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Rewrite net_alerter with presence tracking: baseline on first run, alert on join and rejoin

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n0mad1k
2026-04-06 08:47:48 -04:00
parent 532f5f4a33
commit 0156101f11
1 changed files with 83 additions and 26 deletions
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net_alerter/net_alerter.py
+83 -26
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@@ -1,7 +1,7 @@
#!/usr/bin/env python3
"""
net_alerter.py — Alert on new devices joining the local network.
Runs via cron, sends Matrix messages when unknown MACs appear.
net_alerter.py — Presence-tracking network monitor.
Baseline on first run (silent). Alerts on join and rejoin.
"""
import json
@@ -13,7 +13,7 @@ import subprocess
import sys
import urllib.parse
import urllib.request
from datetime import datetime
from datetime import datetime, timezone
from pathlib import Path
# --- Config (overridable via env) ---
@@ -26,18 +26,30 @@ DB_PATH = Path(os.getenv("NET_ALERTER_DB", "/opt/net_alerter/devices.db"))
ENV_PATH = Path(os.getenv("NET_ALERTER_ENV", "/opt/net_alerter/.env"))
def now_utc() -> str:
return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
def get_db() -> sqlite3.Connection:
DB_PATH.parent.mkdir(parents=True, exist_ok=True)
conn = sqlite3.connect(DB_PATH)
conn.execute("""
CREATE TABLE IF NOT EXISTS devices (
mac TEXT PRIMARY KEY,
ip TEXT,
name TEXT,
mac TEXT PRIMARY KEY,
ip TEXT,
name TEXT,
first_seen TEXT,
last_seen TEXT
last_seen TEXT,
is_present INTEGER NOT NULL DEFAULT 1,
last_left TEXT
)
""")
# Migrate existing DBs that lack the new columns
existing = {row[1] for row in conn.execute("PRAGMA table_info(devices)")}
if "is_present" not in existing:
conn.execute("ALTER TABLE devices ADD COLUMN is_present INTEGER NOT NULL DEFAULT 1")
if "last_left" not in existing:
conn.execute("ALTER TABLE devices ADD COLUMN last_left TEXT")
conn.commit()
return conn
@@ -64,7 +76,10 @@ def refresh_token() -> str:
token = data.get("access_token", "")
if token and ENV_PATH.exists():
lines = ENV_PATH.read_text().splitlines()
lines = [l if not l.startswith("MATRIX_ACCESS_TOKEN=") else f"MATRIX_ACCESS_TOKEN={token}" for l in lines]
lines = [
f"MATRIX_ACCESS_TOKEN={token}" if l.startswith("MATRIX_ACCESS_TOKEN=") else l
for l in lines
]
ENV_PATH.write_text("\n".join(lines) + "\n")
return token
except Exception as e:
@@ -90,14 +105,14 @@ def _do_send(token: str, msg: str) -> int:
except urllib.error.HTTPError as e:
return e.code
except Exception as e:
print(f"[error] Matrix send failed: {e}", file=sys.stderr)
print(f"[error] Matrix send exception: {e}", file=sys.stderr)
return 0
def send_matrix_alert(msg: str) -> None:
global MATRIX_ACCESS_TOKEN
if not MATRIX_ACCESS_TOKEN:
print(f"[warn] No MATRIX_ACCESS_TOKEN set, skipping alert", file=sys.stderr)
print("[warn] No MATRIX_ACCESS_TOKEN set, skipping alert", file=sys.stderr)
return
code = _do_send(MATRIX_ACCESS_TOKEN, msg)
if code == 401:
@@ -143,7 +158,7 @@ def scan_subnet(cidr: str) -> list[dict]:
return []
devices = []
current = {}
current: dict = {}
for line in out.splitlines():
if line.startswith("Nmap scan report for"):
if current.get("mac"):
@@ -167,43 +182,85 @@ def scan_subnet(cidr: str) -> list[dict]:
def run() -> None:
conn = get_db()
now = datetime.utcnow().strftime("%Y-%m-%dT%H:%M:%SZ")
ts = now_utc()
hostname = socket.gethostname()
subnets = get_local_subnets()
if not subnets:
print("[warn] No local subnets found", file=sys.stderr)
conn.close()
return
new_devices = []
# Collect all MACs visible right now across all subnets
scan_results: dict[str, dict] = {}
for cidr in subnets:
devices = scan_subnet(cidr)
for d in devices:
mac = d["mac"]
row = conn.execute("SELECT mac FROM devices WHERE mac=?", (mac,)).fetchone()
if row is None:
for d in scan_subnet(cidr):
scan_results[d["mac"]] = d
# Is this the first run? (empty DB = baseline mode, no alerts)
row_count = conn.execute("SELECT COUNT(*) FROM devices").fetchone()[0]
baseline_mode = row_count == 0
if baseline_mode:
print(f"[info] Baseline run — seeding {len(scan_results)} devices, no alerts", file=sys.stderr)
alerts: list[tuple[str, dict]] = [] # (event_type, device_dict)
# Process devices currently on the network
for mac, d in scan_results.items():
row = conn.execute(
"SELECT is_present FROM devices WHERE mac=?", (mac,)
).fetchone()
if row is None:
# Brand new device
conn.execute(
"INSERT INTO devices (mac, ip, name, first_seen, last_seen, is_present, last_left) "
"VALUES (?,?,?,?,?,1,NULL)",
(mac, d["ip"], d["name"], ts, ts),
)
if not baseline_mode:
alerts.append(("NEW", d))
else:
is_present = row[0]
if is_present == 0:
# Known device rejoining
conn.execute(
"INSERT INTO devices (mac, ip, name, first_seen, last_seen) VALUES (?,?,?,?,?)",
(mac, d["ip"], d["name"], now, now),
"UPDATE devices SET ip=?, name=?, last_seen=?, is_present=1, last_left=NULL WHERE mac=?",
(d["ip"], d["name"], ts, mac),
)
new_devices.append(d)
if not baseline_mode:
alerts.append(("REJOIN", d))
else:
# Already present — just update last_seen
conn.execute(
"UPDATE devices SET ip=?, name=?, last_seen=? WHERE mac=?",
(d["ip"], d["name"], now, mac),
(d["ip"], d["name"], ts, mac),
)
# Mark devices that were present but didn't appear in this scan as gone
present_in_db = {
row[0] for row in conn.execute("SELECT mac FROM devices WHERE is_present=1")
}
for mac in present_in_db - set(scan_results.keys()):
conn.execute(
"UPDATE devices SET is_present=0, last_left=? WHERE mac=?",
(ts, mac),
)
print(f"[info] Device left: {mac}", file=sys.stderr)
conn.commit()
conn.close()
for d in new_devices:
# Send alerts
for event, d in alerts:
label = d["name"] if d["name"] else "unknown"
tag = "NEW DEVICE" if event == "NEW" else "DEVICE REJOINED"
msg = (
f"[{hostname}] NEW DEVICE\n"
f"[{hostname}] {tag}\n"
f" IP: {d['ip']}\n"
f" MAC: {d['mac']}\n"
f" Name: {label}\n"
f" Time: {now}"
f" Time: {ts}"
)
print(msg)
send_matrix_alert(msg)