anchor.diff:  cancel(Pid, Index, Offset, Len) ->
       forward_message(Pid, {cancel, Index, Offset, Len}).
   
  +
   %% @doc Send a REJECT message to the remote peer.
   %% @end
   -spec reject(pid(), integer(), integer(), integer()) -> ok.
  
positive.code: -spec choke(pid()) -> ok.
  choke(Pid) ->
      forward_message(Pid, choke).
  
  %% @doc UNCHOKE the peer.
  %% end
  
negative.code: request(Pid, {Index, Offset, Size}) ->
      forward_message(Pid, {request, {Index, Offset, Size}}).
  
  
  %% @doc send a PIECE message to the remote peer.
  %% @end
  -spec piece(pid(), integer(), integer(), integer(), binary()) -> ok.
  