anchor.diff:  init_tracer(StreamID, Req, Opts=#{tracer_match_specs := List, tracer_callback := _}) ->
   	case match(List, StreamID, Req, Opts) of
   		false ->
  -			no_tracing;
  +			ok;
   		true ->
   			start_tracer(StreamID, Req, Opts)
   	end;
   %% When the options tracer_match_specs or tracer_callback
   %% are not provided we do not enable tracing.
   init_tracer(_, _, _) ->
  -	no_tracing.
  +	ok.
   
   match([], _, _, _) ->
   	true;
  
positive.code: -spec init(cowboy_stream:streamid(), cowboy_req:req(), cowboy:opts())
  	-> {cowboy_stream:commands(), any()}.
  init(StreamID, Req, Opts) ->
  	Result = init_tracer(StreamID, Req, Opts),
  	{Commands, Next} = cowboy_stream:init(StreamID, Req, Opts),
  	case Result of
  		no_tracing -> {Commands, Next};
  		{tracing, TracerPid} -> {[{spawn, TracerPid, 5000}|Commands], Next}
  	end.
  
  -spec data(cowboy_stream:streamid(), cowboy_stream:fin(), cowboy_req:resp_body(), State)
  	-> {cowboy_stream:commands(), State} when State::any().
  
negative.code: 				send, 'receive', call, return_to, procs, ports,
  				monotonic_timestamp, set_on_spawn, {tracer, TracerPid}
  			]),
  			ok;
  		_ ->
  			ok
  	end.
  
  %% Tracer process.
  