How do I reliably write to a OPC UA server?

I'm trying to write some values to a OPC UA server. In order to do that reliably, I propably need to know the DataType of the node that I'm trying to write to, otherwise it seems I'm prone to getting datatype mismatches.

Let's say my server has a node TestNodeOne with datatype Int16

My API gets told to write the value 3 to that node. Now I need to make a decision: Do I handle the 3 as an Integer or as an UShort? For this, it seems that I would need the data type of my node.

What I've tried

My approach was to just browse the server and create a cache of all it's nodes with the corresponding data type. Here's how that looks:

// Recursively browse entire server
@SuppressWarnings("deprecation")
private HashMap<String, NodeId> browseNode(String indent, OpcUaClient client, NodeId browseRoot, HashMap<String, NodeId> nodesMap) {

    BrowseDescription browse = new BrowseDescription(
            browseRoot,
            BrowseDirection.Forward,
            Identifiers.References,
            true, uint(NodeClass.Object.getValue() | NodeClass.Variable.getValue()),
            uint(BrowseResultMask.All.getValue()));

    try {
        BrowseResult browseResult = client.browse(browse).get();
        List<ReferenceDescription> references = toList(browseResult.getReferences());

        for (ReferenceDescription rd : references) {

            UShort namespaceIndex = rd.getNodeId().getNamespaceIndex();
            String identifier = rd.getNodeId().getIdentifier().toString();
            NodeId node = new NodeId(namespaceIndex, identifier);
            nodesMap.put(rd.getNodeId().getIdentifier().toString(), node);

            logger.info("----------------------------------------------------------------");
            logger.info(identifier);
            logger.info("TYPE " + rd.getTypeDefinition()); // Not the right node
            logger.info("TYPE " + rd.getTypeId().getIdentifier().toString()); // Not the right node
            logger.info("TYPE " + rd.getReferenceTypeId().getIdentifier().toString()); // Not the right node

            rd.getNodeId().local().ifPresent(nodeId -> {
                browseNode(indent + "  ", client, nodeId, nodesMap);
            });
        }

    } catch (InterruptedException | ExecutionException e) {
        logger.error("Browsing nodeId={} failed: {}", browseRoot, e.getMessage(), e);
    }

    return nodesMap;
}

I can't figure out how to get the datatype of a node. I think I'm on the wrong track here. How can I find out the data type of a node?

Solution

The easiest approach is to read the DataType attribute before each write so you know what kind of value to send.

Once you have this working you can try something a little trickier, like caching the DataType so that subsequent writes to the same Node don't need to read the DataType attribute again, and then if a write ever fails with Bad_TypeMismatch you can invalidate the entry in the cache for that Node and then retry the read+write.