extend MQTT integration support with seen filter and variable compression

src/lib/ebus/message.h

@@ -525,6 +525,19 @@ class Message : public AttributedItem {
    */
   time_t getCreateTime() const { return m_createTime; }
 
+  /**
+   * Get the arbitrary state value for data handlers.
+   * @return the state value.
+   */
+  int getDataHandlerState() const { return m_dataHandlerState; }
+
+  /**
+   * Set the arbitrary state value for data handlers.
+   * @param state the new state value.
+   * @return true when the state was changed.
+   */
+  bool setDataHandlerState(int state);
+
   /**
    * Get the time when this message was last seen with reasonable data.
    * @return the time when this message was last seen, or 0.
@@ -660,9 +673,12 @@ class Message : public AttributedItem {
   /** the last seen @a SlaveSymbolString. */
   SlaveSymbolString m_lastSlaveData;
 
-  /** the system time when the message was created. */
+  /** the system time when the message was created or changed in poll priority. */
   time_t m_createTime;
 
+  /** an arbitrary state for data handlers. */
+  int m_dataHandlerState;
+
   /** the system time when the message was last updated, 0 for never. */
   time_t m_lastUpdateTime;