Comment 11 for bug 1941988

Test Steps for dnspython only (no OpenStack Designate required)
----------

1) Setup bind9 for 'example.tld':

 $ sudo apt install bind9

 - /etc/bind/named.conf.options: add in 'options':

 listen-on port 12753 { 127.0.0.1/32; };
 allow-query { any; };
 allow-transfer { any; };

 - /etc/bind/named.conf.local: add:

 zone "example.tld" IN {
   type master;
   file "/etc/bind/example.tld.db";
 };

 - /etc/bind/example.tlb.db: create:

 $TTL 5m
 @ IN SOA ns.example.tld. email.example.tld. 90 4h 15m 8h 4m
 @ IN NS ns.example.tld.
 ns IN A 1.1.1.1
 test IN A 1.2.3.4

 $ sudo systemctl restart named.service

 $ systemctl status named.service | grep Active:
      Active: active (running) since ...

 $ journalctl -u named.service | grep -e example.tld -e 'all zones loaded'
 ... named[3668]: zone example.tld/IN: loaded serial 90
 ... named[3668]: all zones loaded

2) Test the basics and AXFR:

Basics:

 $ dig +noall +authority @127.0.0.1 -p 12753 example.tld
 example.tld. 240 IN SOA ns.example.tld. email.example.tld. 90 14400 900 28800 240

 $ dig +noall +answer @127.0.0.1 -p 12753 ns.example.tld
 ns.example.tld. 300 IN A 1.1.1.1

 $ dig +noall +answer @127.0.0.1 -p 12753 test.example.tld
 test.example.tld. 300 IN A 1.2.3.4

AXFR:

 $ dig +noall +answer @127.0.0.1 -p 12753 example.tld axfr
 example.tld. 300 IN SOA ns.example.tld. email.example.tld. 90 14400 900 28800 240
 example.tld. 300 IN NS ns.example.tld.
 ns.example.tld. 300 IN A 1.1.1.1
 test.example.tld. 300 IN A 1.2.3.4
 example.tld. 300 IN SOA ns.example.tld. email.example.tld. 90 14400 900 28800 240

3) Test AXFR with dnspython:

Check same answers with python:

 $ sudo apt install python3-dnspython

 $ python3 -q

 import dns.query
 import dns.zone

 axfr = dns.zone.from_xfr(dns.query.xfr(where='127.0.0.1', port=12753, zone='example.tld', rdtype=dns.rdatatype.AXFR))
 for node in axfr.nodes.keys():
     print(axfr.nodes[node].to_text(node))

 @ 300 IN SOA ns email 90 14400 900 28800 240
 @ 300 IN NS ns
 ns 300 IN A 1.1.1.1
 test 300 IN A 1.2.3.4

Now set dns.query.xfr(lifetime=None, timeout=not None) to hit the bug:

 axfr = dns.zone.from_xfr(dns.query.xfr(where='127.0.0.1', port=12753, zone='example.tld', rdtype=dns.rdatatype.AXFR, lifetime=None, timeout=30))
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/usr/lib/python3/dist-packages/dns/zone.py", line 1106, in from_xfr
     for r in xfr:
   File "/usr/lib/python3/dist-packages/dns/query.py", line 611, in xfr
     if mexpiration is None or mexpiration > expiration:
 TypeError: '>' not supported between instances of 'float' and 'NoneType'

As reported:

 Aug 25 12:56:43 seal08 designate-mdns[116065]: ERROR designate.dnsutils TypeError: '>' not supported between instances of 'float' and 'NoneType'

4) With the patch applied, the issue doesn't happen.