source: draft-ietf-httpbis/latest/p1-messaging.xml @ 641

Last change on this file since 641 was 641, checked in by julian.reschke@…, 10 years ago

Editorial: make link into RFC2045 more specific

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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 "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' 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 status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38]>
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
52     xmlns:x='http://purl.org/net/xml2rfc/ext'>
53<front>
54
55  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
56
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email>fielding@gbiv.com</email>
70      <uri>http://roy.gbiv.com/</uri>
71    </address>
72  </author>
73
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email>jg@laptop.org</email>
85      <uri>http://www.laptop.org/</uri>
86    </address>
87  </author>
88 
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email>JeffMogul@acm.org</email>
101    </address>
102  </author>
103
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email>henrikn@microsoft.com</email>
115    </address>
116  </author>
117
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email>LMM@acm.org</email>
129      <uri>http://larry.masinter.net/</uri>
130    </address>
131  </author>
132 
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email>paulle@microsoft.com</email>
143    </address>
144  </author>
145   
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email>timbl@w3.org</email>
159      <uri>http://www.w3.org/People/Berners-Lee/</uri>
160    </address>
161  </author>
162
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email>ylafon@w3.org</email>
175      <uri>http://www.raubacapeu.net/people/yves/</uri>
176    </address>
177  </author>
178
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email>julian.reschke@greenbytes.de</email>
190      <uri>http://greenbytes.de/tech/webdav/</uri>
191    </address>
192  </author>
193
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
196
197<abstract>
198<t>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
209</t>
210</abstract>
211
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list (ietf-http-wg@w3.org). The current issues list is
216    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
217    and related documents (including fancy diffs) can be found at
218    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
219  </t>
220  <t>
221    The changes in this draft are summarized in <xref target="changes.since.07"/>.
222  </t>
223</note>
224</front>
225<middle>
226<section title="Introduction" anchor="introduction">
227<t>
228   The Hypertext Transfer Protocol (HTTP) is an application-level
229   request/response protocol that uses extensible semantics and MIME-like
230   message payloads for flexible interaction with network-based hypertext
231   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
232   standard <xref target="RFC3986"/> to indicate request targets and
233   relationships between resources.
234   Messages are passed in a format similar to that used by Internet mail
235   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
236   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
237   between HTTP and MIME messages).
238</t>
239<t>
240   HTTP is a generic interface protocol for information systems. It is
241   designed to hide the details of how a service is implemented by presenting
242   a uniform interface to clients that is independent of the types of
243   resources provided. Likewise, servers do not need to be aware of each
244   client's purpose: an HTTP request can be considered in isolation rather
245   than being associated with a specific type of client or a predetermined
246   sequence of application steps. The result is a protocol that can be used
247   effectively in many different contexts and for which implementations can
248   evolve independently over time.
249</t>
250<t>
251   HTTP is also designed for use as a generic protocol for translating
252   communication to and from other Internet information systems.
253   HTTP proxies and gateways provide access to alternative information
254   services by translating their diverse protocols into a hypertext
255   format that can be viewed and manipulated by clients in the same way
256   as HTTP services.
257</t>
258<t>
259   One consequence of HTTP flexibility is that the protocol cannot be
260   defined in terms of what occurs behind the interface. Instead, we
261   are limited to defining the syntax of communication, the intent
262   of received communication, and the expected behavior of recipients.
263   If the communication is considered in isolation, then successful
264   actions should be reflected in corresponding changes to the
265   observable interface provided by servers. However, since multiple
266   clients may act in parallel and perhaps at cross-purposes, we
267   cannot require that such changes be observable beyond the scope
268   of a single response.
269</t>
270<t>
271   This document is Part 1 of the seven-part specification of HTTP,
272   defining the protocol referred to as "HTTP/1.1" and obsoleting
273   <xref target="RFC2616"/>.
274   Part 1 describes the architectural elements that are used or
275   referred to in HTTP, defines the "http" and "https" URI schemes,
276   describes overall network operation and connection management,
277   and defines HTTP message framing and forwarding requirements.
278   Our goal is to define all of the mechanisms necessary for HTTP message
279   handling that are independent of message semantics, thereby defining the
280   complete set of requirements for message parsers and
281   message-forwarding intermediaries.
282</t>
283
284<section title="Requirements" anchor="intro.requirements">
285<t>
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
289</t>
290<t>
291   An implementation is not compliant if it fails to satisfy one or more
292   of the &MUST; or &REQUIRED; level requirements for the protocols it
293   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
294   level and all the &SHOULD; level requirements for its protocols is said
295   to be "unconditionally compliant"; one that satisfies all the &MUST;
296   level requirements but not all the &SHOULD; level requirements for its
297   protocols is said to be "conditionally compliant."
298</t>
299</section>
300
301<section title="Syntax Notation" anchor="notation">
302<iref primary="true" item="Grammar" subitem="ALPHA"/>
303<iref primary="true" item="Grammar" subitem="CR"/>
304<iref primary="true" item="Grammar" subitem="CRLF"/>
305<iref primary="true" item="Grammar" subitem="CTL"/>
306<iref primary="true" item="Grammar" subitem="DIGIT"/>
307<iref primary="true" item="Grammar" subitem="DQUOTE"/>
308<iref primary="true" item="Grammar" subitem="HEXDIG"/>
309<iref primary="true" item="Grammar" subitem="LF"/>
310<iref primary="true" item="Grammar" subitem="OCTET"/>
311<iref primary="true" item="Grammar" subitem="SP"/>
312<iref primary="true" item="Grammar" subitem="VCHAR"/>
313<iref primary="true" item="Grammar" subitem="WSP"/>
314<t>
315   This specification uses the Augmented Backus-Naur Form (ABNF) notation
316   of <xref target="RFC5234"/>.
317</t>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
339</t>
340
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
356</artwork></figure>
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
361</artwork></figure>
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
366</artwork></figure>
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
373 
374  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
375</artwork></figure> 
376<t>
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
379</t>
380</section>
381
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
389</t>
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
394</t>
395<t>
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
401</t>
402<t>
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
408</t>
409<t>
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
414</t>
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
420</t>
421<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"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429                 ; see <xref target="message.headers"/>
430</artwork></figure>
431<t anchor="rule.token.separators">
432  <x:anchor-alias value="tchar"/>
433  <x:anchor-alias value="token"/>
434   Many HTTP/1.1 header field values consist of words separated by whitespace
435   or special characters. These special characters &MUST; be in a quoted
436   string to be used within a parameter value (as defined in
437   <xref target="transfer.codings"/>).
438</t>
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
440  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
441                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
442                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
443                 
444  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
445</artwork></figure>
446<t anchor="rule.quoted-string">
447  <x:anchor-alias value="quoted-string"/>
448  <x:anchor-alias value="qdtext"/>
449  <x:anchor-alias value="obs-text"/>
450   A string of text is parsed as a single word if it is quoted using
451   double-quote marks.
452</t>
453<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"/>
454  <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>
455  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
456                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
457  <x:ref>obs-text</x:ref>       = %x80-FF
458</artwork></figure>
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
464</t>
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
470</artwork></figure>
471</section>
472
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
481<t>
482  The ABNF rules below are defined in other parts:
483</t>
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
487</artwork></figure>
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
491</artwork></figure>
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
496</artwork></figure>
497</section>
498
499</section>
500</section>
501
502<section title="HTTP architecture" anchor="architecture">
503<t>
504   HTTP was created for the World Wide Web architecture
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
508</t>
509
510<section title="Client/Server Operation" anchor="operation">
511<iref item="client"/>
512<iref item="server"/>
513<iref item="connection"/>
514<t>
515   HTTP is a request/response protocol that operates by exchanging messages
516   across a reliable transport or session-layer connection. An HTTP client
517   is a program that establishes a connection to a server for the purpose
518   of sending one or more HTTP requests.  An HTTP server is a program that
519   accepts connections in order to service HTTP requests by sending HTTP
520   responses.
521</t>
522<iref item="user agent"/>
523<iref item="origin server"/>
524<t>
525   Note that the terms "client" and "server" refer only to the roles that
526   these programs perform for a particular connection.  The same program
527   may act as a client on some connections and a server on others.  We use
528   the term "user agent" to refer to the program that initiates a request,
529   such as a WWW browser, editor, or spider (web-traversing robot), and
530   the term "origin server" to refer to the program that can originate
531   authoritative responses to a request.
532</t>
533<t>
534   Most HTTP communication consists of a retrieval request (GET) for
535   a representation of some resource identified by a URI.  In the
536   simplest case, this may be accomplished via a single connection (v)
537   between the user agent (UA) and the origin server (O).
538</t>
539<figure><artwork type="drawing">
540       request chain ------------------------&gt;
541    UA -------------------v------------------- O
542       &lt;----------------------- response chain
543</artwork></figure>
544<iref item="message"/>
545<iref item="request"/>
546<iref item="response"/>
547<t>
548   A client sends an HTTP request to the server in the form of a request
549   message (<xref target="request"/>), beginning with a method, URI, and
550   protocol version, followed by MIME-like header fields containing
551   request modifiers, client information, and payload metadata, an empty
552   line, and finally the payload body (if any).
553   The server response (<xref target="response"/>) begins with a status line,
554   including the protocol version, a success or error code, and textual
555   reason phrase, followed by MIME-like header fields containing server
556   information, resource metadata, payload metadata, an empty line, and
557   finally the payload body (if any).
558</t>
559<t>
560   The following example illustrates a typical message exchange for a
561   GET request on the URI "http://www.example.com/hello.txt":
562</t>
563<figure><preamble>
564client request:
565</preamble><artwork  type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
566GET /hello.txt HTTP/1.1
567User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
568Host: www.example.com
569Accept: */*
570
571</artwork></figure>
572<figure><preamble>
573server response:
574</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
575HTTP/1.1 200 OK
576Date: Mon, 27 Jul 2009 12:28:53 GMT
577Server: Apache
578Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
579ETag: "34aa387-d-1568eb00"
580Accept-Ranges: bytes
581Content-Length: <x:length-of target="exbody"/>
582Vary: Accept-Encoding
583Content-Type: text/plain
584
585<x:span anchor="exbody">Hello World!
586</x:span></artwork></figure>
587</section>
588
589<section title="Intermediaries" anchor="intermediaries">
590<t>
591   A more complicated situation occurs when one or more intermediaries
592   are present in the request/response chain. There are three common
593   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
594   a single intermediary may act as an origin server, proxy, gateway,
595   or tunnel, switching behavior based on the nature of each request.
596</t>
597<figure><artwork type="drawing">
598       request chain --------------------------------------&gt;
599    UA -----v----- A -----v----- B -----v----- C -----v----- O
600       &lt;------------------------------------- response chain
601</artwork></figure>
602<t>
603   The figure above shows three intermediaries (A, B, and C) between the
604   user agent and origin server. A request or response message that
605   travels the whole chain will pass through four separate connections.
606   Some HTTP communication options
607   may apply only to the connection with the nearest, non-tunnel
608   neighbor, only to the end-points of the chain, or to all connections
609   along the chain. Although the diagram is linear, each participant may
610   be engaged in multiple, simultaneous communications. For example, B
611   may be receiving requests from many clients other than A, and/or
612   forwarding requests to servers other than C, at the same time that it
613   is handling A's request.
614</t>
615<t>
616<iref item="upstream"/><iref item="downstream"/>
617<iref item="inbound"/><iref item="outbound"/>
618   We use the terms "upstream" and "downstream" to describe various
619   requirements in relation to the directional flow of a message:
620   all messages flow from upstream to downstream.
621   Likewise, we use the terms "inbound" and "outbound" to refer to
622   directions in relation to the request path: "inbound" means toward
623   the origin server and "outbound" means toward the user agent.
624</t>
625<t><iref item="proxy"/>
626   A proxy is a message forwarding agent that is selected by the
627   client, usually via local configuration rules, to receive requests
628   for some type(s) of absolute URI and attempt to satisfy those
629   requests via translation through the HTTP interface.  Some translations
630   are minimal, such as for proxy requests for "http" URIs, whereas
631   other requests may require translation to and from entirely different
632   application-layer protocols. Proxies are often used to group an
633   organization's HTTP requests through a common intermediary for the
634   sake of security, annotation services, or shared caching.
635</t>
636<t><iref item="gateway"/><iref item="reverse proxy"/>
637   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
638   as a layer above some other server(s) and translates the received
639   requests to the underlying server's protocol.  Gateways are often
640   used for load balancing or partitioning HTTP services across
641   multiple machines.
642   Unlike a proxy, a gateway receives requests as if it were the
643   origin server for the requested resource; the requesting client
644   will not be aware that it is communicating with a gateway.
645   A gateway communicates with the client as if the gateway is the
646   origin server and thus is subject to all of the requirements on
647   origin servers for that connection.  A gateway communicates
648   with inbound servers using any protocol it desires, including
649   private extensions to HTTP that are outside the scope of this
650   specification.
651</t>
652<t><iref item="tunnel"/>
653   A tunnel acts as a blind relay between two connections
654   without changing the messages. Once active, a tunnel is not
655   considered a party to the HTTP communication, though the tunnel may
656   have been initiated by an HTTP request. A tunnel ceases to exist when
657   both ends of the relayed connection are closed. Tunnels are used to
658   extend a virtual connection through an intermediary, such as when
659   transport-layer security is used to establish private communication
660   through a shared firewall proxy.
661</t>
662</section>
663
664<section title="Caches" anchor="caches">
665<iref item="cache"/>
666<t>
667   Any party to HTTP communication that is not acting as a tunnel may
668   employ an internal cache for handling requests.
669   A cache is a local store of previous response messages and the
670   subsystem that controls its message storage, retrieval, and deletion.
671   A cache stores cacheable responses in order to reduce the response
672   time and network bandwidth consumption on future, equivalent
673   requests. Any client or server may include a cache, though a cache
674   cannot be used by a server while it is acting as a tunnel.
675</t>
676<t>
677   The effect of a cache is that the request/response chain is shortened
678   if one of the participants along the chain has a cached response
679   applicable to that request. The following illustrates the resulting
680   chain if B has a cached copy of an earlier response from O (via C)
681   for a request which has not been cached by UA or A.
682</t>
683<figure><artwork type="drawing">
684          request chain ----------&gt;
685       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
686          &lt;--------- response chain
687</artwork></figure>
688<t><iref item="cacheable"/>
689   A response is cacheable if a cache is allowed to store a copy of
690   the response message for use in answering subsequent requests.
691   Even when a response is cacheable, there may be additional
692   constraints placed by the client or by the origin server on when
693   that cached response can be used for a particular request. HTTP
694   requirements for cache behavior and cacheable responses are
695   defined in &caching-overview;
696</t>
697<t>
698   There are a wide variety of architectures and configurations
699   of caches and proxies deployed across the World Wide Web and
700   inside large organizations. These systems include national hierarchies
701   of proxy caches to save transoceanic bandwidth, systems that
702   broadcast or multicast cache entries, organizations that distribute
703   subsets of cached data via optical media, and so on.
704</t>
705</section>
706
707<section title="Transport Independence" anchor="transport-independence">
708<t>
709  HTTP systems are used in a wide variety of environments, from
710  corporate intranets with high-bandwidth links to long-distance
711  communication over low-power radio links and intermittent connectivity.
712</t>
713<t>
714   HTTP communication usually takes place over TCP/IP connections. The
715   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
716   not preclude HTTP from being implemented on top of any other protocol
717   on the Internet, or on other networks. HTTP only presumes a reliable
718   transport; any protocol that provides such guarantees can be used;
719   the mapping of the HTTP/1.1 request and response structures onto the
720   transport data units of the protocol in question is outside the scope
721   of this specification.
722</t>
723<t>
724   In HTTP/1.0, most implementations used a new connection for each
725   request/response exchange. In HTTP/1.1, a connection may be used for
726   one or more request/response exchanges, although connections may be
727   closed for a variety of reasons (see <xref target="persistent.connections"/>).
728</t>
729</section>
730
731<section title="HTTP Version" anchor="http.version">
732  <x:anchor-alias value="HTTP-Version"/>
733  <x:anchor-alias value="HTTP-Prot-Name"/>
734<t>
735   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
736   of the protocol. The protocol versioning policy is intended to allow
737   the sender to indicate the format of a message and its capacity for
738   understanding further HTTP communication, rather than the features
739   obtained via that communication. No change is made to the version
740   number for the addition of message components which do not affect
741   communication behavior or which only add to extensible field values.
742   The &lt;minor&gt; number is incremented when the changes made to the
743   protocol add features which do not change the general message parsing
744   algorithm, but which may add to the message semantics and imply
745   additional capabilities of the sender. The &lt;major&gt; number is
746   incremented when the format of a message within the protocol is
747   changed. See <xref target="RFC2145"/> for a fuller explanation.
748</t>
749<t>
750   The version of an HTTP message is indicated by an HTTP-Version field
751   in the first line of the message. HTTP-Version is case-sensitive.
752</t>
753<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
754  <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>
755  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
756</artwork></figure>
757<t>
758   Note that the major and minor numbers &MUST; be treated as separate
759   integers and that each &MAY; be incremented higher than a single digit.
760   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
761   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
762   &MUST-NOT; be sent.
763</t>
764<t>
765   An application that sends a request or response message that includes
766   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
767   with this specification. Applications that are at least conditionally
768   compliant with this specification &SHOULD; use an HTTP-Version of
769   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
770   not compatible with HTTP/1.0. For more details on when to send
771   specific HTTP-Version values, see <xref target="RFC2145"/>.
772</t>
773<t>
774   The HTTP version of an application is the highest HTTP version for
775   which the application is at least conditionally compliant.
776</t>
777<t>
778   Proxy and gateway applications need to be careful when forwarding
779   messages in protocol versions different from that of the application.
780   Since the protocol version indicates the protocol capability of the
781   sender, a proxy/gateway &MUST-NOT; send a message with a version
782   indicator which is greater than its actual version. If a higher
783   version request is received, the proxy/gateway &MUST; either downgrade
784   the request version, or respond with an error, or switch to tunnel
785   behavior.
786</t>
787<t>
788   Due to interoperability problems with HTTP/1.0 proxies discovered
789   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
790   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
791   they support. The proxy/gateway's response to that request &MUST; be in
792   the same major version as the request.
793</t>
794<x:note>
795  <t>
796    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
797    of header fields required or forbidden by the versions involved.
798  </t>
799</x:note>
800</section>
801
802<section title="Uniform Resource Identifiers" anchor="uri">
803<iref primary="true" item="resource"/>
804<t>
805   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
806   throughout HTTP as the means for identifying resources. URI references
807   are used to target requests, indicate redirects, and define relationships.
