source: draft-ietf-httpbis/latest/p1-messaging.xml @ 630

Last change on this file since 630 was 630, checked in by fielding@…, 11 years ago

Split the section on overall operation into sections for
client/server operation, intermediaries, caches, and transport independence.
Move most of the terminology section into these sections so that terms
are learned as they are introduced (in context).

  • Property svn:eol-style set to native
File size: 214.4 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY 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<figure><preamble>
560   The following example illustrates a typical message exchange for a
561   GET request on the URI "http://www.example.com/hello.txt":
562</preamble><artwork type="drawing">
563client request:
564
565  GET /hello.txt HTTP/1.1
566  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
567  Host: www.example.com
568  Accept: */*
569
570server response:
571
572  HTTP/1.1 200 OK
573  Date: Mon, 27 Jul 2009 12:28:53 GMT
574  Server: Apache
575  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
576  ETag: "34aa387-d-1568eb00"
577  Accept-Ranges: bytes
578  Content-Length: 13
579  Vary: Accept-Encoding
580  Content-Type: text/plain
581 
582  Hello World!
583</artwork></figure>
584</section>
585
586<section title="Intermediaries" anchor="intermediaries">
587<t>
588   A more complicated situation occurs when one or more intermediaries
589   are present in the request/response chain. There are three common
590   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
591   a single intermediary may act as an origin server, proxy, gateway,
592   or tunnel, switching behavior based on the nature of each request.
593</t>
594<figure><artwork type="drawing">
595       request chain --------------------------------------&gt;
596    UA -----v----- A -----v----- B -----v----- C -----v----- O
597       &lt;------------------------------------- response chain
598</artwork></figure>
599<t>
600   The figure above shows three intermediaries (A, B, and C) between the
601   user agent and origin server. A request or response message that
602   travels the whole chain will pass through four separate connections.
603   Some HTTP communication options
604   may apply only to the connection with the nearest, non-tunnel
605   neighbor, only to the end-points of the chain, or to all connections
606   along the chain. Although the diagram is linear, each participant may
607   be engaged in multiple, simultaneous communications. For example, B
608   may be receiving requests from many clients other than A, and/or
609   forwarding requests to servers other than C, at the same time that it
610   is handling A's request.
611</t>
612<t>
613<iref item="upstream"/><iref item="downstream"/>
614<iref item="inbound"/><iref item="outbound"/>
615   We use the terms "upstream" and "downstream" to describe various
616   requirements in relation to the directional flow of a message:
617   all messages flow from upstream to downstream.
618   Likewise, we use the terms "inbound" and "outbound" to refer to
619   directions in relation to the request path: "inbound" means toward
620   the origin server and "outbound" means toward the user agent.
621</t>
622<t><iref item="proxy"/>
623   A proxy is a message forwarding agent that is selected by the
624   client, usually via local configuration rules, to receive requests
625   for some type(s) of absolute URI and attempt to satisfy those
626   requests via translation through the HTTP interface.  Some translations
627   are minimal, such as for proxy requests for "http" URIs, whereas
628   other requests may require translation to and from entirely different
629   application-layer protocols. Proxies are often used to group an
630   organization's HTTP requests through a common intermediary for the
631   sake of security, annotation services, or shared caching.
632</t>
633<t><iref item="gateway"/><iref item="reverse proxy"/>
634   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
635   as a layer above some other server(s) and translates the received
636   requests to the underlying server's protocol.  Gateways are often
637   used for load balancing or partitioning HTTP services across
638   multiple machines.
639   Unlike a proxy, a gateway receives requests as if it were the
640   origin server for the requested resource; the requesting client
641   will not be aware that it is communicating with a gateway.
642   A gateway communicates with the client as if the gateway is the
643   origin server and thus is subject to all of the requirements on
644   origin servers for that connection.  A gateway communicates
645   with inbound servers using any protocol it desires, including
646   private extensions to HTTP that are outside the scope of this
647   specification.
648</t>
649<t><iref item="tunnel"/>
650   A tunnel acts as a blind relay between two connections
651   without changing the messages. Once active, a tunnel is not
652   considered a party to the HTTP communication, though the tunnel may
653   have been initiated by an HTTP request. A tunnel ceases to exist when
654   both ends of the relayed connection are closed. Tunnels are used to
655   extend a virtual connection through an intermediary, such as when
656   transport-layer security is used to establish private communication
657   through a shared firewall proxy.
658</t>
659</section>
660
661<section title="Caches" anchor="caches">
662<iref item="cache"/>
663<t>
664   Any party to HTTP communication that is not acting as a tunnel may
665   employ an internal cache for handling requests.
666   A cache is a local store of previous response messages and the
667   subsystem that controls its message storage, retrieval, and deletion.
668   A cache stores cacheable responses in order to reduce the response
669   time and network bandwidth consumption on future, equivalent
670   requests. Any client or server may include a cache, though a cache
671   cannot be used by a server while it is acting as a tunnel.
672</t>
673<t>
674   The effect of a cache is that the request/response chain is shortened
675   if one of the participants along the chain has a cached response
676   applicable to that request. The following illustrates the resulting
677   chain if B has a cached copy of an earlier response from O (via C)
678   for a request which has not been cached by UA or A.
679</t>
680<figure><artwork type="drawing">
681          request chain ----------&gt;
682       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
683          &lt;--------- response chain
684</artwork></figure>
685<t><iref item="cacheable"/>
686   A response is cacheable if a cache is allowed to store a copy of
687   the response message for use in answering subsequent requests.
688   Even when a response is cacheable, there may be additional
689   constraints placed by the client or by the origin server on when
690   that cached response can be used for a particular request. HTTP
691   requirements for cache behavior and cacheable responses are
692   defined in &caching;
693</t>
694<t>
695   There are a wide variety of architectures and configurations
696   of caches and proxies deployed across the World Wide Web and
697   inside large organizations. These systems include national hierarchies
698   of proxy caches to save transoceanic bandwidth, systems that
699   broadcast or multicast cache entries, organizations that distribute
700   subsets of cached data via CD-ROM, and so on.
701</t>
702</section>
703
704<section title="Transport Independence" anchor="transport-independence">
705<t>
706  HTTP systems are used in a wide variety of environments, from
707  corporate intranets with high-bandwidth links to long-distance
708  communication over low-power radio links and intermittent connectivity.
709</t>
710<t>
711   HTTP communication usually takes place over TCP/IP connections. The
712   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
713   not preclude HTTP from being implemented on top of any other protocol
714   on the Internet, or on other networks. HTTP only presumes a reliable
715   transport; any protocol that provides such guarantees can be used;
716   the mapping of the HTTP/1.1 request and response structures onto the
717   transport data units of the protocol in question is outside the scope
718   of this specification.
719</t>
720<t>
721   In HTTP/1.0, most implementations used a new connection for each
722   request/response exchange. In HTTP/1.1, a connection may be used for
723   one or more request/response exchanges, although connections may be
724   closed for a variety of reasons (see <xref target="persistent.connections"/>).
725</t>
726</section>
727
728<section title="HTTP Version" anchor="http.version">
729  <x:anchor-alias value="HTTP-Version"/>
730  <x:anchor-alias value="HTTP-Prot-Name"/>
731<t>
732   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
733   of the protocol. The protocol versioning policy is intended to allow
734   the sender to indicate the format of a message and its capacity for
735   understanding further HTTP communication, rather than the features
736   obtained via that communication. No change is made to the version
737   number for the addition of message components which do not affect
738   communication behavior or which only add to extensible field values.
739   The &lt;minor&gt; number is incremented when the changes made to the
740   protocol add features which do not change the general message parsing
741   algorithm, but which may add to the message semantics and imply
742   additional capabilities of the sender. The &lt;major&gt; number is
743   incremented when the format of a message within the protocol is
744   changed. See <xref target="RFC2145"/> for a fuller explanation.
745</t>
746<t>
747   The version of an HTTP message is indicated by an HTTP-Version field
748   in the first line of the message. HTTP-Version is case-sensitive.
749</t>
750<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
751  <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>
752  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
753</artwork></figure>
754<t>
755   Note that the major and minor numbers &MUST; be treated as separate
756   integers and that each &MAY; be incremented higher than a single digit.
757   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
758   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
759   &MUST-NOT; be sent.
760</t>
761<t>
762   An application that sends a request or response message that includes
763   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
764   with this specification. Applications that are at least conditionally
765   compliant with this specification &SHOULD; use an HTTP-Version of
766   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
767   not compatible with HTTP/1.0. For more details on when to send
768   specific HTTP-Version values, see <xref target="RFC2145"/>.
769</t>
770<t>
771   The HTTP version of an application is the highest HTTP version for
772   which the application is at least conditionally compliant.
773</t>
774<t>
775   Proxy and gateway applications need to be careful when forwarding
776   messages in protocol versions different from that of the application.
777   Since the protocol version indicates the protocol capability of the
778   sender, a proxy/gateway &MUST-NOT; send a message with a version
779   indicator which is greater than its actual version. If a higher
780   version request is received, the proxy/gateway &MUST; either downgrade
781   the request version, or respond with an error, or switch to tunnel
782   behavior.
783</t>
784<t>
785   Due to interoperability problems with HTTP/1.0 proxies discovered
786   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
787   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
788   they support. The proxy/gateway's response to that request &MUST; be in
789   the same major version as the request.
790</t>
791<x:note>
792  <t>
793    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
794    of header fields required or forbidden by the versions involved.
795  </t>
796</x:note>
797</section>
798
799<section title="Uniform Resource Identifiers" anchor="uri">
800<iref primary="true" item="resource"/>
801<t>
802   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
803   throughout HTTP as the means for identifying resources. URI references
804   are used to target requests, indicate redirects, and define relationships.
805   HTTP does not limit what a resource may be; it merely defines an interface
806   that can be used to interact with a resource via HTTP. More information on
807   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
808</t>
809  <x:anchor-alias value="URI"/>
810  <x:anchor-alias value="URI-reference"/>
811  <x:anchor-alias value="absolute-URI"/>
812  <x:anchor-alias value="relative-part"/>
813  <x:anchor-alias value="authority"/>
814  <x:anchor-alias value="fragment"/>
815  <x:anchor-alias value="path-abempty"/>
816  <x:anchor-alias value="path-absolute"/>
817  <x:anchor-alias value="port"/>
818  <x:anchor-alias value="query"/>
819  <x:anchor-alias value="uri-host"/>
820  <x:anchor-alias value="partial-URI"/>
821<t>
822   This specification adopts the definitions of "URI-reference",
823   "absolute-URI", "relative-part", "fragment", "port", "host",
824   "path-abempty", "path-absolute", "query", and "authority" from
825   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
826   protocol elements that allow a relative URI without a fragment.
827</t>
828<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"/>
829  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
830  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
831  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
832  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
833  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
834  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
835  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
836  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
837  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
838  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
839  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
840 
841  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
842</artwork></figure>
843<t>
844   Each protocol element in HTTP that allows a URI reference will indicate in
845   its ABNF production whether the element allows only a URI in absolute form
846   (absolute-URI), any relative reference (relative-ref), or some other subset
847   of the URI-reference grammar. Unless otherwise indicated, URI references
848   are parsed relative to the request target (the default base URI for both
849   the request and its corresponding response).
850</t>
851
852<section title="http URI scheme" anchor="http.uri">
853  <x:anchor-alias value="http-URI"/>
854  <iref item="http URI scheme" primary="true"/>
855  <iref item="URI scheme" subitem="http" primary="true"/>
856<t>
857   The "http" URI scheme is hereby defined for the purpose of minting
858   identifiers according to their association with the hierarchical
859   namespace governed by a potential HTTP origin server listening for
860   TCP connections on a given port.
861   The HTTP server is identified via the generic syntax's
862   <x:ref>authority</x:ref> component, which includes a host
863   identifier and optional TCP port, and the remainder of the URI is
864   considered to be identifying data corresponding to a resource for
865   which that server might provide an HTTP interface.
866</t>
867<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
868  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
869</artwork></figure>
870<t>
871   The host identifier within an <x:ref>authority</x:ref> component is
872   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
873   provided as an IP literal or IPv4 address, then the HTTP server is any
874   listener on the indicated TCP port at that IP address. If host is a
875   registered name, then that name is considered an indirect identifier
876   and the recipient might use a name resolution service, such as DNS,
877   to find the address of a listener for that host.
878   The host &MUST-NOT; be empty; if an "http" URI is received with an
879   empty host, then it &MUST; be rejected as invalid.
880   If the port subcomponent is empty or not given, then TCP port 80 is
881   assumed (the default reserved port for WWW services).
882</t>
883<t>
884   Regardless of the form of host identifier, access to that host is not
885   implied by the mere presence of its name or address. The host may or may
886   not exist and, even when it does exist, may or may not be running an
887   HTTP server or listening to the indicated port. The "http" URI scheme
888   makes use of the delegated nature of Internet names and addresses to
889   establish a naming authority (whatever entity has the ability to place
890   an HTTP server at that Internet name or address) and allows that
891   authority to determine which names are valid and how they might be used.
892</t>
893<t>
894   When an "http" URI is used within a context that calls for access to the
895   indicated resource, a client &MAY; attempt access by resolving
896   the host to an IP address, establishing a TCP connection to that address
897   on the indicated port, and sending an HTTP request message to the server
898   containing the URI's identifying data as described in <xref target="request"/>.
899   If the server responds to that request with a non-interim HTTP response
900   message, as described in <xref target="response"/>, then that response
901   is considered an authoritative answer to the client's request.
902</t>
903<t>
904   Although HTTP is independent of the transport protocol, the "http"
905   scheme is specific to TCP-based services because the name delegation
906   process depends on TCP for establishing authority.
907   An HTTP service based on some other underlying connection protocol
908   would presumably be identified using a different URI scheme, just as
909   the "https" scheme (below) is used for servers that require an SSL/TLS
910   transport layer on a connection. Other protocols may also be used to
911   provide access to "http" identified resources --- it is only the
912   authoritative interface used for mapping the namespace that is
913   specific to TCP.
914</t>
915</section>
916
917<section title="https URI scheme" anchor="https.uri">
918   <x:anchor-alias value="https-URI"/>
919   <iref item="https URI scheme"/>
920   <iref item="URI scheme" subitem="https"/>
921<t>
922   The "https" URI scheme is hereby defined for the purpose of minting
923   identifiers according to their association with the hierarchical
924   namespace governed by a potential HTTP origin server listening for
925   SSL/TLS-secured connections on a given TCP port.
926   The host and port are determined in the same way
927   as for the "http" scheme, except that a default TCP port of 443
928   is assumed if the port subcomponent is empty or not given.
929</t>
930<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
931  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
932</artwork></figure>
933<t>
934   The primary difference between the "http" and "https" schemes is
935   that interaction with the latter is required to be secured for
936   privacy through the use of strong encryption. The URI cannot be
937   sent in a request until the connection is secure. Likewise, the
938   default for caching is that each response that would be considered
939   "public" under the "http" scheme is instead treated as "private"
940   and thus not eligible for shared caching.
941</t>
942<t>
943   The process for authoritative access to an "https" identified
944   resource is defined in <xref target="RFC2818"/>.
945</t>
946</section>
947
948<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
949<t>
950   Since the "http" and "https" schemes conform to the URI generic syntax,
951   such URIs are normalized and compared according to the algorithm defined
952   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
953   described above for each scheme.
954</t>
955<t>
956   If the port is equal to the default port for a scheme, the normal
957   form is to elide the port subcomponent. Likewise, an empty path
958   component is equivalent to an absolute path of "/", so the normal
959   form is to provide a path of "/" instead. The scheme and host
960   are case-insensitive and normally provided in lowercase; all
961   other components are compared in a case-sensitive manner.
962   Characters other than those in the "reserved" set are equivalent
963   to their percent-encoded octets (see <xref target="RFC3986"
964   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
965</t>
966<t>
967   For example, the following three URIs are equivalent:
968</t>
969<figure><artwork type="example">
970   http://example.com:80/~smith/home.html
971   http://EXAMPLE.com/%7Esmith/home.html
972   http://EXAMPLE.com:/%7esmith/home.html
973</artwork></figure>
974<t>
975   <cref>[[This paragraph does not belong here. --Roy]]</cref>
976   If path-abempty is the empty string (i.e., there is no slash "/"
977   path separator following the authority), then the "http" URI
978   &MUST; be given as "/" when
979   used as a request-target (<xref target="request-target"/>). If a proxy
980   receives a host name which is not a fully qualified domain name, it
981   &MAY; add its domain to the host name it received. If a proxy receives
982   a fully qualified domain name, the proxy &MUST-NOT; change the host
983   name.
984</t>
985</section>
986
987<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
988<t>
989   <cref>TBS: describe why aliases like webcal are harmful.</cref>
990</t>
991</section>
992</section>
993
994<section title="Use of HTTP for proxy communication" anchor="http.proxy">
995<t>
996   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
997</t>
998</section>
999<section title="Interception of HTTP for access control" anchor="http.intercept">
1000<t>
1001   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
1002</t>
1003</section>
1004<section title="Use of HTTP by other protocols" anchor="http.others">
1005<t>
1006   <cref>TBD: Profiles of HTTP defined by other protocol.
1007   Extensions of HTTP like WebDAV.</cref>
1008</t>
1009</section>
1010<section title="Use of HTTP by media type specification" anchor="http.media">
1011<t>
1012   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
1013</t>
1014</section>
1015</section>
1016
1017<section title="HTTP Message" anchor="http.message">
1018
1019<section title="Message Types" anchor="message.types">
1020  <x:anchor-alias value="generic-message"/>
1021  <x:anchor-alias value="HTTP-message"/>
1022  <x:anchor-alias value="start-line"/>
1023<t>
1024   HTTP messages consist of requests from client to server and responses
1025   from server to client.
