From 03e095b0b21d848b2c905b4a477371b5cf92d49e Mon Sep 17 00:00:00 2001
From: Chris Kuethe <chris.kuethe@gmail.com>
Date: Thu, 2 Jan 2025 13:27:31 -0800
Subject: [PATCH] MQTT Last Will and Testament

Register a message with the MQTT broker to publish if the client
loses connection. Also publish online/offline status - all to a
`status` topic.

avoid global variable
---
 RX_FSK/src/conn-mqtt.cpp | 29 +++++++++++++++++++++--------
 RX_FSK/src/conn-mqtt.h   |  6 ++++++
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/RX_FSK/src/conn-mqtt.cpp b/RX_FSK/src/conn-mqtt.cpp
index d4277dde..a1c50234 100644
--- a/RX_FSK/src/conn-mqtt.cpp
+++ b/RX_FSK/src/conn-mqtt.cpp
@@ -37,7 +37,6 @@ TimerHandle_t mqttReconnectTimer;
 extern t_wifi_state wifi_state;
 char time_str[32];
 
-
 /* Global initalization (on TTGO startup) */
 void MQTT::init() {
 }
@@ -70,10 +69,16 @@ void MQTT::netsetup() {
     if (strlen(sonde.config.mqtt.password) > 0) {
         mqttClient.setCredentials(sonde.config.mqtt.username, sonde.config.mqtt.password);
     }
+
+    char lwt[128];
+    snprintf(lwt, sizeof(lwt), "%sstatus", sonde.config.mqtt.prefix);
+    mqttClient.setWill(lwt, MQTT_QOS, MQTT_RETAIN_TRUE, "lost connection");
+
     MQTT::connectToMqtt();
 }
 
 void MQTT::netshutdown() {
+    publishLwt("offline");
     mqttClient.disconnect(false);  // nice shutdown....
     delay(200);
     mqttClient.disconnect(true);  // force
@@ -91,6 +96,7 @@ void MQTT::updateStation( PosInfo *pi ) {
     unsigned long now = millis();
     if ( (lastMqttUptime == 0) || (now - lastMqttUptime >= sonde.config.mqtt.report_interval) ) {
       MQTT::connectToMqtt();
+      publishLwt("online");
       publishUptime();
       publishPmuInfo();
       publishGps();
@@ -106,6 +112,12 @@ int MQTT::mqttGate(uint flag){
   return ((sonde.config.mqtt.active & flag) && mqttClient.connected());
 }
 
+void MQTT::publishLwt(const char *message) {
+  char lwt[128];
+  snprintf(lwt, sizeof(lwt), "%sstatus", sonde.config.mqtt.prefix);
+  mqttClient.publish(lwt, MQTT_QOS, MQTT_RETAIN_TRUE, message);
+}
+
 int MQTT::connectToMqtt() {
   if(mqttClient.connected())
     return 1;
@@ -115,6 +127,7 @@ int MQTT::connectToMqtt() {
     return 0;
   LOG_D(TAG, "MQTT not connected, connecting....");
   mqttClient.connect();
+  publishLwt("online");
   return 1;
 }
 
@@ -160,7 +173,7 @@ void MQTT::publishUptime()
     LOG_D(TAG, "publishUptime: sending %s\n", payload);
     char topic[128];
     snprintf(topic, 128, "%s%s", sonde.config.mqtt.prefix, "uptime");
-    mqttClient.publish(topic, 1, 1, payload);
+    mqttClient.publish(topic, MQTT_QOS, MQTT_RETAIN_TRUE, payload);
 }
 
 void MQTT::publishPmuInfo()
@@ -187,7 +200,7 @@ void MQTT::publishPmuInfo()
 
     char topic[128];
     snprintf(topic, sizeof(topic), "%s%s", sonde.config.mqtt.prefix, "pmu");
-    mqttClient.publish(topic, 1, 1, payload);
+    mqttClient.publish(topic, MQTT_QOS, MQTT_RETAIN_TRUE, payload);
 }
 
 
@@ -209,7 +222,7 @@ void MQTT::publishGps()
 
     char topic[128];
     snprintf(topic, sizeof(topic), "%s%s", sonde.config.mqtt.prefix, "gps");
-    mqttClient.publish(topic, 1, 1, payload);
+    mqttClient.publish(topic, MQTT_QOS, MQTT_RETAIN_TRUE, payload);
 }
 
 
@@ -225,7 +238,7 @@ void MQTT::publishPeak(double pf, int rssi)
 
     char topic[128];
     snprintf(topic, sizeof(topic), "%s%s", sonde.config.mqtt.prefix, "spectrum");
-    mqttClient.publish(topic, 1, /* retain */ false, payload);
+    mqttClient.publish(topic, MQTT_QOS_NONE, MQTT_RETAIN_FALSE, payload);
 }
 
 // What's the scanner looking at?
@@ -243,7 +256,7 @@ void MQTT::publishQRG(int num, const char* type, char* launchsite, float mhz)
 
     char topic[128];
     snprintf(topic, sizeof(topic), "%s%s", sonde.config.mqtt.prefix, "qrg");
-    mqttClient.publish(topic, 1, /*retain*/ false, payload);
+    mqttClient.publish(topic, MQTT_QOS_NONE, MQTT_RETAIN_FALSE, payload);
 }
 
 
@@ -257,7 +270,7 @@ void MQTT::publishDebug(char *debugmsg)
     snprintf(payload, 256, "{\"msg\": %s}", debugmsg);
     char topic[128];
     snprintf(topic, sizeof(topic), "%s%s", sonde.config.mqtt.prefix, "debug");
-    mqttClient.publish(topic, 1, /*retain*/ false, payload);
+    mqttClient.publish(topic, MQTT_QOS_NONE, MQTT_RETAIN_FALSE, payload);
 }
 
 void MQTT::publishPacket(SondeInfo *si)
@@ -279,7 +292,7 @@ void MQTT::publishPacket(SondeInfo *si)
     char topic[128];
     snprintf(topic, 128, "%s%s", sonde.config.mqtt.prefix, "packet");
     LOG_D(TAG, "publishPacket: %s\n", payload);
-    mqttClient.publish(topic, 1, 1, payload);
+    mqttClient.publish(topic, MQTT_QOS, MQTT_RETAIN_TRUE, payload);
 }
 
 String MQTT::getStatus() {
diff --git a/RX_FSK/src/conn-mqtt.h b/RX_FSK/src/conn-mqtt.h
index cc44ebf5..982932b0 100644
--- a/RX_FSK/src/conn-mqtt.h
+++ b/RX_FSK/src/conn-mqtt.h
@@ -17,6 +17,11 @@
 #define MQTT_SEND_DEBUG 0x80
 #define MQTT_SEND_ANY (MQTT_SEND_UPTIME|MQTT_SEND_SONDE|MQTT_SEND_PMU|MQTT_SEND_GPS|MQTT_SEND_RFINFO|MQTT_SEND_DEBUG)
 
+#define MQTT_QOS_NONE 0
+#define MQTT_QOS 1
+#define MQTT_RETAIN_TRUE true
+#define MQTT_RETAIN_FALSE false
+
 class MQTT : public Conn
 {
 public:
@@ -62,6 +67,7 @@ class MQTT : public Conn
         void publishUptime();
         void publishPmuInfo();
         void publishGps();
+        void publishLwt(const char *message);
         void timeFormat();
         int mqttGate(uint flag);
         int connectToMqtt();