play dns with ruby

dns.rb

#!/usr/bin/env ruby

# Copyright (c) 2009 Samuel Williams. Released under the GNU GPLv3.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

require 'rexec'
require 'rexec/daemon'
require 'rubydns'

# Run as user "daemon"
RUN_AS = "daemon"

# We need to be root in order to bind to privileged port
if RExec.current_user != "root"
  $stderr.puts "Sorry, this command needs to be run as root!"
  exit 1
end

# Helper
Name = Resolv::DNS::Name
IN = Resolv::DNS::Resource::IN

LAB = "xxx.xxx.xxx.xxx"
NET = "yyy.yyy.yyy.yyy"

# The Daemon itself
class DNSServer < RExec::Daemon::Base
  @@var_directory = '/var/'

  def self.run
    # Don't buffer output (for debug purposes)
    $stderr.sync = true

    # Use upstream DNS for name resolution
    $LAB = Resolv::DNS.new(:nameserver => LAB)
    $NET = Resolv::DNS.new(:nameserver => NET)

    # Start the RubyDNS server
    RubyDNS::run_server do
      on(:start) do
        RExec.change_user(RUN_AS)
        logger.level = Logger::INFO
      end
      
      match(/sip\.xxx\.com$/, IN::A) do |match, transaction|
        logger.info "#{match} go through lab"
        transaction.passthrough!($LAB)
      end

      match(/^*\.xxx\.net$/, IN::A) do |match, transaction|
        logger.info "#{match} go through lab"
        transaction.passthrough!($LAB)
      end

      match(/^*\.xxx\..*$/, IN::A) do |match, transaction|
        logger.info "#{match} go through net"
        transaction.passthrough!($NET)
      end

      # Default DNS handler
      otherwise do |transaction|
        logger.info 'go through default'
        transaction.passthrough!($LAB)
      end
    end
  end
end

# RExec daemon runner
DNSServer.daemonize