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draft-ietf-httpbis-messaging-latest.html
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draft-ietf-httpbis-messaging-latest.html
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</style><link rel="Contents" href="#rfc.toc">
<link rel="Author" href="#rfc.authors">
<link rel="License" href="#rfc.copyrightnotice">
<link rel="Index" href="#rfc.index">
<link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
<link rel="Chapter" title="2 Message" href="#rfc.section.2">
<link rel="Chapter" title="3 Request Line" href="#rfc.section.3">
<link rel="Chapter" title="4 Status Line" href="#rfc.section.4">
<link rel="Chapter" title="5 Header Fields" href="#rfc.section.5">
<link rel="Chapter" title="6 Message Body" href="#rfc.section.6">
<link rel="Chapter" title="7 Transfer Codings" href="#rfc.section.7">
<link rel="Chapter" title="8 Handling Incomplete Messages" href="#rfc.section.8">
<link rel="Chapter" title="9 Connection Management" href="#rfc.section.9">
<link rel="Chapter" title="10 Enclosing Messages as Data" href="#rfc.section.10">
<link rel="Chapter" title="11 Security Considerations" href="#rfc.section.11">
<link rel="Chapter" title="12 IANA Considerations" href="#rfc.section.12">
<link rel="Chapter" href="#rfc.section.13" title="13 References">
<link rel="Appendix" title="A Collected ABNF" href="#rfc.section.A">
<link rel="Appendix" title="B Differences between HTTP and MIME" href="#rfc.section.B">
<link rel="Appendix" title="C HTTP Version History" href="#rfc.section.C">
<link rel="Appendix" title="D Change Log" href="#rfc.section.D">
<link rel="Appendix" title="Acknowledgments" href="#rfc.section.unnumbered-1">
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<meta name="dcterms.creator" content="Fielding, R.">
<meta name="dcterms.creator" content="Nottingham, M.">
<meta name="dcterms.creator" content="Reschke, J. F.">
<meta name="dcterms.issued" content="2019-03-26">
<meta name="dct.replaces" content="urn:ietf:rfc:7230">
<meta name="dcterms.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230.">
<meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230.">
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<header>
<table class="header" id="rfc.headerblock">
<tbody>
<tr>
<td class="left">HTTP Working Group</td>
<td class="right">R. Fielding, Editor</td>
</tr>
<tr>
<td class="left">Internet-Draft</td>
<td class="right">Adobe</td>
</tr>
<tr>
<td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc7230">7230</a> (if approved)
</td>
<td class="right">M. Nottingham, Editor</td>
</tr>
<tr>
<td class="left">Intended status: Standards Track</td>
<td class="right">Fastly</td>
</tr>
<tr>
<td class="left">Expires: September 27, 2019</td>
<td class="right">J. Reschke, Editor</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">greenbytes</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">March 26, 2019</td>
</tr>
</tbody>
</table>
<div id="rfc.title">
<h1>HTTP/1.1 Messaging</h1>
<div class="filename"><a href="https://datatracker.ietf.org/doc/draft-ietf-httpbis-messaging" class="smpl">draft-ietf-httpbis-messaging-latest</a></div>
</div>
</header>
<section id="rfc.abstract">
<h2><a href="#rfc.abstract">Abstract</a></h2>
<div id="rfc.abstract.p.1">
<p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for
distributed, collaborative, hypertext information systems. This document specifies
the HTTP/1.1 message syntax, message parsing, connection management, and related security
concerns.<a class="self" href="#rfc.abstract.p.1">¶</a></p>
</div>
<div id="rfc.abstract.p.2">
<p>This document obsoletes portions of RFC 7230.<a class="self" href="#rfc.abstract.p.2">¶</a></p>
</div>
</section>
<section id="rfc.note.1" class="note rfcEditorRemove">
<h2><a href="#rfc.note.1">Editorial Note</a></h2>
<div id="rfc.note.1.p.1">
<p>This note is to be removed before publishing as an RFC.<a class="self" href="#rfc.note.1.p.1">¶</a></p>
</div>
<div id="rfc.note.1.p.2">
<p>Discussion of this draft takes place on the HTTP working group mailing list (ietf-http-wg@w3.org),
which is archived at <<a href="https://lists.w3.org/Archives/Public/ietf-http-wg/">https://lists.w3.org/Archives/Public/ietf-http-wg/</a>>.<a class="self" href="#rfc.note.1.p.2">¶</a></p>
</div>
<div id="rfc.note.1.p.3">
<p>Working Group information can be found at <<a href="https://httpwg.org/">https://httpwg.org/</a>>; source code and issues list for this draft can be found at <<a href="https://github.com/httpwg/http-core">https://github.com/httpwg/http-core</a>>.<a class="self" href="#rfc.note.1.p.3">¶</a></p>
</div>
<div id="rfc.note.1.p.4">
<p>The changes in this draft are summarized in <a href="#changes.since.04" title="Since draft-ietf-httpbis-messaging-04">Appendix D.6</a>.<a class="self" href="#rfc.note.1.p.4">¶</a></p>
</div>
</section>
<section id="rfc.status">
<h2><a href="#rfc.status">Status of This Memo</a></h2>
<div id="rfc.boilerplate.1.p.1">
<p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78
and BCP 79.<a class="self" href="#rfc.boilerplate.1.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.2">
<p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF).
