wifi udp stream activity indicator added

app/lib/ui/providers/wifi_connection_provider.dart

@@ -32,6 +32,53 @@ final wifiLinkErrorReasonProvider = Provider<LinkErrorReason?>((ref) {
   return ref.watch(wifiTransportProvider).lastErrorReason;
 });
 
+/// Zeigt an, ob gerade UDP-Pakete ankommen ("receiving"/"not receiving"),
+/// unabhaengig vom (binaeren) Verbindungszustand - der Socket kann offen
+/// sein (LinkState.connected), ohne dass die Gegenstelle tatsaechlich
+/// sendet. Faellt [_receivingTimeout] nach dem letzten Paket automatisch
+/// wieder auf "not receiving" zurueck, dafuer muss ein Timer laufen statt
+/// nur auf den incoming-Stream zu reagieren.
+class WifiStreamActivityNotifier extends Notifier<bool> {
+  static const _receivingTimeout = Duration(seconds: 2);
+
+  StreamSubscription<void>? _dataSub;
+  StreamSubscription<LinkState>? _stateSub;
+  Timer? _timeoutTimer;
+
+  @override
+  bool build() {
+    final transport = ref.watch(wifiTransportProvider);
+    _dataSub?.cancel();
+    _stateSub?.cancel();
+    _timeoutTimer?.cancel();
+    _dataSub = transport.incoming.listen((_) => _onPacket());
+    _stateSub = transport.state.listen(_onStateChanged);
+    ref.onDispose(() {
+      _dataSub?.cancel();
+      _stateSub?.cancel();
+      _timeoutTimer?.cancel();
+    });
+    return false;
+  }
+
+  void _onPacket() {
+    state = true;
+    _timeoutTimer?.cancel();
+    _timeoutTimer = Timer(_receivingTimeout, () => state = false);
+  }
+
+  void _onStateChanged(LinkState linkState) {
+    if (linkState != LinkState.connected) {
+      _timeoutTimer?.cancel();
+      state = false;
+    }
+  }
+}
+
+final wifiStreamActivityProvider =
+    NotifierProvider<WifiStreamActivityNotifier, bool>(
+        WifiStreamActivityNotifier.new);
+
 /// Ein Eintrag im WLAN-Verbindungsprotokoll (Doku 7).
 class WifiConnectionLogEntry {
   const WifiConnectionLogEntry(this.timestamp, this.message);