source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1454

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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  "foo ,bar,   charlie "
434</artwork></figure>
435<t>
436  But these values would be invalid, as at least one non-empty element is
437  required:
438</t>
439<figure><artwork type="example">
440  ""
441  ","
442  ",   ,"
443</artwork></figure>
444<t>
445  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
446  expanded as explained above.
447</t>
448</section>
449
450<section title="Basic Rules" anchor="basic.rules">
451<t anchor="rule.LWS">
452   This specification uses three rules to denote the use of linear
453   whitespace: OWS (optional whitespace), RWS (required whitespace), and
454   BWS ("bad" whitespace).
455</t>
456<t anchor="rule.OWS">
457   The OWS rule is used where zero or more linear whitespace octets might
458   appear. OWS &SHOULD; either not be produced or be produced as a single
459   SP. Multiple OWS octets that occur within field-content &SHOULD; either
460   be replaced with a single SP or transformed to all SP octets (each
461   octet other than SP replaced with SP) before interpreting the field value
462   or forwarding the message downstream.
463</t>
464<t anchor="rule.RWS">
465   RWS is used when at least one linear whitespace octet is required to
466   separate field tokens. RWS &SHOULD; be produced as a single SP.
467   Multiple RWS octets that occur within field-content &SHOULD; either
468   be replaced with a single SP or transformed to all SP octets before
469   interpreting the field value or forwarding the message downstream.
470</t>
471<t anchor="rule.BWS">
472   BWS is used where the grammar allows optional whitespace for historical
473   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
474   recipients &MUST; accept such bad optional whitespace and remove it before
475   interpreting the field value or forwarding the message downstream.
476</t>
477<t anchor="rule.whitespace">
478  <x:anchor-alias value="BWS"/>
479  <x:anchor-alias value="OWS"/>
480  <x:anchor-alias value="RWS"/>
481  <x:anchor-alias value="obs-fold"/>
482</t>
483<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"/>
484  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
485                 ; "optional" whitespace
486  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
487                 ; "required" whitespace
488  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
489                 ; "bad" whitespace
490  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
491                 ; obsolete line folding
492                 ; see <xref target="field.parsing"/>
493</artwork></figure>
494</section>
495</section>
496</section>
497
498<section title="Architecture" anchor="architecture">
499<t>
500   HTTP was created for the World Wide Web architecture
501   and has evolved over time to support the scalability needs of a worldwide
502   hypertext system. Much of that architecture is reflected in the terminology
503   and syntax productions used to define HTTP.
504</t>
505
506<section title="Client/Server Messaging" anchor="operation">
507<iref primary="true" item="client"/>
508<iref primary="true" item="server"/>
509<iref primary="true" item="connection"/>
510<t>
511   HTTP is a stateless request/response protocol that operates by exchanging
512   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
513   transport or session-layer
514   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
515   program that establishes a connection to a server for the purpose of
516   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
517   program that accepts connections in order to service HTTP requests by
518   sending HTTP responses.
519</t>
520<iref primary="true" item="user agent"/>
521<iref primary="true" item="origin server"/>
522<iref primary="true" item="browser"/>
523<iref primary="true" item="spider"/>
524<iref primary="true" item="sender"/>
525<iref primary="true" item="recipient"/>
526<t>
527   Note that the terms client and server refer only to the roles that
528   these programs perform for a particular connection.  The same program
529   might act as a client on some connections and a server on others.  We use
530   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
531   such as a WWW browser, editor, or spider (web-traversing robot), and
532   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
533   authoritative responses to a request.  For general requirements, we use
534   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
535   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
536   message.
537</t>
538<t>
539   Most HTTP communication consists of a retrieval request (GET) for
540   a representation of some resource identified by a URI.  In the
541   simplest case, this might be accomplished via a single bidirectional
542   connection (===) between the user agent (UA) and the origin server (O).
543</t>
544<figure><artwork type="drawing">
545         request   &gt;
546    UA ======================================= O
547                                &lt;   response
548</artwork></figure>
549<iref primary="true" item="message"/>
550<iref primary="true" item="request"/>
551<iref primary="true" item="response"/>
552<t>
553   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
554   message, beginning with a request-line that includes a method, URI, and
555   protocol version (<xref target="request.line"/>),
556   followed by MIME-like header fields containing
557   request modifiers, client information, and payload metadata
558   (<xref target="header.fields"/>),
559   an empty line to indicate the end of the header section, and finally
560   a message body containing the payload body (if any,
561   <xref target="message.body"/>).
562</t>
563<t>
564   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
565   message, beginning with a status line that
566   includes the protocol version, a success or error code, and textual
567   reason phrase (<xref target="status.line"/>),
568   followed by MIME-like header fields containing server
569   information, resource metadata, and payload metadata
570   (<xref target="header.fields"/>),
571   an empty line to indicate the end of the header section, and finally
572   a message body containing the payload body (if any,
573   <xref target="message.body"/>).
574</t>
575<t>
576   The following example illustrates a typical message exchange for a
577   GET request on the URI "http://www.example.com/hello.txt":
578</t>
579<figure><preamble>
580client request:
581</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
582GET /hello.txt HTTP/1.1
583User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
584Host: www.example.com
585Accept: */*
586
587</artwork></figure>
588<figure><preamble>
589server response:
590</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
591HTTP/1.1 200 OK
592Date: Mon, 27 Jul 2009 12:28:53 GMT
593Server: Apache
594Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
595ETag: "34aa387-d-1568eb00"
596Accept-Ranges: bytes
597Content-Length: <x:length-of target="exbody"/>
598Vary: Accept-Encoding
599Content-Type: text/plain
600
601<x:span anchor="exbody">Hello World!
602</x:span></artwork></figure>
603</section>
604
605<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
606<t>
607   Fundamentally, HTTP is a message-based protocol. Although message bodies can
608   be chunked (<xref target="chunked.encoding"/>) and implementations often
609   make parts of a message available progressively, this is not required, and
610   some widely-used implementations only make a message available when it is
611   complete. Furthermore, while most proxies will progressively stream messages,
612   some amount of buffering will take place, and some proxies might buffer
613   messages to perform transformations, check content or provide other services.
614</t>
615<t>
616   Therefore, extensions to and uses of HTTP cannot rely on the availability of
617   a partial message, or assume that messages will not be buffered. There are
618   strategies that can be used to test for buffering in a given connection, but
619   it should be understood that behaviors can differ across connections, and
620   between requests and responses.
621</t>
622<t>
623   Recipients &MUST; consider every message in a connection in isolation;
624   because HTTP is a stateless protocol, it cannot be assumed that two requests
625   on the same connection are from the same client or share any other common
626   attributes. In particular, intermediaries might mix requests from different
627   clients into a single server connection. Note that some existing HTTP
628   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
629   potentially causing interoperability and security problems.
630</t>
631</section>
632
633<section title="Connections and Transport Independence" anchor="transport-independence">
634<t>
635   HTTP messaging is independent of the underlying transport or
636   session-layer connection protocol(s).  HTTP only presumes a reliable
637   transport with in-order delivery of requests and the corresponding
638   in-order delivery of responses.  The mapping of HTTP request and
639   response structures onto the data units of the underlying transport
640   protocol is outside the scope of this specification.
641</t>
642<t>
643   The specific connection protocols to be used for an interaction
644   are determined by client configuration and the target resource's URI.
645   For example, the "http" URI scheme
646   (<xref target="http.uri"/>) indicates a default connection of TCP
647   over IP, with a default TCP port of 80, but the client might be
648   configured to use a proxy via some other connection port or protocol
649   instead of using the defaults.
650</t>
651<t>
652   A connection might be used for multiple HTTP request/response exchanges,
653   as defined in <xref target="persistent.connections"/>.
654</t>
655</section>
656
657<section title="Intermediaries" anchor="intermediaries">
658<iref primary="true" item="intermediary"/>
659<t>
660   HTTP enables the use of intermediaries to satisfy requests through
661   a chain of connections.  There are three common forms of HTTP
662   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
663   a single intermediary might act as an origin server, proxy, gateway,
664   or tunnel, switching behavior based on the nature of each request.
665</t>
666<figure><artwork type="drawing">
667         &gt;             &gt;             &gt;             &gt;
668    <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>
669               &lt;             &lt;             &lt;             &lt;
670</artwork></figure>
671<t>
672   The figure above shows three intermediaries (A, B, and C) between the
673   user agent and origin server. A request or response message that
674   travels the whole chain will pass through four separate connections.
675   Some HTTP communication options
676   might apply only to the connection with the nearest, non-tunnel
677   neighbor, only to the end-points of the chain, or to all connections
678   along the chain. Although the diagram is linear, each participant might
679   be engaged in multiple, simultaneous communications. For example, B
680   might be receiving requests from many clients other than A, and/or
681   forwarding requests to servers other than C, at the same time that it
682   is handling A's request.
683</t>
684<t>
685<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
686<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
687   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
688   to describe various requirements in relation to the directional flow of a
689   message: all messages flow from upstream to downstream.
690   Likewise, we use the terms inbound and outbound to refer to
691   directions in relation to the request path:
692   "<x:dfn>inbound</x:dfn>" means toward the origin server and
693   "<x:dfn>outbound</x:dfn>" means toward the user agent.
694</t>
695<t><iref primary="true" item="proxy"/>
696   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
697   client, usually via local configuration rules, to receive requests
698   for some type(s) of absolute URI and attempt to satisfy those
699   requests via translation through the HTTP interface.  Some translations
700   are minimal, such as for proxy requests for "http" URIs, whereas
701   other requests might require translation to and from entirely different
702   application-layer protocols. Proxies are often used to group an
703   organization's HTTP requests through a common intermediary for the
704   sake of security, annotation services, or shared caching.
705</t>
706<t>
707<iref primary="true" item="transforming proxy"/>
708<iref primary="true" item="non-transforming proxy"/>
709   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
710   or configured to modify request or response messages in a semantically
711   meaningful way (i.e., modifications, beyond those required by normal
712   HTTP processing, that change the message in a way that would be
713   significant to the original sender or potentially significant to
714   downstream recipients).  For example, a transforming proxy might be
715   acting as a shared annotation server (modifying responses to include
716   references to a local annotation database), a malware filter, a
717   format transcoder, or an intranet-to-Internet privacy filter.  Such
718   transformations are presumed to be desired by the client (or client
719   organization) that selected the proxy and are beyond the scope of
720   this specification.  However, when a proxy is not intended to transform
721   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
722   requirements that preserve HTTP message semantics. See &status-203; and
723   &header-warning; for status and warning codes related to transformations.
724</t>
725<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
726<iref primary="true" item="accelerator"/>
727   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
728   is a receiving agent that acts
729   as a layer above some other server(s) and translates the received
730   requests to the underlying server's protocol.  Gateways are often
731   used to encapsulate legacy or untrusted information services, to
732   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
733   enable partitioning or load-balancing of HTTP services across
734   multiple machines.
735</t>
736<t>
737   A gateway behaves as an origin server on its outbound connection and
738   as a user agent on its inbound connection.
739   All HTTP requirements applicable to an origin server
740   also apply to the outbound communication of a gateway.
741   A gateway communicates with inbound servers using any protocol that
742   it desires, including private extensions to HTTP that are outside
743   the scope of this specification.  However, an HTTP-to-HTTP gateway
744   that wishes to interoperate with third-party HTTP servers &MUST;
745   comply with HTTP user agent requirements on the gateway's inbound
746   connection and &MUST; implement the Connection
747   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
748   header fields for both connections.
749</t>
750<t><iref primary="true" item="tunnel"/>
751   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
752   without changing the messages. Once active, a tunnel is not
753   considered a party to the HTTP communication, though the tunnel might
754   have been initiated by an HTTP request. A tunnel ceases to exist when
755   both ends of the relayed connection are closed. Tunnels are used to
756   extend a virtual connection through an intermediary, such as when
757   transport-layer security is used to establish private communication
758   through a shared firewall proxy.
759</t>
760<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
761<iref primary="true" item="captive portal"/>
762   In addition, there may exist network intermediaries that are not
763   considered part of the HTTP communication but nevertheless act as
764   filters or redirecting agents (usually violating HTTP semantics,
765   causing security problems, and otherwise making a mess of things).
766   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
767   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
768   or "<x:dfn>captive portal</x:dfn>",
769   differs from an HTTP proxy because it has not been selected by the client.
770   Instead, the network intermediary redirects outgoing TCP port 80 packets
771   (and occasionally other common port traffic) to an internal HTTP server.
772   Interception proxies are commonly found on public network access points,
773   as a means of enforcing account subscription prior to allowing use of
774   non-local Internet services, and within corporate firewalls to enforce
775   network usage policies.
776   They are indistinguishable from a man-in-the-middle attack.
777</t>
778</section>
779
780<section title="Caches" anchor="caches">
781<iref primary="true" item="cache"/>
782<t>
783   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
784   subsystem that controls its message storage, retrieval, and deletion.
785   A cache stores cacheable responses in order to reduce the response
786   time and network bandwidth consumption on future, equivalent
787   requests. Any client or server &MAY; employ a cache, though a cache
788   cannot be used by a server while it is acting as a tunnel.
789</t>
790<t>
791   The effect of a cache is that the request/response chain is shortened
792   if one of the participants along the chain has a cached response
793   applicable to that request. The following illustrates the resulting
794   chain if B has a cached copy of an earlier response from O (via C)
795   for a request which has not been cached by UA or A.
796</t>
797<figure><artwork type="drawing">
798            &gt;             &gt;
799       UA =========== A =========== B - - - - - - C - - - - - - O
800                  &lt;             &lt;
801</artwork></figure>
802<t><iref primary="true" item="cacheable"/>
803   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
804   the response message for use in answering subsequent requests.
805   Even when a response is cacheable, there might be additional
806   constraints placed by the client or by the origin server on when
807   that cached response can be used for a particular request. HTTP
808   requirements for cache behavior and cacheable responses are
809   defined in &caching-overview;
810</t>
811<t>
812   There are a wide variety of architectures and configurations
813   of caches and proxies deployed across the World Wide Web and
814   inside large organizations. These systems include national hierarchies
815   of proxy caches to save transoceanic bandwidth, systems that
816   broadcast or multicast cache entries, organizations that distribute
817   subsets of cached data via optical media, and so on.
818</t>
819</section>
820
821<section title="Protocol Versioning" anchor="http.version">
822  <x:anchor-alias value="HTTP-Version"/>
823  <x:anchor-alias value="HTTP-Prot-Name"/>
824<t>
825   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
826   versions of the protocol. This specification defines version "1.1".
827   The protocol version as a whole indicates the sender's compliance
828   with the set of requirements laid out in that version's corresponding
829   specification of HTTP.
830</t>
831<t>
832   The version of an HTTP message is indicated by an HTTP-Version field
833   in the first line of the message. HTTP-Version is case-sensitive.
834</t>
835<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
836  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
837  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
838</artwork></figure>
839<t>
840   The HTTP version number consists of two decimal digits separated by a "."
841   (period or decimal point).  The first digit ("major version") indicates the
842   HTTP messaging syntax, whereas the second digit ("minor version") indicates
843   the highest minor version to which the sender is at least conditionally
844   compliant and able to understand for future communication.  The minor
845   version advertises the sender's communication capabilities even when the
846   sender is only using a backwards-compatible subset of the protocol,
847   thereby letting the recipient know that more advanced features can
848   be used in response (by servers) or in future requests (by clients).
849</t>
850<t>
851   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
852   <xref target="RFC1945"/> or a recipient whose version is unknown,
853   the HTTP/1.1 message is constructed such that it can be interpreted
854   as a valid HTTP/1.0 message if all of the newer features are ignored.
855   This specification places recipient-version requirements on some
856   new features so that a compliant sender will only use compatible
857   features until it has determined, through configuration or the
858   receipt of a message, that the recipient supports HTTP/1.1.
859</t>
860<t>
861   The interpretation of an HTTP header field does not change
862   between minor versions of the same major version, though the default
863   behavior of a recipient in the absence of such a field can change.
864   Unless specified otherwise, header fields defined in HTTP/1.1 are
865   defined for all versions of HTTP/1.x.  In particular, the Host and
866   Connection header fields ought to be implemented by all HTTP/1.x
867   implementations whether or not they advertise compliance with HTTP/1.1.
868</t>
869<t>
870   New header fields can be defined such that, when they are
871   understood by a recipient, they might override or enhance the
872   interpretation of previously defined header fields.  When an
873   implementation receives an unrecognized header field, the recipient
874   &MUST; ignore that header field for local processing regardless of
875   the message's HTTP version.  An unrecognized header field received
876   by a proxy &MUST; be forwarded downstream unless the header field's
877   field-name is listed in the message's Connection header-field
878   (see <xref target="header.connection"/>).
879   These requirements allow HTTP's functionality to be enhanced without
880   requiring prior update of all compliant intermediaries.
881</t>
882<t>
883   Intermediaries that process HTTP messages (i.e., all intermediaries
884   other than those acting as a tunnel) &MUST; send their own HTTP-Version
885   in forwarded messages.  In other words, they &MUST-NOT; blindly
886   forward the first line of an HTTP message without ensuring that the
887   protocol version matches what the intermediary understands, and
888   is at least conditionally compliant to, for both the receiving and
889   sending of messages.  Forwarding an HTTP message without rewriting
890   the HTTP-Version might result in communication errors when downstream
891   recipients use the message sender's version to determine what features
892   are safe to use for later communication with that sender.
893</t>
894<t>
895   An HTTP client &SHOULD; send a request version equal to the highest
896   version for which the client is at least conditionally compliant and
897   whose major version is no higher than the highest version supported
898   by the server, if this is known.  An HTTP client &MUST-NOT; send a
899   version for which it is not at least conditionally compliant.
900</t>
901<t>
902   An HTTP client &MAY; send a lower request version if it is known that
903   the server incorrectly implements the HTTP specification, but only
904   after the client has attempted at least one normal request and determined
905   from the response status or header fields (e.g., Server) that the
906   server improperly handles higher request versions.
907</t>
908<t>
909   An HTTP server &SHOULD; send a response version equal to the highest
910   version for which the server is at least conditionally compliant and
911   whose major version is less than or equal to the one received in the
912   request.  An HTTP server &MUST-NOT; send a version for which it is not
913   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
914   Version Not Supported) response if it cannot send a response using the
915   major version used in the client's request.
916</t>
917<t>
918   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
919   if it is known or suspected that the client incorrectly implements the
920   HTTP specification and is incapable of correctly processing later
921   version responses, such as when a client fails to parse the version
922   number correctly or when an intermediary is known to blindly forward
923   the HTTP-Version even when it doesn't comply with the given minor
924   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
925   performed unless triggered by specific client attributes, such as when
926   one or more of the request header fields (e.g., User-Agent) uniquely
927   match the values sent by a client known to be in error.
928</t>
929<t>
930   The intention of HTTP's versioning design is that the major number
931   will only be incremented if an incompatible message syntax is
932   introduced, and that the minor number will only be incremented when
933   changes made to the protocol have the effect of adding to the message
934   semantics or implying additional capabilities of the sender.  However,
935   the minor version was not incremented for the changes introduced between
936   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
937   is specifically avoiding any such changes to the protocol.
938</t>
939</section>
940
941<section title="Uniform Resource Identifiers" anchor="uri">
942<iref primary="true" item="resource"/>
943<t>
944   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
945   throughout HTTP as the means for identifying resources. URI references
946   are used to target requests, indicate redirects, and define relationships.
947   HTTP does not limit what a resource might be; it merely defines an interface
948   that can be used to interact with a resource via HTTP. More information on
949   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
950</t>
951  <x:anchor-alias value="URI-reference"/>
952  <x:anchor-alias value="absolute-URI"/>
953  <x:anchor-alias value="relative-part"/>
954  <x:anchor-alias value="authority"/>
955  <x:anchor-alias value="path-abempty"/>
956  <x:anchor-alias value="path-absolute"/>
957  <x:anchor-alias value="port"/>
958  <x:anchor-alias value="query"/>
959  <x:anchor-alias value="uri-host"/>
960  <x:anchor-alias value="partial-URI"/>
961<t>
962   This specification adopts the definitions of "URI-reference",
963   "absolute-URI", "relative-part", "port", "host",
964   "path-abempty", "path-absolute", "query", and "authority" from the
965   URI generic syntax <xref target="RFC3986"/>.
966   In addition, we define a partial-URI rule for protocol elements
967   that allow a relative URI but not a fragment.
968</t>
969<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"/>
970  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
971  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
972  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
973  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
974  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
975  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
976  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
977  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
978  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
979 
980  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
981</artwork></figure>
982<t>
983   Each protocol element in HTTP that allows a URI reference will indicate
984   in its ABNF production whether the element allows any form of reference
985   (URI-reference), only a URI in absolute form (absolute-URI), only the
986   path and optional query components, or some combination of the above.
987   Unless otherwise indicated, URI references are parsed relative to the
988   effective request URI, which defines the default base URI for references
989   in both the request and its corresponding response.
990</t>
991
992<section title="http URI scheme" anchor="http.uri">
993  <x:anchor-alias value="http-URI"/>
994  <iref item="http URI scheme" primary="true"/>
995  <iref item="URI scheme" subitem="http" primary="true"/>
996<t>
997   The "http" URI scheme is hereby defined for the purpose of minting
998   identifiers according to their association with the hierarchical
999   namespace governed by a potential HTTP origin server listening for
1000   TCP connections on a given port.
1001</t>
1002<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1003  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1004</artwork></figure>
1005<t>
1006   The HTTP origin server is identified by the generic syntax's
1007   <x:ref>authority</x:ref> component, which includes a host identifier
1008   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1009   The remainder of the URI, consisting of both the hierarchical path
1010   component and optional query component, serves as an identifier for
1011   a potential resource within that origin server's name space.
