arper.py

   1 #!/usr/bin/env python3
   2
   3 import datetime
   4 import logging
   5 import os
   6 from typing import Any, Optional
   7
   8 import argparse_utils
   9 from collect.bidict import BiDict
  10 import config
  11 import exec_utils
  12 import persistent
  13 import string_utils
  14
  15 logger = logging.getLogger(__name__)
  16
  17 cfg = config.add_commandline_args(
  18     f'MAC <--> IP Address mapping table cache ({__file__})',
  19     'Commandline args related to MAC <--> IP Address mapping',
  20 )
  21 cfg.add_argument(
  22     '--arper_cache_location',
  23     default=f'{os.environ["HOME"]}/cache/.arp_table_cache',
  24     metavar='FILENAME',
  25     help='Where to cache the kernel ARP table',
  26 )
  27 cfg.add_argument(
  28     '--arper_cache_max_staleness',
  29     type=argparse_utils.valid_duration,
  30     default=datetime.timedelta(seconds=60 * 60),
  31     metavar='DURATION',
  32     help='Max acceptable age of the kernel arp table cache'
  33 )
  34
  35
  36 @persistent.persistent_autoloaded_singleton()
  37 class Arper(persistent.Persistent):
  38     def __init__(
  39             self, cached_state: Optional[BiDict[str, str]] = None
  40     ) -> None:
  41         self.state = BiDict()
  42         if cached_state is not None:
  43             logger.debug('Loading Arper map from cached state.')
  44             self.state = cached_state
  45         else:
  46             logger.debug('No usable cached state; calling /usr/sbin/arp')
  47             output = exec_utils.cmd(
  48                 '/usr/sbin/arp -a',
  49                 timeout_seconds=5.0
  50             )
  51             for line in output.split('\n'):
  52                 ip = string_utils.extract_ip_v4(line)
  53                 mac = string_utils.extract_mac_address(line)
  54                 if ip is not None and mac is not None:
  55                     mac = mac.lower()
  56                     logger.debug(f'    {mac} => {ip}')
  57                     self.state[mac] = ip
  58
  59     def get_ip_by_mac(self, mac: str) -> Optional[str]:
  60         mac = mac.lower()
  61         return self.state.get(mac, None)
  62
  63     def get_mac_by_ip(self, ip: str) -> Optional[str]:
  64         return self.state.inverse.get(ip, None)
  65
  66     def save(self) -> bool:
  67         logger.debug(
  68             f'Persisting state to {config.config["arper_cache_location"]}'
  69         )
  70         with open(config.config['arper_cache_location'], 'w') as wf:
  71             for (mac, ip) in self.state.items():
  72                 mac = mac.lower()
  73                 print(f'{mac}, {ip}', file=wf)
  74
  75     @classmethod
  76     def load(cls) -> Any:
  77         if persistent.was_file_written_within_n_seconds(
  78                 config.config['arper_cache_location'],
  79                 config.config['arper_cache_max_staleness'].total_seconds(),
  80         ):
  81             logger.debug(
  82                 f'Loading state from {config.config["arper_cache_location"]}'
  83             )
  84             cached_state = BiDict()
  85             with open(config.config['arper_cache_location'], 'r') as rf:
  86                 contents = rf.readlines()
  87                 for line in contents:
  88                     logger.debug(f'ARPER> {line}')
  89                     (mac, ip) = line.split(',')
  90                     mac = mac.strip()
  91                     mac = mac.lower()
  92                     ip = ip.strip()
  93                     cached_state[mac] = ip
  94             return cls(cached_state)
  95         logger.debug('No usable saved state found')
  96         return None