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<title>Nine Nines: Reading the request body</title>
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<h1 class="lined-header"><span>Reading the request body</span></h1>
<div class="paragraph"><p>The Req object also allows you to read the request body.</p></div>
<div class="paragraph"><p>Because the request body can be of any size, all body
reading operations will only work once, as Cowboy will
not cache the result of these operations.</p></div>
<div class="paragraph"><p>Cowboy will not attempt to read the body until you do.
If handler execution ends without reading it, Cowboy
will simply skip it.</p></div>
<div class="paragraph"><p>Cowboy provides different ways to read the request body.
You can read it directly, stream it, but also read and
parse in a single call for form urlencoded formats or
multipart. All of these except multipart are covered in
this chapter. Multipart is covered later on in the guide.</p></div>
<div class="sect1">
<h2 id="_check_for_request_body">Check for request body</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can check whether a body was sent with the request.</p></div>
<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">cowboy_req:has_body</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>It will return <code>true</code> if there is a request body, and
<code>false</code> otherwise.</p></div>
<div class="paragraph"><p>Note that it is generally safe to assume that a body is
sent for <code>POST</code>, <code>PUT</code> and <code>PATCH</code> requests, without
having to explicitly check for it.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_request_body_length">Request body length</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can obtain the body length if it was sent with the
request.</p></div>
<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="color: #009900">Length</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body_length</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>The value returned will be <code>undefined</code> if the length
couldn’t be figured out from the request headers. If
there’s a body but no length is given, this means that
the chunked transfer-encoding was used. You can read
chunked bodies by using the stream functions.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_reading_the_body">Reading the body</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can read the whole body directly in one call.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">Body</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>By default, Cowboy will attempt to read up to a
size of 8MB. You can override this limit as needed.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">Body</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body</span></span>(<span style="color: #009900">Req</span>, [{<span style="font-weight: bold"><span style="color: #000080">length</span></span>, <span style="color: #993399">100000000</span>}])<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>You can also disable it.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">Body</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body</span></span>(<span style="color: #009900">Req</span>, [{<span style="font-weight: bold"><span style="color: #000080">length</span></span>, <span style="color: #FF6600">infinity</span>}])<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>It is recommended that you do not disable it for public
facing websites.</p></div>
<div class="paragraph"><p>If the body is larger than the limit, then Cowboy will return
a <code>more</code> tuple instead, allowing you to stream it if you
would like to.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_streaming_the_body">Streaming the body</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can stream the request body by chunks.</p></div>
<div class="paragraph"><p>Cowboy returns a <code>more</code> tuple when there is more body to
be read, and an <code>ok</code> tuple for the last chunk. This allows
you to loop over all chunks.</p></div>
<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">body_to_console</span></span>(<span style="color: #009900">Req</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:body</span></span>(<span style="color: #009900">Req</span>) <span style="font-weight: bold"><span style="color: #0000FF">of</span></span>
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #000000">io:format</span></span>(<span style="color: #FF0000">"~s"</span>, [<span style="color: #009900">Data</span>]),
<span style="color: #009900">Req2</span>;
{<span style="color: #FF6600">more</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">-></span>
<span style="font-weight: bold"><span style="color: #000000">io:format</span></span>(<span style="color: #FF0000">"~s"</span>, [<span style="color: #009900">Data</span>]),
<span style="font-weight: bold"><span style="color: #000000">body_to_console</span></span>(<span style="color: #009900">Req2</span>)
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>You can of course set the <code>length</code> option to configure the
size of chunks.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_rate_of_data_transmission">Rate of data transmission</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can control the rate of data transmission by setting
options when calling body functions. This applies not only
to the functions described in this chapter, but also to
the multipart functions.</p></div>
<div class="paragraph"><p>The <code>read_length</code> option defines the maximum amount of data
to be received from the socket at once, in bytes.</p></div>
<div class="paragraph"><p>The <code>read_timeout</code> option defines the time Cowboy waits
before that amount is received, in milliseconds.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_transfer_and_content_decoding">Transfer and content decoding</h2>
<div class="sectionbody">
<div class="paragraph"><p>Cowboy will by default decode the chunked transfer-encoding
if any. It will not decode any content-encoding by default.</p></div>
<div class="paragraph"><p>The first time you call a body function you can set the
<code>transfer_decode</code> and <code>content_decode</code> options. If the body
was already started being read these options are simply
ignored.</p></div>
<div class="paragraph"><p>The following example shows how to set both options.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body</span></span>(<span style="color: #009900">Req</span>, [
{<span style="color: #FF6600">transfer_decode</span>, <span style="font-weight: bold"><span style="color: #0000FF">fun</span></span> <span style="font-weight: bold"><span style="color: #000000">transfer_decode</span></span><span style="color: #990000">/</span><span style="color: #993399">2</span>, <span style="color: #009900">TransferState</span>},
{<span style="color: #FF6600">content_decode</span>, <span style="font-weight: bold"><span style="color: #0000FF">fun</span></span> <span style="font-weight: bold"><span style="color: #000000">content_decode</span></span><span style="color: #990000">/</span><span style="color: #993399">1</span>}
])<span style="color: #990000">.</span></tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_reading_a_form_urlencoded_body">Reading a form urlencoded body</h2>
<div class="sectionbody">
<div class="paragraph"><p>You can directly obtain a list of key/value pairs if the
body was sent using the application/x-www-form-urlencoded
content-type.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">KeyValues</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body_qs</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>You can then retrieve an individual value from that list.</p></div>
<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="color: #990000">_</span>, <span style="color: #009900">Lang</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">lists:keyfind</span></span>(<span style="color: #FF6600">lang</span>, <span style="color: #993399">1</span>, <span style="color: #009900">KeyValues</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>You should not attempt to match on the list as the order
of the values is undefined.</p></div>
<div class="paragraph"><p>By default Cowboy will reject bodies with a size above
64KB when using this function. You can override this limit
by setting the <code>length</code> option.</p></div>
<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="color: #FF6600">ok</span>, <span style="color: #009900">KeyValues</span>, <span style="color: #009900">Req2</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body_qs</span></span>(<span style="color: #009900">Req</span>, [{<span style="font-weight: bold"><span style="color: #000080">length</span></span>, <span style="color: #993399">2000000</span>}])<span style="color: #990000">.</span></tt></pre></div></div>
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