system.opcua.callMethod throws ClassCastException when invoking with arguments

Ignition
,
1

Hi, calling a OPCUA method with two InputArguments (ua:String, ua:Int32) does not work. I get a ClassCastException.

result = system.opcua.callMethod("RobotArm", "ns=4;i=532", "ns=4;i=650", ["myArticleId", 100])

java.lang.ClassCastException: java.lang.ClassCastException: class org.eclipse.milo.opcua.sdk.client.nodes.UaVariableNode cannot be cast to class

When calling a method without any InputArguments it works fine:
result = system.opcua.callMethod("RobotArm", "ns=4;i=532", "ns=4;i=653", )

I also turned on the system.opcua.callMethod DEBUG logger. No helpful hints.
Trying to json encode the arguments didn't help either.

The gateway runs on a M1 Mac.

Thanks a lot for help! Toni

2

Hmm, this hints at a perhaps a data modelling problem in the underlying server...

Any chance you can make this OPC UA connection without security and get a Wireshark capture while you call this method? What server is this?

3

It would also be useful if you could provide the full error and stack trace from the logs.

4

I'm using the the opcua-asyncio (GitHub - FreeOpcUa/opcua-asyncio: OPC UA library for python >= 3.7) server. I can invoke the method with the two input arguments with the Prosys OPC UA Browser successfully.

So far I connect to the server without security. So network tracing should be possible.

5

Oh... I don't expect this to work then. Both of those Python OPC UA implementations are broken and they don't seem to care or respond to my bug reports.

1 Like
6

At some point I will rewrite the logic in system.opcua.callMethod that triggers this bug in the Python servers, but it's not a priority right now with all the other work we have going on. It's not a super trivial change.

7

I see. Well, I guess I have to switch to another OPC UA SDK. Thanks anyway.

8

My last post in the thread I linked to has some suggestions.