source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1874

Last change on this file since 1874 was 1874, checked in by fielding@…, 7 years ago

Clarify that conformance applies to both syntax and semantics of HTTP

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 242.3 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                "<xref target='Part2' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56]>
57<?rfc toc="yes" ?>
58<?rfc symrefs="yes" ?>
59<?rfc sortrefs="yes" ?>
60<?rfc compact="yes"?>
61<?rfc subcompact="no" ?>
62<?rfc linkmailto="no" ?>
63<?rfc editing="no" ?>
64<?rfc comments="yes"?>
65<?rfc inline="yes"?>
66<?rfc rfcedstyle="yes"?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
70     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext'>
72<x:link rel="next" basename="p2-semantics"/>
73<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
74<front>
75
76  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
77
78  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
79    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
80    <address>
81      <postal>
82        <street>345 Park Ave</street>
83        <city>San Jose</city>
84        <region>CA</region>
85        <code>95110</code>
86        <country>USA</country>
87      </postal>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
94    <organization abbrev="W3C">World Wide Web Consortium</organization>
95    <address>
96      <postal>
97        <street>W3C / ERCIM</street>
98        <street>2004, rte des Lucioles</street>
99        <city>Sophia-Antipolis</city>
100        <region>AM</region>
101        <code>06902</code>
102        <country>France</country>
103      </postal>
104      <email>ylafon@w3.org</email>
105      <uri>http://www.raubacapeu.net/people/yves/</uri>
106    </address>
107  </author>
108
109  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
110    <organization abbrev="greenbytes">greenbytes GmbH</organization>
111    <address>
112      <postal>
113        <street>Hafenweg 16</street>
114        <city>Muenster</city><region>NW</region><code>48155</code>
115        <country>Germany</country>
116      </postal>
117      <email>julian.reschke@greenbytes.de</email>
118      <uri>http://greenbytes.de/tech/webdav/</uri>
119    </address>
120  </author>
121
122  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
123  <workgroup>HTTPbis Working Group</workgroup>
124
125<abstract>
126<t>
127   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
128   distributed, collaborative, hypertext information systems. HTTP has been in
129   use by the World Wide Web global information initiative since 1990.
130   This document provides an overview of HTTP architecture and its associated
131   terminology, defines the "http" and "https" Uniform Resource Identifier
132   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
133   and describes general security concerns for implementations.
134</t>   
135</abstract>
136
137<note title="Editorial Note (To be removed by RFC Editor)">
138  <t>
139    Discussion of this draft takes place on the HTTPBIS working group
140    mailing list (ietf-http-wg@w3.org), which is archived at
141    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
142  </t>
143  <t>
144    The current issues list is at
145    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
146    documents (including fancy diffs) can be found at
147    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
148  </t>
149  <t>
150    The changes in this draft are summarized in <xref target="changes.since.20"/>.
151  </t>
152</note>
153</front>
154<middle>
155<section title="Introduction" anchor="introduction">
156<t>
157   The Hypertext Transfer Protocol (HTTP) is an application-level
158   request/response protocol that uses extensible semantics and MIME-like
159   message payloads for flexible interaction with network-based hypertext
160   information systems. This document is the first in a series of documents
161   that collectively form the HTTP/1.1 specification:
162   <list style="empty">
163    <t>RFC xxx1: Message Syntax and Routing</t>
164    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
165    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
166    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
167    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
168    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
169   </list>
170</t>
171<t>
172   This HTTP/1.1 specification obsoletes and moves to historic status
173   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
174   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
175   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
176   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
177   for TLS upgrades).
178</t>
179<t>
180   HTTP is a generic interface protocol for information systems. It is
181   designed to hide the details of how a service is implemented by presenting
182   a uniform interface to clients that is independent of the types of
183   resources provided. Likewise, servers do not need to be aware of each
184   client's purpose: an HTTP request can be considered in isolation rather
185   than being associated with a specific type of client or a predetermined
186   sequence of application steps. The result is a protocol that can be used
187   effectively in many different contexts and for which implementations can
188   evolve independently over time.
189</t>
190<t>
191   HTTP is also designed for use as an intermediation protocol for translating
192   communication to and from non-HTTP information systems.
193   HTTP proxies and gateways can provide access to alternative information
194   services by translating their diverse protocols into a hypertext
195   format that can be viewed and manipulated by clients in the same way
196   as HTTP services.
197</t>
198<t>
199   One consequence of HTTP flexibility is that the protocol cannot be
200   defined in terms of what occurs behind the interface. Instead, we
201   are limited to defining the syntax of communication, the intent
202   of received communication, and the expected behavior of recipients.
203   If the communication is considered in isolation, then successful
204   actions ought to be reflected in corresponding changes to the
205   observable interface provided by servers. However, since multiple
206   clients might act in parallel and perhaps at cross-purposes, we
207   cannot require that such changes be observable beyond the scope
208   of a single response.
209</t>
210<t>
211   This document describes the architectural elements that are used or
212   referred to in HTTP, defines the "http" and "https" URI schemes,
213   describes overall network operation and connection management,
214   and defines HTTP message framing and forwarding requirements.
215   Our goal is to define all of the mechanisms necessary for HTTP message
216   handling that are independent of message semantics, thereby defining the
217   complete set of requirements for message parsers and
218   message-forwarding intermediaries.
219</t>
220
221
222<section title="Requirement Notation" anchor="intro.requirements">
223<t>
224   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
225   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
226   document are to be interpreted as described in <xref target="RFC2119"/>.
227</t>
228<t>
229   Conformance criteria and considerations regarding error handling
230   are defined in <xref target="conformance"/>.
231</t>
232</section>
233
234<section title="Syntax Notation" anchor="notation">
235<iref primary="true" item="Grammar" subitem="ALPHA"/>
236<iref primary="true" item="Grammar" subitem="CR"/>
237<iref primary="true" item="Grammar" subitem="CRLF"/>
238<iref primary="true" item="Grammar" subitem="CTL"/>
239<iref primary="true" item="Grammar" subitem="DIGIT"/>
240<iref primary="true" item="Grammar" subitem="DQUOTE"/>
241<iref primary="true" item="Grammar" subitem="HEXDIG"/>
242<iref primary="true" item="Grammar" subitem="HTAB"/>
243<iref primary="true" item="Grammar" subitem="LF"/>
244<iref primary="true" item="Grammar" subitem="OCTET"/>
245<iref primary="true" item="Grammar" subitem="SP"/>
246<iref primary="true" item="Grammar" subitem="VCHAR"/>
247<t>
248   This specification uses the Augmented Backus-Naur Form (ABNF) notation
249   of <xref target="RFC5234"/> with the list rule extension defined in
250   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
251   the collected ABNF with the list rule expanded.
252</t>
253<t anchor="core.rules">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="CTL"/>
256  <x:anchor-alias value="CR"/>
257  <x:anchor-alias value="CRLF"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="DQUOTE"/>
260  <x:anchor-alias value="HEXDIG"/>
261  <x:anchor-alias value="HTAB"/>
262  <x:anchor-alias value="LF"/>
263  <x:anchor-alias value="OCTET"/>
264  <x:anchor-alias value="SP"/>
265  <x:anchor-alias value="VCHAR"/>
266   The following core rules are included by
267   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269   DIGIT (decimal 0-9), DQUOTE (double quote),
270   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271   OCTET (any 8-bit sequence of data), SP (space), and
272   VCHAR (any visible <xref target="USASCII"/> character).
273</t>
274<t>
275   As a convention, ABNF rule names prefixed with "obs-" denote
276   "obsolete" grammar rules that appear for historical reasons.
277</t>
278</section>
279</section>
280
281<section title="Architecture" anchor="architecture">
282<t>
283   HTTP was created for the World Wide Web architecture
284   and has evolved over time to support the scalability needs of a worldwide
285   hypertext system. Much of that architecture is reflected in the terminology
286   and syntax productions used to define HTTP.
287</t>
288
289<section title="Client/Server Messaging" anchor="operation">
290<iref primary="true" item="client"/>
291<iref primary="true" item="server"/>
292<iref primary="true" item="connection"/>
293<t>
294   HTTP is a stateless request/response protocol that operates by exchanging
295   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
296   transport or session-layer
297   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
298   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
299   to a server for the purpose of sending one or more HTTP requests.
300   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
301   in order to service HTTP requests by sending HTTP responses.
302</t>
303<iref primary="true" item="user agent"/>
304<iref primary="true" item="origin server"/>
305<iref primary="true" item="browser"/>
306<iref primary="true" item="spider"/>
307<iref primary="true" item="sender"/>
308<iref primary="true" item="recipient"/>
309<t>
310   The terms client and server refer only to the roles that
311   these programs perform for a particular connection.  The same program
312   might act as a client on some connections and a server on others.  We use
313   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
314   such as a WWW browser, editor, or spider (web-traversing robot), and
315   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
316   authoritative responses to a request.  For general requirements, we use
317   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
318   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
319   message.
320</t>
321<t>
322   HTTP relies upon the Uniform Resource Identifier (URI)
323   standard <xref target="RFC3986"/> to indicate the target resource
324   (<xref target="target-resource"/>) and relationships between resources.
325   Messages are passed in a format similar to that used by Internet mail
326   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
327   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
328   between HTTP and MIME messages).
329</t>
330<t>
331   Most HTTP communication consists of a retrieval request (GET) for
332   a representation of some resource identified by a URI.  In the
333   simplest case, this might be accomplished via a single bidirectional
334   connection (===) between the user agent (UA) and the origin server (O).
335</t>
336<figure><artwork type="drawing">
337         request   &gt;
338    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
339                                &lt;   response
340</artwork></figure>
341<iref primary="true" item="message"/>
342<iref primary="true" item="request"/>
343<iref primary="true" item="response"/>
344<t>
345   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
346   message, beginning with a request-line that includes a method, URI, and
347   protocol version (<xref target="request.line"/>),
348   followed by header fields containing
349   request modifiers, client information, and representation metadata
350   (<xref target="header.fields"/>),
351   an empty line to indicate the end of the header section, and finally
352   a message body containing the payload body (if any,
353   <xref target="message.body"/>).
354</t>
355<t>
356   A server responds to a client's request by sending one or more HTTP
357   <x:dfn>response</x:dfn>
358   messages, each beginning with a status line that
359   includes the protocol version, a success or error code, and textual
360   reason phrase (<xref target="status.line"/>),
361   possibly followed by header fields containing server
362   information, resource metadata, and representation metadata
363   (<xref target="header.fields"/>),
364   an empty line to indicate the end of the header section, and finally
365   a message body containing the payload body (if any,
366   <xref target="message.body"/>).
367</t>
368<t>
369   A connection might be used for multiple request/response exchanges,
370   as defined in <xref target="persistent.connections"/>.
371</t>
372<t>
373   The following example illustrates a typical message exchange for a
374   GET request on the URI "http://www.example.com/hello.txt":
375</t>
376<figure><preamble>
377client request:
378</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
379GET /hello.txt HTTP/1.1
380User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
381Host: www.example.com
382Accept-Language: en, mi
383
384</artwork></figure>
385<figure><preamble>
386server response:
387</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
388HTTP/1.1 200 OK
389Date: Mon, 27 Jul 2009 12:28:53 GMT
390Server: Apache
391Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
392ETag: "34aa387-d-1568eb00"
393Accept-Ranges: bytes
394Content-Length: <x:length-of target="exbody"/>
395Vary: Accept-Encoding
396Content-Type: text/plain
397
398<x:span anchor="exbody">Hello World!
399</x:span></artwork></figure>
400</section>
401
402<section title="Implementation Diversity" anchor="implementation-diversity">
403<t>
404   When considering the design of HTTP, it is easy to fall into a trap of
405   thinking that all user agents are general-purpose browsers and all origin
406   servers are large public websites. That is not the case in practice.
407   Common HTTP user agents include household appliances, stereos, scales,
408   firmware update scripts, command-line programs, mobile apps,
409   and communication devices in a multitude of shapes and sizes.  Likewise,
410   common HTTP origin servers include home automation units, configurable
411   networking components, office machines, autonomous robots, news feeds,
412   traffic cameras, ad selectors, and video delivery platforms.
413</t>
414<t>
415   The term "user agent" does not imply that there is a human user directly
416   interacting with the software agent at the time of a request. In many
417   cases, a user agent is installed or configured to run in the background
418   and save its results for later inspection (or save only a subset of those
419   results that might be interesting or erroneous). Spiders, for example, are
420   typically given a start URI and configured to follow certain behavior while
421   crawling the Web as a hypertext graph.
422</t>
423<t>
424   The implementation diversity of HTTP means that we cannot assume the
425   user agent can make interactive suggestions to a user or provide adequate
426   warning for security or privacy options.  In the few cases where this
427   specification requires reporting of errors to the user, it is acceptable
428   for such reporting to only be observable in an error console or log file.
429   Likewise, requirements that an automated action be confirmed by the user
430   before proceeding can me met via advance configuration choices,
431   run-time options, or simply not proceeding with the unsafe action.
432</t>
433</section>
434
435<section title="Intermediaries" anchor="intermediaries">
436<iref primary="true" item="intermediary"/>
437<t>
438   HTTP enables the use of intermediaries to satisfy requests through
439   a chain of connections.  There are three common forms of HTTP
440   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
441   a single intermediary might act as an origin server, proxy, gateway,
442   or tunnel, switching behavior based on the nature of each request.
443</t>
444<figure><artwork type="drawing">
445         &gt;             &gt;             &gt;             &gt;
446    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
447               &lt;             &lt;             &lt;             &lt;
448</artwork></figure>
449<t>
450   The figure above shows three intermediaries (A, B, and C) between the
451   user agent and origin server. A request or response message that
452   travels the whole chain will pass through four separate connections.
453   Some HTTP communication options
454   might apply only to the connection with the nearest, non-tunnel
455   neighbor, only to the end-points of the chain, or to all connections
456   along the chain. Although the diagram is linear, each participant might
457   be engaged in multiple, simultaneous communications. For example, B
458   might be receiving requests from many clients other than A, and/or
459   forwarding requests to servers other than C, at the same time that it
460   is handling A's request.
461</t>
462<t>
463<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
464<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
465   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
466   to describe various requirements in relation to the directional flow of a
467   message: all messages flow from upstream to downstream.
468   Likewise, we use the terms inbound and outbound to refer to
469   directions in relation to the request path:
470   "<x:dfn>inbound</x:dfn>" means toward the origin server and
471   "<x:dfn>outbound</x:dfn>" means toward the user agent.
472</t>
473<t><iref primary="true" item="proxy"/>
474   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
475   client, usually via local configuration rules, to receive requests
476   for some type(s) of absolute URI and attempt to satisfy those
477   requests via translation through the HTTP interface.  Some translations
478   are minimal, such as for proxy requests for "http" URIs, whereas
479   other requests might require translation to and from entirely different
480   application-layer protocols. Proxies are often used to group an
481   organization's HTTP requests through a common intermediary for the
482   sake of security, annotation services, or shared caching.
483</t>
484<t>
485<iref primary="true" item="transforming proxy"/>
486<iref primary="true" item="non-transforming proxy"/>
487   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
488   or configured to modify request or response messages in a semantically
489   meaningful way (i.e., modifications, beyond those required by normal
490   HTTP processing, that change the message in a way that would be
491   significant to the original sender or potentially significant to
492   downstream recipients).  For example, a transforming proxy might be
493   acting as a shared annotation server (modifying responses to include
494   references to a local annotation database), a malware filter, a
495   format transcoder, or an intranet-to-Internet privacy filter.  Such
496   transformations are presumed to be desired by the client (or client
497   organization) that selected the proxy and are beyond the scope of
498   this specification.  However, when a proxy is not intended to transform
499   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
500   requirements that preserve HTTP message semantics. See &status-203; and
501   &header-warning; for status and warning codes related to transformations.
502</t>
503<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
504<iref primary="true" item="accelerator"/>
505   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
506   is a receiving agent that acts
507   as a layer above some other server(s) and translates the received
508   requests to the underlying server's protocol.  Gateways are often
509   used to encapsulate legacy or untrusted information services, to
510   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
511   enable partitioning or load-balancing of HTTP services across
512   multiple machines.
513</t>
514<t>
515   A gateway behaves as an origin server on its outbound connection and
516   as a user agent on its inbound connection.
517   All HTTP requirements applicable to an origin server
518   also apply to the outbound communication of a gateway.
519   A gateway communicates with inbound servers using any protocol that
520   it desires, including private extensions to HTTP that are outside
521   the scope of this specification.  However, an HTTP-to-HTTP gateway
522   that wishes to interoperate with third-party HTTP servers &MUST;
523   conform to HTTP user agent requirements on the gateway's inbound
524   connection and &MUST; implement the <x:ref>Connection</x:ref>
525   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
526   (<xref target="header.via"/>) header fields for both connections.
527</t>
528<t><iref primary="true" item="tunnel"/>
529   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
530   without changing the messages. Once active, a tunnel is not
531   considered a party to the HTTP communication, though the tunnel might
532   have been initiated by an HTTP request. A tunnel ceases to exist when
533   both ends of the relayed connection are closed. Tunnels are used to
534   extend a virtual connection through an intermediary, such as when
535   transport-layer security is used to establish confidential communication
536   through a shared firewall proxy.
537</t>
538<t><iref primary="true" item="interception proxy"/>
539<iref primary="true" item="transparent proxy"/>
540<iref primary="true" item="captive portal"/>
541   The above categories for intermediary only consider those acting as
542   participants in the HTTP communication.  There are also intermediaries
543   that can act on lower layers of the network protocol stack, filtering or
544   redirecting HTTP traffic without the knowledge or permission of message
545   senders. Network intermediaries often introduce security flaws or
546   interoperability problems by violating HTTP semantics.  For example, an
547   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
548   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
549   "<x:dfn>captive portal</x:dfn>")
550   differs from an HTTP proxy because it is not selected by the client.
551   Instead, an interception proxy filters or redirects outgoing TCP port 80
552   packets (and occasionally other common port traffic).
553   Interception proxies are commonly found on public network access points,
554   as a means of enforcing account subscription prior to allowing use of
555   non-local Internet services, and within corporate firewalls to enforce
556   network usage policies.
557   They are indistinguishable from a man-in-the-middle attack.
558</t>
559<t>
560   HTTP is defined as a stateless protocol, meaning that each request message
561   can be understood in isolation.  Many implementations depend on HTTP's
562   stateless design in order to reuse proxied connections or dynamically
563   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
564   assume that two requests on the same connection are from the same user
565   agent unless the connection is secured and specific to that agent.
566   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
567   been known to violate this requirement, resulting in security and
568   interoperability problems.
569</t>
570</section>
571
572<section title="Caches" anchor="caches">
573<iref primary="true" item="cache"/>
574<t>
575   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
576   subsystem that controls its message storage, retrieval, and deletion.
577   A cache stores cacheable responses in order to reduce the response
578   time and network bandwidth consumption on future, equivalent
579   requests. Any client or server &MAY; employ a cache, though a cache
580   cannot be used by a server while it is acting as a tunnel.
581</t>
582<t>
583   The effect of a cache is that the request/response chain is shortened
584   if one of the participants along the chain has a cached response
585   applicable to that request. The following illustrates the resulting
586   chain if B has a cached copy of an earlier response from O (via C)
587   for a request which has not been cached by UA or A.
588</t>
589<figure><artwork type="drawing">
590            &gt;             &gt;
591       <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> - - - - - - <x:highlight>C</x:highlight> - - - - - - <x:highlight>O</x:highlight>
592                  &lt;             &lt;
593</artwork></figure>
594<t><iref primary="true" item="cacheable"/>
595   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
596   the response message for use in answering subsequent requests.
597   Even when a response is cacheable, there might be additional
598   constraints placed by the client or by the origin server on when
599   that cached response can be used for a particular request. HTTP
600   requirements for cache behavior and cacheable responses are
601   defined in &caching-overview;
602</t>
603<t>
604   There are a wide variety of architectures and configurations
605   of caches and proxies deployed across the World Wide Web and
606   inside large organizations. These systems include national hierarchies
607   of proxy caches to save transoceanic bandwidth, systems that
608   broadcast or multicast cache entries, organizations that distribute
609   subsets of cached data via optical media, and so on.
610</t>
611</section>
612
613<section title="Conformance and Error Handling" anchor="conformance">
614<t>
615   This specification targets conformance criteria according to the role of
616   a participant in HTTP communication.  Hence, HTTP requirements are placed
617   on senders, recipients, clients, servers, user agents, intermediaries,
618   origin servers, proxies, gateways, or caches, depending on what behavior
619   is being constrained by the requirement.
620</t>
621<t>
622   The verb "generate" is used instead of "send" where a requirement
623   differentiates between creating a protocol element and merely forwarding a
624   received element downstream.
625</t>
626<t>
627   An implementation is considered conformant if it complies with all of the
628   requirements associated with the roles it partakes in HTTP. Note that
629   SHOULD-level requirements are relevant here, unless one of the documented
630   exceptions is applicable.
631</t>
632<t>
633   Conformance applies to both the syntax and semantics of HTTP protocol
634   elements. A sender &MUST-NOT; generate protocol elements that convey a
635   meaning that is known by that sender to be false. A sender &MUST-NOT;
636   generate protocol elements that do not match the grammar defined by the
637   ABNF rules for those protocol elements that are applicable to the sender's
638   role. If a received protocol element is processed, the recipient &MUST; be
639   able to parse any value that would match the ABNF rules for that protocol
640   element, excluding only those rules not applicable to the recipient's role.
641</t>
642<t>
643   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
644   protocol element from an invalid construct.  HTTP does not define
645   specific error handling mechanisms except when they have a direct impact
646   on security, since different applications of the protocol require
647   different error handling strategies.  For example, a Web browser might
648   wish to transparently recover from a response where the
649   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
650   whereas a systems control client might consider any form of error recovery
651   to be dangerous.
652</t>
653</section>
654
655<section title="Protocol Versioning" anchor="http.version">
656  <x:anchor-alias value="HTTP-version"/>
657  <x:anchor-alias value="HTTP-name"/>
658<t>
659   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
660   versions of the protocol. This specification defines version "1.1".
661   The protocol version as a whole indicates the sender's conformance
662   with the set of requirements laid out in that version's corresponding
663   specification of HTTP.
664</t>
665<t>
666   The version of an HTTP message is indicated by an HTTP-version field
667   in the first line of the message. HTTP-version is case-sensitive.
668</t>
669<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
670  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
671  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
672</artwork></figure>
673<t>
674   The HTTP version number consists of two decimal digits separated by a "."
675   (period or decimal point).  The first digit ("major version") indicates the
676   HTTP messaging syntax, whereas the second digit ("minor version") indicates
677   the highest minor version to which the sender is
678   conformant and able to understand for future communication.  The minor
679   version advertises the sender's communication capabilities even when the
680   sender is only using a backwards-compatible subset of the protocol,
681   thereby letting the recipient know that more advanced features can
682   be used in response (by servers) or in future requests (by clients).
