nixos/beanstalkd: add openFirewall option

nixos/modules/services/misc/beanstalkd.nix

@@ -28,6 +28,12 @@ in
           example = "0.0.0.0";
         };
       };
+
+      openFirewall = mkOption {
+        type = types.bool;
+        default = false;
+        description = "Whether to open ports in the firewall for the server.";
+      };
     };
   };
 
@@ -35,6 +41,10 @@ in
 
   config = mkIf cfg.enable {
 
+    networking.firewall = mkIf cfg.openFirewall {
+      allowedTCPPorts = [ cfg.listen.port ];
+    };
+
     environment.systemPackages = [ pkg ];
 
     systemd.services.beanstalkd = {