MaintenanceMode.php

<?php

namespace Drupal\Core\Site;

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\State\StateInterface;

/**
 * Provides the default implementation of the maintenance mode service.
 */
class MaintenanceMode implements MaintenanceModeInterface {
    
    /**
     * The state.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructs a new maintenance mode service.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   The state.
     */
    public function __construct(StateInterface $state) {
        $this->state = $state;
    }
    
    /**
     * {@inheritdoc}
     */
    public function applies(RouteMatchInterface $route_match) {
        if (!$this->state
            ->get('system.maintenance_mode')) {
            return FALSE;
        }
        if ($route = $route_match->getRouteObject()) {
            if ($route->getOption('_maintenance_access')) {
                return FALSE;
            }
        }
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function exempt(AccountInterface $account) {
        return $account->hasPermission('access site in maintenance mode');
    }

}