the authority form, the Effective
1670   Request URI is undefined.
1674   Example 1: the Effective Request URI for the message
1676<artwork type="example" x:indent-with="  ">
1677GET /pub/WWW/TheProject.html HTTP/1.1
1681  (received over an insecure TCP connection) is "http", plus "://", plus the
1682  authority component "", plus the request-target
1683  "/pub/WWW/TheProject.html", thus
1684  "".
1689   Example 2: the Effective Request URI for the message
1691<artwork type="example" x:indent-with="  ">
1692GET * HTTP/1.1
1696  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1697  authority component "", thus "".
1701   Effective Request URIs are compared using the rules described in
1702   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1703   be treated as equivalent to an absolute path of "/".
1710<section title="Response" anchor="response">
1711  <x:anchor-alias value="Response"/>
1713   After receiving and interpreting a request message, a server responds
1714   with an HTTP response message.
1716<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1717  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1718                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1719                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1720                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1721                  <x:ref>CRLF</x:ref>
1722                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1725<section title="Status-Line" anchor="status-line">
1726  <x:anchor-alias value="Status-Line"/>
1728   The first line of a Response message is the Status-Line, consisting
1729   of the protocol version followed by a numeric status code and its
1730   associated textual phrase, with each element separated by SP
1731   characters. No CR or LF is allowed except in the final CRLF sequence.
1733<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1734  <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>
1737<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1738  <x:anchor-alias value="Reason-Phrase"/>
1739  <x:anchor-alias value="Status-Code"/>
1741   The Status-Code element is a 3-digit integer result code of the
1742   attempt to understand and satisfy the request. These codes are fully
1743   defined in &status-codes;.  The Reason Phrase exists for the sole
1744   purpose of providing a textual description associated with the numeric
1745   status code, out of deference to earlier Internet application protocols
1746   that were more frequently used with interactive text clients.
1747   A client &SHOULD; ignore the content of the Reason Phrase.
1750   The first digit of the Status-Code defines the class of response. The
1751   last two digits do not have any categorization role. There are 5
1752   values for the first digit:
1753  <list style="symbols">
1754    <t>
1755      1xx: Informational - Request received, continuing process
1756    </t>
1757    <t>
1758      2xx: Success - The action was successfully received,
1759        understood, and accepted
1760    </t>
1761    <t>
1762      3xx: Redirection - Further action must be taken in order to
1763        complete the request
1764    </t>
1765    <t>
1766      4xx: Client Error - The request contains bad syntax or cannot
1767        be fulfilled
1768    </t>
1769    <t>
1770      5xx: Server Error - The server failed to fulfill an apparently
1771        valid request
1772    </t>
1773  </list>
1775<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1776  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1777  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1785<section title="Protocol Parameters" anchor="protocol.parameters">
1787<section title="Date/Time Formats: Full Date" anchor="">
1788  <x:anchor-alias value="HTTP-date"/>
1790   HTTP applications have historically allowed three different formats
1791   for date/time stamps.
1792   However, the preferred format is
1793   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1795<figure><artwork type="example" x:indent-with="  ">
1796Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1799   The other formats are described here only for compatibility with obsolete
1800   implementations.
1802<figure><artwork type="example" x:indent-with="  ">
1803Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1804Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1807   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1808   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1809   only generate the RFC 1123 format for representing HTTP-date values
1810   in header fields. See <xref target="tolerant.applications"/> for further information.
1813   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1814   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1815   equal to UTC (Coordinated Universal Time). This is indicated in the
1816   first two formats by the inclusion of "GMT" as the three-letter
1817   abbreviation for time zone, and &MUST; be assumed when reading the
1818   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1819   additional whitespace beyond that specifically included as SP in the
1820   grammar.
1822<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1823  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1825<t anchor="">
1826  <x:anchor-alias value="rfc1123-date"/>
1827  <x:anchor-alias value="time-of-day"/>
1828  <x:anchor-alias value="hour"/>
1829  <x:anchor-alias value="minute"/>
1830  <x:anchor-alias value="second"/>
1831  <x:anchor-alias value="day-name"/>
1832  <x:anchor-alias value="day"/>
1833  <x:anchor-alias value="month"/>
1834  <x:anchor-alias value="year"/>
1835  <x:anchor-alias value="GMT"/>
1836  Preferred format:
1838<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"/>
1839  <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>
1841  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1842               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1843               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1844               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1845               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1846               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1847               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1849  <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>
1850               ; e.g., 02 Jun 1982
1852  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1853  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1854               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1855               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1856               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1857               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1858               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1859               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1860               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1861               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1862               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1863               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1864               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1865  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1867  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1869  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1870                 ; 00:00:00 - 23:59:59
1872  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1873  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1874  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1877  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1878  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1879  same as those defined for the RFC 5322 constructs
1880  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1882<t anchor="">
1883  <x:anchor-alias value="obs-date"/>
1884  <x:anchor-alias value="rfc850-date"/>
1885  <x:anchor-alias value="asctime-date"/>
1886  <x:anchor-alias value="date1"/>
1887  <x:anchor-alias value="date2"/>
1888  <x:anchor-alias value="date3"/>
1889  <x:anchor-alias value="rfc1123-date"/>
1890  <x:anchor-alias value="day-name-l"/>
1891  Obsolete formats:
1893<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1894  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1896<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1897  <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>
1898  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1899                 ; day-month-year (e.g., 02-Jun-82)
1901  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1902         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1903         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1904         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1905         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1906         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1907         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1909<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1910  <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>
1911  <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> ))
1912                 ; month day (e.g., Jun  2)
1915  <t>
1916    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1917    accepting date values that may have been sent by non-HTTP
1918    applications, as is sometimes the case when retrieving or posting
1919    messages via proxies/gateways to SMTP or NNTP.
1920  </t>
1923  <t>
1924    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1925    to their usage within the protocol stream. Clients and servers are
1926    not required to use these formats for user presentation, request
1927    logging, etc.
1928  </t>
1932<section title="Transfer Codings" anchor="transfer.codings">
1933  <x:anchor-alias value="transfer-coding"/>
1934  <x:anchor-alias value="transfer-extension"/>
1936   Transfer-coding values are used to indicate an encoding
1937   transformation that has been, can be, or may need to be applied to a
1938   payload body in order to ensure "safe transport" through the network.
1939   This differs from a content coding in that the transfer-coding is a
1940   property of the message rather than a property of the representation
1941   that is being transferred.
1943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1944  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1945                          / "compress" ; <xref target="compress.coding"/>
1946                          / "deflate" ; <xref target="deflate.coding"/>
1947                          / "gzip" ; <xref target="gzip.coding"/>
1948                          / <x:ref>transfer-extension</x:ref>
1949  <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> )
1951<t anchor="rule.parameter">
1952  <x:anchor-alias value="attribute"/>
1953  <x:anchor-alias value="transfer-parameter"/>
1954  <x:anchor-alias value="value"/>
1955   Parameters are in the form of attribute/value pairs.
1957<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"/>
1958  <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>
1959  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1960  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1963   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1964   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1965   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1968   Whenever a transfer-coding is applied to a payload body, the set of
1969   transfer-codings &MUST; include "chunked", unless the message indicates it
1970   is terminated by closing the connection. When the "chunked" transfer-coding
1971   is used, it &MUST; be the last transfer-coding applied to form the
1972   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1973   than once to a message-body. These rules allow the recipient to
1974   determine the message-body length of the message (<xref target="message.body.length"/>).
1977   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1978   MIME, which were designed to enable safe transport of binary data over a
1979   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1980   However, safe transport
1981   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1982   the only unsafe characteristic of message-bodies is the difficulty in
1983   determining the exact body length (<xref target="message.body.length"/>), or the desire to
1984   encrypt data over a shared transport.
1987   A server that receives a request message with a transfer-coding it does
1988   not understand &SHOULD; respond with 501 (Not Implemented) and then
1989   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1990   client.
1993<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1994  <iref item="chunked (Coding Format)"/>
1995  <iref item="Coding Format" subitem="chunked"/>
1996  <x:anchor-alias value="chunk"/>
1997  <x:anchor-alias value="Chunked-Body"/>
1998  <x:anchor-alias value="chunk-data"/>
1999  <x:anchor-alias value="chunk-ext"/>
2000  <x:anchor-alias value="chunk-ext-name"/>
2001  <x:anchor-alias value="chunk-ext-val"/>
2002  <x:anchor-alias value="chunk-size"/>
2003  <x:anchor-alias value="last-chunk"/>
2004  <x:anchor-alias value="trailer-part"/>
2005  <x:anchor-alias value="quoted-str-nf"/>
2006  <x:anchor-alias value="qdtext-nf"/>
2008   The chunked encoding modifies the body of a message in order to
2009   transfer it as a series of chunks, each with its own size indicator,
2010   followed by an &OPTIONAL; trailer containing entity-header fields. This
2011   allows dynamically produced content to be transferred along with the
2012   information necessary for the recipient to verify that it has
2013   received the full message.
2015<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"/>
2016  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2017                   <x:ref>last-chunk</x:ref>
2018                   <x:ref>trailer-part</x:ref>
2019                   <x:ref>CRLF</x:ref>
2021  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2022                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2023  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2024  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2026  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2027                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2028  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2029  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2030  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2031  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
2033  <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>
2034                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2035  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2036                 ; <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>
2039   The chunk-size field is a string of hex digits indicating the size of
2040   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2041   zero, followed by the trailer, which is terminated by an empty line.
2044   The trailer allows the sender to include additional HTTP header
2045   fields at the end of the message. The Trailer header field can be
2046   used to indicate which header fields are included in a trailer (see
2047   <xref target="header.trailer"/>).
2050   A server using chunked transfer-coding in a response &MUST-NOT; use the
2051   trailer for any header fields unless at least one of the following is
2052   true:
2053  <list style="numbers">
2054    <t>the request included a TE header field that indicates "trailers" is
2055     acceptable in the transfer-coding of the  response, as described in
2056     <xref target="header.te"/>; or,</t>
2058    <t>the server is the origin server for the response, the trailer
2059     fields consist entirely of optional metadata, and the recipient
2060     could use the message (in a manner acceptable to the origin server)
2061     without receiving this metadata.  In other words, the origin server
2062     is willing to accept the possibility that the trailer fields might
2063     be silently discarded along the path to the client.</t>
2064  </list>
2067   This requirement prevents an interoperability failure when the
2068   message is being received by an HTTP/1.1 (or later) proxy and
2069   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2070   compliance with the protocol would have necessitated a possibly
2071   infinite buffer on the proxy.
2074   A process for decoding the "chunked" transfer-coding
2075   can be represented in pseudo-code as:
2077<figure><artwork type="code">
2078  length := 0
2079  read chunk-size, chunk-ext (if any) and CRLF
2080  while (chunk-size &gt; 0) {
2081     read chunk-data and CRLF
2082     append chunk-data to decoded-body
2083     length := length + chunk-size
2084     read chunk-size and CRLF
2085  }
2086  read header-field
2087  while (header-field not empty) {
2088     append header-field to existing header fields
2089     read header-field
2090  }
2091  Content-Length := length
2092  Remove "chunked" from Transfer-Encoding
2095   All HTTP/1.1 applications &MUST; be able to receive and decode the
2096   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2097   they do not understand.
2101<section title="Compression Codings" anchor="compression.codings">
2103   The codings defined below can be used to compress the payload of a
2104   message.
2107   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2108   is not desirable and is discouraged for future encodings. Their
2109   use here is representative of historical practice, not good
2110   design.
2113   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2114   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2115   equivalent to "gzip" and "compress" respectively.
2118<section title="Compress Coding" anchor="compress.coding">
2119<iref item="compress (Coding Format)"/>
2120<iref item="Coding Format" subitem="compress"/>
2122   The "compress" format is produced by the common UNIX file compression
2123   program "compress". This format is an adaptive Lempel-Ziv-Welch
2124   coding (LZW).
2128<section title="Deflate Coding" anchor="deflate.coding">
2129<iref item="deflate (Coding Format)"/>
2130<iref item="Coding Format" subitem="deflate"/>
2132   The "deflate" format is defined as the "deflate" compression mechanism
2133   (described in <xref target="RFC1951"/>) used inside the "zlib"
2134   data format (<xref target="RFC1950"/>).
2137  <t>
2138    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2139    compressed data without the zlib wrapper.
2140   </t>
2144<section title="Gzip Coding" anchor="gzip.coding">
2145<iref item="gzip (Coding Format)"/>
2146<iref item="Coding Format" subitem="gzip"/>
2148   The "gzip" format is produced by the file compression program
2149   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2150   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2156<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2158   The HTTP Transfer Coding Registry defines the name space for the transfer
2159   coding names.
2162   Registrations &MUST; include the following fields:
2163   <list style="symbols">
2164     <t>Name</t>
2165     <t>Description</t>
2166     <t>Pointer to specification text</t>
2167   </list>
2170   Names of transfer codings &MUST-NOT; overlap with names of content codings
2171   (&content-codings;), unless the encoding transformation is identical (as it
2172   is the case for the compression codings defined in
2173   <xref target="compression.codings"/>).
2176   Values to be added to this name space require expert review and a specification
2177   (see "Expert Review" and "Specification Required" in
2178   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2179   conform to the purpose of transfer coding defined in this section.
2182   The registry itself is maintained at
2183   <eref target=""/>.
2188<section title="Product Tokens" anchor="product.tokens">
2189  <x:anchor-alias value="product"/>
2190  <x:anchor-alias value="product-version"/>
2192   Product tokens are used to allow communicating applications to
2193   identify themselves by software name and version. Most fields using
2194   product tokens also allow sub-products which form a significant part
2195   of the application to be listed, separated by whitespace. By
2196   convention, the products are listed in order of their significance
2197   for identifying the application.
