duration: Duration,
): Int {
  check(!duration.isNegative()) { "$name < 0" }
  val millis = duration.inWholeMilliseconds
  require(millis <= Integer.MAX_VALUE) { "$name too large" }
  require(millis != 0L || !duration.isPositive()) { "$name too small" }
  return millis.toInt()
}

internal fun List<Header>.toHeaders(): Headers {
  val builder = Headers.Builder()
  for ((name, value) in this) {