Ignore:
Timestamp:
14/06/14 11:20:37 (8 years ago)
Author:
julian.reschke@…
Message:

update to latest version of rfc2629.xslt, regen all HTML

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1 edited

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  • draft-ietf-httpbis/05/p1-messaging.html

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    389398      <link rel="Appendix" title="D Terminology" href="#rfc.section.D">
    390399      <link rel="Appendix" title="E Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.E">
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    392401      <link rel="schema.dct" href="http://purl.org/dc/terms/">
    393402      <meta name="dct.creator" content="Fielding, R.">
     
    418427            </tr>
    419428            <tr>
    420                <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
     429               <td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a> (if approved)
    421430               </td>
    422431               <td class="right">J. Gettys</td>
     
    489498      </table>
    490499      <p class="title">HTTP/1.1, part 1: URIs, Connections, and Message Parsing<br><span class="filename">draft-ietf-httpbis-p1-messaging-05</span></p>
    491       <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
    492       <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she
    493          is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section
    494          6 of BCP 79.
    495       </p>
    496       <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note
    497          that other groups may also distribute working documents as Internet-Drafts.
    498       </p>
    499       <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
    500          documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
    501          in progress”.
    502       </p>
    503       <p>The list of current Internet-Drafts can be accessed at <a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>.
    504       </p>
    505       <p>The list of Internet-Draft Shadow Directories can be accessed at <a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>.
    506       </p>
    507       <p>This Internet-Draft will expire on May 20, 2009.</p>
    508       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
     500      <div id="rfc.status">
     501         <h1><a href="#rfc.status">Status of this Memo</a></h1>
     502         <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she
     503            is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section
     504            6 of BCP 79.
     505         </p>
     506         <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note
     507            that other groups may also distribute working documents as Internet-Drafts.
     508         </p>
     509         <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
     510            documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
     511            in progress”.
     512         </p>
     513         <p>The list of current Internet-Drafts can be accessed at <a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>.
     514         </p>
     515         <p>The list of Internet-Draft Shadow Directories can be accessed at <a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>.
     516         </p>
     517         <p>This Internet-Draft will expire on May 20, 2009.</p>
     518      </div>
     519      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    509520      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
    510521         systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 1 of the
     
    513524         (URI) schemes, defines the generic message syntax and parsing requirements for HTTP message frames, and describes general
    514525         security concerns for implementations.
    515       </p> 
    516       <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 
     526      </p>
     527      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
    517528      <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues
    518529         list is at &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/report/11">http://tools.ietf.org/wg/httpbis/trac/report/11</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>&gt;.
    519       </p> 
     530      </p>
    520531      <p>The changes in this draft are summarized in <a href="#changes.since.04" title="Since draft-ietf-httpbis-p1-messaging-04">Appendix&nbsp;E.6</a>.
    521       </p> 
     532      </p>
    522533      <hr class="noprint">
    523534      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    524535      <ul class="toc">
    525          <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    526                <li>1.1&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
    527                <li>1.2&nbsp;&nbsp;&nbsp;<a href="#intro.overall.operation">Overall Operation</a></li>
     536         <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
     537               <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
     538               <li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#intro.overall.operation">Overall Operation</a></li>
    528539            </ul>
    529540         </li>
    530          <li>2.&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a><ul>
    531                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></li>
    532                <li>2.2&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
    533                <li>2.3&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
     541         <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a><ul>
     542               <li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></li>
     543               <li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
     544               <li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
    534545            </ul>
    535546         </li>
    536          <li>3.&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
    537                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
    538                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
    539                      <li>3.2.1&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI scheme</a></li>
    540                      <li>3.2.2&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">URI Comparison</a></li>
     547         <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
     548               <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
     549               <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
     550                     <li><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI scheme</a></li>
     551                     <li><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">URI Comparison</a></li>
    541552                  </ul>
    542553               </li>
    543                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#date.time.formats">Date/Time Formats</a><ul>
    544                      <li>3.3.1&nbsp;&nbsp;&nbsp;<a href="#full.date">Full Date</a></li>
     554               <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#date.time.formats">Date/Time Formats</a><ul>
     555                     <li><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#full.date">Full Date</a></li>
    545556                  </ul>
    546557               </li>
    547                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
    548                      <li>3.4.1&nbsp;&nbsp;&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li>
     558               <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
     559                     <li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li>
    549560                  </ul>
    550561               </li>
    551                <li>3.5&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
     562               <li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
    552563            </ul>
    553564         </li>
    554          <li>4.&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
    555                <li>4.1&nbsp;&nbsp;&nbsp;<a href="#message.types">Message Types</a></li>
    556                <li>4.2&nbsp;&nbsp;&nbsp;<a href="#message.headers">Message Headers</a></li>
    557                <li>4.3&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
    558                <li>4.4&nbsp;&nbsp;&nbsp;<a href="#message.length">Message Length</a></li>
    559                <li>4.5&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
     565         <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
     566               <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#message.types">Message Types</a></li>
     567               <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.headers">Message Headers</a></li>
     568               <li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
     569               <li><a href="#rfc.section.4.4">4.4</a>&nbsp;&nbsp;&nbsp;<a href="#message.length">Message Length</a></li>
     570               <li><a href="#rfc.section.4.5">4.5</a>&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
    560571            </ul>
    561572         </li>
    562          <li>5.&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
    563                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
    564                      <li>5.1.1&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
    565                      <li>5.1.2&nbsp;&nbsp;&nbsp;<a href="#request-uri">Request-URI</a></li>
     573         <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
     574               <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
     575                     <li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
     576                     <li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#request-uri">Request-URI</a></li>
    566577                  </ul>
    567578               </li>
    568                <li>5.2&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
     579               <li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
    569580            </ul>
    570581         </li>
    571          <li>6.&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
    572                <li>6.1&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
    573                      <li>6.1.1&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
     582         <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
     583               <li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
     584                     <li><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
    574585                  </ul>
    575586               </li>
    576587            </ul>
    577588         </li>
    578          <li>7.&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
    579                <li>7.1&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
    580                      <li>7.1.1&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
    581                      <li>7.1.2&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a><ul>
    582                            <li>7.1.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.negotiation">Negotiation</a></li>
    583                            <li>7.1.2.2&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li>
    584                         </ul>
    585                      </li>
    586                      <li>7.1.3&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a></li>
    587                      <li>7.1.4&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
     589         <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
     590               <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
     591                     <li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
     592                     <li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a></li>
     593                     <li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a></li>
     594                     <li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
    588595                  </ul>
    589596               </li>
    590                <li>7.2&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
    591                      <li>7.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
    592                      <li>7.2.2&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
    593                      <li>7.2.3&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
    594                      <li>7.2.4&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
     597               <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
     598                     <li><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
     599                     <li><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
     600                     <li><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
     601                     <li><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
    595602                  </ul>
    596603               </li>
    597604            </ul>
    598605         </li>
    599          <li>8.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul>
    600                <li>8.1&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
    601                <li>8.2&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
    602                <li>8.3&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
    603                      <li>8.3.1&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
     606         <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul>
     607               <li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
     608               <li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
     609               <li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
     610                     <li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
    604611                  </ul>
    605612               </li>
    606                <li>8.4&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
    607                <li>8.5&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
    608                <li>8.6&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
    609                <li>8.7&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
    610                <li>8.8&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li>
    611                <li>8.9&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
     613               <li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
     614               <li><a href="#rfc.section.8.5">8.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
     615               <li><a href="#rfc.section.8.6">8.6</a>&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
     616               <li><a href="#rfc.section.8.7">8.7</a>&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
     617               <li><a href="#rfc.section.8.8">8.8</a>&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li>
     618               <li><a href="#rfc.section.8.9">8.9</a>&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
    612619            </ul>
    613620         </li>
    614          <li>9.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
    615                <li>9.1&nbsp;&nbsp;&nbsp;<a href="#message.header.registration">Message Header Registration</a></li>
    616                <li>9.2&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li>
    617                <li>9.3&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registrations</a><ul>
    618                      <li>9.3.1&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li>
    619                      <li>9.3.2&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li>
     621         <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
     622               <li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#message.header.registration">Message Header Registration</a></li>
     623               <li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li>
     624               <li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registrations</a><ul>
     625                     <li><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li>
     626                     <li><a href="#rfc.section.9.3.2">9.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li>
    620627                  </ul>
    621628               </li>
    622629            </ul>
    623630         </li>
    624          <li>10.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
    625                <li>10.1&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a></li>
    626                <li>10.2&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
    627                <li>10.3&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
    628                <li>10.4&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
    629                <li>10.5&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a></li>
    630                <li>10.6&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
     631         <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
     632               <li><a href="#rfc.section.10.1">10.1</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a></li>
     633               <li><a href="#rfc.section.10.2">10.2</a>&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
     634               <li><a href="#rfc.section.10.3">10.3</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
     635               <li><a href="#rfc.section.10.4">10.4</a>&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
     636               <li><a href="#rfc.section.10.5">10.5</a>&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a></li>
     637               <li><a href="#rfc.section.10.6">10.6</a>&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
    631638            </ul>
    632639         </li>
    633          <li>11.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
    634          <li>12.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
    635                <li>12.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    636                <li>12.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     640         <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
     641         <li><a href="#rfc.section.12">12.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
     642               <li><a href="#rfc.section.12.1">12.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     643               <li><a href="#rfc.section.12.2">12.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    637644            </ul>
    638645         </li>
    639          <li><a href="#rfc.authors">Authors' Addresses</a></li>
    640          <li>A.&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
    641          <li>B.&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
    642          <li>C.&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
    643                <li>C.1&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
    644                      <li>C.1.1&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
     646         <li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
     647         <li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
     648         <li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
     649               <li><a href="#rfc.section.C.1">C.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
     650                     <li><a href="#rfc.section.C.1.1">C.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
    645651                  </ul>
    646652               </li>
    647                <li>C.2&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
    648                <li>C.3&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
    649                <li>C.4&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
     653               <li><a href="#rfc.section.C.2">C.2</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
     654               <li><a href="#rfc.section.C.3">C.3</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
     655               <li><a href="#rfc.section.C.4">C.4</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
    650656            </ul>
    651657         </li>
    652          <li>D.&nbsp;&nbsp;&nbsp;<a href="#terminology">Terminology</a></li>
    653          <li>E.&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
    654                <li>E.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.1">Since RFC2616</a></li>
    655                <li>E.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.2">Since draft-ietf-httpbis-p1-messaging-00</a></li>
    656                <li>E.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.3">Since draft-ietf-httpbis-p1-messaging-01</a></li>
    657                <li>E.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li>
    658                <li>E.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p1-messaging-03</a></li>
    659                <li>E.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p1-messaging-04</a></li>
     658         <li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#terminology">Terminology</a></li>
     659         <li><a href="#rfc.section.E">E.</a>&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
     660               <li><a href="#rfc.section.E.1">E.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.1">Since RFC2616</a></li>
     661               <li><a href="#rfc.section.E.2">E.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.2">Since draft-ietf-httpbis-p1-messaging-00</a></li>
     662               <li><a href="#rfc.section.E.3">E.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.3">Since draft-ietf-httpbis-p1-messaging-01</a></li>
     663               <li><a href="#rfc.section.E.4">E.4</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li>
     664               <li><a href="#rfc.section.E.5">E.5</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p1-messaging-03</a></li>
     665               <li><a href="#rfc.section.E.6">E.6</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p1-messaging-04</a></li>
    660666            </ul>
    661667         </li>
    662668         <li><a href="#rfc.index">Index</a></li>
     669         <li><a href="#rfc.authors">Authors' Addresses</a></li>
    663670         <li><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li>
    664671      </ul>
    665       <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
    666       <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level request/response protocol that uses extensible semantics and
    667          MIME-like message payloads for flexible interaction with network-based hypermedia information systems. HTTP relies upon the
    668          Uniform Resource Identifier (URI) standard <a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> to indicate resource targets for interaction and to identify other resources. Messages are passed in a format similar to that
    669          used by Internet mail <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a> and the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a> (see <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> for the differences between HTTP and MIME messages).
    670       </p>
    671       <p id="rfc.section.1.p.2">HTTP is also designed for use as a generic protocol for translating communication to and from other Internet information systems,
    672          such as USENET news services via NNTP <a href="#RFC3977" id="rfc.xref.RFC3977.1"><cite title="Network News Transfer Protocol (NNTP)">[RFC3977]</cite></a>, file services via FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[RFC959]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[RFC1436]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[WAIS]</cite></a>. HTTP proxies and gateways provide access to alternative information services by translating their diverse protocols into
    673          a hypermedia format that can be viewed and manipulated by clients in the same way as HTTP services.
    674       </p>
    675       <p id="rfc.section.1.p.3">This document is Part 1 of the seven-part specification of HTTP, defining the protocol referred to as "HTTP/1.1" and obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. Part 1 defines how clients determine when to use HTTP, the URI schemes specific to HTTP-based resources, overall network
    676          operation with transport protocol connection management, and HTTP message framing. Our goal is to define all of the mechanisms
    677          necessary for HTTP message handling that are independent of message semantics, thereby defining the complete set of requirements
    678          for an HTTP message relay or generic message parser.
    679       </p>
    680       <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.requirements" href="#intro.requirements">Requirements</a></h2>
    681       <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
    682          in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
    683       </p>
    684       <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
    685       </p>
    686       <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="intro.overall.operation" href="#intro.overall.operation">Overall Operation</a></h2>
    687       <p id="rfc.section.1.2.p.1">HTTP is a request/response protocol. A client sends a request to the server in the form of a request method, URI, and protocol
    688          version, followed by a MIME-like message containing request modifiers, client information, and possible body content over
    689          a connection with a server. The server responds with a status line, including the message's protocol version and a success
    690          or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body
    691          content. The relationship between HTTP and MIME is described in <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
    692       </p>
    693       <p id="rfc.section.1.2.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin
    694          server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin
    695          server (O).
    696       </p>
    697       <div id="rfc.figure.u.1"></div><pre class="drawing">       request chain ------------------------&gt;
     672      <div id="introduction">
     673         <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1>
     674         <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level request/response protocol that uses extensible semantics and
     675            MIME-like message payloads for flexible interaction with network-based hypermedia information systems. HTTP relies upon the
     676            Uniform Resource Identifier (URI) standard <a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> to indicate resource targets for interaction and to identify other resources. Messages are passed in a format similar to that
     677            used by Internet mail <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a> and the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a> (see <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> for the differences between HTTP and MIME messages).
     678         </p>
     679         <p id="rfc.section.1.p.2">HTTP is also designed for use as a generic protocol for translating communication to and from other Internet information systems,
     680            such as USENET news services via NNTP <a href="#RFC3977" id="rfc.xref.RFC3977.1"><cite title="Network News Transfer Protocol (NNTP)">[RFC3977]</cite></a>, file services via FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[RFC959]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[RFC1436]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[WAIS]</cite></a>. HTTP proxies and gateways provide access to alternative information services by translating their diverse protocols into
     681            a hypermedia format that can be viewed and manipulated by clients in the same way as HTTP services.
     682         </p>
     683         <p id="rfc.section.1.p.3">This document is Part 1 of the seven-part specification of HTTP, defining the protocol referred to as "HTTP/1.1" and obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. Part 1 defines how clients determine when to use HTTP, the URI schemes specific to HTTP-based resources, overall network
     684            operation with transport protocol connection management, and HTTP message framing. Our goal is to define all of the mechanisms
     685            necessary for HTTP message handling that are independent of message semantics, thereby defining the complete set of requirements
     686            for an HTTP message relay or generic message parser.
     687         </p>
     688         <div id="intro.requirements">
     689            <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#intro.requirements">Requirements</a></h2>
     690            <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
     691               in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
     692            </p>
     693            <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
     694            </p>
     695         </div>
     696         <div id="intro.overall.operation">
     697            <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#intro.overall.operation">Overall Operation</a></h2>
     698            <p id="rfc.section.1.2.p.1">HTTP is a request/response protocol. A client sends a request to the server in the form of a request method, URI, and protocol
     699               version, followed by a MIME-like message containing request modifiers, client information, and possible body content over
     700               a connection with a server. The server responds with a status line, including the message's protocol version and a success
     701               or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body
     702               content. The relationship between HTTP and MIME is described in <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
     703            </p>
     704            <p id="rfc.section.1.2.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin
     705               server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin
     706               server (O).
     707            </p>
     708            <div id="rfc.figure.u.1"></div><pre class="drawing">       request chain ------------------------&gt;
    698709    UA -------------------v------------------- O
    699710       &lt;----------------------- response chain
    700711</pre><p id="rfc.section.1.2.p.4">A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three
    701          common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its
    702          absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by
    703          the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests
    704          to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages;
    705          tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary
    706          cannot understand the contents of the messages.
    707       </p>
    708       <div id="rfc.figure.u.2"></div><pre class="drawing">       request chain --------------------------------------&gt;
     712               common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its
     713               absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by
     714               the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests
     715               to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages;
     716               tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary
     717               cannot understand the contents of the messages.
     718            </p>
     719            <div id="rfc.figure.u.2"></div><pre class="drawing">       request chain --------------------------------------&gt;
    709720    UA -----v----- A -----v----- B -----v----- C -----v----- O
    710721       &lt;------------------------------------- response chain
    711722</pre><p id="rfc.section.1.2.p.6">The figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response
    712          message that travels the whole chain will pass through four separate connections. This distinction is important because some
    713          HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points
    714          of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple,
    715          simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests
    716          to servers other than C, at the same time that it is handling A's request.
    717       </p>
    718       <p id="rfc.section.1.2.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect
    719          of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response
    720          applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from
    721          O (via C) for a request which has not been cached by UA or A.
    722       </p>
    723       <div id="rfc.figure.u.3"></div><pre class="drawing">          request chain ----------&gt;
     723               message that travels the whole chain will pass through four separate connections. This distinction is important because some
     724               HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points
     725               of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple,
     726               simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests
     727               to servers other than C, at the same time that it is handling A's request.
     728            </p>
     729            <p id="rfc.section.1.2.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect
     730               of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response
     731               applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from
     732               O (via C) for a request which has not been cached by UA or A.
     733            </p>
     734            <div id="rfc.figure.u.3"></div><pre class="drawing">          request chain ----------&gt;
    724735       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
    725736          &lt;--------- response chain
    726737</pre><p id="rfc.section.1.2.p.9">Not all responses are usefully cacheable, and some requests may contain modifiers which place special requirements on cache
    727          behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
    728       </p>
    729       <p id="rfc.section.1.2.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with
    730          or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth,
    731          systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so
    732          on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links
    733          and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while
    734          introducing protocol constructs that meet the needs of those who build web applications that require high reliability and,
    735          failing that, at least reliable indications of failure.
    736       </p>
    737       <p id="rfc.section.1.2.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (&lt;<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>&gt;), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
    738          or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
    739          mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
    740          the scope of this specification.
    741       </p>
    742       <p id="rfc.section.1.2.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may
    743          be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>).
    744       </p>
    745       <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="notation" href="#notation">Notational Conventions and Generic Grammar</a></h1>
    746       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="notation.abnf" href="#notation.abnf">ABNF Extension: #rule</a></h2>
    747       <p id="rfc.section.2.1.p.1">One extension to the ABNF rules of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> is used to improve readability.
    748       </p>
    749       <p id="rfc.section.2.1.p.2">A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at
    750          least &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (OWS). This makes the usual form of lists very easy; a rule such as
    751       </p>
    752       <div id="rfc.figure.u.4"></div><pre class="text"> ( *<a href="#rule.whitespace" class="smpl">OWS</a> element *( *<a href="#rule.whitespace" class="smpl">OWS</a> "," *<a href="#rule.whitespace" class="smpl">OWS</a> element ))</pre><p id="rfc.section.2.1.p.3">can be shown as </p>
    753       <div id="rfc.figure.u.5"></div><pre class="text"> 1#element</pre><p id="rfc.section.2.1.p.4">Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is,
    754          "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required,
    755          at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at
    756          least one; and "1#2element" allows one or two.
    757       </p>
    758       <p id="rfc.section.2.1.p.5"> <span class="comment" id="abnf.list">[<a href="#abnf.list" class="smpl">abnf.list</a>: At a later point of time, we may want to add an appendix containing the whole ABNF, with the list rules expanded to strict
    759             RFC 5234 notation.]</span>
    760       </p>
    761       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="basic.rules" href="#basic.rules">Basic Rules</a></h2>
    762       <div id="core.rules">
    763          <p id="rfc.section.2.2.p.1">                          This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>. The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.3"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CHAR (any <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a> character, excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
    764             HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space) and
    765             WSP (white space).
    766          </p>
     738               behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
     739            </p>
     740            <p id="rfc.section.1.2.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with
     741               or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth,
     742               systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so
     743               on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links
     744               and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while
     745               introducing protocol constructs that meet the needs of those who build web applications that require high reliability and,
     746               failing that, at least reliable indications of failure.
     747            </p>
     748            <p id="rfc.section.1.2.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (&lt;<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>&gt;), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
     749               or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
     750               mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
     751               the scope of this specification.
     752            </p>
     753            <p id="rfc.section.1.2.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may
     754               be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>).
     755            </p>
     756         </div>
    767757      </div>
    768       <div id="rule.CRLF">
    769          <p id="rfc.section.2.2.p.2">  HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described
    770             in <a href="p3-payload.html#media.types" title="Media Types">Section 3.3</a> of <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
    771          </p>
    772       </div>
    773       <div id="rule.LWS">
    774          <p id="rfc.section.2.2.p.3">All linear white space (LWS) in header field-values has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any such linear white space with a single SP before interpreting the field value or forwarding the message downstream.
    775          </p>
    776       </div>
    777       <p id="rfc.section.2.2.p.4">Historically, HTTP/1.1 header field values allow linear white space folding across multiple lines. However, this specification
    778          deprecates its use; senders <em class="bcp14">MUST NOT</em> produce messages that include LWS folding (i.e., use the obs-fold rule), except within the message/http media type (<a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;9.3.1</a>). Receivers <em class="bcp14">SHOULD</em> still parse folded linear white space.
    779       </p>
    780       <p id="rfc.section.2.2.p.5">This specification uses three rules to denote the use of linear white space; BWS ("Bad" White Space), OWS (Optional White
    781          Space), and RWS (Required White Space).
    782       </p>
    783       <p id="rfc.section.2.2.p.6">"Bad" white space is allowed by the BNF, but senders <em class="bcp14">SHOULD NOT</em> produce it in messages. Receivers <em class="bcp14">MUST</em> accept it in incoming messages.
    784       </p>
    785       <p id="rfc.section.2.2.p.7">Required white space is used when at least one linear white space character is required to separate field tokens. In all such
    786          cases, a single SP character <em class="bcp14">SHOULD</em> be used.
    787       </p>
    788       <div id="rule.whitespace">
    789          <p id="rfc.section.2.2.p.8">        </p>
    790       </div>
    791       <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
     758      <div id="notation">
     759         <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a></h1>
     760         <div id="notation.abnf">
     761            <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></h2>
     762            <p id="rfc.section.2.1.p.1">One extension to the ABNF rules of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> is used to improve readability.
     763            </p>
     764            <p id="rfc.section.2.1.p.2">A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at
     765               least &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (OWS). This makes the usual form of lists very easy; a rule such as
     766            </p><span id="rfc.figure.u.4"></span><pre class="text"> ( *<a href="#rule.whitespace" class="smpl">OWS</a> element *( *<a href="#rule.whitespace" class="smpl">OWS</a> "," *<a href="#rule.whitespace" class="smpl">OWS</a> element ))</pre><p id="rfc.section.2.1.p.3">can be shown as </p><span id="rfc.figure.u.5"></span><pre class="text"> 1#element</pre><p id="rfc.section.2.1.p.4">Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is,
     767               "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required,
     768               at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at
     769               least one; and "1#2element" allows one or two.
     770            </p>
     771            <p id="rfc.section.2.1.p.5"><span class="comment" id="abnf.list">[<a href="#abnf.list" class="smpl">abnf.list</a>: At a later point of time, we may want to add an appendix containing the whole ABNF, with the list rules expanded to strict
     772                  RFC 5234 notation.]</span>
     773            </p>
     774         </div>
     775         <div id="basic.rules">
     776            <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a href="#basic.rules">Basic Rules</a></h2>
     777            <div id="core.rules">
     778               <p id="rfc.section.2.2.p.1">             This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>. The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.3"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="https://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CHAR (any <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a> character, excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
     779                  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space) and
     780                  WSP (white space).
     781               </p>
     782            </div>
     783            <div id="rule.CRLF">
     784               <p id="rfc.section.2.2.p.2"> HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described
     785                  in <a href="p3-payload.html#media.types" title="Media Types">Section 3.3</a> of <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
     786               </p>
     787            </div>
     788            <div id="rule.LWS">
     789               <p id="rfc.section.2.2.p.3">All linear white space (LWS) in header field-values has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any such linear white space with a single SP before interpreting the field value or forwarding the message downstream.
     790               </p>
     791            </div>
     792            <p id="rfc.section.2.2.p.4">Historically, HTTP/1.1 header field values allow linear white space folding across multiple lines. However, this specification
     793               deprecates its use; senders <em class="bcp14">MUST NOT</em> produce messages that include LWS folding (i.e., use the obs-fold rule), except within the message/http media type (<a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;9.3.1</a>). Receivers <em class="bcp14">SHOULD</em> still parse folded linear white space.
     794            </p>
     795            <p id="rfc.section.2.2.p.5">This specification uses three rules to denote the use of linear white space; BWS ("Bad" White Space), OWS (Optional White
     796               Space), and RWS (Required White Space).
     797            </p>
     798            <p id="rfc.section.2.2.p.6">"Bad" white space is allowed by the BNF, but senders <em class="bcp14">SHOULD NOT</em> produce it in messages. Receivers <em class="bcp14">MUST</em> accept it in incoming messages.
     799            </p>
     800            <p id="rfc.section.2.2.p.7">Required white space is used when at least one linear white space character is required to separate field tokens. In all such
     801               cases, a single SP character <em class="bcp14">SHOULD</em> be used.
     802            </p>
     803            <div id="rule.whitespace">
     804               <p id="rfc.section.2.2.p.8">    </p>
     805            </div>
     806            <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
    792807                 ; "optional" white space
    793808  <a href="#rule.whitespace" class="smpl">RWS</a>            = 1*( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
     
