How to Restrict Route Matching through Conditions

As you've seen, a route can be made to match only certain routing wildcards (via regular expressions), HTTP methods, or host names. But the routing system can be extended to have an almost infinite flexibility using conditions:

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contact:
    path:     /contact
    defaults: { _controller: AcmeDemoBundle:Main:contact }
    condition: "context.getMethod() in ['GET', 'HEAD'] and request.headers.get('User-Agent') matches '/firefox/i'"

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<?xml version="1.0" encoding="UTF-8" ?>
<routes xmlns="http://symfony.com/schema/routing"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/routing
        http://symfony.com/schema/routing/routing-1.0.xsd">

    <route id="contact" path="/contact">
        <default key="_controller">AcmeDemoBundle:Main:contact</default>
        <condition>context.getMethod() in ['GET', 'HEAD'] and request.headers.get('User-Agent') matches '/firefox/i'</condition>
    </route>
</routes>

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use Symfony\Component\Routing\RouteCollection;
use Symfony\Component\Routing\Route;

$collection = new RouteCollection();
$collection->add('contact', new Route(
    '/contact', array(
        '_controller' => 'AcmeDemoBundle:Main:contact',
    ),
    array(),
    array(),
    '',
    array(),
    array(),
    'context.getMethod() in ["GET", "HEAD"] and request.headers.get("User-Agent") matches "/firefox/i"'
));

return $collection;

The condition is an expression, and you can learn more about its syntax here: The Expression Syntax. With this, the route won't match unless the HTTP method is either GET or HEAD and if the User-Agent header matches firefox.

You can do any complex logic you need in the expression by leveraging two variables that are passed into the expression:

context

An instance of RequestContext, which holds the most fundamental information about the route being matched.

request

The Symfony Request object (see The HttpFoundation Component).

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if (rtrim($pathinfo, '/contact') === '' && (
    in_array($context->getMethod(), array(0 => "GET", 1 => "HEAD"))
    && preg_match("/firefox/i", $request->headers->get("User-Agent"))
)) {
    // ...
}