Fix forward mapping when loading entries from an `etc-hosts` file

[fredmorcos]

• Program: Recursor
• Issue type: Bug report

Short description

Description by @omoerbeek: https://github.com/PowerDNS/pdns/pull/11682#issuecomment-1149744457

I did not look at the code yet, but did a few tests.

Looking at at an example /etc/hosts containing

194.109.6.2     p
194.109.6.3     p
2001:888:0:7::2 p
2001:888:0:7::2 q

I see that dig -t A p succeeds but has one record. dig -t AAAA p gives me an empty answer section. dig -t AAAA q works and gives me a single record.

In an ideal world the forward mapping would work for all cases: two answer records for dig -t A p, one record for dig -t AAAA p and one record for dig -t AAAA q.

Having both an IPv4 and an IPv6 address for the same name is very common. So it would be nice if we would handle at least that case.

I don't know if this is feasible with the current structure, I guess it would mean merging domains in some cases.

The reverse (PTR) mapping should give only the first name encountered for each address. This seems to work as expected.

https://github.com/PowerDNS/pdns/pull/11682#issuecomment-1149781192

To be clear, the behavior above is already present in master, so it is not a regression.

Environment

• Operating system: N/A
• Software version: master
• Software source: any

Steps to reproduce

Available in the description above.

Expected behaviour

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Actual behaviour

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Other information