anchor.diff:      back_process/1,
       front_process/3,
       forward/3,
  +    forward/4,
   
       heart/0
   ]).
  
positive.code:     gen_tcp:send(Client, flip(Data)).
  
  forward(Client, Remote, From) ->
      try
          {ok, Packet} = gen_tcp:recv(Client, 0),
          ok = flip_send(Remote, Packet)
      catch
          Error:Reason ->
              From ! {close},
              exit({Error, Reason})
      end,
      forward(Client, Remote, From).
  
  heart() ->
      timer:sleep(10000),
  
negative.code:                 try
                      flip_send(Back, Endpoint),
  
                      spawn(?MODULE, forward, [Client, Back, From, fun(_Args) ->
                                info ! {touch, {Back}}
                                end]),
                      spawn(?MODULE, forward, [Back, Client, From, fun(_Args) ->
                                info ! {touch, {Back}}
                      end]),
  
                      receive _ -> ok end
                  after
  