Function PeekCompression

internal/compression/compression.go:52–68

PeekCompression detects whether the input stream is compressed and which algorithm is used. If r implements Peek, we will use that directly, otherwise a small number of bytes are buffered to Peek at the gzip/zstd header, and the returned PeekReader can be used as a replacement for the consumed inpu

(r io.Reader)

// of bytes are buffered to Peek at the gzip/zstd header, and the returned
// PeekReader can be used as a replacement for the consumed input io.Reader.
func PeekCompression(r io.Reader) (compression.Compression, PeekReader, error) {
	pr := intoPeekReader(r)

	if isGZip, _, err := checkHeader(pr, gzip.MagicHeader); err != nil {
		return compression.None, pr, err
	} else if isGZip {
		return compression.GZip, pr, nil
	}

	if isZStd, _, err := checkHeader(pr, zstd.MagicHeader); err != nil {
		return compression.None, pr, err
	} else if isZStd {
		return compression.ZStd, pr, nil
	}

	return compression.None, pr, nil
}

// PeekReader is an io.Reader that also implements Peek a la bufio.Reader.
type PeekReader interface {