How to write a socket server in Xbasic


Below is a very basic server that you could expand to use multiple sockets and threads as required. It should give you a good starting point on how to use sockets in Xbasic. It does not implement any specific protocol on top of the sockets: that is left to you.

dim Running as l = .t.        'Set this to .f. from elsewhere to stop the server.
dim ListeningPort as n = 1234 'The correct port should be defined in the protocol specification.

dim ServerSocket as INET::Socket

if ServerSocket.Listen(ListeningPort)

    while Running
        dim WorkerSocket as INET::Socket
        dim AcceptTimeout as n = 10000 '10 seconds

        if ServerSocket.Accept(WorkerSocket,AcceptTimeout)

            'This section could go into a spawned worker thread for maximum scalability
            dim RawRequest as c = ""

            if WorkerSocket.Read(RawRequest)
                'RawRequest now contains at least part of a request from a client. Next:
                ' 1) Verify that the request is complete, and read more from the WorkerSocket if necessary.
                ' 2) Parse RawRequest based on the protocol specification to determine what must be done.
                ' 3) Take some appropriate action based on the parsed request.
                ' 4) Send a response using WorkerSocket.Write() or WorkerSocket.WriteBinary().
                ' 5) Close the socket or loop back to reading, depending on the protocol specification.
                'WorkerSocket.CallResult.Text will have a description of why the Read() failed.
            end if
            'end of section that could go into a worker thread
            'No new client connected within the timeout period.
            'Most servers should just do nothing and loop back around to wait again.
        end if
    end while
    msgbox("Server could not be started: " + ServerSocket.CallResult.Text)
end if
Since Xbasic does not have block-level scoping of variables, Dim WorkerSocket as INET::Socket inside the while loop does not guarantee a new unique socket for each pass. Therefore, spawning threads with unique sockets is non-trivial. Ultimately, this task is better handled by C# or a C++ DLL.

See Also