int sd_bus_is_open(sd_bus *bus);
int sd_bus_is_ready(sd_bus *bus);
sd_bus_is_ready() checks whether the specified connection is fully established, i.e. completed the connection and authentication phases of the protocol and received the Hello() method call response, and is not in the process of being torn down again. It returns zero outside of this state, and positive otherwise. Effectively, this function returns positive while regular messages can be sent or received on the connection.
To be notified when the connection is fully established, use sd_bus_set_connected_signal(3) and install a match for the Connected() signal on the "org.freedesktop.DBus.Local" interface. To be notified when the connection is torn down again, install a match for the Disconnected() signal on the "org.freedesktop.DBus.Local" interface.