808   HTTP does not limit what a resource may be; it merely defines an interface
809   that can be used to interact with a resource via HTTP. More information on
810   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
811</t>
812  <x:anchor-alias value="URI"/>
813  <x:anchor-alias value="URI-reference"/>
814  <x:anchor-alias value="absolute-URI"/>
815  <x:anchor-alias value="relative-part"/>
816  <x:anchor-alias value="authority"/>
817  <x:anchor-alias value="fragment"/>
818  <x:anchor-alias value="path-abempty"/>
819  <x:anchor-alias value="path-absolute"/>
820  <x:anchor-alias value="port"/>
821  <x:anchor-alias value="query"/>
822  <x:anchor-alias value="uri-host"/>
823  <x:anchor-alias value="partial-URI"/>
824<t>
825   This specification adopts the definitions of "URI-reference",
826   "absolute-URI", "relative-part", "fragment", "port", "host",
827   "path-abempty", "path-absolute", "query", and "authority" from
828   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
829   protocol elements that allow a relative URI without a fragment.
830</t>
831<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"/>
832  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
833  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
834  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
835  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
836  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
837  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
838  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
839  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
840  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
841  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
842  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
843 
844  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
845</artwork></figure>
846<t>
847   Each protocol element in HTTP that allows a URI reference will indicate in
848   its ABNF production whether the element allows only a URI in absolute form
849   (absolute-URI), any relative reference (relative-ref), or some other subset
850   of the URI-reference grammar. Unless otherwise indicated, URI references
851   are parsed relative to the request target (the default base URI for both
852   the request and its corresponding response).
853</t>
854
855<section title="http URI scheme" anchor="http.uri">
856  <x:anchor-alias value="http-URI"/>
857  <iref item="http URI scheme" primary="true"/>
858  <iref item="URI scheme" subitem="http" primary="true"/>
859<t>
860   The "http" URI scheme is hereby defined for the purpose of minting
861   identifiers according to their association with the hierarchical
862   namespace governed by a potential HTTP origin server listening for
863   TCP connections on a given port.
864   The HTTP server is identified via the generic syntax's
865   <x:ref>authority</x:ref> component, which includes a host
866   identifier and optional TCP port, and the remainder of the URI is
867   considered to be identifying data corresponding to a resource for
868   which that server might provide an HTTP interface.
869</t>
870<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
871  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
872</artwork></figure>
873<t>
874   The host identifier within an <x:ref>authority</x:ref> component is
875   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
876   provided as an IP literal or IPv4 address, then the HTTP server is any
877   listener on the indicated TCP port at that IP address. If host is a
878   registered name, then that name is considered an indirect identifier
879   and the recipient might use a name resolution service, such as DNS,
880   to find the address of a listener for that host.
881   The host &MUST-NOT; be empty; if an "http" URI is received with an
882   empty host, then it &MUST; be rejected as invalid.
883   If the port subcomponent is empty or not given, then TCP port 80 is
884   assumed (the default reserved port for WWW services).
885</t>
886<t>
887   Regardless of the form of host identifier, access to that host is not
888   implied by the mere presence of its name or address. The host may or may
889   not exist and, even when it does exist, may or may not be running an
890   HTTP server or listening to the indicated port. The "http" URI scheme
891   makes use of the delegated nature of Internet names and addresses to
892   establish a naming authority (whatever entity has the ability to place
893   an HTTP server at that Internet name or address) and allows that
894   authority to determine which names are valid and how they might be used.
895</t>
896<t>
897   When an "http" URI is used within a context that calls for access to the
898   indicated resource, a client &MAY; attempt access by resolving
899   the host to an IP address, establishing a TCP connection to that address
900   on the indicated port, and sending an HTTP request message to the server
901   containing the URI's identifying data as described in <xref target="request"/>.
902   If the server responds to that request with a non-interim HTTP response
903   message, as described in <xref target="response"/>, then that response
904   is considered an authoritative answer to the client's request.
905</t>
906<t>
907   Although HTTP is independent of the transport protocol, the "http"
908   scheme is specific to TCP-based services because the name delegation
909   process depends on TCP for establishing authority.
910   An HTTP service based on some other underlying connection protocol
911   would presumably be identified using a different URI scheme, just as
912   the "https" scheme (below) is used for servers that require an SSL/TLS
913   transport layer on a connection. Other protocols may also be used to
914   provide access to "http" identified resources --- it is only the
915   authoritative interface used for mapping the namespace that is
916   specific to TCP.
917</t>
918</section>
919
920<section title="https URI scheme" anchor="https.uri">
921   <x:anchor-alias value="https-URI"/>
922   <iref item="https URI scheme"/>
923   <iref item="URI scheme" subitem="https"/>
924<t>
925   The "https" URI scheme is hereby defined for the purpose of minting
926   identifiers according to their association with the hierarchical
927   namespace governed by a potential HTTP origin server listening for
928   SSL/TLS-secured connections on a given TCP port.
929   The host and port are determined in the same way
930   as for the "http" scheme, except that a default TCP port of 443
931   is assumed if the port subcomponent is empty or not given.
932</t>
933<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
934  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
935</artwork></figure>
936<t>
937   The primary difference between the "http" and "https" schemes is
938   that interaction with the latter is required to be secured for
939   privacy through the use of strong encryption. The URI cannot be
940   sent in a request until the connection is secure. Likewise, the
941   default for caching is that each response that would be considered
942   "public" under the "http" scheme is instead treated as "private"
943   and thus not eligible for shared caching.
944</t>
945<t>
946   The process for authoritative access to an "https" identified
947   resource is defined in <xref target="RFC2818"/>.
948</t>
949</section>
950
951<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
952<t>
953   Since the "http" and "https" schemes conform to the URI generic syntax,
954   such URIs are normalized and compared according to the algorithm defined
955   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
956   described above for each scheme.
957</t>
958<t>
959   If the port is equal to the default port for a scheme, the normal
960   form is to elide the port subcomponent. Likewise, an empty path
961   component is equivalent to an absolute path of "/", so the normal
962   form is to provide a path of "/" instead. The scheme and host
963   are case-insensitive and normally provided in lowercase; all
964   other components are compared in a case-sensitive manner.
965   Characters other than those in the "reserved" set are equivalent
966   to their percent-encoded octets (see <xref target="RFC3986"
967   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
968</t>
969<t>
970   For example, the following three URIs are equivalent:
971</t>
972<figure><artwork type="example">
973   http://example.com:80/~smith/home.html
974   http://EXAMPLE.com/%7Esmith/home.html
975   http://EXAMPLE.com:/%7esmith/home.html
976</artwork></figure>
977<t>
978   <cref>[[This paragraph does not belong here. --Roy]]</cref>
979   If path-abempty is the empty string (i.e., there is no slash "/"
980   path separator following the authority), then the "http" URI
981   &MUST; be given as "/" when
982   used as a request-target (<xref target="request-target"/>). If a proxy
983   receives a host name which is not a fully qualified domain name, it
984   &MAY; add its domain to the host name it received. If a proxy receives
985   a fully qualified domain name, the proxy &MUST-NOT; change the host
986   name.
987</t>
988</section>
989
990<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
991<t>
992   <cref>TBS: describe why aliases like webcal are harmful.</cref>
993</t>
994</section>
995</section>
996
997<section title="Use of HTTP for proxy communication" anchor="http.proxy">
998<t>
999   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
1000</t>
1001</section>
1002<section title="Interception of HTTP for access control" anchor="http.intercept">
1003<t>
1004   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
1005</t>
1006</section>
1007<section title="Use of HTTP by other protocols" anchor="http.others">
1008<t>
1009   <cref>TBD: Profiles of HTTP defined by other protocol.
1010   Extensions of HTTP like WebDAV.</cref>
1011</t>
1012</section>
1013<section title="Use of HTTP by media type specification" anchor="http.media">
1014<t>
1015   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
1016</t>
1017</section>
1018</section>
1019
1020<section title="HTTP Message" anchor="http.message">
1021
1022<section title="Message Types" anchor="message.types">
1023  <x:anchor-alias value="generic-message"/>
1024  <x:anchor-alias value="HTTP-message"/>
1025  <x:anchor-alias value="start-line"/>
1026<t>
1027   HTTP messages consist of requests from client to server and responses
1028   from server to client.
1029</t>
1030<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1031  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1032</artwork></figure>
1033<t>
1034   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1035   message format of <xref target="RFC5322"/> for transferring entities (the payload
1036   of the message). Both types of message consist of a start-line, zero
1037   or more header fields (also known as "headers"), an empty line (i.e.,
1038   a line with nothing preceding the CRLF) indicating the end of the
1039   header fields, and possibly a message-body.
1040</t>
1041<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1042  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1043                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1044                    <x:ref>CRLF</x:ref>
1045                    [ <x:ref>message-body</x:ref> ]
1046  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1047</artwork></figure>
1048<t>
1049   In the interest of robustness, servers &SHOULD; ignore any empty
1050   line(s) received where a Request-Line is expected. In other words, if
1051   the server is reading the protocol stream at the beginning of a
1052   message and receives a CRLF first, it should ignore the CRLF.
1053</t>
1054<t>
1055   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1056   after a POST request. To restate what is explicitly forbidden by the
1057   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1058   extra CRLF.
1059</t>
1060<t>
1061   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1062   header field. The presence of whitespace might be an attempt to trick a
1063   noncompliant implementation of HTTP into ignoring that field or processing
1064   the next line as a new request, either of which may result in security
1065   issues when implementations within the request chain interpret the
1066   same message differently. HTTP/1.1 servers &MUST; reject such a message
1067   with a 400 (Bad Request) response.
1068</t>
1069</section>
1070
1071<section title="Message Headers" anchor="message.headers">
1072  <x:anchor-alias value="field-content"/>
1073  <x:anchor-alias value="field-name"/>
1074  <x:anchor-alias value="field-value"/>
1075  <x:anchor-alias value="message-header"/>
1076<t>
1077   HTTP header fields follow the same general format as Internet messages in
1078   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1079   of a name followed by a colon (":"), optional whitespace, and the field
1080   value. Field names are case-insensitive.
1081</t>
1082<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"/>
1083  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1084  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1085  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1086  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1087</artwork></figure>
1088<t>
1089   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1090   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1091   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1092   header field-values use only a subset of the US-ASCII charset
1093   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1094   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1095   (obs-text) octets in field-content as opaque data.
1096</t>
1097<t>
1098   No whitespace is allowed between the header field-name and colon. For
1099   security reasons, any request message received containing such whitespace
1100   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1101   whitespace in a response message &MUST; be removed.
1102</t>
1103<t>
1104   The field value &MAY; be preceded by optional whitespace; a single SP is
1105   preferred. The field-value does not include any leading or trailing white
1106   space: OWS occurring before the first non-whitespace character of the
1107   field-value or after the last non-whitespace character of the field-value
1108   is ignored and &MAY; be removed without changing the meaning of the header
1109   field.
1110</t>
1111<t>
1112   Historically, HTTP header field values could be extended over multiple
1113   lines by preceding each extra line with at least one space or horizontal
1114   tab character (line folding). This specification deprecates such line
1115   folding except within the message/http media type
1116   (<xref target="internet.media.type.message.http"/>).
1117   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1118   (i.e., that contain any field-content that matches the obs-fold rule) unless
1119   the message is intended for packaging within the message/http media type.
1120   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1121   obs-fold whitespace with a single SP prior to interpreting the field value
1122   or forwarding the message downstream.
1123</t>
1124<t anchor="rule.comment">
1125  <x:anchor-alias value="comment"/>
1126  <x:anchor-alias value="ctext"/>
1127   Comments can be included in some HTTP header fields by surrounding
1128   the comment text with parentheses. Comments are only allowed in
1129   fields containing "comment" as part of their field value definition.
1130   In all other fields, parentheses are considered part of the field
1131   value.
1132</t>
1133<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1134  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1135  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1136                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1137</artwork></figure>
1138<t>
1139   The order in which header fields with differing field names are
1140   received is not significant. However, it is "good practice" to send
1141   general-header fields first, followed by request-header or response-header
1142   fields, and ending with the entity-header fields.
1143</t>
1144<t>
1145   Multiple message-header fields with the same field-name &MAY; be
1146   present in a message if and only if the entire field-value for that
1147   header field is defined as a comma-separated list [i.e., #(values)].
1148   It &MUST; be possible to combine the multiple header fields into one
1149   "field-name: field-value" pair, without changing the semantics of the
1150   message, by appending each subsequent field-value to the first, each
1151   separated by a comma. The order in which header fields with the same
1152   field-name are received is therefore significant to the
1153   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1154   change the order of these field values when a message is forwarded.
1155</t>
1156<x:note>
1157  <t>
1158   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1159   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1160   can occur multiple times, but does not use the list syntax, and thus cannot
1161   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1162   for details.) Also note that the Set-Cookie2 header specified in
1163   <xref target="RFC2965"/> does not share this problem.
1164  </t>
1165</x:note>
1166 
1167</section>
1168
1169<section title="Message Body" anchor="message.body">
1170  <x:anchor-alias value="message-body"/>
1171<t>
1172   The message-body (if any) of an HTTP message is used to carry the
1173   entity-body associated with the request or response. The message-body
1174   differs from the entity-body only when a transfer-coding has been
1175   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1176</t>
1177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1178  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1179               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1180</artwork></figure>
1181<t>
1182   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1183   applied by an application to ensure safe and proper transfer of the
1184   message. Transfer-Encoding is a property of the message, not of the
1185   entity, and thus &MAY; be added or removed by any application along the
1186   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1187   when certain transfer-codings may be used.)
1188</t>
1189<t>
1190   The rules for when a message-body is allowed in a message differ for
1191   requests and responses.
1192</t>
1193<t>
1194   The presence of a message-body in a request is signaled by the
1195   inclusion of a Content-Length or Transfer-Encoding header field in
1196   the request's message-headers.
1197   When a request message contains both a message-body of non-zero
1198   length and a method that does not define any semantics for that
1199   request message-body, then an origin server &SHOULD; either ignore
1200   the message-body or respond with an appropriate error message
1201   (e.g., 413).  A proxy or gateway, when presented the same request,
1202   &SHOULD; either forward the request inbound with the message-body or
1203   ignore the message-body when determining a response.
1204</t>
1205<t>
1206   For response messages, whether or not a message-body is included with
1207   a message is dependent on both the request method and the response
1208   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1209   &MUST-NOT; include a message-body, even though the presence of entity-header
1210   fields might lead one to believe they do. All 1xx
1211   (informational), 204 (No Content), and 304 (Not Modified) responses
1212   &MUST-NOT; include a message-body. All other responses do include a
1213   message-body, although it &MAY; be of zero length.
1214</t>
1215</section>
1216
1217<section title="Message Length" anchor="message.length">
1218<t>
1219   The transfer-length of a message is the length of the message-body as
1220   it appears in the message; that is, after any transfer-codings have
1221   been applied. When a message-body is included with a message, the
1222   transfer-length of that body is determined by one of the following
1223   (in order of precedence):
1224</t>
1225<t>
1226  <list style="numbers">
1227    <x:lt><t>
1228     Any response message which "&MUST-NOT;" include a message-body (such
1229     as the 1xx, 204, and 304 responses and any response to a HEAD
1230     request) is always terminated by the first empty line after the
1231     header fields, regardless of the entity-header fields present in
1232     the message.
1233    </t></x:lt>
1234    <x:lt><t>
1235     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1236     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1237     is used, the transfer-length is defined by the use of this transfer-coding.
1238     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1239     is not present, the transfer-length is defined by the sender closing the connection.
1240    </t></x:lt>
1241    <x:lt><t>
1242     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1243     value in OCTETs represents both the entity-length and the
1244     transfer-length. The Content-Length header field &MUST-NOT; be sent
1245     if these two lengths are different (i.e., if a Transfer-Encoding
1246     header field is present). If a message is received with both a
1247     Transfer-Encoding header field and a Content-Length header field,
1248     the latter &MUST; be ignored.
1249    </t></x:lt>
1250    <x:lt><t>
1251     If the message uses the media type "multipart/byteranges", and the
1252     transfer-length is not otherwise specified, then this self-delimiting
1253     media type defines the transfer-length. This media type
1254     &MUST-NOT; be used unless the sender knows that the recipient can parse
1255     it; the presence in a request of a Range header with multiple byte-range
1256     specifiers from a 1.1 client implies that the client can parse
1257     multipart/byteranges responses.
1258    <list style="empty"><t>
1259       A range header might be forwarded by a 1.0 proxy that does not
1260       understand multipart/byteranges; in this case the server &MUST;
1261       delimit the message using methods defined in items 1, 3 or 5 of
1262       this section.
1263    </t></list>
1264    </t></x:lt>
1265    <x:lt><t>
1266     By the server closing the connection. (Closing the connection
1267     cannot be used to indicate the end of a request body, since that
1268     would leave no possibility for the server to send back a response.)
1269    </t></x:lt>
1270  </list>
1271</t>
1272<t>
1273   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1274   containing a message-body &MUST; include a valid Content-Length header
1275   field unless the server is known to be HTTP/1.1 compliant. If a
1276   request contains a message-body and a Content-Length is not given,
1277   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1278   determine the length of the message, or with 411 (Length Required) if
1279   it wishes to insist on receiving a valid Content-Length.
1280</t>
1281<t>
1282   All HTTP/1.1 applications that receive entities &MUST; accept the
1283   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1284   to be used for messages when the message length cannot be determined
1285   in advance.
1286</t>
1287<t>
1288   Messages &MUST-NOT; include both a Content-Length header field and a
1289   transfer-coding. If the message does include a
1290   transfer-coding, the Content-Length &MUST; be ignored.
1291</t>
1292<t>
1293   When a Content-Length is given in a message where a message-body is
1294   allowed, its field value &MUST; exactly match the number of OCTETs in
1295   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1296   invalid length is received and detected.
1297</t>
1298</section>
1299
1300<section title="General Header Fields" anchor="general.header.fields">
1301  <x:anchor-alias value="general-header"/>
1302<t>
1303   There are a few header fields which have general applicability for
1304   both request and response messages, but which do not apply to the
1305   entity being transferred. These header fields apply only to the
1306   message being transmitted.
1307</t>
1308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1309  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1310                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1311                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1312                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1313                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1314                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1315                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1316                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1317                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1318</artwork></figure>
1319<t>
1320   General-header field names can be extended reliably only in
1321   combination with a change in the protocol version. However, new or
1322   experimental header fields may be given the semantics of general
1323   header fields if all parties in the communication recognize them to
1324   be general-header fields. Unrecognized header fields are treated as
1325   entity-header fields.
1326</t>
1327</section>
1328</section>
1329
1330<section title="Request" anchor="request">
1331  <x:anchor-alias value="Request"/>
1332<t>
1333   A request message from a client to a server includes, within the
1334   first line of that message, the method to be applied to the resource,
1335   the identifier of the resource, and the protocol version in use.
