/** Returns a byte string that differs from this one by one bit. */
  private fun ByteString.offByOneBit(): ByteString {
    return Buffer()
      .write(this, 0, size - 1)
      .writeByte(this[size - 1].toInt() xor 1)
      .readByteString()
  }

  private fun date(s: String): Date {
    return SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ").run {
      timeZone = TimeZone.getTimeZone("GMT")
      parse(s)
    }