modules: HylaFAX server configuration

This commit adds the following
* the uucp user
* options for HylaFAX server to control startup and modems
* systemd services for HylaFAX server processes
  including faxgettys for modems
* systemd services to maintain the HylaFAX spool area,
  including cleanup with faxcron and faxqclean
* default configuration for all server processes
  for a minimal working configuration

Some notes:

* HylaFAX configuration cannot be initialized with faxsetup
  (as it would be common on other Linux distributions).
  The hylafaxplus package contains a template spool area.
* Modems are controlled by faxgetty.
  Send-only configuration (modems controlled by faxq)
  is not supported by this configuration setup.
* To enable the service, one or more modems must be defined with
  config.services.hylafax.modems .
* Sending mail *should* work:
  HylaFAX will use whatever is in
  config.services.mail.sendmailSetuidWrapper.program
  unless overridden with the sendmailPath option.
* The admin has to create a hosts.hfaxd file somewhere
  (e.g. in /etc) before enabling HylaFAX.
  This file controls access to the server (see hosts.hfaxd(5) ).
  Sadly, HylaFAX does not permit account-based access
  control as is accepts connections via TCP only.
* Active fax polling should work; I can't test it.
* Passive fax polling is not supported by HylaFAX.
* Pager transmissions (with sendpage) are disabled by default.
  I have never tested or used these.
* Incoming data/voice/"extern"al calls
  won't be handled by default.
  I have never tested or used these.

8 files changed, 837 insertions, 0 deletions

diff --git a/nixos/modules/services/networking/hylafax/default.nix b/nixos/modules/services/networking/hylafax/default.nix
new file mode 100644
index 000000000000..6e28e8c5d8bc
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/default.nix
@@ -0,0 +1,29 @@
+{ config, lib, pkgs, ... }:
+
+{
+
+  imports = [
+    ./options.nix
+    ./systemd.nix
+  ];
+
+  config = lib.modules.mkIf config.services.hylafax.enable {
+    environment.systemPackages = [ pkgs.hylafaxplus ];
+    users.users.uucp = {
+      uid = config.ids.uids.uucp;
+      group = "uucp";
+      description = "Unix-to-Unix CoPy system";
+      isSystemUser = true;
+      inherit (config.users.users.nobody) home;
+    };
+    assertions = [{
+      assertion = config.services.hylafax.modems != {};
+      message = ''
+        HylaFAX cannot be used without modems.
+        Please define at least one modem with
+        <option>config.services.hylafax</option>.
+      '';
+    }];
+  };
+
+}
diff --git a/nixos/modules/services/networking/hylafax/faxq-default.nix b/nixos/modules/services/networking/hylafax/faxq-default.nix
new file mode 100644
index 000000000000..a2630ce66b71
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/faxq-default.nix
@@ -0,0 +1,12 @@
+{ ... }:
+
+# see man:hylafax-config(5)
+
+{
+
+  ModemGroup = [ ''"any:.*"'' ];
+  ServerTracing = "0x78701";
+  SessionTracing = "0x78701";
+  UUCPLockDir = "/var/lock";
+
+}
diff --git a/nixos/modules/services/networking/hylafax/faxq-wait.sh b/nixos/modules/services/networking/hylafax/faxq-wait.sh
new file mode 100755
index 000000000000..8c39e9d20c18
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/faxq-wait.sh
@@ -0,0 +1,29 @@
+#! @shell@ -e
+
+# skip this if there are no modems at all
+if ! stat -t "@spoolAreaPath@"/etc/config.* >/dev/null 2>&1
+then
+  exit 0
+fi
+
+echo "faxq started, waiting for modem(s) to initialize..."
