if int64(len(b)) > fr.nb {
		b = b[:fr.nb]
	}
	if len(b) > 0 {
		n, err = fr.r.Read(b)
		fr.nb -= int64(n)
	}
	switch {
	case err == io.EOF && fr.nb > 0:
		return n, io.ErrUnexpectedEOF
	case err == nil && fr.nb == 0:
		return n, io.EOF
	default:
		return n, err
	}
}

func (fr *regFileReader) WriteTo(w io.Writer) (int64, error) {

// are not empty then it will check whether the computed
// match the reference values.
type Reader struct {
	src         io.Reader
	bytesRead   int64
	expectedMin int64
	expectedMax int64

	size       int64
	actualSize int64

	checksum      etag.ETag
	contentSHA256 []byte

	// Content checksum
	contentHash   Checksum
	contentHasher hash.Hash
	disableMD5    bool

	// just ignore these.

	return nil
}

func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, baseOffset int64, err error) {
	// look for directoryEndSignature in the last 1k, then in the last 65k
	var buf []byte
	var directoryEndOffset int64
	for i, bLen := range []int64{1024, 65 * 1024} {
		if bLen > size {
			bLen = size
		}
		buf = make([]byte, int(bLen))