To be awaitable, compatible with async, this is run in threadpool.
        """
        return await super().read(size)

    async def seek(
        self,
        offset: Annotated[
            int,
            Doc(
                """
                The position in bytes to seek to in the file.
                """
            ),
        ],
    ) -> None:
        """
        Move to a position in the file.

It is your responsibility to ensure that your use and/or transfer does not
violate applicable laws. 

For more information, please see http://www.bis.doc.gov

      sinkBuffer.write(maskKey)

      if (length > 0) {
        val payloadStart = sinkBuffer.size
        sinkBuffer.write(payload)

        sinkBuffer.readAndWriteUnsafe(maskCursor!!)
        maskCursor.seek(payloadStart)
        toggleMask(maskCursor, maskKey)
        maskCursor.close()
      }
    } else {
      sinkBuffer.writeByte(b1)
      sinkBuffer.write(payload)
    }

    sink.flush()
  }

    options:
        members:
            - file
            - filename
            - size
            - headers
            - content_type
            - read
            - write
            - seek

		n += w
	}
	if d.idx >= d.length {
		extraBytes := d.idx - d.length
		n -= int(extraBytes)
		if n < 0 {
			n = 0
		}
		err = io.EOF
	}
	return n, err
}

func (d *DummyDataGen) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekStart:
		if offset < 0 {
			return 0, errors.New("Invalid offset")
		}
		d.idx = offset
	case io.SeekCurrent:
		if d.idx+offset < 0 {

* `write(data)`: Writes `data` (`str` or `bytes`) to the file.
* `read(size)`: Reads `size` (`int`) bytes/characters of the file.
* `seek(offset)`: Goes to the byte position `offset` (`int`) in the file.
    * E.g., `await myfile.seek(0)` would go to the start of the file.
    * This is especially useful if you run `await myfile.read()` once and then need to read the contents again.
* `close()`: Closes the file.

* `write(data)`: Escreve `data` (`str` ou `bytes`) no arquivo.
* `read(size)`: Lê `size` (`int`) bytes/caracteres do arquivo.
* `seek(offset)`: Vai para o byte na posição `offset` (`int`) no arquivo.
    * Por exemplo, `await myfile.seek(0)` irá para o início do arquivo.
    * Isso é especialmente útil se você executar `await myfile.read()` uma vez e precisar ler o conteúdo novamente.
* `close()`: Fecha o arquivo.

* `write(data)`: Записує `data` (`str` або `bytes`) у файл.
* `read(size)`: Читає `size` (`int`) байтів/символів з файлу.
* `seek(offset)`: Переміщується до позиції `offset` (`int`) у файлі.
    * Наприклад, `await myfile.seek(0)` поверне курсор на початок файлу.

    if (frameLength > 0L) {
      source.readFully(controlFrameBuffer, frameLength)

      if (!isClient) {
        controlFrameBuffer.readAndWriteUnsafe(maskCursor!!)
        maskCursor.seek(0)
        toggleMask(maskCursor, maskKey!!)
        maskCursor.close()
      }
    }

    when (opcode) {
      OPCODE_CONTROL_PING -> {

    assert await file.read() == b"data"
    assert file.size == 4
    await file.write(b" and more data!")
    assert await file.read() == b""
    assert file.size == 19
    await file.seek(0)
    assert await file.read() == b"data and more data!"