source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1462

Last change on this file since 1462 was 1462, checked in by julian.reschke@…, 8 years ago

Fix examples for list syntax not to include *leading* whitespace (that's not part of the list production) (see #36)

  • Property svn:eol-style set to native
File size: 240.3 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 "October">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' 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-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-code-reasonphr  "<xref target='Part2' x:rel='#status.code.and.reason.phrase' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44]>
45<?rfc toc="yes" ?>
46<?rfc symrefs="yes" ?>
47<?rfc sortrefs="yes" ?>
48<?rfc compact="yes"?>
49<?rfc subcompact="no" ?>
50<?rfc linkmailto="no" ?>
51<?rfc editing="no" ?>
52<?rfc comments="yes"?>
53<?rfc inline="yes"?>
54<?rfc rfcedstyle="yes"?>
55<?rfc-ext allow-markup-in-artwork="yes" ?>
56<?rfc-ext include-references-in-index="yes" ?>
57<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x='http://purl.org/net/xml2rfc/ext'>
60<front>
61
62  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
63
64  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
65    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
66    <address>
67      <postal>
68        <street>345 Park Ave</street>
69        <city>San Jose</city>
70        <region>CA</region>
71        <code>95110</code>
72        <country>USA</country>
73      </postal>
74      <email>fielding@gbiv.com</email>
75      <uri>http://roy.gbiv.com/</uri>
76    </address>
77  </author>
78
79  <author initials="J." surname="Gettys" fullname="Jim Gettys">
80    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
81    <address>
82      <postal>
83        <street>21 Oak Knoll Road</street>
84        <city>Carlisle</city>
85        <region>MA</region>
86        <code>01741</code>
87        <country>USA</country>
88      </postal>
89      <email>jg@freedesktop.org</email>
90      <uri>http://gettys.wordpress.com/</uri>
91    </address>
92  </author>
93 
94  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
95    <organization abbrev="HP">Hewlett-Packard Company</organization>
96    <address>
97      <postal>
98        <street>HP Labs, Large Scale Systems Group</street>
99        <street>1501 Page Mill Road, MS 1177</street>
100        <city>Palo Alto</city>
101        <region>CA</region>
102        <code>94304</code>
103        <country>USA</country>
104      </postal>
105      <email>JeffMogul@acm.org</email>
106    </address>
107  </author>
108
109  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
110    <organization abbrev="Microsoft">Microsoft Corporation</organization>
111    <address>
112      <postal>
113        <street>1 Microsoft Way</street>
114        <city>Redmond</city>
115        <region>WA</region>
116        <code>98052</code>
117        <country>USA</country>
118      </postal>
119      <email>henrikn@microsoft.com</email>
120    </address>
121  </author>
122
123  <author initials="L." surname="Masinter" fullname="Larry Masinter">
124    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
125    <address>
126      <postal>
127        <street>345 Park Ave</street>
128        <city>San Jose</city>
129        <region>CA</region>
130        <code>95110</code>
131        <country>USA</country>
132      </postal>
133      <email>LMM@acm.org</email>
134      <uri>http://larry.masinter.net/</uri>
135    </address>
136  </author>
137 
138  <author initials="P." surname="Leach" fullname="Paul J. Leach">
139    <organization abbrev="Microsoft">Microsoft Corporation</organization>
140    <address>
141      <postal>
142        <street>1 Microsoft Way</street>
143        <city>Redmond</city>
144        <region>WA</region>
145        <code>98052</code>
146      </postal>
147      <email>paulle@microsoft.com</email>
148    </address>
149  </author>
150   
151  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
152    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
153    <address>
154      <postal>
155        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
156        <street>The Stata Center, Building 32</street>
157        <street>32 Vassar Street</street>
158        <city>Cambridge</city>
159        <region>MA</region>
160        <code>02139</code>
161        <country>USA</country>
162      </postal>
163      <email>timbl@w3.org</email>
164      <uri>http://www.w3.org/People/Berners-Lee/</uri>
165    </address>
166  </author>
167
168  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
169    <organization abbrev="W3C">World Wide Web Consortium</organization>
170    <address>
171      <postal>
172        <street>W3C / ERCIM</street>
173        <street>2004, rte des Lucioles</street>
174        <city>Sophia-Antipolis</city>
175        <region>AM</region>
176        <code>06902</code>
177        <country>France</country>
178      </postal>
179      <email>ylafon@w3.org</email>
180      <uri>http://www.raubacapeu.net/people/yves/</uri>
181    </address>
182  </author>
183
184  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
185    <organization abbrev="greenbytes">greenbytes GmbH</organization>
186    <address>
187      <postal>
188        <street>Hafenweg 16</street>
189        <city>Muenster</city><region>NW</region><code>48155</code>
190        <country>Germany</country>
191      </postal>
192      <phone>+49 251 2807760</phone>
193      <facsimile>+49 251 2807761</facsimile>
194      <email>julian.reschke@greenbytes.de</email>
195      <uri>http://greenbytes.de/tech/webdav/</uri>
196    </address>
197  </author>
198
199  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
200  <workgroup>HTTPbis Working Group</workgroup>
201
202<abstract>
203<t>
204   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
205   distributed, collaborative, hypertext information systems. HTTP has been in
206   use by the World Wide Web global information initiative since 1990. This
207   document is Part 1 of the seven-part specification that defines the protocol
208   referred to as "HTTP/1.1" and, taken together, obsoletes
209   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
210   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
211   2068</xref>.
212</t>
213<t>
214   Part 1 provides an overview of HTTP and its associated terminology, defines
215   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
216   the generic message syntax and parsing requirements for HTTP message frames,
217   and describes general security concerns for implementations.
218</t>
219<t>
220   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
221   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
222   (on using CONNECT for TLS upgrades) and moves them to historic status.
223</t>
224</abstract>
225
226<note title="Editorial Note (To be removed by RFC Editor)">
227  <t>
228    Discussion of this draft should take place on the HTTPBIS working group
229    mailing list (ietf-http-wg@w3.org), which is archived at
230    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
231  </t>
232  <t>
233    The current issues list is at
234    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
235    documents (including fancy diffs) can be found at
236    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
237  </t>
238  <t>
239    The changes in this draft are summarized in <xref target="changes.since.16"/>.
240  </t>
241</note>
242</front>
243<middle>
244<section title="Introduction" anchor="introduction">
245<t>
246   The Hypertext Transfer Protocol (HTTP) is an application-level
247   request/response protocol that uses extensible semantics and MIME-like
248   message payloads for flexible interaction with network-based hypertext
249   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
250   standard <xref target="RFC3986"/> to indicate the target resource and
251   relationships between resources.
252   Messages are passed in a format similar to that used by Internet mail
253   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
254   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
255   between HTTP and MIME messages).
256</t>
257<t>
258   HTTP is a generic interface protocol for information systems. It is
259   designed to hide the details of how a service is implemented by presenting
260   a uniform interface to clients that is independent of the types of
261   resources provided. Likewise, servers do not need to be aware of each
262   client's purpose: an HTTP request can be considered in isolation rather
263   than being associated with a specific type of client or a predetermined
264   sequence of application steps. The result is a protocol that can be used
265   effectively in many different contexts and for which implementations can
266   evolve independently over time.
267</t>
268<t>
269   HTTP is also designed for use as an intermediation protocol for translating
270   communication to and from non-HTTP information systems.
271   HTTP proxies and gateways can provide access to alternative information
272   services by translating their diverse protocols into a hypertext
273   format that can be viewed and manipulated by clients in the same way
274   as HTTP services.
275</t>
276<t>
277   One consequence of HTTP flexibility is that the protocol cannot be
278   defined in terms of what occurs behind the interface. Instead, we
279   are limited to defining the syntax of communication, the intent
280   of received communication, and the expected behavior of recipients.
281   If the communication is considered in isolation, then successful
282   actions ought to be reflected in corresponding changes to the
283   observable interface provided by servers. However, since multiple
284   clients might act in parallel and perhaps at cross-purposes, we
285   cannot require that such changes be observable beyond the scope
286   of a single response.
287</t>
288<t>
289   This document is Part 1 of the seven-part specification of HTTP,
290   defining the protocol referred to as "HTTP/1.1", obsoleting
291   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
292   Part 1 describes the architectural elements that are used or
293   referred to in HTTP, defines the "http" and "https" URI schemes,
294   describes overall network operation and connection management,
295   and defines HTTP message framing and forwarding requirements.
296   Our goal is to define all of the mechanisms necessary for HTTP message
297   handling that are independent of message semantics, thereby defining the
298   complete set of requirements for message parsers and
299   message-forwarding intermediaries.
300</t>
301
302<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
303<t>
304   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
305   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
306   document are to be interpreted as described in <xref target="RFC2119"/>.
307</t>
308<t>
309   This document defines conformance criteria for several roles in HTTP
310   communication, including Senders, Recipients, Clients, Servers, User-Agents,
311   Origin Servers, Intermediaries, Proxies and Gateways. See <xref target="architecture"/>
312   for definitions of these terms.
313</t>
314<t>
315   An implementation is considered conformant if it complies with all of the
316   requirements associated with its role(s). Note that SHOULD-level requirements
317   are relevant here, unless one of the documented exceptions is applicable.
318</t>
319<t>
320   This document also uses ABNF to define valid protocol elements
321   (<xref target="notation"/>). In addition to the prose requirements placed
322   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
323</t>
324<t>
325   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
326   protocol element from an invalid construct. However, HTTP does not define
327   specific error handling mechanisms, except in cases where it has direct
328   impact on security. This is because different uses of the protocol require
329   different error handling strategies; for example, a Web browser may wish to
330   transparently recover from a response where the Location header field
331   doesn't parse according to the ABNF, whereby in a systems control protocol
332   using HTTP, this type of error recovery could lead to dangerous consequences.
333</t>
334</section>
335
336<section title="Syntax Notation" anchor="notation">
337<iref primary="true" item="Grammar" subitem="ALPHA"/>
338<iref primary="true" item="Grammar" subitem="CR"/>
339<iref primary="true" item="Grammar" subitem="CRLF"/>
340<iref primary="true" item="Grammar" subitem="CTL"/>
341<iref primary="true" item="Grammar" subitem="DIGIT"/>
342<iref primary="true" item="Grammar" subitem="DQUOTE"/>
343<iref primary="true" item="Grammar" subitem="HEXDIG"/>
344<iref primary="true" item="Grammar" subitem="HTAB"/>
345<iref primary="true" item="Grammar" subitem="LF"/>
346<iref primary="true" item="Grammar" subitem="OCTET"/>
347<iref primary="true" item="Grammar" subitem="SP"/>
348<iref primary="true" item="Grammar" subitem="VCHAR"/>
349<t>
350   This specification uses the Augmented Backus-Naur Form (ABNF) notation
351   of <xref target="RFC5234"/>.
352</t>
353<t anchor="core.rules">
354  <x:anchor-alias value="ALPHA"/>
355  <x:anchor-alias value="CTL"/>
356  <x:anchor-alias value="CR"/>
357  <x:anchor-alias value="CRLF"/>
358  <x:anchor-alias value="DIGIT"/>
359  <x:anchor-alias value="DQUOTE"/>
360  <x:anchor-alias value="HEXDIG"/>
361  <x:anchor-alias value="HTAB"/>
362  <x:anchor-alias value="LF"/>
363  <x:anchor-alias value="OCTET"/>
364  <x:anchor-alias value="SP"/>
365  <x:anchor-alias value="VCHAR"/>
366   The following core rules are included by
367   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
368   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
369   DIGIT (decimal 0-9), DQUOTE (double quote),
370   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
371   OCTET (any 8-bit sequence of data), SP (space), and
372   VCHAR (any visible <xref target="USASCII"/> character).
373</t>
374<t>
375   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
376   "obsolete" grammar rules that appear for historical reasons.
377</t>
378
379<section title="ABNF Extension: #rule" anchor="notation.abnf">
380<t>
381  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
382  improve readability.
383</t>
384<t>
385  A construct "#" is defined, similar to "*", for defining comma-delimited
386  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
387  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
388  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
389</t>
390<figure><preamble>
391  Thus,
392</preamble><artwork type="example">
393  1#element =&gt; element *( OWS "," OWS element )
394</artwork></figure>
395<figure><preamble>
396  and:
397</preamble><artwork type="example">
398  #element =&gt; [ 1#element ]
399</artwork></figure>
400<figure><preamble>
401  and for n &gt;= 1 and m &gt; 1:
402</preamble><artwork type="example">
403  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
404</artwork></figure>
405<t>
406  For compatibility with legacy list rules, recipients &SHOULD; accept empty
407  list elements. In other words, consumers would follow the list productions:
408</t>
409<figure><artwork type="example">
410  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
411 
412  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
413</artwork></figure>
414<t>
415  Note that empty elements do not contribute to the count of elements present,
416  though.
417</t>
418<t>
419  For example, given these ABNF productions:
420</t>
421<figure><artwork type="example">
422  example-list      = 1#example-list-elmt
423  example-list-elmt = token ; see <xref target="field.rules"/> 
424</artwork></figure>
425<t>
426  Then these are valid values for example-list (not including the double
427  quotes, which are present for delimitation only):
428</t>
429<figure><artwork type="example">
430  "foo,bar"
431  "foo ,bar,"
432  "foo , ,bar,charlie   "
433</artwork></figure>
434<t>
435  But these values would be invalid, as at least one non-empty element is
436  required:
437</t>
438<figure><artwork type="example">
439  ""
440  ","
441  ",   ,"
442</artwork></figure>
443<t>
444  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
445  expanded as explained above.
446</t>
447</section>
448
449<section title="Basic Rules" anchor="basic.rules">
450<t anchor="rule.LWS">
451   This specification uses three rules to denote the use of linear
452   whitespace: OWS (optional whitespace), RWS (required whitespace), and
453   BWS ("bad" whitespace).
454</t>
455<t anchor="rule.OWS">
456   The OWS rule is used where zero or more linear whitespace octets might
457   appear. OWS &SHOULD; either not be produced or be produced as a single
458   SP. Multiple OWS octets that occur within field-content &SHOULD; either
459   be replaced with a single SP or transformed to all SP octets (each
460   octet other than SP replaced with SP) before interpreting the field value
461   or forwarding the message downstream.
462</t>
463<t anchor="rule.RWS">
464   RWS is used when at least one linear whitespace octet is required to
465   separate field tokens. RWS &SHOULD; be produced as a single SP.
466   Multiple RWS octets that occur within field-content &SHOULD; either
467   be replaced with a single SP or transformed to all SP octets before
468   interpreting the field value or forwarding the message downstream.
469</t>
470<t anchor="rule.BWS">
471   BWS is used where the grammar allows optional whitespace for historical
472   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
473   recipients &MUST; accept such bad optional whitespace and remove it before
474   interpreting the field value or forwarding the message downstream.
475</t>
476<t anchor="rule.whitespace">
477  <x:anchor-alias value="BWS"/>
478  <x:anchor-alias value="OWS"/>
479  <x:anchor-alias value="RWS"/>
480  <x:anchor-alias value="obs-fold"/>
481</t>
482<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"/>
483  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
484                 ; "optional" whitespace
485  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
486                 ; "required" whitespace
487  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
488                 ; "bad" whitespace
489  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
490                 ; obsolete line folding
491                 ; see <xref target="field.parsing"/>
492</artwork></figure>
493</section>
494</section>
495</section>
496
497<section title="Architecture" anchor="architecture">
498<t>
499   HTTP was created for the World Wide Web architecture
500   and has evolved over time to support the scalability needs of a worldwide
501   hypertext system. Much of that architecture is reflected in the terminology
502   and syntax productions used to define HTTP.
503</t>
504
505<section title="Client/Server Messaging" anchor="operation">
506<iref primary="true" item="client"/>
507<iref primary="true" item="server"/>
508<iref primary="true" item="connection"/>
509<t>
510   HTTP is a stateless request/response protocol that operates by exchanging
511   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
512   transport or session-layer
513   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
514   program that establishes a connection to a server for the purpose of
515   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
516   program that accepts connections in order to service HTTP requests by
517   sending HTTP responses.
518</t>
519<iref primary="true" item="user agent"/>
520<iref primary="true" item="origin server"/>
521<iref primary="true" item="browser"/>
522<iref primary="true" item="spider"/>
523<iref primary="true" item="sender"/>
524<iref primary="true" item="recipient"/>
525<t>
526   Note that the terms client and server refer only to the roles that
527   these programs perform for a particular connection.  The same program
528   might act as a client on some connections and a server on others.  We use
529   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
530   such as a WWW browser, editor, or spider (web-traversing robot), and
531   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
532   authoritative responses to a request.  For general requirements, we use
533   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
534   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
535   message.
536</t>
537<t>
538   Most HTTP communication consists of a retrieval request (GET) for
539   a representation of some resource identified by a URI.  In the
540   simplest case, this might be accomplished via a single bidirectional
541   connection (===) between the user agent (UA) and the origin server (O).
542</t>
543<figure><artwork type="drawing">
544         request   &gt;
545    UA ======================================= O
546                                &lt;   response
547</artwork></figure>
548<iref primary="true" item="message"/>
549<iref primary="true" item="request"/>
550<iref primary="true" item="response"/>
551<t>
552   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
553   message, beginning with a request-line that includes a method, URI, and
554   protocol version (<xref target="request.line"/>),
555   followed by MIME-like header fields containing
556   request modifiers, client information, and payload metadata
557   (<xref target="header.fields"/>),
558   an empty line to indicate the end of the header section, and finally
559   a message body containing the payload body (if any,
560   <xref target="message.body"/>).
561</t>
562<t>
563   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
564   message, beginning with a status line that
565   includes the protocol version, a success or error code, and textual
566   reason phrase (<xref target="status.line"/>),
567   followed by MIME-like header fields containing server
568   information, resource metadata, and payload metadata
569   (<xref target="header.fields"/>),
570   an empty line to indicate the end of the header section, and finally
571   a message body containing the payload body (if any,
572   <xref target="message.body"/>).
573</t>
574<t>
575   The following example illustrates a typical message exchange for a
576   GET request on the URI "http://www.example.com/hello.txt":
577</t>
578<figure><preamble>
579client request:
580</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
581GET /hello.txt HTTP/1.1
582User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
583Host: www.example.com
584Accept: */*
585
586</artwork></figure>
587<figure><preamble>
588server response:
589</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
590HTTP/1.1 200 OK
591Date: Mon, 27 Jul 2009 12:28:53 GMT
592Server: Apache
593Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
594ETag: "34aa387-d-1568eb00"
595Accept-Ranges: bytes
596Content-Length: <x:length-of target="exbody"/>
597Vary: Accept-Encoding
598Content-Type: text/plain
599
600<x:span anchor="exbody">Hello World!
601</x:span></artwork></figure>
602</section>
603
604<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
605<t>
606   Fundamentally, HTTP is a message-based protocol. Although message bodies can
607   be chunked (<xref target="chunked.encoding"/>) and implementations often
608   make parts of a message available progressively, this is not required, and
609   some widely-used implementations only make a message available when it is
610   complete. Furthermore, while most proxies will progressively stream messages,
611   some amount of buffering will take place, and some proxies might buffer
612   messages to perform transformations, check content or provide other services.
613</t>
614<t>
615   Therefore, extensions to and uses of HTTP cannot rely on the availability of
616   a partial message, or assume that messages will not be buffered. There are
617   strategies that can be used to test for buffering in a given connection, but
618   it should be understood that behaviors can differ across connections, and
619   between requests and responses.
620</t>
621<t>
622   Recipients &MUST; consider every message in a connection in isolation;
623   because HTTP is a stateless protocol, it cannot be assumed that two requests
624   on the same connection are from the same client or share any other common
625   attributes. In particular, intermediaries might mix requests from different
626   clients into a single server connection. Note that some existing HTTP
627   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
628   potentially causing interoperability and security problems.
629</t>
630</section>
631
632<section title="Connections and Transport Independence" anchor="transport-independence">
633<t>
634   HTTP messaging is independent of the underlying transport or
635   session-layer connection protocol(s).  HTTP only presumes a reliable
636   transport with in-order delivery of requests and the corresponding
637   in-order delivery of responses.  The mapping of HTTP request and
638   response structures onto the data units of the underlying transport
639   protocol is outside the scope of this specification.
640</t>
641<t>
642   The specific connection protocols to be used for an interaction
643   are determined by client configuration and the target resource's URI.
644   For example, the "http" URI scheme
645   (<xref target="http.uri"/>) indicates a default connection of TCP
646   over IP, with a default TCP port of 80, but the client might be
647   configured to use a proxy via some other connection port or protocol
648   instead of using the defaults.
649</t>
650<t>
651   A connection might be used for multiple HTTP request/response exchanges,
652   as defined in <xref target="persistent.connections"/>.
653</t>
654</section>
655
656<section title="Intermediaries" anchor="intermediaries">
657<iref primary="true" item="intermediary"/>
658<t>
659   HTTP enables the use of intermediaries to satisfy requests through
660   a chain of connections.  There are three common forms of HTTP
661   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
662   a single intermediary might act as an origin server, proxy, gateway,
663   or tunnel, switching behavior based on the nature of each request.
664</t>
665<figure><artwork type="drawing">
666         &gt;             &gt;             &gt;             &gt;
667    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
668               &lt;             &lt;             &lt;             &lt;
669</artwork></figure>
670<t>
671   The figure above shows three intermediaries (A, B, and C) between the
672   user agent and origin server. A request or response message that
673   travels the whole chain will pass through four separate connections.
674   Some HTTP communication options
675   might apply only to the connection with the nearest, non-tunnel
676   neighbor, only to the end-points of the chain, or to all connections
677   along the chain. Although the diagram is linear, each participant might
678   be engaged in multiple, simultaneous communications. For example, B
679   might be receiving requests from many clients other than A, and/or
680   forwarding requests to servers other than C, at the same time that it
681   is handling A's request.
682</t>
683<t>
684<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
685<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
686   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
687   to describe various requirements in relation to the directional flow of a
688   message: all messages flow from upstream to downstream.
689   Likewise, we use the terms inbound and outbound to refer to
690   directions in relation to the request path:
691   "<x:dfn>inbound</x:dfn>" means toward the origin server and
692   "<x:dfn>outbound</x:dfn>" means toward the user agent.
693</t>
694<t><iref primary="true" item="proxy"/>
695   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
696   client, usually via local configuration rules, to receive requests
697   for some type(s) of absolute URI and attempt to satisfy those
698   requests via translation through the HTTP interface.  Some translations
699   are minimal, such as for proxy requests for "http" URIs, whereas
700   other requests might require translation to and from entirely different
701   application-layer protocols. Proxies are often used to group an
702   organization's HTTP requests through a common intermediary for the
703   sake of security, annotation services, or shared caching.
704</t>
705<t>
706<iref primary="true" item="transforming proxy"/>
707<iref primary="true" item="non-transforming proxy"/>
708   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
709   or configured to modify request or response messages in a semantically
710   meaningful way (i.e., modifications, beyond those required by normal
711   HTTP processing, that change the message in a way that would be
712   significant to the original sender or potentially significant to
713   downstream recipients).  For example, a transforming proxy might be
714   acting as a shared annotation server (modifying responses to include
715   references to a local annotation database), a malware filter, a
716   format transcoder, or an intranet-to-Internet privacy filter.  Such
717   transformations are presumed to be desired by the client (or client
718   organization) that selected the proxy and are beyond the scope of
719   this specification.  However, when a proxy is not intended to transform
720   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
721   requirements that preserve HTTP message semantics. See &status-203; and
722   &header-warning; for status and warning codes related to transformations.
