source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 383

Last change on this file since 383 was 373, checked in by fielding@…, 12 years ago

change tactics -- define HTTP architecture instead of when to use HTTP

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for informations systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as a generic protocol for translating
254   communication to and from other Internet information systems, such as
255   USENET news services via NNTP <xref target="RFC3977"/>,
256   file services via FTP <xref target="RFC959"/>,
257   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
258   HTTP proxies and gateways provide access to alternative information
259   services by translating their diverse protocols into a hypermedia
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
262</t>
263<t>
264   One consequence of HTTP flexibility is that we cannot define the protocol
265   in terms of how to implement it behind the interface. Instead, we are
266   limited to restricting the syntax of communication, defining the intent
267   of received communication, and the expected behavior of recipients. If
268   the communication is considered in isolation, then successful actions
269   should be reflected in the observable interface provided by servers.
270   However, since many clients are potentially acting in parallel and
271   perhaps at cross-purposes, it would be meaningless to require that such
272   behavior be observable.
273</t>
274<t>
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1" and obsoleting
277   <xref target="RFC2616"/>.
278   Part 1 defines the URI schemes specific to HTTP-based resources, overall
279   network operation, transport protocol connection management, and HTTP
280   message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for a message parser and transparent
284   message-forwarding intermediaries.
285</t>
286
287<section title="Requirements" anchor="intro.requirements">
288<t>
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
292</t>
293<t>
294   An implementation is not compliant if it fails to satisfy one or more
295   of the &MUST; or &REQUIRED; level requirements for the protocols it
296   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
297   level and all the &SHOULD; level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the &MUST;
299   level requirements but not all the &SHOULD; level requirements for its
300   protocols is said to be "conditionally compliant."
301</t>
302</section>
303
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CHAR"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="HTAB"/>
314<iref primary="true" item="Grammar" subitem="LF"/>
315<iref primary="true" item="Grammar" subitem="OCTET"/>
316<iref primary="true" item="Grammar" subitem="SP"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CHAR"/>
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="HTAB"/>
328  <x:anchor-alias value="LF"/>
329  <x:anchor-alias value="OCTET"/>
330  <x:anchor-alias value="SP"/>
331  <x:anchor-alias value="WSP"/>
332   This specification uses the Augmented Backus-Naur Form (ABNF) notation
333   of <xref target="RFC5234"/>.  The following core rules are included by
334   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
336   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
337   DIGIT (decimal 0-9), DQUOTE (double quote),
338   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
339   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
340   and WSP (white space).
341</t>
342
343<section title="ABNF Extensions" anchor="notation.abnf">
344<t>
345   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
346   improve readability.<cref>The current plan is to remove these extensions prior
347   to the last call draft.</cref>
348</t>
349
350<section title="#rule">
351  <t>
352    A construct "#" is defined, similar to "*", for defining lists of
353    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
354    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
355    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
356    form of lists very easy; a rule such as
357    <figure><artwork type="example">
358 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
359  </t>
360  <t>
361    can be shown as
362    <figure><artwork type="example">
363 1#element</artwork></figure>
364  </t>
365  <t>
366    Wherever this construct is used, null elements are allowed, but do
367    not contribute to the count of elements present. That is,
368    "(element), , (element) " is permitted, but counts as only two
369    elements. Therefore, where at least one element is required, at
370    least one non-null element &MUST; be present. Default values are 0
371    and infinity so that "#element" allows any number, including zero;
372    "1#element" requires at least one; and "1#2element" allows one or
373    two.
374  </t>
375</section>
376
377<section title="implied *LWS" anchor="implied.LWS">
378  <iref item="implied *LWS" primary="true"/>
379    <t>
380      The grammar described by this specification is word-based. Except
381      where noted otherwise, linear white space (LWS) can be included
382      between any two adjacent words (token or quoted-string), and
383      between adjacent words and separators, without changing the
384      interpretation of a field. At least one delimiter (LWS and/or
385      separators) &MUST; exist between any two tokens (for the definition
386      of "token" below), since they would otherwise be interpreted as a
387      single token.
388    </t>
389</section>
390</section>
391
392<section title="Basic Rules" anchor="basic.rules">
393<t anchor="rule.CRLF">
394   HTTP/1.1 defines the sequence CRLF as the end-of-line marker for all
395   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
396   tolerant applications). The end-of-line marker within an entity-body
397   is defined by its associated media type, as described in &media-types;.
398</t>
399<t anchor="rule.LWS">
400  <x:anchor-alias value="LWS"/>
401   HTTP/1.1 header field values can be folded onto multiple lines if the
402   continuation line begins with a space or horizontal tab. All linear
403   white space, including folding, has the same semantics as SP. A
404   recipient &MAY; replace any linear white space with a single SP before
405   interpreting the field value or forwarding the message downstream.
406</t>
407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
408  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
409</artwork></figure>
410<t anchor="rule.TEXT">
411  <x:anchor-alias value="TEXT"/>
412   The TEXT rule is only used for descriptive field contents and values
413   that are not intended to be interpreted by the message parser. Words
414   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
415   <xref target="ISO-8859-1"/> only when encoded according to the rules of
416   <xref target="RFC2047"/>.
417</t>
418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
419  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
420                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
421</artwork></figure>
422<t>
423   A CRLF is allowed in the definition of TEXT only as part of a header
424   field continuation. It is expected that the folding LWS will be
425   replaced with a single SP before interpretation of the TEXT value.
426</t>
427<t anchor="rule.token.separators">
428  <x:anchor-alias value="tchar"/>
429  <x:anchor-alias value="token"/>
430  <x:anchor-alias value="separators"/>
431   Many HTTP/1.1 header field values consist of words separated by LWS
432   or special characters. These special characters &MUST; be in a quoted
433   string to be used within a parameter value (as defined in
434   <xref target="transfer.codings"/>).
435</t>
436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/>
437  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
438                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
439                 / "/" / "[" / "]" / "?" / "="
440                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
441                 
442  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
443                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
444                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
445                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
446                 
447  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
448</artwork></figure>
449<t anchor="rule.comment">
450  <x:anchor-alias value="comment"/>
451  <x:anchor-alias value="ctext"/>
452   Comments can be included in some HTTP header fields by surrounding
453   the comment text with parentheses. Comments are only allowed in
454   fields containing "comment" as part of their field value definition.
455   In all other fields, parentheses are considered part of the field
456   value.
457</t>
458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
459  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
460  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
461</artwork></figure>
462<t anchor="rule.quoted-string">
463  <x:anchor-alias value="quoted-string"/>
464  <x:anchor-alias value="qdtext"/>
465   A string of text is parsed as a single word if it is quoted using
466   double-quote marks.
467</t>
468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
469  <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> )
470  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
471</artwork></figure>
472<t anchor="rule.quoted-pair">
473  <x:anchor-alias value="quoted-pair"/>
474  <x:anchor-alias value="quoted-text"/>
475   The backslash character ("\") &MAY; be used as a single-character
476   quoting mechanism only within quoted-string and comment constructs.
477</t>
478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
479  <x:ref>quoted-text</x:ref>    = %x01-09 /
480                   %x0B-0C /
481                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
482  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
483</artwork></figure>
484</section>
485
486<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
487  <x:anchor-alias value="request-header"/>
488  <x:anchor-alias value="response-header"/>
489  <x:anchor-alias value="accept-params"/>
490  <x:anchor-alias value="entity-body"/>
491  <x:anchor-alias value="entity-header"/>
492  <x:anchor-alias value="Cache-Control"/>
493  <x:anchor-alias value="Pragma"/>
494  <x:anchor-alias value="Warning"/>
495<t>
496  The ABNF rules below are defined in other parts:
497</t>
498<figure><!-- Part2--><artwork type="abnf2616">
499  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
500  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
501</artwork></figure>
502<figure><!-- Part3--><artwork type="abnf2616">
503  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
504  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
505  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
506</artwork></figure>
507<figure><!-- Part6--><artwork type="abnf2616">
508  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
509  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
510  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
511</artwork></figure>
512</section>
513
514</section>
515</section>
516
517<section title="HTTP architecture" anchor="architecture">
518<t>
519   Nevertheless, HTTP was created with a specific architecture in mind, the
520   World Wide Web, and has evolved over time to support the scalability needs
521   of a worldwide hypertext system. Much of that architecture is reflected in
522   the terminology used to define HTTP. This section describes the larger
523   architecture surrounding expected usage of HTTP that is used by this
524   specification to define HTTP.
525</t>
526
527<section title="Uniform Resource Identifiers" anchor="uri">
528<t>
529   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
530   to indicate the target of a request and to identify additional resources related
531   to that resource, the request, or the response. Each protocol element in HTTP
532   that allows a URI reference will indicate in its ABNF whether the element allows
533   only a URI in absolute form, any relative reference, or some limited subset of
534   the URI-reference grammar. Unless otherwise indicated, relative URI references
535   are to be parsed relative to the URI corresponding to the request target
536   (the base URI).
537</t>
538  <x:anchor-alias value="URI-reference"/>
539  <x:anchor-alias value="absolute-URI"/>
540  <x:anchor-alias value="authority"/>
541  <x:anchor-alias value="fragment"/>
542  <x:anchor-alias value="path-abempty"/>
543  <x:anchor-alias value="path-absolute"/>
544  <x:anchor-alias value="port"/>
545  <x:anchor-alias value="query"/>
546  <x:anchor-alias value="uri-host"/>
547<t>
548   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
549   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
550</t>
551<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"/>
552  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
553  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
554  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
555  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
556  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
557  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
558  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
559  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
560</artwork></figure>
561<t>
562   HTTP does not place an a priori limit on the length of
563   a URI. Servers &MUST; be able to handle the URI of any resource they
564   serve, and &SHOULD; be able to handle URIs of unbounded length if they
565   provide GET-based forms that could generate such URIs. A server
566   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
567   than the server can handle (see &status-414;).
568</t>
569<t>
570  <list>
571    <t>
572      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
573      above 255 bytes, because some older client or proxy
574      implementations might not properly support these lengths.
575    </t>
576  </list>
577</t>
578
579<section title="http URI scheme" anchor="http.uri">
580  <x:anchor-alias value="http-URI"/>
581  <iref item="http URI scheme" primary="true"/>
582  <iref item="URI scheme" subitem="http" primary="true"/>
583<t>
584   The "http" scheme is used to locate network resources via the HTTP
585   protocol. This section defines the syntax and semantics for identifiers
586   using the http or https URI schemes.
587</t>
588<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
589  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
590</artwork></figure>
591<t>
592   If the port is empty or not given, port 80 is assumed. The semantics
593   are that the identified resource is located at the server listening
594   for TCP connections on that port of that host, and the Request-URI
595   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
596   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
597   the path-absolute is not present in the URL, it &MUST; be given as "/" when
598   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
599   receives a host name which is not a fully qualified domain name, it
600   &MAY; add its domain to the host name it received. If a proxy receives
601   a fully qualified domain name, the proxy &MUST-NOT; change the host
602   name.
603</t>
604<t><list><t>
605  <iref item="https URI scheme"/>
606  <iref item="URI scheme" subitem="https"/>
607  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
608</t></list></t>
609</section>
610
611<section title="URI Comparison" anchor="uri.comparison">
612<t>
613   When comparing two URIs to decide if they match or not, a client
614   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
615   URIs, with these exceptions:
616  <list style="symbols">
617    <t>A port that is empty or not given is equivalent to the default
618        port for that URI-reference;</t>
619    <t>Comparisons of host names &MUST; be case-insensitive;</t>
620    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
621    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
622  </list>
623</t>
624<t>
625   Characters other than those in the "reserved" set (see
626   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
627   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
628</t>
629<t>
630   For example, the following three URIs are equivalent:
631</t>
632<figure><artwork type="example">
633   http://example.com:80/~smith/home.html
634   http://EXAMPLE.com/%7Esmith/home.html
635   http://EXAMPLE.com:/%7esmith/home.html
636</artwork></figure>
637</section>
638
639<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
640<t>
641</t>
642</section>
643</section>
644
645<section title="Overall Operation" anchor="intro.overall.operation">
646<t>
647   HTTP is a request/response protocol. A client sends a
648   request to the server in the form of a request method, URI, and
649   protocol version, followed by a MIME-like message containing request
650   modifiers, client information, and possible body content over a
651   connection with a server. The server responds with a status line,
652   including the message's protocol version and a success or error code,
653   followed by a MIME-like message containing server information, entity
654   metainformation, and possible entity-body content.
655</t>
656<t>
657   Most HTTP communication is initiated by a user agent and consists of
658   a request to be applied to a resource on some origin server. In the
659   simplest case, this may be accomplished via a single connection (v)
660   between the user agent (UA) and the origin server (O).
661</t>
662<figure><artwork type="drawing">
663       request chain ------------------------&gt;
664    UA -------------------v------------------- O
665       &lt;----------------------- response chain
666</artwork></figure>
667<t>
668   A more complicated situation occurs when one or more intermediaries
669   are present in the request/response chain. There are three common
670   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
671   forwarding agent, receiving requests for a URI in its absolute form,
672   rewriting all or part of the message, and forwarding the reformatted
673   request toward the server identified by the URI. A gateway is a
674   receiving agent, acting as a layer above some other server(s) and, if
675   necessary, translating the requests to the underlying server's
676   protocol. A tunnel acts as a relay point between two connections
677   without changing the messages; tunnels are used when the
678   communication needs to pass through an intermediary (such as a
679   firewall) even when the intermediary cannot understand the contents
680   of the messages.
681</t>
682<figure><artwork type="drawing">
683       request chain --------------------------------------&gt;
684    UA -----v----- A -----v----- B -----v----- C -----v----- O
685       &lt;------------------------------------- response chain
686</artwork></figure>
687<t>
688   The figure above shows three intermediaries (A, B, and C) between the
689   user agent and origin server. A request or response message that
690   travels the whole chain will pass through four separate connections.
691   This distinction is important because some HTTP communication options
692   may apply only to the connection with the nearest, non-tunnel
693   neighbor, only to the end-points of the chain, or to all connections
694   along the chain. Although the diagram is linear, each participant may
695   be engaged in multiple, simultaneous communications. For example, B
696   may be receiving requests from many clients other than A, and/or
697   forwarding requests to servers other than C, at the same time that it
698   is handling A's request.
699</t>
700<t>
701   Any party to the communication which is not acting as a tunnel may
702   employ an internal cache for handling requests. The effect of a cache
703   is that the request/response chain is shortened if one of the
704   participants along the chain has a cached response applicable to that
705   request. The following illustrates the resulting chain if B has a
706   cached copy of an earlier response from O (via C) for a request which
707   has not been cached by UA or A.
708</t>
709<figure><artwork type="drawing">
710          request chain ----------&gt;
711       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
712          &lt;--------- response chain
713</artwork></figure>
714<t>
715   Not all responses are usefully cacheable, and some requests may
716   contain modifiers which place special requirements on cache behavior.
717   HTTP requirements for cache behavior and cacheable responses are
718   defined in &caching;.
719</t>
720<t>
721   In fact, there are a wide variety of architectures and configurations
722   of caches and proxies currently being experimented with or deployed
723   across the World Wide Web. These systems include national hierarchies
724   of proxy caches to save transoceanic bandwidth, systems that
725   broadcast or multicast cache entries, organizations that distribute
726   subsets of cached data via CD-ROM, and so on. HTTP systems are used
727   in corporate intranets over high-bandwidth links, and for access via
728   PDAs with low-power radio links and intermittent connectivity. The
729   goal of HTTP/1.1 is to support the wide diversity of configurations
730   already deployed while introducing protocol constructs that meet the
731   needs of those who build web applications that require high
732   reliability and, failing that, at least reliable indications of
733   failure.
734</t>
735<t>
736   HTTP communication usually takes place over TCP/IP connections. The
737   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
738   not preclude HTTP from being implemented on top of any other protocol
739   on the Internet, or on other networks. HTTP only presumes a reliable
740   transport; any protocol that provides such guarantees can be used;
741   the mapping of the HTTP/1.1 request and response structures onto the
742   transport data units of the protocol in question is outside the scope
743   of this specification.
744</t>
745<t>
746   In HTTP/1.0, most implementations used a new connection for each
747   request/response exchange. In HTTP/1.1, a connection may be used for
748   one or more request/response exchanges, although connections may be
749   closed for a variety of reasons (see <xref target="persistent.connections"/>).
750</t>
751</section>
752
753<section title="Use of HTTP for proxy communication" anchor="http.proxy">
754<t>
755   Configured to use HTTP to proxy HTTP or other protocols.
756</t>
757</section>
758<section title="Interception of HTTP for access control" anchor="http.intercept">
759<t>
760   Interception of HTTP traffic for initiating access control.
761</t>
762</section>
763<section title="Use of HTTP by other protocols" anchor="http.others">
764<t>
765   Profiles of HTTP defined by other protocol.
766   Extensions of HTTP like WebDAV.
767</t>
768</section>
769<section title="Use of HTTP by media type specification" anchor="http.media">
770<t>
771   Instructions on composing HTTP requests via hypertext formats.
772</t>
773</section>
774</section>
775
776<section title="Protocol Parameters" anchor="protocol.parameters">
777
778<section title="HTTP Version" anchor="http.version">
779  <x:anchor-alias value="HTTP-Version"/>
780  <x:anchor-alias value="HTTP-Prot-Name"/>
781<t>
782   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
783   of the protocol. The protocol versioning policy is intended to allow
784   the sender to indicate the format of a message and its capacity for
785   understanding further HTTP communication, rather than the features
786   obtained via that communication. No change is made to the version
787   number for the addition of message components which do not affect
788   communication behavior or which only add to extensible field values.
