Gzip file can contain metadata about the original file, where the file name, the file size, and last modified time are stored in gzip.  The caller can pass the file info in the API with those parameters.  Unfortunately gzip only supports u32-sized data for mtime and file_size, so u64 won't work.  Also file_name is the simple file name being stored, not the path.  e.g. Only file name file.txt in the path /home/me/file1.text should be stored.