723</t>
724<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
725<iref primary="true" item="accelerator"/>
726   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
727   is a receiving agent that acts
728   as a layer above some other server(s) and translates the received
729   requests to the underlying server's protocol.  Gateways are often
730   used to encapsulate legacy or untrusted information services, to
731   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
732   enable partitioning or load-balancing of HTTP services across
733   multiple machines.
734</t>
735<t>
736   A gateway behaves as an origin server on its outbound connection and
737   as a user agent on its inbound connection.
738   All HTTP requirements applicable to an origin server
739   also apply to the outbound communication of a gateway.
740   A gateway communicates with inbound servers using any protocol that
741   it desires, including private extensions to HTTP that are outside
742   the scope of this specification.  However, an HTTP-to-HTTP gateway
743   that wishes to interoperate with third-party HTTP servers &MUST;
744   comply with HTTP user agent requirements on the gateway's inbound
745   connection and &MUST; implement the Connection
746   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
747   header fields for both connections.
748</t>
749<t><iref primary="true" item="tunnel"/>
750   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
751   without changing the messages. Once active, a tunnel is not
752   considered a party to the HTTP communication, though the tunnel might
753   have been initiated by an HTTP request. A tunnel ceases to exist when
754   both ends of the relayed connection are closed. Tunnels are used to
755   extend a virtual connection through an intermediary, such as when
756   transport-layer security is used to establish private communication
757   through a shared firewall proxy.
758</t>
759<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
760<iref primary="true" item="captive portal"/>
761   In addition, there may exist network intermediaries that are not
762   considered part of the HTTP communication but nevertheless act as
763   filters or redirecting agents (usually violating HTTP semantics,
764   causing security problems, and otherwise making a mess of things).
765   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
766   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
767   or "<x:dfn>captive portal</x:dfn>",
768   differs from an HTTP proxy because it has not been selected by the client.
769   Instead, the network intermediary redirects outgoing TCP port 80 packets
770   (and occasionally other common port traffic) to an internal HTTP server.
771   Interception proxies are commonly found on public network access points,
772   as a means of enforcing account subscription prior to allowing use of
773   non-local Internet services, and within corporate firewalls to enforce
774   network usage policies.
775   They are indistinguishable from a man-in-the-middle attack.
776</t>
777</section>
778
779<section title="Caches" anchor="caches">
780<iref primary="true" item="cache"/>
781<t>
782   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
783   subsystem that controls its message storage, retrieval, and deletion.
784   A cache stores cacheable responses in order to reduce the response
785   time and network bandwidth consumption on future, equivalent
786   requests. Any client or server &MAY; employ a cache, though a cache
787   cannot be used by a server while it is acting as a tunnel.
788</t>
789<t>
790   The effect of a cache is that the request/response chain is shortened
791   if one of the participants along the chain has a cached response
792   applicable to that request. The following illustrates the resulting
793   chain if B has a cached copy of an earlier response from O (via C)
794   for a request which has not been cached by UA or A.
795</t>
796<figure><artwork type="drawing">
797            &gt;             &gt;
798       UA =========== A =========== B - - - - - - C - - - - - - O
799                  &lt;             &lt;
800</artwork></figure>
801<t><iref primary="true" item="cacheable"/>
802   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
803   the response message for use in answering subsequent requests.
804   Even when a response is cacheable, there might be additional
805   constraints placed by the client or by the origin server on when
806   that cached response can be used for a particular request. HTTP
807   requirements for cache behavior and cacheable responses are
808   defined in &caching-overview;
809</t>
810<t>
811   There are a wide variety of architectures and configurations
812   of caches and proxies deployed across the World Wide Web and
813   inside large organizations. These systems include national hierarchies
814   of proxy caches to save transoceanic bandwidth, systems that
815   broadcast or multicast cache entries, organizations that distribute
816   subsets of cached data via optical media, and so on.
817</t>
818</section>
819
820<section title="Protocol Versioning" anchor="http.version">
821  <x:anchor-alias value="HTTP-Version"/>
822  <x:anchor-alias value="HTTP-Prot-Name"/>
823<t>
824   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
825   versions of the protocol. This specification defines version "1.1".
826   The protocol version as a whole indicates the sender's compliance
827   with the set of requirements laid out in that version's corresponding
828   specification of HTTP.
829</t>
830<t>
831   The version of an HTTP message is indicated by an HTTP-Version field
832   in the first line of the message. HTTP-Version is case-sensitive.
833</t>
834<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
835  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
836  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
837</artwork></figure>
838<t>
839   The HTTP version number consists of two decimal digits separated by a "."
840   (period or decimal point).  The first digit ("major version") indicates the
841   HTTP messaging syntax, whereas the second digit ("minor version") indicates
842   the highest minor version to which the sender is at least conditionally
843   compliant and able to understand for future communication.  The minor
844   version advertises the sender's communication capabilities even when the
845   sender is only using a backwards-compatible subset of the protocol,
846   thereby letting the recipient know that more advanced features can
847   be used in response (by servers) or in future requests (by clients).
848</t>
849<t>
850   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
851   <xref target="RFC1945"/> or a recipient whose version is unknown,
852   the HTTP/1.1 message is constructed such that it can be interpreted
853   as a valid HTTP/1.0 message if all of the newer features are ignored.
854   This specification places recipient-version requirements on some
855   new features so that a compliant sender will only use compatible
856   features until it has determined, through configuration or the
857   receipt of a message, that the recipient supports HTTP/1.1.
858</t>
859<t>
860   The interpretation of an HTTP header field does not change
861   between minor versions of the same major version, though the default
862   behavior of a recipient in the absence of such a field can change.
863   Unless specified otherwise, header fields defined in HTTP/1.1 are
864   defined for all versions of HTTP/1.x.  In particular, the Host and
865   Connection header fields ought to be implemented by all HTTP/1.x
866   implementations whether or not they advertise compliance with HTTP/1.1.
867</t>
868<t>
869   New header fields can be defined such that, when they are
870   understood by a recipient, they might override or enhance the
871   interpretation of previously defined header fields.  When an
872   implementation receives an unrecognized header field, the recipient
873   &MUST; ignore that header field for local processing regardless of
874   the message's HTTP version.  An unrecognized header field received
875   by a proxy &MUST; be forwarded downstream unless the header field's
876   field-name is listed in the message's Connection header-field
877   (see <xref target="header.connection"/>).
878   These requirements allow HTTP's functionality to be enhanced without
879   requiring prior update of all compliant intermediaries.
880</t>
881<t>
882   Intermediaries that process HTTP messages (i.e., all intermediaries
883   other than those acting as a tunnel) &MUST; send their own HTTP-Version
884   in forwarded messages.  In other words, they &MUST-NOT; blindly
885   forward the first line of an HTTP message without ensuring that the
886   protocol version matches what the intermediary understands, and
887   is at least conditionally compliant to, for both the receiving and
888   sending of messages.  Forwarding an HTTP message without rewriting
889   the HTTP-Version might result in communication errors when downstream
890   recipients use the message sender's version to determine what features
891   are safe to use for later communication with that sender.
892</t>
893<t>
894   An HTTP client &SHOULD; send a request version equal to the highest
895   version for which the client is at least conditionally compliant and
896   whose major version is no higher than the highest version supported
897   by the server, if this is known.  An HTTP client &MUST-NOT; send a
898   version for which it is not at least conditionally compliant.
899</t>
900<t>
901   An HTTP client &MAY; send a lower request version if it is known that
902   the server incorrectly implements the HTTP specification, but only
903   after the client has attempted at least one normal request and determined
904   from the response status or header fields (e.g., Server) that the
905   server improperly handles higher request versions.
906</t>
907<t>
908   An HTTP server &SHOULD; send a response version equal to the highest
909   version for which the server is at least conditionally compliant and
910   whose major version is less than or equal to the one received in the
911   request.  An HTTP server &MUST-NOT; send a version for which it is not
912   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
913   Version Not Supported) response if it cannot send a response using the
914   major version used in the client's request.
915</t>
916<t>
917   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
918   if it is known or suspected that the client incorrectly implements the
919   HTTP specification and is incapable of correctly processing later
920   version responses, such as when a client fails to parse the version
921   number correctly or when an intermediary is known to blindly forward
922   the HTTP-Version even when it doesn't comply with the given minor
923   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
924   performed unless triggered by specific client attributes, such as when
925   one or more of the request header fields (e.g., User-Agent) uniquely
926   match the values sent by a client known to be in error.
927</t>
928<t>
929   The intention of HTTP's versioning design is that the major number
930   will only be incremented if an incompatible message syntax is
931   introduced, and that the minor number will only be incremented when
932   changes made to the protocol have the effect of adding to the message
933   semantics or implying additional capabilities of the sender.  However,
934   the minor version was not incremented for the changes introduced between
935   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
936   is specifically avoiding any such changes to the protocol.
937</t>
938</section>
939
940<section title="Uniform Resource Identifiers" anchor="uri">
941<iref primary="true" item="resource"/>
942<t>
943   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
944   throughout HTTP as the means for identifying resources. URI references
945   are used to target requests, indicate redirects, and define relationships.
946   HTTP does not limit what a resource might be; it merely defines an interface
947   that can be used to interact with a resource via HTTP. More information on
948   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
949</t>
950  <x:anchor-alias value="URI-reference"/>
951  <x:anchor-alias value="absolute-URI"/>
952  <x:anchor-alias value="relative-part"/>
953  <x:anchor-alias value="authority"/>
954  <x:anchor-alias value="path-abempty"/>
955  <x:anchor-alias value="path-absolute"/>
956  <x:anchor-alias value="port"/>
957  <x:anchor-alias value="query"/>
958  <x:anchor-alias value="uri-host"/>
959  <x:anchor-alias value="partial-URI"/>
960<t>
961   This specification adopts the definitions of "URI-reference",
962   "absolute-URI", "relative-part", "port", "host",
963   "path-abempty", "path-absolute", "query", and "authority" from the
964   URI generic syntax <xref target="RFC3986"/>.
965   In addition, we define a partial-URI rule for protocol elements
966   that allow a relative URI but not a fragment.
967</t>
968<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"/>
969  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
970  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
971  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
972  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
973  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
974  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
975  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
976  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
977  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
978 
979  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
980</artwork></figure>
981<t>
982   Each protocol element in HTTP that allows a URI reference will indicate
983   in its ABNF production whether the element allows any form of reference
984   (URI-reference), only a URI in absolute form (absolute-URI), only the
985   path and optional query components, or some combination of the above.
986   Unless otherwise indicated, URI references are parsed relative to the
987   effective request URI, which defines the default base URI for references
988   in both the request and its corresponding response.
989</t>
990
991<section title="http URI scheme" anchor="http.uri">
992  <x:anchor-alias value="http-URI"/>
993  <iref item="http URI scheme" primary="true"/>
994  <iref item="URI scheme" subitem="http" primary="true"/>
995<t>
996   The "http" URI scheme is hereby defined for the purpose of minting
997   identifiers according to their association with the hierarchical
998   namespace governed by a potential HTTP origin server listening for
999   TCP connections on a given port.
1000</t>
1001<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1002  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1003</artwork></figure>
1004<t>
1005   The HTTP origin server is identified by the generic syntax's
1006   <x:ref>authority</x:ref> component, which includes a host identifier
1007   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1008   The remainder of the URI, consisting of both the hierarchical path
1009   component and optional query component, serves as an identifier for
1010   a potential resource within that origin server's name space.
1011</t>
1012<t>
1013   If the host identifier is provided as an IP literal or IPv4 address,
1014   then the origin server is any listener on the indicated TCP port at
1015   that IP address. If host is a registered name, then that name is
1016   considered an indirect identifier and the recipient might use a name
1017   resolution service, such as DNS, to find the address of a listener
1018   for that host.
1019   The host &MUST-NOT; be empty; if an "http" URI is received with an
1020   empty host, then it &MUST; be rejected as invalid.
1021   If the port subcomponent is empty or not given, then TCP port 80 is
1022   assumed (the default reserved port for WWW services).
1023</t>
1024<t>
1025   Regardless of the form of host identifier, access to that host is not
1026   implied by the mere presence of its name or address. The host might or might
1027   not exist and, even when it does exist, might or might not be running an
1028   HTTP server or listening to the indicated port. The "http" URI scheme
1029   makes use of the delegated nature of Internet names and addresses to
1030   establish a naming authority (whatever entity has the ability to place
1031   an HTTP server at that Internet name or address) and allows that
1032   authority to determine which names are valid and how they might be used.
1033</t>
1034<t>
1035   When an "http" URI is used within a context that calls for access to the
1036   indicated resource, a client &MAY; attempt access by resolving
1037   the host to an IP address, establishing a TCP connection to that address
1038   on the indicated port, and sending an HTTP request message
1039   (<xref target="http.message"/>) containing the URI's identifying data
1040   (<xref target="message.routing"/>) to the server.
1041   If the server responds to that request with a non-interim HTTP response
1042   message, as described in &status-code-reasonphr;, then that response
1043   is considered an authoritative answer to the client's request.
1044</t>
1045<t>
1046   Although HTTP is independent of the transport protocol, the "http"
1047   scheme is specific to TCP-based services because the name delegation
1048   process depends on TCP for establishing authority.
1049   An HTTP service based on some other underlying connection protocol
1050   would presumably be identified using a different URI scheme, just as
1051   the "https" scheme (below) is used for servers that require an SSL/TLS
1052   transport layer on a connection. Other protocols might also be used to
1053   provide access to "http" identified resources &mdash; it is only the
1054   authoritative interface used for mapping the namespace that is
1055   specific to TCP.
1056</t>
1057<t>
1058   The URI generic syntax for authority also includes a deprecated
1059   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1060   for including user authentication information in the URI.  Some
1061   implementations make use of the userinfo component for internal
1062   configuration of authentication information, such as within command
1063   invocation options, configuration files, or bookmark lists, even
1064   though such usage might expose a user identifier or password.
1065   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1066   delimiter) when transmitting an "http" URI in a message.  Recipients
1067   of HTTP messages that contain a URI reference &SHOULD; parse for the
1068   existence of userinfo and treat its presence as an error, likely
1069   indicating that the deprecated subcomponent is being used to obscure
1070   the authority for the sake of phishing attacks.
1071</t>
1072</section>
1073
1074<section title="https URI scheme" anchor="https.uri">
1075   <x:anchor-alias value="https-URI"/>
1076   <iref item="https URI scheme"/>
1077   <iref item="URI scheme" subitem="https"/>
1078<t>
1079   The "https" URI scheme is hereby defined for the purpose of minting
1080   identifiers according to their association with the hierarchical
1081   namespace governed by a potential HTTP origin server listening for
1082   SSL/TLS-secured connections on a given TCP port.
1083</t>
1084<t>
1085   All of the requirements listed above for the "http" scheme are also
1086   requirements for the "https" scheme, except that a default TCP port
1087   of 443 is assumed if the port subcomponent is empty or not given,
1088   and the TCP connection &MUST; be secured for privacy through the
1089   use of strong encryption prior to sending the first HTTP request.
1090</t>
1091<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1092  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1093</artwork></figure>
1094<t>
1095   Unlike the "http" scheme, responses to "https" identified requests
1096   are never "public" and thus &MUST-NOT; be reused for shared caching.
1097   They can, however, be reused in a private cache if the message is
1098   cacheable by default in HTTP or specifically indicated as such by
1099   the Cache-Control header field (&header-cache-control;).
1100</t>
1101<t>
1102   Resources made available via the "https" scheme have no shared
1103   identity with the "http" scheme even if their resource identifiers
1104   indicate the same authority (the same host listening to the same
1105   TCP port).  They are distinct name spaces and are considered to be
1106   distinct origin servers.  However, an extension to HTTP that is
1107   defined to apply to entire host domains, such as the Cookie protocol
1108   <xref target="RFC6265"/>, can allow information
1109   set by one service to impact communication with other services
1110   within a matching group of host domains.
1111</t>
1112<t>
1113   The process for authoritative access to an "https" identified
1114   resource is defined in <xref target="RFC2818"/>.
1115</t>
1116</section>
1117
1118<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1119<t>
1120   Since the "http" and "https" schemes conform to the URI generic syntax,
1121   such URIs are normalized and compared according to the algorithm defined
1122   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1123   described above for each scheme.
1124</t>
1125<t>
1126   If the port is equal to the default port for a scheme, the normal
1127   form is to elide the port subcomponent. Likewise, an empty path
1128   component is equivalent to an absolute path of "/", so the normal
1129   form is to provide a path of "/" instead. The scheme and host
1130   are case-insensitive and normally provided in lowercase; all
1131   other components are compared in a case-sensitive manner.
1132   Characters other than those in the "reserved" set are equivalent
1133   to their percent-encoded octets (see <xref target="RFC3986"
1134   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1135</t>
1136<t>
1137   For example, the following three URIs are equivalent:
1138</t>
1139<figure><artwork type="example">
1140   http://example.com:80/~smith/home.html
1141   http://EXAMPLE.com/%7Esmith/home.html
1142   http://EXAMPLE.com:/%7esmith/home.html
1143</artwork></figure>
1144</section>
1145</section>
1146</section>
1147
1148<section title="Message Format" anchor="http.message">
1149<x:anchor-alias value="generic-message"/>
1150<x:anchor-alias value="message.types"/>
1151<x:anchor-alias value="HTTP-message"/>
1152<x:anchor-alias value="start-line"/>
1153<iref item="header section"/>
1154<iref item="headers"/>
1155<iref item="header field"/>
1156<t>
1157   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1158   octets in a format similar to the Internet Message Format
1159   <xref target="RFC5322"/>: zero or more header fields (collectively
1160   referred to as the "headers" or the "header section"), an empty line
1161   indicating the end of the header section, and an optional message-body.
1162</t>
1163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1164  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1165                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1166                    <x:ref>CRLF</x:ref>
1167                    [ <x:ref>message-body</x:ref> ]
1168</artwork></figure>
1169<t>
1170   The normal procedure for parsing an HTTP message is to read the
1171   start-line into a structure, read each header field into a hash
1172   table by field name until the empty line, and then use the parsed
1173   data to determine if a message-body is expected.  If a message-body
1174   has been indicated, then it is read as a stream until an amount
1175   of octets equal to the message-body length is read or the connection
1176   is closed.
1177</t>
1178<t>
1179   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1180   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1181   Parsing an HTTP message as a stream of Unicode characters, without regard
1182   for the specific encoding, creates security vulnerabilities due to the
1183   varying ways that string processing libraries handle invalid multibyte
1184   character sequences that contain the octet LF (%x0A).  String-based
1185   parsers can only be safely used within protocol elements after the element
1186   has been extracted from the message, such as within a header field-value
1187   after message parsing has delineated the individual fields.
1188</t>
1189
1190<section title="Start Line" anchor="start.line">
1191  <x:anchor-alias value="Start-Line"/>
1192<t>
1193   An HTTP message can either be a request from client to server or a
1194   response from server to client.  Syntactically, the two types of message
1195   differ only in the start-line, which is either a Request-Line (for requests)
1196   or a Status-Line (for responses), and in the algorithm for determining
1197   the length of the message-body (<xref target="message.body"/>).
1198   In theory, a client could receive requests and a server could receive
1199   responses, distinguishing them by their different start-line formats,
1200   but in practice servers are implemented to only expect a request
1201   (a response is interpreted as an unknown or invalid request method)
1202   and clients are implemented to only expect a response.
1203</t>
1204<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1205  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1206</artwork></figure>
1207<t>
1208</t>
1209<t>
1210   Implementations &MUST-NOT; send whitespace between the start-line and
1211   the first header field. The presence of such whitespace in a request
1212   might be an attempt to trick a server into ignoring that field or
1213   processing the line after it as a new request, either of which might
1214   result in a security vulnerability if other implementations within
1215   the request chain interpret the same message differently.
1216   Likewise, the presence of such whitespace in a response might be
1217   ignored by some clients or cause others to cease parsing.
1218</t>
1219
1220<section title="Request-Line" anchor="request.line">
1221  <x:anchor-alias value="Request"/>
1222  <x:anchor-alias value="Request-Line"/>
1223<t>
1224   The Request-Line begins with a method token, followed by a single
1225   space (SP), the request-target, another single space (SP), the
1226   protocol version, and ending with CRLF.
1227</t>
1228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1229  <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>
1230</artwork></figure>
1231
1232<section title="Method" anchor="method">
1233  <x:anchor-alias value="Method"/>
1234<t>
1235   The Method token indicates the request method to be performed on the
1236   target resource. The request method is case-sensitive.
1237</t>
1238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1239  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1240</artwork></figure>
1241<t>
1242   See &method; for further information, such as the list of methods defined
1243   by this specification, the IANA registry, and considerations for new methods.
1244</t>
1245</section>
1246
1247<section title="request-target" anchor="request-target">
1248  <x:anchor-alias value="request-target"/>
1249<t>
1250   The request-target identifies the target resource upon which to apply
1251   the request.  The four options for request-target are described in
1252   <xref target="request-target-types"/>.
1253</t>
1254<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1255  <x:ref>request-target</x:ref> = "*"
1256                 / <x:ref>absolute-URI</x:ref>
1257                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1258                 / <x:ref>authority</x:ref>
1259</artwork></figure>
1260<t>
1261   HTTP does not place a pre-defined limit on the length of a request-target.
1262   A server &MUST; be prepared to receive URIs of unbounded length and
1263   respond with the 414 (URI Too Long) status code if the received
1264   request-target would be longer than the server wishes to handle
1265   (see &status-414;).
1266</t>
1267<t>
1268   Various ad-hoc limitations on request-target length are found in practice.
1269   It is &RECOMMENDED; that all HTTP senders and recipients support
1270   request-target lengths of 8000 or more octets.
1271</t>
1272<x:note>
1273  <t>
1274    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1275    are not part of the request-target and thus will not be transmitted
1276    in an HTTP request.
1277  </t>
1278</x:note>
1279</section>
1280</section>
1281
1282<section title="Response Status-Line" anchor="status.line">
1283  <x:anchor-alias value="Response"/>
1284  <x:anchor-alias value="Status-Line"/>
1285<t>
1286   The first line of a Response message is the Status-Line, consisting
1287   of the protocol version, a space (SP), the status code, another space,
1288   a possibly-empty textual phrase describing the status code, and
1289   ending with CRLF.
1290</t>
1291<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1292  <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>
1293</artwork></figure>
1294
1295<section title="Status Code" anchor="status.code">
1296  <x:anchor-alias value="Status-Code"/>
1297<t>
1298   The Status-Code element is a 3-digit integer result code of the attempt to
1299   understand and satisfy the request. See &status-code-reasonphr; for
1300   further information, such as the list of status codes defined by this
1301   specification, the IANA registry, and considerations for new status codes.