+
+for i in `seq @timeoutSec@0 -1 0`  # gracefully timeout
+do
+  sleep 0.1
+  # done if status files exist, but don't mention initialization
+  if \
+    stat -t "@spoolAreaPath@"/status/* >/dev/null 2>&1 \
+    && \
+    ! grep --silent --ignore-case 'initializing server' \
+    "@spoolAreaPath@"/status/*
+  then
+    echo "modem(s) apparently ready"
+    exit 0
+  fi
+  # if i reached 0, modems probably failed to initialize
+  if test $i -eq 0
+  then
+    echo "warning: modem initialization timed out"
+  fi
+done
diff --git a/nixos/modules/services/networking/hylafax/hfaxd-default.nix b/nixos/modules/services/networking/hylafax/hfaxd-default.nix
new file mode 100644
index 000000000000..8999dae57f41
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/hfaxd-default.nix
@@ -0,0 +1,10 @@
+{ ... }:
+
+# see man:hfaxd(8)
+
+{
+
+  ServerTracing = "0x91";
+  XferLogFile = "/clientlog";
+
+}
diff --git a/nixos/modules/services/networking/hylafax/modem-default.nix b/nixos/modules/services/networking/hylafax/modem-default.nix
new file mode 100644
index 000000000000..7529b5b0aafd
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/modem-default.nix
@@ -0,0 +1,22 @@
+{ pkgs, ... }:
+
+# see man:hylafax-config(5)
+
+{
+
+  TagLineFont = "etc/LiberationSans-25.pcf";
+  TagLineLocale = ''en_US.UTF-8'';
+
+  AdminGroup = "root";  # groups that can change server config
+  AnswerRotary = "fax";  # don't accept anything else but faxes
+  LogFileMode = "0640";
+  PriorityScheduling = true;
+  RecvFileMode = "0640";
+  ServerTracing = "0x78701";
+  SessionTracing = "0x78701";
+  UUCPLockDir = "/var/lock";
+
+  SendPageCmd = ''${pkgs.coreutils}/bin/false'';  # prevent pager transmit
+  SendUUCPCmd = ''${pkgs.coreutils}/bin/false'';  # prevent UUCP transmit
+
+}
diff --git a/nixos/modules/services/networking/hylafax/options.nix b/nixos/modules/services/networking/hylafax/options.nix
new file mode 100644
index 000000000000..4ac6d3fa8432
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/options.nix
@@ -0,0 +1,375 @@
+{ config, lib, pkgs, ... }:
+
+let
+
+  inherit (lib.options) literalExample mkEnableOption mkOption;
+  inherit (lib.types) bool enum int lines loaOf nullOr path str submodule;
+  inherit (lib.modules) mkDefault mkIf mkMerge;
+
+  commonDescr = ''
+    Values can be either strings or integers
+    (which will be added to the config file verbatimly)
+    or lists thereof
+    (which will be translated to multiple
+    lines with the same configuration key).
+    Boolean values are translated to "Yes" or "No".
+    The default contains some reasonable
+    configuration to yield an operational system.
+  '';
+
+  str1 = lib.types.addCheck str (s: s!="");  # non-empty string
+  int1 = lib.types.addCheck int (i: i>0);  # positive integer
+
+  configAttrType =
+    # Options in HylaFAX configuration files can be
+    # booleans, strings, integers, or list thereof
+    # representing multiple config directives with the same key.
+    # This type definition resolves all
+    # those types into a list of strings.
+    let
+      inherit (lib.types) attrsOf coercedTo listOf;
+      innerType = coercedTo bool (x: if x then "Yes" else "No")
+        (coercedTo int (toString) str);
+    in
+      attrsOf (coercedTo innerType lib.singleton (listOf innerType));
+
+  cfg = config.services.hylafax;
+
+  modemConfigOptions = { name, config, ... }: {
+    options = {
+      name = mkOption {
+        type = str1;
+        example = "ttyS1";
+        description = ''
+          Name of modem device,
+          will be searched for in <filename>/dev</filename>.
+        '';
+      };
+      type = mkOption {
+        type = str1;
+        example = "cirrus";
+        description = ''
+          Name of modem configuration file,
+          will be searched for in <filename>config</filename>
+          in the spooling area directory.
+        '';
+      };
+      config = mkOption {
+        type = configAttrType;
+        example = {
+          AreaCode = "49";
+          LocalCode = "30";
+          FAXNumber = "123456";
+          LocalIdentifier = "LostInBerlin";
+        };
+        description = ''
+          Attribute set of values for the given modem.
