mutablePos += bytesWritten
      mutableByteCount -= bytesWritten
    }
  }

  /**
   * Copy [byteCount] bytes from the file at [pos] into `sink`. It is the
   * caller's responsibility to make sure there are sufficient bytes to read: if there aren't this
   * method throws an `EOFException`.
   */
  fun read(
    pos: Long,
    sink: Buffer,
    byteCount: Long,
  ) {