start mqtt client (based on paho.mqtt.c), basically works

3rd/paho.mqtt.c/src/MQTTPersistenceDefault.h

@@ -0,0 +1,36 @@
+/*******************************************************************************
+ * Copyright (c) 2009, 2018 IBM Corp.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * and Eclipse Distribution License v1.0 which accompany this distribution. 
+ *
+ * The Eclipse Public License is available at 
+ *    https://www.eclipse.org/legal/epl-2.0/
+ * and the Eclipse Distribution License is available at 
+ *   http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * Contributors:
+ *    Ian Craggs - initial API and implementation and/or initial documentation
+ *******************************************************************************/
+
+#if !defined(MQTTPERSISTENCEDEFAULT_H)
+#define MQTTPERSISTENCEDEFAULT_H
+
+/** Extension of the filename */
+#define MESSAGE_FILENAME_EXTENSION ".msg"
+
+/* prototypes of the functions for the default file system persistence */
+int pstopen(void** handle, const char* clientID, const char* serverURI, void* context); 
+int pstclose(void* handle); 
+int pstput(void* handle, char* key, int bufcount, char* buffers[], int buflens[]); 
+int pstget(void* handle, char* key, char** buffer, int* buflen); 
+int pstremove(void* handle, char* key); 
+int pstkeys(void* handle, char*** keys, int* nkeys); 
+int pstclear(void* handle); 
+int pstcontainskey(void* handle, char* key);
+
+int pstmkdir(char *pPathname);
+
+#endif
+