1026</t>
1027<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1028  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1029</artwork></figure>
1030<t>
1031   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1032   message format of <xref target="RFC5322"/> for transferring entities (the payload
1033   of the message). Both types of message consist of a start-line, zero
1034   or more header fields (also known as "headers"), an empty line (i.e.,
1035   a line with nothing preceding the CRLF) indicating the end of the
1036   header fields, and possibly a message-body.
1037</t>
1038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1039  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1040                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1041                    <x:ref>CRLF</x:ref>
1042                    [ <x:ref>message-body</x:ref> ]
1043  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1044</artwork></figure>
1045<t>
1046   In the interest of robustness, servers &SHOULD; ignore any empty
1047   line(s) received where a Request-Line is expected. In other words, if
1048   the server is reading the protocol stream at the beginning of a
1049   message and receives a CRLF first, it should ignore the CRLF.
1050</t>
1051<t>
1052   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1053   after a POST request. To restate what is explicitly forbidden by the
1054   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1055   extra CRLF.
1056</t>
1057<t>
1058   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1059   header field. The presence of whitespace might be an attempt to trick a
1060   noncompliant implementation of HTTP into ignoring that field or processing
1061   the next line as a new request, either of which may result in security
1062   issues when implementations within the request chain interpret the
1063   same message differently. HTTP/1.1 servers &MUST; reject such a message
1064   with a 400 (Bad Request) response.
1065</t>
1066</section>
1067
1068<section title="Message Headers" anchor="message.headers">
1069  <x:anchor-alias value="field-content"/>
1070  <x:anchor-alias value="field-name"/>
1071  <x:anchor-alias value="field-value"/>
1072  <x:anchor-alias value="message-header"/>
1073<t>
1074   HTTP header fields follow the same general format as Internet messages in
1075   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1076   of a name followed by a colon (":"), optional whitespace, and the field
1077   value. Field names are case-insensitive.
1078</t>
1079<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"/>
1080  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1081  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1082  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1083  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1084</artwork></figure>
1085<t>
1086   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1087   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1088   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1089   header field-values use only a subset of the US-ASCII charset
1090   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1091   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1092   (obs-text) octets in field-content as opaque data.
1093</t>
1094<t>
1095   No whitespace is allowed between the header field-name and colon. For
1096   security reasons, any request message received containing such whitespace
1097   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1098   whitespace in a response message &MUST; be removed.
1099</t>
1100<t>
1101   The field value &MAY; be preceded by optional whitespace; a single SP is
1102   preferred. The field-value does not include any leading or trailing white
1103   space: OWS occurring before the first non-whitespace character of the
1104   field-value or after the last non-whitespace character of the field-value
1105   is ignored and &MAY; be removed without changing the meaning of the header
1106   field.
1107</t>
1108<t>
1109   Historically, HTTP header field values could be extended over multiple
1110   lines by preceding each extra line with at least one space or horizontal
1111   tab character (line folding). This specification deprecates such line
1112   folding except within the message/http media type
1113   (<xref target="internet.media.type.message.http"/>).
1114   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1115   (i.e., that contain any field-content that matches the obs-fold rule) unless
1116   the message is intended for packaging within the message/http media type.
1117   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1118   obs-fold whitespace with a single SP prior to interpreting the field value
1119   or forwarding the message downstream.
1120</t>
1121<t anchor="rule.comment">
1122  <x:anchor-alias value="comment"/>
1123  <x:anchor-alias value="ctext"/>
1124   Comments can be included in some HTTP header fields by surrounding
1125   the comment text with parentheses. Comments are only allowed in
1126   fields containing "comment" as part of their field value definition.
1127   In all other fields, parentheses are considered part of the field
1128   value.
1129</t>
1130<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1131  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1132  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1133                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1134</artwork></figure>
1135<t>
1136   The order in which header fields with differing field names are
1137   received is not significant. However, it is "good practice" to send
1138   general-header fields first, followed by request-header or response-header
1139   fields, and ending with the entity-header fields.
1140</t>
1141<t>
1142   Multiple message-header fields with the same field-name &MAY; be
1143   present in a message if and only if the entire field-value for that
1144   header field is defined as a comma-separated list [i.e., #(values)].
1145   It &MUST; be possible to combine the multiple header fields into one
1146   "field-name: field-value" pair, without changing the semantics of the
1147   message, by appending each subsequent field-value to the first, each
1148   separated by a comma. The order in which header fields with the same
1149   field-name are received is therefore significant to the
1150   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1151   change the order of these field values when a message is forwarded.
1152</t>
1153<x:note>
1154  <t>
1155   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1156   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1157   can occur multiple times, but does not use the list syntax, and thus cannot
1158   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1159   for details.) Also note that the Set-Cookie2 header specified in
1160   <xref target="RFC2965"/> does not share this problem.
1161  </t>
1162</x:note>
1163 
1164</section>
1165
1166<section title="Message Body" anchor="message.body">
1167  <x:anchor-alias value="message-body"/>
1168<t>
1169   The message-body (if any) of an HTTP message is used to carry the
1170   entity-body associated with the request or response. The message-body
1171   differs from the entity-body only when a transfer-coding has been
1172   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1173</t>
1174<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1175  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1176               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1177</artwork></figure>
1178<t>
1179   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1180   applied by an application to ensure safe and proper transfer of the
1181   message. Transfer-Encoding is a property of the message, not of the
1182   entity, and thus &MAY; be added or removed by any application along the
1183   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1184   when certain transfer-codings may be used.)
1185</t>
1186<t>
1187   The rules for when a message-body is allowed in a message differ for
1188   requests and responses.
1189</t>
1190<t>
1191   The presence of a message-body in a request is signaled by the
1192   inclusion of a Content-Length or Transfer-Encoding header field in
1193   the request's message-headers.
1194   When a request message contains both a message-body of non-zero
1195   length and a method that does not define any semantics for that
1196   request message-body, then an origin server &SHOULD; either ignore
1197   the message-body or respond with an appropriate error message
1198   (e.g., 413).  A proxy or gateway, when presented the same request,
1199   &SHOULD; either forward the request inbound with the message-body or
1200   ignore the message-body when determining a response.
1201</t>
1202<t>
1203   For response messages, whether or not a message-body is included with
1204   a message is dependent on both the request method and the response
1205   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1206   &MUST-NOT; include a message-body, even though the presence of entity-header
1207   fields might lead one to believe they do. All 1xx
1208   (informational), 204 (No Content), and 304 (Not Modified) responses
1209   &MUST-NOT; include a message-body. All other responses do include a
1210   message-body, although it &MAY; be of zero length.
1211</t>
1212</section>
1213
1214<section title="Message Length" anchor="message.length">
1215<t>
1216   The transfer-length of a message is the length of the message-body as
1217   it appears in the message; that is, after any transfer-codings have
1218   been applied. When a message-body is included with a message, the
1219   transfer-length of that body is determined by one of the following
1220   (in order of precedence):
1221</t>
1222<t>
1223  <list style="numbers">
1224    <x:lt><t>
1225     Any response message which "&MUST-NOT;" include a message-body (such
1226     as the 1xx, 204, and 304 responses and any response to a HEAD
1227     request) is always terminated by the first empty line after the
1228     header fields, regardless of the entity-header fields present in
1229     the message.
1230    </t></x:lt>
1231    <x:lt><t>
1232     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1233     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1234     is used, the transfer-length is defined by the use of this transfer-coding.
1235     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1236     is not present, the transfer-length is defined by the sender closing the connection.
1237    </t></x:lt>
1238    <x:lt><t>
1239     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1240     value in OCTETs represents both the entity-length and the
1241     transfer-length. The Content-Length header field &MUST-NOT; be sent
1242     if these two lengths are different (i.e., if a Transfer-Encoding
1243     header field is present). If a message is received with both a
1244     Transfer-Encoding header field and a Content-Length header field,
1245     the latter &MUST; be ignored.
1246    </t></x:lt>
1247    <x:lt><t>
1248     If the message uses the media type "multipart/byteranges", and the
1249     transfer-length is not otherwise specified, then this self-delimiting
1250     media type defines the transfer-length. This media type
1251     &MUST-NOT; be used unless the sender knows that the recipient can parse
1252     it; the presence in a request of a Range header with multiple byte-range
1253     specifiers from a 1.1 client implies that the client can parse
1254     multipart/byteranges responses.
1255    <list style="empty"><t>
1256       A range header might be forwarded by a 1.0 proxy that does not
1257       understand multipart/byteranges; in this case the server &MUST;
1258       delimit the message using methods defined in items 1, 3 or 5 of
1259       this section.
1260    </t></list>
1261    </t></x:lt>
1262    <x:lt><t>
1263     By the server closing the connection. (Closing the connection
1264     cannot be used to indicate the end of a request body, since that
1265     would leave no possibility for the server to send back a response.)
1266    </t></x:lt>
1267  </list>
1268</t>
1269<t>
1270   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1271   containing a message-body &MUST; include a valid Content-Length header
1272   field unless the server is known to be HTTP/1.1 compliant. If a
1273   request contains a message-body and a Content-Length is not given,
1274   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1275   determine the length of the message, or with 411 (Length Required) if
1276   it wishes to insist on receiving a valid Content-Length.
1277</t>
1278<t>
1279   All HTTP/1.1 applications that receive entities &MUST; accept the
1280   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1281   to be used for messages when the message length cannot be determined
1282   in advance.
1283</t>
1284<t>
1285   Messages &MUST-NOT; include both a Content-Length header field and a
1286   transfer-coding. If the message does include a
1287   transfer-coding, the Content-Length &MUST; be ignored.
1288</t>
1289<t>
1290   When a Content-Length is given in a message where a message-body is
1291   allowed, its field value &MUST; exactly match the number of OCTETs in
1292   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1293   invalid length is received and detected.
1294</t>
1295</section>
1296
1297<section title="General Header Fields" anchor="general.header.fields">
1298  <x:anchor-alias value="general-header"/>
1299<t>
1300   There are a few header fields which have general applicability for
1301   both request and response messages, but which do not apply to the
1302   entity being transferred. These header fields apply only to the
1303   message being transmitted.
1304</t>
1305<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1306  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1307                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1308                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1309                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1310                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1311                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1312                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1313                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1314                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1315</artwork></figure>
1316<t>
1317   General-header field names can be extended reliably only in
1318   combination with a change in the protocol version. However, new or
1319   experimental header fields may be given the semantics of general
1320   header fields if all parties in the communication recognize them to
1321   be general-header fields. Unrecognized header fields are treated as
1322   entity-header fields.
1323</t>
1324</section>
1325</section>
1326
1327<section title="Request" anchor="request">
1328  <x:anchor-alias value="Request"/>
1329<t>
1330   A request message from a client to a server includes, within the
1331   first line of that message, the method to be applied to the resource,
1332   the identifier of the resource, and the protocol version in use.
1333</t>
1334<!--                 Host                      ; should be moved here eventually -->
1335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1336  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1337                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1338                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1339                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1340                  <x:ref>CRLF</x:ref>
1341                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1342</artwork></figure>
1343
1344<section title="Request-Line" anchor="request-line">
1345  <x:anchor-alias value="Request-Line"/>
1346<t>
1347   The Request-Line begins with a method token, followed by the
1348   request-target and the protocol version, and ending with CRLF. The
1349   elements are separated by SP characters. No CR or LF is allowed
1350   except in the final CRLF sequence.
1351</t>
1352<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1353  <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>
1354</artwork></figure>
1355
1356<section title="Method" anchor="method">
1357  <x:anchor-alias value="Method"/>
1358<t>
1359   The Method  token indicates the method to be performed on the
1360   resource identified by the request-target. The method is case-sensitive.
1361</t>
1362<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1363  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1364</artwork></figure>
1365</section>
1366
1367<section title="request-target" anchor="request-target">
1368  <x:anchor-alias value="request-target"/>
1369<t>
1370   The request-target
1371   identifies the resource upon which to apply the request.
1372</t>
1373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1374  <x:ref>request-target</x:ref> = "*"
1375                 / <x:ref>absolute-URI</x:ref>
1376                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1377                 / <x:ref>authority</x:ref>
1378</artwork></figure>
1379<t>
1380   The four options for request-target are dependent on the nature of the
1381   request. The asterisk "*" means that the request does not apply to a
1382   particular resource, but to the server itself, and is only allowed
1383   when the method used does not necessarily apply to a resource. One
1384   example would be
1385</t>
1386<figure><artwork type="example">
1387  OPTIONS * HTTP/1.1
1388</artwork></figure>
1389<t>
1390   The absolute-URI form is &REQUIRED; when the request is being made to a
1391   proxy. The proxy is requested to forward the request or service it
1392   from a valid cache, and return the response. Note that the proxy &MAY;
1393   forward the request on to another proxy or directly to the server
1394   specified by the absolute-URI. In order to avoid request loops, a
1395   proxy &MUST; be able to recognize all of its server names, including
1396   any aliases, local variations, and the numeric IP address. An example
1397   Request-Line would be:
1398</t>
1399<figure><artwork type="example">
1400  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1401</artwork></figure>
1402<t>
1403   To allow for transition to absolute-URIs in all requests in future
1404   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1405   form in requests, even though HTTP/1.1 clients will only generate
1406   them in requests to proxies.
1407</t>
1408<t>
1409   The authority form is only used by the CONNECT method (&CONNECT;).
1410</t>
1411<t>
1412   The most common form of request-target is that used to identify a
1413   resource on an origin server or gateway. In this case the absolute
1414   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1415   the request-target, and the network location of the URI (authority) &MUST;
1416   be transmitted in a Host header field. For example, a client wishing
1417   to retrieve the resource above directly from the origin server would
1418   create a TCP connection to port 80 of the host "www.example.org" and send
1419   the lines:
1420</t>
1421<figure><artwork type="example">
1422  GET /pub/WWW/TheProject.html HTTP/1.1
1423  Host: www.example.org
1424</artwork></figure>
1425<t>
1426   followed by the remainder of the Request. Note that the absolute path
1427   cannot be empty; if none is present in the original URI, it &MUST; be
1428   given as "/" (the server root).
1429</t>
1430<t>
1431   If a proxy receives a request without any path in the request-target and
1432   the method specified is capable of supporting the asterisk form of
1433   request-target, then the last proxy on the request chain &MUST; forward the
1434   request with "*" as the final request-target.
1435</t>
1436<figure><preamble>   
1437   For example, the request
1438</preamble><artwork type="example">
1439  OPTIONS http://www.example.org:8001 HTTP/1.1
1440</artwork></figure>
1441<figure><preamble>   
1442  would be forwarded by the proxy as
1443</preamble><artwork type="example">
1444  OPTIONS * HTTP/1.1
1445  Host: www.example.org:8001
1446</artwork>
1447<postamble>
1448   after connecting to port 8001 of host "www.example.org".
1449</postamble>
1450</figure>
1451<t>
1452   The request-target is transmitted in the format specified in
1453   <xref target="http.uri"/>. If the request-target is percent-encoded
1454   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1455   &MUST; decode the request-target in order to
1456   properly interpret the request. Servers &SHOULD; respond to invalid
1457   request-targets with an appropriate status code.
1458</t>
1459<t>
1460   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1461   received request-target when forwarding it to the next inbound server,
1462   except as noted above to replace a null path-absolute with "/".
1463</t>
1464<x:note>
1465  <t>
1466    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1467    meaning of the request when the origin server is improperly using
1468    a non-reserved URI character for a reserved purpose.  Implementors
1469    should be aware that some pre-HTTP/1.1 proxies have been known to
1470    rewrite the request-target.
1471  </t>
1472</x:note>
1473<t>
1474   HTTP does not place a pre-defined limit on the length of a request-target.
1475   A server &MUST; be prepared to receive URIs of unbounded length and
1476   respond with the 414 (URI Too Long) status if the received
1477   request-target would be longer than the server wishes to handle
1478   (see &status-414;).
1479</t>
1480<t>
1481   Various ad-hoc limitations on request-target length are found in practice.
1482   It is &RECOMMENDED; that all HTTP senders and recipients support
1483   request-target lengths of 8000 or more OCTETs.
1484</t>
1485</section>
1486</section>
1487
1488<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1489<t>
1490   The exact resource identified by an Internet request is determined by
1491   examining both the request-target and the Host header field.
1492</t>
1493<t>
1494   An origin server that does not allow resources to differ by the
1495   requested host &MAY; ignore the Host header field value when
1496   determining the resource identified by an HTTP/1.1 request. (But see
1497   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1498   for other requirements on Host support in HTTP/1.1.)
1499</t>
1500<t>
1501   An origin server that does differentiate resources based on the host
1502   requested (sometimes referred to as virtual hosts or vanity host
1503   names) &MUST; use the following rules for determining the requested
1504   resource on an HTTP/1.1 request:
1505  <list style="numbers">
1506    <t>If request-target is an absolute-URI, the host is part of the
1507     request-target. Any Host header field value in the request &MUST; be
1508     ignored.</t>
1509    <t>If the request-target is not an absolute-URI, and the request includes
1510     a Host header field, the host is determined by the Host header
1511     field value.</t>
1512    <t>If the host as determined by rule 1 or 2 is not a valid host on
1513     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1514  </list>
1515</t>
1516<t>
1517   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1518   attempt to use heuristics (e.g., examination of the URI path for
1519   something unique to a particular host) in order to determine what
1520   exact resource is being requested.
