lmxopcua/tools/opcuacli-dotnet/Commands/SubscribeCommand.cs

using CliFx;
using CliFx.Attributes;
using CliFx.Infrastructure;
using Opc.Ua;
using Opc.Ua.Client;

namespace OpcUaCli.Commands;

[Command("subscribe", Description = "Monitor a node for value changes")]
public class SubscribeCommand : ICommand
{
    [CommandOption("url", 'u', Description = "OPC UA server endpoint URL", IsRequired = true)]
    public string Url { get; init; } = default!;

    [CommandOption("node", 'n', Description = "Node ID to monitor", IsRequired = true)]
    public string NodeId { get; init; } = default!;

    [CommandOption("interval", 'i', Description = "Polling interval in milliseconds")]
    public int Interval { get; init; } = 1000;

    public async ValueTask ExecuteAsync(IConsole console)
    {
        using var session = await OpcUaHelper.ConnectAsync(Url);

        var subscription = new Subscription(session.DefaultSubscription)
        {
            PublishingInterval = Interval,
            DisplayName = "CLI Subscription"
        };

        var item = new MonitoredItem(subscription.DefaultItem)
        {
            StartNodeId = new NodeId(NodeId),
            DisplayName = NodeId,
            SamplingInterval = Interval
        };

        item.Notification += (_, e) =>
        {
            if (e.NotificationValue is MonitoredItemNotification notification)
            {
                console.Output.WriteLine(
                    $"[{notification.Value.SourceTimestamp:O}] {NodeId} = {notification.Value.Value} ({notification.Value.StatusCode})");
            }
        };

        subscription.AddItem(item);
        session.AddSubscription(subscription);
        await subscription.CreateAsync();

        await console.Output.WriteLineAsync(
            $"Subscribed to {NodeId} (interval: {Interval}ms). Press Ctrl+C to stop.");

        var ct = console.RegisterCancellationHandler();

        try { await Task.Delay(Timeout.Infinite, ct); }
        catch (OperationCanceledException) { }

        await console.Output.WriteLineAsync("Unsubscribed.");
    }
}