nixos/home/routing-common: Dynamically return WAN IP DNS

lib/dns.nix

@@ -67,4 +67,35 @@ rec {
           (a.ipv6.address != null && a.ipv6.genPTR)
           ''@@PTR:${a.ipv6.address}:${toString ndots}@@ IN PTR ${a.name}.${domain}.'';
     };
+
+  ifaceA = { pkgs, iface, skipBroadcasts ? [] }:
+  let
+    extraFilters = concatMapStringsSep " " (b: ''and .broadcast != \"${b}\"'') skipBroadcasts;
+    script = pkgs.writeText "if-${iface}-a.lua" ''
+      local proc = io.popen("${pkgs.iproute2}/bin/ip -j addr show dev ${iface} | ${pkgs.jq}/bin/jq -r '.[0].addr_info[] | select(.family == \"inet\" and .scope == \"global\" ${extraFilters}).local'", "r")
+      assert(proc, "failed to popen")
+
+      local addr_line = proc:read("*l")
+      assert(proc:close(), "command failed")
+      assert(addr_line, "no output from command")
+
+      return addr_line
+    '';
+  in
+    ''A "dofile('${script}')"'';
+
+  lookupIP = { pkgs, hostname, server, type ? "A" }:
+  let
+    script = pkgs.writeScript "drill-${hostname}-${server}.lua" ''
+      local proc = io.popen("${pkgs.ldns}/bin/drill -Q @${server} ${hostname} ${type}", "r")
+      assert(proc, "failed to popen")
+
+      local addr_line = proc:read("*l")
+      assert(proc:close(), "command failed")
+      assert(addr_line, "no output from command")
+
+      return addr_line
+    '';
+  in
+    ''${type} "dofile('${script}')"'';
 }