789   The &lt;minor&gt; number is incremented when the changes made to the
790   protocol add features which do not change the general message parsing
791   algorithm, but which may add to the message semantics and imply
792   additional capabilities of the sender. The &lt;major&gt; number is
793   incremented when the format of a message within the protocol is
794   changed. See <xref target="RFC2145"/> for a fuller explanation.
795</t>
796<t>
797   The version of an HTTP message is indicated by an HTTP-Version field
798   in the first line of the message. HTTP-Version is case-sensitive.
799</t>
800<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
801  <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>
802  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
803</artwork></figure>
804<t>
805   Note that the major and minor numbers &MUST; be treated as separate
806   integers and that each &MAY; be incremented higher than a single digit.
807   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
808   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
809   &MUST-NOT; be sent.
810</t>
811<t>
812   An application that sends a request or response message that includes
813   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
814   with this specification. Applications that are at least conditionally
815   compliant with this specification &SHOULD; use an HTTP-Version of
816   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
817   not compatible with HTTP/1.0. For more details on when to send
818   specific HTTP-Version values, see <xref target="RFC2145"/>.
819</t>
820<t>
821   The HTTP version of an application is the highest HTTP version for
822   which the application is at least conditionally compliant.
823</t>
824<t>
825   Proxy and gateway applications need to be careful when forwarding
826   messages in protocol versions different from that of the application.
827   Since the protocol version indicates the protocol capability of the
828   sender, a proxy/gateway &MUST-NOT; send a message with a version
829   indicator which is greater than its actual version. If a higher
830   version request is received, the proxy/gateway &MUST; either downgrade
831   the request version, or respond with an error, or switch to tunnel
832   behavior.
833</t>
834<t>
835   Due to interoperability problems with HTTP/1.0 proxies discovered
836   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
837   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
838   they support. The proxy/gateway's response to that request &MUST; be in
839   the same major version as the request.
840</t>
841<t>
842  <list>
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>
847  </list>
848</t>
849</section>
850
851<section title="Date/Time Formats" anchor="date.time.formats">
852<section title="Full Date" anchor="full.date">
853  <x:anchor-alias value="HTTP-date"/>
854  <x:anchor-alias value="obsolete-date"/>
855  <x:anchor-alias value="rfc1123-date"/>
856  <x:anchor-alias value="rfc850-date"/>
857  <x:anchor-alias value="asctime-date"/>
858  <x:anchor-alias value="date1"/>
859  <x:anchor-alias value="date2"/>
860  <x:anchor-alias value="date3"/>
861  <x:anchor-alias value="rfc1123-date"/>
862  <x:anchor-alias value="time"/>
863  <x:anchor-alias value="wkday"/>
864  <x:anchor-alias value="weekday"/>
865  <x:anchor-alias value="month"/>
866<t>
867   HTTP applications have historically allowed three different formats
868   for the representation of date/time stamps:
869</t>
870<figure><artwork type="example">
871   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
872   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
873   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
874</artwork></figure>
875<t>
876   The first format is preferred as an Internet standard and represents
877   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
878   <xref target="RFC822"/>). The other formats are described here only for
879   compatibility with obsolete implementations.
880   HTTP/1.1 clients and servers that parse the date value &MUST; accept
881   all three formats (for compatibility with HTTP/1.0), though they &MUST;
882   only generate the RFC 1123 format for representing HTTP-date values
883   in header fields. See <xref target="tolerant.applications"/> for further information.
884</t>
885<t><list><t>
886      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
887      accepting date values that may have been sent by non-HTTP
888      applications, as is sometimes the case when retrieving or posting
889      messages via proxies/gateways to SMTP or NNTP.
890</t></list></t>
891<t>
892   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
893   (GMT), without exception. For the purposes of HTTP, GMT is exactly
894   equal to UTC (Coordinated Universal Time). This is indicated in the
895   first two formats by the inclusion of "GMT" as the three-letter
896   abbreviation for time zone, and &MUST; be assumed when reading the
897   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
898   additional LWS beyond that specifically included as SP in the
899   grammar.
900</t>
901<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
902  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
903  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
904  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
905  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
906  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
907  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
908                 ; day month year (e.g., 02 Jun 1982)
909  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
910                 ; day-month-year (e.g., 02-Jun-82)
911  <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> ))
912                 ; month day (e.g., Jun  2)
913  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
914                 ; 00:00:00 - 23:59:59
915  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
916               / s-Thu / s-Fri / s-Sat / s-Sun
917  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
918               / l-Thu / l-Fri / l-Sat / l-Sun
919  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
920               / s-May / s-Jun / s-Jul / s-Aug
921               / s-Sep / s-Oct / s-Nov / s-Dec
922               
923  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
924
925  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
926  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
927  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
928  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
929  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
930  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
931  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
932
933  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
934  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
935  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
936  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
937  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
938  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
939  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
940
941  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
942  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
943  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
944  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
945  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
946  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
947  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
948  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
949  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
950  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
951  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
952  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
953</artwork></figure>
954<t>
955      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
956      to their usage within the protocol stream. Clients and servers are
957      not required to use these formats for user presentation, request
958      logging, etc.
959</t>
960</section>
961</section>
962
963<section title="Transfer Codings" anchor="transfer.codings">
964  <x:anchor-alias value="parameter"/>
965  <x:anchor-alias value="transfer-coding"/>
966  <x:anchor-alias value="transfer-extension"/>
967<t>
968   Transfer-coding values are used to indicate an encoding
969   transformation that has been, can be, or may need to be applied to an
970   entity-body in order to ensure "safe transport" through the network.
971   This differs from a content coding in that the transfer-coding is a
972   property of the message, not of the original entity.
973</t>
974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
975  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
976  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
977</artwork></figure>
978<t anchor="rule.parameter">
979  <x:anchor-alias value="attribute"/>
980  <x:anchor-alias value="parameter"/>
981  <x:anchor-alias value="value"/>
982   Parameters are in  the form of attribute/value pairs.
983</t>
984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
985  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
986  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
987  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
988</artwork></figure>
989<t>
990   All transfer-coding values are case-insensitive. HTTP/1.1 uses
991   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
992   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
993</t>
994<t>
995   Whenever a transfer-coding is applied to a message-body, the set of
996   transfer-codings &MUST; include "chunked", unless the message indicates it
997   is terminated by closing the connection. When the "chunked" transfer-coding
998   is used, it &MUST; be the last transfer-coding applied to the
999   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1000   than once to a message-body. These rules allow the recipient to
1001   determine the transfer-length of the message (<xref target="message.length"/>).
1002</t>
1003<t>
1004   Transfer-codings are analogous to the Content-Transfer-Encoding
1005   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1006   binary data over a 7-bit transport service. However, safe transport
1007   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1008   the only unsafe characteristic of message-bodies is the difficulty in
1009   determining the exact body length (<xref target="message.length"/>), or the desire to
1010   encrypt data over a shared transport.
1011</t>
1012<t>
1013   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1014   transfer-coding value tokens. Initially, the registry contains the
1015   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1016   "gzip", "compress", and "deflate" (&content-codings;).
1017</t>
1018<t>
1019   New transfer-coding value tokens &SHOULD; be registered in the same way
1020   as new content-coding value tokens (&content-codings;).
1021</t>
1022<t>
1023   A server which receives an entity-body with a transfer-coding it does
1024   not understand &SHOULD; return 501 (Not Implemented), and close the
1025   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1026   client.
1027</t>
1028
1029<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1030  <x:anchor-alias value="chunk"/>
1031  <x:anchor-alias value="Chunked-Body"/>
1032  <x:anchor-alias value="chunk-data"/>
1033  <x:anchor-alias value="chunk-extension"/>
1034  <x:anchor-alias value="chunk-ext-name"/>
1035  <x:anchor-alias value="chunk-ext-val"/>
1036  <x:anchor-alias value="chunk-size"/>
1037  <x:anchor-alias value="last-chunk"/>
1038  <x:anchor-alias value="trailer-part"/>
1039<t>
1040   The chunked encoding modifies the body of a message in order to
1041   transfer it as a series of chunks, each with its own size indicator,
1042   followed by an &OPTIONAL; trailer containing entity-header fields. This
1043   allows dynamically produced content to be transferred along with the
1044   information necessary for the recipient to verify that it has
1045   received the full message.
1046</t>
1047<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-extension"/><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"/>
1048  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1049                   <x:ref>last-chunk</x:ref>
1050                   <x:ref>trailer-part</x:ref>
1051                   <x:ref>CRLF</x:ref>
1052 
1053  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1054                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1055  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1056  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1057 
1058  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1059  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1060  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1061  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1062  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1063</artwork></figure>
1064<t>
1065   The chunk-size field is a string of hex digits indicating the size of
1066   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1067   zero, followed by the trailer, which is terminated by an empty line.
1068</t>
1069<t>
1070   The trailer allows the sender to include additional HTTP header
1071   fields at the end of the message. The Trailer header field can be
1072   used to indicate which header fields are included in a trailer (see
1073   <xref target="header.trailer"/>).
1074</t>
1075<t>
1076   A server using chunked transfer-coding in a response &MUST-NOT; use the
1077   trailer for any header fields unless at least one of the following is
1078   true:
1079  <list style="numbers">
1080    <t>the request included a TE header field that indicates "trailers" is
1081     acceptable in the transfer-coding of the  response, as described in
1082     <xref target="header.te"/>; or,</t>
1083
1084    <t>the server is the origin server for the response, the trailer
1085     fields consist entirely of optional metadata, and the recipient
1086     could use the message (in a manner acceptable to the origin server)
1087     without receiving this metadata.  In other words, the origin server
1088     is willing to accept the possibility that the trailer fields might
1089     be silently discarded along the path to the client.</t>
1090  </list>
1091</t>
1092<t>
1093   This requirement prevents an interoperability failure when the
1094   message is being received by an HTTP/1.1 (or later) proxy and
1095   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1096   compliance with the protocol would have necessitated a possibly
1097   infinite buffer on the proxy.
1098</t>
1099<t>
1100   A process for decoding the "chunked" transfer-coding
1101   can be represented in pseudo-code as:
1102</t>
1103<figure><artwork type="code">
1104    length := 0
1105    read chunk-size, chunk-extension (if any) and CRLF
1106    while (chunk-size &gt; 0) {
1107       read chunk-data and CRLF
1108       append chunk-data to entity-body
1109       length := length + chunk-size
1110       read chunk-size and CRLF
1111    }
1112    read entity-header
1113    while (entity-header not empty) {
1114       append entity-header to existing header fields
1115       read entity-header
1116    }
1117    Content-Length := length
1118    Remove "chunked" from Transfer-Encoding
1119</artwork></figure>
1120<t>
1121   All HTTP/1.1 applications &MUST; be able to receive and decode the
1122   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1123   they do not understand.
1124</t>
1125</section>
1126</section>
1127
1128<section title="Product Tokens" anchor="product.tokens">
1129  <x:anchor-alias value="product"/>
1130  <x:anchor-alias value="product-version"/>
1131<t>
1132   Product tokens are used to allow communicating applications to
1133   identify themselves by software name and version. Most fields using
1134   product tokens also allow sub-products which form a significant part
1135   of the application to be listed, separated by white space. By
1136   convention, the products are listed in order of their significance
1137   for identifying the application.
1138</t>
1139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1140  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1141  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1142</artwork></figure>
1143<t>
1144   Examples:
1145</t>
1146<figure><artwork type="example">
1147    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1148    Server: Apache/0.8.4
1149</artwork></figure>
1150<t>
1151   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1152   used for advertising or other non-essential information. Although any
1153   token character &MAY; appear in a product-version, this token &SHOULD;
1154   only be used for a version identifier (i.e., successive versions of
1155   the same product &SHOULD; only differ in the product-version portion of
1156   the product value).
1157</t>
1158</section>
1159
1160</section>
1161
1162<section title="HTTP Message" anchor="http.message">
1163
1164<section title="Message Types" anchor="message.types">
1165  <x:anchor-alias value="generic-message"/>
1166  <x:anchor-alias value="HTTP-message"/>
1167  <x:anchor-alias value="start-line"/>
1168<t>
1169   HTTP messages consist of requests from client to server and responses
1170   from server to client.
1171</t>
1172<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1173  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1174</artwork></figure>
1175<t>
1176   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1177   message format of <xref target="RFC5322"/> for transferring entities (the payload
1178   of the message). Both types of message consist of a start-line, zero
1179   or more header fields (also known as "headers"), an empty line (i.e.,
1180   a line with nothing preceding the CRLF) indicating the end of the
1181   header fields, and possibly a message-body.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1184  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1185                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1186                    <x:ref>CRLF</x:ref>
1187                    [ <x:ref>message-body</x:ref> ]
1188  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1189</artwork></figure>
1190<t>
1191   In the interest of robustness, servers &SHOULD; ignore any empty
1192   line(s) received where a Request-Line is expected. In other words, if
1193   the server is reading the protocol stream at the beginning of a
1194   message and receives a CRLF first, it should ignore the CRLF.
1195</t>
1196<t>
1197   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1198   after a POST request. To restate what is explicitly forbidden by the
1199   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1200   extra CRLF.
1201</t>
1202</section>
1203
1204<section title="Message Headers" anchor="message.headers">
1205  <x:anchor-alias value="field-content"/>
1206  <x:anchor-alias value="field-name"/>
1207  <x:anchor-alias value="field-value"/>
1208  <x:anchor-alias value="message-header"/>
1209<t>
1210   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1211   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1212   entity-header (&entity-header-fields;) fields, follow the same generic format as
1213   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1214   of a name followed by a colon (":") and the field value. Field names
1215   are case-insensitive. The field value &MAY; be preceded by any amount
1216   of LWS, though a single SP is preferred. Header fields can be
1217   extended over multiple lines by preceding each extra line with at
1218   least one SP or HTAB. Applications ought to follow "common form", where
1219   one is known or indicated, when generating HTTP constructs, since
1220   there might exist some implementations that fail to accept anything
1221   beyond the common forms.
1222</t>
1223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-header"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1224  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1225  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1226  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1227  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1228                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1229                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1230                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1231</artwork></figure>
1232<t>
1233   The field-content does not include any leading or trailing LWS:
1234   linear white space occurring before the first non-whitespace
1235   character of the field-value or after the last non-whitespace
1236   character of the field-value. Such leading or trailing LWS &MAY; be
1237   removed without changing the semantics of the field value. Any LWS
1238   that occurs between field-content &MAY; be replaced with a single SP
1239   before interpreting the field value or forwarding the message
1240   downstream.
1241</t>
1242<t>
1243   The order in which header fields with differing field names are
1244   received is not significant. However, it is "good practice" to send
1245   general-header fields first, followed by request-header or response-header
1246   fields, and ending with the entity-header fields.
1247</t>
1248<t>
1249   Multiple message-header fields with the same field-name &MAY; be
1250   present in a message if and only if the entire field-value for that
1251   header field is defined as a comma-separated list [i.e., #(values)].
1252   It &MUST; be possible to combine the multiple header fields into one
1253   "field-name: field-value" pair, without changing the semantics of the
1254   message, by appending each subsequent field-value to the first, each
1255   separated by a comma. The order in which header fields with the same
1256   field-name are received is therefore significant to the
1257   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1258   change the order of these field values when a message is forwarded.
1259</t>
1260<t>
1261  <list><t>
1262   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1263   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1264   can occur multiple times, but does not use the list syntax, and thus cannot
1265   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1266   for details.) Also note that the Set-Cookie2 header specified in
1267   <xref target="RFC2965"/> does not share this problem.
1268  </t></list>
1269</t>
1270 
1271</section>
1272
1273<section title="Message Body" anchor="message.body">
1274  <x:anchor-alias value="message-body"/>
1275<t>
1276   The message-body (if any) of an HTTP message is used to carry the
1277   entity-body associated with the request or response. The message-body
1278   differs from the entity-body only when a transfer-coding has been
1279   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1280</t>
1281<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1282  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1283               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1284</artwork></figure>
1285<t>
1286   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1287   applied by an application to ensure safe and proper transfer of the
1288   message. Transfer-Encoding is a property of the message, not of the
1289   entity, and thus &MAY; be added or removed by any application along the
1290   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1291   when certain transfer-codings may be used.)
1292</t>
1293<t>
1294   The rules for when a message-body is allowed in a message differ for
1295   requests and responses.
1296</t>
1297<t>
1298   The presence of a message-body in a request is signaled by the
1299   inclusion of a Content-Length or Transfer-Encoding header field in
1300   the request's message-headers. A message-body &MUST-NOT; be included in
1301   a request if the specification of the request method (&method;)
1302   explicitly disallows an entity-body in requests.
1303   When a request message contains both a message-body of non-zero
1304   length and a method that does not define any semantics for that
1305   request message-body, then an origin server &SHOULD; either ignore
1306   the message-body or respond with an appropriate error message
1307   (e.g., 413).  A proxy or gateway, when presented the same request,
1308   &SHOULD; either forward the request inbound with the message-body or
1309   ignore the message-body when determining a response.
1310</t>
1311<t>
1312   For response messages, whether or not a message-body is included with
1313   a message is dependent on both the request method and the response
1314   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1315   &MUST-NOT; include a message-body, even though the presence of entity-header
1316   fields might lead one to believe they do. All 1xx
1317   (informational), 204 (No Content), and 304 (Not Modified) responses
1318   &MUST-NOT; include a message-body. All other responses do include a
1319   message-body, although it &MAY; be of zero length.
