source: draft-ietf-httpbis/latest/p1-messaging.xml @ 398

Last change on this file since 398 was 398, checked in by julian.reschke@…, 11 years ago

Resolve #63, #74, #94, #111: Issues around TEXT rule closed with revision [395] (closes #63, #74, #94, #111)

  • Property svn:eol-style set to native
File size: 201.9 KB
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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.05"/>.
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="CR"/>
307<iref primary="true" item="Grammar" subitem="CRLF"/>
308<iref primary="true" item="Grammar" subitem="CTL"/>
309<iref primary="true" item="Grammar" subitem="DIGIT"/>
310<iref primary="true" item="Grammar" subitem="DQUOTE"/>
311<iref primary="true" item="Grammar" subitem="HEXDIG"/>
312<iref primary="true" item="Grammar" subitem="LF"/>
313<iref primary="true" item="Grammar" subitem="OCTET"/>
314<iref primary="true" item="Grammar" subitem="SP"/>
315<iref primary="true" item="Grammar" subitem="VCHAR"/>
316<iref primary="true" item="Grammar" subitem="WSP"/>
317<t anchor="core.rules">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CTL"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="CRLF"/>
322  <x:anchor-alias value="DIGIT"/>
323  <x:anchor-alias value="DQUOTE"/>
324  <x:anchor-alias value="HEXDIG"/>
325  <x:anchor-alias value="LF"/>
326  <x:anchor-alias value="OCTET"/>
327  <x:anchor-alias value="SP"/>
328  <x:anchor-alias value="VCHAR"/>
329  <x:anchor-alias value="WSP"/>
330   This specification uses the Augmented Backus-Naur Form (ABNF) notation
331   of <xref target="RFC5234"/>.  The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (white space).
339</t>
340
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
350    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
351    form of lists very easy; a rule such as
352    <figure><artwork type="example">
353 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
354  </t>
355  <t>
356    can be shown as
357    <figure><artwork type="example">
358 1#element</artwork></figure>
359  </t>
360  <t>
361    Wherever this construct is used, null elements are allowed, but do
362    not contribute to the count of elements present. That is,
363    "(element), , (element) " is permitted, but counts as only two
364    elements. Therefore, where at least one element is required, at
365    least one non-null element &MUST; be present. Default values are 0
366    and infinity so that "#element" allows any number, including zero;
367    "1#element" requires at least one; and "1#2element" allows one or
368    two.
369  </t>
370  <t>
371    <cref anchor="abnf.list">
372      At a later point of time, we may want to add an appendix containing
373      the whole ABNF, with the list rules expanded to strict RFC 5234
374      notation.
375    </cref>
376  </t>
377</section>
378
379<section title="Basic Rules" anchor="basic.rules">
380<t anchor="rule.CRLF">
381  <x:anchor-alias value="CRLF"/>
382   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
383   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
384   tolerant applications). The end-of-line marker within an entity-body
385   is defined by its associated media type, as described in &media-types;.
386</t>
387<t anchor="rule.LWS">
388   This specification uses three rules to denote the use of linear
389   whitespace: OWS (optional whitespace), RWS (required whitespace), and
390   BWS ("bad" whitespace).
391</t>
392<t>
393   The OWS rule is used where zero or more linear white space characters may
394   appear. OWS &SHOULD; either not be produced or be produced as a single SP
395   character. Multiple OWS characters that occur within field-content &SHOULD;
396   be replaced with a single SP before interpreting the field value or
397   forwarding the message downstream.
398</t>
399<t>
400   RWS is used when at least one linear white space character is required to
401   separate field tokens. RWS &SHOULD; be produced as a single SP character.
402   Multiple RWS characters that occur within field-content &SHOULD; be
403   replaced with a single SP before interpreting the field value or
404   forwarding the message downstream.
405</t>
406<t>
407   BWS is used where the grammar allows optional whitespace for historical
408   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
409   recipients &MUST; accept such bad optional whitespace and remove it before
410   interpreting the field value or forwarding the message downstream.
411</t>
412<t anchor="rule.whitespace">
413  <x:anchor-alias value="BWS"/>
414  <x:anchor-alias value="OWS"/>
415  <x:anchor-alias value="RWS"/>
416  <x:anchor-alias value="obs-fold"/>
417</t>
418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
419  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
420                 ; "optional" white space
421  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
422                 ; "required" white space
423  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
424                 ; "bad" white space
425  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
426</artwork></figure>
427<t anchor="rule.token.separators">
428  <x:anchor-alias value="tchar"/>
429  <x:anchor-alias value="token"/>
430   Many HTTP/1.1 header field values consist of words separated by whitespace
431   or special characters. These special characters &MUST; be in a quoted
432   string to be used within a parameter value (as defined in
433   <xref target="transfer.codings"/>).
434</t>
435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
436  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
437                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
438                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
439                 
440  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
441</artwork></figure>
442<t anchor="rule.quoted-string">
443  <x:anchor-alias value="quoted-string"/>
444  <x:anchor-alias value="qdtext"/>
445  <x:anchor-alias value="obs-text"/>
446   A string of text is parsed as a single word if it is quoted using
447   double-quote marks.
448</t>
449<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
450  <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>
451  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
452  <x:ref>obs-text</x:ref>       = %x80-FF
453</artwork></figure>
454<t anchor="rule.quoted-pair">
455  <x:anchor-alias value="quoted-pair"/>
456  <x:anchor-alias value="quoted-text"/>
457   The backslash character ("\") &MAY; be used as a single-character
458   quoting mechanism only within quoted-string and comment constructs.
459</t>
460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
461  <x:ref>quoted-text</x:ref>    = %x01-09 /
462                   %x0B-0C /
463                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
464  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
465</artwork></figure>
466</section>
467
468<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
469  <x:anchor-alias value="request-header"/>
470  <x:anchor-alias value="response-header"/>
471  <x:anchor-alias value="accept-params"/>
472  <x:anchor-alias value="entity-body"/>
473  <x:anchor-alias value="entity-header"/>
474  <x:anchor-alias value="Cache-Control"/>
475  <x:anchor-alias value="Pragma"/>
476  <x:anchor-alias value="Warning"/>
477<t>
478  The ABNF rules below are defined in other parts:
479</t>
480<figure><!-- Part2--><artwork type="abnf2616">
481  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
482  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
483</artwork></figure>
484<figure><!-- Part3--><artwork type="abnf2616">
485  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
486  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
487  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
488</artwork></figure>
489<figure><!-- Part6--><artwork type="abnf2616">
490  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
491  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
492  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
493</artwork></figure>
494</section>
495
496</section>
497</section>
498
499<section title="HTTP architecture" anchor="architecture">
500<t>
501   HTTP was created with a specific architecture in mind, the World Wide Web,
502   and has evolved over time to support the scalability needs of a worldwide
503   hypertext system. Much of that architecture is reflected in the terminology
504   and syntax productions used to define HTTP.
505</t>
506
507<section title="Uniform Resource Identifiers" anchor="uri">
508<t>
509   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
510   throughout HTTP as the means for identifying resources. URI references
511   are used to target requests, redirect responses, and define relationships.
512   HTTP does not limit what a resource may be; it merely defines an interface
513   that can be used to interact with a resource via HTTP. More information on
514   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
515</t>
516  <x:anchor-alias value="URI"/>
517  <x:anchor-alias value="URI-reference"/>
518  <x:anchor-alias value="absolute-URI"/>
519  <x:anchor-alias value="relative-part"/>
520  <x:anchor-alias value="authority"/>
521  <x:anchor-alias value="fragment"/>
522  <x:anchor-alias value="path-abempty"/>
523  <x:anchor-alias value="path-absolute"/>
524  <x:anchor-alias value="port"/>
525  <x:anchor-alias value="query"/>
526  <x:anchor-alias value="uri-host"/>
527  <x:anchor-alias value="partial-URI"/>
528<t>
529   This specification adopts the definitions of "URI-reference",
530   "absolute-URI", "relative-part", "fragment", "port", "host",
531   "path-abempty", "path-absolute", "query", and "authority" from
532   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
533   protocol elements that allow a relative URI without a fragment.
534</t>
535<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"/>
536  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
537  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
538  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
539  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
540  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
541  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
542  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
543  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
544  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
545  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
546  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
547 
548  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
549</artwork></figure>
550<t>
551   Each protocol element in HTTP that allows a URI reference will indicate in
552   its ABNF production whether the element allows only a URI in absolute form
553   (absolute-URI), any relative reference (relative-ref), or some other subset
554   of the URI-reference grammar. Unless otherwise indicated, URI references
555   are parsed relative to the request target (the default base URI for both
556   the request and its corresponding response).
557</t>
558
559<section title="http URI scheme" anchor="http.uri">
560  <x:anchor-alias value="http-URI"/>
561  <iref item="http URI scheme" primary="true"/>
562  <iref item="URI scheme" subitem="http" primary="true"/>
563<t>
564   The "http" scheme is used to locate network resources via the HTTP
565   protocol. This section defines the syntax and semantics for identifiers
566   using the http or https URI schemes.
567</t>
568<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
569  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
570</artwork></figure>
571<t>
572   If the port is empty or not given, port 80 is assumed. The semantics
573   are that the identified resource is located at the server listening
574   for TCP connections on that port of that host, and the request-target
575   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
576   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
577   the path-absolute is not present in the URL, it &MUST; be given as "/" when
578   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
579   receives a host name which is not a fully qualified domain name, it
580   &MAY; add its domain to the host name it received. If a proxy receives
581   a fully qualified domain name, the proxy &MUST-NOT; change the host
582   name.
583</t>
584<t><list><t>
585  <iref item="https URI scheme"/>
586  <iref item="URI scheme" subitem="https"/>
587  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
588</t></list></t>
589</section>
590
591<section title="URI Comparison" anchor="uri.comparison">
592<t>
593   When comparing two URIs to decide if they match or not, a client
594   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
595   URIs, with these exceptions:
596  <list style="symbols">
597    <t>A port that is empty or not given is equivalent to the default
598        port for that URI-reference;</t>
599    <t>Comparisons of host names &MUST; be case-insensitive;</t>
600    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
601    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
602  </list>
603</t>
604<t>
605   Characters other than those in the "reserved" set (see
606   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
607   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
608</t>
609<t>
610   For example, the following three URIs are equivalent:
611</t>
612<figure><artwork type="example">
613   http://example.com:80/~smith/home.html
614   http://EXAMPLE.com/%7Esmith/home.html
615   http://EXAMPLE.com:/%7esmith/home.html
616</artwork></figure>
617</section>
618
619<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
620<t>
621</t>
622</section>
623</section>
624
625<section title="Overall Operation" anchor="intro.overall.operation">
626<t>
627   HTTP is a request/response protocol. A client sends a
628   request to the server in the form of a request method, URI, and
629   protocol version, followed by a MIME-like message containing request
630   modifiers, client information, and possible body content over a
631   connection with a server. The server responds with a status line,
632   including the message's protocol version and a success or error code,
633   followed by a MIME-like message containing server information, entity
634   metainformation, and possible entity-body content.
635</t>
636<t>
637   Most HTTP communication is initiated by a user agent and consists of
638   a request to be applied to a resource on some origin server. In the
639   simplest case, this may be accomplished via a single connection (v)
640   between the user agent (UA) and the origin server (O).
641</t>
642<figure><artwork type="drawing">
643       request chain ------------------------&gt;
644    UA -------------------v------------------- O
645       &lt;----------------------- response chain
646</artwork></figure>
647<t>
648   A more complicated situation occurs when one or more intermediaries
649   are present in the request/response chain. There are three common
650   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
651   forwarding agent, receiving requests for a URI in its absolute form,
652   rewriting all or part of the message, and forwarding the reformatted
653   request toward the server identified by the URI. A gateway is a
654   receiving agent, acting as a layer above some other server(s) and, if
655   necessary, translating the requests to the underlying server's
656   protocol. A tunnel acts as a relay point between two connections
657   without changing the messages; tunnels are used when the
658   communication needs to pass through an intermediary (such as a
659   firewall) even when the intermediary cannot understand the contents
660   of the messages.
661</t>
662<figure><artwork type="drawing">
663       request chain --------------------------------------&gt;
664    UA -----v----- A -----v----- B -----v----- C -----v----- O
665       &lt;------------------------------------- response chain
666</artwork></figure>
667<t>
668   The figure above shows three intermediaries (A, B, and C) between the
669   user agent and origin server. A request or response message that
670   travels the whole chain will pass through four separate connections.
671   This distinction is important because some HTTP communication options
672   may apply only to the connection with the nearest, non-tunnel
673   neighbor, only to the end-points of the chain, or to all connections
674   along the chain. Although the diagram is linear, each participant may
675   be engaged in multiple, simultaneous communications. For example, B
676   may be receiving requests from many clients other than A, and/or
677   forwarding requests to servers other than C, at the same time that it
678   is handling A's request.
679</t>
680<t>
681   Any party to the communication which is not acting as a tunnel may
682   employ an internal cache for handling requests. The effect of a cache
683   is that the request/response chain is shortened if one of the
684   participants along the chain has a cached response applicable to that
685   request. The following illustrates the resulting chain if B has a
686   cached copy of an earlier response from O (via C) for a request which
687   has not been cached by UA or A.
688</t>
689<figure><artwork type="drawing">
690          request chain ----------&gt;
691       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
692          &lt;--------- response chain
693</artwork></figure>
694<t>
695   Not all responses are usefully cacheable, and some requests may
696   contain modifiers which place special requirements on cache behavior.
697   HTTP requirements for cache behavior and cacheable responses are
698   defined in &caching;.
699</t>
700<t>
701   In fact, there are a wide variety of architectures and configurations
702   of caches and proxies currently being experimented with or deployed
703   across the World Wide Web. These systems include national hierarchies
704   of proxy caches to save transoceanic bandwidth, systems that
705   broadcast or multicast cache entries, organizations that distribute
706   subsets of cached data via CD-ROM, and so on. HTTP systems are used
707   in corporate intranets over high-bandwidth links, and for access via
708   PDAs with low-power radio links and intermittent connectivity. The
709   goal of HTTP/1.1 is to support the wide diversity of configurations
710   already deployed while introducing protocol constructs that meet the
711   needs of those who build web applications that require high
712   reliability and, failing that, at least reliable indications of
713   failure.
714</t>
715<t>
716   HTTP communication usually takes place over TCP/IP connections. The
717   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
718   not preclude HTTP from being implemented on top of any other protocol
719   on the Internet, or on other networks. HTTP only presumes a reliable
720   transport; any protocol that provides such guarantees can be used;
721   the mapping of the HTTP/1.1 request and response structures onto the
722   transport data units of the protocol in question is outside the scope
723   of this specification.
724</t>
725<t>
726   In HTTP/1.0, most implementations used a new connection for each
727   request/response exchange. In HTTP/1.1, a connection may be used for
728   one or more request/response exchanges, although connections may be
729   closed for a variety of reasons (see <xref target="persistent.connections"/>).
730</t>
731</section>
732
733<section title="Use of HTTP for proxy communication" anchor="http.proxy">
734<t>
735   Configured to use HTTP to proxy HTTP or other protocols.
736</t>
737</section>
738<section title="Interception of HTTP for access control" anchor="http.intercept">
739<t>
740   Interception of HTTP traffic for initiating access control.
741</t>
742</section>
743<section title="Use of HTTP by other protocols" anchor="http.others">
744<t>
745   Profiles of HTTP defined by other protocol.
746   Extensions of HTTP like WebDAV.
747</t>
748</section>
749<section title="Use of HTTP by media type specification" anchor="http.media">
750<t>
751   Instructions on composing HTTP requests via hypertext formats.
752</t>
753</section>
754</section>
755
756<section title="Protocol Parameters" anchor="protocol.parameters">
757
758<section title="HTTP Version" anchor="http.version">
759  <x:anchor-alias value="HTTP-Version"/>
760  <x:anchor-alias value="HTTP-Prot-Name"/>
761<t>
762   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
763   of the protocol. The protocol versioning policy is intended to allow
764   the sender to indicate the format of a message and its capacity for
765   understanding further HTTP communication, rather than the features
766   obtained via that communication. No change is made to the version
767   number for the addition of message components which do not affect
768   communication behavior or which only add to extensible field values.
769   The &lt;minor&gt; number is incremented when the changes made to the
770   protocol add features which do not change the general message parsing
771   algorithm, but which may add to the message semantics and imply
772   additional capabilities of the sender. The &lt;major&gt; number is
773   incremented when the format of a message within the protocol is
774   changed. See <xref target="RFC2145"/> for a fuller explanation.
775</t>
776<t>
777   The version of an HTTP message is indicated by an HTTP-Version field
778   in the first line of the message. HTTP-Version is case-sensitive.
779</t>
780<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
781  <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>
782  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
783</artwork></figure>
784<t>
785   Note that the major and minor numbers &MUST; be treated as separate
786   integers and that each &MAY; be incremented higher than a single digit.
787   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
788   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
789   &MUST-NOT; be sent.
790</t>
791<t>
792   An application that sends a request or response message that includes
793   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
794   with this specification. Applications that are at least conditionally
795   compliant with this specification &SHOULD; use an HTTP-Version of
796   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
797   not compatible with HTTP/1.0. For more details on when to send
798   specific HTTP-Version values, see <xref target="RFC2145"/>.
799</t>
800<t>
801   The HTTP version of an application is the highest HTTP version for
802   which the application is at least conditionally compliant.
803</t>
804<t>
805   Proxy and gateway applications need to be careful when forwarding
806   messages in protocol versions different from that of the application.
