RouteMethodSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Routing\RouteBuildEvent;
use Drupal\Core\Routing\RoutingEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Provides a default value for the HTTP method restriction on routes.
 *
 * Most routes will only deal with GET and POST requests, so we restrict them to
 * those two if nothing else is specified. This is necessary to give other
 * routes a chance during the route matching process when they are listening
 * for example to DELETE requests on the same path. A typical use case are REST
 * web service routes that use the full spectrum of HTTP methods.
 */
class RouteMethodSubscriber implements EventSubscriberInterface {
    
    /**
     * Sets a default value of GET|POST for the _method route property.
     *
     * @param \Drupal\Core\Routing\RouteBuildEvent $event
     *   The event containing the build routes.
     */
    public function onRouteBuilding(RouteBuildEvent $event) {
        foreach ($event->getRouteCollection() as $route) {
            $methods = $route->getMethods();
            if (empty($methods)) {
                $route->setMethods([
                    'GET',
                    'POST',
                ]);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        // Set a higher priority to ensure that routes get the default HTTP methods
        // as early as possible.
        $events[RoutingEvents::ALTER][] = [
            'onRouteBuilding',
            5000,
        ];
        return $events;
    }

}