source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1868

Last change on this file since 1868 was 1868, checked in by fielding@…, 7 years ago

State that the q in qvalues is case-sensitive. Addresses #378

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 242.1 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                "<xref target='Part2' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56]>
57<?rfc toc="yes" ?>
58<?rfc symrefs="yes" ?>
59<?rfc sortrefs="yes" ?>
60<?rfc compact="yes"?>
61<?rfc subcompact="no" ?>
62<?rfc linkmailto="no" ?>
63<?rfc editing="no" ?>
64<?rfc comments="yes"?>
65<?rfc inline="yes"?>
66<?rfc rfcedstyle="yes"?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
70     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext'>
72<x:link rel="next" basename="p2-semantics"/>
73<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
74<front>
75
76  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
77
78  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
79    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
80    <address>
81      <postal>
82        <street>345 Park Ave</street>
83        <city>San Jose</city>
84        <region>CA</region>
85        <code>95110</code>
86        <country>USA</country>
87      </postal>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
94    <organization abbrev="W3C">World Wide Web Consortium</organization>
95    <address>
96      <postal>
97        <street>W3C / ERCIM</street>
98        <street>2004, rte des Lucioles</street>
99        <city>Sophia-Antipolis</city>
100        <region>AM</region>
101        <code>06902</code>
102        <country>France</country>
103      </postal>
104      <email>ylafon@w3.org</email>
105      <uri>http://www.raubacapeu.net/people/yves/</uri>
106    </address>
107  </author>
108
109  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
110    <organization abbrev="greenbytes">greenbytes GmbH</organization>
111    <address>
112      <postal>
113        <street>Hafenweg 16</street>
114        <city>Muenster</city><region>NW</region><code>48155</code>
115        <country>Germany</country>
116      </postal>
117      <email>julian.reschke@greenbytes.de</email>
118      <uri>http://greenbytes.de/tech/webdav/</uri>
119    </address>
120  </author>
121
122  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
123  <workgroup>HTTPbis Working Group</workgroup>
124
125<abstract>
126<t>
127   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
128   distributed, collaborative, hypertext information systems. HTTP has been in
129   use by the World Wide Web global information initiative since 1990.
130   This document provides an overview of HTTP architecture and its associated
131   terminology, defines the "http" and "https" Uniform Resource Identifier
132   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
133   and describes general security concerns for implementations.
134</t>   
135</abstract>
136
137<note title="Editorial Note (To be removed by RFC Editor)">
138  <t>
139    Discussion of this draft takes place on the HTTPBIS working group
140    mailing list (ietf-http-wg@w3.org), which is archived at
141    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
142  </t>
143  <t>
144    The current issues list is at
145    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
146    documents (including fancy diffs) can be found at
147    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
148  </t>
149  <t>
150    The changes in this draft are summarized in <xref target="changes.since.20"/>.
151  </t>
152</note>
153</front>
154<middle>
155<section title="Introduction" anchor="introduction">
156<t>
157   The Hypertext Transfer Protocol (HTTP) is an application-level
158   request/response protocol that uses extensible semantics and MIME-like
159   message payloads for flexible interaction with network-based hypertext
160   information systems. This document is the first in a series of documents
161   that collectively form the HTTP/1.1 specification:
162   <list style="empty">
163    <t>RFC xxx1: Message Syntax and Routing</t>
164    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
165    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
166    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
167    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
168    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
169   </list>
170</t>
171<t>
172   This HTTP/1.1 specification obsoletes and moves to historic status
173   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
174   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
175   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
176   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
177   for TLS upgrades).
178</t>
179<t>
180   HTTP is a generic interface protocol for information systems. It is
181   designed to hide the details of how a service is implemented by presenting
182   a uniform interface to clients that is independent of the types of
183   resources provided. Likewise, servers do not need to be aware of each
184   client's purpose: an HTTP request can be considered in isolation rather
185   than being associated with a specific type of client or a predetermined
186   sequence of application steps. The result is a protocol that can be used
187   effectively in many different contexts and for which implementations can
188   evolve independently over time.
189</t>
190<t>
191   HTTP is also designed for use as an intermediation protocol for translating
192   communication to and from non-HTTP information systems.
193   HTTP proxies and gateways can provide access to alternative information
194   services by translating their diverse protocols into a hypertext
195   format that can be viewed and manipulated by clients in the same way
196   as HTTP services.
197</t>
198<t>
199   One consequence of HTTP flexibility is that the protocol cannot be
200   defined in terms of what occurs behind the interface. Instead, we
201   are limited to defining the syntax of communication, the intent
202   of received communication, and the expected behavior of recipients.
203   If the communication is considered in isolation, then successful
204   actions ought to be reflected in corresponding changes to the
205   observable interface provided by servers. However, since multiple
206   clients might act in parallel and perhaps at cross-purposes, we
207   cannot require that such changes be observable beyond the scope
208   of a single response.
209</t>
210<t>
211   This document describes the architectural elements that are used or
212   referred to in HTTP, defines the "http" and "https" URI schemes,
213   describes overall network operation and connection management,
214   and defines HTTP message framing and forwarding requirements.
215   Our goal is to define all of the mechanisms necessary for HTTP message
216   handling that are independent of message semantics, thereby defining the
217   complete set of requirements for message parsers and
218   message-forwarding intermediaries.
219</t>
220
221
222<section title="Requirement Notation" anchor="intro.requirements">
223<t>
224   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
225   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
226   document are to be interpreted as described in <xref target="RFC2119"/>.
227</t>
228<t>
229   Conformance criteria and considerations regarding error handling
230   are defined in <xref target="conformance"/>.
231</t>
232</section>
233
234<section title="Syntax Notation" anchor="notation">
235<iref primary="true" item="Grammar" subitem="ALPHA"/>
236<iref primary="true" item="Grammar" subitem="CR"/>
237<iref primary="true" item="Grammar" subitem="CRLF"/>
238<iref primary="true" item="Grammar" subitem="CTL"/>
239<iref primary="true" item="Grammar" subitem="DIGIT"/>
240<iref primary="true" item="Grammar" subitem="DQUOTE"/>
241<iref primary="true" item="Grammar" subitem="HEXDIG"/>
242<iref primary="true" item="Grammar" subitem="HTAB"/>
243<iref primary="true" item="Grammar" subitem="LF"/>
244<iref primary="true" item="Grammar" subitem="OCTET"/>
245<iref primary="true" item="Grammar" subitem="SP"/>
246<iref primary="true" item="Grammar" subitem="VCHAR"/>
247<t>
248   This specification uses the Augmented Backus-Naur Form (ABNF) notation
249   of <xref target="RFC5234"/> with the list rule extension defined in
250   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
251   the collected ABNF with the list rule expanded.
252</t>
253<t anchor="core.rules">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="CTL"/>
256  <x:anchor-alias value="CR"/>
257  <x:anchor-alias value="CRLF"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="DQUOTE"/>
260  <x:anchor-alias value="HEXDIG"/>
261  <x:anchor-alias value="HTAB"/>
262  <x:anchor-alias value="LF"/>
263  <x:anchor-alias value="OCTET"/>
264  <x:anchor-alias value="SP"/>
265  <x:anchor-alias value="VCHAR"/>
266   The following core rules are included by
267   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269   DIGIT (decimal 0-9), DQUOTE (double quote),
270   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271   OCTET (any 8-bit sequence of data), SP (space), and
272   VCHAR (any visible <xref target="USASCII"/> character).
273</t>
274<t>
275   As a convention, ABNF rule names prefixed with "obs-" denote
276   "obsolete" grammar rules that appear for historical reasons.
277</t>
278</section>
279</section>
280
281<section title="Architecture" anchor="architecture">
282<t>
283   HTTP was created for the World Wide Web architecture
284   and has evolved over time to support the scalability needs of a worldwide
285   hypertext system. Much of that architecture is reflected in the terminology
286   and syntax productions used to define HTTP.
287</t>
288
289<section title="Client/Server Messaging" anchor="operation">
290<iref primary="true" item="client"/>
291<iref primary="true" item="server"/>
292<iref primary="true" item="connection"/>
293<t>
294   HTTP is a stateless request/response protocol that operates by exchanging
295   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
296   transport or session-layer
297   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
298   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
299   to a server for the purpose of sending one or more HTTP requests.
300   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
301   in order to service HTTP requests by sending HTTP responses.
302</t>
303<iref primary="true" item="user agent"/>
304<iref primary="true" item="origin server"/>
305<iref primary="true" item="browser"/>
306<iref primary="true" item="spider"/>
307<iref primary="true" item="sender"/>
308<iref primary="true" item="recipient"/>
309<t>
310   The terms client and server refer only to the roles that
311   these programs perform for a particular connection.  The same program
312   might act as a client on some connections and a server on others.  We use
313   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
314   such as a WWW browser, editor, or spider (web-traversing robot), and
315   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
316   authoritative responses to a request.  For general requirements, we use
317   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
318   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
319   message.
320</t>
321<t>
322   HTTP relies upon the Uniform Resource Identifier (URI)
323   standard <xref target="RFC3986"/> to indicate the target resource
324   (<xref target="target-resource"/>) and relationships between resources.
325   Messages are passed in a format similar to that used by Internet mail
326   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
327   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
328   between HTTP and MIME messages).
329</t>
330<t>
331   Most HTTP communication consists of a retrieval request (GET) for
332   a representation of some resource identified by a URI.  In the
333   simplest case, this might be accomplished via a single bidirectional
334   connection (===) between the user agent (UA) and the origin server (O).
335</t>
336<figure><artwork type="drawing">
337         request   &gt;
338    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
339                                &lt;   response
340</artwork></figure>
341<iref primary="true" item="message"/>
342<iref primary="true" item="request"/>
343<iref primary="true" item="response"/>
344<t>
345   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
346   message, beginning with a request-line that includes a method, URI, and
347   protocol version (<xref target="request.line"/>),
348   followed by header fields containing
349   request modifiers, client information, and representation metadata
350   (<xref target="header.fields"/>),
351   an empty line to indicate the end of the header section, and finally
352   a message body containing the payload body (if any,
353   <xref target="message.body"/>).
354</t>
355<t>
356   A server responds to a client's request by sending one or more HTTP
357   <x:dfn>response</x:dfn>
358   messages, each beginning with a status line that
359   includes the protocol version, a success or error code, and textual
360   reason phrase (<xref target="status.line"/>),
361   possibly followed by header fields containing server
362   information, resource metadata, and representation metadata
363   (<xref target="header.fields"/>),
364   an empty line to indicate the end of the header section, and finally
365   a message body containing the payload body (if any,
366   <xref target="message.body"/>).
367</t>
368<t>
369   A connection might be used for multiple request/response exchanges,
370   as defined in <xref target="persistent.connections"/>.
371</t>
372<t>
373   The following example illustrates a typical message exchange for a
374   GET request on the URI "http://www.example.com/hello.txt":
375</t>
376<figure><preamble>
377client request:
378</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
379GET /hello.txt HTTP/1.1
380User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
381Host: www.example.com
382Accept-Language: en, mi
383
384</artwork></figure>
385<figure><preamble>
386server response:
387</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
388HTTP/1.1 200 OK
389Date: Mon, 27 Jul 2009 12:28:53 GMT
390Server: Apache
391Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
392ETag: "34aa387-d-1568eb00"
393Accept-Ranges: bytes
394Content-Length: <x:length-of target="exbody"/>
395Vary: Accept-Encoding
396Content-Type: text/plain
397
398<x:span anchor="exbody">Hello World!
399</x:span></artwork></figure>
400</section>
401
402<section title="Implementation Diversity" anchor="implementation-diversity">
403<t>
404   When considering the design of HTTP, it is easy to fall into a trap of
405   thinking that all user agents are general-purpose browsers and all origin
406   servers are large public websites. That is not the case in practice.
407   Common HTTP user agents include household appliances, stereos, scales,
408   firmware update scripts, command-line programs, mobile apps,
409   and communication devices in a multitude of shapes and sizes.  Likewise,
410   common HTTP origin servers include home automation units, configurable
411   networking components, office machines, autonomous robots, news feeds,
412   traffic cameras, ad selectors, and video delivery platforms.
413</t>
414<t>
415   The term "user agent" does not imply that there is a human user directly
416   interacting with the software agent at the time of a request. In many
417   cases, a user agent is installed or configured to run in the background
418   and save its results for later inspection (or save only a subset of those
419   results that might be interesting or erroneous). Spiders, for example, are
420   typically given a start URI and configured to follow certain behavior while
421   crawling the Web as a hypertext graph.
422</t>
423<t>
424   The implementation diversity of HTTP means that we cannot assume the
425   user agent can make interactive suggestions to a user or provide adequate
426   warning for security or privacy options.  In the few cases where this
427   specification requires reporting of errors to the user, it is acceptable
428   for such reporting to only be observable in an error console or log file.
429   Likewise, requirements that an automated action be confirmed by the user
430   before proceeding can me met via advance configuration choices,
431   run-time options, or simply not proceeding with the unsafe action.
432</t>
433</section>
434
435<section title="Intermediaries" anchor="intermediaries">
436<iref primary="true" item="intermediary"/>
437<t>
438   HTTP enables the use of intermediaries to satisfy requests through
439   a chain of connections.  There are three common forms of HTTP
440   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
441   a single intermediary might act as an origin server, proxy, gateway,
442   or tunnel, switching behavior based on the nature of each request.
443</t>
444<figure><artwork type="drawing">
445         &gt;             &gt;             &gt;             &gt;
446    <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>
447               &lt;             &lt;             &lt;             &lt;
448</artwork></figure>
449<t>
450   The figure above shows three intermediaries (A, B, and C) between the
451   user agent and origin server. A request or response message that
452   travels the whole chain will pass through four separate connections.
453   Some HTTP communication options
454   might apply only to the connection with the nearest, non-tunnel
455   neighbor, only to the end-points of the chain, or to all connections
456   along the chain. Although the diagram is linear, each participant might
457   be engaged in multiple, simultaneous communications. For example, B
458   might be receiving requests from many clients other than A, and/or
459   forwarding requests to servers other than C, at the same time that it
460   is handling A's request.
461</t>
462<t>
463<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
464<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
465   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
466   to describe various requirements in relation to the directional flow of a
467   message: all messages flow from upstream to downstream.
468   Likewise, we use the terms inbound and outbound to refer to
469   directions in relation to the request path:
470   "<x:dfn>inbound</x:dfn>" means toward the origin server and
471   "<x:dfn>outbound</x:dfn>" means toward the user agent.
472</t>
473<t><iref primary="true" item="proxy"/>
474   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
475   client, usually via local configuration rules, to receive requests
476   for some type(s) of absolute URI and attempt to satisfy those
477   requests via translation through the HTTP interface.  Some translations
478   are minimal, such as for proxy requests for "http" URIs, whereas
479   other requests might require translation to and from entirely different
480   application-layer protocols. Proxies are often used to group an
481   organization's HTTP requests through a common intermediary for the
482   sake of security, annotation services, or shared caching.
483</t>
484<t>
485<iref primary="true" item="transforming proxy"/>
486<iref primary="true" item="non-transforming proxy"/>
487   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
488   or configured to modify request or response messages in a semantically
489   meaningful way (i.e., modifications, beyond those required by normal
490   HTTP processing, that change the message in a way that would be
491   significant to the original sender or potentially significant to
492   downstream recipients).  For example, a transforming proxy might be
493   acting as a shared annotation server (modifying responses to include
494   references to a local annotation database), a malware filter, a
495   format transcoder, or an intranet-to-Internet privacy filter.  Such
496   transformations are presumed to be desired by the client (or client
497   organization) that selected the proxy and are beyond the scope of
498   this specification.  However, when a proxy is not intended to transform
499   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
500   requirements that preserve HTTP message semantics. See &status-203; and
501   &header-warning; for status and warning codes related to transformations.
502</t>
503<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
504<iref primary="true" item="accelerator"/>
505   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
506   is a receiving agent that acts
507   as a layer above some other server(s) and translates the received
508   requests to the underlying server's protocol.  Gateways are often
509   used to encapsulate legacy or untrusted information services, to
510   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
511   enable partitioning or load-balancing of HTTP services across
512   multiple machines.
513</t>
514<t>
515   A gateway behaves as an origin server on its outbound connection and
516   as a user agent on its inbound connection.
517   All HTTP requirements applicable to an origin server
518   also apply to the outbound communication of a gateway.
519   A gateway communicates with inbound servers using any protocol that
520   it desires, including private extensions to HTTP that are outside
521   the scope of this specification.  However, an HTTP-to-HTTP gateway
522   that wishes to interoperate with third-party HTTP servers &MUST;
523   conform to HTTP user agent requirements on the gateway's inbound
524   connection and &MUST; implement the <x:ref>Connection</x:ref>
525   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
526   (<xref target="header.via"/>) header fields for both connections.
527</t>
528<t><iref primary="true" item="tunnel"/>
529   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
530   without changing the messages. Once active, a tunnel is not
531   considered a party to the HTTP communication, though the tunnel might
532   have been initiated by an HTTP request. A tunnel ceases to exist when
533   both ends of the relayed connection are closed. Tunnels are used to
534   extend a virtual connection through an intermediary, such as when
535   transport-layer security is used to establish confidential communication
536   through a shared firewall proxy.
537</t>
538<t><iref primary="true" item="interception proxy"/>
539<iref primary="true" item="transparent proxy"/>
540<iref primary="true" item="captive portal"/>
541   The above categories for intermediary only consider those acting as
542   participants in the HTTP communication.  There are also intermediaries
543   that can act on lower layers of the network protocol stack, filtering or
544   redirecting HTTP traffic without the knowledge or permission of message
545   senders. Network intermediaries often introduce security flaws or
546   interoperability problems by violating HTTP semantics.  For example, an
547   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
548   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
549   "<x:dfn>captive portal</x:dfn>")
550   differs from an HTTP proxy because it is not selected by the client.
551   Instead, an interception proxy filters or redirects outgoing TCP port 80
552   packets (and occasionally other common port traffic).
553   Interception proxies are commonly found on public network access points,
554   as a means of enforcing account subscription prior to allowing use of
555   non-local Internet services, and within corporate firewalls to enforce
556   network usage policies.
557   They are indistinguishable from a man-in-the-middle attack.
558</t>
559<t>
560   HTTP is defined as a stateless protocol, meaning that each request message
561   can be understood in isolation.  Many implementations depend on HTTP's
562   stateless design in order to reuse proxied connections or dynamically
563   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
564   assume that two requests on the same connection are from the same user
565   agent unless the connection is secured and specific to that agent.
566   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
567   been known to violate this requirement, resulting in security and
568   interoperability problems.
569</t>
570</section>
571
572<section title="Caches" anchor="caches">
573<iref primary="true" item="cache"/>
574<t>
575   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
576   subsystem that controls its message storage, retrieval, and deletion.
577   A cache stores cacheable responses in order to reduce the response
578   time and network bandwidth consumption on future, equivalent
579   requests. Any client or server &MAY; employ a cache, though a cache
580   cannot be used by a server while it is acting as a tunnel.
581</t>
582<t>
583   The effect of a cache is that the request/response chain is shortened
584   if one of the participants along the chain has a cached response
585   applicable to that request. The following illustrates the resulting
586   chain if B has a cached copy of an earlier response from O (via C)
587   for a request which has not been cached by UA or A.
588</t>
589<figure><artwork type="drawing">
590            &gt;             &gt;
591       <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>
592                  &lt;             &lt;
593</artwork></figure>
594<t><iref primary="true" item="cacheable"/>
595   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
596   the response message for use in answering subsequent requests.
597   Even when a response is cacheable, there might be additional
598   constraints placed by the client or by the origin server on when
599   that cached response can be used for a particular request. HTTP
600   requirements for cache behavior and cacheable responses are
601   defined in &caching-overview;
602</t>
603<t>
604   There are a wide variety of architectures and configurations
605   of caches and proxies deployed across the World Wide Web and
606   inside large organizations. These systems include national hierarchies
607   of proxy caches to save transoceanic bandwidth, systems that
608   broadcast or multicast cache entries, organizations that distribute
609   subsets of cached data via optical media, and so on.
610</t>
611</section>
612
613<section title="Conformance and Error Handling" anchor="conformance">
614<t>
615   This specification targets conformance criteria according to the role of
616   a participant in HTTP communication.  Hence, HTTP requirements are placed
617   on senders, recipients, clients, servers, user agents, intermediaries,
618   origin servers, proxies, gateways, or caches, depending on what behavior
619   is being constrained by the requirement.
620</t>
621<t>
622   The verb "generate" is used instead of "send" where a requirement
623   differentiates between creating a protocol element and merely forwarding a
624   received element downstream.
625</t>
626<t>
627   An implementation is considered conformant if it complies with all of the
628   requirements associated with the roles it partakes in HTTP. Note that
629   SHOULD-level requirements are relevant here, unless one of the documented
630   exceptions is applicable.
631</t>
632<t>
633   In addition to the prose requirements placed upon them, senders &MUST-NOT;
634   generate protocol elements that do not match the grammar defined by the
635   ABNF rules for those protocol elements that are applicable to the sender's
636   role. If a received protocol element is processed, the recipient &MUST; be
637   able to parse any value that would match the ABNF rules for that protocol
638   element, excluding only those rules not applicable to the recipient's role.
639</t>
640<t>
641   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
642   protocol element from an invalid construct.  HTTP does not define
643   specific error handling mechanisms except when they have a direct impact
644   on security, since different applications of the protocol require
645   different error handling strategies.  For example, a Web browser might
646   wish to transparently recover from a response where the
647   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
648   whereas a systems control client might consider any form of error recovery
649   to be dangerous.
650</t>
651</section>
652
653<section title="Protocol Versioning" anchor="http.version">
654  <x:anchor-alias value="HTTP-version"/>
655  <x:anchor-alias value="HTTP-name"/>
656<t>
657   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
658   versions of the protocol. This specification defines version "1.1".
659   The protocol version as a whole indicates the sender's conformance
660   with the set of requirements laid out in that version's corresponding
661   specification of HTTP.
662</t>
663<t>
664   The version of an HTTP message is indicated by an HTTP-version field
665   in the first line of the message. HTTP-version is case-sensitive.
666</t>
667<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
668  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
669  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
670</artwork></figure>
671<t>
672   The HTTP version number consists of two decimal digits separated by a "."
673   (period or decimal point).  The first digit ("major version") indicates the
674   HTTP messaging syntax, whereas the second digit ("minor version") indicates
675   the highest minor version to which the sender is
676   conformant and able to understand for future communication.  The minor
677   version advertises the sender's communication capabilities even when the
678   sender is only using a backwards-compatible subset of the protocol,
679   thereby letting the recipient know that more advanced features can
680   be used in response (by servers) or in future requests (by clients).
681</t>
682<t>
683   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
684   <xref target="RFC1945"/> or a recipient whose version is unknown,
685   the HTTP/1.1 message is constructed such that it can be interpreted
686   as a valid HTTP/1.0 message if all of the newer features are ignored.
687   This specification places recipient-version requirements on some
688   new features so that a conformant sender will only use compatible
689   features until it has determined, through configuration or the
690   receipt of a message, that the recipient supports HTTP/1.1.
691</t>
692<t>
693   The interpretation of a header field does not change between minor
694   versions of the same major HTTP version, though the default
695   behavior of a recipient in the absence of such a field can change.
