protected function registerHTTPServerInterface(INabuHTTPServerInterface $interface) : bool
    {
        $hash = $interface->getHash();
        if (is_array($this->http_server_interface_list) && array_key_exists($hash, $this->http_server_interface_list)) {
            throw new ENabuHTTPException(
                ENabuHTTPException::ERROR_HTTP_SERVER_INSTANCE_ALREADY_REGISTERED,
                array(get_class($interface))
            );
        }

        if ($this->http_server_interface_list === null) {
            $this->http_server_interface_list = array($hash => $interface);
        } else {
            $this->http_server_interface_list[$hash] = $interface;
        }

        return $interface->init();
    }