source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1905

Last change on this file since 1905 was 1905, checked in by fielding@…, 7 years ago

(editorial) define payload within representation

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  • Property svn:mime-type set to text/xml
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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' x:rel='#payload' 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 resource               "<xref target='Part2' x:rel='#resource' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57]>
58<?rfc toc="yes" ?>
59<?rfc symrefs="yes" ?>
60<?rfc sortrefs="yes" ?>
61<?rfc compact="yes"?>
62<?rfc subcompact="no" ?>
63<?rfc linkmailto="no" ?>
64<?rfc editing="no" ?>
65<?rfc comments="yes"?>
66<?rfc inline="yes"?>
67<?rfc rfcedstyle="yes"?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
71     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
72     xmlns:x='http://purl.org/net/xml2rfc/ext'>
73<x:link rel="next" basename="p2-semantics"/>
74<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
75<front>
76
77  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
78
79  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
80    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
81    <address>
82      <postal>
83        <street>345 Park Ave</street>
84        <city>San Jose</city>
85        <region>CA</region>
86        <code>95110</code>
87        <country>USA</country>
88      </postal>
89      <email>fielding@gbiv.com</email>
90      <uri>http://roy.gbiv.com/</uri>
91    </address>
92  </author>
93
94  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
95    <organization abbrev="W3C">World Wide Web Consortium</organization>
96    <address>
97      <postal>
98        <street>W3C / ERCIM</street>
99        <street>2004, rte des Lucioles</street>
100        <city>Sophia-Antipolis</city>
101        <region>AM</region>
102        <code>06902</code>
103        <country>France</country>
104      </postal>
105      <email>ylafon@w3.org</email>
106      <uri>http://www.raubacapeu.net/people/yves/</uri>
107    </address>
108  </author>
109
110  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
111    <organization abbrev="greenbytes">greenbytes GmbH</organization>
112    <address>
113      <postal>
114        <street>Hafenweg 16</street>
115        <city>Muenster</city><region>NW</region><code>48155</code>
116        <country>Germany</country>
117      </postal>
118      <email>julian.reschke@greenbytes.de</email>
119      <uri>http://greenbytes.de/tech/webdav/</uri>
120    </address>
121  </author>
122
123  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
124  <workgroup>HTTPbis Working Group</workgroup>
125
126<abstract>
127<t>
128   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
129   distributed, collaborative, hypertext information systems. HTTP has been in
130   use by the World Wide Web global information initiative since 1990.
131   This document provides an overview of HTTP architecture and its associated
132   terminology, defines the "http" and "https" Uniform Resource Identifier
133   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
134   and describes general security concerns for implementations.
135</t>   
136</abstract>
137
138<note title="Editorial Note (To be removed by RFC Editor)">
139  <t>
140    Discussion of this draft takes place on the HTTPBIS working group
141    mailing list (ietf-http-wg@w3.org), which is archived at
142    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
143  </t>
144  <t>
145    The current issues list is at
146    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
147    documents (including fancy diffs) can be found at
148    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
149  </t>
150  <t>
151    The changes in this draft are summarized in <xref target="changes.since.20"/>.
152  </t>
153</note>
154</front>
155<middle>
156<section title="Introduction" anchor="introduction">
157<t>
158   The Hypertext Transfer Protocol (HTTP) is an application-level
159   request/response protocol that uses extensible semantics and MIME-like
160   message payloads for flexible interaction with network-based hypertext
161   information systems. This document is the first in a series of documents
162   that collectively form the HTTP/1.1 specification:
163   <list style="empty">
164    <t>RFC xxx1: Message Syntax and Routing</t>
165    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
166    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
167    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
168    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
169    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
170   </list>
171</t>
172<t>
173   This HTTP/1.1 specification obsoletes and moves to historic status
174   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
175   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
176   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
177   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
178   for TLS upgrades).
179</t>
180<t>
181   HTTP is a generic interface protocol for information systems. It is
182   designed to hide the details of how a service is implemented by presenting
183   a uniform interface to clients that is independent of the types of
184   resources provided. Likewise, servers do not need to be aware of each
185   client's purpose: an HTTP request can be considered in isolation rather
186   than being associated with a specific type of client or a predetermined
187   sequence of application steps. The result is a protocol that can be used
188   effectively in many different contexts and for which implementations can
189   evolve independently over time.
190</t>
191<t>
192   HTTP is also designed for use as an intermediation protocol for translating
193   communication to and from non-HTTP information systems.
194   HTTP proxies and gateways can provide access to alternative information
195   services by translating their diverse protocols into a hypertext
196   format that can be viewed and manipulated by clients in the same way
197   as HTTP services.
198</t>
199<t>
200   One consequence of HTTP flexibility is that the protocol cannot be
201   defined in terms of what occurs behind the interface. Instead, we
202   are limited to defining the syntax of communication, the intent
203   of received communication, and the expected behavior of recipients.
204   If the communication is considered in isolation, then successful
205   actions ought to be reflected in corresponding changes to the
206   observable interface provided by servers. However, since multiple
207   clients might act in parallel and perhaps at cross-purposes, we
208   cannot require that such changes be observable beyond the scope
209   of a single response.
210</t>
211<t>
212   This document describes the architectural elements that are used or
213   referred to in HTTP, defines the "http" and "https" URI schemes,
214   describes overall network operation and connection management,
215   and defines HTTP message framing and forwarding requirements.
216   Our goal is to define all of the mechanisms necessary for HTTP message
217   handling that are independent of message semantics, thereby defining the
218   complete set of requirements for message parsers and
219   message-forwarding intermediaries.
220</t>
221
222
223<section title="Requirement Notation" anchor="intro.requirements">
224<t>
225   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
226   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
227   document are to be interpreted as described in <xref target="RFC2119"/>.
228</t>
229<t>
230   Conformance criteria and considerations regarding error handling
231   are defined in <xref target="conformance"/>.
232</t>
233</section>
234
235<section title="Syntax Notation" anchor="notation">
236<iref primary="true" item="Grammar" subitem="ALPHA"/>
237<iref primary="true" item="Grammar" subitem="CR"/>
238<iref primary="true" item="Grammar" subitem="CRLF"/>
239<iref primary="true" item="Grammar" subitem="CTL"/>
240<iref primary="true" item="Grammar" subitem="DIGIT"/>
241<iref primary="true" item="Grammar" subitem="DQUOTE"/>
242<iref primary="true" item="Grammar" subitem="HEXDIG"/>
243<iref primary="true" item="Grammar" subitem="HTAB"/>
244<iref primary="true" item="Grammar" subitem="LF"/>
245<iref primary="true" item="Grammar" subitem="OCTET"/>
246<iref primary="true" item="Grammar" subitem="SP"/>
247<iref primary="true" item="Grammar" subitem="VCHAR"/>
248<t>
249   This specification uses the Augmented Backus-Naur Form (ABNF) notation
250   of <xref target="RFC5234"/> with the list rule extension defined in
251   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
252   the collected ABNF with the list rule expanded.
253</t>
254<t anchor="core.rules">
255  <x:anchor-alias value="ALPHA"/>
256  <x:anchor-alias value="CTL"/>
257  <x:anchor-alias value="CR"/>
258  <x:anchor-alias value="CRLF"/>
259  <x:anchor-alias value="DIGIT"/>
260  <x:anchor-alias value="DQUOTE"/>
261  <x:anchor-alias value="HEXDIG"/>
262  <x:anchor-alias value="HTAB"/>
263  <x:anchor-alias value="LF"/>
264  <x:anchor-alias value="OCTET"/>
265  <x:anchor-alias value="SP"/>
266  <x:anchor-alias value="VCHAR"/>
267   The following core rules are included by
268   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
269   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
270   DIGIT (decimal 0-9), DQUOTE (double quote),
271   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
272   OCTET (any 8-bit sequence of data), SP (space), and
273   VCHAR (any visible <xref target="USASCII"/> character).
274</t>
275<t>
276   As a convention, ABNF rule names prefixed with "obs-" denote
277   "obsolete" grammar rules that appear for historical reasons.
278</t>
279</section>
280</section>
281
282<section title="Architecture" anchor="architecture">
283<t>
284   HTTP was created for the World Wide Web architecture
285   and has evolved over time to support the scalability needs of a worldwide
286   hypertext system. Much of that architecture is reflected in the terminology
287   and syntax productions used to define HTTP.
288</t>
289
290<section title="Client/Server Messaging" anchor="operation">
291<iref primary="true" item="client"/>
292<iref primary="true" item="server"/>
293<iref primary="true" item="connection"/>
294<t>
295   HTTP is a stateless request/response protocol that operates by exchanging
296   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
297   transport or session-layer
298   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
299   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
300   to a server for the purpose of sending one or more HTTP requests.
301   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
302   in order to service HTTP requests by sending HTTP responses.
303</t>
304<iref primary="true" item="user agent"/>
305<iref primary="true" item="origin server"/>
306<iref primary="true" item="browser"/>
307<iref primary="true" item="spider"/>
308<iref primary="true" item="sender"/>
309<iref primary="true" item="recipient"/>
310<t>
311   The terms client and server refer only to the roles that
312   these programs perform for a particular connection.  The same program
313   might act as a client on some connections and a server on others.  We use
314   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
315   such as a WWW browser, editor, or spider (web-traversing robot), and
316   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
317   authoritative responses to a request.  For general requirements, we use
318   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
319   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
320   message.
321</t>
322<t>
323   HTTP relies upon the Uniform Resource Identifier (URI)
324   standard <xref target="RFC3986"/> to indicate the target resource
325   (<xref target="target-resource"/>) and relationships between resources.
326   Messages are passed in a format similar to that used by Internet mail
327   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
328   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
329   between HTTP and MIME messages).
330</t>
331<t>
332   Most HTTP communication consists of a retrieval request (GET) for
333   a representation of some resource identified by a URI.  In the
334   simplest case, this might be accomplished via a single bidirectional
335   connection (===) between the user agent (UA) and the origin server (O).
336</t>
337<figure><artwork type="drawing">
338         request   &gt;
339    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
340                                &lt;   response
341</artwork></figure>
342<iref primary="true" item="message"/>
343<iref primary="true" item="request"/>
344<iref primary="true" item="response"/>
345<t>
346   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
347   message, beginning with a request-line that includes a method, URI, and
348   protocol version (<xref target="request.line"/>),
349   followed by header fields containing
350   request modifiers, client information, and representation metadata
351   (<xref target="header.fields"/>),
352   an empty line to indicate the end of the header section, and finally
353   a message body containing the payload body (if any,
354   <xref target="message.body"/>).
355</t>
356<t>
357   A server responds to a client's request by sending one or more HTTP
358   <x:dfn>response</x:dfn>
359   messages, each beginning with a status line that
360   includes the protocol version, a success or error code, and textual
361   reason phrase (<xref target="status.line"/>),
362   possibly followed by header fields containing server
363   information, resource metadata, and representation metadata
364   (<xref target="header.fields"/>),
365   an empty line to indicate the end of the header section, and finally
366   a message body containing the payload body (if any,
367   <xref target="message.body"/>).
368</t>
369<t>
370   A connection might be used for multiple request/response exchanges,
371   as defined in <xref target="persistent.connections"/>.
372</t>
373<t>
374   The following example illustrates a typical message exchange for a
375   GET request on the URI "http://www.example.com/hello.txt":
376</t>
377<figure><preamble>
378client request:
379</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
380GET /hello.txt HTTP/1.1
381User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
382Host: www.example.com
383Accept-Language: en, mi
384
385</artwork></figure>
386<figure><preamble>
387server response:
388</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
389HTTP/1.1 200 OK
390Date: Mon, 27 Jul 2009 12:28:53 GMT
391Server: Apache
392Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
393ETag: "34aa387-d-1568eb00"
394Accept-Ranges: bytes
395Content-Length: <x:length-of target="exbody"/>
396Vary: Accept-Encoding
397Content-Type: text/plain
398
399<x:span anchor="exbody">Hello World!
400</x:span></artwork></figure>
401</section>
402
403<section title="Implementation Diversity" anchor="implementation-diversity">
404<t>
405   When considering the design of HTTP, it is easy to fall into a trap of
406   thinking that all user agents are general-purpose browsers and all origin
407   servers are large public websites. That is not the case in practice.
408   Common HTTP user agents include household appliances, stereos, scales,
409   firmware update scripts, command-line programs, mobile apps,
410   and communication devices in a multitude of shapes and sizes.  Likewise,
411   common HTTP origin servers include home automation units, configurable
412   networking components, office machines, autonomous robots, news feeds,
413   traffic cameras, ad selectors, and video delivery platforms.
414</t>
415<t>
416   The term "user agent" does not imply that there is a human user directly
417   interacting with the software agent at the time of a request. In many
418   cases, a user agent is installed or configured to run in the background
419   and save its results for later inspection (or save only a subset of those
420   results that might be interesting or erroneous). Spiders, for example, are
421   typically given a start URI and configured to follow certain behavior while
422   crawling the Web as a hypertext graph.
423</t>
424<t>
425   The implementation diversity of HTTP means that we cannot assume the
426   user agent can make interactive suggestions to a user or provide adequate
427   warning for security or privacy options.  In the few cases where this
428   specification requires reporting of errors to the user, it is acceptable
429   for such reporting to only be observable in an error console or log file.
430   Likewise, requirements that an automated action be confirmed by the user
431   before proceeding can me met via advance configuration choices,
432   run-time options, or simply not proceeding with the unsafe action.
433</t>
434</section>
435
436<section title="Intermediaries" anchor="intermediaries">
437<iref primary="true" item="intermediary"/>
438<t>
439   HTTP enables the use of intermediaries to satisfy requests through
440   a chain of connections.  There are three common forms of HTTP
441   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
442   a single intermediary might act as an origin server, proxy, gateway,
443   or tunnel, switching behavior based on the nature of each request.
444</t>
445<figure><artwork type="drawing">
446         &gt;             &gt;             &gt;             &gt;
447    <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>
448               &lt;             &lt;             &lt;             &lt;
449</artwork></figure>
450<t>
451   The figure above shows three intermediaries (A, B, and C) between the
452   user agent and origin server. A request or response message that
453   travels the whole chain will pass through four separate connections.
454   Some HTTP communication options
455   might apply only to the connection with the nearest, non-tunnel
456   neighbor, only to the end-points of the chain, or to all connections
457   along the chain. Although the diagram is linear, each participant might
458   be engaged in multiple, simultaneous communications. For example, B
459   might be receiving requests from many clients other than A, and/or
460   forwarding requests to servers other than C, at the same time that it
461   is handling A's request.
462</t>
463<t>
464<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
465<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
466   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
467   to describe various requirements in relation to the directional flow of a
468   message: all messages flow from upstream to downstream.
469   Likewise, we use the terms inbound and outbound to refer to
470   directions in relation to the request path:
471   "<x:dfn>inbound</x:dfn>" means toward the origin server and
472   "<x:dfn>outbound</x:dfn>" means toward the user agent.
473</t>
474<t><iref primary="true" item="proxy"/>
475   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
476   client, usually via local configuration rules, to receive requests
477   for some type(s) of absolute URI and attempt to satisfy those
478   requests via translation through the HTTP interface.  Some translations
479   are minimal, such as for proxy requests for "http" URIs, whereas
480   other requests might require translation to and from entirely different
481   application-level protocols. Proxies are often used to group an
482   organization's HTTP requests through a common intermediary for the
483   sake of security, annotation services, or shared caching.
484</t>
485<t>
486<iref primary="true" item="transforming proxy"/>
487<iref primary="true" item="non-transforming proxy"/>
488   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
489   or configured to modify request or response messages in a semantically
490   meaningful way (i.e., modifications, beyond those required by normal
491   HTTP processing, that change the message in a way that would be
492   significant to the original sender or potentially significant to
493   downstream recipients).  For example, a transforming proxy might be
494   acting as a shared annotation server (modifying responses to include
495   references to a local annotation database), a malware filter, a
496   format transcoder, or an intranet-to-Internet privacy filter.  Such
497   transformations are presumed to be desired by the client (or client
498   organization) that selected the proxy and are beyond the scope of
499   this specification.  However, when a proxy is not intended to transform
500   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
501   requirements that preserve HTTP message semantics. See &status-203; and
502   &header-warning; for status and warning codes related to transformations.
503</t>
504<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
505<iref primary="true" item="accelerator"/>
506   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
507   is a receiving agent that acts
508   as a layer above some other server(s) and translates the received
509   requests to the underlying server's protocol.  Gateways are often
510   used to encapsulate legacy or untrusted information services, to
511   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
512   enable partitioning or load-balancing of HTTP services across
513   multiple machines.
514</t>
515<t>
516   A gateway behaves as an origin server on its outbound connection and
517   as a user agent on its inbound connection.
518   All HTTP requirements applicable to an origin server
519   also apply to the outbound communication of a gateway.
520   A gateway communicates with inbound servers using any protocol that
521   it desires, including private extensions to HTTP that are outside
522   the scope of this specification.  However, an HTTP-to-HTTP gateway
523   that wishes to interoperate with third-party HTTP servers &MUST;
524   conform to HTTP user agent requirements on the gateway's inbound
525   connection and &MUST; implement the <x:ref>Connection</x:ref>
526   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
527   (<xref target="header.via"/>) header fields for both connections.
528</t>
529<t><iref primary="true" item="tunnel"/>
530   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
531   without changing the messages. Once active, a tunnel is not
532   considered a party to the HTTP communication, though the tunnel might
533   have been initiated by an HTTP request. A tunnel ceases to exist when
534   both ends of the relayed connection are closed. Tunnels are used to
535   extend a virtual connection through an intermediary, such as when
536   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
537   establish confidential communication through a shared firewall proxy.
538</t>
539<t><iref primary="true" item="interception proxy"/>
540<iref primary="true" item="transparent proxy"/>
541<iref primary="true" item="captive portal"/>
542   The above categories for intermediary only consider those acting as
543   participants in the HTTP communication.  There are also intermediaries
544   that can act on lower layers of the network protocol stack, filtering or
545   redirecting HTTP traffic without the knowledge or permission of message
546   senders. Network intermediaries often introduce security flaws or
547   interoperability problems by violating HTTP semantics.  For example, an
548   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
549   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
550   "<x:dfn>captive portal</x:dfn>")
551   differs from an HTTP proxy because it is not selected by the client.
552   Instead, an interception proxy filters or redirects outgoing TCP port 80
553   packets (and occasionally other common port traffic).
554   Interception proxies are commonly found on public network access points,
555   as a means of enforcing account subscription prior to allowing use of
556   non-local Internet services, and within corporate firewalls to enforce
557   network usage policies.
558   They are indistinguishable from a man-in-the-middle attack.
559</t>
560<t>
561   HTTP is defined as a stateless protocol, meaning that each request message
562   can be understood in isolation.  Many implementations depend on HTTP's
563   stateless design in order to reuse proxied connections or dynamically
564   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
565   assume that two requests on the same connection are from the same user
566   agent unless the connection is secured and specific to that agent.
567   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
568   been known to violate this requirement, resulting in security and
569   interoperability problems.
570</t>
571</section>
572
573<section title="Caches" anchor="caches">
574<iref primary="true" item="cache"/>
575<t>
576   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
577   subsystem that controls its message storage, retrieval, and deletion.
578   A cache stores cacheable responses in order to reduce the response
579   time and network bandwidth consumption on future, equivalent
580   requests. Any client or server &MAY; employ a cache, though a cache
581   cannot be used by a server while it is acting as a tunnel.
582</t>
583<t>
584   The effect of a cache is that the request/response chain is shortened
585   if one of the participants along the chain has a cached response
586   applicable to that request. The following illustrates the resulting
587   chain if B has a cached copy of an earlier response from O (via C)
588   for a request which has not been cached by UA or A.
589</t>
590<figure><artwork type="drawing">
591            &gt;             &gt;
592       <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>
593                  &lt;             &lt;
594</artwork></figure>
595<t><iref primary="true" item="cacheable"/>
596   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
597   the response message for use in answering subsequent requests.
598   Even when a response is cacheable, there might be additional
599   constraints placed by the client or by the origin server on when
600   that cached response can be used for a particular request. HTTP
601   requirements for cache behavior and cacheable responses are
602   defined in &caching-overview;
603</t>
604<t>
605   There are a wide variety of architectures and configurations
606   of caches and proxies deployed across the World Wide Web and
607   inside large organizations. These systems include national hierarchies
608   of proxy caches to save transoceanic bandwidth, systems that
609   broadcast or multicast cache entries, organizations that distribute
610   subsets of cached data via optical media, and so on.
611</t>
612</section>
613
614<section title="Conformance and Error Handling" anchor="conformance">
615<t>
616   This specification targets conformance criteria according to the role of
617   a participant in HTTP communication.  Hence, HTTP requirements are placed
618   on senders, recipients, clients, servers, user agents, intermediaries,
619   origin servers, proxies, gateways, or caches, depending on what behavior
620   is being constrained by the requirement. Additional (social) requirements
621   are placed on implementations, resource owners, and protocol element
622   registrations when they apply beyond the scope of a single communication.
623</t>
624<t>
625   The verb "generate" is used instead of "send" where a requirement
626   differentiates between creating a protocol element and merely forwarding a
627   received element downstream.
628</t>
629<t>
630   An implementation is considered conformant if it complies with all of the
631   requirements associated with the roles it partakes in HTTP. Note that
632   SHOULD-level requirements are relevant here, unless one of the documented
633   exceptions is applicable.
634</t>
635<t>
636   Conformance applies to both the syntax and semantics of HTTP protocol
637   elements. A sender &MUST-NOT; generate protocol elements that convey a
638   meaning that is known by that sender to be false. A sender &MUST-NOT;
639   generate protocol elements that do not match the grammar defined by the
640   ABNF rules for those protocol elements that are applicable to the sender's
641   role. If a received protocol element is processed, the recipient &MUST; be
642   able to parse any value that would match the ABNF rules for that protocol
643   element, excluding only those rules not applicable to the recipient's role.
644</t>
645<t>
646   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
647   protocol element from an invalid construct.  HTTP does not define
648   specific error handling mechanisms except when they have a direct impact
649   on security, since different applications of the protocol require
650   different error handling strategies.  For example, a Web browser might
651   wish to transparently recover from a response where the
652   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
653   whereas a systems control client might consider any form of error recovery
654   to be dangerous.
655</t>
656</section>
657
658<section title="Protocol Versioning" anchor="http.version">
659  <x:anchor-alias value="HTTP-version"/>
660  <x:anchor-alias value="HTTP-name"/>
661<t>
662   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
663   versions of the protocol. This specification defines version "1.1".
664   The protocol version as a whole indicates the sender's conformance
665   with the set of requirements laid out in that version's corresponding
666   specification of HTTP.
667</t>
668<t>
669   The version of an HTTP message is indicated by an HTTP-version field
670   in the first line of the message. HTTP-version is case-sensitive.
671</t>
672<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
673  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
674  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
675</artwork></figure>
676<t>
677   The HTTP version number consists of two decimal digits separated by a "."
678   (period or decimal point).  The first digit ("major version") indicates the
679   HTTP messaging syntax, whereas the second digit ("minor version") indicates
680   the highest minor version to which the sender is
681   conformant and able to understand for future communication.  The minor
682   version advertises the sender's communication capabilities even when the
683   sender is only using a backwards-compatible subset of the protocol,
684   thereby letting the recipient know that more advanced features can
685   be used in response (by servers) or in future requests (by clients).