683</t>
684<t>
685   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
686   <xref target="RFC1945"/> or a recipient whose version is unknown,
687   the HTTP/1.1 message is constructed such that it can be interpreted
688   as a valid HTTP/1.0 message if all of the newer features are ignored.
689   This specification places recipient-version requirements on some
690   new features so that a conformant sender will only use compatible
691   features until it has determined, through configuration or the
692   receipt of a message, that the recipient supports HTTP/1.1.
693</t>
694<t>
695   The interpretation of a header field does not change between minor
696   versions of the same major HTTP version, though the default
697   behavior of a recipient in the absence of such a field can change.
698   Unless specified otherwise, header fields defined in HTTP/1.1 are
699   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
700   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
701   HTTP/1.x implementations whether or not they advertise conformance with
702   HTTP/1.1.
703</t>
704<t>
705   New header fields can be defined such that, when they are
706   understood by a recipient, they might override or enhance the
707   interpretation of previously defined header fields.  When an
708   implementation receives an unrecognized header field, the recipient
709   &MUST; ignore that header field for local processing regardless of
710   the message's HTTP version.  An unrecognized header field received
711   by a proxy &MUST; be forwarded downstream unless the header field's
712   field-name is listed in the message's <x:ref>Connection</x:ref> header field
713   (see <xref target="header.connection"/>).
714   These requirements allow HTTP's functionality to be enhanced without
715   requiring prior update of deployed intermediaries.
716</t>
717<t>
718   Intermediaries that process HTTP messages (i.e., all intermediaries
719   other than those acting as tunnels) &MUST; send their own HTTP-version
720   in forwarded messages.  In other words, they &MUST-NOT; blindly
721   forward the first line of an HTTP message without ensuring that the
722   protocol version in that message matches a version to which that
723   intermediary is conformant for both the receiving and
724   sending of messages.  Forwarding an HTTP message without rewriting
725   the HTTP-version might result in communication errors when downstream
726   recipients use the message sender's version to determine what features
727   are safe to use for later communication with that sender.
728</t>
729<t>
730   An HTTP client &SHOULD; send a request version equal to the highest
731   version to which the client is conformant and
732   whose major version is no higher than the highest version supported
733   by the server, if this is known.  An HTTP client &MUST-NOT; send a
734   version to which it is not conformant.
735</t>
736<t>
737   An HTTP client &MAY; send a lower request version if it is known that
738   the server incorrectly implements the HTTP specification, but only
739   after the client has attempted at least one normal request and determined
740   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
741   the server improperly handles higher request versions.
742</t>
743<t>
744   An HTTP server &SHOULD; send a response version equal to the highest
745   version to which the server is conformant and
746   whose major version is less than or equal to the one received in the
747   request.  An HTTP server &MUST-NOT; send a version to which it is not
748   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
749   Supported)</x:ref> response if it cannot send a response using the
750   major version used in the client's request.
751</t>
752<t>
753   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
754   if it is known or suspected that the client incorrectly implements the
755   HTTP specification and is incapable of correctly processing later
756   version responses, such as when a client fails to parse the version
757   number correctly or when an intermediary is known to blindly forward
758   the HTTP-version even when it doesn't conform to the given minor
759   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
760   performed unless triggered by specific client attributes, such as when
761   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
762   uniquely match the values sent by a client known to be in error.
763</t>
764<t>
765   The intention of HTTP's versioning design is that the major number
766   will only be incremented if an incompatible message syntax is
767   introduced, and that the minor number will only be incremented when
768   changes made to the protocol have the effect of adding to the message
769   semantics or implying additional capabilities of the sender.  However,
770   the minor version was not incremented for the changes introduced between
771   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
772   is specifically avoiding any such changes to the protocol.
773</t>
774</section>
775
776<section title="Uniform Resource Identifiers" anchor="uri">
777<iref primary="true" item="resource"/>
778<t>
779   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
780   throughout HTTP as the means for identifying resources. URI references
781   are used to target requests, indicate redirects, and define relationships.
782   HTTP does not limit what a resource might be; it merely defines an interface
783   that can be used to interact with a resource via HTTP. More information on
784   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
785</t>
786  <x:anchor-alias value="URI-reference"/>
787  <x:anchor-alias value="absolute-URI"/>
788  <x:anchor-alias value="relative-part"/>
789  <x:anchor-alias value="authority"/>
790  <x:anchor-alias value="path-abempty"/>
791  <x:anchor-alias value="path-absolute"/>
792  <x:anchor-alias value="port"/>
793  <x:anchor-alias value="query"/>
794  <x:anchor-alias value="uri-host"/>
795  <x:anchor-alias value="partial-URI"/>
796<t>
797   This specification adopts the definitions of "URI-reference",
798   "absolute-URI", "relative-part", "port", "host",
799   "path-abempty", "path-absolute", "query", and "authority" from the
800   URI generic syntax <xref target="RFC3986"/>.
801   In addition, we define a partial-URI rule for protocol elements
802   that allow a relative URI but not a fragment.
803</t>
804<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>
805  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
806  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
807  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
808  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
809  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
810  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
811  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
812  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
813  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
814 
815  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
816</artwork></figure>
817<t>
818   Each protocol element in HTTP that allows a URI reference will indicate
819   in its ABNF production whether the element allows any form of reference
820   (URI-reference), only a URI in absolute form (absolute-URI), only the
821   path and optional query components, or some combination of the above.
822   Unless otherwise indicated, URI references are parsed
823   relative to the effective request URI
824   (<xref target="effective.request.uri"/>).
825</t>
826
827<section title="http URI scheme" anchor="http.uri">
828  <x:anchor-alias value="http-URI"/>
829  <iref item="http URI scheme" primary="true"/>
830  <iref item="URI scheme" subitem="http" primary="true"/>
831<t>
832   The "http" URI scheme is hereby defined for the purpose of minting
833   identifiers according to their association with the hierarchical
834   namespace governed by a potential HTTP origin server listening for
835   TCP connections on a given port.
836</t>
837<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
838  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
839</artwork></figure>
840<t>
841   The HTTP origin server is identified by the generic syntax's
842   <x:ref>authority</x:ref> component, which includes a host identifier
843   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
844   The remainder of the URI, consisting of both the hierarchical path
845   component and optional query component, serves as an identifier for
846   a potential resource within that origin server's name space.
847</t>
848<t>
849   If the host identifier is provided as an IP literal or IPv4 address,
850   then the origin server is any listener on the indicated TCP port at
851   that IP address. If host is a registered name, then that name is
852   considered an indirect identifier and the recipient might use a name
853   resolution service, such as DNS, to find the address of a listener
854   for that host.
855   The host &MUST-NOT; be empty; if an "http" URI is received with an
856   empty host, then it &MUST; be rejected as invalid.
857   If the port subcomponent is empty or not given, then TCP port 80 is
858   assumed (the default reserved port for WWW services).
859</t>
860<t>
861   Regardless of the form of host identifier, access to that host is not
862   implied by the mere presence of its name or address. The host might or might
863   not exist and, even when it does exist, might or might not be running an
864   HTTP server or listening to the indicated port. The "http" URI scheme
865   makes use of the delegated nature of Internet names and addresses to
866   establish a naming authority (whatever entity has the ability to place
867   an HTTP server at that Internet name or address) and allows that
868   authority to determine which names are valid and how they might be used.
869</t>
870<t>
871   When an "http" URI is used within a context that calls for access to the
872   indicated resource, a client &MAY; attempt access by resolving
873   the host to an IP address, establishing a TCP connection to that address
874   on the indicated port, and sending an HTTP request message
875   (<xref target="http.message"/>) containing the URI's identifying data
876   (<xref target="message.routing"/>) to the server.
877   If the server responds to that request with a non-interim HTTP response
878   message, as described in &status-codes;, then that response
879   is considered an authoritative answer to the client's request.
880</t>
881<t>
882   Although HTTP is independent of the transport protocol, the "http"
883   scheme is specific to TCP-based services because the name delegation
884   process depends on TCP for establishing authority.
885   An HTTP service based on some other underlying connection protocol
886   would presumably be identified using a different URI scheme, just as
887   the "https" scheme (below) is used for servers that require an SSL/TLS
888   transport layer on a connection. Other protocols might also be used to
889   provide access to "http" identified resources &mdash; it is only the
890   authoritative interface used for mapping the namespace that is
891   specific to TCP.
892</t>
893<t>
894   The URI generic syntax for authority also includes a deprecated
895   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
896   for including user authentication information in the URI.  Some
897   implementations make use of the userinfo component for internal
898   configuration of authentication information, such as within command
899   invocation options, configuration files, or bookmark lists, even
900   though such usage might expose a user identifier or password.
901   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
902   delimiter) when transmitting an "http" URI in a message.  Recipients
903   of HTTP messages that contain a URI reference &SHOULD; parse for the
904   existence of userinfo and treat its presence as an error, likely
905   indicating that the deprecated subcomponent is being used to obscure
906   the authority for the sake of phishing attacks.
907</t>
908</section>
909
910<section title="https URI scheme" anchor="https.uri">
911   <x:anchor-alias value="https-URI"/>
912   <iref item="https URI scheme"/>
913   <iref item="URI scheme" subitem="https"/>
914<t>
915   The "https" URI scheme is hereby defined for the purpose of minting
916   identifiers according to their association with the hierarchical
917   namespace governed by a potential HTTP origin server listening for
918   SSL/TLS-secured connections on a given TCP port.
919</t>
920<t>
921   All of the requirements listed above for the "http" scheme are also
922   requirements for the "https" scheme, except that a default TCP port
923   of 443 is assumed if the port subcomponent is empty or not given,
924   and the TCP connection &MUST; be secured through the
925   use of strong encryption prior to sending the first HTTP request.
926</t>
927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
928  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
929</artwork></figure>
930<t>
931   Unlike the "http" scheme, responses to "https" identified requests
932   are never "public" and thus &MUST-NOT; be reused for shared caching.
933   They can, however, be reused in a private cache if the message is
934   cacheable by default in HTTP or specifically indicated as such by
935   the Cache-Control header field (&header-cache-control;).
936</t>
937<t>
938   Resources made available via the "https" scheme have no shared
939   identity with the "http" scheme even if their resource identifiers
940   indicate the same authority (the same host listening to the same
941   TCP port).  They are distinct name spaces and are considered to be
942   distinct origin servers.  However, an extension to HTTP that is
943   defined to apply to entire host domains, such as the Cookie protocol
944   <xref target="RFC6265"/>, can allow information
945   set by one service to impact communication with other services
946   within a matching group of host domains.
947</t>
948<t>
949   The process for authoritative access to an "https" identified
950   resource is defined in <xref target="RFC2818"/>.
951</t>
952</section>
953
954<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
955<t>
956   Since the "http" and "https" schemes conform to the URI generic syntax,
957   such URIs are normalized and compared according to the algorithm defined
958   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
959   described above for each scheme.
960</t>
961<t>
962   If the port is equal to the default port for a scheme, the normal
963   form is to elide the port subcomponent. Likewise, an empty path
964   component is equivalent to an absolute path of "/", so the normal
965   form is to provide a path of "/" instead. The scheme and host
966   are case-insensitive and normally provided in lowercase; all
967   other components are compared in a case-sensitive manner.
968   Characters other than those in the "reserved" set are equivalent
969   to their percent-encoded octets (see <xref target="RFC3986"
970   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
971</t>
972<t>
973   For example, the following three URIs are equivalent:
974</t>
975<figure><artwork type="example">
976   http://example.com:80/~smith/home.html
977   http://EXAMPLE.com/%7Esmith/home.html
978   http://EXAMPLE.com:/%7esmith/home.html
979</artwork></figure>
980</section>
981</section>
982</section>
983
984<section title="Message Format" anchor="http.message">
985<x:anchor-alias value="generic-message"/>
986<x:anchor-alias value="message.types"/>
987<x:anchor-alias value="HTTP-message"/>
988<x:anchor-alias value="start-line"/>
989<iref item="header section"/>
990<iref item="headers"/>
991<iref item="header field"/>
992<t>
993   All HTTP/1.1 messages consist of a start-line followed by a sequence of
994   octets in a format similar to the Internet Message Format
995   <xref target="RFC5322"/>: zero or more header fields (collectively
996   referred to as the "headers" or the "header section"), an empty line
997   indicating the end of the header section, and an optional message body.
998</t>
999<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1000  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1001                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1002                   <x:ref>CRLF</x:ref>
1003                   [ <x:ref>message-body</x:ref> ]
1004</artwork></figure>
1005<t>
1006   The normal procedure for parsing an HTTP message is to read the
1007   start-line into a structure, read each header field into a hash
1008   table by field name until the empty line, and then use the parsed
1009   data to determine if a message body is expected.  If a message body
1010   has been indicated, then it is read as a stream until an amount
1011   of octets equal to the message body length is read or the connection
1012   is closed.
1013</t>
1014<t>
1015   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1016   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1017   Parsing an HTTP message as a stream of Unicode characters, without regard
1018   for the specific encoding, creates security vulnerabilities due to the
1019   varying ways that string processing libraries handle invalid multibyte
1020   character sequences that contain the octet LF (%x0A).  String-based
1021   parsers can only be safely used within protocol elements after the element
1022   has been extracted from the message, such as within a header field-value
1023   after message parsing has delineated the individual fields.
1024</t>
1025<t>
1026   An HTTP message can be parsed as a stream for incremental processing or
1027   forwarding downstream.  However, recipients cannot rely on incremental
1028   delivery of partial messages, since some implementations will buffer or
1029   delay message forwarding for the sake of network efficiency, security
1030   checks, or payload transformations.
1031</t>
1032
1033<section title="Start Line" anchor="start.line">
1034  <x:anchor-alias value="Start-Line"/>
1035<t>
1036   An HTTP message can either be a request from client to server or a
1037   response from server to client.  Syntactically, the two types of message
1038   differ only in the start-line, which is either a request-line (for requests)
1039   or a status-line (for responses), and in the algorithm for determining
1040   the length of the message body (<xref target="message.body"/>).
1041   In theory, a client could receive requests and a server could receive
1042   responses, distinguishing them by their different start-line formats,
1043   but in practice servers are implemented to only expect a request
1044   (a response is interpreted as an unknown or invalid request method)
1045   and clients are implemented to only expect a response.
1046</t>
1047<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1048  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1049</artwork></figure>
1050<t>
1051   Implementations &MUST-NOT; send whitespace between the start-line and
1052   the first header field. The presence of such whitespace in a request
1053   might be an attempt to trick a server into ignoring that field or
1054   processing the line after it as a new request, either of which might
1055   result in a security vulnerability if other implementations within
1056   the request chain interpret the same message differently.
1057   Likewise, the presence of such whitespace in a response might be
1058   ignored by some clients or cause others to cease parsing.
1059</t>
1060
1061<section title="Request Line" anchor="request.line">
1062  <x:anchor-alias value="Request"/>
1063  <x:anchor-alias value="request-line"/>
1064<t>
1065   A request-line begins with a method token, followed by a single
1066   space (SP), the request-target, another single space (SP), the
1067   protocol version, and ending with CRLF.
1068</t>
1069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1070  <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>
1071</artwork></figure>
1072<t>
1073   A server &MUST; be able to parse any received message that begins
1074   with a request-line and matches the ABNF rule for HTTP-message.
1075</t>
1076<iref primary="true" item="method"/>
1077<t anchor="method">
1078   The method token indicates the request method to be performed on the
1079   target resource. The request method is case-sensitive.
1080</t>
1081<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1082  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1083</artwork></figure>
1084<t>
1085   The methods defined by this specification can be found in
1086   &methods;, along with information regarding the HTTP method registry
1087   and considerations for defining new methods.
1088</t>
1089<iref item="request-target"/>
1090<t>
1091   The request-target identifies the target resource upon which to apply
1092   the request, as defined in <xref target="request-target"/>.
1093</t>
1094<t>
1095   No whitespace is allowed inside the method, request-target, and
1096   protocol version.  Hence, recipients typically parse the request-line
1097   into its component parts by splitting on the SP characters.
1098</t>
1099<t>
1100   Unfortunately, some user agents fail to properly encode hypertext
1101   references that have embedded whitespace, sending the characters
1102   directly instead of properly percent-encoding the disallowed characters.
1103   Recipients of an invalid request-line &SHOULD; respond with either a
1104   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1105   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1106   attempt to autocorrect and then process the request without a redirect,
1107   since the invalid request-line might be deliberately crafted to bypass
1108   security filters along the request chain.
1109</t>
1110<t>
1111   HTTP does not place a pre-defined limit on the length of a request-line.
1112   A server that receives a method longer than any that it implements
1113   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1114   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1115   A server &MUST; be prepared to receive URIs of unbounded length and
1116   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1117   request-target would be longer than the server wishes to handle
1118   (see &status-414;).
1119</t>
1120<t>
1121   Various ad-hoc limitations on request-line length are found in practice.
1122   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1123   minimum, request-line lengths of up to 8000 octets.
1124</t>
1125</section>
1126
1127<section title="Status Line" anchor="status.line">
1128  <x:anchor-alias value="response"/>
1129  <x:anchor-alias value="status-line"/>
1130  <x:anchor-alias value="status-code"/>
1131  <x:anchor-alias value="reason-phrase"/>
1132<t>
1133   The first line of a response message is the status-line, consisting
1134   of the protocol version, a space (SP), the status code, another space,
1135   a possibly-empty textual phrase describing the status code, and
1136   ending with CRLF.
1137</t>
1138<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1139  <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>
1140</artwork></figure>
1141<t>
1142   A client &MUST; be able to parse any received message that begins
1143   with a status-line and matches the ABNF rule for HTTP-message.
1144</t>
1145<t>
1146   The status-code element is a 3-digit integer code describing the
1147   result of the server's attempt to understand and satisfy the client's
1148   corresponding request. The rest of the response message is to be
1149   interpreted in light of the semantics defined for that status code.
1150   See &status-codes; for information about the semantics of status codes,
1151   including the classes of status code (indicated by the first digit),
1152   the status codes defined by this specification, considerations for the
1153   definition of new status codes, and the IANA registry.
1154</t>
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1156  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1157</artwork></figure>
1158<t>   
1159   The reason-phrase element exists for the sole purpose of providing a
1160   textual description associated with the numeric status code, mostly
1161   out of deference to earlier Internet application protocols that were more
1162   frequently used with interactive text clients. A client &SHOULD; ignore
1163   the reason-phrase content.
1164</t>
1165<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1166  <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> )
1167</artwork></figure>
1168</section>
1169</section>
1170
1171<section title="Header Fields" anchor="header.fields">
1172  <x:anchor-alias value="header-field"/>
1173  <x:anchor-alias value="field-content"/>
1174  <x:anchor-alias value="field-name"/>
1175  <x:anchor-alias value="field-value"/>
1176  <x:anchor-alias value="obs-fold"/>
1177<t>
1178   Each HTTP header field consists of a case-insensitive field name
1179   followed by a colon (":"), optional whitespace, and the field value.
1180</t>
1181<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"/>
1182  <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>
1183  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1184  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1185  <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> )
1186  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1187                 ; obsolete line folding
1188                 ; see <xref target="field.parsing"/>
1189</artwork></figure>
1190<t>
1191   The field-name token labels the corresponding field-value as having the
1192   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1193   header field is defined in &header-date; as containing the origination
1194   timestamp for the message in which it appears.
1195</t>
1196<t>
1197   HTTP header fields are fully extensible: there is no limit on the
1198   introduction of new field names, each presumably defining new semantics,
1199   or on the number of header fields used in a given message.  Existing
1200   fields are defined in each part of this specification and in many other
1201   specifications outside the standards process.
1202   New header fields can be introduced without changing the protocol version
1203   if their defined semantics allow them to be safely ignored by recipients
1204   that do not recognize them.
1205</t>
1206<t>
1207   New HTTP header fields &SHOULD; be registered with IANA in the
1208   Message Header Field Registry, as described in &iana-header-registry;.
1209   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1210   field-name is listed in the <x:ref>Connection</x:ref> header field
1211   (<xref target="header.connection"/>) or the proxy is specifically
1212   configured to block or otherwise transform such fields.
1213   Unrecognized header fields &SHOULD; be ignored by other recipients.
1214</t>
1215<t>
1216   The order in which header fields with differing field names are
1217   received is not significant. However, it is "good practice" to send
1218   header fields that contain control data first, such as <x:ref>Host</x:ref>
1219   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1220   can decide when not to handle a message as early as possible.  A server
1221   &MUST; wait until the entire header section is received before interpreting
1222   a request message, since later header fields might include conditionals,
1223   authentication credentials, or deliberately misleading duplicate
1224   header fields that would impact request processing.
1225</t>
1226<t>
1227   Multiple header fields with the same field name &MUST-NOT; be
1228   sent in a message unless the entire field value for that
1229   header field is defined as a comma-separated list [i.e., #(values)].
1230   Multiple header fields with the same field name can be combined into
1231   one "field-name: field-value" pair, without changing the semantics of the
1232   message, by appending each subsequent field value to the combined
1233   field value in order, separated by a comma. The order in which
1234   header fields with the same field name are received is therefore
1235   significant to the interpretation of the combined field value;
1236   a proxy &MUST-NOT; change the order of these field values when
1237   forwarding a message.
1238</t>
1239<x:note>
1240  <t>
1241   &Note; The "Set-Cookie" header field as implemented in
1242   practice can occur multiple times, but does not use the list syntax, and
1243   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1244   for details.) Also note that the Set-Cookie2 header field specified in
1245   <xref target="RFC2965"/> does not share this problem.
1246  </t>
1247</x:note>
1248
1249<section title="Whitespace" anchor="whitespace">
1250<t anchor="rule.LWS">
1251   This specification uses three rules to denote the use of linear
1252   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1253   BWS ("bad" whitespace).
1254</t>
1255<t anchor="rule.OWS">
1256   The OWS rule is used where zero or more linear whitespace octets might
1257   appear. OWS &SHOULD; either not be produced or be produced as a single
1258   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1259   be replaced with a single SP or transformed to all SP octets (each
1260   octet other than SP replaced with SP) before interpreting the field value
1261   or forwarding the message downstream.
1262</t>
1263<t anchor="rule.RWS">
1264   RWS is used when at least one linear whitespace octet is required to
1265   separate field tokens. RWS &SHOULD; be produced as a single SP.
1266   Multiple RWS octets that occur within field-content &SHOULD; either
1267   be replaced with a single SP or transformed to all SP octets before
1268   interpreting the field value or forwarding the message downstream.
1269</t>
1270<t anchor="rule.BWS">
1271   BWS is used where the grammar allows optional whitespace, for historical
1272   reasons, but senders &SHOULD-NOT; produce it in messages;
1273   recipients &MUST; accept such bad optional whitespace and remove it before
1274   interpreting the field value or forwarding the message downstream.
