On Thu, 28 Jun 2012, Dan Fandrich wrote:

>> periodically send a NOOP instruction to the ftp server on the control
>> channel, but I don't think I have this capability if libcurl is handling
>> the ftp transfer, correct?
>
> Correct. Adding NOOP support on the ftp control channel has been suggested
> in the past, but nobody has stepped up and submitted any code that
> implements it.

It is even worse. The NOOP approach has been tested in the wild, and the harsh
reality is that there are a number of FTP server implementations that don't
read the control channel while the transfer is in progress, which thus makes
the solution just end up with sad faces all over. TCP-based keep-alive is the
only somewhat universally working way to keep the control connection alive.

-- 
  / daniel.haxx.se
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