+          ${commonDescr}
+          Options defined here override options in
+          <option>commonModemConfig</option> for this modem.
+        '';
+      };
+    };
+    config.name = mkDefault name;
+    config.config.Include = [ "config/${config.type}" ];
+  };
+
+  defaultConfig =
+    let
+      inherit (config.security) wrapperDir;
+      inherit (config.services.mail.sendmailSetuidWrapper) program;
+      mkIfDefault = cond: value: mkIf cond (mkDefault value);
+      noWrapper = config.services.mail.sendmailSetuidWrapper==null;
+      # If a sendmail setuid wrapper exists,
+      # we add the path to the default configuration file.
+      # Otherwise, we use `false` to provoke
+      # an error if hylafax tries to use it.
+      c.sendmailPath = mkMerge [
+        (mkIfDefault noWrapper ''${pkgs.coreutils}/bin/false'')
+        (mkIfDefault (!noWrapper) ''${wrapperDir}/${program}'')
+      ];
+      importDefaultConfig = file:
+        lib.attrsets.mapAttrs
+        (lib.trivial.const mkDefault)
+        (import file { inherit pkgs; });
+      c.commonModemConfig = importDefaultConfig ./modem-default.nix;
+      c.faxqConfig = importDefaultConfig ./faxq-default.nix;
+      c.hfaxdConfig = importDefaultConfig ./hfaxd-default.nix;
+    in
+      c;
+
+  localConfig =
+    let
+      c.hfaxdConfig.UserAccessFile = cfg.userAccessFile;
+      c.faxqConfig = lib.attrsets.mapAttrs
+        (lib.trivial.const (v: mkIf (v!=null) v))
+        {
+          AreaCode = cfg.areaCode;
+          CountryCode = cfg.countryCode;
+          LongDistancePrefix = cfg.longDistancePrefix;
+          InternationalPrefix = cfg.internationalPrefix;
+        };
+      c.commonModemConfig = c.faxqConfig;
+    in
+      c;
+
+in
+
+
+{
+
+
+  options.services.hylafax = {
+
+    enable = mkEnableOption ''HylaFAX server'';
+
+    autostart = mkOption {
+      type = bool;
+      default = true;
+      example = false;
+      description = ''
+        Autostart the HylaFAX queue manager at system start.
+        If this is <literal>false</literal>, the queue manager
+        will still be started if there are pending
+        jobs or if a user tries to connect to it.
+      '';
+    };
+
+    countryCode = mkOption {
+      type = nullOr str1;
+      default = null;
+      example = "49";
+      description = ''Country code for server and all modems.'';
+    };
+
+    areaCode = mkOption {
+      type = nullOr str1;
+      default = null;
+      example = "30";
+      description = ''Area code for server and all modems.'';
+    };
+
+    longDistancePrefix = mkOption {
+      type = nullOr str;
+      default = null;
+      example = "0";
+      description = ''Long distance prefix for server and all modems.'';
+    };
+
+    internationalPrefix = mkOption {
+      type = nullOr str;
+      default = null;
+      example = "00";
+      description = ''International prefix for server and all modems.'';
+    };
+
+    spoolAreaPath = mkOption {
+      type = path;
+      default = "/var/spool/fax";
+      description = ''
+        The spooling area will be created/maintained
+        at the location given here.
+      '';
+    };
+
+    userAccessFile = mkOption {
+      type = path;
+      default = "/etc/hosts.hfaxd";
+      description = ''
+        The <filename>hosts.hfaxd</filename>
+        file entry in the spooling area
+        will be symlinked to the location given here.
+        This file must exist and be
+        readable only by the <literal>uucp</literal> user.
+        See hosts.hfaxd(5) for details.
+        This configuration permits access for all users:
+        <literal>
+          environment.etc."hosts.hfaxd" = {
+            mode = "0600";
+            user = "uucp";
+            text = ".*";
+          };
+        </literal>
+        Note that host-based access can be controlled with
+        <option>config.systemd.sockets.hylafax-hfaxd.listenStreams</option>;
+        by default, only 127.0.0.1 is permitted to connect.
