RouterListener::onKernelRequest

RouterListener.php

<?php
//vendor/symfony/http-kernel/EventListener/RouterListener.php
public function onKernelRequest(RequestEvent $event)
{
    $request = $event->getRequest();
    // add attributes based on the request (routing)
    try {
        $parameters = $this->matcher->matchRequest($request);
        $request->attributes->add($parameters);
        unset($parameters['_route'], $parameters['_controller']);
        $request->attributes->set('_route_params', $parameters);
    } catch (ResourceNotFoundException $e) {
        $message = sprintf('No route found for "%s %s"', $request->getMethod(), $request->getPathInfo());
        throw new NotFoundHttpException($message, $e);
    } catch (MethodNotAllowedException $e) {
        $message = sprintf('No route found for "%s %s": Method Not Allowed (Allow: %s)', $request->getMethod(), $request->getPathInfo(), implode(', ', $e->getAllowedMethods()));
        throw new MethodNotAllowedHttpException($e->getAllowedMethods(), $message, $e);
    }
}