1275</t>
1276<t anchor="rule.whitespace">
1277  <x:anchor-alias value="BWS"/>
1278  <x:anchor-alias value="OWS"/>
1279  <x:anchor-alias value="RWS"/>
1280</t>
1281<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"/>
1282  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1283                 ; "optional" whitespace
1284  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1285                 ; "required" whitespace
1286  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1287                 ; "bad" whitespace
1288</artwork></figure>
1289</section>
1290
1291<section title="Field Parsing" anchor="field.parsing">
1292<t>
1293   No whitespace is allowed between the header field-name and colon.
1294   In the past, differences in the handling of such whitespace have led to
1295   security vulnerabilities in request routing and response handling.
1296   Any received request message that contains whitespace between a header
1297   field-name and colon &MUST; be rejected with a response code of 400
1298   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1299   message before forwarding the message downstream.
1300</t>
1301<t>
1302   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1303   preferred. The field value does not include any leading or trailing white
1304   space: OWS occurring before the first non-whitespace octet of the
1305   field value or after the last non-whitespace octet of the field value
1306   is ignored and &SHOULD; be removed before further processing (as this does
1307   not change the meaning of the header field).
1308</t>
1309<t>
1310   Historically, HTTP header field values could be extended over multiple
1311   lines by preceding each extra line with at least one space or horizontal
1312   tab (obs-fold). This specification deprecates such line
1313   folding except within the message/http media type
1314   (<xref target="internet.media.type.message.http"/>).
1315   HTTP senders &MUST-NOT; produce messages that include line folding
1316   (i.e., that contain any field-value that matches the obs-fold rule) unless
1317   the message is intended for packaging within the message/http media type.
1318   HTTP recipients &SHOULD; accept line folding and replace any embedded
1319   obs-fold whitespace with either a single SP or a matching number of SP
1320   octets (to avoid buffer copying) prior to interpreting the field value or
1321   forwarding the message downstream.
1322</t>
1323<t>
1324   Historically, HTTP has allowed field content with text in the ISO-8859-1
1325   <xref target="ISO-8859-1"/> character encoding and supported other
1326   character sets only through use of <xref target="RFC2047"/> encoding.
1327   In practice, most HTTP header field values use only a subset of the
1328   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1329   header fields &SHOULD; limit their field values to US-ASCII octets.
1330   Recipients &SHOULD; treat other (obs-text) octets in field content as
1331   opaque data.
1332</t>
1333</section>
1334
1335<section title="Field Length" anchor="field.length">
1336<t>
1337   HTTP does not place a pre-defined limit on the length of header fields,
1338   either in isolation or as a set. A server &MUST; be prepared to receive
1339   request header fields of unbounded length and respond with a <x:ref>4xx
1340   (Client Error)</x:ref> status code if the received header field(s) would be
1341   longer than the server wishes to handle.
1342</t>
1343<t>
1344   A client that receives response header fields that are longer than it wishes
1345   to handle can only treat it as a server error.
1346</t>
1347<t>
1348   Various ad-hoc limitations on header field length are found in practice. It
1349   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1350   combined header fields have 4000 or more octets.
1351</t>
1352</section>
1353
1354<section title="Field value components" anchor="field.components">
1355<t anchor="rule.token.separators">
1356  <x:anchor-alias value="tchar"/>
1357  <x:anchor-alias value="token"/>
1358  <x:anchor-alias value="special"/>
1359  <x:anchor-alias value="word"/>
1360   Many HTTP header field values consist of words (token or quoted-string)
1361   separated by whitespace or special characters. These special characters
1362   &MUST; be in a quoted string to be used within a parameter value (as defined
1363   in <xref target="transfer.codings"/>).
1364</t>
1365<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>
1366  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1367
1368  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1369<!--
1370  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1371 -->
1372  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1373                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1374                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1375                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1376
1377  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1378                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1379                 / "]" / "?" / "=" / "{" / "}"
1380</artwork></figure>
1381<t anchor="rule.quoted-string">
1382  <x:anchor-alias value="quoted-string"/>
1383  <x:anchor-alias value="qdtext"/>
1384  <x:anchor-alias value="obs-text"/>
1385   A string of text is parsed as a single word if it is quoted using
1386   double-quote marks.
1387</t>
1388<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"/>
1389  <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>
1390  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1391  <x:ref>obs-text</x:ref>       = %x80-FF
1392</artwork></figure>
1393<t anchor="rule.quoted-pair">
1394  <x:anchor-alias value="quoted-pair"/>
1395   The backslash octet ("\") can be used as a single-octet
1396   quoting mechanism within quoted-string constructs:
1397</t>
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1399  <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> )
1400</artwork></figure>
1401<t>
1402   Recipients that process the value of the quoted-string &MUST; handle a
1403   quoted-pair as if it were replaced by the octet following the backslash.
1404</t>
1405<t>
1406   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1407   escaping (i.e., other than DQUOTE and the backslash octet).
1408</t>
1409<t anchor="rule.comment">
1410  <x:anchor-alias value="comment"/>
1411  <x:anchor-alias value="ctext"/>
1412   Comments can be included in some HTTP header fields by surrounding
1413   the comment text with parentheses. Comments are only allowed in
1414   fields containing "comment" as part of their field value definition.
1415</t>
1416<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1417  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1418  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1419</artwork></figure>
1420<t anchor="rule.quoted-cpair">
1421  <x:anchor-alias value="quoted-cpair"/>
1422   The backslash octet ("\") can be used as a single-octet
1423   quoting mechanism within comment constructs:
1424</t>
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1426  <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> )
1427</artwork></figure>
1428<t>
1429   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1430   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1431</t>
1432</section>
1433
1434</section>
1435
1436<section title="Message Body" anchor="message.body">
1437  <x:anchor-alias value="message-body"/>
1438<t>
1439   The message body (if any) of an HTTP message is used to carry the
1440   payload body of that request or response.  The message body is
1441   identical to the payload body unless a transfer coding has been
1442   applied, as described in <xref target="header.transfer-encoding"/>.
1443</t>
1444<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1445  <x:ref>message-body</x:ref> = *OCTET
1446</artwork></figure>
1447<t>
1448   The rules for when a message body is allowed in a message differ for
1449   requests and responses.
1450</t>
1451<t>
1452   The presence of a message body in a request is signaled by a
1453   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1454   field. Request message framing is independent of method semantics,
1455   even if the method does not define any use for a message body.
1456</t>
1457<t>
1458   The presence of a message body in a response depends on both
1459   the request method to which it is responding and the response
1460   status code (<xref target="status.line"/>).
1461   Responses to the HEAD request method never include a message body
1462   because the associated response header fields (e.g.,
1463   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1464   indicate what their values would have been if the request method had been
1465   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1466   mode instead of having a message body.
1467   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1468   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1469   All other responses do include a message body, although the body
1470   &MAY; be of zero length.
1471</t>
1472
1473<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1474  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1475  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" 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  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1564  <x:anchor-alias value="Content-Length"/>
1565<t>
1566   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1567   and the payload body length can be determined prior to being transferred, a
1568   Content-Length header field &SHOULD; be sent to indicate the length of the
1569   payload body that is either present as the message body, for requests
1570   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1571   would have been present had the request been an unconditional GET.  The
1572   length is expressed as a decimal number of octets.
1573</t>
1574<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1575  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1576</artwork></figure>
1577<t>
1578   An example is
1579</t>
1580<figure><artwork type="example">
1581  Content-Length: 3495
1582</artwork></figure>
1583<t>
1584   In the case of a response to a HEAD request, Content-Length indicates
1585   the size of the payload body (without any potential transfer-coding)
1586   that would have been sent had the request been a GET.
1587   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1588   to a GET request, Content-Length indicates the size of the payload body (without
1589   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1590   response.
1591</t>
1592<t>
1593   Any Content-Length field value greater than or equal to zero is valid.
1594   Since there is no predefined limit to the length of an HTTP payload,
1595   recipients &SHOULD; anticipate potentially large decimal numerals and
1596   prevent parsing errors due to integer conversion overflows
1597   (<xref target="attack.protocol.element.size.overflows"/>).
1598</t>
1599<t>
1600   If a message is received that has multiple Content-Length header fields
1601   with field-values consisting of the same decimal value, or a single
1602   Content-Length header field with a field value containing a list of
1603   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1604   duplicate Content-Length header fields have been generated or combined by an
1605   upstream message processor, then the recipient &MUST; either reject the
1606   message as invalid or replace the duplicated field-values with a single
1607   valid Content-Length field containing that decimal value prior to
1608   determining the message body length.
1609</t>
1610<x:note>
1611  <t>
1612   &Note; HTTP's use of Content-Length for message framing differs
1613   significantly from the same field's use in MIME, where it is an optional
1614   field used only within the "message/external-body" media-type.
1615  </t>
1616</x:note>
1617</section>
1618
1619<section title="Message Body Length" anchor="message.body.length">
1620<t>
1621   The length of a message body is determined by one of the following
1622   (in order of precedence):
1623</t>
1624<t>
1625  <list style="numbers">
1626    <x:lt><t>
1627     Any response to a HEAD request and any response with a
1628     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1629     <x:ref>304 (Not Modified)</x:ref> status code is always
1630     terminated by the first empty line after the header fields, regardless of
1631     the header fields present in the message, and thus cannot contain a
1632     message body.
1633    </t></x:lt>
1634    <x:lt><t>
1635     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1636     connection will become a tunnel immediately after the empty line that
1637     concludes the header fields.  A client &MUST; ignore any
1638     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1639     fields received in such a message.
1640    </t></x:lt>
1641    <x:lt><t>
1642     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1643     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1644     is the final encoding, the message body length is determined by reading
1645     and decoding the chunked data until the transfer-coding indicates the
1646     data is complete.
1647    </t>
1648    <t>
1649     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1650     response and the "chunked" transfer-coding is not the final encoding, the
1651     message body length is determined by reading the connection until it is
1652     closed by the server.
1653     If a Transfer-Encoding header field is present in a request and the
1654     "chunked" transfer-coding is not the final encoding, the message body
1655     length cannot be determined reliably; the server &MUST; respond with
1656     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1657    </t>
1658    <t>
1659     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1660     and a <x:ref>Content-Length</x:ref> header field, the
1661     Transfer-Encoding overrides the Content-Length.
1662     Such a message might indicate an attempt to perform request or response
1663     smuggling (bypass of security-related checks on message routing or content)
1664     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1665     be removed, prior to forwarding the message downstream, or replaced with
1666     the real message body length after the transfer-coding is decoded.
1667    </t></x:lt>
1668    <x:lt><t>
1669     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1670     either multiple <x:ref>Content-Length</x:ref> header fields having
1671     differing field-values or a single Content-Length header field having an
1672     invalid value, then the message framing is invalid and &MUST; be treated
1673     as an error to prevent request or response smuggling.
1674     If this is a request message, the server &MUST; respond with
1675     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1676     If this is a response message received by a proxy, the proxy
1677     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1678     status code as its downstream response, and then close the connection.
1679     If this is a response message received by a user-agent, it &MUST; be
1680     treated as an error by discarding the message and closing the connection.
1681    </t></x:lt>
1682    <x:lt><t>
1683     If a valid <x:ref>Content-Length</x:ref> header field is present without
1684     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1685     message body length in octets.  If the actual number of octets sent in
1686     the message is less than the indicated Content-Length, the recipient
1687     &MUST; consider the message to be incomplete and treat the connection
1688     as no longer usable.
1689     If the actual number of octets sent in the message is more than the indicated
1690     Content-Length, the recipient &MUST; only process the message body up to the
1691     field value's number of octets; the remainder of the message &MUST; either
1692     be discarded or treated as the next message in a pipeline.  For the sake of
1693     robustness, a user-agent &MAY; attempt to detect and correct such an error
1694     in message framing if it is parsing the response to the last request on
1695     a connection and the connection has been closed by the server.
1696    </t></x:lt>
1697    <x:lt><t>
1698     If this is a request message and none of the above are true, then the
1699     message body length is zero (no message body is present).
1700    </t></x:lt>
1701    <x:lt><t>
1702     Otherwise, this is a response message without a declared message body
1703     length, so the message body length is determined by the number of octets
1704     received prior to the server closing the connection.
1705    </t></x:lt>
1706  </list>
1707</t>
1708<t>
1709   Since there is no way to distinguish a successfully completed,
1710   close-delimited message from a partially-received message interrupted
1711   by network failure, implementations &SHOULD; use encoding or
1712   length-delimited messages whenever possible.  The close-delimiting
1713   feature exists primarily for backwards compatibility with HTTP/1.0.
1714</t>
1715<t>
1716   A server &MAY; reject a request that contains a message body but
1717   not a <x:ref>Content-Length</x:ref> by responding with
1718   <x:ref>411 (Length Required)</x:ref>.
1719</t>
1720<t>
1721   Unless a transfer-coding other than "chunked" has been applied,
1722   a client that sends a request containing a message body &SHOULD;
1723   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1724   length is known in advance, rather than the "chunked" encoding, since some
1725   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1726   status code even though they understand the chunked encoding.  This
1727   is typically because such services are implemented via a gateway that
1728   requires a content-length in advance of being called and the server
1729   is unable or unwilling to buffer the entire request before processing.
1730</t>
1731<t>
1732   A client that sends a request containing a message body &MUST; include a
1733   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1734   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1735   the form of specific user configuration or by remembering the version of a
1736   prior received response.
1737</t>
1738</section>
1739</section>
1740
1741<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1742<t>
1743   Request messages that are prematurely terminated, possibly due to a
1744   canceled connection or a server-imposed time-out exception, &MUST;
1745   result in closure of the connection; sending an error response
1746   prior to closing the connection is &OPTIONAL;.
1747</t>
1748<t>
1749   Response messages that are prematurely terminated, usually by closure
1750   of the connection prior to receiving the expected number of octets or by
1751   failure to decode a transfer-encoded message body, &MUST; be recorded
1752   as incomplete.  A response that terminates in the middle of the header
1753   block (before the empty line is received) cannot be assumed to convey the
1754   full semantics of the response and &MUST; be treated as an error.
1755</t>
1756<t>
1757   A message body that uses the chunked transfer encoding is
1758   incomplete if the zero-sized chunk that terminates the encoding has not
1759   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1760   incomplete if the size of the message body received (in octets) is less than
1761   the value given by Content-Length.  A response that has neither chunked
1762   transfer encoding nor Content-Length is terminated by closure of the
1763   connection, and thus is considered complete regardless of the number of
1764   message body octets received, provided that the header block was received
1765   intact.
1766</t>
1767<t>
1768   A user agent &MUST-NOT; render an incomplete response message body as if
1769   it were complete (i.e., some indication needs to be given to the user that an
1770   error occurred).  Cache requirements for incomplete responses are defined
1771   in &cache-incomplete;.
1772</t>
1773<t>
1774   A server &MUST; read the entire request message body or close
1775   the connection after sending its response, since otherwise the
1776   remaining data on a persistent connection would be misinterpreted
1777   as the next request.  Likewise,
1778   a client &MUST; read the entire response message body if it intends
1779   to reuse the same connection for a subsequent request.  Pipelining
1780   multiple requests on a connection is described in <xref target="pipelining"/>.
1781</t>
1782</section>
1783
1784<section title="Message Parsing Robustness" anchor="message.robustness">
1785<t>
1786   Older HTTP/1.0 client implementations might send an extra CRLF
1787   after a POST request as a lame workaround for some early server
1788   applications that failed to read message body content that was
1789   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1790   preface or follow a request with an extra CRLF.  If terminating
1791   the request message body with a line-ending is desired, then the
1792   client &MUST; include the terminating CRLF octets as part of the
1793   message body length.
1794</t>
1795<t>
1796   In the interest of robustness, servers &SHOULD; ignore at least one
1797   empty line received where a request-line is expected. In other words, if
1798   the server is reading the protocol stream at the beginning of a
1799   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1800   Likewise, although the line terminator for the start-line and header
1801   fields is the sequence CRLF, we recommend that recipients recognize a
1802   single LF as a line terminator and ignore any CR.
1803</t>
1804<t>
1805   When a server listening only for HTTP request messages, or processing
1806   what appears from the start-line to be an HTTP request message,
1807   receives a sequence of octets that does not match the HTTP-message
1808   grammar aside from the robustness exceptions listed above, the
1809   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1810</t>
1811</section>
1812</section>
1813
1814<section title="Transfer Codings" anchor="transfer.codings">
1815  <x:anchor-alias value="transfer-coding"/>
1816  <x:anchor-alias value="transfer-extension"/>
1817<t>
1818   Transfer-coding values are used to indicate an encoding
1819   transformation that has been, can be, or might need to be applied to a
1820   payload body in order to ensure "safe transport" through the network.
1821   This differs from a content coding in that the transfer-coding is a
1822   property of the message rather than a property of the representation
1823   that is being transferred.
1824</t>
1825<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1826  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1827                     / "compress" ; <xref target="compress.coding"/>
1828                     / "deflate" ; <xref target="deflate.coding"/>
1829                     / "gzip" ; <xref target="gzip.coding"/>
1830                     / <x:ref>transfer-extension</x:ref>
1831  <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> )
1832</artwork></figure>
1833<t anchor="rule.parameter">
1834  <x:anchor-alias value="attribute"/>
1835  <x:anchor-alias value="transfer-parameter"/>
1836  <x:anchor-alias value="value"/>
1837   Parameters are in the form of attribute/value pairs.
1838</t>
1839<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"/>
1840  <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>
1841  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1842  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1843</artwork></figure>
1844<t>
1845   All transfer-coding values are case-insensitive and &SHOULD; be registered
1846   within the HTTP Transfer Coding registry, as defined in
1847   <xref target="transfer.coding.registry"/>.
1848   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1849   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1850   header fields.
1851</t>
1852
1853<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1854  <iref item="chunked (Coding Format)"/>
1855  <iref item="Coding Format" subitem="chunked"/>
1856  <x:anchor-alias value="chunk"/>
1857  <x:anchor-alias value="chunked-body"/>
1858  <x:anchor-alias value="chunk-data"/>
1859  <x:anchor-alias value="chunk-ext"/>
1860  <x:anchor-alias value="chunk-ext-name"/>
1861  <x:anchor-alias value="chunk-ext-val"/>
1862  <x:anchor-alias value="chunk-size"/>
1863  <x:anchor-alias value="last-chunk"/>
1864  <x:anchor-alias value="trailer-part"/>
1865  <x:anchor-alias value="quoted-str-nf"/>
1866  <x:anchor-alias value="qdtext-nf"/>
1867<t>
1868   The chunked encoding modifies the body of a message in order to
1869   transfer it as a series of chunks, each with its own size indicator,
1870   followed by an &OPTIONAL; trailer containing header fields. This
1871   allows dynamically produced content to be transferred along with the
1872   information necessary for the recipient to verify that it has
1873   received the full message.
1874</t>
1875<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"/>
1876  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1877                   <x:ref>last-chunk</x:ref>
1878                   <x:ref>trailer-part</x:ref>
1879                   <x:ref>CRLF</x:ref>
1880 
1881  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1882                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1883  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1884  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1885 
1886  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1887  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1888  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1889  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1890  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1891 
1892  <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>
1893                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1894  <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>
1895</artwork></figure>
1896<t>
1897   Chunk extensions within the chucked encoding are deprecated.
1898   Senders &SHOULD-NOT; send chunk-ext.
1899   Definition of new chunk extensions is discouraged.
1900</t>
1901<t>
1902   The chunk-size field is a string of hex digits indicating the size of
1903   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1904   zero, followed by the trailer, which is terminated by an empty line.
1905</t>
1906
1907<section title="Trailer" anchor="header.trailer">
1908  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1909  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
1910  <x:anchor-alias value="Trailer"/>
1911<t>
1912   A trailer allows the sender to include additional fields at the end of a
1913   chunked message in order to supply metadata that might be dynamically
1914   generated while the message body is sent, such as a message integrity
1915   check, digital signature, or post-processing status.
1916   The trailer &MUST-NOT; contain fields that need to be known before a
1917   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1918   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1919</t>
1920<t>
1921   When a message includes a message body encoded with the chunked
1922   transfer-coding and the sender desires to send metadata in the form of
1923   trailer fields at the end of the message, the sender &SHOULD; send a
1924   <x:ref>Trailer</x:ref> header field before the message body to indicate
1925   which fields will be present in the trailers. This allows the recipient
1926   to prepare for receipt of that metadata before it starts processing the body,
1927   which is useful if the message is being streamed and the recipient wishes
1928   to confirm an integrity check on the fly.
1929</t>
1930<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1931  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1932</artwork></figure>
1933<t>
1934   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1935   chunked message body &SHOULD; send an empty trailer.
1936</t>
1937<t>
1938   A server &MUST; send an empty trailer with the chunked transfer-coding
1939   unless at least one of the following is true:
1940  <list style="numbers">
1941    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1942    "trailers" is acceptable in the transfer-coding of the response, as
1943    described in <xref target="header.te"/>; or,</t>
1944     
1945    <t>the trailer fields consist entirely of optional metadata and the
1946    recipient could use the message (in a manner acceptable to the server where
1947    the field originated) without receiving that metadata. In other words,
1948    the server that generated the header field is willing to accept the
1949    possibility that the trailer fields might be silently discarded along
1950    the path to the client.</t>
1951  </list>
1952</t>
1953<t>
1954   The above requirement prevents the need for an infinite buffer when a
1955   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1956   an HTTP/1.0 recipient.
1957</t>
1958</section>
1959
1960<section title="Decoding chunked" anchor="decoding.chunked">
1961<t>
1962   A process for decoding the "chunked" transfer-coding
1963   can be represented in pseudo-code as:
1964</t>
1965<figure><artwork type="code">
1966  length := 0
1967  read chunk-size, chunk-ext (if any) and CRLF
1968  while (chunk-size &gt; 0) {
1969     read chunk-data and CRLF
1970     append chunk-data to decoded-body
1971     length := length + chunk-size
1972     read chunk-size and CRLF
1973  }
1974  read header-field
1975  while (header-field not empty) {
1976     append header-field to existing header fields
1977     read header-field
1978  }
1979  Content-Length := length
1980  Remove "chunked" from Transfer-Encoding
1981  Remove Trailer from existing header fields
1982</artwork></figure>
1983<t>
1984   All recipients &MUST; be able to receive and decode the
1985   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1986   they do not understand.
1987</t>
1988</section>
1989</section>
1990
1991<section title="Compression Codings" anchor="compression.codings">
1992<t>
1993   The codings defined below can be used to compress the payload of a
1994   message.
1995</t>
1996
1997<section title="Compress Coding" anchor="compress.coding">
1998<iref item="compress (Coding Format)"/>
1999<iref item="Coding Format" subitem="compress"/>
2000<t>
2001   The "compress" format is produced by the common UNIX file compression
2002   program "compress". This format is an adaptive Lempel-Ziv-Welch
2003   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2004   equivalent to "compress".