Note that other groups may also distribute working documents as Internet-Drafts. The
list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>.<a class="self" href="#rfc.boilerplate.1.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.3">
<p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated,
replaced, or obsoleted by other documents at any time. It is inappropriate to use
Internet-Drafts as reference material or to cite them other than as “work in progress”.<a class="self" href="#rfc.boilerplate.1.p.3">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.4">
<p>This Internet-Draft will expire on September 27, 2019.<a class="self" href="#rfc.boilerplate.1.p.4">¶</a></p>
</div>
</section>
<section id="rfc.copyrightnotice">
<h2><a href="#rfc.copyrightnotice">Copyright Notice</a></h2>
<div id="rfc.boilerplate.2.p.1">
<p>Copyright © 2019 IETF Trust and the persons identified as the document authors. All
rights reserved.<a class="self" href="#rfc.boilerplate.2.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.2">
<p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating
to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect to this document.
Code Components extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.<a class="self" href="#rfc.boilerplate.2.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.3">
<p>This document may contain material from IETF Documents or IETF Contributions published
or made publicly available before November 10, 2008. The person(s) controlling the
copyright in some of this material may not have granted the IETF Trust the right to
allow modifications of such material outside the IETF Standards Process. Without obtaining
an adequate license from the person(s) controlling the copyright in such materials,
this document may not be modified outside the IETF Standards Process, and derivative
works of it may not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other than English.<a class="self" href="#rfc.boilerplate.2.p.3">¶</a></p>
</div>
</section>
<hr class="noprint">
<nav id="rfc.toc">
<h2 class="np"><a href="#rfc.toc">Table of Contents</a></h2>
<ul class="toc">
<li><a href="#rfc.section.1">1.</a> <a href="#introduction">Introduction</a><ul>
<li><a href="#rfc.section.1.1">1.1.</a> <a href="#intro.requirements">Requirements Notation</a></li>
<li><a href="#rfc.section.1.2">1.2.</a> <a href="#notation">Syntax Notation</a></li>
</ul>
</li>
<li><a href="#rfc.section.2">2.</a> <a href="#http.message">Message</a><ul>
<li><a href="#rfc.section.2.1">2.1.</a> <a href="#message.format">Message Format</a></li>
<li><a href="#rfc.section.2.2">2.2.</a> <a href="#http.version">HTTP Version</a></li>
<li><a href="#rfc.section.2.3">2.3.</a> <a href="#message.parsing">Message Parsing</a></li>
</ul>
</li>
<li><a href="#rfc.section.3">3.</a> <a href="#request.line">Request Line</a><ul>
<li><a href="#rfc.section.3.1">3.1.</a> <a href="#request.method">Method</a></li>
<li><a href="#rfc.section.3.2">3.2.</a> <a href="#request.target">Request Target</a><ul>
<li><a href="#rfc.section.3.2.1">3.2.1.</a> <a href="#origin-form">origin-form</a></li>
<li><a href="#rfc.section.3.2.2">3.2.2.</a> <a href="#absolute-form">absolute-form</a></li>
<li><a href="#rfc.section.3.2.3">3.2.3.</a> <a href="#authority-form">authority-form</a></li>
<li><a href="#rfc.section.3.2.4">3.2.4.</a> <a href="#asterisk-form">asterisk-form</a></li>
</ul>
</li>
<li><a href="#rfc.section.3.3">3.3.</a> <a href="#h1.effective.request.uri">Effective Request URI</a></li>
</ul>
</li>
<li><a href="#rfc.section.4">4.</a> <a href="#status.line">Status Line</a></li>
<li><a href="#rfc.section.5">5.</a> <a href="#header.fields">Header Fields</a><ul>
<li><a href="#rfc.section.5.1">5.1.</a> <a href="#field.parsing">Header Field Parsing</a></li>
<li><a href="#rfc.section.5.2">5.2.</a> <a href="#line.folding">Obsolete Line Folding</a></li>