686</t>
687<t>
688   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
689   <xref target="RFC1945"/> or a recipient whose version is unknown,
690   the HTTP/1.1 message is constructed such that it can be interpreted
691   as a valid HTTP/1.0 message if all of the newer features are ignored.
692   This specification places recipient-version requirements on some
693   new features so that a conformant sender will only use compatible
694   features until it has determined, through configuration or the
695   receipt of a message, that the recipient supports HTTP/1.1.
696</t>
697<t>
698   The interpretation of a header field does not change between minor
699   versions of the same major HTTP version, though the default
700   behavior of a recipient in the absence of such a field can change.
701   Unless specified otherwise, header fields defined in HTTP/1.1 are
702   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
703   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
704   HTTP/1.x implementations whether or not they advertise conformance with
705   HTTP/1.1.
706</t>
707<t>
708   New header fields can be defined such that, when they are
709   understood by a recipient, they might override or enhance the
710   interpretation of previously defined header fields.  When an
711   implementation receives an unrecognized header field, the recipient
712   &MUST; ignore that header field for local processing regardless of
713   the message's HTTP version.  An unrecognized header field received
714   by a proxy &MUST; be forwarded downstream unless the header field's
715   field-name is listed in the message's <x:ref>Connection</x:ref> header field
716   (see <xref target="header.connection"/>).
717   These requirements allow HTTP's functionality to be enhanced without
718   requiring prior update of deployed intermediaries.
719</t>
720<t>
721   Intermediaries that process HTTP messages (i.e., all intermediaries
722   other than those acting as tunnels) &MUST; send their own HTTP-version
723   in forwarded messages.  In other words, they &MUST-NOT; blindly
724   forward the first line of an HTTP message without ensuring that the
725   protocol version in that message matches a version to which that
726   intermediary is conformant for both the receiving and
727   sending of messages.  Forwarding an HTTP message without rewriting
728   the HTTP-version might result in communication errors when downstream
729   recipients use the message sender's version to determine what features
730   are safe to use for later communication with that sender.
731</t>
732<t>
733   An HTTP client &SHOULD; send a request version equal to the highest
734   version to which the client is conformant and
735   whose major version is no higher than the highest version supported
736   by the server, if this is known.  An HTTP client &MUST-NOT; send a
737   version to which it is not conformant.
738</t>
739<t>
740   An HTTP client &MAY; send a lower request version if it is known that
741   the server incorrectly implements the HTTP specification, but only
742   after the client has attempted at least one normal request and determined
743   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
744   the server improperly handles higher request versions.
745</t>
746<t>
747   An HTTP server &SHOULD; send a response version equal to the highest
748   version to which the server is conformant and
749   whose major version is less than or equal to the one received in the
750   request.  An HTTP server &MUST-NOT; send a version to which it is not
751   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
752   Supported)</x:ref> response if it cannot send a response using the
753   major version used in the client's request.
754</t>
755<t>
756   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
757   if it is known or suspected that the client incorrectly implements the
758   HTTP specification and is incapable of correctly processing later
759   version responses, such as when a client fails to parse the version
760   number correctly or when an intermediary is known to blindly forward
761   the HTTP-version even when it doesn't conform to the given minor
762   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
763   performed unless triggered by specific client attributes, such as when
764   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
765   uniquely match the values sent by a client known to be in error.
766</t>
767<t>
768   The intention of HTTP's versioning design is that the major number
769   will only be incremented if an incompatible message syntax is
770   introduced, and that the minor number will only be incremented when
771   changes made to the protocol have the effect of adding to the message
772   semantics or implying additional capabilities of the sender.  However,
773   the minor version was not incremented for the changes introduced between
774   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
775   is specifically avoiding any such changes to the protocol.
776</t>
777</section>
778
779<section title="Uniform Resource Identifiers" anchor="uri">
780<iref primary="true" item="resource"/>
781<t>
782   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
783   throughout HTTP as the means for identifying resources (&resource;).
784   URI references are used to target requests, indicate redirects, and define
785   relationships.
786</t>
787  <x:anchor-alias value="URI-reference"/>
788  <x:anchor-alias value="absolute-URI"/>
789  <x:anchor-alias value="relative-part"/>
790  <x:anchor-alias value="authority"/>
791  <x:anchor-alias value="path-abempty"/>
792  <x:anchor-alias value="path-absolute"/>
793  <x:anchor-alias value="port"/>
794  <x:anchor-alias value="query"/>
795  <x:anchor-alias value="uri-host"/>
796  <x:anchor-alias value="partial-URI"/>
797<t>
798   This specification adopts the definitions of "URI-reference",
799   "absolute-URI", "relative-part", "port", "host",
800   "path-abempty", "path-absolute", "query", and "authority" from the
801   URI generic syntax.
802   In addition, we define a partial-URI rule for protocol elements
803   that allow a relative URI but not a fragment.
804</t>
805<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>
806  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
807  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
808  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
809  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
810  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
811  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
812  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
813  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
814  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
815 
816  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
817</artwork></figure>
818<t>
819   Each protocol element in HTTP that allows a URI reference will indicate
820   in its ABNF production whether the element allows any form of reference
821   (URI-reference), only a URI in absolute form (absolute-URI), only the
822   path and optional query components, or some combination of the above.
823   Unless otherwise indicated, URI references are parsed
824   relative to the effective request URI
825   (<xref target="effective.request.uri"/>).
826</t>
827
828<section title="http URI scheme" anchor="http.uri">
829  <x:anchor-alias value="http-URI"/>
830  <iref item="http URI scheme" primary="true"/>
831  <iref item="URI scheme" subitem="http" primary="true"/>
832<t>
833   The "http" URI scheme is hereby defined for the purpose of minting
834   identifiers according to their association with the hierarchical
835   namespace governed by a potential HTTP origin server listening for
836   TCP connections on a given port.
837</t>
838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
839  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
840</artwork></figure>
841<t>
842   The HTTP origin server is identified by the generic syntax's
843   <x:ref>authority</x:ref> component, which includes a host identifier
844   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
845   The remainder of the URI, consisting of both the hierarchical path
846   component and optional query component, serves as an identifier for
847   a potential resource within that origin server's name space.
848</t>
849<t>
850   If the host identifier is provided as an IP literal or IPv4 address,
851   then the origin server is any listener on the indicated TCP port at
852   that IP address. If host is a registered name, then that name is
853   considered an indirect identifier and the recipient might use a name
854   resolution service, such as DNS, to find the address of a listener
855   for that host.
856   The host &MUST-NOT; be empty; if an "http" URI is received with an
857   empty host, then it &MUST; be rejected as invalid.
858   If the port subcomponent is empty or not given, then TCP port 80 is
859   assumed (the default reserved port for WWW services).
860</t>
861<t>
862   Regardless of the form of host identifier, access to that host is not
863   implied by the mere presence of its name or address. The host might or might
864   not exist and, even when it does exist, might or might not be running an
865   HTTP server or listening to the indicated port. The "http" URI scheme
866   makes use of the delegated nature of Internet names and addresses to
867   establish a naming authority (whatever entity has the ability to place
868   an HTTP server at that Internet name or address) and allows that
869   authority to determine which names are valid and how they might be used.
870</t>
871<t>
872   When an "http" URI is used within a context that calls for access to the
873   indicated resource, a client &MAY; attempt access by resolving
874   the host to an IP address, establishing a TCP connection to that address
875   on the indicated port, and sending an HTTP request message
876   (<xref target="http.message"/>) containing the URI's identifying data
877   (<xref target="message.routing"/>) to the server.
878   If the server responds to that request with a non-interim HTTP response
879   message, as described in &status-codes;, then that response
880   is considered an authoritative answer to the client's request.
881</t>
882<t>
883   Although HTTP is independent of the transport protocol, the "http"
884   scheme is specific to TCP-based services because the name delegation
885   process depends on TCP for establishing authority.
886   An HTTP service based on some other underlying connection protocol
887   would presumably be identified using a different URI scheme, just as
888   the "https" scheme (below) is used for resources that require an
889   end-to-end secured connection. Other protocols might also be used to
890   provide access to "http" identified resources &mdash; it is only the
891   authoritative interface used for mapping the namespace that is
892   specific to TCP.
893</t>
894<t>
895   The URI generic syntax for authority also includes a deprecated
896   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
897   for including user authentication information in the URI.  Some
898   implementations make use of the userinfo component for internal
899   configuration of authentication information, such as within command
900   invocation options, configuration files, or bookmark lists, even
901   though such usage might expose a user identifier or password.
902   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
903   delimiter) when transmitting an "http" URI in a message.  Recipients
904   of HTTP messages that contain a URI reference &SHOULD; parse for the
905   existence of userinfo and treat its presence as an error, likely
906   indicating that the deprecated subcomponent is being used to obscure
907   the authority for the sake of phishing attacks.
908</t>
909</section>
910
911<section title="https URI scheme" anchor="https.uri">
912   <x:anchor-alias value="https-URI"/>
913   <iref item="https URI scheme"/>
914   <iref item="URI scheme" subitem="https"/>
915<t>
916   The "https" URI scheme is hereby defined for the purpose of minting
917   identifiers according to their association with the hierarchical
918   namespace governed by a potential HTTP origin server listening to a
919   given TCP port for TLS-secured connections <xref target="RFC5246"/>.
920</t>
921<t>
922   All of the requirements listed above for the "http" scheme are also
923   requirements for the "https" scheme, except that a default TCP port
924   of 443 is assumed if the port subcomponent is empty or not given,
925   and the TCP connection &MUST; be secured, end-to-end, through the
926   use of strong encryption prior to sending the first HTTP request.
927</t>
928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
929  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
930</artwork></figure>
931<t>
932   Unlike the "http" scheme, responses to "https" identified requests
933   are never "public" and thus &MUST-NOT; be reused for shared caching.
934   They can, however, be reused in a private cache if the message is
935   cacheable by default in HTTP or specifically indicated as such by
936   the Cache-Control header field (&header-cache-control;).
937</t>
938<t>
939   Resources made available via the "https" scheme have no shared
940   identity with the "http" scheme even if their resource identifiers
941   indicate the same authority (the same host listening to the same
942   TCP port).  They are distinct name spaces and are considered to be
943   distinct origin servers.  However, an extension to HTTP that is
944   defined to apply to entire host domains, such as the Cookie protocol
945   <xref target="RFC6265"/>, can allow information
946   set by one service to impact communication with other services
947   within a matching group of host domains.
948</t>
949<t>
950   The process for authoritative access to an "https" identified
951   resource is defined in <xref target="RFC2818"/>.
952</t>
953</section>
954
955<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
956<t>
957   Since the "http" and "https" schemes conform to the URI generic syntax,
958   such URIs are normalized and compared according to the algorithm defined
959   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
960   described above for each scheme.
961</t>
962<t>
963   If the port is equal to the default port for a scheme, the normal
964   form is to elide the port subcomponent. Likewise, an empty path
965   component is equivalent to an absolute path of "/", so the normal
966   form is to provide a path of "/" instead. The scheme and host
967   are case-insensitive and normally provided in lowercase; all
968   other components are compared in a case-sensitive manner.
969   Characters other than those in the "reserved" set are equivalent
970   to their percent-encoded octets (see <xref target="RFC3986"
971   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
972</t>
973<t>
974   For example, the following three URIs are equivalent:
975</t>
976<figure><artwork type="example">
977   http://example.com:80/~smith/home.html
978   http://EXAMPLE.com/%7Esmith/home.html
979   http://EXAMPLE.com:/%7esmith/home.html
980</artwork></figure>
981</section>
982</section>
983</section>
984
985<section title="Message Format" anchor="http.message">
986<x:anchor-alias value="generic-message"/>
987<x:anchor-alias value="message.types"/>
988<x:anchor-alias value="HTTP-message"/>
989<x:anchor-alias value="start-line"/>
990<iref item="header section"/>
991<iref item="headers"/>
992<iref item="header field"/>
993<t>
994   All HTTP/1.1 messages consist of a start-line followed by a sequence of
995   octets in a format similar to the Internet Message Format
996   <xref target="RFC5322"/>: zero or more header fields (collectively
997   referred to as the "headers" or the "header section"), an empty line
998   indicating the end of the header section, and an optional message body.
999</t>
1000<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1001  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1002                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1003                   <x:ref>CRLF</x:ref>
1004                   [ <x:ref>message-body</x:ref> ]
1005</artwork></figure>
1006<t>
1007   The normal procedure for parsing an HTTP message is to read the
1008   start-line into a structure, read each header field into a hash
1009   table by field name until the empty line, and then use the parsed
1010   data to determine if a message body is expected.  If a message body
1011   has been indicated, then it is read as a stream until an amount
1012   of octets equal to the message body length is read or the connection
1013   is closed.
1014</t>
1015<t>
1016   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1017   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1018   Parsing an HTTP message as a stream of Unicode characters, without regard
1019   for the specific encoding, creates security vulnerabilities due to the
1020   varying ways that string processing libraries handle invalid multibyte
1021   character sequences that contain the octet LF (%x0A).  String-based
1022   parsers can only be safely used within protocol elements after the element
1023   has been extracted from the message, such as within a header field-value
1024   after message parsing has delineated the individual fields.
1025</t>
1026<t>
1027   An HTTP message can be parsed as a stream for incremental processing or
1028   forwarding downstream.  However, recipients cannot rely on incremental
1029   delivery of partial messages, since some implementations will buffer or
1030   delay message forwarding for the sake of network efficiency, security
1031   checks, or payload transformations.
1032</t>
1033
1034<section title="Start Line" anchor="start.line">
1035  <x:anchor-alias value="Start-Line"/>
1036<t>
1037   An HTTP message can either be a request from client to server or a
1038   response from server to client.  Syntactically, the two types of message
1039   differ only in the start-line, which is either a request-line (for requests)
1040   or a status-line (for responses), and in the algorithm for determining
1041   the length of the message body (<xref target="message.body"/>).
1042   In theory, a client could receive requests and a server could receive
1043   responses, distinguishing them by their different start-line formats,
1044   but in practice servers are implemented to only expect a request
1045   (a response is interpreted as an unknown or invalid request method)
1046   and clients are implemented to only expect a response.
1047</t>
1048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1049  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1050</artwork></figure>
1051<t>
1052   A sender &MUST-NOT; send whitespace between the start-line and
1053   the first header field. The presence of such whitespace in a request
1054   might be an attempt to trick a server into ignoring that field or
1055   processing the line after it as a new request, either of which might
1056   result in a security vulnerability if other implementations within
1057   the request chain interpret the same message differently.
1058   Likewise, the presence of such whitespace in a response might be
1059   ignored by some clients or cause others to cease parsing.
1060</t>
1061
1062<section title="Request Line" anchor="request.line">
1063  <x:anchor-alias value="Request"/>
1064  <x:anchor-alias value="request-line"/>
1065<t>
1066   A request-line begins with a method token, followed by a single
1067   space (SP), the request-target, another single space (SP), the
1068   protocol version, and ending with CRLF.
1069</t>
1070<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1071  <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>
1072</artwork></figure>
1073<t>
1074   A server &MUST; be able to parse any received message that begins
1075   with a request-line and matches the ABNF rule for HTTP-message.
1076</t>
1077<iref primary="true" item="method"/>
1078<t anchor="method">
1079   The method token indicates the request method to be performed on the
1080   target resource. The request method is case-sensitive.
1081</t>
1082<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1083  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1084</artwork></figure>
1085<t>
1086   The methods defined by this specification can be found in
1087   &methods;, along with information regarding the HTTP method registry
1088   and considerations for defining new methods.
1089</t>
1090<iref item="request-target"/>
1091<t>
1092   The request-target identifies the target resource upon which to apply
1093   the request, as defined in <xref target="request-target"/>.
1094</t>
1095<t>
1096   No whitespace is allowed inside the method, request-target, and
1097   protocol version.  Hence, recipients typically parse the request-line
1098   into its component parts by splitting on the SP characters.
1099</t>
1100<t>
1101   Unfortunately, some user agents fail to properly encode hypertext
1102   references that have embedded whitespace, sending the characters
1103   directly instead of properly percent-encoding the disallowed characters.
1104   Recipients of an invalid request-line &SHOULD; respond with either a
1105   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1106   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1107   attempt to autocorrect and then process the request without a redirect,
1108   since the invalid request-line might be deliberately crafted to bypass
1109   security filters along the request chain.
1110</t>
1111<t>
1112   HTTP does not place a pre-defined limit on the length of a request-line.
1113   A server that receives a method longer than any that it implements
1114   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1115   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1116   A server &MUST; be prepared to receive URIs of unbounded length and
1117   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1118   request-target would be longer than the server wishes to handle
1119   (see &status-414;).
1120</t>
1121<t>
1122   Various ad-hoc limitations on request-line length are found in practice.
1123   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1124   minimum, request-line lengths of up to 8000 octets.
1125</t>
1126</section>
1127
1128<section title="Status Line" anchor="status.line">
1129  <x:anchor-alias value="response"/>
1130  <x:anchor-alias value="status-line"/>
1131  <x:anchor-alias value="status-code"/>
1132  <x:anchor-alias value="reason-phrase"/>
1133<t>
1134   The first line of a response message is the status-line, consisting
1135   of the protocol version, a space (SP), the status code, another space,
1136   a possibly-empty textual phrase describing the status code, and
1137   ending with CRLF.
1138</t>
1139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1140  <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>
1141</artwork></figure>
1142<t>
1143   A client &MUST; be able to parse any received message that begins
1144   with a status-line and matches the ABNF rule for HTTP-message.
1145</t>
1146<t>
1147   The status-code element is a 3-digit integer code describing the
1148   result of the server's attempt to understand and satisfy the client's
1149   corresponding request. The rest of the response message is to be
1150   interpreted in light of the semantics defined for that status code.
1151   See &status-codes; for information about the semantics of status codes,
1152   including the classes of status code (indicated by the first digit),
1153   the status codes defined by this specification, considerations for the
1154   definition of new status codes, and the IANA registry.
1155</t>
1156<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1157  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1158</artwork></figure>
1159<t>   
1160   The reason-phrase element exists for the sole purpose of providing a
1161   textual description associated with the numeric status code, mostly
1162   out of deference to earlier Internet application protocols that were more
1163   frequently used with interactive text clients. A client &SHOULD; ignore
1164   the reason-phrase content.
1165</t>
1166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1167  <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> )
1168</artwork></figure>
1169</section>
1170</section>
1171
1172<section title="Header Fields" anchor="header.fields">
1173  <x:anchor-alias value="header-field"/>
1174  <x:anchor-alias value="field-content"/>
1175  <x:anchor-alias value="field-name"/>
1176  <x:anchor-alias value="field-value"/>
1177  <x:anchor-alias value="obs-fold"/>
1178<t>
1179   Each HTTP header field consists of a case-insensitive field name
1180   followed by a colon (":"), optional whitespace, and the field value.
1181</t>
1182<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"/>
1183  <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>
1184  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1185  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1186  <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> )
1187  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1188                 ; obsolete line folding
1189                 ; see <xref target="field.parsing"/>
1190</artwork></figure>
1191<t>
1192   The field-name token labels the corresponding field-value as having the
1193   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1194   header field is defined in &header-date; as containing the origination
1195   timestamp for the message in which it appears.
1196</t>
1197<t>
1198   HTTP header fields are fully extensible: there is no limit on the
1199   introduction of new field names, each presumably defining new semantics,
1200   or on the number of header fields used in a given message.  Existing
1201   fields are defined in each part of this specification and in many other
1202   specifications outside the standards process.
1203   New header fields can be introduced without changing the protocol version
1204   if their defined semantics allow them to be safely ignored by recipients
1205   that do not recognize them.
1206</t>
1207<t>
1208   New HTTP header fields &SHOULD; be registered with IANA in the
1209   Message Header Field Registry, as described in &iana-header-registry;.
1210   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1211   field-name is listed in the <x:ref>Connection</x:ref> header field
1212   (<xref target="header.connection"/>) or the proxy is specifically
1213   configured to block or otherwise transform such fields.
1214   Unrecognized header fields &SHOULD; be ignored by other recipients.
1215</t>
1216<t>
1217   The order in which header fields with differing field names are
1218   received is not significant. However, it is "good practice" to send
1219   header fields that contain control data first, such as <x:ref>Host</x:ref>
1220   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1221   can decide when not to handle a message as early as possible.  A server
1222   &MUST; wait until the entire header section is received before interpreting
1223   a request message, since later header fields might include conditionals,
1224   authentication credentials, or deliberately misleading duplicate
1225   header fields that would impact request processing.
1226</t>
1227<t>
1228   Multiple header fields with the same field name &MUST-NOT; be
1229   sent in a message unless the entire field value for that
1230   header field is defined as a comma-separated list [i.e., #(values)].
1231   Multiple header fields with the same field name can be combined into
1232   one "field-name: field-value" pair, without changing the semantics of the
1233   message, by appending each subsequent field value to the combined
1234   field value in order, separated by a comma. The order in which
1235   header fields with the same field name are received is therefore
1236   significant to the interpretation of the combined field value;
1237   a proxy &MUST-NOT; change the order of these field values when
1238   forwarding a message.
1239</t>
1240<x:note>
1241  <t>
1242   &Note; The "Set-Cookie" header field as implemented in
1243   practice can occur multiple times, but does not use the list syntax, and
1244   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1245   for details.) Also note that the Set-Cookie2 header field specified in
1246   <xref target="RFC2965"/> does not share this problem.
1247  </t>
1248</x:note>
1249
1250<section title="Whitespace" anchor="whitespace">
1251<t anchor="rule.LWS">
1252   This specification uses three rules to denote the use of linear
1253   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1254   BWS ("bad" whitespace).
1255</t>
1256<t anchor="rule.OWS">
1257   The OWS rule is used where zero or more linear whitespace octets might
1258   appear. OWS &SHOULD; either not be produced or be produced as a single
1259   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1260   be replaced with a single SP or transformed to all SP octets (each
1261   octet other than SP replaced with SP) before interpreting the field value
1262   or forwarding the message downstream.
1263</t>
1264<t anchor="rule.RWS">
1265   RWS is used when at least one linear whitespace octet is required to
1266   separate field tokens. RWS &SHOULD; be produced as a single SP.
1267   Multiple RWS octets that occur within field-content &SHOULD; either
1268   be replaced with a single SP or transformed to all SP octets before
1269   interpreting the field value or forwarding the message downstream.
1270</t>
1271<t anchor="rule.BWS">
1272   BWS is used where the grammar allows optional whitespace, for historical
1273   reasons, but senders &SHOULD-NOT; produce it in messages;
1274   recipients &MUST; accept such bad optional whitespace and remove it before
1275   interpreting the field value or forwarding the message downstream.
