Re: When using ActiveMode of FTPS on Curl for Windows, it takes polling timeout time (1000msec) to establish DataConnection.

From: Stefan Eissing via curl-library <curl-library_at_lists.haxx.se>
Date: Wed, 4 Sep 2024 13:59:24 +0200

> Am 04.09.2024 um 13:41 schrieb Yoshimasa Ohno via curl-library <curl-library_at_lists.haxx.se>:
>
> Thanks for the response!
>
> I tried a local build including
> https://github.com/curl/curl/commit/a07ba37b5e88a89bf4bcc6b0c927f7a42d7ea4f2
> Unfortunately, it did not solve the problem I am experiencing in my environment.
>
> Even just adding printf debugging.
> I don't know where the real cause is, because the problem is no longer reproduced.
>
> One of the conditions for the occurrence of the Dalay problem seems to be that the ReceivedServerConnect function exits in the socket unestablished state.
> ReceivedServerConnect function seems to occur when the following, unestablished state comes through.
> https://github.com/curl/curl/blob/6a9b71037a441eac28d3c7f629ac5801c01f99e2/lib/ftp.c#L572C1-L573C22
> case 0: /* Server connect is not received yet */
> break; /* loop */
>
> When a problem occurs, there is a delay of timeout time (standard is 1 second, extended that way if modified) in the following WSAWaitForMultipleEvents.
> https://github.com/curl/curl/blob/6a9b71037a441eac28d3c7f629ac5801c01f99e2/lib/multi.c#L1366
> else { /* now wait... if not ready during the pre-check (pollrc == 0) */
> WSAWaitForMultipleEvents(1, &multi->wsa_event, FALSE, (DWORD)timeout_ms,
> FALSE);
> }
>
> Is there anything I can try?

Can you produce a log file via 'curl -v --trace-config all' of such a situation?

As you describe it, the delay happens when the first check on the listening socket does
not find anything and curl goes POLLing for socket events. The arriving server connect
should then trigger the processing right away, but maybe there is something else in play here.

- Stefan

> 2024年9月3日(火) 16:59 Stefan Eissing via curl-library <curl-library_at_lists.haxx.se>:
> I created https://github.com/curl/curl/pull/14766 as a fix for this.
>
> The bug was that the socket was not using POLLIN, but POLLOUT. So it never
> triggered an event when the FTP server tried to connect. That led to the
> connect only being noticed a second later when curl checks on all transfers.
>
> Hope this works for you.
>
>
> > Am 03.09.2024 um 08:13 schrieb Daniel Stenberg via curl-library <curl-library_at_lists.haxx.se>:
> >
> > On Sat, 31 Aug 2024, Yoshimasa Ohno via curl-library wrote:
> >
> >> I found that the timeout argument of curl_multi_poll, the literal 1000, was having an effect. Changing this to 3000 resulted in a 3 second wait.
> >
> > We believe there might be a bug in the code that sets what socket activity curl should wait for when waiting for the connect to happen. (A regression)
> >
> > Stefan is going to try to get a fix made and submitted soon.
> >
> > --
> >
> > / daniel.haxx.se
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Received on 2024-09-04