UDPEchoClientTimeout.java

import java.net.*;  // for DatagramSocket, DatagramPacket, and InetAddress
import java.io.*;   // for IOException

public class UDPEchoClientTimeout {
  // Resend timeout (milliseconds)
  private static final int TIMEOUT = 3000;
  // Maximum retransmissions
  private static final int MAXTRIES = 5;

  public static void main(String[] args) throws IOException {

    if ((args.length < 2) || (args.length > 3))  // Test for correct # of args
      throw new IllegalArgumentException("Parameter(s): <Server> <Word> [<Port>]");

    InetAddress serverAddress = InetAddress.getByName(args[0]);  // Server address
    // Convert input String to bytes using the default character encoding
    

    int servPort = (args.length == 3) ? Integer.parseInt(args[2]) : 7;

    DatagramSocket socket = new DatagramSocket();

    socket.setSoTimeout(TIMEOUT);  // Maximum receive blocking time (milliseconds)
    
    for (int num = 0; num < 9001; num++) {
      byte[] bytesToSend = String.format("%4d. %s", num + 1, args[1]).getBytes();
      DatagramPacket sendPacket = new DatagramPacket(bytesToSend,  // Sending packet
          bytesToSend.length, serverAddress, servPort);

      DatagramPacket receivePacket =                              // Receiving packet
          new DatagramPacket(new byte[bytesToSend.length], bytesToSend.length);
    
      int tries = 0;      // Packets may be lost, so we have to keep trying
      boolean receivedResponse = false;
      do {
        socket.send(sendPacket);          // Send the echo string
        try {
          socket.receive(receivePacket);  // Attempt echo reply reception

          if (!receivePacket.getAddress().equals(serverAddress))  // Check source
            throw new IOException("Received packet from an unknown source");

          receivedResponse = true;
        } catch (InterruptedIOException e) {  // We did not get anything
          tries += 1;
          System.out.println("Timed out, " + (MAXTRIES-tries) + " more tries...");
        }
      } while ((!receivedResponse) && (tries < MAXTRIES));
      
      if (receivedResponse)
        System.out.println("Received: " + new String(receivePacket.getData()));
      else
        System.out.println("No response -- giving up.");
    }

    socket.close();
  }
}