Client - Server on same machine using UDP

Question

I am trying to simulate a Client - Server scenario on my machine in c#. But when i am executing it an exception pops up saying:

No such host is known

My code:

namespace TCPClient
{
    public class Program
    {
        public static void Main(string[] args)
        {
            UdpClient udpc = new UdpClient(args[0], 2055);
            IPEndPoint ep = null;
            while (true)
            {
                Console.Write("Name: ");
                string name = Console.ReadLine();
                if (name == "") break;
                byte[] sdata = Encoding.ASCII.GetBytes(name);
                udpc.Send(sdata, sdata.Length);
                byte[] rdata = udpc.Receive(ref ep);
                string job = Encoding.ASCII.GetString(rdata);
                Console.WriteLine(job);
            }
        }
    }
}

I don't understand where I'm going wrong.

score 1 · Answer 1 · answered Nov 14 '13 at 05:36

thanks Dev's ! your answers were helpful, however I found an easiest way for the same.

 public class Program
 {
    public static void Main(string[] args)
    {
        UdpClient udpc = new UdpClient( System.Net.Dns.GetHostName(), 2055);
        IPEndPoint ep = null;
        while (true)
        {
            Console.Write("Name: ");
            string name = Console.ReadLine();
            if (name == "") break;
            byte[] sdata = Encoding.ASCII.GetBytes(name);
            udpc.Send(sdata, sdata.Length);
            byte[] rdata = udpc.Receive(ref ep);
            string job = Encoding.ASCII.GetString(rdata);
            Console.WriteLine(job);
        }
    }
 }

score 0 · Answer 2 · answered Nov 13 '13 at 13:34

Isolate the issue. You're calling new UdpClient(args[0], 2055) and udpc.Receive(ref ep) that can throw this exception, but don't say which one does. Either debug it or try it with a constant string:

string host = args[0];
new UdpClient(host, 2055);

You'll then see that host is most probably not an existing hostname. If it is, check what you are doing with ep: nothing, so it will be null. I guess you'll want to listen to any UDP datagram as explained in the documentation, so specify the endpoint:

ep = new IPEndPoint(IPAddress.Any, 0);

score 0 · Answer 3 · edited May 23 '17 at 12:19

I do believe your issue lies within this call:

byte[] rdata = udpc.Receive(ref ep)

The problem is that, in order to be able to listen to any incoming content, you need first to bind the UdpClient to a valid endpoint - like this:

IPEndPoint ep = new IPEndPoint(IPAddress.Any, 8192);
//You will be listening to port 8192.

Also, keep in mind that you can't both listen AND emit from the same UdpClient; You'll need two clients, and if you want to use the same IP Port for both, you'll need to initialize the class using the SocketOptionName.ReuseAddress parameter. A good example is provided on the following post:

Connecting two UDP clients to one port (Send and Receive)

Client - Server on same machine using UDP

3 Answers3