    797812  <a href="#rule.whitespace" class="smpl">obs-fold</a>       = <a href="#core.rules" class="smpl">CRLF</a>
    798813</pre><div id="rule.TEXT">
    799          <p id="rfc.section.2.2.p.10"> The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message
    800             parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> only when encoded according to the rules of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>.
    801          </p>
    802       </div>
    803       <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  <a href="#rule.TEXT" class="smpl">TEXT</a>           = %x20-7E / %x80-FF / <a href="#rule.whitespace" class="smpl">OWS</a>
     814               <p id="rfc.section.2.2.p.10"> The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message
     815                  parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> only when encoded according to the rules of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>.
     816               </p>
     817            </div>
     818            <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  <a href="#rule.TEXT" class="smpl">TEXT</a>           = %x20-7E / %x80-FF / <a href="#rule.whitespace" class="smpl">OWS</a>
    804819                 ; any <a href="#core.rules" class="smpl">OCTET</a> except <a href="#core.rules" class="smpl">CTL</a>s, but including <a href="#rule.whitespace" class="smpl">OWS</a>
    805820</pre><p id="rfc.section.2.2.p.12">A CRLF is allowed in the definition of TEXT only as part of a header field continuation. It is expected that the folding LWS
    806          will be replaced with a single SP before interpretation of the TEXT value.
    807       </p>
    808       <div id="rule.token.separators">
    809          <p id="rfc.section.2.2.p.13">    Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>).
    810          </p>
    811       </div>
    812       <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span>  <a href="#rule.token.separators" class="smpl">tchar</a>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
     821               will be replaced with a single SP before interpretation of the TEXT value.
     822            </p>
     823            <div id="rule.token.separators">
     824               <p id="rfc.section.2.2.p.13">  Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>).
     825               </p>
     826            </div>
     827            <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span>  <a href="#rule.token.separators" class="smpl">tchar</a>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
    813828                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
    814829                 / <a href="#core.rules" class="smpl">DIGIT</a> / <a href="#core.rules" class="smpl">ALPHA</a>
     
    816831  <a href="#rule.token.separators" class="smpl">token</a>          = 1*<a href="#rule.token.separators" class="smpl">tchar</a>
    817832</pre><div id="rule.comment">
    818          <p id="rfc.section.2.2.p.15">    Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
    819             in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part
    820             of the field value.
    821          </p>
    822       </div>
    823       <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span>  <a href="#rule.comment" class="smpl">comment</a>        = "(" *( <a href="#rule.comment" class="smpl">ctext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> / <a href="#rule.comment" class="smpl">comment</a> ) ")"
     833               <p id="rfc.section.2.2.p.15">  Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
     834                  in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part
     835                  of the field value.
     836               </p>
     837            </div>
     838            <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span>  <a href="#rule.comment" class="smpl">comment</a>        = "(" *( <a href="#rule.comment" class="smpl">ctext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> / <a href="#rule.comment" class="smpl">comment</a> ) ")"
    824839  <a href="#rule.comment" class="smpl">ctext</a>          = &lt;any <a href="#rule.TEXT" class="smpl">TEXT</a> excluding "(" and ")"&gt;
    825840</pre><div id="rule.quoted-string">
    826          <p id="rfc.section.2.2.p.17">    A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
    827       </div>
    828       <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span>  <a href="#rule.quoted-string" class="smpl">quoted-string</a>  = <a href="#core.rules" class="smpl">DQUOTE</a> *(<a href="#rule.quoted-string" class="smpl">qdtext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a>
     841               <p id="rfc.section.2.2.p.17">  A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
     842            </div>
     843            <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span>  <a href="#rule.quoted-string" class="smpl">quoted-string</a>  = <a href="#core.rules" class="smpl">DQUOTE</a> *(<a href="#rule.quoted-string" class="smpl">qdtext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a>
    829844  <a href="#rule.quoted-string" class="smpl">qdtext</a>         = &lt;any <a href="#rule.TEXT" class="smpl">TEXT</a> excluding <a href="#core.rules" class="smpl">DQUOTE</a> and "\"&gt;
    830845</pre><div id="rule.quoted-pair">
    831          <p id="rfc.section.2.2.p.19">    The backslash character ("\") <em class="bcp14">MAY</em> be used as a single-character quoting mechanism only within quoted-string and comment constructs.
    832          </p>
    833       </div>
    834       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>  <a href="#rule.quoted-pair" class="smpl">quoted-text</a>    = %x01-09 /
     846               <p id="rfc.section.2.2.p.19">  The backslash character ("\") <em class="bcp14">MAY</em> be used as a single-character quoting mechanism only within quoted-string and comment constructs.
     847               </p>
     848            </div>
     849            <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>  <a href="#rule.quoted-pair" class="smpl">quoted-text</a>    = %x01-09 /
    835850                   %x0B-0C /
    836851                   %x0E-FF ; Characters excluding NUL, <a href="#core.rules" class="smpl">CR</a> and <a href="#core.rules" class="smpl">LF</a>
    837852  <a href="#rule.quoted-pair" class="smpl">quoted-pair</a>    = "\" <a href="#rule.quoted-pair" class="smpl">quoted-text</a>
    838 </pre><h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h2>
    839       <p id="rfc.section.2.3.p.1">The ABNF rules below are defined in other parts:</p>
    840       <div id="rfc.figure.u.12"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">request-header</a>  = &lt;request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a>&gt;
     853</pre></div>
     854         <div id="abnf.dependencies">
     855            <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h2>
     856            <p id="rfc.section.2.3.p.1">The ABNF rules below are defined in other parts:</p>
     857            <div id="rfc.figure.u.12"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">request-header</a>  = &lt;request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a>&gt;
    841858  <a href="#abnf.dependencies" class="smpl">response-header</a> = &lt;response-header, defined in <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a>&gt;
    842859</pre><div id="rfc.figure.u.13"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">accept-params</a>   = &lt;accept-params, defined in <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept" title="Accept">Section 6.1</a>&gt;
     
    846863  <a href="#abnf.dependencies" class="smpl">Pragma</a>          = &lt;Pragma, defined in <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.pragma" title="Pragma">Section 16.4</a>&gt;
    847864  <a href="#abnf.dependencies" class="smpl">Warning</a>         = &lt;Warning, defined in <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.warning" title="Warning">Section 16.6</a>&gt;
    848 </pre><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1>
    849       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="http.version" href="#http.version">HTTP Version</a></h2>
    850       <p id="rfc.section.3.1.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
    851          to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
    852          than the features obtained via that communication. No change is made to the version number for the addition of message components
    853          which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
    854          when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may
    855          add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
    856          of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation.
    857       </p>
    858       <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p>
    859       <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span>  <a href="#http.version" class="smpl">HTTP-Version</a>   = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a>
     865</pre></div>
     866      </div>
     867      <div id="protocol.parameters">
     868         <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#protocol.parameters">Protocol Parameters</a></h1>
     869         <div id="http.version">
     870            <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#http.version">HTTP Version</a></h2>
     871            <p id="rfc.section.3.1.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
     872               to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
     873               than the features obtained via that communication. No change is made to the version number for the addition of message components
     874               which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
     875               when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may
     876               add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
     877               of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation.
     878            </p>
     879            <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p>
     880            <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span>  <a href="#http.version" class="smpl">HTTP-Version</a>   = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a>
    860881  <a href="#http.version" class="smpl">HTTP-Prot-Name</a> = %x48.54.54.50 ; "HTTP", case-sensitive
    861882</pre><p id="rfc.section.3.1.p.4">Note that the major and minor numbers <em class="bcp14">MUST</em> be treated as separate integers and that each <em class="bcp14">MAY</em> be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3.
    862          Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
    863       </p>
    864       <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
    865          specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
    866          see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>.
    867       </p>
    868       <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
    869       <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
    870          application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
    871          the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
    872       </p>
    873       <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
    874       </p>
    875       <p id="rfc.section.3.1.p.9"> </p>
    876       <ul class="empty">
    877          <li> <b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved.
    878          </li>
    879       </ul>
    880       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="uri" href="#uri">Uniform Resource Identifiers</a></h2>
    881       <p id="rfc.section.3.2.p.1">Uniform Resource Identifiers (URIs) <a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> are used in HTTP to indicate the target of a request and to identify additional resources related to that resource, the request,
    882          or the response. Each protocol element in HTTP that allows a URI reference will indicate in its ABNF whether the element allows
    883          only a URI in absolute form, any relative reference, or some limited subset of the URI-reference grammar. Unless otherwise
    884          indicated, relative URI references are to be parsed relative to the URI corresponding to the request target (the base URI).
    885       </p>
    886       <p id="rfc.section.3.2.p.2">This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port", "host", "path-abempty",
    887          "path-absolute", "query", and "authority" from <a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>:
    888       </p>
    889       <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span><span id="rfc.iref.g.23"></span>  <a href="#uri" class="smpl">absolute-URI</a>   = &lt;absolute-URI, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.4"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>&gt;
    890   <a href="#uri" class="smpl">authority</a>     = &lt;authority, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.5"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2">Section 3.2</a>&gt;
    891   <a href="#uri" class="smpl">fragment</a>      = &lt;fragment, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.6"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.5">Section 3.5</a>&gt;
    892   <a href="#uri" class="smpl">path-abempty</a>  = &lt;path-abempty, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.7"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
    893   <a href="#uri" class="smpl">path-absolute</a> = &lt;path-absolute, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.8"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
    894   <a href="#uri" class="smpl">port</a>          = &lt;port, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.9"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.3">Section 3.2.3</a>&gt;
    895   <a href="#uri" class="smpl">query</a>         = &lt;query, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.10"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.4">Section 3.4</a>&gt;
    896   <a href="#uri" class="smpl">uri-host</a>      = &lt;host, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.11"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>&gt;
     883               Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
     884            </p>
     885            <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
     886               specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
     887               see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>.
     888            </p>
     889            <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
     890            <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
     891               application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
     892               the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
     893            </p>
     894            <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
     895            </p>
     896            <p id="rfc.section.3.1.p.9"></p>
     897            <ul class="empty">
     898               <li><b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved.
     899               </li>
     900            </ul>
     901         </div>
     902         <div id="uri">
     903            <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a href="#uri">Uniform Resource Identifiers</a></h2>
     904            <p id="rfc.section.3.2.p.1">Uniform Resource Identifiers (URIs) <a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> are used in HTTP to indicate the target of a request and to identify additional resources related to that resource, the request,
     905               or the response. Each protocol element in HTTP that allows a URI reference will indicate in its ABNF whether the element allows
     906               only a URI in absolute form, any relative reference, or some limited subset of the URI-reference grammar. Unless otherwise
     907               indicated, relative URI references are to be parsed relative to the URI corresponding to the request target (the base URI).
     908            </p>
     909            <p id="rfc.section.3.2.p.2">This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port", "host", "path-abempty",
     910               "path-absolute", "query", and "authority" from <a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>:
     911            </p>
     912            <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span><span id="rfc.iref.g.23"></span>  <a href="#uri" class="smpl">absolute-URI</a>   = &lt;absolute-URI, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.4"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>&gt;
     913  <a href="#uri" class="smpl">authority</a>     = &lt;authority, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.5"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2">Section 3.2</a>&gt;
     914  <a href="#uri" class="smpl">fragment</a>      = &lt;fragment, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.6"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.5">Section 3.5</a>&gt;
     915  <a href="#uri" class="smpl">path-abempty</a>  = &lt;path-abempty, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.7"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
     916  <a href="#uri" class="smpl">path-absolute</a> = &lt;path-absolute, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.8"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
     917  <a href="#uri" class="smpl">port</a>          = &lt;port, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.9"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.3">Section 3.2.3</a>&gt;
     918  <a href="#uri" class="smpl">query</a>         = &lt;query, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.10"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.4">Section 3.4</a>&gt;
     919  <a href="#uri" class="smpl">uri-host</a>      = &lt;host, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.11"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>&gt;
    897920
    898   <a href="#uri" class="smpl">relative-part</a> = &lt;relative-part, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.12"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>&gt;
     921  <a href="#uri" class="smpl">relative-part</a> = &lt;relative-part, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.12"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>&gt;
    899922  <a href="#uri" class="smpl">relativeURI</a>   = <a href="#uri" class="smpl">relative-part</a> [ "?" <a href="#uri" class="smpl">query</a> ]
    900923</pre><p id="rfc.section.3.2.p.4">HTTP does not place an a priori limit on the length of a URI. Servers <em class="bcp14">MUST</em> be able to handle the URI of any resource they serve, and <em class="bcp14">SHOULD</em> be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server <em class="bcp14">SHOULD</em> return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see <a href="p2-semantics.html#status.414" title="414 Request-URI Too Long">Section 9.4.15</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    901       </p>
    902       <p id="rfc.section.3.2.p.5"> </p>
    903       <ul class="empty">
    904          <li> <b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations
    905             might not properly support these lengths.
    906          </li>
    907       </ul>
    908       <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a id="http.uri" href="#http.uri">http URI scheme</a></h3>
    909       <div id="rfc.iref.h.1"></div>
    910       <div id="rfc.iref.u.1"></div>
    911       <p id="rfc.section.3.2.1.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the syntax and semantics
    912          for identifiers using the http or https URI schemes.
    913       </p>
    914       <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.24"></span>  <a href="#http.uri" class="smpl">http-URI</a> = "http:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
     924            </p>
     925            <p id="rfc.section.3.2.p.5"></p>
     926            <ul class="empty">
     927               <li><b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations
     928                  might not properly support these lengths.
     929               </li>
     930            </ul>
     931            <div id="http.uri">
     932               <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a href="#http.uri">http URI scheme</a></h3>
     933               <div id="rfc.iref.h.1"></div>
     934               <div id="rfc.iref.u.1"></div>
     935               <p id="rfc.section.3.2.1.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the syntax and semantics
     936                  for identifiers using the http or https URI schemes.
     937               </p>
     938               <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.24"></span>  <a href="#http.uri" class="smpl">http-URI</a> = "http:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
    915939</pre><p id="rfc.section.3.2.1.p.3">If the port is empty or not given, port 80 is assumed. The semantics are that the identified resource is located at the server
    916          listening for TCP connections on that port of that host, and the Request-URI for the resource is path-absolute (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>). If the path-absolute is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
    917       </p>
    918       <ul class="empty">
    919          <li> <span id="rfc.iref.h.2"></span>  <span id="rfc.iref.u.2"></span>  <b>Note:</b> the "https" scheme is defined in <a href="#RFC2818" id="rfc.xref.RFC2818.1"><cite title="HTTP Over TLS">[RFC2818]</cite></a>.
    920          </li>
    921       </ul>
    922       <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a id="uri.comparison" href="#uri.comparison">URI Comparison</a></h3>
    923       <p id="rfc.section.3.2.2.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions:
    924       </p>
    925       <ul>
    926          <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li>
    927          <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive;
    928          </li>
    929          <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive;
    930          </li>
    931          <li>An empty path-absolute is equivalent to an path-absolute of "/".</li>
    932       </ul>
    933       <p id="rfc.section.3.2.2.p.2">Characters other than those in the "reserved" set (see <a href="#RFC3986" id="rfc.xref.RFC3986.13"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-2.2">Section 2.2</a>) are equivalent to their ""%" <a href="#core.rules" class="smpl">HEXDIG</a>  <a href="#core.rules" class="smpl">HEXDIG</a>" encoding.
    934       </p>
    935       <p id="rfc.section.3.2.2.p.3">For example, the following three URIs are equivalent:</p>
    936       <div id="rfc.figure.u.18"></div><pre class="text">   http://example.com:80/~smith/home.html
     940                  listening for TCP connections on that port of that host, and the Request-URI for the resource is path-absolute (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>). If the path-absolute is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
     941               </p>
     942               <ul class="empty">
     943                  <li><span id="rfc.iref.h.2"></span> <span id="rfc.iref.u.2"></span> <b>Note:</b> the "https" scheme is defined in <a href="#RFC2818" id="rfc.xref.RFC2818.1"><cite title="HTTP Over TLS">[RFC2818]</cite></a>.
     944                  </li>
     945               </ul>
     946            </div>
     947            <div id="uri.comparison">
     948               <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a href="#uri.comparison">URI Comparison</a></h3>
     949               <p id="rfc.section.3.2.2.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions:
     950               </p>
     951               <ul>
     952                  <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li>
     953                  <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive;
     954                  </li>
     955                  <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive;
     956                  </li>
     957                  <li>An empty path-absolute is equivalent to an path-absolute of "/".</li>
     958               </ul>
     959               <p id="rfc.section.3.2.2.p.2">Characters other than those in the "reserved" set (see <a href="#RFC3986" id="rfc.xref.RFC3986.13"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-2.2">Section 2.2</a>) are equivalent to their ""%" <a href="#core.rules" class="smpl">HEXDIG</a> <a href="#core.rules" class="smpl">HEXDIG</a>" encoding.
     960               </p>
     961               <p id="rfc.section.3.2.2.p.3">For example, the following three URIs are equivalent:</p>
     962               <div id="rfc.figure.u.18"></div><pre class="text">   http://example.com:80/~smith/home.html
    937963   http://EXAMPLE.com/%7Esmith/home.html
    938964   http://EXAMPLE.com:/%7esmith/home.html
    939 </pre><h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="date.time.formats" href="#date.time.formats">Date/Time Formats</a></h2>
    940       <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;<a id="full.date" href="#full.date">Full Date</a></h3>
    941       <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p>
    942       <div id="rfc.figure.u.19"></div><pre class="text">   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
     965</pre></div>
     966         </div>
     967         <div id="date.time.formats">
     968            <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a href="#date.time.formats">Date/Time Formats</a></h2>
     969            <div id="full.date">
     970               <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;<a href="#full.date">Full Date</a></h3>
     971               <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p>
     972               <div id="rfc.figure.u.19"></div><pre class="text">   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
    943973   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
    944974   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
    945975</pre><p id="rfc.section.3.3.1.p.3">The first format is preferred as an Internet standard and represents a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a> (an update to <a href="#RFC822" id="rfc.xref.RFC822.1"><cite title="Standard for the format of ARPA Internet text messages">[RFC822]</cite></a>). The other formats are described here only for compatibility with obsolete implementations. HTTP/1.1 clients and servers
    946          that parse the date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for further information.
    947       </p>
    948       <ul class="empty">
    949          <li> <b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications,
    950             as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
    951          </li>
    952       </ul>
    953       <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
    954          Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
    955          time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar.
    956       </p>
    957       <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span>  <a href="#full.date" class="smpl">HTTP-date</a>    = <a href="#full.date" class="smpl">rfc1123-date</a> / <a href="#full.date" class="smpl">obsolete-date</a>
     976                  that parse the date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for further information.
     977               </p>
     978               <ul class="empty">
     979                  <li><b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications,
     980                     as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
     981                  </li>
     982               </ul>
     983               <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
     984                  Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
     985                  time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar.
     986               </p>
     987               <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span>  <a href="#full.date" class="smpl">HTTP-date</a>    = <a href="#full.date" class="smpl">rfc1123-date</a> / <a href="#full.date" class="smpl">obsolete-date</a>
    958988  <a href="#full.date" class="smpl">obsolete-date</a> = <a href="#full.date" class="smpl">rfc850-date</a> / <a href="#full.date" class="smpl">asctime-date</a>
    959989  <a href="#full.date" class="smpl">rfc1123-date</a> = <a href="#full.date" class="smpl">wkday</a> "," <a href="#core.rules" class="smpl">SP</a> date1 <a href="#core.rules" class="smpl">SP</a> time <a href="#core.rules" class="smpl">SP</a> GMT
     
    10061036  s-Nov = %x4E.6F.76 ; "Nov", case-sensitive
    10071037  s-Dec = %x44.65.63 ; "Dec", case-sensitive
    1008 </pre><p id="rfc.section.3.3.1.p.7"> <b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
    1009          are not required to use these formats for user presentation, request logging, etc.
    1010       </p>
    1011       <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="transfer.codings" href="#transfer.codings">Transfer Codings</a></h2>
    1012       <p id="rfc.section.3.4.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to
    1013          an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding
    1014          is a property of the message, not of the original entity.
    1015       </p>
    1016       <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" / <a href="#transfer.codings" class="smpl">transfer-extension</a>
     1038</pre><p id="rfc.section.3.3.1.p.7"><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
     1039                  are not required to use these formats for user presentation, request logging, etc.
     1040               </p>
     1041            </div>
     1042         </div>
     1043         <div id="transfer.codings">
     1044            <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#transfer.codings">Transfer Codings</a></h2>
     1045            <p id="rfc.section.3.4.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to
     1046               an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding
     1047               is a property of the message, not of the original entity.
     1048            </p>
     1049            <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" / <a href="#transfer.codings" class="smpl">transfer-extension</a>
    10171050  <a href="#transfer.codings" class="smpl">transfer-extension</a>      = <a href="#rule.token.separators" class="smpl">token</a> *( <a href="#rule.whitespace" class="smpl">OWS</a> ";" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#transfer.codings" class="smpl">parameter</a> )
    10181051</pre><div id="rule.parameter">
    1019          <p id="rfc.section.3.4.p.3">      Parameters are in the form of attribute/value pairs.</p>
    1020       </div>
    1021       <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span>  <a href="#transfer.codings" class="smpl">parameter</a>               = <a href="#rule.parameter" class="smpl">attribute</a> <a href="#rule.whitespace" class="smpl">BWS</a> "=" <a href="#rule.whitespace" class="smpl">BWS</a> <a href="#rule.parameter" class="smpl">value</a>
     1052               <p id="rfc.section.3.4.p.3">   Parameters are in the form of attribute/value pairs.</p>
     1053            </div>
     1054            <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span>  <a href="#transfer.codings" class="smpl">parameter</a>               = <a href="#rule.parameter" class="smpl">attribute</a> <a href="#rule.whitespace" class="smpl">BWS</a> "=" <a href="#rule.whitespace" class="smpl">BWS</a> <a href="#rule.parameter" class="smpl">value</a>
    10221055  <a href="#rule.parameter" class="smpl">attribute</a>               = <a href="#rule.token.separators" class="smpl">token</a>
    10231056  <a href="#rule.parameter" class="smpl">value</a>                   = <a href="#rule.token.separators" class="smpl">token</a> / <a href="#rule.quoted-string" class="smpl">quoted-string</a>
    10241057</pre><p id="rfc.section.3.4.p.5">All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer-coding values in the TE header field (<a href="#header.te" id="rfc.xref.header.te.1" title="TE">Section&nbsp;8.5</a>) and in the Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.1" title="Transfer-Encoding">Section&nbsp;8.7</a>).
    1025       </p>
    1026       <p id="rfc.section.3.4.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message indicates it is terminated by closing the connection. When the "chunked" transfer-coding
    1027          is used, it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message
    1028          (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>).
    1029       </p>
    1030       <p id="rfc.section.3.4.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has
    1031          a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty
    1032          in determining the exact body length (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>), or the desire to encrypt data over a shared transport.
    1033       </p>
    1034       <p id="rfc.section.3.4.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry
    1035          contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a>), "gzip", "compress", and "deflate" (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
    1036       </p>
    1037       <p id="rfc.section.3.4.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.8"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
    1038       </p>
    1039       <p id="rfc.section.3.4.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return 501 (Not Implemented), and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
    1040       </p>
    1041       <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;<a id="chunked.transfer.encoding" href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3>
    1042       <p id="rfc.section.3.4.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
    1043          indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information
    1044          necessary for the recipient to verify that it has received the full message.
    1045       </p>
    1046       <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span><span id="rfc.iref.g.46"></span><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span>  <a href="#chunked.transfer.encoding" class="smpl">Chunked-Body</a>   = *<a href="#chunked.transfer.encoding" class="smpl">chunk</a>
     1058            </p>
     1059            <p id="rfc.section.3.4.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message indicates it is terminated by closing the connection. When the "chunked" transfer-coding
     1060               is used, it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message
     1061               (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>).
     1062            </p>
     1063            <p id="rfc.section.3.4.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has
     1064               a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty
     1065               in determining the exact body length (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>), or the desire to encrypt data over a shared transport.
     1066            </p>
     1067            <p id="rfc.section.3.4.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry
     1068               contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a>), "gzip", "compress", and "deflate" (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
     1069            </p>
     1070            <p id="rfc.section.3.4.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.8"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>).
     1071            </p>
     1072            <p id="rfc.section.3.4.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return 501 (Not Implemented), and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
     1073            </p>
     1074            <div id="chunked.transfer.encoding">
     1075               <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3>
     1076               <p id="rfc.section.3.4.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
     1077                  indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information
     1078                  necessary for the recipient to verify that it has received the full message.
     1079               </p>
     1080               <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span><span id="rfc.iref.g.46"></span><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span>  <a href="#chunked.transfer.encoding" class="smpl">Chunked-Body</a>   = *<a href="#chunked.transfer.encoding" class="smpl">chunk</a>
    10471081                   <a href="#chunked.transfer.encoding" class="smpl">last-chunk</a>
    10481082                   <a href="#chunked.transfer.encoding" class="smpl">trailer-part</a>
     