696   Unless specified otherwise, header fields defined in HTTP/1.1 are
697   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
698   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
699   HTTP/1.x implementations whether or not they advertise conformance with
700   HTTP/1.1.
701</t>
702<t>
703   New header fields can be defined such that, when they are
704   understood by a recipient, they might override or enhance the
705   interpretation of previously defined header fields.  When an
706   implementation receives an unrecognized header field, the recipient
707   &MUST; ignore that header field for local processing regardless of
708   the message's HTTP version.  An unrecognized header field received
709   by a proxy &MUST; be forwarded downstream unless the header field's
710   field-name is listed in the message's <x:ref>Connection</x:ref> header field
711   (see <xref target="header.connection"/>).
712   These requirements allow HTTP's functionality to be enhanced without
713   requiring prior update of deployed intermediaries.
714</t>
715<t>
716   Intermediaries that process HTTP messages (i.e., all intermediaries
717   other than those acting as tunnels) &MUST; send their own HTTP-version
718   in forwarded messages.  In other words, they &MUST-NOT; blindly
719   forward the first line of an HTTP message without ensuring that the
720   protocol version in that message matches a version to which that
721   intermediary is conformant for both the receiving and
722   sending of messages.  Forwarding an HTTP message without rewriting
723   the HTTP-version might result in communication errors when downstream
724   recipients use the message sender's version to determine what features
725   are safe to use for later communication with that sender.
726</t>
727<t>
728   An HTTP client &SHOULD; send a request version equal to the highest
729   version to which the client is conformant and
730   whose major version is no higher than the highest version supported
731   by the server, if this is known.  An HTTP client &MUST-NOT; send a
732   version to which it is not conformant.
733</t>
734<t>
735   An HTTP client &MAY; send a lower request version if it is known that
736   the server incorrectly implements the HTTP specification, but only
737   after the client has attempted at least one normal request and determined
738   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
739   the server improperly handles higher request versions.
740</t>
741<t>
742   An HTTP server &SHOULD; send a response version equal to the highest
743   version to which the server is conformant and
744   whose major version is less than or equal to the one received in the
745   request.  An HTTP server &MUST-NOT; send a version to which it is not
746   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
747   Supported)</x:ref> response if it cannot send a response using the
748   major version used in the client's request.
749</t>
750<t>
751   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
752   if it is known or suspected that the client incorrectly implements the
753   HTTP specification and is incapable of correctly processing later
754   version responses, such as when a client fails to parse the version
755   number correctly or when an intermediary is known to blindly forward
756   the HTTP-version even when it doesn't conform to the given minor
757   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
758   performed unless triggered by specific client attributes, such as when
759   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
760   uniquely match the values sent by a client known to be in error.
761</t>
762<t>
763   The intention of HTTP's versioning design is that the major number
764   will only be incremented if an incompatible message syntax is
765   introduced, and that the minor number will only be incremented when
766   changes made to the protocol have the effect of adding to the message
767   semantics or implying additional capabilities of the sender.  However,
768   the minor version was not incremented for the changes introduced between
769   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
770   is specifically avoiding any such changes to the protocol.
771</t>
772</section>
773
774<section title="Uniform Resource Identifiers" anchor="uri">
775<iref primary="true" item="resource"/>
776<t>
777   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
778   throughout HTTP as the means for identifying resources. URI references
779   are used to target requests, indicate redirects, and define relationships.
780   HTTP does not limit what a resource might be; it merely defines an interface
781   that can be used to interact with a resource via HTTP. More information on
782   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
783</t>
784  <x:anchor-alias value="URI-reference"/>
785  <x:anchor-alias value="absolute-URI"/>
786  <x:anchor-alias value="relative-part"/>
787  <x:anchor-alias value="authority"/>
788  <x:anchor-alias value="path-abempty"/>
789  <x:anchor-alias value="path-absolute"/>
790  <x:anchor-alias value="port"/>
791  <x:anchor-alias value="query"/>
792  <x:anchor-alias value="uri-host"/>
793  <x:anchor-alias value="partial-URI"/>
794<t>
795   This specification adopts the definitions of "URI-reference",
796   "absolute-URI", "relative-part", "port", "host",
797   "path-abempty", "path-absolute", "query", and "authority" from the
798   URI generic syntax <xref target="RFC3986"/>.
799   In addition, we define a partial-URI rule for protocol elements
800   that allow a relative URI but not a fragment.
801</t>
802<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><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"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
803  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
804  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
805  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
806  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
807  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
808  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
809  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
810  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
811  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
812 
813  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
814</artwork></figure>
815<t>
816   Each protocol element in HTTP that allows a URI reference will indicate
817   in its ABNF production whether the element allows any form of reference
818   (URI-reference), only a URI in absolute form (absolute-URI), only the
819   path and optional query components, or some combination of the above.
820   Unless otherwise indicated, URI references are parsed
821   relative to the effective request URI
822   (<xref target="effective.request.uri"/>).
823</t>
824
825<section title="http URI scheme" anchor="http.uri">
826  <x:anchor-alias value="http-URI"/>
827  <iref item="http URI scheme" primary="true"/>
828  <iref item="URI scheme" subitem="http" primary="true"/>
829<t>
830   The "http" URI scheme is hereby defined for the purpose of minting
831   identifiers according to their association with the hierarchical
832   namespace governed by a potential HTTP origin server listening for
833   TCP connections on a given port.
834</t>
835<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
836  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
837</artwork></figure>
838<t>
839   The HTTP origin server is identified by the generic syntax's
840   <x:ref>authority</x:ref> component, which includes a host identifier
841   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
842   The remainder of the URI, consisting of both the hierarchical path
843   component and optional query component, serves as an identifier for
844   a potential resource within that origin server's name space.
845</t>
846<t>
847   If the host identifier is provided as an IP literal or IPv4 address,
848   then the origin server is any listener on the indicated TCP port at
849   that IP address. If host is a registered name, then that name is
850   considered an indirect identifier and the recipient might use a name
851   resolution service, such as DNS, to find the address of a listener
852   for that host.
853   The host &MUST-NOT; be empty; if an "http" URI is received with an
854   empty host, then it &MUST; be rejected as invalid.
855   If the port subcomponent is empty or not given, then TCP port 80 is
856   assumed (the default reserved port for WWW services).
857</t>
858<t>
859   Regardless of the form of host identifier, access to that host is not
860   implied by the mere presence of its name or address. The host might or might
861   not exist and, even when it does exist, might or might not be running an
862   HTTP server or listening to the indicated port. The "http" URI scheme
863   makes use of the delegated nature of Internet names and addresses to
864   establish a naming authority (whatever entity has the ability to place
865   an HTTP server at that Internet name or address) and allows that
866   authority to determine which names are valid and how they might be used.
867</t>
868<t>
869   When an "http" URI is used within a context that calls for access to the
870   indicated resource, a client &MAY; attempt access by resolving
871   the host to an IP address, establishing a TCP connection to that address
872   on the indicated port, and sending an HTTP request message
873   (<xref target="http.message"/>) containing the URI's identifying data
874   (<xref target="message.routing"/>) to the server.
875   If the server responds to that request with a non-interim HTTP response
876   message, as described in &status-codes;, then that response
877   is considered an authoritative answer to the client's request.
878</t>
879<t>
880   Although HTTP is independent of the transport protocol, the "http"
881   scheme is specific to TCP-based services because the name delegation
882   process depends on TCP for establishing authority.
883   An HTTP service based on some other underlying connection protocol
884   would presumably be identified using a different URI scheme, just as
885   the "https" scheme (below) is used for servers that require an SSL/TLS
886   transport layer on a connection. Other protocols might also be used to
887   provide access to "http" identified resources &mdash; it is only the
888   authoritative interface used for mapping the namespace that is
889   specific to TCP.
890</t>
891<t>
892   The URI generic syntax for authority also includes a deprecated
893   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
894   for including user authentication information in the URI.  Some
895   implementations make use of the userinfo component for internal
896   configuration of authentication information, such as within command
897   invocation options, configuration files, or bookmark lists, even
898   though such usage might expose a user identifier or password.
899   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
900   delimiter) when transmitting an "http" URI in a message.  Recipients
901   of HTTP messages that contain a URI reference &SHOULD; parse for the
902   existence of userinfo and treat its presence as an error, likely
903   indicating that the deprecated subcomponent is being used to obscure
904   the authority for the sake of phishing attacks.
905</t>
906</section>
907
908<section title="https URI scheme" anchor="https.uri">
909   <x:anchor-alias value="https-URI"/>
910   <iref item="https URI scheme"/>
911   <iref item="URI scheme" subitem="https"/>
912<t>
913   The "https" URI scheme is hereby defined for the purpose of minting
914   identifiers according to their association with the hierarchical
915   namespace governed by a potential HTTP origin server listening for
916   SSL/TLS-secured connections on a given TCP port.
917</t>
918<t>
919   All of the requirements listed above for the "http" scheme are also
920   requirements for the "https" scheme, except that a default TCP port
921   of 443 is assumed if the port subcomponent is empty or not given,
922   and the TCP connection &MUST; be secured through the
923   use of strong encryption prior to sending the first HTTP request.
924</t>
925<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
926  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
927</artwork></figure>
928<t>
929   Unlike the "http" scheme, responses to "https" identified requests
930   are never "public" and thus &MUST-NOT; be reused for shared caching.
931   They can, however, be reused in a private cache if the message is
932   cacheable by default in HTTP or specifically indicated as such by
933   the Cache-Control header field (&header-cache-control;).
934</t>
935<t>
936   Resources made available via the "https" scheme have no shared
937   identity with the "http" scheme even if their resource identifiers
938   indicate the same authority (the same host listening to the same
939   TCP port).  They are distinct name spaces and are considered to be
940   distinct origin servers.  However, an extension to HTTP that is
941   defined to apply to entire host domains, such as the Cookie protocol
942   <xref target="RFC6265"/>, can allow information
943   set by one service to impact communication with other services
944   within a matching group of host domains.
945</t>
946<t>
947   The process for authoritative access to an "https" identified
948   resource is defined in <xref target="RFC2818"/>.
949</t>
950</section>
951
952<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
953<t>
954   Since the "http" and "https" schemes conform to the URI generic syntax,
955   such URIs are normalized and compared according to the algorithm defined
956   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
957   described above for each scheme.
958</t>
959<t>
960   If the port is equal to the default port for a scheme, the normal
961   form is to elide the port subcomponent. Likewise, an empty path
962   component is equivalent to an absolute path of "/", so the normal
963   form is to provide a path of "/" instead. The scheme and host
964   are case-insensitive and normally provided in lowercase; all
965   other components are compared in a case-sensitive manner.
966   Characters other than those in the "reserved" set are equivalent
967   to their percent-encoded octets (see <xref target="RFC3986"
968   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
969</t>
970<t>
971   For example, the following three URIs are equivalent:
972</t>
973<figure><artwork type="example">
974   http://example.com:80/~smith/home.html
975   http://EXAMPLE.com/%7Esmith/home.html
976   http://EXAMPLE.com:/%7esmith/home.html
977</artwork></figure>
978</section>
979</section>
980</section>
981
982<section title="Message Format" anchor="http.message">
983<x:anchor-alias value="generic-message"/>
984<x:anchor-alias value="message.types"/>
985<x:anchor-alias value="HTTP-message"/>
986<x:anchor-alias value="start-line"/>
987<iref item="header section"/>
988<iref item="headers"/>
989<iref item="header field"/>
990<t>
991   All HTTP/1.1 messages consist of a start-line followed by a sequence of
992   octets in a format similar to the Internet Message Format
993   <xref target="RFC5322"/>: zero or more header fields (collectively
994   referred to as the "headers" or the "header section"), an empty line
995   indicating the end of the header section, and an optional message body.
996</t>
997<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
998  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
999                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1000                   <x:ref>CRLF</x:ref>
1001                   [ <x:ref>message-body</x:ref> ]
1002</artwork></figure>
1003<t>
1004   The normal procedure for parsing an HTTP message is to read the
1005   start-line into a structure, read each header field into a hash
1006   table by field name until the empty line, and then use the parsed
1007   data to determine if a message body is expected.  If a message body
1008   has been indicated, then it is read as a stream until an amount
1009   of octets equal to the message body length is read or the connection
1010   is closed.
1011</t>
1012<t>
1013   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1014   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1015   Parsing an HTTP message as a stream of Unicode characters, without regard
1016   for the specific encoding, creates security vulnerabilities due to the
1017   varying ways that string processing libraries handle invalid multibyte
1018   character sequences that contain the octet LF (%x0A).  String-based
1019   parsers can only be safely used within protocol elements after the element
1020   has been extracted from the message, such as within a header field-value
1021   after message parsing has delineated the individual fields.
1022</t>
1023<t>
1024   An HTTP message can be parsed as a stream for incremental processing or
1025   forwarding downstream.  However, recipients cannot rely on incremental
1026   delivery of partial messages, since some implementations will buffer or
1027   delay message forwarding for the sake of network efficiency, security
1028   checks, or payload transformations.
1029</t>
1030
1031<section title="Start Line" anchor="start.line">
1032  <x:anchor-alias value="Start-Line"/>
1033<t>
1034   An HTTP message can either be a request from client to server or a
1035   response from server to client.  Syntactically, the two types of message
1036   differ only in the start-line, which is either a request-line (for requests)
1037   or a status-line (for responses), and in the algorithm for determining
1038   the length of the message body (<xref target="message.body"/>).
1039   In theory, a client could receive requests and a server could receive
1040   responses, distinguishing them by their different start-line formats,
1041   but in practice servers are implemented to only expect a request
1042   (a response is interpreted as an unknown or invalid request method)
1043   and clients are implemented to only expect a response.
1044</t>
1045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1046  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1047</artwork></figure>
1048<t>
1049   Implementations &MUST-NOT; send whitespace between the start-line and
1050   the first header field. The presence of such whitespace in a request
1051   might be an attempt to trick a server into ignoring that field or
1052   processing the line after it as a new request, either of which might
1053   result in a security vulnerability if other implementations within
1054   the request chain interpret the same message differently.
1055   Likewise, the presence of such whitespace in a response might be
1056   ignored by some clients or cause others to cease parsing.
1057</t>
1058
1059<section title="Request Line" anchor="request.line">
1060  <x:anchor-alias value="Request"/>
1061  <x:anchor-alias value="request-line"/>
1062<t>
1063   A request-line begins with a method token, followed by a single
1064   space (SP), the request-target, another single space (SP), the
1065   protocol version, and ending with CRLF.
1066</t>
1067<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1068  <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>
1069</artwork></figure>
1070<t>
1071   A server &MUST; be able to parse any received message that begins
1072   with a request-line and matches the ABNF rule for HTTP-message.
1073</t>
1074<iref primary="true" item="method"/>
1075<t anchor="method">
1076   The method token indicates the request method to be performed on the
1077   target resource. The request method is case-sensitive.
1078</t>
1079<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1080  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1081</artwork></figure>
1082<t>
1083   The methods defined by this specification can be found in
1084   &methods;, along with information regarding the HTTP method registry
1085   and considerations for defining new methods.
1086</t>
1087<iref item="request-target"/>
1088<t>
1089   The request-target identifies the target resource upon which to apply
1090   the request, as defined in <xref target="request-target"/>.
1091</t>
1092<t>
1093   No whitespace is allowed inside the method, request-target, and
1094   protocol version.  Hence, recipients typically parse the request-line
1095   into its component parts by splitting on the SP characters.
1096</t>
1097<t>
1098   Unfortunately, some user agents fail to properly encode hypertext
1099   references that have embedded whitespace, sending the characters
1100   directly instead of properly percent-encoding the disallowed characters.
1101   Recipients of an invalid request-line &SHOULD; respond with either a
1102   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1103   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1104   attempt to autocorrect and then process the request without a redirect,
1105   since the invalid request-line might be deliberately crafted to bypass
1106   security filters along the request chain.
1107</t>
1108<t>
1109   HTTP does not place a pre-defined limit on the length of a request-line.
1110   A server that receives a method longer than any that it implements
1111   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1112   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1113   A server &MUST; be prepared to receive URIs of unbounded length and
1114   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1115   request-target would be longer than the server wishes to handle
1116   (see &status-414;).
1117</t>
1118<t>
1119   Various ad-hoc limitations on request-line length are found in practice.
1120   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1121   minimum, request-line lengths of up to 8000 octets.
1122</t>
1123</section>
1124
1125<section title="Status Line" anchor="status.line">
1126  <x:anchor-alias value="response"/>
1127  <x:anchor-alias value="status-line"/>
1128  <x:anchor-alias value="status-code"/>
1129  <x:anchor-alias value="reason-phrase"/>
1130<t>
1131   The first line of a response message is the status-line, consisting
1132   of the protocol version, a space (SP), the status code, another space,
1133   a possibly-empty textual phrase describing the status code, and
1134   ending with CRLF.
1135</t>
1136<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1137  <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>
1138</artwork></figure>
1139<t>
1140   A client &MUST; be able to parse any received message that begins
1141   with a status-line and matches the ABNF rule for HTTP-message.
1142</t>
1143<t>
1144   The status-code element is a 3-digit integer code describing the
1145   result of the server's attempt to understand and satisfy the client's
1146   corresponding request. The rest of the response message is to be
1147   interpreted in light of the semantics defined for that status code.
1148   See &status-codes; for information about the semantics of status codes,
1149   including the classes of status code (indicated by the first digit),
1150   the status codes defined by this specification, considerations for the
1151   definition of new status codes, and the IANA registry.
1152</t>
1153<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1154  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1155</artwork></figure>
1156<t>   
1157   The reason-phrase element exists for the sole purpose of providing a
1158   textual description associated with the numeric status code, mostly
1159   out of deference to earlier Internet application protocols that were more
1160   frequently used with interactive text clients. A client &SHOULD; ignore
1161   the reason-phrase content.
1162</t>
1163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1164  <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> )
1165</artwork></figure>
1166</section>
1167</section>
1168
1169<section title="Header Fields" anchor="header.fields">
1170  <x:anchor-alias value="header-field"/>
1171  <x:anchor-alias value="field-content"/>
1172  <x:anchor-alias value="field-name"/>
1173  <x:anchor-alias value="field-value"/>
1174  <x:anchor-alias value="obs-fold"/>
1175<t>
1176   Each HTTP header field consists of a case-insensitive field name
1177   followed by a colon (":"), optional whitespace, and the field value.
1178</t>
1179<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"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1180  <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>
1181  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1182  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1183  <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> )
1184  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1185                 ; obsolete line folding
1186                 ; see <xref target="field.parsing"/>
1187</artwork></figure>
1188<t>
1189   The field-name token labels the corresponding field-value as having the
1190   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1191   header field is defined in &header-date; as containing the origination
1192   timestamp for the message in which it appears.
1193</t>
1194<t>
1195   HTTP header fields are fully extensible: there is no limit on the
1196   introduction of new field names, each presumably defining new semantics,
1197   or on the number of header fields used in a given message.  Existing
1198   fields are defined in each part of this specification and in many other
1199   specifications outside the standards process.
1200   New header fields can be introduced without changing the protocol version
1201   if their defined semantics allow them to be safely ignored by recipients
1202   that do not recognize them.
1203</t>
1204<t>
1205   New HTTP header fields &SHOULD; be registered with IANA in the
1206   Message Header Field Registry, as described in &iana-header-registry;.
1207   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1208   field-name is listed in the <x:ref>Connection</x:ref> header field
1209   (<xref target="header.connection"/>) or the proxy is specifically
1210   configured to block or otherwise transform such fields.
1211   Unrecognized header fields &SHOULD; be ignored by other recipients.
1212</t>
1213<t>
1214   The order in which header fields with differing field names are
1215   received is not significant. However, it is "good practice" to send
1216   header fields that contain control data first, such as <x:ref>Host</x:ref>
1217   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1218   can decide when not to handle a message as early as possible.  A server
1219   &MUST; wait until the entire header section is received before interpreting
1220   a request message, since later header fields might include conditionals,
1221   authentication credentials, or deliberately misleading duplicate
1222   header fields that would impact request processing.
1223</t>
1224<t>
1225   Multiple header fields with the same field name &MUST-NOT; be
1226   sent in a message unless the entire field value for that
1227   header field is defined as a comma-separated list [i.e., #(values)].
1228   Multiple header fields with the same field name can be combined into
1229   one "field-name: field-value" pair, without changing the semantics of the
1230   message, by appending each subsequent field value to the combined
1231   field value in order, separated by a comma. The order in which
1232   header fields with the same field name are received is therefore
1233   significant to the interpretation of the combined field value;
1234   a proxy &MUST-NOT; change the order of these field values when
1235   forwarding a message.
1236</t>
1237<x:note>
1238  <t>
1239   &Note; The "Set-Cookie" header field as implemented in
1240   practice can occur multiple times, but does not use the list syntax, and
1241   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1242   for details.) Also note that the Set-Cookie2 header field specified in
1243   <xref target="RFC2965"/> does not share this problem.
1244  </t>
1245</x:note>
1246
1247<section title="Whitespace" anchor="whitespace">
1248<t anchor="rule.LWS">
1249   This specification uses three rules to denote the use of linear
1250   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1251   BWS ("bad" whitespace).
1252</t>
1253<t anchor="rule.OWS">
1254   The OWS rule is used where zero or more linear whitespace octets might
1255   appear. OWS &SHOULD; either not be produced or be produced as a single
1256   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1257   be replaced with a single SP or transformed to all SP octets (each
1258   octet other than SP replaced with SP) before interpreting the field value
1259   or forwarding the message downstream.
1260</t>
1261<t anchor="rule.RWS">
1262   RWS is used when at least one linear whitespace octet is required to
1263   separate field tokens. RWS &SHOULD; be produced as a single SP.
1264   Multiple RWS octets that occur within field-content &SHOULD; either
1265   be replaced with a single SP or transformed to all SP octets before
1266   interpreting the field value or forwarding the message downstream.
1267</t>
1268<t anchor="rule.BWS">
1269   BWS is used where the grammar allows optional whitespace, for historical
1270   reasons, but senders &SHOULD-NOT; produce it in messages;
1271   recipients &MUST; accept such bad optional whitespace and remove it before
1272   interpreting the field value or forwarding the message downstream.
1273</t>
1274<t anchor="rule.whitespace">
1275  <x:anchor-alias value="BWS"/>
1276  <x:anchor-alias value="OWS"/>
1277  <x:anchor-alias value="RWS"/>
1278</t>
1279<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"/>
1280  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1281                 ; "optional" whitespace
1282  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1283                 ; "required" whitespace
1284  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1285                 ; "bad" whitespace
1286</artwork></figure>
1287</section>
1288
1289<section title="Field Parsing" anchor="field.parsing">
1290<t>
1291   No whitespace is allowed between the header field-name and colon.
1292   In the past, differences in the handling of such whitespace have led to
1293   security vulnerabilities in request routing and response handling.
1294   Any received request message that contains whitespace between a header
1295   field-name and colon &MUST; be rejected with a response code of 400
1296   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1297   message before forwarding the message downstream.
1298</t>
1299<t>
1300   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1301   preferred. The field value does not include any leading or trailing white
1302   space: OWS occurring before the first non-whitespace octet of the
1303   field value or after the last non-whitespace octet of the field value
1304   is ignored and &SHOULD; be removed before further processing (as this does
1305   not change the meaning of the header field).
