require 'socket'
require 'ipaddr'

class Multicast
  
  # listen for multicast messages
  # call block when recive any
  #
  # passes 2 elemnts to block, message, info
  # 
  # * MSG: #{msg} 
  # * from #{info[2]} 
  # * (#{info[3]})/#{info[1]} 
  # * length: #{msg.size}"
  def self.listen(address, port, &block)
    
    ip =  IPAddr.new(address).hton + IPAddr.new("0.0.0.0").hton

    sock = UDPSocket.new
    sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, ip)
    sock.bind(Socket::INADDR_ANY, port)

    loop do
      msg, info = sock.recvfrom(1024)
      block.call(msg, info)
    end
  end
  
  def self.propagate(ip,port, message)
    begin
      socket = UDPSocket.open
      socket.setsockopt(Socket::IPPROTO_IP, Socket::IP_TTL, [1].pack('i'))
      socket.send(message, 0, ip, port)
    ensure
      socket.close 
    end
  end
end