1320</t>
1321</section>
1322
1323<section title="Message Length" anchor="message.length">
1324<t>
1325   The transfer-length of a message is the length of the message-body as
1326   it appears in the message; that is, after any transfer-codings have
1327   been applied. When a message-body is included with a message, the
1328   transfer-length of that body is determined by one of the following
1329   (in order of precedence):
1330</t>
1331<t>
1332  <list style="numbers">
1333    <x:lt><t>
1334     Any response message which "&MUST-NOT;" include a message-body (such
1335     as the 1xx, 204, and 304 responses and any response to a HEAD
1336     request) is always terminated by the first empty line after the
1337     header fields, regardless of the entity-header fields present in
1338     the message.
1339    </t></x:lt>
1340    <x:lt><t>
1341     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1342     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1343     is used, the transfer-length is defined by the use of this transfer-coding.
1344     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1345     is not present, the transfer-length is defined by the sender closing the connection.
1346    </t></x:lt>
1347    <x:lt><t>
1348     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1349     decimal value in OCTETs represents both the entity-length and the
1350     transfer-length. The Content-Length header field &MUST-NOT; be sent
1351     if these two lengths are different (i.e., if a Transfer-Encoding
1352     header field is present). If a message is received with both a
1353     Transfer-Encoding header field and a Content-Length header field,
1354     the latter &MUST; be ignored.
1355    </t></x:lt>
1356    <x:lt><t>
1357     If the message uses the media type "multipart/byteranges", and the
1358     transfer-length is not otherwise specified, then this self-delimiting
1359     media type defines the transfer-length. This media type
1360     &MUST-NOT; be used unless the sender knows that the recipient can parse
1361     it; the presence in a request of a Range header with multiple byte-range
1362     specifiers from a 1.1 client implies that the client can parse
1363     multipart/byteranges responses.
1364    <list style="empty"><t>
1365       A range header might be forwarded by a 1.0 proxy that does not
1366       understand multipart/byteranges; in this case the server &MUST;
1367       delimit the message using methods defined in items 1, 3 or 5 of
1368       this section.
1369    </t></list>
1370    </t></x:lt>
1371    <x:lt><t>
1372     By the server closing the connection. (Closing the connection
1373     cannot be used to indicate the end of a request body, since that
1374     would leave no possibility for the server to send back a response.)
1375    </t></x:lt>
1376  </list>
1377</t>
1378<t>
1379   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1380   containing a message-body &MUST; include a valid Content-Length header
1381   field unless the server is known to be HTTP/1.1 compliant. If a
1382   request contains a message-body and a Content-Length is not given,
1383   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1384   determine the length of the message, or with 411 (Length Required) if
1385   it wishes to insist on receiving a valid Content-Length.
1386</t>
1387<t>
1388   All HTTP/1.1 applications that receive entities &MUST; accept the
1389   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1390   to be used for messages when the message length cannot be determined
1391   in advance.
1392</t>
1393<t>
1394   Messages &MUST-NOT; include both a Content-Length header field and a
1395   transfer-coding. If the message does include a
1396   transfer-coding, the Content-Length &MUST; be ignored.
1397</t>
1398<t>
1399   When a Content-Length is given in a message where a message-body is
1400   allowed, its field value &MUST; exactly match the number of OCTETs in
1401   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1402   invalid length is received and detected.
1403</t>
1404</section>
1405
1406<section title="General Header Fields" anchor="general.header.fields">
1407  <x:anchor-alias value="general-header"/>
1408<t>
1409   There are a few header fields which have general applicability for
1410   both request and response messages, but which do not apply to the
1411   entity being transferred. These header fields apply only to the
1412   message being transmitted.
1413</t>
1414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1415  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1416                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1417                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1418                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1419                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1420                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1421                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1422                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1423                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1424</artwork></figure>
1425<t>
1426   General-header field names can be extended reliably only in
1427   combination with a change in the protocol version. However, new or
1428   experimental header fields may be given the semantics of general
1429   header fields if all parties in the communication recognize them to
1430   be general-header fields. Unrecognized header fields are treated as
1431   entity-header fields.
1432</t>
1433</section>
1434</section>
1435
1436<section title="Request" anchor="request">
1437  <x:anchor-alias value="Request"/>
1438<t>
1439   A request message from a client to a server includes, within the
1440   first line of that message, the method to be applied to the resource,
1441   the identifier of the resource, and the protocol version in use.
1442</t>
1443<!--                 Host                      ; should be moved here eventually -->
1444<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1445  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1446                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1447                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1448                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1449                  <x:ref>CRLF</x:ref>
1450                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1451</artwork></figure>
1452
1453<section title="Request-Line" anchor="request-line">
1454  <x:anchor-alias value="Request-Line"/>
1455<t>
1456   The Request-Line begins with a method token, followed by the
1457   Request-URI and the protocol version, and ending with CRLF. The
1458   elements are separated by SP characters. No CR or LF is allowed
1459   except in the final CRLF sequence.
1460</t>
1461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1462  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>Request-URI</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1463</artwork></figure>
1464
1465<section title="Method" anchor="method">
1466  <x:anchor-alias value="Method"/>
1467<t>
1468   The Method  token indicates the method to be performed on the
1469   resource identified by the Request-URI. The method is case-sensitive.
1470</t>
1471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1472  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1473</artwork></figure>
1474</section>
1475
1476<section title="Request-URI" anchor="request-uri">
1477  <x:anchor-alias value="Request-URI"/>
1478<t>
1479   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1480   identifies the resource upon which to apply the request.
1481</t>
1482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1483  <x:ref>Request-URI</x:ref>    = "*"
1484                 / <x:ref>absolute-URI</x:ref>
1485                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1486                 / <x:ref>authority</x:ref>
1487</artwork></figure>
1488<t>
1489   The four options for Request-URI are dependent on the nature of the
1490   request. The asterisk "*" means that the request does not apply to a
1491   particular resource, but to the server itself, and is only allowed
1492   when the method used does not necessarily apply to a resource. One
1493   example would be
1494</t>
1495<figure><artwork type="example">
1496    OPTIONS * HTTP/1.1
1497</artwork></figure>
1498<t>
1499   The absolute-URI form is &REQUIRED; when the request is being made to a
1500   proxy. The proxy is requested to forward the request or service it
1501   from a valid cache, and return the response. Note that the proxy &MAY;
1502   forward the request on to another proxy or directly to the server
1503   specified by the absolute-URI. In order to avoid request loops, a
1504   proxy &MUST; be able to recognize all of its server names, including
1505   any aliases, local variations, and the numeric IP address. An example
1506   Request-Line would be:
1507</t>
1508<figure><artwork type="example">
1509    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1510</artwork></figure>
1511<t>
1512   To allow for transition to absolute-URIs in all requests in future
1513   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1514   form in requests, even though HTTP/1.1 clients will only generate
1515   them in requests to proxies.
1516</t>
1517<t>
1518   The authority form is only used by the CONNECT method (&CONNECT;).
1519</t>
1520<t>
1521   The most common form of Request-URI is that used to identify a
1522   resource on an origin server or gateway. In this case the absolute
1523   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1524   the Request-URI, and the network location of the URI (authority) &MUST;
1525   be transmitted in a Host header field. For example, a client wishing
1526   to retrieve the resource above directly from the origin server would
1527   create a TCP connection to port 80 of the host "www.example.org" and send
1528   the lines:
1529</t>
1530<figure><artwork type="example">
1531    GET /pub/WWW/TheProject.html HTTP/1.1
1532    Host: www.example.org
1533</artwork></figure>
1534<t>
1535   followed by the remainder of the Request. Note that the absolute path
1536   cannot be empty; if none is present in the original URI, it &MUST; be
1537   given as "/" (the server root).
1538</t>
1539<t>
1540   The Request-URI is transmitted in the format specified in
1541   <xref target="http.uri"/>. If the Request-URI is encoded using the
1542   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1543   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1544   &MUST; decode the Request-URI in order to
1545   properly interpret the request. Servers &SHOULD; respond to invalid
1546   Request-URIs with an appropriate status code.
1547</t>
1548<t>
1549   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1550   received Request-URI when forwarding it to the next inbound server,
1551   except as noted above to replace a null path-absolute with "/".
1552</t>
1553<t>
1554  <list><t>
1555      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1556      meaning of the request when the origin server is improperly using
1557      a non-reserved URI character for a reserved purpose.  Implementors
1558      should be aware that some pre-HTTP/1.1 proxies have been known to
1559      rewrite the Request-URI.
1560  </t></list>
1561</t>
1562</section>
1563</section>
1564
1565<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1566<t>
1567   The exact resource identified by an Internet request is determined by
1568   examining both the Request-URI and the Host header field.
1569</t>
1570<t>
1571   An origin server that does not allow resources to differ by the
1572   requested host &MAY; ignore the Host header field value when
1573   determining the resource identified by an HTTP/1.1 request. (But see
1574   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1575   for other requirements on Host support in HTTP/1.1.)
1576</t>
1577<t>
1578   An origin server that does differentiate resources based on the host
1579   requested (sometimes referred to as virtual hosts or vanity host
1580   names) &MUST; use the following rules for determining the requested
1581   resource on an HTTP/1.1 request:
1582  <list style="numbers">
1583    <t>If Request-URI is an absolute-URI, the host is part of the
1584     Request-URI. Any Host header field value in the request &MUST; be
1585     ignored.</t>
1586    <t>If the Request-URI is not an absolute-URI, and the request includes
1587     a Host header field, the host is determined by the Host header
1588     field value.</t>
1589    <t>If the host as determined by rule 1 or 2 is not a valid host on
1590     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1591  </list>
1592</t>
1593<t>
1594   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1595   attempt to use heuristics (e.g., examination of the URI path for
1596   something unique to a particular host) in order to determine what
1597   exact resource is being requested.
1598</t>
1599</section>
1600
1601</section>
1602
1603
1604<section title="Response" anchor="response">
1605  <x:anchor-alias value="Response"/>
1606<t>
1607   After receiving and interpreting a request message, a server responds
1608   with an HTTP response message.
1609</t>
1610<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1611  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1612                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1613                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1614                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1615                  <x:ref>CRLF</x:ref>
1616                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1617</artwork></figure>
1618
1619<section title="Status-Line" anchor="status-line">
1620  <x:anchor-alias value="Status-Line"/>
1621<t>
1622   The first line of a Response message is the Status-Line, consisting
1623   of the protocol version followed by a numeric status code and its
1624   associated textual phrase, with each element separated by SP
1625   characters. No CR or LF is allowed except in the final CRLF sequence.
1626</t>
1627<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1628  <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>
1629</artwork></figure>
1630
1631<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1632  <x:anchor-alias value="Reason-Phrase"/>
1633  <x:anchor-alias value="Status-Code"/>
1634<t>
1635   The Status-Code element is a 3-digit integer result code of the
1636   attempt to understand and satisfy the request. These codes are fully
1637   defined in &status-codes;.  The Reason Phrase exists for the sole
1638   purpose of providing a textual description associated with the numeric
1639   status code, out of deference to earlier Internet application protocols
1640   that were more frequently used with interactive text clients.
1641   A client &SHOULD; ignore the content of the Reason Phrase.
1642</t>
1643<t>
1644   The first digit of the Status-Code defines the class of response. The
1645   last two digits do not have any categorization role. There are 5
1646   values for the first digit:
1647  <list style="symbols">
1648    <t>
1649      1xx: Informational - Request received, continuing process
1650    </t>
1651    <t>
1652      2xx: Success - The action was successfully received,
1653        understood, and accepted
1654    </t>
1655    <t>
1656      3xx: Redirection - Further action must be taken in order to
1657        complete the request
1658    </t>
1659    <t>
1660      4xx: Client Error - The request contains bad syntax or cannot
1661        be fulfilled
1662    </t>
1663    <t>
1664      5xx: Server Error - The server failed to fulfill an apparently
1665        valid request
1666    </t>
1667  </list>
1668</t>
1669<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"/>
1670  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1671  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1672</artwork></figure>
1673</section>
1674</section>
1675
1676</section>
1677
1678
1679<section title="Connections" anchor="connections">
1680
1681<section title="Persistent Connections" anchor="persistent.connections">
1682
1683<section title="Purpose" anchor="persistent.purpose">
1684<t>
1685   Prior to persistent connections, a separate TCP connection was
1686   established to fetch each URL, increasing the load on HTTP servers
1687   and causing congestion on the Internet. The use of inline images and
1688   other associated data often require a client to make multiple
1689   requests of the same server in a short amount of time. Analysis of
1690   these performance problems and results from a prototype
1691   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1692   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1693   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1694   T/TCP <xref target="Tou1998"/>.
1695</t>
1696<t>
1697   Persistent HTTP connections have a number of advantages:
1698  <list style="symbols">
1699      <t>
1700        By opening and closing fewer TCP connections, CPU time is saved
1701        in routers and hosts (clients, servers, proxies, gateways,
1702        tunnels, or caches), and memory used for TCP protocol control
1703        blocks can be saved in hosts.
1704      </t>
1705      <t>
1706        HTTP requests and responses can be pipelined on a connection.
1707        Pipelining allows a client to make multiple requests without
1708        waiting for each response, allowing a single TCP connection to
1709        be used much more efficiently, with much lower elapsed time.
1710      </t>
1711      <t>
1712        Network congestion is reduced by reducing the number of packets
1713        caused by TCP opens, and by allowing TCP sufficient time to
1714        determine the congestion state of the network.
1715      </t>
1716      <t>
1717        Latency on subsequent requests is reduced since there is no time
1718        spent in TCP's connection opening handshake.
1719      </t>
1720      <t>
1721        HTTP can evolve more gracefully, since errors can be reported
1722        without the penalty of closing the TCP connection. Clients using
1723        future versions of HTTP might optimistically try a new feature,
1724        but if communicating with an older server, retry with old
1725        semantics after an error is reported.
1726      </t>
1727    </list>
1728</t>
1729<t>
1730   HTTP implementations &SHOULD; implement persistent connections.
1731</t>
1732</section>
1733
1734<section title="Overall Operation" anchor="persistent.overall">
1735<t>
1736   A significant difference between HTTP/1.1 and earlier versions of
1737   HTTP is that persistent connections are the default behavior of any
1738   HTTP connection. That is, unless otherwise indicated, the client
1739   &SHOULD; assume that the server will maintain a persistent connection,
1740   even after error responses from the server.
1741</t>
1742<t>
1743   Persistent connections provide a mechanism by which a client and a
1744   server can signal the close of a TCP connection. This signaling takes
1745   place using the Connection header field (<xref target="header.connection"/>). Once a close
1746   has been signaled, the client &MUST-NOT; send any more requests on that
1747   connection.
1748</t>
1749
1750<section title="Negotiation" anchor="persistent.negotiation">
1751<t>
1752   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1753   maintain a persistent connection unless a Connection header including
1754   the connection-token "close" was sent in the request. If the server
1755   chooses to close the connection immediately after sending the
1756   response, it &SHOULD; send a Connection header including the
1757   connection-token close.
1758</t>
1759<t>
1760   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1761   decide to keep it open based on whether the response from a server
1762   contains a Connection header with the connection-token close. In case
1763   the client does not want to maintain a connection for more than that
1764   request, it &SHOULD; send a Connection header including the
1765   connection-token close.
1766</t>
1767<t>
1768   If either the client or the server sends the close token in the
1769   Connection header, that request becomes the last one for the
1770   connection.
1771</t>
1772<t>
1773   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1774   maintained for HTTP versions less than 1.1 unless it is explicitly
1775   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1776   compatibility with HTTP/1.0 clients.
1777</t>
1778<t>
1779   In order to remain persistent, all messages on the connection &MUST;
1780   have a self-defined message length (i.e., one not defined by closure
1781   of the connection), as described in <xref target="message.length"/>.
1782</t>
1783</section>
1784
1785<section title="Pipelining" anchor="pipelining">
1786<t>
1787   A client that supports persistent connections &MAY; "pipeline" its
1788   requests (i.e., send multiple requests without waiting for each
1789   response). A server &MUST; send its responses to those requests in the
1790   same order that the requests were received.
1791</t>
1792<t>
1793   Clients which assume persistent connections and pipeline immediately
1794   after connection establishment &SHOULD; be prepared to retry their
1795   connection if the first pipelined attempt fails. If a client does
1796   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1797   persistent. Clients &MUST; also be prepared to resend their requests if
1798   the server closes the connection before sending all of the
1799   corresponding responses.
1800</t>
1801<t>
1802   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1803   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1804   premature termination of the transport connection could lead to
1805   indeterminate results. A client wishing to send a non-idempotent
1806   request &SHOULD; wait to send that request until it has received the
1807   response status for the previous request.
1808</t>
1809</section>
1810</section>
1811
1812<section title="Proxy Servers" anchor="persistent.proxy">
1813<t>
1814   It is especially important that proxies correctly implement the
1815   properties of the Connection header field as specified in <xref target="header.connection"/>.
1816</t>
1817<t>
1818   The proxy server &MUST; signal persistent connections separately with
1819   its clients and the origin servers (or other proxy servers) that it
1820   connects to. Each persistent connection applies to only one transport
1821   link.
1822</t>
1823<t>
1824   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1825   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1826   discussion of the problems with the Keep-Alive header implemented by
1827   many HTTP/1.0 clients).
