packages/moxxmpp/lib/src/xeps/xep_0384/xep_0384.dart

@@ -1,6 +1,8 @@
 import 'dart:async';
+import 'dart:collection';
 import 'dart:convert';
 import 'package:meta/meta.dart';
+import 'package:moxlib/moxlib.dart';
 import 'package:moxxmpp/src/events.dart';
 import 'package:moxxmpp/src/jid.dart';
 import 'package:moxxmpp/src/managers/base.dart';
@@ -23,6 +25,7 @@ import 'package:moxxmpp/src/xeps/xep_0384/errors.dart';
 import 'package:moxxmpp/src/xeps/xep_0384/helpers.dart';
 import 'package:moxxmpp/src/xeps/xep_0384/types.dart';
 import 'package:omemo_dart/omemo_dart.dart';
+import 'package:synchronized/synchronized.dart';
 
 const _doNotEncryptList = [
   // XEP-0033
@@ -40,7 +43,17 @@ const _doNotEncryptList = [
   DoNotEncrypt('stanza-id', stableIdXmlns),
 ];
 
-abstract class BaseOmemoManager extends XmppManagerBase {
+abstract class OmemoManager extends XmppManagerBase {
+  OmemoManager() : _handlerLock = Lock(), _handlerFutures = {}, super();
+
+  final Lock _handlerLock;
+  final Map<JID, Queue<Completer<void>>> _handlerFutures;
+
+  final Map<JID, List<int>> _deviceMap = {};
+
+  // Mapping whether we already tried to subscribe to the JID's devices node
+  final Map<JID, bool> _subscriptionMap = {};
+  
   @override
   String getId() => omemoManager;
 
@@ -114,29 +127,58 @@ abstract class BaseOmemoManager extends XmppManagerBase {
       } else {
         // Someone published to their device list node
         logger.finest('Got devices $ids');
+        _deviceMap[jid] = ids;
       }
 
-      // Tell the OmemoManager
-      (await getOmemoManager())
-        .onDeviceListUpdate(jid.toString(), ids);
-
       // Generate an event
       getAttributes().sendEvent(OmemoDeviceListUpdatedEvent(jid, ids));
     }
   }
   
   @visibleForOverriding
-  Future<OmemoManager> getOmemoManager();
+  Future<OmemoSessionManager> getSessionManager();
 
+  /// Wrapper around using getSessionManager and then calling encryptToJids on it.
+  Future<EncryptionResult> _encryptToJids(List<String> jids, String? plaintext, { List<OmemoBundle>? newSessions }) async {
+    final session = await getSessionManager();
+    return session.encryptToJids(jids, plaintext, newSessions: newSessions);
+  }
+
+  /// Wrapper around using getSessionManager and then calling encryptToJids on it.
+  Future<String?> _decryptMessage(List<int>? ciphertext, String senderJid, int senderDeviceId, List<EncryptedKey> keys, int sendTimestamp) async {
+    final session = await getSessionManager();
+    return session.decryptMessage(
+      ciphertext,
+      senderJid,
+      senderDeviceId,
+      keys,
+      sendTimestamp,
+    );
+  }
   
   /// Wrapper around using getSessionManager and then calling getDeviceId on it.
-  Future<int> _getDeviceId() async => (await getOmemoManager()).getDeviceId();
+  Future<int> _getDeviceId() async {
+    final session = await getSessionManager();
+    return session.getDeviceId();
+  }
 
   /// Wrapper around using getSessionManager and then calling getDeviceId on it.
   Future<OmemoBundle> _getDeviceBundle() async {
-    final om = await getOmemoManager();
+    final session = await getSessionManager();
-    final device = await om.getDevice();
+    return session.getDeviceBundle();
-    return device.toBundle();
+  }
+
+  /// Wrapper around using getSessionManager and then calling isRatchetAcknowledged on it.
+  Future<bool> _isRatchetAcknowledged(String jid, int deviceId) async {
+    final session = await getSessionManager();
+    return session.isRatchetAcknowledged(jid, deviceId);
+  }
+
+  /// Wrapper around checking if [jid] appears in the session manager's device map.
+  Future<bool> _hasSessionWith(String jid) async {
+    final session = await getSessionManager();
+    final deviceMap = await session.getDeviceMap();
+    return deviceMap.containsKey(jid);
   }
   