2005</t>
2006</section>
2007
2008<section title="Deflate Coding" anchor="deflate.coding">
2009<iref item="deflate (Coding Format)"/>
2010<iref item="Coding Format" subitem="deflate"/>
2011<t>
2012   The "deflate" format is defined as the "deflate" compression mechanism
2013   (described in <xref target="RFC1951"/>) used inside the "zlib"
2014   data format (<xref target="RFC1950"/>).
2015</t>
2016<x:note>
2017  <t>
2018    &Note; Some incorrect implementations send the "deflate"
2019    compressed data without the zlib wrapper.
2020   </t>
2021</x:note>
2022</section>
2023
2024<section title="Gzip Coding" anchor="gzip.coding">
2025<iref item="gzip (Coding Format)"/>
2026<iref item="Coding Format" subitem="gzip"/>
2027<t>
2028   The "gzip" format is produced by the file compression program
2029   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2030   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2031   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2032</t>
2033</section>
2034
2035</section>
2036
2037<section title="TE" anchor="header.te">
2038  <iref primary="true" item="TE header field" x:for-anchor=""/>
2039  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2040  <x:anchor-alias value="TE"/>
2041  <x:anchor-alias value="t-codings"/>
2042  <x:anchor-alias value="t-ranking"/>
2043  <x:anchor-alias value="rank"/>
2044<t>
2045   The "TE" header field in a request indicates what transfer-codings,
2046   besides "chunked", the client is willing to accept in response, and
2047   whether or not the client is willing to accept trailer fields in a
2048   chunked transfer-coding.
2049</t>
2050<t>
2051   The TE field-value consists of a comma-separated list of transfer-coding
2052   names, each allowing for optional parameters (as described in
2053   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2054   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2055   chunked is always acceptable for HTTP/1.1 recipients.
2056</t>
2057<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"/>
2058  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2059  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2060  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2061  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2062             / ( "1" [ "." 0*3("0") ] )
2063</artwork></figure>
2064<t>
2065   Three examples of TE use are below.
2066</t>
2067<figure><artwork type="example">
2068  TE: deflate
2069  TE:
2070  TE: trailers, deflate;q=0.5
2071</artwork></figure>
2072<t>
2073   The presence of the keyword "trailers" indicates that the client is
2074   willing to accept trailer fields in a chunked transfer-coding,
2075   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2076   any downstream clients. For chained requests, this implies that either:
2077   (a) all downstream clients are willing to accept trailer fields in the
2078   forwarded response; or,
2079   (b) the client will attempt to buffer the response on behalf of downstream
2080   recipients.
2081   Note that HTTP/1.1 does not define any means to limit the size of a
2082   chunked response such that a client can be assured of buffering the
2083   entire response.
2084</t>
2085<t>
2086   When multiple transfer-codings are acceptable, the client &MAY; rank the
2087   codings by preference using a case-insensitive "q" parameter (similar to
2088   the qvalues used in content negotiation fields, &qvalue;). The rank value
2089   is a real number in the range 0 through 1, where 0.001 is the least
2090   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2091</t>
2092<t>
2093   If the TE field-value is empty or if no TE field is present, the only
2094   acceptable transfer-coding is "chunked". A message with no transfer-coding
2095   is always acceptable.
2096</t>
2097<t>
2098   Since the TE header field only applies to the immediate connection,
2099   a sender of TE &MUST; also send a "TE" connection option within the
2100   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2101   in order to prevent the TE field from being forwarded by intermediaries
2102   that do not support its semantics.
2103</t>
2104</section>
2105</section>
2106
2107<section title="Message Routing" anchor="message.routing">
2108<t>
2109   HTTP request message routing is determined by each client based on the
2110   target resource, the client's proxy configuration, and
2111   establishment or reuse of an inbound connection.  The corresponding
2112   response routing follows the same connection chain back to the client.
2113</t>
2114
2115<section title="Identifying a Target Resource" anchor="target-resource">
2116  <iref primary="true" item="target resource"/>
2117  <iref primary="true" item="target URI"/>
2118  <x:anchor-alias value="target resource"/>
2119  <x:anchor-alias value="target URI"/>
2120<t>
2121   HTTP is used in a wide variety of applications, ranging from
2122   general-purpose computers to home appliances.  In some cases,
2123   communication options are hard-coded in a client's configuration.
2124   However, most HTTP clients rely on the same resource identification
2125   mechanism and configuration techniques as general-purpose Web browsers.
2126</t>
2127<t>
2128   HTTP communication is initiated by a user agent for some purpose.
2129   The purpose is a combination of request semantics, which are defined in
2130   <xref target="Part2"/>, and a target resource upon which to apply those
2131   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2132   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2133   would resolve to its absolute form in order to obtain the
2134   "<x:dfn>target URI</x:dfn>".  The target URI
2135   excludes the reference's fragment identifier component, if any,
2136   since fragment identifiers are reserved for client-side processing
2137   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2138</t>
2139</section>
2140
2141<section title="Connecting Inbound" anchor="connecting.inbound">
2142<t>
2143   Once the target URI is determined, a client needs to decide whether
2144   a network request is necessary to accomplish the desired semantics and,
2145   if so, where that request is to be directed.
2146</t>
2147<t>
2148   If the client has a response cache and the request semantics can be
2149   satisfied by a cache (<xref target="Part6"/>), then the request is
2150   usually directed to the cache first.
2151</t>
2152<t>
2153   If the request is not satisfied by a cache, then a typical client will
2154   check its configuration to determine whether a proxy is to be used to
2155   satisfy the request.  Proxy configuration is implementation-dependent,
2156   but is often based on URI prefix matching, selective authority matching,
2157   or both, and the proxy itself is usually identified by an "http" or
2158   "https" URI.  If a proxy is applicable, the client connects inbound by
2159   establishing (or reusing) a connection to that proxy.
2160</t>
2161<t>
2162   If no proxy is applicable, a typical client will invoke a handler routine,
2163   usually specific to the target URI's scheme, to connect directly
2164   to an authority for the target resource.  How that is accomplished is
2165   dependent on the target URI scheme and defined by its associated
2166   specification, similar to how this specification defines origin server
2167   access for resolution of the "http" (<xref target="http.uri"/>) and
2168   "https" (<xref target="https.uri"/>) schemes.
2169</t>
2170<t>
2171   HTTP requirements regarding connection management are defined in
2172   <xref target="connection.management"/>.
2173</t>
2174</section>
2175
2176<section title="Request Target" anchor="request-target">
2177<t>
2178   Once an inbound connection is obtained,
2179   the client sends an HTTP request message (<xref target="http.message"/>)
2180   with a request-target derived from the target URI.
2181   There are four distinct formats for the request-target, depending on both
2182   the method being requested and whether the request is to a proxy.
2183</t>   
2184<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"/>
2185  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2186                 / <x:ref>absolute-form</x:ref>
2187                 / <x:ref>authority-form</x:ref>
2188                 / <x:ref>asterisk-form</x:ref>
2189
2190  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2191  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2192  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2193  <x:ref>asterisk-form</x:ref>  = "*"
2194</artwork></figure>
2195<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2196   The most common form of request-target is the origin-form.
2197   When making a request directly to an origin server, other than a CONNECT
2198   or server-wide OPTIONS request (as detailed below),
2199   a client &MUST; send only the absolute path and query components of
2200   the target URI as the request-target.
2201   If the target URI's path component is empty, then the client &MUST; send
2202   "/" as the path within the origin-form of request-target.
2203   A <x:ref>Host</x:ref> header field is also sent, as defined in
2204   <xref target="header.host"/>, containing the target URI's
2205   authority component (excluding any userinfo).
2206</t>
2207<t>
2208   For example, a client wishing to retrieve a representation of the resource
2209   identified as
2210</t>
2211<figure><artwork x:indent-with="  " type="example">
2212http://www.example.org/where?q=now
2213</artwork></figure>
2214<t>
2215   directly from the origin server would open (or reuse) a TCP connection
2216   to port 80 of the host "www.example.org" and send the lines:
2217</t>
2218<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2219GET /where?q=now HTTP/1.1
2220Host: www.example.org
2221</artwork></figure>
2222<t>
2223   followed by the remainder of the request message.
2224</t>
2225<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2226   When making a request to a proxy, other than a CONNECT or server-wide
2227   OPTIONS request (as detailed below), a client &MUST; send the target URI
2228   in absolute-form as the request-target.
2229   The proxy is requested to either service that request from a valid cache,
2230   if possible, or make the same request on the client's behalf to either
2231   the next inbound proxy server or directly to the origin server indicated
2232   by the request-target.  Requirements on such "forwarding" of messages are
2233   defined in <xref target="message.forwarding"/>.
2234</t>
2235<t>
2236   An example absolute-form of request-line would be:
2237</t>
2238<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2239GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2240</artwork></figure>
2241<t>
2242   To allow for transition to the absolute-form for all requests in some
2243   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2244   in requests, even though HTTP/1.1 clients will only send them in requests
2245   to proxies.
2246</t>
2247<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2248   The authority-form of request-target is only used for CONNECT requests
2249   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2250   one or more proxies, a client &MUST; send only the target URI's
2251   authority component (excluding any userinfo) as the request-target.
2252   For example,
2253</t>
2254<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2255CONNECT www.example.com:80 HTTP/1.1
2256</artwork></figure>
2257<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2258   The asterisk-form of request-target is only used for a server-wide
2259   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2260   for the server as a whole, as opposed to a specific named resource of
2261   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2262   For example,
2263</t>
2264<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2265OPTIONS * HTTP/1.1
2266</artwork></figure>
2267<t>
2268   If a proxy receives an OPTIONS request with an absolute-form of
2269   request-target in which the URI has an empty path and no query component,
2270   then the last proxy on the request chain &MUST; send a request-target
2271   of "*" when it forwards the request to the indicated origin server.
2272</t>
2273<figure><preamble>   
2274   For example, the request
2275</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2276OPTIONS http://www.example.org:8001 HTTP/1.1
2277</artwork></figure>
2278<figure><preamble>   
2279  would be forwarded by the final proxy as
2280</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2281OPTIONS * HTTP/1.1
2282Host: www.example.org:8001
2283</artwork>
2284<postamble>
2285   after connecting to port 8001 of host "www.example.org".
2286</postamble>
2287</figure>
2288</section>
2289
2290<section title="Host" anchor="header.host">
2291  <iref primary="true" item="Host header field" x:for-anchor=""/>
2292  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2293  <x:anchor-alias value="Host"/>
2294<t>
2295   The "Host" header field in a request provides the host and port
2296   information from the target URI, enabling the origin
2297   server to distinguish among resources while servicing requests
2298   for multiple host names on a single IP address.  Since the Host
2299   field-value is critical information for handling a request, it
2300   &SHOULD; be sent as the first header field following the request-line.
2301</t>
2302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2303  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2304</artwork></figure>
2305<t>
2306   A client &MUST; send a Host header field in all HTTP/1.1 request
2307   messages.  If the target URI includes an authority component, then
2308   the Host field-value &MUST; be identical to that authority component
2309   after excluding any userinfo (<xref target="http.uri"/>).
2310   If the authority component is missing or undefined for the target URI,
2311   then the Host header field &MUST; be sent with an empty field-value.
2312</t>
2313<t>
2314   For example, a GET request to the origin server for
2315   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2316</t>
2317<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2318GET /pub/WWW/ HTTP/1.1
2319Host: www.example.org
2320</artwork></figure>
2321<t>
2322   The Host header field &MUST; be sent in an HTTP/1.1 request even
2323   if the request-target is in the absolute-form, since this
2324   allows the Host information to be forwarded through ancient HTTP/1.0
2325   proxies that might not have implemented Host.
2326</t>
2327<t>
2328   When a proxy receives a request with an absolute-form of
2329   request-target, the proxy &MUST; ignore the received
2330   Host header field (if any) and instead replace it with the host
2331   information of the request-target.  If the proxy forwards the request,
2332   it &MUST; generate a new Host field-value based on the received
2333   request-target rather than forward the received Host field-value.
2334</t>
2335<t>
2336   Since the Host header field acts as an application-level routing
2337   mechanism, it is a frequent target for malware seeking to poison
2338   a shared cache or redirect a request to an unintended server.
2339   An interception proxy is particularly vulnerable if it relies on
2340   the Host field-value for redirecting requests to internal
2341   servers, or for use as a cache key in a shared cache, without
2342   first verifying that the intercepted connection is targeting a
2343   valid IP address for that host.
2344</t>
2345<t>
2346   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2347   to any HTTP/1.1 request message that lacks a Host header field and
2348   to any request message that contains more than one Host header field
2349   or a Host header field with an invalid field-value.
2350</t>
2351</section>
2352
2353<section title="Effective Request URI" anchor="effective.request.uri">
2354  <iref primary="true" item="effective request URI"/>
2355<t>
2356   A server that receives an HTTP request message &MUST; reconstruct
2357   the user agent's original target URI, based on the pieces of information
2358   learned from the request-target, <x:ref>Host</x:ref> header field, and
2359   connection context, in order to identify the intended target resource and
2360   properly service the request. The URI derived from this reconstruction
2361   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2362</t>
2363<t>
2364   For a user agent, the effective request URI is the target URI.
2365</t>
2366<t>
2367   If the request-target is in absolute-form, then the effective request URI
2368   is the same as the request-target.  Otherwise, the effective request URI
2369   is constructed as follows.
2370</t>
2371<t>
2372   If the request is received over an SSL/TLS-secured TCP connection,
2373   then the effective request URI's scheme is "https"; otherwise, the
2374   scheme is "http".
2375</t>
2376<t>
2377   If the request-target is in authority-form, then the effective
2378   request URI's authority component is the same as the request-target.
2379   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2380   non-empty field-value, then the authority component is the same as the
2381   Host field-value. Otherwise, the authority component is the concatenation of
2382   the default host name configured for the server, a colon (":"), and the
2383   connection's incoming TCP port number in decimal form.
2384</t>
2385<t>
2386   If the request-target is in authority-form or asterisk-form, then the
2387   effective request URI's combined path and query component is empty.
2388   Otherwise, the combined path and query component is the same as the
2389   request-target.
2390</t>
2391<t>
2392   The components of the effective request URI, once determined as above,
2393   can be combined into absolute-URI form by concatenating the scheme,
2394   "://", authority, and combined path and query component.
2395</t>
2396<figure>
2397<preamble>
2398   Example 1: the following message received over an insecure TCP connection
2399</preamble> 
2400<artwork type="example" x:indent-with="  ">
2401GET /pub/WWW/TheProject.html HTTP/1.1
2402Host: www.example.org:8080
2403</artwork>
2404</figure>
2405<figure>
2406<preamble>
2407  has an effective request URI of
2408</preamble>
2409<artwork type="example" x:indent-with="  ">
2410http://www.example.org:8080/pub/WWW/TheProject.html
2411</artwork>
2412</figure>
2413<figure>
2414<preamble>
2415   Example 2: the following message received over an SSL/TLS-secured TCP
2416   connection
2417</preamble> 
2418<artwork type="example" x:indent-with="  ">
2419OPTIONS * HTTP/1.1
2420Host: www.example.org
2421</artwork>
2422</figure>
2423<figure>
2424<preamble>
2425  has an effective request URI of
2426</preamble>
2427<artwork type="example" x:indent-with="  ">
2428https://www.example.org
2429</artwork>
2430</figure>
2431<t>
2432   An origin server that does not allow resources to differ by requested
2433   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2434   with a configured server name when constructing the effective request URI.
2435</t>
2436<t>
2437   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2438   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2439   something unique to a particular host) in order to guess the
2440   effective request URI's authority component.
2441</t>
2442</section>
2443
2444<section title="Message Forwarding" anchor="message.forwarding">
2445<t>
2446   As described in <xref target="intermediaries"/>, intermediaries can serve
2447   a variety of roles in the processing of HTTP requests and responses.
2448   Some intermediaries are used to improve performance or availability.
2449   Others are used for access control or to filter content.
2450   Since an HTTP stream has characteristics similar to a pipe-and-filter
2451   architecture, there are no inherent limits to the extent an intermediary
2452   can enhance (or interfere) with either direction of the stream.
2453</t>
2454<t>
2455   Intermediaries that forward a message &MUST; implement the
2456   <x:ref>Connection</x:ref> header field, as specified in
2457   <xref target="header.connection"/>, to exclude fields that are only
2458   intended for the incoming connection.
2459</t>
2460<t>
2461   In order to avoid request loops, a proxy that forwards requests to other
2462   proxies &MUST; be able to recognize and exclude all of its own server
2463   names, including any aliases, local variations, or literal IP addresses.
2464</t>
2465</section>
2466
2467<section title="Via" anchor="header.via">
2468  <iref primary="true" item="Via header field" x:for-anchor=""/>
2469  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2470  <x:anchor-alias value="pseudonym"/>
2471  <x:anchor-alias value="received-by"/>
2472  <x:anchor-alias value="received-protocol"/>
2473  <x:anchor-alias value="Via"/>
2474<t>
2475   The "Via" header field &MUST; be sent by a proxy or gateway
2476   in forwarded messages to
2477   indicate the intermediate protocols and recipients between the user
2478   agent and the server on requests, and between the origin server and
2479   the client on responses. It is analogous to the "Received" field
2480   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2481   Via is used in HTTP for tracking message forwards,
2482   avoiding request loops, and identifying the protocol capabilities of
2483   all senders along the request/response chain.
2484</t>
2485<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"/>
2486  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2487                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2488  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2489  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2490  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2491</artwork></figure>
2492<t>
2493   The received-protocol indicates the protocol version of the message
2494   received by the server or client along each segment of the
2495   request/response chain. The received-protocol version is appended to
2496   the Via field value when the message is forwarded so that information
2497   about the protocol capabilities of upstream applications remains
2498   visible to all recipients.
2499</t>
2500<t>
2501   The protocol-name is excluded if and only if it would be "HTTP". The
2502   received-by field is normally the host and optional port number of a
2503   recipient server or client that subsequently forwarded the message.
2504   However, if the real host is considered to be sensitive information,
2505   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2506   be assumed to be the default port of the received-protocol.
2507</t>
2508<t>
2509   Multiple Via field values represent each proxy or gateway that has
2510   forwarded the message. Each recipient &MUST; append its information
2511   such that the end result is ordered according to the sequence of
2512   forwarding applications.
2513</t>
2514<t>
2515   Comments &MAY; be used in the Via header field to identify the software
2516   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2517   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2518   are optional and &MAY; be removed by any recipient prior to forwarding the
2519   message.
2520</t>
2521<t>
2522   For example, a request message could be sent from an HTTP/1.0 user
2523   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2524   forward the request to a public proxy at p.example.net, which completes
2525   the request by forwarding it to the origin server at www.example.com.
2526   The request received by www.example.com would then have the following
2527   Via header field:
2528</t>
2529<figure><artwork type="example">
2530  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2531</artwork></figure>
2532<t>
2533   A proxy or gateway used as a portal through a network firewall
2534   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2535   region unless it is explicitly enabled to do so. If not enabled, the
2536   received-by host of any host behind the firewall &SHOULD; be replaced
2537   by an appropriate pseudonym for that host.
2538</t>
2539<t>
2540   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2541   field entries into a single such entry if the entries have identical
2542   received-protocol values. For example,
2543</t>
2544<figure><artwork type="example">
2545  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2546</artwork></figure>
2547<t>
2548  could be collapsed to
2549</t>
2550<figure><artwork type="example">
2551  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2552</artwork></figure>
2553<t>
2554   Senders &SHOULD-NOT; combine multiple entries unless they are all
2555   under the same organizational control and the hosts have already been
2556   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2557   have different received-protocol values.
2558</t>
2559</section>
2560
2561<section title="Message Transforming" anchor="message.transforming">
2562<t>
2563   If a proxy receives a request-target with a host name that is not a
2564   fully qualified domain name, it &MAY; add its own domain to the host name
2565   it received when forwarding the request.  A proxy &MUST-NOT; change the
2566   host name if it is a fully qualified domain name.
2567</t>
2568<t>
2569   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2570   parts of the received request-target when forwarding it to the next inbound
2571   server, except as noted above to replace an empty path with "/" or "*".
2572</t>
2573<t>
2574   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2575   though it &MAY; change the message body through application or removal
2576   of a transfer-coding (<xref target="transfer.codings"/>).
2577</t>
2578<t>
2579   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2580   information about the end points of the communication chain, the resource
2581   state, or the selected representation.
2582</t>
2583<t>
2584   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2585   request or response, and it &MUST-NOT; add any of these fields if not
2586   already present:
2587  <list style="symbols">
2588    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2589    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2590    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2591    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2592    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2593    <t><x:ref>Server</x:ref> (&header-server;)</t>
2594  </list>
2595</t>
2596<t>
2597   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2598   header field (&header-expires;) if already present in a response, but
2599   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2600   identical to that of the <x:ref>Date</x:ref> header field.
2601</t>
2602<t>
2603   A proxy &MUST-NOT; modify or add any of the following fields in a
2604   message that contains the no-transform cache-control directive:
2605  <list style="symbols">
2606    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2607    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2608    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2609  </list>
2610</t>
2611<t>
2612   A transforming proxy &MAY; modify or add these fields to a message
2613   that does not include no-transform, but if it does so, it &MUST; add a
2614   Warning 214 (Transformation applied) if one does not already appear
2615   in the message (see &header-warning;).
2616</t>
2617<x:note>
2618  <t>
2619    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2620    cause authentication failures if stronger authentication
2621    mechanisms are introduced in later versions of HTTP. Such
2622    authentication mechanisms &MAY; rely on the values of header fields
2623    not listed here.
2624  </t>
2625</x:note>
2626</section>
2627
2628<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2629<t>
2630   HTTP does not include a request identifier for associating a given
2631   request message with its corresponding one or more response messages.
2632   Hence, it relies on the order of response arrival to correspond exactly
2633   to the order in which requests are made on the same connection.
2634   More than one response message per request only occurs when one or more
2635   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2636   to the same request.
2637</t>
2638<t>
2639   A client that uses persistent connections and sends more than one request
2640   per connection &MUST; maintain a list of outstanding requests in the
2641   order sent on that connection and &MUST; associate each received response
2642   message to the highest ordered request that has not yet received a final
2643   (non-<x:ref>1xx</x:ref>) response.
2644</t>
2645</section>
2646</section>
2647
2648<section title="Connection Management" anchor="connection.management">
2649<t>
2650   HTTP messaging is independent of the underlying transport or
2651   session-layer connection protocol(s).  HTTP only presumes a reliable
2652   transport with in-order delivery of requests and the corresponding
2653   in-order delivery of responses.  The mapping of HTTP request and
2654   response structures onto the data units of an underlying transport
2655   protocol is outside the scope of this specification.
2656</t>
2657<t>
2658   As described in <xref target="connecting.inbound"/>, the specific
2659   connection protocols to be used for an HTTP interaction are determined by
2660   client configuration and the <x:ref>target URI</x:ref>.
2661   For example, the "http" URI scheme
2662   (<xref target="http.uri"/>) indicates a default connection of TCP
2663   over IP, with a default TCP port of 80, but the client might be
2664   configured to use a proxy via some other connection, port, or protocol.