1521</t>
1522</section>
1523
1524</section>
1525
1526
1527<section title="Response" anchor="response">
1528  <x:anchor-alias value="Response"/>
1529<t>
1530   After receiving and interpreting a request message, a server responds
1531   with an HTTP response message.
1532</t>
1533<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1534  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1535                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1536                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1537                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1538                  <x:ref>CRLF</x:ref>
1539                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1540</artwork></figure>
1541
1542<section title="Status-Line" anchor="status-line">
1543  <x:anchor-alias value="Status-Line"/>
1544<t>
1545   The first line of a Response message is the Status-Line, consisting
1546   of the protocol version followed by a numeric status code and its
1547   associated textual phrase, with each element separated by SP
1548   characters. No CR or LF is allowed except in the final CRLF sequence.
1549</t>
1550<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1551  <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>
1552</artwork></figure>
1553
1554<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1555  <x:anchor-alias value="Reason-Phrase"/>
1556  <x:anchor-alias value="Status-Code"/>
1557<t>
1558   The Status-Code element is a 3-digit integer result code of the
1559   attempt to understand and satisfy the request. These codes are fully
1560   defined in &status-codes;.  The Reason Phrase exists for the sole
1561   purpose of providing a textual description associated with the numeric
1562   status code, out of deference to earlier Internet application protocols
1563   that were more frequently used with interactive text clients.
1564   A client &SHOULD; ignore the content of the Reason Phrase.
1565</t>
1566<t>
1567   The first digit of the Status-Code defines the class of response. The
1568   last two digits do not have any categorization role. There are 5
1569   values for the first digit:
1570  <list style="symbols">
1571    <t>
1572      1xx: Informational - Request received, continuing process
1573    </t>
1574    <t>
1575      2xx: Success - The action was successfully received,
1576        understood, and accepted
1577    </t>
1578    <t>
1579      3xx: Redirection - Further action must be taken in order to
1580        complete the request
1581    </t>
1582    <t>
1583      4xx: Client Error - The request contains bad syntax or cannot
1584        be fulfilled
1585    </t>
1586    <t>
1587      5xx: Server Error - The server failed to fulfill an apparently
1588        valid request
1589    </t>
1590  </list>
1591</t>
1592<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"/>
1593  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1594  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1595</artwork></figure>
1596</section>
1597</section>
1598
1599</section>
1600
1601
1602<section title="Protocol Parameters" anchor="protocol.parameters">
1603
1604<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1605  <x:anchor-alias value="HTTP-date"/>
1606<t>
1607   HTTP applications have historically allowed three different formats
1608   for the representation of date/time stamps:
1609</t>
1610<figure><artwork type="example">
1611  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1612  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1613  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1614</artwork></figure>
1615<t>
1616   The first format is preferred as an Internet standard and represents
1617   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1618   other formats are described here only for
1619   compatibility with obsolete implementations.
1620   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1621   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1622   only generate the RFC 1123 format for representing HTTP-date values
1623   in header fields. See <xref target="tolerant.applications"/> for further information.
1624</t>
1625<t>
1626   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1627   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1628   equal to UTC (Coordinated Universal Time). This is indicated in the
1629   first two formats by the inclusion of "GMT" as the three-letter
1630   abbreviation for time zone, and &MUST; be assumed when reading the
1631   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1632   additional whitespace beyond that specifically included as SP in the
1633   grammar.
1634</t>
1635<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1636  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1637</artwork></figure>
1638<t anchor="preferred.date.format">
1639  <x:anchor-alias value="rfc1123-date"/>
1640  <x:anchor-alias value="time-of-day"/>
1641  <x:anchor-alias value="hour"/>
1642  <x:anchor-alias value="minute"/>
1643  <x:anchor-alias value="second"/>
1644  <x:anchor-alias value="day-name"/>
1645  <x:anchor-alias value="day"/>
1646  <x:anchor-alias value="month"/>
1647  <x:anchor-alias value="year"/>
1648  <x:anchor-alias value="GMT"/>
1649  Preferred format:
1650</t>
1651<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"/>
1652  <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>
1653
1654  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1655               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1656               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1657               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1658               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1659               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1660               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1661               
1662  <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>
1663               ; e.g., 02 Jun 1982
1664
1665  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1666  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1667               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1668               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1669               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1670               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1671               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1672               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1673               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1674               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1675               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1676               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1677               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1678  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1679
1680  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1681
1682  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1683                 ; 00:00:00 - 23:59:59
1684                 
1685  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1686  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1687  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1688</artwork></figure>
1689<t>
1690  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1691  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1692  same as those defined for the RFC 5322 constructs
1693  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1694</t>
1695<t anchor="obsolete.date.formats">
1696  <x:anchor-alias value="obs-date"/>
1697  <x:anchor-alias value="rfc850-date"/>
1698  <x:anchor-alias value="asctime-date"/>
1699  <x:anchor-alias value="date1"/>
1700  <x:anchor-alias value="date2"/>
1701  <x:anchor-alias value="date3"/>
1702  <x:anchor-alias value="rfc1123-date"/>
1703  <x:anchor-alias value="day-name-l"/>
1704  Obsolete formats:
1705</t>
1706<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1707  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1708</artwork></figure>
1709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1710  <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>
1711  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1712                 ; day-month-year (e.g., 02-Jun-82)
1713
1714  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1715         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1716         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1717         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1718         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1719         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1720         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1721</artwork></figure>
1722<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1723  <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>
1724  <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> ))
1725                 ; month day (e.g., Jun  2)
1726</artwork></figure>
1727<x:note>
1728  <t>
1729    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1730    accepting date values that may have been sent by non-HTTP
1731    applications, as is sometimes the case when retrieving or posting
1732    messages via proxies/gateways to SMTP or NNTP.
1733  </t>
1734</x:note>
1735<x:note>
1736  <t>
1737    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1738    to their usage within the protocol stream. Clients and servers are
1739    not required to use these formats for user presentation, request
1740    logging, etc.
1741  </t>
1742</x:note>
1743</section>
1744
1745<section title="Transfer Codings" anchor="transfer.codings">
1746  <x:anchor-alias value="transfer-coding"/>
1747  <x:anchor-alias value="transfer-extension"/>
1748<t>
1749   Transfer-coding values are used to indicate an encoding
1750   transformation that has been, can be, or may need to be applied to an
1751   entity-body in order to ensure "safe transport" through the network.
1752   This differs from a content coding in that the transfer-coding is a
1753   property of the message, not of the original entity.
1754</t>
1755<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1756  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
1757  <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> )
1758</artwork></figure>
1759<t anchor="rule.parameter">
1760  <x:anchor-alias value="attribute"/>
1761  <x:anchor-alias value="transfer-parameter"/>
1762  <x:anchor-alias value="value"/>
1763   Parameters are in  the form of attribute/value pairs.
1764</t>
1765<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"/>
1766  <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>
1767  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1768  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1769</artwork></figure>
1770<t>
1771   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1772   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1773   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1774</t>
1775<t>
1776   Whenever a transfer-coding is applied to a message-body, the set of
1777   transfer-codings &MUST; include "chunked", unless the message indicates it
1778   is terminated by closing the connection. When the "chunked" transfer-coding
1779   is used, it &MUST; be the last transfer-coding applied to the
1780   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1781   than once to a message-body. These rules allow the recipient to
1782   determine the transfer-length of the message (<xref target="message.length"/>).
1783</t>
1784<t>
1785   Transfer-codings are analogous to the Content-Transfer-Encoding
1786   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1787   binary data over a 7-bit transport service. However, safe transport
1788   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1789   the only unsafe characteristic of message-bodies is the difficulty in
1790   determining the exact body length (<xref target="message.length"/>), or the desire to
1791   encrypt data over a shared transport.
1792</t>
1793<t>
1794   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1795   transfer-coding value tokens. Initially, the registry contains the
1796   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1797   "gzip", "compress", and "deflate" (&content-codings;).
1798</t>
1799<t>
1800   New transfer-coding value tokens &SHOULD; be registered in the same way
1801   as new content-coding value tokens (&content-codings;).
1802</t>
1803<t>
1804   A server which receives an entity-body with a transfer-coding it does
1805   not understand &SHOULD; return 501 (Not Implemented), and close the
1806   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1807   client.
1808</t>
1809
1810<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1811  <x:anchor-alias value="chunk"/>
1812  <x:anchor-alias value="Chunked-Body"/>
1813  <x:anchor-alias value="chunk-data"/>
1814  <x:anchor-alias value="chunk-ext"/>
1815  <x:anchor-alias value="chunk-ext-name"/>
1816  <x:anchor-alias value="chunk-ext-val"/>
1817  <x:anchor-alias value="chunk-size"/>
1818  <x:anchor-alias value="last-chunk"/>
1819  <x:anchor-alias value="trailer-part"/>
1820<t>
1821   The chunked encoding modifies the body of a message in order to
1822   transfer it as a series of chunks, each with its own size indicator,
1823   followed by an &OPTIONAL; trailer containing entity-header fields. This
1824   allows dynamically produced content to be transferred along with the
1825   information necessary for the recipient to verify that it has
1826   received the full message.
1827</t>
1828<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"/>
1829  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1830                   <x:ref>last-chunk</x:ref>
1831                   <x:ref>trailer-part</x:ref>
1832                   <x:ref>CRLF</x:ref>
1833 
1834  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1835                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1836  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1837  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1838 
1839  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1840                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1841  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1842  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1843  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1844  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1845</artwork></figure>
1846<t>
1847   The chunk-size field is a string of hex digits indicating the size of
1848   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1849   zero, followed by the trailer, which is terminated by an empty line.
1850</t>
1851<t>
1852   The trailer allows the sender to include additional HTTP header
1853   fields at the end of the message. The Trailer header field can be
1854   used to indicate which header fields are included in a trailer (see
1855   <xref target="header.trailer"/>).
1856</t>
1857<t>
1858   A server using chunked transfer-coding in a response &MUST-NOT; use the
1859   trailer for any header fields unless at least one of the following is
1860   true:
1861  <list style="numbers">
1862    <t>the request included a TE header field that indicates "trailers" is
1863     acceptable in the transfer-coding of the  response, as described in
1864     <xref target="header.te"/>; or,</t>
1865
1866    <t>the server is the origin server for the response, the trailer
1867     fields consist entirely of optional metadata, and the recipient
1868     could use the message (in a manner acceptable to the origin server)
1869     without receiving this metadata.  In other words, the origin server
1870     is willing to accept the possibility that the trailer fields might
1871     be silently discarded along the path to the client.</t>
1872  </list>
1873</t>
1874<t>
1875   This requirement prevents an interoperability failure when the
1876   message is being received by an HTTP/1.1 (or later) proxy and
1877   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1878   compliance with the protocol would have necessitated a possibly
1879   infinite buffer on the proxy.
1880</t>
1881<t>
1882   A process for decoding the "chunked" transfer-coding
1883   can be represented in pseudo-code as:
1884</t>
1885<figure><artwork type="code">
1886  length := 0
1887  read chunk-size, chunk-ext (if any) and CRLF
1888  while (chunk-size &gt; 0) {
1889     read chunk-data and CRLF
1890     append chunk-data to entity-body
1891     length := length + chunk-size
1892     read chunk-size and CRLF
1893  }
1894  read entity-header
1895  while (entity-header not empty) {
1896     append entity-header to existing header fields
1897     read entity-header
1898  }
1899  Content-Length := length
1900  Remove "chunked" from Transfer-Encoding
1901</artwork></figure>
1902<t>
1903   All HTTP/1.1 applications &MUST; be able to receive and decode the
1904   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1905   they do not understand.
1906</t>
1907</section>
1908</section>
1909
1910<section title="Product Tokens" anchor="product.tokens">
1911  <x:anchor-alias value="product"/>
1912  <x:anchor-alias value="product-version"/>
1913<t>
1914   Product tokens are used to allow communicating applications to
1915   identify themselves by software name and version. Most fields using
1916   product tokens also allow sub-products which form a significant part
1917   of the application to be listed, separated by whitespace. By
1918   convention, the products are listed in order of their significance
1919   for identifying the application.
1920</t>
1921<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1922  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1923  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1924</artwork></figure>
1925<t>
1926   Examples:
1927</t>
1928<figure><artwork type="example">
1929  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1930  Server: Apache/0.8.4
1931</artwork></figure>
1932<t>
1933   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1934   used for advertising or other non-essential information. Although any
1935   token character &MAY; appear in a product-version, this token &SHOULD;
1936   only be used for a version identifier (i.e., successive versions of
1937   the same product &SHOULD; only differ in the product-version portion of
1938   the product value).
1939</t>
1940</section>
1941
1942<section title="Quality Values" anchor="quality.values">
1943  <x:anchor-alias value="qvalue"/>
1944<t>
1945   Both transfer codings (TE request header, <xref target="header.te"/>)
1946   and content negotiation (&content.negotiation;) use short "floating point"
1947   numbers to indicate the relative importance ("weight") of various
1948   negotiable parameters.  A weight is normalized to a real number in
1949   the range 0 through 1, where 0 is the minimum and 1 the maximum
1950   value. If a parameter has a quality value of 0, then content with
1951   this parameter is `not acceptable' for the client. HTTP/1.1
1952   applications &MUST-NOT; generate more than three digits after the
1953   decimal point. User configuration of these values &SHOULD; also be
1954   limited in this fashion.
1955</t>
1956<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1957  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1958                 / ( "1" [ "." 0*3("0") ] )
1959</artwork></figure>
1960<x:note>
1961  <t>
1962     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1963     relative degradation in desired quality.
1964  </t>
1965</x:note>
1966</section>
1967
1968</section>
1969
1970<section title="Connections" anchor="connections">
1971
1972<section title="Persistent Connections" anchor="persistent.connections">
1973
1974<section title="Purpose" anchor="persistent.purpose">
1975<t>
1976   Prior to persistent connections, a separate TCP connection was
1977   established to fetch each URL, increasing the load on HTTP servers
1978   and causing congestion on the Internet. The use of inline images and
1979   other associated data often require a client to make multiple
1980   requests of the same server in a short amount of time. Analysis of
1981   these performance problems and results from a prototype
1982   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1983   measurements of actual HTTP/1.1 implementations show good
1984   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1985   T/TCP <xref target="Tou1998"/>.
1986</t>
1987<t>
1988   Persistent HTTP connections have a number of advantages:
1989  <list style="symbols">
1990      <t>
1991        By opening and closing fewer TCP connections, CPU time is saved
1992        in routers and hosts (clients, servers, proxies, gateways,
1993        tunnels, or caches), and memory used for TCP protocol control
1994        blocks can be saved in hosts.
1995      </t>
1996      <t>
1997        HTTP requests and responses can be pipelined on a connection.
1998        Pipelining allows a client to make multiple requests without
1999        waiting for each response, allowing a single TCP connection to
2000        be used much more efficiently, with much lower elapsed time.
2001      </t>
2002      <t>
2003        Network congestion is reduced by reducing the number of packets
2004        caused by TCP opens, and by allowing TCP sufficient time to
2005        determine the congestion state of the network.
2006      </t>
2007      <t>
2008        Latency on subsequent requests is reduced since there is no time
2009        spent in TCP's connection opening handshake.
2010      </t>
2011      <t>
2012        HTTP can evolve more gracefully, since errors can be reported
2013        without the penalty of closing the TCP connection. Clients using
2014        future versions of HTTP might optimistically try a new feature,
2015        but if communicating with an older server, retry with old
2016        semantics after an error is reported.
2017      </t>
2018    </list>
2019</t>
2020<t>
2021   HTTP implementations &SHOULD; implement persistent connections.
2022</t>
2023</section>
2024
2025<section title="Overall Operation" anchor="persistent.overall">
2026<t>
2027   A significant difference between HTTP/1.1 and earlier versions of
2028   HTTP is that persistent connections are the default behavior of any
2029   HTTP connection. That is, unless otherwise indicated, the client
2030   &SHOULD; assume that the server will maintain a persistent connection,
2031   even after error responses from the server.
2032</t>
2033<t>
2034   Persistent connections provide a mechanism by which a client and a
2035   server can signal the close of a TCP connection. This signaling takes
2036   place using the Connection header field (<xref target="header.connection"/>). Once a close
2037   has been signaled, the client &MUST-NOT; send any more requests on that
2038   connection.
2039</t>
2040
2041<section title="Negotiation" anchor="persistent.negotiation">
2042<t>
2043   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2044   maintain a persistent connection unless a Connection header including
2045   the connection-token "close" was sent in the request. If the server
2046   chooses to close the connection immediately after sending the
2047   response, it &SHOULD; send a Connection header including the
2048   connection-token close.
2049</t>
2050<t>
2051   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2052   decide to keep it open based on whether the response from a server
2053   contains a Connection header with the connection-token close. In case
2054   the client does not want to maintain a connection for more than that
2055   request, it &SHOULD; send a Connection header including the
2056   connection-token close.
2057</t>
2058<t>
2059   If either the client or the server sends the close token in the
2060   Connection header, that request becomes the last one for the
2061   connection.
2062</t>
2063<t>
2064   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2065   maintained for HTTP versions less than 1.1 unless it is explicitly
2066   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2067   compatibility with HTTP/1.0 clients.
2068</t>
2069<t>
2070   In order to remain persistent, all messages on the connection &MUST;
2071   have a self-defined message length (i.e., one not defined by closure
2072   of the connection), as described in <xref target="message.length"/>.
2073</t>
2074</section>
2075
2076<section title="Pipelining" anchor="pipelining">
2077<t>
2078   A client that supports persistent connections &MAY; "pipeline" its
2079   requests (i.e., send multiple requests without waiting for each
2080   response). A server &MUST; send its responses to those requests in the
2081   same order that the requests were received.