807   Since the protocol version indicates the protocol capability of the
808   sender, a proxy/gateway &MUST-NOT; send a message with a version
809   indicator which is greater than its actual version. If a higher
810   version request is received, the proxy/gateway &MUST; either downgrade
811   the request version, or respond with an error, or switch to tunnel
812   behavior.
813</t>
814<t>
815   Due to interoperability problems with HTTP/1.0 proxies discovered
816   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
817   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
818   they support. The proxy/gateway's response to that request &MUST; be in
819   the same major version as the request.
820</t>
821<t>
822  <list>
823    <t>
824      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
825      of header fields required or forbidden by the versions involved.
826    </t>
827  </list>
828</t>
829</section>
830
831<section title="Date/Time Formats" anchor="date.time.formats">
832<section title="Full Date" anchor="full.date">
833  <x:anchor-alias value="HTTP-date"/>
834  <x:anchor-alias value="obsolete-date"/>
835  <x:anchor-alias value="rfc1123-date"/>
836  <x:anchor-alias value="rfc850-date"/>
837  <x:anchor-alias value="asctime-date"/>
838  <x:anchor-alias value="date1"/>
839  <x:anchor-alias value="date2"/>
840  <x:anchor-alias value="date3"/>
841  <x:anchor-alias value="rfc1123-date"/>
842  <x:anchor-alias value="time"/>
843  <x:anchor-alias value="wkday"/>
844  <x:anchor-alias value="weekday"/>
845  <x:anchor-alias value="month"/>
846<t>
847   HTTP applications have historically allowed three different formats
848   for the representation of date/time stamps:
849</t>
850<figure><artwork type="example">
851   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
852   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
853   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
854</artwork></figure>
855<t>
856   The first format is preferred as an Internet standard and represents
857   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
858   other formats are described here only for
859   compatibility with obsolete implementations.
860   HTTP/1.1 clients and servers that parse the date value &MUST; accept
861   all three formats (for compatibility with HTTP/1.0), though they &MUST;
862   only generate the RFC 1123 format for representing HTTP-date values
863   in header fields. See <xref target="tolerant.applications"/> for further information.
864</t>
865<t><list><t>
866      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
867      accepting date values that may have been sent by non-HTTP
868      applications, as is sometimes the case when retrieving or posting
869      messages via proxies/gateways to SMTP or NNTP.
870</t></list></t>
871<t>
872   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
873   (GMT), without exception. For the purposes of HTTP, GMT is exactly
874   equal to UTC (Coordinated Universal Time). This is indicated in the
875   first two formats by the inclusion of "GMT" as the three-letter
876   abbreviation for time zone, and &MUST; be assumed when reading the
877   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
878   additional whitespace beyond that specifically included as SP in the
879   grammar.
880</t>
881<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"/>
882  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
883  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
884  <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
885  <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
886  <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>
887  <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>
888                 ; day month year (e.g., 02 Jun 1982)
889  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
890                 ; day-month-year (e.g., 02-Jun-82)
891  <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> ))
892                 ; month day (e.g., Jun  2)
893  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
894                 ; 00:00:00 - 23:59:59
895  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
896               / s-Thu / s-Fri / s-Sat / s-Sun
897  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
898               / l-Thu / l-Fri / l-Sat / l-Sun
899  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
900               / s-May / s-Jun / s-Jul / s-Aug
901               / s-Sep / s-Oct / s-Nov / s-Dec
902               
903  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
904
905  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
906  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
907  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
908  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
909  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
910  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
911  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
912
913  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
914  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
915  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
916  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
917  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
918  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
919  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
920
921  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
922  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
923  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
924  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
925  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
926  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
927  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
928  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
929  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
930  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
931  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
932  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
933</artwork></figure>
934<t>
935      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
936      to their usage within the protocol stream. Clients and servers are
937      not required to use these formats for user presentation, request
938      logging, etc.
939</t>
940</section>
941</section>
942
943<section title="Transfer Codings" anchor="transfer.codings">
944  <x:anchor-alias value="parameter"/>
945  <x:anchor-alias value="transfer-coding"/>
946  <x:anchor-alias value="transfer-extension"/>
947<t>
948   Transfer-coding values are used to indicate an encoding
949   transformation that has been, can be, or may need to be applied to an
950   entity-body in order to ensure "safe transport" through the network.
951   This differs from a content coding in that the transfer-coding is a
952   property of the message, not of the original entity.
953</t>
954<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
955  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
956  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
957</artwork></figure>
958<t anchor="rule.parameter">
959  <x:anchor-alias value="attribute"/>
960  <x:anchor-alias value="parameter"/>
961  <x:anchor-alias value="value"/>
962   Parameters are in  the form of attribute/value pairs.
963</t>
964<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"/>
965  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
966  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
967  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
968</artwork></figure>
969<t>
970   All transfer-coding values are case-insensitive. HTTP/1.1 uses
971   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
972   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
973</t>
974<t>
975   Whenever a transfer-coding is applied to a message-body, the set of
976   transfer-codings &MUST; include "chunked", unless the message indicates it
977   is terminated by closing the connection. When the "chunked" transfer-coding
978   is used, it &MUST; be the last transfer-coding applied to the
979   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
980   than once to a message-body. These rules allow the recipient to
981   determine the transfer-length of the message (<xref target="message.length"/>).
982</t>
983<t>
984   Transfer-codings are analogous to the Content-Transfer-Encoding
985   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
986   binary data over a 7-bit transport service. However, safe transport
987   has a different focus for an 8bit-clean transfer protocol. In HTTP,
988   the only unsafe characteristic of message-bodies is the difficulty in
989   determining the exact body length (<xref target="message.length"/>), or the desire to
990   encrypt data over a shared transport.
991</t>
992<t>
993   The Internet Assigned Numbers Authority (IANA) acts as a registry for
994   transfer-coding value tokens. Initially, the registry contains the
995   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
996   "gzip", "compress", and "deflate" (&content-codings;).
997</t>
998<t>
999   New transfer-coding value tokens &SHOULD; be registered in the same way
1000   as new content-coding value tokens (&content-codings;).
1001</t>
1002<t>
1003   A server which receives an entity-body with a transfer-coding it does
1004   not understand &SHOULD; return 501 (Not Implemented), and close the
1005   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1006   client.
1007</t>
1008
1009<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1010  <x:anchor-alias value="chunk"/>
1011  <x:anchor-alias value="Chunked-Body"/>
1012  <x:anchor-alias value="chunk-data"/>
1013  <x:anchor-alias value="chunk-ext"/>
1014  <x:anchor-alias value="chunk-ext-name"/>
1015  <x:anchor-alias value="chunk-ext-val"/>
1016  <x:anchor-alias value="chunk-size"/>
1017  <x:anchor-alias value="last-chunk"/>
1018  <x:anchor-alias value="trailer-part"/>
1019<t>
1020   The chunked encoding modifies the body of a message in order to
1021   transfer it as a series of chunks, each with its own size indicator,
1022   followed by an &OPTIONAL; trailer containing entity-header fields. This
1023   allows dynamically produced content to be transferred along with the
1024   information necessary for the recipient to verify that it has
1025   received the full message.
1026</t>
1027<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1028  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1029                   <x:ref>last-chunk</x:ref>
1030                   <x:ref>trailer-part</x:ref>
1031                   <x:ref>CRLF</x:ref>
1032 
1033  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1034                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1035  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1036  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1037 
1038  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1039                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1040  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1041  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1042  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1043  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1044</artwork></figure>
1045<t>
1046   The chunk-size field is a string of hex digits indicating the size of
1047   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1048   zero, followed by the trailer, which is terminated by an empty line.
1049</t>
1050<t>
1051   The trailer allows the sender to include additional HTTP header
1052   fields at the end of the message. The Trailer header field can be
1053   used to indicate which header fields are included in a trailer (see
1054   <xref target="header.trailer"/>).
1055</t>
1056<t>
1057   A server using chunked transfer-coding in a response &MUST-NOT; use the
1058   trailer for any header fields unless at least one of the following is
1059   true:
1060  <list style="numbers">
1061    <t>the request included a TE header field that indicates "trailers" is
1062     acceptable in the transfer-coding of the  response, as described in
1063     <xref target="header.te"/>; or,</t>
1064
1065    <t>the server is the origin server for the response, the trailer
1066     fields consist entirely of optional metadata, and the recipient
1067     could use the message (in a manner acceptable to the origin server)
1068     without receiving this metadata.  In other words, the origin server
1069     is willing to accept the possibility that the trailer fields might
1070     be silently discarded along the path to the client.</t>
1071  </list>
1072</t>
1073<t>
1074   This requirement prevents an interoperability failure when the
1075   message is being received by an HTTP/1.1 (or later) proxy and
1076   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1077   compliance with the protocol would have necessitated a possibly
1078   infinite buffer on the proxy.
1079</t>
1080<t>
1081   A process for decoding the "chunked" transfer-coding
1082   can be represented in pseudo-code as:
1083</t>
1084<figure><artwork type="code">
1085  length := 0
1086  read chunk-size, chunk-ext (if any) and CRLF
1087  while (chunk-size &gt; 0) {
1088     read chunk-data and CRLF
1089     append chunk-data to entity-body
1090     length := length + chunk-size
1091     read chunk-size and CRLF
1092  }
1093  read entity-header
1094  while (entity-header not empty) {
1095     append entity-header to existing header fields
1096     read entity-header
1097  }
1098  Content-Length := length
1099  Remove "chunked" from Transfer-Encoding
1100</artwork></figure>
1101<t>
1102   All HTTP/1.1 applications &MUST; be able to receive and decode the
1103   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1104   they do not understand.
1105</t>
1106</section>
1107</section>
1108
1109<section title="Product Tokens" anchor="product.tokens">
1110  <x:anchor-alias value="product"/>
1111  <x:anchor-alias value="product-version"/>
1112<t>
1113   Product tokens are used to allow communicating applications to
1114   identify themselves by software name and version. Most fields using
1115   product tokens also allow sub-products which form a significant part
1116   of the application to be listed, separated by white space. By
1117   convention, the products are listed in order of their significance
1118   for identifying the application.
1119</t>
1120<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1121  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1122  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1123</artwork></figure>
1124<t>
1125   Examples:
1126</t>
1127<figure><artwork type="example">
1128    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1129    Server: Apache/0.8.4
1130</artwork></figure>
1131<t>
1132   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1133   used for advertising or other non-essential information. Although any
1134   token character &MAY; appear in a product-version, this token &SHOULD;
1135   only be used for a version identifier (i.e., successive versions of
1136   the same product &SHOULD; only differ in the product-version portion of
1137   the product value).
1138</t>
1139</section>
1140
1141</section>
1142
1143<section title="HTTP Message" anchor="http.message">
1144
1145<section title="Message Types" anchor="message.types">
1146  <x:anchor-alias value="generic-message"/>
1147  <x:anchor-alias value="HTTP-message"/>
1148  <x:anchor-alias value="start-line"/>
1149<t>
1150   HTTP messages consist of requests from client to server and responses
1151   from server to client.
1152</t>
1153<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1154  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1155</artwork></figure>
1156<t>
1157   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1158   message format of <xref target="RFC5322"/> for transferring entities (the payload
1159   of the message). Both types of message consist of a start-line, zero
1160   or more header fields (also known as "headers"), an empty line (i.e.,
1161   a line with nothing preceding the CRLF) indicating the end of the
1162   header fields, and possibly a message-body.
1163</t>
1164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1165  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1166                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1167                    <x:ref>CRLF</x:ref>
1168                    [ <x:ref>message-body</x:ref> ]
1169  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1170</artwork></figure>
1171<t>
1172   In the interest of robustness, servers &SHOULD; ignore any empty
1173   line(s) received where a Request-Line is expected. In other words, if
1174   the server is reading the protocol stream at the beginning of a
1175   message and receives a CRLF first, it should ignore the CRLF.
1176</t>
1177<t>
1178   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1179   after a POST request. To restate what is explicitly forbidden by the
1180   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1181   extra CRLF.
1182</t>
1183<t>
1184   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1185   header field. The presence of whitespace might be an attempt to trick a
1186   noncompliant implementation of HTTP into ignoring that field or processing
1187   the next line as a new request, either of which may result in security
1188   issues when implementations within the request chain interpret the
1189   same message differently. HTTP/1.1 servers &MUST; reject such a message
1190   with a 400 (Bad Request) response.
1191</t>
1192</section>
1193
1194<section title="Message Headers" anchor="message.headers">
1195  <x:anchor-alias value="field-content"/>
1196  <x:anchor-alias value="field-name"/>
1197  <x:anchor-alias value="field-value"/>
1198  <x:anchor-alias value="message-header"/>
1199<t>
1200   HTTP header fields follow the same general format as Internet messages in
1201   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1202   of a name followed by a colon (":"), optional whitespace, and the field
1203   value. Field names are case-insensitive.
1204</t>
1205<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"/>
1206  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1207  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1208  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1209  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1210</artwork></figure>
1211<t>
1212   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1213   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1214   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1215   header field-values use only a subset of the US-ASCII charset
1216   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1217   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1218   (obs-text) octets in field-content as opaque data.
1219</t>
1220<t>
1221   No whitespace is allowed between the header field-name and colon. For
1222   security reasons, any request message received containing such whitespace
1223   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1224   whitespace in a response message &MUST; be removed.
1225</t>
1226<t>
1227   The field value &MAY; be preceded by optional white space; a single SP is
1228   preferred. The field-value does not include any leading or trailing white
1229   space: OWS occurring before the first non-whitespace character of the
1230   field-value or after the last non-whitespace character of the field-value
1231   is ignored and &MAY; be removed without changing the meaning of the header
1232   field.
1233</t>
1234<t>
1235   Historically, HTTP header field values could be extended over multiple
1236   lines by preceding each extra line with at least one space or horizontal
1237   tab character (line folding). This specification deprecates such line
1238   folding except within the message/http media type
1239   (<xref target="internet.media.type.message.http"/>).
1240   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1241   (i.e., that contain any field-content that matches the obs-fold rule) unless
1242   the message is intended for packaging within the message/http media type.
1243   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1244   obs-fold whitespace with a single SP prior to interpreting the field value
1245   or forwarding the message downstream.
1246</t>
1247<t anchor="rule.comment">
1248  <x:anchor-alias value="comment"/>
1249  <x:anchor-alias value="ctext"/>
1250   Comments can be included in some HTTP header fields by surrounding
1251   the comment text with parentheses. Comments are only allowed in
1252   fields containing "comment" as part of their field value definition.
1253   In all other fields, parentheses are considered part of the field
1254   value.
1255</t>
1256<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1257  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1258  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1259</artwork></figure>
1260<t>
1261   The order in which header fields with differing field names are
1262   received is not significant. However, it is "good practice" to send
1263   general-header fields first, followed by request-header or response-header
1264   fields, and ending with the entity-header fields.
1265</t>
1266<t>
1267   Multiple message-header fields with the same field-name &MAY; be
1268   present in a message if and only if the entire field-value for that
1269   header field is defined as a comma-separated list [i.e., #(values)].
1270   It &MUST; be possible to combine the multiple header fields into one
1271   "field-name: field-value" pair, without changing the semantics of the
1272   message, by appending each subsequent field-value to the first, each
1273   separated by a comma. The order in which header fields with the same
1274   field-name are received is therefore significant to the
1275   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1276   change the order of these field values when a message is forwarded.
1277</t>
1278<t>
1279  <list><t>
1280   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1281   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1282   can occur multiple times, but does not use the list syntax, and thus cannot
1283   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1284   for details.) Also note that the Set-Cookie2 header specified in
1285   <xref target="RFC2965"/> does not share this problem.
1286  </t></list>
1287</t>
1288 
1289</section>
1290
1291<section title="Message Body" anchor="message.body">
1292  <x:anchor-alias value="message-body"/>
1293<t>
1294   The message-body (if any) of an HTTP message is used to carry the
1295   entity-body associated with the request or response. The message-body
1296   differs from the entity-body only when a transfer-coding has been
1297   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1298</t>
1299<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1300  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1301               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1302</artwork></figure>
1303<t>
1304   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1305   applied by an application to ensure safe and proper transfer of the
1306   message. Transfer-Encoding is a property of the message, not of the
1307   entity, and thus &MAY; be added or removed by any application along the
1308   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1309   when certain transfer-codings may be used.)
1310</t>
1311<t>
1312   The rules for when a message-body is allowed in a message differ for
1313   requests and responses.
1314</t>
1315<t>
1316   The presence of a message-body in a request is signaled by the
1317   inclusion of a Content-Length or Transfer-Encoding header field in
1318   the request's message-headers. A message-body &MUST-NOT; be included in
1319   a request if the specification of the request method (&method;)
1320   explicitly disallows an entity-body in requests.
1321   When a request message contains both a message-body of non-zero
1322   length and a method that does not define any semantics for that
1323   request message-body, then an origin server &SHOULD; either ignore
1324   the message-body or respond with an appropriate error message
1325   (e.g., 413).  A proxy or gateway, when presented the same request,
1326   &SHOULD; either forward the request inbound with the message-body or
1327   ignore the message-body when determining a response.
1328</t>
1329<t>
1330   For response messages, whether or not a message-body is included with
1331   a message is dependent on both the request method and the response
1332   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1333   &MUST-NOT; include a message-body, even though the presence of entity-header
1334   fields might lead one to believe they do. All 1xx
1335   (informational), 204 (No Content), and 304 (Not Modified) responses
1336   &MUST-NOT; include a message-body. All other responses do include a
1337   message-body, although it &MAY; be of zero length.
