func parseSizeFromContentRange(h http.Header) (sz int64, err error) {
	cr := h.Get(xhttp.ContentRange)
	if cr == "" {
		return sz, fmt.Errorf("Content-Range not set")
	}
	parts := contentRangeRegexp.FindStringSubmatch(cr)
	if len(parts) != 4 {
		return sz, fmt.Errorf("invalid Content-Range header %s", cr)
	}
	if parts[3] == "*" {
		return -1, nil
	}
	var usz uint64
	usz, err = strconv.ParseUint(parts[3], 10, 64)

	if blockSize > 0 && blockSize%dataBlocks != 0 {
		sz++
	}
	return
}

var rePartNum = regexp.MustCompile("/part\\.([0-9]+)/")

func getPartNum(s string) int {
	if m := rePartNum.FindStringSubmatch(s); len(m) > 1 {
		n, _ := strconv.Atoi(m[1])
		return n
	}
	return 1

pkg regexp, method (*Regexp) FindReaderSubmatchIndex(io.RuneReader) []int
pkg regexp, method (*Regexp) FindString(string) string
pkg regexp, method (*Regexp) FindStringIndex(string) []int
pkg regexp, method (*Regexp) FindStringSubmatch(string) []string
pkg regexp, method (*Regexp) FindStringSubmatchIndex(string) []int
pkg regexp, method (*Regexp) FindSubmatch([]uint8) [][]uint8
pkg regexp, method (*Regexp) FindSubmatchIndex([]uint8) []int