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Delays when uploading to Win2003 IIS 6.0 FTP server

From: Mehmet Bozkurt <mehmet.bozkurt_at_xware.se>
Date: Fri, 1 Oct 2010 16:23:42 +0200

Ok, I'm just going to throw this one out here on the mailing list cause I'm
running out of ideas.

But I'm having a kind of odd behavior when uploading multiple files to the
mentioned ftp server, using libcurl.
The behavior I'm seeing is that after the last data transfer there is about
a 2 second delay until the
final server response "226 Transfer Complete" is returned. This does not
happen for each run, but often enough
to make the delay noticeable. Running the same test scenario against the
same ftp server with a different ftp client does not show of any such
delays.
However, running the libcurl client against a vsFTPd (running on FreeBSD) I
don't see the delay at all, but the ftp command/responses are slightly
different compared to the IIS case because vsFTP supports EPORT, IIS 6
supports PORT only. Another difference is the FTP data packet size,
uploading to IIS the size is 1460*3 and a final 1158 bytes, for
vsFTP the packet size is 1448*3 and a final 1194 bytes.

I've attached a picture of the network traffic captured with Wireshark where
these delays are visible.

So my question is that if there is a possibility of libcurl keeping the data
connection open for a while,
in some cases, and then closing it, indicating and EOF?

Cheers,
Mehmet.

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wireshark.jpg
Received on 2010-10-01