Question

I’m new to UDP. Using a test environment, I am able to send/receive a single UDP message. However, I’m trying to figure out how to receive multiple UDP messages. I’d like MyListener service to receive UDP packets all day long, whenever I send them. I appreciate any help.

PS – As noted below in an answer, if I put a while(true) around my DoSomethingWithThisText, that will work while debugging. However, it won’t work when trying to run MyListener as a service, because Start will never get past the while(true) loop.

My listener service looks like this…

public class MyListener
{
    private udpClient udpListener;
    private int udpPort = 51551;

    public void Start()
    {
        udpListener = new UdpClient(udpPort);
        IPEndPoint listenerEndPoint = new IPEndPoint(IPAddress.Any, udpPort);
        Byte[] message = udpListener.Receive(ref listenerEndPoint);

        Console.WriteLine(Encoding.UTF8.GetString(message));
        DoSomethingWithThisText(Encoding.UTF8.GetString(message));
    }
}

My sender looks like this:

static void Main(string[] args)
{
    IPAddress ipAddress = new IPAddress(new byte[] { 127, 0, 0, 1 });
    int port = 51551;

    //define some variables.

    Console.Read();
    UdpClient client = new UdpClient();
    client.Connect(new System.Net.IPEndPoint(ipAddress, port));
    Byte[] message = Encoding.UTF8.GetBytes(string.Format("var1={0}&var2={1}&var3={2}", new string[] { v1, v2, v3 }));
    client.Send(message, message.Length);
    client.Close();
    Console.WriteLine(string.Format("Sent message");
    Console.Read();
}

Answer 1

I ended up using Microsoft’s asynchronous methods, found here – BeginReceive and EndReceive .

Like Microsoft suggests, I call BeginReceive within my Start method like this:

UdpState s = new UdpState();
s.e = listenerEP;
s.u = udpListener;

udpListener.BeginReceive(new AsyncCallback(ReceiveCallback), s);

However, to get the listener to continue receiving messages, I call BeginReceive AGAIN within the ReceiveCallback function, recursively. This, of course, is a potential memory leak, but I’ve yet to encounter problems in my regression testing.

private void ReceiveCallback(IAsyncResult ar)
{
    UdpClient u = (UdpClient)((UdpState)ar.AsyncState).u;
    IPEndPoint e = (IPEndPoint)((UdpState)ar.AsyncState).e;

    UdpState s = new UdpState();
    s.e = e;
    s.u = u;
    udpListener.BeginReceive(new AsyncCallback(ReceiveCallback), s); 

    Byte[] messageBytes = u.EndReceive(ar, ref e);
    string messageString = Encoding.ASCII.GetString(messageBytes);

    DoSomethingWithThisText(messageString);
}