2082</t>
2083<t>
2084   Clients which assume persistent connections and pipeline immediately
2085   after connection establishment &SHOULD; be prepared to retry their
2086   connection if the first pipelined attempt fails. If a client does
2087   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2088   persistent. Clients &MUST; also be prepared to resend their requests if
2089   the server closes the connection before sending all of the
2090   corresponding responses.
2091</t>
2092<t>
2093   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2094   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2095   premature termination of the transport connection could lead to
2096   indeterminate results. A client wishing to send a non-idempotent
2097   request &SHOULD; wait to send that request until it has received the
2098   response status for the previous request.
2099</t>
2100</section>
2101</section>
2102
2103<section title="Proxy Servers" anchor="persistent.proxy">
2104<t>
2105   It is especially important that proxies correctly implement the
2106   properties of the Connection header field as specified in <xref target="header.connection"/>.
2107</t>
2108<t>
2109   The proxy server &MUST; signal persistent connections separately with
2110   its clients and the origin servers (or other proxy servers) that it
2111   connects to. Each persistent connection applies to only one transport
2112   link.
2113</t>
2114<t>
2115   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2116   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2117   for information and discussion of the problems with the Keep-Alive header
2118   implemented by many HTTP/1.0 clients).
2119</t>
2120</section>
2121
2122<section title="Practical Considerations" anchor="persistent.practical">
2123<t>
2124   Servers will usually have some time-out value beyond which they will
2125   no longer maintain an inactive connection. Proxy servers might make
2126   this a higher value since it is likely that the client will be making
2127   more connections through the same server. The use of persistent
2128   connections places no requirements on the length (or existence) of
2129   this time-out for either the client or the server.
2130</t>
2131<t>
2132   When a client or server wishes to time-out it &SHOULD; issue a graceful
2133   close on the transport connection. Clients and servers &SHOULD; both
2134   constantly watch for the other side of the transport close, and
2135   respond to it as appropriate. If a client or server does not detect
2136   the other side's close promptly it could cause unnecessary resource
2137   drain on the network.
2138</t>
2139<t>
2140   A client, server, or proxy &MAY; close the transport connection at any
2141   time. For example, a client might have started to send a new request
2142   at the same time that the server has decided to close the "idle"
2143   connection. From the server's point of view, the connection is being
2144   closed while it was idle, but from the client's point of view, a
2145   request is in progress.
2146</t>
2147<t>
2148   This means that clients, servers, and proxies &MUST; be able to recover
2149   from asynchronous close events. Client software &SHOULD; reopen the
2150   transport connection and retransmit the aborted sequence of requests
2151   without user interaction so long as the request sequence is
2152   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2153   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2154   human operator the choice of retrying the request(s). Confirmation by
2155   user-agent software with semantic understanding of the application
2156   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2157   be repeated if the second sequence of requests fails.
2158</t>
2159<t>
2160   Servers &SHOULD; always respond to at least one request per connection,
2161   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2162   middle of transmitting a response, unless a network or client failure
2163   is suspected.
2164</t>
2165<t>
2166   Clients that use persistent connections &SHOULD; limit the number of
2167   simultaneous connections that they maintain to a given server. A
2168   single-user client &SHOULD-NOT; maintain more than 2 connections with
2169   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2170   another server or proxy, where N is the number of simultaneously
2171   active users. These guidelines are intended to improve HTTP response
2172   times and avoid congestion.
2173</t>
2174</section>
2175</section>
2176
2177<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2178
2179<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2180<t>
2181   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2182   flow control mechanisms to resolve temporary overloads, rather than
2183   terminating connections with the expectation that clients will retry.
2184   The latter technique can exacerbate network congestion.
2185</t>
2186</section>
2187
2188<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2189<t>
2190   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2191   the network connection for an error status while it is transmitting
2192   the request. If the client sees an error status, it &SHOULD;
2193   immediately cease transmitting the body. If the body is being sent
2194   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2195   empty trailer &MAY; be used to prematurely mark the end of the message.
2196   If the body was preceded by a Content-Length header, the client &MUST;
2197   close the connection.
2198</t>
2199</section>
2200
2201<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2202<t>
2203   The purpose of the 100 (Continue) status (see &status-100;) is to
2204   allow a client that is sending a request message with a request body
2205   to determine if the origin server is willing to accept the request
2206   (based on the request headers) before the client sends the request
2207   body. In some cases, it might either be inappropriate or highly
2208   inefficient for the client to send the body if the server will reject
2209   the message without looking at the body.
2210</t>
2211<t>
2212   Requirements for HTTP/1.1 clients:
2213  <list style="symbols">
2214    <t>
2215        If a client will wait for a 100 (Continue) response before
2216        sending the request body, it &MUST; send an Expect request-header
2217        field (&header-expect;) with the "100-continue" expectation.
2218    </t>
2219    <t>
2220        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2221        with the "100-continue" expectation if it does not intend
2222        to send a request body.
2223    </t>
2224  </list>
2225</t>
2226<t>
2227   Because of the presence of older implementations, the protocol allows
2228   ambiguous situations in which a client may send "Expect: 100-continue"
2229   without receiving either a 417 (Expectation Failed) status
2230   or a 100 (Continue) status. Therefore, when a client sends this
2231   header field to an origin server (possibly via a proxy) from which it
2232   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2233   for an indefinite period before sending the request body.
2234</t>
2235<t>
2236   Requirements for HTTP/1.1 origin servers:
2237  <list style="symbols">
2238    <t> Upon receiving a request which includes an Expect request-header
2239        field with the "100-continue" expectation, an origin server &MUST;
2240        either respond with 100 (Continue) status and continue to read
2241        from the input stream, or respond with a final status code. The
2242        origin server &MUST-NOT; wait for the request body before sending
2243        the 100 (Continue) response. If it responds with a final status
2244        code, it &MAY; close the transport connection or it &MAY; continue
2245        to read and discard the rest of the request.  It &MUST-NOT;
2246        perform the requested method if it returns a final status code.
2247    </t>
2248    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2249        the request message does not include an Expect request-header
2250        field with the "100-continue" expectation, and &MUST-NOT; send a
2251        100 (Continue) response if such a request comes from an HTTP/1.0
2252        (or earlier) client. There is an exception to this rule: for
2253        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2254        status in response to an HTTP/1.1 PUT or POST request that does
2255        not include an Expect request-header field with the "100-continue"
2256        expectation. This exception, the purpose of which is
2257        to minimize any client processing delays associated with an
2258        undeclared wait for 100 (Continue) status, applies only to
2259        HTTP/1.1 requests, and not to requests with any other HTTP-version
2260        value.
2261    </t>
2262    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2263        already received some or all of the request body for the
2264        corresponding request.
2265    </t>
2266    <t> An origin server that sends a 100 (Continue) response &MUST;
2267    ultimately send a final status code, once the request body is
2268        received and processed, unless it terminates the transport
2269        connection prematurely.
2270    </t>
2271    <t> If an origin server receives a request that does not include an
2272        Expect request-header field with the "100-continue" expectation,
2273        the request includes a request body, and the server responds
2274        with a final status code before reading the entire request body
2275        from the transport connection, then the server &SHOULD-NOT;  close
2276        the transport connection until it has read the entire request,
2277        or until the client closes the connection. Otherwise, the client
2278        might not reliably receive the response message. However, this
2279        requirement is not be construed as preventing a server from
2280        defending itself against denial-of-service attacks, or from
2281        badly broken client implementations.
2282      </t>
2283    </list>
2284</t>
2285<t>
2286   Requirements for HTTP/1.1 proxies:
2287  <list style="symbols">
2288    <t> If a proxy receives a request that includes an Expect request-header
2289        field with the "100-continue" expectation, and the proxy
2290        either knows that the next-hop server complies with HTTP/1.1 or
2291        higher, or does not know the HTTP version of the next-hop
2292        server, it &MUST; forward the request, including the Expect header
2293        field.
2294    </t>
2295    <t> If the proxy knows that the version of the next-hop server is
2296        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2297        respond with a 417 (Expectation Failed) status.
2298    </t>
2299    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2300        numbers received from recently-referenced next-hop servers.
2301    </t>
2302    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2303        request message was received from an HTTP/1.0 (or earlier)
2304        client and did not include an Expect request-header field with
2305        the "100-continue" expectation. This requirement overrides the
2306        general rule for forwarding of 1xx responses (see &status-1xx;).
2307    </t>
2308  </list>
2309</t>
2310</section>
2311
2312<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2313<t>
2314   If an HTTP/1.1 client sends a request which includes a request body,
2315   but which does not include an Expect request-header field with the
2316   "100-continue" expectation, and if the client is not directly
2317   connected to an HTTP/1.1 origin server, and if the client sees the
2318   connection close before receiving any status from the server, the
2319   client &SHOULD; retry the request.  If the client does retry this
2320   request, it &MAY; use the following "binary exponential backoff"
2321   algorithm to be assured of obtaining a reliable response:
2322  <list style="numbers">
2323    <t>
2324      Initiate a new connection to the server
2325    </t>
2326    <t>
2327      Transmit the request-headers
2328    </t>
2329    <t>
2330      Initialize a variable R to the estimated round-trip time to the
2331         server (e.g., based on the time it took to establish the
2332         connection), or to a constant value of 5 seconds if the round-trip
2333         time is not available.
2334    </t>
2335    <t>
2336       Compute T = R * (2**N), where N is the number of previous
2337         retries of this request.
2338    </t>
2339    <t>
2340       Wait either for an error response from the server, or for T
2341         seconds (whichever comes first)
2342    </t>
2343    <t>
2344       If no error response is received, after T seconds transmit the
2345         body of the request.
2346    </t>
2347    <t>
2348       If client sees that the connection is closed prematurely,
2349         repeat from step 1 until the request is accepted, an error
2350         response is received, or the user becomes impatient and
2351         terminates the retry process.
2352    </t>
2353  </list>
2354</t>
2355<t>
2356   If at any point an error status is received, the client
2357  <list style="symbols">
2358      <t>&SHOULD-NOT;  continue and</t>
2359
2360      <t>&SHOULD; close the connection if it has not completed sending the
2361        request message.</t>
2362    </list>
2363</t>
2364</section>
2365</section>
2366</section>
2367
2368
2369<section title="Header Field Definitions" anchor="header.fields">
2370<t>
2371   This section defines the syntax and semantics of HTTP/1.1 header fields
2372   related to message framing and transport protocols.
2373</t>
2374<t>
2375   For entity-header fields, both sender and recipient refer to either the
2376   client or the server, depending on who sends and who receives the entity.
2377</t>
2378
2379<section title="Connection" anchor="header.connection">
2380  <iref primary="true" item="Connection header" x:for-anchor=""/>
2381  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2382  <x:anchor-alias value="Connection"/>
2383  <x:anchor-alias value="connection-token"/>
2384  <x:anchor-alias value="Connection-v"/>
2385<t>
2386   The general-header field "Connection" allows the sender to specify
2387   options that are desired for that particular connection and &MUST-NOT;
2388   be communicated by proxies over further connections.
2389</t>
2390<t>
2391   The Connection header's value has the following grammar:
2392</t>
2393<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"/>
2394  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2395  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2396  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2397</artwork></figure>
2398<t>
2399   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2400   message is forwarded and, for each connection-token in this field,
2401   remove any header field(s) from the message with the same name as the
2402   connection-token. Connection options are signaled by the presence of
2403   a connection-token in the Connection header field, not by any
2404   corresponding additional header field(s), since the additional header
2405   field may not be sent if there are no parameters associated with that
2406   connection option.
2407</t>
2408<t>
2409   Message headers listed in the Connection header &MUST-NOT; include
2410   end-to-end headers, such as Cache-Control.
2411</t>
2412<t>
2413   HTTP/1.1 defines the "close" connection option for the sender to
2414   signal that the connection will be closed after completion of the
2415   response. For example,
2416</t>
2417<figure><artwork type="example">
2418  Connection: close
2419</artwork></figure>
2420<t>
2421   in either the request or the response header fields indicates that
2422   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2423   after the current request/response is complete.
2424</t>
2425<t>
2426   An HTTP/1.1 client that does not support persistent connections &MUST;
2427   include the "close" connection option in every request message.
2428</t>
2429<t>
2430   An HTTP/1.1 server that does not support persistent connections &MUST;
2431   include the "close" connection option in every response message that
2432   does not have a 1xx (informational) status code.
2433</t>
2434<t>
2435   A system receiving an HTTP/1.0 (or lower-version) message that
2436   includes a Connection header &MUST;, for each connection-token in this
2437   field, remove and ignore any header field(s) from the message with
2438   the same name as the connection-token. This protects against mistaken
2439   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2440</t>
2441</section>
2442
2443<section title="Content-Length" anchor="header.content-length">
2444  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2445  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2446  <x:anchor-alias value="Content-Length"/>
2447  <x:anchor-alias value="Content-Length-v"/>
2448<t>
2449   The entity-header field "Content-Length" indicates the size of the
2450   entity-body, in number of OCTETs, sent to the recipient or,
2451   in the case of the HEAD method, the size of the entity-body that
2452   would have been sent had the request been a GET.
2453</t>
2454<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2455  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2456  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2457</artwork></figure>
2458<t>
2459   An example is
2460</t>
2461<figure><artwork type="example">
2462  Content-Length: 3495
2463</artwork></figure>
2464<t>
2465   Applications &SHOULD; use this field to indicate the transfer-length of
2466   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2467</t>
2468<t>
2469   Any Content-Length greater than or equal to zero is a valid value.
2470   <xref target="message.length"/> describes how to determine the length of a message-body
2471   if a Content-Length is not given.
2472</t>
2473<t>
2474   Note that the meaning of this field is significantly different from
2475   the corresponding definition in MIME, where it is an optional field
2476   used within the "message/external-body" content-type. In HTTP, it
2477   &SHOULD; be sent whenever the message's length can be determined prior
2478   to being transferred, unless this is prohibited by the rules in
2479   <xref target="message.length"/>.
2480</t>
2481</section>
2482
2483<section title="Date" anchor="header.date">
2484  <iref primary="true" item="Date header" x:for-anchor=""/>
2485  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2486  <x:anchor-alias value="Date"/>
2487  <x:anchor-alias value="Date-v"/>
2488<t>
2489   The general-header field "Date" represents the date and time at which
2490   the message was originated, having the same semantics as orig-date in
2491   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2492   HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2493   it &MUST; be sent in rfc1123-date format.
2494</t>
2495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2496  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2497  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2498</artwork></figure>
2499<t>
2500   An example is
2501</t>
2502<figure><artwork type="example">
2503  Date: Tue, 15 Nov 1994 08:12:31 GMT
2504</artwork></figure>
2505<t>
2506   Origin servers &MUST; include a Date header field in all responses,
2507   except in these cases:
2508  <list style="numbers">
2509      <t>If the response status code is 100 (Continue) or 101 (Switching
2510         Protocols), the response &MAY; include a Date header field, at
2511         the server's option.</t>
2512
2513      <t>If the response status code conveys a server error, e.g. 500
2514         (Internal Server Error) or 503 (Service Unavailable), and it is
2515         inconvenient or impossible to generate a valid Date.</t>
2516
2517      <t>If the server does not have a clock that can provide a
2518         reasonable approximation of the current time, its responses
2519         &MUST-NOT; include a Date header field. In this case, the rules
2520         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2521  </list>
2522</t>
2523<t>
2524   A received message that does not have a Date header field &MUST; be
2525   assigned one by the recipient if the message will be cached by that
2526   recipient or gatewayed via a protocol which requires a Date. An HTTP
2527   implementation without a clock &MUST-NOT; cache responses without
2528   revalidating them on every use. An HTTP cache, especially a shared
2529   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2530   clock with a reliable external standard.
2531</t>
2532<t>
2533   Clients &SHOULD; only send a Date header field in messages that include
2534   an entity-body, as in the case of the PUT and POST requests, and even
2535   then it is optional. A client without a clock &MUST-NOT; send a Date
2536   header field in a request.
2537</t>
2538<t>
2539   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2540   time subsequent to the generation of the message. It &SHOULD; represent
2541   the best available approximation of the date and time of message
2542   generation, unless the implementation has no means of generating a
2543   reasonably accurate date and time. In theory, the date ought to
2544   represent the moment just before the entity is generated. In
2545   practice, the date can be generated at any time during the message
2546   origination without affecting its semantic value.
2547</t>
2548
2549<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2550<t>
2551   Some origin server implementations might not have a clock available.
2552   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2553   values to a response, unless these values were associated
2554   with the resource by a system or user with a reliable clock. It &MAY;
2555   assign an Expires value that is known, at or before server
2556   configuration time, to be in the past (this allows "pre-expiration"
2557   of responses without storing separate Expires values for each
2558   resource).
2559</t>
2560</section>
2561</section>
2562
2563<section title="Host" anchor="header.host">
2564  <iref primary="true" item="Host header" x:for-anchor=""/>
2565  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2566  <x:anchor-alias value="Host"/>
2567  <x:anchor-alias value="Host-v"/>
2568<t>
2569   The request-header field "Host" specifies the Internet host and port
2570   number of the resource being requested, as obtained from the original
2571   URI given by the user or referring resource (generally an http URI,
2572   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2573   the naming authority of the origin server or gateway given by the
2574   original URL. This allows the origin server or gateway to
2575   differentiate between internally-ambiguous URLs, such as the root "/"
2576   URL of a server for multiple host names on a single IP address.
2577</t>
2578<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2579  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2580  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2581</artwork></figure>
2582<t>
2583   A "host" without any trailing port information implies the default
2584   port for the service requested (e.g., "80" for an HTTP URL). For
2585   example, a request on the origin server for
2586   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2587</t>
2588<figure><artwork type="example">
2589  GET /pub/WWW/ HTTP/1.1
2590  Host: www.example.org
2591</artwork></figure>
2592<t>
2593   A client &MUST; include a Host header field in all HTTP/1.1 request
2594   messages. If the requested URI does not include an Internet host
2595   name for the service being requested, then the Host header field &MUST;
2596   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2597   request message it forwards does contain an appropriate Host header
2598   field that identifies the service being requested by the proxy. All
2599   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2600   status code to any HTTP/1.1 request message which lacks a Host header
2601   field.