+      '';
+    };
+
+    sendmailPath = mkOption {
+      type = path;
+      example = literalExample "''${pkgs.postfix}/bin/sendmail";
+      # '' ;  # fix vim
+      description = ''
+        Path to <filename>sendmail</filename> program.
+        The default uses the local sendmail wrapper
+        (see <option>config.services.mail.sendmailSetuidWrapper</option>),
+        otherwise the <filename>false</filename>
+        binary to cause an error if used.
+      '';
+    };
+
+    hfaxdConfig = mkOption {
+      type = configAttrType;
+      example.RecvqProtection = "0400";
+      description = ''
+        Attribute set of lines for the global
+        hfaxd config file <filename>etc/hfaxd.conf</filename>.
+        ${commonDescr}
+      '';
+    };
+
+    faxqConfig = mkOption {
+      type = configAttrType;
+      example = {
+        InternationalPrefix = "00";
+        LongDistancePrefix = "0";
+      };
+      description = ''
+        Attribute set of lines for the global
+        faxq config file <filename>etc/config</filename>.
+        ${commonDescr}
+      '';
+    };
+
+    commonModemConfig = mkOption {
+      type = configAttrType;
+      example = {
+        InternationalPrefix = "00";
+        LongDistancePrefix = "0";
+      };
+      description = ''
+        Attribute set of default values for
+        modem config files <filename>etc/config.*</filename>.
+        ${commonDescr}
+        Think twice before changing
+        paths of fax-processing scripts.
+      '';
+    };
+
+    modems = mkOption {
+      type = loaOf (submodule [ modemConfigOptions ]);
+      default = {};
+      example.ttyS1 = {
+        type = "cirrus";
+        config = {
+          FAXNumber = "123456";
+          LocalIdentifier = "Smith";
+        };
+      };
+      description = ''
+        Description of installed modems.
+        At least on modem must be defined
+        to enable the HylaFAX server.
+      '';
+    };
+
+    spoolExtraInit = mkOption {
+      type = lines;
+      default = "";
+      example = ''chmod 0755 .  # everyone may read my faxes'';
+      description = ''
+        Additional shell code that is executed within the
+        spooling area directory right after its setup.
+      '';
+    };
+
+    faxcron.enable.spoolInit = mkEnableOption ''
+      Purge old files from the spooling area with
+      <filename>faxcron</filename>
+      each time the spooling area is initialized.
+    '';
+    faxcron.enable.frequency = mkOption {
+      type = nullOr str1;
+      default = null;
+      example = "daily";
+      description = ''
+        Purge old files from the spooling area with
+        <filename>faxcron</filename> with the given frequency
+        (see systemd.time(7)).
+      '';
+    };
+    faxcron.infoDays = mkOption {
+      type = int1;
+      default = 30;
+      description = ''
+        Set the expiration time for data in the
+        remote machine information directory in days.
+      '';
+    };
+    faxcron.logDays = mkOption {
+      type = int1;
+      default = 30;
+      description = ''
+        Set the expiration time for
+        session trace log files in days.
+      '';
+    };
+    faxcron.rcvDays = mkOption {
+      type = int1;
+      default = 7;
+      description = ''
+        Set the expiration time for files in
+        the received facsimile queue in days.
+      '';
+    };
+
+    faxqclean.enable.spoolInit = mkEnableOption ''
+      Purge old files from the spooling area with
+      <filename>faxqclean</filename>
+      each time the spooling area is initialized.
+    '';
+    faxqclean.enable.frequency = mkOption {
+      type = nullOr str1;
+      default = null;
+      example = "daily";
+      description = ''
+        Purge old files from the spooling area with
+        <filename>faxcron</filename> with the given frequency
+        (see systemd.time(7)).
+      '';
+    };
+    faxqclean.archiving = mkOption {
+      type = enum [ "never" "as-flagged" "always" ];
+      default = "as-flagged";
+      example = "always";
+      description = ''
+        Enable or suppress job archiving:
+        <literal>never</literal> disables job archiving,
+        <literal>as-flagged</literal> archives jobs that
+        have been flagged for archiving by sendfax,
+        <literal>always</literal> forces archiving of all jobs.
+        See also sendfax(1) and faxqclean(8).
