Auto Discovery Cleanup (jellyfin#10793)

* Call GetSmartApiUrl directly in UdpServer.RespondToV2Message

GetSmartApiUrl already returns PublishedServerUrl if set.

* Rewrite auto discovery using UdpClient and BackgroundService

* Respect network address settings in AutoDiscoveryHost

* Always listen on broadcast address in Linux for auto-discovery

* Await udp server tasks in AutoDiscoveryHost

* Only bind to broadcast addresses for IPv4

* Only bind to broadcast if IPv4 is enabled

Jellyfin.Server/Startup.cs

@@ -6,14 +6,14 @@
 using System.Text;
 using Jellyfin.Api.Middleware;
 using Jellyfin.MediaEncoding.Hls.Extensions;
+using Jellyfin.Networking;
 using Jellyfin.Networking.HappyEyeballs;
 using Jellyfin.Server.Extensions;
 using Jellyfin.Server.HealthChecks;
 using Jellyfin.Server.Implementations;
 using Jellyfin.Server.Implementations.Extensions;
 using Jellyfin.Server.Infrastructure;
 using MediaBrowser.Common.Net;
-using MediaBrowser.Controller;
 using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Extensions;
 using Microsoft.AspNetCore.Builder;
@@ -121,6 +121,8 @@ public void ConfigureServices(IServiceCollection services)
                 .AddCheck<DbContextFactoryHealthCheck<JellyfinDbContext>>(nameof(JellyfinDbContext));
 
             services.AddHlsPlaylistGenerator();
+
+            services.AddHostedService<AutoDiscoveryHost>();
         }
 
         /// <summary>

src/Jellyfin.Networking/AutoDiscoveryHost.cs

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Net;
+using MediaBrowser.Controller;
+using MediaBrowser.Model.ApiClient;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Jellyfin.Networking;
+
+/// <summary>
+/// <see cref="BackgroundService"/> responsible for responding to auto-discovery messages.
+/// </summary>
+public sealed class AutoDiscoveryHost : BackgroundService
+{
+    /// <summary>
+    /// The port to listen on for auto-discovery messages.
+    /// </summary>
+    private const int PortNumber = 7359;
+
+    private readonly ILogger<AutoDiscoveryHost> _logger;
+    private readonly IServerApplicationHost _appHost;
+    private readonly IConfigurationManager _configurationManager;
+    private readonly INetworkManager _networkManager;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AutoDiscoveryHost" /> class.
+    /// </summary>
+    /// <param name="logger">The <see cref="ILogger{AutoDiscoveryHost}"/>.</param>
+    /// <param name="appHost">The <see cref="IServerApplicationHost"/>.</param>
+    /// <param name="configurationManager">The <see cref="IConfigurationManager"/>.</param>
+    /// <param name="networkManager">The <see cref="INetworkManager"/>.</param>
+    public AutoDiscoveryHost(
+        ILogger<AutoDiscoveryHost> logger,
+        IServerApplicationHost appHost,
+        IConfigurationManager configurationManager,
+        INetworkManager networkManager)
+    {
+        _logger = logger;
+        _appHost = appHost;
+        _configurationManager = configurationManager;
+        _networkManager = networkManager;
+    }
+
+    /// <inheritdoc />
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var networkConfig = _configurationManager.GetNetworkConfiguration();
+        if (!networkConfig.AutoDiscovery)
+        {
+            return;
+        }
+
+        var udpServers = new List<Task>();
+        // Linux needs to bind to the broadcast addresses to receive broadcast traffic
+        if (OperatingSystem.IsLinux() && networkConfig.EnableIPv4)
+        {
+            udpServers.Add(ListenForAutoDiscoveryMessage(IPAddress.Broadcast, stoppingToken));
+        }
+
+        udpServers.AddRange(_networkManager.GetInternalBindAddresses()
+            .Select(intf => ListenForAutoDiscoveryMessage(
+                OperatingSystem.IsLinux() && intf.AddressFamily == AddressFamily.InterNetwork
+                    ? NetworkUtils.GetBroadcastAddress(intf.Subnet)
+                    : intf.Address,
+                stoppingToken)));
+
+        await Task.WhenAll(udpServers).ConfigureAwait(false);
+    }
+
+    private async Task ListenForAutoDiscoveryMessage(IPAddress address, CancellationToken cancellationToken)
+    {
+        using var udpClient = new UdpClient(new IPEndPoint(address, PortNumber));
+        udpClient.MulticastLoopback = false;
+
+        while (!cancellationToken.IsCancellationRequested)
+        {
+            try
+            {
+                var result = await udpClient.ReceiveAsync(cancellationToken).ConfigureAwait(false);
+                var text = Encoding.UTF8.GetString(result.Buffer);
+                if (text.Contains("who is JellyfinServer?", StringComparison.OrdinalIgnoreCase))
+                {
+                    await RespondToV2Message(udpClient, result.RemoteEndPoint, cancellationToken).ConfigureAwait(false);
+                }
+            }
+            catch (SocketException ex)
+            {
+                _logger.LogError(ex, "Failed to receive data from socket");
+            }
+            catch (OperationCanceledException)
+            {
+                _logger.LogDebug("Broadcast socket operation cancelled");
+            }
+        }
+    }
+
+    private async Task RespondToV2Message(UdpClient udpClient, IPEndPoint endpoint, CancellationToken cancellationToken)
+    {
+        var localUrl = _appHost.GetSmartApiUrl(endpoint.Address);
+        if (string.IsNullOrEmpty(localUrl))
+        {
+            _logger.LogWarning("Unable to respond to server discovery request because the local ip address could not be determined.");
+            return;
+        }
+
+        var response = new ServerDiscoveryInfo(localUrl, _appHost.SystemId, _appHost.FriendlyName);
+
+        try
+        {
+            _logger.LogDebug("Sending AutoDiscovery response");
+            await udpClient
+                .SendAsync(JsonSerializer.SerializeToUtf8Bytes(response).AsMemory(), endpoint, cancellationToken)
+                .ConfigureAwait(false);
+        }
+        catch (SocketException ex)
+        {
+            _logger.LogError(ex, "Error sending response message");
+        }
+    }
+}