this.withLock {
      if (closed) throw IOException("closed")
      this.maxFrameSize = peerSettings.getMaxFrameSize(maxFrameSize)
      if (peerSettings.headerTableSize != -1) {
        hpackWriter.resizeHeaderTable(peerSettings.headerTableSize)
      }
      frameHeader(
        streamId = 0,
        length = 0,
        type = TYPE_SETTINGS,
        flags = FLAG_ACK,
      )
      sink.flush()
    }
  }