1012</t>
1013<t>
1014   If the host identifier is provided as an IP literal or IPv4 address,
1015   then the origin server is any listener on the indicated TCP port at
1016   that IP address. If host is a registered name, then that name is
1017   considered an indirect identifier and the recipient might use a name
1018   resolution service, such as DNS, to find the address of a listener
1019   for that host.
1020   The host &MUST-NOT; be empty; if an "http" URI is received with an
1021   empty host, then it &MUST; be rejected as invalid.
1022   If the port subcomponent is empty or not given, then TCP port 80 is
1023   assumed (the default reserved port for WWW services).
1024</t>
1025<t>
1026   Regardless of the form of host identifier, access to that host is not
1027   implied by the mere presence of its name or address. The host might or might
1028   not exist and, even when it does exist, might or might not be running an
1029   HTTP server or listening to the indicated port. The "http" URI scheme
1030   makes use of the delegated nature of Internet names and addresses to
1031   establish a naming authority (whatever entity has the ability to place
1032   an HTTP server at that Internet name or address) and allows that
1033   authority to determine which names are valid and how they might be used.
1034</t>
1035<t>
1036   When an "http" URI is used within a context that calls for access to the
1037   indicated resource, a client &MAY; attempt access by resolving
1038   the host to an IP address, establishing a TCP connection to that address
1039   on the indicated port, and sending an HTTP request message
1040   (<xref target="http.message"/>) containing the URI's identifying data
1041   (<xref target="message.routing"/>) to the server.
1042   If the server responds to that request with a non-interim HTTP response
1043   message, as described in &status-code-reasonphr;, then that response
1044   is considered an authoritative answer to the client's request.
1045</t>
1046<t>
1047   Although HTTP is independent of the transport protocol, the "http"
1048   scheme is specific to TCP-based services because the name delegation
1049   process depends on TCP for establishing authority.
1050   An HTTP service based on some other underlying connection protocol
1051   would presumably be identified using a different URI scheme, just as
1052   the "https" scheme (below) is used for servers that require an SSL/TLS
1053   transport layer on a connection. Other protocols might also be used to
1054   provide access to "http" identified resources &mdash; it is only the
1055   authoritative interface used for mapping the namespace that is
1056   specific to TCP.
1057</t>
1058<t>
1059   The URI generic syntax for authority also includes a deprecated
1060   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1061   for including user authentication information in the URI.  Some
1062   implementations make use of the userinfo component for internal
1063   configuration of authentication information, such as within command
1064   invocation options, configuration files, or bookmark lists, even
1065   though such usage might expose a user identifier or password.
1066   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1067   delimiter) when transmitting an "http" URI in a message.  Recipients
1068   of HTTP messages that contain a URI reference &SHOULD; parse for the
1069   existence of userinfo and treat its presence as an error, likely
1070   indicating that the deprecated subcomponent is being used to obscure
1071   the authority for the sake of phishing attacks.
1072</t>
1073</section>
1074
1075<section title="https URI scheme" anchor="https.uri">
1076   <x:anchor-alias value="https-URI"/>
1077   <iref item="https URI scheme"/>
1078   <iref item="URI scheme" subitem="https"/>
1079<t>
1080   The "https" URI scheme is hereby defined for the purpose of minting
1081   identifiers according to their association with the hierarchical
1082   namespace governed by a potential HTTP origin server listening for
1083   SSL/TLS-secured connections on a given TCP port.
1084</t>
1085<t>
1086   All of the requirements listed above for the "http" scheme are also
1087   requirements for the "https" scheme, except that a default TCP port
1088   of 443 is assumed if the port subcomponent is empty or not given,
1089   and the TCP connection &MUST; be secured for privacy through the
1090   use of strong encryption prior to sending the first HTTP request.
1091</t>
1092<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1093  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1094</artwork></figure>
1095<t>
1096   Unlike the "http" scheme, responses to "https" identified requests
1097   are never "public" and thus &MUST-NOT; be reused for shared caching.
1098   They can, however, be reused in a private cache if the message is
1099   cacheable by default in HTTP or specifically indicated as such by
1100   the Cache-Control header field (&header-cache-control;).
1101</t>
1102<t>
1103   Resources made available via the "https" scheme have no shared
1104   identity with the "http" scheme even if their resource identifiers
1105   indicate the same authority (the same host listening to the same
1106   TCP port).  They are distinct name spaces and are considered to be
1107   distinct origin servers.  However, an extension to HTTP that is
1108   defined to apply to entire host domains, such as the Cookie protocol
1109   <xref target="RFC6265"/>, can allow information
1110   set by one service to impact communication with other services
1111   within a matching group of host domains.
1112</t>
1113<t>
1114   The process for authoritative access to an "https" identified
1115   resource is defined in <xref target="RFC2818"/>.
1116</t>
1117</section>
1118
1119<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1120<t>
1121   Since the "http" and "https" schemes conform to the URI generic syntax,
1122   such URIs are normalized and compared according to the algorithm defined
1123   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1124   described above for each scheme.
1125</t>
1126<t>
1127   If the port is equal to the default port for a scheme, the normal
1128   form is to elide the port subcomponent. Likewise, an empty path
1129   component is equivalent to an absolute path of "/", so the normal
1130   form is to provide a path of "/" instead. The scheme and host
1131   are case-insensitive and normally provided in lowercase; all
1132   other components are compared in a case-sensitive manner.
1133   Characters other than those in the "reserved" set are equivalent
1134   to their percent-encoded octets (see <xref target="RFC3986"
1135   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1136</t>
1137<t>
1138   For example, the following three URIs are equivalent:
1139</t>
1140<figure><artwork type="example">
1141   http://example.com:80/~smith/home.html
1142   http://EXAMPLE.com/%7Esmith/home.html
1143   http://EXAMPLE.com:/%7esmith/home.html
1144</artwork></figure>
1145</section>
1146</section>
1147</section>
1148
1149<section title="Message Format" anchor="http.message">
1150<x:anchor-alias value="generic-message"/>
1151<x:anchor-alias value="message.types"/>
1152<x:anchor-alias value="HTTP-message"/>
1153<x:anchor-alias value="start-line"/>
1154<iref item="header section"/>
1155<iref item="headers"/>
1156<iref item="header field"/>
1157<t>
1158   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1159   octets in a format similar to the Internet Message Format
1160   <xref target="RFC5322"/>: zero or more header fields (collectively
1161   referred to as the "headers" or the "header section"), an empty line
1162   indicating the end of the header section, and an optional message-body.
1163</t>
1164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1165  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1166                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1167                    <x:ref>CRLF</x:ref>
1168                    [ <x:ref>message-body</x:ref> ]
1169</artwork></figure>
1170<t>
1171   The normal procedure for parsing an HTTP message is to read the
1172   start-line into a structure, read each header field into a hash
1173   table by field name until the empty line, and then use the parsed
1174   data to determine if a message-body is expected.  If a message-body
1175   has been indicated, then it is read as a stream until an amount
1176   of octets equal to the message-body length is read or the connection
1177   is closed.
1178</t>
1179<t>
1180   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1181   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1182   Parsing an HTTP message as a stream of Unicode characters, without regard
1183   for the specific encoding, creates security vulnerabilities due to the
1184   varying ways that string processing libraries handle invalid multibyte
1185   character sequences that contain the octet LF (%x0A).  String-based
1186   parsers can only be safely used within protocol elements after the element
1187   has been extracted from the message, such as within a header field-value
1188   after message parsing has delineated the individual fields.
1189</t>
1190
1191<section title="Start Line" anchor="start.line">
1192  <x:anchor-alias value="Start-Line"/>
1193<t>
1194   An HTTP message can either be a request from client to server or a
1195   response from server to client.  Syntactically, the two types of message
1196   differ only in the start-line, which is either a Request-Line (for requests)
1197   or a Status-Line (for responses), and in the algorithm for determining
1198   the length of the message-body (<xref target="message.body"/>).
1199   In theory, a client could receive requests and a server could receive
1200   responses, distinguishing them by their different start-line formats,
1201   but in practice servers are implemented to only expect a request
1202   (a response is interpreted as an unknown or invalid request method)
1203   and clients are implemented to only expect a response.
1204</t>
1205<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1206  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1207</artwork></figure>
1208<t>
1209</t>
1210<t>
1211   Implementations &MUST-NOT; send whitespace between the start-line and
1212   the first header field. The presence of such whitespace in a request
1213   might be an attempt to trick a server into ignoring that field or
1214   processing the line after it as a new request, either of which might
1215   result in a security vulnerability if other implementations within
1216   the request chain interpret the same message differently.
1217   Likewise, the presence of such whitespace in a response might be
1218   ignored by some clients or cause others to cease parsing.
1219</t>
1220
1221<section title="Request-Line" anchor="request.line">
1222  <x:anchor-alias value="Request"/>
1223  <x:anchor-alias value="Request-Line"/>
1224<t>
1225   The Request-Line begins with a method token, followed by a single
1226   space (SP), the request-target, another single space (SP), the
1227   protocol version, and ending with CRLF.
1228</t>
1229<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1230  <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>
1231</artwork></figure>
1232
1233<section title="Method" anchor="method">
1234  <x:anchor-alias value="Method"/>
1235<t>
1236   The Method token indicates the request method to be performed on the
1237   target resource. The request method is case-sensitive.
1238</t>
1239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1240  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1241</artwork></figure>
1242<t>
1243   See &method; for further information, such as the list of methods defined
1244   by this specification, the IANA registry, and considerations for new methods.
1245</t>
1246</section>
1247
1248<section title="request-target" anchor="request-target">
1249  <x:anchor-alias value="request-target"/>
1250<t>
1251   The request-target identifies the target resource upon which to apply
1252   the request.  The four options for request-target are described in
1253   <xref target="request-target-types"/>.
1254</t>
1255<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1256  <x:ref>request-target</x:ref> = "*"
1257                 / <x:ref>absolute-URI</x:ref>
1258                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1259                 / <x:ref>authority</x:ref>
1260</artwork></figure>
1261<t>
1262   HTTP does not place a pre-defined limit on the length of a request-target.
1263   A server &MUST; be prepared to receive URIs of unbounded length and
1264   respond with the 414 (URI Too Long) status code if the received
1265   request-target would be longer than the server wishes to handle
1266   (see &status-414;).
1267</t>
1268<t>
1269   Various ad-hoc limitations on request-target length are found in practice.
1270   It is &RECOMMENDED; that all HTTP senders and recipients support
1271   request-target lengths of 8000 or more octets.
1272</t>
1273<x:note>
1274  <t>
1275    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1276    are not part of the request-target and thus will not be transmitted
1277    in an HTTP request.
1278  </t>
1279</x:note>
1280</section>
1281</section>
1282
1283<section title="Response Status-Line" anchor="status.line">
1284  <x:anchor-alias value="Response"/>
1285  <x:anchor-alias value="Status-Line"/>
1286<t>
1287   The first line of a Response message is the Status-Line, consisting
1288   of the protocol version, a space (SP), the status code, another space,
1289   a possibly-empty textual phrase describing the status code, and
1290   ending with CRLF.
1291</t>
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1293  <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>
1294</artwork></figure>
1295
1296<section title="Status Code" anchor="status.code">
1297  <x:anchor-alias value="Status-Code"/>
1298<t>
1299   The Status-Code element is a 3-digit integer result code of the attempt to
1300   understand and satisfy the request. See &status-code-reasonphr; for
1301   further information, such as the list of status codes defined by this
1302   specification, the IANA registry, and considerations for new status codes.
1303</t>
1304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1305  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1306</artwork></figure>
1307</section>
1308
1309<section title="Reason Phrase" anchor="reason.phrase">
1310  <x:anchor-alias value="Reason-Phrase"/>
1311<t>   
1312   The Reason Phrase exists for the sole purpose of providing a textual
1313   description associated with the numeric status code, out of deference to
1314   earlier Internet application protocols that were more frequently used with
1315   interactive text clients. A client &SHOULD; ignore the content of the Reason
1316   Phrase.
1317</t>
1318<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1319  <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> )
1320</artwork></figure>
1321</section>
1322</section>
1323
1324</section>
1325
1326<section title="Header Fields" anchor="header.fields">
1327  <x:anchor-alias value="header-field"/>
1328  <x:anchor-alias value="field-content"/>
1329  <x:anchor-alias value="field-name"/>
1330  <x:anchor-alias value="field-value"/>
1331  <x:anchor-alias value="OWS"/>
1332<t>
1333   Each HTTP header field consists of a case-insensitive field name
1334   followed by a colon (":"), optional whitespace, and the field value.
1335</t>
1336<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"/>
1337  <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>
1338  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1339  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1340  <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> )
1341</artwork></figure>
1342<t>
1343   The field-name token labels the corresponding field-value as having the
1344   semantics defined by that header field.  For example, the Date header field
1345   is defined in &header-date; as containing the origination
1346   timestamp for the message in which it appears.
1347</t>
1348<t>
1349   HTTP header fields are fully extensible: there is no limit on the
1350   introduction of new field names, each presumably defining new semantics,
1351   or on the number of header fields used in a given message.  Existing
1352   fields are defined in each part of this specification and in many other
1353   specifications outside the standards process.
1354   New header fields can be introduced without changing the protocol version
1355   if their defined semantics allow them to be safely ignored by recipients
1356   that do not recognize them.
1357</t>
1358<t>
1359   New HTTP header fields &SHOULD; be registered with IANA according
1360   to the procedures in &cons-new-header-fields;.
1361   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1362   field-name is listed in the Connection header field
1363   (<xref target="header.connection"/>) or the proxy is specifically
1364   configured to block or otherwise transform such fields.
1365   Unrecognized header fields &SHOULD; be ignored by other recipients.
1366</t>
1367<t>
1368   The order in which header fields with differing field names are
1369   received is not significant. However, it is "good practice" to send
1370   header fields that contain control data first, such as Host on
1371   requests and Date on responses, so that implementations can decide
1372   when not to handle a message as early as possible.  A server &MUST;
1373   wait until the entire header section is received before interpreting
1374   a request message, since later header fields might include conditionals,
1375   authentication credentials, or deliberately misleading duplicate
1376   header fields that would impact request processing.
1377</t>
1378<t>
1379   Multiple header fields with the same field name &MUST-NOT; be
1380   sent in a message unless the entire field value for that
1381   header field is defined as a comma-separated list [i.e., #(values)].
1382   Multiple header fields with the same field name can be combined into
1383   one "field-name: field-value" pair, without changing the semantics of the
1384   message, by appending each subsequent field value to the combined
1385   field value in order, separated by a comma. The order in which
1386   header fields with the same field name are received is therefore
1387   significant to the interpretation of the combined field value;
1388   a proxy &MUST-NOT; change the order of these field values when
1389   forwarding a message.
1390</t>
1391<x:note>
1392  <t>
1393   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1394   practice can occur multiple times, but does not use the list syntax, and
1395   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1396   for details.) Also note that the Set-Cookie2 header field specified in
1397   <xref target="RFC2965"/> does not share this problem.
1398  </t>
1399</x:note>
1400
1401<section title="Field Parsing" anchor="field.parsing">
1402<t>
1403   No whitespace is allowed between the header field-name and colon.
1404   In the past, differences in the handling of such whitespace have led to
1405   security vulnerabilities in request routing and response handling.
1406   Any received request message that contains whitespace between a header
1407   field-name and colon &MUST; be rejected with a response code of 400
1408   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1409   message before forwarding the message downstream.
1410</t>
1411<t>
1412   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1413   preferred. The field value does not include any leading or trailing white
1414   space: OWS occurring before the first non-whitespace octet of the
1415   field value or after the last non-whitespace octet of the field value
1416   is ignored and &SHOULD; be removed before further processing (as this does
1417   not change the meaning of the header field).
1418</t>
1419<t>
1420   Historically, HTTP header field values could be extended over multiple
1421   lines by preceding each extra line with at least one space or horizontal
1422   tab (obs-fold). This specification deprecates such line
1423   folding except within the message/http media type
1424   (<xref target="internet.media.type.message.http"/>).
1425   HTTP senders &MUST-NOT; produce messages that include line folding
1426   (i.e., that contain any field-content that matches the obs-fold rule) unless
1427   the message is intended for packaging within the message/http media type.
1428   HTTP recipients &SHOULD; accept line folding and replace any embedded
1429   obs-fold whitespace with either a single SP or a matching number of SP
1430   octets (to avoid buffer copying) prior to interpreting the field value or
1431   forwarding the message downstream.
1432</t>
1433<t>
1434   Historically, HTTP has allowed field content with text in the ISO-8859-1
1435   <xref target="ISO-8859-1"/> character encoding and supported other
1436   character sets only through use of <xref target="RFC2047"/> encoding.
1437   In practice, most HTTP header field values use only a subset of the
1438   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1439   header fields &SHOULD; limit their field values to US-ASCII octets.
1440   Recipients &SHOULD; treat other (obs-text) octets in field content as
1441   opaque data.
1442</t>
1443</section>
1444
1445<section title="Field Length" anchor="field.length">
1446<t>
1447   HTTP does not place a pre-defined limit on the length of header fields,
1448   either in isolation or as a set. A server &MUST; be prepared to receive
1449   request header fields of unbounded length and respond with a 4xx status
1450   code if the received header field(s) would be longer than the server wishes
1451   to handle.
1452</t>
1453<t>
1454   A client that receives response headers that are longer than it wishes to
1455   handle can only treat it as a server error.
1456</t>
1457<t>
1458   Various ad-hoc limitations on header length are found in practice. It is
1459   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1460   combined header fields have 4000 or more octets.
1461</t>
1462</section>
1463
1464<section title="Common Field ABNF Rules" anchor="field.rules">
1465<t anchor="rule.token.separators">
1466  <x:anchor-alias value="tchar"/>
1467  <x:anchor-alias value="token"/>
1468  <x:anchor-alias value="special"/>
1469  <x:anchor-alias value="word"/>
1470   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1471   separated by whitespace or special characters. These special characters
1472   &MUST; be in a quoted string to be used within a parameter value (as defined
1473   in <xref target="transfer.codings"/>).
1474</t>
1475<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"/>
1476  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1477
1478  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1479<!--
1480  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1481 -->
1482  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1483                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1484                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1485                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1486
1487  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1488                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1489                 / "]" / "?" / "=" / "{" / "}"
1490</artwork></figure>
1491<t anchor="rule.quoted-string">
1492  <x:anchor-alias value="quoted-string"/>
1493  <x:anchor-alias value="qdtext"/>
1494  <x:anchor-alias value="obs-text"/>
1495   A string of text is parsed as a single word if it is quoted using
1496   double-quote marks.
1497</t>
1498<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"/>
1499  <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>
1500  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1501  <x:ref>obs-text</x:ref>       = %x80-FF
1502</artwork></figure>
1503<t anchor="rule.quoted-pair">
1504  <x:anchor-alias value="quoted-pair"/>
1505   The backslash octet ("\") can be used as a single-octet
1506   quoting mechanism within quoted-string constructs:
1507</t>
1508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1509  <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> )
1510</artwork></figure>
1511<t>
1512   Recipients that process the value of the quoted-string &MUST; handle a
1513   quoted-pair as if it were replaced by the octet following the backslash.
1514</t>
1515<t>
1516   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1517   escaping (i.e., other than DQUOTE and the backslash octet).
1518</t>
1519<t anchor="rule.comment">
1520  <x:anchor-alias value="comment"/>
1521  <x:anchor-alias value="ctext"/>
1522   Comments can be included in some HTTP header fields by surrounding
1523   the comment text with parentheses. Comments are only allowed in
1524   fields containing "comment" as part of their field value definition.
1525</t>
1526<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1527  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1528  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1529</artwork></figure>
1530<t anchor="rule.quoted-cpair">
1531  <x:anchor-alias value="quoted-cpair"/>
1532   The backslash octet ("\") can be used as a single-octet
1533   quoting mechanism within comment constructs:
1534</t>
1535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1536  <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> )
1537</artwork></figure>
1538<t>
1539   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1540   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1541</t>
1542</section>
1543</section>
1544
1545<section title="Message Body" anchor="message.body">
1546  <x:anchor-alias value="message-body"/>
1547<t>
1548   The message-body (if any) of an HTTP message is used to carry the
1549   payload body associated with the request or response.
1550</t>
1551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1552  <x:ref>message-body</x:ref> = *OCTET
1553</artwork></figure>
1554<t>
1555   The message-body differs from the payload body only when a transfer-coding
1556   has been applied, as indicated by the Transfer-Encoding header field
1557   (<xref target="header.transfer-encoding"/>).  If more than one
1558   Transfer-Encoding header field is present in a message, the multiple
1559   field-values &MUST; be combined into one field-value, according to the
1560   algorithm defined in <xref target="header.fields"/>, before determining
1561   the message-body length.
1562</t>
1563<t>
1564   When one or more transfer-codings are applied to a payload in order to
1565   form the message-body, the Transfer-Encoding header field &MUST; contain
1566   the list of transfer-codings applied. Transfer-Encoding is a property of
1567   the message, not of the payload, and thus &MAY; be added or removed by
1568   any implementation along the request/response chain under the constraints
1569   found in <xref target="transfer.codings"/>.
1570</t>
1571<t>
1572   If a message is received that has multiple Content-Length header fields
1573   (<xref target="header.content-length"/>) with field-values consisting
1574   of the same decimal value, or a single Content-Length header field with
1575   a field value containing a list of identical decimal values (e.g.,
1576   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1577   header fields have been generated or combined by an upstream message
1578   processor, then the recipient &MUST; either reject the message as invalid
1579   or replace the duplicated field-values with a single valid Content-Length
1580   field containing that decimal value prior to determining the message-body
1581   length.
1582</t>
1583<t>
1584   The rules for when a message-body is allowed in a message differ for
1585   requests and responses.
