nixos/duplicati: Add dataDir to service

Other services such as minecraft-server and plex allow configuration of
the dataDir option, allowing the files stored by each service to be in a
custom location.

Co-authored-by: Aaron Andersen <aaron@fosslib.net>

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -253,6 +253,13 @@
           configuration.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The option <literal>services.duplicati.dataDir</literal> has
+          been added to allow changing the location of duplicati’s
+          files.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
 </section>

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -101,3 +101,5 @@ In addition to numerous new and upgraded packages, this release has the followin
   e.g. Wayland.
 
 - The `services.stubby` module was converted to a [settings-style](https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md) configuration.
+
+- The option `services.duplicati.dataDir` has been added to allow changing the location of duplicati's files.

nixos/modules/services/backup/duplicati.nix

@@ -18,6 +18,20 @@ in
         '';
       };
 
+      dataDir = mkOption {
+        type = types.str;
+        default = "/var/lib/duplicati";
+        description = ''
+          The directory where Duplicati stores its data files.
+
+          <note><para>
+            If left as the default value this directory will automatically be created
+            before the Duplicati server starts, otherwise you are responsible for ensuring
+            the directory exists with appropriate ownership and permissions.
+          </para></note>
+        '';
+      };
+
       interface = mkOption {
         default = "127.0.0.1";
         type = types.str;
@@ -45,20 +59,23 @@ in
       description = "Duplicati backup";
       after = [ "network.target" ];
       wantedBy = [ "multi-user.target" ];
-      serviceConfig = {
-        User = cfg.user;
-        Group = "duplicati";
-        StateDirectory = "duplicati";
-        ExecStart = "${pkgs.duplicati}/bin/duplicati-server --webservice-interface=${cfg.interface} --webservice-port=${toString cfg.port} --server-datafolder=/var/lib/duplicati";
-        Restart = "on-failure";
-      };
+      serviceConfig = mkMerge [
+        {
+          User = cfg.user;
+          Group = "duplicati";
+          ExecStart = "${pkgs.duplicati}/bin/duplicati-server --webservice-interface=${cfg.interface} --webservice-port=${toString cfg.port} --server-datafolder=${cfg.dataDir}";
+          Restart = "on-failure";
+        }
+        (mkIf (cfg.dataDir == "/var/lib/duplicati") {
+          StateDirectory = "duplicati";
+        })
+      ];
     };
 
     users.users = lib.optionalAttrs (cfg.user == "duplicati") {
       duplicati = {
         uid = config.ids.uids.duplicati;
-        home = "/var/lib/duplicati";
-        createHome = true;
+        home = cfg.dataDir;
         group = "duplicati";
       };
     };