CTT Attributes Write Value Test fails for null Values

[johannwesely]

Hi, im currently testing our Milo Server with CTT now in the Attribute Write Value test i have lots of failures.

I figured out using wireshark this happens because our Server has initaly null Values set, CTT reads the values and wants to write them back and gets BadTypeMismatch. Now i checked in Milo Dev1.0 why this happens and came to the Solution that in Server UaVariableNode Line 250 the server Throws the BadTypeMismatch when the value to write is null. I changed the Line to
Object o = variant.getValue(); if (o == null) return value;
Now i have a lot More green but still some Failures left do you think this could be a solution.

I also tried to initalize the Values before Starting CTT Testscripts and this works also. But can you tell me if null Values should be possible to write ? I cannot find a mention in OpcUa Spec?

[kevinherron]

Whether or not a server allows null values to be written is up to the implementation. The way the SDK is currently written does not support it. I think originally I didn't support it at the attribute level in the UaNodes either, but that seems to have been relaxed a bit.

You should just provide valid initial values for the purpose of CTT testing and chase remaining legitimate errors.

[johannwesely]

Ah okay I liked the idea of null Values for Inital Values. Because later I dont know if our Process has written for example an 0 value or if it is still the inital 0. But Thanks for your Information saves me some time.

[kevinherron]

You can use null or 0 + Uncertain_InitialValue StatusCode in that situation.

Null values work internally, they just don't work when written by an external client.

There's also certain attributes that aren't allowed to have null values (any attribute that is a structure).

And there's some weird behavior you'll see with optional attributes, because when reading an optional attribute null is used to decide Bad_AttributeIdInvalid should be returned because it's not supported/implemented.