X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=arper.py;h=b4c079edcc750307356b60fdba39ca5b43f5c38a;hb=532df2c5b57c7517dfb3dddd8c1358fbadf8baf3;hp=bdd97ac2c93b8109fcfb187f5bc7b455fad7a009;hpb=713a609bd19d491de03debf8a4a6ddf2540b13dc;p=python_utils.git diff --git a/arper.py b/arper.py index bdd97ac..b4c079e 100644 --- a/arper.py +++ b/arper.py @@ -1,5 +1,7 @@ #!/usr/bin/env python3 +# © Copyright 2021-2022, Scott Gasch + """A caching layer around the kernel's network mapping between IPs and MACs""" @@ -28,14 +30,20 @@ cfg = config.add_commandline_args( ) cfg.add_argument( '--arper_cache_location', - default=f'{os.environ["HOME"]}/cache/.arp_table_cache', + default=site_config.get_config().arper_cache_file, metavar='FILENAME', help='Where to cache the kernel ARP table', ) +cfg.add_argument( + '--arper_supplimental_cache_location', + default=site_config.get_config(site_config.other_location()).arper_cache_file, + metavar='FILENAME', + help='Where someone else is caching the kernel ARP table', +) 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', ) @@ -49,17 +57,38 @@ cfg.add_argument( @persistent.persistent_autoloaded_singleton() # type: ignore class Arper(persistent.Persistent): - def __init__(self, cached_state: Optional[BiDict] = None) -> None: + """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, + cached_supplimental_state: Optional[BiDict] = None, + ) -> None: self.state = BiDict() - if cached_state is not None: - logger.debug('Loading Arper map from cached state.') - self.state = cached_state + if cached_local_state is not None: + logger.debug('Loading Arper map from cached local state.') + self.state = cached_local_state else: logger.debug('No usable cached state; calling /usr/sbin/arp') self.update_from_arp_scan() self.update_from_arp() 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('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('%s <-> %s', mac, ip) def update_from_arp_scan(self): network_spec = site_config.get_config().network @@ -76,7 +105,7 @@ class Arper(persistent.Persistent): 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): @@ -90,7 +119,7 @@ class Arper(persistent.Persistent): 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]: @@ -101,39 +130,65 @@ class Arper(persistent.Persistent): return self.state.inverse.get(ip, None) @classmethod - @overrides - def load(cls) -> Any: - cache_file = config.config['arper_cache_location'] + def load_state( + cls, + cache_file: str, + freshness_threshold_sec: int, + state: BiDict, + ): + if not file_utils.file_is_readable(cache_file): + logger.debug('Can\'t read %s', cache_file) + return if persistent.was_file_written_within_n_seconds( cache_file, - config.config['arper_cache_max_staleness'].total_seconds(), + freshness_threshold_sec, ): - logger.debug(f'Loading state from {cache_file}') - cached_state = BiDict() + 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() ip = ip.strip() - cached_state[mac] = ip - if len(cached_state) > config.config['arper_min_entries_to_be_valid']: - return cls(cached_state) - else: - msg = f'{cache_file} is invalid: only {len(cached_state)} entries. Deleting it.' - logger.warning(msg) - warnings.warn(msg, stacklevel=2) + state[mac] = ip + count += 1 + else: + logger.debug('%s is too stale.', cache_file) + + @classmethod + @overrides + def load(cls) -> Any: + local_state: BiDict = BiDict() + cache_file = config.config['arper_cache_location'] + max_staleness = config.config['arper_cache_max_staleness'].total_seconds() + 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.' + logger.warning(msg) + warnings.warn(msg, stacklevel=2) + try: os.remove(cache_file) - logger.debug('No usable saved state found') + except Exception: + pass + + supplimental_state: BiDict = BiDict() + cache_file = config.config['arper_supplimental_cache_location'] + max_staleness = config.config['arper_cache_max_staleness'].total_seconds() + logger.debug('Trying to suppliment arper state from %s', cache_file) + cls.load_state(cache_file, max_staleness, supplimental_state) + 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() @@ -141,6 +196,8 @@ class Arper(persistent.Persistent): 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