nixos/schleuder: init module and accompanying test

Co-Authored-By: Martin Weinelt <hexa@darmstadt.ccc.de>
Co-Authored-By: Cole Helbling <cole.helbling@determinate.systems>

2 files changed, 163 insertions, 0 deletions

diff --git a/nixos/modules/module-list.nix b/nixos/modules/module-list.nix
index 43ae28ac02c5f..3aae26f385439 100644
--- a/nixos/modules/module-list.nix
+++ b/nixos/modules/module-list.nix
@@ -516,6 +516,7 @@
   ./services/mail/rspamd.nix
   ./services/mail/rss2email.nix
   ./services/mail/roundcube.nix
+  ./services/mail/schleuder.nix
   ./services/mail/sympa.nix
   ./services/mail/nullmailer.nix
   ./services/matrix/appservice-discord.nix
diff --git a/nixos/modules/services/mail/schleuder.nix b/nixos/modules/services/mail/schleuder.nix
new file mode 100644
index 0000000000000..7ba15f1070bde
--- /dev/null
+++ b/nixos/modules/services/mail/schleuder.nix
@@ -0,0 +1,162 @@
+{ config, pkgs, lib, ... }:
+let
+  cfg = config.services.schleuder;
+  settingsFormat = pkgs.formats.yaml { };
+  postfixMap = entries: lib.concatStringsSep "\n" (lib.mapAttrsToList (name: value: "${name} ${value}") entries);
+  writePostfixMap = name: entries: pkgs.writeText name (postfixMap entries);
+  configScript = pkgs.writeScript "schleuder-cfg" ''
+    #!${pkgs.runtimeShell}
+    set -exuo pipefail
+    umask 0077
+    ${pkgs.yq}/bin/yq \
+      --slurpfile overrides <(${pkgs.yq}/bin/yq . <${lib.escapeShellArg cfg.extraSettingsFile}) \
+      < ${settingsFormat.generate "schleuder.yml" cfg.settings} \
+      '. * $overrides[0]' \
+      > /etc/schleuder/schleuder.yml
+    chown schleuder: /etc/schleuder/schleuder.yml
+  '';
+in
+{
+  options.services.schleuder = {
+    enable = lib.mkEnableOption "Schleuder secure remailer";
+    enablePostfix = lib.mkEnableOption "automatic postfix integration" // { default = true; };
+    lists = lib.mkOption {
+      description = ''
+        List of list addresses that should be handled by Schleuder.
+
+        Note that this is only handled by the postfix integration, and
+        the setup of the lists, their members and their keys has to be
+        performed separately via schleuder's API, using a tool such as
+        schleuder-cli.
+      '';
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [ "widget-team@example.com" "security@example.com" ];
+    };
+    /* maybe one day....
+      domains = lib.mkOption {
+      description = "Domains for which all mail should be handled by Schleuder.";
+      type = lib.types.listOf lib.types.str;
+      default = [];
+      example = ["securelists.example.com"];
+      };
+    */
+    settings = lib.mkOption {
+      description = ''
+        Settings for schleuder.yml.
+
+        Check the <link xlink:href="https://0xacab.org/schleuder/schleuder/blob/master/etc/schleuder.yml">example configuration</link> for possible values.
+      '';
+      type = lib.types.submodule {
+        freeformType = settingsFormat.type;
+        options.keyserver = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            Key server from which to fetch and update keys.
+
+            Note that NixOS uses a different default from upstream, since the upstream default sks-keyservers.net is deprecated.
+          '';
+          default = "keys.openpgp.org";
+        };
+      };
+      default = { };
+    };
+    extraSettingsFile = lib.mkOption {
+      description = "YAML file to merge into the schleuder config at runtime. This can be used for secrets such as API keys.";
+      type = lib.types.nullOr lib.types.path;
+      default = null;
+    };
+    listDefaults = lib.mkOption {
+      description = ''
+        Default settings for lists (list-defaults.yml).
+
+        Check the <link xlink:href="https://0xacab.org/schleuder/schleuder/-/blob/master/etc/list-defaults.yml">example configuration</link> for possible values.