1338</t>
1339</section>
1340
1341<section title="Message Length" anchor="message.length">
1342<t>
1343   The transfer-length of a message is the length of the message-body as
1344   it appears in the message; that is, after any transfer-codings have
1345   been applied. When a message-body is included with a message, the
1346   transfer-length of that body is determined by one of the following
1347   (in order of precedence):
1348</t>
1349<t>
1350  <list style="numbers">
1351    <x:lt><t>
1352     Any response message which "&MUST-NOT;" include a message-body (such
1353     as the 1xx, 204, and 304 responses and any response to a HEAD
1354     request) is always terminated by the first empty line after the
1355     header fields, regardless of the entity-header fields present in
1356     the message.
1357    </t></x:lt>
1358    <x:lt><t>
1359     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1360     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1361     is used, the transfer-length is defined by the use of this transfer-coding.
1362     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1363     is not present, the transfer-length is defined by the sender closing the connection.
1364    </t></x:lt>
1365    <x:lt><t>
1366     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1367     decimal value in OCTETs represents both the entity-length and the
1368     transfer-length. The Content-Length header field &MUST-NOT; be sent
1369     if these two lengths are different (i.e., if a Transfer-Encoding
1370     header field is present). If a message is received with both a
1371     Transfer-Encoding header field and a Content-Length header field,
1372     the latter &MUST; be ignored.
1373    </t></x:lt>
1374    <x:lt><t>
1375     If the message uses the media type "multipart/byteranges", and the
1376     transfer-length is not otherwise specified, then this self-delimiting
1377     media type defines the transfer-length. This media type
1378     &MUST-NOT; be used unless the sender knows that the recipient can parse
1379     it; the presence in a request of a Range header with multiple byte-range
1380     specifiers from a 1.1 client implies that the client can parse
1381     multipart/byteranges responses.
1382    <list style="empty"><t>
1383       A range header might be forwarded by a 1.0 proxy that does not
1384       understand multipart/byteranges; in this case the server &MUST;
1385       delimit the message using methods defined in items 1, 3 or 5 of
1386       this section.
1387    </t></list>
1388    </t></x:lt>
1389    <x:lt><t>
1390     By the server closing the connection. (Closing the connection
1391     cannot be used to indicate the end of a request body, since that
1392     would leave no possibility for the server to send back a response.)
1393    </t></x:lt>
1394  </list>
1395</t>
1396<t>
1397   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1398   containing a message-body &MUST; include a valid Content-Length header
1399   field unless the server is known to be HTTP/1.1 compliant. If a
1400   request contains a message-body and a Content-Length is not given,
1401   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1402   determine the length of the message, or with 411 (Length Required) if
1403   it wishes to insist on receiving a valid Content-Length.
1404</t>
1405<t>
1406   All HTTP/1.1 applications that receive entities &MUST; accept the
1407   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1408   to be used for messages when the message length cannot be determined
1409   in advance.
1410</t>
1411<t>
1412   Messages &MUST-NOT; include both a Content-Length header field and a
1413   transfer-coding. If the message does include a
1414   transfer-coding, the Content-Length &MUST; be ignored.
1415</t>
1416<t>
1417   When a Content-Length is given in a message where a message-body is
1418   allowed, its field value &MUST; exactly match the number of OCTETs in
1419   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1420   invalid length is received and detected.
1421</t>
1422</section>
1423
1424<section title="General Header Fields" anchor="general.header.fields">
1425  <x:anchor-alias value="general-header"/>
1426<t>
1427   There are a few header fields which have general applicability for
1428   both request and response messages, but which do not apply to the
1429   entity being transferred. These header fields apply only to the
1430   message being transmitted.
1431</t>
1432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1433  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1434                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1435                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1436                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1437                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1438                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1439                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1440                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1441                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1442</artwork></figure>
1443<t>
1444   General-header field names can be extended reliably only in
1445   combination with a change in the protocol version. However, new or
1446   experimental header fields may be given the semantics of general
1447   header fields if all parties in the communication recognize them to
1448   be general-header fields. Unrecognized header fields are treated as
1449   entity-header fields.
1450</t>
1451</section>
1452</section>
1453
1454<section title="Request" anchor="request">
1455  <x:anchor-alias value="Request"/>
1456<t>
1457   A request message from a client to a server includes, within the
1458   first line of that message, the method to be applied to the resource,
1459   the identifier of the resource, and the protocol version in use.
1460</t>
1461<!--                 Host                      ; should be moved here eventually -->
1462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1463  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1464                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1465                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1466                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1467                  <x:ref>CRLF</x:ref>
1468                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1469</artwork></figure>
1470
1471<section title="Request-Line" anchor="request-line">
1472  <x:anchor-alias value="Request-Line"/>
1473<t>
1474   The Request-Line begins with a method token, followed by the
1475   request-target and the protocol version, and ending with CRLF. The
1476   elements are separated by SP characters. No CR or LF is allowed
1477   except in the final CRLF sequence.
1478</t>
1479<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1480  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1481</artwork></figure>
1482
1483<section title="Method" anchor="method">
1484  <x:anchor-alias value="Method"/>
1485<t>
1486   The Method  token indicates the method to be performed on the
1487   resource identified by the request-target. The method is case-sensitive.
1488</t>
1489<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1490  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1491</artwork></figure>
1492</section>
1493
1494<section title="request-target" anchor="request-target">
1495  <x:anchor-alias value="request-target"/>
1496<t>
1497   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1498   identifies the resource upon which to apply the request.
1499</t>
1500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1501  <x:ref>request-target</x:ref>    = "*"
1502                 / <x:ref>absolute-URI</x:ref>
1503                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1504                 / <x:ref>authority</x:ref>
1505</artwork></figure>
1506<t>
1507   The four options for request-target are dependent on the nature of the
1508   request. The asterisk "*" means that the request does not apply to a
1509   particular resource, but to the server itself, and is only allowed
1510   when the method used does not necessarily apply to a resource. One
1511   example would be
1512</t>
1513<figure><artwork type="example">
1514    OPTIONS * HTTP/1.1
1515</artwork></figure>
1516<t>
1517   The absolute-URI form is &REQUIRED; when the request is being made to a
1518   proxy. The proxy is requested to forward the request or service it
1519   from a valid cache, and return the response. Note that the proxy &MAY;
1520   forward the request on to another proxy or directly to the server
1521   specified by the absolute-URI. In order to avoid request loops, a
1522   proxy &MUST; be able to recognize all of its server names, including
1523   any aliases, local variations, and the numeric IP address. An example
1524   Request-Line would be:
1525</t>
1526<figure><artwork type="example">
1527    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1528</artwork></figure>
1529<t>
1530   To allow for transition to absolute-URIs in all requests in future
1531   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1532   form in requests, even though HTTP/1.1 clients will only generate
1533   them in requests to proxies.
1534</t>
1535<t>
1536   The authority form is only used by the CONNECT method (&CONNECT;).
1537</t>
1538<t>
1539   The most common form of request-target is that used to identify a
1540   resource on an origin server or gateway. In this case the absolute
1541   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1542   the request-target, and the network location of the URI (authority) &MUST;
1543   be transmitted in a Host header field. For example, a client wishing
1544   to retrieve the resource above directly from the origin server would
1545   create a TCP connection to port 80 of the host "www.example.org" and send
1546   the lines:
1547</t>
1548<figure><artwork type="example">
1549    GET /pub/WWW/TheProject.html HTTP/1.1
1550    Host: www.example.org
1551</artwork></figure>
1552<t>
1553   followed by the remainder of the Request. Note that the absolute path
1554   cannot be empty; if none is present in the original URI, it &MUST; be
1555   given as "/" (the server root).
1556</t>
1557<t>
1558   The request-target is transmitted in the format specified in
1559   <xref target="http.uri"/>. If the request-target is encoded using the
1560   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1561   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1562   &MUST; decode the request-target in order to
1563   properly interpret the request. Servers &SHOULD; respond to invalid
1564   request-targets with an appropriate status code.
1565</t>
1566<t>
1567   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1568   received request-target when forwarding it to the next inbound server,
1569   except as noted above to replace a null path-absolute with "/".
1570</t>
1571<t>
1572  <list><t>
1573      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1574      meaning of the request when the origin server is improperly using
1575      a non-reserved URI character for a reserved purpose.  Implementors
1576      should be aware that some pre-HTTP/1.1 proxies have been known to
1577      rewrite the request-target.
1578  </t></list>
1579</t>
1580<t>
1581   HTTP does not place a pre-defined limit on the length of a request-target.
1582   A server &MUST; be prepared to receive URIs of unbounded length and
1583   respond with the 414 (URI too long) status if the received
1584   request-target would be longer than the server wishes to handle
1585   (see &status-414;).
1586</t>
1587<t>
1588   Various ad-hoc limitations on request-target length are found in practice.
1589   It is &RECOMMENDED; that all HTTP senders and recipients support
1590   request-target lengths of 8000 or more OCTETs.
1591</t>
1592</section>
1593</section>
1594
1595<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1596<t>
1597   The exact resource identified by an Internet request is determined by
1598   examining both the request-target and the Host header field.
1599</t>
1600<t>
1601   An origin server that does not allow resources to differ by the
1602   requested host &MAY; ignore the Host header field value when
1603   determining the resource identified by an HTTP/1.1 request. (But see
1604   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1605   for other requirements on Host support in HTTP/1.1.)
1606</t>
1607<t>
1608   An origin server that does differentiate resources based on the host
1609   requested (sometimes referred to as virtual hosts or vanity host
1610   names) &MUST; use the following rules for determining the requested
1611   resource on an HTTP/1.1 request:
1612  <list style="numbers">
1613    <t>If request-target is an absolute-URI, the host is part of the
1614     request-target. Any Host header field value in the request &MUST; be
1615     ignored.</t>
1616    <t>If the request-target is not an absolute-URI, and the request includes
1617     a Host header field, the host is determined by the Host header
1618     field value.</t>
1619    <t>If the host as determined by rule 1 or 2 is not a valid host on
1620     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1621  </list>
1622</t>
1623<t>
1624   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1625   attempt to use heuristics (e.g., examination of the URI path for
1626   something unique to a particular host) in order to determine what
1627   exact resource is being requested.
1628</t>
1629</section>
1630
1631</section>
1632
1633
1634<section title="Response" anchor="response">
1635  <x:anchor-alias value="Response"/>
1636<t>
1637   After receiving and interpreting a request message, a server responds
1638   with an HTTP response message.
1639</t>
1640<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1641  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1642                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1643                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1644                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1645                  <x:ref>CRLF</x:ref>
1646                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1647</artwork></figure>
1648
1649<section title="Status-Line" anchor="status-line">
1650  <x:anchor-alias value="Status-Line"/>
1651<t>
1652   The first line of a Response message is the Status-Line, consisting
1653   of the protocol version followed by a numeric status code and its
1654   associated textual phrase, with each element separated by SP
1655   characters. No CR or LF is allowed except in the final CRLF sequence.
1656</t>
1657<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1658  <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>
1659</artwork></figure>
1660
1661<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1662  <x:anchor-alias value="Reason-Phrase"/>
1663  <x:anchor-alias value="Status-Code"/>
1664<t>
1665   The Status-Code element is a 3-digit integer result code of the
1666   attempt to understand and satisfy the request. These codes are fully
1667   defined in &status-codes;.  The Reason Phrase exists for the sole
1668   purpose of providing a textual description associated with the numeric
1669   status code, out of deference to earlier Internet application protocols
1670   that were more frequently used with interactive text clients.
1671   A client &SHOULD; ignore the content of the Reason Phrase.
1672</t>
1673<t>
1674   The first digit of the Status-Code defines the class of response. The
1675   last two digits do not have any categorization role. There are 5
1676   values for the first digit:
1677  <list style="symbols">
1678    <t>
1679      1xx: Informational - Request received, continuing process
1680    </t>
1681    <t>
1682      2xx: Success - The action was successfully received,
1683        understood, and accepted
1684    </t>
1685    <t>
1686      3xx: Redirection - Further action must be taken in order to
1687        complete the request
1688    </t>
1689    <t>
1690      4xx: Client Error - The request contains bad syntax or cannot
1691        be fulfilled
1692    </t>
1693    <t>
1694      5xx: Server Error - The server failed to fulfill an apparently
1695        valid request
1696    </t>
1697  </list>
1698</t>
1699<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"/>
1700  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1701  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1702</artwork></figure>
1703</section>
1704</section>
1705
1706</section>
1707
1708
1709<section title="Connections" anchor="connections">
1710
1711<section title="Persistent Connections" anchor="persistent.connections">
1712
1713<section title="Purpose" anchor="persistent.purpose">
1714<t>
1715   Prior to persistent connections, a separate TCP connection was
1716   established to fetch each URL, increasing the load on HTTP servers
1717   and causing congestion on the Internet. The use of inline images and
1718   other associated data often require a client to make multiple
1719   requests of the same server in a short amount of time. Analysis of
1720   these performance problems and results from a prototype
1721   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1722   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1723   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1724   T/TCP <xref target="Tou1998"/>.
1725</t>
1726<t>
1727   Persistent HTTP connections have a number of advantages:
1728  <list style="symbols">
1729      <t>
1730        By opening and closing fewer TCP connections, CPU time is saved
1731        in routers and hosts (clients, servers, proxies, gateways,
1732        tunnels, or caches), and memory used for TCP protocol control
1733        blocks can be saved in hosts.
1734      </t>
1735      <t>
1736        HTTP requests and responses can be pipelined on a connection.
1737        Pipelining allows a client to make multiple requests without
1738        waiting for each response, allowing a single TCP connection to
1739        be used much more efficiently, with much lower elapsed time.
1740      </t>
1741      <t>
1742        Network congestion is reduced by reducing the number of packets
1743        caused by TCP opens, and by allowing TCP sufficient time to
1744        determine the congestion state of the network.
1745      </t>
1746      <t>
1747        Latency on subsequent requests is reduced since there is no time
1748        spent in TCP's connection opening handshake.
1749      </t>
1750      <t>
1751        HTTP can evolve more gracefully, since errors can be reported
1752        without the penalty of closing the TCP connection. Clients using
1753        future versions of HTTP might optimistically try a new feature,
1754        but if communicating with an older server, retry with old
1755        semantics after an error is reported.
1756      </t>
1757    </list>
1758</t>
1759<t>
1760   HTTP implementations &SHOULD; implement persistent connections.
1761</t>
1762</section>
1763
1764<section title="Overall Operation" anchor="persistent.overall">
1765<t>
1766   A significant difference between HTTP/1.1 and earlier versions of
1767   HTTP is that persistent connections are the default behavior of any
1768   HTTP connection. That is, unless otherwise indicated, the client
1769   &SHOULD; assume that the server will maintain a persistent connection,
1770   even after error responses from the server.
1771</t>
1772<t>
1773   Persistent connections provide a mechanism by which a client and a
1774   server can signal the close of a TCP connection. This signaling takes
1775   place using the Connection header field (<xref target="header.connection"/>). Once a close
1776   has been signaled, the client &MUST-NOT; send any more requests on that
1777   connection.
1778</t>
1779
1780<section title="Negotiation" anchor="persistent.negotiation">
1781<t>
1782   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1783   maintain a persistent connection unless a Connection header including
1784   the connection-token "close" was sent in the request. If the server
1785   chooses to close the connection immediately after sending the
1786   response, it &SHOULD; send a Connection header including the
1787   connection-token close.
1788</t>
1789<t>
1790   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1791   decide to keep it open based on whether the response from a server
1792   contains a Connection header with the connection-token close. In case
1793   the client does not want to maintain a connection for more than that
1794   request, it &SHOULD; send a Connection header including the
1795   connection-token close.
1796</t>
1797<t>
1798   If either the client or the server sends the close token in the
1799   Connection header, that request becomes the last one for the
1800   connection.
1801</t>
1802<t>
1803   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1804   maintained for HTTP versions less than 1.1 unless it is explicitly
1805   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1806   compatibility with HTTP/1.0 clients.
1807</t>
1808<t>
1809   In order to remain persistent, all messages on the connection &MUST;
1810   have a self-defined message length (i.e., one not defined by closure
1811   of the connection), as described in <xref target="message.length"/>.
1812</t>
1813</section>
1814
1815<section title="Pipelining" anchor="pipelining">
1816<t>
1817   A client that supports persistent connections &MAY; "pipeline" its
1818   requests (i.e., send multiple requests without waiting for each
1819   response). A server &MUST; send its responses to those requests in the
1820   same order that the requests were received.
1821</t>
1822<t>
1823   Clients which assume persistent connections and pipeline immediately
1824   after connection establishment &SHOULD; be prepared to retry their
1825   connection if the first pipelined attempt fails. If a client does
1826   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1827   persistent. Clients &MUST; also be prepared to resend their requests if
1828   the server closes the connection before sending all of the
1829   corresponding responses.
1830</t>
1831<t>
1832   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1833   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1834   premature termination of the transport connection could lead to
1835   indeterminate results. A client wishing to send a non-idempotent
1836   request &SHOULD; wait to send that request until it has received the
1837   response status for the previous request.
1838</t>
1839</section>
1840</section>
1841
1842<section title="Proxy Servers" anchor="persistent.proxy">
1843<t>
1844   It is especially important that proxies correctly implement the
1845   properties of the Connection header field as specified in <xref target="header.connection"/>.
1846</t>
1847<t>
1848   The proxy server &MUST; signal persistent connections separately with
1849   its clients and the origin servers (or other proxy servers) that it
1850   connects to. Each persistent connection applies to only one transport
1851   link.
1852</t>
1853<t>
1854   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1855   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1856   discussion of the problems with the Keep-Alive header implemented by
1857   many HTTP/1.0 clients).
1858</t>
1859</section>
1860
1861<section title="Practical Considerations" anchor="persistent.practical">
1862<t>
1863   Servers will usually have some time-out value beyond which they will
1864   no longer maintain an inactive connection. Proxy servers might make
1865   this a higher value since it is likely that the client will be making
1866   more connections through the same server. The use of persistent
1867   connections places no requirements on the length (or existence) of
1868   this time-out for either the client or the server.
