Milo SDK 0.68 can read a scalar server diagnostic with the standard client read call, but the available evidence does not establish an SDK-specific diagnostics wrapper or a confirmed session-diagnostics node. Treat the successful server-summary read and the null session result as separate cases; a null value alone does not prove that the selected node is wrong.
Confirmed server-summary read
The demonstrated Kotlin call reads a source-timestamped value with a maximum-age argument of 0.0. For Identifiers.Server_ServerDiagnostics_ServerDiagnosticsSummary_CurrentSessionCount, the returned payload is handled as UInteger.
opcUaClient.readValue(
0.0,
TimestampsToReturn.Source,
nodeId
).get().value.value?.let { it as UInteger }Why the session read remains unresolved
Applying the same scalar cast to a session-related node produces null, but the evidence does not identify the node, its declared data type, access status, or returned diagnostic metadata. The failure could involve node selection, a non-scalar value, unavailable diagnostics, or a read result without a usable payload. Do not select one cause until the complete read result is examined.
| Observation | Confirmed conclusion | Still unknown |
|---|---|---|
| Server summary returns a value | The shown read pattern works for the specified current-session-count node. | Whether Milo provides a higher-level diagnostics API. |
| Session-oriented read returns null | No usable payload reached the cast. | Correct node, declared type, access state, and server-side availability. |
Diagnostic decision procedure
- Retain the complete result returned by
readValue; do not immediately reduce it tovalue.value. - Record the exact session-related node selected and inspect the returned value metadata before casting.
- Determine whether the payload is scalar or structured and cast only to the type actually returned.
- Compare that result with the known-working server-summary read to separate a general client-read problem from a node-specific problem.
Using SDK types safely
The evidence supports UInteger only for the demonstrated current-session-count value. It does not establish the correct Milo type for session diagnostics. Keep the payload uncast until its declared or returned type is known; otherwise, a scalar assumption can conceal the distinction between an unavailable value and a structured diagnostic value.
FAQ
How do I read CurrentSessionCount with Milo SDK 0.68?
Call readValue(0.0, TimestampsToReturn.Source, nodeId) with Identifiers.Server_ServerDiagnostics_ServerDiagnosticsSummary_CurrentSessionCount, then handle the demonstrated payload as UInteger.
Does a null Milo session diagnostics value mean the NodeId is wrong?
No. Null confirms only that no usable payload reached the cast; inspect the complete read result, exact node, and returned type before concluding that the node is wrong.
Can I cast all OPC UA diagnostics values to UInteger?
No. The evidence supports UInteger only for the demonstrated current-session-count node. Determine whether each session diagnostic is scalar or structured before casting it.