2665</t>
2666<t>
2667   HTTP implementations are expected to engage in connection management,
2668   which includes maintaining the state of current connections,
2669   establishing a new connection or reusing an existing connection,
2670   processing messages received on a connection, detecting connection
2671   failures, and closing each connection.
2672   Most clients maintain multiple connections in parallel, including
2673   more than one connection per server endpoint.
2674   Most servers are designed to maintain thousands of concurrent connections,
2675   while controlling request queues to enable fair use and detect
2676   denial of service attacks.
2677</t>
2678
2679<section title="Connection" anchor="header.connection">
2680  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2681  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2682  <iref primary="true" item="close" x:for-anchor=""/>
2683  <x:anchor-alias value="Connection"/>
2684  <x:anchor-alias value="connection-option"/>
2685  <x:anchor-alias value="close"/>
2686<t>
2687   The "Connection" header field allows the sender to indicate desired
2688   control options for the current connection.  In order to avoid confusing
2689   downstream recipients, a proxy or gateway &MUST; remove or replace any
2690   received connection options before forwarding the message.
2691</t>
2692<t>
2693   When a header field is used to supply control information for or about
2694   the current connection, the sender &SHOULD; list the corresponding
2695   field-name within the "Connection" header field.
2696   A proxy or gateway &MUST; parse a received Connection
2697   header field before a message is forwarded and, for each
2698   connection-option in this field, remove any header field(s) from
2699   the message with the same name as the connection-option, and then
2700   remove the Connection header field itself (or replace it with the
2701   intermediary's own connection options for the forwarded message).
2702</t>
2703<t>
2704   Hence, the Connection header field provides a declarative way of
2705   distinguishing header fields that are only intended for the
2706   immediate recipient ("hop-by-hop") from those fields that are
2707   intended for all recipients on the chain ("end-to-end"), enabling the
2708   message to be self-descriptive and allowing future connection-specific
2709   extensions to be deployed without fear that they will be blindly
2710   forwarded by older intermediaries.
2711</t>
2712<t>
2713   The Connection header field's value has the following grammar:
2714</t>
2715<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2716  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2717  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2718</artwork></figure>
2719<t>
2720   Connection options are case-insensitive.
2721</t>
2722<t>
2723   A sender &MUST-NOT; include field-names in the Connection header
2724   field-value for fields that are defined as expressing constraints
2725   for all recipients in the request or response chain, such as the
2726   Cache-Control header field (&header-cache-control;).
2727</t>
2728<t>
2729   The connection options do not have to correspond to a header field
2730   present in the message, since a connection-specific header field
2731   might not be needed if there are no parameters associated with that
2732   connection option.  Recipients that trigger certain connection
2733   behavior based on the presence of connection options &MUST; do so
2734   based on the presence of the connection-option rather than only the
2735   presence of the optional header field.  In other words, if the
2736   connection option is received as a header field but not indicated
2737   within the Connection field-value, then the recipient &MUST; ignore
2738   the connection-specific header field because it has likely been
2739   forwarded by an intermediary that is only partially conformant.
2740</t>
2741<t>
2742   When defining new connection options, specifications ought to
2743   carefully consider existing deployed header fields and ensure
2744   that the new connection option does not share the same name as
2745   an unrelated header field that might already be deployed.
2746   Defining a new connection option essentially reserves that potential
2747   field-name for carrying additional information related to the
2748   connection option, since it would be unwise for senders to use
2749   that field-name for anything else.
2750</t>
2751<t>
2752   The "<x:dfn>close</x:dfn>" connection option is defined for a
2753   sender to signal that this connection will be closed after completion of
2754   the response. For example,
2755</t>
2756<figure><artwork type="example">
2757  Connection: close
2758</artwork></figure>
2759<t>
2760   in either the request or the response header fields indicates that
2761   the connection &SHOULD; be closed after the current request/response
2762   is complete (<xref target="persistent.tear-down"/>).
2763</t>
2764<t>
2765   A client that does not support persistent connections &MUST;
2766   send the "close" connection option in every request message.
2767</t>
2768<t>
2769   A server that does not support persistent connections &MUST;
2770   send the "close" connection option in every response message that
2771   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2772</t>
2773</section>
2774
2775<section title="Persistent Connections" anchor="persistent.connections">
2776  <x:anchor-alias value="persistent connections"/>
2777<t>
2778   HTTP was originally designed to use a separate connection for each
2779   request/response pair. As the Web evolved and embedded requests became
2780   common for inline images, the connection establishment overhead was
2781   a significant drain on performance and a concern for Internet congestion.
2782   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2783   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2784   to improve performance for some requests. However, these extensions were
2785   insufficient for dynamically generated responses and difficult to use
2786   with intermediaries.
2787</t>
2788<t>
2789   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2790   which allow multiple requests and responses to be carried over a single
2791   connection. The "<x:ref>close</x:ref>" connection-option is used to
2792   signal that a connection will close after the current request/response.
2793   Persistent connections have a number of advantages:
2794  <list style="symbols">
2795      <t>
2796        By opening and closing fewer connections, CPU time is saved
2797        in routers and hosts (clients, servers, proxies, gateways,
2798        tunnels, or caches), and memory used for protocol control
2799        blocks can be saved in hosts.
2800      </t>
2801      <t>
2802        Most requests and responses can be pipelined on a connection.
2803        Pipelining allows a client to make multiple requests without
2804        waiting for each response, allowing a single connection to
2805        be used much more efficiently and with less overall latency.
2806      </t>
2807      <t>
2808        For TCP connections, network congestion is reduced by eliminating the
2809        packets associated with the three way handshake and graceful close
2810        procedures, and by allowing sufficient time to determine the
2811        congestion state of the network.
2812      </t>
2813      <t>
2814        Latency on subsequent requests is reduced since there is no time
2815        spent in the connection opening handshake.
2816      </t>
2817      <t>
2818        HTTP can evolve more gracefully, since most errors can be reported
2819        without the penalty of closing the connection. Clients using
2820        future versions of HTTP might optimistically try a new feature,
2821        but if communicating with an older server, retry with old
2822        semantics after an error is reported.
2823      </t>
2824    </list>
2825</t>
2826<t>
2827   HTTP implementations &SHOULD; implement persistent connections.
2828</t>
2829   
2830<section title="Establishment" anchor="persistent.establishment">
2831<t>
2832   It is beyond the scope of this specification to describe how connections
2833   are established via various transport or session-layer protocols.
2834   Each connection applies to only one transport link.
2835</t>
2836<t>
2837   A recipient determines whether a connection is persistent or not based on
2838   the most recently received message's protocol version and
2839   <x:ref>Connection</x:ref> header field (if any):
2840   <list style="symbols">
2841     <t>If the <x:ref>close</x:ref> connection option is present, the
2842        connection will not persist after the current response; else,</t>
2843     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2844        persist after the current response; else,</t>
2845     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2846        connection option is present, the recipient is not a proxy, and
2847        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2848        the connection will persist after the current response; otherwise,</t>
2849     <t>The connection will close after the current response.</t>
2850   </list>
2851</t>
2852<t>
2853   A proxy server &MUST-NOT; maintain a persistent connection with an
2854   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2855   information and discussion of the problems with the Keep-Alive header field
2856   implemented by many HTTP/1.0 clients).
2857</t>
2858</section>
2859
2860<section title="Reuse" anchor="persistent.reuse">
2861<t>
2862   In order to remain persistent, all messages on a connection &MUST;
2863   have a self-defined message length (i.e., one not defined by closure
2864   of the connection), as described in <xref target="message.body"/>.
2865</t>
2866<t>
2867   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2868   persistent connection until a <x:ref>close</x:ref> connection option
2869   is received in a request.
2870</t>
2871<t>
2872   A client &MAY; reuse a persistent connection until it sends or receives
2873   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2874   without a "keep-alive" connection option.
2875</t>
2876<t>
2877   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2878   maintained for HTTP versions less than 1.1 unless it is explicitly
2879   signaled.
2880   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2881   for more information on backward compatibility with HTTP/1.0 clients.
2882</t>
2883
2884<section title="Pipelining" anchor="pipelining">
2885<t>
2886   A client that supports persistent connections &MAY; "pipeline" its
2887   requests (i.e., send multiple requests without waiting for each
2888   response). A server &MUST; send its responses to those requests in the
2889   same order that the requests were received.
2890</t>
2891<t>
2892   Clients which assume persistent connections and pipeline immediately
2893   after connection establishment &SHOULD; be prepared to retry their
2894   connection if the first pipelined attempt fails. If a client does
2895   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2896   persistent. Clients &MUST; also be prepared to resend their requests if
2897   the server closes the connection before sending all of the
2898   corresponding responses.
2899</t>
2900<t>
2901   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2902   or non-idempotent sequences of request methods (see &idempotent-methods;).
2903   Otherwise, a premature termination of the transport connection could lead
2904   to indeterminate results. A client wishing to send a non-idempotent
2905   request &SHOULD; wait to send that request until it has received the
2906   response status line for the previous request.
2907</t>
2908</section>
2909
2910<section title="Retrying Requests" anchor="persistent.retrying.requests">
2911<t>
2912   Senders can close the transport connection at any time. Therefore,
2913   clients, servers, and proxies &MUST; be able to recover
2914   from asynchronous close events. Client software &MAY; reopen the
2915   transport connection and retransmit the aborted sequence of requests
2916   without user interaction so long as the request sequence is
2917   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2918   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2919   human operator the choice of retrying the request(s). Confirmation by
2920   user-agent software with semantic understanding of the application
2921   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2922   be repeated if the second sequence of requests fails.
2923</t>
2924</section>
2925</section>
2926   
2927<section title="Concurrency" anchor="persistent.concurrency">
2928<t>
2929   Clients &SHOULD; limit the number of simultaneous
2930   connections that they maintain to a given server.
2931</t>
2932<t>
2933   Previous revisions of HTTP gave a specific number of connections as a
2934   ceiling, but this was found to be impractical for many applications. As a
2935   result, this specification does not mandate a particular maximum number of
2936   connections, but instead encourages clients to be conservative when opening
2937   multiple connections.
2938</t>
2939<t>
2940   Multiple connections are typically used to avoid the "head-of-line
2941   blocking" problem, wherein a request that takes significant server-side
2942   processing and/or has a large payload blocks subsequent requests on the
2943   same connection. However, each connection consumes server resources.
2944   Furthermore, using multiple connections can cause undesirable side effects
2945   in congested networks.
2946</t>
2947<t>
2948   Note that servers might reject traffic that they deem abusive, including an
2949   excessive number of connections from a client.
2950</t>
2951</section>
2952
2953<section title="Failures and Time-outs" anchor="persistent.failures">
2954<t>
2955   Servers will usually have some time-out value beyond which they will
2956   no longer maintain an inactive connection. Proxy servers might make
2957   this a higher value since it is likely that the client will be making
2958   more connections through the same server. The use of persistent
2959   connections places no requirements on the length (or existence) of
2960   this time-out for either the client or the server.
2961</t>
2962<t>
2963   When a client or server wishes to time-out it &SHOULD; issue a graceful
2964   close on the transport connection. Clients and servers &SHOULD; both
2965   constantly watch for the other side of the transport close, and
2966   respond to it as appropriate. If a client or server does not detect
2967   the other side's close promptly it could cause unnecessary resource
2968   drain on the network.
2969</t>
2970<t>
2971   A client, server, or proxy &MAY; close the transport connection at any
2972   time. For example, a client might have started to send a new request
2973   at the same time that the server has decided to close the "idle"
2974   connection. From the server's point of view, the connection is being
2975   closed while it was idle, but from the client's point of view, a
2976   request is in progress.
2977</t>
2978<t>
2979   Servers &SHOULD; maintain persistent connections and allow the underlying
2980   transport's flow control mechanisms to resolve temporary overloads, rather
2981   than terminate connections with the expectation that clients will retry.
2982   The latter technique can exacerbate network congestion.
2983</t>
2984<t>
2985   A client sending a message body &SHOULD; monitor
2986   the network connection for an error status code while it is transmitting
2987   the request. If the client sees an error status code, it &SHOULD;
2988   immediately cease transmitting the body and close the connection.
2989</t>
2990</section>
2991   
2992<section title="Tear-down" anchor="persistent.tear-down">
2993  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2994  <iref primary="false" item="close" x:for-anchor=""/>
2995<t>
2996   The <x:ref>Connection</x:ref> header field
2997   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
2998   connection option that a sender &SHOULD; send when it wishes to close
2999   the connection after the current request/response pair.
3000</t>
3001<t>
3002   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3003   send further requests on that connection (after the one containing
3004   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3005   final response message corresponding to this request.
3006</t>
3007<t>
3008   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3009   initiate a lingering close of the connection after it sends the final
3010   response to the request that contained <x:ref>close</x:ref>.
3011   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3012   in its final response on that connection. The server &MUST-NOT; process
3013   any further requests received on that connection.
3014</t>
3015<t>
3016   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3017   initiate a lingering close of the connection after it sends the
3018   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3019   any further requests received on that connection.
3020</t>
3021<t>
3022   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3023   cease sending requests on that connection and close the connection
3024   after reading the response message containing the close; if additional
3025   pipelined requests had been sent on the connection, the client &SHOULD;
3026   assume that they will not be processed by the server.
3027</t>
3028<t>
3029   If a server performs an immediate close of a TCP connection, there is a
3030   significant risk that the client will not be able to read the last HTTP
3031   response.  If the server receives additional data from the client on a
3032   fully-closed connection, such as another request that was sent by the
3033   client before receiving the server's response, the server's TCP stack will
3034   send a reset packet to the client; unfortunately, the reset packet might
3035   erase the client's unacknowledged input buffers before they can be read
3036   and interpreted by the client's HTTP parser.
3037</t>
3038<t>
3039   To avoid the TCP reset problem, a server can perform a lingering close on a
3040   connection by closing only the write side of the read/write connection
3041   (a half-close) and continuing to read from the connection until the
3042   connection is closed by the client or the server is reasonably certain
3043   that its own TCP stack has received the client's acknowledgement of the
3044   packet(s) containing the server's last response. It is then safe for the
3045   server to fully close the connection.
3046</t>
3047<t>
3048   It is unknown whether the reset problem is exclusive to TCP or might also
3049   be found in other transport connection protocols.
3050</t>
3051</section>
3052</section>
3053
3054<section title="Upgrade" anchor="header.upgrade">
3055  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3056  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3057  <x:anchor-alias value="Upgrade"/>
3058  <x:anchor-alias value="protocol"/>
3059  <x:anchor-alias value="protocol-name"/>
3060  <x:anchor-alias value="protocol-version"/>
3061<t>
3062   The "Upgrade" header field is intended to provide a simple mechanism
3063   for transitioning from HTTP/1.1 to some other protocol on the same
3064   connection.  A client &MAY; send a list of protocols in the Upgrade
3065   header field of a request to invite the server to switch to one or
3066   more of those protocols before sending the final response.
3067   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3068   Protocols)</x:ref> responses to indicate which protocol(s) are being
3069   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3070   responses to indicate acceptable protocols.
3071   A server &MAY; send an Upgrade header field in any other response to
3072   indicate that they might be willing to upgrade to one of the
3073   specified protocols for a future request.
3074</t>
3075<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3076  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3077
3078  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3079  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3080  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3081</artwork></figure>
3082<t>
3083   For example,
3084</t>
3085<figure><artwork type="example">
3086  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3087</artwork></figure>
3088<t>
3089   Upgrade eases the difficult transition between incompatible protocols by
3090   allowing the client to initiate a request in the more commonly
3091   supported protocol while indicating to the server that it would like
3092   to use a "better" protocol if available (where "better" is determined
3093   by the server, possibly according to the nature of the request method
3094   or target resource).
3095</t>
3096<t>
3097   Upgrade cannot be used to insist on a protocol change; its acceptance and
3098   use by the server is optional. The capabilities and nature of the
3099   application-layer communication after the protocol change is entirely
3100   dependent upon the new protocol chosen, although the first action
3101   after changing the protocol &MUST; be a response to the initial HTTP
3102   request that contained the Upgrade header field.
3103</t>
3104<t>
3105   For example, if the Upgrade header field is received in a GET request
3106   and the server decides to switch protocols, then it &MUST; first respond
3107   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3108   then immediately follow that with the new protocol's equivalent of a
3109   response to a GET on the target resource.  This allows a connection to be
3110   upgraded to protocols with the same semantics as HTTP without the
3111   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3112   protocols unless the received message semantics can be honored by the new
3113   protocol; an OPTIONS request can be honored by any protocol.
3114</t>
3115<t>
3116   When Upgrade is sent, a sender &MUST; also send a
3117   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3118   that contains the "upgrade" connection option, in order to prevent Upgrade
3119   from being accidentally forwarded by intermediaries that might not implement
3120   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3121   is received in an HTTP/1.0 request.
3122</t>
3123<t>
3124   The Upgrade header field only applies to switching application-layer
3125   protocols on the existing transport-layer connection; it cannot be used
3126   to switch to a protocol on a different connection. For that purpose, it is
3127   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3128   (&status-3xx;).
3129</t>
3130<t>
3131   This specification only defines the protocol name "HTTP" for use by
3132   the family of Hypertext Transfer Protocols, as defined by the HTTP
3133   version rules of <xref target="http.version"/> and future updates to this
3134   specification. Additional tokens can be registered with IANA using the
3135   registration procedure defined in <xref target="upgrade.token.registry"/>.
3136</t>
3137</section>
3138</section>
3139
3140<section title="IANA Considerations" anchor="IANA.considerations">
3141
3142<section title="Header Field Registration" anchor="header.field.registration">
3143<t>
3144   HTTP header fields are registered within the Message Header Field Registry
3145   <xref target="RFC3864"/> maintained by IANA at
3146   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3147</t>
3148<t>
3149   This document defines the following HTTP header fields, so their
3150   associated registry entries shall be updated according to the permanent
3151   registrations below:
3152</t>
3153<?BEGININC p1-messaging.iana-headers ?>
3154<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3155<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3156   <ttcol>Header Field Name</ttcol>
3157   <ttcol>Protocol</ttcol>
3158   <ttcol>Status</ttcol>
3159   <ttcol>Reference</ttcol>
3160
3161   <c>Connection</c>
3162   <c>http</c>
3163   <c>standard</c>
3164   <c>
3165      <xref target="header.connection"/>
3166   </c>
3167   <c>Content-Length</c>
3168   <c>http</c>
3169   <c>standard</c>
3170   <c>
3171      <xref target="header.content-length"/>
3172   </c>
3173   <c>Host</c>
3174   <c>http</c>
3175   <c>standard</c>
3176   <c>
3177      <xref target="header.host"/>
3178   </c>
3179   <c>TE</c>
3180   <c>http</c>
3181   <c>standard</c>
3182   <c>
3183      <xref target="header.te"/>
3184   </c>
3185   <c>Trailer</c>
3186   <c>http</c>
3187   <c>standard</c>
3188   <c>
3189      <xref target="header.trailer"/>
3190   </c>
3191   <c>Transfer-Encoding</c>
3192   <c>http</c>
3193   <c>standard</c>
3194   <c>
3195      <xref target="header.transfer-encoding"/>
3196   </c>
3197   <c>Upgrade</c>
3198   <c>http</c>
3199   <c>standard</c>
3200   <c>
3201      <xref target="header.upgrade"/>
3202   </c>
3203   <c>Via</c>
3204   <c>http</c>
3205   <c>standard</c>
3206   <c>
3207      <xref target="header.via"/>
3208   </c>
3209</texttable>
3210<!--(END)-->
3211<?ENDINC p1-messaging.iana-headers ?>
3212<t>
3213   Furthermore, the header field-name "Close" shall be registered as
3214   "reserved", since using that name as an HTTP header field might
3215   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3216   header field (<xref target="header.connection"/>).
3217</t>
3218<texttable align="left" suppress-title="true">
3219   <ttcol>Header Field Name</ttcol>
3220   <ttcol>Protocol</ttcol>
3221   <ttcol>Status</ttcol>
3222   <ttcol>Reference</ttcol>
3223
3224   <c>Close</c>
3225   <c>http</c>
3226   <c>reserved</c>
3227   <c>
3228      <xref target="header.field.registration"/>
3229   </c>
3230</texttable>
3231<t>
3232   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3233</t>
3234</section>
3235
3236<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3237<t>
3238   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3239   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3240</t>
3241<t>
3242   This document defines the following URI schemes, so their
3243   associated registry entries shall be updated according to the permanent
3244   registrations below:
3245</t>
3246<texttable align="left" suppress-title="true">
3247   <ttcol>URI Scheme</ttcol>
3248   <ttcol>Description</ttcol>
3249   <ttcol>Reference</ttcol>
3250
3251   <c>http</c>
3252   <c>Hypertext Transfer Protocol</c>
3253   <c><xref target="http.uri"/></c>
3254
3255   <c>https</c>
3256   <c>Hypertext Transfer Protocol Secure</c>
3257   <c><xref target="https.uri"/></c>
3258</texttable>
3259</section>
3260
3261<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3262<t>
3263   This document serves as the specification for the Internet media types
3264   "message/http" and "application/http". The following is to be registered with
3265   IANA (see <xref target="RFC4288"/>).
3266</t>
3267<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3268<iref item="Media Type" subitem="message/http" primary="true"/>
3269<iref item="message/http Media Type" primary="true"/>
3270<t>
3271   The message/http type can be used to enclose a single HTTP request or
3272   response message, provided that it obeys the MIME restrictions for all
3273   "message" types regarding line length and encodings.
3274</t>
3275<t>
3276  <list style="hanging" x:indent="12em">
3277    <t hangText="Type name:">
3278      message
3279    </t>
3280    <t hangText="Subtype name:">
3281      http
3282    </t>
3283    <t hangText="Required parameters:">
3284      none
3285    </t>
3286    <t hangText="Optional parameters:">
3287      version, msgtype
3288      <list style="hanging">
3289        <t hangText="version:">
3290          The HTTP-version number of the enclosed message
3291          (e.g., "1.1"). If not present, the version can be
3292          determined from the first line of the body.
3293        </t>
3294        <t hangText="msgtype:">
3295          The message type &mdash; "request" or "response". If not
3296          present, the type can be determined from the first
3297          line of the body.
