[dio] Test typed responses

dio/CHANGELOG.md

@@ -7,12 +7,14 @@ See the [Migration Guide][] for the complete breaking changes list.**
 
 - The minimum supported Dart version has been bumped from `2.15.0` to `2.19.0`.
 - Remove `DefaultHttpClientAdapter` which was deprecated in `5.0.0`.
-- Remove `IOHttpClientAdapter.onHttpClientCreate` which was deprecated in `5.2.0`
+- Remove `IOHttpClientAdapter.onHttpClientCreate` which was deprecated in `5.2.0`.
 - Remove `DioError` and `DioErrorType` which was deprecated in `5.2.0`.
 - Remove `DefaultTransformer` which was deprecated in `5.0.0`.
 - `IOHttpClientAdapter` no longer sets a custom `HttpClient.idleTimeout`. A custom `HttpClient` can be provided via
   `IOHttpClientAdapter.createHttpClient` if customisation is required.
-- Make use of Isolate.run for the BackgroundTransformer
+- Make use of `Isolate.run` in the BackgroundTransformer.
+- Respect nullability of generic type parameter in `dio`s request methods like `get<String()` vs `get<String?>()`.
+  Follow the [Migration Guide][] for more details.
 
 ## Unreleased
 

dio/doc/migration_guide.md

@@ -23,6 +23,29 @@ When new content need to be added to the migration guide, make sure they're foll
 - `IOHttpClientAdapter.onHttpClientCreate` which was deprecated in `5.2.0` has been removed - use `IOHttpClientAdapter.createHttpClient` instead.
 - `DioError` and `DioErrorType` which was deprecated in `5.2.0` has been removed - use `DioException` and `DioExceptionType` instead.
 - `DefaultTransformer` which was deprecated in `5.0.0` has been removed - use `BackgroundTransformer` instead.
+- The nullability of the generic type parameter in `dio`s request methods is now respected for the responses' `data`.
+
+> [!WARNING]
+> The migration depends on your use case and API responses.
+> If in doubt make the type nullable and correctly handle the null case.
+> DO NOT just delete the null checks if they are shown to be redundant, but think about the impact.
+
+Before:
+```dart
+Response<String?> response = await Dio().get<String>('https://example.com');
+String data = response.data!;
+```
+
+After:
+```dart
+Response<String> response = await Dio().get<String>('https://example.com');
+String data = response.data;
+```
+Or:
+```dart
+Response<String?> response = await Dio().get<String?>('https://example.com');
+String? data = response.data;
+```
 
 ## 5.0.0
 

dio/lib/src/dio/dio_for_native.dart

@@ -102,7 +102,7 @@ class DioForNative extends DioMixin implements Dio {
     int received = 0;
 
     // Stream<Uint8List>
-    final stream = response.data!.stream;
+    final stream = response.data.stream;
     bool compressed = false;
     int total = 0;
     final contentEncoding = response.headers.value(

dio/lib/src/dio_mixin.dart

@@ -525,6 +525,7 @@ abstract class DioMixin implements Dio {
       // Make sure headers and [ResponseBody.headers] are the same instance.
       responseBody.headers = headers.map;
       final ret = Response<dynamic>(
+        data: null,
         headers: headers,
         requestOptions: reqOpt,
         redirects: responseBody.redirects ?? [],
@@ -567,7 +568,6 @@ abstract class DioMixin implements Dio {
   }
 
   bool _isValidToken(String token) {
-    _checkNotNullable(token, 'token');
     // from https://www.rfc-editor.org/rfc/rfc2616#page-15
     //
     // CTL            = <any US-ASCII control character
@@ -714,7 +714,7 @@ abstract class DioMixin implements Dio {
         requestOptions: requestOptions,
       );
     } else if (response is! Response<T>) {
-      final T? data = response.data as T?;
+      final T data = response.data as T;
       final Headers headers;
       if (data is ResponseBody) {
         headers = Headers.fromMap(
@@ -739,22 +739,6 @@ abstract class DioMixin implements Dio {
   }
 }
 
-/// A null-check function for function parameters in Null Safety enabled code.
-///
-/// Because Dart does not have full null safety until all legacy code has been
-/// removed from a program, a non-nullable parameter can still end up with a
-/// `null` value. This function can be used to guard those functions against
-/// null arguments. It throws a [TypeError] because we are really seeing
-/// the failure to assign `null` to a non-nullable type.
-///
-/// See http://dartbug.com/40614 for context.
-T _checkNotNullable<T extends Object>(T value, String name) {
-  if ((value as dynamic) == null) {
-    throw NotNullableError<T>(name);
-  }
-  return value;
-}
-
 /// A [TypeError] thrown by [_checkNotNullable].
 class NotNullableError<T> extends Error implements TypeError {
   NotNullableError(this._name);

dio/lib/src/response.dart

@@ -11,7 +11,7 @@ import 'redirect_record.dart';
 /// in anytime, typically by [Interceptor] and [Transformer].
 class Response<T> {
   Response({
-    this.data,
+    required this.data,
     required this.requestOptions,
     this.statusCode,
     this.statusMessage,
@@ -27,7 +27,7 @@ class Response<T> {
   ///
   /// The content could have been transformed by the [Transformer]
   /// before it can use eventually.
-  T? data;
+  T data;
 
