blob: e01efac0041095e0d5d31e746bb1a3ef9bbfbfca [file] [log] [blame]
// Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:async';
/// A transformer that converts a broadcast stream into a single-subscription
/// stream.
///
/// This buffers the broadcast stream's events, which means that it starts
/// listening to a stream as soon as it's bound.
///
/// This also casts the source stream's events to type `T`. If the cast fails,
/// the result stream will emit a [CastError]. This behavior is deprecated, and
/// should not be relied upon.
class SingleSubscriptionTransformer<S, T> implements StreamTransformer<S, T> {
const SingleSubscriptionTransformer();
Stream<T> bind(Stream<S> stream) {
var subscription;
var controller = new StreamController<T>(sync: true,
onCancel: () => subscription.cancel());
subscription = stream.listen((value) {
// TODO(nweiz): When we release a new major version, get rid of the second
// type parameter and avoid this conversion.
try {
controller.add(value as T);
} on CastError catch (error, stackTrace) {
controller.addError(error, stackTrace);
}
}, onError: controller.addError, onDone: controller.close);
return controller.stream;
}
}