#!/usr/bin/env python3
+# © Copyright 2021-2022, Scott Gasch
+
"""A caching layer around the kernel's network mapping between IPs and MACs"""
cfg.add_argument(
'--arper_cache_max_staleness',
type=argparse_utils.valid_duration,
- default=datetime.timedelta(seconds=60 * 15),
+ default=datetime.timedelta(seconds=60 * 30),
metavar='DURATION',
help='Max acceptable age of the kernel arp table cache',
)
@persistent.persistent_autoloaded_singleton() # type: ignore
class Arper(persistent.Persistent):
+ """A caching layer around the kernel's network mapping between IPs and
+ MACs. This class restores persisted state that expires
+ periodically (see --arper_cache_max_staleness) at program startup
+ time. If it's unable to use the file's contents, it queries the
+ kernel (via arp) and uses an auxillary utility called arp-scan to
+ query the network. If it has to do this there's a latency hit but
+ it persists the collected data in the cache file. Either way, the
+ class behaves as a global singleton hosting this data thereafter.
+
+ """
+
def __init__(
self,
cached_local_state: Optional[BiDict] = None,
if len(self.state) < config.config['arper_min_entries_to_be_valid']:
raise Exception(f'Arper didn\'t find enough entries; only got {len(self.state)}.')
if cached_supplimental_state is not None:
- logger.debug(f'Also added {len(cached_supplimental_state)} supplimental entries.')
+ logger.debug('Also added %d supplimental entries.', len(cached_supplimental_state))
for mac, ip in cached_supplimental_state.items():
self.state[mac] = ip
for mac, ip in self.state.items():
- logger.debug(f'{mac} <-> {ip}')
+ logger.debug('%s <-> %s', mac, ip)
def update_from_arp_scan(self):
network_spec = site_config.get_config().network
mac = string_utils.extract_mac_address(line)
if ip is not None and mac is not None and mac != 'UNKNOWN' and ip != 'UNKNOWN':
mac = mac.lower()
- logger.debug(f'ARPER: {mac} => {ip}')
+ logger.debug('ARPER: %s => %s', mac, ip)
self.state[mac] = ip
def update_from_arp(self):
mac = string_utils.extract_mac_address(line)
if ip is not None and mac is not None and mac != 'UNKNOWN' and ip != 'UNKNOWN':
mac = mac.lower()
- logger.debug(f'ARPER: {mac} => {ip}')
+ logger.debug('ARPER: %s => %s', mac, ip)
self.state[mac] = ip
def get_ip_by_mac(self, mac: str) -> Optional[str]:
return self.state.inverse.get(ip, None)
@classmethod
- def load_state(cls, cache_file: str, freshness_threshold_sec: int, state: BiDict):
+ def load_state(
+ cls,
+ cache_file: str,
+ freshness_threshold_sec: int,
+ state: BiDict,
+ ):
if not file_utils.file_is_readable(cache_file):
- logger.debug(f'Can\'t read {cache_file}')
- return None
+ logger.debug('Can\'t read %s', cache_file)
+ return
if persistent.was_file_written_within_n_seconds(
cache_file,
freshness_threshold_sec,
):
- logger.debug(f'Loading state from {cache_file}')
+ logger.debug('Loading state from %s', cache_file)
count = 0
with open(cache_file, 'r') as rf:
contents = rf.readlines()
for line in contents:
line = line[:-1]
- logger.debug(f'ARPER:{cache_file}> {line}')
+ logger.debug('ARPER:%s> %s', cache_file, line)
(mac, ip) = line.split(',')
mac = mac.strip()
mac = mac.lower()
state[mac] = ip
count += 1
else:
- logger.debug(f'{cache_file} is too stale.')
+ logger.debug('%s is too stale.', cache_file)
@classmethod
@overrides
def load(cls) -> Any:
- local_state = BiDict()
+ local_state: BiDict = BiDict()
cache_file = config.config['arper_cache_location']
max_staleness = config.config['arper_cache_max_staleness'].total_seconds()
- logger.debug(f'Trying to load main arper cache from {cache_file}...')
+ logger.debug('Trying to load main arper cache from %s...', cache_file)
cls.load_state(cache_file, max_staleness, local_state)
if len(local_state) <= config.config['arper_min_entries_to_be_valid']:
msg = f'{cache_file} is invalid: only {len(local_state)} entries. Deleting it.'
except Exception:
pass
- supplimental_state = BiDict()
+ supplimental_state: BiDict = BiDict()
cache_file = config.config['arper_supplimental_cache_location']
max_staleness = config.config['arper_cache_max_staleness'].total_seconds()
- logger.debug(f'Trying to suppliment arper state from {cache_file}...')
+ logger.debug('Trying to suppliment arper state from %s', cache_file)
cls.load_state(cache_file, max_staleness, supplimental_state)
- if len(supplimental_state) == 0:
- supplimental_state = None
-
if len(local_state) > 0:
return cls(local_state, supplimental_state)
return None
@overrides
def save(self) -> bool:
if len(self.state) > config.config['arper_min_entries_to_be_valid']:
- logger.debug(f'Persisting state to {config.config["arper_cache_location"]}')
+ logger.debug('Persisting state to %s', config.config["arper_cache_location"])
with file_utils.FileWriter(config.config['arper_cache_location']) as wf:
for (mac, ip) in self.state.items():
mac = mac.lower()
return True
else:
logger.warning(
- f'Only saw {len(self.state)} entries; needed at least {config.config["arper_min_entries_to_be_valid"]} to bother persisting.'
+ 'Only saw %d entries; needed at least %d to bother persisting.',
+ len(self.state),
+ config.config["arper_min_entries_to_be_valid"],
)
return False
projects / python_utils.git / blobdiff