Keeping track of nodes subscribed by clients

[TheNailDev]

Hello there,

I'm programming a server and would like to keep track which items are currently subscribed by clients.
My current idea is to use Server.subscribe_server_callback to react to subscriptions and "unsubscriptions" (is that a real word?).
Based of the example server-callback.py I am now able to detect which nodes a client subscribes.

My problem is that I don't know how to detect for which node the subscription was cancelled in case of an ItemSubscriptionDeleted callback. The event object is not of the same type as the event object during the creation of subscriptions, so I can't just copy my logic from the detection of a new subscription. I might be missing something really simple but I don't have the correct idea.

Here is a simplified version of my code. (Mostly ripped from the example I mentioned.)

def create_monitored_items(event, dispatcher):
    #Get node id of newly subscribed item
    print("Monitored Item")     
    for idx in range(len(event.response_params)) :
        if (event.response_params[idx].StatusCode.is_good()) :
            nodeId = event.request_params.ItemsToCreate[idx].ItemToMonitor.NodeId
            print(f"Node {nodeId} was subscribed")
         
    
def delete_monitored_items(event, dispatcher):
    #How do i get the node id of the unsubscribed item?
    ???
    nodeId = ???
    print(f"Node {nodeId} was unsubscribed")

...
server.subscribe_server_callback(CallbackType.ItemSubscriptionCreated, create_monitored_items)    
server.subscribe_server_callback(CallbackType.ItemSubscriptionDeleted, delete_monitored_items)
...

I hope somebody knows what I should do.

[oroulet]

I am not sure I competely undertsand but the SubscriptionResult should contain some "handle" that you should find back in "params" of subcsriptoin deletes

[oroulet]

so if save your nodes in a Dict[Hanlde, List[nodes]] you can get back to what nodes have been unsubscribed

[TheNailDev]

Yes. Thank you. That was what I was missing.
Using the combination of SubscriptionId and MonitoredItemId I am able to uniquely identify each subscribed node.

Im adding the edited handle methods in case anybody would like to do something similar

def create_monitored_items(event, dispatcher):
    for idx in range(len(event.response_params)) :
        if (event.response_params[idx].StatusCode.is_good()) :
            nodeId = event.request_params.ItemsToCreate[idx].ItemToMonitor.NodeId
            subscription_id = event.request_params.SubscriptionId
            monitored_item_id = event.response_params[idx].MonitoredItemId
            #Save the connection between node id and the handle ids
            ...
         
def delete_monitored_items(event, dispatcher):
    for idx in range(len(event.response_params)) :
        if (event.response_params[idx].is_good()) :
            subscription_id = event.request_params.SubscriptionId
            monitored_item_id = event.request_params.MonitoredItemIds[idx]
            #Use handle ids to get node id of unsubscribed nodes
            ...