1302</t>
1303<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1304  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1305</artwork></figure>
1306</section>
1307
1308<section title="Reason Phrase" anchor="reason.phrase">
1309  <x:anchor-alias value="Reason-Phrase"/>
1310<t>   
1311   The Reason Phrase exists for the sole purpose of providing a textual
1312   description associated with the numeric status code, out of deference to
1313   earlier Internet application protocols that were more frequently used with
1314   interactive text clients. A client &SHOULD; ignore the content of the Reason
1315   Phrase.
1316</t>
1317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1318  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1319</artwork></figure>
1320</section>
1321</section>
1322
1323</section>
1324
1325<section title="Header Fields" anchor="header.fields">
1326  <x:anchor-alias value="header-field"/>
1327  <x:anchor-alias value="field-content"/>
1328  <x:anchor-alias value="field-name"/>
1329  <x:anchor-alias value="field-value"/>
1330  <x:anchor-alias value="OWS"/>
1331<t>
1332   Each HTTP header field consists of a case-insensitive field name
1333   followed by a colon (":"), optional whitespace, and the field value.
1334</t>
1335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1336  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1337  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1338  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1339  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1340</artwork></figure>
1341<t>
1342   The field-name token labels the corresponding field-value as having the
1343   semantics defined by that header field.  For example, the Date header field
1344   is defined in &header-date; as containing the origination
1345   timestamp for the message in which it appears.
1346</t>
1347<t>
1348   HTTP header fields are fully extensible: there is no limit on the
1349   introduction of new field names, each presumably defining new semantics,
1350   or on the number of header fields used in a given message.  Existing
1351   fields are defined in each part of this specification and in many other
1352   specifications outside the standards process.
1353   New header fields can be introduced without changing the protocol version
1354   if their defined semantics allow them to be safely ignored by recipients
1355   that do not recognize them.
1356</t>
1357<t>
1358   New HTTP header fields &SHOULD; be registered with IANA according
1359   to the procedures in &cons-new-header-fields;.
1360   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1361   field-name is listed in the Connection header field
1362   (<xref target="header.connection"/>) or the proxy is specifically
1363   configured to block or otherwise transform such fields.
1364   Unrecognized header fields &SHOULD; be ignored by other recipients.
1365</t>
1366<t>
1367   The order in which header fields with differing field names are
1368   received is not significant. However, it is "good practice" to send
1369   header fields that contain control data first, such as Host on
1370   requests and Date on responses, so that implementations can decide
1371   when not to handle a message as early as possible.  A server &MUST;
1372   wait until the entire header section is received before interpreting
1373   a request message, since later header fields might include conditionals,
1374   authentication credentials, or deliberately misleading duplicate
1375   header fields that would impact request processing.
1376</t>
1377<t>
1378   Multiple header fields with the same field name &MUST-NOT; be
1379   sent in a message unless the entire field value for that
1380   header field is defined as a comma-separated list [i.e., #(values)].
1381   Multiple header fields with the same field name can be combined into
1382   one "field-name: field-value" pair, without changing the semantics of the
1383   message, by appending each subsequent field value to the combined
1384   field value in order, separated by a comma. The order in which
1385   header fields with the same field name are received is therefore
1386   significant to the interpretation of the combined field value;
1387   a proxy &MUST-NOT; change the order of these field values when
1388   forwarding a message.
1389</t>
1390<x:note>
1391  <t>
1392   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1393   practice can occur multiple times, but does not use the list syntax, and
1394   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1395   for details.) Also note that the Set-Cookie2 header field specified in
1396   <xref target="RFC2965"/> does not share this problem.
1397  </t>
1398</x:note>
1399
1400<section title="Field Parsing" anchor="field.parsing">
1401<t>
1402   No whitespace is allowed between the header field-name and colon.
1403   In the past, differences in the handling of such whitespace have led to
1404   security vulnerabilities in request routing and response handling.
1405   Any received request message that contains whitespace between a header
1406   field-name and colon &MUST; be rejected with a response code of 400
1407   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1408   message before forwarding the message downstream.
1409</t>
1410<t>
1411   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1412   preferred. The field value does not include any leading or trailing white
1413   space: OWS occurring before the first non-whitespace octet of the
1414   field value or after the last non-whitespace octet of the field value
1415   is ignored and &SHOULD; be removed before further processing (as this does
1416   not change the meaning of the header field).
1417</t>
1418<t>
1419   Historically, HTTP header field values could be extended over multiple
1420   lines by preceding each extra line with at least one space or horizontal
1421   tab (obs-fold). This specification deprecates such line
1422   folding except within the message/http media type
1423   (<xref target="internet.media.type.message.http"/>).
1424   HTTP senders &MUST-NOT; produce messages that include line folding
1425   (i.e., that contain any field-content that matches the obs-fold rule) unless
1426   the message is intended for packaging within the message/http media type.
1427   HTTP recipients &SHOULD; accept line folding and replace any embedded
1428   obs-fold whitespace with either a single SP or a matching number of SP
1429   octets (to avoid buffer copying) prior to interpreting the field value or
1430   forwarding the message downstream.
1431</t>
1432<t>
1433   Historically, HTTP has allowed field content with text in the ISO-8859-1
1434   <xref target="ISO-8859-1"/> character encoding and supported other
1435   character sets only through use of <xref target="RFC2047"/> encoding.
1436   In practice, most HTTP header field values use only a subset of the
1437   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1438   header fields &SHOULD; limit their field values to US-ASCII octets.
1439   Recipients &SHOULD; treat other (obs-text) octets in field content as
1440   opaque data.
1441</t>
1442</section>
1443
1444<section title="Field Length" anchor="field.length">
1445<t>
1446   HTTP does not place a pre-defined limit on the length of header fields,
1447   either in isolation or as a set. A server &MUST; be prepared to receive
1448   request header fields of unbounded length and respond with a 4xx status
1449   code if the received header field(s) would be longer than the server wishes
1450   to handle.
1451</t>
1452<t>
1453   A client that receives response headers that are longer than it wishes to
1454   handle can only treat it as a server error.
1455</t>
1456<t>
1457   Various ad-hoc limitations on header length are found in practice. It is
1458   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1459   combined header fields have 4000 or more octets.
1460</t>
1461</section>
1462
1463<section title="Common Field ABNF Rules" anchor="field.rules">
1464<t anchor="rule.token.separators">
1465  <x:anchor-alias value="tchar"/>
1466  <x:anchor-alias value="token"/>
1467  <x:anchor-alias value="special"/>
1468  <x:anchor-alias value="word"/>
1469   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1470   separated by whitespace or special characters. These special characters
1471   &MUST; be in a quoted string to be used within a parameter value (as defined
1472   in <xref target="transfer.codings"/>).
1473</t>
1474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
1475  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1476
1477  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1478<!--
1479  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1480 -->
1481  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1482                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1483                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1484                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1485
1486  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1487                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1488                 / "]" / "?" / "=" / "{" / "}"
1489</artwork></figure>
1490<t anchor="rule.quoted-string">
1491  <x:anchor-alias value="quoted-string"/>
1492  <x:anchor-alias value="qdtext"/>
1493  <x:anchor-alias value="obs-text"/>
1494   A string of text is parsed as a single word if it is quoted using
1495   double-quote marks.
1496</t>
1497<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"/>
1498  <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>
1499  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1500  <x:ref>obs-text</x:ref>       = %x80-FF
1501</artwork></figure>
1502<t anchor="rule.quoted-pair">
1503  <x:anchor-alias value="quoted-pair"/>
1504   The backslash octet ("\") can be used as a single-octet
1505   quoting mechanism within quoted-string constructs:
1506</t>
1507<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1508  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1509</artwork></figure>
1510<t>
1511   Recipients that process the value of the quoted-string &MUST; handle a
1512   quoted-pair as if it were replaced by the octet following the backslash.
1513</t>
1514<t>
1515   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1516   escaping (i.e., other than DQUOTE and the backslash octet).
1517</t>
1518<t anchor="rule.comment">
1519  <x:anchor-alias value="comment"/>
1520  <x:anchor-alias value="ctext"/>
1521   Comments can be included in some HTTP header fields by surrounding
1522   the comment text with parentheses. Comments are only allowed in
1523   fields containing "comment" as part of their field value definition.
1524</t>
1525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1526  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1527  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1528</artwork></figure>
1529<t anchor="rule.quoted-cpair">
1530  <x:anchor-alias value="quoted-cpair"/>
1531   The backslash octet ("\") can be used as a single-octet
1532   quoting mechanism within comment constructs:
1533</t>
1534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1535  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1536</artwork></figure>
1537<t>
1538   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1539   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1540</t>
1541</section>
1542</section>
1543
1544<section title="Message Body" anchor="message.body">
1545  <x:anchor-alias value="message-body"/>
1546<t>
1547   The message-body (if any) of an HTTP message is used to carry the
1548   payload body associated with the request or response.
1549</t>
1550<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1551  <x:ref>message-body</x:ref> = *OCTET
1552</artwork></figure>
1553<t>
1554   The message-body differs from the payload body only when a transfer-coding
1555   has been applied, as indicated by the Transfer-Encoding header field
1556   (<xref target="header.transfer-encoding"/>).  If more than one
1557   Transfer-Encoding header field is present in a message, the multiple
1558   field-values &MUST; be combined into one field-value, according to the
1559   algorithm defined in <xref target="header.fields"/>, before determining
1560   the message-body length.
1561</t>
1562<t>
1563   When one or more transfer-codings are applied to a payload in order to
1564   form the message-body, the Transfer-Encoding header field &MUST; contain
1565   the list of transfer-codings applied. Transfer-Encoding is a property of
1566   the message, not of the payload, and thus &MAY; be added or removed by
1567   any implementation along the request/response chain under the constraints
1568   found in <xref target="transfer.codings"/>.
1569</t>
1570<t>
1571   If a message is received that has multiple Content-Length header fields
1572   (<xref target="header.content-length"/>) with field-values consisting
1573   of the same decimal value, or a single Content-Length header field with
1574   a field value containing a list of identical decimal values (e.g.,
1575   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1576   header fields have been generated or combined by an upstream message
1577   processor, then the recipient &MUST; either reject the message as invalid
1578   or replace the duplicated field-values with a single valid Content-Length
1579   field containing that decimal value prior to determining the message-body
1580   length.
1581</t>
1582<t>
1583   The rules for when a message-body is allowed in a message differ for
1584   requests and responses.
1585</t>
1586<t>
1587   The presence of a message-body in a request is signaled by the
1588   inclusion of a Content-Length or Transfer-Encoding header field in
1589   the request's header fields, even if the request method does not
1590   define any use for a message-body.  This allows the request
1591   message framing algorithm to be independent of method semantics.
1592</t>
1593<t>
1594   For response messages, whether or not a message-body is included with
1595   a message is dependent on both the request method and the response
1596   status code (<xref target="status.code"/>).
1597   Responses to the HEAD request method never include a message-body
1598   because the associated response header fields (e.g., Transfer-Encoding,
1599   Content-Length, etc.) only indicate what their values would have been
1600   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1601   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1602   All other responses do include a message-body, although the body
1603   &MAY; be of zero length.
1604</t>
1605<t>
1606   The length of the message-body is determined by one of the following
1607   (in order of precedence):
1608</t>
1609<t>
1610  <list style="numbers">
1611    <x:lt><t>
1612     Any response to a HEAD request and any response with a status
1613     code of 100-199, 204, or 304 is always terminated by the first
1614     empty line after the header fields, regardless of the header
1615     fields present in the message, and thus cannot contain a message-body.
1616    </t></x:lt>
1617    <x:lt><t>
1618     If a Transfer-Encoding header field is present
1619     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1620     is the final encoding, the message-body length is determined by reading
1621     and decoding the chunked data until the transfer-coding indicates the
1622     data is complete.
1623    </t>
1624    <t>
1625     If a Transfer-Encoding header field is present in a response and the
1626     "chunked" transfer-coding is not the final encoding, the message-body
1627     length is determined by reading the connection until it is closed by
1628     the server.
1629     If a Transfer-Encoding header field is present in a request and the
1630     "chunked" transfer-coding is not the final encoding, the message-body
1631     length cannot be determined reliably; the server &MUST; respond with
1632     the 400 (Bad Request) status code and then close the connection.
1633    </t>
1634    <t>
1635     If a message is received with both a Transfer-Encoding header field
1636     and a Content-Length header field, the Transfer-Encoding overrides
1637     the Content-Length.
1638     Such a message might indicate an attempt to perform request or response
1639     smuggling (bypass of security-related checks on message routing or content)
1640     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1641     be removed, prior to forwarding the message downstream, or replaced with
1642     the real message-body length after the transfer-coding is decoded.
1643    </t></x:lt>
1644    <x:lt><t>
1645     If a message is received without Transfer-Encoding and with either
1646     multiple Content-Length header fields having differing field-values or
1647     a single Content-Length header field having an invalid value, then the
1648     message framing is invalid and &MUST; be treated as an error to
1649     prevent request or response smuggling.
1650     If this is a request message, the server &MUST; respond with
1651     a 400 (Bad Request) status code and then close the connection.
1652     If this is a response message received by a proxy, the proxy
1653     &MUST; discard the received response, send a 502 (Bad Gateway)
1654     status code as its downstream response, and then close the connection.
1655     If this is a response message received by a user-agent, it &MUST; be
1656     treated as an error by discarding the message and closing the connection.
1657    </t></x:lt>
1658    <x:lt><t>
1659     If a valid Content-Length header field
1660     is present without Transfer-Encoding, its decimal value defines the
1661     message-body length in octets.  If the actual number of octets sent in
1662     the message is less than the indicated Content-Length, the recipient
1663     &MUST; consider the message to be incomplete and treat the connection
1664     as no longer usable.
1665     If the actual number of octets sent in the message is more than the indicated
1666     Content-Length, the recipient &MUST; only process the message-body up to the
1667     field value's number of octets; the remainder of the message &MUST; either
1668     be discarded or treated as the next message in a pipeline.  For the sake of
1669     robustness, a user-agent &MAY; attempt to detect and correct such an error
1670     in message framing if it is parsing the response to the last request on
1671     a connection and the connection has been closed by the server.
1672    </t></x:lt>
1673    <x:lt><t>
1674     If this is a request message and none of the above are true, then the
1675     message-body length is zero (no message-body is present).
1676    </t></x:lt>
1677    <x:lt><t>
1678     Otherwise, this is a response message without a declared message-body
1679     length, so the message-body length is determined by the number of octets
1680     received prior to the server closing the connection.
1681    </t></x:lt>
1682  </list>
1683</t>
1684<t>
1685   Since there is no way to distinguish a successfully completed,
1686   close-delimited message from a partially-received message interrupted
1687   by network failure, implementations &SHOULD; use encoding or
1688   length-delimited messages whenever possible.  The close-delimiting
1689   feature exists primarily for backwards compatibility with HTTP/1.0.
1690</t>
1691<t>
1692   A server &MAY; reject a request that contains a message-body but
1693   not a Content-Length by responding with 411 (Length Required).
1694</t>
1695<t>
1696   Unless a transfer-coding other than "chunked" has been applied,
1697   a client that sends a request containing a message-body &SHOULD;
1698   use a valid Content-Length header field if the message-body length
1699   is known in advance, rather than the "chunked" encoding, since some
1700   existing services respond to "chunked" with a 411 (Length Required)
1701   status code even though they understand the chunked encoding.  This
1702   is typically because such services are implemented via a gateway that
1703   requires a content-length in advance of being called and the server
1704   is unable or unwilling to buffer the entire request before processing.
1705</t>
1706<t>
1707   A client that sends a request containing a message-body &MUST; include a
1708   valid Content-Length header field if it does not know the server will
1709   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1710   of specific user configuration or by remembering the version of a prior
1711   received response.
1712</t>
1713</section>
1714
1715<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1716<t>
1717   Request messages that are prematurely terminated, possibly due to a
1718   cancelled connection or a server-imposed time-out exception, &MUST;
1719   result in closure of the connection; sending an HTTP/1.1 error response
1720   prior to closing the connection is &OPTIONAL;.
1721</t>
1722<t>
1723   Response messages that are prematurely terminated, usually by closure
1724   of the connection prior to receiving the expected number of octets or by
1725   failure to decode a transfer-encoded message-body, &MUST; be recorded
1726   as incomplete.  A response that terminates in the middle of the header
1727   block (before the empty line is received) cannot be assumed to convey the
1728   full semantics of the response and &MUST; be treated as an error.
1729</t>
1730<t>
1731   A message-body that uses the chunked transfer encoding is
1732   incomplete if the zero-sized chunk that terminates the encoding has not
1733   been received.  A message that uses a valid Content-Length is incomplete
1734   if the size of the message-body received (in octets) is less than the
1735   value given by Content-Length.  A response that has neither chunked
1736   transfer encoding nor Content-Length is terminated by closure of the
1737   connection, and thus is considered complete regardless of the number of
1738   message-body octets received, provided that the header block was received
1739   intact.
1740</t>
1741<t>
1742   A user agent &MUST-NOT; render an incomplete response message-body as if
1743   it were complete (i.e., some indication must be given to the user that an
1744   error occurred).  Cache requirements for incomplete responses are defined
1745   in &cache-incomplete;.
1746</t>
1747<t>
1748   A server &MUST; read the entire request message-body or close
1749   the connection after sending its response, since otherwise the
1750   remaining data on a persistent connection would be misinterpreted
1751   as the next request.  Likewise,
1752   a client &MUST; read the entire response message-body if it intends
1753   to reuse the same connection for a subsequent request.  Pipelining
1754   multiple requests on a connection is described in <xref target="pipelining"/>.
1755</t>
1756</section>
1757
1758<section title="Message Parsing Robustness" anchor="message.robustness">
1759<t>
1760   Older HTTP/1.0 client implementations might send an extra CRLF
1761   after a POST request as a lame workaround for some early server
1762   applications that failed to read message-body content that was
1763   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1764   preface or follow a request with an extra CRLF.  If terminating
1765   the request message-body with a line-ending is desired, then the
1766   client &MUST; include the terminating CRLF octets as part of the
1767   message-body length.
1768</t>
1769<t>
1770   In the interest of robustness, servers &SHOULD; ignore at least one
1771   empty line received where a Request-Line is expected. In other words, if
1772   the server is reading the protocol stream at the beginning of a
1773   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1774   Likewise, although the line terminator for the start-line and header
1775   fields is the sequence CRLF, we recommend that recipients recognize a
1776   single LF as a line terminator and ignore any CR.
1777</t>
1778<t>
1779   When a server listening only for HTTP request messages, or processing
1780   what appears from the start-line to be an HTTP request message,
1781   receives a sequence of octets that does not match the HTTP-message
1782   grammar aside from the robustness exceptions listed above, the
1783   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1784</t>
1785</section>
1786</section>
1787
1788<section title="Message Routing" anchor="message.routing">
1789<t>
1790   In most cases, the user agent is provided a URI reference
1791   from which it determines an absolute URI for identifying the target
1792   resource.  When a request to the resource is initiated, all or part
1793   of that URI is used to construct the HTTP request-target.
1794</t>
1795
1796<section title="Types of Request Target" anchor="request-target-types">
1797<t>
1798   The four options for request-target are dependent on the nature of the
1799   request.
1800</t>   
1801<t><iref item="asterisk form (of request-target)"/>
1802   The asterisk "*" form of request-target, which &MUST-NOT; be used
1803   with any request method other than OPTIONS, means that the request
1804   applies to the server as a whole (the listening process) rather than
1805   to a specific named resource at that server.  For example,
1806</t>
1807<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1808OPTIONS * HTTP/1.1
1809</artwork></figure>
1810<t><iref item="absolute-URI form (of request-target)"/>
1811   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1812   proxy. The proxy is requested to either forward the request or service it
1813   from a valid cache, and then return the response. Note that the proxy &MAY;
1814   forward the request on to another proxy or directly to the server
1815   specified by the absolute-URI. In order to avoid request loops, a
1816   proxy that forwards requests to other proxies &MUST; be able to
1817   recognize and exclude all of its own server names, including
1818   any aliases, local variations, and the numeric IP address. An example
1819   Request-Line would be:
1820</t>
1821<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1822GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1823</artwork></figure>
1824<t>
1825   To allow for transition to absolute-URIs in all requests in future
1826   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1827   form in requests, even though HTTP/1.1 clients will only generate
1828   them in requests to proxies.
1829</t>
1830<t>
1831   If a proxy receives a host name that is not a fully qualified domain
1832   name, it &MAY; add its domain to the host name it received. If a proxy
1833   receives a fully qualified domain name, the proxy &MUST-NOT; change
1834   the host name.
1835</t>
1836<t><iref item="authority form (of request-target)"/>
1837   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1838</t>
1839<t><iref item="origin form (of request-target)"/>
1840   The most common form of request-target is that used when making
1841   a request to an origin server ("origin form").
1842   In this case, the absolute path and query components of the URI
1843   &MUST; be transmitted as the request-target, and the authority component
1844   &MUST; be transmitted in a Host header field. For example, a client wishing
1845   to retrieve a representation of the resource, as identified above,
1846   directly from the origin server would open (or reuse) a TCP connection
1847   to port 80 of the host "www.example.org" and send the lines:
1848</t>
1849<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1850GET /pub/WWW/TheProject.html HTTP/1.1
1851Host: www.example.org
1852</artwork></figure>
1853<t>
1854   followed by the remainder of the Request. Note that the origin form
1855   of request-target always starts with an absolute path; if the target
1856   resource's URI path is empty, then an absolute path of "/" &MUST; be
1857   provided in the request-target.
1858</t>
1859<t>
1860   If a proxy receives an OPTIONS request with an absolute-URI form of
1861   request-target in which the URI has an empty path and no query component,
1862   then the last proxy on the request chain &MUST; use a request-target
1863   of "*" when it forwards the request to the indicated origin server.
1864</t>
1865<figure><preamble>   
1866   For example, the request
1867</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1868OPTIONS http://www.example.org:8001 HTTP/1.1
1869</artwork></figure>
1870<figure><preamble>   
1871  would be forwarded by the final proxy as
1872</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1873OPTIONS * HTTP/1.1
1874Host: www.example.org:8001
1875</artwork>
1876<postamble>
1877   after connecting to port 8001 of host "www.example.org".
1878</postamble>
1879</figure>
1880<t>
1881   The request-target is transmitted in the format specified in
1882   <xref target="http.uri"/>. If the request-target is percent-encoded
1883   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1884   &MUST; decode the request-target in order to
1885   properly interpret the request. Servers &SHOULD; respond to invalid
1886   request-targets with an appropriate status code.
1887</t>
1888<t>
1889   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1890   received request-target when forwarding it to the next inbound server,
1891   except as noted above to replace a null path-absolute with "/" or "*".
1892</t>
1893<x:note>
1894  <t>
1895    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1896    meaning of the request when the origin server is improperly using
1897    a non-reserved URI character for a reserved purpose.  Implementors
1898    need to be aware that some pre-HTTP/1.1 proxies have been known to
1899    rewrite the request-target.
1900  </t>
1901</x:note>
1902</section>
1903
1904<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1905<t>
1906   The exact resource identified by an Internet request is determined by
1907   examining both the request-target and the Host header field.
1908</t>
1909<t>
1910   An origin server that does not allow resources to differ by the
1911   requested host &MAY; ignore the Host header field value when
1912   determining the resource identified by an HTTP/1.1 request. (But see
1913   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1914   for other requirements on Host support in HTTP/1.1.)
1915</t>
1916<t>
1917   An origin server that does differentiate resources based on the host
1918   requested (sometimes referred to as virtual hosts or vanity host
1919   names) &MUST; use the following rules for determining the requested
1920   resource on an HTTP/1.1 request:
1921  <list style="numbers">
1922    <t>If request-target is an absolute-URI, the host is part of the
1923     request-target. Any Host header field value in the request &MUST; be
1924     ignored.</t>
1925    <t>If the request-target is not an absolute-URI, and the request includes
1926     a Host header field, the host is determined by the Host header
1927     field value.</t>
1928    <t>If the host as determined by rule 1 or 2 is not a valid host on
1929     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1930  </list>
1931</t>
1932<t>
1933   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1934   attempt to use heuristics (e.g., examination of the URI path for
1935   something unique to a particular host) in order to determine what
1936   exact resource is being requested.
