DioCacheInterceptor breaks error handling

[fischermario]

The onError handler of DioCacheInterceptor is not able to hand over error handling to the next interceptor in the pipeline. After the onError handler is finished an exception occurs that is not cought by the subsequent interceptor(s).

Please consider the following example:

late CacheOptions cacheOptions;
late CacheStore cacheStore;
Dio dio = Dio(BaseOptions(
  receiveTimeout: const Duration(milliseconds: 2000),
  connectTimeout: const Duration(milliseconds: 2000),
  sendTimeout: const Duration(milliseconds: 2000),
  receiveDataWhenStatusError: true,
));
getTemporaryDirectory().then((dir) async {
  cacheStore = FileCacheStore(dir.path);
  cacheOptions = CacheOptions(
    store: cacheStore,
    // We will use cache functionality on demand
    policy: CachePolicy.noCache,
  );
  dio.interceptors.addAll([
    DioCacheInterceptor(
      options: cacheOptions,
    ),
    InterceptorsWrapper(
      onError: (err, handler) {
        debugPrint('CAUGHT error: $err');
        handler.resolve(
          Response(
            requestOptions: err.requestOptions,
            statusCode: 500,
          ),
        );
      },
    ),
  ]);
  Response resp = await dio.get('https://httpbin.org/delay/10');
  debugPrint(resp.statusCode.toString());
}

Changing this line to

class DioCacheInterceptor extends QueuedInterceptor {

fixes this problem (I can create a PR if interested).

I have also informed the Dio project about this behavior here.

Is there a particular reason why you chose to extend "Interceptor" instead of "QueuedInterceptor"?

[llfbandit]

I don't use QueuedInterceptor because of concurrency concern. There's no need to stream each request because of this package.
That said, dio should follow interceptor chain setup...

[kuhnroyal]

Edit: Meant to post in the dio issue.