+      '';
+    };
+    faxqclean.doneqMinutes = mkOption {
+      type = int1;
+      default = 15;
+      example = literalExample ''24*60'';
+      description = ''
+        Set the job
+        age threshold (in minutes) that controls how long
+        jobs may reside in the doneq directory.
+      '';
+    };
+    faxqclean.docqMinutes = mkOption {
+      type = int1;
+      default = 60;
+      example = literalExample ''24*60'';
+      description = ''
+        Set the document
+        age threshold (in minutes) that controls how long
+        unreferenced files may reside in the docq directory.
+      '';
+    };
+
+  };
+
+
+  config.services.hylafax =
+    mkIf
+    (config.services.hylafax.enable)
+    (mkMerge [ defaultConfig localConfig ])
+  ;
+
+}
diff --git a/nixos/modules/services/networking/hylafax/spool.sh b/nixos/modules/services/networking/hylafax/spool.sh
new file mode 100755
index 000000000000..31e930e8c597
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/spool.sh
@@ -0,0 +1,111 @@
+#! @shell@ -e
+
+# The following lines create/update the HylaFAX spool directory:
+# Subdirectories/files with persistent data are kept,
+# other directories/files are removed/recreated,
+# mostly from the template spool
+# directory in the HylaFAX package.
+
+# This block explains how the spool area is
+# derived from the spool template in the HylaFAX package:
+#
+#                  + capital letter: directory; file otherwise
+#                  + P/p: persistent directory
+#                  + F/f: directory with symlinks per entry
+#                  + T/t: temporary data
+#                  + S/s: single symlink into package
+#                  |
+#                  | + u: change ownership to uucp:uucp
+#                  | + U: ..also change access mode to user-only
+#                  | |
+# archive          P U
+# bin              S
+# client           T u  (client connection info)
+# config           S
+# COPYRIGHT        s
+# dev              T u  (maybe some FIFOs)
+# docq             P U
+# doneq            P U
+# etc              F    contains customized config files!
+# etc/hosts.hfaxd  f
+# etc/xferfaxlog   f
+# info             P u  (database of called devices)
+# log              P u  (communication logs)
+# pollq            P U
+# recvq            P u
+# sendq            P U
+# status           T u  (modem status info files)
+# tmp              T U
+
+
+shopt -s dotglob  # if bash sees "*", it also includes dot files
+lnsym () { ln --symbol "$@" ; }
+lnsymfrc () { ln --symbolic --force "$@" ; }
+cprd () { cp --remove-destination "$@" ; }
+update () { install --owner=@faxuser@ --group=@faxgroup@ "$@" ; }
+
+
+## create/update spooling area
+
+update --mode=0750 -d "@spoolAreaPath@"
+cd "@spoolAreaPath@"
+
+persist=(archive docq doneq info log pollq recvq sendq)
+
+# remove entries that don't belong here
+touch dummy  # ensure "*" resolves to something
+for k in *
+do
+  keep=0
+  for j in "${persist[@]}" xferfaxlog clientlog faxcron.lastrun
+  do
+    if test "$k" == "$j"
+    then
+      keep=1
+      break
+    fi
+  done
+  if test "$keep" == "0"
+  then
+    rm --recursive "$k"
+  fi
+done
+
+# create persistent data directories (unless they exist already)
+update --mode=0700 -d "${persist[@]}"
+chmod 0755 info log recvq
+
+# create ``xferfaxlog``, ``faxcron.lastrun``, ``clientlog``
