* on [ExchangeCodec], which handles the actual I/O.
 */
class Exchange(
  internal val call: RealCall,
  internal val eventListener: EventListener,
  internal val finder: ExchangeFinder,
  private val codec: ExchangeCodec,
) {
  /** True if the request body need not complete before the response body starts. */
  internal var isDuplex: Boolean = false
    private set