<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="">
<meta name="author" content="Loïc Hoguin based on a design from (Soft10) Pol Cámara">
<meta name="generator" content="Hugo 0.37.1" />
<title>Nine Nines: cowboy_req:read_part(3)</title>
<link href='https://fonts.googleapis.com/css?family=Open+Sans:400,700,400italic' rel='stylesheet' type='text/css'>
<link href="/css/99s.css?r=1" rel="stylesheet">
<link rel="shortcut icon" href="/img/ico/favicon.ico">
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="/img/ico/apple-touch-icon-114.png">
<link rel="apple-touch-icon-precomposed" sizes="72x72" href="/img/ico/apple-touch-icon-72.png">
<link rel="apple-touch-icon-precomposed" href="/img/ico/apple-touch-icon-57.png">
</head>
<body class="">
<header id="page-head">
<div id="topbar" class="container">
<div class="row">
<div class="span2">
<h1 id="logo"><a href="/" title="99s">99s</a></h1>
</div>
<div class="span10">
<div id="side-header">
<nav>
<ul>
<li><a title="Hear my thoughts" href="/articles">Articles</a></li>
<li><a title="Watch my talks" href="/talks">Talks</a></li>
<li class="active"><a title="Read the docs" href="/docs">Documentation</a></li>
<li><a title="Request my services" href="/services">Consulting & Training</a></li>
</ul>
</nav>
<ul id="social">
<li>
<a href="https://github.com/ninenines" title="Check my Github repositories"><img src="/img/ico_github.png" data-hover="/img/ico_github_alt.png" alt="Github"></a>
</li>
<li>
<a title="Contact me" href="mailto:[email protected]"><img src="/img/ico_mail.png" data-hover="/img/ico_mail_alt.png"></a>
</li>
</ul>
</div>
</div>
</div>
</div>
</header>
<div id="contents" class="two_col">
<div class="container">
<div class="row">
<div id="docs" class="span9 maincol">
<h1 class="lined-header"><span>cowboy_req:read_part(3)</span></h1>
<div class="sect1">
<h2 id="_name">Name</h2>
<div class="sectionbody">
<div class="paragraph"><p>cowboy_req:read_part - Read the next multipart headers</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">Description</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #000000">read_part</span></span>(<span style="color: #009900">Req</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:req</span></span>())
<span style="color: #990000">-></span> <span style="font-weight: bold"><span style="color: #000000">read_part</span></span>(<span style="color: #009900">Req</span>, #{})
<span style="font-weight: bold"><span style="color: #000000">read_part</span></span>(<span style="color: #009900">Req</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:req</span></span>(), <span style="color: #009900">Opts</span>)
<span style="color: #990000">-></span> {<span style="color: #FF6600">ok</span>, <span style="color: #009900">Headers</span>, <span style="color: #009900">Req</span>} | {<span style="color: #FF6600">done</span>, <span style="color: #009900">Req</span>}
<span style="color: #009900">Opts</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_body_opts</span></span>()
<span style="color: #009900">Headers</span> <span style="color: #990000">::</span> #{<span style="font-weight: bold"><span style="color: #000080">binary</span></span>() <span style="color: #990000">=></span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>()}</tt></pre></div></div>
<div class="paragraph"><p>Read the next part of a multipart body.</p></div>
<div class="paragraph"><p>This function reads the request body and parses it as
multipart. Each parts of a multipart representation have
their own headers and body. This function parses and returns
headers. Examples of multipart media types are
<code>multipart/form-data</code> and <code>multipart/byteranges</code>.</p></div>
<div class="paragraph"><p>Cowboy will skip any data remaining until the beginning of
the next part. This includes the preamble to the multipart
message but also the body of a previous part if it hasn’t
been read. Both are skipped automatically when calling this
function.</p></div>
<div class="paragraph"><p>Cowboy will read the body before parsing in chunks of size
up to 64KB, with a period of 5 seconds. This is tailored for
reading part headers and might not be the most efficient for
skipping the previous part’s body.</p></div>
<div class="paragraph"><p>The headers returned are MIME headers, <strong>NOT</strong> HTTP headers.
They can be parsed using the functions from the <code>cow_multipart</code>
module. In addition, the <code>cow_multipart:form_data/1</code> function
can be used to quickly extract information from <code>multipart/form-data</code>
representations.</p></div>
<div class="paragraph"><p>Once a part has been read, it can not be read again.</p></div>
<div class="paragraph"><p>Once the body has been read, Cowboy sets the content-length
header if it was not previously provided.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_arguments">Arguments</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
Req
</dt>
<dd>
<p>
The Req object.
</p>
</dd>
<dt class="hdlist1">
Opts
</dt>
<dd>
<p>
A map of body reading options. Please refer to
<a href="../cowboy_req.read_body">cowboy_req:read_body(3)</a>
for details about each option.
</p>
<div class="paragraph"><p>This function defaults the <code>length</code> to 64KB and the <code>period</code>
to 5 seconds.</p></div>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_return_value">Return value</h2>
<div class="sectionbody">
<div class="paragraph"><p>An <code>ok</code> tuple is returned containing the next part’s headers
as a map.</p></div>
<div class="paragraph"><p>A <code>done</code> tuple is returned if there are no more parts to read.</p></div>
<div class="paragraph"><p>The Req object returned in the tuple must be used for that point
onward. It contains a more up to date representation of the request.
For example it may have an added content-length header once the
body has been read.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_changelog">Changelog</h2>
<div class="sectionbody">
<div class="ulist"><ul>
<li>
<p>
<strong>2.0</strong>: Function introduced. Replaces <code>part/1,2</code>.
