bf := bufio.NewReader(r)
	switch f := detect(bf); f {
	case formatGzip:
		gz, err := gzip.NewReader(bf)
		if err != nil {
			return err
		}
		defer gz.Close()
		r = gz
	case formatS2:
		r = s2.NewReader(bf)
	case formatZstd:
		// Limit to 16 MiB per stream.
		dec, err := zstd.NewReader(bf, zstd.WithDecoderMaxWindow(16<<20))