MQTT Client Retain Feature (#793)

Optionally allow MQTT client to publish specific messages with
the retain flag set.

default/current behavior should not be impacted.

MyConfig.h

@@ -805,6 +805,12 @@
 #endif
 #endif
 
+/**
+ * @def MY_MQTT_CLIENT_PUBLISH_RETAIN
+ * @brief Enables MQTT client to set the retain flag when publishing specific messages.
+ */
+//#define MY_MQTT_CLIENT_PUBLISH_RETAIN
+
 // Static ip address of gateway (if this is disabled, DHCP will be used)
 //#define MY_IP_ADDRESS 192,168,178,66
 
@@ -982,4 +988,5 @@
 #define MY_RFM95_ATC_MODE_DISABLED
 #define MY_RFM95_RST_PIN
 #define MY_INDICATION_HANDLER
+#define MY_MQTT_CLIENT_PUBLISH_RETAIN
 #endif

core/MyGatewayTransportMQTTClient.cpp

@@ -56,7 +56,13 @@ bool gatewayTransportSend(MyMessage &message)
 	setIndication(INDICATION_GW_TX);
 	char *topic = protocolFormatMQTTTopic(MY_MQTT_PUBLISH_TOPIC_PREFIX, message);
 	debug(PSTR("Sending message on topic: %s\n"), topic);
-	return _MQTT_client.publish(topic, message.getString(_convBuffer));
+	#ifdef MY_MQTT_CLIENT_PUBLISH_RETAIN
+	bool retain = mGetCommand(message) == C_SET || 
+		(mGetCommand(message) == C_INTERNAL && message.type == I_BATTERY_LEVEL);
+	#else
+	bool retain = false;
+	#endif
+	return _MQTT_client.publish(topic, message.getString(_convBuffer), retain);
 }
 
 void incomingMQTT(char* topic, uint8_t* payload, unsigned int length)

keywords.txt

@@ -130,6 +130,7 @@ MY_W5100_SPI_EN	LITERAL1
 MY_MQTT_SUBSCRIBE_TOPIC_PREFIX	LITERAL1
 MY_MQTT_PUBLISH_TOPIC_PREFIX	LITERAL1
 MY_MQTT_CLIENT_ID	LITERAL1
+MY_MQTT_CLIENT_PUBLISH_RETAIN	LITERAL1
 MY_GATEWAY_MQTT_CLIENT	LITERAL1
 MY_DISABLE_REMOTE_RESET	LITERAL1
 MY_RS485_DE_PIN	LITERAL1