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/*******************************************************************************
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 * File: DHCPTable.java
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 * Author: Ira W. Snyder (devel@irasnyder.com)
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 * License: GNU General Public License v2
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 * Class: CS380 - Computer Networking
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 *
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 * Assignment: Project #3
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 * Date Last Modified: 2006-02-15
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 *
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 * Purpose: Implement a DHCPTable, which will give out addresses in the range
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 * 134.71.24.1 - 134.71.24.100. It always gives out the lowest available
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 * address in the range. Addresses time out after 8 seconds.
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 ******************************************************************************/
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import java.util.Date;
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public class DHCPTable
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{
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    /* Instance Variables */
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    private DHCPTableEntry[] table = new DHCPTableEntry[100];
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    private IPAddr lowestIP = new IPAddr("134.71.24.1");
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    private IPAddr highestIP = new IPAddr("134.71.24.100");
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    private long timeoutMS = 8000; // 8000 millisec by default
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    /**
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     * Method: DHCPTable constructor
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     * Purpose: Construct a DHCPTable entry
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     */
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    public DHCPTable ()
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    {
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        int i;
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        final String startStr = "134.71.24.";
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        IPAddr ip = null;
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        // Add every possible IP Address to the table
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        for (i=1; i<=table.length; i++)
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        {
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            ip = new IPAddr (startStr + i);
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            table[i-1] = new DHCPTableEntry("", ip, 0);
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        }
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    }
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    /**
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     * Method: getFirstFreeEntry
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     * Purpose: Get the first free entry in the table
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     */
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    private DHCPTableEntry getFirstFreeEntry ()
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    {
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        int i = 0;
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        // Simple sequential search for an empty entry
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        for (i=0; i<table.length; i++)
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            if (table[i].getLeaseStart() == 0)
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                return table[i];
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        throw new ArrayIndexOutOfBoundsException();
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    }
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    /**
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     * Method: addEntry
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     * Purpose: Add an entry to the table for a given Hardware Address.
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     * This returns the table entry, so that all of it's information can be used.
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     */
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    public DHCPTableEntry addEntry (String HWAddr)
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    {
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        long curTime = new Date().getTime();
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        DHCPTableEntry e = getFirstFreeEntry();
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        e.setHWAddr (HWAddr);
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        e.setLeaseStart (curTime);
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        return e;
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    }
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    /**
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     * Method: timeoutEntry
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     * Purpose: See if the entry for the given IP Address has timed out,
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     * return a copy of the entry if it has expired, or return null if we
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     * have not timed out yet.
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     */
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    public DHCPTableEntry timeoutEntry (IPAddr ip)
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    {
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        int i = ip.getField(3) - 1;
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        long curTime = new Date().getTime();
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        DHCPTableEntry e = null;
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        // Check if it has expired
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        if (curTime > (table[i].getLeaseStart() + timeoutMS))
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        {
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            // Make a copy of the object
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            e = new DHCPTableEntry (table[i].getHWAddr(),
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                                    table[i].getIPAddr(),
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                                    table[i].getLeaseStart());
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            table[i].setHWAddr ("");
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            table[i].setLeaseStart (0);
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            return e;
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        }
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        return null;
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    }
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}
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