    10611095  <a href="#chunked.transfer.encoding" class="smpl">trailer-part</a>   = *(<a href="#abnf.dependencies" class="smpl">entity-header</a> <a href="#core.rules" class="smpl">CRLF</a>)
    10621096</pre><p id="rfc.section.3.4.1.p.3">The chunk-size field is a string of hex digits indicating the size of the chunk-data in octets. The chunked encoding is ended
    1063          by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line.
    1064       </p>
    1065       <p id="rfc.section.3.4.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
    1066          can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;8.6</a>).
    1067       </p>
    1068       <p id="rfc.section.3.4.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
    1069       </p>
    1070       <ol>
    1071          <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
    1072             described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;8.5</a>; or,
    1073          </li>
    1074          <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
    1075             could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
    1076             server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
    1077          </li>
    1078       </ol>
    1079       <p id="rfc.section.3.4.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
    1080          forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
    1081          infinite buffer on the proxy.
    1082       </p>
    1083       <p id="rfc.section.3.4.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p>
    1084       <div id="rfc.figure.u.24"></div><pre class="text">  length := 0
     1097                  by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line.
     1098               </p>
     1099               <p id="rfc.section.3.4.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
     1100                  can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;8.6</a>).
     1101               </p>
     1102               <p id="rfc.section.3.4.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
     1103               </p>
     1104               <ol>
     1105                  <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
     1106                     described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;8.5</a>; or,
     1107                  </li>
     1108                  <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
     1109                     could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
     1110                     server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
     1111                  </li>
     1112               </ol>
     1113               <p id="rfc.section.3.4.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
     1114                  forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
     1115                  infinite buffer on the proxy.
     1116               </p>
     1117               <p id="rfc.section.3.4.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p>
     1118               <div id="rfc.figure.u.24"></div><pre class="text">  length := 0
    10851119  read chunk-size, chunk-ext (if any) and CRLF
    10861120  while (chunk-size &gt; 0) {
     
    10981132  Remove "chunked" from Transfer-Encoding
    10991133</pre><p id="rfc.section.3.4.1.p.9">All HTTP/1.1 applications <em class="bcp14">MUST</em> be able to receive and decode the "chunked" transfer-coding, and <em class="bcp14">MUST</em> ignore chunk-ext extensions they do not understand.
    1100       </p>
    1101       <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h2>
    1102       <p id="rfc.section.3.5.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
    1103          using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
    1104          space. By convention, the products are listed in order of their significance for identifying the application.
    1105       </p>
    1106       <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.51"></span><span id="rfc.iref.g.52"></span>  <a href="#product.tokens" class="smpl">product</a>         = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]
     1134               </p>
     1135            </div>
     1136         </div>
     1137         <div id="product.tokens">
     1138            <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a href="#product.tokens">Product Tokens</a></h2>
     1139            <p id="rfc.section.3.5.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
     1140               using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
     1141               space. By convention, the products are listed in order of their significance for identifying the application.
     1142            </p>
     1143            <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.51"></span><span id="rfc.iref.g.52"></span>  <a href="#product.tokens" class="smpl">product</a>         = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]
    11071144  <a href="#product.tokens" class="smpl">product-version</a> = <a href="#rule.token.separators" class="smpl">token</a>
    11081145</pre><p id="rfc.section.3.5.p.3">Examples:</p>
    1109       <div id="rfc.figure.u.26"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     1146            <div id="rfc.figure.u.26"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    11101147    Server: Apache/0.8.4
    11111148</pre><p id="rfc.section.3.5.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token character <em class="bcp14">MAY</em> appear in a product-version, this token <em class="bcp14">SHOULD</em> only be used for a version identifier (i.e., successive versions of the same product <em class="bcp14">SHOULD</em> only differ in the product-version portion of the product value).
    1112       </p>
    1113       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="http.message" href="#http.message">HTTP Message</a></h1>
    1114       <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="message.types" href="#message.types">Message Types</a></h2>
    1115       <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p>
    1116       <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.53"></span>  <a href="#message.types" class="smpl">HTTP-message</a>   = <a href="#request" class="smpl">Request</a> / <a href="#response" class="smpl">Response</a>     ; HTTP/1.1 messages
     1149            </p>
     1150         </div>
     1151      </div>
     1152      <div id="http.message">
     1153         <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#http.message">HTTP Message</a></h1>
     1154         <div id="message.types">
     1155            <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a href="#message.types">Message Types</a></h2>
     1156            <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p>
     1157            <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.53"></span>  <a href="#message.types" class="smpl">HTTP-message</a>   = <a href="#request" class="smpl">Request</a> / <a href="#response" class="smpl">Response</a>     ; HTTP/1.1 messages
    11171158</pre><p id="rfc.section.4.1.p.3">Request (<a href="#request" title="Request">Section&nbsp;5</a>) and Response (<a href="#response" title="Response">Section&nbsp;6</a>) messages use the generic message format of <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a> for transferring entities (the payload of the message). Both types of message consist of a start-line, zero or more header
    1118          fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header
    1119          fields, and possibly a message-body.
    1120       </p>
    1121       <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span>  <a href="#message.types" class="smpl">generic-message</a> = <a href="#message.types" class="smpl">start-line</a>
     1159               fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header
     1160               fields, and possibly a message-body.
     1161            </p>
     1162            <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span>  <a href="#message.types" class="smpl">generic-message</a> = <a href="#message.types" class="smpl">start-line</a>
    11221163                    *(<a href="#message.headers" class="smpl">message-header</a> <a href="#core.rules" class="smpl">CRLF</a>)
    11231164                    <a href="#core.rules" class="smpl">CRLF</a>
     
    11251166  <a href="#message.types" class="smpl">start-line</a>      = <a href="#request-line" class="smpl">Request-Line</a> / <a href="#status-line" class="smpl">Status-Line</a>
    11261167</pre><p id="rfc.section.4.1.p.5">In the interest of robustness, servers <em class="bcp14">SHOULD</em> ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol
    1127          stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.
    1128       </p>
    1129       <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden
    1130          by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF.
    1131       </p>
    1132       <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="message.headers" href="#message.headers">Message Headers</a></h2>
    1133       <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>), request-header (<a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), response-header (<a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), and entity-header (<a href="p3-payload.html#entity.header.fields" title="Entity Header Fields">Section 4.1</a> of <a href="#Part3" id="rfc.xref.Part3.9"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) fields, follow the same generic format as that given in <a href="http://tools.ietf.org/html/rfc5322#section-2.1">Section 2.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The
    1134          field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding
    1135          each extra line with at least one SP or HTAB. Applications ought to follow "common form", where one is known or indicated,
    1136          when generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common
    1137          forms.
    1138       </p>
    1139       <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span>  <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ <a href="#message.headers" class="smpl">field-value</a> ]
     1168               stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.
     1169            </p>
     1170            <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden
     1171               by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF.
     1172            </p>
     1173         </div>
     1174         <div id="message.headers">
     1175            <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#message.headers">Message Headers</a></h2>
     1176            <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>), request-header (<a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), response-header (<a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), and entity-header (<a href="p3-payload.html#entity.header.fields" title="Entity Header Fields">Section 4.1</a> of <a href="#Part3" id="rfc.xref.Part3.9"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) fields, follow the same generic format as that given in <a href="https://tools.ietf.org/html/rfc5322#section-2.1">Section 2.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The
     1177               field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding
     1178               each extra line with at least one SP or HTAB. Applications ought to follow "common form", where one is known or indicated,
     1179               when generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common
     1180               forms.
     1181            </p>
     1182            <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span>  <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ <a href="#message.headers" class="smpl">field-value</a> ]
    11401183  <a href="#message.headers" class="smpl">field-name</a>     = <a href="#rule.token.separators" class="smpl">token</a>
    11411184  <a href="#message.headers" class="smpl">field-value</a>    = *( <a href="#message.headers" class="smpl">field-content</a> / <a href="#rule.whitespace" class="smpl">OWS</a> )
    11421185  <a href="#message.headers" class="smpl">field-content</a>  = &lt;field content&gt;
    1143 </pre><p id="rfc.section.4.2.p.3"> <span class="comment" id="rfc.comment.1">[<a href="#rfc.comment.1" class="smpl">rfc.comment.1</a>: whitespace between field-name and colon is an error and MUST NOT be accepted]</span>
    1144       </p>
    1145       <p id="rfc.section.4.2.p.4">The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace
    1146          character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
    1147       </p>
    1148       <p id="rfc.section.4.2.p.5">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
    1149          to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header
    1150          fields.
    1151       </p>
    1152       <p id="rfc.section.4.2.p.6">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e.,
    1153          #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics
    1154          of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header
    1155          fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and
    1156          thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded.
    1157       </p>
    1158       <p id="rfc.section.4.2.p.7"> </p>
    1159       <ul class="empty">
    1160          <li> <b>Note:</b> the "Set-Cookie" header as implemented in practice (as opposed to how it is specified in <a href="#RFC2109" id="rfc.xref.RFC2109.1"><cite title="HTTP State Management Mechanism">[RFC2109]</cite></a>) can occur multiple times, but does not use the list syntax, and thus cannot be combined into a single line. (See Appendix
    1161             A.2.3 of <a href="#Kri2001" id="rfc.xref.Kri2001.1"><cite title="HTTP Cookies: Standards, Privacy, and Politics">[Kri2001]</cite></a> for details.) Also note that the Set-Cookie2 header specified in <a href="#RFC2965" id="rfc.xref.RFC2965.1"><cite title="HTTP State Management Mechanism">[RFC2965]</cite></a> does not share this problem.
    1162          </li>
    1163       </ul>
    1164       <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="message.body" href="#message.body">Message Body</a></h2>
    1165       <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The
    1166          message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding
    1167          header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;8.7</a>).
    1168       </p>
    1169       <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.60"></span>  <a href="#message.body" class="smpl">message-body</a> = <a href="#abnf.dependencies" class="smpl">entity-body</a>
     1186</pre><p id="rfc.section.4.2.p.3"><span class="comment" id="rfc.comment.1">[<a href="#rfc.comment.1" class="smpl">rfc.comment.1</a>: whitespace between field-name and colon is an error and MUST NOT be accepted]</span>
     1187            </p>
     1188            <p id="rfc.section.4.2.p.4">The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace
     1189               character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
     1190            </p>
     1191            <p id="rfc.section.4.2.p.5">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
     1192               to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header
     1193               fields.
     1194            </p>
     1195            <p id="rfc.section.4.2.p.6">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e.,
     1196               #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics
     1197               of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header
     1198               fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and
     1199               thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded.
     1200            </p>
     1201            <p id="rfc.section.4.2.p.7"></p>
     1202            <ul class="empty">
     1203               <li><b>Note:</b> the "Set-Cookie" header as implemented in practice (as opposed to how it is specified in <a href="#RFC2109" id="rfc.xref.RFC2109.1"><cite title="HTTP State Management Mechanism">[RFC2109]</cite></a>) can occur multiple times, but does not use the list syntax, and thus cannot be combined into a single line. (See Appendix
     1204                  A.2.3 of <a href="#Kri2001" id="rfc.xref.Kri2001.1"><cite title="HTTP Cookies: Standards, Privacy, and Politics">[Kri2001]</cite></a> for details.) Also note that the Set-Cookie2 header specified in <a href="#RFC2965" id="rfc.xref.RFC2965.1"><cite title="HTTP State Management Mechanism">[RFC2965]</cite></a> does not share this problem.
     1205               </li>
     1206            </ul>
     1207         </div>
     1208         <div id="message.body">
     1209            <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#message.body">Message Body</a></h2>
     1210            <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The
     1211               message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding
     1212               header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;8.7</a>).
     1213            </p>
     1214            <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.60"></span>  <a href="#message.body" class="smpl">message-body</a> = <a href="#abnf.dependencies" class="smpl">entity-body</a>
    11701215               / &lt;entity-body encoded as per <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>&gt;
    11711216</pre><p id="rfc.section.4.3.p.3">Transfer-Encoding <em class="bcp14">MUST</em> be used to indicate any transfer-codings applied by an application to ensure safe and proper transfer of the message. Transfer-Encoding
    1172          is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a> places restrictions on when certain transfer-codings may be used.)
    1173       </p>
    1174       <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
    1175       <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
    1176          in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="p2-semantics.html#method" title="Method">Section 3</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) explicitly disallows an entity-body in requests. When a request message contains both a message-body of non-zero length
    1177          and a method that does not define any semantics for that request message-body, then an origin server <em class="bcp14">SHOULD</em> either ignore the message-body or respond with an appropriate error message (e.g., 413). A proxy or gateway, when presented
    1178          the same request, <em class="bcp14">SHOULD</em> either forward the request inbound with the message-body or ignore the message-body when determining a response.
    1179       </p>
    1180       <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
    1181          the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational),
    1182          204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length.
    1183       </p>
    1184       <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a id="message.length" href="#message.length">Message Length</a></h2>
    1185       <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings
    1186          have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of
    1187          the following (in order of precedence):
    1188       </p>
    1189       <p id="rfc.section.4.4.p.2"> </p>
    1190       <ol>
    1191          <li>
    1192             <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated
    1193                by the first empty line after the header fields, regardless of the entity-header fields present in the message.
    1194             </p>
    1195          </li>
    1196          <li>
    1197             <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;8.7</a>) is present and the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>) is used, the transfer-length is defined by the use of this transfer-coding. If a Transfer-Encoding header field is present
    1198                and the "chunked" transfer-coding is not present, the transfer-length is defined by the sender closing the connection.
    1199             </p>
    1200          </li>
    1201          <li>
    1202             <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;8.2</a>) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length header
    1203                field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received
    1204                with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored.
    1205             </p>
    1206          </li>
    1207          <li>
    1208             <p>If the message uses the media type "multipart/byteranges", and the transfer-length is not otherwise specified, then this self-delimiting
    1209                media type defines the transfer-length. This media type <em class="bcp14">MUST NOT</em> be used unless the sender knows that the recipient can parse it; the presence in a request of a Range header with multiple
    1210                byte-range specifiers from a 1.1 client implies that the client can parse multipart/byteranges responses.
    1211             </p>
    1212             <ul class="empty">
    1213                <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section.
    1214                </li>
    1215             </ul>
    1216          </li>
    1217          <li>
    1218             <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since
    1219                that would leave no possibility for the server to send back a response.)
    1220             </p>
    1221          </li>
    1222       </ol>
    1223       <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body
    1224          and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with 400 (Bad Request) if it cannot determine the length of the message, or with 411 (Length Required) if it wishes
    1225          to insist on receiving a valid Content-Length.
    1226       </p>
    1227       <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance.
    1228       </p>
    1229       <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a transfer-coding. If the message does include a transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored.
    1230       </p>
    1231       <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected.
    1232       </p>
    1233       <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a>&nbsp;<a id="general.header.fields" href="#general.header.fields">General Header Fields</a></h2>
    1234       <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
    1235          to the entity being transferred. These header fields apply only to the message being transmitted.
    1236       </p>
    1237       <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.61"></span>  <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a>            ; <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 16.2</a>
     1217               is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a> places restrictions on when certain transfer-codings may be used.)
     1218            </p>
     1219            <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
     1220            <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
     1221               in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="p2-semantics.html#method" title="Method">Section 3</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) explicitly disallows an entity-body in requests. When a request message contains both a message-body of non-zero length
     1222               and a method that does not define any semantics for that request message-body, then an origin server <em class="bcp14">SHOULD</em> either ignore the message-body or respond with an appropriate error message (e.g., 413). A proxy or gateway, when presented
     1223               the same request, <em class="bcp14">SHOULD</em> either forward the request inbound with the message-body or ignore the message-body when determining a response.
     1224            </p>
     1225            <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
     1226               the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational),
     1227               204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length.
     1228            </p>
     1229         </div>
     1230         <div id="message.length">
     1231            <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a href="#message.length">Message Length</a></h2>
     1232            <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings
     1233               have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of
     1234               the following (in order of precedence):
     1235            </p>
     1236            <p id="rfc.section.4.4.p.2"></p>
     1237            <ol>
     1238               <li>
     1239                  <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated
     1240                     by the first empty line after the header fields, regardless of the entity-header fields present in the message.
     1241                  </p>
     1242               </li>
     1243               <li>
     1244                  <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;8.7</a>) is present and the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>) is used, the transfer-length is defined by the use of this transfer-coding. If a Transfer-Encoding header field is present
     1245                     and the "chunked" transfer-coding is not present, the transfer-length is defined by the sender closing the connection.
     1246                  </p>
     1247               </li>
     1248               <li>
     1249                  <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;8.2</a>) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length header
     1250                     field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received
     1251                     with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored.
     1252                  </p>
     1253               </li>
     1254               <li>
     1255                  <p>If the message uses the media type "multipart/byteranges", and the transfer-length is not otherwise specified, then this self-delimiting
     1256                     media type defines the transfer-length. This media type <em class="bcp14">MUST NOT</em> be used unless the sender knows that the recipient can parse it; the presence in a request of a Range header with multiple
     1257                     byte-range specifiers from a 1.1 client implies that the client can parse multipart/byteranges responses.
     1258                  </p>
     1259                  <ul class="empty">
     1260                     <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section.
     1261                     </li>
     1262                  </ul>
     1263               </li>
     1264               <li>
     1265                  <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since
     1266                     that would leave no possibility for the server to send back a response.)
     1267                  </p>
     1268               </li>
     1269            </ol>
     1270            <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body
     1271               and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with 400 (Bad Request) if it cannot determine the length of the message, or with 411 (Length Required) if it wishes
     1272               to insist on receiving a valid Content-Length.
     1273            </p>
     1274            <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance.
     1275            </p>
     1276            <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a transfer-coding. If the message does include a transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored.
     1277            </p>
     1278            <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected.
     1279            </p>
     1280         </div>
     1281         <div id="general.header.fields">
     1282            <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a>&nbsp;<a href="#general.header.fields">General Header Fields</a></h2>
     1283            <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
     1284               to the entity being transferred. These header fields apply only to the message being transmitted.
     1285            </p>
     1286            <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.61"></span>  <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a>            ; <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 16.2</a>
    12381287                 / <a href="#header.connection" class="smpl">Connection</a>               ; <a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section&nbsp;8.1</a>
    12391288                 / <a href="#header.date" class="smpl">Date</a>                     ; <a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section&nbsp;8.3</a>
     
    12451294                 / <a href="#abnf.dependencies" class="smpl">Warning</a>                  ; <a href="#Part6" id="rfc.xref.Part6.7"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.warning" title="Warning">Section 16.6</a>
    12461295</pre><p id="rfc.section.4.5.p.3">General-header field names can be extended reliably only in combination with a change in the protocol version. However, new
    1247          or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize
    1248          them to be general-header fields. Unrecognized header fields are treated as entity-header fields.
    1249       </p>
    1250       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="request" href="#request">Request</a></h1>
    1251       <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
    1252          resource, the identifier of the resource, and the protocol version in use.
    1253       </p>
    1254       <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.62"></span>  <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;5.1</a>
     1296               or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize
     1297               them to be general-header fields. Unrecognized header fields are treated as entity-header fields.
     1298            </p>
     1299         </div>
     1300      </div>
     1301      <div id="request">
     1302         <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a href="#request">Request</a></h1>
     1303         <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
     1304            resource, the identifier of the resource, and the protocol version in use.
     1305         </p>
     1306         <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.62"></span>  <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;5.1</a>
    12551307                  *(( <a href="#general.header.fields" class="smpl">general-header</a>        ; <a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>
    12561308                   / <a href="#abnf.dependencies" class="smpl">request-header</a>         ; <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a>
     