   /// Determines what child elements of a stanza should be encrypted. If shouldEncrypt
@@ -163,9 +205,11 @@ abstract class BaseOmemoManager extends XmppManagerBase {
   /// an attached payload, if [children] is not null, or an empty OMEMO message if
   /// [children] is null. This function takes care of creating the affix elements as
   /// specified by both XEP-0420 and XEP-0384.
-  /// [toJid] is the list of JIDs the payload should be encrypted for.
+  /// [jids] is the list of JIDs the payload should be encrypted for.
-  String _buildEnvelope(List<XMLNode> children, String toJid) {
+  Future<XMLNode> _encryptChildren(List<XMLNode>? children, List<String> jids, String toJid, List<OmemoBundle> newSessions) async {
-    final payload = XMLNode.xmlns(
+    XMLNode? payload;
+    if (children != null) {
+      payload = XMLNode.xmlns(
         tag: 'envelope',
         xmlns: sceXmlns,
         children: [
@@ -201,13 +245,16 @@ abstract class BaseOmemoManager extends XmppManagerBase {
           */
         ],
       );
-
-    return payload.toXml();
     }
 
-  XMLNode _buildEncryptedElement(EncryptionResult result, String recipientJid, int deviceId) {
+    final encryptedEnvelope = await _encryptToJids(
+      jids,
+      payload?.toXml(),
+      newSessions: newSessions,
+    );
+
     final keyElements = <String, List<XMLNode>>{};
-    for (final key in result.encryptedKeys) {
+    for (final key in encryptedEnvelope.encryptedKeys) {
       final keyElement = XMLNode(
         tag: 'key',
         attributes: <String, String>{
@@ -235,11 +282,11 @@ abstract class BaseOmemoManager extends XmppManagerBase {
     }).toList();
 
     var payloadElement = <XMLNode>[];
-    if (result.ciphertext != null) {
+    if (payload != null) {
       payloadElement = [
         XMLNode(
           tag: 'payload',
-          text: base64.encode(result.ciphertext!),
+          text: base64.encode(encryptedEnvelope.ciphertext!),
         ),
       ];
     }
@@ -252,7 +299,7 @@ abstract class BaseOmemoManager extends XmppManagerBase {
         XMLNode(
           tag: 'header',
           attributes: <String, String>{
-            'sid': deviceId.toString(),
+            'sid': (await _getDeviceId()).toString(),
           },
           children: keysElements,
         ),
@@ -260,18 +307,136 @@ abstract class BaseOmemoManager extends XmppManagerBase {
     );
   }
 
