Function ForLookup

framework/dns/norm.go:41–53

ForLookup converts the domain into a canonical form suitable for table lookups and other comparisons. TL;DR Use this instead of strings.ToLower to prepare domain for lookups. Domains that contain invalid UTF-8 or invalid A-label domains are simply converted to local-case using strings.ToLower, but

(domain string)

// domains are simply converted to local-case using strings.ToLower, but the
// error is also returned.
func ForLookup(domain string) (string, error) {
	uDomain, err := idna.ToUnicode(domain)
	if err != nil {
		return strings.ToLower(domain), err
	}

	// Side note: strings.ToLower does not support full case-folding, so it is
	// important to apply NFC normalization first.
	uDomain = norm.NFC.String(uDomain)
	uDomain = strings.ToLower(uDomain)
	uDomain = strings.TrimSuffix(uDomain, ".")
	return uDomain, nil
}

// Equal reports whether domain1 and domain2 are equivalent as defined by
// IDNA2008 (RFC 5890).