}

func lastBoundary(fd *formInfo, b []byte) int {
	i := len(b)
	info, p := lastRuneStart(fd, b)
	if p == -1 {
		return -1
	}
	if info.size == 0 { // ends with incomplete rune
		if p == 0 { // starts with incomplete rune
			return -1
		}
		i = p
		info, p = lastRuneStart(fd, b[:i])
		if p == -1 { // incomplete UTF-8 encoding or non-starter bytes without a starter
			return i
		}

}

func lastBoundary(fd *formInfo, b []byte) int {
	i := len(b)
	info, p := lastRuneStart(fd, b)
	if p == -1 {
		return -1
	}
	if info.size == 0 { // ends with incomplete rune
		if p == 0 { // starts with incomplete rune
			return -1
		}
		i = p
		info, p = lastRuneStart(fd, b[:i])
		if p == -1 { // incomplete UTF-8 encoding or non-starter bytes without a starter
			return i
		}