1586</t>
1587<t>
1588   The presence of a message-body in a request is signaled by the
1589   inclusion of a Content-Length or Transfer-Encoding header field in
1590   the request's header fields, even if the request method does not
1591   define any use for a message-body.  This allows the request
1592   message framing algorithm to be independent of method semantics.
1593</t>
1594<t>
1595   For response messages, whether or not a message-body is included with
1596   a message is dependent on both the request method and the response
1597   status code (<xref target="status.code"/>).
1598   Responses to the HEAD request method never include a message-body
1599   because the associated response header fields (e.g., Transfer-Encoding,
1600   Content-Length, etc.) only indicate what their values would have been
1601   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1602   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1603   All other responses do include a message-body, although the body
1604   &MAY; be of zero length.
1605</t>
1606<t>
1607   The length of the message-body is determined by one of the following
1608   (in order of precedence):
1609</t>
1610<t>
1611  <list style="numbers">
1612    <x:lt><t>
1613     Any response to a HEAD request and any response with a status
1614     code of 100-199, 204, or 304 is always terminated by the first
1615     empty line after the header fields, regardless of the header
1616     fields present in the message, and thus cannot contain a message-body.
1617    </t></x:lt>
1618    <x:lt><t>
1619     If a Transfer-Encoding header field is present
1620     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1621     is the final encoding, the message-body length is determined by reading
1622     and decoding the chunked data until the transfer-coding indicates the
1623     data is complete.
1624    </t>
1625    <t>
1626     If a Transfer-Encoding header field is present in a response and the
1627     "chunked" transfer-coding is not the final encoding, the message-body
1628     length is determined by reading the connection until it is closed by
1629     the server.
1630     If a Transfer-Encoding header field is present in a request and the
1631     "chunked" transfer-coding is not the final encoding, the message-body
1632     length cannot be determined reliably; the server &MUST; respond with
1633     the 400 (Bad Request) status code and then close the connection.
1634    </t>
1635    <t>
1636     If a message is received with both a Transfer-Encoding header field
1637     and a Content-Length header field, the Transfer-Encoding overrides
1638     the Content-Length.
1639     Such a message might indicate an attempt to perform request or response
1640     smuggling (bypass of security-related checks on message routing or content)
1641     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1642     be removed, prior to forwarding the message downstream, or replaced with
1643     the real message-body length after the transfer-coding is decoded.
1644    </t></x:lt>
1645    <x:lt><t>
1646     If a message is received without Transfer-Encoding and with either
1647     multiple Content-Length header fields having differing field-values or
1648     a single Content-Length header field having an invalid value, then the
1649     message framing is invalid and &MUST; be treated as an error to
1650     prevent request or response smuggling.
1651     If this is a request message, the server &MUST; respond with
1652     a 400 (Bad Request) status code and then close the connection.
1653     If this is a response message received by a proxy, the proxy
1654     &MUST; discard the received response, send a 502 (Bad Gateway)
1655     status code as its downstream response, and then close the connection.
1656     If this is a response message received by a user-agent, it &MUST; be
1657     treated as an error by discarding the message and closing the connection.
1658    </t></x:lt>
1659    <x:lt><t>
1660     If a valid Content-Length header field
1661     is present without Transfer-Encoding, its decimal value defines the
1662     message-body length in octets.  If the actual number of octets sent in
1663     the message is less than the indicated Content-Length, the recipient
1664     &MUST; consider the message to be incomplete and treat the connection
1665     as no longer usable.
1666     If the actual number of octets sent in the message is more than the indicated
1667     Content-Length, the recipient &MUST; only process the message-body up to the
1668     field value's number of octets; the remainder of the message &MUST; either
1669     be discarded or treated as the next message in a pipeline.  For the sake of
1670     robustness, a user-agent &MAY; attempt to detect and correct such an error
1671     in message framing if it is parsing the response to the last request on
1672     a connection and the connection has been closed by the server.
1673    </t></x:lt>
1674    <x:lt><t>
1675     If this is a request message and none of the above are true, then the
1676     message-body length is zero (no message-body is present).
1677    </t></x:lt>
1678    <x:lt><t>
1679     Otherwise, this is a response message without a declared message-body
1680     length, so the message-body length is determined by the number of octets
1681     received prior to the server closing the connection.
1682    </t></x:lt>
1683  </list>
1684</t>
1685<t>
1686   Since there is no way to distinguish a successfully completed,
1687   close-delimited message from a partially-received message interrupted
1688   by network failure, implementations &SHOULD; use encoding or
1689   length-delimited messages whenever possible.  The close-delimiting
1690   feature exists primarily for backwards compatibility with HTTP/1.0.
1691</t>
1692<t>
1693   A server &MAY; reject a request that contains a message-body but
1694   not a Content-Length by responding with 411 (Length Required).
1695</t>
1696<t>
1697   Unless a transfer-coding other than "chunked" has been applied,
1698   a client that sends a request containing a message-body &SHOULD;
1699   use a valid Content-Length header field if the message-body length
1700   is known in advance, rather than the "chunked" encoding, since some
1701   existing services respond to "chunked" with a 411 (Length Required)
1702   status code even though they understand the chunked encoding.  This
1703   is typically because such services are implemented via a gateway that
1704   requires a content-length in advance of being called and the server
1705   is unable or unwilling to buffer the entire request before processing.
1706</t>
1707<t>
1708   A client that sends a request containing a message-body &MUST; include a
1709   valid Content-Length header field if it does not know the server will
1710   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1711   of specific user configuration or by remembering the version of a prior
1712   received response.
1713</t>
1714</section>
1715
1716<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1717<t>
1718   Request messages that are prematurely terminated, possibly due to a
1719   cancelled connection or a server-imposed time-out exception, &MUST;
1720   result in closure of the connection; sending an HTTP/1.1 error response
1721   prior to closing the connection is &OPTIONAL;.
1722</t>
1723<t>
1724   Response messages that are prematurely terminated, usually by closure
1725   of the connection prior to receiving the expected number of octets or by
1726   failure to decode a transfer-encoded message-body, &MUST; be recorded
1727   as incomplete.  A response that terminates in the middle of the header
1728   block (before the empty line is received) cannot be assumed to convey the
1729   full semantics of the response and &MUST; be treated as an error.
1730</t>
1731<t>
1732   A message-body that uses the chunked transfer encoding is
1733   incomplete if the zero-sized chunk that terminates the encoding has not
1734   been received.  A message that uses a valid Content-Length is incomplete
1735   if the size of the message-body received (in octets) is less than the
1736   value given by Content-Length.  A response that has neither chunked
1737   transfer encoding nor Content-Length is terminated by closure of the
1738   connection, and thus is considered complete regardless of the number of
1739   message-body octets received, provided that the header block was received
1740   intact.
1741</t>
1742<t>
1743   A user agent &MUST-NOT; render an incomplete response message-body as if
1744   it were complete (i.e., some indication must be given to the user that an
1745   error occurred).  Cache requirements for incomplete responses are defined
1746   in &cache-incomplete;.
1747</t>
1748<t>
1749   A server &MUST; read the entire request message-body or close
1750   the connection after sending its response, since otherwise the
1751   remaining data on a persistent connection would be misinterpreted
1752   as the next request.  Likewise,
1753   a client &MUST; read the entire response message-body if it intends
1754   to reuse the same connection for a subsequent request.  Pipelining
1755   multiple requests on a connection is described in <xref target="pipelining"/>.
1756</t>
1757</section>
1758
1759<section title="Message Parsing Robustness" anchor="message.robustness">
1760<t>
1761   Older HTTP/1.0 client implementations might send an extra CRLF
1762   after a POST request as a lame workaround for some early server
1763   applications that failed to read message-body content that was
1764   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1765   preface or follow a request with an extra CRLF.  If terminating
1766   the request message-body with a line-ending is desired, then the
1767   client &MUST; include the terminating CRLF octets as part of the
1768   message-body length.
1769</t>
1770<t>
1771   In the interest of robustness, servers &SHOULD; ignore at least one
1772   empty line received where a Request-Line is expected. In other words, if
1773   the server is reading the protocol stream at the beginning of a
1774   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1775   Likewise, although the line terminator for the start-line and header
1776   fields is the sequence CRLF, we recommend that recipients recognize a
1777   single LF as a line terminator and ignore any CR.
1778</t>
1779<t>
1780   When a server listening only for HTTP request messages, or processing
1781   what appears from the start-line to be an HTTP request message,
1782   receives a sequence of octets that does not match the HTTP-message
1783   grammar aside from the robustness exceptions listed above, the
1784   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1785</t>
1786</section>
1787</section>
1788
1789<section title="Message Routing" anchor="message.routing">
1790<t>
1791   In most cases, the user agent is provided a URI reference
1792   from which it determines an absolute URI for identifying the target
1793   resource.  When a request to the resource is initiated, all or part
1794   of that URI is used to construct the HTTP request-target.
1795</t>
1796
1797<section title="Types of Request Target" anchor="request-target-types">
1798<t>
1799   The four options for request-target are dependent on the nature of the
1800   request.
1801</t>   
1802<t><iref item="asterisk form (of request-target)"/>
1803   The asterisk "*" form of request-target, which &MUST-NOT; be used
1804   with any request method other than OPTIONS, means that the request
1805   applies to the server as a whole (the listening process) rather than
1806   to a specific named resource at that server.  For example,
1807</t>
1808<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1809OPTIONS * HTTP/1.1
1810</artwork></figure>
1811<t><iref item="absolute-URI form (of request-target)"/>
1812   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1813   proxy. The proxy is requested to either forward the request or service it
1814   from a valid cache, and then return the response. Note that the proxy &MAY;
1815   forward the request on to another proxy or directly to the server
1816   specified by the absolute-URI. In order to avoid request loops, a
1817   proxy that forwards requests to other proxies &MUST; be able to
1818   recognize and exclude all of its own server names, including
1819   any aliases, local variations, and the numeric IP address. An example
1820   Request-Line would be:
1821</t>
1822<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1823GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1824</artwork></figure>
1825<t>
1826   To allow for transition to absolute-URIs in all requests in future
1827   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1828   form in requests, even though HTTP/1.1 clients will only generate
1829   them in requests to proxies.
1830</t>
1831<t>
1832   If a proxy receives a host name that is not a fully qualified domain
1833   name, it &MAY; add its domain to the host name it received. If a proxy
1834   receives a fully qualified domain name, the proxy &MUST-NOT; change
1835   the host name.
1836</t>
1837<t><iref item="authority form (of request-target)"/>
1838   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1839</t>
1840<t><iref item="origin form (of request-target)"/>
1841   The most common form of request-target is that used when making
1842   a request to an origin server ("origin form").
1843   In this case, the absolute path and query components of the URI
1844   &MUST; be transmitted as the request-target, and the authority component
1845   &MUST; be transmitted in a Host header field. For example, a client wishing
1846   to retrieve a representation of the resource, as identified above,
1847   directly from the origin server would open (or reuse) a TCP connection
1848   to port 80 of the host "www.example.org" and send the lines:
1849</t>
1850<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1851GET /pub/WWW/TheProject.html HTTP/1.1
1852Host: www.example.org
1853</artwork></figure>
1854<t>
1855   followed by the remainder of the Request. Note that the origin form
1856   of request-target always starts with an absolute path; if the target
1857   resource's URI path is empty, then an absolute path of "/" &MUST; be
1858   provided in the request-target.
1859</t>
1860<t>
1861   If a proxy receives an OPTIONS request with an absolute-URI form of
1862   request-target in which the URI has an empty path and no query component,
1863   then the last proxy on the request chain &MUST; use a request-target
1864   of "*" when it forwards the request to the indicated origin server.
1865</t>
1866<figure><preamble>   
1867   For example, the request
1868</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1869OPTIONS http://www.example.org:8001 HTTP/1.1
1870</artwork></figure>
1871<figure><preamble>   
1872  would be forwarded by the final proxy as
1873</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1874OPTIONS * HTTP/1.1
1875Host: www.example.org:8001
1876</artwork>
1877<postamble>
1878   after connecting to port 8001 of host "www.example.org".
1879</postamble>
1880</figure>
1881<t>
1882   The request-target is transmitted in the format specified in
1883   <xref target="http.uri"/>. If the request-target is percent-encoded
1884   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1885   &MUST; decode the request-target in order to
1886   properly interpret the request. Servers &SHOULD; respond to invalid
1887   request-targets with an appropriate status code.
1888</t>
1889<t>
1890   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1891   received request-target when forwarding it to the next inbound server,
1892   except as noted above to replace a null path-absolute with "/" or "*".
1893</t>
1894<x:note>
1895  <t>
1896    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1897    meaning of the request when the origin server is improperly using
1898    a non-reserved URI character for a reserved purpose.  Implementors
1899    need to be aware that some pre-HTTP/1.1 proxies have been known to
1900    rewrite the request-target.
1901  </t>
1902</x:note>
1903</section>
1904
1905<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1906<t>
1907   The exact resource identified by an Internet request is determined by
1908   examining both the request-target and the Host header field.
1909</t>
1910<t>
1911   An origin server that does not allow resources to differ by the
1912   requested host &MAY; ignore the Host header field value when
1913   determining the resource identified by an HTTP/1.1 request. (But see
1914   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1915   for other requirements on Host support in HTTP/1.1.)
1916</t>
1917<t>
1918   An origin server that does differentiate resources based on the host
1919   requested (sometimes referred to as virtual hosts or vanity host
1920   names) &MUST; use the following rules for determining the requested
1921   resource on an HTTP/1.1 request:
1922  <list style="numbers">
1923    <t>If request-target is an absolute-URI, the host is part of the
1924     request-target. Any Host header field value in the request &MUST; be
1925     ignored.</t>
1926    <t>If the request-target is not an absolute-URI, and the request includes
1927     a Host header field, the host is determined by the Host header
1928     field value.</t>
1929    <t>If the host as determined by rule 1 or 2 is not a valid host on
1930     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1931  </list>
1932</t>
1933<t>
1934   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1935   attempt to use heuristics (e.g., examination of the URI path for
1936   something unique to a particular host) in order to determine what
1937   exact resource is being requested.
1938</t>
1939</section>
1940
1941<section title="Effective Request URI" anchor="effective.request.uri">
1942  <iref primary="true" item="effective request URI"/>
1943  <iref primary="true" item="target resource"/>
1944<t>
1945   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1946   for the target resource; instead, the URI needs to be inferred from the
1947   request-target, Host header field, and connection context. The result of
1948   this process is called the "effective request URI".  The "target resource"
1949   is the resource identified by the effective request URI.
1950</t>
1951<t>
1952   If the request-target is an absolute-URI, then the effective request URI is
1953   the request-target.
1954</t>
1955<t>
1956   If the request-target uses the path-absolute form or the asterisk form,
1957   and the Host header field is present, then the effective request URI is
1958   constructed by concatenating
1959</t>
1960<t>
1961  <list style="symbols">
1962    <t>
1963      the scheme name: "http" if the request was received over an insecure
1964      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1965      connection,
1966    </t>
1967    <t>
1968      the octet sequence "://",
1969    </t>
1970    <t>
1971      the authority component, as specified in the Host header field
1972      (<xref target="header.host"/>), and
1973    </t>
1974    <t>
1975      the request-target obtained from the Request-Line, unless the
1976      request-target is just the asterisk "*".
1977    </t>
1978  </list>
1979</t>
1980<t>
1981   If the request-target uses the path-absolute form or the asterisk form,
1982   and the Host header field is not present, then the effective request URI is
1983   undefined.
1984</t>
1985<t>
1986   Otherwise, when request-target uses the authority form, the effective
1987   request URI is undefined.
1988</t>
1989<figure>
1990<preamble>
1991   Example 1: the effective request URI for the message
1992</preamble> 
1993<artwork type="example" x:indent-with="  ">
1994GET /pub/WWW/TheProject.html HTTP/1.1
1995Host: www.example.org:8080
1996</artwork>
1997<postamble>
1998  (received over an insecure TCP connection) is "http", plus "://", plus the
1999  authority component "www.example.org:8080", plus the request-target
2000  "/pub/WWW/TheProject.html", thus
2001  "http://www.example.org:8080/pub/WWW/TheProject.html".
2002</postamble>
2003</figure>
2004<figure>
2005<preamble>
2006   Example 2: the effective request URI for the message
2007</preamble> 
2008<artwork type="example" x:indent-with="  ">
2009OPTIONS * HTTP/1.1
2010Host: www.example.org
2011</artwork>
2012<postamble>
2013  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2014  authority component "www.example.org", thus "https://www.example.org".
2015</postamble>
2016</figure>
2017<t>
2018   Effective request URIs are compared using the rules described in
2019   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2020   be treated as equivalent to an absolute path of "/".
2021</t> 
2022</section>
2023</section>
2024
2025
2026<section title="Protocol Parameters" anchor="protocol.parameters">
2027
2028<section title="Transfer Codings" anchor="transfer.codings">
2029  <x:anchor-alias value="transfer-coding"/>
2030  <x:anchor-alias value="transfer-extension"/>
2031<t>
2032   Transfer-coding values are used to indicate an encoding
2033   transformation that has been, can be, or might need to be applied to a
2034   payload body in order to ensure "safe transport" through the network.
2035   This differs from a content coding in that the transfer-coding is a
2036   property of the message rather than a property of the representation
2037   that is being transferred.
2038</t>
2039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2040  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2041                          / "compress" ; <xref target="compress.coding"/>
2042                          / "deflate" ; <xref target="deflate.coding"/>
2043                          / "gzip" ; <xref target="gzip.coding"/>
2044                          / <x:ref>transfer-extension</x:ref>
2045  <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> )
2046</artwork></figure>
2047<t anchor="rule.parameter">
2048  <x:anchor-alias value="attribute"/>
2049  <x:anchor-alias value="transfer-parameter"/>
2050  <x:anchor-alias value="value"/>
2051   Parameters are in the form of attribute/value pairs.
2052</t>
2053<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"/>
2054  <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>
2055  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2056  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2057</artwork></figure>
2058<t>
2059   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2060   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2061   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2062</t>
2063<t>
2064   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2065   MIME, which were designed to enable safe transport of binary data over a
2066   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2067   However, safe transport
2068   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2069   the only unsafe characteristic of message-bodies is the difficulty in
2070   determining the exact message body length (<xref target="message.body"/>),
2071   or the desire to encrypt data over a shared transport.
2072</t>
2073<t>
2074   A server that receives a request message with a transfer-coding it does
2075   not understand &SHOULD; respond with 501 (Not Implemented) and then
2076   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2077   client.
2078</t>
2079
2080<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2081  <iref item="chunked (Coding Format)"/>
2082  <iref item="Coding Format" subitem="chunked"/>
2083  <x:anchor-alias value="chunk"/>
2084  <x:anchor-alias value="Chunked-Body"/>
2085  <x:anchor-alias value="chunk-data"/>
2086  <x:anchor-alias value="chunk-ext"/>
2087  <x:anchor-alias value="chunk-ext-name"/>
2088  <x:anchor-alias value="chunk-ext-val"/>
2089  <x:anchor-alias value="chunk-size"/>
2090  <x:anchor-alias value="last-chunk"/>
2091  <x:anchor-alias value="trailer-part"/>
2092  <x:anchor-alias value="quoted-str-nf"/>
2093  <x:anchor-alias value="qdtext-nf"/>
2094<t>
2095   The chunked encoding modifies the body of a message in order to
2096   transfer it as a series of chunks, each with its own size indicator,
2097   followed by an &OPTIONAL; trailer containing header fields. This
2098   allows dynamically produced content to be transferred along with the
2099   information necessary for the recipient to verify that it has
2100   received the full message.
2101</t>
2102<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"/>
2103  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2104                   <x:ref>last-chunk</x:ref>
2105                   <x:ref>trailer-part</x:ref>
2106                   <x:ref>CRLF</x:ref>
2107 
2108  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2109                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2110  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2111  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2112 
2113  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2114                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2115  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2116  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2117  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2118  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2119 
2120  <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>
2121                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2122  <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>
2123</artwork></figure>
2124<t>
2125   The chunk-size field is a string of hex digits indicating the size of
2126   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2127   zero, followed by the trailer, which is terminated by an empty line.
2128</t>
2129<t>
2130   The trailer allows the sender to include additional HTTP header
2131   fields at the end of the message. The Trailer header field can be
2132   used to indicate which header fields are included in a trailer (see
2133   <xref target="header.trailer"/>).
2134</t>
2135<t>
2136   A server using chunked transfer-coding in a response &MUST-NOT; use the
2137   trailer for any header fields unless at least one of the following is
2138   true:
2139  <list style="numbers">
2140    <t>the request included a TE header field that indicates "trailers" is
2141     acceptable in the transfer-coding of the  response, as described in
2142     <xref target="header.te"/>; or,</t>
2143     
2144    <t>the trailer fields consist entirely of optional metadata, and the
2145    recipient could use the message (in a manner acceptable to the server where
2146    the field originated) without receiving it. In other words, the server that
2147    generated the header (often but not always the origin server) is willing to
2148    accept the possibility that the trailer fields might be silently discarded
2149    along the path to the client.</t>
2150  </list>
2151</t>
2152<t>
2153   This requirement prevents an interoperability failure when the
2154   message is being received by an HTTP/1.1 (or later) proxy and
2155   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2156   compliance with the protocol would have necessitated a possibly
2157   infinite buffer on the proxy.
2158</t>
2159<t>
2160   A process for decoding the "chunked" transfer-coding
2161   can be represented in pseudo-code as:
2162</t>
2163<figure><artwork type="code">
2164  length := 0
2165  read chunk-size, chunk-ext (if any) and CRLF
2166  while (chunk-size &gt; 0) {
2167     read chunk-data and CRLF
2168     append chunk-data to decoded-body
2169     length := length + chunk-size
2170     read chunk-size and CRLF
2171  }
2172  read header-field
2173  while (header-field not empty) {
2174     append header-field to existing header fields
2175     read header-field
2176  }
2177  Content-Length := length
2178  Remove "chunked" from Transfer-Encoding
2179</artwork></figure>
2180<t>
2181   All HTTP/1.1 applications &MUST; be able to receive and decode the
2182   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2183   they do not understand.
