source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1894

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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-level 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 (TLS, <xref target="RFC5246"/>) is used to
536   establish confidential communication 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. Additional (social) requirements
620   are placed on implementations, resource owners, and protocol element
621   registrations when they apply beyond the scope of a single communication.
622</t>
623<t>
624   The verb "generate" is used instead of "send" where a requirement
625   differentiates between creating a protocol element and merely forwarding a
626   received element downstream.
627</t>
628<t>
629   An implementation is considered conformant if it complies with all of the
630   requirements associated with the roles it partakes in HTTP. Note that
631   SHOULD-level requirements are relevant here, unless one of the documented
632   exceptions is applicable.
633</t>
634<t>
635   Conformance applies to both the syntax and semantics of HTTP protocol
636   elements. A sender &MUST-NOT; generate protocol elements that convey a
637   meaning that is known by that sender to be false. A sender &MUST-NOT;
638   generate protocol elements that do not match the grammar defined by the
639   ABNF rules for those protocol elements that are applicable to the sender's
640   role. If a received protocol element is processed, the recipient &MUST; be
641   able to parse any value that would match the ABNF rules for that protocol
642   element, excluding only those rules not applicable to the recipient's role.
643</t>
644<t>
645   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
646   protocol element from an invalid construct.  HTTP does not define
647   specific error handling mechanisms except when they have a direct impact
648   on security, since different applications of the protocol require
649   different error handling strategies.  For example, a Web browser might
650   wish to transparently recover from a response where the
651   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
652   whereas a systems control client might consider any form of error recovery
653   to be dangerous.
654</t>
655</section>
656
657<section title="Protocol Versioning" anchor="http.version">
658  <x:anchor-alias value="HTTP-version"/>
659  <x:anchor-alias value="HTTP-name"/>
660<t>
661   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
662   versions of the protocol. This specification defines version "1.1".
663   The protocol version as a whole indicates the sender's conformance
664   with the set of requirements laid out in that version's corresponding
665   specification of HTTP.
666</t>
667<t>
668   The version of an HTTP message is indicated by an HTTP-version field
669   in the first line of the message. HTTP-version is case-sensitive.
670</t>
671<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
672  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
673  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
674</artwork></figure>
675<t>
676   The HTTP version number consists of two decimal digits separated by a "."
677   (period or decimal point).  The first digit ("major version") indicates the
678   HTTP messaging syntax, whereas the second digit ("minor version") indicates
679   the highest minor version to which the sender is
680   conformant and able to understand for future communication.  The minor
681   version advertises the sender's communication capabilities even when the
682   sender is only using a backwards-compatible subset of the protocol,
683   thereby letting the recipient know that more advanced features can
684   be used in response (by servers) or in future requests (by clients).
685</t>
686<t>
687   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
688   <xref target="RFC1945"/> or a recipient whose version is unknown,
689   the HTTP/1.1 message is constructed such that it can be interpreted
690   as a valid HTTP/1.0 message if all of the newer features are ignored.
691   This specification places recipient-version requirements on some
692   new features so that a conformant sender will only use compatible
693   features until it has determined, through configuration or the
694   receipt of a message, that the recipient supports HTTP/1.1.
695</t>
696<t>
697   The interpretation of a header field does not change between minor
698   versions of the same major HTTP version, though the default
699   behavior of a recipient in the absence of such a field can change.
700   Unless specified otherwise, header fields defined in HTTP/1.1 are
701   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
702   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
703   HTTP/1.x implementations whether or not they advertise conformance with
704   HTTP/1.1.
705</t>
706<t>
707   New header fields can be defined such that, when they are
708   understood by a recipient, they might override or enhance the
709   interpretation of previously defined header fields.  When an
710   implementation receives an unrecognized header field, the recipient
711   &MUST; ignore that header field for local processing regardless of
712   the message's HTTP version.  An unrecognized header field received
713   by a proxy &MUST; be forwarded downstream unless the header field's
714   field-name is listed in the message's <x:ref>Connection</x:ref> header field
715   (see <xref target="header.connection"/>).
716   These requirements allow HTTP's functionality to be enhanced without
717   requiring prior update of deployed intermediaries.
718</t>
719<t>
720   Intermediaries that process HTTP messages (i.e., all intermediaries
721   other than those acting as tunnels) &MUST; send their own HTTP-version
722   in forwarded messages.  In other words, they &MUST-NOT; blindly
723   forward the first line of an HTTP message without ensuring that the
724   protocol version in that message matches a version to which that
725   intermediary is conformant for both the receiving and
726   sending of messages.  Forwarding an HTTP message without rewriting
727   the HTTP-version might result in communication errors when downstream
728   recipients use the message sender's version to determine what features
729   are safe to use for later communication with that sender.
730</t>
731<t>
732   An HTTP client &SHOULD; send a request version equal to the highest
733   version to which the client is conformant and
734   whose major version is no higher than the highest version supported
735   by the server, if this is known.  An HTTP client &MUST-NOT; send a
736   version to which it is not conformant.
737</t>
738<t>
739   An HTTP client &MAY; send a lower request version if it is known that
740   the server incorrectly implements the HTTP specification, but only
741   after the client has attempted at least one normal request and determined
742   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
743   the server improperly handles higher request versions.
744</t>
745<t>
746   An HTTP server &SHOULD; send a response version equal to the highest
747   version to which the server is conformant and
748   whose major version is less than or equal to the one received in the
749   request.  An HTTP server &MUST-NOT; send a version to which it is not
750   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
751   Supported)</x:ref> response if it cannot send a response using the
752   major version used in the client's request.
753</t>
754<t>
755   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
756   if it is known or suspected that the client incorrectly implements the
757   HTTP specification and is incapable of correctly processing later
758   version responses, such as when a client fails to parse the version
759   number correctly or when an intermediary is known to blindly forward
760   the HTTP-version even when it doesn't conform to the given minor
761   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
762   performed unless triggered by specific client attributes, such as when
763   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
764   uniquely match the values sent by a client known to be in error.
765</t>
766<t>
767   The intention of HTTP's versioning design is that the major number
768   will only be incremented if an incompatible message syntax is
769   introduced, and that the minor number will only be incremented when
770   changes made to the protocol have the effect of adding to the message
771   semantics or implying additional capabilities of the sender.  However,
772   the minor version was not incremented for the changes introduced between
773   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
774   is specifically avoiding any such changes to the protocol.
775</t>
776</section>
777
778<section title="Uniform Resource Identifiers" anchor="uri">
779<iref primary="true" item="resource"/>
780<t>
781   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
782   throughout HTTP as the means for identifying resources. URI references
783   are used to target requests, indicate redirects, and define relationships.
784   HTTP does not limit what a resource might be; it merely defines an interface
785   that can be used to interact with a resource via HTTP. More information on
786   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
787</t>
788  <x:anchor-alias value="URI-reference"/>
789  <x:anchor-alias value="absolute-URI"/>
790  <x:anchor-alias value="relative-part"/>
791  <x:anchor-alias value="authority"/>
792  <x:anchor-alias value="path-abempty"/>
793  <x:anchor-alias value="path-absolute"/>
794  <x:anchor-alias value="port"/>
795  <x:anchor-alias value="query"/>
796  <x:anchor-alias value="uri-host"/>
797  <x:anchor-alias value="partial-URI"/>
798<t>
799   This specification adopts the definitions of "URI-reference",
800   "absolute-URI", "relative-part", "port", "host",
801   "path-abempty", "path-absolute", "query", and "authority" from the
802   URI generic syntax <xref target="RFC3986"/>.
803   In addition, we define a partial-URI rule for protocol elements
804   that allow a relative URI but not a fragment.
805</t>
806<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>
807  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
808  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
809  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
810  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
811  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
812  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
813  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
814  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
815  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
816 
817  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
818</artwork></figure>
819<t>
820   Each protocol element in HTTP that allows a URI reference will indicate
821   in its ABNF production whether the element allows any form of reference
822   (URI-reference), only a URI in absolute form (absolute-URI), only the
823   path and optional query components, or some combination of the above.
824   Unless otherwise indicated, URI references are parsed
825   relative to the effective request URI
826   (<xref target="effective.request.uri"/>).
827</t>
828
829<section title="http URI scheme" anchor="http.uri">
830  <x:anchor-alias value="http-URI"/>
831  <iref item="http URI scheme" primary="true"/>
832  <iref item="URI scheme" subitem="http" primary="true"/>
833<t>
834   The "http" URI scheme is hereby defined for the purpose of minting
835   identifiers according to their association with the hierarchical
836   namespace governed by a potential HTTP origin server listening for
837   TCP connections on a given port.
838</t>
839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
840  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
841</artwork></figure>
842<t>
843   The HTTP origin server is identified by the generic syntax's
844   <x:ref>authority</x:ref> component, which includes a host identifier
845   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
846   The remainder of the URI, consisting of both the hierarchical path
847   component and optional query component, serves as an identifier for
848   a potential resource within that origin server's name space.
849</t>
850<t>
851   If the host identifier is provided as an IP literal or IPv4 address,
852   then the origin server is any listener on the indicated TCP port at
853   that IP address. If host is a registered name, then that name is
854   considered an indirect identifier and the recipient might use a name
855   resolution service, such as DNS, to find the address of a listener
856   for that host.
857   The host &MUST-NOT; be empty; if an "http" URI is received with an
858   empty host, then it &MUST; be rejected as invalid.
859   If the port subcomponent is empty or not given, then TCP port 80 is
860   assumed (the default reserved port for WWW services).
861</t>
862<t>
863   Regardless of the form of host identifier, access to that host is not
864   implied by the mere presence of its name or address. The host might or might
865   not exist and, even when it does exist, might or might not be running an
866   HTTP server or listening to the indicated port. The "http" URI scheme
867   makes use of the delegated nature of Internet names and addresses to
868   establish a naming authority (whatever entity has the ability to place
869   an HTTP server at that Internet name or address) and allows that
870   authority to determine which names are valid and how they might be used.
871</t>
872<t>
873   When an "http" URI is used within a context that calls for access to the
874   indicated resource, a client &MAY; attempt access by resolving
875   the host to an IP address, establishing a TCP connection to that address
876   on the indicated port, and sending an HTTP request message
877   (<xref target="http.message"/>) containing the URI's identifying data
878   (<xref target="message.routing"/>) to the server.
879   If the server responds to that request with a non-interim HTTP response
880   message, as described in &status-codes;, then that response
881   is considered an authoritative answer to the client's request.
882</t>
883<t>
884   Although HTTP is independent of the transport protocol, the "http"
885   scheme is specific to TCP-based services because the name delegation
886   process depends on TCP for establishing authority.
887   An HTTP service based on some other underlying connection protocol
888   would presumably be identified using a different URI scheme, just as
889   the "https" scheme (below) is used for servers that require an SSL/TLS
890   transport layer on a connection. Other protocols might also be used to
891   provide access to "http" identified resources &mdash; it is only the
892   authoritative interface used for mapping the namespace that is
893   specific to TCP.
894</t>
895<t>
896   The URI generic syntax for authority also includes a deprecated
897   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
898   for including user authentication information in the URI.  Some
899   implementations make use of the userinfo component for internal
900   configuration of authentication information, such as within command
901   invocation options, configuration files, or bookmark lists, even
902   though such usage might expose a user identifier or password.
903   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
904   delimiter) when transmitting an "http" URI in a message.  Recipients
905   of HTTP messages that contain a URI reference &SHOULD; parse for the
906   existence of userinfo and treat its presence as an error, likely
907   indicating that the deprecated subcomponent is being used to obscure
908   the authority for the sake of phishing attacks.
909</t>
910</section>
911
912<section title="https URI scheme" anchor="https.uri">
913   <x:anchor-alias value="https-URI"/>
914   <iref item="https URI scheme"/>
915   <iref item="URI scheme" subitem="https"/>
916<t>
917   The "https" URI scheme is hereby defined for the purpose of minting
918   identifiers according to their association with the hierarchical
919   namespace governed by a potential HTTP origin server listening for
920   SSL/TLS-secured connections on a given TCP port.
921</t>
922<t>
923   All of the requirements listed above for the "http" scheme are also
924   requirements for the "https" scheme, except that a default TCP port
925   of 443 is assumed if the port subcomponent is empty or not given,
926   and the TCP connection &MUST; be secured through the
927   use of strong encryption prior to sending the first HTTP request.
928</t>
929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
930  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
931</artwork></figure>
932<t>
933   Unlike the "http" scheme, responses to "https" identified requests
934   are never "public" and thus &MUST-NOT; be reused for shared caching.
935   They can, however, be reused in a private cache if the message is
936   cacheable by default in HTTP or specifically indicated as such by
937   the Cache-Control header field (&header-cache-control;).
938</t>
939<t>
940   Resources made available via the "https" scheme have no shared
941   identity with the "http" scheme even if their resource identifiers
942   indicate the same authority (the same host listening to the same
943   TCP port).  They are distinct name spaces and are considered to be
944   distinct origin servers.  However, an extension to HTTP that is
945   defined to apply to entire host domains, such as the Cookie protocol
946   <xref target="RFC6265"/>, can allow information
947   set by one service to impact communication with other services
948   within a matching group of host domains.
949</t>
950<t>
951   The process for authoritative access to an "https" identified
952   resource is defined in <xref target="RFC2818"/>.
953</t>
954</section>
955
956<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
957<t>
958   Since the "http" and "https" schemes conform to the URI generic syntax,
959   such URIs are normalized and compared according to the algorithm defined
960   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
961   described above for each scheme.
962</t>
963<t>
964   If the port is equal to the default port for a scheme, the normal
965   form is to elide the port subcomponent. Likewise, an empty path
966   component is equivalent to an absolute path of "/", so the normal
967   form is to provide a path of "/" instead. The scheme and host
968   are case-insensitive and normally provided in lowercase; all
969   other components are compared in a case-sensitive manner.
970   Characters other than those in the "reserved" set are equivalent
971   to their percent-encoded octets (see <xref target="RFC3986"
972   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
973</t>
974<t>
975   For example, the following three URIs are equivalent:
976</t>
977<figure><artwork type="example">
978   http://example.com:80/~smith/home.html
979   http://EXAMPLE.com/%7Esmith/home.html
980   http://EXAMPLE.com:/%7esmith/home.html
981</artwork></figure>
982</section>
983</section>
984</section>
985
986<section title="Message Format" anchor="http.message">
987<x:anchor-alias value="generic-message"/>
988<x:anchor-alias value="message.types"/>
989<x:anchor-alias value="HTTP-message"/>
990<x:anchor-alias value="start-line"/>
991<iref item="header section"/>
992<iref item="headers"/>
993<iref item="header field"/>
994<t>
995   All HTTP/1.1 messages consist of a start-line followed by a sequence of
996   octets in a format similar to the Internet Message Format
997   <xref target="RFC5322"/>: zero or more header fields (collectively
998   referred to as the "headers" or the "header section"), an empty line
999   indicating the end of the header section, and an optional message body.
1000</t>
1001<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1002  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1003                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1004                   <x:ref>CRLF</x:ref>
1005                   [ <x:ref>message-body</x:ref> ]
1006</artwork></figure>
1007<t>
1008   The normal procedure for parsing an HTTP message is to read the
1009   start-line into a structure, read each header field into a hash
1010   table by field name until the empty line, and then use the parsed
1011   data to determine if a message body is expected.  If a message body
1012   has been indicated, then it is read as a stream until an amount
1013   of octets equal to the message body length is read or the connection
1014   is closed.
1015</t>
1016<t>
1017   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1018   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1019   Parsing an HTTP message as a stream of Unicode characters, without regard
1020   for the specific encoding, creates security vulnerabilities due to the
1021   varying ways that string processing libraries handle invalid multibyte
1022   character sequences that contain the octet LF (%x0A).  String-based
1023   parsers can only be safely used within protocol elements after the element
1024   has been extracted from the message, such as within a header field-value
1025   after message parsing has delineated the individual fields.
1026</t>
1027<t>
1028   An HTTP message can be parsed as a stream for incremental processing or
1029   forwarding downstream.  However, recipients cannot rely on incremental
1030   delivery of partial messages, since some implementations will buffer or
1031   delay message forwarding for the sake of network efficiency, security
1032   checks, or payload transformations.
1033</t>
1034
1035<section title="Start Line" anchor="start.line">
1036  <x:anchor-alias value="Start-Line"/>
1037<t>
1038   An HTTP message can either be a request from client to server or a
1039   response from server to client.  Syntactically, the two types of message
1040   differ only in the start-line, which is either a request-line (for requests)
1041   or a status-line (for responses), and in the algorithm for determining
1042   the length of the message body (<xref target="message.body"/>).
1043   In theory, a client could receive requests and a server could receive
1044   responses, distinguishing them by their different start-line formats,
1045   but in practice servers are implemented to only expect a request
1046   (a response is interpreted as an unknown or invalid request method)
1047   and clients are implemented to only expect a response.
1048</t>
1049<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1050  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1051</artwork></figure>
1052<t>
1053   A sender &MUST-NOT; send whitespace between the start-line and
1054   the first header field. The presence of such whitespace in a request
1055   might be an attempt to trick a server into ignoring that field or
1056   processing the line after it as a new request, either of which might
1057   result in a security vulnerability if other implementations within
1058   the request chain interpret the same message differently.
1059   Likewise, the presence of such whitespace in a response might be
1060   ignored by some clients or cause others to cease parsing.
1061</t>
1062
1063<section title="Request Line" anchor="request.line">
1064  <x:anchor-alias value="Request"/>
1065  <x:anchor-alias value="request-line"/>
1066<t>
1067   A request-line begins with a method token, followed by a single
1068   space (SP), the request-target, another single space (SP), the
1069   protocol version, and ending with CRLF.
1070</t>
1071<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1072  <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>
1073</artwork></figure>
1074<t>
1075   A server &MUST; be able to parse any received message that begins
1076   with a request-line and matches the ABNF rule for HTTP-message.
1077</t>
1078<iref primary="true" item="method"/>
1079<t anchor="method">
1080   The method token indicates the request method to be performed on the
1081   target resource. The request method is case-sensitive.
1082</t>
1083<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1084  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1085</artwork></figure>
1086<t>
1087   The methods defined by this specification can be found in
1088   &methods;, along with information regarding the HTTP method registry
1089   and considerations for defining new methods.
1090</t>
1091<iref item="request-target"/>
1092<t>
1093   The request-target identifies the target resource upon which to apply
1094   the request, as defined in <xref target="request-target"/>.
1095</t>
1096<t>
1097   No whitespace is allowed inside the method, request-target, and
1098   protocol version.  Hence, recipients typically parse the request-line
1099   into its component parts by splitting on the SP characters.
1100</t>
1101<t>
1102   Unfortunately, some user agents fail to properly encode hypertext
1103   references that have embedded whitespace, sending the characters
1104   directly instead of properly percent-encoding the disallowed characters.
1105   Recipients of an invalid request-line &SHOULD; respond with either a
1106   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1107   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1108   attempt to autocorrect and then process the request without a redirect,
1109   since the invalid request-line might be deliberately crafted to bypass
1110   security filters along the request chain.
1111</t>
1112<t>
1113   HTTP does not place a pre-defined limit on the length of a request-line.
1114   A server that receives a method longer than any that it implements
1115   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1116   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1117   A server &MUST; be prepared to receive URIs of unbounded length and
1118   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1119   request-target would be longer than the server wishes to handle
1120   (see &status-414;).