    12581310                  <a href="#core.rules" class="smpl">CRLF</a>
    12591311                  [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#message.body" title="Message Body">Section&nbsp;4.3</a>
    1260 </pre><h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="request-line" href="#request-line">Request-Line</a></h2>
    1261       <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The
    1262          elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
    1263       </p>
    1264       <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.63"></span>  <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">CRLF</a>
    1265 </pre><h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a id="method" href="#method">Method</a></h3>
    1266       <p id="rfc.section.5.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the Request-URI. The method is case-sensitive.</p>
    1267       <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span>  <a href="#method" class="smpl">Method</a>         = <a href="#rule.token.separators" class="smpl">token</a>
    1268 </pre><h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a id="request-uri" href="#request-uri">Request-URI</a></h3>
    1269       <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>) and identifies the resource upon which to apply the request.
    1270       </p>
    1271       <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.66"></span>  <a href="#request-uri" class="smpl">Request-URI</a>    = "*"
     1312</pre><div id="request-line">
     1313            <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a href="#request-line">Request-Line</a></h2>
     1314            <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The
     1315               elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
     1316            </p>
     1317            <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.63"></span>  <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">CRLF</a>
     1318</pre><div id="method">
     1319               <h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a href="#method">Method</a></h3>
     1320               <p id="rfc.section.5.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the Request-URI. The method is case-sensitive.</p>
     1321               <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span>  <a href="#method" class="smpl">Method</a>         = <a href="#rule.token.separators" class="smpl">token</a>
     1322</pre></div>
     1323            <div id="request-uri">
     1324               <h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a href="#request-uri">Request-URI</a></h3>
     1325               <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>) and identifies the resource upon which to apply the request.
     1326               </p>
     1327               <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.66"></span>  <a href="#request-uri" class="smpl">Request-URI</a>    = "*"
    12721328                 / <a href="#uri" class="smpl">absolute-URI</a>
    12731329                 / ( <a href="#uri" class="smpl">path-absolute</a> [ "?" <a href="#uri" class="smpl">query</a> ] )
    12741330                 / <a href="#uri" class="smpl">authority</a>
    12751331</pre><p id="rfc.section.5.1.2.p.3">The four options for Request-URI are dependent on the nature of the request. The asterisk "*" means that the request does
    1276          not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily
    1277          apply to a resource. One example would be
    1278       </p>
    1279       <div id="rfc.figure.u.36"></div><pre class="text">    OPTIONS * HTTP/1.1
     1332                  not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily
     1333                  apply to a resource. One example would be
     1334               </p>
     1335               <div id="rfc.figure.u.36"></div><pre class="text">    OPTIONS * HTTP/1.1
    12801336</pre><p id="rfc.section.5.1.2.p.5">The absolute-URI form is <em class="bcp14">REQUIRED</em> when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache,
    1281          and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absolute-URI. In order to avoid request
    1282          loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
    1283          Request-Line would be:
    1284       </p>
    1285       <div id="rfc.figure.u.37"></div><pre class="text">    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
     1337                  and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absolute-URI. In order to avoid request
     1338                  loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
     1339                  Request-Line would be:
     1340               </p>
     1341               <div id="rfc.figure.u.37"></div><pre class="text">    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
    12861342</pre><p id="rfc.section.5.1.2.p.7">To allow for transition to absolute-URIs in all requests in future versions of HTTP, all HTTP/1.1 servers <em class="bcp14">MUST</em> accept the absolute-URI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies.
    1287       </p>
    1288       <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 8.9</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    1289       </p>
    1290       <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute
    1291          path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>, path-absolute) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
    1292          server would create a TCP connection to port 80 of the host "www.example.org" and send the lines:
    1293       </p>
    1294       <div id="rfc.figure.u.38"></div><pre class="text">    GET /pub/WWW/TheProject.html HTTP/1.1
     1343               </p>
     1344               <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 8.9</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
     1345               </p>
     1346               <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute
     1347                  path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>, path-absolute) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
     1348                  server would create a TCP connection to port 80 of the host "www.example.org" and send the lines:
     1349               </p>
     1350               <div id="rfc.figure.u.38"></div><pre class="text">    GET /pub/WWW/TheProject.html HTTP/1.1
    12951351    Host: www.example.org
    12961352</pre><p id="rfc.section.5.1.2.p.11">followed by the remainder of the Request. Note that the absolute path cannot be empty; if none is present in the original
    1297          URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
    1298       </p>
    1299       <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>. If the Request-URI is encoded using the "% <a href="#core.rules" class="smpl">HEXDIG</a>  <a href="#core.rules" class="smpl">HEXDIG</a>" encoding (<a href="#RFC3986" id="rfc.xref.RFC3986.14"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-2.4">Section 2.4</a>), the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code.
    1300       </p>
    1301       <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received Request-URI when forwarding it to the next inbound server, except as noted
    1302          above to replace a null path-absolute with "/".
    1303       </p>
    1304       <p id="rfc.section.5.1.2.p.14"> </p>
    1305       <ul class="empty">
    1306          <li> <b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
    1307             a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been
    1308             known to rewrite the Request-URI.
    1309          </li>
    1310       </ul>
    1311       <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="the.resource.identified.by.a.request" href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
    1312       <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p>
    1313       <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;C.1.1</a> for other requirements on Host support in HTTP/1.1.)
    1314       </p>
    1315       <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
    1316          vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
    1317       </p>
    1318       <ol>
    1319          <li>If Request-URI is an absolute-URI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
    1320          </li>
    1321          <li>If the Request-URI is not an absolute-URI, and the request includes a Host header field, the host is determined by the Host
    1322             header field value.
    1323          </li>
    1324          <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message.
    1325          </li>
    1326       </ol>
    1327       <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
    1328          what exact resource is being requested.
    1329       </p>
    1330       <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="response" href="#response">Response</a></h1>
    1331       <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
    1332       <div id="rfc.figure.u.39"></div><pre class="inline"><span id="rfc.iref.g.67"></span>  <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;6.1</a>
     1353                  URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
     1354               </p>
     1355               <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>. If the Request-URI is encoded using the "% <a href="#core.rules" class="smpl">HEXDIG</a> <a href="#core.rules" class="smpl">HEXDIG</a>" encoding (<a href="#RFC3986" id="rfc.xref.RFC3986.14"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-2.4">Section 2.4</a>), the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code.
     1356               </p>
     1357               <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received Request-URI when forwarding it to the next inbound server, except as noted
     1358                  above to replace a null path-absolute with "/".
     1359               </p>
     1360               <p id="rfc.section.5.1.2.p.14"></p>
     1361               <ul class="empty">
     1362                  <li><b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
     1363                     a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been
     1364                     known to rewrite the Request-URI.
     1365                  </li>
     1366               </ul>
     1367            </div>
     1368         </div>
     1369         <div id="the.resource.identified.by.a.request">
     1370            <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
     1371            <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p>
     1372            <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;C.1.1</a> for other requirements on Host support in HTTP/1.1.)
     1373            </p>
     1374            <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
     1375               vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
     1376            </p>
     1377            <ol>
     1378               <li>If Request-URI is an absolute-URI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
     1379               </li>
     1380               <li>If the Request-URI is not an absolute-URI, and the request includes a Host header field, the host is determined by the Host
     1381                  header field value.
     1382               </li>
     1383               <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message.
     1384               </li>
     1385            </ol>
     1386            <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
     1387               what exact resource is being requested.
     1388            </p>
     1389         </div>
     1390      </div>
     1391      <div id="response">
     1392         <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#response">Response</a></h1>
     1393         <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
     1394         <div id="rfc.figure.u.39"></div><pre class="inline"><span id="rfc.iref.g.67"></span>  <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;6.1</a>
    13331395                  *(( <a href="#general.header.fields" class="smpl">general-header</a>        ; <a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>
    13341396                   / <a href="#abnf.dependencies" class="smpl">response-header</a>        ; <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a>
     