2199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2200  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2201  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2204   Examples:
2206<figure><artwork type="example">
2207  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2208  Server: Apache/0.8.4
2211   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2212   used for advertising or other non-essential information. Although any
2213   token character &MAY; appear in a product-version, this token &SHOULD;
2214   only be used for a version identifier (i.e., successive versions of
2215   the same product &SHOULD; only differ in the product-version portion of
2216   the product value).
2220<section title="Quality Values" anchor="quality.values">
2221  <x:anchor-alias value="qvalue"/>
2223   Both transfer codings (TE request header, <xref target="header.te"/>)
2224   and content negotiation (&content.negotiation;) use short "floating point"
2225   numbers to indicate the relative importance ("weight") of various
2226   negotiable parameters.  A weight is normalized to a real number in
2227   the range 0 through 1, where 0 is the minimum and 1 the maximum
2228   value. If a parameter has a quality value of 0, then content with
2229   this parameter is "not acceptable" for the client. HTTP/1.1
2230   applications &MUST-NOT; generate more than three digits after the
2231   decimal point. User configuration of these values &SHOULD; also be
2232   limited in this fashion.
2234<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2235  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2236                 / ( "1" [ "." 0*3("0") ] )
2239  <t>
2240     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2241     relative degradation in desired quality.
2242  </t>
2248<section title="Connections" anchor="connections">
2250<section title="Persistent Connections" anchor="persistent.connections">
2252<section title="Purpose" anchor="persistent.purpose">
2254   Prior to persistent connections, a separate TCP connection was
2255   established to fetch each URL, increasing the load on HTTP servers
2256   and causing congestion on the Internet. The use of inline images and
2257   other associated data often requires a client to make multiple
2258   requests of the same server in a short amount of time. Analysis of
2259   these performance problems and results from a prototype
2260   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2261   measurements of actual HTTP/1.1 implementations show good
2262   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2263   T/TCP <xref target="Tou1998"/>.
2266   Persistent HTTP connections have a number of advantages:
2267  <list style="symbols">
2268      <t>
2269        By opening and closing fewer TCP connections, CPU time is saved
2270        in routers and hosts (clients, servers, proxies, gateways,
2271        tunnels, or caches), and memory used for TCP protocol control
2272        blocks can be saved in hosts.
2273      </t>
2274      <t>
2275        HTTP requests and responses can be pipelined on a connection.
2276        Pipelining allows a client to make multiple requests without
2277        waiting for each response, allowing a single TCP connection to
2278        be used much more efficiently, with much lower elapsed time.
2279      </t>
2280      <t>
2281        Network congestion is reduced by reducing the number of packets
2282        caused by TCP opens, and by allowing TCP sufficient time to
2283        determine the congestion state of the network.
2284      </t>
2285      <t>
2286        Latency on subsequent requests is reduced since there is no time
2287        spent in TCP's connection opening handshake.
2288      </t>
2289      <t>
2290        HTTP can evolve more gracefully, since errors can be reported
2291        without the penalty of closing the TCP connection. Clients using
2292        future versions of HTTP might optimistically try a new feature,
2293        but if communicating with an older server, retry with old
2294        semantics after an error is reported.
2295      </t>
2296    </list>
2299   HTTP implementations &SHOULD; implement persistent connections.
2303<section title="Overall Operation" anchor="persistent.overall">
2305   A significant difference between HTTP/1.1 and earlier versions of
2306   HTTP is that persistent connections are the default behavior of any
2307   HTTP connection. That is, unless otherwise indicated, the client
2308   &SHOULD; assume that the server will maintain a persistent connection,
2309   even after error responses from the server.
2312   Persistent connections provide a mechanism by which a client and a
2313   server can signal the close of a TCP connection. This signaling takes
2314   place using the Connection header field (<xref target="header.connection"/>). Once a close
2315   has been signaled, the client &MUST-NOT; send any more requests on that
2316   connection.
2319<section title="Negotiation" anchor="persistent.negotiation">
2321   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2322   maintain a persistent connection unless a Connection header including
2323   the connection-token "close" was sent in the request. If the server
2324   chooses to close the connection immediately after sending the
2325   response, it &SHOULD; send a Connection header including the
2326   connection-token "close".
2329   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2330   decide to keep it open based on whether the response from a server
2331   contains a Connection header with the connection-token close. In case
2332   the client does not want to maintain a connection for more than that
2333   request, it &SHOULD; send a Connection header including the
2334   connection-token close.
2337   If either the client or the server sends the close token in the
2338   Connection header, that request becomes the last one for the
2339   connection.
2342   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2343   maintained for HTTP versions less than 1.1 unless it is explicitly
2344   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2345   compatibility with HTTP/1.0 clients.
2348   In order to remain persistent, all messages on the connection &MUST;
2349   have a self-defined message length (i.e., one not defined by closure
2350   of the connection), as described in <xref target="message.body.length"/>.
2354<section title="Pipelining" anchor="pipelining">
2356   A client that supports persistent connections &MAY; "pipeline" its
2357   requests (i.e., send multiple requests without waiting for each
2358   response). A server &MUST; send its responses to those requests in the
2359   same order that the requests were received.
2362   Clients which assume persistent connections and pipeline immediately
2363   after connection establishment &SHOULD; be prepared to retry their
2364   connection if the first pipelined attempt fails. If a client does
2365   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2366   persistent. Clients &MUST; also be prepared to resend their requests if
2367   the server closes the connection before sending all of the
2368   corresponding responses.
2371   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2372   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2373   premature termination of the transport connection could lead to
2374   indeterminate results. A client wishing to send a non-idempotent
2375   request &SHOULD; wait to send that request until it has received the
2376   response status for the previous request.
2381<section title="Proxy Servers" anchor="persistent.proxy">
2383   It is especially important that proxies correctly implement the
2384   properties of the Connection header field as specified in <xref target="header.connection"/>.
2387   The proxy server &MUST; signal persistent connections separately with
2388   its clients and the origin servers (or other proxy servers) that it
2389   connects to. Each persistent connection applies to only one transport
2390   link.
2393   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2394   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2395   for information and discussion of the problems with the Keep-Alive header
2396   implemented by many HTTP/1.0 clients).
2399<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2401  <cref anchor="TODO-end-to-end" source="jre">
2402    Restored from <eref target=""/>.
2403    See also <eref target=""/>.
2404  </cref>
2407   For the purpose of defining the behavior of caches and non-caching
2408   proxies, we divide HTTP headers into two categories:
2409  <list style="symbols">
2410      <t>End-to-end headers, which are  transmitted to the ultimate
2411        recipient of a request or response. End-to-end headers in
2412        responses MUST be stored as part of a cache entry and &MUST; be
2413        transmitted in any response formed from a cache entry.</t>
2415      <t>Hop-by-hop headers, which are meaningful only for a single
2416        transport-level connection, and are not stored by caches or
2417        forwarded by proxies.</t>
2418  </list>
2421   The following HTTP/1.1 headers are hop-by-hop headers:
2422  <list style="symbols">
2423      <t>Connection</t>
2424      <t>Keep-Alive</t>
2425      <t>Proxy-Authenticate</t>
2426      <t>Proxy-Authorization</t>
2427      <t>TE</t>
2428      <t>Trailer</t>
2429      <t>Transfer-Encoding</t>
2430      <t>Upgrade</t>
2431  </list>
2434   All other headers defined by HTTP/1.1 are end-to-end headers.
2437   Other hop-by-hop headers &MUST; be listed in a Connection header
2438   (<xref target="header.connection"/>).
2442<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2444  <cref anchor="TODO-non-mod-headers" source="jre">
2445    Restored from <eref target=""/>.
2446    See also <eref target=""/>.
2447  </cref>
2450   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2451   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2452   modify an end-to-end header unless the definition of that header requires
2453   or specifically allows that.
2456   A transparent proxy &MUST-NOT; modify any of the following fields in a
2457   request or response, and it &MUST-NOT; add any of these fields if not
2458   already present:
2459  <list style="symbols">
2460      <t>Content-Location</t>
2461      <t>Content-MD5</t>
2462      <t>ETag</t>
2463      <t>Last-Modified</t>
2464  </list>
2467   A transparent proxy &MUST-NOT; modify any of the following fields in a
2468   response:
2469  <list style="symbols">
2470    <t>Expires</t>
2471  </list>
2474   but it &MAY; add any of these fields if not already present. If an
2475   Expires header is added, it &MUST; be given a field-value identical to
2476   that of the Date header in that response.
2479   A proxy &MUST-NOT; modify or add any of the following fields in a
2480   message that contains the no-transform cache-control directive, or in
2481   any request:
2482  <list style="symbols">
2483    <t>Content-Encoding</t>
2484    <t>Content-Range</t>
2485    <t>Content-Type</t>
2486  </list>
2489   A non-transparent proxy &MAY; modify or add these fields to a message
2490   that does not include no-transform, but if it does so, it &MUST; add a
2491   Warning 214 (Transformation applied) if one does not already appear
2492   in the message (see &header-warning;).
2495  <t>
2496    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2497    cause authentication failures if stronger authentication
2498    mechanisms are introduced in later versions of HTTP. Such
2499    authentication mechanisms &MAY; rely on the values of header fields
2500    not listed here.
2501  </t>
2504   A transparent proxy &MUST; preserve the message payload (&payload;),
2505   though it &MAY; change the message-body through application or removal
2506   of a transfer-coding (<xref target="transfer.codings"/>).
2512<section title="Practical Considerations" anchor="persistent.practical">
2514   Servers will usually have some time-out value beyond which they will
2515   no longer maintain an inactive connection. Proxy servers might make
2516   this a higher value since it is likely that the client will be making
2517   more connections through the same server. The use of persistent
2518   connections places no requirements on the length (or existence) of
2519   this time-out for either the client or the server.
2522   When a client or server wishes to time-out it &SHOULD; issue a graceful
2523   close on the transport connection. Clients and servers &SHOULD; both
2524   constantly watch for the other side of the transport close, and
2525   respond to it as appropriate. If a client or server does not detect
2526   the other side's close promptly it could cause unnecessary resource
2527   drain on the network.
2530   A client, server, or proxy &MAY; close the transport connection at any
2531   time. For example, a client might have started to send a new request
2532   at the same time that the server has decided to close the "idle"
2533   connection. From the server's point of view, the connection is being
2534   closed while it was idle, but from the client's point of view, a
2535   request is in progress.
2538   This means that clients, servers, and proxies &MUST; be able to recover
2539   from asynchronous close events. Client software &SHOULD; reopen the
2540   transport connection and retransmit the aborted sequence of requests
2541   without user interaction so long as the request sequence is
2542   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2543   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2544   human operator the choice of retrying the request(s). Confirmation by
2545   user-agent software with semantic understanding of the application
2546   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2547   be repeated if the second sequence of requests fails.
2550   Servers &SHOULD; always respond to at least one request per connection,
2551   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2552   middle of transmitting a response, unless a network or client failure
2553   is suspected.
2556   Clients (including proxies) &SHOULD; limit the number of simultaneous
2557   connections that they maintain to a given server (including proxies).
2560   Previous revisions of HTTP gave a specific number of connections as a
2561   ceiling, but this was found to be impractical for many applications. As a
2562   result, this specification does not mandate a particular maximum number of
2563   connections, but instead encourages clients to be conservative when opening
2564   multiple connections.
2567   In particular, while using multiple connections avoids the "head-of-line
2568   blocking" problem (whereby a request that takes significant server-side
2569   processing and/or has a large payload can block subsequent requests on the
2570   same connection), each connection used consumes server resources (sometimes
2571   significantly), and furthermore using multiple connections can cause
2572   undesirable side effects in congested networks.
2575   Note that servers might reject traffic that they deem abusive, including an
2576   excessive number of connections from a client.
2581<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2583<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2585   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2586   flow control mechanisms to resolve temporary overloads, rather than
2587   terminating connections with the expectation that clients will retry.
2588   The latter technique can exacerbate network congestion.
2592<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2594   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2595   the network connection for an error status while it is transmitting
2596   the request. If the client sees an error status, it &SHOULD;
2597   immediately cease transmitting the body. If the body is being sent
2598   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2599   empty trailer &MAY; be used to prematurely mark the end of the message.
2600   If the body was preceded by a Content-Length header, the client &MUST;
2601   close the connection.
2605<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2607   The purpose of the 100 (Continue) status (see &status-100;) is to
2608   allow a client that is sending a request message with a request body
2609   to determine if the origin server is willing to accept the request
2610   (based on the request headers) before the client sends the request
2611   body. In some cases, it might either be inappropriate or highly
2612   inefficient for the client to send the body if the server will reject
2613   the message without looking at the body.
2616   Requirements for HTTP/1.1 clients:
2617  <list style="symbols">
2618    <t>
2619        If a client will wait for a 100 (Continue) response before
2620        sending the request body, it &MUST; send an Expect request-header
2621        field (&header-expect;) with the "100-continue" expectation.
2622    </t>
2623    <t>
2624        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2625        with the "100-continue" expectation if it does not intend
2626        to send a request body.
2627    </t>
2628  </list>
2631   Because of the presence of older implementations, the protocol allows
2632   ambiguous situations in which a client may send "Expect: 100-continue"
2633   without receiving either a 417 (Expectation Failed) status
2634   or a 100 (Continue) status. Therefore, when a client sends this
2635   header field to an origin server (possibly via a proxy) from which it
2636   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2637   for an indefinite period before sending the request body.
2640   Requirements for HTTP/1.1 origin servers:
2641  <list style="symbols">
2642    <t> Upon receiving a request which includes an Expect request-header
2643        field with the "100-continue" expectation, an origin server &MUST;
2644        either respond with 100 (Continue) status and continue to read
2645        from the input stream, or respond with a final status code. The
2646        origin server &MUST-NOT; wait for the request body before sending
2647        the 100 (Continue) response. If it responds with a final status
2648        code, it &MAY; close the transport connection or it &MAY; continue
2649        to read and discard the rest of the request.  It &MUST-NOT;
2650        perform the requested method if it returns a final status code.