1121</t>
1122<t>
1123   Various ad-hoc limitations on request-line length are found in practice.
1124   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1125   minimum, request-line lengths of up to 8000 octets.
1126</t>
1127</section>
1128
1129<section title="Status Line" anchor="status.line">
1130  <x:anchor-alias value="response"/>
1131  <x:anchor-alias value="status-line"/>
1132  <x:anchor-alias value="status-code"/>
1133  <x:anchor-alias value="reason-phrase"/>
1134<t>
1135   The first line of a response message is the status-line, consisting
1136   of the protocol version, a space (SP), the status code, another space,
1137   a possibly-empty textual phrase describing the status code, and
1138   ending with CRLF.
1139</t>
1140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1141  <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>
1142</artwork></figure>
1143<t>
1144   A client &MUST; be able to parse any received message that begins
1145   with a status-line and matches the ABNF rule for HTTP-message.
1146</t>
1147<t>
1148   The status-code element is a 3-digit integer code describing the
1149   result of the server's attempt to understand and satisfy the client's
1150   corresponding request. The rest of the response message is to be
1151   interpreted in light of the semantics defined for that status code.
1152   See &status-codes; for information about the semantics of status codes,
1153   including the classes of status code (indicated by the first digit),
1154   the status codes defined by this specification, considerations for the
1155   definition of new status codes, and the IANA registry.
1156</t>
1157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1158  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1159</artwork></figure>
1160<t>   
1161   The reason-phrase element exists for the sole purpose of providing a
1162   textual description associated with the numeric status code, mostly
1163   out of deference to earlier Internet application protocols that were more
1164   frequently used with interactive text clients. A client &SHOULD; ignore
1165   the reason-phrase content.
1166</t>
1167<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1168  <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> )
1169</artwork></figure>
1170</section>
1171</section>
1172
1173<section title="Header Fields" anchor="header.fields">
1174  <x:anchor-alias value="header-field"/>
1175  <x:anchor-alias value="field-content"/>
1176  <x:anchor-alias value="field-name"/>
1177  <x:anchor-alias value="field-value"/>
1178  <x:anchor-alias value="obs-fold"/>
1179<t>
1180   Each HTTP header field consists of a case-insensitive field name
1181   followed by a colon (":"), optional whitespace, and the field value.
1182</t>
1183<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"/>
1184  <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>
1185  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1186  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1187  <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> )
1188  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1189                 ; obsolete line folding
1190                 ; see <xref target="field.parsing"/>
1191</artwork></figure>
1192<t>
1193   The field-name token labels the corresponding field-value as having the
1194   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1195   header field is defined in &header-date; as containing the origination
1196   timestamp for the message in which it appears.
1197</t>
1198<t>
1199   HTTP header fields are fully extensible: there is no limit on the
1200   introduction of new field names, each presumably defining new semantics,
1201   or on the number of header fields used in a given message.  Existing
1202   fields are defined in each part of this specification and in many other
1203   specifications outside the standards process.
1204   New header fields can be introduced without changing the protocol version
1205   if their defined semantics allow them to be safely ignored by recipients
1206   that do not recognize them.
1207</t>
1208<t>
1209   New HTTP header fields &SHOULD; be registered with IANA in the
1210   Message Header Field Registry, as described in &iana-header-registry;.
1211   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1212   field-name is listed in the <x:ref>Connection</x:ref> header field
1213   (<xref target="header.connection"/>) or the proxy is specifically
1214   configured to block or otherwise transform such fields.
1215   Unrecognized header fields &SHOULD; be ignored by other recipients.
1216</t>
1217<t>
1218   The order in which header fields with differing field names are
1219   received is not significant. However, it is "good practice" to send
1220   header fields that contain control data first, such as <x:ref>Host</x:ref>
1221   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1222   can decide when not to handle a message as early as possible.  A server
1223   &MUST; wait until the entire header section is received before interpreting
1224   a request message, since later header fields might include conditionals,
1225   authentication credentials, or deliberately misleading duplicate
1226   header fields that would impact request processing.
1227</t>
1228<t>
1229   Multiple header fields with the same field name &MUST-NOT; be
1230   sent in a message unless the entire field value for that
1231   header field is defined as a comma-separated list [i.e., #(values)].
1232   Multiple header fields with the same field name can be combined into
1233   one "field-name: field-value" pair, without changing the semantics of the
1234   message, by appending each subsequent field value to the combined
1235   field value in order, separated by a comma. The order in which
1236   header fields with the same field name are received is therefore
1237   significant to the interpretation of the combined field value;
1238   a proxy &MUST-NOT; change the order of these field values when
1239   forwarding a message.
1240</t>
1241<x:note>
1242  <t>
1243   &Note; The "Set-Cookie" header field as implemented in
1244   practice can occur multiple times, but does not use the list syntax, and
1245   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1246   for details.) Also note that the Set-Cookie2 header field specified in
1247   <xref target="RFC2965"/> does not share this problem.
1248  </t>
1249</x:note>
1250
1251<section title="Whitespace" anchor="whitespace">
1252<t anchor="rule.LWS">
1253   This specification uses three rules to denote the use of linear
1254   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1255   BWS ("bad" whitespace).
1256</t>
1257<t anchor="rule.OWS">
1258   The OWS rule is used where zero or more linear whitespace octets might
1259   appear. OWS &SHOULD; either not be produced or be produced as a single
1260   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1261   be replaced with a single SP or transformed to all SP octets (each
1262   octet other than SP replaced with SP) before interpreting the field value
1263   or forwarding the message downstream.
1264</t>
1265<t anchor="rule.RWS">
1266   RWS is used when at least one linear whitespace octet is required to
1267   separate field tokens. RWS &SHOULD; be produced as a single SP.
1268   Multiple RWS octets that occur within field-content &SHOULD; either
1269   be replaced with a single SP or transformed to all SP octets before
1270   interpreting the field value or forwarding the message downstream.
1271</t>
1272<t anchor="rule.BWS">
1273   BWS is used where the grammar allows optional whitespace, for historical
1274   reasons, but senders &SHOULD-NOT; produce it in messages;
1275   recipients &MUST; accept such bad optional whitespace and remove it before
1276   interpreting the field value or forwarding the message downstream.
1277</t>
1278<t anchor="rule.whitespace">
1279  <x:anchor-alias value="BWS"/>
1280  <x:anchor-alias value="OWS"/>
1281  <x:anchor-alias value="RWS"/>
1282</t>
1283<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"/>
1284  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1285                 ; "optional" whitespace
1286  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1287                 ; "required" whitespace
1288  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1289                 ; "bad" whitespace
1290</artwork></figure>
1291</section>
1292
1293<section title="Field Parsing" anchor="field.parsing">
1294<t>
1295   No whitespace is allowed between the header field-name and colon.
1296   In the past, differences in the handling of such whitespace have led to
1297   security vulnerabilities in request routing and response handling.
1298   Any received request message that contains whitespace between a header
1299   field-name and colon &MUST; be rejected with a response code of 400
1300   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1301   message before forwarding the message downstream.
1302</t>
1303<t>
1304   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1305   preferred. The field value does not include any leading or trailing white
1306   space: OWS occurring before the first non-whitespace octet of the
1307   field value or after the last non-whitespace octet of the field value
1308   is ignored and &SHOULD; be removed before further processing (as this does
1309   not change the meaning of the header field).
1310</t>
1311<t>
1312   Historically, HTTP header field values could be extended over multiple
1313   lines by preceding each extra line with at least one space or horizontal
1314   tab (obs-fold). This specification deprecates such line
1315   folding except within the message/http media type
1316   (<xref target="internet.media.type.message.http"/>).
1317   HTTP senders &MUST-NOT; produce messages that include line folding
1318   (i.e., that contain any field-value that matches the obs-fold rule) unless
1319   the message is intended for packaging within the message/http media type.
1320   HTTP recipients &SHOULD; accept line folding and replace any embedded
1321   obs-fold whitespace with either a single SP or a matching number of SP
1322   octets (to avoid buffer copying) prior to interpreting the field value or
1323   forwarding the message downstream.
1324</t>
1325<t>
1326   Historically, HTTP has allowed field content with text in the ISO-8859-1
1327   <xref target="ISO-8859-1"/> character encoding and supported other
1328   character sets only through use of <xref target="RFC2047"/> encoding.
1329   In practice, most HTTP header field values use only a subset of the
1330   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1331   header fields &SHOULD; limit their field values to US-ASCII octets.
1332   Recipients &SHOULD; treat other (obs-text) octets in field content as
1333   opaque data.
1334</t>
1335</section>
1336
1337<section title="Field Length" anchor="field.length">
1338<t>
1339   HTTP does not place a pre-defined limit on the length of header fields,
1340   either in isolation or as a set. A server &MUST; be prepared to receive
1341   request header fields of unbounded length and respond with a <x:ref>4xx
1342   (Client Error)</x:ref> status code if the received header field(s) would be
1343   longer than the server wishes to handle.
1344</t>
1345<t>
1346   A client that receives response header fields that are longer than it wishes
1347   to handle can only treat it as a server error.
1348</t>
1349<t>
1350   Various ad-hoc limitations on header field length are found in practice. It
1351   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1352   combined header fields have 4000 or more octets.
1353</t>
1354</section>
1355
1356<section title="Field value components" anchor="field.components">
1357<t anchor="rule.token.separators">
1358  <x:anchor-alias value="tchar"/>
1359  <x:anchor-alias value="token"/>
1360  <x:anchor-alias value="special"/>
1361  <x:anchor-alias value="word"/>
1362   Many HTTP header field values consist of words (token or quoted-string)
1363   separated by whitespace or special characters. These special characters
1364   &MUST; be in a quoted string to be used within a parameter value (as defined
1365   in <xref target="transfer.codings"/>).
1366</t>
1367<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>
1368  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1369
1370  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1371<!--
1372  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1373 -->
1374  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1375                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1376                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1377                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1378
1379  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1380                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1381                 / "]" / "?" / "=" / "{" / "}"
1382</artwork></figure>
1383<t anchor="rule.quoted-string">
1384  <x:anchor-alias value="quoted-string"/>
1385  <x:anchor-alias value="qdtext"/>
1386  <x:anchor-alias value="obs-text"/>
1387   A string of text is parsed as a single word if it is quoted using
1388   double-quote marks.
1389</t>
1390<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"/>
1391  <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>
1392  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1393  <x:ref>obs-text</x:ref>       = %x80-FF
1394</artwork></figure>
1395<t anchor="rule.quoted-pair">
1396  <x:anchor-alias value="quoted-pair"/>
1397   The backslash octet ("\") can be used as a single-octet
1398   quoting mechanism within quoted-string constructs:
1399</t>
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1401  <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> )
1402</artwork></figure>
1403<t>
1404   Recipients that process the value of the quoted-string &MUST; handle a
1405   quoted-pair as if it were replaced by the octet following the backslash.
1406</t>
1407<t>
1408   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1409   escaping (i.e., other than DQUOTE and the backslash octet).
1410</t>
1411<t anchor="rule.comment">
1412  <x:anchor-alias value="comment"/>
1413  <x:anchor-alias value="ctext"/>
1414   Comments can be included in some HTTP header fields by surrounding
1415   the comment text with parentheses. Comments are only allowed in
1416   fields containing "comment" as part of their field value definition.
1417</t>
1418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1419  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1420  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1421</artwork></figure>
1422<t anchor="rule.quoted-cpair">
1423  <x:anchor-alias value="quoted-cpair"/>
1424   The backslash octet ("\") can be used as a single-octet
1425   quoting mechanism within comment constructs:
1426</t>
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1428  <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> )
1429</artwork></figure>
1430<t>
1431   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1432   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1433</t>
1434</section>
1435
1436</section>
1437
1438<section title="Message Body" anchor="message.body">
1439  <x:anchor-alias value="message-body"/>
1440<t>
1441   The message body (if any) of an HTTP message is used to carry the
1442   payload body of that request or response.  The message body is
1443   identical to the payload body unless a transfer coding has been
1444   applied, as described in <xref target="header.transfer-encoding"/>.
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1447  <x:ref>message-body</x:ref> = *OCTET
1448</artwork></figure>
1449<t>
1450   The rules for when a message body is allowed in a message differ for
1451   requests and responses.
1452</t>
1453<t>
1454   The presence of a message body in a request is signaled by a
1455   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1456   field. Request message framing is independent of method semantics,
1457   even if the method does not define any use for a message body.
1458</t>
1459<t>
1460   The presence of a message body in a response depends on both
1461   the request method to which it is responding and the response
1462   status code (<xref target="status.line"/>).
1463   Responses to the HEAD request method never include a message body
1464   because the associated response header fields (e.g.,
1465   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1466   indicate what their values would have been if the request method had been
1467   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1468   mode instead of having a message body.
1469   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1470   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1471   All other responses do include a message body, although the body
1472   &MAY; be of zero length.
1473</t>
1474
1475<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1476  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1477  <x:anchor-alias value="Transfer-Encoding"/>
1478<t>
1479   When one or more transfer codings are applied to a payload body in order
1480   to form the message body, a Transfer-Encoding header field &MUST; be sent
1481   in the message and &MUST; contain the list of corresponding
1482   transfer-coding names in the same order that they were applied.
1483   Transfer codings are defined in <xref target="transfer.codings"/>.
1484</t>
1485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1486  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1487</artwork></figure>
1488<t>
1489   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1490   MIME, which was designed to enable safe transport of binary data over a
1491   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1492   However, safe transport has a different focus for an 8bit-clean transfer
1493   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1494   accurately delimit a dynamically generated payload and to distinguish
1495   payload encodings that are only applied for transport efficiency or
1496   security from those that are characteristics of the target resource.
1497</t>
1498<t>
1499   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1500   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1501   crucial role in delimiting messages when the payload body size is not
1502   known in advance.
1503   When the "chunked" transfer-coding is used, it &MUST; be the last
1504   transfer-coding applied to form the message body and &MUST-NOT;
1505   be applied more than once in a message body.
1506   If any transfer-coding is applied to a request payload body,
1507   the final transfer-coding applied &MUST; be "chunked".
1508   If any transfer-coding is applied to a response payload body, then either
1509   the final transfer-coding applied &MUST; be "chunked" or
1510   the message &MUST; be terminated by closing the connection.
1511</t>
1512<figure><preamble>
1513   For example,
1514</preamble><artwork type="example">
1515  Transfer-Encoding: gzip, chunked
1516</artwork><postamble>
1517   indicates that the payload body has been compressed using the gzip
1518   coding and then chunked using the chunked coding while forming the
1519   message body.
1520</postamble></figure>
1521<t>
1522   If more than one Transfer-Encoding header field is present in a message,
1523   the multiple field-values &MUST; be combined into one field-value,
1524   according to the algorithm defined in <xref target="header.fields"/>,
1525   before determining the message body length.
1526</t>
1527<t>
1528   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1529   Transfer-Encoding is a property of the message, not of the payload, and thus
1530   &MAY; be added or removed by any implementation along the request/response
1531   chain. Additional information about the encoding parameters &MAY; be
1532   provided by other header fields not defined by this specification.
1533</t>
1534<t>
1535   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1536   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1537   neither of which includes a message body,
1538   to indicate that the origin server would have applied a transfer coding
1539   to the message body if the request had been an unconditional GET.
1540   This indication is not required, however, because any recipient on
1541   the response chain (including the origin server) can remove transfer
1542   codings when they are not needed.
1543</t>
1544<t>
1545   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1546   implementations advertising only HTTP/1.0 support will not understand
1547   how to process a transfer-encoded payload.
1548   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1549   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1550   might be in the form of specific user configuration or by remembering the
1551   version of a prior received response.
1552   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1553   the corresponding request indicates HTTP/1.1 (or later).
1554</t>
1555<t>
1556   A server that receives a request message with a transfer-coding it does
1557   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1558   close the connection.
1559</t>
1560</section>
1561
1562<section title="Content-Length" anchor="header.content-length">
1563  <iref primary="true" item="Content-Length header field" 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, a server &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  <x:anchor-alias value="Trailer"/>
1910<t>
1911   A trailer allows the sender to include additional fields at the end of a
1912   chunked message in order to supply metadata that might be dynamically
1913   generated while the message body is sent, such as a message integrity
1914   check, digital signature, or post-processing status.
1915   The trailer &MUST-NOT; contain fields that need to be known before a
1916   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1917   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1918</t>
1919<t>
1920   When a message includes a message body encoded with the chunked
1921   transfer-coding and the sender desires to send metadata in the form of
1922   trailer fields at the end of the message, the sender &SHOULD; send a
1923   <x:ref>Trailer</x:ref> header field before the message body to indicate
1924   which fields will be present in the trailers. This allows the recipient
1925   to prepare for receipt of that metadata before it starts processing the body,
1926   which is useful if the message is being streamed and the recipient wishes
1927   to confirm an integrity check on the fly.
1928</t>
1929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1930  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1931</artwork></figure>
1932<t>
1933   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1934   chunked message body &SHOULD; send an empty trailer.
1935</t>
1936<t>
1937   A server &MUST; send an empty trailer with the chunked transfer-coding
1938   unless at least one of the following is true:
1939  <list style="numbers">
1940    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1941    "trailers" is acceptable in the transfer-coding of the response, as
1942    described in <xref target="header.te"/>; or,</t>
1943     
1944    <t>the trailer fields consist entirely of optional metadata and the
1945    recipient could use the message (in a manner acceptable to the server where
1946    the field originated) without receiving that metadata. In other words,
1947    the server that generated the header field is willing to accept the
1948    possibility that the trailer fields might be silently discarded along
1949    the path to the client.</t>
1950  </list>
1951</t>
1952<t>
1953   The above requirement prevents the need for an infinite buffer when a
1954   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1955   an HTTP/1.0 recipient.
1956</t>
1957</section>
1958
1959<section title="Decoding chunked" anchor="decoding.chunked">
1960<t>
1961   A process for decoding the "chunked" transfer-coding
1962   can be represented in pseudo-code as:
1963</t>
1964<figure><artwork type="code">
1965  length := 0
1966  read chunk-size, chunk-ext (if any) and CRLF
1967  while (chunk-size &gt; 0) {
1968     read chunk-data and CRLF
1969     append chunk-data to decoded-body
1970     length := length + chunk-size
1971     read chunk-size and CRLF
1972  }
1973  read header-field
1974  while (header-field not empty) {
1975     append header-field to existing header fields
1976     read header-field
1977  }
1978  Content-Length := length
1979  Remove "chunked" from Transfer-Encoding
1980  Remove Trailer from existing header fields
1981</artwork></figure>
1982<t>
1983   All recipients &MUST; be able to receive and decode the
1984   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1985   they do not understand.
1986</t>
1987</section>
1988</section>
1989
1990<section title="Compression Codings" anchor="compression.codings">
1991<t>
1992   The codings defined below can be used to compress the payload of a
1993   message.
1994</t>
1995
1996<section title="Compress Coding" anchor="compress.coding">
1997<iref item="compress (Coding Format)"/>
1998<iref item="Coding Format" subitem="compress"/>
1999<t>
2000   The "compress" format is produced by the common UNIX file compression
2001   program "compress". This format is an adaptive Lempel-Ziv-Welch
2002   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2003   equivalent to "compress".
2004</t>
2005</section>
2006
2007<section title="Deflate Coding" anchor="deflate.coding">
2008<iref item="deflate (Coding Format)"/>
2009<iref item="Coding Format" subitem="deflate"/>
2010<t>
2011   The "deflate" format is defined as the "deflate" compression mechanism
2012   (described in <xref target="RFC1951"/>) used inside the "zlib"
2013   data format (<xref target="RFC1950"/>).
