source: draft-ietf-httpbis/latest/p1-messaging.xml @ 538

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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 "March">
16  <!ENTITY ID-YEAR "2009">
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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x='http://purl.org/net/xml2rfc/ext'>
54<front>
55
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
57
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email>fielding@gbiv.com</email>
71      <uri>http://roy.gbiv.com/</uri>
72    </address>
73  </author>
74
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization>One Laptop per Child</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email>jg@laptop.org</email>
86      <uri>http://www.laptop.org/</uri>
87    </address>
88  </author>
89 
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email>JeffMogul@acm.org</email>
102    </address>
103  </author>
104
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email>henrikn@microsoft.com</email>
116    </address>
117  </author>
118
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email>LMM@acm.org</email>
130      <uri>http://larry.masinter.net/</uri>
131    </address>
132  </author>
133 
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email>paulle@microsoft.com</email>
144    </address>
145  </author>
146   
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email>timbl@w3.org</email>
160      <uri>http://www.w3.org/People/Berners-Lee/</uri>
161    </address>
162  </author>
163
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email>ylafon@w3.org</email>
176      <uri>http://www.raubacapeu.net/people/yves/</uri>
177    </address>
178  </author>
179
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>   
189      <facsimile>+49 251 2807761</facsimile>   
190      <email>julian.reschke@greenbytes.de</email>       
191      <uri>http://greenbytes.de/tech/webdav/</uri>     
192    </address>
193  </author>
194
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
197
198<abstract>
199<t>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.05"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate resource targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
238   between HTTP and MIME messages).
239</t>
240<t>
241   HTTP is a generic interface protocol for informations systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
250</t>
251<t>
252   HTTP is also designed for use as a generic protocol for translating
253   communication to and from other Internet information systems, such as
254   USENET news services via NNTP <xref target="RFC3977"/>,
255   file services via FTP <xref target="RFC959"/>,
256   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
257   HTTP proxies and gateways provide access to alternative information
258   services by translating their diverse protocols into a hypertext
259   format that can be viewed and manipulated by clients in the same way
260   as HTTP services.
261</t>
262<t>
263   One consequence of HTTP flexibility is that the protocol cannot be defined
264   in terms of what occurs behind the interface. Instead, we are
265   limited to defining the syntax of communication, the intent
266   of received communication, and the expected behavior of recipients. If
267   the communication is considered in isolation, then successful actions
268   should be reflected in the observable interface provided by servers.
269   However, since many clients are potentially acting in parallel and
270   perhaps at cross-purposes, it would be meaningless to require that such
271   behavior be observable.
272</t>
273<t>
274   This document is Part 1 of the seven-part specification of HTTP,
275   defining the protocol referred to as "HTTP/1.1" and obsoleting
276   <xref target="RFC2616"/>.
277   Part 1 defines the URI schemes specific to HTTP-based resources, overall
278   network operation, transport protocol connection management, and HTTP
279   message framing and forwarding requirements.
280   Our goal is to define all of the mechanisms necessary for HTTP message
281   handling that are independent of message semantics, thereby defining the
282   complete set of requirements for a message parser and transparent
283   message-forwarding intermediaries.
284</t>
285
286<section title="Requirements" anchor="intro.requirements">
287<t>
288   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
289   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
290   document are to be interpreted as described in <xref target="RFC2119"/>.
291</t>
292<t>
293   An implementation is not compliant if it fails to satisfy one or more
294   of the &MUST; or &REQUIRED; level requirements for the protocols it
295   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
296   level and all the &SHOULD; level requirements for its protocols is said
297   to be "unconditionally compliant"; one that satisfies all the &MUST;
298   level requirements but not all the &SHOULD; level requirements for its
299   protocols is said to be "conditionally compliant."
300</t>
301</section>
302
303<section title="Syntax Notation" anchor="notation">
304<iref primary="true" item="Grammar" subitem="ALPHA"/>
305<iref primary="true" item="Grammar" subitem="CR"/>
306<iref primary="true" item="Grammar" subitem="CRLF"/>
307<iref primary="true" item="Grammar" subitem="CTL"/>
308<iref primary="true" item="Grammar" subitem="DIGIT"/>
309<iref primary="true" item="Grammar" subitem="DQUOTE"/>
310<iref primary="true" item="Grammar" subitem="HEXDIG"/>
311<iref primary="true" item="Grammar" subitem="LF"/>
312<iref primary="true" item="Grammar" subitem="OCTET"/>
313<iref primary="true" item="Grammar" subitem="SP"/>
314<iref primary="true" item="Grammar" subitem="VCHAR"/>
315<iref primary="true" item="Grammar" subitem="WSP"/>
316<t anchor="core.rules">
317  <x:anchor-alias value="ALPHA"/>
318  <x:anchor-alias value="CTL"/>
319  <x:anchor-alias value="CR"/>
320  <x:anchor-alias value="CRLF"/>
321  <x:anchor-alias value="DIGIT"/>
322  <x:anchor-alias value="DQUOTE"/>
323  <x:anchor-alias value="HEXDIG"/>
324  <x:anchor-alias value="LF"/>
325  <x:anchor-alias value="OCTET"/>
326  <x:anchor-alias value="SP"/>
327  <x:anchor-alias value="VCHAR"/>
328  <x:anchor-alias value="WSP"/>
329   This specification uses the Augmented Backus-Naur Form (ABNF) notation
330   of <xref target="RFC5234"/>.  The following core rules are included by
331   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
332   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
333   DIGIT (decimal 0-9), DQUOTE (double quote),
334   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
335   OCTET (any 8-bit sequence of data), SP (space),
336   VCHAR (any visible <xref target="USASCII"/> character),
337   and WSP (whitespace).
338</t>
339
340<section title="ABNF Extension: #rule" anchor="notation.abnf">
341  <t>
342    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
343    improve readability.
344  </t>
345  <t>
346    A construct "#" is defined, similar to "*", for defining lists of
347    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
348    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
349    (",") and optional whitespace (OWS).   
350  </t>
351  <figure><preamble>
352    Thus,
353</preamble><artwork type="example">
354  1#element =&gt; element *( OWS "," OWS element )
355</artwork></figure>
356  <figure><preamble>
357    and:
358</preamble><artwork type="example">
359  #element =&gt; [ 1#element ]
360</artwork></figure>
361  <figure><preamble>
362    and for n &gt;= 1 and m &gt; 1:
363</preamble><artwork type="example">
364  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
365</artwork></figure>
366  <t>
367    For compatibility with legacy list rules, recipients &SHOULD; accept empty
368    list elements. In other words, consumers would follow the list productions:
369  </t>
370<figure><artwork type="example">
371  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
372 
373  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
374</artwork></figure> 
375<t>
376  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
377  expanded as explained above.
378</t>
379</section>
380
381<section title="Basic Rules" anchor="basic.rules">
382<t anchor="rule.CRLF">
383  <x:anchor-alias value="CRLF"/>
384   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
385   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
386   tolerant applications). The end-of-line marker within an entity-body
387   is defined by its associated media type, as described in &media-types;.
388</t>
389<t anchor="rule.LWS">
390   This specification uses three rules to denote the use of linear
391   whitespace: OWS (optional whitespace), RWS (required whitespace), and
392   BWS ("bad" whitespace).
393</t>
394<t>
395   The OWS rule is used where zero or more linear whitespace characters may
396   appear. OWS &SHOULD; either not be produced or be produced as a single SP
397   character. Multiple OWS characters that occur within field-content &SHOULD;
398   be replaced with a single SP before interpreting the field value or
399   forwarding the message downstream.
400</t>
401<t>
402   RWS is used when at least one linear whitespace character is required to
403   separate field tokens. RWS &SHOULD; be produced as a single SP character.
404   Multiple RWS characters that occur within field-content &SHOULD; be
405   replaced with a single SP before interpreting the field value or
406   forwarding the message downstream.
407</t>
408<t>
409   BWS is used where the grammar allows optional whitespace for historical
410   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
411   recipients &MUST; accept such bad optional whitespace and remove it before
412   interpreting the field value or forwarding the message downstream.
413</t>
414<t anchor="rule.whitespace">
415  <x:anchor-alias value="BWS"/>
416  <x:anchor-alias value="OWS"/>
417  <x:anchor-alias value="RWS"/>
418  <x:anchor-alias value="obs-fold"/>
419</t>
420<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"/>
421  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
422                 ; "optional" whitespace
423  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
424                 ; "required" whitespace
425  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
426                 ; "bad" whitespace
427  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
428                 ; see <xref target="message.headers"/>
429</artwork></figure>
430<t anchor="rule.token.separators">
431  <x:anchor-alias value="tchar"/>
432  <x:anchor-alias value="token"/>
433   Many HTTP/1.1 header field values consist of words separated by whitespace
434   or special characters. These special characters &MUST; be in a quoted
435   string to be used within a parameter value (as defined in
436   <xref target="transfer.codings"/>).
437</t>
438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
439  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
440                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
441                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
442                 
443  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
444</artwork></figure>
445<t anchor="rule.quoted-string">
446  <x:anchor-alias value="quoted-string"/>
447  <x:anchor-alias value="qdtext"/>
448  <x:anchor-alias value="obs-text"/>
449   A string of text is parsed as a single word if it is quoted using
450   double-quote marks.
451</t>
452<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"/>
453  <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>
454  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
455  <x:ref>obs-text</x:ref>       = %x80-FF
456</artwork></figure>
457<t anchor="rule.quoted-pair">
458  <x:anchor-alias value="quoted-pair"/>
459  <x:anchor-alias value="quoted-text"/>
460   The backslash character ("\") &MAY; be used as a single-character
461   quoting mechanism only within quoted-string and comment constructs.
462</t>
463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
464  <x:ref>quoted-text</x:ref>    = %x01-09 /
465                   %x0B-0C /
466                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
467  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
468</artwork></figure>
469</section>
470
471<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
472  <x:anchor-alias value="request-header"/>
473  <x:anchor-alias value="response-header"/>
474  <x:anchor-alias value="entity-body"/>
475  <x:anchor-alias value="entity-header"/>
476  <x:anchor-alias value="Cache-Control"/>
477  <x:anchor-alias value="Pragma"/>
478  <x:anchor-alias value="Warning"/>
479<t>
480  The ABNF rules below are defined in other parts:
481</t>
482<figure><!-- Part2--><artwork type="abnf2616">
483  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
484  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
485</artwork></figure>
486<figure><!-- Part3--><artwork type="abnf2616">
487  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
488  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
489</artwork></figure>
490<figure><!-- Part6--><artwork type="abnf2616">
491  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
492  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
493  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
494</artwork></figure>
495</section>
496
497</section>
498</section>
499
500<section title="HTTP architecture" anchor="architecture">
501<t>
502   HTTP was created with a specific architecture in mind, the World Wide Web,
503   and has evolved over time to support the scalability needs of a worldwide
504   hypertext system. Much of that architecture is reflected in the terminology
505   and syntax productions used to define HTTP.
506</t>
507
508<section title="Uniform Resource Identifiers" anchor="uri">
509<t>
510   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
511   throughout HTTP as the means for identifying resources. URI references
512   are used to target requests, redirect responses, and define relationships.
513   HTTP does not limit what a resource may be; it merely defines an interface
514   that can be used to interact with a resource via HTTP. More information on
515   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
516</t>
517  <x:anchor-alias value="URI"/>
518  <x:anchor-alias value="URI-reference"/>
519  <x:anchor-alias value="absolute-URI"/>
520  <x:anchor-alias value="relative-part"/>
521  <x:anchor-alias value="authority"/>
522  <x:anchor-alias value="fragment"/>
523  <x:anchor-alias value="path-abempty"/>
524  <x:anchor-alias value="path-absolute"/>
525  <x:anchor-alias value="port"/>
526  <x:anchor-alias value="query"/>
527  <x:anchor-alias value="uri-host"/>
528  <x:anchor-alias value="partial-URI"/>
529<t>
530   This specification adopts the definitions of "URI-reference",
531   "absolute-URI", "relative-part", "fragment", "port", "host",
532   "path-abempty", "path-absolute", "query", and "authority" from
533   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
534   protocol elements that allow a relative URI without a fragment.
535</t>
536<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"/>
537  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
538  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
539  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
540  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
541  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
542  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
543  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
544  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
545  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
546  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
547  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
548 
549  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
550</artwork></figure>
551<t>
552   Each protocol element in HTTP that allows a URI reference will indicate in
553   its ABNF production whether the element allows only a URI in absolute form
554   (absolute-URI), any relative reference (relative-ref), or some other subset
555   of the URI-reference grammar. Unless otherwise indicated, URI references
556   are parsed relative to the request target (the default base URI for both
557   the request and its corresponding response).
558</t>
559
560<section title="http URI scheme" anchor="http.uri">
561  <x:anchor-alias value="http-URI"/>
562  <iref item="http URI scheme" primary="true"/>
563  <iref item="URI scheme" subitem="http" primary="true"/>
564<t>
565   The "http" scheme is used to locate network resources via the HTTP
566   protocol.
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</section>
585
586<section title="https URI scheme" anchor="https.uri">
587   <iref item="https URI scheme"/>
588   <iref item="URI scheme" subitem="https"/>
589<t>
590   <cref>TBD: Define and explain purpose of https scheme.</cref>
591</t>
592<t><list><t>
593  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
594</t></list></t>
595</section>
596
597<section title="URI Comparison" anchor="uri.comparison">
598<t>
599   When comparing two URIs to decide if they match or not, a client
600   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
601   URIs, with these exceptions:
602  <list style="symbols">
603    <t>A port that is empty or not given is equivalent to the default
604        port for that URI-reference;</t>
605    <t>Comparisons of host names &MUST; be case-insensitive;</t>
606    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
607    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
608    <t>Characters other than those in the "reserved" set are equivalent to their
609       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
610    </t>
611  </list>
612</t>
613<t>
614   For example, the following three URIs are equivalent:
615</t>
616<figure><artwork type="example">
617   http://example.com:80/~smith/home.html
618   http://EXAMPLE.com/%7Esmith/home.html
619   http://EXAMPLE.com:/%7esmith/home.html
620</artwork></figure>
621</section>
622
623<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
624<t>
625</t>
626</section>
627</section>
628
629<section title="Overall Operation" anchor="intro.overall.operation">
630<t>
631   HTTP is a request/response protocol. A client sends a
632   request to the server in the form of a request method, URI, and
633   protocol version, followed by a MIME-like message containing request
634   modifiers, client information, and possible body content over a
635   connection with a server. The server responds with a status line,
636   including the message's protocol version and a success or error code,
637   followed by a MIME-like message containing server information, entity
638   metainformation, and possible entity-body content.
639</t>
640<t>
641   Most HTTP communication is initiated by a user agent and consists of
642   a request to be applied to a resource on some origin server. In the
643   simplest case, this may be accomplished via a single connection (v)
644   between the user agent (UA) and the origin server (O).
645</t>
646<figure><artwork type="drawing">
647       request chain ------------------------&gt;
648    UA -------------------v------------------- O
649       &lt;----------------------- response chain
650</artwork></figure>
651<t>
652   A more complicated situation occurs when one or more intermediaries
653   are present in the request/response chain. There are three common
654   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
655   forwarding agent, receiving requests for a URI in its absolute form,
656   rewriting all or part of the message, and forwarding the reformatted
657   request toward the server identified by the URI. A gateway is a
658   receiving agent, acting as a layer above some other server(s) and, if
659   necessary, translating the requests to the underlying server's
660   protocol. A tunnel acts as a relay point between two connections
661   without changing the messages; tunnels are used when the
662   communication needs to pass through an intermediary (such as a
663   firewall) even when the intermediary cannot understand the contents
664   of the messages.
665</t>
666<figure><artwork type="drawing">
667       request chain --------------------------------------&gt;
668    UA -----v----- A -----v----- B -----v----- C -----v----- O
669       &lt;------------------------------------- response chain
670</artwork></figure>
671<t>
672   The figure above shows three intermediaries (A, B, and C) between the
673   user agent and origin server. A request or response message that
674   travels the whole chain will pass through four separate connections.
675   This distinction is important because some HTTP communication options
676   may apply only to the connection with the nearest, non-tunnel
677   neighbor, only to the end-points of the chain, or to all connections
678   along the chain. Although the diagram is linear, each participant may
679   be engaged in multiple, simultaneous communications. For example, B
680   may be receiving requests from many clients other than A, and/or
681   forwarding requests to servers other than C, at the same time that it
682   is handling A's request.
683</t>
684<t>
685   Any party to the communication which is not acting as a tunnel may
686   employ an internal cache for handling requests. The effect of a cache
687   is that the request/response chain is shortened if one of the
688   participants along the chain has a cached response applicable to that
689   request. The following illustrates the resulting chain if B has a
690   cached copy of an earlier response from O (via C) for a request which
691   has not been cached by UA or A.
692</t>
693<figure><artwork type="drawing">
694          request chain ----------&gt;
695       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
696          &lt;--------- response chain
697</artwork></figure>
698<t>
699   Not all responses are usefully cacheable, and some requests may
700   contain modifiers which place special requirements on cache behavior.
701   HTTP requirements for cache behavior and cacheable responses are
702   defined in &caching;.
703</t>
704<t>
705   In fact, there are a wide variety of architectures and configurations
706   of caches and proxies currently being experimented with or deployed
707   across the World Wide Web. These systems include national hierarchies
708   of proxy caches to save transoceanic bandwidth, systems that
709   broadcast or multicast cache entries, organizations that distribute
710   subsets of cached data via CD-ROM, and so on. HTTP systems are used
711   in corporate intranets over high-bandwidth links, and for access via
712   PDAs with low-power radio links and intermittent connectivity. The
713   goal of HTTP/1.1 is to support the wide diversity of configurations
714   already deployed while introducing protocol constructs that meet the
715   needs of those who build web applications that require high
716   reliability and, failing that, at least reliable indications of
717   failure.
718</t>
719<t>
720   HTTP communication usually takes place over TCP/IP connections. The
721   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
722   not preclude HTTP from being implemented on top of any other protocol
723   on the Internet, or on other networks. HTTP only presumes a reliable
724   transport; any protocol that provides such guarantees can be used;
725   the mapping of the HTTP/1.1 request and response structures onto the
726   transport data units of the protocol in question is outside the scope
727   of this specification.
728</t>
729<t>
730   In HTTP/1.0, most implementations used a new connection for each
731   request/response exchange. In HTTP/1.1, a connection may be used for
732   one or more request/response exchanges, although connections may be
733   closed for a variety of reasons (see <xref target="persistent.connections"/>).
734</t>
735</section>
736
737<section title="Use of HTTP for proxy communication" anchor="http.proxy">
738<t>
739   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
740</t>
741</section>
742<section title="Interception of HTTP for access control" anchor="http.intercept">
743<t>
744   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
745</t>
746</section>
747<section title="Use of HTTP by other protocols" anchor="http.others">
748<t>
749   <cref>TBD: Profiles of HTTP defined by other protocol.