+touch clientlog faxcron.lastrun xferfaxlog
+chown @faxuser@:@faxgroup@ clientlog faxcron.lastrun xferfaxlog
+
+# create symlinks for frozen directories/files
+lnsym --target-directory=. "@hylafax@"/spool/{COPYRIGHT,bin,config}
+
+# create empty temporary directories
+update --mode=0700 -d client dev status
+update -d tmp
+
+
+## create and fill etc
+
+install -d "@spoolAreaPath@/etc"
+cd "@spoolAreaPath@/etc"
+
+# create symlinks to all files in template's etc
+lnsym --target-directory=. "@hylafax@/spool/etc"/*
+
+# set LOCKDIR in setup.cache
+sed --regexp-extended 's|^(UUCP_LOCKDIR=).*$|\1'"'@lockPath@'|g" --in-place setup.cache
+
+# etc/{xferfaxlog,lastrun} are stored in the spool root
+lnsymfrc --target-directory=. ../xferfaxlog
+lnsymfrc --no-target-directory ../faxcron.lastrun lastrun
+
+# etc/hosts.hfaxd is provided by the NixOS configuration
+lnsymfrc --no-target-directory "@userAccessFile@" hosts.hfaxd
+
+# etc/config and etc/config.${DEVID} must be copied:
+# hfaxd reads these file after locking itself up in a chroot
+cprd --no-target-directory "@globalConfigPath@" config
+cprd --target-directory=. "@modemConfigPath@"/*
diff --git a/nixos/modules/services/networking/hylafax/systemd.nix b/nixos/modules/services/networking/hylafax/systemd.nix
new file mode 100644
index 000000000000..91d9c1a37da6
--- /dev/null
+++ b/nixos/modules/services/networking/hylafax/systemd.nix
@@ -0,0 +1,249 @@
+{ config, lib, pkgs, ... }:
+
+
+let
+
+  inherit (lib) mkIf mkMerge;
+  inherit (lib) concatStringsSep optionalString;
+
+  cfg = config.services.hylafax;
+  mapModems = lib.flip map (lib.attrValues cfg.modems);
+
+  mkConfigFile = name: conf:
+    # creates hylafax config file,
+    # makes sure "Include" is listed *first*
+    let
+      mkLines = conf:
+        (lib.concatLists
+        (lib.flip lib.mapAttrsToList conf
+        (k: map (v: ''${k}: ${v}'')
+      )));
+      include = mkLines { Include = conf.Include or []; };
+      other = mkLines ( conf // { Include = []; } );
+    in
+      pkgs.writeText ''hylafax-config${name}''
+      (concatStringsSep "\n" (include ++ other));
+
+  globalConfigPath = mkConfigFile "" cfg.faxqConfig;
+
+  modemConfigPath =
+    let
+      mkModemConfigFile = { config, name, ... }:
+        mkConfigFile ''.${name}''
+        (cfg.commonModemConfig // config);
+      mkLine = { name, type, ... }@modem: ''
+        # check if modem config file exists:
+        test -f "${pkgs.hylafaxplus}/spool/config/${type}"
+        ln \
+          --symbolic \
+          --no-target-directory \
+          "${mkModemConfigFile modem}" \
+          "$out/config.${name}"
+      '';
+    in
+      pkgs.runCommand "hylafax-config-modems" {}
+      ''mkdir --parents "$out/" ${concatStringsSep "\n" (mapModems mkLine)}'';
+
+  setupSpoolScript = pkgs.substituteAll {
+    name = "hylafax-setup-spool.sh";
+    src = ./spool.sh;
+    isExecutable = true;
+    inherit (pkgs.stdenv) shell;
+    hylafax = pkgs.hylafaxplus;
+    faxuser = "uucp";
+    faxgroup = "uucp";
+    lockPath = "/var/lock";
+    inherit globalConfigPath modemConfigPath;
+    inherit (cfg) sendmailPath spoolAreaPath userAccessFile;
+  };
+
+  waitFaxqScript = pkgs.substituteAll {
+    # This script checks the modems status files
+    # and waits until all modems report readiness.
