nixos/anki-sync-server: add setting (#344724)

nixos/modules/services/misc/anki-sync-server.md

@@ -42,6 +42,15 @@ Here, `passwordFile` is the path to a file containing just the password in
 plaintext. Make sure to set permissions to make this file unreadable to any
 user besides root.
 
+By default, synced data are stored in */var/lib/anki-sync-server/*ankiuser**.
+You can change the directory by using `services.anki-sync-server.baseDirectory`
+
+```nix
+{
+  services.anki-sync-server.baseDirectory = "/home/anki/data";
+}
+```
+
 By default, the server listen address {option}`services.anki-sync-server.host`
 is set to localhost, listening on port
 {option}`services.anki-sync-server.port`, and does not open the firewall. This

nixos/modules/services/misc/anki-sync-server.nix

@@ -59,6 +59,13 @@ in {
       description = "Port number anki-sync-server listens to.";
     };
 
+    baseDirectory = mkOption {
+      type = types.str;
+      default = "%S/%N";
+      description = "Base directory where user(s) synchronized data will be stored.";
+    };
+
+
     openFirewall = mkOption {
       default = false;
       type = types.bool;
@@ -114,7 +121,7 @@ in {
       wantedBy = ["multi-user.target"];
       path = [cfg.package];
       environment = {
-        SYNC_BASE = "%S/%N";
+        SYNC_BASE = cfg.baseDirectory;
         SYNC_HOST = specEscape cfg.address;
         SYNC_PORT = toString cfg.port;
       };