// Externally, Next iterates through the tar archive as if it is a series of
	// files. Internally, the tar format often uses fake "files" to add meta
	// data that describes the next file. These meta data "files" should not
	// normally be visible to the outside. As such, this loop iterates through
	// one or more "header files" until it finds a "normal file".
	format := FormatUSTAR | FormatPAX | FormatGNU
	for {

	files := r.fileList
	i := sort.Search(len(files), func(i int) bool {
		idir, _, _ := split(files[i].name)
		return idir >= dir
	})
	j := sort.Search(len(files), func(j int) bool {
		jdir, _, _ := split(files[j].name)
		return jdir > dir
	})
	return files[i:j]
}

type openDir struct {
	e      *fileListEntry
	files  []fileListEntry
	offset int
}