1937</t>
1938</section>
1939
1940<section title="Effective Request URI" anchor="effective.request.uri">
1941  <iref primary="true" item="effective request URI"/>
1942  <iref primary="true" item="target resource"/>
1943<t>
1944   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1945   for the target resource; instead, the URI needs to be inferred from the
1946   request-target, Host header field, and connection context. The result of
1947   this process is called the "effective request URI".  The "target resource"
1948   is the resource identified by the effective request URI.
1949</t>
1950<t>
1951   If the request-target is an absolute-URI, then the effective request URI is
1952   the request-target.
1953</t>
1954<t>
1955   If the request-target uses the path-absolute form or the asterisk form,
1956   and the Host header field is present, then the effective request URI is
1957   constructed by concatenating
1958</t>
1959<t>
1960  <list style="symbols">
1961    <t>
1962      the scheme name: "http" if the request was received over an insecure
1963      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1964      connection,
1965    </t>
1966    <t>
1967      the octet sequence "://",
1968    </t>
1969    <t>
1970      the authority component, as specified in the Host header field
1971      (<xref target="header.host"/>), and
1972    </t>
1973    <t>
1974      the request-target obtained from the Request-Line, unless the
1975      request-target is just the asterisk "*".
1976    </t>
1977  </list>
1978</t>
1979<t>
1980   If the request-target uses the path-absolute form or the asterisk form,
1981   and the Host header field is not present, then the effective request URI is
1982   undefined.
1983</t>
1984<t>
1985   Otherwise, when request-target uses the authority form, the effective
1986   request URI is undefined.
1987</t>
1988<figure>
1989<preamble>
1990   Example 1: the effective request URI for the message
1991</preamble> 
1992<artwork type="example" x:indent-with="  ">
1993GET /pub/WWW/TheProject.html HTTP/1.1
1994Host: www.example.org:8080
1995</artwork>
1996<postamble>
1997  (received over an insecure TCP connection) is "http", plus "://", plus the
1998  authority component "www.example.org:8080", plus the request-target
1999  "/pub/WWW/TheProject.html", thus
2000  "http://www.example.org:8080/pub/WWW/TheProject.html".
2001</postamble>
2002</figure>
2003<figure>
2004<preamble>
2005   Example 2: the effective request URI for the message
2006</preamble> 
2007<artwork type="example" x:indent-with="  ">
2008OPTIONS * HTTP/1.1
2009Host: www.example.org
2010</artwork>
2011<postamble>
2012  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2013  authority component "www.example.org", thus "https://www.example.org".
2014</postamble>
2015</figure>
2016<t>
2017   Effective request URIs are compared using the rules described in
2018   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2019   be treated as equivalent to an absolute path of "/".
2020</t> 
2021</section>
2022</section>
2023
2024
2025<section title="Protocol Parameters" anchor="protocol.parameters">
2026
2027<section title="Transfer Codings" anchor="transfer.codings">
2028  <x:anchor-alias value="transfer-coding"/>
2029  <x:anchor-alias value="transfer-extension"/>
2030<t>
2031   Transfer-coding values are used to indicate an encoding
2032   transformation that has been, can be, or might need to be applied to a
2033   payload body in order to ensure "safe transport" through the network.
2034   This differs from a content coding in that the transfer-coding is a
2035   property of the message rather than a property of the representation
2036   that is being transferred.
2037</t>
2038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2039  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2040                          / "compress" ; <xref target="compress.coding"/>
2041                          / "deflate" ; <xref target="deflate.coding"/>
2042                          / "gzip" ; <xref target="gzip.coding"/>
2043                          / <x:ref>transfer-extension</x:ref>
2044  <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> )
2045</artwork></figure>
2046<t anchor="rule.parameter">
2047  <x:anchor-alias value="attribute"/>
2048  <x:anchor-alias value="transfer-parameter"/>
2049  <x:anchor-alias value="value"/>
2050   Parameters are in the form of attribute/value pairs.
2051</t>
2052<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"/>
2053  <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>
2054  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2055  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2056</artwork></figure>
2057<t>
2058   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2059   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2060   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2061</t>
2062<t>
2063   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2064   MIME, which were designed to enable safe transport of binary data over a
2065   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2066   However, safe transport
2067   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2068   the only unsafe characteristic of message-bodies is the difficulty in
2069   determining the exact message body length (<xref target="message.body"/>),
2070   or the desire to encrypt data over a shared transport.
2071</t>
2072<t>
2073   A server that receives a request message with a transfer-coding it does
2074   not understand &SHOULD; respond with 501 (Not Implemented) and then
2075   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2076   client.
2077</t>
2078
2079<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2080  <iref item="chunked (Coding Format)"/>
2081  <iref item="Coding Format" subitem="chunked"/>
2082  <x:anchor-alias value="chunk"/>
2083  <x:anchor-alias value="Chunked-Body"/>
2084  <x:anchor-alias value="chunk-data"/>
2085  <x:anchor-alias value="chunk-ext"/>
2086  <x:anchor-alias value="chunk-ext-name"/>
2087  <x:anchor-alias value="chunk-ext-val"/>
2088  <x:anchor-alias value="chunk-size"/>
2089  <x:anchor-alias value="last-chunk"/>
2090  <x:anchor-alias value="trailer-part"/>
2091  <x:anchor-alias value="quoted-str-nf"/>
2092  <x:anchor-alias value="qdtext-nf"/>
2093<t>
2094   The chunked encoding modifies the body of a message in order to
2095   transfer it as a series of chunks, each with its own size indicator,
2096   followed by an &OPTIONAL; trailer containing header fields. This
2097   allows dynamically produced content to be transferred along with the
2098   information necessary for the recipient to verify that it has
2099   received the full message.
2100</t>
2101<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"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
2102  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2103                   <x:ref>last-chunk</x:ref>
2104                   <x:ref>trailer-part</x:ref>
2105                   <x:ref>CRLF</x:ref>
2106 
2107  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2108                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2109  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2110  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2111 
2112  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2113                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2114  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2115  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2116  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2117  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2118 
2119  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
2120                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2121  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2122</artwork></figure>
2123<t>
2124   The chunk-size field is a string of hex digits indicating the size of
2125   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2126   zero, followed by the trailer, which is terminated by an empty line.
2127</t>
2128<t>
2129   The trailer allows the sender to include additional HTTP header
2130   fields at the end of the message. The Trailer header field can be
2131   used to indicate which header fields are included in a trailer (see
2132   <xref target="header.trailer"/>).
2133</t>
2134<t>
2135   A server using chunked transfer-coding in a response &MUST-NOT; use the
2136   trailer for any header fields unless at least one of the following is
2137   true:
2138  <list style="numbers">
2139    <t>the request included a TE header field that indicates "trailers" is
2140     acceptable in the transfer-coding of the  response, as described in
2141     <xref target="header.te"/>; or,</t>
2142     
2143    <t>the trailer fields consist entirely of optional metadata, and the
2144    recipient could use the message (in a manner acceptable to the server where
2145    the field originated) without receiving it. In other words, the server that
2146    generated the header (often but not always the origin server) is willing to
2147    accept the possibility that the trailer fields might be silently discarded
2148    along the path to the client.</t>
2149  </list>
2150</t>
2151<t>
2152   This requirement prevents an interoperability failure when the
2153   message is being received by an HTTP/1.1 (or later) proxy and
2154   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2155   compliance with the protocol would have necessitated a possibly
2156   infinite buffer on the proxy.
2157</t>
2158<t>
2159   A process for decoding the "chunked" transfer-coding
2160   can be represented in pseudo-code as:
2161</t>
2162<figure><artwork type="code">
2163  length := 0
2164  read chunk-size, chunk-ext (if any) and CRLF
2165  while (chunk-size &gt; 0) {
2166     read chunk-data and CRLF
2167     append chunk-data to decoded-body
2168     length := length + chunk-size
2169     read chunk-size and CRLF
2170  }
2171  read header-field
2172  while (header-field not empty) {
2173     append header-field to existing header fields
2174     read header-field
2175  }
2176  Content-Length := length
2177  Remove "chunked" from Transfer-Encoding
2178</artwork></figure>
2179<t>
2180   All HTTP/1.1 applications &MUST; be able to receive and decode the
2181   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2182   they do not understand.
2183</t>
2184<t>
2185   Since "chunked" is the only transfer-coding required to be understood
2186   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2187   on a persistent connection.  Whenever a transfer-coding is applied to
2188   a payload body in a request, the final transfer-coding applied &MUST;
2189   be "chunked".  If a transfer-coding is applied to a response payload
2190   body, then either the final transfer-coding applied &MUST; be "chunked"
2191   or the message &MUST; be terminated by closing the connection. When the
2192   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2193   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2194   be applied more than once in a message-body.
2195</t>
2196</section>
2197
2198<section title="Compression Codings" anchor="compression.codings">
2199<t>
2200   The codings defined below can be used to compress the payload of a
2201   message.
2202</t>
2203<x:note><t>
2204   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2205   is not desirable and is discouraged for future encodings. Their
2206   use here is representative of historical practice, not good
2207   design.
2208</t></x:note>
2209<x:note><t>
2210   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2211   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2212   equivalent to "gzip" and "compress" respectively.
2213</t></x:note>
2214
2215<section title="Compress Coding" anchor="compress.coding">
2216<iref item="compress (Coding Format)"/>
2217<iref item="Coding Format" subitem="compress"/>
2218<t>
2219   The "compress" format is produced by the common UNIX file compression
2220   program "compress". This format is an adaptive Lempel-Ziv-Welch
2221   coding (LZW).
2222</t>
2223</section>
2224
2225<section title="Deflate Coding" anchor="deflate.coding">
2226<iref item="deflate (Coding Format)"/>
2227<iref item="Coding Format" subitem="deflate"/>
2228<t>
2229   The "deflate" format is defined as the "deflate" compression mechanism
2230   (described in <xref target="RFC1951"/>) used inside the "zlib"
2231   data format (<xref target="RFC1950"/>).
2232</t>
2233<x:note>
2234  <t>
2235    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2236    compressed data without the zlib wrapper.
2237   </t>
2238</x:note>
2239</section>
2240
2241<section title="Gzip Coding" anchor="gzip.coding">
2242<iref item="gzip (Coding Format)"/>
2243<iref item="Coding Format" subitem="gzip"/>
2244<t>
2245   The "gzip" format is produced by the file compression program
2246   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2247   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2248</t>
2249</section>
2250
2251</section>
2252
2253<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2254<t>
2255   The HTTP Transfer Coding Registry defines the name space for the transfer
2256   coding names.
2257</t>
2258<t>
2259   Registrations &MUST; include the following fields:
2260   <list style="symbols">
2261     <t>Name</t>
2262     <t>Description</t>
2263     <t>Pointer to specification text</t>
2264   </list>
2265</t>
2266<t>
2267   Names of transfer codings &MUST-NOT; overlap with names of content codings
2268   (&content-codings;), unless the encoding transformation is identical (as it
2269   is the case for the compression codings defined in
2270   <xref target="compression.codings"/>).
2271</t>
2272<t>
2273   Values to be added to this name space require a specification
2274   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2275   conform to the purpose of transfer coding defined in this section.
2276</t>
2277<t>
2278   The registry itself is maintained at
2279   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2280</t>
2281</section>
2282</section>
2283
2284<section title="Product Tokens" anchor="product.tokens">
2285  <x:anchor-alias value="product"/>
2286  <x:anchor-alias value="product-version"/>
2287<t>
2288   Product tokens are used to allow communicating applications to
2289   identify themselves by software name and version. Most fields using
2290   product tokens also allow sub-products which form a significant part
2291   of the application to be listed, separated by whitespace. By
2292   convention, the products are listed in order of their significance
2293   for identifying the application.
2294</t>
2295<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2296  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2297  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2298</artwork></figure>
2299<t>
2300   Examples:
2301</t>
2302<figure><artwork type="example">
2303  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2304  Server: Apache/0.8.4
2305</artwork></figure>
2306<t>
2307   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2308   used for advertising or other non-essential information. Although any
2309   token octet &MAY; appear in a product-version, this token &SHOULD;
2310   only be used for a version identifier (i.e., successive versions of
2311   the same product &SHOULD; only differ in the product-version portion of
2312   the product value).
2313</t>
2314</section>
2315
2316<section title="Quality Values" anchor="quality.values">
2317  <x:anchor-alias value="qvalue"/>
2318<t>
2319   Both transfer codings (TE request header field, <xref target="header.te"/>)
2320   and content negotiation (&content.negotiation;) use short "floating point"
2321   numbers to indicate the relative importance ("weight") of various
2322   negotiable parameters.  A weight is normalized to a real number in
2323   the range 0 through 1, where 0 is the minimum and 1 the maximum
2324   value. If a parameter has a quality value of 0, then content with
2325   this parameter is "not acceptable" for the client. HTTP/1.1
2326   applications &MUST-NOT; generate more than three digits after the
2327   decimal point. User configuration of these values &SHOULD; also be
2328   limited in this fashion.
2329</t>
2330<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2331  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2332                 / ( "1" [ "." 0*3("0") ] )
2333</artwork></figure>
2334<x:note>
2335  <t>
2336     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2337     relative degradation in desired quality.
2338  </t>
2339</x:note>
2340</section>
2341
2342</section>
2343
2344<section title="Connections" anchor="connections">
2345
2346<section title="Persistent Connections" anchor="persistent.connections">
2347
2348<section title="Purpose" anchor="persistent.purpose">
2349<t>
2350   Prior to persistent connections, a separate TCP connection was
2351   established for each request, increasing the load on HTTP servers
2352   and causing congestion on the Internet. The use of inline images and
2353   other associated data often requires a client to make multiple
2354   requests of the same server in a short amount of time. Analysis of
2355   these performance problems and results from a prototype
2356   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2357   measurements of actual HTTP/1.1 implementations show good
2358   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2359   T/TCP <xref target="Tou1998"/>.
2360</t>
2361<t>
2362   Persistent HTTP connections have a number of advantages:
2363  <list style="symbols">
2364      <t>
2365        By opening and closing fewer TCP connections, CPU time is saved
2366        in routers and hosts (clients, servers, proxies, gateways,
2367        tunnels, or caches), and memory used for TCP protocol control
2368        blocks can be saved in hosts.
2369      </t>
2370      <t>
2371        HTTP requests and responses can be pipelined on a connection.
2372        Pipelining allows a client to make multiple requests without
2373        waiting for each response, allowing a single TCP connection to
2374        be used much more efficiently, with much lower elapsed time.
2375      </t>
2376      <t>
2377        Network congestion is reduced by reducing the number of packets
2378        caused by TCP opens, and by allowing TCP sufficient time to
2379        determine the congestion state of the network.
2380      </t>
2381      <t>
2382        Latency on subsequent requests is reduced since there is no time
2383        spent in TCP's connection opening handshake.
2384      </t>
2385      <t>
2386        HTTP can evolve more gracefully, since errors can be reported
2387        without the penalty of closing the TCP connection. Clients using
2388        future versions of HTTP might optimistically try a new feature,
2389        but if communicating with an older server, retry with old
2390        semantics after an error is reported.
2391      </t>
2392    </list>
2393</t>
2394<t>
2395   HTTP implementations &SHOULD; implement persistent connections.
2396</t>
2397</section>
2398
2399<section title="Overall Operation" anchor="persistent.overall">
2400<t>
2401   A significant difference between HTTP/1.1 and earlier versions of
2402   HTTP is that persistent connections are the default behavior of any
2403   HTTP connection. That is, unless otherwise indicated, the client
2404   &SHOULD; assume that the server will maintain a persistent connection,
2405   even after error responses from the server.
2406</t>
2407<t>
2408   Persistent connections provide a mechanism by which a client and a
2409   server can signal the close of a TCP connection. This signaling takes
2410   place using the Connection header field (<xref target="header.connection"/>). Once a close
2411   has been signaled, the client &MUST-NOT; send any more requests on that
2412   connection.
2413</t>
2414
2415<section title="Negotiation" anchor="persistent.negotiation">
2416<t>
2417   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2418   maintain a persistent connection unless a Connection header field including
2419   the connection-token "close" was sent in the request. If the server
2420   chooses to close the connection immediately after sending the
2421   response, it &SHOULD; send a Connection header field including the
2422   connection-token "close".
2423</t>
2424<t>
2425   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2426   decide to keep it open based on whether the response from a server
2427   contains a Connection header field with the connection-token close. In case
2428   the client does not want to maintain a connection for more than that
2429   request, it &SHOULD; send a Connection header field including the
2430   connection-token close.
2431</t>
2432<t>
2433   If either the client or the server sends the close token in the
2434   Connection header field, that request becomes the last one for the
2435   connection.
2436</t>
2437<t>
2438   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2439   maintained for HTTP versions less than 1.1 unless it is explicitly
2440   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2441   compatibility with HTTP/1.0 clients.
2442</t>
2443<t>
2444   In order to remain persistent, all messages on the connection &MUST;
2445   have a self-defined message length (i.e., one not defined by closure
2446   of the connection), as described in <xref target="message.body"/>.
2447</t>
2448</section>
2449
2450<section title="Pipelining" anchor="pipelining">
2451<t>
2452   A client that supports persistent connections &MAY; "pipeline" its
2453   requests (i.e., send multiple requests without waiting for each
2454   response). A server &MUST; send its responses to those requests in the
2455   same order that the requests were received.
2456</t>
2457<t>
2458   Clients which assume persistent connections and pipeline immediately
2459   after connection establishment &SHOULD; be prepared to retry their
2460   connection if the first pipelined attempt fails. If a client does
2461   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2462   persistent. Clients &MUST; also be prepared to resend their requests if
2463   the server closes the connection before sending all of the
2464   corresponding responses.
2465</t>
2466<t>
2467   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2468   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2469   premature termination of the transport connection could lead to
2470   indeterminate results. A client wishing to send a non-idempotent
2471   request &SHOULD; wait to send that request until it has received the
2472   response status line for the previous request.
2473</t>
2474</section>
2475</section>
2476
2477<section title="Proxy Servers" anchor="persistent.proxy">
2478<t>
2479   It is especially important that proxies correctly implement the
2480   properties of the Connection header field as specified in <xref target="header.connection"/>.
2481</t>
2482<t>
2483   The proxy server &MUST; signal persistent connections separately with
2484   its clients and the origin servers (or other proxy servers) that it
2485   connects to. Each persistent connection applies to only one transport
2486   link.
2487</t>
2488<t>
2489   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2490   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2491   for information and discussion of the problems with the Keep-Alive header field
2492   implemented by many HTTP/1.0 clients).
2493</t>
2494
2495<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2496<!--<t>
2497  <cref anchor="TODO-end-to-end" source="jre">
2498    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2499    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2500  </cref>
2501</t>-->
2502<t>
2503   For the purpose of defining the behavior of caches and non-caching
2504   proxies, we divide HTTP header fields into two categories:
2505  <list style="symbols">
2506      <t>End-to-end header fields, which are  transmitted to the ultimate
2507        recipient of a request or response. End-to-end header fields in
2508        responses MUST be stored as part of a cache entry and &MUST; be
2509        transmitted in any response formed from a cache entry.</t>
2510
2511      <t>Hop-by-hop header fields, which are meaningful only for a single
2512        transport-level connection, and are not stored by caches or
2513        forwarded by proxies.</t>
2514  </list>
2515</t>
2516<t>
2517   The following HTTP/1.1 header fields are hop-by-hop header fields:
2518  <list style="symbols">
2519      <t>Connection</t>
2520      <t>Keep-Alive</t>
2521      <t>Proxy-Authenticate</t>
2522      <t>Proxy-Authorization</t>
2523      <t>TE</t>
2524      <t>Trailer</t>
2525      <t>Transfer-Encoding</t>
2526      <t>Upgrade</t>
2527  </list>
2528</t>
2529<t>
2530   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2531</t>
2532<t>
2533   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2534   (<xref target="header.connection"/>).
2535</t>
2536</section>
2537
2538<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2539<!--<t>
2540  <cref anchor="TODO-non-mod-headers" source="jre">
2541    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2542    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2543  </cref>
2544</t>-->
2545<t>
2546   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2547   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2548   modify an end-to-end header field unless the definition of that header field requires
2549   or specifically allows that.
2550</t>
2551<t>
2552   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2553   request or response, and it &MUST-NOT; add any of these fields if not
2554   already present:
2555  <list style="symbols">
2556    <t>Allow</t>
2557    <t>Content-Location</t>
2558    <t>Content-MD5</t>
2559    <t>ETag</t>
2560    <t>Last-Modified</t>
2561    <t>Server</t>
2562  </list>
2563</t>
2564<t>
2565   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2566   response:
2567  <list style="symbols">
2568    <t>Expires</t>
2569  </list>
2570</t>
2571<t>
2572   but it &MAY; add any of these fields if not already present. If an
2573   Expires header field is added, it &MUST; be given a field-value identical to
2574   that of the Date header field in that response.
2575</t>
2576<t>
2577   A proxy &MUST-NOT; modify or add any of the following fields in a
2578   message that contains the no-transform cache-control directive, or in
2579   any request:
2580  <list style="symbols">
2581    <t>Content-Encoding</t>
2582    <t>Content-Range</t>
2583    <t>Content-Type</t>
2584  </list>
2585</t>
2586<t>
2587   A transforming proxy &MAY; modify or add these fields to a message
2588   that does not include no-transform, but if it does so, it &MUST; add a
2589   Warning 214 (Transformation applied) if one does not already appear
2590   in the message (see &header-warning;).
2591</t>
2592<x:note>
2593  <t>
2594    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2595    cause authentication failures if stronger authentication
2596    mechanisms are introduced in later versions of HTTP. Such
2597    authentication mechanisms &MAY; rely on the values of header fields
2598    not listed here.
2599  </t>
2600</x:note>
2601<t>
2602   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2603   though it &MAY; change the message-body through application or removal
2604   of a transfer-coding (<xref target="transfer.codings"/>).
2605</t>
2606</section>
2607
2608</section>
2609
2610<section title="Practical Considerations" anchor="persistent.practical">
2611<t>
2612   Servers will usually have some time-out value beyond which they will
2613   no longer maintain an inactive connection. Proxy servers might make
2614   this a higher value since it is likely that the client will be making
2615   more connections through the same server. The use of persistent
2616   connections places no requirements on the length (or existence) of
2617   this time-out for either the client or the server.
2618</t>
2619<t>
2620   When a client or server wishes to time-out it &SHOULD; issue a graceful
2621   close on the transport connection. Clients and servers &SHOULD; both
2622   constantly watch for the other side of the transport close, and
2623   respond to it as appropriate. If a client or server does not detect
2624   the other side's close promptly it could cause unnecessary resource
2625   drain on the network.
2626</t>
2627<t>
2628   A client, server, or proxy &MAY; close the transport connection at any
2629   time. For example, a client might have started to send a new request
2630   at the same time that the server has decided to close the "idle"
2631   connection. From the server's point of view, the connection is being
2632   closed while it was idle, but from the client's point of view, a
2633   request is in progress.