750   Extensions of HTTP like WebDAV.</cref>
751</t>
752</section>
753<section title="Use of HTTP by media type specification" anchor="http.media">
754<t>
755   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
756</t>
757</section>
758</section>
759
760<section title="Protocol Parameters" anchor="protocol.parameters">
761
762<section title="HTTP Version" anchor="http.version">
763  <x:anchor-alias value="HTTP-Version"/>
764  <x:anchor-alias value="HTTP-Prot-Name"/>
765<t>
766   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
767   of the protocol. The protocol versioning policy is intended to allow
768   the sender to indicate the format of a message and its capacity for
769   understanding further HTTP communication, rather than the features
770   obtained via that communication. No change is made to the version
771   number for the addition of message components which do not affect
772   communication behavior or which only add to extensible field values.
773   The &lt;minor&gt; number is incremented when the changes made to the
774   protocol add features which do not change the general message parsing
775   algorithm, but which may add to the message semantics and imply
776   additional capabilities of the sender. The &lt;major&gt; number is
777   incremented when the format of a message within the protocol is
778   changed. See <xref target="RFC2145"/> for a fuller explanation.
779</t>
780<t>
781   The version of an HTTP message is indicated by an HTTP-Version field
782   in the first line of the message. HTTP-Version is case-sensitive.
783</t>
784<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
785  <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>
786  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
787</artwork></figure>
788<t>
789   Note that the major and minor numbers &MUST; be treated as separate
790   integers and that each &MAY; be incremented higher than a single digit.
791   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
792   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
793   &MUST-NOT; be sent.
794</t>
795<t>
796   An application that sends a request or response message that includes
797   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
798   with this specification. Applications that are at least conditionally
799   compliant with this specification &SHOULD; use an HTTP-Version of
800   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
801   not compatible with HTTP/1.0. For more details on when to send
802   specific HTTP-Version values, see <xref target="RFC2145"/>.
803</t>
804<t>
805   The HTTP version of an application is the highest HTTP version for
806   which the application is at least conditionally compliant.
807</t>
808<t>
809   Proxy and gateway applications need to be careful when forwarding
810   messages in protocol versions different from that of the application.
811   Since the protocol version indicates the protocol capability of the
812   sender, a proxy/gateway &MUST-NOT; send a message with a version
813   indicator which is greater than its actual version. If a higher
814   version request is received, the proxy/gateway &MUST; either downgrade
815   the request version, or respond with an error, or switch to tunnel
816   behavior.
817</t>
818<t>
819   Due to interoperability problems with HTTP/1.0 proxies discovered
820   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
821   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
822   they support. The proxy/gateway's response to that request &MUST; be in
823   the same major version as the request.
824</t>
825<t>
826  <list>
827    <t>
828      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
829      of header fields required or forbidden by the versions involved.
830    </t>
831  </list>
832</t>
833</section>
834
835<section title="Date/Time Formats" anchor="date.time.formats">
836<section title="Full Date" anchor="full.date">
837  <x:anchor-alias value="HTTP-date"/>
838  <x:anchor-alias value="obsolete-date"/>
839  <x:anchor-alias value="rfc1123-date"/>
840  <x:anchor-alias value="rfc850-date"/>
841  <x:anchor-alias value="asctime-date"/>
842  <x:anchor-alias value="date1"/>
843  <x:anchor-alias value="date2"/>
844  <x:anchor-alias value="date3"/>
845  <x:anchor-alias value="rfc1123-date"/>
846  <x:anchor-alias value="time"/>
847  <x:anchor-alias value="wkday"/>
848  <x:anchor-alias value="weekday"/>
849  <x:anchor-alias value="month"/>
850<t>
851   HTTP applications have historically allowed three different formats
852   for the representation of date/time stamps:
853</t>
854<figure><artwork type="example">
855  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
856  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
857  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
858</artwork></figure>
859<t>
860   The first format is preferred as an Internet standard and represents
861   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
862   other formats are described here only for
863   compatibility with obsolete implementations.
864   HTTP/1.1 clients and servers that parse the date value &MUST; accept
865   all three formats (for compatibility with HTTP/1.0), though they &MUST;
866   only generate the RFC 1123 format for representing HTTP-date values
867   in header fields. See <xref target="tolerant.applications"/> for further information.
868</t>
869<t><list><t>
870      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
871      accepting date values that may have been sent by non-HTTP
872      applications, as is sometimes the case when retrieving or posting
873      messages via proxies/gateways to SMTP or NNTP.
874</t></list></t>
875<t>
876   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
877   (GMT), without exception. For the purposes of HTTP, GMT is exactly
878   equal to UTC (Coordinated Universal Time). This is indicated in the
879   first two formats by the inclusion of "GMT" as the three-letter
880   abbreviation for time zone, and &MUST; be assumed when reading the
881   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
882   additional whitespace beyond that specifically included as SP in the
883   grammar.
884</t>
885<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"/>
886  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
887  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
888  <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
889  <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
890  <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>
891  <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>
892                 ; day month year (e.g., 02 Jun 1982)
893  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
894                 ; day-month-year (e.g., 02-Jun-82)
895  <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> ))
896                 ; month day (e.g., Jun  2)
897  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
898                 ; 00:00:00 - 23:59:59
899  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
900               / s-Thu / s-Fri / s-Sat / s-Sun
901  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
902               / l-Thu / l-Fri / l-Sat / l-Sun
903  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
904               / s-May / s-Jun / s-Jul / s-Aug
905               / s-Sep / s-Oct / s-Nov / s-Dec
906               
907  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
908
909  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
910  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
911  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
912  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
913  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
914  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
915  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
916
917  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
918  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
919  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
920  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
921  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
922  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
923  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
924
925  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
926  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
927  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
928  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
929  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
930  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
931  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
932  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
933  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
934  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
935  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
936  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
937</artwork></figure>
938<t>
939      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
940      to their usage within the protocol stream. Clients and servers are
941      not required to use these formats for user presentation, request
942      logging, etc.
943</t>
944</section>
945</section>
946
947<section title="Transfer Codings" anchor="transfer.codings">
948  <x:anchor-alias value="parameter"/>
949  <x:anchor-alias value="transfer-coding"/>
950  <x:anchor-alias value="transfer-extension"/>
951<t>
952   Transfer-coding values are used to indicate an encoding
953   transformation that has been, can be, or may need to be applied to an
954   entity-body in order to ensure "safe transport" through the network.
955   This differs from a content coding in that the transfer-coding is a
956   property of the message, not of the original entity.
957</t>
958<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
959  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
960  <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> )
961</artwork></figure>
962<t anchor="rule.parameter">
963  <x:anchor-alias value="attribute"/>
964  <x:anchor-alias value="parameter"/>
965  <x:anchor-alias value="value"/>
966   Parameters are in  the form of attribute/value pairs.
967</t>
968<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"/>
969  <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>
970  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
971  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
972</artwork></figure>
973<t>
974   All transfer-coding values are case-insensitive. HTTP/1.1 uses
975   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
976   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
977</t>
978<t>
979   Whenever a transfer-coding is applied to a message-body, the set of
980   transfer-codings &MUST; include "chunked", unless the message indicates it
981   is terminated by closing the connection. When the "chunked" transfer-coding
982   is used, it &MUST; be the last transfer-coding applied to the
983   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
984   than once to a message-body. These rules allow the recipient to
985   determine the transfer-length of the message (<xref target="message.length"/>).
986</t>
987<t>
988   Transfer-codings are analogous to the Content-Transfer-Encoding
989   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
990   binary data over a 7-bit transport service. However, safe transport
991   has a different focus for an 8bit-clean transfer protocol. In HTTP,
992   the only unsafe characteristic of message-bodies is the difficulty in
993   determining the exact body length (<xref target="message.length"/>), or the desire to
994   encrypt data over a shared transport.
995</t>
996<t>
997   The Internet Assigned Numbers Authority (IANA) acts as a registry for
998   transfer-coding value tokens. Initially, the registry contains the
999   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1000   "gzip", "compress", and "deflate" (&content-codings;).
1001</t>
1002<t>
1003   New transfer-coding value tokens &SHOULD; be registered in the same way
1004   as new content-coding value tokens (&content-codings;).
1005</t>
1006<t>
1007   A server which receives an entity-body with a transfer-coding it does
1008   not understand &SHOULD; return 501 (Not Implemented), and close the
1009   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1010   client.
1011</t>
1012
1013<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1014  <x:anchor-alias value="chunk"/>
1015  <x:anchor-alias value="Chunked-Body"/>
1016  <x:anchor-alias value="chunk-data"/>
1017  <x:anchor-alias value="chunk-ext"/>
1018  <x:anchor-alias value="chunk-ext-name"/>
1019  <x:anchor-alias value="chunk-ext-val"/>
1020  <x:anchor-alias value="chunk-size"/>
1021  <x:anchor-alias value="last-chunk"/>
1022  <x:anchor-alias value="trailer-part"/>
1023<t>
1024   The chunked encoding modifies the body of a message in order to
1025   transfer it as a series of chunks, each with its own size indicator,
1026   followed by an &OPTIONAL; trailer containing entity-header fields. This
1027   allows dynamically produced content to be transferred along with the
1028   information necessary for the recipient to verify that it has
1029   received the full message.
1030</t>
1031<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"/>
1032  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1033                   <x:ref>last-chunk</x:ref>
1034                   <x:ref>trailer-part</x:ref>
1035                   <x:ref>CRLF</x:ref>
1036 
1037  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1038                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1039  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1040  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1041 
1042  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1043                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1044  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1045  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1046  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1047  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1048</artwork></figure>
1049<t>
1050   The chunk-size field is a string of hex digits indicating the size of
1051   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1052   zero, followed by the trailer, which is terminated by an empty line.
1053</t>
1054<t>
1055   The trailer allows the sender to include additional HTTP header
1056   fields at the end of the message. The Trailer header field can be
1057   used to indicate which header fields are included in a trailer (see
1058   <xref target="header.trailer"/>).
1059</t>
1060<t>
1061   A server using chunked transfer-coding in a response &MUST-NOT; use the
1062   trailer for any header fields unless at least one of the following is
1063   true:
1064  <list style="numbers">
1065    <t>the request included a TE header field that indicates "trailers" is
1066     acceptable in the transfer-coding of the  response, as described in
1067     <xref target="header.te"/>; or,</t>
1068
1069    <t>the server is the origin server for the response, the trailer
1070     fields consist entirely of optional metadata, and the recipient
1071     could use the message (in a manner acceptable to the origin server)
1072     without receiving this metadata.  In other words, the origin server
1073     is willing to accept the possibility that the trailer fields might
1074     be silently discarded along the path to the client.</t>
1075  </list>
1076</t>
1077<t>
1078   This requirement prevents an interoperability failure when the
1079   message is being received by an HTTP/1.1 (or later) proxy and
1080   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1081   compliance with the protocol would have necessitated a possibly
1082   infinite buffer on the proxy.
1083</t>
1084<t>
1085   A process for decoding the "chunked" transfer-coding
1086   can be represented in pseudo-code as:
1087</t>
1088<figure><artwork type="code">
1089  length := 0
1090  read chunk-size, chunk-ext (if any) and CRLF
1091  while (chunk-size &gt; 0) {
1092     read chunk-data and CRLF
1093     append chunk-data to entity-body
1094     length := length + chunk-size
1095     read chunk-size and CRLF
1096  }
1097  read entity-header
1098  while (entity-header not empty) {
1099     append entity-header to existing header fields
1100     read entity-header
1101  }
1102  Content-Length := length
1103  Remove "chunked" from Transfer-Encoding
1104</artwork></figure>
1105<t>
1106   All HTTP/1.1 applications &MUST; be able to receive and decode the
1107   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1108   they do not understand.
1109</t>
1110</section>
1111</section>
1112
1113<section title="Product Tokens" anchor="product.tokens">
1114  <x:anchor-alias value="product"/>
1115  <x:anchor-alias value="product-version"/>
1116<t>
1117   Product tokens are used to allow communicating applications to
1118   identify themselves by software name and version. Most fields using
1119   product tokens also allow sub-products which form a significant part
1120   of the application to be listed, separated by whitespace. By
1121   convention, the products are listed in order of their significance
1122   for identifying the application.
1123</t>
1124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1125  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1126  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1127</artwork></figure>
1128<t>
1129   Examples:
1130</t>
1131<figure><artwork type="example">
1132  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1133  Server: Apache/0.8.4
1134</artwork></figure>
1135<t>
1136   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1137   used for advertising or other non-essential information. Although any
1138   token character &MAY; appear in a product-version, this token &SHOULD;
1139   only be used for a version identifier (i.e., successive versions of
1140   the same product &SHOULD; only differ in the product-version portion of
1141   the product value).
1142</t>
1143</section>
1144
1145<section title="Quality Values" anchor="quality.values">
1146  <x:anchor-alias value="qvalue"/>
1147<t>
1148   Both transfer codings (TE request header, <xref target="header.te"/>)
1149   and content negotiation (&content.negotiation;) use short "floating point"
1150   numbers to indicate the relative importance ("weight") of various
1151   negotiable parameters.  A weight is normalized to a real number in
1152   the range 0 through 1, where 0 is the minimum and 1 the maximum
1153   value. If a parameter has a quality value of 0, then content with
1154   this parameter is `not acceptable' for the client. HTTP/1.1
1155   applications &MUST-NOT; generate more than three digits after the
1156   decimal point. User configuration of these values &SHOULD; also be
1157   limited in this fashion.
1158</t>
1159<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1160  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1161                 / ( "1" [ "." 0*3("0") ] )
1162</artwork></figure>
1163<x:note>
1164  <t>
1165     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1166     relative degradation in desired quality.
1167  </t>
1168</x:note>
1169</section>
1170
1171</section>
1172
1173<section title="HTTP Message" anchor="http.message">
1174
1175<section title="Message Types" anchor="message.types">
1176  <x:anchor-alias value="generic-message"/>
1177  <x:anchor-alias value="HTTP-message"/>
1178  <x:anchor-alias value="start-line"/>
1179<t>
1180   HTTP messages consist of requests from client to server and responses
1181   from server to client.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1184  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1185</artwork></figure>
1186<t>
1187   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1188   message format of <xref target="RFC5322"/> for transferring entities (the payload
1189   of the message). Both types of message consist of a start-line, zero
1190   or more header fields (also known as "headers"), an empty line (i.e.,
1191   a line with nothing preceding the CRLF) indicating the end of the
1192   header fields, and possibly a message-body.
1193</t>
1194<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1195  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1196                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1197                    <x:ref>CRLF</x:ref>
1198                    [ <x:ref>message-body</x:ref> ]
1199  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1200</artwork></figure>
1201<t>
1202   In the interest of robustness, servers &SHOULD; ignore any empty
1203   line(s) received where a Request-Line is expected. In other words, if
1204   the server is reading the protocol stream at the beginning of a
1205   message and receives a CRLF first, it should ignore the CRLF.
1206</t>
1207<t>
1208   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1209   after a POST request. To restate what is explicitly forbidden by the
1210   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1211   extra CRLF.
1212</t>
1213<t>
1214   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1215   header field. The presence of whitespace might be an attempt to trick a
1216   noncompliant implementation of HTTP into ignoring that field or processing
1217   the next line as a new request, either of which may result in security
1218   issues when implementations within the request chain interpret the
1219   same message differently. HTTP/1.1 servers &MUST; reject such a message
1220   with a 400 (Bad Request) response.
1221</t>
1222</section>
1223
1224<section title="Message Headers" anchor="message.headers">
1225  <x:anchor-alias value="field-content"/>
1226  <x:anchor-alias value="field-name"/>
1227  <x:anchor-alias value="field-value"/>
1228  <x:anchor-alias value="message-header"/>
1229<t>
1230   HTTP header fields follow the same general format as Internet messages in
1231   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1232   of a name followed by a colon (":"), optional whitespace, and the field
1233   value. Field names are case-insensitive.
1234</t>
1235<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"/>
1236  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1237  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1238  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1239  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1240</artwork></figure>
1241<t>
1242   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1243   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1244   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1245   header field-values use only a subset of the US-ASCII charset
1246   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1247   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1248   (obs-text) octets in field-content as opaque data.
1249</t>
1250<t>
1251   No whitespace is allowed between the header field-name and colon. For
1252   security reasons, any request message received containing such whitespace
1253   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1254   whitespace in a response message &MUST; be removed.
1255</t>
1256<t>
1257   The field value &MAY; be preceded by optional whitespace; a single SP is
1258   preferred. The field-value does not include any leading or trailing white
1259   space: OWS occurring before the first non-whitespace character of the
1260   field-value or after the last non-whitespace character of the field-value
1261   is ignored and &MAY; be removed without changing the meaning of the header
1262   field.
1263</t>
1264<t>
1265   Historically, HTTP header field values could be extended over multiple
1266   lines by preceding each extra line with at least one space or horizontal
1267   tab character (line folding). This specification deprecates such line
1268   folding except within the message/http media type
1269   (<xref target="internet.media.type.message.http"/>).
1270   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1271   (i.e., that contain any field-content that matches the obs-fold rule) unless
1272   the message is intended for packaging within the message/http media type.
1273   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1274   obs-fold whitespace with a single SP prior to interpreting the field value
1275   or forwarding the message downstream.
1276</t>
1277<t anchor="rule.comment">
1278  <x:anchor-alias value="comment"/>
1279  <x:anchor-alias value="ctext"/>
1280   Comments can be included in some HTTP header fields by surrounding
1281   the comment text with parentheses. Comments are only allowed in
1282   fields containing "comment" as part of their field value definition.
1283   In all other fields, parentheses are considered part of the field
1284   value.
1285</t>
1286<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1287  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1288  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1289</artwork></figure>
1290<t>
1291   The order in which header fields with differing field names are
1292   received is not significant. However, it is "good practice" to send
1293   general-header fields first, followed by request-header or response-header
1294   fields, and ending with the entity-header fields.
1295</t>
1296<t>
1297   Multiple message-header fields with the same field-name &MAY; be
1298   present in a message if and only if the entire field-value for that
1299   header field is defined as a comma-separated list [i.e., #(values)].
1300   It &MUST; be possible to combine the multiple header fields into one
1301   "field-name: field-value" pair, without changing the semantics of the
1302   message, by appending each subsequent field-value to the first, each
1303   separated by a comma. The order in which header fields with the same
1304   field-name are received is therefore significant to the
1305   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1306   change the order of these field values when a message is forwarded.
1307</t>
1308<t>
1309  <list><t>
1310   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1311   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1312   can occur multiple times, but does not use the list syntax, and thus cannot
1313   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1314   for details.) Also note that the Set-Cookie2 header specified in
1315   <xref target="RFC2965"/> does not share this problem.
1316  </t></list>
1317</t>
1318 
1319</section>
1320
1321<section title="Message Body" anchor="message.body">
1322  <x:anchor-alias value="message-body"/>
1323<t>
1324   The message-body (if any) of an HTTP message is used to carry the
1325   entity-body associated with the request or response. The message-body
1326   differs from the entity-body only when a transfer-coding has been
1327   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1328</t>
1329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1330  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1331               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1332</artwork></figure>
1333<t>
1334   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1335   applied by an application to ensure safe and proper transfer of the
1336   message. Transfer-Encoding is a property of the message, not of the
1337   entity, and thus &MAY; be added or removed by any application along the
1338   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1339   when certain transfer-codings may be used.)
