Improve performance of byte data on IO platform (cfug#1838)

dio/CHANGELOG.md

@@ -11,6 +11,7 @@ See the [Migration Guide][] for the complete breaking changes list.**
 - `IOHttpClientAdapter.onHttpClientCreate` has been deprecated and is scheduled for removal in
   Dio 6.0.0 - Please use the replacement `IOHttpClientAdapter.createHttpClient` instead.
 - Using `CancelToken` no longer closes and re-creates `HttpClient` for each request when `IOHttpClientAdapter` is used. 
+- Improve performance when sending binary data (`List<int>`/`Uint8List`). 
 
 ## 5.1.2
 

dio/lib/src/dio_mixin.dart

@@ -636,14 +636,24 @@ abstract class DioMixin implements Dio {
         options.headers[Headers.contentLengthHeader] = length.toString();
       } else {
         final List<int> bytes;
-        // Call request transformer.
-        final data = await transformer.transformRequest(options);
-        if (options.requestEncoder != null) {
-          bytes = options.requestEncoder!(data, options);
+
+        if (data is Uint8List) {
+          // Handle binary data which does not need to be transformed
+          bytes = data;
+        } else if (data is List<int>) {
+          // Handle binary data which does not need to be transformed
+          bytes = Uint8List.fromList(data);
         } else {
-          //Default convert to utf8
-          bytes = utf8.encode(data);
+          // Call request transformer for anything else
+          final transformed = await transformer.transformRequest(options);
+          if (options.requestEncoder != null) {
+            bytes = options.requestEncoder!(transformed, options);
+          } else {
+            // Default convert to utf8
+            bytes = utf8.encode(transformed);
+          }
         }
+
         // support data sending progress
         length = bytes.length;
         options.headers[Headers.contentLengthHeader] = length.toString();

dio/test/mock/http_mock.dart

@@ -1,5 +1,6 @@
 import 'dart:io';
 
+import 'package:dio/dio.dart';
 import 'package:mockito/annotations.dart';
 
 import 'http_mock.mocks.dart';
@@ -13,6 +14,7 @@ final httpClientMock = MockHttpClient();
     MockSpec<HttpClientRequest>(),
     MockSpec<HttpClientResponse>(),
     MockSpec<HttpHeaders>(),
+    MockSpec<Transformer>(),
   ],
 )
 class MockHttpOverrides extends HttpOverrides {

dio/test/mock/http_mock.mocks.dart

@@ -6,6 +6,9 @@ import 'dart:async' as _i4;
 import 'dart:convert' as _i3;
 import 'dart:io' as _i2;
 
+import 'package:dio/src/adapter.dart' as _i7;
+import 'package:dio/src/options.dart' as _i6;
+import 'package:dio/src/transformer.dart' as _i5;
 import 'package:mockito/mockito.dart' as _i1;
 
 // ignore_for_file: type=lint
@@ -654,3 +657,23 @@ class MockHttpHeaders extends _i1.Mock implements _i2.HttpHeaders {
   void clear() => super.noSuchMethod(Invocation.method(#clear, []),
       returnValueForMissingStub: null);
 }
+
+/// A class which mocks [Transformer].
+///
+/// See the documentation for Mockito's code generation for more information.
+class MockTransformer extends _i1.Mock implements _i5.Transformer {
+  MockTransformer() {
+    _i1.throwOnMissingStub(this);
+  }
+
+  @override
+  _i4.Future<String> transformRequest(_i6.RequestOptions? options) =>
+      (super.noSuchMethod(Invocation.method(#transformRequest, [options]),
+          returnValue: Future<String>.value('')) as _i4.Future<String>);
+  @override
+  _i4.Future<dynamic> transformResponse(
+          _i6.RequestOptions? options, _i7.ResponseBody? response) =>
+      (super.noSuchMethod(
+          Invocation.method(#transformResponse, [options, response]),
+          returnValue: Future<dynamic>.value()) as _i4.Future<dynamic>);
+}

dio/test/upload_stream_test.dart → dio/test/upload_test.dart

@@ -3,27 +3,37 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:dio/dio.dart';
+import 'package:mockito/mockito.dart';
 import 'package:test/test.dart';
 
+import 'mock/http_mock.mocks.dart';
+
 void main() {
-  final dio = Dio()
-    ..options.baseUrl = 'https://httpbun.com/'
-    ..interceptors.add(
-      QueuedInterceptorsWrapper(
-        onRequest: (options, handler) async {
-          // Delay 1 second before requests to avoid request too frequently.
-          await Future.delayed(const Duration(seconds: 1));
-          handler.next(options);
-        },
-      ),
+  late Dio dio;
+
+  setUp(() {
+    dio = Dio()..options.baseUrl = 'https://httpbun.com/';
+  });
+
+  test('binary data should not be transformed', () async {
+    final bytes = List.generate(1024, (index) => index);
+    final transformer = MockTransformer();
+    when(transformer.transformResponse(any, any)).thenAnswer(
+      (i) => i.positionalArguments[1],
+    );
+    final r = await dio.put(
+      '/put',
+      data: bytes,
     );
+    verifyNever(transformer.transformRequest(any));
+    expect(r.statusCode, 200);
+  });
 
   test('stream', () async {
-    Response r;
     const str = 'hello 😌';
     final bytes = utf8.encode(str).toList();
     final stream = Stream.fromIterable(bytes.map((e) => [e]));
-    r = await dio.put(
+    final r = await dio.put(
       '/put',
       data: stream,
       options: Options(