1869</t>
1870<t>
1871   When a client or server wishes to time-out it &SHOULD; issue a graceful
1872   close on the transport connection. Clients and servers &SHOULD; both
1873   constantly watch for the other side of the transport close, and
1874   respond to it as appropriate. If a client or server does not detect
1875   the other side's close promptly it could cause unnecessary resource
1876   drain on the network.
1877</t>
1878<t>
1879   A client, server, or proxy &MAY; close the transport connection at any
1880   time. For example, a client might have started to send a new request
1881   at the same time that the server has decided to close the "idle"
1882   connection. From the server's point of view, the connection is being
1883   closed while it was idle, but from the client's point of view, a
1884   request is in progress.
1885</t>
1886<t>
1887   This means that clients, servers, and proxies &MUST; be able to recover
1888   from asynchronous close events. Client software &SHOULD; reopen the
1889   transport connection and retransmit the aborted sequence of requests
1890   without user interaction so long as the request sequence is
1891   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1892   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1893   human operator the choice of retrying the request(s). Confirmation by
1894   user-agent software with semantic understanding of the application
1895   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1896   be repeated if the second sequence of requests fails.
1897</t>
1898<t>
1899   Servers &SHOULD; always respond to at least one request per connection,
1900   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1901   middle of transmitting a response, unless a network or client failure
1902   is suspected.
1903</t>
1904<t>
1905   Clients that use persistent connections &SHOULD; limit the number of
1906   simultaneous connections that they maintain to a given server. A
1907   single-user client &SHOULD-NOT; maintain more than 2 connections with
1908   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1909   another server or proxy, where N is the number of simultaneously
1910   active users. These guidelines are intended to improve HTTP response
1911   times and avoid congestion.
1912</t>
1913</section>
1914</section>
1915
1916<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1917
1918<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1919<t>
1920   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1921   flow control mechanisms to resolve temporary overloads, rather than
1922   terminating connections with the expectation that clients will retry.
1923   The latter technique can exacerbate network congestion.
1924</t>
1925</section>
1926
1927<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1928<t>
1929   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1930   the network connection for an error status while it is transmitting
1931   the request. If the client sees an error status, it &SHOULD;
1932   immediately cease transmitting the body. If the body is being sent
1933   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1934   empty trailer &MAY; be used to prematurely mark the end of the message.
1935   If the body was preceded by a Content-Length header, the client &MUST;
1936   close the connection.
1937</t>
1938</section>
1939
1940<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1941<t>
1942   The purpose of the 100 (Continue) status (see &status-100;) is to
1943   allow a client that is sending a request message with a request body
1944   to determine if the origin server is willing to accept the request
1945   (based on the request headers) before the client sends the request
1946   body. In some cases, it might either be inappropriate or highly
1947   inefficient for the client to send the body if the server will reject
1948   the message without looking at the body.
1949</t>
1950<t>
1951   Requirements for HTTP/1.1 clients:
1952  <list style="symbols">
1953    <t>
1954        If a client will wait for a 100 (Continue) response before
1955        sending the request body, it &MUST; send an Expect request-header
1956        field (&header-expect;) with the "100-continue" expectation.
1957    </t>
1958    <t>
1959        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1960        with the "100-continue" expectation if it does not intend
1961        to send a request body.
1962    </t>
1963  </list>
1964</t>
1965<t>
1966   Because of the presence of older implementations, the protocol allows
1967   ambiguous situations in which a client may send "Expect: 100-continue"
1968   without receiving either a 417 (Expectation Failed) status
1969   or a 100 (Continue) status. Therefore, when a client sends this
1970   header field to an origin server (possibly via a proxy) from which it
1971   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1972   for an indefinite period before sending the request body.
1973</t>
1974<t>
1975   Requirements for HTTP/1.1 origin servers:
1976  <list style="symbols">
1977    <t> Upon receiving a request which includes an Expect request-header
1978        field with the "100-continue" expectation, an origin server &MUST;
1979        either respond with 100 (Continue) status and continue to read
1980        from the input stream, or respond with a final status code. The
1981        origin server &MUST-NOT; wait for the request body before sending
1982        the 100 (Continue) response. If it responds with a final status
1983        code, it &MAY; close the transport connection or it &MAY; continue
1984        to read and discard the rest of the request.  It &MUST-NOT;
1985        perform the requested method if it returns a final status code.
1986    </t>
1987    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1988        the request message does not include an Expect request-header
1989        field with the "100-continue" expectation, and &MUST-NOT; send a
1990        100 (Continue) response if such a request comes from an HTTP/1.0
1991        (or earlier) client. There is an exception to this rule: for
1992        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1993        status in response to an HTTP/1.1 PUT or POST request that does
1994        not include an Expect request-header field with the "100-continue"
1995        expectation. This exception, the purpose of which is
1996        to minimize any client processing delays associated with an
1997        undeclared wait for 100 (Continue) status, applies only to
1998        HTTP/1.1 requests, and not to requests with any other HTTP-version
1999        value.
2000    </t>
2001    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2002        already received some or all of the request body for the
2003        corresponding request.
2004    </t>
2005    <t> An origin server that sends a 100 (Continue) response &MUST;
2006    ultimately send a final status code, once the request body is
2007        received and processed, unless it terminates the transport
2008        connection prematurely.
2009    </t>
2010    <t> If an origin server receives a request that does not include an
2011        Expect request-header field with the "100-continue" expectation,
2012        the request includes a request body, and the server responds
2013        with a final status code before reading the entire request body
2014        from the transport connection, then the server &SHOULD-NOT;  close
2015        the transport connection until it has read the entire request,
2016        or until the client closes the connection. Otherwise, the client
2017        might not reliably receive the response message. However, this
2018        requirement is not be construed as preventing a server from
2019        defending itself against denial-of-service attacks, or from
2020        badly broken client implementations.
2021      </t>
2022    </list>
2023</t>
2024<t>
2025   Requirements for HTTP/1.1 proxies:
2026  <list style="symbols">
2027    <t> If a proxy receives a request that includes an Expect request-header
2028        field with the "100-continue" expectation, and the proxy
2029        either knows that the next-hop server complies with HTTP/1.1 or
2030        higher, or does not know the HTTP version of the next-hop
2031        server, it &MUST; forward the request, including the Expect header
2032        field.
2033    </t>
2034    <t> If the proxy knows that the version of the next-hop server is
2035        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2036        respond with a 417 (Expectation Failed) status.
2037    </t>
2038    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2039        numbers received from recently-referenced next-hop servers.
2040    </t>
2041    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2042        request message was received from an HTTP/1.0 (or earlier)
2043        client and did not include an Expect request-header field with
2044        the "100-continue" expectation. This requirement overrides the
2045        general rule for forwarding of 1xx responses (see &status-1xx;).
2046    </t>
2047  </list>
2048</t>
2049</section>
2050
2051<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2052<t>
2053   If an HTTP/1.1 client sends a request which includes a request body,
2054   but which does not include an Expect request-header field with the
2055   "100-continue" expectation, and if the client is not directly
2056   connected to an HTTP/1.1 origin server, and if the client sees the
2057   connection close before receiving any status from the server, the
2058   client &SHOULD; retry the request.  If the client does retry this
2059   request, it &MAY; use the following "binary exponential backoff"
2060   algorithm to be assured of obtaining a reliable response:
2061  <list style="numbers">
2062    <t>
2063      Initiate a new connection to the server
2064    </t>
2065    <t>
2066      Transmit the request-headers
2067    </t>
2068    <t>
2069      Initialize a variable R to the estimated round-trip time to the
2070         server (e.g., based on the time it took to establish the
2071         connection), or to a constant value of 5 seconds if the round-trip
2072         time is not available.
2073    </t>
2074    <t>
2075       Compute T = R * (2**N), where N is the number of previous
2076         retries of this request.
2077    </t>
2078    <t>
2079       Wait either for an error response from the server, or for T
2080         seconds (whichever comes first)
2081    </t>
2082    <t>
2083       If no error response is received, after T seconds transmit the
2084         body of the request.
2085    </t>
2086    <t>
2087       If client sees that the connection is closed prematurely,
2088         repeat from step 1 until the request is accepted, an error
2089         response is received, or the user becomes impatient and
2090         terminates the retry process.
2091    </t>
2092  </list>
2093</t>
2094<t>
2095   If at any point an error status is received, the client
2096  <list style="symbols">
2097      <t>&SHOULD-NOT;  continue and</t>
2098
2099      <t>&SHOULD; close the connection if it has not completed sending the
2100        request message.</t>
2101    </list>
2102</t>
2103</section>
2104</section>
2105</section>
2106
2107
2108<section title="Header Field Definitions" anchor="header.fields">
2109<t>
2110   This section defines the syntax and semantics of HTTP/1.1 header fields
2111   related to message framing and transport protocols.
2112</t>
2113<t>
2114   For entity-header fields, both sender and recipient refer to either the
2115   client or the server, depending on who sends and who receives the entity.
2116</t>
2117
2118<section title="Connection" anchor="header.connection">
2119  <iref primary="true" item="Connection header" x:for-anchor=""/>
2120  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2121  <x:anchor-alias value="Connection"/>
2122  <x:anchor-alias value="connection-token"/>
2123  <x:anchor-alias value="Connection-v"/>
2124<t>
2125   The general-header field "Connection" allows the sender to specify
2126   options that are desired for that particular connection and &MUST-NOT;
2127   be communicated by proxies over further connections.
2128</t>
2129<t>
2130   The Connection header's value has the following grammar:
2131</t>
2132<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2133  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2134  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2135  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2136</artwork></figure>
2137<t>
2138   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2139   message is forwarded and, for each connection-token in this field,
2140   remove any header field(s) from the message with the same name as the
2141   connection-token. Connection options are signaled by the presence of
2142   a connection-token in the Connection header field, not by any
2143   corresponding additional header field(s), since the additional header
2144   field may not be sent if there are no parameters associated with that
2145   connection option.
2146</t>
2147<t>
2148   Message headers listed in the Connection header &MUST-NOT; include
2149   end-to-end headers, such as Cache-Control.
2150</t>
2151<t>
2152   HTTP/1.1 defines the "close" connection option for the sender to
2153   signal that the connection will be closed after completion of the
2154   response. For example,
2155</t>
2156<figure><artwork type="example">
2157  Connection: close
2158</artwork></figure>
2159<t>
2160   in either the request or the response header fields indicates that
2161   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2162   after the current request/response is complete.
2163</t>
2164<t>
2165   An HTTP/1.1 client that does not support persistent connections &MUST;
2166   include the "close" connection option in every request message.
2167</t>
2168<t>
2169   An HTTP/1.1 server that does not support persistent connections &MUST;
2170   include the "close" connection option in every response message that
2171   does not have a 1xx (informational) status code.
2172</t>
2173<t>
2174   A system receiving an HTTP/1.0 (or lower-version) message that
2175   includes a Connection header &MUST;, for each connection-token in this
2176   field, remove and ignore any header field(s) from the message with
2177   the same name as the connection-token. This protects against mistaken
2178   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2179</t>
2180</section>
2181
2182<section title="Content-Length" anchor="header.content-length">
2183  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2184  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2185  <x:anchor-alias value="Content-Length"/>
2186  <x:anchor-alias value="Content-Length-v"/>
2187<t>
2188   The entity-header field "Content-Length" indicates the size of the
2189   entity-body, in decimal number of OCTETs, sent to the recipient or,
2190   in the case of the HEAD method, the size of the entity-body that
2191   would have been sent had the request been a GET.
2192</t>
2193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2194  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2195  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2196</artwork></figure>
2197<t>
2198   An example is
2199</t>
2200<figure><artwork type="example">
2201  Content-Length: 3495
2202</artwork></figure>
2203<t>
2204   Applications &SHOULD; use this field to indicate the transfer-length of
2205   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2206</t>
2207<t>
2208   Any Content-Length greater than or equal to zero is a valid value.
2209   <xref target="message.length"/> describes how to determine the length of a message-body
2210   if a Content-Length is not given.
2211</t>
2212<t>
2213   Note that the meaning of this field is significantly different from
2214   the corresponding definition in MIME, where it is an optional field
2215   used within the "message/external-body" content-type. In HTTP, it
2216   &SHOULD; be sent whenever the message's length can be determined prior
2217   to being transferred, unless this is prohibited by the rules in
2218   <xref target="message.length"/>.
2219</t>
2220</section>
2221
2222<section title="Date" anchor="header.date">
2223  <iref primary="true" item="Date header" x:for-anchor=""/>
2224  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2225  <x:anchor-alias value="Date"/>
2226  <x:anchor-alias value="Date-v"/>
2227<t>
2228   The general-header field "Date" represents the date and time at which
2229   the message was originated, having the same semantics as orig-date in
2230   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2231   HTTP-date, as described in <xref target="full.date"/>;
2232   it &MUST; be sent in rfc1123-date format.
2233</t>
2234<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2235  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2236  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2237</artwork></figure>
2238<t>
2239   An example is
2240</t>
2241<figure><artwork type="example">
2242  Date: Tue, 15 Nov 1994 08:12:31 GMT
2243</artwork></figure>
2244<t>
2245   Origin servers &MUST; include a Date header field in all responses,
2246   except in these cases:
2247  <list style="numbers">
2248      <t>If the response status code is 100 (Continue) or 101 (Switching
2249         Protocols), the response &MAY; include a Date header field, at
2250         the server's option.</t>
2251
2252      <t>If the response status code conveys a server error, e.g. 500
2253         (Internal Server Error) or 503 (Service Unavailable), and it is
2254         inconvenient or impossible to generate a valid Date.</t>
2255
2256      <t>If the server does not have a clock that can provide a
2257         reasonable approximation of the current time, its responses
2258         &MUST-NOT; include a Date header field. In this case, the rules
2259         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2260  </list>
2261</t>
2262<t>
2263   A received message that does not have a Date header field &MUST; be
2264   assigned one by the recipient if the message will be cached by that
2265   recipient or gatewayed via a protocol which requires a Date. An HTTP
2266   implementation without a clock &MUST-NOT; cache responses without
2267   revalidating them on every use. An HTTP cache, especially a shared
2268   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2269   clock with a reliable external standard.
2270</t>
2271<t>
2272   Clients &SHOULD; only send a Date header field in messages that include
2273   an entity-body, as in the case of the PUT and POST requests, and even
2274   then it is optional. A client without a clock &MUST-NOT; send a Date
2275   header field in a request.
2276</t>
2277<t>
2278   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2279   time subsequent to the generation of the message. It &SHOULD; represent
2280   the best available approximation of the date and time of message
2281   generation, unless the implementation has no means of generating a
2282   reasonably accurate date and time. In theory, the date ought to
2283   represent the moment just before the entity is generated. In
2284   practice, the date can be generated at any time during the message
2285   origination without affecting its semantic value.
2286</t>
2287
2288<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2289<t>
2290   Some origin server implementations might not have a clock available.
2291   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2292   values to a response, unless these values were associated
2293   with the resource by a system or user with a reliable clock. It &MAY;
2294   assign an Expires value that is known, at or before server
2295   configuration time, to be in the past (this allows "pre-expiration"
2296   of responses without storing separate Expires values for each
2297   resource).
2298</t>
2299</section>
2300</section>
2301
2302<section title="Host" anchor="header.host">
2303  <iref primary="true" item="Host header" x:for-anchor=""/>
2304  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2305  <x:anchor-alias value="Host"/>
2306  <x:anchor-alias value="Host-v"/>
2307<t>
2308   The request-header field "Host" specifies the Internet host and port
2309   number of the resource being requested, as obtained from the original
2310   URI given by the user or referring resource (generally an http URI,
2311   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2312   the naming authority of the origin server or gateway given by the
2313   original URL. This allows the origin server or gateway to
2314   differentiate between internally-ambiguous URLs, such as the root "/"
2315   URL of a server for multiple host names on a single IP address.
2316</t>
2317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2318  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2319  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2320</artwork></figure>
2321<t>
2322   A "host" without any trailing port information implies the default
2323   port for the service requested (e.g., "80" for an HTTP URL). For
2324   example, a request on the origin server for
2325   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2326</t>
2327<figure><artwork type="example">
2328  GET /pub/WWW/ HTTP/1.1
2329  Host: www.example.org
2330</artwork></figure>
2331<t>
2332   A client &MUST; include a Host header field in all HTTP/1.1 request
2333   messages. If the requested URI does not include an Internet host
2334   name for the service being requested, then the Host header field &MUST;
2335   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2336   request message it forwards does contain an appropriate Host header
2337   field that identifies the service being requested by the proxy. All
2338   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2339   status code to any HTTP/1.1 request message which lacks a Host header
2340   field.
2341</t>
2342<t>
2343   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2344   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2345   for other requirements relating to Host.
2346</t>
2347</section>
2348
2349<section title="TE" anchor="header.te">
2350  <iref primary="true" item="TE header" x:for-anchor=""/>
2351  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2352  <x:anchor-alias value="TE"/>
2353  <x:anchor-alias value="TE-v"/>
2354  <x:anchor-alias value="t-codings"/>
2355<t>
2356   The request-header field "TE" indicates what extension transfer-codings
2357   it is willing to accept in the response and whether or not it is
2358   willing to accept trailer fields in a chunked transfer-coding. Its
2359   value may consist of the keyword "trailers" and/or a comma-separated
2360   list of extension transfer-coding names with optional accept
2361   parameters (as described in <xref target="transfer.codings"/>).
2362</t>
2363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2364  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2365  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2366  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2367</artwork></figure>
2368<t>
2369   The presence of the keyword "trailers" indicates that the client is
2370   willing to accept trailer fields in a chunked transfer-coding, as
2371   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2372   transfer-coding values even though it does not itself represent a
2373   transfer-coding.