1336</t>
1337<!--                 Host                      ; should be moved here eventually -->
1338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1339  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1340                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1341                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1342                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1343                  <x:ref>CRLF</x:ref>
1344                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1345</artwork></figure>
1346
1347<section title="Request-Line" anchor="request-line">
1348  <x:anchor-alias value="Request-Line"/>
1349<t>
1350   The Request-Line begins with a method token, followed by the
1351   request-target and the protocol version, and ending with CRLF. The
1352   elements are separated by SP characters. No CR or LF is allowed
1353   except in the final CRLF sequence.
1354</t>
1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1356  <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>
1357</artwork></figure>
1358
1359<section title="Method" anchor="method">
1360  <x:anchor-alias value="Method"/>
1361<t>
1362   The Method  token indicates the method to be performed on the
1363   resource identified by the request-target. The method is case-sensitive.
1364</t>
1365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1366  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1367</artwork></figure>
1368</section>
1369
1370<section title="request-target" anchor="request-target">
1371  <x:anchor-alias value="request-target"/>
1372<t>
1373   The request-target
1374   identifies the resource upon which to apply the request.
1375</t>
1376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1377  <x:ref>request-target</x:ref> = "*"
1378                 / <x:ref>absolute-URI</x:ref>
1379                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1380                 / <x:ref>authority</x:ref>
1381</artwork></figure>
1382<t>
1383   The four options for request-target are dependent on the nature of the
1384   request. The asterisk "*" means that the request does not apply to a
1385   particular resource, but to the server itself, and is only allowed
1386   when the method used does not necessarily apply to a resource. One
1387   example would be
1388</t>
1389<figure><artwork type="example">
1390  OPTIONS * HTTP/1.1
1391</artwork></figure>
1392<t>
1393   The absolute-URI form is &REQUIRED; when the request is being made to a
1394   proxy. The proxy is requested to forward the request or service it
1395   from a valid cache, and return the response. Note that the proxy &MAY;
1396   forward the request on to another proxy or directly to the server
1397   specified by the absolute-URI. In order to avoid request loops, a
1398   proxy &MUST; be able to recognize all of its server names, including
1399   any aliases, local variations, and the numeric IP address. An example
1400   Request-Line would be:
1401</t>
1402<figure><artwork type="example">
1403  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1404</artwork></figure>
1405<t>
1406   To allow for transition to absolute-URIs in all requests in future
1407   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1408   form in requests, even though HTTP/1.1 clients will only generate
1409   them in requests to proxies.
1410</t>
1411<t>
1412   The authority form is only used by the CONNECT method (&CONNECT;).
1413</t>
1414<t>
1415   The most common form of request-target is that used to identify a
1416   resource on an origin server or gateway. In this case the absolute
1417   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1418   the request-target, and the network location of the URI (authority) &MUST;
1419   be transmitted in a Host header field. For example, a client wishing
1420   to retrieve the resource above directly from the origin server would
1421   create a TCP connection to port 80 of the host "www.example.org" and send
1422   the lines:
1423</t>
1424<figure><artwork type="example">
1425  GET /pub/WWW/TheProject.html HTTP/1.1
1426  Host: www.example.org
1427</artwork></figure>
1428<t>
1429   followed by the remainder of the Request. Note that the absolute path
1430   cannot be empty; if none is present in the original URI, it &MUST; be
1431   given as "/" (the server root).
1432</t>
1433<t>
1434   If a proxy receives a request without any path in the request-target and
1435   the method specified is capable of supporting the asterisk form of
1436   request-target, then the last proxy on the request chain &MUST; forward the
1437   request with "*" as the final request-target.
1438</t>
1439<figure><preamble>   
1440   For example, the request
1441</preamble><artwork type="example">
1442  OPTIONS http://www.example.org:8001 HTTP/1.1
1443</artwork></figure>
1444<figure><preamble>   
1445  would be forwarded by the proxy as
1446</preamble><artwork type="example">
1447  OPTIONS * HTTP/1.1
1448  Host: www.example.org:8001
1449</artwork>
1450<postamble>
1451   after connecting to port 8001 of host "www.example.org".
1452</postamble>
1453</figure>
1454<t>
1455   The request-target is transmitted in the format specified in
1456   <xref target="http.uri"/>. If the request-target is percent-encoded
1457   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1458   &MUST; decode the request-target in order to
1459   properly interpret the request. Servers &SHOULD; respond to invalid
1460   request-targets with an appropriate status code.
1461</t>
1462<t>
1463   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1464   received request-target when forwarding it to the next inbound server,
1465   except as noted above to replace a null path-absolute with "/".
1466</t>
1467<x:note>
1468  <t>
1469    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1470    meaning of the request when the origin server is improperly using
1471    a non-reserved URI character for a reserved purpose.  Implementors
1472    should be aware that some pre-HTTP/1.1 proxies have been known to
1473    rewrite the request-target.
1474  </t>
1475</x:note>
1476<t>
1477   HTTP does not place a pre-defined limit on the length of a request-target.
1478   A server &MUST; be prepared to receive URIs of unbounded length and
1479   respond with the 414 (URI Too Long) status if the received
1480   request-target would be longer than the server wishes to handle
1481   (see &status-414;).
1482</t>
1483<t>
1484   Various ad-hoc limitations on request-target length are found in practice.
1485   It is &RECOMMENDED; that all HTTP senders and recipients support
1486   request-target lengths of 8000 or more OCTETs.
1487</t>
1488</section>
1489</section>
1490
1491<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1492<t>
1493   The exact resource identified by an Internet request is determined by
1494   examining both the request-target and the Host header field.
1495</t>
1496<t>
1497   An origin server that does not allow resources to differ by the
1498   requested host &MAY; ignore the Host header field value when
1499   determining the resource identified by an HTTP/1.1 request. (But see
1500   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1501   for other requirements on Host support in HTTP/1.1.)
1502</t>
1503<t>
1504   An origin server that does differentiate resources based on the host
1505   requested (sometimes referred to as virtual hosts or vanity host
1506   names) &MUST; use the following rules for determining the requested
1507   resource on an HTTP/1.1 request:
1508  <list style="numbers">
1509    <t>If request-target is an absolute-URI, the host is part of the
1510     request-target. Any Host header field value in the request &MUST; be
1511     ignored.</t>
1512    <t>If the request-target is not an absolute-URI, and the request includes
1513     a Host header field, the host is determined by the Host header
1514     field value.</t>
1515    <t>If the host as determined by rule 1 or 2 is not a valid host on
1516     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1517  </list>
1518</t>
1519<t>
1520   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1521   attempt to use heuristics (e.g., examination of the URI path for
1522   something unique to a particular host) in order to determine what
1523   exact resource is being requested.
1524</t>
1525</section>
1526
1527</section>
1528
1529
1530<section title="Response" anchor="response">
1531  <x:anchor-alias value="Response"/>
1532<t>
1533   After receiving and interpreting a request message, a server responds
1534   with an HTTP response message.
1535</t>
1536<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1537  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1538                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1539                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1540                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1541                  <x:ref>CRLF</x:ref>
1542                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1543</artwork></figure>
1544
1545<section title="Status-Line" anchor="status-line">
1546  <x:anchor-alias value="Status-Line"/>
1547<t>
1548   The first line of a Response message is the Status-Line, consisting
1549   of the protocol version followed by a numeric status code and its
1550   associated textual phrase, with each element separated by SP
1551   characters. No CR or LF is allowed except in the final CRLF sequence.
1552</t>
1553<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1554  <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>
1555</artwork></figure>
1556
1557<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1558  <x:anchor-alias value="Reason-Phrase"/>
1559  <x:anchor-alias value="Status-Code"/>
1560<t>
1561   The Status-Code element is a 3-digit integer result code of the
1562   attempt to understand and satisfy the request. These codes are fully
1563   defined in &status-codes;.  The Reason Phrase exists for the sole
1564   purpose of providing a textual description associated with the numeric
1565   status code, out of deference to earlier Internet application protocols
1566   that were more frequently used with interactive text clients.
1567   A client &SHOULD; ignore the content of the Reason Phrase.
1568</t>
1569<t>
1570   The first digit of the Status-Code defines the class of response. The
1571   last two digits do not have any categorization role. There are 5
1572   values for the first digit:
1573  <list style="symbols">
1574    <t>
1575      1xx: Informational - Request received, continuing process
1576    </t>
1577    <t>
1578      2xx: Success - The action was successfully received,
1579        understood, and accepted
1580    </t>
1581    <t>
1582      3xx: Redirection - Further action must be taken in order to
1583        complete the request
1584    </t>
1585    <t>
1586      4xx: Client Error - The request contains bad syntax or cannot
1587        be fulfilled
1588    </t>
1589    <t>
1590      5xx: Server Error - The server failed to fulfill an apparently
1591        valid request
1592    </t>
1593  </list>
1594</t>
1595<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"/>
1596  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1597  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1598</artwork></figure>
1599</section>
1600</section>
1601
1602</section>
1603
1604
1605<section title="Protocol Parameters" anchor="protocol.parameters">
1606
1607<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1608  <x:anchor-alias value="HTTP-date"/>
1609<t>
1610   HTTP applications have historically allowed three different formats
1611   for the representation of date/time stamps:
1612</t>
1613<figure><artwork type="example">
1614  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1615  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1616  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1617</artwork></figure>
1618<t>
1619   The first format is preferred as an Internet standard and represents
1620   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1621   other formats are described here only for
1622   compatibility with obsolete implementations.
1623   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1624   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1625   only generate the RFC 1123 format for representing HTTP-date values
1626   in header fields. See <xref target="tolerant.applications"/> for further information.
1627</t>
1628<t>
1629   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1630   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1631   equal to UTC (Coordinated Universal Time). This is indicated in the
1632   first two formats by the inclusion of "GMT" as the three-letter
1633   abbreviation for time zone, and &MUST; be assumed when reading the
1634   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1635   additional whitespace beyond that specifically included as SP in the
1636   grammar.
1637</t>
1638<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1639  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1640</artwork></figure>
1641<t anchor="preferred.date.format">
1642  <x:anchor-alias value="rfc1123-date"/>
1643  <x:anchor-alias value="time-of-day"/>
1644  <x:anchor-alias value="hour"/>
1645  <x:anchor-alias value="minute"/>
1646  <x:anchor-alias value="second"/>
1647  <x:anchor-alias value="day-name"/>
1648  <x:anchor-alias value="day"/>
1649  <x:anchor-alias value="month"/>
1650  <x:anchor-alias value="year"/>
1651  <x:anchor-alias value="GMT"/>
1652  Preferred format:
1653</t>
1654<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
1655  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1656
1657  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1658               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1659               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1660               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1661               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1662               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1663               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1664               
1665  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1666               ; e.g., 02 Jun 1982
1667
1668  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1669  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1670               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1671               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1672               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1673               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1674               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1675               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1676               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1677               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1678               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1679               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1680               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1681  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1682
1683  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1684
1685  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1686                 ; 00:00:00 - 23:59:59
1687                 
1688  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1689  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1690  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1691</artwork></figure>
1692<t>
1693  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1694  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1695  same as those defined for the RFC 5322 constructs
1696  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1697</t>
1698<t anchor="obsolete.date.formats">
1699  <x:anchor-alias value="obs-date"/>
1700  <x:anchor-alias value="rfc850-date"/>
1701  <x:anchor-alias value="asctime-date"/>
1702  <x:anchor-alias value="date1"/>
1703  <x:anchor-alias value="date2"/>
1704  <x:anchor-alias value="date3"/>
1705  <x:anchor-alias value="rfc1123-date"/>
1706  <x:anchor-alias value="day-name-l"/>
1707  Obsolete formats:
1708</t>
1709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1710  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1711</artwork></figure>
1712<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1713  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1714  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1715                 ; day-month-year (e.g., 02-Jun-82)
1716
1717  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1718         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1719         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1720         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1721         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1722         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1723         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1724</artwork></figure>
1725<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1726  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1727  <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> ))
1728                 ; month day (e.g., Jun  2)
1729</artwork></figure>
1730<x:note>
1731  <t>
1732    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1733    accepting date values that may have been sent by non-HTTP
1734    applications, as is sometimes the case when retrieving or posting
1735    messages via proxies/gateways to SMTP or NNTP.
1736  </t>
1737</x:note>
1738<x:note>
1739  <t>
1740    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1741    to their usage within the protocol stream. Clients and servers are
1742    not required to use these formats for user presentation, request
1743    logging, etc.
1744  </t>
1745</x:note>
1746</section>
1747
1748<section title="Transfer Codings" anchor="transfer.codings">
1749  <x:anchor-alias value="transfer-coding"/>
1750  <x:anchor-alias value="transfer-extension"/>
1751<t>
1752   Transfer-coding values are used to indicate an encoding
1753   transformation that has been, can be, or may need to be applied to an
1754   entity-body in order to ensure "safe transport" through the network.
1755   This differs from a content coding in that the transfer-coding is a
1756   property of the message, not of the original entity.
1757</t>
1758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1759  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
1760  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1761</artwork></figure>
1762<t anchor="rule.parameter">
1763  <x:anchor-alias value="attribute"/>
1764  <x:anchor-alias value="transfer-parameter"/>
1765  <x:anchor-alias value="value"/>
1766   Parameters are in  the form of attribute/value pairs.
1767</t>
1768<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1769  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1770  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1771  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1772</artwork></figure>
1773<t>
1774   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1775   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1776   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1777</t>
1778<t>
1779   Whenever a transfer-coding is applied to a message-body, the set of
1780   transfer-codings &MUST; include "chunked", unless the message indicates it
1781   is terminated by closing the connection. When the "chunked" transfer-coding
1782   is used, it &MUST; be the last transfer-coding applied to the
1783   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1784   than once to a message-body. These rules allow the recipient to
1785   determine the transfer-length of the message (<xref target="message.length"/>).
1786</t>
1787<t>
1788   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1789   MIME, which were designed to enable safe transport of binary data over a
1790   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1791   However, safe transport
1792   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1793   the only unsafe characteristic of message-bodies is the difficulty in
1794   determining the exact body length (<xref target="message.length"/>), or the desire to
1795   encrypt data over a shared transport.
1796</t>
1797<t>
1798   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1799   transfer-coding value tokens. Initially, the registry contains the
1800   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1801   "gzip", "compress", and "deflate" (&content-codings;).
1802</t>
1803<t>
1804   New transfer-coding value tokens &SHOULD; be registered in the same way
1805   as new content-coding value tokens (&content-codings;).
1806</t>
1807<t>
1808   A server which receives an entity-body with a transfer-coding it does
1809   not understand &SHOULD; return 501 (Not Implemented), and close the
1810   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1811   client.
1812</t>
1813
1814<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1815  <x:anchor-alias value="chunk"/>
1816  <x:anchor-alias value="Chunked-Body"/>
1817  <x:anchor-alias value="chunk-data"/>
1818  <x:anchor-alias value="chunk-ext"/>
1819  <x:anchor-alias value="chunk-ext-name"/>
1820  <x:anchor-alias value="chunk-ext-val"/>
1821  <x:anchor-alias value="chunk-size"/>
1822  <x:anchor-alias value="last-chunk"/>
1823  <x:anchor-alias value="trailer-part"/>
1824<t>
1825   The chunked encoding modifies the body of a message in order to
1826   transfer it as a series of chunks, each with its own size indicator,
1827   followed by an &OPTIONAL; trailer containing entity-header fields. This
1828   allows dynamically produced content to be transferred along with the
1829   information necessary for the recipient to verify that it has
1830   received the full message.
1831</t>
1832<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"/>
1833  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1834                   <x:ref>last-chunk</x:ref>
1835                   <x:ref>trailer-part</x:ref>
1836                   <x:ref>CRLF</x:ref>
1837 
1838  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1839                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1840  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1841  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1842 
1843  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1844                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1845  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1846  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1847  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1848  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1849</artwork></figure>
1850<t>
1851   The chunk-size field is a string of hex digits indicating the size of
1852   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1853   zero, followed by the trailer, which is terminated by an empty line.
1854</t>
1855<t>
1856   The trailer allows the sender to include additional HTTP header
1857   fields at the end of the message. The Trailer header field can be
1858   used to indicate which header fields are included in a trailer (see
1859   <xref target="header.trailer"/>).
1860</t>
1861<t>
1862   A server using chunked transfer-coding in a response &MUST-NOT; use the
1863   trailer for any header fields unless at least one of the following is
1864   true:
1865  <list style="numbers">
1866    <t>the request included a TE header field that indicates "trailers" is
1867     acceptable in the transfer-coding of the  response, as described in
1868     <xref target="header.te"/>; or,</t>
1869
1870    <t>the server is the origin server for the response, the trailer
1871     fields consist entirely of optional metadata, and the recipient
1872     could use the message (in a manner acceptable to the origin server)
1873     without receiving this metadata.  In other words, the origin server
1874     is willing to accept the possibility that the trailer fields might
1875     be silently discarded along the path to the client.</t>
1876  </list>
1877</t>
1878<t>
1879   This requirement prevents an interoperability failure when the
1880   message is being received by an HTTP/1.1 (or later) proxy and
1881   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1882   compliance with the protocol would have necessitated a possibly
1883   infinite buffer on the proxy.
1884</t>
1885<t>
1886   A process for decoding the "chunked" transfer-coding
1887   can be represented in pseudo-code as:
1888</t>
1889<figure><artwork type="code">
1890  length := 0
1891  read chunk-size, chunk-ext (if any) and CRLF
1892  while (chunk-size &gt; 0) {
1893     read chunk-data and CRLF
1894     append chunk-data to entity-body
1895     length := length + chunk-size
1896     read chunk-size and CRLF
1897  }
1898  read entity-header
1899  while (entity-header not empty) {
1900     append entity-header to existing header fields
1901     read entity-header
1902  }
1903  Content-Length := length
1904  Remove "chunked" from Transfer-Encoding
1905</artwork></figure>
1906<t>
1907   All HTTP/1.1 applications &MUST; be able to receive and decode the
1908   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1909   they do not understand.
1910</t>
1911</section>
1912</section>
1913
1914<section title="Product Tokens" anchor="product.tokens">
1915  <x:anchor-alias value="product"/>
1916  <x:anchor-alias value="product-version"/>
1917<t>
1918   Product tokens are used to allow communicating applications to
1919   identify themselves by software name and version. Most fields using
1920   product tokens also allow sub-products which form a significant part
1921   of the application to be listed, separated by whitespace. By
1922   convention, the products are listed in order of their significance
1923   for identifying the application.
