Issue #934: Be sure to clear _user_delete in _json_object_put_maybe_free() to avoid calling it twice. Add a test to check.

json_object.c

@@ -303,6 +303,7 @@ static inline int _json_object_put_maybe_free(struct json_object *jso, int free_
 
 	if (jso->_user_delete)
 		jso->_user_delete(jso, jso->_userdata);
+	jso->_user_delete = NULL;
 
 	switch (jso->o_type)
 	{

json_object.h

@@ -259,7 +259,7 @@ JSON_EXPORT void *json_object_get_userdata(json_object *jso);
  * The user_delete parameter is optional and may be passed as NULL, even if
  * the userdata parameter is non-NULL.  It will be called just before the
  * json_object is deleted, after it's reference count goes to zero
- * (see json_object_put()).
+ * (see json_object_put()) but before any child objects are freed.
  * If this is not provided, it is up to the caller to free the userdata at
  * an appropriate time. (i.e. after the json_object is deleted)
  *
@@ -293,7 +293,7 @@ JSON_EXPORT void json_object_set_userdata(json_object *jso, void *userdata,
  * The user_delete parameter is optional and may be passed as NULL, even if
  * the userdata parameter is non-NULL.  It will be called just before the
  * json_object is deleted, after it's reference count goes to zero
- * (see json_object_put()).
+ * (see json_object_put()) but before any child objects are freed.
  * If this is not provided, it is up to the caller to free the userdata at
  * an appropriate time. (i.e. after the json_object is deleted)
  *

tests/test_deep_nesting.c

@@ -56,6 +56,37 @@ static void test_deep_nesting_tostring(const char *str)
 	json_tokener_free(tok);
 }
 
+struct userdata_test {
+	int userdata_val;
+	char *p;
+};
+/*
+ * Check that the user_delete function is only called once, even with the
+ * newer code to avoid deeply nested calls during json_object_put().
+ */
+static void user_delete_test(struct json_object *jso, void *userdata_in)
+{
+	struct userdata_test *userdata = (struct userdata_test *)userdata_in;
+	printf("in user_delete, userdata_val=%d\n", userdata->userdata_val);
+	fflush(stdout);
+	userdata->userdata_val = 0;
+	userdata->p[0] = 'x';
+	userdata->p[8191] = 'x';
+	free(userdata->p);
+}
+static void test_nesting_with_user_delete(void)
+{
+	json_object *jso;
+	struct userdata_test userdata_val = {
+		1, malloc(8192)
+	};
+
+ 	jso = json_object_new_object();
+	json_object_set_userdata(jso, &userdata_val, user_delete_test);
+	json_object_object_add(jso, "somekey", json_object_new_string("foo"));
+	json_object_put(jso);
+}
+
 int main(int argc, char **argv)
 {
 	char *str;	
@@ -77,5 +108,7 @@ int main(int argc, char **argv)
 
 	free(str);
 
+	test_nesting_with_user_delete();
+
 	return EXIT_SUCCESS;
 }