IPv6 issues with curl 7.87.0 + c-ares 1.16.1

Hi!

I am upgrading our version of curl and c-ares on an embedded device, and
after upgrading, I find that on a system where IPv6 setup is incomplete
(only internal network configured [1]), I am unable to perform any https
requests; IPv4 fall-back does not happen.

We were using curl 7.54.0 with c-ares 1.12.0 and OpenSSL 1.1.1s, with these
version HTTPS requests [2] work as expected (i.e, I get the IPv4 fall-back).

After upgrading to curl 7.87.0 with c-ares 1.18.1, connections are no longer
going through (it looks like it is trying IPv6 only and timing out).

Keeping curl 7.87.0 but building with c-ares 1.12.0, connections *do* work,
and if I drop-in the 1.18.1 c-ares (libcares.so.2.4.1) they still work, so
it seems like an unintended side-effect of the interaction between the two
versions.

I have not tested whether this also happens on x86, my builds are on an
embedded powerpc e500mc device.

In summary:

    curl                          c-ares   result
    7.54.0 built against 1.12.0 + 1.12.0 = OK
    7.87.0 built against 1.18.1 + 1.18.1 = FAIL
    7.87.0 built against 1.12.0 + 1.12.0 = OK
    7.87.0 built against 1.12.0 + 1.18.1 = OK!!


[1]
   $ ip -6 addr
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536
       inet6 ::1/128 scope host
          valid_lft forever preferred_lft forever
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP100> mtu 1500 qlen 1000
       inet6 2a06:2400:1:0:224:64ff:fe00:1f63/64 scope global dynamic
          valid_lft 2591992sec preferred_lft 604792sec
       inet6 fe80::224:64ff:fe00:1f63/64 scope link
          valid_lft forever preferred_lft forever
   3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP100> mtu 1500 qlen 1000
       inet6 2a06:2400:1:1030:224:64ff:fe00:1f64/64 scope global dynamic
          valid_lft 2592000sec preferred_lft 604800sec
       inet6 fe80::224:64ff:fe00:1f64/64 scope link
          valid_lft forever preferred_lft forever
   4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP100> mtu 1500 qlen 1000
       inet6 2a06:2400:1:0:224:64ff:fe00:1f65/64 scope global dynamic
          valid_lft 2591992sec preferred_lft 604792sec
       inet6 fe80::224:64ff:fe00:1f65/64 scope link
          valid_lft forever preferred_lft forever

[2] (sorry for the slight URL obfuscation; nothing fun there, just trying
      to avoid unintended traffic; response will echo the IP you connected
      from, so I can easily tell if it used IPv4 or IPv6)
   curl $(base64 -d <<<aHR0cHM6Ly9saWNlbnNlLm1pY3JvYW5hbHl0aWNzLm9yZy9waW5n)

-- 
\\// Peter - http://www.softwolves.pp.se/
-- 
Unsubscribe: https://lists.haxx.se/listinfo/curl-users
Etiquette:   https://curl.se/mail/etiquette.html