1306</t>
1307<t>
1308   Historically, HTTP header field values could be extended over multiple
1309   lines by preceding each extra line with at least one space or horizontal
1310   tab (obs-fold). This specification deprecates such line
1311   folding except within the message/http media type
1312   (<xref target="internet.media.type.message.http"/>).
1313   HTTP senders &MUST-NOT; produce messages that include line folding
1314   (i.e., that contain any field-value that matches the obs-fold rule) unless
1315   the message is intended for packaging within the message/http media type.
1316   HTTP recipients &SHOULD; accept line folding and replace any embedded
1317   obs-fold whitespace with either a single SP or a matching number of SP
1318   octets (to avoid buffer copying) prior to interpreting the field value or
1319   forwarding the message downstream.
1320</t>
1321<t>
1322   Historically, HTTP has allowed field content with text in the ISO-8859-1
1323   <xref target="ISO-8859-1"/> character encoding and supported other
1324   character sets only through use of <xref target="RFC2047"/> encoding.
1325   In practice, most HTTP header field values use only a subset of the
1326   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1327   header fields &SHOULD; limit their field values to US-ASCII octets.
1328   Recipients &SHOULD; treat other (obs-text) octets in field content as
1329   opaque data.
1330</t>
1331</section>
1332
1333<section title="Field Length" anchor="field.length">
1334<t>
1335   HTTP does not place a pre-defined limit on the length of header fields,
1336   either in isolation or as a set. A server &MUST; be prepared to receive
1337   request header fields of unbounded length and respond with a <x:ref>4xx
1338   (Client Error)</x:ref> status code if the received header field(s) would be
1339   longer than the server wishes to handle.
1340</t>
1341<t>
1342   A client that receives response header fields that are longer than it wishes
1343   to handle can only treat it as a server error.
1344</t>
1345<t>
1346   Various ad-hoc limitations on header field length are found in practice. It
1347   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1348   combined header fields have 4000 or more octets.
1349</t>
1350</section>
1351
1352<section title="Field value components" anchor="field.components">
1353<t anchor="rule.token.separators">
1354  <x:anchor-alias value="tchar"/>
1355  <x:anchor-alias value="token"/>
1356  <x:anchor-alias value="special"/>
1357  <x:anchor-alias value="word"/>
1358   Many HTTP header field values consist of words (token or quoted-string)
1359   separated by whitespace or special characters. These special characters
1360   &MUST; be in a quoted string to be used within a parameter value (as defined
1361   in <xref target="transfer.codings"/>).
1362</t>
1363<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"><!--unused production--></iref>
1364  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1365
1366  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1367<!--
1368  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1369 -->
1370  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1371                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1372                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1373                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1374
1375  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1376                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1377                 / "]" / "?" / "=" / "{" / "}"
1378</artwork></figure>
1379<t anchor="rule.quoted-string">
1380  <x:anchor-alias value="quoted-string"/>
1381  <x:anchor-alias value="qdtext"/>
1382  <x:anchor-alias value="obs-text"/>
1383   A string of text is parsed as a single word if it is quoted using
1384   double-quote marks.
1385</t>
1386<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"/>
1387  <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>
1388  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1389  <x:ref>obs-text</x:ref>       = %x80-FF
1390</artwork></figure>
1391<t anchor="rule.quoted-pair">
1392  <x:anchor-alias value="quoted-pair"/>
1393   The backslash octet ("\") can be used as a single-octet
1394   quoting mechanism within quoted-string constructs:
1395</t>
1396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1397  <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> )
1398</artwork></figure>
1399<t>
1400   Recipients that process the value of the quoted-string &MUST; handle a
1401   quoted-pair as if it were replaced by the octet following the backslash.
1402</t>
1403<t>
1404   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1405   escaping (i.e., other than DQUOTE and the backslash octet).
1406</t>
1407<t anchor="rule.comment">
1408  <x:anchor-alias value="comment"/>
1409  <x:anchor-alias value="ctext"/>
1410   Comments can be included in some HTTP header fields by surrounding
1411   the comment text with parentheses. Comments are only allowed in
1412   fields containing "comment" as part of their field value definition.
1413</t>
1414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1415  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1416  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1417</artwork></figure>
1418<t anchor="rule.quoted-cpair">
1419  <x:anchor-alias value="quoted-cpair"/>
1420   The backslash octet ("\") can be used as a single-octet
1421   quoting mechanism within comment constructs:
1422</t>
1423<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1424  <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> )
1425</artwork></figure>
1426<t>
1427   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1428   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1429</t>
1430</section>
1431
1432</section>
1433
1434<section title="Message Body" anchor="message.body">
1435  <x:anchor-alias value="message-body"/>
1436<t>
1437   The message body (if any) of an HTTP message is used to carry the
1438   payload body of that request or response.  The message body is
1439   identical to the payload body unless a transfer coding has been
1440   applied, as described in <xref target="header.transfer-encoding"/>.
1441</t>
1442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1443  <x:ref>message-body</x:ref> = *OCTET
1444</artwork></figure>
1445<t>
1446   The rules for when a message body is allowed in a message differ for
1447   requests and responses.
1448</t>
1449<t>
1450   The presence of a message body in a request is signaled by a
1451   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1452   field. Request message framing is independent of method semantics,
1453   even if the method does not define any use for a message body.
1454</t>
1455<t>
1456   The presence of a message body in a response depends on both
1457   the request method to which it is responding and the response
1458   status code (<xref target="status.line"/>).
1459   Responses to the HEAD request method never include a message body
1460   because the associated response header fields (e.g.,
1461   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1462   indicate what their values would have been if the request method had been
1463   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1464   mode instead of having a message body.
1465   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1466   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1467   All other responses do include a message body, although the body
1468   &MAY; be of zero length.
1469</t>
1470
1471<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1472  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1473  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1474  <x:anchor-alias value="Transfer-Encoding"/>
1475<t>
1476   When one or more transfer codings are applied to a payload body in order
1477   to form the message body, a Transfer-Encoding header field &MUST; be sent
1478   in the message and &MUST; contain the list of corresponding
1479   transfer-coding names in the same order that they were applied.
1480   Transfer codings are defined in <xref target="transfer.codings"/>.
1481</t>
1482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1483  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1484</artwork></figure>
1485<t>
1486   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1487   MIME, which was designed to enable safe transport of binary data over a
1488   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1489   However, safe transport has a different focus for an 8bit-clean transfer
1490   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1491   accurately delimit a dynamically generated payload and to distinguish
1492   payload encodings that are only applied for transport efficiency or
1493   security from those that are characteristics of the target resource.
1494</t>
1495<t>
1496   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1497   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1498   crucial role in delimiting messages when the payload body size is not
1499   known in advance.
1500   When the "chunked" transfer-coding is used, it &MUST; be the last
1501   transfer-coding applied to form the message body and &MUST-NOT;
1502   be applied more than once in a message body.
1503   If any transfer-coding is applied to a request payload body,
1504   the final transfer-coding applied &MUST; be "chunked".
1505   If any transfer-coding is applied to a response payload body, then either
1506   the final transfer-coding applied &MUST; be "chunked" or
1507   the message &MUST; be terminated by closing the connection.
1508</t>
1509<figure><preamble>
1510   For example,
1511</preamble><artwork type="example">
1512  Transfer-Encoding: gzip, chunked
1513</artwork><postamble>
1514   indicates that the payload body has been compressed using the gzip
1515   coding and then chunked using the chunked coding while forming the
1516   message body.
1517</postamble></figure>
1518<t>
1519   If more than one Transfer-Encoding header field is present in a message,
1520   the multiple field-values &MUST; be combined into one field-value,
1521   according to the algorithm defined in <xref target="header.fields"/>,
1522   before determining the message body length.
1523</t>
1524<t>
1525   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1526   Transfer-Encoding is a property of the message, not of the payload, and thus
1527   &MAY; be added or removed by any implementation along the request/response
1528   chain. Additional information about the encoding parameters &MAY; be
1529   provided by other header fields not defined by this specification.
1530</t>
1531<t>
1532   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1533   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1534   neither of which includes a message body,
1535   to indicate that the origin server would have applied a transfer coding
1536   to the message body if the request had been an unconditional GET.
1537   This indication is not required, however, because any recipient on
1538   the response chain (including the origin server) can remove transfer
1539   codings when they are not needed.
1540</t>
1541<t>
1542   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1543   implementations advertising only HTTP/1.0 support will not understand
1544   how to process a transfer-encoded payload.
1545   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1546   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1547   might be in the form of specific user configuration or by remembering the
1548   version of a prior received response.
1549   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1550   the corresponding request indicates HTTP/1.1 (or later).
1551</t>
1552<t>
1553   A server that receives a request message with a transfer-coding it does
1554   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1555   close the connection.
1556</t>
1557</section>
1558
1559<section title="Content-Length" anchor="header.content-length">
1560  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1561  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1562  <x:anchor-alias value="Content-Length"/>
1563<t>
1564   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1565   and the payload body length can be determined prior to being transferred, a
1566   Content-Length header field &SHOULD; be sent to indicate the length of the
1567   payload body that is either present as the message body, for requests
1568   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1569   would have been present had the request been an unconditional GET.  The
1570   length is expressed as a decimal number of octets.
1571</t>
1572<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1573  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1574</artwork></figure>
1575<t>
1576   An example is
1577</t>
1578<figure><artwork type="example">
1579  Content-Length: 3495
1580</artwork></figure>
1581<t>
1582   In the case of a response to a HEAD request, Content-Length indicates
1583   the size of the payload body (without any potential transfer-coding)
1584   that would have been sent had the request been a GET.
1585   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1586   to a GET request, Content-Length indicates the size of the payload body (without
1587   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1588   response.
1589</t>
1590<t>
1591   Any Content-Length field value greater than or equal to zero is valid.
1592   Since there is no predefined limit to the length of an HTTP payload,
1593   recipients &SHOULD; anticipate potentially large decimal numerals and
1594   prevent parsing errors due to integer conversion overflows
1595   (<xref target="attack.protocol.element.size.overflows"/>).
1596</t>
1597<t>
1598   If a message is received that has multiple Content-Length header fields
1599   with field-values consisting of the same decimal value, or a single
1600   Content-Length header field with a field value containing a list of
1601   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1602   duplicate Content-Length header fields have been generated or combined by an
1603   upstream message processor, then the recipient &MUST; either reject the
1604   message as invalid or replace the duplicated field-values with a single
1605   valid Content-Length field containing that decimal value prior to
1606   determining the message body length.
1607</t>
1608<x:note>
1609  <t>
1610   &Note; HTTP's use of Content-Length for message framing differs
1611   significantly from the same field's use in MIME, where it is an optional
1612   field used only within the "message/external-body" media-type.
1613  </t>
1614</x:note>
1615</section>
1616
1617<section title="Message Body Length" anchor="message.body.length">
1618<t>
1619   The length of a message body is determined by one of the following
1620   (in order of precedence):
1621</t>
1622<t>
1623  <list style="numbers">
1624    <x:lt><t>
1625     Any response to a HEAD request and any response with a
1626     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1627     <x:ref>304 (Not Modified)</x:ref> status code is always
1628     terminated by the first empty line after the header fields, regardless of
1629     the header fields present in the message, and thus cannot contain a
1630     message body.
1631    </t></x:lt>
1632    <x:lt><t>
1633     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1634     connection will become a tunnel immediately after the empty line that
1635     concludes the header fields.  A client &MUST; ignore any
1636     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1637     fields received in such a message.
1638    </t></x:lt>
1639    <x:lt><t>
1640     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1641     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1642     is the final encoding, the message body length is determined by reading
1643     and decoding the chunked data until the transfer-coding indicates the
1644     data is complete.
1645    </t>
1646    <t>
1647     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1648     response and the "chunked" transfer-coding is not the final encoding, the
1649     message body length is determined by reading the connection until it is
1650     closed by the server.
1651     If a Transfer-Encoding header field is present in a request and the
1652     "chunked" transfer-coding is not the final encoding, the message body
1653     length cannot be determined reliably; the server &MUST; respond with
1654     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1655    </t>
1656    <t>
1657     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1658     and a <x:ref>Content-Length</x:ref> header field, the
1659     Transfer-Encoding overrides the Content-Length.
1660     Such a message might indicate an attempt to perform request or response
1661     smuggling (bypass of security-related checks on message routing or content)
1662     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1663     be removed, prior to forwarding the message downstream, or replaced with
1664     the real message body length after the transfer-coding is decoded.
1665    </t></x:lt>
1666    <x:lt><t>
1667     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1668     either multiple <x:ref>Content-Length</x:ref> header fields having
1669     differing field-values or a single Content-Length header field having an
1670     invalid value, then the message framing is invalid and &MUST; be treated
1671     as an error to prevent request or response smuggling.
1672     If this is a request message, the server &MUST; respond with
1673     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1674     If this is a response message received by a proxy, the proxy
1675     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1676     status code as its downstream response, and then close the connection.
1677     If this is a response message received by a user-agent, it &MUST; be
1678     treated as an error by discarding the message and closing the connection.
1679    </t></x:lt>
1680    <x:lt><t>
1681     If a valid <x:ref>Content-Length</x:ref> header field is present without
1682     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1683     message body length in octets.  If the actual number of octets sent in
1684     the message is less than the indicated Content-Length, the recipient
1685     &MUST; consider the message to be incomplete and treat the connection
1686     as no longer usable.
1687     If the actual number of octets sent in the message is more than the indicated
1688     Content-Length, the recipient &MUST; only process the message body up to the
1689     field value's number of octets; the remainder of the message &MUST; either
1690     be discarded or treated as the next message in a pipeline.  For the sake of
1691     robustness, a user-agent &MAY; attempt to detect and correct such an error
1692     in message framing if it is parsing the response to the last request on
1693     a connection and the connection has been closed by the server.
1694    </t></x:lt>
1695    <x:lt><t>
1696     If this is a request message and none of the above are true, then the
1697     message body length is zero (no message body is present).
1698    </t></x:lt>
1699    <x:lt><t>
1700     Otherwise, this is a response message without a declared message body
1701     length, so the message body length is determined by the number of octets
1702     received prior to the server closing the connection.
1703    </t></x:lt>
1704  </list>
1705</t>
1706<t>
1707   Since there is no way to distinguish a successfully completed,
1708   close-delimited message from a partially-received message interrupted
1709   by network failure, implementations &SHOULD; use encoding or
1710   length-delimited messages whenever possible.  The close-delimiting
1711   feature exists primarily for backwards compatibility with HTTP/1.0.
1712</t>
1713<t>
1714   A server &MAY; reject a request that contains a message body but
1715   not a <x:ref>Content-Length</x:ref> by responding with
1716   <x:ref>411 (Length Required)</x:ref>.
1717</t>
1718<t>
1719   Unless a transfer-coding other than "chunked" has been applied,
1720   a client that sends a request containing a message body &SHOULD;
1721   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1722   length is known in advance, rather than the "chunked" encoding, since some
1723   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1724   status code even though they understand the chunked encoding.  This
1725   is typically because such services are implemented via a gateway that
1726   requires a content-length in advance of being called and the server
1727   is unable or unwilling to buffer the entire request before processing.
1728</t>
1729<t>
1730   A client that sends a request containing a message body &MUST; include a
1731   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1732   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1733   the form of specific user configuration or by remembering the version of a
1734   prior received response.
1735</t>
1736</section>
1737</section>
1738
1739<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1740<t>
1741   Request messages that are prematurely terminated, possibly due to a
1742   canceled connection or a server-imposed time-out exception, &MUST;
1743   result in closure of the connection; sending an error response
1744   prior to closing the connection is &OPTIONAL;.
1745</t>
1746<t>
1747   Response messages that are prematurely terminated, usually by closure
1748   of the connection prior to receiving the expected number of octets or by
1749   failure to decode a transfer-encoded message body, &MUST; be recorded
1750   as incomplete.  A response that terminates in the middle of the header
1751   block (before the empty line is received) cannot be assumed to convey the
1752   full semantics of the response and &MUST; be treated as an error.
1753</t>
1754<t>
1755   A message body that uses the chunked transfer encoding is
1756   incomplete if the zero-sized chunk that terminates the encoding has not
1757   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1758   incomplete if the size of the message body received (in octets) is less than
1759   the value given by Content-Length.  A response that has neither chunked
1760   transfer encoding nor Content-Length is terminated by closure of the
1761   connection, and thus is considered complete regardless of the number of
1762   message body octets received, provided that the header block was received
1763   intact.
1764</t>
1765<t>
1766   A user agent &MUST-NOT; render an incomplete response message body as if
1767   it were complete (i.e., some indication needs to be given to the user that an
1768   error occurred).  Cache requirements for incomplete responses are defined
1769   in &cache-incomplete;.
1770</t>
1771<t>
1772   A server &MUST; read the entire request message body or close
1773   the connection after sending its response, since otherwise the
1774   remaining data on a persistent connection would be misinterpreted
1775   as the next request.  Likewise,
1776   a client &MUST; read the entire response message body if it intends
1777   to reuse the same connection for a subsequent request.  Pipelining
1778   multiple requests on a connection is described in <xref target="pipelining"/>.
1779</t>
1780</section>
1781
1782<section title="Message Parsing Robustness" anchor="message.robustness">
1783<t>
1784   Older HTTP/1.0 client implementations might send an extra CRLF
1785   after a POST request as a lame workaround for some early server
1786   applications that failed to read message body content that was
1787   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1788   preface or follow a request with an extra CRLF.  If terminating
1789   the request message body with a line-ending is desired, then the
1790   client &MUST; include the terminating CRLF octets as part of the
1791   message body length.
1792</t>
1793<t>
1794   In the interest of robustness, servers &SHOULD; ignore at least one
1795   empty line received where a request-line is expected. In other words, if
1796   the server is reading the protocol stream at the beginning of a
1797   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1798   Likewise, although the line terminator for the start-line and header
1799   fields is the sequence CRLF, we recommend that recipients recognize a
1800   single LF as a line terminator and ignore any CR.
1801</t>
1802<t>
1803   When a server listening only for HTTP request messages, or processing
1804   what appears from the start-line to be an HTTP request message,
1805   receives a sequence of octets that does not match the HTTP-message
1806   grammar aside from the robustness exceptions listed above, the
1807   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1808</t>
1809</section>
1810</section>
1811
1812<section title="Transfer Codings" anchor="transfer.codings">
1813  <x:anchor-alias value="transfer-coding"/>
1814  <x:anchor-alias value="transfer-extension"/>
1815<t>
1816   Transfer-coding values are used to indicate an encoding
1817   transformation that has been, can be, or might need to be applied to a
1818   payload body in order to ensure "safe transport" through the network.
1819   This differs from a content coding in that the transfer-coding is a
1820   property of the message rather than a property of the representation
1821   that is being transferred.
1822</t>
1823<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1824  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1825                     / "compress" ; <xref target="compress.coding"/>
1826                     / "deflate" ; <xref target="deflate.coding"/>
1827                     / "gzip" ; <xref target="gzip.coding"/>
1828                     / <x:ref>transfer-extension</x:ref>
1829  <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> )
1830</artwork></figure>
1831<t anchor="rule.parameter">
1832  <x:anchor-alias value="attribute"/>
1833  <x:anchor-alias value="transfer-parameter"/>
1834  <x:anchor-alias value="value"/>
1835   Parameters are in the form of attribute/value pairs.
1836</t>
1837<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"/>
1838  <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>
1839  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1840  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1841</artwork></figure>
1842<t>
1843   All transfer-coding values are case-insensitive and &SHOULD; be registered
1844   within the HTTP Transfer Coding registry, as defined in
1845   <xref target="transfer.coding.registry"/>.
1846   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1847   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1848   header fields.
1849</t>
1850
1851<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1852  <iref item="chunked (Coding Format)"/>
1853  <iref item="Coding Format" subitem="chunked"/>
1854  <x:anchor-alias value="chunk"/>
1855  <x:anchor-alias value="chunked-body"/>
1856  <x:anchor-alias value="chunk-data"/>
1857  <x:anchor-alias value="chunk-ext"/>
1858  <x:anchor-alias value="chunk-ext-name"/>
1859  <x:anchor-alias value="chunk-ext-val"/>
1860  <x:anchor-alias value="chunk-size"/>
1861  <x:anchor-alias value="last-chunk"/>
1862  <x:anchor-alias value="trailer-part"/>
1863  <x:anchor-alias value="quoted-str-nf"/>
1864  <x:anchor-alias value="qdtext-nf"/>
1865<t>
1866   The chunked encoding modifies the body of a message in order to
1867   transfer it as a series of chunks, each with its own size indicator,
1868   followed by an &OPTIONAL; trailer containing header fields. This
1869   allows dynamically produced content to be transferred along with the
1870   information necessary for the recipient to verify that it has
1871   received the full message.
1872</t>
1873<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><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"/>
1874  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1875                   <x:ref>last-chunk</x:ref>
1876                   <x:ref>trailer-part</x:ref>
1877                   <x:ref>CRLF</x:ref>
1878 
1879  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1880                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1881  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1882  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1883 
1884  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1885  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1886  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1887  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1888  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1889 
1890  <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>
1891                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1892  <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>
1893</artwork></figure>
1894<t>
1895   Chunk extensions within the chucked encoding are deprecated.
1896   Senders &SHOULD-NOT; send chunk-ext.
1897   Definition of new chunk extensions is discouraged.
1898</t>
1899<t>
1900   The chunk-size field is a string of hex digits indicating the size of
1901   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1902   zero, followed by the trailer, which is terminated by an empty line.
1903</t>
1904
1905<section title="Trailer" anchor="header.trailer">
1906  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1907  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
1908  <x:anchor-alias value="Trailer"/>
1909<t>
1910   A trailer allows the sender to include additional fields at the end of a
1911   chunked message in order to supply metadata that might be dynamically
1912   generated while the message body is sent, such as a message integrity
1913   check, digital signature, or post-processing status.
1914   The trailer &MUST-NOT; contain fields that need to be known before a
1915   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1916   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1917</t>
1918<t>
1919   When a message includes a message body encoded with the chunked
1920   transfer-coding and the sender desires to send metadata in the form of
1921   trailer fields at the end of the message, the sender &SHOULD; send a
1922   <x:ref>Trailer</x:ref> header field before the message body to indicate
1923   which fields will be present in the trailers. This allows the recipient
1924   to prepare for receipt of that metadata before it starts processing the body,
1925   which is useful if the message is being streamed and the recipient wishes
1926   to confirm an integrity check on the fly.
1927</t>
1928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1929  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1930</artwork></figure>
1931<t>
1932   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1933   chunked message body &SHOULD; send an empty trailer.
1934</t>
1935<t>
1936   A server &MUST; send an empty trailer with the chunked transfer-coding
1937   unless at least one of the following is true:
1938  <list style="numbers">
1939    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1940    "trailers" is acceptable in the transfer-coding of the response, as
1941    described in <xref target="header.te"/>; or,</t>
1942     
1943    <t>the trailer fields consist entirely of optional metadata and the
1944    recipient could use the message (in a manner acceptable to the server where
1945    the field originated) without receiving that metadata. In other words,
1946    the server that generated the header field is willing to accept the
1947    possibility that the trailer fields might be silently discarded along
1948    the path to the client.</t>
1949  </list>
1950</t>
1951<t>
1952   The above requirement prevents the need for an infinite buffer when a
1953   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1954   an HTTP/1.0 recipient.
