ipaddress.reverse_pointer returns nonsense if prefixed input is given

Bug report

ipaddress.reverse_pointer does not seem to validate its input at all. For example:

$ python3
Python 3.10.4 (main, Apr  2 2022, 09:04:19) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ipaddress
>>> ipaddress.ip_network('2001:db8:1:2:3:4:5::/64',False).reverse_pointer
'4.6./.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa'
>>> 

This is very obviously wrong.

In this case of prefixed input, the output should be cut to the appropriate prefix length, yielding
2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa as output. It is ok to assume /128 as the default, converting 2001:db8:1:2:3:4:5:: to 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa, but input longer than that is an error.

Prefixed address strings are for example important when generating zone names for the server side of IPv6 reverse DNS. Run-of-the-mill network client software is unlikely to use this for addresses shorter than /128, but for the server side it is an important use case.

Greetings
Marc

Inizia eseguendo il riproduttore Python segnalato e seguendo il punto di ingresso ipaddress.reverse_pointer per capire come vengono gestiti gli input con prefisso. Il lavoro è completato quando un input IPv6 con prefisso produce un nome di puntatore inverso troncato alla lunghezza del prefisso, l’input predefinito senza prefisso viene trattato come /128 e un input superiore a /128 viene rifiutato.