anchor.diff:      {ok, ResReq} =
           case xprof_tracer_handler:capture_stop(MFA) of
               ok ->
  -                cowboy_req:reply(204, Req);
  +                cowboy_req:reply(204, ?HDR_NO_CONTENT, Req);
               {error, not_found} ->
                   cowboy_req:reply(404, Req)
           end,
  
positive.code:     {ok, ResReq} = case lists:member(Spec, [<<"all">>, <<"pause">>]) of
                         true ->
                             xprof_tracer:trace(list_to_atom(binary_to_list(Spec))),
                             cowboy_req:reply(204, Req);
                         false ->
                             lager:info("Wrong spec for tracing: ~p",[Spec]),
                             cowboy_req:reply(400, Req)
  
negative.code:     {ok, ResReq} =
          case xprof_tracer:monitor(Query) of
              ok ->
                  cowboy_req:reply(204, ?HDR_NO_CONTENT, Req);
              {error, already_traced} ->
                  cowboy_req:reply(204, ?HDR_NO_CONTENT, Req);
              _Error ->
                  cowboy_req:reply(400, Req)
          end,
  