Function runeBoundary

internal/mailparse/parse.go:95–100

runeBoundary returns the largest index <= n that doesn't split a UTF-8 rune, so truncating at it never yields an invalid encoding.

(s string, n int)

// runeBoundary returns the largest index <= n that doesn't split a UTF-8 rune,
// so truncating at it never yields an invalid encoding.
func runeBoundary(s string, n int) int {
	for n > 0 && !utf8RuneStart(s[n]) {
		n--
	}
	return n
}

func utf8RuneStart(b byte) bool { return b&0xC0 != 0x80 }