[SOLVED] UDP Discovery Code Unable to Receive UDP Broadcast.

Question

Hi. I need to write a mobile app (Xamarin) to send a UDP broadcast, then have a desktop app (WPF/WinForms) listen to the UDP broadcast. I got the sample from the link below, but it is not working. The Xamarin app seems okay (on a Samsung phone), but the desktop app never gets past the "listener.Receive(ref ...)" statement. I would appreciate help. Thanks.

https://learn.microsoft.com/en-us/dotnet/framework/network-programming/using-udp-services

Xamarin Server:

    private void StartUdpDiscovery()  
    {  
        Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);  

        IPAddress broadcast = IPAddress.Parse("192.168.1.255");  

        //byte[] sendbuf = Encoding.ASCII.GetBytes(args[0]);  
        IPEndPoint ep = new IPEndPoint(broadcast, 11000);  

        byte[] data = new byte[2]; //broadcast data  
        data[0] = 0x0A;  
        data[1] = 0x60;  
        s.SendTo(data, ep);  

        Console.WriteLine("Message sent to the broadcast address");  
    }  

Desktop Client/Listener:

    private void StartUdpListener()  
    {  
        UdpClient listener = new UdpClient(listenPort);  
        //IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);  
        IPEndPoint groupEP = new IPEndPoint(IPAddress.Parse("192.168.1.255"), listenPort);  

        try  
        {  
            while (true)  
            {  
                Console.WriteLine("Waiting for broadcast");  
                byte[] bytes = listener.Receive(ref groupEP); // NOTE: THE DEBUGGER STALLS HERE AND NEVER MOVES ON...  

                Console.WriteLine($"Received broadcast from {groupEP} :");  
                Console.WriteLine($" {Encoding.ASCII.GetString(bytes, 0, bytes.Length)}");  
            }  
        }  
        catch (SocketException e)  
        {  
            Console.WriteLine(e);  
        }  
        finally  
        {  
            listener.Close();  
        }  
    }  

Answer 1

Hi StoutGamer,

Welcome to our Microsoft Q&A platform!

The sample provided in the documentation works fine in my test.

Please note that you should use the IP address of your "Desktop Client device", rather than "192.168.1.255".

And ensure that your mobile app and desktop app are on the same network segment.

For example,

mobile: 192.168.1.100
desktop: 192.168.1.101

Regards,
Kyle

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