+    name = "hylafax-faxq-wait-start.sh";
+    src = ./faxq-wait.sh;
+    isExecutable = true;
+    timeoutSec = toString 10;
+    inherit (pkgs.stdenv) shell;
+    inherit (cfg) spoolAreaPath;
+  };
+
+  sockets."hylafax-hfaxd" = {
+    description = "HylaFAX server socket";
+    documentation = [ "man:hfaxd(8)" ];
+    wantedBy = [ "multi-user.target" ];
+    listenStreams = [ "127.0.0.1:4559" ];
+    socketConfig.FreeBind = true;
+    socketConfig.Accept = true;
+  };
+
+  paths."hylafax-faxq" = {
+    description = "HylaFAX queue manager sendq watch";
+    documentation = [ "man:faxq(8)" "man:sendq(5)" ];
+    wantedBy = [ "multi-user.target" ];
+    pathConfig.PathExistsGlob = [ ''${cfg.spoolAreaPath}/sendq/q*'' ];
+  };
+
+  timers = mkMerge [
+    (
+      mkIf (cfg.faxcron.enable.frequency!=null)
+      { "hylafax-faxcron".timerConfig.Persistent = true; }
+    )
+    (
+      mkIf (cfg.faxqclean.enable.frequency!=null)
+      { "hylafax-faxqclean".timerConfig.Persistent = true; }
+    )
+  ];
+
+  hardenService =
+    # Add some common systemd service hardening settings,
+    # but allow each service (here) to override
+    # settings by explicitely setting those to `null`.
+    # More hardening would be nice but makes
+    # customizing hylafax setups very difficult.
+    # If at all, it should only be added along
+    # with some options to customize it.
+    let
+      hardening = {
+        PrivateDevices = true;  # breaks /dev/tty...
+        PrivateNetwork = true;
+        PrivateTmp = true;
+        ProtectControlGroups = true;
+        #ProtectHome = true;  # breaks custom spool dirs
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        #ProtectSystem = "strict";  # breaks custom spool dirs
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+      };
+      filter = key: value: (value != null) || ! (lib.hasAttr key hardening);
+      apply = service: lib.filterAttrs filter (hardening // (service.serviceConfig or {}));
+    in
+      service: service // { serviceConfig = apply service; };
+
+  services."hylafax-spool" = {
+    description = "HylaFAX spool area preparation";
+    documentation = [ "man:hylafax-server(4)" ];
+    script = ''
+      ${setupSpoolScript}
+      cd "${cfg.spoolAreaPath}"
+      ${cfg.spoolExtraInit}
+      if ! test -f "${cfg.spoolAreaPath}/etc/hosts.hfaxd"
+      then
+        echo hosts.hfaxd is missing
+        exit 1
+      fi
+    '';
+    serviceConfig.ExecStop = ''${setupSpoolScript}'';
+    serviceConfig.RemainAfterExit = true;
+    serviceConfig.Type = "oneshot";
+    unitConfig.RequiresMountsFor = [ cfg.spoolAreaPath ];
+  };
+
+  services."hylafax-faxq" = {
+    description = "HylaFAX queue manager";
+    documentation = [ "man:faxq(8)" ];
+    requires = [ "hylafax-spool.service" ];
+    after = [ "hylafax-spool.service" ];
+    wants = mapModems ( { name, ... }: ''hylafax-faxgetty@${name}.service'' );
+    wantedBy = mkIf cfg.autostart [ "multi-user.target" ];
+    serviceConfig.Type = "forking";
+    serviceConfig.ExecStart = ''${pkgs.hylafaxplus}/spool/bin/faxq -q "${cfg.spoolAreaPath}"'';
+    # This delays the "readiness" of this service until
+    # all modems are initialized (or a timeout is reached).
+    # Otherwise, sending a fax with the fax service
+    # stopped will always yield a failed send attempt:
+    # The fax service is started when the job is created with
+    # `sendfax`, but modems need some time to initialize.