1955</t>
1956</section>
1957
1958<section title="Decoding chunked" anchor="decoding.chunked">
1959<t>
1960   A process for decoding the "chunked" transfer-coding
1961   can be represented in pseudo-code as:
1962</t>
1963<figure><artwork type="code">
1964  length := 0
1965  read chunk-size, chunk-ext (if any) and CRLF
1966  while (chunk-size &gt; 0) {
1967     read chunk-data and CRLF
1968     append chunk-data to decoded-body
1969     length := length + chunk-size
1970     read chunk-size and CRLF
1971  }
1972  read header-field
1973  while (header-field not empty) {
1974     append header-field to existing header fields
1975     read header-field
1976  }
1977  Content-Length := length
1978  Remove "chunked" from Transfer-Encoding
1979  Remove Trailer from existing header fields
1980</artwork></figure>
1981<t>
1982   All recipients &MUST; be able to receive and decode the
1983   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1984   they do not understand.
1985</t>
1986</section>
1987</section>
1988
1989<section title="Compression Codings" anchor="compression.codings">
1990<t>
1991   The codings defined below can be used to compress the payload of a
1992   message.
1993</t>
1994
1995<section title="Compress Coding" anchor="compress.coding">
1996<iref item="compress (Coding Format)"/>
1997<iref item="Coding Format" subitem="compress"/>
1998<t>
1999   The "compress" format is produced by the common UNIX file compression
2000   program "compress". This format is an adaptive Lempel-Ziv-Welch
2001   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2002   equivalent to "compress".
2003</t>
2004</section>
2005
2006<section title="Deflate Coding" anchor="deflate.coding">
2007<iref item="deflate (Coding Format)"/>
2008<iref item="Coding Format" subitem="deflate"/>
2009<t>
2010   The "deflate" format is defined as the "deflate" compression mechanism
2011   (described in <xref target="RFC1951"/>) used inside the "zlib"
2012   data format (<xref target="RFC1950"/>).
2013</t>
2014<x:note>
2015  <t>
2016    &Note; Some incorrect implementations send the "deflate"
2017    compressed data without the zlib wrapper.
2018   </t>
2019</x:note>
2020</section>
2021
2022<section title="Gzip Coding" anchor="gzip.coding">
2023<iref item="gzip (Coding Format)"/>
2024<iref item="Coding Format" subitem="gzip"/>
2025<t>
2026   The "gzip" format is produced by the file compression program
2027   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2028   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2029   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2030</t>
2031</section>
2032
2033</section>
2034
2035<section title="TE" anchor="header.te">
2036  <iref primary="true" item="TE header field" x:for-anchor=""/>
2037  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2038  <x:anchor-alias value="TE"/>
2039  <x:anchor-alias value="t-codings"/>
2040  <x:anchor-alias value="t-ranking"/>
2041  <x:anchor-alias value="rank"/>
2042<t>
2043   The "TE" header field in a request indicates what transfer-codings,
2044   besides "chunked", the client is willing to accept in response, and
2045   whether or not the client is willing to accept trailer fields in a
2046   chunked transfer-coding.
2047</t>
2048<t>
2049   The TE field-value consists of a comma-separated list of transfer-coding
2050   names, each allowing for optional parameters (as described in
2051   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2052   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2053   chunked is always acceptable for HTTP/1.1 recipients.
2054</t>
2055<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="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/>
2056  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2057  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2058  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2059  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2060             / ( "1" [ "." 0*3("0") ] )
2061</artwork></figure>
2062<t>
2063   Three examples of TE use are below.
2064</t>
2065<figure><artwork type="example">
2066  TE: deflate
2067  TE:
2068  TE: trailers, deflate;q=0.5
2069</artwork></figure>
2070<t>
2071   The presence of the keyword "trailers" indicates that the client is
2072   willing to accept trailer fields in a chunked transfer-coding,
2073   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2074   any downstream clients. For chained requests, this implies that either:
2075   (a) all downstream clients are willing to accept trailer fields in the
2076   forwarded response; or,
2077   (b) the client will attempt to buffer the response on behalf of downstream
2078   recipients.
2079   Note that HTTP/1.1 does not define any means to limit the size of a
2080   chunked response such that a client can be assured of buffering the
2081   entire response.
2082</t>
2083<t>
2084   When multiple transfer-codings are acceptable, the client &MAY; rank the
2085   codings by preference using a case-insensitive "q" parameter (similar to
2086   the qvalues used in content negotiation fields, &qvalue;). The rank value
2087   is a real number in the range 0 through 1, where 0.001 is the least
2088   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2089</t>
2090<t>
2091   If the TE field-value is empty or if no TE field is present, the only
2092   acceptable transfer-coding is "chunked". A message with no transfer-coding
2093   is always acceptable.
2094</t>
2095<t>
2096   Since the TE header field only applies to the immediate connection,
2097   a sender of TE &MUST; also send a "TE" connection option within the
2098   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2099   in order to prevent the TE field from being forwarded by intermediaries
2100   that do not support its semantics.
2101</t>
2102</section>
2103</section>
2104
2105<section title="Message Routing" anchor="message.routing">
2106<t>
2107   HTTP request message routing is determined by each client based on the
2108   target resource, the client's proxy configuration, and
2109   establishment or reuse of an inbound connection.  The corresponding
2110   response routing follows the same connection chain back to the client.
2111</t>
2112
2113<section title="Identifying a Target Resource" anchor="target-resource">
2114  <iref primary="true" item="target resource"/>
2115  <iref primary="true" item="target URI"/>
2116  <x:anchor-alias value="target resource"/>
2117  <x:anchor-alias value="target URI"/>
2118<t>
2119   HTTP is used in a wide variety of applications, ranging from
2120   general-purpose computers to home appliances.  In some cases,
2121   communication options are hard-coded in a client's configuration.
2122   However, most HTTP clients rely on the same resource identification
2123   mechanism and configuration techniques as general-purpose Web browsers.
2124</t>
2125<t>
2126   HTTP communication is initiated by a user agent for some purpose.
2127   The purpose is a combination of request semantics, which are defined in
2128   <xref target="Part2"/>, and a target resource upon which to apply those
2129   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2130   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2131   would resolve to its absolute form in order to obtain the
2132   "<x:dfn>target URI</x:dfn>".  The target URI
2133   excludes the reference's fragment identifier component, if any,
2134   since fragment identifiers are reserved for client-side processing
2135   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2136</t>
2137</section>
2138
2139<section title="Connecting Inbound" anchor="connecting.inbound">
2140<t>
2141   Once the target URI is determined, a client needs to decide whether
2142   a network request is necessary to accomplish the desired semantics and,
2143   if so, where that request is to be directed.
2144</t>
2145<t>
2146   If the client has a response cache and the request semantics can be
2147   satisfied by a cache (<xref target="Part6"/>), then the request is
2148   usually directed to the cache first.
2149</t>
2150<t>
2151   If the request is not satisfied by a cache, then a typical client will
2152   check its configuration to determine whether a proxy is to be used to
2153   satisfy the request.  Proxy configuration is implementation-dependent,
2154   but is often based on URI prefix matching, selective authority matching,
2155   or both, and the proxy itself is usually identified by an "http" or
2156   "https" URI.  If a proxy is applicable, the client connects inbound by
2157   establishing (or reusing) a connection to that proxy.
2158</t>
2159<t>
2160   If no proxy is applicable, a typical client will invoke a handler routine,
2161   usually specific to the target URI's scheme, to connect directly
2162   to an authority for the target resource.  How that is accomplished is
2163   dependent on the target URI scheme and defined by its associated
2164   specification, similar to how this specification defines origin server
2165   access for resolution of the "http" (<xref target="http.uri"/>) and
2166   "https" (<xref target="https.uri"/>) schemes.
2167</t>
2168<t>
2169   HTTP requirements regarding connection management are defined in
2170   <xref target="connection.management"/>.
2171</t>
2172</section>
2173
2174<section title="Request Target" anchor="request-target">
2175<t>
2176   Once an inbound connection is obtained,
2177   the client sends an HTTP request message (<xref target="http.message"/>)
2178   with a request-target derived from the target URI.
2179   There are four distinct formats for the request-target, depending on both
2180   the method being requested and whether the request is to a proxy.
2181</t>   
2182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2183  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2184                 / <x:ref>absolute-form</x:ref>
2185                 / <x:ref>authority-form</x:ref>
2186                 / <x:ref>asterisk-form</x:ref>
2187
2188  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2189  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2190  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2191  <x:ref>asterisk-form</x:ref>  = "*"
2192</artwork></figure>
2193<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2194   The most common form of request-target is the origin-form.
2195   When making a request directly to an origin server, other than a CONNECT
2196   or server-wide OPTIONS request (as detailed below),
2197   a client &MUST; send only the absolute path and query components of
2198   the target URI as the request-target.
2199   If the target URI's path component is empty, then the client &MUST; send
2200   "/" as the path within the origin-form of request-target.
2201   A <x:ref>Host</x:ref> header field is also sent, as defined in
2202   <xref target="header.host"/>, containing the target URI's
2203   authority component (excluding any userinfo).
2204</t>
2205<t>
2206   For example, a client wishing to retrieve a representation of the resource
2207   identified as
2208</t>
2209<figure><artwork x:indent-with="  " type="example">
2210http://www.example.org/where?q=now
2211</artwork></figure>
2212<t>
2213   directly from the origin server would open (or reuse) a TCP connection
2214   to port 80 of the host "www.example.org" and send the lines:
2215</t>
2216<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2217GET /where?q=now HTTP/1.1
2218Host: www.example.org
2219</artwork></figure>
2220<t>
2221   followed by the remainder of the request message.
2222</t>
2223<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2224   When making a request to a proxy, other than a CONNECT or server-wide
2225   OPTIONS request (as detailed below), a client &MUST; send the target URI
2226   in absolute-form as the request-target.
2227   The proxy is requested to either service that request from a valid cache,
2228   if possible, or make the same request on the client's behalf to either
2229   the next inbound proxy server or directly to the origin server indicated
2230   by the request-target.  Requirements on such "forwarding" of messages are
2231   defined in <xref target="message.forwarding"/>.
2232</t>
2233<t>
2234   An example absolute-form of request-line would be:
2235</t>
2236<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2237GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2238</artwork></figure>
2239<t>
2240   To allow for transition to the absolute-form for all requests in some
2241   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2242   in requests, even though HTTP/1.1 clients will only send them in requests
2243   to proxies.
2244</t>
2245<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2246   The authority-form of request-target is only used for CONNECT requests
2247   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2248   one or more proxies, a client &MUST; send only the target URI's
2249   authority component (excluding any userinfo) as the request-target.
2250   For example,
2251</t>
2252<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2253CONNECT www.example.com:80 HTTP/1.1
2254</artwork></figure>
2255<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2256   The asterisk-form of request-target is only used for a server-wide
2257   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2258   for the server as a whole, as opposed to a specific named resource of
2259   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2260   For example,
2261</t>
2262<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2263OPTIONS * HTTP/1.1
2264</artwork></figure>
2265<t>
2266   If a proxy receives an OPTIONS request with an absolute-form of
2267   request-target in which the URI has an empty path and no query component,
2268   then the last proxy on the request chain &MUST; send a request-target
2269   of "*" when it forwards the request to the indicated origin server.
2270</t>
2271<figure><preamble>   
2272   For example, the request
2273</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2274OPTIONS http://www.example.org:8001 HTTP/1.1
2275</artwork></figure>
2276<figure><preamble>   
2277  would be forwarded by the final proxy as
2278</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2279OPTIONS * HTTP/1.1
2280Host: www.example.org:8001
2281</artwork>
2282<postamble>
2283   after connecting to port 8001 of host "www.example.org".
2284</postamble>
2285</figure>
2286</section>
2287
2288<section title="Host" anchor="header.host">
2289  <iref primary="true" item="Host header field" x:for-anchor=""/>
2290  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2291  <x:anchor-alias value="Host"/>
2292<t>
2293   The "Host" header field in a request provides the host and port
2294   information from the target URI, enabling the origin
2295   server to distinguish among resources while servicing requests
2296   for multiple host names on a single IP address.  Since the Host
2297   field-value is critical information for handling a request, it
2298   &SHOULD; be sent as the first header field following the request-line.
2299</t>
2300<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2301  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2302</artwork></figure>
2303<t>
2304   A client &MUST; send a Host header field in all HTTP/1.1 request
2305   messages.  If the target URI includes an authority component, then
2306   the Host field-value &MUST; be identical to that authority component
2307   after excluding any userinfo (<xref target="http.uri"/>).
2308   If the authority component is missing or undefined for the target URI,
2309   then the Host header field &MUST; be sent with an empty field-value.
2310</t>
2311<t>
2312   For example, a GET request to the origin server for
2313   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2314</t>
2315<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2316GET /pub/WWW/ HTTP/1.1
2317Host: www.example.org
2318</artwork></figure>
2319<t>
2320   The Host header field &MUST; be sent in an HTTP/1.1 request even
2321   if the request-target is in the absolute-form, since this
2322   allows the Host information to be forwarded through ancient HTTP/1.0
2323   proxies that might not have implemented Host.
2324</t>
2325<t>
2326   When a proxy receives a request with an absolute-form of
2327   request-target, the proxy &MUST; ignore the received
2328   Host header field (if any) and instead replace it with the host
2329   information of the request-target.  If the proxy forwards the request,
2330   it &MUST; generate a new Host field-value based on the received
2331   request-target rather than forward the received Host field-value.
2332</t>
2333<t>
2334   Since the Host header field acts as an application-level routing
2335   mechanism, it is a frequent target for malware seeking to poison
2336   a shared cache or redirect a request to an unintended server.
2337   An interception proxy is particularly vulnerable if it relies on
2338   the Host field-value for redirecting requests to internal
2339   servers, or for use as a cache key in a shared cache, without
2340   first verifying that the intercepted connection is targeting a
2341   valid IP address for that host.
2342</t>
2343<t>
2344   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2345   to any HTTP/1.1 request message that lacks a Host header field and
2346   to any request message that contains more than one Host header field
2347   or a Host header field with an invalid field-value.
2348</t>
2349</section>
2350
2351<section title="Effective Request URI" anchor="effective.request.uri">
2352  <iref primary="true" item="effective request URI"/>
2353<t>
2354   A server that receives an HTTP request message &MUST; reconstruct
2355   the user agent's original target URI, based on the pieces of information
2356   learned from the request-target, <x:ref>Host</x:ref> header field, and
2357   connection context, in order to identify the intended target resource and
2358   properly service the request. The URI derived from this reconstruction
2359   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2360</t>
2361<t>
2362   For a user agent, the effective request URI is the target URI.
2363</t>
2364<t>
2365   If the request-target is in absolute-form, then the effective request URI
2366   is the same as the request-target.  Otherwise, the effective request URI
2367   is constructed as follows.
2368</t>
2369<t>
2370   If the request is received over an SSL/TLS-secured TCP connection,
2371   then the effective request URI's scheme is "https"; otherwise, the
2372   scheme is "http".
2373</t>
2374<t>
2375   If the request-target is in authority-form, then the effective
2376   request URI's authority component is the same as the request-target.
2377   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2378   non-empty field-value, then the authority component is the same as the
2379   Host field-value. Otherwise, the authority component is the concatenation of
2380   the default host name configured for the server, a colon (":"), and the
2381   connection's incoming TCP port number in decimal form.
2382</t>
2383<t>
2384   If the request-target is in authority-form or asterisk-form, then the
2385   effective request URI's combined path and query component is empty.
2386   Otherwise, the combined path and query component is the same as the
2387   request-target.
2388</t>
2389<t>
2390   The components of the effective request URI, once determined as above,
2391   can be combined into absolute-URI form by concatenating the scheme,
2392   "://", authority, and combined path and query component.
2393</t>
2394<figure>
2395<preamble>
2396   Example 1: the following message received over an insecure TCP connection
2397</preamble> 
2398<artwork type="example" x:indent-with="  ">
2399GET /pub/WWW/TheProject.html HTTP/1.1
2400Host: www.example.org:8080
2401</artwork>
2402</figure>
2403<figure>
2404<preamble>
2405  has an effective request URI of
2406</preamble>
2407<artwork type="example" x:indent-with="  ">
2408http://www.example.org:8080/pub/WWW/TheProject.html
2409</artwork>
2410</figure>
2411<figure>
2412<preamble>
2413   Example 2: the following message received over an SSL/TLS-secured TCP
2414   connection
2415</preamble> 
2416<artwork type="example" x:indent-with="  ">
2417OPTIONS * HTTP/1.1
2418Host: www.example.org
2419</artwork>
2420</figure>
2421<figure>
2422<preamble>
2423  has an effective request URI of
2424</preamble>
2425<artwork type="example" x:indent-with="  ">
2426https://www.example.org
2427</artwork>
2428</figure>
2429<t>
2430   An origin server that does not allow resources to differ by requested
2431   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2432   with a configured server name when constructing the effective request URI.
2433</t>
2434<t>
2435   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2436   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2437   something unique to a particular host) in order to guess the
2438   effective request URI's authority component.
2439</t>
2440</section>
2441
2442<section title="Message Forwarding" anchor="message.forwarding">
2443<t>
2444   As described in <xref target="intermediaries"/>, intermediaries can serve
2445   a variety of roles in the processing of HTTP requests and responses.
2446   Some intermediaries are used to improve performance or availability.
2447   Others are used for access control or to filter content.
2448   Since an HTTP stream has characteristics similar to a pipe-and-filter
2449   architecture, there are no inherent limits to the extent an intermediary
2450   can enhance (or interfere) with either direction of the stream.
2451</t>
2452<t>
2453   Intermediaries that forward a message &MUST; implement the
2454   <x:ref>Connection</x:ref> header field, as specified in
2455   <xref target="header.connection"/>, to exclude fields that are only
2456   intended for the incoming connection.
2457</t>
2458<t>
2459   In order to avoid request loops, a proxy that forwards requests to other
2460   proxies &MUST; be able to recognize and exclude all of its own server
2461   names, including any aliases, local variations, or literal IP addresses.
2462</t>
2463</section>
2464
2465<section title="Via" anchor="header.via">
2466  <iref primary="true" item="Via header field" x:for-anchor=""/>
2467  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2468  <x:anchor-alias value="pseudonym"/>
2469  <x:anchor-alias value="received-by"/>
2470  <x:anchor-alias value="received-protocol"/>
2471  <x:anchor-alias value="Via"/>
2472<t>
2473   The "Via" header field &MUST; be sent by a proxy or gateway
2474   in forwarded messages to
2475   indicate the intermediate protocols and recipients between the user
2476   agent and the server on requests, and between the origin server and
2477   the client on responses. It is analogous to the "Received" field
2478   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2479   Via is used in HTTP for tracking message forwards,
2480   avoiding request loops, and identifying the protocol capabilities of
2481   all senders along the request/response chain.
2482</t>
2483<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"/>
2484  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2485                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2486  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2487  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2488  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2489</artwork></figure>
2490<t>
2491   The received-protocol indicates the protocol version of the message
2492   received by the server or client along each segment of the
2493   request/response chain. The received-protocol version is appended to
2494   the Via field value when the message is forwarded so that information
2495   about the protocol capabilities of upstream applications remains
2496   visible to all recipients.
2497</t>
2498<t>
2499   The protocol-name is excluded if and only if it would be "HTTP". The
2500   received-by field is normally the host and optional port number of a
2501   recipient server or client that subsequently forwarded the message.
2502   However, if the real host is considered to be sensitive information,
2503   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2504   be assumed to be the default port of the received-protocol.
2505</t>
2506<t>
2507   Multiple Via field values represent each proxy or gateway that has
2508   forwarded the message. Each recipient &MUST; append its information
2509   such that the end result is ordered according to the sequence of
2510   forwarding applications.
2511</t>
2512<t>
2513   Comments &MAY; be used in the Via header field to identify the software
2514   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2515   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2516   are optional and &MAY; be removed by any recipient prior to forwarding the
2517   message.
2518</t>
2519<t>
2520   For example, a request message could be sent from an HTTP/1.0 user
2521   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2522   forward the request to a public proxy at p.example.net, which completes
2523   the request by forwarding it to the origin server at www.example.com.
2524   The request received by www.example.com would then have the following
2525   Via header field:
2526</t>
2527<figure><artwork type="example">
2528  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2529</artwork></figure>
2530<t>
2531   A proxy or gateway used as a portal through a network firewall
2532   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2533   region unless it is explicitly enabled to do so. If not enabled, the
2534   received-by host of any host behind the firewall &SHOULD; be replaced
2535   by an appropriate pseudonym for that host.
2536</t>
2537<t>
2538   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2539   field entries into a single such entry if the entries have identical
2540   received-protocol values. For example,
2541</t>
2542<figure><artwork type="example">
2543  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2544</artwork></figure>
2545<t>
2546  could be collapsed to
2547</t>
2548<figure><artwork type="example">
2549  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2550</artwork></figure>
2551<t>
2552   Senders &SHOULD-NOT; combine multiple entries unless they are all
2553   under the same organizational control and the hosts have already been
2554   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2555   have different received-protocol values.
2556</t>
2557</section>
2558
2559<section title="Message Transforming" anchor="message.transforming">
2560<t>
2561   If a proxy receives a request-target with a host name that is not a
2562   fully qualified domain name, it &MAY; add its own domain to the host name
2563   it received when forwarding the request.  A proxy &MUST-NOT; change the
2564   host name if it is a fully qualified domain name.
2565</t>
2566<t>
2567   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2568   parts of the received request-target when forwarding it to the next inbound
2569   server, except as noted above to replace an empty path with "/" or "*".
2570</t>
2571<t>
2572   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2573   though it &MAY; change the message body through application or removal
2574   of a transfer-coding (<xref target="transfer.codings"/>).
2575</t>
2576<t>
2577   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2578   information about the end points of the communication chain, the resource
2579   state, or the selected representation.
2580</t>
2581<t>
2582   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2583   request or response, and it &MUST-NOT; add any of these fields if not
2584   already present:
2585  <list style="symbols">
2586    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2587    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2588    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2589    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2590    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2591    <t><x:ref>Server</x:ref> (&header-server;)</t>
2592  </list>
2593</t>
2594<t>
2595   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2596   header field (&header-expires;) if already present in a response, but
2597   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2598   identical to that of the <x:ref>Date</x:ref> header field.
2599</t>
2600<t>
2601   A proxy &MUST-NOT; modify or add any of the following fields in a
2602   message that contains the no-transform cache-control directive:
2603  <list style="symbols">
2604    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2605    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2606    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2607  </list>
2608</t>
2609<t>
2610   A transforming proxy &MAY; modify or add these fields to a message
2611   that does not include no-transform, but if it does so, it &MUST; add a
2612   Warning 214 (Transformation applied) if one does not already appear
2613   in the message (see &header-warning;).
2614</t>
2615<x:note>
2616  <t>
2617    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2618    cause authentication failures if stronger authentication
2619    mechanisms are introduced in later versions of HTTP. Such
2620    authentication mechanisms &MAY; rely on the values of header fields
2621    not listed here.
