timeout method

Stream<T> timeout(
  1. Duration timeLimit, {
  2. void onTimeout(
    1. EventSink<T> sink
    )?,
})

Creates a new stream with the same events as this stream.

When someone is listening on the returned stream and more than timeLimit passes without any event being emitted by this stream, the onTimeout function is called, which can then emit further events on the returned stream.

The countdown starts when the returned stream is listened to, and is restarted when an event from this stream is emitted, or when listening on the returned stream is paused and resumed. The countdown is stopped when listening on the returned stream is paused or cancelled. No new countdown is started when a countdown completes and the onTimeout function is called, even if events are emitted. If the delay between events of this stream is multiple times timeLimit, at most one timeout will happen between events.

The onTimeout function is called with one argument: an EventSink that allows putting events into the returned stream. This EventSink is only valid during the call to onTimeout. Calling EventSink.close on the sink passed to onTimeout closes the returned stream, and no further events are processed.

If onTimeout is omitted, a timeout will emit a TimeoutException into the error channel of the returned stream. If the call to onTimeout throws, the error is emitted as an error on the returned stream.

The returned stream is a broadcast stream if this stream is. If a broadcast stream is listened to more than once, each subscription will have its individually timer that starts counting on listen, and the subscriptions' timers can be paused individually.

Example:

Future<String> waitTask() async {
  return await Future.delayed(
      const Duration(seconds: 4), () => 'Complete');
}
final stream = Stream<String>.fromFuture(waitTask())
    .timeout(const Duration(seconds: 2), onTimeout: (controller) {
  print('TimeOut occurred');
  controller.close();
});

stream.listen(print, onDone: () => print('Done'));

// Outputs:
// TimeOut occurred
// Done

Implementation

Stream<T> timeout(Duration timeLimit, {void onTimeout(EventSink<T> sink)?}) {
  _StreamControllerBase<T> controller;
  if (isBroadcast) {
    controller = new _SyncBroadcastStreamController<T>(null, null);
  } else {
    controller = new _SyncStreamController<T>(null, null, null, null);
  }

  Zone zone = Zone.current;
  // Register callback immediately.
  _TimerCallback timeoutCallback;
  if (onTimeout == null) {
    timeoutCallback = () {
      controller.addError(
          new TimeoutException("No stream event", timeLimit), null);
    };
  } else {
    var registeredOnTimeout =
        zone.registerUnaryCallback<void, EventSink<T>>(onTimeout);
    var wrapper = new _ControllerEventSinkWrapper<T>(null);
    timeoutCallback = () {
      wrapper._sink = controller; // Only valid during call.
      zone.runUnaryGuarded(registeredOnTimeout, wrapper);
      wrapper._sink = null;
    };
  }

  // All further setup happens inside `onListen`.
  controller.onListen = () {
    Timer timer = zone.createTimer(timeLimit, timeoutCallback);
    var subscription = this.listen(null);
    // Set up event forwarding. Each data or error event resets the timer
    subscription
      ..onData((T event) {
        timer.cancel();
        timer = zone.createTimer(timeLimit, timeoutCallback);
        // Controller is synchronous, and the call might close the stream
        // and cancel the timer,
        // so create the Timer before calling into add();
        // issue: https://github.com/dart-lang/sdk/issues/37565
        controller.add(event);
      })
      ..onError((Object error, StackTrace stackTrace) {
        timer.cancel();
        timer = zone.createTimer(timeLimit, timeoutCallback);
        controller._addError(
            error, stackTrace); // Avoid Zone error replacement.
      })
      ..onDone(() {
        timer.cancel();
        controller.close();
      });
    // Set up further controller callbacks.
    controller.onCancel = () {
      timer.cancel();
      return subscription.cancel();
    };
    if (!isBroadcast) {
      controller
        ..onPause = () {
          timer.cancel();
          subscription.pause();
        }
        ..onResume = () {
          subscription.resume();
          timer = zone.createTimer(timeLimit, timeoutCallback);
        };
    }
  };

  return controller.stream;
}