Warp/apps/mobile/lib/matrix/sliding_sync.dart

import 'package:matrix/matrix.dart';

/// Simplified Sliding Sync (MSC4186) for the famedly SDK, which only knows
/// `/sync`.
///
/// The SDK's sync loop calls [Client.sync] and processes what it returns:
/// rooms, timelines, to-device messages, device lists, key counts. This
/// client answers that call with a sliding sync request instead, rewritten
/// into the `/sync` response the loop expects. Everything downstream —
/// decryption, the database, timelines, notifications — is unchanged.
///
/// What it buys is the first sync. A classic initial sync sends every room
/// with its full state before anything can be drawn; here the first
/// request asks for the 20 most recent rooms with a handful of state events
/// each, so the room list appears at once, and the next requests widen the
/// window to every room.
///
/// The SDK's token (`prevBatch`) becomes `ss1|<pos>|<to-device since>`. A
/// classic token, or none, starts a new connection; so does
/// `M_UNKNOWN_POS`, the server saying it has forgotten the connection
/// (after a restart, or 30 idle minutes). A server that doesn't advertise
/// `org.matrix.simplified_msc3575` gets plain `/sync`.
class WarpClient extends Client {
  WarpClient(
    super.clientName, {
    required super.database,
    super.verificationMethods,
    super.supportedLoginTypes,
    super.nativeImplementations,
    super.logLevel,
    super.importantStateEvents,
    super.onSoftLogout,
  });

  /// Turns sliding sync off, for a server whose implementation misbehaves.
  bool slidingSyncEnabled = true;

  /// Whether the homeserver has sliding sync; null until asked.
  bool? _serverHasSliding;
  Uri? _askedHomeserver;

  /// How many rooms each list asks for; grows to the list's count.
  int _window = firstWindow;

  static const firstWindow = 20;
  static const maxWindow = 1000;
  static const _connId = 'warp-mobile';

  /// Whether the last sync used sliding sync, for the settings screen.
  bool get usingSlidingSync => _serverHasSliding == true && slidingSyncEnabled;

  @override
  Future<SyncUpdate> sync({
    String? filter,
    String? since,
    bool? fullState,
    PresenceType? setPresence,
    int? timeout,
    bool? useStateAfter,
  }) async {
    if (slidingSyncEnabled && await _hasSliding()) {
      final token = SlidingToken.parse(since);
      try {
        return await _slidingSync(token, timeout, setPresence);
      } on MatrixException catch (e) {
        if (e.errcode != 'M_UNKNOWN_POS') rethrow;
        Logs().i('Sliding sync connection expired; starting a new one');
        _window = firstWindow;
        return _slidingSync(
          SlidingToken(null, token.toDeviceSince),
          null,
          setPresence,
        );
      }
    }
    // A sliding sync token means nothing to /sync: start over.
    final classicSince = since != null && SlidingToken.isSliding(since)
        ? null
        : since;
    return super.sync(
      filter: filter,
      since: classicSince,
      fullState: fullState,
      setPresence: setPresence,
      timeout: classicSince == null ? null : timeout,
      useStateAfter: useStateAfter,
    );
  }

  Future<bool> _hasSliding() async {
    if (_askedHomeserver != homeserver) {
      _serverHasSliding = null;
      _askedHomeserver = homeserver;
    }
    if (_serverHasSliding != null) return _serverHasSliding!;
    try {
      final versions = await getVersions();
      _serverHasSliding =
          versions.unstableFeatures?['org.matrix.simplified_msc3575'] == true;
    } catch (e) {
      Logs().w('Could not ask the server about sliding sync', e);
      return false;
    }
    Logs().i(
      _serverHasSliding!
          ? 'Using Simplified Sliding Sync'
          : 'The server has no sliding sync; using /sync',
    );
    return _serverHasSliding!;
  }

  Future<SyncUpdate> _slidingSync(
    SlidingToken token,
    int? timeout,
    PresenceType? setPresence,
  ) async {
    final response = await request(
      RequestType.POST,
      '/client/unstable/org.matrix.simplified_msc3575/sync',
      query: {
        'pos': ?token.pos,
        // A new connection answers at once; only an established one waits.
        if (token.pos != null && timeout != null) 'timeout': '$timeout',
        if (setPresence != null) 'set_presence': setPresence.name,
      },
      data: slidingRequest(
        window: _window,
        toDeviceSince: token.toDeviceSince,
        connId: _connId,
      ),
    );