2651    </t>
2652    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2653        the request message does not include an Expect request-header
2654        field with the "100-continue" expectation, and &MUST-NOT; send a
2655        100 (Continue) response if such a request comes from an HTTP/1.0
2656        (or earlier) client. There is an exception to this rule: for
2657        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2658        status in response to an HTTP/1.1 PUT or POST request that does
2659        not include an Expect request-header field with the "100-continue"
2660        expectation. This exception, the purpose of which is
2661        to minimize any client processing delays associated with an
2662        undeclared wait for 100 (Continue) status, applies only to
2663        HTTP/1.1 requests, and not to requests with any other HTTP-version
2664        value.
2665    </t>
2666    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2667        already received some or all of the request body for the
2668        corresponding request.
2669    </t>
2670    <t> An origin server that sends a 100 (Continue) response &MUST;
2671    ultimately send a final status code, once the request body is
2672        received and processed, unless it terminates the transport
2673        connection prematurely.
2674    </t>
2675    <t> If an origin server receives a request that does not include an
2676        Expect request-header field with the "100-continue" expectation,
2677        the request includes a request body, and the server responds
2678        with a final status code before reading the entire request body
2679        from the transport connection, then the server &SHOULD-NOT;  close
2680        the transport connection until it has read the entire request,
2681        or until the client closes the connection. Otherwise, the client
2682        might not reliably receive the response message. However, this
2683        requirement is not be construed as preventing a server from
2684        defending itself against denial-of-service attacks, or from
2685        badly broken client implementations.
2686      </t>
2687    </list>
2690   Requirements for HTTP/1.1 proxies:
2691  <list style="symbols">
2692    <t> If a proxy receives a request that includes an Expect request-header
2693        field with the "100-continue" expectation, and the proxy
2694        either knows that the next-hop server complies with HTTP/1.1 or
2695        higher, or does not know the HTTP version of the next-hop
2696        server, it &MUST; forward the request, including the Expect header
2697        field.
2698    </t>
2699    <t> If the proxy knows that the version of the next-hop server is
2700        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2701        respond with a 417 (Expectation Failed) status.
2702    </t>
2703    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2704        numbers received from recently-referenced next-hop servers.
2705    </t>
2706    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2707        request message was received from an HTTP/1.0 (or earlier)
2708        client and did not include an Expect request-header field with
2709        the "100-continue" expectation. This requirement overrides the
2710        general rule for forwarding of 1xx responses (see &status-1xx;).
2711    </t>
2712  </list>
2716<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2718   If an HTTP/1.1 client sends a request which includes a request body,
2719   but which does not include an Expect request-header field with the
2720   "100-continue" expectation, and if the client is not directly
2721   connected to an HTTP/1.1 origin server, and if the client sees the
2722   connection close before receiving any status from the server, the
2723   client &SHOULD; retry the request.  If the client does retry this
2724   request, it &MAY; use the following "binary exponential backoff"
2725   algorithm to be assured of obtaining a reliable response:
2726  <list style="numbers">
2727    <t>
2728      Initiate a new connection to the server
2729    </t>
2730    <t>
2731      Transmit the request-headers
2732    </t>
2733    <t>
2734      Initialize a variable R to the estimated round-trip time to the
2735         server (e.g., based on the time it took to establish the
2736         connection), or to a constant value of 5 seconds if the round-trip
2737         time is not available.
2738    </t>
2739    <t>
2740       Compute T = R * (2**N), where N is the number of previous
2741         retries of this request.
2742    </t>
2743    <t>
2744       Wait either for an error response from the server, or for T
2745         seconds (whichever comes first)
2746    </t>
2747    <t>
2748       If no error response is received, after T seconds transmit the
2749         body of the request.
2750    </t>
2751    <t>
2752       If client sees that the connection is closed prematurely,
2753         repeat from step 1 until the request is accepted, an error
2754         response is received, or the user becomes impatient and
2755         terminates the retry process.
2756    </t>
2757  </list>
2760   If at any point an error status is received, the client
2761  <list style="symbols">
2762      <t>&SHOULD-NOT;  continue and</t>
2764      <t>&SHOULD; close the connection if it has not completed sending the
2765        request message.</t>
2766    </list>
2773<section title="Miscellaneous notes that may disappear" anchor="misc">
2774<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2776   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2780<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2782   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2786<section title="Interception of HTTP for access control" anchor="http.intercept">
2788   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2792<section title="Use of HTTP by other protocols" anchor="http.others">
2794   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2795   Extensions of HTTP like WebDAV.</cref>
2799<section title="Use of HTTP by media type specification" anchor="">
2801   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2806<section title="Header Field Definitions" anchor="header.field.definitions">
2808   This section defines the syntax and semantics of HTTP/1.1 header fields
2809   related to message framing and transport protocols.
2812   For entity-header fields, both sender and recipient refer to either the
2813   client or the server, depending on who sends and who receives the entity.
2816<section title="Connection" anchor="header.connection">
2817  <iref primary="true" item="Connection header" x:for-anchor=""/>
2818  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2819  <x:anchor-alias value="Connection"/>
2820  <x:anchor-alias value="connection-token"/>
2821  <x:anchor-alias value="Connection-v"/>
2823   The "Connection" general-header field allows the sender to specify
2824   options that are desired for that particular connection and &MUST-NOT;
2825   be communicated by proxies over further connections.
2828   The Connection header's value has the following grammar:
2830<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2831  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2832  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2833  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2836   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2837   message is forwarded and, for each connection-token in this field,
2838   remove any header field(s) from the message with the same name as the
2839   connection-token. Connection options are signaled by the presence of
2840   a connection-token in the Connection header field, not by any
2841   corresponding additional header field(s), since the additional header
2842   field may not be sent if there are no parameters associated with that
2843   connection option.
2846   Message headers listed in the Connection header &MUST-NOT; include
2847   end-to-end headers, such as Cache-Control.
2850   HTTP/1.1 defines the "close" connection option for the sender to
2851   signal that the connection will be closed after completion of the
2852   response. For example,
2854<figure><artwork type="example">
2855  Connection: close
2858   in either the request or the response header fields indicates that
2859   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2860   after the current request/response is complete.
2863   An HTTP/1.1 client that does not support persistent connections &MUST;
2864   include the "close" connection option in every request message.
2867   An HTTP/1.1 server that does not support persistent connections &MUST;
2868   include the "close" connection option in every response message that
2869   does not have a 1xx (Informational) status code.
2872   A system receiving an HTTP/1.0 (or lower-version) message that
2873   includes a Connection header &MUST;, for each connection-token in this
2874   field, remove and ignore any header field(s) from the message with
2875   the same name as the connection-token. This protects against mistaken
2876   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2880<section title="Content-Length" anchor="header.content-length">
2881  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2882  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2883  <x:anchor-alias value="Content-Length"/>
2884  <x:anchor-alias value="Content-Length-v"/>
2886   The "Content-Length" header field indicates the size of the
2887   message-body, in decimal number of octets, for any message other than
2888   a response to the HEAD method or a response with a status code of 304.
2889   In the case of responses to the HEAD method, it indicates the size of
2890   the payload body (not including any potential transfer-coding) that
2891   would have been sent had the request been a GET.
2892   In the case of the 304 (Not Modified) response, it indicates the size of
2893   the payload body (not including any potential transfer-coding) that
2894   would have been sent in a 200 (OK) response.
2896<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2897  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2898  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2901   An example is
2903<figure><artwork type="example">
2904  Content-Length: 3495
2907   Implementations &SHOULD; use this field to indicate the message-body
2908   length when no transfer-coding is being applied and the
2909   payload's body length can be determined prior to being transferred.
2912   Any Content-Length greater than or equal to zero is a valid value.
2913   <xref target="message.body.length"/> describes how to determine the length of a message-body
2914   if a Content-Length is not given.
2917   Note that the meaning of this field is significantly different from
2918   the corresponding definition in MIME, where it is an optional field
2919   used within the "message/external-body" content-type.
2923<section title="Date" anchor="">
2924  <iref primary="true" item="Date header" x:for-anchor=""/>
2925  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2926  <x:anchor-alias value="Date"/>
2927  <x:anchor-alias value="Date-v"/>
2929   The "Date" general-header field represents the date and time at which
2930   the message was originated, having the same semantics as the Origination
2931   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2932   The field value is an HTTP-date, as described in <xref target=""/>;
2933   it &MUST; be sent in rfc1123-date format.
2935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2936  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2937  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2940   An example is
2942<figure><artwork type="example">
2943  Date: Tue, 15 Nov 1994 08:12:31 GMT
2946   Origin servers &MUST; include a Date header field in all responses,
2947   except in these cases:
2948  <list style="numbers">
2949      <t>If the response status code is 100 (Continue) or 101 (Switching
2950         Protocols), the response &MAY; include a Date header field, at
2951         the server's option.</t>
2953      <t>If the response status code conveys a server error, e.g., 500
2954         (Internal Server Error) or 503 (Service Unavailable), and it is
2955         inconvenient or impossible to generate a valid Date.</t>
2957      <t>If the server does not have a clock that can provide a
2958         reasonable approximation of the current time, its responses
2959         &MUST-NOT; include a Date header field. In this case, the rules
2960         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2961  </list>
2964   A received message that does not have a Date header field &MUST; be
2965   assigned one by the recipient if the message will be cached by that
2966   recipient or gatewayed via a protocol which requires a Date. An HTTP
2967   implementation without a clock &MUST-NOT; cache responses without
2968   revalidating them on every use. An HTTP cache, especially a shared
2969   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2970   clock with a reliable external standard.
2973   Clients &SHOULD; only send a Date header field in messages that include
2974   a payload, as is usually the case for PUT and POST requests, and even
2975   then it is optional. A client without a clock &MUST-NOT; send a Date
2976   header field in a request.
2979   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2980   time subsequent to the generation of the message. It &SHOULD; represent
2981   the best available approximation of the date and time of message
2982   generation, unless the implementation has no means of generating a
2983   reasonably accurate date and time. In theory, the date ought to
2984   represent the moment just before the payload is generated. In
2985   practice, the date can be generated at any time during the message
2986   origination without affecting its semantic value.
2989<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2991   Some origin server implementations might not have a clock available.
2992   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2993   values to a response, unless these values were associated
2994   with the resource by a system or user with a reliable clock. It &MAY;
2995   assign an Expires value that is known, at or before server
2996   configuration time, to be in the past (this allows "pre-expiration"
2997   of responses without storing separate Expires values for each
2998   resource).
3003<section title="Host" anchor="">
3004  <iref primary="true" item="Host header" x:for-anchor=""/>
3005  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3006  <x:anchor-alias value="Host"/>
3007  <x:anchor-alias value="Host-v"/>
3009   The "Host" request-header field specifies the Internet host and port
3010   number of the resource being requested, allowing the origin server or
3011   gateway to differentiate between internally-ambiguous URLs, such as the root
3012   "/" URL of a server for multiple host names on a single IP address.
3015   The Host field value &MUST; represent the naming authority of the origin
3016   server or gateway given by the original URL obtained from the user or
3017   referring resource (generally an http URI, as described in
3018   <xref target="http.uri"/>).
3020<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3021  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3022  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3025   A "host" without any trailing port information implies the default
3026   port for the service requested (e.g., "80" for an HTTP URL). For
3027   example, a request on the origin server for
3028   &lt;; would properly include:
3030<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3031GET /pub/WWW/ HTTP/1.1
3035   A client &MUST; include a Host header field in all HTTP/1.1 request
3036   messages. If the requested URI does not include an Internet host
3037   name for the service being requested, then the Host header field &MUST;
3038   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3039   request message it forwards does contain an appropriate Host header
3040   field that identifies the service being requested by the proxy. All
3041   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3042   status code to any HTTP/1.1 request message which lacks a Host header
3043   field.
3046   See Sections <xref target="" format="counter"/>
3047   and <xref target="" format="counter"/>
3048   for other requirements relating to Host.
3052<section title="TE" anchor="header.te">
3053  <iref primary="true" item="TE header" x:for-anchor=""/>
3054  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3055  <x:anchor-alias value="TE"/>
3056  <x:anchor-alias value="TE-v"/>
3057  <x:anchor-alias value="t-codings"/>
3058  <x:anchor-alias value="te-params"/>
3059  <x:anchor-alias value="te-ext"/>
3061   The "TE" request-header field indicates what extension transfer-codings
3062   it is willing to accept in the response, and whether or not it is
3063   willing to accept trailer fields in a chunked transfer-coding.
3066   Its value may consist of the keyword "trailers" and/or a comma-separated
3067   list of extension transfer-coding names with optional accept
3068   parameters (as described in <xref target="transfer.codings"/>).
3070<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3071  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3072  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3073  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3074  <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> )
3075  <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> ]
3078   The presence of the keyword "trailers" indicates that the client is
3079   willing to accept trailer fields in a chunked transfer-coding, as
3080   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3081   transfer-coding values even though it does not itself represent a
3082   transfer-coding.
3085   Examples of its use are:
3087<figure><artwork type="example">
3088  TE: deflate
3089  TE:
3090  TE: trailers, deflate;q=0.5
3093   The TE header field only applies to the immediate connection.
3094   Therefore, the keyword &MUST; be supplied within a Connection header
3095   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3098   A server tests whether a transfer-coding is acceptable, according to
3099   a TE field, using these rules:
3100  <list style="numbers">
3101    <x:lt>
3102      <t>The "chunked" transfer-coding is always acceptable. If the
3103         keyword "trailers" is listed, the client indicates that it is
3104         willing to accept trailer fields in the chunked response on
3105         behalf of itself and any downstream clients. The implication is
3106         that, if given, the client is stating that either all
3107         downstream clients are willing to accept trailer fields in the
3108         forwarded response, or that it will attempt to buffer the
3109         response on behalf of downstream recipients.
