HttpExample.dart

HttpClient client = new HttpClient();
var _downloadData = List<int>();
var fileSave = new File('./logo.png');
client.getUrl(Uri.parse("https://fluttermaster.com/wp-content/uploads/2018/08/fluttermaster.com-logo-web-header.png"))
  .then((HttpClientRequest request) {
    return request.close();
  })
  .then((HttpClientResponse response) {
    response.listen((d) => _downloadData.addAll(d),
      onDone: () {
        fileSave.writeAsBytes(_downloadData);
      }
    );
  });