How do I see or what gets invoked if someone changes values in the server?

[jnsw]

I am using the server implementation and want to do stuff, if someone changes values on the server. Do we have a callback routine or something for this?

[kevinherron]

Your AddressSpace will receive a call to the write method.

If you’re using a ManagedAddressSpace like the example you can install an AttributeFilter or AttributeObserver on the Node you’re interested in. Or override the write method and make sure to call super when done looking at what is happening.

[jnsw]

Thanks, that worked like a charm.
I have another question: Can we know if the fired AttributeChange is from the "outside", so an OPC UA Client changed the value instead of ourselfes?

[kevinherron]

If you’re using the AttributeFilter mechanism the context will have an Optional containing a Session on it.

[MiproHTy]

I've been banging my head to get this to work. Can someone please show example how the AttributeFilter is going to need to be implemented and how values are updated to server from the software itself so that it doesnt trigger the AttributeChange?

The only time i got this working is when using
misoNodes.get(i).getFilterChain().addLast( new AttributeLoggingFilter(), AttributeFilters.getValue( ctx -> new DataValue(new Variant(value)) ) );
Thats when AttributeChange doesnt trigger BUT when i'm updating about 100 variables in server in a loop which sleeps every 500ms i get StackOverFlow in about 10 seconds. So i think im using this wrong and there is correct way to do this?

[kevinherron]

You don't need an AttributeFilter if you are updating the values by some other means (your loop in this case). AttributeFilter is a way to "intercept" calls to get the value of an attribute, either for a Node that you don't fully "control" or didn't instantiate, or that you aren't setting the attribute values on by some other means.

[MiproHTy]

Thank you for still answering :)

My problem was that when using AttributeObserver on nodes what i created i get AttributeChanged even when i write myself the value to node. My ugly workaround is now this:
Nodes.get(i).removeAttributeObserver(myObs);
Nodes.get(i).setValue(new DataValue(new Variant(value)));
Nodes.get(i).addAttributeObserver(myObs);

So when i update myself the values in the server my observer will not fire and if client writes i get the attributechanged.
Do you have suggestions how this should have been done?

[kevinherron]

No, it's working as intended. Why does your AttributeObserver being notified of the attribute change lead to an infinite loop or stack overflow?

[MiproHTy]

Nodes.get(i).getFilterChain().addLast( new AttributeLoggingFilter(), AttributeFilters.getValue( ctx -> new DataValue(new Variant(value)) ) );
If you run this code in a loop it stackoverflows.

[kevinherron]

Why would you continue to add filters in a loop? That’s also a memory leak.