3110      </t><t>
3111         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3112         chunked response such that a client can be assured of buffering
3113         the entire response.</t>
3114    </x:lt>
3115    <x:lt>
3116      <t>If the transfer-coding being tested is one of the transfer-codings
3117         listed in the TE field, then it is acceptable unless it
3118         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3119         qvalue of 0 means "not acceptable.")</t>
3120    </x:lt>
3121    <x:lt>
3122      <t>If multiple transfer-codings are acceptable, then the
3123         acceptable transfer-coding with the highest non-zero qvalue is
3124         preferred.  The "chunked" transfer-coding always has a qvalue
3125         of 1.</t>
3126    </x:lt>
3127  </list>
3130   If the TE field-value is empty or if no TE field is present, the only
3131   transfer-coding is "chunked". A message with no transfer-coding is
3132   always acceptable.
3136<section title="Trailer" anchor="header.trailer">
3137  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3138  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3139  <x:anchor-alias value="Trailer"/>
3140  <x:anchor-alias value="Trailer-v"/>
3142   The "Trailer" general-header field indicates that the given set of
3143   header fields is present in the trailer of a message encoded with
3144   chunked transfer-coding.
3146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3147  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3148  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3151   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3152   message using chunked transfer-coding with a non-empty trailer. Doing
3153   so allows the recipient to know which header fields to expect in the
3154   trailer.
3157   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3158   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3159   trailer fields in a "chunked" transfer-coding.
3162   Message header fields listed in the Trailer header field &MUST-NOT;
3163   include the following header fields:
3164  <list style="symbols">
3165    <t>Transfer-Encoding</t>
3166    <t>Content-Length</t>
3167    <t>Trailer</t>
3168  </list>
3172<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3173  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3174  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3175  <x:anchor-alias value="Transfer-Encoding"/>
3176  <x:anchor-alias value="Transfer-Encoding-v"/>
3178   The "Transfer-Encoding" general-header field indicates what transfer-codings
3179   (if any) have been applied to the message body. It differs from
3180   Content-Encoding (&content-codings;) in that transfer-codings are a property
3181   of the message (and therefore are removed by intermediaries), whereas
3182   content-codings are not.
3184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3185  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3186                        <x:ref>Transfer-Encoding-v</x:ref>
3187  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3190   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3192<figure><artwork type="example">
3193  Transfer-Encoding: chunked
3196   If multiple encodings have been applied to an entity, the transfer-codings
3197   &MUST; be listed in the order in which they were applied.
3198   Additional information about the encoding parameters &MAY; be provided
3199   by other entity-header fields not defined by this specification.
3202   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3203   header.
3207<section title="Upgrade" anchor="header.upgrade">
3208  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3209  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3210  <x:anchor-alias value="Upgrade"/>
3211  <x:anchor-alias value="Upgrade-v"/>
3213   The "Upgrade" general-header field allows the client to specify what
3214   additional communication protocols it would like to use, if the server
3215   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3216   header field within a 101 (Switching Protocols) response to indicate which
3217   protocol(s) are being switched to.
3219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3220  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3221  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3224   For example,
3226<figure><artwork type="example">
3227  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3230   The Upgrade header field is intended to provide a simple mechanism
3231   for transition from HTTP/1.1 to some other, incompatible protocol. It
3232   does so by allowing the client to advertise its desire to use another
3233   protocol, such as a later version of HTTP with a higher major version
3234   number, even though the current request has been made using HTTP/1.1.
3235   This eases the difficult transition between incompatible protocols by
3236   allowing the client to initiate a request in the more commonly
3237   supported protocol while indicating to the server that it would like
3238   to use a "better" protocol if available (where "better" is determined
3239   by the server, possibly according to the nature of the method and/or
3240   resource being requested).
3243   The Upgrade header field only applies to switching application-layer
3244   protocols upon the existing transport-layer connection. Upgrade
3245   cannot be used to insist on a protocol change; its acceptance and use
3246   by the server is optional. The capabilities and nature of the
3247   application-layer communication after the protocol change is entirely
3248   dependent upon the new protocol chosen, although the first action
3249   after changing the protocol &MUST; be a response to the initial HTTP
3250   request containing the Upgrade header field.
3253   The Upgrade header field only applies to the immediate connection.
3254   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3255   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3256   HTTP/1.1 message.
3259   The Upgrade header field cannot be used to indicate a switch to a
3260   protocol on a different connection. For that purpose, it is more
3261   appropriate to use a 301, 302, 303, or 305 redirection response.
3264   This specification only defines the protocol name "HTTP" for use by
3265   the family of Hypertext Transfer Protocols, as defined by the HTTP
3266   version rules of <xref target="http.version"/> and future updates to this
3267   specification. Additional tokens can be registered with IANA using the
3268   registration procedure defined below. 
3271<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3273   The HTTP Upgrade Token Registry defines the name space for product
3274   tokens used to identify protocols in the Upgrade header field.
3275   Each registered token should be associated with one or a set of
3276   specifications, and with contact information.
3279   Registrations should be allowed on a First Come First Served basis as
3280   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3281   specifications need not be IETF documents or be subject to IESG review, but
3282   should obey the following rules:
3283  <list style="numbers">
3284    <t>A token, once registered, stays registered forever.</t>
3285    <t>The registration &MUST; name a responsible party for the
3286       registration.</t>
3287    <t>The registration &MUST; name a point of contact.</t>
3288    <t>The registration &MAY; name the documentation required for the
3289       token.</t>
3290    <t>The responsible party &MAY; change the registration at any time.
3291       The IANA will keep a record of all such changes, and make them
3292       available upon request.</t>
3293    <t>The responsible party for the first registration of a "product"
3294       token &MUST; approve later registrations of a "version" token
3295       together with that "product" token before they can be registered.</t>
3296    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3297       for a token. This will normally only be used in the case when a
3298       responsible party cannot be contacted.</t>
3299  </list>
3302   It is not required that specifications for upgrade tokens be made
3303   publicly available, but the contact information for the registration
3304   should be.
3311<section title="Via" anchor="header.via">
3312  <iref primary="true" item="Via header" x:for-anchor=""/>
3313  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3314  <x:anchor-alias value="protocol-name"/>
3315  <x:anchor-alias value="protocol-version"/>
3316  <x:anchor-alias value="pseudonym"/>
3317  <x:anchor-alias value="received-by"/>
3318  <x:anchor-alias value="received-protocol"/>
3319  <x:anchor-alias value="Via"/>
3320  <x:anchor-alias value="Via-v"/>
3322   The "Via" general-header field &MUST; be used by gateways and proxies to
3323   indicate the intermediate protocols and recipients between the user
3324   agent and the server on requests, and between the origin server and
3325   the client on responses. It is analogous to the "Received" field defined in
3326   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3327   avoiding request loops, and identifying the protocol capabilities of
3328   all senders along the request/response chain.
3330<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3331  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3332  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3333                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3334  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3335  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3336  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3337  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3338  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3341   The received-protocol indicates the protocol version of the message
3342   received by the server or client along each segment of the
3343   request/response chain. The received-protocol version is appended to
3344   the Via field value when the message is forwarded so that information
3345   about the protocol capabilities of upstream applications remains
3346   visible to all recipients.
3349   The protocol-name is optional if and only if it would be "HTTP". The
3350   received-by field is normally the host and optional port number of a
3351   recipient server or client that subsequently forwarded the message.
3352   However, if the real host is considered to be sensitive information,
3353   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3354   be assumed to be the default port of the received-protocol.
3357   Multiple Via field values represent each proxy or gateway that has
3358   forwarded the message. Each recipient &MUST; append its information
3359   such that the end result is ordered according to the sequence of
3360   forwarding applications.
3363   Comments &MAY; be used in the Via header field to identify the software
3364   of the recipient proxy or gateway, analogous to the User-Agent and
3365   Server header fields. However, all comments in the Via field are
3366   optional and &MAY; be removed by any recipient prior to forwarding the
3367   message.
3370   For example, a request message could be sent from an HTTP/1.0 user
3371   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3372   forward the request to a public proxy at, which completes
3373   the request by forwarding it to the origin server at
3374   The request received by would then have the following
3375   Via header field:
3377<figure><artwork type="example">
3378  Via: 1.0 fred, 1.1 (Apache/1.1)
3381   Proxies and gateways used as a portal through a network firewall
3382   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3383   the firewall region. This information &SHOULD; only be propagated if
3384   explicitly enabled. If not enabled, the received-by host of any host
3385   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3386   for that host.
3389   For organizations that have strong privacy requirements for hiding
3390   internal structures, a proxy &MAY; combine an ordered subsequence of
3391   Via header field entries with identical received-protocol values into
3392   a single such entry. For example,
3394<figure><artwork type="example">
3395  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3398  could be collapsed to
3400<figure><artwork type="example">
3401  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3404   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3405   under the same organizational control and the hosts have already been
3406   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3407   have different received-protocol values.
3413<section title="IANA Considerations" anchor="IANA.considerations">
3415<section title="Message Header Registration" anchor="message.header.registration">
3417   The Message Header Registry located at <eref target=""/> should be updated
3418   with the permanent registrations below (see <xref target="RFC3864"/>):
3420<?BEGININC p1-messaging.iana-headers ?>
3421<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3422<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3423   <ttcol>Header Field Name</ttcol>
3424   <ttcol>Protocol</ttcol>
3425   <ttcol>Status</ttcol>
3426   <ttcol>Reference</ttcol>
3428   <c>Connection</c>
3429   <c>http</c>
3430   <c>standard</c>
3431   <c>
3432      <xref target="header.connection"/>
3433   </c>
3434   <c>Content-Length</c>
3435   <c>http</c>
3436   <c>standard</c>
3437   <c>
3438      <xref target="header.content-length"/>
3439   </c>
3440   <c>Date</c>
3441   <c>http</c>
3442   <c>standard</c>
3443   <c>
3444      <xref target=""/>
3445   </c>
3446   <c>Host</c>
3447   <c>http</c>
3448   <c>standard</c>
3449   <c>
3450      <xref target=""/>
3451   </c>
3452   <c>TE</c>
3453   <c>http</c>
3454   <c>standard</c>
3455   <c>
3456      <xref target="header.te"/>
3457   </c>
3458   <c>Trailer</c>
3459   <c>http</c>
3460   <c>standard</c>
3461   <c>
3462      <xref target="header.trailer"/>
3463   </c>
3464   <c>Transfer-Encoding</c>
3465   <c>http</c>
3466   <c>standard</c>
3467   <c>
3468      <xref target="header.transfer-encoding"/>
3469   </c>
3470   <c>Upgrade</c>
3471   <c>http</c>
3472   <c>standard</c>
3473   <c>
3474      <xref target="header.upgrade"/>
3475   </c>
3476   <c>Via</c>
3477   <c>http</c>
3478   <c>standard</c>
3479   <c>
3480      <xref target="header.via"/>
3481   </c>
3484<?ENDINC p1-messaging.iana-headers ?>
3486   The change controller is: "IETF ( - Internet Engineering Task Force".
3490<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3492   The entries for the "http" and "https" URI Schemes in the registry located at
3493   <eref target=""/>
3494   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3495   and <xref target="https.uri" format="counter"/> of this document
3496   (see <xref target="RFC4395"/>).
3500<section title="Internet Media Type Registrations" anchor="">
3502   This document serves as the specification for the Internet media types
3503   "message/http" and "application/http". The following is to be registered with
3504   IANA (see <xref target="RFC4288"/>).
3506<section title="Internet Media Type message/http" anchor="">
3507<iref item="Media Type" subitem="message/http" primary="true"/>
3508<iref item="message/http Media Type" primary="true"/>
3510   The message/http type can be used to enclose a single HTTP request or
3511   response message, provided that it obeys the MIME restrictions for all
3512   "message" types regarding line length and encodings.
3515  <list style="hanging" x:indent="12em">
3516    <t hangText="Type name:">
3517      message
3518    </t>
3519    <t hangText="Subtype name:">
3520      http
3521    </t>
3522    <t hangText="Required parameters:">
3523      none
3524    </t>
3525    <t hangText="Optional parameters:">
3526      version, msgtype
3527      <list style="hanging">
3528        <t hangText="version:">
3529          The HTTP-Version number of the enclosed message
3530          (e.g., "1.1"). If not present, the version can be
3531          determined from the first line of the body.
3532        </t>
3533        <t hangText="msgtype:">
3534          The message type -- "request" or "response". If not
3535          present, the type can be determined from the first
3536          line of the body.
3537        </t>
3538      </list>
3539    </t>
3540    <t hangText="Encoding considerations:">
3541      only "7bit", "8bit", or "binary" are permitted
3542    </t>
3543    <t hangText="Security considerations:">
3544      none
3545    </t>
3546    <t hangText="Interoperability considerations:">
3547      none
3548    </t>
3549    <t hangText="Published specification:">
3550      This specification (see <xref target=""/>).
3551    </t>
3552    <t hangText="Applications that use this media type:">
3553    </t>
3554    <t hangText="Additional information:">
3555      <list style="hanging">
3556        <t hangText="Magic number(s):">none</t>
3557        <t hangText="File extension(s):">none</t>
3558        <t hangText="Macintosh file type code(s):">none</t>
3559      </list>
3560    </t>
3561    <t hangText="Person and email address to contact for further information:">
3562      See Authors Section.
3563    </t>
3564    <t hangText="Intended usage:">
3565      COMMON
3566    </t>
3567    <t hangText="Restrictions on usage:">
3568      none
3569    </t>
3570    <t hangText="Author/Change controller:">
3571      IESG
3572    </t>
3573  </list>
3576<section title="Internet Media Type application/http" anchor="">
3577<iref item="Media Type" subitem="application/http" primary="true"/>
3578<iref item="application/http Media Type" primary="true"/>
3580   The application/http type can be used to enclose a pipeline of one or more
3581   HTTP request or response messages (not intermixed).
3584  <list style="hanging" x:indent="12em">
3585    <t hangText="Type name:">
3586      application
3587    </t>
3588    <t hangText="Subtype name:">
3589      http
3590    </t>
3591    <t hangText="Required parameters:">
3592      none
3593    </t>
3594    <t hangText="Optional parameters:">
3595      version, msgtype
3596      <list style="hanging">
3597        <t hangText="version:">
3598          The HTTP-Version number of the enclosed messages
3599          (e.g., "1.1"). If not present, the version can be
3600          determined from the first line of the body.
