Reverse Lookup fails on uppercase "IN-ADDR.ARPA"

[PhaedrusTheGreek]

Under Logstash 5.6.5, reverse lookups will fail when the case of the in-addr.arpa zone name is in anything other than lower case. This was not reproducible under Win2k16 or Bind 9.9.4 (default CentOS 7), but was reproducible under a custom bind 9.10.6 installation that has since changed behaviour to preserve case sensitivity.

A zone configured like this would pass:

zone "1.168.192.in-addr.arpa" IN {
        type master;
        file "1.168.192.IN-ADDR.ARPA";
        allow-update { none; };
};

But the slightest difference in case in the zone name would case a failure:

zone "1.168.192.IN-addr.arpa" IN {
        type master;
        file "1.168.192.IN-ADDR.ARPA";
        allow-update { none; };
};

Some extra debugging reveals this error:

 DNS: couldn't resolve the address. {:field=>"message", :value=>"192.168.1.10", :message=>"no name for 192.168.1.10"}

Which (as best as I could tell) traces back to Ruby's Resolv::DNS.getaddresses failing to be case insensitive as it should be , according to RFC 4343.

OK now the good news - The bug tested fixed as of Logstash 6.0.0! So, problem solved!!