1276</t>
1277<t anchor="rule.whitespace">
1278  <x:anchor-alias value="BWS"/>
1279  <x:anchor-alias value="OWS"/>
1280  <x:anchor-alias value="RWS"/>
1281</t>
1282<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"/>
1283  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1284                 ; "optional" whitespace
1285  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1286                 ; "required" whitespace
1287  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1288                 ; "bad" whitespace
1289</artwork></figure>
1290</section>
1291
1292<section title="Field Parsing" anchor="field.parsing">
1293<t>
1294   No whitespace is allowed between the header field-name and colon.
1295   In the past, differences in the handling of such whitespace have led to
1296   security vulnerabilities in request routing and response handling.
1297   Any received request message that contains whitespace between a header
1298   field-name and colon &MUST; be rejected with a response code of 400
1299   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1300   message before forwarding the message downstream.
1301</t>
1302<t>
1303   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1304   preferred. The field value does not include any leading or trailing white
1305   space: OWS occurring before the first non-whitespace octet of the
1306   field value or after the last non-whitespace octet of the field value
1307   is ignored and &SHOULD; be removed before further processing (as this does
1308   not change the meaning of the header field).
1309</t>
1310<t>
1311   Historically, HTTP header field values could be extended over multiple
1312   lines by preceding each extra line with at least one space or horizontal
1313   tab (obs-fold). This specification deprecates such line
1314   folding except within the message/http media type
1315   (<xref target="internet.media.type.message.http"/>).
1316   HTTP senders &MUST-NOT; produce messages that include line folding
1317   (i.e., that contain any field-value that matches the obs-fold rule) unless
1318   the message is intended for packaging within the message/http media type.
1319   HTTP recipients &SHOULD; accept line folding and replace any embedded
1320   obs-fold whitespace with either a single SP or a matching number of SP
1321   octets (to avoid buffer copying) prior to interpreting the field value or
1322   forwarding the message downstream.
1323</t>
1324<t>
1325   Historically, HTTP has allowed field content with text in the ISO-8859-1
1326   <xref target="ISO-8859-1"/> character encoding and supported other
1327   character sets only through use of <xref target="RFC2047"/> encoding.
1328   In practice, most HTTP header field values use only a subset of the
1329   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1330   header fields &SHOULD; limit their field values to US-ASCII octets.
1331   Recipients &SHOULD; treat other (obs-text) octets in field content as
1332   opaque data.
1333</t>
1334</section>
1335
1336<section title="Field Length" anchor="field.length">
1337<t>
1338   HTTP does not place a pre-defined limit on the length of header fields,
1339   either in isolation or as a set. A server &MUST; be prepared to receive
1340   request header fields of unbounded length and respond with a <x:ref>4xx
1341   (Client Error)</x:ref> status code if the received header field(s) would be
1342   longer than the server wishes to handle.
1343</t>
1344<t>
1345   A client that receives response header fields that are longer than it wishes
1346   to handle can only treat it as a server error.
1347</t>
1348<t>
1349   Various ad-hoc limitations on header field length are found in practice. It
1350   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1351   combined header fields have 4000 or more octets.
1352</t>
1353</section>
1354
1355<section title="Field value components" anchor="field.components">
1356<t anchor="rule.token.separators">
1357  <x:anchor-alias value="tchar"/>
1358  <x:anchor-alias value="token"/>
1359  <x:anchor-alias value="special"/>
1360  <x:anchor-alias value="word"/>
1361   Many HTTP header field values consist of words (token or quoted-string)
1362   separated by whitespace or special characters. These special characters
1363   &MUST; be in a quoted string to be used within a parameter value (as defined
1364   in <xref target="transfer.codings"/>).
1365</t>
1366<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>
1367  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1368
1369  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1370<!--
1371  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1372 -->
1373  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1374                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1375                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1376                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1377
1378  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1379                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1380                 / "]" / "?" / "=" / "{" / "}"
1381</artwork></figure>
1382<t anchor="rule.quoted-string">
1383  <x:anchor-alias value="quoted-string"/>
1384  <x:anchor-alias value="qdtext"/>
1385  <x:anchor-alias value="obs-text"/>
1386   A string of text is parsed as a single word if it is quoted using
1387   double-quote marks.
1388</t>
1389<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"/>
1390  <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>
1391  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1392  <x:ref>obs-text</x:ref>       = %x80-FF
1393</artwork></figure>
1394<t anchor="rule.quoted-pair">
1395  <x:anchor-alias value="quoted-pair"/>
1396   The backslash octet ("\") can be used as a single-octet
1397   quoting mechanism within quoted-string constructs:
1398</t>
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1400  <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> )
1401</artwork></figure>
1402<t>
1403   Recipients that process the value of the quoted-string &MUST; handle a
1404   quoted-pair as if it were replaced by the octet following the backslash.
1405</t>
1406<t>
1407   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1408   escaping (i.e., other than DQUOTE and the backslash octet).
1409</t>
1410<t anchor="rule.comment">
1411  <x:anchor-alias value="comment"/>
1412  <x:anchor-alias value="ctext"/>
1413   Comments can be included in some HTTP header fields by surrounding
1414   the comment text with parentheses. Comments are only allowed in
1415   fields containing "comment" as part of their field value definition.
1416</t>
1417<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1418  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1419  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1420</artwork></figure>
1421<t anchor="rule.quoted-cpair">
1422  <x:anchor-alias value="quoted-cpair"/>
1423   The backslash octet ("\") can be used as a single-octet
1424   quoting mechanism within comment constructs:
1425</t>
1426<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1427  <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> )
1428</artwork></figure>
1429<t>
1430   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1431   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1432</t>
1433</section>
1434
1435</section>
1436
1437<section title="Message Body" anchor="message.body">
1438  <x:anchor-alias value="message-body"/>
1439<t>
1440   The message body (if any) of an HTTP message is used to carry the
1441   payload body of that request or response.  The message body is
1442   identical to the payload body unless a transfer coding has been
1443   applied, as described in <xref target="header.transfer-encoding"/>.
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1446  <x:ref>message-body</x:ref> = *OCTET
1447</artwork></figure>
1448<t>
1449   The rules for when a message body is allowed in a message differ for
1450   requests and responses.
1451</t>
1452<t>
1453   The presence of a message body in a request is signaled by a
1454   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1455   field. Request message framing is independent of method semantics,
1456   even if the method does not define any use for a message body.
1457</t>
1458<t>
1459   The presence of a message body in a response depends on both
1460   the request method to which it is responding and the response
1461   status code (<xref target="status.line"/>).
1462   Responses to the HEAD request method never include a message body
1463   because the associated response header fields (e.g.,
1464   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1465   indicate what their values would have been if the request method had been
1466   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1467   mode instead of having a message body.
1468   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1469   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1470   All other responses do include a message body, although the body
1471   &MAY; be of zero length.
1472</t>
1473
1474<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1475  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1476  <x:anchor-alias value="Transfer-Encoding"/>
1477<t>
1478   When one or more transfer codings are applied to a payload body in order
1479   to form the message body, a Transfer-Encoding header field &MUST; be sent
1480   in the message and &MUST; contain the list of corresponding
1481   transfer-coding names in the same order that they were applied.
1482   Transfer codings are defined in <xref target="transfer.codings"/>.
1483</t>
1484<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1485  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1486</artwork></figure>
1487<t>
1488   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1489   MIME, which was designed to enable safe transport of binary data over a
1490   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1491   However, safe transport has a different focus for an 8bit-clean transfer
1492   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1493   accurately delimit a dynamically generated payload and to distinguish
1494   payload encodings that are only applied for transport efficiency or
1495   security from those that are characteristics of the target resource.
1496</t>
1497<t>
1498   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1499   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1500   crucial role in delimiting messages when the payload body size is not
1501   known in advance.
1502   When the "chunked" transfer-coding is used, it &MUST; be the last
1503   transfer-coding applied to form the message body and &MUST-NOT;
1504   be applied more than once in a message body.
1505   If any transfer-coding is applied to a request payload body,
1506   the final transfer-coding applied &MUST; be "chunked".
1507   If any transfer-coding is applied to a response payload body, then either
1508   the final transfer-coding applied &MUST; be "chunked" or
1509   the message &MUST; be terminated by closing the connection.
1510</t>
1511<figure><preamble>
1512   For example,
1513</preamble><artwork type="example">
1514  Transfer-Encoding: gzip, chunked
1515</artwork><postamble>
1516   indicates that the payload body has been compressed using the gzip
1517   coding and then chunked using the chunked coding while forming the
1518   message body.
1519</postamble></figure>
1520<t>
1521   If more than one Transfer-Encoding header field is present in a message,
1522   the multiple field-values &MUST; be combined into one field-value,
1523   according to the algorithm defined in <xref target="header.fields"/>,
1524   before determining the message body length.
1525</t>
1526<t>
1527   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1528   Transfer-Encoding is a property of the message, not of the payload, and thus
1529   &MAY; be added or removed by any implementation along the request/response
1530   chain. Additional information about the encoding parameters &MAY; be
1531   provided by other header fields not defined by this specification.
1532</t>
1533<t>
1534   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1535   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1536   neither of which includes a message body,
1537   to indicate that the origin server would have applied a transfer coding
1538   to the message body if the request had been an unconditional GET.
1539   This indication is not required, however, because any recipient on
1540   the response chain (including the origin server) can remove transfer
1541   codings when they are not needed.
1542</t>
1543<t>
1544   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1545   implementations advertising only HTTP/1.0 support will not understand
1546   how to process a transfer-encoded payload.
1547   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1548   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1549   might be in the form of specific user configuration or by remembering the
1550   version of a prior received response.
1551   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1552   the corresponding request indicates HTTP/1.1 (or later).
1553</t>
1554<t>
1555   A server that receives a request message with a transfer-coding it does
1556   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1557   close the connection.
1558</t>
1559</section>
1560
1561<section title="Content-Length" anchor="header.content-length">
1562  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1563  <x:anchor-alias value="Content-Length"/>
1564<t>
1565   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1566   and the payload body length can be determined prior to being transferred, a
1567   Content-Length header field &SHOULD; be sent to indicate the length of the
1568   payload body that is either present as the message body, for requests
1569   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1570   would have been present had the request been an unconditional GET.  The
1571   length is expressed as a decimal number of octets.
1572</t>
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1574  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1575</artwork></figure>
1576<t>
1577   An example is
1578</t>
1579<figure><artwork type="example">
1580  Content-Length: 3495
1581</artwork></figure>
1582<t>
1583   In the case of a response to a HEAD request, Content-Length indicates
1584   the size of the payload body (without any potential transfer-coding)
1585   that would have been sent had the request been a GET.
1586   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1587   to a GET request, Content-Length indicates the size of the payload body (without
1588   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1589   response.
1590</t>
1591<t>
1592   Any Content-Length field value greater than or equal to zero is valid.
1593   Since there is no predefined limit to the length of an HTTP payload,
1594   recipients &SHOULD; anticipate potentially large decimal numerals and
1595   prevent parsing errors due to integer conversion overflows
1596   (<xref target="attack.protocol.element.size.overflows"/>).
1597</t>
1598<t>
1599   If a message is received that has multiple Content-Length header fields
1600   with field-values consisting of the same decimal value, or a single
1601   Content-Length header field with a field value containing a list of
1602   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1603   duplicate Content-Length header fields have been generated or combined by an
1604   upstream message processor, then the recipient &MUST; either reject the
1605   message as invalid or replace the duplicated field-values with a single
1606   valid Content-Length field containing that decimal value prior to
1607   determining the message body length.
1608</t>
1609<x:note>
1610  <t>
1611   &Note; HTTP's use of Content-Length for message framing differs
1612   significantly from the same field's use in MIME, where it is an optional
1613   field used only within the "message/external-body" media-type.
1614  </t>
1615</x:note>
1616</section>
1617
1618<section title="Message Body Length" anchor="message.body.length">
1619<t>
1620   The length of a message body is determined by one of the following
1621   (in order of precedence):
1622</t>
1623<t>
1624  <list style="numbers">
1625    <x:lt><t>
1626     Any response to a HEAD request and any response with a
1627     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1628     <x:ref>304 (Not Modified)</x:ref> status code is always
1629     terminated by the first empty line after the header fields, regardless of
1630     the header fields present in the message, and thus cannot contain a
1631     message body.
1632    </t></x:lt>
1633    <x:lt><t>
1634     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1635     connection will become a tunnel immediately after the empty line that
1636     concludes the header fields.  A client &MUST; ignore any
1637     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1638     fields received in such a message.
1639    </t></x:lt>
1640    <x:lt><t>
1641     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1642     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1643     is the final encoding, the message body length is determined by reading
1644     and decoding the chunked data until the transfer-coding indicates the
1645     data is complete.
1646    </t>
1647    <t>
1648     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1649     response and the "chunked" transfer-coding is not the final encoding, the
1650     message body length is determined by reading the connection until it is
1651     closed by the server.
1652     If a Transfer-Encoding header field is present in a request and the
1653     "chunked" transfer-coding is not the final encoding, the message body
1654     length cannot be determined reliably; the server &MUST; respond with
1655     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1656    </t>
1657    <t>
1658     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1659     and a <x:ref>Content-Length</x:ref> header field, the
1660     Transfer-Encoding overrides the Content-Length.
1661     Such a message might indicate an attempt to perform request or response
1662     smuggling (bypass of security-related checks on message routing or content)
1663     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1664     be removed, prior to forwarding the message downstream, or replaced with
1665     the real message body length after the transfer-coding is decoded.
1666    </t></x:lt>
1667    <x:lt><t>
1668     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1669     either multiple <x:ref>Content-Length</x:ref> header fields having
1670     differing field-values or a single Content-Length header field having an
1671     invalid value, then the message framing is invalid and &MUST; be treated
1672     as an error to prevent request or response smuggling.
1673     If this is a request message, the server &MUST; respond with
1674     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1675     If this is a response message received by a proxy, the proxy
1676     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1677     status code as its downstream response, and then close the connection.
1678     If this is a response message received by a user-agent, it &MUST; be
1679     treated as an error by discarding the message and closing the connection.
1680    </t></x:lt>
1681    <x:lt><t>
1682     If a valid <x:ref>Content-Length</x:ref> header field is present without
1683     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1684     message body length in octets.  If the actual number of octets sent in
1685     the message is less than the indicated Content-Length, the recipient
1686     &MUST; consider the message to be incomplete and treat the connection
1687     as no longer usable.
1688     If the actual number of octets sent in the message is more than the indicated
1689     Content-Length, the recipient &MUST; only process the message body up to the
1690     field value's number of octets; the remainder of the message &MUST; either
1691     be discarded or treated as the next message in a pipeline.  For the sake of
1692     robustness, a user-agent &MAY; attempt to detect and correct such an error
1693     in message framing if it is parsing the response to the last request on
1694     a connection and the connection has been closed by the server.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If this is a request message and none of the above are true, then the
1698     message body length is zero (no message body is present).
1699    </t></x:lt>
1700    <x:lt><t>
1701     Otherwise, this is a response message without a declared message body
1702     length, so the message body length is determined by the number of octets
1703     received prior to the server closing the connection.
1704    </t></x:lt>
1705  </list>
1706</t>
1707<t>
1708   Since there is no way to distinguish a successfully completed,
1709   close-delimited message from a partially-received message interrupted
1710   by network failure, a server &SHOULD; use encoding or
1711   length-delimited messages whenever possible.  The close-delimiting
1712   feature exists primarily for backwards compatibility with HTTP/1.0.
1713</t>
1714<t>
1715   A server &MAY; reject a request that contains a message body but
1716   not a <x:ref>Content-Length</x:ref> by responding with
1717   <x:ref>411 (Length Required)</x:ref>.
1718</t>
1719<t>
1720   Unless a transfer-coding other than "chunked" has been applied,
1721   a client that sends a request containing a message body &SHOULD;
1722   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1723   length is known in advance, rather than the "chunked" encoding, since some
1724   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1725   status code even though they understand the chunked encoding.  This
1726   is typically because such services are implemented via a gateway that
1727   requires a content-length in advance of being called and the server
1728   is unable or unwilling to buffer the entire request before processing.
1729</t>
1730<t>
1731   A client that sends a request containing a message body &MUST; include a
1732   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1733   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1734   the form of specific user configuration or by remembering the version of a
1735   prior received response.
1736</t>
1737</section>
1738</section>
1739
1740<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1741<t>
1742   Request messages that are prematurely terminated, possibly due to a
1743   canceled connection or a server-imposed time-out exception, &MUST;
1744   result in closure of the connection; sending an error response
1745   prior to closing the connection is &OPTIONAL;.
1746</t>
1747<t>
1748   Response messages that are prematurely terminated, usually by closure
1749   of the connection prior to receiving the expected number of octets or by
1750   failure to decode a transfer-encoded message body, &MUST; be recorded
1751   as incomplete.  A response that terminates in the middle of the header
1752   block (before the empty line is received) cannot be assumed to convey the
1753   full semantics of the response and &MUST; be treated as an error.
1754</t>
1755<t>
1756   A message body that uses the chunked transfer encoding is
1757   incomplete if the zero-sized chunk that terminates the encoding has not
1758   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1759   incomplete if the size of the message body received (in octets) is less than
1760   the value given by Content-Length.  A response that has neither chunked
1761   transfer encoding nor Content-Length is terminated by closure of the
1762   connection, and thus is considered complete regardless of the number of
1763   message body octets received, provided that the header block was received
1764   intact.
1765</t>
1766<t>
1767   A user agent &MUST-NOT; render an incomplete response message body as if
1768   it were complete (i.e., some indication needs to be given to the user that an
1769   error occurred).  Cache requirements for incomplete responses are defined
1770   in &cache-incomplete;.
1771</t>
1772<t>
1773   A server &MUST; read the entire request message body or close
1774   the connection after sending its response, since otherwise the
1775   remaining data on a persistent connection would be misinterpreted
1776   as the next request.  Likewise,
1777   a client &MUST; read the entire response message body if it intends
1778   to reuse the same connection for a subsequent request.  Pipelining
1779   multiple requests on a connection is described in <xref target="pipelining"/>.
1780</t>
1781</section>
1782
1783<section title="Message Parsing Robustness" anchor="message.robustness">
1784<t>
1785   Older HTTP/1.0 client implementations might send an extra CRLF
1786   after a POST request as a lame workaround for some early server
1787   applications that failed to read message body content that was
1788   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1789   preface or follow a request with an extra CRLF.  If terminating
1790   the request message body with a line-ending is desired, then the
1791   client &MUST; include the terminating CRLF octets as part of the
1792   message body length.
1793</t>
1794<t>
1795   In the interest of robustness, servers &SHOULD; ignore at least one
1796   empty line received where a request-line is expected. In other words, if
1797   the server is reading the protocol stream at the beginning of a
1798   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1799   Likewise, although the line terminator for the start-line and header
1800   fields is the sequence CRLF, we recommend that recipients recognize a
1801   single LF as a line terminator and ignore any CR.
1802</t>
1803<t>
1804   When a server listening only for HTTP request messages, or processing
1805   what appears from the start-line to be an HTTP request message,
1806   receives a sequence of octets that does not match the HTTP-message
1807   grammar aside from the robustness exceptions listed above, the
1808   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1809</t>
1810</section>
1811</section>
1812
1813<section title="Transfer Codings" anchor="transfer.codings">
1814  <x:anchor-alias value="transfer-coding"/>
1815  <x:anchor-alias value="transfer-extension"/>
1816<t>
1817   Transfer-coding values are used to indicate an encoding
1818   transformation that has been, can be, or might need to be applied to a
1819   payload body in order to ensure "safe transport" through the network.
1820   This differs from a content coding in that the transfer-coding is a
1821   property of the message rather than a property of the representation
1822   that is being transferred.
1823</t>
1824<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1825  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1826                     / "compress" ; <xref target="compress.coding"/>
1827                     / "deflate" ; <xref target="deflate.coding"/>
1828                     / "gzip" ; <xref target="gzip.coding"/>
1829                     / <x:ref>transfer-extension</x:ref>
1830  <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> )
1831</artwork></figure>
1832<t anchor="rule.parameter">
1833  <x:anchor-alias value="attribute"/>
1834  <x:anchor-alias value="transfer-parameter"/>
1835  <x:anchor-alias value="value"/>
1836   Parameters are in the form of attribute/value pairs.
1837</t>
1838<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"/>
1839  <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>
1840  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1841  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1842</artwork></figure>
1843<t>
1844   All transfer-coding values are case-insensitive and &SHOULD; be registered
1845   within the HTTP Transfer Coding registry, as defined in
1846   <xref target="transfer.coding.registry"/>.
1847   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1848   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1849   header fields.
1850</t>
1851
1852<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1853  <iref item="chunked (Coding Format)"/>
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  <x:anchor-alias value="Trailer"/>
1908<t>
1909   A trailer allows the sender to include additional fields at the end of a
1910   chunked message in order to supply metadata that might be dynamically
1911   generated while the message body is sent, such as a message integrity
1912   check, digital signature, or post-processing status.
1913   The trailer &MUST-NOT; contain fields that need to be known before a
1914   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1915   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1916</t>
1917<t>
1918   When a message includes a message body encoded with the chunked
1919   transfer-coding and the sender desires to send metadata in the form of
1920   trailer fields at the end of the message, the sender &SHOULD; send a
1921   <x:ref>Trailer</x:ref> header field before the message body to indicate
1922   which fields will be present in the trailers. This allows the recipient
1923   to prepare for receipt of that metadata before it starts processing the body,
1924   which is useful if the message is being streamed and the recipient wishes
1925   to confirm an integrity check on the fly.
1926</t>
1927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1928  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1929</artwork></figure>
1930<t>
1931   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1932   chunked message body &SHOULD; send an empty trailer.
1933</t>
1934<t>
1935   A server &MUST; send an empty trailer with the chunked transfer-coding
1936   unless at least one of the following is true:
1937  <list style="numbers">
1938    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1939    "trailers" is acceptable in the transfer-coding of the response, as
1940    described in <xref target="header.te"/>; or,</t>
1941     
1942    <t>the trailer fields consist entirely of optional metadata and the
1943    recipient could use the message (in a manner acceptable to the server where
1944    the field originated) without receiving that metadata. In other words,
1945    the server that generated the header field is willing to accept the
1946    possibility that the trailer fields might be silently discarded along
1947    the path to the client.</t>
1948  </list>
1949</t>
1950<t>
1951   The above requirement prevents the need for an infinite buffer when a
1952   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1953   an HTTP/1.0 recipient.
1954</t>
1955</section>
1956
1957<section title="Decoding chunked" anchor="decoding.chunked">
1958<t>
1959   A process for decoding the "chunked" transfer-coding
1960   can be represented in pseudo-code as:
1961</t>
1962<figure><artwork type="code">
1963  length := 0
1964  read chunk-size, chunk-ext (if any) and CRLF
1965  while (chunk-size &gt; 0) {
1966     read chunk-data and CRLF
1967     append chunk-data to decoded-body
1968     length := length + chunk-size
1969     read chunk-size and CRLF
1970  }
1971  read header-field
1972  while (header-field not empty) {
1973     append header-field to existing header fields
1974     read header-field
1975  }
1976  Content-Length := length
1977  Remove "chunked" from Transfer-Encoding
1978  Remove Trailer from existing header fields
1979</artwork></figure>
1980<t>
1981   All recipients &MUST; be able to receive and decode the
1982   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1983   they do not understand.