2374</t>
2375<t>
2376   Examples of its use are:
2377</t>
2378<figure><artwork type="example">
2379  TE: deflate
2380  TE:
2381  TE: trailers, deflate;q=0.5
2382</artwork></figure>
2383<t>
2384   The TE header field only applies to the immediate connection.
2385   Therefore, the keyword &MUST; be supplied within a Connection header
2386   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2387</t>
2388<t>
2389   A server tests whether a transfer-coding is acceptable, according to
2390   a TE field, using these rules:
2391  <list style="numbers">
2392    <x:lt>
2393      <t>The "chunked" transfer-coding is always acceptable. If the
2394         keyword "trailers" is listed, the client indicates that it is
2395         willing to accept trailer fields in the chunked response on
2396         behalf of itself and any downstream clients. The implication is
2397         that, if given, the client is stating that either all
2398         downstream clients are willing to accept trailer fields in the
2399         forwarded response, or that it will attempt to buffer the
2400         response on behalf of downstream recipients.
2401      </t><t>
2402         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2403         chunked response such that a client can be assured of buffering
2404         the entire response.</t>
2405    </x:lt>
2406    <x:lt>
2407      <t>If the transfer-coding being tested is one of the transfer-codings
2408         listed in the TE field, then it is acceptable unless it
2409         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2410         qvalue of 0 means "not acceptable.")</t>
2411    </x:lt>
2412    <x:lt>
2413      <t>If multiple transfer-codings are acceptable, then the
2414         acceptable transfer-coding with the highest non-zero qvalue is
2415         preferred.  The "chunked" transfer-coding always has a qvalue
2416         of 1.</t>
2417    </x:lt>
2418  </list>
2419</t>
2420<t>
2421   If the TE field-value is empty or if no TE field is present, the only
2422   transfer-coding  is "chunked". A message with no transfer-coding is
2423   always acceptable.
2424</t>
2425</section>
2426
2427<section title="Trailer" anchor="header.trailer">
2428  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2429  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2430  <x:anchor-alias value="Trailer"/>
2431  <x:anchor-alias value="Trailer-v"/>
2432<t>
2433   The general field "Trailer" indicates that the given set of
2434   header fields is present in the trailer of a message encoded with
2435   chunked transfer-coding.
2436</t>
2437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2438  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2439  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2440</artwork></figure>
2441<t>
2442   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2443   message using chunked transfer-coding with a non-empty trailer. Doing
2444   so allows the recipient to know which header fields to expect in the
2445   trailer.
2446</t>
2447<t>
2448   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2449   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2450   trailer fields in a "chunked" transfer-coding.
2451</t>
2452<t>
2453   Message header fields listed in the Trailer header field &MUST-NOT;
2454   include the following header fields:
2455  <list style="symbols">
2456    <t>Transfer-Encoding</t>
2457    <t>Content-Length</t>
2458    <t>Trailer</t>
2459  </list>
2460</t>
2461</section>
2462
2463<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2464  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2465  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2466  <x:anchor-alias value="Transfer-Encoding"/>
2467  <x:anchor-alias value="Transfer-Encoding-v"/>
2468<t>
2469   The general-header "Transfer-Encoding" field indicates what (if any)
2470   type of transformation has been applied to the message body in order
2471   to safely transfer it between the sender and the recipient. This
2472   differs from the content-coding in that the transfer-coding is a
2473   property of the message, not of the entity.
2474</t>
2475<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2476  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2477                        <x:ref>Transfer-Encoding-v</x:ref>
2478  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2479</artwork></figure>
2480<t>
2481   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2482</t>
2483<figure><artwork type="example">
2484  Transfer-Encoding: chunked
2485</artwork></figure>
2486<t>
2487   If multiple encodings have been applied to an entity, the transfer-codings
2488   &MUST; be listed in the order in which they were applied.
2489   Additional information about the encoding parameters &MAY; be provided
2490   by other entity-header fields not defined by this specification.
2491</t>
2492<t>
2493   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2494   header.
2495</t>
2496</section>
2497
2498<section title="Upgrade" anchor="header.upgrade">
2499  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2500  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2501  <x:anchor-alias value="Upgrade"/>
2502  <x:anchor-alias value="Upgrade-v"/>
2503<t>
2504   The general-header "Upgrade" allows the client to specify what
2505   additional communication protocols it supports and would like to use
2506   if the server finds it appropriate to switch protocols. The server
2507   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2508   response to indicate which protocol(s) are being switched.
2509</t>
2510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2511  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2512  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2513</artwork></figure>
2514<t>
2515   For example,
2516</t>
2517<figure><artwork type="example">
2518  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2519</artwork></figure>
2520<t>
2521   The Upgrade header field is intended to provide a simple mechanism
2522   for transition from HTTP/1.1 to some other, incompatible protocol. It
2523   does so by allowing the client to advertise its desire to use another
2524   protocol, such as a later version of HTTP with a higher major version
2525   number, even though the current request has been made using HTTP/1.1.
2526   This eases the difficult transition between incompatible protocols by
2527   allowing the client to initiate a request in the more commonly
2528   supported protocol while indicating to the server that it would like
2529   to use a "better" protocol if available (where "better" is determined
2530   by the server, possibly according to the nature of the method and/or
2531   resource being requested).
2532</t>
2533<t>
2534   The Upgrade header field only applies to switching application-layer
2535   protocols upon the existing transport-layer connection. Upgrade
2536   cannot be used to insist on a protocol change; its acceptance and use
2537   by the server is optional. The capabilities and nature of the
2538   application-layer communication after the protocol change is entirely
2539   dependent upon the new protocol chosen, although the first action
2540   after changing the protocol &MUST; be a response to the initial HTTP
2541   request containing the Upgrade header field.
2542</t>
2543<t>
2544   The Upgrade header field only applies to the immediate connection.
2545   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2546   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2547   HTTP/1.1 message.
2548</t>
2549<t>
2550   The Upgrade header field cannot be used to indicate a switch to a
2551   protocol on a different connection. For that purpose, it is more
2552   appropriate to use a 301, 302, 303, or 305 redirection response.
2553</t>
2554<t>
2555   This specification only defines the protocol name "HTTP" for use by
2556   the family of Hypertext Transfer Protocols, as defined by the HTTP
2557   version rules of <xref target="http.version"/> and future updates to this
2558   specification. Any token can be used as a protocol name; however, it
2559   will only be useful if both the client and server associate the name
2560   with the same protocol.
2561</t>
2562</section>
2563
2564<section title="Via" anchor="header.via">
2565  <iref primary="true" item="Via header" x:for-anchor=""/>
2566  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2567  <x:anchor-alias value="protocol-name"/>
2568  <x:anchor-alias value="protocol-version"/>
2569  <x:anchor-alias value="pseudonym"/>
2570  <x:anchor-alias value="received-by"/>
2571  <x:anchor-alias value="received-protocol"/>
2572  <x:anchor-alias value="Via"/>
2573  <x:anchor-alias value="Via-v"/>
2574<t>
2575   The general-header field "Via" &MUST; be used by gateways and proxies to
2576   indicate the intermediate protocols and recipients between the user
2577   agent and the server on requests, and between the origin server and
2578   the client on responses. It is analogous to the "Received" field defined in
2579   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2580   avoiding request loops, and identifying the protocol capabilities of
2581   all senders along the request/response chain.
2582</t>
2583<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2584  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2585  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2586                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2587  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2588  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2589  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2590  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2591  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2592</artwork></figure>
2593<t>
2594   The received-protocol indicates the protocol version of the message
2595   received by the server or client along each segment of the
2596   request/response chain. The received-protocol version is appended to
2597   the Via field value when the message is forwarded so that information
2598   about the protocol capabilities of upstream applications remains
2599   visible to all recipients.
2600</t>
2601<t>
2602   The protocol-name is optional if and only if it would be "HTTP". The
2603   received-by field is normally the host and optional port number of a
2604   recipient server or client that subsequently forwarded the message.
2605   However, if the real host is considered to be sensitive information,
2606   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2607   be assumed to be the default port of the received-protocol.
2608</t>
2609<t>
2610   Multiple Via field values represents each proxy or gateway that has
2611   forwarded the message. Each recipient &MUST; append its information
2612   such that the end result is ordered according to the sequence of
2613   forwarding applications.
2614</t>
2615<t>
2616   Comments &MAY; be used in the Via header field to identify the software
2617   of the recipient proxy or gateway, analogous to the User-Agent and
2618   Server header fields. However, all comments in the Via field are
2619   optional and &MAY; be removed by any recipient prior to forwarding the
2620   message.
2621</t>
2622<t>
2623   For example, a request message could be sent from an HTTP/1.0 user
2624   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2625   forward the request to a public proxy at p.example.net, which completes
2626   the request by forwarding it to the origin server at www.example.com.
2627   The request received by www.example.com would then have the following
2628   Via header field:
2629</t>
2630<figure><artwork type="example">
2631  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2632</artwork></figure>
2633<t>
2634   Proxies and gateways used as a portal through a network firewall
2635   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2636   the firewall region. This information &SHOULD; only be propagated if
2637   explicitly enabled. If not enabled, the received-by host of any host
2638   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2639   for that host.
2640</t>
2641<t>
2642   For organizations that have strong privacy requirements for hiding
2643   internal structures, a proxy &MAY; combine an ordered subsequence of
2644   Via header field entries with identical received-protocol values into
2645   a single such entry. For example,
2646</t>
2647<figure><artwork type="example">
2648  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2649</artwork></figure>
2650<t>
2651        could be collapsed to
2652</t>
2653<figure><artwork type="example">
2654  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2655</artwork></figure>
2656<t>
2657   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2658   under the same organizational control and the hosts have already been
2659   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2660   have different received-protocol values.
2661</t>
2662</section>
2663
2664</section>
2665
2666<section title="IANA Considerations" anchor="IANA.considerations">
2667<section title="Message Header Registration" anchor="message.header.registration">
2668<t>
2669   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2670   with the permanent registrations below (see <xref target="RFC3864"/>):
2671</t>
2672<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2673<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2674   <ttcol>Header Field Name</ttcol>
2675   <ttcol>Protocol</ttcol>
2676   <ttcol>Status</ttcol>
2677   <ttcol>Reference</ttcol>
2678
2679   <c>Connection</c>
2680   <c>http</c>
2681   <c>standard</c>
2682   <c>
2683      <xref target="header.connection"/>
2684   </c>
2685   <c>Content-Length</c>
2686   <c>http</c>
2687   <c>standard</c>
2688   <c>
2689      <xref target="header.content-length"/>
2690   </c>
2691   <c>Date</c>
2692   <c>http</c>
2693   <c>standard</c>
2694   <c>
2695      <xref target="header.date"/>
2696   </c>
2697   <c>Host</c>
2698   <c>http</c>
2699   <c>standard</c>
2700   <c>
2701      <xref target="header.host"/>
2702   </c>
2703   <c>TE</c>
2704   <c>http</c>
2705   <c>standard</c>
2706   <c>
2707      <xref target="header.te"/>
2708   </c>
2709   <c>Trailer</c>
2710   <c>http</c>
2711   <c>standard</c>
2712   <c>
2713      <xref target="header.trailer"/>
2714   </c>
2715   <c>Transfer-Encoding</c>
2716   <c>http</c>
2717   <c>standard</c>
2718   <c>
2719      <xref target="header.transfer-encoding"/>
2720   </c>
2721   <c>Upgrade</c>
2722   <c>http</c>
2723   <c>standard</c>
2724   <c>
2725      <xref target="header.upgrade"/>
2726   </c>
2727   <c>Via</c>
2728   <c>http</c>
2729   <c>standard</c>
2730   <c>
2731      <xref target="header.via"/>
2732   </c>
2733</texttable>
2734<!--(END)-->
2735<t>
2736   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2737</t>
2738</section>
2739
2740<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2741<t>
2742   The entry for the "http" URI Scheme in the registry located at
2743   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2744   should be updated to point to <xref target="http.uri"/> of this document
2745   (see <xref target="RFC4395"/>).
2746</t>
2747</section>
2748
2749<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2750<t>
2751   This document serves as the specification for the Internet media types
2752   "message/http" and "application/http". The following is to be registered with
2753   IANA (see <xref target="RFC4288"/>).
2754</t>
2755<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2756<iref item="Media Type" subitem="message/http" primary="true"/>
2757<iref item="message/http Media Type" primary="true"/>
2758<t>
2759   The message/http type can be used to enclose a single HTTP request or
2760   response message, provided that it obeys the MIME restrictions for all
2761   "message" types regarding line length and encodings.
2762</t>
2763<t>
2764  <list style="hanging" x:indent="12em">
2765    <t hangText="Type name:">
2766      message
2767    </t>
2768    <t hangText="Subtype name:">
2769      http
2770    </t>
2771    <t hangText="Required parameters:">
2772      none
2773    </t>
2774    <t hangText="Optional parameters:">
2775      version, msgtype
2776      <list style="hanging">
2777        <t hangText="version:">
2778          The HTTP-Version number of the enclosed message
2779          (e.g., "1.1"). If not present, the version can be
2780          determined from the first line of the body.
2781        </t>
2782        <t hangText="msgtype:">
2783          The message type -- "request" or "response". If not
2784          present, the type can be determined from the first
2785          line of the body.
2786        </t>
2787      </list>
2788    </t>
2789    <t hangText="Encoding considerations:">
2790      only "7bit", "8bit", or "binary" are permitted
2791    </t>
2792    <t hangText="Security considerations:">
2793      none
2794    </t>
2795    <t hangText="Interoperability considerations:">
2796      none
2797    </t>
2798    <t hangText="Published specification:">
2799      This specification (see <xref target="internet.media.type.message.http"/>).
2800    </t>
2801    <t hangText="Applications that use this media type:">
2802    </t>
2803    <t hangText="Additional information:">
2804      <list style="hanging">
2805        <t hangText="Magic number(s):">none</t>
2806        <t hangText="File extension(s):">none</t>
2807        <t hangText="Macintosh file type code(s):">none</t>
2808      </list>
2809    </t>
2810    <t hangText="Person and email address to contact for further information:">
2811      See Authors Section.
2812    </t>
2813                <t hangText="Intended usage:">
2814                  COMMON
2815    </t>
2816                <t hangText="Restrictions on usage:">
2817                  none
2818    </t>
2819    <t hangText="Author/Change controller:">
2820      IESG
2821    </t>
2822  </list>
2823</t>
2824</section>
2825<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2826<iref item="Media Type" subitem="application/http" primary="true"/>
2827<iref item="application/http Media Type" primary="true"/>
2828<t>
2829   The application/http type can be used to enclose a pipeline of one or more
2830   HTTP request or response messages (not intermixed).
2831</t>
2832<t>
2833  <list style="hanging" x:indent="12em">
2834    <t hangText="Type name:">
2835      application
2836    </t>
2837    <t hangText="Subtype name:">
2838      http
2839    </t>
2840    <t hangText="Required parameters:">
2841      none
2842    </t>
2843    <t hangText="Optional parameters:">
2844      version, msgtype
2845      <list style="hanging">
2846        <t hangText="version:">
2847          The HTTP-Version number of the enclosed messages
2848          (e.g., "1.1"). If not present, the version can be
2849          determined from the first line of the body.
2850        </t>
2851        <t hangText="msgtype:">
2852          The message type -- "request" or "response". If not
2853          present, the type can be determined from the first
2854          line of the body.
2855        </t>
2856      </list>
2857    </t>
2858    <t hangText="Encoding considerations:">
2859      HTTP messages enclosed by this type
2860      are in "binary" format; use of an appropriate
2861      Content-Transfer-Encoding is required when
2862      transmitted via E-mail.
2863    </t>
2864    <t hangText="Security considerations:">
2865      none
2866    </t>
2867    <t hangText="Interoperability considerations:">
2868      none
2869    </t>
2870    <t hangText="Published specification:">
2871      This specification (see <xref target="internet.media.type.application.http"/>).
2872    </t>
2873    <t hangText="Applications that use this media type:">
2874    </t>
2875    <t hangText="Additional information:">
2876      <list style="hanging">
2877        <t hangText="Magic number(s):">none</t>
2878        <t hangText="File extension(s):">none</t>
2879        <t hangText="Macintosh file type code(s):">none</t>
2880      </list>
2881    </t>
2882    <t hangText="Person and email address to contact for further information:">
2883      See Authors Section.
2884    </t>
2885                <t hangText="Intended usage:">
2886                  COMMON
2887    </t>
2888                <t hangText="Restrictions on usage:">
2889                  none
2890    </t>
2891    <t hangText="Author/Change controller:">
2892      IESG
2893    </t>
2894  </list>
2895</t>
2896</section>
2897</section>
2898
2899</section>
2900
2901<section title="Security Considerations" anchor="security.considerations">
2902<t>
2903   This section is meant to inform application developers, information
2904   providers, and users of the security limitations in HTTP/1.1 as
2905   described by this document. The discussion does not include
2906   definitive solutions to the problems revealed, though it does make
2907   some suggestions for reducing security risks.
2908</t>
2909
2910<section title="Personal Information" anchor="personal.information">
2911<t>
2912   HTTP clients are often privy to large amounts of personal information
2913   (e.g. the user's name, location, mail address, passwords, encryption
2914   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2915   leakage of this information.
2916   We very strongly recommend that a convenient interface be provided
2917   for the user to control dissemination of such information, and that
2918   designers and implementors be particularly careful in this area.
2919   History shows that errors in this area often create serious security
2920   and/or privacy problems and generate highly adverse publicity for the
2921   implementor's company.
