[Room] Clear outbound session only if devices changed

lib/src/client.dart

@@ -755,7 +755,7 @@ class Client {
       sessions.forEach((olm.Session session) => session?.free());
     });
     rooms.forEach((Room room) {
-      room.clearOutboundGroupSession();
+      room.clearOutboundGroupSession(wipe: true);
       room.sessionKeys.values.forEach((SessionKey sessionKey) {
         sessionKey.inboundGroupSession?.free();
       });
@@ -986,22 +986,6 @@ class Client {
     }
   }
 
-  /// Clears the outboundGroupSession from all rooms where this user is
-  /// participating. Should be called when the user's devices list has changed.
-  void _clearOutboundGroupSessionsByUserId(String userId) {
-    for (Room room in rooms) {
-      if (!room.encrypted) continue;
-      room.requestParticipants().then((List<User> users) {
-        if (users.indexWhere((u) =>
-                u.id == userId &&
-                [Membership.join, Membership.invite].contains(u.membership)) !=
-            -1) {
-          room.clearOutboundGroupSession();
-        }
-      });
-    }
-  }
-
   void _handleDeviceListsEvents(Map<String, dynamic> deviceLists) {
     if (deviceLists["changed"] is List) {
       for (final userId in deviceLists["changed"]) {
@@ -1010,7 +994,6 @@ class Client {
         }
       }
       for (final userId in deviceLists["left"]) {
-        _clearOutboundGroupSessionsByUserId(userId);
         if (_userDeviceKeys.containsKey(userId)) {
           _userDeviceKeys.remove(userId);
         }
@@ -1489,13 +1472,14 @@ class Client {
             }
           }
           _userDeviceKeys[userId].outdated = false;
-          if (_userDeviceKeys[userId].deviceKeys.toString() !=
-              oldKeys.toString()) {
-            _clearOutboundGroupSessionsByUserId(userId);
-          }
         }
       }
       await this.storeAPI?.storeUserDeviceKeys(userDeviceKeys);
+      rooms.forEach((Room room) {
+        if (room.encrypted) {
+          room.clearOutboundGroupSession();
+        }
+      });
     } catch (e) {
       print("[LibOlm] Unable to update user device keys: " + e.toString());
     }

lib/src/room.dart

@@ -84,12 +84,20 @@ class Room {
   olm.OutboundGroupSession get outboundGroupSession => _outboundGroupSession;
   olm.OutboundGroupSession _outboundGroupSession;
 
+  List<String> _outboundGroupSessionDevices;
+
   /// Clears the existing outboundGroupSession, tries to create a new one and
   /// stores it as an ingoingGroupSession in the [sessionKeys]. Then sends the
   /// new session encrypted with olm to all non-blocked devices using
   /// to-device-messaging.
   Future<void> createOutboundGroupSession() async {
-    await clearOutboundGroupSession();
+    await clearOutboundGroupSession(wipe: true);
+    List<DeviceKeys> deviceKeys = await getUserDeviceKeys();
+    _outboundGroupSessionDevices = [];
+    for (DeviceKeys keys in deviceKeys) {
+      _outboundGroupSessionDevices.add(keys.deviceId);
+    }
+    _outboundGroupSessionDevices.sort();
     try {
       _outboundGroupSession = olm.OutboundGroupSession();
       _outboundGroupSession.create();
@@ -110,7 +118,6 @@ class Room {
       "session_key": _outboundGroupSession.session_key(),
     };
     setSessionKey(rawSession["session_id"], rawSession);
-    List<DeviceKeys> deviceKeys = await getUserDeviceKeys();
     try {
       await client.sendToDevice(deviceKeys, "m.room_key", rawSession);
     } catch (e) {
@@ -127,17 +134,35 @@ class Room {
     await client.storeAPI?.setItem(
         "/clients/${client.deviceID}/rooms/${this.id}/outbound_group_session",
         _outboundGroupSession.pickle(client.userID));
+    await client.storeAPI?.setItem(
+        "/clients/${client.deviceID}/rooms/${this.id}/outbound_group_session_devices",
+        json.encode(_outboundGroupSessionDevices));
     return;
   }
 
