#!/bin/bash

RULESET="table inet uni {
	chain gtfo {
		reject with icmpx type host-unreachable
		drop
	}

	chain filter_in_tcp {
		tcp dport vmap {
			   80 : accept,
			   81 : accept,
			  443 : accept,
			  931 : accept,
			 5001 : accept,
			 5201 : accept,
		}
		tcp dport vmap {
			 6800-6999  : accept,
			33434-33499 : accept,
		}

		drop
	}

	chain filter_in_udp {
		udp dport vmap {
			   53 : accept,
			  123 : accept,
			  846 : accept,
			  849 : accept,
			 5001 : accept,
			 5201 : accept,
		}
		udp dport vmap {
			 5300-5399  : accept,
			 6800-6999  : accept,
			33434-33499 : accept,
		}

		drop
	}

	chain filter_in {
		type filter hook input priority 0; policy drop;

		ct state vmap {
			invalid     : drop,
			established : accept,
			related     : accept,
			untracked   : accept,
		}

		ct status vmap {
			dnat : accept,
			snat : accept,
		}

		iif lo  accept

		meta iifgroup {100-199}  accept

		meta l4proto tcp  goto filter_in_tcp
		meta l4proto udp  goto filter_in_udp

		icmp type vmap {
			echo-request : accept,
		}
		ip6 nexthdr icmpv6 icmpv6 type vmap {
			echo-request : accept,
		}
	}

	chain filter_fwd_ifgroup {
		meta iifgroup . oifgroup vmap {
		          100 .  10 : accept,
		          100 . 100 : accept,
		          100 . 101 : accept,
		          101 . 101 : accept,
		}
		goto gtfo
	}

	chain filter_fwd {
		type filter hook forward priority 0; policy drop;

		fib daddr type broadcast  drop

		ct state vmap {
			invalid     : drop,
			established : accept,
			related     : accept,
			untracked   : accept,
		}

		ct status vmap {
			dnat : accept,
			snat : accept,
		}

		meta iifgroup {100-199}  goto filter_fwd_ifgroup
	}

	chain nat_fwd_tun {
		meta l4proto tcp redirect to :15
		udp dport 53 redirect to :13
		goto gtfo
	}

	chain nat_dns_dnstc     { meta l4proto udp redirect to :5300 ; drop ; }
	chain nat_dns_this_5301 { meta l4proto udp redirect to :5301 ; drop ; }
	chain nat_dns_moon_5301  { meta nfproto ipv4 meta l4proto udp dnat to 240.0.1.2:5301 ; drop ; }
	chain nat_dns_moon_5302  { meta nfproto ipv4 meta l4proto udp dnat to 240.0.1.2:5302 ; drop ; }
	chain nat_dns_moon_5303  { meta nfproto ipv4 meta l4proto udp dnat to 240.0.1.2:5303 ; drop ; }

	chain nat_dns_acme {
		udp length 47-63 @th,160,128 0x0e373135363130333131303735353203 \
			goto nat_dns_dnstc

		udp length 62-78 @th,160,128 0x0e31393032383939353831343037320e \
			goto nat_dns_this_5301

		udp length 62-78 @th,160,128 0x0e31363436323733373931323934300e \
			goto nat_dns_moon_5301

		udp length 62-78 @th,160,128 0x0e32393535373539353636383732310e \
			goto nat_dns_moon_5302

		udp length 62-78 @th,160,128 0x0e38353439353637323038363633390e \
			goto nat_dns_moon_5303

		drop
	}

	chain nat_prerouting {
		type nat hook prerouting priority -100; policy accept;

		iifgroup 10 udp dport 53 goto nat_dns_acme
		iifgroup 10 accept

		ip  daddr 198.19.0.0/16  goto nat_fwd_tun
		ip6 daddr fc00::/8       goto nat_fwd_tun

		tcp dport 53 redirect to :25302
		udp dport 53 redirect to :25302
	}

	chain nat_output {
		type nat hook output priority -100; policy accept;

		ip  daddr 198.19.0.0/16  goto nat_fwd_tun
		ip6 daddr fc00::/8       goto nat_fwd_tun
	}

	chain nat_postrouting {
		type nat hook postrouting priority 100; policy accept;

		oif != lo masquerade
	}

	chain mangle_forward {
		type filter hook forward priority -150; policy accept;

		tcp flags & (syn | rst) == syn tcp option maxseg size set rt mtu
	}
}"

$NFT -o -c -f - <<< $RULESET