Thanks, I understand that the "onRoomUnavailable" is a condition in bottleneck, not in bottleneck_lobby. (I make a mistake previous post)
In my original design, the room id is an identify to tell friends to join my game, like "xoros's game".
The available room list is maintained in game lobby (bottleneck_lobby, not in bottleneck). So player could choice the game which he/she want to join.
I need to check the server code and bottleneck plugin if you wish to get a available room id in bottleneck plugin. (when I have time. I'm making a new sprite bank recently, sorry.)