bug#42535: 28.0.50; macOS test failure: echo-server-with-dns

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Tue, 04 Aug 2020 17:02:14 +0200, Lars Ingebrigtsen <larsi@gnus.org> said:

    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >> Then either we need to accept that this test can fail on some systems,
    >> or we risk calling the wrath of <insert large internet company> down
    >> upon us by putting one of their public servers in the test. Or we just
    >> use www.gnu.org

    Lars> We can't use anything external -- that'd fail a lot more than using
    Lars> (system-name).

    Lars> But we should just disable this test if (system-name) doesn't resolve.
    Lars> That should be easy enough to check for.  

    Lars> (network-lookup-address-info (system-name))
    Lars> => ([127 0 1 1 0])

    Lars> So reasonable values here would be 127 as the first octet on ipv4...

Why restrict yourself to IPv4?

(network-lookup-address-info (system-name))
=> ([0 0 0 0 0 0 0 1 0] [127 0 0 1 0])

Note that strictly speaking this doesnʼt test DNS, since in my case
itʼs just looking in /etc/hosts, but it does test the resolver.

Robert