-  /// Clears the existing outboundGroupSession.
-  Future<void> clearOutboundGroupSession() async {
+  /// Clears the existing outboundGroupSession but first checks if the participating
+  /// devices have been changed. Returns false if the session has not been cleared because
+  /// it wasn't necessary.
+  Future<bool> clearOutboundGroupSession({bool wipe = false}) async {
+    if (!wipe && this._outboundGroupSessionDevices != null) {
+      List<DeviceKeys> deviceKeys = await getUserDeviceKeys();
+      List<String> outboundGroupSessionDevices = [];
+      for (DeviceKeys keys in deviceKeys) {
+        outboundGroupSessionDevices.add(keys.deviceId);
+      }
+      outboundGroupSessionDevices.sort();
+      if (outboundGroupSessionDevices.toString() ==
+          this._outboundGroupSessionDevices.toString()) {
+        return false;
+      }
+    }
+    this._outboundGroupSessionDevices == null;
     await client.storeAPI?.setItem(
         "/clients/${client.deviceID}/rooms/${this.id}/outbound_group_session",
         null);
     this._outboundGroupSession?.free();
     this._outboundGroupSession = null;
-    return;
+    return true;
   }
 
   /// Key-Value store of session ids to the session keys. Only m.megolm.v1.aes-sha2
@@ -861,6 +886,13 @@ class Room {
               e.toString());
         }
       }
+      final String outboundGroupSessionDevicesString = await client.storeAPI
+          .getItem(
+              "/clients/${client.deviceID}/rooms/${this.id}/outbound_group_session_devices");
+      if (outboundGroupSessionDevicesString != null) {
+        this._outboundGroupSessionDevices =
+            List<String>.from(json.decode(outboundGroupSessionDevicesString));
+      }
       final String sessionKeysPickle = await client.storeAPI
           .getItem("/clients/${client.deviceID}/rooms/${this.id}/session_keys");
       if (sessionKeysPickle?.isNotEmpty ?? false) {

test/client_test.dart

@@ -563,7 +563,7 @@ void main() {
     });
     test('Test invalidate outboundGroupSessions', () async {
       if (matrix.encryptionEnabled) {
-        await matrix.rooms[1].clearOutboundGroupSession();
+        await matrix.rooms[1].clearOutboundGroupSession(wipe: true);
         expect(matrix.rooms[1].outboundGroupSession == null, true);
         await matrix.rooms[1].createOutboundGroupSession();
         expect(matrix.rooms[1].outboundGroupSession != null, true);
@@ -589,7 +589,7 @@ void main() {
           }
         });
         await Future.delayed(Duration(milliseconds: 50));
-        expect(matrix.rooms[1].outboundGroupSession == null, true);
+        expect(matrix.rooms[1].outboundGroupSession != null, true);
       }
     });
     DeviceKeys deviceKeys = DeviceKeys.fromJson({

test/fake_matrix_api.dart

@@ -603,6 +603,24 @@ class FakeMatrixApi extends MockClient {
               {"type": "m.login.password"}
             ]
           },
+      "/client/r0/rooms/!696r7674:example.com/members": (var req) => {
+            "chunk": [
+              {
+                "content": {
+                  "membership": "join",
+                  "avatar_url": "mxc://example.org/SEsfnsuifSDFSSEF",
+                  "displayname": "Alice Margatroid"
+                },
+                "type": "m.room.member",
+                "event_id": "§143273582443PhrSn:example.org",
+                "room_id": "!636q39766251:example.com",
+                "sender": "@alice:example.com",
+                "origin_server_ts": 1432735824653,
+                "unsigned": {"age": 1234},
+                "state_key": "@alice:example.com"
+              }
+            ]
+          },
       "/client/r0/rooms/!726s6s6q:example.com/members": (var req) => {
             "chunk": [
               {

test/room_test.dart

@@ -406,7 +406,7 @@ void main() {
 
     test('clearOutboundGroupSession', () async {
       if (!room.client.encryptionEnabled) return;
-      await room.clearOutboundGroupSession();
+      await room.clearOutboundGroupSession(wipe: true);
       expect(room.outboundGroupSession == null, true);
     });