Validate domain patterns

domainutil/util.go

@@ -79,10 +79,12 @@ func DomainSuffix(url string) string {
 // If no TLD is found in provided url, this function returns empty string.
 func Domain(url string) string {
 	domain, top := stripURLParts(url), ""
+	if !isDomainName(domain){
+		return ""
+	}
 	parts := strings.Split(domain, ".")
 	currentTld := *tlds
 	foundTld := false
-
 	// Cycle trough parts in reverse
 	if len(parts) > 1 {
 		for i := len(parts) - 1; i >= 0; i-- {
@@ -194,3 +196,59 @@ func Password(url string) string {
 	}
 	return auth[1]
 }
+// isDomainName checks if a string is a presentation-format domain name
+// (currently restricted to hostname-compatible "preferred name" LDH labels and
+// SRV-like "underscore labels"; see golang.org/issue/12421).
+func isDomainName(s string) bool {
+	// See RFC 1035, RFC 3696.
+	// Presentation format has dots before every label except the first, and the
+	// terminal empty label is optional here because we assume fully-qualified
+	// (absolute) input. We must therefore reserve space for the first and last
+	// labels' length octets in wire format, where they are necessary and the
+	// maximum total length is 255.
+	// So our _effective_ maximum is 253, but 254 is not rejected if the last
+	// character is a dot.
+	l := len(s)
+	if l == 0 || l > 254 || l == 254 && s[l-1] != '.' {
+		return false
+	}
+
+	last := byte('.')
+	nonNumeric := false // true once we've seen a letter or hyphen
+	partlen := 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		switch {
+		default:
+			return false
+		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_':
+			nonNumeric = true
+			partlen++
+		case '0' <= c && c <= '9':
+			// fine
+			partlen++
+		case c == '-':
+			// Byte before dash cannot be dot.
+			if last == '.' {
+				return false
+			}
+			partlen++
+			nonNumeric = true
+		case c == '.':
+			// Byte before dot cannot be dot, dash.
+			if last == '.' || last == '-' {
+				return false
+			}
+			if partlen > 63 || partlen == 0 {
+				return false
+			}
+			partlen = 0
+		}
+		last = c
+	}
+	if last == '-' || partlen > 63 {
+		return false
+	}
+
+	return nonNumeric
+}