1340</t>
1341<t>
1342   The rules for when a message-body is allowed in a message differ for
1343   requests and responses.
1344</t>
1345<t>
1346   The presence of a message-body in a request is signaled by the
1347   inclusion of a Content-Length or Transfer-Encoding header field in
1348   the request's message-headers. A message-body &MUST-NOT; be included in
1349   a request if the specification of the request method (&method;)
1350   explicitly disallows an entity-body in requests.
1351   When a request message contains both a message-body of non-zero
1352   length and a method that does not define any semantics for that
1353   request message-body, then an origin server &SHOULD; either ignore
1354   the message-body or respond with an appropriate error message
1355   (e.g., 413).  A proxy or gateway, when presented the same request,
1356   &SHOULD; either forward the request inbound with the message-body or
1357   ignore the message-body when determining a response.
1358</t>
1359<t>
1360   For response messages, whether or not a message-body is included with
1361   a message is dependent on both the request method and the response
1362   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1363   &MUST-NOT; include a message-body, even though the presence of entity-header
1364   fields might lead one to believe they do. All 1xx
1365   (informational), 204 (No Content), and 304 (Not Modified) responses
1366   &MUST-NOT; include a message-body. All other responses do include a
1367   message-body, although it &MAY; be of zero length.
1368</t>
1369</section>
1370
1371<section title="Message Length" anchor="message.length">
1372<t>
1373   The transfer-length of a message is the length of the message-body as
1374   it appears in the message; that is, after any transfer-codings have
1375   been applied. When a message-body is included with a message, the
1376   transfer-length of that body is determined by one of the following
1377   (in order of precedence):
1378</t>
1379<t>
1380  <list style="numbers">
1381    <x:lt><t>
1382     Any response message which "&MUST-NOT;" include a message-body (such
1383     as the 1xx, 204, and 304 responses and any response to a HEAD
1384     request) is always terminated by the first empty line after the
1385     header fields, regardless of the entity-header fields present in
1386     the message.
1387    </t></x:lt>
1388    <x:lt><t>
1389     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1390     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1391     is used, the transfer-length is defined by the use of this transfer-coding.
1392     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1393     is not present, the transfer-length is defined by the sender closing the connection.
1394    </t></x:lt>
1395    <x:lt><t>
1396     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1397     decimal value in OCTETs represents both the entity-length and the
1398     transfer-length. The Content-Length header field &MUST-NOT; be sent
1399     if these two lengths are different (i.e., if a Transfer-Encoding
1400     header field is present). If a message is received with both a
1401     Transfer-Encoding header field and a Content-Length header field,
1402     the latter &MUST; be ignored.
1403    </t></x:lt>
1404    <x:lt><t>
1405     If the message uses the media type "multipart/byteranges", and the
1406     transfer-length is not otherwise specified, then this self-delimiting
1407     media type defines the transfer-length. This media type
1408     &MUST-NOT; be used unless the sender knows that the recipient can parse
1409     it; the presence in a request of a Range header with multiple byte-range
1410     specifiers from a 1.1 client implies that the client can parse
1411     multipart/byteranges responses.
1412    <list style="empty"><t>
1413       A range header might be forwarded by a 1.0 proxy that does not
1414       understand multipart/byteranges; in this case the server &MUST;
1415       delimit the message using methods defined in items 1, 3 or 5 of
1416       this section.
1417    </t></list>
1418    </t></x:lt>
1419    <x:lt><t>
1420     By the server closing the connection. (Closing the connection
1421     cannot be used to indicate the end of a request body, since that
1422     would leave no possibility for the server to send back a response.)
1423    </t></x:lt>
1424  </list>
1425</t>
1426<t>
1427   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1428   containing a message-body &MUST; include a valid Content-Length header
1429   field unless the server is known to be HTTP/1.1 compliant. If a
1430   request contains a message-body and a Content-Length is not given,
1431   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1432   determine the length of the message, or with 411 (Length Required) if
1433   it wishes to insist on receiving a valid Content-Length.
1434</t>
1435<t>
1436   All HTTP/1.1 applications that receive entities &MUST; accept the
1437   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1438   to be used for messages when the message length cannot be determined
1439   in advance.
1440</t>
1441<t>
1442   Messages &MUST-NOT; include both a Content-Length header field and a
1443   transfer-coding. If the message does include a
1444   transfer-coding, the Content-Length &MUST; be ignored.
1445</t>
1446<t>
1447   When a Content-Length is given in a message where a message-body is
1448   allowed, its field value &MUST; exactly match the number of OCTETs in
1449   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1450   invalid length is received and detected.
1451</t>
1452</section>
1453
1454<section title="General Header Fields" anchor="general.header.fields">
1455  <x:anchor-alias value="general-header"/>
1456<t>
1457   There are a few header fields which have general applicability for
1458   both request and response messages, but which do not apply to the
1459   entity being transferred. These header fields apply only to the
1460   message being transmitted.
1461</t>
1462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1463  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1464                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1465                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1466                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1467                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1468                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1469                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1470                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1471                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1472</artwork></figure>
1473<t>
1474   General-header field names can be extended reliably only in
1475   combination with a change in the protocol version. However, new or
1476   experimental header fields may be given the semantics of general
1477   header fields if all parties in the communication recognize them to
1478   be general-header fields. Unrecognized header fields are treated as
1479   entity-header fields.
1480</t>
1481</section>
1482</section>
1483
1484<section title="Request" anchor="request">
1485  <x:anchor-alias value="Request"/>
1486<t>
1487   A request message from a client to a server includes, within the
1488   first line of that message, the method to be applied to the resource,
1489   the identifier of the resource, and the protocol version in use.
1490</t>
1491<!--                 Host                      ; should be moved here eventually -->
1492<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1493  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1494                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1495                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1496                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1497                  <x:ref>CRLF</x:ref>
1498                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1499</artwork></figure>
1500
1501<section title="Request-Line" anchor="request-line">
1502  <x:anchor-alias value="Request-Line"/>
1503<t>
1504   The Request-Line begins with a method token, followed by the
1505   request-target and the protocol version, and ending with CRLF. The
1506   elements are separated by SP characters. No CR or LF is allowed
1507   except in the final CRLF sequence.
1508</t>
1509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1510  <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>
1511</artwork></figure>
1512
1513<section title="Method" anchor="method">
1514  <x:anchor-alias value="Method"/>
1515<t>
1516   The Method  token indicates the method to be performed on the
1517   resource identified by the request-target. The method is case-sensitive.
1518</t>
1519<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1520  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1521</artwork></figure>
1522</section>
1523
1524<section title="request-target" anchor="request-target">
1525  <x:anchor-alias value="request-target"/>
1526<t>
1527   The request-target
1528   identifies the resource upon which to apply the request.
1529</t>
1530<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1531  <x:ref>request-target</x:ref> = "*"
1532                 / <x:ref>absolute-URI</x:ref>
1533                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1534                 / <x:ref>authority</x:ref>
1535</artwork></figure>
1536<t>
1537   The four options for request-target are dependent on the nature of the
1538   request. The asterisk "*" means that the request does not apply to a
1539   particular resource, but to the server itself, and is only allowed
1540   when the method used does not necessarily apply to a resource. One
1541   example would be
1542</t>
1543<figure><artwork type="example">
1544  OPTIONS * HTTP/1.1
1545</artwork></figure>
1546<t>
1547   The absolute-URI form is &REQUIRED; when the request is being made to a
1548   proxy. The proxy is requested to forward the request or service it
1549   from a valid cache, and return the response. Note that the proxy &MAY;
1550   forward the request on to another proxy or directly to the server
1551   specified by the absolute-URI. In order to avoid request loops, a
1552   proxy &MUST; be able to recognize all of its server names, including
1553   any aliases, local variations, and the numeric IP address. An example
1554   Request-Line would be:
1555</t>
1556<figure><artwork type="example">
1557  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1558</artwork></figure>
1559<t>
1560   To allow for transition to absolute-URIs in all requests in future
1561   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1562   form in requests, even though HTTP/1.1 clients will only generate
1563   them in requests to proxies.
1564</t>
1565<t>
1566   The authority form is only used by the CONNECT method (&CONNECT;).
1567</t>
1568<t>
1569   The most common form of request-target is that used to identify a
1570   resource on an origin server or gateway. In this case the absolute
1571   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1572   the request-target, and the network location of the URI (authority) &MUST;
1573   be transmitted in a Host header field. For example, a client wishing
1574   to retrieve the resource above directly from the origin server would
1575   create a TCP connection to port 80 of the host "www.example.org" and send
1576   the lines:
1577</t>
1578<figure><artwork type="example">
1579  GET /pub/WWW/TheProject.html HTTP/1.1
1580  Host: www.example.org
1581</artwork></figure>
1582<t>
1583   followed by the remainder of the Request. Note that the absolute path
1584   cannot be empty; if none is present in the original URI, it &MUST; be
1585   given as "/" (the server root).
1586</t>
1587<t>
1588   If a proxy receives a request without any path in the request-target and
1589   the method specified is capable of supporting the asterisk form of
1590   request-target, then the last proxy on the request chain &MUST; forward the
1591   request with "*" as the final request-target.
1592</t>
1593<figure><preamble>   
1594   For example, the request
1595</preamble><artwork type="example">
1596  OPTIONS http://www.example.org:8001 HTTP/1.1
1597</artwork></figure>
1598<figure><preamble>   
1599  would be forwarded by the proxy as
1600</preamble><artwork type="example">
1601  OPTIONS * HTTP/1.1
1602  Host: www.example.org:8001
1603</artwork>
1604<postamble>
1605   after connecting to port 8001 of host "www.example.org".
1606</postamble>
1607</figure>
1608<t>
1609   The request-target is transmitted in the format specified in
1610   <xref target="http.uri"/>. If the request-target is percent-encoded
1611   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1612   &MUST; decode the request-target in order to
1613   properly interpret the request. Servers &SHOULD; respond to invalid
1614   request-targets with an appropriate status code.
1615</t>
1616<t>
1617   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1618   received request-target when forwarding it to the next inbound server,
1619   except as noted above to replace a null path-absolute with "/".
1620</t>
1621<t>
1622  <list><t>
1623      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1624      meaning of the request when the origin server is improperly using
1625      a non-reserved URI character for a reserved purpose.  Implementors
1626      should be aware that some pre-HTTP/1.1 proxies have been known to
1627      rewrite the request-target.
1628  </t></list>
1629</t>
1630<t>
1631   HTTP does not place a pre-defined limit on the length of a request-target.
1632   A server &MUST; be prepared to receive URIs of unbounded length and
1633   respond with the 414 (URI Too Long) status if the received
1634   request-target would be longer than the server wishes to handle
1635   (see &status-414;).
1636</t>
1637<t>
1638   Various ad-hoc limitations on request-target length are found in practice.
1639   It is &RECOMMENDED; that all HTTP senders and recipients support
1640   request-target lengths of 8000 or more OCTETs.
1641</t>
1642</section>
1643</section>
1644
1645<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1646<t>
1647   The exact resource identified by an Internet request is determined by
1648   examining both the request-target and the Host header field.
1649</t>
1650<t>
1651   An origin server that does not allow resources to differ by the
1652   requested host &MAY; ignore the Host header field value when
1653   determining the resource identified by an HTTP/1.1 request. (But see
1654   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1655   for other requirements on Host support in HTTP/1.1.)
1656</t>
1657<t>
1658   An origin server that does differentiate resources based on the host
1659   requested (sometimes referred to as virtual hosts or vanity host
1660   names) &MUST; use the following rules for determining the requested
1661   resource on an HTTP/1.1 request:
1662  <list style="numbers">
1663    <t>If request-target is an absolute-URI, the host is part of the
1664     request-target. Any Host header field value in the request &MUST; be
1665     ignored.</t>
1666    <t>If the request-target is not an absolute-URI, and the request includes
1667     a Host header field, the host is determined by the Host header
1668     field value.</t>
1669    <t>If the host as determined by rule 1 or 2 is not a valid host on
1670     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1671  </list>
1672</t>
1673<t>
1674   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1675   attempt to use heuristics (e.g., examination of the URI path for
1676   something unique to a particular host) in order to determine what
1677   exact resource is being requested.
1678</t>
1679</section>
1680
1681</section>
1682
1683
1684<section title="Response" anchor="response">
1685  <x:anchor-alias value="Response"/>
1686<t>
1687   After receiving and interpreting a request message, a server responds
1688   with an HTTP response message.
1689</t>
1690<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1691  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1692                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1693                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1694                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1695                  <x:ref>CRLF</x:ref>
1696                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1697</artwork></figure>
1698
1699<section title="Status-Line" anchor="status-line">
1700  <x:anchor-alias value="Status-Line"/>
1701<t>
1702   The first line of a Response message is the Status-Line, consisting
1703   of the protocol version followed by a numeric status code and its
1704   associated textual phrase, with each element separated by SP
1705   characters. No CR or LF is allowed except in the final CRLF sequence.
1706</t>
1707<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1708  <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>
1709</artwork></figure>
1710
1711<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1712  <x:anchor-alias value="Reason-Phrase"/>
1713  <x:anchor-alias value="Status-Code"/>
1714<t>
1715   The Status-Code element is a 3-digit integer result code of the
1716   attempt to understand and satisfy the request. These codes are fully
1717   defined in &status-codes;.  The Reason Phrase exists for the sole
1718   purpose of providing a textual description associated with the numeric
1719   status code, out of deference to earlier Internet application protocols
1720   that were more frequently used with interactive text clients.
1721   A client &SHOULD; ignore the content of the Reason Phrase.
1722</t>
1723<t>
1724   The first digit of the Status-Code defines the class of response. The
1725   last two digits do not have any categorization role. There are 5
1726   values for the first digit:
1727  <list style="symbols">
1728    <t>
1729      1xx: Informational - Request received, continuing process
1730    </t>
1731    <t>
1732      2xx: Success - The action was successfully received,
1733        understood, and accepted
1734    </t>
1735    <t>
1736      3xx: Redirection - Further action must be taken in order to
1737        complete the request
1738    </t>
1739    <t>
1740      4xx: Client Error - The request contains bad syntax or cannot
1741        be fulfilled
1742    </t>
1743    <t>
1744      5xx: Server Error - The server failed to fulfill an apparently
1745        valid request
1746    </t>
1747  </list>
1748</t>
1749<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"/>
1750  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1751  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1752</artwork></figure>
1753</section>
1754</section>
1755
1756</section>
1757
1758
1759<section title="Connections" anchor="connections">
1760
1761<section title="Persistent Connections" anchor="persistent.connections">
1762
1763<section title="Purpose" anchor="persistent.purpose">
1764<t>
1765   Prior to persistent connections, a separate TCP connection was
1766   established to fetch each URL, increasing the load on HTTP servers
1767   and causing congestion on the Internet. The use of inline images and
1768   other associated data often require a client to make multiple
1769   requests of the same server in a short amount of time. Analysis of
1770   these performance problems and results from a prototype
1771   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1772   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1773   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1774   T/TCP <xref target="Tou1998"/>.
1775</t>
1776<t>
1777   Persistent HTTP connections have a number of advantages:
1778  <list style="symbols">
1779      <t>
1780        By opening and closing fewer TCP connections, CPU time is saved
1781        in routers and hosts (clients, servers, proxies, gateways,
1782        tunnels, or caches), and memory used for TCP protocol control
1783        blocks can be saved in hosts.
1784      </t>
1785      <t>
1786        HTTP requests and responses can be pipelined on a connection.
1787        Pipelining allows a client to make multiple requests without
1788        waiting for each response, allowing a single TCP connection to
1789        be used much more efficiently, with much lower elapsed time.
1790      </t>
1791      <t>
1792        Network congestion is reduced by reducing the number of packets
1793        caused by TCP opens, and by allowing TCP sufficient time to
1794        determine the congestion state of the network.
1795      </t>
1796      <t>
1797        Latency on subsequent requests is reduced since there is no time
1798        spent in TCP's connection opening handshake.
1799      </t>
1800      <t>
1801        HTTP can evolve more gracefully, since errors can be reported
1802        without the penalty of closing the TCP connection. Clients using
1803        future versions of HTTP might optimistically try a new feature,
1804        but if communicating with an older server, retry with old
1805        semantics after an error is reported.
1806      </t>
1807    </list>
1808</t>
1809<t>
1810   HTTP implementations &SHOULD; implement persistent connections.
1811</t>
1812</section>
1813
1814<section title="Overall Operation" anchor="persistent.overall">
1815<t>
1816   A significant difference between HTTP/1.1 and earlier versions of
1817   HTTP is that persistent connections are the default behavior of any
1818   HTTP connection. That is, unless otherwise indicated, the client
1819   &SHOULD; assume that the server will maintain a persistent connection,
1820   even after error responses from the server.
1821</t>
1822<t>
1823   Persistent connections provide a mechanism by which a client and a
1824   server can signal the close of a TCP connection. This signaling takes
1825   place using the Connection header field (<xref target="header.connection"/>). Once a close
1826   has been signaled, the client &MUST-NOT; send any more requests on that
1827   connection.
1828</t>
1829
1830<section title="Negotiation" anchor="persistent.negotiation">
1831<t>
1832   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1833   maintain a persistent connection unless a Connection header including
1834   the connection-token "close" was sent in the request. If the server
1835   chooses to close the connection immediately after sending the
1836   response, it &SHOULD; send a Connection header including the
1837   connection-token close.
1838</t>
1839<t>
1840   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1841   decide to keep it open based on whether the response from a server
1842   contains a Connection header with the connection-token close. In case
1843   the client does not want to maintain a connection for more than that
1844   request, it &SHOULD; send a Connection header including the
1845   connection-token close.
1846</t>
1847<t>
1848   If either the client or the server sends the close token in the
1849   Connection header, that request becomes the last one for the
1850   connection.
1851</t>
1852<t>
1853   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1854   maintained for HTTP versions less than 1.1 unless it is explicitly
1855   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1856   compatibility with HTTP/1.0 clients.
1857</t>
1858<t>
1859   In order to remain persistent, all messages on the connection &MUST;
1860   have a self-defined message length (i.e., one not defined by closure
1861   of the connection), as described in <xref target="message.length"/>.
1862</t>
1863</section>
1864
1865<section title="Pipelining" anchor="pipelining">
1866<t>
1867   A client that supports persistent connections &MAY; "pipeline" its
1868   requests (i.e., send multiple requests without waiting for each
1869   response). A server &MUST; send its responses to those requests in the
1870   same order that the requests were received.
1871</t>
1872<t>
1873   Clients which assume persistent connections and pipeline immediately
1874   after connection establishment &SHOULD; be prepared to retry their
1875   connection if the first pipelined attempt fails. If a client does
1876   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1877   persistent. Clients &MUST; also be prepared to resend their requests if
1878   the server closes the connection before sending all of the
1879   corresponding responses.
1880</t>
1881<t>
1882   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1883   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1884   premature termination of the transport connection could lead to
1885   indeterminate results. A client wishing to send a non-idempotent
1886   request &SHOULD; wait to send that request until it has received the
1887   response status for the previous request.
