/* udpserver.java */
import java.io.*;
import java.net.*;

public class udpserver {
    public static void main(String[] args) throws IOException
    {
	DatagramSocket sock = null;
        byte recvbuf[] = new byte[4096];
        byte sendbuf[];
        InetAddress client = null;
        DatagramPacket p = null;
        int port = 0;
        int clientPort = 0;
   
	if (args.length != 1) 
	{
        System.err.println(
           "usage java udpserver port");
	System.exit(0);
	}
        try {
           port = Integer.parseInt(args[0]);
        }
        catch (NumberFormatException e) {
	    System.err.println("Arg was not a number");
            System.exit(0);
        }
        try {
            sock = new DatagramSocket(port);
        } catch (IOException e) {
            System.err.println("Could not listen on port: "+ port);
            System.exit(1);
        }
            while(true) {
		p = new DatagramPacket(recvbuf, 4096);           
                sock.receive(p);
                String s = new String(p.getData(),0,p.getLength());
                System.out.println("Client sent " + s);


                client = p.getAddress();
	    clientPort = p.getPort();
            String reply = "I got your message";
            sendbuf = reply.getBytes();
	    DatagramPacket sendPacket = new DatagramPacket(sendbuf, 
							   sendbuf.length, 
							   client, 
							   clientPort);
	    sock.send(sendPacket);
	    }
    }
}