2602</t>
2603<t>
2604   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2605   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2606   for other requirements relating to Host.
2607</t>
2608</section>
2609
2610<section title="TE" anchor="header.te">
2611  <iref primary="true" item="TE header" x:for-anchor=""/>
2612  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2613  <x:anchor-alias value="TE"/>
2614  <x:anchor-alias value="TE-v"/>
2615  <x:anchor-alias value="t-codings"/>
2616  <x:anchor-alias value="te-params"/>
2617  <x:anchor-alias value="te-ext"/>
2618<t>
2619   The request-header field "TE" indicates what extension transfer-codings
2620   it is willing to accept in the response and whether or not it is
2621   willing to accept trailer fields in a chunked transfer-coding. Its
2622   value may consist of the keyword "trailers" and/or a comma-separated
2623   list of extension transfer-coding names with optional accept
2624   parameters (as described in <xref target="transfer.codings"/>).
2625</t>
2626<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"/>
2627  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2628  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2629  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2630  <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> )
2631  <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> ) ]
2632</artwork></figure>
2633<t>
2634   The presence of the keyword "trailers" indicates that the client is
2635   willing to accept trailer fields in a chunked transfer-coding, as
2636   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2637   transfer-coding values even though it does not itself represent a
2638   transfer-coding.
2639</t>
2640<t>
2641   Examples of its use are:
2642</t>
2643<figure><artwork type="example">
2644  TE: deflate
2645  TE:
2646  TE: trailers, deflate;q=0.5
2647</artwork></figure>
2648<t>
2649   The TE header field only applies to the immediate connection.
2650   Therefore, the keyword &MUST; be supplied within a Connection header
2651   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2652</t>
2653<t>
2654   A server tests whether a transfer-coding is acceptable, according to
2655   a TE field, using these rules:
2656  <list style="numbers">
2657    <x:lt>
2658      <t>The "chunked" transfer-coding is always acceptable. If the
2659         keyword "trailers" is listed, the client indicates that it is
2660         willing to accept trailer fields in the chunked response on
2661         behalf of itself and any downstream clients. The implication is
2662         that, if given, the client is stating that either all
2663         downstream clients are willing to accept trailer fields in the
2664         forwarded response, or that it will attempt to buffer the
2665         response on behalf of downstream recipients.
2666      </t><t>
2667         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2668         chunked response such that a client can be assured of buffering
2669         the entire response.</t>
2670    </x:lt>
2671    <x:lt>
2672      <t>If the transfer-coding being tested is one of the transfer-codings
2673         listed in the TE field, then it is acceptable unless it
2674         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2675         qvalue of 0 means "not acceptable.")</t>
2676    </x:lt>
2677    <x:lt>
2678      <t>If multiple transfer-codings are acceptable, then the
2679         acceptable transfer-coding with the highest non-zero qvalue is
2680         preferred.  The "chunked" transfer-coding always has a qvalue
2681         of 1.</t>
2682    </x:lt>
2683  </list>
2684</t>
2685<t>
2686   If the TE field-value is empty or if no TE field is present, the only
2687   transfer-coding is "chunked". A message with no transfer-coding is
2688   always acceptable.
2689</t>
2690</section>
2691
2692<section title="Trailer" anchor="header.trailer">
2693  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2694  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2695  <x:anchor-alias value="Trailer"/>
2696  <x:anchor-alias value="Trailer-v"/>
2697<t>
2698   The general field "Trailer" indicates that the given set of
2699   header fields is present in the trailer of a message encoded with
2700   chunked transfer-coding.
2701</t>
2702<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2703  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2704  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2705</artwork></figure>
2706<t>
2707   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2708   message using chunked transfer-coding with a non-empty trailer. Doing
2709   so allows the recipient to know which header fields to expect in the
2710   trailer.
2711</t>
2712<t>
2713   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2714   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2715   trailer fields in a "chunked" transfer-coding.
2716</t>
2717<t>
2718   Message header fields listed in the Trailer header field &MUST-NOT;
2719   include the following header fields:
2720  <list style="symbols">
2721    <t>Transfer-Encoding</t>
2722    <t>Content-Length</t>
2723    <t>Trailer</t>
2724  </list>
2725</t>
2726</section>
2727
2728<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2729  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2730  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2731  <x:anchor-alias value="Transfer-Encoding"/>
2732  <x:anchor-alias value="Transfer-Encoding-v"/>
2733<t>
2734   The general-header "Transfer-Encoding" field indicates what (if any)
2735   type of transformation has been applied to the message body in order
2736   to safely transfer it between the sender and the recipient. This
2737   differs from the content-coding in that the transfer-coding is a
2738   property of the message, not of the entity.
2739</t>
2740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2741  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2742                        <x:ref>Transfer-Encoding-v</x:ref>
2743  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2744</artwork></figure>
2745<t>
2746   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2747</t>
2748<figure><artwork type="example">
2749  Transfer-Encoding: chunked
2750</artwork></figure>
2751<t>
2752   If multiple encodings have been applied to an entity, the transfer-codings
2753   &MUST; be listed in the order in which they were applied.
2754   Additional information about the encoding parameters &MAY; be provided
2755   by other entity-header fields not defined by this specification.
2756</t>
2757<t>
2758   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2759   header.
2760</t>
2761</section>
2762
2763<section title="Upgrade" anchor="header.upgrade">
2764  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2765  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2766  <x:anchor-alias value="Upgrade"/>
2767  <x:anchor-alias value="Upgrade-v"/>
2768<t>
2769   The general-header "Upgrade" allows the client to specify what
2770   additional communication protocols it supports and would like to use
2771   if the server finds it appropriate to switch protocols. The server
2772   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2773   response to indicate which protocol(s) are being switched.
2774</t>
2775<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2776  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2777  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2778</artwork></figure>
2779<t>
2780   For example,
2781</t>
2782<figure><artwork type="example">
2783  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2784</artwork></figure>
2785<t>
2786   The Upgrade header field is intended to provide a simple mechanism
2787   for transition from HTTP/1.1 to some other, incompatible protocol. It
2788   does so by allowing the client to advertise its desire to use another
2789   protocol, such as a later version of HTTP with a higher major version
2790   number, even though the current request has been made using HTTP/1.1.
2791   This eases the difficult transition between incompatible protocols by
2792   allowing the client to initiate a request in the more commonly
2793   supported protocol while indicating to the server that it would like
2794   to use a "better" protocol if available (where "better" is determined
2795   by the server, possibly according to the nature of the method and/or
2796   resource being requested).
2797</t>
2798<t>
2799   The Upgrade header field only applies to switching application-layer
2800   protocols upon the existing transport-layer connection. Upgrade
2801   cannot be used to insist on a protocol change; its acceptance and use
2802   by the server is optional. The capabilities and nature of the
2803   application-layer communication after the protocol change is entirely
2804   dependent upon the new protocol chosen, although the first action
2805   after changing the protocol &MUST; be a response to the initial HTTP
2806   request containing the Upgrade header field.
2807</t>
2808<t>
2809   The Upgrade header field only applies to the immediate connection.
2810   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2811   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2812   HTTP/1.1 message.
2813</t>
2814<t>
2815   The Upgrade header field cannot be used to indicate a switch to a
2816   protocol on a different connection. For that purpose, it is more
2817   appropriate to use a 301, 302, 303, or 305 redirection response.
2818</t>
2819<t>
2820   This specification only defines the protocol name "HTTP" for use by
2821   the family of Hypertext Transfer Protocols, as defined by the HTTP
2822   version rules of <xref target="http.version"/> and future updates to this
2823   specification. Any token can be used as a protocol name; however, it
2824   will only be useful if both the client and server associate the name
2825   with the same protocol.
2826</t>
2827</section>
2828
2829<section title="Via" anchor="header.via">
2830  <iref primary="true" item="Via header" x:for-anchor=""/>
2831  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2832  <x:anchor-alias value="protocol-name"/>
2833  <x:anchor-alias value="protocol-version"/>
2834  <x:anchor-alias value="pseudonym"/>
2835  <x:anchor-alias value="received-by"/>
2836  <x:anchor-alias value="received-protocol"/>
2837  <x:anchor-alias value="Via"/>
2838  <x:anchor-alias value="Via-v"/>
2839<t>
2840   The general-header field "Via" &MUST; be used by gateways and proxies to
2841   indicate the intermediate protocols and recipients between the user
2842   agent and the server on requests, and between the origin server and
2843   the client on responses. It is analogous to the "Received" field defined in
2844   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2845   avoiding request loops, and identifying the protocol capabilities of
2846   all senders along the request/response chain.
2847</t>
2848<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"/>
2849  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2850  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2851                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2852  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2853  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2854  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2855  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2856  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2857</artwork></figure>
2858<t>
2859   The received-protocol indicates the protocol version of the message
2860   received by the server or client along each segment of the
2861   request/response chain. The received-protocol version is appended to
2862   the Via field value when the message is forwarded so that information
2863   about the protocol capabilities of upstream applications remains
2864   visible to all recipients.
2865</t>
2866<t>
2867   The protocol-name is optional if and only if it would be "HTTP". The
2868   received-by field is normally the host and optional port number of a
2869   recipient server or client that subsequently forwarded the message.
2870   However, if the real host is considered to be sensitive information,
2871   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2872   be assumed to be the default port of the received-protocol.
2873</t>
2874<t>
2875   Multiple Via field values represents each proxy or gateway that has
2876   forwarded the message. Each recipient &MUST; append its information
2877   such that the end result is ordered according to the sequence of
2878   forwarding applications.
2879</t>
2880<t>
2881   Comments &MAY; be used in the Via header field to identify the software
2882   of the recipient proxy or gateway, analogous to the User-Agent and
2883   Server header fields. However, all comments in the Via field are
2884   optional and &MAY; be removed by any recipient prior to forwarding the
2885   message.
2886</t>
2887<t>
2888   For example, a request message could be sent from an HTTP/1.0 user
2889   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2890   forward the request to a public proxy at p.example.net, which completes
2891   the request by forwarding it to the origin server at www.example.com.
2892   The request received by www.example.com would then have the following
2893   Via header field:
2894</t>
2895<figure><artwork type="example">
2896  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2897</artwork></figure>
2898<t>
2899   Proxies and gateways used as a portal through a network firewall
2900   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2901   the firewall region. This information &SHOULD; only be propagated if
2902   explicitly enabled. If not enabled, the received-by host of any host
2903   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2904   for that host.
2905</t>
2906<t>
2907   For organizations that have strong privacy requirements for hiding
2908   internal structures, a proxy &MAY; combine an ordered subsequence of
2909   Via header field entries with identical received-protocol values into
2910   a single such entry. For example,
2911</t>
2912<figure><artwork type="example">
2913  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2914</artwork></figure>
2915<t>
2916        could be collapsed to
2917</t>
2918<figure><artwork type="example">
2919  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2920</artwork></figure>
2921<t>
2922   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2923   under the same organizational control and the hosts have already been
2924   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2925   have different received-protocol values.
2926</t>
2927</section>
2928
2929</section>
2930
2931<section title="IANA Considerations" anchor="IANA.considerations">
2932<section title="Message Header Registration" anchor="message.header.registration">
2933<t>
2934   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2935   with the permanent registrations below (see <xref target="RFC3864"/>):
2936</t>
2937<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2938<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2939   <ttcol>Header Field Name</ttcol>
2940   <ttcol>Protocol</ttcol>
2941   <ttcol>Status</ttcol>
2942   <ttcol>Reference</ttcol>
2943
2944   <c>Connection</c>
2945   <c>http</c>
2946   <c>standard</c>
2947   <c>
2948      <xref target="header.connection"/>
2949   </c>
2950   <c>Content-Length</c>
2951   <c>http</c>
2952   <c>standard</c>
2953   <c>
2954      <xref target="header.content-length"/>
2955   </c>
2956   <c>Date</c>
2957   <c>http</c>
2958   <c>standard</c>
2959   <c>
2960      <xref target="header.date"/>
2961   </c>
2962   <c>Host</c>
2963   <c>http</c>
2964   <c>standard</c>
2965   <c>
2966      <xref target="header.host"/>
2967   </c>
2968   <c>TE</c>
2969   <c>http</c>
2970   <c>standard</c>
2971   <c>
2972      <xref target="header.te"/>
2973   </c>
2974   <c>Trailer</c>
2975   <c>http</c>
2976   <c>standard</c>
2977   <c>
2978      <xref target="header.trailer"/>
2979   </c>
2980   <c>Transfer-Encoding</c>
2981   <c>http</c>
2982   <c>standard</c>
2983   <c>
2984      <xref target="header.transfer-encoding"/>
2985   </c>
2986   <c>Upgrade</c>
2987   <c>http</c>
2988   <c>standard</c>
2989   <c>
2990      <xref target="header.upgrade"/>
2991   </c>
2992   <c>Via</c>
2993   <c>http</c>
2994   <c>standard</c>
2995   <c>
2996      <xref target="header.via"/>
2997   </c>
2998</texttable>
2999<!--(END)-->
3000<t>
3001   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3002</t>
3003</section>
3004
3005<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3006<t>
3007   The entry for the "http" URI Scheme in the registry located at
3008   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3009   should be updated to point to <xref target="http.uri"/> of this document
3010   (see <xref target="RFC4395"/>).
3011</t>
3012</section>
3013
3014<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3015<t>
3016   This document serves as the specification for the Internet media types
3017   "message/http" and "application/http". The following is to be registered with
3018   IANA (see <xref target="RFC4288"/>).
3019</t>
3020<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3021<iref item="Media Type" subitem="message/http" primary="true"/>
3022<iref item="message/http Media Type" primary="true"/>
3023<t>
3024   The message/http type can be used to enclose a single HTTP request or
3025   response message, provided that it obeys the MIME restrictions for all
3026   "message" types regarding line length and encodings.
3027</t>
3028<t>
3029  <list style="hanging" x:indent="12em">
3030    <t hangText="Type name:">
3031      message
3032    </t>
3033    <t hangText="Subtype name:">
3034      http
3035    </t>
3036    <t hangText="Required parameters:">
3037      none
3038    </t>
3039    <t hangText="Optional parameters:">
3040      version, msgtype
3041      <list style="hanging">
3042        <t hangText="version:">
3043          The HTTP-Version number of the enclosed message
3044          (e.g., "1.1"). If not present, the version can be
3045          determined from the first line of the body.
3046        </t>
3047        <t hangText="msgtype:">
3048          The message type -- "request" or "response". If not
3049          present, the type can be determined from the first
3050          line of the body.
3051        </t>
3052      </list>
3053    </t>
3054    <t hangText="Encoding considerations:">
3055      only "7bit", "8bit", or "binary" are permitted
3056    </t>
3057    <t hangText="Security considerations:">
3058      none
3059    </t>
3060    <t hangText="Interoperability considerations:">
3061      none
3062    </t>
3063    <t hangText="Published specification:">
3064      This specification (see <xref target="internet.media.type.message.http"/>).
3065    </t>
3066    <t hangText="Applications that use this media type:">
3067    </t>
3068    <t hangText="Additional information:">
3069      <list style="hanging">
3070        <t hangText="Magic number(s):">none</t>
3071        <t hangText="File extension(s):">none</t>
3072        <t hangText="Macintosh file type code(s):">none</t>
3073      </list>
3074    </t>
3075    <t hangText="Person and email address to contact for further information:">
3076      See Authors Section.
3077    </t>
3078    <t hangText="Intended usage:">
3079      COMMON
3080    </t>
3081    <t hangText="Restrictions on usage:">
3082      none
3083    </t>
3084    <t hangText="Author/Change controller:">
3085      IESG
3086    </t>
3087  </list>
3088</t>
3089</section>
3090<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3091<iref item="Media Type" subitem="application/http" primary="true"/>
3092<iref item="application/http Media Type" primary="true"/>
3093<t>
3094   The application/http type can be used to enclose a pipeline of one or more
3095   HTTP request or response messages (not intermixed).
3096</t>
3097<t>
3098  <list style="hanging" x:indent="12em">
3099    <t hangText="Type name:">
3100      application
3101    </t>
3102    <t hangText="Subtype name:">
3103      http
3104    </t>
3105    <t hangText="Required parameters:">
3106      none
3107    </t>
3108    <t hangText="Optional parameters:">
3109      version, msgtype
3110      <list style="hanging">
3111        <t hangText="version:">
3112          The HTTP-Version number of the enclosed messages
3113          (e.g., "1.1"). If not present, the version can be
3114          determined from the first line of the body.
3115        </t>
3116        <t hangText="msgtype:">
3117          The message type -- "request" or "response". If not
3118          present, the type can be determined from the first
3119          line of the body.
3120        </t>
3121      </list>
3122    </t>
3123    <t hangText="Encoding considerations:">
3124      HTTP messages enclosed by this type
3125      are in "binary" format; use of an appropriate
3126      Content-Transfer-Encoding is required when
3127      transmitted via E-mail.
