The "site chksize" [bytecount] extension
This command allows an FTP client to register an expected byte count with the server so the size of the next uploaded file can be checked against that count before being committed to NetStorage. If the counts do not match, the transfer attempt returns an error. If there is some other error during transfer, the byte count setting is discarded and must be re-registered before retrying the upload.
ftp> quote "site chksize 400000" 200 Size check set to 400000