2634</t>
2635<t>
2636   Clients (including proxies) &SHOULD; limit the number of simultaneous
2637   connections that they maintain to a given server (including proxies).
2638</t>
2639<t>
2640   Previous revisions of HTTP gave a specific number of connections as a
2641   ceiling, but this was found to be impractical for many applications. As a
2642   result, this specification does not mandate a particular maximum number of
2643   connections, but instead encourages clients to be conservative when opening
2644   multiple connections.
2645</t>
2646<t>
2647   In particular, while using multiple connections avoids the "head-of-line
2648   blocking" problem (whereby a request that takes significant server-side
2649   processing and/or has a large payload can block subsequent requests on the
2650   same connection), each connection used consumes server resources (sometimes
2651   significantly), and furthermore using multiple connections can cause
2652   undesirable side effects in congested networks.
2653</t>
2654<t>
2655   Note that servers might reject traffic that they deem abusive, including an
2656   excessive number of connections from a client.
2657</t>
2658</section>
2659
2660<section title="Retrying Requests" anchor="persistent.retrying.requests">
2661<t>
2662   Senders can close the transport connection at any time. Therefore,
2663   clients, servers, and proxies &MUST; be able to recover
2664   from asynchronous close events. Client software &MAY; reopen the
2665   transport connection and retransmit the aborted sequence of requests
2666   without user interaction so long as the request sequence is
2667   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2668   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2669   human operator the choice of retrying the request(s). Confirmation by
2670   user-agent software with semantic understanding of the application
2671   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2672   be repeated if the second sequence of requests fails.
2673</t>
2674</section>
2675
2676</section>
2677
2678<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2679
2680<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2681<t>
2682   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2683   flow control mechanisms to resolve temporary overloads, rather than
2684   terminating connections with the expectation that clients will retry.
2685   The latter technique can exacerbate network congestion.
2686</t>
2687</section>
2688
2689<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2690<t>
2691   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2692   the network connection for an error status code while it is transmitting
2693   the request. If the client sees an error status code, it &SHOULD;
2694   immediately cease transmitting the body. If the body is being sent
2695   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2696   empty trailer &MAY; be used to prematurely mark the end of the message.
2697   If the body was preceded by a Content-Length header field, the client &MUST;
2698   close the connection.
2699</t>
2700</section>
2701
2702<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2703<t>
2704   The purpose of the 100 (Continue) status code (see &status-100;) is to
2705   allow a client that is sending a request message with a request body
2706   to determine if the origin server is willing to accept the request
2707   (based on the request header fields) before the client sends the request
2708   body. In some cases, it might either be inappropriate or highly
2709   inefficient for the client to send the body if the server will reject
2710   the message without looking at the body.
2711</t>
2712<t>
2713   Requirements for HTTP/1.1 clients:
2714  <list style="symbols">
2715    <t>
2716        If a client will wait for a 100 (Continue) response before
2717        sending the request body, it &MUST; send an Expect header
2718        field (&header-expect;) with the "100-continue" expectation.
2719    </t>
2720    <t>
2721        A client &MUST-NOT; send an Expect header field (&header-expect;)
2722        with the "100-continue" expectation if it does not intend
2723        to send a request body.
2724    </t>
2725  </list>
2726</t>
2727<t>
2728   Because of the presence of older implementations, the protocol allows
2729   ambiguous situations in which a client might send "Expect: 100-continue"
2730   without receiving either a 417 (Expectation Failed)
2731   or a 100 (Continue) status code. Therefore, when a client sends this
2732   header field to an origin server (possibly via a proxy) from which it
2733   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2734   wait for an indefinite period before sending the request body.
2735</t>
2736<t>
2737   Requirements for HTTP/1.1 origin servers:
2738  <list style="symbols">
2739    <t> Upon receiving a request which includes an Expect header
2740        field with the "100-continue" expectation, an origin server &MUST;
2741        either respond with 100 (Continue) status code and continue to read
2742        from the input stream, or respond with a final status code. The
2743        origin server &MUST-NOT; wait for the request body before sending
2744        the 100 (Continue) response. If it responds with a final status
2745        code, it &MAY; close the transport connection or it &MAY; continue
2746        to read and discard the rest of the request.  It &MUST-NOT;
2747        perform the request method if it returns a final status code.
2748    </t>
2749    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2750        the request message does not include an Expect header
2751        field with the "100-continue" expectation, and &MUST-NOT; send a
2752        100 (Continue) response if such a request comes from an HTTP/1.0
2753        (or earlier) client. There is an exception to this rule: for
2754        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2755        status code in response to an HTTP/1.1 PUT or POST request that does
2756        not include an Expect header field with the "100-continue"
2757        expectation. This exception, the purpose of which is
2758        to minimize any client processing delays associated with an
2759        undeclared wait for 100 (Continue) status code, applies only to
2760        HTTP/1.1 requests, and not to requests with any other HTTP-version
2761        value.
2762    </t>
2763    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2764        already received some or all of the request body for the
2765        corresponding request.
2766    </t>
2767    <t> An origin server that sends a 100 (Continue) response &MUST;
2768    ultimately send a final status code, once the request body is
2769        received and processed, unless it terminates the transport
2770        connection prematurely.
2771    </t>
2772    <t> If an origin server receives a request that does not include an
2773        Expect header field with the "100-continue" expectation,
2774        the request includes a request body, and the server responds
2775        with a final status code before reading the entire request body
2776        from the transport connection, then the server &SHOULD-NOT;  close
2777        the transport connection until it has read the entire request,
2778        or until the client closes the connection. Otherwise, the client
2779        might not reliably receive the response message. However, this
2780        requirement is not be construed as preventing a server from
2781        defending itself against denial-of-service attacks, or from
2782        badly broken client implementations.
2783      </t>
2784    </list>
2785</t>
2786<t>
2787   Requirements for HTTP/1.1 proxies:
2788  <list style="symbols">
2789    <t> If a proxy receives a request that includes an Expect header
2790        field with the "100-continue" expectation, and the proxy
2791        either knows that the next-hop server complies with HTTP/1.1 or
2792        higher, or does not know the HTTP version of the next-hop
2793        server, it &MUST; forward the request, including the Expect header
2794        field.
2795    </t>
2796    <t> If the proxy knows that the version of the next-hop server is
2797        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2798        respond with a 417 (Expectation Failed) status code.
2799    </t>
2800    <t> Proxies &SHOULD; maintain a record of the HTTP version
2801        numbers received from recently-referenced next-hop servers.
2802    </t>
2803    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2804        request message was received from an HTTP/1.0 (or earlier)
2805        client and did not include an Expect header field with
2806        the "100-continue" expectation. This requirement overrides the
2807        general rule for forwarding of 1xx responses (see &status-1xx;).
2808    </t>
2809  </list>
2810</t>
2811</section>
2812
2813</section>
2814</section>
2815
2816
2817<section title="Miscellaneous notes that might disappear" anchor="misc">
2818<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2819<t>
2820   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2821</t>
2822</section>
2823
2824<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2825<t>
2826   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2827</t>
2828</section>
2829
2830<section title="Interception of HTTP for access control" anchor="http.intercept">
2831<t>
2832   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2833</t>
2834</section>
2835
2836<section title="Use of HTTP by other protocols" anchor="http.others">
2837<t>
2838   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2839   Extensions of HTTP like WebDAV.</cref>
2840</t>
2841
2842</section>
2843<section title="Use of HTTP by media type specification" anchor="http.media">
2844<t>
2845   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2846</t>
2847</section>
2848</section>
2849
2850<section title="Header Field Definitions" anchor="header.field.definitions">
2851<t>
2852   This section defines the syntax and semantics of HTTP header fields
2853   related to message origination, framing, and routing.
2854</t>
2855<texttable align="left">
2856  <ttcol>Header Field Name</ttcol>
2857  <ttcol>Defined in...</ttcol>
2858 
2859  <c>Connection</c> <c><xref target="header.connection"/></c>
2860  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2861  <c>Host</c> <c><xref target="header.host"/></c>
2862  <c>TE</c> <c><xref target="header.te"/></c>
2863  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2864  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2865  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2866  <c>Via</c> <c><xref target="header.via"/></c>
2867</texttable>
2868
2869<section title="Connection" anchor="header.connection">
2870  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2871  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2872  <x:anchor-alias value="Connection"/>
2873  <x:anchor-alias value="connection-token"/>
2874<t>
2875   The "Connection" header field allows the sender to specify
2876   options that are desired only for that particular connection.
2877   Such connection options &MUST; be removed or replaced before the
2878   message can be forwarded downstream by a proxy or gateway.
2879   This mechanism also allows the sender to indicate which HTTP
2880   header fields used in the message are only intended for the
2881   immediate recipient ("hop-by-hop"), as opposed to all recipients
2882   on the chain ("end-to-end"), enabling the message to be
2883   self-descriptive and allowing future connection-specific extensions
2884   to be deployed in HTTP without fear that they will be blindly
2885   forwarded by previously deployed intermediaries.
2886</t>
2887<t>
2888   The Connection header field's value has the following grammar:
2889</t>
2890<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2891  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2892  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2893</artwork></figure>
2894<t>
2895   A proxy or gateway &MUST; parse a received Connection
2896   header field before a message is forwarded and, for each
2897   connection-token in this field, remove any header field(s) from
2898   the message with the same name as the connection-token, and then
2899   remove the Connection header field itself or replace it with the
2900   sender's own connection options for the forwarded message.
2901</t>
2902<t>
2903   A sender &MUST-NOT; include field-names in the Connection header
2904   field-value for fields that are defined as expressing constraints
2905   for all recipients in the request or response chain, such as the
2906   Cache-Control header field (&header-cache-control;).
2907</t>
2908<t>
2909   The connection options do not have to correspond to a header field
2910   present in the message, since a connection-specific header field
2911   might not be needed if there are no parameters associated with that
2912   connection option.  Recipients that trigger certain connection
2913   behavior based on the presence of connection options &MUST; do so
2914   based on the presence of the connection-token rather than only the
2915   presence of the optional header field.  In other words, if the
2916   connection option is received as a header field but not indicated
2917   within the Connection field-value, then the recipient &MUST; ignore
2918   the connection-specific header field because it has likely been
2919   forwarded by an intermediary that is only partially compliant.
2920</t>
2921<t>
2922   When defining new connection options, specifications ought to
2923   carefully consider existing deployed header fields and ensure
2924   that the new connection-token does not share the same name as
2925   an unrelated header field that might already be deployed.
2926   Defining a new connection-token essentially reserves that potential
2927   field-name for carrying additional information related to the
2928   connection option, since it would be unwise for senders to use
2929   that field-name for anything else.
2930</t>
2931<t>
2932   HTTP/1.1 defines the "close" connection option for the sender to
2933   signal that the connection will be closed after completion of the
2934   response. For example,
2935</t>
2936<figure><artwork type="example">
2937  Connection: close
2938</artwork></figure>
2939<t>
2940   in either the request or the response header fields indicates that
2941   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2942   after the current request/response is complete.
2943</t>
2944<t>
2945   An HTTP/1.1 client that does not support persistent connections &MUST;
2946   include the "close" connection option in every request message.
2947</t>
2948<t>
2949   An HTTP/1.1 server that does not support persistent connections &MUST;
2950   include the "close" connection option in every response message that
2951   does not have a 1xx (Informational) status code.
2952</t>
2953</section>
2954
2955<section title="Content-Length" anchor="header.content-length">
2956  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2957  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2958  <x:anchor-alias value="Content-Length"/>
2959<t>
2960   The "Content-Length" header field indicates the size of the
2961   message-body, in decimal number of octets, for any message other than
2962   a response to a HEAD request or a response with a status code of 304.
2963   In the case of a response to a HEAD request, Content-Length indicates
2964   the size of the payload body (not including any potential transfer-coding)
2965   that would have been sent had the request been a GET.
2966   In the case of a 304 (Not Modified) response to a GET request,
2967   Content-Length indicates the size of the payload body (not including
2968   any potential transfer-coding) that would have been sent in a 200 (OK)
2969   response.
2970</t>
2971<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2972  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
2973</artwork></figure>
2974<t>
2975   An example is
2976</t>
2977<figure><artwork type="example">
2978  Content-Length: 3495
2979</artwork></figure>
2980<t>
2981   Implementations &SHOULD; use this field to indicate the message-body
2982   length when no transfer-coding is being applied and the
2983   payload's body length can be determined prior to being transferred.
2984   <xref target="message.body"/> describes how recipients determine the length
2985   of a message-body.
2986</t>
2987<t>
2988   Any Content-Length greater than or equal to zero is a valid value.
2989</t>
2990<t>
2991   Note that the use of this field in HTTP is significantly different from
2992   the corresponding definition in MIME, where it is an optional field
2993   used within the "message/external-body" content-type.
2994</t>
2995</section>
2996
2997<section title="Host" anchor="header.host">
2998  <iref primary="true" item="Host header field" x:for-anchor=""/>
2999  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3000  <x:anchor-alias value="Host"/>
3001<t>
3002   The "Host" header field in a request provides the host and port
3003   information from the target resource's URI, enabling the origin
3004   server to distinguish between resources while servicing requests
3005   for multiple host names on a single IP address.  Since the Host
3006   field-value is critical information for handling a request, it
3007   &SHOULD; be sent as the first header field following the Request-Line.
3008</t>
3009<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3010  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3011</artwork></figure>
3012<t>
3013   A client &MUST; send a Host header field in all HTTP/1.1 request
3014   messages.  If the target resource's URI includes an authority
3015   component, then the Host field-value &MUST; be identical to that
3016   authority component after excluding any userinfo (<xref target="http.uri"/>).
3017   If the authority component is missing or undefined for the target
3018   resource's URI, then the Host header field &MUST; be sent with an
3019   empty field-value.
3020</t>
3021<t>
3022   For example, a GET request to the origin server for
3023   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3024</t>
3025<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3026GET /pub/WWW/ HTTP/1.1
3027Host: www.example.org
3028</artwork></figure>
3029<t>
3030   The Host header field &MUST; be sent in an HTTP/1.1 request even
3031   if the request-target is in the form of an absolute-URI, since this
3032   allows the Host information to be forwarded through ancient HTTP/1.0
3033   proxies that might not have implemented Host.
3034</t>
3035<t>
3036   When an HTTP/1.1 proxy receives a request with a request-target in
3037   the form of an absolute-URI, the proxy &MUST; ignore the received
3038   Host header field (if any) and instead replace it with the host
3039   information of the request-target.  When a proxy forwards a request,
3040   it &MUST; generate the Host header field based on the received
3041   absolute-URI rather than the received Host.
3042</t>
3043<t>
3044   Since the Host header field acts as an application-level routing
3045   mechanism, it is a frequent target for malware seeking to poison
3046   a shared cache or redirect a request to an unintended server.
3047   An interception proxy is particularly vulnerable if it relies on
3048   the Host header field value for redirecting requests to internal
3049   servers, or for use as a cache key in a shared cache, without
3050   first verifying that the intercepted connection is targeting a
3051   valid IP address for that host.
3052</t>
3053<t>
3054   A server &MUST; respond with a 400 (Bad Request) status code to
3055   any HTTP/1.1 request message that lacks a Host header field and
3056   to any request message that contains more than one Host header field
3057   or a Host header field with an invalid field-value.
3058</t>
3059<t>
3060   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3061   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3062   for other requirements relating to Host.
3063</t>
3064</section>
3065
3066<section title="TE" anchor="header.te">
3067  <iref primary="true" item="TE header field" x:for-anchor=""/>
3068  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3069  <x:anchor-alias value="TE"/>
3070  <x:anchor-alias value="t-codings"/>
3071  <x:anchor-alias value="te-params"/>
3072  <x:anchor-alias value="te-ext"/>
3073<t>
3074   The "TE" header field indicates what extension transfer-codings
3075   it is willing to accept in the response, and whether or not it is
3076   willing to accept trailer fields in a chunked transfer-coding.
3077</t>
3078<t>
3079   Its value consists of the keyword "trailers" and/or a comma-separated
3080   list of extension transfer-coding names with optional accept
3081   parameters (as described in <xref target="transfer.codings"/>).
3082</t>
3083<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3084  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3085  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3086  <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> )
3087  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3088</artwork></figure>
3089<t>
3090   The presence of the keyword "trailers" indicates that the client is
3091   willing to accept trailer fields in a chunked transfer-coding, as
3092   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3093   transfer-coding values even though it does not itself represent a
3094   transfer-coding.
3095</t>
3096<t>
3097   Examples of its use are:
3098</t>
3099<figure><artwork type="example">
3100  TE: deflate
3101  TE:
3102  TE: trailers, deflate;q=0.5
3103</artwork></figure>
3104<t>
3105   The TE header field only applies to the immediate connection.
3106   Therefore, the keyword &MUST; be supplied within a Connection header
3107   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3108</t>
3109<t>
3110   A server tests whether a transfer-coding is acceptable, according to
3111   a TE field, using these rules:
3112  <list style="numbers">
3113    <x:lt>
3114      <t>The "chunked" transfer-coding is always acceptable. If the
3115         keyword "trailers" is listed, the client indicates that it is
3116         willing to accept trailer fields in the chunked response on
3117         behalf of itself and any downstream clients. The implication is
3118         that, if given, the client is stating that either all
3119         downstream clients are willing to accept trailer fields in the
3120         forwarded response, or that it will attempt to buffer the
3121         response on behalf of downstream recipients.
3122      </t><t>
3123         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3124         chunked response such that a client can be assured of buffering
3125         the entire response.</t>
3126    </x:lt>
3127    <x:lt>
3128      <t>If the transfer-coding being tested is one of the transfer-codings
3129         listed in the TE field, then it is acceptable unless it
3130         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3131         qvalue of 0 means "not acceptable".)</t>
3132    </x:lt>
3133    <x:lt>
3134      <t>If multiple transfer-codings are acceptable, then the
3135         acceptable transfer-coding with the highest non-zero qvalue is
3136         preferred.  The "chunked" transfer-coding always has a qvalue
3137         of 1.</t>
3138    </x:lt>
3139  </list>
3140</t>
3141<t>
3142   If the TE field-value is empty or if no TE field is present, the only
3143   transfer-coding is "chunked". A message with no transfer-coding is
3144   always acceptable.
3145</t>
3146</section>
3147
3148<section title="Trailer" anchor="header.trailer">
3149  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3150  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3151  <x:anchor-alias value="Trailer"/>
3152<t>
3153   The "Trailer" header field indicates that the given set of
3154   header fields is present in the trailer of a message encoded with
3155   chunked transfer-coding.
3156</t>
3157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3158  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3159</artwork></figure>
3160<t>
3161   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3162   message using chunked transfer-coding with a non-empty trailer. Doing
3163   so allows the recipient to know which header fields to expect in the
3164   trailer.
3165</t>
3166<t>
3167   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3168   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3169   trailer fields in a "chunked" transfer-coding.
3170</t>
3171<t>
3172   Message header fields listed in the Trailer header field &MUST-NOT;
3173   include the following header fields:
3174  <list style="symbols">
3175    <t>Transfer-Encoding</t>
3176    <t>Content-Length</t>
3177    <t>Trailer</t>
3178  </list>
3179</t>
3180</section>
3181
3182<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3183  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3184  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3185  <x:anchor-alias value="Transfer-Encoding"/>
3186<t>
3187   The "Transfer-Encoding" header field indicates what transfer-codings
3188   (if any) have been applied to the message body. It differs from
3189   Content-Encoding (&content-codings;) in that transfer-codings are a property
3190   of the message (and therefore are removed by intermediaries), whereas
3191   content-codings are not.
3192</t>
3193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3194  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3195</artwork></figure>
3196<t>
3197   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3198</t>
3199<figure><artwork type="example">
3200  Transfer-Encoding: chunked
3201</artwork></figure>
3202<t>
3203   If multiple encodings have been applied to a representation, the transfer-codings
3204   &MUST; be listed in the order in which they were applied.
3205   Additional information about the encoding parameters &MAY; be provided
3206   by other header fields not defined by this specification.
3207</t>
3208<t>
3209   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3210   header field.
3211</t>
3212</section>
3213
3214<section title="Upgrade" anchor="header.upgrade">
3215  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3216  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3217  <x:anchor-alias value="Upgrade"/>
3218<t>
3219   The "Upgrade" header field allows the client to specify what
3220   additional communication protocols it would like to use, if the server
3221   chooses to switch protocols. Servers can use it to indicate what protocols
3222   they are willing to switch to.
3223</t>
3224<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3225  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3226</artwork></figure>
3227<t>
3228   For example,
3229</t>
3230<figure><artwork type="example">
3231  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3232</artwork></figure>
3233<t>
3234   The Upgrade header field is intended to provide a simple mechanism
3235   for transition from HTTP/1.1 to some other, incompatible protocol. It
3236   does so by allowing the client to advertise its desire to use another
3237   protocol, such as a later version of HTTP with a higher major version
3238   number, even though the current request has been made using HTTP/1.1.
3239   This eases the difficult transition between incompatible protocols by
3240   allowing the client to initiate a request in the more commonly
3241   supported protocol while indicating to the server that it would like
3242   to use a "better" protocol if available (where "better" is determined
3243   by the server, possibly according to the nature of the request method
3244   or target resource).
3245</t>
3246<t>
3247   The Upgrade header field only applies to switching application-layer
3248   protocols upon the existing transport-layer connection. Upgrade
3249   cannot be used to insist on a protocol change; its acceptance and use
3250   by the server is optional. The capabilities and nature of the
3251   application-layer communication after the protocol change is entirely
3252   dependent upon the new protocol chosen, although the first action
3253   after changing the protocol &MUST; be a response to the initial HTTP
3254   request containing the Upgrade header field.
3255</t>
3256<t>
3257   The Upgrade header field only applies to the immediate connection.
3258   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3259   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3260   HTTP/1.1 message.
3261</t>
3262<t>
3263   The Upgrade header field cannot be used to indicate a switch to a
3264   protocol on a different connection. For that purpose, it is more
3265   appropriate to use a 3xx redirection response (&status-3xx;).
3266</t>
3267<t>
3268   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3269   Protocols) responses to indicate which protocol(s) are being switched to,
3270   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3271   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3272   response to indicate that they are willing to upgrade to one of the
3273   specified protocols.
3274</t>
3275<t>
3276   This specification only defines the protocol name "HTTP" for use by
3277   the family of Hypertext Transfer Protocols, as defined by the HTTP
3278   version rules of <xref target="http.version"/> and future updates to this
3279   specification. Additional tokens can be registered with IANA using the
3280   registration procedure defined below. 
3281</t>
3282
3283<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3284<t>
3285   The HTTP Upgrade Token Registry defines the name space for product
3286   tokens used to identify protocols in the Upgrade header field.
3287   Each registered token is associated with contact information and
3288   an optional set of specifications that details how the connection
3289   will be processed after it has been upgraded.
3290</t>
3291<t>
3292   Registrations are allowed on a First Come First Served basis as
3293   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3294   specifications need not be IETF documents or be subject to IESG review.
3295   Registrations are subject to the following rules:
3296  <list style="numbers">
3297    <t>A token, once registered, stays registered forever.</t>
3298    <t>The registration &MUST; name a responsible party for the
3299       registration.</t>
3300    <t>The registration &MUST; name a point of contact.</t>
3301    <t>The registration &MAY; name a set of specifications associated with that
3302       token. Such specifications need not be publicly available.</t>
3303    <t>The responsible party &MAY; change the registration at any time.
