Debian Bug #1059582: dig might crash or fail on multiple queries over different DNS transports (a stream transport -> UDP)

When performing multiple queries over different transports, dig might fail (or crash with abort() in the case of 9.18).

For example:

dig @dns.google 'www.example.com' IN A +tls +keepalive +keepopen 'www.example.net' IN A

The problem reveals itself when a query is performed over a stream transport and a subsequent one is performed over UDP.

That happens due to broken port selection logic while selecting a port for UDP. As the result dig would try to send a UDP query over the port number used for the previously used transport.

For more details, see here.