Hi,

I just noticed that since Alpine release 3.16.x the curl option
--dns-server does not work anymore. The following error message is
displayed:

       curl: option --dns-server: the installed libcurl version
doesn't support this

After some investigation I found that Curl (7.83.x) changed how the
build manages c-ares.

       configure: remove support for "embedded ares" #8397
       https://github.com/curl/curl/pull/8397)

Based on the commit comment the option --enable-ares must now be
explicitly given.

I'm now wondering how to proceed. Is this something that can be
changed in Alpine? Should a defect be opened? Submit a patch? What
would be the preferred method?

Thank you in advance,

Fred

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On Fri, Jan 13, 2023 at 12:01:12PM -0500, Frederick Lafleche wrote:
> Hi,
> 
> I just noticed that since Alpine release 3.16.x the curl option
> --dns-server does not work anymore. The following error message is
> displayed:
> 
>        curl: option --dns-server: the installed libcurl version
> doesn't support this
> 
> After some investigation I found that Curl (7.83.x) changed how the
> build manages c-ares.
> 
>        configure: remove support for "embedded ares" #8397
>        https://github.com/curl/curl/pull/8397)
> 
> Based on the commit comment the option --enable-ares must now be
> explicitly given.
> 
> I'm now wondering how to proceed. Is this something that can be
> changed in Alpine? Should a defect be opened? Submit a patch? What
> would be the preferred method?
> 
> Thank you in advance,
> 
> Fred

If I look at the buildlogs for curl on 3.15[0] or 3.14[1], I see:

> checking whether to enable c-ares for DNS lookups... no

so c-ares was not enabled then either. The pull request that you refer
to mentions:

> In March 2010 (commit 4259d2d) we removed the embedded 'ares'
> directory from the curl source tree 

So c-ares was already not embedded for a long time, and hence, could not
have been used.

The history of the curl package also does not show c-ares was ever
pulled in as a dependency. So my conclusion is that whatever has changed
since 3.16, it's not the lack of c-ares that causes the issue.

Comparing the configure output of those buildlogs, I do not see any
obvious differences which could explain why it's no longer supported.

This issue[2] mentions:

> The option --dns-servers only works if libcurl was built to use c-ares
> and it seems your build does not. Previously curl would just silently
> ignore that problem, but it still wouldn't (couldn't) use the option.

So apparently, it would have never worked, curl just didn't complain
about it.

Kevin

[0]:https://build.alpinelinux.org/buildlogs/build-3-15-x86_64/main/curl/curl-7.80.0-r5.log
[1]:https://build.alpinelinux.org/buildlogs/build-3-14-x86_64/main/curl/curl-7.79.1-r4.log
[2]:https://github.com/curl/curl/issues/8551#issuecomment-1060280243