Amazon Dash→LIFX Power

dash.py

#!/usr/bin/env python
# Detect Amazon Dash button network broadcast, toggle LIFX power based on MAC.
#
# Usage, with Amazon Dash buttons connected to LAN WiFi (see below for setup):
#
# 0. Configure `BUTTONS` with MAC to LIFX selector & `LIFX` with token.
# 1. Configure network firewall to block WAN out from dash MAC.
# 2. Install dependencies with `pip install requests scapy` on Python 3.
# 3. Run as root.
#
# Alternatively, to run Scapy without root:
#
#     setcap cap_net_raw=eip /path/to/python
#     setcap cap_net_raw=eip `which tcpdump`
#
# Note that this `setcap` usage opens up raw socket access to all users.
#
# This packet-sniffing program can run anywhere on the LAN from a non-WiFi
# hard-wired host. On button press, the dash button connects to WiFi and issues
# a DHCP request in order to get its IP and DNS settings. This DHCP request
# (with related ARP packets) is broadcast on the network. The following program
# detects the DHCP request by sniffing LAN traffic and dispatches the connected
# Python function.
#
# A simple debounce method ensures that only one dispatch is made within a few
# seconds, to avoid dispatch on multiple DHCP packets for the same button
# press. The connection is passive in that no response is sent to the dash
# button. The observed behavior of the dash button is a blinking white LED that
# eventually times out. While the white LED is lit, additional button presses
# do nothing, as no further DHCP request is made. The button then powers down
# about half a minute later, and a button press during an unlit LED then starts
# the process again, issuing a new DHCP request, to be picked up by this
# packet-sniffing program.
#
# Meaning, after pressing the dash button, wait until the white LED is unlit
# before attempting to press the button again.
#
# Altogether, this process is slow and takes several seconds.
#
# To get an Amazon Dash button onto local WiFI, noting that a button may need
# an attempted setting of amzn_ssid via `curl` (which fails) before it accepts
# the .wav payload:
#
# blog.christophermullins.com/2019/12/20/rescue-your-amazon-dash-buttons/
#
# LIFX personal access token:
#
# cloud.lifx.com/settings


import datetime

import requests
from scapy.all import Ether, sniff


LIFX = '0123456789abcdef01234567890abcdef01234567890abcdef01234567890abc'

BUTTONS = {
  '01:23:45:67:89:AB': 'd0123456789a',
  '12:34:56:78:9A:BC': 'group_id:0123456789abcdef0123456789abcdef',
}


LAST_SEEN = {}
DEBOUNCE_SECONDS = 25


def toggle(selector):
    requests.post(
        f'https://api.lifx.com/v1/lights/{selector}/toggle',
        headers={'Authorization': f'Bearer {LIFX}'})


def detect_button(pkt):
    MAC = pkt[Ether].src.upper()
    if MAC in BUTTONS:
        now = datetime.datetime.now()
        timestamp = int(now.timestamp())
        if timestamp > LAST_SEEN.get(MAC, 0) + DEBOUNCE_SECONDS:
            LAST_SEEN[MAC] = timestamp
            print(now.strftime(f'%Y-%m-%d %H:%M:%S - {MAC}'))
            toggle(BUTTONS[MAC])


def main():
    # Performance Note:
    #
    # Filter on ARP, not DHCP, as Scapy provides a simple means to specify
    # `filter='arp'`. Otherwise, filtering on DHCP requires filter syntax with
    # UDP packets and additional processing to detect DHCP layer.
    sniff(prn=detect_button, filter='arp', store=0)


if __name__ == '__main__':
    main()

Tested with:

• Raspberry Pi 3 with fully updated Raspian "Buster" OS as of 2020-04-18.
• Python 3.7.3, Scapy 2.4.3, Requests 2.23.0.
• Amazon Dash buttons model JK29LP.