2014</t>
2015<x:note>
2016  <t>
2017    &Note; Some incorrect implementations send the "deflate"
2018    compressed data without the zlib wrapper.
2019   </t>
2020</x:note>
2021</section>
2022
2023<section title="Gzip Coding" anchor="gzip.coding">
2024<iref item="gzip (Coding Format)"/>
2025<iref item="Coding Format" subitem="gzip"/>
2026<t>
2027   The "gzip" format is produced by the file compression program
2028   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2029   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2030   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2031</t>
2032</section>
2033
2034</section>
2035
2036<section title="TE" anchor="header.te">
2037  <iref primary="true" item="TE header field" x:for-anchor=""/>
2038  <x:anchor-alias value="TE"/>
2039  <x:anchor-alias value="t-codings"/>
2040  <x:anchor-alias value="t-ranking"/>
2041  <x:anchor-alias value="rank"/>
2042<t>
2043   The "TE" header field in a request indicates what transfer-codings,
2044   besides "chunked", the client is willing to accept in response, and
2045   whether or not the client is willing to accept trailer fields in a
2046   chunked transfer-coding.
2047</t>
2048<t>
2049   The TE field-value consists of a comma-separated list of transfer-coding
2050   names, each allowing for optional parameters (as described in
2051   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2052   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2053   chunked is always acceptable for HTTP/1.1 recipients.
2054</t>
2055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/>
2056  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2057  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2058  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2059  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2060             / ( "1" [ "." 0*3("0") ] )
2061</artwork></figure>
2062<t>
2063   Three examples of TE use are below.
2064</t>
2065<figure><artwork type="example">
2066  TE: deflate
2067  TE:
2068  TE: trailers, deflate;q=0.5
2069</artwork></figure>
2070<t>
2071   The presence of the keyword "trailers" indicates that the client is
2072   willing to accept trailer fields in a chunked transfer-coding,
2073   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2074   any downstream clients. For chained requests, this implies that either:
2075   (a) all downstream clients are willing to accept trailer fields in the
2076   forwarded response; or,
2077   (b) the client will attempt to buffer the response on behalf of downstream
2078   recipients.
2079   Note that HTTP/1.1 does not define any means to limit the size of a
2080   chunked response such that a client can be assured of buffering the
2081   entire response.
2082</t>
2083<t>
2084   When multiple transfer-codings are acceptable, the client &MAY; rank the
2085   codings by preference using a case-insensitive "q" parameter (similar to
2086   the qvalues used in content negotiation fields, &qvalue;). The rank value
2087   is a real number in the range 0 through 1, where 0.001 is the least
2088   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2089</t>
2090<t>
2091   If the TE field-value is empty or if no TE field is present, the only
2092   acceptable transfer-coding is "chunked". A message with no transfer-coding
2093   is always acceptable.
2094</t>
2095<t>
2096   Since the TE header field only applies to the immediate connection,
2097   a sender of TE &MUST; also send a "TE" connection option within the
2098   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2099   in order to prevent the TE field from being forwarded by intermediaries
2100   that do not support its semantics.
2101</t>
2102</section>
2103</section>
2104
2105<section title="Message Routing" anchor="message.routing">
2106<t>
2107   HTTP request message routing is determined by each client based on the
2108   target resource, the client's proxy configuration, and
2109   establishment or reuse of an inbound connection.  The corresponding
2110   response routing follows the same connection chain back to the client.
2111</t>
2112
2113<section title="Identifying a Target Resource" anchor="target-resource">
2114  <iref primary="true" item="target resource"/>
2115  <iref primary="true" item="target URI"/>
2116  <x:anchor-alias value="target resource"/>
2117  <x:anchor-alias value="target URI"/>
2118<t>
2119   HTTP is used in a wide variety of applications, ranging from
2120   general-purpose computers to home appliances.  In some cases,
2121   communication options are hard-coded in a client's configuration.
2122   However, most HTTP clients rely on the same resource identification
2123   mechanism and configuration techniques as general-purpose Web browsers.
2124</t>
2125<t>
2126   HTTP communication is initiated by a user agent for some purpose.
2127   The purpose is a combination of request semantics, which are defined in
2128   <xref target="Part2"/>, and a target resource upon which to apply those
2129   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2130   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2131   would resolve to its absolute form in order to obtain the
2132   "<x:dfn>target URI</x:dfn>".  The target URI
2133   excludes the reference's fragment identifier component, if any,
2134   since fragment identifiers are reserved for client-side processing
2135   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2136</t>
2137</section>
2138
2139<section title="Connecting Inbound" anchor="connecting.inbound">
2140<t>
2141   Once the target URI is determined, a client needs to decide whether
2142   a network request is necessary to accomplish the desired semantics and,
2143   if so, where that request is to be directed.
2144</t>
2145<t>
2146   If the client has a response cache and the request semantics can be
2147   satisfied by a cache (<xref target="Part6"/>), then the request is
2148   usually directed to the cache first.
2149</t>
2150<t>
2151   If the request is not satisfied by a cache, then a typical client will
2152   check its configuration to determine whether a proxy is to be used to
2153   satisfy the request.  Proxy configuration is implementation-dependent,
2154   but is often based on URI prefix matching, selective authority matching,
2155   or both, and the proxy itself is usually identified by an "http" or
2156   "https" URI.  If a proxy is applicable, the client connects inbound by
2157   establishing (or reusing) a connection to that proxy.
2158</t>
2159<t>
2160   If no proxy is applicable, a typical client will invoke a handler routine,
2161   usually specific to the target URI's scheme, to connect directly
2162   to an authority for the target resource.  How that is accomplished is
2163   dependent on the target URI scheme and defined by its associated
2164   specification, similar to how this specification defines origin server
2165   access for resolution of the "http" (<xref target="http.uri"/>) and
2166   "https" (<xref target="https.uri"/>) schemes.
2167</t>
2168<t>
2169   HTTP requirements regarding connection management are defined in
2170   <xref target="connection.management"/>.
2171</t>
2172</section>
2173
2174<section title="Request Target" anchor="request-target">
2175<t>
2176   Once an inbound connection is obtained,
2177   the client sends an HTTP request message (<xref target="http.message"/>)
2178   with a request-target derived from the target URI.
2179   There are four distinct formats for the request-target, depending on both
2180   the method being requested and whether the request is to a proxy.
2181</t>   
2182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2183  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2184                 / <x:ref>absolute-form</x:ref>
2185                 / <x:ref>authority-form</x:ref>
2186                 / <x:ref>asterisk-form</x:ref>
2187
2188  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2189  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2190  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2191  <x:ref>asterisk-form</x:ref>  = "*"
2192</artwork></figure>
2193<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2194   The most common form of request-target is the origin-form.
2195   When making a request directly to an origin server, other than a CONNECT
2196   or server-wide OPTIONS request (as detailed below),
2197   a client &MUST; send only the absolute path and query components of
2198   the target URI as the request-target.
2199   If the target URI's path component is empty, then the client &MUST; send
2200   "/" as the path within the origin-form of request-target.
2201   A <x:ref>Host</x:ref> header field is also sent, as defined in
2202   <xref target="header.host"/>, containing the target URI's
2203   authority component (excluding any userinfo).
2204</t>
2205<t>
2206   For example, a client wishing to retrieve a representation of the resource
2207   identified as
2208</t>
2209<figure><artwork x:indent-with="  " type="example">
2210http://www.example.org/where?q=now
2211</artwork></figure>
2212<t>
2213   directly from the origin server would open (or reuse) a TCP connection
2214   to port 80 of the host "www.example.org" and send the lines:
2215</t>
2216<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2217GET /where?q=now HTTP/1.1
2218Host: www.example.org
2219</artwork></figure>
2220<t>
2221   followed by the remainder of the request message.
2222</t>
2223<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2224   When making a request to a proxy, other than a CONNECT or server-wide
2225   OPTIONS request (as detailed below), a client &MUST; send the target URI
2226   in absolute-form as the request-target.
2227   The proxy is requested to either service that request from a valid cache,
2228   if possible, or make the same request on the client's behalf to either
2229   the next inbound proxy server or directly to the origin server indicated
2230   by the request-target.  Requirements on such "forwarding" of messages are
2231   defined in <xref target="message.forwarding"/>.
2232</t>
2233<t>
2234   An example absolute-form of request-line would be:
2235</t>
2236<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2237GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2238</artwork></figure>
2239<t>
2240   To allow for transition to the absolute-form for all requests in some
2241   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2242   in requests, even though HTTP/1.1 clients will only send them in requests
2243   to proxies.
2244</t>
2245<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2246   The authority-form of request-target is only used for CONNECT requests
2247   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2248   one or more proxies, a client &MUST; send only the target URI's
2249   authority component (excluding any userinfo) as the request-target.
2250   For example,
2251</t>
2252<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2253CONNECT www.example.com:80 HTTP/1.1
2254</artwork></figure>
2255<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2256   The asterisk-form of request-target is only used for a server-wide
2257   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2258   for the server as a whole, as opposed to a specific named resource of
2259   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2260   For example,
2261</t>
2262<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2263OPTIONS * HTTP/1.1
2264</artwork></figure>
2265<t>
2266   If a proxy receives an OPTIONS request with an absolute-form of
2267   request-target in which the URI has an empty path and no query component,
2268   then the last proxy on the request chain &MUST; send a request-target
2269   of "*" when it forwards the request to the indicated origin server.
2270</t>
2271<figure><preamble>   
2272   For example, the request
2273</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2274OPTIONS http://www.example.org:8001 HTTP/1.1
2275</artwork></figure>
2276<figure><preamble>   
2277  would be forwarded by the final proxy as
2278</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2279OPTIONS * HTTP/1.1
2280Host: www.example.org:8001
2281</artwork>
2282<postamble>
2283   after connecting to port 8001 of host "www.example.org".
2284</postamble>
2285</figure>
2286</section>
2287
2288<section title="Host" anchor="header.host">
2289  <iref primary="true" item="Host header field" x:for-anchor=""/>
2290  <x:anchor-alias value="Host"/>
2291<t>
2292   The "Host" header field in a request provides the host and port
2293   information from the target URI, enabling the origin
2294   server to distinguish among resources while servicing requests
2295   for multiple host names on a single IP address.  Since the Host
2296   field-value is critical information for handling a request, it
2297   &SHOULD; be sent as the first header field following the request-line.
2298</t>
2299<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2300  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2301</artwork></figure>
2302<t>
2303   A client &MUST; send a Host header field in all HTTP/1.1 request
2304   messages.  If the target URI includes an authority component, then
2305   the Host field-value &MUST; be identical to that authority component
2306   after excluding any userinfo (<xref target="http.uri"/>).
2307   If the authority component is missing or undefined for the target URI,
2308   then the Host header field &MUST; be sent with an empty field-value.
2309</t>
2310<t>
2311   For example, a GET request to the origin server for
2312   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2313</t>
2314<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2315GET /pub/WWW/ HTTP/1.1
2316Host: www.example.org
2317</artwork></figure>
2318<t>
2319   The Host header field &MUST; be sent in an HTTP/1.1 request even
2320   if the request-target is in the absolute-form, since this
2321   allows the Host information to be forwarded through ancient HTTP/1.0
2322   proxies that might not have implemented Host.
2323</t>
2324<t>
2325   When a proxy receives a request with an absolute-form of
2326   request-target, the proxy &MUST; ignore the received
2327   Host header field (if any) and instead replace it with the host
2328   information of the request-target.  If the proxy forwards the request,
2329   it &MUST; generate a new Host field-value based on the received
2330   request-target rather than forward the received Host field-value.
2331</t>
2332<t>
2333   Since the Host header field acts as an application-level routing
2334   mechanism, it is a frequent target for malware seeking to poison
2335   a shared cache or redirect a request to an unintended server.
2336   An interception proxy is particularly vulnerable if it relies on
2337   the Host field-value for redirecting requests to internal
2338   servers, or for use as a cache key in a shared cache, without
2339   first verifying that the intercepted connection is targeting a
2340   valid IP address for that host.
2341</t>
2342<t>
2343   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2344   to any HTTP/1.1 request message that lacks a Host header field and
2345   to any request message that contains more than one Host header field
2346   or a Host header field with an invalid field-value.
2347</t>
2348</section>
2349
2350<section title="Effective Request URI" anchor="effective.request.uri">
2351  <iref primary="true" item="effective request URI"/>
2352<t>
2353   A server that receives an HTTP request message &MUST; reconstruct
2354   the user agent's original target URI, based on the pieces of information
2355   learned from the request-target, <x:ref>Host</x:ref> header field, and
2356   connection context, in order to identify the intended target resource and
2357   properly service the request. The URI derived from this reconstruction
2358   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2359</t>
2360<t>
2361   For a user agent, the effective request URI is the target URI.
2362</t>
2363<t>
2364   If the request-target is in absolute-form, then the effective request URI
2365   is the same as the request-target.  Otherwise, the effective request URI
2366   is constructed as follows.
2367</t>
2368<t>
2369   If the request is received over an SSL/TLS-secured TCP connection,
2370   then the effective request URI's scheme is "https"; otherwise, the
2371   scheme is "http".
2372</t>
2373<t>
2374   If the request-target is in authority-form, then the effective
2375   request URI's authority component is the same as the request-target.
2376   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2377   non-empty field-value, then the authority component is the same as the
2378   Host field-value. Otherwise, the authority component is the concatenation of
2379   the default host name configured for the server, a colon (":"), and the
2380   connection's incoming TCP port number in decimal form.
2381</t>
2382<t>
2383   If the request-target is in authority-form or asterisk-form, then the
2384   effective request URI's combined path and query component is empty.
2385   Otherwise, the combined path and query component is the same as the
2386   request-target.
2387</t>
2388<t>
2389   The components of the effective request URI, once determined as above,
2390   can be combined into absolute-URI form by concatenating the scheme,
2391   "://", authority, and combined path and query component.
2392</t>
2393<figure>
2394<preamble>
2395   Example 1: the following message received over an insecure TCP connection
2396</preamble> 
2397<artwork type="example" x:indent-with="  ">
2398GET /pub/WWW/TheProject.html HTTP/1.1
2399Host: www.example.org:8080
2400</artwork>
2401</figure>
2402<figure>
2403<preamble>
2404  has an effective request URI of
2405</preamble>
2406<artwork type="example" x:indent-with="  ">
2407http://www.example.org:8080/pub/WWW/TheProject.html
2408</artwork>
2409</figure>
2410<figure>
2411<preamble>
2412   Example 2: the following message received over an SSL/TLS-secured TCP
2413   connection
2414</preamble> 
2415<artwork type="example" x:indent-with="  ">
2416OPTIONS * HTTP/1.1
2417Host: www.example.org
2418</artwork>
2419</figure>
2420<figure>
2421<preamble>
2422  has an effective request URI of
2423</preamble>
2424<artwork type="example" x:indent-with="  ">
2425https://www.example.org
2426</artwork>
2427</figure>
2428<t>
2429   An origin server that does not allow resources to differ by requested
2430   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2431   with a configured server name when constructing the effective request URI.
2432</t>
2433<t>
2434   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2435   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2436   something unique to a particular host) in order to guess the
2437   effective request URI's authority component.
2438</t>
2439</section>
2440
2441<section title="Message Forwarding" anchor="message.forwarding">
2442<t>
2443   As described in <xref target="intermediaries"/>, intermediaries can serve
2444   a variety of roles in the processing of HTTP requests and responses.
2445   Some intermediaries are used to improve performance or availability.
2446   Others are used for access control or to filter content.
2447   Since an HTTP stream has characteristics similar to a pipe-and-filter
2448   architecture, there are no inherent limits to the extent an intermediary
2449   can enhance (or interfere) with either direction of the stream.
2450</t>
2451<t>
2452   Intermediaries that forward a message &MUST; implement the
2453   <x:ref>Connection</x:ref> header field, as specified in
2454   <xref target="header.connection"/>, to exclude fields that are only
2455   intended for the incoming connection.
2456</t>
2457<t>
2458   In order to avoid request loops, a proxy that forwards requests to other
2459   proxies &MUST; be able to recognize and exclude all of its own server
2460   names, including any aliases, local variations, or literal IP addresses.
2461</t>
2462</section>
2463
2464<section title="Via" anchor="header.via">
2465  <iref primary="true" item="Via header field" x:for-anchor=""/>
2466  <x:anchor-alias value="pseudonym"/>
2467  <x:anchor-alias value="received-by"/>
2468  <x:anchor-alias value="received-protocol"/>
2469  <x:anchor-alias value="Via"/>
2470<t>
2471   The "Via" header field &MUST; be sent by a proxy or gateway
2472   in forwarded messages to
2473   indicate the intermediate protocols and recipients between the user
2474   agent and the server on requests, and between the origin server and
2475   the client on responses. It is analogous to the "Received" field
2476   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2477   Via is used in HTTP for tracking message forwards,
2478   avoiding request loops, and identifying the protocol capabilities of
2479   all senders along the request/response chain.
2480</t>
2481<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"/>
2482  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2483                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2484  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2485  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2486  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2487</artwork></figure>
2488<t>
2489   The received-protocol indicates the protocol version of the message
2490   received by the server or client along each segment of the
2491   request/response chain. The received-protocol version is appended to
2492   the Via field value when the message is forwarded so that information
2493   about the protocol capabilities of upstream applications remains
2494   visible to all recipients.
2495</t>
2496<t>
2497   The protocol-name is excluded if and only if it would be "HTTP". The
2498   received-by field is normally the host and optional port number of a
2499   recipient server or client that subsequently forwarded the message.
2500   However, if the real host is considered to be sensitive information,
2501   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2502   be assumed to be the default port of the received-protocol.
2503</t>
2504<t>
2505   Multiple Via field values represent each proxy or gateway that has
2506   forwarded the message. Each recipient &MUST; append its information
2507   such that the end result is ordered according to the sequence of
2508   forwarding applications.
2509</t>
2510<t>
2511   Comments &MAY; be used in the Via header field to identify the software
2512   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2513   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2514   are optional and &MAY; be removed by any recipient prior to forwarding the
2515   message.
2516</t>
2517<t>
2518   For example, a request message could be sent from an HTTP/1.0 user
2519   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2520   forward the request to a public proxy at p.example.net, which completes
2521   the request by forwarding it to the origin server at www.example.com.
2522   The request received by www.example.com would then have the following
2523   Via header field:
2524</t>
2525<figure><artwork type="example">
2526  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2527</artwork></figure>
2528<t>
2529   A proxy or gateway used as a portal through a network firewall
2530   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2531   region unless it is explicitly enabled to do so. If not enabled, the
2532   received-by host of any host behind the firewall &SHOULD; be replaced
2533   by an appropriate pseudonym for that host.
2534</t>
2535<t>
2536   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2537   field entries into a single such entry if the entries have identical
2538   received-protocol values. For example,
2539</t>
2540<figure><artwork type="example">
2541  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2542</artwork></figure>
2543<t>
2544  could be collapsed to
2545</t>
2546<figure><artwork type="example">
2547  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2548</artwork></figure>
2549<t>
2550   Senders &SHOULD-NOT; combine multiple entries unless they are all
2551   under the same organizational control and the hosts have already been
2552   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2553   have different received-protocol values.