1924</t>
1925<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1926  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1927  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1928</artwork></figure>
1929<t>
1930   Examples:
1931</t>
1932<figure><artwork type="example">
1933  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1934  Server: Apache/0.8.4
1935</artwork></figure>
1936<t>
1937   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1938   used for advertising or other non-essential information. Although any
1939   token character &MAY; appear in a product-version, this token &SHOULD;
1940   only be used for a version identifier (i.e., successive versions of
1941   the same product &SHOULD; only differ in the product-version portion of
1942   the product value).
1943</t>
1944</section>
1945
1946<section title="Quality Values" anchor="quality.values">
1947  <x:anchor-alias value="qvalue"/>
1948<t>
1949   Both transfer codings (TE request header, <xref target="header.te"/>)
1950   and content negotiation (&content.negotiation;) use short "floating point"
1951   numbers to indicate the relative importance ("weight") of various
1952   negotiable parameters.  A weight is normalized to a real number in
1953   the range 0 through 1, where 0 is the minimum and 1 the maximum
1954   value. If a parameter has a quality value of 0, then content with
1955   this parameter is `not acceptable' for the client. HTTP/1.1
1956   applications &MUST-NOT; generate more than three digits after the
1957   decimal point. User configuration of these values &SHOULD; also be
1958   limited in this fashion.
1959</t>
1960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1961  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1962                 / ( "1" [ "." 0*3("0") ] )
1963</artwork></figure>
1964<x:note>
1965  <t>
1966     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1967     relative degradation in desired quality.
1968  </t>
1969</x:note>
1970</section>
1971
1972</section>
1973
1974<section title="Connections" anchor="connections">
1975
1976<section title="Persistent Connections" anchor="persistent.connections">
1977
1978<section title="Purpose" anchor="persistent.purpose">
1979<t>
1980   Prior to persistent connections, a separate TCP connection was
1981   established to fetch each URL, increasing the load on HTTP servers
1982   and causing congestion on the Internet. The use of inline images and
1983   other associated data often require a client to make multiple
1984   requests of the same server in a short amount of time. Analysis of
1985   these performance problems and results from a prototype
1986   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1987   measurements of actual HTTP/1.1 implementations show good
1988   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1989   T/TCP <xref target="Tou1998"/>.
1990</t>
1991<t>
1992   Persistent HTTP connections have a number of advantages:
1993  <list style="symbols">
1994      <t>
1995        By opening and closing fewer TCP connections, CPU time is saved
1996        in routers and hosts (clients, servers, proxies, gateways,
1997        tunnels, or caches), and memory used for TCP protocol control
1998        blocks can be saved in hosts.
1999      </t>
2000      <t>
2001        HTTP requests and responses can be pipelined on a connection.
2002        Pipelining allows a client to make multiple requests without
2003        waiting for each response, allowing a single TCP connection to
2004        be used much more efficiently, with much lower elapsed time.
2005      </t>
2006      <t>
2007        Network congestion is reduced by reducing the number of packets
2008        caused by TCP opens, and by allowing TCP sufficient time to
2009        determine the congestion state of the network.
2010      </t>
2011      <t>
2012        Latency on subsequent requests is reduced since there is no time
2013        spent in TCP's connection opening handshake.
2014      </t>
2015      <t>
2016        HTTP can evolve more gracefully, since errors can be reported
2017        without the penalty of closing the TCP connection. Clients using
2018        future versions of HTTP might optimistically try a new feature,
2019        but if communicating with an older server, retry with old
2020        semantics after an error is reported.
2021      </t>
2022    </list>
2023</t>
2024<t>
2025   HTTP implementations &SHOULD; implement persistent connections.
2026</t>
2027</section>
2028
2029<section title="Overall Operation" anchor="persistent.overall">
2030<t>
2031   A significant difference between HTTP/1.1 and earlier versions of
2032   HTTP is that persistent connections are the default behavior of any
2033   HTTP connection. That is, unless otherwise indicated, the client
2034   &SHOULD; assume that the server will maintain a persistent connection,
2035   even after error responses from the server.
2036</t>
2037<t>
2038   Persistent connections provide a mechanism by which a client and a
2039   server can signal the close of a TCP connection. This signaling takes
2040   place using the Connection header field (<xref target="header.connection"/>). Once a close
2041   has been signaled, the client &MUST-NOT; send any more requests on that
2042   connection.
2043</t>
2044
2045<section title="Negotiation" anchor="persistent.negotiation">
2046<t>
2047   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2048   maintain a persistent connection unless a Connection header including
2049   the connection-token "close" was sent in the request. If the server
2050   chooses to close the connection immediately after sending the
2051   response, it &SHOULD; send a Connection header including the
2052   connection-token close.
2053</t>
2054<t>
2055   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2056   decide to keep it open based on whether the response from a server
2057   contains a Connection header with the connection-token close. In case
2058   the client does not want to maintain a connection for more than that
2059   request, it &SHOULD; send a Connection header including the
2060   connection-token close.
2061</t>
2062<t>
2063   If either the client or the server sends the close token in the
2064   Connection header, that request becomes the last one for the
2065   connection.
2066</t>
2067<t>
2068   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2069   maintained for HTTP versions less than 1.1 unless it is explicitly
2070   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2071   compatibility with HTTP/1.0 clients.
2072</t>
2073<t>
2074   In order to remain persistent, all messages on the connection &MUST;
2075   have a self-defined message length (i.e., one not defined by closure
2076   of the connection), as described in <xref target="message.length"/>.
2077</t>
2078</section>
2079
2080<section title="Pipelining" anchor="pipelining">
2081<t>
2082   A client that supports persistent connections &MAY; "pipeline" its
2083   requests (i.e., send multiple requests without waiting for each
2084   response). A server &MUST; send its responses to those requests in the
2085   same order that the requests were received.
2086</t>
2087<t>
2088   Clients which assume persistent connections and pipeline immediately
2089   after connection establishment &SHOULD; be prepared to retry their
2090   connection if the first pipelined attempt fails. If a client does
2091   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2092   persistent. Clients &MUST; also be prepared to resend their requests if
2093   the server closes the connection before sending all of the
2094   corresponding responses.
2095</t>
2096<t>
2097   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2098   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2099   premature termination of the transport connection could lead to
2100   indeterminate results. A client wishing to send a non-idempotent
2101   request &SHOULD; wait to send that request until it has received the
2102   response status for the previous request.
2103</t>
2104</section>
2105</section>
2106
2107<section title="Proxy Servers" anchor="persistent.proxy">
2108<t>
2109   It is especially important that proxies correctly implement the
2110   properties of the Connection header field as specified in <xref target="header.connection"/>.
2111</t>
2112<t>
2113   The proxy server &MUST; signal persistent connections separately with
2114   its clients and the origin servers (or other proxy servers) that it
2115   connects to. Each persistent connection applies to only one transport
2116   link.
2117</t>
2118<t>
2119   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2120   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2121   for information and discussion of the problems with the Keep-Alive header
2122   implemented by many HTTP/1.0 clients).
2123</t>
2124</section>
2125
2126<section title="Practical Considerations" anchor="persistent.practical">
2127<t>
2128   Servers will usually have some time-out value beyond which they will
2129   no longer maintain an inactive connection. Proxy servers might make
2130   this a higher value since it is likely that the client will be making
2131   more connections through the same server. The use of persistent
2132   connections places no requirements on the length (or existence) of
2133   this time-out for either the client or the server.
2134</t>
2135<t>
2136   When a client or server wishes to time-out it &SHOULD; issue a graceful
2137   close on the transport connection. Clients and servers &SHOULD; both
2138   constantly watch for the other side of the transport close, and
2139   respond to it as appropriate. If a client or server does not detect
2140   the other side's close promptly it could cause unnecessary resource
2141   drain on the network.
2142</t>
2143<t>
2144   A client, server, or proxy &MAY; close the transport connection at any
2145   time. For example, a client might have started to send a new request
2146   at the same time that the server has decided to close the "idle"
2147   connection. From the server's point of view, the connection is being
2148   closed while it was idle, but from the client's point of view, a
2149   request is in progress.
2150</t>
2151<t>
2152   This means that clients, servers, and proxies &MUST; be able to recover
2153   from asynchronous close events. Client software &SHOULD; reopen the
2154   transport connection and retransmit the aborted sequence of requests
2155   without user interaction so long as the request sequence is
2156   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2157   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2158   human operator the choice of retrying the request(s). Confirmation by
2159   user-agent software with semantic understanding of the application
2160   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2161   be repeated if the second sequence of requests fails.
2162</t>
2163<t>
2164   Servers &SHOULD; always respond to at least one request per connection,
2165   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2166   middle of transmitting a response, unless a network or client failure
2167   is suspected.
2168</t>
2169<t>
2170   Clients that use persistent connections &SHOULD; limit the number of
2171   simultaneous connections that they maintain to a given server. A
2172   single-user client &SHOULD-NOT; maintain more than 2 connections with
2173   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2174   another server or proxy, where N is the number of simultaneously
2175   active users. These guidelines are intended to improve HTTP response
2176   times and avoid congestion.
2177</t>
2178</section>
2179</section>
2180
2181<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2182
2183<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2184<t>
2185   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2186   flow control mechanisms to resolve temporary overloads, rather than
2187   terminating connections with the expectation that clients will retry.
2188   The latter technique can exacerbate network congestion.
2189</t>
2190</section>
2191
2192<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2193<t>
2194   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2195   the network connection for an error status while it is transmitting
2196   the request. If the client sees an error status, it &SHOULD;
2197   immediately cease transmitting the body. If the body is being sent
2198   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2199   empty trailer &MAY; be used to prematurely mark the end of the message.
2200   If the body was preceded by a Content-Length header, the client &MUST;
2201   close the connection.
2202</t>
2203</section>
2204
2205<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2206<t>
2207   The purpose of the 100 (Continue) status (see &status-100;) is to
2208   allow a client that is sending a request message with a request body
2209   to determine if the origin server is willing to accept the request
2210   (based on the request headers) before the client sends the request
2211   body. In some cases, it might either be inappropriate or highly
2212   inefficient for the client to send the body if the server will reject
2213   the message without looking at the body.
2214</t>
2215<t>
2216   Requirements for HTTP/1.1 clients:
2217  <list style="symbols">
2218    <t>
2219        If a client will wait for a 100 (Continue) response before
2220        sending the request body, it &MUST; send an Expect request-header
2221        field (&header-expect;) with the "100-continue" expectation.
2222    </t>
2223    <t>
2224        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2225        with the "100-continue" expectation if it does not intend
2226        to send a request body.
2227    </t>
2228  </list>
2229</t>
2230<t>
2231   Because of the presence of older implementations, the protocol allows
2232   ambiguous situations in which a client may send "Expect: 100-continue"
2233   without receiving either a 417 (Expectation Failed) status
2234   or a 100 (Continue) status. Therefore, when a client sends this
2235   header field to an origin server (possibly via a proxy) from which it
2236   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2237   for an indefinite period before sending the request body.
2238</t>
2239<t>
2240   Requirements for HTTP/1.1 origin servers:
2241  <list style="symbols">
2242    <t> Upon receiving a request which includes an Expect request-header
2243        field with the "100-continue" expectation, an origin server &MUST;
2244        either respond with 100 (Continue) status and continue to read
2245        from the input stream, or respond with a final status code. The
2246        origin server &MUST-NOT; wait for the request body before sending
2247        the 100 (Continue) response. If it responds with a final status
2248        code, it &MAY; close the transport connection or it &MAY; continue
2249        to read and discard the rest of the request.  It &MUST-NOT;
2250        perform the requested method if it returns a final status code.
2251    </t>
2252    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2253        the request message does not include an Expect request-header
2254        field with the "100-continue" expectation, and &MUST-NOT; send a
2255        100 (Continue) response if such a request comes from an HTTP/1.0
2256        (or earlier) client. There is an exception to this rule: for
2257        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2258        status in response to an HTTP/1.1 PUT or POST request that does
2259        not include an Expect request-header field with the "100-continue"
2260        expectation. This exception, the purpose of which is
2261        to minimize any client processing delays associated with an
2262        undeclared wait for 100 (Continue) status, applies only to
2263        HTTP/1.1 requests, and not to requests with any other HTTP-version
2264        value.
2265    </t>
2266    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2267        already received some or all of the request body for the
2268        corresponding request.
2269    </t>
2270    <t> An origin server that sends a 100 (Continue) response &MUST;
2271    ultimately send a final status code, once the request body is
2272        received and processed, unless it terminates the transport
2273        connection prematurely.
2274    </t>
2275    <t> If an origin server receives a request that does not include an
2276        Expect request-header field with the "100-continue" expectation,
2277        the request includes a request body, and the server responds
2278        with a final status code before reading the entire request body
2279        from the transport connection, then the server &SHOULD-NOT;  close
2280        the transport connection until it has read the entire request,
2281        or until the client closes the connection. Otherwise, the client
2282        might not reliably receive the response message. However, this
2283        requirement is not be construed as preventing a server from
2284        defending itself against denial-of-service attacks, or from
2285        badly broken client implementations.
2286      </t>
2287    </list>
2288</t>
2289<t>
2290   Requirements for HTTP/1.1 proxies:
2291  <list style="symbols">
2292    <t> If a proxy receives a request that includes an Expect request-header
2293        field with the "100-continue" expectation, and the proxy
2294        either knows that the next-hop server complies with HTTP/1.1 or
2295        higher, or does not know the HTTP version of the next-hop
2296        server, it &MUST; forward the request, including the Expect header
2297        field.
2298    </t>
2299    <t> If the proxy knows that the version of the next-hop server is
2300        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2301        respond with a 417 (Expectation Failed) status.
2302    </t>
2303    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2304        numbers received from recently-referenced next-hop servers.
2305    </t>
2306    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2307        request message was received from an HTTP/1.0 (or earlier)
2308        client and did not include an Expect request-header field with
2309        the "100-continue" expectation. This requirement overrides the
2310        general rule for forwarding of 1xx responses (see &status-1xx;).
2311    </t>
2312  </list>
2313</t>
2314</section>
2315
2316<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2317<t>
2318   If an HTTP/1.1 client sends a request which includes a request body,
2319   but which does not include an Expect request-header field with the
2320   "100-continue" expectation, and if the client is not directly
2321   connected to an HTTP/1.1 origin server, and if the client sees the
2322   connection close before receiving any status from the server, the
2323   client &SHOULD; retry the request.  If the client does retry this
2324   request, it &MAY; use the following "binary exponential backoff"
2325   algorithm to be assured of obtaining a reliable response:
2326  <list style="numbers">
2327    <t>
2328      Initiate a new connection to the server
2329    </t>
2330    <t>
2331      Transmit the request-headers
2332    </t>
2333    <t>
2334      Initialize a variable R to the estimated round-trip time to the
2335         server (e.g., based on the time it took to establish the
2336         connection), or to a constant value of 5 seconds if the round-trip
2337         time is not available.
2338    </t>
2339    <t>
2340       Compute T = R * (2**N), where N is the number of previous
2341         retries of this request.
2342    </t>
2343    <t>
2344       Wait either for an error response from the server, or for T
2345         seconds (whichever comes first)
2346    </t>
2347    <t>
2348       If no error response is received, after T seconds transmit the
2349         body of the request.
2350    </t>
2351    <t>
2352       If client sees that the connection is closed prematurely,
2353         repeat from step 1 until the request is accepted, an error
2354         response is received, or the user becomes impatient and
2355         terminates the retry process.
2356    </t>
2357  </list>
2358</t>
2359<t>
2360   If at any point an error status is received, the client
2361  <list style="symbols">
2362      <t>&SHOULD-NOT;  continue and</t>
2363
2364      <t>&SHOULD; close the connection if it has not completed sending the
2365        request message.</t>
2366    </list>
2367</t>
2368</section>
2369</section>
2370</section>
2371
2372
2373<section title="Header Field Definitions" anchor="header.fields">
2374<t>
2375   This section defines the syntax and semantics of HTTP/1.1 header fields
2376   related to message framing and transport protocols.
2377</t>
2378<t>
2379   For entity-header fields, both sender and recipient refer to either the
2380   client or the server, depending on who sends and who receives the entity.
2381</t>
2382
2383<section title="Connection" anchor="header.connection">
2384  <iref primary="true" item="Connection header" x:for-anchor=""/>
2385  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2386  <x:anchor-alias value="Connection"/>
2387  <x:anchor-alias value="connection-token"/>
2388  <x:anchor-alias value="Connection-v"/>
2389<t>
2390   The general-header field "Connection" allows the sender to specify
2391   options that are desired for that particular connection and &MUST-NOT;
2392   be communicated by proxies over further connections.
2393</t>
2394<t>
2395   The Connection header's value has the following grammar:
2396</t>
2397<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"/>
2398  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2399  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2400  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2401</artwork></figure>
2402<t>
2403   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2404   message is forwarded and, for each connection-token in this field,
2405   remove any header field(s) from the message with the same name as the
2406   connection-token. Connection options are signaled by the presence of
2407   a connection-token in the Connection header field, not by any
2408   corresponding additional header field(s), since the additional header
2409   field may not be sent if there are no parameters associated with that
2410   connection option.
2411</t>
2412<t>
2413   Message headers listed in the Connection header &MUST-NOT; include
2414   end-to-end headers, such as Cache-Control.
2415</t>
2416<t>
2417   HTTP/1.1 defines the "close" connection option for the sender to
2418   signal that the connection will be closed after completion of the
2419   response. For example,
2420</t>
2421<figure><artwork type="example">
2422  Connection: close
2423</artwork></figure>
2424<t>
2425   in either the request or the response header fields indicates that
2426   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2427   after the current request/response is complete.
2428</t>
2429<t>
2430   An HTTP/1.1 client that does not support persistent connections &MUST;
2431   include the "close" connection option in every request message.
2432</t>
2433<t>
2434   An HTTP/1.1 server that does not support persistent connections &MUST;
2435   include the "close" connection option in every response message that
2436   does not have a 1xx (informational) status code.
2437</t>
2438<t>
2439   A system receiving an HTTP/1.0 (or lower-version) message that
2440   includes a Connection header &MUST;, for each connection-token in this
2441   field, remove and ignore any header field(s) from the message with
2442   the same name as the connection-token. This protects against mistaken
2443   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2444</t>
2445</section>
2446
2447<section title="Content-Length" anchor="header.content-length">
2448  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2449  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2450  <x:anchor-alias value="Content-Length"/>
2451  <x:anchor-alias value="Content-Length-v"/>
2452<t>
2453   The entity-header field "Content-Length" indicates the size of the
2454   entity-body, in number of OCTETs, sent to the recipient or,
2455   in the case of the HEAD method, the size of the entity-body that
2456   would have been sent had the request been a GET.
