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("username", 'U', Description = "Username for authentication")]
    public string? Username { get; init; }

    [CommandOption("password", 'P', Description = "Password for authentication")]
    public string? Password { get; init; }

    [CommandOption("security", 'S', Description = "Transport security: none, sign, encrypt (default: none)")]
    public string Security { get; init; } = "none";

    [CommandOption("failover-urls", 'F', Description = "Comma-separated failover endpoint URLs for redundancy")]
    public string? FailoverUrls { get; init; }

    [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)
    {
        var urls = FailoverUrlParser.Parse(Url, FailoverUrls);
        var hasFailover = urls.Length > 1;

        if (hasFailover)
        {
            await RunWithFailoverAsync(console, urls);
        }
        else
        {
            await RunSimpleAsync(console);
        }
    }

    private async Task RunSimpleAsync(IConsole console)
    {
        using var session = await OpcUaHelper.ConnectAsync(Url, Username, Password, Security);
        var (subscription, item) = await CreateSubscriptionAsync(session);
        await console.Output.WriteLineAsync($"Subscribed to {NodeId} (interval: {Interval}ms). Press Ctrl+C to stop.");

        var ct = console.RegisterCancellationHandler();
        await MonitorLoopAsync(session, subscription, item, ct);
        await console.Output.WriteLineAsync("Unsubscribed.");
    }

    private async Task RunWithFailoverAsync(IConsole console, string[] urls)
    {
        using var failover = new OpcUaFailoverHelper(urls, Username, Password, Security);
        var session = await failover.ConnectAsync();

        Subscription? subscription = null;
        MonitoredItem? item = null;
        var subLock = new object();

        (subscription, item) = await CreateSubscriptionAsync(session);
        await console.Output.WriteLineAsync(
            $"Subscribed to {NodeId} (interval: {Interval}ms, failover enabled). Press Ctrl+C to stop.");

        // Install failover handler
        failover.OnFailover += (oldUrl, newUrl) =>
        {
            Console.WriteLine($"  [failover] Switched from {oldUrl} to {newUrl}");
        };

        failover.InstallKeepAliveHandler(async newSession =>
        {
            try
            {
                var (newSub, newItem) = await CreateSubscriptionAsync(newSession);
                lock (subLock)
                {
                    subscription = newSub;
                    item = newItem;
                }
                Console.WriteLine($"  [failover] Re-subscribed to {NodeId} on {failover.CurrentEndpointUrl}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"  [failover] Failed to re-subscribe: {ex.Message}");
            }
        });

        var ct = console.RegisterCancellationHandler();

        int tick = 0;
        while (!ct.IsCancellationRequested)
        {
            await Task.Delay(2000, ct).ContinueWith(_ => { });
            tick++;

            Session? currentSession;
            MonitoredItem? currentItem;
            Subscription? currentSub;
            lock (subLock)
            {
                currentSession = failover.Session;
                currentSub = subscription;
                currentItem = item;
            }

            Console.WriteLine(
                $"  [tick {tick}] Server={failover.CurrentEndpointUrl}, Connected={currentSession?.Connected}, " +
                $"Sub.Id={currentSub?.Id}, " +
                $"LastValue={((currentItem?.LastValue as MonitoredItemNotification)?.Value?.Value)} " +
                $"({((currentItem?.LastValue as MonitoredItemNotification)?.Value?.StatusCode)})");
        }

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

    private async Task<(Subscription, MonitoredItem)> CreateSubscriptionAsync(Session session)
    {
        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.WriteLine(
                    $"[{notification.Value.SourceTimestamp:O}] {NodeId} = {notification.Value.Value} ({notification.Value.StatusCode})");
            }
        };

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

        return (subscription, item);
    }

    private static async Task MonitorLoopAsync(Session session, Subscription subscription, MonitoredItem item, CancellationToken ct)
    {
        int tick = 0;
        while (!ct.IsCancellationRequested)
        {
            await Task.Delay(2000, ct).ContinueWith(_ => { });
            tick++;
            Console.WriteLine(
                $"  [tick {tick}] Session={session.Connected}, Sub.Id={subscription.Id}, " +
                $"PublishingEnabled={subscription.PublishingEnabled}, " +
                $"MonitoredItemCount={subscription.MonitoredItemCount}, " +
                $"ItemStatus={item.Status?.Id}, " +
                $"LastNotification={((item.LastValue as MonitoredItemNotification)?.Value?.Value)} ({((item.LastValue as MonitoredItemNotification)?.Value?.StatusCode)})");
        }
    }
}