OPC UA BadNodeIdUnknown: Resolving Numeric NodeIds

BadNodeIdUnknown occurs here because the client constructs a string NodeId for Temperature, while the server exposes that variable with numeric NodeId NS4|Numeric|23. Keep OpcUa_Attributes_Value; changing the attribute does not correct an invalid NodeId.

Identify the NodeId mismatch

The configuration entry NS4/Variable01 =Temperature passes a string into setNodeId(..., g_nsIndex). That creates a string-identifier NodeId. The server instead expects numeric identifier 23, so the address does not exist and the read returns BadNodeIdUnknown.

Separate NodeId, BrowseName, and DisplayName

A NodeId contains a namespace index and exactly one identifier. The supported identifier types are numeric, string, GUID, and ByteString. A node does not simultaneously use its numeric identifier and BrowseName as interchangeable addresses.

BrowseName identifies a node within a browse path. DisplayName is localized text intended for user interfaces. A browsing client receives the full NodeId in each browse result, displays the returned name, and retains the NodeId for reads and subscriptions. Seeing Temperature in a browse tree therefore does not mean the variable has a string NodeId.

Choose a production addressing strategy

Do not treat namespace index 4 as persistent. Store the namespace URI plus the identifier, read the server's NamespaceArray at startup, find the URI's current index, and replace the stored index before reading. If the numeric identifier itself can change during development, either stabilize the server's NodeId or resolve the node from a known browse path.

Configure and read the variable

1. Inspect the browse result or attribute view and confirm both the identifier type and identifier. For the reported server, Temperature is NS4|Numeric|23.
2. Retain NS4/NameSpaceUri = http://www.unifiedautomation.com/customprovider/ and resolve its current namespace index from NamespaceArray when the session starts.
3. If retaining numeric NodeIds, enhance client_cpp_sdk.cpp so readConfiguration accepts numeric NodeId syntax. UaNodeId::fromXmlString can parse ns=1;i=123 for a numeric identifier or ns=1;s=stringnodeid for a string identifier; then replace the parsed namespace index with the index resolved from the URI.
4. If retaining the sample's string-only configuration logic, change the server variable to use a string NodeId and configure that exact string identifier.
5. Build each read request with the resolved NodeId and OpcUa_Attributes_Value.

nodesToRead.create(count);
for (i = 0; i < count; i++)
{
    g_VariableNodeIds[i].copyTo(&nodesToRead[i].NodeId);
    nodesToRead[i].AttributeId = OpcUa_Attributes_Value;
}

Setting Identifier.Numeric = 23 and IdentifierType = OpcUa_IdentifierType_Numeric proved the diagnosis, but hardcoding those fields inside the read loop is only a test. Construct the correct NodeId during configuration processing so reads and subscriptions use the same resolved address.

Verify the correction

1. Dump or inspect the constructed NodeId before the read. Confirm the namespace index matches the URI's current position and the identifier is numeric 23, unless the server was changed to a string identifier.
2. Read with OpcUa_Attributes_Value and confirm that BadNodeIdUnknown no longer occurs and the returned value is the server's temperature.
3. Create a subscription using the same NodeId and confirm that value changes arrive. Successful reads and subscriptions were reported after changing the server variables to string NodeIds.

If browsing succeeds but reading still fails, compare the full browsed NodeId against the constructed read NodeId. Matching display text is insufficient; namespace index, identifier type, and identifier value must all address the same node.

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