1984</t>
1985</section>
1986</section>
1987
1988<section title="Compression Codings" anchor="compression.codings">
1989<t>
1990   The codings defined below can be used to compress the payload of a
1991   message.
1992</t>
1993
1994<section title="Compress Coding" anchor="compress.coding">
1995<iref item="compress (Coding Format)"/>
1996<t>
1997   The "compress" format is produced by the common UNIX file compression
1998   program "compress". This format is an adaptive Lempel-Ziv-Welch
1999   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2000   equivalent to "compress".
2001</t>
2002</section>
2003
2004<section title="Deflate Coding" anchor="deflate.coding">
2005<iref item="deflate (Coding Format)"/>
2006<t>
2007   The "deflate" format is defined as the "deflate" compression mechanism
2008   (described in <xref target="RFC1951"/>) used inside the "zlib"
2009   data format (<xref target="RFC1950"/>).
2010</t>
2011<x:note>
2012  <t>
2013    &Note; Some incorrect implementations send the "deflate"
2014    compressed data without the zlib wrapper.
2015   </t>
2016</x:note>
2017</section>
2018
2019<section title="Gzip Coding" anchor="gzip.coding">
2020<iref item="gzip (Coding Format)"/>
2021<t>
2022   The "gzip" format is produced by the file compression program
2023   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2024   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2025   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2026</t>
2027</section>
2028
2029</section>
2030
2031<section title="TE" anchor="header.te">
2032  <iref primary="true" item="TE header field" x:for-anchor=""/>
2033  <x:anchor-alias value="TE"/>
2034  <x:anchor-alias value="t-codings"/>
2035  <x:anchor-alias value="t-ranking"/>
2036  <x:anchor-alias value="rank"/>
2037<t>
2038   The "TE" header field in a request indicates what transfer-codings,
2039   besides "chunked", the client is willing to accept in response, and
2040   whether or not the client is willing to accept trailer fields in a
2041   chunked transfer-coding.
2042</t>
2043<t>
2044   The TE field-value consists of a comma-separated list of transfer-coding
2045   names, each allowing for optional parameters (as described in
2046   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2047   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2048   chunked is always acceptable for HTTP/1.1 recipients.
2049</t>
2050<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"/>
2051  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2052  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2053  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2054  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2055             / ( "1" [ "." 0*3("0") ] )
2056</artwork></figure>
2057<t>
2058   Three examples of TE use are below.
2059</t>
2060<figure><artwork type="example">
2061  TE: deflate
2062  TE:
2063  TE: trailers, deflate;q=0.5
2064</artwork></figure>
2065<t>
2066   The presence of the keyword "trailers" indicates that the client is
2067   willing to accept trailer fields in a chunked transfer-coding,
2068   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2069   any downstream clients. For chained requests, this implies that either:
2070   (a) all downstream clients are willing to accept trailer fields in the
2071   forwarded response; or,
2072   (b) the client will attempt to buffer the response on behalf of downstream
2073   recipients.
2074   Note that HTTP/1.1 does not define any means to limit the size of a
2075   chunked response such that a client can be assured of buffering the
2076   entire response.
2077</t>
2078<t>
2079   When multiple transfer-codings are acceptable, the client &MAY; rank the
2080   codings by preference using a case-insensitive "q" parameter (similar to
2081   the qvalues used in content negotiation fields, &qvalue;). The rank value
2082   is a real number in the range 0 through 1, where 0.001 is the least
2083   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2084</t>
2085<t>
2086   If the TE field-value is empty or if no TE field is present, the only
2087   acceptable transfer-coding is "chunked". A message with no transfer-coding
2088   is always acceptable.
2089</t>
2090<t>
2091   Since the TE header field only applies to the immediate connection,
2092   a sender of TE &MUST; also send a "TE" connection option within the
2093   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2094   in order to prevent the TE field from being forwarded by intermediaries
2095   that do not support its semantics.
2096</t>
2097</section>
2098</section>
2099
2100<section title="Message Routing" anchor="message.routing">
2101<t>
2102   HTTP request message routing is determined by each client based on the
2103   target resource, the client's proxy configuration, and
2104   establishment or reuse of an inbound connection.  The corresponding
2105   response routing follows the same connection chain back to the client.
2106</t>
2107
2108<section title="Identifying a Target Resource" anchor="target-resource">
2109  <iref primary="true" item="target resource"/>
2110  <iref primary="true" item="target URI"/>
2111  <x:anchor-alias value="target resource"/>
2112  <x:anchor-alias value="target URI"/>
2113<t>
2114   HTTP is used in a wide variety of applications, ranging from
2115   general-purpose computers to home appliances.  In some cases,
2116   communication options are hard-coded in a client's configuration.
2117   However, most HTTP clients rely on the same resource identification
2118   mechanism and configuration techniques as general-purpose Web browsers.
2119</t>
2120<t>
2121   HTTP communication is initiated by a user agent for some purpose.
2122   The purpose is a combination of request semantics, which are defined in
2123   <xref target="Part2"/>, and a target resource upon which to apply those
2124   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2125   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2126   would resolve to its absolute form in order to obtain the
2127   "<x:dfn>target URI</x:dfn>".  The target URI
2128   excludes the reference's fragment identifier component, if any,
2129   since fragment identifiers are reserved for client-side processing
2130   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2131</t>
2132</section>
2133
2134<section title="Connecting Inbound" anchor="connecting.inbound">
2135<t>
2136   Once the target URI is determined, a client needs to decide whether
2137   a network request is necessary to accomplish the desired semantics and,
2138   if so, where that request is to be directed.
2139</t>
2140<t>
2141   If the client has a response cache and the request semantics can be
2142   satisfied by a cache (<xref target="Part6"/>), then the request is
2143   usually directed to the cache first.
2144</t>
2145<t>
2146   If the request is not satisfied by a cache, then a typical client will
2147   check its configuration to determine whether a proxy is to be used to
2148   satisfy the request.  Proxy configuration is implementation-dependent,
2149   but is often based on URI prefix matching, selective authority matching,
2150   or both, and the proxy itself is usually identified by an "http" or
2151   "https" URI.  If a proxy is applicable, the client connects inbound by
2152   establishing (or reusing) a connection to that proxy.
2153</t>
2154<t>
2155   If no proxy is applicable, a typical client will invoke a handler routine,
2156   usually specific to the target URI's scheme, to connect directly
2157   to an authority for the target resource.  How that is accomplished is
2158   dependent on the target URI scheme and defined by its associated
2159   specification, similar to how this specification defines origin server
2160   access for resolution of the "http" (<xref target="http.uri"/>) and
2161   "https" (<xref target="https.uri"/>) schemes.
2162</t>
2163<t>
2164   HTTP requirements regarding connection management are defined in
2165   <xref target="connection.management"/>.
2166</t>
2167</section>
2168
2169<section title="Request Target" anchor="request-target">
2170<t>
2171   Once an inbound connection is obtained,
2172   the client sends an HTTP request message (<xref target="http.message"/>)
2173   with a request-target derived from the target URI.
2174   There are four distinct formats for the request-target, depending on both
2175   the method being requested and whether the request is to a proxy.
2176</t>   
2177<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"/>
2178  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2179                 / <x:ref>absolute-form</x:ref>
2180                 / <x:ref>authority-form</x:ref>
2181                 / <x:ref>asterisk-form</x:ref>
2182
2183  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2184  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2185  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2186  <x:ref>asterisk-form</x:ref>  = "*"
2187</artwork></figure>
2188<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2189   The most common form of request-target is the origin-form.
2190   When making a request directly to an origin server, other than a CONNECT
2191   or server-wide OPTIONS request (as detailed below),
2192   a client &MUST; send only the absolute path and query components of
2193   the target URI as the request-target.
2194   If the target URI's path component is empty, then the client &MUST; send
2195   "/" as the path within the origin-form of request-target.
2196   A <x:ref>Host</x:ref> header field is also sent, as defined in
2197   <xref target="header.host"/>, containing the target URI's
2198   authority component (excluding any userinfo).
2199</t>
2200<t>
2201   For example, a client wishing to retrieve a representation of the resource
2202   identified as
2203</t>
2204<figure><artwork x:indent-with="  " type="example">
2205http://www.example.org/where?q=now
2206</artwork></figure>
2207<t>
2208   directly from the origin server would open (or reuse) a TCP connection
2209   to port 80 of the host "www.example.org" and send the lines:
2210</t>
2211<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2212GET /where?q=now HTTP/1.1
2213Host: www.example.org
2214</artwork></figure>
2215<t>
2216   followed by the remainder of the request message.
2217</t>
2218<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2219   When making a request to a proxy, other than a CONNECT or server-wide
2220   OPTIONS request (as detailed below), a client &MUST; send the target URI
2221   in absolute-form as the request-target.
2222   The proxy is requested to either service that request from a valid cache,
2223   if possible, or make the same request on the client's behalf to either
2224   the next inbound proxy server or directly to the origin server indicated
2225   by the request-target.  Requirements on such "forwarding" of messages are
2226   defined in <xref target="message.forwarding"/>.
2227</t>
2228<t>
2229   An example absolute-form of request-line would be:
2230</t>
2231<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2232GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2233</artwork></figure>
2234<t>
2235   To allow for transition to the absolute-form for all requests in some
2236   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2237   in requests, even though HTTP/1.1 clients will only send them in requests
2238   to proxies.
2239</t>
2240<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2241   The authority-form of request-target is only used for CONNECT requests
2242   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2243   one or more proxies, a client &MUST; send only the target URI's
2244   authority component (excluding any userinfo) as the request-target.
2245   For example,
2246</t>
2247<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2248CONNECT www.example.com:80 HTTP/1.1
2249</artwork></figure>
2250<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2251   The asterisk-form of request-target is only used for a server-wide
2252   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2253   for the server as a whole, as opposed to a specific named resource of
2254   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2255   For example,
2256</t>
2257<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2258OPTIONS * HTTP/1.1
2259</artwork></figure>
2260<t>
2261   If a proxy receives an OPTIONS request with an absolute-form of
2262   request-target in which the URI has an empty path and no query component,
2263   then the last proxy on the request chain &MUST; send a request-target
2264   of "*" when it forwards the request to the indicated origin server.
2265</t>
2266<figure><preamble>   
2267   For example, the request
2268</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2269OPTIONS http://www.example.org:8001 HTTP/1.1
2270</artwork></figure>
2271<figure><preamble>   
2272  would be forwarded by the final proxy as
2273</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2274OPTIONS * HTTP/1.1
2275Host: www.example.org:8001
2276</artwork>
2277<postamble>
2278   after connecting to port 8001 of host "www.example.org".
2279</postamble>
2280</figure>
2281</section>
2282
2283<section title="Host" anchor="header.host">
2284  <iref primary="true" item="Host header field" x:for-anchor=""/>
2285  <x:anchor-alias value="Host"/>
2286<t>
2287   The "Host" header field in a request provides the host and port
2288   information from the target URI, enabling the origin
2289   server to distinguish among resources while servicing requests
2290   for multiple host names on a single IP address.  Since the Host
2291   field-value is critical information for handling a request, it
2292   &SHOULD; be sent as the first header field following the request-line.
2293</t>
2294<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2295  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2296</artwork></figure>
2297<t>
2298   A client &MUST; send a Host header field in all HTTP/1.1 request
2299   messages.  If the target URI includes an authority component, then
2300   the Host field-value &MUST; be identical to that authority component
2301   after excluding any userinfo (<xref target="http.uri"/>).
2302   If the authority component is missing or undefined for the target URI,
2303   then the Host header field &MUST; be sent with an empty field-value.
2304</t>
2305<t>
2306   For example, a GET request to the origin server for
2307   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2308</t>
2309<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2310GET /pub/WWW/ HTTP/1.1
2311Host: www.example.org
2312</artwork></figure>
2313<t>
2314   The Host header field &MUST; be sent in an HTTP/1.1 request even
2315   if the request-target is in the absolute-form, since this
2316   allows the Host information to be forwarded through ancient HTTP/1.0
2317   proxies that might not have implemented Host.
2318</t>
2319<t>
2320   When a proxy receives a request with an absolute-form of
2321   request-target, the proxy &MUST; ignore the received
2322   Host header field (if any) and instead replace it with the host
2323   information of the request-target.  If the proxy forwards the request,
2324   it &MUST; generate a new Host field-value based on the received
2325   request-target rather than forward the received Host field-value.
2326</t>
2327<t>
2328   Since the Host header field acts as an application-level routing
2329   mechanism, it is a frequent target for malware seeking to poison
2330   a shared cache or redirect a request to an unintended server.
2331   An interception proxy is particularly vulnerable if it relies on
2332   the Host field-value for redirecting requests to internal
2333   servers, or for use as a cache key in a shared cache, without
2334   first verifying that the intercepted connection is targeting a
2335   valid IP address for that host.
2336</t>
2337<t>
2338   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2339   to any HTTP/1.1 request message that lacks a Host header field and
2340   to any request message that contains more than one Host header field
2341   or a Host header field with an invalid field-value.
2342</t>
2343</section>
2344
2345<section title="Effective Request URI" anchor="effective.request.uri">
2346  <iref primary="true" item="effective request URI"/>
2347<t>
2348   A server that receives an HTTP request message &MUST; reconstruct
2349   the user agent's original target URI, based on the pieces of information
2350   learned from the request-target, <x:ref>Host</x:ref> header field, and
2351   connection context, in order to identify the intended target resource and
2352   properly service the request. The URI derived from this reconstruction
2353   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2354</t>
2355<t>
2356   For a user agent, the effective request URI is the target URI.
2357</t>
2358<t>
2359   If the request-target is in absolute-form, then the effective request URI
2360   is the same as the request-target.  Otherwise, the effective request URI
2361   is constructed as follows.
2362</t>
2363<t>
2364   If the request is received over a TLS-secured TCP connection,
2365   then the effective request URI's scheme is "https"; otherwise, the
2366   scheme is "http".
2367</t>
2368<t>
2369   If the request-target is in authority-form, then the effective
2370   request URI's authority component is the same as the request-target.
2371   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2372   non-empty field-value, then the authority component is the same as the
2373   Host field-value. Otherwise, the authority component is the concatenation of
2374   the default host name configured for the server, a colon (":"), and the
2375   connection's incoming TCP port number in decimal form.
2376</t>
2377<t>
2378   If the request-target is in authority-form or asterisk-form, then the
2379   effective request URI's combined path and query component is empty.
2380   Otherwise, the combined path and query component is the same as the
2381   request-target.
2382</t>
2383<t>
2384   The components of the effective request URI, once determined as above,
2385   can be combined into absolute-URI form by concatenating the scheme,
2386   "://", authority, and combined path and query component.
2387</t>
2388<figure>
2389<preamble>
2390   Example 1: the following message received over an insecure TCP connection
2391</preamble> 
2392<artwork type="example" x:indent-with="  ">
2393GET /pub/WWW/TheProject.html HTTP/1.1
2394Host: www.example.org:8080
2395</artwork>
2396</figure>
2397<figure>
2398<preamble>
2399  has an effective request URI of
2400</preamble>
2401<artwork type="example" x:indent-with="  ">
2402http://www.example.org:8080/pub/WWW/TheProject.html
2403</artwork>
2404</figure>
2405<figure>
2406<preamble>
2407   Example 2: the following message received over a TLS-secured TCP connection
2408</preamble> 
2409<artwork type="example" x:indent-with="  ">
2410OPTIONS * HTTP/1.1
2411Host: www.example.org
2412</artwork>
2413</figure>
2414<figure>
2415<preamble>
2416  has an effective request URI of
2417</preamble>
2418<artwork type="example" x:indent-with="  ">
2419https://www.example.org
2420</artwork>
2421</figure>
2422<t>
2423   An origin server that does not allow resources to differ by requested
2424   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2425   with a configured server name when constructing the effective request URI.
2426</t>
2427<t>
2428   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2429   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2430   something unique to a particular host) in order to guess the
2431   effective request URI's authority component.
2432</t>
2433</section>
2434
2435<section title="Message Forwarding" anchor="message.forwarding">
2436<t>
2437   As described in <xref target="intermediaries"/>, intermediaries can serve
2438   a variety of roles in the processing of HTTP requests and responses.
2439   Some intermediaries are used to improve performance or availability.
2440   Others are used for access control or to filter content.
2441   Since an HTTP stream has characteristics similar to a pipe-and-filter
2442   architecture, there are no inherent limits to the extent an intermediary
2443   can enhance (or interfere) with either direction of the stream.
2444</t>
2445<t>
2446   Intermediaries that forward a message &MUST; implement the
2447   <x:ref>Connection</x:ref> header field, as specified in
2448   <xref target="header.connection"/>, to exclude fields that are only
2449   intended for the incoming connection.
2450</t>
2451<t>
2452   In order to avoid request loops, a proxy that forwards requests to other
2453   proxies &MUST; be able to recognize and exclude all of its own server
2454   names, including any aliases, local variations, or literal IP addresses.
2455</t>
2456</section>
2457
2458<section title="Via" anchor="header.via">
2459  <iref primary="true" item="Via header field" x:for-anchor=""/>
2460  <x:anchor-alias value="pseudonym"/>
2461  <x:anchor-alias value="received-by"/>
2462  <x:anchor-alias value="received-protocol"/>
2463  <x:anchor-alias value="Via"/>
2464<t>
2465   The "Via" header field &MUST; be sent by a proxy or gateway
2466   in forwarded messages to
2467   indicate the intermediate protocols and recipients between the user
2468   agent and the server on requests, and between the origin server and
2469   the client on responses. It is analogous to the "Received" field
2470   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2471   Via is used in HTTP for tracking message forwards,
2472   avoiding request loops, and identifying the protocol capabilities of
2473   all senders along the request/response chain.
2474</t>
2475<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"/>
2476  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2477                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2478  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2479  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2480  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2481</artwork></figure>
2482<t>
2483   The received-protocol indicates the protocol version of the message
2484   received by the server or client along each segment of the
2485   request/response chain. The received-protocol version is appended to
2486   the Via field value when the message is forwarded so that information
2487   about the protocol capabilities of upstream applications remains
2488   visible to all recipients.
2489</t>
2490<t>
2491   The protocol-name is excluded if and only if it would be "HTTP". The
2492   received-by field is normally the host and optional port number of a
2493   recipient server or client that subsequently forwarded the message.
2494   However, if the real host is considered to be sensitive information,
2495   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2496   be assumed to be the default port of the received-protocol.
2497</t>
2498<t>
2499   Multiple Via field values represent each proxy or gateway that has
2500   forwarded the message. Each recipient &MUST; append its information
2501   such that the end result is ordered according to the sequence of
2502   forwarding applications.
2503</t>
2504<t>
2505   Comments &MAY; be used in the Via header field to identify the software
2506   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2507   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2508   are optional and &MAY; be removed by any recipient prior to forwarding the
2509   message.
2510</t>
2511<t>
2512   For example, a request message could be sent from an HTTP/1.0 user
2513   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2514   forward the request to a public proxy at p.example.net, which completes
2515   the request by forwarding it to the origin server at www.example.com.
2516   The request received by www.example.com would then have the following
2517   Via header field:
2518</t>
2519<figure><artwork type="example">
2520  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2521</artwork></figure>
2522<t>
2523   A proxy or gateway used as a portal through a network firewall
2524   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2525   region unless it is explicitly enabled to do so. If not enabled, the
2526   received-by host of any host behind the firewall &SHOULD; be replaced
2527   by an appropriate pseudonym for that host.
2528</t>
2529<t>
2530   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2531   field entries into a single such entry if the entries have identical
2532   received-protocol values. For example,
2533</t>
2534<figure><artwork type="example">
2535  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2536</artwork></figure>
2537<t>
2538  could be collapsed to
2539</t>
2540<figure><artwork type="example">
2541  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2542</artwork></figure>
2543<t>
2544   Senders &SHOULD-NOT; combine multiple entries unless they are all
2545   under the same organizational control and the hosts have already been
2546   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2547   have different received-protocol values.
2548</t>
2549</section>
2550
2551<section title="Message Transforming" anchor="message.transforming">
2552<t>
2553   If a proxy receives a request-target with a host name that is not a
2554   fully qualified domain name, it &MAY; add its own domain to the host name
2555   it received when forwarding the request.  A proxy &MUST-NOT; change the
2556   host name if it is a fully qualified domain name.
2557</t>
2558<t>
2559   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2560   parts of the received request-target when forwarding it to the next inbound
2561   server, except as noted above to replace an empty path with "/" or "*".
2562</t>
2563<t>
2564   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2565   though it &MAY; change the message body through application or removal
2566   of a transfer-coding (<xref target="transfer.codings"/>).
2567</t>
2568<t>
2569   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2570   information about the end points of the communication chain, the resource
2571   state, or the selected representation.
2572</t>
2573<t>
2574   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2575   request or response, and it &MUST-NOT; add any of these fields if not
2576   already present:
2577  <list style="symbols">
2578    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2579    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2580    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2581    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2582    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2583    <t><x:ref>Server</x:ref> (&header-server;)</t>
2584  </list>
2585</t>
2586<t>
2587   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2588   header field (&header-expires;) if already present in a response, but
2589   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2590   identical to that of the <x:ref>Date</x:ref> header field.
2591</t>
2592<t>
2593   A proxy &MUST-NOT; modify or add any of the following fields in a
2594   message that contains the no-transform cache-control directive:
2595  <list style="symbols">
2596    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2597    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2598    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2599  </list>
2600</t>
2601<t>
2602   A transforming proxy &MAY; modify or add these fields to a message
2603   that does not include no-transform, but if it does so, it &MUST; add a
2604   Warning 214 (Transformation applied) if one does not already appear
2605   in the message (see &header-warning;).
2606</t>
2607<x:note>
2608  <t>
2609    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2610    cause authentication failures if stronger authentication
2611    mechanisms are introduced in later versions of HTTP. Such
2612    authentication mechanisms &MAY; rely on the values of header fields
2613    not listed here.
2614  </t>
2615</x:note>
2616</section>
2617
2618<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2619<t>
2620   HTTP does not include a request identifier for associating a given
2621   request message with its corresponding one or more response messages.
2622   Hence, it relies on the order of response arrival to correspond exactly
2623   to the order in which requests are made on the same connection.
2624   More than one response message per request only occurs when one or more
2625   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2626   to the same request.
2627</t>
2628<t>
2629   A client that uses persistent connections and sends more than one request
2630   per connection &MUST; maintain a list of outstanding requests in the
2631   order sent on that connection and &MUST; associate each received response
2632   message to the highest ordered request that has not yet received a final
2633   (non-<x:ref>1xx</x:ref>) response.
2634</t>
2635</section>
2636</section>
2637
2638<section title="Connection Management" anchor="connection.management">
2639<t>
2640   HTTP messaging is independent of the underlying transport or
2641   session-layer connection protocol(s).  HTTP only presumes a reliable
2642   transport with in-order delivery of requests and the corresponding
2643   in-order delivery of responses.  The mapping of HTTP request and
2644   response structures onto the data units of an underlying transport
2645   protocol is outside the scope of this specification.
2646</t>
2647<t>
2648   As described in <xref target="connecting.inbound"/>, the specific
2649   connection protocols to be used for an HTTP interaction are determined by
2650   client configuration and the <x:ref>target URI</x:ref>.
