Change:
# Test printing via CUPS. <del> import ./make-test.nix ({pkgs, ... }: { </del> <ins> import ./make-test.nix ({pkgs, ... }: let printingServer = startWhenNeeded: { services.printing.enable = true; services.printing.startWhenNeeded = startWhenNeeded; services.printing.listenAddresses = [ "*:631" ]; services.printing.defaultShared = true; services.printing.extraConf = '' <Location /> Order allow,deny Allow from all </Location> ''; networking.firewall.allowedTCPPorts = [ 631 ]; # Add a HP Deskjet printer connected via USB to the server. hardware.printers.ensurePrinters = [{ name = "DeskjetLocal"; deviceUri = "usb://foobar/printers/foobar"; model = "drv:///sample.drv/deskjet.ppd"; }]; }; printingClient = startWhenNeeded: { services.printing.enable = true; services.printing.startWhenNeeded = startWhenNeeded; # Add printer to the client as well, via IPP. hardware.printers.ensurePrinters = [{ name = "DeskjetRemote"; deviceUri = "ipp://${if startWhenNeeded then "socketActivatedServer" else "serviceServer"}/printers/DeskjetLocal"; model = "drv:///sample.drv/deskjet.ppd"; }]; hardware.printers.ensureDefaultPrinter = "DeskjetRemote"; }; in { </ins> name = "printing"; meta = with pkgs.stdenv.lib.maintainers; { maintainers = [ domenkozar eelco matthewbauer ]; }; nodes = { <ins> socketActivatedServer = { ... }: (printingServer true); serviceServer = { ... }: (printingServer false); </ins> <del> server = { ... }: { services.printing.enable = true; services.printing.listenAddresses = [ "*:631" ]; services.printing.defaultShared = true; services.printing.extraConf = '' <Location /> Order allow,deny Allow from all </Location> ''; networking.firewall.allowedTCPPorts = [ 631 ]; }; client = { ... }: { services.printing.enable = true; }; </del> <ins> socketActivatedClient = { ... }: (printingClient true); serviceClient = { ... }: (printingClient false); </ins> }; testScript = '' startAll; <del> $client->succeed("lpstat -r") =~ /scheduler is running/ or die; # check local encrypted connections work without error $client->succeed("lpstat -E -r") =~ /scheduler is running/ or die; # Test that UNIX socket is used for connections. $client->succeed("lpstat -H") =~ "/run/cups/cups.sock" or die; # Test that HTTP server is available too. $client->succeed("curl --fail http://localhost:631/"); $client->succeed("curl --fail http://server:631/"); $server->fail("curl --fail --connect-timeout 2  http://client:631/"); # Add a HP Deskjet printer connected via USB to the server. $server->succeed("lpadmin -p DeskjetLocal -E -v usb://foobar/printers/foobar"); # Add it to the client as well via IPP. $client->succeed("lpadmin -p DeskjetRemote -E -v ipp://server/printers/DeskjetLocal"); $client->succeed("lpadmin -d DeskjetRemote"); # Do some status checks. $client->succeed("lpstat -a") =~ /DeskjetRemote accepting requests/ or die; $client->succeed("lpstat -h server:631 -a") =~ /DeskjetLocal accepting requests/ or die; $client->succeed("cupsdisable DeskjetRemote"); $client->succeed("lpq") =~ /DeskjetRemote is not ready.*no entries/s or die; $client->succeed("cupsenable DeskjetRemote"); $client->succeed("lpq") =~ /DeskjetRemote is ready.*no entries/s or die; # Test printing various file types. foreach my $file ("${pkgs.groff.doc}/share/doc/*/examples/mom/penguin.pdf", "${pkgs.groff.doc}/share/doc/*/meref.ps", "${pkgs.cups.out}/share/doc/cups/images/cups.png", "${pkgs.pcre.doc}/share/doc/pcre/pcre.txt") { $file =~ /([^/]*)$/; my $fn = $1; subtest "print $fn", sub { # Print the file on the client. $client->succeed("lp $file"); $client->sleep(10); $client->succeed("lpq") =~ /active.*root.*$fn/ or die; # Ensure that a raw PCL file appeared in the server's queue # (showing that the right filters have been applied).  Of # course, since there is no actual USB printer attached, the # file will stay in the queue forever. $server->waitForFile("/var/spool/cups/d*-001"); $server->sleep(10); $server->succeed("lpq -a") =~ /$fn/ or die; # Delete the job on the client.  