ddclient: T5612: Improve dual stack support for dyndns2 protocol

dyndns2 protocol in ddclient honors dual stack for selective servers
because of the way it is implemented in ddclient.

We formalize the well known servers that support dual stack in a list
and check against it when validating the configuration.

1 files changed, 8 insertions, 4 deletions

diff --git a/src/conf_mode/dns_dynamic.py b/src/conf_mode/dns_dynamic.py
index 2885f3e37..5150574a8 100755
--- a/src/conf_mode/dns_dynamic.py
+++ b/src/conf_mode/dns_dynamic.py
@@ -30,7 +30,7 @@ config_file = r'/run/ddclient/ddclient.conf'
 systemd_override = r'/run/systemd/system/ddclient.service.d/override.conf'
 
 # Protocols that require zone
-zone_allowed = ['cloudflare', 'godaddy', 'hetzner', 'gandi', 'nfsn']
+zone_required = ['cloudflare', 'godaddy', 'hetzner', 'gandi', 'nfsn']
 
 # Protocols that do not require username
 username_unnecessary = ['1984', 'cloudflare', 'cloudns', 'duckdns', 'freemyip', 'hetzner', 'keysystems', 'njalla']
@@ -41,6 +41,10 @@ ttl_supported = ['cloudflare', 'gandi', 'hetzner', 'dnsexit', 'godaddy', 'nfsn']
 # Protocols that support both IPv4 and IPv6
 dualstack_supported = ['cloudflare', 'dyndns2', 'freedns', 'njalla']
 
+# dyndns2 protocol in ddclient honors dual stack for selective servers
+# because of the way it is implemented in ddclient
+dyndns_dualstack_servers = ['members.dyndns.org', 'dynv6.com']
+
 def get_config(config=None):
     if config:
         conf = config
@@ -86,10 +90,10 @@ def verify(dyndns):
                     if field not in config:
                         raise ConfigError(f'"{field.replace("_", "-")}" {error_msg}')
 
-                if config['protocol'] in zone_allowed and 'zone' not in config:
+                if config['protocol'] in zone_required and 'zone' not in config:
                         raise ConfigError(f'"zone" {error_msg}')
 
-                if config['protocol'] not in zone_allowed and 'zone' in config:
+                if config['protocol'] not in zone_required and 'zone' in config:
                         raise ConfigError(f'"{config["protocol"]}" does not support "zone"')
 
                 if config['protocol'] not in username_unnecessary:
@@ -104,7 +108,7 @@ def verify(dyndns):
                         raise ConfigError(f'"{config["protocol"]}" does not support '
                                           f'both IPv4 and IPv6 at the same time')
                     # dyndns2 protocol in ddclient honors dual stack only for dyn.com (dyndns.org)
-                    if config['protocol'] == 'dyndns2' and 'server' in config and config['server'] != 'members.dyndns.org':
+                    if config['protocol'] == 'dyndns2' and 'server' in config and config['server'] not in dyndns_dualstack_servers:
                         raise ConfigError(f'"{config["protocol"]}" does not support '
                                           f'both IPv4 and IPv6 at the same time for "{config["server"]}"')