migration_to_4.x.md

Migration to 4.x

This guide is primarily for users with prior dio 3.x experience who want to learn about the new features and changes in dio 4.x .

New Features

1. Interceptors: Add handler for Interceptor APIs which can specify the subsequent interceptors processing logic more finely（whether to skip them or not)）
2. Support multiple encoding styles ( options.listFormat ) for request List parameters.
3. Make keys of request headers be case-insensitive.
4. New API: Future<Response> dio.fetch( RequestOptions ).
5. New API: RequestOptions options.compose(BaseOptions baseOpt,...).

Breaking Changes

1. Null safety support (Dart >=2.12).

2. The Interceptor APIs signature has changed.

3. Rename options.merge to options.copyWith.

4. Rename DioErrorType enums from uppercase to camel style.

5. Delete dio.resolve and dio.reject APIs (use handler instead in interceptors).

6. Class BaseOptions no longer inherits from Options class.

7. Change requestStream type of HttpClientAdapter.fetch from Stream<List<int>> to Stream<Uint8List>.

8. Download API: Add real uri and redirect information to headers.