Initial commit: Fava NixOS module

.gitignore

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+result

fava.nix

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+{ config, lib, pkgs, domain ? null, ... }:
+
+with lib;
+
+let
+  cfg = config.services.fava;
+
+in {
+  options.services.fava = {
+    enable = mkEnableOption "Fava web interface for Beancount";
+
+    ledgerFile = mkOption {
+      type = types.path;
+      default = "/var/lib/fava/ledger.beancount";
+      description = "Path to the beancount ledger file";
+    };
+
+    host = mkOption {
+      type = types.str;
+      default = "127.0.0.1";
+      description = "Host address to bind to";
+    };
+
+    port = mkOption {
+      type = types.port;
+      default = 5000;
+      description = "Port to run Fava on";
+    };
+
+    user = mkOption {
+      type = types.str;
+      default = "fava";
+      description = "User account under which Fava runs";
+    };
+
+    group = mkOption {
+      type = types.str;
+      default = "fava";
+      description = "Group under which Fava runs";
+    };
+
+    dataDir = mkOption {
+      type = types.path;
+      default = "/var/lib/fava";
+      description = "Directory for Fava data and ledger files";
+    };
+
+    openFirewall = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Open the firewall port for Fava";
+    };
+
+    extraOptions = mkOption {
+      type = types.listOf types.str;
+      default = [];
+      description = "Additional command-line options to pass to Fava";
+      example = [ "--read-only" "--incognito" ];
+    };
+
+    nginx = {
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = "Enable nginx reverse proxy for Fava";
+      };
+
+      subdomain = mkOption {
+        type = types.str;
+        default = "fava";
+        description = "Subdomain for Fava (e.g., 'fava' for fava.domain.com)";
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # Create system user and group
+    users.users.${cfg.user} = {
+      isSystemUser = true;
+      group = cfg.group;
+      home = cfg.dataDir;
+      createHome = true;
+      description = "Fava service user";
+    };
+
+    users.groups.${cfg.group} = {};
+
+    # Ensure data directory and ledger file exist with correct permissions
+    systemd.tmpfiles.rules = [
+      "d ${cfg.dataDir} 0750 ${cfg.user} ${cfg.group} - -"
+      "f ${cfg.ledgerFile} 0640 ${cfg.user} ${cfg.group} - -"
+    ];
+
+    # Fava systemd service
+    systemd.services.fava = {
+      description = "Fava - Web interface for Beancount";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        Type = "simple";
+        User = cfg.user;
+        Group = cfg.group;
+        WorkingDirectory = cfg.dataDir;
+
+        ExecStart = "${pkgs.fava}/bin/fava ${cfg.ledgerFile} --host ${cfg.host} --port ${toString cfg.port} ${concatStringsSep " " cfg.extraOptions}";
+
+        Restart = "on-failure";
+        RestartSec = "5s";
+
+        # Security hardening
+        NoNewPrivileges = true;
+        PrivateHome = true;
+        PrivateTmp = true;
+        PrivateDevices = true;
+        ProtectHome = true;
+        ProtectSystem = "full";
+        ProtectKernelTunables = true;
+        ProtectKernelModules = true;
+        ProtectControlGroups = true;
+        RestrictAddressFamilies = [ "AF_UNIX" "AF_INET" "AF_INET6" ];
+        RestrictNamespaces = true;
+        LockPersonality = true;
+        MemoryDenyWriteExecute = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        PrivateMounts = true;
+
+        # Allow read/write access to data directory
+        ReadWritePaths = [ cfg.dataDir ];
+      };
+    };
+
+    # Nginx reverse proxy configuration (optional)
+    services.nginx.virtualHosts = mkIf (cfg.nginx.enable && domain != null) {
+      "${cfg.nginx.subdomain}.${domain}" = {
+        forceSSL = true;
+        enableACME = true;
+        locations."/" = {
+          proxyPass = "http://${cfg.host}:${toString cfg.port}";
+          proxyWebsockets = true;
+          extraConfig = ''
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_buffering off;
+          '';
+        };
+      };
+    };
+
+    # Open firewall port if requested
+    networking.firewall.allowedTCPPorts = mkIf cfg.openFirewall [ cfg.port ];
+  };
+}

flake.nix

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+{
+  description = "Fava (Beancount web UI) NixOS module";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = { self, nixpkgs }: {
+    nixosModules.fava = import ./fava.nix;
+    nixosModules.default = self.nixosModules.fava;
+  };
+}