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<title>Nine Nines: The Req object</title>
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<h1 class="lined-header"><span>The Req object</span></h1>
<div class="paragraph"><p>The Req object is a variable used for obtaining information
about a request, read its body or send a response.</p></div>
<div class="paragraph"><p>It is not really an object in the object-oriented sense.
It is a simple map that can be directly accessed or
used when calling functions from the <code>cowboy_req</code> module.</p></div>
<div class="paragraph"><p>The Req object is the subject of a few different chapters.
In this chapter we will learn about the Req object and
look at how to retrieve information about the request.</p></div>
<div class="sect1">
<h2 id="_direct_access">Direct access</h2>
<div class="sectionbody">
<div class="paragraph"><p>The Req map contains a number of fields which are documented
and can be accessed directly. They are the fields that have
a direct mapping to HTTP: the request <code>method</code>; the HTTP
<code>version</code> used; the effective URI components <code>scheme</code>,
<code>host</code>, <code>port</code>, <code>path</code> and <code>qs</code>; the request <code>headers</code>;
and the connection <code>peer</code> address and port.</p></div>
<div class="paragraph"><p>Note that the <code>version</code> field can be used to determine
whether a connection is using HTTP/2.</p></div>
<div class="paragraph"><p>To access a field, you can simply match in the function
head. The following example sends a simple "Hello world!"
response when the <code>method</code> is GET, and a 405 error
otherwise.</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
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">init</span></span>(<span style="color: #009900">Req0</span><span style="color: #990000">=</span>#{<span style="color: #FF6600">method</span> <span style="color: #990000">:=</span> <span style="color: #990000"><<</span><span style="color: #FF0000">"GET"</span><span style="color: #990000">>></span>}, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
<span style="color: #009900">Req</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:reply</span></span>(<span style="color: #993399">200</span>, #{
<span style="color: #990000"><<</span><span style="color: #FF0000">"content-type"</span><span style="color: #990000">>></span> <span style="color: #990000">=></span> <span style="color: #990000"><<</span><span style="color: #FF0000">"text/plain"</span><span style="color: #990000">>></span>
}, <span style="color: #990000"><<</span><span style="color: #FF0000">"Hello world!"</span><span style="color: #990000">>></span>, <span style="color: #009900">Req0</span>),
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>};
<span style="font-weight: bold"><span style="color: #000000">init</span></span>(<span style="color: #009900">Req0</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
<span style="color: #009900">Req</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:reply</span></span>(<span style="color: #993399">405</span>, #{
<span style="color: #990000"><<</span><span style="color: #FF0000">"allow"</span><span style="color: #990000">>></span> <span style="color: #990000">=></span> <span style="color: #990000"><<</span><span style="color: #FF0000">"GET"</span><span style="color: #990000">>></span>
}, <span style="color: #009900">Req0</span>),
{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>}<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Any other field is internal and should not be accessed.
They may change in future releases, including maintenance
releases, without notice.</p></div>
<div class="paragraph"><p>Modifying the Req object, while allowed, is not recommended
unless strictly necessary. If adding new fields, make sure
to namespace the field names so that no conflict can occur
with future Cowboy updates or third party projects.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_introduction_to_the_cowboy_req_interface">Introduction to the cowboy_req interface</h2>
<div class="sectionbody">
<div class="paragraph"><p>Functions in the <code>cowboy_req</code> module provide access to
the request information but also various operations that
are common when dealing with HTTP requests.</p></div>
<div class="paragraph"><p>All the functions that begin with a verb indicate an action.
Other functions simply return the corresponding value
(sometimes that value does need to be built, but the
cost of the operation is equivalent to retrieving a value).</p></div>
<div class="paragraph"><p>Some of the <code>cowboy_req</code> functions return an updated Req
object. They are the read, reply, set and delete functions.
