port_forwarding.rb

#!/usr/bin/ruby -w

require 'socket'

server = TCPServer.open(7788)
loop do
  Thread.start(server.accept) do |client|
    remote = TCPSocket.open("bbs.csie.ntnu.edu.tw", 23)
    Thread.start do
      while s = remote.getc do
        client.write s.chr
      end
    end
    Thread.start do
      while s = client.getc do
        remote.write s.chr
      end
    end
  end
end