proof-of-concept for server discovery emulation

- currently always on

Author: Chaphasilor

lib/components/LoginScreen/login_flow.dart

@@ -290,6 +290,7 @@ class JellyfinServerClientDiscovery {
               .finest("Received datagram: ${utf8.decode(datagram.data)}");
           final response = ClientDiscoveryResponse.fromJson(
               jsonDecode(utf8.decode(datagram.data)));
+          _clientDiscoveryLogger.fine("Received discovery response from ${datagram.address}:${datagram.port}: ${jsonEncode(response)}");
           onServerFound(response);
         }
       }

lib/main.dart

@@ -20,6 +20,7 @@ import 'package:finamp/services/keep_screen_on_helper.dart';
 import 'package:finamp/services/offline_listen_helper.dart';
 import 'package:finamp/services/playback_history_service.dart';
 import 'package:finamp/services/queue_service.dart';
+import 'package:finamp/services/server_discovery_emulation_service.dart';
 import 'package:finamp/services/theme_provider.dart';
 import 'package:audio_service/audio_service.dart';
 import 'package:audio_session/audio_session.dart';
@@ -340,6 +341,7 @@ Future<void> _setupPlaybackServices() async {
   await GetIt.instance<QueueService>().initializePlayer();
   GetIt.instance.registerSingleton(PlaybackHistoryService());
   GetIt.instance.registerSingleton(AudioServiceHelper());
+  GetIt.instance.registerSingleton(JellyfinServerDiscoveryEmulationService());
 }
 
 /// Migrates the old DownloadLocations list to a map

lib/models/jellyfin_models.dart

@@ -3802,6 +3802,7 @@ class ClientDiscoveryResponse {
 
   factory ClientDiscoveryResponse.fromJson(Map<String, dynamic> json) =>
       _$ClientDiscoveryResponseFromJson(json);
+  Map<String, dynamic> toJson() => _$ClientDiscoveryResponseToJson(this);
 }
 
 /// LyricMetadata model.

lib/services/server_discovery_emulation_service.dart

@@ -0,0 +1,69 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:finamp/models/jellyfin_models.dart';
+import 'package:finamp/services/finamp_user_helper.dart';
+import 'package:get_it/get_it.dart';
+import 'package:logging/logging.dart';
+
+/// Used for discovering Jellyfin servers on the local network
+/// https://jellyfin.org/docs/general/networking/#port-bindings
+/// For some reason it's always being referred to as "client discovery" in the Jellyfin docs, even though we're actually discovering servers
+class JellyfinServerDiscoveryEmulationService {
+  static final _serverDiscoveryEmulationLogger = Logger("JellyfinServerDiscoveryEmulation");
+
+  final _finampUserHelper = GetIt.instance<FinampUserHelper>();
+
+  late RawDatagramSocket socket;
+  bool isDisposed = false;
+
+  JellyfinServerDiscoveryEmulationService() {
+    advertiseServer();
+  }
+
+  void advertiseServer() async {
+
+    const discoveryMessage =
+        "who is JellyfinServer?"; // doesn't seem to be case sensitive, but the Kotlin SDK uses this capitalization
+    final broadcastAddress =
+        InternetAddress("255.255.255.255"); // UDP broadcast address
+    const discoveryPort = 7359; // Jellyfin client discovery port
+
+    socket = await RawDatagramSocket.bind(InternetAddress.anyIPv4, discoveryPort);
+    socket.broadcastEnabled =
+        true; // important to allow sending to broadcast address
+    socket.multicastHops = 5; // to account for weird network setups
+
+    _serverDiscoveryEmulationLogger.fine("Advertising server on port $discoveryPort");
+
+    socket.listen((event) {
+      if (event == RawSocketEvent.read) {
+        final datagram = socket.receive();
+        if (datagram != null) {
+          _serverDiscoveryEmulationLogger
+              .finest("Received datagram: ${utf8.decode(datagram.data)}");
+          final requestMessage = utf8.decode(datagram.data);
+          if (requestMessage.toLowerCase().contains(discoveryMessage.toLowerCase())) {
+            _serverDiscoveryEmulationLogger.fine("Received discovery message from ${datagram.address}:${datagram.port}");
+            // Respond with the server's information
+            final response = ClientDiscoveryResponse(
+              address: _finampUserHelper.currentUser?.baseUrl,
+              endpointAddress: _finampUserHelper.currentUser?.baseUrl,
+              id: _finampUserHelper.currentUser?.serverId,
+              name: "Jellyfin Server (provided by Finamp)",
+            );
+            final responseMessage = jsonEncode(response);
+            _serverDiscoveryEmulationLogger.finest("Sending discovery response: $responseMessage");
+            socket.send(utf8.encode(responseMessage), datagram.address, datagram.port);
+            _serverDiscoveryEmulationLogger.fine("Sent discovery response to ${datagram.address}:${datagram.port}");
+          }
+        }
+      }
+    });
+  }
+
+  void dispose() {
+    isDisposed = true;
+    socket.close();
+  }
+}