Have you tried c-ares? http://c-ares.haxx.se/

Not yet. I have had a quick look at ldns (https://www.nlnetlabs.nl/projects/ldns/) which supports parsing DNS packets from wire. I will probably replace the DNS implementation with either libldns or c-ares.

ldns is synchronous so all your queries will block. libunbound (https://www.unbound.net/documentation/libunbound.html), like c-ares, is an async C resolver library from the authors of ldns.

Ah, that would mean that I would have the libraries handle the resolving. I was currently only thinking about keeping the single socket which is used in order to only use the parsing functions from the libraries.

Ah, you are correct. There is also dnscache, which is part of the same suite. However, it does not do what you are attempting to do.