Drop retry if queued

[r3a1d3a1]

Hey Vitaly,

Thanks for the handy project!
I've not worked with Rust before, so I was wondering whether you could add a few lines of code to do what the title suggests.
More precisely, if I dig e.g. google.com twice in a row very quickly, I'd like the second request to get ignored. (Since the first one is already pending.) Or ideally, but probably involving more code, return a cached response once the first one is resolved.

Thanks again!

P.S. The min-ttl functionality of this project is my main usage, so if you've abandoned this, but know another repo with the same capability, please let me know :)

[vi]

I haven't used dnscache for myself for a long time.

If you need just minttl then maybe a simpler DNS proxy (without cache) can be implemented that just patches TTL without other things?