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<h1 class="lined-header"><span>cowboy_req:parse_header(3)</span></h1>

<div class="sect1">
<h2 id="_name">Name</h2>
<div class="sectionbody">
<div class="paragraph"><p>cowboy_req:parse_header - Parse the given 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">parse_header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>)          <span style="color: #990000">-&gt;</span> <span style="color: #009900">ParsedValue</span> | <span style="color: #009900">Default</span>
<span style="font-weight: bold"><span style="color: #000000">parse_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">-&gt;</span> <span style="color: #009900">ParsedValue</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="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">ParsedValue</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">any</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>Parse 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>The type of the parsed value varies depending on
the header. Similarly, the default value when calling
<code>cowboy_req:parse_header/2</code> differs depending on the
header.</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 parsed header value varies depending on the header.
When the header is missing, the default argument is returned.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_headers">Headers</h2>
<div class="sectionbody">
<div class="paragraph"><p>The following snippets detail the types returned by the
different headers. Unless mentioned otherwise, the
default value when the header is missing will be <code>undefined</code>:</p></div>
<div class="listingblock">
<div class="title">accept</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"accept"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>)
    <span style="color: #990000">-&gt;</span> [{{<span style="color: #009900">Type</span>, <span style="color: #009900">SubType</span>, <span style="color: #009900">Params</span>}, <span style="color: #009900">Quality</span>, <span style="color: #009900">AcceptExt</span>}]

<span style="color: #009900">Type</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">%% case insensitive</span></span>
<span style="color: #009900">SubType</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">%% case insensitive</span></span>
<span style="color: #009900">Params</span>    <span style="color: #990000">::</span> [{<span style="color: #009900">Key</span>, <span style="color: #009900">Value</span>}]
<span style="color: #009900">Quality</span>   <span style="color: #990000">::</span> <span style="color: #993399">0</span><span style="color: #990000">..</span><span style="color: #993399">1000</span>
<span style="color: #009900">AcceptExt</span> <span style="color: #990000">::</span> [<span style="color: #009900">Key</span> | {<span style="color: #009900">Key</span>, <span style="color: #009900">Value</span>}]
<span style="color: #009900">Key</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">%% case insensitive</span></span>
<span style="color: #009900">Value</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">%% case sensitive</span></span></tt></pre></div></div>
<div class="listingblock">
<div class="title">accept-charset, accept-encoding and accept-language</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">parse_header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> [{<span style="color: #009900">Value</span>, <span style="color: #009900">Quality</span>}]

<span style="color: #009900">Name</span>    <span style="color: #990000">::</span> <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"accept-charset"</span><span style="color: #990000">&gt;&gt;</span>
         | <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"accept-encoding"</span><span style="color: #990000">&gt;&gt;</span>
         | <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"accept-language"</span><span style="color: #990000">&gt;&gt;</span>
<span style="color: #009900">Value</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">%% case insensitive</span></span>
<span style="color: #009900">Quality</span> <span style="color: #990000">::</span> <span style="color: #993399">0</span><span style="color: #990000">..</span><span style="color: #993399">1000</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">authorization</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"authorization"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>)
    <span style="color: #990000">-&gt;</span> {<span style="color: #FF6600">basic</span>, <span style="color: #009900">Username</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>(), <span style="color: #009900">Password</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>()}
     | {<span style="color: #FF6600">bearer</span>, <span style="color: #009900">Token</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>()}
     | {<span style="color: #FF6600">digest</span>, [{<span style="color: #009900">Key</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>(), <span style="color: #009900">Value</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000080">binary</span></span>()}]}</tt></pre></div></div>
<div class="listingblock">
<div class="title">content-length</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"content-length"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> <span style="font-weight: bold"><span style="color: #000000">non_neg_integer</span></span>()</tt></pre></div></div>
<div class="paragraph"><p>When the content-length header is missing, <code>0</code> is returned.</p></div>
<div class="listingblock">
<div class="title">content-type</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"content-type"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>)
    <span style="color: #990000">-&gt;</span> {<span style="color: #009900">Type</span>, <span style="color: #009900">SubType</span>, <span style="color: #009900">Params</span>}