-  /// For usage with omemo_dart's OmemoManager.
+  /// A logging wrapper around acking the ratchet with [jid] with identifier [deviceId].
-  Future<void> sendEmptyMessageImpl(EncryptionResult result, String toJid) async {
+  Future<void> _ackRatchet(String jid, int deviceId) async {
+    logger.finest('Acking ratchet $jid:$deviceId');
+    final session = await getSessionManager();
+    await session.ratchetAcknowledged(jid, deviceId);
+  }
+
+  /// Figure out if new sessions need to be built. [toJid] is the JID of the entity we
+  /// want to send a message to. [children] refers to the unencrypted children of the
+  /// message. They are required to be passed because shouldIgnoreUnackedRatchets is
+  /// called here.
+  ///
+  /// Either returns a list of bundles we "need" to build a session with or an OmemoError.
+  Future<Result<OmemoError, List<OmemoBundle>>> _findNewSessions(JID toJid, List<XMLNode> children) async {
+    final ownJid = getAttributes().getFullJID().toBare();
+    final session = await getSessionManager();
+    final ownId = await session.getDeviceId();
+
+    // Ignore our own device if it is the only published device on our devices node
+    if (toJid.toBare() == ownJid) {
+      final deviceList = await getDeviceList(ownJid);
+      if (deviceList.isType<List<int>>()) {
+        final devices = deviceList.get<List<int>>();
+        if (devices.length == 1 && devices.first == ownId) {
+          return const Result(<OmemoBundle>[]);
+        }
+      }
+    }
+
+    final newSessions = List<OmemoBundle>.empty(growable: true);
+    final sessionAvailable = await _hasSessionWith(toJid.toString());   
+    if (!sessionAvailable) {
+      logger.finest('No session for $toJid. Retrieving bundles to build a new session.');
+      final result = await retrieveDeviceBundles(toJid);
+      if (result.isType<List<OmemoBundle>>()) {
+        final bundles = result.get<List<OmemoBundle>>();
+
+        if (ownJid == toJid) {
+          logger.finest('Requesting bundles for own JID. Ignoring current device');
+          newSessions.addAll(bundles.where((bundle) => bundle.id != ownId));
+        } else {
+          newSessions.addAll(bundles);
+        }
+      } else {
+        logger.warning('Failed to retrieve device bundles for $toJid');
+        return Result(OmemoNotSupportedForContactException());
+      }
+
+      if (!_subscriptionMap.containsKey(toJid)) {
+        await subscribeToDeviceList(toJid);
+      }
+    } else {
+      final toBare = toJid.toBare();
+      final ratchetSessions = (await session.getDeviceMap())[toBare.toString()]!;
+      final deviceMapRaw = await getDeviceList(toBare);
+      if (!_subscriptionMap.containsKey(toBare)) {
+        unawaited(subscribeToDeviceList(toBare));
+      }
+
+      if (deviceMapRaw.isType<OmemoError>()) {
+        logger.warning('Failed to get device list');
+        return Result(UnknownOmemoError());
+      }
+
+      final deviceList = deviceMapRaw.get<List<int>>();
+      for (final id in deviceList) {
+        // We already have a session with that device
+        if (ratchetSessions.contains(id)) continue;
+
+        // Ignore requests for our own device.
+        if (toJid == ownJid && id == ownId) {
+          logger.finest('Attempted to request bundle for our own device $id, which is the current device. Skipping request...');
+          continue;
+        }
+
+        logger.finest('Retrieving bundle for $toJid:$id');
+        final bundle = await retrieveDeviceBundle(toJid, id);
+        if (bundle.isType<OmemoBundle>()) {
+          newSessions.add(bundle.get<OmemoBundle>());
+        } else {
+          logger.warning('Failed to retrieve bundle for $toJid:$id');
+        }
+      }
+    }
+    
+    return Result(newSessions);
+  }
+
+  /// Sends an empty Omemo message to [toJid].
+  ///
+  /// If [findNewSessions] is true, then
+  /// new devices will be looked for first before sending the message. This means that
+  /// the new sessions will be included in the empty Omemo message. If false, then no
+  /// new sessions will be looked for before encrypting.
+  ///
+  /// [calledFromCriticalSection] MUST NOT be used from outside the manager. If true, then
+  /// sendEmptyMessage will not attempt to enter the critical section guarding the
+  /// encryption and decryption. If false, then the critical section will be entered before
+  /// encryption and left after sending the message.
+  Future<void> sendEmptyMessage(JID toJid, {
+    bool findNewSessions = false,
+    @protected
+    bool calledFromCriticalSection = false,
+  }) async {
+    if (!calledFromCriticalSection) {
+      final completer = await _handlerEntry(toJid);
+      if (completer != null) {
+        await completer.future;
+      }
+    }
+
+    var newSessions = <OmemoBundle>[];
+    if (findNewSessions) {
+      final result = await _findNewSessions(toJid, <XMLNode>[]);
+      if (!result.isType<OmemoError>()) newSessions = result.get<List<OmemoBundle>>();
+    }
+
+    final empty = await _encryptChildren(
+      null,
+      [toJid.toString()],
+      toJid.toString(),
+      newSessions,
+    );
+
     await getAttributes().sendStanza(
       Stanza.message(
-        to: toJid,
+        to: toJid.toString(),
         type: 'chat',
         children: [
-          _buildEncryptedElement(
+          empty,
-            result,
-            toJid,
-            await _getDeviceId(),
-          ),
 
