add will message on <device>/status topic, so status is always available even when offline.

add wifi/bssid topic to track which AP is connected
fix reconnect breaking out of loop

src/lib/mqtt.cpp

@@ -5,18 +5,39 @@ TaskHandle_t mqttTaskHandle = NULL;
 WiFiClient wifiClient;
 PubSubClient client(wifiClient);
 
+// avoid circular deps, just forward declare externs used here.
+bool hasLightLevel();
+float getLightLevel();
+String getMyHostname();
+
 void onMqttCallback(char* topic, byte* payload, unsigned int length)
 {
     Serial.println("MQTT message arrived");
 }
 
+const String getDeviceTopic()
+{
+    const String hostname = getMyHostname();
+    const String rootTopic = preferences.getString("mqttRootTopic", DEFAULT_MQTT_ROOTTOPIC);
+    String fullTopic = rootTopic;
+    if (!rootTopic.endsWith("/") && rootTopic != "")
+    {
+        fullTopic += "/";
+    }
+    fullTopic += hostname + "/";
+    return String(fullTopic);
+}
+
 boolean connectMqtt()
 {
-    boolean result = client.connect("btclockClient");
+    const String willTopic = getDeviceTopic() + "status";
+    boolean result = client.connect("btclockClient", willTopic.c_str(), 0, true, "offline");
     if (!result)
     {
         Serial.println("[MQTT] could not connect");
+        return result;
     }
+    publish("status", "online", true);
     return result;
 }
 
@@ -43,11 +64,6 @@ void setupMqtt()
     connectMqtt();
 }
 
-// avoid circular deps, just forward declare externs used here.
-bool hasLightLevel();
-float getLightLevel();
-String getMyHostname();
-
 void mqttTask(void *pvParameters)
 {
     int t=0;
@@ -61,7 +77,7 @@ void mqttTask(void *pvParameters)
             {
                 // reconnect
                 if (!connectMqtt())
-                    return;
+                    continue;
             }
 
             if (hasLightLevel())
@@ -74,6 +90,7 @@ void mqttTask(void *pvParameters)
                 int8_t rssi = WiFi.RSSI();
                 std::string rssi_s = std::to_string(static_cast<int>(rssi));
                 publish("wifi/rssi", rssi_s.c_str());
+                publish("wifi/bssid", WiFi.BSSIDstr().c_str());
             }
             std::string heap_free_s = std::to_string(static_cast<int>(ESP.getFreeHeap()));
             publish("mem/heap_free", heap_free_s.c_str());
@@ -89,6 +106,11 @@ void setupMqttTask()
 }
 
 void publish(const char *topic, const char *value)
+{
+    publish(topic, value, false);
+}
+
+void publish(const char *topic, const char *value, boolean retain)
 {
     if (!client.connected())
     {
@@ -96,16 +118,9 @@ void publish(const char *topic, const char *value)
         return;
     }
 
-    const String hostname = getMyHostname();
+    const String fullTopic = getDeviceTopic() + topic;
-    const String rootTopic = preferences.getString("mqttRootTopic", DEFAULT_MQTT_ROOTTOPIC);
-    String fullTopic = rootTopic;
-    if (!rootTopic.endsWith("/") && rootTopic != "")
-    {
-        fullTopic += "/";
-    }
-    fullTopic += hostname + "/" + topic;
 
-    if (!client.publish(fullTopic.c_str(), value))
+    if (!client.publish(fullTopic.c_str(), value, retain))
     {
         Serial.println("[MQTT] could not write");
     }

src/lib/mqtt.hpp

@@ -6,4 +6,5 @@
 
 void setupMqtt();
 void setupMqttTask();
-void publish(const char *key, const char *value);
+void publish(const char *topic, const char *value);
+void publish(const char *topic, const char *value, boolean retain);