3298        </t>
3299      </list>
3300    </t>
3301    <t hangText="Encoding considerations:">
3302      only "7bit", "8bit", or "binary" are permitted
3303    </t>
3304    <t hangText="Security considerations:">
3305      none
3306    </t>
3307    <t hangText="Interoperability considerations:">
3308      none
3309    </t>
3310    <t hangText="Published specification:">
3311      This specification (see <xref target="internet.media.type.message.http"/>).
3312    </t>
3313    <t hangText="Applications that use this media type:">
3314    </t>
3315    <t hangText="Additional information:">
3316      <list style="hanging">
3317        <t hangText="Magic number(s):">none</t>
3318        <t hangText="File extension(s):">none</t>
3319        <t hangText="Macintosh file type code(s):">none</t>
3320      </list>
3321    </t>
3322    <t hangText="Person and email address to contact for further information:">
3323      See Authors Section.
3324    </t>
3325    <t hangText="Intended usage:">
3326      COMMON
3327    </t>
3328    <t hangText="Restrictions on usage:">
3329      none
3330    </t>
3331    <t hangText="Author/Change controller:">
3332      IESG
3333    </t>
3334  </list>
3335</t>
3336</section>
3337<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3338<iref item="Media Type" subitem="application/http" primary="true"/>
3339<iref item="application/http Media Type" primary="true"/>
3340<t>
3341   The application/http type can be used to enclose a pipeline of one or more
3342   HTTP request or response messages (not intermixed).
3343</t>
3344<t>
3345  <list style="hanging" x:indent="12em">
3346    <t hangText="Type name:">
3347      application
3348    </t>
3349    <t hangText="Subtype name:">
3350      http
3351    </t>
3352    <t hangText="Required parameters:">
3353      none
3354    </t>
3355    <t hangText="Optional parameters:">
3356      version, msgtype
3357      <list style="hanging">
3358        <t hangText="version:">
3359          The HTTP-version number of the enclosed messages
3360          (e.g., "1.1"). If not present, the version can be
3361          determined from the first line of the body.
3362        </t>
3363        <t hangText="msgtype:">
3364          The message type &mdash; "request" or "response". If not
3365          present, the type can be determined from the first
3366          line of the body.
3367        </t>
3368      </list>
3369    </t>
3370    <t hangText="Encoding considerations:">
3371      HTTP messages enclosed by this type
3372      are in "binary" format; use of an appropriate
3373      Content-Transfer-Encoding is required when
3374      transmitted via E-mail.
3375    </t>
3376    <t hangText="Security considerations:">
3377      none
3378    </t>
3379    <t hangText="Interoperability considerations:">
3380      none
3381    </t>
3382    <t hangText="Published specification:">
3383      This specification (see <xref target="internet.media.type.application.http"/>).
3384    </t>
3385    <t hangText="Applications that use this media type:">
3386    </t>
3387    <t hangText="Additional information:">
3388      <list style="hanging">
3389        <t hangText="Magic number(s):">none</t>
3390        <t hangText="File extension(s):">none</t>
3391        <t hangText="Macintosh file type code(s):">none</t>
3392      </list>
3393    </t>
3394    <t hangText="Person and email address to contact for further information:">
3395      See Authors Section.
3396    </t>
3397    <t hangText="Intended usage:">
3398      COMMON
3399    </t>
3400    <t hangText="Restrictions on usage:">
3401      none
3402    </t>
3403    <t hangText="Author/Change controller:">
3404      IESG
3405    </t>
3406  </list>
3407</t>
3408</section>
3409</section>
3410
3411<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3412<t>
3413   The HTTP Transfer Coding Registry defines the name space for transfer
3414   coding names.
3415</t>
3416<t>
3417   Registrations &MUST; include the following fields:
3418   <list style="symbols">
3419     <t>Name</t>
3420     <t>Description</t>
3421     <t>Pointer to specification text</t>
3422   </list>
3423</t>
3424<t>
3425   Names of transfer codings &MUST-NOT; overlap with names of content codings
3426   (&content-codings;) unless the encoding transformation is identical, as
3427   is the case for the compression codings defined in
3428   <xref target="compression.codings"/>.
3429</t>
3430<t>
3431   Values to be added to this name space require IETF Review (see
3432   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3433   conform to the purpose of transfer coding defined in this section.
3434   Use of program names for the identification of encoding formats
3435   is not desirable and is discouraged for future encodings.
3436</t>
3437<t>
3438   The registry itself is maintained at
3439   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3440</t>
3441</section>
3442
3443<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3444<t>
3445   The HTTP Transfer Coding Registry shall be updated with the registrations
3446   below:
3447</t>
3448<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3449   <ttcol>Name</ttcol>
3450   <ttcol>Description</ttcol>
3451   <ttcol>Reference</ttcol>
3452   <c>chunked</c>
3453   <c>Transfer in a series of chunks</c>
3454   <c>
3455      <xref target="chunked.encoding"/>
3456   </c>
3457   <c>compress</c>
3458   <c>UNIX "compress" program method</c>
3459   <c>
3460      <xref target="compress.coding"/>
3461   </c>
3462   <c>deflate</c>
3463   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3464   the "zlib" data format (<xref target="RFC1950"/>)
3465   </c>
3466   <c>
3467      <xref target="deflate.coding"/>
3468   </c>
3469   <c>gzip</c>
3470   <c>Same as GNU zip <xref target="RFC1952"/></c>
3471   <c>
3472      <xref target="gzip.coding"/>
3473   </c>
3474</texttable>
3475</section>
3476
3477<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3478<t>
3479   The HTTP Upgrade Token Registry defines the name space for protocol-name
3480   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3481   field. Each registered protocol name is associated with contact information
3482   and an optional set of specifications that details how the connection
3483   will be processed after it has been upgraded.
3484</t>
3485<t>
3486   Registrations happen on a "First Come First Served" basis (see
3487   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3488   following rules:
3489  <list style="numbers">
3490    <t>A protocol-name token, once registered, stays registered forever.</t>
3491    <t>The registration &MUST; name a responsible party for the
3492       registration.</t>
3493    <t>The registration &MUST; name a point of contact.</t>
3494    <t>The registration &MAY; name a set of specifications associated with
3495       that token. Such specifications need not be publicly available.</t>
3496    <t>The registration &SHOULD; name a set of expected "protocol-version"
3497       tokens associated with that token at the time of registration.</t>
3498    <t>The responsible party &MAY; change the registration at any time.
3499       The IANA will keep a record of all such changes, and make them
3500       available upon request.</t>
3501    <t>The IESG &MAY; reassign responsibility for a protocol token.
3502       This will normally only be used in the case when a
3503       responsible party cannot be contacted.</t>
3504  </list>
3505</t>
3506<t>
3507   This registration procedure for HTTP Upgrade Tokens replaces that
3508   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3509</t>
3510</section>
3511
3512<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3513<t>
3514   The HTTP Upgrade Token Registry shall be updated with the registration
3515   below:
3516</t>
3517<texttable align="left" suppress-title="true">
3518   <ttcol>Value</ttcol>
3519   <ttcol>Description</ttcol>
3520   <ttcol>Expected Version Tokens</ttcol>
3521   <ttcol>Reference</ttcol>
3522
3523   <c>HTTP</c>
3524   <c>Hypertext Transfer Protocol</c>
3525   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3526   <c><xref target="http.version"/></c>
3527</texttable>
3528<t>
3529   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3530</t>
3531</section>
3532
3533</section>
3534
3535<section title="Security Considerations" anchor="security.considerations">
3536<t>
3537   This section is meant to inform application developers, information
3538   providers, and users of the security limitations in HTTP/1.1 as
3539   described by this document. The discussion does not include
3540   definitive solutions to the problems revealed, though it does make
3541   some suggestions for reducing security risks.
3542</t>
3543
3544<section title="Personal Information" anchor="personal.information">
3545<t>
3546   HTTP clients are often privy to large amounts of personal information,
3547   including both information provided by the user to interact with resources
3548   (e.g., the user's name, location, mail address, passwords, encryption
3549   keys, etc.) and information about the user's browsing activity over
3550   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3551   prevent unintentional leakage of this information.
3552</t>
3553</section>
3554
3555<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3556<t>
3557   A server is in the position to save personal data about a user's
3558   requests which might identify their reading patterns or subjects of
3559   interest.  In particular, log information gathered at an intermediary
3560   often contains a history of user agent interaction, across a multitude
3561   of sites, that can be traced to individual users.
3562</t>
3563<t>
3564   HTTP log information is confidential in nature; its handling is often
3565   constrained by laws and regulations.  Log information needs to be securely
3566   stored and appropriate guidelines followed for its analysis.
3567   Anonymization of personal information within individual entries helps,
3568   but is generally not sufficient to prevent real log traces from being
3569   re-identified based on correlation with other access characteristics.
3570   As such, access traces that are keyed to a specific client should not
3571   be published even if the key is pseudonymous.
3572</t>
3573<t>
3574   To minimize the risk of theft or accidental publication, log information
3575   should be purged of personally identifiable information, including
3576   user identifiers, IP addresses, and user-provided query parameters,
3577   as soon as that information is no longer necessary to support operational
3578   needs for security, auditing, or fraud control.
3579</t>
3580</section>
3581
3582<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3583<t>
3584   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3585   the documents returned by HTTP requests to be only those that were
3586   intended by the server administrators. If an HTTP server translates
3587   HTTP URIs directly into file system calls, the server &MUST; take
3588   special care not to serve files that were not intended to be
3589   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3590   other operating systems use ".." as a path component to indicate a
3591   directory level above the current one. On such a system, an HTTP
3592   server &MUST; disallow any such construct in the request-target if it
3593   would otherwise allow access to a resource outside those intended to
3594   be accessible via the HTTP server. Similarly, files intended for
3595   reference only internally to the server (such as access control
3596   files, configuration files, and script code) &MUST; be protected from
3597   inappropriate retrieval, since they might contain sensitive
3598   information. Experience has shown that minor bugs in such HTTP server
3599   implementations have turned into security risks.
3600</t>
3601</section>
3602
3603<section title="DNS-related Attacks" anchor="dns.related.attacks">
3604<t>
3605   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3606   generally prone to security attacks based on the deliberate misassociation
3607   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3608   cautious in assuming the validity of an IP number/DNS name association unless
3609   the response is protected by DNSSec (<xref target="RFC4033"/>).
3610</t>
3611</section>
3612
3613<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3614<t>
3615   By their very nature, HTTP intermediaries are men-in-the-middle, and
3616   represent an opportunity for man-in-the-middle attacks. Compromise of
3617   the systems on which the intermediaries run can result in serious security
3618   and privacy problems. Intermediaries have access to security-related
3619   information, personal information about individual users and
3620   organizations, and proprietary information belonging to users and
3621   content providers. A compromised intermediary, or an intermediary
3622   implemented or configured without regard to security and privacy
3623   considerations, might be used in the commission of a wide range of
3624   potential attacks.
3625</t>
3626<t>
3627   Intermediaries that contain a shared cache are especially vulnerable
3628   to cache poisoning attacks.
3629</t>
3630<t>
3631   Implementers need to consider the privacy and security
3632   implications of their design and coding decisions, and of the
3633   configuration options they provide to operators (especially the
3634   default configuration).
3635</t>
3636<t>
3637   Users need to be aware that intermediaries are no more trustworthy than
3638   the people who run them; HTTP itself cannot solve this problem.
3639</t>
3640</section>
3641
3642<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3643<t>
3644   Because HTTP uses mostly textual, character-delimited fields, attackers can
3645   overflow buffers in implementations, and/or perform a Denial of Service
3646   against implementations that accept fields with unlimited lengths.
3647</t>
3648<t>
3649   To promote interoperability, this specification makes specific
3650   recommendations for minimum size limits on request-line
3651   (<xref target="request.line"/>)
3652   and blocks of header fields (<xref target="header.fields"/>). These are
3653   minimum recommendations, chosen to be supportable even by implementations
3654   with limited resources; it is expected that most implementations will
3655   choose substantially higher limits.
3656</t>
3657<t>
3658   This specification also provides a way for servers to reject messages that
3659   have request-targets that are too long (&status-414;) or request entities
3660   that are too large (&status-4xx;).
3661</t>
3662<t>
3663   Other fields (including but not limited to request methods, response status
3664   phrases, header field-names, and body chunks) &SHOULD; be limited by
3665   implementations carefully, so as to not impede interoperability.
3666</t>
3667</section>
3668</section>
3669
3670<section title="Acknowledgments" anchor="acks">
3671<t>
3672   This edition of HTTP builds on the many contributions that went into
3673   <xref target="RFC1945" format="none">RFC 1945</xref>,
3674   <xref target="RFC2068" format="none">RFC 2068</xref>,
3675   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3676   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3677   substantial contributions made by the previous authors, editors, and
3678   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3679   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3680   Paul J. Leach, and Mark Nottingham.
3681   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3682   acknowledgements from prior revisions.
3683</t>
3684<t>
3685   Since 1999, the following contributors have helped improve the HTTP
3686   specification by reporting bugs, asking smart questions, drafting or
3687   reviewing text, and evaluating open issues:
3688</t>
3689<?BEGININC acks ?>
3690<t>Adam Barth,
3691Adam Roach,
3692Addison Phillips,
3693Adrian Chadd,
3694Adrien W. de Croy,
3695Alan Ford,
3696Alan Ruttenberg,
3697Albert Lunde,
3698Alek Storm,
3699Alex Rousskov,
3700Alexandre Morgaut,
3701Alexey Melnikov,
3702Alisha Smith,
3703Amichai Rothman,
3704Amit Klein,
3705Amos Jeffries,
3706Andreas Maier,
3707Andreas Petersson,
3708Anil Sharma,
3709Anne van Kesteren,
3710Anthony Bryan,
3711Asbjorn Ulsberg,
3712Balachander Krishnamurthy,
3713Barry Leiba,
3714Ben Laurie,
3715Benjamin Niven-Jenkins,
3716Bil Corry,
3717Bill Burke,
3718Bjoern Hoehrmann,
3719Bob Scheifler,
3720Boris Zbarsky,
3721Brett Slatkin,
3722Brian Kell,
3723Brian McBarron,
3724Brian Pane,
3725Brian Smith,
3726Bryce Nesbitt,
3727Cameron Heavon-Jones,
3728Carl Kugler,
3729Carsten Bormann,
3730Charles Fry,
3731Chris Newman,
3732Cyrus Daboo,
3733Dale Robert Anderson,
3734Dan Wing,
3735Dan Winship,
3736Daniel Stenberg,
3737Dave Cridland,
3738Dave Crocker,
3739Dave Kristol,
3740David Booth,
3741David Singer,
3742David W. Morris,
3743Diwakar Shetty,
3744Dmitry Kurochkin,
3745Drummond Reed,
3746Duane Wessels,
3747Edward Lee,
3748Eliot Lear,
3749Eran Hammer-Lahav,
3750Eric D. Williams,
3751Eric J. Bowman,
3752Eric Lawrence,
3753Eric Rescorla,
3754Erik Aronesty,
3755Evan Prodromou,
3756Florian Weimer,
3757Frank Ellermann,
3758Fred Bohle,
3759Gabriel Montenegro,
3760Geoffrey Sneddon,
3761Gervase Markham,
3762Grahame Grieve,
3763Greg Wilkins,
3764Harald Tveit Alvestrand,
3765Harry Halpin,
3766Helge Hess,
3767Henrik Nordstrom,
3768Henry S. Thompson,
3769Henry Story,
3770Herbert van de Sompel,
3771Howard Melman,
3772Hugo Haas,
3773Ian Fette,
3774Ian Hickson,
3775Ido Safruti,
3776Ingo Struck,
3777J. Ross Nicoll,
3778James H. Manger,
3779James Lacey,
3780James M. Snell,
3781Jamie Lokier,
3782Jan Algermissen,
3783Jeff Hodges (who came up with the term 'effective Request-URI'),
3784Jeff Walden,
3785Jim Luther,
3786Joe D. Williams,
3787Joe Gregorio,
3788Joe Orton,
3789John C. Klensin,
3790John C. Mallery,
3791John Cowan,
3792John Kemp,
3793John Panzer,
3794John Schneider,
3795John Stracke,
3796John Sullivan,
3797Jonas Sicking,
3798Jonathan Billington,
3799Jonathan Moore,
3800Jonathan Rees,
3801Jonathan Silvera,
3802Jordi Ros,
3803Joris Dobbelsteen,
3804Josh Cohen,
3805Julien Pierre,
3806Jungshik Shin,
3807Justin Chapweske,
3808Justin Erenkrantz,
3809Justin James,
3810Kalvinder Singh,
3811Karl Dubost,
3812Keith Hoffman,
3813Keith Moore,
3814Koen Holtman,
3815Konstantin Voronkov,
3816Kris Zyp,
3817Lisa Dusseault,
3818Maciej Stachowiak,
3819Marc Schneider,
3820Marc Slemko,
3821Mark Baker,
3822Mark Pauley,
3823Mark Watson,
3824Markus Isomaki,
3825Markus Lanthaler,
3826Martin J. Duerst,
3827Martin Musatov,
3828Martin Nilsson,
3829Martin Thomson,
3830Matt Lynch,
3831Matthew Cox,
3832Max Clark,
3833Michael Burrows,
3834Michael Hausenblas,
3835Mike Amundsen,
3836Mike Belshe,
3837Mike Kelly,
3838Mike Schinkel,
3839Miles Sabin,
3840Murray S. Kucherawy,
3841Mykyta Yevstifeyev,
3842Nathan Rixham,
3843Nicholas Shanks,
3844Nico Williams,
3845Nicolas Alvarez,
3846Nicolas Mailhot,
3847Noah Slater,
3848Pablo Castro,
3849Pat Hayes,
3850Patrick R. McManus,
3851Paul E. Jones,
3852Paul Hoffman,
3853Paul Marquess,
3854Peter Lepeska,
3855Peter Saint-Andre,
3856Peter Watkins,
3857Phil Archer,
3858Philippe Mougin,
3859Phillip Hallam-Baker,
3860Poul-Henning Kamp,
3861Preethi Natarajan,
3862Rajeev Bector,
3863Ray Polk,
3864Reto Bachmann-Gmuer,
3865Richard Cyganiak,
3866Robert Brewer,
3867Robert Collins,
3868Robert O'Callahan,
3869Robert Olofsson,
3870Robert Sayre,
3871Robert Siemer,
3872Robert de Wilde,
3873Roberto Javier Godoy,
3874Roberto Peon,
3875Ronny Widjaja,
3876S. Mike Dierken,
3877Salvatore Loreto,
3878Sam Johnston,
3879Sam Ruby,
3880Scott Lawrence (who maintained the original issues list),
3881Sean B. Palmer,
3882Shane McCarron,
3883Stefan Eissing,
3884Stefan Tilkov,
3885Stefanos Harhalakis,
3886Stephane Bortzmeyer,
3887Stephen Farrell,
3888Stephen Ludin,
3889Stuart Williams,
3890Subbu Allamaraju,
3891Sylvain Hellegouarch,
3892Tapan Divekar,
3893Tatsuya Hayashi,
3894Ted Hardie,
3895Thomas Broyer,
3896Thomas Nordin,
3897Thomas Roessler,
3898Tim Bray,
3899Tim Morgan,
3900Tim Olsen,
3901Tom Zhou,
3902Travis Snoozy,
3903Tyler Close,
3904Vincent Murphy,
3905Wenbo Zhu,
3906Werner Baumann,
3907Wilbur Streett,
3908Wilfredo Sanchez Vega,
3909William A. Rowe Jr.,
3910William Chan,
3911Willy Tarreau,
3912Xiaoshu Wang,
3913Yaron Goland,
3914Yngve Nysaeter Pettersen,
3915Yoav Nir,
3916Yogesh Bang,
3917Yutaka Oiwa,
3918Zed A. Shaw, and
3919Zhong Yu.