3128    </t>
3129    <t hangText="Security considerations:">
3130      none
3131    </t>
3132    <t hangText="Interoperability considerations:">
3133      none
3134    </t>
3135    <t hangText="Published specification:">
3136      This specification (see <xref target="internet.media.type.application.http"/>).
3137    </t>
3138    <t hangText="Applications that use this media type:">
3139    </t>
3140    <t hangText="Additional information:">
3141      <list style="hanging">
3142        <t hangText="Magic number(s):">none</t>
3143        <t hangText="File extension(s):">none</t>
3144        <t hangText="Macintosh file type code(s):">none</t>
3145      </list>
3146    </t>
3147    <t hangText="Person and email address to contact for further information:">
3148      See Authors Section.
3149    </t>
3150    <t hangText="Intended usage:">
3151      COMMON
3152    </t>
3153    <t hangText="Restrictions on usage:">
3154      none
3155    </t>
3156    <t hangText="Author/Change controller:">
3157      IESG
3158    </t>
3159  </list>
3160</t>
3161</section>
3162</section>
3163
3164</section>
3165
3166<section title="Security Considerations" anchor="security.considerations">
3167<t>
3168   This section is meant to inform application developers, information
3169   providers, and users of the security limitations in HTTP/1.1 as
3170   described by this document. The discussion does not include
3171   definitive solutions to the problems revealed, though it does make
3172   some suggestions for reducing security risks.
3173</t>
3174
3175<section title="Personal Information" anchor="personal.information">
3176<t>
3177   HTTP clients are often privy to large amounts of personal information
3178   (e.g. the user's name, location, mail address, passwords, encryption
3179   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3180   leakage of this information.
3181   We very strongly recommend that a convenient interface be provided
3182   for the user to control dissemination of such information, and that
3183   designers and implementors be particularly careful in this area.
3184   History shows that errors in this area often create serious security
3185   and/or privacy problems and generate highly adverse publicity for the
3186   implementor's company.
3187</t>
3188</section>
3189
3190<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3191<t>
3192   A server is in the position to save personal data about a user's
3193   requests which might identify their reading patterns or subjects of
3194   interest. This information is clearly confidential in nature and its
3195   handling can be constrained by law in certain countries. People using
3196   HTTP to provide data are responsible for ensuring that
3197   such material is not distributed without the permission of any
3198   individuals that are identifiable by the published results.
3199</t>
3200</section>
3201
3202<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3203<t>
3204   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3205   the documents returned by HTTP requests to be only those that were
3206   intended by the server administrators. If an HTTP server translates
3207   HTTP URIs directly into file system calls, the server &MUST; take
3208   special care not to serve files that were not intended to be
3209   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3210   other operating systems use ".." as a path component to indicate a
3211   directory level above the current one. On such a system, an HTTP
3212   server &MUST; disallow any such construct in the request-target if it
3213   would otherwise allow access to a resource outside those intended to
3214   be accessible via the HTTP server. Similarly, files intended for
3215   reference only internally to the server (such as access control
3216   files, configuration files, and script code) &MUST; be protected from
3217   inappropriate retrieval, since they might contain sensitive
3218   information. Experience has shown that minor bugs in such HTTP server
3219   implementations have turned into security risks.
3220</t>
3221</section>
3222
3223<section title="DNS Spoofing" anchor="dns.spoofing">
3224<t>
3225   Clients using HTTP rely heavily on the Domain Name Service, and are
3226   thus generally prone to security attacks based on the deliberate
3227   mis-association of IP addresses and DNS names. Clients need to be
3228   cautious in assuming the continuing validity of an IP number/DNS name
3229   association.
3230</t>
3231<t>
3232   In particular, HTTP clients &SHOULD; rely on their name resolver for
3233   confirmation of an IP number/DNS name association, rather than
3234   caching the result of previous host name lookups. Many platforms
3235   already can cache host name lookups locally when appropriate, and
3236   they &SHOULD; be configured to do so. It is proper for these lookups to
3237   be cached, however, only when the TTL (Time To Live) information
3238   reported by the name server makes it likely that the cached
3239   information will remain useful.
3240</t>
3241<t>
3242   If HTTP clients cache the results of host name lookups in order to
3243   achieve a performance improvement, they &MUST; observe the TTL
3244   information reported by DNS.
3245</t>
3246<t>
3247   If HTTP clients do not observe this rule, they could be spoofed when
3248   a previously-accessed server's IP address changes. As network
3249   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3250   possibility of this form of attack will grow. Observing this
3251   requirement thus reduces this potential security vulnerability.
3252</t>
3253<t>
3254   This requirement also improves the load-balancing behavior of clients
3255   for replicated servers using the same DNS name and reduces the
3256   likelihood of a user's experiencing failure in accessing sites which
3257   use that strategy.
3258</t>
3259</section>
3260
3261<section title="Proxies and Caching" anchor="attack.proxies">
3262<t>
3263   By their very nature, HTTP proxies are men-in-the-middle, and
3264   represent an opportunity for man-in-the-middle attacks. Compromise of
3265   the systems on which the proxies run can result in serious security
3266   and privacy problems. Proxies have access to security-related
3267   information, personal information about individual users and
3268   organizations, and proprietary information belonging to users and
3269   content providers. A compromised proxy, or a proxy implemented or
3270   configured without regard to security and privacy considerations,
3271   might be used in the commission of a wide range of potential attacks.
3272</t>
3273<t>
3274   Proxy operators should protect the systems on which proxies run as
3275   they would protect any system that contains or transports sensitive
3276   information. In particular, log information gathered at proxies often
3277   contains highly sensitive personal information, and/or information
3278   about organizations. Log information should be carefully guarded, and
3279   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3280</t>
3281<t>
3282   Proxy implementors should consider the privacy and security
3283   implications of their design and coding decisions, and of the
3284   configuration options they provide to proxy operators (especially the
3285   default configuration).
3286</t>
3287<t>
3288   Users of a proxy need to be aware that they are no trustworthier than
3289   the people who run the proxy; HTTP itself cannot solve this problem.
3290</t>
3291<t>
3292   The judicious use of cryptography, when appropriate, may suffice to
3293   protect against a broad range of security and privacy attacks. Such
3294   cryptography is beyond the scope of the HTTP/1.1 specification.
3295</t>
3296</section>
3297
3298<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3299<t>
3300   They exist. They are hard to defend against. Research continues.
3301   Beware.
3302</t>
3303</section>
3304</section>
3305
3306<section title="Acknowledgments" anchor="ack">
3307<t>
3308   HTTP has evolved considerably over the years. It has
3309   benefited from a large and active developer community--the many
3310   people who have participated on the www-talk mailing list--and it is
3311   that community which has been most responsible for the success of
3312   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3313   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3314   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3315   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3316   VanHeyningen deserve special recognition for their efforts in
3317   defining early aspects of the protocol.
3318</t>
3319<t>
3320   This document has benefited greatly from the comments of all those
3321   participating in the HTTP-WG. In addition to those already mentioned,
3322   the following individuals have contributed to this specification:
3323</t>
3324<t>
3325   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3326   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3327   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3328   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3329   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3330   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3331   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3332   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3333   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3334   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3335   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3336   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3337   Josh Cohen.
3338</t>
3339<t>
3340   Thanks to the "cave men" of Palo Alto. You know who you are.
3341</t>
3342<t>
3343   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3344   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3345   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3346   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3347   Larry Masinter for their help. And thanks go particularly to Jeff
3348   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3349</t>
3350<t>
3351   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3352   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3353   discovery of many of the problems that this document attempts to
3354   rectify.
3355</t>
3356<t>
3357   This specification makes heavy use of the augmented BNF and generic
3358   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3359   reuses many of the definitions provided by Nathaniel Borenstein and
3360   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3361   specification will help reduce past confusion over the relationship
3362   between HTTP and Internet mail message formats.
3363</t>
3364</section>
3365
3366</middle>
3367<back>
3368
3369<references title="Normative References">
3370
3371<reference anchor="ISO-8859-1">
3372  <front>
3373    <title>
3374     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3375    </title>
3376    <author>
3377      <organization>International Organization for Standardization</organization>
3378    </author>
3379    <date year="1998"/>
3380  </front>
3381  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3382</reference>
3383
3384<reference anchor="Part2">
3385  <front>
3386    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3387    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3388      <organization abbrev="Day Software">Day Software</organization>
3389      <address><email>fielding@gbiv.com</email></address>
3390    </author>
3391    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3392      <organization>One Laptop per Child</organization>
3393      <address><email>jg@laptop.org</email></address>
3394    </author>
3395    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3396      <organization abbrev="HP">Hewlett-Packard Company</organization>
3397      <address><email>JeffMogul@acm.org</email></address>
3398    </author>
3399    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3400      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3401      <address><email>henrikn@microsoft.com</email></address>
3402    </author>
3403    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3404      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3405      <address><email>LMM@acm.org</email></address>
3406    </author>
3407    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3408      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3409      <address><email>paulle@microsoft.com</email></address>
3410    </author>
3411    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3412      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3413      <address><email>timbl@w3.org</email></address>
3414    </author>
3415    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3416      <organization abbrev="W3C">World Wide Web Consortium</organization>
3417      <address><email>ylafon@w3.org</email></address>
3418    </author>
3419    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3420      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3421      <address><email>julian.reschke@greenbytes.de</email></address>
3422    </author>
3423    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3424  </front>
3425  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3426  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3427</reference>
3428
3429<reference anchor="Part3">
3430  <front>
3431    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3432    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3433      <organization abbrev="Day Software">Day Software</organization>
3434      <address><email>fielding@gbiv.com</email></address>
3435    </author>
3436    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3437      <organization>One Laptop per Child</organization>
3438      <address><email>jg@laptop.org</email></address>
3439    </author>
3440    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3441      <organization abbrev="HP">Hewlett-Packard Company</organization>
3442      <address><email>JeffMogul@acm.org</email></address>
3443    </author>
3444    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3445      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3446      <address><email>henrikn@microsoft.com</email></address>
3447    </author>
3448    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3449      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3450      <address><email>LMM@acm.org</email></address>
3451    </author>
3452    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3453      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3454      <address><email>paulle@microsoft.com</email></address>
3455    </author>
3456    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3457      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3458      <address><email>timbl@w3.org</email></address>
3459    </author>
3460    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3461      <organization abbrev="W3C">World Wide Web Consortium</organization>
3462      <address><email>ylafon@w3.org</email></address>
3463    </author>
3464    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3465      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3466      <address><email>julian.reschke@greenbytes.de</email></address>
3467    </author>
3468    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3469  </front>
3470  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3471  <x:source href="p3-payload.xml" basename="p3-payload"/>
3472</reference>
3473
3474<reference anchor="Part5">
3475  <front>
3476    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3477    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3478      <organization abbrev="Day Software">Day Software</organization>
3479      <address><email>fielding@gbiv.com</email></address>
3480    </author>
3481    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3482      <organization>One Laptop per Child</organization>
3483      <address><email>jg@laptop.org</email></address>
3484    </author>
3485    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3486      <organization abbrev="HP">Hewlett-Packard Company</organization>
3487      <address><email>JeffMogul@acm.org</email></address>
3488    </author>
3489    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3490      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3491      <address><email>henrikn@microsoft.com</email></address>
3492    </author>
3493    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3494      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3495      <address><email>LMM@acm.org</email></address>
3496    </author>
3497    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3498      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3499      <address><email>paulle@microsoft.com</email></address>
3500    </author>
3501    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3502      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3503      <address><email>timbl@w3.org</email></address>
3504    </author>
3505    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3506      <organization abbrev="W3C">World Wide Web Consortium</organization>
3507      <address><email>ylafon@w3.org</email></address>
3508    </author>
3509    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3510      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3511      <address><email>julian.reschke@greenbytes.de</email></address>
3512    </author>
3513    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3514  </front>
3515  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3516  <x:source href="p5-range.xml" basename="p5-range"/>
3517</reference>
3518
3519<reference anchor="Part6">
3520  <front>
3521    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3522    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3523      <organization abbrev="Day Software">Day Software</organization>
3524      <address><email>fielding@gbiv.com</email></address>
3525    </author>
3526    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3527      <organization>One Laptop per Child</organization>
3528      <address><email>jg@laptop.org</email></address>
3529    </author>
3530    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3531      <organization abbrev="HP">Hewlett-Packard Company</organization>
3532      <address><email>JeffMogul@acm.org</email></address>
3533    </author>
3534    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3535      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3536      <address><email>henrikn@microsoft.com</email></address>
3537    </author>
3538    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3539      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3540      <address><email>LMM@acm.org</email></address>
3541    </author>
3542    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3543      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3544      <address><email>paulle@microsoft.com</email></address>
3545    </author>
3546    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3547      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3548      <address><email>timbl@w3.org</email></address>
3549    </author>
3550    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3551      <organization abbrev="W3C">World Wide Web Consortium</organization>
3552      <address><email>ylafon@w3.org</email></address>
3553    </author>
3554    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3555      <organization />
3556      <address><email>mnot@mnot.net</email></address>
3557    </author>
3558    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3559      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3560      <address><email>julian.reschke@greenbytes.de</email></address>
3561    </author>
3562    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3563  </front>
3564  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3565  <x:source href="p6-cache.xml" basename="p6-cache"/>
3566</reference>
3567
3568<reference anchor="RFC5234">
3569  <front>
3570    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3571    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3572      <organization>Brandenburg InternetWorking</organization>
3573      <address>
3574      <postal>
3575      <street>675 Spruce Dr.</street>
3576      <city>Sunnyvale</city>
3577      <region>CA</region>
3578      <code>94086</code>
3579      <country>US</country></postal>
3580      <phone>+1.408.246.8253</phone>
3581      <email>dcrocker@bbiw.net</email></address> 
3582    </author>
3583    <author initials="P." surname="Overell" fullname="Paul Overell">
3584      <organization>THUS plc.</organization>
3585      <address>
3586      <postal>
3587      <street>1/2 Berkeley Square</street>
3588      <street>99 Berkely Street</street>
3589      <city>Glasgow</city>
3590      <code>G3 7HR</code>
3591      <country>UK</country></postal>
3592      <email>paul.overell@thus.net</email></address>
3593    </author>
3594    <date month="January" year="2008"/>
3595  </front>
3596  <seriesInfo name="STD" value="68"/>
3597  <seriesInfo name="RFC" value="5234"/>
3598</reference>
3599
3600<reference anchor="RFC2119">
3601  <front>
3602    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3603    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3604      <organization>Harvard University</organization>
3605      <address><email>sob@harvard.edu</email></address>
3606    </author>
3607    <date month="March" year="1997"/>
3608  </front>
3609  <seriesInfo name="BCP" value="14"/>
3610  <seriesInfo name="RFC" value="2119"/>
3611</reference>
3612
3613<reference anchor="RFC3986">
3614 <front>
3615  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3616  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3617    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3618    <address>
3619       <email>timbl@w3.org</email>
3620       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3621    </address>
3622  </author>
3623  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3624    <organization abbrev="Day Software">Day Software</organization>
3625    <address>
3626      <email>fielding@gbiv.com</email>
3627      <uri>http://roy.gbiv.com/</uri>
3628    </address>
3629  </author>
3630  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3631    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3632    <address>
3633      <email>LMM@acm.org</email>
3634      <uri>http://larry.masinter.net/</uri>
3635    </address>
3636  </author>
3637  <date month='January' year='2005'></date>
3638 </front>
3639 <seriesInfo name="RFC" value="3986"/>
3640 <seriesInfo name="STD" value="66"/>
3641</reference>
3642
3643<reference anchor="USASCII">
3644  <front>
3645    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3646    <author>
3647      <organization>American National Standards Institute</organization>
3648    </author>
3649    <date year="1986"/>
3650  </front>
3651  <seriesInfo name="ANSI" value="X3.4"/>
3652</reference>
3653
3654</references>
3655
3656<references title="Informative References">
3657
3658<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3659  <front>
3660    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3661    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3662      <organization/>
3663    </author>
3664    <author initials="J." surname="Gettys" fullname="J. Gettys">
3665      <organization/>
3666    </author>