2922</t>
2923</section>
2924
2925<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2926<t>
2927   A server is in the position to save personal data about a user's
2928   requests which might identify their reading patterns or subjects of
2929   interest. This information is clearly confidential in nature and its
2930   handling can be constrained by law in certain countries. People using
2931   HTTP to provide data are responsible for ensuring that
2932   such material is not distributed without the permission of any
2933   individuals that are identifiable by the published results.
2934</t>
2935</section>
2936
2937<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2938<t>
2939   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2940   the documents returned by HTTP requests to be only those that were
2941   intended by the server administrators. If an HTTP server translates
2942   HTTP URIs directly into file system calls, the server &MUST; take
2943   special care not to serve files that were not intended to be
2944   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2945   other operating systems use ".." as a path component to indicate a
2946   directory level above the current one. On such a system, an HTTP
2947   server &MUST; disallow any such construct in the request-target if it
2948   would otherwise allow access to a resource outside those intended to
2949   be accessible via the HTTP server. Similarly, files intended for
2950   reference only internally to the server (such as access control
2951   files, configuration files, and script code) &MUST; be protected from
2952   inappropriate retrieval, since they might contain sensitive
2953   information. Experience has shown that minor bugs in such HTTP server
2954   implementations have turned into security risks.
2955</t>
2956</section>
2957
2958<section title="DNS Spoofing" anchor="dns.spoofing">
2959<t>
2960   Clients using HTTP rely heavily on the Domain Name Service, and are
2961   thus generally prone to security attacks based on the deliberate
2962   mis-association of IP addresses and DNS names. Clients need to be
2963   cautious in assuming the continuing validity of an IP number/DNS name
2964   association.
2965</t>
2966<t>
2967   In particular, HTTP clients &SHOULD; rely on their name resolver for
2968   confirmation of an IP number/DNS name association, rather than
2969   caching the result of previous host name lookups. Many platforms
2970   already can cache host name lookups locally when appropriate, and
2971   they &SHOULD; be configured to do so. It is proper for these lookups to
2972   be cached, however, only when the TTL (Time To Live) information
2973   reported by the name server makes it likely that the cached
2974   information will remain useful.
2975</t>
2976<t>
2977   If HTTP clients cache the results of host name lookups in order to
2978   achieve a performance improvement, they &MUST; observe the TTL
2979   information reported by DNS.
2980</t>
2981<t>
2982   If HTTP clients do not observe this rule, they could be spoofed when
2983   a previously-accessed server's IP address changes. As network
2984   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2985   possibility of this form of attack will grow. Observing this
2986   requirement thus reduces this potential security vulnerability.
2987</t>
2988<t>
2989   This requirement also improves the load-balancing behavior of clients
2990   for replicated servers using the same DNS name and reduces the
2991   likelihood of a user's experiencing failure in accessing sites which
2992   use that strategy.
2993</t>
2994</section>
2995
2996<section title="Proxies and Caching" anchor="attack.proxies">
2997<t>
2998   By their very nature, HTTP proxies are men-in-the-middle, and
2999   represent an opportunity for man-in-the-middle attacks. Compromise of
3000   the systems on which the proxies run can result in serious security
3001   and privacy problems. Proxies have access to security-related
3002   information, personal information about individual users and
3003   organizations, and proprietary information belonging to users and
3004   content providers. A compromised proxy, or a proxy implemented or
3005   configured without regard to security and privacy considerations,
3006   might be used in the commission of a wide range of potential attacks.
3007</t>
3008<t>
3009   Proxy operators should protect the systems on which proxies run as
3010   they would protect any system that contains or transports sensitive
3011   information. In particular, log information gathered at proxies often
3012   contains highly sensitive personal information, and/or information
3013   about organizations. Log information should be carefully guarded, and
3014   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3015</t>
3016<t>
3017   Proxy implementors should consider the privacy and security
3018   implications of their design and coding decisions, and of the
3019   configuration options they provide to proxy operators (especially the
3020   default configuration).
3021</t>
3022<t>
3023   Users of a proxy need to be aware that they are no trustworthier than
3024   the people who run the proxy; HTTP itself cannot solve this problem.
3025</t>
3026<t>
3027   The judicious use of cryptography, when appropriate, may suffice to
3028   protect against a broad range of security and privacy attacks. Such
3029   cryptography is beyond the scope of the HTTP/1.1 specification.
3030</t>
3031</section>
3032
3033<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3034<t>
3035   They exist. They are hard to defend against. Research continues.
3036   Beware.
3037</t>
3038</section>
3039</section>
3040
3041<section title="Acknowledgments" anchor="ack">
3042<t>
3043   HTTP has evolved considerably over the years. It has
3044   benefited from a large and active developer community--the many
3045   people who have participated on the www-talk mailing list--and it is
3046   that community which has been most responsible for the success of
3047   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3048   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3049   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3050   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3051   VanHeyningen deserve special recognition for their efforts in
3052   defining early aspects of the protocol.
3053</t>
3054<t>
3055   This document has benefited greatly from the comments of all those
3056   participating in the HTTP-WG. In addition to those already mentioned,
3057   the following individuals have contributed to this specification:
3058</t>
3059<t>
3060   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3061   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3062   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3063   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3064   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3065   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3066   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3067   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3068   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3069   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3070   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3071   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3072   Josh Cohen.
3073</t>
3074<t>
3075   Thanks to the "cave men" of Palo Alto. You know who you are.
3076</t>
3077<t>
3078   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3079   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3080   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3081   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3082   Larry Masinter for their help. And thanks go particularly to Jeff
3083   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3084</t>
3085<t>
3086   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3087   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3088   discovery of many of the problems that this document attempts to
3089   rectify.
3090</t>
3091<t>
3092   This specification makes heavy use of the augmented BNF and generic
3093   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3094   reuses many of the definitions provided by Nathaniel Borenstein and
3095   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3096   specification will help reduce past confusion over the relationship
3097   between HTTP and Internet mail message formats.
3098</t>
3099</section>
3100
3101</middle>
3102<back>
3103
3104<references title="Normative References">
3105
3106<reference anchor="ISO-8859-1">
3107  <front>
3108    <title>
3109     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3110    </title>
3111    <author>
3112      <organization>International Organization for Standardization</organization>
3113    </author>
3114    <date year="1998"/>
3115  </front>
3116  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3117</reference>
3118
3119<reference anchor="Part2">
3120  <front>
3121    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3122    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3123      <organization abbrev="Day Software">Day Software</organization>
3124      <address><email>fielding@gbiv.com</email></address>
3125    </author>
3126    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3127      <organization>One Laptop per Child</organization>
3128      <address><email>jg@laptop.org</email></address>
3129    </author>
3130    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3131      <organization abbrev="HP">Hewlett-Packard Company</organization>
3132      <address><email>JeffMogul@acm.org</email></address>
3133    </author>
3134    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3135      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3136      <address><email>henrikn@microsoft.com</email></address>
3137    </author>
3138    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3139      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3140      <address><email>LMM@acm.org</email></address>
3141    </author>
3142    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3143      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3144      <address><email>paulle@microsoft.com</email></address>
3145    </author>
3146    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3147      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3148      <address><email>timbl@w3.org</email></address>
3149    </author>
3150    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3151      <organization abbrev="W3C">World Wide Web Consortium</organization>
3152      <address><email>ylafon@w3.org</email></address>
3153    </author>
3154    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3155      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3156      <address><email>julian.reschke@greenbytes.de</email></address>
3157    </author>
3158    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3159  </front>
3160  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3161  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3162</reference>
3163
3164<reference anchor="Part3">
3165  <front>
3166    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3167    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3168      <organization abbrev="Day Software">Day Software</organization>
3169      <address><email>fielding@gbiv.com</email></address>
3170    </author>
3171    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3172      <organization>One Laptop per Child</organization>
3173      <address><email>jg@laptop.org</email></address>
3174    </author>
3175    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3176      <organization abbrev="HP">Hewlett-Packard Company</organization>
3177      <address><email>JeffMogul@acm.org</email></address>
3178    </author>
3179    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3180      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3181      <address><email>henrikn@microsoft.com</email></address>
3182    </author>
3183    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3184      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3185      <address><email>LMM@acm.org</email></address>
3186    </author>
3187    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3188      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3189      <address><email>paulle@microsoft.com</email></address>
3190    </author>
3191    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3192      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3193      <address><email>timbl@w3.org</email></address>
3194    </author>
3195    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3196      <organization abbrev="W3C">World Wide Web Consortium</organization>
3197      <address><email>ylafon@w3.org</email></address>
3198    </author>
3199    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3200      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3201      <address><email>julian.reschke@greenbytes.de</email></address>
3202    </author>
3203    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3204  </front>
3205  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3206  <x:source href="p3-payload.xml" basename="p3-payload"/>
3207</reference>
3208
3209<reference anchor="Part5">
3210  <front>
3211    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3212    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3213      <organization abbrev="Day Software">Day Software</organization>
3214      <address><email>fielding@gbiv.com</email></address>
3215    </author>
3216    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3217      <organization>One Laptop per Child</organization>
3218      <address><email>jg@laptop.org</email></address>
3219    </author>
3220    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3221      <organization abbrev="HP">Hewlett-Packard Company</organization>
3222      <address><email>JeffMogul@acm.org</email></address>
3223    </author>
3224    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3225      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3226      <address><email>henrikn@microsoft.com</email></address>
3227    </author>
3228    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3229      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3230      <address><email>LMM@acm.org</email></address>
3231    </author>
3232    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3233      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3234      <address><email>paulle@microsoft.com</email></address>
3235    </author>
3236    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3237      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3238      <address><email>timbl@w3.org</email></address>
3239    </author>
3240    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3241      <organization abbrev="W3C">World Wide Web Consortium</organization>
3242      <address><email>ylafon@w3.org</email></address>
3243    </author>
3244    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3245      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3246      <address><email>julian.reschke@greenbytes.de</email></address>
3247    </author>
3248    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3249  </front>
3250  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3251  <x:source href="p5-range.xml" basename="p5-range"/>
3252</reference>
3253
3254<reference anchor="Part6">
3255  <front>
3256    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3257    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3258      <organization abbrev="Day Software">Day Software</organization>
3259      <address><email>fielding@gbiv.com</email></address>
3260    </author>
3261    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3262      <organization>One Laptop per Child</organization>
3263      <address><email>jg@laptop.org</email></address>
3264    </author>
3265    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3266      <organization abbrev="HP">Hewlett-Packard Company</organization>
3267      <address><email>JeffMogul@acm.org</email></address>
3268    </author>
3269    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3270      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3271      <address><email>henrikn@microsoft.com</email></address>
3272    </author>
3273    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3274      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3275      <address><email>LMM@acm.org</email></address>
3276    </author>
3277    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3278      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3279      <address><email>paulle@microsoft.com</email></address>
3280    </author>
3281    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3282      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3283      <address><email>timbl@w3.org</email></address>
3284    </author>
3285    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3286      <organization abbrev="W3C">World Wide Web Consortium</organization>
3287      <address><email>ylafon@w3.org</email></address>
3288    </author>
3289    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3290      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3291      <address><email>julian.reschke@greenbytes.de</email></address>
3292    </author>
3293    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3294  </front>
3295  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3296  <x:source href="p6-cache.xml" basename="p6-cache"/>
3297</reference>
3298
3299<reference anchor="RFC5234">
3300  <front>
3301    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3302    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3303      <organization>Brandenburg InternetWorking</organization>
3304      <address>
3305      <postal>
3306      <street>675 Spruce Dr.</street>
3307      <city>Sunnyvale</city>
3308      <region>CA</region>
3309      <code>94086</code>
3310      <country>US</country></postal>
3311      <phone>+1.408.246.8253</phone>
3312      <email>dcrocker@bbiw.net</email></address> 
3313    </author>
3314    <author initials="P." surname="Overell" fullname="Paul Overell">
3315      <organization>THUS plc.</organization>
3316      <address>
3317      <postal>
3318      <street>1/2 Berkeley Square</street>
3319      <street>99 Berkely Street</street>
3320      <city>Glasgow</city>
3321      <code>G3 7HR</code>
3322      <country>UK</country></postal>
3323      <email>paul.overell@thus.net</email></address>
3324    </author>
3325    <date month="January" year="2008"/>
3326  </front>
3327  <seriesInfo name="STD" value="68"/>
3328  <seriesInfo name="RFC" value="5234"/>
3329</reference>
3330
3331<reference anchor="RFC2045">
3332  <front>
3333    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3334    <author initials="N." surname="Freed" fullname="Ned Freed">
3335      <organization>Innosoft International, Inc.</organization>
3336      <address><email>ned@innosoft.com</email></address>
3337    </author>
3338    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3339      <organization>First Virtual Holdings</organization>
3340      <address><email>nsb@nsb.fv.com</email></address>
3341    </author>
3342    <date month="November" year="1996"/>
3343  </front>
3344  <seriesInfo name="RFC" value="2045"/>
3345</reference>
3346
3347<reference anchor="RFC2119">
3348  <front>
3349    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3350    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3351      <organization>Harvard University</organization>
3352      <address><email>sob@harvard.edu</email></address>
3353    </author>
3354    <date month="March" year="1997"/>
3355  </front>
3356  <seriesInfo name="BCP" value="14"/>
3357  <seriesInfo name="RFC" value="2119"/>
3358</reference>
3359
3360<reference anchor="RFC3986">
3361 <front>
3362  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3363  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3364    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3365    <address>
3366       <email>timbl@w3.org</email>
3367       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3368    </address>
3369  </author>
3370  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3371    <organization abbrev="Day Software">Day Software</organization>
3372    <address>
3373      <email>fielding@gbiv.com</email>
3374      <uri>http://roy.gbiv.com/</uri>
3375    </address>
3376  </author>
3377  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3378    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3379    <address>
3380      <email>LMM@acm.org</email>
3381      <uri>http://larry.masinter.net/</uri>
3382    </address>
3383  </author>
3384  <date month='January' year='2005'></date>
3385 </front>
3386 <seriesInfo name="RFC" value="3986"/>
3387 <seriesInfo name="STD" value="66"/>
3388</reference>
3389
3390<reference anchor="USASCII">
3391  <front>
3392    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3393    <author>
3394      <organization>American National Standards Institute</organization>
3395    </author>
3396    <date year="1986"/>
3397  </front>
3398  <seriesInfo name="ANSI" value="X3.4"/>
3399</reference>
3400
3401</references>
3402
3403<references title="Informative References">
3404
3405<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3406  <front>
3407    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3408    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3409      <organization/>
3410    </author>
3411    <author initials="J." surname="Gettys" fullname="J. Gettys">
3412      <organization/>
3413    </author>
3414    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3415      <organization/>
3416    </author>
3417    <author initials="H." surname="Lie" fullname="H. Lie">
3418      <organization/>
3419    </author>
3420    <author initials="C." surname="Lilley" fullname="C. Lilley">
3421      <organization/>
3422    </author>
3423    <date year="1997" month="September"/>
3424  </front>
3425  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3426</reference>
3427
3428<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3429  <front>
3430    <title>Improving HTTP Latency</title>
3431    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3432      <organization/>
3433    </author>
3434    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3435      <organization/>
3436    </author>
3437    <date year="1995" month="December"/>
3438  </front>
3439  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3440</reference>
3441
3442<reference anchor="RFC959">
3443  <front>
3444    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3445    <author initials="J." surname="Postel" fullname="J. Postel">
3446      <organization>Information Sciences Institute (ISI)</organization>
3447    </author>
3448    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3449      <organization/>
3450    </author>
3451    <date month="October" year="1985"/>
3452  </front>
3453  <seriesInfo name="STD" value="9"/>
3454  <seriesInfo name="RFC" value="959"/>
3455</reference>
3456
3457<reference anchor="RFC1123">
3458  <front>
3459    <title>Requirements for Internet Hosts - Application and Support</title>
3460    <author initials="R." surname="Braden" fullname="Robert Braden">
3461      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3462      <address><email>Braden@ISI.EDU</email></address>
3463    </author>
3464    <date month="October" year="1989"/>
3465  </front>
3466  <seriesInfo name="STD" value="3"/>
3467  <seriesInfo name="RFC" value="1123"/>
3468</reference>
3469
3470<reference anchor="RFC1305">
3471  <front>
3472    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3473    <author initials="D." surname="Mills" fullname="David L. Mills">
