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: 2006-02-05

 *

 * 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 int sendCount = 0;

    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 String readPacket (int maxlen)

    {

        byte[] buf = new byte[maxlen];

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

        try {

            socket.receive (packet);

        } catch (IOException e) {

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

            e.printStackTrace();

            return null;

        }

        System.out.println ("Recieved Packet. Len: " + packet.getLength());

        String s = new String (buf, 0, packet.getLength() /*- 1*/);

        return s;

    }

    /**

     * Method: writePacket()

     * Purpose: write a message to the last client that sent us a message,

     * while dropping every n-th message, as specified by the client.

     */

    public static boolean writePacket (String msg)

    {

        if (sendCount == dropEvery && !msg.equals("QUIT"))

        {

            System.out.println ("Dropped a packet");

            sendCount = 0; // reset the sendCount

            return true;   // "Fake" send

        }

        else { sendCount++; }

        InetAddress address = packet.getAddress();

        int port = packet.getPort();

        byte[] buf = msg.getBytes();

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

        try {

            socket.send (packet);

        } catch (IOException e) {

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

            e.printStackTrace();

            return false;

        }

        return true;

    }

    /**

     * Method: calcDrops()

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

     * every n-th message.

     */

    public static int calcDrops (String s)

    {

        String dropRegex = "^DROP(\\d*)(.*)$";

        Pattern p = Pattern.compile(dropRegex);

        Matcher m = p.matcher(s);

        if (m.matches())

            return Integer.parseInt(m.group(1));

        return -1;

    }

    /**

     * 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;

        socket = new DatagramSocket(portNumber);

        packet = null;

        String s;

        // Try to get a "timeout info" packet

        while (!done)

        {

            s = readPacket (8);

            dropEvery = calcDrops(s);

            if (dropEvery != -1)

            {

                done = true;

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

            }

            writePacket (s);

        }

        done = false;

        // Keep reading until we get a quit packet

        while (!done)

        {

            s = readPacket (5);

            // Check and see if we got a quit message

            if (s.equals("QUIT"))

            {

                done = true;

                writePacket(s);

                continue;

            }

            try {

                s = P2_EncDec.convert4B (s);

            } catch (IllegalArgumentException e) {

                System.out.println ("Recieved a bad packet");

                s = "BADVAL";

            }

            writePacket (s);

        }

        // Close the socket

        socket.close();

    }

}