3667    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3668      <organization/>
3669    </author>
3670    <author initials="H." surname="Lie" fullname="H. Lie">
3671      <organization/>
3672    </author>
3673    <author initials="C." surname="Lilley" fullname="C. Lilley">
3674      <organization/>
3675    </author>
3676    <date year="1997" month="September"/>
3677  </front>
3678  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3679</reference>
3680
3681<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3682  <front>
3683    <title>Improving HTTP Latency</title>
3684    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3685      <organization/>
3686    </author>
3687    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3688      <organization/>
3689    </author>
3690    <date year="1995" month="December"/>
3691  </front>
3692  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3693</reference>
3694
3695<reference anchor="RFC1123">
3696  <front>
3697    <title>Requirements for Internet Hosts - Application and Support</title>
3698    <author initials="R." surname="Braden" fullname="Robert Braden">
3699      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3700      <address><email>Braden@ISI.EDU</email></address>
3701    </author>
3702    <date month="October" year="1989"/>
3703  </front>
3704  <seriesInfo name="STD" value="3"/>
3705  <seriesInfo name="RFC" value="1123"/>
3706</reference>
3707
3708<reference anchor="RFC1305">
3709  <front>
3710    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3711    <author initials="D." surname="Mills" fullname="David L. Mills">
3712      <organization>University of Delaware, Electrical Engineering Department</organization>
3713      <address><email>mills@udel.edu</email></address>
3714    </author>
3715    <date month="March" year="1992"/>
3716  </front>
3717  <seriesInfo name="RFC" value="1305"/>
3718</reference>
3719
3720<reference anchor="RFC1900">
3721  <front>
3722    <title>Renumbering Needs Work</title>
3723    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3724      <organization>CERN, Computing and Networks Division</organization>
3725      <address><email>brian@dxcoms.cern.ch</email></address>
3726    </author>
3727    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3728      <organization>cisco Systems</organization>
3729      <address><email>yakov@cisco.com</email></address>
3730    </author>
3731    <date month="February" year="1996"/>
3732  </front>
3733  <seriesInfo name="RFC" value="1900"/>
3734</reference>
3735
3736<reference anchor="RFC1945">
3737  <front>
3738    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3739    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3740      <organization>MIT, Laboratory for Computer Science</organization>
3741      <address><email>timbl@w3.org</email></address>
3742    </author>
3743    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3744      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3745      <address><email>fielding@ics.uci.edu</email></address>
3746    </author>
3747    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3748      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3749      <address><email>frystyk@w3.org</email></address>
3750    </author>
3751    <date month="May" year="1996"/>
3752  </front>
3753  <seriesInfo name="RFC" value="1945"/>
3754</reference>
3755
3756<reference anchor="RFC2045">
3757  <front>
3758    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3759    <author initials="N." surname="Freed" fullname="Ned Freed">
3760      <organization>Innosoft International, Inc.</organization>
3761      <address><email>ned@innosoft.com</email></address>
3762    </author>
3763    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3764      <organization>First Virtual Holdings</organization>
3765      <address><email>nsb@nsb.fv.com</email></address>
3766    </author>
3767    <date month="November" year="1996"/>
3768  </front>
3769  <seriesInfo name="RFC" value="2045"/>
3770</reference>
3771
3772<reference anchor="RFC2047">
3773  <front>
3774    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3775    <author initials="K." surname="Moore" fullname="Keith Moore">
3776      <organization>University of Tennessee</organization>
3777      <address><email>moore@cs.utk.edu</email></address>
3778    </author>
3779    <date month="November" year="1996"/>
3780  </front>
3781  <seriesInfo name="RFC" value="2047"/>
3782</reference>
3783
3784<reference anchor="RFC2068">
3785  <front>
3786    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3787    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3788      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3789      <address><email>fielding@ics.uci.edu</email></address>
3790    </author>
3791    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3792      <organization>MIT Laboratory for Computer Science</organization>
3793      <address><email>jg@w3.org</email></address>
3794    </author>
3795    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3796      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3797      <address><email>mogul@wrl.dec.com</email></address>
3798    </author>
3799    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3800      <organization>MIT Laboratory for Computer Science</organization>
3801      <address><email>frystyk@w3.org</email></address>
3802    </author>
3803    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3804      <organization>MIT Laboratory for Computer Science</organization>
3805      <address><email>timbl@w3.org</email></address>
3806    </author>
3807    <date month="January" year="1997"/>
3808  </front>
3809  <seriesInfo name="RFC" value="2068"/>
3810</reference>
3811
3812<reference anchor='RFC2109'>
3813  <front>
3814    <title>HTTP State Management Mechanism</title>
3815    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3816      <organization>Bell Laboratories, Lucent Technologies</organization>
3817      <address><email>dmk@bell-labs.com</email></address>
3818    </author>
3819    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3820      <organization>Netscape Communications Corp.</organization>
3821      <address><email>montulli@netscape.com</email></address>
3822    </author>
3823    <date year='1997' month='February' />
3824  </front>
3825  <seriesInfo name='RFC' value='2109' />
3826</reference>
3827
3828<reference anchor="RFC2145">
3829  <front>
3830    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3831    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3832      <organization>Western Research Laboratory</organization>
3833      <address><email>mogul@wrl.dec.com</email></address>
3834    </author>
3835    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3836      <organization>Department of Information and Computer Science</organization>
3837      <address><email>fielding@ics.uci.edu</email></address>
3838    </author>
3839    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3840      <organization>MIT Laboratory for Computer Science</organization>
3841      <address><email>jg@w3.org</email></address>
3842    </author>
3843    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3844      <organization>W3 Consortium</organization>
3845      <address><email>frystyk@w3.org</email></address>
3846    </author>
3847    <date month="May" year="1997"/>
3848  </front>
3849  <seriesInfo name="RFC" value="2145"/>
3850</reference>
3851
3852<reference anchor="RFC2616">
3853  <front>
3854    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3855    <author initials="R." surname="Fielding" fullname="R. Fielding">
3856      <organization>University of California, Irvine</organization>
3857      <address><email>fielding@ics.uci.edu</email></address>
3858    </author>
3859    <author initials="J." surname="Gettys" fullname="J. Gettys">
3860      <organization>W3C</organization>
3861      <address><email>jg@w3.org</email></address>
3862    </author>
3863    <author initials="J." surname="Mogul" fullname="J. Mogul">
3864      <organization>Compaq Computer Corporation</organization>
3865      <address><email>mogul@wrl.dec.com</email></address>
3866    </author>
3867    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3868      <organization>MIT Laboratory for Computer Science</organization>
3869      <address><email>frystyk@w3.org</email></address>
3870    </author>
3871    <author initials="L." surname="Masinter" fullname="L. Masinter">
3872      <organization>Xerox Corporation</organization>
3873      <address><email>masinter@parc.xerox.com</email></address>
3874    </author>
3875    <author initials="P." surname="Leach" fullname="P. Leach">
3876      <organization>Microsoft Corporation</organization>
3877      <address><email>paulle@microsoft.com</email></address>
3878    </author>
3879    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3880      <organization>W3C</organization>
3881      <address><email>timbl@w3.org</email></address>
3882    </author>
3883    <date month="June" year="1999"/>
3884  </front>
3885  <seriesInfo name="RFC" value="2616"/>
3886</reference>
3887
3888<reference anchor='RFC2818'>
3889  <front>
3890    <title>HTTP Over TLS</title>
3891    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3892      <organization>RTFM, Inc.</organization>
3893      <address><email>ekr@rtfm.com</email></address>
3894    </author>
3895    <date year='2000' month='May' />
3896  </front>
3897  <seriesInfo name='RFC' value='2818' />
3898</reference>
3899
3900<reference anchor='RFC2965'>
3901  <front>
3902    <title>HTTP State Management Mechanism</title>
3903    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3904      <organization>Bell Laboratories, Lucent Technologies</organization>
3905      <address><email>dmk@bell-labs.com</email></address>
3906    </author>
3907    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3908      <organization>Epinions.com, Inc.</organization>
3909      <address><email>lou@montulli.org</email></address>
3910    </author>
3911    <date year='2000' month='October' />
3912  </front>
3913  <seriesInfo name='RFC' value='2965' />
3914</reference>
3915
3916<reference anchor='RFC3864'>
3917  <front>
3918    <title>Registration Procedures for Message Header Fields</title>
3919    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3920      <organization>Nine by Nine</organization>
3921      <address><email>GK-IETF@ninebynine.org</email></address>
3922    </author>
3923    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3924      <organization>BEA Systems</organization>
3925      <address><email>mnot@pobox.com</email></address>
3926    </author>
3927    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3928      <organization>HP Labs</organization>
3929      <address><email>JeffMogul@acm.org</email></address>
3930    </author>
3931    <date year='2004' month='September' />
3932  </front>
3933  <seriesInfo name='BCP' value='90' />
3934  <seriesInfo name='RFC' value='3864' />
3935</reference>
3936
3937<reference anchor="RFC4288">
3938  <front>
3939    <title>Media Type Specifications and Registration Procedures</title>
3940    <author initials="N." surname="Freed" fullname="N. Freed">
3941      <organization>Sun Microsystems</organization>
3942      <address>
3943        <email>ned.freed@mrochek.com</email>
3944      </address>
3945    </author>
3946    <author initials="J." surname="Klensin" fullname="J. Klensin">
3947      <organization/>
3948      <address>
3949        <email>klensin+ietf@jck.com</email>
3950      </address>
3951    </author>
3952    <date year="2005" month="December"/>
3953  </front>
3954  <seriesInfo name="BCP" value="13"/>
3955  <seriesInfo name="RFC" value="4288"/>
3956</reference>
3957
3958<reference anchor='RFC4395'>
3959  <front>
3960    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3961    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3962      <organization>AT&amp;T Laboratories</organization>
3963      <address>
3964        <email>tony+urireg@maillennium.att.com</email>
3965      </address>
3966    </author>
3967    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3968      <organization>Qualcomm, Inc.</organization>
3969      <address>
3970        <email>hardie@qualcomm.com</email>
3971      </address>
3972    </author>
3973    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3974      <organization>Adobe Systems</organization>
3975      <address>
3976        <email>LMM@acm.org</email>
3977      </address>
3978    </author>
3979    <date year='2006' month='February' />
3980  </front>
3981  <seriesInfo name='BCP' value='115' />
3982  <seriesInfo name='RFC' value='4395' />
3983</reference>
3984
3985<reference anchor="RFC5322">
3986  <front>
3987    <title>Internet Message Format</title>
3988    <author initials="P." surname="Resnick" fullname="P. Resnick">
3989      <organization>Qualcomm Incorporated</organization>
3990    </author>
3991    <date year="2008" month="October"/>
3992  </front> 
3993  <seriesInfo name="RFC" value="5322"/>
3994</reference>
3995
3996<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3997  <front>
3998    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3999    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4000      <organization/>
4001    </author>
4002    <date year="2001" month="November"/>
4003  </front>
4004  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4005</reference>
4006
4007<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4008  <front>
4009  <title>Analysis of HTTP Performance Problems</title>
4010  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4011    <organization/>
4012  </author>
4013  <date/>
4014  </front>
4015</reference>
4016
4017<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4018  <front>
4019  <title>Analysis of HTTP Performance</title>
4020  <author initials="J." surname="Touch" fullname="Joe Touch">
4021    <organization>USC/Information Sciences Institute</organization>
4022    <address><email>touch@isi.edu</email></address>
4023  </author>
4024  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4025    <organization>USC/Information Sciences Institute</organization>
4026    <address><email>johnh@isi.edu</email></address>
4027  </author>
4028  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4029    <organization>USC/Information Sciences Institute</organization>
4030    <address><email>katia@isi.edu</email></address>
4031  </author>
4032  <date year="1998" month="Aug"/>
4033  </front>
4034  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4035  <annotation>(original report dated Aug. 1996)</annotation>
4036</reference>
4037
4038</references>
4039
4040
4041<section title="Tolerant Applications" anchor="tolerant.applications">
4042<t>
4043   Although this document specifies the requirements for the generation
4044   of HTTP/1.1 messages, not all applications will be correct in their
4045   implementation. We therefore recommend that operational applications
4046   be tolerant of deviations whenever those deviations can be
4047   interpreted unambiguously.
4048</t>
4049<t>
4050   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4051   tolerant when parsing the Request-Line. In particular, they &SHOULD;
4052   accept any amount of WSP characters between fields, even though
4053   only a single SP is required.
4054</t>
4055<t>
4056   The line terminator for message-header fields is the sequence CRLF.
4057   However, we recommend that applications, when parsing such headers,
4058   recognize a single LF as a line terminator and ignore the leading CR.
4059</t>
4060<t>
4061   The character set of an entity-body &SHOULD; be labeled as the lowest
4062   common denominator of the character codes used within that body, with
4063   the exception that not labeling the entity is preferred over labeling
4064   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4065</t>
4066<t>
4067   Additional rules for requirements on parsing and encoding of dates
4068   and other potential problems with date encodings include:
4069</t>
4070<t>
4071  <list style="symbols">
4072     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4073        which appears to be more than 50 years in the future is in fact
4074        in the past (this helps solve the "year 2000" problem).</t>
4075
4076     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4077        Expires date as earlier than the proper value, but &MUST-NOT;
4078        internally represent a parsed Expires date as later than the
4079        proper value.</t>
4080
4081     <t>All expiration-related calculations &MUST; be done in GMT. The
4082        local time zone &MUST-NOT; influence the calculation or comparison
4083        of an age or expiration time.</t>
4084
4085     <t>If an HTTP header incorrectly carries a date value with a time
4086        zone other than GMT, it &MUST; be converted into GMT using the
4087        most conservative possible conversion.</t>
4088  </list>
4089</t>
4090</section>
4091
4092<section title="Compatibility with Previous Versions" anchor="compatibility">
4093<t>
4094   HTTP has been in use by the World-Wide Web global information initiative
4095   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4096   was a simple protocol for hypertext data transfer across the Internet
4097   with only a single method and no metadata.
4098   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4099   methods and MIME-like messaging that could include metadata about the data
4100   transferred and modifiers on the request/response semantics. However,
4101   HTTP/1.0 did not sufficiently take into consideration the effects of
4102   hierarchical proxies, caching, the need for persistent connections, or
4103   name-based virtual hosts. The proliferation of incompletely-implemented
4104   applications calling themselves "HTTP/1.0" further necessitated a
4105   protocol version change in order for two communicating applications
4106   to determine each other's true capabilities.
4107</t>
4108<t>
4109   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4110   requirements that enable reliable implementations, adding only
4111   those new features that will either be safely ignored by an HTTP/1.0
4112   recipient or only sent when communicating with a party advertising
4113   compliance with HTTP/1.1.
4114</t>
4115<t>
4116   It is beyond the scope of a protocol specification to mandate
4117   compliance with previous versions. HTTP/1.1 was deliberately
4118   designed, however, to make supporting previous versions easy. It is
4119   worth noting that, at the time of composing this specification
4120   (1996), we would expect commercial HTTP/1.1 servers to:
4121  <list style="symbols">
4122     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4123        1.1 requests;</t>
4124
4125     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4126        1.1;</t>
4127
4128     <t>respond appropriately with a message in the same major version
4129        used by the client.</t>
4130  </list>
4131</t>
4132<t>
4133   And we would expect HTTP/1.1 clients to:
4134  <list style="symbols">
4135     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4136        responses;</t>
4137
4138     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4139        1.1.</t>
4140  </list>
4141</t>
4142<t>
4143   For most implementations of HTTP/1.0, each connection is established
4144   by the client prior to the request and closed by the server after
4145   sending the response. Some implementations implement the Keep-Alive
4146   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4147</t>
4148
4149<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4150<t>
4151   This section summarizes major differences between versions HTTP/1.0
4152   and HTTP/1.1.
4153</t>
4154
4155<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">
4156<t>
4157   The requirements that clients and servers support the Host request-header,
4158   report an error if the Host request-header (<xref target="header.host"/>) is
4159   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4160   are among the most important changes defined by this
4161   specification.
4162</t>
4163<t>
4164   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4165   addresses and servers; there was no other established mechanism for
4166   distinguishing the intended server of a request than the IP address
4167   to which that request was directed. The changes outlined above will
4168   allow the Internet, once older HTTP clients are no longer common, to
4169   support multiple Web sites from a single IP address, greatly
4170   simplifying large operational Web servers, where allocation of many
4171   IP addresses to a single host has created serious problems. The
4172   Internet will also be able to recover the IP addresses that have been
4173   allocated for the sole purpose of allowing special-purpose domain
4174   names to be used in root-level HTTP URLs. Given the rate of growth of
4175   the Web, and the number of servers already deployed, it is extremely
4176   important that all implementations of HTTP (including updates to
4177   existing HTTP/1.0 applications) correctly implement these
4178   requirements:
4179  <list style="symbols">
4180     <t>Both clients and servers &MUST; support the Host request-header.</t>
4181
4182     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4183
4184     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4185        request does not include a Host request-header.</t>
4186
4187     <t>Servers &MUST; accept absolute URIs.</t>
4188  </list>
4189</t>
4190</section>
4191</section>
4192
4193<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4194<t>
4195   Some clients and servers might wish to be compatible with some
4196   previous implementations of persistent connections in HTTP/1.0
4197   clients and servers. Persistent connections in HTTP/1.0 are
4198   explicitly negotiated as they are not the default behavior. HTTP/1.0
4199   experimental implementations of persistent connections are faulty,
4200   and the new facilities in HTTP/1.1 are designed to rectify these
4201   problems. The problem was that some existing 1.0 clients may be
4202   sending Keep-Alive to a proxy server that doesn't understand
4203   Connection, which would then erroneously forward it to the next
4204   inbound server, which would establish the Keep-Alive connection and
4205   result in a hung HTTP/1.0 proxy waiting for the close on the
4206   response. The result is that HTTP/1.0 clients must be prevented from
4207   using Keep-Alive when talking to proxies.
4208</t>
4209<t>
4210   However, talking to proxies is the most important use of persistent
4211   connections, so that prohibition is clearly unacceptable. Therefore,
4212   we need some other mechanism for indicating a persistent connection
4213   is desired, which is safe to use even when talking to an old proxy
4214   that ignores Connection. Persistent connections are the default for
4215   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4216   declaring non-persistence. See <xref target="header.connection"/>.
4217</t>
4218<t>
4219   The original HTTP/1.0 form of persistent connections (the Connection:
4220   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4221</t>
4222</section>
4223
4224<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4225<t>
4226   This specification has been carefully audited to correct and
4227   disambiguate key word usage; RFC 2068 had many problems in respect to
4228   the conventions laid out in <xref target="RFC2119"/>.