3601        </t>
3602        <t hangText="msgtype:">
3603          The message type -- "request" or "response". If not
3604          present, the type can be determined from the first
3605          line of the body.
3606        </t>
3607      </list>
3608    </t>
3609    <t hangText="Encoding considerations:">
3610      HTTP messages enclosed by this type
3611      are in "binary" format; use of an appropriate
3612      Content-Transfer-Encoding is required when
3613      transmitted via E-mail.
3614    </t>
3615    <t hangText="Security considerations:">
3616      none
3617    </t>
3618    <t hangText="Interoperability considerations:">
3619      none
3620    </t>
3621    <t hangText="Published specification:">
3622      This specification (see <xref target=""/>).
3623    </t>
3624    <t hangText="Applications that use this media type:">
3625    </t>
3626    <t hangText="Additional information:">
3627      <list style="hanging">
3628        <t hangText="Magic number(s):">none</t>
3629        <t hangText="File extension(s):">none</t>
3630        <t hangText="Macintosh file type code(s):">none</t>
3631      </list>
3632    </t>
3633    <t hangText="Person and email address to contact for further information:">
3634      See Authors Section.
3635    </t>
3636    <t hangText="Intended usage:">
3637      COMMON
3638    </t>
3639    <t hangText="Restrictions on usage:">
3640      none
3641    </t>
3642    <t hangText="Author/Change controller:">
3643      IESG
3644    </t>
3645  </list>
3650<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3652   The registration procedure for HTTP Transfer Codings is now defined by
3653   <xref target="transfer.coding.registry"/> of this document.
3656   The HTTP Transfer Codings Registry located at <eref target=""/>
3657   should be updated with the registrations below:
3659<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3660   <ttcol>Name</ttcol>
3661   <ttcol>Description</ttcol>
3662   <ttcol>Reference</ttcol>
3663   <c>chunked</c>
3664   <c>Transfer in a series of chunks</c>
3665   <c>
3666      <xref target="chunked.encoding"/>
3667   </c>
3668   <c>compress</c>
3669   <c>UNIX "compress" program method</c>
3670   <c>
3671      <xref target="compress.coding"/>
3672   </c>
3673   <c>deflate</c>
3674   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3675   the "zlib" data format (<xref target="RFC1950"/>)
3676   </c>
3677   <c>
3678      <xref target="deflate.coding"/>
3679   </c>
3680   <c>gzip</c>
3681   <c>Same as GNU zip <xref target="RFC1952"/></c>
3682   <c>
3683      <xref target="gzip.coding"/>
3684   </c>
3688<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3690   The registration procedure for HTTP Upgrade Tokens -- previously defined
3691   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3692   by <xref target="upgrade.token.registry"/> of this document.
3695   The HTTP Status Code Registry located at <eref target=""/>
3696   should be updated with the registration below:
3698<texttable align="left" suppress-title="true">
3699   <ttcol>Value</ttcol>
3700   <ttcol>Description</ttcol>
3701   <ttcol>Reference</ttcol>
3703   <c>HTTP</c>
3704   <c>Hypertext Transfer Protocol</c>
3705   <c><xref target="http.version"/> of this specification</c>
3706<!-- IANA should add this without our instructions; emailed on June 05, 2009
3707   <c>TLS/1.0</c>
3708   <c>Transport Layer Security</c>
3709   <c><xref target="RFC2817"/></c> -->
3716<section title="Security Considerations" anchor="security.considerations">
3718   This section is meant to inform application developers, information
3719   providers, and users of the security limitations in HTTP/1.1 as
3720   described by this document. The discussion does not include
3721   definitive solutions to the problems revealed, though it does make
3722   some suggestions for reducing security risks.
3725<section title="Personal Information" anchor="personal.information">
3727   HTTP clients are often privy to large amounts of personal information
3728   (e.g., the user's name, location, mail address, passwords, encryption
3729   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3730   leakage of this information.
3731   We very strongly recommend that a convenient interface be provided
3732   for the user to control dissemination of such information, and that
3733   designers and implementors be particularly careful in this area.
3734   History shows that errors in this area often create serious security
3735   and/or privacy problems and generate highly adverse publicity for the
3736   implementor's company.
3740<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3742   A server is in the position to save personal data about a user's
3743   requests which might identify their reading patterns or subjects of
3744   interest. This information is clearly confidential in nature and its
3745   handling can be constrained by law in certain countries. People using
3746   HTTP to provide data are responsible for ensuring that
3747   such material is not distributed without the permission of any
3748   individuals that are identifiable by the published results.
3752<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3754   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3755   the documents returned by HTTP requests to be only those that were
3756   intended by the server administrators. If an HTTP server translates
3757   HTTP URIs directly into file system calls, the server &MUST; take
3758   special care not to serve files that were not intended to be
3759   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3760   other operating systems use ".." as a path component to indicate a
3761   directory level above the current one. On such a system, an HTTP
3762   server &MUST; disallow any such construct in the request-target if it
3763   would otherwise allow access to a resource outside those intended to
3764   be accessible via the HTTP server. Similarly, files intended for
3765   reference only internally to the server (such as access control
3766   files, configuration files, and script code) &MUST; be protected from
3767   inappropriate retrieval, since they might contain sensitive
3768   information. Experience has shown that minor bugs in such HTTP server
3769   implementations have turned into security risks.
3773<section title="DNS Spoofing" anchor="dns.spoofing">
3775   Clients using HTTP rely heavily on the Domain Name Service, and are
3776   thus generally prone to security attacks based on the deliberate
3777   mis-association of IP addresses and DNS names. Clients need to be
3778   cautious in assuming the continuing validity of an IP number/DNS name
3779   association.
3782   In particular, HTTP clients &SHOULD; rely on their name resolver for
3783   confirmation of an IP number/DNS name association, rather than
3784   caching the result of previous host name lookups. Many platforms
3785   already can cache host name lookups locally when appropriate, and
3786   they &SHOULD; be configured to do so. It is proper for these lookups to
3787   be cached, however, only when the TTL (Time To Live) information
3788   reported by the name server makes it likely that the cached
3789   information will remain useful.
3792   If HTTP clients cache the results of host name lookups in order to
3793   achieve a performance improvement, they &MUST; observe the TTL
3794   information reported by DNS.
3797   If HTTP clients do not observe this rule, they could be spoofed when
3798   a previously-accessed server's IP address changes. As network
3799   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3800   possibility of this form of attack will grow. Observing this
3801   requirement thus reduces this potential security vulnerability.
3804   This requirement also improves the load-balancing behavior of clients
3805   for replicated servers using the same DNS name and reduces the
3806   likelihood of a user's experiencing failure in accessing sites which
3807   use that strategy.
3811<section title="Proxies and Caching" anchor="attack.proxies">
3813   By their very nature, HTTP proxies are men-in-the-middle, and
3814   represent an opportunity for man-in-the-middle attacks. Compromise of
3815   the systems on which the proxies run can result in serious security
3816   and privacy problems. Proxies have access to security-related
3817   information, personal information about individual users and
3818   organizations, and proprietary information belonging to users and
3819   content providers. A compromised proxy, or a proxy implemented or
3820   configured without regard to security and privacy considerations,
3821   might be used in the commission of a wide range of potential attacks.
3824   Proxy operators should protect the systems on which proxies run as
3825   they would protect any system that contains or transports sensitive
3826   information. In particular, log information gathered at proxies often
3827   contains highly sensitive personal information, and/or information
3828   about organizations. Log information should be carefully guarded, and
3829   appropriate guidelines for use should be developed and followed.
3830   (<xref target="abuse.of.server.log.information"/>).
3833   Proxy implementors should consider the privacy and security
3834   implications of their design and coding decisions, and of the
3835   configuration options they provide to proxy operators (especially the
3836   default configuration).
3839   Users of a proxy need to be aware that proxies are no trustworthier than
3840   the people who run them; HTTP itself cannot solve this problem.
3843   The judicious use of cryptography, when appropriate, may suffice to
3844   protect against a broad range of security and privacy attacks. Such
3845   cryptography is beyond the scope of the HTTP/1.1 specification.
3849<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3851   They exist. They are hard to defend against. Research continues.
3852   Beware.
3857<section title="Acknowledgments" anchor="ack">
3859   HTTP has evolved considerably over the years. It has
3860   benefited from a large and active developer community--the many
3861   people who have participated on the www-talk mailing list--and it is
3862   that community which has been most responsible for the success of
3863   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3864   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3865   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3866   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3867   VanHeyningen deserve special recognition for their efforts in
3868   defining early aspects of the protocol.
3871   This document has benefited greatly from the comments of all those
3872   participating in the HTTP-WG. In addition to those already mentioned,
3873   the following individuals have contributed to this specification:
3876   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3877   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3878   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3879   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3880   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3881   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3882   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3883   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3884   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3885   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3886   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3887   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3890   Thanks to the "cave men" of Palo Alto. You know who you are.
3893   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3894   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3895   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3896   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3897   Larry Masinter for their help. And thanks go particularly to Jeff
3898   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3901   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3902   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3903   discovery of many of the problems that this document attempts to
3904   rectify.
3907   This specification makes heavy use of the augmented BNF and generic
3908   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3909   reuses many of the definitions provided by Nathaniel Borenstein and
3910   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3911   specification will help reduce past confusion over the relationship
3912   between HTTP and Internet mail message formats.
3919<references title="Normative References">
3921<reference anchor="ISO-8859-1">
3922  <front>
3923    <title>
3924     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3925    </title>
3926    <author>
3927      <organization>International Organization for Standardization</organization>
3928    </author>
3929    <date year="1998"/>
3930  </front>
3931  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3934<reference anchor="Part2">
3935  <front>
3936    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3937    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3938      <organization abbrev="Day Software">Day Software</organization>
3939      <address><email></email></address>
3940    </author>
3941    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3942      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3943      <address><email></email></address>
3944    </author>
3945    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3946      <organization abbrev="HP">Hewlett-Packard Company</organization>
3947      <address><email></email></address>
3948    </author>
3949    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3950      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3951      <address><email></email></address>
3952    </author>
3953    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3954      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3955      <address><email></email></address>
3956    </author>
3957    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3958      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3959      <address><email></email></address>
3960    </author>
3961    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3962      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3963      <address><email></email></address>
3964    </author>
3965    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3966      <organization abbrev="W3C">World Wide Web Consortium</organization>
3967      <address><email></email></address>
3968    </author>
3969    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3970      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3971      <address><email></email></address>
3972    </author>
3973    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3974  </front>
3975  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3976  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3979<reference anchor="Part3">
3980  <front>
3981    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3982    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3983      <organization abbrev="Day Software">Day Software</organization>
3984      <address><email></email></address>
3985    </author>
3986    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3987      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3988      <address><email></email></address>
3989    </author>
3990    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3991      <organization abbrev="HP">Hewlett-Packard Company</organization>
3992      <address><email></email></address>
3993    </author>
3994    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3995      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3996      <address><email></email></address>
3997    </author>
3998    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3999      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4000      <address><email></email></address>
4001    </author>
4002    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4003      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4004      <address><email></email></address>
4005    </author>
4006    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4007      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4008      <address><email></email></address>
4009    </author>
4010    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4011      <organization abbrev="W3C">World Wide Web Consortium</organization>
4012      <address><email></email></address>
4013    </author>
4014    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4015      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4016      <address><email></email></address>
4017    </author>
4018    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4019  </front>
4020  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4021  <x:source href="p3-payload.xml" basename="p3-payload"/>
4024<reference anchor="Part5">
4025  <front>
4026    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4027    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4028      <organization abbrev="Day Software">Day Software</organization>
4029      <address><email></email></address>
4030    </author>
4031    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4032      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4033      <address><email></email></address>
4034    </author>
4035    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4036      <organization abbrev="HP">Hewlett-Packard Company</organization>
4037      <address><email></email></address>
4038    </author>
4039    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4040      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4041      <address><email></email></address>
4042    </author>
4043    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4044      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4045      <address><email></email></address>
4046    </author>
4047    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4048      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4049      <address><email></email></address>
4050    </author>
4051    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4052      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4053      <address><email></email></address>
4054    </author>
4055    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4056      <organization abbrev="W3C">World Wide Web Consortium</organization>
4057      <address><email></email></address>
4058    </author>
4059    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4060      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4061      <address><email></email></address>
4062    </author>
4063    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4064  </front>
4065  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4066  <x:source href="p5-range.xml" basename="p5-range"/>
4069<reference anchor="Part6">
4070  <front>
4071    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4072    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4073      <organization abbrev="Day Software">Day Software</organization>
4074      <address><email></email></address>
4075    </author>
4076    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4077      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4078      <address><email></email></address>
4079    </author>
4080    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4081      <organization abbrev="HP">Hewlett-Packard Company</organization>
4082      <address><email></email></address>
4083    </author>
4084    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4085      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4086      <address><email></email></address>
4087    </author>
4088    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4089      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4090      <address><email></email></address>
4091    </author>
4092    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4093      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4094      <address><email></email></address>
4095    </author>
4096    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4097      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4098      <address><email></email></address>
4099    </author>
4100    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4101      <organization abbrev="W3C">World Wide Web Consortium</organization>
4102      <address><email></email></address>
4103    </author>
4104    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4105      <address><email></email></address>
4106    </author>
4107    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4108      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4109      <address><email></email></address>
4110    </author>
4111    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4112  </front>
4113  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4114  <x:source href="p6-cache.xml" basename="p6-cache"/>
4117<reference anchor="RFC5234">
4118  <front>
4119    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4120    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4121      <organization>Brandenburg InternetWorking</organization>
4122      <address>
4123        <email></email>
4124      </address> 
4125    </author>
4126    <author initials="P." surname="Overell" fullname="Paul Overell">
4127      <organization>THUS plc.</organization>
4128      <address>
4129        <email></email>
4130      </address>
4131    </author>
4132    <date month="January" year="2008"/>
4133  </front>
4134  <seriesInfo name="STD" value="68"/>
4135  <seriesInfo name="RFC" value="5234"/>
4138<reference anchor="RFC2119">
4139  <front>
4140    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4141    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4142      <organization>Harvard University</organization>
4143      <address><email></email></address>
4144    </author>
4145    <date month="March" year="1997"/>
4146  </front>
4147  <seriesInfo name="BCP" value="14"/>
4148  <seriesInfo name="RFC" value="2119"/>
4151<reference anchor="RFC3986">
4152 <front>
4153  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4154  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4155    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4156    <address>
4157       <email></email>
4158       <uri></uri>
4159    </address>
4160  </author>
4161  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4162    <organization abbrev="Day Software">Day Software</organization>
4163    <address>
4164      <email></email>
4165      <uri></uri>
4166    </address>
4167  </author>
4168  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4169    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4170    <address>
4171      <email></email>
4172      <uri></uri>
4173    </address>
4174  </author>
4175  <date month='January' year='2005'></date>
4176 </front>
4177 <seriesInfo name="RFC" value="3986"/>
4178 <seriesInfo name="STD" value="66"/>
4181<reference anchor="USASCII">
4182  <front>
4183    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4184    <author>
4185      <organization>American National Standards Institute</organization>
4186    </author>
4187    <date year="1986"/>
4188  </front>
4189  <seriesInfo name="ANSI" value="X3.4"/>
4192<reference anchor="RFC1950">
4193  <front>
4194    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4195    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4196      <organization>Aladdin Enterprises</organization>
4197      <address><email></email></address>
4198    </author>
4199    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4200    <date month="May" year="1996"/>
4201  </front>
4202  <seriesInfo name="RFC" value="1950"/>
4203  <annotation>
4204    RFC 1950 is an Informational RFC, thus it may be less stable than
4205    this specification. On the other hand, this downward reference was
4206    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4207    therefore it is unlikely to cause problems in practice. See also
4208    <xref target="BCP97"/>.
