nixos/mautrix-signal: add module

- [db-rest](https://github.com/derhuerst/db-rest), a wrapper around Deutsche Bahn's internal API for public transport data. Available as [services.db-rest](#opt-services.db-rest.enable).

- [mautrix-signal](https://github.com/mautrix/signal), a Matrix-Signal puppeting bridge. Available as [services.mautrix-signal](#opt-services.mautrix-signal.enable).

- [Anki Sync Server](https://docs.ankiweb.net/sync-server.html), the official sync server built into recent versions of Anki. Available as [services.anki-sync-server](#opt-services.anki-sync-server.enable).

The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been marked deprecated and will be dropped after 24.05 due to lack of maintenance of the anki-sync-server software.

  ./services/matrix/maubot.nix

  ./services/matrix/mautrix-facebook.nix

  ./services/matrix/mautrix-meta.nix

  ./services/matrix/mautrix-signal.nix

  ./services/matrix/mautrix-telegram.nix

  ./services/matrix/mautrix-whatsapp.nix

  ./services/matrix/mjolnir.nix

{ lib

, config

, pkgs

, ...

}:

let

  cfg = config.services.mautrix-signal;

  dataDir = "/var/lib/mautrix-signal";

  registrationFile = "${dataDir}/signal-registration.yaml";

  settingsFile = "${dataDir}/config.yaml";

  settingsFileUnsubstituted = settingsFormat.generate "mautrix-signal-config-unsubstituted.json" cfg.settings;

  settingsFormat = pkgs.formats.json { };

  appservicePort = 29328;

  # to be used with a list of lib.mkIf values

  optOneOf = lib.lists.findFirst (value: value.condition) (lib.mkIf false null);

  mkDefaults = lib.mapAttrsRecursive (n: v: lib.mkDefault v);

  defaultConfig = {

    homeserver.address = "http://localhost:8448";

    appservice = {

      hostname = "[::]";

      port = appservicePort;

      database.type = "sqlite3";

      database.uri = "file:${dataDir}/mautrix-signal.db?_txlock=immediate";

      id = "signal";

      bot = {

        username = "signalbot";

        displayname = "Signal Bridge Bot";

      };

      as_token = "";

      hs_token = "";

    };

    bridge = {

      username_template = "signal_{{.}}";

      displayname_template = "{{or .ProfileName .PhoneNumber \"Unknown user\"}}";

      double_puppet_server_map = { };

      login_shared_secret_map = { };

      command_prefix = "!signal";

      permissions."*" = "relay";

      relay.enabled = true;

    };

    logging = {

      min_level = "info";

      writers = lib.singleton {

        type = "stdout";

        format = "pretty-colored";

        time_format = " ";

      };

    };

  };

in

{

  options.services.mautrix-signal = {

    enable = lib.mkEnableOption "mautrix-signal, a Matrix-Signal puppeting bridge.";

    settings = lib.mkOption {

      apply = lib.recursiveUpdate defaultConfig;

      type = settingsFormat.type;

      default = defaultConfig;

      description = ''

        {file}`config.yaml` configuration as a Nix attribute set.

        Configuration options should match those described in

        [example-config.yaml](https://github.com/mautrix/signal/blob/master/example-config.yaml).

        Secret tokens should be specified using {option}`environmentFile`

        instead of this world-readable attribute set.

      '';

      example = {

        appservice = {

          database = {

            type = "postgres";

            uri = "postgresql:///mautrix_signal?host=/run/postgresql";

          };

          id = "signal";

          ephemeral_events = false;

        };

        bridge = {

          history_sync = {

            request_full_sync = true;

          };

          private_chat_portal_meta = true;

          mute_bridging = true;

          encryption = {

            allow = true;

            default = true;

            require = true;

          };

          provisioning = {

            shared_secret = "disable";

          };

          permissions = {

            "example.com" = "user";

          };

        };

      };

    };

    environmentFile = lib.mkOption {

      type = lib.types.nullOr lib.types.path;

      default = null;

      description = ''

        File containing environment variables to be passed to the mautrix-signal service.

        If an environment variable `MAUTRIX_SIGNAL_BRIDGE_LOGIN_SHARED_SECRET` is set,

        then its value will be used in the configuration file for the option

        `login_shared_secret_map` without leaking it to the store, using the configured

        `homeserver.domain` as key.

        See [here](https://github.com/mautrix/signal/blob/main/example-config.yaml)

        for the documentation of `login_shared_secret_map`.

      '';

    };

    serviceDependencies = lib.mkOption {

      type = with lib.types; listOf str;

      default = (lib.optional config.services.matrix-synapse.enable config.services.matrix-synapse.serviceUnit)

        ++ (lib.optional config.services.matrix-conduit.enable "conduit.service");

      defaultText = lib.literalExpression ''

        (optional config.services.matrix-synapse.enable config.services.matrix-synapse.serviceUnit)

        ++ (optional config.services.matrix-conduit.enable "conduit.service")

      '';

      description = ''

        List of systemd units to require and wait for when starting the application service.

