Add print server for label printer to have it easily usable via SSH

Add and configure a print server for the Brother P-touch QL 500 label
printer, so that it can be easily used via SSH.

Do the following to make that work:
- Configure the print server host.
- Package printer-driver-ptouch to have a working driver for the label
  printer.
- Configure CUPS.
- Add a script "forcecommand-lpr-wrapper", which works together with the
  ForceCommand sshd_config option and wraps lpr to provide an easy
  interface to use the Brother QL 500 label printer via SSH.
- Add a print user and configure SSH to have the
  "forcecommand-lpr-wrapper" script accessible without a password using
  the print user via SSH.

config/hosts/ptouch-print-server/configuration.nix

@@ -0,0 +1,7 @@
+{ ... }:
+
+{
+  networking.hostName = "ptouch-print-server";
+
+  system.stateVersion = "23.11";
+}

config/hosts/ptouch-print-server/default.nix

@@ -0,0 +1,9 @@
+{ ... }:
+
+{
+  imports = [
+    ./configuration.nix
+    ./networking.nix
+    ./printing.nix
+  ];
+}

config/hosts/ptouch-print-server/forcecommand-lpr-wrapper/forcecommand-lpr-wrapper.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+# A script for usage with the ForceCommand sshd_config option.
+# It calls lpr with some standard arguments, but also parses
+# SSH_ORIGINAL_COMMAND to potentially provide a different set of arguments to
+# lpr.
+#
+# This wrapper is written for interacting with the Brother QL 500 label printer.
+#
+# The following options can be provided as an SSH command and this script will
+# then pass them to the lpr call: <MediaType> <PageSize>
+# - MediaType can be one of:
+#   - Labels
+#   - Tape (this is the default)
+# - PageSize can be one of:
+#   - 12mm
+#   - 12mm-circular
+#   - 17x54mm
+#   - 17x87mm
+#   - 23x23mm
+#   - 24mm-circular
+#   - 29mm
+#   - 29x90mm
+#   - 38mm
+#   - 38x90mm
+#   - 50mm
+#   - 54mm
+#   - 58mm-circular
+#   - 62mm
+#   - 62x29mm
+#   - 62x100mm
+#   - Custom.WIDTHxHEIGHT (with WIDTH and HEIGHT needing to be either one to
+#     three digits)
+#   - label-wide (this being a convenience alias for Custom.62x35mm and it also
+#     being the default)
+#   - label-item (this being a convenience alias for 38x90mm)
+# 
+# So using these options in a complete setup would look like this for example:
+# cat label-item.pdf | ssh print@ptouch-print-server.z9.ccchh.net labels label-item
+# This being equivalent to:
+# cat label-item.pdf | ssh print@ptouch-print-server.z9.ccchh.net Labels 38x90mm
+#
+# The options are case-insensitive.
+#
+# The options are derived from: lpoptions -p Brother-QL-500 -l
+
+import os, re, subprocess
+
+mediaType = "Tape"
+pageSize = "Custom.62x35mm"
+
+def parseGivenOptions():
+    givenOptionsString = os.environ["SSH_ORIGINAL_COMMAND"]
+    givenOptionsIterator = iter(givenOptionsString.split(" "))
+
+    givenMediaType = next(givenOptionsIterator, "")
+    givenPageSize = next(givenOptionsIterator, "")
+
+    global mediaType
+    if givenMediaType.lower() == "labels":
+        mediaType = "Labels"
+    elif givenMediaType.lower() == "tape":
+        mediaType = "Tape"
+
+    global pageSize
+    pageSizeRegex = re.compile(r"^((12mm(-circular)?)|(24mm-circular)|(58mm-circular)|(((17x(54|87))|(23x23)|((29|38)(x90)?)|(62x(29|100))|50|54|62)mm))$", re.ASCII | re.IGNORECASE)
+    pageSizeMatch = pageSizeRegex.match(givenPageSize)
+    pageSizeCustomRegex = re.compile(r"^custom\.(\d{1,3})x(\d{1,3})$", re.ASCII | re.IGNORECASE)
+    pageSizeCustomMatch = pageSizeCustomRegex.match(givenPageSize)
+    if givenPageSize.lower() == "label-wide":
+        pageSize = "Custom.62x35mm"
+    elif givenPageSize.lower() == "label-item":
+        pageSize = "38x90mm"
+    elif pageSizeMatch:
+        pageSize = givenPageSize.lower()
+    elif pageSizeCustomMatch:
+        width = pageSizeCustomMatch.group(1)
+        height = pageSizeCustomMatch.group(2)
+        pageSize = "Custom.{}x{}".format(width, height)
+
+if "SSH_ORIGINAL_COMMAND" in os.environ:
+    parseGivenOptions()
+
+subprocess.run(["lpr", "-P", "Brother-QL-500", "-o", "MediaType={}".format(mediaType), "-o", "PageSize={}".format(pageSize)])