</ul>
</li>
<li><a href="#rfc.section.6">6.</a> <a href="#message.body">Message Body</a><ul>
<li><a href="#rfc.section.6.1">6.1.</a> <a href="#header.transfer-encoding">Transfer-Encoding</a></li>
<li><a href="#rfc.section.6.2">6.2.</a> <a href="#body.content-length">Content-Length</a></li>
<li><a href="#rfc.section.6.3">6.3.</a> <a href="#message.body.length">Message Body Length</a></li>
</ul>
</li>
<li><a href="#rfc.section.7">7.</a> <a href="#transfer.codings">Transfer Codings</a><ul>
<li><a href="#rfc.section.7.1">7.1.</a> <a href="#chunked.encoding">Chunked Transfer Coding</a><ul>
<li><a href="#rfc.section.7.1.1">7.1.1.</a> <a href="#chunked.extension">Chunk Extensions</a></li>
<li><a href="#rfc.section.7.1.2">7.1.2.</a> <a href="#chunked.trailer.part">Chunked Trailer Part</a></li>
<li><a href="#rfc.section.7.1.3">7.1.3.</a> <a href="#decoding.chunked">Decoding Chunked</a></li>
</ul>
</li>
<li><a href="#rfc.section.7.2">7.2.</a> <a href="#compression.codings">Transfer Codings for Compression</a></li>
<li><a href="#rfc.section.7.3">7.3.</a> <a href="#transfer.coding.registry">Transfer Coding Registry</a></li>
<li><a href="#rfc.section.7.4">7.4.</a> <a href="#header.te">TE</a></li>
</ul>
</li>
<li><a href="#rfc.section.8">8.</a> <a href="#incomplete.messages">Handling Incomplete Messages</a></li>
<li><a href="#rfc.section.9">9.</a> <a href="#connection.management">Connection Management</a><ul>
<li><a href="#rfc.section.9.1">9.1.</a> <a href="#header.connection">Connection</a></li>
<li><a href="#rfc.section.9.2">9.2.</a> <a href="#persistent.establishment">Establishment</a></li>
<li><a href="#rfc.section.9.3">9.3.</a> <a href="#associating.response.to.request">Associating a Response to a Request</a></li>
<li><a href="#rfc.section.9.4">9.4.</a> <a href="#persistent.connections">Persistence</a><ul>
<li><a href="#rfc.section.9.4.1">9.4.1.</a> <a href="#persistent.retrying.requests">Retrying Requests</a></li>
<li><a href="#rfc.section.9.4.2">9.4.2.</a> <a href="#pipelining">Pipelining</a></li>
</ul>
</li>
<li><a href="#rfc.section.9.5">9.5.</a> <a href="#persistent.concurrency">Concurrency</a></li>
<li><a href="#rfc.section.9.6">9.6.</a> <a href="#persistent.failures">Failures and Timeouts</a></li>
<li><a href="#rfc.section.9.7">9.7.</a> <a href="#persistent.tear-down">Tear-down</a></li>
<li><a href="#rfc.section.9.8">9.8.</a> <a href="#header.upgrade">Upgrade</a><ul>
<li><a href="#rfc.section.9.8.1">9.8.1.</a> <a href="#upgrade.protocol.names">Upgrade Protocol Names</a></li>
<li><a href="#rfc.section.9.8.2">9.8.2.</a> <a href="#upgrade.token.registry">Upgrade Token Registry</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#rfc.section.10">10.</a> <a href="#enclosing.messages">Enclosing Messages as Data</a><ul>
<li><a href="#rfc.section.10.1">10.1.</a> <a href="#media.type.message.http">Media Type message/http</a></li>
<li><a href="#rfc.section.10.2">10.2.</a> <a href="#media.type.application.http">Media Type application/http</a></li>
</ul>
</li>
<li><a href="#rfc.section.11">11.</a> <a href="#security.considerations">Security Considerations</a><ul>
<li><a href="#rfc.section.11.1">11.1.</a> <a href="#response.splitting">Response Splitting</a></li>
<li><a href="#rfc.section.11.2">11.2.</a> <a href="#request.smuggling">Request Smuggling</a></li>
<li><a href="#rfc.section.11.3">11.3.</a> <a href="#message.integrity">Message Integrity</a></li>
<li><a href="#rfc.section.11.4">11.4.</a> <a href="#message.confidentiality">Message Confidentiality</a></li>
</ul>
</li>
<li><a href="#rfc.section.12">12.</a> <a href="#IANA.considerations">IANA Considerations</a><ul>
<li><a href="#rfc.section.12.1">12.1.</a> <a href="#header.field.registration">Header Field Registration</a></li>
<li><a href="#rfc.section.12.2">12.2.</a> <a href="#media.type.http">Media Type Registration</a></li>