    // Widen the window to every room, once the first rooms are drawn.
    final lists = response['lists'];
    if (lists is Map) {
      var count = 0;
      for (final list in lists.values) {
        if (list is Map && list['count'] is int) {
          count = count > list['count'] ? count : list['count'] as int;
        }
      }
      if (count > _window) _window = count > maxWindow ? maxWindow : count;
    }

    final extensions = response['extensions'];
    final toDevice = extensions is Map ? extensions['to_device'] : null;
    final next = SlidingToken(
      response['pos'] as String?,
      (toDevice is Map ? toDevice['next_batch'] as String? : null) ??
          token.toDeviceSince,
    );
    return SyncUpdate.fromJson(
      slidingToSyncJson(response, userId: userID!, nextBatch: next.toString()),
    );
  }
}

/// The state each room is sent with: what the room list and the room
/// screen draw, what encryption needs, and calls. The members are the
/// timeline's senders and the user; direct chats get all of theirs (two
/// people), so their names come out right.
const slidingRequiredState = [
  ['m.room.create', ''],
  ['m.room.name', ''],
  ['m.room.avatar', ''],
  ['m.room.topic', ''],
  ['m.room.canonical_alias', ''],
  ['m.room.encryption', ''],
  ['m.room.power_levels', ''],
  ['m.room.join_rules', ''],
  ['m.room.history_visibility', ''],
  ['m.room.guest_access', ''],
  ['m.room.tombstone', ''],
  ['m.room.pinned_events', ''],
  ['m.space.child', '*'],
  ['m.space.parent', '*'],
  ['m.room.member', r'$LAZY'],
  ['m.room.member', r'$ME'],
  ['org.matrix.msc3401.call.member', '*'],
];

/// The request body: two lists (rooms, and direct chats with all their
/// members) over the same window, and the extensions encryption needs.
Map<String, Object?> slidingRequest({
  required int window,
  required String? toDeviceSince,
  required String connId,
}) {
  final ranges = [
    [0, window - 1],
  ];
  return {
    'conn_id': connId,
    'lists': {
      'rooms': {
        'ranges': ranges,
        'timeline_limit': 10,
        'required_state': slidingRequiredState,
        'filters': {'is_dm': false},
      },
      'dms': {
        'ranges': ranges,
        'timeline_limit': 10,
        'required_state': [
          ...slidingRequiredState,
          ['m.room.member', '*'],
        ],
        'filters': {'is_dm': true},
      },
    },
    'extensions': {
      'to_device': {'enabled': true, 'since': ?toDeviceSince},
      'e2ee': {'enabled': true},
      'account_data': {'enabled': true},
      'receipts': {'enabled': true},
      'typing': {'enabled': true},
    },
  };
}

/// The SDK's sync token while sliding sync is in use.
class SlidingToken {
  const SlidingToken(this.pos, this.toDeviceSince);

  final String? pos;
  final String? toDeviceSince;

  static const _prefix = 'ss1|';

  static bool isSliding(String token) => token.startsWith(_prefix);

  /// Reads a token; a classic `/sync` token, or none, is a new connection.
  factory SlidingToken.parse(String? token) {
    if (token == null || !isSliding(token)) {
      return const SlidingToken(null, null);
    }
    final parts = token.substring(_prefix.length).split('|');
    String? part(int i) =>
        parts.length > i && parts[i].isNotEmpty ? parts[i] : null;
    return SlidingToken(part(0), part(1));
  }

  @override
  String toString() => '$_prefix${pos ?? ''}|${toDeviceSince ?? ''}';
}

/// Rewrites a sliding sync response into the `/sync` response with the
/// same news, for [SyncUpdate.fromJson].
///
/// A room with `invite_state` is an invite and one with `knock_state` a
/// knock. Any other room is joined, unless the user's own latest membership
/// in what was sent is a leave or a ban: sliding sync keeps rooms the user
/// left while the connection was open in its lists, which is how a client
/// hears that one is gone.
Map<String, Object?> slidingToSyncJson(
  Map<String, Object?> response, {
  required String userId,
  required String nextBatch,
}) {
  final join = <String, Map<String, Object?>>{};
  final invite = <String, Object?>{};
  final knock = <String, Object?>{};
  final leave = <String, Object?>{};