2457</t>
2458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2459  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2460  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2461</artwork></figure>
2462<t>
2463   An example is
2464</t>
2465<figure><artwork type="example">
2466  Content-Length: 3495
2467</artwork></figure>
2468<t>
2469   Applications &SHOULD; use this field to indicate the transfer-length of
2470   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2471</t>
2472<t>
2473   Any Content-Length greater than or equal to zero is a valid value.
2474   <xref target="message.length"/> describes how to determine the length of a message-body
2475   if a Content-Length is not given.
2476</t>
2477<t>
2478   Note that the meaning of this field is significantly different from
2479   the corresponding definition in MIME, where it is an optional field
2480   used within the "message/external-body" content-type. In HTTP, it
2481   &SHOULD; be sent whenever the message's length can be determined prior
2482   to being transferred, unless this is prohibited by the rules in
2483   <xref target="message.length"/>.
2484</t>
2485</section>
2486
2487<section title="Date" anchor="header.date">
2488  <iref primary="true" item="Date header" x:for-anchor=""/>
2489  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2490  <x:anchor-alias value="Date"/>
2491  <x:anchor-alias value="Date-v"/>
2492<t>
2493   The general-header field "Date" represents the date and time at which
2494   the message was originated, having the same semantics as orig-date in
2495   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2496   HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2497   it &MUST; be sent in rfc1123-date format.
2498</t>
2499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2500  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2501  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2502</artwork></figure>
2503<t>
2504   An example is
2505</t>
2506<figure><artwork type="example">
2507  Date: Tue, 15 Nov 1994 08:12:31 GMT
2508</artwork></figure>
2509<t>
2510   Origin servers &MUST; include a Date header field in all responses,
2511   except in these cases:
2512  <list style="numbers">
2513      <t>If the response status code is 100 (Continue) or 101 (Switching
2514         Protocols), the response &MAY; include a Date header field, at
2515         the server's option.</t>
2516
2517      <t>If the response status code conveys a server error, e.g. 500
2518         (Internal Server Error) or 503 (Service Unavailable), and it is
2519         inconvenient or impossible to generate a valid Date.</t>
2520
2521      <t>If the server does not have a clock that can provide a
2522         reasonable approximation of the current time, its responses
2523         &MUST-NOT; include a Date header field. In this case, the rules
2524         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2525  </list>
2526</t>
2527<t>
2528   A received message that does not have a Date header field &MUST; be
2529   assigned one by the recipient if the message will be cached by that
2530   recipient or gatewayed via a protocol which requires a Date. An HTTP
2531   implementation without a clock &MUST-NOT; cache responses without
2532   revalidating them on every use. An HTTP cache, especially a shared
2533   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2534   clock with a reliable external standard.
2535</t>
2536<t>
2537   Clients &SHOULD; only send a Date header field in messages that include
2538   an entity-body, as in the case of the PUT and POST requests, and even
2539   then it is optional. A client without a clock &MUST-NOT; send a Date
2540   header field in a request.
2541</t>
2542<t>
2543   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2544   time subsequent to the generation of the message. It &SHOULD; represent
2545   the best available approximation of the date and time of message
2546   generation, unless the implementation has no means of generating a
2547   reasonably accurate date and time. In theory, the date ought to
2548   represent the moment just before the entity is generated. In
2549   practice, the date can be generated at any time during the message
2550   origination without affecting its semantic value.
2551</t>
2552
2553<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2554<t>
2555   Some origin server implementations might not have a clock available.
2556   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2557   values to a response, unless these values were associated
2558   with the resource by a system or user with a reliable clock. It &MAY;
2559   assign an Expires value that is known, at or before server
2560   configuration time, to be in the past (this allows "pre-expiration"
2561   of responses without storing separate Expires values for each
2562   resource).
2563</t>
2564</section>
2565</section>
2566
2567<section title="Host" anchor="header.host">
2568  <iref primary="true" item="Host header" x:for-anchor=""/>
2569  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2570  <x:anchor-alias value="Host"/>
2571  <x:anchor-alias value="Host-v"/>
2572<t>
2573   The request-header field "Host" specifies the Internet host and port
2574   number of the resource being requested, as obtained from the original
2575   URI given by the user or referring resource (generally an http URI,
2576   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2577   the naming authority of the origin server or gateway given by the
2578   original URL. This allows the origin server or gateway to
2579   differentiate between internally-ambiguous URLs, such as the root "/"
2580   URL of a server for multiple host names on a single IP address.
2581</t>
2582<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2583  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2584  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2585</artwork></figure>
2586<t>
2587   A "host" without any trailing port information implies the default
2588   port for the service requested (e.g., "80" for an HTTP URL). For
2589   example, a request on the origin server for
2590   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2591</t>
2592<figure><artwork type="example">
2593  GET /pub/WWW/ HTTP/1.1
2594  Host: www.example.org
2595</artwork></figure>
2596<t>
2597   A client &MUST; include a Host header field in all HTTP/1.1 request
2598   messages. If the requested URI does not include an Internet host
2599   name for the service being requested, then the Host header field &MUST;
2600   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2601   request message it forwards does contain an appropriate Host header
2602   field that identifies the service being requested by the proxy. All
2603   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2604   status code to any HTTP/1.1 request message which lacks a Host header
2605   field.
2606</t>
2607<t>
2608   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2609   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2610   for other requirements relating to Host.
2611</t>
2612</section>
2613
2614<section title="TE" anchor="header.te">
2615  <iref primary="true" item="TE header" x:for-anchor=""/>
2616  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2617  <x:anchor-alias value="TE"/>
2618  <x:anchor-alias value="TE-v"/>
2619  <x:anchor-alias value="t-codings"/>
2620  <x:anchor-alias value="te-params"/>
2621  <x:anchor-alias value="te-ext"/>
2622<t>
2623   The request-header field "TE" indicates what extension transfer-codings
2624   it is willing to accept in the response and whether or not it is
2625   willing to accept trailer fields in a chunked transfer-coding. Its
2626   value may consist of the keyword "trailers" and/or a comma-separated
2627   list of extension transfer-coding names with optional accept
2628   parameters (as described in <xref target="transfer.codings"/>).
2629</t>
2630<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"/>
2631  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2632  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2633  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2634  <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> )
2635  <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> ) ]
2636</artwork></figure>
2637<t>
2638   The presence of the keyword "trailers" indicates that the client is
2639   willing to accept trailer fields in a chunked transfer-coding, as
2640   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2641   transfer-coding values even though it does not itself represent a
2642   transfer-coding.
2643</t>
2644<t>
2645   Examples of its use are:
2646</t>
2647<figure><artwork type="example">
2648  TE: deflate
2649  TE:
2650  TE: trailers, deflate;q=0.5
2651</artwork></figure>
2652<t>
2653   The TE header field only applies to the immediate connection.
2654   Therefore, the keyword &MUST; be supplied within a Connection header
2655   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2656</t>
2657<t>
2658   A server tests whether a transfer-coding is acceptable, according to
2659   a TE field, using these rules:
2660  <list style="numbers">
2661    <x:lt>
2662      <t>The "chunked" transfer-coding is always acceptable. If the
2663         keyword "trailers" is listed, the client indicates that it is
2664         willing to accept trailer fields in the chunked response on
2665         behalf of itself and any downstream clients. The implication is
2666         that, if given, the client is stating that either all
2667         downstream clients are willing to accept trailer fields in the
2668         forwarded response, or that it will attempt to buffer the
2669         response on behalf of downstream recipients.
2670      </t><t>
2671         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2672         chunked response such that a client can be assured of buffering
2673         the entire response.</t>
2674    </x:lt>
2675    <x:lt>
2676      <t>If the transfer-coding being tested is one of the transfer-codings
2677         listed in the TE field, then it is acceptable unless it
2678         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2679         qvalue of 0 means "not acceptable.")</t>
2680    </x:lt>
2681    <x:lt>
2682      <t>If multiple transfer-codings are acceptable, then the
2683         acceptable transfer-coding with the highest non-zero qvalue is
2684         preferred.  The "chunked" transfer-coding always has a qvalue
2685         of 1.</t>
2686    </x:lt>
2687  </list>
2688</t>
2689<t>
2690   If the TE field-value is empty or if no TE field is present, the only
2691   transfer-coding is "chunked". A message with no transfer-coding is
2692   always acceptable.
2693</t>
2694</section>
2695
2696<section title="Trailer" anchor="header.trailer">
2697  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2698  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2699  <x:anchor-alias value="Trailer"/>
2700  <x:anchor-alias value="Trailer-v"/>
2701<t>
2702   The general field "Trailer" indicates that the given set of
2703   header fields is present in the trailer of a message encoded with
2704   chunked transfer-coding.
2705</t>
2706<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2707  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2708  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2709</artwork></figure>
2710<t>
2711   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2712   message using chunked transfer-coding with a non-empty trailer. Doing
2713   so allows the recipient to know which header fields to expect in the
2714   trailer.
2715</t>
2716<t>
2717   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2718   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2719   trailer fields in a "chunked" transfer-coding.
2720</t>
2721<t>
2722   Message header fields listed in the Trailer header field &MUST-NOT;
2723   include the following header fields:
2724  <list style="symbols">
2725    <t>Transfer-Encoding</t>
2726    <t>Content-Length</t>
2727    <t>Trailer</t>
2728  </list>
2729</t>
2730</section>
2731
2732<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2733  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2734  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2735  <x:anchor-alias value="Transfer-Encoding"/>
2736  <x:anchor-alias value="Transfer-Encoding-v"/>
2737<t>
2738   The general-header "Transfer-Encoding" field indicates what (if any)
2739   type of transformation has been applied to the message body in order
2740   to safely transfer it between the sender and the recipient. This
2741   differs from the content-coding in that the transfer-coding is a
2742   property of the message, not of the entity.
2743</t>
2744<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2745  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2746                        <x:ref>Transfer-Encoding-v</x:ref>
2747  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2748</artwork></figure>
2749<t>
2750   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2751</t>
2752<figure><artwork type="example">
2753  Transfer-Encoding: chunked
2754</artwork></figure>
2755<t>
2756   If multiple encodings have been applied to an entity, the transfer-codings
2757   &MUST; be listed in the order in which they were applied.
2758   Additional information about the encoding parameters &MAY; be provided
2759   by other entity-header fields not defined by this specification.
2760</t>
2761<t>
2762   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2763   header.
2764</t>
2765</section>
2766
2767<section title="Upgrade" anchor="header.upgrade">
2768  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2769  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2770  <x:anchor-alias value="Upgrade"/>
2771  <x:anchor-alias value="Upgrade-v"/>
2772<t>
2773   The general-header "Upgrade" allows the client to specify what
2774   additional communication protocols it supports and would like to use
2775   if the server finds it appropriate to switch protocols. The server
2776   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2777   response to indicate which protocol(s) are being switched.
2778</t>
2779<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2780  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2781  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2782</artwork></figure>
2783<t>
2784   For example,
2785</t>
2786<figure><artwork type="example">
2787  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2788</artwork></figure>
2789<t>
2790   The Upgrade header field is intended to provide a simple mechanism
2791   for transition from HTTP/1.1 to some other, incompatible protocol. It
2792   does so by allowing the client to advertise its desire to use another
2793   protocol, such as a later version of HTTP with a higher major version
2794   number, even though the current request has been made using HTTP/1.1.
2795   This eases the difficult transition between incompatible protocols by
2796   allowing the client to initiate a request in the more commonly
2797   supported protocol while indicating to the server that it would like
2798   to use a "better" protocol if available (where "better" is determined
2799   by the server, possibly according to the nature of the method and/or
2800   resource being requested).
2801</t>
2802<t>
2803   The Upgrade header field only applies to switching application-layer
2804   protocols upon the existing transport-layer connection. Upgrade
2805   cannot be used to insist on a protocol change; its acceptance and use
2806   by the server is optional. The capabilities and nature of the
2807   application-layer communication after the protocol change is entirely
2808   dependent upon the new protocol chosen, although the first action
2809   after changing the protocol &MUST; be a response to the initial HTTP
2810   request containing the Upgrade header field.
2811</t>
2812<t>
2813   The Upgrade header field only applies to the immediate connection.
2814   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2815   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2816   HTTP/1.1 message.
2817</t>
2818<t>
2819   The Upgrade header field cannot be used to indicate a switch to a
2820   protocol on a different connection. For that purpose, it is more
2821   appropriate to use a 301, 302, 303, or 305 redirection response.
2822</t>
2823<t>
2824   This specification only defines the protocol name "HTTP" for use by
2825   the family of Hypertext Transfer Protocols, as defined by the HTTP
2826   version rules of <xref target="http.version"/> and future updates to this
2827   specification. Any token can be used as a protocol name; however, it
2828   will only be useful if both the client and server associate the name
2829   with the same protocol.
2830</t>
2831</section>
2832
2833<section title="Via" anchor="header.via">
2834  <iref primary="true" item="Via header" x:for-anchor=""/>
2835  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2836  <x:anchor-alias value="protocol-name"/>
2837  <x:anchor-alias value="protocol-version"/>
2838  <x:anchor-alias value="pseudonym"/>
2839  <x:anchor-alias value="received-by"/>
2840  <x:anchor-alias value="received-protocol"/>
2841  <x:anchor-alias value="Via"/>
2842  <x:anchor-alias value="Via-v"/>
2843<t>
2844   The general-header field "Via" &MUST; be used by gateways and proxies to
2845   indicate the intermediate protocols and recipients between the user
2846   agent and the server on requests, and between the origin server and
2847   the client on responses. It is analogous to the "Received" field defined in
2848   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2849   avoiding request loops, and identifying the protocol capabilities of
2850   all senders along the request/response chain.
2851</t>
2852<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"/>
2853  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2854  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2855                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2856  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2857  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2858  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2859  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2860  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2861</artwork></figure>
2862<t>
2863   The received-protocol indicates the protocol version of the message
2864   received by the server or client along each segment of the
2865   request/response chain. The received-protocol version is appended to
2866   the Via field value when the message is forwarded so that information
2867   about the protocol capabilities of upstream applications remains
2868   visible to all recipients.
2869</t>
2870<t>
2871   The protocol-name is optional if and only if it would be "HTTP". The
2872   received-by field is normally the host and optional port number of a
2873   recipient server or client that subsequently forwarded the message.
2874   However, if the real host is considered to be sensitive information,
2875   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2876   be assumed to be the default port of the received-protocol.
2877</t>
2878<t>
2879   Multiple Via field values represents each proxy or gateway that has
2880   forwarded the message. Each recipient &MUST; append its information
2881   such that the end result is ordered according to the sequence of
2882   forwarding applications.
2883</t>
2884<t>
2885   Comments &MAY; be used in the Via header field to identify the software
2886   of the recipient proxy or gateway, analogous to the User-Agent and
2887   Server header fields. However, all comments in the Via field are
2888   optional and &MAY; be removed by any recipient prior to forwarding the
2889   message.
2890</t>
2891<t>
2892   For example, a request message could be sent from an HTTP/1.0 user
2893   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2894   forward the request to a public proxy at p.example.net, which completes
2895   the request by forwarding it to the origin server at www.example.com.
2896   The request received by www.example.com would then have the following
2897   Via header field:
2898</t>
2899<figure><artwork type="example">
2900  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2901</artwork></figure>
2902<t>
2903   Proxies and gateways used as a portal through a network firewall
2904   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2905   the firewall region. This information &SHOULD; only be propagated if
2906   explicitly enabled. If not enabled, the received-by host of any host
2907   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2908   for that host.
2909</t>
2910<t>
2911   For organizations that have strong privacy requirements for hiding
2912   internal structures, a proxy &MAY; combine an ordered subsequence of
2913   Via header field entries with identical received-protocol values into
2914   a single such entry. For example,
2915</t>
2916<figure><artwork type="example">
2917  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2918</artwork></figure>
2919<t>
2920        could be collapsed to
2921</t>
2922<figure><artwork type="example">
2923  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2924</artwork></figure>
2925<t>
2926   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2927   under the same organizational control and the hosts have already been
2928   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2929   have different received-protocol values.
2930</t>
2931</section>
2932
2933</section>
2934
2935<section title="IANA Considerations" anchor="IANA.considerations">
2936<section title="Message Header Registration" anchor="message.header.registration">
2937<t>
2938   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2939   with the permanent registrations below (see <xref target="RFC3864"/>):
2940</t>
2941<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2942<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2943   <ttcol>Header Field Name</ttcol>
2944   <ttcol>Protocol</ttcol>
2945   <ttcol>Status</ttcol>
2946   <ttcol>Reference</ttcol>
2947
2948   <c>Connection</c>
2949   <c>http</c>
2950   <c>standard</c>
2951   <c>
2952      <xref target="header.connection"/>
2953   </c>
2954   <c>Content-Length</c>
2955   <c>http</c>
2956   <c>standard</c>
2957   <c>
2958      <xref target="header.content-length"/>
2959   </c>
2960   <c>Date</c>
2961   <c>http</c>
2962   <c>standard</c>
2963   <c>
2964      <xref target="header.date"/>
2965   </c>
2966   <c>Host</c>
2967   <c>http</c>
2968   <c>standard</c>
2969   <c>
2970      <xref target="header.host"/>
2971   </c>
2972   <c>TE</c>
2973   <c>http</c>
2974   <c>standard</c>
2975   <c>
2976      <xref target="header.te"/>
2977   </c>
2978   <c>Trailer</c>
2979   <c>http</c>
2980   <c>standard</c>
2981   <c>
2982      <xref target="header.trailer"/>
2983   </c>
2984   <c>Transfer-Encoding</c>
2985   <c>http</c>
2986   <c>standard</c>
2987   <c>
2988      <xref target="header.transfer-encoding"/>
2989   </c>
2990   <c>Upgrade</c>
2991   <c>http</c>
2992   <c>standard</c>
2993   <c>
2994      <xref target="header.upgrade"/>
2995   </c>
2996   <c>Via</c>
2997   <c>http</c>
2998   <c>standard</c>
2999   <c>
3000      <xref target="header.via"/>
3001   </c>
3002</texttable>
3003<!--(END)-->
3004<t>
3005   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3006</t>
3007</section>
3008
3009<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3010<t>
3011   The entry for the "http" URI Scheme in the registry located at
3012   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3013   should be updated to point to <xref target="http.uri"/> of this document
3014   (see <xref target="RFC4395"/>).
3015</t>
3016</section>
3017
3018<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3019<t>
3020   This document serves as the specification for the Internet media types
3021   "message/http" and "application/http". The following is to be registered with
3022   IANA (see <xref target="RFC4288"/>).
3023</t>
3024<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3025<iref item="Media Type" subitem="message/http" primary="true"/>
3026<iref item="message/http Media Type" primary="true"/>
3027<t>
3028   The message/http type can be used to enclose a single HTTP request or
3029   response message, provided that it obeys the MIME restrictions for all
3030   "message" types regarding line length and encodings.