    13361398                  <a href="#core.rules" class="smpl">CRLF</a>
    13371399                  [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#message.body" title="Message Body">Section&nbsp;4.3</a>
    1338 </pre><h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="status-line" href="#status-line">Status-Line</a></h2>
    1339       <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
    1340          and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
    1341          CRLF sequence.
    1342       </p>
    1343       <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.68"></span>  <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#core.rules" class="smpl">CRLF</a>
    1344 </pre><h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;<a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
    1345       <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
    1346          are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 9</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code,
    1347          out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A
    1348          client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase.
    1349       </p>
    1350       <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
    1351          There are 5 values for the first digit:
    1352       </p>
    1353       <ul>
    1354          <li>1xx: Informational - Request received, continuing process</li>
    1355          <li>2xx: Success - The action was successfully received, understood, and accepted</li>
    1356          <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
    1357          <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
    1358          <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
    1359       </ul>
    1360       <div id="rfc.figure.u.41"></div><pre class="inline"><span id="rfc.iref.g.69"></span><span id="rfc.iref.g.70"></span><span id="rfc.iref.g.71"></span>  <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a>    = 3<a href="#core.rules" class="smpl">DIGIT</a>
     1400</pre><div id="status-line">
     1401            <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#status-line">Status-Line</a></h2>
     1402            <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
     1403               and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
     1404               CRLF sequence.
     1405            </p>
     1406            <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.68"></span>  <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#core.rules" class="smpl">CRLF</a>
     1407</pre><div id="status.code.and.reason.phrase">
     1408               <h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
     1409               <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
     1410                  are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 9</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code,
     1411                  out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A
     1412                  client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase.
     1413               </p>
     1414               <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
     1415                  There are 5 values for the first digit:
     1416               </p>
     1417               <ul>
     1418                  <li>1xx: Informational - Request received, continuing process</li>
     1419                  <li>2xx: Success - The action was successfully received, understood, and accepted</li>
     1420                  <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
     1421                  <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
     1422                  <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
     1423               </ul>
     1424               <div id="rfc.figure.u.41"></div><pre class="inline"><span id="rfc.iref.g.69"></span><span id="rfc.iref.g.70"></span><span id="rfc.iref.g.71"></span>  <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a>    = 3<a href="#core.rules" class="smpl">DIGIT</a>
    13611425  <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a>  = *&lt;<a href="#rule.TEXT" class="smpl">TEXT</a>, excluding <a href="#core.rules" class="smpl">CR</a>, <a href="#core.rules" class="smpl">LF</a>&gt;
    1362 </pre><h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="connections" href="#connections">Connections</a></h1>
    1363       <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="persistent.connections" href="#persistent.connections">Persistent Connections</a></h2>
    1364       <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a id="persistent.purpose" href="#persistent.purpose">Purpose</a></h3>
    1365       <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
    1366          servers and causing congestion on the Internet. The use of inline images and other associated data often require a client
    1367          to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
    1368          from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a>  <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (<cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2068.2">RFC 2068</cite>) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>.
    1369       </p>
    1370       <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
    1371       <ul>
    1372          <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
    1373             tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
    1374          </li>
    1375          <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
    1376             waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
    1377          </li>
    1378          <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
    1379             determine the congestion state of the network.
    1380          </li>
    1381          <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
    1382          <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
    1383             future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
    1384             semantics after an error is reported.
    1385          </li>
    1386       </ul>
    1387       <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
    1388       </p>
    1389       <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a id="persistent.overall" href="#persistent.overall">Overall Operation</a></h3>
    1390       <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
    1391          of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
    1392       </p>
    1393       <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
    1394          takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;8.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
    1395       </p>
    1396       <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a>&nbsp;<a id="persistent.negotiation" href="#persistent.negotiation">Negotiation</a></h4>
    1397       <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
    1398          "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
    1399       </p>
    1400       <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
    1401          a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
    1402          that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
    1403       </p>
    1404       <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
    1405          connection.
    1406       </p>
    1407       <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;C.2</a> for more information on backward compatibility with HTTP/1.0 clients.
    1408       </p>
    1409       <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
    1410       </p>
    1411       <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a>&nbsp;<a id="pipelining" href="#pipelining">Pipelining</a></h4>
    1412       <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
    1413       </p>
    1414       <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
    1415       </p>
    1416       <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
    1417          send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request.
    1418       </p>
    1419       <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a id="persistent.proxy" href="#persistent.proxy">Proxy Servers</a></h3>
    1420       <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;8.1</a>.
    1421       </p>
    1422       <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
    1423          to. Each persistent connection applies to only one transport link.
    1424       </p>
    1425       <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
    1426       </p>
    1427       <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;<a id="persistent.practical" href="#persistent.practical">Practical Considerations</a></h3>
    1428       <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
    1429          might make this a higher value since it is likely that the client will be making more connections through the same server.
    1430          The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
    1431          or the server.
    1432       </p>
    1433       <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
    1434          not detect the other side's close promptly it could cause unnecessary resource drain on the network.
    1435       </p>
    1436       <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
    1437          that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
    1438          while it was idle, but from the client's point of view, a request is in progress.
    1439       </p>
    1440       <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
    1441          sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.12"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
    1442          of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
    1443       </p>
    1444       <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
    1445       </p>
    1446       <p id="rfc.section.7.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines
    1447          are intended to improve HTTP response times and avoid congestion.
    1448       </p>
    1449       <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="message.transmission.requirements" href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
    1450       <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a id="persistent.flow" href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
    1451       <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
    1452          connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
    1453       </p>
    1454       <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a id="persistent.monitor" href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
    1455       <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status,
    1456          it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
    1457       </p>
    1458       <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
    1459       <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 9.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
    1460          to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
    1461          be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
    1462          at the body.
    1463       </p>
    1464       <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
    1465       <ul>
    1466          <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation.
    1467          </li>
    1468          <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.15"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body.
    1469          </li>
    1470       </ul>
    1471       <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect:
    1472          100-continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client
    1473          sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the
    1474          client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
    1475       </p>
    1476       <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
    1477       <ul>
    1478          <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final status code.
    1479             The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
    1480          </li>
    1481          <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue"
    1482             expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this
    1483             rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header
    1484             field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays
    1485             associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 requests, and not to requests with
    1486             any other HTTP-version value.
    1487          </li>
    1488          <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request.
    1489          </li>
    1490          <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
    1491             prematurely.
    1492          </li>
    1493          <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
    1494             the request includes a request body, and the server responds with a final status code before reading the entire request body
    1495             from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
    1496             the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
    1497             server from defending itself against denial-of-service attacks, or from badly broken client implementations.
    1498          </li>
    1499       </ul>
    1500       <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
    1501       <ul>
    1502          <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
    1503             either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
    1504             server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
    1505          </li>
    1506          <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status.
    1507          </li>
    1508          <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
    1509          </li>
    1510          <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include
    1511             an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding
    1512             of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 9.1</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    1513          </li>
    1514       </ul>
    1515       <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;<a id="connection.premature" href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
    1516       <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
    1517          with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
    1518          client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
    1519       </p>
    1520       <ol>
    1521          <li>Initiate a new connection to the server</li>
    1522          <li>Transmit the request-headers</li>
    1523          <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
    1524             or to a constant value of 5 seconds if the round-trip time is not available.
    1525          </li>
    1526          <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
    1527          <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
    1528          <li>If no error response is received, after T seconds transmit the body of the request.</li>
    1529          <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
    1530             is received, or the user becomes impatient and terminates the retry process.
    1531          </li>
    1532       </ol>
    1533       <p id="rfc.section.7.2.4.p.2">If at any point an error status is received, the client </p>
    1534       <ul>
    1535          <li><em class="bcp14">SHOULD NOT</em> continue and
    1536          </li>
    1537          <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
    1538          </li>
    1539       </ul>
    1540       <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
    1541       <p id="rfc.section.8.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p>
    1542       <p id="rfc.section.8.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
    1543          receives the entity.
    1544       </p>
    1545       <div id="rfc.iref.c.1"></div>
    1546       <div id="rfc.iref.h.3"></div>
    1547       <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a id="header.connection" href="#header.connection">Connection</a></h2>
    1548       <p id="rfc.section.8.1.p.1">The general-header field "Connection" allows the sender to specify options that are desired for that particular connection
    1549          and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections.
    1550       </p>
    1551       <p id="rfc.section.8.1.p.2">The Connection header's value has the following grammar:</p>
    1552       <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.72"></span><span id="rfc.iref.g.73"></span><span id="rfc.iref.g.74"></span>  <a href="#header.connection" class="smpl">Connection</a>       = "Connection" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.connection" class="smpl">Connection-v</a>
     1426</pre></div>
     1427         </div>
     1428      </div>
     1429      <div id="connections">
     1430         <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#connections">Connections</a></h1>
     1431         <div id="persistent.connections">
     1432            <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#persistent.connections">Persistent Connections</a></h2>
     1433            <div id="persistent.purpose">
     1434               <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a href="#persistent.purpose">Purpose</a></h3>
     1435               <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
     1436                  servers and causing congestion on the Internet. The use of inline images and other associated data often require a client
     1437                  to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
     1438                  from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a> <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (<cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2068.2">RFC 2068</cite>) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>.
     1439               </p>
     1440               <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
     1441               <ul>
     1442                  <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
     1443                     tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
     1444                  </li>
     1445                  <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
     1446                     waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
     1447                  </li>
     1448                  <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
     1449                     determine the congestion state of the network.
     1450                  </li>
     1451                  <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
     1452                  <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
     1453                     future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
     1454                     semantics after an error is reported.
     1455                  </li>
     1456               </ul>
     1457               <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
     1458               </p>
     1459            </div>
     1460            <div id="persistent.overall">
     1461               <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a href="#persistent.overall">Overall Operation</a></h3>
     1462               <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
     1463                  of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
     1464               </p>
     1465               <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
     1466                  takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;8.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
     1467               </p>
     1468               <div id="persistent.negotiation">
     1469                  <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a>&nbsp;<a href="#persistent.negotiation">Negotiation</a></h4>
     1470                  <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
     1471                     "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
     1472                  </p>
     1473                  <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
     1474                     a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
     1475                     that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
     1476                  </p>
     1477                  <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
     1478                     connection.
     1479                  </p>
     1480                  <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;C.2</a> for more information on backward compatibility with HTTP/1.0 clients.
     1481                  </p>
     1482                  <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
     1483                  </p>
     1484               </div>
     1485               <div id="pipelining">
     1486                  <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a>&nbsp;<a href="#pipelining">Pipelining</a></h4>
     1487                  <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
     1488                  </p>
     1489                  <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
     1490                  </p>
     1491                  <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
     1492                     send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request.
     1493                  </p>
     1494               </div>
     1495            </div>
     1496            <div id="persistent.proxy">
     1497               <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a href="#persistent.proxy">Proxy Servers</a></h3>
     1498               <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;8.1</a>.
     1499               </p>
     1500               <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
     1501                  to. Each persistent connection applies to only one transport link.
     1502               </p>
     1503               <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
     1504               </p>
     1505            </div>
     1506            <div id="persistent.practical">
     1507               <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;<a href="#persistent.practical">Practical Considerations</a></h3>
     1508               <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
     1509                  might make this a higher value since it is likely that the client will be making more connections through the same server.
     1510                  The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
     1511                  or the server.
     1512               </p>
     1513               <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
     1514                  not detect the other side's close promptly it could cause unnecessary resource drain on the network.
     1515               </p>
     1516               <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
     1517                  that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
     1518                  while it was idle, but from the client's point of view, a request is in progress.
     1519               </p>
     1520               <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
     1521                  sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.12"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
     1522                  of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
     1523               </p>
     1524               <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
     1525               </p>
     1526               <p id="rfc.section.7.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines
     1527                  are intended to improve HTTP response times and avoid congestion.
     1528               </p>
     1529            </div>
     1530         </div>
     1531         <div id="message.transmission.requirements">
     1532            <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
     1533            <div id="persistent.flow">
     1534               <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
     1535               <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
     1536                  connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
     1537               </p>
     1538            </div>
     1539            <div id="persistent.monitor">
     1540               <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
     1541               <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status,
     1542                  it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
     1543               </p>
     1544            </div>
     1545            <div id="use.of.the.100.status">
     1546               <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
     1547               <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 9.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
     1548                  to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
     1549                  be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
     1550                  at the body.
     1551               </p>
     1552               <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
     1553               <ul>
     1554                  <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation.
     1555                  </li>
     1556                  <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.15"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body.
     1557                  </li>
     1558               </ul>
     1559               <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect:
     1560                  100-continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client
     1561                  sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the
     1562                  client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
     1563               </p>
     1564               <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
     1565               <ul>
     1566                  <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final status code.
     1567                     The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
     1568                  </li>
     1569                  <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue"
     1570                     expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this
     1571                     rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header
     1572                     field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays
     1573                     associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 requests, and not to requests with
     1574                     any other HTTP-version value.
     1575                  </li>
     1576                  <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request.
     1577                  </li>
     1578                  <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
     1579                     prematurely.
     1580                  </li>
     1581                  <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
     1582                     the request includes a request body, and the server responds with a final status code before reading the entire request body
     1583                     from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
     1584                     the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
     1585                     server from defending itself against denial-of-service attacks, or from badly broken client implementations.
     1586                  </li>
     1587               </ul>
     1588               <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
     1589               <ul>
     1590                  <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
     1591                     either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
     1592                     server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
     1593                  </li>
     1594                  <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status.
     1595                  </li>
     1596                  <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
     1597                  </li>
     1598                  <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include
     1599                     an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding
     1600                     of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 9.1</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
     1601                  </li>
     1602               </ul>
     1603            </div>
     1604            <div id="connection.premature">
     1605               <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
     1606               <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
     1607                  with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
     1608                  client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
     1609               </p>
     1610               <ol>
     1611                  <li>Initiate a new connection to the server</li>
     1612                  <li>Transmit the request-headers</li>
     1613                  <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
     1614                     or to a constant value of 5 seconds if the round-trip time is not available.
     1615                  </li>
     1616                  <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
     1617                  <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
     1618                  <li>If no error response is received, after T seconds transmit the body of the request.</li>
     1619                  <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
     1620                     is received, or the user becomes impatient and terminates the retry process.
     1621                  </li>
     1622               </ol>
     1623               <p id="rfc.section.7.2.4.p.2">If at any point an error status is received, the client </p>
     1624               <ul>
     1625                  <li><em class="bcp14">SHOULD NOT</em> continue and
     1626                  </li>
     1627                  <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
     1628                  </li>
     1629               </ul>
     1630            </div>
     1631         </div>
     1632      </div>
     1633      <div id="header.fields">
     1634         <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#header.fields">Header Field Definitions</a></h1>
     1635         <p id="rfc.section.8.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p>
     1636         <p id="rfc.section.8.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
     1637            receives the entity.
     1638         </p>
     1639         <div id="header.connection">
     1640            <div id="rfc.iref.c.1"></div>
     1641            <div id="rfc.iref.h.3"></div>
     1642            <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#header.connection">Connection</a></h2>
     1643            <p id="rfc.section.8.1.p.1">The general-header field "Connection" allows the sender to specify options that are desired for that particular connection
     1644               and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections.
     1645            </p>
     1646            <p id="rfc.section.8.1.p.2">The Connection header's value has the following grammar:</p>
     1647            <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.72"></span><span id="rfc.iref.g.73"></span><span id="rfc.iref.g.74"></span>  <a href="#header.connection" class="smpl">Connection</a>       = "Connection" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.connection" class="smpl">Connection-v</a>
    15531648  <a href="#header.connection" class="smpl">Connection-v</a>     = 1#<a href="#header.connection" class="smpl">connection-token</a>
    15541649  <a href="#header.connection" class="smpl">connection-token</a> = <a href="#rule.token.separators" class="smpl">token</a>
    15551650</pre><p id="rfc.section.8.1.p.4">HTTP/1.1 proxies <em class="bcp14">MUST</em> parse the Connection header field before a message is forwarded and, for each connection-token in this field, remove any header
    1556          field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a
    1557          connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional
    1558          header field may not be sent if there are no parameters associated with that connection option.
    1559       </p>
    1560       <p id="rfc.section.8.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control.
    1561       </p>
    1562       <p id="rfc.section.8.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion
    1563          of the response. For example,
    1564       </p>
    1565       <div id="rfc.figure.u.43"></div><pre class="text">  Connection: close
     1651               field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a
     1652               connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional
     1653               header field may not be sent if there are no parameters associated with that connection option.
     1654            </p>
     1655            <p id="rfc.section.8.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control.
     1656            </p>
     1657            <p id="rfc.section.8.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion
     1658               of the response. For example,
     1659            </p>
     1660            <div id="rfc.figure.u.43"></div><pre class="text">  Connection: close
    15661661</pre><p id="rfc.section.8.1.p.8">in either the request or the response header fields indicates that the connection <em class="bcp14">SHOULD NOT</em> be considered `persistent' (<a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>) after the current request/response is complete.
    1567       </p>
    1568       <p id="rfc.section.8.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message.
    1569       </p>
    1570       <p id="rfc.section.8.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (informational) status code.
    1571       </p>
    1572       <p id="rfc.section.8.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the
    1573          connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;C.2</a>.
    1574       </p>
    1575       <div id="rfc.iref.c.2"></div>
    1576       <div id="rfc.iref.h.4"></div>
    1577       <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a id="header.content-length" href="#header.content-length">Content-Length</a></h2>
    1578       <p id="rfc.section.8.2.p.1">The entity-header field "Content-Length" indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient
    1579          or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.
    1580       </p>
    1581       <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span>  <a href="#header.content-length" class="smpl">Content-Length</a>   = "Content-Length" ":" <a href="#rule.whitespace" class="smpl">OWS</a> 1*<a href="#header.content-length" class="smpl">Content-Length-v</a>
     1662            </p>
     1663            <p id="rfc.section.8.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message.
     1664            </p>
     1665            <p id="rfc.section.8.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (informational) status code.
     1666            </p>
     1667            <p id="rfc.section.8.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the
     1668               connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;C.2</a>.
     1669            </p>
     1670         </div>
     1671         <div id="header.content-length">
     1672            <div id="rfc.iref.c.2"></div>
     1673            <div id="rfc.iref.h.4"></div>
     1674            <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#header.content-length">Content-Length</a></h2>
     1675            <p id="rfc.section.8.2.p.1">The entity-header field "Content-Length" indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient
     1676               or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.
     1677            </p>
     1678            <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span>  <a href="#header.content-length" class="smpl">Content-Length</a>   = "Content-Length" ":" <a href="#rule.whitespace" class="smpl">OWS</a> 1*<a href="#header.content-length" class="smpl">Content-Length-v</a>
    15821679  <a href="#header.content-length" class="smpl">Content-Length-v</a> = 1*<a href="#core.rules" class="smpl">DIGIT</a>
    15831680</pre><p id="rfc.section.8.2.p.3">An example is</p>
    1584       <div id="rfc.figure.u.45"></div><pre class="text">  Content-Length: 3495
     1681            <div id="rfc.figure.u.45"></div><pre class="text">  Content-Length: 3495
    15851682</pre><p id="rfc.section.8.2.p.5">Applications <em class="bcp14">SHOULD</em> use this field to indicate the transfer-length of the message-body, unless this is prohibited by the rules in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
    1586       </p>
    1587       <p id="rfc.section.8.2.p.6">Any Content-Length greater than or equal to zero is a valid value. <a href="#message.length" title="Message Length">Section&nbsp;4.4</a> describes how to determine the length of a message-body if a Content-Length is not given.
    1588       </p>
    1589       <p id="rfc.section.8.2.p.7">Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional
    1590          field used within the "message/external-body" content-type. In HTTP, it <em class="bcp14">SHOULD</em> be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules
    1591          in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
    1592       </p>
    1593       <div id="rfc.iref.d.1"></div>
    1594       <div id="rfc.iref.h.5"></div>
    1595       <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a id="header.date" href="#header.date">Date</a></h2>
    1596       <p id="rfc.section.8.3.p.1">The general-header field "Date" represents the date and time at which the message was originated, having the same semantics
    1597          as orig-date in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as described in <a href="#full.date" title="Full Date">Section&nbsp;3.3.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
    1598       </p>
    1599       <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.77"></span><span id="rfc.iref.g.78"></span>  <a href="#header.date" class="smpl">Date</a>   = "Date" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.date" class="smpl">Date-v</a>
     1683            </p>
     1684            <p id="rfc.section.8.2.p.6">Any Content-Length greater than or equal to zero is a valid value. <a href="#message.length" title="Message Length">Section&nbsp;4.4</a> describes how to determine the length of a message-body if a Content-Length is not given.
     1685            </p>
     1686            <p id="rfc.section.8.2.p.7">Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional
     1687               field used within the "message/external-body" content-type. In HTTP, it <em class="bcp14">SHOULD</em> be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules
     1688               in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
     1689            </p>
     1690         </div>
     1691         <div id="header.date">
     1692            <div id="rfc.iref.d.1"></div>
     1693            <div id="rfc.iref.h.5"></div>
     1694            <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#header.date">Date</a></h2>
     1695            <p id="rfc.section.8.3.p.1">The general-header field "Date" represents the date and time at which the message was originated, having the same semantics
     1696               as orig-date in <a href="https://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as described in <a href="#full.date" title="Full Date">Section&nbsp;3.3.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
     1697            </p>
     1698            <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.77"></span><span id="rfc.iref.g.78"></span>  <a href="#header.date" class="smpl">Date</a>   = "Date" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.date" class="smpl">Date-v</a>
    16001699  <a href="#header.date" class="smpl">Date-v</a> = <a href="#full.date" class="smpl">HTTP-date</a>
    16011700</pre><p id="rfc.section.8.3.p.3">An example is</p>
    1602       <div id="rfc.figure.u.47"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
     1701            <div id="rfc.figure.u.47"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
    16031702</pre><p id="rfc.section.8.3.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases:
    1604       </p>
    1605       <ol>
    1606          <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option.
    1607          </li>
    1608          <li>If the response status code conveys a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it
    1609             is inconvenient or impossible to generate a valid Date.
    1610          </li>
    1611          <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section&nbsp;8.3.1</a>  <em class="bcp14">MUST</em> be followed.
    1612          </li>
    1613       </ol>
    1614       <p id="rfc.section.8.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires
    1615          a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
    1616       </p>
    1617       <p id="rfc.section.8.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include an entity-body, as in the case of the PUT and POST requests, and even
    1618          then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request.
    1619       </p>
    1620       <p id="rfc.section.8.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means
    1621          of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the entity
    1622          is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic
    1623          value.
    1624       </p>
    1625       <h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a id="clockless.origin.server.operation" href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3>
    1626       <p id="rfc.section.8.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or
    1627          user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration"
    1628          of responses without storing separate Expires values for each resource).
    1629       </p>
    1630       <div id="rfc.iref.h.6"></div>
    1631       <div id="rfc.iref.h.7"></div>
    1632       <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a id="header.host" href="#header.host">Host</a></h2>
    1633       <p id="rfc.section.8.4.p.1">The request-header field "Host" specifies the Internet host and port number of the resource being requested, as obtained from
    1634          the original URI given by the user or referring resource (generally an HTTP URL, as described in <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>). The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL. This allows the origin server or
    1635          gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple host names on
    1636          a single IP address.
    1637       </p>
    1638       <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span>  <a href="#header.host" class="smpl">Host</a>   = "Host" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.host" class="smpl">Host-v</a>
     1703            </p>
     1704            <ol>
     1705               <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option.
     1706               </li>
     1707               <li>If the response status code conveys a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it
     1708                  is inconvenient or impossible to generate a valid Date.
     1709               </li>
     1710               <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section&nbsp;8.3.1</a> <em class="bcp14">MUST</em> be followed.
     1711               </li>
     1712            </ol>
     1713            <p id="rfc.section.8.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires
     1714               a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
     1715            </p>
     1716            <p id="rfc.section.8.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include an entity-body, as in the case of the PUT and POST requests, and even
     1717               then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request.
     1718            </p>
     1719            <p id="rfc.section.8.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means
     1720               of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the entity
     1721               is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic
     1722               value.
     1723            </p>
     1724            <div id="clockless.origin.server.operation">
     1725               <h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3>
     1726               <p id="rfc.section.8.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or
     1727                  user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration"
     1728                  of responses without storing separate Expires values for each resource).
     1729               </p>
     1730            </div>
     1731         </div>
     1732         <div id="header.host">
     1733            <div id="rfc.iref.h.6"></div>
     1734            <div id="rfc.iref.h.7"></div>
     1735            <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a href="#header.host">Host</a></h2>
     1736            <p id="rfc.section.8.4.p.1">The request-header field "Host" specifies the Internet host and port number of the resource being requested, as obtained from
     1737               the original URI given by the user or referring resource (generally an HTTP URL, as described in <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>). The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL. This allows the origin server or
     1738               gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple host names on
     1739               a single IP address.
     1740            </p>
     1741            <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span>  <a href="#header.host" class="smpl">Host</a>   = "Host" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.host" class="smpl">Host-v</a>
    16391742  <a href="#header.host" class="smpl">Host-v</a> = <a href="#uri" class="smpl">uri-host</a> [ ":" <a href="#uri" class="smpl">port</a> ] ; <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a>
    16401743</pre><p id="rfc.section.8.4.p.3">A "host" without any trailing port information implies the default port for the service requested (e.g., "80" for an HTTP
    1641          URL). For example, a request on the origin server for &lt;http://www.example.org/pub/WWW/&gt; would properly include:
    1642       </p>
    1643       <div id="rfc.figure.u.49"></div><pre class="text">  GET /pub/WWW/ HTTP/1.1
     1744               URL). For example, a request on the origin server for &lt;http://www.example.org/pub/WWW/&gt; would properly include:
     1745            </p>
     1746            <div id="rfc.figure.u.49"></div><pre class="text">  GET /pub/WWW/ HTTP/1.1
    16441747  Host: www.example.org
    16451748</pre><p id="rfc.section.8.4.p.5">A client <em class="bcp14">MUST</em> include a Host header field in all HTTP/1.1 request messages. If the requested URI does not include an Internet host name
    1646          for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being
    1647          requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field.
    1648       </p>
    1649       <p id="rfc.section.8.4.p.6">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">5.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">C.1.1</a> for other requirements relating to Host.
    1650       </p>
    1651       <div id="rfc.iref.t.1"></div>
    1652       <div id="rfc.iref.h.8"></div>
    1653       <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a id="header.te" href="#header.te">TE</a></h2>
    1654       <p id="rfc.section.8.5.p.1">The request-header field "TE" indicates what extension transfer-codings it is willing to accept in the response and whether
    1655          or not it is willing to accept trailer fields in a chunked transfer-coding. Its value may consist of the keyword "trailers"
    1656          and/or a comma-separated list of extension transfer-coding names with optional accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>).
    1657       </p>
    1658       <div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span>  <a href="#header.te" class="smpl">TE</a>        = "TE" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.te" class="smpl">TE-v</a>
     1749               for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being
     1750               requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field.
     1751            </p>
     1752            <p id="rfc.section.8.4.p.6">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">5.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">C.1.1</a> for other requirements relating to Host.
     1753            </p>
     1754         </div>
     1755         <div id="header.te">
     1756            <div id="rfc.iref.t.1"></div>
     1757            <div id="rfc.iref.h.8"></div>
     1758            <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a href="#header.te">TE</a></h2>
     1759            <p id="rfc.section.8.5.p.1">The request-header field "TE" indicates what extension transfer-codings it is willing to accept in the response and whether
     1760               or not it is willing to accept trailer fields in a chunked transfer-coding. Its value may consist of the keyword "trailers"
     1761               and/or a comma-separated list of extension transfer-coding names with optional accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>).
     1762            </p>
     1763            <div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span>  <a href="#header.te" class="smpl">TE</a>        = "TE" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.te" class="smpl">TE-v</a>
    16591764  <a href="#header.te" class="smpl">TE-v</a>      = #<a href="#header.te" class="smpl">t-codings</a>
    16601765  <a href="#header.te" class="smpl">t-codings</a> = "trailers" / ( <a href="#transfer.codings" class="smpl">transfer-extension</a> [ <a href="#abnf.dependencies" class="smpl">accept-params</a> ] )
    16611766</pre><p id="rfc.section.8.5.p.3">The presence of the keyword "trailers" indicates that the client is willing to accept trailer fields in a chunked transfer-coding,
    1662          as defined in <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.
    1663       </p>
    1664       <p id="rfc.section.8.5.p.4">Examples of its use are:</p>
    1665       <div id="rfc.figure.u.51"></div><pre class="text">  TE: deflate
     1767               as defined in <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.
     1768            </p>
     1769            <p id="rfc.section.8.5.p.4">Examples of its use are:</p>
     1770            <div id="rfc.figure.u.51"></div><pre class="text">  TE: deflate
    16661771  TE:
    16671772  TE: trailers, deflate;q=0.5
    16681773</pre><p id="rfc.section.8.5.p.6">The TE header field only applies to the immediate connection. Therefore, the keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.4" title="Connection">Section&nbsp;8.1</a>) whenever TE is present in an HTTP/1.1 message.
    1669       </p>
    1670       <p id="rfc.section.8.5.p.7">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p>
    1671       <ol>
    1672          <li>
    1673             <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing
    1674                to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that,
    1675                if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response,
    1676                or that it will attempt to buffer the response on behalf of downstream recipients.
    1677             </p>
    1678             <p> <b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering
    1679                the entire response.
    1680             </p>
    1681          </li>
    1682          <li>
    1683             <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it
    1684                is accompanied by a qvalue of 0. (As defined in <a href="p3-payload.html#quality.values" title="Quality Values">Section 3.4</a> of <a href="#Part3" id="rfc.xref.Part3.12"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, a qvalue of 0 means "not acceptable.")
    1685             </p>
    1686          </li>
    1687          <li>
    1688             <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred.
    1689                The "chunked" transfer-coding always has a qvalue of 1.
    1690             </p>
    1691          </li>
    1692       </ol>
    1693       <p id="rfc.section.8.5.p.8">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding
    1694          is always acceptable.
    1695       </p>
    1696       <div id="rfc.iref.t.2"></div>
    1697       <div id="rfc.iref.h.9"></div>
    1698       <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a id="header.trailer" href="#header.trailer">Trailer</a></h2>
    1699       <p id="rfc.section.8.6.p.1">The general field "Trailer" indicates that the given set of header fields is present in the trailer of a message encoded with
    1700          chunked transfer-coding.
    1701       </p>
    1702       <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.84"></span><span id="rfc.iref.g.85"></span>  <a href="#header.trailer" class="smpl">Trailer</a>   = "Trailer" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.trailer" class="smpl">Trailer-v</a>
     1774            </p>
     1775            <p id="rfc.section.8.5.p.7">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p>
     1776            <ol>
     1777               <li>
     1778                  <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing
     1779                     to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that,
     1780                     if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response,
     1781                     or that it will attempt to buffer the response on behalf of downstream recipients.
     1782                  </p>
     1783                  <p><b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering
     1784                     the entire response.
     1785                  </p>
     1786               </li>
     1787               <li>
     1788                  <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it
     1789                     is accompanied by a qvalue of 0. (As defined in <a href="p3-payload.html#quality.values" title="Quality Values">Section 3.4</a> of <a href="#Part3" id="rfc.xref.Part3.12"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, a qvalue of 0 means "not acceptable.")
     1790                  </p>
     1791               </li>
     1792               <li>
     1793                  <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred.
     1794                     The "chunked" transfer-coding always has a qvalue of 1.
     1795                  </p>
     1796               </li>
     1797            </ol>
     1798            <p id="rfc.section.8.5.p.8">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding
     1799               is always acceptable.
     1800            </p>
     1801         </div>
     1802         <div id="header.trailer">
     1803            <div id="rfc.iref.t.2"></div>
     1804            <div id="rfc.iref.h.9"></div>
     1805            <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a href="#header.trailer">Trailer</a></h2>
     1806            <p id="rfc.section.8.6.p.1">The general field "Trailer" indicates that the given set of header fields is present in the trailer of a message encoded with
     1807               chunked transfer-coding.
     1808            </p>
     1809            <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.84"></span><span id="rfc.iref.g.85"></span>  <a href="#header.trailer" class="smpl">Trailer</a>   = "Trailer" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.trailer" class="smpl">Trailer-v</a>
    17031810  <a href="#header.trailer" class="smpl">Trailer-v</a> = 1#<a href="#message.headers" class="smpl">field-name</a>
    17041811</pre><p id="rfc.section.8.6.p.3">An HTTP/1.1 message <em class="bcp14">SHOULD</em> include a Trailer header field in a message using chunked transfer-coding with a non-empty trailer. Doing so allows the recipient
    1705          to know which header fields to expect in the trailer.
    1706       </p>
    1707       <p id="rfc.section.8.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding.
    1708       </p>
    1709       <p id="rfc.section.8.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields:
    1710       </p>
    1711       <ul>
    1712          <li>Transfer-Encoding</li>
    1713          <li>Content-Length</li>
    1714          <li>Trailer</li>
    1715       </ul>
    1716       <div id="rfc.iref.t.3"></div>
    1717       <div id="rfc.iref.h.10"></div>
    1718       <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a>&nbsp;<a id="header.transfer-encoding" href="#header.transfer-encoding">Transfer-Encoding</a></h2>
    1719       <p id="rfc.section.8.7.p.1">The general-header "Transfer-Encoding" field indicates what (if any) type of transformation has been applied to the message
    1720          body in order to safely transfer it between the sender and the recipient. This differs from the content-coding in that the
    1721          transfer-coding is a property of the message, not of the entity.
    1722       </p>
    1723       <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.86"></span><span id="rfc.iref.g.87"></span>  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>   = "Transfer-Encoding" ":" <a href="#rule.whitespace" class="smpl">OWS</a>
     1812               to know which header fields to expect in the trailer.
     1813            </p>
     1814            <p id="rfc.section.8.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding.
     1815            </p>
     1816            <p id="rfc.section.8.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields:
     1817            </p>
     1818            <ul>
     1819               <li>Transfer-Encoding</li>
     1820               <li>Content-Length</li>
     1821               <li>Trailer</li>
     1822            </ul>
     1823         </div>
     1824         <div id="header.transfer-encoding">
     1825            <div id="rfc.iref.t.3"></div>
     1826            <div id="rfc.iref.h.10"></div>
     1827            <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a>&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></h2>
     1828            <p id="rfc.section.8.7.p.1">The general-header "Transfer-Encoding" field indicates what (if any) type of transformation has been applied to the message
     1829               body in order to safely transfer it between the sender and the recipient. This differs from the content-coding in that the
     1830               transfer-coding is a property of the message, not of the entity.
     1831            </p>
     1832            <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.86"></span><span id="rfc.iref.g.87"></span>  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>   = "Transfer-Encoding" ":" <a href="#rule.whitespace" class="smpl">OWS</a>
    17241833                        <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding-v</a>
    17251834  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding-v</a> = 1#<a href="#transfer.codings" class="smpl">transfer-coding</a>
    17261835</pre><p id="rfc.section.8.7.p.3">Transfer-codings are defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.4</a>. An example is:
    1727       </p>
    1728       <div id="rfc.figure.u.54"></div><pre class="text">  Transfer-Encoding: chunked
     1836            </p>
     1837            <div id="rfc.figure.u.54"></div><pre class="text">  Transfer-Encoding: chunked
    17291838</pre><p id="rfc.section.8.7.p.5">If multiple encodings have been applied to an entity, the transfer-codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other entity-header fields not defined by this specification.
    1730       </p>
    1731       <p id="rfc.section.8.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p>
    1732       <div id="rfc.iref.u.3"></div>
    1733       <div id="rfc.iref.h.11"></div>
    1734       <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a>&nbsp;<a id="header.upgrade" href="#header.upgrade">Upgrade</a></h2>
    1735       <p id="rfc.section.8.8.p.1">The general-header "Upgrade" allows the client to specify what additional communication protocols it supports and would like
    1736          to use if the server finds it appropriate to switch protocols. The server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched.
    1737       </p>
    1738       <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>  <a href="#header.upgrade" class="smpl">Upgrade</a>   = "Upgrade" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.upgrade" class="smpl">Upgrade-v</a>
     1839            </p>
     1840            <p id="rfc.section.8.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p>
     1841         </div>
     1842         <div id="header.upgrade">
     1843            <div id="rfc.iref.u.3"></div>
     1844            <div id="rfc.iref.h.11"></div>
     1845            <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a>&nbsp;<a href="#header.upgrade">Upgrade</a></h2>
     1846            <p id="rfc.section.8.8.p.1">The general-header "Upgrade" allows the client to specify what additional communication protocols it supports and would like
     1847               to use if the server finds it appropriate to switch protocols. The server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched.
     1848            </p>
     1849            <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>  <a href="#header.upgrade" class="smpl">Upgrade</a>   = "Upgrade" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.upgrade" class="smpl">Upgrade-v</a>
    17391850  <a href="#header.upgrade" class="smpl">Upgrade-v</a> = 1#<a href="#product.tokens" class="smpl">product</a>
    17401851</pre><p id="rfc.section.8.8.p.3">For example,</p>
    1741       <div id="rfc.figure.u.56"></div><pre class="text">  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
     1852            <div id="rfc.figure.u.56"></div><pre class="text">  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
    17421853</pre><p id="rfc.section.8.8.p.5">The Upgrade header field is intended to provide a simple mechanism for transition from HTTP/1.1 to some other, incompatible
    1743          protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP
    1744          with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult
    1745          transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol
    1746          while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by
    1747          the server, possibly according to the nature of the method and/or resource being requested).
    1748       </p>
    1749       <p id="rfc.section.8.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection.
    1750          Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities
    1751          and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen,
    1752          although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field.
    1753       </p>
    1754       <p id="rfc.section.8.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.5" title="Connection">Section&nbsp;8.1</a>) whenever Upgrade is present in an HTTP/1.1 message.
    1755       </p>
    1756       <p id="rfc.section.8.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it
    1757          is more appropriate to use a 301, 302, 303, or 305 redirection response.
    1758       </p>
    1759       <p id="rfc.section.8.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined
    1760          by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section&nbsp;3.1</a> and future updates to this specification. Any token can be used as a protocol name; however, it will only be useful if both
    1761          the client and server associate the name with the same protocol.
    1762       </p>
    1763       <div id="rfc.iref.v.1"></div>
    1764       <div id="rfc.iref.h.12"></div>
    1765       <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a>&nbsp;<a id="header.via" href="#header.via">Via</a></h2>
    1766       <p id="rfc.section.8.9.p.1">The general-header field "Via" <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server
    1767          on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.7">Section 3.6.7</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities
    1768          of all senders along the request/response chain.
    1769       </p>
    1770       <div id="rfc.figure.u.57"></div><pre class="inline"><span id="rfc.iref.g.90"></span><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span><span id="rfc.iref.g.93"></span><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span>  <a href="#header.via" class="smpl">Via</a>               = "Via" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.via" class="smpl">Via-v</a>
     1854               protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP
     1855               with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult
     1856               transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol
     1857               while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by
     1858               the server, possibly according to the nature of the method and/or resource being requested).
     1859            </p>
     1860            <p id="rfc.section.8.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection.
     1861               Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities
     1862               and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen,
     1863               although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field.
     1864            </p>
     1865            <p id="rfc.section.8.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.5" title="Connection">Section&nbsp;8.1</a>) whenever Upgrade is present in an HTTP/1.1 message.
     1866            </p>
     1867            <p id="rfc.section.8.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it
     1868               is more appropriate to use a 301, 302, 303, or 305 redirection response.
     1869            </p>
     1870            <p id="rfc.section.8.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined
     1871               by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section&nbsp;3.1</a> and future updates to this specification. Any token can be used as a protocol name; however, it will only be useful if both
     1872               the client and server associate the name with the same protocol.
     1873            </p>
     1874         </div>
     1875         <div id="header.via">
     1876            <div id="rfc.iref.v.1"></div>
     1877            <div id="rfc.iref.h.12"></div>
     1878            <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a>&nbsp;<a href="#header.via">Via</a></h2>
     1879            <p id="rfc.section.8.9.p.1">The general-header field "Via" <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server
     1880               on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="https://tools.ietf.org/html/rfc5322#section-3.6.7">Section 3.6.7</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities
     1881               of all senders along the request/response chain.
     1882            </p>
     1883            <div id="rfc.figure.u.57"></div><pre class="inline"><span id="rfc.iref.g.90"></span><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span><span id="rfc.iref.g.93"></span><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span>  <a href="#header.via" class="smpl">Via</a>               = "Via" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.via" class="smpl">Via-v</a>
    17711884  <a href="#header.via" class="smpl">Via-v</a>             = 1#( <a href="#header.via" class="smpl">received-protocol</a> <a href="#rule.whitespace" class="smpl">RWS</a> <a href="#header.via" class="smpl">received-by</a>
    17721885                          [ <a href="#rule.whitespace" class="smpl">RWS</a> <a href="#rule.comment" class="smpl">comment</a> ] )
     
