Dont complete on fail in Reactive Swift

Question

I have a function capturing events from an api which works great. The only issue is i dont want the stream to be complete when it fails.

    public func getDeviceEvent(deviceUID: String) -> SignalProducer<DeviceEvent, HTTPConnectorError> {
        return SignalProducer<DeviceEvent, HTTPConnectorError> { observer, _ in
            self.getDeviceEvent(deviceUID: deviceUID) { result in
                switch result {
                case .success(let deviceEvent):
                    observer.send(value: deviceEvent)
                    observer.sendCompleted()
                case .failure(let error):
                    observer.send(error: error)
                }
            }
        }
    }

    private func getDeviceEvent(deviceUID: String, completion: @escaping (Result<DeviceEvent, HTTPConnectorError>) -> Void) {
        httpConnector.request(authenticated: true, target: .deviceLocationEvent(deviceID: deviceUID), parse: makeParser(), completion: completion)
    }

Is there a way i can keep the stream going? i know there is retry but i don't want to add a number of times i just want it to continue.

If the HTTP request fails, what ought to happen? Do you want to keep retrying until it succeeds? — jjoelson, Dec 18 '19 at 01:48
When the request fails i dont want the stream to complete, or i want to re-trigger the stream but still pass the error so the ui can display it — Wazza, Dec 18 '19 at 09:17

score 1 · Accepted Answer · answered Dec 22 '19 at 22:55

You could create your own version of retry which retries indefinitely (I've included a version here that pauses for a given interval after each failure):

extension SignalProducer {
    func retry() -> SignalProducer<Value, Never> {
        flatMapError { _ in
            self.retry()
        }
    }

    func retry(interval: TimeInterval, on scheduler: DateScheduler) -> SignalProducer<Value, Never> {
        flatMapError { _ in
            SignalProducer<Value, Never>.empty
                .delay(interval, on: scheduler)
                .concat(self.retry(interval: interval, on: scheduler))
        }
    }
}

Then you can use on(failed:) to display something to the user on each failure while retrying indefinitely:

getDeviceEvent(deviceUID: someDeviceUID)
    .on(failed: { error in
        print(error)
        // Display this to the user
    })
    .retry(interval: 1.0, on: QueueScheduler())
    .take(during: self.lifetime)
    .startWithValues { value in
        print(value)
    }

This snippet assumes self is a view controller; take(during: self.lifetime) will then stop the operation when the current view controller deallocates. You ought to do something like this to prevent this retrying forever in the worst case.

Dont complete on fail in Reactive Swift

1 Answers1