class Net::POP3Command

def uidl(num = nil)
  if num
    res = check_response(critical { get_response('UIDL %d', num) })
    return res.split(/ /)[1]
  else
    critical {
      getok('UIDL')
      table = {}
      @socket.each_list_item do |line|
        num, uid = line.split(' ')
        table[num.to_i] = uid
      end
      return table
    }
  end
end