Minor Description
Even though the RFC does not explicitly say this, the example replies showed in the RFC enclose all file paths in double quotes. I'm not sure if there are any FTP clients that look for double quotes presence. A smart FTP client could always grab the checksum from the last token in the reply, where each token is separated by one or more white spaces. In order to offer best compatibility, I would recommend enclosing the file paths in double quotes when they contain any spaces.