While ignoring the returned Req will not cause incorrect
behavior for some of them, it is highly recommended to
always keep and use the last returned Req object. The
manual for <code>cowboy_req</code> details these functions and what
modifications are done to the Req object.</p></div>
<div class="paragraph"><p>Some of the calls to <code>cowboy_req</code> have side effects. This
is the case of the read and reply functions. Cowboy reads
the request body or replies immediately when the function
is called.</p></div>
<div class="paragraph"><p>All functions will crash if something goes wrong. There
is usually no need to catch these errors, Cowboy will
send the appropriate 4xx or 5xx response depending on
where the crash occurred.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_request_method">Request method</h2>
<div class="sectionbody">
<div class="paragraph"><p>The request method can be retrieved directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">method</span> <span style="color: #990000">:=</span> <span style="color: #009900">Method</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>Or using a function:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Method</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:method</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>The method is a case sensitive binary string. Standard
methods include GET, HEAD, OPTIONS, PATCH, POST, PUT
or DELETE.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_http_version">HTTP version</h2>
<div class="sectionbody">
<div class="paragraph"><p>The HTTP version is informational. It does not indicate that
the client implements the protocol well or fully.</p></div>
<div class="paragraph"><p>There is typically no need to change behavior based on the
HTTP version: Cowboy already does it for you.</p></div>
<div class="paragraph"><p>It can be useful in some cases, though. For example, one may
want to redirect HTTP/1.1 clients to use Websocket, while HTTP/2
clients keep using HTTP/2.</p></div>
<div class="paragraph"><p>The HTTP version can be retrieved directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">version</span> <span style="color: #990000">:=</span> <span style="color: #009900">Version</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>Or using a function:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Version</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:version</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Cowboy defines the <code>'HTTP/1.0'</code>, <code>'HTTP/1.1'</code> and <code>'HTTP/2'</code>
versions. Custom protocols can define their own values as
atoms.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_effective_request_uri">Effective request URI</h2>
<div class="sectionbody">
<div class="paragraph"><p>The scheme, host, port, path and query string components
of the effective request URI can all be retrieved directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{
<span style="color: #FF6600">scheme</span> <span style="color: #990000">:=</span> <span style="color: #009900">Scheme</span>,
<span style="color: #FF6600">host</span> <span style="color: #990000">:=</span> <span style="color: #009900">Host</span>,
<span style="color: #FF6600">port</span> <span style="color: #990000">:=</span> <span style="color: #009900">Port</span>,
<span style="color: #FF6600">path</span> <span style="color: #990000">:=</span> <span style="color: #009900">Path</span>,
<span style="color: #FF6600">qs</span> <span style="color: #990000">:=</span> <span style="color: #009900">Qs</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>Or using the related functions:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Scheme</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:scheme</span></span>(<span style="color: #009900">Req</span>),
<span style="color: #009900">Host</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:host</span></span>(<span style="color: #009900">Req</span>),
<span style="color: #009900">Port</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:port</span></span>(<span style="color: #009900">Req</span>),
<span style="color: #009900">Path</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:path</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span>
<span style="color: #009900">Qs</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:qs</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>The scheme and host are lowercased case insensitive binary
strings. The port is an integer representing the port number.
The path and query string are case sensitive binary strings.</p></div>
<div class="paragraph"><p>Cowboy defines only the <code><<"http">></code> and <code><<"https">></code> schemes.
