Rails - Apr 2006 - Netmask validator

Sharing the wealth. I just finished working on a custom netmask  
validator and thought others might benefit. Of course, comments and  
suggestions are welcome.

def validates_netmask(*attr_names)
  configuration = { :only_numbers => ''must only use numbers as octet
values'',
                    :range => ''has one or more octet values that are
> 255'',
                    :invalid => ''is invalid'' }
  configuration.update(attr_names.pop) if attr_names.last.is_a?(Hash)

  validates_each attr_names do |record, attr_name, value|
    # Test for non-numeric values
    record.errors.add(attr_name, configuration[:only_numbers]) unless  
value.tr(''.'', '''') =~ /^\d+$/

    # Make binary string from octets
    binary = ''''
    value.split(''.'').each do |octet|
      binary << ''%08b'' % octet
    end

    # Test for octet values > 255
    record.errors.add(attr_name, configuration[:range]) if binary.length > 32

    # Test for valid netmask (contiguous binary string of 1''s)
    record.errors.add(attr_name, configuration[:invalid]) if  
binary.include? ''01''
  end
end

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