           // Add a storage hint in case this is a message
           // Taken from the example at
@@ -282,28 +447,10 @@ abstract class BaseOmemoManager extends XmppManagerBase {
       awaitable: false,
       encrypted: true,
     );
+
+    if (!calledFromCriticalSection) {
+      await _handlerExit(toJid);
     }
-
-  /// Send a heartbeat message to [jid].
-  Future<void> sendOmemoHeartbeat(String jid) async {
-    final om = await getOmemoManager();
-    await om.sendOmemoHeartbeat(jid);
-  }
-  
-  /// For usage with omemo_dart's OmemoManager
-  Future<List<int>?> fetchDeviceList(String jid) async {
-    final result = await getDeviceList(JID.fromString(jid));
-    if (result.isType<OmemoError>()) return null;
-
-    return result.get<List<int>>();
-  }
-
-  /// For usage with omemo_dart's OmemoManager
-  Future<OmemoBundle?> fetchDeviceBundle(String jid, int id) async {
-    final result = await retrieveDeviceBundle(JID.fromString(jid), id);
-    if (result.isType<OmemoError>()) return null;
-
-    return result.get<OmemoBundle>();
   }
   
   Future<StanzaHandlerData> _onOutgoingStanza(Stanza stanza, StanzaHandlerData state) async {
@@ -314,7 +461,6 @@ abstract class BaseOmemoManager extends XmppManagerBase {
 
     if (stanza.to == null) {
       // We cannot encrypt in this case.
-      logger.finest('Not encrypting since stanza.to is null');
       return state;
     }
 
@@ -326,6 +472,33 @@ abstract class BaseOmemoManager extends XmppManagerBase {
       logger.finest('shouldEncryptStanza returned true for message to $toJid.');
     }
     
+    final completer = await _handlerEntry(toJid);
+    if (completer != null) {
+      await completer.future;
+    }
+
+    final newSessions = List<OmemoBundle>.empty(growable: true);
+    // Try to find new sessions for [toJid].
+    final resultToJid = await _findNewSessions(toJid, stanza.children);
+    if (resultToJid.isType<List<OmemoBundle>>()) {
+      newSessions.addAll(resultToJid.get<List<OmemoBundle>>());
+    } else {
+      if (resultToJid.isType<OmemoNotSupportedForContactException>()) {
+        await _handlerExit(toJid);
+        return state.copyWith(
+          cancel: true,
+          cancelReason: resultToJid.get<OmemoNotSupportedForContactException>(),
+        );
+      }
+    }
+
+    // Try to find new sessions for our own Jid.
+    final ownJid = getAttributes().getFullJID().toBare();
+    final resultOwnJid = await _findNewSessions(ownJid, stanza.children);
+    if (resultOwnJid.isType<List<OmemoBundle>>()) {
+      newSessions.addAll(resultOwnJid.get<List<OmemoBundle>>());
+    }
+    
     final toEncrypt = List<XMLNode>.empty(growable: true);
     final children = List<XMLNode>.empty(growable: true);
     for (final child in stanza.children) {
@@ -336,40 +509,76 @@ abstract class BaseOmemoManager extends XmppManagerBase {
       }
     }
 