They are chosen so that the scheme will only be <code><<"https">></code>
for requests on secure HTTP/1.1 or HTTP/2 connections.</p></div>
<div class="paragraph"><p>The effective request URI itself can be reconstructed with
the <code>cowboy_req:uri/1,2</code> function. By default, an absolute
URI is returned:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
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">%% </span></span><span style="text-decoration: underline"><span style="color: #0000FF">scheme://host</span></span><span style="font-style: italic"><span style="color: #9A1900">[:port]/path[?qs]</span></span>
<span style="color: #009900">URI</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:uri</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Options are available to either disable or replace some
or all of the components. Various URIs or URI formats can
be generated this way, including the origin form:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
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">%% /path[?qs]</span></span>
<span style="color: #009900">URI</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:uri</span></span>(<span style="color: #009900">Req</span>, #{<span style="color: #0000FF">host</span> <span style="color: #990000">=></span> <span style="color: #000080">undefined</span>})<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>The protocol relative form:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
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">%% //host[:port]/path[?qs]</span></span>
<span style="color: #009900">URI</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:uri</span></span>(<span style="color: #009900">Req</span>, #{<span style="color: #0000FF">scheme</span> <span style="color: #990000">=></span> <span style="color: #000080">undefined</span>})<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>The absolute URI without a query string:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">URI</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:uri</span></span>(<span style="color: #009900">Req</span>, #{<span style="color: #0000FF">qs</span> <span style="color: #990000">=></span> <span style="color: #000080">undefined</span>})<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>A different host:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">URI</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:uri</span></span>(<span style="color: #009900">Req</span>, #{<span style="color: #0000FF">host</span> <span style="color: #990000">=></span> <span style="color: #990000"><<</span><span style="color: #FF0000">"example.org"</span><span style="color: #990000">>></span>})<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>And any other combination.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_bindings">Bindings</h2>
<div class="sectionbody">
<div class="paragraph"><p>Bindings are the host and path components that you chose
to extract when defining the routes of your application.
They are only available after the routing.</p></div>
<div class="paragraph"><p>Cowboy provides functions to retrieve one or all bindings.</p></div>
<div class="paragraph"><p>To retrieve a single value:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Value</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:binding</span></span>(<span style="color: #FF6600">userid</span>, <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>When attempting to retrieve a value that was not bound,
<code>undefined</code> will be returned. A different default value
can be provided:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Value</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:binding</span></span>(<span style="color: #FF6600">userid</span>, <span style="color: #009900">Req</span>, <span style="color: #993399">42</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>To retrieve everything that was bound:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">Bindings</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:bindings</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>They are returned as a map, with keys being atoms.</p></div>
<div class="paragraph"><p>The Cowboy router also allows you to capture many host
or path segments at once using the <code>...</code> qualifier.</p></div>
<div class="paragraph"><p>To retrieve the segments captured from the host name:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">HostInfo</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:host_info</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>And the path segments:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">PathInfo</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:path_info</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Cowboy will return <code>undefined</code> if <code>...</code> was not used
in the route.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_query_parameters">Query parameters</h2>
<div class="sectionbody">
<div class="paragraph"><p>Cowboy provides two functions to access query parameters.
You can use the first to get the entire list of parameters.</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">QsVals</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:parse_qs</span></span>(<span style="color: #009900">Req</span>),
{<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: #990000"><<</span><span style="color: #FF0000">"lang"</span><span style="color: #990000">>></span>, <span style="color: #993399">1</span>, <span style="color: #009900">QsVals</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Cowboy will only parse the query string, and not do any
transformation. This function may therefore return duplicates,
or parameter names without an associated value. The order of
the list returned is undefined.</p></div>
<div class="paragraph"><p>When a query string is <code>key=1&key=2</code>, the list returned will
contain two parameters of name <code>key</code>.</p></div>
<div class="paragraph"><p>The same is true when trying to use the PHP-style suffix <code>[]</code>.
When a query string is <code>key[]=1&key[]=2</code>, the list returned will
contain two parameters of name <code>key[]</code>.</p></div>
<div class="paragraph"><p>When a query string is simply <code>key</code>, Cowboy will return the
list <code>[{<<"key">>, true}]</code>, using <code>true</code> to indicate that the
parameter <code>key</code> was defined, but with no value.</p></div>
<div class="paragraph"><p>The second function Cowboy provides allows you to match out
only the parameters you are interested in, and at the same
time do any post processing you require using <a href="../constraints">constraints</a>.
