fix(mobile): recover stale relay sessions

Co-authored-by: Tom Brow <tomb@block.xyz>
Signed-off-by: Tom Brow <tomb@block.xyz>

mobile/lib/shared/relay/relay_session.dart

@@ -78,17 +78,21 @@ class RelaySessionNotifier extends Notifier<SessionState> {
   RelaySessionNotifier({
     http.Client? httpClient,
     RelaySocketFactory socketFactory = RelaySocket.new,
+    DateTime Function()? now,
   }) : _httpClient = httpClient,
-       _socketFactory = socketFactory;
+       _socketFactory = socketFactory,
+       _now = now ?? DateTime.now;
 
   final http.Client? _httpClient;
   final RelaySocketFactory _socketFactory;
+  final DateTime Function() _now;
 
   static const _baseReconnectDelayMs = 1000;
   static const _maxReconnectDelayMs = 30000;
   static const _eventBatchMs = 16;
   static const _reconnectReplaySkewSeconds = 5;
   static const _maxRecentDeliveryKeys = 5000;
+  static const _backgroundGraceDuration = Duration(seconds: 5);
 
   RelaySocket? _socket;
   final Map<String, _HistorySubscription> _historySubscriptions = {};
@@ -99,6 +103,7 @@ class RelaySessionNotifier extends Notifier<SessionState> {
   Timer? _reconnectTimer;
   Timer? _flushTimer;
   Timer? _backgroundGraceTimer;
+  DateTime? _backgroundedAt;
   int _reconnectDelayMs = _baseReconnectDelayMs;
   int _subIdCounter = 0;
   bool _disposed = false;
@@ -315,8 +320,9 @@ class RelaySessionNotifier extends Notifier<SessionState> {
 
   /// Called by the app lifecycle provider when the app goes to background.
   void onAppPaused() {
+    _backgroundedAt = _now();
     _backgroundGraceTimer?.cancel();
-    _backgroundGraceTimer = Timer(const Duration(seconds: 5), _pauseNow);
+    _backgroundGraceTimer = Timer(_backgroundGraceDuration, _pauseNow);
   }
 
   void _pauseNow() {
@@ -331,12 +337,18 @@ class RelaySessionNotifier extends Notifier<SessionState> {
   /// Called by the app lifecycle provider when the app returns to foreground.
   void onAppResumed() {
     _paused = false;
+    final backgroundedAt = _backgroundedAt;
+    _backgroundedAt = null;
     _backgroundGraceTimer?.cancel();
     _backgroundGraceTimer = null;
 
-    // If still connected, nothing to do — the socket survived the background
-    // grace window.
-    if (state.status == SessionStatus.connected) return;
+    final backgroundedLongEnoughToRequireReconnect =
+        backgroundedAt != null &&
+        _now().difference(backgroundedAt) >= _backgroundGraceDuration;
+    if (!backgroundedLongEnoughToRequireReconnect &&
+        state.status == SessionStatus.connected) {
+      return;
+    }
 
     // Cancel any in-flight reconnect backoff timer so we reconnect immediately
     // instead of waiting for the (possibly large) exponential delay.
@@ -650,6 +662,7 @@ class RelaySessionNotifier extends Notifier<SessionState> {
     _reconnectTimer?.cancel();
     _flushTimer?.cancel();
     _backgroundGraceTimer?.cancel();
+    _backgroundedAt = null;
     _cancelAllHistory(null);
     _rejectAllPending(null);
     _recentDeliveryKeys.clear();

mobile/lib/shared/relay/relay_socket.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 
 import 'package:flutter/foundation.dart';
 import 'package:nostr/nostr.dart' as nostr;
+import 'package:web_socket_channel/io.dart';
 import 'package:web_socket_channel/web_socket_channel.dart';
 
 import 'nostr_models.dart';
@@ -30,6 +31,12 @@ Exception classifyRelayAuthFailure(String message) {
 }
 
 class RelaySocket {
+  /// Interval for sending a ping and awaiting its pong before disconnecting.
+  static const pingInterval = Duration(seconds: 30);
+
+  @visibleForTesting
+  static Duration debugPingInterval = pingInterval;
+
   final String _wsUrl;
   final String? _nsec;
   final void Function(List<dynamic> message) _onMessage;
@@ -63,7 +70,10 @@ class RelaySocket {
     _state = SocketState.connecting;
 