3304       The IANA will keep a record of all such changes, and make them
3305       available upon request.</t>
3306    <t>The responsible party for the first registration of a "product"
3307       token &MUST; approve later registrations of a "version" token
3308       together with that "product" token before they can be registered.</t>
3309    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3310       for a token. This will normally only be used in the case when a
3311       responsible party cannot be contacted.</t>
3312  </list>
3313</t>
3314</section>
3315
3316
3317</section>
3318
3319<section title="Via" anchor="header.via">
3320  <iref primary="true" item="Via header field" x:for-anchor=""/>
3321  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3322  <x:anchor-alias value="protocol-name"/>
3323  <x:anchor-alias value="protocol-version"/>
3324  <x:anchor-alias value="pseudonym"/>
3325  <x:anchor-alias value="received-by"/>
3326  <x:anchor-alias value="received-protocol"/>
3327  <x:anchor-alias value="Via"/>
3328<t>
3329   The "Via" header field &MUST; be sent by a proxy or gateway to
3330   indicate the intermediate protocols and recipients between the user
3331   agent and the server on requests, and between the origin server and
3332   the client on responses. It is analogous to the "Received" field
3333   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3334   and is intended to be used for tracking message forwards,
3335   avoiding request loops, and identifying the protocol capabilities of
3336   all senders along the request/response chain.
3337</t>
3338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3339  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3340                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3341  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3342  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3343  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3344  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3345  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3346</artwork></figure>
3347<t>
3348   The received-protocol indicates the protocol version of the message
3349   received by the server or client along each segment of the
3350   request/response chain. The received-protocol version is appended to
3351   the Via field value when the message is forwarded so that information
3352   about the protocol capabilities of upstream applications remains
3353   visible to all recipients.
3354</t>
3355<t>
3356   The protocol-name is excluded if and only if it would be "HTTP". The
3357   received-by field is normally the host and optional port number of a
3358   recipient server or client that subsequently forwarded the message.
3359   However, if the real host is considered to be sensitive information,
3360   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3361   be assumed to be the default port of the received-protocol.
3362</t>
3363<t>
3364   Multiple Via field values represent each proxy or gateway that has
3365   forwarded the message. Each recipient &MUST; append its information
3366   such that the end result is ordered according to the sequence of
3367   forwarding applications.
3368</t>
3369<t>
3370   Comments &MAY; be used in the Via header field to identify the software
3371   of each recipient, analogous to the User-Agent and Server header fields.
3372   However, all comments in the Via field are optional and &MAY; be removed
3373   by any recipient prior to forwarding the message.
3374</t>
3375<t>
3376   For example, a request message could be sent from an HTTP/1.0 user
3377   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3378   forward the request to a public proxy at p.example.net, which completes
3379   the request by forwarding it to the origin server at www.example.com.
3380   The request received by www.example.com would then have the following
3381   Via header field:
3382</t>
3383<figure><artwork type="example">
3384  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3385</artwork></figure>
3386<t>
3387   A proxy or gateway used as a portal through a network firewall
3388   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3389   region unless it is explicitly enabled to do so. If not enabled, the
3390   received-by host of any host behind the firewall &SHOULD; be replaced
3391   by an appropriate pseudonym for that host.
3392</t>
3393<t>
3394   For organizations that have strong privacy requirements for hiding
3395   internal structures, a proxy or gateway &MAY; combine an ordered
3396   subsequence of Via header field entries with identical received-protocol
3397   values into a single such entry. For example,
3398</t>
3399<figure><artwork type="example">
3400  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3401</artwork></figure>
3402<t>
3403  could be collapsed to
3404</t>
3405<figure><artwork type="example">
3406  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3407</artwork></figure>
3408<t>
3409   Senders &SHOULD-NOT; combine multiple entries unless they are all
3410   under the same organizational control and the hosts have already been
3411   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3412   have different received-protocol values.
3413</t>
3414</section>
3415
3416</section>
3417
3418<section title="IANA Considerations" anchor="IANA.considerations">
3419
3420<section title="Header Field Registration" anchor="header.field.registration">
3421<t>
3422   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3423   with the permanent registrations below (see <xref target="RFC3864"/>):
3424</t>
3425<?BEGININC p1-messaging.iana-headers ?>
3426<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3427<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3428   <ttcol>Header Field Name</ttcol>
3429   <ttcol>Protocol</ttcol>
3430   <ttcol>Status</ttcol>
3431   <ttcol>Reference</ttcol>
3432
3433   <c>Connection</c>
3434   <c>http</c>
3435   <c>standard</c>
3436   <c>
3437      <xref target="header.connection"/>
3438   </c>
3439   <c>Content-Length</c>
3440   <c>http</c>
3441   <c>standard</c>
3442   <c>
3443      <xref target="header.content-length"/>
3444   </c>
3445   <c>Host</c>
3446   <c>http</c>
3447   <c>standard</c>
3448   <c>
3449      <xref target="header.host"/>
3450   </c>
3451   <c>TE</c>
3452   <c>http</c>
3453   <c>standard</c>
3454   <c>
3455      <xref target="header.te"/>
3456   </c>
3457   <c>Trailer</c>
3458   <c>http</c>
3459   <c>standard</c>
3460   <c>
3461      <xref target="header.trailer"/>
3462   </c>
3463   <c>Transfer-Encoding</c>
3464   <c>http</c>
3465   <c>standard</c>
3466   <c>
3467      <xref target="header.transfer-encoding"/>
3468   </c>
3469   <c>Upgrade</c>
3470   <c>http</c>
3471   <c>standard</c>
3472   <c>
3473      <xref target="header.upgrade"/>
3474   </c>
3475   <c>Via</c>
3476   <c>http</c>
3477   <c>standard</c>
3478   <c>
3479      <xref target="header.via"/>
3480   </c>
3481</texttable>
3482<!--(END)-->
3483<?ENDINC p1-messaging.iana-headers ?>
3484<t>
3485   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3486   HTTP header field would be in conflict with the use of the "close" connection
3487   option for the "Connection" header field (<xref target="header.connection"/>).
3488</t>
3489<texttable align="left" suppress-title="true">
3490   <ttcol>Header Field Name</ttcol>
3491   <ttcol>Protocol</ttcol>
3492   <ttcol>Status</ttcol>
3493   <ttcol>Reference</ttcol>
3494
3495   <c>Close</c>
3496   <c>http</c>
3497   <c>reserved</c>
3498   <c>
3499      <xref target="header.field.registration"/>
3500   </c>
3501</texttable>
3502<t>
3503   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3504</t>
3505</section>
3506
3507<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3508<t>
3509   The entries for the "http" and "https" URI Schemes in the registry located at
3510   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3511   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3512   and <xref target="https.uri" format="counter"/> of this document
3513   (see <xref target="RFC4395"/>).
3514</t>
3515</section>
3516
3517<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3518<t>
3519   This document serves as the specification for the Internet media types
3520   "message/http" and "application/http". The following is to be registered with
3521   IANA (see <xref target="RFC4288"/>).
3522</t>
3523<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3524<iref item="Media Type" subitem="message/http" primary="true"/>
3525<iref item="message/http Media Type" primary="true"/>
3526<t>
3527   The message/http type can be used to enclose a single HTTP request or
3528   response message, provided that it obeys the MIME restrictions for all
3529   "message" types regarding line length and encodings.
3530</t>
3531<t>
3532  <list style="hanging" x:indent="12em">
3533    <t hangText="Type name:">
3534      message
3535    </t>
3536    <t hangText="Subtype name:">
3537      http
3538    </t>
3539    <t hangText="Required parameters:">
3540      none
3541    </t>
3542    <t hangText="Optional parameters:">
3543      version, msgtype
3544      <list style="hanging">
3545        <t hangText="version:">
3546          The HTTP-Version number of the enclosed message
3547          (e.g., "1.1"). If not present, the version can be
3548          determined from the first line of the body.
3549        </t>
3550        <t hangText="msgtype:">
3551          The message type &mdash; "request" or "response". If not
3552          present, the type can be determined from the first
3553          line of the body.
3554        </t>
3555      </list>
3556    </t>
3557    <t hangText="Encoding considerations:">
3558      only "7bit", "8bit", or "binary" are permitted
3559    </t>
3560    <t hangText="Security considerations:">
3561      none
3562    </t>
3563    <t hangText="Interoperability considerations:">
3564      none
3565    </t>
3566    <t hangText="Published specification:">
3567      This specification (see <xref target="internet.media.type.message.http"/>).
3568    </t>
3569    <t hangText="Applications that use this media type:">
3570    </t>
3571    <t hangText="Additional information:">
3572      <list style="hanging">
3573        <t hangText="Magic number(s):">none</t>
3574        <t hangText="File extension(s):">none</t>
3575        <t hangText="Macintosh file type code(s):">none</t>
3576      </list>
3577    </t>
3578    <t hangText="Person and email address to contact for further information:">
3579      See Authors Section.
3580    </t>
3581    <t hangText="Intended usage:">
3582      COMMON
3583    </t>
3584    <t hangText="Restrictions on usage:">
3585      none
3586    </t>
3587    <t hangText="Author/Change controller:">
3588      IESG
3589    </t>
3590  </list>
3591</t>
3592</section>
3593<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3594<iref item="Media Type" subitem="application/http" primary="true"/>
3595<iref item="application/http Media Type" primary="true"/>
3596<t>
3597   The application/http type can be used to enclose a pipeline of one or more
3598   HTTP request or response messages (not intermixed).
3599</t>
3600<t>
3601  <list style="hanging" x:indent="12em">
3602    <t hangText="Type name:">
3603      application
3604    </t>
3605    <t hangText="Subtype name:">
3606      http
3607    </t>
3608    <t hangText="Required parameters:">
3609      none
3610    </t>
3611    <t hangText="Optional parameters:">
3612      version, msgtype
3613      <list style="hanging">
3614        <t hangText="version:">
3615          The HTTP-Version number of the enclosed messages
3616          (e.g., "1.1"). If not present, the version can be
3617          determined from the first line of the body.
3618        </t>
3619        <t hangText="msgtype:">
3620          The message type &mdash; "request" or "response". If not
3621          present, the type can be determined from the first
3622          line of the body.
3623        </t>
3624      </list>
3625    </t>
3626    <t hangText="Encoding considerations:">
3627      HTTP messages enclosed by this type
3628      are in "binary" format; use of an appropriate
3629      Content-Transfer-Encoding is required when
3630      transmitted via E-mail.
3631    </t>
3632    <t hangText="Security considerations:">
3633      none
3634    </t>
3635    <t hangText="Interoperability considerations:">
3636      none
3637    </t>
3638    <t hangText="Published specification:">
3639      This specification (see <xref target="internet.media.type.application.http"/>).
3640    </t>
3641    <t hangText="Applications that use this media type:">
3642    </t>
3643    <t hangText="Additional information:">
3644      <list style="hanging">
3645        <t hangText="Magic number(s):">none</t>
3646        <t hangText="File extension(s):">none</t>
3647        <t hangText="Macintosh file type code(s):">none</t>
3648      </list>
3649    </t>
3650    <t hangText="Person and email address to contact for further information:">
3651      See Authors Section.
3652    </t>
3653    <t hangText="Intended usage:">
3654      COMMON
3655    </t>
3656    <t hangText="Restrictions on usage:">
3657      none
3658    </t>
3659    <t hangText="Author/Change controller:">
3660      IESG
3661    </t>
3662  </list>
3663</t>
3664</section>
3665</section>
3666
3667<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3668<t>
3669   The registration procedure for HTTP Transfer Codings is now defined by
3670   <xref target="transfer.coding.registry"/> of this document.
3671</t>
3672<t>
3673   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3674   shall be updated with the registrations below:
3675</t>
3676<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3677   <ttcol>Name</ttcol>
3678   <ttcol>Description</ttcol>
3679   <ttcol>Reference</ttcol>
3680   <c>chunked</c>
3681   <c>Transfer in a series of chunks</c>
3682   <c>
3683      <xref target="chunked.encoding"/>
3684   </c>
3685   <c>compress</c>
3686   <c>UNIX "compress" program method</c>
3687   <c>
3688      <xref target="compress.coding"/>
3689   </c>
3690   <c>deflate</c>
3691   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3692   the "zlib" data format (<xref target="RFC1950"/>)
3693   </c>
3694   <c>
3695      <xref target="deflate.coding"/>
3696   </c>
3697   <c>gzip</c>
3698   <c>Same as GNU zip <xref target="RFC1952"/></c>
3699   <c>
3700      <xref target="gzip.coding"/>
3701   </c>
3702</texttable>
3703</section>
3704
3705<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3706<t>
3707   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3708   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3709   by <xref target="upgrade.token.registry"/> of this document.
3710</t>
3711<t>
3712   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3713   shall be updated with the registration below:
3714</t>
3715<texttable align="left" suppress-title="true">
3716   <ttcol>Value</ttcol>
3717   <ttcol>Description</ttcol>
3718   <ttcol>Reference</ttcol>
3719
3720   <c>HTTP</c>
3721   <c>Hypertext Transfer Protocol</c> 
3722   <c><xref target="http.version"/> of this specification</c>
3723
3724</texttable>
3725</section>
3726
3727</section>
3728
3729<section title="Security Considerations" anchor="security.considerations">
3730<t>
3731   This section is meant to inform application developers, information
3732   providers, and users of the security limitations in HTTP/1.1 as
3733   described by this document. The discussion does not include
3734   definitive solutions to the problems revealed, though it does make
3735   some suggestions for reducing security risks.
3736</t>
3737
3738<section title="Personal Information" anchor="personal.information">
3739<t>
3740   HTTP clients are often privy to large amounts of personal information
3741   (e.g., the user's name, location, mail address, passwords, encryption
3742   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3743   leakage of this information.
3744   We very strongly recommend that a convenient interface be provided
3745   for the user to control dissemination of such information, and that
3746   designers and implementors be particularly careful in this area.
3747   History shows that errors in this area often create serious security
3748   and/or privacy problems and generate highly adverse publicity for the
3749   implementor's company.
3750</t>
3751</section>
3752
3753<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3754<t>
3755   A server is in the position to save personal data about a user's
3756   requests which might identify their reading patterns or subjects of
3757   interest. This information is clearly confidential in nature and its
3758   handling can be constrained by law in certain countries. People using
3759   HTTP to provide data are responsible for ensuring that
3760   such material is not distributed without the permission of any
3761   individuals that are identifiable by the published results.
3762</t>
3763</section>
3764
3765<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3766<t>
3767   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3768   the documents returned by HTTP requests to be only those that were
3769   intended by the server administrators. If an HTTP server translates
3770   HTTP URIs directly into file system calls, the server &MUST; take
3771   special care not to serve files that were not intended to be
3772   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3773   other operating systems use ".." as a path component to indicate a
3774   directory level above the current one. On such a system, an HTTP
3775   server &MUST; disallow any such construct in the request-target if it
3776   would otherwise allow access to a resource outside those intended to
3777   be accessible via the HTTP server. Similarly, files intended for
3778   reference only internally to the server (such as access control
3779   files, configuration files, and script code) &MUST; be protected from
3780   inappropriate retrieval, since they might contain sensitive
3781   information. Experience has shown that minor bugs in such HTTP server
3782   implementations have turned into security risks.
3783</t>
3784</section>
3785
3786<section title="DNS-related Attacks" anchor="dns.related.attacks">
3787<t>
3788   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3789   generally prone to security attacks based on the deliberate misassociation
3790   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3791   cautious in assuming the validity of an IP number/DNS name association unless
3792   the response is protected by DNSSec (<xref target="RFC4033"/>).
3793</t>
3794</section>
3795
3796<section title="Proxies and Caching" anchor="attack.proxies">
3797<t>
3798   By their very nature, HTTP proxies are men-in-the-middle, and
3799   represent an opportunity for man-in-the-middle attacks. Compromise of
3800   the systems on which the proxies run can result in serious security
3801   and privacy problems. Proxies have access to security-related
3802   information, personal information about individual users and
3803   organizations, and proprietary information belonging to users and
3804   content providers. A compromised proxy, or a proxy implemented or
3805   configured without regard to security and privacy considerations,
3806   might be used in the commission of a wide range of potential attacks.
3807</t>
3808<t>
3809   Proxy operators need to protect the systems on which proxies run as
3810   they would protect any system that contains or transports sensitive
3811   information. In particular, log information gathered at proxies often
3812   contains highly sensitive personal information, and/or information
3813   about organizations. Log information needs to be carefully guarded, and
3814   appropriate guidelines for use need to be developed and followed.
3815   (<xref target="abuse.of.server.log.information"/>).
3816</t>
3817<t>
3818   Proxy implementors need to consider the privacy and security
3819   implications of their design and coding decisions, and of the
3820   configuration options they provide to proxy operators (especially the
3821   default configuration).
3822</t>
3823<t>
3824   Users of a proxy need to be aware that proxies are no trustworthier than
3825   the people who run them; HTTP itself cannot solve this problem.
3826</t>
3827<t>
3828   The judicious use of cryptography, when appropriate, might suffice to
3829   protect against a broad range of security and privacy attacks. Such
3830   cryptography is beyond the scope of the HTTP/1.1 specification.
3831</t>
3832</section>
3833
3834<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3835<t>
3836   Because HTTP uses mostly textual, character-delimited fields, attackers can
3837   overflow buffers in implementations, and/or perform a Denial of Service
3838   against implementations that accept fields with unlimited lengths.
3839</t>
3840<t>
3841   To promote interoperability, this specification makes specific
3842   recommendations for size limits on request-targets (<xref target="request-target"/>)
3843   and blocks of header fields (<xref target="header.fields"/>). These are
3844   minimum recommendations, chosen to be supportable even by implementations
3845   with limited resources; it is expected that most implementations will choose
3846   substantially higher limits.
3847</t>
3848<t>
3849   This specification also provides a way for servers to reject messages that
3850   have request-targets that are too long (&status-414;) or request entities
3851   that are too large (&status-4xx;).
3852</t>
3853<t>
3854   Other fields (including but not limited to request methods, response status
3855   phrases, header field-names, and body chunks) &SHOULD; be limited by
3856   implementations carefully, so as to not impede interoperability.
3857</t>
3858</section>
3859
3860<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3861<t>
3862   They exist. They are hard to defend against. Research continues.
3863   Beware.
3864</t>
3865</section>
3866</section>
3867
3868<section title="Acknowledgments" anchor="acks">
3869<t>
3870   This document revision builds on the work that went into
3871   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3872   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3873   acknowledgements.
3874</t>
3875<t>
3876   Since 1999, many contributors have helped by reporting bugs, asking
3877   smart questions, drafting and reviewing text, and discussing open issues:
3878</t>
3879<?BEGININC acks ?>
3880<t>Adam Barth,
3881Adam Roach,
3882Addison Phillips,
3883Adrian Chadd,
3884Adrien de Croy,
3885Alan Ford,
3886Alan Ruttenberg,
3887Albert Lunde,
3888Alex Rousskov,
3889Alexey Melnikov,
3890Alisha Smith,
3891Amichai Rothman,
3892Amit Klein,
3893Amos Jeffries,
3894Andreas Maier,
3895Andreas Petersson,
3896Anne van Kesteren,
3897Anthony Bryan,
3898Asbjorn Ulsberg,
3899Balachander Krishnamurthy,
3900Barry Leiba,
3901Ben Laurie,
3902Benjamin Niven-Jenkins,
3903Bil Corry,
3904Bill Burke,
3905Bjoern Hoehrmann,
3906Bob Scheifler,
3907Boris Zbarsky,
3908Brett Slatkin,
3909Brian Kell,
3910Brian McBarron,
3911Brian Pane,
3912Brian Smith,
3913Bryce Nesbitt,
3914Carl Kugler,
3915Charles Fry,
3916Chris Newman,
3917Cyrus Daboo,
3918Dale Robert Anderson,
3919Dan Winship,
3920Daniel Stenberg,
3921Dave Cridland,
3922Dave Crocker,
3923Dave Kristol,
3924David Booth,
3925David Singer,
3926David W. Morris,
3927Diwakar Shetty,
3928Drummond Reed,
3929Duane Wessels,
3930Edward Lee,
3931Eliot Lear,
3932Eran Hammer-Lahav,
3933Eric D. Williams,
3934Eric J. Bowman,
3935Eric Lawrence,
3936Erik Aronesty,
3937Florian Weimer,
3938Frank Ellermann,
3939Fred Bohle,
3940Geoffrey Sneddon,
3941Gervase Markham,
3942Greg Wilkins,
3943Harald Tveit Alvestrand,
3944Harry Halpin,
3945Helge Hess,
3946Henrik Nordstrom,
3947Henry S. Thompson,
3948Henry Story,
3949Howard Melman,
3950Hugo Haas,
3951Ian Hickson,
3952Ingo Struck,
3953J. Ross Nicoll,
3954James H. Manger,
3955James Lacey,
3956James M. Snell,
3957Jamie Lokier,
3958Jan Algermissen,
3959Jeff Hodges (for coming up with the term 'effective Request-URI'),
3960Jeff Walden,
3961Jim Luther,
3962Joe D. Williams,
3963Joe Gregorio,
3964Joe Orton,
3965John C. Klensin,
3966John C. Mallery,
3967John Cowan,
3968John Kemp,
3969John Panzer,
3970John Schneider,
3971John Stracke,
3972Jonas Sicking,
3973Jonathan Moore,
3974Jonathan Rees,
3975Jordi Ros,
3976Joris Dobbelsteen,
3977Josh Cohen,
3978Julien Pierre,
3979Jungshik Shin,
3980Justin Chapweske,
3981Justin Erenkrantz,
3982Justin James,
3983Kalvinder Singh,
3984Karl Dubost,
3985Keith Hoffman,
3986Keith Moore,
3987Koen Holtman,
3988Konstantin Voronkov,
3989Kris Zyp,
3990Lisa Dusseault,
3991Maciej Stachowiak,
3992Marc Schneider,
3993Marc Slemko,
3994Mark Baker,
3995Mark Nottingham (Working Group chair),
3996Mark Pauley,
3997Martin J. Duerst,
3998Martin Thomson,
3999Matt Lynch,
4000Matthew Cox,
4001Max Clark,
4002Michael Burrows,
4003Michael Hausenblas,
4004Mike Amundsen,
4005Mike Kelly,
4006Mike Schinkel,
4007Miles Sabin,
4008Mykyta Yevstifeyev,
4009Nathan Rixham,
4010Nicholas Shanks,
4011Nico Williams,
4012Nicolas Alvarez,
4013Noah Slater,
4014Pablo Castro,
4015Pat Hayes,
4016Patrick R. McManus,
4017Paul E. Jones,
4018Paul Hoffman,
4019Paul Marquess,
4020Peter Saint-Andre,
4021Peter Watkins,
4022Phil Archer,
4023Phillip Hallam-Baker,
4024Poul-Henning Kamp,
4025Preethi Natarajan,
4026Reto Bachmann-Gmuer,
4027Richard Cyganiak,
4028Robert Brewer,
4029Robert Collins,
4030Robert O'Callahan,
4031Robert Olofsson,
4032Robert Sayre,
4033Robert Siemer,
4034Robert de Wilde,
4035Roberto Javier Godoy,
4036Ronny Widjaja,
4037S. Mike Dierken,
4038Salvatore Loreto,
4039Sam Johnston,
4040Sam Ruby,
4041Scott Lawrence (for maintaining the original issues list),
4042Sean B. Palmer,
4043Shane McCarron,
4044Stefan Eissing,
4045Stefan Tilkov,
4046Stefanos Harhalakis,
4047Stephane Bortzmeyer,
4048Stuart Williams,
4049Subbu Allamaraju,
4050Sylvain Hellegouarch,
4051Tapan Divekar,
4052Thomas Broyer,
4053Thomas Nordin,
4054Thomas Roessler,
4055Tim Morgan,
4056Tim Olsen,
4057Travis Snoozy,
4058Tyler Close,
4059Vincent Murphy,
4060Wenbo Zhu,
4061Werner Baumann,
4062Wilbur Streett,
4063Wilfredo Sanchez Vega,
4064William A. Rowe Jr.,
4065William Chan,
4066Willy Tarreau,
4067Xiaoshu Wang,
4068Yaron Goland,
4069Yngve Nysaeter Pettersen,
4070Yogesh Bang,
4071Yutaka Oiwa, and
4072Zed A. Shaw.
