[Bug]: NotifyCharacteristic throws BleException "Characteristic notification descriptor not found"

[gianisimone]

[Bug]: NotifyCharacteristic throws BleException "Characteristic notification descriptor not found"

[aritchie]

Android has always looked for a notification characteristic because it is required. This has never been any different.

[gianisimone]

@aritchie thank you for your reply. I can guarantee that with 2.7.2 subscribing to the characteristic which had no descriptor with WhenNotificationReceived actually worked. The OnNext was called perfectly even if the EnableNotifications failed to complete.

[aritchie]

Then send a reproducible case with the issue!

[gianisimone]

@aritchie Yes, sure.
This is the code using the v3 of Shiny:

private async Task WhenConnected(IPeripheral P)
{
    var characteristics = await P.GetAllCharacteristicsAsync();
    Command = characteristics.FirstOrDefault(c => c.Uuid == BLECharacteristicCommandUuid);    

    if(Command != null) 
    {
        P.NotifyCharacteristic(Command).ObserveOn(RxApp.MainThreadScheduler).Subscribe(notification =>
        {
            Log($"COMMAND CHANGED {Encoding.UTF8.GetString(notification.Data)}");
        },
        (notifyEx) => Log($"Error while enabling notifications for COMMAND. {notifyEx.Message}"));
    }
}
// peripheral is IPeripheral
whenConnected = peripheral.WhenConnected().Subscribe(conn => _ = WhenConnected(conn));

In this example, when calling NotifyCharacteristic the error handler is called and I am not able to process any notifications in the OnNext handler.

This is the code I have for version 2.7.2

var d = await peripheral.GetAllCharacteristics();
d.FirstOrDefault(_ => _.Uuid.ToGuid() == BT_CHARACTERISTIC_COMMAND_UUID);

if(d != null)
{
    TaskCompletionSource<bool> enableCommandNotificationTask = new TaskCompletionSource<bool>();

    CommandNotifyDisposable = Command.WhenNotificationReceived().Subscribe(g =>
    {
        Log(string.Format("COMMAND CHANGED {0}", Encoding.UTF8.GetString(g.Data)));
    }, 
    err => Log("Error"));

    Command.EnableNotifications(true).Subscribe(encd =>
    {
        Log("Command notifications enabled");
    }, 
    err =>
    {
        Log(string.Format("Error while enabling notifications for command {0}", err.Message));
    });
}

The EnableNotifications calls the error method, however, when a notification is received on the characteristic which has no descriptor, the OnNext is called properly.

If you need more details let me know

[aritchie]

Ok so really this is more of a feature request. You would like the methods NotifyCharacteristic to be EnableNotification with a separate hook method. This is something I can consider for a future release, but honestly, I don't want to support the non-standard cases. I also merged these methods because people don't understand subscribing/unsubscribing/resubscribing post reconnect. It's a support case I don't want again

[gianisimone]

Yes, I would like to be able to process any notification received on the a Characteristic even if it has no descriptor.
Is there something I could do to workaround that Exception at the moment?

[aritchie]

Not with the current implementation that I can think of. You can always create your own implementation.