     try {
-      _channel = WebSocketChannel.connect(Uri.parse(_wsUrl));
+      _channel = IOWebSocketChannel.connect(
+        Uri.parse(_wsUrl),
+        pingInterval: debugPingInterval,
+      );
       await _channel!.ready;
     } catch (e) {
       _state = SocketState.disconnected;

mobile/pubspec.lock

@@ -274,7 +274,7 @@ packages:
     source: hosted
     version: "0.3.5+2"
   crypto:
-    dependency: transitive
+    dependency: "direct dev"
     description:
       name: crypto
       sha256: c8ea0233063ba03258fbcf2ca4d6dadfefe14f02fab57702265467a19f27fadf

mobile/pubspec.yaml

@@ -47,6 +47,7 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   flutter_lints: ^6.0.0
+  crypto: ^3.0.7
   custom_lint: ^0.8.0
   riverpod_lint: ^3.1.0
   mocktail: ^1.0.4

mobile/test/shared/relay/relay_session_test.dart

@@ -260,6 +260,120 @@ void main() {
     expect(session.state.status, SessionStatus.disconnected);
   });
 
+  test(
+    'resume reconnects a stale connected session after a long pause',
+    () async {
+      final sockets = <_ControlledRelaySocket>[];
+      final keychain = nostr.Keys.generate();
+      var now = DateTime(2026, 8, 2, 12);
+      final session = RelaySessionNotifier(
+        now: () => now,
+        socketFactory:
+            ({
+              required wsUrl,
+              required nsec,
+              required onMessage,
+              required onConnected,
+              required onDisconnected,
+            }) {
+              final socket = _ControlledRelaySocket(
+                wsUrl: wsUrl,
+                nsec: nsec,
+                onMessage: onMessage,
+                onConnected: onConnected,
+                onDisconnected: onDisconnected,
+              );
+              sockets.add(socket);
+              return socket;
+            },
+      );
+      final container = ProviderContainer(
+        overrides: [
+          relaySessionProvider.overrideWith(() => session),
+          relayConfigProvider.overrideWith(
+            () => _FakeRelayConfigNotifier(
+              baseUrl: 'https://relay.example',
+              nsec: keychain.nsec,
+            ),
+          ),
+          authProvider.overrideWith(() => _AuthenticatedAuthNotifier()),
+        ],
+      );
+      addTearDown(container.dispose);
+      await container.read(authProvider.future);
+      final subscription = container.listen(relaySessionProvider, (_, _) {});
+      addTearDown(subscription.close);
+      await Future<void>.delayed(Duration.zero);
+      sockets.single.connectSuccessfully();
+
+      session.onAppPaused();
+      now = now.add(const Duration(minutes: 5));
+      session.onAppResumed();
+      await Future<void>.delayed(Duration.zero);
+
+      expect(sockets, hasLength(2));
+      expect(sockets.first.disposeCalls, 1);
+      expect(session.state.status, SessionStatus.reconnecting);
+    },
+  );
+
+  test(
+    'resume keeps a connected session within the background grace period',
+    () async {
+      final sockets = <_ControlledRelaySocket>[];
+      final keychain = nostr.Keys.generate();
+      var now = DateTime(2026, 8, 2, 12);
+      final session = RelaySessionNotifier(
+        now: () => now,
+        socketFactory:
+            ({
+              required wsUrl,
+              required nsec,
+              required onMessage,
+              required onConnected,
+              required onDisconnected,
+            }) {
+              final socket = _ControlledRelaySocket(
+                wsUrl: wsUrl,
+                nsec: nsec,
+                onMessage: onMessage,
+                onConnected: onConnected,
+                onDisconnected: onDisconnected,
+              );
+              sockets.add(socket);
+              return socket;
+            },
+      );
+      final container = ProviderContainer(
+        overrides: [
+          relaySessionProvider.overrideWith(() => session),
+          relayConfigProvider.overrideWith(
+            () => _FakeRelayConfigNotifier(
+              baseUrl: 'https://relay.example',
+              nsec: keychain.nsec,
+            ),
+          ),
+          authProvider.overrideWith(() => _AuthenticatedAuthNotifier()),
+        ],
+      );
+      addTearDown(container.dispose);
+      await container.read(authProvider.future);
+      final subscription = container.listen(relaySessionProvider, (_, _) {});
+      addTearDown(subscription.close);
+      await Future<void>.delayed(Duration.zero);
+      sockets.single.connectSuccessfully();
+
+      session.onAppPaused();
+      now = now.add(const Duration(seconds: 4));
+      session.onAppResumed();
+      await Future<void>.delayed(Duration.zero);
+
+      expect(sockets, hasLength(1));
+      expect(sockets.single.disposeCalls, 0);
+      expect(session.state.status, SessionStatus.connected);
+    },
+  );
+
   test('delivers the same live event to each matching subscription', () async {
     final session = RelaySessionNotifier();
     final firstEvents = <NostrEvent>[];
@@ -402,6 +516,7 @@ class _AuthenticatedAuthNotifier extends AuthNotifier {
 class _ControlledRelaySocket extends RelaySocket {
   final void Function() _connected;
   final void Function(Object? error) _disconnected;
+  int disposeCalls = 0;
 
