local_ip for rails' controller

local_ip.rb

module ::ActionController
  class Request
    unless method_defined?(:local_ip)
      require "socket"
      require "ipaddr"

      def local_ip
        f = Socket.do_not_reverse_lookup
        Socket.do_not_reverse_lookup = true
        ip = IPAddr.new(remote_ip)
        UDPSocket.open(ip.family) do |s|
          s.connect(ip.to_s, 1)
          IPAddr.new(s.addr.last).native.to_s
        end
      ensure
        Socket.do_not_reverse_lookup = f
      end
    end
  end
end

if __FILE__ == $0
  require "test/unit"

  class LocalIPTest < Test::Unit::TestCase
    def test_local_ip
      request = ::ActionController::TestRequest.new
      request.remote_addr = "127.0.0.1"
      assert_equal "127.0.0.1", request.local_ip
      request.remote_addr = "127.0.0.2"
      assert_equal "127.0.0.2", request.local_ip
      request.remote_addr = "::1"
      assert_equal "::1", request.local_ip
      request.remote_addr = "::ffff:127.0.0.1"
      assert_equal "127.0.0.1", request.local_ip
    end
  end
end