this.withLock {
      if (closed) throw IOException("closed")
      var flags = FLAG_NONE
      if (outFinished) flags = flags or FLAG_END_STREAM
      dataFrame(streamId, flags, source, byteCount)
    }
  }

  @Throws(IOException::class)
  fun dataFrame(
    streamId: Int,
    flags: Int,
    buffer: Buffer?,
    byteCount: Int,
  ) {
    frameHeader(
      streamId = streamId,