2554</t>
2555</section>
2556
2557<section title="Message Transforming" anchor="message.transforming">
2558<t>
2559   If a proxy receives a request-target with a host name that is not a
2560   fully qualified domain name, it &MAY; add its own domain to the host name
2561   it received when forwarding the request.  A proxy &MUST-NOT; change the
2562   host name if it is a fully qualified domain name.
2563</t>
2564<t>
2565   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2566   parts of the received request-target when forwarding it to the next inbound
2567   server, except as noted above to replace an empty path with "/" or "*".
2568</t>
2569<t>
2570   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2571   though it &MAY; change the message body through application or removal
2572   of a transfer-coding (<xref target="transfer.codings"/>).
2573</t>
2574<t>
2575   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2576   information about the end points of the communication chain, the resource
2577   state, or the selected representation.
2578</t>
2579<t>
2580   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2581   request or response, and it &MUST-NOT; add any of these fields if not
2582   already present:
2583  <list style="symbols">
2584    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2585    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2586    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2587    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2588    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2589    <t><x:ref>Server</x:ref> (&header-server;)</t>
2590  </list>
2591</t>
2592<t>
2593   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2594   header field (&header-expires;) if already present in a response, but
2595   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2596   identical to that of the <x:ref>Date</x:ref> header field.
2597</t>
2598<t>
2599   A proxy &MUST-NOT; modify or add any of the following fields in a
2600   message that contains the no-transform cache-control directive:
2601  <list style="symbols">
2602    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2603    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2604    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2605  </list>
2606</t>
2607<t>
2608   A transforming proxy &MAY; modify or add these fields to a message
2609   that does not include no-transform, but if it does so, it &MUST; add a
2610   Warning 214 (Transformation applied) if one does not already appear
2611   in the message (see &header-warning;).
2612</t>
2613<x:note>
2614  <t>
2615    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2616    cause authentication failures if stronger authentication
2617    mechanisms are introduced in later versions of HTTP. Such
2618    authentication mechanisms &MAY; rely on the values of header fields
2619    not listed here.
2620  </t>
2621</x:note>
2622</section>
2623
2624<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2625<t>
2626   HTTP does not include a request identifier for associating a given
2627   request message with its corresponding one or more response messages.
2628   Hence, it relies on the order of response arrival to correspond exactly
2629   to the order in which requests are made on the same connection.
2630   More than one response message per request only occurs when one or more
2631   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2632   to the same request.
2633</t>
2634<t>
2635   A client that uses persistent connections and sends more than one request
2636   per connection &MUST; maintain a list of outstanding requests in the
2637   order sent on that connection and &MUST; associate each received response
2638   message to the highest ordered request that has not yet received a final
2639   (non-<x:ref>1xx</x:ref>) response.
2640</t>
2641</section>
2642</section>
2643
2644<section title="Connection Management" anchor="connection.management">
2645<t>
2646   HTTP messaging is independent of the underlying transport or
2647   session-layer connection protocol(s).  HTTP only presumes a reliable
2648   transport with in-order delivery of requests and the corresponding
2649   in-order delivery of responses.  The mapping of HTTP request and
2650   response structures onto the data units of an underlying transport
2651   protocol is outside the scope of this specification.
2652</t>
2653<t>
2654   As described in <xref target="connecting.inbound"/>, the specific
2655   connection protocols to be used for an HTTP interaction are determined by
2656   client configuration and the <x:ref>target URI</x:ref>.
2657   For example, the "http" URI scheme
2658   (<xref target="http.uri"/>) indicates a default connection of TCP
2659   over IP, with a default TCP port of 80, but the client might be
2660   configured to use a proxy via some other connection, port, or protocol.
2661</t>
2662<t>
2663   HTTP implementations are expected to engage in connection management,
2664   which includes maintaining the state of current connections,
2665   establishing a new connection or reusing an existing connection,
2666   processing messages received on a connection, detecting connection
2667   failures, and closing each connection.
2668   Most clients maintain multiple connections in parallel, including
2669   more than one connection per server endpoint.
2670   Most servers are designed to maintain thousands of concurrent connections,
2671   while controlling request queues to enable fair use and detect
2672   denial of service attacks.
2673</t>
2674
2675<section title="Connection" anchor="header.connection">
2676  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2677  <iref primary="true" item="close" x:for-anchor=""/>
2678  <x:anchor-alias value="Connection"/>
2679  <x:anchor-alias value="connection-option"/>
2680  <x:anchor-alias value="close"/>
2681<t>
2682   The "Connection" header field allows the sender to indicate desired
2683   control options for the current connection.  In order to avoid confusing
2684   downstream recipients, a proxy or gateway &MUST; remove or replace any
2685   received connection options before forwarding the message.
2686</t>
2687<t>
2688   When a header field is used to supply control information for or about
2689   the current connection, the sender &SHOULD; list the corresponding
2690   field-name within the "Connection" header field.
2691   A proxy or gateway &MUST; parse a received Connection
2692   header field before a message is forwarded and, for each
2693   connection-option in this field, remove any header field(s) from
2694   the message with the same name as the connection-option, and then
2695   remove the Connection header field itself (or replace it with the
2696   intermediary's own connection options for the forwarded message).
2697</t>
2698<t>
2699   Hence, the Connection header field provides a declarative way of
2700   distinguishing header fields that are only intended for the
2701   immediate recipient ("hop-by-hop") from those fields that are
2702   intended for all recipients on the chain ("end-to-end"), enabling the
2703   message to be self-descriptive and allowing future connection-specific
2704   extensions to be deployed without fear that they will be blindly
2705   forwarded by older intermediaries.
2706</t>
2707<t>
2708   The Connection header field's value has the following grammar:
2709</t>
2710<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2711  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2712  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2713</artwork></figure>
2714<t>
2715   Connection options are case-insensitive.
2716</t>
2717<t>
2718   A sender &MUST-NOT; include field-names in the Connection header
2719   field-value for fields that are defined as expressing constraints
2720   for all recipients in the request or response chain, such as the
2721   Cache-Control header field (&header-cache-control;).
2722</t>
2723<t>
2724   The connection options do not have to correspond to a header field
2725   present in the message, since a connection-specific header field
2726   might not be needed if there are no parameters associated with that
2727   connection option.  Recipients that trigger certain connection
2728   behavior based on the presence of connection options &MUST; do so
2729   based on the presence of the connection-option rather than only the
2730   presence of the optional header field.  In other words, if the
2731   connection option is received as a header field but not indicated
2732   within the Connection field-value, then the recipient &MUST; ignore
2733   the connection-specific header field because it has likely been
2734   forwarded by an intermediary that is only partially conformant.
2735</t>
2736<t>
2737   When defining new connection options, specifications ought to
2738   carefully consider existing deployed header fields and ensure
2739   that the new connection option does not share the same name as
2740   an unrelated header field that might already be deployed.
2741   Defining a new connection option essentially reserves that potential
2742   field-name for carrying additional information related to the
2743   connection option, since it would be unwise for senders to use
2744   that field-name for anything else.
2745</t>
2746<t>
2747   The "<x:dfn>close</x:dfn>" connection option is defined for a
2748   sender to signal that this connection will be closed after completion of
2749   the response. For example,
2750</t>
2751<figure><artwork type="example">
2752  Connection: close
2753</artwork></figure>
2754<t>
2755   in either the request or the response header fields indicates that
2756   the connection &SHOULD; be closed after the current request/response
2757   is complete (<xref target="persistent.tear-down"/>).
2758</t>
2759<t>
2760   A client that does not support persistent connections &MUST;
2761   send the "close" connection option in every request message.
2762</t>
2763<t>
2764   A server that does not support persistent connections &MUST;
2765   send the "close" connection option in every response message that
2766   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2767</t>
2768</section>
2769
2770<section title="Persistent Connections" anchor="persistent.connections">
2771  <x:anchor-alias value="persistent connections"/>
2772<t>
2773   HTTP was originally designed to use a separate connection for each
2774   request/response pair. As the Web evolved and embedded requests became
2775   common for inline images, the connection establishment overhead was
2776   a significant drain on performance and a concern for Internet congestion.
2777   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2778   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2779   to improve performance for some requests. However, these extensions were
2780   insufficient for dynamically generated responses and difficult to use
2781   with intermediaries.
2782</t>
2783<t>
2784   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2785   which allow multiple requests and responses to be carried over a single
2786   connection. The "<x:ref>close</x:ref>" connection-option is used to
2787   signal that a connection will close after the current request/response.
2788   Persistent connections have a number of advantages:
2789  <list style="symbols">
2790      <t>
2791        By opening and closing fewer connections, CPU time is saved
2792        in routers and hosts (clients, servers, proxies, gateways,
2793        tunnels, or caches), and memory used for protocol control
2794        blocks can be saved in hosts.
2795      </t>
2796      <t>
2797        Most requests and responses can be pipelined on a connection.
2798        Pipelining allows a client to make multiple requests without
2799        waiting for each response, allowing a single connection to
2800        be used much more efficiently and with less overall latency.
2801      </t>
2802      <t>
2803        For TCP connections, network congestion is reduced by eliminating the
2804        packets associated with the three way handshake and graceful close
2805        procedures, and by allowing sufficient time to determine the
2806        congestion state of the network.
2807      </t>
2808      <t>
2809        Latency on subsequent requests is reduced since there is no time
2810        spent in the connection opening handshake.
2811      </t>
2812      <t>
2813        HTTP can evolve more gracefully, since most errors can be reported
2814        without the penalty of closing the connection. Clients using
2815        future versions of HTTP might optimistically try a new feature,
2816        but if communicating with an older server, retry with old
2817        semantics after an error is reported.
2818      </t>
2819    </list>
2820</t>
2821<t>
2822   HTTP implementations &SHOULD; implement persistent connections.
2823</t>
2824   
2825<section title="Establishment" anchor="persistent.establishment">
2826<t>
2827   It is beyond the scope of this specification to describe how connections
2828   are established via various transport or session-layer protocols.
2829   Each connection applies to only one transport link.
2830</t>
2831<t>
2832   A recipient determines whether a connection is persistent or not based on
2833   the most recently received message's protocol version and
2834   <x:ref>Connection</x:ref> header field (if any):
2835   <list style="symbols">
2836     <t>If the <x:ref>close</x:ref> connection option is present, the
2837        connection will not persist after the current response; else,</t>
2838     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2839        persist after the current response; else,</t>
2840     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2841        connection option is present, the recipient is not a proxy, and
2842        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2843        the connection will persist after the current response; otherwise,</t>
2844     <t>The connection will close after the current response.</t>
2845   </list>
2846</t>
2847<t>
2848   A proxy server &MUST-NOT; maintain a persistent connection with an
2849   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2850   information and discussion of the problems with the Keep-Alive header field
2851   implemented by many HTTP/1.0 clients).
2852</t>
2853</section>
2854
2855<section title="Reuse" anchor="persistent.reuse">
2856<t>
2857   In order to remain persistent, all messages on a connection &MUST;
2858   have a self-defined message length (i.e., one not defined by closure
2859   of the connection), as described in <xref target="message.body"/>.
2860</t>
2861<t>
2862   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2863   persistent connection until a <x:ref>close</x:ref> connection option
2864   is received in a request.
2865</t>
2866<t>
2867   A client &MAY; reuse a persistent connection until it sends or receives
2868   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2869   without a "keep-alive" connection option.
2870</t>
2871<t>
2872   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2873   maintained for HTTP versions less than 1.1 unless it is explicitly
2874   signaled.
2875   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2876   for more information on backward compatibility with HTTP/1.0 clients.
2877</t>
2878
2879<section title="Pipelining" anchor="pipelining">
2880<t>
2881   A client that supports persistent connections &MAY; "pipeline" its
2882   requests (i.e., send multiple requests without waiting for each
2883   response). A server &MUST; send its responses to those requests in the
2884   same order that the requests were received.
2885</t>
2886<t>
2887   Clients which assume persistent connections and pipeline immediately
2888   after connection establishment &SHOULD; be prepared to retry their
2889   connection if the first pipelined attempt fails. If a client does
2890   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2891   persistent. Clients &MUST; also be prepared to resend their requests if
2892   the server closes the connection before sending all of the
2893   corresponding responses.
2894</t>
2895<t>
2896   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods
2897   or non-idempotent sequences of request methods (see &idempotent-methods;).
2898   Otherwise, a premature termination of the transport connection could lead
2899   to indeterminate results. A client wishing to send a non-idempotent
2900   request &SHOULD; wait to send that request until it has received the
2901   response status line for the previous request.
2902</t>
2903</section>
2904
2905<section title="Retrying Requests" anchor="persistent.retrying.requests">
2906<t>
2907   Senders can close the transport connection at any time. Therefore,
2908   clients, servers, and proxies &MUST; be able to recover
2909   from asynchronous close events. Client software &MAY; reopen the
2910   transport connection and retransmit the aborted sequence of requests
2911   without user interaction so long as the request sequence is
2912   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2913   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2914   human operator the choice of retrying the request(s). Confirmation by
2915   user-agent software with semantic understanding of the application
2916   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2917   be repeated if the second sequence of requests fails.
2918</t>
2919</section>
2920</section>
2921   
2922<section title="Concurrency" anchor="persistent.concurrency">
2923<t>
2924   Clients &SHOULD; limit the number of simultaneous
2925   connections that they maintain to a given server.
2926</t>
2927<t>
2928   Previous revisions of HTTP gave a specific number of connections as a
2929   ceiling, but this was found to be impractical for many applications. As a
2930   result, this specification does not mandate a particular maximum number of
2931   connections, but instead encourages clients to be conservative when opening
2932   multiple connections.
2933</t>
2934<t>
2935   Multiple connections are typically used to avoid the "head-of-line
2936   blocking" problem, wherein a request that takes significant server-side
2937   processing and/or has a large payload blocks subsequent requests on the
2938   same connection. However, each connection consumes server resources.
2939   Furthermore, using multiple connections can cause undesirable side effects
2940   in congested networks.
2941</t>
2942<t>
2943   Note that servers might reject traffic that they deem abusive, including an
2944   excessive number of connections from a client.
2945</t>
2946</section>
2947
2948<section title="Failures and Time-outs" anchor="persistent.failures">
2949<t>
2950   Servers will usually have some time-out value beyond which they will
2951   no longer maintain an inactive connection. Proxy servers might make
2952   this a higher value since it is likely that the client will be making
2953   more connections through the same server. The use of persistent
2954   connections places no requirements on the length (or existence) of
2955   this time-out for either the client or the server.
2956</t>
2957<t>
2958   When a client or server wishes to time-out it &SHOULD; issue a graceful
2959   close on the transport connection. Clients and servers &SHOULD; both
2960   constantly watch for the other side of the transport close, and
2961   respond to it as appropriate. If a client or server does not detect
2962   the other side's close promptly it could cause unnecessary resource
2963   drain on the network.
2964</t>
2965<t>
2966   A client, server, or proxy &MAY; close the transport connection at any
2967   time. For example, a client might have started to send a new request
2968   at the same time that the server has decided to close the "idle"
2969   connection. From the server's point of view, the connection is being
2970   closed while it was idle, but from the client's point of view, a
2971   request is in progress.
2972</t>
2973<t>
2974   Servers &SHOULD; maintain persistent connections and allow the underlying
2975   transport's flow control mechanisms to resolve temporary overloads, rather
2976   than terminate connections with the expectation that clients will retry.
2977   The latter technique can exacerbate network congestion.
2978</t>
2979<t>
2980   A client sending a message body &SHOULD; monitor
2981   the network connection for an error status code while it is transmitting
2982   the request. If the client sees an error status code, it &SHOULD;
2983   immediately cease transmitting the body and close the connection.
2984</t>
2985</section>
2986   
2987<section title="Tear-down" anchor="persistent.tear-down">
2988  <iref primary="false" item="Connection header field" x:for-anchor=""/>
2989  <iref primary="false" item="close" x:for-anchor=""/>
2990<t>
2991   The <x:ref>Connection</x:ref> header field
2992   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
2993   connection option that a sender &SHOULD; send when it wishes to close
2994   the connection after the current request/response pair.
2995</t>
2996<t>
2997   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
2998   send further requests on that connection (after the one containing
2999   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3000   final response message corresponding to this request.
3001</t>
3002<t>
3003   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3004   initiate a lingering close of the connection after it sends the final
3005   response to the request that contained <x:ref>close</x:ref>.
3006   The server &SHOULD; include a <x:ref>close</x:ref> connection option
3007   in its final response on that connection. The server &MUST-NOT; process
3008   any further requests received on that connection.
3009</t>
3010<t>
3011   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3012   initiate a lingering close of the connection after it sends the
3013   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3014   any further requests received on that connection.
3015</t>
3016<t>
3017   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3018   cease sending requests on that connection and close the connection
3019   after reading the response message containing the close; if additional
3020   pipelined requests had been sent on the connection, the client &SHOULD;
3021   assume that they will not be processed by the server.
3022</t>
3023<t>
3024   If a server performs an immediate close of a TCP connection, there is a
3025   significant risk that the client will not be able to read the last HTTP
3026   response.  If the server receives additional data from the client on a
3027   fully-closed connection, such as another request that was sent by the
3028   client before receiving the server's response, the server's TCP stack will
3029   send a reset packet to the client; unfortunately, the reset packet might
3030   erase the client's unacknowledged input buffers before they can be read
3031   and interpreted by the client's HTTP parser.
3032</t>
3033<t>
3034   To avoid the TCP reset problem, a server can perform a lingering close on a
3035   connection by closing only the write side of the read/write connection
3036   (a half-close) and continuing to read from the connection until the
3037   connection is closed by the client or the server is reasonably certain
3038   that its own TCP stack has received the client's acknowledgement of the
3039   packet(s) containing the server's last response. It is then safe for the
3040   server to fully close the connection.
3041</t>
3042<t>
3043   It is unknown whether the reset problem is exclusive to TCP or might also
3044   be found in other transport connection protocols.
3045</t>
3046</section>
3047</section>
3048
3049<section title="Upgrade" anchor="header.upgrade">
3050  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3051  <x:anchor-alias value="Upgrade"/>
3052  <x:anchor-alias value="protocol"/>
3053  <x:anchor-alias value="protocol-name"/>
3054  <x:anchor-alias value="protocol-version"/>
3055<t>
3056   The "Upgrade" header field is intended to provide a simple mechanism
3057   for transitioning from HTTP/1.1 to some other protocol on the same
3058   connection.  A client &MAY; send a list of protocols in the Upgrade
3059   header field of a request to invite the server to switch to one or
3060   more of those protocols before sending the final response.
3061   A server &MUST; send an Upgrade header field in <x:ref>101 (Switching
3062   Protocols)</x:ref> responses to indicate which protocol(s) are being
3063   switched to, and &MUST; send it in <x:ref>426 (Upgrade Required)</x:ref>
3064   responses to indicate acceptable protocols.
3065   A server &MAY; send an Upgrade header field in any other response to
3066   indicate that they might be willing to upgrade to one of the
3067   specified protocols for a future request.
3068</t>
3069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3070  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3071
3072  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3073  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3074  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3075</artwork></figure>
3076<t>
3077   For example,
3078</t>
3079<figure><artwork type="example">
3080  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3081</artwork></figure>
3082<t>
3083   Upgrade eases the difficult transition between incompatible protocols by
3084   allowing the client to initiate a request in the more commonly
3085   supported protocol while indicating to the server that it would like
3086   to use a "better" protocol if available (where "better" is determined
3087   by the server, possibly according to the nature of the request method
3088   or target resource).
