fix: bind to multicast ip on macOS

Bind to the multicast IP instead of the unicast IP like Linux. Unlike Linux, macOS does not require(and actually does not allow) bind to 255.255.255.255 to receive broadcast packets.

Signed-off-by: gnattu <gnattuoc@me.com>

src/Jellyfin.Networking/AutoDiscoveryHost.cs

@@ -11,6 +11,7 @@ using MediaBrowser.Common.Configuration;
 using MediaBrowser.Common.Net;
 using MediaBrowser.Controller;
 using MediaBrowser.Model.ApiClient;
+using MediaBrowser.Model.Net;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 
@@ -50,6 +51,25 @@ public sealed class AutoDiscoveryHost : BackgroundService
         _networkManager = networkManager;
     }
 
+    private static IPAddress GetBindAddress(IPData intf)
+    {
+        if (intf.AddressFamily == AddressFamily.InterNetwork)
+        {
+            if (OperatingSystem.IsLinux())
+            {
+                return NetworkUtils.GetBroadcastAddress(intf.Subnet);
+            }
+
+            if (OperatingSystem.IsMacOS())
+            {
+                // macOS kernel does not allow bind to 127:255:255:255
+                return IPAddress.IsLoopback(intf.Address) ? intf.Address : NetworkUtils.GetBroadcastAddress(intf.Subnet);
+            }
+        }
+
+        return intf.Address;
+    }
+
     /// <inheritdoc />
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
@@ -63,24 +83,23 @@ public sealed class AutoDiscoveryHost : BackgroundService
         // Linux needs to bind to the broadcast addresses to receive broadcast traffic
         if (OperatingSystem.IsLinux() && networkConfig.EnableIPv4)
         {
-            udpServers.Add(ListenForAutoDiscoveryMessage(IPAddress.Broadcast, stoppingToken));
+            udpServers.Add(ListenForAutoDiscoveryMessage(IPAddress.Broadcast, IPAddress.Broadcast, stoppingToken));
         }
 
         udpServers.AddRange(_networkManager.GetInternalBindAddresses()
             .Select(intf => ListenForAutoDiscoveryMessage(
-                OperatingSystem.IsLinux() && intf.AddressFamily == AddressFamily.InterNetwork
-                    ? NetworkUtils.GetBroadcastAddress(intf.Subnet)
-                    : intf.Address,
+                GetBindAddress(intf),
+                intf.Address,
                 stoppingToken)));
 
         await Task.WhenAll(udpServers).ConfigureAwait(false);
     }
 
-    private async Task ListenForAutoDiscoveryMessage(IPAddress address, CancellationToken cancellationToken)
+    private async Task ListenForAutoDiscoveryMessage(IPAddress listenAddress, IPAddress respondAddress, CancellationToken cancellationToken)
     {
         try
         {
-            using var udpClient = new UdpClient(new IPEndPoint(address, PortNumber));
+            using var udpClient = new UdpClient(new IPEndPoint(listenAddress, PortNumber));
             udpClient.MulticastLoopback = false;
 
             while (!cancellationToken.IsCancellationRequested)
@@ -91,7 +110,7 @@ public sealed class AutoDiscoveryHost : BackgroundService
                     var text = Encoding.UTF8.GetString(result.Buffer);
                     if (text.Contains("who is JellyfinServer?", StringComparison.OrdinalIgnoreCase))
                     {
-                        await RespondToV2Message(udpClient, result.RemoteEndPoint, cancellationToken).ConfigureAwait(false);
+                        await RespondToV2Message(respondAddress, result.RemoteEndPoint, cancellationToken).ConfigureAwait(false);
                     }
                 }
                 catch (SocketException ex)
@@ -107,11 +126,11 @@ public sealed class AutoDiscoveryHost : BackgroundService
         catch (Exception ex)
         {
             // Exception in this function will prevent the background service from restarting in-process.
-            _logger.LogError(ex, "Unable to bind to {Address}:{Port}", address, PortNumber);
+            _logger.LogError(ex, "Unable to bind to {Address}:{Port}", listenAddress, PortNumber);
         }
     }
 
-    private async Task RespondToV2Message(UdpClient udpClient, IPEndPoint endpoint, CancellationToken cancellationToken)
+    private async Task RespondToV2Message(IPAddress responderIp, IPEndPoint endpoint, CancellationToken cancellationToken)
     {
         var localUrl = _appHost.GetSmartApiUrl(endpoint.Address);
         if (string.IsNullOrEmpty(localUrl))
@@ -122,10 +141,11 @@ public sealed class AutoDiscoveryHost : BackgroundService
 
         var response = new ServerDiscoveryInfo(localUrl, _appHost.SystemId, _appHost.FriendlyName);
 
+        using var responder = new UdpClient(new IPEndPoint(responderIp, PortNumber));
         try
         {
             _logger.LogDebug("Sending AutoDiscovery response");
-            await udpClient
+            await responder
                 .SendAsync(JsonSerializer.SerializeToUtf8Bytes(response).AsMemory(), endpoint, cancellationToken)
                 .ConfigureAwait(false);
         }