1828</t>
1829</section>
1830
1831<section title="Practical Considerations" anchor="persistent.practical">
1832<t>
1833   Servers will usually have some time-out value beyond which they will
1834   no longer maintain an inactive connection. Proxy servers might make
1835   this a higher value since it is likely that the client will be making
1836   more connections through the same server. The use of persistent
1837   connections places no requirements on the length (or existence) of
1838   this time-out for either the client or the server.
1839</t>
1840<t>
1841   When a client or server wishes to time-out it &SHOULD; issue a graceful
1842   close on the transport connection. Clients and servers &SHOULD; both
1843   constantly watch for the other side of the transport close, and
1844   respond to it as appropriate. If a client or server does not detect
1845   the other side's close promptly it could cause unnecessary resource
1846   drain on the network.
1847</t>
1848<t>
1849   A client, server, or proxy &MAY; close the transport connection at any
1850   time. For example, a client might have started to send a new request
1851   at the same time that the server has decided to close the "idle"
1852   connection. From the server's point of view, the connection is being
1853   closed while it was idle, but from the client's point of view, a
1854   request is in progress.
1855</t>
1856<t>
1857   This means that clients, servers, and proxies &MUST; be able to recover
1858   from asynchronous close events. Client software &SHOULD; reopen the
1859   transport connection and retransmit the aborted sequence of requests
1860   without user interaction so long as the request sequence is
1861   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1862   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1863   human operator the choice of retrying the request(s). Confirmation by
1864   user-agent software with semantic understanding of the application
1865   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1866   be repeated if the second sequence of requests fails.
1867</t>
1868<t>
1869   Servers &SHOULD; always respond to at least one request per connection,
1870   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1871   middle of transmitting a response, unless a network or client failure
1872   is suspected.
1873</t>
1874<t>
1875   Clients that use persistent connections &SHOULD; limit the number of
1876   simultaneous connections that they maintain to a given server. A
1877   single-user client &SHOULD-NOT; maintain more than 2 connections with
1878   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1879   another server or proxy, where N is the number of simultaneously
1880   active users. These guidelines are intended to improve HTTP response
1881   times and avoid congestion.
1882</t>
1883</section>
1884</section>
1885
1886<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1887
1888<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1889<t>
1890   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1891   flow control mechanisms to resolve temporary overloads, rather than
1892   terminating connections with the expectation that clients will retry.
1893   The latter technique can exacerbate network congestion.
1894</t>
1895</section>
1896
1897<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1898<t>
1899   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1900   the network connection for an error status while it is transmitting
1901   the request. If the client sees an error status, it &SHOULD;
1902   immediately cease transmitting the body. If the body is being sent
1903   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1904   empty trailer &MAY; be used to prematurely mark the end of the message.
1905   If the body was preceded by a Content-Length header, the client &MUST;
1906   close the connection.
1907</t>
1908</section>
1909
1910<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1911<t>
1912   The purpose of the 100 (Continue) status (see &status-100;) is to
1913   allow a client that is sending a request message with a request body
1914   to determine if the origin server is willing to accept the request
1915   (based on the request headers) before the client sends the request
1916   body. In some cases, it might either be inappropriate or highly
1917   inefficient for the client to send the body if the server will reject
1918   the message without looking at the body.
1919</t>
1920<t>
1921   Requirements for HTTP/1.1 clients:
1922  <list style="symbols">
1923    <t>
1924        If a client will wait for a 100 (Continue) response before
1925        sending the request body, it &MUST; send an Expect request-header
1926        field (&header-expect;) with the "100-continue" expectation.
1927    </t>
1928    <t>
1929        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1930        with the "100-continue" expectation if it does not intend
1931        to send a request body.
1932    </t>
1933  </list>
1934</t>
1935<t>
1936   Because of the presence of older implementations, the protocol allows
1937   ambiguous situations in which a client may send "Expect: 100-continue"
1938   without receiving either a 417 (Expectation Failed) status
1939   or a 100 (Continue) status. Therefore, when a client sends this
1940   header field to an origin server (possibly via a proxy) from which it
1941   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1942   for an indefinite period before sending the request body.
1943</t>
1944<t>
1945   Requirements for HTTP/1.1 origin servers:
1946  <list style="symbols">
1947    <t> Upon receiving a request which includes an Expect request-header
1948        field with the "100-continue" expectation, an origin server &MUST;
1949        either respond with 100 (Continue) status and continue to read
1950        from the input stream, or respond with a final status code. The
1951        origin server &MUST-NOT; wait for the request body before sending
1952        the 100 (Continue) response. If it responds with a final status
1953        code, it &MAY; close the transport connection or it &MAY; continue
1954        to read and discard the rest of the request.  It &MUST-NOT;
1955        perform the requested method if it returns a final status code.
1956    </t>
1957    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1958        the request message does not include an Expect request-header
1959        field with the "100-continue" expectation, and &MUST-NOT; send a
1960        100 (Continue) response if such a request comes from an HTTP/1.0
1961        (or earlier) client. There is an exception to this rule: for
1962        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1963        status in response to an HTTP/1.1 PUT or POST request that does
1964        not include an Expect request-header field with the "100-continue"
1965        expectation. This exception, the purpose of which is
1966        to minimize any client processing delays associated with an
1967        undeclared wait for 100 (Continue) status, applies only to
1968        HTTP/1.1 requests, and not to requests with any other HTTP-version
1969        value.
1970    </t>
1971    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1972        already received some or all of the request body for the
1973        corresponding request.
1974    </t>
1975    <t> An origin server that sends a 100 (Continue) response &MUST;
1976    ultimately send a final status code, once the request body is
1977        received and processed, unless it terminates the transport
1978        connection prematurely.
1979    </t>
1980    <t> If an origin server receives a request that does not include an
1981        Expect request-header field with the "100-continue" expectation,
1982        the request includes a request body, and the server responds
1983        with a final status code before reading the entire request body
1984        from the transport connection, then the server &SHOULD-NOT;  close
1985        the transport connection until it has read the entire request,
1986        or until the client closes the connection. Otherwise, the client
1987        might not reliably receive the response message. However, this
1988        requirement is not be construed as preventing a server from
1989        defending itself against denial-of-service attacks, or from
1990        badly broken client implementations.
1991      </t>
1992    </list>
1993</t>
1994<t>
1995   Requirements for HTTP/1.1 proxies:
1996  <list style="symbols">
1997    <t> If a proxy receives a request that includes an Expect request-header
1998        field with the "100-continue" expectation, and the proxy
1999        either knows that the next-hop server complies with HTTP/1.1 or
2000        higher, or does not know the HTTP version of the next-hop
2001        server, it &MUST; forward the request, including the Expect header
2002        field.
2003    </t>
2004    <t> If the proxy knows that the version of the next-hop server is
2005        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2006        respond with a 417 (Expectation Failed) status.
2007    </t>
2008    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2009        numbers received from recently-referenced next-hop servers.
2010    </t>
2011    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2012        request message was received from an HTTP/1.0 (or earlier)
2013        client and did not include an Expect request-header field with
2014        the "100-continue" expectation. This requirement overrides the
2015        general rule for forwarding of 1xx responses (see &status-1xx;).
2016    </t>
2017  </list>
2018</t>
2019</section>
2020
2021<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2022<t>
2023   If an HTTP/1.1 client sends a request which includes a request body,
2024   but which does not include an Expect request-header field with the
2025   "100-continue" expectation, and if the client is not directly
2026   connected to an HTTP/1.1 origin server, and if the client sees the
2027   connection close before receiving any status from the server, the
2028   client &SHOULD; retry the request.  If the client does retry this
2029   request, it &MAY; use the following "binary exponential backoff"
2030   algorithm to be assured of obtaining a reliable response:
2031  <list style="numbers">
2032    <t>
2033      Initiate a new connection to the server
2034    </t>
2035    <t>
2036      Transmit the request-headers
2037    </t>
2038    <t>
2039      Initialize a variable R to the estimated round-trip time to the
2040         server (e.g., based on the time it took to establish the
2041         connection), or to a constant value of 5 seconds if the round-trip
2042         time is not available.
2043    </t>
2044    <t>
2045       Compute T = R * (2**N), where N is the number of previous
2046         retries of this request.
2047    </t>
2048    <t>
2049       Wait either for an error response from the server, or for T
2050         seconds (whichever comes first)
2051    </t>
2052    <t>
2053       If no error response is received, after T seconds transmit the
2054         body of the request.
2055    </t>
2056    <t>
2057       If client sees that the connection is closed prematurely,
2058         repeat from step 1 until the request is accepted, an error
2059         response is received, or the user becomes impatient and
2060         terminates the retry process.
2061    </t>
2062  </list>
2063</t>
2064<t>
2065   If at any point an error status is received, the client
2066  <list style="symbols">
2067      <t>&SHOULD-NOT;  continue and</t>
2068
2069      <t>&SHOULD; close the connection if it has not completed sending the
2070        request message.</t>
2071    </list>
2072</t>
2073</section>
2074</section>
2075</section>
2076
2077
2078<section title="Header Field Definitions" anchor="header.fields">
2079<t>
2080   This section defines the syntax and semantics of HTTP/1.1 header fields
2081   related to message framing and transport protocols.
2082</t>
2083<t>
2084   For entity-header fields, both sender and recipient refer to either the
2085   client or the server, depending on who sends and who receives the entity.
2086</t>
2087
2088<section title="Connection" anchor="header.connection">
2089  <iref primary="true" item="Connection header" x:for-anchor=""/>
2090  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2091  <x:anchor-alias value="Connection"/>
2092  <x:anchor-alias value="connection-token"/>
2093<t>
2094   The Connection general-header field allows the sender to specify
2095   options that are desired for that particular connection and &MUST-NOT;
2096   be communicated by proxies over further connections.
2097</t>
2098<t>
2099   The Connection header has the following grammar:
2100</t>
2101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2102  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2103  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2104</artwork></figure>
2105<t>
2106   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2107   message is forwarded and, for each connection-token in this field,
2108   remove any header field(s) from the message with the same name as the
2109   connection-token. Connection options are signaled by the presence of
2110   a connection-token in the Connection header field, not by any
2111   corresponding additional header field(s), since the additional header
2112   field may not be sent if there are no parameters associated with that
2113   connection option.
2114</t>
2115<t>
2116   Message headers listed in the Connection header &MUST-NOT; include
2117   end-to-end headers, such as Cache-Control.
2118</t>
2119<t>
2120   HTTP/1.1 defines the "close" connection option for the sender to
2121   signal that the connection will be closed after completion of the
2122   response. For example,
2123</t>
2124<figure><artwork type="example">
2125    Connection: close
2126</artwork></figure>
2127<t>
2128   in either the request or the response header fields indicates that
2129   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2130   after the current request/response is complete.
2131</t>
2132<t>
2133   An HTTP/1.1 client that does not support persistent connections &MUST;
2134   include the "close" connection option in every request message.
2135</t>
2136<t>
2137   An HTTP/1.1 server that does not support persistent connections &MUST;
2138   include the "close" connection option in every response message that
2139   does not have a 1xx (informational) status code.
2140</t>
2141<t>
2142   A system receiving an HTTP/1.0 (or lower-version) message that
2143   includes a Connection header &MUST;, for each connection-token in this
2144   field, remove and ignore any header field(s) from the message with
2145   the same name as the connection-token. This protects against mistaken
2146   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2147</t>
2148</section>
2149
2150<section title="Content-Length" anchor="header.content-length">
2151  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2152  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2153  <x:anchor-alias value="Content-Length"/>
2154<t>
2155   The Content-Length entity-header field indicates the size of the
2156   entity-body, in decimal number of OCTETs, sent to the recipient or,
2157   in the case of the HEAD method, the size of the entity-body that
2158   would have been sent had the request been a GET.
2159</t>
2160<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2161  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2162</artwork></figure>
2163<t>
2164   An example is
2165</t>
2166<figure><artwork type="example">
2167    Content-Length: 3495
2168</artwork></figure>
2169<t>
2170   Applications &SHOULD; use this field to indicate the transfer-length of
2171   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2172</t>
2173<t>
2174   Any Content-Length greater than or equal to zero is a valid value.
2175   <xref target="message.length"/> describes how to determine the length of a message-body
2176   if a Content-Length is not given.
2177</t>
2178<t>
2179   Note that the meaning of this field is significantly different from
2180   the corresponding definition in MIME, where it is an optional field
2181   used within the "message/external-body" content-type. In HTTP, it
2182   &SHOULD; be sent whenever the message's length can be determined prior
2183   to being transferred, unless this is prohibited by the rules in
2184   <xref target="message.length"/>.
2185</t>
2186</section>
2187
2188<section title="Date" anchor="header.date">
2189  <iref primary="true" item="Date header" x:for-anchor=""/>
2190  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2191  <x:anchor-alias value="Date"/>
2192<t>
2193   The Date general-header field represents the date and time at which
2194   the message was originated, having the same semantics as orig-date in
2195   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2196   HTTP-date, as described in <xref target="full.date"/>;
2197   it &MUST; be sent in rfc1123-date format.
2198</t>
2199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2200  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2201</artwork></figure>
2202<t>
2203   An example is
2204</t>
2205<figure><artwork type="example">
2206    Date: Tue, 15 Nov 1994 08:12:31 GMT
2207</artwork></figure>
2208<t>
2209   Origin servers &MUST; include a Date header field in all responses,
2210   except in these cases:
2211  <list style="numbers">
2212      <t>If the response status code is 100 (Continue) or 101 (Switching
2213         Protocols), the response &MAY; include a Date header field, at
2214         the server's option.</t>
2215
2216      <t>If the response status code conveys a server error, e.g. 500
2217         (Internal Server Error) or 503 (Service Unavailable), and it is
2218         inconvenient or impossible to generate a valid Date.</t>
2219
2220      <t>If the server does not have a clock that can provide a
2221         reasonable approximation of the current time, its responses
2222         &MUST-NOT; include a Date header field. In this case, the rules
2223         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2224  </list>
2225</t>
2226<t>
2227   A received message that does not have a Date header field &MUST; be
2228   assigned one by the recipient if the message will be cached by that
2229   recipient or gatewayed via a protocol which requires a Date. An HTTP
2230   implementation without a clock &MUST-NOT; cache responses without
2231   revalidating them on every use. An HTTP cache, especially a shared
2232   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2233   clock with a reliable external standard.
2234</t>
2235<t>
2236   Clients &SHOULD; only send a Date header field in messages that include
2237   an entity-body, as in the case of the PUT and POST requests, and even
2238   then it is optional. A client without a clock &MUST-NOT; send a Date
2239   header field in a request.
2240</t>
2241<t>
2242   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2243   time subsequent to the generation of the message. It &SHOULD; represent
2244   the best available approximation of the date and time of message
2245   generation, unless the implementation has no means of generating a
2246   reasonably accurate date and time. In theory, the date ought to
2247   represent the moment just before the entity is generated. In
2248   practice, the date can be generated at any time during the message
2249   origination without affecting its semantic value.
2250</t>
2251
2252<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2253<t>
2254   Some origin server implementations might not have a clock available.
2255   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2256   values to a response, unless these values were associated
2257   with the resource by a system or user with a reliable clock. It &MAY;
2258   assign an Expires value that is known, at or before server
2259   configuration time, to be in the past (this allows "pre-expiration"
2260   of responses without storing separate Expires values for each
2261   resource).
2262</t>
2263</section>
2264</section>
2265
2266<section title="Host" anchor="header.host">
2267  <iref primary="true" item="Host header" x:for-anchor=""/>
2268  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2269  <x:anchor-alias value="Host"/>
2270<t>
2271   The Host request-header field specifies the Internet host and port
2272   number of the resource being requested, as obtained from the original
2273   URI given by the user or referring resource (generally an http URI,
2274   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2275   the naming authority of the origin server or gateway given by the
2276   original URL. This allows the origin server or gateway to
2277   differentiate between internally-ambiguous URLs, such as the root "/"
2278   URL of a server for multiple host names on a single IP address.
2279</t>
2280<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2281  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2282</artwork></figure>
2283<t>
2284   A "host" without any trailing port information implies the default
2285   port for the service requested (e.g., "80" for an HTTP URL). For
2286   example, a request on the origin server for
2287   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2288</t>
2289<figure><artwork type="example">
2290    GET /pub/WWW/ HTTP/1.1
2291    Host: www.example.org
2292</artwork></figure>
2293<t>
2294   A client &MUST; include a Host header field in all HTTP/1.1 request
2295   messages. If the requested URI does not include an Internet host
2296   name for the service being requested, then the Host header field &MUST;
2297   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2298   request message it forwards does contain an appropriate Host header
2299   field that identifies the service being requested by the proxy. All
2300   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2301   status code to any HTTP/1.1 request message which lacks a Host header
2302   field.
2303</t>
2304<t>
2305   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2306   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2307   for other requirements relating to Host.
2308</t>
2309</section>
2310
2311<section title="TE" anchor="header.te">
2312  <iref primary="true" item="TE header" x:for-anchor=""/>
2313  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2314  <x:anchor-alias value="TE"/>
2315  <x:anchor-alias value="t-codings"/>
2316<t>
2317   The TE request-header field indicates what extension transfer-codings
2318   it is willing to accept in the response and whether or not it is
2319   willing to accept trailer fields in a chunked transfer-coding. Its
2320   value may consist of the keyword "trailers" and/or a comma-separated
2321   list of extension transfer-coding names with optional accept
2322   parameters (as described in <xref target="transfer.codings"/>).