      '';

    };

    registerToSynapse = lib.mkOption {

      type = lib.types.bool;

      default = config.services.matrix-synapse.enable;

      defaultText = lib.literalExpression ''

        config.services.matrix-synapse.enable

      '';

      description = ''

        Whether to add the bridge's app service registration file to

        `services.matrix-synapse.settings.app_service_config_files`.

      '';

    };

  };

  config = lib.mkIf cfg.enable {

    users.users.mautrix-signal = {

      isSystemUser = true;

      group = "mautrix-signal";

      home = dataDir;

      description = "Mautrix-Signal bridge user";

    };

    users.groups.mautrix-signal = { };

    services.matrix-synapse = lib.mkIf cfg.registerToSynapse {

      settings.app_service_config_files = [ registrationFile ];

    };

    systemd.services.matrix-synapse = lib.mkIf cfg.registerToSynapse {

      serviceConfig.SupplementaryGroups = [ "mautrix-signal" ];

    };

    # Note: this is defined here to avoid the docs depending on `config`

    services.mautrix-signal.settings.homeserver = optOneOf (with config.services; [

      (lib.mkIf matrix-synapse.enable (mkDefaults {

        domain = matrix-synapse.settings.server_name;

      }))

      (lib.mkIf matrix-conduit.enable (mkDefaults {

        domain = matrix-conduit.settings.global.server_name;

        address = "http://localhost:${toString matrix-conduit.settings.global.port}";

      }))

    ]);

    systemd.services.mautrix-signal = {

      description = "mautrix-signal, a Matrix-Signal puppeting bridge.";

      wantedBy = [ "multi-user.target" ];

      wants = [ "network-online.target" ] ++ cfg.serviceDependencies;

      after = [ "network-online.target" ] ++ cfg.serviceDependencies;

      # ffmpeg is required for conversion of voice messages

      path = [ pkgs.ffmpeg-headless ];

      preStart = ''

        # substitute the settings file by environment variables

        # in this case read from EnvironmentFile

        test -f '${settingsFile}' && rm -f '${settingsFile}'

        old_umask=$(umask)

        umask 0177

        ${pkgs.envsubst}/bin/envsubst \

          -o '${settingsFile}' \

          -i '${settingsFileUnsubstituted}'

        umask $old_umask

        # generate the appservice's registration file if absent

        if [ ! -f '${registrationFile}' ]; then

          ${pkgs.mautrix-signal}/bin/mautrix-signal \

            --generate-registration \

            --config='${settingsFile}' \

            --registration='${registrationFile}'

        fi

        chmod 640 ${registrationFile}

        umask 0177

        # 1. Overwrite registration tokens in config

        # 2. If environment variable MAUTRIX_SIGNAL_BRIDGE_LOGIN_SHARED_SECRET

        #    is set, set it as the login shared secret value for the configured

        #    homeserver domain.

        ${pkgs.yq}/bin/yq -s '.[0].appservice.as_token = .[1].as_token

          | .[0].appservice.hs_token = .[1].hs_token

          | .[0]

          | if env.MAUTRIX_SIGNAL_BRIDGE_LOGIN_SHARED_SECRET then .bridge.login_shared_secret_map.[.homeserver.domain] = env.MAUTRIX_SIGNAL_BRIDGE_LOGIN_SHARED_SECRET else . end' \

          '${settingsFile}' '${registrationFile}' > '${settingsFile}.tmp'

        mv '${settingsFile}.tmp' '${settingsFile}'

        umask $old_umask

      '';

      serviceConfig = {

        User = "mautrix-signal";

        Group = "mautrix-signal";

        EnvironmentFile = cfg.environmentFile;

        StateDirectory = baseNameOf dataDir;

        WorkingDirectory = dataDir;

        ExecStart = ''

          ${pkgs.mautrix-signal}/bin/mautrix-signal \

          --config='${settingsFile}' \

          --registration='${registrationFile}'

        '';

        LockPersonality = true;

        MemoryDenyWriteExecute = true;

        NoNewPrivileges = true;

        PrivateDevices = true;

        PrivateTmp = true;

        PrivateUsers = true;

        ProtectClock = true;

        ProtectControlGroups = true;

        ProtectHome = true;

        ProtectHostname = true;

        ProtectKernelLogs = true;

        ProtectKernelModules = true;

        ProtectKernelTunables = true;

        ProtectSystem = "strict";

        Restart = "on-failure";

        RestartSec = "30s";

        RestrictRealtime = true;

        RestrictSUIDSGID = true;

        SystemCallArchitectures = "native";

        SystemCallErrorNumber = "EPERM";

        SystemCallFilter = [ "@system-service" ];

        Type = "simple";

        UMask = 0027;

      };

      restartTriggers = [ settingsFileUnsubstituted ];

    };

  };

  meta.maintainers = with lib.maintainers; [ niklaskorz ];

}