feat: Serialise the Double Ratchet

test/serialisation_test.dart

@@ -2,7 +2,7 @@ import 'package:omemo_dart/omemo_dart.dart';
 import 'package:test/test.dart';
 
 void main() {
-  test('Test serialising and deserialising Device', () async {
+  test('Test serialising and deserialising the Device', () async {
     // Generate a random session
     final oldSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
     final oldDevice = await oldSession.getDevice();
@@ -21,4 +21,50 @@ void main() {
       expect(await newDevice.opks[entry.key]!.equals(entry.value), true);
     }
   });
+
+  test('Test serialising and deserialising the OmemoDoubleRatchet', () async {
+    // Generate a random ratchet
+    const aliceJid = 'alice@server.example';
+    const bobJid = 'bob@other.server.example';
+    final aliceSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+    final bobSession = await OmemoSessionManager.generateNewIdentity(opkAmount: 1);
+    final aliceMessage = await aliceSession.encryptToJid(
+      bobJid,
+      'Hello Bob!',
+      newSessions: [
+        await (await bobSession.getDevice()).toBundle(),
+      ],
+    );
+    await bobSession.decryptMessage(
+      aliceMessage.ciphertext,
+      aliceJid,
+      (await aliceSession.getDevice()).id,
+      aliceMessage.encryptedKeys,
+    );
+    final aliceOld = aliceSession.getRatchet((await bobSession.getDevice()).id);
+    final aliceSerialised = await aliceOld.toJson();
+    final aliceNew = OmemoDoubleRatchet.fromJson(aliceSerialised);
+
+    expect(await aliceOld.dhs.equals(aliceNew.dhs), true);
+    if (aliceOld.dhr == null) {
+      expect(aliceNew.dhr, null);
+    } else {
+      expect(await aliceOld.dhr!.equals(aliceNew.dhr!), true);
+    }
+    expect(listsEqual(aliceOld.rk, aliceNew.rk), true);
+    if (aliceOld.cks == null) {
+      expect(aliceNew.cks, null);
+    } else {
+      expect(listsEqual(aliceOld.cks!, aliceNew.cks!), true);
+    }
+    if (aliceOld.ckr == null) {
+      expect(aliceNew.ckr, null);
+    } else {
+      expect(listsEqual(aliceOld.ckr!, aliceNew.ckr!), true);
+    }
+    expect(aliceOld.ns, aliceNew.ns);
+    expect(aliceOld.nr, aliceNew.nr);
+    expect(aliceOld.pn, aliceNew.pn);
+    expect(listsEqual(aliceOld.sessionAd, aliceNew.sessionAd), true);
+  });
 }