3031</t>
3032<t>
3033  <list style="hanging" x:indent="12em">
3034    <t hangText="Type name:">
3035      message
3036    </t>
3037    <t hangText="Subtype name:">
3038      http
3039    </t>
3040    <t hangText="Required parameters:">
3041      none
3042    </t>
3043    <t hangText="Optional parameters:">
3044      version, msgtype
3045      <list style="hanging">
3046        <t hangText="version:">
3047          The HTTP-Version number of the enclosed message
3048          (e.g., "1.1"). If not present, the version can be
3049          determined from the first line of the body.
3050        </t>
3051        <t hangText="msgtype:">
3052          The message type -- "request" or "response". If not
3053          present, the type can be determined from the first
3054          line of the body.
3055        </t>
3056      </list>
3057    </t>
3058    <t hangText="Encoding considerations:">
3059      only "7bit", "8bit", or "binary" are permitted
3060    </t>
3061    <t hangText="Security considerations:">
3062      none
3063    </t>
3064    <t hangText="Interoperability considerations:">
3065      none
3066    </t>
3067    <t hangText="Published specification:">
3068      This specification (see <xref target="internet.media.type.message.http"/>).
3069    </t>
3070    <t hangText="Applications that use this media type:">
3071    </t>
3072    <t hangText="Additional information:">
3073      <list style="hanging">
3074        <t hangText="Magic number(s):">none</t>
3075        <t hangText="File extension(s):">none</t>
3076        <t hangText="Macintosh file type code(s):">none</t>
3077      </list>
3078    </t>
3079    <t hangText="Person and email address to contact for further information:">
3080      See Authors Section.
3081    </t>
3082    <t hangText="Intended usage:">
3083      COMMON
3084    </t>
3085    <t hangText="Restrictions on usage:">
3086      none
3087    </t>
3088    <t hangText="Author/Change controller:">
3089      IESG
3090    </t>
3091  </list>
3092</t>
3093</section>
3094<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3095<iref item="Media Type" subitem="application/http" primary="true"/>
3096<iref item="application/http Media Type" primary="true"/>
3097<t>
3098   The application/http type can be used to enclose a pipeline of one or more
3099   HTTP request or response messages (not intermixed).
3100</t>
3101<t>
3102  <list style="hanging" x:indent="12em">
3103    <t hangText="Type name:">
3104      application
3105    </t>
3106    <t hangText="Subtype name:">
3107      http
3108    </t>
3109    <t hangText="Required parameters:">
3110      none
3111    </t>
3112    <t hangText="Optional parameters:">
3113      version, msgtype
3114      <list style="hanging">
3115        <t hangText="version:">
3116          The HTTP-Version number of the enclosed messages
3117          (e.g., "1.1"). If not present, the version can be
3118          determined from the first line of the body.
3119        </t>
3120        <t hangText="msgtype:">
3121          The message type -- "request" or "response". If not
3122          present, the type can be determined from the first
3123          line of the body.
3124        </t>
3125      </list>
3126    </t>
3127    <t hangText="Encoding considerations:">
3128      HTTP messages enclosed by this type
3129      are in "binary" format; use of an appropriate
3130      Content-Transfer-Encoding is required when
3131      transmitted via E-mail.
3132    </t>
3133    <t hangText="Security considerations:">
3134      none
3135    </t>
3136    <t hangText="Interoperability considerations:">
3137      none
3138    </t>
3139    <t hangText="Published specification:">
3140      This specification (see <xref target="internet.media.type.application.http"/>).
3141    </t>
3142    <t hangText="Applications that use this media type:">
3143    </t>
3144    <t hangText="Additional information:">
3145      <list style="hanging">
3146        <t hangText="Magic number(s):">none</t>
3147        <t hangText="File extension(s):">none</t>
3148        <t hangText="Macintosh file type code(s):">none</t>
3149      </list>
3150    </t>
3151    <t hangText="Person and email address to contact for further information:">
3152      See Authors Section.
3153    </t>
3154    <t hangText="Intended usage:">
3155      COMMON
3156    </t>
3157    <t hangText="Restrictions on usage:">
3158      none
3159    </t>
3160    <t hangText="Author/Change controller:">
3161      IESG
3162    </t>
3163  </list>
3164</t>
3165</section>
3166</section>
3167
3168</section>
3169
3170<section title="Security Considerations" anchor="security.considerations">
3171<t>
3172   This section is meant to inform application developers, information
3173   providers, and users of the security limitations in HTTP/1.1 as
3174   described by this document. The discussion does not include
3175   definitive solutions to the problems revealed, though it does make
3176   some suggestions for reducing security risks.
3177</t>
3178
3179<section title="Personal Information" anchor="personal.information">
3180<t>
3181   HTTP clients are often privy to large amounts of personal information
3182   (e.g. the user's name, location, mail address, passwords, encryption
3183   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3184   leakage of this information.
3185   We very strongly recommend that a convenient interface be provided
3186   for the user to control dissemination of such information, and that
3187   designers and implementors be particularly careful in this area.
3188   History shows that errors in this area often create serious security
3189   and/or privacy problems and generate highly adverse publicity for the
3190   implementor's company.
3191</t>
3192</section>
3193
3194<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3195<t>
3196   A server is in the position to save personal data about a user's
3197   requests which might identify their reading patterns or subjects of
3198   interest. This information is clearly confidential in nature and its
3199   handling can be constrained by law in certain countries. People using
3200   HTTP to provide data are responsible for ensuring that
3201   such material is not distributed without the permission of any
3202   individuals that are identifiable by the published results.
3203</t>
3204</section>
3205
3206<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3207<t>
3208   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3209   the documents returned by HTTP requests to be only those that were
3210   intended by the server administrators. If an HTTP server translates
3211   HTTP URIs directly into file system calls, the server &MUST; take
3212   special care not to serve files that were not intended to be
3213   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3214   other operating systems use ".." as a path component to indicate a
3215   directory level above the current one. On such a system, an HTTP
3216   server &MUST; disallow any such construct in the request-target if it
3217   would otherwise allow access to a resource outside those intended to
3218   be accessible via the HTTP server. Similarly, files intended for
3219   reference only internally to the server (such as access control
3220   files, configuration files, and script code) &MUST; be protected from
3221   inappropriate retrieval, since they might contain sensitive
3222   information. Experience has shown that minor bugs in such HTTP server
3223   implementations have turned into security risks.
3224</t>
3225</section>
3226
3227<section title="DNS Spoofing" anchor="dns.spoofing">
3228<t>
3229   Clients using HTTP rely heavily on the Domain Name Service, and are
3230   thus generally prone to security attacks based on the deliberate
3231   mis-association of IP addresses and DNS names. Clients need to be
3232   cautious in assuming the continuing validity of an IP number/DNS name
3233   association.
3234</t>
3235<t>
3236   In particular, HTTP clients &SHOULD; rely on their name resolver for
3237   confirmation of an IP number/DNS name association, rather than
3238   caching the result of previous host name lookups. Many platforms
3239   already can cache host name lookups locally when appropriate, and
3240   they &SHOULD; be configured to do so. It is proper for these lookups to
3241   be cached, however, only when the TTL (Time To Live) information
3242   reported by the name server makes it likely that the cached
3243   information will remain useful.
3244</t>
3245<t>
3246   If HTTP clients cache the results of host name lookups in order to
3247   achieve a performance improvement, they &MUST; observe the TTL
3248   information reported by DNS.
3249</t>
3250<t>
3251   If HTTP clients do not observe this rule, they could be spoofed when
3252   a previously-accessed server's IP address changes. As network
3253   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3254   possibility of this form of attack will grow. Observing this
3255   requirement thus reduces this potential security vulnerability.
3256</t>
3257<t>
3258   This requirement also improves the load-balancing behavior of clients
3259   for replicated servers using the same DNS name and reduces the
3260   likelihood of a user's experiencing failure in accessing sites which
3261   use that strategy.
3262</t>
3263</section>
3264
3265<section title="Proxies and Caching" anchor="attack.proxies">
3266<t>
3267   By their very nature, HTTP proxies are men-in-the-middle, and
3268   represent an opportunity for man-in-the-middle attacks. Compromise of
3269   the systems on which the proxies run can result in serious security
3270   and privacy problems. Proxies have access to security-related
3271   information, personal information about individual users and
3272   organizations, and proprietary information belonging to users and
3273   content providers. A compromised proxy, or a proxy implemented or
3274   configured without regard to security and privacy considerations,
3275   might be used in the commission of a wide range of potential attacks.
3276</t>
3277<t>
3278   Proxy operators should protect the systems on which proxies run as
3279   they would protect any system that contains or transports sensitive
3280   information. In particular, log information gathered at proxies often
3281   contains highly sensitive personal information, and/or information
3282   about organizations. Log information should be carefully guarded, and
3283   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3284</t>
3285<t>
3286   Proxy implementors should consider the privacy and security
3287   implications of their design and coding decisions, and of the
3288   configuration options they provide to proxy operators (especially the
3289   default configuration).
3290</t>
3291<t>
3292   Users of a proxy need to be aware that they are no trustworthier than
3293   the people who run the proxy; HTTP itself cannot solve this problem.
3294</t>
3295<t>
3296   The judicious use of cryptography, when appropriate, may suffice to
3297   protect against a broad range of security and privacy attacks. Such
3298   cryptography is beyond the scope of the HTTP/1.1 specification.
3299</t>
3300</section>
3301
3302<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3303<t>
3304   They exist. They are hard to defend against. Research continues.
3305   Beware.
3306</t>
3307</section>
3308</section>
3309
3310<section title="Acknowledgments" anchor="ack">
3311<t>
3312   HTTP has evolved considerably over the years. It has
3313   benefited from a large and active developer community--the many
3314   people who have participated on the www-talk mailing list--and it is
3315   that community which has been most responsible for the success of
3316   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3317   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3318   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3319   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3320   VanHeyningen deserve special recognition for their efforts in
3321   defining early aspects of the protocol.
3322</t>
3323<t>
3324   This document has benefited greatly from the comments of all those
3325   participating in the HTTP-WG. In addition to those already mentioned,
3326   the following individuals have contributed to this specification:
3327</t>
3328<t>
3329   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3330   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3331   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3332   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3333   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3334   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3335   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3336   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3337   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3338   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3339   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3340   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3341   Josh Cohen.
3342</t>
3343<t>
3344   Thanks to the "cave men" of Palo Alto. You know who you are.
3345</t>
3346<t>
3347   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3348   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3349   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3350   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3351   Larry Masinter for their help. And thanks go particularly to Jeff
3352   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3353</t>
3354<t>
3355   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3356   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3357   discovery of many of the problems that this document attempts to
3358   rectify.
3359</t>
3360<t>
3361   This specification makes heavy use of the augmented BNF and generic
3362   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3363   reuses many of the definitions provided by Nathaniel Borenstein and
3364   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3365   specification will help reduce past confusion over the relationship
3366   between HTTP and Internet mail message formats.
3367</t>
3368</section>
3369
3370</middle>
3371<back>
3372
3373<references title="Normative References">
3374
3375<reference anchor="ISO-8859-1">
3376  <front>
3377    <title>
3378     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3379    </title>
3380    <author>
3381      <organization>International Organization for Standardization</organization>
3382    </author>
3383    <date year="1998"/>
3384  </front>
3385  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3386</reference>
3387
3388<reference anchor="Part2">
3389  <front>
3390    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3391    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3392      <organization abbrev="Day Software">Day Software</organization>
3393      <address><email>fielding@gbiv.com</email></address>
3394    </author>
3395    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3396      <organization>One Laptop per Child</organization>
3397      <address><email>jg@laptop.org</email></address>
3398    </author>
3399    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3400      <organization abbrev="HP">Hewlett-Packard Company</organization>
3401      <address><email>JeffMogul@acm.org</email></address>
3402    </author>
3403    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3404      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3405      <address><email>henrikn@microsoft.com</email></address>
3406    </author>
3407    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3408      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3409      <address><email>LMM@acm.org</email></address>
3410    </author>
3411    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3412      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3413      <address><email>paulle@microsoft.com</email></address>
3414    </author>
3415    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3416      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3417      <address><email>timbl@w3.org</email></address>
3418    </author>
3419    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3420      <organization abbrev="W3C">World Wide Web Consortium</organization>
3421      <address><email>ylafon@w3.org</email></address>
3422    </author>
3423    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3424      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3425      <address><email>julian.reschke@greenbytes.de</email></address>
3426    </author>
3427    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3428  </front>
3429  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3430  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3431</reference>
3432
3433<reference anchor="Part3">
3434  <front>
3435    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3436    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3437      <organization abbrev="Day Software">Day Software</organization>
3438      <address><email>fielding@gbiv.com</email></address>
3439    </author>
3440    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3441      <organization>One Laptop per Child</organization>
3442      <address><email>jg@laptop.org</email></address>
3443    </author>
3444    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3445      <organization abbrev="HP">Hewlett-Packard Company</organization>
3446      <address><email>JeffMogul@acm.org</email></address>
3447    </author>
3448    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3449      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3450      <address><email>henrikn@microsoft.com</email></address>
3451    </author>
3452    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3453      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3454      <address><email>LMM@acm.org</email></address>
3455    </author>
3456    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3457      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3458      <address><email>paulle@microsoft.com</email></address>
3459    </author>
3460    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3461      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3462      <address><email>timbl@w3.org</email></address>
3463    </author>
3464    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3465      <organization abbrev="W3C">World Wide Web Consortium</organization>
3466      <address><email>ylafon@w3.org</email></address>
3467    </author>
3468    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3469      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3470      <address><email>julian.reschke@greenbytes.de</email></address>
3471    </author>
3472    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3473  </front>
3474  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3475  <x:source href="p3-payload.xml" basename="p3-payload"/>
3476</reference>
3477
3478<reference anchor="Part5">
3479  <front>
3480    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3481    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3482      <organization abbrev="Day Software">Day Software</organization>
3483      <address><email>fielding@gbiv.com</email></address>
3484    </author>
3485    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3486      <organization>One Laptop per Child</organization>
3487      <address><email>jg@laptop.org</email></address>
3488    </author>
3489    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3490      <organization abbrev="HP">Hewlett-Packard Company</organization>
3491      <address><email>JeffMogul@acm.org</email></address>
3492    </author>
3493    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3494      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3495      <address><email>henrikn@microsoft.com</email></address>
3496    </author>
3497    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3498      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3499      <address><email>LMM@acm.org</email></address>
3500    </author>
3501    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3502      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3503      <address><email>paulle@microsoft.com</email></address>
3504    </author>
3505    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3506      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3507      <address><email>timbl@w3.org</email></address>
3508    </author>
3509    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3510      <organization abbrev="W3C">World Wide Web Consortium</organization>
3511      <address><email>ylafon@w3.org</email></address>
3512    </author>
3513    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3514      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3515      <address><email>julian.reschke@greenbytes.de</email></address>
3516    </author>
3517    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3518  </front>
3519  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3520  <x:source href="p5-range.xml" basename="p5-range"/>
3521</reference>
3522
3523<reference anchor="Part6">
3524  <front>
3525    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3526    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3527      <organization abbrev="Day Software">Day Software</organization>
3528      <address><email>fielding@gbiv.com</email></address>
3529    </author>
3530    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3531      <organization>One Laptop per Child</organization>
3532      <address><email>jg@laptop.org</email></address>
3533    </author>
3534    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3535      <organization abbrev="HP">Hewlett-Packard Company</organization>
3536      <address><email>JeffMogul@acm.org</email></address>
3537    </author>
3538    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3539      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3540      <address><email>henrikn@microsoft.com</email></address>
3541    </author>
3542    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3543      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3544      <address><email>LMM@acm.org</email></address>
3545    </author>
3546    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3547      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3548      <address><email>paulle@microsoft.com</email></address>
3549    </author>
3550    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3551      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3552      <address><email>timbl@w3.org</email></address>
3553    </author>
3554    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3555      <organization abbrev="W3C">World Wide Web Consortium</organization>
3556      <address><email>ylafon@w3.org</email></address>
3557    </author>
3558    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3559      <organization />
3560      <address><email>mnot@mnot.net</email></address>
3561    </author>
3562    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3563      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3564      <address><email>julian.reschke@greenbytes.de</email></address>
3565    </author>
3566    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3567  </front>
3568  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3569  <x:source href="p6-cache.xml" basename="p6-cache"/>
3570</reference>
3571
3572<reference anchor="RFC5234">
3573  <front>
3574    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3575    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3576      <organization>Brandenburg InternetWorking</organization>
3577      <address>
3578      <postal>
3579      <street>675 Spruce Dr.</street>
3580      <city>Sunnyvale</city>
3581      <region>CA</region>
3582      <code>94086</code>
3583      <country>US</country></postal>
3584      <phone>+1.408.246.8253</phone>
3585      <email>dcrocker@bbiw.net</email></address> 
3586    </author>
3587    <author initials="P." surname="Overell" fullname="Paul Overell">
3588      <organization>THUS plc.</organization>
3589      <address>
3590      <postal>
3591      <street>1/2 Berkeley Square</street>
3592      <street>99 Berkely Street</street>
3593      <city>Glasgow</city>
3594      <code>G3 7HR</code>
3595      <country>UK</country></postal>
3596      <email>paul.overell@thus.net</email></address>
3597    </author>
3598    <date month="January" year="2008"/>
3599  </front>
3600  <seriesInfo name="STD" value="68"/>
3601  <seriesInfo name="RFC" value="5234"/>
3602</reference>
3603
3604<reference anchor="RFC2119">
3605  <front>
3606    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3607    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3608      <organization>Harvard University</organization>
3609      <address><email>sob@harvard.edu</email></address>
3610    </author>
3611    <date month="March" year="1997"/>
