sane: Add support for the unfree Fujitsu ScanSnap drivers

This adds the scanner files already linked from the
`etc/sane.d/epjitsu.conf` file, which are extracted from the Windows
drivers and mirrored on GitHub.

Being a Japanese hardware vendor, Fujitsu’s software release &
licensing methods are horrifying, but their scanners are some of the
best, so we should definitly have discoverable support for them, which
this patch hopefully adds.

Inspiration was taken from the following sources:
https://www.josharcher.uk/code/install-scansnap-s1300-drivers-linux/
https://ubuntuforums.org/archive/index.php/t-1461915.html
https://github.com/stevleibelt/scansnap-firmware

nixos/modules/services/hardware/sane.nix

@@ -4,7 +4,10 @@ with lib;
 
 let
 
-  pkg = pkgs.sane-backends;
+  pkg = pkgs.sane-backends.override {
+    scanSnapDriversUnfree = config.hardware.sane.drivers.scanSnap.enable;
+    scanSnapDriversPackage = config.hardware.sane.drivers.scanSnap.package;
+  };
 
   sanedConf = pkgs.writeTextFile {
     name = "saned.conf";
@@ -98,6 +101,28 @@ in
       '';
     };
 
+    hardware.sane.drivers.scanSnap.enable = mkOption {
+      type = types.bool;
+      default = false;
+      example = true;
+      description = ''
+        Whether to enable drivers for the Fujitsu ScanSnap scanners.
+
+        The driver files are unfree and extracted from the Windows driver image.
+      '';
+    };
+
+    hardware.sane.drivers.scanSnap.package = mkOption {
+      type = types.package;
+      default = pkgs.sane-drivers.epjitsu;
+      description = ''
+        Epjitsu driver package to use. Useful if you want to extract the driver files yourself.
+
+        The process is described in the <literal>/etc/sane.d/epjitsu.conf</literal> file in
+        the <literal>sane-backends</literal> package.
+      '';
+    };
+
     services.saned.enable = mkOption {
       type = types.bool;
       default = false;

pkgs/applications/graphics/sane/backends/default.nix

@@ -2,12 +2,16 @@
 , gettext, pkg-config, python3
 , avahi, libgphoto2, libieee1284, libjpeg, libpng, libtiff, libusb1, libv4l, net-snmp
 , curl, systemd, libxml2, poppler
+, sane-drivers
 
 # List of { src name backend } attibute sets - see installFirmware below:
 , extraFirmware ? []
 
 # For backwards compatibility with older setups; use extraFirmware instead:
 , gt68xxFirmware ? null, snapscanFirmware ? null
+
+# Not included by default, scan snap drivers require fetching of unfree binaries.
+, scanSnapDriversUnfree ? false, scanSnapDriversPackage ? sane-drivers.epjitsu
 }:
 
 stdenv.mkDerivation {
@@ -88,7 +92,14 @@ stdenv.mkDerivation {
 
     # net.conf conflicts with the file generated by the nixos module
     rm $out/etc/sane.d/net.conf
-  '' + lib.concatStrings (builtins.map installFirmware compatFirmware);
+
+  ''
+  + lib.optionalString scanSnapDriversUnfree ''
+    # the ScanSnap drivers live under the epjitsu subdirectory, which was already created by the build but is empty.
+    rmdir $out/share/sane/epjitsu
+    ln -svT ${scanSnapDriversPackage} $out/share/sane/epjitsu
+  ''
+  + lib.concatStrings (builtins.map installFirmware compatFirmware);
 
   meta = with lib; {
     description = "SANE (Scanner Access Now Easy) backends";

pkgs/applications/graphics/sane/drivers.nix

@@ -0,0 +1,13 @@
+{ lib, fetchFromGitHub }:
+
+{
+  # Fujitsu ScanSnap
+  epjitsu = fetchFromGitHub {
+    name = "scansnap-firmware";
+    owner = "stevleibelt";
+    repo = "scansnap-firmware";
+    rev = "96c3a8b2a4e4f1ccc4e5827c5eb5598084fd17c8";
+    sha256 = "1inchnvaqyw9d0skpg8hp5rpn27c09q58lsr42by4bahpbx5qday";
+    meta.license = lib.licenses.unfree;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -31830,6 +31830,8 @@ in
 
   sane-backends = callPackage ../applications/graphics/sane/backends (config.sane or {});
 
+  sane-drivers = callPackage ../applications/graphics/sane/drivers.nix {};
+
   senv = callPackage ../applications/misc/senv { };
 
   brlaser = callPackage ../misc/cups/drivers/brlaser { };