On Thursday 04 November 2010 17:35:37 Number Cruncher wrote:
> I'm the reporter for
> https://bugzilla.redhat.com/show_bug.cgi?id=649347 and just have a
> couple of additional remarks.

Thank you for gathering the info.

> Firstly, how come you're sending ABOR anyway? Why doesn't the client
> want to receive the whole file and instead tear down the transfer mid-flow?

Because anaconda/yum developers are busy guys and they refuse to wait till
the download is finished.

> Secondly, I'd agree you absolutely have to wait for the ABOR response.
> RFC959 outlines 2 cases for the server to handle when receiving this
> command; either the server responds with 226 (abor successful) or a 426
> then 226. In the trace you mentioned, the server is in the middle of a

Right, that is what RF959 says.

> transfer process when it notices the socket reset, long before it sees
> the ABOR. I think there might be a bug with VSFTPD in that it eventually
> returns a 225 (not 226) "Data connection open; no transfer in progress"
> even though it uses FTP_ABOR_NOCONN in the source code.
>
> You don't know at the time of sending ABOR and closing the connection
> whether the server will process the closure before processing the ABOR.
> So wait for a response; if it's 426 then also wait for a final response
> to the original ABOR.

It does not solve the following case:

3) > ABOR
   < 226 File send OK.
   < 225 No transfer to ABOR.

I would be reluctant to continuously adjust our ABOR handling rules, so that
they cope with more and more buggy FTP server implementations. We need to
figure out something more generic I guess.

> I can't believe we're still wrestling with fiddly connection race
> conditions in a 30-year old network protocol!

Is there actually any other FTP client successfully providing such a feature?
I would be happy to look at its code...

Kamil
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Received on 2010-11-04