anchor.diff:  |                                                          |
   | Push plugin for Dart.                                    |
   |                                                          |
  -| LastModified: Jun 06, 2021                               |
  +| LastModified: Jun 24, 2021                               |
   | Author: Ma Bingyao <andot@hprose.com>                    |
   |                                                          |
   \*________________________________________________________*/
  
positive.code:   final _responders = <String, Completer<Map<String, List<Message>>>>{};
    final _timers = <String, Completer<bool>>{};
    Service service;
    int messageQueueMaxLength = 10;
    Duration timeout = const Duration(minutes: 2);
    Duration heartbeat = const Duration(seconds: 10);
    void Function(String id, String topic, ServiceContext context) onSubscribe;
  
negative.code:   bool unicast(dynamic data, String topic, String id, [String from = '']) {
      if (_messages.containsKey(id) && _messages[id].containsKey(topic)) {
        final messages = _messages[id][topic];
        messages.add(Message(data, from));
        _response(id);
        return true;
      }
      return false;
    }
  