2184</t>
2185<t>
2186   Since "chunked" is the only transfer-coding required to be understood
2187   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2188   on a persistent connection.  Whenever a transfer-coding is applied to
2189   a payload body in a request, the final transfer-coding applied &MUST;
2190   be "chunked".  If a transfer-coding is applied to a response payload
2191   body, then either the final transfer-coding applied &MUST; be "chunked"
2192   or the message &MUST; be terminated by closing the connection. When the
2193   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2194   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2195   be applied more than once in a message-body.
2196</t>
2197</section>
2198
2199<section title="Compression Codings" anchor="compression.codings">
2200<t>
2201   The codings defined below can be used to compress the payload of a
2202   message.
2203</t>
2204<x:note><t>
2205   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2206   is not desirable and is discouraged for future encodings. Their
2207   use here is representative of historical practice, not good
2208   design.
2209</t></x:note>
2210<x:note><t>
2211   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2212   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2213   equivalent to "gzip" and "compress" respectively.
2214</t></x:note>
2215
2216<section title="Compress Coding" anchor="compress.coding">
2217<iref item="compress (Coding Format)"/>
2218<iref item="Coding Format" subitem="compress"/>
2219<t>
2220   The "compress" format is produced by the common UNIX file compression
2221   program "compress". This format is an adaptive Lempel-Ziv-Welch
2222   coding (LZW).
2223</t>
2224</section>
2225
2226<section title="Deflate Coding" anchor="deflate.coding">
2227<iref item="deflate (Coding Format)"/>
2228<iref item="Coding Format" subitem="deflate"/>
2229<t>
2230   The "deflate" format is defined as the "deflate" compression mechanism
2231   (described in <xref target="RFC1951"/>) used inside the "zlib"
2232   data format (<xref target="RFC1950"/>).
2233</t>
2234<x:note>
2235  <t>
2236    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2237    compressed data without the zlib wrapper.
2238   </t>
2239</x:note>
2240</section>
2241
2242<section title="Gzip Coding" anchor="gzip.coding">
2243<iref item="gzip (Coding Format)"/>
2244<iref item="Coding Format" subitem="gzip"/>
2245<t>
2246   The "gzip" format is produced by the file compression program
2247   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2248   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2249</t>
2250</section>
2251
2252</section>
2253
2254<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2255<t>
2256   The HTTP Transfer Coding Registry defines the name space for the transfer
2257   coding names.
2258</t>
2259<t>
2260   Registrations &MUST; include the following fields:
2261   <list style="symbols">
2262     <t>Name</t>
2263     <t>Description</t>
2264     <t>Pointer to specification text</t>
2265   </list>
2266</t>
2267<t>
2268   Names of transfer codings &MUST-NOT; overlap with names of content codings
2269   (&content-codings;), unless the encoding transformation is identical (as it
2270   is the case for the compression codings defined in
2271   <xref target="compression.codings"/>).
2272</t>
2273<t>
2274   Values to be added to this name space require a specification
2275   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2276   conform to the purpose of transfer coding defined in this section.
2277</t>
2278<t>
2279   The registry itself is maintained at
2280   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2281</t>
2282</section>
2283</section>
2284
2285<section title="Product Tokens" anchor="product.tokens">
2286  <x:anchor-alias value="product"/>
2287  <x:anchor-alias value="product-version"/>
2288<t>
2289   Product tokens are used to allow communicating applications to
2290   identify themselves by software name and version. Most fields using
2291   product tokens also allow sub-products which form a significant part
2292   of the application to be listed, separated by whitespace. By
2293   convention, the products are listed in order of their significance
2294   for identifying the application.
2295</t>
2296<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2297  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2298  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2299</artwork></figure>
2300<t>
2301   Examples:
2302</t>
2303<figure><artwork type="example">
2304  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2305  Server: Apache/0.8.4
2306</artwork></figure>
2307<t>
2308   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2309   used for advertising or other non-essential information. Although any
2310   token octet &MAY; appear in a product-version, this token &SHOULD;
2311   only be used for a version identifier (i.e., successive versions of
2312   the same product &SHOULD; only differ in the product-version portion of
2313   the product value).
2314</t>
2315</section>
2316
2317<section title="Quality Values" anchor="quality.values">
2318  <x:anchor-alias value="qvalue"/>
2319<t>
2320   Both transfer codings (TE request header field, <xref target="header.te"/>)
2321   and content negotiation (&content.negotiation;) use short "floating point"
2322   numbers to indicate the relative importance ("weight") of various
2323   negotiable parameters.  A weight is normalized to a real number in
2324   the range 0 through 1, where 0 is the minimum and 1 the maximum
2325   value. If a parameter has a quality value of 0, then content with
2326   this parameter is "not acceptable" for the client. HTTP/1.1
2327   applications &MUST-NOT; generate more than three digits after the
2328   decimal point. User configuration of these values &SHOULD; also be
2329   limited in this fashion.
2330</t>
2331<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2332  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2333                 / ( "1" [ "." 0*3("0") ] )
2334</artwork></figure>
2335<x:note>
2336  <t>
2337     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2338     relative degradation in desired quality.
2339  </t>
2340</x:note>
2341</section>
2342
2343</section>
2344
2345<section title="Connections" anchor="connections">
2346
2347<section title="Persistent Connections" anchor="persistent.connections">
2348
2349<section title="Purpose" anchor="persistent.purpose">
2350<t>
2351   Prior to persistent connections, a separate TCP connection was
2352   established for each request, increasing the load on HTTP servers
2353   and causing congestion on the Internet. The use of inline images and
2354   other associated data often requires a client to make multiple
2355   requests of the same server in a short amount of time. Analysis of
2356   these performance problems and results from a prototype
2357   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2358   measurements of actual HTTP/1.1 implementations show good
2359   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2360   T/TCP <xref target="Tou1998"/>.
2361</t>
2362<t>
2363   Persistent HTTP connections have a number of advantages:
2364  <list style="symbols">
2365      <t>
2366        By opening and closing fewer TCP connections, CPU time is saved
2367        in routers and hosts (clients, servers, proxies, gateways,
2368        tunnels, or caches), and memory used for TCP protocol control
2369        blocks can be saved in hosts.
2370      </t>
2371      <t>
2372        HTTP requests and responses can be pipelined on a connection.
2373        Pipelining allows a client to make multiple requests without
2374        waiting for each response, allowing a single TCP connection to
2375        be used much more efficiently, with much lower elapsed time.
2376      </t>
2377      <t>
2378        Network congestion is reduced by reducing the number of packets
2379        caused by TCP opens, and by allowing TCP sufficient time to
2380        determine the congestion state of the network.
2381      </t>
2382      <t>
2383        Latency on subsequent requests is reduced since there is no time
2384        spent in TCP's connection opening handshake.
2385      </t>
2386      <t>
2387        HTTP can evolve more gracefully, since errors can be reported
2388        without the penalty of closing the TCP connection. Clients using
2389        future versions of HTTP might optimistically try a new feature,
2390        but if communicating with an older server, retry with old
2391        semantics after an error is reported.
2392      </t>
2393    </list>
2394</t>
2395<t>
2396   HTTP implementations &SHOULD; implement persistent connections.
2397</t>
2398</section>
2399
2400<section title="Overall Operation" anchor="persistent.overall">
2401<t>
2402   A significant difference between HTTP/1.1 and earlier versions of
2403   HTTP is that persistent connections are the default behavior of any
2404   HTTP connection. That is, unless otherwise indicated, the client
2405   &SHOULD; assume that the server will maintain a persistent connection,
2406   even after error responses from the server.
2407</t>
2408<t>
2409   Persistent connections provide a mechanism by which a client and a
2410   server can signal the close of a TCP connection. This signaling takes
2411   place using the Connection header field (<xref target="header.connection"/>). Once a close
2412   has been signaled, the client &MUST-NOT; send any more requests on that
2413   connection.
2414</t>
2415
2416<section title="Negotiation" anchor="persistent.negotiation">
2417<t>
2418   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2419   maintain a persistent connection unless a Connection header field including
2420   the connection-token "close" was sent in the request. If the server
2421   chooses to close the connection immediately after sending the
2422   response, it &SHOULD; send a Connection header field including the
2423   connection-token "close".
2424</t>
2425<t>
2426   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2427   decide to keep it open based on whether the response from a server
2428   contains a Connection header field with the connection-token close. In case
2429   the client does not want to maintain a connection for more than that
2430   request, it &SHOULD; send a Connection header field including the
2431   connection-token close.
2432</t>
2433<t>
2434   If either the client or the server sends the close token in the
2435   Connection header field, that request becomes the last one for the
2436   connection.
2437</t>
2438<t>
2439   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2440   maintained for HTTP versions less than 1.1 unless it is explicitly
2441   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2442   compatibility with HTTP/1.0 clients.
2443</t>
2444<t>
2445   In order to remain persistent, all messages on the connection &MUST;
2446   have a self-defined message length (i.e., one not defined by closure
2447   of the connection), as described in <xref target="message.body"/>.
2448</t>
2449</section>
2450
2451<section title="Pipelining" anchor="pipelining">
2452<t>
2453   A client that supports persistent connections &MAY; "pipeline" its
2454   requests (i.e., send multiple requests without waiting for each
2455   response). A server &MUST; send its responses to those requests in the
2456   same order that the requests were received.
2457</t>
2458<t>
2459   Clients which assume persistent connections and pipeline immediately
2460   after connection establishment &SHOULD; be prepared to retry their
2461   connection if the first pipelined attempt fails. If a client does
2462   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2463   persistent. Clients &MUST; also be prepared to resend their requests if
2464   the server closes the connection before sending all of the
2465   corresponding responses.
2466</t>
2467<t>
2468   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2469   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2470   premature termination of the transport connection could lead to
2471   indeterminate results. A client wishing to send a non-idempotent
2472   request &SHOULD; wait to send that request until it has received the
2473   response status line for the previous request.
2474</t>
2475</section>
2476</section>
2477
2478<section title="Proxy Servers" anchor="persistent.proxy">
2479<t>
2480   It is especially important that proxies correctly implement the
2481   properties of the Connection header field as specified in <xref target="header.connection"/>.
2482</t>
2483<t>
2484   The proxy server &MUST; signal persistent connections separately with
2485   its clients and the origin servers (or other proxy servers) that it
2486   connects to. Each persistent connection applies to only one transport
2487   link.
2488</t>
2489<t>
2490   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2491   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2492   for information and discussion of the problems with the Keep-Alive header field
2493   implemented by many HTTP/1.0 clients).
2494</t>
2495
2496<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2497<!--<t>
2498  <cref anchor="TODO-end-to-end" source="jre">
2499    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2500    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2501  </cref>
2502</t>-->
2503<t>
2504   For the purpose of defining the behavior of caches and non-caching
2505   proxies, we divide HTTP header fields into two categories:
2506  <list style="symbols">
2507      <t>End-to-end header fields, which are  transmitted to the ultimate
2508        recipient of a request or response. End-to-end header fields in
2509        responses MUST be stored as part of a cache entry and &MUST; be
2510        transmitted in any response formed from a cache entry.</t>
2511
2512      <t>Hop-by-hop header fields, which are meaningful only for a single
2513        transport-level connection, and are not stored by caches or
2514        forwarded by proxies.</t>
2515  </list>
2516</t>
2517<t>
2518   The following HTTP/1.1 header fields are hop-by-hop header fields:
2519  <list style="symbols">
2520      <t>Connection</t>
2521      <t>Keep-Alive</t>
2522      <t>Proxy-Authenticate</t>
2523      <t>Proxy-Authorization</t>
2524      <t>TE</t>
2525      <t>Trailer</t>
2526      <t>Transfer-Encoding</t>
2527      <t>Upgrade</t>
2528  </list>
2529</t>
2530<t>
2531   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2532</t>
2533<t>
2534   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2535   (<xref target="header.connection"/>).
2536</t>
2537</section>
2538
2539<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2540<!--<t>
2541  <cref anchor="TODO-non-mod-headers" source="jre">
2542    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2543    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2544  </cref>
2545</t>-->
2546<t>
2547   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2548   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2549   modify an end-to-end header field unless the definition of that header field requires
2550   or specifically allows that.
2551</t>
2552<t>
2553   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2554   request or response, and it &MUST-NOT; add any of these fields if not
2555   already present:
2556  <list style="symbols">
2557    <t>Allow</t>
2558    <t>Content-Location</t>
2559    <t>Content-MD5</t>
2560    <t>ETag</t>
2561    <t>Last-Modified</t>
2562    <t>Server</t>
2563  </list>
2564</t>
2565<t>
2566   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2567   response:
2568  <list style="symbols">
2569    <t>Expires</t>
2570  </list>
2571</t>
2572<t>
2573   but it &MAY; add any of these fields if not already present. If an
2574   Expires header field is added, it &MUST; be given a field-value identical to
2575   that of the Date header field in that response.
2576</t>
2577<t>
2578   A proxy &MUST-NOT; modify or add any of the following fields in a
2579   message that contains the no-transform cache-control directive, or in
2580   any request:
2581  <list style="symbols">
2582    <t>Content-Encoding</t>
2583    <t>Content-Range</t>
2584    <t>Content-Type</t>
2585  </list>
2586</t>
2587<t>
2588   A transforming proxy &MAY; modify or add these fields to a message
2589   that does not include no-transform, but if it does so, it &MUST; add a
2590   Warning 214 (Transformation applied) if one does not already appear
2591   in the message (see &header-warning;).
2592</t>
2593<x:note>
2594  <t>
2595    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2596    cause authentication failures if stronger authentication
2597    mechanisms are introduced in later versions of HTTP. Such
2598    authentication mechanisms &MAY; rely on the values of header fields
2599    not listed here.
2600  </t>
2601</x:note>
2602<t>
2603   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2604   though it &MAY; change the message-body through application or removal
2605   of a transfer-coding (<xref target="transfer.codings"/>).
2606</t>
2607</section>
2608
2609</section>
2610
2611<section title="Practical Considerations" anchor="persistent.practical">
2612<t>
2613   Servers will usually have some time-out value beyond which they will
2614   no longer maintain an inactive connection. Proxy servers might make
2615   this a higher value since it is likely that the client will be making
2616   more connections through the same server. The use of persistent
2617   connections places no requirements on the length (or existence) of
2618   this time-out for either the client or the server.
2619</t>
2620<t>
2621   When a client or server wishes to time-out it &SHOULD; issue a graceful
2622   close on the transport connection. Clients and servers &SHOULD; both
2623   constantly watch for the other side of the transport close, and
2624   respond to it as appropriate. If a client or server does not detect
2625   the other side's close promptly it could cause unnecessary resource
2626   drain on the network.
2627</t>
2628<t>
2629   A client, server, or proxy &MAY; close the transport connection at any
2630   time. For example, a client might have started to send a new request
2631   at the same time that the server has decided to close the "idle"
2632   connection. From the server's point of view, the connection is being
2633   closed while it was idle, but from the client's point of view, a
2634   request is in progress.
2635</t>
2636<t>
2637   Servers &SHOULD; always respond to at least one request per connection,
2638   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2639   middle of transmitting a response, unless a network or client failure
2640   is suspected.
2641</t>
2642<t>
2643   Clients (including proxies) &SHOULD; limit the number of simultaneous
2644   connections that they maintain to a given server (including proxies).
2645</t>
2646<t>
2647   Previous revisions of HTTP gave a specific number of connections as a
2648   ceiling, but this was found to be impractical for many applications. As a
2649   result, this specification does not mandate a particular maximum number of
2650   connections, but instead encourages clients to be conservative when opening
2651   multiple connections.
2652</t>
2653<t>
2654   In particular, while using multiple connections avoids the "head-of-line
2655   blocking" problem (whereby a request that takes significant server-side
2656   processing and/or has a large payload can block subsequent requests on the
2657   same connection), each connection used consumes server resources (sometimes
2658   significantly), and furthermore using multiple connections can cause
2659   undesirable side effects in congested networks.
2660</t>
2661<t>
2662   Note that servers might reject traffic that they deem abusive, including an
2663   excessive number of connections from a client.
2664</t>
2665</section>
2666
2667<section title="Retrying Requests" anchor="persistent.retrying.requests">
2668<t>
2669   Senders can close the transport connection at any time. Therefore,
2670   clients, servers, and proxies &MUST; be able to recover
2671   from asynchronous close events. Client software &MAY; reopen the
2672   transport connection and retransmit the aborted sequence of requests
2673   without user interaction so long as the request sequence is
2674   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2675   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2676   human operator the choice of retrying the request(s). Confirmation by
2677   user-agent software with semantic understanding of the application
2678   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2679   be repeated if the second sequence of requests fails.
2680</t>
2681</section>
2682
2683</section>
2684
2685<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2686
2687<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2688<t>
2689   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2690   flow control mechanisms to resolve temporary overloads, rather than
2691   terminating connections with the expectation that clients will retry.
2692   The latter technique can exacerbate network congestion.
2693</t>
2694</section>
2695
2696<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2697<t>
2698   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2699   the network connection for an error status code while it is transmitting
2700   the request. If the client sees an error status code, it &SHOULD;
2701   immediately cease transmitting the body. If the body is being sent
2702   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2703   empty trailer &MAY; be used to prematurely mark the end of the message.
2704   If the body was preceded by a Content-Length header field, the client &MUST;
2705   close the connection.
2706</t>
2707</section>
2708
2709<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2710<t>
2711   The purpose of the 100 (Continue) status code (see &status-100;) is to
2712   allow a client that is sending a request message with a request body
2713   to determine if the origin server is willing to accept the request
2714   (based on the request header fields) before the client sends the request
2715   body. In some cases, it might either be inappropriate or highly
2716   inefficient for the client to send the body if the server will reject
2717   the message without looking at the body.
2718</t>
2719<t>
2720   Requirements for HTTP/1.1 clients:
2721  <list style="symbols">
2722    <t>
2723        If a client will wait for a 100 (Continue) response before
2724        sending the request body, it &MUST; send an Expect header
2725        field (&header-expect;) with the "100-continue" expectation.
2726    </t>
2727    <t>
2728        A client &MUST-NOT; send an Expect header field (&header-expect;)
2729        with the "100-continue" expectation if it does not intend
2730        to send a request body.
2731    </t>
2732  </list>
2733</t>
2734<t>
2735   Because of the presence of older implementations, the protocol allows
2736   ambiguous situations in which a client might send "Expect: 100-continue"
2737   without receiving either a 417 (Expectation Failed)
2738   or a 100 (Continue) status code. Therefore, when a client sends this
2739   header field to an origin server (possibly via a proxy) from which it
2740   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2741   wait for an indefinite period before sending the request body.
2742</t>
2743<t>
2744   Requirements for HTTP/1.1 origin servers:
2745  <list style="symbols">
2746    <t> Upon receiving a request which includes an Expect header
2747        field with the "100-continue" expectation, an origin server &MUST;
2748        either respond with 100 (Continue) status code and continue to read
2749        from the input stream, or respond with a final status code. The
2750        origin server &MUST-NOT; wait for the request body before sending
2751        the 100 (Continue) response. If it responds with a final status
2752        code, it &MAY; close the transport connection or it &MAY; continue
2753        to read and discard the rest of the request.  It &MUST-NOT;
2754        perform the request method if it returns a final status code.
2755    </t>
2756    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2757        the request message does not include an Expect header
2758        field with the "100-continue" expectation, and &MUST-NOT; send a
2759        100 (Continue) response if such a request comes from an HTTP/1.0
2760        (or earlier) client. There is an exception to this rule: for
2761        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2762        status code in response to an HTTP/1.1 PUT or POST request that does
2763        not include an Expect header field with the "100-continue"
2764        expectation. This exception, the purpose of which is
2765        to minimize any client processing delays associated with an
2766        undeclared wait for 100 (Continue) status code, applies only to
2767        HTTP/1.1 requests, and not to requests with any other HTTP-version
2768        value.
2769    </t>
2770    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2771        already received some or all of the request body for the
2772        corresponding request.
2773    </t>
2774    <t> An origin server that sends a 100 (Continue) response &MUST;
2775    ultimately send a final status code, once the request body is
2776        received and processed, unless it terminates the transport
2777        connection prematurely.
2778    </t>
2779    <t> If an origin server receives a request that does not include an
2780        Expect header field with the "100-continue" expectation,
2781        the request includes a request body, and the server responds
2782        with a final status code before reading the entire request body
2783        from the transport connection, then the server &SHOULD-NOT;  close
2784        the transport connection until it has read the entire request,
2785        or until the client closes the connection. Otherwise, the client
2786        might not reliably receive the response message. However, this
2787        requirement is not be construed as preventing a server from
2788        defending itself against denial-of-service attacks, or from
2789        badly broken client implementations.
2790      </t>
2791    </list>
2792</t>
2793<t>
2794   Requirements for HTTP/1.1 proxies:
2795  <list style="symbols">
2796    <t> If a proxy receives a request that includes an Expect header
2797        field with the "100-continue" expectation, and the proxy
2798        either knows that the next-hop server complies with HTTP/1.1 or
2799        higher, or does not know the HTTP version of the next-hop
2800        server, it &MUST; forward the request, including the Expect header
2801        field.
2802    </t>
2803    <t> If the proxy knows that the version of the next-hop server is
2804        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2805        respond with a 417 (Expectation Failed) status code.
2806    </t>
2807    <t> Proxies &SHOULD; maintain a record of the HTTP version
2808        numbers received from recently-referenced next-hop servers.
2809    </t>
2810    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2811        request message was received from an HTTP/1.0 (or earlier)
2812        client and did not include an Expect header field with
2813        the "100-continue" expectation. This requirement overrides the
2814        general rule for forwarding of 1xx responses (see &status-1xx;).