3089</t>
3090<t>
3091   Upgrade cannot be used to insist on a protocol change; its acceptance and
3092   use by the server is optional. The capabilities and nature of the
3093   application-level communication after the protocol change is entirely
3094   dependent upon the new protocol chosen, although the first action
3095   after changing the protocol &MUST; be a response to the initial HTTP
3096   request that contained the Upgrade header field.
3097</t>
3098<t>
3099   For example, if the Upgrade header field is received in a GET request
3100   and the server decides to switch protocols, then it &MUST; first respond
3101   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3102   then immediately follow that with the new protocol's equivalent of a
3103   response to a GET on the target resource.  This allows a connection to be
3104   upgraded to protocols with the same semantics as HTTP without the
3105   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3106   protocols unless the received message semantics can be honored by the new
3107   protocol; an OPTIONS request can be honored by any protocol.
3108</t>
3109<t>
3110   When Upgrade is sent, a sender &MUST; also send a
3111   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3112   that contains the "upgrade" connection option, in order to prevent Upgrade
3113   from being accidentally forwarded by intermediaries that might not implement
3114   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3115   is received in an HTTP/1.0 request.
3116</t>
3117<t>
3118   The Upgrade header field only applies to switching application-level
3119   protocols on the existing connection; it cannot be used
3120   to switch to a protocol on a different connection. For that purpose, it is
3121   more appropriate to use a <x:ref>3xx (Redirection)</x:ref> response
3122   (&status-3xx;).
3123</t>
3124<t>
3125   This specification only defines the protocol name "HTTP" for use by
3126   the family of Hypertext Transfer Protocols, as defined by the HTTP
3127   version rules of <xref target="http.version"/> and future updates to this
3128   specification. Additional tokens can be registered with IANA using the
3129   registration procedure defined in <xref target="upgrade.token.registry"/>.
3130</t>
3131</section>
3132</section>
3133
3134<section title="IANA Considerations" anchor="IANA.considerations">
3135
3136<section title="Header Field Registration" anchor="header.field.registration">
3137<t>
3138   HTTP header fields are registered within the Message Header Field Registry
3139   <xref target="RFC3864"/> maintained by IANA at
3140   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3141</t>
3142<t>
3143   This document defines the following HTTP header fields, so their
3144   associated registry entries shall be updated according to the permanent
3145   registrations below:
3146</t>
3147<?BEGININC p1-messaging.iana-headers ?>
3148<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3149<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3150   <ttcol>Header Field Name</ttcol>
3151   <ttcol>Protocol</ttcol>
3152   <ttcol>Status</ttcol>
3153   <ttcol>Reference</ttcol>
3154
3155   <c>Connection</c>
3156   <c>http</c>
3157   <c>standard</c>
3158   <c>
3159      <xref target="header.connection"/>
3160   </c>
3161   <c>Content-Length</c>
3162   <c>http</c>
3163   <c>standard</c>
3164   <c>
3165      <xref target="header.content-length"/>
3166   </c>
3167   <c>Host</c>
3168   <c>http</c>
3169   <c>standard</c>
3170   <c>
3171      <xref target="header.host"/>
3172   </c>
3173   <c>TE</c>
3174   <c>http</c>
3175   <c>standard</c>
3176   <c>
3177      <xref target="header.te"/>
3178   </c>
3179   <c>Trailer</c>
3180   <c>http</c>
3181   <c>standard</c>
3182   <c>
3183      <xref target="header.trailer"/>
3184   </c>
3185   <c>Transfer-Encoding</c>
3186   <c>http</c>
3187   <c>standard</c>
3188   <c>
3189      <xref target="header.transfer-encoding"/>
3190   </c>
3191   <c>Upgrade</c>
3192   <c>http</c>
3193   <c>standard</c>
3194   <c>
3195      <xref target="header.upgrade"/>
3196   </c>
3197   <c>Via</c>
3198   <c>http</c>
3199   <c>standard</c>
3200   <c>
3201      <xref target="header.via"/>
3202   </c>
3203</texttable>
3204<!--(END)-->
3205<?ENDINC p1-messaging.iana-headers ?>
3206<t>
3207   Furthermore, the header field-name "Close" shall be registered as
3208   "reserved", since using that name as an HTTP header field might
3209   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3210   header field (<xref target="header.connection"/>).
3211</t>
3212<texttable align="left" suppress-title="true">
3213   <ttcol>Header Field Name</ttcol>
3214   <ttcol>Protocol</ttcol>
3215   <ttcol>Status</ttcol>
3216   <ttcol>Reference</ttcol>
3217
3218   <c>Close</c>
3219   <c>http</c>
3220   <c>reserved</c>
3221   <c>
3222      <xref target="header.field.registration"/>
3223   </c>
3224</texttable>
3225<t>
3226   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3227</t>
3228</section>
3229
3230<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3231<t>
3232   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3233   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3234</t>
3235<t>
3236   This document defines the following URI schemes, so their
3237   associated registry entries shall be updated according to the permanent
3238   registrations below:
3239</t>
3240<texttable align="left" suppress-title="true">
3241   <ttcol>URI Scheme</ttcol>
3242   <ttcol>Description</ttcol>
3243   <ttcol>Reference</ttcol>
3244
3245   <c>http</c>
3246   <c>Hypertext Transfer Protocol</c>
3247   <c><xref target="http.uri"/></c>
3248
3249   <c>https</c>
3250   <c>Hypertext Transfer Protocol Secure</c>
3251   <c><xref target="https.uri"/></c>
3252</texttable>
3253</section>
3254
3255<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3256<t>
3257   This document serves as the specification for the Internet media types
3258   "message/http" and "application/http". The following is to be registered with
3259   IANA (see <xref target="RFC4288"/>).
3260</t>
3261<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3262<iref item="Media Type" subitem="message/http" primary="true"/>
3263<iref item="message/http Media Type" primary="true"/>
3264<t>
3265   The message/http type can be used to enclose a single HTTP request or
3266   response message, provided that it obeys the MIME restrictions for all
3267   "message" types regarding line length and encodings.
3268</t>
3269<t>
3270  <list style="hanging" x:indent="12em">
3271    <t hangText="Type name:">
3272      message
3273    </t>
3274    <t hangText="Subtype name:">
3275      http
3276    </t>
3277    <t hangText="Required parameters:">
3278      none
3279    </t>
3280    <t hangText="Optional parameters:">
3281      version, msgtype
3282      <list style="hanging">
3283        <t hangText="version:">
3284          The HTTP-version number of the enclosed message
3285          (e.g., "1.1"). If not present, the version can be
3286          determined from the first line of the body.
3287        </t>
3288        <t hangText="msgtype:">
3289          The message type &mdash; "request" or "response". If not
3290          present, the type can be determined from the first
3291          line of the body.
3292        </t>
3293      </list>
3294    </t>
3295    <t hangText="Encoding considerations:">
3296      only "7bit", "8bit", or "binary" are permitted
3297    </t>
3298    <t hangText="Security considerations:">
3299      none
3300    </t>
3301    <t hangText="Interoperability considerations:">
3302      none
3303    </t>
3304    <t hangText="Published specification:">
3305      This specification (see <xref target="internet.media.type.message.http"/>).
3306    </t>
3307    <t hangText="Applications that use this media type:">
3308    </t>
3309    <t hangText="Additional information:">
3310      <list style="hanging">
3311        <t hangText="Magic number(s):">none</t>
3312        <t hangText="File extension(s):">none</t>
3313        <t hangText="Macintosh file type code(s):">none</t>
3314      </list>
3315    </t>
3316    <t hangText="Person and email address to contact for further information:">
3317      See Authors Section.
3318    </t>
3319    <t hangText="Intended usage:">
3320      COMMON
3321    </t>
3322    <t hangText="Restrictions on usage:">
3323      none
3324    </t>
3325    <t hangText="Author/Change controller:">
3326      IESG
3327    </t>
3328  </list>
3329</t>
3330</section>
3331<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3332<iref item="Media Type" subitem="application/http" primary="true"/>
3333<iref item="application/http Media Type" primary="true"/>
3334<t>
3335   The application/http type can be used to enclose a pipeline of one or more
3336   HTTP request or response messages (not intermixed).
3337</t>
3338<t>
3339  <list style="hanging" x:indent="12em">
3340    <t hangText="Type name:">
3341      application
3342    </t>
3343    <t hangText="Subtype name:">
3344      http
3345    </t>
3346    <t hangText="Required parameters:">
3347      none
3348    </t>
3349    <t hangText="Optional parameters:">
3350      version, msgtype
3351      <list style="hanging">
3352        <t hangText="version:">
3353          The HTTP-version number of the enclosed messages
3354          (e.g., "1.1"). If not present, the version can be
3355          determined from the first line of the body.
3356        </t>
3357        <t hangText="msgtype:">
3358          The message type &mdash; "request" or "response". If not
3359          present, the type can be determined from the first
3360          line of the body.
3361        </t>
3362      </list>
3363    </t>
3364    <t hangText="Encoding considerations:">
3365      HTTP messages enclosed by this type
3366      are in "binary" format; use of an appropriate
3367      Content-Transfer-Encoding is required when
3368      transmitted via E-mail.
3369    </t>
3370    <t hangText="Security considerations:">
3371      none
3372    </t>
3373    <t hangText="Interoperability considerations:">
3374      none
3375    </t>
3376    <t hangText="Published specification:">
3377      This specification (see <xref target="internet.media.type.application.http"/>).
3378    </t>
3379    <t hangText="Applications that use this media type:">
3380    </t>
3381    <t hangText="Additional information:">
3382      <list style="hanging">
3383        <t hangText="Magic number(s):">none</t>
3384        <t hangText="File extension(s):">none</t>
3385        <t hangText="Macintosh file type code(s):">none</t>
3386      </list>
3387    </t>
3388    <t hangText="Person and email address to contact for further information:">
3389      See Authors Section.
3390    </t>
3391    <t hangText="Intended usage:">
3392      COMMON
3393    </t>
3394    <t hangText="Restrictions on usage:">
3395      none
3396    </t>
3397    <t hangText="Author/Change controller:">
3398      IESG
3399    </t>
3400  </list>
3401</t>
3402</section>
3403</section>
3404
3405<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3406<t>
3407   The HTTP Transfer Coding Registry defines the name space for transfer
3408   coding names.
3409</t>
3410<t>
3411   Registrations &MUST; include the following fields:
3412   <list style="symbols">
3413     <t>Name</t>
3414     <t>Description</t>
3415     <t>Pointer to specification text</t>
3416   </list>
3417</t>
3418<t>
3419   Names of transfer codings &MUST-NOT; overlap with names of content codings
3420   (&content-codings;) unless the encoding transformation is identical, as
3421   is the case for the compression codings defined in
3422   <xref target="compression.codings"/>.
3423</t>
3424<t>
3425   Values to be added to this name space require IETF Review (see
3426   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3427   conform to the purpose of transfer coding defined in this section.
3428   Use of program names for the identification of encoding formats
3429   is not desirable and is discouraged for future encodings.
3430</t>
3431<t>
3432   The registry itself is maintained at
3433   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3434</t>
3435</section>
3436
3437<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3438<t>
3439   The HTTP Transfer Coding Registry shall be updated with the registrations
3440   below:
3441</t>
3442<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3443   <ttcol>Name</ttcol>
3444   <ttcol>Description</ttcol>
3445   <ttcol>Reference</ttcol>
3446   <c>chunked</c>
3447   <c>Transfer in a series of chunks</c>
3448   <c>
3449      <xref target="chunked.encoding"/>
3450   </c>
3451   <c>compress</c>
3452   <c>UNIX "compress" program method</c>
3453   <c>
3454      <xref target="compress.coding"/>
3455   </c>
3456   <c>deflate</c>
3457   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3458   the "zlib" data format (<xref target="RFC1950"/>)
3459   </c>
3460   <c>
3461      <xref target="deflate.coding"/>
3462   </c>
3463   <c>gzip</c>
3464   <c>Same as GNU zip <xref target="RFC1952"/></c>
3465   <c>
3466      <xref target="gzip.coding"/>
3467   </c>
3468</texttable>
3469</section>
3470
3471<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3472<t>
3473   The HTTP Upgrade Token Registry defines the name space for protocol-name
3474   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3475   field. Each registered protocol name is associated with contact information
3476   and an optional set of specifications that details how the connection
3477   will be processed after it has been upgraded.
3478</t>
3479<t>
3480   Registrations happen on a "First Come First Served" basis (see
3481   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3482   following rules:
3483  <list style="numbers">
3484    <t>A protocol-name token, once registered, stays registered forever.</t>
3485    <t>The registration &MUST; name a responsible party for the
3486       registration.</t>
3487    <t>The registration &MUST; name a point of contact.</t>
3488    <t>The registration &MAY; name a set of specifications associated with
3489       that token. Such specifications need not be publicly available.</t>
3490    <t>The registration &SHOULD; name a set of expected "protocol-version"
3491       tokens associated with that token at the time of registration.</t>
3492    <t>The responsible party &MAY; change the registration at any time.
3493       The IANA will keep a record of all such changes, and make them
3494       available upon request.</t>
3495    <t>The IESG &MAY; reassign responsibility for a protocol token.
3496       This will normally only be used in the case when a
3497       responsible party cannot be contacted.</t>
3498  </list>
3499</t>
3500<t>
3501   This registration procedure for HTTP Upgrade Tokens replaces that
3502   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3503</t>
3504</section>
3505
3506<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3507<t>
3508   The HTTP Upgrade Token Registry shall be updated with the registration
3509   below:
3510</t>
3511<texttable align="left" suppress-title="true">
3512   <ttcol>Value</ttcol>
3513   <ttcol>Description</ttcol>
3514   <ttcol>Expected Version Tokens</ttcol>
3515   <ttcol>Reference</ttcol>
3516
3517   <c>HTTP</c>
3518   <c>Hypertext Transfer Protocol</c>
3519   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3520   <c><xref target="http.version"/></c>
3521</texttable>
3522<t>
3523   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3524</t>
3525</section>
3526
3527</section>
3528
3529<section title="Security Considerations" anchor="security.considerations">
3530<t>
3531   This section is meant to inform application developers, information
3532   providers, and users of the security limitations in HTTP/1.1 as
3533   described by this document. The discussion does not include
3534   definitive solutions to the problems revealed, though it does make
3535   some suggestions for reducing security risks.
3536</t>
3537
3538<section title="Personal Information" anchor="personal.information">
3539<t>
3540   HTTP clients are often privy to large amounts of personal information,
3541   including both information provided by the user to interact with resources
3542   (e.g., the user's name, location, mail address, passwords, encryption
3543   keys, etc.) and information about the user's browsing activity over
3544   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3545   prevent unintentional leakage of this information.
3546</t>
3547</section>
3548
3549<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3550<t>
3551   A server is in the position to save personal data about a user's
3552   requests which might identify their reading patterns or subjects of
3553   interest.  In particular, log information gathered at an intermediary
3554   often contains a history of user agent interaction, across a multitude
3555   of sites, that can be traced to individual users.
3556</t>
3557<t>
3558   HTTP log information is confidential in nature; its handling is often
3559   constrained by laws and regulations.  Log information needs to be securely
3560   stored and appropriate guidelines followed for its analysis.
3561   Anonymization of personal information within individual entries helps,
3562   but is generally not sufficient to prevent real log traces from being
3563   re-identified based on correlation with other access characteristics.
3564   As such, access traces that are keyed to a specific client should not
3565   be published even if the key is pseudonymous.
3566</t>
3567<t>
3568   To minimize the risk of theft or accidental publication, log information
3569   should be purged of personally identifiable information, including
3570   user identifiers, IP addresses, and user-provided query parameters,
3571   as soon as that information is no longer necessary to support operational
3572   needs for security, auditing, or fraud control.
3573</t>
3574</section>
3575
3576<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3577<t>
3578   Origin servers &SHOULD; be careful to restrict
3579   the documents returned by HTTP requests to be only those that were
3580   intended by the server administrators. If an HTTP server translates
3581   HTTP URIs directly into file system calls, the server &MUST; take
3582   special care not to serve files that were not intended to be
3583   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3584   other operating systems use ".." as a path component to indicate a
3585   directory level above the current one. On such a system, an HTTP
3586   server &MUST; disallow any such construct in the request-target if it
3587   would otherwise allow access to a resource outside those intended to
3588   be accessible via the HTTP server. Similarly, files intended for
3589   reference only internally to the server (such as access control
3590   files, configuration files, and script code) &MUST; be protected from
3591   inappropriate retrieval, since they might contain sensitive
3592   information.
3593</t>
3594</section>
3595
3596<section title="DNS-related Attacks" anchor="dns.related.attacks">
3597<t>
3598   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3599   generally prone to security attacks based on the deliberate misassociation
3600   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3601   cautious in assuming the validity of an IP number/DNS name association unless
3602   the response is protected by DNSSec (<xref target="RFC4033"/>).
3603</t>
3604</section>
3605
3606<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3607<t>
3608   By their very nature, HTTP intermediaries are men-in-the-middle, and
3609   represent an opportunity for man-in-the-middle attacks. Compromise of
3610   the systems on which the intermediaries run can result in serious security
3611   and privacy problems. Intermediaries have access to security-related
3612   information, personal information about individual users and
3613   organizations, and proprietary information belonging to users and
3614   content providers. A compromised intermediary, or an intermediary
3615   implemented or configured without regard to security and privacy
3616   considerations, might be used in the commission of a wide range of
3617   potential attacks.
3618</t>
3619<t>
3620   Intermediaries that contain a shared cache are especially vulnerable
3621   to cache poisoning attacks.
3622</t>
3623<t>
3624   Implementers need to consider the privacy and security
3625   implications of their design and coding decisions, and of the
3626   configuration options they provide to operators (especially the
3627   default configuration).
3628</t>
3629<t>
3630   Users need to be aware that intermediaries are no more trustworthy than
3631   the people who run them; HTTP itself cannot solve this problem.
3632</t>
3633</section>
3634
3635<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3636<t>
3637   Because HTTP uses mostly textual, character-delimited fields, attackers can
3638   overflow buffers in implementations, and/or perform a Denial of Service
3639   against implementations that accept fields with unlimited lengths.
3640</t>
3641<t>
3642   To promote interoperability, this specification makes specific
3643   recommendations for minimum size limits on request-line
3644   (<xref target="request.line"/>)
3645   and blocks of header fields (<xref target="header.fields"/>). These are
3646   minimum recommendations, chosen to be supportable even by implementations
3647   with limited resources; it is expected that most implementations will
3648   choose substantially higher limits.
3649</t>
3650<t>
3651   This specification also provides a way for servers to reject messages that
3652   have request-targets that are too long (&status-414;) or request entities
3653   that are too large (&status-4xx;).
3654</t>
3655<t>
3656   Recipients &SHOULD; carefully limit the extent to which they read other
3657   fields, including (but not limited to) request methods, response status
3658   phrases, header field-names, and body chunks, so as to avoid denial of
3659   service attacks without impeding interoperability.
3660</t>
3661</section>
3662</section>
3663
3664<section title="Acknowledgments" anchor="acks">
3665<t>
3666   This edition of HTTP builds on the many contributions that went into
3667   <xref target="RFC1945" format="none">RFC 1945</xref>,
3668   <xref target="RFC2068" format="none">RFC 2068</xref>,
3669   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3670   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3671   substantial contributions made by the previous authors, editors, and
3672   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3673   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3674   Paul J. Leach, and Mark Nottingham.
