Assuming this mysterious server program is actually accessed by other existing clients, that might be the place to start. Assuming a network and not native socket, you should be able to capture all network traffic using wireshark or tcpdump. Try some sample commands on the working client, and look at the corresponding network traffic. That would probably get you basic functions. If you need to do something for which no client currently exists, then you are scr*wed. The request/response could be just about anything.