C＃UDP握手错误

Question

I have a program that will broadcast on 255.255.255.255 . First it will broadcast a message to request for LOCATION then listens for the reply. If the broadcast is starting with LOCATION: it will get the location string. Here is my code:

UDPCommunication Class

 class UDPCommunication
 {
    public void BroadcastMessage(string message, int port)
    {
        BroadcastMessage(Encoding.ASCII.GetBytes(message), port);
    }

    private static void BroadcastMessage(byte[] message, int port)
    {
        using (var sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram,
         ProtocolType.Udp))
        {
            sock.EnableBroadcast = true;
            sock.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, true);

            var iep = new IPEndPoint(IPAddress.Broadcast, port);

            sock.SendTo(message, iep);
        }
    }

    public void ReceiveBroadcastMessage(Action<EndPoint, string> receivedAction, int port)
    {
        ReceiveBroadcastMessage((ep, data) =>
        {
            var stringData = Encoding.ASCII.GetString(data);
            receivedAction(ep, stringData);
        }, port);
    }

    private void ReceiveBroadcastMessage(Action<EndPoint, byte[]> receivedAction, int port)
    {
        using (var sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
        {
            var ep = new IPEndPoint(IPAddress.Any, port) as EndPoint;
            sock.Bind(ep);

            while (true)
            {
                var buffer = new byte[1024];
                var recv = sock.ReceiveFrom(buffer, ref ep);

                var data = new byte[recv];

                Array.Copy(buffer, 0, data, 0, recv);

                receivedAction(ep, data);

                Thread.Sleep(500);
                Application.DoEvents();
            }
        }
    }
}

Form1.cs
    public event EventHandler BroadcastMessageArrived;
    public event EventHandler LocationReceived;
    string location = null;
    string ReceivedMessage = null;
    bool WorkDone = false;
    UDPCommunication UDP = new UDPCommunication();
    private void Form1_Load(object sender, EventArgs e)
    {
        BroadcastMessageArrived += new EventHandler(OnBroadcastMessageArrived);
        LocationReceived += new EventHandler(Form1_LocationReceived);

        backgroundWorker1.RunWorkerAsync();

        UDP.BroadcastMessage("GATE_REQUEST_LOCATION", 15000); 

        while (!WorkDone) ;

        LogGlobally(string.Format("Location now set to: ", Gate_Application.Properties.Settings.Default.Location));
}

    void OnBroadcastMessageArrived(object sender, EventArgs e)
    {
        Console.WriteLine("Message received: {0}", ReceivedMessage); // Never being called
        if (ReceivedMessage.StartsWith("LOCATION:"))
        {
            string[] LocationString = ReceivedMessage.Split(':');
            location = LocationString[1];
            EventHandler handler = LocationReceived;
            if (handler != null)
            {
                handler(this, e);
            }
            return;
        }
    }

    void Form1_LocationReceived(object sender, EventArgs e)
    {
        Gate_Application.Properties.Settings.Default.Location = location;
        Gate_Application.Properties.Settings.Default.Save();
        WorkDone = true;
        return;
    }

With my code above, I tried sending a broadcast LOCATION:SZ but it never showed the message on the console. I suspect the problem is with the while loop which it won't breakoff even WorkDone is =true Please help! Thanks!

Answer 1

I am not clear - did you even receive the message? If not:

Almost all network hardware drops packets addressed 255.255.255.255 unconditionally (imagine how one could flood networks if they didn't).

Try broadcast to a more specific subnet, eg: 192.168.0.255