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

net_alerter/net_alerter.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 """
-net_alerter.py — Alert on new devices joining the local network.
+net_alerter.py — Presence-tracking network monitor.
-Runs via cron, sends Matrix messages when unknown MACs appear.
+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) ---
@@ -26,6 +26,10 @@ 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)
@@ -35,9 +39,17 @@ def get_db() -> sqlite3.Connection:
             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 scan_subnet(cidr):
-        for d in devices:
+            scan_results[d["mac"]] = d
-            mac = d["mac"]
+
-            row = conn.execute("SELECT mac FROM devices WHERE mac=?", (mac,)).fetchone()
+    # 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) VALUES (?,?,?,?,?)",
+                "INSERT INTO devices (mac, ip, name, first_seen, last_seen, is_present, last_left) "
-                    (mac, d["ip"], d["name"], now, now),
+                "VALUES (?,?,?,?,?,1,NULL)",
+                (mac, d["ip"], d["name"], ts, ts),
             )
-                new_devices.append(d)
+            if not baseline_mode:
+                alerts.append(("NEW", d))
         else:
+            is_present = row[0]
+            if is_present == 0:
+                # Known device rejoining
+                conn.execute(
+                    "UPDATE devices SET ip=?, name=?, last_seen=?, is_present=1, last_left=NULL WHERE mac=?",
+                    (d["ip"], d["name"], ts, mac),
+                )
+                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)