node opc-ua - how do i discover a variable in a server? - node.js

Question

I am learning node opc-ua and have followed the example provided in the GitHub page for the sample_server.js and simple_client.js.
In the sample_server I add a variable when constructing the address space of the server such as:
//this code is in the server
addressSpace.addVariable({
componentOf: device,
nodeId: "ns=1;s=variable_1",
browseName: "MyVariable1",
dataType: "Double",
value: {
get: function () {
return new opcua.Variant({ dataType: opcua.DataType.Double, value: variable1 });
}
}
});
Here is the whole server code for reference:
var opcua = require("node-opcua");
var server = new opcua.OPCUAServer({
port: 4334, // the port of the listening socket of the server
resourcePath: "UA/MyLittleServer", // this path will be added to the endpoint resource name
buildInfo: {
productName: "MySampleServer1",
buildNumber: "7658",
buildDate: new Date(2014, 5, 2)
}
});
server.initialize(post_initialize);
function post_initialize() {
console.log("initialized");
construct_my_address_space(server, function () {
server.start(function () {
console.log("Server is now listening ... ( press CTRL+C to stop)");
console.log("port ", server.endpoints[0].port);
var endpointUrl = server.endpoints[0].endpointDescriptions()[0].endpointUrl;
console.log(" the primary server endpoint url is ", endpointUrl);
});
});
}
function construct_my_address_space(server, callback) {
var addressSpace = server.engine.addressSpace;
// declare a new object
var device = addressSpace.addObject({
organizedBy: addressSpace.rootFolder.objects,
browseName: "MyDevice"
});
// add a variable named MyVariable1 to the newly created folder "MyDevice"
var variable1 = 1;
// emulate variable1 changing every 500 ms
setInterval(function () { variable1 += 1; }, 500);
addressSpace.addVariable({
componentOf: device,
nodeId: "ns=1;s=variable_1",
browseName: "MyVariable1",
dataType: "Double",
value: {
get: function () {
return new opcua.Variant({ dataType: opcua.DataType.Double, value: variable1 });
}
}
});
callback();
}
Now, in the client i want to discover this variable by name or the full nodeId.
I am using the sample provided to browse the session to the server but in the return i only see FolderType, Objects, Types and Views and can not locate this variable anywhere.
Here is the client code:
var opcua = require("node-opcua");
var async = require("async");
var client = new opcua.OPCUAClient();
var endpointUrl = "opc.tcp://" + require("os").hostname() + ":4334/UA/MyLittleServer";
var the_session, the_subscription;
async.series([
// step 1 : connect to
function (callback) {
client.connect(endpointUrl, function (err) {
if (err) {
console.log(" cannot connect to endpoint :", endpointUrl);
} else {
console.log("connected !");
}
callback(err);
});
},
// step 2 : createSession
function (callback) {
client.createSession(function (err, session) {
if (!err) {
the_session = session;
}
callback(err);
});
},
// step 3 : browse
function (callback) {
the_session.browse("RootFolder", function (err, browse_result) {
if (!err) {
console.log('Result of browsing: ', browse_result);
browse_result[0].references.forEach(function (reference) {
console.log('browsing: ', reference.browseName);
console.log(reference);
console.log("**************************************");
});
}
callback(err);
});
},
/* step 4 : read a variable with readVariableValue
function (callback) {
the_session.readVariableValue("ns=1;s=variable_1", function (err, dataValue) {
if (!err) {
console.log(" var 1 = ", dataValue.toString());
}
callback(err);
});
},
// step 4' : read a variable with read
function (callback) {
var max_age = 0;
var nodes_to_read = [
{ nodeId: "ns=1;s=variable_1", attributeId: opcua.AttributeIds.Value }
];
the_session.read(nodes_to_read, max_age, function (err, nodes_to_read, dataValues) {
if (!err) {
console.log(" variable 1 = ", dataValues[0]);
}
callback(err);
});
},
*/
// step 5: install a subscription and install a monitored item for 10 seconds
function (callback) {
the_subscription = new opcua.ClientSubscription(the_session, {
requestedPublishingInterval: 1000,
requestedLifetimeCount: 10,
requestedMaxKeepAliveCount: 2,
maxNotificationsPerPublish: 10,
publishingEnabled: true,
priority: 10
});
the_subscription.on("started", function () {
console.log("subscription started for 2 seconds - subscriptionId=", the_subscription.subscriptionId);
}).on("keepalive", function () {
console.log("keepalive");
}).on("terminated", function () {
callback();
});
setTimeout(function () {
the_subscription.terminate();
}, 10000);
// install monitored item
var monitoredItem = the_subscription.monitor({
nodeId: opcua.resolveNodeId("ns=1;s=variable_1"),
attributeId: opcua.AttributeIds.Value
},
{
samplingInterval: 100,
discardOldest: true,
queueSize: 10
},
opcua.read_service.TimestampsToReturn.Both
);
console.log("-------------------------------------");
monitoredItem.on("changed", function (dataValue) {
console.log("variable_1 = ", dataValue.value.value);
});
},
// close session
function (callback) {
the_session.close(function (err) {
if (err) {
console.log("session closed failed ?");
} else{
console.log("session closed!");
}
callback();
});
}
],
function (err) {
if (err) {
console.log(" failure ", err);
} else {
console.log("done!");
}
client.disconnect(function () { });
});
Thanks in advance

Answer 1

You need to drill down from from the rootFolder and investigate the various objects until you find the variable you want to monitor, with a series of browseNode.
The best option is to use a free OPCUA client from a commercial vendor such as UAExpert or Prosys OPC UA Client to name a few.
You can also use opcua-commander: This little utility will allow you to explore the address space of the server and find the node you're looking for. ( source code available on github )