QueuedInterceptors strange behavior

[bustazone]

Package

dio

Version

5.9.0

Operating-System

iOS

Adapter

Default Dio

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! Doctor found issues in 1 category.

Dart Version

3.9.0

Steps to Reproduce

I've found a problem with the performance of the QueuedInterceptors.
I have a really complex interceptors distribution so it's easier to describe the problem with an example.
I'd like to clarify that maybe it's no a bug but a lack of clear documentation.

Let's see the case:

To start, I have 4 interceptors (I1, I2, I3, I4) and I passed it to dio with:
instance.interceptors.addAll([I1, I2, I3, I4]);
Each interceptor is a queued inteceptor (beaceause the order of execution is very important) and has different functionality in onResponse and onError.
So the Idea is to chain the Interceptors with the following order:

OutGoing: I1(onRequest) -> I2(onRequest) -> I3(onRequest) -> I4(onRequest)
Incoming: I4(onResponse|onError) -> I3(onResponse|onError) -> I2(onResponse|onError) -> I1(onResponse|onError)

The goal is that each interceptor get the state of the previous one, i.e.: if the onResponse function of I3 returns a handler.reject it has to be followed by the execution of the I2 onError function.

Here comes the problems:

• Actually the outgoing order is good I1(onRequest) -> I2(onRequest) -> I3(onRequest) -> I4(onRequest) but when the call incomes from network I see the same execution order (I1(onRequest) -> I2(onRequest) -> I3(onRequest) -> I4(onRequest)).
• The other problem is that when I execute a handler.reject the call returns an exception directly instead of execute the onError of the next Interceptor.

In order to clarify, that the dummy code for the test:

Test interceptor:

import 'package:dio/dio.dart';

class DioNetTestErrorInterceptor extends QueuedInterceptor {
  final String id;
  DioNetTestErrorInterceptor(this.id);

  @override
  void onRequest(
    RequestOptions options,
    RequestInterceptorHandler handler,
  ) async {
    print('[DioNetTestErrorInterceptor-$id] onRequest');
    return handler.next(options);
  }

  @override
  void onResponse(Response response, ResponseInterceptorHandler handler) async {
    print('[DioNetTestErrorInterceptor-$id] onResponse');

    if (id == '4') {
      final dioError = DioException(
        requestOptions: response.requestOptions,
        error: 'Fake error',
        type: DioExceptionType.badResponse,
        response: Response(
          requestOptions: response.requestOptions,
          statusCode: 500,
          data: {"code": 900, "message": "Fake error"},
        ),
      );
      return handler.reject(dioError);
    } else {
      return handler.next(response);
    }
  }

  @override
  void onError(DioException err, ErrorInterceptorHandler handler) {
    print('[DioNetTestErrorInterceptor-$id] onError');
    return handler.next(err);
  }
}

Dio instance creation:

Dio newInstance = Dio(options);
newInstance.interceptors.addAll([
	DioNetTestErrorInterceptor(1),
	DioNetTestErrorInterceptor(2),
	DioNetTestErrorInterceptor(3),
	DioNetTestErrorInterceptor(4),
])

Expected Result

Start Call
[DioNetTestErrorInterceptor-1] onRequest
[DioNetTestErrorInterceptor-2] onRequest
[DioNetTestErrorInterceptor-3] onRequest
[DioNetTestErrorInterceptor-4] onRequest
[DioNetTestErrorInterceptor-4] onResponse
[DioNetTestErrorInterceptor-3] onError
[DioNetTestErrorInterceptor-2] onError
[DioNetTestErrorInterceptor-1] onError
End Call

Actual Result

Start Call
[DioNetTestErrorInterceptor-1] onRequest
[DioNetTestErrorInterceptor-2] onRequest
[DioNetTestErrorInterceptor-3] onRequest
[DioNetTestErrorInterceptor-4] onRequest
[DioNetTestErrorInterceptor-1] onResponse
End Call

[AlexV525]

1. Queued interceptors are meant to be FIFO, so 1234 -> 4321 does not follow any of the regular sequences. Maybe you'll need to aggregate your interceptors as a chain externally.
2. There is no way to specify callFollowingErrorInterceptor when calling reject in an error interceptor. I'll look into it and see if we can expose the behavior or not.