throw AssertionError("Invalid IPv6 address: '$host'")
  }

  val result = idnToAscii(host) ?: return null
  if (result.isEmpty()) return null
  if (result.containsInvalidHostnameAsciiCodes()) return null
  if (result.containsInvalidLabelLengths()) return null

  return result
}

internal fun idnToAscii(host: String): String? {
  val bufferA = Buffer().writeUtf8(host)
  val bufferB = Buffer()