<li><a href="#rfc.section.12.3">12.3.</a> <a href="#transfer.coding.registration">Transfer Coding Registration</a></li>
<li><a href="#rfc.section.12.4">12.4.</a> <a href="#upgrade.token.registration">Upgrade Token Registration</a></li>
</ul>
</li>
<li><a href="#rfc.section.13">13.</a> <a href="#rfc.references">References</a><ul>
<li><a href="#rfc.section.13.1">13.1.</a> <a href="#rfc.references.1">Normative References</a></li>
<li><a href="#rfc.section.13.2">13.2.</a> <a href="#rfc.references.2">Informative References</a></li>
</ul>
</li>
<li><a href="#rfc.section.A">Appendix A.</a> <a href="#collected.abnf">Collected ABNF</a></li>
<li><a href="#rfc.section.B">Appendix B.</a> <a href="#differences.between.http.and.mime">Differences between HTTP and MIME</a><ul>
<li><a href="#rfc.section.B.1">B.1.</a> <a href="#mime-version">MIME-Version</a></li>
<li><a href="#rfc.section.B.2">B.2.</a> <a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
<li><a href="#rfc.section.B.3">B.3.</a> <a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
<li><a href="#rfc.section.B.4">B.4.</a> <a href="#conversion.content-encoding">Conversion of Content-Encoding</a></li>
<li><a href="#rfc.section.B.5">B.5.</a> <a href="#conversion.content-transfer-encoding">Conversion of Content-Transfer-Encoding</a></li>
<li><a href="#rfc.section.B.6">B.6.</a> <a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
</ul>
</li>
<li><a href="#rfc.section.C">Appendix C.</a> <a href="#compatibility">HTTP Version History</a><ul>
<li><a href="#rfc.section.C.1">C.1.</a> <a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
<li><a href="#rfc.section.C.1.1">C.1.1.</a> <a href="#changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses">Multihomed Web Servers</a></li>
<li><a href="#rfc.section.C.1.2">C.1.2.</a> <a href="#compatibility.with.http.1.0.persistent.connections">Keep-Alive Connections</a></li>
<li><a href="#rfc.section.C.1.3">C.1.3.</a> <a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li>
</ul>
</li>
<li><a href="#rfc.section.C.2">C.2.</a> <a href="#changes.from.rfc.7230">Changes from RFC 7230</a></li>
</ul>
</li>
<li><a href="#rfc.section.D">Appendix D.</a> <a href="#change.log">Change Log</a><ul>
<li><a href="#rfc.section.D.1">D.1.</a> <a href="#changes.since.publication.as.rfc">Between RFC7230 and draft 00</a></li>
<li><a href="#rfc.section.D.2">D.2.</a> <a href="#changes.since.00">Since draft-ietf-httpbis-messaging-00</a></li>
<li><a href="#rfc.section.D.3">D.3.</a> <a href="#changes.since.01">Since draft-ietf-httpbis-messaging-01</a></li>
<li><a href="#rfc.section.D.4">D.4.</a> <a href="#changes.since.02">Since draft-ietf-httpbis-messaging-02</a></li>
<li><a href="#rfc.section.D.5">D.5.</a> <a href="#changes.since.03">Since draft-ietf-httpbis-messaging-03</a></li>
<li><a href="#rfc.section.D.6">D.6.</a> <a href="#changes.since.04">Since draft-ietf-httpbis-messaging-04</a></li>
</ul>
</li>
<li><a href="#acks">Acknowledgments</a></li>
<li><a href="#rfc.index">Index</a></li>
<li><a href="#rfc.authors">Authors' Addresses</a></li>
</ul>
</nav>
<section id="introduction">
<h2 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a href="#introduction">Introduction</a></h2>
<div id="rfc.section.1.p.1" class="avoidbreakafter">
<p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level request/response
protocol that uses extensible semantics and self-descriptive messages for flexible
interaction with network-based hypertext information systems. HTTP is defined by a
series of documents that collectively form the HTTP/1.1 specification:<a class="self" href="#rfc.section.1.p.1">¶</a></p>
</div>
<div id="rfc.section.1.p.2">
<ul>
<li>"HTTP Semantics" <a href="#Semantics" id="rfc.xref.Semantics.1"><cite title="HTTP Semantics">[Semantics]</cite></a></li>
