I know how to do this with Windows sockets, but how do I bind a UDP listen socket to the first available port?  I want to send a packet from client to the server to subscribe to data and tell the server what port to send the subscribed data to.  I don't care what port the client listens to.  If I hard code it, I can only run a single client on a PC.  I want to bind to the first available one so I can run as many clients on the same PC as I want.