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

/**
 * This class, and its several inner classes, provide a simple
 * echo server for TCP and UDP. 
 */
public class DualServer
{    
    protected Thread tcpThread;
    protected Thread udpThread;

    /**
     * Default port on which to provide TCP and UDP
     * echo services.
     * This is not final, so a caller could change it
     * to provide echo services on a different port.
     */
    public static int ECHO_PORT = 7;

    /** 
     * Create a DualServer object to offer echo service
     * on TCP and UDP ports on the default IP address.
     */
    public DualServer() {
	try {
	    tcpThread = new StreamEchoService(ECHO_PORT);
	} catch (IOException ie) {
	    System.err.println("Couldn't start TCP echo service: " + ie);
	}
	try {
	    udpThread = new DatagramEchoService(ECHO_PORT);
	} catch (IOException ie) {
	    System.err.println("Couldn't start UDP echo service: " + ie);
	}
    }

    /**
     * Start up this echo service.
     */
    public void start() {
	tcpThread.start();
	udpThread.start();
	return;
    }
	

    static class DatagramEchoService extends Thread
    {
	DatagramSocket ds;

	DatagramEchoService(int port) 
		throws IOException 
	{
	    super("datagram service");
	    ds = new DatagramSocket(port);
	}
	private static final int LEN = 65530;
	public void run() {
	    DatagramPacket dp;
	    dp = new DatagramPacket(new byte[LEN], LEN);
	    while (true) {
		try {
		    dp.setLength(LEN);
		    ds.receive(dp);
		    ds.send(dp);
		}
		catch (IOException e) {
		    System.err.println("Exception on UDP service: " + e);
		}
	    }
	}
    }

    static class StreamEchoServer extends Thread {
	private Socket s;

	public StreamEchoServer(Socket cs) {
	    super("server");
	    s = cs;
	}
	public void run() {
	    InputStream is = null;
	    OutputStream os = null;
	    try {
		is = s.getInputStream();
		os = s.getOutputStream();
		byte [] buf = new byte[1024];
		int cc;
		do {
		    cc = is.read(buf);
		    if (cc > 0) os.write(buf, 0, cc);
		} while (cc >= 0);
	    }
	    catch (IOException ie) { }
	    finally {
		try { is.close(); } catch (IOException ie) { }
		try { os.close(); } catch (IOException ie) { }
		try { s.close(); } catch (IOException ie) { }
	    }
	}
    }

    static class StreamEchoService extends Thread
    {
	ServerSocket ss;

	StreamEchoService(int port) 
		throws IOException
	{
	    super("stream service");
	    ss = new ServerSocket(port);
	}

	public void run() {
	    Socket cs;
	    while(true) {
		try {
		    cs = ss.accept();
		    (new StreamEchoServer(cs)).start();
		}
		catch (IOException ie) { break; }
	    }
	}
    }

    /**
     * Test main - test out the echo server on its
     * default port, or on a port specified by args[0].
     */
    public static void main(String args[]) {
	if (args.length > 0) {
	    try {
		int prt = Integer.parseInt(args[0]);
		if (prt > 0 && prt < 65535)
		    ECHO_PORT = prt;
	    } 
	    catch (Exception e) { }
	}
	System.out.println("Starting echo service on port " + ECHO_PORT);
	DualServer ds = new DualServer();
	ds.start();
	return;
    }
}