The first frame of the JSON parser stack is never used; it's substituted with a separate bson_t in bson_json_reader_bson_t.bson. Much of the code would be simpler if we use bson_json_reader_bson_t.stack[0].bson as the root object instead. Additionally, there are many checks for "bson_json_reader_bson_t.n > 0" which I believe are always true as the parser descends into the JSON object.