Function read_engine_json_line 

fn read_engine_json_line<R: Read>(
    stdout: &mut BufReader<R>,
) -> Result<String, String>

One response is one JSON object/array per line. A linked library may print warnings to stdout before the JSON line (e.g. Warning: thread locking is not implemented), which would break serde_json::from_str on the first read_line. Skip lines until one starts with { or [.