Daybreak/Daybreak.API/Services/ApiAdvertisingService.cs

using Daybreak.Shared.Models;
using Daybreak.Shared.Services.MDns;
using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using System.Extensions.Core;

namespace Daybreak.API.Services;

public sealed class ApiAdvertisingService(
    IServer server,
    IMDnsService mDnsService,
    IHostApplicationLifetime lifetime,
    ILogger<ApiAdvertisingService> logger) : IHostedService
{
    private const string ProcessIdPlaceholder = "{PID}";
    private const string ServiceName = $"daybreak-api-{ProcessIdPlaceholder}";
    private const string ServiceSubType = "daybreak-api";
    private readonly IServerAddressesFeature serverAddressesFeature = server.Features.Get<IServerAddressesFeature>() ?? throw new InvalidOperationException("Server does not support addresses feature.");
    private readonly IMDnsService mDnsService = mDnsService;
    private readonly IHostApplicationLifetime lifetime = lifetime;
    private readonly ILogger<ApiAdvertisingService> logger = logger;

    private DnsRegistrationToken? dnsToken;

    public Task StartAsync(CancellationToken cancellationToken)
    {
        this.lifetime.ApplicationStarted.Register(this.RegisterDomain);
        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        this.dnsToken?.Dispose();
        return Task.CompletedTask;
    }

    private void RegisterDomain()
    {
        var scopedLogger = this.logger.CreateScopedLogger();
        var addresses = this.serverAddressesFeature?.Addresses.ToArray() ?? [];
        var port = addresses
            .Select(a => new Uri(a).Port)
            .Distinct()
            .FirstOrDefault();

        scopedLogger.LogInformation("Found port {port}", port);
        if (port is 0)
        {
            throw new InvalidOperationException("Unable to start advertising service. No port found");
        }

        var dnsEntry = ServiceName.Replace(ProcessIdPlaceholder, Environment.ProcessId.ToString());
        scopedLogger.LogInformation("Advertising service {service}:{port}", dnsEntry, port);
        this.dnsToken = this.mDnsService.RegisterDomain(dnsEntry, (ushort)port, ServiceSubType);
    }
}