MethodFilter.php

<?php

namespace Drupal\Core\Routing;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Exception\MethodNotAllowedException;
use Symfony\Component\Routing\RouteCollection;

/**
 * Filters routes based on the HTTP method.
 */
class MethodFilter implements FilterInterface {
    
    /**
     * {@inheritdoc}
     */
    public function filter(RouteCollection $collection, Request $request) {
        $method = $request->getMethod();
        $all_supported_methods = [];
        foreach ($collection->all() as $name => $route) {
            $supported_methods = $route->getMethods();
            // A route not restricted to specific methods allows any method. If this
            // is the case, we'll also have at least one route left in the collection,
            // hence we don't need to calculate the set of all supported methods.
            if (empty($supported_methods)) {
                continue;
            }
            // If the GET method is allowed we also need to allow the HEAD method
            // since HEAD is a GET method that doesn't return the body.
            if (in_array('GET', $supported_methods, TRUE)) {
                $supported_methods[] = 'HEAD';
            }
            if (!in_array($method, $supported_methods, TRUE)) {
                $all_supported_methods[] = $supported_methods;
                $collection->remove($name);
            }
        }
        if (count($collection)) {
            return $collection;
        }
        throw new MethodNotAllowedException(array_unique(array_merge(...$all_supported_methods)));
    }

}