Domain validator + tests (unwired)

smtpd/utils.go

@@ -38,3 +38,54 @@ func JoinStringList(listOfStrings *list.List) string {
 	}
 	return strings.Join(s, ",")
 }
+
+// ValidateDomainPart returns true if the domain part complies to RFC3696, RFC1035
+func ValidateDomainPart(domain string) bool {
+	if len(domain) == 0 {
+		return false
+	}
+	if len(domain) > 255 {
+		return false
+	}
+	if domain[len(domain)-1] != '.' {
+		domain += "."
+	}
+	prev := '.'
+	labelLen := 0
+	hasLetters := false
+
+	for _, c := range domain {
+		switch {
+		case ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_':
+			// Must contain some of these to be a valid label
+			hasLetters = true
+			labelLen++
+		case '0' <= c && c <= '9':
+			labelLen++
+		case c == '-':
+			if prev == '.' {
+				// Cannot lead with hyphen
+				return false
+			}
+		case c == '.':
+			if prev == '.' || prev == '-' {
+				// Cannot end with hyphen or double-dot
+				return false
+			}
+			if labelLen > 63 {
+				return false
+			}
+			if !hasLetters {
+				return false
+			}
+			labelLen = 0
+			hasLetters = false
+		default:
+			// Unknown character
+			return false
+		}
+		prev = c
+	}
+
+	return true
+}