Call OPCUA method with struct input argument using node-opcua - node-opcua

Question

I am trying to interface with an RFID reader which implements an OPC-UA server according to this specification.
I am trying to call the method ScanStart which takes the ScanSettings struct as an input argument (an AutoID datatype) but despite reading through the examples and documentation I can't figure out a way to do this.
Using UAExpert I can call the method and enter the values for the struct using the GUI which produces the following dump in wireshark:
ArraySize: 1
[0]: Variant
Variant Type: ExtensionObject (0x16)
Value: ExtensionObject
TypeId: ExpandedNodeId
EncodingMask: 0x01, EncodingMask: Four byte encoded Numeric
.... 0001 = EncodingMask: Four byte encoded Numeric (0x1)
.0.. .... = has server index: False
0... .... = has namespace uri: False
Namespace Index: 3
Identifier Numeric: 5015
EncodingMask: 0x01, has binary body
.... ...1 = has binary body: True
.... ..0. = has xml body: False
ByteString: 0000000000000000000000000000000000
Has anyone successfully managed to register an ExtensionObject for passing to a method call using node-opcua? At this point I am happy to just send the ByteString above without needing to encode/decode the struct as it is always static.
Apparently there is a constructExtensionObject method. The client code I have for this is:
(async () => {
const client = OPCUAClient.create({ endpoint_must_exist: false});
client.on("backoff", () => console.log("Backoff: trying to connect to ", endpointUri));
await client.withSessionAsync(endpointUri, async (session) => {
let scanSettings = {
Duration: 0,
Cyles: 0,
DataAvailble: false
};
const nodeID = new NodeId(NodeIdType.STRING, "rfr310.ScanStart.InputArguments", 4);
const extObj = session.constructExtensionObject(nodeID, scanSettings);
const methodsToCall = [
{
objectId: "ns=4;s=rfr310",
methodId: "ns=4;s=rfr310.ScanStart",
inputArguments: [extObj]
}
];
extObj.then(() => {
session.call(methodsToCall,(err,results) => {
if (err) {
console.log(err);
} else {
console.log(results);
}
});
}).catch(() => {
})
});
})();
produces the error "dispose when pendingTransactions is not empty", which is caught by the extObj.catch()
What am I doing wrong? I'm fairly certain this is a promise handling issue on my part...
Any help is appreciated!

Answer 1

OK so I finally got there. Here is the method to call an OPC-UA method with a struct input argument using node-opcua:
const { OPCUAClient, NodeId, NodeIdType, DataType} = require("node-opcua");
const endpointUri = "opc.tcp://<your-endpoint>:<your-port>";
(async () => {
const client = OPCUAClient.create({ endpoint_must_exist: false});
client.on("backoff", () => console.log("Backoff: trying to connect to ", endpointUri));
await client.withSessionAsync(endpointUri, async (session) => {
// Scan settings value input
const scanSettingsParams = {
duration: 0,
cycles : 0,
dataAvailable : false,
locationType: 0
};
try {
// NodeID for InputArguments struct type (inherits from ScanSettings)
const nodeID = new NodeId(NodeIdType.NUMERIC, 3010, 3);
// Create ExtensionObject for InputArguments
const scanSettingsObj = await session.constructExtensionObject(nodeID, scanSettingsParams);
// Populate Method call with ExtensionObject as InputArgument
const methodToCall = {
objectId: "ns=4;s=rfr310",
methodId: "ns=4;s=rfr310.ScanStart",
inputArguments: [
{
dataType: DataType.ExtensionObject,
value: scanSettingsObj
}
]
};
// Call method, passing ScanSettings as input argument
session.call(methodToCall,(err,results) => {
if (err) {
console.log(err);
} else {
console.log(results);
}
});
} catch (err) {
console.log(err);
}
});
})();