anchor.diff:    case call(Req, State, timeout, Backend) of
       no_call ->
         next(Req, State, fun open_connection/2);
  +    ?HANDLE_ERROR(State);
       {Timeout, Req2, HandlerState} ->
         State2 = State#state{handler_state = HandlerState,
                              timeout = Timeout},
  
positive.code:   case call(Req, State, res_headers, ResHeaders) of
      no_call ->
        next(Req, State, fun reply/2);
      {FilteredHeaders, Req2, HandlerState} ->
        next(Req2, State#state{handler_state = HandlerState,
                               res_headers = FilteredHeaders}, fun reply/2)
  
negative.code:   case call(Req, State, forwarded_header_prefix) of
      no_call ->
        next(Req, State, fun request_id/2);
      ?HANDLE_ERROR(State);
      {{_, _, _, _} = Headers, Req2, HandlerState} ->
        ForwardedHeaders = format_forwarded_headers(Req, Headers),
        State2 = State#state{handler_state = HandlerState,
  