erlang cowboy 404 onresponse_hook

gistfile1.erl

%% Hook for the above onresponse tests.
onresponse_hook(Status, Headers, Req) ->
  case Status of
    404 -> 
      {ok, Html} = file:read_file("www/404.html"),
      {ok, Req2} = cowboy_http_req:reply(404, [], Html, Req),
      Req2;
    _ ->
      Req
  end.


   cowboy:start_listener(http, 100, 
      cowboy_tcp_transport, [{port, config(http_port)}],
      cowboy_http_protocol, [
                              {dispatch, Dispatch},
                              {onresponse, fun onresponse_hook/3}
                            ]
                         ), ok.