4229</t>
4230<t>
4231   Transfer-coding and message lengths all interact in ways that
4232   required fixing exactly when chunked encoding is used (to allow for
4233   transfer encoding that may not be self delimiting); it was important
4234   to straighten out exactly how message lengths are computed. (Sections
4235   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4236   <xref target="header.content-length" format="counter"/>,
4237   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4238</t>
4239<t>
4240   The use and interpretation of HTTP version numbers has been clarified
4241   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4242   version they support to deal with problems discovered in HTTP/1.0
4243   implementations (<xref target="http.version"/>)
4244</t>
4245<t>
4246   Quality Values of zero should indicate that "I don't want something"
4247   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4248</t>
4249<t>
4250   Transfer-coding had significant problems, particularly with
4251   interactions with chunked encoding. The solution is that transfer-codings
4252   become as full fledged as content-codings. This involves
4253   adding an IANA registry for transfer-codings (separate from content
4254   codings), a new header field (TE) and enabling trailer headers in the
4255   future. Transfer encoding is a major performance benefit, so it was
4256   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4257   interoperability problem that could have occurred due to interactions
4258   between authentication trailers, chunked encoding and HTTP/1.0
4259   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4260   and <xref target="header.te" format="counter"/>)
4261</t>
4262</section>
4263
4264<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4265<t>
4266  Empty list elements in list productions have been deprecated.
4267  (<xref target="notation.abnf"/>)
4268</t>
4269<t>
4270  Rules about implicit linear whitespace between certain grammar productions
4271  have been removed; now it's only allowed when specifically pointed out
4272  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4273  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4274  Non-ASCII content in header fields and reason phrase has been obsoleted and
4275  made opaque (the TEXT rule was removed)
4276  (<xref target="basic.rules"/>)
4277</t>
4278<t>
4279  Clarify that HTTP-Version is case sensitive.
4280  (<xref target="http.version"/>)
4281</t>
4282<t>
4283  Remove reference to non-existant identity transfer-coding value tokens.
4284  (Sections <xref format="counter" target="transfer.codings"/> and
4285  <xref format="counter" target="message.length"/>)
4286</t>
4287<t>
4288  Clarification that the chunk length does not include
4289  the count of the octets in the chunk header and trailer.
4290  (<xref target="chunked.transfer.encoding"/>)
4291</t>
4292<t>
4293  Require that invalid whitespace around field-names be rejected.
4294  (<xref target="message.headers"/>)
4295</t>
4296<t>
4297  Update use of abs_path production from RFC1808 to the path-absolute + query
4298  components of RFC3986.
4299  (<xref target="request-target"/>)
4300</t>
4301<t>
4302  Clarify exactly when close connection options must be sent.
4303  (<xref target="header.connection"/>)
4304</t>
4305</section>
4306</section>
4307
4308<section title="Terminology" anchor="terminology">
4309<t>
4310   This specification uses a number of terms to refer to the roles
4311   played by participants in, and objects of, the HTTP communication.
4312</t>
4313<t>
4314  <iref item="content negotiation"/>
4315  <x:dfn>content negotiation</x:dfn>
4316  <list>
4317    <t>
4318      The mechanism for selecting the appropriate representation when
4319      servicing a request, as described in &content.negotiation;. The
4320      representation of entities in any response can be negotiated
4321      (including error responses).
4322    </t>
4323  </list>
4324</t>
4325<t>
4326  <iref item="entity"/>
4327  <x:dfn>entity</x:dfn>
4328  <list>
4329    <t>
4330      The information transferred as the payload of a request or
4331      response. An entity consists of metadata in the form of
4332      entity-header fields and content in the form of an entity-body, as
4333      described in &entity;.
4334    </t>
4335  </list>
4336</t>
4337<t>
4338  <iref item="representation"/>
4339  <x:dfn>representation</x:dfn>
4340  <list>
4341    <t>
4342      An entity included with a response that is subject to content
4343      negotiation, as described in &content.negotiation;. There may exist multiple
4344      representations associated with a particular response status.
4345    </t>
4346  </list>
4347</t>
4348<t>
4349  <iref item="variant"/>
4350  <x:dfn>variant</x:dfn>
4351  <list>
4352    <t>
4353      A resource may have one, or more than one, representation(s)
4354      associated with it at any given instant. Each of these
4355      representations is termed a `variant'.  Use of the term `variant'
4356      does not necessarily imply that the resource is subject to content
4357      negotiation.
4358    </t>
4359  </list>
4360</t>
4361</section>
4362
4363<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4364<figure>
4365<artwork type="abnf" name="p1-messaging.parsed-abnf">
4366<x:ref>BWS</x:ref> = OWS
4367
4368<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4369<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4370<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4371<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4372 connection-token ] )
4373<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4374<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4375
4376<x:ref>Date</x:ref> = "Date:" OWS Date-v
4377<x:ref>Date-v</x:ref> = HTTP-date
4378
4379<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4380
4381<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4382<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4383<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4384<x:ref>HTTP-message</x:ref> = Request / Response
4385<x:ref>Host</x:ref> = "Host:" OWS Host-v
4386<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4387
4388<x:ref>Method</x:ref> = token
4389
4390<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4391
4392<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4393
4394<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4395<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4396<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4397 entity-header ) CRLF ) CRLF [ message-body ]
4398<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4399<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4400 entity-header ) CRLF ) CRLF [ message-body ]
4401
4402<x:ref>Status-Code</x:ref> = 3DIGIT
4403<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4404
4405<x:ref>TE</x:ref> = "TE:" OWS TE-v
4406<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4407<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4408<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4409<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4410<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4411 transfer-coding ] )
4412
4413<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4414<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4415<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4416<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4417
4418<x:ref>Via</x:ref> = "Via:" OWS Via-v
4419<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4420 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4421 ] )
4422
4423<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4424
4425<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4426<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4427<x:ref>attribute</x:ref> = token
4428<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4429
4430<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4431<x:ref>chunk-data</x:ref> = 1*OCTET
4432<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4433<x:ref>chunk-ext-name</x:ref> = token
4434<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4435<x:ref>chunk-size</x:ref> = 1*HEXDIG
4436<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4437<x:ref>connection-token</x:ref> = token
4438<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4439 / %x2A-5B ; '*'-'['
4440 / %x5D-7E ; ']'-'~'
4441 / obs-text
4442
4443<x:ref>date1</x:ref> = day SP month SP year
4444<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4445<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4446<x:ref>day</x:ref> = 2DIGIT
4447<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4448 / %x54.75.65 ; Tue
4449 / %x57.65.64 ; Wed
4450 / %x54.68.75 ; Thu
4451 / %x46.72.69 ; Fri
4452 / %x53.61.74 ; Sat
4453 / %x53.75.6E ; Sun
4454<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4455 / %x54.75.65.73.64.61.79 ; Tuesday
4456 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4457 / %x54.68.75.72.73.64.61.79 ; Thursday
4458 / %x46.72.69.64.61.79 ; Friday
4459 / %x53.61.74.75.72.64.61.79 ; Saturday
4460 / %x53.75.6E.64.61.79 ; Sunday
4461
4462<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4463<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4464
4465<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4466<x:ref>field-name</x:ref> = token
4467<x:ref>field-value</x:ref> = *( field-content / OWS )
4468<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4469
4470<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4471 / Transfer-Encoding / Upgrade / Via / Warning
4472<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4473 message-body ]
4474
4475<x:ref>hour</x:ref> = 2DIGIT
4476<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4477<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4478
4479<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4480
4481<x:ref>message-body</x:ref> = entity-body /
4482 &lt;entity-body encoded as per Transfer-Encoding&gt;
4483<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4484<x:ref>minute</x:ref> = 2DIGIT
4485<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4486 / %x46.65.62 ; Feb
4487 / %x4D.61.72 ; Mar
4488 / %x41.70.72 ; Apr
4489 / %x4D.61.79 ; May
4490 / %x4A.75.6E ; Jun
4491 / %x4A.75.6C ; Jul
4492 / %x41.75.67 ; Aug
4493 / %x53.65.70 ; Sep
4494 / %x4F.63.74 ; Oct
4495 / %x4E.6F.76 ; Nov
4496 / %x44.65.63 ; Dec
4497
4498<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4499<x:ref>obs-fold</x:ref> = CRLF
4500<x:ref>obs-text</x:ref> = %x80-FF
4501
4502<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4503<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4504<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4505<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4506<x:ref>product</x:ref> = token [ "/" product-version ]
4507<x:ref>product-version</x:ref> = token
4508<x:ref>protocol-name</x:ref> = token
4509<x:ref>protocol-version</x:ref> = token
4510<x:ref>pseudonym</x:ref> = token
4511
4512<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4513 / %x5D-7E ; ']'-'~'
4514 / obs-text
4515<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4516<x:ref>quoted-pair</x:ref> = "\" quoted-text
4517<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4518<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4519<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4520
4521<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4522<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4523<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4524<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4525<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4526 / authority
4527<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4528<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4529<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4530
4531<x:ref>second</x:ref> = 2DIGIT
4532<x:ref>start-line</x:ref> = Request-Line / Status-Line
4533
4534<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4535<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4536 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4537<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4538<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4539<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4540<x:ref>token</x:ref> = 1*tchar
4541<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4542<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4543<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4544<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4545
4546<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4547
4548<x:ref>value</x:ref> = token / quoted-string
4549
4550<x:ref>year</x:ref> = 4DIGIT
4551</artwork>
4552</figure>
4553<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4554; Chunked-Body defined but not used
4555; Content-Length defined but not used
4556; HTTP-message defined but not used
4557; Host defined but not used
4558; TE defined but not used
4559; URI defined but not used
4560; URI-reference defined but not used
4561; fragment defined but not used
4562; generic-message defined but not used
4563; http-URI defined but not used
4564; https-URI defined but not used
4565; partial-URI defined but not used
4566</artwork></figure></section>
4567
4568<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4569
4570<section title="Since RFC2616">
4571<t>
4572  Extracted relevant partitions from <xref target="RFC2616"/>.
4573</t>
4574</section>
4575
4576<section title="Since draft-ietf-httpbis-p1-messaging-00">
4577<t>
4578  Closed issues:
4579  <list style="symbols"> 
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4582      "HTTP Version should be case sensitive"
4583      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4584    </t>
4585    <t>
4586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4587      "'unsafe' characters"
4588      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4592      "Chunk Size Definition"
4593      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4597      "Message Length"
4598      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4599    </t>
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4602      "Media Type Registrations"
4603      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4604    </t>
4605    <t>
4606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4607      "URI includes query"
4608      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4612      "No close on 1xx responses"
4613      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4614    </t>
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4617      "Remove 'identity' token references"
4618      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4619    </t>
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4622      "Import query BNF"
4623    </t>
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4626      "qdtext BNF"
4627    </t>
4628    <t>
4629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4630      "Normative and Informative references"
4631    </t>
4632    <t>
4633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4634      "RFC2606 Compliance"
4635    </t>
4636    <t>
4637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4638      "RFC977 reference"
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4642      "RFC1700 references"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4646      "inconsistency in date format explanation"
4647    </t>
4648    <t>
4649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4650      "Date reference typo"
4651    </t>
4652    <t>
4653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4654      "Informative references"
4655    </t>
4656    <t>
4657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4658      "ISO-8859-1 Reference"
4659    </t>
4660    <t>
4661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4662      "Normative up-to-date references"
4663    </t>
4664  </list>
4665</t>
4666<t>
4667  Other changes:
4668  <list style="symbols"> 
4669    <t>
4670      Update media type registrations to use RFC4288 template.
4671    </t>
4672    <t>
4673      Use names of RFC4234 core rules DQUOTE and WSP,
4674      fix broken ABNF for chunk-data
4675      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4676    </t>
4677  </list>
4678</t>
4679</section>
4680
4681<section title="Since draft-ietf-httpbis-p1-messaging-01">
4682<t>
4683  Closed issues:
4684  <list style="symbols"> 
4685    <t>
4686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4687      "Bodies on GET (and other) requests"
4688    </t>
4689    <t>
4690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4691      "Updating to RFC4288"
4692    </t>
4693    <t>
4694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4695      "Status Code and Reason Phrase"
4696    </t>
4697    <t>
4698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4699      "rel_path not used"
4700    </t>
4701  </list>
4702</t>
4703<t>
4704  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4705  <list style="symbols"> 
4706    <t>
4707      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4708      "trailer-part").
4709    </t>
4710    <t>
4711      Avoid underscore character in rule names ("http_URL" ->
4712      "http-URL", "abs_path" -> "path-absolute").
4713    </t>
4714    <t>
4715      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4716      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4717      have to be updated when switching over to RFC3986.
4718    </t>
4719    <t>
4720      Synchronize core rules with RFC5234.
4721    </t>
4722    <t>
4723      Get rid of prose rules that span multiple lines.
4724    </t>
4725    <t>
4726      Get rid of unused rules LOALPHA and UPALPHA.
4727    </t>
4728    <t>
4729      Move "Product Tokens" section (back) into Part 1, as "token" is used
4730      in the definition of the Upgrade header.
4731    </t>
4732    <t>
4733      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4734    </t>
4735    <t>
4736      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4737    </t>
4738  </list>
4739</t>
4740</section>
4741
4742<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4743<t>
4744  Closed issues:
4745  <list style="symbols"> 
4746    <t>
4747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4748      "HTTP-date vs. rfc1123-date"
4749    </t>
4750    <t>
4751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4752      "WS in quoted-pair"
4753    </t>
4754  </list>
4755</t>
4756<t>
4757  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4758  <list style="symbols"> 
4759    <t>
4760      Reference RFC 3984, and update header registrations for headers defined
4761      in this document.
4762    </t>
4763  </list>
4764</t>
4765<t>
4766  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4767  <list style="symbols"> 
4768    <t>
4769      Replace string literals when the string really is case-sensitive (HTTP-Version).
4770    </t>
4771  </list>
4772</t>
4773</section>
4774
4775<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4776<t>
4777  Closed issues:
4778  <list style="symbols"> 
4779    <t>
4780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4781      "Connection closing"
4782    </t>
4783    <t>
4784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4785      "Move registrations and registry information to IANA Considerations"
4786    </t>
4787    <t>
4788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4789      "need new URL for PAD1995 reference"
4790    </t>
4791    <t>
4792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4793      "IANA Considerations: update HTTP URI scheme registration"
4794    </t>
4795    <t>
4796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4797      "Cite HTTPS URI scheme definition"
4798    </t>
4799    <t>
4800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4801      "List-type headers vs Set-Cookie"
4802    </t>
4803  </list>
4804</t>
4805<t>
4806  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4807  <list style="symbols"> 
4808    <t>
4809      Replace string literals when the string really is case-sensitive (HTTP-Date).
4810    </t>
4811    <t>
4812      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4813    </t>
4814  </list>
4815</t>
4816</section>
4817
4818<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4819<t>
4820  Closed issues:
4821  <list style="symbols"> 
4822    <t>
4823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4824      "Out-of-date reference for URIs"
4825    </t>
4826    <t>
4827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4828      "RFC 2822 is updated by RFC 5322"
4829    </t>
4830  </list>
4831</t>
4832<t>
4833  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4834  <list style="symbols"> 
4835    <t>
4836      Use "/" instead of "|" for alternatives.
4837    </t>
4838    <t>
4839      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4840    </t>
4841    <t>
4842      Only reference RFC 5234's core rules.
4843    </t>
4844    <t>
4845      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4846      whitespace ("OWS") and required whitespace ("RWS").
4847    </t>
4848    <t>
4849      Rewrite ABNFs to spell out whitespace rules, factor out
4850      header value format definitions.
4851    </t>
4852  </list>
4853</t>
4854</section>
4855
4856<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4857<t>
4858  Closed issues:
4859  <list style="symbols"> 
4860    <t>
4861      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4862      "Header LWS"
4863    </t>
4864    <t>
4865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4866      "Sort 1.3 Terminology"
4867    </t>
4868    <t>
4869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4870      "RFC2047 encoded words"
4871    </t>
4872    <t>
4873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4874      "Character Encodings in TEXT"
4875    </t>
4876    <t>
4877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4878      "Line Folding"
4879    </t>
4880    <t>
4881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4882      "OPTIONS * and proxies"
4883    </t>
4884    <t>
4885      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4886      "Reason-Phrase BNF"
4887    </t>
4888    <t>
4889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4890      "Use of TEXT"
4891    </t>
4892    <t>
4893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4894      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4895    </t>
4896    <t>
4897      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4898      "RFC822 reference left in discussion of date formats"
4899    </t>
4900  </list>
4901</t>
4902<t>
4903  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4904  <list style="symbols"> 
4905    <t>
4906      Rewrite definition of list rules, deprecate empty list elements.
4907    </t>
4908    <t>
4909      Add appendix containing collected and expanded ABNF.
4910    </t>
4911  </list>
4912</t>
4913<t>
4914  Other changes:
4915  <list style="symbols"> 
4916    <t>
4917      Rewrite introduction; add mostly new Architecture Section.
4918    </t>
4919    <t>
4920      Move definition of quality values from Part 3 into Part 1;
4921      make TE request header grammar independent of accept-params (defined in Part 3).
4922    </t>
4923  </list>
4924</t>
4925</section>
4926
4927<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4928<t>
4929  Closed issues:
4930  <list style="symbols"> 
4931    <t>
4932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
4933      "base for numeric protocol elements"
4934    </t>
4935    <t>
4936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
4937      "comment ABNF"
4938    </t>
4939  </list>
4940</t>
4941<t>
4942  Partly resolved issues:
4943  <list style="symbols"> 
4944    <t>
4945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4946      "205 Bodies" (took out language that implied that there may be
4947      methods for which a request body MUST NOT be included)
4948    </t>
4949    <t>
4950      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
4951      "editorial improvements around HTTP-date"
4952    </t>
4953  </list>
4954</t>
4955</section>
4956
4957<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
4958<t>
4959  Closed issues:
4960  <list style="symbols"> 
4961    <t>
4962      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
4963      "IP addresses in URLs"
4964    </t>
4965  </list>
4966</t>
4967
4968</section>
4969
4970</section>
4971
4972</back>
4973</rfc>
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