macOS daemon that logs home Wi-Fi bandwidth usage to Postgres. Built to prove to my dad I'm not the one killing our 1.2TB data cap.

network-usage-tracker.py

import json
import os
import subprocess
import time
import psycopg2

TARGET_ROUTER_MAC = ""
STATE_FILE = "/Users/zayd/wifi_tracker/state.json"
DB_CONFIG = ""

def get_router_mac():
    try:
        gateway_ip = (
            subprocess.check_output(
                "route -n get default | grep gateway | awk '{print $2}'", shell=True
            )
            .decode("utf-8")
            .strip()
        )

        arp_out = subprocess.check_output(f"arp {gateway_ip}", shell=True).decode(
            "utf-8"
        )

        parts = arp_out.split()
        for i, part in enumerate(parts):
            if part == "at":
                return parts[i + 1]
    except Exception:
        return None
    return None


def get_bytes():
    try:
        res = subprocess.check_output(["netstat", "-b", "-I", "en0"]).decode("utf-8")
        lines = res.split("\n")
        parts = lines[1].split()
        return int(parts[6]), int(parts[9])
    except Exception:
        return 0, 0


def main():
    current_mac = get_router_mac()
    curr_rx, curr_tx = get_bytes()

    prev_state = {}
    if os.path.exists(STATE_FILE):
        with open(STATE_FILE, "r") as f:
            prev_state = json.load(f)

    # We only log if we were on the target router LAST time and THIS time
    # This ensures the delta happened entirely on the target network
    if (
        prev_state.get("router_mac") == TARGET_ROUTER_MAC
        and current_mac == TARGET_ROUTER_MAC
    ):
        delta_rx = curr_rx - prev_state.get("rx", 0)
        delta_tx = curr_tx - prev_state.get("tx", 0)

        # Check for reboot/counter rollover (if current < prev, something reset)
        if delta_rx >= 0 and delta_tx >= 0:
            # CONNECT AND LOG
            try:
                conn = psycopg2.connect(DB_CONFIG)
                cur = conn.cursor()
                cur.execute(
                    """
                    INSERT INTO wifi_logs (network_mac_address, rx_bytes_delta, tx_bytes_delta, total_bytes_delta)
                    VALUES (%s, %s, %s, %s)
                """,
                    (current_mac, delta_rx, delta_tx, delta_rx + delta_tx),
                )
                conn.commit()
                cur.close()
                conn.close()
            except Exception as e:
                print(f"DB Error: {e}")

    # Update state file
    new_state = {
        "router_mac": current_mac,
        "rx": curr_rx,
        "tx": curr_tx,
        "timestamp": time.time(),
    }

    with open(STATE_FILE, "w") as f:
        json.dump(new_state, f)


if __name__ == "__main__":
    main()