    17771890  <a href="#header.via" class="smpl">pseudonym</a>         = <a href="#rule.token.separators" class="smpl">token</a>
    17781891</pre><p id="rfc.section.8.9.p.3">The received-protocol indicates the protocol version of the message received by the server or client along each segment of
    1779          the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded
    1780          so that information about the protocol capabilities of upstream applications remains visible to all recipients.
    1781       </p>
    1782       <p id="rfc.section.8.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port
    1783          number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to
    1784          be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol.
    1785       </p>
    1786       <p id="rfc.section.8.9.p.5">Multiple Via field values represents each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications.
    1787       </p>
    1788       <p id="rfc.section.8.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and
    1789          Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message.
    1790       </p>
    1791       <p id="rfc.section.8.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses
    1792          HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin
    1793          server at www.example.com. The request received by www.example.com would then have the following Via header field:
    1794       </p>
    1795       <div id="rfc.figure.u.58"></div><pre class="text">  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
     1892               the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded
     1893               so that information about the protocol capabilities of upstream applications remains visible to all recipients.
     1894            </p>
     1895            <p id="rfc.section.8.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port
     1896               number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to
     1897               be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol.
     1898            </p>
     1899            <p id="rfc.section.8.9.p.5">Multiple Via field values represents each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications.
     1900            </p>
     1901            <p id="rfc.section.8.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and
     1902               Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message.
     1903            </p>
     1904            <p id="rfc.section.8.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses
     1905               HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin
     1906               server at www.example.com. The request received by www.example.com would then have the following Via header field:
     1907            </p>
     1908            <div id="rfc.figure.u.58"></div><pre class="text">  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
    17961909</pre><p id="rfc.section.8.9.p.9">Proxies and gateways used as a portal through a network firewall <em class="bcp14">SHOULD NOT</em>, by default, forward the names and ports of hosts within the firewall region. This information <em class="bcp14">SHOULD</em> only be propagated if explicitly enabled. If not enabled, the received-by host of any host behind the firewall <em class="bcp14">SHOULD</em> be replaced by an appropriate pseudonym for that host.
    1797       </p>
    1798       <p id="rfc.section.8.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry.
    1799          For example,
    1800       </p>
    1801       <div id="rfc.figure.u.59"></div><pre class="text">  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
     1910            </p>
     1911            <p id="rfc.section.8.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry.
     1912               For example,
     1913            </p>
     1914            <div id="rfc.figure.u.59"></div><pre class="text">  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
    18021915</pre><p id="rfc.section.8.9.p.12">could be collapsed to</p>
    1803       <div id="rfc.figure.u.60"></div><pre class="text">  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
     1916            <div id="rfc.figure.u.60"></div><pre class="text">  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
    18041917</pre><p id="rfc.section.8.9.p.14">Applications <em class="bcp14">SHOULD NOT</em> combine multiple entries unless they are all under the same organizational control and the hosts have already been replaced
    1805          by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values.
    1806       </p>
    1807       <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    1808       <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a id="message.header.registration" href="#message.header.registration">Message Header Registration</a></h2>
    1809       <p id="rfc.section.9.1.p.1">The Message Header Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; should be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
    1810       </p>
    1811       <div id="rfc.table.1">
    1812          <div id="iana.header.registration.table"></div>
    1813          <table class="tt full left" cellpadding="3" cellspacing="0">
    1814             <thead>
    1815                <tr>
    1816                   <th>Header Field Name</th>
    1817                   <th>Protocol</th>
    1818                   <th>Status</th>
    1819                   <th>Reference</th>
    1820                </tr>
    1821             </thead>
    1822             <tbody>
    1823                <tr>
    1824                   <td class="left">Connection</td>
    1825                   <td class="left">http</td>
    1826                   <td class="left">standard</td>
    1827                   <td class="left"> <a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;8.1</a>
    1828                   </td>
    1829                </tr>
    1830                <tr>
    1831                   <td class="left">Content-Length</td>
    1832                   <td class="left">http</td>
    1833                   <td class="left">standard</td>
    1834                   <td class="left"> <a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section&nbsp;8.2</a>
    1835                   </td>
    1836                </tr>
    1837                <tr>
    1838                   <td class="left">Date</td>
    1839                   <td class="left">http</td>
    1840                   <td class="left">standard</td>
    1841                   <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;8.3</a>
    1842                   </td>
    1843                </tr>
    1844                <tr>
    1845                   <td class="left">Host</td>
    1846                   <td class="left">http</td>
    1847                   <td class="left">standard</td>
    1848                   <td class="left"> <a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section&nbsp;8.4</a>
    1849                   </td>
    1850                </tr>
    1851                <tr>
    1852                   <td class="left">TE</td>
    1853                   <td class="left">http</td>
    1854                   <td class="left">standard</td>
    1855                   <td class="left"> <a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;8.5</a>
    1856                   </td>
    1857                </tr>
    1858                <tr>
    1859                   <td class="left">Trailer</td>
    1860                   <td class="left">http</td>
    1861                   <td class="left">standard</td>
    1862                   <td class="left"> <a href="#header.trailer" id="rfc.xref.header.trailer.3" title="Trailer">Section&nbsp;8.6</a>
    1863                   </td>
    1864                </tr>
    1865                <tr>
    1866                   <td class="left">Transfer-Encoding</td>
    1867                   <td class="left">http</td>
    1868                   <td class="left">standard</td>
    1869                   <td class="left"> <a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.5" title="Transfer-Encoding">Section&nbsp;8.7</a>
    1870                   </td>
    1871                </tr>
    1872                <tr>
    1873                   <td class="left">Upgrade</td>
    1874                   <td class="left">http</td>
    1875                   <td class="left">standard</td>
    1876                   <td class="left"> <a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section&nbsp;8.8</a>
    1877                   </td>
    1878                </tr>
    1879                <tr>
    1880                   <td class="left">Via</td>
    1881                   <td class="left">http</td>
    1882                   <td class="left">standard</td>
    1883                   <td class="left"> <a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;8.9</a>
    1884                   </td>
    1885                </tr>
    1886             </tbody>
    1887          </table>
     1918               by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values.
     1919            </p>
     1920         </div>
    18881921      </div>
    1889       <p id="rfc.section.9.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    1890       <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a id="uri.scheme.registration" href="#uri.scheme.registration">URI Scheme Registration</a></h2>
    1891       <p id="rfc.section.9.2.p.1">The entry for the "http" URI Scheme in the registry located at &lt;<a href="http://www.iana.org/assignments/uri-schemes.html">http://www.iana.org/assignments/uri-schemes.html</a>&gt; should be updated to point to <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a> of this document (see <a href="#RFC4395" id="rfc.xref.RFC4395.1"><cite title="Guidelines and Registration Procedures for New URI Schemes">[RFC4395]</cite></a>).
    1892       </p>
    1893       <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a id="internet.media.type.http" href="#internet.media.type.http">Internet Media Type Registrations</a></h2>
    1894       <p id="rfc.section.9.3.p.1">This document serves as the specification for the Internet media types "message/http" and "application/http". The following
    1895          is to be registered with IANA (see <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>).
    1896       </p>
    1897       <div id="rfc.iref.m.1"></div>
    1898       <div id="rfc.iref.m.2"></div>
    1899       <h3 id="rfc.section.9.3.1"><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;<a id="internet.media.type.message.http" href="#internet.media.type.message.http">Internet Media Type message/http</a></h3>
    1900       <p id="rfc.section.9.3.1.p.1">The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions
    1901          for all "message" types regarding line length and encodings.
    1902       </p>
    1903       <p id="rfc.section.9.3.1.p.2"> </p>
    1904       <dl>
    1905          <dt>Type name:</dt>
    1906          <dd>message</dd>
    1907          <dt>Subtype name:</dt>
    1908          <dd>http</dd>
    1909          <dt>Required parameters:</dt>
    1910          <dd>none</dd>
    1911          <dt>Optional parameters:</dt>
    1912          <dd>version, msgtype
    1913             <dl>
    1914                <dt>version:</dt>
    1915                <dd>The HTTP-Version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first
    1916                   line of the body.
    1917                </dd>
    1918                <dt>msgtype:</dt>
    1919                <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
    1920             </dl>
    1921          </dd>
    1922          <dt>Encoding considerations:</dt>
    1923          <dd>only "7bit", "8bit", or "binary" are permitted</dd>
    1924          <dt>Security considerations:</dt>
    1925          <dd>none</dd>
    1926          <dt>Interoperability considerations:</dt>
    1927          <dd>none</dd>
    1928          <dt>Published specification:</dt>
    1929          <dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;9.3.1</a>).
    1930          </dd>
    1931          <dt>Applications that use this media type:</dt>
    1932          <dt>Additional information:</dt>
    1933          <dd>
    1934             <dl>
    1935                <dt>Magic number(s):</dt>
    1936                <dd>none</dd>
    1937                <dt>File extension(s):</dt>
    1938                <dd>none</dd>
    1939                <dt>Macintosh file type code(s):</dt>
    1940                <dd>none</dd>
    1941             </dl>
    1942          </dd>
    1943          <dt>Person and email address to contact for further information:</dt>
    1944          <dd>See Authors Section.</dd>
    1945          <dt>Intended usage:</dt>
    1946          <dd>COMMON</dd>
    1947          <dt>Restrictions on usage:</dt>
    1948          <dd>none</dd>
    1949          <dt>Author/Change controller:</dt>
    1950          <dd>IESG</dd>
    1951       </dl>
    1952       <div id="rfc.iref.m.3"></div>
    1953       <div id="rfc.iref.a.1"></div>
    1954       <h3 id="rfc.section.9.3.2"><a href="#rfc.section.9.3.2">9.3.2</a>&nbsp;<a id="internet.media.type.application.http" href="#internet.media.type.application.http">Internet Media Type application/http</a></h3>
    1955       <p id="rfc.section.9.3.2.p.1">The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).</p>
    1956       <p id="rfc.section.9.3.2.p.2"> </p>
    1957       <dl>
    1958          <dt>Type name:</dt>
    1959          <dd>application</dd>
    1960          <dt>Subtype name:</dt>
    1961          <dd>http</dd>
    1962          <dt>Required parameters:</dt>
    1963          <dd>none</dd>
    1964          <dt>Optional parameters:</dt>
    1965          <dd>version, msgtype
    1966             <dl>
    1967                <dt>version:</dt>
    1968                <dd>The HTTP-Version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first
    1969                   line of the body.
    1970                </dd>
    1971                <dt>msgtype:</dt>
    1972                <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
    1973             </dl>
    1974          </dd>
    1975          <dt>Encoding considerations:</dt>
    1976          <dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when
    1977             transmitted via E-mail.
    1978          </dd>
    1979          <dt>Security considerations:</dt>
    1980          <dd>none</dd>
    1981          <dt>Interoperability considerations:</dt>
    1982          <dd>none</dd>
    1983          <dt>Published specification:</dt>
    1984          <dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Section&nbsp;9.3.2</a>).
    1985          </dd>
    1986          <dt>Applications that use this media type:</dt>
    1987          <dt>Additional information:</dt>
    1988          <dd>
    1989             <dl>
    1990                <dt>Magic number(s):</dt>
    1991                <dd>none</dd>
    1992                <dt>File extension(s):</dt>
    1993                <dd>none</dd>
    1994                <dt>Macintosh file type code(s):</dt>
    1995                <dd>none</dd>
    1996             </dl>
    1997          </dd>
    1998          <dt>Person and email address to contact for further information:</dt>
    1999          <dd>See Authors Section.</dd>
    2000          <dt>Intended usage:</dt>
    2001          <dd>COMMON</dd>
    2002          <dt>Restrictions on usage:</dt>
    2003          <dd>none</dd>
    2004          <dt>Author/Change controller:</dt>
    2005          <dd>IESG</dd>
    2006       </dl>
    2007       <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    2008       <p id="rfc.section.10.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
    2009          as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
    2010          make some suggestions for reducing security risks.
    2011       </p>
    2012       <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a>&nbsp;<a id="personal.information" href="#personal.information">Personal Information</a></h2>
    2013       <p id="rfc.section.10.1.p.1">HTTP clients are often privy to large amounts of personal information (e.g. the user's name, location, mail address, passwords,
    2014          encryption keys, etc.), and <em class="bcp14">SHOULD</em> be very careful to prevent unintentional leakage of this information. We very strongly recommend that a convenient interface
    2015          be provided for the user to control dissemination of such information, and that designers and implementors be particularly
    2016          careful in this area. History shows that errors in this area often create serious security and/or privacy problems and generate
    2017          highly adverse publicity for the implementor's company.
    2018       </p>
    2019       <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a>&nbsp;<a id="abuse.of.server.log.information" href="#abuse.of.server.log.information">Abuse of Server Log Information</a></h2>
    2020       <p id="rfc.section.10.2.p.1">A server is in the position to save personal data about a user's requests which might identify their reading patterns or subjects
    2021          of interest. This information is clearly confidential in nature and its handling can be constrained by law in certain countries.
    2022          People using HTTP to provide data are responsible for ensuring that such material is not distributed without the permission
    2023          of any individuals that are identifiable by the published results.
    2024       </p>
    2025       <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a>&nbsp;<a id="attack.pathname" href="#attack.pathname">Attacks Based On File and Path Names</a></h2>
    2026       <p id="rfc.section.10.3.p.1">Implementations of HTTP origin servers <em class="bcp14">SHOULD</em> be careful to restrict the documents returned by HTTP requests to be only those that were intended by the server administrators.
    2027          If an HTTP server translates HTTP URIs directly into file system calls, the server <em class="bcp14">MUST</em> take special care not to serve files that were not intended to be delivered to HTTP clients. For example, UNIX, Microsoft
    2028          Windows, and other operating systems use ".." as a path component to indicate a directory level above the current one. On
    2029          such a system, an HTTP server <em class="bcp14">MUST</em> disallow any such construct in the Request-URI if it would otherwise allow access to a resource outside those intended to
    2030          be accessible via the HTTP server. Similarly, files intended for reference only internally to the server (such as access control
    2031          files, configuration files, and script code) <em class="bcp14">MUST</em> be protected from inappropriate retrieval, since they might contain sensitive information. Experience has shown that minor
    2032          bugs in such HTTP server implementations have turned into security risks.
    2033       </p>
    2034       <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a>&nbsp;<a id="dns.spoofing" href="#dns.spoofing">DNS Spoofing</a></h2>
    2035       <p id="rfc.section.10.4.p.1">Clients using HTTP rely heavily on the Domain Name Service, and are thus generally prone to security attacks based on the
    2036          deliberate mis-association of IP addresses and DNS names. Clients need to be cautious in assuming the continuing validity
    2037          of an IP number/DNS name association.
    2038       </p>
    2039       <p id="rfc.section.10.4.p.2">In particular, HTTP clients <em class="bcp14">SHOULD</em> rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous
    2040          host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they <em class="bcp14">SHOULD</em> be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information
    2041          reported by the name server makes it likely that the cached information will remain useful.
    2042       </p>
    2043       <p id="rfc.section.10.4.p.3">If HTTP clients cache the results of host name lookups in order to achieve a performance improvement, they <em class="bcp14">MUST</em> observe the TTL information reported by DNS.
    2044       </p>
    2045       <p id="rfc.section.10.4.p.4">If HTTP clients do not observe this rule, they could be spoofed when a previously-accessed server's IP address changes. As
    2046          network renumbering is expected to become increasingly common <a href="#RFC1900" id="rfc.xref.RFC1900.2"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>, the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability.
    2047       </p>
    2048       <p id="rfc.section.10.4.p.5">This requirement also improves the load-balancing behavior of clients for replicated servers using the same DNS name and reduces
    2049          the likelihood of a user's experiencing failure in accessing sites which use that strategy.
    2050       </p>
    2051       <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a>&nbsp;<a id="attack.proxies" href="#attack.proxies">Proxies and Caching</a></h2>
    2052       <p id="rfc.section.10.5.p.1">By their very nature, HTTP proxies are men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Compromise
    2053          of the systems on which the proxies run can result in serious security and privacy problems. Proxies have access to security-related
    2054          information, personal information about individual users and organizations, and proprietary information belonging to users
    2055          and content providers. A compromised proxy, or a proxy implemented or configured without regard to security and privacy considerations,
    2056          might be used in the commission of a wide range of potential attacks.
    2057       </p>
    2058       <p id="rfc.section.10.5.p.2">Proxy operators should protect the systems on which proxies run as they would protect any system that contains or transports
    2059          sensitive information. In particular, log information gathered at proxies often contains highly sensitive personal information,
    2060          and/or information about organizations. Log information should be carefully guarded, and appropriate guidelines for use developed
    2061          and followed. (<a href="#abuse.of.server.log.information" title="Abuse of Server Log Information">Section&nbsp;10.2</a>).
    2062       </p>
    2063       <p id="rfc.section.10.5.p.3">Proxy implementors should consider the privacy and security implications of their design and coding decisions, and of the
    2064          configuration options they provide to proxy operators (especially the default configuration).
    2065       </p>
    2066       <p id="rfc.section.10.5.p.4">Users of a proxy need to be aware that they are no trustworthier than the people who run the proxy; HTTP itself cannot solve
    2067          this problem.
    2068       </p>
    2069       <p id="rfc.section.10.5.p.5">The judicious use of cryptography, when appropriate, may suffice to protect against a broad range of security and privacy
    2070          attacks. Such cryptography is beyond the scope of the HTTP/1.1 specification.
    2071       </p>
    2072       <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a>&nbsp;<a id="attack.DoS" href="#attack.DoS">Denial of Service Attacks on Proxies</a></h2>
    2073       <p id="rfc.section.10.6.p.1">They exist. They are hard to defend against. Research continues. Beware.</p>
    2074       <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
    2075       <p id="rfc.section.11.p.1">HTTP has evolved considerably over the years. It has benefited from a large and active developer community--the many people
    2076          who have participated on the www-talk mailing list--and it is that community which has been most responsible for the success
    2077          of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly, Bob Denny, John Franks,
    2078          Jean-Francois Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett, Tony Sanders,
    2079          and Marc VanHeyningen deserve special recognition for their efforts in defining early aspects of the protocol.
    2080       </p>
    2081       <p id="rfc.section.11.p.2">This document has benefited greatly from the comments of all those participating in the HTTP-WG. In addition to those already
    2082          mentioned, the following individuals have contributed to this specification:
    2083       </p>
    2084       <p id="rfc.section.11.p.3">Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf, Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman
    2085          Czyborra, Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann,
    2086          Bob Jernigan, Shel Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol, Daniel LaLiberte, Ben
    2087          Laurie, Paul J. Leach, Albert Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris, Gavin Nicol, Ross
    2088          Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz, Allan
    2089          M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink, Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
    2090          Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.
    2091       </p>
    2092       <p id="rfc.section.11.p.4">Thanks to the "cave men" of Palo Alto. You know who you are.</p>
    2093       <p id="rfc.section.11.p.5">Jim Gettys (the editor of <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>) wishes particularly to thank Roy Fielding, the editor of <a href="#RFC2068" id="rfc.xref.RFC2068.5"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, along with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott
    2094          Lawrence, and Larry Masinter for their help. And thanks go particularly to Jeff Mogul and Scott Lawrence for performing the
    2095          "MUST/MAY/SHOULD" audit.
    2096       </p>
    2097       <p id="rfc.section.11.p.6">The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik Frystyk implemented RFC 2068 early, and we wish to thank
    2098          them for the discovery of many of the problems that this document attempts to rectify.
    2099       </p>
    2100       <p id="rfc.section.11.p.7">This specification makes heavy use of the augmented BNF and generic constructs defined by David H. Crocker for <a href="#RFC5234" id="rfc.xref.RFC5234.4"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>. Similarly, it reuses many of the definitions provided by Nathaniel Borenstein and Ned Freed for MIME <a href="#RFC2045" id="rfc.xref.RFC2045.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. We hope that their inclusion in this specification will help reduce past confusion over the relationship between HTTP and
    2101          Internet mail message formats.
    2102       </p>
     1922      <div id="IANA.considerations">
     1923         <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1>
     1924         <div id="message.header.registration">
     1925            <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#message.header.registration">Message Header Registration</a></h2>
     1926            <p id="rfc.section.9.1.p.1">The Message Header Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; should be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
     1927            </p>
     1928            <div id="rfc.table.1">
     1929               <div id="iana.header.registration.table"></div>
     1930               <table class="tt full left" cellpadding="3" cellspacing="0">
     1931                  <thead>
     1932                     <tr>
     1933                        <th>Header Field Name</th>
     1934                        <th>Protocol</th>
     1935                        <th>Status</th>
     1936                        <th>Reference</th>
     1937                     </tr>
     1938                  </thead>
     1939                  <tbody>
     1940                     <tr>
     1941                        <td class="left">Connection</td>
     1942                        <td class="left">http</td>
     1943                        <td class="left">standard</td>
     1944                        <td class="left"><a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;8.1</a>
     1945                        </td>
     1946                     </tr>
     1947                     <tr>
     1948                        <td class="left">Content-Length</td>
     1949                        <td class="left">http</td>
     1950                        <td class="left">standard</td>
     1951                        <td class="left"><a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section&nbsp;8.2</a>
     1952                        </td>
     1953                     </tr>
     1954                     <tr>
     1955                        <td class="left">Date</td>
     1956                        <td class="left">http</td>
     1957                        <td class="left">standard</td>
     1958                        <td class="left"><a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;8.3</a>
     1959                        </td>
     1960                     </tr>
     1961                     <tr>
     1962                        <td class="left">Host</td>
     1963                        <td class="left">http</td>
     1964                        <td class="left">standard</td>
     1965                        <td class="left"><a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section&nbsp;8.4</a>
     1966                        </td>
     1967                     </tr>
     1968                     <tr>
     1969                        <td class="left">TE</td>
     1970                        <td class="left">http</td>
     1971                        <td class="left">standard</td>
     1972                        <td class="left"><a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;8.5</a>
     1973                        </td>
     1974                     </tr>
     1975                     <tr>
     1976                        <td class="left">Trailer</td>
     1977                        <td class="left">http</td>
     1978                        <td class="left">standard</td>
     1979                        <td class="left"><a href="#header.trailer" id="rfc.xref.header.trailer.3" title="Trailer">Section&nbsp;8.6</a>
     1980                        </td>
     1981                     </tr>
     1982                     <tr>
     1983                        <td class="left">Transfer-Encoding</td>
     1984                        <td class="left">http</td>
     1985                        <td class="left">standard</td>
     1986                        <td class="left"><a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.5" title="Transfer-Encoding">Section&nbsp;8.7</a>
     1987                        </td>
     1988                     </tr>
     1989                     <tr>
     1990                        <td class="left">Upgrade</td>
     1991                        <td class="left">http</td>
     1992                        <td class="left">standard</td>
     1993                        <td class="left"><a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section&nbsp;8.8</a>
     1994                        </td>
     1995                     </tr>
     1996                     <tr>
     1997                        <td class="left">Via</td>
     1998                        <td class="left">http</td>
     1999                        <td class="left">standard</td>
     2000                        <td class="left"><a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;8.9</a>
     2001                        </td>
     2002                     </tr>
     2003                  </tbody>
     2004               </table>
     2005            </div>
     2006            <p id="rfc.section.9.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
     2007         </div>
     2008         <div id="uri.scheme.registration">
     2009            <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></h2>
     2010            <p id="rfc.section.9.2.p.1">The entry for the "http" URI Scheme in the registry located at &lt;<a href="http://www.iana.org/assignments/uri-schemes.html">http://www.iana.org/assignments/uri-schemes.html</a>&gt; should be updated to point to <a href="#http.uri" title="http URI scheme">Section&nbsp;3.2.1</a> of this document (see <a href="#RFC4395" id="rfc.xref.RFC4395.1"><cite title="Guidelines and Registration Procedures for New URI Schemes">[RFC4395]</cite></a>).
     2011            </p>
     2012         </div>
     2013         <div id="internet.media.type.http">
     2014            <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a href="#internet.media.type.http">Internet Media Type Registrations</a></h2>
     2015            <p id="rfc.section.9.3.p.1">This document serves as the specification for the Internet media types "message/http" and "application/http". The following
     2016               is to be registered with IANA (see <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>).
     2017            </p>
     2018            <div id="internet.media.type.message.http">
     2019               <div id="rfc.iref.m.1"></div>
     2020               <div id="rfc.iref.m.2"></div>
     2021               <h3 id="rfc.section.9.3.1"><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></h3>
     2022               <p id="rfc.section.9.3.1.p.1">The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions
     2023                  for all "message" types regarding line length and encodings.
     2024               </p>
     2025               <p id="rfc.section.9.3.1.p.2"></p>
     2026               <dl>
     2027                  <dt>Type name:</dt>
     2028                  <dd>message</dd>
     2029                  <dt>Subtype name:</dt>
     2030                  <dd>http</dd>
     2031                  <dt>Required parameters:</dt>
     2032                  <dd>none</dd>
     2033                  <dt>Optional parameters:</dt>
     2034                  <dd>version, msgtype
     2035                     <dl>
     2036                        <dt>version:</dt>
     2037                        <dd>The HTTP-Version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first
     2038                           line of the body.
     2039                        </dd>
     2040                        <dt>msgtype:</dt>
     2041                        <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
     2042                     </dl>
     2043                  </dd>
     2044                  <dt>Encoding considerations:</dt>
     2045                  <dd>only "7bit", "8bit", or "binary" are permitted</dd>
     2046                  <dt>Security considerations:</dt>
     2047                  <dd>none</dd>
     2048                  <dt>Interoperability considerations:</dt>
     2049                  <dd>none</dd>
     2050                  <dt>Published specification:</dt>
     2051                  <dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;9.3.1</a>).
     2052                  </dd>
     2053                  <dt>Applications that use this media type:</dt>
     2054                  <dt>Additional information:</dt>
     2055                  <dd>
     2056                     <dl>
     2057                        <dt>Magic number(s):</dt>
     2058                        <dd>none</dd>
     2059                        <dt>File extension(s):</dt>
     2060                        <dd>none</dd>
     2061                        <dt>Macintosh file type code(s):</dt>
     2062                        <dd>none</dd>
     2063                     </dl>
     2064                  </dd>
     2065                  <dt>Person and email address to contact for further information:</dt>
     2066                  <dd>See Authors Section.</dd>
     2067                  <dt>Intended usage:</dt>
     2068                  <dd>COMMON</dd>
     2069                  <dt>Restrictions on usage:</dt>
     2070                  <dd>none</dd>
     2071                  <dt>Author/Change controller:</dt>
     2072                  <dd>IESG</dd>
     2073               </dl>
     2074            </div>
     2075            <div id="internet.media.type.application.http">
     2076               <div id="rfc.iref.m.3"></div>
     2077               <div id="rfc.iref.a.1"></div>
     2078               <h3 id="rfc.section.9.3.2"><a href="#rfc.section.9.3.2">9.3.2</a>&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></h3>
     2079               <p id="rfc.section.9.3.2.p.1">The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).</p>
     2080               <p id="rfc.section.9.3.2.p.2"></p>
     2081               <dl>
     2082                  <dt>Type name:</dt>
     2083                  <dd>application</dd>
     2084                  <dt>Subtype name:</dt>
     2085                  <dd>http</dd>
     2086                  <dt>Required parameters:</dt>
     2087                  <dd>none</dd>
     2088                  <dt>Optional parameters:</dt>
     2089                  <dd>version, msgtype
     2090                     <dl>
     2091                        <dt>version:</dt>
     2092                        <dd>The HTTP-Version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first
     2093                           line of the body.
     2094                        </dd>
     2095                        <dt>msgtype:</dt>
     2096                        <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
     2097                     </dl>
     2098                  </dd>
     2099                  <dt>Encoding considerations:</dt>
     2100                  <dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when
     2101                     transmitted via E-mail.
     2102                  </dd>
     2103                  <dt>Security considerations:</dt>
     2104                  <dd>none</dd>
     2105                  <dt>Interoperability considerations:</dt>
     2106                  <dd>none</dd>
     2107                  <dt>Published specification:</dt>
     2108                  <dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Section&nbsp;9.3.2</a>).
     2109                  </dd>
     2110                  <dt>Applications that use this media type:</dt>
     2111                  <dt>Additional information:</dt>
     2112                  <dd>
     2113                     <dl>
     2114                        <dt>Magic number(s):</dt>
     2115                        <dd>none</dd>
     2116                        <dt>File extension(s):</dt>
     2117                        <dd>none</dd>
     2118                        <dt>Macintosh file type code(s):</dt>
     2119                        <dd>none</dd>
     2120                     </dl>
     2121                  </dd>
     2122                  <dt>Person and email address to contact for further information:</dt>
     2123                  <dd>See Authors Section.</dd>
     2124                  <dt>Intended usage:</dt>
     2125                  <dd>COMMON</dd>
     2126                  <dt>Restrictions on usage:</dt>
     2127                  <dd>none</dd>
     2128                  <dt>Author/Change controller:</dt>
     2129                  <dd>IESG</dd>
     2130               </dl>
     2131            </div>
     2132         </div>
     2133      </div>
     2134      <div id="security.considerations">
     2135         <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a href="#security.considerations">Security Considerations</a></h1>
     2136         <p id="rfc.section.10.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
     2137            as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
     2138            make some suggestions for reducing security risks.
     2139         </p>
     2140         <div id="personal.information">
     2141            <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a>&nbsp;<a href="#personal.information">Personal Information</a></h2>
     2142            <p id="rfc.section.10.1.p.1">HTTP clients are often privy to large amounts of personal information (e.g. the user's name, location, mail address, passwords,
     2143               encryption keys, etc.), and <em class="bcp14">SHOULD</em> be very careful to prevent unintentional leakage of this information. We very strongly recommend that a convenient interface
     2144               be provided for the user to control dissemination of such information, and that designers and implementors be particularly
     2145               careful in this area. History shows that errors in this area often create serious security and/or privacy problems and generate
     2146               highly adverse publicity for the implementor's company.
     2147            </p>
     2148         </div>
     2149         <div id="abuse.of.server.log.information">
     2150            <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a>&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></h2>
     2151            <p id="rfc.section.10.2.p.1">A server is in the position to save personal data about a user's requests which might identify their reading patterns or subjects
     2152               of interest. This information is clearly confidential in nature and its handling can be constrained by law in certain countries.
     2153               People using HTTP to provide data are responsible for ensuring that such material is not distributed without the permission
     2154               of any individuals that are identifiable by the published results.
     2155            </p>
     2156         </div>
     2157         <div id="attack.pathname">
     2158            <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a>&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></h2>
     2159            <p id="rfc.section.10.3.p.1">Implementations of HTTP origin servers <em class="bcp14">SHOULD</em> be careful to restrict the documents returned by HTTP requests to be only those that were intended by the server administrators.
     2160               If an HTTP server translates HTTP URIs directly into file system calls, the server <em class="bcp14">MUST</em> take special care not to serve files that were not intended to be delivered to HTTP clients. For example, UNIX, Microsoft
     2161               Windows, and other operating systems use ".." as a path component to indicate a directory level above the current one. On
     2162               such a system, an HTTP server <em class="bcp14">MUST</em> disallow any such construct in the Request-URI if it would otherwise allow access to a resource outside those intended to
     2163               be accessible via the HTTP server. Similarly, files intended for reference only internally to the server (such as access control
     2164               files, configuration files, and script code) <em class="bcp14">MUST</em> be protected from inappropriate retrieval, since they might contain sensitive information. Experience has shown that minor
     2165               bugs in such HTTP server implementations have turned into security risks.
     2166            </p>
     2167         </div>
     2168         <div id="dns.spoofing">
     2169            <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a>&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></h2>
     2170            <p id="rfc.section.10.4.p.1">Clients using HTTP rely heavily on the Domain Name Service, and are thus generally prone to security attacks based on the
     2171               deliberate mis-association of IP addresses and DNS names. Clients need to be cautious in assuming the continuing validity
     2172               of an IP number/DNS name association.
     2173            </p>
     2174            <p id="rfc.section.10.4.p.2">In particular, HTTP clients <em class="bcp14">SHOULD</em> rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous
     2175               host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they <em class="bcp14">SHOULD</em> be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information
     2176               reported by the name server makes it likely that the cached information will remain useful.
     2177            </p>
     2178            <p id="rfc.section.10.4.p.3">If HTTP clients cache the results of host name lookups in order to achieve a performance improvement, they <em class="bcp14">MUST</em> observe the TTL information reported by DNS.
     2179            </p>
     2180            <p id="rfc.section.10.4.p.4">If HTTP clients do not observe this rule, they could be spoofed when a previously-accessed server's IP address changes. As
     2181               network renumbering is expected to become increasingly common <a href="#RFC1900" id="rfc.xref.RFC1900.2"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>, the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability.
     2182            </p>
     2183            <p id="rfc.section.10.4.p.5">This requirement also improves the load-balancing behavior of clients for replicated servers using the same DNS name and reduces
     2184               the likelihood of a user's experiencing failure in accessing sites which use that strategy.
     2185            </p>
     2186         </div>
     2187         <div id="attack.proxies">
     2188            <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a>&nbsp;<a href="#attack.proxies">Proxies and Caching</a></h2>
     2189            <p id="rfc.section.10.5.p.1">By their very nature, HTTP proxies are men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Compromise
     2190               of the systems on which the proxies run can result in serious security and privacy problems. Proxies have access to security-related
     2191               information, personal information about individual users and organizations, and proprietary information belonging to users
     2192               and content providers. A compromised proxy, or a proxy implemented or configured without regard to security and privacy considerations,
     2193               might be used in the commission of a wide range of potential attacks.
     2194            </p>
     2195            <p id="rfc.section.10.5.p.2">Proxy operators should protect the systems on which proxies run as they would protect any system that contains or transports
     2196               sensitive information. In particular, log information gathered at proxies often contains highly sensitive personal information,
     2197               and/or information about organizations. Log information should be carefully guarded, and appropriate guidelines for use developed
     2198               and followed. (<a href="#abuse.of.server.log.information" title="Abuse of Server Log Information">Section&nbsp;10.2</a>).
     2199            </p>
     2200            <p id="rfc.section.10.5.p.3">Proxy implementors should consider the privacy and security implications of their design and coding decisions, and of the
     2201               configuration options they provide to proxy operators (especially the default configuration).
     2202            </p>
     2203            <p id="rfc.section.10.5.p.4">Users of a proxy need to be aware that they are no trustworthier than the people who run the proxy; HTTP itself cannot solve
     2204               this problem.
     2205            </p>
     2206            <p id="rfc.section.10.5.p.5">The judicious use of cryptography, when appropriate, may suffice to protect against a broad range of security and privacy
     2207               attacks. Such cryptography is beyond the scope of the HTTP/1.1 specification.
     2208            </p>
     2209         </div>
     2210         <div id="attack.DoS">
     2211            <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a>&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></h2>
     2212            <p id="rfc.section.10.6.p.1">They exist. They are hard to defend against. Research continues. Beware.</p>
     2213         </div>
     2214      </div>
     2215      <div id="ack">
     2216         <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a href="#ack">Acknowledgments</a></h1>
     2217         <p id="rfc.section.11.p.1">HTTP has evolved considerably over the years. It has benefited from a large and active developer community--the many people
     2218            who have participated on the www-talk mailing list--and it is that community which has been most responsible for the success
     2219            of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly, Bob Denny, John Franks,
     2220            Jean-Francois Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett, Tony Sanders,
     2221            and Marc VanHeyningen deserve special recognition for their efforts in defining early aspects of the protocol.
     2222         </p>
     2223         <p id="rfc.section.11.p.2">This document has benefited greatly from the comments of all those participating in the HTTP-WG. In addition to those already
     2224            mentioned, the following individuals have contributed to this specification:
     2225         </p>
     2226         <p id="rfc.section.11.p.3">Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf, Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman
     2227            Czyborra, Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann,
     2228            Bob Jernigan, Shel Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol, Daniel LaLiberte, Ben
     2229            Laurie, Paul J. Leach, Albert Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris, Gavin Nicol, Ross
     2230            Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz, Allan
     2231            M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink, Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
     2232            Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.
     2233         </p>
     2234         <p id="rfc.section.11.p.4">Thanks to the "cave men" of Palo Alto. You know who you are.</p>
     2235         <p id="rfc.section.11.p.5">Jim Gettys (the editor of <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>) wishes particularly to thank Roy Fielding, the editor of <a href="#RFC2068" id="rfc.xref.RFC2068.5"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, along with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott
     2236            Lawrence, and Larry Masinter for their help. And thanks go particularly to Jeff Mogul and Scott Lawrence for performing the
     2237            "MUST/MAY/SHOULD" audit.
     2238         </p>
     2239         <p id="rfc.section.11.p.6">The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik Frystyk implemented RFC 2068 early, and we wish to thank
     2240            them for the discovery of many of the problems that this document attempts to rectify.
     2241         </p>
     2242         <p id="rfc.section.11.p.7">This specification makes heavy use of the augmented BNF and generic constructs defined by David H. Crocker for <a href="#RFC5234" id="rfc.xref.RFC5234.4"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>. Similarly, it reuses many of the definitions provided by Nathaniel Borenstein and Ned Freed for MIME <a href="#RFC2045" id="rfc.xref.RFC2045.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. We hope that their inclusion in this specification will help reduce past confusion over the relationship between HTTP and
     2243            Internet mail message formats.
     2244         </p>
     2245      </div>
    21032246      <h1 id="rfc.references"><a id="rfc.section.12" href="#rfc.section.12">12.</a> References
    21042247      </h1>
    21052248      <h2 id="rfc.references.1"><a href="#rfc.section.12.1" id="rfc.section.12.1">12.1</a> Normative References
    21062249      </h2>
    2107       <table>                     
     2250      <table>
    21082251         <tr>
    21092252            <td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td>
     
