code: def get_recover_position(gzfile, last_good_position):
      # type: (gzip.GzipFile, int) -> int
      
      with closing(mmap.mmap(gzfile.fileno(), 0, access=mmap.ACCESS_READ)) as m:
          return m.find(GZIP_SIGNATURE, last_good_position + 1)
docs: Return position of a next gzip stream in a GzipFile, 
      or -1 if it is not found.
      
      XXX: caller must ensure that the same last_good_position
      is not used multiple times for the same gzfile.