fuuko/nar-serve: Use NixOS module

Since it does not provide a `package` option, it has to be overriden
with an overlay.

machines/fuuko/services/binary-cache.nix

@@ -59,43 +59,18 @@ in
             (lib.splitString "\n" config.services.nginx.commonHttpConfig))}
           add_header Access-Control-Allow-Origin https://hydra.sbruder.de;
         '';
-        "/nix/store/".proxyPass = "http://localhost:${config.systemd.services.nar-serve.environment.PORT}";
+        "/nix/store/".proxyPass = "http://localhost:${toString config.services.nar-serve.port}";
       };
     };
   };
 
   systemd.services.nginx.serviceConfig.ReadWritePaths = lib.singleton binaryCachePath;
 
-  # TODO 21.05: Replace with upstream module
-  systemd.services.nar-serve =
-    let
-      # TODO: remove once new version is released and in nixpkgs
-      nar-serve = pkgs.nar-serve.overrideAttrs (o: o // {
-        version = "unstable-2021-04-08";
-
-        src = pkgs.fetchFromGitHub {
-          owner = "numtide";
-          repo = "nar-serve";
-          rev = "4243b0efa41910dfa4be8b9936ae460699d3f8f0";
-          sha256 = "0mjs3yilf5rixm67wk4h4jji54dsc0w3vfxd561pvfbxplbmgh3c";
-        };
-      });
-    in
-    {
-      after = [ "network.target" ];
-      wantedBy = [ "multi-user.target" ];
-
-      environment = {
-        PORT = "8383";
-        NAR_CACHE_URL = "file://${binaryCachePath}";
+  services.nar-serve = {
+    enable = true;
+    cacheURL = "file://${binaryCachePath}";
   };
 
-      serviceConfig = {
-        Restart = "always";
-        RestartSec = "5s";
-        ExecStart = "${nar-serve}/bin/nar-serve";
-        DynamicUser = true;
-        StandardOutput = "null"; # nar-server logs multiple lines on every request
-      };
-    };
+  # nar-serve logs multiple lines on every request
+  systemd.services.nar-serve.serviceConfig.StandardOutput = "null";
 }

pkgs/default.nix

@@ -48,4 +48,16 @@ in
     doCheck = prev.stdenv.isi686;
     checkTarget = "run_self_test";
   });
+
+  # TODO: remove once new version (> 0.3.0) is released and in nixpkgs
+  nar-serve = prev.nar-serve.overrideAttrs (o: o // {
+    version = "unstable-2021-04-08";
+
+    src = prev.fetchFromGitHub {
+      owner = "numtide";
+      repo = "nar-serve";
+      rev = "4243b0efa41910dfa4be8b9936ae460699d3f8f0";
+      sha256 = "0mjs3yilf5rixm67wk4h4jji54dsc0w3vfxd561pvfbxplbmgh3c";
+    };
+  });
 }