(PECL gupnp >= 0.1.0)
gupnp_root_device_get_available — Check whether root device is available
$root_device
Get whether or not root_device is available (announcing its presence).
root_device
A root device identifier, returned by gupnp_root_device_new().
成功时返回 TRUE， 或者在失败时返回 FALSE.
TRUE
FALSE