nixos/dae: fix override existed config issue

nixos/modules/services/networking/dae.nix

···
 
       package = mkPackageOptionMD pkgs "dae" { };
 
+
       assets = mkOption {
         type = with types;(listOf path);
         default = with pkgs; [ v2ray-geoip v2ray-domain-list-community ];
···
       };
 
       configFile = mkOption {
-        type = types.path;
-        default = "/etc/dae/config.dae";
+        type = with types; (nullOr path);
+        default = null;
         example = "/path/to/your/config.dae";
         description = mdDoc ''
           The path of dae config file, end with `.dae`.
···
       };
 
       config = mkOption {
-        type = types.str;
-        default = ''
-          global{}
-          routing{}
-        '';
+        type = with types; (nullOr str);
+        default = null;
         description = mdDoc ''
+          WARNING: This option will expose store your config unencrypted world-readable in the nix store.
           Config text for dae.
 
           See <https://github.com/daeuniverse/dae/blob/main/example.dae>.
···
       environment.systemPackages = [ cfg.package ];
       systemd.packages = [ cfg.package ];
 
-      environment.etc."dae/config.dae" = {
-        mode = "0400";
-        source = pkgs.writeText "config.dae" cfg.config;
-      };
-
       networking = lib.mkIf cfg.openFirewall.enable {
         firewall =
           let portToOpen = cfg.openFirewall.port;
···
       systemd.services.dae =
         let
           daeBin = lib.getExe cfg.package;
-          TxChecksumIpGenericWorkaround = with lib;(getExe pkgs.writeShellApplication {
-            name = "disable-tx-checksum-ip-generic";
-            text = with pkgs; ''
-              iface=$(${iproute2}/bin/ip route | ${lib.getExe gawk} '/default/ {print $5}')
-              ${lib.getExe ethtool} -K "$iface" tx-checksum-ip-generic off
-            '';
-          });
+
+          configPath =
+            if cfg.configFile != null
+            then cfg.configFile else pkgs.writeText "config.dae" cfg.config;
+
+          TxChecksumIpGenericWorkaround = with lib;
+            (getExe pkgs.writeShellApplication {
+              name = "disable-tx-checksum-ip-generic";
+              text = with pkgs; ''
+                iface=$(${iproute2}/bin/ip route | ${lib.getExe gawk} '/default/ {print $5}')
+                ${lib.getExe ethtool} -K "$iface" tx-checksum-ip-generic off
+              '';
+            });
         in
         {
           wantedBy = [ "multi-user.target" ];
           serviceConfig = {
-            ExecStartPre = [ "" "${daeBin} validate -c ${cfg.configFile}" ]
+            LoadCredential = [ "config.dae:${configPath}" ];
+            ExecStartPre = [ "" "${daeBin} validate -c \${CREDENTIALS_DIRECTORY}/config.dae" ]
               ++ (with lib; optional cfg.disableTxChecksumIpGeneric TxChecksumIpGenericWorkaround);
-            ExecStart = [ "" "${daeBin} run --disable-timestamp -c ${cfg.configFile}" ];
+            ExecStart = [ "" "${daeBin} run --disable-timestamp -c \${CREDENTIALS_DIRECTORY}/config.dae" ];
             Environment = "DAE_LOCATION_ASSET=${cfg.assetsPath}";
           };
         };
···
         }
 
         {
-          assertion = !((config.services.dae.config != "global{}\nrouting{}\n")
-            && (config.services.dae.configFile != "/etc/dae/config.dae"));
+          assertion = !((config.services.dae.config != null)
+            && (config.services.dae.configFile != null));
           message = ''
             Option `config` and `configFile` could not be set
             at the same time.
+          '';
+        }
+
+        {
+          assertion = !((config.services.dae.config == null)
+            && (config.services.dae.configFile == null));
+          message = ''
+            Either `config` or `configFile` should be set.
           '';
         }
       ];

nixos/tests/dae.nix

···
     };
     services.dae = {
       enable = true;
+      config = ''
+        global{}
+        routing{}
+      '';
     };
   };