Before a client can connect to a server, it must know the network address on which the server accepts connections.
Network addresses consist of a host address or name, and a port number.
Port numbers are 16 bit unsigned integers. This function signals an error if the chosen port is unusable. You will probably want to write a loop using handler-case , catching conditions of type error, since this function does not signal more specific conditions. If port is unavailable for any reason, this signals an error. When a client connects to this port, the acceptance mechanism makes a wire structure and invokes the on-connect function.