Based on a list of IP ranges and country (format: "<from> <to> <country>", look up where an IP is located.

ip_locator.rb

class IPLocator
  attr_accessor :ranges
  
  def initialize(filename)
    self.ranges = []
    
    File.open(filename).each do |line|
      if not line.start_with? '#'
        start, stop, country = line.split
        self.ranges << IPRange.new(start.to_i, stop.to_i, country)
      end
    end
  end
  
  def lookup(ip, fallback = 'ZZ')
    ipn = ip.is_a?(String) ? self.class.parse_ip(ip) : ip.to_i
    index = self.class.bisect_right(self.ranges, IPRange.new(ipn, nil, nil)) - 1
    range = self.ranges[index]
    range && range.includes?(ipn) ? range.country.gsub(/ZZ/, fallback) : nil
  rescue => ex
    Airbrake.notify(ex)
    nil
  end  
  
  def self.parse_ip(ip)
    ip.split('.').collect(&:to_i).inject { |memo,x| x + (memo << 8) }
  end
  
  def self.bisect_right(a, x)
    lo, hi = 0, a.size

    while lo < hi
      mid = (lo+hi) / 2
      if x < a[mid]
        hi = mid
      else
        lo = mid + 1
      end
    end
    
    return lo
  end
  
  class IPRange
    include Comparable
    attr_accessor :start, :stop, :country

    def initialize(start, stop, country)
      self.start = start
      self.stop = stop
      self.country = country
    end

    def <=>(another)
      self.start <=> another.start
    end
    
    def includes?(ip)
      ip.between?(self.start, self.stop)
    end
  end
end