2622  </t>
2623</x:note>
2624</section>
2625
2626<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2627<t>
2628   HTTP does not include a request identifier for associating a given
2629   request message with its corresponding one or more response messages.
2630   Hence, it relies on the order of response arrival to correspond exactly
2631   to the order in which requests are made on the same connection.
2632   More than one response message per request only occurs when one or more
2633   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2634   to the same request.
2635</t>
2636<t>
2637   A client that uses persistent connections and sends more than one request
2638   per connection &MUST; maintain a list of outstanding requests in the
2639   order sent on that connection and &MUST; associate each received response
2640   message to the highest ordered request that has not yet received a final
2641   (non-<x:ref>1xx</x:ref>) response.
2642</t>
2643</section>
2644</section>
2645
2646<section title="Connection Management" anchor="connection.management">
2647<t>
2648   HTTP messaging is independent of the underlying transport or
2649   session-layer connection protocol(s).  HTTP only presumes a reliable
2650   transport with in-order delivery of requests and the corresponding
2651   in-order delivery of responses.  The mapping of HTTP request and
2652   response structures onto the data units of an underlying transport
2653   protocol is outside the scope of this specification.
2654</t>
2655<t>
2656   As described in <xref target="connecting.inbound"/>, the specific
2657   connection protocols to be used for an HTTP interaction are determined by
2658   client configuration and the <x:ref>target URI</x:ref>.
2659   For example, the "http" URI scheme
2660   (<xref target="http.uri"/>) indicates a default connection of TCP
2661   over IP, with a default TCP port of 80, but the client might be
2662   configured to use a proxy via some other connection, port, or protocol.
2663</t>
2664<t>
2665   HTTP implementations are expected to engage in connection management,
2666   which includes maintaining the state of current connections,
2667   establishing a new connection or reusing an existing connection,
2668   processing messages received on a connection, detecting connection
2669   failures, and closing each connection.
2670   Most clients maintain multiple connections in parallel, including
2671   more than one connection per server endpoint.
2672   Most servers are designed to maintain thousands of concurrent connections,
2673   while controlling request queues to enable fair use and detect
2674   denial of service attacks.
2675</t>
2676
2677<section title="Connection" anchor="header.connection">
2678  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2679  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2680  <iref primary="true" item="close" x:for-anchor=""/>
2681  <x:anchor-alias value="Connection"/>
2682  <x:anchor-alias value="connection-option"/>
2683  <x:anchor-alias value="close"/>
2684<t>
2685   The "Connection" header field allows the sender to indicate desired
2686   control options for the current connection.  In order to avoid confusing
2687   downstream recipients, a proxy or gateway &MUST; remove or replace any
2688   received connection options before forwarding the message.
2689</t>
2690<t>
2691   When a header field is used to supply control information for or about
2692   the current connection, the sender &SHOULD; list the corresponding
2693   field-name within the "Connection" header field.
2694   A proxy or gateway &MUST; parse a received Connection
2695   header field before a message is forwarded and, for each
2696   connection-option in this field, remove any header field(s) from
2697   the message with the same name as the connection-option, and then
2698   remove the Connection header field itself (or replace it with the
2699   intermediary's own connection options for the forwarded message).
2700</t>
2701<t>
2702   Hence, the Connection header field provides a declarative way of
2703   distinguishing header fields that are only intended for the
2704   immediate recipient ("hop-by-hop") from those fields that are
2705   intended for all recipients on the chain ("end-to-end"), enabling the
2706   message to be self-descriptive and allowing future connection-specific
2707   extensions to be deployed without fear that they will be blindly
2708   forwarded by older intermediaries.
2709</t>
2710<t>
2711   The Connection header field's value has the following grammar:
2712</t>
2713<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2714  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2715  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2716</artwork></figure>
2717<t>
2718   Connection options are case-insensitive.
2719</t>
2720<t>
2721   A sender &MUST-NOT; include field-names in the Connection header
2722   field-value for fields that are defined as expressing constraints
2723   for all recipients in the request or response chain, such as the
2724   Cache-Control header field (&header-cache-control;).
2725</t>
2726<t>
2727   The connection options do not have to correspond to a header field
2728   present in the message, since a connection-specific header field
2729   might not be needed if there are no parameters associated with that
2730   connection option.  Recipients that trigger certain connection
2731   behavior based on the presence of connection options &MUST; do so
2732   based on the presence of the connection-option rather than only the
2733   presence of the optional header field.  In other words, if the
2734   connection option is received as a header field but not indicated
2735   within the Connection field-value, then the recipient &MUST; ignore
2736   the connection-specific header field because it has likely been
2737   forwarded by an intermediary that is only partially conformant.
2738</t>
2739<t>
2740   When defining new connection options, specifications ought to
2741   carefully consider existing deployed header fields and ensure
2742   that the new connection option does not share the same name as
2743   an unrelated header field that might already be deployed.
2744   Defining a new connection option essentially reserves that potential
2745   field-name for carrying additional information related to the
2746   connection option, since it would be unwise for senders to use
2747   that field-name for anything else.
2748</t>
2749<t>
2750   The "<x:dfn>close</x:dfn>" connection option is defined for a
2751   sender to signal that this connection will be closed after completion of
2752   the response. For example,
2753</t>
2754<figure><artwork type="example">
2755  Connection: close
2756</artwork></figure>
2757<t>
2758   in either the request or the response header fields indicates that
2759   the connection &SHOULD; be closed after the current request/response
2760   is complete (<xref target="persistent.tear-down"/>).
2761</t>
2762<t>
2763   A client that does not support persistent connections &MUST;
2764   send the "close" connection option in every request message.
2765</t>
2766<t>
2767   A server that does not support persistent connections &MUST;
2768   send the "close" connection option in every response message that
2769   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2770</t>
2771</section>
2772
2773<section title="Persistent Connections" anchor="persistent.connections">
2774  <x:anchor-alias value="persistent connections"/>
2775<t>
2776   HTTP was originally designed to use a separate connection for each
2777   request/response pair. As the Web evolved and embedded requests became
2778   common for inline images, the connection establishment overhead was
2779   a significant drain on performance and a concern for Internet congestion.
2780   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2781   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2782   to improve performance for some requests. However, these extensions were
2783   insufficient for dynamically generated responses and difficult to use
2784   with intermediaries.
2785</t>
2786<t>
2787   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2788   which allow multiple requests and responses to be carried over a single
2789   connection. The "<x:ref>close</x:ref>" connection-option is used to
2790   signal that a connection will close after the current request/response.
2791   Persistent connections have a number of advantages:
2792  <list style="symbols">
2793      <t>
2794        By opening and closing fewer connections, CPU time is saved
2795        in routers and hosts (clients, servers, proxies, gateways,
2796        tunnels, or caches), and memory used for protocol control
2797        blocks can be saved in hosts.
2798      </t>
2799      <t>
2800        Most requests and responses can be pipelined on a connection.
2801        Pipelining allows a client to make multiple requests without
2802        waiting for each response, allowing a single connection to
2803        be used much more efficiently and with less overall latency.
2804      </t>
2805      <t>
2806        Network congestion is reduced by reducing the number of packets
2807        caused by connection establishment and tear-down, and by allowing
2808        sufficient time for send/receive windows to adjust to the
2809        available network bandwidth.
2810      </t>
2811      <t>
2812        Latency on subsequent requests is reduced since there is no time
2813        spent in the connection opening handshake.
2814      </t>
2815      <t>
2816        HTTP can evolve more gracefully, since most errors can be reported
2817        without the penalty of closing the connection. Clients using
2818        future versions of HTTP might optimistically try a new feature,
2819        but if communicating with an older server, retry with old
2820        semantics after an error is reported.
2821      </t>
2822    </list>
2823</t>
2824<t>
2825   HTTP implementations &SHOULD; implement persistent connections.
2826</t>
2827   
2828<section title="Establishment" anchor="persistent.establishment">
2829<t>
2830   It is beyond the scope of this specification to describe how connections
2831   are established via various transport or session-layer protocols.
2832   Each connection applies to only one transport link.
2833</t>
2834<t>
2835   A recipient determines whether a connection is persistent or not based on
2836   the most recently received message's protocol version and
2837   <x:ref>Connection</x:ref> header field (if any):
2838   <list style="symbols">
2839     <t>If the <x:ref>close</x:ref> connection option is present, the
2840        connection will not persist after the current response; else,</t>
2841     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2842        persist after the current response; else,</t>
2843     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2844        connection option is present, the recipient is not a proxy, and
2845        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2846        the connection will persist after the current response; otherwise,</t>
2847     <t>The connection will close after the current response.</t>
2848   </list>
2849</t>
2850<t>
2851   A proxy server &MUST-NOT; maintain a persistent connection with an
2852   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2853   information and discussion of the problems with the Keep-Alive header field
2854   implemented by many HTTP/1.0 clients).
2855</t>
2856</section>
2857
2858<section title="Reuse" anchor="persistent.reuse">
2859<t>
2860   In order to remain persistent, all messages on a connection &MUST;
2861   have a self-defined message length (i.e., one not defined by closure
2862   of the connection), as described in <xref target="message.body"/>.
2863</t>
2864<t>
2865   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2866   persistent connection until a <x:ref>close</x:ref> connection option
2867   is received in a request.
2868</t>
2869<t>
2870   A client &MAY; reuse a persistent connection until it sends or receives
2871   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2872   without a "keep-alive" connection option.
2873</t>
2874<t>
2875   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2876   maintained for HTTP versions less than 1.1 unless it is explicitly
2877   signaled.
2878   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2879   for more information on backward compatibility with HTTP/1.0 clients.
2880</t>
2881
2882<section title="Pipelining" anchor="pipelining">
2883<t>
2884   A client that supports persistent connections &MAY; "pipeline" its
2885   requests (i.e., send multiple requests without waiting for each
2886   response). A server &MUST; send its responses to those requests in the
2887   same order that the requests were received.
2888</t>
2889<t>
2890   Clients which assume persistent connections and pipeline immediately
2891   after connection establishment &SHOULD; be prepared to retry their
2892   connection if the first pipelined attempt fails. If a client does
2893   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2894   persistent. Clients &MUST; also be prepared to resend their requests if
2895   the server closes the connection before sending all of the
2896   corresponding responses.
2897</t>
2898<t>
2899   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2900   or non-idempotent sequences of request methods (see &idempotent-methods;).
2901   Otherwise, a premature termination of the transport connection could lead
2902   to indeterminate results. A client wishing to send a non-idempotent
2903   request &SHOULD; wait to send that request until it has received the
2904   response status line for the previous request.
2905</t>
2906</section>
2907
2908<section title="Retrying Requests" anchor="persistent.retrying.requests">
2909<t>
2910   Senders can close the transport connection at any time. Therefore,
2911   clients, servers, and proxies &MUST; be able to recover
2912   from asynchronous close events. Client software &MAY; reopen the
2913   transport connection and retransmit the aborted sequence of requests
2914   without user interaction so long as the request sequence is
2915   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2916   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2917   human operator the choice of retrying the request(s). Confirmation by
2918   user-agent software with semantic understanding of the application
2919   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2920   be repeated if the second sequence of requests fails.
2921</t>
2922</section>
2923</section>
2924   
2925<section title="Concurrency" anchor="persistent.concurrency">
2926<t>
2927   Clients &SHOULD; limit the number of simultaneous
2928   connections that they maintain to a given server.
2929</t>
2930<t>
2931   Previous revisions of HTTP gave a specific number of connections as a
2932   ceiling, but this was found to be impractical for many applications. As a
2933   result, this specification does not mandate a particular maximum number of
2934   connections, but instead encourages clients to be conservative when opening
2935   multiple connections.
2936</t>
2937<t>
2938   Multiple connections are typically used to avoid the "head-of-line
2939   blocking" problem, wherein a request that takes significant server-side
2940   processing and/or has a large payload blocks subsequent requests on the
2941   same connection. However, each connection consumes server resources.
2942   Furthermore, using multiple connections can cause undesirable side effects
2943   in congested networks.
2944</t>
2945<t>
2946   Note that servers might reject traffic that they deem abusive, including an
2947   excessive number of connections from a client.
2948</t>
2949</section>
2950
2951<section title="Failures and Time-outs" anchor="persistent.failures">
2952<t>
2953   Servers will usually have some time-out value beyond which they will
2954   no longer maintain an inactive connection. Proxy servers might make
2955   this a higher value since it is likely that the client will be making
2956   more connections through the same server. The use of persistent
2957   connections places no requirements on the length (or existence) of
2958   this time-out for either the client or the server.
2959</t>
2960<t>
2961   When a client or server wishes to time-out it &SHOULD; issue a graceful
2962   close on the transport connection. Clients and servers &SHOULD; both
2963   constantly watch for the other side of the transport close, and
2964   respond to it as appropriate. If a client or server does not detect
2965   the other side's close promptly it could cause unnecessary resource
2966   drain on the network.
2967</t>
2968<t>
2969   A client, server, or proxy &MAY; close the transport connection at any
2970   time. For example, a client might have started to send a new request
2971   at the same time that the server has decided to close the "idle"
2972   connection. From the server's point of view, the connection is being
2973   closed while it was idle, but from the client's point of view, a
2974   request is in progress.
2975</t>
2976<t>
2977   Servers &SHOULD; maintain persistent connections and allow the underlying
2978   transport's flow control mechanisms to resolve temporary overloads, rather
2979   than terminate connections with the expectation that clients will retry.
2980   The latter technique can exacerbate network congestion.
2981</t>
2982<t>
2983   A client sending a message body &SHOULD; monitor
2984   the network connection for an error status code while it is transmitting
2985   the request. If the client sees an error status code, it &SHOULD;
2986   immediately cease transmitting the body and close the connection.
2987</t>
2988</section>
2989   
2990<section title="Tear-down" anchor="persistent.tear-down">
2991  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2992  <iref primary="false" item="close" x:for-anchor=""/>
2993<t>
2994   The <x:ref>Connection</x:ref> header field
2995   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
2996   connection option that a sender &SHOULD; send when it wishes to close
2997   the connection after the current request/response pair.
2998</t>
2999<t>
3000   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3001   send further requests on that connection (after the one containing
3002   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3003   final response message corresponding to this request.
3004</t>
3005<t>
3006   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3007   initiate a lingering close of the connection after it sends the final
3008   response to the request that contained <x:ref>close</x:ref>.
3009   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3010   in its final response on that connection. The server &MUST-NOT; process
3011   any further requests received on that connection.
3012</t>
3013<t>
3014   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3015   initiate a lingering close of the connection after it sends the
3016   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3017   any further requests received on that connection.
3018</t>
3019<t>
3020   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3021   cease sending requests on that connection and close the connection
3022   after reading the response message containing the close; if additional
3023   pipelined requests had been sent on the connection, the client &SHOULD;
3024   assume that they will not be processed by the server.
3025</t>
3026<t>
3027   If a server performs an immediate close of a TCP connection, there is a
3028   significant risk that the client will not be able to read the last HTTP
3029   response.  If the server receives additional data from the client on a
3030   fully-closed connection, such as another request that was sent by the
3031   client before receiving the server's response, the server's TCP stack will
3032   send a reset packet to the client; unfortunately, the reset packet might
3033   erase the client's unacknowledged input buffers before they can be read
3034   and interpreted by the client's HTTP parser.
3035</t>
3036<t>
3037   To avoid the TCP reset problem, a server can perform a lingering close on a
3038   connection by closing only the write side of the read/write connection
3039   (a half-close) and continuing to read from the connection until the
3040   connection is closed by the client or the server is reasonably certain
3041   that its own TCP stack has received the client's acknowledgement of the
3042   packet(s) containing the server's last response. It is then safe for the
3043   server to fully close the connection.
3044</t>
3045<t>
3046   It is unknown whether the reset problem is exclusive to TCP or might also
3047   be found in other transport connection protocols.
3048</t>
3049</section>
3050</section>
3051
3052<section title="Upgrade" anchor="header.upgrade">
3053  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3054  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3055  <x:anchor-alias value="Upgrade"/>
3056  <x:anchor-alias value="protocol"/>
3057  <x:anchor-alias value="protocol-name"/>
3058  <x:anchor-alias value="protocol-version"/>
3059<t>
3060   The "Upgrade" header field is intended to provide a simple mechanism
3061   for transitioning from HTTP/1.1 to some other protocol on the same
3062   connection.  A client &MAY; send a list of protocols in the Upgrade
3063   header field of a request to invite the server to switch to one or
3064   more of those protocols before sending the final response.
3065   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3066   Protocols)</x:ref> responses to indicate which protocol(s) are being
3067   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3068   responses to indicate acceptable protocols.
3069   A server &MAY; send an Upgrade header field in any other response to
3070   indicate that they might be willing to upgrade to one of the
3071   specified protocols for a future request.
3072</t>
3073<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3074  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3075
3076  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3077  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3078  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3079</artwork></figure>
3080<t>
3081   For example,
3082</t>
3083<figure><artwork type="example">
3084  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3085</artwork></figure>
3086<t>
3087   Upgrade eases the difficult transition between incompatible protocols by
3088   allowing the client to initiate a request in the more commonly
3089   supported protocol while indicating to the server that it would like
3090   to use a "better" protocol if available (where "better" is determined
3091   by the server, possibly according to the nature of the request method
3092   or target resource).
3093</t>
3094<t>
3095   Upgrade cannot be used to insist on a protocol change; its acceptance and
3096   use by the server is optional. The capabilities and nature of the
3097   application-layer communication after the protocol change is entirely
3098   dependent upon the new protocol chosen, although the first action
3099   after changing the protocol &MUST; be a response to the initial HTTP
3100   request that contained the Upgrade header field.
3101</t>
3102<t>
3103   For example, if the Upgrade header field is received in a GET request
3104   and the server decides to switch protocols, then it &MUST; first respond
3105   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3106   then immediately follow that with the new protocol's equivalent of a
3107   response to a GET on the target resource.  This allows a connection to be
3108   upgraded to protocols with the same semantics as HTTP without the
3109   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3110   protocols unless the received message semantics can be honored by the new
3111   protocol; an OPTIONS request can be honored by any protocol.
3112</t>
3113<t>
3114   When Upgrade is sent, a sender &MUST; also send a
3115   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3116   that contains the "upgrade" connection option, in order to prevent Upgrade
3117   from being accidentally forwarded by intermediaries that might not implement
3118   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3119   is received in an HTTP/1.0 request.
3120</t>
3121<t>
3122   The Upgrade header field only applies to switching application-layer
3123   protocols on the existing transport-layer connection; it cannot be used
3124   to switch to a protocol on a different connection. For that purpose, it is
3125   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3126   (&status-3xx;).
3127</t>
3128<t>
3129   This specification only defines the protocol name "HTTP" for use by
3130   the family of Hypertext Transfer Protocols, as defined by the HTTP
3131   version rules of <xref target="http.version"/> and future updates to this
3132   specification. Additional tokens can be registered with IANA using the
3133   registration procedure defined in <xref target="upgrade.token.registry"/>.
3134</t>
3135</section>
3136</section>
3137
3138<section title="IANA Considerations" anchor="IANA.considerations">
3139
3140<section title="Header Field Registration" anchor="header.field.registration">
3141<t>
3142   HTTP header fields are registered within the Message Header Field Registry
3143   <xref target="RFC3864"/> maintained by IANA at
3144   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3145</t>
3146<t>
3147   This document defines the following HTTP header fields, so their
3148   associated registry entries shall be updated according to the permanent
3149   registrations below:
3150</t>
3151<?BEGININC p1-messaging.iana-headers ?>
3152<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3153<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3154   <ttcol>Header Field Name</ttcol>
3155   <ttcol>Protocol</ttcol>
3156   <ttcol>Status</ttcol>
3157   <ttcol>Reference</ttcol>
3158
3159   <c>Connection</c>
3160   <c>http</c>
3161   <c>standard</c>
3162   <c>
3163      <xref target="header.connection"/>
3164   </c>
3165   <c>Content-Length</c>
3166   <c>http</c>
3167   <c>standard</c>
3168   <c>
3169      <xref target="header.content-length"/>
3170   </c>
3171   <c>Host</c>
3172   <c>http</c>
3173   <c>standard</c>
3174   <c>
3175      <xref target="header.host"/>
3176   </c>
3177   <c>TE</c>
3178   <c>http</c>
3179   <c>standard</c>
3180   <c>
3181      <xref target="header.te"/>
3182   </c>
3183   <c>Trailer</c>
3184   <c>http</c>
3185   <c>standard</c>
3186   <c>
3187      <xref target="header.trailer"/>
3188   </c>
3189   <c>Transfer-Encoding</c>
3190   <c>http</c>
3191   <c>standard</c>
3192   <c>
3193      <xref target="header.transfer-encoding"/>
3194   </c>
3195   <c>Upgrade</c>
3196   <c>http</c>
3197   <c>standard</c>
3198   <c>
3199      <xref target="header.upgrade"/>
3200   </c>
3201   <c>Via</c>
3202   <c>http</c>
3203   <c>standard</c>
3204   <c>
3205      <xref target="header.via"/>
3206   </c>
3207</texttable>
3208<!--(END)-->
3209<?ENDINC p1-messaging.iana-headers ?>
3210<t>
3211   Furthermore, the header field-name "Close" shall be registered as
3212   "reserved", since using that name as an HTTP header field might
3213   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3214   header field (<xref target="header.connection"/>).
3215</t>
3216<texttable align="left" suppress-title="true">
3217   <ttcol>Header Field Name</ttcol>
3218   <ttcol>Protocol</ttcol>
3219   <ttcol>Status</ttcol>
3220   <ttcol>Reference</ttcol>
3221
3222   <c>Close</c>
3223   <c>http</c>
3224   <c>reserved</c>
3225   <c>
3226      <xref target="header.field.registration"/>
3227   </c>
3228</texttable>
3229<t>
3230   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3231</t>
3232</section>
3233
3234<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3235<t>
3236   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3237   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3238</t>
3239<t>
3240   This document defines the following URI schemes, so their
3241   associated registry entries shall be updated according to the permanent
3242   registrations below:
3243</t>
3244<texttable align="left" suppress-title="true">
3245   <ttcol>URI Scheme</ttcol>
3246   <ttcol>Description</ttcol>
3247   <ttcol>Reference</ttcol>
3248
3249   <c>http</c>
3250   <c>Hypertext Transfer Protocol</c>
3251   <c><xref target="http.uri"/></c>
3252
3253   <c>https</c>
3254   <c>Hypertext Transfer Protocol Secure</c>
3255   <c><xref target="https.uri"/></c>
3256</texttable>
3257</section>
3258
3259<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3260<t>
3261   This document serves as the specification for the Internet media types
3262   "message/http" and "application/http". The following is to be registered with
3263   IANA (see <xref target="RFC4288"/>).
3264</t>
3265<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3266<iref item="Media Type" subitem="message/http" primary="true"/>
3267<iref item="message/http Media Type" primary="true"/>
3268<t>
3269   The message/http type can be used to enclose a single HTTP request or
3270   response message, provided that it obeys the MIME restrictions for all
3271   "message" types regarding line length and encodings.
