private fun String.isAscii() = length == utf8Size().toInt()

  /**
   * Returns true if [hostname] matches the domain name [pattern].
   *
   * @param hostname lower-case host name.
   * @param pattern domain name pattern from certificate. May be a wildcard pattern such as
   *     `*.android.com`.
   */
  private fun verifyHostname(
    hostname: String?,
    pattern: String?,