2651   For example, the "http" URI scheme
2652   (<xref target="http.uri"/>) indicates a default connection of TCP
2653   over IP, with a default TCP port of 80, but the client might be
2654   configured to use a proxy via some other connection, port, or protocol.
2655</t>
2656<t>
2657   HTTP implementations are expected to engage in connection management,
2658   which includes maintaining the state of current connections,
2659   establishing a new connection or reusing an existing connection,
2660   processing messages received on a connection, detecting connection
2661   failures, and closing each connection.
2662   Most clients maintain multiple connections in parallel, including
2663   more than one connection per server endpoint.
2664   Most servers are designed to maintain thousands of concurrent connections,
2665   while controlling request queues to enable fair use and detect
2666   denial of service attacks.
2667</t>
2668
2669<section title="Connection" anchor="header.connection">
2670  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2671  <iref primary="true" item="close" x:for-anchor=""/>
2672  <x:anchor-alias value="Connection"/>
2673  <x:anchor-alias value="connection-option"/>
2674  <x:anchor-alias value="close"/>
2675<t>
2676   The "Connection" header field allows the sender to indicate desired
2677   control options for the current connection.  In order to avoid confusing
2678   downstream recipients, a proxy or gateway &MUST; remove or replace any
2679   received connection options before forwarding the message.
2680</t>
2681<t>
2682   When a header field is used to supply control information for or about
2683   the current connection, the sender &SHOULD; list the corresponding
2684   field-name within the "Connection" header field.
2685   A proxy or gateway &MUST; parse a received Connection
2686   header field before a message is forwarded and, for each
2687   connection-option in this field, remove any header field(s) from
2688   the message with the same name as the connection-option, and then
2689   remove the Connection header field itself (or replace it with the
2690   intermediary's own connection options for the forwarded message).
2691</t>
2692<t>
2693   Hence, the Connection header field provides a declarative way of
2694   distinguishing header fields that are only intended for the
2695   immediate recipient ("hop-by-hop") from those fields that are
2696   intended for all recipients on the chain ("end-to-end"), enabling the
2697   message to be self-descriptive and allowing future connection-specific
2698   extensions to be deployed without fear that they will be blindly
2699   forwarded by older intermediaries.
2700</t>
2701<t>
2702   The Connection header field's value has the following grammar:
2703</t>
2704<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2705  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2706  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2707</artwork></figure>
2708<t>
2709   Connection options are case-insensitive.
2710</t>
2711<t>
2712   A sender &MUST-NOT; include field-names in the Connection header
2713   field-value for fields that are defined as expressing constraints
2714   for all recipients in the request or response chain, such as the
2715   Cache-Control header field (&header-cache-control;).
2716</t>
2717<t>
2718   The connection options do not have to correspond to a header field
2719   present in the message, since a connection-specific header field
2720   might not be needed if there are no parameters associated with that
2721   connection option.  Recipients that trigger certain connection
2722   behavior based on the presence of connection options &MUST; do so
2723   based on the presence of the connection-option rather than only the
2724   presence of the optional header field.  In other words, if the
2725   connection option is received as a header field but not indicated
2726   within the Connection field-value, then the recipient &MUST; ignore
2727   the connection-specific header field because it has likely been
2728   forwarded by an intermediary that is only partially conformant.
2729</t>
2730<t>
2731   When defining new connection options, specifications ought to
2732   carefully consider existing deployed header fields and ensure
2733   that the new connection option does not share the same name as
2734   an unrelated header field that might already be deployed.
2735   Defining a new connection option essentially reserves that potential
2736   field-name for carrying additional information related to the
2737   connection option, since it would be unwise for senders to use
2738   that field-name for anything else.
2739</t>
2740<t>
2741   The "<x:dfn>close</x:dfn>" connection option is defined for a
2742   sender to signal that this connection will be closed after completion of
2743   the response. For example,
2744</t>
2745<figure><artwork type="example">
2746  Connection: close
2747</artwork></figure>
2748<t>
2749   in either the request or the response header fields indicates that
2750   the connection &SHOULD; be closed after the current request/response
2751   is complete (<xref target="persistent.tear-down"/>).
2752</t>
2753<t>
2754   A client that does not support persistent connections &MUST;
2755   send the "close" connection option in every request message.
2756</t>
2757<t>
2758   A server that does not support persistent connections &MUST;
2759   send the "close" connection option in every response message that
2760   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2761</t>
2762</section>
2763
2764<section title="Persistent Connections" anchor="persistent.connections">
2765  <x:anchor-alias value="persistent connections"/>
2766<t>
2767   HTTP was originally designed to use a separate connection for each
2768   request/response pair. As the Web evolved and embedded requests became
2769   common for inline images, the connection establishment overhead was
2770   a significant drain on performance and a concern for Internet congestion.
2771   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2772   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2773   to improve performance for some requests. However, these extensions were
2774   insufficient for dynamically generated responses and difficult to use
2775   with intermediaries.
2776</t>
2777<t>
2778   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2779   which allow multiple requests and responses to be carried over a single
2780   connection. The "<x:ref>close</x:ref>" connection-option is used to
2781   signal that a connection will close after the current request/response.
2782   Persistent connections have a number of advantages:
2783  <list style="symbols">
2784      <t>
2785        By opening and closing fewer connections, CPU time is saved
2786        in routers and hosts (clients, servers, proxies, gateways,
2787        tunnels, or caches), and memory used for protocol control
2788        blocks can be saved in hosts.
2789      </t>
2790      <t>
2791        Most requests and responses can be pipelined on a connection.
2792        Pipelining allows a client to make multiple requests without
2793        waiting for each response, allowing a single connection to
2794        be used much more efficiently and with less overall latency.
2795      </t>
2796      <t>
2797        For TCP connections, network congestion is reduced by eliminating the
2798        packets associated with the three way handshake and graceful close
2799        procedures, and by allowing sufficient time to determine the
2800        congestion state of the network.
2801      </t>
2802      <t>
2803        Latency on subsequent requests is reduced since there is no time
2804        spent in the connection opening handshake.
2805      </t>
2806      <t>
2807        HTTP can evolve more gracefully, since most errors can be reported
2808        without the penalty of closing the connection. Clients using
2809        future versions of HTTP might optimistically try a new feature,
2810        but if communicating with an older server, retry with old
2811        semantics after an error is reported.
2812      </t>
2813    </list>
2814</t>
2815<t>
2816   HTTP implementations &SHOULD; implement persistent connections.
2817</t>
2818   
2819<section title="Establishment" anchor="persistent.establishment">
2820<t>
2821   It is beyond the scope of this specification to describe how connections
2822   are established via various transport or session-layer protocols.
2823   Each connection applies to only one transport link.
2824</t>
2825<t>
2826   A recipient determines whether a connection is persistent or not based on
2827   the most recently received message's protocol version and
2828   <x:ref>Connection</x:ref> header field (if any):
2829   <list style="symbols">
2830     <t>If the <x:ref>close</x:ref> connection option is present, the
2831        connection will not persist after the current response; else,</t>
2832     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2833        persist after the current response; else,</t>
2834     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2835        connection option is present, the recipient is not a proxy, and
2836        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2837        the connection will persist after the current response; otherwise,</t>
2838     <t>The connection will close after the current response.</t>
2839   </list>
2840</t>
2841<t>
2842   A proxy server &MUST-NOT; maintain a persistent connection with an
2843   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2844   information and discussion of the problems with the Keep-Alive header field
2845   implemented by many HTTP/1.0 clients).
2846</t>
2847</section>
2848
2849<section title="Reuse" anchor="persistent.reuse">
2850<t>
2851   In order to remain persistent, all messages on a connection &MUST;
2852   have a self-defined message length (i.e., one not defined by closure
2853   of the connection), as described in <xref target="message.body"/>.
2854</t>
2855<t>
2856   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2857   persistent connection until a <x:ref>close</x:ref> connection option
2858   is received in a request.
2859</t>
2860<t>
2861   A client &MAY; reuse a persistent connection until it sends or receives
2862   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2863   without a "keep-alive" connection option.
2864</t>
2865<t>
2866   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2867   maintained for HTTP versions less than 1.1 unless it is explicitly
2868   signaled.
2869   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2870   for more information on backward compatibility with HTTP/1.0 clients.
2871</t>
2872
2873<section title="Pipelining" anchor="pipelining">
2874<t>
2875   A client that supports persistent connections &MAY; "pipeline" its
2876   requests (i.e., send multiple requests without waiting for each
2877   response). A server &MUST; send its responses to those requests in the
2878   same order that the requests were received.
2879</t>
2880<t>
2881   Clients which assume persistent connections and pipeline immediately
2882   after connection establishment &SHOULD; be prepared to retry their
2883   connection if the first pipelined attempt fails. If a client does
2884   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2885   persistent. Clients &MUST; also be prepared to resend their requests if
2886   the server closes the connection before sending all of the
2887   corresponding responses.
2888</t>
2889<t>
2890   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2891   or non-idempotent sequences of request methods (see &idempotent-methods;).
2892   Otherwise, a premature termination of the transport connection could lead
2893   to indeterminate results. A client wishing to send a non-idempotent
2894   request &SHOULD; wait to send that request until it has received the
2895   response status line for the previous request.
2896</t>
2897</section>
2898
2899<section title="Retrying Requests" anchor="persistent.retrying.requests">
2900<t>
2901   Senders can close the transport connection at any time. Therefore,
2902   clients, servers, and proxies &MUST; be able to recover
2903   from asynchronous close events. Client software &MAY; reopen the
2904   transport connection and retransmit the aborted sequence of requests
2905   without user interaction so long as the request sequence is
2906   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2907   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2908   human operator the choice of retrying the request(s). Confirmation by
2909   user-agent software with semantic understanding of the application
2910   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2911   be repeated if the second sequence of requests fails.
2912</t>
2913</section>
2914</section>
2915   
2916<section title="Concurrency" anchor="persistent.concurrency">
2917<t>
2918   Clients &SHOULD; limit the number of simultaneous
2919   connections that they maintain to a given server.
2920</t>
2921<t>
2922   Previous revisions of HTTP gave a specific number of connections as a
2923   ceiling, but this was found to be impractical for many applications. As a
2924   result, this specification does not mandate a particular maximum number of
2925   connections, but instead encourages clients to be conservative when opening
2926   multiple connections.
2927</t>
2928<t>
2929   Multiple connections are typically used to avoid the "head-of-line
2930   blocking" problem, wherein a request that takes significant server-side
2931   processing and/or has a large payload blocks subsequent requests on the
2932   same connection. However, each connection consumes server resources.
2933   Furthermore, using multiple connections can cause undesirable side effects
2934   in congested networks.
2935</t>
2936<t>
2937   Note that servers might reject traffic that they deem abusive, including an
2938   excessive number of connections from a client.
2939</t>
2940</section>
2941
2942<section title="Failures and Time-outs" anchor="persistent.failures">
2943<t>
2944   Servers will usually have some time-out value beyond which they will
2945   no longer maintain an inactive connection. Proxy servers might make
2946   this a higher value since it is likely that the client will be making
2947   more connections through the same server. The use of persistent
2948   connections places no requirements on the length (or existence) of
2949   this time-out for either the client or the server.
2950</t>
2951<t>
2952   When a client or server wishes to time-out it &SHOULD; issue a graceful
2953   close on the transport connection. Clients and servers &SHOULD; both
2954   constantly watch for the other side of the transport close, and
2955   respond to it as appropriate. If a client or server does not detect
2956   the other side's close promptly it could cause unnecessary resource
2957   drain on the network.
2958</t>
2959<t>
2960   A client, server, or proxy &MAY; close the transport connection at any
2961   time. For example, a client might have started to send a new request
2962   at the same time that the server has decided to close the "idle"
2963   connection. From the server's point of view, the connection is being
2964   closed while it was idle, but from the client's point of view, a
2965   request is in progress.
2966</t>
2967<t>
2968   Servers &SHOULD; maintain persistent connections and allow the underlying
2969   transport's flow control mechanisms to resolve temporary overloads, rather
2970   than terminate connections with the expectation that clients will retry.
2971   The latter technique can exacerbate network congestion.
2972</t>
2973<t>
2974   A client sending a message body &SHOULD; monitor
2975   the network connection for an error status code while it is transmitting
2976   the request. If the client sees an error status code, it &SHOULD;
2977   immediately cease transmitting the body and close the connection.
2978</t>
2979</section>
2980   
2981<section title="Tear-down" anchor="persistent.tear-down">
2982  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2983  <iref primary="false" item="close" x:for-anchor=""/>
2984<t>
2985   The <x:ref>Connection</x:ref> header field
2986   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
2987   connection option that a sender &SHOULD; send when it wishes to close
2988   the connection after the current request/response pair.
2989</t>
2990<t>
2991   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
2992   send further requests on that connection (after the one containing
2993   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
2994   final response message corresponding to this request.
2995</t>
2996<t>
2997   A server that receives a <x:ref>close</x:ref> connection option &MUST;
2998   initiate a lingering close of the connection after it sends the final
2999   response to the request that contained <x:ref>close</x:ref>.
3000   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3001   in its final response on that connection. The server &MUST-NOT; process
3002   any further requests received on that connection.
3003</t>
3004<t>
3005   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3006   initiate a lingering close of the connection after it sends the
3007   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3008   any further requests received on that connection.
3009</t>
3010<t>
3011   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3012   cease sending requests on that connection and close the connection
3013   after reading the response message containing the close; if additional
3014   pipelined requests had been sent on the connection, the client &SHOULD;
3015   assume that they will not be processed by the server.
3016</t>
3017<t>
3018   If a server performs an immediate close of a TCP connection, there is a
3019   significant risk that the client will not be able to read the last HTTP
3020   response.  If the server receives additional data from the client on a
3021   fully-closed connection, such as another request that was sent by the
3022   client before receiving the server's response, the server's TCP stack will
3023   send a reset packet to the client; unfortunately, the reset packet might
3024   erase the client's unacknowledged input buffers before they can be read
3025   and interpreted by the client's HTTP parser.
3026</t>
3027<t>
3028   To avoid the TCP reset problem, a server can perform a lingering close on a
3029   connection by closing only the write side of the read/write connection
3030   (a half-close) and continuing to read from the connection until the
3031   connection is closed by the client or the server is reasonably certain
3032   that its own TCP stack has received the client's acknowledgement of the
3033   packet(s) containing the server's last response. It is then safe for the
3034   server to fully close the connection.
3035</t>
3036<t>
3037   It is unknown whether the reset problem is exclusive to TCP or might also
3038   be found in other transport connection protocols.
3039</t>
3040</section>
3041</section>
3042
3043<section title="Upgrade" anchor="header.upgrade">
3044  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3045  <x:anchor-alias value="Upgrade"/>
3046  <x:anchor-alias value="protocol"/>
3047  <x:anchor-alias value="protocol-name"/>
3048  <x:anchor-alias value="protocol-version"/>
3049<t>
3050   The "Upgrade" header field is intended to provide a simple mechanism
3051   for transitioning from HTTP/1.1 to some other protocol on the same
3052   connection.  A client &MAY; send a list of protocols in the Upgrade
3053   header field of a request to invite the server to switch to one or
3054   more of those protocols before sending the final response.
3055   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3056   Protocols)</x:ref> responses to indicate which protocol(s) are being
3057   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3058   responses to indicate acceptable protocols.
3059   A server &MAY; send an Upgrade header field in any other response to
3060   indicate that they might be willing to upgrade to one of the
3061   specified protocols for a future request.
3062</t>
3063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3064  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3065
3066  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3067  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3068  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3069</artwork></figure>
3070<t>
3071   For example,
3072</t>
3073<figure><artwork type="example">
3074  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3075</artwork></figure>
3076<t>
3077   Upgrade eases the difficult transition between incompatible protocols by
3078   allowing the client to initiate a request in the more commonly
3079   supported protocol while indicating to the server that it would like
3080   to use a "better" protocol if available (where "better" is determined
3081   by the server, possibly according to the nature of the request method
3082   or target resource).
3083</t>
3084<t>
3085   Upgrade cannot be used to insist on a protocol change; its acceptance and
3086   use by the server is optional. The capabilities and nature of the
3087   application-level communication after the protocol change is entirely
3088   dependent upon the new protocol chosen, although the first action
3089   after changing the protocol &MUST; be a response to the initial HTTP
3090   request that contained the Upgrade header field.
3091</t>
3092<t>
3093   For example, if the Upgrade header field is received in a GET request
3094   and the server decides to switch protocols, then it &MUST; first respond
3095   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3096   then immediately follow that with the new protocol's equivalent of a
3097   response to a GET on the target resource.  This allows a connection to be
3098   upgraded to protocols with the same semantics as HTTP without the
3099   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3100   protocols unless the received message semantics can be honored by the new
3101   protocol; an OPTIONS request can be honored by any protocol.
3102</t>
3103<t>
3104   When Upgrade is sent, a sender &MUST; also send a
3105   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3106   that contains the "upgrade" connection option, in order to prevent Upgrade
3107   from being accidentally forwarded by intermediaries that might not implement
3108   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3109   is received in an HTTP/1.0 request.
3110</t>
3111<t>
3112   The Upgrade header field only applies to switching application-level
3113   protocols on the existing connection; it cannot be used
3114   to switch to a protocol on a different connection. For that purpose, it is
3115   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3116   (&status-3xx;).
3117</t>
3118<t>
3119   This specification only defines the protocol name "HTTP" for use by
3120   the family of Hypertext Transfer Protocols, as defined by the HTTP
3121   version rules of <xref target="http.version"/> and future updates to this
3122   specification. Additional tokens can be registered with IANA using the
3123   registration procedure defined in <xref target="upgrade.token.registry"/>.
3124</t>
3125</section>
3126</section>
3127
3128<section title="IANA Considerations" anchor="IANA.considerations">
3129
3130<section title="Header Field Registration" anchor="header.field.registration">
3131<t>
3132   HTTP header fields are registered within the Message Header Field Registry
3133   <xref target="RFC3864"/> maintained by IANA at
3134   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3135</t>
3136<t>
3137   This document defines the following HTTP header fields, so their
3138   associated registry entries shall be updated according to the permanent
3139   registrations below:
3140</t>
3141<?BEGININC p1-messaging.iana-headers ?>
3142<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3143<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3144   <ttcol>Header Field Name</ttcol>
3145   <ttcol>Protocol</ttcol>
3146   <ttcol>Status</ttcol>
3147   <ttcol>Reference</ttcol>
3148
3149   <c>Connection</c>
3150   <c>http</c>
3151   <c>standard</c>
3152   <c>
3153      <xref target="header.connection"/>
3154   </c>
3155   <c>Content-Length</c>
3156   <c>http</c>
3157   <c>standard</c>
3158   <c>
3159      <xref target="header.content-length"/>
3160   </c>
3161   <c>Host</c>
3162   <c>http</c>
3163   <c>standard</c>
3164   <c>
3165      <xref target="header.host"/>
3166   </c>
3167   <c>TE</c>
3168   <c>http</c>
3169   <c>standard</c>
3170   <c>
3171      <xref target="header.te"/>
3172   </c>
3173   <c>Trailer</c>
3174   <c>http</c>
3175   <c>standard</c>
3176   <c>
3177      <xref target="header.trailer"/>
3178   </c>
3179   <c>Transfer-Encoding</c>
3180   <c>http</c>
3181   <c>standard</c>
3182   <c>
3183      <xref target="header.transfer-encoding"/>
3184   </c>
3185   <c>Upgrade</c>
3186   <c>http</c>
3187   <c>standard</c>
3188   <c>
3189      <xref target="header.upgrade"/>
3190   </c>
3191   <c>Via</c>
3192   <c>http</c>
3193   <c>standard</c>
3194   <c>
3195      <xref target="header.via"/>
3196   </c>
3197</texttable>
3198<!--(END)-->
3199<?ENDINC p1-messaging.iana-headers ?>
3200<t>
3201   Furthermore, the header field-name "Close" shall be registered as
3202   "reserved", since using that name as an HTTP header field might
3203   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3204   header field (<xref target="header.connection"/>).
3205</t>
3206<texttable align="left" suppress-title="true">
3207   <ttcol>Header Field Name</ttcol>
3208   <ttcol>Protocol</ttcol>
3209   <ttcol>Status</ttcol>
3210   <ttcol>Reference</ttcol>
3211
3212   <c>Close</c>
3213   <c>http</c>
3214   <c>reserved</c>
3215   <c>
3216      <xref target="header.field.registration"/>
3217   </c>
3218</texttable>
3219<t>
3220   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3221</t>
3222</section>
3223
3224<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3225<t>
3226   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3227   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3228</t>
3229<t>
3230   This document defines the following URI schemes, so their
3231   associated registry entries shall be updated according to the permanent
3232   registrations below:
3233</t>
3234<texttable align="left" suppress-title="true">
3235   <ttcol>URI Scheme</ttcol>
3236   <ttcol>Description</ttcol>
3237   <ttcol>Reference</ttcol>
3238
3239   <c>http</c>
3240   <c>Hypertext Transfer Protocol</c>
3241   <c><xref target="http.uri"/></c>
3242
3243   <c>https</c>
3244   <c>Hypertext Transfer Protocol Secure</c>
3245   <c><xref target="https.uri"/></c>
3246</texttable>
3247</section>
3248
3249<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3250<t>
3251   This document serves as the specification for the Internet media types
3252   "message/http" and "application/http". The following is to be registered with
3253   IANA (see <xref target="RFC4288"/>).
3254</t>
3255<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3256<iref item="Media Type" subitem="message/http" primary="true"/>
3257<iref item="message/http Media Type" primary="true"/>
3258<t>
3259   The message/http type can be used to enclose a single HTTP request or
3260   response message, provided that it obeys the MIME restrictions for all
3261   "message" types regarding line length and encodings.
3262</t>
3263<t>
3264  <list style="hanging" x:indent="12em">
3265    <t hangText="Type name:">
3266      message
3267    </t>
3268    <t hangText="Subtype name:">
3269      http
3270    </t>
3271    <t hangText="Required parameters:">
3272      none
3273    </t>
3274    <t hangText="Optional parameters:">
3275      version, msgtype
3276      <list style="hanging">
3277        <t hangText="version:">
3278          The HTTP-version number of the enclosed message
3279          (e.g., "1.1"). If not present, the version can be
3280          determined from the first line of the body.
3281        </t>
3282        <t hangText="msgtype:">
3283          The message type &mdash; "request" or "response". If not
3284          present, the type can be determined from the first
3285          line of the body.
