Idea: Automatically unsubscribe unknown notification handles

[crishoj]

ads-client detects incoming notifications for unknown handles, which indicates that previously an ADS subscription was not properly unsubscribed.

In our application code, we detect this by error message /Notification received with unknown handle \((\d+)\)/ and unsubscribe the handle with a raw ADS command:

    const handle = Number.parseInt(matches[1])
    const payload = Buffer.alloc(4)
    payload.writeUInt32LE(handle, 0)
    ads.sendAdsCommand({ adsCommand: 7, payload: payload })

This works, but could be more convenient, with one or more of these changes:

• Use a dedicated error class, e.g. StaleSubscriptionHandleError with a handle: number property.
• Expose an unsubscribeRaw(handle: number) method.
• Automatically unsubscribe unknown handles (but do emit a warning).

[jisotalo]

That sounds like a good idea.

I can't see any reason why deleting unknown ADS notifications received for that port could cause issues. They just use resources.

Perhaps the unsubscribe() could also accept numerical handle. That would allow users to do whatever they like:

public async unsubscribe(subscription: ActiveSubscription | number): Promise<void> {
//...
}

We could automatically delete all unknown notifications, and write a WARNING: to the console. It could also be a setting such as deleteUnknownSubscriptions which defaults to true.