How to call logout in API service class when API throws 401 error - flutter

Question

I am working with flutter bloc in my project which is working great.
I have an API service class which uses Dio for making API requests. I am using an Interceptors for handling error. What I am trying to achieve is whenever API throws 401 error I want to logout the user and show login page. I will also be invalidating the token.
So my question is,
If I want to logout the user as soon as 401 occur ie. from API service class do I call logout event which is defined in the Authentication Bloc. To do so I will have to have instance of Authentication Bloc in API Service class. Is this approach correct? or is there any other simpler ways to achieve this.
class APIService{
...
onError: (DioError error, handler) async {
if (error.response?.statusCode == 401){
//invalidate the token
//Do I call the logout event of authentication bloc here?
}
}
...
}

Answer 1

You can do it, but this is not correct way.
You should handle errors somewhere above in interactors or blocks. There are quite a few ways to implement this. For example, you can use base loading block, something like this:
abstract class LoadingBloc<Event, T> extends Bloc<Event, LoadingState<T>> {
LoadingBloc([LoadingState<T>? state, this.authBloc])
: super(state ?? const LoadingInitialState());
T? get result => state.as<LoadingCompleteState<T>>()?.result;
final AuthenticationBloc? authBloc;
#protected
Future<void> load(
AsyncValueGetter<T> block,
Emitter<LoadingState<T>> emit,
) async {
assert(state is! LoadingProgressState);
emit(const LoadingProgressState());
try {
final result = await block();
if (!isClosed) {
emit(LoadingCompleteState(result));
}
} catch (error, stackTrace) {
print(error);
print(stackTrace);
if (!isClosed) {
if (error is DioError && error.response?.statusCode == 401) {
authBloc.add(LogOutState(error));
} else {
emit(const LoadingErrorState(RawException()));
}
}
}
}
}
Example:
class FirstBloc extends LoadingBloc<FistBloctEvent, FistBloctState>{
FirstBloc(Authentication authBlock):super(authBlock);
}
class SecondBloc extends LoadingBloc<SecondBloctEvent, SecondBloctState>{
SecondBloc(Authentication authBlock):super(authBlock);
}
States for your blocs:
#immutable
abstract class LoadingState<T> extends Equatable {
const LoadingState();
#override
List<Object?> get props => const [];
}
class LoadingInitialState<T> extends LoadingState<T> {
const LoadingInitialState();
}
class LoadingCompleteState<T> extends LoadingState<T> {
final T result;
const LoadingCompleteState(this.result);
#override
List<Object?> get props => [result];
}
class LoadingErrorState<T> extends LoadingState<T> {
final Exception error;
const LoadingErrorState(this.error);
#override
List<Object?> get props => [error];
}
As an option also, if you are using interceptors you could use wrapper, where you will override methods onRequest(..), onError(..):
class RequestHandler extends QueuedInterceptorsWrapper {
final Dio _dio;
RequestHandler({
required Dio dio,
required this.networkBlockRepository,
}) : _dio = dio {
_dio.interceptors.add(this);
}
void close() {
_dio.interceptors.remove(this);
_citySubscription?.cancel();
}
#override
Future<void> onRequest(..) ...
#override
Future<void> onError(..) ...
}