nixos/searx: declarative configuration

nixos/modules/services/networking/searx.nix

@@ -3,32 +3,130 @@
 with lib;
 
 let
-
+  dataDir = "/var/lib/searx";
   cfg = config.services.searx;
 
-  configFile = cfg.configFile;
+  hasEngines =
+    builtins.hasAttr "engines" cfg.settings &&
+    cfg.settings.engines != { };
+
+  # Script to merge NixOS settings with
+  # the default settings.yml bundled in searx.
+  mergeConfig = ''
+    cd ${dataDir}
+    # find the default settings.yml
+    default=$(find '${cfg.package}/' -name settings.yml)
+
+    # write NixOS settings as JSON
+    cat <<'EOF' > settings.json
+      ${builtins.toJSON cfg.settings}
+    EOF
+
+    ${optionalString hasEngines ''
+      # extract and convert the default engines array to an object
+      ${pkgs.yq-go}/bin/yq r "$default" engines -j | \
+      ${pkgs.jq}/bin/jq 'reduce .[] as $e ({}; .[$e.name] = $e)' \
+        > engines.json
+
+      # merge and update the NixOS engines with the newly created object
+      cp settings.json temp.json
+      ${pkgs.jq}/bin/jq -s '. as [$s, $e] | $s | .engines |=
+        ($e * . | to_entries | map (.value))' \
+        temp.json engines.json > settings.json
+
+      # clean up temporary files
+      rm {engines,temp}.json
+    ''}
+
+    # merge the default and NixOS settings
+    ${pkgs.yq-go}/bin/yq m -P settings.json "$default" > settings.yml
+    rm settings.json
+
+    # substitute environment variables
+    env -0 | while IFS='=' read -r -d ''' n v; do
+      sed "s#@$n@#$v#g" -i settings.yml
+    done
+  '';
 
 in
 
 {
 
+  imports = [
+    (mkRenamedOptionModule
+      [ "services" "searx" "configFile" ]
+      [ "services" "searx" "settingsFile" ])
+  ];
+
   ###### interface
 
   options = {
 
     services.searx = {
 
-      enable = mkEnableOption
-        "the searx server. See https://github.com/asciimoo/searx";
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        relatedPackages = [ "searx" ];
+        description = "Whether to enable Searx, the meta search engine.";
+      };
 
-      configFile = mkOption {
+      environmentFile = mkOption {
         type = types.nullOr types.path;
         default = null;
-        description = "
-          The path of the Searx server configuration file. If no file
-          is specified, a default file is used (default config file has
-          debug mode enabled).
-        ";
+        description = ''
+          Environment file (see <literal>systemd.exec(5)</literal>
+          "EnvironmentFile=" section for the syntax) to define variables for
+          Searx. This option can be used to safely include secret keys into the
+          Searx configuration.
+        '';
+      };
+
+      settings = mkOption {
+        type = types.attrs;
+        default = { };
+        example = literalExample ''
+          { server.port = 8080;
+            server.bind_address = "0.0.0.0";
+            server.secret_key = "@SEARX_SECRET_KEY@";
+
+            engines.wolframalpha =
+              { shortcut = "wa";
+                api_key = "@WOLFRAM_API_KEY@";
+                engine = "wolframalpha_api";
+              };
+          }
+        '';
+        description = ''
+          Searx settings. These will be merged with (taking precedence over)
+          the default configuration. It's also possible to refer to
+          environment variables
+          (defined in <xref linkend="opt-services.searx.environmentFile"/>)
+          using the syntax <literal>@VARIABLE_NAME@</literal>.
+          <note>
+            <para>
+              For available settings, see the Searx
+              <link xlink:href="https://searx.github.io/searx/admin/settings.html">docs</link>.
+            </para>
+          </note>
+        '';
+      };
+
+      settingsFile = mkOption {
+        type = types.path;
+        default = "${dataDir}/settings.yml";
+        description = ''
+          The path of the Searx server settings.yml file. If no file is
+          specified, a default file is used (default config file has debug mode
+          enabled). Note: setting this options overrides
+          <xref linkend="opt-services.searx.settings"/>.
+          <warning>
+            <para>
+              This file, along with any secret key it contains, will be copied
+              into the world-readable Nix store.
+            </para>
+          </warning>
+        '';
       };
 
       package = mkOption {
@@ -46,30 +144,20 @@ in
   ###### implementation
 
   config = mkIf config.services.searx.enable {
-
-    users.users.searx =
-      { uid = config.ids.uids.searx;
-        description = "Searx user";
-        createHome = true;
-        home = "/var/lib/searx";
-      };
-
-    users.groups.searx =
-      { gid = config.ids.gids.searx;
-      };
-
-    systemd.services.searx =
-      {
-        description = "Searx server, the meta search engine.";
-        after = [ "network.target" ];
-        wantedBy = [ "multi-user.target" ];
-        serviceConfig = {
-          User = "searx";
-          ExecStart = "${cfg.package}/bin/searx-run";
-        };
-      } // (optionalAttrs (configFile != null) {
-        environment.SEARX_SETTINGS_PATH = configFile;
-      });
+    systemd.services.searx = {
+      description = "Searx server, the meta search engine.";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        User = "searx";
+        DynamicUser = true;
+        ExecStart = "${cfg.package}/bin/searx-run";
+        StateDirectory = "searx";
+      } // optionalAttrs (cfg.environmentFile != null)
+        { EnvironmentFile = builtins.toPath cfg.environmentFile; };
+      environment.SEARX_SETTINGS_PATH = cfg.settingsFile;
+      preStart = mergeConfig;
+    };
 
     environment.systemPackages = [ cfg.package ];