Subversion Repositories programming

/*******************************************************************************
 * File: P2_Client.java
 * Author: Ira W. Snyder (devel@irasnyder.com)
 * License: GNU General Public License v2
 * Class: CS380 - Computer Networking
 *
 * Assignment: Project #2
 * Date Last Modified: 2006-02-05
 *
 * Purpose: Implement a simple client allowing the user to send datagrams
 * to P2_Server, which will decode them from 4B to 5B encoding. The client
 * will retransmit any packets that do not recieve a reply.
 ******************************************************************************/

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

public class P2_Client
{
    private static int soTimeout = 3000; // 3000 ms timeout = 3 sec
    private static DatagramSocket socket;
    private static DatagramPacket packet;
    private static int portNumber = 1337;

    /**
     * Method: readPacket()
     * Purpose: Read a packet on the currently opened DatagramSocket,
     * and return it as a String.
     */
    public static String readPacket (int maxlen)
    {
        byte[] buf = new byte[maxlen];
        packet = new DatagramPacket (buf, buf.length);

        try {
            socket.receive (packet);
        } catch (SocketTimeoutException e) {
            System.out.println ("Read timed out, requesting retransmit");
            return null;
        } catch (PortUnreachableException e) {
            System.out.println ("Caught PortUnreachableException, are you" +
                                " sure the server is running?");
            System.exit(1);
        } catch (IOException e) {
            System.out.println ("Caught exception in readPacket()");
            e.printStackTrace();
            return null;
        }

        return new String (buf, 0, packet.getLength()/*- 1*/);
    }

    /**
     * Method: writePacket()
     * Purpose: Send a packet to localhost:portNumber.
     */
    public static boolean writePacket (String msg) throws Exception
    {
        InetAddress address = InetAddress.getLocalHost();
        int port = portNumber;

        byte[] buf = msg.getBytes();
        packet = new DatagramPacket (buf, buf.length, address, port);

        try {
            socket.send (packet);
        } catch (PortUnreachableException e) {
            System.out.println ("Caught PortUnreachableException, are " +
                                "you sure the server is running?");
            System.exit(1);
        } catch (IOException e) {
            System.out.println ("Caught exception in writePacket()");
            e.printStackTrace();
            return false;
        }

        return true;
    }

    /**
     * Method: guaranteedTransmit()
     * Purpose: A wrapper around readPacket() and writePacket() that implements
     * a reliable transmit mechanism. It allows you to specify a maximum number
     * of times to try resending a packet.
     */
    public static String guaranteedTransmit (String msg, int maxlen, int maxRetries) throws Exception
    {
        String reply = null;
        int retries = 0;

        writePacket (msg);
        reply = readPacket (maxlen);

        while (reply == null && retries < maxRetries)
        {
            System.err.println ("Packet lost, retransmitting...");
            writePacket (msg);
            reply = readPacket (maxlen);
            retries++;
        }

        return reply;
    }

    /**
     * Method: main()
     * Purpose: This will accept input from the user, and attempt to send it
     * to the corresponding server, which will convert the messages from 4B
     * to 5B encoding.
     */
    public static void main (String[] args) throws Exception
    {
        int dropHowMany = 0;
        socket = new DatagramSocket();
        socket.connect (InetAddress.getLocalHost(), portNumber);
        socket.setSoTimeout (soTimeout);

        BufferedReader kbd = new BufferedReader (
                                 new InputStreamReader (
                                     System.in));

        try {
            dropHowMany = Integer.parseInt(args[0]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.err.println ("You need to call the program with \'java P2_Client <num>\'");
            System.exit(1);
        }

        String msg = new String("DROP" + dropHowMany);
        String reply = guaranteedTransmit (msg, 6, 1);

        if (!reply.equals(msg))
        {
            System.err.println ("Unable to inform the server how often to drop packets");
            System.exit(1);
        }

        System.out.print ("% decode: ");
        msg = kbd.readLine();
        boolean done = false;

        while (!done)
        {
            reply = guaranteedTransmit (msg, 6, 1);

            if (reply.equals("QUIT"))
            {
                done = true;
                continue;
            }

            System.out.println ("-> reply: " + reply);
            System.out.print ("% decode: ");
            msg = kbd.readLine();
        }

        // Close the socket
        socket.close();
    }
}