3675   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3676   acknowledgements from prior revisions.
3677</t>
3678<t>
3679   Since 1999, the following contributors have helped improve the HTTP
3680   specification by reporting bugs, asking smart questions, drafting or
3681   reviewing text, and evaluating open issues:
3682</t>
3683<?BEGININC acks ?>
3684<t>Adam Barth,
3685Adam Roach,
3686Addison Phillips,
3687Adrian Chadd,
3688Adrien W. de Croy,
3689Alan Ford,
3690Alan Ruttenberg,
3691Albert Lunde,
3692Alek Storm,
3693Alex Rousskov,
3694Alexandre Morgaut,
3695Alexey Melnikov,
3696Alisha Smith,
3697Amichai Rothman,
3698Amit Klein,
3699Amos Jeffries,
3700Andreas Maier,
3701Andreas Petersson,
3702Anil Sharma,
3703Anne van Kesteren,
3704Anthony Bryan,
3705Asbjorn Ulsberg,
3706Balachander Krishnamurthy,
3707Barry Leiba,
3708Ben Laurie,
3709Benjamin Niven-Jenkins,
3710Bil Corry,
3711Bill Burke,
3712Bjoern Hoehrmann,
3713Bob Scheifler,
3714Boris Zbarsky,
3715Brett Slatkin,
3716Brian Kell,
3717Brian McBarron,
3718Brian Pane,
3719Brian Smith,
3720Bryce Nesbitt,
3721Cameron Heavon-Jones,
3722Carl Kugler,
3723Carsten Bormann,
3724Charles Fry,
3725Chris Newman,
3726Cyrus Daboo,
3727Dale Robert Anderson,
3728Dan Wing,
3729Dan Winship,
3730Daniel Stenberg,
3731Dave Cridland,
3732Dave Crocker,
3733Dave Kristol,
3734David Booth,
3735David Singer,
3736David W. Morris,
3737Diwakar Shetty,
3738Dmitry Kurochkin,
3739Drummond Reed,
3740Duane Wessels,
3741Edward Lee,
3742Eliot Lear,
3743Eran Hammer-Lahav,
3744Eric D. Williams,
3745Eric J. Bowman,
3746Eric Lawrence,
3747Eric Rescorla,
3748Erik Aronesty,
3749Evan Prodromou,
3750Florian Weimer,
3751Frank Ellermann,
3752Fred Bohle,
3753Gabriel Montenegro,
3754Geoffrey Sneddon,
3755Gervase Markham,
3756Grahame Grieve,
3757Greg Wilkins,
3758Harald Tveit Alvestrand,
3759Harry Halpin,
3760Helge Hess,
3761Henrik Nordstrom,
3762Henry S. Thompson,
3763Henry Story,
3764Herbert van de Sompel,
3765Howard Melman,
3766Hugo Haas,
3767Ian Fette,
3768Ian Hickson,
3769Ido Safruti,
3770Ingo Struck,
3771J. Ross Nicoll,
3772James H. Manger,
3773James Lacey,
3774James M. Snell,
3775Jamie Lokier,
3776Jan Algermissen,
3777Jeff Hodges (who came up with the term 'effective Request-URI'),
3778Jeff Walden,
3779Jim Luther,
3780Joe D. Williams,
3781Joe Gregorio,
3782Joe Orton,
3783John C. Klensin,
3784John C. Mallery,
3785John Cowan,
3786John Kemp,
3787John Panzer,
3788John Schneider,
3789John Stracke,
3790John Sullivan,
3791Jonas Sicking,
3792Jonathan Billington,
3793Jonathan Moore,
3794Jonathan Rees,
3795Jonathan Silvera,
3796Jordi Ros,
3797Joris Dobbelsteen,
3798Josh Cohen,
3799Julien Pierre,
3800Jungshik Shin,
3801Justin Chapweske,
3802Justin Erenkrantz,
3803Justin James,
3804Kalvinder Singh,
3805Karl Dubost,
3806Keith Hoffman,
3807Keith Moore,
3808Koen Holtman,
3809Konstantin Voronkov,
3810Kris Zyp,
3811Lisa Dusseault,
3812Maciej Stachowiak,
3813Marc Schneider,
3814Marc Slemko,
3815Mark Baker,
3816Mark Pauley,
3817Mark Watson,
3818Markus Isomaki,
3819Markus Lanthaler,
3820Martin J. Duerst,
3821Martin Musatov,
3822Martin Nilsson,
3823Martin Thomson,
3824Matt Lynch,
3825Matthew Cox,
3826Max Clark,
3827Michael Burrows,
3828Michael Hausenblas,
3829Mike Amundsen,
3830Mike Belshe,
3831Mike Kelly,
3832Mike Schinkel,
3833Miles Sabin,
3834Murray S. Kucherawy,
3835Mykyta Yevstifeyev,
3836Nathan Rixham,
3837Nicholas Shanks,
3838Nico Williams,
3839Nicolas Alvarez,
3840Nicolas Mailhot,
3841Noah Slater,
3842Pablo Castro,
3843Pat Hayes,
3844Patrick R. McManus,
3845Paul E. Jones,
3846Paul Hoffman,
3847Paul Marquess,
3848Peter Lepeska,
3849Peter Saint-Andre,
3850Peter Watkins,
3851Phil Archer,
3852Philippe Mougin,
3853Phillip Hallam-Baker,
3854Poul-Henning Kamp,
3855Preethi Natarajan,
3856Rajeev Bector,
3857Ray Polk,
3858Reto Bachmann-Gmuer,
3859Richard Cyganiak,
3860Robert Brewer,
3861Robert Collins,
3862Robert O'Callahan,
3863Robert Olofsson,
3864Robert Sayre,
3865Robert Siemer,
3866Robert de Wilde,
3867Roberto Javier Godoy,
3868Roberto Peon,
3869Ronny Widjaja,
3870S. Mike Dierken,
3871Salvatore Loreto,
3872Sam Johnston,
3873Sam Ruby,
3874Scott Lawrence (who maintained the original issues list),
3875Sean B. Palmer,
3876Shane McCarron,
3877Stefan Eissing,
3878Stefan Tilkov,
3879Stefanos Harhalakis,
3880Stephane Bortzmeyer,
3881Stephen Farrell,
3882Stephen Ludin,
3883Stuart Williams,
3884Subbu Allamaraju,
3885Sylvain Hellegouarch,
3886Tapan Divekar,
3887Tatsuya Hayashi,
3888Ted Hardie,
3889Thomas Broyer,
3890Thomas Nordin,
3891Thomas Roessler,
3892Tim Bray,
3893Tim Morgan,
3894Tim Olsen,
3895Tom Zhou,
3896Travis Snoozy,
3897Tyler Close,
3898Vincent Murphy,
3899Wenbo Zhu,
3900Werner Baumann,
3901Wilbur Streett,
3902Wilfredo Sanchez Vega,
3903William A. Rowe Jr.,
3904William Chan,
3905Willy Tarreau,
3906Xiaoshu Wang,
3907Yaron Goland,
3908Yngve Nysaeter Pettersen,
3909Yoav Nir,
3910Yogesh Bang,
3911Yutaka Oiwa,
3912Zed A. Shaw, and
3913Zhong Yu.
3914</t>
3915<?ENDINC acks ?>
3916</section>
3917
3918</middle>
3919<back>
3920
3921<references title="Normative References">
3922
3923<reference anchor="Part2">
3924  <front>
3925    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
3926    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3927      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3928      <address><email>fielding@gbiv.com</email></address>
3929    </author>
3930    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3931      <organization abbrev="W3C">World Wide Web Consortium</organization>
3932      <address><email>ylafon@w3.org</email></address>
3933    </author>
3934    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3935      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3936      <address><email>julian.reschke@greenbytes.de</email></address>
3937    </author>
3938    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3939  </front>
3940  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3941  <x:source href="p2-semantics.xml" basename="p2-semantics">
3942    <x:defines>1xx (Informational)</x:defines>
3943    <x:defines>1xx</x:defines>
3944    <x:defines>100 (Continue)</x:defines>
3945    <x:defines>101 (Switching Protocols)</x:defines>
3946    <x:defines>2xx (Successful)</x:defines>
3947    <x:defines>2xx</x:defines>
3948    <x:defines>200 (OK)</x:defines>
3949    <x:defines>204 (No Content)</x:defines>
3950    <x:defines>3xx (Redirection)</x:defines>
3951    <x:defines>3xx</x:defines>
3952    <x:defines>301 (Moved Permanently)</x:defines>
3953    <x:defines>4xx (Client Error)</x:defines>
3954    <x:defines>4xx</x:defines>
3955    <x:defines>400 (Bad Request)</x:defines>
3956    <x:defines>405 (Method Not Allowed)</x:defines>
3957    <x:defines>411 (Length Required)</x:defines>
3958    <x:defines>414 (URI Too Long)</x:defines>
3959    <x:defines>417 (Expectation Failed)</x:defines>
3960    <x:defines>426 (Upgrade Required)</x:defines>
3961    <x:defines>501 (Not Implemented)</x:defines>
3962    <x:defines>502 (Bad Gateway)</x:defines>
3963    <x:defines>505 (HTTP Version Not Supported)</x:defines>
3964    <x:defines>Allow</x:defines>
3965    <x:defines>Content-Encoding</x:defines>
3966    <x:defines>Content-Location</x:defines>
3967    <x:defines>Content-Type</x:defines>
3968    <x:defines>Date</x:defines>
3969    <x:defines>Expect</x:defines>
3970    <x:defines>Location</x:defines>
3971    <x:defines>Server</x:defines>
3972    <x:defines>User-Agent</x:defines>
3973  </x:source>
3974</reference>
3975
3976<reference anchor="Part4">
3977  <front>
3978    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
3979    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
3980      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3981      <address><email>fielding@gbiv.com</email></address>
3982    </author>
3983    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
3984      <organization abbrev="W3C">World Wide Web Consortium</organization>
3985      <address><email>ylafon@w3.org</email></address>
3986    </author>
3987    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
3988      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3989      <address><email>julian.reschke@greenbytes.de</email></address>
3990    </author>
3991    <date month="&ID-MONTH;" year="&ID-YEAR;" />
3992  </front>
3993  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
3994  <x:source basename="p4-conditional" href="p4-conditional.xml">
3995    <x:defines>304 (Not Modified)</x:defines>
3996    <x:defines>ETag</x:defines>
3997    <x:defines>Last-Modified</x:defines>
3998  </x:source>
3999</reference>
4000
4001<reference anchor="Part5">
4002  <front>
4003    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4004    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4005      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4006      <address><email>fielding@gbiv.com</email></address>
4007    </author>
4008    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4009      <organization abbrev="W3C">World Wide Web Consortium</organization>
4010      <address><email>ylafon@w3.org</email></address>
4011    </author>
4012    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4013      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4014      <address><email>julian.reschke@greenbytes.de</email></address>
4015    </author>
4016    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4017  </front>
4018  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4019  <x:source href="p5-range.xml" basename="p5-range">
4020    <x:defines>Content-Range</x:defines>
4021  </x:source>
4022</reference>
4023
4024<reference anchor="Part6">
4025  <front>
4026    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4027    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4028      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4029      <address><email>fielding@gbiv.com</email></address>
4030    </author>
4031    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4032      <organization abbrev="W3C">World Wide Web Consortium</organization>
4033      <address><email>ylafon@w3.org</email></address>
4034    </author>
4035    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4036      <address><email>mnot@mnot.net</email></address>
4037    </author>
4038    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4039      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4040      <address><email>julian.reschke@greenbytes.de</email></address>
4041    </author>
4042    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4043  </front>
4044  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4045  <x:source href="p6-cache.xml" basename="p6-cache">
4046    <x:defines>Expires</x:defines>
4047  </x:source>
4048</reference>
4049
4050<reference anchor="Part7">
4051  <front>
4052    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4053    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4054      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4055      <address><email>fielding@gbiv.com</email></address>
4056    </author>
4057    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4058      <organization abbrev="W3C">World Wide Web Consortium</organization>
4059      <address><email>ylafon@w3.org</email></address>
4060    </author>
4061    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4062      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4063      <address><email>julian.reschke@greenbytes.de</email></address>
4064    </author>
4065    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4066  </front>
4067  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4068  <x:source href="p7-auth.xml" basename="p7-auth">
4069    <x:defines>Proxy-Authenticate</x:defines>
4070    <x:defines>Proxy-Authorization</x:defines>
4071  </x:source>
4072</reference>
4073
4074<reference anchor="RFC5234">
4075  <front>
4076    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4077    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4078      <organization>Brandenburg InternetWorking</organization>
4079      <address>
4080        <email>dcrocker@bbiw.net</email>
4081      </address> 
4082    </author>
4083    <author initials="P." surname="Overell" fullname="Paul Overell">
4084      <organization>THUS plc.</organization>
4085      <address>
4086        <email>paul.overell@thus.net</email>
4087      </address>
4088    </author>
4089    <date month="January" year="2008"/>
4090  </front>
4091  <seriesInfo name="STD" value="68"/>
4092  <seriesInfo name="RFC" value="5234"/>
4093</reference>
4094
4095<reference anchor="RFC2119">
4096  <front>
4097    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4098    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4099      <organization>Harvard University</organization>
4100      <address><email>sob@harvard.edu</email></address>
4101    </author>
4102    <date month="March" year="1997"/>
4103  </front>
4104  <seriesInfo name="BCP" value="14"/>
4105  <seriesInfo name="RFC" value="2119"/>
4106</reference>
4107
4108<reference anchor="RFC3986">
4109 <front>
4110  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4111  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4113    <address>
4114       <email>timbl@w3.org</email>
4115       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4116    </address>
4117  </author>
4118  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4119    <organization abbrev="Day Software">Day Software</organization>
4120    <address>
4121      <email>fielding@gbiv.com</email>
4122      <uri>http://roy.gbiv.com/</uri>
4123    </address>
4124  </author>
4125  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4126    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4127    <address>
4128      <email>LMM@acm.org</email>
4129      <uri>http://larry.masinter.net/</uri>
4130    </address>
4131  </author>
4132  <date month='January' year='2005'></date>
4133 </front>
4134 <seriesInfo name="STD" value="66"/>
4135 <seriesInfo name="RFC" value="3986"/>
4136</reference>
4137
4138<reference anchor="USASCII">
4139  <front>
4140    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4141    <author>
4142      <organization>American National Standards Institute</organization>
4143    </author>
4144    <date year="1986"/>
4145  </front>
4146  <seriesInfo name="ANSI" value="X3.4"/>
4147</reference>
4148
4149<reference anchor="RFC1950">
4150  <front>
4151    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4152    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4153      <organization>Aladdin Enterprises</organization>
4154      <address><email>ghost@aladdin.com</email></address>
4155    </author>
4156    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4157    <date month="May" year="1996"/>
4158  </front>
4159  <seriesInfo name="RFC" value="1950"/>
4160  <!--<annotation>
4161    RFC 1950 is an Informational RFC, thus it might be less stable than
4162    this specification. On the other hand, this downward reference was
4163    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4164    therefore it is unlikely to cause problems in practice. See also
4165    <xref target="BCP97"/>.
4166  </annotation>-->
4167</reference>
4168
4169<reference anchor="RFC1951">
4170  <front>
4171    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4172    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4173      <organization>Aladdin Enterprises</organization>
4174      <address><email>ghost@aladdin.com</email></address>
4175    </author>
4176    <date month="May" year="1996"/>
4177  </front>
4178  <seriesInfo name="RFC" value="1951"/>
4179  <!--<annotation>
4180    RFC 1951 is an Informational RFC, thus it might be less stable than
4181    this specification. On the other hand, this downward reference was
4182    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4183    therefore it is unlikely to cause problems in practice. See also
4184    <xref target="BCP97"/>.
4185  </annotation>-->
4186</reference>
4187
4188<reference anchor="RFC1952">
4189  <front>
4190    <title>GZIP file format specification version 4.3</title>
4191    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4192      <organization>Aladdin Enterprises</organization>
4193      <address><email>ghost@aladdin.com</email></address>
4194    </author>
4195    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4196      <address><email>gzip@prep.ai.mit.edu</email></address>
4197    </author>
4198    <author initials="M." surname="Adler" fullname="Mark Adler">
4199      <address><email>madler@alumni.caltech.edu</email></address>
4200    </author>
4201    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4202      <address><email>ghost@aladdin.com</email></address>
4203    </author>
4204    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4205      <address><email>randeg@alumni.rpi.edu</email></address>
4206    </author>
4207    <date month="May" year="1996"/>
4208  </front>
4209  <seriesInfo name="RFC" value="1952"/>
4210  <!--<annotation>
4211    RFC 1952 is an Informational RFC, thus it might be less stable than
4212    this specification. On the other hand, this downward reference was
4213    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4214    therefore it is unlikely to cause problems in practice. See also
4215    <xref target="BCP97"/>.
