arper.py

   1 #!/usr/bin/env python3
   2
   3 """A caching layer around the kernel's network mapping between IPs and MACs"""
   4
   5
   6 import datetime
   7 import logging
   8 import os
   9 import warnings
  10 from typing import Any, Optional
  11
  12 from overrides import overrides
  13
  14 import argparse_utils
  15 import config
  16 import exec_utils
  17 import file_utils
  18 import persistent
  19 import site_config
  20 import string_utils
  21 from collect.bidict import BiDict
  22
  23 logger = logging.getLogger(__name__)
  24
  25 cfg = config.add_commandline_args(
  26     f'MAC <--> IP Address mapping table cache ({__file__})',
  27     'Commandline args related to MAC <--> IP Address mapping',
  28 )
  29 cfg.add_argument(
  30     '--arper_cache_location',
  31     default=site_config.get_config().arper_cache_file,
  32     metavar='FILENAME',
  33     help='Where to cache the kernel ARP table',
  34 )
  35 cfg.add_argument(
  36     '--arper_supplimental_cache_location',
  37     default=site_config.get_config(site_config.other_location()).arper_cache_file,
  38     metavar='FILENAME',
  39     help='Where someone else is caching the kernel ARP table',
  40 )
  41 cfg.add_argument(
  42     '--arper_cache_max_staleness',
  43     type=argparse_utils.valid_duration,
  44     default=datetime.timedelta(seconds=60 * 15),
  45     metavar='DURATION',
  46     help='Max acceptable age of the kernel arp table cache',
  47 )
  48 cfg.add_argument(
  49     '--arper_min_entries_to_be_valid',
  50     type=int,
  51     default=site_config.get_config().arper_minimum_device_count,
  52     help='Min number of arp entries to bother persisting.',
  53 )
  54
  55
  56 @persistent.persistent_autoloaded_singleton()  # type: ignore
  57 class Arper(persistent.Persistent):
  58     def __init__(
  59         self,
  60         cached_local_state: Optional[BiDict] = None,
  61         cached_supplimental_state: Optional[BiDict] = None,
  62     ) -> None:
  63         self.state = BiDict()
  64         if cached_local_state is not None:
  65             logger.debug('Loading Arper map from cached local state.')
  66             self.state = cached_local_state
  67         else:
  68             logger.debug('No usable cached state; calling /usr/sbin/arp')
  69             self.update_from_arp_scan()
  70             self.update_from_arp()
  71         if len(self.state) < config.config['arper_min_entries_to_be_valid']:
  72             raise Exception(f'Arper didn\'t find enough entries; only got {len(self.state)}.')
  73         if cached_supplimental_state is not None:
  74             logger.debug(f'Also added {len(cached_supplimental_state)} supplimental entries.')
  75             for mac, ip in cached_supplimental_state.items():
  76                 self.state[mac] = ip
  77         for mac, ip in self.state.items():
  78             logger.debug(f'{mac} <-> {ip}')
  79
  80     def update_from_arp_scan(self):
  81         network_spec = site_config.get_config().network
  82         try:
  83             output = exec_utils.cmd(
  84                 f'/usr/local/bin/arp-scan --retry=6 --timeout 350 --backoff=1.4 --random --numeric --plain --ignoredups {network_spec}',
  85                 timeout_seconds=10.0,
  86             )
  87         except Exception as e:
  88             logger.exception(e)
  89             return
  90         for line in output.split('\n'):
  91             ip = string_utils.extract_ip_v4(line)
  92             mac = string_utils.extract_mac_address(line)
  93             if ip is not None and mac is not None and mac != 'UNKNOWN' and ip != 'UNKNOWN':
  94                 mac = mac.lower()
  95                 logger.debug(f'ARPER: {mac} => {ip}')
  96                 self.state[mac] = ip
  97
  98     def update_from_arp(self):
  99         try:
 100             output = exec_utils.cmd('/usr/sbin/arp -a', timeout_seconds=10.0)
 101         except Exception as e:
 102             logger.exception(e)
 103             return
 104         for line in output.split('\n'):
 105             ip = string_utils.extract_ip_v4(line)
 106             mac = string_utils.extract_mac_address(line)
 107             if ip is not None and mac is not None and mac != 'UNKNOWN' and ip != 'UNKNOWN':
 108                 mac = mac.lower()
 109                 logger.debug(f'ARPER: {mac} => {ip}')
 110                 self.state[mac] = ip
 111
 112     def get_ip_by_mac(self, mac: str) -> Optional[str]:
 113         mac = mac.lower()
 114         return self.state.get(mac, None)
 115
 116     def get_mac_by_ip(self, ip: str) -> Optional[str]:
 117         return self.state.inverse.get(ip, None)
 118
 119     @classmethod
 120     def load_state(cls, cache_file: str, freshness_threshold_sec: int, state: BiDict):
 121         if not file_utils.file_is_readable(cache_file):
 122             logger.debug(f'Can\'t read {cache_file}')
 123             return None
 124         if persistent.was_file_written_within_n_seconds(
 125             cache_file,
 126             freshness_threshold_sec,
 127         ):
 128             logger.debug(f'Loading state from {cache_file}')
 129             count = 0
 130             with open(cache_file, 'r') as rf:
 131                 contents = rf.readlines()
 132                 for line in contents:
 133                     line = line[:-1]
 134                     logger.debug(f'ARPER:{cache_file}> {line}')
 135                     (mac, ip) = line.split(',')
 136                     mac = mac.strip()
 137                     mac = mac.lower()
 138                     ip = ip.strip()
 139                     state[mac] = ip
 140                     count += 1
 141         else:
 142             logger.debug(f'{cache_file} is too stale.')
 143
 144     @classmethod
 145     @overrides
 146     def load(cls) -> Any:
 147         local_state = BiDict()
 148         cache_file = config.config['arper_cache_location']
 149         max_staleness = config.config['arper_cache_max_staleness'].total_seconds()
 150         logger.debug(f'Trying to load main arper cache from {cache_file}...')
 151         cls.load_state(cache_file, max_staleness, local_state)
 152         if len(local_state) <= config.config['arper_min_entries_to_be_valid']:
 153             msg = f'{cache_file} is invalid: only {len(local_state)} entries.  Deleting it.'
 154             logger.warning(msg)
 155             warnings.warn(msg, stacklevel=2)
 156             try:
 157                 os.remove(cache_file)
 158             except Exception:
 159                 pass
 160
 161         supplimental_state = BiDict()
 162         cache_file = config.config['arper_supplimental_cache_location']
 163         max_staleness = config.config['arper_cache_max_staleness'].total_seconds()
 164         logger.debug(f'Trying to suppliment arper state from {cache_file}...')
 165         cls.load_state(cache_file, max_staleness, supplimental_state)
 166         if len(supplimental_state) == 0:
 167             supplimental_state = None
 168
 169         if len(local_state) > 0:
 170             return cls(local_state, supplimental_state)
 171         return None
 172
 173     @overrides
 174     def save(self) -> bool:
 175         if len(self.state) > config.config['arper_min_entries_to_be_valid']:
 176             logger.debug(f'Persisting state to {config.config["arper_cache_location"]}')
 177             with file_utils.FileWriter(config.config['arper_cache_location']) as wf:
 178                 for (mac, ip) in self.state.items():
 179                     mac = mac.lower()
 180                     print(f'{mac}, {ip}', file=wf)
 181             return True
 182         else:
 183             logger.warning(
 184                 f'Only saw {len(self.state)} entries; needed at least {config.config["arper_min_entries_to_be_valid"]} to bother persisting.'
 185             )
 186             return False