-    logger.finest('Beginning encryption');
+    final jidsToEncryptFor = <String>[JID.fromString(stanza.to!).toBare().toString()];
-    final om = await getOmemoManager();
+    // Prevent encrypting to self if there is only one device (ours).
-    final result = await om.onOutgoingStanza(
+    if (await _hasSessionWith(ownJid.toString())) {
-      OmemoOutgoingStanza(
+      jidsToEncryptFor.add(ownJid.toString());
-        [toJid.toString()],
+    }
-        _buildEnvelope(toEncrypt, toJid.toString()),
+
-      ),
+    try {
+      logger.finest('Encrypting stanza');
+      final encrypted = await _encryptChildren(
+        toEncrypt,
+        jidsToEncryptFor,
+        stanza.to!,
+        newSessions,
       );
       logger.finest('Encryption done');
 
-    final encrypted = _buildEncryptedElement(
-      result,
-      toJid.toString(),
-      await _getDeviceId(),
-    );
       children.add(encrypted);
 
-    // Only add message specific metadata when actually sending a message
+      // Only add EME when sending a message
       if (stanza.tag == 'message') {
-      children
+        children.add(buildEmeElement(ExplicitEncryptionType.omemo2));
-        // Add EME data
+      }
-        ..add(buildEmeElement(ExplicitEncryptionType.omemo2))
+
       // Add a storage hint in case this is a message
       // Taken from the example at
       // https://xmpp.org/extensions/xep-0384.html#message-structure-description.
-        ..add(MessageProcessingHint.store.toXml());
+      if (stanza.tag == 'message') {
+        children.add(MessageProcessingHint.store.toXml());
       }
       
+      await _handlerExit(toJid);
       return state.copyWith(
         stanza: state.stanza.copyWith(
           children: children,
         ),
         encrypted: true,
       );
+    } catch (ex) {
+      logger.severe('Encryption failed! $ex');
+      await _handlerExit(toJid);
+      return state.copyWith(
+        cancel: true,
+        cancelReason: EncryptionFailedException(),
+        other: {
+          ...state.other,
+          'encryption_error': ex,
+        },
+      );
+    }
+  }
+
+  /// This function returns true if the encryption scheme should ignore unacked ratchets
+  /// and don't try to build a new ratchet even though there are unacked ones.
+  /// The current logic is that chat states with no body ignore the "ack" state of the
+  /// ratchets.
+  ///
+  /// This function may be overriden. By default, the ack status of the ratchet is ignored
+  /// if we're sending a message containing chatstates or chat markers and the message does
+  /// not contain a <body /> element.
+  @visibleForOverriding
+  bool shouldIgnoreUnackedRatchets(List<XMLNode> children) {
+    return listContains(
+      children,
+      (XMLNode child) {
+        return child.attributes['xmlns'] == chatStateXmlns || child.attributes['xmlns'] == chatMarkersXmlns;
+      },
+    ) && !listContains(
+      children,
+      (XMLNode child) => child.tag == 'body',
+    );
   }
 
   /// This function is called whenever a message is to be encrypted. If it returns true,
@@ -378,12 +587,48 @@ abstract class BaseOmemoManager extends XmppManagerBase {
   @visibleForOverriding
   Future<bool> shouldEncryptStanza(JID toJid, Stanza stanza);
   
+  /// Wrapper function that attempts to enter the encryption/decryption critical section.
+  /// In case the critical section could be entered, null is returned. If not, then a
+  /// Completer is returned whose future will resolve once the critical section can be
+  /// entered.
+  Future<Completer<void>?> _handlerEntry(JID fromJid) async {
+    return _handlerLock.synchronized(() {
+      if (_handlerFutures.containsKey(fromJid)) {
+        final c = Completer<void>();
+        _handlerFutures[fromJid]!.addLast(c);
+        return c;
+      }
+
+      _handlerFutures[fromJid] = Queue();
+      return null;
+    });
+  }
+
+  /// Wrapper function that exits the critical section.
+  Future<void> _handlerExit(JID fromJid) async {
+    await _handlerLock.synchronized(() {
+      if (_handlerFutures.containsKey(fromJid)) {
+        if (_handlerFutures[fromJid]!.isEmpty) {
+          _handlerFutures.remove(fromJid);
+          return;
+        }
+
+        _handlerFutures[fromJid]!.removeFirst().complete();
+      }
+    });
+  }
+  
   Future<StanzaHandlerData> _onIncomingStanza(Stanza stanza, StanzaHandlerData state) async {
     final encrypted = stanza.firstTag('encrypted', xmlns: omemoXmlns);
     if (encrypted == null) return state;
     if (stanza.from == null) return state;
 