   /// The [RequestOptions] used for the corresponding request.
   RequestOptions requestOptions;

dio/test/options_test.dart

@@ -357,9 +357,9 @@ void main() {
     // Regression: https://github.com/cfug/dio/issues/1834
     final r11 = await dio.get('');
     expect(r11.data, '');
-    final r12 = await dio.get<Map>('');
+    final r12 = await dio.get<Map?>('');
     expect(r12.data, null);
-    final r13 = await dio.get<Map<String, Object>>('');
+    final r13 = await dio.get<Map<String, Object>?>('');
     expect(r13.data, null);
   });
 

dio/test/request_integration_test.dart

@@ -327,7 +327,7 @@ void main() {
         );
         expect(response.data, isA<List>());
         expect(response.data, isNotEmpty);
-        expect(response.data![0], 1);
+        expect(response.data[0], 1);
       });
     });
 

dio/test/timeout_test.dart

@@ -37,14 +37,16 @@ void main() {
           );
 
         dio.options.connectTimeout = Duration(milliseconds: 5);
-        await dio
-            .get('/')
-            .catchError((e) => Response(requestOptions: RequestOptions()));
+        await dio.get('/').catchError((e) => Response(
+              requestOptions: RequestOptions(),
+              data: null,
+            ));
         expect(client.connectionTimeout, dio.options.connectTimeout);
         dio.options.connectTimeout = Duration(milliseconds: 10);
-        await dio
-            .get('/')
-            .catchError((e) => Response(requestOptions: RequestOptions()));
+        await dio.get('/').catchError((e) => Response(
+              requestOptions: RequestOptions(),
+              data: null,
+            ));
         expect(client.connectionTimeout, dio.options.connectTimeout);
       }, testOn: 'vm');
     });

dio/test/utils.dart

@@ -112,6 +112,25 @@ Future<void> startServer() async {
         return;
       }
 
+      if (path == '/null-response') {
+        response.headers.contentType = ContentType('text', 'plain');
+        response
+          ..statusCode = 200
+          ..contentLength = -1;
+        response.close();
+        return;
+      }
+
+      if (path == '/non-null-response') {
+        response.headers.contentType = ContentType('text', 'plain');
+        response
+          ..statusCode = 200
+          ..contentLength = -1
+          ..write('response');
+        response.close();
+        return;
+      }
+
       final requestBodyBytes = await ByteStream(request).toBytes();
       final encodingName = request.uri.queryParameters['response-encoding'];
       final outputEncoding = encodingName == null

example/lib/generic.dart

@@ -42,5 +42,5 @@ void main() async {
 
   // This is the recommended way.
   final r = await dio.get<String>('https://baidu.com');
-  print(r.data?.length);
+  print(r.data.length);
 }

example_flutter_app/lib/main.dart

@@ -54,7 +54,7 @@ class _MyHomePageState extends State<MyHomePage> {
                       .then((r) {
                     setState(() {
                       print(r.data);
-                      _text = r.data!.replaceAll(RegExp(r'\s'), '');
+                      _text = r.data.replaceAll(RegExp(r'\s'), '');
                     });
                   });
                 } catch (e) {

example_flutter_app/lib/routes/request.dart

@@ -26,7 +26,7 @@ class _RequestRouteState extends State<RequestRoute> {
               onPressed: () {
                 dio.get<String>('https://httpbin.org/get').then((r) {
                   setState(() {
-                    _text = r.data!;
+                    _text = r.data;
                   });
                 });
               },

plugins/cookie_manager/test/cookies_test.dart

@@ -42,6 +42,7 @@ void main() {
     final firstRequestOptions = RequestOptions(baseUrl: exampleUrl);
 
     final mockResponse = Response(
+      data: null,
       requestOptions: firstRequestOptions,
       headers: Headers.fromMap(
         {HttpHeaders.setCookieHeader: mockFirstRequestCookies},
@@ -77,6 +78,7 @@ void main() {
       final requestOptions = RequestOptions(baseUrl: exampleUrl);
 
       final mockResponse = Response(
+        data: null,
         requestOptions: requestOptions,
         headers: Headers.fromMap(
           {HttpHeaders.setCookieHeader: mockResponseCookies},

plugins/native_dio_adapter/example/lib/main.dart

@@ -84,7 +84,7 @@ class _MyHomePageState extends State<MyHomePage> {
         return AlertDialog(
           title: Text('Response ${response.statusCode}'),
           content: SingleChildScrollView(
-            child: Text(response.data ?? 'No response'),
+            child: Text(response.data),
           ),
           actions: [
             MaterialButton(
@@ -120,7 +120,7 @@ class _MyHomePageState extends State<MyHomePage> {
         return AlertDialog(
           title: Text('Response ${response.statusCode}'),
           content: SingleChildScrollView(
-            child: Text(response.data ?? 'No response'),
+            child: Text(response.data),
           ),
           actions: [
             MaterialButton(