UDP packet Sent once but received thrice

Hi,

I am writing a simple code to send and receive data on a udp socket.

the code works ok except for the data is getting received thrice .

I am new to this so please bare with me... :)

<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>

Socket server = new Socket(AddressFamily.InterNetwork,SocketType.Dgram,

ProtocolType.Udp);

server.EnableBroadcast = false;

server.ExclusiveAddressUse = false;

IPEndPoint iep = new IPEndPoint(IPAddress.Parse("224.100.0.1"), 9050);

byte[] data = Encoding.ASCII.GetBytes(textBox1.Text.Trim());

server.SendTo(data, iep);

server.Close();

<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>

private void OnReceive(IAsyncResult ar)

{

try

{

UdpClient u = (UdpClient)((UdpState)(ar.AsyncState)).u;

IPEndPoint e = (IPEndPoint)((UdpState)(ar.AsyncState)).e;

UdpState s = new UdpState();

s.e = e;

s.u = u;

Byte[] receiveBytes = u.EndReceive(ar,ref e);

string receiveString = Encoding.ASCII.GetString(receiveBytes);

s.e = e;

listBox1.Items.Add("Received:" + receiveString+e.Address.ToString());

u.BeginReceive(new AsyncCallback(OnReceive), s);

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

private void Form1_Load(object sender, EventArgs e)

{

CheckForIllegalCrossThreadCalls = false;//Will remove later

}

private void StartReceive_Click(object sender, EventArgs eA)

{

IPEndPoint iep = new IPEndPoint(IPAddress.Parse("224.100.0.1"), 9050);

IPEndPoint e = new IPEndPoint(IPAddress.Any, 9050);

UdpClient u = new UdpClient(e);

u.Client.Blocking = false;

UdpState s = new UdpState();

s.e = e;

s.u = u;

s.u.Client.DontFragment = true;

s.u.Client.Ttl = 1;

listBox1.Items.Add("listening for messages");

u.JoinMulticastGroup( IPAddress.Parse("224.100.0.1"));

u.BeginReceive(new AsyncCallback(OnReceive), s);

}

public class UdpState

{

public IPEndPoint e;

public UdpClient u;

}

1 Reply

Know the answer? Post it — somebody with the same question will find it here.

Sam Hobbs14y ago
I would somehow ensure that the send is being done only once. You assume it is but the cause of problems such as this are often overlooked due to invalid assumptions. You can simply put a breakpoint on the line that does the send then debug the sender. Do the same for StartReceive_Click in the client. I realize that it is unlikely that the receive code is executed more than once per click but if it is executed more than once then that would be a problem and it is easy enough to eliminate that as a possibility.

Finally, I am not sure you need JoinMulticastGroup. I do not know what it does. I do not know how it works. I assume it is the problem but if so then I cannot help.