def _get_ip_lookup_cache() -> IPLookupCache:
"""A file based fall-back DNS cache in case resolution fails"""
if _config_cache.exists("ip_lookup"):
# Return already created and initialized cache
return cast(IPLookupCache, _config_cache.get("ip_lookup", IPLookupCache))
cache = cast(IPLookupCache, _config_cache.get("ip_lookup", IPLookupCache))
cache.load_persisted()
return cache
def _ip_to_hostname(config_cache, ip):
# type: (config.ConfigCache, Optional[HostAddress]) -> Optional[HostName]
if not _config_cache.exists("ip_to_hostname"):
cache = _config_cache.get_dict("ip_to_hostname")
for host in config_cache.all_active_realhosts():
try:
cache[ip_lookup.lookup_ipv4_address(host)] = host
except Exception:
pass
else:
cache = _config_cache.get_dict("ip_to_hostname")
return cache.get(ip)