Add Connection error callback to fix issue 1148

src/MQTTAsync.c

@@ -1644,6 +1644,26 @@ int MQTTAsync_setConnected(MQTTAsync handle, void* context, MQTTAsync_connected*
 	return rc;
 }
 
+int MQTTAsync_setConnectionError(MQTTAsync handle, void* context, MQTTAsync_connectionError* ce)
+{
+	int rc = MQTTASYNC_SUCCESS;
+	MQTTAsyncs* m = handle;
+
+	FUNC_ENTRY;
+	MQTTAsync_lock_mutex(mqttasync_mutex);
+
+	if (m == NULL || m->c->connect_state != NOT_IN_PROGRESS)
+		rc = MQTTASYNC_FAILURE;
+	else
+	{
+		m->connection_error_context = context;
+		m->connection_error = ce;
+	}
+
+	MQTTAsync_unlock_mutex(mqttasync_mutex);
+	FUNC_EXIT_RC(rc);
+	return rc;
+}
 
 int MQTTAsync_setUpdateConnectOptions(MQTTAsync handle, void* context, MQTTAsync_updateConnectOptions* updateOptions)
 {

src/MQTTAsync.h

@@ -429,6 +429,25 @@ typedef void MQTTAsync_connectionLost(void* context, char* cause);
  */
 typedef void MQTTAsync_connected(void* context, char* cause);
 
+/**
+ * This is a callback function, which will be called when the client library
+ * have some errors during connection process. This is superfluous when the
+ * connection is made in response to a MQTTAsync_connect call, because the
+ * onFailure callback can be used.  It is intended for use when automatic
+ * reconnect is enabled or after MQTTAsync_reconnect() function, so that when
+ * a connection attempt failed in the background, the application is notified
+ * and can take any required actions.
+ *
+ * <b>Note:</b> Neither MQTTAsync_create() nor MQTTAsync_destroy() should be
+ * called within this callback.
+ * @param context A pointer to any application-specific context. The
+ * the <i>context</i> pointer is passed to each of the callback functions to
+ * provide access to the context information in the callback.
+ * @param code A numeric code identifying the error.
+ * @param message Optional text explaining the error. Can be NULL.
+ */
+typedef void MQTTAsync_connectionError(void* context, int code, const char *message);
+
 /**
  * This is a callback function, which will be called when the client
  * library receives a disconnect packet from the server. This applies to MQTT V5 and above only.
@@ -889,6 +908,21 @@ LIBMQTT_API int MQTTAsync_setDeliveryCompleteCallback(MQTTAsync handle, void* co
  */
 LIBMQTT_API int MQTTAsync_setConnected(MQTTAsync handle, void* context, MQTTAsync_connected* co);
 
+/**
+ * This function sets the callback function for a situation when there is
+ * a problem connecting to the broker after calling the MQTTAsync_connect(),
+ * MQTTAsync_reconnect() or automatic reconnection functions.
+ * @param handle A valid client handle from a successful call to
+ * MQTTAsync_create().
+ * @param context A pointer to any application-specific context. The
+ * the <i>context</i> pointer is passed to each of the callback functions to
+ * provide access to the context information in the callback.
+ * @param ce A pointer to an MQTTAsync_connectionError() callback
+ * function.  NULL removes the callback setting.
+ * @return ::MQTTASYNC_SUCCESS if the callbacks were correctly set,
+ * ::MQTTASYNC_FAILURE if an error occurred.
+ */
+LIBMQTT_API int MQTTAsync_setConnectionError(MQTTAsync handle, void* context, MQTTAsync_connectionError* ce);
 
 /**
  * Reconnects a client with the previously used connect options.  Connect

src/MQTTAsyncUtils.c

@@ -1504,6 +1504,11 @@ static int MQTTAsync_processCommand(void)
 					command->client->connect.onFailure5 = NULL;
 					command->client->connect.onSuccess5 = NULL;
 				}
+				if (command->client->connection_error) {
+					Log(TRACE_MIN, -1, "Calling connection error for client %s", command->client->c->clientID);
+					(*(command->client->connection_error))(command->client->connection_error_context,
+														   MQTTASYNC_OPERATION_INCOMPLETE, NULL);
+				}      
 			}
 			command->client->c->connect_state = DISCONNECTING;
 			MQTTAsync_checkDisconnect(command->client, &command->command);
@@ -1577,6 +1582,10 @@ static int MQTTAsync_processCommand(void)
 				Log(TRACE_MIN, -1, "Calling command failure for client %s", command->client->c->clientID);
 				(*(command->command.onFailure5))(command->command.context, &data);
 			}
+			if (command->client->connection_error) {
+				Log(TRACE_MIN, -1, "Calling connection error for client %s", command->client->c->clientID);
+				(*(command->client->connection_error))(command->client->connection_error_context, rc, NULL);
+			}
 			if (command->command.type == CONNECT)
 			{
 				command->client->connect = command->command;
@@ -1668,6 +1677,10 @@ static void nextOrClose(MQTTAsyncs* m, int rc, char* message)
 			m->connect.onFailure5 = NULL;
 			m->connect.onSuccess5 = NULL;
 		}
+		if (m->connection_error) {
+			Log(TRACE_MIN, -1, "Calling connection error for client %s", m->c->clientID);
+			(*(m->connection_error))(m->connection_error_context, rc, message);
+		}
 		if (connectionLost_called == 0 && m->cl && was_connected)
 		{
 			Log(TRACE_MIN, -1, "Calling connectionLost for client %s", m->c->clientID);

src/MQTTAsyncUtils.h

@@ -104,6 +104,9 @@ typedef struct MQTTAsync_struct
 	MQTTAsync_connected* connected;
 	void* connected_context; /* the context to be associated with the connected callback*/
 
+	MQTTAsync_connectionError* connection_error;
+	void* connection_error_context; /* the context to be associated with the connection error callback*/
+
 	MQTTAsync_disconnected* disconnected;
 	void* disconnected_context; /* the context to be associated with the disconnected callback*/