sockets - UDP multicasting. C#

Question

I try to send message to all members of the group. Sender:

// Create socket
        Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

        // Multicast IP-address
        IPAddress ip = IPAddress.Parse("224.168.55.25");

        // Join multicast group
        s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(ip));

        // TTL
        s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 2);

        // Create an endpoint
        IPEndPoint ipep = new IPEndPoint(ip, 4567);

        // Connect to the endpoint
        s.Connect(ipep);

        // Scan message
         while (true)
        {
            byte[] buffer = new byte[1024];
            string msg = Console.ReadLine();
            buffer = Encoding.ASCII.GetBytes(msg);
            s.Send(buffer, buffer.Length, SocketFlags.None);
            if (msg.Equals("Bye!", StringComparison.Ordinal))
                break;
        }

        // Close socket
        s.Close();

Receiver:

// Create new socket
        Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

        // Create IP endpoint
        IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 4567);

        // Bind endpoint to the socket
        s.Bind(ipep);

        // Multicast IP-address
        IPAddress ip = IPAddress.Parse("224.168.55.25");

        // Add socket to the multicast group
        s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(ip, IPAddress.Any));

        // Receive messages
        while (true)
        {
            byte[] data = new byte[1024];
            s.Receive(data);
            string str = System.Text.Encoding.ASCII.GetString(data, 0, data.Length);
            Console.WriteLine(str.Trim());
            if (str.Equals("Bye!", StringComparison.Ordinal))
            {
                break;
            }
        }

I don't uderstand why there is a lot of free space between messages when I print them to screen on the client side? Why loop in the Receiver program doesn't stop after receiveing message Bye!? How can I fix this problems?

Thank you very much!

Answer 1

You are creating a udp socket. Udp sockets are not connection oriented. So it just receives messages and has no idea about the state of the sender. Even if the sender socket closes, the receiver would keep on listening. I hope I have understood your question correctly.

if (strData.Trim().Equals("Bye!", StringComparison.Ordinal))
{
                Console.WriteLine("that's right");
                break;
}