Merge pull request #182360 from Yarny0/cups-pdf

cups-pdf(-to-pdf): init

1 files changed, 185 insertions, 0 deletions

diff --git a/nixos/modules/services/printing/cups-pdf.nix b/nixos/modules/services/printing/cups-pdf.nix
new file mode 100644
index 000000000000..07f24367132f
--- /dev/null
+++ b/nixos/modules/services/printing/cups-pdf.nix
@@ -0,0 +1,185 @@
+{ config, lib, pkgs, ... }:
+
+let
+
+  # cups calls its backends as user `lp` (which is good!),
+  # but cups-pdf wants to be called as `root`, so it can change ownership of files.
+  # We add a suid wrapper and a wrapper script to trick cups into calling the suid wrapper.
+  # Note that a symlink to the suid wrapper alone wouldn't suffice, cups would complain
+  # > File "/nix/store/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-cups-progs/lib/cups/backend/cups-pdf" has insecure permissions (0104554/uid=0/gid=20)
+
+  # wrapper script that redirects calls to the suid wrapper
+  cups-pdf-wrapper = pkgs.writeTextFile {
+    name = "${pkgs.cups-pdf-to-pdf.name}-wrapper.sh";
+    executable = true;
+    destination = "/lib/cups/backend/cups-pdf";
+    checkPhase = ''
+      ${pkgs.stdenv.shellDryRun} "$target"
+      ${lib.getExe pkgs.shellcheck} "$target"
+    '';
+    text = ''
+      #! ${pkgs.runtimeShell}
+      exec "${config.security.wrapperDir}/cups-pdf" "$@"
+    '';
+  };
+
+  # wrapped cups-pdf package that uses the suid wrapper
+  cups-pdf-wrapped = pkgs.buildEnv {
+    name = "${pkgs.cups-pdf-to-pdf.name}-wrapped";
+    # using the wrapper as first path ensures it is used
+    paths = [ cups-pdf-wrapper pkgs.cups-pdf-to-pdf ];
+    ignoreCollisions = true;
+  };
+
+  instanceSettings = name: {
+    freeformType = with lib.types; nullOr (oneOf [ int str path package ]);
+    # override defaults:
+    # inject instance name into paths,
+    # also avoid conflicts between user names and special dirs
+    options.Out = lib.mkOption {
+      type = with lib.types; nullOr singleLineStr;
+      default = "/var/spool/cups-pdf-${name}/users/\${USER}";
+      defaultText = "/var/spool/cups-pdf-{instance-name}/users/\${USER}";
+      example = "\${HOME}/cups-pdf";
+      description = lib.mdDoc ''
+        output directory;
+        `''${HOME}` will be expanded to the user's home directory,
+        `''${USER}` will be expanded to the user name.
+      '';
+    };
+    options.AnonDirName = lib.mkOption {
+      type = with lib.types; nullOr singleLineStr;
+      default = "/var/spool/cups-pdf-${name}/anonymous";
+      defaultText = "/var/spool/cups-pdf-{instance-name}/anonymous";
+      example = "/var/lib/cups-pdf";
+      description = lib.mdDoc "path for anonymously created PDF files";
+    };
+    options.Spool = lib.mkOption {
+      type = with lib.types; nullOr singleLineStr;
+      default = "/var/spool/cups-pdf-${name}/spool";
+      defaultText = "/var/spool/cups-pdf-{instance-name}/spool";
+      example = "/var/lib/cups-pdf";
+      description = lib.mdDoc "spool directory";
+    };
+    options.Anonuser = lib.mkOption {
+      type = lib.types.singleLineStr;
+      default = "root";
+      description = lib.mdDoc ''
+        User for anonymous PDF creation.
+        An empty string disables this feature.
+      '';
+    };
+    options.GhostScript = lib.mkOption {
+      type = with lib.types; nullOr path;
+      default = lib.getExe pkgs.ghostscript;
+      defaultText = lib.literalExpression "lib.getExe pkgs.ghostscript";
+      example = lib.literalExpression ''''${pkgs.ghostscript}/bin/ps2pdf'';
+      description = lib.mdDoc "location of GhostScript binary";
+    };
+  };
+
+  instanceConfig = { name, config, ... }: {
+    options = {
+      enable = (lib.mkEnableOption (lib.mdDoc "this cups-pdf instance")) // { default = true; };
+      installPrinter = (lib.mkEnableOption (lib.mdDoc ''
