update utils.py to include failover-dependencies

README.md

@@ -17,6 +17,35 @@ NFTables documentation: [docs.o-x-l.com](https://docs.o-x-l.com/firewall/nftable
 
 ----
 
+## Install
+
+* Create directories:
+
+   ```bash
+   mkdir -p /var/local/lib/nftables_addons /etc/nftables.d/addons/
+   ```
+
+* Add the script-files:
+
+   * [util.py](https://github.com/O-X-L/nftables_addon_dns/blob/latest/lib/util.py)
+   * [iplist.py](https://github.com/O-X-L/nftables_addon_dns/blob/latest/lib/dns.py)
+
+* Add the config file:
+
+   `/etc/nftables.d/addons/dns.json`
+
+* Optional: Create a service user
+
+   * Add sudoers privileges
+   * Allow to read lib-dir
+   * Allow to write to addons-config-dir
+
+* Add cron or systemd-timer to execute the script on a schedule: `python3 /var/local/lib/nftables_addons/dns.py`
+
+* Test it and verify it's working as expected
+
+----
+
 ## Result
 
 ```text
@@ -52,7 +81,7 @@ cat /etc/nftables.d/addons/dns.nft
 
 2. The script is executed
 
-    `python3 /usr/lib/nftables/dns.py`
+    `python3 /var/local/lib/nftables_addons/dns.py`
 
   * It will load the configuration
   * Resolve IPv4 and IPv6 (_if enabled_) for all configured variables

lib/util.py

@@ -34,7 +34,14 @@
 FILE_HEADER = '# Auto-Generated config - DO NOT EDIT MANUALLY!\n\n'
 
 
-def format_var(name: str, data: list, version: int) -> str:
+def ensure_list(data: (str, list)) -> list:
+    if isinstance(data, list):
+        return data
+
+    return [data]
+
+
+def format_var(name: str, data: list, version: int, as_set: bool = True, fallback: str = None) -> str:
     if version not in FALLBACK_VAR_VALUE:
         version = 4
 
@@ -43,10 +50,17 @@ def format_var(name: str, data: list, version: int) -> str:
     if append not in [None, ' ', '']:
         name = f'{name}_{append}'
 
-    raw = f"define { name } = {{ %s }}"
+    if as_set or len(data) > 1:
+        raw = f"define { name } = {{ %s }}"
+
+    else:
+        raw = f"define { name } = %s"
 
     if len(data) == 0:
-        return raw % FALLBACK_VAR_VALUE[version]
+        if fallback is None:
+            return raw % FALLBACK_VAR_VALUE[version]
+
+        return raw % fallback
 
     return raw % ', '.join(map(str, data))