Added mDNS advertising for simple LAN access to UI

[cbattlegear]

Added basic mDNS advertising to the BlazorServer setup.
UI will now advertise on the LAN at http://wowbot.local:5000.

This makes the prompt properly pop up from Windows to allow access to the program and makes accessing the UI significantly easier from remote devices.

[Xian55]

Gooday, interesting request.

Personally there are times when i'm running the application on the same network on two different computers (main pc where im developing + one lower specced machine which where i can run longer session to gather data). For this specific use case i would assume i would ran into dns name collision in the same network.

Which at that point having a unique name in the same network seems rather an obstacle then a benefit.

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Secondly Makaretu.Dns.Multicast v0.27.0 a 7 years old.

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Also some notices about the PR in general:

GetLocalIPAddresses() is called on every mDNS query received. This iterates all network interfaces which is relatively expensive. Consider caching the result and refreshing periodically or on network change events.

Missing using - List<IPAddress> is used but System.Collections.Generic isn't in the using statements (may be a global using).

Null safety in StopAsync - _serviceProfile could be null if StartAsync failed early:

 _serviceDiscovery?.Unadvertise(_serviceProfile);  // _serviceProfile could be null

run.bat fallback - If mDNS fails (unsupported network, etc.), wowbot.local won't resolve and the browser will fail to open. The old localhost was a safer default.

[cbattlegear]

Totally! This came from helping out a friend who didn't have a bunch of context about networking and trying to explain how to reach the UI from another computer in their house.

I'll get that IP caching in, that makes total sense. The System.Collections.Generic was removed via Intellisense, I'll throw it in the using properly.

And I'll get that null safety check, that was just me working too fast.

Thanks for the review on it and I'll get the code up shortly!

[Xian55]

I had time to think about it, how about making this feature guarded by a feature flag ? like a command line argument ?

[cbattlegear]

That's actually what I was working on setting up as we speak, the system by default probes for wowbot.local and won't advertise if it already exists. By default if you are running one instance you get wowbot.local.

I changed the batch back to localhost to prevent it not working if there is a conflict.

And the part I am working on currently is making a command line argument you can use with the dotnet run call to pick a custom mDNS name to be advertised.

So if you wanted you could have a fleet all advertising unique DNS names based on whatever you had put in your run.bat or on the cmd.

[cbattlegear]

Ok! Got the caching, null safety, custom mDNS names, and documentation handled, also moved to a fork of the mdns library that is significantly newer/up to date.

[Xian55]

Since .NET 9 introduced System.Threading.Lock it's the recommended approach now.

[cbattlegear]

Implemented as requested 49c876c

[Xian55]

After reading more about the mDNS topic in Windows there's a requirement

  ┌────────────────────┬───────────────┬──────────────────────────────────────────────────────┐
  │         OS         │    Status     │                        Notes                         │
  ├────────────────────┼───────────────┼──────────────────────────────────────────────────────┤
  │ Windows 10 1809+   │ Built-in      │ Microsoft added native mDNS resolution               │
  ├────────────────────┼───────────────┼──────────────────────────────────────────────────────┤
  │ Windows 10 (older) │ Needs Bonjour │ Install iTunes or Bonjour Print Services             │
  └────────────────────┴───────────────┴──────────────────────────────────────────────────────┘

I'm aware that many people are still running the "project" under a Virtual machine where even Windows ?7? could be installed 👀

[Xian55]

Doesn't account for launchSettings.json or appsettings.json Kestrel config.

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Recommendation

 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.AspNetCore.Hosting.Server.Features;

public sealed class MdnsAdvertisingService : IHostedService, IDisposable
{
    private readonly ILogger<MdnsAdvertisingService> _logger;
    private readonly IServer _server;
    private readonly IHostApplicationLifetime _lifetime;
    private readonly string _hostname;

    private int _port = 5000; // fallback
    private CancellationTokenRegistration _startedRegistration;

    public MdnsAdvertisingService(
        ILogger<MdnsAdvertisingService> logger,
        IServer server,
        IHostApplicationLifetime lifetime)
    {
        _logger = logger;
        _server = server;
        _lifetime = lifetime;
        _hostname = Environment.GetEnvironmentVariable("MDNS_HOSTNAME") ?? "wowbot";
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        // Server addresses aren't available until after Kestrel binds
        // Wait for ApplicationStarted event
        _startedRegistration = _lifetime.ApplicationStarted.Register(() =>
        {
            var addressFeature = _server.Features.Get<IServerAddressesFeature>();
            if (addressFeature != null)
            {
                foreach (var address in addressFeature.Addresses)
                {
                    if (Uri.TryCreate(address, UriKind.Absolute, out var uri))
                    {
                        _port = uri.Port;
                        _logger.LogDebug("mDNS: Detected server port {Port} from {Address}", _port, address);
                        break;
                    }
                }
            }

            // Now start advertising with the correct port
            StartAdvertising();
        });

        return Task.CompletedTask;
    }

[cbattlegear]

Implemented as requested in 57b0511

[Xian55]

It would be nice when the feature is not used, then the service its won't be registered in the Dependency Injection container.

[cbattlegear]

Added USE_MDNS env var check, if it is not null it will load the service
d69eac7

[Xian55]

Thanks, its shaping better and better, i have no more nitpicks, i like the capability, however i do not want this to be the default behaviour of accessing the BlazorServer portal, however those who want to opt it can do so!

From my end this is acceptable, i will squash and merge! Thank you for the contribution! 🙇