function engine($arg='curl') {
		$arg=strtolower($arg);
		$flags=[
			'curl'=>extension_loaded('curl'),
			'stream'=>ini_get('allow_url_fopen'),
			'socket'=>function_exists('fsockopen')
		];
		if ($flags[$arg])
			return $this->wrapper=$arg;
		foreach ($flags as $key=>$val)
			if ($val)
				return $this->wrapper=$key;
		user_error(self::E_Request,E_USER_ERROR);
	}