It should disappear on the # server as well. $client->succeed("lprm"); $client->sleep(10); $client->succeed("lpq -a") =~ /no entries/; Machine::retry sub { return 1 if $server->succeed("lpq -a") =~ /no entries/; </del> <ins> # Make sure that cups is up on both sides. $serviceServer->waitForUnit("cups.service"); $serviceClient->waitForUnit("cups.service"); # wait until cups is fully initialized and ensure-printers has executed with 10s delay $serviceClient->sleep(20); $socketActivatedClient->waitUntilSucceeds("systemctl status ensure-printers | grep -q -E 'code=exited, status=0/SUCCESS'"); sub testPrinting { my ($client, $server) = (@_); my $clientHostname = $client->name(); my $serverHostname = $server->name(); $client->succeed("lpstat -r") =~ /scheduler is running/ or die; # Test that UNIX socket is used for connections. $client->succeed("lpstat -H") =~ "/var/run/cups/cups.sock" or die; # Test that HTTP server is available too. $client->succeed("curl --fail http://localhost:631/"); $client->succeed("curl --fail http://$serverHostname:631/"); $server->fail("curl --fail --connect-timeout 2  http://$clientHostname:631/"); # Do some status checks. $client->succeed("lpstat -a") =~ /DeskjetRemote accepting requests/ or die; $client->succeed("lpstat -h $serverHostname:631 -a") =~ /DeskjetLocal accepting requests/ or die; $client->succeed("cupsdisable DeskjetRemote"); $client->succeed("lpq") =~ /DeskjetRemote is not ready.*no entries/s or die; $client->succeed("cupsenable DeskjetRemote"); $client->succeed("lpq") =~ /DeskjetRemote is ready.*no entries/s or die; # Test printing various file types. foreach my $file ("${pkgs.groff.doc}/share/doc/*/examples/mom/penguin.pdf", "${pkgs.groff.doc}/share/doc/*/meref.ps", "${pkgs.cups.out}/share/doc/cups/images/cups.png", "${pkgs.pcre.doc}/share/doc/pcre/pcre.txt") { $file =~ /([^/]*)$/; my $fn = $1; subtest "print $fn", sub { # Print the file on the client. $client->succeed("lp $file"); $client->waitUntilSucceeds("lpq | grep -q -E 'active.*root.*$fn'"); # Ensure that a raw PCL file appeared in the server's queue # (showing that the right filters have been applied).  Of # course, since there is no actual USB printer attached, the # file will stay in the queue forever. $server->waitForFile("/var/spool/cups/d*-001"); $server->waitUntilSucceeds("lpq -a | grep -q -E '$fn'"); # Delete the job on the client.  It should disappear on the # server as well. $client->succeed("lprm"); $client->waitUntilSucceeds("lpq -a | grep -q -E 'no entries'"); Machine::retry sub { return 1 if $server->succeed("lpq -a") =~ /no entries/; }; # The queue is empty already, so this should be safe. # Otherwise, pairs of "c*"-"d*-001" files might persist. $server->execute("rm /var/spool/cups/*"); </ins> }; <del> # The queue is empty already, so this should be safe. # Otherwise, pairs of "c*"-"d*-001" files might persist. $server->execute("rm /var/spool/cups/*"); }; </del> <ins> } </ins> } <del> ''; </del> <ins> testPrinting($serviceClient, $serviceServer); testPrinting($socketActivatedClient, $socketActivatedServer); ''; </ins> })

Discussion:
Allow configuration of a cups printer by pointing at a ppd file and specifying a single URL in Currently, such configuration requires clicking through a web-interface. 09
I actually ran into problems with the imperative configuration. I configured my printer (samsung scx3200) and after a system upgrade i was unable to print anymore. An error was shown in the cups web interface for the printer: "unable to load PPD, /nix/store/.... no such file or directory". It looks like the driver i used was garbage-collected. That would not happen with a declarative configuration. However i am certain that this module is no easy piece of work because it requires deep insight into how cups works.
Interestingly for my driver it just copy them to . Does the files within this directory has references to the nix store?
I created a half-stateful solution similar to , which uses etc. to create the configured printers and force them in the right configuration, without having to touch the deep parts of cups. Works quite well, still have to see how it works on printer driver updates, though. Will pose a PR when that succeeds.
PR: please go and test it. :)
Upvote this! Will test on weekend. (looks better, than my own unconditional injection of ppd into /var/.../cups)
Hi, I just stumbled over this issue by accident and realized I'm using something similar in my machines own printing config. So I'm thinking it might help you if I'd share this code with you. Sorry for just dumping this file here. I've been planning to clean it up and suggest my module via a pull-request on its own, but I haven't found the time to do so yet. Still, I hope my module contains some usable ideas towards declarative printer config (e.g. set options, and check that each declared printer has its backend and ppd file installed).