nixos/sing-box: add configFile option

nixos/modules/services/networking/sing-box.nix

@@ -12,7 +12,10 @@ in
 {
 
   meta = {
-    maintainers = with lib.maintainers; [ nickcao ];
+    maintainers = with lib.maintainers; [
+      nickcao
+      oluceps
+    ];
   };
 
   options = {
@@ -34,47 +37,82 @@ in
           containing the value the option should be set to.
         '';
       };
+      configFile = lib.mkOption {
+        type = with lib.types; nullOr path;
+        default = null;
+        description = ''
+          The path of file that contains sing-box configuration.
+        '';
+      };
     };
   };
 
-  config = lib.mkIf cfg.enable {
-    assertions =
-      let
-        rules = cfg.settings.route.rules or [ ];
-      in
-      [
-        {
-          assertion = !lib.any (r: r ? source_geoip || r ? geoip) rules;
-          message = ''
-            Deprecated option `services.sing-box.settings.route.rules.*.{source_geoip,geoip}` is set.
-            See https://sing-box.sagernet.org/migration/#migrate-geoip-to-rule-sets for migration instructions.
-          '';
-        }
-        {
-          assertion = !lib.any (r: r ? geosite) rules;
+  config = lib.mkIf cfg.enable (
+    let
+      useConfigFile = cfg.configFile != null;
+    in
+    {
+      assertions =
+        (lib.singleton {
+          assertion =
+            let
+              settingsSet = cfg.settings != { };
+            in
+            useConfigFile -> !settingsSet;
           message = ''
-            Deprecated option `services.sing-box.settings.route.rules.*.geosite` is set.
-            See https://sing-box.sagernet.org/migration/#migrate-geosite-to-rule-sets for migration instructions.
+            `services.sing-box.settings` or `services.sing-box.configFile` must be set exclusively.
           '';
-        }
-      ];
+        })
+        ++ (lib.optionals (!useConfigFile) (
+          let
+            rules = cfg.settings.route.rules or [ ];
+          in
+          [
+            {
+              assertion = !lib.any (r: r ? source_geoip || r ? geoip) rules;
+              message = ''
+                Deprecated option `services.sing-box.settings.route.rules.*.{source_geoip,geoip}` is set.
+                See https://sing-box.sagernet.org/migration/#migrate-geoip-to-rule-sets for migration instructions.
+              '';
+            }
+            {
+              assertion = !lib.any (r: r ? geosite) rules;
+              message = ''
+                Deprecated option `services.sing-box.settings.route.rules.*.geosite` is set.
+                See https://sing-box.sagernet.org/migration/#migrate-geosite-to-rule-sets for migration instructions.
+              '';
+            }
+          ]
+        ));
 
-    systemd.packages = [ cfg.package ];
+      systemd.packages = [ cfg.package ];
 
-    systemd.services.sing-box = {
-      preStart = utils.genJqSecretsReplacementSnippet cfg.settings "/run/sing-box/config.json";
-      serviceConfig = {
-        StateDirectory = "sing-box";
-        StateDirectoryMode = "0700";
-        RuntimeDirectory = "sing-box";
-        RuntimeDirectoryMode = "0700";
-        ExecStart = [
-          ""
-          "${lib.getExe cfg.package} -D \${STATE_DIRECTORY} -C \${RUNTIME_DIRECTORY} run"
-        ];
+      systemd.services.sing-box = {
+
+        preStart = lib.mkIf (!useConfigFile) (
+          utils.genJqSecretsReplacementSnippet cfg.settings "/run/sing-box/config.json"
+        );
+
+        serviceConfig = {
+          StateDirectory = "sing-box";
+          StateDirectoryMode = "0700";
+          RuntimeDirectory = "sing-box";
+          RuntimeDirectoryMode = "0700";
+          LoadCredential = lib.mkIf useConfigFile [ ("config.json:" + cfg.configFile) ];
+          ExecStart = [
+            ""
+            (
+              let
+                configArgs =
+                  if useConfigFile then "-c $\{CREDENTIALS_DIRECTORY}/config.json" else "-C \${RUNTIME_DIRECTORY}";
+              in
+              "${lib.getExe cfg.package} -D \${STATE_DIRECTORY} ${configArgs} run"
+            )
+          ];
+        };
+        wantedBy = [ "multi-user.target" ];
       };
-      wantedBy = [ "multi-user.target" ];
-    };
-  };
+    }
+  );
 
 }

nixos/tests/sing-box.nix

@@ -210,17 +210,21 @@ import ./make-test-python.nix (
 
           services.sing-box = {
             enable = true;
-            settings = {
-              inbounds = [
-                vmessInbound
-              ];
-              outbounds = [
-                {
-                  type = "direct";
-                  tag = "outbound:direct";
+            configFile = toString (
+              pkgs.writeText "test-sing-box-json-config" (
+                builtins.toJSON {
+                  inbounds = [
+                    vmessInbound
+                  ];
+                  outbounds = [
+                    {
+                      type = "direct";
+                      tag = "outbound:direct";
+                    }
+                  ];
                 }
-              ];
-            };
+              )
+            );
           };
         };