3612  </front>
3613  <seriesInfo name="BCP" value="14"/>
3614  <seriesInfo name="RFC" value="2119"/>
3615</reference>
3616
3617<reference anchor="RFC3986">
3618 <front>
3619  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3620  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3621    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3622    <address>
3623       <email>timbl@w3.org</email>
3624       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3625    </address>
3626  </author>
3627  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3628    <organization abbrev="Day Software">Day Software</organization>
3629    <address>
3630      <email>fielding@gbiv.com</email>
3631      <uri>http://roy.gbiv.com/</uri>
3632    </address>
3633  </author>
3634  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3635    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3636    <address>
3637      <email>LMM@acm.org</email>
3638      <uri>http://larry.masinter.net/</uri>
3639    </address>
3640  </author>
3641  <date month='January' year='2005'></date>
3642 </front>
3643 <seriesInfo name="RFC" value="3986"/>
3644 <seriesInfo name="STD" value="66"/>
3645</reference>
3646
3647<reference anchor="USASCII">
3648  <front>
3649    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3650    <author>
3651      <organization>American National Standards Institute</organization>
3652    </author>
3653    <date year="1986"/>
3654  </front>
3655  <seriesInfo name="ANSI" value="X3.4"/>
3656</reference>
3657
3658</references>
3659
3660<references title="Informative References">
3661
3662<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3663  <front>
3664    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3665    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3666      <organization/>
3667    </author>
3668    <author initials="J." surname="Gettys" fullname="J. Gettys">
3669      <organization/>
3670    </author>
3671    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3672      <organization/>
3673    </author>
3674    <author initials="H." surname="Lie" fullname="H. Lie">
3675      <organization/>
3676    </author>
3677    <author initials="C." surname="Lilley" fullname="C. Lilley">
3678      <organization/>
3679    </author>
3680    <date year="1997" month="September"/>
3681  </front>
3682  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3683</reference>
3684
3685<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3686  <front>
3687    <title>Improving HTTP Latency</title>
3688    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3689      <organization/>
3690    </author>
3691    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3692      <organization/>
3693    </author>
3694    <date year="1995" month="December"/>
3695  </front>
3696  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3697</reference>
3698
3699<reference anchor="RFC1123">
3700  <front>
3701    <title>Requirements for Internet Hosts - Application and Support</title>
3702    <author initials="R." surname="Braden" fullname="Robert Braden">
3703      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3704      <address><email>Braden@ISI.EDU</email></address>
3705    </author>
3706    <date month="October" year="1989"/>
3707  </front>
3708  <seriesInfo name="STD" value="3"/>
3709  <seriesInfo name="RFC" value="1123"/>
3710</reference>
3711
3712<reference anchor="RFC1305">
3713  <front>
3714    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3715    <author initials="D." surname="Mills" fullname="David L. Mills">
3716      <organization>University of Delaware, Electrical Engineering Department</organization>
3717      <address><email>mills@udel.edu</email></address>
3718    </author>
3719    <date month="March" year="1992"/>
3720  </front>
3721  <seriesInfo name="RFC" value="1305"/>
3722</reference>
3723
3724<reference anchor="RFC1900">
3725  <front>
3726    <title>Renumbering Needs Work</title>
3727    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3728      <organization>CERN, Computing and Networks Division</organization>
3729      <address><email>brian@dxcoms.cern.ch</email></address>
3730    </author>
3731    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3732      <organization>cisco Systems</organization>
3733      <address><email>yakov@cisco.com</email></address>
3734    </author>
3735    <date month="February" year="1996"/>
3736  </front>
3737  <seriesInfo name="RFC" value="1900"/>
3738</reference>
3739
3740<reference anchor="RFC1945">
3741  <front>
3742    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3743    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3744      <organization>MIT, Laboratory for Computer Science</organization>
3745      <address><email>timbl@w3.org</email></address>
3746    </author>
3747    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3748      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3749      <address><email>fielding@ics.uci.edu</email></address>
3750    </author>
3751    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3752      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3753      <address><email>frystyk@w3.org</email></address>
3754    </author>
3755    <date month="May" year="1996"/>
3756  </front>
3757  <seriesInfo name="RFC" value="1945"/>
3758</reference>
3759
3760<reference anchor="RFC2045">
3761  <front>
3762    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3763    <author initials="N." surname="Freed" fullname="Ned Freed">
3764      <organization>Innosoft International, Inc.</organization>
3765      <address><email>ned@innosoft.com</email></address>
3766    </author>
3767    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3768      <organization>First Virtual Holdings</organization>
3769      <address><email>nsb@nsb.fv.com</email></address>
3770    </author>
3771    <date month="November" year="1996"/>
3772  </front>
3773  <seriesInfo name="RFC" value="2045"/>
3774</reference>
3775
3776<reference anchor="RFC2047">
3777  <front>
3778    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3779    <author initials="K." surname="Moore" fullname="Keith Moore">
3780      <organization>University of Tennessee</organization>
3781      <address><email>moore@cs.utk.edu</email></address>
3782    </author>
3783    <date month="November" year="1996"/>
3784  </front>
3785  <seriesInfo name="RFC" value="2047"/>
3786</reference>
3787
3788<reference anchor="RFC2068">
3789  <front>
3790    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3791    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3792      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3793      <address><email>fielding@ics.uci.edu</email></address>
3794    </author>
3795    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3796      <organization>MIT Laboratory for Computer Science</organization>
3797      <address><email>jg@w3.org</email></address>
3798    </author>
3799    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3800      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3801      <address><email>mogul@wrl.dec.com</email></address>
3802    </author>
3803    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3804      <organization>MIT Laboratory for Computer Science</organization>
3805      <address><email>frystyk@w3.org</email></address>
3806    </author>
3807    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3808      <organization>MIT Laboratory for Computer Science</organization>
3809      <address><email>timbl@w3.org</email></address>
3810    </author>
3811    <date month="January" year="1997"/>
3812  </front>
3813  <seriesInfo name="RFC" value="2068"/>
3814</reference>
3815
3816<reference anchor='RFC2109'>
3817  <front>
3818    <title>HTTP State Management Mechanism</title>
3819    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3820      <organization>Bell Laboratories, Lucent Technologies</organization>
3821      <address><email>dmk@bell-labs.com</email></address>
3822    </author>
3823    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3824      <organization>Netscape Communications Corp.</organization>
3825      <address><email>montulli@netscape.com</email></address>
3826    </author>
3827    <date year='1997' month='February' />
3828  </front>
3829  <seriesInfo name='RFC' value='2109' />
3830</reference>
3831
3832<reference anchor="RFC2145">
3833  <front>
3834    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3835    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3836      <organization>Western Research Laboratory</organization>
3837      <address><email>mogul@wrl.dec.com</email></address>
3838    </author>
3839    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3840      <organization>Department of Information and Computer Science</organization>
3841      <address><email>fielding@ics.uci.edu</email></address>
3842    </author>
3843    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3844      <organization>MIT Laboratory for Computer Science</organization>
3845      <address><email>jg@w3.org</email></address>
3846    </author>
3847    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3848      <organization>W3 Consortium</organization>
3849      <address><email>frystyk@w3.org</email></address>
3850    </author>
3851    <date month="May" year="1997"/>
3852  </front>
3853  <seriesInfo name="RFC" value="2145"/>
3854</reference>
3855
3856<reference anchor="RFC2616">
3857  <front>
3858    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3859    <author initials="R." surname="Fielding" fullname="R. Fielding">
3860      <organization>University of California, Irvine</organization>
3861      <address><email>fielding@ics.uci.edu</email></address>
3862    </author>
3863    <author initials="J." surname="Gettys" fullname="J. Gettys">
3864      <organization>W3C</organization>
3865      <address><email>jg@w3.org</email></address>
3866    </author>
3867    <author initials="J." surname="Mogul" fullname="J. Mogul">
3868      <organization>Compaq Computer Corporation</organization>
3869      <address><email>mogul@wrl.dec.com</email></address>
3870    </author>
3871    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3872      <organization>MIT Laboratory for Computer Science</organization>
3873      <address><email>frystyk@w3.org</email></address>
3874    </author>
3875    <author initials="L." surname="Masinter" fullname="L. Masinter">
3876      <organization>Xerox Corporation</organization>
3877      <address><email>masinter@parc.xerox.com</email></address>
3878    </author>
3879    <author initials="P." surname="Leach" fullname="P. Leach">
3880      <organization>Microsoft Corporation</organization>
3881      <address><email>paulle@microsoft.com</email></address>
3882    </author>
3883    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3884      <organization>W3C</organization>
3885      <address><email>timbl@w3.org</email></address>
3886    </author>
3887    <date month="June" year="1999"/>
3888  </front>
3889  <seriesInfo name="RFC" value="2616"/>
3890</reference>
3891
3892<reference anchor='RFC2818'>
3893  <front>
3894    <title>HTTP Over TLS</title>
3895    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3896      <organization>RTFM, Inc.</organization>
3897      <address><email>ekr@rtfm.com</email></address>
3898    </author>
3899    <date year='2000' month='May' />
3900  </front>
3901  <seriesInfo name='RFC' value='2818' />
3902</reference>
3903
3904<reference anchor='RFC2965'>
3905  <front>
3906    <title>HTTP State Management Mechanism</title>
3907    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3908      <organization>Bell Laboratories, Lucent Technologies</organization>
3909      <address><email>dmk@bell-labs.com</email></address>
3910    </author>
3911    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3912      <organization>Epinions.com, Inc.</organization>
3913      <address><email>lou@montulli.org</email></address>
3914    </author>
3915    <date year='2000' month='October' />
3916  </front>
3917  <seriesInfo name='RFC' value='2965' />
3918</reference>
3919
3920<reference anchor='RFC3864'>
3921  <front>
3922    <title>Registration Procedures for Message Header Fields</title>
3923    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3924      <organization>Nine by Nine</organization>
3925      <address><email>GK-IETF@ninebynine.org</email></address>
3926    </author>
3927    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3928      <organization>BEA Systems</organization>
3929      <address><email>mnot@pobox.com</email></address>
3930    </author>
3931    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3932      <organization>HP Labs</organization>
3933      <address><email>JeffMogul@acm.org</email></address>
3934    </author>
3935    <date year='2004' month='September' />
3936  </front>
3937  <seriesInfo name='BCP' value='90' />
3938  <seriesInfo name='RFC' value='3864' />
3939</reference>
3940
3941<reference anchor="RFC4288">
3942  <front>
3943    <title>Media Type Specifications and Registration Procedures</title>
3944    <author initials="N." surname="Freed" fullname="N. Freed">
3945      <organization>Sun Microsystems</organization>
3946      <address>
3947        <email>ned.freed@mrochek.com</email>
3948      </address>
3949    </author>
3950    <author initials="J." surname="Klensin" fullname="J. Klensin">
3951      <organization/>
3952      <address>
3953        <email>klensin+ietf@jck.com</email>
3954      </address>
3955    </author>
3956    <date year="2005" month="December"/>
3957  </front>
3958  <seriesInfo name="BCP" value="13"/>
3959  <seriesInfo name="RFC" value="4288"/>
3960</reference>
3961
3962<reference anchor='RFC4395'>
3963  <front>
3964    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3965    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3966      <organization>AT&amp;T Laboratories</organization>
3967      <address>
3968        <email>tony+urireg@maillennium.att.com</email>
3969      </address>
3970    </author>
3971    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3972      <organization>Qualcomm, Inc.</organization>
3973      <address>
3974        <email>hardie@qualcomm.com</email>
3975      </address>
3976    </author>
3977    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3978      <organization>Adobe Systems</organization>
3979      <address>
3980        <email>LMM@acm.org</email>
3981      </address>
3982    </author>
3983    <date year='2006' month='February' />
3984  </front>
3985  <seriesInfo name='BCP' value='115' />
3986  <seriesInfo name='RFC' value='4395' />
3987</reference>
3988
3989<reference anchor="RFC5322">
3990  <front>
3991    <title>Internet Message Format</title>
3992    <author initials="P." surname="Resnick" fullname="P. Resnick">
3993      <organization>Qualcomm Incorporated</organization>
3994    </author>
3995    <date year="2008" month="October"/>
3996  </front> 
3997  <seriesInfo name="RFC" value="5322"/>
3998</reference>
3999
4000<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4001  <front>
4002    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4003    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4004      <organization/>
4005    </author>
4006    <date year="2001" month="November"/>
4007  </front>
4008  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4009</reference>
4010
4011<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4012  <front>
4013  <title>Analysis of HTTP Performance Problems</title>
4014  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4015    <organization/>
4016  </author>
4017  <date/>
4018  </front>
4019</reference>
4020
4021<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4022  <front>
4023  <title>Analysis of HTTP Performance</title>
4024  <author initials="J." surname="Touch" fullname="Joe Touch">
4025    <organization>USC/Information Sciences Institute</organization>
4026    <address><email>touch@isi.edu</email></address>
4027  </author>
4028  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4029    <organization>USC/Information Sciences Institute</organization>
4030    <address><email>johnh@isi.edu</email></address>
4031  </author>
4032  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4033    <organization>USC/Information Sciences Institute</organization>
4034    <address><email>katia@isi.edu</email></address>
4035  </author>
4036  <date year="1998" month="Aug"/>
4037  </front>
4038  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4039  <annotation>(original report dated Aug. 1996)</annotation>
4040</reference>
4041
4042</references>
4043
4044
4045<section title="Tolerant Applications" anchor="tolerant.applications">
4046<t>
4047   Although this document specifies the requirements for the generation
4048   of HTTP/1.1 messages, not all applications will be correct in their
4049   implementation. We therefore recommend that operational applications
4050   be tolerant of deviations whenever those deviations can be
4051   interpreted unambiguously.
4052</t>
4053<t>
4054   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4055   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4056   accept any amount of WSP characters between fields, even though
4057   only a single SP is required.
4058</t>
4059<t>
4060   The line terminator for message-header fields is the sequence CRLF.
4061   However, we recommend that applications, when parsing such headers,
4062   recognize a single LF as a line terminator and ignore the leading CR.
4063</t>
4064<t>
4065   The character set of an entity-body &SHOULD; be labeled as the lowest
4066   common denominator of the character codes used within that body, with
4067   the exception that not labeling the entity is preferred over labeling
4068   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4069</t>
4070<t>
4071   Additional rules for requirements on parsing and encoding of dates
4072   and other potential problems with date encodings include:
4073</t>
4074<t>
4075  <list style="symbols">
4076     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4077        which appears to be more than 50 years in the future is in fact
4078        in the past (this helps solve the "year 2000" problem).</t>
4079
4080     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4081        Expires date as earlier than the proper value, but &MUST-NOT;
4082        internally represent a parsed Expires date as later than the
4083        proper value.</t>
4084
4085     <t>All expiration-related calculations &MUST; be done in GMT. The
4086        local time zone &MUST-NOT; influence the calculation or comparison
4087        of an age or expiration time.</t>
4088
4089     <t>If an HTTP header incorrectly carries a date value with a time
4090        zone other than GMT, it &MUST; be converted into GMT using the
4091        most conservative possible conversion.</t>
4092  </list>
4093</t>
4094</section>
4095
4096<section title="Compatibility with Previous Versions" anchor="compatibility">
4097<t>
4098   HTTP has been in use by the World-Wide Web global information initiative
4099   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4100   was a simple protocol for hypertext data transfer across the Internet
4101   with only a single method and no metadata.
4102   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4103   methods and MIME-like messaging that could include metadata about the data
4104   transferred and modifiers on the request/response semantics. However,
4105   HTTP/1.0 did not sufficiently take into consideration the effects of
4106   hierarchical proxies, caching, the need for persistent connections, or
4107   name-based virtual hosts. The proliferation of incompletely-implemented
4108   applications calling themselves "HTTP/1.0" further necessitated a
4109   protocol version change in order for two communicating applications
4110   to determine each other's true capabilities.
4111</t>
4112<t>
4113   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4114   requirements that enable reliable implementations, adding only
4115   those new features that will either be safely ignored by an HTTP/1.0
4116   recipient or only sent when communicating with a party advertising
4117   compliance with HTTP/1.1.
4118</t>
4119<t>
4120   It is beyond the scope of a protocol specification to mandate
4121   compliance with previous versions. HTTP/1.1 was deliberately
4122   designed, however, to make supporting previous versions easy. It is
4123   worth noting that, at the time of composing this specification
4124   (1996), we would expect commercial HTTP/1.1 servers to:
4125  <list style="symbols">
4126     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4127        1.1 requests;</t>
4128
4129     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4130        1.1;</t>
4131
4132     <t>respond appropriately with a message in the same major version
4133        used by the client.</t>
4134  </list>
4135</t>
4136<t>
4137   And we would expect HTTP/1.1 clients to:
4138  <list style="symbols">
4139     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4140        responses;</t>
4141
4142     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4143        1.1.</t>
4144  </list>
4145</t>
4146<t>
4147   For most implementations of HTTP/1.0, each connection is established
4148   by the client prior to the request and closed by the server after
4149   sending the response. Some implementations implement the Keep-Alive
4150   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4151</t>
4152
4153<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4154<t>
4155   This section summarizes major differences between versions HTTP/1.0
4156   and HTTP/1.1.
4157</t>
4158
4159<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">
4160<t>
4161   The requirements that clients and servers support the Host request-header,
4162   report an error if the Host request-header (<xref target="header.host"/>) is
4163   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4164   are among the most important changes defined by this
4165   specification.
4166</t>
4167<t>
4168   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4169   addresses and servers; there was no other established mechanism for
4170   distinguishing the intended server of a request than the IP address
4171   to which that request was directed. The changes outlined above will
4172   allow the Internet, once older HTTP clients are no longer common, to
4173   support multiple Web sites from a single IP address, greatly
4174   simplifying large operational Web servers, where allocation of many
4175   IP addresses to a single host has created serious problems. The
4176   Internet will also be able to recover the IP addresses that have been
4177   allocated for the sole purpose of allowing special-purpose domain
4178   names to be used in root-level HTTP URLs. Given the rate of growth of
4179   the Web, and the number of servers already deployed, it is extremely
4180   important that all implementations of HTTP (including updates to
4181   existing HTTP/1.0 applications) correctly implement these
4182   requirements:
4183  <list style="symbols">
4184     <t>Both clients and servers &MUST; support the Host request-header.</t>
4185
4186     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4187
4188     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4189        request does not include a Host request-header.</t>
4190
4191     <t>Servers &MUST; accept absolute URIs.</t>
4192  </list>
4193</t>
4194</section>
4195</section>
4196
4197<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4198<t>
4199   Some clients and servers might wish to be compatible with some
4200   previous implementations of persistent connections in HTTP/1.0
4201   clients and servers. Persistent connections in HTTP/1.0 are
4202   explicitly negotiated as they are not the default behavior. HTTP/1.0
4203   experimental implementations of persistent connections are faulty,
4204   and the new facilities in HTTP/1.1 are designed to rectify these
4205   problems. The problem was that some existing 1.0 clients may be
4206   sending Keep-Alive to a proxy server that doesn't understand
4207   Connection, which would then erroneously forward it to the next
4208   inbound server, which would establish the Keep-Alive connection and
4209   result in a hung HTTP/1.0 proxy waiting for the close on the
4210   response. The result is that HTTP/1.0 clients must be prevented from
4211   using Keep-Alive when talking to proxies.
4212</t>
4213<t>
4214   However, talking to proxies is the most important use of persistent
4215   connections, so that prohibition is clearly unacceptable. Therefore,
4216   we need some other mechanism for indicating a persistent connection
4217   is desired, which is safe to use even when talking to an old proxy
4218   that ignores Connection. Persistent connections are the default for
4219   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4220   declaring non-persistence. See <xref target="header.connection"/>.
