feat: Periodically fetch ssss secrets from other devices

lib/encryption/encryption.dart

@@ -96,6 +96,10 @@ class Encryption {
       // some ssss thing. We can do this in the background
       unawaited(Zone.root.run(() => ssss.handleToDeviceEvent(event)));
     }
+    if (event.sender == client.userID) {
+      // maybe we need to re-try SSSS secrets
+      unawaited(Zone.root.run(() => ssss.periodicallyRequestMissingCache()));
+    }
   }
 
   Future<void> handleEventUpdate(EventUpdate update) async {
@@ -111,6 +115,11 @@ class Encryption {
       unawaited(Zone.root
           .run(() => keyVerificationManager.handleEventUpdate(update)));
     }
+    if (update.content['sender'] == client.userID &&
+        !update.content['unsigned'].containsKey('transaction_id')) {
+      // maybe we need to re-try SSSS secrets
+      unawaited(Zone.root.run(() => ssss.periodicallyRequestMissingCache()));
+    }
   }
 
   Future<ToDeviceEvent> decryptToDeviceEvent(ToDeviceEvent event) async {

lib/encryption/key_manager.dart

@@ -451,11 +451,16 @@ class KeyManager {
       try {
         await loadSingleKey(room.id, sessionId);
       } catch (err, stacktrace) {
+        if (err is MatrixException && err.errcode == 'M_NOT_FOUND') {
+          Logs.info(
+              '[KeyManager] Key not in online key backup, requesting it from other devices...');
+        } else {
           Logs.error(
               '[KeyManager] Failed to access online key backup: ' +
                   err.toString(),
               stacktrace);
         }
+      }
       if (!hadPreviously &&
           getInboundGroupSession(room.id, sessionId, senderKey) != null) {
         return; // we managed to load the session from online backup, no need to care about it now

lib/encryption/ssss.dart

@@ -258,18 +258,27 @@ class SSSS {
     }
   }
 
-  Future<void> maybeRequestAll(List<DeviceKeys> devices) async {
+  Future<void> maybeRequestAll([List<DeviceKeys> devices]) async {
     for (final type in CACHE_TYPES) {
+      if (keyIdsFromType(type) != null) {
         final secret = await getCached(type);
         if (secret == null) {
           await request(type, devices);
         }
       }
     }
+  }
 
-  Future<void> request(String type, List<DeviceKeys> devices) async {
+  Future<void> request(String type, [List<DeviceKeys> devices]) async {
     // only send to own, verified devices
     Logs.info('[SSSS] Requesting type ${type}...');
+    if (devices == null || devices.isEmpty) {
+      if (!client.userDeviceKeys.containsKey(client.userID)) {
+        Logs.warning('[SSSS] User does not have any devices');
+        return;
+      }
+      devices = client.userDeviceKeys[client.userID].deviceKeys.values.toList();
+    }
     devices.removeWhere((DeviceKeys d) =>
         d.userId != client.userID ||
         !d.verified ||
@@ -294,6 +303,27 @@ class SSSS {
     });
   }
 
+  DateTime _lastCacheRequest;
+  bool _isPeriodicallyRequestingMissingCache = false;
+  Future<void> periodicallyRequestMissingCache() async {
+    if (_isPeriodicallyRequestingMissingCache ||
+        (_lastCacheRequest != null &&
+            DateTime.now()
+                .subtract(Duration(minutes: 15))
+                .isBefore(_lastCacheRequest)) ||
+        client.isUnknownSession) {
+      // we are already requesting right now or we attempted to within the last 15 min
+      return;
+    }
+    _lastCacheRequest = DateTime.now();
+    _isPeriodicallyRequestingMissingCache = true;
+    try {
+      await maybeRequestAll();
+    } finally {
+      _isPeriodicallyRequestingMissingCache = false;
+    }
+  }
+
   Future<void> handleToDeviceEvent(ToDeviceEvent event) async {
     if (event.type == 'm.secret.request') {
       // got a request to share a secret

test/encryption/key_verification_test.dart

@@ -32,7 +32,7 @@ class MockSSSS extends SSSS {
 
   bool requestedSecrets = false;
   @override
-  Future<void> maybeRequestAll(List<DeviceKeys> devices) async {
+  Future<void> maybeRequestAll([List<DeviceKeys> devices]) async {
     requestedSecrets = true;
     final handle = open();
     handle.unlock(recoveryKey: SSSS_KEY);

test/encryption/ssss_test.dart

@@ -30,6 +30,19 @@ import 'package:olm/olm.dart' as olm;
 import '../fake_client.dart';
 import '../fake_matrix_api.dart';
 
+class MockSSSS extends SSSS {
+  MockSSSS(Encryption encryption) : super(encryption);
+
+  bool requestedSecrets = false;
+  @override
+  Future<void> maybeRequestAll([List<DeviceKeys> devices]) async {
+    requestedSecrets = true;
+    final handle = open();
+    handle.unlock(recoveryKey: SSSS_KEY);
+    await handle.maybeCacheAll();
+  }
+}
+
 void main() {
   group('SSSS', () {
     var olmEnabled = true;
@@ -392,6 +405,18 @@ void main() {
       expect(client.encryption.ssss.pendingShareRequests.length, 3);
     });
 
+    test('periodicallyRequestMissingCache', () async {
+      client.userDeviceKeys[client.userID].masterKey.setDirectVerified(true);
+      client.encryption.ssss = MockSSSS(client.encryption);
+      (client.encryption.ssss as MockSSSS).requestedSecrets = false;
+      await client.encryption.ssss.periodicallyRequestMissingCache();
+      expect((client.encryption.ssss as MockSSSS).requestedSecrets, true);
+      // it should only retry once every 15 min
+      (client.encryption.ssss as MockSSSS).requestedSecrets = false;
+      await client.encryption.ssss.periodicallyRequestMissingCache();
+      expect((client.encryption.ssss as MockSSSS).requestedSecrets, false);
+    });
+
     test('dispose client', () async {
       await client.dispose(closeDatabase: true);
     });