RE: losing an FTP connection

[Scott Klement <klemscot@xxxxxxxxxxxx>]

RETR is "retrieve".  Its used to download a file from the beginning,
not to restart it.

REST is used when "re-getting" a file where you left off.  You send
it an argument of the byte position where you left off, usually.

I've written some FTP clients, but as to what happens when a file is
only partially sent -- that would depend on what the server chooses
to do.   The OS/400 FTP server does many different things to accomodate
its rather unusual file/library system.

I believe that when you do a PUT to a QSYS.LIB file, it will first
receive it in the ROOT file system, then copy it to QSYS.LIB after
doing some other things to it  (finding the max record length?)

FTP has two connections at any given time.  A "control" connection
and a "data" connection.   The control connection is where commands
and status messages are sent to/from the server.    The data connection
is just a channel for sending the raw file data through.

When a transfer starts, messages are sent on the control connection so
that both ends know that its starting successfully.   Likewise, when
that file transfer completes, a message is sent saying that it is 
completed.

So, its certainly possible for the software to detect that a partial
file was sent -- but its up to the specific software implementation
to decide how to handle it.

On Wed, 28 Feb 2001, Joe Pluta wrote:

> Actually, there is a specific FTP command, (RETR, I think), that
> determines whether or not transfers can be restarted.  Typically, an
> FTP client will perform an initial RETR to see if the FTP server
> supports the command.  Some do, some don't.  If the RETR is
> successful, then the client knows it can resume a transfer from where
> it failed.  So, in fact, both the client AND the server must have the
> resume capability in order for restart to work.
> 
> Joe
> 

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