config/hosts/ptouch-print-server/forcecommand-lpr-wrapper/setup.py

@@ -0,0 +1,7 @@
+from distutils.core import setup
+
+setup(
+    name = "forcecommand-lpr-wrapper",
+    version = "0.0.1",
+    scripts = ["./forcecommand-lpr-wrapper.py"]
+)

config/hosts/ptouch-print-server/networking.nix

@@ -0,0 +1,23 @@
+{ ... }:
+
+{
+  networking = {
+    interfaces.net0 = {
+      ipv4.addresses = [
+        {
+          address = "10.31.208.13";
+          prefixLength = 25;
+        }
+      ];
+    };
+    defaultGateway = "10.31.208.1";
+    nameservers = [
+      "10.31.208.1"
+    ];
+  };
+
+  systemd.network.links."10-net0" = {
+    matchConfig.MACAddress = "BC:24:11:F2:CF:8F";
+    linkConfig.Name = "net0";
+  };
+}

config/hosts/ptouch-print-server/printing.nix

@@ -0,0 +1,104 @@
+# Sources for this configuration:
+# - https://nixos.wiki/wiki/Printing
+
+{ pkgs, lib, ... }:
+
+let
+  # https://github.com/philpem/printer-driver-ptouch
+  printer-driver-ptouch = pkgs.stdenv.mkDerivation rec {
+    pname = "printer-driver-ptouch";
+    version = "1.7";
+
+    src = pkgs.fetchgit {
+      url = "https://github.com/philpem/printer-driver-ptouch";
+      rev = "v${version}";
+      hash = "sha256-3ZotSHn7lERp53hAzx47Ct/k565rEoensCcltwX/Xls=";
+    };
+
+    nativeBuildInputs = [
+      pkgs.autoreconfHook
+      pkgs.perl
+    ];
+
+    buildInputs = [
+      pkgs.cups
+      pkgs.libpng
+      pkgs.perlPackages.XMLLibXML
+      pkgs.foomatic-db-engine
+    ];
+
+    patches = [
+      # Add this patch to have the package actually build sucessfully.
+      # https://github.com/philpem/printer-driver-ptouch/pull/35
+      (pkgs.fetchpatch {
+        name = "fix-brother-ql-600.xml.patch";
+        url = "https://patch-diff.githubusercontent.com/raw/philpem/printer-driver-ptouch/pull/35.patch";
+        hash = "sha256-y5bHKFeRXx8Wdl1++l4QNGgiY41LY5uzrRdOlaZyF9I=";
+      })
+    ];
+
+    # Used the following as a reference on how to generate the ppd files.
+    # https://salsa.debian.org/printing-team/ptouch-driver/-/blob/4ba5d2c490ea1230374aa4b0bf711bf77f1ab0c7/debian/rules#L34
+    postInstall = ''
+      mkdir -p $out/share/cups
+      FOOMATICDB=$out/share/foomatic ${pkgs.foomatic-db-engine}/bin/foomatic-compiledb -t ppd -d $out/share/cups/model
+      rm -r $out/share/foomatic
+    '';
+
+    postPatch = ''
+      patchShebangs --build foomaticalize
+    '';
+  };
+  forcecommand-lpr-wrapper = pkgs.python3Packages.buildPythonApplication {
+    name = "forcecommand-lpr-wrapper";
+    src = ./forcecommand-lpr-wrapper;
+
+    propagatedBuildInputs = [
+      pkgs.cups
+    ];
+  };
+in
+{
+  services.printing = {
+    enable = true;
+    drivers = [ printer-driver-ptouch ];
+    stateless = true;
+  };
+
+  hardware.printers = {
+    ensurePrinters = [
+      {
+        name = "Brother-QL-500";
+        location = "Z9";
+        deviceUri = "usb://Brother/QL-500?serial=J8Z249208";
+        model = "Brother-QL-500-ptouch-ql.ppd";
+        ppdOptions = {
+          PageSize = "Custom.62x35mm";
+        };
+      }
+    ];
+    ensureDefaultPrinter = "Brother-QL-500";
+  };
+
+  users.users.print = {
+    isNormalUser = true;
+    description = "User for printing via SSH.";
+    password = "";
+  };
+
+  # PasswordAuthentication being set to false just puts "auth required
+  # pam_deny.so # deny (order 12400)" for pam.d/sshd, so enable
+  # PasswordAuthentication to have it not do that.
+  services.openssh.settings.PasswordAuthentication = lib.mkForce true;
+  # The following doesn't need to be set in order for empty passwords to work
+  # apparently:
+  # security.pam.services.sshd.allowNullPassword = true;
+  services.openssh.extraConfig = ''
+    Match User print
+      PubkeyAuthentication no
+      AuthenticationMethods none
+      PermitEmptyPasswords yes
+      ForceCommand ${forcecommand-lpr-wrapper}/bin/forcecommand-lpr-wrapper.py 
+    Match User *
+  '';
+}