<li>"HTTP Caching" <a href="#Caching" id="rfc.xref.Caching.1"><cite title="HTTP Caching">[Caching]</cite></a></li>
<li>"HTTP/1.1 Messaging" (this document)</li>
</ul>
</div>
<div id="rfc.section.1.p.3">
<p>This document defines HTTP/1.1 message syntax and framing requirements and their associated
connection management. Our goal is to define all of the mechanisms necessary for HTTP/1.1
message handling that are independent of message semantics, thereby defining the complete
set of requirements for message parsers and message-forwarding intermediaries.<a class="self" href="#rfc.section.1.p.3">¶</a></p>
</div>
<div id="rfc.section.1.p.4">
<p>This document obsoletes the portions of <cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing" id="rfc.xref.RFC7230.1">RFC 7230</cite> related to HTTP/1.1 messaging and connection management, with the changes being summarized
in <a href="#changes.from.rfc.7230" title="Changes from RFC 7230">Appendix C.2</a>. The other parts of <cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing" id="rfc.xref.RFC7230.2">RFC 7230</cite> are obsoleted by "HTTP Semantics" <a href="#Semantics" id="rfc.xref.Semantics.2"><cite title="HTTP Semantics">[Semantics]</cite></a>.<a class="self" href="#rfc.section.1.p.4">¶</a></p>
</div>
<section id="intro.requirements">
<h3 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1.</a> <a href="#intro.requirements">Requirements Notation</a></h3>
<div id="rfc.section.1.1.p.1">
<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD
NOT", "RECOMMENDED", "MAY", and "OPTIONAL" 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>.<a class="self" href="#rfc.section.1.1.p.1">¶</a></p>
</div>
<div id="rfc.section.1.1.p.2">
<p>Conformance criteria and considerations regarding error handling are defined in <a href="draft-ietf-httpbis-semantics-latest.html#conformance" title="Conformance">Section 3</a> of <a href="#Semantics" id="rfc.xref.Semantics.3"><cite title="HTTP Semantics">[Semantics]</cite></a>.<a class="self" href="#rfc.section.1.1.p.2">¶</a></p>
</div>
</section>
<section id="notation">
<h3 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2.</a> <a href="#notation">Syntax Notation</a></h3>
<div id="rfc.section.1.2.p.1">
<p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, extended with the notation for case-sensitivity in strings defined in <a href="#RFC7405" id="rfc.xref.RFC7405.1"><cite title="Case-Sensitive String Support in ABNF">[RFC7405]</cite></a>.<a class="self" href="#rfc.section.1.2.p.1">¶</a></p>
</div>
<div id="rfc.section.1.2.p.2">
<p>It also uses a list extension, defined in <a href="draft-ietf-httpbis-semantics-latest.html#abnf.extension" title="ABNF List Extension: #rule">Section 11</a> of <a href="#Semantics" id="rfc.xref.Semantics.4"><cite title="HTTP Semantics">[Semantics]</cite></a>, that allows for compact definition of comma-separated lists using a '#' operator
(similar to how the '*' operator indicates repetition). <a href="#collected.abnf" title="Collected ABNF">Appendix A</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.2">¶</a></p>
</div>
<div id="rfc.section.1.2.p.3">
<p>As a convention, ABNF rule names prefixed with "obs-" denote "obsolete" grammar rules
that appear for historical reasons.<a class="self" href="#rfc.section.1.2.p.3">¶</a></p>
</div>
<div id="rfc.section.1.2.p.4">
<p id="core.rules"> The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><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), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal
0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible <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).<a class="self" href="#rfc.section.1.2.p.4">¶</a></p>
</div>
<div id="rfc.section.1.2.p.5" class="avoidbreakafter">
<p id="imported.rules"> The rules below are defined in <a href="#Semantics" id="rfc.xref.Semantics.5"><cite title="HTTP Semantics">[Semantics]</cite></a>:<a class="self" href="#rfc.section.1.2.p.5">¶</a></p>
