How to detect FTP file transfer completion?

Question

I am writing a script that polls an FTP site for files and downloads them locally as and when available. The files are deposited to the FTP site randomly by various source parties. I need a way to be able to detect if the file on the FTP site has been transferred over completely by the source party, before downloading them. Any thoughts on how to go about this?

Answer 1

If you cannot manipulate the FTP server itself the only way of checking that comes to my mind is polling the filesize and if the filesize doesn't change for a longer time you can be quite sure the upload has finished. But nobody can guarantee. Ideally you can adapt the FTP server and make it execute some script after finishing some upload.

Some pseudo-code:

my %filesizes;
my %processed;

sub poll {
    foreach (@files_on_ftp) {
         if($_->filesize == $filesizes{$_->filename} and not $processed{$_->filename}) {
             process($_);
             $processed{$_->filename)++;
         }
    }
}