#!/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__)
)
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',
)
@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(
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:
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()
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
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