+      '';
+      type = settingsFormat.type;
+      default = { };
+    };
+  };
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = !(cfg.settings.api ? valid_api_keys);
+        message = ''
+          services.schleuder.settings.api.valid_api_keys is set. Defining API keys via NixOS config results in them being copied to the world-readable Nix store. Please use the extraSettingsFile option to store API keys in a non-public location.
+        '';
+      }
+      {
+        assertion = !(lib.any (db: db ? password) (lib.attrValues cfg.settings.database or {}));
+        message = ''
+          A password is defined for at least one database in services.schleuder.settings.database. Defining passwords via NixOS config results in them being copied to the world-readable Nix store. Please use the extraSettingsFile option to store database passwords in a non-public location.
+        '';
+      }
+    ];
+    users.users.schleuder.isSystemUser = true;
+    users.users.schleuder.group = "schleuder";
+    users.groups.schleuder = {};
+    environment.systemPackages = [
+      pkgs.schleuder-cli
+    ];
+    services.postfix = lib.mkIf cfg.enablePostfix {
+      extraMasterConf = ''
+        schleuder  unix  -       n       n       -       -       pipe
+          flags=DRhu user=schleuder argv=/${pkgs.schleuder}/bin/schleuder work ''${recipient}
+      '';
+      transport = lib.mkIf (cfg.lists != [ ]) (postfixMap (lib.genAttrs cfg.lists (_: "schleuder:")));
+      extraConfig = ''
+        schleuder_destination_recipient_limit = 1
+      '';
+      # review: does this make sense?
+      localRecipients = lib.mkIf (cfg.lists != [ ]) cfg.lists;
+    };
+    systemd.services = let commonServiceConfig = {
+      # We would have liked to use DynamicUser, but since the default
+      # database is SQLite and lives in StateDirectory, and that same
+      # database needs to be readable from the postfix service, this
+      # isn't trivial to do.
+      User = "schleuder";
+      StateDirectory = "schleuder";
+      StateDirectoryMode = "0700";
+    }; in
+      {
+        schleuder-init = {
+          serviceConfig = commonServiceConfig // {
+            ExecStartPre = lib.mkIf (cfg.extraSettingsFile != null) [
+              "+${configScript}"
+            ];
+            ExecStart = [ "${pkgs.schleuder}/bin/schleuder install" ];
+            Type = "oneshot";
+          };
+        };
+        schleuder-api-daemon = {
+          after = [ "local-fs.target" "network.target" "schleuder-init.service" ];
+          wantedBy = [ "multi-user.target" ];
+          requires = [ "schleuder-init.service" ];
+          serviceConfig = commonServiceConfig // {
+            ExecStart = [ "${pkgs.schleuder}/bin/schleuder-api-daemon" ];
+          };
+        };
+        schleuder-weekly-key-maintenance = {
+          after = [ "local-fs.target" "network.target" ];
+          startAt = "weekly";
+          serviceConfig = commonServiceConfig // {
+            ExecStart = [
+              "${pkgs.schleuder}/bin/schleuder refresh_keys"
+              "${pkgs.schleuder}/bin/schleuder check_keys"
+            ];
+          };
+        };
+      };
+
+    environment.etc."schleuder/schleuder.yml" = lib.mkIf (cfg.extraSettingsFile == null) {
+      source = settingsFormat.generate "schleuder.yml" cfg.settings;
+    };
+    environment.etc."schleuder/list-defaults.yml".source = settingsFormat.generate "list-defaults.yml" cfg.listDefaults;
+
+    services.schleuder = {
+      #lists_dir = "/var/lib/schleuder.lists";
+      settings.filters_dir = lib.mkDefault "/var/lib/schleuder/filters";
+      settings.keyword_handlers_dir = lib.mkDefault "/var/lib/schleuder/keyword_handlers";
+    };
+  };
+}