for i, c := range b {
		if c != 0 {
			return i, errWriteHole
		}
	}
	return len(b), nil
}

// ensureEOF checks whether r is at EOF, reporting ErrWriteTooLong if not so.
func ensureEOF(r io.Reader) error {
	n, err := tryReadFull(r, []byte{0})
	switch {
	case n > 0:
		return ErrWriteTooLong
	case err == io.EOF:
		return nil
	default:
		return err
	}

// form directly bypassing decompression, compression, and validation.
func (w *Writer) Copy(f *File) error {
	r, err := f.OpenRaw()
	if err != nil {
		return err
	}
	// Copy the FileHeader so w doesn't store a pointer to the data
	// of f's entire archive. See #65499.
	fh := f.FileHeader
	fw, err := w.CreateRaw(&fh)
	if err != nil {
		return err
	}
	_, err = io.Copy(fw, r)
	return err
}