2323</t>
2324<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2325  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2326  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2327</artwork></figure>
2328<t>
2329   The presence of the keyword "trailers" indicates that the client is
2330   willing to accept trailer fields in a chunked transfer-coding, as
2331   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2332   transfer-coding values even though it does not itself represent a
2333   transfer-coding.
2334</t>
2335<t>
2336   Examples of its use are:
2337</t>
2338<figure><artwork type="example">
2339    TE: deflate
2340    TE:
2341    TE: trailers, deflate;q=0.5
2342</artwork></figure>
2343<t>
2344   The TE header field only applies to the immediate connection.
2345   Therefore, the keyword &MUST; be supplied within a Connection header
2346   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2347</t>
2348<t>
2349   A server tests whether a transfer-coding is acceptable, according to
2350   a TE field, using these rules:
2351  <list style="numbers">
2352    <x:lt>
2353      <t>The "chunked" transfer-coding is always acceptable. If the
2354         keyword "trailers" is listed, the client indicates that it is
2355         willing to accept trailer fields in the chunked response on
2356         behalf of itself and any downstream clients. The implication is
2357         that, if given, the client is stating that either all
2358         downstream clients are willing to accept trailer fields in the
2359         forwarded response, or that it will attempt to buffer the
2360         response on behalf of downstream recipients.
2361      </t><t>
2362         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2363         chunked response such that a client can be assured of buffering
2364         the entire response.</t>
2365    </x:lt>
2366    <x:lt>
2367      <t>If the transfer-coding being tested is one of the transfer-codings
2368         listed in the TE field, then it is acceptable unless it
2369         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2370         qvalue of 0 means "not acceptable.")</t>
2371    </x:lt>
2372    <x:lt>
2373      <t>If multiple transfer-codings are acceptable, then the
2374         acceptable transfer-coding with the highest non-zero qvalue is
2375         preferred.  The "chunked" transfer-coding always has a qvalue
2376         of 1.</t>
2377    </x:lt>
2378  </list>
2379</t>
2380<t>
2381   If the TE field-value is empty or if no TE field is present, the only
2382   transfer-coding  is "chunked". A message with no transfer-coding is
2383   always acceptable.
2384</t>
2385</section>
2386
2387<section title="Trailer" anchor="header.trailer">
2388  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2389  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2390  <x:anchor-alias value="Trailer"/>
2391<t>
2392   The Trailer general field value indicates that the given set of
2393   header fields is present in the trailer of a message encoded with
2394   chunked transfer-coding.
2395</t>
2396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2397  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2398</artwork></figure>
2399<t>
2400   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2401   message using chunked transfer-coding with a non-empty trailer. Doing
2402   so allows the recipient to know which header fields to expect in the
2403   trailer.
2404</t>
2405<t>
2406   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2407   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2408   trailer fields in a "chunked" transfer-coding.
2409</t>
2410<t>
2411   Message header fields listed in the Trailer header field &MUST-NOT;
2412   include the following header fields:
2413  <list style="symbols">
2414    <t>Transfer-Encoding</t>
2415    <t>Content-Length</t>
2416    <t>Trailer</t>
2417  </list>
2418</t>
2419</section>
2420
2421<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2422  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2423  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2424  <x:anchor-alias value="Transfer-Encoding"/>
2425<t>
2426   The Transfer-Encoding general-header field indicates what (if any)
2427   type of transformation has been applied to the message body in order
2428   to safely transfer it between the sender and the recipient. This
2429   differs from the content-coding in that the transfer-coding is a
2430   property of the message, not of the entity.
2431</t>
2432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2433  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2434</artwork></figure>
2435<t>
2436   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2437</t>
2438<figure><artwork type="example">
2439  Transfer-Encoding: chunked
2440</artwork></figure>
2441<t>
2442   If multiple encodings have been applied to an entity, the transfer-codings
2443   &MUST; be listed in the order in which they were applied.
2444   Additional information about the encoding parameters &MAY; be provided
2445   by other entity-header fields not defined by this specification.
2446</t>
2447<t>
2448   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2449   header.
2450</t>
2451</section>
2452
2453<section title="Upgrade" anchor="header.upgrade">
2454  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2455  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2456  <x:anchor-alias value="Upgrade"/>
2457<t>
2458   The Upgrade general-header allows the client to specify what
2459   additional communication protocols it supports and would like to use
2460   if the server finds it appropriate to switch protocols. The server
2461   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2462   response to indicate which protocol(s) are being switched.
2463</t>
2464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2465  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2466</artwork></figure>
2467<t>
2468   For example,
2469</t>
2470<figure><artwork type="example">
2471    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2472</artwork></figure>
2473<t>
2474   The Upgrade header field is intended to provide a simple mechanism
2475   for transition from HTTP/1.1 to some other, incompatible protocol. It
2476   does so by allowing the client to advertise its desire to use another
2477   protocol, such as a later version of HTTP with a higher major version
2478   number, even though the current request has been made using HTTP/1.1.
2479   This eases the difficult transition between incompatible protocols by
2480   allowing the client to initiate a request in the more commonly
2481   supported protocol while indicating to the server that it would like
2482   to use a "better" protocol if available (where "better" is determined
2483   by the server, possibly according to the nature of the method and/or
2484   resource being requested).
2485</t>
2486<t>
2487   The Upgrade header field only applies to switching application-layer
2488   protocols upon the existing transport-layer connection. Upgrade
2489   cannot be used to insist on a protocol change; its acceptance and use
2490   by the server is optional. The capabilities and nature of the
2491   application-layer communication after the protocol change is entirely
2492   dependent upon the new protocol chosen, although the first action
2493   after changing the protocol &MUST; be a response to the initial HTTP
2494   request containing the Upgrade header field.
2495</t>
2496<t>
2497   The Upgrade header field only applies to the immediate connection.
2498   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2499   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2500   HTTP/1.1 message.
2501</t>
2502<t>
2503   The Upgrade header field cannot be used to indicate a switch to a
2504   protocol on a different connection. For that purpose, it is more
2505   appropriate to use a 301, 302, 303, or 305 redirection response.
2506</t>
2507<t>
2508   This specification only defines the protocol name "HTTP" for use by
2509   the family of Hypertext Transfer Protocols, as defined by the HTTP
2510   version rules of <xref target="http.version"/> and future updates to this
2511   specification. Any token can be used as a protocol name; however, it
2512   will only be useful if both the client and server associate the name
2513   with the same protocol.
2514</t>
2515</section>
2516
2517<section title="Via" anchor="header.via">
2518  <iref primary="true" item="Via header" x:for-anchor=""/>
2519  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2520  <x:anchor-alias value="protocol-name"/>
2521  <x:anchor-alias value="protocol-version"/>
2522  <x:anchor-alias value="pseudonym"/>
2523  <x:anchor-alias value="received-by"/>
2524  <x:anchor-alias value="received-protocol"/>
2525  <x:anchor-alias value="Via"/>
2526<t>
2527   The Via general-header field &MUST; be used by gateways and proxies to
2528   indicate the intermediate protocols and recipients between the user
2529   agent and the server on requests, and between the origin server and
2530   the client on responses. It is analogous to the "Received" field defined in
2531   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2532   avoiding request loops, and identifying the protocol capabilities of
2533   all senders along the request/response chain.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2536  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2537  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2538  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2539  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2540  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2541  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2542</artwork></figure>
2543<t>
2544   The received-protocol indicates the protocol version of the message
2545   received by the server or client along each segment of the
2546   request/response chain. The received-protocol version is appended to
2547   the Via field value when the message is forwarded so that information
2548   about the protocol capabilities of upstream applications remains
2549   visible to all recipients.
2550</t>
2551<t>
2552   The protocol-name is optional if and only if it would be "HTTP". The
2553   received-by field is normally the host and optional port number of a
2554   recipient server or client that subsequently forwarded the message.
2555   However, if the real host is considered to be sensitive information,
2556   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2557   be assumed to be the default port of the received-protocol.
2558</t>
2559<t>
2560   Multiple Via field values represents each proxy or gateway that has
2561   forwarded the message. Each recipient &MUST; append its information
2562   such that the end result is ordered according to the sequence of
2563   forwarding applications.
2564</t>
2565<t>
2566   Comments &MAY; be used in the Via header field to identify the software
2567   of the recipient proxy or gateway, analogous to the User-Agent and
2568   Server header fields. However, all comments in the Via field are
2569   optional and &MAY; be removed by any recipient prior to forwarding the
2570   message.
2571</t>
2572<t>
2573   For example, a request message could be sent from an HTTP/1.0 user
2574   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2575   forward the request to a public proxy at p.example.net, which completes
2576   the request by forwarding it to the origin server at www.example.com.
2577   The request received by www.example.com would then have the following
2578   Via header field:
2579</t>
2580<figure><artwork type="example">
2581    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2582</artwork></figure>
2583<t>
2584   Proxies and gateways used as a portal through a network firewall
2585   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2586   the firewall region. This information &SHOULD; only be propagated if
2587   explicitly enabled. If not enabled, the received-by host of any host
2588   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2589   for that host.
2590</t>
2591<t>
2592   For organizations that have strong privacy requirements for hiding
2593   internal structures, a proxy &MAY; combine an ordered subsequence of
2594   Via header field entries with identical received-protocol values into
2595   a single such entry. For example,
2596</t>
2597<figure><artwork type="example">
2598    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2599</artwork></figure>
2600<t>
2601        could be collapsed to
2602</t>
2603<figure><artwork type="example">
2604    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2605</artwork></figure>
2606<t>
2607   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2608   under the same organizational control and the hosts have already been
2609   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2610   have different received-protocol values.
2611</t>
2612</section>
2613
2614</section>
2615
2616<section title="IANA Considerations" anchor="IANA.considerations">
2617<section title="Message Header Registration" anchor="message.header.registration">
2618<t>
2619   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2620   with the permanent registrations below (see <xref target="RFC3864"/>):
2621</t>
2622<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2623<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2624   <ttcol>Header Field Name</ttcol>
2625   <ttcol>Protocol</ttcol>
2626   <ttcol>Status</ttcol>
2627   <ttcol>Reference</ttcol>
2628
2629   <c>Connection</c>
2630   <c>http</c>
2631   <c>standard</c>
2632   <c>
2633      <xref target="header.connection"/>
2634   </c>
2635   <c>Content-Length</c>
2636   <c>http</c>
2637   <c>standard</c>
2638   <c>
2639      <xref target="header.content-length"/>
2640   </c>
2641   <c>Date</c>
2642   <c>http</c>
2643   <c>standard</c>
2644   <c>
2645      <xref target="header.date"/>
2646   </c>
2647   <c>Host</c>
2648   <c>http</c>
2649   <c>standard</c>
2650   <c>
2651      <xref target="header.host"/>
2652   </c>
2653   <c>TE</c>
2654   <c>http</c>
2655   <c>standard</c>
2656   <c>
2657      <xref target="header.te"/>
2658   </c>
2659   <c>Trailer</c>
2660   <c>http</c>
2661   <c>standard</c>
2662   <c>
2663      <xref target="header.trailer"/>
2664   </c>
2665   <c>Transfer-Encoding</c>
2666   <c>http</c>
2667   <c>standard</c>
2668   <c>
2669      <xref target="header.transfer-encoding"/>
2670   </c>
2671   <c>Upgrade</c>
2672   <c>http</c>
2673   <c>standard</c>
2674   <c>
2675      <xref target="header.upgrade"/>
2676   </c>
2677   <c>Via</c>
2678   <c>http</c>
2679   <c>standard</c>
2680   <c>
2681      <xref target="header.via"/>
2682   </c>
2683</texttable>
2684<!--(END)-->
2685<t>
2686   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2687</t>
2688</section>
2689
2690<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2691<t>
2692   The entry for the "http" URI Scheme in the registry located at
2693   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2694   should be updated to point to <xref target="http.uri"/> of this document
2695   (see <xref target="RFC4395"/>).
2696</t>
2697</section>
2698
2699<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2700<t>
2701   This document serves as the specification for the Internet media types
2702   "message/http" and "application/http". The following is to be registered with
2703   IANA (see <xref target="RFC4288"/>).
2704</t>
2705<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2706<iref item="Media Type" subitem="message/http" primary="true"/>
2707<iref item="message/http Media Type" primary="true"/>
2708<t>
2709   The message/http type can be used to enclose a single HTTP request or
2710   response message, provided that it obeys the MIME restrictions for all
2711   "message" types regarding line length and encodings.
2712</t>
2713<t>
2714  <list style="hanging" x:indent="12em">
2715    <t hangText="Type name:">
2716      message
2717    </t>
2718    <t hangText="Subtype name:">
2719      http
2720    </t>
2721    <t hangText="Required parameters:">
2722      none
2723    </t>
2724    <t hangText="Optional parameters:">
2725      version, msgtype
2726      <list style="hanging">
2727        <t hangText="version:">
2728          The HTTP-Version number of the enclosed message
2729          (e.g., "1.1"). If not present, the version can be
2730          determined from the first line of the body.
2731        </t>
2732        <t hangText="msgtype:">
2733          The message type -- "request" or "response". If not
2734          present, the type can be determined from the first
2735          line of the body.
2736        </t>
2737      </list>
2738    </t>
2739    <t hangText="Encoding considerations:">
2740      only "7bit", "8bit", or "binary" are permitted
2741    </t>
2742    <t hangText="Security considerations:">
2743      none
2744    </t>
2745    <t hangText="Interoperability considerations:">
2746      none
2747    </t>
2748    <t hangText="Published specification:">
2749      This specification (see <xref target="internet.media.type.message.http"/>).
2750    </t>
2751    <t hangText="Applications that use this media type:">
2752    </t>
2753    <t hangText="Additional information:">
2754      <list style="hanging">
2755        <t hangText="Magic number(s):">none</t>
2756        <t hangText="File extension(s):">none</t>
2757        <t hangText="Macintosh file type code(s):">none</t>
2758      </list>
2759    </t>
2760    <t hangText="Person and email address to contact for further information:">
2761      See Authors Section.
2762    </t>
2763                <t hangText="Intended usage:">
2764                  COMMON
2765    </t>
2766                <t hangText="Restrictions on usage:">
2767                  none
2768    </t>
2769    <t hangText="Author/Change controller:">
2770      IESG
2771    </t>
2772  </list>
2773</t>
2774</section>
2775<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2776<iref item="Media Type" subitem="application/http" primary="true"/>
2777<iref item="application/http Media Type" primary="true"/>
2778<t>
2779   The application/http type can be used to enclose a pipeline of one or more
2780   HTTP request or response messages (not intermixed).
2781</t>
2782<t>
2783  <list style="hanging" x:indent="12em">
2784    <t hangText="Type name:">
2785      application
2786    </t>
2787    <t hangText="Subtype name:">
2788      http
2789    </t>
2790    <t hangText="Required parameters:">
2791      none
2792    </t>
2793    <t hangText="Optional parameters:">
2794      version, msgtype
2795      <list style="hanging">
2796        <t hangText="version:">
2797          The HTTP-Version number of the enclosed messages
2798          (e.g., "1.1"). If not present, the version can be
2799          determined from the first line of the body.
2800        </t>
2801        <t hangText="msgtype:">
2802          The message type -- "request" or "response". If not
2803          present, the type can be determined from the first
2804          line of the body.
2805        </t>
2806      </list>
2807    </t>
2808    <t hangText="Encoding considerations:">
2809      HTTP messages enclosed by this type
2810      are in "binary" format; use of an appropriate
2811      Content-Transfer-Encoding is required when
2812      transmitted via E-mail.
2813    </t>
2814    <t hangText="Security considerations:">
2815      none
2816    </t>
2817    <t hangText="Interoperability considerations:">
2818      none
2819    </t>
2820    <t hangText="Published specification:">
2821      This specification (see <xref target="internet.media.type.application.http"/>).
2822    </t>
2823    <t hangText="Applications that use this media type:">
2824    </t>
2825    <t hangText="Additional information:">
2826      <list style="hanging">
2827        <t hangText="Magic number(s):">none</t>
2828        <t hangText="File extension(s):">none</t>
2829        <t hangText="Macintosh file type code(s):">none</t>
2830      </list>
2831    </t>
2832    <t hangText="Person and email address to contact for further information:">
2833      See Authors Section.
2834    </t>
2835                <t hangText="Intended usage:">
2836                  COMMON
2837    </t>
2838                <t hangText="Restrictions on usage:">
2839                  none
2840    </t>
2841    <t hangText="Author/Change controller:">
2842      IESG
2843    </t>
2844  </list>
2845</t>
2846</section>
2847</section>
2848
2849</section>
2850
2851<section title="Security Considerations" anchor="security.considerations">
2852<t>
2853   This section is meant to inform application developers, information
2854   providers, and users of the security limitations in HTTP/1.1 as
2855   described by this document. The discussion does not include
2856   definitive solutions to the problems revealed, though it does make
2857   some suggestions for reducing security risks.
2858</t>
2859
2860<section title="Personal Information" anchor="personal.information">
2861<t>
2862   HTTP clients are often privy to large amounts of personal information
2863   (e.g. the user's name, location, mail address, passwords, encryption
2864   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2865   leakage of this information.
2866   We very strongly recommend that a convenient interface be provided
2867   for the user to control dissemination of such information, and that
2868   designers and implementors be particularly careful in this area.
2869   History shows that errors in this area often create serious security
2870   and/or privacy problems and generate highly adverse publicity for the
2871   implementor's company.