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_examples">Examples</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="title">Read all parts</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #000000">acc_multipart</span></span>(<span style="color: #009900">Req0</span>, <span style="color: #009900">Acc</span>) <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #0000FF">case</span></span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_part</span></span>(<span style="color: #009900">Req0</span>) <span style="font-weight: bold"><span style="color: #0000FF">of</span></span>
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Headers</span>, <span style="color: #009900">Req1</span>} <span style="color: #990000">-></span>
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Body</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">stream_body</span></span>(<span style="color: #009900">Req1</span>, <span style="color: #990000"><<>></span>),
<span style="font-weight: bold"><span style="color: #000000">acc_multipart</span></span>(<span style="color: #009900">Req</span>, [{<span style="color: #009900">Headers</span>, <span style="color: #009900">Body</span>}|<span style="color: #009900">Acc</span>]);
{<span style="color: #FF6600">done</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-></span>
{<span style="font-weight: bold"><span style="color: #000000">lists:reverse</span></span>(<span style="color: #009900">Acc</span>), <span style="color: #009900">Req</span>}
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span>
<span style="font-weight: bold"><span style="color: #000000">stream_body</span></span>(<span style="color: #009900">Req0</span>, <span style="color: #009900">Acc</span>) <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #0000FF">case</span></span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_part_body</span></span>(<span style="color: #009900">Req0</span>) <span style="font-weight: bold"><span style="color: #0000FF">of</span></span>
{<span style="color: #FF6600">more</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #000000">stream_body</span></span>(<span style="color: #009900">Req</span>, <span style="color: #990000"><<</span> <span style="color: #009900">Acc</span><span style="color: #990000">/</span><span style="font-weight: bold"><span style="color: #000080">binary</span></span>, <span style="color: #009900">Data</span><span style="color: #990000">/</span><span style="font-weight: bold"><span style="color: #000080">binary</span></span> <span style="color: #990000">>></span>);
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-></span>
{<span style="color: #FF6600">ok</span>, <span style="color: #990000"><<</span> <span style="color: #009900">Acc</span><span style="color: #990000">/</span><span style="font-weight: bold"><span style="color: #000080">binary</span></span>, <span style="color: #009900">Data</span><span style="color: #990000">/</span><span style="font-weight: bold"><span style="color: #000080">binary</span></span> <span style="color: #990000">>></span>, <span style="color: #009900">Req</span>}
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Read all part headers, skipping bodies</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #000000">skip_body_multipart</span></span>(<span style="color: #009900">Req0</span>, <span style="color: #009900">Acc</span>) <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #0000FF">case</span></span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_part</span></span>(<span style="color: #009900">Req0</span>) <span style="font-weight: bold"><span style="color: #0000FF">of</span></span>
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Headers</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #000000">skip_body_multipart</span></span>(<span style="color: #009900">Req</span>, [<span style="color: #009900">Headers</span>|<span style="color: #009900">Acc</span>]);
{<span style="color: #FF6600">done</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-></span>
{<span style="font-weight: bold"><span style="color: #000000">lists:reverse</span></span>(<span style="color: #009900">Acc</span>), <span style="color: #009900">Req</span>}
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Read a part header in larger chunks</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Headers</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_part</span></span>(<span style="color: #009900">Req0</span>, #{<span style="font-weight: bold"><span style="color: #000080">length</span></span> <span style="color: #990000">=></span> <span style="color: #993399">1000000</span>})<span style="color: #990000">.</span></tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">See also</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="../cowboy_req">cowboy_req(3)</a>,
<a href="../cowboy_req.has_body">cowboy_req:has_body(3)</a>,
<a href="../cowboy_req.body_length">cowboy_req:body_length(3)</a>,
<a href="../cowboy_req.read_body">cowboy_req:read_body(3)</a>,
<a href="../cowboy_req.read_urlencoded_body">cowboy_req:read_urlencoded_body(3)</a>,
<a href="../cowboy_req.read_part_body">cowboy_req:read_part_body(3)</a></p></div>
</div>
</div>
</div>
<div class="span3 sidecol">
<h3>
Cowboy
2.2
Function Reference
</h3>
<ul>
<li><a href="/docs/en/cowboy/2.2/guide">User Guide</a></li>
<li><a href="/docs/en/cowboy/2.2/manual">Function Reference</a></li>
</ul>
<h4 id="docs-nav">Navigation</h4>
<h4>Version select</h4>
<ul>
<li><a href="/docs/en/cowboy/2.4/manual">2.4</a></li>
<li><a href="/docs/en/cowboy/2.3/manual">2.3</a></li>
<li><a href="/docs/en/cowboy/2.2/manual">2.2</a></li>
<li><a href="/docs/en/cowboy/2.1/manual">2.1</a></li>
<li><a href="/docs/en/cowboy/2.0/manual">2.0</a></li>
<li><a href="/docs/en/cowboy/1.0/manual">1.0</a></li>
</ul>
</div>
</div>
</div>
</div>
<footer>
<div class="container">
<div class="row">
<div class="span6">
<p id="scroll-top"><a href="#">↑ Scroll to top</a></p>
<nav>
<ul>
<li><a href="mailto:[email protected]" title="Contact us">Contact us</a></li><li><a href="https://github.com/ninenines/ninenines.github.io" title="Github repository">Contribute to this site</a></li>
</ul>
</nav>
</div>
<div class="span6 credits">
<p><img src="/img/footer_logo.png"></p>
<p>Copyright © Loïc Hoguin 2012-2018</p>
</div>
</div>
</div>
</footer>
<script src="/js/custom.js"></script>
</body>
</html>