     final fromJid = JID.fromString(stanza.from!).toBare();
+    final completer = await _handlerEntry(fromJid);
+    if (completer != null) {
+      await completer.future;
+    }
+    
     final header = encrypted.firstTag('header')!;
     final payloadElement = encrypted.firstTag('payload');
     final keys = List<EncryptedKey>.empty(growable: true);
@@ -404,36 +649,56 @@ abstract class BaseOmemoManager extends XmppManagerBase {
     final ourJid = getAttributes().getFullJID();
     final sid = int.parse(header.attributes['sid']! as String);
 
-    final om = await getOmemoManager();
+    // Ensure that if we receive a message from a device that we don't know about, we
-    final result = await om.onIncomingStanza(
+    // ensure that _deviceMap is up-to-date.
-      OmemoIncomingStanza(
+    final devices = _deviceMap[fromJid] ?? <int>[];
-        fromJid.toString(),
+    if (!devices.contains(sid)) {
-        sid,
+      await getDeviceList(fromJid);
-        state.delayedDelivery?.timestamp.millisecondsSinceEpoch ?? DateTime.now().millisecondsSinceEpoch,
-        keys,
-        payloadElement?.innerText(),
-      ),
-    );
-
-    final children = stanza.children.where(
-      (child) => child.tag != 'encrypted' || child.attributes['xmlns'] != omemoXmlns,
-    ).toList();
-    final other = Map<String, dynamic>.from(state.other);
-    if (result.error != null) {
-      other['encryption_error'] = result.error;
     }
 
-    if (result.payload != null) {
+    String? decrypted;
-      final envelope = XMLNode.fromString(result.payload!);
+    try {
-      children.addAll(
+      decrypted = await _decryptMessage(
-        envelope.firstTag('content')!.children,
+        payloadElement != null ? base64.decode(payloadElement.innerText()) : null,
+        fromJid.toString(),
+        sid,
+        keys,
+        state.delayedDelivery?.timestamp.millisecondsSinceEpoch ?? DateTime.now().millisecondsSinceEpoch,
       );
+    } catch (ex) {
+      logger.warning('Error occurred during message decryption: $ex');
 
+      await _handlerExit(fromJid);
+      return state.copyWith(
+        other: {
+          ...state.other,
+          'encryption_error': ex,
+        },
+      );
+    }
+    
+    final isAcked = await _isRatchetAcknowledged(fromJid.toString(), sid);
+    if (!isAcked) {
+      // Unacked ratchet decrypted this message
+      if (decrypted != null) {
+        // The message is not empty, i.e. contains content
+        logger.finest('Received non-empty OMEMO encrypted message for unacked ratchet. Acking with empty OMEMO message.');
+
+        await _ackRatchet(fromJid.toString(), sid);
+        await sendEmptyMessage(fromJid, calledFromCriticalSection: true);
+
+        final envelope = XMLNode.fromString(decrypted);
+        final children = stanza.children.where(
+          (child) => child.tag != 'encrypted' || child.attributes['xmlns'] != omemoXmlns,
+        ).toList()
+          ..addAll(envelope.firstTag('content')!.children);
+
+        final other = Map<String, dynamic>.from(state.other);
         if (!checkAffixElements(envelope, stanza.from!, ourJid)) {
           other['encryption_error'] = InvalidAffixElementsException();
         }
-    }
 