1888</t>
1889</section>
1890</section>
1891
1892<section title="Proxy Servers" anchor="persistent.proxy">
1893<t>
1894   It is especially important that proxies correctly implement the
1895   properties of the Connection header field as specified in <xref target="header.connection"/>.
1896</t>
1897<t>
1898   The proxy server &MUST; signal persistent connections separately with
1899   its clients and the origin servers (or other proxy servers) that it
1900   connects to. Each persistent connection applies to only one transport
1901   link.
1902</t>
1903<t>
1904   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1905   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1906   discussion of the problems with the Keep-Alive header implemented by
1907   many HTTP/1.0 clients).
1908</t>
1909</section>
1910
1911<section title="Practical Considerations" anchor="persistent.practical">
1912<t>
1913   Servers will usually have some time-out value beyond which they will
1914   no longer maintain an inactive connection. Proxy servers might make
1915   this a higher value since it is likely that the client will be making
1916   more connections through the same server. The use of persistent
1917   connections places no requirements on the length (or existence) of
1918   this time-out for either the client or the server.
1919</t>
1920<t>
1921   When a client or server wishes to time-out it &SHOULD; issue a graceful
1922   close on the transport connection. Clients and servers &SHOULD; both
1923   constantly watch for the other side of the transport close, and
1924   respond to it as appropriate. If a client or server does not detect
1925   the other side's close promptly it could cause unnecessary resource
1926   drain on the network.
1927</t>
1928<t>
1929   A client, server, or proxy &MAY; close the transport connection at any
1930   time. For example, a client might have started to send a new request
1931   at the same time that the server has decided to close the "idle"
1932   connection. From the server's point of view, the connection is being
1933   closed while it was idle, but from the client's point of view, a
1934   request is in progress.
1935</t>
1936<t>
1937   This means that clients, servers, and proxies &MUST; be able to recover
1938   from asynchronous close events. Client software &SHOULD; reopen the
1939   transport connection and retransmit the aborted sequence of requests
1940   without user interaction so long as the request sequence is
1941   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1942   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1943   human operator the choice of retrying the request(s). Confirmation by
1944   user-agent software with semantic understanding of the application
1945   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1946   be repeated if the second sequence of requests fails.
1947</t>
1948<t>
1949   Servers &SHOULD; always respond to at least one request per connection,
1950   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1951   middle of transmitting a response, unless a network or client failure
1952   is suspected.
1953</t>
1954<t>
1955   Clients that use persistent connections &SHOULD; limit the number of
1956   simultaneous connections that they maintain to a given server. A
1957   single-user client &SHOULD-NOT; maintain more than 2 connections with
1958   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1959   another server or proxy, where N is the number of simultaneously
1960   active users. These guidelines are intended to improve HTTP response
1961   times and avoid congestion.
1962</t>
1963</section>
1964</section>
1965
1966<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1967
1968<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1969<t>
1970   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1971   flow control mechanisms to resolve temporary overloads, rather than
1972   terminating connections with the expectation that clients will retry.
1973   The latter technique can exacerbate network congestion.
1974</t>
1975</section>
1976
1977<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1978<t>
1979   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1980   the network connection for an error status while it is transmitting
1981   the request. If the client sees an error status, it &SHOULD;
1982   immediately cease transmitting the body. If the body is being sent
1983   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1984   empty trailer &MAY; be used to prematurely mark the end of the message.
1985   If the body was preceded by a Content-Length header, the client &MUST;
1986   close the connection.
1987</t>
1988</section>
1989
1990<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1991<t>
1992   The purpose of the 100 (Continue) status (see &status-100;) is to
1993   allow a client that is sending a request message with a request body
1994   to determine if the origin server is willing to accept the request
1995   (based on the request headers) before the client sends the request
1996   body. In some cases, it might either be inappropriate or highly
1997   inefficient for the client to send the body if the server will reject
1998   the message without looking at the body.
1999</t>
2000<t>
2001   Requirements for HTTP/1.1 clients:
2002  <list style="symbols">
2003    <t>
2004        If a client will wait for a 100 (Continue) response before
2005        sending the request body, it &MUST; send an Expect request-header
2006        field (&header-expect;) with the "100-continue" expectation.
2007    </t>
2008    <t>
2009        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2010        with the "100-continue" expectation if it does not intend
2011        to send a request body.
2012    </t>
2013  </list>
2014</t>
2015<t>
2016   Because of the presence of older implementations, the protocol allows
2017   ambiguous situations in which a client may send "Expect: 100-continue"
2018   without receiving either a 417 (Expectation Failed) status
2019   or a 100 (Continue) status. Therefore, when a client sends this
2020   header field to an origin server (possibly via a proxy) from which it
2021   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2022   for an indefinite period before sending the request body.
2023</t>
2024<t>
2025   Requirements for HTTP/1.1 origin servers:
2026  <list style="symbols">
2027    <t> Upon receiving a request which includes an Expect request-header
2028        field with the "100-continue" expectation, an origin server &MUST;
2029        either respond with 100 (Continue) status and continue to read
2030        from the input stream, or respond with a final status code. The
2031        origin server &MUST-NOT; wait for the request body before sending
2032        the 100 (Continue) response. If it responds with a final status
2033        code, it &MAY; close the transport connection or it &MAY; continue
2034        to read and discard the rest of the request.  It &MUST-NOT;
2035        perform the requested method if it returns a final status code.
2036    </t>
2037    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2038        the request message does not include an Expect request-header
2039        field with the "100-continue" expectation, and &MUST-NOT; send a
2040        100 (Continue) response if such a request comes from an HTTP/1.0
2041        (or earlier) client. There is an exception to this rule: for
2042        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2043        status in response to an HTTP/1.1 PUT or POST request that does
2044        not include an Expect request-header field with the "100-continue"
2045        expectation. This exception, the purpose of which is
2046        to minimize any client processing delays associated with an
2047        undeclared wait for 100 (Continue) status, applies only to
2048        HTTP/1.1 requests, and not to requests with any other HTTP-version
2049        value.
2050    </t>
2051    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2052        already received some or all of the request body for the
2053        corresponding request.
2054    </t>
2055    <t> An origin server that sends a 100 (Continue) response &MUST;
2056    ultimately send a final status code, once the request body is
2057        received and processed, unless it terminates the transport
2058        connection prematurely.
2059    </t>
2060    <t> If an origin server receives a request that does not include an
2061        Expect request-header field with the "100-continue" expectation,
2062        the request includes a request body, and the server responds
2063        with a final status code before reading the entire request body
2064        from the transport connection, then the server &SHOULD-NOT;  close
2065        the transport connection until it has read the entire request,
2066        or until the client closes the connection. Otherwise, the client
2067        might not reliably receive the response message. However, this
2068        requirement is not be construed as preventing a server from
2069        defending itself against denial-of-service attacks, or from
2070        badly broken client implementations.
2071      </t>
2072    </list>
2073</t>
2074<t>
2075   Requirements for HTTP/1.1 proxies:
2076  <list style="symbols">
2077    <t> If a proxy receives a request that includes an Expect request-header
2078        field with the "100-continue" expectation, and the proxy
2079        either knows that the next-hop server complies with HTTP/1.1 or
2080        higher, or does not know the HTTP version of the next-hop
2081        server, it &MUST; forward the request, including the Expect header
2082        field.
2083    </t>
2084    <t> If the proxy knows that the version of the next-hop server is
2085        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2086        respond with a 417 (Expectation Failed) status.
2087    </t>
2088    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2089        numbers received from recently-referenced next-hop servers.
2090    </t>
2091    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2092        request message was received from an HTTP/1.0 (or earlier)
2093        client and did not include an Expect request-header field with
2094        the "100-continue" expectation. This requirement overrides the
2095        general rule for forwarding of 1xx responses (see &status-1xx;).
2096    </t>
2097  </list>
2098</t>
2099</section>
2100
2101<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2102<t>
2103   If an HTTP/1.1 client sends a request which includes a request body,
2104   but which does not include an Expect request-header field with the
2105   "100-continue" expectation, and if the client is not directly
2106   connected to an HTTP/1.1 origin server, and if the client sees the
2107   connection close before receiving any status from the server, the
2108   client &SHOULD; retry the request.  If the client does retry this
2109   request, it &MAY; use the following "binary exponential backoff"
2110   algorithm to be assured of obtaining a reliable response:
2111  <list style="numbers">
2112    <t>
2113      Initiate a new connection to the server
2114    </t>
2115    <t>
2116      Transmit the request-headers
2117    </t>
2118    <t>
2119      Initialize a variable R to the estimated round-trip time to the
2120         server (e.g., based on the time it took to establish the
2121         connection), or to a constant value of 5 seconds if the round-trip
2122         time is not available.
2123    </t>
2124    <t>
2125       Compute T = R * (2**N), where N is the number of previous
2126         retries of this request.
2127    </t>
2128    <t>
2129       Wait either for an error response from the server, or for T
2130         seconds (whichever comes first)
2131    </t>
2132    <t>
2133       If no error response is received, after T seconds transmit the
2134         body of the request.
2135    </t>
2136    <t>
2137       If client sees that the connection is closed prematurely,
2138         repeat from step 1 until the request is accepted, an error
2139         response is received, or the user becomes impatient and
2140         terminates the retry process.
2141    </t>
2142  </list>
2143</t>
2144<t>
2145   If at any point an error status is received, the client
2146  <list style="symbols">
2147      <t>&SHOULD-NOT;  continue and</t>
2148
2149      <t>&SHOULD; close the connection if it has not completed sending the
2150        request message.</t>
2151    </list>
2152</t>
2153</section>
2154</section>
2155</section>
2156
2157
2158<section title="Header Field Definitions" anchor="header.fields">
2159<t>
2160   This section defines the syntax and semantics of HTTP/1.1 header fields
2161   related to message framing and transport protocols.
2162</t>
2163<t>
2164   For entity-header fields, both sender and recipient refer to either the
2165   client or the server, depending on who sends and who receives the entity.
2166</t>
2167
2168<section title="Connection" anchor="header.connection">
2169  <iref primary="true" item="Connection header" x:for-anchor=""/>
2170  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2171  <x:anchor-alias value="Connection"/>
2172  <x:anchor-alias value="connection-token"/>
2173  <x:anchor-alias value="Connection-v"/>
2174<t>
2175   The general-header field "Connection" allows the sender to specify
2176   options that are desired for that particular connection and &MUST-NOT;
2177   be communicated by proxies over further connections.
2178</t>
2179<t>
2180   The Connection header's value has the following grammar:
2181</t>
2182<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"/>
2183  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2184  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2185  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2186</artwork></figure>
2187<t>
2188   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2189   message is forwarded and, for each connection-token in this field,
2190   remove any header field(s) from the message with the same name as the
2191   connection-token. Connection options are signaled by the presence of
2192   a connection-token in the Connection header field, not by any
2193   corresponding additional header field(s), since the additional header
2194   field may not be sent if there are no parameters associated with that
2195   connection option.
2196</t>
2197<t>
2198   Message headers listed in the Connection header &MUST-NOT; include
2199   end-to-end headers, such as Cache-Control.
2200</t>
2201<t>
2202   HTTP/1.1 defines the "close" connection option for the sender to
2203   signal that the connection will be closed after completion of the
2204   response. For example,
2205</t>
2206<figure><artwork type="example">
2207  Connection: close
2208</artwork></figure>
2209<t>
2210   in either the request or the response header fields indicates that
2211   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2212   after the current request/response is complete.
2213</t>
2214<t>
2215   An HTTP/1.1 client that does not support persistent connections &MUST;
2216   include the "close" connection option in every request message.
2217</t>
2218<t>
2219   An HTTP/1.1 server that does not support persistent connections &MUST;
2220   include the "close" connection option in every response message that
2221   does not have a 1xx (informational) status code.
2222</t>
2223<t>
2224   A system receiving an HTTP/1.0 (or lower-version) message that
2225   includes a Connection header &MUST;, for each connection-token in this
2226   field, remove and ignore any header field(s) from the message with
2227   the same name as the connection-token. This protects against mistaken
2228   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2229</t>
2230</section>
2231
2232<section title="Content-Length" anchor="header.content-length">
2233  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2234  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2235  <x:anchor-alias value="Content-Length"/>
2236  <x:anchor-alias value="Content-Length-v"/>
2237<t>
2238   The entity-header field "Content-Length" indicates the size of the
2239   entity-body, in decimal number of OCTETs, sent to the recipient or,
2240   in the case of the HEAD method, the size of the entity-body that
2241   would have been sent had the request been a GET.
2242</t>
2243<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2244  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2245  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2246</artwork></figure>
2247<t>
2248   An example is
2249</t>
2250<figure><artwork type="example">
2251  Content-Length: 3495
2252</artwork></figure>
2253<t>
2254   Applications &SHOULD; use this field to indicate the transfer-length of
2255   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2256</t>
2257<t>
2258   Any Content-Length greater than or equal to zero is a valid value.
2259   <xref target="message.length"/> describes how to determine the length of a message-body
2260   if a Content-Length is not given.
2261</t>
2262<t>
2263   Note that the meaning of this field is significantly different from
2264   the corresponding definition in MIME, where it is an optional field
2265   used within the "message/external-body" content-type. In HTTP, it
2266   &SHOULD; be sent whenever the message's length can be determined prior
2267   to being transferred, unless this is prohibited by the rules in
2268   <xref target="message.length"/>.
2269</t>
2270</section>
2271
2272<section title="Date" anchor="header.date">
2273  <iref primary="true" item="Date header" x:for-anchor=""/>
2274  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2275  <x:anchor-alias value="Date"/>
2276  <x:anchor-alias value="Date-v"/>
2277<t>
2278   The general-header field "Date" represents the date and time at which
2279   the message was originated, having the same semantics as orig-date in
2280   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2281   HTTP-date, as described in <xref target="full.date"/>;
2282   it &MUST; be sent in rfc1123-date format.
2283</t>
2284<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2285  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2286  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2287</artwork></figure>
2288<t>
2289   An example is
2290</t>
2291<figure><artwork type="example">
2292  Date: Tue, 15 Nov 1994 08:12:31 GMT
2293</artwork></figure>
2294<t>
2295   Origin servers &MUST; include a Date header field in all responses,
2296   except in these cases:
2297  <list style="numbers">
2298      <t>If the response status code is 100 (Continue) or 101 (Switching
2299         Protocols), the response &MAY; include a Date header field, at
2300         the server's option.</t>
2301
2302      <t>If the response status code conveys a server error, e.g. 500
2303         (Internal Server Error) or 503 (Service Unavailable), and it is
2304         inconvenient or impossible to generate a valid Date.</t>
2305
2306      <t>If the server does not have a clock that can provide a
2307         reasonable approximation of the current time, its responses
2308         &MUST-NOT; include a Date header field. In this case, the rules
2309         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2310  </list>
2311</t>
2312<t>
2313   A received message that does not have a Date header field &MUST; be
2314   assigned one by the recipient if the message will be cached by that
2315   recipient or gatewayed via a protocol which requires a Date. An HTTP
2316   implementation without a clock &MUST-NOT; cache responses without
2317   revalidating them on every use. An HTTP cache, especially a shared
2318   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2319   clock with a reliable external standard.
2320</t>
2321<t>
2322   Clients &SHOULD; only send a Date header field in messages that include
2323   an entity-body, as in the case of the PUT and POST requests, and even
2324   then it is optional. A client without a clock &MUST-NOT; send a Date
2325   header field in a request.
2326</t>
2327<t>
2328   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2329   time subsequent to the generation of the message. It &SHOULD; represent
2330   the best available approximation of the date and time of message
2331   generation, unless the implementation has no means of generating a
2332   reasonably accurate date and time. In theory, the date ought to
2333   represent the moment just before the entity is generated. In
2334   practice, the date can be generated at any time during the message
2335   origination without affecting its semantic value.
2336</t>
2337
2338<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2339<t>
2340   Some origin server implementations might not have a clock available.
2341   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2342   values to a response, unless these values were associated
2343   with the resource by a system or user with a reliable clock. It &MAY;
2344   assign an Expires value that is known, at or before server
2345   configuration time, to be in the past (this allows "pre-expiration"
2346   of responses without storing separate Expires values for each
2347   resource).
2348</t>
2349</section>
2350</section>
2351
2352<section title="Host" anchor="header.host">
2353  <iref primary="true" item="Host header" x:for-anchor=""/>
2354  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2355  <x:anchor-alias value="Host"/>
2356  <x:anchor-alias value="Host-v"/>
2357<t>
2358   The request-header field "Host" specifies the Internet host and port
2359   number of the resource being requested, as obtained from the original
2360   URI given by the user or referring resource (generally an http URI,
2361   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2362   the naming authority of the origin server or gateway given by the
2363   original URL. This allows the origin server or gateway to
2364   differentiate between internally-ambiguous URLs, such as the root "/"
2365   URL of a server for multiple host names on a single IP address.
2366</t>
2367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2368  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2369  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2370</artwork></figure>
2371<t>
2372   A "host" without any trailing port information implies the default
2373   port for the service requested (e.g., "80" for an HTTP URL). For
2374   example, a request on the origin server for
2375   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2376</t>
2377<figure><artwork type="example">
2378  GET /pub/WWW/ HTTP/1.1
2379  Host: www.example.org
2380</artwork></figure>
2381<t>
2382   A client &MUST; include a Host header field in all HTTP/1.1 request
2383   messages. If the requested URI does not include an Internet host
2384   name for the service being requested, then the Host header field &MUST;
2385   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2386   request message it forwards does contain an appropriate Host header
2387   field that identifies the service being requested by the proxy. All
2388   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2389   status code to any HTTP/1.1 request message which lacks a Host header
2390   field.
2391</t>
2392<t>
2393   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2394   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2395   for other requirements relating to Host.
2396</t>
2397</section>
2398
2399<section title="TE" anchor="header.te">
2400  <iref primary="true" item="TE header" x:for-anchor=""/>
2401  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2402  <x:anchor-alias value="TE"/>
2403  <x:anchor-alias value="TE-v"/>
2404  <x:anchor-alias value="t-codings"/>
2405  <x:anchor-alias value="te-params"/>
2406  <x:anchor-alias value="te-ext"/>
2407<t>
2408   The request-header field "TE" indicates what extension transfer-codings
2409   it is willing to accept in the response and whether or not it is
2410   willing to accept trailer fields in a chunked transfer-coding. Its
2411   value may consist of the keyword "trailers" and/or a comma-separated
2412   list of extension transfer-coding names with optional accept
2413   parameters (as described in <xref target="transfer.codings"/>).
2414</t>
2415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2416  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2417  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2418  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2419  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2420  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2421</artwork></figure>
2422<t>
2423   The presence of the keyword "trailers" indicates that the client is
2424   willing to accept trailer fields in a chunked transfer-coding, as
2425   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2426   transfer-coding values even though it does not itself represent a
2427   transfer-coding.