    21122255         <tr>
    21132256            <td class="reference"><b id="Part2">[Part2]</b></td>
    2114             <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-05">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p2-semantics-05 (work in progress), November&nbsp;2008.
     2257            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-05">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p2-semantics-05 (work in progress), November&nbsp;2008.
    21152258            </td>
    21162259         </tr>
    21172260         <tr>
    21182261            <td class="reference"><b id="Part3">[Part3]</b></td>
    2119             <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-05">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p3-payload-05 (work in progress), November&nbsp;2008.
     2262            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-05">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p3-payload-05 (work in progress), November&nbsp;2008.
    21202263            </td>
    21212264         </tr>
    21222265         <tr>
    21232266            <td class="reference"><b id="Part5">[Part5]</b></td>
    2124             <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-05">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p5-range-05 (work in progress), November&nbsp;2008.
     2267            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p5-range-05">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p5-range-05 (work in progress), November&nbsp;2008.
    21252268            </td>
    21262269         </tr>
    21272270         <tr>
    21282271            <td class="reference"><b id="Part6">[Part6]</b></td>
    2129             <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-05 (work in progress), November&nbsp;2008.
     2272            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-05 (work in progress), November&nbsp;2008.
    21302273            </td>
    21312274         </tr>
    21322275         <tr>
    21332276            <td class="reference"><b id="RFC2045">[RFC2045]</b></td>
    2134             <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC&nbsp;2045, November&nbsp;1996.
     2277            <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="https://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC&nbsp;2045, November&nbsp;1996.
    21352278            </td>
    21362279         </tr>
    21372280         <tr>
    21382281            <td class="reference"><b id="RFC2047">[RFC2047]</b></td>
    2139             <td class="top"><a href="mailto:moore@cs.utk.edu" title="University of Tennessee">Moore, K.</a>, “<a href="http://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>”, RFC&nbsp;2047, November&nbsp;1996.
     2282            <td class="top"><a href="mailto:moore@cs.utk.edu" title="University of Tennessee">Moore, K.</a>, “<a href="https://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>”, RFC&nbsp;2047, November&nbsp;1996.
    21402283            </td>
    21412284         </tr>
    21422285         <tr>
    21432286            <td class="reference"><b id="RFC2119">[RFC2119]</b></td>
    2144             <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.
     2287            <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.
    21452288            </td>
    21462289         </tr>
    21472290         <tr>
    21482291            <td class="reference"><b id="RFC3986">[RFC3986]</b></td>
    2149             <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R.</a>, and <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">L. Masinter</a>, “<a href="http://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>”, RFC&nbsp;3986, STD&nbsp;66, January&nbsp;2005.
     2292            <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R.</a>, and <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">L. Masinter</a>, “<a href="https://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>”, RFC&nbsp;3986, STD&nbsp;66, January&nbsp;2005.
    21502293            </td>
    21512294         </tr>
    21522295         <tr>
    21532296            <td class="reference"><b id="RFC5234">[RFC5234]</b></td>
    2154             <td class="top"><a href="mailto:dcrocker@bbiw.net" title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a href="mailto:paul.overell@thus.net" title="THUS plc.">P. Overell</a>, “<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.
     2297            <td class="top"><a href="mailto:dcrocker@bbiw.net" title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a href="mailto:paul.overell@thus.net" title="THUS plc.">P. Overell</a>, “<a href="https://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.
    21552298            </td>
    21562299         </tr>
     
    21622305      <h2 id="rfc.references.2"><a href="#rfc.section.12.2" id="rfc.section.12.2">12.2</a> Informative References
    21632306      </h2>
    2164       <table>                                               
     2307      <table>
    21652308         <tr>
    21662309            <td class="reference"><b id="Kri2001">[Kri2001]</b></td>
     
    21812324         <tr>
    21822325            <td class="reference"><b id="RFC1123">[RFC1123]</b></td>
    2183             <td class="top"><a href="mailto:Braden@ISI.EDU" title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="http://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD&nbsp;3, RFC&nbsp;1123, October&nbsp;1989.
     2326            <td class="top"><a href="mailto:Braden@ISI.EDU" title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="https://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD&nbsp;3, RFC&nbsp;1123, October&nbsp;1989.
    21842327            </td>
    21852328         </tr>
    21862329         <tr>
    21872330            <td class="reference"><b id="RFC1305">[RFC1305]</b></td>
    2188             <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="http://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC&nbsp;1305, March&nbsp;1992.
     2331            <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="https://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC&nbsp;1305, March&nbsp;1992.
    21892332            </td>
    21902333         </tr>
    21912334         <tr>
    21922335            <td class="reference"><b id="RFC1436">[RFC1436]</b></td>
    2193             <td class="top"><a href="mailto:fxa@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Anklesaria, F.</a>, <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">McCahill, M.</a>, <a href="mailto:lindner@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Lindner, P.</a>, <a href="mailto:dmj@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Johnson, D.</a>, <a href="mailto:daniel@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Torrey, D.</a>, and <a href="mailto:alberti@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">B. Alberti</a>, “<a href="http://tools.ietf.org/html/rfc1436">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</a>”, RFC&nbsp;1436, March&nbsp;1993.
     2336            <td class="top"><a href="mailto:fxa@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Anklesaria, F.</a>, <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">McCahill, M.</a>, <a href="mailto:lindner@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Lindner, P.</a>, <a href="mailto:dmj@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Johnson, D.</a>, <a href="mailto:daniel@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Torrey, D.</a>, and <a href="mailto:alberti@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">B. Alberti</a>, “<a href="https://tools.ietf.org/html/rfc1436">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</a>”, RFC&nbsp;1436, March&nbsp;1993.
    21942337            </td>
    21952338         </tr>
    21962339         <tr>
    21972340            <td class="reference"><b id="RFC1900">[RFC1900]</b></td>
    2198             <td class="top"><a href="mailto:brian@dxcoms.cern.ch" title="CERN, Computing and Networks Division">Carpenter, B.</a> and <a href="mailto:yakov@cisco.com" title="cisco Systems">Y. Rekhter</a>, “<a href="http://tools.ietf.org/html/rfc1900">Renumbering Needs Work</a>”, RFC&nbsp;1900, February&nbsp;1996.
     2341            <td class="top"><a href="mailto:brian@dxcoms.cern.ch" title="CERN, Computing and Networks Division">Carpenter, B.</a> and <a href="mailto:yakov@cisco.com" title="cisco Systems">Y. Rekhter</a>, “<a href="https://tools.ietf.org/html/rfc1900">Renumbering Needs Work</a>”, RFC&nbsp;1900, February&nbsp;1996.
    21992342            </td>
    22002343         </tr>
    22012344         <tr>
    22022345            <td class="reference"><b id="RFC1945">[RFC1945]</b></td>
    2203             <td class="top"><a href="mailto:timbl@w3.org" title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium, MIT Laboratory for Computer Science">H. Nielsen</a>, “<a href="http://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC&nbsp;1945, May&nbsp;1996.
     2346            <td class="top"><a href="mailto:timbl@w3.org" title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium, MIT Laboratory for Computer Science">H. Nielsen</a>, “<a href="https://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC&nbsp;1945, May&nbsp;1996.
    22042347            </td>
    22052348         </tr>
    22062349         <tr>
    22072350            <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
    2208             <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2068, January&nbsp;1997.
     2351            <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="https://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2068, January&nbsp;1997.
    22092352            </td>
    22102353         </tr>
    22112354         <tr>
    22122355            <td class="reference"><b id="RFC2109">[RFC2109]</b></td>
    2213             <td class="top"><a href="mailto:dmk@bell-labs.com" title="Bell Laboratories, Lucent Technologies">Kristol, D.</a> and <a href="mailto:montulli@netscape.com" title="Netscape Communications Corp.">L. Montulli</a>, “<a href="http://tools.ietf.org/html/rfc2109">HTTP State Management Mechanism</a>”, RFC&nbsp;2109, February&nbsp;1997.
     2356            <td class="top"><a href="mailto:dmk@bell-labs.com" title="Bell Laboratories, Lucent Technologies">Kristol, D.</a> and <a href="mailto:montulli@netscape.com" title="Netscape Communications Corp.">L. Montulli</a>, “<a href="https://tools.ietf.org/html/rfc2109">HTTP State Management Mechanism</a>”, RFC&nbsp;2109, February&nbsp;1997.
    22142357            </td>
    22152358         </tr>
    22162359         <tr>
    22172360            <td class="reference"><b id="RFC2145">[RFC2145]</b></td>
    2218             <td class="top"><a href="mailto:mogul@wrl.dec.com" title="Western Research Laboratory">Mogul, J.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium">H. Nielsen</a>, “<a href="http://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>”, RFC&nbsp;2145, May&nbsp;1997.
     2361            <td class="top"><a href="mailto:mogul@wrl.dec.com" title="Western Research Laboratory">Mogul, J.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium">H. Nielsen</a>, “<a href="https://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>”, RFC&nbsp;2145, May&nbsp;1997.
    22192362            </td>
    22202363         </tr>
    22212364         <tr>
    22222365            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
    2223             <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2616, June&nbsp;1999.
     2366            <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="https://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2616, June&nbsp;1999.
    22242367            </td>
    22252368         </tr>
    22262369         <tr>
    22272370            <td class="reference"><b id="RFC2818">[RFC2818]</b></td>
    2228             <td class="top"><a href="mailto:ekr@rtfm.com" title="RTFM, Inc.">Rescorla, E.</a>, “<a href="http://tools.ietf.org/html/rfc2818">HTTP Over TLS</a>”, RFC&nbsp;2818, May&nbsp;2000.
     2371            <td class="top"><a href="mailto:ekr@rtfm.com" title="RTFM, Inc.">Rescorla, E.</a>, “<a href="https://tools.ietf.org/html/rfc2818">HTTP Over TLS</a>”, RFC&nbsp;2818, May&nbsp;2000.
    22292372            </td>
    22302373         </tr>
    22312374         <tr>
    22322375            <td class="reference"><b id="RFC2965">[RFC2965]</b></td>
    2233             <td class="top"><a href="mailto:dmk@bell-labs.com" title="Bell Laboratories, Lucent Technologies">Kristol, D.</a> and <a href="mailto:lou@montulli.org" title="Epinions.com, Inc.">L. Montulli</a>, “<a href="http://tools.ietf.org/html/rfc2965">HTTP State Management Mechanism</a>”, RFC&nbsp;2965, October&nbsp;2000.
     2376            <td class="top"><a href="mailto:dmk@bell-labs.com" title="Bell Laboratories, Lucent Technologies">Kristol, D.</a> and <a href="mailto:lou@montulli.org" title="Epinions.com, Inc.">L. Montulli</a>, “<a href="https://tools.ietf.org/html/rfc2965">HTTP State Management Mechanism</a>”, RFC&nbsp;2965, October&nbsp;2000.
    22342377            </td>
    22352378         </tr>
    22362379         <tr>
    22372380            <td class="reference"><b id="RFC3864">[RFC3864]</b></td>
    2238             <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.
     2381            <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="https://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.
    22392382            </td>
    22402383         </tr>
    22412384         <tr>
    22422385            <td class="reference"><b id="RFC3977">[RFC3977]</b></td>
    2243             <td class="top"><a href="mailto:clive@demon.net" title="THUS plc">Feather, C.</a>, “<a href="http://tools.ietf.org/html/rfc3977">Network News Transfer Protocol (NNTP)</a>”, RFC&nbsp;3977, October&nbsp;2006.
     2386            <td class="top"><a href="mailto:clive@demon.net" title="THUS plc">Feather, C.</a>, “<a href="https://tools.ietf.org/html/rfc3977">Network News Transfer Protocol (NNTP)</a>”, RFC&nbsp;3977, October&nbsp;2006.
    22442387            </td>
    22452388         </tr>
    22462389         <tr>
    22472390            <td class="reference"><b id="RFC4288">[RFC4288]</b></td>
    2248             <td class="top"><a href="mailto:ned.freed@mrochek.com" title="Sun Microsystems">Freed, N.</a> and <a href="mailto:klensin+ietf@jck.com">J. Klensin</a>, “<a href="http://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP&nbsp;13, RFC&nbsp;4288, December&nbsp;2005.
     2391            <td class="top"><a href="mailto:ned.freed@mrochek.com" title="Sun Microsystems">Freed, N.</a> and <a href="mailto:klensin+ietf@jck.com">J. Klensin</a>, “<a href="https://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP&nbsp;13, RFC&nbsp;4288, December&nbsp;2005.
    22492392            </td>
    22502393         </tr>
    22512394         <tr>
    22522395            <td class="reference"><b id="RFC4395">[RFC4395]</b></td>
    2253             <td class="top"><a href="mailto:tony+urireg@maillennium.att.com" title="AT&amp;T Laboratories">Hansen, T.</a>, <a href="mailto:hardie@qualcomm.com" title="Qualcomm, Inc.">Hardie, T.</a>, and <a href="mailto:LMM@acm.org" title="Adobe Systems">L. Masinter</a>, “<a href="http://tools.ietf.org/html/rfc4395">Guidelines and Registration Procedures for New URI Schemes</a>”, BCP&nbsp;115, RFC&nbsp;4395, February&nbsp;2006.
     2396            <td class="top"><a href="mailto:tony+urireg@maillennium.att.com" title="AT&amp;T Laboratories">Hansen, T.</a>, <a href="mailto:hardie@qualcomm.com" title="Qualcomm, Inc.">Hardie, T.</a>, and <a href="mailto:LMM@acm.org" title="Adobe Systems">L. Masinter</a>, “<a href="https://tools.ietf.org/html/rfc4395">Guidelines and Registration Procedures for New URI Schemes</a>”, BCP&nbsp;115, RFC&nbsp;4395, February&nbsp;2006.
    22542397            </td>
    22552398         </tr>
    22562399         <tr>
    22572400            <td class="reference"><b id="RFC5322">[RFC5322]</b></td>
    2258             <td class="top">Resnick, P., “<a href="http://tools.ietf.org/html/rfc5322">Internet Message Format</a>”, RFC&nbsp;5322, October&nbsp;2008.
     2401            <td class="top">Resnick, P., “<a href="https://tools.ietf.org/html/rfc5322">Internet Message Format</a>”, RFC&nbsp;5322, October&nbsp;2008.
    22592402            </td>
    22602403         </tr>
    22612404         <tr>
    22622405            <td class="reference"><b id="RFC822">[RFC822]</b></td>
    2263             <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="http://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD&nbsp;11, RFC&nbsp;822, August&nbsp;1982.
     2406            <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="https://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD&nbsp;11, RFC&nbsp;822, August&nbsp;1982.
    22642407            </td>
    22652408         </tr>
    22662409         <tr>
    22672410            <td class="reference"><b id="RFC959">[RFC959]</b></td>
    2268             <td class="top">Postel, J. and J. Reynolds, “<a href="http://tools.ietf.org/html/rfc959">File Transfer Protocol</a>”, STD&nbsp;9, RFC&nbsp;959, October&nbsp;1985.
     2411            <td class="top">Postel, J. and J. Reynolds, “<a href="https://tools.ietf.org/html/rfc959">File Transfer Protocol</a>”, STD&nbsp;9, RFC&nbsp;959, October&nbsp;1985.
    22692412            </td>
    22702413         </tr>
     
