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Re: Curl Issue with ftp protocol

From: Daniel Stenberg <>
Date: Tue, 9 Aug 2011 10:54:30 +0200 (CEST)

On Tue, 9 Aug 2011, Arun venkatesh wrote:

> though i havent encountered this problem yet, but still curious to knw if
> curl have a mechanism to trigger keep alives on control channel? if yes pls
> let me knw how ths can be achieved by using libcurl..

The only way that works somewhat reliably is to set the TCP-level keepalive
options on that connection. That's what the command line tool does with the
--keepalive-time option.

"Somewhat" because not all operating systems allow that to be done in a
sensible way.

Years ago we tried to make the control connection send occasional "NOOP" FTP
commands to keep it alive during data transfers, but too many FTP servers
don't support that (they basically don't read the control connection while a
transfer is in progress) and it then makes far too many transfers unreliable.

FTP is in many ways a protocol that doesn't match many of the current
paradigms of internet use...

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Received on 2011-08-09