2428</t>
2429<t>
2430   Examples of its use are:
2431</t>
2432<figure><artwork type="example">
2433  TE: deflate
2434  TE:
2435  TE: trailers, deflate;q=0.5
2436</artwork></figure>
2437<t>
2438   The TE header field only applies to the immediate connection.
2439   Therefore, the keyword &MUST; be supplied within a Connection header
2440   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2441</t>
2442<t>
2443   A server tests whether a transfer-coding is acceptable, according to
2444   a TE field, using these rules:
2445  <list style="numbers">
2446    <x:lt>
2447      <t>The "chunked" transfer-coding is always acceptable. If the
2448         keyword "trailers" is listed, the client indicates that it is
2449         willing to accept trailer fields in the chunked response on
2450         behalf of itself and any downstream clients. The implication is
2451         that, if given, the client is stating that either all
2452         downstream clients are willing to accept trailer fields in the
2453         forwarded response, or that it will attempt to buffer the
2454         response on behalf of downstream recipients.
2455      </t><t>
2456         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2457         chunked response such that a client can be assured of buffering
2458         the entire response.</t>
2459    </x:lt>
2460    <x:lt>
2461      <t>If the transfer-coding being tested is one of the transfer-codings
2462         listed in the TE field, then it is acceptable unless it
2463         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2464         qvalue of 0 means "not acceptable.")</t>
2465    </x:lt>
2466    <x:lt>
2467      <t>If multiple transfer-codings are acceptable, then the
2468         acceptable transfer-coding with the highest non-zero qvalue is
2469         preferred.  The "chunked" transfer-coding always has a qvalue
2470         of 1.</t>
2471    </x:lt>
2472  </list>
2473</t>
2474<t>
2475   If the TE field-value is empty or if no TE field is present, the only
2476   transfer-coding is "chunked". A message with no transfer-coding is
2477   always acceptable.
2478</t>
2479</section>
2480
2481<section title="Trailer" anchor="header.trailer">
2482  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2483  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2484  <x:anchor-alias value="Trailer"/>
2485  <x:anchor-alias value="Trailer-v"/>
2486<t>
2487   The general field "Trailer" indicates that the given set of
2488   header fields is present in the trailer of a message encoded with
2489   chunked transfer-coding.
2490</t>
2491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2492  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2493  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2494</artwork></figure>
2495<t>
2496   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2497   message using chunked transfer-coding with a non-empty trailer. Doing
2498   so allows the recipient to know which header fields to expect in the
2499   trailer.
2500</t>
2501<t>
2502   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2503   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2504   trailer fields in a "chunked" transfer-coding.
2505</t>
2506<t>
2507   Message header fields listed in the Trailer header field &MUST-NOT;
2508   include the following header fields:
2509  <list style="symbols">
2510    <t>Transfer-Encoding</t>
2511    <t>Content-Length</t>
2512    <t>Trailer</t>
2513  </list>
2514</t>
2515</section>
2516
2517<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2518  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2519  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2520  <x:anchor-alias value="Transfer-Encoding"/>
2521  <x:anchor-alias value="Transfer-Encoding-v"/>
2522<t>
2523   The general-header "Transfer-Encoding" field indicates what (if any)
2524   type of transformation has been applied to the message body in order
2525   to safely transfer it between the sender and the recipient. This
2526   differs from the content-coding in that the transfer-coding is a
2527   property of the message, not of the entity.
2528</t>
2529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2530  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2531                        <x:ref>Transfer-Encoding-v</x:ref>
2532  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2533</artwork></figure>
2534<t>
2535   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2536</t>
2537<figure><artwork type="example">
2538  Transfer-Encoding: chunked
2539</artwork></figure>
2540<t>
2541   If multiple encodings have been applied to an entity, the transfer-codings
2542   &MUST; be listed in the order in which they were applied.
2543   Additional information about the encoding parameters &MAY; be provided
2544   by other entity-header fields not defined by this specification.
2545</t>
2546<t>
2547   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2548   header.
2549</t>
2550</section>
2551
2552<section title="Upgrade" anchor="header.upgrade">
2553  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2554  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2555  <x:anchor-alias value="Upgrade"/>
2556  <x:anchor-alias value="Upgrade-v"/>
2557<t>
2558   The general-header "Upgrade" allows the client to specify what
2559   additional communication protocols it supports and would like to use
2560   if the server finds it appropriate to switch protocols. The server
2561   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2562   response to indicate which protocol(s) are being switched.
2563</t>
2564<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2565  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2566  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2567</artwork></figure>
2568<t>
2569   For example,
2570</t>
2571<figure><artwork type="example">
2572  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2573</artwork></figure>
2574<t>
2575   The Upgrade header field is intended to provide a simple mechanism
2576   for transition from HTTP/1.1 to some other, incompatible protocol. It
2577   does so by allowing the client to advertise its desire to use another
2578   protocol, such as a later version of HTTP with a higher major version
2579   number, even though the current request has been made using HTTP/1.1.
2580   This eases the difficult transition between incompatible protocols by
2581   allowing the client to initiate a request in the more commonly
2582   supported protocol while indicating to the server that it would like
2583   to use a "better" protocol if available (where "better" is determined
2584   by the server, possibly according to the nature of the method and/or
2585   resource being requested).
2586</t>
2587<t>
2588   The Upgrade header field only applies to switching application-layer
2589   protocols upon the existing transport-layer connection. Upgrade
2590   cannot be used to insist on a protocol change; its acceptance and use
2591   by the server is optional. The capabilities and nature of the
2592   application-layer communication after the protocol change is entirely
2593   dependent upon the new protocol chosen, although the first action
2594   after changing the protocol &MUST; be a response to the initial HTTP
2595   request containing the Upgrade header field.
2596</t>
2597<t>
2598   The Upgrade header field only applies to the immediate connection.
2599   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2600   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2601   HTTP/1.1 message.
2602</t>
2603<t>
2604   The Upgrade header field cannot be used to indicate a switch to a
2605   protocol on a different connection. For that purpose, it is more
2606   appropriate to use a 301, 302, 303, or 305 redirection response.
2607</t>
2608<t>
2609   This specification only defines the protocol name "HTTP" for use by
2610   the family of Hypertext Transfer Protocols, as defined by the HTTP
2611   version rules of <xref target="http.version"/> and future updates to this
2612   specification. Any token can be used as a protocol name; however, it
2613   will only be useful if both the client and server associate the name
2614   with the same protocol.
2615</t>
2616</section>
2617
2618<section title="Via" anchor="header.via">
2619  <iref primary="true" item="Via header" x:for-anchor=""/>
2620  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2621  <x:anchor-alias value="protocol-name"/>
2622  <x:anchor-alias value="protocol-version"/>
2623  <x:anchor-alias value="pseudonym"/>
2624  <x:anchor-alias value="received-by"/>
2625  <x:anchor-alias value="received-protocol"/>
2626  <x:anchor-alias value="Via"/>
2627  <x:anchor-alias value="Via-v"/>
2628<t>
2629   The general-header field "Via" &MUST; be used by gateways and proxies to
2630   indicate the intermediate protocols and recipients between the user
2631   agent and the server on requests, and between the origin server and
2632   the client on responses. It is analogous to the "Received" field defined in
2633   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2634   avoiding request loops, and identifying the protocol capabilities of
2635   all senders along the request/response chain.
2636</t>
2637<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"/>
2638  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2639  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2640                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2641  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2642  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2643  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2644  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2645  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2646</artwork></figure>
2647<t>
2648   The received-protocol indicates the protocol version of the message
2649   received by the server or client along each segment of the
2650   request/response chain. The received-protocol version is appended to
2651   the Via field value when the message is forwarded so that information
2652   about the protocol capabilities of upstream applications remains
2653   visible to all recipients.
2654</t>
2655<t>
2656   The protocol-name is optional if and only if it would be "HTTP". The
2657   received-by field is normally the host and optional port number of a
2658   recipient server or client that subsequently forwarded the message.
2659   However, if the real host is considered to be sensitive information,
2660   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2661   be assumed to be the default port of the received-protocol.
2662</t>
2663<t>
2664   Multiple Via field values represents each proxy or gateway that has
2665   forwarded the message. Each recipient &MUST; append its information
2666   such that the end result is ordered according to the sequence of
2667   forwarding applications.
2668</t>
2669<t>
2670   Comments &MAY; be used in the Via header field to identify the software
2671   of the recipient proxy or gateway, analogous to the User-Agent and
2672   Server header fields. However, all comments in the Via field are
2673   optional and &MAY; be removed by any recipient prior to forwarding the
2674   message.
2675</t>
2676<t>
2677   For example, a request message could be sent from an HTTP/1.0 user
2678   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2679   forward the request to a public proxy at p.example.net, which completes
2680   the request by forwarding it to the origin server at www.example.com.
2681   The request received by www.example.com would then have the following
2682   Via header field:
2683</t>
2684<figure><artwork type="example">
2685  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2686</artwork></figure>
2687<t>
2688   Proxies and gateways used as a portal through a network firewall
2689   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2690   the firewall region. This information &SHOULD; only be propagated if
2691   explicitly enabled. If not enabled, the received-by host of any host
2692   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2693   for that host.
2694</t>
2695<t>
2696   For organizations that have strong privacy requirements for hiding
2697   internal structures, a proxy &MAY; combine an ordered subsequence of
2698   Via header field entries with identical received-protocol values into
2699   a single such entry. For example,
2700</t>
2701<figure><artwork type="example">
2702  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2703</artwork></figure>
2704<t>
2705        could be collapsed to
2706</t>
2707<figure><artwork type="example">
2708  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2709</artwork></figure>
2710<t>
2711   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2712   under the same organizational control and the hosts have already been
2713   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2714   have different received-protocol values.
2715</t>
2716</section>
2717
2718</section>
2719
2720<section title="IANA Considerations" anchor="IANA.considerations">
2721<section title="Message Header Registration" anchor="message.header.registration">
2722<t>
2723   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2724   with the permanent registrations below (see <xref target="RFC3864"/>):
2725</t>
2726<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2727<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2728   <ttcol>Header Field Name</ttcol>
2729   <ttcol>Protocol</ttcol>
2730   <ttcol>Status</ttcol>
2731   <ttcol>Reference</ttcol>
2732
2733   <c>Connection</c>
2734   <c>http</c>
2735   <c>standard</c>
2736   <c>
2737      <xref target="header.connection"/>
2738   </c>
2739   <c>Content-Length</c>
2740   <c>http</c>
2741   <c>standard</c>
2742   <c>
2743      <xref target="header.content-length"/>
2744   </c>
2745   <c>Date</c>
2746   <c>http</c>
2747   <c>standard</c>
2748   <c>
2749      <xref target="header.date"/>
2750   </c>
2751   <c>Host</c>
2752   <c>http</c>
2753   <c>standard</c>
2754   <c>
2755      <xref target="header.host"/>
2756   </c>
2757   <c>TE</c>
2758   <c>http</c>
2759   <c>standard</c>
2760   <c>
2761      <xref target="header.te"/>
2762   </c>
2763   <c>Trailer</c>
2764   <c>http</c>
2765   <c>standard</c>
2766   <c>
2767      <xref target="header.trailer"/>
2768   </c>
2769   <c>Transfer-Encoding</c>
2770   <c>http</c>
2771   <c>standard</c>
2772   <c>
2773      <xref target="header.transfer-encoding"/>
2774   </c>
2775   <c>Upgrade</c>
2776   <c>http</c>
2777   <c>standard</c>
2778   <c>
2779      <xref target="header.upgrade"/>
2780   </c>
2781   <c>Via</c>
2782   <c>http</c>
2783   <c>standard</c>
2784   <c>
2785      <xref target="header.via"/>
2786   </c>
2787</texttable>
2788<!--(END)-->
2789<t>
2790   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2791</t>
2792</section>
2793
2794<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2795<t>
2796   The entry for the "http" URI Scheme in the registry located at
2797   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2798   should be updated to point to <xref target="http.uri"/> of this document
2799   (see <xref target="RFC4395"/>).
2800</t>
2801</section>
2802
2803<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2804<t>
2805   This document serves as the specification for the Internet media types
2806   "message/http" and "application/http". The following is to be registered with
2807   IANA (see <xref target="RFC4288"/>).
2808</t>
2809<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2810<iref item="Media Type" subitem="message/http" primary="true"/>
2811<iref item="message/http Media Type" primary="true"/>
2812<t>
2813   The message/http type can be used to enclose a single HTTP request or
2814   response message, provided that it obeys the MIME restrictions for all
2815   "message" types regarding line length and encodings.
2816</t>
2817<t>
2818  <list style="hanging" x:indent="12em">
2819    <t hangText="Type name:">
2820      message
2821    </t>
2822    <t hangText="Subtype name:">
2823      http
2824    </t>
2825    <t hangText="Required parameters:">
2826      none
2827    </t>
2828    <t hangText="Optional parameters:">
2829      version, msgtype
2830      <list style="hanging">
2831        <t hangText="version:">
2832          The HTTP-Version number of the enclosed message
2833          (e.g., "1.1"). If not present, the version can be
2834          determined from the first line of the body.
2835        </t>
2836        <t hangText="msgtype:">
2837          The message type -- "request" or "response". If not
2838          present, the type can be determined from the first
2839          line of the body.
2840        </t>
2841      </list>
2842    </t>
2843    <t hangText="Encoding considerations:">
2844      only "7bit", "8bit", or "binary" are permitted
2845    </t>
2846    <t hangText="Security considerations:">
2847      none
2848    </t>
2849    <t hangText="Interoperability considerations:">
2850      none
2851    </t>
2852    <t hangText="Published specification:">
2853      This specification (see <xref target="internet.media.type.message.http"/>).
2854    </t>
2855    <t hangText="Applications that use this media type:">
2856    </t>
2857    <t hangText="Additional information:">
2858      <list style="hanging">
2859        <t hangText="Magic number(s):">none</t>
2860        <t hangText="File extension(s):">none</t>
2861        <t hangText="Macintosh file type code(s):">none</t>
2862      </list>
2863    </t>
2864    <t hangText="Person and email address to contact for further information:">
2865      See Authors Section.
2866    </t>
2867                <t hangText="Intended usage:">
2868                  COMMON
2869    </t>
2870                <t hangText="Restrictions on usage:">
2871                  none
2872    </t>
2873    <t hangText="Author/Change controller:">
2874      IESG
2875    </t>
2876  </list>
2877</t>
2878</section>
2879<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2880<iref item="Media Type" subitem="application/http" primary="true"/>
2881<iref item="application/http Media Type" primary="true"/>
2882<t>
2883   The application/http type can be used to enclose a pipeline of one or more
2884   HTTP request or response messages (not intermixed).
2885</t>
2886<t>
2887  <list style="hanging" x:indent="12em">
2888    <t hangText="Type name:">
2889      application
2890    </t>
2891    <t hangText="Subtype name:">
2892      http
2893    </t>
2894    <t hangText="Required parameters:">
2895      none
2896    </t>
2897    <t hangText="Optional parameters:">
2898      version, msgtype
2899      <list style="hanging">
2900        <t hangText="version:">
2901          The HTTP-Version number of the enclosed messages
2902          (e.g., "1.1"). If not present, the version can be
2903          determined from the first line of the body.
2904        </t>
2905        <t hangText="msgtype:">
2906          The message type -- "request" or "response". If not
2907          present, the type can be determined from the first
2908          line of the body.
2909        </t>
2910      </list>
2911    </t>
2912    <t hangText="Encoding considerations:">
2913      HTTP messages enclosed by this type
2914      are in "binary" format; use of an appropriate
2915      Content-Transfer-Encoding is required when
2916      transmitted via E-mail.
2917    </t>
2918    <t hangText="Security considerations:">
2919      none
2920    </t>
2921    <t hangText="Interoperability considerations:">
2922      none
2923    </t>
2924    <t hangText="Published specification:">
2925      This specification (see <xref target="internet.media.type.application.http"/>).
2926    </t>
2927    <t hangText="Applications that use this media type:">
2928    </t>
2929    <t hangText="Additional information:">
2930      <list style="hanging">
2931        <t hangText="Magic number(s):">none</t>
2932        <t hangText="File extension(s):">none</t>
2933        <t hangText="Macintosh file type code(s):">none</t>
2934      </list>
2935    </t>
2936    <t hangText="Person and email address to contact for further information:">
2937      See Authors Section.
2938    </t>
2939                <t hangText="Intended usage:">
2940                  COMMON
2941    </t>
2942                <t hangText="Restrictions on usage:">
2943                  none
2944    </t>
2945    <t hangText="Author/Change controller:">
2946      IESG
2947    </t>
2948  </list>
2949</t>
2950</section>
2951</section>
2952
2953</section>
2954
2955<section title="Security Considerations" anchor="security.considerations">
2956<t>
2957   This section is meant to inform application developers, information
2958   providers, and users of the security limitations in HTTP/1.1 as
2959   described by this document. The discussion does not include
2960   definitive solutions to the problems revealed, though it does make
2961   some suggestions for reducing security risks.
2962</t>
2963
2964<section title="Personal Information" anchor="personal.information">
2965<t>
2966   HTTP clients are often privy to large amounts of personal information
2967   (e.g. the user's name, location, mail address, passwords, encryption
2968   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2969   leakage of this information.
2970   We very strongly recommend that a convenient interface be provided
2971   for the user to control dissemination of such information, and that
2972   designers and implementors be particularly careful in this area.
2973   History shows that errors in this area often create serious security
2974   and/or privacy problems and generate highly adverse publicity for the
2975   implementor's company.
2976</t>
2977</section>
2978
2979<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2980<t>
2981   A server is in the position to save personal data about a user's
2982   requests which might identify their reading patterns or subjects of
2983   interest. This information is clearly confidential in nature and its
2984   handling can be constrained by law in certain countries. People using
2985   HTTP to provide data are responsible for ensuring that
2986   such material is not distributed without the permission of any
2987   individuals that are identifiable by the published results.
2988</t>
2989</section>
2990
2991<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2992<t>
2993   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2994   the documents returned by HTTP requests to be only those that were
2995   intended by the server administrators. If an HTTP server translates
2996   HTTP URIs directly into file system calls, the server &MUST; take
2997   special care not to serve files that were not intended to be
2998   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2999   other operating systems use ".." as a path component to indicate a
3000   directory level above the current one. On such a system, an HTTP
3001   server &MUST; disallow any such construct in the request-target if it
3002   would otherwise allow access to a resource outside those intended to
3003   be accessible via the HTTP server. Similarly, files intended for
3004   reference only internally to the server (such as access control
3005   files, configuration files, and script code) &MUST; be protected from
3006   inappropriate retrieval, since they might contain sensitive
3007   information. Experience has shown that minor bugs in such HTTP server
3008   implementations have turned into security risks.
3009</t>
3010</section>
3011
3012<section title="DNS Spoofing" anchor="dns.spoofing">
3013<t>
3014   Clients using HTTP rely heavily on the Domain Name Service, and are
3015   thus generally prone to security attacks based on the deliberate
3016   mis-association of IP addresses and DNS names. Clients need to be
3017   cautious in assuming the continuing validity of an IP number/DNS name
3018   association.
3019</t>
3020<t>
3021   In particular, HTTP clients &SHOULD; rely on their name resolver for
3022   confirmation of an IP number/DNS name association, rather than
3023   caching the result of previous host name lookups. Many platforms
3024   already can cache host name lookups locally when appropriate, and
3025   they &SHOULD; be configured to do so. It is proper for these lookups to
3026   be cached, however, only when the TTL (Time To Live) information
3027   reported by the name server makes it likely that the cached
3028   information will remain useful.
