A request with an interceptor, which produces an error, makes the code stuck.

[yehorh]

Package

dio

Version

5.4.1

Operating-System

Android

Output of flutter doctor -v

flutter doctor -v
[✓] Flutter (Channel stable, 3.19.3, on macOS 14.4 23E214 darwin-arm64, locale en-UA)
    • Flutter version 3.19.3 on channel stable at /Users/yehorh/opt/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision ba39319843 (6 days ago), 2024-03-07 15:22:21 -0600
    • Engine revision 2e4ba9c6fb
    • Dart version 3.3.1
    • DevTools version 2.31.1

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0-rc1)
    • Android SDK at /Users/yehorh/Library/Android/sdk
    • Platform android-34, build-tools 34.0.0-rc1
    • Java binary at: /Users/yehorh/Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15E204a
    • CocoaPods version 1.14.3

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.2)
    • Android Studio at /Users/yehorh/Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] IntelliJ IDEA Ultimate Edition (version 2023.3.5)
    • IntelliJ at /Users/yehorh/Applications/IntelliJ IDEA Ultimate.app
    • Flutter plugin version 78.3.1
    • Dart plugin version 233.14888

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (4 available)            
    • sdk gphone64 arm64 (mobile) • emulator-5554             • android-arm64  • Android 13 (API 33) (emulator)
    • yiPhone (mobile)            • 00008101-000E28880AD2001E • ios            • iOS 17.4 21E219
    • macOS (desktop)             • macos                     • darwin-arm64   • macOS 14.4 23E214 darwin-arm64
    • Chrome (web)                • chrome                    • web-javascript • Google Chrome 122.0.6261.128

[✓] Network resources
    • All expected network resources are available.

• No issues found!

Dart Version

3.3.1

Steps to Reproduce

Here is a minimal example; I can't understand why the error isn't caught in any way, and everything that follows the request never executes.

tried on Android and macOS

import 'package:dio/dio.dart';

Future<void> main() async {
  final dio = Dio();

  dio.interceptors.add(InterceptorWithError());

  try {
    final response = await dio.get('https://google.com');
  } catch (e, st) {
    print('Unreachable code');
  }

  print('Unreachable code too');
}

class InterceptorWithError extends Interceptor {
  @override
  Future<void> onRequest(
    RequestOptions options,
    RequestInterceptorHandler handler,
  ) async {
    throw Exception('some error');
    return handler.next(options);
  }

  @override
  Future<void> onResponse(
    Response response,
    ResponseInterceptorHandler handler,
  ) async {
    handler.next(response);
  }

  @override
  Future<void> onError(
    DioException err,
    ErrorInterceptorHandler handler,
  ) async {
    handler.next(err);
  }
}

Expected Result

Errors from broken requests must be caught.

Actual Result

The program stops when executing a request, and the subsequent code becomes unreachable.

[yehorh]

It seems I have broken the interface contract.
I have overridden synchronous functions with asynchronous functions.

The override_on_non_overriding_member lint hasn't helped me this time.

[khamidjon]

the same problem is happening with our project too.

[sdgroot]

We're currently experiencing the same issue using the following interactor to refresh an access token and retry the request, using Dio v5.4.3+1. The request never finishes executing and no exceptions are caught in the try/catch block.

try {
  final body = {...};
  final options = Options(extra: {'authenticated': true}, validateStatus: (status) => status == 200);
  final response = await _dio.post('...', data: body, options: options);
  // We never get here
} on DioException catch (error, trace) {
  // We never get here
}

class AuthInterceptor extends Interceptor {
  final Dio _dio;
  final Future<String?> Function() _getAccessToken;

  AuthInterceptor({
    required Dio dio,
    required Future<String?> Function() getAccessToken,
  })  : _dio = dio,
        _getAccessToken = getAccessToken;

  @override
  Future<void> onRequest(RequestOptions options, RequestInterceptorHandler handler) async {
    // If the request is not authenticated, continue without adding the Authorization header
    if (options.extra['authenticated'] == false) {
      return handler.next(options);
    }

    // Try to retrieve a valid (non-expired) access token for the Authorization header.
    // If no token could be retrieved, we don't add the header.
    final String? accessToken = await _getAccessToken();
    if (accessToken != null) {
      options.headers['Authorization'] = 'Bearer $accessToken';
    }

    // Continue request
    return handler.next(options);
  }

  @override
  FutureOr<void> onError(DioException error, ErrorInterceptorHandler handler) async {
    final Response? response = error.response;

    // We're only interested in handling the 401 header here. Let other errors pass through.
    if (response == null || response.statusCode != 401) {
      return handler.next(error);
    }

    final RequestOptions options = response.requestOptions;

    // If the request was already retried we back off and let the error pass through.
    if (options.extra['retried'] == true) {
      return handler.next(error); // also tried handler.reject(error) with same result
    }

    // Add flag to indicate that we retried the request, to prevent infinite retries.
    options.extra['retried'] = true;

    // Retry the request. A refresh token will be added to the request in the [onRequest]
    // handler, when available.
    return handler.resolve(await _dio.fetch(options));
  }
}

[romandrahan]

@sdgroot

is this part from your code using the same _dio instance as the main app thread (final response = await _dio.post('...', data: body, options: options);?

// Retry the request. A refresh token will be added to the request in the [onRequest]
// handler, when available.
return handler.resolve(await _dio.fetch(options));

for token interceptors it's better to use QueuedInterceptor and separate Dio instance which do retries, see https://github.com/cfug/dio/blob/main/example/lib/queued_interceptor_crsftoken.dart