<span style="color: #009900">Type</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">%% case insensitive</span></span>
<span style="color: #009900">SubType</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">%% case insensitive</span></span>
<span style="color: #009900">Params</span>    <span style="color: #990000">::</span> [{<span style="color: #009900">Key</span>, <span style="color: #009900">Value</span>}]
<span style="color: #009900">Key</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">%% case insensitive</span></span>
<span style="color: #009900">Value</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">%% case sensitive;</span></span></tt></pre></div></div>
<div class="paragraph"><p>Note that the value for the charset parameter is case insensitive
and returned as a lowercase binary string.</p></div>
<div class="listingblock">
<div class="title">cookie</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"cookie"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> [{<span style="color: #009900">Name</span>, <span style="color: #009900">Value</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">%% case sensitive</span></span>
<span style="color: #009900">Value</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">%% case sensitive</span></span></tt></pre></div></div>
<div class="paragraph"><p>When the cookie header is missing, <code>[]</code> is returned.</p></div>
<div class="paragraph"><p>While an empty cookie header is not valid, some clients do
send it. Cowboy will in this case also return <code>[]</code>.</p></div>
<div class="listingblock">
<div class="title">expect</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"expect"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> <span style="color: #FF6600">continue</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">if-match and if-none-match</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">parse_header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>)
    <span style="color: #990000">-&gt;</span> <span style="color: #FF6600">'*'</span> | [{<span style="color: #FF6600">weak</span> | <span style="color: #FF6600">strong</span>, <span style="color: #009900">OpaqueTag</span>}]

<span style="color: #009900">Name</span>      <span style="color: #990000">::</span> <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"if-match"</span><span style="color: #990000">&gt;&gt;</span>
           | <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"if-none-match"</span><span style="color: #990000">&gt;&gt;</span>
<span style="color: #009900">OpaqueTag</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">%% case sensitive</span></span></tt></pre></div></div>
<div class="listingblock">
<div class="title">if-modified-since and if-unmodified-since</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">parse_header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> <span style="font-weight: bold"><span style="color: #000000">calendar:datetime</span></span>()</tt></pre></div></div>
<div class="listingblock">
<div class="title">range</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"range"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> {<span style="color: #009900">From</span>, <span style="color: #009900">To</span>} | <span style="color: #009900">Final</span>

<span style="color: #009900">From</span>  <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">non_neg_integer</span></span>()
<span style="color: #009900">To</span>    <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">non_neg_integer</span></span>() | <span style="color: #FF6600">infinity</span>
<span style="color: #009900">Final</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">neg_integer</span></span>()</tt></pre></div></div>
<div class="listingblock">
<div class="title">sec-websocket-extensions</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"sec-websocket-extensions"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>)
    <span style="color: #990000">-&gt;</span> [{<span style="color: #009900">Extension</span>, <span style="color: #009900">Params</span>}]

<span style="color: #009900">Extension</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">%% case sensitive</span></span>
<span style="color: #009900">Params</span>    <span style="color: #990000">::</span> [<span style="color: #009900">Key</span> | {<span style="color: #009900">Key</span>, <span style="color: #009900">Value</span>}]
<span style="color: #009900">Key</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">%% case sensitive</span></span>
<span style="color: #009900">Value</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">%% case sensitive</span></span></tt></pre></div></div>
<div class="listingblock">
<div class="title">sec-websocket-protocol and upgrade</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">parse_header</span></span>(<span style="color: #009900">Name</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> [<span style="color: #009900">Token</span>]

<span style="color: #009900">Name</span>  <span style="color: #990000">::</span> <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"sec-websocket-protocol"</span><span style="color: #990000">&gt;&gt;</span>
       | <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"upgrade"</span><span style="color: #990000">&gt;&gt;</span>
<span style="color: #009900">Token</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">%% case insensitive</span></span></tt></pre></div></div>
<div class="listingblock">
<div class="title">x-forwarded-for</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">parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"x-forwarded-for"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> [<span style="color: #009900">Token</span>]

<span style="color: #009900">Token</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">%% case sensitive</span></span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Unknown headers</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">parse_header</span></span>(<span style="color: #990000">_</span>, <span style="color: #009900">Req</span>) <span style="color: #990000">-&gt;</span> {<span style="color: #000080">undefined</span>, <span style="color: #009900">RawValue</span>}</tt></pre></div></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 parsed 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">Parse the accept header with a custom 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="font-style: italic"><span style="color: #9A1900">%% Accept everything when header is missing.</span></span>
<span style="color: #009900">Accept</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:parse_header</span></span>(<span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"accept"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</span>,
    [{{ <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"*"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #990000">&lt;&lt;</span><span style="color: #FF0000">"*"</span><span style="color: #990000">&gt;&gt;</span>, []}, <span style="color: #993399">1000</span>, []}])<span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Parse the content-length 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="font-style: italic"><span style="color: #9A1900">%% Default content-length is 0.</span></span>
<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">&lt;&lt;</span><span style="color: #FF0000">"content-length"</span><span style="color: #990000">&gt;&gt;</span>, <span style="color: #009900">Req</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.header">cowboy_req:header(3)</a>,
<a href="../cowboy_req.headers">cowboy_req:headers(3)</a></p></div>
</div>
</div>





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<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>
	
	
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<h4>Version select</h4>
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		<li><a href="/docs/en/cowboy/2.0/manual">2.0</a></li>
	
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