Consult the principle of remotely modifying the read and write attributes of files on the FTP serve

Hi,
I am a Chinese college student. I am learning the implementation principle of FTP recently, which may need to be used in my design. In the process of using WinSCP, I found that after logging into the FTP server, I can directly modify the read and write attributes of the server-side file function, I am very interested in this, can you guide me how this is achieved, I may use and develop the same function.
Thanks all!

To change file permissions, WinSCP uses non-standard SITE CHMOD command, which is supported by some FTP servers. For example by ProFTPD:
http://www.proftpd.org/docs/howto/FTP.html#SITE_CHMOD