stasis: Remove stringfields and lock from change message.

When a subscribe or unsubscribe occurs a message is published
containing this information. This change makes it so that the
message no longer uses stringfields or a lock, as both are not
really needed for the message.

Change-Id: I3f4831931d79f94fd979baf48048738df5dc1632

include/asterisk/stasis.h

@@ -806,11 +806,9 @@ int stasis_subscription_final_message(struct stasis_subscription *sub, struct st
  * \since 12
  */
 struct stasis_subscription_change {
-	AST_DECLARE_STRING_FIELDS(
-		AST_STRING_FIELD(uniqueid);	/*!< The unique ID associated with this subscription */
-		AST_STRING_FIELD(description);	/*!< The description of the change to the subscription associated with the uniqueid */
-	);
-	struct stasis_topic *topic;		/*!< The topic the subscription is/was subscribing to */
+	struct stasis_topic *topic; /*!< The topic the subscription is/was subscribing to */
+	char *uniqueid;             /*!< The unique ID associated with this subscription */
+	char description[0];        /*!< The description of the change to the subscription associated with the uniqueid */
 };
 
 /*!

main/stasis.c

@@ -1077,22 +1077,23 @@ static void subscription_change_dtor(void *obj)
 {
 	struct stasis_subscription_change *change = obj;
 
-	ast_string_field_free_memory(change);
 	ao2_cleanup(change->topic);
 }
 
 static struct stasis_subscription_change *subscription_change_alloc(struct stasis_topic *topic, const char *uniqueid, const char *description)
 {
+	size_t description_len = strlen(description) + 1;
 	struct stasis_subscription_change *change;
 
-	change = ao2_alloc(sizeof(struct stasis_subscription_change), subscription_change_dtor);
-	if (!change || ast_string_field_init(change, 128)) {
-		ao2_cleanup(change);
+	change = ao2_alloc_options(sizeof(*change) + description_len + strlen(uniqueid) + 1,
+		subscription_change_dtor, AO2_ALLOC_OPT_LOCK_NOLOCK);
+	if (!change) {
 		return NULL;
 	}
 
-	ast_string_field_set(change, uniqueid, uniqueid);
-	ast_string_field_set(change, description, description);
+	strcpy(change->description, description); /* SAFE */
+	change->uniqueid = change->description + description_len;
+	strcpy(change->uniqueid, uniqueid); /* SAFE */
 	ao2_ref(topic, +1);
 	change->topic = topic;