feat: Ratchets should overwrite each other

lib/src/omemo/sessionmanager.dart

@@ -110,21 +110,22 @@ class OmemoSessionManager {
       // Add the bundle Id
       if (!_deviceMap.containsKey(jid)) {
         _deviceMap[jid] = [deviceId];
-      } else {
-        _deviceMap[jid]!.add(deviceId);
-      }
 
         // Commit the device map
         _eventStreamController.add(DeviceMapModifiedEvent(_deviceMap));
+      } else {
+        // Prevent having the same device multiple times in the list
+        if (!_deviceMap[jid]!.contains(deviceId)) {
+          _deviceMap[jid]!.add(deviceId);
+
+          // Commit the device map
+          _eventStreamController.add(DeviceMapModifiedEvent(_deviceMap));
+        }
+      }
 
       // Add the ratchet session
       final key = RatchetMapKey(jid, deviceId);
-      if (!_ratchetMap.containsKey(key)) {
       _ratchetMap[key] = ratchet;
-      } else {
-        // TODO(PapaTutuWawa): What do we do now?
-        throw Exception();
-      }
 
       // Commit the ratchet
       _eventStreamController.add(RatchetModifiedEvent(jid, deviceId, ratchet));

test/omemo_test.dart

@@ -543,4 +543,75 @@ void main() {
       true,
     );
   });
+
+  test('Test overwriting sessions', () async {
+    const aliceJid = 'alice@server.example';
+    const bobJid = 'bob@other.server.example';
+    // Alice and Bob generate their sessions
+    final aliceSession = await OmemoSessionManager.generateNewIdentity(
+      aliceJid,
+      AlwaysTrustingTrustManager(),
+      opkAmount: 1,
+    );
+    final bobSession = await OmemoSessionManager.generateNewIdentity(
+      bobJid,
+      AlwaysTrustingTrustManager(),
+      opkAmount: 2,
+    );
+
+    // Alice sends Bob a message
+    final msg1 = await aliceSession.encryptToJid(
+      bobJid,
+      'Hallo Welt',
+      newSessions: [
+        await (await bobSession.getDevice()).toBundle(),
+      ],
+    );
+    await bobSession.decryptMessage(
+      msg1.ciphertext,
+      aliceJid,
+      (await aliceSession.getDevice()).id,
+      msg1.encryptedKeys,
+    );
+    final aliceRatchet1 = aliceSession.getRatchet(
+      bobJid,
+      (await bobSession.getDevice()).id,
+    );
+    final bobRatchet1 = bobSession.getRatchet(
+      aliceJid,
+      (await aliceSession.getDevice()).id,
+    );
+
+    // Alice is impatient and immediately sends another message before the original one
+    // can be acknowledged by Bob
+    final msg2 = await aliceSession.encryptToJid(
+      bobJid,
+      "Why don't you answer?",
+      newSessions: [
+        await (await bobSession.getDevice()).toBundle(),
+      ],
+    );
+    await bobSession.decryptMessage(
+      msg2.ciphertext,
+      aliceJid,
+      (await aliceSession.getDevice()).id,
+      msg2.encryptedKeys,
+    );
+    final aliceRatchet2 = aliceSession.getRatchet(
+      bobJid,
+      (await bobSession.getDevice()).id,
+    );
+    final bobRatchet2 = bobSession.getRatchet(
+      aliceJid,
+      (await aliceSession.getDevice()).id,
+    );
+
+    // Both should only have one ratchet
+    expect(aliceSession.getRatchetMap().length, 1);
+    expect(bobSession.getRatchetMap().length, 1);
+    
+    // The ratchets should both be different
+    expect(await aliceRatchet1.equals(aliceRatchet2), false);
+    expect(await bobRatchet1.equals(bobRatchet2), false);
+  });
 }