4216  </annotation>-->
4217</reference>
4218
4219</references>
4220
4221<references title="Informative References">
4222
4223<reference anchor="ISO-8859-1">
4224  <front>
4225    <title>
4226     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4227    </title>
4228    <author>
4229      <organization>International Organization for Standardization</organization>
4230    </author>
4231    <date year="1998"/>
4232  </front>
4233  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4234</reference>
4235
4236<reference anchor='RFC1919'>
4237  <front>
4238    <title>Classical versus Transparent IP Proxies</title>
4239    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4240      <address><email>mchatel@pax.eunet.ch</email></address>
4241    </author>
4242    <date year='1996' month='March' />
4243  </front>
4244  <seriesInfo name='RFC' value='1919' />
4245</reference>
4246
4247<reference anchor="RFC1945">
4248  <front>
4249    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4250    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4251      <organization>MIT, Laboratory for Computer Science</organization>
4252      <address><email>timbl@w3.org</email></address>
4253    </author>
4254    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4255      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4256      <address><email>fielding@ics.uci.edu</email></address>
4257    </author>
4258    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4259      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4260      <address><email>frystyk@w3.org</email></address>
4261    </author>
4262    <date month="May" year="1996"/>
4263  </front>
4264  <seriesInfo name="RFC" value="1945"/>
4265</reference>
4266
4267<reference anchor="RFC2045">
4268  <front>
4269    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4270    <author initials="N." surname="Freed" fullname="Ned Freed">
4271      <organization>Innosoft International, Inc.</organization>
4272      <address><email>ned@innosoft.com</email></address>
4273    </author>
4274    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4275      <organization>First Virtual Holdings</organization>
4276      <address><email>nsb@nsb.fv.com</email></address>
4277    </author>
4278    <date month="November" year="1996"/>
4279  </front>
4280  <seriesInfo name="RFC" value="2045"/>
4281</reference>
4282
4283<reference anchor="RFC2047">
4284  <front>
4285    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4286    <author initials="K." surname="Moore" fullname="Keith Moore">
4287      <organization>University of Tennessee</organization>
4288      <address><email>moore@cs.utk.edu</email></address>
4289    </author>
4290    <date month="November" year="1996"/>
4291  </front>
4292  <seriesInfo name="RFC" value="2047"/>
4293</reference>
4294
4295<reference anchor="RFC2068">
4296  <front>
4297    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4298    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4299      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4300      <address><email>fielding@ics.uci.edu</email></address>
4301    </author>
4302    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4303      <organization>MIT Laboratory for Computer Science</organization>
4304      <address><email>jg@w3.org</email></address>
4305    </author>
4306    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4307      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4308      <address><email>mogul@wrl.dec.com</email></address>
4309    </author>
4310    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4311      <organization>MIT Laboratory for Computer Science</organization>
4312      <address><email>frystyk@w3.org</email></address>
4313    </author>
4314    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4315      <organization>MIT Laboratory for Computer Science</organization>
4316      <address><email>timbl@w3.org</email></address>
4317    </author>
4318    <date month="January" year="1997"/>
4319  </front>
4320  <seriesInfo name="RFC" value="2068"/>
4321</reference>
4322
4323<reference anchor="RFC2145">
4324  <front>
4325    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4326    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4327      <organization>Western Research Laboratory</organization>
4328      <address><email>mogul@wrl.dec.com</email></address>
4329    </author>
4330    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4331      <organization>Department of Information and Computer Science</organization>
4332      <address><email>fielding@ics.uci.edu</email></address>
4333    </author>
4334    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4335      <organization>MIT Laboratory for Computer Science</organization>
4336      <address><email>jg@w3.org</email></address>
4337    </author>
4338    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4339      <organization>W3 Consortium</organization>
4340      <address><email>frystyk@w3.org</email></address>
4341    </author>
4342    <date month="May" year="1997"/>
4343  </front>
4344  <seriesInfo name="RFC" value="2145"/>
4345</reference>
4346
4347<reference anchor="RFC2616">
4348  <front>
4349    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4350    <author initials="R." surname="Fielding" fullname="R. Fielding">
4351      <organization>University of California, Irvine</organization>
4352      <address><email>fielding@ics.uci.edu</email></address>
4353    </author>
4354    <author initials="J." surname="Gettys" fullname="J. Gettys">
4355      <organization>W3C</organization>
4356      <address><email>jg@w3.org</email></address>
4357    </author>
4358    <author initials="J." surname="Mogul" fullname="J. Mogul">
4359      <organization>Compaq Computer Corporation</organization>
4360      <address><email>mogul@wrl.dec.com</email></address>
4361    </author>
4362    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4363      <organization>MIT Laboratory for Computer Science</organization>
4364      <address><email>frystyk@w3.org</email></address>
4365    </author>
4366    <author initials="L." surname="Masinter" fullname="L. Masinter">
4367      <organization>Xerox Corporation</organization>
4368      <address><email>masinter@parc.xerox.com</email></address>
4369    </author>
4370    <author initials="P." surname="Leach" fullname="P. Leach">
4371      <organization>Microsoft Corporation</organization>
4372      <address><email>paulle@microsoft.com</email></address>
4373    </author>
4374    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4375      <organization>W3C</organization>
4376      <address><email>timbl@w3.org</email></address>
4377    </author>
4378    <date month="June" year="1999"/>
4379  </front>
4380  <seriesInfo name="RFC" value="2616"/>
4381</reference>
4382
4383<reference anchor='RFC2817'>
4384  <front>
4385    <title>Upgrading to TLS Within HTTP/1.1</title>
4386    <author initials='R.' surname='Khare' fullname='R. Khare'>
4387      <organization>4K Associates / UC Irvine</organization>
4388      <address><email>rohit@4K-associates.com</email></address>
4389    </author>
4390    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4391      <organization>Agranat Systems, Inc.</organization>
4392      <address><email>lawrence@agranat.com</email></address>
4393    </author>
4394    <date year='2000' month='May' />
4395  </front>
4396  <seriesInfo name='RFC' value='2817' />
4397</reference>
4398
4399<reference anchor='RFC2818'>
4400  <front>
4401    <title>HTTP Over TLS</title>
4402    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4403      <organization>RTFM, Inc.</organization>
4404      <address><email>ekr@rtfm.com</email></address>
4405    </author>
4406    <date year='2000' month='May' />
4407  </front>
4408  <seriesInfo name='RFC' value='2818' />
4409</reference>
4410
4411<reference anchor='RFC2965'>
4412  <front>
4413    <title>HTTP State Management Mechanism</title>
4414    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4415      <organization>Bell Laboratories, Lucent Technologies</organization>
4416      <address><email>dmk@bell-labs.com</email></address>
4417    </author>
4418    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4419      <organization>Epinions.com, Inc.</organization>
4420      <address><email>lou@montulli.org</email></address>
4421    </author>
4422    <date year='2000' month='October' />
4423  </front>
4424  <seriesInfo name='RFC' value='2965' />
4425</reference>
4426
4427<reference anchor='RFC3040'>
4428  <front>
4429    <title>Internet Web Replication and Caching Taxonomy</title>
4430    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4431      <organization>Equinix, Inc.</organization>
4432    </author>
4433    <author initials='I.' surname='Melve' fullname='I. Melve'>
4434      <organization>UNINETT</organization>
4435    </author>
4436    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4437      <organization>CacheFlow Inc.</organization>
4438    </author>
4439    <date year='2001' month='January' />
4440  </front>
4441  <seriesInfo name='RFC' value='3040' />
4442</reference>
4443
4444<reference anchor='RFC3864'>
4445  <front>
4446    <title>Registration Procedures for Message Header Fields</title>
4447    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4448      <organization>Nine by Nine</organization>
4449      <address><email>GK-IETF@ninebynine.org</email></address>
4450    </author>
4451    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4452      <organization>BEA Systems</organization>
4453      <address><email>mnot@pobox.com</email></address>
4454    </author>
4455    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4456      <organization>HP Labs</organization>
4457      <address><email>JeffMogul@acm.org</email></address>
4458    </author>
4459    <date year='2004' month='September' />
4460  </front>
4461  <seriesInfo name='BCP' value='90' />
4462  <seriesInfo name='RFC' value='3864' />
4463</reference>
4464
4465<reference anchor='RFC4033'>
4466  <front>
4467    <title>DNS Security Introduction and Requirements</title>
4468    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4469    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4470    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4471    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4472    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4473    <date year='2005' month='March' />
4474  </front>
4475  <seriesInfo name='RFC' value='4033' />
4476</reference>
4477
4478<reference anchor="RFC4288">
4479  <front>
4480    <title>Media Type Specifications and Registration Procedures</title>
4481    <author initials="N." surname="Freed" fullname="N. Freed">
4482      <organization>Sun Microsystems</organization>
4483      <address>
4484        <email>ned.freed@mrochek.com</email>
4485      </address>
4486    </author>
4487    <author initials="J." surname="Klensin" fullname="J. Klensin">
4488      <address>
4489        <email>klensin+ietf@jck.com</email>
4490      </address>
4491    </author>
4492    <date year="2005" month="December"/>
4493  </front>
4494  <seriesInfo name="BCP" value="13"/>
4495  <seriesInfo name="RFC" value="4288"/>
4496</reference>
4497
4498<reference anchor='RFC4395'>
4499  <front>
4500    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4501    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4502      <organization>AT&amp;T Laboratories</organization>
4503      <address>
4504        <email>tony+urireg@maillennium.att.com</email>
4505      </address>
4506    </author>
4507    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4508      <organization>Qualcomm, Inc.</organization>
4509      <address>
4510        <email>hardie@qualcomm.com</email>
4511      </address>
4512    </author>
4513    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4514      <organization>Adobe Systems</organization>
4515      <address>
4516        <email>LMM@acm.org</email>
4517      </address>
4518    </author>
4519    <date year='2006' month='February' />
4520  </front>
4521  <seriesInfo name='BCP' value='115' />
4522  <seriesInfo name='RFC' value='4395' />
4523</reference>
4524
4525<reference anchor='RFC4559'>
4526  <front>
4527    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4528    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4529    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4530    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4531    <date year='2006' month='June' />
4532  </front>
4533  <seriesInfo name='RFC' value='4559' />
4534</reference>
4535
4536<reference anchor='RFC5226'>
4537  <front>
4538    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4539    <author initials='T.' surname='Narten' fullname='T. Narten'>
4540      <organization>IBM</organization>
4541      <address><email>narten@us.ibm.com</email></address>
4542    </author>
4543    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4544      <organization>Google</organization>
4545      <address><email>Harald@Alvestrand.no</email></address>
4546    </author>
4547    <date year='2008' month='May' />
4548  </front>
4549  <seriesInfo name='BCP' value='26' />
4550  <seriesInfo name='RFC' value='5226' />
4551</reference>
4552
4553<reference anchor='RFC5246'>
4554   <front>
4555      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4556      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4557         <organization />
4558      </author>
4559      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4560         <organization>RTFM, Inc.</organization>
4561      </author>
4562      <date year='2008' month='August' />
4563   </front>
4564   <seriesInfo name='RFC' value='5246' />
4565</reference>
4566
4567<reference anchor="RFC5322">
4568  <front>
4569    <title>Internet Message Format</title>
4570    <author initials="P." surname="Resnick" fullname="P. Resnick">
4571      <organization>Qualcomm Incorporated</organization>
4572    </author>
4573    <date year="2008" month="October"/>
4574  </front> 
4575  <seriesInfo name="RFC" value="5322"/>
4576</reference>
4577
4578<reference anchor="RFC6265">
4579  <front>
4580    <title>HTTP State Management Mechanism</title>
4581    <author initials="A." surname="Barth" fullname="Adam Barth">
4582      <organization abbrev="U.C. Berkeley">
4583        University of California, Berkeley
4584      </organization>
4585      <address><email>abarth@eecs.berkeley.edu</email></address>
4586    </author>
4587    <date year="2011" month="April" />
4588  </front>
4589  <seriesInfo name="RFC" value="6265"/>
4590</reference>
4591
4592<!--<reference anchor='BCP97'>
4593  <front>
4594    <title>Handling Normative References to Standards-Track Documents</title>
4595    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4596      <address>
4597        <email>klensin+ietf@jck.com</email>
4598      </address>
4599    </author>
4600    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4601      <organization>MIT</organization>
4602      <address>
4603        <email>hartmans-ietf@mit.edu</email>
4604      </address>
4605    </author>
4606    <date year='2007' month='June' />
4607  </front>
4608  <seriesInfo name='BCP' value='97' />
4609  <seriesInfo name='RFC' value='4897' />
4610</reference>-->
4611
4612<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4613  <front>
4614    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4615    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4616    <date year="2001" month="November"/>
4617  </front>
4618  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4619</reference>
4620
4621</references>
4622
4623
4624<section title="HTTP Version History" anchor="compatibility">
4625<t>
4626   HTTP has been in use by the World-Wide Web global information initiative
4627   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4628   was a simple protocol for hypertext data transfer across the Internet
4629   with only a single request method (GET) and no metadata.
4630   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4631   methods and MIME-like messaging that could include metadata about the data
4632   transferred and modifiers on the request/response semantics. However,
4633   HTTP/1.0 did not sufficiently take into consideration the effects of
4634   hierarchical proxies, caching, the need for persistent connections, or
4635   name-based virtual hosts. The proliferation of incompletely-implemented
4636   applications calling themselves "HTTP/1.0" further necessitated a
4637   protocol version change in order for two communicating applications
4638   to determine each other's true capabilities.
4639</t>
4640<t>
4641   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4642   requirements that enable reliable implementations, adding only
4643   those new features that will either be safely ignored by an HTTP/1.0
4644   recipient or only sent when communicating with a party advertising
4645   conformance with HTTP/1.1.
4646</t>
4647<t>
4648   It is beyond the scope of a protocol specification to mandate
4649   conformance with previous versions. HTTP/1.1 was deliberately
4650   designed, however, to make supporting previous versions easy.
4651   We would expect a general-purpose HTTP/1.1 server to understand
4652   any valid request in the format of HTTP/1.0 and respond appropriately
4653   with an HTTP/1.1 message that only uses features understood (or
4654   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4655   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4656</t>
4657<t>
4658   Since HTTP/0.9 did not support header fields in a request,
4659   there is no mechanism for it to support name-based virtual
4660   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4661   field).  Any server that implements name-based virtual hosts
4662   ought to disable support for HTTP/0.9.  Most requests that
4663   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4664   requests wherein a buggy client failed to properly encode
4665   linear whitespace found in a URI reference and placed in
4666   the request-target.
4667</t>
4668
4669<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4670<t>
4671   This section summarizes major differences between versions HTTP/1.0
4672   and HTTP/1.1.
4673</t>
4674
4675<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4676<t>
4677   The requirements that clients and servers support the <x:ref>Host</x:ref>
4678   header field (<xref target="header.host"/>), report an error if it is
4679   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4680   are among the most important changes defined by HTTP/1.1.
4681</t>
4682<t>
4683   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4684   addresses and servers; there was no other established mechanism for
4685   distinguishing the intended server of a request than the IP address
4686   to which that request was directed. The <x:ref>Host</x:ref> header field was
4687   introduced during the development of HTTP/1.1 and, though it was
4688   quickly implemented by most HTTP/1.0 browsers, additional requirements
4689   were placed on all HTTP/1.1 requests in order to ensure complete
4690   adoption.  At the time of this writing, most HTTP-based services
4691   are dependent upon the Host header field for targeting requests.
4692</t>
4693</section>
4694
4695<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4696<t>
4697   In HTTP/1.0, each connection is established by the client prior to the
4698   request and closed by the server after sending the response. However, some
4699   implementations implement the explicitly negotiated ("Keep-Alive") version
4700   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4701   target="RFC2068"/>.
4702</t>
4703<t>
4704   Some clients and servers might wish to be compatible with these previous
4705   approaches to persistent connections, by explicitly negotiating for them
4706   with a "Connection: keep-alive" request header field. However, some
4707   experimental implementations of HTTP/1.0 persistent connections are faulty;
4708   for example, if a HTTP/1.0 proxy server doesn't understand
4709   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4710   to the next inbound server, which would result in a hung connection.
4711</t>
4712<t>
4713   One attempted solution was the introduction of a Proxy-Connection header
4714   field, targeted specifically at proxies. In practice, this was also
4715   unworkable, because proxies are often deployed in multiple layers, bringing
4716   about the same problem discussed above.
4717</t>
4718<t>
4719   As a result, clients are encouraged not to send the Proxy-Connection header
4720   field in any requests.
4721</t>
4722<t>
4723   Clients are also encouraged to consider the use of Connection: keep-alive
4724   in requests carefully; while they can enable persistent connections with
4725   HTTP/1.0 servers, clients using them need will need to monitor the
4726   connection for "hung" requests (which indicate that the client ought stop
4727   sending the header field), and this mechanism ought not be used by clients
4728   at all when a proxy is being used.
4729</t>
4730</section>
4731
4732<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4733<t>
4734   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4735   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4736   any transfer-coding prior to forwarding a message via a MIME-compliant
4737   protocol.
4738</t>
4739</section>
4740
4741</section>
4742
4743<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4744<t>
4745  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4746  sensitive. Restrict the version numbers to be single digits due to the fact
4747  that implementations are known to handle multi-digit version numbers
4748  incorrectly.
4749  (<xref target="http.version"/>)
4750</t>
4751<t>
4752  Require that invalid whitespace around field-names be rejected.
4753  Change ABNF productions for header fields to only define the field value.
4754  (<xref target="header.fields"/>)
4755</t>
4756<t>
4757  Rules about implicit linear whitespace between certain grammar productions
4758  have been removed; now whitespace is only allowed where specifically
4759  defined in the ABNF.
4760  (<xref target="whitespace"/>)
4761</t>
4762<t> 
4763  The NUL octet is no longer allowed in comment and quoted-string
4764  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4765  Non-ASCII content in header fields and reason phrase has been obsoleted and
4766  made opaque (the TEXT rule was removed).
4767  (<xref target="field.components"/>)
4768</t>
4769<t>
4770  Require recipients to handle bogus "<x:ref>Content-Length</x:ref>" header
4771  fields as errors.
4772  (<xref target="message.body"/>)
4773</t>
4774<t>
4775  Remove reference to non-existent identity transfer-coding value tokens.
4776  (Sections <xref format="counter" target="message.body"/> and
4777  <xref format="counter" target="transfer.codings"/>)
4778</t>
4779<t>
4780  Clarification that the chunk length does not include the count of the octets
4781  in the chunk header and trailer. Furthermore disallowed line folding
4782  in chunk extensions, and deprecate their use.
4783  (<xref target="chunked.encoding"/>)
4784</t>
4785<t>
4786  Update use of abs_path production from RFC 1808 to the path-absolute + query
4787  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4788  request method only.
4789  (<xref target="request-target"/>)
4790</t>
4791<t>
4792  Clarify exactly when "close" connection options have to be sent; drop
4793  notion of header fields being "hop-by-hop" without being listed in the
4794  Connection header field.
4795  (<xref target="header.connection"/>)
4796</t>
4797<t>
4798  Remove hard limit of two connections per server.
4799  Remove requirement to retry a sequence of requests as long it was idempotent.
4800  Remove requirements about when servers are allowed to close connections
4801  prematurely.
4802  (<xref target="persistent.connections"/>)
4803</t>
4804<t>
4805  Remove requirement to retry requests under certain circumstances when the
4806  server prematurely closes the connection.
4807  (<xref target="persistent.reuse"/>)
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  Registration of Transfer Codings now requires IETF Review
4816  (<xref target="transfer.coding.registry"/>)
4817</t>
4818<t>
4819  Take over the Upgrade Token Registry, previously defined in
4820  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4821  (<xref target="upgrade.token.registry"/>)
4822</t>
4823<t>
4824  Empty list elements in list productions have been deprecated.
4825  (<xref target="abnf.extension"/>)
4826</t>
4827</section>
4828</section>
4829
4830<section title="ABNF list extension: #rule" anchor="abnf.extension">
4831<t>
4832  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4833  improve readability in the definitions of some header field values.
4834</t>
4835<t>
4836  A construct "#" is defined, similar to "*", for defining comma-delimited
4837  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4838  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4839  comma (",") and optional whitespace (OWS).   
4840</t>
4841<figure><preamble>
4842  Thus,
4843</preamble><artwork type="example">
4844  1#element =&gt; element *( OWS "," OWS element )
4845</artwork></figure>
4846<figure><preamble>
4847  and:
4848</preamble><artwork type="example">
4849  #element =&gt; [ 1#element ]
4850</artwork></figure>
4851<figure><preamble>
4852  and for n &gt;= 1 and m &gt; 1:
4853</preamble><artwork type="example">
4854  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4855</artwork></figure>
4856<t>
4857  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4858  list elements. In other words, consumers would follow the list productions:
4859</t>
4860<figure><artwork type="example">
4861  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4862 
4863  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4864</artwork></figure>
4865<t>
4866  Note that empty elements do not contribute to the count of elements present,
4867  though.
4868</t>
4869<t>
4870  For example, given these ABNF productions:
4871</t>
4872<figure><artwork type="example">
4873  example-list      = 1#example-list-elmt
4874  example-list-elmt = token ; see <xref target="field.components"/> 
4875</artwork></figure>
4876<t>
4877  Then these are valid values for example-list (not including the double
4878  quotes, which are present for delimitation only):
4879</t>
4880<figure><artwork type="example">
4881  "foo,bar"
4882  "foo ,bar,"
4883  "foo , ,bar,charlie   "
4884</artwork></figure>
4885<t>
4886  But these values would be invalid, as at least one non-empty element is
4887  required:
4888</t>
4889<figure><artwork type="example">
4890  ""
4891  ","
4892  ",   ,"
4893</artwork></figure>
4894<t>
4895  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4896  expanded as explained above.