4209  </annotation>
4212<reference anchor="RFC1951">
4213  <front>
4214    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4215    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4216      <organization>Aladdin Enterprises</organization>
4217      <address><email></email></address>
4218    </author>
4219    <date month="May" year="1996"/>
4220  </front>
4221  <seriesInfo name="RFC" value="1951"/>
4222  <annotation>
4223    RFC 1951 is an Informational RFC, thus it may be less stable than
4224    this specification. On the other hand, this downward reference was
4225    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4226    therefore it is unlikely to cause problems in practice. See also
4227    <xref target="BCP97"/>.
4228  </annotation>
4231<reference anchor="RFC1952">
4232  <front>
4233    <title>GZIP file format specification version 4.3</title>
4234    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4235      <organization>Aladdin Enterprises</organization>
4236      <address><email></email></address>
4237    </author>
4238    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4239      <address><email></email></address>
4240    </author>
4241    <author initials="M." surname="Adler" fullname="Mark Adler">
4242      <address><email></email></address>
4243    </author>
4244    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4245      <address><email></email></address>
4246    </author>
4247    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4248      <address><email></email></address>
4249    </author>
4250    <date month="May" year="1996"/>
4251  </front>
4252  <seriesInfo name="RFC" value="1952"/>
4253  <annotation>
4254    RFC 1952 is an Informational RFC, thus it may be less stable than
4255    this specification. On the other hand, this downward reference was
4256    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4257    therefore it is unlikely to cause problems in practice. See also
4258    <xref target="BCP97"/>.
4259  </annotation>
4264<references title="Informative References">
4266<reference anchor="Nie1997" target="">
4267  <front>
4268    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4269    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4270    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4271    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4272    <author initials="H." surname="Lie" fullname="H. Lie"/>
4273    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4274    <date year="1997" month="September"/>
4275  </front>
4276  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4279<reference anchor="Pad1995" target="">
4280  <front>
4281    <title>Improving HTTP Latency</title>
4282    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4283    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4284    <date year="1995" month="December"/>
4285  </front>
4286  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4289<reference anchor="RFC1123">
4290  <front>
4291    <title>Requirements for Internet Hosts - Application and Support</title>
4292    <author initials="R." surname="Braden" fullname="Robert Braden">
4293      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4294      <address><email>Braden@ISI.EDU</email></address>
4295    </author>
4296    <date month="October" year="1989"/>
4297  </front>
4298  <seriesInfo name="STD" value="3"/>
4299  <seriesInfo name="RFC" value="1123"/>
4302<reference anchor="RFC1305">
4303  <front>
4304    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4305    <author initials="D." surname="Mills" fullname="David L. Mills">
4306      <organization>University of Delaware, Electrical Engineering Department</organization>
4307      <address><email></email></address>
4308    </author>
4309    <date month="March" year="1992"/>
4310  </front>
4311  <seriesInfo name="RFC" value="1305"/>
4314<reference anchor="RFC1900">
4315  <front>
4316    <title>Renumbering Needs Work</title>
4317    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4318      <organization>CERN, Computing and Networks Division</organization>
4319      <address><email></email></address>
4320    </author>
4321    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4322      <organization>cisco Systems</organization>
4323      <address><email></email></address>
4324    </author>
4325    <date month="February" year="1996"/>
4326  </front>
4327  <seriesInfo name="RFC" value="1900"/>
4330<reference anchor="RFC1945">
4331  <front>
4332    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4333    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4334      <organization>MIT, Laboratory for Computer Science</organization>
4335      <address><email></email></address>
4336    </author>
4337    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4338      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4339      <address><email></email></address>
4340    </author>
4341    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4342      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4343      <address><email></email></address>
4344    </author>
4345    <date month="May" year="1996"/>
4346  </front>
4347  <seriesInfo name="RFC" value="1945"/>
4350<reference anchor="RFC2045">
4351  <front>
4352    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4353    <author initials="N." surname="Freed" fullname="Ned Freed">
4354      <organization>Innosoft International, Inc.</organization>
4355      <address><email></email></address>
4356    </author>
4357    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4358      <organization>First Virtual Holdings</organization>
4359      <address><email></email></address>
4360    </author>
4361    <date month="November" year="1996"/>
4362  </front>
4363  <seriesInfo name="RFC" value="2045"/>
4366<reference anchor="RFC2047">
4367  <front>
4368    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4369    <author initials="K." surname="Moore" fullname="Keith Moore">
4370      <organization>University of Tennessee</organization>
4371      <address><email></email></address>
4372    </author>
4373    <date month="November" year="1996"/>
4374  </front>
4375  <seriesInfo name="RFC" value="2047"/>
4378<reference anchor="RFC2068">
4379  <front>
4380    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4381    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4382      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4383      <address><email></email></address>
4384    </author>
4385    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4386      <organization>MIT Laboratory for Computer Science</organization>
4387      <address><email></email></address>
4388    </author>
4389    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4390      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4391      <address><email></email></address>
4392    </author>
4393    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4394      <organization>MIT Laboratory for Computer Science</organization>
4395      <address><email></email></address>
4396    </author>
4397    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4398      <organization>MIT Laboratory for Computer Science</organization>
4399      <address><email></email></address>
4400    </author>
4401    <date month="January" year="1997"/>
4402  </front>
4403  <seriesInfo name="RFC" value="2068"/>
4406<reference anchor='RFC2109'>
4407  <front>
4408    <title>HTTP State Management Mechanism</title>
4409    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4410      <organization>Bell Laboratories, Lucent Technologies</organization>
4411      <address><email></email></address>
4412    </author>
4413    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4414      <organization>Netscape Communications Corp.</organization>
4415      <address><email></email></address>
4416    </author>
4417    <date year='1997' month='February' />
4418  </front>
4419  <seriesInfo name='RFC' value='2109' />
4422<reference anchor="RFC2145">
4423  <front>
4424    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4425    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4426      <organization>Western Research Laboratory</organization>
4427      <address><email></email></address>
4428    </author>
4429    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4430      <organization>Department of Information and Computer Science</organization>
4431      <address><email></email></address>
4432    </author>
4433    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4434      <organization>MIT Laboratory for Computer Science</organization>
4435      <address><email></email></address>
4436    </author>
4437    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4438      <organization>W3 Consortium</organization>
4439      <address><email></email></address>
4440    </author>
4441    <date month="May" year="1997"/>
4442  </front>
4443  <seriesInfo name="RFC" value="2145"/>
4446<reference anchor="RFC2616">
4447  <front>
4448    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4449    <author initials="R." surname="Fielding" fullname="R. Fielding">
4450      <organization>University of California, Irvine</organization>
4451      <address><email></email></address>
4452    </author>
4453    <author initials="J." surname="Gettys" fullname="J. Gettys">
4454      <organization>W3C</organization>
4455      <address><email></email></address>
4456    </author>
4457    <author initials="J." surname="Mogul" fullname="J. Mogul">
4458      <organization>Compaq Computer Corporation</organization>
4459      <address><email></email></address>
4460    </author>
4461    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4462      <organization>MIT Laboratory for Computer Science</organization>
4463      <address><email></email></address>
4464    </author>
4465    <author initials="L." surname="Masinter" fullname="L. Masinter">
4466      <organization>Xerox Corporation</organization>
4467      <address><email></email></address>
4468    </author>
4469    <author initials="P." surname="Leach" fullname="P. Leach">
4470      <organization>Microsoft Corporation</organization>
4471      <address><email></email></address>
4472    </author>
4473    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4474      <organization>W3C</organization>
4475      <address><email></email></address>
4476    </author>
4477    <date month="June" year="1999"/>
4478  </front>
4479  <seriesInfo name="RFC" value="2616"/>
4482<reference anchor='RFC2817'>
4483  <front>
4484    <title>Upgrading to TLS Within HTTP/1.1</title>
4485    <author initials='R.' surname='Khare' fullname='R. Khare'>
4486      <organization>4K Associates / UC Irvine</organization>
4487      <address><email></email></address>
4488    </author>
4489    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4490      <organization>Agranat Systems, Inc.</organization>
4491      <address><email></email></address>
4492    </author>
4493    <date year='2000' month='May' />
4494  </front>
4495  <seriesInfo name='RFC' value='2817' />
4498<reference anchor='RFC2818'>
4499  <front>
4500    <title>HTTP Over TLS</title>
4501    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4502      <organization>RTFM, Inc.</organization>
4503      <address><email></email></address>
4504    </author>
4505    <date year='2000' month='May' />
4506  </front>
4507  <seriesInfo name='RFC' value='2818' />
4510<reference anchor='RFC2965'>
4511  <front>
4512    <title>HTTP State Management Mechanism</title>
4513    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4514      <organization>Bell Laboratories, Lucent Technologies</organization>
4515      <address><email></email></address>
4516    </author>
4517    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4518      <organization>, Inc.</organization>
4519      <address><email></email></address>
4520    </author>
4521    <date year='2000' month='October' />
4522  </front>
4523  <seriesInfo name='RFC' value='2965' />
4526<reference anchor='RFC3864'>
4527  <front>
4528    <title>Registration Procedures for Message Header Fields</title>
4529    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4530      <organization>Nine by Nine</organization>
4531      <address><email></email></address>
4532    </author>
4533    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4534      <organization>BEA Systems</organization>
4535      <address><email></email></address>
4536    </author>
4537    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4538      <organization>HP Labs</organization>
4539      <address><email></email></address>
4540    </author>
4541    <date year='2004' month='September' />
4542  </front>
4543  <seriesInfo name='BCP' value='90' />
4544  <seriesInfo name='RFC' value='3864' />
4547<reference anchor="RFC4288">
4548  <front>
4549    <title>Media Type Specifications and Registration Procedures</title>
4550    <author initials="N." surname="Freed" fullname="N. Freed">
4551      <organization>Sun Microsystems</organization>
4552      <address>
4553        <email></email>
4554      </address>
4555    </author>
4556    <author initials="J." surname="Klensin" fullname="J. Klensin">
4557      <address>
4558        <email></email>
4559      </address>
4560    </author>
4561    <date year="2005" month="December"/>
4562  </front>
4563  <seriesInfo name="BCP" value="13"/>
4564  <seriesInfo name="RFC" value="4288"/>
4567<reference anchor='RFC4395'>
4568  <front>
4569    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4570    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4571      <organization>AT&amp;T Laboratories</organization>
4572      <address>
4573        <email></email>
4574      </address>
4575    </author>
4576    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4577      <organization>Qualcomm, Inc.</organization>
4578      <address>
4579        <email></email>
4580      </address>
4581    </author>
4582    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4583      <organization>Adobe Systems</organization>
4584      <address>
4585        <email></email>
4586      </address>
4587    </author>
4588    <date year='2006' month='February' />
4589  </front>
4590  <seriesInfo name='BCP' value='115' />
4591  <seriesInfo name='RFC' value='4395' />
4594<reference anchor='RFC5226'>
4595  <front>
4596    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4597    <author initials='T.' surname='Narten' fullname='T. Narten'>
4598      <organization>IBM</organization>
4599      <address><email></email></address>
4600    </author>
4601    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4602      <organization>Google</organization>
4603      <address><email></email></address>
4604    </author>
4605    <date year='2008' month='May' />
4606  </front>
4607  <seriesInfo name='BCP' value='26' />
4608  <seriesInfo name='RFC' value='5226' />
4611<reference anchor="RFC5322">
4612  <front>
4613    <title>Internet Message Format</title>
4614    <author initials="P." surname="Resnick" fullname="P. Resnick">
4615      <organization>Qualcomm Incorporated</organization>
4616    </author>
4617    <date year="2008" month="October"/>
4618  </front>
4619  <seriesInfo name="RFC" value="5322"/>
4622<reference anchor='BCP97'>
4623  <front>
4624    <title>Handling Normative References to Standards-Track Documents</title>
4625    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4626      <address>
4627        <email></email>
4628      </address>
4629    </author>
4630    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4631      <organization>MIT</organization>
4632      <address>
4633        <email></email>
4634      </address>
4635    </author>
4636    <date year='2007' month='June' />
4637  </front>
4638  <seriesInfo name='BCP' value='97' />
4639  <seriesInfo name='RFC' value='4897' />
4642<reference anchor="Kri2001" target="">
4643  <front>
4644    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4645    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4646    <date year="2001" month="November"/>
4647  </front>
4648  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4651<reference anchor="Spe" target="">
4652  <front>
4653    <title>Analysis of HTTP Performance Problems</title>
4654    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4655    <date/>
4656  </front>
4659<reference anchor="Tou1998" target="">
4660  <front>
4661  <title>Analysis of HTTP Performance</title>
4662  <author initials="J." surname="Touch" fullname="Joe Touch">
4663    <organization>USC/Information Sciences Institute</organization>
4664    <address><email></email></address>
4665  </author>
4666  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4667    <organization>USC/Information Sciences Institute</organization>
4668    <address><email></email></address>
4669  </author>
4670  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4671    <organization>USC/Information Sciences Institute</organization>
4672    <address><email></email></address>
4673  </author>
4674  <date year="1998" month="Aug"/>
4675  </front>
4676  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4677  <annotation>(original report dated Aug. 1996)</annotation>
4683<section title="Tolerant Applications" anchor="tolerant.applications">
4685   Although this document specifies the requirements for the generation
4686   of HTTP/1.1 messages, not all applications will be correct in their
4687   implementation. We therefore recommend that operational applications
4688   be tolerant of deviations whenever those deviations can be
4689   interpreted unambiguously.