    22842427         </tr>
    22852428      </table>
    2286       <div class="avoidbreak">
    2287          <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
    2288          <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
    2289                (editor)
    2290                <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Day Software</span><span class="adr"><span class="street-address vcardline">23 Corporate Plaza DR, Suite 280</span><span class="vcardline"><span class="locality">Newport Beach</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">92660</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline tel">Phone: <a href="tel:+1-949-706-5300"><span class="value">+1-949-706-5300</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+1-949-706-5305"><span class="value">+1-949-706-5305</span></a></span><span class="vcardline">EMail: <a href="mailto:fielding@gbiv.com"><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address>
    2291          <address class="vcard"><span class="vcardline"><span class="fn">Jim Gettys</span><span class="n hidden"><span class="family-name">Gettys</span><span class="given-name">Jim</span></span></span><span class="org vcardline">One Laptop per Child</span><span class="adr"><span class="street-address vcardline">21 Oak Knoll Road</span><span class="vcardline"><span class="locality">Carlisle</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">01741</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:jg@laptop.org"><span class="email">jg@laptop.org</span></a></span><span class="vcardline">URI: <a href="http://www.laptop.org/" class="url">http://www.laptop.org/</a></span></address>
    2292          <address class="vcard"><span class="vcardline"><span class="fn">Jeffrey C. Mogul</span><span class="n hidden"><span class="family-name">Mogul</span><span class="given-name">Jeffrey C.</span></span></span><span class="org vcardline">Hewlett-Packard Company</span><span class="adr"><span class="street-address vcardline">HP Labs, Large Scale Systems Group</span><span class="street-address vcardline">1501 Page Mill Road, MS 1177</span><span class="vcardline"><span class="locality">Palo Alto</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">94304</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:JeffMogul@acm.org"><span class="email">JeffMogul@acm.org</span></a></span></address>
    2293          <address class="vcard"><span class="vcardline"><span class="fn">Henrik Frystyk Nielsen</span><span class="n hidden"><span class="family-name">Frystyk</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:henrikn@microsoft.com"><span class="email">henrikn@microsoft.com</span></a></span></address>
    2294          <address class="vcard"><span class="vcardline"><span class="fn">Larry Masinter</span><span class="n hidden"><span class="family-name">Masinter</span><span class="given-name">Larry</span></span></span><span class="org vcardline">Adobe Systems, Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:LMM@acm.org"><span class="email">LMM@acm.org</span></a></span><span class="vcardline">URI: <a href="http://larry.masinter.net/" class="url">http://larry.masinter.net/</a></span></address>
    2295          <address class="vcard"><span class="vcardline"><span class="fn">Paul J. Leach</span><span class="n hidden"><span class="family-name">Leach</span><span class="given-name">Paul J.</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span></span><span class="vcardline">EMail: <a href="mailto:paulle@microsoft.com"><span class="email">paulle@microsoft.com</span></a></span></address>
    2296          <address class="vcard"><span class="vcardline"><span class="fn">Tim Berners-Lee</span><span class="n hidden"><span class="family-name">Berners-Lee</span><span class="given-name">Tim</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">MIT Computer Science and Artificial Intelligence Laboratory</span><span class="street-address vcardline">The Stata Center, Building 32</span><span class="street-address vcardline">32 Vassar Street</span><span class="vcardline"><span class="locality">Cambridge</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">02139</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:timbl@w3.org"><span class="email">timbl@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.w3.org/People/Berners-Lee/" class="url">http://www.w3.org/People/Berners-Lee/</a></span></address>
    2297          <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span>
    2298                (editor)
    2299                <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span>&nbsp;<span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">EMail: <a href="mailto:ylafon@w3.org"><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address>
    2300          <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span>
    2301                (editor)
    2302                <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span>&nbsp;<span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline tel">Phone: <a href="tel:+492512807760"><span class="value">+49 251 2807760</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+492512807761"><span class="value">+49 251 2807761</span></a></span><span class="vcardline">EMail: <a href="mailto:julian.reschke@greenbytes.de"><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address>
     2429      <div id="tolerant.applications">
     2430         <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></h1>
     2431         <p id="rfc.section.A.p.1">Although this document specifies the requirements for the generation of HTTP/1.1 messages, not all applications will be correct
     2432            in their implementation. We therefore recommend that operational applications be tolerant of deviations whenever those deviations
     2433            can be interpreted unambiguously.
     2434         </p>
     2435         <p id="rfc.section.A.p.2">Clients <em class="bcp14">SHOULD</em> be tolerant in parsing the Status-Line and servers tolerant when parsing the Request-Line. In particular, they <em class="bcp14">SHOULD</em> accept any amount of SP or HTAB characters between fields, even though only a single SP is required.
     2436         </p>
     2437         <p id="rfc.section.A.p.3">The line terminator for message-header fields is the sequence CRLF. However, we recommend that applications, when parsing
     2438            such headers, recognize a single LF as a line terminator and ignore the leading CR.
     2439         </p>
     2440         <p id="rfc.section.A.p.4">The character set of an entity-body <em class="bcp14">SHOULD</em> be labeled as the lowest common denominator of the character codes used within that body, with the exception that not labeling
     2441            the entity is preferred over labeling the entity with the labels US-ASCII or ISO-8859-1. See <a href="#Part3" id="rfc.xref.Part3.13"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
     2442         </p>
     2443         <p id="rfc.section.A.p.5">Additional rules for requirements on parsing and encoding of dates and other potential problems with date encodings include:</p>
     2444         <p id="rfc.section.A.p.6"></p>
     2445         <ul>
     2446            <li>HTTP/1.1 clients and caches <em class="bcp14">SHOULD</em> assume that an RFC-850 date which appears to be more than 50 years in the future is in fact in the past (this helps solve
     2447               the "year 2000" problem).
     2448            </li>
     2449            <li>An HTTP/1.1 implementation <em class="bcp14">MAY</em> internally represent a parsed Expires date as earlier than the proper value, but <em class="bcp14">MUST NOT</em> internally represent a parsed Expires date as later than the proper value.
     2450            </li>
     2451            <li>All expiration-related calculations <em class="bcp14">MUST</em> be done in GMT. The local time zone <em class="bcp14">MUST NOT</em> influence the calculation or comparison of an age or expiration time.
     2452            </li>
     2453            <li>If an HTTP header incorrectly carries a date value with a time zone other than GMT, it <em class="bcp14">MUST</em> be converted into GMT using the most conservative possible conversion.
     2454            </li>
     2455         </ul>
    23032456      </div>
    2304       <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="tolerant.applications" href="#tolerant.applications">Tolerant Applications</a></h1>
    2305       <p id="rfc.section.A.p.1">Although this document specifies the requirements for the generation of HTTP/1.1 messages, not all applications will be correct
    2306          in their implementation. We therefore recommend that operational applications be tolerant of deviations whenever those deviations
    2307          can be interpreted unambiguously.
    2308       </p>
    2309       <p id="rfc.section.A.p.2">Clients <em class="bcp14">SHOULD</em> be tolerant in parsing the Status-Line and servers tolerant when parsing the Request-Line. In particular, they <em class="bcp14">SHOULD</em> accept any amount of SP or HTAB characters between fields, even though only a single SP is required.
    2310       </p>
    2311       <p id="rfc.section.A.p.3">The line terminator for message-header fields is the sequence CRLF. However, we recommend that applications, when parsing
    2312          such headers, recognize a single LF as a line terminator and ignore the leading CR.
    2313       </p>
    2314       <p id="rfc.section.A.p.4">The character set of an entity-body <em class="bcp14">SHOULD</em> be labeled as the lowest common denominator of the character codes used within that body, with the exception that not labeling
    2315          the entity is preferred over labeling the entity with the labels US-ASCII or ISO-8859-1. See <a href="#Part3" id="rfc.xref.Part3.13"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
    2316       </p>
    2317       <p id="rfc.section.A.p.5">Additional rules for requirements on parsing and encoding of dates and other potential problems with date encodings include:</p>
    2318       <p id="rfc.section.A.p.6"> </p>
    2319       <ul>
    2320          <li>HTTP/1.1 clients and caches <em class="bcp14">SHOULD</em> assume that an RFC-850 date which appears to be more than 50 years in the future is in fact in the past (this helps solve
    2321             the "year 2000" problem).
    2322          </li>
    2323          <li>An HTTP/1.1 implementation <em class="bcp14">MAY</em> internally represent a parsed Expires date as earlier than the proper value, but <em class="bcp14">MUST NOT</em> internally represent a parsed Expires date as later than the proper value.
    2324          </li>
    2325          <li>All expiration-related calculations <em class="bcp14">MUST</em> be done in GMT. The local time zone <em class="bcp14">MUST NOT</em> influence the calculation or comparison of an age or expiration time.
    2326          </li>
    2327          <li>If an HTTP header incorrectly carries a date value with a time zone other than GMT, it <em class="bcp14">MUST</em> be converted into GMT using the most conservative possible conversion.
    2328          </li>
    2329       </ul>
    2330       <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="conversion.of.date.formats" href="#conversion.of.date.formats">Conversion of Date Formats</a></h1>
    2331       <p id="rfc.section.B.p.1">HTTP/1.1 uses a restricted set of date formats (<a href="#full.date" title="Full Date">Section&nbsp;3.3.1</a>) to simplify the process of date comparison. Proxies and gateways from other protocols <em class="bcp14">SHOULD</em> ensure that any Date header field present in a message conforms to one of the HTTP/1.1 formats and rewrite the date if necessary.
    2332       </p>
    2333       <h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a>&nbsp;<a id="compatibility" href="#compatibility">Compatibility with Previous Versions</a></h1>
    2334       <p id="rfc.section.C.p.1">HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, later referred
    2335          to as HTTP/0.9, was a simple protocol for hypertext data transfer across the Internet with only a single method and no metadata.
    2336          HTTP/1.0, as defined by <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, added a range of request methods and MIME-like messaging that could include metadata about the data transferred and modifiers
    2337          on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration the effects of hierarchical
    2338          proxies, caching, the need for persistent connections, or name-based virtual hosts. The proliferation of incompletely-implemented
    2339          applications calling themselves "HTTP/1.0" further necessitated a protocol version change in order for two communicating applications
    2340          to determine each other's true capabilities.
    2341       </p>
    2342       <p id="rfc.section.C.p.2">HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations, adding
    2343          only those new features that will either be safely ignored by an HTTP/1.0 recipient or only sent when communicating with a
    2344          party advertising compliance with HTTP/1.1.
    2345       </p>
    2346       <p id="rfc.section.C.p.3">It is beyond the scope of a protocol specification to mandate compliance with previous versions. HTTP/1.1 was deliberately
    2347          designed, however, to make supporting previous versions easy. It is worth noting that, at the time of composing this specification
    2348          (1996), we would expect commercial HTTP/1.1 servers to:
    2349       </p>
    2350       <ul>
    2351          <li>recognize the format of the Request-Line for HTTP/0.9, 1.0, and 1.1 requests;</li>
    2352          <li>understand any valid request in the format of HTTP/0.9, 1.0, or 1.1;</li>
    2353          <li>respond appropriately with a message in the same major version used by the client.</li>
    2354       </ul>
    2355       <p id="rfc.section.C.p.4">And we would expect HTTP/1.1 clients to: </p>
    2356       <ul>
    2357          <li>recognize the format of the Status-Line for HTTP/1.0 and 1.1 responses;</li>
    2358          <li>understand any valid response in the format of HTTP/0.9, 1.0, or 1.1.</li>
    2359       </ul>
    2360       <p id="rfc.section.C.p.5">For most implementations of HTTP/1.0, each connection is established by the client prior to the request and closed by the
    2361          server after sending the response. Some implementations implement the Keep-Alive version of persistent connections described
    2362          in <a href="http://tools.ietf.org/html/rfc2068#section-19.7.1">Section 19.7.1</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.6"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.
    2363       </p>
    2364       <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a>&nbsp;<a id="changes.from.1.0" href="#changes.from.1.0">Changes from HTTP/1.0</a></h2>
    2365       <p id="rfc.section.C.1.p.1">This section summarizes major differences between versions HTTP/1.0 and HTTP/1.1.</p>
    2366       <h3 id="rfc.section.C.1.1"><a href="#rfc.section.C.1.1">C.1.1</a>&nbsp;<a id="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></h3>
    2367       <p id="rfc.section.C.1.1.p.1">The requirements that clients and servers support the Host request-header, report an error if the Host request-header (<a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;8.4</a>) is missing from an HTTP/1.1 request, and accept absolute URIs (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>) are among the most important changes defined by this specification.
    2368       </p>
    2369       <p id="rfc.section.C.1.1.p.2">Older HTTP/1.0 clients assumed a one-to-one relationship of IP addresses and servers; there was no other established mechanism
    2370          for distinguishing the intended server of a request than the IP address to which that request was directed. The changes outlined
    2371          above will allow the Internet, once older HTTP clients are no longer common, to support multiple Web sites from a single IP
    2372          address, greatly simplifying large operational Web servers, where allocation of many IP addresses to a single host has created
    2373          serious problems. The Internet will also be able to recover the IP addresses that have been allocated for the sole purpose
    2374          of allowing special-purpose domain names to be used in root-level HTTP URLs. Given the rate of growth of the Web, and the
    2375          number of servers already deployed, it is extremely important that all implementations of HTTP (including updates to existing
    2376          HTTP/1.0 applications) correctly implement these requirements:
    2377       </p>
    2378       <ul>
    2379          <li>Both clients and servers <em class="bcp14">MUST</em> support the Host request-header.
    2380          </li>
    2381          <li>A client that sends an HTTP/1.1 request <em class="bcp14">MUST</em> send a Host header.
    2382          </li>
    2383          <li>Servers <em class="bcp14">MUST</em> report a 400 (Bad Request) error if an HTTP/1.1 request does not include a Host request-header.
    2384          </li>
    2385          <li>Servers <em class="bcp14">MUST</em> accept absolute URIs.
    2386          </li>
    2387       </ul>
    2388       <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a>&nbsp;<a id="compatibility.with.http.1.0.persistent.connections" href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></h2>
    2389       <p id="rfc.section.C.2.p.1">Some clients and servers might wish to be compatible with some previous implementations of persistent connections in HTTP/1.0
    2390          clients and servers. Persistent connections in HTTP/1.0 are explicitly negotiated as they are not the default behavior. HTTP/1.0
    2391          experimental implementations of persistent connections are faulty, and the new facilities in HTTP/1.1 are designed to rectify
    2392          these problems. The problem was that some existing 1.0 clients may be sending Keep-Alive to a proxy server that doesn't understand
    2393          Connection, which would then erroneously forward it to the next inbound server, which would establish the Keep-Alive connection
    2394          and result in a hung HTTP/1.0 proxy waiting for the close on the response. The result is that HTTP/1.0 clients must be prevented
    2395          from using Keep-Alive when talking to proxies.
    2396       </p>
    2397       <p id="rfc.section.C.2.p.2">However, talking to proxies is the most important use of persistent connections, so that prohibition is clearly unacceptable.
    2398          Therefore, we need some other mechanism for indicating a persistent connection is desired, which is safe to use even when
    2399          talking to an old proxy that ignores Connection. Persistent connections are the default for HTTP/1.1 messages; we introduce
    2400          a new keyword (Connection: close) for declaring non-persistence. See <a href="#header.connection" id="rfc.xref.header.connection.7" title="Connection">Section&nbsp;8.1</a>.
    2401       </p>
    2402       <p id="rfc.section.C.2.p.3">The original HTTP/1.0 form of persistent connections (the Connection: Keep-Alive and Keep-Alive header) is documented in <a href="#RFC2068" id="rfc.xref.RFC2068.7"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.
    2403       </p>
    2404       <h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a>&nbsp;<a id="changes.from.rfc.2068" href="#changes.from.rfc.2068">Changes from RFC 2068</a></h2>
    2405       <p id="rfc.section.C.3.p.1">This specification has been carefully audited to correct and disambiguate key word usage; RFC 2068 had many problems in respect
    2406          to the conventions laid out in <a href="#RFC2119" id="rfc.xref.RFC2119.2"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
    2407       </p>
    2408       <p id="rfc.section.C.3.p.2">Transfer-coding and message lengths all interact in ways that required fixing exactly when chunked encoding is used (to allow
    2409          for transfer encoding that may not be self delimiting); it was important to straighten out exactly how message lengths are
    2410          computed. (Sections <a href="#transfer.codings" title="Transfer Codings">3.4</a>, <a href="#message.length" title="Message Length">4.4</a>, <a href="#header.content-length" id="rfc.xref.header.content-length.3" title="Content-Length">8.2</a>, see also <a href="#Part3" id="rfc.xref.Part3.14"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> and <a href="#Part6" id="rfc.xref.Part6.8"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>)
    2411       </p>
    2412       <p id="rfc.section.C.3.p.3">The use and interpretation of HTTP version numbers has been clarified by <a href="#RFC2145" id="rfc.xref.RFC2145.3"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>. Require proxies to upgrade requests to highest protocol version they support to deal with problems discovered in HTTP/1.0
    2413          implementations (<a href="#http.version" title="HTTP Version">Section&nbsp;3.1</a>)
    2414       </p>
    2415       <p id="rfc.section.C.3.p.4">Transfer-coding had significant problems, particularly with interactions with chunked encoding. The solution is that transfer-codings
    2416          become as full fledged as content-codings. This involves adding an IANA registry for transfer-codings (separate from content
    2417          codings), a new header field (TE) and enabling trailer headers in the future. Transfer encoding is a major performance benefit,
    2418          so it was worth fixing <a href="#Nie1997" id="rfc.xref.Nie1997.2"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. TE also solves another, obscure, downward interoperability problem that could have occurred due to interactions between
    2419          authentication trailers, chunked encoding and HTTP/1.0 clients.(Section <a href="#transfer.codings" title="Transfer Codings">3.4</a>, <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">3.4.1</a>, and <a href="#header.te" id="rfc.xref.header.te.4" title="TE">8.5</a>)
    2420       </p>
    2421       <h2 id="rfc.section.C.4"><a href="#rfc.section.C.4">C.4</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2>
    2422       <p id="rfc.section.C.4.p.1">Rules about implicit linear white space between certain grammar productions have been removed; now it's only allowed when
    2423          specifically pointed out in the ABNF. The CHAR rule does not allow the NUL character anymore (this affects the comment and
    2424          quoted-string rules). Furthermore, the quoted-pair rule does not allow escaping NUL, CR or LF anymore. (<a href="#basic.rules" title="Basic Rules">Section&nbsp;2.2</a>)
    2425       </p>
    2426       <p id="rfc.section.C.4.p.2">Clarify that HTTP-Version is case sensitive. (<a href="#http.version" title="HTTP Version">Section&nbsp;3.1</a>)
    2427       </p>
    2428       <p id="rfc.section.C.4.p.3">Remove reference to non-existant identity transfer-coding value tokens. (Sections <a href="#transfer.codings" title="Transfer Codings">3.4</a> and <a href="#message.length" title="Message Length">4.4</a>)
    2429       </p>
    2430       <p id="rfc.section.C.4.p.4">Clarification that the chunk length does not include the count of the octets in the chunk header and trailer. (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.4.1</a>)
    2431       </p>
    2432       <p id="rfc.section.C.4.p.5">Update use of abs_path production from RFC1808 to the path-absolute + query components of RFC3986. (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>)
    2433       </p>
    2434       <p id="rfc.section.C.4.p.6">Clarify exactly when close connection options must be sent. (<a href="#header.connection" id="rfc.xref.header.connection.8" title="Connection">Section&nbsp;8.1</a>)
    2435       </p>
    2436       <h1 id="rfc.section.D"><a href="#rfc.section.D">D.</a>&nbsp;<a id="terminology" href="#terminology">Terminology</a></h1>
    2437       <p id="rfc.section.D.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.</p>
    2438       <p id="rfc.section.D.p.2"> <span id="rfc.iref.c.3"></span>  <dfn>connection</dfn> 
    2439       </p>
    2440       <ul class="empty">
    2441          <li>A transport layer virtual circuit established between two programs for the purpose of communication.</li>
    2442       </ul>
    2443       <p id="rfc.section.D.p.3"> <span id="rfc.iref.m.4"></span>  <dfn>message</dfn> 
    2444       </p>
    2445       <ul class="empty">
    2446          <li>The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in <a href="#http.message" title="HTTP Message">Section&nbsp;4</a> and transmitted via the connection.
    2447          </li>
    2448       </ul>
    2449       <p id="rfc.section.D.p.4"> <span id="rfc.iref.r.1"></span>  <dfn>request</dfn> 
    2450       </p>
    2451       <ul class="empty">
    2452          <li>An HTTP request message, as defined in <a href="#request" title="Request">Section&nbsp;5</a>.
    2453          </li>
    2454       </ul>
    2455       <p id="rfc.section.D.p.5"> <span id="rfc.iref.r.2"></span>  <dfn>response</dfn> 
    2456       </p>
    2457       <ul class="empty">
    2458          <li>An HTTP response message, as defined in <a href="#response" title="Response">Section&nbsp;6</a>.
    2459          </li>
    2460       </ul>
    2461       <p id="rfc.section.D.p.6"> <span id="rfc.iref.r.3"></span>  <dfn>resource</dfn> 
    2462       </p>
    2463       <ul class="empty">
    2464          <li>A network data object or service that can be identified by a URI, as defined in <a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or
    2465             vary in other ways.
    2466          </li>
    2467       </ul>
    2468       <p id="rfc.section.D.p.7"> <span id="rfc.iref.e.1"></span>  <dfn>entity</dfn> 
    2469       </p>
    2470       <ul class="empty">
    2471          <li>The information transferred as the payload of a request or response. An entity consists of metainformation in the form of
    2472             entity-header fields and content in the form of an entity-body, as described in <a href="p3-payload.html#entity" title="Entity">Section 4</a> of <a href="#Part3" id="rfc.xref.Part3.15"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
    2473          </li>
    2474       </ul>
    2475       <p id="rfc.section.D.p.8"> <span id="rfc.iref.r.4"></span>  <dfn>representation</dfn> 
    2476       </p>
    2477       <ul class="empty">
    2478          <li>An entity included with a response that is subject to content negotiation, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.16"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. There may exist multiple representations associated with a particular response status.
    2479          </li>
    2480       </ul>
    2481       <p id="rfc.section.D.p.9"> <span id="rfc.iref.c.4"></span>  <dfn>content negotiation</dfn> 
    2482       </p>
    2483       <ul class="empty">
    2484          <li>The mechanism for selecting the appropriate representation when servicing a request, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.17"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. The representation of entities in any response can be negotiated (including error responses).
    2485          </li>
    2486       </ul>
    2487       <p id="rfc.section.D.p.10"> <span id="rfc.iref.v.2"></span>  <dfn>variant</dfn> 
    2488       </p>
    2489       <ul class="empty">
    2490          <li>A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations
    2491             is termed a `variant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation.
    2492          </li>
    2493       </ul>
    2494       <p id="rfc.section.D.p.11"> <span id="rfc.iref.c.5"></span>  <dfn>client</dfn> 
    2495       </p>
    2496       <ul class="empty">
    2497          <li>A program that establishes connections for the purpose of sending requests.</li>
    2498       </ul>
    2499       <p id="rfc.section.D.p.12"> <span id="rfc.iref.u.4"></span>  <dfn>user agent</dfn> 
    2500       </p>
    2501       <ul class="empty">
    2502          <li>The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user
    2503             tools.
    2504          </li>
    2505       </ul>
    2506       <p id="rfc.section.D.p.13"> <span id="rfc.iref.s.1"></span>  <dfn>server</dfn> 
    2507       </p>
    2508       <ul class="empty">
    2509          <li>An application program that accepts connections in order to service requests by sending back responses. Any given program
    2510             may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the
    2511             program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as
    2512             an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.
    2513          </li>
    2514       </ul>
    2515       <p id="rfc.section.D.p.14"> <span id="rfc.iref.o.1"></span>  <dfn>origin server</dfn> 
    2516       </p>
    2517       <ul class="empty">
    2518          <li>The server on which a given resource resides or is to be created.</li>
    2519       </ul>
    2520       <p id="rfc.section.D.p.15"> <span id="rfc.iref.p.1"></span>  <dfn>proxy</dfn> 
    2521       </p>
    2522       <ul class="empty">
    2523          <li>An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients.
    2524             Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy <em class="bcp14">MUST</em> implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify
    2525             the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is
    2526             a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation
    2527</