Add support for MQTT retain flag

add retain flag to constructor
add setRetain function

Author: rjwats

Diff for: lib/framework/MqttPubSub.h

@@ -33,11 +33,20 @@ class MqttPub : virtual public MqttConnector<T> {
           StatefulService<T>* statefulService,
           AsyncMqttClient* mqttClient,
           const String& pubTopic = "",
+          bool retain = false,
           size_t bufferSize = DEFAULT_BUFFER_SIZE) :
-      MqttConnector<T>(statefulService, mqttClient, bufferSize), _stateReader(stateReader), _pubTopic(pubTopic) {
+      MqttConnector<T>(statefulService, mqttClient, bufferSize),
+      _stateReader(stateReader),
+      _pubTopic(pubTopic),
+      _retain(retain) {
     MqttConnector<T>::_statefulService->addUpdateHandler([&](const String& originId) { publish(); }, false);
   }
 
+  void setRetain(const bool retain) {
+    _retain = retain;
+    publish();
+  }
+
   void setPubTopic(const String& pubTopic) {
     _pubTopic = pubTopic;
     publish();
@@ -51,6 +60,7 @@ class MqttPub : virtual public MqttConnector<T> {
  private:
   JsonStateReader<T> _stateReader;
   String _pubTopic;
+  bool _retain;
 
   void publish() {
     if (_pubTopic.length() > 0 && MqttConnector<T>::_mqttClient->connected()) {
@@ -64,7 +74,7 @@ class MqttPub : virtual public MqttConnector<T> {
       serializeJson(json, payload);
 
       // publish the payload
-      MqttConnector<T>::_mqttClient->publish(_pubTopic.c_str(), 0, false, payload.c_str());
+      MqttConnector<T>::_mqttClient->publish(_pubTopic.c_str(), 0, _retain, payload.c_str());
     }
   }
 };
@@ -145,9 +155,10 @@ class MqttPubSub : public MqttPub<T>, public MqttSub<T> {
              AsyncMqttClient* mqttClient,
              const String& pubTopic = "",
              const String& subTopic = "",
+             bool retain = false,
              size_t bufferSize = DEFAULT_BUFFER_SIZE) :
       MqttConnector<T>(statefulService, mqttClient, bufferSize),
-      MqttPub<T>(stateReader, statefulService, mqttClient, pubTopic, bufferSize),
+      MqttPub<T>(stateReader, statefulService, mqttClient, pubTopic, retain, bufferSize),
       MqttSub<T>(stateUpdater, statefulService, mqttClient, subTopic, bufferSize) {
   }