4692   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4693   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4694   &SHOULD; accept any amount of WSP characters between fields, even though
4695   only a single SP is required.
4698   The line terminator for header fields is the sequence CRLF.
4699   However, we recommend that applications, when parsing such headers,
4700   recognize a single LF as a line terminator and ignore the leading CR.
4703   The character set of a representation &SHOULD; be labeled as the lowest
4704   common denominator of the character codes used within that representation, with
4705   the exception that not labeling the representation is preferred over labeling
4706   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4709   Additional rules for requirements on parsing and encoding of dates
4710   and other potential problems with date encodings include:
4713  <list style="symbols">
4714     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4715        which appears to be more than 50 years in the future is in fact
4716        in the past (this helps solve the "year 2000" problem).</t>
4718     <t>Although all date formats are specified to be case-sensitive,
4719        recipients &SHOULD; match day, week and timezone names
4720        case-insensitively.</t>
4722     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4723        Expires date as earlier than the proper value, but &MUST-NOT;
4724        internally represent a parsed Expires date as later than the
4725        proper value.</t>
4727     <t>All expiration-related calculations &MUST; be done in GMT. The
4728        local time zone &MUST-NOT; influence the calculation or comparison
4729        of an age or expiration time.</t>
4731     <t>If an HTTP header incorrectly carries a date value with a time
4732        zone other than GMT, it &MUST; be converted into GMT using the
4733        most conservative possible conversion.</t>
4734  </list>
4738<section title="Compatibility with Previous Versions" anchor="compatibility">
4740   HTTP has been in use by the World-Wide Web global information initiative
4741   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4742   was a simple protocol for hypertext data transfer across the Internet
4743   with only a single method and no metadata.
4744   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4745   methods and MIME-like messaging that could include metadata about the data
4746   transferred and modifiers on the request/response semantics. However,
4747   HTTP/1.0 did not sufficiently take into consideration the effects of
4748   hierarchical proxies, caching, the need for persistent connections, or
4749   name-based virtual hosts. The proliferation of incompletely-implemented
4750   applications calling themselves "HTTP/1.0" further necessitated a
4751   protocol version change in order for two communicating applications
4752   to determine each other's true capabilities.
4755   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4756   requirements that enable reliable implementations, adding only
4757   those new features that will either be safely ignored by an HTTP/1.0
4758   recipient or only sent when communicating with a party advertising
4759   compliance with HTTP/1.1.
4762   It is beyond the scope of a protocol specification to mandate
4763   compliance with previous versions. HTTP/1.1 was deliberately
4764   designed, however, to make supporting previous versions easy. It is
4765   worth noting that, at the time of composing this specification, we would
4766   expect general-purpose HTTP/1.1 servers to:
4767  <list style="symbols">
4768     <t>understand any valid request in the format of HTTP/1.0 and
4769        1.1;</t>
4771     <t>respond appropriately with a message in the same major version
4772        used by the client.</t>
4773  </list>
4776   And we would expect HTTP/1.1 clients to:
4777  <list style="symbols">
4778     <t>understand any valid response in the format of HTTP/1.0 or
4779        1.1.</t>
4780  </list>
4783   For most implementations of HTTP/1.0, each connection is established
4784   by the client prior to the request and closed by the server after
4785   sending the response. Some implementations implement the Keep-Alive
4786   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4789<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4791   This section summarizes major differences between versions HTTP/1.0
4792   and HTTP/1.1.
4795<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4797   The requirements that clients and servers support the Host request-header,
4798   report an error if the Host request-header (<xref target=""/>) is
4799   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4800   are among the most important changes defined by this
4801   specification.
4804   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4805   addresses and servers; there was no other established mechanism for
4806   distinguishing the intended server of a request than the IP address
4807   to which that request was directed. The changes outlined above will
4808   allow the Internet, once older HTTP clients are no longer common, to
4809   support multiple Web sites from a single IP address, greatly
4810   simplifying large operational Web servers, where allocation of many
4811   IP addresses to a single host has created serious problems. The
4812   Internet will also be able to recover the IP addresses that have been
4813   allocated for the sole purpose of allowing special-purpose domain
4814   names to be used in root-level HTTP URLs. Given the rate of growth of
4815   the Web, and the number of servers already deployed, it is extremely
4816   important that all implementations of HTTP (including updates to
4817   existing HTTP/1.0 applications) correctly implement these
4818   requirements:
4819  <list style="symbols">
4820     <t>Both clients and servers &MUST; support the Host request-header.</t>
4822     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4824     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4825        request does not include a Host request-header.</t>
4827     <t>Servers &MUST; accept absolute URIs.</t>
4828  </list>
4833<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4835   Some clients and servers might wish to be compatible with some
4836   previous implementations of persistent connections in HTTP/1.0
4837   clients and servers. Persistent connections in HTTP/1.0 are
4838   explicitly negotiated as they are not the default behavior. HTTP/1.0
4839   experimental implementations of persistent connections are faulty,
4840   and the new facilities in HTTP/1.1 are designed to rectify these
4841   problems. The problem was that some existing HTTP/1.0 clients may be
4842   sending Keep-Alive to a proxy server that doesn't understand
4843   Connection, which would then erroneously forward it to the next
4844   inbound server, which would establish the Keep-Alive connection and
4845   result in a hung HTTP/1.0 proxy waiting for the close on the
4846   response. The result is that HTTP/1.0 clients must be prevented from
4847   using Keep-Alive when talking to proxies.
4850   However, talking to proxies is the most important use of persistent
4851   connections, so that prohibition is clearly unacceptable. Therefore,
4852   we need some other mechanism for indicating a persistent connection
4853   is desired, which is safe to use even when talking to an old proxy
4854   that ignores Connection. Persistent connections are the default for
4855   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4856   declaring non-persistence. See <xref target="header.connection"/>.
4859   The original HTTP/1.0 form of persistent connections (the Connection:
4860   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4864<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4866   This specification has been carefully audited to correct and
4867   disambiguate key word usage; RFC 2068 had many problems in respect to
4868   the conventions laid out in <xref target="RFC2119"/>.
4871   Transfer-coding and message lengths all interact in ways that
4872   required fixing exactly when chunked encoding is used (to allow for
4873   transfer encoding that may not be self delimiting); it was important
4874   to straighten out exactly how message lengths are computed. (Sections
4875   <xref target="transfer.codings" format="counter"/>, <xref target="message.body.length" format="counter"/>,
4876   <xref target="header.content-length" format="counter"/>,
4877   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4880   The use and interpretation of HTTP version numbers has been clarified
4881   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4882   version they support to deal with problems discovered in HTTP/1.0
4883   implementations (<xref target="http.version"/>)
4886   Quality Values of zero should indicate that "I don't want something"
4887   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4890   Transfer-coding had significant problems, particularly with
4891   interactions with chunked encoding. The solution is that transfer-codings
4892   become as full fledged as content-codings. This involves
4893   adding an IANA registry for transfer-codings (separate from content
4894   codings), a new header field (TE) and enabling trailer headers in the
4895   future. Transfer encoding is a major performance benefit, so it was
4896   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4897   interoperability problem that could have occurred due to interactions
4898   between authentication trailers, chunked encoding and HTTP/1.0
4899   clients.(Section
4900   <xref target="transfer.codings" format="counter"/>,
4901   <xref target="chunked.encoding" format="counter"/>,
4902   <xref target="non-modifiable.headers" format="counter"/>,
4903   and <xref target="header.te" format="counter"/>)
4906  Proxies should be able to add Content-Length when appropriate.
4907  (<xref target="non-modifiable.headers"/>)
4911<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4913  Empty list elements in list productions have been deprecated.
4914  (<xref target="notation.abnf"/>)
4917  Rules about implicit linear whitespace between certain grammar productions
4918  have been removed; now it's only allowed when specifically pointed out
4919  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4920  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4921  Non-ASCII content in header fields and reason phrase has been obsoleted and
4922  made opaque (the TEXT rule was removed)
4923  (<xref target="basic.rules"/>)
4926  Clarify that HTTP-Version is case sensitive.
4927  (<xref target="http.version"/>)
4930  Remove reference to non-existent identity transfer-coding value tokens.
4931  (Sections <xref format="counter" target="transfer.codings"/> and
4932  <xref format="counter" target="message.body.length"/>)
4935  Require that invalid whitespace around field-names be rejected.
4936  (<xref target="header.fields"/>)
4939  Update use of abs_path production from RFC1808 to the path-absolute + query
4940  components of RFC3986.
4941  (<xref target="request-target"/>)
4944  Clarification that the chunk length does not include the count of the octets
4945  in the chunk header and trailer. Furthermore disallowed line folding
4946  in chunk extensions.
4947  (<xref target="chunked.encoding"/>)
4950  Remove hard limit of two connections per server.
4951  (<xref target="persistent.practical"/>)
4954  Clarify exactly when close connection options must be sent.
4955  (<xref target="header.connection"/>)
4960<?BEGININC p1-messaging.abnf-appendix ?>
4961<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4963<artwork type="abnf" name="p1-messaging.parsed-abnf">
4964<x:ref>BWS</x:ref> = OWS
4966<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4967<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4968<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4969<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4970 connection-token ] )
4971<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4972<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4974<x:ref>Date</x:ref> = "Date:" OWS Date-v
4975<x:ref>Date-v</x:ref> = HTTP-date
4977<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4979<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4980<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4981<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4982<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4983 ]
4984<x:ref>Host</x:ref> = "Host:" OWS Host-v
4985<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4987<x:ref>Method</x:ref> = token
4989<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4991<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4993<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4994<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4995<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4996 entity-header ) CRLF ) CRLF [ message-body ]
4997<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4998<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4999 entity-header ) CRLF ) CRLF [ message-body ]
5001<x:ref>Status-Code</x:ref> = 3DIGIT
5002<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5004<x:ref>TE</x:ref> = "TE:" OWS TE-v
5005<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5006<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5007<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5008<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5009<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5010 transfer-coding ] )
5012<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5013<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5014<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5016<x:ref>Via</x:ref> = "Via:" OWS Via-v
5017<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5018 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5019 ] )
5021<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5023<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5024<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5025<x:ref>attribute</x:ref> = token
5026<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5028<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5029<x:ref>chunk-data</x:ref> = 1*OCTET
5030<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5031<x:ref>chunk-ext-name</x:ref> = token
5032<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5033<x:ref>chunk-size</x:ref> = 1*HEXDIG
5034<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5035<x:ref>connection-token</x:ref> = token
5036<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5037 / %x2A-5B ; '*'-'['
5038 / %x5D-7E ; ']'-'~'
5039 / obs-text
5041<x:ref>date1</x:ref> = day SP month SP year
5042<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5043<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5044<x:ref>day</x:ref> = 2DIGIT
5045<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5046 / %x54.75.65 ; Tue
5047 / %x57.65.64 ; Wed
5048 / %x54.68.75 ; Thu
5049 / %x46.72.69 ; Fri
5050 / %x53.61.74 ; Sat
5051 / %x53.75.6E ; Sun
5052<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5053 / %x54. ; Tuesday
5054 / %x57.65.64.6E. ; Wednesday
5055 / %x54. ; Thursday
5056 / %x46. ; Friday
5057 / %x53. ; Saturday
5058 / %x53.75.6E.64.61.79 ; Sunday
5060<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
5062<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5063<x:ref>field-name</x:ref> = token
5064<x:ref>field-value</x:ref> = *( field-content / OWS )
5066<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5067 / Transfer-Encoding / Upgrade / Via / Warning
5069<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5070<x:ref>hour</x:ref> = 2DIGIT
5071<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5072<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5074<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5076<x:ref>message-body</x:ref> = *OCTET
5077<x:ref>minute</x:ref> = 2DIGIT
5078<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5079 / %x46.65.62 ; Feb
5080 / %x4D.61.72 ; Mar
5081 / %x41.70.72 ; Apr
5082 / %x4D.61.79 ; May
5083 / %x4A.75.6E ; Jun
5084 / %x4A.75.6C ; Jul
5085 / %x41.75.67 ; Aug
5086 / %x53.65.70 ; Sep
5087 / %x4F.63.74 ; Oct
5088 / %x4E.6F.76 ; Nov
5089 / %x44.65.63 ; Dec
5091<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5092<x:ref>obs-fold</x:ref> = CRLF
5093<x:ref>obs-text</x:ref> = %x80-FF
5095<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5096<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5097<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5098<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5099<x:ref>product</x:ref> = token [ "/" product-version ]
5100<x:ref>product-version</x:ref> = token
5101<x:ref>protocol-name</x:ref> = token
5102<x:ref>protocol-version</x:ref> = token
5103<x:ref>pseudonym</x:ref> = token
5105<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5106 / %x5D-7E ; ']'-'~'
5107 / obs-text
5108<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5109 / %x5D-7E ; ']'-'~'
5110 / obs-text
5111<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5112<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5113<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5114<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5115<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5116<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5118<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5119<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5120<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5121<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5122<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5123 / authority
5124<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5125<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5126<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5128<x:ref>second</x:ref> = 2DIGIT
5129<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5130 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5131<x:ref>start-line</x:ref> = Request-Line / Status-Line
5133<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5134<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5135 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5136<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5137<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5138<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5139<x:ref>token</x:ref> = 1*tchar
5140<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5141<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5142 transfer-extension
5143<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5144<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5146<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5148<x:ref>value</x:ref> = word
5150<x:ref>word</x:ref> = token / quoted-string
5152<x:ref>year</x:ref> = 4DIGIT
5155<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5156; Chunked-Body defined but not used
5157; Content-Length defined but not used
5158; HTTP-message defined but not used
5159; Host defined but not used
5160; Request defined but not used
5161; Response defined but not used
5162; TE defined but not used
5163; URI-reference defined but not used
5164; http-URI defined but not used
5165; https-URI defined but not used
5166; partial-URI defined but not used
5167; special defined but not used
5169<?ENDINC p1-messaging.abnf-appendix ?>
5171<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5173<section title="Since RFC2616">