4897</t>
4898</section>
4899
4900<?BEGININC p1-messaging.abnf-appendix ?>
4901<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4902<figure>
4903<artwork type="abnf" name="p1-messaging.parsed-abnf">
4904<x:ref>BWS</x:ref> = OWS
4905
4906<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4907 connection-option ] )
4908<x:ref>Content-Length</x:ref> = 1*DIGIT
4909
4910<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4911 ]
4912<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4913<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4914<x:ref>Host</x:ref> = uri-host [ ":" port ]
4915
4916<x:ref>OWS</x:ref> = *( SP / HTAB )
4917
4918<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4919
4920<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4921<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4922<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4923 transfer-coding ] )
4924
4925<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4926<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4927
4928<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4929 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4930 comment ] ) ] )
4931
4932<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4933<x:ref>absolute-form</x:ref> = absolute-URI
4934<x:ref>asterisk-form</x:ref> = "*"
4935<x:ref>attribute</x:ref> = token
4936<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4937<x:ref>authority-form</x:ref> = authority
4938
4939<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4940<x:ref>chunk-data</x:ref> = 1*OCTET
4941<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4942<x:ref>chunk-ext-name</x:ref> = token
4943<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4944<x:ref>chunk-size</x:ref> = 1*HEXDIG
4945<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4946<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4947<x:ref>connection-option</x:ref> = token
4948<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4949 / %x2A-5B ; '*'-'['
4950 / %x5D-7E ; ']'-'~'
4951 / obs-text
4952
4953<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4954<x:ref>field-name</x:ref> = token
4955<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4956
4957<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4958<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4959<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4960
4961<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4962
4963<x:ref>message-body</x:ref> = *OCTET
4964<x:ref>method</x:ref> = token
4965
4966<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4967<x:ref>obs-text</x:ref> = %x80-FF
4968<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4969
4970<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4971<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4972<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4973<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4974<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4975<x:ref>protocol-name</x:ref> = token
4976<x:ref>protocol-version</x:ref> = token
4977<x:ref>pseudonym</x:ref> = token
4978
4979<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4980 / %x5D-7E ; ']'-'~'
4981 / obs-text
4982<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4983 / %x5D-7E ; ']'-'~'
4984 / obs-text
4985<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4986<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4987<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4988<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4989<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4990
4991<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4992<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4993<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4994<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4995<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4996<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4997<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4998 asterisk-form
4999
5000<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5001 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5002<x:ref>start-line</x:ref> = request-line / status-line
5003<x:ref>status-code</x:ref> = 3DIGIT
5004<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5005
5006<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5007<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5008<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5009 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5010<x:ref>token</x:ref> = 1*tchar
5011<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5012<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5013 transfer-extension
5014<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5015<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5016
5017<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5018
5019<x:ref>value</x:ref> = word
5020
5021<x:ref>word</x:ref> = token / quoted-string
5022</artwork>
5023</figure>
5024</section>
5025<?ENDINC p1-messaging.abnf-appendix ?>
5026
5027<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5028
5029<section title="Since RFC 2616">
5030<t>
5031  Extracted relevant partitions from <xref target="RFC2616"/>.
5032</t>
5033</section>
5034
5035<section title="Since draft-ietf-httpbis-p1-messaging-00">
5036<t>
5037  Closed issues:
5038  <list style="symbols"> 
5039    <t>
5040      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5041      "HTTP Version should be case sensitive"
5042      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5043    </t>
5044    <t>
5045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5046      "'unsafe' characters"
5047      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5048    </t>
5049    <t>
5050      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5051      "Chunk Size Definition"
5052      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5053    </t>
5054    <t>
5055      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5056      "Message Length"
5057      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5058    </t>
5059    <t>
5060      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5061      "Media Type Registrations"
5062      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5063    </t>
5064    <t>
5065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5066      "URI includes query"
5067      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5068    </t>
5069    <t>
5070      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5071      "No close on 1xx responses"
5072      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5073    </t>
5074    <t>
5075      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5076      "Remove 'identity' token references"
5077      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5078    </t>
5079    <t>
5080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5081      "Import query BNF"
5082    </t>
5083    <t>
5084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5085      "qdtext BNF"
5086    </t>
5087    <t>
5088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5089      "Normative and Informative references"
5090    </t>
5091    <t>
5092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5093      "RFC2606 Compliance"
5094    </t>
5095    <t>
5096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5097      "RFC977 reference"
5098    </t>
5099    <t>
5100      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5101      "RFC1700 references"
5102    </t>
5103    <t>
5104      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5105      "inconsistency in date format explanation"
5106    </t>
5107    <t>
5108      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5109      "Date reference typo"
5110    </t>
5111    <t>
5112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5113      "Informative references"
5114    </t>
5115    <t>
5116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5117      "ISO-8859-1 Reference"
5118    </t>
5119    <t>
5120      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5121      "Normative up-to-date references"
5122    </t>
5123  </list>
5124</t>
5125<t>
5126  Other changes:
5127  <list style="symbols"> 
5128    <t>
5129      Update media type registrations to use RFC4288 template.
5130    </t>
5131    <t>
5132      Use names of RFC4234 core rules DQUOTE and HTAB,
5133      fix broken ABNF for chunk-data
5134      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5135    </t>
5136  </list>
5137</t>
5138</section>
5139
5140<section title="Since draft-ietf-httpbis-p1-messaging-01">
5141<t>
5142  Closed issues:
5143  <list style="symbols"> 
5144    <t>
5145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5146      "Bodies on GET (and other) requests"
5147    </t>
5148    <t>
5149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5150      "Updating to RFC4288"
5151    </t>
5152    <t>
5153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5154      "Status Code and Reason Phrase"
5155    </t>
5156    <t>
5157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5158      "rel_path not used"
5159    </t>
5160  </list>
5161</t>
5162<t>
5163  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5164  <list style="symbols"> 
5165    <t>
5166      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5167      "trailer-part").
5168    </t>
5169    <t>
5170      Avoid underscore character in rule names ("http_URL" ->
5171      "http-URL", "abs_path" -> "path-absolute").
5172    </t>
5173    <t>
5174      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5175      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5176      have to be updated when switching over to RFC3986.
5177    </t>
5178    <t>
5179      Synchronize core rules with RFC5234.
5180    </t>
5181    <t>
5182      Get rid of prose rules that span multiple lines.
5183    </t>
5184    <t>
5185      Get rid of unused rules LOALPHA and UPALPHA.
5186    </t>
5187    <t>
5188      Move "Product Tokens" section (back) into Part 1, as "token" is used
5189      in the definition of the Upgrade header field.
5190    </t>
5191    <t>
5192      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5193    </t>
5194    <t>
5195      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5196    </t>
5197  </list>
5198</t>
5199</section>
5200
5201<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5202<t>
5203  Closed issues:
5204  <list style="symbols"> 
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5207      "HTTP-date vs. rfc1123-date"
5208    </t>
5209    <t>
5210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5211      "WS in quoted-pair"
5212    </t>
5213  </list>
5214</t>
5215<t>
5216  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5217  <list style="symbols"> 
5218    <t>
5219      Reference RFC 3984, and update header field registrations for header
5220      fields defined in this document.
5221    </t>
5222  </list>
5223</t>
5224<t>
5225  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5226  <list style="symbols"> 
5227    <t>
5228      Replace string literals when the string really is case-sensitive (HTTP-version).
5229    </t>
5230  </list>
5231</t>
5232</section>
5233
5234<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5235<t>
5236  Closed issues:
5237  <list style="symbols"> 
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5240      "Connection closing"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5244      "Move registrations and registry information to IANA Considerations"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5248      "need new URL for PAD1995 reference"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5252      "IANA Considerations: update HTTP URI scheme registration"
5253    </t>
5254    <t>
5255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5256      "Cite HTTPS URI scheme definition"
5257    </t>
5258    <t>
5259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5260      "List-type header fields vs Set-Cookie"
5261    </t>
5262  </list>
5263</t>
5264<t>
5265  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5266  <list style="symbols"> 
5267    <t>
5268      Replace string literals when the string really is case-sensitive (HTTP-Date).
5269    </t>
5270    <t>
5271      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5272    </t>
5273  </list>
5274</t>
5275</section>
5276
5277<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5278<t>
5279  Closed issues:
5280  <list style="symbols"> 
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5283      "Out-of-date reference for URIs"
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5287      "RFC 2822 is updated by RFC 5322"
5288    </t>
5289  </list>
5290</t>
5291<t>
5292  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5293  <list style="symbols"> 
5294    <t>
5295      Use "/" instead of "|" for alternatives.
5296    </t>
5297    <t>
5298      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5299    </t>
5300    <t>
5301      Only reference RFC 5234's core rules.
5302    </t>
5303    <t>
5304      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5305      whitespace ("OWS") and required whitespace ("RWS").
5306    </t>
5307    <t>
5308      Rewrite ABNFs to spell out whitespace rules, factor out
5309      header field value format definitions.
5310    </t>
5311  </list>
5312</t>
5313</section>
5314
5315<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5316<t>
5317  Closed issues:
5318  <list style="symbols"> 
5319    <t>
5320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5321      "Header LWS"
5322    </t>
5323    <t>
5324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5325      "Sort 1.3 Terminology"
5326    </t>
5327    <t>
5328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5329      "RFC2047 encoded words"
5330    </t>
5331    <t>
5332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5333      "Character Encodings in TEXT"
5334    </t>
5335    <t>
5336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5337      "Line Folding"
5338    </t>
5339    <t>
5340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5341      "OPTIONS * and proxies"
5342    </t>
5343    <t>
5344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5345      "reason-phrase BNF"
5346    </t>
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5349      "Use of TEXT"
5350    </t>
5351    <t>
5352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5353      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5354    </t>
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5357      "RFC822 reference left in discussion of date formats"
5358    </t>
5359  </list>
5360</t>
5361<t>
5362  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5363  <list style="symbols"> 
5364    <t>
5365      Rewrite definition of list rules, deprecate empty list elements.
5366    </t>
5367    <t>
5368      Add appendix containing collected and expanded ABNF.
5369    </t>
5370  </list>
5371</t>
5372<t>
5373  Other changes:
5374  <list style="symbols"> 
5375    <t>
5376      Rewrite introduction; add mostly new Architecture Section.
5377    </t>
5378    <t>
5379      Move definition of quality values from Part 3 into Part 1;
5380      make TE request header field grammar independent of accept-params (defined in Part 3).
5381    </t>
5382  </list>
5383</t>
5384</section>
5385
5386<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5387<t>
5388  Closed issues:
5389  <list style="symbols"> 
5390    <t>
5391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5392      "base for numeric protocol elements"
5393    </t>
5394    <t>
5395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5396      "comment ABNF"
5397    </t>
5398  </list>
5399</t>
5400<t>
5401  Partly resolved issues:
5402  <list style="symbols"> 
5403    <t>
5404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5405      "205 Bodies" (took out language that implied that there might be
5406      methods for which a request body MUST NOT be included)
5407    </t>
5408    <t>
5409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5410      "editorial improvements around HTTP-date"
5411    </t>
5412  </list>
5413</t>
5414</section>
5415
5416<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5417<t>
5418  Closed issues:
5419  <list style="symbols"> 
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5422      "Repeating single-value header fields"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5426      "increase connection limit"
5427    </t>
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5430      "IP addresses in URLs"
5431    </t>
5432    <t>
5433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5434      "take over HTTP Upgrade Token Registry"
5435    </t>
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5438      "CR and LF in chunk extension values"
5439    </t>
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5442      "HTTP/0.9 support"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5446      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5447    </t>
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5450      "move definitions of gzip/deflate/compress to part 1"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5454      "disallow control characters in quoted-pair"
5455    </t>
5456  </list>
5457</t>
5458<t>
5459  Partly resolved issues:
5460  <list style="symbols"> 
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5463      "update IANA requirements wrt Transfer-Coding values" (add the
5464      IANA Considerations subsection)
5465    </t>
5466  </list>
5467</t>
5468</section>
5469
5470<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5471<t>
5472  Closed issues:
5473  <list style="symbols"> 
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5476      "header parsing, treatment of leading and trailing OWS"
5477    </t>
5478  </list>
5479</t>
5480<t>
5481  Partly resolved issues:
5482  <list style="symbols"> 
5483    <t>
5484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5485      "Placement of 13.5.1 and 13.5.2"
5486    </t>
5487    <t>
5488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5489      "use of term "word" when talking about header field structure"
5490    </t>
5491  </list>
5492</t>
5493</section>
5494
5495<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5496<t>
5497  Closed issues:
5498  <list style="symbols"> 
5499    <t>
5500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5501      "Clarification of the term 'deflate'"
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5505      "OPTIONS * and proxies"
5506    </t>
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5509      "MIME-Version not listed in P1, general header fields"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5513      "IANA registry for content/transfer encodings"
5514    </t>
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5517      "Case-sensitivity of HTTP-date"
5518    </t>
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5521      "use of term "word" when talking about header field structure"
5522    </t>
5523  </list>
5524</t>
5525<t>
5526  Partly resolved issues:
5527  <list style="symbols"> 
5528    <t>
5529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5530      "Term for the requested resource's URI"
5531    </t>
5532  </list>
5533</t>
5534</section>
5535
5536<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5537<t>
5538  Closed issues:
5539  <list style="symbols">
5540    <t>
5541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5542      "Connection Closing"
5543    </t>
5544    <t>
5545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5546      "Delimiting messages with multipart/byteranges"
5547    </t>
5548    <t>
5549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5550      "Handling multiple Content-Length header fields"
5551    </t>
5552    <t>
5553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5554      "Clarify entity / representation / variant terminology"
5555    </t>
5556    <t>
5557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5558      "consider removing the 'changes from 2068' sections"
5559    </t>
5560  </list>
5561</t>
5562<t>
5563  Partly resolved issues:
5564  <list style="symbols"> 
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5567      "HTTP(s) URI scheme definitions"
5568    </t>
5569  </list>
5570</t>
5571</section>
5572
5573<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5574<t>
5575  Closed issues:
5576  <list style="symbols">
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5579      "Trailer requirements"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5583      "Text about clock requirement for caches belongs in p6"
5584    </t>
5585    <t>
5586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5587      "effective request URI: handling of missing host in HTTP/1.0"
5588    </t>
5589    <t>
5590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5591      "confusing Date requirements for clients"
5592    </t>
5593  </list>
5594</t>
5595<t>
5596  Partly resolved issues:
5597  <list style="symbols"> 
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5600      "Handling multiple Content-Length header fields"
5601    </t>
5602  </list>
5603</t>
5604</section>
5605
5606<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5607<t>
5608  Closed issues:
5609  <list style="symbols">
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5612      "RFC2145 Normative"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5616      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5620      "define 'transparent' proxy"
5621    </t>
5622    <t>
5623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5624      "Header Field Classification"
5625    </t>
5626    <t>
5627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5628      "Is * usable as a request-uri for new methods?"
5629    </t>
5630    <t>
5631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5632      "Migrate Upgrade details from RFC2817"
5633    </t>
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5636      "untangle ABNFs for header fields"
5637    </t>
5638    <t>
5639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5640      "update RFC 2109 reference"
5641    </t>
5642  </list>
5643</t>
5644</section>
5645
5646<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5647<t>
5648  Closed issues:
5649  <list style="symbols">
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5652      "Allow is not in 13.5.2"
5653    </t>
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5656      "Handling multiple Content-Length header fields"
5657    </t>
5658    <t>
5659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5660      "untangle ABNFs for header fields"
5661    </t>
5662    <t>
5663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5664      "Content-Length ABNF broken"
5665    </t>
5666  </list>
5667</t>
5668</section>
5669
5670<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5671<t>
5672  Closed issues:
5673  <list style="symbols">
5674    <t>
5675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5676      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5677    </t>
5678    <t>
5679      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5680      "Recommend minimum sizes for protocol elements"
5681    </t>
5682    <t>
5683      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5684      "Set expectations around buffering"
5685    </t>
5686    <t>
5687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5688      "Considering messages in isolation"
5689    </t>
5690  </list>
5691</t>
5692</section>
5693
5694<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5695<t>
5696  Closed issues:
5697  <list style="symbols">
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5700      "DNS Spoofing / DNS Binding advice"
5701    </t>
5702    <t>
5703      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5704      "move RFCs 2145, 2616, 2817 to Historic status"
5705    </t>
5706    <t>
5707      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5708      "\-escaping in quoted strings"
5709    </t>
5710    <t>
5711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5712      "'Close' should be reserved in the HTTP header field registry"
5713    </t>
5714  </list>
5715</t>
5716</section>
5717
5718<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5719<t>
5720  Closed issues:
5721  <list style="symbols">
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5724      "Document HTTP's error-handling philosophy"
5725    </t>
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5728      "Explain header field registration"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5732      "Revise Acknowledgements Sections"
5733    </t>
5734    <t>
5735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5736      "Retrying Requests"
5737    </t>
5738    <t>
5739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5740      "Closing the connection on server error"
5741    </t>
5742  </list>
5743</t>
5744</section>
5745
5746<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5747<t>
5748  Closed issues:
5749  <list style="symbols">
5750    <t>
5751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5752      "Proxy-Connection and Keep-Alive"
5753    </t>
5754    <t>
5755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5756      "Clarify 'User Agent'"
5757    </t>
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5760      "Define non-final responses"
5761    </t>
5762    <t>
5763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5764      "intended maturity level vs normative references"
5765    </t>
5766    <t>
5767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5768      "Intermediary rewriting of queries"
5769    </t>
5770  </list>
5771</t>
5772</section>
5773
5774<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5775<t>
5776  Closed issues:
5777  <list style="symbols">
5778    <t>
5779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5780      "message-body in CONNECT response"
5781    </t>
5782    <t>
5783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5784      "Misplaced text on connection handling in p2"
5785    </t>
5786    <t>
5787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5788      "wording of line folding rule"
5789    </t>
5790    <t>
5791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5792      "chunk-extensions"
5793    </t>
5794    <t>
5795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5796      "make IANA policy definitions consistent"
5797    </t>
5798  </list>
5799</t>
5800</section>
5801
5802<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5803<t>
5804  Closed issues:
5805  <list style="symbols">
5806    <t>
5807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5808      "make IANA policy definitions consistent"
5809    </t>
5810    <t>
5811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5812      "clarify connection header field values are case-insensitive"
5813    </t>
5814    <t>
5815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5816      "ABNF requirements for recipients"
5817    </t>
5818    <t>
5819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5820      "note introduction of new IANA registries as normative changes"
5821    </t>
5822    <t>
5823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5824      "Reference to ISO-8859-1 is informative"
5825    </t>
5826  </list>
5827</t>
5828</section>
5829
5830<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5831<t>
5832  Closed issues:
5833  <list style="symbols"> 
5834    <t>
5835      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/378"/>:
5836      "is 'q=' case-sensitive?"
5837    </t>
5838  </list>
5839</t>
5840<t>
5841  Other changes:
5842  <list style="symbols">
5843    <t>
5844      Drop notion of header fields being "hop-by-hop" without being listed in
5845      the Connection header field.     
5846    </t>
5847    <t>
5848      Section about connection management rewritten; dropping some historic
5849      information.
5850    </t>
5851    <t>
5852      Move description of "100-continue" into Part 2.
5853    </t>
5854    <t>
5855      Rewrite the persistent connection and Upgrade requirements to be
5856      actionable by role and consistent with the rest of HTTP.
5857    </t>
5858  </list>
5859</t>
5860</section>
5861
5862</section>
5863
5864</back>
5865</rfc>
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