🥅 Throw if cancelled before established (#2251)

#2207

dio/CHANGELOG.md

@@ -12,6 +12,8 @@ See the [Migration Guide][] for the complete breaking changes list.**
 - Split the Web implementation to `package:dio_web_adapter`.
 - Add FusedTransformer for improved performance when decoding JSON.
 - Improves `InterceptorState.toString()`.
+- If the `CancelToken` got canceled before making requests,
+  throws the exception directly rather than cut actual HTTP requests afterward.
 
 ## 5.4.3+1
 

dio/lib/src/dio_mixin.dart

@@ -337,7 +337,11 @@ abstract class DioMixin implements Dio {
     Options? options,
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
-  }) {
+  }) async {
+    if (cancelToken != null && cancelToken.isCancelled) {
+      throw cancelToken.cancelError!;
+    }
+
     final requestOptions = (options ?? Options()).compose(
       this.options,
       path,

dio/test/cancel_token_test.dart

@@ -87,5 +87,29 @@ void main() {
         verify(request.abort()).called(1);
       }
     });
+
+    test('throws if cancelled before making requests', () async {
+      final cancelToken = CancelToken();
+
+      bool walkThroughHandlers = false;
+      final interceptor = QueuedInterceptorsWrapper(
+        onRequest: (options, handler) {
+          walkThroughHandlers = true;
+          handler.next(options);
+        },
+      );
+
+      cancelToken.cancel();
+      final dio = Dio();
+      dio.interceptors.add(interceptor);
+      await expectLater(
+        () => dio.get('/test', cancelToken: cancelToken),
+        throwsDioException(
+          DioExceptionType.cancel,
+          matcher: isA<DioException>(),
+        ),
+      );
+      expect(walkThroughHandlers, isFalse);
+    });
   });
 }