pattern: String?,
  ): Boolean {
    var hostname = hostname
    var pattern = pattern
    if (hostname.isNullOrEmpty() ||
      hostname.startsWith(".") ||
      hostname.endsWith("..")
    ) {
      // Invalid domain name.
      return false
    }
    if (pattern.isNullOrEmpty() ||
      pattern.startsWith(".") ||
      pattern.endsWith("..")
    ) {
      // Invalid pattern.