Validate an IP Address (with Mask)

Question

I have ip addresses and a mask such as 10.1.1.1/32. I would like to check if 10.1.1.1 is inside that range. Is there a library or utility that would do

Answer 1

Here is a version that takes subnet descriptions in several common ways, including IPv6.

Based on the other code posted here. On IPv4 addresses it might work slower than the approach of performing binary operations on bare int's.

package de.c3oe.tryanderror;
import java.math.BigInteger;
import java.net.InetAddress;
import java.net.UnknownHostException;

/**
 * @author c3oe.de, based on snippets from Scott Plante, John Kugelmann
 */
public class Subnet
{
    final private int bytesSubnetCount;
    final private BigInteger bigMask;
    final private BigInteger bigSubnetMasked;

    /** For use via format "192.168.0.0/24" or "2001:db8:85a3:880:0:0:0:0/57" */
    public Subnet( final InetAddress subnetAddress, final int bits )
    {
        this.bytesSubnetCount = subnetAddress.getAddress().length; // 4 or 16
        this.bigMask = BigInteger.valueOf( -1 ).shiftLeft( this.bytesSubnetCount*8 - bits ); // mask = -1 << 32 - bits
        this.bigSubnetMasked = new BigInteger( subnetAddress.getAddress() ).and( this.bigMask );
    }

    /** For use via format "192.168.0.0/255.255.255.0" or single address */
    public Subnet( final InetAddress subnetAddress, final InetAddress mask )
    {
        this.bytesSubnetCount = subnetAddress.getAddress().length;
        this.bigMask = null == mask ? BigInteger.valueOf( -1 ) : new BigInteger( mask.getAddress() ); // no mask given case is handled here.
        this.bigSubnetMasked = new BigInteger( subnetAddress.getAddress() ).and( this.bigMask );
    }

    /**
     * Subnet factory method.
     * @param subnetMask format: "192.168.0.0/24" or "192.168.0.0/255.255.255.0"
     *      or single address or "2001:db8:85a3:880:0:0:0:0/57"
     * @return a new instance
     * @throws UnknownHostException thrown if unsupported subnet mask.
     */
    public static Subnet createInstance( final String subnetMask )
            throws UnknownHostException
    {
        final String[] stringArr = subnetMask.split("/");
        if ( 2 > stringArr.length )
            return new Subnet( InetAddress.getByName( stringArr[ 0 ] ), (InetAddress)null );
        else if ( stringArr[ 1 ].contains(".") || stringArr[ 1 ].contains(":") )
            return new Subnet( InetAddress.getByName( stringArr[ 0 ] ), InetAddress.getByName( stringArr[ 1 ] ) );
        else
            return new Subnet( InetAddress.getByName( stringArr[ 0 ] ), Integer.parseInt( stringArr[ 1 ] ) );
    }

    public boolean isInNet( final InetAddress address )
    {
        final byte[] bytesAddress = address.getAddress();
        if ( this.bytesSubnetCount != bytesAddress.length )
            return false;
        final BigInteger bigAddress = new BigInteger( bytesAddress );
        return  bigAddress.and( this.bigMask ).equals( this.bigSubnetMasked );
    }

    @Override
    final public boolean equals( Object obj )
    {
        if ( ! (obj instanceof Subnet) )
            return false;
        final Subnet other = (Subnet)obj;
        return  this.bigSubnetMasked.equals( other.bigSubnetMasked ) &&
                this.bigMask.equals( other.bigMask ) &&
                this.bytesSubnetCount == other.bytesSubnetCount;
    }

    @Override
    final public int hashCode()
    {
        return this.bytesSubnetCount;
    }

    @Override
    public String toString()
    {
        final StringBuilder buf = new StringBuilder();
        bigInteger2IpString( buf, this.bigSubnetMasked, this.bytesSubnetCount );
        buf.append( '/' );
        bigInteger2IpString( buf, this.bigMask, this.bytesSubnetCount );
        return buf.toString();
    }

    static private void bigInteger2IpString( final StringBuilder buf, final BigInteger bigInteger, final int displayBytes )
    {
        final boolean isIPv4 = 4 == displayBytes;
        byte[] bytes = bigInteger.toByteArray();
        int diffLen = displayBytes - bytes.length;
        final byte fillByte = 0 > (int)bytes[ 0 ] ? (byte)0xFF : (byte)0x00;

        int integer;
        for ( int i = 0; i < displayBytes; i++ )
        {
            if ( 0 < i && ! isIPv4 && i % 2 == 0 )
                buf.append( ':' );
            else if ( 0 < i && isIPv4 )
                buf.append( '.' );
            integer = 0xFF & (i < diffLen ? fillByte : bytes[ i - diffLen ]);
            if ( ! isIPv4 && 0x10 > integer )
                buf.append( '0' );
            buf.append( isIPv4 ? integer : Integer.toHexString( integer ) );
        }
    }
}