X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=arper.py;h=ffe4b7431746d6178badd3ec099ce9796663a1a8;hb=57acb381eb927bcafd5a0c496e4fec8917f361a7;hp=29a8a121870175c8a469c8158fe087b290f40fe0;hpb=17e8082381dbbf691dfb19fb1b38a97e48d6ab87;p=python_utils.git diff --git a/arper.py b/arper.py index 29a8a12..ffe4b74 100644 --- a/arper.py +++ b/arper.py @@ -1,23 +1,26 @@ #!/usr/bin/env python3 +# © Copyright 2021-2022, Scott Gasch + """A caching layer around the kernel's network mapping between IPs and MACs""" + import datetime import logging import os -from typing import Any, Optional import warnings +from typing import Any, Optional from overrides import overrides import argparse_utils -from collect.bidict import BiDict import config import exec_utils import file_utils import persistent -import string_utils import site_config +import string_utils +from collect.bidict import BiDict logger = logging.getLogger(__name__) @@ -27,14 +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', ) @@ -46,23 +55,53 @@ cfg.add_argument( ) -@persistent.persistent_autoloaded_singleton() +@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: + """For most purposes, ignore the arguments. Because this is a + Persistent subclass the decorator will handle invoking our load + and save methods to read/write persistent state transparently. + + Args: + cached_local_state: local state to initialize mapping + cached_supplimental_state: remote state to initialize mapping + """ + 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() + 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)}.' - ) + 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): + """Internal method to initialize our state via a call to arp-scan.""" - def update_from_arp_scan(self): network_spec = site_config.get_config().network try: output = exec_utils.cmd( @@ -75,17 +114,14 @@ class Arper(persistent.Persistent): for line in output.split('\n'): ip = string_utils.extract_ip_v4(line) mac = string_utils.extract_mac_address(line) - if ( - ip is not None - and mac is not None - and mac != 'UNKNOWN' - and ip != 'UNKNOWN' - ): + 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): + def _update_from_arp(self): + """Internal method to initialize our state via a call to arp.""" + try: output = exec_utils.cmd('/usr/sbin/arp -a', timeout_seconds=10.0) except Exception as e: @@ -94,57 +130,110 @@ class Arper(persistent.Persistent): for line in output.split('\n'): ip = string_utils.extract_ip_v4(line) mac = string_utils.extract_mac_address(line) - if ( - ip is not None - and mac is not None - and mac != 'UNKNOWN' - and ip != 'UNKNOWN' - ): + 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]: - mac = mac.lower() - return self.state.get(mac, None) + """Given a MAC address, see if we know it's IP address and, if so, + return it. If not, return None. + + Args: + mac: the MAC address to lookup. Should be formatted like + ab:cd:ef:g1:23:45. + + Returns: + The IPv4 address associated with that MAC address (as a string) + or None if it's not known. + """ + m = string_utils.extract_mac_address(mac) + if not m: + return None + m = m.lower() + if not string_utils.is_mac_address(m): + return None + return self.state.get(m, None) def get_mac_by_ip(self, ip: str) -> Optional[str]: + """Given an IPv4 address (as a string), check to see if we know what + MAC address is associated with it and, if so, return it. If not, + return None. + + Args: + ip: the IPv4 address to look up. + + Returns: + The associated MAC address, if known. Or None if not. + """ 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, + ): + """Internal helper method behind load.""" + + 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: + """Internal helper method to fulfull Persistent requirements.""" + + 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: + """Internal helper method to fulfull Persistent requirements.""" + 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() @@ -152,6 +241,8 @@ 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