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

lib/default.nix

@@ -8,6 +8,18 @@ let
   inherit (lib.flake) defaultSystems;
 in
 rec {
+  pow =
+    let
+      pow' = base: exponent: value:
+        # FIXME: It will silently overflow on values > 2**62 :(
+        # The value will become negative or zero in this case
+        if exponent == 0
+        then 1
+        else if exponent <= 1
+        then value
+        else (pow' base (exponent - 1) (value * base));
+    in base: exponent: pow' base exponent base;
+
   attrsToNVList = mapAttrsToList nameValuePair;
 
   inherit (import ./net.nix { inherit lib; }) net;
@@ -29,6 +41,8 @@ rec {
       ports = checked (elemAt m 1);
     };
 
+  netBroadcast = net': net.cidr.host ((pow 2 (net.cidr.size net')) - 1) net';
+
   mkDefaultSystemsPkgs = path: args': genAttrs defaultSystems (system: import path ((args' system) // { inherit system; }));
   mkApp = program: { type = "app"; inherit program; };
   mkShellApp = pkgs: name: text: mkApp (pkgs.writeShellScript name text).outPath;

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}')"'';
 }