4073</t>
4074<?ENDINC acks ?>
4075</section>
4076
4077</middle>
4078<back>
4079
4080<references title="Normative References">
4081
4082<reference anchor="ISO-8859-1">
4083  <front>
4084    <title>
4085     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4086    </title>
4087    <author>
4088      <organization>International Organization for Standardization</organization>
4089    </author>
4090    <date year="1998"/>
4091  </front>
4092  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4093</reference>
4094
4095<reference anchor="Part2">
4096  <front>
4097    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4098    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4099      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4100      <address><email>fielding@gbiv.com</email></address>
4101    </author>
4102    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4103      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4104      <address><email>jg@freedesktop.org</email></address>
4105    </author>
4106    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4107      <organization abbrev="HP">Hewlett-Packard Company</organization>
4108      <address><email>JeffMogul@acm.org</email></address>
4109    </author>
4110    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4111      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4112      <address><email>henrikn@microsoft.com</email></address>
4113    </author>
4114    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4115      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4116      <address><email>LMM@acm.org</email></address>
4117    </author>
4118    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4119      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4120      <address><email>paulle@microsoft.com</email></address>
4121    </author>
4122    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4123      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4124      <address><email>timbl@w3.org</email></address>
4125    </author>
4126    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4127      <organization abbrev="W3C">World Wide Web Consortium</organization>
4128      <address><email>ylafon@w3.org</email></address>
4129    </author>
4130    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4131      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4132      <address><email>julian.reschke@greenbytes.de</email></address>
4133    </author>
4134    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4135  </front>
4136  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4137  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4138</reference>
4139
4140<reference anchor="Part3">
4141  <front>
4142    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4143    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4144      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4145      <address><email>fielding@gbiv.com</email></address>
4146    </author>
4147    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4148      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4149      <address><email>jg@freedesktop.org</email></address>
4150    </author>
4151    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4152      <organization abbrev="HP">Hewlett-Packard Company</organization>
4153      <address><email>JeffMogul@acm.org</email></address>
4154    </author>
4155    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4156      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4157      <address><email>henrikn@microsoft.com</email></address>
4158    </author>
4159    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4160      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4161      <address><email>LMM@acm.org</email></address>
4162    </author>
4163    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4164      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4165      <address><email>paulle@microsoft.com</email></address>
4166    </author>
4167    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4168      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4169      <address><email>timbl@w3.org</email></address>
4170    </author>
4171    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4172      <organization abbrev="W3C">World Wide Web Consortium</organization>
4173      <address><email>ylafon@w3.org</email></address>
4174    </author>
4175    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4176      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4177      <address><email>julian.reschke@greenbytes.de</email></address>
4178    </author>
4179    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4180  </front>
4181  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4182  <x:source href="p3-payload.xml" basename="p3-payload"/>
4183</reference>
4184
4185<reference anchor="Part6">
4186  <front>
4187    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4188    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4189      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4190      <address><email>fielding@gbiv.com</email></address>
4191    </author>
4192    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4193      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4194      <address><email>jg@freedesktop.org</email></address>
4195    </author>
4196    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4197      <organization abbrev="HP">Hewlett-Packard Company</organization>
4198      <address><email>JeffMogul@acm.org</email></address>
4199    </author>
4200    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4201      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4202      <address><email>henrikn@microsoft.com</email></address>
4203    </author>
4204    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4205      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4206      <address><email>LMM@acm.org</email></address>
4207    </author>
4208    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4209      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4210      <address><email>paulle@microsoft.com</email></address>
4211    </author>
4212    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4213      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4214      <address><email>timbl@w3.org</email></address>
4215    </author>
4216    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4217      <organization abbrev="W3C">World Wide Web Consortium</organization>
4218      <address><email>ylafon@w3.org</email></address>
4219    </author>
4220    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4221      <organization>Rackspace</organization>
4222      <address><email>mnot@mnot.net</email></address>
4223    </author>
4224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4226      <address><email>julian.reschke@greenbytes.de</email></address>
4227    </author>
4228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4229  </front>
4230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4231  <x:source href="p6-cache.xml" basename="p6-cache"/>
4232</reference>
4233
4234<reference anchor="RFC5234">
4235  <front>
4236    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4237    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4238      <organization>Brandenburg InternetWorking</organization>
4239      <address>
4240        <email>dcrocker@bbiw.net</email>
4241      </address> 
4242    </author>
4243    <author initials="P." surname="Overell" fullname="Paul Overell">
4244      <organization>THUS plc.</organization>
4245      <address>
4246        <email>paul.overell@thus.net</email>
4247      </address>
4248    </author>
4249    <date month="January" year="2008"/>
4250  </front>
4251  <seriesInfo name="STD" value="68"/>
4252  <seriesInfo name="RFC" value="5234"/>
4253</reference>
4254
4255<reference anchor="RFC2119">
4256  <front>
4257    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4258    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4259      <organization>Harvard University</organization>
4260      <address><email>sob@harvard.edu</email></address>
4261    </author>
4262    <date month="March" year="1997"/>
4263  </front>
4264  <seriesInfo name="BCP" value="14"/>
4265  <seriesInfo name="RFC" value="2119"/>
4266</reference>
4267
4268<reference anchor="RFC3986">
4269 <front>
4270  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4271  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4272    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4273    <address>
4274       <email>timbl@w3.org</email>
4275       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4276    </address>
4277  </author>
4278  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4279    <organization abbrev="Day Software">Day Software</organization>
4280    <address>
4281      <email>fielding@gbiv.com</email>
4282      <uri>http://roy.gbiv.com/</uri>
4283    </address>
4284  </author>
4285  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4286    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4287    <address>
4288      <email>LMM@acm.org</email>
4289      <uri>http://larry.masinter.net/</uri>
4290    </address>
4291  </author>
4292  <date month='January' year='2005'></date>
4293 </front>
4294 <seriesInfo name="STD" value="66"/>
4295 <seriesInfo name="RFC" value="3986"/>
4296</reference>
4297
4298<reference anchor="USASCII">
4299  <front>
4300    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4301    <author>
4302      <organization>American National Standards Institute</organization>
4303    </author>
4304    <date year="1986"/>
4305  </front>
4306  <seriesInfo name="ANSI" value="X3.4"/>
4307</reference>
4308
4309<reference anchor="RFC1950">
4310  <front>
4311    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4312    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4313      <organization>Aladdin Enterprises</organization>
4314      <address><email>ghost@aladdin.com</email></address>
4315    </author>
4316    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4317    <date month="May" year="1996"/>
4318  </front>
4319  <seriesInfo name="RFC" value="1950"/>
4320  <annotation>
4321    RFC 1950 is an Informational RFC, thus it might be less stable than
4322    this specification. On the other hand, this downward reference was
4323    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4324    therefore it is unlikely to cause problems in practice. See also
4325    <xref target="BCP97"/>.
4326  </annotation>
4327</reference>
4328
4329<reference anchor="RFC1951">
4330  <front>
4331    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4332    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4333      <organization>Aladdin Enterprises</organization>
4334      <address><email>ghost@aladdin.com</email></address>
4335    </author>
4336    <date month="May" year="1996"/>
4337  </front>
4338  <seriesInfo name="RFC" value="1951"/>
4339  <annotation>
4340    RFC 1951 is an Informational RFC, thus it might be less stable than
4341    this specification. On the other hand, this downward reference was
4342    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4343    therefore it is unlikely to cause problems in practice. See also
4344    <xref target="BCP97"/>.
4345  </annotation>
4346</reference>
4347
4348<reference anchor="RFC1952">
4349  <front>
4350    <title>GZIP file format specification version 4.3</title>
4351    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4352      <organization>Aladdin Enterprises</organization>
4353      <address><email>ghost@aladdin.com</email></address>
4354    </author>
4355    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4356      <address><email>gzip@prep.ai.mit.edu</email></address>
4357    </author>
4358    <author initials="M." surname="Adler" fullname="Mark Adler">
4359      <address><email>madler@alumni.caltech.edu</email></address>
4360    </author>
4361    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4362      <address><email>ghost@aladdin.com</email></address>
4363    </author>
4364    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4365      <address><email>randeg@alumni.rpi.edu</email></address>
4366    </author>
4367    <date month="May" year="1996"/>
4368  </front>
4369  <seriesInfo name="RFC" value="1952"/>
4370  <annotation>
4371    RFC 1952 is an Informational RFC, thus it might be less stable than
4372    this specification. On the other hand, this downward reference was
4373    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4374    therefore it is unlikely to cause problems in practice. See also
4375    <xref target="BCP97"/>.
4376  </annotation>
4377</reference>
4378
4379</references>
4380
4381<references title="Informative References">
4382
4383<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4384  <front>
4385    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4386    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4387    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4388    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4389    <author initials="H." surname="Lie" fullname="H. Lie"/>
4390    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4391    <date year="1997" month="September"/>
4392  </front>
4393  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4394</reference>
4395
4396<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4397  <front>
4398    <title>Improving HTTP Latency</title>
4399    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4400    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4401    <date year="1995" month="December"/>
4402  </front>
4403  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4404</reference>
4405
4406<reference anchor='RFC1919'>
4407  <front>
4408    <title>Classical versus Transparent IP Proxies</title>
4409    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4410      <address><email>mchatel@pax.eunet.ch</email></address>
4411    </author>
4412    <date year='1996' month='March' />
4413  </front>
4414  <seriesInfo name='RFC' value='1919' />
4415</reference>
4416
4417<reference anchor="RFC1945">
4418  <front>
4419    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4420    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4421      <organization>MIT, Laboratory for Computer Science</organization>
4422      <address><email>timbl@w3.org</email></address>
4423    </author>
4424    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4425      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4426      <address><email>fielding@ics.uci.edu</email></address>
4427    </author>
4428    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4429      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4430      <address><email>frystyk@w3.org</email></address>
4431    </author>
4432    <date month="May" year="1996"/>
4433  </front>
4434  <seriesInfo name="RFC" value="1945"/>
4435</reference>
4436
4437<reference anchor="RFC2045">
4438  <front>
4439    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4440    <author initials="N." surname="Freed" fullname="Ned Freed">
4441      <organization>Innosoft International, Inc.</organization>
4442      <address><email>ned@innosoft.com</email></address>
4443    </author>
4444    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4445      <organization>First Virtual Holdings</organization>
4446      <address><email>nsb@nsb.fv.com</email></address>
4447    </author>
4448    <date month="November" year="1996"/>
4449  </front>
4450  <seriesInfo name="RFC" value="2045"/>
4451</reference>
4452
4453<reference anchor="RFC2047">
4454  <front>
4455    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4456    <author initials="K." surname="Moore" fullname="Keith Moore">
4457      <organization>University of Tennessee</organization>
4458      <address><email>moore@cs.utk.edu</email></address>
4459    </author>
4460    <date month="November" year="1996"/>
4461  </front>
4462  <seriesInfo name="RFC" value="2047"/>
4463</reference>
4464
4465<reference anchor="RFC2068">
4466  <front>
4467    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4468    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4469      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4470      <address><email>fielding@ics.uci.edu</email></address>
4471    </author>
4472    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4473      <organization>MIT Laboratory for Computer Science</organization>
4474      <address><email>jg@w3.org</email></address>
4475    </author>
4476    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4477      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4478      <address><email>mogul@wrl.dec.com</email></address>
4479    </author>
4480    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4481      <organization>MIT Laboratory for Computer Science</organization>
4482      <address><email>frystyk@w3.org</email></address>
4483    </author>
4484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4485      <organization>MIT Laboratory for Computer Science</organization>
4486      <address><email>timbl@w3.org</email></address>
4487    </author>
4488    <date month="January" year="1997"/>
4489  </front>
4490  <seriesInfo name="RFC" value="2068"/>
4491</reference>
4492
4493<reference anchor="RFC2145">
4494  <front>
4495    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4496    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4497      <organization>Western Research Laboratory</organization>
4498      <address><email>mogul@wrl.dec.com</email></address>
4499    </author>
4500    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4501      <organization>Department of Information and Computer Science</organization>
4502      <address><email>fielding@ics.uci.edu</email></address>
4503    </author>
4504    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4505      <organization>MIT Laboratory for Computer Science</organization>
4506      <address><email>jg@w3.org</email></address>
4507    </author>
4508    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4509      <organization>W3 Consortium</organization>
4510      <address><email>frystyk@w3.org</email></address>
4511    </author>
4512    <date month="May" year="1997"/>
4513  </front>
4514  <seriesInfo name="RFC" value="2145"/>
4515</reference>
4516
4517<reference anchor="RFC2616">
4518  <front>
4519    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4520    <author initials="R." surname="Fielding" fullname="R. Fielding">
4521      <organization>University of California, Irvine</organization>
4522      <address><email>fielding@ics.uci.edu</email></address>
4523    </author>
4524    <author initials="J." surname="Gettys" fullname="J. Gettys">
4525      <organization>W3C</organization>
4526      <address><email>jg@w3.org</email></address>
4527    </author>
4528    <author initials="J." surname="Mogul" fullname="J. Mogul">
4529      <organization>Compaq Computer Corporation</organization>
4530      <address><email>mogul@wrl.dec.com</email></address>
4531    </author>
4532    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4533      <organization>MIT Laboratory for Computer Science</organization>
4534      <address><email>frystyk@w3.org</email></address>
4535    </author>
4536    <author initials="L." surname="Masinter" fullname="L. Masinter">
4537      <organization>Xerox Corporation</organization>
4538      <address><email>masinter@parc.xerox.com</email></address>
4539    </author>
4540    <author initials="P." surname="Leach" fullname="P. Leach">
4541      <organization>Microsoft Corporation</organization>
4542      <address><email>paulle@microsoft.com</email></address>
4543    </author>
4544    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4545      <organization>W3C</organization>
4546      <address><email>timbl@w3.org</email></address>
4547    </author>
4548    <date month="June" year="1999"/>
4549  </front>
4550  <seriesInfo name="RFC" value="2616"/>
4551</reference>
4552
4553<reference anchor='RFC2817'>
4554  <front>
4555    <title>Upgrading to TLS Within HTTP/1.1</title>
4556    <author initials='R.' surname='Khare' fullname='R. Khare'>
4557      <organization>4K Associates / UC Irvine</organization>
4558      <address><email>rohit@4K-associates.com</email></address>
4559    </author>
4560    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4561      <organization>Agranat Systems, Inc.</organization>
4562      <address><email>lawrence@agranat.com</email></address>
4563    </author>
4564    <date year='2000' month='May' />
4565  </front>
4566  <seriesInfo name='RFC' value='2817' />
4567</reference>
4568
4569<reference anchor='RFC2818'>
4570  <front>
4571    <title>HTTP Over TLS</title>
4572    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4573      <organization>RTFM, Inc.</organization>
4574      <address><email>ekr@rtfm.com</email></address>
4575    </author>
4576    <date year='2000' month='May' />
4577  </front>
4578  <seriesInfo name='RFC' value='2818' />
4579</reference>
4580
4581<reference anchor='RFC2965'>
4582  <front>
4583    <title>HTTP State Management Mechanism</title>
4584    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4585      <organization>Bell Laboratories, Lucent Technologies</organization>
4586      <address><email>dmk@bell-labs.com</email></address>
4587    </author>
4588    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4589      <organization>Epinions.com, Inc.</organization>
4590      <address><email>lou@montulli.org</email></address>
4591    </author>
4592    <date year='2000' month='October' />
4593  </front>
4594  <seriesInfo name='RFC' value='2965' />
4595</reference>
4596
4597<reference anchor='RFC3040'>
4598  <front>
4599    <title>Internet Web Replication and Caching Taxonomy</title>
4600    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4601      <organization>Equinix, Inc.</organization>
4602    </author>
4603    <author initials='I.' surname='Melve' fullname='I. Melve'>
4604      <organization>UNINETT</organization>
4605    </author>
4606    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4607      <organization>CacheFlow Inc.</organization>
4608    </author>
4609    <date year='2001' month='January' />
4610  </front>
4611  <seriesInfo name='RFC' value='3040' />
4612</reference>
4613
4614<reference anchor='RFC3864'>
4615  <front>
4616    <title>Registration Procedures for Message Header Fields</title>
4617    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4618      <organization>Nine by Nine</organization>
4619      <address><email>GK-IETF@ninebynine.org</email></address>
4620    </author>
4621    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4622      <organization>BEA Systems</organization>
4623      <address><email>mnot@pobox.com</email></address>
4624    </author>
4625    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4626      <organization>HP Labs</organization>
4627      <address><email>JeffMogul@acm.org</email></address>
4628    </author>
4629    <date year='2004' month='September' />
4630  </front>
4631  <seriesInfo name='BCP' value='90' />
4632  <seriesInfo name='RFC' value='3864' />
4633</reference>
4634
4635<reference anchor='RFC4033'>
4636  <front>
4637    <title>DNS Security Introduction and Requirements</title>
4638    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4639    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4640    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4641    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4642    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4643    <date year='2005' month='March' />
4644  </front>
4645  <seriesInfo name='RFC' value='4033' />
4646</reference>
4647
4648<reference anchor="RFC4288">
4649  <front>
4650    <title>Media Type Specifications and Registration Procedures</title>
4651    <author initials="N." surname="Freed" fullname="N. Freed">
4652      <organization>Sun Microsystems</organization>
4653      <address>
4654        <email>ned.freed@mrochek.com</email>
4655      </address>
4656    </author>
4657    <author initials="J." surname="Klensin" fullname="J. Klensin">
4658      <address>
4659        <email>klensin+ietf@jck.com</email>
4660      </address>
4661    </author>
4662    <date year="2005" month="December"/>
4663  </front>
4664  <seriesInfo name="BCP" value="13"/>
4665  <seriesInfo name="RFC" value="4288"/>
4666</reference>
4667
4668<reference anchor='RFC4395'>
4669  <front>
4670    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4671    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4672      <organization>AT&amp;T Laboratories</organization>
4673      <address>
4674        <email>tony+urireg@maillennium.att.com</email>
4675      </address>
4676    </author>
4677    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4678      <organization>Qualcomm, Inc.</organization>
4679      <address>
4680        <email>hardie@qualcomm.com</email>
4681      </address>
4682    </author>
4683    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4684      <organization>Adobe Systems</organization>
4685      <address>
4686        <email>LMM@acm.org</email>
4687      </address>
4688    </author>
4689    <date year='2006' month='February' />
4690  </front>
4691  <seriesInfo name='BCP' value='115' />
4692  <seriesInfo name='RFC' value='4395' />
4693</reference>
4694
4695<reference anchor='RFC4559'>
4696  <front>
4697    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4698    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4699    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4700    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4701    <date year='2006' month='June' />
4702  </front>
4703  <seriesInfo name='RFC' value='4559' />
4704</reference>
4705
4706<reference anchor='RFC5226'>
4707  <front>
4708    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4709    <author initials='T.' surname='Narten' fullname='T. Narten'>
4710      <organization>IBM</organization>
4711      <address><email>narten@us.ibm.com</email></address>
4712    </author>
4713    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4714      <organization>Google</organization>
4715      <address><email>Harald@Alvestrand.no</email></address>
4716    </author>
4717    <date year='2008' month='May' />
4718  </front>
4719  <seriesInfo name='BCP' value='26' />
4720  <seriesInfo name='RFC' value='5226' />
4721</reference>
4722
4723<reference anchor="RFC5322">
4724  <front>
4725    <title>Internet Message Format</title>
4726    <author initials="P." surname="Resnick" fullname="P. Resnick">
4727      <organization>Qualcomm Incorporated</organization>
4728    </author>
4729    <date year="2008" month="October"/>
4730  </front> 
4731  <seriesInfo name="RFC" value="5322"/>
4732</reference>
4733
4734<reference anchor="RFC6265">
4735  <front>
4736    <title>HTTP State Management Mechanism</title>
4737    <author initials="A." surname="Barth" fullname="Adam Barth">
4738      <organization abbrev="U.C. Berkeley">
4739        University of California, Berkeley
4740      </organization>
4741      <address><email>abarth@eecs.berkeley.edu</email></address>
4742    </author>
4743    <date year="2011" month="April" />
4744  </front>
4745  <seriesInfo name="RFC" value="6265"/>
4746</reference>
4747
4748<reference anchor='BCP97'>
4749  <front>
4750    <title>Handling Normative References to Standards-Track Documents</title>
4751    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4752      <address>
4753        <email>klensin+ietf@jck.com</email>
4754      </address>
4755    </author>
4756    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4757      <organization>MIT</organization>
4758      <address>
4759        <email>hartmans-ietf@mit.edu</email>
4760      </address>
4761    </author>
4762    <date year='2007' month='June' />
4763  </front>
4764  <seriesInfo name='BCP' value='97' />
4765  <seriesInfo name='RFC' value='4897' />
4766</reference>
4767
4768<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4769  <front>
4770    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4771    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4772    <date year="2001" month="November"/>
4773  </front>
4774  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4775</reference>
4776
4777<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4778  <front>
4779    <title>Analysis of HTTP Performance Problems</title>
4780    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4781    <date/>
4782  </front>
4783</reference>
4784
4785<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4786  <front>
4787  <title>Analysis of HTTP Performance</title>
4788  <author initials="J." surname="Touch" fullname="Joe Touch">
4789    <organization>USC/Information Sciences Institute</organization>
4790    <address><email>touch@isi.edu</email></address>
4791  </author>
4792  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4793    <organization>USC/Information Sciences Institute</organization>
4794    <address><email>johnh@isi.edu</email></address>
4795  </author>
4796  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4797    <organization>USC/Information Sciences Institute</organization>
4798    <address><email>katia@isi.edu</email></address>
4799  </author>
4800  <date year="1998" month="Aug"/>
4801  </front>
4802  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4803  <annotation>(original report dated Aug. 1996)</annotation>
4804</reference>
4805
4806</references>
4807
4808
4809<section title="HTTP Version History" anchor="compatibility">
4810<t>
4811   HTTP has been in use by the World-Wide Web global information initiative
4812   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4813   was a simple protocol for hypertext data transfer across the Internet
4814   with only a single request method (GET) and no metadata.
4815   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4816   methods and MIME-like messaging that could include metadata about the data
4817   transferred and modifiers on the request/response semantics. However,
4818   HTTP/1.0 did not sufficiently take into consideration the effects of
4819   hierarchical proxies, caching, the need for persistent connections, or
4820   name-based virtual hosts. The proliferation of incompletely-implemented
4821   applications calling themselves "HTTP/1.0" further necessitated a
4822   protocol version change in order for two communicating applications
4823   to determine each other's true capabilities.
