nixos/shelfmark: init module

Adds a NixOS service module with DynamicUser, configurable host/port,
data and ingest directories, environment variable passthrough, and
systemd hardening (per NixOS/nixpkgs#377827).

nixos/modules/module-list.nix

@@ -957,6 +957,7 @@
   ./services/misc/servarr/sonarr.nix
   ./services/misc/servarr/whisparr.nix
   ./services/misc/serviio.nix
+  ./services/misc/shelfmark.nix
   ./services/misc/shoko.nix
   ./services/misc/sickbeard.nix
   ./services/misc/snapper.nix

nixos/modules/services/misc/shelfmark.nix

@@ -0,0 +1,131 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
+let
+  cfg = config.services.shelfmark;
+in
+{
+  options.services.shelfmark = {
+
+    enable = lib.mkEnableOption "Shelfmark, a self-hosted book and audiobook search and download interface";
+
+    package = lib.mkPackageOption pkgs "shelfmark" { };
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Open the appropriate ports in the firewall for Shelfmark.";
+    };
+
+    environment = lib.mkOption {
+      type = lib.types.submodule {
+        freeformType = lib.types.attrsOf lib.types.str;
+        options = {
+          FLASK_HOST = lib.mkOption {
+            type = lib.types.str;
+            default = "127.0.0.1";
+            example = "0.0.0.0";
+            description = "The IP address to bind the Shelfmark server to.";
+          };
+
+          FLASK_PORT = lib.mkOption {
+            type = lib.types.port;
+            default = 8084;
+            apply = toString;
+            description = "TCP port for the Shelfmark web interface.";
+          };
+
+          ENABLE_LOGGING = lib.mkOption {
+            type = lib.types.bool;
+            apply = toString;
+            default = false;
+            description = "Whether to enable file logging. Disabled by default since systemd captures console output via journald.";
+          };
+
+          CONFIG_DIR = lib.mkOption {
+            type = lib.types.path;
+            default = "/var/lib/shelfmark";
+            description = "Directory for Shelfmark configuration, database, and artwork cache.";
+          };
+        };
+      };
+      default = { };
+      example = {
+        SEARCH_MODE = "universal";
+        LOG_LEVEL = "DEBUG";
+      };
+      description = ''
+        Environment variables to pass to the Shelfmark service.
+        See <https://github.com/calibrain/shelfmark/blob/main/docs/environment-variables.md>
+        for available options.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+
+    systemd.services.shelfmark = {
+      description = "Shelfmark - book and audiobook search and download interface";
+      after = [ "network-online.target" ];
+      wants = [ "network-online.target" ];
+      wantedBy = [ "multi-user.target" ];
+      inherit (cfg) environment;
+      serviceConfig = {
+        DynamicUser = true;
+        ExecStart = "${lib.getExe cfg.package} -b ${cfg.environment.FLASK_HOST}:${cfg.environment.FLASK_PORT}";
+        StateDirectory = "shelfmark";
+
+        ProtectSystem = "strict";
+        ProtectHome = true;
+        PrivateTmp = true;
+        PrivateDevices = true;
+        PrivateMounts = true;
+        ProtectControlGroups = true;
+        ProtectKernelTunables = true;
+        RestrictSUIDSGID = true;
+        RemoveIPC = true;
+        UMask = "0077";
+
+        CapabilityBoundingSet = [ "" ];
+        NoNewPrivileges = true;
+
+        ProtectKernelModules = true;
+        ProtectKernelLogs = true;
+        ProtectClock = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = [
+          "@system-service"
+          "~@privileged"
+          "~@resources"
+        ];
+
+        RestrictAddressFamilies = [
+          "AF_INET"
+          "AF_INET6"
+          "AF_UNIX"
+        ];
+
+        PrivateUsers = true;
+
+        LockPersonality = true;
+        ProtectHostname = true;
+        RestrictRealtime = true;
+        RestrictNamespaces = true;
+        ProtectProc = "invisible";
+        ProcSubset = "pid";
+        DeviceAllow = [ "" ];
+      };
+    };
+
+    networking.firewall = lib.mkIf cfg.openFirewall {
+      allowedTCPPorts = [ (lib.toInt cfg.environment.FLASK_PORT) ];
+    };
+  };
+
+  meta = {
+    maintainers = with lib.maintainers; [ jamiemagee ];
+  };
+}