3272</t>
3273<t>
3274  <list style="hanging" x:indent="12em">
3275    <t hangText="Type name:">
3276      message
3277    </t>
3278    <t hangText="Subtype name:">
3279      http
3280    </t>
3281    <t hangText="Required parameters:">
3282      none
3283    </t>
3284    <t hangText="Optional parameters:">
3285      version, msgtype
3286      <list style="hanging">
3287        <t hangText="version:">
3288          The HTTP-version number of the enclosed message
3289          (e.g., "1.1"). If not present, the version can be
3290          determined from the first line of the body.
3291        </t>
3292        <t hangText="msgtype:">
3293          The message type &mdash; "request" or "response". If not
3294          present, the type can be determined from the first
3295          line of the body.
3296        </t>
3297      </list>
3298    </t>
3299    <t hangText="Encoding considerations:">
3300      only "7bit", "8bit", or "binary" are permitted
3301    </t>
3302    <t hangText="Security considerations:">
3303      none
3304    </t>
3305    <t hangText="Interoperability considerations:">
3306      none
3307    </t>
3308    <t hangText="Published specification:">
3309      This specification (see <xref target="internet.media.type.message.http"/>).
3310    </t>
3311    <t hangText="Applications that use this media type:">
3312    </t>
3313    <t hangText="Additional information:">
3314      <list style="hanging">
3315        <t hangText="Magic number(s):">none</t>
3316        <t hangText="File extension(s):">none</t>
3317        <t hangText="Macintosh file type code(s):">none</t>
3318      </list>
3319    </t>
3320    <t hangText="Person and email address to contact for further information:">
3321      See Authors Section.
3322    </t>
3323    <t hangText="Intended usage:">
3324      COMMON
3325    </t>
3326    <t hangText="Restrictions on usage:">
3327      none
3328    </t>
3329    <t hangText="Author/Change controller:">
3330      IESG
3331    </t>
3332  </list>
3333</t>
3334</section>
3335<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3336<iref item="Media Type" subitem="application/http" primary="true"/>
3337<iref item="application/http Media Type" primary="true"/>
3338<t>
3339   The application/http type can be used to enclose a pipeline of one or more
3340   HTTP request or response messages (not intermixed).
3341</t>
3342<t>
3343  <list style="hanging" x:indent="12em">
3344    <t hangText="Type name:">
3345      application
3346    </t>
3347    <t hangText="Subtype name:">
3348      http
3349    </t>
3350    <t hangText="Required parameters:">
3351      none
3352    </t>
3353    <t hangText="Optional parameters:">
3354      version, msgtype
3355      <list style="hanging">
3356        <t hangText="version:">
3357          The HTTP-version number of the enclosed messages
3358          (e.g., "1.1"). If not present, the version can be
3359          determined from the first line of the body.
3360        </t>
3361        <t hangText="msgtype:">
3362          The message type &mdash; "request" or "response". If not
3363          present, the type can be determined from the first
3364          line of the body.
3365        </t>
3366      </list>
3367    </t>
3368    <t hangText="Encoding considerations:">
3369      HTTP messages enclosed by this type
3370      are in "binary" format; use of an appropriate
3371      Content-Transfer-Encoding is required when
3372      transmitted via E-mail.
3373    </t>
3374    <t hangText="Security considerations:">
3375      none
3376    </t>
3377    <t hangText="Interoperability considerations:">
3378      none
3379    </t>
3380    <t hangText="Published specification:">
3381      This specification (see <xref target="internet.media.type.application.http"/>).
3382    </t>
3383    <t hangText="Applications that use this media type:">
3384    </t>
3385    <t hangText="Additional information:">
3386      <list style="hanging">
3387        <t hangText="Magic number(s):">none</t>
3388        <t hangText="File extension(s):">none</t>
3389        <t hangText="Macintosh file type code(s):">none</t>
3390      </list>
3391    </t>
3392    <t hangText="Person and email address to contact for further information:">
3393      See Authors Section.
3394    </t>
3395    <t hangText="Intended usage:">
3396      COMMON
3397    </t>
3398    <t hangText="Restrictions on usage:">
3399      none
3400    </t>
3401    <t hangText="Author/Change controller:">
3402      IESG
3403    </t>
3404  </list>
3405</t>
3406</section>
3407</section>
3408
3409<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3410<t>
3411   The HTTP Transfer Coding Registry defines the name space for transfer
3412   coding names.
3413</t>
3414<t>
3415   Registrations &MUST; include the following fields:
3416   <list style="symbols">
3417     <t>Name</t>
3418     <t>Description</t>
3419     <t>Pointer to specification text</t>
3420   </list>
3421</t>
3422<t>
3423   Names of transfer codings &MUST-NOT; overlap with names of content codings
3424   (&content-codings;) unless the encoding transformation is identical, as
3425   is the case for the compression codings defined in
3426   <xref target="compression.codings"/>.
3427</t>
3428<t>
3429   Values to be added to this name space require IETF Review (see
3430   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3431   conform to the purpose of transfer coding defined in this section.
3432   Use of program names for the identification of encoding formats
3433   is not desirable and is discouraged for future encodings.
3434</t>
3435<t>
3436   The registry itself is maintained at
3437   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3438</t>
3439</section>
3440
3441<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3442<t>
3443   The HTTP Transfer Coding Registry shall be updated with the registrations
3444   below:
3445</t>
3446<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3447   <ttcol>Name</ttcol>
3448   <ttcol>Description</ttcol>
3449   <ttcol>Reference</ttcol>
3450   <c>chunked</c>
3451   <c>Transfer in a series of chunks</c>
3452   <c>
3453      <xref target="chunked.encoding"/>
3454   </c>
3455   <c>compress</c>
3456   <c>UNIX "compress" program method</c>
3457   <c>
3458      <xref target="compress.coding"/>
3459   </c>
3460   <c>deflate</c>
3461   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3462   the "zlib" data format (<xref target="RFC1950"/>)
3463   </c>
3464   <c>
3465      <xref target="deflate.coding"/>
3466   </c>
3467   <c>gzip</c>
3468   <c>Same as GNU zip <xref target="RFC1952"/></c>
3469   <c>
3470      <xref target="gzip.coding"/>
3471   </c>
3472</texttable>
3473</section>
3474
3475<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3476<t>
3477   The HTTP Upgrade Token Registry defines the name space for protocol-name
3478   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3479   field. Each registered protocol name is associated with contact information
3480   and an optional set of specifications that details how the connection
3481   will be processed after it has been upgraded.
3482</t>
3483<t>
3484   Registrations happen on a "First Come First Served" basis (see
3485   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3486   following rules:
3487  <list style="numbers">
3488    <t>A protocol-name token, once registered, stays registered forever.</t>
3489    <t>The registration &MUST; name a responsible party for the
3490       registration.</t>
3491    <t>The registration &MUST; name a point of contact.</t>
3492    <t>The registration &MAY; name a set of specifications associated with
3493       that token. Such specifications need not be publicly available.</t>
3494    <t>The registration &SHOULD; name a set of expected "protocol-version"
3495       tokens associated with that token at the time of registration.</t>
3496    <t>The responsible party &MAY; change the registration at any time.
3497       The IANA will keep a record of all such changes, and make them
3498       available upon request.</t>
3499    <t>The IESG &MAY; reassign responsibility for a protocol token.
3500       This will normally only be used in the case when a
3501       responsible party cannot be contacted.</t>
3502  </list>
3503</t>
3504<t>
3505   This registration procedure for HTTP Upgrade Tokens replaces that
3506   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3507</t>
3508</section>
3509
3510<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3511<t>
3512   The HTTP Upgrade Token Registry shall be updated with the registration
3513   below:
3514</t>
3515<texttable align="left" suppress-title="true">
3516   <ttcol>Value</ttcol>
3517   <ttcol>Description</ttcol>
3518   <ttcol>Expected Version Tokens</ttcol>
3519   <ttcol>Reference</ttcol>
3520
3521   <c>HTTP</c>
3522   <c>Hypertext Transfer Protocol</c>
3523   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3524   <c><xref target="http.version"/></c>
3525</texttable>
3526<t>
3527   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3528</t>
3529</section>
3530
3531</section>
3532
3533<section title="Security Considerations" anchor="security.considerations">
3534<t>
3535   This section is meant to inform application developers, information
3536   providers, and users of the security limitations in HTTP/1.1 as
3537   described by this document. The discussion does not include
3538   definitive solutions to the problems revealed, though it does make
3539   some suggestions for reducing security risks.
3540</t>
3541
3542<section title="Personal Information" anchor="personal.information">
3543<t>
3544   HTTP clients are often privy to large amounts of personal information,
3545   including both information provided by the user to interact with resources
3546   (e.g., the user's name, location, mail address, passwords, encryption
3547   keys, etc.) and information about the user's browsing activity over
3548   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3549   prevent unintentional leakage of this information.
3550</t>
3551</section>
3552
3553<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3554<t>
3555   A server is in the position to save personal data about a user's
3556   requests which might identify their reading patterns or subjects of
3557   interest.  In particular, log information gathered at an intermediary
3558   often contains a history of user agent interaction, across a multitude
3559   of sites, that can be traced to individual users.
3560</t>
3561<t>
3562   HTTP log information is confidential in nature; its handling is often
3563   constrained by laws and regulations.  Log information needs to be securely
3564   stored and appropriate guidelines followed for its analysis.
3565   Anonymization of personal information within individual entries helps,
3566   but is generally not sufficient to prevent real log traces from being
3567   re-identified based on correlation with other access characteristics.
3568   As such, access traces that are keyed to a specific client should not
3569   be published even if the key is pseudonymous.
3570</t>
3571<t>
3572   To minimize the risk of theft or accidental publication, log information
3573   should be purged of personally identifiable information, including
3574   user identifiers, IP addresses, and user-provided query parameters,
3575   as soon as that information is no longer necessary to support operational
3576   needs for security, auditing, or fraud control.
3577</t>
3578</section>
3579
3580<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3581<t>
3582   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3583   the documents returned by HTTP requests to be only those that were
3584   intended by the server administrators. If an HTTP server translates
3585   HTTP URIs directly into file system calls, the server &MUST; take
3586   special care not to serve files that were not intended to be
3587   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3588   other operating systems use ".." as a path component to indicate a
3589   directory level above the current one. On such a system, an HTTP
3590   server &MUST; disallow any such construct in the request-target if it
3591   would otherwise allow access to a resource outside those intended to
3592   be accessible via the HTTP server. Similarly, files intended for
3593   reference only internally to the server (such as access control
3594   files, configuration files, and script code) &MUST; be protected from
3595   inappropriate retrieval, since they might contain sensitive
3596   information. Experience has shown that minor bugs in such HTTP server
3597   implementations have turned into security risks.
3598</t>
3599</section>
3600
3601<section title="DNS-related Attacks" anchor="dns.related.attacks">
3602<t>
3603   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3604   generally prone to security attacks based on the deliberate misassociation
3605   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3606   cautious in assuming the validity of an IP number/DNS name association unless
3607   the response is protected by DNSSec (<xref target="RFC4033"/>).
3608</t>
3609</section>
3610
3611<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3612<t>
3613   By their very nature, HTTP intermediaries are men-in-the-middle, and
3614   represent an opportunity for man-in-the-middle attacks. Compromise of
3615   the systems on which the intermediaries run can result in serious security
3616   and privacy problems. Intermediaries have access to security-related
3617   information, personal information about individual users and
3618   organizations, and proprietary information belonging to users and
3619   content providers. A compromised intermediary, or an intermediary
3620   implemented or configured without regard to security and privacy
3621   considerations, might be used in the commission of a wide range of
3622   potential attacks.
3623</t>
3624<t>
3625   Intermediaries that contain a shared cache are especially vulnerable
3626   to cache poisoning attacks.
3627</t>
3628<t>
3629   Implementers need to consider the privacy and security
3630   implications of their design and coding decisions, and of the
3631   configuration options they provide to operators (especially the
3632   default configuration).
3633</t>
3634<t>
3635   Users need to be aware that intermediaries are no more trustworthy than
3636   the people who run them; HTTP itself cannot solve this problem.
3637</t>
3638</section>
3639
3640<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3641<t>
3642   Because HTTP uses mostly textual, character-delimited fields, attackers can
3643   overflow buffers in implementations, and/or perform a Denial of Service
3644   against implementations that accept fields with unlimited lengths.
3645</t>
3646<t>
3647   To promote interoperability, this specification makes specific
3648   recommendations for minimum size limits on request-line
3649   (<xref target="request.line"/>)
3650   and blocks of header fields (<xref target="header.fields"/>). These are
3651   minimum recommendations, chosen to be supportable even by implementations
3652   with limited resources; it is expected that most implementations will
3653   choose substantially higher limits.
3654</t>
3655<t>
3656   This specification also provides a way for servers to reject messages that
3657   have request-targets that are too long (&status-414;) or request entities
3658   that are too large (&status-4xx;).
3659</t>
3660<t>
3661   Other fields (including but not limited to request methods, response status
3662   phrases, header field-names, and body chunks) &SHOULD; be limited by
3663   implementations carefully, so as to not impede interoperability.
3664</t>
3665</section>
3666</section>
3667
3668<section title="Acknowledgments" anchor="acks">
3669<t>
3670   This edition of HTTP builds on the many contributions that went into
3671   <xref target="RFC1945" format="none">RFC 1945</xref>,
3672   <xref target="RFC2068" format="none">RFC 2068</xref>,
3673   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3674   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3675   substantial contributions made by the previous authors, editors, and
3676   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3677   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3678   Paul J. Leach, and Mark Nottingham.
3679   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3680   acknowledgements from prior revisions.
3681</t>
3682<t>
3683   Since 1999, the following contributors have helped improve the HTTP
3684   specification by reporting bugs, asking smart questions, drafting or
3685   reviewing text, and evaluating open issues:
3686</t>
3687<?BEGININC acks ?>
3688<t>Adam Barth,
3689Adam Roach,
3690Addison Phillips,
3691Adrian Chadd,
3692Adrien W. de Croy,
3693Alan Ford,
3694Alan Ruttenberg,
3695Albert Lunde,
3696Alek Storm,
3697Alex Rousskov,
3698Alexandre Morgaut,
3699Alexey Melnikov,
3700Alisha Smith,
3701Amichai Rothman,
3702Amit Klein,
3703Amos Jeffries,
3704Andreas Maier,
3705Andreas Petersson,
3706Anil Sharma,
3707Anne van Kesteren,
3708Anthony Bryan,
3709Asbjorn Ulsberg,
3710Balachander Krishnamurthy,
3711Barry Leiba,
3712Ben Laurie,
3713Benjamin Niven-Jenkins,
3714Bil Corry,
3715Bill Burke,
3716Bjoern Hoehrmann,
3717Bob Scheifler,
3718Boris Zbarsky,
3719Brett Slatkin,
3720Brian Kell,
3721Brian McBarron,
3722Brian Pane,
3723Brian Smith,
3724Bryce Nesbitt,
3725Cameron Heavon-Jones,
3726Carl Kugler,
3727Carsten Bormann,
3728Charles Fry,
3729Chris Newman,
3730Cyrus Daboo,
3731Dale Robert Anderson,
3732Dan Wing,
3733Dan Winship,
3734Daniel Stenberg,
3735Dave Cridland,
3736Dave Crocker,
3737Dave Kristol,
3738David Booth,
3739David Singer,
3740David W. Morris,
3741Diwakar Shetty,
3742Dmitry Kurochkin,
3743Drummond Reed,
3744Duane Wessels,
3745Edward Lee,
3746Eliot Lear,
3747Eran Hammer-Lahav,
3748Eric D. Williams,
3749Eric J. Bowman,
3750Eric Lawrence,
3751Eric Rescorla,
3752Erik Aronesty,
3753Florian Weimer,
3754Frank Ellermann,
3755Fred Bohle,
3756Gabriel Montenegro,
3757Geoffrey Sneddon,
3758Gervase Markham,
3759Grahame Grieve,
3760Greg Wilkins,
3761Harald Tveit Alvestrand,
3762Harry Halpin,
3763Helge Hess,
3764Henrik Nordstrom,
3765Henry S. Thompson,
3766Henry Story,
3767Herbert van de Sompel,
3768Howard Melman,
3769Hugo Haas,
3770Ian Fette,
3771Ian Hickson,
3772Ido Safruti,
3773Ingo Struck,
3774J. Ross Nicoll,
3775James H. Manger,
3776James Lacey,
3777James M. Snell,
3778Jamie Lokier,
3779Jan Algermissen,
3780Jeff Hodges (who came up with the term 'effective Request-URI'),
3781Jeff Walden,
3782Jim Luther,
3783Joe D. Williams,
3784Joe Gregorio,
3785Joe Orton,
3786John C. Klensin,
3787John C. Mallery,
3788John Cowan,
3789John Kemp,
3790John Panzer,
3791John Schneider,
3792John Stracke,
3793John Sullivan,
3794Jonas Sicking,
3795Jonathan Billington,
3796Jonathan Moore,
3797Jonathan Rees,
3798Jonathan Silvera,
3799Jordi Ros,
3800Joris Dobbelsteen,
3801Josh Cohen,
3802Julien Pierre,
3803Jungshik Shin,
3804Justin Chapweske,
3805Justin Erenkrantz,
3806Justin James,
3807Kalvinder Singh,
3808Karl Dubost,
3809Keith Hoffman,
3810Keith Moore,
3811Koen Holtman,
3812Konstantin Voronkov,
3813Kris Zyp,
3814Lisa Dusseault,
3815Maciej Stachowiak,
3816Marc Schneider,
3817Marc Slemko,
3818Mark Baker,
3819Mark Pauley,
3820Mark Watson,
3821Markus Isomaki,
3822Markus Lanthaler,
3823Martin J. Duerst,
3824Martin Musatov,
3825Martin Nilsson,
3826Martin Thomson,
3827Matt Lynch,
3828Matthew Cox,
3829Max Clark,
3830Michael Burrows,
3831Michael Hausenblas,
3832Mike Amundsen,
3833Mike Belshe,
3834Mike Kelly,
3835Mike Schinkel,
3836Miles Sabin,
3837Murray S. Kucherawy,
3838Mykyta Yevstifeyev,
3839Nathan Rixham,
3840Nicholas Shanks,
3841Nico Williams,
3842Nicolas Alvarez,
3843Nicolas Mailhot,
3844Noah Slater,
3845Pablo Castro,
3846Pat Hayes,
3847Patrick R. McManus,
3848Paul E. Jones,
3849Paul Hoffman,
3850Paul Marquess,
3851Peter Lepeska,
3852Peter Saint-Andre,
3853Peter Watkins,
3854Phil Archer,
3855Philippe Mougin,
3856Phillip Hallam-Baker,
3857Poul-Henning Kamp,
3858Preethi Natarajan,
3859Rajeev Bector,
3860Ray Polk,
3861Reto Bachmann-Gmuer,
3862Richard Cyganiak,
3863Robert Brewer,
3864Robert Collins,
3865Robert O'Callahan,
3866Robert Olofsson,
3867Robert Sayre,
3868Robert Siemer,
3869Robert de Wilde,
3870Roberto Javier Godoy,
3871Roberto Peon,
3872Ronny Widjaja,
3873S. Mike Dierken,
3874Salvatore Loreto,
3875Sam Johnston,
3876Sam Ruby,
3877Scott Lawrence (who maintained the original issues list),
3878Sean B. Palmer,
3879Shane McCarron,
3880Stefan Eissing,
3881Stefan Tilkov,
3882Stefanos Harhalakis,
3883Stephane Bortzmeyer,
3884Stephen Farrell,
3885Stephen Ludin,
3886Stuart Williams,
3887Subbu Allamaraju,
3888Sylvain Hellegouarch,
3889Tapan Divekar,
3890Tatsuya Hayashi,
3891Ted Hardie,
3892Thomas Broyer,
3893Thomas Nordin,
3894Thomas Roessler,
3895Tim Bray,
3896Tim Morgan,
3897Tim Olsen,
3898Tom Zhou,
3899Travis Snoozy,
3900Tyler Close,
3901Vincent Murphy,
3902Wenbo Zhu,
3903Werner Baumann,
3904Wilbur Streett,
3905Wilfredo Sanchez Vega,
3906William A. Rowe Jr.,
3907William Chan,
3908Willy Tarreau,
3909Xiaoshu Wang,
3910Yaron Goland,
3911Yngve Nysaeter Pettersen,
3912Yoav Nir,
3913Yogesh Bang,
3914Yutaka Oiwa,
3915Zed A. Shaw, and
3916Zhong Yu.