2815    </t>
2816  </list>
2817</t>
2818</section>
2819
2820</section>
2821</section>
2822
2823
2824<section title="Miscellaneous notes that might disappear" anchor="misc">
2825<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2826<t>
2827   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2828</t>
2829</section>
2830
2831<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2832<t>
2833   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2834</t>
2835</section>
2836
2837<section title="Interception of HTTP for access control" anchor="http.intercept">
2838<t>
2839   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2840</t>
2841</section>
2842
2843<section title="Use of HTTP by other protocols" anchor="http.others">
2844<t>
2845   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2846   Extensions of HTTP like WebDAV.</cref>
2847</t>
2848
2849</section>
2850<section title="Use of HTTP by media type specification" anchor="http.media">
2851<t>
2852   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2853</t>
2854</section>
2855</section>
2856
2857<section title="Header Field Definitions" anchor="header.field.definitions">
2858<t>
2859   This section defines the syntax and semantics of HTTP header fields
2860   related to message origination, framing, and routing.
2861</t>
2862<texttable align="left">
2863  <ttcol>Header Field Name</ttcol>
2864  <ttcol>Defined in...</ttcol>
2865 
2866  <c>Connection</c> <c><xref target="header.connection"/></c>
2867  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2868  <c>Host</c> <c><xref target="header.host"/></c>
2869  <c>TE</c> <c><xref target="header.te"/></c>
2870  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2871  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2872  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2873  <c>Via</c> <c><xref target="header.via"/></c>
2874</texttable>
2875
2876<section title="Connection" anchor="header.connection">
2877  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2878  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2879  <x:anchor-alias value="Connection"/>
2880  <x:anchor-alias value="connection-token"/>
2881<t>
2882   The "Connection" header field allows the sender to specify
2883   options that are desired only for that particular connection.
2884   Such connection options &MUST; be removed or replaced before the
2885   message can be forwarded downstream by a proxy or gateway.
2886   This mechanism also allows the sender to indicate which HTTP
2887   header fields used in the message are only intended for the
2888   immediate recipient ("hop-by-hop"), as opposed to all recipients
2889   on the chain ("end-to-end"), enabling the message to be
2890   self-descriptive and allowing future connection-specific extensions
2891   to be deployed in HTTP without fear that they will be blindly
2892   forwarded by previously deployed intermediaries.
2893</t>
2894<t>
2895   The Connection header field's value has the following grammar:
2896</t>
2897<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2898  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2899  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2900</artwork></figure>
2901<t>
2902   A proxy or gateway &MUST; parse a received Connection
2903   header field before a message is forwarded and, for each
2904   connection-token in this field, remove any header field(s) from
2905   the message with the same name as the connection-token, and then
2906   remove the Connection header field itself or replace it with the
2907   sender's own connection options for the forwarded message.
2908</t>
2909<t>
2910   A sender &MUST-NOT; include field-names in the Connection header
2911   field-value for fields that are defined as expressing constraints
2912   for all recipients in the request or response chain, such as the
2913   Cache-Control header field (&header-cache-control;).
2914</t>
2915<t>
2916   The connection options do not have to correspond to a header field
2917   present in the message, since a connection-specific header field
2918   might not be needed if there are no parameters associated with that
2919   connection option.  Recipients that trigger certain connection
2920   behavior based on the presence of connection options &MUST; do so
2921   based on the presence of the connection-token rather than only the
2922   presence of the optional header field.  In other words, if the
2923   connection option is received as a header field but not indicated
2924   within the Connection field-value, then the recipient &MUST; ignore
2925   the connection-specific header field because it has likely been
2926   forwarded by an intermediary that is only partially compliant.
2927</t>
2928<t>
2929   When defining new connection options, specifications ought to
2930   carefully consider existing deployed header fields and ensure
2931   that the new connection-token does not share the same name as
2932   an unrelated header field that might already be deployed.
2933   Defining a new connection-token essentially reserves that potential
2934   field-name for carrying additional information related to the
2935   connection option, since it would be unwise for senders to use
2936   that field-name for anything else.
2937</t>
2938<t>
2939   HTTP/1.1 defines the "close" connection option for the sender to
2940   signal that the connection will be closed after completion of the
2941   response. For example,
2942</t>
2943<figure><artwork type="example">
2944  Connection: close
2945</artwork></figure>
2946<t>
2947   in either the request or the response header fields indicates that
2948   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2949   after the current request/response is complete.
2950</t>
2951<t>
2952   An HTTP/1.1 client that does not support persistent connections &MUST;
2953   include the "close" connection option in every request message.
2954</t>
2955<t>
2956   An HTTP/1.1 server that does not support persistent connections &MUST;
2957   include the "close" connection option in every response message that
2958   does not have a 1xx (Informational) status code.
2959</t>
2960</section>
2961
2962<section title="Content-Length" anchor="header.content-length">
2963  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2964  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2965  <x:anchor-alias value="Content-Length"/>
2966<t>
2967   The "Content-Length" header field indicates the size of the
2968   message-body, in decimal number of octets, for any message other than
2969   a response to a HEAD request or a response with a status code of 304.
2970   In the case of a response to a HEAD request, Content-Length indicates
2971   the size of the payload body (not including any potential transfer-coding)
2972   that would have been sent had the request been a GET.
2973   In the case of a 304 (Not Modified) response to a GET request,
2974   Content-Length indicates the size of the payload body (not including
2975   any potential transfer-coding) that would have been sent in a 200 (OK)
2976   response.
2977</t>
2978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2979  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
2980</artwork></figure>
2981<t>
2982   An example is
2983</t>
2984<figure><artwork type="example">
2985  Content-Length: 3495
2986</artwork></figure>
2987<t>
2988   Implementations &SHOULD; use this field to indicate the message-body
2989   length when no transfer-coding is being applied and the
2990   payload's body length can be determined prior to being transferred.
2991   <xref target="message.body"/> describes how recipients determine the length
2992   of a message-body.
2993</t>
2994<t>
2995   Any Content-Length greater than or equal to zero is a valid value.
2996</t>
2997<t>
2998   Note that the use of this field in HTTP is significantly different from
2999   the corresponding definition in MIME, where it is an optional field
3000   used within the "message/external-body" content-type.
3001</t>
3002</section>
3003
3004<section title="Host" anchor="header.host">
3005  <iref primary="true" item="Host header field" x:for-anchor=""/>
3006  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3007  <x:anchor-alias value="Host"/>
3008<t>
3009   The "Host" header field in a request provides the host and port
3010   information from the target resource's URI, enabling the origin
3011   server to distinguish between resources while servicing requests
3012   for multiple host names on a single IP address.  Since the Host
3013   field-value is critical information for handling a request, it
3014   &SHOULD; be sent as the first header field following the Request-Line.
3015</t>
3016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3017  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3018</artwork></figure>
3019<t>
3020   A client &MUST; send a Host header field in all HTTP/1.1 request
3021   messages.  If the target resource's URI includes an authority
3022   component, then the Host field-value &MUST; be identical to that
3023   authority component after excluding any userinfo (<xref target="http.uri"/>).
3024   If the authority component is missing or undefined for the target
3025   resource's URI, then the Host header field &MUST; be sent with an
3026   empty field-value.
3027</t>
3028<t>
3029   For example, a GET request to the origin server for
3030   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3031</t>
3032<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3033GET /pub/WWW/ HTTP/1.1
3034Host: www.example.org
3035</artwork></figure>
3036<t>
3037   The Host header field &MUST; be sent in an HTTP/1.1 request even
3038   if the request-target is in the form of an absolute-URI, since this
3039   allows the Host information to be forwarded through ancient HTTP/1.0
3040   proxies that might not have implemented Host.
3041</t>
3042<t>
3043   When an HTTP/1.1 proxy receives a request with a request-target in
3044   the form of an absolute-URI, the proxy &MUST; ignore the received
3045   Host header field (if any) and instead replace it with the host
3046   information of the request-target.  When a proxy forwards a request,
3047   it &MUST; generate the Host header field based on the received
3048   absolute-URI rather than the received Host.
3049</t>
3050<t>
3051   Since the Host header field acts as an application-level routing
3052   mechanism, it is a frequent target for malware seeking to poison
3053   a shared cache or redirect a request to an unintended server.
3054   An interception proxy is particularly vulnerable if it relies on
3055   the Host header field value for redirecting requests to internal
3056   servers, or for use as a cache key in a shared cache, without
3057   first verifying that the intercepted connection is targeting a
3058   valid IP address for that host.
3059</t>
3060<t>
3061   A server &MUST; respond with a 400 (Bad Request) status code to
3062   any HTTP/1.1 request message that lacks a Host header field and
3063   to any request message that contains more than one Host header field
3064   or a Host header field with an invalid field-value.
3065</t>
3066<t>
3067   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3068   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3069   for other requirements relating to Host.
3070</t>
3071</section>
3072
3073<section title="TE" anchor="header.te">
3074  <iref primary="true" item="TE header field" x:for-anchor=""/>
3075  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3076  <x:anchor-alias value="TE"/>
3077  <x:anchor-alias value="t-codings"/>
3078  <x:anchor-alias value="te-params"/>
3079  <x:anchor-alias value="te-ext"/>
3080<t>
3081   The "TE" header field indicates what extension transfer-codings
3082   it is willing to accept in the response, and whether or not it is
3083   willing to accept trailer fields in a chunked transfer-coding.
3084</t>
3085<t>
3086   Its value consists of the keyword "trailers" and/or a comma-separated
3087   list of extension transfer-coding names with optional accept
3088   parameters (as described in <xref target="transfer.codings"/>).
3089</t>
3090<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"/>
3091  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3092  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3093  <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> )
3094  <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> ]
3095</artwork></figure>
3096<t>
3097   The presence of the keyword "trailers" indicates that the client is
3098   willing to accept trailer fields in a chunked transfer-coding, as
3099   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3100   transfer-coding values even though it does not itself represent a
3101   transfer-coding.
3102</t>
3103<t>
3104   Examples of its use are:
3105</t>
3106<figure><artwork type="example">
3107  TE: deflate
3108  TE:
3109  TE: trailers, deflate;q=0.5
3110</artwork></figure>
3111<t>
3112   The TE header field only applies to the immediate connection.
3113   Therefore, the keyword &MUST; be supplied within a Connection header
3114   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3115</t>
3116<t>
3117   A server tests whether a transfer-coding is acceptable, according to
3118   a TE field, using these rules:
3119  <list style="numbers">
3120    <x:lt>
3121      <t>The "chunked" transfer-coding is always acceptable. If the
3122         keyword "trailers" is listed, the client indicates that it is
3123         willing to accept trailer fields in the chunked response on
3124         behalf of itself and any downstream clients. The implication is
3125         that, if given, the client is stating that either all
3126         downstream clients are willing to accept trailer fields in the
3127         forwarded response, or that it will attempt to buffer the
3128         response on behalf of downstream recipients.
3129      </t><t>
3130         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3131         chunked response such that a client can be assured of buffering
3132         the entire response.</t>
3133    </x:lt>
3134    <x:lt>
3135      <t>If the transfer-coding being tested is one of the transfer-codings
3136         listed in the TE field, then it is acceptable unless it
3137         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3138         qvalue of 0 means "not acceptable".)</t>
3139    </x:lt>
3140    <x:lt>
3141      <t>If multiple transfer-codings are acceptable, then the
3142         acceptable transfer-coding with the highest non-zero qvalue is
3143         preferred.  The "chunked" transfer-coding always has a qvalue
3144         of 1.</t>
3145    </x:lt>
3146  </list>
3147</t>
3148<t>
3149   If the TE field-value is empty or if no TE field is present, the only
3150   transfer-coding is "chunked". A message with no transfer-coding is
3151   always acceptable.
3152</t>
3153</section>
3154
3155<section title="Trailer" anchor="header.trailer">
3156  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3157  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3158  <x:anchor-alias value="Trailer"/>
3159<t>
3160   The "Trailer" header field indicates that the given set of
3161   header fields is present in the trailer of a message encoded with
3162   chunked transfer-coding.
3163</t>
3164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3165  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3166</artwork></figure>
3167<t>
3168   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3169   message using chunked transfer-coding with a non-empty trailer. Doing
3170   so allows the recipient to know which header fields to expect in the
3171   trailer.
3172</t>
3173<t>
3174   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3175   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3176   trailer fields in a "chunked" transfer-coding.
3177</t>
3178<t>
3179   Message header fields listed in the Trailer header field &MUST-NOT;
3180   include the following header fields:
3181  <list style="symbols">
3182    <t>Transfer-Encoding</t>
3183    <t>Content-Length</t>
3184    <t>Trailer</t>
3185  </list>
3186</t>
3187</section>
3188
3189<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3190  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3191  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3192  <x:anchor-alias value="Transfer-Encoding"/>
3193<t>
3194   The "Transfer-Encoding" header field indicates what transfer-codings
3195   (if any) have been applied to the message body. It differs from
3196   Content-Encoding (&content-codings;) in that transfer-codings are a property
3197   of the message (and therefore are removed by intermediaries), whereas
3198   content-codings are not.
3199</t>
3200<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3201  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3202</artwork></figure>
3203<t>
3204   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3205</t>
3206<figure><artwork type="example">
3207  Transfer-Encoding: chunked
3208</artwork></figure>
3209<t>
3210   If multiple encodings have been applied to a representation, the transfer-codings
3211   &MUST; be listed in the order in which they were applied.
3212   Additional information about the encoding parameters &MAY; be provided
3213   by other header fields not defined by this specification.
3214</t>
3215<t>
3216   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3217   header field.
3218</t>
3219</section>
3220
3221<section title="Upgrade" anchor="header.upgrade">
3222  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3223  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3224  <x:anchor-alias value="Upgrade"/>
3225<t>
3226   The "Upgrade" header field allows the client to specify what
3227   additional communication protocols it would like to use, if the server
3228   chooses to switch protocols. Servers can use it to indicate what protocols
3229   they are willing to switch to.
3230</t>
3231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3232  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3233</artwork></figure>
3234<t>
3235   For example,
3236</t>
3237<figure><artwork type="example">
3238  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3239</artwork></figure>
3240<t>
3241   The Upgrade header field is intended to provide a simple mechanism
3242   for transition from HTTP/1.1 to some other, incompatible protocol. It
3243   does so by allowing the client to advertise its desire to use another
3244   protocol, such as a later version of HTTP with a higher major version
3245   number, even though the current request has been made using HTTP/1.1.
3246   This eases the difficult transition between incompatible protocols by
3247   allowing the client to initiate a request in the more commonly
3248   supported protocol while indicating to the server that it would like
3249   to use a "better" protocol if available (where "better" is determined
3250   by the server, possibly according to the nature of the request method
3251   or target resource).
3252</t>
3253<t>
3254   The Upgrade header field only applies to switching application-layer
3255   protocols upon the existing transport-layer connection. Upgrade
3256   cannot be used to insist on a protocol change; its acceptance and use
3257   by the server is optional. The capabilities and nature of the
3258   application-layer communication after the protocol change is entirely
3259   dependent upon the new protocol chosen, although the first action
3260   after changing the protocol &MUST; be a response to the initial HTTP
3261   request containing the Upgrade header field.
3262</t>
3263<t>
3264   The Upgrade header field only applies to the immediate connection.
3265   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3266   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3267   HTTP/1.1 message.
3268</t>
3269<t>
3270   The Upgrade header field cannot be used to indicate a switch to a
3271   protocol on a different connection. For that purpose, it is more
3272   appropriate to use a 3xx redirection response (&status-3xx;).
3273</t>
3274<t>
3275   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3276   Protocols) responses to indicate which protocol(s) are being switched to,
3277   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3278   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3279   response to indicate that they are willing to upgrade to one of the
3280   specified protocols.
3281</t>
3282<t>
3283   This specification only defines the protocol name "HTTP" for use by
3284   the family of Hypertext Transfer Protocols, as defined by the HTTP
3285   version rules of <xref target="http.version"/> and future updates to this
3286   specification. Additional tokens can be registered with IANA using the
3287   registration procedure defined below. 
3288</t>
3289
3290<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3291<t>
3292   The HTTP Upgrade Token Registry defines the name space for product
3293   tokens used to identify protocols in the Upgrade header field.
3294   Each registered token is associated with contact information and
3295   an optional set of specifications that details how the connection
3296   will be processed after it has been upgraded.
3297</t>
3298<t>
3299   Registrations are allowed on a First Come First Served basis as
3300   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3301   specifications need not be IETF documents or be subject to IESG review.
3302   Registrations are subject to the following rules:
3303  <list style="numbers">
3304    <t>A token, once registered, stays registered forever.</t>
3305    <t>The registration &MUST; name a responsible party for the
3306       registration.</t>
3307    <t>The registration &MUST; name a point of contact.</t>
3308    <t>The registration &MAY; name a set of specifications associated with that
3309       token. Such specifications need not be publicly available.</t>
3310    <t>The responsible party &MAY; change the registration at any time.
3311       The IANA will keep a record of all such changes, and make them
3312       available upon request.</t>
3313    <t>The responsible party for the first registration of a "product"
3314       token &MUST; approve later registrations of a "version" token
3315       together with that "product" token before they can be registered.</t>
3316    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3317       for a token. This will normally only be used in the case when a
3318       responsible party cannot be contacted.</t>
3319  </list>
3320</t>
3321</section>
3322
3323
3324</section>
3325
3326<section title="Via" anchor="header.via">
3327  <iref primary="true" item="Via header field" x:for-anchor=""/>
3328  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3329  <x:anchor-alias value="protocol-name"/>
3330  <x:anchor-alias value="protocol-version"/>
3331  <x:anchor-alias value="pseudonym"/>
3332  <x:anchor-alias value="received-by"/>
3333  <x:anchor-alias value="received-protocol"/>
3334  <x:anchor-alias value="Via"/>
3335<t>
3336   The "Via" header field &MUST; be sent by a proxy or gateway to
3337   indicate the intermediate protocols and recipients between the user
3338   agent and the server on requests, and between the origin server and
3339   the client on responses. It is analogous to the "Received" field
3340   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3341   and is intended to be used for tracking message forwards,
3342   avoiding request loops, and identifying the protocol capabilities of
3343   all senders along the request/response chain.
3344</t>
3345<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"/>
3346  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3347                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3348  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3349  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3350  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3351  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3352  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3353</artwork></figure>
3354<t>
3355   The received-protocol indicates the protocol version of the message
3356   received by the server or client along each segment of the
3357   request/response chain. The received-protocol version is appended to
3358   the Via field value when the message is forwarded so that information
3359   about the protocol capabilities of upstream applications remains
3360   visible to all recipients.
3361</t>
3362<t>
3363   The protocol-name is excluded if and only if it would be "HTTP". The
3364   received-by field is normally the host and optional port number of a
3365   recipient server or client that subsequently forwarded the message.
3366   However, if the real host is considered to be sensitive information,
3367   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3368   be assumed to be the default port of the received-protocol.
3369</t>
3370<t>
3371   Multiple Via field values represent each proxy or gateway that has
3372   forwarded the message. Each recipient &MUST; append its information
3373   such that the end result is ordered according to the sequence of
3374   forwarding applications.
3375</t>
3376<t>
3377   Comments &MAY; be used in the Via header field to identify the software
3378   of each recipient, analogous to the User-Agent and Server header fields.
3379   However, all comments in the Via field are optional and &MAY; be removed
3380   by any recipient prior to forwarding the message.
3381</t>
3382<t>
3383   For example, a request message could be sent from an HTTP/1.0 user
3384   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3385   forward the request to a public proxy at p.example.net, which completes
3386   the request by forwarding it to the origin server at www.example.com.
3387   The request received by www.example.com would then have the following
3388   Via header field:
3389</t>
3390<figure><artwork type="example">
3391  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3392</artwork></figure>
3393<t>
3394   A proxy or gateway used as a portal through a network firewall
3395   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3396   region unless it is explicitly enabled to do so. If not enabled, the
3397   received-by host of any host behind the firewall &SHOULD; be replaced
3398   by an appropriate pseudonym for that host.
3399</t>
3400<t>
3401   For organizations that have strong privacy requirements for hiding
3402   internal structures, a proxy or gateway &MAY; combine an ordered
3403   subsequence of Via header field entries with identical received-protocol
3404   values into a single such entry. For example,
3405</t>
3406<figure><artwork type="example">
3407  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3408</artwork></figure>
3409<t>
3410  could be collapsed to
3411</t>
3412<figure><artwork type="example">
3413  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3414</artwork></figure>
3415<t>
3416   Senders &SHOULD-NOT; combine multiple entries unless they are all
3417   under the same organizational control and the hosts have already been
3418   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3419   have different received-protocol values.
3420</t>
3421</section>
3422
3423</section>
3424
3425<section title="IANA Considerations" anchor="IANA.considerations">
3426
3427<section title="Header Field Registration" anchor="header.field.registration">
3428<t>
3429   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3430   with the permanent registrations below (see <xref target="RFC3864"/>):
3431</t>
3432<?BEGININC p1-messaging.iana-headers ?>
3433<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3434<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3435   <ttcol>Header Field Name</ttcol>
3436   <ttcol>Protocol</ttcol>
3437   <ttcol>Status</ttcol>
3438   <ttcol>Reference</ttcol>
3439
3440   <c>Connection</c>
3441   <c>http</c>
3442   <c>standard</c>
3443   <c>
3444      <xref target="header.connection"/>
3445   </c>
3446   <c>Content-Length</c>
3447   <c>http</c>
3448   <c>standard</c>
3449   <c>
3450      <xref target="header.content-length"/>
3451   </c>
3452   <c>Host</c>
3453   <c>http</c>
3454   <c>standard</c>
3455   <c>
3456      <xref target="header.host"/>
3457   </c>
3458   <c>TE</c>
3459   <c>http</c>
3460   <c>standard</c>
3461   <c>
3462      <xref target="header.te"/>
3463   </c>
3464   <c>Trailer</c>
3465   <c>http</c>
3466   <c>standard</c>
3467   <c>
3468      <xref target="header.trailer"/>
3469   </c>
3470   <c>Transfer-Encoding</c>
3471   <c>http</c>
3472   <c>standard</c>
3473   <c>
3474      <xref target="header.transfer-encoding"/>
3475   </c>
3476   <c>Upgrade</c>
3477   <c>http</c>
3478   <c>standard</c>
3479   <c>
3480      <xref target="header.upgrade"/>
3481   </c>
3482   <c>Via</c>
3483   <c>http</c>
3484   <c>standard</c>
3485   <c>
3486      <xref target="header.via"/>
3487   </c>
3488</texttable>
3489<!--(END)-->
3490<?ENDINC p1-messaging.iana-headers ?>
3491<t>
3492   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3493   HTTP header field would be in conflict with the use of the "close" connection
3494   option for the "Connection" header field (<xref target="header.connection"/>).