3920</t>
3921<?ENDINC acks ?>
3922</section>
3923
3924</middle>
3925<back>
3926
3927<references title="Normative References">
3928
3929<reference anchor="Part2">
3930  <front>
3931    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3932    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3933      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3934      <address><email>fielding@gbiv.com</email></address>
3935    </author>
3936    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3937      <organization abbrev="W3C">World Wide Web Consortium</organization>
3938      <address><email>ylafon@w3.org</email></address>
3939    </author>
3940    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3941      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3942      <address><email>julian.reschke@greenbytes.de</email></address>
3943    </author>
3944    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3945  </front>
3946  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3947  <x:source href="p2-semantics.xml" basename="p2-semantics">
3948    <x:defines>1xx (Informational)</x:defines>
3949    <x:defines>1xx</x:defines>
3950    <x:defines>100 (Continue)</x:defines>
3951    <x:defines>101 (Switching Protocols)</x:defines>
3952    <x:defines>2xx (Successful)</x:defines>
3953    <x:defines>2xx</x:defines>
3954    <x:defines>200 (OK)</x:defines>
3955    <x:defines>204 (No Content)</x:defines>
3956    <x:defines>3xx (Redirection)</x:defines>
3957    <x:defines>3xx</x:defines>
3958    <x:defines>301 (Moved Permanently)</x:defines>
3959    <x:defines>4xx (Client Error)</x:defines>
3960    <x:defines>4xx</x:defines>
3961    <x:defines>400 (Bad Request)</x:defines>
3962    <x:defines>405 (Method Not Allowed)</x:defines>
3963    <x:defines>411 (Length Required)</x:defines>
3964    <x:defines>414 (URI Too Long)</x:defines>
3965    <x:defines>417 (Expectation Failed)</x:defines>
3966    <x:defines>426 (Upgrade Required)</x:defines>
3967    <x:defines>501 (Not Implemented)</x:defines>
3968    <x:defines>502 (Bad Gateway)</x:defines>
3969    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3970    <x:defines>Allow</x:defines>
3971    <x:defines>Content-Encoding</x:defines>
3972    <x:defines>Content-Location</x:defines>
3973    <x:defines>Content-Type</x:defines>
3974    <x:defines>Date</x:defines>
3975    <x:defines>Expect</x:defines>
3976    <x:defines>Location</x:defines>
3977    <x:defines>Server</x:defines>
3978    <x:defines>User-Agent</x:defines>
3979  </x:source>
3980</reference>
3981
3982<reference anchor="Part4">
3983  <front>
3984    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3985    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3986      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3987      <address><email>fielding@gbiv.com</email></address>
3988    </author>
3989    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3990      <organization abbrev="W3C">World Wide Web Consortium</organization>
3991      <address><email>ylafon@w3.org</email></address>
3992    </author>
3993    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3994      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3995      <address><email>julian.reschke@greenbytes.de</email></address>
3996    </author>
3997    <date month="&ID-MONTH;" year="&ID-YEAR;" />
3998  </front>
3999  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4000  <x:source basename="p4-conditional" href="p4-conditional.xml">
4001    <x:defines>304 (Not Modified)</x:defines>
4002    <x:defines>ETag</x:defines>
4003    <x:defines>Last-Modified</x:defines>
4004  </x:source>
4005</reference>
4006
4007<reference anchor="Part5">
4008  <front>
4009    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4010    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4011      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4012      <address><email>fielding@gbiv.com</email></address>
4013    </author>
4014    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4015      <organization abbrev="W3C">World Wide Web Consortium</organization>
4016      <address><email>ylafon@w3.org</email></address>
4017    </author>
4018    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4019      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4020      <address><email>julian.reschke@greenbytes.de</email></address>
4021    </author>
4022    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4023  </front>
4024  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4025  <x:source href="p5-range.xml" basename="p5-range">
4026    <x:defines>Content-Range</x:defines>
4027  </x:source>
4028</reference>
4029
4030<reference anchor="Part6">
4031  <front>
4032    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4033    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4034      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4035      <address><email>fielding@gbiv.com</email></address>
4036    </author>
4037    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4038      <organization abbrev="W3C">World Wide Web Consortium</organization>
4039      <address><email>ylafon@w3.org</email></address>
4040    </author>
4041    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4042      <address><email>mnot@mnot.net</email></address>
4043    </author>
4044    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4045      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4046      <address><email>julian.reschke@greenbytes.de</email></address>
4047    </author>
4048    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4049  </front>
4050  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4051  <x:source href="p6-cache.xml" basename="p6-cache">
4052    <x:defines>Expires</x:defines>
4053  </x:source>
4054</reference>
4055
4056<reference anchor="Part7">
4057  <front>
4058    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4059    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4060      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4061      <address><email>fielding@gbiv.com</email></address>
4062    </author>
4063    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4064      <organization abbrev="W3C">World Wide Web Consortium</organization>
4065      <address><email>ylafon@w3.org</email></address>
4066    </author>
4067    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4068      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4069      <address><email>julian.reschke@greenbytes.de</email></address>
4070    </author>
4071    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4072  </front>
4073  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4074  <x:source href="p7-auth.xml" basename="p7-auth">
4075    <x:defines>Proxy-Authenticate</x:defines>
4076    <x:defines>Proxy-Authorization</x:defines>
4077  </x:source>
4078</reference>
4079
4080<reference anchor="RFC5234">
4081  <front>
4082    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4083    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4084      <organization>Brandenburg InternetWorking</organization>
4085      <address>
4086        <email>dcrocker@bbiw.net</email>
4087      </address> 
4088    </author>
4089    <author initials="P." surname="Overell" fullname="Paul Overell">
4090      <organization>THUS plc.</organization>
4091      <address>
4092        <email>paul.overell@thus.net</email>
4093      </address>
4094    </author>
4095    <date month="January" year="2008"/>
4096  </front>
4097  <seriesInfo name="STD" value="68"/>
4098  <seriesInfo name="RFC" value="5234"/>
4099</reference>
4100
4101<reference anchor="RFC2119">
4102  <front>
4103    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4104    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4105      <organization>Harvard University</organization>
4106      <address><email>sob@harvard.edu</email></address>
4107    </author>
4108    <date month="March" year="1997"/>
4109  </front>
4110  <seriesInfo name="BCP" value="14"/>
4111  <seriesInfo name="RFC" value="2119"/>
4112</reference>
4113
4114<reference anchor="RFC3986">
4115 <front>
4116  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4117  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4118    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4119    <address>
4120       <email>timbl@w3.org</email>
4121       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4122    </address>
4123  </author>
4124  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4125    <organization abbrev="Day Software">Day Software</organization>
4126    <address>
4127      <email>fielding@gbiv.com</email>
4128      <uri>http://roy.gbiv.com/</uri>
4129    </address>
4130  </author>
4131  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4132    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4133    <address>
4134      <email>LMM@acm.org</email>
4135      <uri>http://larry.masinter.net/</uri>
4136    </address>
4137  </author>
4138  <date month='January' year='2005'></date>
4139 </front>
4140 <seriesInfo name="STD" value="66"/>
4141 <seriesInfo name="RFC" value="3986"/>
4142</reference>
4143
4144<reference anchor="USASCII">
4145  <front>
4146    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4147    <author>
4148      <organization>American National Standards Institute</organization>
4149    </author>
4150    <date year="1986"/>
4151  </front>
4152  <seriesInfo name="ANSI" value="X3.4"/>
4153</reference>
4154
4155<reference anchor="RFC1950">
4156  <front>
4157    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4158    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4159      <organization>Aladdin Enterprises</organization>
4160      <address><email>ghost@aladdin.com</email></address>
4161    </author>
4162    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4163    <date month="May" year="1996"/>
4164  </front>
4165  <seriesInfo name="RFC" value="1950"/>
4166  <!--<annotation>
4167    RFC 1950 is an Informational RFC, thus it might be less stable than
4168    this specification. On the other hand, this downward reference was
4169    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4170    therefore it is unlikely to cause problems in practice. See also
4171    <xref target="BCP97"/>.
4172  </annotation>-->
4173</reference>
4174
4175<reference anchor="RFC1951">
4176  <front>
4177    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4178    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4179      <organization>Aladdin Enterprises</organization>
4180      <address><email>ghost@aladdin.com</email></address>
4181    </author>
4182    <date month="May" year="1996"/>
4183  </front>
4184  <seriesInfo name="RFC" value="1951"/>
4185  <!--<annotation>
4186    RFC 1951 is an Informational RFC, thus it might be less stable than
4187    this specification. On the other hand, this downward reference was
4188    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4189    therefore it is unlikely to cause problems in practice. See also
4190    <xref target="BCP97"/>.
4191  </annotation>-->
4192</reference>
4193
4194<reference anchor="RFC1952">
4195  <front>
4196    <title>GZIP file format specification version 4.3</title>
4197    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4198      <organization>Aladdin Enterprises</organization>
4199      <address><email>ghost@aladdin.com</email></address>
4200    </author>
4201    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4202      <address><email>gzip@prep.ai.mit.edu</email></address>
4203    </author>
4204    <author initials="M." surname="Adler" fullname="Mark Adler">
4205      <address><email>madler@alumni.caltech.edu</email></address>
4206    </author>
4207    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4208      <address><email>ghost@aladdin.com</email></address>
4209    </author>
4210    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4211      <address><email>randeg@alumni.rpi.edu</email></address>
4212    </author>
4213    <date month="May" year="1996"/>
4214  </front>
4215  <seriesInfo name="RFC" value="1952"/>
4216  <!--<annotation>
4217    RFC 1952 is an Informational RFC, thus it might be less stable than
4218    this specification. On the other hand, this downward reference was
4219    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4220    therefore it is unlikely to cause problems in practice. See also
4221    <xref target="BCP97"/>.
4222  </annotation>-->
4223</reference>
4224
4225</references>
4226
4227<references title="Informative References">
4228
4229<reference anchor="ISO-8859-1">
4230  <front>
4231    <title>
4232     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4233    </title>
4234    <author>
4235      <organization>International Organization for Standardization</organization>
4236    </author>
4237    <date year="1998"/>
4238  </front>
4239  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4240</reference>
4241
4242<reference anchor='RFC1919'>
4243  <front>
4244    <title>Classical versus Transparent IP Proxies</title>
4245    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4246      <address><email>mchatel@pax.eunet.ch</email></address>
4247    </author>
4248    <date year='1996' month='March' />
4249  </front>
4250  <seriesInfo name='RFC' value='1919' />
4251</reference>
4252
4253<reference anchor="RFC1945">
4254  <front>
4255    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4256    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4257      <organization>MIT, Laboratory for Computer Science</organization>
4258      <address><email>timbl@w3.org</email></address>
4259    </author>
4260    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4261      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4262      <address><email>fielding@ics.uci.edu</email></address>
4263    </author>
4264    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4265      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4266      <address><email>frystyk@w3.org</email></address>
4267    </author>
4268    <date month="May" year="1996"/>
4269  </front>
4270  <seriesInfo name="RFC" value="1945"/>
4271</reference>
4272
4273<reference anchor="RFC2045">
4274  <front>
4275    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4276    <author initials="N." surname="Freed" fullname="Ned Freed">
4277      <organization>Innosoft International, Inc.</organization>
4278      <address><email>ned@innosoft.com</email></address>
4279    </author>
4280    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4281      <organization>First Virtual Holdings</organization>
4282      <address><email>nsb@nsb.fv.com</email></address>
4283    </author>
4284    <date month="November" year="1996"/>
4285  </front>
4286  <seriesInfo name="RFC" value="2045"/>
4287</reference>
4288
4289<reference anchor="RFC2047">
4290  <front>
4291    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4292    <author initials="K." surname="Moore" fullname="Keith Moore">
4293      <organization>University of Tennessee</organization>
4294      <address><email>moore@cs.utk.edu</email></address>
4295    </author>
4296    <date month="November" year="1996"/>
4297  </front>
4298  <seriesInfo name="RFC" value="2047"/>
4299</reference>
4300
4301<reference anchor="RFC2068">
4302  <front>
4303    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4304    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4305      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4306      <address><email>fielding@ics.uci.edu</email></address>
4307    </author>
4308    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4309      <organization>MIT Laboratory for Computer Science</organization>
4310      <address><email>jg@w3.org</email></address>
4311    </author>
4312    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4313      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4314      <address><email>mogul@wrl.dec.com</email></address>
4315    </author>
4316    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4317      <organization>MIT Laboratory for Computer Science</organization>
4318      <address><email>frystyk@w3.org</email></address>
4319    </author>
4320    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4321      <organization>MIT Laboratory for Computer Science</organization>
4322      <address><email>timbl@w3.org</email></address>
4323    </author>
4324    <date month="January" year="1997"/>
4325  </front>
4326  <seriesInfo name="RFC" value="2068"/>
4327</reference>
4328
4329<reference anchor="RFC2145">
4330  <front>
4331    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4332    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4333      <organization>Western Research Laboratory</organization>
4334      <address><email>mogul@wrl.dec.com</email></address>
4335    </author>
4336    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4337      <organization>Department of Information and Computer Science</organization>
4338      <address><email>fielding@ics.uci.edu</email></address>
4339    </author>
4340    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4341      <organization>MIT Laboratory for Computer Science</organization>
4342      <address><email>jg@w3.org</email></address>
4343    </author>
4344    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4345      <organization>W3 Consortium</organization>
4346      <address><email>frystyk@w3.org</email></address>
4347    </author>
4348    <date month="May" year="1997"/>
4349  </front>
4350  <seriesInfo name="RFC" value="2145"/>
4351</reference>
4352
4353<reference anchor="RFC2616">
4354  <front>
4355    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4356    <author initials="R." surname="Fielding" fullname="R. Fielding">
4357      <organization>University of California, Irvine</organization>
4358      <address><email>fielding@ics.uci.edu</email></address>
4359    </author>
4360    <author initials="J." surname="Gettys" fullname="J. Gettys">
4361      <organization>W3C</organization>
4362      <address><email>jg@w3.org</email></address>
4363    </author>
4364    <author initials="J." surname="Mogul" fullname="J. Mogul">
4365      <organization>Compaq Computer Corporation</organization>
4366      <address><email>mogul@wrl.dec.com</email></address>
4367    </author>
4368    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4369      <organization>MIT Laboratory for Computer Science</organization>
4370      <address><email>frystyk@w3.org</email></address>
4371    </author>
4372    <author initials="L." surname="Masinter" fullname="L. Masinter">
4373      <organization>Xerox Corporation</organization>
4374      <address><email>masinter@parc.xerox.com</email></address>
4375    </author>
4376    <author initials="P." surname="Leach" fullname="P. Leach">
4377      <organization>Microsoft Corporation</organization>
4378      <address><email>paulle@microsoft.com</email></address>
4379    </author>
4380    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4381      <organization>W3C</organization>
4382      <address><email>timbl@w3.org</email></address>
4383    </author>
4384    <date month="June" year="1999"/>
4385  </front>
4386  <seriesInfo name="RFC" value="2616"/>
4387</reference>
4388
4389<reference anchor='RFC2817'>
4390  <front>
4391    <title>Upgrading to TLS Within HTTP/1.1</title>
4392    <author initials='R.' surname='Khare' fullname='R. Khare'>
4393      <organization>4K Associates / UC Irvine</organization>
4394      <address><email>rohit@4K-associates.com</email></address>
4395    </author>
4396    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4397      <organization>Agranat Systems, Inc.</organization>
4398      <address><email>lawrence@agranat.com</email></address>
4399    </author>
4400    <date year='2000' month='May' />
4401  </front>
4402  <seriesInfo name='RFC' value='2817' />
4403</reference>
4404
4405<reference anchor='RFC2818'>
4406  <front>
4407    <title>HTTP Over TLS</title>
4408    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4409      <organization>RTFM, Inc.</organization>
4410      <address><email>ekr@rtfm.com</email></address>
4411    </author>
4412    <date year='2000' month='May' />
4413  </front>
4414  <seriesInfo name='RFC' value='2818' />
4415</reference>
4416
4417<reference anchor='RFC2965'>
4418  <front>
4419    <title>HTTP State Management Mechanism</title>
4420    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4421      <organization>Bell Laboratories, Lucent Technologies</organization>
4422      <address><email>dmk@bell-labs.com</email></address>
4423    </author>
4424    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4425      <organization>Epinions.com, Inc.</organization>
4426      <address><email>lou@montulli.org</email></address>
4427    </author>
4428    <date year='2000' month='October' />
4429  </front>
4430  <seriesInfo name='RFC' value='2965' />
4431</reference>
4432
4433<reference anchor='RFC3040'>
4434  <front>
4435    <title>Internet Web Replication and Caching Taxonomy</title>
4436    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4437      <organization>Equinix, Inc.</organization>
4438    </author>
4439    <author initials='I.' surname='Melve' fullname='I. Melve'>
4440      <organization>UNINETT</organization>
4441    </author>
4442    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4443      <organization>CacheFlow Inc.</organization>
4444    </author>
4445    <date year='2001' month='January' />
4446  </front>
4447  <seriesInfo name='RFC' value='3040' />
4448</reference>
4449
4450<reference anchor='RFC3864'>
4451  <front>
4452    <title>Registration Procedures for Message Header Fields</title>
4453    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4454      <organization>Nine by Nine</organization>
4455      <address><email>GK-IETF@ninebynine.org</email></address>
4456    </author>
4457    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4458      <organization>BEA Systems</organization>
4459      <address><email>mnot@pobox.com</email></address>
4460    </author>
4461    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4462      <organization>HP Labs</organization>
4463      <address><email>JeffMogul@acm.org</email></address>
4464    </author>
4465    <date year='2004' month='September' />
4466  </front>
4467  <seriesInfo name='BCP' value='90' />
4468  <seriesInfo name='RFC' value='3864' />
4469</reference>
4470
4471<reference anchor='RFC4033'>
4472  <front>
4473    <title>DNS Security Introduction and Requirements</title>
4474    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4475    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4476    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4477    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4478    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4479    <date year='2005' month='March' />
4480  </front>
4481  <seriesInfo name='RFC' value='4033' />
4482</reference>
4483
4484<reference anchor="RFC4288">
4485  <front>
4486    <title>Media Type Specifications and Registration Procedures</title>
4487    <author initials="N." surname="Freed" fullname="N. Freed">
4488      <organization>Sun Microsystems</organization>
4489      <address>
4490        <email>ned.freed@mrochek.com</email>
4491      </address>
4492    </author>
4493    <author initials="J." surname="Klensin" fullname="J. Klensin">
4494      <address>
4495        <email>klensin+ietf@jck.com</email>
4496      </address>
4497    </author>
4498    <date year="2005" month="December"/>
4499  </front>
4500  <seriesInfo name="BCP" value="13"/>
4501  <seriesInfo name="RFC" value="4288"/>
4502</reference>
4503
4504<reference anchor='RFC4395'>
4505  <front>
4506    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4507    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4508      <organization>AT&amp;T Laboratories</organization>
4509      <address>
4510        <email>tony+urireg@maillennium.att.com</email>
4511      </address>
4512    </author>
4513    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4514      <organization>Qualcomm, Inc.</organization>
4515      <address>
4516        <email>hardie@qualcomm.com</email>
4517      </address>
4518    </author>
4519    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4520      <organization>Adobe Systems</organization>
4521      <address>
4522        <email>LMM@acm.org</email>
4523      </address>
4524    </author>
4525    <date year='2006' month='February' />
4526  </front>
4527  <seriesInfo name='BCP' value='115' />
4528  <seriesInfo name='RFC' value='4395' />
4529</reference>
4530
4531<reference anchor='RFC4559'>
4532  <front>
4533    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4534    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4535    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4536    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4537    <date year='2006' month='June' />
4538  </front>
4539  <seriesInfo name='RFC' value='4559' />
4540</reference>
4541
4542<reference anchor='RFC5226'>
4543  <front>
4544    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4545    <author initials='T.' surname='Narten' fullname='T. Narten'>
4546      <organization>IBM</organization>
4547      <address><email>narten@us.ibm.com</email></address>
4548    </author>
4549    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4550      <organization>Google</organization>
4551      <address><email>Harald@Alvestrand.no</email></address>
4552    </author>
4553    <date year='2008' month='May' />
4554  </front>
4555  <seriesInfo name='BCP' value='26' />
4556  <seriesInfo name='RFC' value='5226' />
4557</reference>
4558
4559<reference anchor="RFC5322">
4560  <front>
4561    <title>Internet Message Format</title>
4562    <author initials="P." surname="Resnick" fullname="P. Resnick">
4563      <organization>Qualcomm Incorporated</organization>
4564    </author>
4565    <date year="2008" month="October"/>
4566  </front> 
4567  <seriesInfo name="RFC" value="5322"/>
4568</reference>
4569
4570<reference anchor="RFC6265">
4571  <front>
4572    <title>HTTP State Management Mechanism</title>
4573    <author initials="A." surname="Barth" fullname="Adam Barth">
4574      <organization abbrev="U.C. Berkeley">
4575        University of California, Berkeley
4576      </organization>
4577      <address><email>abarth@eecs.berkeley.edu</email></address>
4578    </author>
4579    <date year="2011" month="April" />
4580  </front>
4581  <seriesInfo name="RFC" value="6265"/>
4582</reference>
4583
4584<!--<reference anchor='BCP97'>
4585  <front>
4586    <title>Handling Normative References to Standards-Track Documents</title>
4587    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4588      <address>
4589        <email>klensin+ietf@jck.com</email>
4590      </address>
4591    </author>
4592    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4593      <organization>MIT</organization>
4594      <address>
4595        <email>hartmans-ietf@mit.edu</email>
4596      </address>
4597    </author>
4598    <date year='2007' month='June' />
4599  </front>
4600  <seriesInfo name='BCP' value='97' />
4601  <seriesInfo name='RFC' value='4897' />
4602</reference>-->
4603
4604<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4605  <front>
4606    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4607    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4608    <date year="2001" month="November"/>
4609  </front>
4610  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4611</reference>
4612
4613</references>
4614
4615
4616<section title="HTTP Version History" anchor="compatibility">
4617<t>
4618   HTTP has been in use by the World-Wide Web global information initiative
4619   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4620   was a simple protocol for hypertext data transfer across the Internet
4621   with only a single request method (GET) and no metadata.
4622   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4623   methods and MIME-like messaging that could include metadata about the data
4624   transferred and modifiers on the request/response semantics. However,
4625   HTTP/1.0 did not sufficiently take into consideration the effects of
4626   hierarchical proxies, caching, the need for persistent connections, or
4627   name-based virtual hosts. The proliferation of incompletely-implemented
4628   applications calling themselves "HTTP/1.0" further necessitated a
4629   protocol version change in order for two communicating applications
4630   to determine each other's true capabilities.
4631</t>
4632<t>
4633   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4634   requirements that enable reliable implementations, adding only
4635   those new features that will either be safely ignored by an HTTP/1.0
4636   recipient or only sent when communicating with a party advertising
4637   conformance with HTTP/1.1.
4638</t>
4639<t>
4640   It is beyond the scope of a protocol specification to mandate
4641   conformance with previous versions. HTTP/1.1 was deliberately
4642   designed, however, to make supporting previous versions easy.
4643   We would expect a general-purpose HTTP/1.1 server to understand
4644   any valid request in the format of HTTP/1.0 and respond appropriately
4645   with an HTTP/1.1 message that only uses features understood (or
4646   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4647   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4648</t>
4649<t>
4650   Since HTTP/0.9 did not support header fields in a request,
4651   there is no mechanism for it to support name-based virtual
4652   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4653   field).  Any server that implements name-based virtual hosts
4654   ought to disable support for HTTP/0.9.  Most requests that
4655   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4656   requests wherein a buggy client failed to properly encode
4657   linear whitespace found in a URI reference and placed in
4658   the request-target.
4659</t>
4660
4661<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4662<t>
4663   This section summarizes major differences between versions HTTP/1.0
4664   and HTTP/1.1.
4665</t>
4666
4667<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4668<t>
4669   The requirements that clients and servers support the <x:ref>Host</x:ref>
4670   header field (<xref target="header.host"/>), report an error if it is
4671   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4672   are among the most important changes defined by HTTP/1.1.
4673</t>
4674<t>
4675   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4676   addresses and servers; there was no other established mechanism for
4677   distinguishing the intended server of a request than the IP address
4678   to which that request was directed. The <x:ref>Host</x:ref> header field was
4679   introduced during the development of HTTP/1.1 and, though it was
4680   quickly implemented by most HTTP/1.0 browsers, additional requirements
4681   were placed on all HTTP/1.1 requests in order to ensure complete
4682   adoption.  At the time of this writing, most HTTP-based services
4683   are dependent upon the Host header field for targeting requests.
4684</t>
4685</section>
4686
4687<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4688<t>
4689   In HTTP/1.0, each connection is established by the client prior to the
4690   request and closed by the server after sending the response. However, some
4691   implementations implement the explicitly negotiated ("Keep-Alive") version
4692   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4693   target="RFC2068"/>.
4694</t>
4695<t>
4696   Some clients and servers might wish to be compatible with these previous
4697   approaches to persistent connections, by explicitly negotiating for them
4698   with a "Connection: keep-alive" request header field. However, some
4699   experimental implementations of HTTP/1.0 persistent connections are faulty;
4700   for example, if a HTTP/1.0 proxy server doesn't understand
4701   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4702   to the next inbound server, which would result in a hung connection.
4703</t>
4704<t>
4705   One attempted solution was the introduction of a Proxy-Connection header
4706   field, targeted specifically at proxies. In practice, this was also
4707   unworkable, because proxies are often deployed in multiple layers, bringing
4708   about the same problem discussed above.
4709</t>
4710<t>
4711   As a result, clients are encouraged not to send the Proxy-Connection header
4712   field in any requests.
4713</t>
4714<t>
4715   Clients are also encouraged to consider the use of Connection: keep-alive
4716   in requests carefully; while they can enable persistent connections with
4717   HTTP/1.0 servers, clients using them need will need to monitor the
4718   connection for "hung" requests (which indicate that the client ought stop
4719   sending the header field), and this mechanism ought not be used by clients
4720   at all when a proxy is being used.
4721</t>
4722</section>
4723
4724<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4725<t>
4726   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4727   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4728   any transfer-coding prior to forwarding a message via a MIME-compliant
4729   protocol.
4730</t>
4731</section>
4732
4733</section>
4734
4735<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4736<t>
4737  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4738  sensitive. Restrict the version numbers to be single digits due to the fact
4739  that implementations are known to handle multi-digit version numbers
4740  incorrectly.
4741  (<xref target="http.version"/>)
4742</t>
4743<t>
4744  Update use of abs_path production from RFC 1808 to the path-absolute + query
4745  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4746  request method only.