2872</t>
2873</section>
2874
2875<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2876<t>
2877   A server is in the position to save personal data about a user's
2878   requests which might identify their reading patterns or subjects of
2879   interest. This information is clearly confidential in nature and its
2880   handling can be constrained by law in certain countries. People using
2881   HTTP to provide data are responsible for ensuring that
2882   such material is not distributed without the permission of any
2883   individuals that are identifiable by the published results.
2884</t>
2885</section>
2886
2887<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2888<t>
2889   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2890   the documents returned by HTTP requests to be only those that were
2891   intended by the server administrators. If an HTTP server translates
2892   HTTP URIs directly into file system calls, the server &MUST; take
2893   special care not to serve files that were not intended to be
2894   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2895   other operating systems use ".." as a path component to indicate a
2896   directory level above the current one. On such a system, an HTTP
2897   server &MUST; disallow any such construct in the Request-URI if it
2898   would otherwise allow access to a resource outside those intended to
2899   be accessible via the HTTP server. Similarly, files intended for
2900   reference only internally to the server (such as access control
2901   files, configuration files, and script code) &MUST; be protected from
2902   inappropriate retrieval, since they might contain sensitive
2903   information. Experience has shown that minor bugs in such HTTP server
2904   implementations have turned into security risks.
2905</t>
2906</section>
2907
2908<section title="DNS Spoofing" anchor="dns.spoofing">
2909<t>
2910   Clients using HTTP rely heavily on the Domain Name Service, and are
2911   thus generally prone to security attacks based on the deliberate
2912   mis-association of IP addresses and DNS names. Clients need to be
2913   cautious in assuming the continuing validity of an IP number/DNS name
2914   association.
2915</t>
2916<t>
2917   In particular, HTTP clients &SHOULD; rely on their name resolver for
2918   confirmation of an IP number/DNS name association, rather than
2919   caching the result of previous host name lookups. Many platforms
2920   already can cache host name lookups locally when appropriate, and
2921   they &SHOULD; be configured to do so. It is proper for these lookups to
2922   be cached, however, only when the TTL (Time To Live) information
2923   reported by the name server makes it likely that the cached
2924   information will remain useful.
2925</t>
2926<t>
2927   If HTTP clients cache the results of host name lookups in order to
2928   achieve a performance improvement, they &MUST; observe the TTL
2929   information reported by DNS.
2930</t>
2931<t>
2932   If HTTP clients do not observe this rule, they could be spoofed when
2933   a previously-accessed server's IP address changes. As network
2934   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2935   possibility of this form of attack will grow. Observing this
2936   requirement thus reduces this potential security vulnerability.
2937</t>
2938<t>
2939   This requirement also improves the load-balancing behavior of clients
2940   for replicated servers using the same DNS name and reduces the
2941   likelihood of a user's experiencing failure in accessing sites which
2942   use that strategy.
2943</t>
2944</section>
2945
2946<section title="Proxies and Caching" anchor="attack.proxies">
2947<t>
2948   By their very nature, HTTP proxies are men-in-the-middle, and
2949   represent an opportunity for man-in-the-middle attacks. Compromise of
2950   the systems on which the proxies run can result in serious security
2951   and privacy problems. Proxies have access to security-related
2952   information, personal information about individual users and
2953   organizations, and proprietary information belonging to users and
2954   content providers. A compromised proxy, or a proxy implemented or
2955   configured without regard to security and privacy considerations,
2956   might be used in the commission of a wide range of potential attacks.
2957</t>
2958<t>
2959   Proxy operators should protect the systems on which proxies run as
2960   they would protect any system that contains or transports sensitive
2961   information. In particular, log information gathered at proxies often
2962   contains highly sensitive personal information, and/or information
2963   about organizations. Log information should be carefully guarded, and
2964   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2965</t>
2966<t>
2967   Proxy implementors should consider the privacy and security
2968   implications of their design and coding decisions, and of the
2969   configuration options they provide to proxy operators (especially the
2970   default configuration).
2971</t>
2972<t>
2973   Users of a proxy need to be aware that they are no trustworthier than
2974   the people who run the proxy; HTTP itself cannot solve this problem.
2975</t>
2976<t>
2977   The judicious use of cryptography, when appropriate, may suffice to
2978   protect against a broad range of security and privacy attacks. Such
2979   cryptography is beyond the scope of the HTTP/1.1 specification.
2980</t>
2981</section>
2982
2983<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2984<t>
2985   They exist. They are hard to defend against. Research continues.
2986   Beware.
2987</t>
2988</section>
2989</section>
2990
2991<section title="Acknowledgments" anchor="ack">
2992<t>
2993   HTTP has evolved considerably over the years. It has
2994   benefited from a large and active developer community--the many
2995   people who have participated on the www-talk mailing list--and it is
2996   that community which has been most responsible for the success of
2997   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2998   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2999   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3000   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3001   VanHeyningen deserve special recognition for their efforts in
3002   defining early aspects of the protocol.
3003</t>
3004<t>
3005   This document has benefited greatly from the comments of all those
3006   participating in the HTTP-WG. In addition to those already mentioned,
3007   the following individuals have contributed to this specification:
3008</t>
3009<t>
3010   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3011   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3012   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3013   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3014   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3015   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3016   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3017   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3018   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3019   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3020   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3021   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3022   Josh Cohen.
3023</t>
3024<t>
3025   Thanks to the "cave men" of Palo Alto. You know who you are.
3026</t>
3027<t>
3028   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3029   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3030   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3031   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3032   Larry Masinter for their help. And thanks go particularly to Jeff
3033   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3034</t>
3035<t>
3036   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3037   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3038   discovery of many of the problems that this document attempts to
3039   rectify.
3040</t>
3041<t>
3042   This specification makes heavy use of the augmented BNF and generic
3043   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3044   reuses many of the definitions provided by Nathaniel Borenstein and
3045   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3046   specification will help reduce past confusion over the relationship
3047   between HTTP and Internet mail message formats.
3048</t>
3049</section>
3050
3051</middle>
3052<back>
3053
3054<references title="Normative References">
3055
3056<reference anchor="ISO-8859-1">
3057  <front>
3058    <title>
3059     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3060    </title>
3061    <author>
3062      <organization>International Organization for Standardization</organization>
3063    </author>
3064    <date year="1998"/>
3065  </front>
3066  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3067</reference>
3068
3069<reference anchor="Part2">
3070  <front>
3071    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3072    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3073      <organization abbrev="Day Software">Day Software</organization>
3074      <address><email>fielding@gbiv.com</email></address>
3075    </author>
3076    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3077      <organization>One Laptop per Child</organization>
3078      <address><email>jg@laptop.org</email></address>
3079    </author>
3080    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3081      <organization abbrev="HP">Hewlett-Packard Company</organization>
3082      <address><email>JeffMogul@acm.org</email></address>
3083    </author>
3084    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3085      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3086      <address><email>henrikn@microsoft.com</email></address>
3087    </author>
3088    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3089      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3090      <address><email>LMM@acm.org</email></address>
3091    </author>
3092    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3093      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3094      <address><email>paulle@microsoft.com</email></address>
3095    </author>
3096    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3097      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3098      <address><email>timbl@w3.org</email></address>
3099    </author>
3100    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3101      <organization abbrev="W3C">World Wide Web Consortium</organization>
3102      <address><email>ylafon@w3.org</email></address>
3103    </author>
3104    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3105      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3106      <address><email>julian.reschke@greenbytes.de</email></address>
3107    </author>
3108    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3109  </front>
3110  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3111  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3112</reference>
3113
3114<reference anchor="Part3">
3115  <front>
3116    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3118      <organization abbrev="Day Software">Day Software</organization>
3119      <address><email>fielding@gbiv.com</email></address>
3120    </author>
3121    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3122      <organization>One Laptop per Child</organization>
3123      <address><email>jg@laptop.org</email></address>
3124    </author>
3125    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3126      <organization abbrev="HP">Hewlett-Packard Company</organization>
3127      <address><email>JeffMogul@acm.org</email></address>
3128    </author>
3129    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3130      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3131      <address><email>henrikn@microsoft.com</email></address>
3132    </author>
3133    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3134      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3135      <address><email>LMM@acm.org</email></address>
3136    </author>
3137    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3138      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3139      <address><email>paulle@microsoft.com</email></address>
3140    </author>
3141    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3142      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3143      <address><email>timbl@w3.org</email></address>
3144    </author>
3145    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3146      <organization abbrev="W3C">World Wide Web Consortium</organization>
3147      <address><email>ylafon@w3.org</email></address>
3148    </author>
3149    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3150      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3151      <address><email>julian.reschke@greenbytes.de</email></address>
3152    </author>
3153    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3154  </front>
3155  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3156  <x:source href="p3-payload.xml" basename="p3-payload"/>
3157</reference>
3158
3159<reference anchor="Part5">
3160  <front>
3161    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3162    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3163      <organization abbrev="Day Software">Day Software</organization>
3164      <address><email>fielding@gbiv.com</email></address>
3165    </author>
3166    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3167      <organization>One Laptop per Child</organization>
3168      <address><email>jg@laptop.org</email></address>
3169    </author>
3170    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3171      <organization abbrev="HP">Hewlett-Packard Company</organization>
3172      <address><email>JeffMogul@acm.org</email></address>
3173    </author>
3174    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3175      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3176      <address><email>henrikn@microsoft.com</email></address>
3177    </author>
3178    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3179      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3180      <address><email>LMM@acm.org</email></address>
3181    </author>
3182    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3184      <address><email>paulle@microsoft.com</email></address>
3185    </author>
3186    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3187      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3188      <address><email>timbl@w3.org</email></address>
3189    </author>
3190    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3191      <organization abbrev="W3C">World Wide Web Consortium</organization>
3192      <address><email>ylafon@w3.org</email></address>
3193    </author>
3194    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3195      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3196      <address><email>julian.reschke@greenbytes.de</email></address>
3197    </author>
3198    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3199  </front>
3200  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3201  <x:source href="p5-range.xml" basename="p5-range"/>
3202</reference>
3203
3204<reference anchor="Part6">
3205  <front>
3206    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3207    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3208      <organization abbrev="Day Software">Day Software</organization>
3209      <address><email>fielding@gbiv.com</email></address>
3210    </author>
3211    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3212      <organization>One Laptop per Child</organization>
3213      <address><email>jg@laptop.org</email></address>
3214    </author>
3215    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3216      <organization abbrev="HP">Hewlett-Packard Company</organization>
3217      <address><email>JeffMogul@acm.org</email></address>
3218    </author>
3219    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3220      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3221      <address><email>henrikn@microsoft.com</email></address>
3222    </author>
3223    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3224      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3225      <address><email>LMM@acm.org</email></address>
3226    </author>
3227    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3228      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3229      <address><email>paulle@microsoft.com</email></address>
3230    </author>
3231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3232      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3233      <address><email>timbl@w3.org</email></address>
3234    </author>
3235    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3236      <organization abbrev="W3C">World Wide Web Consortium</organization>
3237      <address><email>ylafon@w3.org</email></address>
3238    </author>
3239    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3240      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3241      <address><email>julian.reschke@greenbytes.de</email></address>
3242    </author>
3243    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3244  </front>
3245  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3246  <x:source href="p6-cache.xml" basename="p6-cache"/>
3247</reference>
3248
3249<reference anchor="RFC5234">
3250  <front>
3251    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3252    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3253      <organization>Brandenburg InternetWorking</organization>
3254      <address>
3255      <postal>
3256      <street>675 Spruce Dr.</street>
3257      <city>Sunnyvale</city>
3258      <region>CA</region>
3259      <code>94086</code>
3260      <country>US</country></postal>
3261      <phone>+1.408.246.8253</phone>
3262      <email>dcrocker@bbiw.net</email></address> 
3263    </author>
3264    <author initials="P." surname="Overell" fullname="Paul Overell">
3265      <organization>THUS plc.</organization>
3266      <address>
3267      <postal>
3268      <street>1/2 Berkeley Square</street>
3269      <street>99 Berkely Street</street>
3270      <city>Glasgow</city>
3271      <code>G3 7HR</code>
3272      <country>UK</country></postal>
3273      <email>paul.overell@thus.net</email></address>
3274    </author>
3275    <date month="January" year="2008"/>
3276  </front>
3277  <seriesInfo name="STD" value="68"/>
3278  <seriesInfo name="RFC" value="5234"/>
3279</reference>
3280
3281<reference anchor="RFC2045">
3282  <front>
3283    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3284    <author initials="N." surname="Freed" fullname="Ned Freed">
3285      <organization>Innosoft International, Inc.</organization>
3286      <address><email>ned@innosoft.com</email></address>
3287    </author>
3288    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3289      <organization>First Virtual Holdings</organization>
3290      <address><email>nsb@nsb.fv.com</email></address>
3291    </author>
3292    <date month="November" year="1996"/>
3293  </front>
3294  <seriesInfo name="RFC" value="2045"/>
3295</reference>
3296
3297<reference anchor="RFC2047">
3298  <front>
3299    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3300    <author initials="K." surname="Moore" fullname="Keith Moore">
3301      <organization>University of Tennessee</organization>
3302      <address><email>moore@cs.utk.edu</email></address>
3303    </author>
3304    <date month="November" year="1996"/>
3305  </front>
3306  <seriesInfo name="RFC" value="2047"/>
3307</reference>
3308
3309<reference anchor="RFC2119">
3310  <front>
3311    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3312    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3313      <organization>Harvard University</organization>
3314      <address><email>sob@harvard.edu</email></address>
3315    </author>
3316    <date month="March" year="1997"/>
3317  </front>
3318  <seriesInfo name="BCP" value="14"/>
3319  <seriesInfo name="RFC" value="2119"/>
3320</reference>
3321
3322<reference anchor="RFC3986">
3323 <front>
3324  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3325  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3326    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3327    <address>
3328       <email>timbl@w3.org</email>
3329       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3330    </address>
3331  </author>
3332  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3333    <organization abbrev="Day Software">Day Software</organization>
3334    <address>
3335      <email>fielding@gbiv.com</email>
3336      <uri>http://roy.gbiv.com/</uri>
3337    </address>
3338  </author>
3339  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3340    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3341    <address>
3342      <email>LMM@acm.org</email>
3343      <uri>http://larry.masinter.net/</uri>
3344    </address>
3345  </author>
3346  <date month='January' year='2005'></date>
3347 </front>
3348 <seriesInfo name="RFC" value="3986"/>
3349 <seriesInfo name="STD" value="66"/>
3350</reference>
3351
3352<reference anchor="USASCII">
3353  <front>
3354    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3355    <author>
3356      <organization>American National Standards Institute</organization>
3357    </author>
3358    <date year="1986"/>
3359  </front>
3360  <seriesInfo name="ANSI" value="X3.4"/>
3361</reference>
3362
3363</references>
3364
3365<references title="Informative References">
3366
3367<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3368  <front>
3369    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3370    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3371      <organization/>
3372    </author>
3373    <author initials="J." surname="Gettys" fullname="J. Gettys">
3374      <organization/>
3375    </author>
3376    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3377      <organization/>
3378    </author>
3379    <author initials="H." surname="Lie" fullname="H. Lie">
3380      <organization/>
3381    </author>
3382    <author initials="C." surname="Lilley" fullname="C. Lilley">
3383      <organization/>
3384    </author>
3385    <date year="1997" month="September"/>
3386  </front>
3387  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3388</reference>
3389
3390<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3391  <front>
3392    <title>Improving HTTP Latency</title>
3393    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3394      <organization/>
3395    </author>
3396    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3397      <organization/>
3398    </author>
3399    <date year="1995" month="December"/>
3400  </front>
3401  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3402</reference>
3403
3404<reference anchor="RFC822">
3405  <front>