5175  Extracted relevant partitions from <xref target="RFC2616"/>.
5179<section title="Since draft-ietf-httpbis-p1-messaging-00">
5181  Closed issues:
5182  <list style="symbols">
5183    <t>
5184      <eref target=""/>:
5185      "HTTP Version should be case sensitive"
5186      (<eref target=""/>)
5187    </t>
5188    <t>
5189      <eref target=""/>:
5190      "'unsafe' characters"
5191      (<eref target=""/>)
5192    </t>
5193    <t>
5194      <eref target=""/>:
5195      "Chunk Size Definition"
5196      (<eref target=""/>)
5197    </t>
5198    <t>
5199      <eref target=""/>:
5200      "Message Length"
5201      (<eref target=""/>)
5202    </t>
5203    <t>
5204      <eref target=""/>:
5205      "Media Type Registrations"
5206      (<eref target=""/>)
5207    </t>
5208    <t>
5209      <eref target=""/>:
5210      "URI includes query"
5211      (<eref target=""/>)
5212    </t>
5213    <t>
5214      <eref target=""/>:
5215      "No close on 1xx responses"
5216      (<eref target=""/>)
5217    </t>
5218    <t>
5219      <eref target=""/>:
5220      "Remove 'identity' token references"
5221      (<eref target=""/>)
5222    </t>
5223    <t>
5224      <eref target=""/>:
5225      "Import query BNF"
5226    </t>
5227    <t>
5228      <eref target=""/>:
5229      "qdtext BNF"
5230    </t>
5231    <t>
5232      <eref target=""/>:
5233      "Normative and Informative references"
5234    </t>
5235    <t>
5236      <eref target=""/>:
5237      "RFC2606 Compliance"
5238    </t>
5239    <t>
5240      <eref target=""/>:
5241      "RFC977 reference"
5242    </t>
5243    <t>
5244      <eref target=""/>:
5245      "RFC1700 references"
5246    </t>
5247    <t>
5248      <eref target=""/>:
5249      "inconsistency in date format explanation"
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "Date reference typo"
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "Informative references"
5258    </t>
5259    <t>
5260      <eref target=""/>:
5261      "ISO-8859-1 Reference"
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "Normative up-to-date references"
5266    </t>
5267  </list>
5270  Other changes:
5271  <list style="symbols">
5272    <t>
5273      Update media type registrations to use RFC4288 template.
5274    </t>
5275    <t>
5276      Use names of RFC4234 core rules DQUOTE and WSP,
5277      fix broken ABNF for chunk-data
5278      (work in progress on <eref target=""/>)
5279    </t>
5280  </list>
5284<section title="Since draft-ietf-httpbis-p1-messaging-01">
5286  Closed issues:
5287  <list style="symbols">
5288    <t>
5289      <eref target=""/>:
5290      "Bodies on GET (and other) requests"
5291    </t>
5292    <t>
5293      <eref target=""/>:
5294      "Updating to RFC4288"
5295    </t>
5296    <t>
5297      <eref target=""/>:
5298      "Status Code and Reason Phrase"
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "rel_path not used"
5303    </t>
5304  </list>
5307  Ongoing work on ABNF conversion (<eref target=""/>):
5308  <list style="symbols">
5309    <t>
5310      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5311      "trailer-part").
5312    </t>
5313    <t>
5314      Avoid underscore character in rule names ("http_URL" ->
5315      "http-URL", "abs_path" -> "path-absolute").
5316    </t>
5317    <t>
5318      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5319      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5320      have to be updated when switching over to RFC3986.
5321    </t>
5322    <t>
5323      Synchronize core rules with RFC5234.
5324    </t>
5325    <t>
5326      Get rid of prose rules that span multiple lines.
5327    </t>
5328    <t>
5329      Get rid of unused rules LOALPHA and UPALPHA.
5330    </t>
5331    <t>
5332      Move "Product Tokens" section (back) into Part 1, as "token" is used
5333      in the definition of the Upgrade header.
5334    </t>
5335    <t>
5336      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5337    </t>
5338    <t>
5339      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5340    </t>
5341  </list>
5345<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5347  Closed issues:
5348  <list style="symbols">
5349    <t>
5350      <eref target=""/>:
5351      "HTTP-date vs. rfc1123-date"
5352    </t>
5353    <t>
5354      <eref target=""/>:
5355      "WS in quoted-pair"
5356    </t>
5357  </list>
5360  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5361  <list style="symbols">
5362    <t>
5363      Reference RFC 3984, and update header registrations for headers defined
5364      in this document.
5365    </t>
5366  </list>
5369  Ongoing work on ABNF conversion (<eref target=""/>):
5370  <list style="symbols">
5371    <t>
5372      Replace string literals when the string really is case-sensitive (HTTP-Version).
5373    </t>
5374  </list>
5378<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5380  Closed issues:
5381  <list style="symbols">
5382    <t>
5383      <eref target=""/>:
5384      "Connection closing"
5385    </t>
5386    <t>
5387      <eref target=""/>:
5388      "Move registrations and registry information to IANA Considerations"
5389    </t>
5390    <t>
5391      <eref target=""/>:
5392      "need new URL for PAD1995 reference"
5393    </t>
5394    <t>
5395      <eref target=""/>:
5396      "IANA Considerations: update HTTP URI scheme registration"
5397    </t>
5398    <t>
5399      <eref target=""/>:
5400      "Cite HTTPS URI scheme definition"
5401    </t>
5402    <t>
5403      <eref target=""/>:
5404      "List-type headers vs Set-Cookie"
5405    </t>
5406  </list>
5409  Ongoing work on ABNF conversion (<eref target=""/>):
5410  <list style="symbols">
5411    <t>
5412      Replace string literals when the string really is case-sensitive (HTTP-Date).
5413    </t>
5414    <t>
5415      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5416    </t>
5417  </list>
5421<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5423  Closed issues:
5424  <list style="symbols">
5425    <t>
5426      <eref target=""/>:
5427      "Out-of-date reference for URIs"
5428    </t>
5429    <t>
5430      <eref target=""/>:
5431      "RFC 2822 is updated by RFC 5322"
5432    </t>
5433  </list>
5436  Ongoing work on ABNF conversion (<eref target=""/>):
5437  <list style="symbols">
5438    <t>
5439      Use "/" instead of "|" for alternatives.
5440    </t>
5441    <t>
5442      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5443    </t>
5444    <t>
5445      Only reference RFC 5234's core rules.
5446    </t>
5447    <t>
5448      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5449      whitespace ("OWS") and required whitespace ("RWS").
5450    </t>
5451    <t>
5452      Rewrite ABNFs to spell out whitespace rules, factor out
5453      header value format definitions.
5454    </t>
5455  </list>
5459<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5461  Closed issues:
5462  <list style="symbols">
5463    <t>
5464      <eref target=""/>:
5465      "Header LWS"
5466    </t>
5467    <t>
5468      <eref target=""/>:
5469      "Sort 1.3 Terminology"
5470    </t>
5471    <t>
5472      <eref target=""/>:
5473      "RFC2047 encoded words"
5474    </t>
5475    <t>
5476      <eref target=""/>:
5477      "Character Encodings in TEXT"
5478    </t>
5479    <t>
5480      <eref target=""/>:
5481      "Line Folding"
5482    </t>
5483    <t>
5484      <eref target=""/>:
5485      "OPTIONS * and proxies"
5486    </t>
5487    <t>
5488      <eref target=""/>:
5489      "Reason-Phrase BNF"
5490    </t>
5491    <t>
5492      <eref target=""/>:
5493      "Use of TEXT"
5494    </t>
5495    <t>
5496      <eref target=""/>:
5497      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5498    </t>
5499    <t>
5500      <eref target=""/>:
5501      "RFC822 reference left in discussion of date formats"
5502    </t>
5503  </list>
5506  Final work on ABNF conversion (<eref target=""/>):
5507  <list style="symbols">
5508    <t>
5509      Rewrite definition of list rules, deprecate empty list elements.
5510    </t>
5511    <t>
5512      Add appendix containing collected and expanded ABNF.
5513    </t>
5514  </list>
5517  Other changes:
5518  <list style="symbols">
5519    <t>
5520      Rewrite introduction; add mostly new Architecture Section.
5521    </t>
5522    <t>
5523      Move definition of quality values from Part 3 into Part 1;
5524      make TE request header grammar independent of accept-params (defined in Part 3).
5525    </t>
5526  </list>
5530<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5532  Closed issues:
5533  <list style="symbols">
5534    <t>
5535      <eref target=""/>:
5536      "base for numeric protocol elements"
5537    </t>
5538    <t>
5539      <eref target=""/>:
5540      "comment ABNF"
5541    </t>
5542  </list>
5545  Partly resolved issues:
5546  <list style="symbols">
5547    <t>
5548      <eref target=""/>:
5549      "205 Bodies" (took out language that implied that there may be
5550      methods for which a request body MUST NOT be included)
5551    </t>
5552    <t>
5553      <eref target=""/>:
5554      "editorial improvements around HTTP-date"
5555    </t>
5556  </list>
5560<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5562  Closed issues:
5563  <list style="symbols">
5564    <t>
5565      <eref target=""/>:
5566      "Repeating single-value headers"
5567    </t>
5568    <t>
5569      <eref target=""/>:
5570      "increase connection limit"
5571    </t>
5572    <t>
5573      <eref target=""/>:
5574      "IP addresses in URLs"
5575    </t>
5576    <t>
5577      <eref target=""/>:
5578      "take over HTTP Upgrade Token Registry"
5579    </t>
5580    <t>
5581      <eref target=""/>:
5582      "CR and LF in chunk extension values"
5583    </t>
5584    <t>
5585      <eref target=""/>:
5586      "HTTP/0.9 support"
5587    </t>
5588    <t>
5589      <eref target=""/>:
5590      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5591    </t>
5592    <t>
5593      <eref target=""/>:
5594      "move definitions of gzip/deflate/compress to part 1"
5595    </t>
5596    <t>
5597      <eref target=""/>:
5598      "disallow control characters in quoted-pair"
5599    </t>
5600  </list>
5603  Partly resolved issues:
5604  <list style="symbols">
5605    <t>
5606      <eref target=""/>:
5607      "update IANA requirements wrt Transfer-Coding values" (add the
5608      IANA Considerations subsection)
5609    </t>
5610  </list>
5614<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5616  Closed issues:
5617  <list style="symbols">
5618    <t>
5619      <eref target=""/>:
5620      "header parsing, treatment of leading and trailing OWS"
5621    </t>
5622  </list>
5625  Partly resolved issues:
5626  <list style="symbols">
5627    <t>
5628      <eref target=""/>:
5629      "Placement of 13.5.1 and 13.5.2"
5630    </t>
5631    <t>
5632      <eref target=""/>:
5633      "use of term "word" when talking about header structure"
5634    </t>
5635  </list>
5639<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5641  Closed issues:
5642  <list style="symbols">
5643    <t>
5644      <eref target=""/>:
5645      "Clarification of the term 'deflate'"
5646    </t>
5647    <t>
5648      <eref target=""/>:
5649      "OPTIONS * and proxies"
5650    </t>
5651    <t>
5652      <eref target=""/>:
5653      "IANA registry for content/transfer encodings"
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "Case-sensitivity of HTTP-date"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "use of term "word" when talking about header structure"
5662    </t>
5663  </list>
5666  Partly resolved issues:
5667  <list style="symbols">
5668    <t>
5669      <eref target=""/>:
5670      "Term for the requested resource's URI"
5671    </t>
5672  </list>
5676<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5678  None yet.
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