test udp port https://wiki.itadmins.net/network/tcp_udp_ping sudo watch -n 5 "nmap -P0 -sU -p54321 127.0.0.1" this creates a zero-len udp package, that is used to mock a request
also testable as real dns proxy on linux: cargo build sudo RUST_BACKTRACE=1 ./target/debug/httpsdns 0.0.0.0:53 put a new line with "nameserver 127.0.0.1" in /etc/resolf.conf (obviously: comment out the old with a # or backup it otherwise)