Issue #260: add a check to prevent trivial loops in the object tree, even though it is up to the callers to avoid doing so in more complex cases.

json_object.c

@@ -459,6 +459,12 @@ int json_object_object_add_ex(struct json_object* jso,
 	existing_entry = (opts & JSON_C_OBJECT_ADD_KEY_IS_NEW) ? NULL : 
 			      lh_table_lookup_entry_w_hash(jso->o.c_object,
 							   (const void *)key, hash);
+
+	// The caller must avoid creating loops in the object tree, but do a
+	// quick check anyway to make sure we're not creating a trivial loop.
+	if (jso == val)
+		return -1;
+
 	if (!existing_entry)
 	{
 		const void *const k = (opts & JSON_C_OBJECT_KEY_IS_CONSTANT) ?

tests/test1.c

@@ -205,6 +205,12 @@ int main(int argc, char **argv)
 	printf("my_array.to_string()=%s\n", json_object_to_json_string(my_array));
 
 	my_object = json_object_new_object();
+	int rc = json_object_object_add(my_object, "abc", my_object);
+	if (rc != -1)
+	{
+		printf("ERROR: able to successfully add object to itself!\n");
+		fflush(stdout);
+	}
 	json_object_object_add(my_object, "abc", json_object_new_int(12));
 	json_object_object_add(my_object, "foo", json_object_new_string("bar"));
 	json_object_object_add(my_object, "bool0", json_object_new_boolean(0));