4824</t>
4825<t>
4826   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4827   requirements that enable reliable implementations, adding only
4828   those new features that will either be safely ignored by an HTTP/1.0
4829   recipient or only sent when communicating with a party advertising
4830   compliance with HTTP/1.1.
4831</t>
4832<t>
4833   It is beyond the scope of a protocol specification to mandate
4834   compliance with previous versions. HTTP/1.1 was deliberately
4835   designed, however, to make supporting previous versions easy.
4836   We would expect a general-purpose HTTP/1.1 server to understand
4837   any valid request in the format of HTTP/1.0 and respond appropriately
4838   with an HTTP/1.1 message that only uses features understood (or
4839   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4840   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4841</t>
4842<t>
4843   Since HTTP/0.9 did not support header fields in a request,
4844   there is no mechanism for it to support name-based virtual
4845   hosts (selection of resource by inspection of the Host header
4846   field).  Any server that implements name-based virtual hosts
4847   ought to disable support for HTTP/0.9.  Most requests that
4848   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4849   requests wherein a buggy client failed to properly encode
4850   linear whitespace found in a URI reference and placed in
4851   the request-target.
4852</t>
4853
4854<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4855<t>
4856   This section summarizes major differences between versions HTTP/1.0
4857   and HTTP/1.1.
4858</t>
4859
4860<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4861<t>
4862   The requirements that clients and servers support the Host header
4863   field (<xref target="header.host"/>), report an error if it is
4864   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4865   are among the most important changes defined by HTTP/1.1.
4866</t>
4867<t>
4868   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4869   addresses and servers; there was no other established mechanism for
4870   distinguishing the intended server of a request than the IP address
4871   to which that request was directed. The Host header field was
4872   introduced during the development of HTTP/1.1 and, though it was
4873   quickly implemented by most HTTP/1.0 browsers, additional requirements
4874   were placed on all HTTP/1.1 requests in order to ensure complete
4875   adoption.  At the time of this writing, most HTTP-based services
4876   are dependent upon the Host header field for targeting requests.
4877</t>
4878</section>
4879
4880<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4881<t>
4882   For most implementations of HTTP/1.0, each connection is established
4883   by the client prior to the request and closed by the server after
4884   sending the response. However, some implementations implement the
4885   Keep-Alive version of persistent connections described in
4886   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4887</t>
4888<t>
4889   Some clients and servers might wish to be compatible with some
4890   previous implementations of persistent connections in HTTP/1.0
4891   clients and servers. Persistent connections in HTTP/1.0 are
4892   explicitly negotiated as they are not the default behavior. HTTP/1.0
4893   experimental implementations of persistent connections are faulty,
4894   and the new facilities in HTTP/1.1 are designed to rectify these
4895   problems. The problem was that some existing HTTP/1.0 clients might
4896   send Keep-Alive to a proxy server that doesn't understand
4897   Connection, which would then erroneously forward it to the next
4898   inbound server, which would establish the Keep-Alive connection and
4899   result in a hung HTTP/1.0 proxy waiting for the close on the
4900   response. The result is that HTTP/1.0 clients must be prevented from
4901   using Keep-Alive when talking to proxies.
4902</t>
4903<t>
4904   However, talking to proxies is the most important use of persistent
4905   connections, so that prohibition is clearly unacceptable. Therefore,
4906   we need some other mechanism for indicating a persistent connection
4907   is desired, which is safe to use even when talking to an old proxy
4908   that ignores Connection. Persistent connections are the default for
4909   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4910   declaring non-persistence. See <xref target="header.connection"/>.
4911</t>
4912</section>
4913</section>
4914
4915<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4916<t>
4917  Empty list elements in list productions have been deprecated.
4918  (<xref target="notation.abnf"/>)
4919</t>
4920<t>
4921  Rules about implicit linear whitespace between certain grammar productions
4922  have been removed; now it's only allowed when specifically pointed out
4923  in the ABNF.
4924  (<xref target="basic.rules"/>)
4925</t>
4926<t>
4927  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4928  sensitive. Restrict the version numbers to be single digits due to the fact
4929  that implementations are known to handle multi-digit version numbers
4930  incorrectly.
4931  (<xref target="http.version"/>)
4932</t>
4933<t>
4934  Require that invalid whitespace around field-names be rejected.
4935  (<xref target="header.fields"/>)
4936</t>
4937<t> 
4938  The NUL octet is no longer allowed in comment and quoted-string
4939  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4940  Non-ASCII content in header fields and reason phrase has been obsoleted and
4941  made opaque (the TEXT rule was removed).
4942  (<xref target="field.rules"/>)
4943</t>
4944<t>
4945  Require recipients to handle bogus Content-Length header fields as errors.
4946  (<xref target="message.body"/>)
4947</t>
4948<t>
4949  Remove reference to non-existent identity transfer-coding value tokens.
4950  (Sections <xref format="counter" target="message.body"/> and
4951  <xref format="counter" target="transfer.codings"/>)
4952</t>
4953<t>
4954  Update use of abs_path production from RFC 1808 to the path-absolute + query
4955  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4956  request method only.
4957  (<xref target="request-target"/>)
4958</t>
4959<t>
4960  Clarification that the chunk length does not include the count of the octets
4961  in the chunk header and trailer. Furthermore disallowed line folding
4962  in chunk extensions.
4963  (<xref target="chunked.encoding"/>)
4964</t>
4965<t>
4966  Remove hard limit of two connections per server.
4967  Remove requirement to retry a sequence of requests as long it was idempotent.
4968  Remove requirements about when servers are allowed to close connections
4969  prematurely.
4970  (<xref target="persistent.practical"/>)
4971</t>
4972<t>
4973  Remove requirement to retry requests under certain cirumstances when the
4974  server prematurely closes the connection.
4975  (<xref target="message.transmission.requirements"/>)
4976</t>
4977<t>
4978  Change ABNF productions for header fields to only define the field value.
4979  (<xref target="header.field.definitions"/>)
4980</t>
4981<t>
4982  Clarify exactly when close connection options must be sent.
4983  (<xref target="header.connection"/>)
4984</t>
4985<t>
4986  Define the semantics of the "Upgrade" header field in responses other than
4987  101 (this was incorporated from <xref target="RFC2817"/>).
4988  (<xref target="header.upgrade"/>)
4989</t>
4990</section>
4991</section>
4992
4993<?BEGININC p1-messaging.abnf-appendix ?>
4994<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4995<figure>
4996<artwork type="abnf" name="p1-messaging.parsed-abnf">
4997<x:ref>BWS</x:ref> = OWS
4998
4999<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5000<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5001 connection-token ] )
5002<x:ref>Content-Length</x:ref> = 1*DIGIT
5003
5004<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5005<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5006<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5007 ]
5008<x:ref>Host</x:ref> = uri-host [ ":" port ]
5009
5010<x:ref>Method</x:ref> = token
5011
5012<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5013
5014<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5015<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5016<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5017
5018<x:ref>Status-Code</x:ref> = 3DIGIT
5019<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5020
5021<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5022<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5023<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5024 transfer-coding ] )
5025
5026<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5027<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5028
5029<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5030 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5031 )
5032
5033<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5034<x:ref>attribute</x:ref> = token
5035<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5036
5037<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5038<x:ref>chunk-data</x:ref> = 1*OCTET
5039<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5040<x:ref>chunk-ext-name</x:ref> = token
5041<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5042<x:ref>chunk-size</x:ref> = 1*HEXDIG
5043<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5044<x:ref>connection-token</x:ref> = token
5045<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5046 / %x2A-5B ; '*'-'['
5047 / %x5D-7E ; ']'-'~'
5048 / obs-text
5049
5050<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5051<x:ref>field-name</x:ref> = token
5052<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5053
5054<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5055<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5056<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5057
5058<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5059
5060<x:ref>message-body</x:ref> = *OCTET
5061
5062<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5063<x:ref>obs-text</x:ref> = %x80-FF
5064
5065<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5066<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5067<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5068<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5069<x:ref>product</x:ref> = token [ "/" product-version ]
5070<x:ref>product-version</x:ref> = token
5071<x:ref>protocol-name</x:ref> = token
5072<x:ref>protocol-version</x:ref> = token
5073<x:ref>pseudonym</x:ref> = token
5074
5075<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5076 / %x5D-7E ; ']'-'~'
5077 / obs-text
5078<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5079 / %x5D-7E ; ']'-'~'
5080 / obs-text
5081<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5082<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5083<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5084<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5085<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5086<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5087
5088<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5089<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5090<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5091<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5092 / authority
5093
5094<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5095 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5096<x:ref>start-line</x:ref> = Request-Line / Status-Line
5097
5098<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5099<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5100 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5101<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5102<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5103<x:ref>token</x:ref> = 1*tchar
5104<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5105<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5106 transfer-extension
5107<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5108<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5109
5110<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5111
5112<x:ref>value</x:ref> = word
5113
5114<x:ref>word</x:ref> = token / quoted-string
5115</artwork>
5116</figure>
5117<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5118; Chunked-Body defined but not used
5119; Connection defined but not used
5120; Content-Length defined but not used
5121; HTTP-message defined but not used
5122; Host defined but not used
5123; TE defined but not used
5124; Trailer defined but not used
5125; Transfer-Encoding defined but not used
5126; URI-reference defined but not used
5127; Upgrade defined but not used
5128; Via defined but not used
5129; http-URI defined but not used
5130; https-URI defined but not used
5131; partial-URI defined but not used
5132; special defined but not used
5133</artwork></figure></section>
5134<?ENDINC p1-messaging.abnf-appendix ?>
5135
5136<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5137
5138<section title="Since RFC 2616">
5139<t>
5140  Extracted relevant partitions from <xref target="RFC2616"/>.
5141</t>
5142</section>
5143
5144<section title="Since draft-ietf-httpbis-p1-messaging-00">
5145<t>
5146  Closed issues:
5147  <list style="symbols"> 
5148    <t>
5149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5150      "HTTP Version should be case sensitive"
5151      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5155      "'unsafe' characters"
5156      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5160      "Chunk Size Definition"
5161      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5162    </t>
5163    <t>
5164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5165      "Message Length"
5166      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5167    </t>
5168    <t>
5169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5170      "Media Type Registrations"
5171      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5175      "URI includes query"
5176      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5177    </t>
5178    <t>
5179      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5180      "No close on 1xx responses"
5181      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5182    </t>
5183    <t>
5184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5185      "Remove 'identity' token references"
5186      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5187    </t>
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5190      "Import query BNF"
5191    </t>
5192    <t>
5193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5194      "qdtext BNF"
5195    </t>
5196    <t>
5197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5198      "Normative and Informative references"
5199    </t>
5200    <t>
5201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5202      "RFC2606 Compliance"
5203    </t>
5204    <t>
5205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5206      "RFC977 reference"
5207    </t>
5208    <t>
5209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5210      "RFC1700 references"
5211    </t>
5212    <t>
5213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5214      "inconsistency in date format explanation"
5215    </t>
5216    <t>
5217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5218      "Date reference typo"
5219    </t>
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5222      "Informative references"
5223    </t>
5224    <t>
5225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5226      "ISO-8859-1 Reference"
5227    </t>
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5230      "Normative up-to-date references"
5231    </t>
5232  </list>
5233</t>
5234<t>
5235  Other changes:
5236  <list style="symbols"> 
5237    <t>
5238      Update media type registrations to use RFC4288 template.
5239    </t>
5240    <t>
5241      Use names of RFC4234 core rules DQUOTE and HTAB,
5242      fix broken ABNF for chunk-data
5243      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5244    </t>
5245  </list>
5246</t>
5247</section>
5248
5249<section title="Since draft-ietf-httpbis-p1-messaging-01">
5250<t>
5251  Closed issues:
5252  <list style="symbols"> 
5253    <t>
5254      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5255      "Bodies on GET (and other) requests"
5256    </t>
5257    <t>
5258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5259      "Updating to RFC4288"
5260    </t>
5261    <t>
5262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5263      "Status Code and Reason Phrase"
5264    </t>
5265    <t>
5266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5267      "rel_path not used"
5268    </t>
5269  </list>
5270</t>
5271<t>
5272  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5273  <list style="symbols"> 
5274    <t>
5275      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5276      "trailer-part").
5277    </t>
5278    <t>
5279      Avoid underscore character in rule names ("http_URL" ->
5280      "http-URL", "abs_path" -> "path-absolute").
5281    </t>
5282    <t>
5283      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5284      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5285      have to be updated when switching over to RFC3986.
5286    </t>
5287    <t>
5288      Synchronize core rules with RFC5234.
5289    </t>
5290    <t>
5291      Get rid of prose rules that span multiple lines.
5292    </t>
5293    <t>
5294      Get rid of unused rules LOALPHA and UPALPHA.
5295    </t>
5296    <t>
5297      Move "Product Tokens" section (back) into Part 1, as "token" is used
5298      in the definition of the Upgrade header field.
5299    </t>
5300    <t>
5301      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5302    </t>
5303    <t>
5304      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5305    </t>
5306  </list>
5307</t>
5308</section>
5309
5310<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5311<t>
5312  Closed issues:
5313  <list style="symbols"> 
5314    <t>
5315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5316      "HTTP-date vs. rfc1123-date"
5317    </t>
5318    <t>
5319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5320      "WS in quoted-pair"
5321    </t>
5322  </list>
5323</t>
5324<t>
5325  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5326  <list style="symbols"> 
5327    <t>
5328      Reference RFC 3984, and update header field registrations for headers defined
5329      in this document.
5330    </t>
5331  </list>
5332</t>
5333<t>
5334  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5335  <list style="symbols"> 
5336    <t>
5337      Replace string literals when the string really is case-sensitive (HTTP-Version).
5338    </t>
5339  </list>
5340</t>
5341</section>
5342
5343<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5344<t>
5345  Closed issues:
5346  <list style="symbols"> 
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5349      "Connection closing"
5350    </t>
5351    <t>
5352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5353      "Move registrations and registry information to IANA Considerations"
5354    </t>
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5357      "need new URL for PAD1995 reference"
5358    </t>
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5361      "IANA Considerations: update HTTP URI scheme registration"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5365      "Cite HTTPS URI scheme definition"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5369      "List-type headers vs Set-Cookie"
5370    </t>
5371  </list>
5372</t>
5373<t>
5374  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5375  <list style="symbols"> 
5376    <t>
5377      Replace string literals when the string really is case-sensitive (HTTP-Date).
5378    </t>
5379    <t>
5380      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5381    </t>
5382  </list>
5383</t>
5384</section>
5385
5386<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5387<t>
5388  Closed issues:
5389  <list style="symbols"> 
5390    <t>
5391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5392      "Out-of-date reference for URIs"
5393    </t>
5394    <t>
5395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5396      "RFC 2822 is updated by RFC 5322"
5397    </t>
5398  </list>
5399</t>
5400<t>
5401  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5402  <list style="symbols"> 
5403    <t>
5404      Use "/" instead of "|" for alternatives.
5405    </t>
5406    <t>
5407      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5408    </t>
5409    <t>
5410      Only reference RFC 5234's core rules.
5411    </t>
5412    <t>
5413      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5414      whitespace ("OWS") and required whitespace ("RWS").
5415    </t>
5416    <t>
5417      Rewrite ABNFs to spell out whitespace rules, factor out
5418      header field value format definitions.
5419    </t>
5420  </list>
5421</t>
5422</section>
5423
5424<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5425<t>
5426  Closed issues:
5427  <list style="symbols"> 
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5430      "Header LWS"
5431    </t>
5432    <t>
5433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5434      "Sort 1.3 Terminology"
5435    </t>
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5438      "RFC2047 encoded words"
5439    </t>
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5442      "Character Encodings in TEXT"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5446      "Line Folding"
5447    </t>
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5450      "OPTIONS * and proxies"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5454      "Reason-Phrase BNF"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5458      "Use of TEXT"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5462      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5463    </t>
5464    <t>
5465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5466      "RFC822 reference left in discussion of date formats"
5467    </t>
5468  </list>
5469</t>
5470<t>
5471  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5472  <list style="symbols"> 
5473    <t>
5474      Rewrite definition of list rules, deprecate empty list elements.
5475    </t>
5476    <t>
5477      Add appendix containing collected and expanded ABNF.
5478    </t>
5479  </list>
5480</t>
5481<t>
5482  Other changes:
5483  <list style="symbols"> 
5484    <t>
5485      Rewrite introduction; add mostly new Architecture Section.
5486    </t>
5487    <t>
5488      Move definition of quality values from Part 3 into Part 1;
5489      make TE request header field grammar independent of accept-params (defined in Part 3).
5490    </t>
5491  </list>
5492</t>
5493</section>
5494
5495<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5496<t>
5497  Closed issues:
5498  <list style="symbols"> 
5499    <t>
5500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5501      "base for numeric protocol elements"
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5505      "comment ABNF"
5506    </t>
5507  </list>
5508</t>
5509<t>
5510  Partly resolved issues:
5511  <list style="symbols"> 
5512    <t>
5513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5514      "205 Bodies" (took out language that implied that there might be
5515      methods for which a request body MUST NOT be included)
5516    </t>
5517    <t>
5518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5519      "editorial improvements around HTTP-date"
5520    </t>
5521  </list>
5522</t>
5523</section>
5524
5525<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5526<t>
5527  Closed issues:
5528  <list style="symbols"> 
5529    <t>
5530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5531      "Repeating single-value headers"
5532    </t>
5533    <t>
5534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5535      "increase connection limit"
5536    </t>
5537    <t>
5538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5539      "IP addresses in URLs"
5540    </t>
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5543      "take over HTTP Upgrade Token Registry"
5544    </t>
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5547      "CR and LF in chunk extension values"
5548    </t>
5549    <t>
5550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5551      "HTTP/0.9 support"
5552    </t>
5553    <t>
5554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5555      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5559      "move definitions of gzip/deflate/compress to part 1"
5560    </t>
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5563      "disallow control characters in quoted-pair"
5564    </t>
5565  </list>
5566</t>
5567<t>
5568  Partly resolved issues:
5569  <list style="symbols"> 
5570    <t>
5571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5572      "update IANA requirements wrt Transfer-Coding values" (add the
5573      IANA Considerations subsection)
5574    </t>
5575  </list>
5576</t>
5577</section>
5578
5579<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5580<t>
5581  Closed issues:
5582  <list style="symbols"> 
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5585      "header parsing, treatment of leading and trailing OWS"
5586    </t>
5587  </list>
5588</t>
5589<t>
5590  Partly resolved issues:
5591  <list style="symbols"> 
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5594      "Placement of 13.5.1 and 13.5.2"
5595    </t>
5596    <t>
5597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5598      "use of term "word" when talking about header structure"
5599    </t>
5600  </list>
5601</t>
5602</section>
5603
5604<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5605<t>
5606  Closed issues:
5607  <list style="symbols"> 
5608    <t>
5609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5610      "Clarification of the term 'deflate'"
5611    </t>
5612    <t>
5613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5614      "OPTIONS * and proxies"
5615    </t>
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5618      "MIME-Version not listed in P1, general header fields"
5619    </t>
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5622      "IANA registry for content/transfer encodings"
5623    </t>
5624    <t>
5625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5626      "Case-sensitivity of HTTP-date"
5627    </t>
5628    <t>
5629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5630      "use of term "word" when talking about header structure"
5631    </t>
5632  </list>
5633</t>
5634<t>
5635  Partly resolved issues:
5636  <list style="symbols"> 
5637    <t>
5638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5639      "Term for the requested resource's URI"
5640    </t>
5641  </list>
5642</t>
5643</section>
5644
5645<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5646<t>
5647  Closed issues:
5648  <list style="symbols">
5649    <t>
5650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5651      "Connection Closing"
5652    </t>
5653    <t>
5654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5655      "Delimiting messages with multipart/byteranges"
5656    </t>
5657    <t>
5658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5659      "Handling multiple Content-Length headers"
5660    </t>
5661    <t>
5662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5663      "Clarify entity / representation / variant terminology"
5664    </t>
5665    <t>
5666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5667      "consider removing the 'changes from 2068' sections"
5668    </t>
5669  </list>
5670</t>
5671<t>
5672  Partly resolved issues:
5673  <list style="symbols"> 
5674    <t>
5675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5676      "HTTP(s) URI scheme definitions"
5677    </t>
5678  </list>
5679</t>
5680</section>
5681
5682<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5683<t>
5684  Closed issues:
5685  <list style="symbols">
5686    <t>
5687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5688      "Trailer requirements"
5689    </t>
5690    <t>
5691      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5692      "Text about clock requirement for caches belongs in p6"
5693    </t>
5694    <t>
5695      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5696      "effective request URI: handling of missing host in HTTP/1.0"
5697    </t>
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5700      "confusing Date requirements for clients"
5701    </t>
5702  </list>
5703</t>
5704<t>
5705  Partly resolved issues:
5706  <list style="symbols"> 
5707    <t>
5708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5709      "Handling multiple Content-Length headers"
5710    </t>
5711  </list>
5712</t>
5713</section>
5714
5715<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5716<t>
5717  Closed issues:
5718  <list style="symbols">
5719    <t>
5720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5721      "RFC2145 Normative"
5722    </t>
5723    <t>
5724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5725      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5726    </t>
5727    <t>
5728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5729      "define 'transparent' proxy"
5730    </t>
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5733      "Header Classification"
5734    </t>
5735    <t>
5736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5737      "Is * usable as a request-uri for new methods?"
5738    </t>
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5741      "Migrate Upgrade details from RFC2817"
5742    </t>
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5745      "untangle ABNFs for header fields"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5749      "update RFC 2109 reference"
5750    </t>
5751  </list>
5752</t>
5753</section>
5754
5755<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5756<t>
5757  Closed issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5761      "Allow is not in 13.5.2"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5765      "Handling multiple Content-Length headers"
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5769      "untangle ABNFs for header fields"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5773      "Content-Length ABNF broken"
5774    </t>
5775  </list>
5776</t>
5777</section>
5778
5779<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5780<t>
5781  Closed issues:
5782  <list style="symbols">
5783    <t>
5784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5785      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5786    </t>
5787    <t>
5788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5789      "Recommend minimum sizes for protocol elements"
5790    </t>
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5793      "Set expectations around buffering"
5794    </t>
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5797      "Considering messages in isolation"
5798    </t>
5799  </list>
5800</t>
5801</section>
5802
5803<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5804<t>
5805  Closed issues:
5806  <list style="symbols">
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5809      "DNS Spoofing / DNS Binding advice"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5813      "move RFCs 2145, 2616, 2817 to Historic status"
5814    </t>
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5817      "\-escaping in quoted strings"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5821      "'Close' should be reserved in the HTTP header field registry"
5822    </t>
5823  </list>
5824</t>
5825</section>
5826
5827<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5828<t>
5829  Closed issues:
5830  <list style="symbols">
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5833      "Document HTTP's error-handling philosophy"
5834    </t>
5835    <t>
5836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5837      "Explain header registration"
5838    </t>
5839    <t>
5840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5841      "Revise Acknowledgements Sections"
5842    </t>
5843    <t>
5844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5845      "Retrying Requests"
5846    </t>
5847    <t>
5848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5849      "Closing the connection on server error"
5850    </t>
5851  </list>
5852</t>
5853</section>
5854
5855</section>
5856
5857</back>
5858</rfc>
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