Read Complex structure |OPC UA Implementation

[yurimedici86]

Hi, I am new to OPC ua and I am having problems reading structure data in a server from an opc ua client.

My code is very simple:

ComplexTypeSystem complexTypeSystem = new ComplexTypeSystem(uaClient.Session);
await complexTypeSystem.Load().ConfigureAwait(false);

EncodeableFactory.GlobalFactory.AddEncodeableType(typeof(ConfigType));

var conf = uaClient.Session.Call("ns=6;s=::Program", "ns=6;s=::Program:TestGetConfig");


IEncodeable confEncod = ExtensionObject.ToEncodeable((ExtensionObject)conf[0]);
ConfigType configuration = confEncod as ConfigType;
ConfigType casted = (ConfigType)confEncod ;
 

Where ConfigType is a C# class with properties equal to PLC server structure i want read :

public class ConfigType: EncodeableObject
{
        public override ExpandedNodeId TypeId => ExpandedNodeId.Parse("nsu=http://br-automation.com/OpcUa/PLC/PV/;i=100020");

public override ExpandedNodeId BinaryEncodingId => ExpandedNodeId.Parse("nsu=http://br-automation.com/OpcUa/PLC/PV/;i=100021");

public override ExpandedNodeId XmlEncodingId => NodeId.Null;

public override void Decode(IDecoder decoder)
{
}

public override void Encode(IEncoder encoder)
{

                 }

public ushort param1
{
   get;
   set;
}

public ushort param2
{
    get;
    set;
}

}

The properties value of Conf variable after call method are good but the type of Conf[0].body variable is "Opc.Ua.ComplexTyper.ne=6.i=99999.6.ConfigType" so confEncod is of the same type and configuration is null.

If i try a direct cast the error is

'Unable to cast object of type 'Opc.Ua.ComplexTypes.ns=6;i=99999.6.ConfigType' to type 'Quickstarts.ConsoleReferenceClient.ConfigType'

Anyone can help me?

Thanks a lot

[lkomanetz]

I haven't used EncodableObject yet but did solve this issue a different but similar way. First thing I do is create the data structure to mimic what the OPC-UA server is saying. We'll just say it looks like this:

public class MyObject
{
    public int SomeNumber { get; set; }
    public string SomeText { get; set; }
    public float SomeFloat { get; set; }
}

Then I use a combination of recursion and reflection to parse the ExtensionObject's body (which I think is always a byte[]). I'm using the built-in BinaryDecoder to do the heavy lifting of knowing how everything is encoded. Now I can do something like the below snippet and get the data in the way I want it.

var vector = await plc.ReadAsync<Vector>(vectorTag);
Console.WriteLine($"[{vector.X}, {vectory.Y}, {vector.Z}]");

The object could have a property that is an object itself which is where the recursion comes in. I just have to account for the various types in my switch. Hopefully this helps! One thing to note is that I'm still working on figuring out how to go the other direction. I can serialize the data structure to the correct byte array but it won't let me write to the tag. I think I have to have the ExpandedNodeId value for the type within the ExtensionObject I'm trying to write.

public TOutput FromBytes<TOutput>(byte[] bytes, IServiceMessageContext ctx)
{
    var decoder = new BinaryDecoder(bytes, ctx);
    var outputResult = DeserializeTo(typeof(TOutput), bytes, decoder);
    return (TOutput)outputResult;
}
static object DeserializeTo(Type t, byte[] bytes, BinaryDecoder decoder)
{
    var outputInstance = Activactor.CreateInstance(t);
    var properties = t.GetTypeInfo().GetProperties();

    foreach (var p in properties)
    {
        object? value = p.PropertyType switch
        {
            Type { Name: nameof(Int16) } => decoder.ReadInt16(p.Name),
            Type { Name: "Int16[]" } => decoder.ReadInt16Array(p.Name),
            /* etc. */
            Type { IsClass: true } childType => DeserializeTo(childType, bytes, decoder),
            _ => null
        };
        p.SetValue(outputInstance, value);
    }

    return outputInstance;
}

[lkomanetz]

It is something I've looked into a little bit but for what I'm trying to do I haven't been able to figure out a way for it to work. Essentially I'm working on a wrapper library that abstracts out some of the areas that make things more complicated when you're trying to do simple IO. Basically it looks like this right now...

using var plc = await PlcConnection.OpenAsync("opc.ua://localhost:4840?opcConfig=/path/to/opc.config.xml&listenerInterval=100");
var allTags = plc.GetPlcTags();
var numberTag = allTags.Single(t => t.Name.EndsWith("SomeNumber"));
int currentValue = await plc.ReadAsync<int>(numberTag); // We'll just say it is 5
int newValue = currentValue + 2;
await plc.WriteAsync(numberTag, newValue); // Writes 7 to the tag.

And for listening to tag changes

plc.TagChanged += (sender, args) =>
{
    Console.WriteLine($"Tag: {args.Tag.Name}\tValue: {args.Value}"); // args.Value is of type object
};
plc.StartListeningTo(numberTag, floatTag);
await Task.Delay(10_000);
plc.StopListeningTo(numberTag, floatTag);

With that goal in mind I haven't been able to figure out how to use EncodableObject.

[yurimedici86]

I'm working on the same kind of library for wrap opc.ua library. Now i'm working on write method. do you use encoding functions for writing?

[lkomanetz]

Yes I do. Basically the same thing but in reverse and the byte[] gets put into an ExtensionObject. The byte[] that it creates is identical with what is read from this OPC-UA library if all you do is parse the bytes into an object and then encode it back to bytes. I haven't confirmed yet but I think the correct type id you receive when you read the tag has to be a part of the extension object as well otherwise it won't write. I'm using the Prosys simulated OPC-UA server but I don't know how to create extension objects to test so I've been using an actual controller with an embedded server.

[yurimedici86]

I have some problem with the encodig of data. Witch IServiceMessageContext i have to use for write and read?
Thanks

[lkomanetz]

The Session is being treated like a singleton. That seems like how it wants to be used. So I'm really only using Session.MessageContext. If you are able to figure out how to get the extension object's type ID when browsing instead of having to read it first, cache it, and then use it for a later write that would be amazing. In my wrapper you have to get the list of PLC tags at some point in order to read / write. It just feels like information that should be available when you're recursively browsing nodes.