code: func IsArchive(header []byte) bool {
  	compression := archive.DetectCompression(header)
  	if compression != archive.Uncompressed {
  		return true
  	}
  	r := tar.NewReader(bytes.NewBuffer(header))
  	_, err := r.Next()
  	return err == nil
  }
docs: // IsArchive checks for the magic bytes of a tar or any supported compression
  // algorithm.