3406    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3407    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3408      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3409      <address><email>DCrocker@UDel-Relay</email></address>
3410    </author>
3411    <date month="August" day="13" year="1982"/>
3412  </front>
3413  <seriesInfo name="STD" value="11"/>
3414  <seriesInfo name="RFC" value="822"/>
3415</reference>
3416
3417<reference anchor="RFC959">
3418  <front>
3419    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3420    <author initials="J." surname="Postel" fullname="J. Postel">
3421      <organization>Information Sciences Institute (ISI)</organization>
3422    </author>
3423    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3424      <organization/>
3425    </author>
3426    <date month="October" year="1985"/>
3427  </front>
3428  <seriesInfo name="STD" value="9"/>
3429  <seriesInfo name="RFC" value="959"/>
3430</reference>
3431
3432<reference anchor="RFC1123">
3433  <front>
3434    <title>Requirements for Internet Hosts - Application and Support</title>
3435    <author initials="R." surname="Braden" fullname="Robert Braden">
3436      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3437      <address><email>Braden@ISI.EDU</email></address>
3438    </author>
3439    <date month="October" year="1989"/>
3440  </front>
3441  <seriesInfo name="STD" value="3"/>
3442  <seriesInfo name="RFC" value="1123"/>
3443</reference>
3444
3445<reference anchor="RFC1305">
3446  <front>
3447    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3448    <author initials="D." surname="Mills" fullname="David L. Mills">
3449      <organization>University of Delaware, Electrical Engineering Department</organization>
3450      <address><email>mills@udel.edu</email></address>
3451    </author>
3452    <date month="March" year="1992"/>
3453  </front>
3454  <seriesInfo name="RFC" value="1305"/>
3455</reference>
3456
3457<reference anchor="RFC1436">
3458  <front>
3459    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3460    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3461      <organization>University of Minnesota, Computer and Information Services</organization>
3462      <address><email>fxa@boombox.micro.umn.edu</email></address>
3463    </author>
3464    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3465      <organization>University of Minnesota, Computer and Information Services</organization>
3466      <address><email>mpm@boombox.micro.umn.edu</email></address>
3467    </author>
3468    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3469      <organization>University of Minnesota, Computer and Information Services</organization>
3470      <address><email>lindner@boombox.micro.umn.edu</email></address>
3471    </author>
3472    <author initials="D." surname="Johnson" fullname="David Johnson">
3473      <organization>University of Minnesota, Computer and Information Services</organization>
3474      <address><email>dmj@boombox.micro.umn.edu</email></address>
3475    </author>
3476    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3477      <organization>University of Minnesota, Computer and Information Services</organization>
3478      <address><email>daniel@boombox.micro.umn.edu</email></address>
3479    </author>
3480    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3481      <organization>University of Minnesota, Computer and Information Services</organization>
3482      <address><email>alberti@boombox.micro.umn.edu</email></address>
3483    </author>
3484    <date month="March" year="1993"/>
3485  </front>
3486  <seriesInfo name="RFC" value="1436"/>
3487</reference>
3488
3489<reference anchor="RFC1900">
3490  <front>
3491    <title>Renumbering Needs Work</title>
3492    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3493      <organization>CERN, Computing and Networks Division</organization>
3494      <address><email>brian@dxcoms.cern.ch</email></address>
3495    </author>
3496    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3497      <organization>cisco Systems</organization>
3498      <address><email>yakov@cisco.com</email></address>
3499    </author>
3500    <date month="February" year="1996"/>
3501  </front>
3502  <seriesInfo name="RFC" value="1900"/>
3503</reference>
3504
3505<reference anchor="RFC1945">
3506  <front>
3507    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3508    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3509      <organization>MIT, Laboratory for Computer Science</organization>
3510      <address><email>timbl@w3.org</email></address>
3511    </author>
3512    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3513      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3514      <address><email>fielding@ics.uci.edu</email></address>
3515    </author>
3516    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3517      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3518      <address><email>frystyk@w3.org</email></address>
3519    </author>
3520    <date month="May" year="1996"/>
3521  </front>
3522  <seriesInfo name="RFC" value="1945"/>
3523</reference>
3524
3525<reference anchor="RFC2068">
3526  <front>
3527    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3528    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3529      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3530      <address><email>fielding@ics.uci.edu</email></address>
3531    </author>
3532    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3533      <organization>MIT Laboratory for Computer Science</organization>
3534      <address><email>jg@w3.org</email></address>
3535    </author>
3536    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3537      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3538      <address><email>mogul@wrl.dec.com</email></address>
3539    </author>
3540    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3541      <organization>MIT Laboratory for Computer Science</organization>
3542      <address><email>frystyk@w3.org</email></address>
3543    </author>
3544    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3545      <organization>MIT Laboratory for Computer Science</organization>
3546      <address><email>timbl@w3.org</email></address>
3547    </author>
3548    <date month="January" year="1997"/>
3549  </front>
3550  <seriesInfo name="RFC" value="2068"/>
3551</reference>
3552
3553<reference anchor='RFC2109'>
3554  <front>
3555    <title>HTTP State Management Mechanism</title>
3556    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3557      <organization>Bell Laboratories, Lucent Technologies</organization>
3558      <address><email>dmk@bell-labs.com</email></address>
3559    </author>
3560    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3561      <organization>Netscape Communications Corp.</organization>
3562      <address><email>montulli@netscape.com</email></address>
3563    </author>
3564    <date year='1997' month='February' />
3565  </front>
3566  <seriesInfo name='RFC' value='2109' />
3567</reference>
3568
3569<reference anchor="RFC2145">
3570  <front>
3571    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3572    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3573      <organization>Western Research Laboratory</organization>
3574      <address><email>mogul@wrl.dec.com</email></address>
3575    </author>
3576    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3577      <organization>Department of Information and Computer Science</organization>
3578      <address><email>fielding@ics.uci.edu</email></address>
3579    </author>
3580    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3581      <organization>MIT Laboratory for Computer Science</organization>
3582      <address><email>jg@w3.org</email></address>
3583    </author>
3584    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3585      <organization>W3 Consortium</organization>
3586      <address><email>frystyk@w3.org</email></address>
3587    </author>
3588    <date month="May" year="1997"/>
3589  </front>
3590  <seriesInfo name="RFC" value="2145"/>
3591</reference>
3592
3593<reference anchor="RFC2616">
3594  <front>
3595    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3596    <author initials="R." surname="Fielding" fullname="R. Fielding">
3597      <organization>University of California, Irvine</organization>
3598      <address><email>fielding@ics.uci.edu</email></address>
3599    </author>
3600    <author initials="J." surname="Gettys" fullname="J. Gettys">
3601      <organization>W3C</organization>
3602      <address><email>jg@w3.org</email></address>
3603    </author>
3604    <author initials="J." surname="Mogul" fullname="J. Mogul">
3605      <organization>Compaq Computer Corporation</organization>
3606      <address><email>mogul@wrl.dec.com</email></address>
3607    </author>
3608    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3609      <organization>MIT Laboratory for Computer Science</organization>
3610      <address><email>frystyk@w3.org</email></address>
3611    </author>
3612    <author initials="L." surname="Masinter" fullname="L. Masinter">
3613      <organization>Xerox Corporation</organization>
3614      <address><email>masinter@parc.xerox.com</email></address>
3615    </author>
3616    <author initials="P." surname="Leach" fullname="P. Leach">
3617      <organization>Microsoft Corporation</organization>
3618      <address><email>paulle@microsoft.com</email></address>
3619    </author>
3620    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3621      <organization>W3C</organization>
3622      <address><email>timbl@w3.org</email></address>
3623    </author>
3624    <date month="June" year="1999"/>
3625  </front>
3626  <seriesInfo name="RFC" value="2616"/>
3627</reference>
3628
3629<reference anchor='RFC2818'>
3630  <front>
3631    <title>HTTP Over TLS</title>
3632    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3633      <organization>RTFM, Inc.</organization>
3634      <address><email>ekr@rtfm.com</email></address>
3635    </author>
3636    <date year='2000' month='May' />
3637  </front>
3638  <seriesInfo name='RFC' value='2818' />
3639</reference>
3640
3641<reference anchor='RFC2965'>
3642  <front>
3643    <title>HTTP State Management Mechanism</title>
3644    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3645      <organization>Bell Laboratories, Lucent Technologies</organization>
3646      <address><email>dmk@bell-labs.com</email></address>
3647    </author>
3648    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3649      <organization>Epinions.com, Inc.</organization>
3650      <address><email>lou@montulli.org</email></address>
3651    </author>
3652    <date year='2000' month='October' />
3653  </front>
3654  <seriesInfo name='RFC' value='2965' />
3655</reference>
3656
3657<reference anchor='RFC3864'>
3658  <front>
3659    <title>Registration Procedures for Message Header Fields</title>
3660    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3661      <organization>Nine by Nine</organization>
3662      <address><email>GK-IETF@ninebynine.org</email></address>
3663    </author>
3664    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3665      <organization>BEA Systems</organization>
3666      <address><email>mnot@pobox.com</email></address>
3667    </author>
3668    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3669      <organization>HP Labs</organization>
3670      <address><email>JeffMogul@acm.org</email></address>
3671    </author>
3672    <date year='2004' month='September' />
3673  </front>
3674  <seriesInfo name='BCP' value='90' />
3675  <seriesInfo name='RFC' value='3864' />
3676</reference>
3677
3678<reference anchor='RFC3977'>
3679  <front>
3680    <title>Network News Transfer Protocol (NNTP)</title>
3681    <author initials='C.' surname='Feather' fullname='C. Feather'>
3682      <organization>THUS plc</organization>
3683      <address><email>clive@demon.net</email></address>
3684    </author>
3685    <date year='2006' month='October' />
3686  </front>
3687  <seriesInfo name="RFC" value="3977"/>
3688</reference>
3689
3690<reference anchor="RFC4288">
3691  <front>
3692    <title>Media Type Specifications and Registration Procedures</title>
3693    <author initials="N." surname="Freed" fullname="N. Freed">
3694      <organization>Sun Microsystems</organization>
3695      <address>
3696        <email>ned.freed@mrochek.com</email>
3697      </address>
3698    </author>
3699    <author initials="J." surname="Klensin" fullname="J. Klensin">
3700      <organization/>
3701      <address>
3702        <email>klensin+ietf@jck.com</email>
3703      </address>
3704    </author>
3705    <date year="2005" month="December"/>
3706  </front>
3707  <seriesInfo name="BCP" value="13"/>
3708  <seriesInfo name="RFC" value="4288"/>
3709</reference>
3710
3711<reference anchor='RFC4395'>
3712  <front>
3713    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3714    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3715      <organization>AT&amp;T Laboratories</organization>
3716      <address>
3717        <email>tony+urireg@maillennium.att.com</email>
3718      </address>
3719    </author>
3720    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3721      <organization>Qualcomm, Inc.</organization>
3722      <address>
3723        <email>hardie@qualcomm.com</email>
3724      </address>
3725    </author>
3726    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3727      <organization>Adobe Systems</organization>
3728      <address>
3729        <email>LMM@acm.org</email>
3730      </address>
3731    </author>
3732    <date year='2006' month='February' />
3733  </front>
3734  <seriesInfo name='BCP' value='115' />
3735  <seriesInfo name='RFC' value='4395' />
3736</reference>
3737
3738<reference anchor="RFC5322">
3739  <front>
3740    <title>Internet Message Format</title>
3741    <author initials="P." surname="Resnick" fullname="P. Resnick">
3742      <organization>Qualcomm Incorporated</organization>
3743    </author>
3744    <date year="2008" month="October"/>
3745  </front>
3746  <seriesInfo name="RFC" value="5322"/>
3747</reference>
3748
3749<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3750  <front>
3751    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3752    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3753      <organization/>
3754    </author>
3755    <date year="2001" month="November"/>
3756  </front>
3757  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3758</reference>
3759
3760<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3761  <front>
3762  <title>Analysis of HTTP Performance Problems</title>
3763  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3764    <organization/>
3765  </author>
3766  <date/>
3767  </front>
3768</reference>
3769
3770<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3771  <front>
3772  <title>Analysis of HTTP Performance</title>
3773  <author initials="J." surname="Touch" fullname="Joe Touch">
3774    <organization>USC/Information Sciences Institute</organization>
3775    <address><email>touch@isi.edu</email></address>
3776  </author>
3777  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3778    <organization>USC/Information Sciences Institute</organization>
3779    <address><email>johnh@isi.edu</email></address>
3780  </author>
3781  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3782    <organization>USC/Information Sciences Institute</organization>
3783    <address><email>katia@isi.edu</email></address>
3784  </author>
3785  <date year="1998" month="Aug"/>
3786  </front>
3787  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3788  <annotation>(original report dated Aug. 1996)</annotation>
3789</reference>
3790
3791<reference anchor="WAIS">
3792  <front>
3793    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3794    <author initials="F." surname="Davis" fullname="F. Davis">
3795      <organization>Thinking Machines Corporation</organization>
3796    </author>
3797    <author initials="B." surname="Kahle" fullname="B. Kahle">
3798      <organization>Thinking Machines Corporation</organization>
3799    </author>
3800    <author initials="H." surname="Morris" fullname="H. Morris">
3801      <organization>Thinking Machines Corporation</organization>
3802    </author>
3803    <author initials="J." surname="Salem" fullname="J. Salem">
3804      <organization>Thinking Machines Corporation</organization>
3805    </author>
3806    <author initials="T." surname="Shen" fullname="T. Shen">
3807      <organization>Thinking Machines Corporation</organization>
3808    </author>
3809    <author initials="R." surname="Wang" fullname="R. Wang">
3810      <organization>Thinking Machines Corporation</organization>
3811    </author>
3812    <author initials="J." surname="Sui" fullname="J. Sui">
3813      <organization>Thinking Machines Corporation</organization>
3814    </author>
3815    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3816      <organization>Thinking Machines Corporation</organization>
3817    </author>
3818    <date month="April" year="1990"/>
3819  </front>
3820  <seriesInfo name="Thinking Machines Corporation" value=""/>
3821</reference>
3822
3823</references>
3824
3825
3826<section title="Tolerant Applications" anchor="tolerant.applications">
3827<t>
3828   Although this document specifies the requirements for the generation
3829   of HTTP/1.1 messages, not all applications will be correct in their
3830   implementation. We therefore recommend that operational applications
3831   be tolerant of deviations whenever those deviations can be
3832   interpreted unambiguously.
3833</t>
3834<t>
3835   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3836   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3837   accept any amount of SP or HTAB characters between fields, even though
3838   only a single SP is required.
3839</t>
3840<t>
3841   The line terminator for message-header fields is the sequence CRLF.
3842   However, we recommend that applications, when parsing such headers,
3843   recognize a single LF as a line terminator and ignore the leading CR.
3844</t>
3845<t>
3846   The character set of an entity-body &SHOULD; be labeled as the lowest
3847   common denominator of the character codes used within that body, with
3848   the exception that not labeling the entity is preferred over labeling
3849   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3850</t>
3851<t>
3852   Additional rules for requirements on parsing and encoding of dates
3853   and other potential problems with date encodings include:
3854</t>
3855<t>
3856  <list style="symbols">
3857     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3858        which appears to be more than 50 years in the future is in fact
3859        in the past (this helps solve the "year 2000" problem).</t>
3860
3861     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3862        Expires date as earlier than the proper value, but &MUST-NOT;
3863        internally represent a parsed Expires date as later than the
3864        proper value.</t>
3865
3866     <t>All expiration-related calculations &MUST; be done in GMT. The
3867        local time zone &MUST-NOT; influence the calculation or comparison
3868        of an age or expiration time.</t>
3869
3870     <t>If an HTTP header incorrectly carries a date value with a time
3871        zone other than GMT, it &MUST; be converted into GMT using the
3872        most conservative possible conversion.</t>
3873  </list>
3874</t>
3875</section>
3876
3877<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3878<t>
3879   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3880   simplify the process of date comparison. Proxies and gateways from
3881   other protocols &SHOULD; ensure that any Date header field present in a
3882   message conforms to one of the HTTP/1.1 formats and rewrite the date
3883   if necessary.
3884</t>
3885</section>
3886
3887<section title="Compatibility with Previous Versions" anchor="compatibility">
3888<t>
3889   HTTP has been in use by the World-Wide Web global information initiative
3890   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3891   was a simple protocol for hypertext data transfer across the Internet
3892   with only a single method and no metadata.
3893   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3894   methods and MIME-like messaging that could include metadata about the data
3895   transferred and modifiers on the request/response semantics. However,
3896   HTTP/1.0 did not sufficiently take into consideration the effects of
3897   hierarchical proxies, caching, the need for persistent connections, or
3898   name-based virtual hosts. The proliferation of incompletely-implemented
3899   applications calling themselves "HTTP/1.0" further necessitated a
3900   protocol version change in order for two communicating applications
3901   to determine each other's true capabilities.
3902</t>
3903<t>
3904   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3905   requirements that enable reliable implementations, adding only
3906   those new features that will either be safely ignored by an HTTP/1.0
3907   recipient or only sent when communicating with a party advertising
3908   compliance with HTTP/1.1.
3909</t>
3910<t>
3911   It is beyond the scope of a protocol specification to mandate
3912   compliance with previous versions. HTTP/1.1 was deliberately
3913   designed, however, to make supporting previous versions easy. It is
3914   worth noting that, at the time of composing this specification
3915   (1996), we would expect commercial HTTP/1.1 servers to:
3916  <list style="symbols">
3917     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3918        1.1 requests;</t>
3919
3920     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3921        1.1;</t>
3922
3923     <t>respond appropriately with a message in the same major version
3924        used by the client.</t>
3925  </list>
3926</t>
3927<t>
3928   And we would expect HTTP/1.1 clients to:
3929  <list style="symbols">
3930     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3931        responses;</t>
3932
3933     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3934        1.1.</t>
3935  </list>
3936</t>
3937<t>
3938   For most implementations of HTTP/1.0, each connection is established
3939   by the client prior to the request and closed by the server after
3940   sending the response. Some implementations implement the Keep-Alive
3941   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3942</t>
3943
3944<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3945<t>
3946   This section summarizes major differences between versions HTTP/1.0
3947   and HTTP/1.1.
3948</t>
3949
3950<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
3951<t>
3952   The requirements that clients and servers support the Host request-header,
3953   report an error if the Host request-header (<xref target="header.host"/>) is
3954   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3955   are among the most important changes defined by this
3956   specification.
