nixos/spacecookie: add openFirewall option

Convenience shortcut which automatically configures the firewall to open
the port which is also configured for the spacecookie service.

nixos/modules/services/networking/spacecookie.nix

···
         '';
       };
 
+      openFirewall = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether to open the necessary port in the firewall for spacecookie.
+        '';
+      };
+
       port = mkOption {
         type = types.port;
         default = 70;
         description = ''
-          Port the gopher service should be exposed on. The
-          firewall is not opened automatically.
+          Port the gopher service should be exposed on.
         '';
       };
 
···
         # AF_INET replaced by BindIPv6Only=both
         RestrictAddressFamilies = "AF_UNIX AF_INET6";
       };
+    };
+
+    networking.firewall = mkIf cfg.openFirewall {
+      allowedTCPPorts = [ cfg.port ];
     };
   };
 }

nixos/tests/spacecookie.nix

···
     name = "spacecookie";
     nodes = {
       ${gopherHost} = {
-        networking.firewall.allowedTCPPorts = [ 70 ];
         systemd.services.spacecookie = {
           preStart = ''
             mkdir -p ${gopherRoot}/directory
···
           enable = true;
           root = gopherRoot;
           hostname = gopherHost;
+          openFirewall = true;
         };
       };