3286        </t>
3287      </list>
3288    </t>
3289    <t hangText="Encoding considerations:">
3290      only "7bit", "8bit", or "binary" are permitted
3291    </t>
3292    <t hangText="Security considerations:">
3293      none
3294    </t>
3295    <t hangText="Interoperability considerations:">
3296      none
3297    </t>
3298    <t hangText="Published specification:">
3299      This specification (see <xref target="internet.media.type.message.http"/>).
3300    </t>
3301    <t hangText="Applications that use this media type:">
3302    </t>
3303    <t hangText="Additional information:">
3304      <list style="hanging">
3305        <t hangText="Magic number(s):">none</t>
3306        <t hangText="File extension(s):">none</t>
3307        <t hangText="Macintosh file type code(s):">none</t>
3308      </list>
3309    </t>
3310    <t hangText="Person and email address to contact for further information:">
3311      See Authors Section.
3312    </t>
3313    <t hangText="Intended usage:">
3314      COMMON
3315    </t>
3316    <t hangText="Restrictions on usage:">
3317      none
3318    </t>
3319    <t hangText="Author/Change controller:">
3320      IESG
3321    </t>
3322  </list>
3323</t>
3324</section>
3325<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3326<iref item="Media Type" subitem="application/http" primary="true"/>
3327<iref item="application/http Media Type" primary="true"/>
3328<t>
3329   The application/http type can be used to enclose a pipeline of one or more
3330   HTTP request or response messages (not intermixed).
3331</t>
3332<t>
3333  <list style="hanging" x:indent="12em">
3334    <t hangText="Type name:">
3335      application
3336    </t>
3337    <t hangText="Subtype name:">
3338      http
3339    </t>
3340    <t hangText="Required parameters:">
3341      none
3342    </t>
3343    <t hangText="Optional parameters:">
3344      version, msgtype
3345      <list style="hanging">
3346        <t hangText="version:">
3347          The HTTP-version number of the enclosed messages
3348          (e.g., "1.1"). If not present, the version can be
3349          determined from the first line of the body.
3350        </t>
3351        <t hangText="msgtype:">
3352          The message type &mdash; "request" or "response". If not
3353          present, the type can be determined from the first
3354          line of the body.
3355        </t>
3356      </list>
3357    </t>
3358    <t hangText="Encoding considerations:">
3359      HTTP messages enclosed by this type
3360      are in "binary" format; use of an appropriate
3361      Content-Transfer-Encoding is required when
3362      transmitted via E-mail.
3363    </t>
3364    <t hangText="Security considerations:">
3365      none
3366    </t>
3367    <t hangText="Interoperability considerations:">
3368      none
3369    </t>
3370    <t hangText="Published specification:">
3371      This specification (see <xref target="internet.media.type.application.http"/>).
3372    </t>
3373    <t hangText="Applications that use this media type:">
3374    </t>
3375    <t hangText="Additional information:">
3376      <list style="hanging">
3377        <t hangText="Magic number(s):">none</t>
3378        <t hangText="File extension(s):">none</t>
3379        <t hangText="Macintosh file type code(s):">none</t>
3380      </list>
3381    </t>
3382    <t hangText="Person and email address to contact for further information:">
3383      See Authors Section.
3384    </t>
3385    <t hangText="Intended usage:">
3386      COMMON
3387    </t>
3388    <t hangText="Restrictions on usage:">
3389      none
3390    </t>
3391    <t hangText="Author/Change controller:">
3392      IESG
3393    </t>
3394  </list>
3395</t>
3396</section>
3397</section>
3398
3399<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3400<t>
3401   The HTTP Transfer Coding Registry defines the name space for transfer
3402   coding names.
3403</t>
3404<t>
3405   Registrations &MUST; include the following fields:
3406   <list style="symbols">
3407     <t>Name</t>
3408     <t>Description</t>
3409     <t>Pointer to specification text</t>
3410   </list>
3411</t>
3412<t>
3413   Names of transfer codings &MUST-NOT; overlap with names of content codings
3414   (&content-codings;) unless the encoding transformation is identical, as
3415   is the case for the compression codings defined in
3416   <xref target="compression.codings"/>.
3417</t>
3418<t>
3419   Values to be added to this name space require IETF Review (see
3420   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3421   conform to the purpose of transfer coding defined in this section.
3422   Use of program names for the identification of encoding formats
3423   is not desirable and is discouraged for future encodings.
3424</t>
3425<t>
3426   The registry itself is maintained at
3427   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3428</t>
3429</section>
3430
3431<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3432<t>
3433   The HTTP Transfer Coding Registry shall be updated with the registrations
3434   below:
3435</t>
3436<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3437   <ttcol>Name</ttcol>
3438   <ttcol>Description</ttcol>
3439   <ttcol>Reference</ttcol>
3440   <c>chunked</c>
3441   <c>Transfer in a series of chunks</c>
3442   <c>
3443      <xref target="chunked.encoding"/>
3444   </c>
3445   <c>compress</c>
3446   <c>UNIX "compress" program method</c>
3447   <c>
3448      <xref target="compress.coding"/>
3449   </c>
3450   <c>deflate</c>
3451   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3452   the "zlib" data format (<xref target="RFC1950"/>)
3453   </c>
3454   <c>
3455      <xref target="deflate.coding"/>
3456   </c>
3457   <c>gzip</c>
3458   <c>Same as GNU zip <xref target="RFC1952"/></c>
3459   <c>
3460      <xref target="gzip.coding"/>
3461   </c>
3462</texttable>
3463</section>
3464
3465<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3466<t>
3467   The HTTP Upgrade Token Registry defines the name space for protocol-name
3468   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3469   field. Each registered protocol name is associated with contact information
3470   and an optional set of specifications that details how the connection
3471   will be processed after it has been upgraded.
3472</t>
3473<t>
3474   Registrations happen on a "First Come First Served" basis (see
3475   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3476   following rules:
3477  <list style="numbers">
3478    <t>A protocol-name token, once registered, stays registered forever.</t>
3479    <t>The registration &MUST; name a responsible party for the
3480       registration.</t>
3481    <t>The registration &MUST; name a point of contact.</t>
3482    <t>The registration &MAY; name a set of specifications associated with
3483       that token. Such specifications need not be publicly available.</t>
3484    <t>The registration &SHOULD; name a set of expected "protocol-version"
3485       tokens associated with that token at the time of registration.</t>
3486    <t>The responsible party &MAY; change the registration at any time.
3487       The IANA will keep a record of all such changes, and make them
3488       available upon request.</t>
3489    <t>The IESG &MAY; reassign responsibility for a protocol token.
3490       This will normally only be used in the case when a
3491       responsible party cannot be contacted.</t>
3492  </list>
3493</t>
3494<t>
3495   This registration procedure for HTTP Upgrade Tokens replaces that
3496   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3497</t>
3498</section>
3499
3500<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3501<t>
3502   The HTTP Upgrade Token Registry shall be updated with the registration
3503   below:
3504</t>
3505<texttable align="left" suppress-title="true">
3506   <ttcol>Value</ttcol>
3507   <ttcol>Description</ttcol>
3508   <ttcol>Expected Version Tokens</ttcol>
3509   <ttcol>Reference</ttcol>
3510
3511   <c>HTTP</c>
3512   <c>Hypertext Transfer Protocol</c>
3513   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3514   <c><xref target="http.version"/></c>
3515</texttable>
3516<t>
3517   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3518</t>
3519</section>
3520
3521</section>
3522
3523<section title="Security Considerations" anchor="security.considerations">
3524<t>
3525   This section is meant to inform application developers, information
3526   providers, and users of the security limitations in HTTP/1.1 as
3527   described by this document. The discussion does not include
3528   definitive solutions to the problems revealed, though it does make
3529   some suggestions for reducing security risks.
3530</t>
3531
3532<section title="Personal Information" anchor="personal.information">
3533<t>
3534   HTTP clients are often privy to large amounts of personal information,
3535   including both information provided by the user to interact with resources
3536   (e.g., the user's name, location, mail address, passwords, encryption
3537   keys, etc.) and information about the user's browsing activity over
3538   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3539   prevent unintentional leakage of this information.
3540</t>
3541</section>
3542
3543<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3544<t>
3545   A server is in the position to save personal data about a user's
3546   requests which might identify their reading patterns or subjects of
3547   interest.  In particular, log information gathered at an intermediary
3548   often contains a history of user agent interaction, across a multitude
3549   of sites, that can be traced to individual users.
3550</t>
3551<t>
3552   HTTP log information is confidential in nature; its handling is often
3553   constrained by laws and regulations.  Log information needs to be securely
3554   stored and appropriate guidelines followed for its analysis.
3555   Anonymization of personal information within individual entries helps,
3556   but is generally not sufficient to prevent real log traces from being
3557   re-identified based on correlation with other access characteristics.
3558   As such, access traces that are keyed to a specific client should not
3559   be published even if the key is pseudonymous.
3560</t>
3561<t>
3562   To minimize the risk of theft or accidental publication, log information
3563   should be purged of personally identifiable information, including
3564   user identifiers, IP addresses, and user-provided query parameters,
3565   as soon as that information is no longer necessary to support operational
3566   needs for security, auditing, or fraud control.
3567</t>
3568</section>
3569
3570<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3571<t>
3572   Origin servers &SHOULD; be careful to restrict
3573   the documents returned by HTTP requests to be only those that were
3574   intended by the server administrators. If an HTTP server translates
3575   HTTP URIs directly into file system calls, the server &MUST; take
3576   special care not to serve files that were not intended to be
3577   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3578   other operating systems use ".." as a path component to indicate a
3579   directory level above the current one. On such a system, an HTTP
3580   server &MUST; disallow any such construct in the request-target if it
3581   would otherwise allow access to a resource outside those intended to
3582   be accessible via the HTTP server. Similarly, files intended for
3583   reference only internally to the server (such as access control
3584   files, configuration files, and script code) &MUST; be protected from
3585   inappropriate retrieval, since they might contain sensitive
3586   information.
3587</t>
3588</section>
3589
3590<section title="DNS-related Attacks" anchor="dns.related.attacks">
3591<t>
3592   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3593   generally prone to security attacks based on the deliberate misassociation
3594   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3595   cautious in assuming the validity of an IP number/DNS name association unless
3596   the response is protected by DNSSec (<xref target="RFC4033"/>).
3597</t>
3598</section>
3599
3600<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3601<t>
3602   By their very nature, HTTP intermediaries are men-in-the-middle, and
3603   represent an opportunity for man-in-the-middle attacks. Compromise of
3604   the systems on which the intermediaries run can result in serious security
3605   and privacy problems. Intermediaries have access to security-related
3606   information, personal information about individual users and
3607   organizations, and proprietary information belonging to users and
3608   content providers. A compromised intermediary, or an intermediary
3609   implemented or configured without regard to security and privacy
3610   considerations, might be used in the commission of a wide range of
3611   potential attacks.
3612</t>
3613<t>
3614   Intermediaries that contain a shared cache are especially vulnerable
3615   to cache poisoning attacks.
3616</t>
3617<t>
3618   Implementers need to consider the privacy and security
3619   implications of their design and coding decisions, and of the
3620   configuration options they provide to operators (especially the
3621   default configuration).
3622</t>
3623<t>
3624   Users need to be aware that intermediaries are no more trustworthy than
3625   the people who run them; HTTP itself cannot solve this problem.
3626</t>
3627</section>
3628
3629<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3630<t>
3631   Because HTTP uses mostly textual, character-delimited fields, attackers can
3632   overflow buffers in implementations, and/or perform a Denial of Service
3633   against implementations that accept fields with unlimited lengths.
3634</t>
3635<t>
3636   To promote interoperability, this specification makes specific
3637   recommendations for minimum size limits on request-line
3638   (<xref target="request.line"/>)
3639   and blocks of header fields (<xref target="header.fields"/>). These are
3640   minimum recommendations, chosen to be supportable even by implementations
3641   with limited resources; it is expected that most implementations will
3642   choose substantially higher limits.
3643</t>
3644<t>
3645   This specification also provides a way for servers to reject messages that
3646   have request-targets that are too long (&status-414;) or request entities
3647   that are too large (&status-4xx;).
3648</t>
3649<t>
3650   Recipients &SHOULD; carefully limit the extent to which they read other
3651   fields, including (but not limited to) request methods, response status
3652   phrases, header field-names, and body chunks, so as to avoid denial of
3653   service attacks without impeding interoperability.
3654</t>
3655</section>
3656</section>
3657
3658<section title="Acknowledgments" anchor="acks">
3659<t>
3660   This edition of HTTP builds on the many contributions that went into
3661   <xref target="RFC1945" format="none">RFC 1945</xref>,
3662   <xref target="RFC2068" format="none">RFC 2068</xref>,
3663   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3664   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3665   substantial contributions made by the previous authors, editors, and
3666   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3667   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3668   Paul J. Leach, and Mark Nottingham.
3669   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3670   acknowledgements from prior revisions.
3671</t>
3672<t>
3673   Since 1999, the following contributors have helped improve the HTTP
3674   specification by reporting bugs, asking smart questions, drafting or
3675   reviewing text, and evaluating open issues:
3676</t>
3677<?BEGININC acks ?>
3678<t>Adam Barth,
3679Adam Roach,
3680Addison Phillips,
3681Adrian Chadd,
3682Adrien W. de Croy,
3683Alan Ford,
3684Alan Ruttenberg,
3685Albert Lunde,
3686Alek Storm,
3687Alex Rousskov,
3688Alexandre Morgaut,
3689Alexey Melnikov,
3690Alisha Smith,
3691Amichai Rothman,
3692Amit Klein,
3693Amos Jeffries,
3694Andreas Maier,
3695Andreas Petersson,
3696Anil Sharma,
3697Anne van Kesteren,
3698Anthony Bryan,
3699Asbjorn Ulsberg,
3700Balachander Krishnamurthy,
3701Barry Leiba,
3702Ben Laurie,
3703Benjamin Niven-Jenkins,
3704Bil Corry,
3705Bill Burke,
3706Bjoern Hoehrmann,
3707Bob Scheifler,
3708Boris Zbarsky,
3709Brett Slatkin,
3710Brian Kell,
3711Brian McBarron,
3712Brian Pane,
3713Brian Smith,
3714Bryce Nesbitt,
3715Cameron Heavon-Jones,
3716Carl Kugler,
3717Carsten Bormann,
3718Charles Fry,
3719Chris Newman,
3720Cyrus Daboo,
3721Dale Robert Anderson,
3722Dan Wing,
3723Dan Winship,
3724Daniel Stenberg,
3725Dave Cridland,
3726Dave Crocker,
3727Dave Kristol,
3728David Booth,
3729David Singer,
3730David W. Morris,
3731Diwakar Shetty,
3732Dmitry Kurochkin,
3733Drummond Reed,
3734Duane Wessels,
3735Edward Lee,
3736Eliot Lear,
3737Eran Hammer-Lahav,
3738Eric D. Williams,
3739Eric J. Bowman,
3740Eric Lawrence,
3741Eric Rescorla,
3742Erik Aronesty,
3743Evan Prodromou,
3744Florian Weimer,
3745Frank Ellermann,
3746Fred Bohle,
3747Gabriel Montenegro,
3748Geoffrey Sneddon,
3749Gervase Markham,
3750Grahame Grieve,
3751Greg Wilkins,
3752Harald Tveit Alvestrand,
3753Harry Halpin,
3754Helge Hess,
3755Henrik Nordstrom,
3756Henry S. Thompson,
3757Henry Story,
3758Herbert van de Sompel,
3759Howard Melman,
3760Hugo Haas,
3761Ian Fette,
3762Ian Hickson,
3763Ido Safruti,
3764Ingo Struck,
3765J. Ross Nicoll,
3766James H. Manger,
3767James Lacey,
3768James M. Snell,
3769Jamie Lokier,
3770Jan Algermissen,
3771Jeff Hodges (who came up with the term 'effective Request-URI'),
3772Jeff Walden,
3773Jim Luther,
3774Joe D. Williams,
3775Joe Gregorio,
3776Joe Orton,
3777John C. Klensin,
3778John C. Mallery,
3779John Cowan,
3780John Kemp,
3781John Panzer,
3782John Schneider,
3783John Stracke,
3784John Sullivan,
3785Jonas Sicking,
3786Jonathan Billington,
3787Jonathan Moore,
3788Jonathan Rees,
3789Jonathan Silvera,
3790Jordi Ros,
3791Joris Dobbelsteen,
3792Josh Cohen,
3793Julien Pierre,
3794Jungshik Shin,
3795Justin Chapweske,
3796Justin Erenkrantz,
3797Justin James,
3798Kalvinder Singh,
3799Karl Dubost,
3800Keith Hoffman,
3801Keith Moore,
3802Koen Holtman,
3803Konstantin Voronkov,
3804Kris Zyp,
3805Lisa Dusseault,
3806Maciej Stachowiak,
3807Marc Schneider,
3808Marc Slemko,
3809Mark Baker,
3810Mark Pauley,
3811Mark Watson,
3812Markus Isomaki,
3813Markus Lanthaler,
3814Martin J. Duerst,
3815Martin Musatov,
3816Martin Nilsson,
3817Martin Thomson,
3818Matt Lynch,
3819Matthew Cox,
3820Max Clark,
3821Michael Burrows,
3822Michael Hausenblas,
3823Mike Amundsen,
3824Mike Belshe,
3825Mike Kelly,
3826Mike Schinkel,
3827Miles Sabin,
3828Murray S. Kucherawy,
3829Mykyta Yevstifeyev,
3830Nathan Rixham,
3831Nicholas Shanks,
3832Nico Williams,
3833Nicolas Alvarez,
3834Nicolas Mailhot,
3835Noah Slater,
3836Pablo Castro,
3837Pat Hayes,
3838Patrick R. McManus,
3839Paul E. Jones,
3840Paul Hoffman,
3841Paul Marquess,
3842Peter Lepeska,
3843Peter Saint-Andre,
3844Peter Watkins,
3845Phil Archer,
3846Philippe Mougin,
3847Phillip Hallam-Baker,
3848Poul-Henning Kamp,
3849Preethi Natarajan,
3850Rajeev Bector,
3851Ray Polk,
3852Reto Bachmann-Gmuer,
3853Richard Cyganiak,
3854Robert Brewer,
3855Robert Collins,
3856Robert O'Callahan,
3857Robert Olofsson,
3858Robert Sayre,
3859Robert Siemer,
3860Robert de Wilde,
3861Roberto Javier Godoy,
3862Roberto Peon,
3863Ronny Widjaja,
3864S. Mike Dierken,
3865Salvatore Loreto,
3866Sam Johnston,
3867Sam Ruby,
3868Scott Lawrence (who maintained the original issues list),
3869Sean B. Palmer,
3870Shane McCarron,
3871Stefan Eissing,
3872Stefan Tilkov,
3873Stefanos Harhalakis,
3874Stephane Bortzmeyer,
3875Stephen Farrell,
3876Stephen Ludin,
3877Stuart Williams,
3878Subbu Allamaraju,
3879Sylvain Hellegouarch,
3880Tapan Divekar,
3881Tatsuya Hayashi,
3882Ted Hardie,
3883Thomas Broyer,
3884Thomas Nordin,
3885Thomas Roessler,
3886Tim Bray,
3887Tim Morgan,
3888Tim Olsen,
3889Tom Zhou,
3890Travis Snoozy,
3891Tyler Close,
3892Vincent Murphy,
3893Wenbo Zhu,
3894Werner Baumann,
3895Wilbur Streett,
3896Wilfredo Sanchez Vega,
3897William A. Rowe Jr.,
3898William Chan,
3899Willy Tarreau,
3900Xiaoshu Wang,
3901Yaron Goland,
3902Yngve Nysaeter Pettersen,
3903Yoav Nir,
3904Yogesh Bang,
3905Yutaka Oiwa,
3906Zed A. Shaw, and
3907Zhong Yu.
