feat: Allow removing a ratchet session

lib/src/omemo/events.dart

@@ -12,6 +12,14 @@ class RatchetModifiedEvent extends OmemoEvent {
   final OmemoDoubleRatchet ratchet;
 }
 
+/// Triggered when a ratchet has been removed and should be removed from storage.
+class RatchetRemovedEvent extends OmemoEvent {
+
+  RatchetRemovedEvent(this.jid, this.deviceId);
+  final String jid;
+  final int deviceId;
+}
+
 /// Triggered when the device map has been modified
 class DeviceMapModifiedEvent extends OmemoEvent {
 

lib/src/omemo/sessionmanager.dart

@@ -3,7 +3,8 @@ import 'dart:convert';
 import 'package:collection/collection.dart';
 import 'package:cryptography/cryptography.dart';
 import 'package:hex/hex.dart';
-import 'package:meta/meta.dart'; import 'package:omemo_dart/src/crypto.dart';
+import 'package:meta/meta.dart';
+import 'package:omemo_dart/src/crypto.dart';
 import 'package:omemo_dart/src/double_ratchet/double_ratchet.dart';
 import 'package:omemo_dart/src/errors.dart';
 import 'package:omemo_dart/src/helpers.dart';
@@ -93,6 +94,7 @@ class OmemoSessionManager {
   /// A stream that receives events regarding the session
   Stream<OmemoEvent> get eventStream => _eventStreamController.stream;
 
+  /// Returns our own device.
   Future<Device> getDevice() async {
     Device? dev;
     await _deviceLock.synchronized(() async {
@@ -403,11 +405,31 @@ class OmemoSessionManager {
     Map<String, List<int>>? map;
 
     await _lock.synchronized(() async {
-        map = _deviceMap;
+      map = _deviceMap;
     });
 
     return map!;
   }
+
+  /// Removes the ratchet identified by [jid] and [deviceId] from the session manager.
+  /// Also triggers events for commiting the new device map to storage and removing
+  /// the old ratchet.
+  Future<void> removeRatchet(String jid, int deviceId) async {
+    await _lock.synchronized(() async {
+      // Remove the ratchet
+      _ratchetMap.remove(RatchetMapKey(jid, deviceId));
+      // Commit it
+      _eventStreamController.add(RatchetRemovedEvent(jid, deviceId));
+
+      // Remove the device from jid
+      _deviceMap[jid]!.remove(deviceId);
+      if (_deviceMap[jid]!.isEmpty) {
+        _deviceMap.remove(jid);
+      }
+      // Commit it
+      _eventStreamController.add(DeviceMapModifiedEvent(_deviceMap));
+    });
+  }
   
   @visibleForTesting
   OmemoDoubleRatchet getRatchet(String jid, int deviceId) => _ratchetMap[RatchetMapKey(jid, deviceId)]!;

test/omemo_test.dart

@@ -422,4 +422,81 @@ void main() {
       expect(messageText, aliceReceivedMessage);
     }
   });
+
+  group('Test removing a ratchet', () {
+    test('Test removing a ratchet when the user has multiple', () async {
+      const aliceJid = 'alice@server.local';
+      const bobJid = 'bob@some.server.local';
+      final aliceSession = await OmemoSessionManager.generateNewIdentity(
+        aliceJid,
+        AlwaysTrustingTrustManager(),
+        opkAmount: 1,
+      );
+      final bobSession1 = await OmemoSessionManager.generateNewIdentity(
+        bobJid,
+        AlwaysTrustingTrustManager(),
+        opkAmount: 1,
+      );
+      final bobSession2 = await OmemoSessionManager.generateNewIdentity(
+        bobJid,
+        AlwaysTrustingTrustManager(),
+        opkAmount: 1,
+      );
+
+      // Alice sends a message to those two Bobs
+      final aliceMessage = await aliceSession.encryptToJid(
+        bobJid,
+        'Hallo Welt',
+        newSessions: [
+          await (await bobSession1.getDevice()).toBundle(),
+          await (await bobSession2.getDevice()).toBundle(),
+        ],
+      );
+
+      // One of those two sessions is broken, so Alice removes the session2 ratchet
+      final id1 = (await bobSession1.getDevice()).id;
+      final id2 = (await bobSession2.getDevice()).id;
+      await aliceSession.removeRatchet(bobJid, id1);
+
+      final map = await aliceSession.getRatchetMap();
+      expect(map.containsKey(RatchetMapKey(bobJid, id1)), false);
+      expect(map.containsKey(RatchetMapKey(bobJid, id2)), true);
+      final deviceMap = await aliceSession.getDeviceMap();
+      expect(deviceMap.containsKey(bobJid), true);
+      expect(deviceMap[bobJid], [id2]);
+    });
+
+    test('Test removing a ratchet when the user has only one', () async {
+      const aliceJid = 'alice@server.local';
+      const bobJid = 'bob@some.server.local';
+      final aliceSession = await OmemoSessionManager.generateNewIdentity(
+        aliceJid,
+        AlwaysTrustingTrustManager(),
+        opkAmount: 1,
+      );
+      final bobSession = await OmemoSessionManager.generateNewIdentity(
+        bobJid,
+        AlwaysTrustingTrustManager(),
+        opkAmount: 1,
+      );
+
+      // Alice sends a message to those two Bobs
+      final aliceMessage = await aliceSession.encryptToJid(
+        bobJid,
+        'Hallo Welt',
+        newSessions: [
+          await (await bobSession.getDevice()).toBundle(),
+        ],
+      );
+
+      // One of those two sessions is broken, so Alice removes the session2 ratchet
+      final id = (await bobSession.getDevice()).id;
+      await aliceSession.removeRatchet(bobJid, id);
+
+      final map = await aliceSession.getRatchetMap();
+      expect(map.containsKey(RatchetMapKey(bobJid, id)), false);
+      final deviceMap = await aliceSession.getDeviceMap();
+      expect(deviceMap.containsKey(bobJid), false);
+    });
+  });
 }