3917</t>
3918<?ENDINC acks ?>
3919</section>
3920
3921</middle>
3922<back>
3923
3924<references title="Normative References">
3925
3926<reference anchor="Part2">
3927  <front>
3928    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3929    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3930      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3931      <address><email>fielding@gbiv.com</email></address>
3932    </author>
3933    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3934      <organization abbrev="W3C">World Wide Web Consortium</organization>
3935      <address><email>ylafon@w3.org</email></address>
3936    </author>
3937    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3938      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3939      <address><email>julian.reschke@greenbytes.de</email></address>
3940    </author>
3941    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3942  </front>
3943  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3944  <x:source href="p2-semantics.xml" basename="p2-semantics">
3945    <x:defines>1xx (Informational)</x:defines>
3946    <x:defines>1xx</x:defines>
3947    <x:defines>100 (Continue)</x:defines>
3948    <x:defines>101 (Switching Protocols)</x:defines>
3949    <x:defines>2xx (Successful)</x:defines>
3950    <x:defines>2xx</x:defines>
3951    <x:defines>200 (OK)</x:defines>
3952    <x:defines>204 (No Content)</x:defines>
3953    <x:defines>3xx (Redirection)</x:defines>
3954    <x:defines>3xx</x:defines>
3955    <x:defines>301 (Moved Permanently)</x:defines>
3956    <x:defines>4xx (Client Error)</x:defines>
3957    <x:defines>4xx</x:defines>
3958    <x:defines>400 (Bad Request)</x:defines>
3959    <x:defines>405 (Method Not Allowed)</x:defines>
3960    <x:defines>411 (Length Required)</x:defines>
3961    <x:defines>414 (URI Too Long)</x:defines>
3962    <x:defines>417 (Expectation Failed)</x:defines>
3963    <x:defines>426 (Upgrade Required)</x:defines>
3964    <x:defines>501 (Not Implemented)</x:defines>
3965    <x:defines>502 (Bad Gateway)</x:defines>
3966    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3967    <x:defines>Allow</x:defines>
3968    <x:defines>Content-Encoding</x:defines>
3969    <x:defines>Content-Location</x:defines>
3970    <x:defines>Content-Type</x:defines>
3971    <x:defines>Date</x:defines>
3972    <x:defines>Expect</x:defines>
3973    <x:defines>Location</x:defines>
3974    <x:defines>Server</x:defines>
3975    <x:defines>User-Agent</x:defines>
3976  </x:source>
3977</reference>
3978
3979<reference anchor="Part4">
3980  <front>
3981    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3982    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3983      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3984      <address><email>fielding@gbiv.com</email></address>
3985    </author>
3986    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3987      <organization abbrev="W3C">World Wide Web Consortium</organization>
3988      <address><email>ylafon@w3.org</email></address>
3989    </author>
3990    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3991      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3992      <address><email>julian.reschke@greenbytes.de</email></address>
3993    </author>
3994    <date month="&ID-MONTH;" year="&ID-YEAR;" />
3995  </front>
3996  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
3997  <x:source basename="p4-conditional" href="p4-conditional.xml">
3998    <x:defines>304 (Not Modified)</x:defines>
3999    <x:defines>ETag</x:defines>
4000    <x:defines>Last-Modified</x:defines>
4001  </x:source>
4002</reference>
4003
4004<reference anchor="Part5">
4005  <front>
4006    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4007    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4008      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4009      <address><email>fielding@gbiv.com</email></address>
4010    </author>
4011    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4012      <organization abbrev="W3C">World Wide Web Consortium</organization>
4013      <address><email>ylafon@w3.org</email></address>
4014    </author>
4015    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4016      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4017      <address><email>julian.reschke@greenbytes.de</email></address>
4018    </author>
4019    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4020  </front>
4021  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4022  <x:source href="p5-range.xml" basename="p5-range">
4023    <x:defines>Content-Range</x:defines>
4024  </x:source>
4025</reference>
4026
4027<reference anchor="Part6">
4028  <front>
4029    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4030    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4031      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4032      <address><email>fielding@gbiv.com</email></address>
4033    </author>
4034    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4035      <organization abbrev="W3C">World Wide Web Consortium</organization>
4036      <address><email>ylafon@w3.org</email></address>
4037    </author>
4038    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4039      <address><email>mnot@mnot.net</email></address>
4040    </author>
4041    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4042      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4043      <address><email>julian.reschke@greenbytes.de</email></address>
4044    </author>
4045    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4046  </front>
4047  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4048  <x:source href="p6-cache.xml" basename="p6-cache">
4049    <x:defines>Expires</x:defines>
4050  </x:source>
4051</reference>
4052
4053<reference anchor="Part7">
4054  <front>
4055    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4056    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4057      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4058      <address><email>fielding@gbiv.com</email></address>
4059    </author>
4060    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4061      <organization abbrev="W3C">World Wide Web Consortium</organization>
4062      <address><email>ylafon@w3.org</email></address>
4063    </author>
4064    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4065      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4066      <address><email>julian.reschke@greenbytes.de</email></address>
4067    </author>
4068    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4069  </front>
4070  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4071  <x:source href="p7-auth.xml" basename="p7-auth">
4072    <x:defines>Proxy-Authenticate</x:defines>
4073    <x:defines>Proxy-Authorization</x:defines>
4074  </x:source>
4075</reference>
4076
4077<reference anchor="RFC5234">
4078  <front>
4079    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4080    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4081      <organization>Brandenburg InternetWorking</organization>
4082      <address>
4083        <email>dcrocker@bbiw.net</email>
4084      </address> 
4085    </author>
4086    <author initials="P." surname="Overell" fullname="Paul Overell">
4087      <organization>THUS plc.</organization>
4088      <address>
4089        <email>paul.overell@thus.net</email>
4090      </address>
4091    </author>
4092    <date month="January" year="2008"/>
4093  </front>
4094  <seriesInfo name="STD" value="68"/>
4095  <seriesInfo name="RFC" value="5234"/>
4096</reference>
4097
4098<reference anchor="RFC2119">
4099  <front>
4100    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4101    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4102      <organization>Harvard University</organization>
4103      <address><email>sob@harvard.edu</email></address>
4104    </author>
4105    <date month="March" year="1997"/>
4106  </front>
4107  <seriesInfo name="BCP" value="14"/>
4108  <seriesInfo name="RFC" value="2119"/>
4109</reference>
4110
4111<reference anchor="RFC3986">
4112 <front>
4113  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4114  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4115    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4116    <address>
4117       <email>timbl@w3.org</email>
4118       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4119    </address>
4120  </author>
4121  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4122    <organization abbrev="Day Software">Day Software</organization>
4123    <address>
4124      <email>fielding@gbiv.com</email>
4125      <uri>http://roy.gbiv.com/</uri>
4126    </address>
4127  </author>
4128  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4129    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4130    <address>
4131      <email>LMM@acm.org</email>
4132      <uri>http://larry.masinter.net/</uri>
4133    </address>
4134  </author>
4135  <date month='January' year='2005'></date>
4136 </front>
4137 <seriesInfo name="STD" value="66"/>
4138 <seriesInfo name="RFC" value="3986"/>
4139</reference>
4140
4141<reference anchor="USASCII">
4142  <front>
4143    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4144    <author>
4145      <organization>American National Standards Institute</organization>
4146    </author>
4147    <date year="1986"/>
4148  </front>
4149  <seriesInfo name="ANSI" value="X3.4"/>
4150</reference>
4151
4152<reference anchor="RFC1950">
4153  <front>
4154    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4155    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4156      <organization>Aladdin Enterprises</organization>
4157      <address><email>ghost@aladdin.com</email></address>
4158    </author>
4159    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4160    <date month="May" year="1996"/>
4161  </front>
4162  <seriesInfo name="RFC" value="1950"/>
4163  <!--<annotation>
4164    RFC 1950 is an Informational RFC, thus it might be less stable than
4165    this specification. On the other hand, this downward reference was
4166    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4167    therefore it is unlikely to cause problems in practice. See also
4168    <xref target="BCP97"/>.
4169  </annotation>-->
4170</reference>
4171
4172<reference anchor="RFC1951">
4173  <front>
4174    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4175    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4176      <organization>Aladdin Enterprises</organization>
4177      <address><email>ghost@aladdin.com</email></address>
4178    </author>
4179    <date month="May" year="1996"/>
4180  </front>
4181  <seriesInfo name="RFC" value="1951"/>
4182  <!--<annotation>
4183    RFC 1951 is an Informational RFC, thus it might be less stable than
4184    this specification. On the other hand, this downward reference was
4185    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4186    therefore it is unlikely to cause problems in practice. See also
4187    <xref target="BCP97"/>.
4188  </annotation>-->
4189</reference>
4190
4191<reference anchor="RFC1952">
4192  <front>
4193    <title>GZIP file format specification version 4.3</title>
4194    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4195      <organization>Aladdin Enterprises</organization>
4196      <address><email>ghost@aladdin.com</email></address>
4197    </author>
4198    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4199      <address><email>gzip@prep.ai.mit.edu</email></address>
4200    </author>
4201    <author initials="M." surname="Adler" fullname="Mark Adler">
4202      <address><email>madler@alumni.caltech.edu</email></address>
4203    </author>
4204    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4205      <address><email>ghost@aladdin.com</email></address>
4206    </author>
4207    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4208      <address><email>randeg@alumni.rpi.edu</email></address>
4209    </author>
4210    <date month="May" year="1996"/>
4211  </front>
4212  <seriesInfo name="RFC" value="1952"/>
4213  <!--<annotation>
4214    RFC 1952 is an Informational RFC, thus it might be less stable than
4215    this specification. On the other hand, this downward reference was
4216    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4217    therefore it is unlikely to cause problems in practice. See also
4218    <xref target="BCP97"/>.
4219  </annotation>-->
4220</reference>
4221
4222</references>
4223
4224<references title="Informative References">
4225
4226<reference anchor="ISO-8859-1">
4227  <front>
4228    <title>
4229     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4230    </title>
4231    <author>
4232      <organization>International Organization for Standardization</organization>
4233    </author>
4234    <date year="1998"/>
4235  </front>
4236  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4237</reference>
4238
4239<reference anchor='RFC1919'>
4240  <front>
4241    <title>Classical versus Transparent IP Proxies</title>
4242    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4243      <address><email>mchatel@pax.eunet.ch</email></address>
4244    </author>
4245    <date year='1996' month='March' />
4246  </front>
4247  <seriesInfo name='RFC' value='1919' />
4248</reference>
4249
4250<reference anchor="RFC1945">
4251  <front>
4252    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4253    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4254      <organization>MIT, Laboratory for Computer Science</organization>
4255      <address><email>timbl@w3.org</email></address>
4256    </author>
4257    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4258      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4259      <address><email>fielding@ics.uci.edu</email></address>
4260    </author>
4261    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4262      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4263      <address><email>frystyk@w3.org</email></address>
4264    </author>
4265    <date month="May" year="1996"/>
4266  </front>
4267  <seriesInfo name="RFC" value="1945"/>
4268</reference>
4269
4270<reference anchor="RFC2045">
4271  <front>
4272    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4273    <author initials="N." surname="Freed" fullname="Ned Freed">
4274      <organization>Innosoft International, Inc.</organization>
4275      <address><email>ned@innosoft.com</email></address>
4276    </author>
4277    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4278      <organization>First Virtual Holdings</organization>
4279      <address><email>nsb@nsb.fv.com</email></address>
4280    </author>
4281    <date month="November" year="1996"/>
4282  </front>
4283  <seriesInfo name="RFC" value="2045"/>
4284</reference>
4285
4286<reference anchor="RFC2047">
4287  <front>
4288    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4289    <author initials="K." surname="Moore" fullname="Keith Moore">
4290      <organization>University of Tennessee</organization>
4291      <address><email>moore@cs.utk.edu</email></address>
4292    </author>
4293    <date month="November" year="1996"/>
4294  </front>
4295  <seriesInfo name="RFC" value="2047"/>
4296</reference>
4297
4298<reference anchor="RFC2068">
4299  <front>
4300    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4301    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4302      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4303      <address><email>fielding@ics.uci.edu</email></address>
4304    </author>
4305    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4306      <organization>MIT Laboratory for Computer Science</organization>
4307      <address><email>jg@w3.org</email></address>
4308    </author>
4309    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4310      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4311      <address><email>mogul@wrl.dec.com</email></address>
4312    </author>
4313    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4314      <organization>MIT Laboratory for Computer Science</organization>
4315      <address><email>frystyk@w3.org</email></address>
4316    </author>
4317    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4318      <organization>MIT Laboratory for Computer Science</organization>
4319      <address><email>timbl@w3.org</email></address>
4320    </author>
4321    <date month="January" year="1997"/>
4322  </front>
4323  <seriesInfo name="RFC" value="2068"/>
4324</reference>
4325
4326<reference anchor="RFC2145">
4327  <front>
4328    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4329    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4330      <organization>Western Research Laboratory</organization>
4331      <address><email>mogul@wrl.dec.com</email></address>
4332    </author>
4333    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4334      <organization>Department of Information and Computer Science</organization>
4335      <address><email>fielding@ics.uci.edu</email></address>
4336    </author>
4337    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4338      <organization>MIT Laboratory for Computer Science</organization>
4339      <address><email>jg@w3.org</email></address>
4340    </author>
4341    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4342      <organization>W3 Consortium</organization>
4343      <address><email>frystyk@w3.org</email></address>
4344    </author>
4345    <date month="May" year="1997"/>
4346  </front>
4347  <seriesInfo name="RFC" value="2145"/>
4348</reference>
4349
4350<reference anchor="RFC2616">
4351  <front>
4352    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4353    <author initials="R." surname="Fielding" fullname="R. Fielding">
4354      <organization>University of California, Irvine</organization>
4355      <address><email>fielding@ics.uci.edu</email></address>
4356    </author>
4357    <author initials="J." surname="Gettys" fullname="J. Gettys">
4358      <organization>W3C</organization>
4359      <address><email>jg@w3.org</email></address>
4360    </author>
4361    <author initials="J." surname="Mogul" fullname="J. Mogul">
4362      <organization>Compaq Computer Corporation</organization>
4363      <address><email>mogul@wrl.dec.com</email></address>
4364    </author>
4365    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4366      <organization>MIT Laboratory for Computer Science</organization>
4367      <address><email>frystyk@w3.org</email></address>
4368    </author>
4369    <author initials="L." surname="Masinter" fullname="L. Masinter">
4370      <organization>Xerox Corporation</organization>
4371      <address><email>masinter@parc.xerox.com</email></address>
4372    </author>
4373    <author initials="P." surname="Leach" fullname="P. Leach">
4374      <organization>Microsoft Corporation</organization>
4375      <address><email>paulle@microsoft.com</email></address>
4376    </author>
4377    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4378      <organization>W3C</organization>
4379      <address><email>timbl@w3.org</email></address>
4380    </author>
4381    <date month="June" year="1999"/>
4382  </front>
4383  <seriesInfo name="RFC" value="2616"/>
4384</reference>
4385
4386<reference anchor='RFC2817'>
4387  <front>
4388    <title>Upgrading to TLS Within HTTP/1.1</title>
4389    <author initials='R.' surname='Khare' fullname='R. Khare'>
4390      <organization>4K Associates / UC Irvine</organization>
4391      <address><email>rohit@4K-associates.com</email></address>
4392    </author>
4393    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4394      <organization>Agranat Systems, Inc.</organization>
4395      <address><email>lawrence@agranat.com</email></address>
4396    </author>
4397    <date year='2000' month='May' />
4398  </front>
4399  <seriesInfo name='RFC' value='2817' />
4400</reference>
4401
4402<reference anchor='RFC2818'>
4403  <front>
4404    <title>HTTP Over TLS</title>
4405    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4406      <organization>RTFM, Inc.</organization>
4407      <address><email>ekr@rtfm.com</email></address>
4408    </author>
4409    <date year='2000' month='May' />
4410  </front>
4411  <seriesInfo name='RFC' value='2818' />
4412</reference>
4413
4414<reference anchor='RFC2965'>
4415  <front>
4416    <title>HTTP State Management Mechanism</title>
4417    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4418      <organization>Bell Laboratories, Lucent Technologies</organization>
4419      <address><email>dmk@bell-labs.com</email></address>
4420    </author>
4421    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4422      <organization>Epinions.com, Inc.</organization>
4423      <address><email>lou@montulli.org</email></address>
4424    </author>
4425    <date year='2000' month='October' />
4426  </front>
4427  <seriesInfo name='RFC' value='2965' />
4428</reference>
4429
4430<reference anchor='RFC3040'>
4431  <front>
4432    <title>Internet Web Replication and Caching Taxonomy</title>
4433    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4434      <organization>Equinix, Inc.</organization>
4435    </author>
4436    <author initials='I.' surname='Melve' fullname='I. Melve'>
4437      <organization>UNINETT</organization>
4438    </author>
4439    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4440      <organization>CacheFlow Inc.</organization>
4441    </author>
4442    <date year='2001' month='January' />
4443  </front>
4444  <seriesInfo name='RFC' value='3040' />
4445</reference>
4446
4447<reference anchor='RFC3864'>
4448  <front>
4449    <title>Registration Procedures for Message Header Fields</title>
4450    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4451      <organization>Nine by Nine</organization>
4452      <address><email>GK-IETF@ninebynine.org</email></address>
4453    </author>
4454    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4455      <organization>BEA Systems</organization>
4456      <address><email>mnot@pobox.com</email></address>
4457    </author>
4458    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4459      <organization>HP Labs</organization>
4460      <address><email>JeffMogul@acm.org</email></address>
4461    </author>
4462    <date year='2004' month='September' />
4463  </front>
4464  <seriesInfo name='BCP' value='90' />
4465  <seriesInfo name='RFC' value='3864' />
4466</reference>
4467
4468<reference anchor='RFC4033'>
4469  <front>
4470    <title>DNS Security Introduction and Requirements</title>
4471    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4472    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4473    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4474    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4475    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4476    <date year='2005' month='March' />
4477  </front>
4478  <seriesInfo name='RFC' value='4033' />
4479</reference>
4480
4481<reference anchor="RFC4288">
4482  <front>
4483    <title>Media Type Specifications and Registration Procedures</title>
4484    <author initials="N." surname="Freed" fullname="N. Freed">
4485      <organization>Sun Microsystems</organization>
4486      <address>
4487        <email>ned.freed@mrochek.com</email>
4488      </address>
4489    </author>
4490    <author initials="J." surname="Klensin" fullname="J. Klensin">
4491      <address>
4492        <email>klensin+ietf@jck.com</email>
4493      </address>
4494    </author>
4495    <date year="2005" month="December"/>
4496  </front>
4497  <seriesInfo name="BCP" value="13"/>
4498  <seriesInfo name="RFC" value="4288"/>
4499</reference>
4500
4501<reference anchor='RFC4395'>
4502  <front>
4503    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4504    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4505      <organization>AT&amp;T Laboratories</organization>
4506      <address>
4507        <email>tony+urireg@maillennium.att.com</email>
4508      </address>
4509    </author>
4510    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4511      <organization>Qualcomm, Inc.</organization>
4512      <address>
4513        <email>hardie@qualcomm.com</email>
4514      </address>
4515    </author>
4516    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4517      <organization>Adobe Systems</organization>
4518      <address>
4519        <email>LMM@acm.org</email>
4520      </address>
4521    </author>
4522    <date year='2006' month='February' />
4523  </front>
4524  <seriesInfo name='BCP' value='115' />
4525  <seriesInfo name='RFC' value='4395' />
4526</reference>
4527
4528<reference anchor='RFC4559'>
4529  <front>
4530    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4531    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4532    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4533    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4534    <date year='2006' month='June' />
4535  </front>
4536  <seriesInfo name='RFC' value='4559' />
4537</reference>
4538
4539<reference anchor='RFC5226'>
4540  <front>
4541    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4542    <author initials='T.' surname='Narten' fullname='T. Narten'>
4543      <organization>IBM</organization>
4544      <address><email>narten@us.ibm.com</email></address>
4545    </author>
4546    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4547      <organization>Google</organization>
4548      <address><email>Harald@Alvestrand.no</email></address>
4549    </author>
4550    <date year='2008' month='May' />
4551  </front>
4552  <seriesInfo name='BCP' value='26' />
4553  <seriesInfo name='RFC' value='5226' />
4554</reference>
4555
4556<reference anchor="RFC5322">
4557  <front>
4558    <title>Internet Message Format</title>
4559    <author initials="P." surname="Resnick" fullname="P. Resnick">
4560      <organization>Qualcomm Incorporated</organization>
4561    </author>
4562    <date year="2008" month="October"/>
4563  </front> 
4564  <seriesInfo name="RFC" value="5322"/>
4565</reference>
4566
4567<reference anchor="RFC6265">
4568  <front>
4569    <title>HTTP State Management Mechanism</title>
4570    <author initials="A." surname="Barth" fullname="Adam Barth">
4571      <organization abbrev="U.C. Berkeley">
4572        University of California, Berkeley
4573      </organization>
4574      <address><email>abarth@eecs.berkeley.edu</email></address>
4575    </author>
4576    <date year="2011" month="April" />
4577  </front>
4578  <seriesInfo name="RFC" value="6265"/>
4579</reference>
4580
4581<!--<reference anchor='BCP97'>
4582  <front>
4583    <title>Handling Normative References to Standards-Track Documents</title>
4584    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4585      <address>
4586        <email>klensin+ietf@jck.com</email>
4587      </address>
4588    </author>
4589    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4590      <organization>MIT</organization>
4591      <address>
4592        <email>hartmans-ietf@mit.edu</email>
4593      </address>
4594    </author>
4595    <date year='2007' month='June' />
4596  </front>
4597  <seriesInfo name='BCP' value='97' />
4598  <seriesInfo name='RFC' value='4897' />
4599</reference>-->
4600
4601<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4602  <front>
4603    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4604    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4605    <date year="2001" month="November"/>
4606  </front>
4607  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4608</reference>
4609
4610</references>
4611
4612
4613<section title="HTTP Version History" anchor="compatibility">
4614<t>
4615   HTTP has been in use by the World-Wide Web global information initiative
4616   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4617   was a simple protocol for hypertext data transfer across the Internet
4618   with only a single request method (GET) and no metadata.
4619   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4620   methods and MIME-like messaging that could include metadata about the data
4621   transferred and modifiers on the request/response semantics. However,
4622   HTTP/1.0 did not sufficiently take into consideration the effects of
4623   hierarchical proxies, caching, the need for persistent connections, or
4624   name-based virtual hosts. The proliferation of incompletely-implemented
4625   applications calling themselves "HTTP/1.0" further necessitated a
4626   protocol version change in order for two communicating applications
4627   to determine each other's true capabilities.
4628</t>
4629<t>
4630   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4631   requirements that enable reliable implementations, adding only
4632   those new features that will either be safely ignored by an HTTP/1.0
4633   recipient or only sent when communicating with a party advertising
4634   conformance with HTTP/1.1.
4635</t>
4636<t>
4637   It is beyond the scope of a protocol specification to mandate
4638   conformance with previous versions. HTTP/1.1 was deliberately
4639   designed, however, to make supporting previous versions easy.
4640   We would expect a general-purpose HTTP/1.1 server to understand
4641   any valid request in the format of HTTP/1.0 and respond appropriately
4642   with an HTTP/1.1 message that only uses features understood (or
4643   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4644   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4645</t>
4646<t>
4647   Since HTTP/0.9 did not support header fields in a request,
4648   there is no mechanism for it to support name-based virtual
4649   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4650   field).  Any server that implements name-based virtual hosts
4651   ought to disable support for HTTP/0.9.  Most requests that
4652   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4653   requests wherein a buggy client failed to properly encode
4654   linear whitespace found in a URI reference and placed in
4655   the request-target.
4656</t>
4657
4658<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4659<t>
4660   This section summarizes major differences between versions HTTP/1.0
4661   and HTTP/1.1.
4662</t>
4663
4664<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4665<t>
4666   The requirements that clients and servers support the <x:ref>Host</x:ref>
4667   header field (<xref target="header.host"/>), report an error if it is
4668   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4669   are among the most important changes defined by HTTP/1.1.
4670</t>
4671<t>
4672   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4673   addresses and servers; there was no other established mechanism for
4674   distinguishing the intended server of a request than the IP address
4675   to which that request was directed. The <x:ref>Host</x:ref> header field was
4676   introduced during the development of HTTP/1.1 and, though it was
4677   quickly implemented by most HTTP/1.0 browsers, additional requirements
4678   were placed on all HTTP/1.1 requests in order to ensure complete
4679   adoption.  At the time of this writing, most HTTP-based services
4680   are dependent upon the Host header field for targeting requests.
4681</t>
4682</section>
4683
4684<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4685<t>
4686   In HTTP/1.0, each connection is established by the client prior to the
4687   request and closed by the server after sending the response. However, some
4688   implementations implement the explicitly negotiated ("Keep-Alive") version
4689   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4690   target="RFC2068"/>.
4691</t>
4692<t>
4693   Some clients and servers might wish to be compatible with these previous
4694   approaches to persistent connections, by explicitly negotiating for them
4695   with a "Connection: keep-alive" request header field. However, some
4696   experimental implementations of HTTP/1.0 persistent connections are faulty;
4697   for example, if a HTTP/1.0 proxy server doesn't understand
4698   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4699   to the next inbound server, which would result in a hung connection.
4700</t>
4701<t>
4702   One attempted solution was the introduction of a Proxy-Connection header
4703   field, targeted specifically at proxies. In practice, this was also
4704   unworkable, because proxies are often deployed in multiple layers, bringing
4705   about the same problem discussed above.
4706</t>
4707<t>
4708   As a result, clients are encouraged not to send the Proxy-Connection header
4709   field in any requests.
4710</t>
4711<t>
4712   Clients are also encouraged to consider the use of Connection: keep-alive
4713   in requests carefully; while they can enable persistent connections with
4714   HTTP/1.0 servers, clients using them need will need to monitor the
4715   connection for "hung" requests (which indicate that the client ought stop
4716   sending the header field), and this mechanism ought not be used by clients
4717   at all when a proxy is being used.