3474      <organization>University of Delaware, Electrical Engineering Department</organization>
3475      <address><email>mills@udel.edu</email></address>
3476    </author>
3477    <date month="March" year="1992"/>
3478  </front>
3479  <seriesInfo name="RFC" value="1305"/>
3480</reference>
3481
3482<reference anchor="RFC1436">
3483  <front>
3484    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3485    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3486      <organization>University of Minnesota, Computer and Information Services</organization>
3487      <address><email>fxa@boombox.micro.umn.edu</email></address>
3488    </author>
3489    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3490      <organization>University of Minnesota, Computer and Information Services</organization>
3491      <address><email>mpm@boombox.micro.umn.edu</email></address>
3492    </author>
3493    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3494      <organization>University of Minnesota, Computer and Information Services</organization>
3495      <address><email>lindner@boombox.micro.umn.edu</email></address>
3496    </author>
3497    <author initials="D." surname="Johnson" fullname="David Johnson">
3498      <organization>University of Minnesota, Computer and Information Services</organization>
3499      <address><email>dmj@boombox.micro.umn.edu</email></address>
3500    </author>
3501    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3502      <organization>University of Minnesota, Computer and Information Services</organization>
3503      <address><email>daniel@boombox.micro.umn.edu</email></address>
3504    </author>
3505    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3506      <organization>University of Minnesota, Computer and Information Services</organization>
3507      <address><email>alberti@boombox.micro.umn.edu</email></address>
3508    </author>
3509    <date month="March" year="1993"/>
3510  </front>
3511  <seriesInfo name="RFC" value="1436"/>
3512</reference>
3513
3514<reference anchor="RFC1900">
3515  <front>
3516    <title>Renumbering Needs Work</title>
3517    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3518      <organization>CERN, Computing and Networks Division</organization>
3519      <address><email>brian@dxcoms.cern.ch</email></address>
3520    </author>
3521    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3522      <organization>cisco Systems</organization>
3523      <address><email>yakov@cisco.com</email></address>
3524    </author>
3525    <date month="February" year="1996"/>
3526  </front>
3527  <seriesInfo name="RFC" value="1900"/>
3528</reference>
3529
3530<reference anchor="RFC1945">
3531  <front>
3532    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3533    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3534      <organization>MIT, Laboratory for Computer Science</organization>
3535      <address><email>timbl@w3.org</email></address>
3536    </author>
3537    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3538      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3539      <address><email>fielding@ics.uci.edu</email></address>
3540    </author>
3541    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3542      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3543      <address><email>frystyk@w3.org</email></address>
3544    </author>
3545    <date month="May" year="1996"/>
3546  </front>
3547  <seriesInfo name="RFC" value="1945"/>
3548</reference>
3549
3550<reference anchor="RFC2047">
3551  <front>
3552    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3553    <author initials="K." surname="Moore" fullname="Keith Moore">
3554      <organization>University of Tennessee</organization>
3555      <address><email>moore@cs.utk.edu</email></address>
3556    </author>
3557    <date month="November" year="1996"/>
3558  </front>
3559  <seriesInfo name="RFC" value="2047"/>
3560</reference>
3561
3562<reference anchor="RFC2068">
3563  <front>
3564    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3565    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3566      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3567      <address><email>fielding@ics.uci.edu</email></address>
3568    </author>
3569    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3570      <organization>MIT Laboratory for Computer Science</organization>
3571      <address><email>jg@w3.org</email></address>
3572    </author>
3573    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3574      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3575      <address><email>mogul@wrl.dec.com</email></address>
3576    </author>
3577    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3578      <organization>MIT Laboratory for Computer Science</organization>
3579      <address><email>frystyk@w3.org</email></address>
3580    </author>
3581    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3582      <organization>MIT Laboratory for Computer Science</organization>
3583      <address><email>timbl@w3.org</email></address>
3584    </author>
3585    <date month="January" year="1997"/>
3586  </front>
3587  <seriesInfo name="RFC" value="2068"/>
3588</reference>
3589
3590<reference anchor='RFC2109'>
3591  <front>
3592    <title>HTTP State Management Mechanism</title>
3593    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3594      <organization>Bell Laboratories, Lucent Technologies</organization>
3595      <address><email>dmk@bell-labs.com</email></address>
3596    </author>
3597    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3598      <organization>Netscape Communications Corp.</organization>
3599      <address><email>montulli@netscape.com</email></address>
3600    </author>
3601    <date year='1997' month='February' />
3602  </front>
3603  <seriesInfo name='RFC' value='2109' />
3604</reference>
3605
3606<reference anchor="RFC2145">
3607  <front>
3608    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3609    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3610      <organization>Western Research Laboratory</organization>
3611      <address><email>mogul@wrl.dec.com</email></address>
3612    </author>
3613    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3614      <organization>Department of Information and Computer Science</organization>
3615      <address><email>fielding@ics.uci.edu</email></address>
3616    </author>
3617    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3618      <organization>MIT Laboratory for Computer Science</organization>
3619      <address><email>jg@w3.org</email></address>
3620    </author>
3621    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3622      <organization>W3 Consortium</organization>
3623      <address><email>frystyk@w3.org</email></address>
3624    </author>
3625    <date month="May" year="1997"/>
3626  </front>
3627  <seriesInfo name="RFC" value="2145"/>
3628</reference>
3629
3630<reference anchor="RFC2616">
3631  <front>
3632    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3633    <author initials="R." surname="Fielding" fullname="R. Fielding">
3634      <organization>University of California, Irvine</organization>
3635      <address><email>fielding@ics.uci.edu</email></address>
3636    </author>
3637    <author initials="J." surname="Gettys" fullname="J. Gettys">
3638      <organization>W3C</organization>
3639      <address><email>jg@w3.org</email></address>
3640    </author>
3641    <author initials="J." surname="Mogul" fullname="J. Mogul">
3642      <organization>Compaq Computer Corporation</organization>
3643      <address><email>mogul@wrl.dec.com</email></address>
3644    </author>
3645    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3646      <organization>MIT Laboratory for Computer Science</organization>
3647      <address><email>frystyk@w3.org</email></address>
3648    </author>
3649    <author initials="L." surname="Masinter" fullname="L. Masinter">
3650      <organization>Xerox Corporation</organization>
3651      <address><email>masinter@parc.xerox.com</email></address>
3652    </author>
3653    <author initials="P." surname="Leach" fullname="P. Leach">
3654      <organization>Microsoft Corporation</organization>
3655      <address><email>paulle@microsoft.com</email></address>
3656    </author>
3657    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3658      <organization>W3C</organization>
3659      <address><email>timbl@w3.org</email></address>
3660    </author>
3661    <date month="June" year="1999"/>
3662  </front>
3663  <seriesInfo name="RFC" value="2616"/>
3664</reference>
3665
3666<reference anchor='RFC2818'>
3667  <front>
3668    <title>HTTP Over TLS</title>
3669    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3670      <organization>RTFM, Inc.</organization>
3671      <address><email>ekr@rtfm.com</email></address>
3672    </author>
3673    <date year='2000' month='May' />
3674  </front>
3675  <seriesInfo name='RFC' value='2818' />
3676</reference>
3677
3678<reference anchor='RFC2965'>
3679  <front>
3680    <title>HTTP State Management Mechanism</title>
3681    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3682      <organization>Bell Laboratories, Lucent Technologies</organization>
3683      <address><email>dmk@bell-labs.com</email></address>
3684    </author>
3685    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3686      <organization>Epinions.com, Inc.</organization>
3687      <address><email>lou@montulli.org</email></address>
3688    </author>
3689    <date year='2000' month='October' />
3690  </front>
3691  <seriesInfo name='RFC' value='2965' />
3692</reference>
3693
3694<reference anchor='RFC3864'>
3695  <front>
3696    <title>Registration Procedures for Message Header Fields</title>
3697    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3698      <organization>Nine by Nine</organization>
3699      <address><email>GK-IETF@ninebynine.org</email></address>
3700    </author>
3701    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3702      <organization>BEA Systems</organization>
3703      <address><email>mnot@pobox.com</email></address>
3704    </author>
3705    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3706      <organization>HP Labs</organization>
3707      <address><email>JeffMogul@acm.org</email></address>
3708    </author>
3709    <date year='2004' month='September' />
3710  </front>
3711  <seriesInfo name='BCP' value='90' />
3712  <seriesInfo name='RFC' value='3864' />
3713</reference>
3714
3715<reference anchor='RFC3977'>
3716  <front>
3717    <title>Network News Transfer Protocol (NNTP)</title>
3718    <author initials='C.' surname='Feather' fullname='C. Feather'>
3719      <organization>THUS plc</organization>
3720      <address><email>clive@demon.net</email></address>
3721    </author>
3722    <date year='2006' month='October' />
3723  </front>
3724  <seriesInfo name="RFC" value="3977"/>
3725</reference>
3726
3727<reference anchor="RFC4288">
3728  <front>
3729    <title>Media Type Specifications and Registration Procedures</title>
3730    <author initials="N." surname="Freed" fullname="N. Freed">
3731      <organization>Sun Microsystems</organization>
3732      <address>
3733        <email>ned.freed@mrochek.com</email>
3734      </address>
3735    </author>
3736    <author initials="J." surname="Klensin" fullname="J. Klensin">
3737      <organization/>
3738      <address>
3739        <email>klensin+ietf@jck.com</email>
3740      </address>
3741    </author>
3742    <date year="2005" month="December"/>
3743  </front>
3744  <seriesInfo name="BCP" value="13"/>
3745  <seriesInfo name="RFC" value="4288"/>
3746</reference>
3747
3748<reference anchor='RFC4395'>
3749  <front>
3750    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3751    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3752      <organization>AT&amp;T Laboratories</organization>
3753      <address>
3754        <email>tony+urireg@maillennium.att.com</email>
3755      </address>
3756    </author>
3757    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3758      <organization>Qualcomm, Inc.</organization>
3759      <address>
3760        <email>hardie@qualcomm.com</email>
3761      </address>
3762    </author>
3763    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3764      <organization>Adobe Systems</organization>
3765      <address>
3766        <email>LMM@acm.org</email>
3767      </address>
3768    </author>
3769    <date year='2006' month='February' />
3770  </front>
3771  <seriesInfo name='BCP' value='115' />
3772  <seriesInfo name='RFC' value='4395' />
3773</reference>
3774
3775<reference anchor="RFC5322">
3776  <front>
3777    <title>Internet Message Format</title>
3778    <author initials="P." surname="Resnick" fullname="P. Resnick">
3779      <organization>Qualcomm Incorporated</organization>
3780    </author>
3781    <date year="2008" month="October"/>
3782  </front> 
3783  <seriesInfo name="RFC" value="5322"/>
3784</reference>
3785
3786<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3787  <front>
3788    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3789    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3790      <organization/>
3791    </author>
3792    <date year="2001" month="November"/>
3793  </front>
3794  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3795</reference>
3796
3797<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3798  <front>
3799  <title>Analysis of HTTP Performance Problems</title>
3800  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3801    <organization/>
3802  </author>
3803  <date/>
3804  </front>
3805</reference>
3806
3807<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3808  <front>
3809  <title>Analysis of HTTP Performance</title>
3810  <author initials="J." surname="Touch" fullname="Joe Touch">
3811    <organization>USC/Information Sciences Institute</organization>
3812    <address><email>touch@isi.edu</email></address>
3813  </author>
3814  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3815    <organization>USC/Information Sciences Institute</organization>
3816    <address><email>johnh@isi.edu</email></address>
3817  </author>
3818  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3819    <organization>USC/Information Sciences Institute</organization>
3820    <address><email>katia@isi.edu</email></address>
3821  </author>
3822  <date year="1998" month="Aug"/>
3823  </front>
3824  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3825  <annotation>(original report dated Aug. 1996)</annotation>
3826</reference>
3827
3828<reference anchor="WAIS">
3829  <front>
3830    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3831    <author initials="F." surname="Davis" fullname="F. Davis">
3832      <organization>Thinking Machines Corporation</organization>
3833    </author>
3834    <author initials="B." surname="Kahle" fullname="B. Kahle">
3835      <organization>Thinking Machines Corporation</organization>
3836    </author>
3837    <author initials="H." surname="Morris" fullname="H. Morris">
3838      <organization>Thinking Machines Corporation</organization>
3839    </author>
3840    <author initials="J." surname="Salem" fullname="J. Salem">
3841      <organization>Thinking Machines Corporation</organization>
3842    </author>
3843    <author initials="T." surname="Shen" fullname="T. Shen">
3844      <organization>Thinking Machines Corporation</organization>
3845    </author>
3846    <author initials="R." surname="Wang" fullname="R. Wang">
3847      <organization>Thinking Machines Corporation</organization>
3848    </author>
3849    <author initials="J." surname="Sui" fullname="J. Sui">
3850      <organization>Thinking Machines Corporation</organization>
3851    </author>
3852    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3853      <organization>Thinking Machines Corporation</organization>
3854    </author>
3855    <date month="April" year="1990"/>
3856  </front>
3857  <seriesInfo name="Thinking Machines Corporation" value=""/>
3858</reference>
3859
3860</references>
3861
3862
3863<section title="Tolerant Applications" anchor="tolerant.applications">
3864<t>
3865   Although this document specifies the requirements for the generation
3866   of HTTP/1.1 messages, not all applications will be correct in their
3867   implementation. We therefore recommend that operational applications
3868   be tolerant of deviations whenever those deviations can be
3869   interpreted unambiguously.
3870</t>
3871<t>
3872   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3873   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3874   accept any amount of WSP characters between fields, even though
3875   only a single SP is required.
3876</t>
3877<t>
3878   The line terminator for message-header fields is the sequence CRLF.
3879   However, we recommend that applications, when parsing such headers,
3880   recognize a single LF as a line terminator and ignore the leading CR.
3881</t>
3882<t>
3883   The character set of an entity-body &SHOULD; be labeled as the lowest
3884   common denominator of the character codes used within that body, with
3885   the exception that not labeling the entity is preferred over labeling
3886   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3887</t>
3888<t>
3889   Additional rules for requirements on parsing and encoding of dates
3890   and other potential problems with date encodings include:
3891</t>
3892<t>
3893  <list style="symbols">
3894     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3895        which appears to be more than 50 years in the future is in fact
3896        in the past (this helps solve the "year 2000" problem).</t>
3897
3898     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3899        Expires date as earlier than the proper value, but &MUST-NOT;
3900        internally represent a parsed Expires date as later than the
3901        proper value.</t>
3902
3903     <t>All expiration-related calculations &MUST; be done in GMT. The
3904        local time zone &MUST-NOT; influence the calculation or comparison
3905        of an age or expiration time.</t>
3906
3907     <t>If an HTTP header incorrectly carries a date value with a time
3908        zone other than GMT, it &MUST; be converted into GMT using the
3909        most conservative possible conversion.</t>
3910  </list>
3911</t>
3912</section>
3913
3914<section title="Compatibility with Previous Versions" anchor="compatibility">
3915<t>
3916   HTTP has been in use by the World-Wide Web global information initiative
3917   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3918   was a simple protocol for hypertext data transfer across the Internet
3919   with only a single method and no metadata.
3920   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3921   methods and MIME-like messaging that could include metadata about the data
3922   transferred and modifiers on the request/response semantics. However,
3923   HTTP/1.0 did not sufficiently take into consideration the effects of
3924   hierarchical proxies, caching, the need for persistent connections, or
3925   name-based virtual hosts. The proliferation of incompletely-implemented
3926   applications calling themselves "HTTP/1.0" further necessitated a
3927   protocol version change in order for two communicating applications
3928   to determine each other's true capabilities.
3929</t>
3930<t>
3931   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3932   requirements that enable reliable implementations, adding only
3933   those new features that will either be safely ignored by an HTTP/1.0
3934   recipient or only sent when communicating with a party advertising
3935   compliance with HTTP/1.1.
3936</t>
3937<t>
3938   It is beyond the scope of a protocol specification to mandate
3939   compliance with previous versions. HTTP/1.1 was deliberately
3940   designed, however, to make supporting previous versions easy. It is
3941   worth noting that, at the time of composing this specification
3942   (1996), we would expect commercial HTTP/1.1 servers to:
3943  <list style="symbols">
3944     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3945        1.1 requests;</t>
3946
3947     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3948        1.1;</t>
3949
3950     <t>respond appropriately with a message in the same major version
3951        used by the client.</t>
3952  </list>
3953</t>
3954<t>
3955   And we would expect HTTP/1.1 clients to:
3956  <list style="symbols">
3957     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3958        responses;</t>
3959
3960     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3961        1.1.</t>
3962  </list>
3963</t>
3964<t>
3965   For most implementations of HTTP/1.0, each connection is established
3966   by the client prior to the request and closed by the server after
3967   sending the response. Some implementations implement the Keep-Alive
3968   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3969</t>
3970
3971<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3972<t>
3973   This section summarizes major differences between versions HTTP/1.0
3974   and HTTP/1.1.
3975</t>
3976
3977<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">
3978<t>
3979   The requirements that clients and servers support the Host request-header,
3980   report an error if the Host request-header (<xref target="header.host"/>) is
3981   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3982   are among the most important changes defined by this
3983   specification.
3984</t>
3985<t>
3986   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3987   addresses and servers; there was no other established mechanism for
3988   distinguishing the intended server of a request than the IP address
3989   to which that request was directed. The changes outlined above will
3990   allow the Internet, once older HTTP clients are no longer common, to
3991   support multiple Web sites from a single IP address, greatly
3992   simplifying large operational Web servers, where allocation of many
3993   IP addresses to a single host has created serious problems. The
3994   Internet will also be able to recover the IP addresses that have been
3995   allocated for the sole purpose of allowing special-purpose domain
3996   names to be used in root-level HTTP URLs. Given the rate of growth of
3997   the Web, and the number of servers already deployed, it is extremely
3998   important that all implementations of HTTP (including updates to
3999   existing HTTP/1.0 applications) correctly implement these
4000   requirements:
4001  <list style="symbols">
4002     <t>Both clients and servers &MUST; support the Host request-header.</t>
4003
4004     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4005
4006     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4007        request does not include a Host request-header.</t>
4008
4009     <t>Servers &MUST; accept absolute URIs.</t>
4010  </list>
4011</t>
4012</section>
4013</section>
4014
4015<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4016<t>
4017   Some clients and servers might wish to be compatible with some
4018   previous implementations of persistent connections in HTTP/1.0
4019   clients and servers. Persistent connections in HTTP/1.0 are
4020   explicitly negotiated as they are not the default behavior. HTTP/1.0
4021   experimental implementations of persistent connections are faulty,
4022   and the new facilities in HTTP/1.1 are designed to rectify these
4023   problems. The problem was that some existing 1.0 clients may be
4024   sending Keep-Alive to a proxy server that doesn't understand
4025   Connection, which would then erroneously forward it to the next
4026   inbound server, which would establish the Keep-Alive connection and
4027   result in a hung HTTP/1.0 proxy waiting for the close on the
4028   response. The result is that HTTP/1.0 clients must be prevented from
4029   using Keep-Alive when talking to proxies.
