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();

    }

}