nixos-config/machines/fuuko/services/scan.nix

{ lib, pkgs, ... }:
{
  users.users.scan = {
    home = "/var/lib/scans";
    isSystemUser = true;
    # this is a low-risk account and since the only thing the account can do is
    # login to the ftp server from my home network, you can also sniff the
    # password since the connection is unencrypted
    password = "meeB3laodoo8na3z";
  };

  systemd.tmpfiles.rules = [
    "d /var/lib/scans 0755 scan root 7d"
  ];

  sbruder.restic.system.extraExcludes = [ "/var/lib/scans" ];

  services.vsftpd = {
    enable = true;
    writeEnable = true;
    localUsers = true;
    userlist = [ "scan" ];
    extraConfig = ''
      # I only want this to be reachable from within my home network. Since
      # IPv6 has all ports forwarded, it is disabled here.
      listen=YES
      listen_ipv6=NO

      # user’s shell is nologin
      check_shell=NO

      # scans should be readable
      local_umask=022

      pasv_min_port=30000
      pasv_max_port=30009
    '';
  };

  services.nginx.virtualHosts."scan.sbruder.de" = {
    enableACME = true;
    forceSSL = true;

    locations."/" = {
      root = "/var/lib/scans";

      extraConfig = ''
        autoindex on;

        allow 192.168.100.0/24;
        allow 2001:470:1f0b:abc::/64;
        deny all;
      '';
    };
  };

  networking.firewall = {
    allowedTCPPorts = [ 21 ];
    allowedTCPPortRanges = [{ from = 30000; to = 30009; }];
  };

  systemd.services.scan-converter = {
    wantedBy = [ "multi-user.target" ];
    script = ''
      set -euo pipefail
      ${pkgs.inotify-tools}/bin/inotifywait -m --include "\.tif$" -e close_write /var/lib/scans | while read path action file; do
          echo "Converting ''${file}…"
          ${pkgs.imagemagick}/bin/convert -strip "/var/lib/scans/$file" "/var/lib/scans/''${file%.*}.png"
          rm "/var/lib/scans/$file"
      done
    '';
    serviceConfig = {
      User = "scan";
      Restart = "always";

      # systemd-analyze --no-pager security scan-converter.service
      CapabilityBoundingSet = null;
      PrivateDevices = true;
      PrivateNetwork = true;
      PrivateTmp = true;
      PrivateUsers = true;
      ProtectHome = true;
      RestrictNamespaces = true;
      SystemCallFilter = "@system-service";
    };
  };
}