4030</t>
4031<t>
4032   However, talking to proxies is the most important use of persistent
4033   connections, so that prohibition is clearly unacceptable. Therefore,
4034   we need some other mechanism for indicating a persistent connection
4035   is desired, which is safe to use even when talking to an old proxy
4036   that ignores Connection. Persistent connections are the default for
4037   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4038   declaring non-persistence. See <xref target="header.connection"/>.
4039</t>
4040<t>
4041   The original HTTP/1.0 form of persistent connections (the Connection:
4042   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4043</t>
4044</section>
4045
4046<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4047<t>
4048   This specification has been carefully audited to correct and
4049   disambiguate key word usage; RFC 2068 had many problems in respect to
4050   the conventions laid out in <xref target="RFC2119"/>.
4051</t>
4052<t>
4053   Transfer-coding and message lengths all interact in ways that
4054   required fixing exactly when chunked encoding is used (to allow for
4055   transfer encoding that may not be self delimiting); it was important
4056   to straighten out exactly how message lengths are computed. (Sections
4057   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4058   <xref target="header.content-length" format="counter"/>,
4059   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4060</t>
4061<t>
4062   The use and interpretation of HTTP version numbers has been clarified
4063   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4064   version they support to deal with problems discovered in HTTP/1.0
4065   implementations (<xref target="http.version"/>)
4066</t>
4067<t>
4068   Transfer-coding had significant problems, particularly with
4069   interactions with chunked encoding. The solution is that transfer-codings
4070   become as full fledged as content-codings. This involves
4071   adding an IANA registry for transfer-codings (separate from content
4072   codings), a new header field (TE) and enabling trailer headers in the
4073   future. Transfer encoding is a major performance benefit, so it was
4074   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4075   interoperability problem that could have occurred due to interactions
4076   between authentication trailers, chunked encoding and HTTP/1.0
4077   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4078   and <xref target="header.te" format="counter"/>)
4079</t>
4080</section>
4081
4082<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4083<t>
4084  Rules about implicit linear white space between certain grammar productions
4085  have been removed; now it's only allowed when specifically pointed out
4086  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4087  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4088  Non-ASCII content in header fields and reason phrase has been obsoleted and
4089  made opaque (the TEXT rule was removed)
4090  (<xref target="basic.rules"/>)
4091</t>
4092<t>
4093  Clarify that HTTP-Version is case sensitive.
4094  (<xref target="http.version"/>)
4095</t>
4096<t>
4097  Remove reference to non-existant identity transfer-coding value tokens.
4098  (Sections <xref format="counter" target="transfer.codings"/> and
4099  <xref format="counter" target="message.length"/>)
4100</t>
4101<t>
4102  Clarification that the chunk length does not include
4103  the count of the octets in the chunk header and trailer.
4104  (<xref target="chunked.transfer.encoding"/>)
4105</t>
4106<t>
4107  Require that invalid whitespace around field-names be rejected.
4108  (<xref target="message.headers"/>)
4109</t>
4110<t>
4111  Update use of abs_path production from RFC1808 to the path-absolute + query
4112  components of RFC3986.
4113  (<xref target="request-target"/>)
4114</t>
4115<t>
4116  Clarify exactly when close connection options must be sent.
4117  (<xref target="header.connection"/>)
4118</t>
4119</section>
4120</section>
4121
4122<section title="Terminology" anchor="terminology">
4123<t>
4124   This specification uses a number of terms to refer to the roles
4125   played by participants in, and objects of, the HTTP communication.
4126</t>
4127<t>
4128  <iref item="connection"/>
4129  <x:dfn>connection</x:dfn>
4130  <list>
4131    <t>
4132      A transport layer virtual circuit established between two programs
4133      for the purpose of communication.
4134    </t>
4135  </list>
4136</t>
4137<t>
4138  <iref item="message"/>
4139  <x:dfn>message</x:dfn>
4140  <list>
4141    <t>
4142      The basic unit of HTTP communication, consisting of a structured
4143      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4144      transmitted via the connection.
4145    </t>
4146  </list>
4147</t>
4148<t>
4149  <iref item="request"/>
4150  <x:dfn>request</x:dfn>
4151  <list>
4152    <t>
4153      An HTTP request message, as defined in <xref target="request"/>.
4154    </t>
4155  </list>
4156</t>
4157<t>
4158  <iref item="response"/>
4159  <x:dfn>response</x:dfn>
4160  <list>
4161    <t>
4162      An HTTP response message, as defined in <xref target="response"/>.
4163    </t>
4164  </list>
4165</t>
4166<t>
4167  <iref item="resource"/>
4168  <x:dfn>resource</x:dfn>
4169  <list>
4170    <t>
4171      A network data object or service that can be identified by a URI,
4172      as defined in <xref target="uri"/>. Resources may be available in multiple
4173      representations (e.g. multiple languages, data formats, size, and
4174      resolutions) or vary in other ways.
4175    </t>
4176  </list>
4177</t>
4178<t>
4179  <iref item="entity"/>
4180  <x:dfn>entity</x:dfn>
4181  <list>
4182    <t>
4183      The information transferred as the payload of a request or
4184      response. An entity consists of metainformation in the form of
4185      entity-header fields and content in the form of an entity-body, as
4186      described in &entity;.
4187    </t>
4188  </list>
4189</t>
4190<t>
4191  <iref item="representation"/>
4192  <x:dfn>representation</x:dfn>
4193  <list>
4194    <t>
4195      An entity included with a response that is subject to content
4196      negotiation, as described in &content.negotiation;. There may exist multiple
4197      representations associated with a particular response status.
4198    </t>
4199  </list>
4200</t>
4201<t>
4202  <iref item="content negotiation"/>
4203  <x:dfn>content negotiation</x:dfn>
4204  <list>
4205    <t>
4206      The mechanism for selecting the appropriate representation when
4207      servicing a request, as described in &content.negotiation;. The
4208      representation of entities in any response can be negotiated
4209      (including error responses).
4210    </t>
4211  </list>
4212</t>
4213<t>
4214  <iref item="variant"/>
4215  <x:dfn>variant</x:dfn>
4216  <list>
4217    <t>
4218      A resource may have one, or more than one, representation(s)
4219      associated with it at any given instant. Each of these
4220      representations is termed a `variant'.  Use of the term `variant'
4221      does not necessarily imply that the resource is subject to content
4222      negotiation.
4223    </t>
4224  </list>
4225</t>
4226<t>
4227  <iref item="client"/>
4228  <x:dfn>client</x:dfn>
4229  <list>
4230    <t>
4231      A program that establishes connections for the purpose of sending
4232      requests.
4233    </t>
4234  </list>
4235</t>
4236<t>
4237  <iref item="user agent"/>
4238  <x:dfn>user agent</x:dfn>
4239  <list>
4240    <t>
4241      The client which initiates a request. These are often browsers,
4242      editors, spiders (web-traversing robots), or other end user tools.
4243    </t>
4244  </list>
4245</t>
4246<t>
4247  <iref item="server"/>
4248  <x:dfn>server</x:dfn>
4249  <list>
4250    <t>
4251      An application program that accepts connections in order to
4252      service requests by sending back responses. Any given program may
4253      be capable of being both a client and a server; our use of these
4254      terms refers only to the role being performed by the program for a
4255      particular connection, rather than to the program's capabilities
4256      in general. Likewise, any server may act as an origin server,
4257      proxy, gateway, or tunnel, switching behavior based on the nature
4258      of each request.
4259    </t>
4260  </list>
4261</t>
4262<t>
4263  <iref item="origin server"/>
4264  <x:dfn>origin server</x:dfn>
4265  <list>
4266    <t>
4267      The server on which a given resource resides or is to be created.
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  <iref item="proxy"/>
4273  <x:dfn>proxy</x:dfn>
4274  <list>
4275    <t>
4276      An intermediary program which acts as both a server and a client
4277      for the purpose of making requests on behalf of other clients.
4278      Requests are serviced internally or by passing them on, with
4279      possible translation, to other servers. A proxy &MUST; implement
4280      both the client and server requirements of this specification. A
4281      "transparent proxy" is a proxy that does not modify the request or
4282      response beyond what is required for proxy authentication and
4283      identification. A "non-transparent proxy" is a proxy that modifies
4284      the request or response in order to provide some added service to
4285      the user agent, such as group annotation services, media type
4286      transformation, protocol reduction, or anonymity filtering. Except
4287      where either transparent or non-transparent behavior is explicitly
4288      stated, the HTTP proxy requirements apply to both types of
4289      proxies.
4290    </t>
4291  </list>
4292</t>
4293<t>
4294  <iref item="gateway"/>
4295  <x:dfn>gateway</x:dfn>
4296  <list>
4297    <t>
4298      A server which acts as an intermediary for some other server.
4299      Unlike a proxy, a gateway receives requests as if it were the
4300      origin server for the requested resource; the requesting client
4301      may not be aware that it is communicating with a gateway.
4302    </t>
4303  </list>
4304</t>
4305<t>
4306  <iref item="tunnel"/>
4307  <x:dfn>tunnel</x:dfn>
4308  <list>
4309    <t>
4310      An intermediary program which is acting as a blind relay between
4311      two connections. Once active, a tunnel is not considered a party
4312      to the HTTP communication, though the tunnel may have been
4313      initiated by an HTTP request. The tunnel ceases to exist when both
4314      ends of the relayed connections are closed.
4315    </t>
4316  </list>
4317</t>
4318<t>
4319  <iref item="cache"/>
4320  <x:dfn>cache</x:dfn>
4321  <list>
4322    <t>
4323      A program's local store of response messages and the subsystem
4324      that controls its message storage, retrieval, and deletion. A
4325      cache stores cacheable responses in order to reduce the response
4326      time and network bandwidth consumption on future, equivalent
4327      requests. Any client or server may include a cache, though a cache
4328      cannot be used by a server that is acting as a tunnel.
4329    </t>
4330  </list>
4331</t>
4332<t>
4333  <iref item="cacheable"/>
4334  <x:dfn>cacheable</x:dfn>
4335  <list>
4336    <t>
4337      A response is cacheable if a cache is allowed to store a copy of
4338      the response message for use in answering subsequent requests. The
4339      rules for determining the cacheability of HTTP responses are
4340      defined in &caching;. Even if a resource is cacheable, there may
4341      be additional constraints on whether a cache can use the cached
4342      copy for a particular request.
4343    </t>
4344  </list>
4345</t>
4346<t>
4347  <iref item="upstream"/>
4348  <iref item="downstream"/>
4349  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4350  <list>
4351    <t>
4352      Upstream and downstream describe the flow of a message: all
4353      messages flow from upstream to downstream.
4354    </t>
4355  </list>
4356</t>
4357<t>
4358  <iref item="inbound"/>
4359  <iref item="outbound"/>
4360  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4361  <list>
4362    <t>
4363      Inbound and outbound refer to the request and response paths for
4364      messages: "inbound" means "traveling toward the origin server",
4365      and "outbound" means "traveling toward the user agent"
4366    </t>
4367  </list>
4368</t>
4369</section>
4370
4371<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4372
4373<section title="Since RFC2616">
4374<t>
4375  Extracted relevant partitions from <xref target="RFC2616"/>.
4376</t>
4377</section>
4378
4379<section title="Since draft-ietf-httpbis-p1-messaging-00">
4380<t>
4381  Closed issues:
4382  <list style="symbols"> 
4383    <t>
4384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4385      "HTTP Version should be case sensitive"
4386      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4387    </t>
4388    <t>
4389      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4390      "'unsafe' characters"
4391      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4392    </t>
4393    <t>
4394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4395      "Chunk Size Definition"
4396      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4400      "Message Length"
4401      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4402    </t>
4403    <t>
4404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4405      "Media Type Registrations"
4406      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4407    </t>
4408    <t>
4409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4410      "URI includes query"
4411      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4412    </t>
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4415      "No close on 1xx responses"
4416      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4417    </t>
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4420      "Remove 'identity' token references"
4421      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4422    </t>
4423    <t>
4424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4425      "Import query BNF"
4426    </t>
4427    <t>
4428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4429      "qdtext BNF"
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4433      "Normative and Informative references"
4434    </t>
4435    <t>
4436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4437      "RFC2606 Compliance"
4438    </t>
4439    <t>
4440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4441      "RFC977 reference"
4442    </t>
4443    <t>
4444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4445      "RFC1700 references"
4446    </t>
4447    <t>
4448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4449      "inconsistency in date format explanation"
4450    </t>
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4453      "Date reference typo"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4457      "Informative references"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4461      "ISO-8859-1 Reference"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4465      "Normative up-to-date references"
4466    </t>
4467  </list>
4468</t>
4469<t>
4470  Other changes:
4471  <list style="symbols"> 
4472    <t>
4473      Update media type registrations to use RFC4288 template.
4474    </t>
4475    <t>
4476      Use names of RFC4234 core rules DQUOTE and WSP,
4477      fix broken ABNF for chunk-data
4478      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4479    </t>
4480  </list>
4481</t>
4482</section>
4483
4484<section title="Since draft-ietf-httpbis-p1-messaging-01">
4485<t>
4486  Closed issues:
4487  <list style="symbols"> 
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4490      "Bodies on GET (and other) requests"
4491    </t>
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4494      "Updating to RFC4288"
4495    </t>
4496    <t>
4497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4498      "Status Code and Reason Phrase"
4499    </t>
4500    <t>
4501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4502      "rel_path not used"
4503    </t>
4504  </list>
4505</t>
4506<t>
4507  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4508  <list style="symbols"> 
4509    <t>
4510      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4511      "trailer-part").
4512    </t>
4513    <t>
4514      Avoid underscore character in rule names ("http_URL" ->
4515      "http-URL", "abs_path" -> "path-absolute").
4516    </t>
4517    <t>
4518      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4519      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4520      have to be updated when switching over to RFC3986.
4521    </t>
4522    <t>
4523      Synchronize core rules with RFC5234.
4524    </t>
4525    <t>
4526      Get rid of prose rules that span multiple lines.
4527    </t>
4528    <t>
4529      Get rid of unused rules LOALPHA and UPALPHA.
4530    </t>
4531    <t>
4532      Move "Product Tokens" section (back) into Part 1, as "token" is used
4533      in the definition of the Upgrade header.
4534    </t>
4535    <t>
4536      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4537    </t>
4538    <t>
4539      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4540    </t>
4541  </list>
4542</t>
4543</section>
4544
4545<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4546<t>
4547  Closed issues:
4548  <list style="symbols"> 
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4551      "HTTP-date vs. rfc1123-date"
4552    </t>
4553    <t>
4554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4555      "WS in quoted-pair"
4556    </t>
4557  </list>
4558</t>
4559<t>
4560  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4561  <list style="symbols"> 
4562    <t>
4563      Reference RFC 3984, and update header registrations for headers defined
4564      in this document.
4565    </t>
4566  </list>
4567</t>
4568<t>
4569  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4570  <list style="symbols"> 
4571    <t>
4572      Replace string literals when the string really is case-sensitive (HTTP-Version).
4573    </t>
4574  </list>
4575</t>
4576</section>
4577
4578<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4579<t>
4580  Closed issues:
4581  <list style="symbols"> 
4582    <t>
4583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4584      "Connection closing"
4585    </t>
4586    <t>
4587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4588      "Move registrations and registry information to IANA Considerations"
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4592      "need new URL for PAD1995 reference"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4596      "IANA Considerations: update HTTP URI scheme registration"
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4600      "Cite HTTPS URI scheme definition"
4601    </t>
4602    <t>
4603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4604      "List-type headers vs Set-Cookie"
4605    </t>
4606  </list>
4607</t>
4608<t>
4609  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4610  <list style="symbols"> 
4611    <t>
4612      Replace string literals when the string really is case-sensitive (HTTP-Date).
4613    </t>
4614    <t>
4615      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4616    </t>
4617  </list>
4618</t>
4619</section>
4620
4621<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4622<t>
4623  Closed issues:
4624  <list style="symbols"> 
4625    <t>
4626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4627      "Out-of-date reference for URIs"
4628    </t>
4629    <t>
4630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4631      "RFC 2822 is updated by RFC 5322"
4632    </t>
4633  </list>
4634</t>
4635<t>
4636  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4637  <list style="symbols"> 
4638    <t>
4639      Use "/" instead of "|" for alternatives.
4640    </t>
4641    <t>
4642      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4643    </t>
4644    <t>
4645      Only reference RFC 5234's core rules.
4646    </t>
4647    <t>
4648      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4649      whitespace ("OWS") and required whitespace ("RWS").
4650    </t>
4651    <t>
4652      Rewrite ABNFs to spell out whitespace rules, factor out
4653      header value format definitions.
4654    </t>
4655  </list>
4656</t>
4657</section>
4658
4659<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4660<t>
4661  Closed issues:
4662  <list style="symbols"> 
4663    <t>
4664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4665      "Header LWS"
4666    </t>
4667    <t>
4668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4669      "RFC2047 encoded words"
4670    </t>
4671    <t>
4672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4673      "Character Encodings in TEXT"
4674    </t>
4675    <t>
4676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4677      "Line Folding"
4678    </t>
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4681      "Reason-Phrase BNF"
4682    </t>
4683    <t>
4684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4685      "Use of TEXT"
4686    </t>
4687    <t>
4688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4689      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4690    </t>
4691    <t>
4692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4693      "RFC822 reference left in discussion of date formats"
4694    </t>
4695  </list>
4696</t>
4697<t>
4698  Other changes:
4699  <list style="symbols"> 
4700    <t>
4701      Rewrite introduction; add mostly new Architecture Section.
4702    </t>
4703  </list>
4704</t>
4705</section>
4706
4707</section>
4708
4709</back>
4710</rfc>
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