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<h1 class="lined-header"><span>cowboy_req:read_part(3)</span></h1>
<h2 id="_name">Name</h2>
<p>cowboy_req:read_part - Read the next multipart headers</p>
<h2 id="_description">Description</h2>
<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">read_part</font></b>(<font color="#009900">Req</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_req:req</font></b>())
<font color="#990000">-></font> <b><font color="#000000">read_part</font></b>(<font color="#009900">Req</font>, #{})
<b><font color="#000000">read_part</font></b>(<font color="#009900">Req</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_req:req</font></b>(), <font color="#009900">Opts</font>)
<font color="#990000">-></font> {<font color="#FF6600">ok</font>, <font color="#009900">Headers</font>, <font color="#009900">Req</font>} | {<font color="#FF6600">done</font>, <font color="#009900">Req</font>}
<font color="#009900">Opts</font> <font color="#990000">::</font> <b><font color="#000000">cowboy_req:read_body_opts</font></b>()
<font color="#009900">Headers</font> <font color="#990000">::</font> #{<b><font color="#000080">binary</font></b>() <font color="#990000">=></font> <b><font color="#000080">binary</font></b>()}</tt></pre>
</div></div>
<p>Read the next part of a multipart body.</p>
<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>
<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>
<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>
<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>
<!-- @todo Proper link to cow_multipart:form_data.-->
<p>Once a part has been read, it can not be read again.</p>
<p>Once the body has been read, Cowboy sets the content-length header if it was not previously provided.</p>
<!-- @todo Limit the maximum size of multipart headers.-->
<h2 id="_arguments">Arguments</h2>
<dl><dt>Req</dt>
<dd><p>The Req object.</p>
</dd>
<dt>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>
<p>This function defaults the <code>length</code> to 64KB and the <code>period</code> to 5 seconds.</p>
</dd>
</dl>
<h2 id="_return_value">Return value</h2>
<p>An <code>ok</code> tuple is returned containing the next part's headers as a map.</p>
<p>A <code>done</code> tuple is returned if there are no more parts to read.</p>
<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>
<h2 id="_changelog">Changelog</h2>
<ul><li><strong>2.0</strong>: Function introduced. Replaces <code>part/1,2</code>.
</li>
</ul>
<h2 id="_examples">Examples</h2>
<div class="listingblock"><div class="title">Read all parts</div>
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">acc_multipart</font></b>(<font color="#009900">Req0</font>, <font color="#009900">Acc</font>) <font color="#990000">-></font>
<b><font color="#0000FF">case</font></b> <b><font color="#000000">cowboy_req:read_part</font></b>(<font color="#009900">Req0</font>) <b><font color="#0000FF">of</font></b>
{<font color="#FF6600">ok</font>, <font color="#009900">Headers</font>, <font color="#009900">Req1</font>} <font color="#990000">-></font>
{<font color="#FF6600">ok</font>, <font color="#009900">Body</font>, <font color="#009900">Req</font>} <font color="#990000">=</font> <b><font color="#000000">stream_body</font></b>(<font color="#009900">Req1</font>, <font color="#990000"><<>></font>),
<b><font color="#000000">acc_multipart</font></b>(<font color="#009900">Req</font>, [{<font color="#009900">Headers</font>, <font color="#009900">Body</font>}|<font color="#009900">Acc</font>]);
{<font color="#FF6600">done</font>, <font color="#009900">Req</font>} <font color="#990000">-></font>
{<b><font color="#000000">lists:reverse</font></b>(<font color="#009900">Acc</font>), <font color="#009900">Req</font>}
<b><font color="#0000FF">end</font></b><font color="#990000">.</font>
<b><font color="#000000">stream_body</font></b>(<font color="#009900">Req0</font>, <font color="#009900">Acc</font>) <font color="#990000">-></font>
<b><font color="#0000FF">case</font></b> <b><font color="#000000">cowboy_req:read_part_body</font></b>(<font color="#009900">Req0</font>) <b><font color="#0000FF">of</font></b>
{<font color="#FF6600">more</font>, <font color="#009900">Data</font>, <font color="#009900">Req</font>} <font color="#990000">-></font>
<b><font color="#000000">stream_body</font></b>(<font color="#009900">Req</font>, <font color="#990000"><<</font> <font color="#009900">Acc</font><font color="#990000">/</font><b><font color="#000080">binary</font></b>, <font color="#009900">Data</font><font color="#990000">/</font><b><font color="#000080">binary</font></b> <font color="#990000">>></font>);
{<font color="#FF6600">ok</font>, <font color="#009900">Data</font>, <font color="#009900">Req</font>} <font color="#990000">-></font>
{<font color="#FF6600">ok</font>, <font color="#990000"><<</font> <font color="#009900">Acc</font><font color="#990000">/</font><b><font color="#000080">binary</font></b>, <font color="#009900">Data</font><font color="#990000">/</font><b><font color="#000080">binary</font></b> <font color="#990000">>></font>, <font color="#009900">Req</font>}
<b><font color="#0000FF">end</font></b><font color="#990000">.</font></tt></pre>
</div></div>
<div class="listingblock"><div class="title">Read all part headers, skipping bodies</div>
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><b><font color="#000000">skip_body_multipart</font></b>(<font color="#009900">Req0</font>, <font color="#009900">Acc</font>) <font color="#990000">-></font>
<b><font color="#0000FF">case</font></b> <b><font color="#000000">cowboy_req:read_part</font></b>(<font color="#009900">Req0</font>) <b><font color="#0000FF">of</font></b>
{<font color="#FF6600">ok</font>, <font color="#009900">Headers</font>, <font color="#009900">Req</font>} <font color="#990000">-></font>
<b><font color="#000000">skip_body_multipart</font></b>(<font color="#009900">Req</font>, [<font color="#009900">Headers</font>|<font color="#009900">Acc</font>]);
{<font color="#FF6600">done</font>, <font color="#009900">Req</font>} <font color="#990000">-></font>
{<b><font color="#000000">lists:reverse</font></b>(<font color="#009900">Acc</font>), <font color="#009900">Req</font>}
<b><font color="#0000FF">end</font></b><font color="#990000">.</font></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 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>{<font color="#FF6600">ok</font>, <font color="#009900">Headers</font>, <font color="#009900">Req</font>} <font color="#990000">=</font> <b><font color="#000000">cowboy_req:read_part</font></b>(<font color="#009900">Req0</font>, #{<b><font color="#000080">length</font></b> <font color="#990000">=></font> <font color="#993399">1000000</font>})<font color="#990000">.</font></tt></pre>
</div></div>
<h2 id="_see_also">See also</h2>
<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 class="span3 sidecol">
<h3>
Cowboy
2.0
Function Reference
</h3>
<ul>
<li><a href="/docs/en/cowboy/2.0/guide">User Guide</a></li>
<li><a href="/docs/en/cowboy/2.0/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>
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