This function returns a map.</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">id</span> <span style="color: #990000">:=</span> <span style="color: #009900">ID</span>, <span style="color: #FF6600">lang</span> <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">cowboy_req:match_qs</span></span>([<span style="color: #FF6600">id</span>, <span style="color: #FF6600">lang</span>], <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Constraints can be applied automatically. The following
snippet will crash when the <code>id</code> parameter is not an integer,
or when the <code>lang</code> parameter is empty. At the same time, the
value for <code>id</code> will be converted to an integer term:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">QsMap</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:match_qs</span></span>([{<span style="color: #FF6600">id</span>, <span style="color: #FF6600">int</span>}, {<span style="color: #FF6600">lang</span>, <span style="color: #FF6600">nonempty</span>}], <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>A default value may also be provided. The default will be used
if the <code>lang</code> key is not found. It will not be used if
the key is found but has an empty value.</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">lang</span> <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">cowboy_req:match_qs</span></span>([{<span style="color: #FF6600">lang</span>, [], <span style="color: #990000"><<</span><span style="color: #FF0000">"en-US"</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>If no default is provided and the value is missing, the
query string is deemed invalid and the process will crash.</p></div>
<div class="paragraph"><p>When the query string is <code>key=1&key=2</code>, the value for <code>key</code>
will be the list <code>[1, 2]</code>. Parameter names do not need to
include the PHP-style suffix. Constraints may be used to
ensure that only one value was passed through.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_headers">Headers</h2>
<div class="sectionbody">
<div class="paragraph"><p>Header values can be retrieved either as a binary string
or parsed into a more meaningful representation.</p></div>
<div class="paragraph"><p>The get the raw value:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">HeaderVal</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-type"</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>Cowboy expects all header names to be provided as lowercase
binary strings. This is true for both requests and responses,
regardless of the underlying protocol.</p></div>
<div class="paragraph"><p>When the header is missing from the request, <code>undefined</code>
will be returned. A different default can be provided:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">HeaderVal</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-type"</span><span style="color: #990000">>></span>, <span style="color: #009900">Req</span>, <span style="color: #990000"><<</span><span style="color: #FF0000">"text/plain"</span><span style="color: #990000">>></span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>All headers can be retrieved at once, either directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
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">AllHeaders</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>Or using a function:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">AllHeaders</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:headers</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Cowboy provides equivalent functions to parse individual
headers. There is no function to parse all headers at once.</p></div>
<div class="paragraph"><p>To parse a specific header:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">ParsedVal</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"><<</span><span style="color: #FF0000">"content-type"</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>An exception will be thrown if it doesn’t know how to parse the
given header, or if the value is invalid. The list of known headers
and default values can be found in the manual.</p></div>
<div class="paragraph"><p>When the header is missing, <code>undefined</code> is returned. You can
change the default value. Note that it should be the parsed value
directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">ParsedVal</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"><<</span><span style="color: #FF0000">"content-type"</span><span style="color: #990000">>></span>, <span style="color: #009900">Req</span>,
{<span style="color: #990000"><<</span><span style="color: #FF0000">"text"</span><span style="color: #990000">>></span>, <span style="color: #990000"><<</span><span style="color: #FF0000">"plain"</span><span style="color: #990000">>></span>, []})<span style="color: #990000">.</span></tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_peer">Peer</h2>
<div class="sectionbody">
<div class="paragraph"><p>The peer address and port number for the connection can be
retrieved either directly or using a function.</p></div>
<div class="paragraph"><p>To retrieve the peer directly:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">peer</span> <span style="color: #990000">:=</span> {<span style="color: #009900">IP</span>, <span style="color: #009900">Port</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>And using a function:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>{<span style="color: #009900">IP</span>, <span style="color: #009900">Port</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:peer</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="paragraph"><p>Note that the peer corresponds to the remote end of the
connection to the server, which may or may not be the
client itself. It may also be a proxy or a gateway.</p></div>
</div>
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