</div>
<div id="rfc.section.1.2.p.6"><pre class="inline prettyprint lang-ietf_abnf"> <a href="draft-ietf-httpbis-semantics-latest.html#whitespace" class="smpl">BWS</a> = <BWS, see <a href="#Semantics" id="rfc.xref.Semantics.6"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#whitespace" title="Whitespace">Section 4.3</a>>
<a href="draft-ietf-httpbis-semantics-latest.html#whitespace" class="smpl">OWS</a> = <OWS, see <a href="#Semantics" id="rfc.xref.Semantics.7"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#whitespace" title="Whitespace">Section 4.3</a>>
<a href="draft-ietf-httpbis-semantics-latest.html#whitespace" class="smpl">RWS</a> = <RWS, see <a href="#Semantics" id="rfc.xref.Semantics.8"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#whitespace" title="Whitespace">Section 4.3</a>>
<a href="#imported.rules" class="smpl">absolute-URI</a> = <absolute-URI, see <a href="#RFC3986" id="rfc.xref.RFC3986.1"><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>>
<a href="#imported.rules" class="smpl">absolute-path</a> = <absolute-path, see <a href="#Semantics" id="rfc.xref.Semantics.9"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#uri" title="Uniform Resource Identifiers">Section 2.4</a>>
<a href="#imported.rules" class="smpl">authority</a> = <authority, see <a href="#RFC3986" id="rfc.xref.RFC3986.2"><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>>
<a href="#imported.rules" class="smpl">comment</a> = <comment, see <a href="#Semantics" id="rfc.xref.Semantics.10"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.components" title="Header Field Value Components">Section 4.2.3</a>>
<a href="#imported.rules" class="smpl">field-name</a> = <field-name, see <a href="#Semantics" id="rfc.xref.Semantics.11"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.values" title="Header Field Values">Section 4.2</a>>
<a href="#imported.rules" class="smpl">field-value</a> = <field-value, see <a href="#Semantics" id="rfc.xref.Semantics.12"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.values" title="Header Field Values">Section 4.2</a>>
<a href="#imported.rules" class="smpl">obs-text</a> = <obs-text, see <a href="#Semantics" id="rfc.xref.Semantics.13"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.components" title="Header Field Value Components">Section 4.2.3</a>>
<a href="draft-ietf-httpbis-semantics-latest.html#uri" class="smpl">port</a> = <port, see <a href="#RFC3986" id="rfc.xref.RFC3986.3"><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>>
<a href="#imported.rules" class="smpl">query</a> = <query, see <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-3.4">Section 3.4</a>>
<a href="#imported.rules" class="smpl">quoted-string</a> = <quoted-string, see <a href="#Semantics" id="rfc.xref.Semantics.14"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.components" title="Header Field Value Components">Section 4.2.3</a>>
<a href="#imported.rules" class="smpl">token</a> = <token, see <a href="#Semantics" id="rfc.xref.Semantics.15"><cite title="HTTP Semantics">[Semantics]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#field.components" title="Header Field Value Components">Section 4.2.3</a>>
<a href="draft-ietf-httpbis-semantics-latest.html#uri" class="smpl">uri-host</a> = <host, see <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-3.2.2">Section 3.2.2</a>>
</pre></div>
</section>
</section>
<section id="http.message">
<h2 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a href="#http.message">Message</a></h2>
<section id="message.format">
<h3 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1.</a> <a href="#message.format">Message Format</a></h3>
<div id="rfc.section.2.1.p.1">
<p>All HTTP/1.1 messages consist of a start-line followed by a sequence of octets in