   _ControlledRelaySocket({
     required super.wsUrl,
@@ -416,7 +531,9 @@ class _ControlledRelaySocket extends RelaySocket {
   Future<void> connect() async {}
 
   @override
-  void dispose() {}
+  void dispose() {
+    disposeCalls++;
+  }
 
   void connectSuccessfully() => _connected();
 

mobile/test/shared/relay/relay_socket_liveness_test.dart

@@ -0,0 +1,111 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:buzz/shared/relay/relay_socket.dart';
+import 'package:crypto/crypto.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+/// A server that completes the WS handshake then never speaks again: no pongs,
+/// no close frame. Only a client-side ping timeout can notice.
+Future<ServerSocket> _silentAfterHandshakeServer() async {
+  final server = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
+  server.listen((client) {
+    client.listen(
+      (data) {
+        final match = RegExp(
+          r'Sec-WebSocket-Key: (.*)\r\n',
+          caseSensitive: false,
+        ).firstMatch(String.fromCharCodes(data));
+        if (match == null) return;
+        final accept = base64.encode(
+          sha1
+              .convert(
+                utf8.encode(
+                  '${match.group(1)!.trim()}258EAFA5-E914-47DA-95CA-C5AB0DC85B11',
+                ),
+              )
+              .bytes,
+        );
+        client.write(
+          'HTTP/1.1 101 Switching Protocols\r\n'
+          'Upgrade: websocket\r\nConnection: Upgrade\r\n'
+          'Sec-WebSocket-Accept: $accept\r\n\r\n',
+        );
+      },
+      onError: (_) {},
+      onDone: () {},
+    );
+  });
+  return server;
+}
+
+void main() {
+  const testPingInterval = Duration(milliseconds: 150);
+
+  setUp(() {
+    RelaySocket.debugPingInterval = testPingInterval;
+  });
+
+  tearDown(() {
+    RelaySocket.debugPingInterval = RelaySocket.pingInterval;
+  });
+
+  test('detects a peer that stops answering pings', () async {
+    final server = await _silentAfterHandshakeServer();
+
+    final disconnected = Completer<Object?>();
+    final socket = RelaySocket(
+      wsUrl: 'ws://127.0.0.1:${server.port}',
+      nsec: null,
+      onMessage: (_) {},
+      onConnected: () {},
+      onDisconnected: (error) {
+        if (!disconnected.isCompleted) disconnected.complete(error);
+      },
+    );
+    unawaited(socket.connect());
+
+    var detected = true;
+    try {
+      await disconnected.future.timeout(testPingInterval * 4);
+    } on TimeoutException {
+      detected = false;
+    }
+
+    expect(
+      detected,
+      isTrue,
+      reason:
+          'RelaySocket must surface an unanswered ping through onDisconnected',
+    );
+
+    socket.dispose();
+    await server.close();
+  });
+
+  test('keeps an idle but healthy peer connected', () async {
+    final server = await HttpServer.bind(InternetAddress.loopbackIPv4, 0);
+    server.transform(WebSocketTransformer()).listen((ws) {
+      // A healthy relay answers pings without sending application data.
+      ws.listen((_) {}, onError: (_) {}, onDone: () {});
+    });
+
+    var tornDown = false;
+    final socket = RelaySocket(
+      wsUrl: 'ws://127.0.0.1:${server.port}',
+      nsec: null,
+      onMessage: (_) {},
+      onConnected: () {},
+      onDisconnected: (_) => tornDown = true,
+    );
+    unawaited(socket.connect());
+
+    await Future<void>.delayed(testPingInterval * 4);
+
+    expect(tornDown, isFalse);
+
+    await socket.disconnect();
+    await server.close(force: true);
+  });
+}