+    serviceConfig.ExecStartPost = [ ''${waitFaxqScript}'' ];
+    # faxquit fails if the pipe is already gone
+    # (e.g. the service is already stopping)
+    serviceConfig.ExecStop = ''-${pkgs.hylafaxplus}/spool/bin/faxquit -q "${cfg.spoolAreaPath}"'';
+    # disable some systemd hardening settings
+    serviceConfig.PrivateDevices = null;
+    serviceConfig.RestrictRealtime = null;
+  };
+
+  services."hylafax-hfaxd@" = {
+    description = "HylaFAX server";
+    documentation = [ "man:hfaxd(8)" ];
+    after = [ "hylafax-faxq.service" ];
+    requires = [ "hylafax-faxq.service" ];
+    serviceConfig.StandardInput = "socket";
+    serviceConfig.StandardOutput = "socket";
+    serviceConfig.ExecStart = ''${pkgs.hylafaxplus}/spool/bin/hfaxd -q "${cfg.spoolAreaPath}" -d -I'';
+    unitConfig.RequiresMountsFor = [ cfg.userAccessFile ];
+    # disable some systemd hardening settings
+    serviceConfig.PrivateDevices = null;
+    serviceConfig.PrivateNetwork = null;
+  };
+
+  services."hylafax-faxcron" = rec {
+    description = "HylaFAX spool area maintenance";
+    documentation = [ "man:faxcron(8)" ];
+    after = [ "hylafax-spool.service" ];
+    requires = [ "hylafax-spool.service" ];
+    wantedBy = mkIf cfg.faxcron.enable.spoolInit requires;
+    startAt = mkIf (cfg.faxcron.enable.frequency!=null) cfg.faxcron.enable.frequency;
+    serviceConfig.ExecStart = concatStringsSep " " [
+      ''${pkgs.hylafaxplus}/spool/bin/faxcron''
+      ''-q "${cfg.spoolAreaPath}"''
+      ''-info ${toString cfg.faxcron.infoDays}''
+      ''-log  ${toString cfg.faxcron.logDays}''
+      ''-rcv  ${toString cfg.faxcron.rcvDays}''
+    ];
+  };
+
+  services."hylafax-faxqclean" = rec {
+    description = "HylaFAX spool area queue cleaner";
+    documentation = [ "man:faxqclean(8)" ];
+    after = [ "hylafax-spool.service" ];
+    requires = [ "hylafax-spool.service" ];
+    wantedBy = mkIf cfg.faxqclean.enable.spoolInit requires;
+    startAt = mkIf (cfg.faxqclean.enable.frequency!=null) cfg.faxqclean.enable.frequency;
+    serviceConfig.ExecStart = concatStringsSep " " [
+      ''${pkgs.hylafaxplus}/spool/bin/faxqclean''
+      ''-q "${cfg.spoolAreaPath}"''
+      ''-v''
+      (optionalString (cfg.faxqclean.archiving!="never") ''-a'')
+      (optionalString (cfg.faxqclean.archiving=="always")  ''-A'')
+      ''-j ${toString (cfg.faxqclean.doneqMinutes*60)}''
+      ''-d ${toString (cfg.faxqclean.docqMinutes*60)}''
+    ];
+  };
+
+  mkFaxgettyService = { name, ... }:
+    lib.nameValuePair ''hylafax-faxgetty@${name}'' rec {
+      description = "HylaFAX faxgetty for %I";
+      documentation = [ "man:faxgetty(8)" ];
+      bindsTo = [ "dev-%i.device" ];
+      requires = [ "hylafax-spool.service" ];
+      after = bindsTo ++ requires;
+      before = [ "hylafax-faxq.service" "getty.target" ];
+      unitConfig.StopWhenUnneeded = true;
+      unitConfig.AssertFileNotEmpty = ''${cfg.spoolAreaPath}/etc/config.%I'';
+      serviceConfig.UtmpIdentifier = "%I";
+      serviceConfig.TTYPath = "/dev/%I";
+      serviceConfig.Restart = "always";
+      serviceConfig.KillMode = "process";
+      serviceConfig.IgnoreSIGPIPE = false;
+      serviceConfig.ExecStart = ''-${pkgs.hylafaxplus}/spool/bin/faxgetty -q "${cfg.spoolAreaPath}" /dev/%I'';
+      # faxquit fails if the pipe is already gone
+      # (e.g. the service is already stopping)
+      serviceConfig.ExecStop = ''-${pkgs.hylafaxplus}/spool/bin/faxquit -q "${cfg.spoolAreaPath}" %I'';
+      # disable some systemd hardening settings
+      serviceConfig.PrivateDevices = null;
+      serviceConfig.RestrictRealtime = null;
+    };
+
+  modemServices =
+    lib.listToAttrs (mapModems mkFaxgettyService);
+
+in
+
+{
+  config.systemd = mkIf cfg.enable {
+    inherit sockets timers paths;
+    services = lib.mapAttrs (lib.const hardenService) (services // modemServices);
+  };
+}