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: 2006-02-08

 *

 * 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;

    private static int packetNum = 0;

    /**

     * Method: verifyInput()

     * Purpose: Verify the user's input before it is sent out to the

     * server for translation.

     */

    public static boolean verifyInput (String s)

    {

        int i;

        // Check for QUIT message

        if (s.equals("QUIT"))

            return true;

        // If it's not a QUIT, it must be 0's and 1's only

        for (i=0; i<s.length(); i++)

            if (!(s.charAt(i) == '0' || s.charAt(i) == '1'))

                return false;

        // Everything was a 0 or 1, good!

        return true;

    }

    /**

     * Method: readPacket()

     * Purpose: Read a packet on the currently opened DatagramSocket,

     * and return it as a P2_Packet.

     */

    public static P2_Packet readPacket ()

    {

        byte[] buf = new byte[256];

        packet = new DatagramPacket (buf, buf.length);

        // Try to recieve a packet from the server, and catch all possible

        // exceptions that can happen.

        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;

        }

        // Convert the bytes to a P2_Packet, then return them.

        return new P2_Packet (packet.getData());

    }

    /**

     * Method: writePacket()

     * Purpose: Send a packet to localhost:portNumber.

     */

    public static boolean writePacket (byte type, byte[] data, int packetNum)

    {

        InetAddress address = null;

        int port = portNumber;

        // Try to get the localhost address. If this fail's, we've got major

        // problems going on, so just exit.

        try {

            address = InetAddress.getLocalHost();

        } catch (UnknownHostException e) {

            System.err.println ("Caught UnknownHostException in writePacket(), " +

                                "are you sure the system is working?");

            System.exit(1);

        }

        // Create the new packet

        byte[] buf = P2_Packet.createPacket (type, data, packetNum);

        packet = new DatagramPacket (buf, buf.length, address, port);

        // Try to send the packet, and catch all of the possible errors.

        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;

        }

        // We sent successfully, so return true.

        return true;

    }

    /**

     * Method: guaranteedTransmit()

     * Purpose: A wrapper around readPacket() and writePacket() that implements

     * a reliable transmit mechanism.

     */

    public static P2_Packet guaranteedTransmit (byte type, byte[] data)

    {

        P2_Packet reply;

        int retries = 0;

        // Send a packet, and wait for a reply

        writePacket (type, data, packetNum);

        reply = readPacket ();

        // If the read timed out, keep trying to send until it gets through

        while (reply == null)

        {

            System.err.println ("Packet lost, retransmitting...");

            writePacket (type, data, packetNum);

            reply = readPacket ();

            retries++;

        }

        // Reset the packetNum if we had to retry sending a packet.

        // The packetNum is used to control the server's dropping

        // of packets.

        if (retries > 0)

            packetNum = 0;

        packetNum++;

        return reply;

    }

    /**

     * Method: guaranteedTransmit()

     * Purpose: A simplified version of the guaranteedTransmit() above.

     */

    public static P2_Packet guaranteedTransmit (byte type)

    {

        byte[] pData = { 0 };

        return guaranteedTransmit (type, pData);

    }

    /**

     * 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);

        // Set the socket's timeout to 3 seconds

        socket.setSoTimeout (soTimeout);

        BufferedReader kbd = new BufferedReader (

                                 new InputStreamReader (

                                     System.in));

        // Parse the first command-line argument into an int, and use that

        // to inform the server how often to drop packets.

        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;

        byte[] pData = { (byte)dropHowMany };

        P2_Packet reply = guaranteedTransmit (P2_Packet.DROP, pData);

        // Check to make sure our packet informing the server how often to drop

        // packets was recieved successfully.

        if (reply.getPacketType() != P2_Packet.DROP)

        {

            System.err.println ("Unable to inform the server how often to drop packets");

            System.exit(1);

        }

        boolean done = false;

        // Keep running until the user decides that they don't want to

        // decode any more 4B numbers.

        while (!done)

        {

            System.out.print ("% decode: ");

            msg = kbd.readLine ();

            // Check user input

            if (!verifyInput(msg))

            {

                System.out.println ("Bad input, try again...");

                continue;

            }

            // Check for a QUIT message

            if (msg.equals("QUIT"))

            {

                reply = guaranteedTransmit (P2_Packet.QUIT);

                done = true;

                continue;

            }

            reply = guaranteedTransmit (P2_Packet.TRANSREQ, P2_EncDec.convertToByteArray(msg));

            // Check for a bad packet from the server

            if (reply.getPacketType() == P2_Packet.BADPACKET)

                System.out.println ("-> reply: BAD REQUEST");

            else

                System.out.println ("-> reply: " + 

                        P2_EncDec.convertToString(reply.getPacketData()));

        }

        // Close the socket

        socket.close();

    }

}