nixos/tests/printing: test cases for domain socket only config

Add two new vm tests for the printing configuration that
test `listenAddresses = []`, i.e., the situation where cups
only listens on the unix domain socket `/run/cups/cups.sock`.

This helps catching bugs like this:

OpenPrinting/cups#985
NixOS#337748

nixos/tests/all-tests.nix

@@ -809,8 +809,10 @@ in {
   predictable-interface-names = handleTest ./predictable-interface-names.nix {};
   pretalx = runTest ./web-apps/pretalx.nix;
   pretix = runTest ./web-apps/pretix.nix;
-  printing-socket = handleTest ./printing.nix { socket = true; };
-  printing-service = handleTest ./printing.nix { socket = false; };
+  printing-socket = handleTest ./printing.nix { socket = true; listenTcp = true; };
+  printing-service = handleTest ./printing.nix { socket = false; listenTcp = true; };
+  printing-socket-notcp = handleTest ./printing.nix { socket = true; listenTcp = false; };
+  printing-service-notcp = handleTest ./printing.nix { socket = false; listenTcp = false; };
   private-gpt = handleTest ./private-gpt.nix {};
   privoxy = handleTest ./privoxy.nix {};
   prometheus = handleTest ./prometheus {};

nixos/tests/printing.nix

@@ -3,6 +3,7 @@
 import ./make-test-python.nix (
 { pkgs
 , socket ? true # whether to use socket activation
+, listenTcp ? true # whether to open port 631 on client
 , ...
 }:
 
@@ -35,9 +36,10 @@ import ./make-test-python.nix (
     }];
   };
 
-  nodes.client = { ... }: {
+  nodes.client = { lib, ... }: {
     services.printing.enable = true;
     services.printing.startWhenNeeded = socket;
+    services.printing.listenAddresses = lib.mkIf (!listenTcp) [];
     # Add printer to the client as well, via IPP.
     hardware.printers.ensurePrinters = [{
       name = "DeskjetRemote";
@@ -63,7 +65,7 @@ import ./make-test-python.nix (
         assert "/var/run/cups/cups.sock" in client.succeed("lpstat -H")
 
     with subtest("HTTP server is available too"):
-        client.succeed("curl --fail http://localhost:631/")
+        ${pkgs.lib.optionalString listenTcp ''client.succeed("curl --fail http://localhost:631/")''}
         client.succeed(f"curl --fail http://{server.name}:631/")
         server.fail(f"curl --fail --connect-timeout 2 http://{client.name}:631/")
 

pkgs/misc/cups/default.nix

@@ -141,6 +141,8 @@ stdenv.mkDerivation rec {
       cups-pdf
       printing-service
       printing-socket
+      printing-service-notcp
+      printing-socket-notcp
     ;
   };