3029</t>
3030<t>
3031   If HTTP clients cache the results of host name lookups in order to
3032   achieve a performance improvement, they &MUST; observe the TTL
3033   information reported by DNS.
3034</t>
3035<t>
3036   If HTTP clients do not observe this rule, they could be spoofed when
3037   a previously-accessed server's IP address changes. As network
3038   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3039   possibility of this form of attack will grow. Observing this
3040   requirement thus reduces this potential security vulnerability.
3041</t>
3042<t>
3043   This requirement also improves the load-balancing behavior of clients
3044   for replicated servers using the same DNS name and reduces the
3045   likelihood of a user's experiencing failure in accessing sites which
3046   use that strategy.
3047</t>
3048</section>
3049
3050<section title="Proxies and Caching" anchor="attack.proxies">
3051<t>
3052   By their very nature, HTTP proxies are men-in-the-middle, and
3053   represent an opportunity for man-in-the-middle attacks. Compromise of
3054   the systems on which the proxies run can result in serious security
3055   and privacy problems. Proxies have access to security-related
3056   information, personal information about individual users and
3057   organizations, and proprietary information belonging to users and
3058   content providers. A compromised proxy, or a proxy implemented or
3059   configured without regard to security and privacy considerations,
3060   might be used in the commission of a wide range of potential attacks.
3061</t>
3062<t>
3063   Proxy operators should protect the systems on which proxies run as
3064   they would protect any system that contains or transports sensitive
3065   information. In particular, log information gathered at proxies often
3066   contains highly sensitive personal information, and/or information
3067   about organizations. Log information should be carefully guarded, and
3068   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3069</t>
3070<t>
3071   Proxy implementors should consider the privacy and security
3072   implications of their design and coding decisions, and of the
3073   configuration options they provide to proxy operators (especially the
3074   default configuration).
3075</t>
3076<t>
3077   Users of a proxy need to be aware that they are no trustworthier than
3078   the people who run the proxy; HTTP itself cannot solve this problem.
3079</t>
3080<t>
3081   The judicious use of cryptography, when appropriate, may suffice to
3082   protect against a broad range of security and privacy attacks. Such
3083   cryptography is beyond the scope of the HTTP/1.1 specification.
3084</t>
3085</section>
3086
3087<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3088<t>
3089   They exist. They are hard to defend against. Research continues.
3090   Beware.
3091</t>
3092</section>
3093</section>
3094
3095<section title="Acknowledgments" anchor="ack">
3096<t>
3097   HTTP has evolved considerably over the years. It has
3098   benefited from a large and active developer community--the many
3099   people who have participated on the www-talk mailing list--and it is
3100   that community which has been most responsible for the success of
3101   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3102   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3103   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3104   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3105   VanHeyningen deserve special recognition for their efforts in
3106   defining early aspects of the protocol.
3107</t>
3108<t>
3109   This document has benefited greatly from the comments of all those
3110   participating in the HTTP-WG. In addition to those already mentioned,
3111   the following individuals have contributed to this specification:
3112</t>
3113<t>
3114   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3115   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3116   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3117   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3118   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3119   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3120   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3121   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3122   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3123   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3124   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3125   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3126   Josh Cohen.
3127</t>
3128<t>
3129   Thanks to the "cave men" of Palo Alto. You know who you are.
3130</t>
3131<t>
3132   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3133   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3134   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3135   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3136   Larry Masinter for their help. And thanks go particularly to Jeff
3137   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3138</t>
3139<t>
3140   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3141   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3142   discovery of many of the problems that this document attempts to
3143   rectify.
3144</t>
3145<t>
3146   This specification makes heavy use of the augmented BNF and generic
3147   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3148   reuses many of the definitions provided by Nathaniel Borenstein and
3149   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3150   specification will help reduce past confusion over the relationship
3151   between HTTP and Internet mail message formats.
3152</t>
3153</section>
3154
3155</middle>
3156<back>
3157
3158<references title="Normative References">
3159
3160<reference anchor="ISO-8859-1">
3161  <front>
3162    <title>
3163     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3164    </title>
3165    <author>
3166      <organization>International Organization for Standardization</organization>
3167    </author>
3168    <date year="1998"/>
3169  </front>
3170  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3171</reference>
3172
3173<reference anchor="Part2">
3174  <front>
3175    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3176    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3177      <organization abbrev="Day Software">Day Software</organization>
3178      <address><email>fielding@gbiv.com</email></address>
3179    </author>
3180    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3181      <organization>One Laptop per Child</organization>
3182      <address><email>jg@laptop.org</email></address>
3183    </author>
3184    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3185      <organization abbrev="HP">Hewlett-Packard Company</organization>
3186      <address><email>JeffMogul@acm.org</email></address>
3187    </author>
3188    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3189      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3190      <address><email>henrikn@microsoft.com</email></address>
3191    </author>
3192    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3193      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3194      <address><email>LMM@acm.org</email></address>
3195    </author>
3196    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3197      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3198      <address><email>paulle@microsoft.com</email></address>
3199    </author>
3200    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3201      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3202      <address><email>timbl@w3.org</email></address>
3203    </author>
3204    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3205      <organization abbrev="W3C">World Wide Web Consortium</organization>
3206      <address><email>ylafon@w3.org</email></address>
3207    </author>
3208    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3209      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3210      <address><email>julian.reschke@greenbytes.de</email></address>
3211    </author>
3212    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3213  </front>
3214  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3215  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3216</reference>
3217
3218<reference anchor="Part3">
3219  <front>
3220    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3221    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3222      <organization abbrev="Day Software">Day Software</organization>
3223      <address><email>fielding@gbiv.com</email></address>
3224    </author>
3225    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3226      <organization>One Laptop per Child</organization>
3227      <address><email>jg@laptop.org</email></address>
3228    </author>
3229    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3230      <organization abbrev="HP">Hewlett-Packard Company</organization>
3231      <address><email>JeffMogul@acm.org</email></address>
3232    </author>
3233    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3234      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3235      <address><email>henrikn@microsoft.com</email></address>
3236    </author>
3237    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3238      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3239      <address><email>LMM@acm.org</email></address>
3240    </author>
3241    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3242      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3243      <address><email>paulle@microsoft.com</email></address>
3244    </author>
3245    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3246      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3247      <address><email>timbl@w3.org</email></address>
3248    </author>
3249    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3250      <organization abbrev="W3C">World Wide Web Consortium</organization>
3251      <address><email>ylafon@w3.org</email></address>
3252    </author>
3253    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3254      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3255      <address><email>julian.reschke@greenbytes.de</email></address>
3256    </author>
3257    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3258  </front>
3259  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3260  <x:source href="p3-payload.xml" basename="p3-payload"/>
3261</reference>
3262
3263<reference anchor="Part5">
3264  <front>
3265    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3266    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3267      <organization abbrev="Day Software">Day Software</organization>
3268      <address><email>fielding@gbiv.com</email></address>
3269    </author>
3270    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3271      <organization>One Laptop per Child</organization>
3272      <address><email>jg@laptop.org</email></address>
3273    </author>
3274    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3275      <organization abbrev="HP">Hewlett-Packard Company</organization>
3276      <address><email>JeffMogul@acm.org</email></address>
3277    </author>
3278    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3279      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3280      <address><email>henrikn@microsoft.com</email></address>
3281    </author>
3282    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3283      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3284      <address><email>LMM@acm.org</email></address>
3285    </author>
3286    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3287      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3288      <address><email>paulle@microsoft.com</email></address>
3289    </author>
3290    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3291      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3292      <address><email>timbl@w3.org</email></address>
3293    </author>
3294    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3295      <organization abbrev="W3C">World Wide Web Consortium</organization>
3296      <address><email>ylafon@w3.org</email></address>
3297    </author>
3298    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3299      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3300      <address><email>julian.reschke@greenbytes.de</email></address>
3301    </author>
3302    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3303  </front>
3304  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3305  <x:source href="p5-range.xml" basename="p5-range"/>
3306</reference>
3307
3308<reference anchor="Part6">
3309  <front>
3310    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3311    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3312      <organization abbrev="Day Software">Day Software</organization>
3313      <address><email>fielding@gbiv.com</email></address>
3314    </author>
3315    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3316      <organization>One Laptop per Child</organization>
3317      <address><email>jg@laptop.org</email></address>
3318    </author>
3319    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3320      <organization abbrev="HP">Hewlett-Packard Company</organization>
3321      <address><email>JeffMogul@acm.org</email></address>
3322    </author>
3323    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3324      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3325      <address><email>henrikn@microsoft.com</email></address>
3326    </author>
3327    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3328      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3329      <address><email>LMM@acm.org</email></address>
3330    </author>
3331    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3332      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3333      <address><email>paulle@microsoft.com</email></address>
3334    </author>
3335    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3336      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3337      <address><email>timbl@w3.org</email></address>
3338    </author>
3339    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3340      <organization abbrev="W3C">World Wide Web Consortium</organization>
3341      <address><email>ylafon@w3.org</email></address>
3342    </author>
3343    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3344      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3345      <address><email>julian.reschke@greenbytes.de</email></address>
3346    </author>
3347    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3348  </front>
3349  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3350  <x:source href="p6-cache.xml" basename="p6-cache"/>
3351</reference>
3352
3353<reference anchor="RFC5234">
3354  <front>
3355    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3356    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3357      <organization>Brandenburg InternetWorking</organization>
3358      <address>
3359      <postal>
3360      <street>675 Spruce Dr.</street>
3361      <city>Sunnyvale</city>
3362      <region>CA</region>
3363      <code>94086</code>
3364      <country>US</country></postal>
3365      <phone>+1.408.246.8253</phone>
3366      <email>dcrocker@bbiw.net</email></address> 
3367    </author>
3368    <author initials="P." surname="Overell" fullname="Paul Overell">
3369      <organization>THUS plc.</organization>
3370      <address>
3371      <postal>
3372      <street>1/2 Berkeley Square</street>
3373      <street>99 Berkely Street</street>
3374      <city>Glasgow</city>
3375      <code>G3 7HR</code>
3376      <country>UK</country></postal>
3377      <email>paul.overell@thus.net</email></address>
3378    </author>
3379    <date month="January" year="2008"/>
3380  </front>
3381  <seriesInfo name="STD" value="68"/>
3382  <seriesInfo name="RFC" value="5234"/>
3383</reference>
3384
3385<reference anchor="RFC2119">
3386  <front>
3387    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3388    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3389      <organization>Harvard University</organization>
3390      <address><email>sob@harvard.edu</email></address>
3391    </author>
3392    <date month="March" year="1997"/>
3393  </front>
3394  <seriesInfo name="BCP" value="14"/>
3395  <seriesInfo name="RFC" value="2119"/>
3396</reference>
3397
3398<reference anchor="RFC3986">
3399 <front>
3400  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3401  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3402    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3403    <address>
3404       <email>timbl@w3.org</email>
3405       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3406    </address>
3407  </author>
3408  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3409    <organization abbrev="Day Software">Day Software</organization>
3410    <address>
3411      <email>fielding@gbiv.com</email>
3412      <uri>http://roy.gbiv.com/</uri>
3413    </address>
3414  </author>
3415  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3416    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3417    <address>
3418      <email>LMM@acm.org</email>
3419      <uri>http://larry.masinter.net/</uri>
3420    </address>
3421  </author>
3422  <date month='January' year='2005'></date>
3423 </front>
3424 <seriesInfo name="RFC" value="3986"/>
3425 <seriesInfo name="STD" value="66"/>
3426</reference>
3427
3428<reference anchor="USASCII">
3429  <front>
3430    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3431    <author>
3432      <organization>American National Standards Institute</organization>
3433    </author>
3434    <date year="1986"/>
3435  </front>
3436  <seriesInfo name="ANSI" value="X3.4"/>
3437</reference>
3438
3439</references>
3440
3441<references title="Informative References">
3442
3443<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3444  <front>
3445    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3446    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3447      <organization/>
3448    </author>
3449    <author initials="J." surname="Gettys" fullname="J. Gettys">
3450      <organization/>
3451    </author>
3452    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3453      <organization/>
3454    </author>
3455    <author initials="H." surname="Lie" fullname="H. Lie">
3456      <organization/>
3457    </author>
3458    <author initials="C." surname="Lilley" fullname="C. Lilley">
3459      <organization/>
3460    </author>
3461    <date year="1997" month="September"/>
3462  </front>
3463  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3464</reference>
3465
3466<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3467  <front>
3468    <title>Improving HTTP Latency</title>
3469    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3470      <organization/>
3471    </author>
3472    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3473      <organization/>
3474    </author>
3475    <date year="1995" month="December"/>
3476  </front>
3477  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3478</reference>
3479
3480<reference anchor="RFC959">
3481  <front>
3482    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3483    <author initials="J." surname="Postel" fullname="J. Postel">
3484      <organization>Information Sciences Institute (ISI)</organization>
3485    </author>
3486    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3487      <organization/>
3488    </author>
3489    <date month="October" year="1985"/>
3490  </front>
3491  <seriesInfo name="STD" value="9"/>
3492  <seriesInfo name="RFC" value="959"/>
3493</reference>
3494
3495<reference anchor="RFC1123">
3496  <front>
3497    <title>Requirements for Internet Hosts - Application and Support</title>
3498    <author initials="R." surname="Braden" fullname="Robert Braden">
3499      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3500      <address><email>Braden@ISI.EDU</email></address>
3501    </author>
3502    <date month="October" year="1989"/>
3503  </front>
3504  <seriesInfo name="STD" value="3"/>
3505  <seriesInfo name="RFC" value="1123"/>
3506</reference>
3507
3508<reference anchor="RFC1305">
3509  <front>
3510    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3511    <author initials="D." surname="Mills" fullname="David L. Mills">
3512      <organization>University of Delaware, Electrical Engineering Department</organization>
3513      <address><email>mills@udel.edu</email></address>
3514    </author>
3515    <date month="March" year="1992"/>
3516  </front>
3517  <seriesInfo name="RFC" value="1305"/>
3518</reference>
3519
3520<reference anchor="RFC1436">
3521  <front>
3522    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3523    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3524      <organization>University of Minnesota, Computer and Information Services</organization>
3525      <address><email>fxa@boombox.micro.umn.edu</email></address>
3526    </author>
3527    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3528      <organization>University of Minnesota, Computer and Information Services</organization>
3529      <address><email>mpm@boombox.micro.umn.edu</email></address>
3530    </author>
3531    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3532      <organization>University of Minnesota, Computer and Information Services</organization>
3533      <address><email>lindner@boombox.micro.umn.edu</email></address>
3534    </author>
3535    <author initials="D." surname="Johnson" fullname="David Johnson">
3536      <organization>University of Minnesota, Computer and Information Services</organization>
3537      <address><email>dmj@boombox.micro.umn.edu</email></address>
3538    </author>
3539    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3540      <organization>University of Minnesota, Computer and Information Services</organization>
3541      <address><email>daniel@boombox.micro.umn.edu</email></address>
3542    </author>
3543    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3544      <organization>University of Minnesota, Computer and Information Services</organization>
3545      <address><email>alberti@boombox.micro.umn.edu</email></address>
3546    </author>
3547    <date month="March" year="1993"/>
3548  </front>
3549  <seriesInfo name="RFC" value="1436"/>
3550</reference>
3551
3552<reference anchor="RFC1900">
3553  <front>
3554    <title>Renumbering Needs Work</title>
3555    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3556      <organization>CERN, Computing and Networks Division</organization>
3557      <address><email>brian@dxcoms.cern.ch</email></address>
3558    </author>
3559    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3560      <organization>cisco Systems</organization>
3561      <address><email>yakov@cisco.com</email></address>
3562    </author>
3563    <date month="February" year="1996"/>
3564  </front>
3565  <seriesInfo name="RFC" value="1900"/>
3566</reference>
3567
3568<reference anchor="RFC1945">
3569  <front>
3570    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3571    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3572      <organization>MIT, Laboratory for Computer Science</organization>
3573      <address><email>timbl@w3.org</email></address>
3574    </author>
3575    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3576      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3577      <address><email>fielding@ics.uci.edu</email></address>
3578    </author>
3579    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3580      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3581      <address><email>frystyk@w3.org</email></address>
3582    </author>
3583    <date month="May" year="1996"/>
3584  </front>
3585  <seriesInfo name="RFC" value="1945"/>
3586</reference>
3587
3588<reference anchor="RFC2045">
3589  <front>
3590    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3591    <author initials="N." surname="Freed" fullname="Ned Freed">
3592      <organization>Innosoft International, Inc.</organization>
3593      <address><email>ned@innosoft.com</email></address>
3594    </author>
3595    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3596      <organization>First Virtual Holdings</organization>
3597      <address><email>nsb@nsb.fv.com</email></address>
3598    </author>
3599    <date month="November" year="1996"/>
3600  </front>
3601  <seriesInfo name="RFC" value="2045"/>
3602</reference>
3603
3604<reference anchor="RFC2047">
3605  <front>
3606    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3607    <author initials="K." surname="Moore" fullname="Keith Moore">
3608      <organization>University of Tennessee</organization>
3609      <address><email>moore@cs.utk.edu</email></address>
3610    </author>
3611    <date month="November" year="1996"/>
3612  </front>
3613  <seriesInfo name="RFC" value="2047"/>
3614</reference>
3615
3616<reference anchor="RFC2068">
3617  <front>
3618    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3619    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3620      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3621      <address><email>fielding@ics.uci.edu</email></address>
3622    </author>
