Stream - .addStream(), pipe()

main.dart

import 'dart:async';

var stream = Stream.fromIterable([1, 2, 3, 4, 5]);

void main() {
  final controller1 = new StreamController();
  final controller2 = new StreamController();

  controller1.addStream(stream);

  final doubler =
      new StreamTransformer.fromHandlers(handleData: (data, sink) {
      sink.add(data * 2);
  });

  controller1.stream.transform(doubler).pipe(controller2);
  controller2.stream.listen((data) => print(data));

}