4747  (<xref target="request-target"/>)
4748</t>
4749<t>
4750  Require that invalid whitespace around field-names be rejected.
4751  (<xref target="header.fields"/>)
4752</t>
4753<t>
4754  Rules about implicit linear whitespace between certain grammar productions
4755  have been removed; now whitespace is only allowed where specifically
4756  defined in the ABNF.
4757  (<xref target="whitespace"/>)
4758</t>
4759<t> 
4760  The NUL octet is no longer allowed in comment and quoted-string
4761  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4762  Non-ASCII content in header fields and reason phrase has been obsoleted and
4763  made opaque (the TEXT rule was removed).
4764  (<xref target="field.components"/>)
4765</t>
4766<t>
4767  Empty list elements in list productions have been deprecated.
4768  (<xref target="abnf.extension"/>)
4769</t>
4770<t>
4771  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4772  fields as errors.
4773  (<xref target="message.body"/>)
4774</t>
4775<t>
4776  Remove reference to non-existent identity transfer-coding value tokens.
4777  (Sections <xref format="counter" target="message.body"/> and
4778  <xref format="counter" target="transfer.codings"/>)
4779</t>
4780<t>
4781  Clarification that the chunk length does not include the count of the octets
4782  in the chunk header and trailer. Furthermore disallowed line folding
4783  in chunk extensions, and deprecate their use.
4784  (<xref target="chunked.encoding"/>)
4785</t>
4786<t>
4787  Registration of Transfer Codings now requires IETF Review
4788  (<xref target="transfer.coding.registry"/>)
4789</t>
4790<t>
4791  Remove hard limit of two connections per server.
4792  Remove requirement to retry a sequence of requests as long it was idempotent.
4793  Remove requirements about when servers are allowed to close connections
4794  prematurely.
4795  (<xref target="persistent.connections"/>)
4796</t>
4797<t>
4798  Remove requirement to retry requests under certain circumstances when the
4799  server prematurely closes the connection.
4800  (<xref target="persistent.reuse"/>)
4801</t>
4802<t>
4803  Change ABNF productions for header fields to only define the field value.
4804</t>
4805<t>
4806  Clarify exactly when "close" connection options have to be sent.
4807  (<xref target="header.connection"/>)
4808</t>
4809<t>
4810  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4811  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4812  (<xref target="header.upgrade"/>)
4813</t>
4814<t>
4815  Take over the Upgrade Token Registry, previously defined in
4816  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4817  (<xref target="upgrade.token.registry"/>)
4818</t>
4819</section>
4820</section>
4821
4822<section title="ABNF list extension: #rule" anchor="abnf.extension">
4823<t>
4824  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4825  improve readability in the definitions of some header field values.
4826</t>
4827<t>
4828  A construct "#" is defined, similar to "*", for defining comma-delimited
4829  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4830  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4831  comma (",") and optional whitespace (OWS).   
4832</t>
4833<figure><preamble>
4834  Thus,
4835</preamble><artwork type="example">
4836  1#element =&gt; element *( OWS "," OWS element )
4837</artwork></figure>
4838<figure><preamble>
4839  and:
4840</preamble><artwork type="example">
4841  #element =&gt; [ 1#element ]
4842</artwork></figure>
4843<figure><preamble>
4844  and for n &gt;= 1 and m &gt; 1:
4845</preamble><artwork type="example">
4846  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4847</artwork></figure>
4848<t>
4849  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4850  list elements. In other words, consumers would follow the list productions:
4851</t>
4852<figure><artwork type="example">
4853  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4854 
4855  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4856</artwork></figure>
4857<t>
4858  Note that empty elements do not contribute to the count of elements present,
4859  though.
4860</t>
4861<t>
4862  For example, given these ABNF productions:
4863</t>
4864<figure><artwork type="example">
4865  example-list      = 1#example-list-elmt
4866  example-list-elmt = token ; see <xref target="field.components"/> 
4867</artwork></figure>
4868<t>
4869  Then these are valid values for example-list (not including the double
4870  quotes, which are present for delimitation only):
4871</t>
4872<figure><artwork type="example">
4873  "foo,bar"
4874  "foo ,bar,"
4875  "foo , ,bar,charlie   "
4876</artwork></figure>
4877<t>
4878  But these values would be invalid, as at least one non-empty element is
4879  required:
4880</t>
4881<figure><artwork type="example">
4882  ""
4883  ","
4884  ",   ,"
4885</artwork></figure>
4886<t>
4887  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4888  expanded as explained above.
4889</t>
4890</section>
4891
4892<?BEGININC p1-messaging.abnf-appendix ?>
4893<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4894<figure>
4895<artwork type="abnf" name="p1-messaging.parsed-abnf">
4896<x:ref>BWS</x:ref> = OWS
4897
4898<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4899 connection-option ] )
4900<x:ref>Content-Length</x:ref> = 1*DIGIT
4901
4902<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4903 ]
4904<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4905<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4906<x:ref>Host</x:ref> = uri-host [ ":" port ]
4907
4908<x:ref>OWS</x:ref> = *( SP / HTAB )
4909
4910<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4911
4912<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4913<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4914<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4915 transfer-coding ] )
4916
4917<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4918<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4919
4920<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4921 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4922 comment ] ) ] )
4923
4924<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4925<x:ref>absolute-form</x:ref> = absolute-URI
4926<x:ref>asterisk-form</x:ref> = "*"
4927<x:ref>attribute</x:ref> = token
4928<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4929<x:ref>authority-form</x:ref> = authority
4930
4931<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4932<x:ref>chunk-data</x:ref> = 1*OCTET
4933<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4934<x:ref>chunk-ext-name</x:ref> = token
4935<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4936<x:ref>chunk-size</x:ref> = 1*HEXDIG
4937<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4938<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4939<x:ref>connection-option</x:ref> = token
4940<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4941 / %x2A-5B ; '*'-'['
4942 / %x5D-7E ; ']'-'~'
4943 / obs-text
4944
4945<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4946<x:ref>field-name</x:ref> = token
4947<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4948
4949<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4950<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4951<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4952
4953<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4954
4955<x:ref>message-body</x:ref> = *OCTET
4956<x:ref>method</x:ref> = token
4957
4958<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4959<x:ref>obs-text</x:ref> = %x80-FF
4960<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4961
4962<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4963<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4964<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4965<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4966<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4967<x:ref>protocol-name</x:ref> = token
4968<x:ref>protocol-version</x:ref> = token
4969<x:ref>pseudonym</x:ref> = token
4970
4971<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4972 / %x5D-7E ; ']'-'~'
4973 / obs-text
4974<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4975 / %x5D-7E ; ']'-'~'
4976 / obs-text
4977<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4978<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4979<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4980<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4981<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4982
4983<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4984<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4985<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4986<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4987<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4988<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4989<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4990 asterisk-form
4991
4992<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4993 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4994<x:ref>start-line</x:ref> = request-line / status-line
4995<x:ref>status-code</x:ref> = 3DIGIT
4996<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
4997
4998<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
4999<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5000<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5001 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5002<x:ref>token</x:ref> = 1*tchar
5003<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5004<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5005 transfer-extension
5006<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5007<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5008
5009<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5010
5011<x:ref>value</x:ref> = word
5012
5013<x:ref>word</x:ref> = token / quoted-string
5014</artwork>
5015</figure>
5016</section>
5017<?ENDINC p1-messaging.abnf-appendix ?>
5018
5019<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5020
5021<section title="Since RFC 2616">
5022<t>
5023  Extracted relevant partitions from <xref target="RFC2616"/>.
5024</t>
5025</section>
5026
5027<section title="Since draft-ietf-httpbis-p1-messaging-00">
5028<t>
5029  Closed issues:
5030  <list style="symbols"> 
5031    <t>
5032      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5033      "HTTP Version should be case sensitive"
5034      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5035    </t>
5036    <t>
5037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5038      "'unsafe' characters"
5039      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5040    </t>
5041    <t>
5042      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5043      "Chunk Size Definition"
5044      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5045    </t>
5046    <t>
5047      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5048      "Message Length"
5049      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5050    </t>
5051    <t>
5052      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5053      "Media Type Registrations"
5054      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5055    </t>
5056    <t>
5057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5058      "URI includes query"
5059      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5060    </t>
5061    <t>
5062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5063      "No close on 1xx responses"
5064      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5065    </t>
5066    <t>
5067      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5068      "Remove 'identity' token references"
5069      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5070    </t>
5071    <t>
5072      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5073      "Import query BNF"
5074    </t>
5075    <t>
5076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5077      "qdtext BNF"
5078    </t>
5079    <t>
5080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5081      "Normative and Informative references"
5082    </t>
5083    <t>
5084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5085      "RFC2606 Compliance"
5086    </t>
5087    <t>
5088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5089      "RFC977 reference"
5090    </t>
5091    <t>
5092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5093      "RFC1700 references"
5094    </t>
5095    <t>
5096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5097      "inconsistency in date format explanation"
5098    </t>
5099    <t>
5100      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5101      "Date reference typo"
5102    </t>
5103    <t>
5104      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5105      "Informative references"
5106    </t>
5107    <t>
5108      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5109      "ISO-8859-1 Reference"
5110    </t>
5111    <t>
5112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5113      "Normative up-to-date references"
5114    </t>
5115  </list>
5116</t>
5117<t>
5118  Other changes:
5119  <list style="symbols"> 
5120    <t>
5121      Update media type registrations to use RFC4288 template.
5122    </t>
5123    <t>
5124      Use names of RFC4234 core rules DQUOTE and HTAB,
5125      fix broken ABNF for chunk-data
5126      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5127    </t>
5128  </list>
5129</t>
5130</section>
5131
5132<section title="Since draft-ietf-httpbis-p1-messaging-01">
5133<t>
5134  Closed issues:
5135  <list style="symbols"> 
5136    <t>
5137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5138      "Bodies on GET (and other) requests"
5139    </t>
5140    <t>
5141      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5142      "Updating to RFC4288"
5143    </t>
5144    <t>
5145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5146      "Status Code and Reason Phrase"
5147    </t>
5148    <t>
5149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5150      "rel_path not used"
5151    </t>
5152  </list>
5153</t>
5154<t>
5155  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5156  <list style="symbols"> 
5157    <t>
5158      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5159      "trailer-part").
5160    </t>
5161    <t>
5162      Avoid underscore character in rule names ("http_URL" ->
5163      "http-URL", "abs_path" -> "path-absolute").
5164    </t>
5165    <t>
5166      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5167      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5168      have to be updated when switching over to RFC3986.
5169    </t>
5170    <t>
5171      Synchronize core rules with RFC5234.
5172    </t>
5173    <t>
5174      Get rid of prose rules that span multiple lines.
5175    </t>
5176    <t>
5177      Get rid of unused rules LOALPHA and UPALPHA.
5178    </t>
5179    <t>
5180      Move "Product Tokens" section (back) into Part 1, as "token" is used
5181      in the definition of the Upgrade header field.
5182    </t>
5183    <t>
5184      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5185    </t>
5186    <t>
5187      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5188    </t>
5189  </list>
5190</t>
5191</section>
5192
5193<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5194<t>
5195  Closed issues:
5196  <list style="symbols"> 
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5199      "HTTP-date vs. rfc1123-date"
5200    </t>
5201    <t>
5202      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5203      "WS in quoted-pair"
5204    </t>
5205  </list>
5206</t>
5207<t>
5208  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5209  <list style="symbols"> 
5210    <t>
5211      Reference RFC 3984, and update header field registrations for header
5212      fields defined in this document.
5213    </t>
5214  </list>
5215</t>
5216<t>
5217  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5218  <list style="symbols"> 
5219    <t>
5220      Replace string literals when the string really is case-sensitive (HTTP-version).
5221    </t>
5222  </list>
5223</t>
5224</section>
5225
5226<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5227<t>
5228  Closed issues:
5229  <list style="symbols"> 
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5232      "Connection closing"
5233    </t>
5234    <t>
5235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5236      "Move registrations and registry information to IANA Considerations"
5237    </t>
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5240      "need new URL for PAD1995 reference"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5244      "IANA Considerations: update HTTP URI scheme registration"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5248      "Cite HTTPS URI scheme definition"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5252      "List-type header fields vs Set-Cookie"
5253    </t>
5254  </list>
5255</t>
5256<t>
5257  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5258  <list style="symbols"> 
5259    <t>
5260      Replace string literals when the string really is case-sensitive (HTTP-Date).
5261    </t>
5262    <t>
5263      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5264    </t>
5265  </list>
5266</t>
5267</section>
5268
5269<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5270<t>
5271  Closed issues:
5272  <list style="symbols"> 
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5275      "Out-of-date reference for URIs"
5276    </t>
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5279      "RFC 2822 is updated by RFC 5322"
5280    </t>
5281  </list>
5282</t>
5283<t>
5284  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5285  <list style="symbols"> 
5286    <t>
5287      Use "/" instead of "|" for alternatives.
5288    </t>
5289    <t>
5290      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5291    </t>
5292    <t>
5293      Only reference RFC 5234's core rules.
5294    </t>
5295    <t>
5296      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5297      whitespace ("OWS") and required whitespace ("RWS").
5298    </t>
5299    <t>
5300      Rewrite ABNFs to spell out whitespace rules, factor out
5301      header field value format definitions.
5302    </t>
5303  </list>
5304</t>
5305</section>
5306
5307<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5308<t>
5309  Closed issues:
5310  <list style="symbols"> 
5311    <t>
5312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5313      "Header LWS"
5314    </t>
5315    <t>
5316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5317      "Sort 1.3 Terminology"
5318    </t>
5319    <t>
5320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5321      "RFC2047 encoded words"
5322    </t>
5323    <t>
5324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5325      "Character Encodings in TEXT"
5326    </t>
5327    <t>
5328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5329      "Line Folding"
5330    </t>
5331    <t>
5332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5333      "OPTIONS * and proxies"
5334    </t>
5335    <t>
5336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5337      "reason-phrase BNF"
5338    </t>
5339    <t>
5340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5341      "Use of TEXT"
5342    </t>
5343    <t>
5344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5345      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5346    </t>
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5349      "RFC822 reference left in discussion of date formats"
5350    </t>
5351  </list>
5352</t>
5353<t>
5354  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5355  <list style="symbols"> 
5356    <t>
5357      Rewrite definition of list rules, deprecate empty list elements.
5358    </t>
5359    <t>
5360      Add appendix containing collected and expanded ABNF.
5361    </t>
5362  </list>
5363</t>
5364<t>
5365  Other changes:
5366  <list style="symbols"> 
5367    <t>
5368      Rewrite introduction; add mostly new Architecture Section.
5369    </t>
5370    <t>
5371      Move definition of quality values from Part 3 into Part 1;
5372      make TE request header field grammar independent of accept-params (defined in Part 3).
5373    </t>
5374  </list>
5375</t>
5376</section>
5377
5378<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5379<t>
5380  Closed issues:
5381  <list style="symbols"> 
5382    <t>
5383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5384      "base for numeric protocol elements"
5385    </t>
5386    <t>
5387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5388      "comment ABNF"
5389    </t>
5390  </list>
5391</t>
5392<t>
5393  Partly resolved issues:
5394  <list style="symbols"> 
5395    <t>
5396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5397      "205 Bodies" (took out language that implied that there might be
5398      methods for which a request body MUST NOT be included)
5399    </t>
5400    <t>
5401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5402      "editorial improvements around HTTP-date"
5403    </t>
5404  </list>
5405</t>
5406</section>
5407
5408<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5409<t>
5410  Closed issues:
5411  <list style="symbols"> 
5412    <t>
5413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5414      "Repeating single-value header fields"
5415    </t>
5416    <t>
5417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5418      "increase connection limit"
5419    </t>
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5422      "IP addresses in URLs"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5426      "take over HTTP Upgrade Token Registry"
5427    </t>
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5430      "CR and LF in chunk extension values"
5431    </t>
5432    <t>
5433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5434      "HTTP/0.9 support"
5435    </t>
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5438      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5439    </t>
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5442      "move definitions of gzip/deflate/compress to part 1"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5446      "disallow control characters in quoted-pair"
5447    </t>
5448  </list>
5449</t>
5450<t>
5451  Partly resolved issues:
5452  <list style="symbols"> 
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5455      "update IANA requirements wrt Transfer-Coding values" (add the
5456      IANA Considerations subsection)
5457    </t>
5458  </list>
5459</t>
5460</section>
5461
5462<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5463<t>
5464  Closed issues:
5465  <list style="symbols"> 
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5468      "header parsing, treatment of leading and trailing OWS"
5469    </t>
5470  </list>
5471</t>
5472<t>
5473  Partly resolved issues:
5474  <list style="symbols"> 
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5477      "Placement of 13.5.1 and 13.5.2"
5478    </t>
5479    <t>
5480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5481      "use of term "word" when talking about header field structure"
5482    </t>
5483  </list>
5484</t>
5485</section>
5486
5487<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5488<t>
5489  Closed issues:
5490  <list style="symbols"> 
5491    <t>
5492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5493      "Clarification of the term 'deflate'"
5494    </t>
5495    <t>
5496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5497      "OPTIONS * and proxies"
5498    </t>
5499    <t>
5500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5501      "MIME-Version not listed in P1, general header fields"
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5505      "IANA registry for content/transfer encodings"
5506    </t>
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5509      "Case-sensitivity of HTTP-date"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5513      "use of term "word" when talking about header field structure"
5514    </t>
5515  </list>
5516</t>
5517<t>
5518  Partly resolved issues:
5519  <list style="symbols"> 
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5522      "Term for the requested resource's URI"
5523    </t>
5524  </list>
5525</t>
5526</section>
5527
5528<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5529<t>
5530  Closed issues:
5531  <list style="symbols">
5532    <t>
5533      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5534      "Connection Closing"
5535    </t>
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5538      "Delimiting messages with multipart/byteranges"
5539    </t>
5540    <t>
5541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5542      "Handling multiple Content-Length header fields"
5543    </t>
5544    <t>
5545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5546      "Clarify entity / representation / variant terminology"
5547    </t>
5548    <t>
5549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5550      "consider removing the 'changes from 2068' sections"
5551    </t>
5552  </list>
5553</t>
5554<t>
5555  Partly resolved issues:
5556  <list style="symbols"> 
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5559      "HTTP(s) URI scheme definitions"
5560    </t>
5561  </list>
5562</t>
5563</section>
5564
5565<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5566<t>
5567  Closed issues:
5568  <list style="symbols">
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5571      "Trailer requirements"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5575      "Text about clock requirement for caches belongs in p6"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5579      "effective request URI: handling of missing host in HTTP/1.0"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5583      "confusing Date requirements for clients"
5584    </t>
5585  </list>
5586</t>
5587<t>
5588  Partly resolved issues:
5589  <list style="symbols"> 
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5592      "Handling multiple Content-Length header fields"
5593    </t>
5594  </list>
5595</t>
5596</section>
5597
5598<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5599<t>
5600  Closed issues:
5601  <list style="symbols">
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5604      "RFC2145 Normative"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5608      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5609    </t>
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5612      "define 'transparent' proxy"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5616      "Header Field Classification"
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5620      "Is * usable as a request-uri for new methods?"
5621    </t>
5622    <t>
5623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5624      "Migrate Upgrade details from RFC2817"
5625    </t>
5626    <t>
5627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5628      "untangle ABNFs for header fields"
5629    </t>
5630    <t>
5631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5632      "update RFC 2109 reference"
5633    </t>
5634  </list>
5635</t>
5636</section>
5637
5638<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5639<t>
5640  Closed issues:
5641  <list style="symbols">
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5644      "Allow is not in 13.5.2"
5645    </t>
5646    <t>
5647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5648      "Handling multiple Content-Length header fields"
5649    </t>
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5652      "untangle ABNFs for header fields"
5653    </t>
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5656      "Content-Length ABNF broken"
5657    </t>
5658  </list>
5659</t>
5660</section>
5661
5662<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5663<t>
5664  Closed issues:
5665  <list style="symbols">
5666    <t>
5667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5668      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5669    </t>
5670    <t>
5671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5672      "Recommend minimum sizes for protocol elements"
5673    </t>
5674    <t>
5675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5676      "Set expectations around buffering"
5677    </t>
5678    <t>
5679      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5680      "Considering messages in isolation"
5681    </t>
5682  </list>
5683</t>
5684</section>
5685
5686<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5687<t>
5688  Closed issues:
5689  <list style="symbols">
5690    <t>
5691      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5692      "DNS Spoofing / DNS Binding advice"
5693    </t>
5694    <t>
5695      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5696      "move RFCs 2145, 2616, 2817 to Historic status"
5697    </t>
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5700      "\-escaping in quoted strings"
5701    </t>
5702    <t>
5703      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5704      "'Close' should be reserved in the HTTP header field registry"
5705    </t>
5706  </list>
5707</t>
5708</section>
5709
5710<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5711<t>
5712  Closed issues:
5713  <list style="symbols">
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5716      "Document HTTP's error-handling philosophy"
5717    </t>
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5720      "Explain header field registration"
5721    </t>
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5724      "Revise Acknowledgements Sections"
5725    </t>
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5728      "Retrying Requests"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5732      "Closing the connection on server error"
5733    </t>
5734  </list>
5735</t>
5736</section>
5737
5738<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5739<t>
5740  Closed issues:
5741  <list style="symbols">
5742    <t>
5743      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5744      "Proxy-Connection and Keep-Alive"
5745    </t>
5746    <t>
5747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5748      "Clarify 'User Agent'"
5749    </t>
5750    <t>
5751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5752      "Define non-final responses"
5753    </t>
5754    <t>
5755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5756      "intended maturity level vs normative references"
5757    </t>
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5760      "Intermediary rewriting of queries"
5761    </t>
5762  </list>
5763</t>
5764</section>
5765
5766<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5767<t>
5768  Closed issues:
5769  <list style="symbols">
5770    <t>
5771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5772      "message-body in CONNECT response"
5773    </t>
5774    <t>
5775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5776      "Misplaced text on connection handling in p2"
5777    </t>
5778    <t>
5779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5780      "wording of line folding rule"
5781    </t>
5782    <t>
5783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5784      "chunk-extensions"
5785    </t>
5786    <t>
5787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5788      "make IANA policy definitions consistent"
5789    </t>
5790  </list>
5791</t>
5792</section>
5793
5794<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5795<t>
5796  Closed issues:
5797  <list style="symbols">
5798    <t>
5799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5800      "make IANA policy definitions consistent"
5801    </t>
5802    <t>
5803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5804      "clarify connection header field values are case-insensitive"
5805    </t>
5806    <t>
5807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5808      "ABNF requirements for recipients"
5809    </t>
5810    <t>
5811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5812      "note introduction of new IANA registries as normative changes"
5813    </t>
5814    <t>
5815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5816      "Reference to ISO-8859-1 is informative"
5817    </t>
5818  </list>
5819</t>
5820</section>
5821
5822<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5823<t>
5824  None yet.
5825</t>
5826</section>
5827
5828</section>
5829
5830</back>
5831</rfc>
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