Session.php

<?php

namespace Drupal\Core\StackMiddleware;

use Symfony\Component\DependencyInjection\ContainerAwareTrait;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\HttpKernelInterface;

/**
 * Wrap session logic around a HTTP request.
 *
 * Note, the session service is not injected into this class in order to prevent
 * premature initialization of session storage (database). Instead the session
 * service is retrieved from the container only when handling the request.
 */
class Session implements HttpKernelInterface {
    use ContainerAwareTrait;
    
    /**
     * The wrapped HTTP kernel.
     *
     * @var \Symfony\Component\HttpKernel\HttpKernelInterface
     */
    protected $httpKernel;
    
    /**
     * The session service name.
     *
     * @var string
     */
    protected $sessionServiceName;
    
    /**
     * Constructs a Session stack middleware object.
     *
     * @param \Symfony\Component\HttpKernel\HttpKernelInterface $http_kernel
     *   The decorated kernel.
     * @param string $service_name
     *   The name of the session service, defaults to "session".
     */
    public function __construct(HttpKernelInterface $http_kernel, $service_name = 'session') {
        $this->httpKernel = $http_kernel;
        $this->sessionServiceName = $service_name;
    }
    
    /**
     * {@inheritdoc}
     */
    public function handle(Request $request, $type = self::MASTER_REQUEST, $catch = TRUE) {
        if ($type === self::MASTER_REQUEST && PHP_SAPI !== 'cli') {
            $session = $this->container
                ->get($this->sessionServiceName);
            $session->start();
            $request->setSession($session);
        }
        $result = $this->httpKernel
            ->handle($request, $type, $catch);
        if ($type === self::MASTER_REQUEST && $request->hasSession()) {
            $request->getSession()
                ->save();
        }
        return $result;
    }

}