As you mention, TCP's checksumming should guarantee that whatever data is
delivered to you is valid.

TCP connections can terminate abnormally (reset) if the physical connection
is lost or extremely poor, so you might receive only a partial amount of
data for a file, but I assume the curl FTP client code will detect this
condition and return an error, so you will be aware of this condition.

So basically you should not have to worry about the integrity of any data
you receive and should only have to worry about retry/resume/retransmit if
the ftp engine reports an error during transfer.

That's been my experience with other ftp implementations, I haven't
actually used curl's ftp implementation but I trust it is similar.

                                                                                                                                       
                      Alejandro Escalante
                      <alejandro_escalante_medina_at_ya To: curl-library_at_lists.sourceforge.net
                      hoo.com.mx> cc:
                      Sent by: Subject: about FTP reliability...
                      curl-library-admin_at_lists.sourc
                      eforge.net
                                                                                                                                       
                                                                                                                                       
                      10/25/2002 07:04 PM
                      Please respond to curl-library
                                                                                                                                       
                                                                                                                                       

I'm currently developing an unattended file transfer application based on
FTP (libcurl works great, by the way, thank you very much), that is mean to
replace a defective, old piece of code that used to cause trouble.

My boss has concerns about the reliability of FTP because the old program
used to lose files or to get them corrupted to the other side because we do
have ocasional network failures and intermittences. The new software deals
reasonably well on most conditions, I guess, but I don't know if it's
possible that data may get corrupted without libcurl, or my software, for
the case, noticing. I know that FTP, being a TCP based protocol, has
provisions for these situations, but anyway I wanted to be on the safe side
and ask for your experience on this.

If there's a big chance of getting corrupted data without notice, we might
need to develop additional code for checksum checking and the like, and
that's expensive...

So, the questions is: how reliable is FTP, on your own experience?

Thanks in advance,

Alejandro Escalante

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Received on 2002-10-26