3908</t>
3909<?ENDINC acks ?>
3910</section>
3911
3912</middle>
3913<back>
3914
3915<references title="Normative References">
3916
3917<reference anchor="Part2">
3918  <front>
3919    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3920    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3921      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3922      <address><email>fielding@gbiv.com</email></address>
3923    </author>
3924    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3925      <organization abbrev="W3C">World Wide Web Consortium</organization>
3926      <address><email>ylafon@w3.org</email></address>
3927    </author>
3928    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3929      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3930      <address><email>julian.reschke@greenbytes.de</email></address>
3931    </author>
3932    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3933  </front>
3934  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3935  <x:source href="p2-semantics.xml" basename="p2-semantics">
3936    <x:defines>1xx (Informational)</x:defines>
3937    <x:defines>1xx</x:defines>
3938    <x:defines>100 (Continue)</x:defines>
3939    <x:defines>101 (Switching Protocols)</x:defines>
3940    <x:defines>2xx (Successful)</x:defines>
3941    <x:defines>2xx</x:defines>
3942    <x:defines>200 (OK)</x:defines>
3943    <x:defines>204 (No Content)</x:defines>
3944    <x:defines>3xx (Redirection)</x:defines>
3945    <x:defines>3xx</x:defines>
3946    <x:defines>301 (Moved Permanently)</x:defines>
3947    <x:defines>4xx (Client Error)</x:defines>
3948    <x:defines>4xx</x:defines>
3949    <x:defines>400 (Bad Request)</x:defines>
3950    <x:defines>405 (Method Not Allowed)</x:defines>
3951    <x:defines>411 (Length Required)</x:defines>
3952    <x:defines>414 (URI Too Long)</x:defines>
3953    <x:defines>417 (Expectation Failed)</x:defines>
3954    <x:defines>426 (Upgrade Required)</x:defines>
3955    <x:defines>501 (Not Implemented)</x:defines>
3956    <x:defines>502 (Bad Gateway)</x:defines>
3957    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3958    <x:defines>Allow</x:defines>
3959    <x:defines>Content-Encoding</x:defines>
3960    <x:defines>Content-Location</x:defines>
3961    <x:defines>Content-Type</x:defines>
3962    <x:defines>Date</x:defines>
3963    <x:defines>Expect</x:defines>
3964    <x:defines>Location</x:defines>
3965    <x:defines>Server</x:defines>
3966    <x:defines>User-Agent</x:defines>
3967  </x:source>
3968</reference>
3969
3970<reference anchor="Part4">
3971  <front>
3972    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3973    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3974      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3975      <address><email>fielding@gbiv.com</email></address>
3976    </author>
3977    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3978      <organization abbrev="W3C">World Wide Web Consortium</organization>
3979      <address><email>ylafon@w3.org</email></address>
3980    </author>
3981    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3982      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3983      <address><email>julian.reschke@greenbytes.de</email></address>
3984    </author>
3985    <date month="&ID-MONTH;" year="&ID-YEAR;" />
3986  </front>
3987  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
3988  <x:source basename="p4-conditional" href="p4-conditional.xml">
3989    <x:defines>304 (Not Modified)</x:defines>
3990    <x:defines>ETag</x:defines>
3991    <x:defines>Last-Modified</x:defines>
3992  </x:source>
3993</reference>
3994
3995<reference anchor="Part5">
3996  <front>
3997    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
3998    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3999      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4000      <address><email>fielding@gbiv.com</email></address>
4001    </author>
4002    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4003      <organization abbrev="W3C">World Wide Web Consortium</organization>
4004      <address><email>ylafon@w3.org</email></address>
4005    </author>
4006    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4007      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4008      <address><email>julian.reschke@greenbytes.de</email></address>
4009    </author>
4010    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4011  </front>
4012  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4013  <x:source href="p5-range.xml" basename="p5-range">
4014    <x:defines>Content-Range</x:defines>
4015  </x:source>
4016</reference>
4017
4018<reference anchor="Part6">
4019  <front>
4020    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4021    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4022      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4023      <address><email>fielding@gbiv.com</email></address>
4024    </author>
4025    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4026      <organization abbrev="W3C">World Wide Web Consortium</organization>
4027      <address><email>ylafon@w3.org</email></address>
4028    </author>
4029    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4030      <address><email>mnot@mnot.net</email></address>
4031    </author>
4032    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4033      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4034      <address><email>julian.reschke@greenbytes.de</email></address>
4035    </author>
4036    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4037  </front>
4038  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4039  <x:source href="p6-cache.xml" basename="p6-cache">
4040    <x:defines>Expires</x:defines>
4041  </x:source>
4042</reference>
4043
4044<reference anchor="Part7">
4045  <front>
4046    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4047    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4048      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4049      <address><email>fielding@gbiv.com</email></address>
4050    </author>
4051    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4052      <organization abbrev="W3C">World Wide Web Consortium</organization>
4053      <address><email>ylafon@w3.org</email></address>
4054    </author>
4055    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4056      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4057      <address><email>julian.reschke@greenbytes.de</email></address>
4058    </author>
4059    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4060  </front>
4061  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4062  <x:source href="p7-auth.xml" basename="p7-auth">
4063    <x:defines>Proxy-Authenticate</x:defines>
4064    <x:defines>Proxy-Authorization</x:defines>
4065  </x:source>
4066</reference>
4067
4068<reference anchor="RFC5234">
4069  <front>
4070    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4071    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4072      <organization>Brandenburg InternetWorking</organization>
4073      <address>
4074        <email>dcrocker@bbiw.net</email>
4075      </address> 
4076    </author>
4077    <author initials="P." surname="Overell" fullname="Paul Overell">
4078      <organization>THUS plc.</organization>
4079      <address>
4080        <email>paul.overell@thus.net</email>
4081      </address>
4082    </author>
4083    <date month="January" year="2008"/>
4084  </front>
4085  <seriesInfo name="STD" value="68"/>
4086  <seriesInfo name="RFC" value="5234"/>
4087</reference>
4088
4089<reference anchor="RFC2119">
4090  <front>
4091    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4092    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4093      <organization>Harvard University</organization>
4094      <address><email>sob@harvard.edu</email></address>
4095    </author>
4096    <date month="March" year="1997"/>
4097  </front>
4098  <seriesInfo name="BCP" value="14"/>
4099  <seriesInfo name="RFC" value="2119"/>
4100</reference>
4101
4102<reference anchor="RFC3986">
4103 <front>
4104  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4105  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4106    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4107    <address>
4108       <email>timbl@w3.org</email>
4109       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4110    </address>
4111  </author>
4112  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4113    <organization abbrev="Day Software">Day Software</organization>
4114    <address>
4115      <email>fielding@gbiv.com</email>
4116      <uri>http://roy.gbiv.com/</uri>
4117    </address>
4118  </author>
4119  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4120    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4121    <address>
4122      <email>LMM@acm.org</email>
4123      <uri>http://larry.masinter.net/</uri>
4124    </address>
4125  </author>
4126  <date month='January' year='2005'></date>
4127 </front>
4128 <seriesInfo name="STD" value="66"/>
4129 <seriesInfo name="RFC" value="3986"/>
4130</reference>
4131
4132<reference anchor="USASCII">
4133  <front>
4134    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4135    <author>
4136      <organization>American National Standards Institute</organization>
4137    </author>
4138    <date year="1986"/>
4139  </front>
4140  <seriesInfo name="ANSI" value="X3.4"/>
4141</reference>
4142
4143<reference anchor="RFC1950">
4144  <front>
4145    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4146    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4147      <organization>Aladdin Enterprises</organization>
4148      <address><email>ghost@aladdin.com</email></address>
4149    </author>
4150    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4151    <date month="May" year="1996"/>
4152  </front>
4153  <seriesInfo name="RFC" value="1950"/>
4154  <!--<annotation>
4155    RFC 1950 is an Informational RFC, thus it might be less stable than
4156    this specification. On the other hand, this downward reference was
4157    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4158    therefore it is unlikely to cause problems in practice. See also
4159    <xref target="BCP97"/>.
4160  </annotation>-->
4161</reference>
4162
4163<reference anchor="RFC1951">
4164  <front>
4165    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4166    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4167      <organization>Aladdin Enterprises</organization>
4168      <address><email>ghost@aladdin.com</email></address>
4169    </author>
4170    <date month="May" year="1996"/>
4171  </front>
4172  <seriesInfo name="RFC" value="1951"/>
4173  <!--<annotation>
4174    RFC 1951 is an Informational RFC, thus it might be less stable than
4175    this specification. On the other hand, this downward reference was
4176    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4177    therefore it is unlikely to cause problems in practice. See also
4178    <xref target="BCP97"/>.
4179  </annotation>-->
4180</reference>
4181
4182<reference anchor="RFC1952">
4183  <front>
4184    <title>GZIP file format specification version 4.3</title>
4185    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4186      <organization>Aladdin Enterprises</organization>
4187      <address><email>ghost@aladdin.com</email></address>
4188    </author>
4189    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4190      <address><email>gzip@prep.ai.mit.edu</email></address>
4191    </author>
4192    <author initials="M." surname="Adler" fullname="Mark Adler">
4193      <address><email>madler@alumni.caltech.edu</email></address>
4194    </author>
4195    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4196      <address><email>ghost@aladdin.com</email></address>
4197    </author>
4198    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4199      <address><email>randeg@alumni.rpi.edu</email></address>
4200    </author>
4201    <date month="May" year="1996"/>
4202  </front>
4203  <seriesInfo name="RFC" value="1952"/>
4204  <!--<annotation>
4205    RFC 1952 is an Informational RFC, thus it might be less stable than
4206    this specification. On the other hand, this downward reference was
4207    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4208    therefore it is unlikely to cause problems in practice. See also
4209    <xref target="BCP97"/>.
4210  </annotation>-->
4211</reference>
4212
4213</references>
4214
4215<references title="Informative References">
4216
4217<reference anchor="ISO-8859-1">
4218  <front>
4219    <title>
4220     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4221    </title>
4222    <author>
4223      <organization>International Organization for Standardization</organization>
4224    </author>
4225    <date year="1998"/>
4226  </front>
4227  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4228</reference>
4229
4230<reference anchor='RFC1919'>
4231  <front>
4232    <title>Classical versus Transparent IP Proxies</title>
4233    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4234      <address><email>mchatel@pax.eunet.ch</email></address>
4235    </author>
4236    <date year='1996' month='March' />
4237  </front>
4238  <seriesInfo name='RFC' value='1919' />
4239</reference>
4240
4241<reference anchor="RFC1945">
4242  <front>
4243    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4244    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4245      <organization>MIT, Laboratory for Computer Science</organization>
4246      <address><email>timbl@w3.org</email></address>
4247    </author>
4248    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4249      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4250      <address><email>fielding@ics.uci.edu</email></address>
4251    </author>
4252    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4253      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4254      <address><email>frystyk@w3.org</email></address>
4255    </author>
4256    <date month="May" year="1996"/>
4257  </front>
4258  <seriesInfo name="RFC" value="1945"/>
4259</reference>
4260
4261<reference anchor="RFC2045">
4262  <front>
4263    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4264    <author initials="N." surname="Freed" fullname="Ned Freed">
4265      <organization>Innosoft International, Inc.</organization>
4266      <address><email>ned@innosoft.com</email></address>
4267    </author>
4268    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4269      <organization>First Virtual Holdings</organization>
4270      <address><email>nsb@nsb.fv.com</email></address>
4271    </author>
4272    <date month="November" year="1996"/>
4273  </front>
4274  <seriesInfo name="RFC" value="2045"/>
4275</reference>
4276
4277<reference anchor="RFC2047">
4278  <front>
4279    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4280    <author initials="K." surname="Moore" fullname="Keith Moore">
4281      <organization>University of Tennessee</organization>
4282      <address><email>moore@cs.utk.edu</email></address>
4283    </author>
4284    <date month="November" year="1996"/>
4285  </front>
4286  <seriesInfo name="RFC" value="2047"/>
4287</reference>
4288
4289<reference anchor="RFC2068">
4290  <front>
4291    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4292    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4293      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4294      <address><email>fielding@ics.uci.edu</email></address>
4295    </author>
4296    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4297      <organization>MIT Laboratory for Computer Science</organization>
4298      <address><email>jg@w3.org</email></address>
4299    </author>
4300    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4301      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4302      <address><email>mogul@wrl.dec.com</email></address>
4303    </author>
4304    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4305      <organization>MIT Laboratory for Computer Science</organization>
4306      <address><email>frystyk@w3.org</email></address>
4307    </author>
4308    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4309      <organization>MIT Laboratory for Computer Science</organization>
4310      <address><email>timbl@w3.org</email></address>
4311    </author>
4312    <date month="January" year="1997"/>
4313  </front>
4314  <seriesInfo name="RFC" value="2068"/>
4315</reference>
4316
4317<reference anchor="RFC2145">
4318  <front>
4319    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4320    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4321      <organization>Western Research Laboratory</organization>
4322      <address><email>mogul@wrl.dec.com</email></address>
4323    </author>
4324    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4325      <organization>Department of Information and Computer Science</organization>
4326      <address><email>fielding@ics.uci.edu</email></address>
4327    </author>
4328    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4329      <organization>MIT Laboratory for Computer Science</organization>
4330      <address><email>jg@w3.org</email></address>
4331    </author>
4332    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4333      <organization>W3 Consortium</organization>
4334      <address><email>frystyk@w3.org</email></address>
4335    </author>
4336    <date month="May" year="1997"/>
4337  </front>
4338  <seriesInfo name="RFC" value="2145"/>
4339</reference>
4340
4341<reference anchor="RFC2616">
4342  <front>
4343    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4344    <author initials="R." surname="Fielding" fullname="R. Fielding">
4345      <organization>University of California, Irvine</organization>
4346      <address><email>fielding@ics.uci.edu</email></address>
4347    </author>
4348    <author initials="J." surname="Gettys" fullname="J. Gettys">
4349      <organization>W3C</organization>
4350      <address><email>jg@w3.org</email></address>
4351    </author>
4352    <author initials="J." surname="Mogul" fullname="J. Mogul">
4353      <organization>Compaq Computer Corporation</organization>
4354      <address><email>mogul@wrl.dec.com</email></address>
4355    </author>
4356    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4357      <organization>MIT Laboratory for Computer Science</organization>
4358      <address><email>frystyk@w3.org</email></address>
4359    </author>
4360    <author initials="L." surname="Masinter" fullname="L. Masinter">
4361      <organization>Xerox Corporation</organization>
4362      <address><email>masinter@parc.xerox.com</email></address>
4363    </author>
4364    <author initials="P." surname="Leach" fullname="P. Leach">
4365      <organization>Microsoft Corporation</organization>
4366      <address><email>paulle@microsoft.com</email></address>
4367    </author>
4368    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4369      <organization>W3C</organization>
4370      <address><email>timbl@w3.org</email></address>
4371    </author>
4372    <date month="June" year="1999"/>
4373  </front>
4374  <seriesInfo name="RFC" value="2616"/>
4375</reference>
4376
4377<reference anchor='RFC2817'>
4378  <front>
4379    <title>Upgrading to TLS Within HTTP/1.1</title>
4380    <author initials='R.' surname='Khare' fullname='R. Khare'>
4381      <organization>4K Associates / UC Irvine</organization>
4382      <address><email>rohit@4K-associates.com</email></address>
4383    </author>
4384    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4385      <organization>Agranat Systems, Inc.</organization>
4386      <address><email>lawrence@agranat.com</email></address>
4387    </author>
4388    <date year='2000' month='May' />
4389  </front>
4390  <seriesInfo name='RFC' value='2817' />
4391</reference>
4392
4393<reference anchor='RFC2818'>
4394  <front>
4395    <title>HTTP Over TLS</title>
4396    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4397      <organization>RTFM, Inc.</organization>
4398      <address><email>ekr@rtfm.com</email></address>
4399    </author>
4400    <date year='2000' month='May' />
4401  </front>
4402  <seriesInfo name='RFC' value='2818' />
4403</reference>
4404
4405<reference anchor='RFC2965'>
4406  <front>
4407    <title>HTTP State Management Mechanism</title>
4408    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4409      <organization>Bell Laboratories, Lucent Technologies</organization>
4410      <address><email>dmk@bell-labs.com</email></address>
4411    </author>
4412    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4413      <organization>Epinions.com, Inc.</organization>
4414      <address><email>lou@montulli.org</email></address>
4415    </author>
4416    <date year='2000' month='October' />
4417  </front>
4418  <seriesInfo name='RFC' value='2965' />
4419</reference>
4420
4421<reference anchor='RFC3040'>
4422  <front>
4423    <title>Internet Web Replication and Caching Taxonomy</title>
4424    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4425      <organization>Equinix, Inc.</organization>
4426    </author>
4427    <author initials='I.' surname='Melve' fullname='I. Melve'>
4428      <organization>UNINETT</organization>
4429    </author>
4430    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4431      <organization>CacheFlow Inc.</organization>
4432    </author>
4433    <date year='2001' month='January' />
4434  </front>
4435  <seriesInfo name='RFC' value='3040' />
4436</reference>
4437
4438<reference anchor='RFC3864'>
4439  <front>
4440    <title>Registration Procedures for Message Header Fields</title>
4441    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4442      <organization>Nine by Nine</organization>
4443      <address><email>GK-IETF@ninebynine.org</email></address>
4444    </author>
4445    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4446      <organization>BEA Systems</organization>
4447      <address><email>mnot@pobox.com</email></address>
4448    </author>
4449    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4450      <organization>HP Labs</organization>
4451      <address><email>JeffMogul@acm.org</email></address>
4452    </author>
4453    <date year='2004' month='September' />
4454  </front>
4455  <seriesInfo name='BCP' value='90' />
4456  <seriesInfo name='RFC' value='3864' />
4457</reference>
4458
4459<reference anchor='RFC4033'>
4460  <front>
4461    <title>DNS Security Introduction and Requirements</title>
4462    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4463    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4464    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4465    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4466    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4467    <date year='2005' month='March' />
4468  </front>
4469  <seriesInfo name='RFC' value='4033' />
4470</reference>
4471
4472<reference anchor="RFC4288">
4473  <front>
4474    <title>Media Type Specifications and Registration Procedures</title>
4475    <author initials="N." surname="Freed" fullname="N. Freed">
4476      <organization>Sun Microsystems</organization>
4477      <address>
4478        <email>ned.freed@mrochek.com</email>
4479      </address>
4480    </author>
4481    <author initials="J." surname="Klensin" fullname="J. Klensin">
4482      <address>
4483        <email>klensin+ietf@jck.com</email>
4484      </address>
4485    </author>
4486    <date year="2005" month="December"/>
4487  </front>
4488  <seriesInfo name="BCP" value="13"/>
4489  <seriesInfo name="RFC" value="4288"/>
4490</reference>
4491
4492<reference anchor='RFC4395'>
4493  <front>
4494    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4495    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4496      <organization>AT&amp;T Laboratories</organization>
4497      <address>
4498        <email>tony+urireg@maillennium.att.com</email>
4499      </address>
4500    </author>
4501    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4502      <organization>Qualcomm, Inc.</organization>
4503      <address>
4504        <email>hardie@qualcomm.com</email>
4505      </address>
4506    </author>
4507    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4508      <organization>Adobe Systems</organization>
4509      <address>
4510        <email>LMM@acm.org</email>
4511      </address>
4512    </author>
4513    <date year='2006' month='February' />
4514  </front>
4515  <seriesInfo name='BCP' value='115' />
4516  <seriesInfo name='RFC' value='4395' />
4517</reference>
4518
4519<reference anchor='RFC4559'>
4520  <front>
4521    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4522    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4523    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4524    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4525    <date year='2006' month='June' />
4526  </front>
4527  <seriesInfo name='RFC' value='4559' />
4528</reference>
4529
4530<reference anchor='RFC5226'>
4531  <front>
4532    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4533    <author initials='T.' surname='Narten' fullname='T. Narten'>
4534      <organization>IBM</organization>
4535      <address><email>narten@us.ibm.com</email></address>
4536    </author>
4537    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4538      <organization>Google</organization>
4539      <address><email>Harald@Alvestrand.no</email></address>
4540    </author>
4541    <date year='2008' month='May' />
4542  </front>
4543  <seriesInfo name='BCP' value='26' />
4544  <seriesInfo name='RFC' value='5226' />
4545</reference>
4546
4547<reference anchor='RFC5246'>
4548   <front>
4549      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4550      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4551         <organization />
4552      </author>
4553      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4554         <organization>RTFM, Inc.</organization>
4555      </author>
4556      <date year='2008' month='August' />
4557   </front>
4558   <seriesInfo name='RFC' value='5246' />
4559</reference>
4560
4561<reference anchor="RFC5322">
4562  <front>
4563    <title>Internet Message Format</title>
4564    <author initials="P." surname="Resnick" fullname="P. Resnick">
4565      <organization>Qualcomm Incorporated</organization>
4566    </author>
4567    <date year="2008" month="October"/>
4568  </front> 
4569  <seriesInfo name="RFC" value="5322"/>
4570</reference>
4571
4572<reference anchor="RFC6265">
4573  <front>
4574    <title>HTTP State Management Mechanism</title>
4575    <author initials="A." surname="Barth" fullname="Adam Barth">
4576      <organization abbrev="U.C. Berkeley">
4577        University of California, Berkeley
4578      </organization>
4579      <address><email>abarth@eecs.berkeley.edu</email></address>
4580    </author>
4581    <date year="2011" month="April" />
4582  </front>
4583  <seriesInfo name="RFC" value="6265"/>
4584</reference>
4585
4586<!--<reference anchor='BCP97'>
4587  <front>
4588    <title>Handling Normative References to Standards-Track Documents</title>
4589    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4590      <address>
4591        <email>klensin+ietf@jck.com</email>
4592      </address>
4593    </author>
4594    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4595      <organization>MIT</organization>
4596      <address>
4597        <email>hartmans-ietf@mit.edu</email>
4598      </address>
4599    </author>
4600    <date year='2007' month='June' />
4601  </front>
4602  <seriesInfo name='BCP' value='97' />
4603  <seriesInfo name='RFC' value='4897' />
4604</reference>-->
4605
4606<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4607  <front>
4608    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4609    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4610    <date year="2001" month="November"/>
4611  </front>
4612  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4613</reference>
4614
4615</references>
4616
4617
4618<section title="HTTP Version History" anchor="compatibility">
4619<t>
4620   HTTP has been in use by the World-Wide Web global information initiative
4621   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4622   was a simple protocol for hypertext data transfer across the Internet
4623   with only a single request method (GET) and no metadata.
4624   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4625   methods and MIME-like messaging that could include metadata about the data
4626   transferred and modifiers on the request/response semantics. However,
4627   HTTP/1.0 did not sufficiently take into consideration the effects of
4628   hierarchical proxies, caching, the need for persistent connections, or
4629   name-based virtual hosts. The proliferation of incompletely-implemented
4630   applications calling themselves "HTTP/1.0" further necessitated a
4631   protocol version change in order for two communicating applications
4632   to determine each other's true capabilities.
4633</t>
4634<t>
4635   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4636   requirements that enable reliable implementations, adding only
4637   those new features that will either be safely ignored by an HTTP/1.0
4638   recipient or only sent when communicating with a party advertising
4639   conformance with HTTP/1.1.
4640</t>
4641<t>
4642   It is beyond the scope of a protocol specification to mandate
4643   conformance with previous versions. HTTP/1.1 was deliberately
4644   designed, however, to make supporting previous versions easy.
4645   We would expect a general-purpose HTTP/1.1 server to understand
4646   any valid request in the format of HTTP/1.0 and respond appropriately
4647   with an HTTP/1.1 message that only uses features understood (or
4648   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4649   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4650</t>
4651<t>
4652   Since HTTP/0.9 did not support header fields in a request,
4653   there is no mechanism for it to support name-based virtual
4654   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4655   field).  Any server that implements name-based virtual hosts
4656   ought to disable support for HTTP/0.9.  Most requests that
4657   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4658   requests wherein a buggy client failed to properly encode
4659   linear whitespace found in a URI reference and placed in
4660   the request-target.
4661</t>
4662
4663<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4664<t>
4665   This section summarizes major differences between versions HTTP/1.0
4666   and HTTP/1.1.
4667</t>
4668
4669<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4670<t>
4671   The requirements that clients and servers support the <x:ref>Host</x:ref>
4672   header field (<xref target="header.host"/>), report an error if it is
4673   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4674   are among the most important changes defined by HTTP/1.1.
4675</t>
4676<t>
4677   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4678   addresses and servers; there was no other established mechanism for
4679   distinguishing the intended server of a request than the IP address
4680   to which that request was directed. The <x:ref>Host</x:ref> header field was
4681   introduced during the development of HTTP/1.1 and, though it was
4682   quickly implemented by most HTTP/1.0 browsers, additional requirements
4683   were placed on all HTTP/1.1 requests in order to ensure complete
4684   adoption.  At the time of this writing, most HTTP-based services
4685   are dependent upon the Host header field for targeting requests.
4686</t>
4687</section>
4688
4689<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4690<t>
4691   In HTTP/1.0, each connection is established by the client prior to the
4692   request and closed by the server after sending the response. However, some
4693   implementations implement the explicitly negotiated ("Keep-Alive") version
4694   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4695   target="RFC2068"/>.
4696</t>
4697<t>
4698   Some clients and servers might wish to be compatible with these previous
4699   approaches to persistent connections, by explicitly negotiating for them
4700   with a "Connection: keep-alive" request header field. However, some
4701   experimental implementations of HTTP/1.0 persistent connections are faulty;
4702   for example, if a HTTP/1.0 proxy server doesn't understand
4703   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4704   to the next inbound server, which would result in a hung connection.
4705</t>
4706<t>
4707   One attempted solution was the introduction of a Proxy-Connection header
4708   field, targeted specifically at proxies. In practice, this was also
4709   unworkable, because proxies are often deployed in multiple layers, bringing
4710   about the same problem discussed above.
4711</t>
4712<t>
4713   As a result, clients are encouraged not to send the Proxy-Connection header
4714   field in any requests.
4715</t>
4716<t>
4717   Clients are also encouraged to consider the use of Connection: keep-alive
4718   in requests carefully; while they can enable persistent connections with
4719   HTTP/1.0 servers, clients using them need will need to monitor the
4720   connection for "hung" requests (which indicate that the client ought stop
4721   sending the header field), and this mechanism ought not be used by clients
4722   at all when a proxy is being used.
4723</t>
4724</section>
4725
4726<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4727<t>
4728   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4729   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4730   any transfer-coding prior to forwarding a message via a MIME-compliant
4731   protocol.
4732</t>
4733</section>
4734
4735</section>
4736
4737<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4738<t>
4739  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4740  sensitive. Restrict the version numbers to be single digits due to the fact
4741  that implementations are known to handle multi-digit version numbers
4742  incorrectly.
4743  (<xref target="http.version"/>)
4744</t>
4745<t>
4746  Require that invalid whitespace around field-names be rejected.
4747  Change ABNF productions for header fields to only define the field value.
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  Require recipients to handle bogus "<x:ref>Content-Length</x:ref>" header
4765  fields as errors.
