dynamicdns: Fix adding null domain into configuration

When old configuration is not set and is exported with new code into newer
format, the result is a domain added with domain name 'null'. This causes issues
with UI not showing configuration and with null domain being added into
configurations of various daemons.

Tests:

- To reproduce the issue, switch to a revision with old dynamicdns code. Then
switch to a latest version without the fix. A 'null' domain is added to
configuration.

- To reproduce the issue, switch to a revision with old dynamicdns code. Then
switch to a latest version with the fix. A 'null' domain is not added to
configuration.

- With null domain in the configuration. Start FreedomBox with the fix. The null
domain should be removed and null domain should not be announced to other
daemons.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

actions/dynamicdns

@@ -106,7 +106,10 @@ def subcommand_export_config(_):
                               and _active_config.exists()):
         enabled = True
 
-    output_config = {'enabled': enabled, 'domains': {domain['domain']: domain}}
+    output_config = {'enabled': enabled, 'domains': {}}
+    if domain['domain']:
+        output_config['domains'][domain['domain']] = domain
+
     print(json.dumps(output_config))
 
 

plinth/modules/dynamicdns/__init__.py

@@ -258,7 +258,18 @@ def get_config():
     """Return the current configuration."""
     default_config = {'domains': {}}
     config = kvstore.get_default('dynamicdns_config', '{}')
-    return json.loads(config) or default_config
+    config = json.loads(config) or default_config
+    return _fix_corrupt_config(config)
+
+
+def _fix_corrupt_config(config):
+    """Fix malformed configuration result of bug in older version."""
+    if 'null' not in config['domains']:
+        return config
+
+    del config['domains']['null']
+    set_config(config)
+    return config
 
 
 def set_config(config):