publish method
Implementation
Future<void> publish(
String topic, {
bool retain = false,
MqttQos qos = MqttQos.qos0,
bool dup = false,
Uint8List? payload,
}) {
var msg = MqttMessagePublish();
msg.fixedHead.retain = retain;
msg.fixedHead.qos = qos;
msg.fixedHead.dup = dup;
msg.toTopic(topic);
msg.data = payload ?? Uint8List(0);
_send(msg);
return Future.value();
}