3623    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3624      <organization>MIT Laboratory for Computer Science</organization>
3625      <address><email>jg@w3.org</email></address>
3626    </author>
3627    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3628      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3629      <address><email>mogul@wrl.dec.com</email></address>
3630    </author>
3631    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3632      <organization>MIT Laboratory for Computer Science</organization>
3633      <address><email>frystyk@w3.org</email></address>
3634    </author>
3635    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3636      <organization>MIT Laboratory for Computer Science</organization>
3637      <address><email>timbl@w3.org</email></address>
3638    </author>
3639    <date month="January" year="1997"/>
3640  </front>
3641  <seriesInfo name="RFC" value="2068"/>
3642</reference>
3643
3644<reference anchor='RFC2109'>
3645  <front>
3646    <title>HTTP State Management Mechanism</title>
3647    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3648      <organization>Bell Laboratories, Lucent Technologies</organization>
3649      <address><email>dmk@bell-labs.com</email></address>
3650    </author>
3651    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3652      <organization>Netscape Communications Corp.</organization>
3653      <address><email>montulli@netscape.com</email></address>
3654    </author>
3655    <date year='1997' month='February' />
3656  </front>
3657  <seriesInfo name='RFC' value='2109' />
3658</reference>
3659
3660<reference anchor="RFC2145">
3661  <front>
3662    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3663    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3664      <organization>Western Research Laboratory</organization>
3665      <address><email>mogul@wrl.dec.com</email></address>
3666    </author>
3667    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3668      <organization>Department of Information and Computer Science</organization>
3669      <address><email>fielding@ics.uci.edu</email></address>
3670    </author>
3671    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3672      <organization>MIT Laboratory for Computer Science</organization>
3673      <address><email>jg@w3.org</email></address>
3674    </author>
3675    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3676      <organization>W3 Consortium</organization>
3677      <address><email>frystyk@w3.org</email></address>
3678    </author>
3679    <date month="May" year="1997"/>
3680  </front>
3681  <seriesInfo name="RFC" value="2145"/>
3682</reference>
3683
3684<reference anchor="RFC2616">
3685  <front>
3686    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3687    <author initials="R." surname="Fielding" fullname="R. Fielding">
3688      <organization>University of California, Irvine</organization>
3689      <address><email>fielding@ics.uci.edu</email></address>
3690    </author>
3691    <author initials="J." surname="Gettys" fullname="J. Gettys">
3692      <organization>W3C</organization>
3693      <address><email>jg@w3.org</email></address>
3694    </author>
3695    <author initials="J." surname="Mogul" fullname="J. Mogul">
3696      <organization>Compaq Computer Corporation</organization>
3697      <address><email>mogul@wrl.dec.com</email></address>
3698    </author>
3699    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3700      <organization>MIT Laboratory for Computer Science</organization>
3701      <address><email>frystyk@w3.org</email></address>
3702    </author>
3703    <author initials="L." surname="Masinter" fullname="L. Masinter">
3704      <organization>Xerox Corporation</organization>
3705      <address><email>masinter@parc.xerox.com</email></address>
3706    </author>
3707    <author initials="P." surname="Leach" fullname="P. Leach">
3708      <organization>Microsoft Corporation</organization>
3709      <address><email>paulle@microsoft.com</email></address>
3710    </author>
3711    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3712      <organization>W3C</organization>
3713      <address><email>timbl@w3.org</email></address>
3714    </author>
3715    <date month="June" year="1999"/>
3716  </front>
3717  <seriesInfo name="RFC" value="2616"/>
3718</reference>
3719
3720<reference anchor='RFC2818'>
3721  <front>
3722    <title>HTTP Over TLS</title>
3723    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3724      <organization>RTFM, Inc.</organization>
3725      <address><email>ekr@rtfm.com</email></address>
3726    </author>
3727    <date year='2000' month='May' />
3728  </front>
3729  <seriesInfo name='RFC' value='2818' />
3730</reference>
3731
3732<reference anchor='RFC2965'>
3733  <front>
3734    <title>HTTP State Management Mechanism</title>
3735    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3736      <organization>Bell Laboratories, Lucent Technologies</organization>
3737      <address><email>dmk@bell-labs.com</email></address>
3738    </author>
3739    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3740      <organization>Epinions.com, Inc.</organization>
3741      <address><email>lou@montulli.org</email></address>
3742    </author>
3743    <date year='2000' month='October' />
3744  </front>
3745  <seriesInfo name='RFC' value='2965' />
3746</reference>
3747
3748<reference anchor='RFC3864'>
3749  <front>
3750    <title>Registration Procedures for Message Header Fields</title>
3751    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3752      <organization>Nine by Nine</organization>
3753      <address><email>GK-IETF@ninebynine.org</email></address>
3754    </author>
3755    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3756      <organization>BEA Systems</organization>
3757      <address><email>mnot@pobox.com</email></address>
3758    </author>
3759    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3760      <organization>HP Labs</organization>
3761      <address><email>JeffMogul@acm.org</email></address>
3762    </author>
3763    <date year='2004' month='September' />
3764  </front>
3765  <seriesInfo name='BCP' value='90' />
3766  <seriesInfo name='RFC' value='3864' />
3767</reference>
3768
3769<reference anchor='RFC3977'>
3770  <front>
3771    <title>Network News Transfer Protocol (NNTP)</title>
3772    <author initials='C.' surname='Feather' fullname='C. Feather'>
3773      <organization>THUS plc</organization>
3774      <address><email>clive@demon.net</email></address>
3775    </author>
3776    <date year='2006' month='October' />
3777  </front>
3778  <seriesInfo name="RFC" value="3977"/>
3779</reference>
3780
3781<reference anchor="RFC4288">
3782  <front>
3783    <title>Media Type Specifications and Registration Procedures</title>
3784    <author initials="N." surname="Freed" fullname="N. Freed">
3785      <organization>Sun Microsystems</organization>
3786      <address>
3787        <email>ned.freed@mrochek.com</email>
3788      </address>
3789    </author>
3790    <author initials="J." surname="Klensin" fullname="J. Klensin">
3791      <organization/>
3792      <address>
3793        <email>klensin+ietf@jck.com</email>
3794      </address>
3795    </author>
3796    <date year="2005" month="December"/>
3797  </front>
3798  <seriesInfo name="BCP" value="13"/>
3799  <seriesInfo name="RFC" value="4288"/>
3800</reference>
3801
3802<reference anchor='RFC4395'>
3803  <front>
3804    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3805    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3806      <organization>AT&amp;T Laboratories</organization>
3807      <address>
3808        <email>tony+urireg@maillennium.att.com</email>
3809      </address>
3810    </author>
3811    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3812      <organization>Qualcomm, Inc.</organization>
3813      <address>
3814        <email>hardie@qualcomm.com</email>
3815      </address>
3816    </author>
3817    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3818      <organization>Adobe Systems</organization>
3819      <address>
3820        <email>LMM@acm.org</email>
3821      </address>
3822    </author>
3823    <date year='2006' month='February' />
3824  </front>
3825  <seriesInfo name='BCP' value='115' />
3826  <seriesInfo name='RFC' value='4395' />
3827</reference>
3828
3829<reference anchor="RFC5322">
3830  <front>
3831    <title>Internet Message Format</title>
3832    <author initials="P." surname="Resnick" fullname="P. Resnick">
3833      <organization>Qualcomm Incorporated</organization>
3834    </author>
3835    <date year="2008" month="October"/>
3836  </front> 
3837  <seriesInfo name="RFC" value="5322"/>
3838</reference>
3839
3840<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3841  <front>
3842    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3843    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3844      <organization/>
3845    </author>
3846    <date year="2001" month="November"/>
3847  </front>
3848  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3849</reference>
3850
3851<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3852  <front>
3853  <title>Analysis of HTTP Performance Problems</title>
3854  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3855    <organization/>
3856  </author>
3857  <date/>
3858  </front>
3859</reference>
3860
3861<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3862  <front>
3863  <title>Analysis of HTTP Performance</title>
3864  <author initials="J." surname="Touch" fullname="Joe Touch">
3865    <organization>USC/Information Sciences Institute</organization>
3866    <address><email>touch@isi.edu</email></address>
3867  </author>
3868  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3869    <organization>USC/Information Sciences Institute</organization>
3870    <address><email>johnh@isi.edu</email></address>
3871  </author>
3872  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3873    <organization>USC/Information Sciences Institute</organization>
3874    <address><email>katia@isi.edu</email></address>
3875  </author>
3876  <date year="1998" month="Aug"/>
3877  </front>
3878  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3879  <annotation>(original report dated Aug. 1996)</annotation>
3880</reference>
3881
3882<reference anchor="WAIS">
3883  <front>
3884    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3885    <author initials="F." surname="Davis" fullname="F. Davis">
3886      <organization>Thinking Machines Corporation</organization>
3887    </author>
3888    <author initials="B." surname="Kahle" fullname="B. Kahle">
3889      <organization>Thinking Machines Corporation</organization>
3890    </author>
3891    <author initials="H." surname="Morris" fullname="H. Morris">
3892      <organization>Thinking Machines Corporation</organization>
3893    </author>
3894    <author initials="J." surname="Salem" fullname="J. Salem">
3895      <organization>Thinking Machines Corporation</organization>
3896    </author>
3897    <author initials="T." surname="Shen" fullname="T. Shen">
3898      <organization>Thinking Machines Corporation</organization>
3899    </author>
3900    <author initials="R." surname="Wang" fullname="R. Wang">
3901      <organization>Thinking Machines Corporation</organization>
3902    </author>
3903    <author initials="J." surname="Sui" fullname="J. Sui">
3904      <organization>Thinking Machines Corporation</organization>
3905    </author>
3906    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3907      <organization>Thinking Machines Corporation</organization>
3908    </author>
3909    <date month="April" year="1990"/>
3910  </front>
3911  <seriesInfo name="Thinking Machines Corporation" value=""/>
3912</reference>
3913
3914</references>
3915
3916
3917<section title="Tolerant Applications" anchor="tolerant.applications">
3918<t>
3919   Although this document specifies the requirements for the generation
3920   of HTTP/1.1 messages, not all applications will be correct in their
3921   implementation. We therefore recommend that operational applications
3922   be tolerant of deviations whenever those deviations can be
3923   interpreted unambiguously.
3924</t>
3925<t>
3926   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3927   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3928   accept any amount of WSP characters between fields, even though
3929   only a single SP is required.
3930</t>
3931<t>
3932   The line terminator for message-header fields is the sequence CRLF.
3933   However, we recommend that applications, when parsing such headers,
3934   recognize a single LF as a line terminator and ignore the leading CR.
3935</t>
3936<t>
3937   The character set of an entity-body &SHOULD; be labeled as the lowest
3938   common denominator of the character codes used within that body, with
3939   the exception that not labeling the entity is preferred over labeling
3940   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3941</t>
3942<t>
3943   Additional rules for requirements on parsing and encoding of dates
3944   and other potential problems with date encodings include:
3945</t>
3946<t>
3947  <list style="symbols">
3948     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3949        which appears to be more than 50 years in the future is in fact
3950        in the past (this helps solve the "year 2000" problem).</t>
3951
3952     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3953        Expires date as earlier than the proper value, but &MUST-NOT;
3954        internally represent a parsed Expires date as later than the
3955        proper value.</t>
3956
3957     <t>All expiration-related calculations &MUST; be done in GMT. The
3958        local time zone &MUST-NOT; influence the calculation or comparison
3959        of an age or expiration time.</t>
3960
3961     <t>If an HTTP header incorrectly carries a date value with a time
3962        zone other than GMT, it &MUST; be converted into GMT using the
3963        most conservative possible conversion.</t>
3964  </list>
3965</t>
3966</section>
3967
3968<section title="Compatibility with Previous Versions" anchor="compatibility">
3969<t>
3970   HTTP has been in use by the World-Wide Web global information initiative
3971   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3972   was a simple protocol for hypertext data transfer across the Internet
3973   with only a single method and no metadata.
3974   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3975   methods and MIME-like messaging that could include metadata about the data
3976   transferred and modifiers on the request/response semantics. However,
3977   HTTP/1.0 did not sufficiently take into consideration the effects of
3978   hierarchical proxies, caching, the need for persistent connections, or
3979   name-based virtual hosts. The proliferation of incompletely-implemented
3980   applications calling themselves "HTTP/1.0" further necessitated a
3981   protocol version change in order for two communicating applications
3982   to determine each other's true capabilities.
3983</t>
3984<t>
3985   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3986   requirements that enable reliable implementations, adding only
3987   those new features that will either be safely ignored by an HTTP/1.0
3988   recipient or only sent when communicating with a party advertising
3989   compliance with HTTP/1.1.
3990</t>
3991<t>
3992   It is beyond the scope of a protocol specification to mandate
3993   compliance with previous versions. HTTP/1.1 was deliberately
3994   designed, however, to make supporting previous versions easy. It is
3995   worth noting that, at the time of composing this specification
3996   (1996), we would expect commercial HTTP/1.1 servers to:
3997  <list style="symbols">
3998     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3999        1.1 requests;</t>
4000
4001     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4002        1.1;</t>
4003
4004     <t>respond appropriately with a message in the same major version
4005        used by the client.</t>
4006  </list>
4007</t>
4008<t>
4009   And we would expect HTTP/1.1 clients to:
4010  <list style="symbols">
4011     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4012        responses;</t>
4013
4014     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4015        1.1.</t>
4016  </list>
4017</t>
4018<t>
4019   For most implementations of HTTP/1.0, each connection is established
4020   by the client prior to the request and closed by the server after
4021   sending the response. Some implementations implement the Keep-Alive
4022   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4023</t>
4024
4025<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4026<t>
4027   This section summarizes major differences between versions HTTP/1.0
4028   and HTTP/1.1.
4029</t>
4030
4031<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">
4032<t>
4033   The requirements that clients and servers support the Host request-header,
4034   report an error if the Host request-header (<xref target="header.host"/>) is
4035   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4036   are among the most important changes defined by this
4037   specification.
4038</t>
4039<t>
4040   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4041   addresses and servers; there was no other established mechanism for
4042   distinguishing the intended server of a request than the IP address
4043   to which that request was directed. The changes outlined above will
4044   allow the Internet, once older HTTP clients are no longer common, to
4045   support multiple Web sites from a single IP address, greatly
4046   simplifying large operational Web servers, where allocation of many
4047   IP addresses to a single host has created serious problems. The
4048   Internet will also be able to recover the IP addresses that have been
4049   allocated for the sole purpose of allowing special-purpose domain
4050   names to be used in root-level HTTP URLs. Given the rate of growth of
4051   the Web, and the number of servers already deployed, it is extremely
4052   important that all implementations of HTTP (including updates to
4053   existing HTTP/1.0 applications) correctly implement these
4054   requirements:
4055  <list style="symbols">
4056     <t>Both clients and servers &MUST; support the Host request-header.</t>
4057
4058     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4059
4060     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4061        request does not include a Host request-header.</t>
4062
4063     <t>Servers &MUST; accept absolute URIs.</t>
4064  </list>
4065</t>
4066</section>
4067</section>
4068
4069<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4070<t>
4071   Some clients and servers might wish to be compatible with some
4072   previous implementations of persistent connections in HTTP/1.0
4073   clients and servers. Persistent connections in HTTP/1.0 are
4074   explicitly negotiated as they are not the default behavior. HTTP/1.0
4075   experimental implementations of persistent connections are faulty,
4076   and the new facilities in HTTP/1.1 are designed to rectify these
4077   problems. The problem was that some existing 1.0 clients may be
4078   sending Keep-Alive to a proxy server that doesn't understand
4079   Connection, which would then erroneously forward it to the next
4080   inbound server, which would establish the Keep-Alive connection and
4081   result in a hung HTTP/1.0 proxy waiting for the close on the
4082   response. The result is that HTTP/1.0 clients must be prevented from
4083   using Keep-Alive when talking to proxies.
4084</t>
4085<t>
4086   However, talking to proxies is the most important use of persistent
4087   connections, so that prohibition is clearly unacceptable. Therefore,
4088   we need some other mechanism for indicating a persistent connection
4089   is desired, which is safe to use even when talking to an old proxy
4090   that ignores Connection. Persistent connections are the default for
4091   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4092   declaring non-persistence. See <xref target="header.connection"/>.
4093</t>
4094<t>
4095   The original HTTP/1.0 form of persistent connections (the Connection:
4096   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4097</t>
4098</section>
4099
4100<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4101<t>
4102   This specification has been carefully audited to correct and
4103   disambiguate key word usage; RFC 2068 had many problems in respect to
4104   the conventions laid out in <xref target="RFC2119"/>.
4105</t>
4106<t>
4107   Transfer-coding and message lengths all interact in ways that
4108   required fixing exactly when chunked encoding is used (to allow for
4109   transfer encoding that may not be self delimiting); it was important
4110   to straighten out exactly how message lengths are computed. (Sections
4111   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4112   <xref target="header.content-length" format="counter"/>,
4113   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4114</t>
4115<t>
4116   The use and interpretation of HTTP version numbers has been clarified
4117   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4118   version they support to deal with problems discovered in HTTP/1.0
4119   implementations (<xref target="http.version"/>)
4120</t>
4121<t>
4122   Quality Values of zero should indicate that "I don't want something"
4123   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4124</t>
4125<t>
4126   Transfer-coding had significant problems, particularly with
4127   interactions with chunked encoding. The solution is that transfer-codings
4128   become as full fledged as content-codings. This involves
4129   adding an IANA registry for transfer-codings (separate from content
4130   codings), a new header field (TE) and enabling trailer headers in the
4131   future. Transfer encoding is a major performance benefit, so it was
4132   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4133   interoperability problem that could have occurred due to interactions
4134   between authentication trailers, chunked encoding and HTTP/1.0
4135   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4136   and <xref target="header.te" format="counter"/>)
4137</t>
4138</section>
4139
4140<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4141<t>
4142  Empty list elements in list productions have been deprecated.
4143  (<xref target="notation.abnf"/>)
4144</t>
4145<t>
4146  Rules about implicit linear whitespace between certain grammar productions
4147  have been removed; now it's only allowed when specifically pointed out
4148  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4149  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4150  Non-ASCII content in header fields and reason phrase has been obsoleted and
4151  made opaque (the TEXT rule was removed)
4152  (<xref target="basic.rules"/>)
4153</t>
4154<t>
4155  Clarify that HTTP-Version is case sensitive.
4156  (<xref target="http.version"/>)
4157</t>
4158<t>
4159  Remove reference to non-existant identity transfer-coding value tokens.
4160  (Sections <xref format="counter" target="transfer.codings"/> and
4161  <xref format="counter" target="message.length"/>)
4162</t>
4163<t>
4164  Clarification that the chunk length does not include
4165  the count of the octets in the chunk header and trailer.
4166  (<xref target="chunked.transfer.encoding"/>)
4167</t>
4168<t>
4169  Require that invalid whitespace around field-names be rejected.
4170  (<xref target="message.headers"/>)
4171</t>
4172<t>
4173  Update use of abs_path production from RFC1808 to the path-absolute + query
4174  components of RFC3986.
4175  (<xref target="request-target"/>)
4176</t>
4177<t>
4178  Clarify exactly when close connection options must be sent.
4179  (<xref target="header.connection"/>)
4180</t>
4181</section>
4182</section>
4183
4184<section title="Terminology" anchor="terminology">
4185<t>
4186   This specification uses a number of terms to refer to the roles
4187   played by participants in, and objects of, the HTTP communication.
4188</t>
4189<t>
4190  <iref item="cache"/>
4191  <x:dfn>cache</x:dfn>
4192  <list>
4193    <t>
4194      A program's local store of response messages and the subsystem
4195      that controls its message storage, retrieval, and deletion. A
4196      cache stores cacheable responses in order to reduce the response
4197      time and network bandwidth consumption on future, equivalent
4198      requests. Any client or server may include a cache, though a cache
4199      cannot be used by a server that is acting as a tunnel.
4200    </t>
4201  </list>
4202</t>
4203<t>
4204  <iref item="cacheable"/>
4205  <x:dfn>cacheable</x:dfn>
4206  <list>
4207    <t>
4208      A response is cacheable if a cache is allowed to store a copy of
4209      the response message for use in answering subsequent requests. The
4210      rules for determining the cacheability of HTTP responses are
4211      defined in &caching;. Even if a resource is cacheable, there may
4212      be additional constraints on whether a cache can use the cached
4213      copy for a particular request.
4214    </t>
4215  </list>
4216</t>
4217<t>
4218  <iref item="client"/>
4219  <x:dfn>client</x:dfn>
4220  <list>
4221    <t>
4222      A program that establishes connections for the purpose of sending
4223      requests.
