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

[Robert Pluim]

>>>>> On Tue, 04 Aug 2020 17:16:02 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >> 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])

    Lars> Sure.  So if the first octet is 0 or 127, then we have a resolving
    Lars> (system-name)?  I'm not sure what the rules are on ipv6 for 
localhost...

There is one and only one IPv6 localhost, and itʼs the one
above. There are no currently assigned IPv6 prefixes with a 0 in the
first octet, but in 40 years, who know?

IPv4 localhost is anything in 127.0.0.0/8, so testing the first octet
is enough.

Robert