trusted_proxy_regexp_creator.rb

#!/usr/bin/env ruby

require 'ipaddr'

# Creates a regexp of trusted IP addresses to be used by Rails'
# ActionController::Request::TRUSTED_PROXIES.
#
class TrustedProxyRegexpCreator
  OCTET = '\d{1,3}'
  EDGECAST_IP_FORMAT = /#{OCTET}\.#{OCTET}\.#{OCTET}\.(\*|#{OCTET})/
  EDGECAST_RANGE_FORMAT = /#{EDGECAST_IP_FORMAT} - #{EDGECAST_IP_FORMAT}/

  def initialize(list)
    @ips = list.split("\n").inject([]) do |memo, line|
      case line
      when EDGECAST_RANGE_FORMAT
        expand(line).each { |ip| memo << ip }
        memo
      when EDGECAST_IP_FORMAT
        memo << sanitize(line)
      else
        raise ArgumentError, "Unsupported format: #{line.inspect}"
      end
    end
  end

  def create
    combine(@ips)
  end

  def self.create(list)
    new(list).create
  end

protected

  def sanitize(address)
    address.split('.').map { |octet| octet == '*' ? OCTET : octet }
  end

  def expand(range)
    low, high = range.split(' - ')
    (IPAddr.new(low)..IPAddr.new(high)).map { |ip| sanitize ip.to_s }
  end

  def concat(prefix, suffix)
    [prefix, suffix].compact.join('\.')
  end

  def block(elements)
    elements.one? ? elements.first : "(?:#{elements.join('|')})"
  end

  def suffixable?(elements)
    elements.all? { |octets| octets.size == 2 } && elements.group_by(&:last).one?
  end

  def suffix(elements)
    elements.group_by(&:last).map do |group, octets|
      concat(block(octets.map(&:first)), group)
    end
  end

  def combine(addresses)
    groups = if addresses.all?(&:one?)
      addresses
    else
      addresses.group_by(&:first).map do |group, parts|
        parts = parts.map { |octetes| octetes[1..-1] }

        # shortcut, edgecast blocks can be mainly grouped by the third octet
        concat(group, suffixable?(parts) ? block(suffix(parts)) : combine(parts))
      end
    end

    block(groups)
  end
end

if __FILE__ == $0
  begin
    puts TrustedProxyRegexpCreator.create($stdin.read)
  rescue ArgumentError => error
    $stderr.puts error.message
    exit 1
  end
end