type Reader struct {
	s        []byte
	i        int64 // current reading index
	prevRune int   // index of previous rune; or < 0
}

// Len returns the number of bytes of the unread portion of the
// slice.
func (r *Reader) Len() int {
	if r.i >= int64(len(r.s)) {
		return 0
	}
	return int(int64(len(r.s)) - r.i)
}

// Size returns the original length of the underlying byte slice.

//   - Exactly 0 bytes are read and EOF is hit.
//   - Exactly 1 block of zeros is read and EOF is hit.
//   - At least 2 blocks of zeros are read.
func (tr *Reader) readHeader() (*Header, *block, error) {
	// Two blocks of zero bytes marks the end of the archive.
	if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
		return nil, nil, err // EOF is okay here; exactly 0 bytes read
	}

		r.err = io.EOF
	}
	return r.readCloser.Close()
}

// nextSplit will attempt to skip a number of bytes and
// return the buffer until the next newline occurs.
// The last block will be sent along with an io.EOF.
func (r *Reader) nextSplit(skip int, dst []byte) ([]byte, error) {
	if cap(dst) < skip {
		dst = make([]byte, 0, skip+1024)
	}
	dst = dst[:skip]
	if skip > 0 {
		n, err := io.ReadFull(r.buf, dst)

// result in a different checksum.
func (r *Reader) MD5Current() []byte {
	if r.disableMD5 {
		return r.checksum
	}
	return r.ETag()[:]
}

// SHA256 returns the SHA256 checksum set as reference value.
//
// It corresponds to the checksum that is expected and
// not the actual SHA256 checksum of the content.
func (r *Reader) SHA256() []byte {
	return r.contentSHA256
}

// Read implements a throttled read
func (r *MonitoredReader) Read(buf []byte) (n int, err error) {
	if r.throttle == nil {
		return r.r.Read(buf)
	}
	if r.lastErr != nil {
		err = r.lastErr
		return
	}
	b := r.throttle.Burst()  // maximum available tokens
	need := len(buf)         // number of bytes requested by caller
	hdr := r.opts.HeaderSize // remaining header bytes
	var tokens int           // number of tokens to request

}

// UUIDHash - use uuid to make md5sum
type UUIDHash struct {
	uuid []byte
}

// Write -  implement hash.Hash Write
func (u UUIDHash) Write(p []byte) (n int, err error) {
	return len(p), nil
}

// Sum -  implement md5.Sum
func (u UUIDHash) Sum(b []byte) []byte {
	return u.uuid
}

// Reset -  implement hash.Hash Reset
func (u UUIDHash) Reset() {
	return
}

	//
	// dataDescriptorLen includes the size of the signature but
	// first read just those 4 bytes to see if it exists.
	if _, err := io.ReadFull(r, buf[:4]); err != nil {
		return err
	}
	off := 0
	maybeSig := readBuf(buf[:4])
	if maybeSig.uint32() != dataDescriptorSignature {
		// No data descriptor signature. Keep these four
		// bytes.
		off += 4
	}
	if _, err := io.ReadFull(r, buf[off:12]); err != nil {
		return err

}

// safeCloser will wrap a Reader as a ReadCloser.
// It is safe to call Close while the reader is being used.
type safeCloser struct {
	closed uint32
	r      io.Reader
}

func (s *safeCloser) Read(p []byte) (n int, err error) {
	if atomic.LoadUint32(&s.closed) == 1 {
		return 0, io.EOF
	}
	n, err = s.r.Read(p)
	if atomic.LoadUint32(&s.closed) == 1 {
		return 0, io.EOF
	}
	return n, err
}