+        a CUPS printer queue for this instance.
+        The queue will be named after the instance and will use the {file}`CUPS-PDF_opt.ppd` ppd file.
+        If this is disabled, you need to add the queue yourself to use the instance
+      '')) // { default = true; };
+      confFileText = lib.mkOption {
+        type = lib.types.lines;
+        description = lib.mdDoc ''
+          This will contain the contents of {file}`cups-pdf.conf` for this instance, derived from {option}`settings`.
+          You can use this option to append text to the file.
+        '';
+      };
+      settings = lib.mkOption {
+        type = lib.types.submodule (instanceSettings name);
+        default = {};
+        example = {
+          Out = "\${HOME}/cups-pdf";
+          UserUMask = "0033";
+        };
+        description = lib.mdDoc ''
+          Settings for a cups-pdf instance, see the descriptions in the template config file in the cups-pdf package.
+          The key value pairs declared here will be translated into proper key value pairs for {file}`cups-pdf.conf`.
+          Setting a value to `null` disables the option and removes it from the file.
+        '';
+      };
+    };
+    config.confFileText = lib.pipe config.settings [
+      (lib.filterAttrs (key: value: value != null))
+      (lib.mapAttrs (key: builtins.toString))
+      (lib.mapAttrsToList (key: value: "${key} ${value}\n"))
+      lib.concatStrings
+    ];
+  };
+
+  cupsPdfCfg = config.services.printing.cups-pdf;
+
+  copyConfigFileCmds = lib.pipe cupsPdfCfg.instances [
+    (lib.filterAttrs (name: lib.getAttr "enable"))
+    (lib.mapAttrs (name: lib.getAttr "confFileText"))
+    (lib.mapAttrs (name: pkgs.writeText "cups-pdf-${name}.conf"))
+    (lib.mapAttrsToList (name: confFile: "ln --symbolic --no-target-directory ${confFile} /var/lib/cups/cups-pdf-${name}.conf\n"))
+    lib.concatStrings
+  ];
+
+  printerSettings = lib.pipe cupsPdfCfg.instances [
+    (lib.filterAttrs (name: lib.getAttr "enable"))
+    (lib.filterAttrs (name: lib.getAttr "installPrinter"))
+    (lib.mapAttrsToList (name: instance: (lib.mapAttrs (key: lib.mkDefault) {
+      inherit name;
+      model = "CUPS-PDF_opt.ppd";
+      deviceUri = "cups-pdf:/${name}";
+      description = "virtual printer for cups-pdf instance ${name}";
+      location = instance.settings.Out;
+    })))
+  ];
+
+in
+
+{
+
+  options.services.printing.cups-pdf = {
+    enable = lib.mkEnableOption (lib.mdDoc ''
+      the cups-pdf virtual pdf printer backend.
+      By default, this will install a single printer `pdf`.
+      but this can be changed/extended with {option}`services.printing.cups-pdf.instances`
+    '');
+    instances = lib.mkOption {
+      type = lib.types.attrsOf (lib.types.submodule instanceConfig);
+      default.pdf = {};
+      example.pdf.settings = {
+        Out = "\${HOME}/cups-pdf";
+        UserUMask = "0033";
+      };
+      description = lib.mdDoc ''
+        Permits to raise one or more cups-pdf instances.
+        Each instance is named by an attribute name, and the attribute's values control the instance' configuration.
+      '';
+    };
+  };
+
+  config = lib.mkIf cupsPdfCfg.enable {
+    services.printing.enable = true;
+    services.printing.drivers = [ cups-pdf-wrapped ];
+    hardware.printers.ensurePrinters = printerSettings;
+    # the cups module will install the default config file,
+    # but we don't need it and it would confuse cups-pdf
+    systemd.services.cups.preStart = lib.mkAfter ''
+      rm -f /var/lib/cups/cups-pdf.conf
+      ${copyConfigFileCmds}
+    '';
+    security.wrappers.cups-pdf = {
+      group = "lp";
+      owner = "root";
+      permissions = "+r,ug+x";
+      setuid = true;
+      source = "${pkgs.cups-pdf-to-pdf}/lib/cups/backend/cups-pdf";
+    };
+  };
+
+  meta.maintainers = [ lib.maintainers.yarny ];
+
+}