a format similar to the Internet Message Format <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>: zero or more header fields (collectively referred to as the "headers" or the "header
section"), an empty line indicating the end of the header section, and an optional
message body.<a class="self" href="#rfc.section.2.1.p.1">¶</a></p>
</div>
<div id="rfc.section.2.1.p.2"><pre class="inline prettyprint lang-ietf_abnf"><span id="rfc.iref.g.1"></span> <a href="#message.format" class="smpl">HTTP-message</a> = <a href="#message.format" class="smpl">start-line</a>
*( <a href="#header.fields" class="smpl">header-field</a> <a href="#core.rules" class="smpl">CRLF</a> )
<a href="#core.rules" class="smpl">CRLF</a>
[ <a href="#message.body" class="smpl">message-body</a> ]
</pre></div>
<div id="rfc.section.2.1.p.3">
<p>An HTTP message can be either a request from client to server or a response from server
to client. Syntactically, the two types of message differ only in the start-line,
which is either a request-line (for requests) or a status-line (for responses), and
in the algorithm for determining the length of the message body (<a href="#message.body" title="Message Body">Section 6</a>).<a class="self" href="#rfc.section.2.1.p.3">¶</a></p>
</div>
<div id="rfc.section.2.1.p.4"><pre class="inline prettyprint lang-ietf_abnf"><span id="rfc.iref.g.2"></span> <a href="#message.format" class="smpl">start-line</a> = <a href="#request.line" class="smpl">request-line</a> / <a href="#status.line" class="smpl">status-line</a>
</pre></div>
<div id="rfc.section.2.1.p.5">
<p>In theory, a client could receive requests and a server could receive responses, distinguishing
them by their different start-line formats. In practice, servers are implemented to
only expect a request (a response is interpreted as an unknown or invalid request
method) and clients are implemented to only expect a response.<a class="self" href="#rfc.section.2.1.p.5">¶</a></p>
</div>
<div id="rfc.section.2.1.p.6">
<p>Although HTTP makes use of some protocol elements similar to 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="#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix B</a> for the differences between HTTP and MIME messages.<a class="self" href="#rfc.section.2.1.p.6">¶</a></p>
</div>
</section>
<section id="http.version">
<h3 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2.</a> <a href="#http.version">HTTP Version</a></h3>
<div id="rfc.section.2.2.p.1">
<p>HTTP uses a "<major>.<minor>" numbering scheme to indicate versions of the protocol.
This specification defines version "1.1". <a href="draft-ietf-httpbis-semantics-latest.html#protocol.version" title="Protocol Versioning">Section 3.5</a> of <a href="#Semantics" id="rfc.xref.Semantics.16"><cite title="HTTP Semantics">[Semantics]</cite></a> specifies the semantics of HTTP version numbers.<a class="self" href="#rfc.section.2.2.p.1">¶</a></p>
</div>
<div id="rfc.section.2.2.p.2">
<p>The version of an HTTP/1.x message is indicated by an HTTP-version field in the <a href="#message.format" class="smpl">start-line</a>. HTTP-version is case-sensitive.<a class="self" href="#rfc.section.2.2.p.2">¶</a></p>
</div>
<div id="rfc.section.2.2.p.3"><pre class="inline prettyprint lang-ietf_abnf"><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span> <a href="#http.version" class="smpl">HTTP-version</a> = <a href="#http.version" class="smpl">HTTP-name</a> "/" <a href="#core.rules" class="smpl">DIGIT</a> "." <a href="#core.rules" class="smpl">DIGIT</a>
<a href="#http.version" class="smpl">HTTP-name</a> = %s"HTTP"
</pre></div>
<div id="rfc.section.2.2.p.4">
<p>When an HTTP/1.1 message is sent to an HTTP/1.0 recipient <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a> or a recipient whose version is unknown, the HTTP/1.1 message is constructed such