3957</t>
3958<t>
3959   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3960   addresses and servers; there was no other established mechanism for
3961   distinguishing the intended server of a request than the IP address
3962   to which that request was directed. The changes outlined above will
3963   allow the Internet, once older HTTP clients are no longer common, to
3964   support multiple Web sites from a single IP address, greatly
3965   simplifying large operational Web servers, where allocation of many
3966   IP addresses to a single host has created serious problems. The
3967   Internet will also be able to recover the IP addresses that have been
3968   allocated for the sole purpose of allowing special-purpose domain
3969   names to be used in root-level HTTP URLs. Given the rate of growth of
3970   the Web, and the number of servers already deployed, it is extremely
3971   important that all implementations of HTTP (including updates to
3972   existing HTTP/1.0 applications) correctly implement these
3973   requirements:
3974  <list style="symbols">
3975     <t>Both clients and servers &MUST; support the Host request-header.</t>
3976
3977     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3978
3979     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3980        request does not include a Host request-header.</t>
3981
3982     <t>Servers &MUST; accept absolute URIs.</t>
3983  </list>
3984</t>
3985</section>
3986</section>
3987
3988<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3989<t>
3990   Some clients and servers might wish to be compatible with some
3991   previous implementations of persistent connections in HTTP/1.0
3992   clients and servers. Persistent connections in HTTP/1.0 are
3993   explicitly negotiated as they are not the default behavior. HTTP/1.0
3994   experimental implementations of persistent connections are faulty,
3995   and the new facilities in HTTP/1.1 are designed to rectify these
3996   problems. The problem was that some existing 1.0 clients may be
3997   sending Keep-Alive to a proxy server that doesn't understand
3998   Connection, which would then erroneously forward it to the next
3999   inbound server, which would establish the Keep-Alive connection and
4000   result in a hung HTTP/1.0 proxy waiting for the close on the
4001   response. The result is that HTTP/1.0 clients must be prevented from
4002   using Keep-Alive when talking to proxies.
4003</t>
4004<t>
4005   However, talking to proxies is the most important use of persistent
4006   connections, so that prohibition is clearly unacceptable. Therefore,
4007   we need some other mechanism for indicating a persistent connection
4008   is desired, which is safe to use even when talking to an old proxy
4009   that ignores Connection. Persistent connections are the default for
4010   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4011   declaring non-persistence. See <xref target="header.connection"/>.
4012</t>
4013<t>
4014   The original HTTP/1.0 form of persistent connections (the Connection:
4015   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4016</t>
4017</section>
4018
4019<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4020<t>
4021   This specification has been carefully audited to correct and
4022   disambiguate key word usage; RFC 2068 had many problems in respect to
4023   the conventions laid out in <xref target="RFC2119"/>.
4024</t>
4025<t>
4026   Transfer-coding and message lengths all interact in ways that
4027   required fixing exactly when chunked encoding is used (to allow for
4028   transfer encoding that may not be self delimiting); it was important
4029   to straighten out exactly how message lengths are computed. (Sections
4030   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4031   <xref target="header.content-length" format="counter"/>,
4032   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4033</t>
4034<t>
4035   The use and interpretation of HTTP version numbers has been clarified
4036   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4037   version they support to deal with problems discovered in HTTP/1.0
4038   implementations (<xref target="http.version"/>)
4039</t>
4040<t>
4041   Transfer-coding had significant problems, particularly with
4042   interactions with chunked encoding. The solution is that transfer-codings
4043   become as full fledged as content-codings. This involves
4044   adding an IANA registry for transfer-codings (separate from content
4045   codings), a new header field (TE) and enabling trailer headers in the
4046   future. Transfer encoding is a major performance benefit, so it was
4047   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4048   interoperability problem that could have occurred due to interactions
4049   between authentication trailers, chunked encoding and HTTP/1.0
4050   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4051   and <xref target="header.te" format="counter"/>)
4052</t>
4053</section>
4054
4055<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4056<t>
4057  The CHAR rule does not allow the NUL character anymore (this affects
4058  the comment and quoted-string rules).  Furthermore, the quoted-pair
4059  rule does not allow escaping NUL, CR or LF anymore.
4060  (<xref target="basic.rules"/>)
4061</t>
4062<t>
4063  Clarify that HTTP-Version is case sensitive.
4064  (<xref target="http.version"/>)
4065</t>
4066<t>
4067  Remove reference to non-existant identity transfer-coding value tokens.
4068  (Sections <xref format="counter" target="transfer.codings"/> and
4069  <xref format="counter" target="message.length"/>)
4070</t>
4071<t>
4072  Clarification that the chunk length does not include
4073  the count of the octets in the chunk header and trailer.
4074  (<xref target="chunked.transfer.encoding"/>)
4075</t>
4076<t>
4077  Update use of abs_path production from RFC1808 to the path-absolute + query
4078  components of RFC3986.
4079  (<xref target="request-uri"/>)
4080</t>
4081<t>
4082  Clarify exactly when close connection options must be sent.
4083  (<xref target="header.connection"/>)
4084</t>
4085</section>
4086</section>
4087
4088<section title="Terminology" anchor="terminology">
4089<t>
4090   This specification uses a number of terms to refer to the roles
4091   played by participants in, and objects of, the HTTP communication.
4092</t>
4093<t>
4094  <iref item="connection"/>
4095  <x:dfn>connection</x:dfn>
4096  <list>
4097    <t>
4098      A transport layer virtual circuit established between two programs
4099      for the purpose of communication.
4100    </t>
4101  </list>
4102</t>
4103<t>
4104  <iref item="message"/>
4105  <x:dfn>message</x:dfn>
4106  <list>
4107    <t>
4108      The basic unit of HTTP communication, consisting of a structured
4109      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4110      transmitted via the connection.
4111    </t>
4112  </list>
4113</t>
4114<t>
4115  <iref item="request"/>
4116  <x:dfn>request</x:dfn>
4117  <list>
4118    <t>
4119      An HTTP request message, as defined in <xref target="request"/>.
4120    </t>
4121  </list>
4122</t>
4123<t>
4124  <iref item="response"/>
4125  <x:dfn>response</x:dfn>
4126  <list>
4127    <t>
4128      An HTTP response message, as defined in <xref target="response"/>.
4129    </t>
4130  </list>
4131</t>
4132<t>
4133  <iref item="resource"/>
4134  <x:dfn>resource</x:dfn>
4135  <list>
4136    <t>
4137      A network data object or service that can be identified by a URI,
4138      as defined in <xref target="uri"/>. Resources may be available in multiple
4139      representations (e.g. multiple languages, data formats, size, and
4140      resolutions) or vary in other ways.
4141    </t>
4142  </list>
4143</t>
4144<t>
4145  <iref item="entity"/>
4146  <x:dfn>entity</x:dfn>
4147  <list>
4148    <t>
4149      The information transferred as the payload of a request or
4150      response. An entity consists of metainformation in the form of
4151      entity-header fields and content in the form of an entity-body, as
4152      described in &entity;.
4153    </t>
4154  </list>
4155</t>
4156<t>
4157  <iref item="representation"/>
4158  <x:dfn>representation</x:dfn>
4159  <list>
4160    <t>
4161      An entity included with a response that is subject to content
4162      negotiation, as described in &content.negotiation;. There may exist multiple
4163      representations associated with a particular response status.
4164    </t>
4165  </list>
4166</t>
4167<t>
4168  <iref item="content negotiation"/>
4169  <x:dfn>content negotiation</x:dfn>
4170  <list>
4171    <t>
4172      The mechanism for selecting the appropriate representation when
4173      servicing a request, as described in &content.negotiation;. The
4174      representation of entities in any response can be negotiated
4175      (including error responses).
4176    </t>
4177  </list>
4178</t>
4179<t>
4180  <iref item="variant"/>
4181  <x:dfn>variant</x:dfn>
4182  <list>
4183    <t>
4184      A resource may have one, or more than one, representation(s)
4185      associated with it at any given instant. Each of these
4186      representations is termed a `variant'.  Use of the term `variant'
4187      does not necessarily imply that the resource is subject to content
4188      negotiation.
4189    </t>
4190  </list>
4191</t>
4192<t>
4193  <iref item="client"/>
4194  <x:dfn>client</x:dfn>
4195  <list>
4196    <t>
4197      A program that establishes connections for the purpose of sending
4198      requests.
4199    </t>
4200  </list>
4201</t>
4202<t>
4203  <iref item="user agent"/>
4204  <x:dfn>user agent</x:dfn>
4205  <list>
4206    <t>
4207      The client which initiates a request. These are often browsers,
4208      editors, spiders (web-traversing robots), or other end user tools.
4209    </t>
4210  </list>
4211</t>
4212<t>
4213  <iref item="server"/>
4214  <x:dfn>server</x:dfn>
4215  <list>
4216    <t>
4217      An application program that accepts connections in order to
4218      service requests by sending back responses. Any given program may
4219      be capable of being both a client and a server; our use of these
4220      terms refers only to the role being performed by the program for a
4221      particular connection, rather than to the program's capabilities
4222      in general. Likewise, any server may act as an origin server,
4223      proxy, gateway, or tunnel, switching behavior based on the nature
4224      of each request.
4225    </t>
4226  </list>
4227</t>
4228<t>
4229  <iref item="origin server"/>
4230  <x:dfn>origin server</x:dfn>
4231  <list>
4232    <t>
4233      The server on which a given resource resides or is to be created.
4234    </t>
4235  </list>
4236</t>
4237<t>
4238  <iref item="proxy"/>
4239  <x:dfn>proxy</x:dfn>
4240  <list>
4241    <t>
4242      An intermediary program which acts as both a server and a client
4243      for the purpose of making requests on behalf of other clients.
4244      Requests are serviced internally or by passing them on, with
4245      possible translation, to other servers. A proxy &MUST; implement
4246      both the client and server requirements of this specification. A
4247      "transparent proxy" is a proxy that does not modify the request or
4248      response beyond what is required for proxy authentication and
4249      identification. A "non-transparent proxy" is a proxy that modifies
4250      the request or response in order to provide some added service to
4251      the user agent, such as group annotation services, media type
4252      transformation, protocol reduction, or anonymity filtering. Except
4253      where either transparent or non-transparent behavior is explicitly
4254      stated, the HTTP proxy requirements apply to both types of
4255      proxies.
4256    </t>
4257  </list>
4258</t>
4259<t>
4260  <iref item="gateway"/>
4261  <x:dfn>gateway</x:dfn>
4262  <list>
4263    <t>
4264      A server which acts as an intermediary for some other server.
4265      Unlike a proxy, a gateway receives requests as if it were the
4266      origin server for the requested resource; the requesting client
4267      may not be aware that it is communicating with a gateway.
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  <iref item="tunnel"/>
4273  <x:dfn>tunnel</x:dfn>
4274  <list>
4275    <t>
4276      An intermediary program which is acting as a blind relay between
4277      two connections. Once active, a tunnel is not considered a party
4278      to the HTTP communication, though the tunnel may have been
4279      initiated by an HTTP request. The tunnel ceases to exist when both
4280      ends of the relayed connections are closed.
4281    </t>
4282  </list>
4283</t>
4284<t>
4285  <iref item="cache"/>
4286  <x:dfn>cache</x:dfn>
4287  <list>
4288    <t>
4289      A program's local store of response messages and the subsystem
4290      that controls its message storage, retrieval, and deletion. A
4291      cache stores cacheable responses in order to reduce the response
4292      time and network bandwidth consumption on future, equivalent
4293      requests. Any client or server may include a cache, though a cache
4294      cannot be used by a server that is acting as a tunnel.
4295    </t>
4296  </list>
4297</t>
4298<t>
4299  <iref item="cacheable"/>
4300  <x:dfn>cacheable</x:dfn>
4301  <list>
4302    <t>
4303      A response is cacheable if a cache is allowed to store a copy of
4304      the response message for use in answering subsequent requests. The
4305      rules for determining the cacheability of HTTP responses are
4306      defined in &caching;. Even if a resource is cacheable, there may
4307      be additional constraints on whether a cache can use the cached
4308      copy for a particular request.
4309    </t>
4310  </list>
4311</t>
4312<t>
4313  <iref item="upstream"/>
4314  <iref item="downstream"/>
4315  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4316  <list>
4317    <t>
4318      Upstream and downstream describe the flow of a message: all
4319      messages flow from upstream to downstream.
4320    </t>
4321  </list>
4322</t>
4323<t>
4324  <iref item="inbound"/>
4325  <iref item="outbound"/>
4326  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4327  <list>
4328    <t>
4329      Inbound and outbound refer to the request and response paths for
4330      messages: "inbound" means "traveling toward the origin server",
4331      and "outbound" means "traveling toward the user agent"
4332    </t>
4333  </list>
4334</t>
4335</section>
4336
4337<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4338
4339<section title="Since RFC2616">
4340<t>
4341  Extracted relevant partitions from <xref target="RFC2616"/>.
4342</t>
4343</section>
4344
4345<section title="Since draft-ietf-httpbis-p1-messaging-00">
4346<t>
4347  Closed issues:
4348  <list style="symbols">
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4351      "HTTP Version should be case sensitive"
4352      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4353    </t>
4354    <t>
4355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4356      "'unsafe' characters"
4357      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4358    </t>
4359    <t>
4360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4361      "Chunk Size Definition"
4362      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4363    </t>
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4366      "Message Length"
4367      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4368    </t>
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4371      "Media Type Registrations"
4372      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4373    </t>
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4376      "URI includes query"
4377      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4378    </t>
4379    <t>
4380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4381      "No close on 1xx responses"
4382      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4386      "Remove 'identity' token references"
4387      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4388    </t>
4389    <t>
4390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4391      "Import query BNF"
4392    </t>
4393    <t>
4394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4395      "qdtext BNF"
4396    </t>
4397    <t>
4398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4399      "Normative and Informative references"
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4403      "RFC2606 Compliance"
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4407      "RFC977 reference"
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4411      "RFC1700 references"
4412    </t>
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4415      "inconsistency in date format explanation"
4416    </t>
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4419      "Date reference typo"
4420    </t>
4421    <t>
4422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4423      "Informative references"
4424    </t>
4425    <t>
4426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4427      "ISO-8859-1 Reference"
4428    </t>
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4431      "Normative up-to-date references"
4432    </t>
4433  </list>
4434</t>
4435<t>
4436  Other changes:
4437  <list style="symbols">
4438    <t>
4439      Update media type registrations to use RFC4288 template.
4440    </t>
4441    <t>
4442      Use names of RFC4234 core rules DQUOTE and HTAB,
4443      fix broken ABNF for chunk-data
4444      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4445    </t>
4446  </list>
4447</t>
4448</section>
4449
4450<section title="Since draft-ietf-httpbis-p1-messaging-01">
4451<t>
4452  Closed issues:
4453  <list style="symbols">
4454    <t>
4455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4456      "Bodies on GET (and other) requests"
4457    </t>
4458    <t>
4459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4460      "Updating to RFC4288"
4461    </t>
4462    <t>
4463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4464      "Status Code and Reason Phrase"
4465    </t>
4466    <t>
4467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4468      "rel_path not used"
4469    </t>
4470  </list>
4471</t>
4472<t>
4473  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4474  <list style="symbols">
4475    <t>
4476      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4477      "trailer-part").
4478    </t>
4479    <t>
4480      Avoid underscore character in rule names ("http_URL" ->
4481      "http-URI", "abs_path" -> "path-absolute").
4482    </t>
4483    <t>
4484      Add rules for terms imported from URI spec ("absolute-URI", "authority",
4485      "path-abempty", "path-absolute", "uri-host", "port", "query").
4486    </t>
4487    <t>
4488      Synchronize core rules with RFC5234 (this includes a change to CHAR
4489      which now excludes NUL).
4490    </t>
4491    <t>
4492      Get rid of prose rules that span multiple lines.
4493    </t>
4494    <t>
4495      Get rid of unused rules LOALPHA and UPALPHA.
4496    </t>
4497    <t>
4498      Move "Product Tokens" section (back) into Part 1, as "token" is used
4499      in the definition of the Upgrade header.
4500    </t>
4501    <t>
4502      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4503    </t>
4504    <t>
4505      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4506    </t>
4507  </list>
4508</t>
4509</section>
4510
4511<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4512<t>
4513  Closed issues:
4514  <list style="symbols">
4515    <t>
4516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4517      "HTTP-date vs. rfc1123-date"
4518    </t>
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4521      "WS in quoted-pair"
4522    </t>
4523  </list>
4524</t>
4525<t>
4526  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4527  <list style="symbols">
4528    <t>
4529      Reference RFC 3984, and update header registrations for headers defined
4530      in this document.
4531    </t>
4532  </list>
4533</t>
4534<t>
4535  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4536  <list style="symbols">
4537    <t>
4538      Replace string literals when the string really is case-sensitive (HTTP-Version).
4539    </t>
4540  </list>
4541</t>
4542</section>
4543
4544<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4545<t>
4546  Closed issues:
4547  <list style="symbols">
4548    <t>
4549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4550      "Connection closing"
4551    </t>
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4554      "Move registrations and registry information to IANA Considerations"
4555    </t>
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4558      "need new URL for PAD1995 reference"
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4562      "IANA Considerations: update HTTP URI scheme registration"
4563    </t>
4564    <t>
4565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4566      "Cite HTTPS URI scheme definition"
4567    </t>
4568    <t>
4569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4570      "List-type headers vs Set-Cookie"
4571    </t>
4572  </list>
4573</t>
4574<t>
4575  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4576  <list style="symbols">
4577    <t>
4578      Replace string literals when the string really is case-sensitive (HTTP-Date).
4579    </t>
4580    <t>
4581      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4582    </t>
4583  </list>
4584</t>
4585</section>
4586
4587<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4588<t>
4589  Closed issues:
4590  <list style="symbols">
4591    <t>
4592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4593      "RFC 2822 is updated by RFC 5322"
4594    </t>
4595  </list>
4596</t>
4597<t>
4598  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4599  <list style="symbols">
4600    <t>
4601      Use "/" instead of "|" for alternatives.
4602    </t>
4603    <t>
4604      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4605    </t>
4606  </list>
4607</t>
4608</section>
4609
4610</section>
4611
4612</back>
4613</rfc>
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