WriteValues returning Bad_WriteNotSupported after migrating to Milo 1.0.1

[alexandrenetbr]

Hi Kevin,

I'm migrating an industrial OPC UA client from Milo 0.6.3 to Milo 1.0.1, and I've noticed that all write operations are now returning the following error:

StatusCode[name=Bad_WriteNotSupported, value=0x80730000, quality=bad]

The same code works perfectly with 0.6.3.

Here is a simplified snippet of how I’m performing the writes:

List nodes = tags.stream()
.map(t -> new NodeId(comm.getNamespaceIndex(), t.getFullName()))
.collect(Collectors.toList());

List values = ImmutableList.copyOf(tags.stream()
.map(t -> new DataValue(new Variant(ScalingHelper.scaleToDevice(t, t.getValue())), StatusCode.GOOD,
DateTime.now()))
.toArray(DataValue[]::new));

client.writeValues(nodes, values);

Some details:

• All NodeIds are correct and point to writable tags in KepServerEX (read/write).
• The values match the data types expected by the tags.
• We confirmed the tags are writable using external OPC UA client.

Is there any known breaking change between 0.6.3 and 1.0.1 related to writeValues() or how DataValues should be constructed?

Thanks for your help!

[kevinherron]

It looks like you're including a StatusCode a timestamp value with your write, and it's pretty common to see Bad_WriteNotSupported from Servers when you do this.

Build the DataValue with a null StatusCode and timestamps.

edit: just null timestamps are required, I think. StatusCode isn't nullable now... There's a static helper method for this you can use:

var dv = DataValue.valueOnly(Variant.ofInt32(42));

[kevinherron]

Butchered this response and had to make many edits 😅

[alexandrenetbr]

I actually first tried passing null for the StatusCode, just like I did in Milo 0.6.3. But after migrating to 1.0.1, I started getting this runtime exception:

"org.eclipse.milo.opcua.stack.core.types.builtin.StatusCode.getValue()" because the return value of "org.eclipse.milo.opcua.stack.core.types.builtin.DataValue.getStatusCode()" is null

So now I'm explicitly passing StatusCode.GOOD in the DataValue as a workaround to avoid the null exception above.

Is this the recommended way to write values in Milo 1.0.1, or is there a better approach to ensure compatibility with servers like KepServerEX?

[kevinherron]

Pass StatusCode.GOOD along with null timestamps or use DataValue.valueOnly.

The only thing that changed in 0.6.x -> 1.x is that null isn't allowed for the StatusCode parameter any more. Nothing else really changed, and the fundamental problem is that some/many servers do not accept write values that include timestamps.

The constructor variations on DataValue are biased towards implementing a Server, where you want the timestamps to be part of the value.

[alexandrenetbr]

That was exactly the issue — once I removed the timestamp (i.e., passed null), the write started working perfectly.

Your response speed and clarity are truly impressive — really appreciate the support! Thanks, Kevin!