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Re: Question about DNS timeout in libCurl
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From: Daniel Stenberg via curl-library <curl-library_at_lists.haxx.se>
Date: Fri, 10 Dec 2021 23:34:56 +0100 (CET)
On Fri, 10 Dec 2021, Dmitry Karpov via curl-library wrote:
> While parallel query requests in c-ares are not there yet, I am wondering if
> it is possible to control DNS timeout or expose such control via curl handle
> options in the future? I noticed that libcurl always uses the default c-ares
> timeout value, which is 5s, and happy eyeball DNS timeout also relies on
> that value by hard coding it in the HAPPY_EYEBALLS_DNS_TIMEOUT constant, but
> in some cases, 5s may be a too long wait before switching to a different
> name server.
I agree that 5 seconds is a very long time that should probably be lowered,
but that timeout logic in curl is also only used when an old c-ares version is
used so maybe the effort is better spent elsewhere anyway?
> I am wondering, if you think that doing such changes will be a very risky
> change even as a short-term solution?
I don't think it will be particularly risky, no. I also think we should be
able to lower the default timeout somewhat. I do however think that this is
mostly a problem for c-ares itself to handle. I mean, we don't set any
timeout values at all when we use libc's resolver functions...
Date: Fri, 10 Dec 2021 23:34:56 +0100 (CET)
On Fri, 10 Dec 2021, Dmitry Karpov via curl-library wrote:
> While parallel query requests in c-ares are not there yet, I am wondering if
> it is possible to control DNS timeout or expose such control via curl handle
> options in the future? I noticed that libcurl always uses the default c-ares
> timeout value, which is 5s, and happy eyeball DNS timeout also relies on
> that value by hard coding it in the HAPPY_EYEBALLS_DNS_TIMEOUT constant, but
> in some cases, 5s may be a too long wait before switching to a different
> name server.
I agree that 5 seconds is a very long time that should probably be lowered,
but that timeout logic in curl is also only used when an old c-ares version is
used so maybe the effort is better spent elsewhere anyway?
> I am wondering, if you think that doing such changes will be a very risky
> change even as a short-term solution?
I don't think it will be particularly risky, no. I also think we should be
able to lower the default timeout somewhat. I do however think that this is
mostly a problem for c-ares itself to handle. I mean, we don't set any
timeout values at all when we use libc's resolver functions...
-- / daniel.haxx.se | Commercial curl support up to 24x7 is available! | Private help, bug fixes, support, ports, new features | https://curl.se/support.html -- Unsubscribe: https://lists.haxx.se/listinfo/curl-library Etiquette: https://curl.haxx.se/mail/etiquette.htmlReceived on 2021-12-10