fix: Catch sync/async* exceptions in interceptor's handlers

dio/CHANGELOG.md

@@ -6,6 +6,7 @@ See the [Migration Guide][] for the complete breaking changes list.**
 ## Unreleased
 
 - Fix `receiveTimeout` throws exception after the request has been cancelled.
+- Catch sync/async exceptions in interceptors' handlers.
 
 ## 5.4.1
 

dio/lib/src/dio_mixin.dart

@@ -375,40 +375,45 @@ abstract class DioMixin implements Dio {
     // Convert the request interceptor to a functional callback in which
     // we can handle the return value of interceptor callback.
     FutureOr Function(dynamic) requestInterceptorWrapper(
-      InterceptorSendCallback interceptor,
+      InterceptorSendCallback cb,
     ) {
       return (dynamic incomingState) async {
         final state = incomingState as InterceptorState;
         if (state.type == InterceptorResultType.next) {
           return listenCancelForAsyncTask(
             requestOptions.cancelToken,
-            Future(() {
-              final requestHandler = RequestInterceptorHandler();
-              interceptor(state.data as RequestOptions, requestHandler);
-              return requestHandler.future;
+            Future(() async {
+              final handler = RequestInterceptorHandler();
+              final callback = cb(state.data as RequestOptions, handler);
+              if (callback is Future) {
+                await callback;
+              }
+              return handler.future;
             }),
           );
-        } else {
-          return state;
         }
+        return state;
       };
     }
 
     // Convert the response interceptor to a functional callback in which
     // we can handle the return value of interceptor callback.
     FutureOr<dynamic> Function(dynamic) responseInterceptorWrapper(
-      InterceptorSuccessCallback interceptor,
+      InterceptorSuccessCallback cb,
     ) {
       return (dynamic incomingState) async {
         final state = incomingState as InterceptorState;
         if (state.type == InterceptorResultType.next ||
             state.type == InterceptorResultType.resolveCallFollowing) {
           return listenCancelForAsyncTask(
             requestOptions.cancelToken,
-            Future(() {
-              final responseHandler = ResponseInterceptorHandler();
-              interceptor(state.data as Response, responseHandler);
-              return responseHandler.future;
+            Future(() async {
+              final handler = ResponseInterceptorHandler();
+              final callback = cb(state.data as Response, handler);
+              if (callback is Future) {
+                await callback;
+              }
+              return handler.future;
             }),
           );
         } else {
@@ -420,32 +425,35 @@ abstract class DioMixin implements Dio {
     // Convert the error interceptor to a functional callback in which
     // we can handle the return value of interceptor callback.
     FutureOr<dynamic> Function(Object) errorInterceptorWrapper(
-      InterceptorErrorCallback interceptor,
+      InterceptorErrorCallback cb,
     ) {
       return (error) {
         final state = error is InterceptorState
             ? error
             : InterceptorState(assureDioException(error, requestOptions));
         Future<InterceptorState> handleError() async {
-          final errorHandler = ErrorInterceptorHandler();
-          interceptor(state.data, errorHandler);
-          return errorHandler.future;
+          final handler = ErrorInterceptorHandler();
+          final callback = cb(state.data, handler);
+          if (callback is Future) {
+            await callback;
+          }
+          return handler.future;
         }
 
         // The request has already been cancelled,
         // there is no need to listen for another cancellation.
         if (state.data is DioException &&
             state.data.type == DioExceptionType.cancel) {
           return handleError();
-        } else if (state.type == InterceptorResultType.next ||
+        }
+        if (state.type == InterceptorResultType.next ||
             state.type == InterceptorResultType.rejectCallFollowing) {
           return listenCancelForAsyncTask(
             requestOptions.cancelToken,
             Future(handleError),
           );
-        } else {
-          throw error;
         }
+        throw error;
       };
     }
 
@@ -495,20 +503,21 @@ abstract class DioMixin implements Dio {
       future = future.catchError(errorInterceptorWrapper(fun));
     }
     // Normalize errors, converts errors to [DioException].
-    return future.then<Response<T>>((data) {
+    try {
+      final data = await future;
       return assureResponse<T>(
         data is InterceptorState ? data.data : data,
         requestOptions,
       );
-    }).catchError((Object e) {
+    } catch (e) {
       final isState = e is InterceptorState;
       if (isState) {
         if (e.type == InterceptorResultType.resolve) {
           return assureResponse<T>(e.data, requestOptions);
         }
       }
       throw assureDioException(isState ? e.data : e, requestOptions);
-    });
+    }
   }
 
   Future<Response<dynamic>> _dispatchRequest<T>(RequestOptions reqOpt) async {

dio/lib/src/interceptor.dart

@@ -207,19 +207,19 @@ class Interceptor {
 }
 
 /// The signature of [Interceptor.onRequest].
-typedef InterceptorSendCallback = void Function(
+typedef InterceptorSendCallback = FutureOr<void> Function(
   RequestOptions options,
   RequestInterceptorHandler handler,
 );
 
 /// The signature of [Interceptor.onResponse].
-typedef InterceptorSuccessCallback = void Function(
+typedef InterceptorSuccessCallback = FutureOr<void> Function(
   Response<dynamic> response,
   ResponseInterceptorHandler handler,
 );
 
 /// The signature of [Interceptor.onError].
-typedef InterceptorErrorCallback = void Function(
+typedef InterceptorErrorCallback = FutureOr<void> Function(
   DioException error,
   ErrorInterceptorHandler handler,
 );

dio/test/interceptor_test.dart

@@ -318,6 +318,31 @@ void main() {
       expect(response.data['errCode'], 0);
     });
 
+    test('Caught exceptions before handler called', () async {
+      final dio = Dio();
+      const errorMsg = 'interceptor error';
+      dio.interceptors.add(
+        InterceptorsWrapper(
+          // TODO(EVERYONE): Remove the ignorance once we migrated to a higher version of Dart.
+          // ignore: void_checks
+          onRequest: (response, handler) {
+            throw UnsupportedError(errorMsg);
+          },
+        ),
+      );
+      expect(
+        dio.get('https://www.cloudflare.com'),
+        throwsA(
+          isA<DioException>().having(
+            (dioException) => dioException.error,
+            'Exception',
+            isA<UnsupportedError>()
+                .having((e) => e.message, 'message', errorMsg),
+          ),
+        ),
+      );
+    });
+
     group(ImplyContentTypeInterceptor, () {
       Dio createDio() {
         final dio = Dio();