Provide additional callbacks to register functions for various 'on-connection' failure types:

- Can not connect to the network (WiFi, GSM, ...)
- Can not connect to MQTT broker
- Can not subscribe to MQTT topics.

Author: aentinger

src/ArduinoIoTCloud.h

@@ -66,7 +66,7 @@ enum class ArduinoIoTConnectionStatus
 
 enum class ArduinoIoTCloudEvent : size_t
 {
-  SYNC = 0, CONNECT = 1, DISCONNECT = 2
+  SYNC = 0, CONNECT = 1, DISCONNECT = 2, MOTT_CONNECT_FAILURE = 3, MOTT_SUBSCRIBE_FAILURE = 4
 };
 
 typedef void (*OnCloudEventCallback)(void);
@@ -100,6 +100,11 @@ class ArduinoIoTCloudClass
 
     void addCallback(ArduinoIoTCloudEvent const event, OnCloudEventCallback callback);
 
+    inline void onPhyConnectionFailure   (OnCloudEventCallback func) { if (_connection) _connection->addCallback(NetworkConnectionEvent::CONNECTION_FAILED, func); }
+    inline void onMQTTConnectionFailure  (OnCloudEventCallback func) { addCallback(ArduinoIoTCloudEvent::MOTT_CONNECT_FAILURE, func); }
+    inline void onMQTTSubscriptionFailure(OnCloudEventCallback func) { addCallback(ArduinoIoTCloudEvent::MOTT_SUBSCRIBE_FAILURE, func); }
+
+
 #define addProperty( v, ...) addPropertyReal(v, #v, __VA_ARGS__)
 
     /* The following methods are used for non-LoRa boards which can use the 
@@ -148,7 +153,7 @@ class ArduinoIoTCloudClass
 
     String _thing_id = "";
     String _device_id = "";
-    OnCloudEventCallback _cloud_event_callback[3] = {nullptr};
+    OnCloudEventCallback _cloud_event_callback[5] = {nullptr};
 };
 
 #ifdef HAS_TCP

src/ArduinoIoTCloudTCP.cpp

@@ -354,6 +354,8 @@ ArduinoIoTCloudTCP::State ArduinoIoTCloudTCP::handle_ConnectMqttBroker()
   if (_mqttClient.connect(_brokerAddress.c_str(), _brokerPort))
     return State::SubscribeMqttTopics;
 
+  execCloudEventCallback(ArduinoIoTCloudEvent::MOTT_CONNECT_FAILURE);
+
   DEBUG_ERROR("ArduinoIoTCloudTCP::%s could not connect to %s:%d", __FUNCTION__, _brokerAddress.c_str(), _brokerPort);
   return State::ConnectPhy;
 }
@@ -374,6 +376,7 @@ ArduinoIoTCloudTCP::State ArduinoIoTCloudTCP::handle_SubscribeMqttTopics()
 #if !defined(__AVR__)
     DEBUG_ERROR("Check your thing configuration, and press the reset button on your board.");
 #endif
+    execCloudEventCallback(ArduinoIoTCloudEvent::MOTT_SUBSCRIBE_FAILURE);
     return State::SubscribeMqttTopics;
   }
 
@@ -385,6 +388,7 @@ ArduinoIoTCloudTCP::State ArduinoIoTCloudTCP::handle_SubscribeMqttTopics()
 #if !defined(__AVR__)
       DEBUG_ERROR("Check your thing configuration, and press the reset button on your board.");
 #endif
+      execCloudEventCallback(ArduinoIoTCloudEvent::MOTT_SUBSCRIBE_FAILURE);
       return State::SubscribeMqttTopics;
     }
   }