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="connection"/>
4229  <x:dfn>connection</x:dfn>
4230  <list>
4231    <t>
4232      A transport layer virtual circuit established between two programs
4233      for the purpose of communication.
4234    </t>
4235  </list>
4236</t>
4237<t>
4238  <iref item="content negotiation"/>
4239  <x:dfn>content negotiation</x:dfn>
4240  <list>
4241    <t>
4242      The mechanism for selecting the appropriate representation when
4243      servicing a request, as described in &content.negotiation;. The
4244      representation of entities in any response can be negotiated
4245      (including error responses).
4246    </t>
4247  </list>
4248</t>
4249<t>
4250  <iref item="entity"/>
4251  <x:dfn>entity</x:dfn>
4252  <list>
4253    <t>
4254      The information transferred as the payload of a request or
4255      response. An entity consists of metainformation in the form of
4256      entity-header fields and content in the form of an entity-body, as
4257      described in &entity;.
4258    </t>
4259  </list>
4260</t>
4261<t>
4262  <iref item="gateway"/>
4263  <x:dfn>gateway</x:dfn>
4264  <list>
4265    <t>
4266      A server which acts as an intermediary for some other server.
4267      Unlike a proxy, a gateway receives requests as if it were the
4268      origin server for the requested resource; the requesting client
4269      may not be aware that it is communicating with a gateway.
4270    </t>
4271  </list>
4272</t>
4273<t>
4274  <iref item="inbound"/>
4275  <iref item="outbound"/>
4276  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4277  <list>
4278    <t>
4279      Inbound and outbound refer to the request and response paths for
4280      messages: "inbound" means "traveling toward the origin server",
4281      and "outbound" means "traveling toward the user agent"
4282    </t>
4283  </list>
4284</t>
4285<t>
4286  <iref item="message"/>
4287  <x:dfn>message</x:dfn>
4288  <list>
4289    <t>
4290      The basic unit of HTTP communication, consisting of a structured
4291      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4292      transmitted via the connection.
4293    </t>
4294  </list>
4295</t>
4296<t>
4297  <iref item="origin server"/>
4298  <x:dfn>origin server</x:dfn>
4299  <list>
4300    <t>
4301      The server on which a given resource resides or is to be created.
4302    </t>
4303  </list>
4304</t>
4305<t>
4306  <iref item="proxy"/>
4307  <x:dfn>proxy</x:dfn>
4308  <list>
4309    <t>
4310      An intermediary program which acts as both a server and a client
4311      for the purpose of making requests on behalf of other clients.
4312      Requests are serviced internally or by passing them on, with
4313      possible translation, to other servers. A proxy &MUST; implement
4314      both the client and server requirements of this specification. A
4315      "transparent proxy" is a proxy that does not modify the request or
4316      response beyond what is required for proxy authentication and
4317      identification. A "non-transparent proxy" is a proxy that modifies
4318      the request or response in order to provide some added service to
4319      the user agent, such as group annotation services, media type
4320      transformation, protocol reduction, or anonymity filtering. Except
4321      where either transparent or non-transparent behavior is explicitly
4322      stated, the HTTP proxy requirements apply to both types of
4323      proxies.
4324    </t>
4325  </list>
4326</t>
4327<t>
4328  <iref item="request"/>
4329  <x:dfn>request</x:dfn>
4330  <list>
4331    <t>
4332      An HTTP request message, as defined in <xref target="request"/>.
4333    </t>
4334  </list>
4335</t>
4336<t>
4337  <iref item="resource"/>
4338  <x:dfn>resource</x:dfn>
4339  <list>
4340    <t>
4341      A network data object or service that can be identified by a URI,
4342      as defined in <xref target="uri"/>. Resources may be available in multiple
4343      representations (e.g. multiple languages, data formats, size, and
4344      resolutions) or vary in other ways.
4345    </t>
4346  </list>
4347</t>
4348<t>
4349  <iref item="response"/>
4350  <x:dfn>response</x:dfn>
4351  <list>
4352    <t>
4353      An HTTP response message, as defined in <xref target="response"/>.
4354    </t>
4355  </list>
4356</t>
4357<t>
4358  <iref item="representation"/>
4359  <x:dfn>representation</x:dfn>
4360  <list>
4361    <t>
4362      An entity included with a response that is subject to content
4363      negotiation, as described in &content.negotiation;. There may exist multiple
4364      representations associated with a particular response status.
4365    </t>
4366  </list>
4367</t>
4368<t>
4369  <iref item="server"/>
4370  <x:dfn>server</x:dfn>
4371  <list>
4372    <t>
4373      An application program that accepts connections in order to
4374      service requests by sending back responses. Any given program may
4375      be capable of being both a client and a server; our use of these
4376      terms refers only to the role being performed by the program for a
4377      particular connection, rather than to the program's capabilities
4378      in general. Likewise, any server may act as an origin server,
4379      proxy, gateway, or tunnel, switching behavior based on the nature
4380      of each request.
4381    </t>
4382  </list>
4383</t>
4384<t>
4385  <iref item="tunnel"/>
4386  <x:dfn>tunnel</x:dfn>
4387  <list>
4388    <t>
4389      An intermediary program which is acting as a blind relay between
4390      two connections. Once active, a tunnel is not considered a party
4391      to the HTTP communication, though the tunnel may have been
4392      initiated by an HTTP request. The tunnel ceases to exist when both
4393      ends of the relayed connections are closed.
4394    </t>
4395  </list>
4396</t>
4397<t>
4398  <iref item="upstream"/>
4399  <iref item="downstream"/>
4400  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4401  <list>
4402    <t>
4403      Upstream and downstream describe the flow of a message: all
4404      messages flow from upstream to downstream.
4405    </t>
4406  </list>
4407</t>
4408<t>
4409  <iref item="user agent"/>
4410  <x:dfn>user agent</x:dfn>
4411  <list>
4412    <t>
4413      The client which initiates a request. These are often browsers,
4414      editors, spiders (web-traversing robots), or other end user tools.
4415    </t>
4416  </list>
4417</t>
4418<t>
4419  <iref item="variant"/>
4420  <x:dfn>variant</x:dfn>
4421  <list>
4422    <t>
4423      A resource may have one, or more than one, representation(s)
4424      associated with it at any given instant. Each of these
4425      representations is termed a `variant'.  Use of the term `variant'
4426      does not necessarily imply that the resource is subject to content
4427      negotiation.
4428    </t>
4429  </list>
4430</t>
4431</section>
4432
4433<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4434<figure>
4435<artwork type="abnf" name="p1-messaging.parsed-abnf">
4436<x:ref>BWS</x:ref> = OWS
4437
4438<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4439<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4440<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4441<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4442 connection-token ] )
4443<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4444<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4445
4446<x:ref>Date</x:ref> = "Date:" OWS Date-v
4447<x:ref>Date-v</x:ref> = HTTP-date
4448
4449GMT = %x47.4D.54
4450
4451<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4452<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4453<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4454<x:ref>HTTP-message</x:ref> = Request / Response
4455<x:ref>Host</x:ref> = "Host:" OWS Host-v
4456<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4457
4458<x:ref>Method</x:ref> = token
4459
4460<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4461
4462<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4463
4464<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4465<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4466<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4467 entity-header ) CRLF ) CRLF [ message-body ]
4468<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4469<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4470 entity-header ) CRLF ) CRLF [ message-body ]
4471
4472<x:ref>Status-Code</x:ref> = 3DIGIT
4473<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4474
4475<x:ref>TE</x:ref> = "TE:" OWS TE-v
4476<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4477<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4478<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4479<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4480<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4481 transfer-coding ] )
4482
4483<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4484<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4485<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4486<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4487
4488<x:ref>Via</x:ref> = "Via:" OWS Via-v
4489<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4490 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4491 ] )
4492
4493<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4494
4495<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4496<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4497<x:ref>attribute</x:ref> = token
4498<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4499
4500<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4501<x:ref>chunk-data</x:ref> = 1*OCTET
4502<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4503<x:ref>chunk-ext-name</x:ref> = token
4504<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4505<x:ref>chunk-size</x:ref> = 1*HEXDIG
4506<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4507<x:ref>connection-token</x:ref> = token
4508<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4509
4510<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4511<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4512<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4513
4514<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4515<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4516
4517<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4518<x:ref>field-name</x:ref> = token
4519<x:ref>field-value</x:ref> = *( field-content / OWS )
4520<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4521
4522<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4523 / Transfer-Encoding / Upgrade / Via / Warning
4524<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4525 message-body ]
4526
4527<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4528
4529l-Fri = %x46.72.69.64.61.79
4530l-Mon = %x4D.6F.6E.64.61.79
4531l-Sat = %x53.61.74.75.72.64.61.79
4532l-Sun = %x53.75.6E.64.61.79
4533l-Thu = %x54.68.75.72.73.64.61.79
4534l-Tue = %x54.75.65.73.64.61.79
4535l-Wed = %x57.65.64.6E.65.73.64.61.79
4536<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4537
4538<x:ref>message-body</x:ref> = entity-body /
4539 &lt;entity-body encoded as per Transfer-Encoding&gt;
4540<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4541<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4542 / s-Sep / s-Oct / s-Nov / s-Dec
4543
4544<x:ref>obs-fold</x:ref> = CRLF
4545<x:ref>obs-text</x:ref> = %x80-FF
4546<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4547
4548<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4549<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4550<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4551<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4552<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4553<x:ref>product</x:ref> = token [ "/" product-version ]
4554<x:ref>product-version</x:ref> = token
4555<x:ref>protocol-name</x:ref> = token
4556<x:ref>protocol-version</x:ref> = token
4557<x:ref>pseudonym</x:ref> = token
4558
4559<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4560<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4561<x:ref>quoted-pair</x:ref> = "\" quoted-text
4562<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4563<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4564<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4565
4566<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4567<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4568<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4569<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4570<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4571 / authority
4572<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4573<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4574<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4575
4576s-Apr = %x41.70.72
4577s-Aug = %x41.75.67
4578s-Dec = %x44.65.63
4579s-Feb = %x46.65.62
4580s-Fri = %x46.72.69
4581s-Jan = %x4A.61.6E
4582s-Jul = %x4A.75.6C
4583s-Jun = %x4A.75.6E
4584s-Mar = %x4D.61.72
4585s-May = %x4D.61.79
4586s-Mon = %x4D.6F.6E
4587s-Nov = %x4E.6F.76
4588s-Oct = %x4F.63.74
4589s-Sat = %x53.61.74
4590s-Sep = %x53.65.70
4591s-Sun = %x53.75.6E
4592s-Thu = %x54.68.75
4593s-Tue = %x54.75.65
4594s-Wed = %x57.65.64
4595<x:ref>start-line</x:ref> = Request-Line / Status-Line
4596
4597<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4598<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4599 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4600<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4601<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4602<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4603<x:ref>token</x:ref> = 1*tchar
4604<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4605<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4606<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4607
4608<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4609
4610<x:ref>value</x:ref> = token / quoted-string
4611
4612<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4613<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4614
4615
4616</artwork>
4617</figure>
4618<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4619; Chunked-Body defined but not used
4620; Content-Length defined but not used
4621; HTTP-message defined but not used
4622; Host defined but not used
4623; TE defined but not used
4624; URI defined but not used
4625; URI-reference defined but not used
4626; fragment defined but not used
4627; generic-message defined but not used
4628; http-URI defined but not used
4629; partial-URI defined but not used
4630</artwork></figure></section>
4631
4632<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4633
4634<section title="Since RFC2616">
4635<t>
4636  Extracted relevant partitions from <xref target="RFC2616"/>.
4637</t>
4638</section>
4639
4640<section title="Since draft-ietf-httpbis-p1-messaging-00">
4641<t>
4642  Closed issues:
4643  <list style="symbols"> 
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4646      "HTTP Version should be case sensitive"
4647      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4648    </t>
4649    <t>
4650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4651      "'unsafe' characters"
4652      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4653    </t>
4654    <t>
4655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4656      "Chunk Size Definition"
4657      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4658    </t>
4659    <t>
4660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4661      "Message Length"
4662      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4663    </t>
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4666      "Media Type Registrations"
4667      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4668    </t>
4669    <t>
4670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4671      "URI includes query"
4672      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4673    </t>
4674    <t>
4675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4676      "No close on 1xx responses"
4677      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4678    </t>
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4681      "Remove 'identity' token references"
4682      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4683    </t>
4684    <t>
4685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4686      "Import query BNF"
4687    </t>
4688    <t>
4689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4690      "qdtext BNF"
4691    </t>
4692    <t>
4693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4694      "Normative and Informative references"
4695    </t>
4696    <t>
4697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4698      "RFC2606 Compliance"
4699    </t>
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4702      "RFC977 reference"
4703    </t>
4704    <t>
4705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4706      "RFC1700 references"
4707    </t>
4708    <t>
4709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4710      "inconsistency in date format explanation"
4711    </t>
4712    <t>
4713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4714      "Date reference typo"
4715    </t>
4716    <t>
4717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4718      "Informative references"
4719    </t>
4720    <t>
4721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4722      "ISO-8859-1 Reference"
4723    </t>
4724    <t>
4725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4726      "Normative up-to-date references"
4727    </t>
4728  </list>
4729</t>
4730<t>
4731  Other changes:
4732  <list style="symbols"> 
4733    <t>
4734      Update media type registrations to use RFC4288 template.
4735    </t>
4736    <t>
4737      Use names of RFC4234 core rules DQUOTE and WSP,
4738      fix broken ABNF for chunk-data
4739      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4740    </t>
4741  </list>
4742</t>
4743</section>
4744
4745<section title="Since draft-ietf-httpbis-p1-messaging-01">
4746<t>
4747  Closed issues:
4748  <list style="symbols"> 
4749    <t>
4750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4751      "Bodies on GET (and other) requests"
4752    </t>
4753    <t>
4754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4755      "Updating to RFC4288"
4756    </t>
4757    <t>
4758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4759      "Status Code and Reason Phrase"
4760    </t>
4761    <t>
4762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4763      "rel_path not used"
4764    </t>
4765  </list>
4766</t>
4767<t>
4768  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4769  <list style="symbols"> 
4770    <t>
4771      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4772      "trailer-part").
4773    </t>
4774    <t>
4775      Avoid underscore character in rule names ("http_URL" ->
4776      "http-URL", "abs_path" -> "path-absolute").
4777    </t>
4778    <t>
4779      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4780      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4781      have to be updated when switching over to RFC3986.
4782    </t>
4783    <t>
4784      Synchronize core rules with RFC5234.
4785    </t>
4786    <t>
4787      Get rid of prose rules that span multiple lines.
4788    </t>
4789    <t>
4790      Get rid of unused rules LOALPHA and UPALPHA.
4791    </t>
4792    <t>
4793      Move "Product Tokens" section (back) into Part 1, as "token" is used
4794      in the definition of the Upgrade header.
4795    </t>
4796    <t>
4797      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4798    </t>
4799    <t>
4800      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4801    </t>
4802  </list>
4803</t>
4804</section>
4805
4806<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4807<t>
4808  Closed issues:
4809  <list style="symbols"> 
4810    <t>
4811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4812      "HTTP-date vs. rfc1123-date"
4813    </t>
4814    <t>
4815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4816      "WS in quoted-pair"
4817    </t>
4818  </list>
4819</t>
4820<t>
4821  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4822  <list style="symbols"> 
4823    <t>
4824      Reference RFC 3984, and update header registrations for headers defined
4825      in this document.
4826    </t>
4827  </list>
4828</t>
4829<t>
4830  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4831  <list style="symbols"> 
4832    <t>
4833      Replace string literals when the string really is case-sensitive (HTTP-Version).
4834    </t>
4835  </list>
4836</t>
4837</section>
4838
4839<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4840<t>
4841  Closed issues:
4842  <list style="symbols"> 
4843    <t>
4844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4845      "Connection closing"
4846    </t>
4847    <t>
4848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4849      "Move registrations and registry information to IANA Considerations"
4850    </t>
4851    <t>
4852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4853      "need new URL for PAD1995 reference"
4854    </t>
4855    <t>
4856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4857      "IANA Considerations: update HTTP URI scheme registration"
4858    </t>
4859    <t>
4860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4861      "Cite HTTPS URI scheme definition"
4862    </t>
4863    <t>
4864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4865      "List-type headers vs Set-Cookie"
4866    </t>
4867  </list>
4868</t>
4869<t>
4870  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4871  <list style="symbols"> 
4872    <t>
4873      Replace string literals when the string really is case-sensitive (HTTP-Date).
4874    </t>
4875    <t>
4876      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4877    </t>
4878  </list>
4879</t>
4880</section>
4881
4882<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4883<t>
4884  Closed issues:
4885  <list style="symbols"> 
4886    <t>
4887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4888      "Out-of-date reference for URIs"
4889    </t>
4890    <t>
4891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4892      "RFC 2822 is updated by RFC 5322"
4893    </t>
4894  </list>
4895</t>
4896<t>
4897  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4898  <list style="symbols"> 
4899    <t>
4900      Use "/" instead of "|" for alternatives.
4901    </t>
4902    <t>
4903      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4904    </t>
4905    <t>
4906      Only reference RFC 5234's core rules.
4907    </t>
4908    <t>
4909      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4910      whitespace ("OWS") and required whitespace ("RWS").
4911    </t>
4912    <t>
4913      Rewrite ABNFs to spell out whitespace rules, factor out
4914      header value format definitions.
4915    </t>
4916  </list>
4917</t>
4918</section>
4919
4920<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4921<t>
4922  Closed issues:
4923  <list style="symbols"> 
4924    <t>
4925      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4926      "Header LWS"
4927    </t>
4928    <t>
4929      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4930      "Sort 1.3 Terminology"
4931    </t>
4932    <t>
4933      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4934      "RFC2047 encoded words"
4935    </t>
4936    <t>
4937      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4938      "Character Encodings in TEXT"
4939    </t>
4940    <t>
4941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4942      "Line Folding"
4943    </t>
4944    <t>
4945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4946      "OPTIONS * and proxies"
4947    </t>
4948    <t>
4949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4950      "Reason-Phrase BNF"
4951    </t>
4952    <t>
4953      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4954      "Use of TEXT"
4955    </t>
4956    <t>
4957      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4958      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4959    </t>
4960    <t>
4961      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4962      "RFC822 reference left in discussion of date formats"
4963    </t>
4964  </list>
4965</t>
4966<t>
4967  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4968  <list style="symbols"> 
4969    <t>
4970      Rewrite definition of list rules, deprecate empty list elements.
4971    </t>
4972    <t>
4973      Add appendix containing collected and expanded ABNF.
4974    </t>
4975  </list>
4976</t>
4977<t>
4978  Other changes:
4979  <list style="symbols"> 
4980    <t>
4981      Rewrite introduction; add mostly new Architecture Section.
4982    </t>
4983    <t>
4984      Move definition of quality values from Part 3 into Part 1;
4985      make TE request header grammar independent of accept-params (defined in Part 3).
4986    </t>
4987  </list>
4988</t>
4989</section>
4990
4991</section>
4992
4993</back>
4994</rfc>
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