4718</t>
4719</section>
4720
4721<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4722<t>
4723   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4724   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4725   any transfer-coding prior to forwarding a message via a MIME-compliant
4726   protocol.
4727</t>
4728</section>
4729
4730</section>
4731
4732<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4733<t>
4734  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4735  sensitive. Restrict the version numbers to be single digits due to the fact
4736  that implementations are known to handle multi-digit version numbers
4737  incorrectly.
4738  (<xref target="http.version"/>)
4739</t>
4740<t>
4741  Update use of abs_path production from RFC 1808 to the path-absolute + query
4742  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4743  request method only.
4744  (<xref target="request-target"/>)
4745</t>
4746<t>
4747  Require that invalid whitespace around field-names be rejected.
4748  (<xref target="header.fields"/>)
4749</t>
4750<t>
4751  Rules about implicit linear whitespace between certain grammar productions
4752  have been removed; now whitespace is only allowed where specifically
4753  defined in the ABNF.
4754  (<xref target="whitespace"/>)
4755</t>
4756<t> 
4757  The NUL octet is no longer allowed in comment and quoted-string
4758  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4759  Non-ASCII content in header fields and reason phrase has been obsoleted and
4760  made opaque (the TEXT rule was removed).
4761  (<xref target="field.components"/>)
4762</t>
4763<t>
4764  Empty list elements in list productions have been deprecated.
4765  (<xref target="abnf.extension"/>)
4766</t>
4767<t>
4768  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4769  fields as errors.
4770  (<xref target="message.body"/>)
4771</t>
4772<t>
4773  Remove reference to non-existent identity transfer-coding value tokens.
4774  (Sections <xref format="counter" target="message.body"/> and
4775  <xref format="counter" target="transfer.codings"/>)
4776</t>
4777<t>
4778  Clarification that the chunk length does not include the count of the octets
4779  in the chunk header and trailer. Furthermore disallowed line folding
4780  in chunk extensions, and deprecate their use.
4781  (<xref target="chunked.encoding"/>)
4782</t>
4783<t>
4784  Registration of Transfer Codings now requires IETF Review
4785  (<xref target="transfer.coding.registry"/>)
4786</t>
4787<t>
4788  Remove hard limit of two connections per server.
4789  Remove requirement to retry a sequence of requests as long it was idempotent.
4790  Remove requirements about when servers are allowed to close connections
4791  prematurely.
4792  (<xref target="persistent.connections"/>)
4793</t>
4794<t>
4795  Remove requirement to retry requests under certain circumstances when the
4796  server prematurely closes the connection.
4797  (<xref target="persistent.reuse"/>)
4798</t>
4799<t>
4800  Change ABNF productions for header fields to only define the field value.
4801</t>
4802<t>
4803  Clarify exactly when "close" connection options have to be sent.
4804  (<xref target="header.connection"/>)
4805</t>
4806<t>
4807  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4808  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4809  (<xref target="header.upgrade"/>)
4810</t>
4811<t>
4812  Take over the Upgrade Token Registry, previously defined in
4813  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4814  (<xref target="upgrade.token.registry"/>)
4815</t>
4816</section>
4817</section>
4818
4819<section title="ABNF list extension: #rule" anchor="abnf.extension">
4820<t>
4821  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4822  improve readability in the definitions of some header field values.
4823</t>
4824<t>
4825  A construct "#" is defined, similar to "*", for defining comma-delimited
4826  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4827  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4828  comma (",") and optional whitespace (OWS).   
4829</t>
4830<figure><preamble>
4831  Thus,
4832</preamble><artwork type="example">
4833  1#element =&gt; element *( OWS "," OWS element )
4834</artwork></figure>
4835<figure><preamble>
4836  and:
4837</preamble><artwork type="example">
4838  #element =&gt; [ 1#element ]
4839</artwork></figure>
4840<figure><preamble>
4841  and for n &gt;= 1 and m &gt; 1:
4842</preamble><artwork type="example">
4843  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4844</artwork></figure>
4845<t>
4846  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4847  list elements. In other words, consumers would follow the list productions:
4848</t>
4849<figure><artwork type="example">
4850  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4851 
4852  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4853</artwork></figure>
4854<t>
4855  Note that empty elements do not contribute to the count of elements present,
4856  though.
4857</t>
4858<t>
4859  For example, given these ABNF productions:
4860</t>
4861<figure><artwork type="example">
4862  example-list      = 1#example-list-elmt
4863  example-list-elmt = token ; see <xref target="field.components"/> 
4864</artwork></figure>
4865<t>
4866  Then these are valid values for example-list (not including the double
4867  quotes, which are present for delimitation only):
4868</t>
4869<figure><artwork type="example">
4870  "foo,bar"
4871  "foo ,bar,"
4872  "foo , ,bar,charlie   "
4873</artwork></figure>
4874<t>
4875  But these values would be invalid, as at least one non-empty element is
4876  required:
4877</t>
4878<figure><artwork type="example">
4879  ""
4880  ","
4881  ",   ,"
4882</artwork></figure>
4883<t>
4884  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4885  expanded as explained above.
4886</t>
4887</section>
4888
4889<?BEGININC p1-messaging.abnf-appendix ?>
4890<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4891<figure>
4892<artwork type="abnf" name="p1-messaging.parsed-abnf">
4893<x:ref>BWS</x:ref> = OWS
4894
4895<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4896 connection-option ] )
4897<x:ref>Content-Length</x:ref> = 1*DIGIT
4898
4899<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4900 ]
4901<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4902<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4903<x:ref>Host</x:ref> = uri-host [ ":" port ]
4904
4905<x:ref>OWS</x:ref> = *( SP / HTAB )
4906
4907<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4908
4909<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4910<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4911<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4912 transfer-coding ] )
4913
4914<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4915<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4916
4917<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4918 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4919 comment ] ) ] )
4920
4921<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4922<x:ref>absolute-form</x:ref> = absolute-URI
4923<x:ref>asterisk-form</x:ref> = "*"
4924<x:ref>attribute</x:ref> = token
4925<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4926<x:ref>authority-form</x:ref> = authority
4927
4928<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4929<x:ref>chunk-data</x:ref> = 1*OCTET
4930<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4931<x:ref>chunk-ext-name</x:ref> = token
4932<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4933<x:ref>chunk-size</x:ref> = 1*HEXDIG
4934<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4935<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4936<x:ref>connection-option</x:ref> = token
4937<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4938 / %x2A-5B ; '*'-'['
4939 / %x5D-7E ; ']'-'~'
4940 / obs-text
4941
4942<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4943<x:ref>field-name</x:ref> = token
4944<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4945
4946<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4947<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4948<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4949
4950<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4951
4952<x:ref>message-body</x:ref> = *OCTET
4953<x:ref>method</x:ref> = token
4954
4955<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4956<x:ref>obs-text</x:ref> = %x80-FF
4957<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4958
4959<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4960<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4961<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4962<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4963<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4964<x:ref>protocol-name</x:ref> = token
4965<x:ref>protocol-version</x:ref> = token
4966<x:ref>pseudonym</x:ref> = token
4967
4968<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4969 / %x5D-7E ; ']'-'~'
4970 / obs-text
4971<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4972 / %x5D-7E ; ']'-'~'
4973 / obs-text
4974<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4975<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4976<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4977<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4978<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4979
4980<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4981<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4982<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4983<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4984<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4985<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4986<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4987 asterisk-form
4988
4989<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4990 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4991<x:ref>start-line</x:ref> = request-line / status-line
4992<x:ref>status-code</x:ref> = 3DIGIT
4993<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
4994
4995<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
4996<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
4997<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4998 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4999<x:ref>token</x:ref> = 1*tchar
5000<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5001<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5002 transfer-extension
5003<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5004<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5005
5006<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5007
5008<x:ref>value</x:ref> = word
5009
5010<x:ref>word</x:ref> = token / quoted-string
5011</artwork>
5012</figure>
5013</section>
5014<?ENDINC p1-messaging.abnf-appendix ?>
5015
5016<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5017
5018<section title="Since RFC 2616">
5019<t>
5020  Extracted relevant partitions from <xref target="RFC2616"/>.
5021</t>
5022</section>
5023
5024<section title="Since draft-ietf-httpbis-p1-messaging-00">
5025<t>
5026  Closed issues:
5027  <list style="symbols"> 
5028    <t>
5029      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5030      "HTTP Version should be case sensitive"
5031      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5032    </t>
5033    <t>
5034      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5035      "'unsafe' characters"
5036      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5037    </t>
5038    <t>
5039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5040      "Chunk Size Definition"
5041      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5042    </t>
5043    <t>
5044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5045      "Message Length"
5046      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5047    </t>
5048    <t>
5049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5050      "Media Type Registrations"
5051      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5052    </t>
5053    <t>
5054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5055      "URI includes query"
5056      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5057    </t>
5058    <t>
5059      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5060      "No close on 1xx responses"
5061      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5062    </t>
5063    <t>
5064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5065      "Remove 'identity' token references"
5066      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5067    </t>
5068    <t>
5069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5070      "Import query BNF"
5071    </t>
5072    <t>
5073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5074      "qdtext BNF"
5075    </t>
5076    <t>
5077      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5078      "Normative and Informative references"
5079    </t>
5080    <t>
5081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5082      "RFC2606 Compliance"
5083    </t>
5084    <t>
5085      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5086      "RFC977 reference"
5087    </t>
5088    <t>
5089      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5090      "RFC1700 references"
5091    </t>
5092    <t>
5093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5094      "inconsistency in date format explanation"
5095    </t>
5096    <t>
5097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5098      "Date reference typo"
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5102      "Informative references"
5103    </t>
5104    <t>
5105      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5106      "ISO-8859-1 Reference"
5107    </t>
5108    <t>
5109      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5110      "Normative up-to-date references"
5111    </t>
5112  </list>
5113</t>
5114<t>
5115  Other changes:
5116  <list style="symbols"> 
5117    <t>
5118      Update media type registrations to use RFC4288 template.
5119    </t>
5120    <t>
5121      Use names of RFC4234 core rules DQUOTE and HTAB,
5122      fix broken ABNF for chunk-data
5123      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5124    </t>
5125  </list>
5126</t>
5127</section>
5128
5129<section title="Since draft-ietf-httpbis-p1-messaging-01">
5130<t>
5131  Closed issues:
5132  <list style="symbols"> 
5133    <t>
5134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5135      "Bodies on GET (and other) requests"
5136    </t>
5137    <t>
5138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5139      "Updating to RFC4288"
5140    </t>
5141    <t>
5142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5143      "Status Code and Reason Phrase"
5144    </t>
5145    <t>
5146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5147      "rel_path not used"
5148    </t>
5149  </list>
5150</t>
5151<t>
5152  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5153  <list style="symbols"> 
5154    <t>
5155      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5156      "trailer-part").
5157    </t>
5158    <t>
5159      Avoid underscore character in rule names ("http_URL" ->
5160      "http-URL", "abs_path" -> "path-absolute").
5161    </t>
5162    <t>
5163      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5164      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5165      have to be updated when switching over to RFC3986.
5166    </t>
5167    <t>
5168      Synchronize core rules with RFC5234.
5169    </t>
5170    <t>
5171      Get rid of prose rules that span multiple lines.
5172    </t>
5173    <t>
5174      Get rid of unused rules LOALPHA and UPALPHA.
5175    </t>
5176    <t>
5177      Move "Product Tokens" section (back) into Part 1, as "token" is used
5178      in the definition of the Upgrade header field.
5179    </t>
5180    <t>
5181      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5182    </t>
5183    <t>
5184      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5185    </t>
5186  </list>
5187</t>
5188</section>
5189
5190<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5191<t>
5192  Closed issues:
5193  <list style="symbols"> 
5194    <t>
5195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5196      "HTTP-date vs. rfc1123-date"
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5200      "WS in quoted-pair"
5201    </t>
5202  </list>
5203</t>
5204<t>
5205  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5206  <list style="symbols"> 
5207    <t>
5208      Reference RFC 3984, and update header field registrations for header
5209      fields defined in this document.
5210    </t>
5211  </list>
5212</t>
5213<t>
5214  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5215  <list style="symbols"> 
5216    <t>
5217      Replace string literals when the string really is case-sensitive (HTTP-version).
5218    </t>
5219  </list>
5220</t>
5221</section>
5222
5223<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5224<t>
5225  Closed issues:
5226  <list style="symbols"> 
5227    <t>
5228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5229      "Connection closing"
5230    </t>
5231    <t>
5232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5233      "Move registrations and registry information to IANA Considerations"
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5237      "need new URL for PAD1995 reference"
5238    </t>
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5241      "IANA Considerations: update HTTP URI scheme registration"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5245      "Cite HTTPS URI scheme definition"
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5249      "List-type header fields vs Set-Cookie"
5250    </t>
5251  </list>
5252</t>
5253<t>
5254  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5255  <list style="symbols"> 
5256    <t>
5257      Replace string literals when the string really is case-sensitive (HTTP-Date).
5258    </t>
5259    <t>
5260      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5261    </t>
5262  </list>
5263</t>
5264</section>
5265
5266<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5267<t>
5268  Closed issues:
5269  <list style="symbols"> 
5270    <t>
5271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5272      "Out-of-date reference for URIs"
5273    </t>
5274    <t>
5275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5276      "RFC 2822 is updated by RFC 5322"
5277    </t>
5278  </list>
5279</t>
5280<t>
5281  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5282  <list style="symbols"> 
5283    <t>
5284      Use "/" instead of "|" for alternatives.
5285    </t>
5286    <t>
5287      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5288    </t>
5289    <t>
5290      Only reference RFC 5234's core rules.
5291    </t>
5292    <t>
5293      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5294      whitespace ("OWS") and required whitespace ("RWS").
5295    </t>
5296    <t>
5297      Rewrite ABNFs to spell out whitespace rules, factor out
5298      header field value format definitions.
5299    </t>
5300  </list>
5301</t>
5302</section>
5303
5304<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5305<t>
5306  Closed issues:
5307  <list style="symbols"> 
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5310      "Header LWS"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5314      "Sort 1.3 Terminology"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5318      "RFC2047 encoded words"
5319    </t>
5320    <t>
5321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5322      "Character Encodings in TEXT"
5323    </t>
5324    <t>
5325      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5326      "Line Folding"
5327    </t>
5328    <t>
5329      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5330      "OPTIONS * and proxies"
5331    </t>
5332    <t>
5333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5334      "reason-phrase BNF"
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5338      "Use of TEXT"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5342      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5343    </t>
5344    <t>
5345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5346      "RFC822 reference left in discussion of date formats"
5347    </t>
5348  </list>
5349</t>
5350<t>
5351  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5352  <list style="symbols"> 
5353    <t>
5354      Rewrite definition of list rules, deprecate empty list elements.
5355    </t>
5356    <t>
5357      Add appendix containing collected and expanded ABNF.
5358    </t>
5359  </list>
5360</t>
5361<t>
5362  Other changes:
5363  <list style="symbols"> 
5364    <t>
5365      Rewrite introduction; add mostly new Architecture Section.
5366    </t>
5367    <t>
5368      Move definition of quality values from Part 3 into Part 1;
5369      make TE request header field grammar independent of accept-params (defined in Part 3).
5370    </t>
5371  </list>
5372</t>
5373</section>
5374
5375<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5376<t>
5377  Closed issues:
5378  <list style="symbols"> 
5379    <t>
5380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5381      "base for numeric protocol elements"
5382    </t>
5383    <t>
5384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5385      "comment ABNF"
5386    </t>
5387  </list>
5388</t>
5389<t>
5390  Partly resolved issues:
5391  <list style="symbols"> 
5392    <t>
5393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5394      "205 Bodies" (took out language that implied that there might be
5395      methods for which a request body MUST NOT be included)
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5399      "editorial improvements around HTTP-date"
5400    </t>
5401  </list>
5402</t>
5403</section>
5404
5405<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5406<t>
5407  Closed issues:
5408  <list style="symbols"> 
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5411      "Repeating single-value header fields"
5412    </t>
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5415      "increase connection limit"
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5419      "IP addresses in URLs"
5420    </t>
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5423      "take over HTTP Upgrade Token Registry"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5427      "CR and LF in chunk extension values"
5428    </t>
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5431      "HTTP/0.9 support"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5435      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5436    </t>
5437    <t>
5438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5439      "move definitions of gzip/deflate/compress to part 1"
5440    </t>
5441    <t>
5442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5443      "disallow control characters in quoted-pair"
5444    </t>
5445  </list>
5446</t>
5447<t>
5448  Partly resolved issues:
5449  <list style="symbols"> 
5450    <t>
5451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5452      "update IANA requirements wrt Transfer-Coding values" (add the
5453      IANA Considerations subsection)
5454    </t>
5455  </list>
5456</t>
5457</section>
5458
5459<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5460<t>
5461  Closed issues:
5462  <list style="symbols"> 
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5465      "header parsing, treatment of leading and trailing OWS"
5466    </t>
5467  </list>
5468</t>
5469<t>
5470  Partly resolved issues:
5471  <list style="symbols"> 
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5474      "Placement of 13.5.1 and 13.5.2"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5478      "use of term "word" when talking about header field structure"
5479    </t>
5480  </list>
5481</t>
5482</section>
5483
5484<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5485<t>
5486  Closed issues:
5487  <list style="symbols"> 
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5490      "Clarification of the term 'deflate'"
5491    </t>
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5494      "OPTIONS * and proxies"
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5498      "MIME-Version not listed in P1, general header fields"
5499    </t>
5500    <t>
5501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5502      "IANA registry for content/transfer encodings"
5503    </t>
5504    <t>
5505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5506      "Case-sensitivity of HTTP-date"
5507    </t>
5508    <t>
5509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5510      "use of term "word" when talking about header field structure"
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/196"/>:
5519      "Term for the requested resource's URI"
5520    </t>
5521  </list>
5522</t>
5523</section>
5524
5525<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5526<t>
5527  Closed issues:
5528  <list style="symbols">
5529    <t>
5530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5531      "Connection Closing"
5532    </t>
5533    <t>
5534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5535      "Delimiting messages with multipart/byteranges"
5536    </t>
5537    <t>
5538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5539      "Handling multiple Content-Length header fields"
5540    </t>
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5543      "Clarify entity / representation / variant terminology"
5544    </t>
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5547      "consider removing the 'changes from 2068' sections"
5548    </t>
5549  </list>
5550</t>
5551<t>
5552  Partly resolved issues:
5553  <list style="symbols"> 
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5556      "HTTP(s) URI scheme definitions"
5557    </t>
5558  </list>
5559</t>
5560</section>
5561
5562<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5563<t>
5564  Closed issues:
5565  <list style="symbols">
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5568      "Trailer requirements"
5569    </t>
5570    <t>
5571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5572      "Text about clock requirement for caches belongs in p6"
5573    </t>
5574    <t>
5575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5576      "effective request URI: handling of missing host in HTTP/1.0"
5577    </t>
5578    <t>
5579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5580      "confusing Date requirements for clients"
5581    </t>
5582  </list>
5583</t>
5584<t>
5585  Partly resolved issues:
5586  <list style="symbols"> 
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5589      "Handling multiple Content-Length header fields"
5590    </t>
5591  </list>
5592</t>
5593</section>
5594
5595<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5596<t>
5597  Closed issues:
5598  <list style="symbols">
5599    <t>
5600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5601      "RFC2145 Normative"
5602    </t>
5603    <t>
5604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5605      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5606    </t>
5607    <t>
5608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5609      "define 'transparent' proxy"
5610    </t>
5611    <t>
5612      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5613      "Header Field Classification"
5614    </t>
5615    <t>
5616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5617      "Is * usable as a request-uri for new methods?"
5618    </t>
5619    <t>
5620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5621      "Migrate Upgrade details from RFC2817"
5622    </t>
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5625      "untangle ABNFs for header fields"
5626    </t>
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5629      "update RFC 2109 reference"
5630    </t>
5631  </list>
5632</t>
5633</section>
5634
5635<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5636<t>
5637  Closed issues:
5638  <list style="symbols">
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5641      "Allow is not in 13.5.2"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5645      "Handling multiple Content-Length header fields"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5649      "untangle ABNFs for header fields"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5653      "Content-Length ABNF broken"
5654    </t>
5655  </list>
5656</t>
5657</section>
5658
5659<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5660<t>
5661  Closed issues:
5662  <list style="symbols">
5663    <t>
5664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5665      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5666    </t>
5667    <t>
5668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5669      "Recommend minimum sizes for protocol elements"
5670    </t>
5671    <t>
5672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5673      "Set expectations around buffering"
5674    </t>
5675    <t>
5676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5677      "Considering messages in isolation"
5678    </t>
5679  </list>
5680</t>
5681</section>
5682
5683<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5684<t>
5685  Closed issues:
5686  <list style="symbols">
5687    <t>
5688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5689      "DNS Spoofing / DNS Binding advice"
5690    </t>
5691    <t>
5692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5693      "move RFCs 2145, 2616, 2817 to Historic status"
5694    </t>
5695    <t>
5696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5697      "\-escaping in quoted strings"
5698    </t>
5699    <t>
5700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5701      "'Close' should be reserved in the HTTP header field registry"
5702    </t>
5703  </list>
5704</t>
5705</section>
5706
5707<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5708<t>
5709  Closed issues:
5710  <list style="symbols">
5711    <t>
5712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5713      "Document HTTP's error-handling philosophy"
5714    </t>
5715    <t>
5716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5717      "Explain header field registration"
5718    </t>
5719    <t>
5720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5721      "Revise Acknowledgements Sections"
5722    </t>
5723    <t>
5724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5725      "Retrying Requests"
5726    </t>
5727    <t>
5728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5729      "Closing the connection on server error"
5730    </t>
5731  </list>
5732</t>
5733</section>
5734
5735<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5736<t>
5737  Closed issues:
5738  <list style="symbols">
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5741      "Proxy-Connection and Keep-Alive"
5742    </t>
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5745      "Clarify 'User Agent'"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5749      "Define non-final responses"
5750    </t>
5751    <t>
5752      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5753      "intended maturity level vs normative references"
5754    </t>
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5757      "Intermediary rewriting of queries"
5758    </t>
5759  </list>
5760</t>
5761</section>
5762
5763<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5764<t>
5765  Closed issues:
5766  <list style="symbols">
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5769      "message-body in CONNECT response"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5773      "Misplaced text on connection handling in p2"
5774    </t>
5775    <t>
5776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5777      "wording of line folding rule"
5778    </t>
5779    <t>
5780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5781      "chunk-extensions"
5782    </t>
5783    <t>
5784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5785      "make IANA policy definitions consistent"
5786    </t>
5787  </list>
5788</t>
5789</section>
5790
5791<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5792<t>
5793  Closed issues:
5794  <list style="symbols">
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5797      "make IANA policy definitions consistent"
5798    </t>
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5801      "clarify connection header field values are case-insensitive"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5805      "ABNF requirements for recipients"
5806    </t>
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5809      "note introduction of new IANA registries as normative changes"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5813      "Reference to ISO-8859-1 is informative"
5814    </t>
5815  </list>
5816</t>
5817</section>
5818
5819<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5820<t>
5821  None yet.
5822</t>
5823</section>
5824
5825</section>
5826
5827</back>
5828</rfc>
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