  Map<String, Object?> joined(String roomId) =>
      join.putIfAbsent(roomId, () => <String, Object?>{});

  final rooms = response['rooms'];
  if (rooms is Map) {
    for (final entry in rooms.entries) {
      final roomId = entry.key as String;
      final room = entry.value;
      if (room is! Map) continue;

      final inviteState = room['invite_state'];
      if (inviteState is List) {
        invite[roomId] = {
          'invite_state': {'events': inviteState},
        };
        continue;
      }
      final knockState = room['knock_state'];
      if (knockState is List) {
        knock[roomId] = {
          'knock_state': {'events': knockState},
        };
        continue;
      }

      final state = room['required_state'] is List
          ? room['required_state'] as List
          : const [];
      final timeline = room['timeline'] is List
          ? room['timeline'] as List
          : const [];
      final timelineJson = <String, Object?>{
        'events': timeline,
        'limited': room['limited'] == true,
        if (room['prev_batch'] is String) 'prev_batch': room['prev_batch'],
      };

      final own = _ownMembership([...state, ...timeline], userId);
      if (own == 'leave' || own == 'ban') {
        leave[roomId] = {
          'state': {'events': state},
          'timeline': timelineJson,
        };
        continue;
      }

      final heroes = room['heroes'] is List
          ? [
              for (final h in room['heroes'] as List)
                if (h is Map && h['user_id'] is String) h['user_id'],
            ]
          : null;
      joined(roomId).addAll({
        'state': {'events': state},
        'timeline': timelineJson,
        'summary': {
          'm.heroes': ?heroes,
          if (room['joined_count'] is int)
            'm.joined_member_count': room['joined_count'],
          if (room['invited_count'] is int)
            'm.invited_member_count': room['invited_count'],
        },
        'unread_notifications': {
          'notification_count': room['notification_count'] is int
              ? room['notification_count']
              : 0,
          'highlight_count': room['highlight_count'] is int
              ? room['highlight_count']
              : 0,
        },
      });
    }
  }

  final out = <String, Object?>{'next_batch': nextBatch};
  final extensions = response['extensions'];
  if (extensions is Map) {
    // Typing and receipts are per room ephemeral events.
    for (final name in ['typing', 'receipts']) {
      final ext = extensions[name];
      final byRoom = ext is Map ? ext['rooms'] : null;
      if (byRoom is! Map) continue;
      for (final entry in byRoom.entries) {
        final roomId = entry.key as String;
        if (!join.containsKey(roomId) &&
            rooms is Map &&
            rooms[roomId] != null) {
          // Sent as an invite, knock or leave: no ephemeral events there.
          continue;
        }
        final ephemeral =
            (joined(roomId)['ephemeral'] ??= <String, Object?>{'events': []})
                as Map<String, Object?>;
        (ephemeral['events'] as List).add(entry.value);
      }
    }

    final accountData = extensions['account_data'];
    if (accountData is Map) {
      if (accountData['global'] is List) {
        out['account_data'] = {'events': accountData['global']};
      }
      final byRoom = accountData['rooms'];
      if (byRoom is Map) {
        for (final entry in byRoom.entries) {
          final roomId = entry.key as String;
          if (leave.containsKey(roomId)) {
            (leave[roomId] as Map<String, Object?>)['account_data'] = {
              'events': entry.value,
            };
          } else if (!invite.containsKey(roomId) &&
              !knock.containsKey(roomId)) {
            joined(roomId)['account_data'] = {'events': entry.value};
          }
        }
      }
    }

    final toDevice = extensions['to_device'];
    if (toDevice is Map && toDevice['events'] is List) {
      out['to_device'] = {'events': toDevice['events']};
    }

    final e2ee = extensions['e2ee'];
    if (e2ee is Map) {
      if (e2ee['device_lists'] is Map) {
        out['device_lists'] = e2ee['device_lists'];
      }
      if (e2ee['device_one_time_keys_count'] is Map) {
        out['device_one_time_keys_count'] = e2ee['device_one_time_keys_count'];
      }
      if (e2ee['device_unused_fallback_key_types'] is List) {
        out['device_unused_fallback_key_types'] =
            e2ee['device_unused_fallback_key_types'];
      }
    }
  }

  if (join.isNotEmpty ||
      invite.isNotEmpty ||
      knock.isNotEmpty ||
      leave.isNotEmpty) {
    out['rooms'] = {
      if (join.isNotEmpty) 'join': join,
      if (invite.isNotEmpty) 'invite': invite,
      if (knock.isNotEmpty) 'knock': knock,
      if (leave.isNotEmpty) 'leave': leave,
    };
  }
  return out;
}

/// The user's membership as of the last of [events] about them.
String? _ownMembership(List<Object?> events, String userId) {
  String? membership;
  for (final e in events) {
    if (e is Map &&
        e['type'] == 'm.room.member' &&
        e['state_key'] == userId &&
        e['content'] is Map) {
      final m = (e['content'] as Map)['membership'];
      if (m is String) membership = m;
    }
  }
  return membership;
}