class SessionHandler

class SessionHandler extends AbstractProxy implements \SessionHandlerInterface {
    use DependencySerializationTrait;
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Constructs a new SessionHandler instance.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   The request stack.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     */
    public function __construct(RequestStack $request_stack, Connection $connection) {
        $this->requestStack = $request_stack;
        $this->connection = $connection;
    }
    
    /**
     * {@inheritdoc}
     */
    public function open($save_path, $name) {
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function read($sid) {
        $data = '';
        if (!empty($sid)) {
            // Read the session data from the database.
            $query = $this->connection
                ->queryRange('SELECT [session] FROM {sessions} WHERE [sid] = :sid', 0, 1, [
                ':sid' => Crypt::hashBase64($sid),
            ]);
            $data = (string) $query->fetchField();
        }
        return $data;
    }
    
    /**
     * {@inheritdoc}
     */
    public function write($sid, $value) {
        // The exception handler is not active at this point, so we need to do it
        // manually.
        try {
            $request = $this->requestStack
                ->getCurrentRequest();
            $fields = [
                'uid' => $request->getSession()
                    ->get('uid', 0),
                'hostname' => $request->getClientIP(),
                'session' => $value,
                'timestamp' => REQUEST_TIME,
            ];
            $this->connection
                ->merge('sessions')
                ->keys([
                'sid' => Crypt::hashBase64($sid),
            ])
                ->fields($fields)
                ->execute();
            return TRUE;
        } catch (\Exception $exception) {
            require_once DRUPAL_ROOT . '/core/includes/errors.inc';
            // If we are displaying errors, then do so with no possibility of a
            // further uncaught exception being thrown.
            if (error_displayable()) {
                print '<h1>Uncaught exception thrown in session handler.</h1>';
                print '<p>' . Error::renderExceptionSafe($exception) . '</p><hr />';
            }
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function close() {
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function destroy($sid) {
        // Delete session data.
        $this->connection
            ->delete('sessions')
            ->condition('sid', Crypt::hashBase64($sid))
            ->execute();
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function gc($lifetime) {
        // Be sure to adjust 'php_value session.gc_maxlifetime' to a large enough
        // value. For example, if you want user sessions to stay in your database
        // for three weeks before deleting them, you need to set gc_maxlifetime
        // to '1814400'. At that value, only after a user doesn't log in after
        // three weeks (1814400 seconds) will their session be removed.
        $this->connection
            ->delete('sessions')
            ->condition('timestamp', REQUEST_TIME - $lifetime, '<')
            ->execute();
        return TRUE;
    }

}