Re: DNS data not refreshed after CURLOPT_DNS_CACHE_TIMEOUT

On Tue, 1 Sep 2020, Narasimha M wrote:

> Hence, I want to keep the connection and handle for a long time. However
> during this time, there can be changes to the DNS server/data. I would like
> the application to be agnostic to the changes to the DNS. This would have
> been possible if CURL queried the DNS periodically and updated its cache for
> long running handles.

Sure it *could*. It's just code. It could do *anything* if we just add the
code for it. This feature you're asking for has however not been implemented.

> I am still not able to understand the use of CURLOPT_DNS_CACHE_TIMEOUT in
> the context of a given connection which runs for a long time.

curl doesn't resolve the host name AT ALL when it reuses an existing
connection. It doesn't need to so it avoids it. Saves time and resources.

The DNS cache is only used when a host name is resolved. If no resolving is
done, the DNS cache is not used and therefore the timeout also has no meaning.
The entry is since long removed from the DNS cache but the connection is still
there - and working.

> Could you please point me to any example which can illustrate
> CURLOPT_DNS_CACHE_TIMEOUT in context of a given curl handle?

How would a cache timeout even get visualized in an example? There's an
example in the man page for the option:
https://curl.haxx.se/libcurl/c/CURLOPT_DNS_CACHE_TIMEOUT.html

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