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<title>Nine Nines: cowboy_req:header(3)</title>
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<h1 class="lined-header"><span>cowboy_req:header(3)</span></h1>
<div class="sect1">
<h2 id="_name">Name</h2>
<div class="sectionbody">
<div class="paragraph"><p>cowboy_req:header - HTTP header</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">header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-></span> <span style="font-weight: bold"><span style="color: #000000">header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>, <span style="color: #000080">undefined</span>)
<span style="font-weight: bold"><span style="color: #000000">header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">Default</span>) <span style="color: #990000">-></span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>() | <span style="color: #009900">Default</span>
<span style="color: #009900">Name</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>() <span style="font-style: italic"><span style="color: #9A1900">%% lowercase; case insensitive</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">Default</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">any</span></span>()</tt></pre></div></div>
<div class="paragraph"><p>Return the value for the given HTTP header.</p></div>
<div class="paragraph"><p>The header name must be given as a lowercase binary string.
While header names are case insensitive, Cowboy requires them
to be given as lowercase to function properly.</p></div>
<div class="paragraph"><p>Headers can also be obtained using pattern matching:</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">headers</span> <span style="color: #990000">:=</span> #{<span style="color: #009900">Name</span> <span style="color: #990000">:=</span> <span style="color: #009900">Value</span>}} <span style="color: #990000">=</span> <span style="color: #009900">Req</span><span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Note that this snippet will crash if the header is missing.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_arguments">Arguments</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
Name
</dt>
<dd>
<p>
Desired HTTP header name as a lowercase binary string.
</p>
</dd>
<dt class="hdlist1">
Req
</dt>
<dd>
<p>
The Req object.
</p>
</dd>
<dt class="hdlist1">
Default
</dt>
<dd>
<p>
Default value returned when the header is missing.
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_return_value">Return value</h2>
<div class="sectionbody">
<div class="paragraph"><p>The header value is returned as a binary string. When the
header is missing, the default argument is returned.</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>: Only the header value is returned, it is no longer wrapped in a tuple.
</p>
</li>
<li>
<p>
<strong>1.0</strong>: Function introduced.
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_examples">Examples</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="title">Get the accept header</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: #009900">Accept</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:header</span></span>(<span style="color: #990000"><<</span><span style="color: #FF0000">"accept"</span><span style="color: #990000">>></span>, <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Get the content-length header with a default value</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: #009900">Length</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:header</span></span>(<span style="color: #990000"><<</span><span style="color: #FF0000">"content-length"</span><span style="color: #990000">>></span>, <span style="color: #009900">Req</span>, <span style="color: #990000"><<</span><span style="color: #FF0000">"0"</span><span style="color: #990000">>></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.headers">cowboy_req:headers(3)</a>,
<a href="../cowboy_req.parse_header">cowboy_req:parse_header(3)</a></p></div>
</div>
</div>
</div>
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Cowboy
2.1
Function Reference
</h3>
<ul>
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<li><a href="/docs/en/cowboy/2.1/manual">Function Reference</a></li>
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<h4>Version select</h4>
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<li><a href="/docs/en/cowboy/2.2/manual">2.2</a></li>
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<li><a href="/docs/en/cowboy/1.0/manual">1.0</a></li>
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