require 'rev'

def resolve_name(query, success_callback=nil, fail_callback=nil, loop=nil)
  unless query.is_a?(String) && query.length > 0
    raise ArgumentError.new(
      "unexpected argument query (expected String of non-zero length)"
    )
  end
  unless loop.nil? || loop.is_a?(Rev::Loop)
    raise ArgumentError.new(
      "unexpected argument class '#{loop.class}' for loop (expected Nil" +
      " or Rev::Looop)"
    )
  end
  unless success_callback.nil? || success_callback.is_a?(Proc)
    raise ArgumentError.new(
      "unexpected argument class '#{success_callback.class}' for " +
      "success_callback (expected Nil or Proc)"
    )
  end
  unless fail_callback.nil? || fail_callback.is_a?(Proc)
    raise ArgumentError.new(
      "unexpected argument class '#{fail_callback.class}' for " +
      "fail_callback (expected Nil or Proc)"
    )
  end
  aloop = loop.nil? ? Rev::Loop.new() : loop
  answer = nil
  onsuccess = success_callback.nil?     ?
    lambda { |result| answer = result } :
    success_callback
  onfail    = fail_callback.nil? ?
    lambda { onsuccess.(nil)   } :
    fail_callback
  Class.new(Rev::DNSResolver) do
    def initialize(query, on_success, on_fail)
      @on_success = on_success
      @on_fail    = on_fail
      super(query)
    end
    def on_fail
      return @on_fail.nil? ? nil : @on_fail.()
    end
    def on_success(result)
      if @on_success.nil?
        return result
      else
        return @on_success.(result)
      end
    end
  end.new(query, onsuccess, onfail).attach(aloop)
  aloop.run if loop.nil?
  return answer
end

loop = Rev::Loop.new()
def rq(query, loop)
  resolve_name(
    query,
    lambda {|result|
      if result.nil?
        print "'#{query} failed to resolve.\n"
      else
        print "'#{query} resolves to '#{result}'\n"
      end
    },
    nil,
    loop
  )
end
ARGV.each do |query|
  rq(query, loop)
  if query =~ /^\d+\.\d+\.\d+\.\d+$/
    rq(query.split(/\./).reverse.join('.') + '.in-addr.arpa', loop)
  end
end

loop.run

$ ./x.rb www.google.com www.infowest.com \
 www.eq.net hatrack.com eq.net fooaasdvwedf.df \
 127.0.0.1 204.17.177.10
'www.google.com resolves to '74.125.155.103'
'127.0.0.1 resolves to '127.0.0.1'
'www.infowest.com resolves to '204.17.177.250'
'www.eq.net resolves to '69.46.228.43'
'hatrack.com resolves to '66.223.20.195'
'eq.net resolves to '69.46.226.134'
'1.0.0.127.in-addr.arpa failed to resolve.
'204.17.177.10 resolves to '204.17.177.10'
'10.177.17.204.in-addr.arpa failed to resolve.
'fooaasdvwedf.df failed to resolve.