anchor.diff:  
   get_transport(#transport{rcv_pid = Pid}) ->
       gen_server:call(Pid, get_transport).
  +
  +set_filter(#transport{rcv_pid = Pid}, Filter) ->
  +    gen_server:call(Pid, {set_filter, Filter}).
   
   %%%===================================================================
   %%% gen_server callbacks
  
positive.code:          use_zlib/2,
           get_transport/1,
           reset_parser/1,
           stop/1]).
  
  %% gen_server callbacks
  -export([init/1,
  
negative.code:     {ok, NewParser} = exml_stream:reset_parser(Parser),
      {reply, Socket, State#state{parser = NewParser,
                                  compress = {zlib, {Zin,Zout}}}};
  handle_call({set_filter, Filter}, _From, #state{} = S) ->
      {reply, ok, S#state{filter = Filter}};
  handle_call(stop, _From, #state{socket = Socket, ssl = Ssl,
                                  compress = Compress} = State) ->
      StreamEnd = escalus_stanza:stream_end(),
  