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<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 3.1.8
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: #000000">cow_multipart:headers</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 list of key/values.</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 3.1.8
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 3.1.8
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 3.1.8
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
2.0
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/2.0/manual">2.0</a></li>
<li><a href="/docs/en/cowboy/1.0/manual">1.0</a></li>
</ul>
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