Subversion Repositories programming

/*******************************************************************************

 * File: P2_Server.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 server which will listen on UDP port 1337 for

 * incoming datagrams. It will first recieve a message telling it to drop

 * every n-th message. After that it will convert every message it recieves

 * from 4B to 5B encoding, and reply back to the client. It will only exit on

 * receiving the message "QUIT".

 ******************************************************************************/

import java.io.*;

import java.util.*;

import java.net.*;

import java.util.regex.*;

public class P2_Server

{

    private static int portNumber = 1337;

    private static int dropEvery = -1;

    private static boolean dropPacket = false;

    private static DatagramPacket packet;

    private static DatagramSocket socket;

    /**

     * Method: readPacket()

     * Purpose: Read a packet from the currently opened socket.

     * Note: Blocks until it recieves data.

     */

    public static P2_Packet readPacket ()

    {

        byte[] buf = new byte[256];

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

        // Try to recieve data from the client. Catch any

        // exceptions that may occur.

        try {

            socket.receive (packet);

        } catch (IllegalArgumentException e) {

            System.err.println ("Caught exception in readPacket()");

            e.printStackTrace ();

        } catch (IOException e) {

            System.err.println ("Caught exception in readPacket()");

            e.printStackTrace ();

            return null;

        }

        // Convert the packet, and print a status message.

        P2_Packet ret = new P2_Packet (packet.getData());

        System.out.printf ("Recieved a packet: %d bytes -- packetNum: %d\n",

                ret.getPacketDataSize(), ret.getPacketNumber());

        return ret;

    }

    /**

     * Method: writePacket()

     * Purpose: Write a message to the last client that sent us a message.

     */

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

    {

        // Get the address and port of the last message sent to us.

        InetAddress address = packet.getAddress();

        int port = packet.getPort();

        // Set up our packet

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

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

        // Attempt to send the packet

        try {

            socket.send (packet);

        } catch (IOException e) {

            System.out.println ("Caught exception in writePacket()");

            e.printStackTrace();

            return false;

        }

        // It got sent ok

        return true;

    }

    /**

     * Method: writePacket()

     * Purpose: A simplified version of writePacket() above.

     */

    public static boolean writePacket (byte type)

    {

        byte[] pData = { 0 };

        return writePacket (type, pData);

    }

    /**

     * Method: calcDropNum()

     * Purpose: Parse a message sent by the client telling us to drop

     * every n-th message.

     */

    public static int calcDropNum (P2_Packet p)

    {

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

            throw new IllegalArgumentException(); // major problem

        // The byte informing us how often to drop packets is in

        // the first byte only.

        byte[] num = p.getPacketData();

        return (int)num[0];

    }

    /**

     * Method: main()

     * Purpose: Open a listening UDP socket, and convert a client's

     * requests from 4B encoding to 5B encoding.

     */

    public static void main (String[] args) throws Exception

    {

        boolean done = false, droppedLast = false;

        socket = new DatagramSocket(portNumber);

        packet = null;

        String s;

        P2_Packet decodedPacket = null;

        byte[] pData;

        // Try to get a "timeout info" packet

        while (!done)

        {

            decodedPacket = readPacket ();

            dropEvery = calcDropNum (decodedPacket);

            if (dropEvery != -1)

            {

                done = true;

                System.out.println ("dropEvery: " + dropEvery);

            }

            writePacket (P2_Packet.DROP);

        }

        done = false;

        // Keep reading until we get a quit packet

        while (!done)

        {

            decodedPacket = readPacket ();

            // Drop a packet if it is the correct time to do so

            if ((decodedPacket.getPacketNumber() == dropEvery) && !droppedLast)

            {

                System.out.println ("Purposely dropped a packet");

                droppedLast = true;

                continue;

            }

            droppedLast = false;

            // Figure out what type of packet to send in reply

            switch (decodedPacket.getPacketType())

            {

                case P2_Packet.TRANSREQ:

                    try {

                        pData = P2_EncDec.convert4B (decodedPacket.getPacketData());

                        writePacket (P2_Packet.TRANSREPL, pData);

                    } catch (IllegalArgumentException e) {

                        System.err.println ("Received a bad packet");

                        writePacket (P2_Packet.BADPACKET);

                    }

                    break;

                case P2_Packet.QUIT:

                    writePacket (P2_Packet.QUIT);

                    done = true;

                    break;

                default:

                    System.err.println ("Got a packetType that I was not "

                                      + "expecting here.");

                    writePacket (P2_Packet.BADPACKET);

                    break;

            }

        }

        // Close the socket

        socket.close();

    }

}