/** Indicates the reason why this stream was canceled. */
  fun onReset(
    streamId: Int,
    errorCode: ErrorCode,
  )

  companion object {
    @JvmField val CANCEL: PushObserver = PushObserverCancel()

    private class PushObserverCancel : PushObserver {
      override fun onRequest(
        streamId: Int,
        requestHeaders: List<Header>,
      ): Boolean {
        return true
      }

      this.sink = sink
    }

    fun listener(listener: Listener) =
      apply {
        this.listener = listener
      }

    fun pushObserver(pushObserver: PushObserver) =
      apply {
        this.pushObserver = pushObserver
      }

    fun pingIntervalMillis(pingIntervalMillis: Int) =
      apply {
        this.pingIntervalMillis = pingIntervalMillis
      }

  private fun connect(
    peer: MockHttp2Peer,
    pushObserver: PushObserver = IGNORE,
    listener: Http2Connection.Listener = Http2Connection.Listener.REFUSE_INCOMING_STREAMS,
  ): Http2Connection {
    val connection =
      Http2Connection.Builder(true, TaskRunner.INSTANCE)
        .socket(peer.openSocket())
        .pushObserver(pushObserver)
        .listener(listener)
        .build()

    peer.acceptFrame() // PING
    peer.play()

    // Play it back.
    val connection =
      Http2Connection.Builder(true, TaskRunner.INSTANCE)
        .socket(peer.openSocket())
        .pushObserver(Http2ConnectionTest.IGNORE)
        .listener(realConnection)
        .build()
    connection.start(sendConnectionPreface = false)

    // verify the peer received the ACK
    val ackFrame = peer.takeFrame()