Server Node Event Source

[julian-gb]

Hi,

I tried to subscribe to events emitted by the server node. However, it seems events are not emitted by it but the specification states "any OPC UA Server that supports eventing shall expose at least one Node as EventNotifier. The Server Object defined in OPC 10000-5 is used for this purpose."

Is this not implemented or have I done something wrong? I was not able to find a disscussion regrading this topic. Has it maybe already dicussed somewhere?

[AndreasHeine]

it is!

you are using our client right!?
so there are some topics related to events in the past with the eventfilter!

but first things first does it work with ua expert?

[julian-gb]

Yes, tested it with the subscription examples and ua expert. Only when I subscribe directly to the emitting object I'm able to receive events.

Changing and running the client-events.py example while running the server-events.py.

... 
        obj = await client.nodes.root.get_child(["0:Objects", "2:MyObject"])
        _logger.info("MyObject is: %r", obj)

        myevent = await client.nodes.root.get_child(["0:Types", "0:EventTypes", "0:BaseEventType", "2:MyFirstEvent"])
        _logger.info("MyFirstEventType is: %r", myevent)

        msclt = SubHandler()
        sub = await client.create_subscription(100, msclt)
        #handle = await sub.subscribe_events(obj, myevent)
        #handle = await sub.subscribe_events() # use default to subscribe to server base events
        handle = await sub.subscribe_events(client.nodes.server, myevent)
        await asyncio.sleep(10)
        await sub.unsubscribe(handle)
        await sub.delete()
...

Am I missing something?

[AndreasHeine]

ok i looked thru the source-code and the EventGenerator currently only support one emitting node so if you like to emit via server-obj then you need to modify the server-events.py

# emmtiting node myobj
mysecondevgen = await server.get_event_generator(custom_etype, myobj)

# if no emmitting node is set it falls back to server
mysecondevgen = await server.get_event_generator(custom_etype)

    async def get_event_generator(self, etype=None, emitting_node=ua.ObjectIds.Server):
        """
        Returns an event object using an event type from address space.
        Use this object to fire events
        """
        if not etype:
            etype = BaseEvent()
        ev_gen = EventGenerator(self.iserver.isession)
        await ev_gen.init(etype, emitting_node=emitting_node)
        return ev_gen

currently there is something missing:
The "Notifier-Chain" e.g. Server-Obj <-[HasNotifier-Reference or HasEventSource-Reference]- myobj
specreference: https://reference.opcfoundation.org/Core/Part3/v104/docs/7.18

so usually if implemented some day it should be possible to subscribe to server or myobj and recv in both cases the events of myobj

correct my if i am wrong! @oroulet @schroeder-

[schroeder-]

I think you are correct.

[julian-gb]

For now I tried to fix it by adding the following to the end of the trigger method in event_generator.py:

     if self.emitting_node.nodeid is not ua.NodeId(ua.ObjectIds.Server):
          event = copy(self.event)
          event.emitting_node = ua.NodeId(ua.ObjectIds.Server)
          await self.isession.subscription_service.trigger_event(event)

     await self.isession.subscription_service.trigger_event(self.event)

Is the HasNotifier reference required in all cases? Seems to like a more sophisticated extension to the basic event functionality. Otherwise i would assume that the reference between server an emitting node should always been added if a new event generator is created, where the emitting node is not the server node.