Added NixOS module

nix/qddns-module.nix

@@ -0,0 +1,52 @@
+flake:
+{ config, options, lib, pkgs, ...}:
+let
+  cfg = config.services.qddns-server;
+  pkg = flake.defaultPackage.${pkgs.system};
+in
+{
+  options.services.qddns-server = with lib; {
+    enable = mkEnableOption "QDDNS";
+    db = mkOption {
+      default = "postgresql:///pdns";
+      type = types.str;
+      description = "Connection string for PDNS backend database";
+    };
+    sockUser = mkOption {
+      default = cfg.user;
+      type = types.str;
+      description = "The desired owner of the listen socket";
+    };
+    user = mkOption {
+      default = "qddns";
+      type = types.str;
+      description = "The user to run QDDNS as";
+    };
+    group = mkOption {
+      default = "qddns";
+      description = "The group to run QDDNS as";
+      type = types.str;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.sockets.qddns = {
+      enable = true;
+      listenStreams = [ "/run/qddns.sock" ];
+      socketConfig = {
+        SocketUser = cfg.sockUser;
+      };
+    };
+    systemd.services.qddns = {
+      enable = true;
+      script = "${pkg}/bin/qddns-server";
+      wantedBy = [ "multi-user.target" ];
+      environment.QDDNS_SERVER = cfg.db;
+      ServiceConfig = {
+        DynamicUser="yes";
+        User = cfg.user;
+        Group = cfg.group;
+      };
+    };
+  };
+}