Fix mqtt_subscribe does not work

when topic filter string passed to mqtt_subscribe via a local variable, topic
subscribe is success but does not receive anything afterwards.

This patch remove dependency of type of variable passed to mqtt_subscribe

Signed-off-by: Ajay Bhargav <ajay.bhargav@waybyte.in>

Author: ajaybhargav

mqttclient/mqttclient.c

@@ -425,15 +425,16 @@ static message_handlers_t *mqtt_msg_handler_create(const char* topic_filter, mqt
 {
     message_handlers_t *msg_handler = NULL;
 
-    msg_handler = (message_handlers_t *) platform_memory_alloc(sizeof(message_handlers_t));
+    msg_handler = (message_handlers_t *) platform_memory_alloc(sizeof(message_handlers_t) + strlen(topic_filter) + 1);
     if (NULL == msg_handler)
         return NULL;
 
     mqtt_list_init(&msg_handler->list);
 
     msg_handler->qos = qos;
     msg_handler->handler = handler;     /* register  callback handler */
-    msg_handler->topic_filter = topic_filter;
+    msg_handler->topic_filter = (char *)msg_handler + sizeof(message_handlers_t);
+    strcpy(msg_handler->topic_filter, topic_filter);
 
     return msg_handler;
 }

mqttclient/mqttclient.h

@@ -69,7 +69,7 @@ typedef void (*reconnect_handler_t)(void* client, void* reconnect_date);
 typedef struct message_handlers {
     mqtt_list_t         list;
     mqtt_qos_t          qos;
-    const char*         topic_filter;
+    char                *topic_filter;
     message_handler_t   handler;
 } message_handlers_t;