3495</t>
3496<texttable align="left" suppress-title="true">
3497   <ttcol>Header Field Name</ttcol>
3498   <ttcol>Protocol</ttcol>
3499   <ttcol>Status</ttcol>
3500   <ttcol>Reference</ttcol>
3501
3502   <c>Close</c>
3503   <c>http</c>
3504   <c>reserved</c>
3505   <c>
3506      <xref target="header.field.registration"/>
3507   </c>
3508</texttable>
3509<t>
3510   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3511</t>
3512</section>
3513
3514<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3515<t>
3516   The entries for the "http" and "https" URI Schemes in the registry located at
3517   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3518   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3519   and <xref target="https.uri" format="counter"/> of this document
3520   (see <xref target="RFC4395"/>).
3521</t>
3522</section>
3523
3524<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3525<t>
3526   This document serves as the specification for the Internet media types
3527   "message/http" and "application/http". The following is to be registered with
3528   IANA (see <xref target="RFC4288"/>).
3529</t>
3530<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3531<iref item="Media Type" subitem="message/http" primary="true"/>
3532<iref item="message/http Media Type" primary="true"/>
3533<t>
3534   The message/http type can be used to enclose a single HTTP request or
3535   response message, provided that it obeys the MIME restrictions for all
3536   "message" types regarding line length and encodings.
3537</t>
3538<t>
3539  <list style="hanging" x:indent="12em">
3540    <t hangText="Type name:">
3541      message
3542    </t>
3543    <t hangText="Subtype name:">
3544      http
3545    </t>
3546    <t hangText="Required parameters:">
3547      none
3548    </t>
3549    <t hangText="Optional parameters:">
3550      version, msgtype
3551      <list style="hanging">
3552        <t hangText="version:">
3553          The HTTP-Version number of the enclosed message
3554          (e.g., "1.1"). If not present, the version can be
3555          determined from the first line of the body.
3556        </t>
3557        <t hangText="msgtype:">
3558          The message type &mdash; "request" or "response". If not
3559          present, the type can be determined from the first
3560          line of the body.
3561        </t>
3562      </list>
3563    </t>
3564    <t hangText="Encoding considerations:">
3565      only "7bit", "8bit", or "binary" are permitted
3566    </t>
3567    <t hangText="Security considerations:">
3568      none
3569    </t>
3570    <t hangText="Interoperability considerations:">
3571      none
3572    </t>
3573    <t hangText="Published specification:">
3574      This specification (see <xref target="internet.media.type.message.http"/>).
3575    </t>
3576    <t hangText="Applications that use this media type:">
3577    </t>
3578    <t hangText="Additional information:">
3579      <list style="hanging">
3580        <t hangText="Magic number(s):">none</t>
3581        <t hangText="File extension(s):">none</t>
3582        <t hangText="Macintosh file type code(s):">none</t>
3583      </list>
3584    </t>
3585    <t hangText="Person and email address to contact for further information:">
3586      See Authors Section.
3587    </t>
3588    <t hangText="Intended usage:">
3589      COMMON
3590    </t>
3591    <t hangText="Restrictions on usage:">
3592      none
3593    </t>
3594    <t hangText="Author/Change controller:">
3595      IESG
3596    </t>
3597  </list>
3598</t>
3599</section>
3600<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3601<iref item="Media Type" subitem="application/http" primary="true"/>
3602<iref item="application/http Media Type" primary="true"/>
3603<t>
3604   The application/http type can be used to enclose a pipeline of one or more
3605   HTTP request or response messages (not intermixed).
3606</t>
3607<t>
3608  <list style="hanging" x:indent="12em">
3609    <t hangText="Type name:">
3610      application
3611    </t>
3612    <t hangText="Subtype name:">
3613      http
3614    </t>
3615    <t hangText="Required parameters:">
3616      none
3617    </t>
3618    <t hangText="Optional parameters:">
3619      version, msgtype
3620      <list style="hanging">
3621        <t hangText="version:">
3622          The HTTP-Version number of the enclosed messages
3623          (e.g., "1.1"). If not present, the version can be
3624          determined from the first line of the body.
3625        </t>
3626        <t hangText="msgtype:">
3627          The message type &mdash; "request" or "response". If not
3628          present, the type can be determined from the first
3629          line of the body.
3630        </t>
3631      </list>
3632    </t>
3633    <t hangText="Encoding considerations:">
3634      HTTP messages enclosed by this type
3635      are in "binary" format; use of an appropriate
3636      Content-Transfer-Encoding is required when
3637      transmitted via E-mail.
3638    </t>
3639    <t hangText="Security considerations:">
3640      none
3641    </t>
3642    <t hangText="Interoperability considerations:">
3643      none
3644    </t>
3645    <t hangText="Published specification:">
3646      This specification (see <xref target="internet.media.type.application.http"/>).
3647    </t>
3648    <t hangText="Applications that use this media type:">
3649    </t>
3650    <t hangText="Additional information:">
3651      <list style="hanging">
3652        <t hangText="Magic number(s):">none</t>
3653        <t hangText="File extension(s):">none</t>
3654        <t hangText="Macintosh file type code(s):">none</t>
3655      </list>
3656    </t>
3657    <t hangText="Person and email address to contact for further information:">
3658      See Authors Section.
3659    </t>
3660    <t hangText="Intended usage:">
3661      COMMON
3662    </t>
3663    <t hangText="Restrictions on usage:">
3664      none
3665    </t>
3666    <t hangText="Author/Change controller:">
3667      IESG
3668    </t>
3669  </list>
3670</t>
3671</section>
3672</section>
3673
3674<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3675<t>
3676   The registration procedure for HTTP Transfer Codings is now defined by
3677   <xref target="transfer.coding.registry"/> of this document.
3678</t>
3679<t>
3680   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3681   shall be updated with the registrations below:
3682</t>
3683<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3684   <ttcol>Name</ttcol>
3685   <ttcol>Description</ttcol>
3686   <ttcol>Reference</ttcol>
3687   <c>chunked</c>
3688   <c>Transfer in a series of chunks</c>
3689   <c>
3690      <xref target="chunked.encoding"/>
3691   </c>
3692   <c>compress</c>
3693   <c>UNIX "compress" program method</c>
3694   <c>
3695      <xref target="compress.coding"/>
3696   </c>
3697   <c>deflate</c>
3698   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3699   the "zlib" data format (<xref target="RFC1950"/>)
3700   </c>
3701   <c>
3702      <xref target="deflate.coding"/>
3703   </c>
3704   <c>gzip</c>
3705   <c>Same as GNU zip <xref target="RFC1952"/></c>
3706   <c>
3707      <xref target="gzip.coding"/>
3708   </c>
3709</texttable>
3710</section>
3711
3712<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3713<t>
3714   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3715   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3716   by <xref target="upgrade.token.registry"/> of this document.
3717</t>
3718<t>
3719   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3720   shall be updated with the registration below:
3721</t>
3722<texttable align="left" suppress-title="true">
3723   <ttcol>Value</ttcol>
3724   <ttcol>Description</ttcol>
3725   <ttcol>Reference</ttcol>
3726
3727   <c>HTTP</c>
3728   <c>Hypertext Transfer Protocol</c> 
3729   <c><xref target="http.version"/> of this specification</c>
3730
3731</texttable>
3732</section>
3733
3734</section>
3735
3736<section title="Security Considerations" anchor="security.considerations">
3737<t>
3738   This section is meant to inform application developers, information
3739   providers, and users of the security limitations in HTTP/1.1 as
3740   described by this document. The discussion does not include
3741   definitive solutions to the problems revealed, though it does make
3742   some suggestions for reducing security risks.
3743</t>
3744
3745<section title="Personal Information" anchor="personal.information">
3746<t>
3747   HTTP clients are often privy to large amounts of personal information
3748   (e.g., the user's name, location, mail address, passwords, encryption
3749   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3750   leakage of this information.
3751   We very strongly recommend that a convenient interface be provided
3752   for the user to control dissemination of such information, and that
3753   designers and implementors be particularly careful in this area.
3754   History shows that errors in this area often create serious security
3755   and/or privacy problems and generate highly adverse publicity for the
3756   implementor's company.
3757</t>
3758</section>
3759
3760<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3761<t>
3762   A server is in the position to save personal data about a user's
3763   requests which might identify their reading patterns or subjects of
3764   interest. This information is clearly confidential in nature and its
3765   handling can be constrained by law in certain countries. People using
3766   HTTP to provide data are responsible for ensuring that
3767   such material is not distributed without the permission of any
3768   individuals that are identifiable by the published results.
3769</t>
3770</section>
3771
3772<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3773<t>
3774   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3775   the documents returned by HTTP requests to be only those that were
3776   intended by the server administrators. If an HTTP server translates
3777   HTTP URIs directly into file system calls, the server &MUST; take
3778   special care not to serve files that were not intended to be
3779   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3780   other operating systems use ".." as a path component to indicate a
3781   directory level above the current one. On such a system, an HTTP
3782   server &MUST; disallow any such construct in the request-target if it
3783   would otherwise allow access to a resource outside those intended to
3784   be accessible via the HTTP server. Similarly, files intended for
3785   reference only internally to the server (such as access control
3786   files, configuration files, and script code) &MUST; be protected from
3787   inappropriate retrieval, since they might contain sensitive
3788   information. Experience has shown that minor bugs in such HTTP server
3789   implementations have turned into security risks.
3790</t>
3791</section>
3792
3793<section title="DNS-related Attacks" anchor="dns.related.attacks">
3794<t>
3795   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3796   generally prone to security attacks based on the deliberate misassociation
3797   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3798   cautious in assuming the validity of an IP number/DNS name association unless
3799   the response is protected by DNSSec (<xref target="RFC4033"/>).
3800</t>
3801</section>
3802
3803<section title="Proxies and Caching" anchor="attack.proxies">
3804<t>
3805   By their very nature, HTTP proxies are men-in-the-middle, and
3806   represent an opportunity for man-in-the-middle attacks. Compromise of
3807   the systems on which the proxies run can result in serious security
3808   and privacy problems. Proxies have access to security-related
3809   information, personal information about individual users and
3810   organizations, and proprietary information belonging to users and
3811   content providers. A compromised proxy, or a proxy implemented or
3812   configured without regard to security and privacy considerations,
3813   might be used in the commission of a wide range of potential attacks.
3814</t>
3815<t>
3816   Proxy operators need to protect the systems on which proxies run as
3817   they would protect any system that contains or transports sensitive
3818   information. In particular, log information gathered at proxies often
3819   contains highly sensitive personal information, and/or information
3820   about organizations. Log information needs to be carefully guarded, and
3821   appropriate guidelines for use need to be developed and followed.
3822   (<xref target="abuse.of.server.log.information"/>).
3823</t>
3824<t>
3825   Proxy implementors need to consider the privacy and security
3826   implications of their design and coding decisions, and of the
3827   configuration options they provide to proxy operators (especially the
3828   default configuration).
3829</t>
3830<t>
3831   Users of a proxy need to be aware that proxies are no trustworthier than
3832   the people who run them; HTTP itself cannot solve this problem.
3833</t>
3834<t>
3835   The judicious use of cryptography, when appropriate, might suffice to
3836   protect against a broad range of security and privacy attacks. Such
3837   cryptography is beyond the scope of the HTTP/1.1 specification.
3838</t>
3839</section>
3840
3841<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3842<t>
3843   Because HTTP uses mostly textual, character-delimited fields, attackers can
3844   overflow buffers in implementations, and/or perform a Denial of Service
3845   against implementations that accept fields with unlimited lengths.
3846</t>
3847<t>
3848   To promote interoperability, this specification makes specific
3849   recommendations for size limits on request-targets (<xref target="request-target"/>)
3850   and blocks of header fields (<xref target="header.fields"/>). These are
3851   minimum recommendations, chosen to be supportable even by implementations
3852   with limited resources; it is expected that most implementations will choose
3853   substantially higher limits.
3854</t>
3855<t>
3856   This specification also provides a way for servers to reject messages that
3857   have request-targets that are too long (&status-414;) or request entities
3858   that are too large (&status-4xx;).
3859</t>
3860<t>
3861   Other fields (including but not limited to request methods, response status
3862   phrases, header field-names, and body chunks) &SHOULD; be limited by
3863   implementations carefully, so as to not impede interoperability.
3864</t>
3865</section>
3866
3867<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3868<t>
3869   They exist. They are hard to defend against. Research continues.
3870   Beware.
3871</t>
3872</section>
3873</section>
3874
3875<section title="Acknowledgments" anchor="acks">
3876<t>
3877   This document revision builds on the work that went into
3878   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3879   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3880   acknowledgements.
3881</t>
3882<t>
3883   Since 1999, many contributors have helped by reporting bugs, asking
3884   smart questions, drafting and reviewing text, and discussing open issues:
3885</t>
3886<?BEGININC acks ?>
3887<t>Adam Barth,
3888Adam Roach,
3889Addison Phillips,
3890Adrian Chadd,
3891Adrien de Croy,
3892Alan Ford,
3893Alan Ruttenberg,
3894Albert Lunde,
3895Alex Rousskov,
3896Alexey Melnikov,
3897Alisha Smith,
3898Amichai Rothman,
3899Amit Klein,
3900Amos Jeffries,
3901Andreas Maier,
3902Andreas Petersson,
3903Anne van Kesteren,
3904Anthony Bryan,
3905Asbjorn Ulsberg,
3906Balachander Krishnamurthy,
3907Barry Leiba,
3908Ben Laurie,
3909Benjamin Niven-Jenkins,
3910Bil Corry,
3911Bill Burke,
3912Bjoern Hoehrmann,
3913Bob Scheifler,
3914Boris Zbarsky,
3915Brett Slatkin,
3916Brian Kell,
3917Brian McBarron,
3918Brian Pane,
3919Brian Smith,
3920Bryce Nesbitt,
3921Carl Kugler,
3922Charles Fry,
3923Chris Newman,
3924Cyrus Daboo,
3925Dale Robert Anderson,
3926Dan Winship,
3927Daniel Stenberg,
3928Dave Cridland,
3929Dave Crocker,
3930Dave Kristol,
3931David Booth,
3932David Singer,
3933David W. Morris,
3934Diwakar Shetty,
3935Drummond Reed,
3936Duane Wessels,
3937Edward Lee,
3938Eliot Lear,
3939Eran Hammer-Lahav,
3940Eric D. Williams,
3941Eric J. Bowman,
3942Eric Lawrence,
3943Erik Aronesty,
3944Florian Weimer,
3945Frank Ellermann,
3946Fred Bohle,
3947Geoffrey Sneddon,
3948Gervase Markham,
3949Greg Wilkins,
3950Harald Tveit Alvestrand,
3951Harry Halpin,
3952Helge Hess,
3953Henrik Nordstrom,
3954Henry S. Thompson,
3955Henry Story,
3956Howard Melman,
3957Hugo Haas,
3958Ian Hickson,
3959Ingo Struck,
3960J. Ross Nicoll,
3961James H. Manger,
3962James Lacey,
3963James M. Snell,
3964Jamie Lokier,
3965Jan Algermissen,
3966Jeff Hodges (for coming up with the term 'effective Request-URI'),
3967Jeff Walden,
3968Jim Luther,
3969Joe D. Williams,
3970Joe Gregorio,
3971Joe Orton,
3972John C. Klensin,
3973John C. Mallery,
3974John Cowan,
3975John Kemp,
3976John Panzer,
3977John Schneider,
3978John Stracke,
3979Jonas Sicking,
3980Jonathan Moore,
3981Jonathan Rees,
3982Jordi Ros,
3983Joris Dobbelsteen,
3984Josh Cohen,
3985Julien Pierre,
3986Jungshik Shin,
3987Justin Chapweske,
3988Justin Erenkrantz,
3989Justin James,
3990Kalvinder Singh,
3991Karl Dubost,
3992Keith Hoffman,
3993Keith Moore,
3994Koen Holtman,
3995Konstantin Voronkov,
3996Kris Zyp,
3997Lisa Dusseault,
3998Maciej Stachowiak,
3999Marc Schneider,
4000Marc Slemko,
4001Mark Baker,
4002Mark Nottingham (Working Group chair),
4003Mark Pauley,
4004Martin J. Duerst,
4005Martin Thomson,
4006Matt Lynch,
4007Matthew Cox,
4008Max Clark,
4009Michael Burrows,
4010Michael Hausenblas,
4011Mike Amundsen,
4012Mike Kelly,
4013Mike Schinkel,
4014Miles Sabin,
4015Mykyta Yevstifeyev,
4016Nathan Rixham,
4017Nicholas Shanks,
4018Nico Williams,
4019Nicolas Alvarez,
4020Noah Slater,
4021Pablo Castro,
4022Pat Hayes,
4023Patrick R. McManus,
4024Paul E. Jones,
4025Paul Hoffman,
4026Paul Marquess,
4027Peter Saint-Andre,
4028Peter Watkins,
4029Phil Archer,
4030Phillip Hallam-Baker,
4031Poul-Henning Kamp,
4032Preethi Natarajan,
4033Reto Bachmann-Gmuer,
4034Richard Cyganiak,
4035Robert Brewer,
4036Robert Collins,
4037Robert O'Callahan,
4038Robert Olofsson,
4039Robert Sayre,
4040Robert Siemer,
4041Robert de Wilde,
4042Roberto Javier Godoy,
4043Ronny Widjaja,
4044S. Mike Dierken,
4045Salvatore Loreto,
4046Sam Johnston,
4047Sam Ruby,
4048Scott Lawrence (for maintaining the original issues list),
4049Sean B. Palmer,
4050Shane McCarron,
4051Stefan Eissing,
4052Stefan Tilkov,
4053Stefanos Harhalakis,
4054Stephane Bortzmeyer,
4055Stuart Williams,
4056Subbu Allamaraju,
4057Sylvain Hellegouarch,
4058Tapan Divekar,
4059Thomas Broyer,
4060Thomas Nordin,
4061Thomas Roessler,
4062Tim Morgan,
4063Tim Olsen,
4064Travis Snoozy,
4065Tyler Close,
4066Vincent Murphy,
4067Wenbo Zhu,
4068Werner Baumann,
4069Wilbur Streett,
4070Wilfredo Sanchez Vega,
4071William A. Rowe Jr.,
4072William Chan,
4073Willy Tarreau,
4074Xiaoshu Wang,
4075Yaron Goland,
4076Yngve Nysaeter Pettersen,
4077Yogesh Bang,
4078Yutaka Oiwa, and
4079Zed A. Shaw.