+        await _handlerExit(fromJid);
         return state.copyWith(
           encrypted: true,
           stanza: Stanza(
@@ -447,6 +712,55 @@ abstract class BaseOmemoManager extends XmppManagerBase {
           ),
           other: other,
         );
+      } else {
+        logger.info('Received empty OMEMO message for unacked ratchet. Marking $fromJid:$sid as acked');
+        await _ackRatchet(fromJid.toString(), sid);
+
+        final ownId = await (await getSessionManager()).getDeviceId();
+        final kex = keys.any((key) => key.kex && key.rid == ownId);
+        if (kex) {
+          logger.info('Empty OMEMO message contained a kex. Answering.');
+          await sendEmptyMessage(fromJid, calledFromCriticalSection: true);
+        }
+
+        await _handlerExit(fromJid);
+        return state;
+      }
+    } else {
+      // The ratchet that decrypted the message was acked
+      if (decrypted != null) {
+        final envelope = XMLNode.fromString(decrypted);
+
+        final children = stanza.children.where(
+          (child) => child.tag != 'encrypted' || child.attributes['xmlns'] != omemoXmlns,
+        ).toList()
+          ..addAll(envelope.firstTag('content')!.children);
+
+        final other = Map<String, dynamic>.from(state.other);
+        if (!checkAffixElements(envelope, stanza.from!, ourJid)) {
+          other['encryption_error'] = InvalidAffixElementsException();
+        }
+        
+        await _handlerExit(fromJid);
+        return state.copyWith(
+          encrypted: true,
+          stanza: Stanza(
+            to: stanza.to,
+            from: stanza.from,
+            id: stanza.id,
+            type: stanza.type,
+            children: children,
+            tag: stanza.tag,
+            attributes: Map<String, String>.from(stanza.attributes),
+          ),
+          other: other,
+        );
+      } else {
+        logger.info('Received empty OMEMO message on acked ratchet. Doing nothing');
+        await _handlerExit(fromJid);
+        return state;
+      }
+    }
   }
 
   /// Convenience function that attempts to retrieve the raw XML payload from the
@@ -462,12 +776,15 @@ abstract class BaseOmemoManager extends XmppManagerBase {
   
   /// Retrieves the OMEMO device list from [jid].
   Future<Result<OmemoError, List<int>>> getDeviceList(JID jid) async {
+    if (_deviceMap.containsKey(jid)) return Result(_deviceMap[jid]);
+
     final itemsRaw = await _retrieveDeviceListPayload(jid);
     if (itemsRaw.isType<OmemoError>()) return Result(UnknownOmemoError());
 
     final ids = itemsRaw.get<XMLNode>().children
       .map((child) => int.parse(child.attributes['id']! as String))
       .toList();
+    _deviceMap[jid] = ids;
     return Result(ids);
   }
 
@@ -565,9 +882,13 @@ abstract class BaseOmemoManager extends XmppManagerBase {
   }
 
   /// Subscribes to the device list PubSub node of [jid].
-  Future<void> subscribeToDeviceListImpl(String jid) async {
+  Future<void> subscribeToDeviceList(JID jid) async {
     final pm = getAttributes().getManagerById<PubSubManager>(pubsubManager)!;
-    await pm.subscribe(jid, omemoDevicesXmlns);
+    final result = await pm.subscribe(jid.toString(), omemoDevicesXmlns);
+
+    if (!result.isType<PubSubError>()) {
+      _subscriptionMap[jid] = true;
+    }
   }
 
   /// Attempts to find out if [jid] supports omemo:2.

packages/moxxmpp/pubspec.yaml

@@ -20,7 +20,7 @@ dependencies:
    version: ^0.1.5
   omemo_dart:
    hosted: https://git.polynom.me/api/packages/PapaTutuWawa/pub
-    version: ^0.4.0
+   version: ^0.3.2
   random_string: ^2.3.1
   saslprep: ^1.0.2
   synchronized: ^3.0.0+2