import java.net.*;
import java.io.*;

/**
 * This small class simply provides a usable main that
 * can be used to test some kinds of datagram servers.
 * Basically, this program expects to get a host name
 * and port number on the command line.  If the port
 * number is not supplied, it defaults to 7.  The
 * program reads lines from standard input, and packages
 * up each line as a datagram packet.  After sending a
 * packet, it waits for and prints the response.  This
 * program exits on end-of-file.
 */
public class DatagramTest 
{
    public static void main(String args[]) {
	if (args.length < 1) {
	    System.err.println("Usage: java DatagramTest host [port] <file");
	    System.exit(0);
	}

	String host = args[0];
	int port = 7;
	if (args.length > 1) {
	    try {
		port = Integer.parseInt(args[1]);
	    } catch (NumberFormatException nfe) { }
	}
	
	BufferedReader br;
	br = new BufferedReader(new InputStreamReader(System.in));

	InetAddress addr = null;
	try {
	    addr = InetAddress.getByName(host);
	}
	catch (UnknownHostException uhe) {
	    System.err.println("No such host: " + host);
	    System.exit(0);
	}

	/*
	 * The approach used here, send then immediately
	 * receive, will usually work, but is not totally
	 * reliable.  In a very fast network, or with loopback,
	 * it is possible for the response to arrive before
	 * Java manages to crawl from send to receive.
	 */
	DatagramSocket ds = null;
	DatagramPacket rec, send;
	String line;
	rec = new DatagramPacket(new byte[65530], 65530);
	try {
	    ds = new DatagramSocket();
	    while((line = br.readLine()) != null) {
		byte [] buf = line.getBytes();
		if (buf.length > 0) {
		    send = new DatagramPacket(buf, buf.length, addr, port);
		    rec.setLength(65530);
		    ds.send(send);
		    ds.receive(rec);
		    line = new String(rec.getData(), 0, rec.getLength());
		    System.out.println(line);
		}
	    }
	}
	catch (IOException ie) {
	    System.err.println("IO exception in datagram test: " + ie);
	}
	finally {
	    if (ds != null) try {
		ds.close();
	    } catch (Exception e) { }
	}
    }
}