4080</t>
4081<?ENDINC acks ?>
4082</section>
4083
4084</middle>
4085<back>
4086
4087<references title="Normative References">
4088
4089<reference anchor="ISO-8859-1">
4090  <front>
4091    <title>
4092     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4093    </title>
4094    <author>
4095      <organization>International Organization for Standardization</organization>
4096    </author>
4097    <date year="1998"/>
4098  </front>
4099  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4100</reference>
4101
4102<reference anchor="Part2">
4103  <front>
4104    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4105    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4106      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4107      <address><email>fielding@gbiv.com</email></address>
4108    </author>
4109    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4110      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4111      <address><email>jg@freedesktop.org</email></address>
4112    </author>
4113    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4114      <organization abbrev="HP">Hewlett-Packard Company</organization>
4115      <address><email>JeffMogul@acm.org</email></address>
4116    </author>
4117    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4119      <address><email>henrikn@microsoft.com</email></address>
4120    </author>
4121    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4122      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4123      <address><email>LMM@acm.org</email></address>
4124    </author>
4125    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4126      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4127      <address><email>paulle@microsoft.com</email></address>
4128    </author>
4129    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4130      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4131      <address><email>timbl@w3.org</email></address>
4132    </author>
4133    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4134      <organization abbrev="W3C">World Wide Web Consortium</organization>
4135      <address><email>ylafon@w3.org</email></address>
4136    </author>
4137    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4138      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4139      <address><email>julian.reschke@greenbytes.de</email></address>
4140    </author>
4141    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4142  </front>
4143  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4144  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4145</reference>
4146
4147<reference anchor="Part3">
4148  <front>
4149    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4150    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4151      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4152      <address><email>fielding@gbiv.com</email></address>
4153    </author>
4154    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4155      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4156      <address><email>jg@freedesktop.org</email></address>
4157    </author>
4158    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4159      <organization abbrev="HP">Hewlett-Packard Company</organization>
4160      <address><email>JeffMogul@acm.org</email></address>
4161    </author>
4162    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4164      <address><email>henrikn@microsoft.com</email></address>
4165    </author>
4166    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4167      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4168      <address><email>LMM@acm.org</email></address>
4169    </author>
4170    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4171      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4172      <address><email>paulle@microsoft.com</email></address>
4173    </author>
4174    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4175      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4176      <address><email>timbl@w3.org</email></address>
4177    </author>
4178    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4179      <organization abbrev="W3C">World Wide Web Consortium</organization>
4180      <address><email>ylafon@w3.org</email></address>
4181    </author>
4182    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4183      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4184      <address><email>julian.reschke@greenbytes.de</email></address>
4185    </author>
4186    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4187  </front>
4188  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4189  <x:source href="p3-payload.xml" basename="p3-payload"/>
4190</reference>
4191
4192<reference anchor="Part6">
4193  <front>
4194    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4195    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4196      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4197      <address><email>fielding@gbiv.com</email></address>
4198    </author>
4199    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4200      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4201      <address><email>jg@freedesktop.org</email></address>
4202    </author>
4203    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4204      <organization abbrev="HP">Hewlett-Packard Company</organization>
4205      <address><email>JeffMogul@acm.org</email></address>
4206    </author>
4207    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4208      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4209      <address><email>henrikn@microsoft.com</email></address>
4210    </author>
4211    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4212      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4213      <address><email>LMM@acm.org</email></address>
4214    </author>
4215    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4216      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4217      <address><email>paulle@microsoft.com</email></address>
4218    </author>
4219    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4220      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4221      <address><email>timbl@w3.org</email></address>
4222    </author>
4223    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4224      <organization abbrev="W3C">World Wide Web Consortium</organization>
4225      <address><email>ylafon@w3.org</email></address>
4226    </author>
4227    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4228      <organization>Rackspace</organization>
4229      <address><email>mnot@mnot.net</email></address>
4230    </author>
4231    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4232      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4233      <address><email>julian.reschke@greenbytes.de</email></address>
4234    </author>
4235    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4236  </front>
4237  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4238  <x:source href="p6-cache.xml" basename="p6-cache"/>
4239</reference>
4240
4241<reference anchor="RFC5234">
4242  <front>
4243    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4244    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4245      <organization>Brandenburg InternetWorking</organization>
4246      <address>
4247        <email>dcrocker@bbiw.net</email>
4248      </address> 
4249    </author>
4250    <author initials="P." surname="Overell" fullname="Paul Overell">
4251      <organization>THUS plc.</organization>
4252      <address>
4253        <email>paul.overell@thus.net</email>
4254      </address>
4255    </author>
4256    <date month="January" year="2008"/>
4257  </front>
4258  <seriesInfo name="STD" value="68"/>
4259  <seriesInfo name="RFC" value="5234"/>
4260</reference>
4261
4262<reference anchor="RFC2119">
4263  <front>
4264    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4265    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4266      <organization>Harvard University</organization>
4267      <address><email>sob@harvard.edu</email></address>
4268    </author>
4269    <date month="March" year="1997"/>
4270  </front>
4271  <seriesInfo name="BCP" value="14"/>
4272  <seriesInfo name="RFC" value="2119"/>
4273</reference>
4274
4275<reference anchor="RFC3986">
4276 <front>
4277  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4278  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4279    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4280    <address>
4281       <email>timbl@w3.org</email>
4282       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4283    </address>
4284  </author>
4285  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4286    <organization abbrev="Day Software">Day Software</organization>
4287    <address>
4288      <email>fielding@gbiv.com</email>
4289      <uri>http://roy.gbiv.com/</uri>
4290    </address>
4291  </author>
4292  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4293    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4294    <address>
4295      <email>LMM@acm.org</email>
4296      <uri>http://larry.masinter.net/</uri>
4297    </address>
4298  </author>
4299  <date month='January' year='2005'></date>
4300 </front>
4301 <seriesInfo name="STD" value="66"/>
4302 <seriesInfo name="RFC" value="3986"/>
4303</reference>
4304
4305<reference anchor="USASCII">
4306  <front>
4307    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4308    <author>
4309      <organization>American National Standards Institute</organization>
4310    </author>
4311    <date year="1986"/>
4312  </front>
4313  <seriesInfo name="ANSI" value="X3.4"/>
4314</reference>
4315
4316<reference anchor="RFC1950">
4317  <front>
4318    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4319    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4320      <organization>Aladdin Enterprises</organization>
4321      <address><email>ghost@aladdin.com</email></address>
4322    </author>
4323    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4324    <date month="May" year="1996"/>
4325  </front>
4326  <seriesInfo name="RFC" value="1950"/>
4327  <annotation>
4328    RFC 1950 is an Informational RFC, thus it might be less stable than
4329    this specification. On the other hand, this downward reference was
4330    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4331    therefore it is unlikely to cause problems in practice. See also
4332    <xref target="BCP97"/>.
4333  </annotation>
4334</reference>
4335
4336<reference anchor="RFC1951">
4337  <front>
4338    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4339    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4340      <organization>Aladdin Enterprises</organization>
4341      <address><email>ghost@aladdin.com</email></address>
4342    </author>
4343    <date month="May" year="1996"/>
4344  </front>
4345  <seriesInfo name="RFC" value="1951"/>
4346  <annotation>
4347    RFC 1951 is an Informational RFC, thus it might be less stable than
4348    this specification. On the other hand, this downward reference was
4349    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4350    therefore it is unlikely to cause problems in practice. See also
4351    <xref target="BCP97"/>.
4352  </annotation>
4353</reference>
4354
4355<reference anchor="RFC1952">
4356  <front>
4357    <title>GZIP file format specification version 4.3</title>
4358    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4359      <organization>Aladdin Enterprises</organization>
4360      <address><email>ghost@aladdin.com</email></address>
4361    </author>
4362    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4363      <address><email>gzip@prep.ai.mit.edu</email></address>
4364    </author>
4365    <author initials="M." surname="Adler" fullname="Mark Adler">
4366      <address><email>madler@alumni.caltech.edu</email></address>
4367    </author>
4368    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4369      <address><email>ghost@aladdin.com</email></address>
4370    </author>
4371    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4372      <address><email>randeg@alumni.rpi.edu</email></address>
4373    </author>
4374    <date month="May" year="1996"/>
4375  </front>
4376  <seriesInfo name="RFC" value="1952"/>
4377  <annotation>
4378    RFC 1952 is an Informational RFC, thus it might be less stable than
4379    this specification. On the other hand, this downward reference was
4380    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4381    therefore it is unlikely to cause problems in practice. See also
4382    <xref target="BCP97"/>.
4383  </annotation>
4384</reference>
4385
4386</references>
4387
4388<references title="Informative References">
4389
4390<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4391  <front>
4392    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4393    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4394    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4395    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4396    <author initials="H." surname="Lie" fullname="H. Lie"/>
4397    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4398    <date year="1997" month="September"/>
4399  </front>
4400  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4401</reference>
4402
4403<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4404  <front>
4405    <title>Improving HTTP Latency</title>
4406    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4407    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4408    <date year="1995" month="December"/>
4409  </front>
4410  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4411</reference>
4412
4413<reference anchor='RFC1919'>
4414  <front>
4415    <title>Classical versus Transparent IP Proxies</title>
4416    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4417      <address><email>mchatel@pax.eunet.ch</email></address>
4418    </author>
4419    <date year='1996' month='March' />
4420  </front>
4421  <seriesInfo name='RFC' value='1919' />
4422</reference>
4423
4424<reference anchor="RFC1945">
4425  <front>
4426    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4427    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4428      <organization>MIT, Laboratory for Computer Science</organization>
4429      <address><email>timbl@w3.org</email></address>
4430    </author>
4431    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4432      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4433      <address><email>fielding@ics.uci.edu</email></address>
4434    </author>
4435    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4436      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4437      <address><email>frystyk@w3.org</email></address>
4438    </author>
4439    <date month="May" year="1996"/>
4440  </front>
4441  <seriesInfo name="RFC" value="1945"/>
4442</reference>
4443
4444<reference anchor="RFC2045">
4445  <front>
4446    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4447    <author initials="N." surname="Freed" fullname="Ned Freed">
4448      <organization>Innosoft International, Inc.</organization>
4449      <address><email>ned@innosoft.com</email></address>
4450    </author>
4451    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4452      <organization>First Virtual Holdings</organization>
4453      <address><email>nsb@nsb.fv.com</email></address>
4454    </author>
4455    <date month="November" year="1996"/>
4456  </front>
4457  <seriesInfo name="RFC" value="2045"/>
4458</reference>
4459
4460<reference anchor="RFC2047">
4461  <front>
4462    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4463    <author initials="K." surname="Moore" fullname="Keith Moore">
4464      <organization>University of Tennessee</organization>
4465      <address><email>moore@cs.utk.edu</email></address>
4466    </author>
4467    <date month="November" year="1996"/>
4468  </front>
4469  <seriesInfo name="RFC" value="2047"/>
4470</reference>
4471
4472<reference anchor="RFC2068">
4473  <front>
4474    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4475    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4476      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4477      <address><email>fielding@ics.uci.edu</email></address>
4478    </author>
4479    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4480      <organization>MIT Laboratory for Computer Science</organization>
4481      <address><email>jg@w3.org</email></address>
4482    </author>
4483    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4484      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4485      <address><email>mogul@wrl.dec.com</email></address>
4486    </author>
4487    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4488      <organization>MIT Laboratory for Computer Science</organization>
4489      <address><email>frystyk@w3.org</email></address>
4490    </author>
4491    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4492      <organization>MIT Laboratory for Computer Science</organization>
4493      <address><email>timbl@w3.org</email></address>
4494    </author>
4495    <date month="January" year="1997"/>
4496  </front>
4497  <seriesInfo name="RFC" value="2068"/>
4498</reference>
4499
4500<reference anchor="RFC2145">
4501  <front>
4502    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4503    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4504      <organization>Western Research Laboratory</organization>
4505      <address><email>mogul@wrl.dec.com</email></address>
4506    </author>
4507    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4508      <organization>Department of Information and Computer Science</organization>
4509      <address><email>fielding@ics.uci.edu</email></address>
4510    </author>
4511    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4512      <organization>MIT Laboratory for Computer Science</organization>
4513      <address><email>jg@w3.org</email></address>
4514    </author>
4515    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4516      <organization>W3 Consortium</organization>
4517      <address><email>frystyk@w3.org</email></address>
4518    </author>
4519    <date month="May" year="1997"/>
4520  </front>
4521  <seriesInfo name="RFC" value="2145"/>
4522</reference>
4523
4524<reference anchor="RFC2616">
4525  <front>
4526    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4527    <author initials="R." surname="Fielding" fullname="R. Fielding">
4528      <organization>University of California, Irvine</organization>
4529      <address><email>fielding@ics.uci.edu</email></address>
4530    </author>
4531    <author initials="J." surname="Gettys" fullname="J. Gettys">
4532      <organization>W3C</organization>
4533      <address><email>jg@w3.org</email></address>
4534    </author>
4535    <author initials="J." surname="Mogul" fullname="J. Mogul">
4536      <organization>Compaq Computer Corporation</organization>
4537      <address><email>mogul@wrl.dec.com</email></address>
4538    </author>
4539    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4540      <organization>MIT Laboratory for Computer Science</organization>
4541      <address><email>frystyk@w3.org</email></address>
4542    </author>
4543    <author initials="L." surname="Masinter" fullname="L. Masinter">
4544      <organization>Xerox Corporation</organization>
4545      <address><email>masinter@parc.xerox.com</email></address>
4546    </author>
4547    <author initials="P." surname="Leach" fullname="P. Leach">
4548      <organization>Microsoft Corporation</organization>
4549      <address><email>paulle@microsoft.com</email></address>
4550    </author>
4551    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4552      <organization>W3C</organization>
4553      <address><email>timbl@w3.org</email></address>
4554    </author>
4555    <date month="June" year="1999"/>
4556  </front>
4557  <seriesInfo name="RFC" value="2616"/>
4558</reference>
4559
4560<reference anchor='RFC2817'>
4561  <front>
4562    <title>Upgrading to TLS Within HTTP/1.1</title>
4563    <author initials='R.' surname='Khare' fullname='R. Khare'>
4564      <organization>4K Associates / UC Irvine</organization>
4565      <address><email>rohit@4K-associates.com</email></address>
4566    </author>
4567    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4568      <organization>Agranat Systems, Inc.</organization>
4569      <address><email>lawrence@agranat.com</email></address>
4570    </author>
4571    <date year='2000' month='May' />
4572  </front>
4573  <seriesInfo name='RFC' value='2817' />
4574</reference>
4575
4576<reference anchor='RFC2818'>
4577  <front>
4578    <title>HTTP Over TLS</title>
4579    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4580      <organization>RTFM, Inc.</organization>
4581      <address><email>ekr@rtfm.com</email></address>
4582    </author>
4583    <date year='2000' month='May' />
4584  </front>
4585  <seriesInfo name='RFC' value='2818' />
4586</reference>
4587
4588<reference anchor='RFC2965'>
4589  <front>
4590    <title>HTTP State Management Mechanism</title>
4591    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4592      <organization>Bell Laboratories, Lucent Technologies</organization>
4593      <address><email>dmk@bell-labs.com</email></address>
4594    </author>
4595    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4596      <organization>Epinions.com, Inc.</organization>
4597      <address><email>lou@montulli.org</email></address>
4598    </author>
4599    <date year='2000' month='October' />
4600  </front>
4601  <seriesInfo name='RFC' value='2965' />
4602</reference>
4603
4604<reference anchor='RFC3040'>
4605  <front>
4606    <title>Internet Web Replication and Caching Taxonomy</title>
4607    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4608      <organization>Equinix, Inc.</organization>
4609    </author>
4610    <author initials='I.' surname='Melve' fullname='I. Melve'>
4611      <organization>UNINETT</organization>
4612    </author>
4613    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4614      <organization>CacheFlow Inc.</organization>
4615    </author>
4616    <date year='2001' month='January' />
4617  </front>
4618  <seriesInfo name='RFC' value='3040' />
4619</reference>
4620
4621<reference anchor='RFC3864'>
4622  <front>
4623    <title>Registration Procedures for Message Header Fields</title>
4624    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4625      <organization>Nine by Nine</organization>
4626      <address><email>GK-IETF@ninebynine.org</email></address>
4627    </author>
4628    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4629      <organization>BEA Systems</organization>
4630      <address><email>mnot@pobox.com</email></address>
4631    </author>
4632    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4633      <organization>HP Labs</organization>
4634      <address><email>JeffMogul@acm.org</email></address>
4635    </author>
4636    <date year='2004' month='September' />
4637  </front>
4638  <seriesInfo name='BCP' value='90' />
4639  <seriesInfo name='RFC' value='3864' />
4640</reference>
4641
4642<reference anchor='RFC4033'>
4643  <front>
4644    <title>DNS Security Introduction and Requirements</title>
4645    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4646    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4647    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4648    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4649    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4650    <date year='2005' month='March' />
4651  </front>
4652  <seriesInfo name='RFC' value='4033' />
4653</reference>
4654
4655<reference anchor="RFC4288">
4656  <front>
4657    <title>Media Type Specifications and Registration Procedures</title>
4658    <author initials="N." surname="Freed" fullname="N. Freed">
4659      <organization>Sun Microsystems</organization>
4660      <address>
4661        <email>ned.freed@mrochek.com</email>
4662      </address>
4663    </author>
4664    <author initials="J." surname="Klensin" fullname="J. Klensin">
4665      <address>
4666        <email>klensin+ietf@jck.com</email>
4667      </address>
4668    </author>
4669    <date year="2005" month="December"/>
4670  </front>
4671  <seriesInfo name="BCP" value="13"/>
4672  <seriesInfo name="RFC" value="4288"/>
4673</reference>
4674
4675<reference anchor='RFC4395'>
4676  <front>
4677    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4678    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4679      <organization>AT&amp;T Laboratories</organization>
4680      <address>
4681        <email>tony+urireg@maillennium.att.com</email>
4682      </address>
4683    </author>
4684    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4685      <organization>Qualcomm, Inc.</organization>
4686      <address>
4687        <email>hardie@qualcomm.com</email>
4688      </address>
4689    </author>
4690    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4691      <organization>Adobe Systems</organization>
4692      <address>
4693        <email>LMM@acm.org</email>
4694      </address>
4695    </author>
4696    <date year='2006' month='February' />
4697  </front>
4698  <seriesInfo name='BCP' value='115' />
4699  <seriesInfo name='RFC' value='4395' />
4700</reference>
4701
4702<reference anchor='RFC4559'>
4703  <front>
4704    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4705    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4706    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4707    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4708    <date year='2006' month='June' />
4709  </front>
4710  <seriesInfo name='RFC' value='4559' />
4711</reference>
4712
4713<reference anchor='RFC5226'>
4714  <front>
4715    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4716    <author initials='T.' surname='Narten' fullname='T. Narten'>
4717      <organization>IBM</organization>
4718      <address><email>narten@us.ibm.com</email></address>
4719    </author>
4720    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4721      <organization>Google</organization>
4722      <address><email>Harald@Alvestrand.no</email></address>
4723    </author>
4724    <date year='2008' month='May' />
4725  </front>
4726  <seriesInfo name='BCP' value='26' />
4727  <seriesInfo name='RFC' value='5226' />
4728</reference>
4729
4730<reference anchor="RFC5322">
4731  <front>
4732    <title>Internet Message Format</title>
4733    <author initials="P." surname="Resnick" fullname="P. Resnick">
4734      <organization>Qualcomm Incorporated</organization>
4735    </author>
4736    <date year="2008" month="October"/>
4737  </front> 
4738  <seriesInfo name="RFC" value="5322"/>
4739</reference>
4740
4741<reference anchor="RFC6265">
4742  <front>
4743    <title>HTTP State Management Mechanism</title>
4744    <author initials="A." surname="Barth" fullname="Adam Barth">
4745      <organization abbrev="U.C. Berkeley">
4746        University of California, Berkeley
4747      </organization>
4748      <address><email>abarth@eecs.berkeley.edu</email></address>
4749    </author>
4750    <date year="2011" month="April" />
4751  </front>
4752  <seriesInfo name="RFC" value="6265"/>
4753</reference>
4754
4755<reference anchor='BCP97'>
4756  <front>
4757    <title>Handling Normative References to Standards-Track Documents</title>
4758    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4759      <address>
4760        <email>klensin+ietf@jck.com</email>
4761      </address>
4762    </author>
4763    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4764      <organization>MIT</organization>
4765      <address>
4766        <email>hartmans-ietf@mit.edu</email>
4767      </address>
4768    </author>
4769    <date year='2007' month='June' />
4770  </front>
4771  <seriesInfo name='BCP' value='97' />
4772  <seriesInfo name='RFC' value='4897' />
4773</reference>
4774
4775<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4776  <front>
4777    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4778    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4779    <date year="2001" month="November"/>
4780  </front>
4781  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4782</reference>
4783
4784<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4785  <front>
4786    <title>Analysis of HTTP Performance Problems</title>
4787    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4788    <date/>
4789  </front>
4790</reference>
4791
4792<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4793  <front>
4794  <title>Analysis of HTTP Performance</title>
4795  <author initials="J." surname="Touch" fullname="Joe Touch">
4796    <organization>USC/Information Sciences Institute</organization>
4797    <address><email>touch@isi.edu</email></address>
4798  </author>
4799  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4800    <organization>USC/Information Sciences Institute</organization>
4801    <address><email>johnh@isi.edu</email></address>
4802  </author>
4803  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4804    <organization>USC/Information Sciences Institute</organization>
4805    <address><email>katia@isi.edu</email></address>
4806  </author>
4807  <date year="1998" month="Aug"/>
4808  </front>
4809  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4810  <annotation>(original report dated Aug. 1996)</annotation>
4811</reference>
4812
4813</references>
4814
4815
4816<section title="HTTP Version History" anchor="compatibility">
4817<t>
4818   HTTP has been in use by the World-Wide Web global information initiative
4819   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4820   was a simple protocol for hypertext data transfer across the Internet
4821   with only a single request method (GET) and no metadata.
4822   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4823   methods and MIME-like messaging that could include metadata about the data
4824   transferred and modifiers on the request/response semantics. However,
4825   HTTP/1.0 did not sufficiently take into consideration the effects of
4826   hierarchical proxies, caching, the need for persistent connections, or
4827   name-based virtual hosts. The proliferation of incompletely-implemented
4828   applications calling themselves "HTTP/1.0" further necessitated a
4829   protocol version change in order for two communicating applications
4830   to determine each other's true capabilities.
4831</t>
4832<t>
4833   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4834   requirements that enable reliable implementations, adding only
4835   those new features that will either be safely ignored by an HTTP/1.0
4836   recipient or only sent when communicating with a party advertising
4837   compliance with HTTP/1.1.
4838</t>
4839<t>
4840   It is beyond the scope of a protocol specification to mandate
4841   compliance with previous versions. HTTP/1.1 was deliberately
4842   designed, however, to make supporting previous versions easy.
4843   We would expect a general-purpose HTTP/1.1 server to understand
4844   any valid request in the format of HTTP/1.0 and respond appropriately
4845   with an HTTP/1.1 message that only uses features understood (or
4846   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4847   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4848</t>
4849<t>
4850   Since HTTP/0.9 did not support header fields in a request,
4851   there is no mechanism for it to support name-based virtual
4852   hosts (selection of resource by inspection of the Host header
4853   field).  Any server that implements name-based virtual hosts
4854   ought to disable support for HTTP/0.9.  Most requests that
4855   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4856   requests wherein a buggy client failed to properly encode
4857   linear whitespace found in a URI reference and placed in
4858   the request-target.
4859</t>
4860
4861<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4862<t>
4863   This section summarizes major differences between versions HTTP/1.0
4864   and HTTP/1.1.
4865</t>
4866
4867<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4868<t>
4869   The requirements that clients and servers support the Host header
4870   field (<xref target="header.host"/>), report an error if it is
4871   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4872   are among the most important changes defined by HTTP/1.1.