4221</t>
4222<t>
4223   The original HTTP/1.0 form of persistent connections (the Connection:
4224   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4225</t>
4226</section>
4227
4228<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4229<t>
4230   This specification has been carefully audited to correct and
4231   disambiguate key word usage; RFC 2068 had many problems in respect to
4232   the conventions laid out in <xref target="RFC2119"/>.
4233</t>
4234<t>
4235   Transfer-coding and message lengths all interact in ways that
4236   required fixing exactly when chunked encoding is used (to allow for
4237   transfer encoding that may not be self delimiting); it was important
4238   to straighten out exactly how message lengths are computed. (Sections
4239   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4240   <xref target="header.content-length" format="counter"/>,
4241   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4242</t>
4243<t>
4244   The use and interpretation of HTTP version numbers has been clarified
4245   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4246   version they support to deal with problems discovered in HTTP/1.0
4247   implementations (<xref target="http.version"/>)
4248</t>
4249<t>
4250   Quality Values of zero should indicate that "I don't want something"
4251   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4252</t>
4253<t>
4254   Transfer-coding had significant problems, particularly with
4255   interactions with chunked encoding. The solution is that transfer-codings
4256   become as full fledged as content-codings. This involves
4257   adding an IANA registry for transfer-codings (separate from content
4258   codings), a new header field (TE) and enabling trailer headers in the
4259   future. Transfer encoding is a major performance benefit, so it was
4260   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4261   interoperability problem that could have occurred due to interactions
4262   between authentication trailers, chunked encoding and HTTP/1.0
4263   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4264   and <xref target="header.te" format="counter"/>)
4265</t>
4266</section>
4267
4268<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4269<t>
4270  Empty list elements in list productions have been deprecated.
4271  (<xref target="notation.abnf"/>)
4272</t>
4273<t>
4274  Rules about implicit linear whitespace between certain grammar productions
4275  have been removed; now it's only allowed when specifically pointed out
4276  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4277  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4278  Non-ASCII content in header fields and reason phrase has been obsoleted and
4279  made opaque (the TEXT rule was removed)
4280  (<xref target="basic.rules"/>)
4281</t>
4282<t>
4283  Clarify that HTTP-Version is case sensitive.
4284  (<xref target="http.version"/>)
4285</t>
4286<t>
4287  Remove reference to non-existant identity transfer-coding value tokens.
4288  (Sections <xref format="counter" target="transfer.codings"/> and
4289  <xref format="counter" target="message.length"/>)
4290</t>
4291<t>
4292  Clarification that the chunk length does not include
4293  the count of the octets in the chunk header and trailer.
4294  (<xref target="chunked.transfer.encoding"/>)
4295</t>
4296<t>
4297  Require that invalid whitespace around field-names be rejected.
4298  (<xref target="message.headers"/>)
4299</t>
4300<t>
4301  Update use of abs_path production from RFC1808 to the path-absolute + query
4302  components of RFC3986.
4303  (<xref target="request-target"/>)
4304</t>
4305<t>
4306  Clarify exactly when close connection options must be sent.
4307  (<xref target="header.connection"/>)
4308</t>
4309</section>
4310</section>
4311
4312<section title="Terminology" anchor="terminology">
4313<t>
4314   This specification uses a number of terms to refer to the roles
4315   played by participants in, and objects of, the HTTP communication.
4316</t>
4317<t>
4318  <iref item="content negotiation"/>
4319  <x:dfn>content negotiation</x:dfn>
4320  <list>
4321    <t>
4322      The mechanism for selecting the appropriate representation when
4323      servicing a request, as described in &content.negotiation;. The
4324      representation of entities in any response can be negotiated
4325      (including error responses).
4326    </t>
4327  </list>
4328</t>
4329<t>
4330  <iref item="entity"/>
4331  <x:dfn>entity</x:dfn>
4332  <list>
4333    <t>
4334      The information transferred as the payload of a request or
4335      response. An entity consists of metadata in the form of
4336      entity-header fields and content in the form of an entity-body, as
4337      described in &entity;.
4338    </t>
4339  </list>
4340</t>
4341<t>
4342  <iref item="representation"/>
4343  <x:dfn>representation</x:dfn>
4344  <list>
4345    <t>
4346      An entity included with a response that is subject to content
4347      negotiation, as described in &content.negotiation;. There may exist multiple
4348      representations associated with a particular response status.
4349    </t>
4350  </list>
4351</t>
4352<t>
4353  <iref item="variant"/>
4354  <x:dfn>variant</x:dfn>
4355  <list>
4356    <t>
4357      A resource may have one, or more than one, representation(s)
4358      associated with it at any given instant. Each of these
4359      representations is termed a `variant'.  Use of the term `variant'
4360      does not necessarily imply that the resource is subject to content
4361      negotiation.
4362    </t>
4363  </list>
4364</t>
4365</section>
4366
4367<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4368<figure>
4369<artwork type="abnf" name="p1-messaging.parsed-abnf">
4370<x:ref>BWS</x:ref> = OWS
4371
4372<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4373<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4374<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4375<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4376 connection-token ] )
4377<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4378<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4379
4380<x:ref>Date</x:ref> = "Date:" OWS Date-v
4381<x:ref>Date-v</x:ref> = HTTP-date
4382
4383<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4384
4385<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4386<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4387<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4388<x:ref>HTTP-message</x:ref> = Request / Response
4389<x:ref>Host</x:ref> = "Host:" OWS Host-v
4390<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4391
4392<x:ref>Method</x:ref> = token
4393
4394<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4395
4396<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4397
4398<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4399<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4400<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4401 entity-header ) CRLF ) CRLF [ message-body ]
4402<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4403<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4404 entity-header ) CRLF ) CRLF [ message-body ]
4405
4406<x:ref>Status-Code</x:ref> = 3DIGIT
4407<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4408
4409<x:ref>TE</x:ref> = "TE:" OWS TE-v
4410<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4411<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4412<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4413<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4414<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4415 transfer-coding ] )
4416
4417<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4418<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4419<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4420<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4421
4422<x:ref>Via</x:ref> = "Via:" OWS Via-v
4423<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4424 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4425 ] )
4426
4427<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4428
4429<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4430<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4431<x:ref>attribute</x:ref> = token
4432<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4433
4434<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4435<x:ref>chunk-data</x:ref> = 1*OCTET
4436<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4437<x:ref>chunk-ext-name</x:ref> = token
4438<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4439<x:ref>chunk-size</x:ref> = 1*HEXDIG
4440<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4441<x:ref>connection-token</x:ref> = token
4442<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4443 / %x2A-5B ; '*'-'['
4444 / %x5D-7E ; ']'-'~'
4445 / obs-text
4446
4447<x:ref>date1</x:ref> = day SP month SP year
4448<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4449<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4450<x:ref>day</x:ref> = 2DIGIT
4451<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4452 / %x54.75.65 ; Tue
4453 / %x57.65.64 ; Wed
4454 / %x54.68.75 ; Thu
4455 / %x46.72.69 ; Fri
4456 / %x53.61.74 ; Sat
4457 / %x53.75.6E ; Sun
4458<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4459 / %x54.75.65.73.64.61.79 ; Tuesday
4460 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4461 / %x54.68.75.72.73.64.61.79 ; Thursday
4462 / %x46.72.69.64.61.79 ; Friday
4463 / %x53.61.74.75.72.64.61.79 ; Saturday
4464 / %x53.75.6E.64.61.79 ; Sunday
4465
4466<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4467<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4468
4469<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4470<x:ref>field-name</x:ref> = token
4471<x:ref>field-value</x:ref> = *( field-content / OWS )
4472<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4473
4474<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4475 / Transfer-Encoding / Upgrade / Via / Warning
4476<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4477 message-body ]
4478
4479<x:ref>hour</x:ref> = 2DIGIT
4480<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4481<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4482
4483<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4484
4485<x:ref>message-body</x:ref> = entity-body /
4486 &lt;entity-body encoded as per Transfer-Encoding&gt;
4487<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4488<x:ref>minute</x:ref> = 2DIGIT
4489<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4490 / %x46.65.62 ; Feb
4491 / %x4D.61.72 ; Mar
4492 / %x41.70.72 ; Apr
4493 / %x4D.61.79 ; May
4494 / %x4A.75.6E ; Jun
4495 / %x4A.75.6C ; Jul
4496 / %x41.75.67 ; Aug
4497 / %x53.65.70 ; Sep
4498 / %x4F.63.74 ; Oct
4499 / %x4E.6F.76 ; Nov
4500 / %x44.65.63 ; Dec
4501
4502<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4503<x:ref>obs-fold</x:ref> = CRLF
4504<x:ref>obs-text</x:ref> = %x80-FF
4505
4506<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4507<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4508<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4509<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4510<x:ref>product</x:ref> = token [ "/" product-version ]
4511<x:ref>product-version</x:ref> = token
4512<x:ref>protocol-name</x:ref> = token
4513<x:ref>protocol-version</x:ref> = token
4514<x:ref>pseudonym</x:ref> = token
4515
4516<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4517 / %x5D-7E ; ']'-'~'
4518 / obs-text
4519<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4520<x:ref>quoted-pair</x:ref> = "\" quoted-text
4521<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4522<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4523<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4524
4525<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4526<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4527<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4528<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4529<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4530 / authority
4531<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4532<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4533<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4534
4535<x:ref>second</x:ref> = 2DIGIT
4536<x:ref>start-line</x:ref> = Request-Line / Status-Line
4537
4538<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4539<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4540 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4541<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4542<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4543<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4544<x:ref>token</x:ref> = 1*tchar
4545<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4546<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4547<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4548<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4549
4550<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4551
4552<x:ref>value</x:ref> = token / quoted-string
4553
4554<x:ref>year</x:ref> = 4DIGIT
4555</artwork>
4556</figure>
4557<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4558; Chunked-Body defined but not used
4559; Content-Length defined but not used
4560; HTTP-message defined but not used
4561; Host defined but not used
4562; TE defined but not used
4563; URI defined but not used
4564; URI-reference defined but not used
4565; fragment defined but not used
4566; generic-message defined but not used
4567; http-URI defined but not used
4568; https-URI defined but not used
4569; partial-URI defined but not used
4570</artwork></figure></section>
4571
4572<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4573
4574<section title="Since RFC2616">
4575<t>
4576  Extracted relevant partitions from <xref target="RFC2616"/>.
4577</t>
4578</section>
4579
4580<section title="Since draft-ietf-httpbis-p1-messaging-00">
4581<t>
4582  Closed issues:
4583  <list style="symbols"> 
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4586      "HTTP Version should be case sensitive"
4587      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4588    </t>
4589    <t>
4590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4591      "'unsafe' characters"
4592      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4596      "Chunk Size Definition"
4597      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4598    </t>
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4601      "Message Length"
4602      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4606      "Media Type Registrations"
4607      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4608    </t>
4609    <t>
4610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4611      "URI includes query"
4612      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4613    </t>
4614    <t>
4615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4616      "No close on 1xx responses"
4617      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4618    </t>
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4621      "Remove 'identity' token references"
4622      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4623    </t>
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4626      "Import query BNF"
4627    </t>
4628    <t>
4629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4630      "qdtext BNF"
4631    </t>
4632    <t>
4633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4634      "Normative and Informative references"
4635    </t>
4636    <t>
4637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4638      "RFC2606 Compliance"
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4642      "RFC977 reference"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4646      "RFC1700 references"
4647    </t>
4648    <t>
4649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4650      "inconsistency in date format explanation"
4651    </t>
4652    <t>
4653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4654      "Date reference typo"
4655    </t>
4656    <t>
4657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4658      "Informative references"
4659    </t>
4660    <t>
4661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4662      "ISO-8859-1 Reference"
4663    </t>
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4666      "Normative up-to-date references"
4667    </t>
4668  </list>
4669</t>
4670<t>
4671  Other changes:
4672  <list style="symbols"> 
4673    <t>
4674      Update media type registrations to use RFC4288 template.
4675    </t>
4676    <t>
4677      Use names of RFC4234 core rules DQUOTE and WSP,
4678      fix broken ABNF for chunk-data
4679      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4680    </t>
4681  </list>
4682</t>
4683</section>
4684
4685<section title="Since draft-ietf-httpbis-p1-messaging-01">
4686<t>
4687  Closed issues:
4688  <list style="symbols"> 
4689    <t>
4690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4691      "Bodies on GET (and other) requests"
4692    </t>
4693    <t>
4694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4695      "Updating to RFC4288"
4696    </t>
4697    <t>
4698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4699      "Status Code and Reason Phrase"
4700    </t>
4701    <t>
4702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4703      "rel_path not used"
4704    </t>
4705  </list>
4706</t>
4707<t>
4708  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4709  <list style="symbols"> 
4710    <t>
4711      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4712      "trailer-part").
4713    </t>
4714    <t>
4715      Avoid underscore character in rule names ("http_URL" ->
4716      "http-URL", "abs_path" -> "path-absolute").
4717    </t>
4718    <t>
4719      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4720      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4721      have to be updated when switching over to RFC3986.
4722    </t>
4723    <t>
4724      Synchronize core rules with RFC5234.
4725    </t>
4726    <t>
4727      Get rid of prose rules that span multiple lines.
4728    </t>
4729    <t>
4730      Get rid of unused rules LOALPHA and UPALPHA.
4731    </t>
4732    <t>
4733      Move "Product Tokens" section (back) into Part 1, as "token" is used
4734      in the definition of the Upgrade header.
4735    </t>
4736    <t>
4737      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4738    </t>
4739    <t>
4740      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4741    </t>
4742  </list>
4743</t>
4744</section>
4745
4746<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4747<t>
4748  Closed issues:
4749  <list style="symbols"> 
4750    <t>
4751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4752      "HTTP-date vs. rfc1123-date"
4753    </t>
4754    <t>
4755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4756      "WS in quoted-pair"
4757    </t>
4758  </list>
4759</t>
4760<t>
4761  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4762  <list style="symbols"> 
4763    <t>
4764      Reference RFC 3984, and update header registrations for headers defined
4765      in this document.
4766    </t>
4767  </list>
4768</t>
4769<t>
4770  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4771  <list style="symbols"> 
4772    <t>
4773      Replace string literals when the string really is case-sensitive (HTTP-Version).
4774    </t>
4775  </list>
4776</t>
4777</section>
4778
4779<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4780<t>
4781  Closed issues:
4782  <list style="symbols"> 
4783    <t>
4784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4785      "Connection closing"
4786    </t>
4787    <t>
4788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4789      "Move registrations and registry information to IANA Considerations"
4790    </t>
4791    <t>
4792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4793      "need new URL for PAD1995 reference"
4794    </t>
4795    <t>
4796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4797      "IANA Considerations: update HTTP URI scheme registration"
4798    </t>
4799    <t>
4800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4801      "Cite HTTPS URI scheme definition"
4802    </t>
4803    <t>
4804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4805      "List-type headers vs Set-Cookie"
4806    </t>
4807  </list>
4808</t>
4809<t>
4810  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4811  <list style="symbols"> 
4812    <t>
4813      Replace string literals when the string really is case-sensitive (HTTP-Date).
4814    </t>
4815    <t>
4816      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4817    </t>
4818  </list>
4819</t>
4820</section>
4821
4822<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4823<t>
4824  Closed issues:
4825  <list style="symbols"> 
4826    <t>
4827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4828      "Out-of-date reference for URIs"
4829    </t>
4830    <t>
4831      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4832      "RFC 2822 is updated by RFC 5322"
4833    </t>
4834  </list>
4835</t>
4836<t>
4837  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4838  <list style="symbols"> 
4839    <t>
4840      Use "/" instead of "|" for alternatives.
4841    </t>
4842    <t>
4843      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4844    </t>
4845    <t>
4846      Only reference RFC 5234's core rules.
4847    </t>
4848    <t>
4849      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4850      whitespace ("OWS") and required whitespace ("RWS").
4851    </t>
4852    <t>
4853      Rewrite ABNFs to spell out whitespace rules, factor out
4854      header value format definitions.
4855    </t>
4856  </list>
4857</t>
4858</section>
4859
4860<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4861<t>
4862  Closed issues:
4863  <list style="symbols"> 
4864    <t>
4865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4866      "Header LWS"
4867    </t>
4868    <t>
4869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4870      "Sort 1.3 Terminology"
4871    </t>
4872    <t>
4873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4874      "RFC2047 encoded words"
4875    </t>
4876    <t>
4877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4878      "Character Encodings in TEXT"
4879    </t>
4880    <t>
4881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4882      "Line Folding"
4883    </t>
4884    <t>
4885      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4886      "OPTIONS * and proxies"
4887    </t>
4888    <t>
4889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4890      "Reason-Phrase BNF"
4891    </t>
4892    <t>
4893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4894      "Use of TEXT"
4895    </t>
4896    <t>
4897      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4898      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4899    </t>
4900    <t>
4901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4902      "RFC822 reference left in discussion of date formats"
4903    </t>
4904  </list>
4905</t>
4906<t>
4907  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4908  <list style="symbols"> 
4909    <t>
4910      Rewrite definition of list rules, deprecate empty list elements.
4911    </t>
4912    <t>
4913      Add appendix containing collected and expanded ABNF.
4914    </t>
4915  </list>
4916</t>
4917<t>
4918  Other changes:
4919  <list style="symbols"> 
4920    <t>
4921      Rewrite introduction; add mostly new Architecture Section.
4922    </t>
4923    <t>
4924      Move definition of quality values from Part 3 into Part 1;
4925      make TE request header grammar independent of accept-params (defined in Part 3).
4926    </t>
4927  </list>
4928</t>
4929</section>
4930
4931<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4932<t>
4933  Closed issues:
4934  <list style="symbols"> 
4935    <t>
4936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
4937      "base for numeric protocol elements"
4938    </t>
4939    <t>
4940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
4941      "comment ABNF"
4942    </t>
4943  </list>
4944</t>
4945<t>
4946  Partly resolved issues:
4947  <list style="symbols"> 
4948    <t>
4949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4950      "205 Bodies" (took out language that implied that there may be
4951      methods for which a request body MUST NOT be included)
4952    </t>
4953    <t>
4954      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
4955      "editorial improvements around HTTP-date"
4956    </t>
4957  </list>
4958</t>
4959</section>
4960
4961<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
4962<t>
4963  Closed issues:
4964  <list style="symbols"> 
4965    <t>
4966      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
4967      "IP addresses in URLs"
4968    </t>
4969  </list>
4970</t>
4971
4972</section>
4973
4974</section>
4975
4976</back>
4977</rfc>
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