4766  (<xref target="message.body"/>)
4767</t>
4768<t>
4769  Remove reference to non-existent identity transfer-coding value tokens.
4770  (Sections <xref format="counter" target="message.body"/> and
4771  <xref format="counter" target="transfer.codings"/>)
4772</t>
4773<t>
4774  Clarification that the chunk length does not include the count of the octets
4775  in the chunk header and trailer. Furthermore disallowed line folding
4776  in chunk extensions, and deprecate their use.
4777  (<xref target="chunked.encoding"/>)
4778</t>
4779<t>
4780  Update use of abs_path production from RFC 1808 to the path-absolute + query
4781  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4782  request method only.
4783  (<xref target="request-target"/>)
4784</t>
4785<t>
4786  Clarify exactly when "close" connection options have to be sent; drop
4787  notion of header fields being "hop-by-hop" without being listed in the
4788  Connection header field.
4789  (<xref target="header.connection"/>)
4790</t>
4791<t>
4792  Remove hard limit of two connections per server.
4793  Remove requirement to retry a sequence of requests as long it was idempotent.
4794  Remove requirements about when servers are allowed to close connections
4795  prematurely.
4796  (<xref target="persistent.connections"/>)
4797</t>
4798<t>
4799  Remove requirement to retry requests under certain circumstances when the
4800  server prematurely closes the connection.
4801  (<xref target="persistent.reuse"/>)
4802</t>
4803<t>
4804  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4805  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4806  (<xref target="header.upgrade"/>)
4807</t>
4808<t>
4809  Registration of Transfer Codings now requires IETF Review
4810  (<xref target="transfer.coding.registry"/>)
4811</t>
4812<t>
4813  Take over the Upgrade Token Registry, previously defined in
4814  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4815  (<xref target="upgrade.token.registry"/>)
4816</t>
4817<t>
4818  Empty list elements in list productions have been deprecated.
4819  (<xref target="abnf.extension"/>)
4820</t>
4821</section>
4822</section>
4823
4824<section title="ABNF list extension: #rule" anchor="abnf.extension">
4825<t>
4826  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4827  improve readability in the definitions of some header field values.
4828</t>
4829<t>
4830  A construct "#" is defined, similar to "*", for defining comma-delimited
4831  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4832  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4833  comma (",") and optional whitespace (OWS).   
4834</t>
4835<figure><preamble>
4836  Thus,
4837</preamble><artwork type="example">
4838  1#element =&gt; element *( OWS "," OWS element )
4839</artwork></figure>
4840<figure><preamble>
4841  and:
4842</preamble><artwork type="example">
4843  #element =&gt; [ 1#element ]
4844</artwork></figure>
4845<figure><preamble>
4846  and for n &gt;= 1 and m &gt; 1:
4847</preamble><artwork type="example">
4848  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4849</artwork></figure>
4850<t>
4851  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4852  list elements. In other words, consumers would follow the list productions:
4853</t>
4854<figure><artwork type="example">
4855  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4856 
4857  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4858</artwork></figure>
4859<t>
4860  Note that empty elements do not contribute to the count of elements present,
4861  though.
4862</t>
4863<t>
4864  For example, given these ABNF productions:
4865</t>
4866<figure><artwork type="example">
4867  example-list      = 1#example-list-elmt
4868  example-list-elmt = token ; see <xref target="field.components"/> 
4869</artwork></figure>
4870<t>
4871  Then these are valid values for example-list (not including the double
4872  quotes, which are present for delimitation only):
4873</t>
4874<figure><artwork type="example">
4875  "foo,bar"
4876  "foo ,bar,"
4877  "foo , ,bar,charlie   "
4878</artwork></figure>
4879<t>
4880  But these values would be invalid, as at least one non-empty element is
4881  required:
4882</t>
4883<figure><artwork type="example">
4884  ""
4885  ","
4886  ",   ,"
4887</artwork></figure>
4888<t>
4889  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4890  expanded as explained above.
4891</t>
4892</section>
4893
4894<?BEGININC p1-messaging.abnf-appendix ?>
4895<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4896<figure>
4897<artwork type="abnf" name="p1-messaging.parsed-abnf">
4898<x:ref>BWS</x:ref> = OWS
4899
4900<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4901 connection-option ] )
4902<x:ref>Content-Length</x:ref> = 1*DIGIT
4903
4904<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4905 ]
4906<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4907<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4908<x:ref>Host</x:ref> = uri-host [ ":" port ]
4909
4910<x:ref>OWS</x:ref> = *( SP / HTAB )
4911
4912<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4913
4914<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4915<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4916<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4917 transfer-coding ] )
4918
4919<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4920<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4921
4922<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4923 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4924 comment ] ) ] )
4925
4926<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4927<x:ref>absolute-form</x:ref> = absolute-URI
4928<x:ref>asterisk-form</x:ref> = "*"
4929<x:ref>attribute</x:ref> = token
4930<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4931<x:ref>authority-form</x:ref> = authority
4932
4933<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4934<x:ref>chunk-data</x:ref> = 1*OCTET
4935<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4936<x:ref>chunk-ext-name</x:ref> = token
4937<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4938<x:ref>chunk-size</x:ref> = 1*HEXDIG
4939<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4940<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4941<x:ref>connection-option</x:ref> = token
4942<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4943 / %x2A-5B ; '*'-'['
4944 / %x5D-7E ; ']'-'~'
4945 / obs-text
4946
4947<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4948<x:ref>field-name</x:ref> = token
4949<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4950
4951<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4952<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4953<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4954
4955<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4956
4957<x:ref>message-body</x:ref> = *OCTET
4958<x:ref>method</x:ref> = token
4959
4960<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4961<x:ref>obs-text</x:ref> = %x80-FF
4962<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4963
4964<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4965<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4966<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4967<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4968<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4969<x:ref>protocol-name</x:ref> = token
4970<x:ref>protocol-version</x:ref> = token
4971<x:ref>pseudonym</x:ref> = token
4972
4973<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4974 / %x5D-7E ; ']'-'~'
4975 / obs-text
4976<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4977 / %x5D-7E ; ']'-'~'
4978 / obs-text
4979<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4980<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4981<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4982<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4983<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4984
4985<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4986<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4987<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4988<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4989<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4990<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4991<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4992 asterisk-form
4993
4994<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4995 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4996<x:ref>start-line</x:ref> = request-line / status-line
4997<x:ref>status-code</x:ref> = 3DIGIT
4998<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
4999
5000<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5001<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5002<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5003 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5004<x:ref>token</x:ref> = 1*tchar
5005<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5006<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5007 transfer-extension
5008<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5009<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5010
5011<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5012
5013<x:ref>value</x:ref> = word
5014
5015<x:ref>word</x:ref> = token / quoted-string
5016</artwork>
5017</figure>
5018</section>
5019<?ENDINC p1-messaging.abnf-appendix ?>
5020
5021<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5022
5023<section title="Since RFC 2616">
5024<t>
5025  Extracted relevant partitions from <xref target="RFC2616"/>.
5026</t>
5027</section>
5028
5029<section title="Since draft-ietf-httpbis-p1-messaging-00">
5030<t>
5031  Closed issues:
5032  <list style="symbols"> 
5033    <t>
5034      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5035      "HTTP Version should be case sensitive"
5036      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5037    </t>
5038    <t>
5039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5040      "'unsafe' characters"
5041      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5042    </t>
5043    <t>
5044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5045      "Chunk Size Definition"
5046      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5047    </t>
5048    <t>
5049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5050      "Message Length"
5051      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5052    </t>
5053    <t>
5054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5055      "Media Type Registrations"
5056      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5057    </t>
5058    <t>
5059      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5060      "URI includes query"
5061      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5062    </t>
5063    <t>
5064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5065      "No close on 1xx responses"
5066      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5067    </t>
5068    <t>
5069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5070      "Remove 'identity' token references"
5071      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5072    </t>
5073    <t>
5074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5075      "Import query BNF"
5076    </t>
5077    <t>
5078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5079      "qdtext BNF"
5080    </t>
5081    <t>
5082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5083      "Normative and Informative references"
5084    </t>
5085    <t>
5086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5087      "RFC2606 Compliance"
5088    </t>
5089    <t>
5090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5091      "RFC977 reference"
5092    </t>
5093    <t>
5094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5095      "RFC1700 references"
5096    </t>
5097    <t>
5098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5099      "inconsistency in date format explanation"
5100    </t>
5101    <t>
5102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5103      "Date reference typo"
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5107      "Informative references"
5108    </t>
5109    <t>
5110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5111      "ISO-8859-1 Reference"
5112    </t>
5113    <t>
5114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5115      "Normative up-to-date references"
5116    </t>
5117  </list>
5118</t>
5119<t>
5120  Other changes:
5121  <list style="symbols"> 
5122    <t>
5123      Update media type registrations to use RFC4288 template.
5124    </t>
5125    <t>
5126      Use names of RFC4234 core rules DQUOTE and HTAB,
5127      fix broken ABNF for chunk-data
5128      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5129    </t>
5130  </list>
5131</t>
5132</section>
5133
5134<section title="Since draft-ietf-httpbis-p1-messaging-01">
5135<t>
5136  Closed issues:
5137  <list style="symbols"> 
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5140      "Bodies on GET (and other) requests"
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5144      "Updating to RFC4288"
5145    </t>
5146    <t>
5147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5148      "Status Code and Reason Phrase"
5149    </t>
5150    <t>
5151      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5152      "rel_path not used"
5153    </t>
5154  </list>
5155</t>
5156<t>
5157  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5158  <list style="symbols"> 
5159    <t>
5160      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5161      "trailer-part").
5162    </t>
5163    <t>
5164      Avoid underscore character in rule names ("http_URL" ->
5165      "http-URL", "abs_path" -> "path-absolute").
5166    </t>
5167    <t>
5168      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5169      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5170      have to be updated when switching over to RFC3986.
5171    </t>
5172    <t>
5173      Synchronize core rules with RFC5234.
5174    </t>
5175    <t>
5176      Get rid of prose rules that span multiple lines.
5177    </t>
5178    <t>
5179      Get rid of unused rules LOALPHA and UPALPHA.
5180    </t>
5181    <t>
5182      Move "Product Tokens" section (back) into Part 1, as "token" is used
5183      in the definition of the Upgrade header field.
5184    </t>
5185    <t>
5186      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5187    </t>
5188    <t>
5189      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5190    </t>
5191  </list>
5192</t>
5193</section>
5194
5195<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5196<t>
5197  Closed issues:
5198  <list style="symbols"> 
5199    <t>
5200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5201      "HTTP-date vs. rfc1123-date"
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5205      "WS in quoted-pair"
5206    </t>
5207  </list>
5208</t>
5209<t>
5210  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5211  <list style="symbols"> 
5212    <t>
5213      Reference RFC 3984, and update header field registrations for header
5214      fields defined in this document.
5215    </t>
5216  </list>
5217</t>
5218<t>
5219  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5220  <list style="symbols"> 
5221    <t>
5222      Replace string literals when the string really is case-sensitive (HTTP-version).
5223    </t>
5224  </list>
5225</t>
5226</section>
5227
5228<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5229<t>
5230  Closed issues:
5231  <list style="symbols"> 
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5234      "Connection closing"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5238      "Move registrations and registry information to IANA Considerations"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5242      "need new URL for PAD1995 reference"
5243    </t>
5244    <t>
5245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5246      "IANA Considerations: update HTTP URI scheme registration"
5247    </t>
5248    <t>
5249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5250      "Cite HTTPS URI scheme definition"
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5254      "List-type header fields vs Set-Cookie"
5255    </t>
5256  </list>
5257</t>
5258<t>
5259  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5260  <list style="symbols"> 
5261    <t>
5262      Replace string literals when the string really is case-sensitive (HTTP-Date).
5263    </t>
5264    <t>
5265      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5266    </t>
5267  </list>
5268</t>
5269</section>
5270
5271<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5272<t>
5273  Closed issues:
5274  <list style="symbols"> 
5275    <t>
5276      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5277      "Out-of-date reference for URIs"
5278    </t>
5279    <t>
5280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5281      "RFC 2822 is updated by RFC 5322"
5282    </t>
5283  </list>
5284</t>
5285<t>
5286  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5287  <list style="symbols"> 
5288    <t>
5289      Use "/" instead of "|" for alternatives.
5290    </t>
5291    <t>
5292      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5293    </t>
5294    <t>
5295      Only reference RFC 5234's core rules.
5296    </t>
5297    <t>
5298      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5299      whitespace ("OWS") and required whitespace ("RWS").
5300    </t>
5301    <t>
5302      Rewrite ABNFs to spell out whitespace rules, factor out
5303      header field value format definitions.
5304    </t>
5305  </list>
5306</t>
5307</section>
5308
5309<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5310<t>
5311  Closed issues:
5312  <list style="symbols"> 
5313    <t>
5314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5315      "Header LWS"
5316    </t>
5317    <t>
5318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5319      "Sort 1.3 Terminology"
5320    </t>
5321    <t>
5322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5323      "RFC2047 encoded words"
5324    </t>
5325    <t>
5326      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5327      "Character Encodings in TEXT"
5328    </t>
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5331      "Line Folding"
5332    </t>
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5335      "OPTIONS * and proxies"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5339      "reason-phrase BNF"
5340    </t>
5341    <t>
5342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5343      "Use of TEXT"
5344    </t>
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5347      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5348    </t>
5349    <t>
5350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5351      "RFC822 reference left in discussion of date formats"
5352    </t>
5353  </list>
5354</t>
5355<t>
5356  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5357  <list style="symbols"> 
5358    <t>
5359      Rewrite definition of list rules, deprecate empty list elements.
5360    </t>
5361    <t>
5362      Add appendix containing collected and expanded ABNF.
5363    </t>
5364  </list>
5365</t>
5366<t>
5367  Other changes:
5368  <list style="symbols"> 
5369    <t>
5370      Rewrite introduction; add mostly new Architecture Section.
5371    </t>
5372    <t>
5373      Move definition of quality values from Part 3 into Part 1;
5374      make TE request header field grammar independent of accept-params (defined in Part 3).
5375    </t>
5376  </list>
5377</t>
5378</section>
5379
5380<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5381<t>
5382  Closed issues:
5383  <list style="symbols"> 
5384    <t>
5385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5386      "base for numeric protocol elements"
5387    </t>
5388    <t>
5389      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5390      "comment ABNF"
5391    </t>
5392  </list>
5393</t>
5394<t>
5395  Partly resolved issues:
5396  <list style="symbols"> 
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5399      "205 Bodies" (took out language that implied that there might be
5400      methods for which a request body MUST NOT be included)
5401    </t>
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5404      "editorial improvements around HTTP-date"
5405    </t>
5406  </list>
5407</t>
5408</section>
5409
5410<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5411<t>
5412  Closed issues:
5413  <list style="symbols"> 
5414    <t>
5415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5416      "Repeating single-value header fields"
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5420      "increase connection limit"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5424      "IP addresses in URLs"
5425    </t>
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5428      "take over HTTP Upgrade Token Registry"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5432      "CR and LF in chunk extension values"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5436      "HTTP/0.9 support"
5437    </t>
5438    <t>
5439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5440      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5441    </t>
5442    <t>
5443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5444      "move definitions of gzip/deflate/compress to part 1"
5445    </t>
5446    <t>
5447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5448      "disallow control characters in quoted-pair"
5449    </t>
5450  </list>
5451</t>
5452<t>
5453  Partly resolved issues:
5454  <list style="symbols"> 
5455    <t>
5456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5457      "update IANA requirements wrt Transfer-Coding values" (add the
5458      IANA Considerations subsection)
5459    </t>
5460  </list>
5461</t>
5462</section>
5463
5464<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5465<t>
5466  Closed issues:
5467  <list style="symbols"> 
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5470      "header parsing, treatment of leading and trailing OWS"
5471    </t>
5472  </list>
5473</t>
5474<t>
5475  Partly resolved issues:
5476  <list style="symbols"> 
5477    <t>
5478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5479      "Placement of 13.5.1 and 13.5.2"
5480    </t>
5481    <t>
5482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5483      "use of term "word" when talking about header field structure"
5484    </t>
5485  </list>
5486</t>
5487</section>
5488
5489<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5490<t>
5491  Closed issues:
5492  <list style="symbols"> 
5493    <t>
5494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5495      "Clarification of the term 'deflate'"
5496    </t>
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5499      "OPTIONS * and proxies"
5500    </t>
5501    <t>
5502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5503      "MIME-Version not listed in P1, general header fields"
5504    </t>
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5507      "IANA registry for content/transfer encodings"
5508    </t>
5509    <t>
5510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5511      "Case-sensitivity of HTTP-date"
5512    </t>
5513    <t>
5514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5515      "use of term "word" when talking about header field structure"
5516    </t>
5517  </list>
5518</t>
5519<t>
5520  Partly resolved issues:
5521  <list style="symbols"> 
5522    <t>
5523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5524      "Term for the requested resource's URI"
5525    </t>
5526  </list>
5527</t>
5528</section>
5529
5530<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5531<t>
5532  Closed issues:
5533  <list style="symbols">
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5536      "Connection Closing"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5540      "Delimiting messages with multipart/byteranges"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5544      "Handling multiple Content-Length header fields"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5548      "Clarify entity / representation / variant terminology"
5549    </t>
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5552      "consider removing the 'changes from 2068' sections"
5553    </t>
5554  </list>
5555</t>
5556<t>
5557  Partly resolved issues:
5558  <list style="symbols"> 
5559    <t>
5560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5561      "HTTP(s) URI scheme definitions"
5562    </t>
5563  </list>
5564</t>
5565</section>
5566
5567<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5568<t>
5569  Closed issues:
5570  <list style="symbols">
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5573      "Trailer requirements"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5577      "Text about clock requirement for caches belongs in p6"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5581      "effective request URI: handling of missing host in HTTP/1.0"
5582    </t>
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5585      "confusing Date requirements for clients"
5586    </t>
5587  </list>
5588</t>
5589<t>
5590  Partly resolved issues:
5591  <list style="symbols"> 
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5594      "Handling multiple Content-Length header fields"
5595    </t>
5596  </list>
5597</t>
5598</section>
5599
5600<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5601<t>
5602  Closed issues:
5603  <list style="symbols">
5604    <t>
5605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5606      "RFC2145 Normative"
5607    </t>
5608    <t>
5609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5610      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5611    </t>
5612    <t>
5613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5614      "define 'transparent' proxy"
5615    </t>
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5618      "Header Field Classification"
5619    </t>
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5622      "Is * usable as a request-uri for new methods?"
5623    </t>
5624    <t>
5625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5626      "Migrate Upgrade details from RFC2817"
5627    </t>
5628    <t>
5629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5630      "untangle ABNFs for header fields"
5631    </t>
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5634      "update RFC 2109 reference"
5635    </t>
5636  </list>
5637</t>
5638</section>
5639
5640<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5641<t>
5642  Closed issues:
5643  <list style="symbols">
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5646      "Allow is not in 13.5.2"
5647    </t>
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5650      "Handling multiple Content-Length header fields"
5651    </t>
5652    <t>
5653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5654      "untangle ABNFs for header fields"
5655    </t>
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5658      "Content-Length ABNF broken"
5659    </t>
5660  </list>
5661</t>
5662</section>
5663
5664<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5665<t>
5666  Closed issues:
5667  <list style="symbols">
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5670      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5671    </t>
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5674      "Recommend minimum sizes for protocol elements"
5675    </t>
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5678      "Set expectations around buffering"
5679    </t>
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5682      "Considering messages in isolation"
5683    </t>
5684  </list>
5685</t>
5686</section>
5687
5688<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5689<t>
5690  Closed issues:
5691  <list style="symbols">
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5694      "DNS Spoofing / DNS Binding advice"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5698      "move RFCs 2145, 2616, 2817 to Historic status"
5699    </t>
5700    <t>
5701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5702      "\-escaping in quoted strings"
5703    </t>
5704    <t>
5705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5706      "'Close' should be reserved in the HTTP header field registry"
5707    </t>
5708  </list>
5709</t>
5710</section>
5711
5712<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5713<t>
5714  Closed issues:
5715  <list style="symbols">
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5718      "Document HTTP's error-handling philosophy"
5719    </t>
5720    <t>
5721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5722      "Explain header field registration"
5723    </t>
5724    <t>
5725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5726      "Revise Acknowledgements Sections"
5727    </t>
5728    <t>
5729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5730      "Retrying Requests"
5731    </t>
5732    <t>
5733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5734      "Closing the connection on server error"
5735    </t>
5736  </list>
5737</t>
5738</section>
5739
5740<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5741<t>
5742  Closed issues:
5743  <list style="symbols">
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5746      "Proxy-Connection and Keep-Alive"
5747    </t>
5748    <t>
5749      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5750      "Clarify 'User Agent'"
5751    </t>
5752    <t>
5753      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5754      "Define non-final responses"
5755    </t>
5756    <t>
5757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5758      "intended maturity level vs normative references"
5759    </t>
5760    <t>
5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5762      "Intermediary rewriting of queries"
5763    </t>
5764  </list>
5765</t>
5766</section>
5767
5768<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5769<t>
5770  Closed issues:
5771  <list style="symbols">
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5774      "message-body in CONNECT response"
5775    </t>
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5778      "Misplaced text on connection handling in p2"
5779    </t>
5780    <t>
5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5782      "wording of line folding rule"
5783    </t>
5784    <t>
5785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5786      "chunk-extensions"
5787    </t>
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5790      "make IANA policy definitions consistent"
5791    </t>
5792  </list>
5793</t>
5794</section>
5795
5796<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5797<t>
5798  Closed issues:
5799  <list style="symbols">
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5802      "make IANA policy definitions consistent"
5803    </t>
5804    <t>
5805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5806      "clarify connection header field values are case-insensitive"
5807    </t>
5808    <t>
5809      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5810      "ABNF requirements for recipients"
5811    </t>
5812    <t>
5813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5814      "note introduction of new IANA registries as normative changes"
5815    </t>
5816    <t>
5817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5818      "Reference to ISO-8859-1 is informative"
5819    </t>
5820  </list>
5821</t>
5822</section>
5823
5824<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5825<t>
5826  Closed issues:
5827  <list style="symbols"> 
5828    <t>
5829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
5830      "is 'q=' case-sensitive?"
5831    </t>
5832    <t>
5833      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/383"/>:
5834      "Semantics of HTTPS"
5835    </t>
5836  </list>
5837</t>
5838<t>
5839  Other changes:
5840  <list style="symbols">
5841    <t>
5842      Drop notion of header fields being "hop-by-hop" without being listed in
5843      the Connection header field.     
5844    </t>
5845    <t>
5846      Section about connection management rewritten; dropping some historic
5847      information.
5848    </t>
5849    <t>
5850      Move description of "100-continue" into Part 2.
5851    </t>
5852    <t>
5853      Rewrite the persistent connection and Upgrade requirements to be
5854      actionable by role and consistent with the rest of HTTP.
5855    </t>
5856  </list>
5857</t>
5858</section>
5859
5860</section>
5861
5862</back>
5863</rfc>
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