4873</t>
4874<t>
4875   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4876   addresses and servers; there was no other established mechanism for
4877   distinguishing the intended server of a request than the IP address
4878   to which that request was directed. The Host header field was
4879   introduced during the development of HTTP/1.1 and, though it was
4880   quickly implemented by most HTTP/1.0 browsers, additional requirements
4881   were placed on all HTTP/1.1 requests in order to ensure complete
4882   adoption.  At the time of this writing, most HTTP-based services
4883   are dependent upon the Host header field for targeting requests.
4884</t>
4885</section>
4886
4887<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4888<t>
4889   For most implementations of HTTP/1.0, each connection is established
4890   by the client prior to the request and closed by the server after
4891   sending the response. However, some implementations implement the
4892   Keep-Alive version of persistent connections described in
4893   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4894</t>
4895<t>
4896   Some clients and servers might wish to be compatible with some
4897   previous implementations of persistent connections in HTTP/1.0
4898   clients and servers. Persistent connections in HTTP/1.0 are
4899   explicitly negotiated as they are not the default behavior. HTTP/1.0
4900   experimental implementations of persistent connections are faulty,
4901   and the new facilities in HTTP/1.1 are designed to rectify these
4902   problems. The problem was that some existing HTTP/1.0 clients might
4903   send Keep-Alive to a proxy server that doesn't understand
4904   Connection, which would then erroneously forward it to the next
4905   inbound server, which would establish the Keep-Alive connection and
4906   result in a hung HTTP/1.0 proxy waiting for the close on the
4907   response. The result is that HTTP/1.0 clients must be prevented from
4908   using Keep-Alive when talking to proxies.
4909</t>
4910<t>
4911   However, talking to proxies is the most important use of persistent
4912   connections, so that prohibition is clearly unacceptable. Therefore,
4913   we need some other mechanism for indicating a persistent connection
4914   is desired, which is safe to use even when talking to an old proxy
4915   that ignores Connection. Persistent connections are the default for
4916   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4917   declaring non-persistence. See <xref target="header.connection"/>.
4918</t>
4919</section>
4920</section>
4921
4922<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4923<t>
4924  Empty list elements in list productions have been deprecated.
4925  (<xref target="notation.abnf"/>)
4926</t>
4927<t>
4928  Rules about implicit linear whitespace between certain grammar productions
4929  have been removed; now it's only allowed when specifically pointed out
4930  in the ABNF.
4931  (<xref target="basic.rules"/>)
4932</t>
4933<t>
4934  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4935  sensitive. Restrict the version numbers to be single digits due to the fact
4936  that implementations are known to handle multi-digit version numbers
4937  incorrectly.
4938  (<xref target="http.version"/>)
4939</t>
4940<t>
4941  Require that invalid whitespace around field-names be rejected.
4942  (<xref target="header.fields"/>)
4943</t>
4944<t> 
4945  The NUL octet is no longer allowed in comment and quoted-string
4946  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4947  Non-ASCII content in header fields and reason phrase has been obsoleted and
4948  made opaque (the TEXT rule was removed).
4949  (<xref target="field.rules"/>)
4950</t>
4951<t>
4952  Require recipients to handle bogus Content-Length header fields as errors.
4953  (<xref target="message.body"/>)
4954</t>
4955<t>
4956  Remove reference to non-existent identity transfer-coding value tokens.
4957  (Sections <xref format="counter" target="message.body"/> and
4958  <xref format="counter" target="transfer.codings"/>)
4959</t>
4960<t>
4961  Update use of abs_path production from RFC 1808 to the path-absolute + query
4962  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4963  request method only.
4964  (<xref target="request-target"/>)
4965</t>
4966<t>
4967  Clarification that the chunk length does not include the count of the octets
4968  in the chunk header and trailer. Furthermore disallowed line folding
4969  in chunk extensions.
4970  (<xref target="chunked.encoding"/>)
4971</t>
4972<t>
4973  Remove hard limit of two connections per server.
4974  Remove requirement to retry a sequence of requests as long it was idempotent.
4975  (<xref target="persistent.practical"/>)
4976</t>
4977<t>
4978  Remove requirement to retry requests under certain cirumstances when the
4979  server prematurely closes the connection.
4980  (<xref target="message.transmission.requirements"/>)
4981</t>
4982<t>
4983  Change ABNF productions for header fields to only define the field value.
4984  (<xref target="header.field.definitions"/>)
4985</t>
4986<t>
4987  Clarify exactly when close connection options must be sent.
4988  (<xref target="header.connection"/>)
4989</t>
4990<t>
4991  Define the semantics of the "Upgrade" header field in responses other than
4992  101 (this was incorporated from <xref target="RFC2817"/>).
4993  (<xref target="header.upgrade"/>)
4994</t>
4995</section>
4996</section>
4997
4998<?BEGININC p1-messaging.abnf-appendix ?>
4999<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5000<figure>
5001<artwork type="abnf" name="p1-messaging.parsed-abnf">
5002<x:ref>BWS</x:ref> = OWS
5003
5004<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5005<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5006 connection-token ] )
5007<x:ref>Content-Length</x:ref> = 1*DIGIT
5008
5009<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5010<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5011<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5012 ]
5013<x:ref>Host</x:ref> = uri-host [ ":" port ]
5014
5015<x:ref>Method</x:ref> = token
5016
5017<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5018
5019<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5020<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5021<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5022
5023<x:ref>Status-Code</x:ref> = 3DIGIT
5024<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5025
5026<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5027<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5028<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5029 transfer-coding ] )
5030
5031<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5032<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5033
5034<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5035 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5036 )
5037
5038<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5039<x:ref>attribute</x:ref> = token
5040<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5041
5042<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5043<x:ref>chunk-data</x:ref> = 1*OCTET
5044<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5045<x:ref>chunk-ext-name</x:ref> = token
5046<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5047<x:ref>chunk-size</x:ref> = 1*HEXDIG
5048<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5049<x:ref>connection-token</x:ref> = token
5050<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5051 / %x2A-5B ; '*'-'['
5052 / %x5D-7E ; ']'-'~'
5053 / obs-text
5054
5055<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5056<x:ref>field-name</x:ref> = token
5057<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5058
5059<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5060<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5061<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5062
5063<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5064
5065<x:ref>message-body</x:ref> = *OCTET
5066
5067<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5068<x:ref>obs-text</x:ref> = %x80-FF
5069
5070<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5071<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5072<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5073<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5074<x:ref>product</x:ref> = token [ "/" product-version ]
5075<x:ref>product-version</x:ref> = token
5076<x:ref>protocol-name</x:ref> = token
5077<x:ref>protocol-version</x:ref> = token
5078<x:ref>pseudonym</x:ref> = token
5079
5080<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5081 / %x5D-7E ; ']'-'~'
5082 / obs-text
5083<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5084 / %x5D-7E ; ']'-'~'
5085 / obs-text
5086<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5087<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5088<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5089<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5090<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5091<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5092
5093<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5094<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5095<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5096<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5097 / authority
5098
5099<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5100 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5101<x:ref>start-line</x:ref> = Request-Line / Status-Line
5102
5103<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5104<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5105 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5106<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5107<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5108<x:ref>token</x:ref> = 1*tchar
5109<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5110<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5111 transfer-extension
5112<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5113<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5114
5115<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5116
5117<x:ref>value</x:ref> = word
5118
5119<x:ref>word</x:ref> = token / quoted-string
5120</artwork>
5121</figure>
5122<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5123; Chunked-Body defined but not used
5124; Connection defined but not used
5125; Content-Length defined but not used
5126; HTTP-message defined but not used
5127; Host defined but not used
5128; TE defined but not used
5129; Trailer defined but not used
5130; Transfer-Encoding defined but not used
5131; URI-reference defined but not used
5132; Upgrade defined but not used
5133; Via defined but not used
5134; http-URI defined but not used
5135; https-URI defined but not used
5136; partial-URI defined but not used
5137; special defined but not used
5138</artwork></figure></section>
5139<?ENDINC p1-messaging.abnf-appendix ?>
5140
5141<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5142
5143<section title="Since RFC 2616">
5144<t>
5145  Extracted relevant partitions from <xref target="RFC2616"/>.
5146</t>
5147</section>
5148
5149<section title="Since draft-ietf-httpbis-p1-messaging-00">
5150<t>
5151  Closed issues:
5152  <list style="symbols"> 
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5155      "HTTP Version should be case sensitive"
5156      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5160      "'unsafe' characters"
5161      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5162    </t>
5163    <t>
5164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5165      "Chunk Size Definition"
5166      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5167    </t>
5168    <t>
5169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5170      "Message Length"
5171      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5175      "Media Type Registrations"
5176      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5177    </t>
5178    <t>
5179      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5180      "URI includes query"
5181      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5182    </t>
5183    <t>
5184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5185      "No close on 1xx responses"
5186      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5187    </t>
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5190      "Remove 'identity' token references"
5191      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5192    </t>
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5195      "Import query BNF"
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5199      "qdtext BNF"
5200    </t>
5201    <t>
5202      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5203      "Normative and Informative references"
5204    </t>
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5207      "RFC2606 Compliance"
5208    </t>
5209    <t>
5210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5211      "RFC977 reference"
5212    </t>
5213    <t>
5214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5215      "RFC1700 references"
5216    </t>
5217    <t>
5218      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5219      "inconsistency in date format explanation"
5220    </t>
5221    <t>
5222      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5223      "Date reference typo"
5224    </t>
5225    <t>
5226      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5227      "Informative references"
5228    </t>
5229    <t>
5230      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5231      "ISO-8859-1 Reference"
5232    </t>
5233    <t>
5234      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5235      "Normative up-to-date references"
5236    </t>
5237  </list>
5238</t>
5239<t>
5240  Other changes:
5241  <list style="symbols"> 
5242    <t>
5243      Update media type registrations to use RFC4288 template.
5244    </t>
5245    <t>
5246      Use names of RFC4234 core rules DQUOTE and HTAB,
5247      fix broken ABNF for chunk-data
5248      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5249    </t>
5250  </list>
5251</t>
5252</section>
5253
5254<section title="Since draft-ietf-httpbis-p1-messaging-01">
5255<t>
5256  Closed issues:
5257  <list style="symbols"> 
5258    <t>
5259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5260      "Bodies on GET (and other) requests"
5261    </t>
5262    <t>
5263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5264      "Updating to RFC4288"
5265    </t>
5266    <t>
5267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5268      "Status Code and Reason Phrase"
5269    </t>
5270    <t>
5271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5272      "rel_path not used"
5273    </t>
5274  </list>
5275</t>
5276<t>
5277  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5278  <list style="symbols"> 
5279    <t>
5280      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5281      "trailer-part").
5282    </t>
5283    <t>
5284      Avoid underscore character in rule names ("http_URL" ->
5285      "http-URL", "abs_path" -> "path-absolute").
5286    </t>
5287    <t>
5288      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5289      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5290      have to be updated when switching over to RFC3986.
5291    </t>
5292    <t>
5293      Synchronize core rules with RFC5234.
5294    </t>
5295    <t>
5296      Get rid of prose rules that span multiple lines.
5297    </t>
5298    <t>
5299      Get rid of unused rules LOALPHA and UPALPHA.
5300    </t>
5301    <t>
5302      Move "Product Tokens" section (back) into Part 1, as "token" is used
5303      in the definition of the Upgrade header field.
5304    </t>
5305    <t>
5306      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5307    </t>
5308    <t>
5309      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5310    </t>
5311  </list>
5312</t>
5313</section>
5314
5315<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5316<t>
5317  Closed issues:
5318  <list style="symbols"> 
5319    <t>
5320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5321      "HTTP-date vs. rfc1123-date"
5322    </t>
5323    <t>
5324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5325      "WS in quoted-pair"
5326    </t>
5327  </list>
5328</t>
5329<t>
5330  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5331  <list style="symbols"> 
5332    <t>
5333      Reference RFC 3984, and update header field registrations for headers defined
5334      in this document.
5335    </t>
5336  </list>
5337</t>
5338<t>
5339  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5340  <list style="symbols"> 
5341    <t>
5342      Replace string literals when the string really is case-sensitive (HTTP-Version).
5343    </t>
5344  </list>
5345</t>
5346</section>
5347
5348<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5349<t>
5350  Closed issues:
5351  <list style="symbols"> 
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5354      "Connection closing"
5355    </t>
5356    <t>
5357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5358      "Move registrations and registry information to IANA Considerations"
5359    </t>
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5362      "need new URL for PAD1995 reference"
5363    </t>
5364    <t>
5365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5366      "IANA Considerations: update HTTP URI scheme registration"
5367    </t>
5368    <t>
5369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5370      "Cite HTTPS URI scheme definition"
5371    </t>
5372    <t>
5373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5374      "List-type headers vs Set-Cookie"
5375    </t>
5376  </list>
5377</t>
5378<t>
5379  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5380  <list style="symbols"> 
5381    <t>
5382      Replace string literals when the string really is case-sensitive (HTTP-Date).
5383    </t>
5384    <t>
5385      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5386    </t>
5387  </list>
5388</t>
5389</section>
5390
5391<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5392<t>
5393  Closed issues:
5394  <list style="symbols"> 
5395    <t>
5396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5397      "Out-of-date reference for URIs"
5398    </t>
5399    <t>
5400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5401      "RFC 2822 is updated by RFC 5322"
5402    </t>
5403  </list>
5404</t>
5405<t>
5406  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5407  <list style="symbols"> 
5408    <t>
5409      Use "/" instead of "|" for alternatives.
5410    </t>
5411    <t>
5412      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5413    </t>
5414    <t>
5415      Only reference RFC 5234's core rules.
5416    </t>
5417    <t>
5418      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5419      whitespace ("OWS") and required whitespace ("RWS").
5420    </t>
5421    <t>
5422      Rewrite ABNFs to spell out whitespace rules, factor out
5423      header field value format definitions.
5424    </t>
5425  </list>
5426</t>
5427</section>
5428
5429<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5430<t>
5431  Closed issues:
5432  <list style="symbols"> 
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5435      "Header LWS"
5436    </t>
5437    <t>
5438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5439      "Sort 1.3 Terminology"
5440    </t>
5441    <t>
5442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5443      "RFC2047 encoded words"
5444    </t>
5445    <t>
5446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5447      "Character Encodings in TEXT"
5448    </t>
5449    <t>
5450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5451      "Line Folding"
5452    </t>
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5455      "OPTIONS * and proxies"
5456    </t>
5457    <t>
5458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5459      "Reason-Phrase BNF"
5460    </t>
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5463      "Use of TEXT"
5464    </t>
5465    <t>
5466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5467      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5468    </t>
5469    <t>
5470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5471      "RFC822 reference left in discussion of date formats"
5472    </t>
5473  </list>
5474</t>
5475<t>
5476  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5477  <list style="symbols"> 
5478    <t>
5479      Rewrite definition of list rules, deprecate empty list elements.
5480    </t>
5481    <t>
5482      Add appendix containing collected and expanded ABNF.
5483    </t>
5484  </list>
5485</t>
5486<t>
5487  Other changes:
5488  <list style="symbols"> 
5489    <t>
5490      Rewrite introduction; add mostly new Architecture Section.
5491    </t>
5492    <t>
5493      Move definition of quality values from Part 3 into Part 1;
5494      make TE request header field grammar independent of accept-params (defined in Part 3).
5495    </t>
5496  </list>
5497</t>
5498</section>
5499
5500<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5501<t>
5502  Closed issues:
5503  <list style="symbols"> 
5504    <t>
5505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5506      "base for numeric protocol elements"
5507    </t>
5508    <t>
5509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5510      "comment ABNF"
5511    </t>
5512  </list>
5513</t>
5514<t>
5515  Partly resolved issues:
5516  <list style="symbols"> 
5517    <t>
5518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5519      "205 Bodies" (took out language that implied that there might be
5520      methods for which a request body MUST NOT be included)
5521    </t>
5522    <t>
5523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5524      "editorial improvements around HTTP-date"
5525    </t>
5526  </list>
5527</t>
5528</section>
5529
5530<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5531<t>
5532  Closed issues:
5533  <list style="symbols"> 
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5536      "Repeating single-value headers"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5540      "increase connection limit"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5544      "IP addresses in URLs"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5548      "take over HTTP Upgrade Token Registry"
5549    </t>
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5552      "CR and LF in chunk extension values"
5553    </t>
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5556      "HTTP/0.9 support"
5557    </t>
5558    <t>
5559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5560      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5561    </t>
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5564      "move definitions of gzip/deflate/compress to part 1"
5565    </t>
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5568      "disallow control characters in quoted-pair"
5569    </t>
5570  </list>
5571</t>
5572<t>
5573  Partly resolved issues:
5574  <list style="symbols"> 
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5577      "update IANA requirements wrt Transfer-Coding values" (add the
5578      IANA Considerations subsection)
5579    </t>
5580  </list>
5581</t>
5582</section>
5583
5584<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5585<t>
5586  Closed issues:
5587  <list style="symbols"> 
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5590      "header parsing, treatment of leading and trailing OWS"
5591    </t>
5592  </list>
5593</t>
5594<t>
5595  Partly resolved issues:
5596  <list style="symbols"> 
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5599      "Placement of 13.5.1 and 13.5.2"
5600    </t>
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5603      "use of term "word" when talking about header structure"
5604    </t>
5605  </list>
5606</t>
5607</section>
5608
5609<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5610<t>
5611  Closed issues:
5612  <list style="symbols"> 
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5615      "Clarification of the term 'deflate'"
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5619      "OPTIONS * and proxies"
5620    </t>
5621    <t>
5622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5623      "MIME-Version not listed in P1, general header fields"
5624    </t>
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5627      "IANA registry for content/transfer encodings"
5628    </t>
5629    <t>
5630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5631      "Case-sensitivity of HTTP-date"
5632    </t>
5633    <t>
5634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5635      "use of term "word" when talking about header structure"
5636    </t>
5637  </list>
5638</t>
5639<t>
5640  Partly resolved issues:
5641  <list style="symbols"> 
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5644      "Term for the requested resource's URI"
5645    </t>
5646  </list>
5647</t>
5648</section>
5649
5650<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5651<t>
5652  Closed issues:
5653  <list style="symbols">
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5656      "Connection Closing"
5657    </t>
5658    <t>
5659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5660      "Delimiting messages with multipart/byteranges"
5661    </t>
5662    <t>
5663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5664      "Handling multiple Content-Length headers"
5665    </t>
5666    <t>
5667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5668      "Clarify entity / representation / variant terminology"
5669    </t>
5670    <t>
5671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5672      "consider removing the 'changes from 2068' sections"
5673    </t>
5674  </list>
5675</t>
5676<t>
5677  Partly resolved issues:
5678  <list style="symbols"> 
5679    <t>
5680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5681      "HTTP(s) URI scheme definitions"
5682    </t>
5683  </list>
5684</t>
5685</section>
5686
5687<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5688<t>
5689  Closed issues:
5690  <list style="symbols">
5691    <t>
5692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5693      "Trailer requirements"
5694    </t>
5695    <t>
5696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5697      "Text about clock requirement for caches belongs in p6"
5698    </t>
5699    <t>
5700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5701      "effective request URI: handling of missing host in HTTP/1.0"
5702    </t>
5703    <t>
5704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5705      "confusing Date requirements for clients"
5706    </t>
5707  </list>
5708</t>
5709<t>
5710  Partly resolved issues:
5711  <list style="symbols"> 
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5714      "Handling multiple Content-Length headers"
5715    </t>
5716  </list>
5717</t>
5718</section>
5719
5720<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5721<t>
5722  Closed issues:
5723  <list style="symbols">
5724    <t>
5725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5726      "RFC2145 Normative"
5727    </t>
5728    <t>
5729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5730      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5731    </t>
5732    <t>
5733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5734      "define 'transparent' proxy"
5735    </t>
5736    <t>
5737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5738      "Header Classification"
5739    </t>
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5742      "Is * usable as a request-uri for new methods?"
5743    </t>
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5746      "Migrate Upgrade details from RFC2817"
5747    </t>
5748    <t>
5749      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5750      "untangle ABNFs for header fields"
5751    </t>
5752    <t>
5753      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5754      "update RFC 2109 reference"
5755    </t>
5756  </list>
5757</t>
5758</section>
5759
5760<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5761<t>
5762  Closed issues:
5763  <list style="symbols">
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5766      "Allow is not in 13.5.2"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5770      "Handling multiple Content-Length headers"
5771    </t>
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5774      "untangle ABNFs for header fields"
5775    </t>
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5778      "Content-Length ABNF broken"
5779    </t>
5780  </list>
5781</t>
5782</section>
5783
5784<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5785<t>
5786  Closed issues:
5787  <list style="symbols">
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5790      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5794      "Recommend minimum sizes for protocol elements"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5798      "Set expectations around buffering"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5802      "Considering messages in isolation"
5803    </t>
5804  </list>
5805</t>
5806</section>
5807
5808<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5809<t>
5810  Closed issues:
5811  <list style="symbols">
5812    <t>
5813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5814      "DNS Spoofing / DNS Binding advice"
5815    </t>
5816    <t>
5817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5818      "move RFCs 2145, 2616, 2817 to Historic status"
5819    </t>
5820    <t>
5821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5822      "\-escaping in quoted strings"
5823    </t>
5824    <t>
5825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5826      "'Close' should be reserved in the HTTP header field registry"
5827    </t>
5828  </list>
5829</t>
5830</section>
5831
5832<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5833<t>
5834  Closed issues:
5835  <list style="symbols">
5836    <t>
5837      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5838      "Document HTTP's error-handling philosophy"
5839    </t>
5840    <t>
5841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5842      "Explain header registration"
5843    </t>
5844    <t>
5845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5846      "Revise Acknowledgements Sections"
5847    </t>
5848    <t>
5849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5850      "Retrying Requests"
5851    </t>
5852  </list>
5853</t>
5854</section>
5855
5856</section>
5857
5858</back>
5859</rfc>
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